A new type of full scale photovoltaic DC power generation system and its control strategy of modular multilevel converter

This new full scale photovoltaic DC power generation system was proposed to improve the efficiency of the new energy power system. The system consists of two parts: the series DC-DC converter part which realizes the maximum power output of the PV system and the establishment of the high voltage DC bus, and the MMC which realizes the high voltage and high power inverter. In this paper, we paid close attention on the operation principle of modular multilevel converter. Much work had been done to establish the switching state space model based on MMC and AC small-signal model. We put forward a dual-loop three-phase access strategy to grid based on carrier phase-shifted sinusoidal pulse width modulation technique to realize the significant degradation decoupling of modular multilevel converter model, in which MMC outer loop is subjected to the voltage while inner loop is subjected to the current. In this paper, an MMC simulation system with 4kV direct current bus and 5 level voltage is modeled to test the feasibility. And the stability and rapid response of the simulation model is outstanding.