| Integrated Energy System(IES),which is coupled and integrated by heterogeneous energy systems such as electric power system and natural gas pipeline network system,is the physical carrier of Energy Internet.Natural gas pipeline network system is an important national energy infrastructure,as well as an important part of IES.Security is an extremely important factor during the operation of IES and natural gas pipeline network system.Compared with the electric power system,natural gas pipeline network system and IES still lack effective security analysis methods.Based on the classic security region theory of electric power system,this thesis studies the security region of natural gas pipeline network system(NGS-SR)and the security region of IES(IES-SR).The main contributions of this thesis are as follows.First,the general concepts involved in NGS-SR and IES-SR are defined in the standardized way,including operating point,state space,security,security region,security boundary,energy supply capability,etc.The general representations of the models of security region and security boundary are given at the same time.Second,for the natural gas pipeline network system,NGS-SR and gas transmission capability(GTC)curve are found and proposed for the first time,which describe the maximum secure operating range and complete capability limit of the system respectively.The models,solution and application methods of NGS-SR and GTC curve are studied.The related details are as follows.(1)The definition and mathematical model of NGS-SR are proposed.The existence of NGS-SR in natural gas pipeline network system is verified through observation.A method for observing NGS-SR through solving the security boundary is proposed further,which can observe the two-dimensional and three-dimensional figures of any NGS-SR.The application method of NGS-SR is proposed.Based on NGS-SR,the security distance of an operating point can be calculated,so as to evaluate the security and calculate the security margin during the system operation,which can help operators make decisions.(2)The definition,mathematical model,drawing method and indices of GTC curve are proposed.Traditional GTC is only an index of GTC curve,that is,the maximum value of the curve.In addition,there exist other indices such as the minimum value,average value and median of GTC curve,which together with GTC reflect the transmission capability of the system.(3)The existence of NGS-SR and GTC curve,as well as the correctness and advantages of the proposed models and methods,are verified through typical cases.For NGS-SR,it can describe the secure operating range of the system in a visualized way during the security analysis of natural gas pipeline network system.Moreover,NGSSR greatly improves the efficiency of online security analysis of the system,and provides more comprehensive information for security control.For GTC curve,the complete transmission capability limit of the system can be described through the curve,which is beneficial to comprehensively evaluate the gas transmission performance of the pipeline network and find the transmission bottleneck,so as to improve the resource utilization efficiency of the system.Third,aiming at the unified modeling of security region for the IES coupled with heterogeneous energy,the NGS-SR model and IES-SR model based on the energy circuit are proposed,which enjoy the unified standardized mathematical form and are easy to expand.The models,modeling and solution methods of NGS-SR and IES-SR based on the energy circuit are studied.The related details are as follows.(1)The energy circuit model of the heterogeneous energy unified modeling method is introduced.The energy circuit is shown as the electric circuit in the electric power system,and as the gas circuit in the natural gas pipeline network system.The energy circuit model of natural gas pipeline network system under steady state is established,including the gas circuit model and natural gas network equation.(2)The models of NGS-SR and IES-SR based on the energy circuit are proposed.In the model,the network equations are used to describe the process of heterogeneous energy flows,which makes the models have the same mathematical form as the model of security region of electric power system,and feasible to expand to the dynamic situation.(3)The solution methods of NGS-SR and IES-SR models based on energy circuit are proposed,which effectively reduces the difficulty of solving the security region in high-dimensional state space,and can obtain the complete boundary point results of NGS-SR and IES-SR in high-dimensional state space.Furthermore,a security boundary fitting method,which is suitable for the security region in high-dimensional state space,is proposed.The IES-SR security boundary in any dimensional state space can be fitted with controllable accuracy through the fitting method,which effectively improves the practicability of IES-SR.(4)For NGS-SR and IES-SR based on the energy circuit,typical cases are taken to verify the correctness and advantages of the proposed models and solution methods.On the premise of ensuring the correctness and accuracy,the difficulty of solving the models is reduced,which significantly improves the calculation efficiency for NGS-SR and IES-SR.Benefiting from the advantage,the feasibility of calculating the complete boundary points of NGS-SR and IES-SR in high-dimensional state space is improved,which makes it possible to obtain the practical security boundary expressions that contain the complete information of security region in high-dimensional state space. |
