A Capacitors Voltage Balancing Control Strategy of MMC Sub-modules Based on Dynamic Threshold for PV System

The Modular Multilevel Converter (MMC) is considered one of the most promising approaches in the field of High Voltage Direct Current (HVDC) transmission. Aim at the unbalance of capacitors voltage of sub-modules (SMs) and the defect of conventional sorting capacitors voltage balancing strategy in switching frequency, an optimized sorting capacitors voltage balancing strategy based on dynamic threshold has been proposed in this paper. Firstly, the topology and operation principle of MMC were analyzed. The superiority was shown by comparative analysis of the conventional sorting capacitors voltage balancing strategy and the optimized sorting capacitors voltage balancing strategy based on dynamic threshold next. The dynamic threshold that obtained through the closed-loop control of capacitors voltage unbalance factor can help to reduce the switching loss. Finally, a simulation verification carried out in Matlab/Simulink shown that the proposed optimized strategy can reduce the switching frequency while limiting the capacitor voltage unbalance factor in a feasible range.