PQ-U control method of grid-connected PV inverter under weak grid

Under the condition of low short circuit capacity and high grid impedance of weak grid, the grid voltage is easily fluctuated due to the load change, affecting the power quality of the grid. In view of this problem, firstly, this paper analyzes the principle of the grid-connected voltage change caused by the load change. Secondly, an improved voltage-power control method (PQ-U) for three-phase grid-connected PV inverter is proposed. This method changes the output reactive power of PV inverter to maintain the stability of the bus voltage when the inductive or capacitive load changes significantly. Besides, the advantages of PQ-U control method relative to traditional PQ control method are compared and analyzed by Matlab software. The simulation results show that PQ-U control method can maintain the stability of bus voltage in inductive or capacitive load significant change and play a supporting role for weak grid voltage. Finally, experiments are done to verify the validity of the PQ-U control method.