Research On Two-stage Photovoltaic System Control Under Partially Shaded Conditions

To solve the problems caused by fossil energy consumption,it is necessary to develop clean energy industry.Solar energy is widely used as a high-quality clean energy,and photovoltaic power generation has also been a research hotspot of scholars.This paper focuses on the two-stage photovoltaic grid-connected power generation system,mainly to study its MPPT control strategy and inverter control strategy,as well as the LCL filter considering the grid impedance.Firstly,this paper introduces each module of the two-stage photovoltaic grid-connected power generation system in detail,and briefly analyzes the mathematical model of the photovoltaic array and its output characteristics.Introduce the working principle and parameter design of DC / DC circuit and the principle of DC / AC inverter circuit.Briefly describe the DC / AC inverter modulation method and the parameter design of the LCL filter.Then,the multimodal model of the photovoltaic array under partial shadows is analyzed.The MPPT principle and several commonly used MPPT methods are introduced,and then its characteristics are analyzed and compared through simulation.For the pre-stage DC / DC converter,a particle swarm optimization algorithm(PSO)with changing iteration rules and dynamic search speed limits is used to solve the multi-peak problem of photovoltaic cells under shadow conditions.The principle and algorithm flow are introduced in detail,and its superiority is shown through simulation comparison with traditional particle swarm optimization algorithm.The internal equivalent relationship between SPWM and SVPWM is analyzed in detail,and the feasibility of the third harmonic injection method is theoretically confirmed.And for the post-stage DC / AC inverter,the third harmonic injection SPWM control method is used.Secondly,the influence of grid impedance on the stability of the photovoltaic system is studied in detail.The effectiveness and applicability of the third harmonic injection method are verified by simulation.Finally,a two-stage photovoltaic power generation system simulation model was built on the MATLAB / Simulink platform.The simulation results show that the MPPT control based on the improved PSO algorithm has good tracking performance,can adapt to various shadow conditions,and can quickly and accurately track the maximum power point.The entire system has good grid connection characteristics.Through the analysis of the output waveform,it is verified that the SPWM control method injected with third harmonics improves the DC voltage utilization rate.The goal of tracking the maximum power point of the photovoltaic system and having good grid connection characteristics has been achieved.