ADVANCED CONTROL ALGORITHMS + SIMULINK
Contents
1. RexCore TCP IP Development visualization Communication DCOM f OPC RexOPCsv Real time control Fig 1 Structure of REX control system 3 Function block library RexLib 4 REX runtime and diagnostics 5 Configuration of REX 6 OPC OLE for Process Control utilization 2 STRUCTURE OF REX The structure of the REX control system and its rela tions to an environment are shown in fig 1 The top part of the figure contains components of a host development environment which is simul taneously the visualization and operator manage ment environment All current development tools of REX are created for the Windows operating sys tems 95 98 ME NT 2000 XP Standard visualiza tion tools are used some of them are shown in the figure Visualization tools are connected to the con trol system through an OPC interface which uses COM Component Object Model and DCOM Dis tributed COM services or through Automation OLE Automation and various scripts VBScript JScript Visual Basic The bottom part of the figure presents the structure of the target enviroment which implements real time control algorithms In addition to the Windows op erating systems mentioned above also e g Windows CE or Phar Lap ETS can be chosen for the target environment In the case of the Windows operating a _OPCSvr OPC OPC SvM OPCDrv R systems the target and host2. Control Data Access Custom Interface Standard Version 2 04 OPC Foundation REX Controls 2004 Function blocks of the system REX in Czech REX Controls s r o Plze Schlegel M P Balda and M St tina 2001 C MEX blocks industrial control library with application examples In Summaries Volume of the Matlab 2001 Workshop Humusoft s r o Praha pp 361 369 Schlegel M P Balda and M St tina 2002 PID au totuner for industrial use In Proceedings of the conference Control of power amp heating systems Zl n Czech Republic The Mathworks 2001 Using Simulink Version 4 1 Using Simulink Version 4 1 Natick MA
3. environments can be the same even on a single computer The links between host and target environments are carried out by a communication layer in the middle of fig 1 The most frequently used communication protocol is the TCP IP standard which is used as a basis of our own diagnostic protocol of REX 3 FUNCTION BLOCK LIBRARY The control algorithms performed by REX are de veloped using only a special function block library block set called RexLib Schlegel et al 2001 At present the library contains more than 120 function blocks which are compiled for Simulink and each target platform Windows Windows CE and Phar Lap ETS The library contains both simple function blocks similar to the corresponding Simulink blocks and advanced industrial control blocks The most so phisticated function blocks are depicted in fig 2 PIDMA is the full ISA PID controller supplemented with the built in autotuning procedure After start of the autotuner the rectangle pulse is applied to the input of the process and the first three process moments are computed from the pulse response Subsequently the controller parameters are deter mined by a model based design procedure Schlegel et al 2002 REXLANG Fig 2 Examples of advanced function blocks from RexLib Autotuning PID loop with analog output PROCESS gt gt MDL Scope manipul var Dt disturbance si E etpoin
4. store func tion block diagrams in files with the md1 extenstion model These text files are too big to be transferred to some memory limited embedded devices That is why the md1 files are compiled by the RexComp compiler into the binary format rex section 5 2 The configuration of REX is demonstrated on a simple control loop example which is shown in figures 5 6 and 7 The rest of this section explains the mutual relations of all the three figures gt lt EFA_AO_MV_ _IEFA_AL PV LIN_MV Simulation of the process Fig 6 A particular simple control loop configuration example loop md1l EFA__AO_MV Fig 7 The simulation subsystem Simulation of the process of the configuration loop mdl 5 1 RexDraw Graphic editor of function block diagrams The RexDraw program is used for function block diagrams design in a way very similar to the Simulink built in editor Both programs generate files with the md1 extension but there are some differences in their options First of all RexDraw allows to compose md1 files using only blocks from the large library of REX blocks Schlegel et al 2001 All these blocks work in discrete time although many of them are dis cretized for a given sampling period This fact corre sponds to the Simulink Solver options param eters Type Fixed step and discrete no continuous states While a whole Simulink configuration c
5. the properties of the superior objects of the selected block P IDMA Task depicts the diagnostics of the task mtuner e g the measurements of current average mini mum and maximum execution time variables com puting error indications Executive shows the identification and diagnos tic data of the current real time executive instance Active executive e g creation download and last start dates and times memory usage Target identifies the current target device here pavel which is on line e g target device type operating system name and version REX version and build date The program contains also property pages of the other REX control system core objects The appropriate page is activated when a given type object is selected e g a module a driver a trend or an archive Modules pev _nextp Drivers EFADRV Archives Ley prev next EFA QTaskp Level0 t PIprev nexp Levelt b loop Level2 p Level3 p EXEC Fig 5 A main file exec md1 of a simple control loop example 5 CONFIGURATION OF REX REX is configured by creating function block dia grams consisting of a large function block library Schlegel et al 2001 The function block library is available in Simulink and all target platform versions of REX This fact makes it possible to draw function block diagrams in the Simulink built in editor The second possibility is to use REX s own editor Rex Draw Both programs Simulink and RexDraw
6. ADVANCED CONTROL ALGORITHMS SIMULINK COMPATIBILITY REAL TIME OS REX Pavel Balda Milos Schlegel Milan St tina University of West Bohemia in Pilsen Department of Cybernetics Univerzitn 8 306 14 Plze Czech Republic e mail pbalda kky zcu cz Abstract This paper describes the structure and features of a new industrial control system called REX During the system design special attention was paid to the simulation facility of the control algorithms The equivalent behavior of simulation and real time control is guaranteed by a large function blocks library which is implemented for both Simulink and each target platform REX is suitable for building real time control systems of real virtual and remote laboratories REX does not utilize Real Time Workshop by The Mathworks Copyright 2005 IFAC Keywords industrial control system embedded control Simulink OPC real time control system 1 INTRODUCTION There is a rather wide gap between control engineer ing theory and practice The way from the develop ment of a new algorithm to its practical implementa tion is usually very long and laborious because both areas use different tools Currently Matlab Simulink The Mathworks 2001 is perhaps the most widely spread program system used for the development and testing of new algorithms in industrial process control Simulink is more frequently used not only in academic institutions but also in engineering practice Pr
7. acti cal use of standard Simulink blocks is however not without obstacles because these blocks have not been developed for industrial applications To bridge the above mentioned gap a new control system REX has been developed The main design requirements have been as follows e Compatibility with Matlab Simulink e Development of industrial control block library blockset e Openness of the system easy creation of new algorithms e Suitability for the teaching of control engineer ing e Support of industrial standards and internet tech nologies The objective of the paper is to describe briefly the creation of a REX application and to emphasize the possibility of simulating it in Simulink before putting it into operation The REX control system is an open and scalable system which is suitable for embed ded control REX can be easily ported to different platforms with C and C language compilers from dedicated control cards and simple real time execu tives to process stations equipped with standard op erating systems At present REX supports Windows NT 2000 XP Windows CE NET and a hard real time operating system Phar Lap ETS Embedded Tools Suite REX has been used for the building of the remote and virtual laboratory in the department of cybernetics lab fav zcu cz Below is the list of sections following this Introduction 2 Structure of REX Simulink RexComp TCP IP Target File rex
8. elp Dat ae a enw pavel gt Active executive fae Level O Eat mtuner A ASTAT 1 MAN PDIS T RUN i TOIS A ADDDIS I extpv I SWMAN I MCU_SP 0 PIDMA 0 ADD I MCU_HY Variables M Inputs M Outputs 3 01127864E 001 3 00000000E 001 3 00000000E 001 Workspace Task Executive Target V Parameters WM State variables Halt Name vae Connection Type Minimum Maximum 0 00000000E 000 4 00000000E 001 MCU_SP y SWPY iy PIDMA my MCU_HV MANLY GB MDL I SWA1 I Constant Canetvalle ctinput S SINT x For Help press F1 Fig 4 Sample of a RexView program screen contains checkboxes for the selection of the kinds of variable inputs outputs parameters and states The middle part of the page contains the list of selected variables whose values are periodically updated The connections to adjacent blocks are also visible The bottom part makes it possible to enter the values of parameters and to simulate the values of selected in puts In this case the input MAN is selected Its value 1 means that the controller is in the manual mode If we want to switch the controller to the automatic mode directly for the debugging purpose it is sufficient to check the item Constant then to choose the value 0inthe Const value of input field and finally to press the button Set The other property pages in the right hand part of the figure correspond to
9. fers to the signal AI_ PV of the driver with the name EFA in the project main file see fig 5 Similarly the block Goto with the tag EFA__AO_MV refers to the signal AO_MV of the same driver Keeping the rules above guarantees the possibility of transition from real time system simulation in Simulink to real time control in REX without the ne cessity of any configuration file change 6 OPC OLE FOR PROCESS CONTROL UTILIZATION OPC is a relatively new but at present a very widespread standard for automatic control devices data exchange especially for communication of pro cess stations and SCADA Supervisory Control And Data Acquisition or HMI Human Machine Interface levels The current REX version supports the OPC Data Access Specification OPC Foundation 2000 in two ways described below 6 1 RexOPCsv OPC server of the REX system The first way is the OPC Data Access server Rex OPCsv which can be seen in the bottom Target part of fig 1 was created mainly for the purpose of communication with a supervisory level The supre visory system can be an arbitrary system which is OPC Data Access version 2 0 client Today there are tens of such systems on the market some of them are presented in fig 1 The structure shown in fig 1 is applicable if the target environment supports the DCOM standard i e mainly in the Windows operating systems The server can also be launched in the host platform it is necessary
10. for target platforms supporting TCP IP only This struc ture is suitable for large networks Internet where the gateways to local networks are protected against unauthorized access Firewalls For this reason the DCOM packet transfer may be a problem 6 2 OPCDrv I O driver communicating with third party OPC servers The OPCDrv I O driver represents the second way of OPC utilization in REX In contrast to the Rex OPCsv server this driver is an OPC Data Access 2 0 client Thanks to this fact REX can read write inputs outputs of arbitrary devices which are equipped with OPC Data Access servers There are hundreds of such devices produced by many companies on the market 7 CONCLUSION The paper introduces a new control system called REX which is compatible with Matlab Simulink Un der certain circumstances described in section 5 2 it is even possible to move from Simulink simulation to REX real time control and vice versa without any configuration modification Using REX instead of Real Time Workshop RTW or prototyping devices such as dSpace has several advantages e Existence of industrial control blockset RexLib e No need of software licenses for prototype de vices development e Low price of prototype and or final control sys tem application The proposed solution is also suitable for the building of real remote and virtual laboratory control systems REFERENCES OPC Foundation 2000 OLE for Process
11. gnostic information and enables application download and debugging Archive subsystem serves for the archiving of events alarms and historical trends of selected variables 4 2 RexView the diagnostic tool The RexView program makes it possible to watch what is going on in the control system core Therefore it is a very important tool during the debugging of the control system and also in routine operation when a problem occurs The program offers detailed hier archically ordered information about all core subsys tems The communication protocol based on TCP IP makes it possible to connect RexView to a running core on the local computer local area network or re mote network e g through Internet Fig 4 demonstrates one type of the RexView screen A more detailed description of the program is con tained in the user manual The left part of the figure is filled by the hierarchy of control system subsystems and objects The selected P TDMA block is tenth block of the real time subsystem task mtuner in the tree structure The PIDMA block implements the PID controller equipped with a built in autotuner Schlegel et al 2002 The Workspace property page containing the PIDMA block workspace variables is chosen on the right hand part of the screen The top part of the property page 1 Blocks of the given task are ordered in the same way as they are executed in the task RexTune RexView File Target Edit View Settings H
12. mple control loop with autotuning feature based on the RexLib blocks Detailed information about these and other blocks can be found in REX Controls 2004 4 REX RUNTIME AND DIAGNOSTICS The core of REX consists of a program RexCore which runs continually on the target platform Other tools are necessary for watching the control system behavior from the host platform especially during putting the control system into operation This aim is partially satisfied by the already mentioned visualiza tion tools but a detailed view is provided by a program called RexView 4 1 RexCore the control system core RexCore is a rather complicated program performing simultaneously different activities which are usual in control systems Particular activities are executed ac cording to their priorities in the preemptive multitask ing mode The following activities belong to the core subsystems Real time Subsystem takes care of the triggering of tasks and nested fuction blocks and triggering of T O drivers It also collects and renders diagnostic information about the system performance and the timing variables of tasks and drivers Input output Subsystem provides interfaces for the I O drivers of hardware devices which are used to acquire process inputs and to actuate process outputs Algorithmic subsystem includes function block al gorithms which are called from real time subsystem tasks Diagnostic subsystem provides runtime dia
13. nd outputs connected to this driver see paragraph 5 2 for more details loop is the file name the md1 extension is ap pended automatically containing the control task configuration This task is inserted into the control level 0 see the output Leve10 of the block EXEC It is presented in fig 6 The described blocks possess inputs prev previous and outputs next which allow to chain several blocks representing modules I O drivers and control tasks in the configuration The same rule holds for archives not used in the example which are connected to the Archives output of the EXEC block and for tasks of ohter control levels Level1 Level2 and Level13 The only exception to the rule is the block Qtask not used here representing very quick con trol task there can be at most only one such task 5 2 RexComp Compiler of configurations The RexComp program compiles a project main file in md1 format into a binary configuration file of the REX control system Note that the main file exec md1 configuration is shown in fig 5 The com pilation process consists of the following steps 1 Finding of the real time executive block EXEC in the project main file checking of the executive parameters 2 Finding and checking of all control system ob jects which are drawn in the project main file 3 Addition of configuration objects modules drivers archives the quick task and tasks of u
14. onsists of the only one file which can contain many subsystems see the file Loop md1 in fig 6 and the subsystem Simulation of the process in fig 7 any REX configuration consists of at least two files Only one of them is called the project main file in this case the file exec md_1 in fig 5 The project main file specifies the configuration of the RexCore particular subsystems which are described in paragraph 4 1 Our example is very simple the real time executive is represented by the block EXEC the remaining blocks serve the following purposes EFADRV ETS Fast Advantech Driver is one of the REX control system modules This particular mod ule implements the fast driver of several PCI boards by Advantech for the hard real time operat ing system Phar Lap ETS Embedded Tools Suite by VenturCom EFA is an I O driver block Its first parameter is the name of a module implementing the driver in this case EFADRV The next parameter is the name of a configuration file which contains information about 2 The present version of REX supports also other drivers e g Modbus master an slave also over TCP IP standard Advantech driver OPC driver etc see fig 1 the source of control system inputs and destination of outputs in addition to the device parameters For control system design the most important parame ter is the name of the block here it is EFA which determines the prefix of all names of inputs a
15. sed com puting levels 4 Memory allocation and setting of configured blocks parameters 5 Checking of control task connections 6 Whole configuration validation check 7 Storing of the compiled file with the extension rex on the disc During its run the compiler writes out the information about the files being compiled and about possible compilation errors Each of the described steps can fail fatally which results in compilation abort and the binary file is not created Effective transition from simulation in Simulink to realtime control is supported by the following two rules of RexComp 1 All subsystems in md1 files the names of which begin with the word Simulation are skipped i e they are not compiled 2 All blocks From and Goto whose Tag is of the form lt prefix gt __ lt name gt are substituted by standard input and output blocks of the REX system These blocks refer to the I O driver block with the name lt prefix gt Further the sym bolic name lt name gt of an input or an output is searched in the driver configuration The two characters _ underscore serve as the separator of a driver prefix and an input or an output vari able name in the driver The following example demonstrates how these rules work Due to rule 1 the subsystem Simulation of the process is eliminated Rule 2 determines that the block From with the tag EFA__AI_PV is substituted by the standard REX input block which re
16. t hand value a tuner break Dy tuner affirmation DI par set index tuner outputs integrator hold tuner results ips 0 controller parameters ips 1 process moments ips 2 FOPDT processmodel SLEEP HINT 1 set tuner parameters 2 in manual mode MAN 1 TUNE 0 set a working point by hand value hv and wait for steady state 3 TUNE 0 gt 1 starts the autotuning function TBSY 0 gt 1 4 wait for the end of tuning TBSY 1 gt 0 if TE 0 then all is OK 5 check the computed PID parameters in closed loop TAFF 1 MAN 0 change sp or dv Fig 3 Simple autotuning control loop in REX SC2FA is a self tuning controller for lightly damped processes A new algorithm of the frequency do main identification and the standard state space ap proach form the core of the automatic controller design method REXLANG is a special function block which allows the user to write his her own code in the program ming language called RexLang This language sup ports all common C language commands e g if else for while do while switch call ing user defined functions standard math functions and work with indexed arrays RexLang is almost a subset of the C language except for commands input output parameter which map block inputs u0 to u15 outputs yO to y15 and pa rameters p0 to p15 to user defined C language variables Fig 3 demonstrates the example of a si
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