Coordinated Operation And Optimization Of Multi-microgrid In Distribution Network

The problem of energy depletion and environment deterioration makes it eager to find more clean renewable energy sources.So Distributed Generation(DG)is developed soon and used much more widely.With the rapid increasing of DGs in distribution network,it becomes more and more difficult to manage and control these DGs.The development of microgrid provides a new solution to solve the problem.It can integrate DGs,energy storage systems and loads together and make full use of them.A microgrid can not only operate in islanding mode with energy storage systems to meet loads in a small region,but also run in grid-connected mode.With lots of DGs appearing in distribution network,the traditional distribution grid is gradually transferring to a smart power grid.To divide the distribution network into several subsystems can help to manage them effectively,thus occurs the concept of smart power grid with multi-microgrid.The layer structure and interaction of information and energy between microgrids enables the distribution network to run more coordinately and enhances the security and reliability of system.At first,mathematical models of DGs are introduced in detail,which include generation and output models of renewable energy,fuel cost of controllable DGs,charge and discharge model of energy storage systems and electric vehicles.They form the base of the following modeling.Secondly,traditional centralized dispatch mode and new interaction dispatch mode are compared,and layer structure of multi-agent system(MAS)is applied to multi-microgrid system.According to MAS technology,mathematical model is established with the goal of operational cost minimization of the whole system,then a case of a distribution network with two MGs is analyzed,and the result reveals the economic benefits for both distribution network and MGs.Finally,dispatch policies of distribution network with multi-microgrid in peak,flat and off-peak periods according to different electricity purchase prices are put forward.Then a mathematical model of the distribution network with multi-microgrid is established with the goal of operational cost minimization of the system.A case is studied to compare the operation of multi-microgrid system in a separate way and in a combined way to verify effectiveness of policies and model proposed.The result shows that the cooperation of multi-microgrid can not only reduce cost of operation,but also chip peak off and fill valley up to some extent.The electric vehicle(EV)charging station then is added to the model above to be dispatched as a whole.A case of multi-microgrids system with EV charging station is studied,and the different system operation those are disordered charge and order charge and discharge of EVs are compared,and the result shows that the latter can decrease operational cost and reduce dependence on the energy storage system greatly.In view of the external characteristics of a MG as a power source or a load,a microgrid is dispatched in the distribution network as a entity,which can enhance the economy of system to some extent,improve load characteristic and makes mincrogrids orderly interconnect with grid.