When the frequency of weak grid drifts

traditional controllers cannot track the grid frequency without error and achieve zero steady-state error control of the grid-connected current. To this end

an adaptive proportional complex integral（PCI） control strategy for single-phase grid-connected inverters is proposed. This strategy uses an adaptive control method that combines complex-number domain-based proportional complex integral control with frequency-locked loop（FLL）

where the PCI controller is used to eliminate the steady-state error of the grid-connected current

and the FLL is used to track the grid frequency in real time to improve the control accuracy of PCI. The simulation and prototype experiments show that the control strategy can achieve grid-connected current tracking the given signal without difference under grid frequency fluctuations

while reducing the harmonic content of grid-connected current. The research in this paper can provide references for improving the control performance of single-phase grid-connected inverter under frequency drift.