| With the rapid development of distributed power generation technology,the traditional distribution network has gradually transformed into an active distribution network（ADN）by coordinating and controlling a large number of distributed generations（DGs）connected in the network.At the same time,with the proposed goal of "carbon peak and carbon neutrality",the proportion of renewable energy generation continues to increase,squeezing the output of conventional units as a traditional source of flexibility,and the uncertainty and volatility of the output of renewable energy such as wind power make the problem of insufficient flexibility of transmission system increasingly prominent.Therefore,it is of great significance to excavate flexible resources in ADNs to provide flexibility service for transmission network.However,this kind of flexibility trading across different levels of networks requires a reasonable market clearing mechanism as a guarantee to encourage DGs on the distribution network side to respond positively to the flexibility required by the transmission system,the research on relevant market mechanisms is still relatively insufficient.To this end,this paper carries out the following research work on the issues related to the coordination of transmission and distribution network to improve the flexibility of the transmission system:1)Under the background of the power market reform of "separation of transmission and distribution network",in order to respect the autonomous operation characteristics of transmission system operators（TSOs）and distribution system operators（DSOs）,it is advisable to adopt the form of decentralized autonomy and cooperative optimization.The operation framework of hierarchical partition of transmission and distribution system is given,and the decomposed transmission and distribution network is modeled according to the network structure,which provides a foundation for the subsequent research on the clearing model of energy market and flexibility market considering the cooperation of transmission and distribution network.2)Considering the coordination between TSO and DSOs,and taking upward flexibility as the research subject,a two-stage clearing model of energy-flexibility market is proposed.The clearing order of the energy and flexibility market is determined,that is,the day-ahead energy market is cleared first,and then the real-time flexibility market is cleared,and the clearing mechanism of their respective markets is established.Secondly,the market clearing model is established,the idea of hierarchical partition is used to divide the market clearing model into transmission networklevel market clearing sub-model and distribution network-level market clearing sub-model.Then the general consistency form of alternating direction method of multipliers（ADMM）is used to solve the market clearing model to protect data privacy.Finally,a modified IEEE 30-node transmission network and two IEEE 33-node ADNs coupling system are taken as an example to verify the proposed model.The results show that the proposed model can reduce TSO’s cost of purchasing flexibility and improve the economic benefits of ADNs.3)Based on the above research content,the impact of wind power uncertainty and flexibility resource shortage on flexibility clearing is further explored,and downward flexibility is considered in the model.The general consistency form of ADMM is still used to solve the proposed model in a distributed manner,and the modified IEEE 30-node transmission network and the IEEE 33-node ADNs coupling system are used for case studies.The analysis results of the calculation examples show that,compared with the clearing method that the flexibility is only provided by traditional generating units,the flexibility market clearing method that considers the coordination of TSO and DSOs proposed in this paper can effectively cope with the uncertainty of renewable energy output,improve the flexibility and economy of the system operation,better realize the optimal allocation of flexible resources in the whole network,and improve the absorption capacity of renewable energy. |
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