The Control Strategies For Grid-connected Inverter In Distributed Power System

With the constant expansion of the power system, centralized power generation,high-voltage long-distance transmission single grid mode exposed the problem is gettingworse. To compensate for the inadequacies of the grid, distributed generation came intobeing. High power factor, low harmonic pollution power rectifier inverter is the keyequipment of the distributed power generation system. The conventional inverter device hasbeen unable to meet the requirements. Control system is the core of the inverter system,excellent control technology can improve the power factor, output power quality, reduce theimpact on the grid. This thesis focuses on voltage type grid-connected generation system.The main contents are as follows:Firstly, the problems and disadvantages of centralized grid is analyzed. Major newenergy distributed generation systems and research directions of the grid-connected inverteris summarized.Analysis of distributed grid inverter system.The mathematic models in ABC, anddq frame for three-phase voltage source inverter are established. The SVPWM modulationand the filter design method is introduced in detail. Dead-time effect and nonlinear loaddisturbing are pointed as the reasons which causing the waveform distortion insluding.Grid current control methods and characteristics are described. Given in detai dualclosed-loop PI controller design method based on three-phase voltage-type grid invertermathematical modle in rotating coordinate system, the simulation analysis of current loopand voltage loop.Introduction of repetitive control theory, it carried out a detailed theoretical analysis,gives specific repetitive controller design method and specific parameters.The stability of therepetitive controller design simulation.A new control algorithm, PI+repetitive control method is proposed. The simulationmode of three-phase voltage source inverter are built, compare the system of nonlinearloads, dead time and voltage disturbance respectively,the simulation results have shown thatthe inverter under PI+repetitive control can effectively reduce harmonic pollution, enhancepower quality and improve dynamic characteristic of power system.