A Compact Hybrid Multilevel Converter With Wide Operation Range

The miniaturization requirement of modular multilevel converter (MMC) has drawn great attention in offshore wind power integration system. This paper proposes a compact hybrid multilevel converter, which introduces the commutation switches in each phase leg to shape the double half-wave generated by the single arm. The single arm only needs to output half of the maximum voltage of MMC arm, which can achieve the reduction of 75% submodules and highly improve the power density. To achieve energy balance of the phase leg under wide-range modulation ratio, an overlap period is introduced as per phase operating modes changes. During the overlap period, the dc common leg is assigned to one of the three phase legs to forming a circulating current path, and the circulating current is controlled to balance the phase-leg energy at different operating modulation index and power factor. The feasibility of the proposed topology and the wide-range voltage regulation capacity have been verified by the simulation results on the MATLAB/Simulink platform.