Research On Dual-Mode Stability Control Of Microgrid Based On Nonlinear Switching System

With the shortage of fossil energy,environmental pollution,global warming and other problems are becoming more and more serious.Micro-grid systems using clean energy are gaining more and more attention.The microgrid can not only be connected to the large power grid,but also separate the connection of the two when the large power grid fails,and operate independently to ensure the power demand of the load.For the stability of the microgrid system,it is necessary not only to ensure the stability of the grid-connected operation or the island operation,but also to ensure the stability of the microgrid system when the operating mode is switched.The stable switching of the two operating modes can reduce the impact of voltage and current impact on the entire system during the switching process,which is conducive to improving power quality and power supply reliability.Therefore,the stability of microgrid operation mode switching has attracted the attention of scholars.In view of the above problems,it is proposed to apply the nonlinear switching system theory to the microgrid mode switching problem.The idea of the switching system is used to solve the problem of the switching stability of the microgrid inverter operation mode,and the research on the stability of the microgrid system is carried out from the perspective of the switching system.First,consider the grid-connected and island operating modes of the microgrid inverter as two subsystems,and expand the grid-connected and island operating models to build a microgrid switching system model.The backstepping method was used to design the subsystem controllers of the microgrid inverter to ensure the stability of each mode.At the same time,the common Lyapunov function of the subsystems is constructed to ensure the stability of the micro-grid inverter operating mode switching.According to whether the grid voltage and frequency are in the normal operating range,the corresponding switching law is designed.By comparing with traditional P/Q control and V/F control switching,this strategy effectively reduces the voltage and current oscillations that occur during the switching between the two operating modes.The simulation results verify the effectiveness and superiority of the design method.Secondly,consider the problem of uncertain parameters in the microgrid system.The equivalent resistance in the system is a time-varying variable with temperature and is a value that is not easy to measure accurately.It is an uncertain parameter.The adaptive backstepping method was used to design the subsystem controllers of the microgrid inverter respectively.While ensuring the stability of each mode,the parameter substitution law was designed.And the common Lyapunov function of the subsystem is constructed to ensure the stability of the operation mode switching of the microgrid inverter.According to whether the grid voltage and frequency are in the normal operating range,the corresponding switching law is designed.The simulation results verify the effectiveness of the design method and the real-time tracking of adaptive parameters.Finally,considering the uncertain parameters and external interference problems in the microgrid system,a sliding mode control method is introduced to increase the transient response speed of the system and suppress the effects of external disturbances.The sliding mode adaptive backstepping method was used to design the subsystem controllers of the microgrid inverter to ensure the stability of each mode,and to construct a common Lyapunov function of the subsystem to ensure the stability of the microgrid inverter operating mode switching.According to whether the grid voltage and frequency are in the normal operating range,the corresponding switching law is designed.The simulation results verify that the design method improves the transient response speed of the system,reduces the response oscillation amplitude and suppresses the influence of external disturbances.