Power balancing of grid connected PV system based on MMC under different irradiation conditions

When it comes to renewable energy applications, the Modular Multilevel Converter (MMC) is considered as one of the most promising converter topologies. In this paper, the MMC is used for integrating the Photovoltaic (PV) strings to the grid. The PV strings are connected to the MMC submodules (SMs) through a DC-DC converter, which facilitates the independent MPPT implementation. For satisfactory operation of MMC, it is important to maintain a balanced voltage across the SMs. In addition, the total generated power by the PV strings should be uniformly distributed among the three phases. These requirements are considered as challenging tasks during different inhomogeneous irradiation conditions. The proposed method is capable of balancing the SMs capacitor voltages and at the same time inherently generating a DC and fundamental frequency components of the circulating currents inside the MMC without using a controller. These circulating current components are responsible for equally distributing the total generated power by the PV strings among all phases. As a result, balanced three phase currents are injected into the grid. The proposed method is verified through extensive simulation during different irradiation conditions.