Reduced common mode carrier-based modulation strategies for cascaded multilevel inverters

Abstract

This paper presents carrier-based modulation strategies for cascaded multilevel inverters that substantially eliminate common mode voltage on the output phases. The paper begins by developing generic multilevel inverter reference waveforms that use only "allowed" space vectors to achieve reduced common mode voltage. A graphical technique is then proposed that allows various carrier disposition modulation strategies for a diode clamped inverter to be converted to equivalent modulation of a cascaded inverter for any fundamental reference waveform. This graphical technique is confirmed for both alternative phase opposition disposition (APOD) and phase disposition (PD) equivalent modulation of a cascaded inverter, and is then used to create reduced common mode modulation strategies for cascaded inverters from their equivalent counterparts for diode-clamped inverters under both continuous and discontinuous switching conditions. The strategies have been confirmed by both simulation and experimental results obtained using a cascaded five-level inverter.