Research On Power Control Strategy And Seamless Switch Of AC/DC Hybrid Microgrid With PV And Battery

Microgrid is a very important way to use renewable energy.AC/DC Hybrid microgrid combined with photovoltaic and energy storage units,distributed power generation units and load units through power electronic interfaces can supply power for various AC and DC loads in buildings.It has practical application values.The AC/DC hybrid microgrid can be connected to the grid,and can also operate in islanding mode disconnection with the grid.The power control and smooth switch of operation mode is the key to ensure the safe operation of hybrid microgrid system.This paper takes this as the research content,and the main work is as follows.According to the characteristics of the load in buildings,the system structure of the AC/DC hybrid microgrid with PV and battery is given.Two DC bus with different voltage is set for different DC loads.The PV and energy storage unit are connected to both AC and DC side,so that the power can be supplied by both sides.The hybrid energy storage composed of lithium battery and super capacitor meets the demand for energy storage in different operation modes,the effectiveness is verified by Simulink.Based on the analysis of the power balance of AC/DC hybrid microgrid,the power control strategies of the AC and DC sub-microgrid in grid-tied and islanding mode are proposed,the corresponding control of each module converter is given.In order to maximize the function of hybrid energy storage and improve the reliability of microgrid in islanding mode,a power control strategy based on double-side energy storage is proposed for the AC/DC interconnect converter,and corresponding algorithm is given.The correctness of this power control strategy is verified by Simulink.When the microgrid switch from grid-tied to islanding mode,the energy storage inverter needs to switch from PQ control to V/F control.The voltage is uncontrollable during the island detection in unplanned islands,resulting in overvoltage or undervoltage.To solve the above problem,this paper proposes a collaborative control of voltage and current,which uses a voltage controller to control load voltage during the whole operation time.In grid-tied mode,voltage controller keeps power balance with microgrid load and makes a stable output,meanwhile an additional current controller is introduced to regulate output current,and keep power balance between microgrid and the grid.In islanding mode,the current controller quits from working,and the load voltage is still maintained by voltage controller.So the power can be balanced and the output of controller is continuous.Besides,the control mode has been transferred to voltage control mode seamlessly,the seamless switch is achievedA simulation model of AC/DC hybrid microgrid with PV and battery is built in MATLAB/Simulink,the power control strategy for both grid-tied mode and islanding mode as well as the proposed seamless switch control is simulated and verified.At the same time,an experimental system combined with RTDS and DSP controller is built.The circuit of the microgrid system is built in RSCAD and run by RTDS,while the proposed control strategy is implemented by DSP controller.Simulation and experimental results demonstrate the correctness of the proposed control strategy.