Re-evaluation of modulation techniques for neutral-point-clamped inverters with high-order output filters

Evaluation of modulation techniques for neutral-point-clamped inverters has been an extensively investigated theme. The conclusion at present is centered space vector modulation with phase-disposed carrier arrangement gives the best harmonic performance. This conclusion is however drawn at the inverter output terminals or with only a simple L-filter considered. It may therefore not be relevant for applications, where high-order filters are used for better attenuating the switching harmonics. The intention of this paper is thus to investigate the characteristics of different high-order filters, and then re-evaluate different modulation techniques when the inverters are conditioned by these filters. In total, five types of filters are considered with some of them eventually found to output better current quality when the alternative-phase-opposition-disposition carrier arrangement is used. The finding is thus different from common belief, especially in low switching frequencies. The same atypical finding has been found among standard sinusoidal, centered space-vector, and discontinuous modulation techniques when analyzed with the same high-order filters, as proven through simulation.