System minimum load shedding method considering electrical coupling sensitivity

Abstract

The present invention discloses a system minimum load shedding method that takes into account electrical coupling sensitivity, including: constructing a comprehensive sensitivity index based on the IEGS air pressure instability scenario, quantifying the impact of increased electricity and gas loads on the IEGS air pressure, and using the air pressure of the node with the maximum comprehensive sensitivity index as the air pressure weak link; constructing a load shedding sensitivity index for the air pressure weak link, and evaluating the effect of removing the load of each node on the air pressure recovery of the node with the maximum comprehensive sensitivity index when the air pressure is about to become unstable; sorting each load node from large to small according to the load shedding sensitivity index, and removing the electricity / gas load in sequence when the air pressure is about to become unstable, ultimately achieving the minimum load shedding of the IEGS. The present invention analyzes the relationship between the air pressure of each IEGS node and each electricity and gas load, identifies the weak link that affects the stability of the IEGS air pressure, and comprehensively considers the impact of the load changes of each node on the air pressure of the weak link, formulates the minimum load shedding sequence of the IEGS, and ultimately achieves the minimum load shedding across the electricity and gas energy systems.

Description

Technical Field

[0001] The present invention relates to the field of engineering integrated energy systems, and in particular to a system minimum load shedding method considering electrical coupling sensitivity. Background Art

[0002] Natural gas-fired generating units (NGUs) are widely used due to their high controllability, low carbon footprint, and environmental friendliness. Through NGU coupling, power and natural gas systems gradually form an integrated electricity-gas system (IEGS). [1] . In recent years, both electricity and gas loads in IEGS have shown a rapid growth trend. The national "14th Five-Year Plan" electricity demand forecast shows that by 2025, my country's average annual electricity consumption growth rate will remain at 4%-6%; at the same time, with the large-scale utilization of NGU and the promotion of low-carbon policies such as "coal to gas", the proportion of gas-fired power generation in IEGS has increased significantly, and some areas have even experienced insufficient gas supply. The simultaneous rapid growth of both electricity and gas loads poses a huge threat to the safe and stable operation of IEGS. For example: in 2017, Nigeria suffered a nationwide blackout due to insufficient gas supply; in August 2020, Southern California, the United States, suffered a large-scale power outage due to insufficient NGU gas supply due to the rapid growth of electricity load. Load shedding is the last barrier to prevent large-scale power outages in the system. [2] However, compared with the power system, the scenarios and load types faced by IEGS load shedding will change significantly.

[0003] First, IEGS load shedding will face a new scenario where gas pressure destabilizes before voltage. The increase in electricity load will be transmitted to the natural gas system through the NGU, causing the gas load to increase further. Therefore, the gas pressure in the IEGS will decrease as the electricity and gas loads increase. In certain scenarios, it may collapse before the voltage destabilizes. [3] At the same time, there are two load shedding types to choose from: electricity and gas. To minimize the overall losses of IEGS load shedding, it is urgent to consider the minimum load shedding requirements across both electricity and gas energy systems.

[0004] In view of the above characteristics, the original power load shedding strategy is difficult to be directly applied to IEGS. Some scholars have studied the load shedding strategy of IEGS. Reference [4] proposed an optimal load reduction algorithm based on a hierarchical decoupling optimization model, which solves the optimization models of the energy hub, power system and natural gas system respectively to obtain the minimum load shedding amount, thereby improving the accuracy and efficiency of the calculation. Reference [5] proposed an IEGS minimum load reduction algorithm based on a two-stage gas network optimization flow model, which achieves the minimum load shedding of IEGS by alternately optimizing and solving the power system and natural gas system, thereby improving the convergence of the calculation to a certain extent. The above studies all use optimal flow to achieve the minimum load shedding of IEGS. The advantage is that the minimum load shedding amount of IEGS can be calculated, but multiple electricity and gas flow calculations are required. When the system scale is large, the calculation is more complicated and the convergence is difficult to guarantee. [6] Compared with the optimal power flow method, the advantage of the sensitivity method is that it only needs to use some elements of the Jacobian matrix to construct the sensitivity index, thereby analyzing the differential relationship between different variables in the system, and then realizing the identification of weak links and the minimum load shedding of the system. There is no need to perform too much power flow calculation. The physical meaning is clear, the calculation is simple and the speed is fast. However, the disadvantage is that it can only give the load shedding order and cannot directly calculate the minimum load shedding amount quantitatively. [7] In power systems, the sensitivity method is often used to formulate load shedding strategies for large-scale power grids. For example, references [8-9] proposed an emergency load shedding strategy when the system is overloaded, calculating the sensitivity index of the reactive load and active load of each node to the total reactive power. Based on this index, the weak voltage nodes of the system are identified, and a strategy is formulated to prioritize the removal of electrical loads at highly sensitive nodes. However, the above power system sensitivity index can only reflect the differential relationship between voltage and power, and is difficult to apply to IEGS. How to construct the IEGS sensitivity index and formulate the minimum load shedding strategy based on it is an urgent problem to be solved.

[0005] As the coupling between electricity and gas deepens, new scenarios are emerging in integrated electricity-gas systems (IEGS) where gas pressure destabilizes before voltage, and load shedding has expanded from electricity to both electricity and gas. To minimize overall load losses in IEGS, further consideration is needed for minimum load shedding requirements across both the electricity and gas energy systems.

[0006] References

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[0008] [2]WANG Mingshen,MU Yunfei,Jia Hongjie,et al.A preventive controlstrategy for static voltage stability based on an efficient power plant modelof electric vehicles[J].Journal of Modern Power Systems and Clean Energy,2015,3(1):103-113

[0009] [3]JIANG Tao,ZHANG Rufeng,LI Xue,et al.An optimal reactive powerplanning strategy against voltage collapse[J].Applied Energy,2021,283.

[0010] [4]LEI Yunkai,HOU Kai,WANG Yue,et al.I A new reliability as-sessmentapproach for integrated energy systems:using hierarchical decouplingoptimization framework and impactincrement based state enumeration method[J].Applied Energy,2018,210:1237-1250

[0011] [5] Wang Han, Hou Kai, Yu Xiaodan, Jia Hongjie. Resilience assessment and improvement method of electrical interconnection system considering earthquake disaster uncertainty[J]. Proceedings of the CSEE, 2022, 42(03): 853-864.

[0012] [6] ZHANG Zhe, YANG Hang, YIN Xianggen, et al. A Load-Shedding Model Basedon Sensitivity Analysis in on-Line Power System Operation Risk Assessment[J]. ENERGIES, 2018, 11(4).

[0013] [7] Zhao Hongshan, Zhao Yingying. Assessment of vulnerable areas of power grid based on sensitivity technology[J]. Power System Technology, 2008, 32(14): 54-58.

[0014] [8] MMBegovic, AGPhadke. Power system emergency control near voltageinstability[C] / / Proceedings of the 28th IEEE Conference on Decision and Control, Dec. 13-15, 1989, Tampa, FL, USA: 2179-2180.

[0015] [9] MMBegovic, AGPhadke. Control of voltage stability using sensitivity analysis [J]. IEEE Transactions on Power Systems, 1992, 7(1): 114-123. Summary of the Invention

[0016] The present invention provides a system minimum load shedding method that considers electrical coupling sensitivity. This method is used for the preventive control of air pressure instability. By constructing a comprehensive sensitivity index (CSI) and a load shedding sensitivity index (LSSI), the method analyzes the relationship between the air pressure at each IEGS node and the electrical and gas loads. This method identifies the weak links that affect the air pressure stability of the IEGS, comprehensively considers the impact of load changes at each node on the air pressure at the weak links, and formulates the minimum load shedding sequence for the IEGS. Ultimately, the method achieves minimum load shedding across both the electrical and gas energy systems. Details are described below:

[0017] A system minimum load shedding method considering electrical coupling sensitivity, the method comprising:

[0018] Based on the IEGS air pressure instability scenario, a comprehensive sensitivity index was constructed to quantify the impact of electricity and gas load growth on IEGS air pressure. The air pressure at the node with the maximum comprehensive sensitivity index was taken as the weak link of air pressure.

[0019] Aiming at the weak link of air pressure, a load shedding sensitivity index is constructed to evaluate the effect of shedding the load at each node on restoring the air pressure at the node with the largest comprehensive sensitivity index when the air pressure is close to instability.

[0020] The load nodes are sorted from large to small according to the load shedding sensitivity index. When the gas pressure is close to instability, the electric / gas loads are cut off in sequence, and the minimum load shedding of IEGS is finally achieved.

[0021] The method of taking the air pressure of the node with the maximum comprehensive sensitivity index as the weak link of air pressure is as follows:

[0022] The air pressure instability index and the average air pressure-load increment sensitivity are used to characterize the situation respectively, and a comprehensive sensitivity index is constructed by combining the two.

[0023] Furthermore, the air pressure instability index is:

[0024]

[0025] Where, is the air pressure of the current operating point node j; It is the maximum air pressure at the current IEGS operating point.

[0026] The average air pressure-load increment sensitivity is:

[0027]

[0028] Where n gIndicates the number of load nodes in the natural gas system; gas pressure-load increment sensitivity S p-△L Reflects the sensitivity of gas pressure at each node of the IEGS gas network to the growth of total electricity and gas load; The larger the value, the more sensitive the gas pressure at node j in the natural gas system is to the IEGS load growth, and the faster the pressure drops when the load increases;

[0029] Average air pressure-load increment sensitivity To express the decreasing speed of gas pressure at each node of IEGS gas network as the electricity and gas load increases:

[0030]

[0031] Where z is the state label, indicating the zth state of node j; n c Indicates the total number of states calculated from the current operating point to the critical operating point of air pressure stability.

[0032] Furthermore, the load nodes are sorted from large to small according to the load shedding sensitivity index, and the electric / gas loads are shelved in sequence when the gas pressure is about to become unstable. Specifically,

[0033] 1) Gas cut load sensitivity index

[0034]

[0035] Where, e w is a unit row vector whose wth element is 1, p w The air pressure of the weak link of IEGS, LSSI g Reflects the impact of load changes at each node in the gas network on the gas pressure of weak nodes; LSSI, the load shedding sensitivity index of gas network node j g,j The larger the value, the greater the effect of the gas load of the removed node j on the gas pressure of the weak node.

[0036] 2) Power-off load sensitivity index

[0037]

[0038] Where, Indicates the output ratio of the i-th NGU; LSSI g,NGUi Represents the LSSI of the node connected to the i-th NGU in the gas network g The order of cutting off power and gas loads is determined according to the size of the LSSI of the power and gas loads.

[0039] The beneficial effects of the technical solution provided by the present invention are:

[0040] 1. The minimum load shedding strategy obtained by the present invention through sensitivity analysis can minimize the load reduction while ensuring that the IEGS air pressure returns to the minimum level for normal system operation;

[0041] 2. In view of the new characteristics of IEGS load shedding, this invention proposes a system minimum load shedding method that takes into account electrical coupling sensitivity. This method is used to prevent and control air pressure instability. It can minimize the load reduction while ensuring that the IEGS air pressure returns to the minimum level for normal system operation.

[0042] 3. The growth ratio of electricity and gas loads has a significant impact on the identification of weak gas pressure nodes and the formulation of the minimum load shedding sequence. This method considers the different growth ratios of electricity and gas loads in the continuous multi-energy flow model, which can more accurately form the IEGS minimum load shedding strategy.

[0043] 4. The comprehensive sensitivity index defined in the present invention reflects the stability of the static air pressure at each node during the IEGS load growth process. The greater the comprehensive sensitivity index, the easier it is for the node air pressure to reach the static stability limit, and the weaker the node air pressure;

[0044] 5. The load shedding sensitivity index defined in the present invention reflects the impact of changes in electrical and gas loads on the gas pressure of weak links. When shedding loads, prioritizing the removal of loads at nodes with large load shedding sensitivity indexes can minimize the amount of load reduction.

[0045] 6. The present invention takes into account the need for cross-system load shedding in the IEGS load shedding strategy. Compared with shedding a single type of load, the present invention comprehensively evaluates the effects of shedding both electricity and gas loads on gas pressure recovery, which can greatly reduce the load reduction amount and achieve the minimum load shedding of IEGS. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a flow chart of the system minimum load shedding method considering electrical coupling sensitivity in the present invention;

[0047] Figure 2 It is a curve diagram of the change of node gas pressure with the increase of electricity and gas load;

[0048] Figure 3 Schematic diagram of the IEGS structure;

[0049] Figure 4 Identify chromatograms for IEGS air pressure weak links;

[0050] Figure 5 The graph of the air pressure at each node and the comprehensive sensitivity index (CSI) at the static air pressure stability limit state;

[0051] Figure 6 It is the load shedding sensitivity index (LSSI) diagram of electric and gas loads;

[0052] Figure 7 This is the minimum gas pressure recovery diagram after 10MW load is removed from each node;

[0053] Figure 8 The load shedding diagram for the two load shedding strategies when the air pressure recovers Δp;

[0054] Figure 9 Figure 2 is the voltage-reactive load sensitivity index diagram under two scenarios. DETAILED DESCRIPTION

[0055] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0056] A method for minimum load shedding of a system considering electrical coupling sensitivity, see Figure 1 The first step of this method is to solve the static stability limit operating point of the IEGS based on the IEGS steady-state multi-energy flow model and define the IEGS air pressure instability scenario. The second step is to construct a comprehensive sensitivity index (CSI) based on the obtained IEGS air pressure instability scenario to scientifically quantify the impact of the increase in electricity and gas loads on the IEGS air pressure. The air pressure at the node with the largest CSI is most likely to reach the stability limit, which is the weak link of the IEGS air pressure. The third step is to further construct a load shedding sensitivity index (LSSI) for the air pressure weak link identified by the CSI to evaluate the effect of removing the load of each node on the recovery of the air pressure at the CSI maximum node when the air pressure is about to become unstable. The load nodes are sorted from large to small according to the LSSI. When the air pressure is about to become unstable, the electricity / gas loads are removed in sequence to finally achieve the minimum load shedding of the IEGS. The specific steps are as follows:

[0057] Step 1: Construct the IEGS multi-stable energy flow model and pressure instability scenario

[0058] In this step, the static stability limit operating point of the IEGS is obtained based on the IEGS multi-energy flow model, and the IEGS air pressure instability scenario is defined.

[0059] 1-1) IEGS multi-energy flow model

[0060] First, the IEGS steady-state multi-energy flow model is constructed, and then the IEGS continuous multi-energy flow model is constructed.

[0061] 1-1-1) IEGS Steady-State Multi-Energy Flow Model

[0062] The IEGS steady-state multi-energy flow calculation is the core of the steady-state analysis of the electrically coupled integrated energy system and the basis for constructing sensitivity indicators. The IEGS steady-state multi-energy flow model is shown in Equation (1):

[0063]

[0064] Where x = [θ, V, p] is the state variable of IEGS, which are the voltage phase angle and voltage amplitude of the power system except the balance node and the gas pressure of the load node of the natural gas system; u = [P sp ,Q sp ,L sp ] are the control variables of IEGS, which are the active power and reactive power injected into the power system nodes and the gas load injected into the natural gas system nodes respectively; represents the node voltage phasor; Y represents the node admittance matrix; A1 is the node-branch reduced-order correlation matrix; f is the branch flow of the natural gas system; P NGU is the active power output by NGU; L NGU is the natural gas load consumed by the natural gas generator NGU; η ge is the electrical conversion coefficient of NGU, which can be calculated based on the calorific value of natural gas. * indicates the conjugate complex number.

[0065] The energy flow model can be calculated using a unified solution method, and the unified Jacobian matrix is ​​shown in Equation (2).

[0066]

[0067] Where, J ee and J gg Respectively represent the relationship between the power flow and state quantity of the individual electricity and gas systems; J eg and J ge Indicates the coupling relationship between electrical and gas systems.

[0068] 1-1-2) IEGS continuous multi-energy flow model

[0069] By adding the load growth factor to the IEGS steady-state multi-energy flow model, the IEGS continuous multi-energy flow model can be further constructed:

[0070] When the NGU dispatch direction and load growth direction are known, the Continuation Multi-Energy Flow (CMEF) model can be used to solve the static stability limit operating point of the IEGS. To represent the different growth ratios of electricity and gas loads, the electricity and gas load growth coefficients k are introduced into the CMEF. e and k g , as shown in formulas (3)-(6).

[0071]

[0072]

[0073]

[0074]

[0075] Where, the electric load growth factor λ is the total growth of the system electric load; the gas load growth factor λ of the gas grid itself is g is the electrical load growth factor λ multiplied by the electrical conversion coefficient η ge The electricity and gas load growth can be converted to the same dimension (MW); P g,i0 、P l,i0 , Q l,i0 are the initial active power, initial active load and initial reactive load of the generator at power system node i respectively; and are the proportions of generator output growth, active load growth and reactive load growth at power system node i to the total generator output growth, total active load growth and total reactive load growth; L l,m0 is the initial gas demand at node m in the natural gas system; is the proportion of gas load growth at node m in the natural gas system to the total gas load growth.

[0076] 1-2) Construction of IEGS pressure instability scenario

[0077] The IEGS static stability must meet both the static voltage stability of the power system and the static pressure stability of the natural gas system. To determine whether the system has reached its static stability limit, the IEGS static voltage stability index and gas pressure stability index are introduced.

[0078] Whether the voltage is statically stable can be determined by whether the power Jacobian matrix is ​​singular. The IEGS static voltage stability index is shown in formula (3).

[0079]

[0080] Where, δ min For J ee The minimum eigenvalue of .

[0081] Whether the air pressure is statically stable is often measured by the lowest air pressure p of the air network. min The IEGS static air pressure stability index is determined by whether it passes through zero, as shown in formula (4).

[0082]

[0083] During the CMEF calculation process, if the IEGS reaches the static pressure stability limit first, that is, p min First reaches 0, and δ minIf the value is ≥0, it indicates that in this scenario, load growth will eventually cause pressure to destabilize before voltage, resulting in an IEGS pressure instability scenario. The node where the pressure reaches 0 first is the IEGS pressure weak link. The minimum load shedding method in this embodiment of the present invention is primarily designed to prevent such scenarios. When the IEGS is about to reach its static pressure stability limit, load shedding in a prescribed sequence ensures that the IEGS pressure returns to the minimum level for normal system operation while minimizing load reduction.

[0084] Step 2: Construct a Comprehensive Sensitivity Index (CSI) to identify IEGS pressure weaknesses

[0085] In this step, for the above-mentioned IEGS air pressure instability scenario, we first construct the IEGS air pressure-air load sensitivity matrix, and then use the elements in the sensitivity matrix to construct the comprehensive sensitivity index (CSI) to identify the weak links of the IEGS air pressure.

[0086] 2-1) IEGS air pressure-air load sensitivity matrix

[0087] IEGS air pressure-air load sensitivity matrix S p-L It can be calculated by formula (9).

[0088]

[0089] In the high-pressure gas network calculation process, the pressure p appears in the form of pressure squared π. The gas network Jacobian matrix J gg The gas load L deviation value △L is converted into the correction value δΠ of the square of the gas pressure, which can be expressed in the partial differential form of Π and L:

[0090]

[0091] The relationship between Π and p can be expressed by formula (11):

[0092]

[0093] Combining equations (9)-(11), the IEGS air pressure-air load sensitivity matrix can be calculated using equation (12).

[0094]

[0095] Where diag represents the diagonal matrix function; S p-L It reflects the differential relationship between IEGS gas network pressure and gas load. The element in the i-th row and j-th column represents the sensitivity of the gas pressure of the j-th natural gas node to the load change of the i-th natural gas node.

[0096] 2-2) Comprehensive sensitivity index

[0097] Based on the elements in the sensitivity matrix in 2-1), the comprehensive sensitivity index (CSI) can be further constructed to identify the weak links of IEGS pressure. Figure 2 It can be seen that the initial level of node gas pressure and the sensitivity to load growth jointly determine the degree of gas pressure weakness, which can be expressed by the gas pressure instability indicator (GII) and the average gas pressure-load increment sensitivity. Finally, the two are combined to construct CSI.

[0098] 2-2-1) Air pressure instability index

[0099] Analogously to the voltage instability index, the gas pressure instability index is constructed to quantify the impact of the initial gas pressure level. For the natural gas system node j, its gas pressure instability index GII j The calculation is shown in formula (13). j The larger it is, the lower the initial air pressure of the node is, and the easier it is for the air pressure to become unstable.

[0100]

[0101] Where, is the air pressure of the current operating point node j; It is the maximum air pressure at the current IEGS operating point.

[0102] 2-2-2) Average air pressure-load increment sensitivity

[0103] In IEGS, NGU is often used as a control unit, and the active power loss in the transmission network can be approximately ignored. The increase in electric load is equivalent to the increase in NGU output, which is equivalent to the increase in gas load of the gas grid node connected to the NGU (hereinafter referred to as the "gas grid coupling node"). The conversion relationship is shown in Equation (1).

[0104] Therefore, the cross-system electricity and gas load growth can be converted into a single gas load growth. e Indicates the gas load used for NGU power generation; L g Indicates the difference between L e The gas load other than the gas load is set as the gas load of the gas network itself. The total gas load increment ΔL includes the increase ΔL of the gas load of the gas network itself. g , which also includes the gas load increase ΔL caused by the increase in electric load e , as shown in formula (14).

[0105] △L=△L g +△L e (14)

[0106] Assume that the ratio of the load increment of node i in the natural gas system to the total gas load increment △L is K i , linearly combine the elements of the pressure-gas load Jacobian matrix according to the load growth ratio of each node, and finally calculate the pressure-load increment sensitivity of the gas pressure at node j of the natural gas system to the total load increment As shown in formula (15).

[0107]

[0108] Where n g Indicates the number of load nodes in the natural gas system; S p-△L Reflects the sensitivity of gas pressure at each node of the IEGS gas grid to the growth of total electricity and gas load. The larger the value, the more sensitive the gas pressure at node j in the natural gas system is to the IEGS load growth, and the faster the gas pressure drops when the load increases.

[0109] However, since the sensitivity index is derived from the Jacobian matrix, it is inherently highly nonlinear. The sensitivity of a single state alone cannot fully reflect the changes in the IEGS pressure during instability. In power systems, to avoid the limitations of a single-state sensitivity index, power systems often reflect the sensitivity of system node voltages to load growth by calculating the average sensitivity during load growth. Drawing on this idea, CMEF is used to calculate the pressure drop from the current IEGS operating point Ω0 to the static pressure stability limit operating point Ω. lim Between c The average pressure-load increment sensitivity of each state is obtained by taking the average pressure-load increment sensitivity The average air pressure of node j is the load increment sensitivity It can be calculated using formula (16). To express the rate of decrease of gas pressure at each node of IEGS gas network as the electricity and gas load increases.

[0110]

[0111] Where z is the state label, indicating the zth state of node j; n c Indicates the total number of states calculated from the current operating point to the critical operating point of air pressure stability.

[0112] 2-2-3) Comprehensive sensitivity index

[0113] CSI combines GII with Combined together, the comprehensive sensitivity index CSI of gas network node j is jAs shown in Equation (17), the CSI considers both the impact of the node's initial air pressure value and the rate at which the node's air pressure decreases with increasing load. The larger the CSI, the worse the static stability of the node's air pressure and the weaker the node's air pressure. The node with the largest CSI is the IEGS air pressure weak link, thereby enabling the identification of the IEGS air pressure weak link.

[0114]

[0115] Step 3: Construct the load shedding sensitivity index (LSSI) to determine the minimum load shedding sequence for IEGS

[0116] Assume that the weakest node of air pressure identified by CSI is w. After using CSI to identify the weak link of IEGS air pressure, in order to achieve the minimum load shedding, this step further evaluates the impact of removing the load of each node on the air pressure of the weak node when the air pressure is close to instability, and constructs the load shedding sensitivity index LSSI, including: g and load sensitivity index LSSI e .

[0117] 3-1) Gas cut load sensitivity index

[0118] Sensitivity matrix S p-L The jth column vector in represents the influence of the air load change of each node on the air pressure of node j. Therefore, it is advisable to take S p-L The corresponding weak node pressure p w Column vector of the gas shedding load for p w The recovery effect of the element is used as the LSSI of each gas load node, recorded as LSSI g , as shown in formula (18).

[0119]

[0120] Where, e w is a unit row vector whose wth element is 1, p w The air pressure of the weak link of IEGS. LSSI g It can reflect the impact of load changes at each node of the gas network on the gas pressure of weak nodes. LSSI of load shedding sensitivity index of gas network node j g,j The larger the value, the greater the effect of removing the gas load of node j on the pressure of the weak node, and the smaller the load that needs to be removed. Therefore, according to LSSI g Cut off the gas load in order from large to small.

[0121] 3-2) Power-off load sensitivity index

[0122] Assuming that the active power output of the coal-fired unit has reached its maximum and remains unchanged, cutting off the load is equivalent to reducing the active power output of the NGU. NGU Equivalent to reducing L NGU Then the electricity load can be converted into the gas load of the gas grid coupling node. u NGU, then the power-off load sensitivity index LSSI e It can be calculated by formula (19).

[0123]

[0124] Where, Indicates the output ratio of the i-th NGU; LSSI g,NGUi Represents the LSSI of the node connected to the i-th NGU in the gas network g The order of cutting off the power and gas loads can be determined according to the size of the LSSI of the power and gas loads.

[0125] In addition, since the effect of cutting off loads at different nodes in the power grid on restoring gas pressure is almost the same, the electric loads can be cut off in sequence according to the voltage-reactive load sensitivity index, with priority given to cutting off the electric loads that have the greatest impact on the system voltage.

[0126] The embodiment of the present invention uses a typical IEGS to verify the effectiveness of the system minimum load shedding method considering electrical coupling sensitivity. The IEGS is composed of an IEEE 39-node power system and a 22-node gas grid system coupled through two NGUs. Figure 3 As shown, NGU1 connects the grid node E32 and the gas grid node G12, and NGU2 connects E33 and G1. Except for the generators connected to the grid nodes E32 and E33, which are NGUs, all other node generators are coal-fired units. ge =101.12(m 3 ·h -1 ) / MW, air pressure stability limit p lim =0kPa. Since the focus is on proving the effectiveness of the system minimum load shedding method of the present invention considering electrical coupling sensitivity, the following assumptions are made:

[0127] 1) The output ratio of the gas generators is 1:1, and the parameters of the two gas generators are the same; 2) Active power loss is ignored in the transmission network, and the NGU is used as the control unit; 3) The gas load of the gas grid coupling node is all used for NGU power generation, that is, the load increase of the gas grid coupling node is only related to the electric load increment λ, and is not related to the gas grid's own load increment λ g 4) When shedding the load, it is assumed that the output of the coal-fired units in the system has reached the maximum and remains unchanged. The output of the NGU needs to be reduced to meet the demand of the shedding load.

[0128] In order to study the impact of different growth ratios of electricity and gas loads on the minimum load shedding strategy of IEGS under electrical coupling, the following two scenarios are set (the calculation of continuous multi-energy flow CMEF shows that IEGS in both scenarios meets p min reaches 0 first, and the air pressure becomes unstable before the voltage):

[0129] Scenario 1: The electric load of each load node in the power system increases proportionally, and the gas load of each load node in the gas grid increases proportionally except for the coupling node, and the electric load of the power system and the gas load of the natural gas system itself L g Increase in the same increment, that is, the growth coefficients of electricity and gas loads in CMEF are equal, k e =k g =0.5;

[0130] Scenario 2: The electric load of the power system does not increase, and the gas load of each load node in the natural gas system increases proportionally except for the coupling node, that is, k e =0,k g =1.

[0131] 1. Identification of IEGS air pressure weak links

[0132] Calculate the comprehensive sensitivity (CSI), and express the CSI size of each IEGS gas network node using a color spectrum, as shown in the figure below: Figure 4 As shown in the figure, the color spectrum from bottom to top represents the CSI from small to large. As can be seen from the figure, the weakest IEGS pressure nodes in scenarios one and two are G7 and G21, respectively.

[0133] In order to verify the effectiveness of CSI in identifying the weak links of IEGS gas pressure, CMEF simulation was used to obtain the static stability limit operating points of IEGS under two scenarios. Finally, IEGS in the two scenarios reached the static pressure stability limit state when λ was equal to 3520.6MW and 3338.9MW respectively. At this time, the gas pressure at each node of the IEGS gas network and the CSI were Figure 5 As shown in the figure, the pressure at each node shows a significant negative correlation with the CSI when the IEGS pressure approaches instability. This demonstrates that the CSI effectively reflects the static stability of the pressure at each node during load growth. The larger the CSI, the worse the static pressure stability and the weaker the pressure. Furthermore, the pressure at nodes G7 and G21, which have the largest CSIs in both scenarios, eventually reaches the static stability limit first, representing the weakest link in the IEGS pressure.

[0134] 2. Establishment of the minimum load shedding sequence for IEGS

[0135] After determining the IEGS node with the weakest gas pressure, calculate the load shedding sensitivity index LSSI of the electric load (EL) and each gas load node, as follows: Figure 6As shown in the figure. Since the LSSI value is small and the LSSI difference between different nodes is large, in order to intuitively represent the order of LSSI, Figure 6 Take the common logarithm of the LSSI of each load. Grid voltage-reactive load sensitivity index dU L / dQ L like Figure 9 shown.

[0136] According to LSSI and dU L / dQ L Sorting the electricity and gas load nodes, in scenario one, the LSSI for electricity load is already ranked fifth. This means that when the IEGS gas pressure approaches instability, if the four gas grid nodes with the largest LSSI have insufficient load shedding, shedding electricity load will be more effective in restoring the system's weak gas pressure than shedding the remaining gas load, and the required load shedding will be smaller. The following sections will demonstrate the effectiveness of LSSI in minimizing load shedding and the necessity of minimum load shedding across the system.

[0137] 2-1) Effectiveness of LSSI in minimizing load shedding

[0138] When the IEGS gas pressure is close to instability in the two scenarios, the recovery value Δp of the system minimum gas pressure after the 10MW load is cut off at the electric load node E7 and the gas load node respectively is calculated, as follows: Figure 7 As shown in the figure, the triangle represents the removal of electrical load. As can be seen from the figure, the effect of removing equal load at each node on the recovery of air pressure is the same as Figure 6 The LSSI order is basically the same. The larger the LSSI of a node, the greater the effect of shedding equal loads on air pressure recovery, and the loads should be shelved first, which proves the rationality of formulating the minimum load shedding order of IEGS based on LSSI.

[0139] Assuming that the IEGS nodes have sufficient load shedding capacity, select grid node E7 and the gas load nodes with the maximum and minimum LSSI for load shedding. Gradually shear loads at the three nodes until the system minimum pressure returns from 0 kPa to 300 kPa. Stop shedding loads and record the load shedding capacity at each node. Finally, the load shedding capacity at each node (gas load is calculated by η ge converted into MW units) and LSSI sizes are shown in Table 1.

[0140] Table 1 Load shedding at different nodes under two scenarios

[0141]

[0142] The table shows a negative correlation between node LSSI and required load shedding. In scenario one, node G7, which has the highest LSSI, reduces load shedding by approximately 23% and 59.1% compared to node E7 and G6, respectively. In scenario two, node G21 reduces load shedding by approximately 49.3% and 56.7% compared to node E7 and G6, respectively. This demonstrates that prioritizing load shedding at nodes with the highest LSSI during IEGS load shedding can minimize load reduction.

[0143] In addition, compared with scenario 2, the effect of power load shedding on air pressure recovery is significantly improved in scenario 1. Figure 7 As shown by the dashed line, in Scenario 1, the effect of electricity load shedding on gas pressure recovery exceeds that of 80% of the grid's load nodes. This is because, compared to Scenario 2, the proportion of electricity load growth in Scenario 1 is greater, which increases the impact of electricity load changes on gas pressure, and the effect of electricity load shedding on boosting gas pressure in weak links is also greater. This shows that the different growth rates of electricity and gas have a significant impact on the IEGS minimum load shedding strategy.

[0144] 2-2) Consider the necessity of minimum load shedding across the system

[0145] To demonstrate the necessity of considering cross-system load shedding in the IEGS minimum load shedding strategy, assuming that the maximum load shedding per IEGS load node is 5MW, two load shedding strategies are set for comparison in scenario 1: (Both strategies shed load sequentially in descending order of LSSI)

[0146] Strategy 1: Consider cross-system load shedding, which can cut both gas and electricity loads;

[0147] Strategy 2: Do not consider cross-system load shedding, only gas load shedding.

[0148] Let the system minimum pressure be restored from 0kPa to the set pressure level Δp respectively. The load shedding required by the two strategies is as follows: Figure 8 The load node number next to the data point in the figure indicates the load node that needs to be additionally cut off to restore the system air pressure to the current Δp compared to the previous Δp.

[0149] When Δp ≤ 200 kPa, both strategies require only gas load shedding at the four gas grid nodes with the largest LSSI, resulting in the same load shedding amount. However, when Δp ≥ 250 kPa, simply shedding the four nodes with the largest LSSI is no longer sufficient to restore the system pressure to Δp. At this point, following the LSSI order, Strategy 1 sheds the electricity load, while Strategy 2 continues shedding the remaining gas load. As shown in the figure, as Δp increases, Strategy 1 requires less load shedding than Strategy 2. This is because the LSSI of the electricity load nodes is greater than that of the remaining gas load nodes, and shedding the electricity load has a greater impact on restoring the gas grid pressure, requiring less load shedding. Therefore, compared to shedding only the gas load, incorporating cross-system load shedding in the IEGS minimum load shedding strategy can significantly reduce the amount of load reduction, ultimately achieving minimum load shedding for the IEGS.

[0150] Unless otherwise specified, the embodiments of the present invention do not limit the models of the components. Any component that can perform the above functions may be used.

[0151] Those skilled in the art will understand that the accompanying drawings are only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A system minimum load shedding method considering electrical coupling sensitivity, characterized in that: The method comprises: Based on the IEGS air pressure instability scenario, a comprehensive sensitivity index was constructed to quantify the impact of electricity and gas load growth on IEGS air pressure. The air pressure at the node with the maximum comprehensive sensitivity index was taken as the weak link of air pressure. Aiming at the weak link of air pressure, a load shedding sensitivity index is constructed to evaluate the effect of shedding the load at each node on restoring the air pressure at the node with the largest comprehensive sensitivity index when the air pressure is close to instability. The load nodes are sorted from largest to smallest according to the load shedding sensitivity index, and the electrical / gas loads are sequentially cut off when the air pressure is about to become unstable, ultimately achieving the minimum load shedding of the IEGS. The air pressure of the node with the largest comprehensive sensitivity index is taken as the weak link of air pressure in the following specific steps: The pressure instability index and the average pressure-load increment sensitivity are used to characterize the system respectively, and a comprehensive sensitivity index is constructed by combining the two. Wherein, the air pressure instability index is: Where, is the air pressure of the current operating point node j; The maximum air pressure at the current IEGS operating point; The average air pressure-load increment sensitivity is: Where n g Indicates the number of load nodes in the natural gas system; gas pressure-load increment sensitivity S p-ΔL Reflects the sensitivity of gas pressure at each node of the IEGS gas network to the growth of total electricity and gas load; The larger the value, the more sensitive the gas pressure at node j in the natural gas system is to the IEGS load growth, and the faster the pressure drops when the load increases; K i It represents the ratio of the load increment of node i in the natural gas system to the total gas load increment ΔL; is the element in the i-th row and j-th column, indicating the sensitivity of the gas pressure of the j-th gas node to the load change of the i-th gas node; Average air pressure-load increment sensitivity To express the decreasing speed of gas pressure at each node of IEGS gas network as the electricity and gas load increases: Where z is the state label, indicating the zth state of node j; n c Indicates the total number of states calculated from the current operating point to the critical operating point of air pressure stability.

2. A system minimum load shedding method considering electrical coupling sensitivity according to claim 1, characterized in that: The load nodes are sorted from large to small according to the load shedding sensitivity index, and the electric / gas loads are shelved in sequence when the gas pressure is about to become unstable. Specifically: 1) Gas cut load sensitivity index Where, e w is a unit row vector whose wth element is 1, p w is the air pressure of the weak link of IEGS, L is the air load; S p-L Represents the IEGS pressure-gas load sensitivity matrix; LSSI g Reflects the impact of load changes at each node in the gas network on the gas pressure of weak nodes; LSSI, the load shedding sensitivity index of gas network node j g,j The larger the value, the greater the effect of the gas load of the removed node j on the gas pressure of the weak node. 2) Power-off load sensitivity index Where, Indicates the output ratio of the i-th NGU; LSSI g,NGUi Represents the LSSI of the node connected to the i-th NGU in the gas network g The order of cutting off power and gas loads is determined according to the size of the LSSI of the power and gas loads.

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