Asymmetrical carrier phase‐shifted pulse‐width modulation for partly regenerative converter

Abstract

A cascaded H-bridge-based partly regenerative converter is a low-cost scheme to enable a medium-voltage motor drive to feed back the braking energy to the grid. However, its asymmetrical topology induces serious switching harmonic distortion on the motor side when conventional symmetrical carrier phase-shift pulse-width modulation (SCPS-PWM) is used. This study analyses switching harmonic characteristics in detail and proposes an asymmetrical carrier phase-shift pulse-width modulation (ACPS-PWM) method to improve the switching harmonic performance of the partly regenerative converter by eliminating low-frequency switching harmonics. The proposed method transcends the limitation of SCPS-PWM on carrier phase-shift angles, increasing the controllable degrees of freedom that can be used to multiply the apparent switching frequency without extra hardware or software investment. ACPS-PWM is compared with other modulation methods, and the possibilities for other applications are discussed. Experimental results verify the effectiveness of the proposed method.