Unipolar stitched inverter low-frequency harmonics caused by stitching delay

Abstract

Unipolar switched single-phase inverters experience lower switching losses and generate less electro-magnetic interference (EMI) when compared with bipolar switched inverters. However, these benefits come at the expense of increased distortion in the current waveform near the voltage zero crossing. Furthermore, it is demonstrated in this paper that circuit delay is a major cause of the generation of low-frequency harmonics (LFH). A new analytical method to explain why circuit delays are responsible for the generation of LFH in unipolar switched inverters, and not in bipolar switched inverters, is presented. Numerical results calculated from this theory are compared with simulation and experimental results to illustrate this relationship.