Research And Desgin Of Repetitive Controller For Unbalanced Grid-connected There-phase Inverter

Distributed generation is one of the key technologies to solve the problem of power supply.Grid-connected inverter is an important interface between grid and distributed generation.Due to the use of unbalanced load and the mixed use of single-phase and three-phase load,the three-phase voltage of the grid is unbalanced,which makes the three-phase current of grid-connected inverter unbalanced and reduces the power quality injected into the grid.At the same time,the distributed power generation system can provide power for different electrical equipment as well asthe grid.If the inverter is only used for grid-connection,it has a single function and cannot meet the multi-purpose requirements.In view of these problems,this thesis studies and designs the repetitive controller strategy of grid-connected inverter.The main contents are as follows:The topology of grid-connected inverter for three-phase unbalanced power grid is presented.Based on the comparison and analysis of several applicable inverter topologies,combined with the design requirements of this thesis and the characteristics of unbalanced grid voltage,the topology structure of the three-phase four-leg grid-connected inverter with neutral leginductor and LCL filter is designed.Based on this structure,the parameters of key components are calculated and selected.The compound repetitive control strategy of grid-connected inverter is designed for there-phase unbalanced power grid.For the three-phase unbalanced power grid,a decoupled double synchronous reference frame-software PLLwith precise phase-locked is designed,.At the same time,the principle of repetitive control is analyzed.Aiming at the slow dynamic response of repetitive controller,a compound repetitive controller in parallel with PI controller is designed,and digital design of the controller and parameter setting are carried out.Finally,the effectiveness of the proposed method is validated by computer simulation.The off-grid Fractional-order repetitive controller is designed.This thesis analyzes the defects of the compound repetitive controller in controlling the off-grid mode of the inverter,and puts forward an improvement scheme based on Lagrange interpolation.Using FIR filter to approximate the fractional part of the delay link coefficient N,so as to construct the compound repetitive controller with fractional order.Based on this,the parameters are desgined,and finally validated by simulation.The experimental platform of grid-connected inverter under three-phase unbalanced grid is built.According to the overall design scheme,the hardware circuit and software program based on DSP are designed,and the experimental research is carried out.The experimental results verify the precision of thedecoupled double synchronous reference frame-software PLL,the high dynamic response and stability of the compound repetitive controller,and the high efficiency of the off-grid mode of the fractional repetitive controller inverter.