A new multilevel carrier based pulse width modulation method for modular multilevel inverter

Abstract

The multilevel inverters (MLIs) utilization have been increased in recent years due to its advantages such as: staircase waveform quality, better harmonic spectrum, reduced EMI, eliminated common mode voltage and etc. Different methods have been proposed for multilevel inverter modulation that one of them is level-shifted PWM method (LS-PWM). In this paper a new LS-PWM method is introduced that uses rotating carrier waveforms for generation of gate signals of switches to balance switching pattern in all cells for a modular MLI, at all modulation indices. A three phase seven level modular inverter is used to explain the method. This method can be easily extended to an n-level inverter. Simulation has been carried out and results show that the proposed method can balance switching pattern for all cells compare to the conventional LS-PWM while the quality of waveforms has not been changed.