Mode Switch Control of Two-Stage Photovoltaic Inverter after Losing Battery Storage in Islanded Microgrid

In order to deal with the energy shortage and environmental pollution, solar energy has been widely used, which can be organized with the energy storage as the microgrid. In islanded mode of the photovoltaic microgrid, due to the randomness of the output power, the photovoltaic inverter usually needs energy storage to keep power balance. As a result, in the absence of energy storage, photovoltaic inverter should stop working because of the loss of voltage synchronization and balanced power flow. To solve this problem, this paper proposes a mode switch strategy of two-stage photovoltaic inverter, which can operate both with energy storage and in standalone mode according to the state of the islanded microgrid. When working with energy storage, the photovoltaic inverter tracks the power point that derived from the energy management system. After losing the energy storage, the photovoltaic inverter supports the bus voltage and satisfies load demand. Moreover, a method is proposed to achieve seamless switch between these two control modes, where the balanced power flow between the photovoltaic inverter and load is promised at the same time. Finally, the simulation results verify the effectiveness of the proposed control method.