Optimal PWM for the control of multilevel voltage source inverter

The use of multilevel voltage source inverters allows improvements in the quality of the AC side voltage waveforms as well as an increase in the handled power and DC side voltage. In such high power applications only a limited switching frequency is allowed for the PWM control of the converter, giving importance to the optimal exploitation of the few available commutations. In this paper optimal precalculated switching patterns for the control of a generalized multilevel VSI are presented. The problems addressed are the minimization of the global harmonic distortion of the output voltage waveforms as well as the elimination of selected harmonics. Possible sub-optimal simplifications to avoid discontinuities in the switching patterns as the amplitude of the fundamental varies are discussed. Quantization errors and memory requirements for the implementation of a microprocessor controller are briefly analyzed