Analysis Model And Application Research On Heating System Structure And Operation Flexibility

Building a smart integrated energy system with multi-energy synergy is a significant development direction of the green-oriented energy transition in China.As an essential part of the urban integrated energy system,the heating system plays a vital role in ensuring people’s livelihood.With the proposal of the carbon peaking and carbon neutrality strategy,the development of China’s heating system shows various changes in the trend,such as sourcenetwork-load linkage,the multi-energy synergy of fossil and renewable energy sources,and distributed and centralized integration.Under the transition of the energy system,the structural design and operation of the new generation heating system need to be solved urgently.One of the core technical problems lies in achieving flexible matching of thermal energy between supply and demand.On the one hand,the "source-network-load-storage" links of the existing system are generally independent.It is difficult to support the whole process of the "source-network-load-storage" linkage under renewable energy access.On the other hand,the traditional heating system scheduling method focuses on production planning to achieve the total balance of supply and demand in operation.The scheduling strategy of the heating system based on a given load lacks an understanding of the source-load uncertainty and the dynamic transport characteristics of the heating system,making it difficult to achieve real-time balancing under source-load fluctuations.The scientific problem behind the above technical difficulties is the lack of in-depth theoretical understanding of the flexibility of the heating system.This paper focuses on the whole process of "source-network-load-storage" of the heating system.Starting from the modeling of the heating system,combined with the system operating parameters,a general theoretical model of the flexibility of the heating system is established.Then,the structural design and optimal scheduling methods considering supply-demand uncertainty and heating system flexibility are studied in two scenarios: system structure design and operation scheduling.It can support the construction and operation of the multi-energy complementary heating system with renewable energy access.The main innovations and conclusions are as follows:(1)This paper systematically analyzes and clarifies the causes of flexibility in the heating system’s "source-grid-load-storage" link.A generic theoretical model of heating system flexibility is established,and flexibility degree is defined as an index for quantitative analysis of system flexibility.According to different application scenarios,the flexibility of the whole process is decomposed into structure flexibility for structural planning and design scenarios and operation flexibility for operation and scheduling scenarios.(2)For the structural planning and design of the heating system,a steady-state model of the heating system is established,combining structural mechanism and data identification methods.A multi-scenario construction technique is used to simulate supply and demand uncertainty.The comprehensive transport capacity of the heating system to cope with the fluctuation of supply and demand under the change of the topology and working point of the attached components is quantified by combining the steady-state model.Based on it,a quantification method for structure flexibility considering source-supply uncertainty scenarios is developed.Further,a structural planning and design method that considers structure flexibility is proposed.The results of the practical case show that the additional piping and pumps have a positive effect on improving the structure flexibility of the system.(3)For the operation and scheduling of the heating system,a dynamic model of the heating system based on the Laplace transform is established.By converting the complex transport process inside the system into equivalent supply-demand boundary conditions,the explicit analytical expression of the thermal state of the nodes fluctuating with the supply-demand is obtained.It enables a fast solution to the dynamic model.The supply and demand uncertainty model is developed based on the Gram-Charlier Type A series expansion method.The confidence interval estimation is introduced to convert the uncertainty into the interval quantity for the realtime fluctuation of supply and demand.Taking the fluctuation range of supply and demand as the boundary condition of the dynamic model,a quantification method of operation flexibility considering the fluctuation range is formed.Furthermore,an operation scheduling method that considers operation flexibility is proposed.The practical cases show that operation flexibility has different characteristics at different time scales and confidence levels.At the same time,flexible scheduling of heating systems can be achieved after quantifying the delay characteristics and heat loss characteristics of heating systems.Considering heating system transmission delays and heat transfer losses can enable flexible scheduling of heating systems.(4)To improve the flexibility of the heating system structure,a topology optimization method considering construction cost and structure flexibility is proposed.Based on the economical optimization analysis of the topology,the structure flexibility constraints are introduced.Then,an optimal mathematical model of the system structure considering construction cost and structure flexibility is developed and solved using a mixed-integer linear programming method.It realizes the optimization of pipe layout,pipe size,and heating source location selection.The results show that the proposed method can reduce the total length of the pipe network and reduce heat loss.At the same time,it avoids the reduction of local flexibility caused by structural redundancy and high resistance of the pipe network.(5)To improve the flexibility of the operation and scheduling of the heating system,a multiobjective optimal scheduling method that considers operational economy and operation flexibility is proposed.The dynamic model operation boundary is constructed based on the fluctuation interval of supply and demand.Then,a multi-objective optimal scheduling model aiming at maximum operational economy and operation flexibility is established.The optimal compromise solution is obtained using the multi-objective evolutionary algorithm based on decomposition and the technique for order preference by similarity to ideal solution for real-time output of controllable heating sources.Further,the influence of total heat supply and heating source configuration on the optimal value is analyzed.The results show a threshold effect between unit configuration and operation flexibility.It requires a higher operating cost to enhance the operation flexibility.When the unit power rating is increased to a critical value,it no longer provides a gain in dispatch flexibility.The result analysis also shows a threshold effect between the rated power of the heating unit and the operation flexibility.When the rated power increases to a critical value,it no longer provides a gain to the operation flexibility.This paper establishes a generalized theoretical model of heating system flexibility and applies it to structure design and operation scheduling.It breaks through the limitation of theoretical analysis and technical methods for heating system flexibility.The research results can promote the construction and development of multi-energy complementary heating systems in future integrated urban energy systems and provide references for the low-carbon transformation of China’s heating systems.