A Circulating Current Suppression Method for Hybrid Modular Multilevel Converter Based on Multimaterial Devices

The hybrid modular multilevel converter (HMMC) based on multimaterial devices has been proved to achieve a better balance among cost, loss, and feasibility compared with others. However, due to the use of hybrid-frequency modulation method, the implementation of traditional circulating current control strategy would increase output voltage harmonics of the HMMC. In this article, the mechanism of the above problems is analyzed in detail, and the specific circulating current suppression (SCCS) method is proposed. Based on the voltage balancing operation of the high-frequency submodules, the corresponding redundant voltage generated by the low-frequency submodules in the arms is analyzed. By utilizing the redundant voltage levels during the operation of HMMC, the number of inserted submodules is adjusted to reduce the circulating current of the system without compromising the quality of the HMMC output waveform. Finally, the simulation and experimental results verify the effectiveness and feasibility of the proposed SCCS method.