Study On Distributed And Networked Control Methods For Microgrids Based On Multi-Agent Systems

The combustion of nonrenewable fossil fuels causes environmental pollution and energy crisis,and it is worse that fossil fuel-fired electricity generation is the largest source of air pollution in many countries.Therefore,more and more countries switch to the utilization of renewable energy,which appears to be an ideal solution for reducing pollution.In recent years,distributed generators(DGs)using renewable energies has been developing rapidly.Microgrid,as an effective form of distributed power generation,will contribute a lot to improving the utilization of renewable energy,reducing pollution and relieving the crisis of energy.Thus,it's of great significance to improve the reliability and stability of power supply.However,the uncertainty of environmental conditions,the outputs of DGs has obvious randomness,and the load demand is fluctuating at the same time.The microgrid itself with low equivalent inertia,the trend of two-way flow,and the interaction of these factors,make microgrid control very difficult.According to the distributed characteristics of microgrid,to study the distributed and networked control of microgrid provides a new way and method to ensure the safe and reliable operation of microgrid.Based on the distributed multi-agent system(MAS),this paper constructs a two-layer control model of the microgrid,and studies the control and energy management of microgrid.Firstly,a distributed and networked control method for microgrid with communication network is proposed to realize the balance operation of microgrids system and the controllable DG allocation according to capacity.Then,this method is popularized,and a framework for the integration of control and energy management is proposed.This framework can achieve both different control schemes and different energy management objectives.Under this framework,the fault control method of microgrid is proposed,which solves the problem of control and energy management under agent failure.Finally,the digital simulation platform is set up in MATLAB/Simulink,and the proposed control method is tested.The main research contents of this thesis are shown as follows:(1)In order to fit the distributed characteristics of microgrid,based on multi-agent system,this paper establishes a two-layer control model of microgrid,and proposes a distributed networked control method for microgrid with communication network.The two-layer model is employed,where there is a top-layer communication network over a bottom-layer microgrid.Firstly,the construction method of the top-layer communication network is given,and then the general method of deriving the distributed control laws for agent from any communication network is systematically shown.Secondly,it is theoretically proved that as long as the agent adjusts the output of the controllable DGs according to the derived control laws,the allocation of power can be realized by iteration.Finally,the method is evaluated over seven cases via the simulation platform.The test results show that even if the environment and load change drastically at the same time,the derived control laws can guarantee the balance operation of the system and meet the requirements of power allocation according to capacity.(2)In order to improve the universality of the control law,this paper promotes the above-mentioned microgrid control method,proposes an integration framework of control and energy management,and studies the energy management of microgrid under a unified framework.Firstly,the integration framework presented in this paper,uses the two-layer structure with microgrid on the bottom-layer and the communication network on the top-layer.Then,the dynamic weight matrix is designed,and the construction method of the distributed control law is systematically given.It offers a convenient way to achieve different targets of control and energy management by substituting a parameter in the weight matrix.Secondly,it is theoretically proved that as long as the agent adjusts the output of the DGs according to the derived control laws,and the output of DGs will reach the set of control or energy management targets by iteration.Finally,the control law is tested from two aspects of control and energy management via the simulation platform.The test results show that the control law can achieve the control and energy management targets such as equal outputs,outputs according to capacity and the optimal incremental cost when the environment and load change at the same time.(3)In order to improve the robustness of the control law,combined with the above-mentioned integration framework of control and energy management,a fault tolerance control method for microgrid is proposed for the fault of communication network.Because the method can change the control law parameters adaptively,the system can be operated stably regardless of whether the communication network is faulty.Firstly,the method of judging the agent fault in the communication network is given.Then,according to the situation whether information transmission occurs or not,the control laws for controllable agents are changed adaptively.Secondly,if a failed agent functions again,it will collect present information of the DG and the load that it connects.Finally,on the simulation platform,fault tolerance control tests are performed for different types of agent faults.The test results show that,the system does not collapse due to failures of different types of agents,and partly achieve the targets of control and energy management.(4)In order to test the proposed control law,a digital simulation platform is built in MATLAB/Simulink.Firstly,four different types of DG simulation models are developed for microturbines,photovoltaic,wind turbines and battery energy storage system.Then,the basic control methods of four simulation models,such as the active and reactive power control(PQ control)and voltage and frequency control(V/F control)modes,are debugged.Secondly,the four simulation models are combined to establish the microgrid.In the meantime,the agent communication network with different topologies is constructed,which is prepared to realize the distributed and network control.Finally,the digital simulation platform can be used to set the light intensity and the change of wind speed,and adjust the DG outputs according to the control law.Meanwhile,it can set the time delay,package losses,communication link failures and agent fault.