Research On Control Of Single-phase Photovoltaic Grid-connected Power Generation System

With the rapid development of the national distributed photovoltaic power generation industry,photovoltaic grid connected systems are developing towards a trend of miniaturization.Small and medium-sized photovoltaic power grid connected inverters are often used in household use,industrial and commercial rooftops,party and government rooftops,and other places.The complex grid connected environment requires high stability and safe operation of inverters.This article takes the single-phase photovoltaic grid connected power generation system as the research object.Based on the research of photovoltaic cell characteristics,maximum power point tracking,battery charging and discharging control,and grid connected inverter design,a repetitive control auto disturbance rejection control method is adopted to control the grid connected current.Firstly,an overview is given of the composition of the entire photovoltaic grid connected power generation system,mathematical models of photovoltaic cells and batteries are established,and disturbance observation method is selected as the maximum power point tracking control method based on the characteristic curve of photovoltaic cells.Furthermore,the working mode of the bidirectional DC/DC converter was analyzed,and its control under the charging and discharging states of the battery was designed.Secondly,the working principle of single-phase grid connected inverter under unipolar frequency doubling SPWM modulation mode was analyzed.Based on the establishment of the mathematical model of the LCL filter and the analysis of frequency characteristics,the suppression of the resonant peak of the LCL filter by six passive damping methods was analyzed in detail.Finally,the passive damping method of capacitor series resistance was selected for resonant peak suppression,and the parameters of the LCL filter and power switch were calculated.In order to effectively improve the anti-interference ability of the grid connected inverter and reduce the harmonic content of the output current,an improved control method combining repetitive control and auto disturbance rejection was adopted for the grid connected inverter.This control method differs from traditional auto disturbance rejection control in the following aspects: firstly,the auto disturbance rejection control is decoupled to achieve independent adjustment between the tracking performance and anti-interference performance parameters of the controller,reducing the difficulty of parameter adjustment.Then,repetitive control is added to the auto disturbance rejection control,expanding the bandwidth of the auto disturbance rejection controller,improving its ability to suppress intermediate frequency disturbances,and effectively suppressing periodic disturbances.Finally,a simulation model of the photovoltaic grid connected power generation system was built using Matlab/Simulink simulation software,and the maximum power point tracking control,battery charging and discharging control,and grid connected current control were simulated and verified.Detailed simulation and experimental verification were conducted on the improved repetitive control auto disturbance rejection control method.The simulation results of PI control,traditional auto disturbance rejection control,and repetitive control auto disturbance rejection control under normal power grid,weak current grid,and periodic disturbances all showed that the improved algorithm has more advantages and lower harmonic content of the output current waveform.And steady-state and dynamic performance related experiments were conducted on the hardware experimental platform,verifying the effectiveness and feasibility of the adopted control algorithm.