Analysis and Mitigation of Bearing Current in Inverter-Fed IPMSMs Drive System

Voltage source inverters (VSIs) are widely used in electric vehicle due to their high control performance and efficiency in electric motor drive systems. However, the output voltage of the inverter during switching instances generates bearing currents, leading to bearing damage. This article analyzes the relationship between bearing currents and bearing damage, and proposes a new method for reducing bearing currents. First, a precise bearing current measurement system using a current transformer is introduced. This system verifies the phenomenon of bearing damage caused by bearing currents at low speeds. Fourier transform analysis of audio signals from bearings is employed to confirm this phenomenon. Subsequently, a two-phase pulse-width modulation (PWM) method that considers the saliency of interior permanent magnet synchronous machines (IPMSMs) and a capacitive filter topology is presented. The proposed method is validated through experimental results in a commercial electric vehicle drive system. As a result, the bearing current is reduced by 91% compared to that of space vector PWM (SVPWM) method.