Research On MAS Based Distributed Cooperative Control For Micro-grid

After entering the 21st century,people gradually realize that the large-scale use of fossil energy will cause environmental pollution,which is non renewable and the stock of fossil energy is limited.Therefore,new energy has become a hot issue for people to study.Wind energy,solar energy,nuclear energy and other new energy are booming in China.China’s urban power supply mainly depends on the large power grid,because most users in the city are close to the load center;However,for some remote villages or islands,users are far away from the load center,and subject to geographical conditions or power supply costs,it is not realistic to rely on large power grid for power supply;Therefore,the distributed generation represented by the system energy is often used to power these loads,so a variety of distributed generation power support emerges as the times require.But the distributed micro source system in smart grid contains all kinds of power electronic devices.The existence of these components also brings many problems to the grid.For example,the voltage,frequency deviation and power stability problems caused by the primary droop control of isolated micro-grid,and the power quality degradation caused by the access of PCC to unbalanced load.Aiming at the voltage,frequency deviation and power stability problems caused by primary droop control of islanded microgrid,this paper adopts hierarchical control method.Firstly,the droop control method is adopted in the first layer,and the virtual impedance is introduced to decouple the active power and reactive power.Then the parameters of the inner voltage loop and the outer current loop of the quasi PR controller are designed to realize the steady-state control of the signal in the system;Secondly,in the second layer of control system,the secondary controller is regarded as MAS(multi-agent system).The consistency algorithm of distributed secondary controller is used to realize the information exchange of frequency,voltage and current between adjacent control layers.The calculated frequency deviation of the system is fed back to the primary control system and its frequency deviation is eliminated,The voltage deviation parameter is taken as the index value of reactive power iterative calculation,and the distributed micro source capacity is allocated according to the reactive power convergence value.In order to solve the problems of unbalanced system voltage and unreasonable negative sequence current distribution caused by the microgrid system merging into the external network through the common connection point,the system voltage unbalance compensation method is adopted to improve the voltage quality of the microgrid system merging into the common connection point,the negative sequence current of the system is controlled by the dynamic consistency method,and the distributed micro source capacity of the system is distributed,To avoid circulating current between micro sources due to uneven distribution of negative sequence current.