Study On Two-layer Distributed Methods For Control Of Multi-Microgrids And Their Optimization Of Economic Operation

The exploitation and utilization of fossil energy is the main cause of the global energy crisis.In order to alleviate the global energy crisis and improve the environmental quality,the utilization of renewable energy power generation has become the main trend.However,due to the influence of natural conditions and geographical location,the distributed generation using new energy sources such as wind energy and solar energy are uncertain,and direct connection will cause interference to the main grid,which is not conducive to stable operation.In order to improve the permeability of renewable energy,the adjacent renewable energy sources can be integrated into microgrids to generate electricity,using energy manager to interact with the main grid,and control the renewable energy generation according to the dispatching plan,which greatly reduces the impact of the fluctuation of renewable energy on the main grid,as well as improves the reliability of power supply.Due to the limited capacity of the microgrid,the dramatic fluctuation of wind and light,or the instantaneous large connection or shedding of loads,it may reduce the reliability of power supply so that it is difficult to maintain the stable operation of the microgrid.In order to improve the reliability,several microgrids which are close to each other can be combined into multi-microgrids,designing operation strategies to promote power exchange in microgrids,which can alleviate the shortage of power supply.That is significant to the stable operation.However,compared with a single microgrid,the control and optimization of a multi-microgrid system is more complex because not only the coordination between the various distributed generations within each microgrid,but also the energy exchange between microgrids need to be considered.Thus,the research is the key problem of multi-microgrid.In order to realize the coordination control and optimization of multi-microgrid system,this paper studies two-layer distributed control method of multi-microgrid based on multi-agent system and distributed optimal economic dispatching method of multi-microgrid based on the optimal energy flow.A two-layer control model is proposed based on the idea of multi-agent.And the distributed control laws within the microgrid and the control laws between the microgrids are designed to achieve the outputs of distributed generators in proportion to their capacities and the goal of allocating the total power shortage in proportion to the available capacities of microgrids.Further,a distributed optimal economic dispatch method for multi-microgrid system based on optimal energy flow is proposed with the distributed economic operation algorithm,which achieves the objective of minimizing the generation cost of microgrid and optimizing the energy flow between microgrids.Finally,the simulation platform is built.And,simulation cases are designed to verify the effectiveness of the proposed method.The main contents of this paper include:(1)multi-agent system based two-layer distributed control method for multi-microgrid.Firstly,based on multi-agent system,a multi-microgrid two-layer control model is proposed.The upper layer of the model is communication network,including the within-MG network and the between-MG network,and the lower layer is multi-microgrid system.Then,based on the upper communication network,a distributed control algorithm is proposed,and a universal approach for obtaining the expression on arbitrary networks is given.The control law derived from the within-MG network can ensure that the power balance of microgrid and the outputs of dispatchable distributed generations are proportional to their capacities.The power balance of multi-microgrid system can be ensured by the control law derived from the between-MG network.In addition,the convergence of the proposed distributed control algorithm is proved theoretically.Finally,four cases are designed for simulation.The results show that when the power of some microgrids is insufficient due to the drastic fluctuation of load and environment,the phenomenon of insufficient power can be eliminated by power interaction between microgrids,so that the power balance of multi-microgrids can be maintained as a whole.In addition,by comparing the centralized method,the distributed method in this paper has higher fault tolerance.(2)distributed optimal economic dispatching method for multi-microgrid based on optimal energy flow.In order to realize the optimal energy flow among microgrids,based on the alternating direction multiplier method,a distributed optimal method is proposed.the method decomposes the global optimization model into several local optimization models,solved in a distributed way.Finally,the optimal generation power within each microgrid and the optimal power exchange among microgrids are obtained.To optimize the microgrid,a distributed economic operation algorithm is proposed to satisfy the optimal generation power within the microgrid and minimize the generation cost of the microgrid,so as to satisfy the criterion of equal increment among dispatchable distributed generators.Finally,a multi-microgrid simulation model is established.Moreover,three typical cases are carried out to test the performance of the distributed optimal economic dispatching method.After the analysis,the optimal power exchange among microgrids,i.e.the optimal energy flow,is realized by using ADMM algorithm.It is proved that the global optimization of multi-microgrids is solved by a distributed way.At the same time,the dispatchable DGs satisfy the criterion of equal increment rate to minimize the generation cost in the microgrid.In addition,compared with the traditional centralized optimization method,the method proposed in this paper has higher economic efficiency through comparative experiments.(3)construction of multi-microgrid system simulation platform.To test the performance of the proposed method,firstly,in Matlab/Simulink,the models of micro gas turbine,wind power generation and photovoltaic power generation are built.Then,the physical system of the underlying multi-microgrid is built and the control methods of the distributed generation are designed.On this basis,the upper multi-agent communication network is constructed and the rules of information exchange are designed.Finally,the simulation platform can satisfy various distributed control strategies and network topologies.At the same time,it can satisfy the simulation requirement of two-layer distributed control and optimal economic dispatch of multi-microgrid.