Under high-frequency variable loads, EV electrical system is prone to causing bus voltage oscillations and instability. A small-signal model of the vehicle’s electrical system has been established, obtaining the output impedance of the system source-transformer and the input impedance of the motor load. Based on the traditional impedance ratio criterion and combined with the system’s stability margin, the stability determination principle of the vehicle’s electrical system has been derived. By using a Bode diagram for predicting system instability, research is conducted to explore the instability boundary of pure electric vehicle under high-speed conditions. The simulation verification results show that the vehicle’s maximum speed shall not exceed 188 km/h, and torque variation of hub motor will affect vehicle stability, the torque mutation of single hub motor shall not exceed 220 N·m, which is basically consistent with theoretical analysis results. The results prove that this stability determination principle can predict instability boundary of vehicle electrical system to some extent.

Vehicle electrical system  /  Small signal model  /  Impedance ratio  /  Instability prediction  /  Instability boundary