Study On The Control Strategy Of Inverter And Mode Switching In Microgrid

With the increasingly serious energy shortage and environmental problems,distributed generation technology has attracted more and more attention,and the resulting micro-grid has become a hot research topic.Microgrid is a single and controllable independent power generation system composed of distributed generation,load,energy storage devices and control devices.Microgrid has two modes of operation,i.e.grid-connected and island-connected,which can be used as a controllable unit to connect with the large grid,and can also be separated from the main network to become a controllable autonomous system.No matter what mode of operation,the stability control of microgrid is the basic condition to ensure its reliable operation.Therefore,the stable operation and smooth switching of microgrid have been the focus of microgrid research.In this paper,the operation control strategy of microgrid is studied,and effective control methods are designed to make the microgrid operate stably and switch smoothly in island mode.Firstly,several common control strategies of microgrid system and Microgrid inverters are introduced from the aspects of microgrid system and micropower supply,and their control principles and applicable conditions are analyzed.The control principles and methods of three typical micro-sources are described in detail,and the stability of output voltage and frequency of micro-sources under different control strategies is compared by simulation.Secondly,aiming at the micro-source inverters under islanded operation mode of micro-grid,an ADRC sliding mode controller is designed by combining ADRC with sliding mode control method,and the parameters of the controller are optimized by using particle swarm optimization(PSO)algorithm to control the AC side voltage of the inverters.The simulation results show that the AC side voltage and frequency of the inverter under ADRC sliding mode control can track the reference value quickly and accurately when there is parameter perturbation or external disturbance in the islanded operation mode.Thirdly,the small signal model of microgrid independent operation is established,and the concept of switching system is introduced to solve the system stability problem of microgrid operation switching.The grid-connected and island operation modes of micro-grid can be regarded as two subsystems.The small signal model of micro-grid operating independently is transformed into the mathematical model of switching system.The switching controller is designed and the stability of switching system is analyzed to realize smooth switching of operation modes of micro-grid.The correctness and effectiveness of the control strategy are verified by simulation.Finally,based on the proposed micro-grid inverter and system switching control strategy,a micro-grid operation control system is built.The hardware and software are designed,and the validity of the control strategy of micro-source inverters and microgrid switching operation is verified by testing on the experimental platform.