The Operation Strategy And Bidding Mechanism Of Energy Storage In The Electricity Market Based On Flexible State Of Charge

As a highly flexible resource,energy storage can bring many benefits to power systems.Energy storage,as a high-quality demand response resource,can profit by participating in the electricity market.The operation strategy and bidding mechanism of energy storage in the electricity market have been a research hot spot in recent years.According to the technical characteristics of energy storage,this paper proposes the operation mode of energy storage based on the flexible state of charge,and applies it to the operation strategy of market participants and market mechanism design,respectively.The contributions of this paper are summarized as follows.Firstly,the operation mode of energy storage based on the flexible state of charge is proposed.In the optimization model,it can be understood as a relaxation method for the constraints of the final state of charge.Under the flexible state of charge operation mode,the state of charge of the energy storage at the last moment of the optimization period does not necessarily need to be equal to its preset value.In this way,the charging and discharging power of energy storage can be more flexibly decided,thereby further releasing the demand response potential of energy storage.The flexible state of charge not only helps to improve the safety,stability and economy of the power system operation,but also helps to increase the revenue of energy storage and further promote the development of energy storage technology.This paper first systematically expounds the basic content of the flexible state of charge,based on which the new operation model,optimal bidding strategy and new bidding mechanism of energy storage are proposed.Secondly,the optimal bidding strategy for energy storage aggregators based on flexible state of charge under direct load control is proposed.Under direct load control,the aggregator centrally determines power set points according to a single objective function.This paper firstly proposes a new operation model of energy storage aggregators based on flexible state of charge,and then proposes a stochastic programming model of aggregators participating in the electricity market.The core of the new operation model is that the charging demands ofelectric vehicles are considered to be flexible.In the mathematical model,the constraints of satisfying the charging demands of electric vehicles are relaxed and added to the objective function based on the Lagrangian relaxation method.The proposed strategies are verified by the case studies based on the rules and data of a real electricity market.We also compare the results of the traditional operation model and the proposed operation model.Thirdly,the optimal bidding strategy of energy storage aggregators based on flexible state of charge under indirect load control is proposed.Under indirect load control,the energy storages manage their charging schedules according to the retail prices determined by the aggregator.The aggregator looks for economic benefit in the transaction between the grid and the energy storages.The strategic interactions between the aggregator and energy storages can be modeled by the bi-level optimization approaches.The upper-level problem takes the perspective of the aggregator who aims to maximize the profits obtained from the wholesale and retail markets.Given the retail prices,in the lower level,the energy storages maximize their profits and determine the optimal charging and discharging schedules.In order to reduce the difficulty of solving the model without loss of accuracy,this paper,on the one hand,proposes the exact relaxing methods to remove some constraints.On the other hand,this paper proposes the decomposition-based method and the model is divided into several simple problems,which are solved iteratively to obtain the optimal solution.The case studies verify the effectiveness of the proposed relaxation methods and decomposition algorithm.Fourthly,a new bidding mechanism for energy storage is proposed based on flexible state of charge.The innovation of the new mechanism,from the perspective of the energy storage,lies in the what to decide and submit,dispatching method and profit model,etc.The focus is on what to decide for energy storage.Under the new mechanism,energy storage does not need to decide the charging and discharging power for the operation day,but decides the demand response curve and submits it to the system operator,who determines its charging and discharging power in the market clearing process.Under the new mechanism,the charging and discharging power of energy storage can be flexibly adjusted during the operating day according to the demand curves,which quantifies the potential profitopportunities in the subsequent market window.In this case,the revenue of energy storage obtained in the market can be further increased.This paper fully describes the main content of the new mechanism,gives the specific form of the demand response curve,establishes the dispatching model under the new mechanism,and also establishes a long-term dynamic equilibrium model to analyse the impact of the new mechanism on the market.At last,the new mechanism is verified by the case studies.