Study And Design Of Three-Phase Grid-Tied Inverter Based On Multirate Repetitive Control

As the fast development of the new energy distributed generation systems,such as solar and wind energy,grid-tied inverters,the essential interfaces between distributed generation systems and grids,have become hot research topics in the field of new energy.Because a three-phase four-leg inverter has the advantages of high DC voltage utilization and the ability of unbalanced voltage compensation,it attracts more and more attention from scientists and engineers.But some of the key specifications,such as efficiency and THD,still need to be optimized.To solve these problems,multirate repetitive control strategy which has a good steady performance and strong ability of harmonic suppression,is used to research and design a three-phase four-leg grid-tied inverter.The main contents are as follows:On the basis of analyzing requirements of a grid-tied inverter,this thesis chose the three-phase four-leg topological structure by comparing several typical three-phase four-wire inverters,then determined LCL filter structure based on the comparison of several well known filter circuits.Calculating principles of main components parameters were analyzed,and mathematical model of the grid-tied inverter was built and decoupled.The multirate repetitive control strategy was proposed to overcome the calculation delay and sampling frequency restrict of traditional repetitive control.Simplied equivalent structure of the control strategy was put forward,and the system stability was analyzed.Furthermore,this thesis completed research and design of multirate repetitive control strategy based on the mathematical model.The grid-tied inverter controller based on DSP and FPGA was proposed,and hardware and software of the control system were designed.The hardwaredesign contains the peripheral circuit design of core chips,signal processing circuit,drive and protective circuit and so on,while software aspects includes the communication between DSP and FPGA,main program,ADC interrupt control program and external interrupt protection program.On the basis of above research,a 50 kW three-phase four-leg grid-tied inverter test platform was built.Simulation and experiment research were carried out.And the performances under different sampling ration and Q are compared and analyzed.Finally,through parameter optimization,the THD of the output current is as low as 2%,and the efficiency is up to 96% under rated power operation.The experimental results verified the effectiveness of multirate repetitive control strategy.