Distributed Optimization And Control Strategy For DC Microgrids

With the increase of permeability for the renewable energy such as the wind power generation and the photovoltaic power generation,the microgrids that can guarantee the stable operation of the large-scale and diverse distributed generations will play an important role in the future energy Internet.Compared with AC microgrids,DC microgrids have less energy conversion and more convenient control.Moreover,there are no problems such as the transformer inrush current,the frequency synchronization and the reactive power in DC microgrids.Therefore,it is of great theoretical and engineering significance to research the distributed optimization and control strategy of stabilizing bus voltage,load sharing and minimizing global power loss for DC microgrids.Based on the finite-time average consensus algorithm of multi-agent system under the directed graph,the distributed optimization and control algorithms which can be used to minimize global transmission power loss and realize load sharing of the islanded DC microgrids are studied.Firstly,in order to reduce the conversion power loss of the power electronic converter and the transmission power loss of the transmission line in the islanded DC microgrids,the global transmission power loss optimization model is established,and the global transmission loss minimization condition is derived.Further,based on the minimization condition and the finite-time average consensus algorithm under the directed graph,a distributed optimization and control framework that can simultaneously achieve the global average bus voltage regulation and the global transmission power loss minimization of the islanded DC microgrids is proposed.In addition,the load sharing can greatly improve the operating efficiency and the service life of the distributed generations and the energy storage equipments in DC microgrids.However,it is impossible to simultaneously achieve the perfect load sharing and the perfect global transmission power loss minimization.Thus,the more relaxed load sharing condition is proposed.That is,the difference of the per-unit output current between any two distributed sources is less than the assigned maximum allowable deviation.Further,an adaptive optimization weight is proposed to integrate the load sharing and the global transmission power loss minimization.Eventually,the global transmission power loss minimization condition considering load sharing is derived.Based on the minimization condition and the finite-time average consensus algorithm,a distributed optimization and control framework that can simultaneously achieve the global average bus voltage regulation and the global transmission power loss minimization considering load sharing is proposed.These two distributed optimization and control frameworks are independent of the global information of DC microgrids such as the admittance matrix and the load distribution information.Moreover,they only need the strong connected communication network.Finally,the stability of the islanded DC microgrids under these two distributed optimization and control frameworks is analyzed.The simulations are carried out using MATLAB/Simulink.