Phase-Shifting-Transformer-Fed Multimodular Matrix Converter Operated by a New Modulation Strategy

Abstract

Multimodular matrix converters (MMMCs) built with three- to single-phase modules have emerged as a candidate for high-power applications. In order to reach higher voltage and power levels, constituent modules of an MMMC are fed by isolated secondary windings of a phase-shifting transformer, while their outputs are connected in series to supply the load. This paper presents a new modulation strategy for the MMMC. Unlike previously proposed strategies that aim to simultaneously fabricate sinusoidal output voltage and input current, the new method only focuses on generating multilevel output voltage waveforms. Nonetheless, because power balance among modules on a same output phase is guaranteed, and owing to the harmonic elimination capability of the phase-shifting transformer, sinusoidal input current with good quality can still be achieved. Compared with previous methods, the proposed strategy cannot adjust the input power factor but is simpler, more straightforward, and associated with lower switching losses. Its use makes possible the employment of an indirect module structure that significantly reduces the total number of switches and, thereby, the overall semiconductor cost and eliminates the need for complex device commutations, which is essential in direct matrix converter modules. The presented concepts are verified by simulation and experimental results.