2004-01-1240 An Overview of Hardware-In-the-Loop ... - dSPACE

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addition of new requirement, and refinement ofrequirement. The late changes in requirements cause asignificant impact on the development and testing timeof control system software and this iterative loop ofrequirement change, development and testing is notvery efficient. Further, obtaining a prototype vehicleduring the early software developmental phase isextremely difficult and cost prohibitive, especially for anon-OEM (Original Equipment Manufacturer)companies.A Powertrain Control Module (PCM) is one of the mostcomplex electronic embedded control systems in themodern vehicle. The PCM software therefore requires arigorous and through testing of its functionality. In orderto manage the increasing demand of technology in PCMdesign, Visteon Corporation started investigating thepossibilities of using a state-of-the-art HIL system forPCM software development and verification in 1998. HILtechnology is best suited to perform a complete andrigorous testing of the Embedded control systemsoftware of PCM. Visteon anticipated that HILsimulation would improve quality and also reducedevelopment time and cost. At the same time the HILsystem based development and testing will complementthe implementation of model based softwaredevelopment (MBD) technology. The initial strategy wasto implement HIL for PCM software testing only.However, over time it became apparent that the sameimplementation could be easily tailored for theSoftware/Hardware Interface validation as well.Implementation of a HIL system for testing during thedevelopment phase of PCM software also addressesother issues associated with the traditional bench testenvironment. Some of the issues associated with thetraditional bench test environment are uncontrolled andnon-repeatable tests without proper closed loopfeedback to perform a complete system verification andvalidation of the software in real time, difficulty inachieving consistency, manual mode of operation for setpoints, ad hock data capture and test results and thenear impossible task of testing the complex closed loopcontrol algorithms of the PCM software in an open loopbench test environment.Visteon has proven that there are significant benefits ofOpen Loop HIL testing during the initial phase ofsoftware development by performing unit level softwareverification. HIL testing is also used for verification ofthe Software and Hardware Interface of the low-levelplatform software. The integration of HIL systems withcalibration and diagnostic tools also provides significantadvantages with closed loop simulation and testing ofcompletely integrated software in real time on the bench.Several other features of HIL such as test automation,test stimulus generation, and fault-insertion testing areaddressed. These HIL systems use Python, anadvanced test scripting language, to control testsequences and coordinate the variety of interfacesnecessary for a particular test, or a set of tests. Thistest-scripting feature of the HIL system gives the testdeveloper the capability to implement full lights-outtesting scenarios and also allow for exact reproductionfor subsequent DUT (Device Under Test) regressiontesting. The HIL systems also have the capability toinject stimulus signals into the DUT, which can be usedfor a variety of purposes. These include drive cycles foran engine or vehicle test, and also response datahistories for component validation.Finally, the interfaces between the PCM and the plant(Vehicle, Engine, etc) need to be tested. When failuresoccur with sensors or actuators, the PCM generallyneeds to detect these and provide for strategies toovercome them. Using the HIL systems, it is fullypossible to simulate almost any type of failure that acontroller could experience. This failure testing can alsobe performed during critical control periods, which mightnot be possible to implement on the actual target plant.Figure 2 Visteon HIL ArchitectureVISTEON HIL SYSTEMARCHITECTUREThe Visteon HIL software-testing environment is built onmodified dSPACE midsize and/or full size enginesimulators integrated with several off the shelf tools. Thesystem architecture of the Visteon HIL system is shownin block diagram in Figure 2. The Visteon HIL simulatoris housed inside a 19” desktop rack containing a PowerPC processor board for real time computation, aspecialized automotive HIL I/O board, additional I/Ocards, required signal conditioning boards, load boardswith fault simulation capability as the main component ofthe simulator. The system is also equipped with a
emote control power supply. The power supply can becontrolled in real time during simulation, which providesthe capability of vehicle battery simulation The PCM isphysically connected to the HIL simulator by customizedharnesses for I/O routing either directly or throughswitchable breakout boxes. Further, it is possible toattach actual physical component assemblies to the HILsystem using an external interface. The system alsoaccommodates integration of off-the-shelf calibrationand diagnostic tools. The integration of calibration anddiagnostic tools with the HIL system provides thecapability of automated testing of very complexPowertrain control system software. [3]One of the critical parts of this HIL system is the loadsubsystem. It is very critical to have an appropriate loadfor the actuator signals in order for the PCM software towork properly. In order to accommodate the specialcharacteristics of certain actuators the system connectsto a specially designed company proprietary loadsubsystem. The closed loop simulation of the systemrequires appropriate feedback response from theactuator load to satisfy the smart device driver integratedcircuits (IC) and advanced On Board Diagnostics (OBD)system software. Without the appropriate closed loopsystem and actuator load feedback, the PCM controllerwill enter a fault mode and will defeat the purpose ofvalidation of the system software. For the completeclosed loop system simulation another significationrequirement is the representative plant model. The plantmodel should represent the physical behavior of theplant; in our implementation the plant consists of theengine, the transmission and other ancillarycomponents.interfaces. Refer to Figure 3 to see a depiction of someof these interfaces. Below is a list of just some of thephases required to perform HIL testing:• Control of the test sequence to run and ability toregressively test• Injection of test stimulus in real-time• Access to the model parameters and data andcontrol of the simulation state• Access to external devices (Testers, Voltmeters,etc.)• Access to and control of PCM interfaces (diagnostictools)• Ability to generate test documentation and save testdata• Test data analysis during the testThe system chosen to perform the testing must providethe power to perform the above tasks, yet needs to berelatively easy to use in order to minimize testdevelopment costs and allow for changes in the testingprocess. The system chosen by Visteon is the softwaretool ControlDesk ®2 , by dSPACE. ControlDesk providesall of the capabilities needed for a HIL test system,including hardware/model management, data acquisitionand graphical user-interface capabilities. The TestAutomation extension of ControlDesk is based on thepython language, and it provides the interface librariesneeded to automate the tools and programs needed toperform the above listed tasks.A set of plant models suitable for real-time simulationhas been developed and validated in-house, torepresent various automotive subsystems for differentpowertrain applications. The real time executable plantmodels are developed in MATLAB ® , Simulink ®andStateflow ®1 , and are composed of flexible andconfigurable component and sub component models.Physical component and systems are represented inmathematical models. These representative plantmodels are developed with significant and adequatedetail to perform the controller software algorithmverification and validation.TEST AUTOMATION SEQUENCE CONTROL ANDDESIGNPhases of testing and automationThe task of powertrain hardware and software testingusing HIL simulation requires many phases andFigure 3 Interfaces in HIL SystemTest sequences and scripting with pythonPython is an open source language, available on thewww.python.org website. It is an extremely powerful,1MATLAB, Simulink and Stateflow are trademarks of The MathWorks,Inc.2ControlDesk is trademark of dSPACE GmbH.
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