Research On Key Technologies Of Transmission Network Congestion Management Based On Transmission And Distribution Coordination

At present,under the background of the “dual carbon” goal and the continuous deepening of power system reform,the access to massive clean energy in the power grid and the interaction of multi-stakeholders in the market have put forward new requirements for the operation of the power grid.In addition,the strong randomness and large fluctuation of the source and load,as well as the uncertainty and inhomogeneity of the bidirectional power flow,make the power fluctuation and turbulence in the power transmission channel aggravated,and the problem of transmission network congestion appears gradually.Meanwhile,with the continuous access of massive heterogeneous resources on the distribution network side,the “passive” operation mode of the distribution network is changing,the adjustable ability of the distribution network is gradually being tapped,and transmission and distribution coordination has become an important means of transmission network regulation.Therefore,from the perspective of transmission and distribution coordination,it has important research significance and application value to make full use of the adjustable ability of the connected distribution network to alleviate the increasingly serious transmission network congestion problem.Relying on the transmission and distribution coordination framework,this thesis focuses on the key technical problems of transmission network congestion management by fully exploiting the adjustable ability of the distribution network and its supporting ability to the main network.Starting from solving the transmission network congestion problem under multiple time scales,this thesis conducts research from five aspects to deeply analyze the interaction strategy between transmission and distribution networks and achieve effective management of transmission network congestion,including dominance assessment of distribution network response potential,day-ahead congestion management of transmission network oriented to transmission and distribution coordination,intra-day congestion management of transmission network oriented to transmission and distribution coordination,real-time congestion management of transmission network oriented to transmission and distribution coordination,and load control of distribution network in the emergency state of severe congestion of transmission network.The detailed contents of this thesis are as follows:(1)Considering the impact of the distribution network response differences on transmission and distribution collaborative congestion management,a multi-time-scale distribution network response potential dominance evaluation method is researched.The evaluation system of multi-time-scale response potential dominance of distribution network is comprehensively constructed from the perspectives of reliability,economy,sociality,etc.The intuitionistic normal cloud model is utilized to characterize the uncertain information in the evaluation process,and a scoring algorithm considering cloud droplets’ distribution characteristics based on the forward intuitionistic normal cloud generator is introduced to quantify qualitative assessment information,thus effectively avoiding the loss of information.Given the influence of attribute weights on the evaluation result,the indifference threshold-based attribute ratio analysis is used to identify attribute weights.Finally,combined with the TODIM(an acronym in Portuguese for interactive and multicriteria decision-making)method in the context of intuitionistic normal cloud,a distribution network response potential dominance degree evaluation model is constructed to perceive the multi-time scale response potential dominance of the distribution network,and thereby achieve the reasonable characterization of the response interval of the dispatchable resources of the distribution network.This research lays the foundation for the research on the key technologies of transmission network congestion management based on transmission and distribution coordination.(2)Focusing on the day-ahead congestion scheduling dimension of the transmission network,and considering the strong uncertainty and intermittency brought about by massive renewable energy access,a day-ahead two-layer robust scheduling model for transmission and distribution coordination considering the congestion risk is proposed.The uncertainty of renewable energy output is introduced into the two-layer model in the form of intervals.In the upper-layer model,the cooperative dispatching of power plant and distribution network is carried out with the goal of minimizing the risk of transmission grid congestion and optimizing the economics of grid operation.In the lower-layer model,to collect the lines with the largest load shedding after the occurrence of N-1 in the transmission network,the post-N-1 verification model is constructed,and the generated important line constraints are fed back to the upper model.Finally,the interval robust optimization method is used to process the output interval of renewable energy in the model,so as to realize the solution of the two-layer model and obtain the effective day-ahead scheduling strategy of the transmission network.(3)In view of the congestion problem caused by score-load fluctuations during the intraday operation of the transmission network,in the context of the power auxiliary market including the stakeholders of the transmission network,power plant,and distribution network,and based on the operation mode in which the transmission network in the market realizes the transmission network congestion management by purchasing the power adjustment amount of the power plants(or users),an intraday congestion mitigation model of the transmission network considering the participation of transmission and distribution multi-stakeholders is proposed.The proposed model takes into account the interests of power plants,transmission networks,and distribution networks,and realizes the modification of the day-ahead scheduling strategy.Firstly,considering the impact of the improvement in the accuracy of the source-load forecasting process and the fluctuation of the source-load operation process on the day-ahead scheduling strategy,the fuzzy theory is utilized to characterize the uncertainty of the source-load operation in the power grid,which effectively preserves the source-load information.On this basis,the intraday congestion scheduling model of the transmission network with the participation of multi-stakeholders is constructed.The Nash negotiation theory is used to reconstruct the model,and the model is decomposed into the sub-problem of multi-party benefit maximization and the sub-problem of electric energy transaction negotiation and payment,thereby realizing the decoupling of transaction electricity and transaction price.Finally,the proposed model is solved by using the Alternating Direction Method of Multipliers(ADMM)method.The model not only addresses the problem of intraday congestion in the transmission network but also achieves a win-win situation for the interests of multiple parties.(4)For the congestion problem caused by occasional small faults during the real-time operation of the transmission network,a transmission network real-time hierarchical congestion management model considering the hierarchical response capability of the distribution network is proposed,which avoids the traditional congestion mitigation mode of load being directly cut off.Aiming at the difference in the degree of line congestion,the transmission network congestion is studied from the perspectives of multi-distribution network reactive power optimization,multi-distribution network active and reactive power optimization,and distribution network layer demand response.Firstly,facing the problem of mild congestion in the transmission network,the reactive power optimization scheduling model of the active distribution network group is constructed that considers the adjustable margin of network loss under the time section of the distribution network,and the secondorder cone programming method is used to perform convex relation of the power flow in the distribution network to speed up the solution speed of the model.Secondly,for the moderate congestion problem caused by occasional small faults in the transmission network,by combining with the improved target analysis cascade method,a two-layer active and reactive power optimization scheduling model for the multi-distribution network is constructed to further reduce the load on the distribution network side.Finally,for the heavy congestion problem caused by occasional small faults in the transmission network,a twolayer demand response model for the multi-distribution network based on compromise planning is proposed by fully considering the satisfaction of users to minimize the load on the distribution network side and ensure the safe operation of the power grid.(5)Aiming at the serious congestion problem caused by major faults in the transmission network and considering the insufficiency of the load shedding strategy based solely on the load level in the traditional congestion management process,an emergency load sequential cutting strategy based on the power outage loss assessment of the distribution network is proposed.Firstly,an evaluation system for power outage loss of regional distribution network is constructed,and rough-fuzzy set theory is introduced to characterize and deal with the internal uncertainty from attribute information and the diversity of group preferences in the evaluation.On this basis,a two-stage decision-making framework for regional distribution network power outage loss assessment is constructed.In the first stage,the rough-fuzzy best-worst method is introduced to identify the relative weight of each attribute in the power outage loss evaluation system.In the second stage,the MARCOS(Measurement of Alternatives and Ranking according to COmpromise Solution)decision-making method is extended to rough-fuzzy environments and a rough-fuzzy MARCOS method is proposed.This method can make full use of the relationship between the evaluation object and the positive and negative ideal sequences,and obtain the effective load cutting information of each distribution network by calculating the utility function value of the regional distribution network in the power outage loss.Then,considering the complexity of load shedding,the distribution network is set as a load-user with multiple terminals,and on this basis,a load shedding model of the distribution network is constructed by comprehensively considering the economic cost and importance cost of power outage loss and the accuracy of load shedding.Aiming at the difficulty of solving the multi-objective model to meet the requirements of second-level load shedding,the competitive-cum-compensatory decision strategy-based fuzzy goal programming approach is used to transform the model into a single objective problem,so as to realize the secondlevel solution of the proposed model.Finally,the serious congestion problem caused by the major fault of the transmission network can be addressed effectively by the load priority removal of the distribution network.