Effects of switching frequency and motor speed on common mode voltage, common mode current and shaft voltage in PWM inverter-fed induction motors

High-frequency components and large amplitudes of the common mode voltage (CMV) at the motor neutral point generate high-frequency common mode current (CMC) to the ground path and induce voltage on the shaft, which eventually reduces the machine life. This paper presents the effect of switching frequency and motor speed on CMV, CMC and shaft voltage. Three parameters viz. common mode voltage peak factor, common mode current peak factor and shaft voltage peak factor are proposed to define the stresses generated at ground wall insulation and bearings when induction motor is operated with inverter. The results can be used for verifying the feasibility of the mitigation techniques for CMV and bearing currents at different switching frequencies and motor speed.