A phase shift Selective Harmonic Elimination method for balancing capacitor voltages in a seven level Cascaded H-Bridge Rectifier

This paper presents a low switching frequency, selective harmonic elimination (SHE) modulation method which may be applied to a cascaded H-bridge active rectifier. The method is based on a decoupled scheme where the modulation index of each H-bridge cell is controlled independently to enable complete control of power flow through the converter. The method utilises a phase shift between the AC side cell voltages to achieve the required cell power balancing but with reduced distortion in the output waveform when compared with previously presented methods. Practical results from a laboratory based prototype converter are presented to validate the analysis. Although presented for a single phase topology the method can be applied to a three phase converter.