Reduced common-mode modulation strategies for cascaded multilevel inverters

This paper presents 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 and Phase Disposition 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 hath continuous and discontinuous switching conditions. The strategies have been confirmed by both simulation and experimental results obtained using a cascaded five-level inverter. Index Terms--Common-mode voltages, harmonic analysis, multilevel inverters, pulsewidth modulation (PWM).