A Three-Level T-Type Indirect Matrix Converter Based on the Third-Harmonic Injection Technique

An indirect matrix converter (IMC) is a direct ac-ac power converter. As an improvement of the output waveform quality, several types of three-level IMC are proposed and investigated. However, two major problems of these converters still exist. First, in some specific situations, such as wind energy conversion systems and flexible ac transmission systems, these converters’ capabilities of generating input reactive power must be improved greatly. Second, neutral-point voltage balancing is a key challenge to the normal operation of multilevel IMCs, but the control of balancing the neutral-point voltage for multilevel IMCs has not been investigated so far. To address these issues, a three-level T-type indirect MC (3LT2IMC) topology as well as a carrier-based modulation method is proposed. In addition to inheriting the advantages of the third-harmonic injection two-stage MC such as extended input reactive power control range and no need for synchronization in modulation, 3LT2IMC could provide an improved output power quality. Besides, a closed-loop control algorithm for balancing the neutral-point voltage is developed. The presented modulation strategy and control algorithm are generalized and can be extended to other three-level IMCs. Finally, the proposed topology and method are verified by simulation and experimental results.