When an electric vehicle (EV) catches fire, the damaged lithium-ion battery can cause a runaway thermal reaction due to its chemical properties. This makes it difficult to extinguish the fire and releases large amounts of toxic gases such as hydrogen fluoride. Statistics show that the typical amount of water required to extinguish an EV fire is 40 times the amount required for a conventional gasoline-powered vehicle. Given the significant impact temperature has on Li-ion battery performance, improving EV efficiency and safety hinges on an effective Battery Management System (BMS).
For automotive BMS, it’s important to note that the battery pack is not directly connected to the motor. Instead, it interfaces through relays and fuses (as shown in the diagram below). Any disconnection or abnormal connection between these components can lead to unexpected increases in impedance. Since the voltage and current flowing from the battery to the motor are substantial and fluctuate frequently, increased impedance can cause system temperatures to rise and become unstable. In the worst case, this can lead to thermal runaway and fire. An effective way to address this is by simulating voltage scenarios at various points along the high-voltage path. This makes it easy to verify whether the BMS can adequately respond to these conditions and ensure a safer and more reliable system.
Another important consideration is that in an actual vehicle, the battery pack case is connected to the vehicle chassis. Given the high voltage and current directed to the motor, the entire power delivery circuit must maintain a specific impedance relative to the battery pack case to prevent electric shock. If the battery pack case becomes electrified, the entire chassis, including doors, could carry an electric charge, posing a severe shock hazard. This is why it’s vital to verify that the BMS can accurately detect low impedance at each point and take appropriate protective actions. However, the minimum allowable impedance at each point varies based on product design. Therefore, when performing this test, the impedance matching must be properly adjusted for each point to achieve optimal test results.
The Chroma 8630 BMS Power Hardware-in-the-Loop (HIL) Testbed provides a Pack Voltage and Isolation Impedance Simulator that allows users to easily perform the tests mentioned above. The programmable voltage simulator enables replication of various voltage drops caused by poor connections. Its modular nature allows fast and flexible testing of different product designs and characteristics. It offers nine selectable resistance levels (Opened, 200K, 500K, 800K, 1M, 2M, 3M, 5M, and 10M ohms) and utilizes a programmable, modular switching method for simple, efficient, and rapid adjustments to meet the needs of a wide array of specifications, providing an optimally cost-effective test solution.
With 40 years of experience in precision test & measurement instruments, Chroma is a leading provider of automated test systems with a focus on power electronics test applications. As the renewable energy industry surges forward, we’re actively involved in developing test solutions for electric vehicles, energy storage systems, and fuel cells. Our commitment is to provide comprehensive solutions that empower every technological breakthrough, driving the continuous advancement of the industry.