Research On MPPT Control Algorithm For Independent Photovoltaic Power System

With the continuous depletion of traditional fossil energy sources and the growing problem of environmental pollution,solar energy,as a kind of renewable energy with abundant reserves and clean environment,has received wide attention from all over the world.Photovoltaic power generation is one of the most effective ways to use solar energy,however,since the output characteristic of photovoltaic cells has strong nonlinear characteristics,the output power is extremely susceptible to changes in the external environment,and it is impossible to ensure that the photovoltaic power generation system always operates stably at the maximum power point(MPP).Therefore,maximum power point tracking(MPPT)technology is needed to improve the efficiency and power quality of photovoltaic power generation.Aiming at the problems of slow tracking speed and poor stability of the proposed MPPT control algorithm,this thesis designs and improves the MPPT algorithm based on sliding mode variable structure control with independent photovoltaic power generation system as the research object.This thesis first introduces the research background and significance of photovoltaic power generation,and simulation analysis the output characteristics of photovoltaic cells in different external environments.Secondly,by comparing the advantages and disadvantages of various DC-DC converters,the Boost converter is selected as the main circuit of the system,and the circuit design is carried out.Thirdly,the basic principle of photovoltaic power generation system MPPT is introduced,and the working principle,advantages and disadvantages of several common MPPT algorithms are analyzed.Then,the MPPT algorithm based on sliding mode variable structure control is studied.In order to ensure that the system can realize MPPT quickly and stably under the change of external environment,the traditional sliding mode control algorithm is designed by using the difference between the inductor current and the current at the MPP in the Boost converter.At the same time,in order to further reduce the power oscillation of the system under steady state,the traditional sliding mode control algorithm is improved by adding the integral term in the sliding mode switching function and replacing the sign function sgn(s)in the exponential approach rate with the saturation function sat(s),and an improved sliding mode control algorithm was designed.Finally,the simulation model of MPPT algorithm is built in Matlab/Simulink,and the simulation results of different MPPT algorithms are compared and analyzed.The simulation results show that when the external environment is stable,compared with the traditional sliding mode control algorithm,the improved sliding mode control algorithm reduces the fluctuation range of photovoltaic cell output power by 2.7W.Compared with the traditional perturbation and observation method,not only the power fluctuation range is reduced by 3.6W,but also the MPPT time is also shortened by 0.031 s.In the case of changes in the external environment,compared with other MPPT algorithms,the improved sliding mode control algorithm has faster tracking speed and higher tracking accuracy in the system implementation of MPPT.Figure [65] table [8] reference [65]...