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Observations on Electric Hybrid Bus Design - IEA

1. Bottom Low pass filtered z L0s feedforward charging strategy on the N eoplan bus 18 Observations on Electric H ybrid Bus D es gn Comparing different strategies With aid of the simulation program a sensitivity analysis with respect to charging strategy ICE size and battery size has been made T he results for Casel N eoplan in M alm in one route are presented in table 7 1 The busis running the Malmo cycle in all simulations The reason why this bus was chosen for modification was that the bus design is the most modern The over all efficiency of the driving cycle in the simulation is the same as the fuel consumption when the final SO C in the battery isthe same T hefollowing strategies were tested in table 7 1 The first simulation is called M M M angetM otor T his charging strategy is the original in the N eoplan bus T he size of the components in the drivetrain has the original dimensions T he charging strategy on off is run with the ICE off at the beginning and in the later part of the simulation with the ICE on with constant power 75 kW T he low pass filtered charging strategy is altered in steps of 1 3 10 100 and ee seconds With the e time constant this strategy corresponds to the average power discussed in section 7 3 N otethat the fuel consumption is not significantly affected by the charging time constant All the other strategies do involve the time constant z T he battery los
2. 4 Observations on Electric H ybrid Bus D eign With the proposed changes in theoretical simulation model in composition and charging strategy one of the buses studied can reduce the battery weight with 60 96 the fuel consumption with 10 96 and the size of the ICE with 60 9o 13 Outline of the Thesis A general introduction to hybrid vehicles and their main components is given in Chapter 2 The two commercial buses of series hybrid type studied in this report a N eoplan M IC N 8012 and Scania D ab 1200M KII are described in Chapter 3 A construction of a simulation model has been made that include the bus dynamics the ICE and the power flow in the bus see Chapter 4 The simulation model has been verified and calibrated with onboard measurements where comprehensive measurements were made on the buses and their ICEs Internal Combustion Engine see Chapter 5 With the simulation mode a series of sensitivity analysis have been made pointing out suitable motor sizes charging strategies etc of the buses A number of different drive cycles are presented in Chapter 6 A particular way of using the drive cycle as a function of position instead of time is presented The predicted drive cycle proposed in Chapter 7 is based on position measurements of the bus relative to the route A sensitivity analysis with respect to ICE size battery size and charging strategy is presented in Chapter 7 A method for determination of the limit for trans
3. seconds Figure 7 3 T he present charging strategy measured on the Scania bus Power from generator to battery amp drive motor 100 690 700 680 Figure 7 4 T he present charging strategy simulated on the Scania bus Chapte 7 Charging Strategies 71 T here isa delay in the simulated cycle of 30 seconds T he differences in the motor power are due to the Stockholm area has large altitude variation having some measurement and compensation for that in the simulation model would have been recommended but was not feasible due to technical problems with the measurement system in the Stockholm bus There are also differences in the SOC between the measured and the simulated batteries of the buses The total integrated energy consumption of the different components for a cycle isthe same in the both cases 7 3 Alternative Charging Strategies The simulation of any of the following driving cycles is arranged for SOC to end at the same level as it started in this case 75 This makes the fuel consumption and emissions of different cycles comparable T herefore a peak may appear in the ICE power at the end of each driving cycle if the SOC of the battery is too low The different charging strategies are tested on the N eoplan bus Average Power This charging strategy is very simple The ICE and the generator supply the battery and traction motor with the average power consumed by the traction motors In this way
4. e Write smulate and press return e Now Matlab starts its graphical user interface where the simulation program runs A new window opens with buses a piston a battery an electric motor a diagram and different buttons T he interface is shown in Figure 4 1 e A choice between different buses can be done by clicking on the popup menu Select Bus A selection between N eoplan and Scania D AB hybrid buses can be done W hen a bus is chosen a picture of that bus appears in the figure 110 Observations on Electric H ybrid Bus D ei gn e When a bus has been selected all its defaults values appear by the different components T his is the number of cylinders number of battery cells and the size of electric motor These numbers can be changed by the popup menus for each component For example if the ICE sizeisto be reduced with 50 percent the default value number of cylinders can be changed from 6 to 3 by the popup menu e The driving cycle which the bus is going to run during the simulation can be selected by the popup menu Driving Cycle The driving cycle available for the moment is M alm to the O resund bridge Stockholm line 57 Braunschwig and ECE15 When a cycle is chosen it appears in the plot e The Charging strategy is the way the ICE should charge the battery and the electric motors The selection by this popup menu is between the original and different low pass filter constants e The simulation can now be
5. seconds Information Driving distance 7 1 km Average speed 21 5 km h Fuel consumtion 2 1 kg 10km NOx emission 24 6 g 10km HC emission 22 5 g 10km CO emission 0 14 g 10km CO2 emission 4 15 kg 10km Battery losses 0 372 kWh Vehicle specification Neoplan 8012 CNG kerb weight 8780 kg Engine size 145 kW 6 cylinders Electric motor 110 kW Battery 280 cells 60Ah NiMH Figure B 1 Theresult view of the simulation program
6. these electric buses T he battery was charged in a special charger see Figure 9 2 T hedriver had to change the battery when it was empty T his procedure meant some extra work T he bus has to be stopped by the charging station the driver has to go 98 Observations on Electric H ybrid Bus D eign out of the bus and manually operate the switching of batteries Among the drivers it has been a challenge and competition to drive as long as possible without the battery exchange procedure In other words to drive as energy efficient as possible which is a good thing If the driver could be challenged to drive efficiently like in this example somehow even on other kind of vehicles it would of course be a great advantage One of the drivers also told that the batteries behaved like individuals He was able to drive many routes with battery no 5 while he was only able to drive one route with battery no 7 This demonstrates that the battery technology is still is the weakest link in the driving chain T hereis still a lot of work to bedonein this area Figure 9 2 T he battery changing station for the electric busses in U ppsala Chapter 10 Conclusion and Future Work Conclusions Several lessons have been learnt from these half experimental vehicles Some of these are just minor problems with details and some are on the system levd The major conclusions are 1 To be able to write near optimal specifications for a hybrid bus
7. 44 kW ICE and a 30 kW electrical motor produced in 1998 H ellman Peralta and Piotrowski 1998 amp sun G Garner Fi ring Figure 2 4 The planetary gear 2 3 Prime Source of Energy T he prime source of energy can be a fue cell FC or an ICE T he vehicle can also be connected to the electric grid over night for battery charging T his over night charging has little influence on the fuel consumption on a city bus in continuous traffic for 12 hours since a fully charged battery in pure electric mode only will last for a small fraction of the travelled distance during a full days operation 10 Observations on Electric H ybrid Bus D eign With generic FC s hydrogen is used as the primary energy storage but heavy research efforts are made towards reformer based systems with eg methanol as the prime energy source The combustion of hydrogen does not produce any other emission than water and furthermore produces the necessary electrical energy For a basic description of fuel cells in vehicles see M eyer 1998 If hydrogen can be manufactured with favorable emission this technology could be very interesting for the future There are still problems with hydrogen e g it is not so easy to bring hydrogen in a tank on a vehicle A FC hasan efficiency of about 6096 but if the compressor and water pump also are included in the system the efficiency is reduced to 30 This value is comparable to an ICE FC sare still too expensi
8. Observations on Electric H ybrid Bus D eign gt samlig2 vi Diagram Uptb U24 Igen Idede m1 Im2 Ibroms I24dcdc I24gen rpm speed massa lambda Pin Put gasped trottle Tin Tut Tikat Tekat T vatten T ute Tlada S amplings hasttighet i Koll om t ndning till Figure 5 2 O ne page of the LabView program used for collecting data Chapter 5 M easurenents Sensors All sensors are mounted after the bus was built seethe T able 5 1 Table 5 1 Sensor specification Unit Voltage traction system Remark T o calculate the power flow Voltage 24 V system Current from generator Current to D C D C traction system Current to motors 1 amp 2 Current to brake resistor Current to D C D C 24V system Current from generator 24V system Speed ICE ICE behaviour Speed V ehicle Vehicle behaviour Lambda Air Fuel ratio M ass gas Fuel consumption Pressure inlet Corresponds to the torque D iff Pressure C atalyst Check catalyst condition Accelerator D rivers activity Throttle ICE parameter T emperature inlet ICE condition T emperature exhaust gas T emperature before amp after Cat Catalyst condition Temperature C ooling ICE condition T emperature O utside Condition T emperature in the bus u 48 Observations on Electric H ybrid Bus D eign The current and voltage sensors measure the elec
9. Speed rpm CO2 emissions CO emissions _ 2000 z z4 1500 z E EE Zz amp 1000 f 5 500 81 a O o oO NO 0 200 200 2500 3000 Torque Nm 0 1500 Speed rpm Torque Nm 0 1500 Speed rpm Figure 5 9 The emissions from the Saab ICE with ethanol measured after the 3 way catalyst The emissions of NO x and HC are significantly lower for the Saab ICE than for the Cummins ICE The reason for this is that the emissons are measured after a 3 way catalytic converter on the Saab ICE The Cummins ICE is equipped with a oxidizing catalyst with less efficiency The Cummins ICE isalean burn ICE and cannot be equipped with a 3 way catalyst Chapter 6 Driving Cycles W hen specifying aH EV or choosing the individual components performance and size it is important to know the performance requirements like speed limits acceleration and hill climbing ec 6 1 Standard Cycles There are a number of different standard driving cycles for chassis dynamometer testing For example the Braunschweig cycle and the ECE15 The Braunschweig cycle was developed at the Technical University of Braunschweig It is characterized by a lot of starts and stops and high acceleration The ECE 15 cycle is a standard cycle used by car manufacturer the measure fuel consumption it is a theoretical recorded cycle with low acceleration Recently the transient behaviour and the real driving cycles have drawn attention This is the reason for the discussion whether
10. T able 8 3 Table 8 3 Emissions in stationary and transient operation with the same average torque decreasing torque Emission Transient Stationary operation operation CO 96 3 3 0 8 HC ppm 1000 720 02 1 0 0 72 NOx ppm 1400 2500 The lower emission by NOx can be explained by Figure 2 5 The both measuring points has probable a rich mixture of air and fud Stationary Measurements The reason for this performance test is that there have been questions about the influence of the T ES equipment on the emissions T o verify and confirm that the emission measurements by the T ES method have not been influenced by the cooling of the exhaust gases in the bag or any other things in the TES System a stationary test has been done T he ICE was run at a constant speed 2200 rpm and torque 80 N m and the emissions were measured both with the T ES equipment and in the ordinary exhaust pipe In these two different places the emissions were the same So the T ES equipment had no influences on the emissions Conclusions of TES Fast throttle movements can excite the transient behaviour where the lambda control of the ICE has a problem to control the air fuel ratio averageto 1 For the ICE used in the preliminary tests of the TES method reported here the limit for this behaviour starts somewhere in the region between 5 to 10 seconds Faster throttle movements than this limit on a hybrid vehicle with thi
11. as the ICE and generator deliver a constant power average driving power to the traction motor and the battery In this way the battery will deliver all the dynamic variation in tractive power T he losses will be large in the battery due to the power exchange when braking and accelerating A more energy efficient charging strategy is the ICE and generator delivering as much as possible of the instantaneous tractive power The ICE and generator should not produce any power at all when braking When the ICE produces all the instantaneous power the operating point of the ICE has to vary fast Transient operation like that is a source of some of the excess emissions of the ICE An intermediate solution is a charging strategy where the ICE and generator deliver a low pass filtered version of the tractive power and the battery supplies the difference to the instantaneous tractive power T he degree of transient operation is wal defined by the cross over frequency used in the low pass filter T his reduces the electrical power requested and avoids the fast 66 Observations on Electric H ybrid Bus D eign transients in speed and torque range by the ICE T he battery handles only the transient power In this way the losses in the battery and thus the battery size will be reduced This charging strategy with a small battery will only allow a relatively short distance in the emission free zones T he idea with emission free zones can be questioned to d
12. by Lund U niversity T he predicted drive cycle proposed here is based on position measurements of the bus relativeto the route With the proposed changes in composition and charging strategy one of the buses studied can reduce the battery weight with 60 the fue consumption with 10 96 and the size of the CE with 60 96 As a part of the work with measurements on the busses some practical experience of handling the vehicles have been gained some of which are also presented in this report Acknowledgements To accomplish practical experiment and build a test platform with an onboard measuring system in the bus all sensors and computers in the installation needs support from a lot of people A special thank to Bengt Simonsson for his support with the measuring equipment and installation in the busses would also like to thank G etachew D arage and M anne Andersson for help with the installation T he drivers of the bus Ingemar Carlson and project leader Ingvar Bl ckert when testing the onboard measuring system they have been very kind and supported with the bus any timethat was requested For the test bench drive and the emission measuring of the ICE would liketo thank Petter Strand of D epartment of H eat and Power Engineering For the more theoretical part like the simulation mode construction and improvements of my writing would like to send a special thank to my advisor Professor M ats Alak la would also like to thank Karin Jo
13. it is important to know the driving cycles what kind of traffic how steep hills and how many passengers the bus is expected to carry Without such a priori knowledge the hybrid drive train is likely to be overpowered with significantly less than optimal performance in terms of emissions fue consumption and battery losses The ICE must be selected and purposefully designed with regard to average and peak power production This in turn requires a well defined charging strategy The battery size must be limited to a minimum with respect to either the charging strategy or the minimum zero emission driving distance 2 Thecharging strategy is important to minimize exhaust emissions and fuel consumption T he goal should be to supply instantaneous power to the traction and auxiliary systems but without exceeding the limit for transient emission generation with the ICE With such a goal the battery will be minimized with respect to the charging strategy 3 A prediction of the drive cycle should be taken advantage of to improve the charging strategy T his is especially feasible in a city bus route due to 100 Observations on Electric H ybrid Bus D ei gn 4 5 6 the repetitive nature of its operation e g by using information from the GPS sensor or the bus stop information system T he simulations made in this work indicate a reduction of the battery losses with more than 30 when applying prediction to one of the better charging str
14. lot of power the power is supplied by the battery and the generator If the ICE and generator are low pass filtered there will be a time delay by the ICE and generator power and the battery will supply the requested power If the power request is known in advance the ICE and generator power could be increased the seconds before the acceleration T his limits the peak power supplied by the battery e When braking or running down a steep hill the traction motors produce power for charging the battery T he power from the ICE and the generator is low pass filtered The generator will still charge the battery when braking T he charging power for the battery will be large and cause unnecessarily big losses in the battery If these power requests are known in advance the charging power to the battery could be limited to the power from thetraction motors 11 Chapte 7 Charging Strategies Speed Seconds Power to motors battery amp from generator 2 Pes o IS x o o EE M quM ae O es Xx 22 ro E NE pee 95 Alo l gt gt D ane c E UO og PE IEEE Fedha J I at 4 E rrE ra een l l o o o o eo wo wo Seconds Power to motors battery amp from generator Low pass filtered power in advance Seconds 10s Figure 7 6 Top Low pass filtered power with the time constant z
15. low floor even in the back Battery Figure 2 1 Series hybrid vehicle Parallel Hybrid The structure is the parallel hybrid is illustrated in Figure 2 2 The ICE is mechanically connected through a gearbox to the wheels so is the electric motor W hen breaking the electric motor can regenerate power to the battery One of the advantages in comparison with the series hybrid system is that all the energy from the ICE to the wheels does not have to be converted to electricity T his increases the system efficiency Another advantage is that the electrical machine does not have to be so large that it can supply all tractive power van M ierlo 1999 A drawback with the parallel hybrid is that the operating point speed and torque of the ICE cannot be chosen freely due to the mechanical connection of speed through the gearbox to the wheels T his drawback can the neglected by usng a CVT Continuously Variable T ransmission a gear box with a continuously variable gear ratio in the transmission The CVT allows the IC E to beoperated in other points in the speed torque space 8 Observations on Electric H ybrid Bus D eign A simple parallel hybrid vehicle would be an ordinary car equipped with a large electrical starte motor and a large battery Several car producers have made various constellations of this hybrid H onda Insight is the first parallel hybrid vehicle in series production with 5 speed manual gearbox 50 kW ICE and a 10 kW
16. motors there are two steps the power from the generator is AC D C converted and then D C AC converted for the traction motors T he converters are self commutated with IGBT transistor Isolated Gate Bipolar transistor or M OSFETs In the power electronics the switches work by switch frequencies between 1 and 10 kH z T he efficiency of a well designed converter is often more than 98 in most of the working area Blaabjerg 1995 16 Observations on Electric H ybrid Bus D eign 2 6 Energy Storage A hybrid vehicle uses per definition more than one energy source If one is able to store regenerated energy it is possible to improve energy efficiency and possibly emission decrease There are a number of energy storage types available with different drawbacks and advantages Some of the energy storage still needs more development and testing to be commercialised Electrochemical energy storage is the most common one T hese batteries belong to the type of storage where the energy is stored chemically T he drawback is the life cycle size and weight Flywheels could be future mechanical energy storage O ne advantage is a high peak power density 1 kW I M anson 1998 Figure 2 8 illustrates some future and present energy and power storage technologies T he X axis denotes the power density KW kg in a logarithmic scale and the Y axis shows the energy density W h kg in a logarithmic scale T he price is not included in this diagram I
17. multiplying the vehicle mass and acceleration dv F Maus a Maus nd Newton dt 5 1 The resulting force on the vehicle by constant speed will be 2 F ys 8 H friction A C g Posy 5 2 where the first term corresponds to frictions forces and the second one the aerodynamic damping T he coefficients are F N Resulting force M kg W eight of the bus g m s Gravity H friction Rolling friction coefficient A m Bus cross section area C Aerodynamic coefficient Pa kg m X Air density v m s Speed Chapter 5 M easurenents 53 The resulting force with the coefficients inserted for the N eoplan bus will be F 21050 1 46 y 5 3 In Equation 5 4 the measured force in relation to the speed and the coefficients can be seen T he equation is calculated by doing linear regression in the measured values F 600 50 v 0 62 v 5 4 The measured and theoretical results can bee seen in Figure 5 6 The practical and theoretical equations do match reasonably within the speed interval of interest but the assumption of quadratically dependent air resistance loss seems to need improvement T he manufacturer supplied with no information regarding the rolling test Force on the bus 10 Force kN Speed km h Figure 5 6 Aerodynamic and friction force during the rolling test on the N eoplan bus 54 Observations on Electric H ybrid Bus D eign 5 3 ICE in Test Bench The st
18. number of passengers T he input variable for the block is the traction force from the vehicle which in this case is the tractive force of the traction motor and the braking force from the mechanical brakes T he output variables from this block arethetraction force vehicle speed and travelled distance In the block the forces on the vehicle such as friction aerodynamics and slope are summed up together with the traction force F F HEF Friction Aero Slope F F 4 4 Traction is a constant friction and F isthe air resistance of the bus as Aero where F Friction specified in later C hapter 5 2 Acceleration is calculated through N ewton s law a Fg 2 dv 4 5 Mobuss dt T he acceleration is integrated to speed T he speed is integrated to distance Chapter 4 Simulation modd 33 v t ata gt s t voa 4 6 t 0 t 0 The new distance that is reached as well as the speed is sent back to the Control block to be used for the new reference speed and tractive force calculation T he speed is used in the block Electricmotor for calculation of the power use from the batteries and the motor losses GY Paty foes j baca digi F slope mesraluri Figure 4 3 T he mechanical level in the simulation program Electric Traction Motor T he block calculates the power needed for driving the motor the power on the motor axis and losses of the electric traction motor The efficiency of an electrical mac
19. stay out of service for an unusually long time When the vehicle is not in use some other complications does also appear like the battery becoming discharged A larger fleet with special vehicles like hybrid and electric buses would be preferable to collect in one place compared to have them spread out at many placesin Sweden 9 2 Drive and Control System It is very important that the vehicle control system limits the number of warning messages for the driver Too many warning lamps and alarms may cause the driver to reduce attention to them The bus must not lose tractive power control when a side cover is indicating opened These alarm limits 96 Observations on Electric H ybrid Bus D eign Should be very carefully chosen and if possible diverted from the driver to the workshop At nioke ane WS e NS Compressor Turbo 12V Generator Figure 9 1 The back of theN eoplan bus showing the complexity of a hybrid System The complexity has to be watched carefully H aving too many computer Systems talking to each other depending on too many sensors is a dangerous solution O ne of the buses was not able to run on batteries at all when one of ten temperature sensors in the battery was short circuited A cold day when the bus was parked outside during the night the battery signalled too low temperature T he consequence was that the bus was not able to run on battery The cooling fan kept pumping cold air from t
20. to DC DC converter 3 0 ICE off ICE on gt a 2 5 a I 1 i i a fl Il 2 0 lly i i i 4 g n LI T l al 1 LL Lui E CREE T yyl LL 1 0 i F H W EOM e i f 05 li HH 1 420 430 440 450 460 470 480 490 500 Seconds Figure 4 7 TheD C D C auxiliary power consumption on the N eoplan bus In the Scania bus there are only electric motors supplying the servo pump and the air compressor T hese motors consume on average 0 6 and 1 0 kW during a normal driving cycle T he servo pump is depending on how much turning the driver does and the air compressor loads the system continuously The other auxiliary system components lights fans etc consume about 1 5 kW This makes a total consumption of 3 1 kW in the auxiliary system of the Scania bus In the simulation mode the auxiliary power is modeled as an average power consumption that loads the electric system In the future the simulation model has to be further developed in order to achieve a better accuracy T his also requires more sophisticated measurements of the auxiliary power consumers Chapter 5 Measurements To calibrate the simulation model with measurements from the bus under real conditions it is necessary to have a measurement system on the bus T he data from the measuring system is the reference and mean of calibration for the simulation mode If there is anything wrong or missing in this data
21. 0 35 40 51 2 on off 6 2 02 15 24 24 1 31 93 88 3 1 6 2 33 79 24 24 0 22 40 32 4 3 6 233 76 25 24 0 31 62 40 5 10 6 2 37 61 25 26 0 52 68 51 6 100 6 2 47 33 25 37 0 73 61 70 7 oo 6 244 15 23 48 0 76 51 72 8 oo 2 1 95 15 24 17 0 76 51 72 9 10 A 2 22 61 24 22 0 52 68 51 10 10 3 2 16 60 23 24 0 52 68 51 11 10p 6 2 32 60 24 26 0 35 56 40 12 100p 6 2 47 26 23 41 0 70 56 75 13 10p 3 2 04 57 23 22 0 35 53 68 Comments to the results of the simulations by number 1 The original charging strategy of the N eoplan buss The ICE supports with most of the dynamic power In the model there is no transient operation compensation that would have made the emissions from the ICE larger 2 With the on off charging strategy the battery has to take care of all the tractive power parts of the time T his gives relatively high battery losses but a good fuel economy since the ICE runs only at high efficiency An additional problem is that long intermittence may cause the catalytic converter to go out with correspondingly high emissions in the beginning of the next start 80 Observations on Electric H ybrid Bus D eign 3 7 Low pass filtered power from the ICE T he low pass filter time constant T should be small from the battery losses point of view but not too small as the ICE will gradually create transient emissions as the time constant gets shorter T he limit where the ICE starts causin
22. 8 European Conference on Power Electronics and Applications Lausanne Switzerland Stridsberg L 1998 Dual electric motor hybrid power train Electric Vehicle Symposium 15 Brussels Belgium Westerholm M Research Scientist responsible for the Cummins ICE measurements Department of Engine Technology and Energy in Transportation Technical Research Centre V TT of Finland June 2000 Marten Westerholu vtt fi 104 Observations on Electric H ybrid Bus D eign Wiegerman H L N 1998 Fundamental analysis of a battery state regulation technique based on terminal voltage IEEE SAE ALAA 17 Dig Avion Sys Con Seattle WA USA Appendix A The MagnetM otor charging strategy The measurements on the N eoplan bus were performed during an 8 hour shift in traffic between the central station of Malmo and the exhibition by the Oresund bridge Under these tours the power from the generator the fuel consumption and speed of the ICE were measured T hetorque power to ICE and efficiency of the generator and the ICE can be calculated in all these points Thenumber of operating points visited by the ICE with a certain rpm and torque can be seen in figure A 1 As expected the highest peaks are by idling with zero torque T hese peaks are set to zero to see the others that are more interesting T hereis also an apparent ridge of small peaks by 700 rpm that goes high up in the torque register the generator causes this when it st
23. 997 Provmetoder och emissioner vid anv ndningen av alternativa drivmedel KFB Meddelande 1997 24 Sweden Einewall P 2000 Ezirsionsm tning Konst Vetenskap eller hokus pokus department of Heat and Power Engineering Lund University Sweden Hauck B Altimeier J 1998 Test and evaluation of the battery management system with the two wire bus E ctric Vehicle Symposium 15 Brussels Belgium Hellman K Peralta M and Piotrowski G 1998 Evaluation of a Toyota Prius hybrid system EPA420 R 98 006 USA Insightcentral Honda Insight technical description 2001 01 06 http www insightcentral net Hellsing J 1998 Design and Optimization of a Permanent Magnet Motor for a Hybrid Electric Vehicle Lic Thesis Department of Electric Power Engineering Chalmers University of Technology Gothenburg Sweden Hemmingsson M 1999 A Powerflow Control Strategy to Minimize Energy Losses in Hybrid Electric Vehicles Lic Thesis Department of Industrial Electrical Engineering and Automation Lund University Sweden HEV Team 2000 Energy Storage http www engineering sdsu edu hev energy html Department of Mechanical Engineering San Diego State University USA Heywood J B 1988 Internal Combustion ICE Fundamentals 24 edition Singapore Johansson B 2001 Forbranningsmotorer 2001 1 department of Heat and Power Engineering Lund University Sweden Kimura A Abe T Sasaki S 1999 Drive
24. By the time the beginning of the project the Advisor program Advisor was not availably Thus we conclude that we need to build up our own simulation platform to be able to make necessary additions because there is also pedagogic advantages with building a unique simulation model For all simulation programs a lot of parameters are requested like efficiency consumption and emissions T he manufacturer of the components in a particular vehicle could supply these parameters but often the manufacturers are not willing to supply key parameters like the efficiency of ther product It is also required to have a good knowledge about the components in the vehicle as well as the driving cycle T his has been obtained in this work by measurements on the hybrid bus both on the bus in traffic and directly on some of its components 1 2 Main Results The authors main contribution with the work presented in this thesis is e A simulation program for a HEB Hybrid Electric Bus verified via measurements taking all major power conversion processes into account modelling efficiency and emissions given a particular drives cycle and vehicle specification e A predictive charging strategy that utilizes the repetitive nature of a bus route to predict the power need and thus allow a smoother use of the IC E e A method TES for determination of the transient limit expressed as a bandwidth within which the ICE performance can be regarded as stationary
25. E exhaust temperatures The temperatures right before and after the catalyst in Figure 5 4 are within the operating range for the catalyst according to correspondence with Cummins Laing 1999 T helow temperature after the catalyst indicates that it is probably not working properly since the combustion within the catalyst is expected to be exothermic Some weeks after these measurements were done the catalyst broke down and was dismounted The lambda sensor With attached electronic equipment with a very fast responding time 10 ms is mounted on the ICE The sensor has been installed by the exhaust outlet to measure the ratio between fuel and air W ith a fast responding high band with lambda sensor it is possible to measure during transients i e when the CE changes working points T hefuel air ratio is important for the emissions from the ICE T he lambda sensor comes from ETAS Chapter 5 M easurenents 51 The fuel flow sensor for the fuel consumption comes from BRON KH ORST H I TEC The sensor measures the massflow of natural gas T he working range is between 0 36 kg h T he measurement principle is thermal T he sensor are neither sensitive to vibrations nor do they need long straight pipes The response time is below 1 second Figure 5 5 T he massflow sensor for natural gas Pressures in different locations are also measured T he differential pressure over the catalytic converter is recorded O ne reason for this is t
26. ICE runs in transient operation the emissions will increase T hus it is important to know the transient properties of an ICE when designing a hybrid traction system In Chapter 8 a new test procedure to measure the transient behaviours proposed here in this thesis for the first time will be tested on an ICE in atest bench The test procedure gives a hint of how fast it is possible to move between different operation points In a hybrid vehicle the ICE is not the only tractive power source like in an ordinary vehicle and power transients from the ICE can be avoided In order to simulate the time varying behaviour of the hybrid vehicle it is obvious that the ICE has to be properly represented in the modd An ICE in practical use may differ from the one in the test bench the IC E emission depends on many other things like the temperature the flame speed in the combustion and the air fuel ratio Even in atest bench it is very difficult to measure the same emissions by the same working point two days in a row 14 Observations on Electric H ybrid Bus D eign The most important reason for these behaviors is the Lambda variations The Lambda alters between 0 97 and 1 03 with the average value 1 00 and when Lambda differs too much from 1 00 the emissions will increase fast Another reason is also temperature variation in the combustion chamber and in the catalytic converter 2 4 Electrical Machines M ost of the electrical machines used in hybrid ve
27. Observations on Electric Hybrid Bus Design Christian Andersson Licentiate Thesis Department of Industrial Electrical Engineering and Automation D epartment of Industrial Electrical Engineering and Automation Lund Institute of T echnology Lund University P O Box 118 SE 221 00 LUND SWEDEN www iea Ith se ISBN 91 88934 18 7 CODEN LUTED X T EIE 1026 1 117 2001 Christian Andersson Printed in Sweden by U niversitetstryckeriet Lund U niversity Lund 2001 Abstract The work presented here deals with evaluation and optimisation of the tractive system in hybrid electric buses The work is based on analytical simulation models that are verified via measurements The main results of the work are e An optimised composition of the traction system topology regarding the size of the different components in the drive train with respect to the performance and emission at a given drive cycle e A charging strategy taking into account a predicted drive cycle the SOC of the batteries and the instantaneous tractive power e A transient emission measurement T ES method for Internal Combustion Engines The simulation mode concerns all the major power flow vehicle speed temperatures and Internal Combustion Engine ICE parameters of the busses The model is verified through measurements on two hybrid buses in M alm and Stockholm T he ICE models are verified through test bench driving both by an external partner and
28. ampling The ICE measurements are done together with the Department of H eat and Power Engineering Division of Combustion Engineering Fast throttle movements are performed and a special technique for sampling the emission is applied T he ICE used to test this TES method is a 2 3 SAAB ICE the same as in the Scania hybrid bus 8 1 Method The idea with TES is to measure transient emissions with standard emission measurement equipment used for stationary measurements This does not request use of fast responding equipment that is expensive and does not have the same performance 82 Observations on Electric H ybrid Bus D eign The TES method is applied to an ordinary ICE The ICE is mounted in a test bench with additional measurement equipment T he test bench s brake is speed controlled and the ICE is torque controlled The ICE is forced by controlling the speed and torque to continuously change operating point by changing the torque and speed references A repeated behaviour is possible to achieve and in a controlled manner repeatedly excite transient operation Figure 8 1 illustrates how the speed and torque changes Emissions from a certain selected part torque and speed of the transient operation can be sampled by a valve on the exhaust pipe T he valve is opened intermittently in a specific time interval These samples can be gathered for analysis with conventional instruments in a stationary manner T A Valve clo
29. arts to deliver power 106 Observations on Electric H ybrid Bus D ei gn weet Drive points 400 2500 Torque Nm Figure A 1 ICE driving points on the N eoplan bus during one day ThelCE have visited these operating points more than 25 times during 8 hours This is a normal driving point for the ICE All efficiencies by a certain rpm and toque are summarized and an average efficiency values are calculated In figure A 2 the efficiency of the most frequent visited working points are plotted T he efficiency increases as more torque is requested from the ICE W hen the torque is high the efficiency over the ICE and the generator is the highest Appendix A 107 Torque Nm 0 0 Figure A 2 ICE efficiency on theN eoplan bus during one day Appendix B User Manual This is a description of the user manual for the simulation program It is a manual that a person with some computer experience and only little knowledge about M atlab Simulink can handle It could also be interesting to have a description of the simulation program on another leve where modification of the software and more advanced use can be executed This more complicated use has been described in some way in the thesis H ere the purpose is to present a quick introduction into the use of the simulation program Instructions e Start the M atlab program on the computer e Go to the directory where the file 3mulate is placed
30. ategies The transient emission limit expressed as a bandwidth needs to be determined for a particular ICE before implementing the charging strategy M ethods for determination of this limit like the TES method discussed here needs to be developed and applied The error message handling must be made to minimize the number of error situations that disturb the driver or cause the vehicle to cease operation The less important error messages should be available to the workshop personnel only The job to bea driver of a hybrid bus should be given a positive image it Should be regarded as an honour to be picked as a driver of test vehicles like the ones used in this project If such an image is obtained and the driver is properly educated the number of undesired stops due to technical problems is reduced due to the driver s higher willingness and ability to solve problems on the spot Proposals for Future Work Based on the work presented in this report some particular suggestions for additional effort within thefield of hybrid buses are recommended 1 Equip a hybrid bus with a drive line according to the results in this work i e a considerably smaller engine and battery pack of course including the proposed charging strategy Implementation of the proposed route predictive charging strategy in a hybrid bus Further development of the TES method as presented in this report In particular testing different types of ICE s wi
31. ationary characteristics of the ICE s used in two dimension look up tables in the simulation program are based on measurements from test bench driving Torque Nm and speed RPM is used as the in parameter and for example N O x emission g kW h as out parameter T he bench testing gives a good knowledge about how the ICE works in stationary operation but is not valid when the ICE moves too fast in torque or speed T ransient operation is evaluated in C hapter 8 Cummins ICE The Cummins ICE in the N eoplan bus has been run in a test bench by VTT the Technical Research Centre of Finland Westerholm 2000 All regulated emissions particles and some other unregulated emissions have been measured and some results are shown in Figure 5 7 T hese measurements are also used for simulation model calibration Chapter 5 M easurenents 55 NOx emissions HC emissions tA 4 NOXx g kWh HC g kWh So m o a e e a e 2500 2500 2000 A0 1500 200 1000 2000 1500 1000 Speed rpm Torque Nm Speed rpm Torque Nm CO2 emissions CO emissions 000000 D UA AEAN KX CO2 g kWh CO g kWh o o D s x a e eo 2500 2500 2000 2000 1500 1000 200 1500 1000 Speed rpm Torque Nm Speed rpm Torque Nm Figure 5 7 The emissions from the C ummins natural gas ICE Saab ICE The regulated emissions the CO and the efficiency have been measur
32. be avoided The strategy presented below is as simple as effective in limiting the dynamic operation requirements for the ICE T he proposed charging strategy used in the simulation model sets the C E power P as a low pass filtered sum of the tractive power Psa and a proportion of the state of charge error SOC SOC This gives the required ICE power dP _ Practve K SOC SOC P 7 1 dt T ice T is the low pass filter time constant for the ICE The emissions are strongly depending on the selection of z A small z entails a quick change of the ICE operation point and vice versa T he simulations have been made with T equal 1 3 10 100 and ee seconds At a choice of z 1 second the analysis must be made with the reservation that transient effects of the ICE operation are not fully represented The choice of z also affects the minimum battery size needed Smaller battery capacity of course means a lighter battery but the ability to run in an emission free zone will also be reduced It should be observed that the SOC varies very little during the driving cycle no matter which cycle is used T his implies that the present battery size in both the tested buses is too large for hybrid operation but it may still be needed for pure electric operation eg in emission free zones T he distance could be reduced from 15 km to a couple of km for example 5 km T he central part of a city is usually not so large T he battery
33. be the same type of machine Electrical machines differ in behaviour from ICE in many ways Electrical machines have generally good efficiency and can be overloaded for a short time when high power is needed The ICE has a maximum torque by a certain speed while an electric machine has a constant torque during from zero speed to a certain maximum after which it drops as the inverse of the speed increase This makes that an electrical driven vehicle feels stronger at low speeds T he torque density of an electrical machine is high it can reach levels like 30 N m kg Anpalahan 2001 In comparison an ICE torque density is limited to 2 N m kg H eywood 1988 Chapter 2 H ybrid vehicles 15 The Figure 2 7 shows the principal construction of a conventional induction and an outer rotor synchronous machine Stator Rotor Sator Rotor Shafi 4 1 Hearings Diearinas earings Winding Figure 2 7 Induction and synchronous machine 2 5 Power Electronics To connect an AC machine to a traction battery the traction battery voltage has to be connected to some kind of power converter for conversion to AC In some applications the power flows only in one direction for example from the generator to the DC system In other application eg the traction motor where the power flows in both directions more sophisticated power electronics is needed When power goes from the generator to the traction
34. cceleration is 2 14 m s The maximum speed is 58 2 km h and the average speed is 22 4 km h T he driving distance is 10 8 km Chapte 6 Driving Cycles 61 The Braunschweig cycle 60 Speed km h nS C2 AB ol eo eo e eo eo l 0 0 200 400 600 800 1000 1200 1400 1600 1800 Time s Figure 6 2 Speed asa function of time during the Braunschweig cycle 6 2 Local Cycles The Malmo cycle is a randomly selected recording of the bus velocity going from the town centre to an exhibition site at the Oresund bridge at the outskirts of M alm T he cycleis depicted in Figure 6 3 It is not as demanding as the Braunschweig cycle partly reflecting that M alm is a relatively flat city The maximum speed is 49 7 km h the average speed is 20 9 km h and the cycle is 10 5 km long T he maximum acceleration is 1 36 m s It is important to note that when using a standard driving cycle like the Braunschweig City D riving Cycle this will impose too high demands on acceleration on the H EV specified T his result in an overpowered vehicle not able to run near optimal operation with respect to fuel consumption exhaust emissions etc 62 Observations on Electric H ybrid Bus D eign The Malm cycle o o Speed km h D w A ol e eo eo eo eo T 0 1j 1 1 1 1 1 1 0 200 400 600 800 1000 1200 1400 1600 1800 Time s Figure 6 3 Speed as a function of time during the M almo cycle The Stockhol
35. commercial state of development 9 3 Views on the Driver of the Neoplan Hybrid bus The driver of a special vehicle should not be randomly selected among hundreds of drivers It is important that the driver will get a special education and information about the vehicle that he is appointed to drive When a new driver comes to a new vehicle and is not used to the vehicle and some small failure appears some lamp flashing he is not prepared to solve this kind of problem The driver immediately calls for another bus These kinds of situations do not appear as often when the driver is used to the vehicle and has some experience to handle the particular problems related to hybrid buses T he drivers are generally negative to changes compared to their ordinary bus For example some drivers had opinions about the steering wheel and the brake pedal both being too heavy to operate compared to other buses Some had opinions about the place to hang the jacket T hese things can many times be easil y adjusted or changed It is a pity that such small things could affect the general impression of a hybrid buses 9 4 Views on the Driver of the Neoplan Electric bus In U ppsala there are 12 electric busses that also were a part of the project from the beginning N o data collection from these buses has yet been made The drivers of the electric bus were not randomly selected they were purposefully selected Among the drivers it was seen as a privilege to drive
36. cs and consider an adequate description of the vehicle s mechanic electrical and ICE dynamics efficiency and emissions The mode does not consider things like temperature in the passenger compartment or the number of passengers Actually no difference was observed in the measurements between driving a bus filled with passengers and 28 Observations on Electric H ybrid Bus D eign an empty bus One of the reasons to this is that the bus itself is so heavy that the passengers weight does not significantly change the tractive work Another reason is the relation between aerodynamic and friction forces and of course the altitude variation 4 1 Introduction to the Program model D ifferent platforms for programming were evaluated and complete programs for vehicle simulation were evaluated van den Bussche 1998 In some programs it was difficult to make modifications in the simulation program e g with the simulation program Advisor Advisor and was not availably by the beginning of the project Other programs were too expensive N edungadi 1997 M atlab Simulink was chosen as the platform for this simulation model Matlab is well known in the scientific world and has already been used for many hybrid and electric vehicle simulations The hybrid bus is modularly designed in Simulink and fed with input values via M atlab T he simulation program is after calibration by extensive measurements used for structural sensitivity analysis and
37. described as a basis for later simulation model creation 6 Observations on Electric H ybrid Bus D eign 2 1 Introduction The aim with a hybrid drive system is to run the ICE either at the best possible efficiency or at minimum emissions or a combination of both while maintaining the desired vehicle performance This goal can partly be reached already at the design phase by a proper choice of ICE type and size electrical machines type and size battery type and size and charging strategy The charging strategy is the strategy with which the instantaneous ICE power is selected in relation to the driver s power request and the battery SOC State of Charge deviation The size of the ICE is crucial since an oversized ICE means that it will probably run most of the time at too low efficiency This is particularly important for a city bus since it runs and stops frequently and parts of the kinetic energy can be recovered to the battery when it brakes A too large battery pack and ICE will make the bus heavy and expensive while too small traction motors will make the performance too low It is thus important to find the right combination of the different components In a hybrid vehicle the ICE with its fuelling system is the only prime source of energy Night charging is not an alternative when the bus runs a whole day for more then 10 hours T here are lots of possibilities to combine the ICE battery and electrical machines in a drivetra
38. e in some cells and under voltage in others T here are more advanced BM S systems that actively bypass the charging current from the over charged cells In this project the BM S of one of the buses has indicated out of range temperature or voltage in a battery cell block with the consequence that the bus did not move from the place In that situation the question appears how should a BM S system be implemented in a vehicle Chapter 2 H ybrid vehicles 19 2 7 Accessories In any vehicle and certainly in a H EB there are a number of systems that consume energy apart from the traction system Examples of such systems are air conditioning breaking steering and lights Other such systems that are more specific to buses are the opening of doors and lowering of the bus at a bus stop T hese systems could be electric hydraulic or pneumatic T hese different energy forms can be accomplished even when operating the system inn pure electric mode on the battery Since most systems on board a bus are inherited from conventional buses and thus made to be driven by the ICE there is often a dual supply system One example is the air pressure for opening doors etc that is made with a compressor The compressor can either be mechanically coupled to the ICE when the ICE is in operation or driven by a separate electric motor when the ICE isturned off This kind of constellation naturally increases the complexity In an electric hybrid vehicle it would b
39. e preferable to have as many of the accessory systems as possible electric only That would minimize the complexity the cost and often the losses since eg an electrically driven compressor can be a variable speed drive which is favourable from an efficiency point of view 2 8 Driver T he drivers behaviour with respect to driving the bus is naturally a complicated function of very many parameters like traffic density possible delays relative to schedule time of the day state of health passenger behaviour ec that is very hard to model correctly It is thus necessary to use a simplified model in the simulation work described later T hereis an advantage though with a simplified model that the mode will be repeatable which is very important when comparing different technical arrangements A particular note must be made regarding the drivers behaviour After having done numerous measurements on the H EB s in the work with this report it is dear that the accelerator is used in mostly the same way by most of the drivers The accelerator is basically operated in three levels full way down half way and not at all When the bus starts and accelerates the driver pushes the accelerator to the bottom until the bus reaches the desired speed 50 km h and then releases the accelerator to halfway to continue at the same speed or just leave the bus rolling When the driver breaks for a stop he doesn t push the accelerator at all Chapter 3 Case S
40. ed on the Saab ICE of the Scania bus The department of H eat and Power Engineering together with the department of Industrial Electrical Engineering and Automation at the Lund University madethe tests Both gasoline and E85 85 96 ethanol have been used as fuel for the ICE during the bench testing with corresponding adjustment of the fue injection system All these measurements are performed in 46 working points before and after the catalyst Only stationary measurenents were made on the SAAB engine The analysis and detection of CO and CO are made with an infrared instrument 56 Observations on Electric H ybrid Bus D eign called N DIR HC was analysed with a flame ionisation detector FID and NOx was analysed with a chemo luminescence instrument CL Einewall 2000 NOx emissions HC emissions 0 3 z z 0 2 E Bh x U Z z01 0 200 200 0 2000 Torque Nm 0 1500 Speed rpm Torque Nm 1500 Speed rpm CO2 emissions CO emissions 2000 4 m z 1500 N z SONDA WA 1000 x2 BR ANNIN 500 O1 NN IN 0 0 N 200 200 4000 4000 3500 i 3500 3000 3000 2500 2500 0 2000 0 2000 Torque Nm 1500 Speed rpm Torque Nm 1500 Speed rpm Figure 5 8 The emissions from the Saab ICE with gasoline measured after the 3 way Catalyst Chapter 5 M easurenents 57 NOx HC emissions S a 0 3 E 3 A LE Sod SSS 02 SSS E x 20 2 g o 5 o9 T 0 0 200 200 4000 Torque Nm 0 1500
41. ed by 50 Both the generator and the battery supply the traction motor with power at peak load when the ICE is on ThelCE produces a power of 35 kW or 50 kW when running The generator is consequently charging the battery when the tractive power is less than 35 kW or 50 kW respectively The ICE operates at two different speeds 2500 rpm and 3500 rpm with constant torque T he speed of thel CE goes down to 2500 rpm when the speed of the vehicle is below 8 km h and increases to 3500 rpm when the vehicle speed exceeds 8 km h as illustrated in Figure 7 3 This reduces the noise emissions from the ICE at the bus stops This charging strategy needs a large battery as the battery has to take care of all the tractive power variations of the traction motor With this charging strategy recharging by the traction motors is not allowed The reason is that too much power would charge the battery when the generator delivers 50 kW and the traction motors generate 90 kW If the ICE had been controlled in another way or turned off by the braking then regeneration would be possible This charging strategy makes the gasoline consumption rather high In a normal city cycle the average gasoline consumption is 0 6 kg km Observations on Electric H ybrid Bus D eign 10 Speed 700 710 690 640 650 660 670 630 seconds Power from generator to battery amp drive motor Generator Battery MA 650 660 670 640
42. electric motor Insightcentral EREA Electric Motor Generator Battery Figure 2 2 Parallel hybrid vehicle Pow er Split Hybrid It is possible to combine the advantages of paralle and series hybrid vehicle Stridsberg 1998 or by using a planetary gearbox Kimura 1999 as illustrated in Figure 2 3 Such a constellation uses two electrical machines and one CE in connection to a planetary gearbox Battery Electric Machine 2 ca Figure 2 3 Complex hybrid vehicle Chapter 2 H ybrid vehicles 9 In the complex power split hybrids the ICE is connected to the planet carrier wheel see Figure 2 4 The output axis is connected to the ring wheel The electrical machines are connected to the solar wheel as well as the ring wheel Both electrical machines are connected via separate power electronics to the battery If the components in the drive train are well designed this technique allows the ICE to operate at optimal torque and speed for best efficiency Only at one specific speed all the power from the ICE goes directly to the wheels and it acts like a parallel hybrid In all other cases it acts more or less like the series hybrid The choice of configuration depends on what performance the vehicle is designed for and which complexity that is desired for the drivetrain T he first passenger car in series production with this type of gearbox was Toyota Prius with a
43. em ccseeseeseeeeee eee een 41 5 Measurements 43 5 1 Onboard System coiere et rA DROP ERE HE Ub 43 52 Phe Rolling T6st ete et occi ote Melee lead ate n te tee edo 52 5 3 ICE test bench i esci Eo ER ERE RAD EULQ Ae E ena 54 10 11 Driving Cycles 6 1 Standard Cycles r RD 6 2 Locabcycles iue rr tette tete reste snes Charging Strategies 7 1 Present Charging Strategies for the Neoplan bus 7 2 Present Charging Strategies for the Scania Bus 7 5 Alternative Charging Strategies esses Transient Emission Sampling TES Si Methodazsii eee bike aa prpiuR De RP Drei 8 22 Implementation sssssseeee 8 5 Results seit ot lans eoe isto adeo ut osse ect da eden Experience of the Vehicles 9 1 Ir Genetal ic costae eise i eic 9 2 Drive and Control System esses 9 5 Driver Aspects of Neoplan Hybrid bus 9 4 Driver of Neoplan Electric bus esses Conclusion and future work References Appendix A The MM charging strategy Appendix B User manual THSEUCTIONSE 0 ceci does cube Dark uci oua eas Result of the simulation program sse vi Chapter 1 Introduction 1 1 Background Electric traction of vehicles is an old technique and has been used for example 1894 in an electric train Electrical motors have higher torque density than an ICE internal combustion engine and thus the electrical traction system can have a more compact design than the ICE counte
44. ening is 20 and 30 km h respectively in case and II T his means that the tractive force is limited to the maximum that the traction motors can provide up to 20 and 30 km h and the tractive power is limited above this speed with correspondingly reduced tractive force The maximum braking force is always higher than the maximum force the traction motor can provide W hen braking the traction motors are first used to 32 Observations on Electric H ybrid Bus D eign regenerate energy to the battery and the mechanical brakes are engaged in case higher braking force is needed Control of the ICE power corresponds to controlling the power from the generator which supplies the traction motor with power and charges the battery T he generator power is selected based upon the instantaneous tractive power and the present SOC in the battery but the exact charging strategy varies between the buses and is discussed in detail in chapter 7 As an example the present charging strategy of the N eoplan bus can be is seen in Equation 4 3 P C P C harge speed 5 15km h Pprivemotor 12 kW 4 3 harge speed lt 15km h 0 kw To conclude the control block provides the tractive force for mechanical propulsion of the vehicle and the power request from the hybrid generator Mechanical Dynamics In the simulation block called mech dynamics all the mechanical forces in the vehicle are summed up T here is no compensation for wind speed or
45. es it possible to see how the ratio between air and fuel changes when throttle movements are performed W hen lambda differs from 1 for a long time emissions will increase a lot after the 3 way catalyst Example The ICE tries to control the air fuel ratio to an average value in this case 1 for the 3 way catalyst T he operation is performed as a limit cycle around the stochiometric air fuel ratio 1 0 T he lambda value air fuel is lean over 1 0 and the ICE makes lambda richer goes down until it reaches a certain level 0 97 The ICE changes strategy and starts to make the lambda leaner goes up until it reaches a certain level 1 03 T hisis repeated aslong as the ICE applies lambda control and will make the lambda average value to 1 It is important that the average lambda is 1 00 but not that important that the actual value is exactly 1 00 Chapter 8 Transient Emission Sampling T ES 85 e kh RE r i B ag i i Ro es A tas i Emission measure Y Y NDIR Speed Throttle Torque Lambda Magnet measure servo control measure valve HFID GCMS CLA Figure 8 2 TES major equipment for emission sampling N DIR infrared analysis instrument detection of CO and CO H FID flame ionisation detector for HC GCM S gas chronograph and mass spectrometer for emissions detection CLA chemiluminescence instrument for detection of NO
46. esult the power is just put away as heat and could be better utilized for charging the battery Example The wheel motors deliver 40 kW when braking T he battery was charged with 10 kW the seconds before and has the state of charge of 90 The power for the battery islow 10 15 kW and 25 30 kW goes to the brake resistor T his is of course not energy efficient A better way to handle this problem with overcharged battery would be to charge the battery with the generator power only up to SOC 70 or 75 96 and Chapte 7 Charging Strategies 67 then stop charging When the bus is breaking the battery will have a better chance to absorb all the power that the motors generate To verify the simulation model for the N eoplan bus the simulation result is plotted in Figure 7 2 under the measured energy flow There are obvious similarities between the experimental data and the simulation Still there are some minor differences that can be explained by local winds vehicle turns and small height variations that influence the vehicle behaviour and energy consumption To get a better verification of the energy consumption the fue consumption is integrated during a measured cycle Verification is then possible between the simulated and the measured integrated values of the cycle 68 Observations on Electric H ybrid Bus D eign Speed amp accelerator 695 700 705 710 715 720 725 730 735 740 745 Seconds Power to motors brakeres
47. evaluation of charging strategy improvements 4 2 User Interface of the Program The modules in the simulated vehicle constitute of batteries ICE generator electric motor power electronics control block etc M echanical dynamics such as aerodynamics and rolling resistance components are modelled All the components have been chosen to imitate the real bus and its conditions as good as possible T he electrical machines are modelled with look up tables with current and voltage and efficiency as output parameter The battery mode includes a temperature depending resistance In the simulation mode the auxiliary load is considered a constant power The user defined parameter that can be specified in the simulation model is Choice of bus D riving cycle Charging strategy Size of the certain components Chapter 4 Simulation modd 29 T he choice of a special bus defines the default value of ICE battery and electric drive motor T hese default parameters can then be scaled by reducing the number of cylinders cells or using a scale factor i 1 H a AI n LE h 11 At i T sz i M ai AM ch tg E d Li Xi 4n Be pma uno Tirsa je tabact Bus s Pis a a e Engrs jv L x rur ioci i v Nemak wadin Ba rpea ce o Gpp i E Frei Figure 4 1 U ser interface of the hybrid bus simulation program ThelCE simulation mode includes all regulated emissions HC CO and N O x aswell as the fuel c
48. force control of a parallel series hybrid system JSAE Review 20 337 341 Japan Chapter 10 References 103 Laing B M 1999 Referring to e mail correspondence with Mr Laing in December 1999 Bob M Laing Cummins com Malmquist A 1999 Analysis of a Gas Turbine Driven Hybrid Drive System for Heavy Vehicles Ph D Thesis Department of Electric Power Systems Royal Institute of Technology KTH Stockholm Sweden Mason P Howe D H Mellor P Y Wu Z Allen T Atallah K 1998 A Flywheel peak power buffer for electric vehicle Electric Vehicle Symposium 15 Brussels Belgium Meyer A Gorman M Callaghan V 1998 Fuel Cell Systems Development for Automobiles and Commercial Vehicles Electric Vehicle Symposium 15 Brussels Belgtum van Mietlo J 1999 Simulation of a complex parallel series hybrid drive train Electric Vehicle Symposium 16 Beijing China Nedungadi A 1997 A Hybrid Electric Vehicle Modeling and Simulation Toolbox proceedings of Electric Vehicle Symposium 14 Orlando Florida USA Thisdale P 2000 BATTERIES Plug into the future Official Electric Vehicle Symposium 17 magazine Montreal Canada T rngren S 1998 A Study on Modelling and Optimising the Power Train of a Fuel Cell Bus Volvo and Chalmers University of technology Gothenburg Sweden Sutanto D Chan H L and Fok C C 1999 Battery Model for Use in Electric Vehicles and Battery Storage System
49. g transient emissions is somewhere between 3 and 10 seconds T hese are the reasons why 4 10 seconds is selected ice 78 When c the ICE will run on an average power during the whole drive cycle T his power is relatively low and it is thus possibleto reduce the ICE size ThelCE has higher efficiency if the whole torque register of the ICE is used Cutting off cylinders will reduce the ICE size but retain the torque speed characteristics per cylinder W hen only 15 kW is needed a 2 cylinder ICE is sufficient The fuel economy will be good but the battery losses will be large since the battery will take care of the tractive power dynamics 9 10 In this case the ICE power request is not constant but slowly varying and without the high peaks like in example 1 and 2 With the lower power requests from the ICE a smaller ICE can be used see 7 8 In this case the number of cylinders is reduced from 6 to 4 and 3 T his also changes the fuel economy and the emissions 11 13 The last three simulations marked with p are simulated with the predicted cycle The lower battery losses are of special interest in these simulations When the battery does not need to exchange so much energy the overall efficiency is increased Concluding Remarks T he different charging strategies presented in this section are simple in nature and can all be implemented as software changes T he only exception from this rule is the predictive cycle that w
50. gnition is turned off during the night the data acquisition system goes into a sleeping mode Data Acquisition Program The program used for data acquisition is called LabView LabView is a graphical program language for collecting data viewing data and controlling instruments From the beginning it was made for the M acintosh computers and later on ported to the PC platform It is a user friendly environment which a person without large programming experience can use T here are advantages and drawbacks with a graphical user interface compared with text based systems O ne example is when the program grows too big and then it is hard to get a good overview of the program If the LabView program environment is used for viewing collected data the program is very user friendly and allows simple ways of viewing data In the project it has been found that the computations inside the LabView programme in the on board measurement system should be Chapter 5 M easurenents 45 minimized due to the complexity of the data handling of the program environment It is recommendable to store the data on disk as fast as possible without making too many calculations In the subsystem on the highest level of the program all sensor signals are sampled as primary variables T hey are scaled by the D AQ system and sampled with 5 H z During 60 seconds a number of 5 x 60 300 values per variable are stored in the variable Lager see Figure 5 2 46
51. hat in the previous bus a fire started in the back of the bus and a stop in the exhaust pipe by the catalyst was suspected to be the cause The intake pressure is also measured since it is directly linked to the torque of thelCE Other sensors like speed sensors position sensors and a GPS unit are also installed in the bus T he speed sensors get pulses from the internal bus system and convert to a dc voltage which is recorded by the data acquisition system The position sensors are used to get the positions for the throttle and the accelerator pedal of the driver A GPS unit was also installed to log the speed position and the altitude variation this sensor however was too slow and could only be used for calibration of the speed sensor 52 Observations on Electric H ybrid Bus D eign 5 2 The Rolling Test To get the forces on the vehicle when driving at a constant speed no acceleration rolling tests are done T he air and friction forces are speed mass and air density dependent Therolling test is performed like this e The bus accelerates to 70 km h on a long flat road After that the traction motor is turned off e Rolling with the vehicle begins with all brakes released while the speed is logged e Thevehicleis rolling until it stops e Thesame procedure is done from the other direction Some calculations now need to be done The acceleration is calculated through the speed Newton s law calculates the force by
52. he outside which works very good during all seasons but winter T he result of this was that the bus could not run on battery that day If theair during the cold season instead were taken from the passenger compartment this problem would not appear T he different parts used in hybrid vehicle construction must be of the right size and made for the use in the certain application In the ICE case it is neither good to use a too big ICE which can deliver the power for long time without service nor use a small car ICE of theright size but not constructed for this kind of use A small car engine that is used in a hybrid bus is designed to Chapter 9 Experience of the Vehicles 97 run with peak power for a short time under acceleration in a car and then run with reduced power for a longer time It is also designed to run 15 20 000 km between the services D uring one day a hybrid bus will run 12 hours or 12h x 20km h 240 km consuming approximately 6 times as much fue as a small car T his will be equivalent to run the ICE 6 x 240km 1440 km T his means that the ICE during two weeks in the hybrid bus will run as much as it would do in a small car during one year T he ICE bearings valves and other moving parts will be worn out in advance when the ICE is not designed for this application T hese kinds of failures or design mistakes may not appear on a commercial bus and it shows that the hybrid busses still are somewhere between experimental and
53. hicles are alternating current AC machines that is induction or synchronous machines which is due to the development of power electronics for high power and due to the faster control systems available with modern micro controllers In the beginning of the hybrid vehicle development process direct current machines were mostly used due to the simple control O ne of the drawbacks with D C machines was the shorter life cycle and problems with high speed By having brushless permanent magnetic machines this problem is partly overcome Alak la 2000 The induction machine is the very most standardized and the most common of all the electrical machines T here are very few moving parts and the mechanical construction is simple This gives this type of motor long lifetime and it requires a minimum of care T hese advantages in combination with a low price make the induction machines very common Synchronous machines are similar in the mechanical construction to the induction machines M ost synchronous machines used in vehicle traction are permanent magnetic machines which often uses an outer rotor in the permanent synchronous machine T his gives the motor a high torque density typically one order of magnitude higher than that of an ICE T he efficiency of a well designed electrical machine for vehicle application is often higher than 90 in most of its operating space In best operating points the efficiency may reach 97 96 Generator and motor can
54. hine is rather high but is dependent on how it is driven T he losses are mainly of two types e Resistive losses caused by the current in the copper windings T he losses are depending on the current in square e Losses caused by the speed when the magnetic flux is changing eddy current losses and friction when the motor turns Some losses are linear and some are quadratic to the speed 34 Observations on Electric H ybrid Bus D eign The sum of all losses is low compared to an ICE when the motor works at nominal torque and speed W hen the motor power is low the relative losses are higher T hisisillustrated in Figure 4 4 Efficency 600 400 Torque Nm 0 0 Speed rad s Figure 4 4 T he efficiency of an electric motor T hetraction force and speed of the vehicle wheels are converted to traction motor speed and torque T he traction motor speed and torque are used in look up tables for the efficiency of the traction motor and the electric input power is calculated In Figure 4 4 the torque speed and efficiency of a traction motor is plotted Since the efficiency of well designed traction motors are very much alike the same look up table for efficiency is used both for the generator and the traction motors T he specific data used are collected from a licentiate thesis on traction motors for electric vehicles H ellsing 1998 Contact with the manufacturers was taken but they did not supply with any data at all The sa
55. ic converter from a commercial car and a relatively large battery 10 km at battery operation In the Scania bus peak traction power must be collected both from the generator and the battery Toreb makes the energy control system which controls all the energy flow in the bus Table 3 1 contains all other important information about the buses ThelCE and generator are placed in the back of the bus the gasoline fuel tanks in the back and the battery on the roof of the bus Figure 3 3 Casell Scania hybrid bus 3 3 Differences and similarities The main differences between the both the vehicles are the size of the chassis and the size of the ICE T he Scania is a full sized bus 12 m and the N eoplan isa medium sized bus 10 m 26 Observations on Electric H ybrid Bus D eign With the larger size the Scania bus can take more passengers but with the smaller ICE it needs assistance from the battery to supply peak power to the electrical traction motors T he Scania bus is heavier and has a weaker traction motor compared to its weight this makes the performance of the bus lower TheN eoplan bus is both lighter and with the larger ICE it is able to supply the traction motors with peak power and simultaneously charge the batteries The Neoplan bus also has the highest performance due to its higher ratio between peak tractive power and vehicle weight Since both buses are of the same type series hybrid only the size of the components a
56. ient behaviour of an ICE is presented in Chapter 8 T he method is called TES transient Emission Sampling and is based on emission sampling from a cyclic repetition of a torque speed loop A transient emission sampling technique and study is performed on an ICE in Chapter 8 Chapter 2 Hybrid Vehicles A definition of the entity hybrid vehicle is given by Michael T amor at Ford M otor Company A Hybrid vehideisa conventionally fuded and operated vehicle that has been equipped with a power train capable of implementing at leas the first three of the following four hybrid functions 1 Engineshutdown when power demand is zero or negative 2 Enginedown szefor improved thermal efficiency 3 Regenerative braking for recovery and reus of braking energy 4 Engineoff propulson at low power when engineisinedfident A power train that fulfills at least the first three of the four functions above can be composed in a number of different ways where series hybrid parallel hybrid and variants of these are the most common T helCE can be of different types eg Otto Diese Stirling ec T he electric energy storage can also be of several different types like electro chemical batteries electro mechanical flywheels and electro static super capacitors The electrical machines can also be of several different types although they are all rather alike in terms of efficiency In the following sections these topologies and components of them are
57. in series such as series parallel or various combinations of series and parallel here called complex 2 2 Different Hybrid System Series hybrid T he buses in the project are series hybrids In this combination of the hybrid vehicles electrical machines supply all the tractive energy and there are no mechanical connections between the ICE and the wheels The ICE drives a generator that charges the battery and supplies the traction motor with power as shown in Figure 2 1 An advantage is that the ICE can be switched off when driving the vehicle in no emission zones T he working point of the ICE speed and torque can also be chosen freely when running the ICE van M ierlo 1999 A drawback is that the prime energy from the ICE has to pass two electrical machines and power electronics on its way to the wheels This makes the System efficiency relatively low T he energy may also have to be stored in a Chapter 2 H ybrid vehicles 1 battery which further reduces the system efficiency Another drawback is that thetraction motors haveto be ableto convert the peak traction power An electrical vehicle supplied with a small ICE and generator as a range extender can be considered a simple series hybrid vehicle M ost of the existing hybrid buses are series hybrids O ne reason is the way they run with many starts and stops Another reason is that electric wheel motors do not need a rear axis this makes it possible to design the bus with a
58. ing T he velocity is integrated to a distance that is connected to the stop display showing the name of the bus stop W hen the bus stops and the doors are opened for passengers entering or getting off the distance is reset and in a second and a new bus stop shows on the display If the bus passes a bus stop and the distance increases too much a new bus stop is shown on the display automatically The requested power for driving the bus is the sum of the power of the traction motors and all auxiliary systems T his power could be stored together with the position the first time the bus travels the route specified by the driver Theinformation could then be used the second time the bus travels the route Compensation by the new requested power could also be done between the first and second time the bus travels the route W hen the system for power in advance fails or something else happens it can automatically go back to the normal charging strategy Example In Figure 7 6 a simulation with low pass filtered power from the generator is shown The requested power is the same as the previous time but forwarded the same number of seconds 10 s asthe low pass filter constant T helow pass 16 Observations on Electric H ybrid Bus D es gn filtered charging strategy behaves very well in combination with the feed forward power information T he following examples show how e When the bus climbs a hill or accelerates and the traction motors need a
59. ing strategy is similar to average power but a larger ICE and generator are used See figure 7 5 and table 7 1 for number of the fuel economy and battery losses 73 Chapte 7 Charging Strategies Speed 200 Seconds Power to motors battery amp from generator 100 100 D x 9 w o i N p p o Hd4 r 7 74 e LE o OL o e ene aie wa cul e o oO 2 95 Q D E o oo ee ee NEG Qa os o o 2 Y o r 9 o E LJ 2 o o 5 8 N z Oo A o a n o l p o T gt d F l gt lt es l o 1 i ceo o o o v i E 280 240 220 180 Seconds Figure 7 5 Simulated on off amp average charging strategies on the N eoplan bus 74 Observations on Electric H ybrid Bus D eign Low pass Filtered Power With this charging strategy the ICE and generator deliver a low pass filtered version of the tractive power and the battery supplies the rest of the required instantaneous tractive power This reduces the electrical power requested and avoids the fast move in speed and torque by the ICE In this way the losses in the battery as well as the battery size are or can be reduced When an ICE is forced to change operating point fast the instantaneous emissions increase significantly see Chapter 8 Since one of the motivations to design a hybrid drive system is to minimise emissions such dynamic operation must
60. ions point of view the hybrid vehicle also has similar disadvantages as the ICE driven vehicle But there is a small and important difference the CE does not have to produce all the instantaneous power for driving and thereis a freedom to choose operating point for the ICE to keep the state of Charge SOC of the batteries within reasonable limits T he battery assists with the difference between the total power used in the vehicle including tractive power and the power produced by the IC E driven generator The possibility of choosing the working points of the ICE more freely in a hybrid vehicle makes it possible to optimise some parameters T he energy consumption is one parameter and emissions another T o optimise the composition and use of a hybrid electrical vehicle it is necessary to start by defining what qualities and performance or what combinations of these that is regarded as optimal Electrical hybrid vehicle can be built in any conventional type like trucks buses and small cars The electrical vehicle s qualities with a silent and emissions free the ICE turned off operation are particularly interesting in the centre of the city This licentiate thesis describes a scientific evaluation of two commercial hybrid buses with special focus on the design and control of the traction System including the batteries combustion engine and electrical machines T he work is requested by three bus fleet operators in Sweden M alm Stockho
61. iption above on how the systems on board the buses interact is concluded from studies of the documentation that follows the bus This information is not confirmed by Neoplan and there is a possibility that the real implementation differs from the one described in the documentation Observations on Electric H ybrid Bus D eign 24 Air Fuel Gas Flow Control Gas Ignition Main _ Contactor Main Voltage Vehicle Speed jme Driving pe Mode T4 Driver s accelerator X14 blocks Containing 20 cells Voltage Measure Temp gt Mixer Wastegate L Jf Control gt Turbo Idle Control Engine position In Out pressure Engine Controller Coolant temp Exhaust oxygen Left amp right side Motor amp Generator Temp Current Speed Controller Brake Resistor Battery Management Coltroller System Current Ventilation Measure LAir temp Figure 3 2 T he control system and the manufactures of the N eoplan bus Chapter 3 Case sudies 25 3 2 Case Study Il the Scania In casell the bus is a Scania D ab from Sweden It isa full size 12 meters long bus with 66 passengers T he second case is heavier than the first bus due to the size and the construction It has a smaller ICE 2 3 equipped with a 3 way catalyt
62. is often a catalyst converter connected to the ICE This converter needs also to be modelled in some way T he catalyst is highly dependent on the working temperature Several considerations must be emphasized regarding the use of look up tables to represent the ICE in the H EB e Thetables do only represent stationary operating points e The tables do only represent nominal working temperatures of the ICE eg not cold starts e The tables are not valid when the ignition air fuel ratio or the compression is changed When the throttle of the ICE makes fast movements and creates transient torque or speed variations the air fuel ratio deviates temporarily from the desired level This deviation becomes larger when fast transients of the speed and the torque are made on the ICE Thus a complete ICE model should describe these transient effects T his is however difficult and research is still needed before reliable models can be implemented Preliminary results indicate that transients expressed as a bandwidth slower than 1 Hz can be regarded as quasi stationary See Chapter 8 for more information about the transient behaviour and measurement Thus look up tables do not correctly model fast transients but can be regarded as sufficient if the rate of change of operating point expressed as a frequency is lower than 1 Hz Torque and speed are used as in parameters for the look up tables and the fuel consumption or emissions arethe output para
63. istor battery amp from generator 100 l Generator i 50 kW i i 0 695 700 705 710 715 720 725 730 735 740 745 Seconds Figure 7 1 T he present charging strategy measured on the N eoplan bus Power to motors brakeresistor battery amp from generator 100 Generator 700 705 710 715 Figure 7 2 T he present charging strategy simulated on the N eoplan bus Chapte 7 Charging Strategies 69 The differences between the measured and simulated the motor power curves is the local altitude and wind variation The generator and battery power differences can partly be depending on the differences in the state of charge in the battery and the different motor power There is also a little time delay in the simulated the reason for this is that the simulated cycle was extended by 3 seconds in the beginning The brake resistor is an on off module but is simulated as an average power consumer The total integrated power consumption of the different components for a cycle is the same in the both cases 7 2 Present Charging Strategies for the Scania Bus When driving the Scania bus in hybrid mode the voltage of the battery controls the ICE and generator If the voltage of the battery is below a certain level the ICE is started and if the voltage exceeds a certain level the ICE is turned off When the ICE is off the peak power for the traction motor is reduc
64. laced in the Otto engine with ethanol while diesel can be replaced with natural gas CNG in the diese engine When a gasoline ICE runs on ethanol very small adjustments of the fuelling system is required basically it only needs a higher amount of fuel A diesel engine needs spark ignition plugs to run on natural gas a new fuel system and fuel tanks Egeb ck Ahlvik W esterholm 1997 The emissions from an ICE are very complex and are depending on many parameters such as combustion technology thermodynamics and mechanical operations To test and compare different ICEs standardised methods have been developed D ieselnet O ne of these methods is called ECE R49 T he test contains 13 points where the ICE runs in different speeds and torques First the ICE runs on idling and then on different speeds by the maximum torque then idling then by full power speed and final idling again see Figure 2 6 Chapter 2 H ybrid vehicles 13 Load BMEP d AD 60 80 100 Engine Speed Figure 2 6 TheECE R49 ICE test This mapping gives a good description of the fuel consumption and the emissions in stationary operation but do not contain any information about the transient behaviour of the ICE when it is running up and down in speed and torque The traction system has to provide any transient power required by the driver In a hybrid these transients have to be supplied by the traction system to some extent When the
65. lm and U ppsala and performed by IEA at Lund University and dept of Physics at Uppsala University IEA has earlier experience of hybrid vehicle project H emmingsson 1999 The main goal of the work behind this report is to increase the understanding of hybrid buses amongst bus fleet operators in order to make them more competent buyers of hybrid buses To reach this main goal a number of sub goals have been set 1 Thecreation of a simulation model that describes a hybrid bus in enough detail to facilitate evaluation of the effect of changes in the composition or control of the hybrid drive system 2 Detailed measurements on two commercial hybrid buses for calibration of the simulation mode T his in turn requires the design and installation of a measurement system 3 Sensitivity analyses of the effect of changes in the composition or control of the hybrid drive system Particular questions are Chapter 1 Introduction 3 a What is the best size of combustion engine for a given power consumption b Whatisthe best size of the traction battery c Which is the most suitable charging strategy i e how to operate the ICE asa function of the operation of the vehicle There are several commercial simulation programs available for electro hybrid vehicles T hey are often made for specific customers or for specific hybrid structures and do not allow the kind of changes in detail and or topology that we anticipate to need
66. m cycle is a recording of bus line 57 in Stockholm See Figure 6 4 This line is usually trafficked by the hybrid busses In Stockholm there is a large altitude variation with many up and down hills as opposite to the M alm city cycle The altitude variation has large impact on the tractive power when driving the bus this effect is discussed in the next Chapter section 7 2 The maximum speed is 58 km h the average speed is 21 6 km h and the cycle is 7 0 km long The maximum acceleration is 1 3 m s Chapte 6 Driving Cycles 63 Stockholm line 57 60 1 50r 30 Speed km h 20r 0 200 400 600 800 1000 Time s Figure 6 4 Speed as function of time during Stockholm line 57 1200 Chapter 7 Charging Strategies The charging strategy for an H EV is defined as the way the ICE and generator are producing power with respect to the instantaneous power demand of the driver and the auxiliary system and the SOC deviation of the electric energy storage In a H EV this is one of the most important design parameters when optimising a HEV drive train T he choice of charging strategy influences the size of the different components in the drive train In a series hybrid vehicle the operating point of the ICE defined by speed and torque can be chosen freely since no mechanical connection to the wheels exist T his gives a great flexibility in choosing charging strategy for a H EV A simple charging strategy is obtained
67. me look up table for efficiency is used both in motoring and generating mode though in inverse ways see Equation 4 7 o T Pe E when T gt O motordrive 4 7 T 7 when T O generatordrive Chapter 4 Simulation modd 35 ICE Generator The block I CE Generator contains three different sub systems the IC E control the ICE and the Generator The power request for the ICE generator is supplied for the external control block see Figure 4 2 The ICE is connected on the same shaft as the generator this means that the ICE and the generator always have the same speed and steady state torque O ne of the machines must be speed controlled and the other torque controlled by a control system Figure 4 5 Insdethel CE G enerator block in the simulation program The ICE control determines the most suitable speed and torque for the ICE and thus the generator T his torque and speed can be chosen arbitrarily to get the actual power P oT 4 8 To minimize the fuel consumption it is well known that an ICE should be driven on high torque and low speed to have good efficiency But it is not so obvious how the ICE should be driven by what speed and torque when low emission is desired In the Figure 4 6 the optimal torque at a given power for different optimising criteria like minimal fuel consumption minimisation of various emissions and the present implementation of the N eoplan hybrid bus are described for the Cummins ICE The selec
68. meters 38 Observations on Electric H ybrid Bus D eign Efficieny for Cummins Efficiency for Saab E85 4000 200 1500 100 50 2000 Torque Nm 1000 Speed rpm Torque Nm Speed rpm Figure 4 7 Efficiency look up tables for the Cummins and Saab ICE T he efficiency 77 for the ICE is looked up at a certain speed and torque The total fue consumption is calculated by integrating the efficiency multiplied with the ICE power and divided by the specific fuel heating value Quay das dt 4 11 LHV Total Fuel consumption The generator Subsystem is similar to the electric traction motor with look up tables for the efficiency The only difference is that the energy or power can only go in one direction from the axis connected to the ICE via the generator and to the electrical system Start of the CE with the generator machine is not modelled Battery The voltage and current in the battery are estimated from the power that charges or discharges the battery The model of the battery is described as a voltage source where the voltage varies with the state of charge SO C Figure 4 8 The resistors in series with ideal diodes make it possible to mode the battery with different internal resistances at charging and discharging W iegerman 1998 amp Sutanto 1999 Chapter 4 Simulation modd 39 Raus Ua ls KL R U M7 qn Figure 4 8 T he battery model used in the simulation program T he resi
69. nasson for boosting and questioning my ideas regarding the simulation model And finally want to thank Professor Gustaf Olsson and Rose M arie Andersson for reading the drafts of this thesis and improve the language Lund a snowing day in April 2001 Christian Andersson Contents 1 Introduction 1 1 1 Background sa tae sou Sea bees RE Up HO ertet e e Po RI RN tS 1 1 2 Main tesultSc oe ves Dee be vae ve e edu Qua oen DA e te cb A Pe IR 3 1 3 Outline Gf the thesis mH EH es 3 2 Hybrid vehicles 5 21 Introduction oe GLO e e Bee Ne dee Rea Ph rus 6 22 Different hybrid system eie epi pace e tee rH tenes 6 2 3 Prime source Of CNeLgy 6 ee eee n 9 24 Electrical machines 0 cc cece ec ce eee e eee eceeeenneeeceeaeannnes 14 25 Power electronics a een c cece ene e nee ceeeeennneeeeeeeaannnes 15 2 6 NEL Sy Stora enana ne e eT eie e tae RT e gd 16 2 7 JNGCeSSOtleS oe Ao ED ex EP ERS 19 2 07 Dive iecore NUR OU e RORIS CO eM eate oe ade ken 19 3 Case studies 21 3 1 Case study I the Neoplan nse roccia aiiai aa iaa Anaa aan 22 3 2 Case study II the Scama ser e a E E E eie 25 3 3 Differences and similarities ccc cece cece eee e cece eee eeneee eens 25 4 Simulation model 27 41 Introduction to the program model ccc cece eee ee eee 28 4 2 User interface of the program c cece cece cece e eee eee ee es 28 4 3 Prooram models i ce HR INR uM eR 29 44 Auxiliary power syst
70. nd some parameters needs to differ between the simulation models N o exchange of experience has taken place between the drivers of the buses in this project T he reason isthat the different buses traffic two different cities Chapter 4 Simulation Model The simulation model can be built in many different ways To be able to use the model in as many situations as possible the model has to be based on physical principles This gives more freedom to choose parameters in the modd not only to describe different choices of driving mode and components but also to be able to describe the way the vehicle operates In practical use two consecutive driving cycles on the same route are not equal Stopping at a traffic light a bus stop without passenger or stopping for a pedestrian crossing the road are unique actions T he distance the acceleration behaviour and the total stops and starts during one cycle are approximately the same The world model means description of the external conditions around the bus operation In principle the following types of information are necessary to supply 1 theglobal movement of the vehicle which means acceleration speed and position as the functions of time 2 fud consumption emissions and the batteries state of charge as functions of time 3 important components efficiency and losses as functions of time T he model hasto includethelCE the electrical traction machines and the power electroni
71. nds Figure 8 5 T ES torque speed and lambda measured by fast throttle movements Chapter 8 Transient Emission Sampling T ES 91 eo o eo are LR o to eo e eo Torque Nm o eo Az o 20 EE ize 1600 1800 2000 2200 2400 2600 RPM Figure 8 5 Torque as a function of speed by fast throttle movements T hese cycles make a high variation per time unit in both speed dt and torque T dt The speed is going between 1550 rpm and 2500 rpm and the torque is going from 10 Nm to 180 Nm this makes a power variation of approximately 40 kW In table 8 2 and 8 3 the emissions measured with the TES principle as described in this section are compared with the emissions produced in stationary operation at the same operating points as the average torque and speed of the sample valve opening interval Table 8 2 Emissions in stationary and transient operation with the same average torque increasing torque Emission Transient Stationary operation operation CO 96 2 25 0 4 HC ppm 1200 1880 02 96 2 0 0 88 NOx ppm 2200 3500 92 Observations on Electric H ybrid Bus D eign The results from these measurements give a hint that the emissions by the certain load have an overflow of fuel This is also indicated by the lambda sensor Emissions by load reduction can be seen in
72. nductor when switching on lt gt off e n passive components like coils and capacitors depending on the frequency and amplitude of the voltage and current The efficiency of power electronic converters is very high the larger size the better efficiency T he converters used in this bus project are of medium size with peak efficiency around 98 and well above 90 at most operating points Blaabjerg 1995 This is implenented in the simulation model by using look up tables with current and voltage as in parameters and efficiency as out parameter This efficiency curve does vary from 90 to 99 with the lowest values when transforming low power In the block Power electronics all powers from the traction motors generator and auxiliary load are added and divided by the voltage and multiplied by the efficiency for the certain component T hus the total current for the battery is calculated The total current is then divided or multiplied depending on whether the battery is being charged or discharged with the efficiency for the converter See Equation 4 14 P motor PE 0 P U i x TT oio generator 4 an P lr otal generator Tau ECmotor J n P gt 0 U g U motor motor Ua 4 14 Lui i Crotal lt 0 batt 7 powerEl Total i 7 PowerEI Crotal gt 0 where U is the battery voltage the current 7 the efficiency for the different component and P aux the power consumption of the auxiliary s
73. ng and reducing environment T his can be obtained by using a 3 way catalytic converter in the exhaust pipe A modern air fuel ratio control system controls the exhaust to be periodically rich and lean In this way there is both an oxidizing and reducing atmosphere created in the exhaust pipe T he catalyst is active only at high temperatures but can in this way obtain a significant reduction of the three major components in the exhaust gas CO NOx and HC The exhaust gases will be reduced to 99 from the emission after the catalyst reactions H eywood 1988 An ICE that is running lean and is connected to a 3 way catalyst will not be able to reduce the N O x gases A 2 way or an oxidation catalyst converter can be connected and do the same job by oxidising the H C and CO With a proper air fuel ratio that both oxidizes the hydrocarbons and the carbon dioxide and reduces the N O x gases the principal composition of the exhaust gas is dominated by water and carbon dioxide H ere we neglect all the other 12 Observations on Electric H ybrid Bus D es gn components that are present Equation 2 1 shows a simplified summary reaction of the combustion between gasoline and air in lean mixture as function of lambda The coefficients in the equation represent the molar weight g mol of the different substances J ohansson 2001 CH sx A 1 46 O 3 773N 2 1 CO 0 935 H O 4 1 46 0 3 773 A 1 46 N P In general gasoline can be rep
74. onsumption The simulated driving cycles use velocity as a function of time or distance U sing velocity as a function of time can give a wrong result due to accumulated errors If the speed differs from the desired speed too much due to low performance of the vehicle the bus stop will occur at the wrong place after a while If velocity is used as a function of distance this problem will not appear but there might be a problem with the pause time at the bus stop To make it possible for the passengers of the simulated vehicle to get on and off the bus at the bus stop a time delay is added at all bus stops It takes 20 seconds to run a complete simulation of 1800 seconds simulation on a hybrid bus with an average PC 30 Observations on Electric H ybrid Bus D eign 4 3 Program Model T he program s structure can be seen in Figure 4 2 This is an overview of the highest level of the Simulink program Each block can be opened and contains new structures H ere not all the details are described but only the principal configurations are discussed T he full capability of the software is naturally experienced directly at the computer CONTROL Fitr wieziraniz Figure 4 2 The highest level in the simulation program Simulink Control This block has two major functions to control the vehicle traction force with a driver model and to control thel CE power Chapter 4 Simulation modd 3l T hereference speed v comes from a
75. or specification of the engine test bench Sensor Unit rpm Speed Fuel flow g s Pressure inlet bar Fuel pressure bar Torque Nm Valve Open Close Temp cool water C Temp oil C Temp fuel C Temp brake C Temp inlet C Temp before cat C Temp after cat C Lambda sensor Air Fuel The reason why so many temperatures are measured is to check that the ICE fud and cooling has the right working temperature The catalyst temperatures before and after are very important to control that the catalyst has lightened and is active The inlet pressure is depending on the ICE torque and is also used for controlling the magnetic valve by the exhaust pipe The torque measured on the electrical brake is not the same as the ICE torque ThelCE storqueis also used for accelerating the inertia of the brake and the ICE This is the reason why it is important to measure the inlet pressure In stationary operation 84 Observations on Electric H ybrid Bus D eign constant torque and speed the brake torque and the ICE torque would be the same In this case the ICE torque will be calculated afterwards by using the inertia J for the brake and the ICE multiplied with the speed variation and the measured brake torque as described by Equation 8 1 Tie T prate m 8 1 dt Lambda A broadband lambda sensor with very fast response time is also used in the measurement system T he lambda sensor mak
76. ould need a GPS unit with the additional hardware that follows An important consideration in the choice of charging strategy is the need for emission free driving distance as this sets the lower limit for the size of the battery If the emission free driving distance can disregarded it is shown that the 13 charging strategy will improve the fuel consumption with 11 as well as reduce the ICE size with 60 Thesize of the battery can be reduced with 60 96 corresponding to a theoretical reduction of the emission free driving distance from 15 km to 5 km Chapter 8 Transient Emission Sampling TES A hybrid vehicle offers the freedom to choose between the ICE and or the battery as power source T he conclusion from the previous chapters is that the ICE should operate as near its transient limits regarding emissions as possible Thus knowledge of this transient limit is crucial H owever conventional methods for emission measurement are made for stationary operation Egeback W esterholm 1997 In fact most emission measurement techniques are unable to detect transient changes within the time frames necessary for establishing the transient emission limitation of an ICE in real time The instruments response time is too slow Fast responding instruments used by the industry are very expensive and in some cases not so reliable To overcome this problem a transient emission measurement technique is proposed here called TES Transient Emission S
77. rive the bus in the center of a city in pure electric mode and let the suburbs take care of the emissions from the IC E 7 1 Present Charging Strategies for the Neoplan bus The charging strategy when driving in H ybrid M ode with the N eoplan bus works as follows The bus runs on reduced battery power up to 25 km h All the power max 50 kW to the wheel motors comes from the battery and no power comes from the generator T he power limitation to 50 kW is set to protect the batteries since they cannot provide the 90 kW that the traction motors could use themselves but need assistance from the ICE W hen the bus is driven faster than 25 km h the ICE starts to deliver power via the generator Then all the power for the wheel motors max 100 kW comes from the generator Power from the generator also charges the battery The charging power is then approximately 12 kW when going faster than 25 km h and 0 kW when going slower than 20 i e the ICE turns off This is depicted in Figure 7 1 The consequence of this is that the battery state of charge is kept at a high level SO C 29096 When the bus slows down and the motors begin to act like generators energy is fed back into the traction battery T hen the battery may already be charged to a high level and cannot absorb much more regenerated power T he excess regenerated power is then dissipated as heat in a brake resistor The brake resistor only heats the water used for cooling the ICE As a r
78. rpart e g the electrical motor can be mounted in the wheel T he life cycle on an electrical machine is longer than that of an ICE they do not need oil change and do not generate any emissions Another advantage in a vehicle is that they can regenerate the kinetic energy when braking As a traction motor the electrical machine is more suitable than any ICE The problem with an electrical driven vehicle is the amount of energy that must be brought with the vehicle to reach a reasonable driving distance The main energy storage is electro chemical batteries electro mechanical flywheels and electro static super capacitors N o electric bus equipped with these energy storages can store an amount of energy on the bus that is comparable to e g the energy in the diesel tank of a pure diesel bus An important trend for the future of electric vehicles is the use of fuel cells that allow for direct conversion of a high energy medium gas of fluid to electricity In the future the fuel cell vehicle may compete with conventional ICE vehicles One solution to the electrically driven vehicle s energy storage problem is to bring along an ICE and a generator which can assist the electro chemical energy storage with electric energy from chemical energy with high energy 2 Observations on Electric H ybrid Bus D eign density From a driving distance point of a view such a vehicle has the same advantages as the pure ICE driven vehicles From an emiss
79. s Energy W h kg 35 40 55 70 155 125 80 Power W kg 80 120 200 315 260 145 Energy dens W h L 90 90 90 165 200 130 Life cycles 300 1000 600 4600 4600 600 Charge time h 6 8 6 8 6 4 6 4 6 4 6 D riveng range km 75 100 150 250 200 200 Price SEK kW h 1200 5000 7000 The use of the battery management system BM S should increase the batteries life and saving them from dangers like overcharging and discharging when driving and charging One of the problems with a BM S is to establish relevant models of the state of charge SO C how full or empty a battery is for the moment H auck Altimeier 1998 Of course it is easy to measure the current in and out from the battery but the SOC is also depending on several other parameters like resistive losses in the battery that are a function of the temperature charging history ec T here is also another way of handling the energy of the battery having some kind of indication of the energy level of the battery The energy leve could both be a maximum or minimum leve The minimum level is interesting when the battery assist with power and the maximum leve is interesting when power are going to be stored in the battery A battery consists of many cells that are connected in series T hese cells are identical regarding the voltage and resistance in theory but not in reality W hen a battery is charged this may pose a problem with over voltag
80. s particular ICE and engine control system where the electric traction system Chapter 8 Transient Emission Sampling T ES 93 can reduce the transient power from the ICE is thus not recommended from an emissions point of view The limit for transient emission generation expressed as a bandwidth in an ICE is most likely different in different ICE drives It is also possible that this limit may be different for different operating regions of the ICE torque speed plane The T ES method as presented here is a first and preliminary evaluation of the TES method and must only be taken as a indication supporting the intuitive assumption that the must be a limit where the lambda control no longer works properly Other reports do support this assumption Cowart Cheng 2000 Chapter 9 Experience of the Vehicles 9 1 In General In this chapter some general experiences of working with the vehicles used in this project are discussed To have one or two special vehicles in a larger conventional bus fleet causes some problems T he vehicles are unique and have several kinds of unusual properties When a failure occurs in one of these special vehicles special repair methods are needed Service and repair is also needed for the ordinary vehicles in the fleet the special vehicle s needs are placed last or beside the queue If not somebody like the one who isin charge of the bus workshop is particularly assigned to care for the vehicle it might
81. saved or printed by clicking on the proper buttons e Torun the summation program press the button Simulate Result of the Simulation Program In the simulation result view of the simulation program there are 5 different subplots and some text information The text informs about the total driving range and average speed total fuel consumption and the different emissions All subplots can bee zoomed by clicking on the magnifying glass and mark the interesting area with a square around it The first subplot shows the reached speed in m s of the bus T he second subplot shows the variation 96 in state of charge in the battery T he third subplot shows the power kW from the ICE The fourth subplot is the ICE s fuel consumption kg And finally the fifth subplot shows the power kW to the electric motor requested to run the driving cycle 111 Appendix B m s kW kw 15 eo 120 100 80 60 H 40 20 100 10H a Stockholm linje 57 nie QUAM nS TTR TERT AO UE RU lj MANT Tm So 600 TN 1000 seconds Power from ICE Wi DE ERES i aa UNIT Ji MW M 200 ERE zm ma 1000 seconds Power to the drivingmotors 0 400 600 800 1000 seconds 70 5 70 926 69 5 69 68 5 State of Charge l hi lt IT F 4 ssakhjsrs d iL l b 0g m i Loo 4340 r1 popmEELEE I u 200 400 600 800 1000
82. se P3 Valve open Torque RPM Figure 8 1 TES principle for emission sampling 8 2 Implementation The test bench consists of an electrical brake of eddy current type The brake is connected to the outgoing axis of the ICE The brake controls the speed variations It tries to limit the speed of the ICE when it is throttling by increasing the braking torque The ICE is torque controlled by a throttle servo connected to a tone generator for torque reference The tone generator can give triangular or sinusoid reference signals by a chosen frequency amplitude and dc level T hese voltages can easily be adjusted for acting as torque references for the throttle servo An example is ramping the throttle like a triangle forward and backward W hen the speed or torque reaches a certain level a valve by the exhaust pipe is opened for a short time A sample of the emissions is taken by a certain Chapter 8 Transient Emission Sampling T ES 83 torque and speed under a bit of the transient loop T his is done over and over again until a plastic bag is full of these samples O rdinary emission tests can be done on the emissions in the bag as illustrated in Figure 8 2 A time delay can be added to the opening condition of the valve and the emissions in another speed and torque level around the loop can be collected A complete ICE measuring system is connected to the ICE T he sensors are as described in T able 8 1 Table 8 1 Sens
83. servations on Electric H ybrid Bus D eign In the next figure the same speed and torque variations are used as in the previous figure but plotted in a different way torque as a function of speed Thecycleis run through counter clock wise TES cycles 180 zs o eo Torque Nm 3 m E e e eo co eo co eo 40 20 i i i 2250 2300 2350 2400 2450 2500 RPM Figure 8 4 T ES torque as a function of speed by slow throttle movements T hese cycles make a very low variation per time unit in both speed dt and torque T dt The speed is going between 2280 rpm and 2480 rpm and the torque is going from 50 N m to 150 N m this makes a power variation of approximately 30 kW Higher Transient Emissions In the following example the cycle time was 2 5 seconds the speed and torque has thus been varied with higher frequency 0 4 H z than the previous example 0 05 Hz The lambda variation is clearly increased This is a source of transient emissions Chapter 8 Transient Emission Sampling T ES 89 The CE speed and torque are plotted in Figure 8 5 T he emissions were measured both at load increase and load decrease The magnetic valve was opened during 0 5 seconds each cycle Observations on Electric H ybrid Bus D eign 90 97 96 5 96 95 5 2500 2000 7 1500 epquie 100 99 5 Seco
84. ses on the other hand are significantly reduced if the ICE is taking more responsibility for transient traction power T 1 is believed to possibly excite transient behavior T his is supported by results such as presented in Cowart Cheng 2000 where z 3 is regarded as being on the verge to transient operation of the ICE 7 710 is regarded as not exciting any transient operation of the ICE T he peak power of the ICE is still reduced significantly compared to the tractive power 7 7100 the ICE runs almost on average power and battery losses get too large T the ICE runson a constant average power Secondly the size of the ICE is used as a variable parameter The size cannot be altered continuously but in steps of cylinders Even if one cylinder is removed the fuel consumption and exhaust emission per cylinder will remain almost the same ref discussions with Rolf Egnell The efficiency at a given torque and speed combination is modelled as Chapte 7 Charging Strategies 19 unchanged when a cylinder is removed or added H owever a smaller motor cylinders removed must operate at a higher torque cylinder for the same power thus increasing the efficiency See T able 7 1 Table 7 1 e Charging strategy is changed ic No Fue Max HC NOx Batlos Max s cyl f kg ICE g g kWh Power Power fr to Bat kW kW MM 1 6 2 30 87 24 24
85. stance does vary with the temperature of the battery T he battery manufacturer Varta has supplied values of resistance and internal voltage shown in Equation 4 12 A thermal model is included in the battery moda Un Us R I U No cells chrg dis bat U 0 05V aes R _ 0 85 20 Temp chrg dis 1000 The new SOC are calculated through integration and by using the number The electro chemical features of a battery cell are highly depending on the temperature M ost kind of battery cells has their best working point by 20 C T he resistance decrease with the temperature as modelled in Equation 4 11 The losses in the battery both with charging and discharging contribute to heat the cells and is moddled in Equation 4 13 P ATemp H 4 13 i Moen n where H is the heat transfer coefficient C is specific heat capacity m mass of a cell and n is the number of cells in the battery Pow er Electronics All electrical power of the vehicle is connected to the Powe Electronic block in the simulation program reflecting the actual structure of the power system in 40 Observations on Electric H ybrid Bus D eign the bus where all major power consumers generators convert electric energy via power electronic converters This kind of power electronic converters has also some losses where the most important ones are e n the power semi conductor when they are conducting current e Inthe power semi co
86. t would have been very difficult to evaluate that since in most cases the storage is not yet produced in large series and the n umber of cycles that the battery can sustain is hard to predict H EV T eam 2000 Since several of these technologies still are under development there is a lack of predictions for large scale production prizing Chapter 2 H ybrid vehicles 17 Energy Wh kg os Gasoline atat 10 OOD A Hydrogen 1 ana NS 100 SN RA OCS a a Battery Flywheel E C ut S Carbon SS Ultra AS Capacitor capacitors 10 Metal Oxide Capacitor DN NS Power 100 1 O00 10 O00 100 000 W Eg F oF a 4 Avalable now SS Future Projected Figure 2 8 Different energy storage Battery The only energy storage commercially available today for use in hybrid vehicles is conventional batteries T he types of battery used are listed in T able 2 1 Table 2 1 Battery types Lead Acid x Pb ac C heap but not so long lifetime e Better than Lead acid environment problem AMT etalhydride M ore energy and power than N i Cd Lithium polymer iron TP Li p Li ion M aybe the future production just started N atrium N ickel Clorid N a N iCI M aybe the future but at present 18 Observations on Electric H ybrid Bus D eign The next table describes some relevant properties of different batteries for electric vehicles T hisdale 2000 Table 2 2 Battery characteristic
87. table where the speed and distance are described T he speed reference is read from a vector in workspace and can be represented both as a function of time and of travelled distance The driver model used in the simulation program is a PI regulator It is selected due to its simplicity and the ease with which the parameters can be selected intuitively with realistic performance as the result The force of the driver mode is described by the following equation Frraction Kp By PE K Ji vu 4 1 where v is the velocity v the set point of the velocity and Kp and Ki the control parameters of the controller T he proportional and integrative terms are selected according to Equation 4 2 Max tractive force P 10960f max speed 4 2 Max tractive force i 33 96 of max speed Equation 4 2 should be interpreted as a driver that request the full tractive force at a speed error of 10 of the maximal speed and doubles this request about every 3rd second as long as the speed error remains An anti windup function stops the integration in case of a limitation of the requested tractive force This driver model is not validated in any other ways than by showing that the vehicle behaviour is realistic with any of the driving cycles that have been used in this report T he requested tractive force is limited as a function of the speed to account for the field weakening of the traction motors The speed limit for field weak
88. th a comprehensive evaluation of the size position and repetition speed of the loop in the torque speed plane Chapter 11 References Advisor A simulation program 2000 09 05 http www ctts nrel gov analysis advisor html Alak la M 2000 Edmaskinsystem 2000 Industrial Electrical Engineering and Automation LTH Lund University Sweden Anpalahan P 2001 Design of Transverse Flux Machines using Analytical Calculations e Finite Element Analysis Lic Thesis Department of Electrical Engineering Electrical Machines and Power Electronics Royal Institute of Technology KTH Stockholm Sweden Blaabjerg F 1995 Power Losses in PWM VSI Inverter Using NPT or PT IGBT Devices EEE Transactions on power electronics vol 10 No 3 May van den Bussche G 1998 Simulation of the power flow in battery powered busses A polit study Master Thesis Uppsala University Sweden Cowart Jim S and Cheng Wai K 2000 Throttle movement rate effects on transient fuel compensation in a port fuel injected SI ICE SAE technical paper series 2000 01 1937 Paris France Dieselnet ICE emission standards and test procedures 2000 06 01 http www dieselnet com 102 Observations on Electric H ybrid Bus D ei gn Egebiack K Ahlvik P and Westerholm R 1997 Eymzsstonsfaktorer for Jordon drivna med fossila respektive alternativa br nslen KFB Meddelande 1997 22 Sweden Egeb ck K and Westerholm R 1
89. the calibration of the simulation mode will be misguided 5 1 Onboard System The energy on the bus appears in many different forms like kinetic electric and chemical energy T he measuring system is used onboard the vehicle to get infromation about the energy flow vehicle behaviour temperature and some ICE parameters like fuel consumption speed and air fuel ratio From these data it is possible to derive and verify the energy flow as described in the simulation model so that the model can be verified A compact installation is desirable and the measurements system must be insensitive to vibrations dust etc The measurement systems in the buses are built around a commercial data acquisition system from N ational Instruments called SCXI A laptop computer is connected to the SCXI system with the program LabView The analogue data acquisition is done by 16 bits resolution This means that 0 10 V will be resolved in steps of 160 uV It is important that the channels are sampled synchronously since simultaneous measurements of most quantities is needed 44 Observations on Electric H ybrid Bus D eign Figure 5 1 The computer and measuring system assembled in the N eoplan bus All quantities are sampled at a rate of 5 Hz The data are stored on the hard disk of the laptop computer During an ordinary day the total data storage requirement will be 30 MB The transfer to a stationary computer is done with a zip drive W hen the i
90. the ECE15 is a representative driving cycle for a bus since it emanates from a car cycle The cycle is used for emission certification of light duty vehicles in Europe This cycle can easily be optimised by a good chassis dynamometer driver and does not give a good indication of the real fuel consumption and the emissions of the vehicle in real operation 60 Observations on Electric H ybrid Bus D eign The ECE15 cycle Co c o o T T Speed km h n2 Co A C1 O N eo eo eo eo eo eo eo T T TIU I 0 0 200 400 600 800 1000 1200 Time s Figure 6 1 Speed asa function of time during the ECE15 cycle T he speed limits for light duty vehicles are 90 km h and 70 km h for heavy duty vehicles This will make the driven distance slightly shorter for heavy duty vehicles i e 9 94 vs 10 5 km The average speed for heavy duty vehicles is 30 km h while it is 31 7 km h for the light duty ones The maximum read all acceleration in the ECE15 is rather low 1 04 m s This low acceleration makes it easier to optimise the fuel consumption by smooth driving The Braunschweig cycle was developed at the Technical University of Braunschweig Germany to simulate and test an urban bus driving cycle especially when a vehicle is tested on a chassis dynamometer The cycle is frequently used in research when comparing simulation models T his cycle is demanding and contains quick accelerations and retardations The maximum a
91. the ICE and generator can bee made small since the battery will take care of all the dynamic power W hen breaking the peak power will become very large as both the traction motors and the generator will charge the battery T his will create large losses in the battery so a large battery will be needed T his is illustrated in Figure 7 5 and T able 7 1 A large battery is heavy and expensive T he lifetime of the battery is short so this charging strategy is not so good for busses working continuously during 8 12 hours T he average power might be good in a HEV if this power source is for example a fuel cell which peak power is expensive SEK kW or in an electric vehicle that is charged once in a while by the grid and has not so long daily usage time as a city bus A small ICE and generator range extender might then be adequate On Off Power A large ICE and generator deliver power to the battery and traction motor by the ICEs highest efficiency point during the charging time D uring the rest of the time the ICE is switched off This will make the battery losses large since 72 Observations on Electric H ybrid Bus D eign the battery has to supply the traction motor with all the tractive power variations When the ICE is switched off this charging strategy will need large battery capacity One of the advantages with this charging strategy is that the fuel economy is good when the ICE drives by the optimum efficiency point This charg
92. tion of these optimised operating points are based on steady state performance 36 Observations on Electric H ybrid Bus D eign 600 500 ____ 7 _ Ff us eg P Fuel Hc Present NOx 400 7 T z Pd Pd co Pdf 5300 3 o yt e pag D 7 ie t 200 E t aj j 4 Pd Fi 100 S Ag 0 0 20 40 60 80 100 Power kW Figure 4 6 O ptimal torque for several different optimisation criteria with the Cummins CE used in the N eoplan H ybrid case 1 The ICE controller picks the best operating point for the ICE based on a look up table according to Figure 4 6 Based on the selected power and torque the speed reference is subsequently calculated Finally the generator torque reference is calculated by a speed controller Both the ICE and the generator and a regulator adjust the speed to a stationary value T from look up table ice T ice TA EK lo Z Dice ri Ice whereT isthe torque the speed and P the power 4 9 Chapter 4 Simulation modd 37 The mechanical dynamics is solved with N ewton s 2 nd law represented inside the block me in Figure 4 5 d e T Ts 4 10 4 10 ice gen where J isthe inertia for the engine and generator ice gen The ICE subsystem is described in the simulation model with look up tables The model is depending on temperature pressure speed fuel and air humidity H eywood 1988 T here
93. trical power flow in the bus The manufacturer of these sensors is LEM T he sensors use the H all effect and they are galvanically isolated from the respective systen The inaccuracy ist 0 8 T his will make the voltage error at 500 V to 4V and the current error of 100 A to 0 8A See Figure 5 3 for the connection points of the current and voltage transducers Figure 5 3 The current and voltage transducer placement in the N eoplan bus Chapter 5 M easurenents 49 Figure 5 3 T hecurrent transducers around the cables in the power connecting points in the busses At the top the PT B box in theN eoplan bus and at the bottom Grundbulten in the Scania bus The temperature sensors Measuring less than 150 degrees Celsius consist of PT 100 elements which are resistive sensors The temperature sensors measuring above 150 degrees are thermo elements of type K and are only used on the exhaust gases from the ICE The temperatures on both sides of the catalyst are measured to determine whether the catalyst is working or not as illustrated in Figure 5 4 50 Observations on Electric H ybrid Bus D eign Temperature by exhaust outlet before amp after catalyst 600 500 Outlet 400 Before Degres Celsius C2 eo e After 200 Power from the generator kW 100 0 Wt A ae illi A f pi EM Af Bac 3 4 5 6 7 Minutes Figure 5 4 Examples of different C
94. tudies In the present work the drive systems of two different types of hybrid busses have been thoroughly investigated O ne is a N eoplan M etroliner MIC N 8012 GE and the other is a Scania D ab Citybus 1200 M KII The purpose of the investigation has been to aid and verify modeling Thus comprehensive measurements system has been installed and all major energy paths in the vehicles and a number of other quantities are also measured These buses are both pure series hybrid types but represent different concepts in terms of battery size vs ICE size See table 3 1 for more detailed information about the vehicles 22 Observations on Electric H ybrid Bus D eign Table 3 1 Vehicle specification i Case I Case II Vehicle mass 8500 kg 12500 kg Front area 8m 8 5 m Length 10m 12m Generator type PMSM PMSM Generator power 125 kW 55 kW Electric motors type PMSM wheel motor IM Electric motors power 2 x 55 kW 2x 75 kW ICE type Natural gas Gasoline amp E85 ICE size 5 9 2 31 ICE power 145 kW 90 kW Battery Type NiMH NiCd Number of cells 280 270 Battery Energy 60 Ah 80 Ah 3 1 Case Study I the Neoplan Neoplan in Germany makes the bus in case It has a large ICE 5 9 I generator and a battery 15 km at battery operation The genset ICE and generator is able to supply all peak power needed for the traction motors T he bus is designed to take 57 passengers It is a low floor cit
95. ve compared to and ICE and a generator T rngren 1998 As alternative to the conventional ICE there are other types of ICEs like turbines and stirling motors Volvo has built a hybrid bus with a gas turbine M almqvist 1998 In this thesis and in the hybrid vehicles in this project only conventionally fuelled IC E s have been modelled and evaluated There are many similarities between Diesel and Otto engines One important difference is however the air fuel ratio called the lambda A gasoline spark ignition ICE is meant to operate at stochiometric relationship between air and fuel The air fuel ratio is controlled when throttling In a Diesel engine the air flow is constant and the amount of fuel is controlled when accelerating This makes the diesel engine run lean when idling and at low load T hese are the reasons why an Otto gasoline engines run with lambda 1 at the stochiometric ratio while the diesel ICE s require lambda gt 1 4 which is lean burn The emissions in an O tto engine are illustrated in Figure 2 5 Chapter 2 H ybrid vehicles 11 TEE GE cA Rich Scc home tne Lean NO CO and HC ceecentrazioms re te scale Dar eee ea are em amm ee La 0 3 i9 1 4 LI 1 3 13 Air fuel eyuivalenee ratio Figure 2 5 T he emission by different lambda of an Otto engine before the catalytic converter In order to decrease the emission of carbon dioxides hydrocarbons and nitrous gases there has to be both an oxidizi
96. will then have to contain higher power density T he size of the battery can be reduced with 60 96 A drawback with the low pass filtered charging strategy is that the ICE power set point cannot easily be predicted The ICE power is thus some seconds too slow when accelerating and breaking T helCE will still charge the Chapte 7 Charging Strategies 15 battery but causes unnecessary big losses in the battery A possible solution to this problem is presented in the following paragraph Forwarding the Driving Cycle T he best chance to optimise the charging strategy of the ICE and the generator on a hybrid vehicle is when the driving cycle the road topologies and the emission free zones are known in advance In the hybrid bus where the bus often runs the same route many times a day this would not be too difficult to implement Implementation It would be possible to connect the information of the bus stops as a priori information to the system T his can for example be connected to the GPS System for feedback information It could also be a connection to the system that shows the bus stops for the passengers or a combination of the GPS and the display systems T he bus stop information system is connected to the door opening and to the distance between the bus stops W hen the driver starts on a new route he also chooses the route for the passenger stop display T he input signals to the stop display system are velocity and door open
97. x Measurement and control computer 8 3 Result A number of tests with the TES method have been performed where the DC level amplitude and frequency of the throttle servo have been changed The magnetic sample valve can be controlled by speed or torque In the torque case the ICE inlet pressure is used as reference for timing of the sample valve Emissions at Slow Transients In Figure 8 3 one of the tests is performed where torque speed and lambda with very slow throttle movements are shown The repetition time for one cycle isin this case 20s T he small squares show the magnetic valve opening for measurements in both these both points 86 Observations on Electric H ybrid Bus D eign By these slow movements the ICE lambda control still works The lambda control keeps the air fuel ratio near an average of 1 0 The 3 way catalyst converter works and there are no transient emissions due to the very slow transient behaviour Chapter 8 Transient Emission Sampling T ES 87 150 7 d BA e 100 f e 300 305 310 315 320 325 330 335 340 2500 2400 SN vU 2300 De 2200 1 1 1 1 1 300 305 310 315 320 325 330 335 340 RPM Lambda 300 305 310 315 320 325 330 335 340 Seconds Figure 8 3 TES torque speed and lambda measured by slow throttle movements 88 Ob
98. ybus 10 meters long T he chassis is built of composite and coal fibre T his makes the bus very light Theconstruction also is environmental friendly since it is 100 recyclable Chapter 3 Case studies 23 Figure 3 1 Casel N eoplan bus ThelCE and generator are placed in the back of the bus the fuel tanks on the roof and the battery on thefloor in the middle of the bus The power flow control and the name of the manufactures of the systems can be seen in Figure 3 2 in the N eoplan bus The Cummins system controls the ICE through the ICE sensors The fuel air ratio the ignition and idling are controlled The input signal like throttle angleto the CE comes from the M agnetM otor system The Varta BMS sysem measures and to some extent controls temperature current and voltage of the battery It also calculates the State Of Charge SO C of the battery that is delivered to the M agnetM otor system The M agnetM otor control system controls all the other systems the ICE the battery the generator and the motors in a supervisory manner T he input to the M agnetM otor system comes from the driver T he driver s accelerator movements are registered and the M agnetM otor system decides how much and which power source battery or generator is going to supply the requested power In this decision many parameters can be involved like the present State of Charge in the battery and the speed of the vehicle It must be noted that the descr
99. ystem Chapter 4 Simulation modd 41 4 4 Auxiliary Power System The auxiliary system is called Aux power in Figure 4 2 It has influence on the energy consumption of the vehicle since it loads the energy system all the time even during a stop The auxiliary system drives ventilators lights steering brakes and door openings It is very important that the help systems like steering and braking assistance are built in an energy efficient way On a hybrid electric vehicle there is always electric energy available On an ordinary vehicle an ICE is running and mechanical pumps and compressors can be connected On the N eoplan bus there is a dual system with an air compressor and a servo pump mechanically connected to the ICE while the ICE is running When the ICE is turned off there is another system with electric motors driving the servo pump and air compressor This is a rather complex system where the energy is not used efficiently For example it would be better to have an electric motor to assist the steering wheel instead of having a hydraulic System T his would replacethetwo servo pumps Figure 4 7 shows some real measurements on the N eoplan bus of the power of the auxiliary system when the ICE is on and off respectively A small generator supplies power to the 24 volt system when thelCE ison Observations on Electric H ybrid Bus D eign 42 Power

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