Simplified Design of Common-Mode Chokes for Reduction of Motor Ground Currents in Inverter Drives

A simplified design calculation for common-mode chokes for reducing motor ground currents provides insight on the effects of various parameters and allows easy design. Key simplifying assumptions are that the voltage rise time is short compared to the ring period and that the damping is small. Example designs for machines up to 450-mm frame size show how effective ground-current reduction is possible with small inexpensive single-turn chokes.