Flexible Grid-Connection Method for Single-Stage Photovoltaic Inverter Based on Phase-Locked Loop Control for Grid Fundamental Frequency Voltage

In allusion to orientation deviation of grid fundamental frequency voltage and DC voltage collapse of existing grid-connecting photovoltaic(PV) inverter and the impact to power grid due to grid-connection of photovoltaic inverter,a three-loop control method based on phase-locked loop(PLL) control for grid fundamental frequency voltage was proposed and applied to single-stage grid-connecting PV inverter to improve output performance of the inverter and implement flexible grid-connection.Firstly,based on PLL control for grid fundamental frequency voltage,the orientation of grid fundamental frequency voltage was performed and the effect of the orientation was dependent on the designed performance of the PLL;secondly,the three loop-control structure was adopted to avoid DC voltage collapse and decrease total harmonic factor of output current;finally reasonable grid-connecting control logic was adopted to implement flexible grid-connection of PV inverter.The feasibility of the proposed method was verified by experiments,and experiment results showed that using the proposed method both real-time performance of dynamic response and steady state tracking accuracy could be improved.