A Modular Wide Bandwidth High Performance Automotive Lithium-Ion Cell Emulator for Hardware in the Loop Application

The performance of electrical vehicles strongly depends on characteristics of its energy storage system. A typical lithium-ion battery system is supervised by a battery management system to optimize operation and ensure safety over its whole lifecycle. Advanced battery management systems apply sophisticated fast charging procedures and active cell balancing. In future, impedance spectroscopy based on driving current stimulation for online estimation of the energy storage’s state of health can be expected. For efficient development and testing of such battery management systems it is impractical to use real lithium-ion cells in arbitrary condition of state of charge, temperature and state of health. Consequently, hardware in the loop cell emulators are state of the art. Most of them are limited to low frequency operation. In this paper, a novel modular wide bandwidth high performance lithium-ion cell emulator is introduced. The performance is proven by applying a commercial active cell balancing system and by performing electrochemical impedance spectroscopy. One electronic unit emulates a single cell, while multiple of them can be stacked to form a complete energy storage system up to 1000 V. Every module is autonomously operating in stand-alone mode and contains the full computing power for emulating open circuit voltage and output impedance depending on state of charge, temperature and aging. A fast high resolution acquisition stage samples the input current with 18 bit at 5 MSPS. The output cell voltage is generated by a power amplifier with 8 MHz bandwidth and up to ±10 A output current, while the output is fully protected. Leakage current can be measured down to 1 μA. High performance and long term stability is achieved by a self-calibrating system, using one single stable floating Zener reference.