Research On Stability Control Of Isolated Microgrid Based On Switched System

China has become the largest energy producer and consumer in the world.With the rapid development of China’s economy and society,the shortage of traditional fossil energy and carbon oxide pollution are becoming increasingly serious.Micro-grid with clean energy is the main way to achieve ‘carbon peaking and carbon neutralization’.Micro-grid system is divided into grid-connected operation mode and isolated operation mode.Isolated microgrid refers to a controllable and independent microgrid system which contains a variety of distributed power sources and is equipped with energy storage devices to continuously supply power to the load,and which is composed of diesel generator sets and various power electronic devices to ensure the stable operation of the microgrid.It is often used for power supply in remote areas or islands.The reliability and economy of power supply for isolated microgrid system and how to obtain better power quality are still outstanding problems to be solved in microgrid system.In view of the problems of power supply reliability and power quality degradation that may occur during the switching process of main control units in isolated microgrid,this thesis proposes to apply the switched system theory to the switching problem of main control units in isolated microgrid,establish a nonlinear model of inverter control unit of energy storage system combined with VSG(Virtual Synchronous Generator)idea,and establish a switched system model and design a controller jointly with the nonlinear model of synchronous generator to solve the stability problem in the switching process of isolated microgrid.Firstly,the isolated microgrid with the energy storage system as the main control unit and the diesel generator as the main control unit is regarded as two subsystems respectively.The switched subsystem I model is established by using the virtual synchronous generator third-order practical model for the energy storage system,and the synchronous generator model is used as the switched subsystem II model.The backstepping method is used to design the nonlinear controllers of the two subsystems,and the Lyapunov functions of the two subsystems are constructed at the same time,and the switching law of the subsystems is designed.Finally,the stability of the system is verified by the method of multiple Lyapunov functions and dwell time.Secondly,the parameter uncertainty of diesel generator is considered,in which the damping coefficient of synchronous generator is difficult to measure accurately and regarded as an uncertain parameter.To solve the problem of uncertain parameters,the adaptive backstepping method is applied to design controllers for two subsystems,and the parameter replacement rate is designed on the premise of ensuring the stability of the two subsystems.Lyapunov functions of subsystems are constructed to ensure the stability of subsystems.In order to improve the transient response speed of the system,the K-class function is introduced into the design of the virtual stabilization function,and the simulation comparison test is carried out.Finally,considering the problem of parameter uncertainty and external interference in isolated microgrid,based on the third chapter,the improved adaptive backstepping method and sliding mode control method are combined to design controllers for two subsystems respectively,and Lyapunov functions of subsystems are constructed to ensure the stability of subsystems.The simulation results verify the effectiveness of this design method.