THD-optimal staircase modulation of single-phase multilevel inverters

This paper considers the problem of achieving the minimum THD of the staircase-modulated output voltage of single-phase multilevel inverters, with or without elimination of the lowest harmonics. The minimal THD values together with the corresponding necessary step angles (and also dc source ratios when the source values are not constrained to be equal) have been obtained for various waveform cases. The results show that requiring harmonic elimination yields slightly to somewhat worse distortion, and that using unequal dc source voltages is better than using equal ones, as expected.