Research On Maximum Power Point Tracking And Grid Control Of Photovoltaic Power System

As the energy crisis and environment pollution become progressively worse,solar energy is one of the representatives of renewable energy,with the characteristics of large storage capacity,wide availability,clean and pollution-free.Therefore,photovoltaic power generation has become a research hotspot in today's society.The National Energy Development Strategy Outline pointed out that solar power generation has become a major component of China's energy structure adjustment.The distributed photovoltaic grid-connected power generation system with flexible power generation and high energy utilization has been rapidly developed,This paper takes three-phase photovoltaic power generation system as the research object,and conducts in-depth research from the aspects of maximum power point tracking strategy,grid-connected inverter control strategy and phase-locked loop method.The main work of the thesis is as follows:Firstly,after expounding the working principle of photovoltaic cells,this paper simplifies the equivalent circuit to establish the corresponding mathematical model,and analyzes the nonlinear output characteristics of photovoltaic cells with different temperatures and illuminations.This paper makes some studies and compares several maximum power point tracking control methods,and put forward a maximum power point tracking method combining sliding mode control and disturbance control.The MATLAB/Simulink simulation software is used to verify the steady state of the proposed method at the maximum power point.Accuracy and response speed are superior to traditional control algorithms.Secondly,this paper adopts LCL type filter and three-phase full-bridge inverter structure to be the inverter part of photovoltaic grid-connected power generation system.This paper researches the mathematical model of LCL filter in different coordinate systems,introduces the working characteristics of the LCL filter and designs the corresponding parameters.To solve the resonance peak problem generated by LCL filter,the filter is added in the traditional voltage and current double closed loop control.The capacitor current is fed back to the inner loop.At the same time,to reduce the steady-state error caused by the output power variation,the grid-connected current loop is changed to fuzzy PI control to improve the robustness of the system interconnection.The method is verified by MATLAB/Simulink simulation software.Then,this paper establishes the mathematical model of the unbalanced power grid because of the actual imbalance of the power grid,expounds the basic structure of the phase-locked loop and the phase-locking principle of the commonly used SRF-PLL.Several commonly used ones are introduced.After balancing the phase-locking method under the power grid,the phase information problem of the DC component in the grid voltage can not be detected well for the conventional method.A method combining the second-order generalized integrator and the delayed signal cancellation method is designed.The method is verified by MATLAB/Simulink simulation software.Finally,the design process of the 10KW three-phase photovoltaic grid-connected power generation system controller is introduced.According to the overall control structure diagram and technical indicators of the system,the parameters of the main components in the circuit are selected;the hardware circuit and software algorithm design of the system are completed;the experimental test platform is built,the debugging is carried out,and the research content is verified by experiments.The resulting grid-connected current meets the grid-connected standard and can be smoothly connected to the grid.