Abstract: The control strategy is one of the key technologies to ensure the security and stability operation of micro-grid. This paper studies the grid connected/islanding operation control strategy of micro-grid system with energy storage device. In the grid-connected mode, the outer voltage loop and inner current loop strategy is adopted for the grid-connected inverters. In the island mode, the V/f control strategy with the battery system is used to ensure the voltage and frequency of PV system to be stable. In order to reduce the steady state error on tracking the AC voltage, improved V/f control strategy based on double closed-loop quasi PR control strategy is proposed, with which the zero steady-state error control can be achieved in wider frequency band. Meanwhile, the fluctuation of PCC bus voltage is reduced effectively and the power quality is improved. The simulation results verify the effectiveness of the proposed control strategy. 1.Control Mechanism analysis of photovoltaic/battery micro-grid During the normal operation of the microgrid, the inverter operates in the grid-connected mode; when the microgrid is out of order, the battery storage device is added and the inverter operates in the island mode. 1.1 Control mechanism of photovoltaic grid-connected In grid-connected mode, the outer voltage loop and inner current loop strategy are applied for the grid-connected inverters, which can ensure the stable output of the inverter. 1.2 Island control mechanism of battery system In island mode, the battery storage device is added and the V/f control is adopted, which can provide a voltage source, with a constant voltage amplitude and frequency, for the microgrid system, and ensure the voltage and frequency of PV system to be stable.When P is between Pmin and Pmax, the output of the frequency is constant. 1.3 Operation scheme of photovoltaic/battery micro-grid When the Photovoltaic/Battery Micro-grid is operates in the grid-connected mode, the battery system cooperates with the photovoltaic system to provide power with high power quality for the distribution network and the load; when the frequency and voltage of the distribution network or the PCC point are detected to be crossed, the grid connection switch is turned off. In this case, the control mode is converted to island operating mode. 2. Design of the improved V/f control Compared with the traditional V/f control, the improved V/f control strategy, based on double closed-loop quasi PR control strategy, is proposed. It uses the inverter feedback voltage to adjust the AC side voltage, which can ensure the stability of the output voltage. 3. Analysis of simulation result The 400V DC power supply is used in the simulation to replace the output of the PV inverter's pre-stage circuit. The simulation process is as follows: t=0, the master-slaver inverter operates in the grid-connected mode; t=0.2s, the power grid is out of order,while the system is switched to the island mode. At this time,P= 3kW.The results indicate that the fluctuation of PCC bus voltage is reduced effectively and the power quality is improved. 4. Conclusion In the Matlab/Simulink simulation environment, the V/f control model is built for analysis and comparison. The results indicate that the effectiveness and feasibility of this method are verified, and the stability of the optical storage system is improved.