Research On Hierarchical Control Of Multiple Microgrids Based On Flexible DC Interconnection

With the widespread of renewable distributed energy like wind-driven generator and rooftop photovoltaic,there will be more distributed generators in distributed network in the future.While these power sources are unstable,their output power varies according to the strength of wind and sunshine which are constantly changing.If these sources connect to the network directly,the power quality will be severely affected.Microgrid can relieve this problem partly,it is always small-scale so that it can’t absorb much distributed energy effectively and it is easy to go into failure status when it operates alone.Now,the research fields of microgrid technologies are moving to connect several microgrids to become a multiple microgrids system,the stability of operation and the utilization rate of distributed energy of multiple microgrids are better than microgrid system.The work of this paper is as follows:(1)The mathematical model of flexible connected multiple microgrids is deduced,and the mathematical and simulation model of distributed generators and the control strategy of V/f and PQ of VSC are introduced.(2)The structure of flexible connected multiple microgrids based on switch system is established,the main characteristics and advantages of this structure and the new work modes of multiple microgrids are introduced,the hierarchical control strategy is established.The central dispatching layer takes into account the factors such as the charging state of energy storage and the distance between microgrids to realize the matching combination of microgrids.A PQ control strategy based on SOC state value is adopted to distribute the output of energy storage systems.An ameliorated greedy algorithm is adopted to control the working of switch system.(3)The simulation results testify the effectiveness of the structure and strategy:the switch system and parallel mode make the fluctuation of distributed generators output unprevailing to the distributed network,the flexible connected multiple microgrids and its control strategy can achieve active control of power flow,effective utilization of distributed energy,cooperation output of energy storage system.