Research On Control Strategy Of Photovoltaic Power Generation System

With the rapid development of the global economy,the problem of energy shortage and environmental pollution is becoming more and more serious.The development of solar energy has received more and more attention.Under the strong support of the state,the photovoltaic power generation industry has been further developed.In order to improve the photoelectric conversion rate and grid-connected current quality,this paper takes the LCL bipolar photovoltaic grid-connected power generation system as the research object.The control problem of Maximum Power Point Tracking(MPPT)of photovoltaic Power generation system and the current control strategy of grid-connected inverter are deeply studied.The main research contents are as follows:Firstly,the photovoltaic power generation system is introduced,the bipolar photovoltaic power generation system is selected as the research object,and the mathematical model of the photovoltaic cell is established.The simulation model was built in Matlab,and the effects of light intensity and temperature on photovoltaic cells were analyzed through P-U and I-U characteristic curves.Extremum Seeking algorithm is analyzed in detail,and aiming at the contradiction between steady-state oscillation and response speed in traditional disturbance Extremum searching,an improved Extremum searching control algorithm is proposed.Through simulation,it is verified that this method can improve steady-state accuracy with less steady-state oscillation.The theory basis of Active Disturbance Rejection Control(ADRC)is introduced in detail,which lays a theoretical foundation for the Control strategy research in the following paper.Secondly,the principle of pre-stage maximum power point tracking is introduced.The advantages and disadvantages of the existing traditional MPPT control algorithm are analyzed.The MPPT control algorithm has some problems,such as slow tracking speed and steady-state oscillation.The improved Extremum Seeking method without steady-state oscillation proposed in this paper is applied to the maximum power point tracking.In order to solve the coupling problem among PV output voltage,current and load voltage in photovoltaic system,this paper proposes to combine ADRC with extremum search method to realize the decoupling of variables,further improve the tracking speed of the system and reduce steady-state oscillation.The simulation model is built in Matlab and compared with the traditional perturbation observation method to verify the feasibility of the two methods proposed in this paper.The simulation results show that the method proposed in this paper can significantly improve the tracking speed and reduce the steady-state oscillation,so as to achieve the purpose of improving the photoelectric conversion rate.Finally,the modeling of the later-stage LCL type grid-connected inverter is analyzed.In order to deal with the power quality of the grid-connected current,the current control strategy of the grid-connected inverter is studied,and a third-order nonlinear active disturbance rejection controller is constructed as the current controller.In the ADRC,the grid-connected current resonance and other disturbances are regarded as total disturbances,and the extended state observer is used to estimate and offset them.Due to high order adrc parameter itself is complex,difficult in practical engineering application,this paper,the approximate method of third order LCL type inverter in order to a first order system,in order to build the first-order linear ADRC,and approximate time delay problem in the system,on the input signal before entering the extended state observer joined the consistent with the system delay time delay link.The square simulation results show that this method can improve the power quality of grid-connected current.