Research On Multi-peak Power Tracking And Synchronization Technology Of Photovoltaic Inverter Under Weak Grid

With the more and more severe environmental pollution and energy crisis,clean and renewable solar energy is widely used,and photovoltaic power generation technology has developed fastly.There are three main types of grid-connected photovoltaic inverters: single-stage,two-stage and multi-stage.The two-stage structure is easy to control the front and back stages separately,and it is the most widely used circuit structure in practice.This project chooses single-phase two-stage grid-connected photovoltaic inverters as the research object.The former mainly studies the tracking control technology of global maximum power point(MPPT)in complex external environment,especially under partial shadows,to improve energy utilization.The latter mainly studies the new grid-connected synchronization method for weak grid environment to realize the reliable grid-connected photovoltaic inverters.Photovoltaic panels are a kind of non-linear components,whose output voltage and current show obvious non-linear characteristics.In order to maximize the power generation efficiency of photovoltaic power generation system,photovoltaic cells need to work at the maximum output power point.First,this paper analyzes working principle of photovoltaic cells,and establishes the mathematical model of photovoltaic array under partial shading,and its output characteristics are analyzed.Then,the control scheme of Boost circuit for two-stage grid-connected photovoltaic inverters is established.Implementation of multi-peak MPPT control analysis based on two-step method.Secondly,the principle of basic particle swarm optimization(PSO)is introduced,and the implementation method of traditional PSO multi-peak MPPT control and its shortcomings are analyzed.On this basis,an improved PSO MPPT control method is proposed to improve the optimization speed and dynamic performance of photovoltaic power generation system for photovoltaic array output power,so as to better adapt to complex external environment.A simulation model is built in MATLAB/Simulink to verify and compare the three MPPT control methods mentioned above.Then,aiming at the full-bridge inverters,this paper researches the basic thought and working principle of the new frequency-locked loop in weak power grid,designs the filtering link and phase calculation link,establishes the mathematical model of the frequency-locked loop,proves that it has the characteristics of both type I and type II systems,and on this basis,designs the parameters,optimizes the performance of the system,and verifies the differences by simulation.Compared with the common synchronous reference frame phase-locked loop,the frequency-locked loop has advantages under the condition of grid voltage operation.Finally,a hardware circuit experimental platform composed of Boost circuit and full-bridge inverter circuit is designed and built.The MPPT control method and frequency-locked loop synchronization method designed above are implemented on the experimental platform.The experimental results show that the improved particle swarm optimization algorithm can achieve multi-peak MPPT control and has good dynamic performance.The proposed differential frequency-locked loop has better dynamic response performance than the traditional frequency-locked method.