Coordinate Control Strategy For Multi-Microgrids With Three-Phase/Single-Phase Hybrid Structure

With China's new urbanization construction and energy low-carbon transition,microgrids can not only meet the growing power demand of power users,but also promote the consumption of new energy on the spot.With the scale promotion of microgrids,three-phase microgrids and multiple single-phase microgrids are connected in series and in parallel to form the multi-microgrids with three-phase/single-phase hybrid architecture in a similar area.It has become a mainstream multi-microgrids network topology on the user side.Through collaborative interaction,it can not only improve the reliability,stability and economy of user power in the region,but also facilitate the high-density consumption of new energy.The multi-microgrids with three-phase/single-phase hybrid architecture will become an important carrier of structural reform in the supply side of the energy sector.According to whether the multi-microgrids are running or connect to the distribution network,the operation status of the multi-microgrids can be divided into three states: stop,islanded and grid-connected.During three states,the switching process includes black-start recovery and mode transfer between islanded and grid-connected.There are a large number of single-phase source-load-storage devices in the multi-microgrids.Therefore,the randomness of the output of the new energy source,the difference in power consumption habits of users,and other characteristics of the space-time imbalance of the source-load-storage output will lead to unbalanced three-phase power of the system tie-line.It poses new challenges for the coordinated control of the main switching modes of the multi-microgrids(black start recovery,mode transfer between islanded and grid-connected)and operation mode(regional autonomy,grid-connected optimization).Therefore,it is very necessary to study the coordinate control strategy for multi-microgrids with three-phase/single-phase hybrid structure.Considering the three-phase unbalance constraint,this thesis proposes some coordinate control strategies for the multi-microgrids with three-phase/single-phase hybrid structure,including the black start recovery strategy,mode transfer strategy between islanded and grid-connected,regional autonomy strategy and grid-connected optimization strategy.The main jobs of the thesis are as the following.(1)Due to the large number of sub-microgrid and source-load-storage devices,the capacity and priority of the required restoration devices are also quite different.To make the source and load in the network recover fast,reliable and orderly,this thesis proposes a concentrated-distributed black start recovery strategy for the multi-microgrids.A black start main power source is selected by the subjective and objective equilibrium evaluation method combining the Analytic Hierarchy Process and Superiority Matrix.The In-phase sequence sub-microgrid devices are recover dispersedly based on the multistage power circular domain criterion.The final state of unrestored devices decided by the modified accelerated Particle Swarm Optimization with mixed-integer nonlinear programming,and the centralized recovery order optimization is realized by the improved generalized minimum spanning tree method.The effectiveness of the proposed strategy is verified by simulation results based on the DIgSILENT model for the multi-microgrids with three-phase/single-phase hybrid structure.(2)Islanded transfer to grid-connected actively : Considering the number of sub-microgrids and networked paths involved in the grid-connected process,a search strategy for networked paths that takes stability and networking time into account is proposed to achieve stable,rapid,and orderly integration of regional autonomy systems into the distribution network.Grid-connected transfer to Islanded passively:Because the main power source bears the limited power transfer capability of the original tie line,the source-load-storge response is required.A passive mode transfer strategy that takes the timeliness and smoothness into account is proposed to achieve rapid and stable disengagement of the multi-microgrids from the distribution network.Grid-connected transfer to Islanded actively:The islanding combination scheme will affect the overall operational reliability after disconnection from the distribution network.An active mode transfer strategy that takes the decision-making and state switching of the scheme into account is proposed so that the multi-microgrids can smoothly escape the distribution network and be efficient.The effectiveness of the proposed strategy is verified by simulation results based on the DIgSILENT model for the multi-microgrids with three-phase/single-phase hybrid structure.(3)In the case of disconnection from the distribution network,the problem of source and load power loss under multi-zone island isolation will challenge the regional autonomy of the multi-microgrids with three-phase/single-phase hybrid structure.In order to make full use of the resources in the network to achieve a reliable and efficient operation of the system,this thesis proposes a multi-time-scale region autonomy control strategy for the multi-microgrids.Dynamically update island combinations and coupling search switching control through hourly dynamic islanding can achieve overall resource configuration optimization.Sourceload-storage power and state redistribution through minute-level centralized coordination optimization can minimize three-phase unbalance and source-load loss.The source-load-storage power redistribution in each sub-microgrid by using the second-order islanded real-time pow-er control to suppress source-load power fluctuations,so as to maintain the tie-line power to the original setpoint and the three-phase unbalance.The effectiveness of the proposed strategy is verified by simulation results based on the DIgSILENT model for the multi-microgrids with three-phase/single-phase hybrid structure.(4)Under the situation of connecting to the distribution network,in order to make the three-phase unbalanced degree of the system meet the requirements in the case of each sub-microgrid pursuing its own economic benefits,this thesis proposes a multiple time scales algorithm suitable for the multi-microgrids with three-phase/single-phase hybrid structure.The algorithm uses the double-layer rolling optimization structure considering correction of unbalance.A single-microgrid decentralized optimization algorithm that takes reactive power compensation into account is proposed to achieve optimal economic benefits during the forecast period.The Stackbelberg game with multiple leaders-followers is used to correct centralized rolling the power values of sub-microgrid tie lines and optimize system three-phase unbalance in each period.In addition,the day-optimized results of the recently optimized energy storage output are the hourly-optimized tracking targets.It can further refine the three-phase unbalance.The effectiveness of the proposed algorithm is verified by simulation results based on MATLAB programming.The research in this dissertation is supported by the national high technology research and development program(863 program,Research on key technology and demonstration project of smart grid on customers' side based on distributed sources,2014AA052001).