DC- Link Voltage Equalization and Second Ripple Suppression Control Strategy for Three-Phase To Single-Phase Converters

The three-phase to single-phase three-level converter is the core equipment in the advanced traction power supply system. The voltage equalization and second ripple on the dc-link are not conducive to not only distorting the three-phase grid side current and the inverter output voltage, but also leading to the degradation of the life of the power electronic converter devices. In this paper, a three-phase to single-phase three-level converter topology based on a symmetrical half-bridge active power decoupling circuit is proposed. This structure can maintain the balance of the two voltages on the dc-link and decouple the ripple power, thereby ensuring the instantaneous power flow balance between the three-phase grid side and the half-bridge decoupling circuit and the load, and can greatly reduce the number of required passive components and volume. In order to achieve proper closed-loop regulation, a unified coordinated control strategy for voltage equalization and second ripple is proposed.