A novel non-zero sequence choke and its application in output EMI filters for PWM inverters

This paper proposes a novel non-zero sequence choke and analysis of its characteristics when applied as an EMI filter to reduce the common-mode voltage in the PWM inverter. The non-zero sequence choke behaves like an inductor only in the differential-mode circuit, but it has zero impedance in the common-mode circuit. When it is used in series with the capacitors as the EMI filter, the differential-mode currents flowing through capacitors are blocked without any effect on the common-mode voltage reduction. Furthermore, since the zero sequence-choke is very small, the proposed common-mode EMI filter is smaller than the conventional filter. Experimental results on a real drive system confirm the theoretical concepts and verify the feasibility of industrial applications.