Aiming at the problem that the filtering effect of LCL filter becomes worse when the PV system works at low power, this paper presents a control strategy to change the switching frequency according to the instantaneous output power of the inverter. By analysing the design method of each parameter of LCL filter, a single-stage PV grid-connected inverter structure is used to establish the frequency loop based on grid voltage oriented vector control (VOC) to determine the optimal switching frequency under the current power state .The design methods of power detector, frequency calculation and frequency hysteresis comparator are analysed in detail. Finally, the waveforms of grid-connected current before and after frequency conversion are contrasted by MATLAB simulation to verify the feasibility and effectiveness of the inverter control strategy.