Methods To Enhance Power System Flexibility And Acquisition Mechanism For Flexible Ramping Products

As a kind of environmentally friendly and sustainable resource,renewable energy source(RES)is of great significance to alleviate the pressure of energy supply and promote the social and economic development of human beings.However,the inherent variability and uncertainty of intermittent renewable energy generation present great challenges for power system planning and operation,and increase the demand for power system flexibility.There is no universally accepted definition of power system flexibility for now,and most of the research work is still in the stage of theoretical analysis without sufficient exploration and reflection on relevant practical issues.The ability to adjust controllable resources in order to meet the potential movement of system net load is one of the important characteristics of a flexible power system.System net load is defined as the remaining system load not served by renewable energy generation.To address the issue of insufficient upward and downward ramping capability in real-time dispatch,flexible ramping product(FRP)has been proposed and initially implemented by some Independent System Operators(ISOs)in the United States as a new market design.The main function of FRP is to explore flexible capability from dispatchable resources so as to meet potential upward and downward ramping requirements,and thus to enhance power system operational flexibility for effectively responding to various operational conditions.At present,there have been a number of studies on the main features,pricing mechanism,and clearing models of FRP by foreign research institutions.However,there are few reports on domestic related research work.Given this background,focusing on power system flexibility and flexible ramping product,this dissertation explores several research hotspots including flexible resources,settlement of inter-province and inter-area electricity trading,implementation of FRP in enhancing operational flexiblilty of a power system and new providers for FRP.Specifically,the main focuses of this dissertation can be summarized as follows:1)Studies on settlement methods for inter-province and inter-area electricity trading.First of all,the importance of grid interconnection and inter-province/area electricity trading to the enhancement of power system flexibility and RES integration ability is analyzed.It is pointed out proper settlement methods for inter-province/area electricity trading are the basis for ensuring the sustainability of the trading.Secondly,based on the current electricity mode in China Southern Power Grid(CSG),three existing settlement methods are introduced,with detailed examinations on the main disadvantages of the current settlement method in CSG.Finally,to address the disadvantages,a new settlement method considering allocations of unbalanced electric quantity is proposed,and then extended for possible use in the future electricity trading model with multiple power purchasers.The proposed method is based on the actual generating/consuming electric quantity and the ratified transmission loss rates,which makes it more reasonable and convincing than the current method.2)Studies on flexible ramping product and its implementation in enhancing operational flexibility of a power system.Firstly,the part of introduction studies the basic concepts and evaluation methods of power system flexibility,and summarizes the technical and economical characteristics of different types of flexible resources.Besides,FRP is depicted as a kind of improved market operation in order to enhance the power system flexibility,and existing research work about FRP is outlined.Secondly,Chapter 3 examines the impacts of high penetration of intermittent renewable energy generation on power system operational flexibility.Moreover,FRP is introduced with the focuses on basic concepts,main characteristics,pricing mechanism and clearing models,and comparisons with the existing ancillary services are made as well.Finally,two case studies are served for demonstrating the implementation of FRP in enhancing power system operational flexibility.3)Studies on simultaneous provision of flexible ramping product and demand relief by interruptible loads considering economic incentives.First of all,the role of interruptible load(IL)in power system balance and flexibility is analyzed,and a load serving entity is introduced as the mediator between multiple IL customers and system operator.Secondly,with respect to the stable and economic operation of power systems,a stochastic real-time unit commitment model considering ramp requirement and IL provision is established,with an aim of minimizing the expected operating costs.Finally,incentive compatible contracts are designed to encourage customers to reveal their true outage costs,addressing the issues of allocating and reimbursing ILs.The proposed method can effectively reduce the operation cost of power systems by taking advantage of IL participation.On the other hand,the LSE and IL customers can also get well paid under a proper price scheme.4)Studies on provision of flexible ramping product by battery energy storage in day-ahead energy and reserve markets.First of all,based on the physical actions of battery energy storage(BES),different participation modes of BES in day-ahead energy and reserve markets are discussed,as well as the associated revenue and cost streams.A BES aggregator is then introduced as the mediator between large fleets of BESs and power system operators,and offering strategies of the aggregator are proposed.Based on the strategies,an optimisation model for the aggregator to optimally participate in the multiproduct market is established,with the goal of maximizing its monetary benefits.The proposed model considers the battery degradation cost and over-offering risk cost.The BES aggregator can use the proposed method to make optimal decisions in the market and better manage its BES fleets,and the impacts of key factors on the aggregator's profit are also explored.The research content of this dissertation has enriched the current research achievements of power system flexibility,and at the same time can provide a preliminary reference for the study of flexible ramping products in China.