Control Method And Strategy For Smooth Switching Of Microgrid Operation Modes Based On Virtual Generator

In current life,with increasing depletion of energy and environmental issues, distributed generation as an effective way to solve these problems has been booming. The microgrid, as an effective carrying way of distributed generation, can fully take advantages of distributed generation and support each other with grid, which makes users obtain uninterrupted reliable power supply. Microgrid seamless transfer between grid-connected mode and islanding mode is the premise of ensuring normal operation of sensitive load in microgrid, which becomes one of important contents of microgrid research.According to microgrid seamless transfer control problems, the traditional PQ control strategy is studied. By improving traditional PQ control strategy and introducing virtual generator control, this thesis puts forward a perp-synchronization control method to achieve the microgrid seamless transfer between grid-connected mode and islanding mode. The main research contents are listed as follows:1.The microsource interface control strategy is discussed in details. Each module is analyzed in terms of microsource inverter interface modeling, instantaneous power calculation,the basis of virtual generator strategy,voltage and current dual-loop decoupling control theory and voltage space vector pulse width modulation control method.2.For realizing the smooth transition between stand-alone and grid-connected, this thesis puts forward two improvements. First, an indirect control strategy of virtual synchronous generator PQ outer loop with PQ power decoupled and capacitance voltage inner loop is proposed. It not only realizes load voltage smooth transition between stand-alone and grid-connected, but also enhances robustness against line impedance variation in low voltage system.3.A new pre-synchronization control method based virtual reactance is proposed. It does not need any additional synchronization controller, and is helpful to reduce current transient process at the moment of connecting grid.4.The implementation of microgrid seamless transfer control method is given. By MATLAB/Simulink modeling and simulation, the proposed control strategy is verified.