Topology and Modulation Scheme of a Three-Level Third-Harmonic Injection Indirect Matrix Converter

The matrix converter is a direct ac-ac power conversion topology. To improve the output waveform quality of the conventional matrix converter and overcome the drawbacks of the neutral-point clamped matrix converters such as the neutral-point voltage balancing issue, the limited control range of the input reactive power and the need for strict synchronization in the modulations of the rectification and inversion stages, a three-level third-harmonic injection indirect matrix converter, and a neutral-point voltage balancing algorithm are proposed. The topology consists of a line-commutated input voltage selector, a three-level inverter and a third-harmonic injection circuit, where the split dc source voltage of the inverter is formed by two input line-line voltages. Furthermore, by adopting the active power filtering technique and utilizing the third-harmonic injection circuit to compensate the neutral-point current, the neutral-point potential is balanced without extra control effort. In addition, except the advantages such as bidirectional power flow, sinusoidal input-output currents, and multilevel output voltages, the synchronization in modulations is eliminated, and the control range of the input reactive power is extended significantly. Finally, the functionality and effectiveness of the proposed methods are verified by simulations and experimental results.