Sponsored by Pickering Interfaces
A complete physical HIL simulation system based on modular PXI simulation and switching modules
Imagine the challenge. You work for an electric vehicle (EV) startup and design the Hardware-in-the-Loop Simulation (HILS) test system. Everything is new – hardware, software, tools, testers and test code. Still, the system must be as accurate as possible to properly simulate the operating environment. You also work on the electronic control unit (ECU), which monitors and controls the EV batteries. To test them thoroughly, the software must be stressed beyond its normal operating range. To thoroughly test EV battery control algorithms, enhanced simulation with fault insertion is the only way to safely test the software before hitting the road in prototype vehicles.
Hardware in the Loop Simulation for Automotive ECU Systems
During development, HILs are typically used to test the operation of the ECU in a simulated real environment in which the ECU will operate. Instrumentation simulates sensor inputs from an ECU and captures and verifies control outputs from the ECU. Safety-critical controllers typically require certification, where faults including short circuits and open circuits are introduced. The ECU’s response is analyzed to ensure that it operates predictably and safely. Automated defect insertion systems allow verification testing to be performed efficiently in a controlled and repeatable manner.
The automotive environment can often be very harsh, especially for sensors, with wide temperature ranges commonly encountered. Failures can occur due to corrosion, aging, damage or even faulty installation. Due to all the features and options available in vehicles, especially as more and more electronic systems are introduced for ADAS systems, the ECUs are becoming very complex, so the accuracy of HILS is essential for a launch successful.
In an EV, the battery dominates, so the ECU that manages the battery must be very precise, efficient and reliable to ensure safe operation.
Software testing of an electronic battery control unit in an electric vehicle startup
Pickering Interfaces provides products and services to streamline the design, deployment and maintenance of high performance electronic test and verification systems. The company was approached by a team that was designing an electric vehicle start-up’s software test systems for battery ECUs. HIL test systems and benchtop testers are required.
The software testing team faced three challenges. First, he found himself in a very dynamic and changing situation. As a start-up addressing a new market, the product range was always evolving as new requirements emerged. This meant that long-term testing strategies with common test items were difficult to plan and implement. Second, everything was new. The ECU software, hardware and sensors were new. Both hardware and software needed debugging, and sometimes it wasn’t clear whether the problem was due to hardware or software failure. The battery configuration was also new. Indeed, the test team itself – although made up of very experienced personnel – was also new. Finally, the test environment was potentially dangerous. To ensure operational safety limits, actual EV batteries should be tested well above their specified ratings. High currents up to 2000 A and high voltages in the hundreds of volts must be used in a real EV battery for functional safety reasons. Therefore, many redundancies and extreme security precautions were required for conventional testing.
In this context, the team constantly struggled to ensure that the HIL test system design was functionally safe, accurate and reproducible and was able to scale to dynamic hardware and software development cycles. In their own words, it was “a monumental challenge to wring all the rooms simultaneously while adhering to an aggressive schedule.”
Therefore, the software testing platform had to be scalable and very flexible. The decision to use instrumentation based on industry standard PXI and LXI formats was obvious. Yet the EV start-up also decided to use both a fully functional HILS system and flexible benchtop equipment in its software testing strategy.
HIL systems must simulate the environment in which the system will operate not only for security reasons, but also to thoroughly instrument a comprehensive test strategy. This can be achieved using models and simulations or by physical means. Accuracy and repeatability are essential. Models can be very space and cost efficient, but the accuracy or exact replication of the simulation environment can suffer. With batteries, temperature control is essential to avoid thermal runaway. Electric vehicle batteries can easily use more than 100 thermistors. The EV test development team preferred to use programmable resistors as the physical representation of thermistors, because the behavior of a programmable resistor more accurately represents that of a thermistor (which is, of course, a type of resistor). The programmable resistors will also give the full range of characteristics of the actual sensor, including variations with temperature – described by the EV company as the “thermal isotope”. However, with over 100 sensors to simulate, it is necessary to select programmable resistor boards with as many channels as possible to avoid making large test systems. This becomes a trade-off for acquiring enough channels, accuracy, and range versus cost and space. The customer commented that the test system becomes “more complex than the real system to be able to simulate and test all possible eventualities”.
The insertion of faults is another consideration; for example, how do you reproduce and respond to a broken thread? If you are driving a high voltage and current drive relay, in the worst case control currents as high as 50A can be flowing – essentially a welder – so all circuits must be able to handle 50A and respond in a specific time and shut off effectively.
The HIL test system team leader was a long-time user of Pickering products in his previous job. So the team reached out to Pickering to overcome the limitations of their existing HILS systems, which weren’t flexible enough to meet their needs for new test ranges and capabilities. . Lack of support was also an issue. Pickering worked with the team to develop a roadmap for a HILS system more suited to their needs.
A complete physical HILS system based on the following Pickering products:
The HILS system was designed for fully automated operation, performing full physical functional testing overnight without supervision. For more specific granular testing, the EV company also specified benchtop systems based on similar products housed in Pickering’s 2-slot LXI/USB Chassis (model 60-104-001). While with the full HILS system the focus was on the performance, scalability and flexibility of Pickering solutions, the small size was the main advantage of the benchtop tester.
In addition to these benefits, the EV test system development team said Pickering’s long history of providing high-quality switching and simulation products that are easy to use and program was an important reason to choose Pickering. “With all the changes we were going through, it was nice to have something to rely on – that I don’t have to worry about,” the Pickering client said.
Learn more about Hardware-in-the-Loop testing at pickeringtest.com.
Sponsored by Pickering Interfaces
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