Abstract: By taking the peer-to-peer structure microgrid as the research object,a seamless transfer control method for primary control and secondary control is proposed.In the primary control part,the microgrid inverters are controlled in droop mode in both microgrid island mode and grid connected mode.The transient response can be reduced since there’s no need to switch the control algorithm during the microgrid mode transfer period.In the secondary control part,agrid synchronization method based on hierarchical control is proposed,which allows droop-controlled inverters to adjust the frequency,phase,and amplitude of their output voltages to synchronize with the grid,realizing smooth transition from islanded mode to grid connected mode.The inverter control algorithm,frequency restoration and pre-synchronization control algorithm are analyzed in detail,experimental test results presented to validate the effectiveness of the proposed method.