Distributed Optimization For Energy Transactions Among Multi-Microgrid Considering Congestion Management

With the increasing permeability of distributed power in power networks,microgrids have been widely concerned due to the effective distributed power accessing.Their energy trading modes have also become a research focus.At present,the peer-to-peer(P2P)transaction mode which realizes the distributed transaction among microgrids in the electricity market,is applied in some countries.In this mode,microgrids can trade energy freely and obtain corresponding income,where its internal renewable energy can be fully absorbed.In view of the fact that the distributed transaction among microgrids in the electricity market of our country still needs further exploration,P2 P transaction mode provides a new way.However,the complexity and variability of P2 P transactions lead to line congestions in the distribution network,which poses a threat to the safety and stabilization of the distribution network.In order to solve the problem of line congestion in the real-time P2 P energy trading of the microgrid containing renewable energy,this thesis designs an event-triggering rolling horizon optimization framework.By updating the forecast data,the P2 P energy trading scheme of microgrids at the optimized time is corrected online.This framework contains a rich time dimension,composed of three processes: online P2 P energy transaction among microgrids,line congestion detection,and the rescheduling of microgrid transaction scheme.Aiming at this framework,the research work done in this thesis is as follows:Firstly,a discrete-time linear programming model of P2 P power transaction among microgrids is established with the aim of minimizing the operating cost of microgrids.The objective function is rewritten as an augmented Lagrangian function and coupled transactions are separated.The alternate direction multiplier method is used to calculate the objective function.A rolling horizon optimization method is proposed,which realizes the optimization of P2 P energy transaction scheme of microgrids in real-time scenario.Secondly,the occurrence of congestions is defined as an event.The congestion detection process and the rescheduling process of transactions among microgrids are embedded in the rolling horizon optimization window.If line congestions are detected,the system will eliminate the congestion and reschedule the transaction scheme of microgrids.If no congestion is detected,the original transaction scheme is retained.The power flow tracking technology is used to realize the congestion detection,which obtains the specific quantity of congestions and eliminates it.Based on the contribution to the congestion,microgrids are realized to share the congestion cost proportionally.The rescheduling trading scheme of microgrids is designed to ensure the power balance of microgrids through adjusting the output of micro turbines and energy storage devices.This proposed method proves that the eventtriggering rolling horizon optimization framework can solve line congestion problems.Compared with the traditional period-driven rolling horizon optimization framework,the computational time of congestion management scheme is significantly shortened under this proposed framework.Finally,considering the above method may lead to defects of the congestion management scheme contrary to transaction interests of microgrids,this congestion management method is improved.A congestion detection method based on optimal power flow algorithm is designed to obtain the total amount of reduced transactions of each microgrid during congestion.According to the total amount of transactions reduced by each microgrid,a transaction rescheduling scheme of microgrid based on alternating direction multiplier method is designed to ensure the optimal operation cost under the premise of transaction independence of microgrids.This thesis verifies the rationality and effectiveness of the improved congestion management method by designing different simulation examples.The results show that the microgrid can reschedule the transaction scheme according to its own transaction intention under the background of eliminating the line congestion.Therefore,it can be seen that the improved congestion management method can respect the transaction reduction intention of the microgrid,ensure the economic interests of the microgrid to the maximum extent,and have certain flexibility and effectiveness.