Asymmetrical modulation and over-modulation techniques of parallel connected NPC-PWM inverters for AC motor drives

Abstract

A technique of parallel connection of power devices using current sharing reactors for neutral point clamped (NPC) PWM inverters is reported in this paper. The proposed modulation techniques can improve the output characteristics such as output voltage level or output harmonics. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, thus it is anticipated that it will be difficult to analyze the output waveforms. For such waveforms, a frequency analysis approach is described, whose results are verified by experiments.