When the three-phase grid is in imbalance，there will be generated on the DC and AC sides even-numbered and odd-numbered non-characteristic harmonics based on the traditional double-loop control strategy，the active power fluctuates significantly，while the system performance is deteriorated.In view of these problems，a grid control strategy is proposed based on the positive and negative sequence rotating coordinate system，the control strategy being based on grid inverter mathematical models and forms of power fluctuations under unbalanced grid.To suppress the secondary ripple of active power，grid current effective control is achieved.To effectively and quickly separate the positive and negative sequence quantities，a separation method of the instantaneous positive and negative sequence is proposed.The algorithm accuracy is higher and with almost no delay.Experimental results show that the positive and negative sequence separation method is effective，and the active power control strategy is capable of effectively suppressing fluctuations and grid current harmonics，thus improving the steady-state performance.