Reliability Evaluation Of Integrated Energy Systems Considering Flexibility On Demand Side

With the worldwide transition towards low-carbon and environmentally friendly energy utilization,it is of great significance to build an integrated energy system,where the electricity,gas,and heat are coordinated in terms of generation,transmission,and consumption.It can substantially bring down the overall energy utilization cost and promote efficiency,accelerating the realization of China’s blueprints of “peaking carbon dioxide emissions” and “carbon neutrality”.However,the integrated energy systems have different characteristics over traditional electric power systems in the operational phase.On the one hand,in the transmission pipelines,compared with the electric power flow that is usually described by algebraic equations,the natural gas flow in the pipeline networks is described by partial derivative equations.Its time constant is larger than electricity,and the transient process in the operation timescale cannot be neglected.On the other hand,on the demand side,compared with a single type of electricity load in traditional electricity systems,some customers in the integrated energy systems are capable of flexibly adjusting their energy consumption strategies,to better satisfy their comprehensive needs for electricity,heating,and cooling.These factors bring not only opportunities but challenges as well.However,the reliability evaluation of integrated energy systems is still at an early stage.It mainly focuses on the long-term and steady-state reliabilities,while the impacts of gas flow dynamics and the flexibilities of customers on the operational reliabilities are rarely considered.To address the issues above,this thesis aims to fully explore the dynamics on the transmission side and the flexibilities on the demand side,and carry out in-depth research on the reliability of integrated energy systems in the operational phase.This work hopes to provide technical supports for the secure and reliable operation of integrated energy systems.More specifically,the contributions are summarized as follows:(1)The reliability evaluation technique of integrated electricity and gas systems(IEGS)is proposed,considering the complementation of multiple energy demands.Based on the reliability network equivalent approach,the steady-state reliability models of IEGS components are developed.Based on the integrated electricity and gas optimal power flow technique,the contingency state management scheme of IEGS is developed.The nodal reliability of IEGS can be finally obtained.The proposed technique can effectively evaluate the steady-state nodal reliabilities of IEGS,considering the bidirectional energy exchange between the electricity and gas systems,as well as the complementation of multiple energy demands of end-users.It establishes a solid research foundation for the following chapters.(2)Operational reliability evaluation technique of IEGS is proposed,considering the dynamics of gas flow.Compared with Chapter 2,this chapter further focuses on the operational phase.Considering the state transition process and the time-varying state probabilities,as well as the dynamics of gas flow,this chapter uses the time-sequential Monte Carlo simulation method,embedded with a finite-difference scheme,to evaluate the operational reliability of IEGS.Compared with former researches on steady-state-based reliabilities,the technique proposed in this chapter is more practical by accurately simulating the actual operating condition of IEGS.(3)Operational reliability evaluation technique for multi-energy customers is proposed,considering the flexibility on the demand side.Based on Chapter 2,this chapter further explores the flexibility of multi-energy customers by implementing service-based optimal self-scheduling.Based on the proposed generalized customer damage function and imperfect switching model,the operational cost and reliability during the self-scheduling are formulated.The technique proposed in this chapter is capable of optimizing the operating strategies and promoting the reliabilities of multi-energy customers,under the uncertain and fluctuating energy supply.(4)Coordinated operation framework of integrated energy systems is proposed,considering the flexibilities on both transmission and demand sides.Based on the flexibilities of transmission and demand sides studied in chapters 3 and 4,respectively,this chapter further convexifies their mathematical models using Mc Cormick envelope and second-order cone relaxation methods.The Optimization problem is further solved by an enhanced Benders decomposition method,which is embedded with the Lift-and-project cutting plane method and improved with unique solution procedures.The proposed technique in this chapter can effectively utilize the flexibilities of integrated energy systems,providing solid support for the reliable operation of the electricity system.(5)The trade-offs of operational reliabilities in the integrated energy systems considering the flexibilities on both transmission and demand sides are investigated in this chapter.Based on the conclusion from Chapter 5,this chapter continues to develop a look-ahead contingency management scheme for integrated energy systems.By setting different operating strategy preferences,the trade-off of the cost-efficiency and reliability in different operational periods,as well as the trade-off between the reliabilities of electricity and gas systems is investigated.From the operational reliability point of view,this study could guide the system operator of integrated energy systems,on how to balance the operating cost at this moment and the risk hedging in the future moment,and how to balance between the reserve provision of the gas system for the electricity system,and the operating risk of the gas system itself in the future.