Modeling and Analysis of Capacitive Bearing Voltage of In-Wheel Hub Motor Reduction System for Electric Vehicles

This study focuses on the in-wheel hub motor reduction system, analyzing the parasitic capacitances of the hub motor and planetary gear reducer, as well as the voltage division paths of common-mode voltage (CMV) within the two-stage planetary reducer. A CMV loop model for the entire in-wheel hub motor reduction system is constructed. Extensive simulation of the control model and measurement of shaft voltage demonstrate that the introduction of the two-stage planetary reducer significantly reduces the voltage division across the hub bearings. Additionally, the shaft voltage of the motor bearings is slightly lower compared to a standalone motor system. However, the coaxial structure, larger gear pairs, and hub bearing capacitances provide paths for high frequency circulating currents.