Optimal dispatch method for integrated power-gas energy system considering n-1 security criterion

Abstract

The application relates to an electric-gas integrated energy power system optimization scheduling method considering N-1 safety criteria, which comprises the following steps: step S1: a group of partial differential equations are introduced to describe the change of gas temperature in a natural gas system, and full-implicit finite difference method is adopted to discretize the group of partial differential equations; step S2: a large M method is adopted to respectively establish a natural gas system model and a power system model considering N-1 safety criteria; and step S3: the natural gas system model and the power system model obtained in step S2 are coupled to obtain an electric-gas integrated energy power system optimization scheduling model considering N-1 safety criteria and gas thermodynamics. The application effectively improves the reliability of the electric-gas integrated energy power system.

Description

Technical Field

[0001] This invention relates to an optimal scheduling method for an integrated electric-gas energy power system that considers the N-1 safety criterion. Background Technology

[0002] The rapid development of natural gas power generation technology has led to increasingly close coupling between power and natural gas systems. However, the higher the degree of system coupling, the greater the probability of cascading failures. In power systems, transmission lines and other equipment are prone to failure due to environmental factors; similarly, underground gas pipelines are also susceptible to accidents caused by earthquakes, extreme frost, or improper human operation. Therefore, considering the N-1 safety criterion is crucial in integrated power-gas energy systems. On the other hand, gas thermodynamics also significantly affects the assessment of the operating status of natural gas systems. How to balance the N-1 safety criterion with gas thermodynamics is a problem that urgently needs to be solved. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide an optimized scheduling method for an integrated electric-gas energy power system that considers the N-1 safety criterion. This method not only improves system reliability and enables the system to cope with N-1 safety risks, but also avoids errors caused by the isothermal assumption, thus greatly improving accuracy.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] An optimal scheduling method for an integrated electric-gas energy power system considering the N-1 safety criterion includes the following steps:

[0006] Step S1: Introduce a set of partial differential equations to describe the temperature change of the gas in the natural gas system, and discretize them using the fully implicit finite difference method;

[0007] Step S2: Use the Big M method to establish natural gas system models and power system models that consider the N-1 safety criterion respectively;

[0008] Step S3: Couple the natural gas system model and the power system model obtained in step S2 to obtain an optimal scheduling model for the integrated electric-gas energy power system that considers the N-1 safety criterion and gas thermodynamics.

[0009] Furthermore, step S1 specifically includes:

[0010] The temperature changes of gas in a natural gas system are described by a set of partial differential equations, expressed as:

[0011]

[0012] In the formula, k c It is the heat transfer coefficient; cp T represents the specific heat under constant pressure; a T represents ambient temperature; T represents gas temperature. It is the mass flow rate of the gas;

[0013] The above partial differential equation is discretized using the fully implicit finite difference method, and the space-dependent partial differential terms are approximated as follows:

[0014]

[0015] In the formula, H is a state variable that includes gas temperature, pressure, mass flow rate, etc.

[0016] A single state variable H is approximated by the following formula:

[0017]

[0018] Substituting into the difference scheme, the partial differential equation is discretized as

[0019]

[0020] In the formula, T represents the length of the pipe. i and T j Indicates the gas temperature at nodes i and j; Let be the mass flow rate of pipe ij.

[0021] The compressor model is represented as:

[0022]

[0023] For the compressor's horsepower; π i and π i These represent the pressures at nodes i and j, respectively; HV refers to the total calorific value of the natural gas. Indicates the compressor's gas consumption; γ p The energy conversion coefficient of the compressor; and These represent the minimum and maximum compression ratios of the compressor, respectively. and Indicates the minimum and maximum mass flow rates of the compressor;

[0024] The compressor model is simplified to

[0025]

[0026] T j =(1+λ) ij )T i

[0027] In the formula, κ pand λ ij All are constants.

[0028] The momentum equation for a natural gas system is:

[0029]

[0030] In the formula, A represents the cross-sectional area of ​​the pipe; d is the diameter of the pipe; It is the gas constant; It is the compressibility factor of the gas.

[0031] Furthermore, step S2 specifically includes:

[0032] Using the Big M method, the momentum equation in the natural gas system is equivalently replaced by two inequality constraints, expressed as:

[0033]

[0034] In the formula, U ij U is a binary variable representing the operating status of a natural gas pipeline. ij =1 indicates that the pipeline is in normal operating condition; U ij =0 indicates that the pipeline is in a fault state; M G It is a parameter with a preset value;

[0035] Similarly, the pipe thermal model is transformed into inequality constraints using the Big M method, as follows:

[0036]

[0037] When the pipeline is in normal operation, the above two inequality constraints are equivalent to equality constraints; when the pipeline is in a fault state, the above inequality constraints always hold and have no constraint effect.

[0038] Furthermore, step S3 specifically includes:

[0039] The operating constraints of the natural gas system are as follows:

[0040]

[0041] In the formula, and These represent the minimum and maximum mass flow rates of the pipeline, respectively. and These represent the minimum and maximum pressures at the node, respectively.

[0042] The total operating cost of the optimized scheduling model consists of the costs of the coal-fired power generating units and the gas supplier, expressed as:

[0043]

[0044] In the formula, The cost coefficient of a coal-fired power generator; ψ i This represents the cost coefficient of the gas source node; This indicates the power output of a coal-fired generator; This is the output of the gas source node;

[0045] Based on the Big M method, the optimal scheduling model for the electric-gas integrated energy power system, considering the N-1 safety criterion and gas thermodynamics, is expressed as follows:

[0046]

[0047] In the formula, P k,t B is the active power flowing through the transmission line; k The susceptance of the transmission line; N is the phase angle of node i; k N is a binary variable representing the operating status of a transmission line. k =1 indicates that the line is in normal operating condition, N k =0 indicates that the line is in a fault state; M P It is a parameter with a preset value; and These are the minimum and maximum active power that can flow through the line;

[0048] The phase angle constraint is:

[0049]

[0050] In the formula, and Represents the minimum and maximum phase angles of a node.

[0051] An optimized scheduling system for an integrated electric and gas energy power system considering the N-1 safety criterion includes a processor, a memory, and a computer program stored in the memory. When the processor executes the computer program, it specifically performs the steps in the optimized scheduling method for an integrated electric and gas energy power system considering the N-1 safety criterion as described above.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] This invention not only improves the reliability of the integrated electric-gas energy power system, enabling the system to cope with N-1 security risks, but also avoids errors caused by the isothermal assumption, greatly improving the accuracy of dispatching. Attached Figure Description

[0054] Figure 1 This refers to the nodal pressure under isothermal and non-isothermal conditions in one embodiment of the present invention;

[0055] Figure 2 This is the power flow distribution of the power system after an N-1 fault in one embodiment of the present invention. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0057] This invention provides an optimized scheduling method for an integrated electric-gas energy power system considering the N-1 safety criterion, comprising the following steps:

[0058] Step S1: Introduce a set of partial differential equations to describe the temperature change of the gas in the natural gas system, and discretize them using the fully implicit finite difference method;

[0059] In this embodiment, the gas temperature change in the natural gas system is described by a set of partial differential equations, expressed as:

[0060]

[0061] In the formula, k c It is the heat transfer coefficient; c p T represents the specific heat under constant pressure; a T represents ambient temperature; T represents gas temperature. It is the mass flow rate of the gas;

[0062] The above partial differential equation is discretized using the fully implicit finite difference method, and the space-dependent partial differential terms are approximated as follows:

[0063]

[0064] In the formula, H is a state variable that includes gas temperature, pressure, mass flow rate, etc.

[0065] A single state variable H is approximated by the following formula:

[0066]

[0067] Substituting into the difference scheme, the partial differential equation is discretized as

[0068]

[0069] In the formula, T represents the length of the pipe. i and T j Indicates the gas temperature at nodes i and j; Let be the mass flow rate of pipe ij.

[0070] The compressor model is represented as:

[0071]

[0072] For the compressor's horsepower; π i and π i These represent the pressures at nodes i and j, respectively; HV refers to the total calorific value of the natural gas. Indicates the compressor's gas consumption; γ p The energy conversion coefficient of the compressor; and These represent the minimum and maximum compression ratios of the compressor, respectively. and Indicates the minimum and maximum mass flow rates of the compressor;

[0073] The compressor typically consumes 3-5% of the total gas passing through the pipeline, so the compressor model simplifies to...

[0074]

[0075] T j =(1+λ) ij )T i

[0076] In the formula, κ p and λ ij All are constants.

[0077] The momentum equation for a natural gas system is:

[0078]

[0079] In the formula, A represents the cross-sectional area of ​​the pipe; d is the diameter of the pipe; It is the gas constant; It is the compressibility factor of the gas.

[0080] Step S2: Use the Big M method to establish natural gas system models and power system models that consider the N-1 safety criterion respectively;

[0081] In this implementation, to consider the N-1 safety criterion, the Big M method is used to integrate the N-1 safety criterion into the natural gas network model, specifically as follows:

[0082] Using the Big M method, the momentum equation in the natural gas system is equivalently replaced by two inequality constraints, expressed as:

[0083]

[0084] In the formula, U ij U is a binary variable representing the operating status of a natural gas pipeline. ij =1 indicates that the pipeline is in normal operating condition; U ij =0 indicates that the pipeline is in a fault state; M G It is a parameter with a preset value;

[0085] Similarly, the pipe thermal model is transformed into inequality constraints using the Big M method, as follows:

[0086]

[0087] When the pipeline is in normal operation, the above two inequality constraints are equivalent to equality constraints; when the pipeline is in a fault state, the above inequality constraints always hold and have no constraint effect.

[0088] Step S3: Couple the natural gas system model and the power system model obtained in step S2 to obtain an optimal scheduling model for the integrated electric-gas energy power system that considers the N-1 safety criterion and gas thermodynamics.

[0089] In this embodiment, the operating constraints of the natural gas system are as follows:

[0090]

[0091] In the formula, and These represent the minimum and maximum mass flow rates of the pipeline, respectively. and These represent the minimum and maximum pressures at the node, respectively.

[0092] The total operating cost of the optimized scheduling model consists of the costs of the coal-fired power generating units and the gas supplier, expressed as:

[0093]

[0094] In the formula, The cost coefficient of a coal-fired power generator; ψ i This represents the cost coefficient of the gas source node; This indicates the power output of a coal-fired generator; This is the output of the gas source node;

[0095] Based on the Big M method, the optimal scheduling model for the electric-gas integrated energy power system, considering the N-1 safety criterion and gas thermodynamics, is expressed as follows:

[0096]

[0097] In the formula, P k,t B is the active power flowing through the transmission line; k The susceptance of the transmission line; N is the phase angle of node i; k N is a binary variable representing the operating status of a transmission line. k =1 indicates that the line is in normal operating condition, N k =0 indicates that the line is in a fault state; M PIt is a parameter with a preset value; and These are the minimum and maximum active power that can flow through the line;

[0098] The phase angle constraint is:

[0099]

[0100] In the formula, and Represents the minimum and maximum phase angles of a node.

[0101] Example 1:

[0102] In this embodiment, the modified integrated electrical energy test system consists of a 24-node power network and a 25-node natural gas network. The test system includes 7 coal-fired generators and 3 gas turbines. All simulations were performed on the OPTI-MATLAB solver.

[0103] Figure 1 The nodal pressures under isothermal and non-isothermal conditions are presented. It can be seen that the nodal pressures under isothermal and non-isothermal conditions differ significantly, demonstrating the importance of gas thermodynamics in assessing the state of natural gas systems. Therefore, the proposed electric-gas integrated energy power system optimal scheduling model considering the N-1 safety criterion and gas thermodynamics can more accurately assess the operating state of natural gas systems.

[0104] Figure 2 The power flow distribution of the power system after an N-1 fault is presented. It can be seen that after a fault in line 24, the active power of line 29 reaches its upper limit, but does not exceed it. Similarly, after a fault in line 29, the active power of line 24 also reaches its upper limit. This proves the effectiveness of the obtained optimal operating strategy in mitigating N-1 transmission line faults.

[0105] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for optimal scheduling of an integrated electric-gas energy power system considering the N-1 safety criterion, characterized in that, Includes the following steps: Step S1: Introduce a set of partial differential equations to describe the temperature change of the gas in the natural gas system, and discretize them using the fully implicit finite difference method; Step S2: Use the Big M method to establish natural gas system models and power system models that consider the N-1 safety criterion respectively; Step S3: Couple the natural gas system model and the power system model obtained in step S2 to obtain an optimal scheduling model for the integrated electric-gas energy power system that considers the N-1 safety criterion and gas thermodynamics; Step S1 specifically involves: The temperature changes of gas in a natural gas system are described by a set of partial differential equations, expressed as: In the formula, k c It is the heat transfer coefficient; c p T represents the specific heat under constant pressure; a T represents ambient temperature; T represents gas temperature. It is the mass flow rate of the gas; The above partial differential equation is discretized using the fully implicit finite difference method, and the space-dependent partial differential terms are approximated as follows: In the formula, H represents the gas temperature T, pressure π, and mass flow rate. State variables included; A single state variable H is approximated by the following formula: Substituting into the difference scheme, the partial differential equation is discretized as In the formula, T represents the length of the pipe. i and T j Indicates the gas temperature at nodes i and j; Let be the mass flow velocity of pipe ij; The compressor model is represented as: For the compressor's horsepower; π i and π j These represent the pressures at nodes i and j, respectively; HV refers to the total calorific value of the natural gas. Indicates the compressor's gas consumption; γ p The energy conversion coefficient of the compressor; and These represent the minimum and maximum compression ratios of the compressor, respectively. and Indicates the minimum and maximum mass flow rates of the compressor; The compressor model is simplified to T j =(1+λ ij )T i In the formula, κ p and λ ij All are constants; The momentum equation for a natural gas system is: In the formula, A represents the cross-sectional area of ​​the pipe; d is the diameter of the pipe; It is the gas constant; It is the compressibility factor of the gas.

2. The method for optimal scheduling of an integrated electric-gas energy power system considering the N-1 safety criterion according to claim 1, characterized in that, Step S2 specifically includes: Using the Big M method, the momentum equation in the natural gas system is equivalently replaced by two inequality constraints, expressed as: In the formula, U ij U is a binary variable representing the operating status of a natural gas pipeline. ij =1 indicates that the pipeline is in normal operating condition; U ij =0 indicates that the pipeline is in a fault state; M G It is a parameter with a preset value; Similarly, the pipe thermal model is transformed into inequality constraints using the Big M method, as follows: When the pipeline is in normal operation, the above two inequality constraints are equivalent to equality constraints; when the pipeline is in a fault state, the above inequality constraints always hold and have no constraint effect.

3. The method for optimal scheduling of an integrated electric-gas energy power system considering the N-1 safety criterion according to claim 1, characterized in that, Step S3 specifically includes: The operating constraints of the natural gas system are as follows: In the formula, and These represent the minimum and maximum mass flow rates of the pipeline, respectively. and U represents the minimum and maximum pressure at the node, respectively; ij A binary variable representing the operating status of a natural gas pipeline; The total operating cost of the optimized scheduling model consists of the costs of the coal-fired power generating units and the gas supplier, expressed as: In the formula, The cost coefficient of a coal-fired generator; ψ i This represents the cost coefficient of the gas source node; This indicates the power output of a coal-fired generator; This is the output of the gas source node; Based on the Big M method, the optimal scheduling model for the electric-gas integrated energy power system, considering the N-1 safety criterion and gas thermodynamics, is expressed as follows: In the formula, P k,t B is the active power flowing through the transmission line; k The susceptance of the transmission line; N is the phase angle of node i; k N is a binary variable representing the operating status of a transmission line. k =1 indicates that the line is in normal operating condition, N k =0 indicates that the line is in a fault state; M P It is a parameter with a preset value; and These are the minimum and maximum active power that can flow through the line; The phase angle constraint is: In the formula, and Represents the minimum and maximum phase angles of a node.

4. An optimized dispatching system for an integrated electric-gas energy power system considering the N-1 safety criterion, characterized in that, It includes a processor, a memory, and a computer program stored in the memory. When the processor executes the computer program, it specifically performs the steps in the method for optimal scheduling of an integrated electric-gas energy power system considering the N-1 safety criterion as described in any one of claims 1-3.

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