Control Method And Strategy For Switching Of Microgrid Operation Modes Based On Energy Storage System

Energy and environment crisis has prompted countries around the world to turn their attention to distributed generation(DG).Microgrid integrated the distributed energy effectively and made the full use of distributed energy become a reality.At the same time,it improved the power supply reliability and diversification of the distribution network.The switching control of the microgrid operation modes is an important part of the microgrid operation control,and also is the important part of the microgrid stable operation and to reduce the disturbance to the power grid.By taking microgrid with photovoltaic a nd storage based on hybrid energy storage system(HESS)as the research object,control method of smooth switching between the two operation modes of microgrid based on hybrid energy storage system is designed in this paper.Lead-acid battery and super capacitor,which complement each other in function,are selected to form a hybrid energy storage system in this paper.Firstly,the mathematical model of the lead-acid battery,the supercapacitor and the photovoltaic(PV)cell are studied.Under the premise o f meeting the output characteristics,the mathematical model of distributed source studied in this paper is established.On the basis of the analysis of the bidirectional DC/DC circuit,the charge and discharge mode of energy storage unit is studied,and the three-stage charging control of energy storage unit is designed.The hybrid energy storage system control structure of the super capacitor constant voltage discharge and storage battery constant current discharge based on DC bus voltage constant is designed.A maximum power point tracking control system for photovoltaic cells based on perturb & observe method is designed.Simulation results verify the validity of the above control.Control of inverter is an important part of switching control of microgrid operation mode.The mathematical model of three-phase inverter is established in this paper.The principles of PQ control,V/f control and V/f constant voltage and frequency droop control are studied,and the PQ controller and the V/f constant voltage constant frequency controller are designed in this paper.On the basis of the control of microgrid operation and the characteristics of microgrid operation in island mode and grid-connected mode,control method and strategy for smooth switching of microgrid operation modes is designed in this paper.When the microgrid is switched from the grid connected mode to the island mode,the inverter phase compensation and the state compensation are added to ensure that the phase and output power are not mutated,and the impact of the large power grid is reduced during the switching process.At the same time,the power control is used to reduce the impact of the power grid during the switching process.When the microgrid is switched from the island mode to the grid connected mode,the pre synchronization strategy is adopted to make the voltage amplitude and phase of microgrid synchronized with the power grid.At the same time,the inverter adopts state compensation to achieve smooth grid connecting,and to reduce the impact on the power grid.Finally,the model of the microgrid system is built in the Simulink environment,and simulation analyses on the operation of the microgrid and the modes switching are carried on in this paper.The simulation results are compared and a nalyzed.The results show that the control strategy designed in this paper can guarantee the stable operation of microgrid in isolated island mode and grid connected mode.Control method and strategy for switching of microgrid operation modes presented in this paper can achieve the purpose of smooth switching between the microgrid operation modes and reducing the impact on the power grid.As the main power supply of microgrid,Hybrid energy storage system can rapidly response to the power dema nd of microgrid and provide constant voltage and constant frequency support for microgrid.