Study On Control Strategy Of LCL Filter-based Single-phase Photovoltaic Grid-Connected Inverter

In recent years,household photovoltaic power generation equipment has received extensive attention and research in both environmental and economic benefits.One of the issues to be concerned with is the power quality and system stability.During the conversion of direct current to alternating current,the high frequency noise is generated by the inverter of high frequency action,which seriously affects the current quality of the invert bridge output.Although the LCL filter can weaken the high harmonic component,it can generate the resonance peak at the resonant frequency and cause the instability of the system under certain excitation conditions.At the same time,in the process of modulation wave formation,the traditional PI control strategy can not eliminate the steady state error and single control performance.Therefore,3k W LCL single-phase grid-connected inverter is the research object.Theoretical research and simulation verification are carried out to optimize the parameter design of LCL filter,LCL filter resonance peak improvement problem,and optimize the traditional current control strategy.In addition,based on the photovoltaic power generation experiment platform of the research group,the effectiveness of grid current quality and control effect is verified.The main achievements of this dissertation are as follows:(1)Complete the parameter design of LCL filter circuit.In order to meet the requirements of the total harmonic distortion and the actual engineering requirements.The correlation characteristics of LCL filter are analyzed.The optimization method of filter parameters is given by graphical method.The correctness of the design is verified by simulation test.(2)The research of active damping control under digital control is completed.Using capacitive current feedback to solve the problem of resonance peak.At the same time,the stability of the closed-loop system is guaranteed.In order to meet the requirement of system stability margin and grid-connected current,the setting process of system closed-loop parameter is given,and the simulation software is used for rationalization analysis.(3)Complete the study of self-adaptive control strategy.The current controller adopts the nine-point control algorithm to solve the steady-state error of traditional PI control.Then,aiming at the defects of the uncertainty of the 9-point control parameter,this dissertation proposes and studies self-adaptive control strategy based on random forest algorithm and 9-point control algorithm to achieve the control accuracy.Simulation and analysis of self-adaptive control strategy are carried out to verify the superiority of adaptive point control.(4)The experimental platform of LCL single-phase grid-connected inverter control system is completed.The software process of DSP+FPGA and hardware circuit module are designed.According to the indirect control of the contravariant side current,the direct control of the grid-connected current and the self-adaptive control,experimental results verify the effectiveness of the adaptive control.In summary,LCL filter circuit can attenuate high frequency harmonics,and the active damping method of capacitive current feedback under digital control can suppress the resonance peak and optimize the performance of the system.The self-adaptive control based on the nine-point control and random forest algorithm is better than the traditional control strategy,which eliminates the steady state error and meets the requirement of THD parallel network.