Convex Optimization Based Coordinated Scheduling Of Integrated Electricity-Water System With Desalination Plants

Recently,due to the rapid development of Energy Internet and integrated energy system(IES),the interconnection and interdependency between power system and water supply system has drawn the world-wide attention.Plenty of researchers devote efforts to the coordinated planning and operation study of integrated electricity-water system(IEWS).Additionally,seawater desalination is a significant way to produce potable water.The seawater desalination plant powered by renewable energy sources(wind or PV)and arises as an effective solution to the problem of high energy intensity and wind/PV accommodation,which provide noval approach and possibility for the coordination between power system and water system.There have been researches on the power distribution network or micro-grid containing desalination plants;however,the present researches on the optimal scheduling of IES regard desalination plants as controllable loads,and the modelling of desalination plant only considers the power consumption for simplification,which omits the desalination process and security constraints of desalination plants.Besides,under the background of IES,few researches study the coordinated scheduling of desalination plants and IEWS.With regional IEWS and reverse osmosis(RO)desalination plant as the research objective,this paper starts from the optimal energy flow problem,studies the convexification method of optimal power-water flow(OPWF)problem;then,the OPWF problem is extended to co-optimal scheduling problem of IEWS that contains desalination plants;finally,this paper proposes the cooperation mechanism and coordinated scheduling of IEWS and desalination plants that participate in demand response.The primary contribution is summarized as follows:(1)Propose a convex OPWF model of regional IEWS and an algorithm to tighten the relaxation gaps.OPWF problem for regional IEWS is a complex non-linear and non-convex problem.This paper uses variable substitution method and big M trick to address the sign function that denotes the direction of water flow,then uses the second-order cone(SOC)relaxation and convex hull method to transform the non-linear programming(NLP)problem into a mixed-integer convex programming(MICP)problem.Moreover,this paper further proposes to tighten the relaxed constraionts with the convex combination of Mc Cormick envelopes and the penalty convex-concave procedure(P-CCP).The proposed convexification method is validated on testing IEWSs.Simulation results suggest that the proposed method has the advantage of good solvability,high accuracy,fast computational speed and the adaptability to various operation condition and large-scale systems.(2)Propose a co-optimal scheduling method of IEWS considering desalination plant and its operation constraints.Combining the OPWF model,this paper establishes the co-optimal scheduling model of IEWS integrated with wind-powered desalination plants considering the power consumption and security constraints(start-up/shut-down times,power ramping rate,and etc.)of RO process.Concerning that the co-optimal scheduling problem involves multiple time periods and numerous variables,the co-optimal scheduling model is convexified using SOC relaxation,convex hull,and penalty function based on the proposed OPWF model.The proposed method is validated to limit the start-up/shut-down times,decrease system operation cost and facilitate wind accommodation.(3)Propose two coordination mechanisms and scheduling methods of desalination plant and regional IEWS.Considering desalination plants and regional IEWS are operated by various decision-makers,this paper proposes two coordination mechanisms and scheduling and corresponding two-level scheduling frameworks based on incentive-based demand response and price-based demand response mechanism.The proposed coordination mechanisms and scheduling methods are validated on a testing IEWS.The effects of the proposed mechanisms on facilitating wind accommodation,improving load profiles and decrease operation cost are contrasted and analyzed.