Abstract: In photovoltaic grid-connected operation,voltage and current fluctuations occur when the grid voltage is unbalanced,which affects the power quality of the grid and the stability of the system. Combined with voltage compensation control,a constant DC voltage and reactive power control strategy based on voltage compensation control is proposed. The voltage unbalance coefficient is obtained from positive and negative sequence voltages collected through voltage compensation control,and the unbalance degree of power grid voltage is compensated,and the negative sequence current suppression step is introduced. The simulation model before and after the improvement is designed and built in PSCAD respectively,and the dynamic change characteristics of photovoltaic grid-connected power generation system are studied and analyzed.The simulation results show that under the step disturbance of light intensity and temperature,the system can respond quickly and work at the maximum power point,the voltage and current fluctuation range is reduced,and the power quality of the power grid is significantly improved, which verifies the accuracy and effectiveness of the MPPT algorithm and the improved control strategy.