An Improved Three-Phase Multistepped-Voltage Inverter Combined with a Single-Phase Inverter Through Switching Devices

A new multistepped-voltage waveform inverter with a total harmonic distortion (THD) of 6.25 percent is described. The proposed system consists of a three-phase inverter whose conduction intervgl is smaller than 180 °, a triple-frequency single-phase inverter, and power semiconductor switches that link the two inverters. The advantages of the proposed system over conventional stepped-voltage inverters are that it requires only a small number of switching devices, no three-phase output transformers, and an output filter of reduced size. The relation between THD and the number of steps of an output voltage waveform is discussed. Comparison with other stepped voltage inverters and experimental results using power transistors are also presented.