Investigations on a unified controller for a practical hybrid multilevel power converter

Abstract

This paper is devoted to the investigation of a practically feasible and commercially viable hybrid multilevel power converter topology typically suitable for active rectifier or static reactive power compensation applications at distribution voltage levels. This system comprises a three-phase neutral point clamped (NPC) main inverter supported by three auxiliary single-phase H-bridge inverters fed from independent DC links. The main and auxiliary DC link voltages are configured in the ratio 3:1. A multilevel waveform is realized by adding the low-voltage, fast-switching auxiliary inverter outputs to the high-voltage, slow-switching main inverter output. A novel hybrid modulation scheme that incorporates stepped synthesis in conjunction with variable pulse width of the consecutive steps is described. In addition, the performance of a unified controller that enables the regulation of all the DC bus voltages is discussed.