A seamless switching control strategy for operating modes of photovoltaic generation system

The seamless switching of operating modes cannot be implemented by both traditional voltage mode control for islanded photovoltaic (PV) generation system and current mode control for grid-connected PV generation system. For this reason, it is proposed to adopt voltage mode control strategy under above-mentioned two operating modes of PV generation system to avoid the impact due to the switching of control strategies. According to the characteristics of PV generation system, droop control strategies for PV inverter under the islanded operation, grid-connected operation and operating mode switching are designed respectively. Improving the droop control and through dynamic translation of the droop curve, the PV inverter can always output the maximum active power during the grid-connected operation mode and restrain the power deviation under different conditions, meanwhile maintain the DC bus voltage stable; during the islanded operation mode of PV generation system the operating condition of power grid can be traced to mitigate the impact at the moment of grid-connection of PV generation system. The effectiveness of the proposed control strategy is validated by both simulation results and experimental results. Using the proposed control strategy, the PV inverter can meet the requirement of steady state operation of power grid under the islanded operating mode and grid-connected operating mode of PV generation system, and the transient process during the switching of operating modes is smooth and no-impact.