An efficient multilevel-synthesis approach and its application to a 27-level inverter

This paper presents an efficient multilevel-synthesis scheme and its application to a 27-level inverter. In the proposed multilevel scheme, this can be realized by an array of switching devices composing full-bridge inverter modules and proper mixing of each transformer terminal voltage. The most different aspect, compared to the conventional approach, in the synthesis of the multilevel output waveform is the utilization of a combination of transformers rather than the accumulation of capacitor voltage sources. A 27-level inverter consists of three full-bridge modules and their corresponding transformers. Quasi-sinusoidal voltage waves can be generated from a suitable selection of the turns ratio of the transformer. The validity of the proposed system is verified by computer-aided simulation and experimental results using a 500-W prototype, which can generate a 110-V ac output voltage from a 12-V dc input.