Research On Control Strategy Of Grid-connected Inverter In Distributed Generation System

Nowadays distributed generation based on renewable energy has become thedirection of future development in energy industry. As the bridge between power grid anddistributed generation sources, inverter has become a research hotspot. Grid-connectedthree-phase voltage source inverter system is considered as the research object in thispaper. The power control of distributed generation system in grid-connected mode and thecontrol of dc bus voltage are studied. Inverter’s output active and reactive power isdecoupled by controlling its output current, thus the power demand of power grid is met.Firstly, the working principle of voltage source inverter and its mathematicaldescription is introduced. The architecture of grid-connected inverter system is analyzedand the mathematical model of the system in different coordinate systems is established,which lay the foundation of subsequent chapters.Secondly, in view of the nonlinear characteristics and the uncertainties caused byparameter perturbation and external disturbance in actual operation, adaptive controlstrategy is adopted to control classical three-phase voltage source inverter. An adaptivecontroller with the function of interference suppression is designed to control theinverter’s output power by applying adaptive Backstepping technology. Unity powerfactor operation of the system is realized, and stability of dc bus voltage is achieved at thesame time. Both theoretical analysis and simulation results show the effectiveness of theadopted control strategy.Finally, the issue of power tracking control when AC power grid’s demand changes isconsidered. The inverter with an LCL filter is adopted. As the system has an higher order,the control law is derived by using Backstepping recursive control thought. Inconsideration of system uncertainties, such as parameter perturbation in actual operation,the robust control strategy is adopted to design the controller. Active power injected intopower grid is controlled. At the same time, reactive power compensation control isrealized and system stability is guaranteed. Simulation results show that the adoptedcontrol strategy designed for grid-connected inverter with an LCL filter could effectivelycontrol the output power. Moreover, the influence caused by parameter variations to system performance is overcome.