From BMS to Battery Pack: The Importance of Power Hardware-in-the-Loop (HIL) Test Systems
From power output to driving range, the performance of electric vehicles (EVs) heavily relies on the ability to charge and discharge their battery packs. As one of the most crucial EV components, battery packs must meet the highest standards of integrity and safety - hence their classification as the highest ASIL-D requirement level. Today’s EV battery packs incorporate ingenious mechanical designs, extensive battery cell monitoring and management strategies, multiple switch and fuse safety mechanisms, thermal management systems integrated with the vehicle’s heat sources, as well as intricate battery state estimation and safety strategies. Given this complexity, the smallest design flaws could result in sizeable correction costs further down the line, which is why all these aspects demand rigorous testing before the battery pack enters automated production.
We can divide EV battery packs into two system levels: the Battery Management System (BMS) at the first level, and the complete battery pack combining battery cells with other components at the second level.
In a real environment, a BMS may encounter compound failure scenarios, such as battery overheating and communication line failure both within a short period of time. It's important to verify not only the BMS's ability to detect faults effectively but also the promptness and efficacy of its response mechanisms. For instance, the BMS should issue power limitation instructions to other power-consuming devices in the system (like MCUs) within milliseconds. The Power HIL system can use battery and MCU models to instantly simulate the real discharge behavior of the battery pack. Chroma 8630 also generates actual current to the current sensor, which can further correct the impact of the current sensor measurement signal on the SOC calculation algorithm under instantaneous current changes.
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Now for the second system level, where the BMS is combined with battery cells and other components to form a complete battery pack. A battery cycler by itself can only replay specific current records to test the known limits of the battery pack. The battery pack Power HIL, which has a real-time control system, can import a vehicle model to dynamically simulate the current under real driving conditions, further test various driving cycles, and achieve an evaluation of the battery pack with actual power that is equivalent to a real vehicle road test. This includes, for instance, battery pack temperature control and SOC correction under conditions such as rapid acceleration and deceleration, the execution effect of battery performance prediction, etc. Chroma 8610 also has on-board electrical safety testing equipment to test the insulation of the battery pack before and after high-power testing.
From the ISO 26262 perspective, design engineers are advised to implement continuous hazard analysis and risk assessment throughout the development cycle, from the initial design phase to the final verification stages. Early detection and rectification of any flaws in design or manufacturing, alongside latent faults and risks that may be discovered, are sure to be worth the effort. As EV battery packs become more complex, it's becoming increasingly important to apply ISO 26262 principles starting from the BMS level. Implementing a second round of HIL verification at the battery pack level then emerges as a logical and critical next step in the process. The comprehensive Chroma 8610 + 8630 power HIL test platform combo (both platforms can use the same real-time control system) is designed to cover the entire BMS-to-battery pack design process, reducing hardware and software costs as well as user learning curves.