Common-mode voltage reduction for regenerative AC drives

When the conventional space vector PWM (SVPWM) schemes are applied to regenerative AC drives, very high neutral to ground voltages are generated at the motor. This can result in premature failure of the motor bearings and stator winding insulation to ground. The DC bus to ground voltage may also be elevated to very high levels, resulting in failure of various components within the drive. Popular methods to mitigate these issues include synchronization of the carrier wave between the rectifier and inverter and filters at the output of the drive. While synchronization cannot be achieved in all applications and presents significant design trade-offs, filters are bulky, expensive and may not address all issues. In this paper, common-mode voltage (CMV) and common-mode current (CMC) reduction PWM schemes are investigated for their application to regenerative AC drives. It is shown that the CMV can be significantly reduced without PWM carrier synchronization, and without affecting the performance of the drive.