Suppressing low-frequency components of commonmode voltage through reverse injection in three-phase inverter

The output common-mode voltage (CMV) will bring many negative effects in a three-phase inverter, which is controlled by the sinusoidal pulse-width modulation (SPWM) method. The carrier phase-shift method and the carrier-frequency modulation method can reduce the peaks of the CMV at the switching frequency and its harmonic frequencies, but they may cause increase of the low-frequency (LF) baseband harmonics. A new reverse injection scheme is proposed to suppress the LF harmonics. In this scheme, the parameters of the interference peaks are obtained through CMV detection and real-time harmonic parameters estimation. The estimated phase errors from the detection-control delay are amended by the method of temporary addition of the standard phase signal. Then, the sinusoids with a reverse phase to the LF harmonics are generated and injected in the reference sinusoid of each phase to produce the SPWM. Thus, the LF peaks of the CMV are counteracted. The feasibility and the validity of this scheme are verified through the experiments under different control strategies.