Hierarchical Coordination And Master-slave Control Strategy Of Multi-microgrids System With Series And Parallel Structure

The microgrid is a individually controllable system, which contains distributedgeneration (DG), distributed energy storage (DS) and the corresponding load. Microgridhas advantages of autonomous operation, fault recovery, mutually reinforcing, optimizemanagement and coordination. The microgrid is divided into multiple sub-microgrids torealize large-scale distributed generation accessing, enhance reliability and ensurepower quality of microgrid. So the coordination control among DGs, DSs, localload,switch of microgrid and multi-microgrid system should be established, ensure thatthe microgrid can meet the power requirements of the local user under differentoperating conditions.This paper designs two-level hierarchical control scheme ofmulti-microgrid system with series and parallel structure, research micro sourcecontroller(MGCC)’s function of power control, state management and synchronizationcontrol. Analysis operation states and trigger events of the multi-microgrid system,simplify and classified operation states, a scheme of operation state transition isestablished under its current operation state and trigger event. According to thecharacteristics of multi-micro-grid system tie-line power control and synchronizationcontrol,paper design coordination strategy of MGCC. The main contents are as follows:The paper analysis the characteristics of multi-microgrid system with series andparallel structure, designs two-level hierarchical control scheme of multi-microgridsystem,which contains master-slave MGCC. The relationship of sub-microgrids withseries structure is upstream and downstream. When upstream sub-microgrid is islanding,the downstream is islanding. The relationship of sub-microgrids with parallel structureis parallel relationship, the power distribution among sub-microgrids is determined bythe partition coefficient to regulate power of multi-microgrid system. Eachsub-microgrids contains a MGCC, the paper select master MGCC from MGCC tocontrol slave MGCC and Micro source Controller (MC), load controller (LC) of mastersub-microgrid and other MGCC.This paper simplify and classified operation states, a scheme of operation state transition is established. The scheme is based on operation state and trigger event ofmulti-microgrid system, MGCC monitor operation state and trigger event ofmulti-microgrid system, adjust and control components in accordance with apredetermined program to realize state transitions.According to the characteristics of multi-micro-grid system tie-line power controlwith series and parallel structure, paper design coordination strategy of MGCC tocontrol tie-line power of multi-micro-grid system.Master MGCC of multi-micro-gridsystem with series structure generate a control signal of battery power according to thetie-line power signal, and control slave sub-microgrid. MGCC of multi-micro-gridsystem with parallel structure generate control signals of sub-microgrids poweraccording to partition coefficient, to control the battery power and control the tie-linepower.Combined with conditions of multi-micro-grid system synchronization, paperdesign coordination strategy of MGCC when multi-microgrid system is synchronization.Strategy generate control signals according to partition coefficient to control battery andsynchronization, with voltage amplitude, frequency, voltage phase difference ofswitches and the battery power. When the battery reach output limit, it wait for the nexttest, if the local load is reduced to a certain range, sub-microgrid reconnection.The Matlab/Simulink software is used to build multi-microgrid system with seriesand parallel structure, to verify the correctness of the proposed control strategy ofmulti-microgrid system. according to the dynamic characteristics of distributedgeneration, research the dynamic characteristics of tie-line power control andsynchronizing. The results verify the effectiveness and correctness of the proposedcontrol strategy.