Research On Control Strategy Of Microgrid Based On Virtual Synchronous Generator

Microgrid is an effective approach to integrate the advantages of all kinds of distributed resources,to take less impact on distribution grid and improve the economic profits of distributed generations.It has become a hot topic and important direction in distributed generation area.This paper focuses on inverters and its control strategy,and transforms inverter as a virtual synchronous generator according to the behavior and control strategy of synchronous generator and control structure of utility.This paper also establishes the math model of VSG,and designs different kinds of controller applied in different mode.The main content of this paper are as follow:First of all,a survey of the background,concept and development at home and broad of microgrid are provided;Control structures of microgrid and operation strategies of inverters are summarized based on many experimental platforms and projects in many countries.And the problems exsiting in microgird system are given in this paper.Secondly,a microgrid inverter that imitates synchronous generatorvirtual synchronous generator(VSG)is proposed,and fundamental theory and implemental method are explained.An analysis of the influence of each parameter on VSG is proposed.Thirdly,a digital frequency governor and an excitacion controller which extracts from the essence of frequency governor and excitation controller of synchronous generator are designed,and VSG embodies as same as power-frequency characteristic and voltage regulating characteristic as synchronous generator.The math model of active power loop and reactive power loop are established,and this paper anylyzes theinfluence of each parameters to system stability by root locus method,which provides principles for parameter design.Forthly,this paper makes a study of key technology of VSG,such as load sharing and presynchronization.It gives the significance of the harm of load unsharing and presynchronization to VSG.A new load sharing method is proposed,and the parameter of presynchronization is designed.In order to verify the correctness of related principles,through the Matlab/Simulink software.Experiments of the operation of islanding mode,grid-connected mode,mode transfer between the islanding/grid-connected modes,load sharing mode and presynchronization mode have been implemented.The results have verified the effectiveness of the proposed VSG control strategy.