Distributed Robust Control Of Island Microgrid Considering Time-varying Communication Delay

In recent years,with the increasing severity of environmental pollution and energy crisis,the distributed generation technology has attracted the widespread attention.Microgrid,as an effective application means for distributed generation unit to connect to the large power grid,the microgrid can work in different modes according to the situation,it can achieve grid-connected operation by connecting to the large power grid,and also can be separated from the large power grid when the large power grid fails or some special situation occurs,switching to island mode.This flexible working characteristic has made microgrid widely applied and developed.In the island mode,distributed power generation units in the microgrid need to exchange information through the communication network,so as to jointly maintain the voltage and frequency stability of the microgrid.However,many problems,such as delay caused by communication transmission,will do harm to microgrid control.For solving this problem,based on the two-level microgrid control structure combining local primary control and remote secondary control,this thesis proposes the distributed robust method for controlling the microgrid frequency and voltage.The main contents of this thesis are as follows:1.From the perspective of the basic structure,main characteristics and control strategies of the microgrid,the constraints of the microgrid's control performance is analyzed.Then the significance of the communication network to the microgrid control and the applications of the communication network in the microgrid are introduced.Finally,the impact of communication networks on microgrid control and the characteristics of time-varying communication delays in communication networks are analyzed.2.The asymptotic stability of the networked control system with a given robust performance index is analyzed,and the stability of networked control system based on Lyapunov-krasovsky theory and linear matrix inequality method,in the condition of random time-varying delays in communication networks is analyzed,and the conditions for the existence of stability and robustness are given.then the design method of the system's optimal secondary robust controller under the condition of given robust performance indexes is studied.3.Based on the droop control method,the small-signal analysis model of themicrogrid voltage and frequency is established.Then by introducing a distributed secondary robust control strategy,a microgrid closed-loop system analysis model that includes the communication network is obtained,4.Based on the above theoretical research results of the island microgrid model and optimal secondary robust control,a system stability condition and controller optimization design method for distributed control of microgrid system,for the microgrid system with four distributed power sources connected in series are proposed.MATLAB/Simulink simulation platform was used to verify the effectiveness of the robust control strategy in the presence of random time-varying delays and external disturbances.The simulation tests show that the proposed island micro grid secondary robust control strategy can obtain the optimal controller parameters under the permitted robust performance of a given system.And the system can make the microgrid system operated in a stable state and satisfy the given robust performance,in the presence of random time-varying delay,external disturbances and other conditions.