Review and re‐evaluation of modulation techniques for neutral‐point‐clamped inverters with high‐order filters

Abstract

The centred space vector modulation scheme is considered to be the best since it produces the least switching harmonics among the modulation techniques developed for neutral-point-clamped (NPC) inverters. However, this common belief was concluded in the condition when inverters interfaced to the grid with a simple inductor filter. Nevertheless, to achieve an excellent harmonic attenuation performance, higher-order filter is much preferred for NPC inverter. Consequently, the aforementioned common belief may lose its correctness due to the distinctive resonance characteristics accompanied by high-order filters. The objective is to review and re-evaluate the performances of the commonly used modulation techniques for NPC inverters when different high-order filters are applied. Furthermore, this study provides a guide to choose an appropriate modulation scheme when high-order filters are used. The sinusoidal pulse-width modulation with alternative phase opposition disposition shows the best performance since it always ensures high-quality current waveforms when high-order filters are used in NPC inverters. Apparently, this conclusion is against the common belief. Moreover, different conclusions in terms of the performances have also been found for other modulation techniques considered in this review. Finally, to validate the correctness of the analysis and the findings, simulated and experimental results are provided and discussed.