Coordinated Optimization And Control Of Multiple Microgrids In A Distribution Network

The increasing number of microgrids produce serious optimization and control problems when multi-microgrids are connected to power network.The multimicrogrids system is different from traditional distribution network,which is composed by the large amount of microgrids,has brought a number of adverse effects on the operation of the distribution network,such as breaking the monopoly distribution network marketing model,changing the flow direction of power flow in the distribution network,and weakening the overall control of the distribution network.For the sake of the difficulty of global control,the operation level of multimicrogrids system and the absorbtion ability of renewable energy,this thesis studies the optimization and control strategy of multi-microgrids systems in distribution network to promote the healthy development of the distribution network system.Firstly,taking the frequent fluctuations in power when the renewable energy has accesses to microgrid into account,a double level control system is designed,whose upper control system is responsible for optimizing the load distribution of the multi-microgrids in a long time interval,and lower control system adjusts microsources to track the planned power from the upper level and ensure the real-time power balance of multi-microgrids in a short time interval.Thus,this control system enhances the economy and robustness of the multi-microgrids system.Secondly,on the basis of the pricing mechanism of microgrid and distribution network,a trading strategy of multi-microgrids system is designed and a suitable optimization model for the operation of multi-microgrids is proposed.Considering the requirements for the energy storage device-battery in the microgrid,a battery discharge penalty function is used to simulate the battery power generation cost,which is also taken as one part of the optimization objective function.Using the designed discharge penalty function for optimization,the battery can dynamically adjust the charge and discharge strategy according to its own SOC value to achieve the optimal operation of the battery.Thirdly,in the upper-level control system,due to the drawbacks of the centralized optimization method,such as the not good protection of the privacy of various market participants,the high requirements for the construction of the communication system,and the poor robustness of the control system,etc.,a distributed optimization algorithm based on the alternating multiplier method(Alteranting Direction Multiplier Method,ADMM)is designed.The decentralized optimization model of multi-microgrids system is established by analyzing the coupling relationship among nodes in the distribution network.The ADMM algorithm is improved by eliminating the regional coordination variables and used to solve the decentralized optimization model of the multi-microgrids system.The accuracy and effectiveness of the proposed method are verified through simulation analysis.Finally,in the lower level control of the microgrid,a distributed autonomous control scheme is also designed to replace the centralized control.And based on the necessary information exchange with neighboring micro-sources,each micro-source unit realizes dynamic adjustment of unit power in the neighborhood of the optimal operating point with the finite-time control method.Simulation analysis shows that the proposed micro-network distributed autonomous control scheme ensures not only the decentralization but also the economical operation capability of the microgrid.