Development of quasi 24-step voltage source inverter

A new method for reducing harmonics involved in output voltages of a three-phase voltage source inverter is proposed. It is applied to the conventional 6-step inverter with a three-phase autotransformer. By injecting harmonics to the neutral point of the autotransformer from an auxiliary circuit, output voltages of the proposed inverter can be almost the same as a conventional 24-step inverter. In this paper, circuit performances and output voltage waveforms are discussed, and the optimum parameters are determined by taking effect of harmonic reductions. Then, characteristics of the proposed inverter can be clarified by simulation results.