A joint optimization power flow calculation method for power-to-gas system considering hydrogen injection

Abstract

This invention relates to a method for joint optimization power flow calculation of a power-natural gas system considering hydrogen injection, comprising: constructing a natural gas system model considering hydrogen injection, the system model including a natural gas load model, a natural gas source model, a steady-state power flow model within the natural gas pipeline, a natural gas node energy conservation model, and a natural gas mixing model; establishing coupling element models, including an electricity-to-gas facility model and a gas turbine unit model; establishing a power system model; based on the natural gas system model, the coupling element model, and the power system model, constructing a steady-state power-natural gas joint optimization model considering hydrogen injection; and solving the steady-state power-natural gas joint optimization model considering hydrogen injection to obtain the optimal control strategy and operating state of the power-natural gas system. This method can be used to calculate the joint system optimization control strategy and operating state of a power-natural gas system considering hydrogen injection, providing support for ensuring its safe operation.

Description

Technical Field

[0001] This invention relates to the field of integrated energy technology, and in particular to a method for joint optimization of power flow calculation in a power and natural gas system considering hydrogen injection. Background Technology

[0002] Hydrogen, as a clean and efficient energy source, has recently gained increasing attention in many countries as a potential alternative to natural gas. Green hydrogen is typically produced from surplus renewable energy power generation via electricity-to-gas technology, and is therefore considered one of the important energy forms for achieving zero-carbon energy systems. Hydrogen can be transported in several ways, one of which is through pipeline transportation via injection into existing natural gas pipelines. This method not only utilizes existing infrastructure, thus avoiding further investment, but also promotes the decarbonization of existing natural gas systems.

[0003] However, adding hydrogen to existing natural gas transmission systems also brings certain safety hazards and technical problems: 1. Due to hydrogen's lower ignition point and higher combustion rate compared to other gases, it is more likely to cause fire hazards; 2. Traditional natural gas energy equipment is usually designed and commissioned according to the original natural gas composition. If the natural gas composition is changed by adding hydrogen, the energy equipment may operate under non-ideal conditions, resulting in non-ideal combustion; 3. In the natural gas network, pipelines, valves, compressors, and other equipment are also usually designed for the original natural gas composition. Adding hydrogen will affect the natural gas composition and thus affect the lifespan of surface materials such as pipelines; 4. Injecting hydrogen at different locations in the natural gas system will affect the natural gas flow and node pressure. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the technical defects of the existing technology that hydrogen incorporation in natural gas transmission systems will bring certain safety hazards.

[0005] To address the aforementioned technical problems, this invention provides a method for joint optimization power flow calculation of a power-natural gas system considering hydrogen injection, comprising:

[0006] A natural gas system model considering hydrogen injection is constructed. The system model includes a natural gas load model, a natural gas source model, a steady-state power flow model within the natural gas pipeline, a natural gas node energy conservation model, and a natural gas mixing model.

[0007] Establish a coupling element model, which includes an electric-to-gas facility model and a gas turbine unit model;

[0008] Establish a power system model;

[0009] Based on the natural gas system model, the coupling element model, and the power system model, a steady-state power-natural gas joint optimization model considering hydrogen energy injection is constructed.

[0010] The steady-state power-natural gas joint optimization model considering hydrogen injection is solved to obtain the optimal control strategy and operating status of the power-natural gas system.

[0011] Preferably, the natural gas load model is as follows: in, Let the natural gas load at natural gas node i be described by energy. For the natural gas load at natural gas node i, which was originally described by flow rate, GCV gas This represents the total calorific value of natural gas.

[0012] Preferably, the natural gas source model is as follows: in, The natural gas supply described by energy at natural gas node i. For the natural gas supply at node i in the original natural gas system, described by flow rate, GCV i s The total calorific value of the natural gas supplied to the natural gas source of node i;

[0013] Preferably, the steady-state power flow model within the natural gas pipeline is as follows: Where, q i,j R represents the standard natural gas flow rate of the natural gas pipeline between natural gas nodes i and j. air T is the gas constant of air. STP and p STP Standard temperature and air pressure, p i Let D be the gas pressure at natural gas node i. i,j F i,j L i,j These represent the pipe's diameter, Fanning coefficient, and length, respectively, S. i,j Let T be the relative density of the gas inside the pipeline, and Z be the temperature of the natural gas. i,j This is the compressibility coefficient of natural gas.

[0014] Preferably, the natural gas node energy conservation model and the natural gas hybrid model are as follows:

[0015]

[0016] in, Let i be the set of power nodes that link natural gas node i. For power node j e The energy equivalent of natural gas consumed per unit time by the power-to-gas conversion facility. For power node j e A collection of gas turbine units on the ground. For power node je The jth gfu The energy corresponding to the natural gas consumed per unit time by a gas turbine unit. The natural gas flow direction is the direction of natural gas flow into natural gas node i and natural gas node j. in The set, The natural gas flow direction is the direction of natural gas outflow from natural gas node i at natural gas node j. out The set, and From natural gas node j in Flow to i and flow from i to j out The energy of natural gas currents and From natural gas node j in Flow to i and flow from i to j out The flow rate of the natural gas current, GCV i The total calorific value of natural gas node i;

[0017] Let the natural gas flow direction be from natural gas node i to j, then the relative density and total calorific value of the mixed gas are:

[0018]

[0019] Among them, M gas M hy and M air These are the relative molecular masses of natural gas, hydrogen, and air, respectively.

[0020] and The percentages of hydrogen and natural gas in natural gas node i are respectively:

[0021]

[0022] in, For power node j e The output of the power-to-gas conversion facility.

[0023] Preferably, the electro-gas conversion facility model includes: the electro-gas conversion facility consumes electricity to generate hydrogen, and the electro-gas conversion relationship is as follows:

[0024] in, and These represent the power consumption and energy conversion efficiency of the electro-gas conversion facility at node i, respectively.

[0025] The gas turbine model includes:

[0026] in, and These represent the power generation, natural gas consumption rate, and energy conversion efficiency of gas turbine unit j at node i, respectively.

[0027] Preferably, the power system model is established based on a DC model:

[0028] g i,j =(θ i -θ j ) / X i,j ,

[0029] in, Let i be the set of non-gas turbine units. Let J be the power generation capacity of the non-gas turbine unit j at node i. Let g be the electrical load of node i. i,j For the power flow from node i to j, θ i Let θ be the phase angle of node i. j Let X be the phase angle of node j. i,j Let be the reactance of power lines i and j.

[0030] Preferably, the objective of the steady-state power-natural gas joint optimization model considering hydrogen injection is to minimize the operating cost C. T The optimization variables include: the gas production rate of the natural gas source. Node pressure p i Power generation of non-gas turbine units Voltage phase angle θ i Power generation of gas turbine units Hydrogen production rate of the power-to-gas facility And the proportion of hydrogen and natural gas and

[0031] The mathematical model is as follows:

[0032]

[0033] Where EB and GB are sets of power nodes and natural gas nodes, respectively, and cst i,j (·) represents the cost function of non-gas turbine unit j at node i, ρ i Let represent the natural gas supply price of the natural gas source at natural gas node i, and μ represent the subsidy value for producing green hydrogen.

[0034] Preferably, the steady-state power-natural gas joint optimization model considering hydrogen injection satisfies the following constraints:

[0035] Wobbe indicator

[0036] Where, ξ i The range is between 5% and 10%;

[0037] Natural gas composition and gross calorific value constraints:

[0038]

[0039] β min ≤GCV i ≤β max ,

[0040] Where, α i This represents the upper limit of the hydrogen content. β max and β min The upper and lower limits are constraints on the total calorific value.

[0041]

[0042]

[0043] in, and These represent the upper and lower limits of the natural gas production rate from the natural gas source. This is the upper limit for the natural gas consumption rate of power-to-gas conversion facilities. Let i,j be the transmission capacity of natural gas pipelines. Let i be the transmission capacity of power line i,j. and These are the upper and lower limits of power generation for gas turbine units and non-gas turbine units, respectively.

[0044] Preferably, solving the steady-state power-natural gas joint optimization model considering hydrogen injection includes solving the steady-state power-natural gas joint optimization model using the IPOPT solver.

[0045] The technical solution of the present invention has the following advantages compared with the prior art:

[0046] This invention calculates and considers the optimized control strategy and operating status of the combined power and natural gas system under hydrogen injection, and controls its safety indicators such as Wobbe index, mixed natural gas composition, and mixed natural gas calorific value within a reasonable range, providing technical support for ensuring the safe operation of the combined power and natural gas system. Attached Figure Description

[0047] Figure 1 A schematic diagram of a combined power-natural gas system structure that takes hydrogen injection into account. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0049] Reference Figure 1 As shown, the power flow calculation method for a power-natural gas system considering hydrogen injection of the present invention includes the following steps:

[0050] Step 1: Construct a natural gas system model considering hydrogen injection. The system model includes a natural gas load model, a natural gas source model, a steady-state power flow model within the natural gas pipeline, a natural gas node energy conservation model, and a natural gas mixing model.

[0051] Step 2: Establish the coupling element model, which includes the electric-to-gas facility model and the gas turbine unit model.

[0052] Step 3: Establish a power system model.

[0053] Step 4: Based on the natural gas system model, the coupled element model, and the power system model, construct a steady-state power-natural gas joint optimization model considering hydrogen energy injection.

[0054] Step 5: Solve the steady-state power-natural gas joint optimization model considering hydrogen injection to obtain the optimal control strategy and operating status of the power-natural gas system.

[0055] There is no logical order between steps one, two, and three.

[0056] The method of the present invention mainly includes the following steps:

[0057] (1) Constructing a natural gas system model considering hydrogen injection (1.1) Establishing a natural gas load model

[0058] Natural gas load is essentially the energy load generated by burning natural gas to provide heat to energy-consuming devices, such as gas water heaters. Therefore, natural gas load is fundamentally a combustion energy load. In traditional natural gas systems, natural gas load is usually described by the flow rate under standard conditions. This description is simple and effective when the natural gas composition is uniformly distributed throughout the system. However, in natural gas systems considering hydrogen injection, due to distributed hydrogen injection, the natural gas composition is inconsistent at different locations within the system. That is, burning the same volume, mass, or molar amount of natural gas may not provide the same amount of heat. Therefore, the natural gas load originally described by flow rate needs to be transformed as follows:

[0059]

[0060] in, Let represent the natural gas load at natural gas node i, described by energy. This represents the natural gas load at natural gas node i, originally described by flow rate. GCV gas This represents the total calorific value of natural gas.

[0061] (1.2) Establishing a natural gas source model

[0062] Natural gas sources, including natural gas wells and storage facilities, are typically described by flow rates in conventional natural gas systems. Similar to natural gas load, this is converted into energy forms:

[0063]

[0064] in, The natural gas supply described by energy at natural gas node i. This refers to the natural gas supply at node i in the original natural gas system, described by flow rate. GCV i s The total calorific value of the natural gas supplied to the natural gas source of node i.

[0065] (1.3) Establish a steady-state power flow model within the natural gas pipeline

[0066] In high-pressure natural gas transmission systems, we use the Weymouth equation to describe the steady-state power flow model within the pipeline:

[0067]

[0068] Where, q i,j R represents the standard natural gas flow rate of the natural gas pipeline between natural gas nodes i and j. air T is the gas constant for air. STP and p STP Standard temperature and air pressure. i Let D be the gas pressure at natural gas node i. i,j F i,j L i,j These represent the pipe's diameter, Fanning coefficient, and length, respectively. S i,j Z represents the relative density of the gas inside the pipeline. T represents the temperature of the natural gas. i,j This is the compressibility coefficient of natural gas.

[0069] (1.4) Establishing a natural gas node energy conservation and natural gas mixing model

[0070] Unlike traditional natural gas systems that rely on flow rate-based node conservation, in the case of hydrogen injection, node conservation is modeled in terms of energy, meaning the energy flowing into a natural gas node equals the energy flowing out of it.

[0071]

[0072] in, This is the set of power nodes that link natural gas node i. For power node j e The energy corresponding to the natural gas consumed per unit time by the power-to-gas conversion facility. For power node j e A collection of gas turbine units. For power node j e The jth gfu The energy corresponding to the natural gas consumed per unit time by a gas turbine unit. The natural gas flow direction is the direction of natural gas flow into natural gas node i and natural gas node j. in A set of. The natural gas flow direction is the direction of natural gas outflow from natural gas node i at natural gas node j. out A set of. and From natural gas node j in Flow to i and flow from i to j out The energy of the natural gas flow. and From natural gas node j in Flow to i and flow from i to j out The flow rate of the natural gas current. GCV i Let be the total calorific value of natural gas node i.

[0073] It is worth noting that the natural gas composition from upstream pipelines may differ. Therefore, different pipelines mix at their junction, such as natural gas node i, and the mixed gas is then transported downstream again through the pipeline. Therefore, the flow direction of the pipelines needs to be assumed before performing optimized flow calculations. Assuming the natural gas flow direction is from natural gas node i to j, the relative density and total calorific value of the mixed gas can be calculated as follows:

[0074]

[0075] Among them, M gas M hy and M air These are the relative molecular masses of natural gas, hydrogen, and air, respectively. and Let represent the proportions of hydrogen and natural gas at natural gas node i, respectively, measured by the amount of substance, and calculated using the following formula:

[0076]

[0077] in, For power node je The output of the power-to-gas conversion facility is measured by the flow rate under standard conditions.

[0078] (2) Establishing a coupling element model (2.1) Establishing an electric-to-gas conversion facility model

[0079] The power-to-gas conversion facility consumes electricity to produce hydrogen. The conversion relationship is as follows:

[0080]

[0081] in, and These represent the power consumption and energy conversion efficiency of the electro-gas conversion facility at node i, respectively.

[0082] (2.2) Establishing a gas turbine unit model

[0083] Gas turbine units consume natural gas to generate electricity. The conversion relationship is as follows:

[0084]

[0085] in, and These represent the power generation, natural gas consumption rate, and energy conversion efficiency of gas turbine unit j at node i, respectively.

[0086] (3) Establishing a power system model

[0087] The power system model is established based on the DC model:

[0088]

[0089] g i,j =(θ i -θ j ) / X i,j (15)

[0090] in, Let i be the set of non-gas turbine units at node i. Let be the power generation capacity of the non-gas turbine unit j at node i. Let g be the electrical load of node i. i,j Let θ represent the power flow from node i to node j. i Let X be the phase angle of node i. i,j Let be the reactance of power lines i and j.

[0091] (4) Establish a steady-state power and natural gas joint optimization power flow model considering hydrogen injection.

[0092] The objective of the steady-state power and natural gas joint optimization power flow model considering hydrogen injection is to minimize the operating cost C. TThe optimization variables include: (a) the gas production rate of the natural gas source. (b) Nodal pressure p i (c) Power generation of non-gas turbine units (d) Voltage phase angle θ i (e) Power generation of the gas turbine unit (f) Hydrogen production rate of the power-to-gas facility (g) The ratio of hydrogen to natural gas and The mathematical model is as follows:

[0093]

[0094] Here, EB and GB represent the sets of power nodes and natural gas nodes, respectively. i,j (·) represents the cost function of non-gas turbine unit j at node i. ρ i denoted as , where is the natural gas supply price for the natural gas source at natural gas node i. μ represents the subsidy value for producing green hydrogen.

[0095] It conforms to constraints (1)-(15) and the following constraints:

[0096] 4.1) Wobbe Index. The composition of the gas mixture in a natural gas system affects its combustion characteristics, thereby impacting the performance and lifespan of energy-consuming equipment, and even operational safety. The Wobbe index is commonly used to measure the substitutability between different gases. Therefore, this index needs to be constrained within a certain range at each natural gas node:

[0097]

[0098] Where, ξ i This range is typically limited to 5%-10%.

[0099] 4.2) Constraints on natural gas composition and total calorific value:

[0100]

[0101] β min ≤GCV i ≤β max (20)

[0102] Where, α i This represents the upper limit of the hydrogen content. β max and β min This serves as the upper and lower limit constraint for the total calorific value.

[0103] 4.3) Upper and lower bound constraints for other optimization variables:

[0104]

[0105] in, and These are the upper and lower limits of the natural gas production rate of the natural gas source. This is the upper limit for the natural gas consumption rate of the power-to-gas conversion facility. Let be the transmission capacity of natural gas pipelines i and j. Let be the transmission capacity of power lines i and j. and These are the upper and lower limits of power generation for gas turbine units and non-gas turbine units, respectively.

[0106] The above model is a nonlinear programming problem, which can be solved by the IPOPT solver.

[0107] The technical solution of the present invention will be further described and explained below with reference to specific embodiments.

[0108] The reliability of a combined power-gas system consisting of the IEEE Power System Reliability Test System and the Belgian 20-node natural gas transmission system is obtained in a test case.

[0109] First, the parameters of the combined power and natural gas system are initialized. A schematic diagram of the combined power and natural gas system is shown below. Figure 1 As shown, the raw data for the power system and natural gas transmission system included in it comes from the publicly available literature "Grigg C, Wong P, Albrecht P, et al. The IEEE reliability test system-1996. A report prepared by the reliability test system task force of the application of probability methods subcommittee[J]. IEEE Transactions on power systems, 1999, 14(3): 1010-1020." Figure 1 The information can be found in Tables 1, 5, 6, 7, and 12, and in Appendix A of "De Wolf D, Smeers Y. The gas transmission problem solved by an extension of the simplex algorithm[J]. Management Science, 2000, 46(11):1454-1465." Based on this, the present invention makes the following modifications:

[0110] In such Figure 1At the locations shown, gas turbine units and electric-to-gas (EPG) converters were added. Three EPG converters with a gas production capacity of 0.5 MW under normal operating conditions were installed at natural gas nodes 7, 10, and 16. The non-gas turbine units of 12, 20, and 100 MW at power nodes (EB) 15, 13, 14, and 2 in the original power system were replaced with gas turbine units of the same capacity. Their thermal efficiency coefficients were set according to Table 1 of the published document "Unsihuay C, Lima JWM, De Souza AC Z. Modeling the integrated natural gas and electricity optimal power flow [C] / / PowerEngineering Society General Meeting, 2007. IEEE. IEEE, 2007: 1-7." The unit value of natural gas from each gas source in the natural gas system is set according to Table 2 of the publicly available literature "Unsihuay C, Lima JWM, DeSouza AC Z. Modeling the integrated natural gas and electricity optimal powerflow[C] / / Power Engineering Society General Meeting, 2007.IEEE.IEEE, 2007:1-7." The total power load of the power system is set to its peak value, i.e., a constant 2850MW.

[0111] Tables 1-4 present the calculation results of this joint optimization power flow. The total operating cost is 1.80 × 10⁻⁶. 5 $, including the cost of electricity generation 2.84 × 10 4 The cost of natural gas production is $1.69 × 10. 5 $, hydrogen production subsidy 1.70 × 10 4 $.

[0112] Table 1 Natural Gas Production Rate of Natural Gas Source

[0113]

[0114] Table 2 Hydrogen production rate of the power-to-gas conversion facility

[0115]

[0116] Table 3. Gas pressure, hydrogen and natural gas ratios, relative density, total calorific value, and Wobbe index at natural gas nodes.

[0117]

[0118]

[0119] Table 4 Natural Gas Flow in Natural Gas Pipelines

[0120]

[0121]

[0122] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0123] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0124] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0125] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0126] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for combined optimization power flow calculation of power-to-natural gas system considering hydrogen energy injection, characterized in that, The method comprises the following steps: a natural gas system model considering hydrogen energy injection is constructed, the system model comprising a natural gas load model, a natural gas source model, a steady-state flow model in a natural gas pipeline, a natural gas node energy conservation model and a natural gas mixing model; a coupling element model is established, the coupling element model comprising an electric-gas conversion facility model and a gas turbine model; a power system model is established; a steady-state power and natural gas joint optimization model considering hydrogen energy injection is constructed based on the natural gas system model, the coupling element model and the power system model; the steady-state power and natural gas joint optimization model considering hydrogen energy injection is solved to obtain an optimized control strategy and an operating state of the power and natural gas system; The objective of the steady-state power and natural gas joint optimization model considering hydrogen energy injection is to minimize the operation cost C T The optimization variables include: gas production rate of the natural gas source Node gas pressure p i Power generation of non-gas turbine units Voltage phase angle θ i Power generation of gas turbine units Hydrogen production rate of the electric-gas conversion facility And the proportion of hydrogen and natural gas And the mathematical model is as follows: where EB and GB are the sets of electricity and natural gas nodes, respectively, is the set of non-gas units on node i, is the power generation of non-gas unit j on node i, cst i,j (·) is the cost function of non-gas unit j on node i, ρ i is the natural gas supply price of natural gas source on natural gas node i, μ is the subsidy value of producing green hydrogen; the steady-state power and natural gas joint optimization model considering hydrogen energy injection satisfies constraint conditions, the constraint conditions comprising: Wobbe index wherein GCV i is the total heating value of natural gas node i; GCV gas is the total heating value of natural gas; S i,j is the relative density of the gas in the pipe; M gas , M air are the relative molecular mass of natural gas, air, respectively; ξ i ranges between 5% - 10%; a natural gas composition and total heat value constraint: β min ≤GCV i ≤β max , wherein a i is an upper limit for the hydrogen fraction, β max and β min are upper and lower limits for the total heating value; wherein, and are upper and lower bounds on the natural gas production rate from the natural gas source, is an upper bound on the natural gas consumption rate of the electric-to-gas facility, is the transmission capacity of the natural gas pipeline i,j, is the transmission capacity of the electric power line i,j, and are upper and lower bounds on the power generation of the gas and non-gas units, respectively; q i,j is the natural gas flow rate at standard conditions of the natural gas pipeline between nodes i and j; is the power generation of the gas unit j at node i; g i,j is the power flow from node i to j.

2. The method according to claim 1, wherein the steady-state power and natural gas joint optimization model considering hydrogen energy injection satisfies constraint conditions, the constraint conditions comprising: The natural gas load model is: wherein, GCV is the natural gas load at node i described by energy, GCV is the natural gas load at node i originally described by flow rate, gas GCV is the gross calorific value of the natural gas.

3. The method according to claim 2, wherein the steady-state power and natural gas joint optimization model considering hydrogen energy injection satisfies constraint conditions, the constraint conditions comprising: The natural gas source model is: wherein, GCV is the natural gas supply at node i described by energy, GCV is the natural gas supply at node i described by flow rate in the original natural gas system, GCV i s GCV is the total heat value of the natural gas supply of the node i.

4. The method according to claim 3, wherein the steady-state power and natural gas joint optimization model considering hydrogen energy injection satisfies constraint conditions, the constraint conditions comprising: The steady-state flow model in the natural gas pipeline is where q i,j is the natural gas flow rate at standard conditions of the natural gas pipeline between natural gas nodes i and j, R air is the gas constant for air, T STP and p STP are the temperature and pressure at standard conditions, p i , p j are the pressures at natural gas nodes i, j, respectively, D i,j , F i,j , L i,j are the diameter, Fanning coefficient and length of the pipeline, respectively, S i,j is the relative density of the gas in the pipeline, T is the temperature of the natural gas, and Z i,j is the compressibility factor of the natural gas.

5. The method of claim 4, wherein the method is characterized by, the natural gas node energy conservation model and the natural gas mixing model are as follows: wherein, is a set of power nodes linked to natural gas node i, is a set of power nodes linked to natural gas node i, e is the energy corresponding to the natural gas consumed by the electric-to-gas facility at power node j is a set of gas units at power node j e , is the energy corresponding to the natural gas consumed by the j e th gas unit at power node j gfu , is a set of natural gas nodes j in from which natural gas flows into natural gas node i, is a set of natural gas nodes j out from which natural gas flows out of natural gas node i, and are the energy of the natural gas flow from natural gas node j in to i and from i to j out , respectively, and are the flow rate of the natural gas flow from natural gas node j in to i and from i to j out , respectively, GCV i is the gross calorific value of natural gas node i; let the natural gas flow direction be from a natural gas node i to j, then the mixed gas relative density and total heat value are as follows: wherein M gas , M hy and M air are the relative molecular mass of natural gas, hydrogen and air, respectively; and Xi and X2 are the share of hydrogen and natural gas at the natural gas node i, respectively: wherein, is the production of the electricity-to-gas facility of the power node j e .

6. The method according to claim 5, wherein the steady-state power and natural gas joint optimization model considering hydrogen energy injection satisfies constraint conditions, the constraint conditions comprising: The electricity-to-gas facility model comprises: the electricity-to-gas facility consumes electricity to generate hydrogen gas, and the conversion relationship of electricity-to-gas is wherein, and Pi and ηi are the power consumption and energy conversion efficiency of the electric-to-gas facility at node i, respectively. The gas turbine unit model comprises: where, and Pi,j, Gj, and ηi,j are the power output, natural gas consumption rate, and energy conversion efficiency of the gas turbine unit j at node i, respectively.

7. The method according to claim 6, wherein the steady-state power and natural gas joint optimization model considering hydrogen energy injection satisfies constraint conditions, the constraint conditions comprising: the power system model is established according to a direct current model: where, is the set of non-gas units on node i, is the power generation of non-gas unit j on node i, is the power load on node i, g i,j is the power flow from node i to j, θ i is the phase angle of node i, θ j is the phase angle of node j, X i,j is the reactance of power line i,j.

8. The method of claim 1, wherein, the solving of the steady-state power and natural gas joint optimization model considering hydrogen energy injection comprises solving the steady-state power and natural gas joint optimization model by an IPOPT solver.

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