Method and device for acquiring closed-loop current and computer readable storage medium

Abstract

The application discloses a loop closing current acquisition method and device and a computer readable storage medium. The method comprises the following steps: acquiring the injection power measurement value of a plurality of nodes in a target power grid and the voltage measurement value of the plurality of nodes; acquiring the injection current measurement value of the plurality of nodes in the target power grid based on the injection power measurement value of the plurality of nodes and the voltage measurement value of the plurality of nodes; acquiring the dynamic equivalent impedance of the target power grid based on the injection current measurement value of the plurality of nodes and the voltage measurement value of the plurality of nodes; acquiring the loop closing voltage difference between two loop closing points when the target power grid is loop closed; and acquiring the steady-state loop closing current and the transient-state loop closing current based on the loop closing voltage difference and the dynamic equivalent impedance. The application solves the technical problem that the loop closing current is difficult to be accurately acquired in the related art.

Description

Technical Field

[0001] This invention relates to the field of power flow calculation in power systems, and more specifically, to a method, apparatus, and computer-readable storage medium for obtaining closed-loop current. Background Technology

[0002] For power grids in large cities, loop closure is necessary to ensure power supply reliability for major events or to meet maintenance requirements. Loop closure current calculation is fundamental to this process. Inaccurate steady-state current calculations can lead to unreasonable power flow distribution after closure, overloads on some lines, and other problems. Inaccurate transient current calculations can result in excessive inrush current, triggering protection systems and causing closure failure.

[0003] In related technologies, static equivalent impedance is typically used to calculate steady-state and transient loop-closing currents. Specifically, the entire power network is first subjected to Thevenin equivalent impedance to obtain the static equivalent impedance, which is calculated using the unit current method. After obtaining the equivalent impedance, the real-time voltage across the loop is measured at the moment of loop closure. The steady-state current is obtained by dividing the measured real-time voltage by the loop impedance, and the transient current is obtained by multiplying the steady-state current by the transient impulse factor. While this method can obtain both steady-state and transient loop-closing currents, it has the following problems: the generator and load parameters used in the static equivalent impedance are static, while generator impedance and rotating load impedance change with operating conditions and cannot reflect the actual situation; for complex power grids, calculating the equivalent impedance from the network to the loop closure point is difficult, and the calculated loop equivalent impedance is not accurate enough, which leads to inaccurate calculation of the loop current. In other words, related technologies suffer from the technical problem of accurately obtaining the loop current.

[0004] There is currently no effective solution to the above problems. Summary of the Invention

[0005] This invention provides a method, apparatus, and computer-readable storage medium for obtaining closed-loop current, thereby at least solving the technical problem of difficulty in accurately obtaining closed-loop current in related technologies.

[0006] According to one aspect of the present invention, a method for obtaining loop current is provided, comprising: obtaining injected power measurements and voltage measurements of a plurality of nodes in a target power grid; obtaining injected current measurements of the plurality of nodes in the target power grid based on the injected power measurements and voltage measurements of the plurality of nodes; obtaining the dynamic equivalent impedance of the target power grid based on the injected current measurements and voltage measurements of the plurality of nodes; obtaining the loop voltage difference between two loop points when the target power grid is looped; and obtaining steady-state loop current and transient loop current based on the loop voltage difference and the dynamic equivalent impedance.

[0007] Optionally, obtaining the dynamic equivalent impedance of the target power grid based on the injected current measurement values ​​and voltage measurement values ​​of the multiple nodes includes: obtaining the generator dynamic impedance and load dynamic impedance based on the injected current measurement values ​​and voltage measurement values ​​of the multiple nodes in a pre-constructed multi-fault disturbance scenario; obtaining the dynamic equivalent impedance of the target power grid based on the generator dynamic impedance and the load dynamic impedance, and a Thevenin equivalent impedance model with the two loop points as two ports; wherein, the Thevenin equivalent impedance model with the two loop points as two ports is constructed based on the admittance matrix of three node blocks in the target power grid, the three node blocks including: a first node block and a second node block respectively composed of the two loop points, and a third node block composed of other nodes in the multiple nodes of the target power grid except for the two loop points.

[0008] Optionally, the step of obtaining generator dynamic impedance and load dynamic impedance based on a pre-constructed multi-fault disturbance scenario, the injected current measurement values ​​of the multiple nodes, and the voltage measurement values ​​of the multiple nodes, includes: solving an error function based on the voltage measurement values, current measurement values, and power angle measurement values ​​of the multiple nodes to obtain the target voltage model value, target current model value, and target power angle model value corresponding to the minimum error value. The error function is constructed based on the least squares method and is used to characterize the error between the measured values ​​and the corresponding predicted values ​​of multiple power parameters of the power grid, including voltage, current, and power angle. Based on the target voltage model value, target current model value, and target power angle model value corresponding to the minimum error value, and the pre-constructed third-order generator model and integrated load model, the generator dynamic impedance and load dynamic impedance corresponding to the target voltage model value, target current model value, and target power angle model value are obtained. The third-order generator model and the integrated load model are constructed based on the multiple fault disturbance scenarios and the generator dynamic impedance parameters and load dynamic impedance parameters.

[0009] Optionally, it also includes: constructing a third-order model of the generator based on the power angle, angular velocity, q-axis transient reactance, real and imaginary parts of current, d-axis synchronous reactance, d-axis transient reactance, inertial constant, d-axis transient open-circuit time constant, active power output, excitation electromotive force, and the nominal value of synchronous angular velocity of the generator at node k in the target power grid at time t under fault disturbance scenario j; and based on the ratio of kinetic energy to capacity of the induction motor, the d-axis transient internal electromotive force and q-axis transient internal electromotive force of the induction motor, the d-axis current component, and the q-axis current component of the induction motor. A third-order model of the motor is constructed using the d-axis and q-axis voltage components, the rotational speed of the induction motor, and the proportional coefficients of the mechanical rotational angle of the induction motor that are linearly related to the square of the rotational speed and independent of the rotational speed. A ZIP model of the static load is constructed based on the coefficients of constant impedance, constant current, and constant power in the active load, the coefficients of constant impedance, constant current, and constant power in the reactive load, and the initial active and reactive power of the load. Based on the third-order model of the motor and the ZIP model of the static load, the comprehensive load model is obtained.

[0010] Optionally, it further includes: obtaining the node voltage equations of the three node blocks based on the admittance matrix; and eliminating the current parameters of the third node block in the node voltage equations based on Gaussian elimination to obtain the Thevenin equivalent impedance model with the two loop points as two ports.

[0011] Optionally, obtaining the steady-state closing current and transient closing current based on the closing-loop voltage difference and the dynamic equivalent impedance includes: obtaining the steady-state closing current based on the closing-loop voltage difference and the dynamic equivalent impedance; and obtaining the transient closing current based on the steady-state closing current and a predetermined inrush current coefficient, wherein the transient closing current includes: the maximum value of the closing-loop inrush current and the effective value of the closing-loop inrush current.

[0012] Optionally, obtaining the transient closing current based on the steady-state closing current and the predetermined impulse current coefficient includes: according to the following method:

[0013]

[0014] Obtain the maximum value of the closed-loop impact current i M Among them, K M I represents the predetermined impact current coefficient. c The magnitude of the steady-state closed-loop current is represented by the following method:

[0015]

[0016] Obtain the effective value i of the closed-loop impact current t .

[0017] According to another aspect of the present invention, a loop current acquisition device is also provided, comprising: a first acquisition module, configured to acquire injected power measurement values ​​and voltage measurement values ​​of multiple nodes in a target power grid; a second acquisition module, configured to acquire injected current measurement values ​​of multiple nodes in the target power grid based on the injected power measurement values ​​and voltage measurement values ​​of the multiple nodes; a third acquisition module, configured to acquire the dynamic equivalent impedance of the target power grid based on the injected current measurement values ​​and voltage measurement values ​​of the multiple nodes; a fourth acquisition module, configured to acquire the loop voltage difference between two loop points when the target power grid is looped; and a fifth acquisition module, configured to acquire steady-state loop current and transient loop current based on the loop voltage difference and the dynamic equivalent impedance.

[0018] According to another aspect of the present invention, a computer-readable storage medium is also provided, characterized in that the storage medium includes a stored program, wherein, when the program is executed, it controls the device where the storage medium is located to execute the closed-loop current acquisition method described in any one of the above embodiments.

[0019] According to another aspect of the present invention, a computer device is also provided, characterized in that it includes: a memory and a processor, the memory storing a computer program; the processor is configured to execute the computer program stored in the memory, wherein when the computer program is executed, the processor performs the data processing method described in any one of the preceding embodiments.

[0020] In this embodiment of the invention, the injected power measurement values ​​and voltage measurement values ​​of multiple nodes in the target power grid are obtained; based on the injected power measurement values ​​and voltage measurement values ​​of multiple nodes, the injected current measurement values ​​of multiple nodes in the target power grid are obtained; based on the injected current measurement values ​​and voltage measurement values ​​of multiple nodes, the dynamic equivalent impedance of the target power grid is obtained; the loop-closing voltage difference between the two loop-closing points of the target power grid is obtained; and based on the loop-closing voltage difference and the dynamic equivalent impedance, the steady-state loop-closing current and transient loop-closing current are obtained. By obtaining the dynamic equivalent impedance of the target power grid, and obtaining the steady-state loop-closing current and transient loop-closing current based on the dynamic equivalent impedance, the accuracy of the obtained steady-state loop-closing current and transient loop-closing current is high, solving the problem of difficulty in accurately obtaining the loop-closing current in related technologies. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0022] Figure 1This is a flowchart of an optional method for obtaining loop current according to an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of an optional power grid structure before dynamic impedance equivalence processing according to an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of an optional power grid structure after dynamic impedance equivalence processing according to an embodiment of the present invention;

[0025] Figure 4 This is a frame diagram of an optional loop current acquisition device according to an embodiment of the present invention. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0027] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0028] Example 1

[0029] According to an embodiment of the present invention, an embodiment of a method for obtaining loop current is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0030] Figure 1 This is a flowchart of an optional loop current acquisition method according to an embodiment of the present invention, such as... Figure 1 As shown, the method includes the following steps:

[0031] Step S102: Obtain the injected power measurement value and the voltage measurement value of multiple nodes in the target power grid;

[0032] Step S104: Based on the injected power measurement values ​​and voltage measurement values ​​of multiple nodes, obtain the injected current measurement values ​​of multiple nodes in the target power grid;

[0033] Step S106: Based on the injection current measurement values ​​and voltage measurement values ​​of multiple nodes, obtain the dynamic equivalent impedance of the target power grid;

[0034] Step S108: Obtain the loop closing voltage difference between the two loop closing points when the target power grid is closed;

[0035] Step S110: Based on the loop voltage difference and dynamic equivalent impedance, obtain the steady-state loop current and transient loop current.

[0036] In this optional embodiment, the injected power measurement values ​​and voltage measurement values ​​of multiple nodes in the target power grid are obtained; based on the injected power measurement values ​​and voltage measurement values ​​of multiple nodes, the injected current measurement values ​​of multiple nodes in the target power grid are obtained; based on the injected current measurement values ​​and voltage measurement values ​​of multiple nodes, the dynamic equivalent impedance of the target power grid is obtained; the loop-closing voltage difference between the two loop-closing points of the target power grid is obtained; based on the loop-closing voltage difference and the dynamic equivalent impedance, the steady-state loop-closing current and transient loop-closing current are obtained. By obtaining the dynamic equivalent impedance of the target power grid, the steady-state loop-closing current and transient loop-closing current are obtained with high accuracy, solving the problem of difficulty in accurately obtaining the loop-closing current in related technologies.

[0037] As an optional embodiment, the dynamic equivalent impedance of the target power grid is obtained based on the injected current measurements and voltage measurements of multiple nodes. This includes: obtaining the generator dynamic impedance and load dynamic impedance based on a pre-constructed multi-fault disturbance scenario, the injected current measurements and voltage measurements of multiple nodes; and obtaining the dynamic equivalent impedance of the target power grid based on the generator dynamic impedance, load dynamic impedance, and a Thevenin equivalent impedance model with two loop points as two ports. The Thevenin equivalent impedance model with two loop points as two ports is constructed based on the admittance matrices of three node blocks in the target power grid. These three node blocks include: a first node block and a second node block, each composed of two loop points; and a third node block, composed of all nodes in the target power grid except for the two loop points. Based on the pre-constructed multi-fault disturbance scenario and the injected current measurements and voltage measurements of multiple nodes, the dynamic impedance of the generator and load can be calculated in real time, and the dynamic equivalent impedance of the target power grid can be obtained in real time based on the generator dynamic impedance and load dynamic impedance, thus improving the accuracy of the dynamic equivalent impedance.

[0038] As an optional embodiment, based on a pre-constructed multi-fault disturbance scenario, the injected current measurement values ​​of multiple nodes, and the voltage measurement values ​​of multiple nodes, the generator dynamic impedance and load dynamic impedance are obtained, including: solving an error function based on the voltage measurement values, current measurement values, and power angle measurement values ​​of the multiple nodes to obtain the target voltage model value, target current model value, and target power angle model value corresponding to the minimum error value. The error function is constructed based on the least squares method and is used to characterize the error between the measured values ​​and the corresponding predicted values ​​of multiple power parameters of the power grid. The power parameters include voltage, current, and power angle. Based on the target voltage model value, target current model value, and target power angle model value corresponding to the minimum error value, and the pre-constructed third-order generator model and integrated load model, the generator dynamic impedance and load dynamic impedance corresponding to the target voltage model value, target current model value, and target power angle model value are obtained. The third-order generator model and integrated load model are constructed based on multiple fault disturbance scenarios and the generator dynamic impedance parameters and load dynamic impedance parameters. Based on the minimum error values ​​of the model values ​​and measured values ​​of voltage, current and power angle of multiple nodes, the corresponding voltage model values, current model values ​​and power angle model values, as well as the pre-constructed third-order generator model and integrated load model, the generator dynamic impedance and load dynamic impedance corresponding to the target voltage model value, target current model value and target power angle model value can be accurately obtained.

[0039] As an optional embodiment, it further includes: constructing a third-order model of the generator based on the power angle, angular velocity, q-axis transient reactance, real and imaginary parts of current, d-axis synchronous reactance, d-axis transient reactance, inertial constant, d-axis transient open-circuit time constant, active power output, magnetomotive force, and nominal value of synchronous angular velocity of the generator at node k in the target power grid at time t under fault disturbance scenario j; and based on the ratio of kinetic energy to capacity of the induction motor, the d-axis transient internal potential and q-axis transient internal potential of the induction motor, the d-axis current component of the induction motor, and the q-axis... A third-order model of the induction motor is constructed using the current component, d-axis voltage component, q-axis voltage component, induction motor speed, and the proportionality coefficients of the mechanical angle of the induction motor that are linearly related to the square of the speed and independent of the speed. A ZIP model of the static load is constructed based on the coefficients of constant impedance, constant current, and constant power in the active load, the coefficients of constant impedance, constant current, and constant power in the reactive load, and the initial active and reactive power of the load. A comprehensive load model is obtained based on the third-order model of the motor and the ZIP model of the static load. The comprehensive load model obtained using this method can accurately determine the generator dynamic impedance and load dynamic impedance corresponding to the target voltage model value, target current model value, and target power angle model value, thus improving the accuracy of the calculation results.

[0040] As an optional embodiment, the method further includes: obtaining the node voltage equations for the three node blocks based on the admittance matrix; and eliminating the current parameters of the third node block from the node voltage equations using Gaussian elimination to obtain a Thevenin equivalent impedance model with the two loop points as two ports. The Thevenin equivalent impedance model thus determined has high usability, and based on this model, the dynamic equivalent impedance of the target power grid can be accurately obtained.

[0041] As an optional embodiment, the steady-state and transient closing-loop currents are obtained based on the closing-loop voltage difference and dynamic equivalent impedance. This includes: obtaining the steady-state closing-loop current based on the closing-loop voltage difference and dynamic equivalent impedance; and obtaining the transient closing-loop current based on the steady-state closing-loop current and a predetermined inrush current coefficient. The transient closing-loop current includes the maximum value and the effective value of the closing-loop inrush current. The resulting steady-state and transient closing-loop currents are highly accurate, solving the problem of inaccurate current calculations caused by the mismatch between typical impedance and real-time impedance in related technologies.

[0042] Optionally, the transient closing current is obtained based on the steady-state closing current and a predetermined impulse current coefficient, including by the following method:

[0043]

[0044] Obtain the maximum value of the closed-loop inrush current iM; where KM represents the predetermined inrush current coefficient, and Ic represents the amplitude of the steady-state closed-loop current; according to the following method:

[0045]

[0046] Obtain the effective value of the closed-loop inrush current (it). The method described in this optional embodiment for obtaining the maximum and effective values ​​of the closed-loop inrush current is simple and yields highly accurate results.

[0047] Based on the above embodiments and optional embodiments, an optional implementation method is provided, which is described in detail below.

[0048] Calculating the loop-closing current is fundamental to loop-closing operations. Inaccurate steady-state loop-closing current calculations can lead to unreasonable power flow distribution after loop closure, overloads on some lines, and other problems. Inaccurate transient loop-closing current calculations can result in excessive loop-closing inrush current, triggering protection mechanisms and causing loop closure failure. In related technologies, both steady-state and transient loop-closing currents are calculated using static equivalent impedance. Specifically, the entire power network is first subjected to Thevenin equivalent impedance calculation, and the equivalent impedance is calculated using the unit current method. Then, the real-time voltage across the loop-closing point is measured at the moment of loop closure. The steady-state current is obtained by dividing the real-time voltage across the loop-closing point by the loop impedance. The transient loop-closing current is obtained by multiplying the steady-state loop-closing current by the transient inrush coefficient. This method in related technologies has the following drawbacks: First, the generator and load parameters used in calculating the static equivalent impedance are static. However, in actual power grids, generator impedance and rotating load impedance change with operating conditions, so the aforementioned method in related technologies cannot reflect the actual situation. Second, in complex power grids, calculating the equivalent impedance from the network to the loop-closing point is difficult, and the calculated loop-closing equivalent impedance is not accurate enough. In some power grid areas, the failure rate of loop closing due to inaccurate calculation of the loop closing current is as high as 30%. Therefore, accurate and rapid calculation of the loop closing current is crucial. However, a method for accurately obtaining the loop closing current is lacking in related technologies.

[0049] Therefore, this disclosure provides a method for obtaining loop current. This method involves acquiring injected power measurements and voltage measurements at multiple nodes in a target power grid; obtaining injected current measurements at multiple nodes based on these measurements; obtaining the dynamic equivalent impedance of the target power grid based on these measurements; obtaining the loop voltage difference between two loop points when the target power grid is closed; and obtaining the steady-state and transient loop currents based on the loop voltage difference and the dynamic equivalent impedance. The accuracy of the obtained steady-state and transient loop currents is high, solving the problem of accurately obtaining loop current in related technologies. This is described in detail below.

[0050] The loop current acquisition method of this optional embodiment includes the following steps:

[0051] S1. Obtain the real-time injected power and node voltage of all nodes in the network, and calculate the node injected current. The method for calculating the node injected current specifically includes the following steps:

[0052] Step S11: Obtain the real-time injected power and node voltage of each node in the entire network (equivalent to the voltage measurement value in the aforementioned embodiment).

[0053] Step S12: Obtain the node injection current (equivalent to the current measurement value in the aforementioned embodiment) according to the following method:

[0054] I = (I * ) * =(U -1 S) *

[0055] Where I is a matrix composed of node injected currents, U is a matrix composed of node voltages, and S is a matrix composed of apparent power.

[0056] S2: Jointly identify the dynamic impedance parameters of generators and loads based on multiple fault disturbance scenarios, specifically including the following steps:

[0057] Step S21: Set up multiple fault scenarios.

[0058] Step S22, construct the following third-order generator model:

[0059]

[0060] In the formula:

[0061]

[0062] in: These represent the power angle, angular velocity, q-axis transient reactance, real part and imaginary part of the current of the generator at node k under scenario j at time t; X dk 、X′ dk M k 、T′ d0k These represent the d-axis synchronous reactance, d-axis transient reactance, inertial constant, and d-axis transient open-circuit time constant of the generator at node k, respectively. qk P represents the q-axis synchronous reactance of the generator at node k; Gk E fk These represent the active power output and magnetomotive force of the generator at node k, respectively; ω s The synchronous angular velocity has a given value. Let represent the active power of the generator at node k at time t under scenario j. This represents the direct-axis current of the generator at node k in scenario j at time t. Let n represent the quadrature-axis current of the generator at node k in scenario j at time t. G N represents the number of nodes. S This indicates the total number of scenarios.

[0063] Among them, the d-axis synchronous reactance X of the generator at node k dk d-axis transient reactance X′ dk Inertial constant M k d-axis transient open-circuit time constant T′ d0k For the generator to be identified; X dk 、X′ dk Used to calculate the equivalent impedance of a closed loop.

[0064] Step S23: Construct the third-order model of the induction motor as shown below:

[0065]

[0066] In the formula:

[0067]

[0068] in

[0069] T′=(X r +X m ) / R r

[0070] X = X s +X m

[0071] X′=X s +X m X r / (X m +X r )

[0072]

[0073] Where H is the ratio of the kinetic energy to the capacity of the induction motor; E′ d E′ q These are the d-axis transient internal potential and q-axis transient internal potential of the induction motor, respectively; I d I q U d U q These represent the d-axis current component, q-axis current component, d-axis voltage component, and q-axis voltage component of the induction motor, respectively; ω rR represents the rotational speed of the induction motor; the subscript "0" indicates the initial value of each physical quantity; A, B, and C are the proportionality coefficients of the mechanical torque of the induction motor that are linearly related to the square of the rotational speed, linearly related to the rotational speed, and independent of the rotational speed, respectively; s R r These represent the stator resistance and rotor resistance, respectively; T′ represents the transient open-circuit time constant; X s X m X r X, X′, X′ represent the stator reactance, magnetizing reactance, rotor reactance, rotor open-circuit reactance, and short-circuit reactance when the rotor is stationary, respectively.

[0074] The ZIP model for static load is shown below:

[0075]

[0076] Where, k pz k pi k pp These are the coefficients representing the proportions of constant impedance, constant current, and constant power in the active load; k qz k qi k qp These are the coefficients for constant impedance, constant current, and constant power in reactive loads, respectively; P L0 Q L0 P represents the initial active and reactive power of the load. ZIP Q ZIP This represents the equivalent active and reactive power of a static load.

[0077] The load is a comprehensive load model composed of a parallel ZIP model of third-order induction motors.

[0078] Among them, the parameters of the induction motor to be identified are: R s ,X s ,R r ,X r ,X m The static ZIP parameters include: k (A, B, H). pz ,k pp ,k qz ,k qp , where R s ,X s ,R r ,X r ,X m Used to calculate the equivalent impedance of a closed loop.

[0079] Step S24: Establish a dynamic parameter identification model with the objective function of minimizing the least squares error between the model values ​​and measured values ​​of node voltage, current, and power angle. The objective function f(x) is as follows:

[0080]

[0081] In the formula, nT is the number of integration time periods for the measurement data; Let represent the power angle value, real and imaginary parts of the current, and real and imaginary parts of the voltage at time t in scenario j of the generator model. These represent active power and reactive power, respectively. These represent the real and imaginary parts of the power angle measurement, current measurement, and voltage measurement of generator node i at time t under scenario j, as measured by the corresponding synchronous waveform measurement devices. Let n represent the active power measurement value and reactive power measurement value of load node ii at time t in scenario j, respectively. load This indicates the number of load nodes.

[0082] The objective function is constrained by power flow constraints and dynamic parameter inequality constraints.

[0083] Step S25: Solve the above model using the interior point method to obtain the generator dynamic impedance and load dynamic impedance parameters.

[0084] Step S3 involves dividing the power network into three parts based on the two sides of the loop closure point and the remaining nodes, writing out the block node admittance matrices, and updating the node admittance matrices according to the identified dynamic parameters. Specifically, this includes the following steps:

[0085] Step S31: Figure 2 This is a schematic diagram of an optional power grid structure before dynamic impedance equivalence processing according to an embodiment of the present invention; Figure 3 This is a schematic diagram of an optional power grid structure after dynamic impedance equivalence processing according to an embodiment of the present invention. (Refer to...) Figure 2 and Figure 3 As shown, the entire power grid is divided into three parts: node 1 and node 2 each constitute one part, and the remaining nodes constitute one part. Then, the nodal admittance matrix Y of the entire power grid can be written as:

[0086]

[0087] The elements in YEE include generator nodes and load nodes. Each element in the matrix represents the node admittance of each node. Specifically, YEE, YE1, and YE2 are the self-admittance matrix of external node E, the mutual admittance between external node E and node 1, and the mutual admittance between external node E and node 2, respectively. 1E Y 11 Y 12 Y 2E Y 21Let represent the mutual admittance between the merging node 1 and the external node E, the self-admittance of the merging node 1, the mutual admittance between node 1 and node 2, the mutual admittance between the merging node 2 and the external node E, and the mutual admittance between node 2 and node 1, respectively.

[0088] Step S32: Update the nodal admittance matrix based on the real-time identified generator and load dynamic impedance parameters, and the generator nodal self-admittance y. Gii The updated expression is:

[0089]

[0090] Among them, y Gi Generator admittance to ground, generator node self-admittance y Gii Direct-axis transient reactance x d Direct-axis transient reactance x q and subtransient reactance x′ d The function, generator node self-admittance y Gii For generator dynamic parameters; y ij It is the mutual admittance between the generator node and the surrounding interconnected nodes.

[0091] Load node self-admittance y Lii The updated formula is:

[0092]

[0093] Among them, y Li For load admittance to ground, self-admittance y Lii For R s ,X s ,R r ,X r ,X m The function, self-admittance y Lii For load dynamic parameters; y ij It is the mutual admittance between the load node and the surrounding interconnected nodes.

[0094] Then update the nodal admittance matrix Y, since only Y... EE The elements in the table include generator nodes and load nodes; only these need to be updated. The update formula is as follows:

[0095]

[0096] Among them, Y GG Y is the admittance matrix between generator nodes; LL Y is the admittance matrix between load nodes; GL Y is the mutual admittance matrix between the generator node and the load node; LG Let be the mutual admittance matrix between the load node and the generator node; satisfying Direct-axis transient reactance xd Direct-axis transient reactance x q and subtransient reactance x′ d The function represents the generator node self-admittance y. Gii g(R) s ,X s ,R r ,X r ,X m ) is R s ,X s ,R r ,X r ,X m The function represents the load self-admittance, and diag(.) represents taking the diagonal elements.

[0097] S4. Based on the Gaussian elimination method, a Thevenin equivalent impedance model is established with the loop point as the two-port.

[0098] Step S41: Based on the updated block node admittance matrix, write the node voltage equations as follows:

[0099]

[0100] In the formula, UE, U1, and U2 represent the voltages on both sides of the external node and the closing point, respectively; IE, IL1, and IL2 represent the injected currents. YEE, YE1, and YE2 represent the self-admittance matrix of the external node, the mutual admittance between the external node and node 1, and the mutual admittance between the external node and node 2, respectively; Y11 represents the self-admittance of closing point 1; Y22 represents the self-admittance of closing point 2; and Y12 represents the mutual admittance between closing point 1 and closing point 2.

[0101] Step S42, based on Gaussian elimination, eliminate I. E The equivalent impedance of the dynamic loop closure is obtained as follows:

[0102]

[0103] in,

[0104] Among them, i1, i2, i L1 i L2 , and y1, y2, y3, y4 are all functions of the dynamic parameters of the generator and load nodes, which can be expressed as the relationship between the dynamic parameters of the generator and load nodes. Where U eq Z eq These are the equivalent potential and equivalent impedance of the closed loop network, respectively.

[0105] S5. Calculate the steady-state and transient loop closing currents based on the voltage at the loop closing moment and the dynamic equivalent impedance.

[0106] Step S51, calculate the steady-state closed-loop current.

[0107] Based on the Thevenin equivalent circuit, the steady-state closed-loop current I can be obtained. c The calculation formula is as follows:

[0108]

[0109] Step S52, calculate the transient loop current.

[0110] The transient closing current includes the general formula of the closing current impulse, the closing current impulse value, and the closing current effective value, which are calculated separately.

[0111] The calculation model for the closed-loop impact current is shown below:

[0112] Let Z eq =R eq +jX eq Assuming the voltage of the equivalent voltage source varies sinusoidally, R eq and X eq Let U be the equivalent resistance and equivalent reactance, respectively; then the equivalent potential of the closed-loop network can be written as: U eq =E max sin(ωt+φ), based on the equivalence structure of the loop, the differential equation is established as follows:

[0113]

[0114] In the formula, E max The magnitude of the loop closing voltage difference is represented by φ, which represents the phase angle difference between the voltages on both sides of the loop closing point at the moment of closing. j represents the imaginary part; ω represents the angular frequency.

[0115] The particular solution and general solution of the above equation are as follows:

[0116]

[0117]

[0118] In the formula, t represents the decay time. This represents the loop impedance angle after the loop is closed.

[0119] The combined loop impact current i(t), which is the sum of the particular solution and the general solution of the differential equation, is expressed as follows:

[0120]

[0121] As can be seen from the above equation, the inrush current after the loop is closed consists of a periodic component i p (t) and a free decay component i q (t) constitutes. It is a periodic component i pThe magnitude of (t), i q (t) is a non-periodic component that decays exponentially.

[0122] As can be seen from this expression, overall, the closed-loop inrush current and E max That is, the difference in the magnitude of the closed-loop voltage is proportional to, and That is, the impedance of the ring network is inversely proportional to the voltage phase angle difference φ, and the decay time constant is also related to... The equivalent resistance and reactance of the network are relevant. The derivation shows that the magnitude of the loop inrush current is related to the electrical parameters of the loop network and is caused by the voltage difference across the loop closing point.

[0123] The method for obtaining the maximum value of the closed-loop inrush current includes the following steps:

[0124] According to the expression for the closed-loop impact current, when φ-tan -1 When (ωL / R)=kπ(k=0,1,2,…), sin[φ-tan -1 [ωL / R]=0, meaning the attenuation component of the closed-loop impact current is 0, and it directly enters steady state without a decay process. When hour, The inrush current reaches its maximum value.

[0125] In practical closed-loop networks, it is difficult to determine the angle at the moment of closure. Therefore, the calculation is performed based on the most severe possible scenario. That is, the above equation can be simplified to:

[0126]

[0127] From the above equation, we know that when sin(ωt-π / 2)=1, that is, after half a cycle from the moment the loop closes, the loop impact current reaches its maximum value, and its expression is:

[0128]

[0129] Taking a distribution network frequency of 50Hz as an example, its period T = 1 / 50 = 0.02s. Since the closing-loop inrush current reaches its maximum value after half a cycle of closing, t = T / 2 = 0.01s in the above formula. Therefore, the maximum value of the closing-loop inrush current is:

[0130]

[0131] In the above formula, I is the impact coefficient. M I is the amplitude of the closed-loop steady-state current. c This represents the effective value of the steady-state current. In a power system, K... M The value is typically 1.8.

[0132] The method for obtaining the effective value of the closed-loop impulse current includes the following steps:

[0133] Since the current setting value of instantaneous overcurrent protection in relay protection is the effective value of the current, it is necessary to solve for the effective value of the impulse current while calculating the closing-loop impulse current. The effective value, also called the root mean square (RMS) value, refers to the root mean square value of the current over one cycle. Therefore, the impulse current i... q (t) Effective value I t The calculation formula is as follows:

[0134]

[0135] To simplify the calculation process, assume i q If the value of (t) remains constant within a period T centered at time t, then we have i q The effective value of (t) is equal to the instantaneous value, i.e., I q =i q ; and assume i p (t) If the amplitude remains constant during this period, then the relationship between the effective value and the amplitude of the circulating current is:

[0136] Therefore, the above formula can be written as:

[0137]

[0138] at the same time, Substituting into the above formula, we obtain the following effective values:

[0139]

[0140] When K M When I takes the value 1.8, t =1.52I c .

[0141] Using the above optional implementation method, the loop current in a certain regional power grid is calculated. The specific method includes the following steps:

[0142] Step 1: Obtain the real-time injected power and node voltage of each node in the entire network, and calculate the node injected current. The obtained real-time injected power, node voltage, and calculated injected current are shown in Table 1.

[0143] Table 1

[0144]

[0145]

[0146] Step 2: Jointly identify the dynamic impedance parameters of generators and loads based on multiple fault disturbance scenarios. The impedance parameters of some generators in the power grid are shown in Table 2.

[0147] Table 2

[0148]

[0149] The partial load impedances are shown in Table 3:

[0150] Table 3

[0151]

[0152] Step 3: Divide the power network into three parts according to the two sides of the loop point and the remaining nodes, write the block node admittance matrix, and update the node admittance matrix according to the identified dynamic parameters.

[0153] Step 4: Based on Gaussian elimination, establish the Thevenin equivalent impedance model with the loop closure point as the two-port terminal. The relevant parameters for establishing the Thevenin equivalent impedance model with the loop closure point as the two-port terminal based on Gaussian elimination are shown in Table 4.

[0154] Table 4

[0155]

[0156]

[0157] Step 5: Calculate the steady-state and transient loop closing currents based on the voltage at the loop closing moment and the dynamic equivalent impedance.

[0158] The steady-state and transient loop closing currents are shown in Table 5.

[0159]

[0160] Example 2

[0161] According to an embodiment of the present invention, an apparatus for implementing the above-described loop current acquisition method is also provided. Figure 4 This is a frame diagram of an optional loop current acquisition device according to an embodiment of the present invention. (Refer to...) Figure 4 As shown, the device includes a first acquisition module 402, a second acquisition module 404, a third acquisition module 406, a fourth acquisition module 408, and a fifth acquisition module 410, which will be described in detail below.

[0162] The first acquisition module 402 is used to acquire the injected power measurement values ​​and voltage measurement values ​​of multiple nodes in the target power grid; the second acquisition module 404, connected to the first acquisition module 402, is used to acquire the injected current measurement values ​​of multiple nodes in the target power grid based on the injected power measurement values ​​and voltage measurement values ​​of multiple nodes; the third acquisition module 406, connected to the second acquisition module 404, is used to acquire the dynamic equivalent impedance of the target power grid based on the injected current measurement values ​​and voltage measurement values ​​of multiple nodes; the fourth acquisition module 408, connected to the third acquisition module 406, is used to acquire the loop voltage difference between two loop closing points when the target power grid is closed; the fifth acquisition module 410, connected to the fourth acquisition module 408, is used to acquire the steady-state loop closing current and transient loop closing current based on the loop closing voltage difference and the dynamic equivalent impedance.

[0163] It should be noted that the first acquisition module 402, the second acquisition module 404, the third acquisition module 406, the fourth acquisition module 408 and the fifth acquisition module 410 mentioned above correspond to steps S102 to S110 in Embodiment 1. The instances and application scenarios implemented by these modules and the corresponding steps are the same, but they are not limited to the content disclosed in Embodiment 1.

[0164] Example 3

[0165] Embodiments of the present invention may provide a computer-readable storage medium, characterized in that the storage medium includes a stored program, wherein, when the program is executed, it controls the device where the storage medium is located to execute the closed-loop current acquisition method described above.

[0166] An embodiment of the present invention provides a computer device, including: a memory and a processor. The memory stores a computer program; the processor is configured to execute the computer program stored in the memory. When the computer program runs, the processor performs the following data processing method: acquiring injected power measurement values ​​and voltage measurement values ​​of multiple nodes in a target power grid; acquiring injected current measurement values ​​of multiple nodes in the target power grid based on the injected power measurement values ​​and voltage measurement values ​​of multiple nodes; acquiring the dynamic equivalent impedance of the target power grid based on the injected current measurement values ​​and voltage measurement values ​​of multiple nodes; acquiring the loop voltage difference between two loop closing points when the target power grid is closed; and acquiring the steady-state loop closing current and transient loop closing current based on the loop voltage difference and the dynamic equivalent impedance.

[0167] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing the hardware related to the terminal device. The program can be stored in a computer-readable storage medium, which may include: flash drive, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc.

[0168] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0169] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0170] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The device embodiments described above are merely illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For instance, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling, direct coupling, or communication connection may be through some interfaces; the indirect coupling or communication connection between units or modules may be electrical or other forms.

[0171] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0172] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0173] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0174] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for obtaining closed-loop current, characterized in that, include: Acquire the injected power measurement values ​​and voltage measurement values ​​of multiple nodes in the target power grid; Based on the injected power measurement values ​​and voltage measurement values ​​of the multiple nodes, the injected current measurement values ​​of multiple nodes in the target power grid are obtained; Based on the injected current measurement values ​​and voltage measurement values ​​of the multiple nodes, the dynamic equivalent impedance of the target power grid is obtained; Obtain the loop-closing voltage difference between the two loop-closing points when the target power grid is closed; Based on the closed-loop voltage difference and the dynamic equivalent impedance, the steady-state closed-loop current and the transient closed-loop current are obtained; The process of obtaining the dynamic equivalent impedance of the target power grid based on the injected current measurement values ​​and voltage measurement values ​​of the multiple nodes includes: obtaining the generator dynamic impedance and load dynamic impedance based on a pre-constructed multi-fault disturbance scenario, the injected current measurement values ​​of the multiple nodes, and the voltage measurement values ​​of the multiple nodes; obtaining the dynamic equivalent impedance of the target power grid based on the generator dynamic impedance and load dynamic impedance, and a Thevenin equivalent impedance model with the two loop points as two ports; wherein the Thevenin equivalent impedance model with the two loop points as two ports is constructed based on the admittance matrix of three node blocks in the target power grid, the three node blocks including: a first node block and a second node block respectively composed of the two loop points, and a third node block composed of other nodes in the multiple nodes of the target power grid excluding the two loop points.

2. The method according to claim 1, characterized in that, The process of obtaining generator dynamic impedance and load dynamic impedance based on a pre-constructed multi-fault disturbance scenario, the injected current measurements of the multiple nodes, and the voltage measurements of the multiple nodes includes: The error function is solved based on the voltage, current and power angle measurements of the multiple nodes to obtain the target voltage model value, target current model value and target power angle model value corresponding to the minimum error value. The error function is constructed based on the least squares method and is used to characterize the error between the measured values ​​of multiple power parameters of the power grid and the corresponding predicted values ​​of the power parameters, including voltage, current and power angle. Based on the target voltage model value, target current model value, and target power angle model value corresponding to the minimum error value, as well as the pre-constructed third-order generator model and integrated load model, the generator dynamic impedance and load dynamic impedance corresponding to the target voltage model value, target current model value, and target power angle model value are obtained; wherein, the third-order generator model and integrated load model are constructed based on the multiple fault disturbance scenarios, as well as the generator dynamic impedance parameters and load dynamic impedance parameters.

3. The method according to claim 2, characterized in that, Also includes: Based on the power angle, angular velocity, q-axis transient reactance, real and imaginary parts of current, d-axis synchronous reactance, d-axis transient reactance, inertial constant, d-axis transient open-circuit time constant, active power output, magnetomotive force, and nominal value of synchronous angular velocity of the generator at node k in the target power grid at time t under fault disturbance scenario j, a third-order model of the generator is constructed. A third-order model of the induction motor is constructed based on the ratio of kinetic energy to capacity, the transient internal electromotive force of the induction motor along the d-axis and q-axis, the current component along the d-axis, the current component along the q-axis, the voltage component along the d-axis and q-axis, the rotational speed of the induction motor, and the proportional coefficient of the mechanical rotation angle of the induction motor that is linearly related to the square of the rotational speed and the rotational speed and is independent of the rotational speed. Based on the coefficients of constant impedance, constant current and constant power in active load, the coefficients of constant impedance, constant current and constant power in reactive load, and the initial active power and reactive power of the load, a ZIP model of static load is constructed. Based on the third-order model of the motor and the ZIP model of the static load, a comprehensive load model is obtained.

4. The method according to claim 1, characterized in that, Also includes: Based on the admittance matrix, the node voltage equations of the three node blocks are obtained; Based on Gaussian elimination, the current parameters of the third node block in the node voltage equation are eliminated to obtain the Thevenin equivalent impedance model with the two loop points as two ports.

5. The method according to claim 1, characterized in that, Based on the closed-loop voltage difference and the dynamic equivalent impedance, the steady-state closed-loop current and the transient closed-loop current are obtained, including: The steady-state closed-loop current is obtained based on the closed-loop voltage difference and the dynamic equivalent impedance; Based on the steady-state closed-loop current and the predetermined impact current coefficient, the maximum value and effective value of the closed-loop impact current are obtained.

6. The method according to claim 5, characterized in that, Based on the steady-state closed-loop current and the predetermined impact current coefficient, the maximum and effective values ​​of the closed-loop impact current are obtained, including: According to the following method: , Obtain the maximum value of the closed-loop impact current. ; in, Indicates the predetermined impact current coefficient. This represents the magnitude of the steady-state closed-loop current. According to the following method: , Obtain the effective value of the closed-loop impact current .

7. A loop current acquisition device, characterized in that, include: The first acquisition module is used to acquire the injected power measurement value and the voltage measurement value of multiple nodes in the target power grid; The second acquisition module is used to acquire the injection current measurement values ​​of multiple nodes in the target power grid based on the injection power measurement values ​​and the voltage measurement values ​​of the multiple nodes. The third acquisition module is used to acquire the dynamic equivalent impedance of the target power grid based on the injection current measurement value and the voltage measurement value of the multiple nodes. The fourth acquisition module is used to acquire the loop voltage difference between the two loop closing points when the target power grid is closed; The fifth acquisition module is used to acquire the steady-state closing current and the transient closing current based on the closing loop voltage difference and the dynamic equivalent impedance. The third acquisition module is further configured to acquire the generator dynamic impedance and load dynamic impedance based on a pre-constructed multi-fault disturbance scenario, the injected current measurement values ​​of the multiple nodes, and the voltage measurement values ​​of the multiple nodes; and to acquire the dynamic equivalent impedance of the target power grid based on the generator dynamic impedance and load dynamic impedance, and the Thevenin equivalent impedance model with the two loop points as two ports; wherein the Thevenin equivalent impedance model with the two loop points as two ports is constructed based on the admittance matrix of three node blocks in the target power grid, the three node blocks including: a first node block and a second node block respectively composed of the two loop points, and a third node block composed of other nodes in the multiple nodes of the target power grid except for the two loop points.

8. A computer-readable storage medium, characterized in that, The storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the storage medium to perform the loop current acquisition method according to any one of claims 1 to 6.

9. A computer device, characterized in that, include: Memory and processor The memory stores computer programs; The processor is configured to execute a computer program stored in the memory, wherein when the computer program is executed, the processor performs the loop current acquisition method according to any one of claims 1 to 6.

Images