Research On Maximum Power Point Tracking And Grid-connection Control Strategy Of Photovoltaic Power Generation System

In recent years,with increasingly serious problems of energy supply shortage and environmental pollution,which has been caused by the rapid development of the world economy,the importance of development of wind power,photovoltaic or other green energy industries has been gradually attached by countries around the world.With advantages of being green,safe and having many applications,photovoltaic power generation,has gradually played a vital role in boosting to reach the goal of "carbon peaking and carbon neutrality" and sustainable development strategies.However,the power generation efficiency of photovoltaic systems is easily affected by the external environment and the performance of control algorithms.In addition,When the traditional grid-connected control strategy is adopted,it would lead to the unstable DC bus voltage on the inverter side and deteriorate the anti-disturbance performance of the system.Therefore,this paper is devoted to the research on the maximum power point tracking(MPPT)technology and grid-connected control technology for photovoltaic power generation.The main research contents are as follows:(1)Establishment of PV cell model and output characteristics analysis.A simulation model of the PV cell was built through the Simulink platform in MATLAB software.The output characteristics of the PV cell under different light intensities and ambient temperatures were analyzed by the control variable method.At the same time,a PV array simulation model was built to simulate the variation pattern of PV array output characteristics under partial shading conditions,providing a theoretical basis for the research of the maximum power point algorithm.(2)Research on traditional maximum power point tracking algorithms.By the analysis of the basic principle of maximum power point tracking,three traditional MPPT algorithms were simulated and analyzed under uniform light and partial shading conditions respectively.The simulation results show that the traditional MPPT algorithm has a good tracking effect under uniform illumination conditions.But it is easy to fall into local extremes,under partial shading conditions,which leads to tracking failure.(3)The study and simulation validation of a new improved whale algorithm.In view of the drawbacks of the traditional MPPT algorithm,an improved new whale algorithm is proposed by this paper.Firstly,by introducing an improved logistic chaotic mapping to initialize the whale position,the ergodicity of the initial value generation of the whale algorithm was improved.Secondly,by introducing an improved non-linear convergence factor and inertia weight factor,the problems that the algorithm tends to fall into local extremes and oscillate near the maximum power point were solved,so that the accuracy and speed of the algorithm’s search are enhanced.In addition,the improved spiral update method enhances the algorithm’s global search ability.Finally,the simulation model of the MPPT system based on the new whale algorithm was built by the Simulink in MATLAB software.The simulation results have been compared and analyzed in the environment of uniform illumination,local shading and dynamic shading respectively,which validated the effectiveness and superiority of the new whale algorithm.(4)Research on the grid-connected control strategy of PV power generation system.Firstly,after the mathematical model of the three-phase PV grid-connected inverter was established,the operation mode of the PV grid-connected inverter has been analyzed.Secondly,a second-order linear self-anti-disturbance control technique was adopted for the problems of slow dynamic response and poor anti-disturbance capability of the traditional double-loop PI control of the DC-AC PV inverter unit,which was applied to the outer-loop constant DC voltage/reactive power control and the inner-loop current control.Lastly,a simulation has been carried out to compare with the two-loop PI control under the same conditions.The simulation results show that the adopted control method can better stabilize the DC bus voltage under a variety of different operating conditions of disturbance,and have the better dynamic performance and anti-disturbance capability.