Research On Joint Optimal Operation And Dispatch Strategy Of Electricity-gas Integrated System

As an important primary energy,natural gas has the advantages of high calorific value,less pollution,and large reserves.In order to accomplish green power supply and increase the flexibility of power system,the installed capacity of natural gas power generation constantly increases.In addition,the recently emerging power to gas technology can convert the redundant power into natural gas for storage,which provides a technical support for the large-scale storage of renewable energy such as wind and solar energy.The development of gas turbines and power to gas technology realizes the two-way coupling of power system and natural gas system,which makes electricity-gas integrated system a fundamental paradigm in the context of integrated energy systems.The coupling of power system and natural gas system widens the optimization space,but also increases the difficulty of system optimization.i)The reformation and development of the energy structure generate more requirements for the dispatch of electricity-gas integrated system.The system should not only achieve the efficient and reliable energy supply,but also comprehensively consider the impact on the environment.ii)The large-scale wind power integration brings many uncertainties to electricity-gas integrated system.How to improve the system capability to accommodate the uncertain wind power and enhance the system reliability,becomes a dispatch problem.iii)Power system and natural gas system belong to two operation centers.The traditional centralized dispatch cannot meet actual requirements,and hence the decentralized dispatch framework is necessary.To address the above-mentioned problems,this paper carries out the following researches.1)In view of the increasingly serious environmental problems of global warming and air pollution,this paper proposes an environmental-economic dispatch model of electricity-gas integrated system which considers a space-time diffusion control of air pollutants.The traditional emission amount control mode ignores the temporal and spatial distribution of emissions,which cannot effectively reduce the air pollution.While the proposed space-time diffusion control of air pollutants,captures the complex space-time diffusion of pollutant emissions,and considers the environmental protection demands of different regions,and hence reduce the influence on the air pollutant concentration according to local conditions.Furthermore,based on the space-time diffusion control of air pollutants,an environmentaleconomic dispatch model of electricity-gas integrated system is proposed.Compared to the traditional economic dispatch,the environmental-economic dispatch coordinates multiple conflicting objectives,and reduces the impact on the environment with a slight cost sacrifice,Therefore,the comprehensive advantages of electricity-gas integrated system in economic operation and environmental protection are fully explored.2)To optimize and coordinate multiple conflictive objectives in the environmentaleconomic dispatch of electricity-gas integrated system,this paper proposes a two-stage Pareto optimization.Pareto optimization first obtains a Pareto solution set for a multi-objective problem,and the decision makers can select a solution from the Pareto solution set for execution according to the actual dynamically changing requirements or expert experience.However,a huge number of nonlinear constraints in the electricity-gas integrated system cause the computational burden of Pareto solution set,which makes the Pareto optimization of this mode a difficult problem.In view of this,this paper converts the traditional single-stage Pareto optimization to a two-stage Pareto optimization.The first stage uses marginal cost model to linearize the nonconvex natural gas system,and then solves the Pareto solution set for the environmental-economic dispatch of the simplified electricity-gas integrated system,hence the computational efficiency for the Pareto solution set can be improved.In the second stage,decision makers select a best trade-off of objectives from the first-stage Pareto solution set.And then the compromise solution traces the best trade-off of objectives,and uses penalty convex–concave procedure(PCCP)to convexify the nonconvex gas flow transmission,such that the reliability of the compromise solution for operation can be guaranteed.Besides,this paper a novel analytical Pareto optimizer-homogenized adjacent points method(HAPM)for multi-objective problems.HAPM solves a Pareto optimal,evenly and widely distributed Pareto solution set for multi-objective optimization problem using three basic strategies,including reference point homogenization,adjacent point calculation and adjacent point filtration.HAPM solves the problem that the traditional Pareto algorithms cannot search the boundary Pareto solutions,and hence ensures the wide distribution of Pareto solution set.Moreover,the Pareto optimality of HAPM is also proved mathematically.3)To deal with the large-scale integration of uncertain wind power,this paper proposes a stochastic robust dispatch strategy for electricity-gas integrated system.In existing dispatch strategies for uncertainty,stochastic optimization and robust optimization are usually adopted separately,which are difficult to be coordinated.While the proposed stochastic robust dispatch combines these two optimizations and make the dispatch for uncertainty more secure and economic.Specifically speaking,system security constraints are established using affine adjustable robust optimization to ensure the reliable operation of the system in extreme scenarios,while the expected value of operation cost established by stochastic optimization is optimized to ensure the economic operation of the system.This paper adopts Nataf transformation-based three-point estimate to formulate the operation cost expectation of electricity-gas integrated system.Compared to the traditional sampling methods,Nataf transformation-based three-point estimate can accurately approximate the expected value of output variables with a very small sampling scale.Besides,the method can also consider the correlation of wind power.The stochastic robust dispatch arranges the dispatch plan based on the forecast interval of wind power,which ensures the system security in extreme wind scenarios.Besides,the stochastic robust dispatch allocates the wind power fluctuation among adjusting resources according to the operation cost of different resources,such that the actual operation cost can be reduced.4)To guarantee the decentralized autonomy and information privacy of power sub-system and natural gas sub-system,this paper proposes a two-layer convex decentralized optimization.A huge number of nonlinear constraints are contained in electricity-gas integrated system,which challenge the optimality and convergence of the decentralized optimization for the combined system.In view of this,the upper layer adopts PCCP to tightly relax the nonconvex functions in electricity-gas integrated system,and hence the original nonconvex problem is converted into an iterative convex programming.The lower layer adopts alternating direction method of multipliers(ADMM)to solve each step of PCCP in a decentralized mode,namely,the original centralized problem is decomposed into independent sub-problems solved by power system and natural gas system.Since each step of upper-layer PCCP is convex,the convergence of the lower-layer ADMM-based decentralized optimization is ensured.Through the two-layer convex decentralized optimization,power system and natural gas system independently solve their own sub-problems,and exchange few boundary variables,to converge to a high-quality result.Therefore,the decentralized autonomy and information privacy of each sub-system are protected.