Research On Nonlinear Control Strategy Of High Frequency Isolated Quasi Z Source Photovoltaic Grid-connected Inverter

Global energy depletion and energy pollution have become obstacles to the development of all countries.Light energy is an inexhaustible source of energy in green and environmental protection,and has become the fundamental way to solve the energy crisis.In view of the characteristics of photovoltaic power generation,the inverters of the Z source structure have come into being.The research of its topology and control strategy has become the research object of many teachers and students in Colleges and universities.Based on the topology of high frequency isolated quasi Z source inverter,this paper studies the control strategy of high frequency isolated quasi Z source PV grid connected inverter.There is zero point in the right half plane of the transfer function of the direct duty duty ratio of the Z source inverter,which will make the system have a non minimum phase phenomenon.The existence of non minimum phase phenomenon makes the output voltage of high-frequency isolated quasi Z source inverters oscillate when the input disturbance occurs,especially when large disturbances occur.The influence of non minimum phase on the system is more obvious.In view of the nonlinear characteristics of the system,the nonlinear control strategy is adopted for the DC voltage regulator control.This paper first analyzes the research status of Z source inverter nonlinear control strategy for the moment,then study on mathematic model of photovoltaic cell and its output characteristics,the maximum power point tracking several typical methods of photovoltaic power generation system,double step climbing search method to build a photovoltaic power generation system MPPT control simulation model based on verification the feasibility of.Then the high frequency isolated quasi Z source inverter is modeled and its control characteristics are analyzed.The control strategy of high frequency isolated quasi Z source PV grid connected inverter is studied,including modulation strategy,DC link voltage regulation strategy and grid connected current control strategy.The modulation strategy uses a simple boost SPWM control.A nonlinear control multi power reaching law sliding mode control is applied to control the DC link voltage.The sliding surface design and reaching law design are completed,and the reachability and the stability of the sliding mode surface are proved.At the same time,the traditional sliding mode control with the traditional exponential convergence law and the multi power convergence law sliding mode control are compared.The quasi PR regulatoris used to control the closed loop current of the grid,and the 3 parameters of the quasi PR regulator are designed.Finally,the correctness of the designed control strategy is verified by simulation and experiment,the results show that the grid current control loop regulator quasi PR can make the grid current and voltage with the same frequency and phase,phase error,power factor of 1,can follow the reference current change,the steady-state error is small compared with the traditional index;sliding mode control,sliding mode control law make DC link voltage controlling power reaching much faster response speed,higher stability,robustness.