A lithium-ion battery modeling for a HIL-battery simulator

A battery simulator is needed to test battery management systems (BMS) for electric vehicles. A new battery simulator called a Hardware in Loop (HIL)-battery simulator is build. In order to facilitate the electric battery model part of the HIL-battery simulator, a simple and accurate equivalent circuit model for LiFePO₄ batteries is defined. For estimating and identifying the battery parameters from measurement data, tools and processes are implemented based on an open-circuit test and an impedance test. The measurement is applied for discharging and charging a LiFePO₄ battery cell. From the open-circuit test, the open-circuit voltages as a function of state of charge are determined. From the impedance test, the real part and the imaginary part of impedances as a function of state of charge are extracted. By applying Nyquist plot observation of impedances, the parameters of the electric battery model are determined. By fitting curves between the measured impedance and the modeled impedance, the electric battery model is chosen to the second order battery model. This second order battery model can cope the transient behaviors of the LiFePO₄ cell sufficiently. The parameterized battery model is used for the battery simulator on its electric model and the results fulfill the requirements.