A Hybrid Filter for the Suppression of Common-Mode Voltage and Differential-Mode Harmonics in Three-Phase Inverters With CPPM

In the motor systems driven by sinusoidal pulse width modulation (SPWM) three-phase inverters, the peaks of common-mode (CM) voltage are so high that it will cause many negative effects. In this paper, a hybrid filter is presented to reduce the CM voltage (CMV) and the differential-mode (DM) harmonics in a three-phase inverter with carrier peak position modulation (CPPM). Because the use of CPPM strategy in the inverter can ensure that the output CMV will be only two levels in any condition, the simple active CM filter (composed of a half-bridge circuit) in the hybrid filter can effectively suppress the output CMV and CM current. The passive filter in the hybrid filter consists of an added single tuned filter and the original DM low-pass filter. The single tuned filter is designed to lower the DM harmonics, which are aggravated by the CPPM strategy in the carrier frequency band. Through the experiments, the validity of CMV and DM harmonics suppression by the hybrid filter in the three-phase inverter is verified and the calculation-control active CM filter is proved to be the best in the optional schemes.