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

With the acceleration of world industrialization and the excessive consumption of fossil energy,the problem of energy shortage is becoming increasingly prominent and the pressure on the environment is increasing.The transition to new energy has become a trend.Solar energy as a renewable clean energy has been widely used in daily life and industrial production.However,the output characteristics of photovoltaic cells are easily affected by environmental factors,resulting in the low photoelectric conversion efficiency of the system.Moreover,when the traditional PI control method is adopted in the grid-connection link,the grid-connection current harmonic content is more,affecting the power quality.Therefore,the maximum power tracking and grid-connection of single-phase grid-connected photovoltaic power generation system are studied in this paper.Firstly,the working principle of the photovoltaic cell was analyzed and its mathematical model was derived.A simulation model of the photovoltaic cell was built in Matlab/Simulink environment.The I-U and P-U curves of the output of the photovoltaic cell at different temperatures and light intensity were obtained.Secondly,the control principle of MPPT of photovoltaic cells is analyzed.Through the analysis of Boost circuit,it is concluded that the essence of maximum power tracking of photovoltaic cells is to match the load with the internal resistance of photovoltaic cells by controlling its duty cycle.And the parameters of capacitance(C)and inductance(L)in the former Boost circuit are designed.Subsequently,the control effects of common MPPT methods such as constant voltage method,perturbation observation method and conductance increment method are compared and analyzed.Therefore,an adaptive variable step size algorithm based on adaptive filtering is proposed in this paper.This algorithm can simultaneously consider the tracking speed and accuracy of the maximum power point,effectively suppress the system oscillation,and ensure the stable operation of the system.Finally,the overall design of the single-phase bipolar grid-connected photovoltaicpower generation system is completed,the working principle and topology of the back-stage grid-connected inverter are analyzed,as well as the control objectives and control methods of the inverter.The proportional resonance PR control strategy is adopted to solve the problem that the traditional PI control of the inner current loop is easy to produce harmonic components.The simulation results show that the proposed method can ensure that the grid-connected current is in the same frequency and phase with the grid voltage under the conditions of standard conditions and varying light intensity,and the harmonic component in the grid-connected current is low,which proves the superiority of the proposed control method.