Suppressing of common mode voltage on ac motor with changing ground point of DC link in PWM inverter

With the increased application of adjustable-speed drive of AC motor, there has been a growing number of failures such as electromagnetic interference(EMI) caused by common mode current, and bearing current. Especially, bearing current leads to motor bearing material erosion and early mechanical failure. To reduce the bearing current, there are two methods, one is reduce the common mode voltage, and another one is reduce the motor shaft voltage itself. This paper describes the approaches to suppress the Common mode voltage on ac motor with changing the ground point of DC link in PWM inverter.