Multi-scale Operational Analysis Of The Electricity-heat Integrated Energy Systems

With the deterioration of energy crisis and environmental pollution situations worldwide,it is necessary for the energy supply system to improve its energy utilization efficiency,reduce pollutants and carbon dioxide emissions,and transform towards the low-carbon and clean infrastructure.Based on the principle of “multi-energy complementation and cascade utilization”,the Integrated Energy System(IES)can give full play to the complementary and mutually beneficial advantages of electricity,gas,cooling,heat and other energy flows,and has more flexible resources,higher energy utilization efficiency and fewer carbon emissions,which has received worldwide attention recently.Since the consumption of electricity and heat energy is dominant in most industrial,commercial,residential and business load scenarios,the ElectricityHeat Integrated Energy System(EH-IES)is also one of the most widely deployed forms of IES.Different from an individual electric power or district heating system,coupling facilities provide connections and mutual interactions between two energy flows with completely different physical properties.On the one hand,the deep coupling of electricity and heat in the “source-network-loadstorage” links provides huge flexible resources for the system to accommodate renewable energy and to achieve more cost-effective and low-carbon operation;On the other hand,the coordinated operation of heterogeneous energy flows increases the system scale and introduces more nonlinear factors,which poses a huge challenge to the accurate perception of the operation states of such coupled energy system.In view of this,this paper focuses on the topic of multi-scale operational analysis of the Electricity-Heat Integrated Energy Systems.Aiming to provide both theoretical support and a practical analysis tool for the safe,stable,low-carbon,efficient and economic operation of EHIES,a systematic study on the energy flow calculation,system-level multi-process joint simulation and optimal energy flow analysis of EH-IES is carried out.The major research work of this paper is summarized as follows.1)Steady-state energy flow calculation of the integrated electric and heating networks.Firstly,the steady-state energy flow calculation models of power grid,district heating network and coupling facilities are established,among which the model formulation of disrict heating network is improved in that redundant intermediate variables are eliminated.Therefrom a reduceddimension heating network model that only includes nodal outflow temperature vector and nodal net injected heat power vector as variable vectors is derived.Secondly,by further imposing block matrix operations,the improved model formulation of district heating network is transformed into a standard form of non-homogeneous linear equations,which can be efficiently solved by calling some existing well-developed algorithms.Thirdly,the coupling mode of power grid and district heating network is thoroughly analyzed,and a generic decoupling energy flow calculation framework is proposed,under which the energy flows of both networks coupled in any mode can be conveniently and efficiently calculated by leveraging MATPOWER and our self-developed code package---MATHN in this paper.Lastly,the validity and generality of the proposed methods are verified by large,medium and small scale numerical examples.This piece of work provides a steady-state simulation model of electrical and heating networks for the following system-level multi-process joint simulation studies.2)Quasi-dynamic energy flow calculation of the integrated electric and heating networks.Firstly,the time series AC power flow model and the quasi-dynamic district heating network model are established.Secondly,the paper focuses on how to deal with the partial differential equations(PDE)describing the thermal transients of the pipes,and conducts detailed theoretical proof and experimental analysis of the numerical performance of the adopted method.On this basis,two methods are further proposed to solve the quasi-dynamic energy flow model of the district heating network: the decomposition-iteration method and the improved calculation method.The latter method is integrated into our self-developed code package---MATHN,to realize generic energy flow calculation of any given district heating network.Thirdly,considering the ramp rate constraints and the adjusting limits of actuators,the heat sources cannot meet the regulation amplitude and frequency required by the energy flow calculation results in some scenarios.Therefore,an energy flow correction stage is introduced to verify(and correct if violated)the adjusting frequency limits and the ramp rate constraints of the heat sources,so as to obtain closerto-reality energy flow results.Fourthly,under the decoupled solution framework,a time step matching method is proposed to reduce the error occurred in the process of information exchange between the operators of power grid and district heating networks,which also protects the privacy of both operators by revealing only necessary information.Lastly,the feasibility,effectiveness and efficiency of the above quasi-dynamic energy flow calculation methods(including the decomposition-iteration method and the improved calculation method),the decoupled solution framework and the time step matching method are tested through three case studies of different scales.This piece of work provides the quasi-dynamic simulation models of power grid and district heating network for the following system-level multi-process joint simulation study.The work on the discretization,solution and improvement of the quasi-dynamic model of district heating network provides the key network model and pretreatment method for the optimal energy flow analysis of EH-IES.3)Multi-process joint simulation of Electricity-Heat Integrated Energy System.Firstly,the typical application scenarios and physical processes involved in the operation of EH-IES are summarized,based on which,the typical simulation events that may occur in various components are analyzed.Secondly,each component of the system is modeled structurally and encapsulated as a white box module,whose input and output dynamic characteristics are characterized by three types of physical quantities: module inputs,outputs and parameters.Thirdly,to achieve a generic way of solving the system-level simulation model,the “partially-joint solution” strategy is proposed,which incorporates the calculation step flexibility of the “decomposed solution” strategy and the generality advantage of the “joint solution” strategy.Fourthly,two categories of data interfaces(named as “power type” and “energy type”)are further proposed to reduce the error due to information exchange among different data sets.Lastly,the effectiveness of the proposed model and method is verified by numerical case studies.This work can provide simulation support for system security and stability analysis,operation state simulation and dispatch plan verification.4)Optimal energy flow analysis of Electricity-Heat Integrated Energy System.Firstly,considering the uncertainty of renewable energy generations and the operation difference between electric and heating equipment,a hybrid time scale hierarchy for operational optimization of multienergy flows is constructed.Under this hierachy,the optimal energy flow model of ElectricityHeat Integrated Energy System is established by further considering the transmission constraints of power grid and district heating network.In this optimization model,the dynamic transmission constraints of district heating network described by PDEs are discretized into a set of linear equality constraints with the finite difference method,after which some mature software can be directly employed to solve the discretized optimization model efficiently.Secondly,the influence of the spatial and temporal difference step sizes on the optimal energy flow results and the overall computing time is analyzed,based on which an optimal difference step sizes selection method is proposed.Lastly,the effectiveness of the proposed model and methods is verified by numerical case studies.