Research On Hierarchical Control Straregy Based On Milti-agent Theory For Microgrid

In order to solve the problems of frequency and voltage restoration and economic dispatch under the islanded operation mode of microgrid,and to overcome the disadvantage of low reliability caused by the traditional centralized control structure,the hierarchical control of microgrid is combined with the distributed cooperative control for multi-agent system in this thesis which uses the information of each distributed generator and its neighbors to ensure the frequency and voltage with no deviation and proportional power distribution aiming to achieve the microgrid operating economical and reliable.The main research contents of this thesis are as follows:Firstly,the microgrid mathematical model is established.The hierarchical control structure and the common control methods of the microgrid are studied.Aiming at the disadvantage that the primary control adopts droop control and the frequency and voltage cannot be restored to the reference value,a distributed secondary control strategy for microgrid is proposed based on the multi-agent system cooperative control theory.The distributed secondary control strategy is divided into two parts: frequency restoration control and voltage restoration control.Each distributed generator only needs to change information with its adjacent distributed generators such as frequency voltage and active power information,which can realize the seamless adjustment of frequency and voltage restoration and the proportional distribution of the active power.Secondly,aiming at accelerating the convergence,a distributed secondary control strategy based on finite-time consensus algorithm is proposed for the situation that the microgrid system may suffer from sudden external disturbances in actual operation,ensuring that the microgrid system can achieve convergence while achieves the control goal of frequency and voltage with no deviation in a rapid time.Aiming at the problem that the microgrid is susceptible to different distributed generator parameters and line impedance mismatch in the actual o peration process,it is difficult to achieve the reactive power proportional distribution,a reactive power proportional distribution method based on adaptive virtual impedance is studied.The mismatch of reactive power is used to adaptively adjust the parameters of the line impedances to satisfy the control targets of voltage and frequency restoration and power proportional distribution within a finite-time.Finally,a distributed economic dispatch strategy based on finite-time consensus algorithm is proposed with each distributed generators meeting the optimal incremental cost rate operation and minimizing the total operating cost of the microgrid.The control strategy takes two conditions of distributed generator capacity constraints into account.The optimal incremental cost of each distributed generator unit is converge to consistency within a finite-time and obtain the optimal output power which only needs the information of the optimal incremental cost rate and active power.