| Guided by the goal of building a new power system with new energy sources as the mainstay,flexibility,as an important means for system to cope with random power fluctuations,has gradually become one of the important indexes to measure the safe operation of the system.With the increasingly close coupling of electricity,gas and heat energy systems,the integrated energy system(IES)can realize the sharing of flexible resources of different energy systems,enrich the technical means of improving the flexibility of power system,and thus effectively cope with the random fluctuations of renewable energy output.However,there are relatively few researches on the flexibility of integrated energy systems at present,and there is a lack of in-depth discussion on the mutual aid of flexibility between heterogeneous energy systems.Therefore,this paper first quantifies and evaluates the adjustable capability of the integrated energy system and its flexible resources;Then,a day-ahead optimal scheduling strategy for integrated energy systems considering mutual aid of flexibility between multiple energy systems is proposed;Finally,based on the difference of response ability of flexible resources at different time scales,an optimal scheduling method for integrated energy system considering the mutual aid of flexible resources in multiple time scales is proposed to make full use of the flexible regulation capability of heterogeneous energy system to cope with the stochastic power fluctuations of renewable energy such as wind and solar energy.The main work of this paper is as follows:(1)Based on the types and operational characteristics of flexible resources,the quantitative evaluation indexes of flexibility at equipment level and system level are proposed,and an integrated energy system flexibility evaluation index system is established,which takes flexibility margin,renewable energy consumption and operation economy into account.Firstly,based on the concept and basic characteristics of flexibility,the flexible resources of each link within the integrated energy system are explored,and their operational characteristics are analyzed and modeled.Secondly,according to the categories and regulation characteristics of flexible resources,the flexibility quantification and evaluation indicators for flexible resources are put forward.Finally,the flexibility evaluation index system of integrated energy system is established from three perspectives:the flexibility margin of system operation,the renewable energy consumption and the operation cost.The effectiveness of the multi-energy coupling operation mode in promoting wind power consumption and improving system operation economy and flexibility is verified through the simulation results.Meanwhile,the effect of energy storage in different energy forms and load energy substitution on power system flexibility is also verified.(2)Based on the characteristics of flexibility supply and demand interaction between different types of energy systems,a day-ahead optimal scheduling strategy of integrated energy system considering mutual aid of flexibility between multiple energy systems is proposed.Firstly,the flexibility demand caused by the uncertainty of source and load is analyzed.The wind power fluctuation is modeled using the universal generating function method,and the flexibility demand of wind power balance regulation is quantified according to the wind power fluctuation confidence level index.The flexibility demand of load fluctuation is quantified according to the load reserve rate index.The flexibility demand of net load can be obtained by combining the flexibility demand of wind power and load.Secondly,based on the proposed equipment level flexibility indexes,the adjustment capacity of flexible resources between and within different energy systems is quantified,and the components of flexibility supply and demand within different energy subsystems are analyzed.Finally,on the basis of the conventional day-ahead economic dispatching model of the integrated energy system,the relevant constraints reflecting the flexibility supply and demand relationship of energy subsystems are added,and the flexibility supply and demand balance of each energy subsystem is realized through the coordination and mutual aid of the flexibility between multiple energy subsystems.The simulation results show that the proposed scheduling strategy can achieve the mutual aid of power regulation capabilities between different energy systems by coordinating the output of flexible resources,and effectively reduce the occurrence of insufficient flexibility supply.(3)Based on the difference in regulation characteristics of different types of flexible resources,an optimal scheduling strategy of integrated energy system considering the coordination and mutual aid of flexible resources on multiple time scales is proposed.Firstly,the regulation characteristics of flexible resources in different energy forms and different scheduling links are analyzed from three perspectives:command response speed,cumulative adjustment range and adjustment rate.Secondly,considering the transmission inertia of gas and heat energy,the thermal inertia of heating area and dynamic energy storage characteristics of gas and heat pipe network are modeled,and the regulation potential of gas and heat energy system in different time scales is mined.Finally,the multi-time scale coordinated scheduling model of the integrated energy system is established.In the day-ahead stage,on the basis of ensuring the balance of flexibility supply and demand,the power adjustment space of the system is expanded by the thermal inertia of the heating areas.In the intra-day and real-time stage,the power fluctuations caused by wind power prediction errors are suppressed by invoking flexible resources with different regulation characteristics.Therefore,the coordination and mutual aid of flexible resources on multiple time scales are realized.The simulation results show that the proposed scheduling strategy can coordinate the flexible resources with different regulation characteristics in the scheduling of different time scales,which can not only suppress the power fluctuation at the current time scale,but also reserve more power adjustment space for shorter time scales scheduling,so as to better respond to the random fluctuations of wind power on different time scales. |
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