PWM-control methods for common mode voltage minimization - a survey

The common mode voltages produced by fast switching IGBT-PWM inverters are often the reason for bearing damages. These are caused by the current flow through the bearing after breakdown of the bearing lubricating film. The decisive current parts in the medium power range are the electric discharge machining current and the dv/dt-current. They are dependent of internal motor conditions, amplitude and common mode voltage rise. Therefore it is useful to modify the PWM so that these causes can be reduced. In this contribution the known PWM-methods for reduction of common mode voltages are compared with the help of some essential criteria like modulation index, switching frequency, harmonic content, and isolation stressing of motor windings