MODELING AND DAMPING OF HIGH-FREQUENCY LEAKAGE CURRENTS IN PWM INVERTER-FED AC MOTOR DRIVE SYSTEMS

This paper presents an equivalent circuit for high-frequency leakage c urrents in pulsewidth modulation (PWM) inverter-fed ac motors, which f orms a series resonant circuit. The analysis based on the equivalent c ircuit leads to such a conclusion that the connection of a conventiona l common-mode choke or reactor in series between the ac terminals of a PWM inverter and those of an ac motor is not effective to reduce the rms and average values of the leakage current, but effective to reduce the peak value. Furthermore, this paper proposes a common-mode transf ormer which is different in damping principle from the conventional co mmon-mode choke. It is shown theoretically and experimentally that the common-mode transformer is able to reduce the rms value of the leakag e current to 25%, where the core used in the common-mode transformer i s smaller than that of the conventional common-mode choke.