Study on High voltage Grid-Connected PV inverter based on Modular Multilevel Converter

At present, the high-capacity centralized photovoltaic (PV) system is usually connected to the grid by three-phase full-bridge inverter + boost transformer, and its efficiency and power quality can be further improved. Modular multilevel converter (MMC) has a highly modular structure, which is helpful to reduce the loss of the device and realize the redundancy of the device, and it has the advantages of high power quality, high efficiency and flexible control. A high voltage Grid-connected PV inverter based on MMC is proposed in order to realize high voltage grid-connected operation of PV without transformer. It contains Boost DC/DC converters and MMC DC/AC converter. For the front stage circuit, the MPPT (Maximum Power Point Tracking) algorithm is adopted for realizing maximum power point tracking. MMC adopts carrier phase shift modulation, additional average voltage control and voltage balancing control to suppress the imbalance between interphase and sub module voltages. The validity of the structure and control strategy is verified by simulation.