Research On Control Technologies Of Single Phase Grid-tied Inverter With LCL Filter

With the problem of energy is getting worse in recent years, Distributed Generation (DG) is paidwide attention and developed rapidly. As grid-tied inverter is the important unit of DG sets, its outputpower quality will be determined by its design and control, especially for LCL grid-tied inverter. Sothe thesis does deep researches in single phase LCL grid-tied inverter with the three aspects of filterdesign, the current feedback method and the current control method.The thesis introduces a simple and direct design method for LCL filter design based on tworequirements of voltage-current ratio at the switch frequency and resonant frequency. Thevoltage-ratio is derived by the requirments for gird current at the switch frequency and the invertervoltage at the switch frequency according to the analytical expresssion for a modulate method. Withthe approximate expression for LCL filter bode diagram and the equation of resonant frequency, boththe total inductance and the product of the three elements are constant value. The design method isaccomplished according to the optimization objective for the least capaitor and other elements valuerange.Different analysis is carried out for three differernt current feedback method. The output powerfactor is analyzed in the inverter current feedback method. For active damping of grid currentfeedback method, the thesis discusses about the stability due to the PWM delay and the delay in thefeedback of capacitor current. The reason of the resonant problem for the split-capacitor is pointed out.for which the positive damping method is added. The grid voltage feedforward for the above structureis derived for the disturbance of grid voltage.The research on the Proportional-Intergal control and the Proportion-Resonant control isperformed. The design procedure is given for PI control for inverters. The influence of the disturbanceon the forward channel and the backward channel, and the digital delay to the performance of thecontrol system is discussed. Meanwhile, the thesis also devotes itself the design procedure for PRcontrol and points out the relation between PR control and repetetive contol. In addition, thediscretization method and phase compensation for PR control is studied. The dynamic performance ofthe two above control method is obtained by closed loop pole-zero maps.Finally the simulation and experiments are conducted on the simulate models and experimentplatform. The results of simulations and experiments shows that the correctness of the abovetheoretical analysis.