Control Strategy for Modular Multilevel Converter based on Single-phase Power Factor Correction Converter

This paper proposes a novel control strategy for a step-down rectifier that applies a modular multilevel converter (MMC). This paper first discusses the circuit configuration and the proposed control method. The main part of the control system is based on the control method for the single-phase power factor correction converter (PFC converter), which means that the conventional control techniques of the single-phase PFC converter can be simply applied to the MMC. The control elements which achieve step-down rectification and capacitor voltage balancing are added to the main part. Besides, in capacitor voltage balancing of the proposed control method, it is not necessary to design the control parameters. In addition, the operation of the proposed step-down rectifier is confirmed by the simulation. The simulation results show that the proposed converter achieves step-down rectification from the grid voltage of 6.6 kV to the DC voltage of 400 V. Moreover, the step-down rectifier maintains all capacitor voltages constant. Finally, a fundamental operation is confirmed by experiments using a miniature model. As the results, the step-down rectifier converts from the input grid voltage of 200 V to the output DC voltage of 75 V. Besides, the proposed step-down rectifier maintains the capacitor voltage of each cell to the voltage command of 130 V. The maximum error between the voltage command of the cell capacitor and the measured voltage is less than 2%.