Distributed-centralized Coordinated Dispatch Research On Multi-level Grid-connected Microgrid

In order to meet the demand of China for carbon emissions decrease and energy transition,the power system industry’s application of renewable energy is increasing year by year.Distributed generation which depends on renewable energy has the disadvantage of intermittence.Microgrid can effectively alleviate the contradiction between distributed generation and distribution network,which is often presented as multi-layer grid structure composed of feeder level microgrid and user level microgrid in engineering applications.This paper is oriented to multi-level grid-connected microgrids in medium and low voltage levels,and discusses thought of modular microgrid structure and the hierarchical coordinated control.According to different types of distributed generation and energy storage system,this paper analyzes the corresponding operation characteristics and grid connected control circuit,and establishes a model to verify its operation effectiveness.Due to the multi-level structure characteristics of grid connected microgrid,the grid structure of multi-level grid connected microgrid is modularized,in which feeder-level microgrid is formed together with feeder facilities and constructed modular user-level microgrid.Multi-level modular grid connected microgrid reduces line power transmission,simplifies the design process,and improves scalability and operational flexibility through its modular features.In order to reduce the control pressure of the feeder level microgrid control center dealing with the distributed generation and avoid the single point failure of the user-level microgrid control system,this paper constructs a peer-to-peer control structure based on multi-agent system,which controls user-level microgrid controllable distributed generation.The consensus algorithm is used for adjacent communication between agents to reach a consensus on the incremental rate of consumption,that ensure the economic operation goal of the lowest generation cost in the user level microgrid.The example results verify that the user-level microgrid can effectively respond to the port power output command issued by the superior when it is connected to the grid,and it can realize stable independent operation in off grid operation.Equal consumption incremental operation between controllable distributed generators can be achieved as well.Based on the goal of minimum network loss,feeder-level microgrid control center uses centralized control to optimize network loss,issues instructions to direct facilities and userlevel microgrid,and cooperates with the distributed control of user-level microgrid to realize the economic operation principle,forming the distributed centralized collaborative control.In off grid operation,the control center controls direct facilities,which makes the multi-level gridconnected microgrid has independent operation ability.The partially decentralized control structure formed by distributed centralized cooperative control reduces the control pressure of multi-level grid control center,maintains the communication ability between the upper and lower levels,and is suitable for the modular grid structure of multi-level grid-connected microgrid.Based on the IEEE-33 node distribution network,a transformed multi-level grid connected microgrid is formed,and the simulation model is built to verify the feasibility of the optimal centralized control.Moreover,the coordinated operation economy of the user level microgrid with more adjustable margin is better,which proves the effectiveness of the distributed centralized coordinated dispatch.