Font Size: a A A

Research On Control Strategy Of Distributed Generation Units Based On Virtual Impedance And Virtual Synchronous Generator

Posted on:2017-01-09Degree:MasterType:Thesis
Country:ChinaCandidate:Y SuFull Text:PDF
GTID:2322330482980527Subject:Control Engineering
Abstract/Summary:PDF Full Text Request
Nowadays,under the pressure of environmental protection and energy demand,more attention has been put into the related technical field of distributed generation(DG),which can improve the utilization efficiency of the traditional energy resources and make full use of all kinds of renewable energy resources.With the analysis of the challenges of DG and microgrid,this paper mainly searches for the solutions to two problems:On one hand,when the impedance ratio of transmission line is relatively high,the application of traditional power droop control strategy has great obstacles in the environment of middle and low voltage of distribution network and microgrid.Besises,when the virtual impedance is used to solve this problem,the effect of equivalent output impedance of the DG's inverter based on virtual impedance is still needed to be considered.On the other hand,with the increasing penetration of DG,the proportion of the traditional synchronous generator is gradually reduced,which leads to the reduction of the spinning reserve capacity and moment inertia in the power system.Meanwhile,due to the excessively fast speed of response and almost no moment of inertia,the DG units based on power-electronic interface are difficult to participate in the regulation and necessary voltage and frequency support,and lack of effective compatibility with distribution network and microgrid.This paper mainly makes specific design and improvement from two aspects for the control strategy of the DG's inverter for the above problems,.In order to solve the problem above,the control strategy of DG units with high penetration in microgrid is analyzed at first,and a comprehensive control strategy which combines virtual impedance(VI)based on second-order generalizedintegrator(SOGI)with virtual synchronous generator(VSG)is also proposed in this paper.First of all,the background and significance of this research field are described in the beginning,and the necessity of this research is clarified too.Then,it illustrates and analyzes not only the existing problems caused by the large-scale application and high penetration of DG units,but also the development status and challenges of the traditional DG and microgrid.Then,this paper introduces some common control strategies of DG units.Then,the power transmission characteristics and droop control strategy of DG unit are analyzed emphatically,which will lay the foundation for the following study of control strategy based on VI and VSG.After that,due to the problems and limitations which appear in the traditional droop control in the low-voltage distribution network and microgrid,the concept of virtual impedance is introduced and a model based on SOGI is established.In order to prove the advantage of virtual impedance based on SOGI in realizability and system performance improvement,a comparative analysis of different characteristics of inverter's output impedance caused by virtual impedance based on low-pass filter and SOGI is illustrated in detail.Furthermore,after realizing the introduction and improvement of characteristics of VI,an improved droop control strategy of grid-connected inverter is also proposed in this paper.A voltage controlled VSG is proposed to improve the output characteristics of the inverter by totally or partially simulating the frequency and voltage control of a synchronous generator,which aims to improve the operational stability of DG system.At last,based on the two control strategy mentioned above,a simulated model of DG system by Matlab/Simulink is built in this paper.A specific simulation and analysis of this model,and the summary and prospect of the relevant technology are also given in the end of this paper.
Keywords/Search Tags:Distributed Generation, Droop Control, Second-Order Generalized-Integrator, Virtual Impedance, Virtual Synchronous Generator
PDF Full Text Request
Related items