Method for evaluating voltage sag disturbance energy of power distribution network

Abstract

The invention discloses a power distribution network voltage sag disturbance energy evaluation method, and belongs to the technical field of voltage sag governance, and the method comprises the steps: mapping a power system into an elastic system based on a mapping relation; based on the Newton's third law, analyzing distribution characteristics of voltage sag disturbance force borne by each node in the elastic system and restoring force borne by a line after disturbance is finished; based on the nodal disturbance force and the branch restoring force in the elastic system, obtaining the nodal disturbance force and the branch restoring force of the power system; according to the node disturbance force and the branch recovery force, voltage sag disturbance energy in a voltage sag stage and a voltage recovery stage in the power system is obtained; obtaining a single-node voltage sag disturbance energy general formula based on the voltage sag disturbance energy; and evaluating the evolution process of the voltage sag disturbance energy along with time based on the voltage sag disturbance energy general formula. According to the method, the voltage sag problem is analyzed from the energy perspective, a new thought is provided for a voltage sag suppression scheme, and therefore the influence of voltage sag is relieved.

Description

Technical Field

[0001] The present application relates to the technical field of voltage sag control, and in particular to a method for evaluating the disturbance energy of voltage sag in a distribution network. Background Art

[0002] During normal operation, the power system maintains a state of energy exchange and equilibrium. However, a voltage sag is essentially a sudden surge of current drawn from the system during normal operation, causing a deficit in active power and disrupting the system's energy balance. Therefore, a voltage sag is a power quality disturbance and possesses disturbance energy. During normal operation of an active distribution network, the introduction of voltage sag disturbance energy disrupts the system's energy exchange balance. Unable to absorb the voltage sag disturbance energy, some distributed generation units (DGs) disconnect from the grid, causing an even greater energy deficit. However, if a DG successfully withstands a voltage sag, it can modify its operating mode and interact with the system's energy, rapidly attenuating the voltage sag disturbance energy and accelerating the system's return to equilibrium.

[0003] Traditional methods for studying voltage sags have focused on the spatial distribution characteristics of voltage sags. Spatial distribution characteristics reflect the voltage sag level experienced by each node at each time interval. These characteristics serve only as one dimension for characterizing the voltage sag disturbance energy, but cannot accurately characterize the spatial distribution characteristics of the voltage sag disturbance energy, nor can they reflect the temporal evolution of the voltage sag disturbance energy. The temporal characteristics of voltage sag disturbance energy refer to its self-organized evolution and equilibrium over time, while the spatial characteristics refer to its transmission across multiple voltage levels in the power system. The essence of voltage sag control is energy replenishment. Understanding the spatiotemporal distribution characteristics of voltage sag disturbance energy can provide technical support for efficient voltage sag control in active distribution networks.

[0004] Current research on the concept of energy during voltage sags can be divided into two categories. The first category addresses the problem that existing disturbance identification methods ignore the assessment of energy magnitude. This category introduces the relationship between energy entropy and free energy in thermodynamics into power system disturbance analysis, defining the concept of disturbance free energy. This effectively describes the strength of the energy impact of the system after a disturbance, but fails to reflect the evolution of energy in the system over time. The second category maps the power grid topology into a longitudinally stressed elastic network deployed in three-dimensional space, proposes the concept of mapped elastic potential energy, and uses this to study quantitative characterization methods for the active power carrying capacity of power systems. However, these mechanical mapping and elastic potential energy studies are based on analyzing the static stability of the system or low-frequency oscillations after a disturbance, and do not analyze the disturbance energy during the system disturbance. Therefore, it is necessary to propose a method to characterize the voltage sag disturbance energy based on existing methods and study the spatiotemporal distribution characteristics of the voltage sag disturbance energy. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, this application provides a method for evaluating the voltage sag disturbance energy in a distribution network, which analyzes the voltage sag control problem from an energy perspective and can provide new ideas for voltage sag suppression solutions.

[0006] In order to achieve the above-mentioned invention objectives, the technical solutions adopted in this application are: This application provides a method for evaluating the energy of a voltage sag disturbance in a distribution network, comprising: S1: Map the power system into a resilient system based on the mapping relationship; S2: Based on Newton's third law, analyze the distribution characteristics of the voltage sag disturbance force on each node in the elastic system and the restoring force on the line after the disturbance ends; S3: Based on the node disturbance force and branch restoration force in the elastic system, the node disturbance force and branch restoration force of the power system are obtained; S4: According to the node disturbance force and branch recovery force of the power system, the voltage sag disturbance energy generated by the voltage sag during the voltage drop stage and the voltage recovery stage in the power system is obtained; S5: Based on the voltage sag disturbance energy, the general formula of the voltage sag disturbance energy of a single node is obtained; S6: Evaluate the time evolution of the voltage sag disturbance energy of a single node based on the voltage sag disturbance energy general formula.

[0007] Furthermore, the step of mapping the power system into a resilient system based on the mapping relationship in S1 includes: Set the voltage Mapped to the extension or compression of the spring , load power Mapped to the gravity of a heavy object in an elastic system , the admittance of the line in the power system Mapped to the elastic coefficient of the spring , current Mapped to spring force , the mapping relationship is: .

[0008] Furthermore, the S2 specifically includes: S201: Based on the mapping relationship, analyze the voltage sag disturbance force and branch recovery force borne by each node in the radial network elastic system to obtain a mesh network elastic system; S202: Based on the mesh network elastic system, the force analysis of upstream and downstream nodes and multi-branch connections is performed to obtain the node disturbance force and branch restoring force in the elastic system. The expressions of the node disturbance force and branch restoring force in the elastic system are:

[0009]

[0010] in, is the node disturbance force, is the branch restoring force, For the Node number, For the nodes, is the upstream node, is the downstream node, The node after disturbance and The longest length between For nodes and The initial length of the Node after disturbance and The longest length between node and The initial length of the For nodes and The elastic coefficient of the branch between For nodes and The elastic coefficient of the branch between and are two nodes of the branch, For nodes and The elastic constant of the spring between is the spring length.

[0011] Furthermore, the S3 specifically includes: The elastic system parameters of the expressions of the node disturbance force and branch restoring force in the elastic system are converted into power system parameters to obtain the node disturbance force and branch restoring force of the power system. The expressions of the node disturbance force and branch restoring force of the power system are:

[0012]

[0013] in, For nodes and Mutual admittance of the lines, The nodes before and after the disturbance and The change in the voltage difference between For nodes and Mutual admittance of the lines, The nodes before and after the disturbance and The change in the voltage difference between is a node and The mutual admittance between nodes, is the voltage difference between the nodes.

[0014] Furthermore, the S4 specifically includes: S401: During the voltage drop phase, the work done by the node disturbance force and the change in elastic potential energy are analyzed based on the elastic system to obtain an expression for the work done by the node disturbance force; S402: Mapping the work done by the node disturbance force in the elastic system to the power system through a mapping relationship to obtain the initial energy of the voltage sag at the node in the power system; S403: In the voltage recovery phase, the work done by the spring restoring force in the elastic system is analyzed to obtain the voltage sag recovery energy in the elastic system; S404: Obtaining voltage sag recovery energy in the power system based on the voltage sag recovery energy in the elastic system; S405: Obtaining node voltage sag disturbance energy in the power system based on the voltage sag initial energy and the voltage sag recovery energy in the power system.

[0015] Furthermore, the S5 specifically includes: S501: Based on the disturbance energy distribution law of each node in the elastic system during the voltage drop phase, the voltage sag initial energy of a node after the elastic system is mapped to the power system is obtained. The expression of the voltage sag initial energy is:

[0016] in, for The node's neighbors, For nodes and The mutual admittance between For nodes and The change in the voltage difference between is the initial energy of voltage sag; S502: Obtain the voltage sag recovery energy of a certain node according to the voltage sag recovery energy. The voltage sag recovery energy of the certain node is expressed as:

[0017] in, Recover energy for voltage sags, For nodes and The change in the voltage difference between For nodes The voltage, For nodes The voltage, is the integration variable, is a parameter variable; S503: Based on the voltage sag initial energy and the voltage sag recovery energy, a general formula for the time evolution of the voltage sag disturbance energy of a single node is obtained. The general formula for the voltage sag disturbance energy of a single node is: .

[0018] The beneficial effects of this application are: The present application provides a method for evaluating the disturbance energy of voltage sag in a distribution network. The method proposes a new mapping rule for mapping electrodynamic topology to elastic dynamic topology, characterizes the transmission mechanism of node disturbance force and branch restoring force during voltage sag from a spatial perspective, and characterizes the disturbance energy of voltage sag from a temporal and spatial perspective. Based on the characterization results, the spatiotemporal distribution characteristics of the disturbance energy during the voltage sag process can be obtained, the voltage sag control problem can be analyzed from an energy perspective, and new ideas can be provided for voltage sag suppression solutions, namely, the impact of voltage sag can be alleviated by suppressing the transmission of disturbance energy and accelerating the attenuation of disturbance energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0020] Figure 1 A flow chart of a method for evaluating the energy of voltage sag disturbance in a distribution network provided in an embodiment of the present application.

[0021] Figure 2 A schematic structural diagram of a radial network power system model provided in an embodiment of the present application.

[0022] Figure 3 A schematic structural diagram of a radial network elastic system model provided in an embodiment of the present application.

[0023] Figure 4 A schematic structural diagram of a mesh network power system model provided in an embodiment of the present application.

[0024] Figure 5 A schematic diagram of the structure of a mesh network elastic system model provided in an embodiment of the present application.

[0025] Figure 6 A schematic structural diagram of a three-node elastic system model provided in an embodiment of the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of this application.

[0027] The present invention provides a method for evaluating the voltage sag disturbance energy of a distribution network. Figure 1 , Figure 1 FIG. 1 is a flow chart of a method for evaluating the energy of a voltage sag disturbance in a distribution network provided by an embodiment of the present application, including: S1: Map the power system into a resilient system based on the mapping relationship.

[0028] In one embodiment of the present application, the power network mainly includes branch current, node voltage and branch impedance parameters, and the parameter connection is established by Ohm's law, while the elastic network mainly includes branch elastic force, node displacement and branch elastic coefficient parameters, and the connection is established by Hooke's law. The analysis of the two is similar, and the power network can be analyzed using the visual mapping of the elastic network. At the energy level, the analysis of the elastic network is more intuitive and concise, which is more convenient for the definition and analysis of temporary sag energy.

[0029] When a short circuit occurs in a line of the power system, voltage sag events of varying degrees will occur to other nodes in the system. For other nodes, voltage sag is similar to an external disturbance, which will disrupt the balance of their normal operation. In order to characterize the impact and disturbance energy brought by voltage sag to the system and nodes, the power system is mapped into an elastic mechanics network. According to Newton's third law, the voltage sag disturbance force borne by each node and the distribution characteristics of the voltage sag disturbance force in the network are analyzed. Corresponding to the extension or compression of the spring ; Load power It can be compared to the gravity of a heavy object in an elastic system ; Admittance of lines in power systems It can be compared to the elastic coefficient of a spring , current Comparable to the elastic force of a spring The mapping relationship is:

[0030] S2: Based on Newton's third law, analyze the voltage sag disturbance force on each node in the elastic system and the distribution characteristics of the restoring force on the line after the disturbance ends.

[0031] In one embodiment of the present application, when a short circuit fault or heavy load switching occurs, the actual current change is a short circuit fault, which is the most common voltage sag. When a short circuit fault occurs, it is reflected in the power system as a disturbance force in the direction of the load's gravity. To maintain system stability and force balance, the spring force must increase to balance the external force, causing the spring to stretch and the node to displace, which is equivalent to a change in the potential difference between the nodes, manifesting as a rapid drop in voltage amplitude.

[0032] like Figure 2 As shown, Figure 2 A structural diagram of a radial network power system model provided in an embodiment of the present application shows that in a simple radial network power system, four nodes A, B, C, and D are included, where node A is the power source, and nodes B, C, and D are respectively connected to a load B, C, and D. Node B fails at a certain moment, causing a temporary voltage drop in the system.

[0033] In the power system simulation, it can be concluded that when the voltage of node B sags, the voltage sag degree of nodes A and C can be obtained by the voltage values ​​of A and C before and after the sag. and , and thus solve the disturbance force The following analysis of the disturbance force in the elastic system The solution formula of .

[0034] Furthermore, the S2 includes: S201: Based on the mapping relationship, analyze the voltage sag disturbance force and branch recovery force borne by each node in the radial network elastic system to obtain a mesh network elastic system; S202: Based on the mesh network elastic system, analyze the forces acting on upstream and downstream nodes and multi-branch connections to obtain the node disturbance force and branch restoring force in the elastic system.

[0035] In one embodiment of the present application, in a node system connected by springs, the action of forces follows Newton's laws of motion and Hooke's law. The single disturbance force spring node system model is as follows: Figure 3 As shown, Figure 3 This is a schematic diagram of the structure of a radial network elastic system model provided in an embodiment of the present application. Figure 3 Take the simple system consisting of nodes A, B, C, and D connected by springs as an example. Point A is the power source, which is fixed and at the highest point in the elastic system. Assume that the disturbance force When applied to point B, point B will be affected by the combined forces of springs AB and BC, the gravity of block B, and the disturbance force. The forces of springs AB and BC are generated by the spring deformation, and their magnitude follows Hooke's law. Directly change the force balance state of point B, causing it to move. Point C is connected to point B through spring BC, and the force on point C is mainly the elastic force generated by the deformation of spring BC due to the displacement of point B. According to Newton's third law, the forces exerted by spring BC on points B and C are equal in magnitude and opposite in direction. When point B moves downward under the action of the disturbing force, spring BC is stretched, generating a downward pulling force on point C, and point C moves downward under the combined force of the pulling force and its own gravity. The movement process of point D is similar to that of point C. The fundamental reason for the movement of points C and D is that the displacement of point B after the disturbing force causes the change in the elastic force of spring BC, not that it is directly affected by the disturbing force. .

[0036] (1) Force analysis of each node when no disturbance force is applied Node B is pulled upward by spring AB , is pulled downward by spring BC , subject to the gravity of weight B , according to the equilibrium condition:

[0037] The negative sign indicates an upward direction. is the extension of spring AB before disturbance, is the elastic coefficient of spring AB, the positive sign indicates the downward direction, is the elongation of spring BC before disturbance, is the elastic constant of spring BC, is the mass of weight B, is the acceleration due to gravity.

[0038] Node C is pulled upward by spring BC , is pulled downward by spring CD , subject to the gravity of weight C , according to the equilibrium condition:

[0039] in, is the extension of the spring CD before disturbance, is the elastic constant of spring CD, is the mass of weight C.

[0040] Node D is pulled upward by spring CD and the gravity of weight D , according to the equilibrium condition:

[0041] in, is the mass of object D.

[0042] (2) Node force analysis after adding disturbance force Node B is pulled upward by spring AB ( is the elongation of spring AB after disturbance), and is pulled downward by spring BC. ( is the extension of spring BC after disturbance), subject to the gravity of weight B . Subject to downward disturbance force , according to the equilibrium condition:

[0043] Adding the two equations before and after the disturbance at point B yields:

[0044] It can be solved F The values ​​are:

[0045] make , and the simplified result is that the disturbance force on point B is:

[0046] in, is the difference in elongation of spring AB before and after the disturbance, is the difference in elongation of spring BC before and after the disturbance.

[0047] Similarly, the equilibrium equation at point C can be obtained as:

[0048] in, is the elongation of the spring after CD disturbance; Adding the two equations before and after the disturbance at point C yields:

[0049] make , the force change at point C is obtained as:

[0050] in, is the change in force of spring BC before and after the disturbance, is the change in force of spring CD before and after the disturbance.

[0051] From a mechanical perspective, when a perturbation force is introduced at a point in the system, the system will regain equilibrium. The increase in the force of spring BC is transmitted through the system's mechanical forces, causing a corresponding increase in the force of spring CD. Ultimately, the change in the net force at node C is zero, thus maintaining the overall mechanical equilibrium of the system. Similarly, the displacement of nodes not directly affected by the perturbation force is due to the displacement of point B after the perturbation force triggers a change in the spring's force, causing a disturbance in the entire system. While the remaining nodes are not directly affected by the perturbation force, the forces in the lines between them will change accordingly.

[0052] After the disturbance force is added, the forces on branches AB, BC and CD are , and , at this time, the branch undergoes force changes due to the disturbance force on the node. Figure 4 As shown, Figure 4 A structural diagram of a mesh network power system model provided in an embodiment of the present application shows that when multiple nodes are connected by multiple branches, the radial network forms a mesh structure network. Therefore, a force analysis is performed on the single-node disturbed multi-branch model to obtain the disturbance force of each node in the mesh network.

[0053] Point B is subjected to a downward disturbance force, which will cause points C and E to move. The BC and BE springs will both generate elastic forces, which are mapped to the elastic system as follows: Figure 5 As shown, Figure 5 A schematic diagram of the structure of a mesh network elastic system model provided in an embodiment of the present application.

[0054] The force analysis of node B before and after the disturbance is performed as above. The magnitude of the disturbance force can be obtained after calculation:

[0055] in, is the elastic constant of spring BE, is the length of spring BE before disturbance, is the length of spring BE after disturbance. The sign of the upstream node is positive, and that of the downstream node is negative. That is, the force exerted by the upstream node on the fault node is upward, and the force exerted by the downstream node on the fault node is downward. The currents of the corresponding upstream and downstream nodes converge toward the fault node B to supplement the active power shortage at point B.

[0056] That is, in an elastic system, the disturbed force at point B will cause the elastic force of the connected spring to change, thereby causing the force and position of other nodes to change; in an electric power system, after point B is grounded due to a fault, its potential becomes zero potential, forming a huge potential difference with nodes A, C, and E, thereby causing a unidirectional flow of current, and the currents at points A, C, and E all flow to point B.

[0057] At this point, it's necessary to define the upper and lower springs. In a radial network, the power source is assumed to be at the highest vertical point, and current flows from the source along the radial path to each node. In a mesh network, a single node often connects to multiple branches, necessitating the inclusion of upstream and downstream nodes. When a fault occurs at a point, all connected branches will experience power or short-circuit current flowing to that node. Based on the mapping relationship between current and spring tension, we can analyze that the node corresponding to the branch where the current during normal operation and the short-circuit current flow in the same direction after a fault remain unchanged is the upstream node, while the node corresponding to the branch where the current flows in the opposite direction is the downstream node.

[0058] Based on the node disturbance force analysis of upstream and downstream nodes and multi-branch connections, n A total of m nodes, from 1 to n -1 is the upstream node, n +1 to m is the downstream node, then the expression of the modified node disturbance force is obtained:

[0059] in, For the elastic system Node number, For the nodes, is the upstream node, is the downstream node, The node after disturbance and The longest length between For nodes and The initial length of the Node after disturbance and The longest length between node and The initial length of the For nodes and The elastic coefficient of the branch between For nodes and The elastic coefficient of the branch between them.

[0060] S3: Based on the node disturbance force and branch restoring force in the elastic system, the node disturbance force and branch restoring force of the power system are obtained.

[0061] Furthermore, the elastic system parameters of the expression of the node disturbance force in the elastic system are converted into power system parameters to obtain the node disturbance force of the power system. The expression of the node disturbance force of the power system is:

[0062] in, a represents the upstream node, b represents the downstream node, For nodes and The mutual admittance between For nodes and The change in the voltage difference between For nodes and The mutual admittance between For nodes and The change in the voltage difference between the two.

[0063] In a mesh network, the disturbance force on a branch is still related to the branch's own impedance and the voltage of the node to which the branch is connected. The branch restoring force can be expressed as:

[0064] in and are two nodes of the branch, is the elastic constant of the spring between the nodes, is the spring length.

[0065] The branch resilience mapped to the power system is:

[0066] in, is the mutual admittance between nodes, is the voltage difference between the nodes.

[0067] Based on the mapping analysis of node and branch disturbance forces, the voltage sag disturbance energy is characterized by deriving the relationship between disturbance force and energy in Section 3.

[0068] S4: According to the node disturbance force and branch recovery force of the power system, the voltage sag disturbance energy caused by the voltage sag during the voltage drop stage and the voltage recovery stage in the power system is obtained.

[0069] Furthermore, the S4 specifically includes: S401: During the voltage drop phase, the work done by the node disturbance force and the change in elastic potential energy are analyzed based on the elastic system to obtain an expression for the work done by the node disturbance force; S402: Mapping the work done by the node disturbance force in the elastic system to the power system through a mapping relationship to obtain the initial energy of the voltage sag at the node in the power system; S403: In the voltage recovery phase, the work done by the spring restoring force in the elastic system is analyzed to obtain the voltage sag recovery energy in the elastic system; S404: Obtaining voltage sag recovery energy in the power system based on the voltage sag recovery energy in the elastic system; S405: Obtaining node voltage sag disturbance energy in the power system based on the voltage sag initial energy and the voltage sag recovery energy in the power system.

[0070] In one embodiment of the present application, a voltage sag event is divided into two stages: a voltage drop stage and a voltage recovery stage. Therefore, the voltage sag disturbance energy, as a disturbance energy, should be divided into two parts: impact energy and recovery energy.

[0071] During the voltage sag phase, there are voltage sag disturbance forces and voltage sag impact energy. Impact energy is the energy generated by the disturbance force doing work over time. The voltage sag disturbance force is an instantaneous force. When the fault is cleared, the disturbance force disappears, but the impact energy remains. This energy is only transferred and does not disappear instantly. During the voltage recovery phase, there is voltage sag recovery energy. Recovery energy refers to the energy in the voltage recovery phase. It is driven by the system's internal restoring force, with kinetic energy and potential energy converted into each other. The impact energy is then dissipated by system damping (resistive loads, line resistance, and regulation resources).

[0072] From a mechanical perspective, the voltage drop stage is similar to the process in which all the potential energy in an elastic system is converted into kinetic energy, which takes a very short time and can be considered to be completed instantaneously; while in the voltage recovery stage, the system potential energy and kinetic energy coexist, and there is a long-term evolution of energy.

[0073] The following will first define and characterize the voltage sag disturbance energy of the disturbance node in the radial network, dividing it into the voltage drop stage and the voltage recovery stage, and then derive the general formula of the voltage sag disturbance energy in the mesh network.

[0074] (1) Voltage drop stage The energy generated during the voltage drop phase is mapped to the elastic system and can be expressed as the energy generated by the work done by the disturbance force. Figure 6 The three-node elastic system model shown in the figure assumes that the original length of AB before the disturbance is , subject to disturbance force The effect of the force produces a downward (positive) displacement. , that is, AB spring stretches , BC spring shortened .

[0075] Analyze the disturbance energy of point B. Point B is subject to disturbance force. , can be obtained Doing work during the disturbance :

[0076] in, is the elongation of AB spring; The change in elastic potential energy of AB spring is:

[0077] in, is the elastic coefficient of the AB spring in the three-node elastic system model; The change in elastic potential energy of the BC spring is:

[0078] in, is the elastic coefficient of the BC spring in the three-node elastic system model; Disturbance The work done changes the distribution of the elastic potential energy of the entire elastic system, and at this point, the elastic potential energy of both the AB and BC springs changes. From the perspective of force, when the AB spring stretches, its elastic potential energy increases. This energy is converted from the work done by the disturbing force and acts directly on point B, forming part of the disturbance energy at point B. The shortening of the BC spring is also due to the force applied to point B, which exerts a strong force on point B. In other words, the effect of the work done by these two forces on point B is to increase the energy of point B. From the perspective of energy transfer, the changes in the elastic potential energy of these two springs are the result of the interaction between point B and the surrounding components during the disturbance process, and are the accumulation of energy at point B. Therefore, they should be added together to obtain the disturbance energy of point B:

[0079] The value of the work done by the disturbing force is equal to the change in elastic potential energy, and the kinetic energy at point B is It is the result of the influence of the disturbing force, so it can also be considered that the kinetic energy of point B is equal to the work done by the disturbing force.

[0080] Based on the mapping relationship, correspond , and Line admittance corresponding to AB and BC segments and , and Corresponding respectively and , and is the voltage difference between nodes AB and BC in the power system, and the potential energy change mapped to the power system is:

[0081] This part of potential energy is equivalent to the initial energy generated by the voltage sag, that is, the initial energy of the voltage sag, which can be obtained by simulating the completion of the voltage drop stage (that is, the lowest value of the voltage drop) and calculating the initial energy of the voltage sag disturbance energy in the drop stage.

[0082] (2) Voltage recovery stage Segment AB: Let the displacement of node A be , the displacement of node B is , the displacement of node C is , assuming that point A is fixed and has no displacement, the displacement of the AB spring is the displacement of point B , the displacement of BC .

[0083] According to the definition of instantaneous power ( It is force, is the velocity), and the spring force ( is the spring constant, is the displacement), assuming that if the spring force and the displacement velocity of the node If the directions are the same, the power is positive.

[0084] The power of spring AB doing work on node B is:

[0085] in, is the change in the distance between node A and node B, For time, is the derivative operator, is the time derivative of the displacement of node A, The displacement of node B is derived with respect to time.

[0086] Segment BC: Since the expansion and contraction of spring BC is caused by the relative motion of B and C, the instantaneous velocity is the velocity of B relative to C:

[0087] in, is the speed of node B, is the speed of node C; Substituting the definition of instantaneous power, the power of spring BC doing work on node B is:

[0088] in, is the restoring force on spring BC between nodes B and C, is the instantaneous velocity of B relative to C, is the change in displacement between nodes B and C.

[0089] Therefore, during the recovery phase arrive During time, the total work done by the two springs on node B is:

[0090] In the above formula, the lower limit is a constant, and the upper limit is the variable limit integral of the parameter time t. is the displacement of node A, is the displacement of node B, is the displacement of node C, is the change in displacement between nodes A and B, is the change in displacement between nodes B and C. The integrand contains only the integral variable , without parameters .

[0091] Assume that the voltage at node B changes with time as , the voltage difference between nodes A and B, and between nodes B and C is and , analogous to the work done by the restoring force of a spring, in line AB, the power Similar to the power of the restoring force. The voltage sag energy during the voltage recovery phase is:

[0092] is the change in the voltage difference between nodes A and B, is the voltage at node A, is the voltage at node B, is the voltage at node C, The time derivative of the voltage at node A.

[0093] In summary, the voltage sag disturbance energy expression at point B is:

[0094] That is, the voltage sag initial energy generated in the sag stage is subtracted from the voltage sag recovery energy. Therefore, the voltage sag disturbance energy decays over time, which means that the voltage sag disturbance energy gradually disappears in the power system.

[0095] S5: Based on the voltage sag disturbance energy, the general formula of the voltage sag disturbance energy of a single node is obtained.

[0096] S6: Evaluate the time evolution of the voltage sag disturbance energy of a single node based on the voltage sag disturbance energy general formula.

[0097] In one embodiment of the present application, the voltage sag disturbance energy at point B is According to the mapping relationship, the initial energy of the voltage sag corresponds to the change in the elastic potential energy of the spring. The lines between the upstream and downstream nodes and the fault node store energy due to the voltage difference, which is the direct source of the initial energy of the voltage sag.

[0098] Therefore, in an elastic system, the value of the initial energy of the voltage sag at each node is equal to the change in potential energy of the spring between the node and its adjacent nodes. x Node, after mapping the elastic system to the power system, the initial energy of voltage sag is:

[0099] in, for The node's neighbors, For nodes and The mutual admittance between For nodes and The change in the voltage difference between is the initial energy of voltage sag; The expression of energy recovery based on voltage sag in power system , the voltage recovery stage is affected by the branch recovery force, for x The node voltage recovery energy is:

[0100] Therefore, we can get x The function of the node voltage sag disturbance energy evolving over time is as follows:

[0101] The above formula can be used to study the time evolution process of the voltage sag disturbance energy at a single node.

[0102] The present application provides a method for evaluating the disturbance energy of voltage sag in a distribution network. The method proposes a new mapping rule for mapping electrodynamic topology to elastic dynamic topology, characterizes the transmission mechanism of node disturbance force and branch restoring force during voltage sag from a spatial perspective, and characterizes the disturbance energy of voltage sag from a temporal and spatial perspective. Based on the characterization results, the spatiotemporal distribution characteristics of the disturbance energy during the voltage sag process can be obtained, the voltage sag control problem can be analyzed from an energy perspective, and new ideas can be provided for voltage sag suppression solutions, namely, the impact of voltage sag can be alleviated by suppressing the transmission of disturbance energy and accelerating the attenuation of disturbance energy.

[0103] It should be noted that those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of this application, and it should be understood that the scope of protection of this application is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in this application without departing from the essence of this application, and such variations and combinations are still within the scope of protection of this application.

Claims

1. A method for evaluating the disturbance energy of voltage sag in a distribution network, characterized in that: include: S1: Map the power system into a resilient system based on the mapping relationship; S2: Based on Newton's third law, analyze the distribution characteristics of the voltage sag disturbance force on each node in the elastic system and the restoring force on the line after the disturbance ends; S3: Based on the node disturbance force and branch restoration force in the elastic system, the node disturbance force and branch restoration force of the power system are obtained; S4: According to the node disturbance force and branch recovery force of the power system, the voltage sag disturbance energy generated by the voltage sag during the voltage drop stage and the voltage recovery stage in the power system is obtained; S5: Based on the voltage sag disturbance energy, the general formula of the voltage sag disturbance energy of a single node is obtained; S6: Evaluate the time evolution of the voltage sag disturbance energy of a single node based on the voltage sag disturbance energy general formula.

2. The method for evaluating the voltage sag disturbance energy of a distribution network according to claim 1, wherein: In S1, the power system is mapped into a resilient system based on the mapping relationship, including: Set the voltage Mapped to the extension or compression of the spring , load power Mapped to the gravity of a heavy object in an elastic system , the admittance of the line in the power system Mapped to the elastic coefficient of the spring , current Mapped to spring force , the mapping relationship is: 。 3. The method for evaluating the voltage sag disturbance energy of a distribution network according to claim 2, wherein: The S2 specifically includes: S201: Based on the mapping relationship, analyze the voltage sag disturbance force and branch recovery force borne by each node in the radial network elastic system to obtain a mesh network elastic system; S202: Based on the mesh network elastic system, the force analysis of upstream and downstream nodes and multi-branch connections is performed to obtain the node disturbance force and branch restoring force in the elastic system. The expressions of the node disturbance force and branch restoring force in the elastic system are: in, is the node disturbance force, is the branch restoring force, For the Node number, For the nodes, is the upstream node, is the downstream node, The node after disturbance and The longest length between For nodes and The initial length of the Node after disturbance and The longest length between node and The initial length of the For nodes and The elastic coefficient of the branch between For nodes and The elastic coefficient of the branch between and are two nodes of the branch, For nodes and The elastic constant of the spring between is the spring length.

4. The method for evaluating the voltage sag disturbance energy of a distribution network according to claim 3, wherein: The S3 specifically includes: The elastic system parameters of the expressions of the node disturbance force and branch restoring force in the elastic system are converted into power system parameters to obtain the node disturbance force and branch restoring force of the power system. The expressions of the node disturbance force and branch restoring force of the power system are: in, For nodes and Mutual admittance of the lines, The nodes before and after the disturbance and The change in the voltage difference between For nodes and Mutual admittance of the lines, The nodes before and after the disturbance and The change in the voltage difference between is a node and The mutual admittance between nodes, is the voltage difference between the nodes.

5. The method for evaluating the distribution network voltage sag disturbance energy according to claim 4, characterized in that: The S4 specifically includes: S401: During the voltage drop phase, the work done by the node disturbance force and the change in elastic potential energy are analyzed based on the elastic system to obtain an expression for the work done by the node disturbance force; S402: Mapping the work done by the node disturbance force in the elastic system to the power system through a mapping relationship to obtain the initial energy of the voltage sag at the node in the power system; S403: In the voltage recovery phase, the work done by the spring restoring force in the elastic system is analyzed to obtain the voltage sag recovery energy in the elastic system; S404: Obtaining voltage sag recovery energy in the power system based on the voltage sag recovery energy in the elastic system; S405: Obtaining node voltage sag disturbance energy in the power system based on the voltage sag initial energy and the voltage sag recovery energy in the power system.

6. The method for evaluating the voltage sag disturbance energy of a distribution network according to claim 5, characterized in that: The S5 specifically includes: S501: According to the disturbance energy distribution law of each node in the elastic system during the voltage drop stage, the voltage sag initial energy of a node after the elastic system is mapped to the power system is obtained. The expression of the voltage sag initial energy is: in, for The node's neighbors, For nodes and The mutual admittance between For nodes and The change in the voltage difference between is the initial energy of voltage sag; S502: Obtain the voltage sag recovery energy of a certain node according to the voltage sag recovery energy. The voltage sag recovery energy of the certain node is expressed as: in, Recover energy for voltage sags, For nodes and The change in the voltage difference between For nodes The voltage, For nodes The voltage, is the integration variable, is a parameter variable; S503: Based on the voltage sag initial energy and the voltage sag recovery energy, a general formula for the time evolution of the voltage sag disturbance energy of a single node is obtained. The general formula for the voltage sag disturbance energy of a single node is: 。

Images