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Research on Grid-Connected and Off-Grid Switching Distributed Photovoltaic Power System

Photovoltaic power system (PV system) includes grid-connected and off-grid (islanding) types. With the improvement of power supply reliability, it is necessary to provide distributed PV power system with functions of grid-connection and off-grid operation, which as well as being easily switched. This research comparative analyzes on model of AC bus and model of DC bus of grid-connected and off-grid PVsystem and presents the control strategy. In order to safely operate and seamlessly switch grid-connected and off-grid, PV system is furnised constant-power control and constant-voltage frequency control with switching operation. Additionally, the switch junction for off-grid and the public supply system must be connected to the synchronization device for controling system of PV system therefore the PV system can be safely operated and switch from off-grid to grid-connected can be smoothly and rapidly.