Design Of Nonlinear Backstepping Controller For Photovoltaic Grid-Connected Inverter

With the development and popularization of photovoltaic technology,the research of grid-connected photovoltaic technology has become a hot research direction.The grid-connected photovoltaic inverters are the bridge between the whole power grid and renewable energy generation,and are the most critical core part of the whole photovoltaic power generation system.Grid-connected inverters convert DC power into AC power,then feed it into the grid,and maintain the quality of the grid-connected part.Research on grid-connected photovoltaic inverters plays an important role in the development of photovoltaic power generation,and its control strategy is the most important issue.This thesis mainly focuses on the nonlinear control method of three-phase photovoltaic grid-connected inverters.Based on the improved backstepping method,combined with adaptive control,dissipative theory,sliding mode control and fast terminal sliding mode control,the control strategy of three-phase grid-connected photovoltaic inverters is studied in this thesis.The main research results are as follows:(1)In view of the unknown parameters of the three-phase photovoltaic grid-connected inverter model,an improved adaptive control method is adopted to design the controller.Based on the adaptive backstepping method,K-type function is introduced into the virtual function of each step,and an improved controller of three-phase photovoltaic grid-connected inverter is designed.The controller maintains the stability of DC voltage and the grid-connected unit power factor,at the same time,the system state convergence speed is faster and the oscillation amplitude is smaller.(2)Aiming at the problem of unknown parameters and external interference in the three-phase grid-connected photovoltaic inverters model,an improved adaptive backstepping method combined with dissipation theory is adopted to design the controller.In the design process,each link meets the dissipative requirement.At the same time,K-class functions are introduced into the virtual function design of each step.Combining with adaptive control,unknown parameters can be estimated in real time.At the same time,the convergence speed of system state variables can be accelerated and external disturbances can be effectively suppressed.In the design process,the controller of three-phase grid-connected photovoltaic inverters is designed by combining K-function,adaptive backstepping method and dissipation theory,making full use of the non-linear characteristics of the system.(3)An improved adaptive sliding mode control method is adopted to design the controller for the unknown parameters and external disturbances of the three-phase grid-connected photovoltaic inverters.Based on the adaptive backstepping method,the sliding mode control technique is introduced to suppress the influence of external disturbances.In the design of virtual function,K-class function is introduced,which combines with adaptivecontrol and sliding mode control.The adaptive method estimates unknown parameters in real time.K-function accelerates the convergence speed of system state variables.Sliding mode control can suppress external interference.The controller of three-phase grid-connected photovoltaic inverters is designed by combining the above control methods.At the same time,fast terminal sliding mode control is introduced to modify the controller.In addition,an improved nonlinear robust controller is designed.