Resilience of gas interchangeability in hydrogen-blended integrated electricity and gas systems:A transient approach with dynamic gas composition tracking

Green hydrogen can be produced by consuming surplus renewable generations.It can be injected into the natural gas networks,accelerating the decarbonization of energy systems.However,with the fluctuation of renewable energies,the gas composition in the gas network may change dramatically as the hydrogen injection fluctuates.The gas interchangeability may be adversely affected.To investigate the ability to defend the fluctuated hydrogen injection,this paper proposes a gas interchangeability resilience evaluation method for hydrogen-blended integrated electricity and gas systems(H-IEGS).First,gas interchangeability resilience is defined by proposing several novel metrics.Then,A two-stage gas interchangeability management scheme is proposed to accommodate the hydrogen injections.The steady-state optimal electricity and hydrogen-gas energy flow technique is performed first to obtain the desired operating state of the H-IEGS.Then,the dynamic gas composition tracking is implemented to calculate the real-time traveling of hydrogen contents in the gas network,and evaluate the time-varying gas interchangeability metrics.Moreover,to improve the computation efficiency,a self-adaptive linearization technique is proposed and embedded in the solution process of discretized partial derivative equations.Finally,an IEEE 24 bus reliability test system and Belgium natural gas system are used to validate the proposed method.

Real-time Risk-averse Dispatch of an Integrated Electricity and Natural Gas System via Condi-tional Value-at-risk-based Lookup-table Ap-proximate Dynamic Programming

The real-time risk-averse dispatch problem of an integrated electricity and natural gas system(IEGS)is studied in this paper.It is formulated as a real-time conditional value-at-risk(CVaR)-based risk-averse dis-patch model in the Markov decision process framework.Because of its stochasticity,nonconvexity and nonlinearity,the model is difficult to analyze by traditional algorithms in an acceptable time.To address this non-deterministic polynomial-hard problem,a CVaR-based lookup-table approximate dynamic programming(CVaR-ADP)algo-rithm is proposed,and the risk-averse dispatch problem is decoupled into a series of tractable subproblems.The line pack is used as the state variable to describe the impact of one period’s decision on the future.This facilitates the reduction of load shedding and wind power curtailment.Through the proposed method,real-time decisions can be made according to the current information,while the value functions can be used to overview the whole opti-mization horizon to balance the current cost and future risk loss.Numerical simulations indicate that the pro-posed method can effectively measure and control the risk costs in extreme scenarios.Moreover,the decisions can be made within 10 s,which meets the requirement of the real-time dispatch of an IEGS.Index Terms—Integrated electricity and natural gas system,approximate dynamic programming,real-time dispatch,risk-averse,conditional value-at-risk.

Cascading Failure Propagation Simulation in Integrated Electricity and Natural Gas Systems

The sharp increase in the total installed capacity of natural gas generators has intensified the dynamic interaction between the electricity and natural gas systems,which could induce cascading failure propagation across the two systems that deserves intensive research.Considering the distinct time response behaviors of the two systems,this paper discusses an integrated simulation approach to simulate the cascading failure propagation process of integrated electricity and natural gas systems(IEGSs).On one hand,considering instantaneous re-distribution of power flows after the occurrence of disturbance or failure,the steady-state AC power flow model is employed.On the other hand,gas transmission dynamics are represented by dynamic model to capture the details of its transition process.The interactions between the two systems,intensified by energy coupling components(such as gas-fired generator and electricity-driven gas compressor)as well as the switching among the operation modes of compressors during the cascading failure propagation process,are studied.An IEGS composed of the IEEE 30-bus electricity system and a 14-node 15-pipeline gas system is established to illustrate the effectiveness of the proposed simulation approach,in which two energy sub-systems are coupled by compressor and gas-fired generator.Numerical results clearly demonstrate that heterogeneous interactions between electricity and gas systems would trigger the cascading failure propagation between the two coupling systems.

Stochastic Dynamic Economic Dispatch of Wind-integrated Electricity and Natural Gas Systems Considering Security Risk Constraints

As the proportion of wind power generation increases in power systems,it is necessary to develop new ways for wind power accommodation and improve the existing power dispatch model.The power-to-gas technology,which offers a new approach to accommodate surplus wind power,is an excellent way to solve the former.Hence,this paper proposes to involve power-to-gas technology in the integrated electricity and natural gas systems(IEGSs).To solve the latter,on one hand,a new indicator,the scale factor of wind power integration,is introduced into the wind power stochastic model to better describe the uncertainty of grid-connected wind power;on the other hand,for quantizing and minimizing the impact of the uncertainties of wind power and system loads on system security,security risk constraints are established for the IEGS by the conditional value-at-risk method.By considering these two aspects,an MILP formulation of a security-risk based stochastic dynamic economic dispatch model for an IEGS is established,and GUROBI obtained from GAMS is used for the solution.Case studies are conducted on an IEGS consisting of a modified IEEE 39-bus system and the Belgium 20-node natural gas system to examine the effectiveness of the proposed dispatch model.

Reliability evaluation of integrated electricity–gas system utilizing network equivalent and integrated optimal power flow techniques

The wide utilization of gas-fired generation and the rapid development of power-to-gas technologies have led to the intensified integration of electricity and gas systems.The random failures of components in either electricity or gas system may have a considerable impact on the reliabilities of both systems.Therefore,it is necessary to evaluate the reliabilities of electricity and gas systems considering their integration.In this paper,a novel reliability evaluation method for integrated electricity-gas systems(IEGSs)is proposed.First,reliability network equivalents are utilized to represent reliability models of gas-fired generating units,gas sources(GSs),power-to-gas facilities,and other conventional generating units in IEGS.A contingency management schema is then developed considering the coupling between electricity and gas systems based on an optimal power flow technique.Finally,the time-sequential Monte Carlo simulation approach is used to model the chronological characteristics of the corresponding reliability network equivalents.The proposed method is capable to evaluate customers’reliabilities in IEGS,which is illustrated on an integrated IEEE Reliability Test System and Belgium gas transmission system.

Optimal Operation of Integrated Energy Systems Subject to Coupled Demand Constraints of Electricity and Natural Gas

This paper proposes a hybrid multi-objective optimization and game-theoretic approach(HMOGTA)to achieve the optimal operation of integrated energy systems(IESs)consisting of electricity and natural gas(E&G)utility networks,multiple distributed energy stations(DESs),and multiple energy users(EUs).The HMOGTA aims to solve the coordinated operation strategy of the electricity and natural gas networks considering the demand characteristics of DESs and EUs.In the HMOGTA,a hierarchical Stackelberg game model is developed for generating equilibrium strategies of DESs and EUs in each district energy network(DEN).Based on the game results,we obtain the coupling demand constraints of electricity and natural gas(CDCENs)which reflect the relationship between the amounts and prices of electricity and cooling(E&C)that DESs purchase from utility networks.Furthermore,the minimization of conflicting costs of E&G networks considering the CDCENs are solved by a multi-objective optimization method.A case study is conducted on a test IES composed of a 20-node natural gas network,a modified IEEE 30-bus system,and 3 DENs,which verifies the effectiveness of the proposed HMOGTA to realize fair treatment for all participants in the IES.

Coordinated Dispatch of Integrated Electricity-Natural Gas System and the Freight Railway Network

With the significant development of liquefied natural gas(LNG)rail transport,the railway system is increasingly more closely connected with the integrated electricity-natural gas system(IEGS).To coordinate the economic operations of the two systems,this paper innovatively proposes a coordinated dispatch model of IEGS with LNG infrastructures and a freight railway network with LNG transport.First,an operational scheduling model of the railway network,considering energy consumption,is put forward for both LNG transmission and ordinary freight transport.Then,the coordinated dispatch problem of IEGS and the railway network is formulated into a mixed-integer linear programming model via the big M method and a modified incremental linearization approach.Finally,a bi-level optimization algorithm based on generalized benders decomposition(GBD)is presented to solve the coordinated dispatch problem due to the restrictions on exchanging private information.Case studies demonstrate the effectiveness of the proposed model and algorithm as well as the potential benefit for wind power accommodation.

Optimal Energy Reserve Scheduling in Integrated Electricity and Gas Systems Considering Reliability Requirements

With the growing interdependence between the electricity system and the natural gas system,the operation uncertainties in either subsystem,such as wind fluctuations or component failures,could have a magnified impact on the reliability of the whole system due to energy interactions.A joint reserve scheduling model considering the cross-sectorial impacts of operation uncertainties is essential but still insufficient to guarantee the reliable operation of the integrated electricity and natural gas system(IEGS).Therefore,this paper proposes a day-ahead security-constrained unit commitment(SCUC)model for the IEGS to schedule the operation and reserve simultaneously considering reliability requirements.Firstly,the multi-state models for generating units and gas wells are established.Based on the multi-state models,the expected unserved energy cost(EUEC)and the expected wind curtailment cost(EWC)criteria are proposed based on probabilistic methods considering wind fluctuation and random failures of components in IEGS.Furthermore,the EUEC and EWC criteria are incorporated into the day-ahead SCUC model,which is nonconvex and mathematically reformulated into a solvable mixed-integer second-order cone programming(MISOCP)problem.The proposed model is validated using an IEEE 30-bus system and Belgium 20-node natural gas system.Numerical results demonstrate that the proposed model can effectively schedule the energy reserve to guarantee the reliable operation of the IEGS considering the multiple uncertainties in different subsystems and the cross-sectorial failure propagation.

Reliability Assessment of Integrated Electricity and Natural Gas Transmission Systems in Presence of Power-to-gas and Combined Heat and Power Technologies

Assessing the reliability of integrated electricity and gas systems has become an important issue due to the strong dependence of these energy networks through the power-to-gas(P2G)and combined heat and power(CHP)technologies.The current work,initially,presents a detailed energy flow model for the integrated power and natural gas system in light of the P2G and CHP technologies.Considering the simultaneous load flow of networks,a contingency analysis procedure is proposed,and reliability is assessed through sequential Monte Carlo simulations.The current study examines the effect of independent and dependent operation of energy networks on the reliability of the systems.In particular,the effect of employing both P2G and CHP technologies on reliability criteria is evaluated.In addition,a series of sensitivity analysis are performed on the size and site of these technologies to investigate their effects on system reliability.The proposed method is implemented on an integrated IEEE 24-bus electrical power system and 20-node Belgian natural gas system.The simulation procedure certifies the proposed method for reliability assessment is practical and applicable.In addition,the results prove connection between energy networks through P2G and CHP technologies can improve reliability of networks if the site and size of technologies are properly determined.

Many-objective optimization for coordinated operation of integrated electricity and gas network

This paper develops a many-objective optimization model, which contains objectives representing the interests of the electricity and gas networks, as well as the distributed district heating and cooling units, to coordinate the benefits of all parties participated in the integrated energy system(IES). In order to solve the many-objective optimization model efficiently, an improved objective reduction(IOR) approach is proposed, aiming at acquiring the smallest set of objectives. The IOR approach utilizes the Spearman’s rank correlation coefficient to measure the relationship between objectives based on the Pareto-optimal front captured by the multi-objective group search optimizer with adaptive covariance and Lévy flights algorithm, and adopts various strategies to reduce the number of objectives gradually. Simulation studies are conducted on an IES consisting of a modified IEEE 30-bus electricity network and a 15-node gas network. The results show that the many-objective optimization problem is transformed into a bi-objective formulation by the IOR. Furthermore,our approach improves the overall quality of dispatch solutions and alleviates the decision making burden.

Coordinated optimal dispatch and market equilibrium of integrated electric power and natural gas networks with P2G embedded

As power to gas(P2 G) technology gradually matures, the coupling between electricity networks and natural gas networks should ideally evolve synergistically.With the intent of characterizing market behaviors of integrated electric power and natural gas networks(IPGNs)with P2 G facilities, this paper establishes a steady-state model of P2 G and constructs optimal dispatch models of an electricity network and a natural gas network separately. In addition, a concept of slack energy flow(SEF) is proposed as a tool for coordinated optimal dispatch between the two networks. To study how the market pricing mechanism affects coordinated optimal dispatch in an IPGN, a market equilibrium-solving model for an IPGN is constructed according to game theory, with a solution based on the Nikaido-Isoda function. Case studies are conducted on a joint model that combines the modified IEEE 118-node electricity network and the Belgian 20-node gas network.The results show that if the game between an electric power company and a natural gas company reaches market equilibrium, not only can both companies maximize their profits, but also the coordinated operation of the coupling units, i.e., gas turbines and P2 G facilities, will contribute more to renewable energy utilization and carbon emission reduction.

Bi-Level Bidding and Multi-Energy Retail Packages for Integrated Energy Service Providers Considering Multi-Energy Demand Elasticity

How to effectively use the multi-energy demand elasticity of users to bid in the multi-energy market and formulate multi-energy retail packages is an urgent problem which needs to be solved by integrated energy service providers(IESPs)to attract more users and reduce operating costs.This paper presents a unified clearing of electricity and natural gas based on a bi-level bidding and multi-energy retail price formulation method for IESPs considering multi-energy demand elasticity.First,we propose an operating structure of IESPs in the wholesale and retail energy markets.The multi-energy demand elasticity model of retail-side users and a retail price model for electricity,gas,heat and cooling are established.Secondly,a bi-level bidding model for IESPs considering multi-energy demand elasticity is established to provide IESPs with wholesale-side bidding decisions and retail-side energy retail price decisions.Finally,an example is given to verify the proposed method.The results show that the method improves the total social welfare of the electricity and natural gas markets by 7.99%and the profit of IESPs by 1.40%.It can reduce the variance of the electricity,gas,and cooling load curves,especially the reduction of the variance of the electricity load curve can which reach 79.90%.It can be seen that the research in this paper has a positive effect on repairing the limitations of integrated energy trading research and improving the economics of the operation of IESPs.

A Demand Response System for Wind Power Integration: Greenhouse Gas Mitigation and Reduction of Generator Cycling

A smart grid power system for a small region consisting of 1,000 residential homes with electric heating appliances from the demand side,and a generic generation mix of nuclear,hydro,coal,gas and oil-based generators representing the supply side,is investigated using agent-based simulations.The simulation includes a transactive load control in a real-time pricing electricity market.The study investigates the impacts of adding wind power and demand response(DR)on both greenhouse gas(GHG)emissions and generator cycling requirements.The results demonstrate and quantify the effectiveness of DR in mitigating the variability of renewable generation.The extent to which greenhouse gas emissions can be mitigated is found to be highly dependent on the mix of generators and their operational capacity factors.It is expected that the effects of demand response on electricity use can reduce dependency on fossil fuel-based electricity generation.However,the anticipated mitigation of GHG emissions is found to dependent on the number and efficiency of fossil fuel generators,and especially on the capacity factor at which they operate.Therefore,if a generator(the marginal seller)is forced to use less efficient fossil fuel power generation schemes,it will result in higher GHG emissions.The simulations show that DR can yield a small reduction in GHG emissions,but also lead to a smaller increase in emissions in circumstances when,for example,a generator(the marginal seller)is forced to use less efficient fossil fuel power generation schemes.Nonetheless,DR is shown to enhance overall system operation,particularly by facilitating increased penetration of variable renewable electricity generation without jeopardizing grid operation reliability.DR reduces the amount of generator cycling by an increased order of magnitude,thereby reducing wear and tear,improving generator efficiency,and avoiding the need for additional operating reserves.The effectiveness of DR for these uses depends on the participation of responsive loads,and this study highlights the need to maintain a certain degree of diversity of loads to ensure they can provide adequate responsiveness to the changing grid conditions.

计及动态管存的电—气互联系统优化调度与高比例风电消纳

面向高比例风电接入下电—气互联系统(IEGS)的日前优化调度问题,首先提出了风电并网功率比例因子,将其作为控制变量引入风电的随机性模型中,使风电建模可反映风电不确定程度与并网功率的相关性。其次,基于天然气传输的动态管存模型及流量平衡方程,推导了动态管存特性在应对天然气负荷波动时所呈现的缓冲特性机理。进一步地,以IEGS外购能源费用最小为目标,计及动态管存特性,同时引入极限场景的优化方法,建立了含高比例风电的IEGS日前经济调度模型,并对模型进行线性化求解。最后,构建仿真系统,验证了动态管存特性对风电不确定性功率的缓解作用,可有效提升系统运行的灵活性。同时,得出电转气(P2G)设备的应用有利于提升风电消纳能力的结论,但该能力受到风电不确定程度的制约。

电-气综合能源系统的综合灵敏度指标构建方法和应用研究

燃气轮机和电转气(power-to-gas,P2G)技术的日益成熟逐渐加深电力系统和天然气系统的耦合程度。在电-气综合能源系统的联合运行中,子系统的扰动会通过耦合元件跨系统传播,从而影响整个系统的安全运行。为研究电-气综合能源系统中子系统间的相互影响,基于牛顿拉夫逊法建立了统一潮流模型并实现了联合求解,其中天然气系统的状态变量采用牛顿下山法更新,一定程度上避免了初值敏感性。随后,基于统一潮流模型构建了节点电压/节点气压-注入节点功率综合灵敏度指标,同时获取了规范化的电压/气压灵敏度矩阵,可以定量评估系统多种扰动的共同影响并分析耦合系统的相互作用机理。算例分析验证了潮流算法和所提指标的有效性,并讨论了燃气轮机和P2G装置耦合作用下子系统间的影响关系。

电-气互联系统建模与运行优化研究方法评述

基于燃气轮机和电转气(P2G)双向耦合的电-气互联系统(IEGS)是实现高比例可再生能源消纳、提升终端能源利用效率的重要载体。首先,基于电力-天然气流传输特性的对比,阐述了IEGS的内涵及其优势。其次,介绍了IEGS中耦合新设备——P2G的技术原理和建模方法。进一步,围绕IEGS能流建模求解和优化运行调度2个维度,总结综述了相关技术的研究进展。关于优化运行调度的研究进展,主要从基础调度模型、计及系统随机性、计及能流差异性、计及运营管理机制、模型非线性处理方法等5个方面展开论述。最后,对未来IEGS建模和运行优化的研究进行了展望。

基于分立求解的电气耦合综合能源系统多能流联合计算方法

电力系统和天然气系统通过大量的燃气电厂、电转气设备等紧密耦合在一起,构成了电气耦合综合能源系统,本文提出一种基于分立求解的电气耦合能源系统多能流联合计算方法。首先,建立天然气系统、电力系统,以及耦合环节天然气发电机的模型。然后,提出基于分立求解的电气耦合综合能源系统多能流模型,通过读取天然气发电机的有功出力,计算得到其天然气消耗量,更新天然气系统负荷信息,实现电气耦合综合能源系统的解耦,对解耦后的两系统分别独立求解即可得到待求状态变量。最后,通过算例验证了分立求解方法的可行性和准确性。

计及可转移负荷的电-气综合能源系统多目标优化

可再生能源发电、电转气(powertogas,P2G)技术和电动汽车等的快速发展,促进了电-气综合能源系统(integratedelectricity-gasenergysystem,IEGES)的形成和发展。IEGES可以提升多能源系统的经济运行,但同时也引起了新的问题和挑战。在此背景下,研究包括P2G装置、间歇性可再生能源发电机组和电动汽车的IEGES系统的协调运行策略。首先,构建计及可转移负荷的IEGES多目标优化模型,以最小化系统运行成本、弃风弃光量和配电系统网损为优化目标,并考虑配电系统和配气系统相关的运行约束等;然后,应用模糊集理论将多个目标分别转化为隶属度函数,并采用加权综合指标法将多目标转化成单目标,之后采用AMPL/IPOPT商业求解器求解;最后,以修改的54节点配电系统和19节点配气网络所构成的IEGES为例,对所构建的优化模型和采用的求解方法进行说明。

基于稀疏多项式混沌展开的区域电-气联合系统全局灵敏度分析

电-气联合系统中存在大量不确定因素,准确评估这些不确定因素对联合系统的影响是联合系统规划与运行的一项重要内容。该文以区域电-气联合系统为研究对象,考虑电/气负荷、光伏电源和天然气管道参数的不确定性,提出一种基于Sobol′方法和稀疏多项式混沌展开的全局灵敏度分析方法。以IEEE 13配电网和11节点配气网构成的区域电-气联合系统为算例,验证了该文方法的正确性和有效性。算例结果表明,全局灵敏度指标可以量化各种不确定变量及其相互作用对联合系统运行的影响,有助于揭示联合系统运行状态与各种不确定因素之间的复杂关系。仿真结果同时论证了不确定变量的相关性以及天然气管道参数的不确定性对全局灵敏度分析的显著影响。

考虑热备用的气-电耦合园区综合能源系统弹性调度

随着气-电耦合园区综合能源系统IEGS(integrated electricity and gas community system)内部能源耦合程度的逐渐增强和其日益增长的供能可靠性需求,制定合理有效的调度策略增强系统对供能端故障的适应性愈加重要。为此,计及IEGS电、气互补运行特性,制定了考虑蓄热装置热备用的气、电互补多阶段弹性调度策略。首先,计算各个时刻发生气源、电源故障时满足重要负荷所需的最小储能备用容量;然后,基于备用信息进行考虑热备用约束的日前经济调度,若发生源端故障,系统切换至故障运行模式,优先保证重要负荷供能;最后,选取夏季运行日数据进行调度策略的验证分析。结果表明,考虑热备用的IEGS气、电互补弹性调度策略可在不明显改变运行成本的情况下提升系统对源端故障的适应性,保证故障域内重要负荷的可靠供给,具有较强的运行弹性。