Hybrid multi-carrier PWM technique with computationally efficient voltage balancing algorithm for modular multilevel converter

Abstract

Phase-shifted pulse width modulation (PS-PWM) technique is preferred for modular multilevel converters (MMCs) as it has even power distribution and also ensures uniform switch utilization among the submodules (SMs). In contrast, phase disposition PWM (PD-PWM) technique has superior output voltage profile, but suffers from unequal switch utilization. A new PWM technique is proposed in this paper, having the best features of the PS-PWM and PD-PWM. The SM capacitor voltage balancing algorithm has to be incorporated with the modulation scheme to maintain SM voltages at defined voltage level. This paper also presents a modified SM capacitor voltage balancing approach which can be easily implemented with any type of carrier-based PWM technique. The proposed balancing algorithm, as well as PWM technique can be extended to any level of MMC and also applicable to any SM type. The effectiveness of proposed PWM technique is validated for five-level MMC with flying capacitor SMs (FCSM) under different operating conditions against PS-PWM and PD-PWM by simulation results in PLECS platform.