Optimum harmonic reduction with a wide range of modulation indexes for multilevel converters

This paper proposes a novel modulation technique applying in multilevel voltage source converters suitable for high voltage power supplies and flexible ac transmission system (FACTS) devices. The proposed technique can generate output stepped-waveforms with a wide range of modulation indexes and minimized total voltage harmonic distortion. 'The main power devices switch only one time per cycle, suitable for high power applications. For the proposed harmonic reduction technique, the theoretical analysis is presented. By using a systematic method, only the polarities and the number of levels are required to be determined for different modulation levels. Computer simulation results are then provided. To verify the theory and the simulation results, a cascade inverter based hardware prototype including a low cost 8-bit microcontroller and modularized power stage and gate driver circuits, is implemented. Experimental results indicate that the proposed technique is effective for harmonic reduction in multilevel converters, and that both theoretical and simulation results are well validated.