Seamless Transfer Scheme Based on Unified Control Structure for Single-Stage Photovoltaic Inverter

The seamless transfer between islanded and grid-connected modes can be achieved by the voltage-type control inverter based on traditional droop control scheme. However, the grid current cannot be controlled directly when the inverter is connected to the grid, which shows that the grid current is easily distorted by the grid voltage harmonics. Moreover, the dynamics of the grid current may be slow under the traditional droop control. To resolve these issues, a novel seamless transfer scheme between two operation modes with unified control structure is proposed in this paper. Simulation results and experimental results are both presented, showing the feasibility of the proposed scheme.