Method and device for recovering multi-direct-current receiving end system under secondary fault

Abstract

The embodiment of the invention provides a multi-direct-current receiving end system recovery method and device under a secondary fault. The method comprises the steps that an initial recovery scheme meeting all network topology corresponding constraints is generated for a receiving end system; the network topology comprises first network topologies where secondary faults occur in a receiving end system. Each second network topology is formed after a current source is independently arranged at each current conversion bus in the receiving end system; each third network topology is formed after a current source which is equal to a corresponding direct current transmission power per unit value is arranged at each current conversion bus in the receiving end system; and determining a target recovery scheme of the receiving end system according to the prediction rapidity index value and the prediction toughness index value corresponding to the initial recovery scheme. Through the method provided by the invention, the recovery toughness of the receiving end system under the secondary fault is remarkably improved, the adaptability and stability of the system are enhanced, the risk of system locking fault or re-collapse in the recovery process is effectively avoided, and the recovery efficiency and reliability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power systems and their automation, in particular, to a multi-direct-current receiving-end system recovery method and device under secondary faults. BACKGROUND

[0002] Under the background of low-carbon transformation of energy and power in China, high-voltage direct-current transmission has become a backbone channel for large-scale new energy cross-regional consumption due to its own advantages, and a multi-loop direct-current feeding receiving-end system has been formed in load-intensive areas. However, in the receiving-end system, the AC-DC interconnected grid is prone to cause cascading reactions when a fault occurs, increasing the risk of a large-scale blackout.

[0003] Traditional power system recovery is mainly aimed at AC systems and does not involve the resilience improvement of the receiving-end system recovery process under the participation of high-voltage direct current. If the AC grid support strength in the receiving-end system decreases due to secondary faults during the recovery process, it may cause the direct-current system in the receiving-end system to be blocked, and even cause the receiving-end system grid to collapse again. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a multi-direct-current receiving-end system recovery method and device under secondary faults, which generates an initial recovery scheme that meets various network topology constraints, and optimally selects a target recovery scheme by comprehensively considering rapidity and resilience indicators, thereby significantly improving the resilience of the receiving-end system under secondary faults, enhancing the adaptability and stability of the system, effectively avoiding the risk of system blocking failure or collapse again during the recovery process, and improving the recovery efficiency and reliability.

[0005] In a first aspect, an embodiment of the present application provides a multi-direct-current receiving-end system recovery method under secondary faults, which comprises: generating, for the receiving-end system, an initial recovery scheme that meets all network topology corresponding constraints within a current rolling window according to a preset time step; different network topologies correspond to different constraints; the network topologies include each first network topology in which each secondary fault occurs in the receiving-end system, each second network topology in which a current source is separately set at each converter bus in the receiving-end system, and a third network topology in which a current source equal to the corresponding direct-current transmission power per unit is set at all converter buses in the receiving-end system; For each initial recovery scheme, a recovery index value corresponding to the initial recovery scheme is calculated according to a first difference between a predicted rapidity index value corresponding to the initial recovery scheme and a theoretical maximum value of the rapidity index, and a second difference between a predicted resilience index value corresponding to the initial recovery scheme and a theoretical minimum value of the resilience index; wherein the smaller the predicted resilience index value, the higher the resilience level of the receiving-end system; The initial recovery solution with the smallest recovery index value is determined as the target recovery solution of the receiving system.

[0006] In a possible implementation, the network topology includes a fault layer network topology, a fault layer operating network topology, a decision layer startup network topology, and a decision layer operating network topology; The fault layer network topology and the fault layer operating network topology both include all first network topologies; the decision layer startup network topology includes all second network topologies; and the decision layer operating network topology includes the third network topology; Among them, the first network topology corresponding constraint in the fault layer network topology is used to ensure that the changes in the unit's DC output power and node load comply with the system control constraints after each secondary fault occurs in the receiving system, so as to characterize the steady-state operating state of the receiving system after the secondary fault occurs; the first network topology corresponding constraint in the fault layer operating network topology is used to linearize the nonlinear constraint on the output power of the DC transmission system under the secondary fault, and use the multi-infeed short-circuit ratio as a quantitative indicator to evaluate the safe and stable operation capability of the DC under the secondary fault scenario; the second network topology corresponding constraint in the decision layer startup network topology is used to linearize the nonlinear conditions for DC safe startup and determine whether the DC meets the startup requirements based on the current operating state of the system; the third network topology corresponding constraint in the decision layer operating network topology is used to linearize the nonlinear model caused by the product of DC power and node impedance in the calculation of the multi-infeed short-circuit ratio to meet the response constraint.

[0007] In a possible implementation manner, the second network topology corresponding constraint in the fault layer network topology includes: ; ; ; ; ; ; ; ; in, is the transmission power of DC i in the first network topology s at the kth time step, is the set of generators connected to node i, is the active power output of unit g in the first network topology s at time step k, The kth time step in the first network topology s Middle Line j-i-c The meritorious trend on For the k Time step in the first network topology s Middle Line i-j-c Active power flow on the line j-i-c in j is the first end node of the line, j-i-c in i Number the end node of the line. j-i-c in c is the circuit number of the line, For the k Time step in the first network topology s midpoint i The load, For the k Time step in the first network topology s Medium unit g The 0-1 variable of the startup state, For the crew g Required starting power, N is a collection of nodes, S is a set of first network topologies, L is the line set that does not include the generator grounding branch, For the line i-j-c The reactance, For the k Time step in the first network topology s midpoint i and nodes j The phase angle difference between For the k Time-step route i-j-c 0-1 variable of commissioning status, For the first network topology s Middle Line i-j-c A 0-1 variable indicating whether the system is shut down. is an integer, For the line i-j-c The upper limit of active power flow, For the k Time step unit g The meritorious contribution, For the crew g The upper limit of the downward climbing rate, For the crew g The upper limit of the climbing rate for upward climbing, is the duration corresponding to one time step, is the collection of units, For the k Time step unit g In the first network topology s 0-1 variable of the grid-connected state, is the 0-1 variable of the grid-connected state of the unit at the kth time step, k is the 0-1 variable of the grid-connected state of the unit at the kth time step, g is the 0-1 variable of the grid-connected state of the unit at the kth time step, is the 0-1 variable of the grid-connected state of the unit at the kth time step, k is the 0-1 variable of the grid-connected state of the unit at the kth time step, s is the 0-1 variable of the grid-connected state of the unit at the kth time step, i is the 0-1 variable of the grid-connected state of the unit at the kth time step, is the 0-1 variable of the grid-connected state of the unit at the kth time step, k is the 0-1 variable of the grid-connected state of the unit at the kth time step, i is the 0-1 variable of the grid-connected state of the unit at the kth time step, is the 0-1 variable of the grid-connected state of the unit at the kth time step, k is the 0-1 variable of the grid-connected state of the unit at the kth time step,

[0008] In one possible implementation, the second network topology of the fault layer operating network topology corresponds to constraints including: ; ; ; ; ; ; ; ; wherein, is the transmission power of the DC in the first network topology at the kth time step, k is the transmission power of the DC in the first network topology at the kth time step, s is the current value on the line in the first network topology at the kth time step, i is the current value on the line in the first network topology at the kth time step, is the current value on the line in the first network topology at the kth time step, k is the current value on the line in the first network topology at the kth time step, s is the current value on the line in the first network topology at the kth time step, j-i-c is the current value on the line in the first network topology at the kth time step, j-i-c is the current value on the line in the first network topology at the kth time step, j is the current value on the line in the first network topology at the kth time step, j-i-c is the current value on the line in the first network topology at the kth time step, i is the current value on the line in the first network topology at the kth time step, j-i-c is the current value on the line in the first network topology at the kth time step, c is the current value on the line in the first network topology at the kth time step, is the current value on the line in the first network topology at the kth time step, k is the current value on the line in the first network topology at the kth time step, s is the current value on the line in the first network topology at the kth time step, i-j-c is the current value on the line in the first network topology at the kth time step, is the current value on the line in the first network topology at the kth time step, is the current value on the line in the first network topology at the kth time step, is the current value on the line in the first network topology at the kth time step, is the current value on the line in the first network topology at the kth time step, is the current value on the line in the first network topology at the kth time step, k is the current value on the line in the first network topology at the kth time step,i-j-c 0-1 variable of the in-service state, is an integer, s 0-1 variable of the line i-j-c whether out of service, is an integer, reactance of the line i-j-c is an integer, is an integer, k voltage value of the node s in the first network topology i at the t-th time step, voltage value of the node k in the first network topology s at the t-th time step, j is an integer, minimum starting power of the t-th DC, i rated capacity of the t-th DC, is an integer, i 0-1 variable of the starting state of the DC before and after the t-th time step, k 0-1 variable of the starting state of the DC i in the first network topology at the t-th time step, k 0-1 variable of the starting state of the DC s in the first network topology i at the t-th time step, is an integer, k multi-infeed short-circuit ratio index of the DC s in the first network topology i at the t-th time step, is the minimum short-circuit ratio under the premise of ensuring stable operation of the receiving end system.

[0009] In a possible implementation, the predicted resilience index value corresponding to each initial recovery scheme is calculated by the following formula: ; wherein, is the predicted resilience index value corresponding to the initial recovery scheme, is the resilience index value of the first network topology s at the k-th time step in the recovery process; p is the p-th time step in the preset recovery time domain, that is, the first time step in the current rolling window in the preset recovery time domain; is calculated by the following formula: ; ; ; ; ; ​in, is the high risk function value, is the load loss of the system under the secondary fault scenario w, For expectations, is the set of secondary failure scenarios, is the probability of occurrence of secondary failure scenario w, High-risk markers, is the medium risk function value, is a medium-risk marker factor, is a high-risk urgency factor, is a high-conformity loss cutoff point. It is the low load loss cut-off point.

[0010] In a possible implementation, calculating the recovery index value corresponding to the initial recovery scheme based on a first difference between the predicted rapidity index value corresponding to the initial recovery scheme and a theoretical maximum value of the rapidity index, and a second difference between the predicted toughness index value corresponding to the initial recovery scheme and a theoretical minimum value of the toughness index, includes: Calculating a standardized rapidity index value according to a first difference between the predicted rapidity index value corresponding to the initial recovery plan and a theoretical maximum value of the rapidity index, and a third difference between the theoretical maximum value of the rapidity index and a theoretical minimum value of the rapidity index; Calculating a normalized toughness index value according to a second difference between the predicted toughness index value corresponding to the initial recovery plan and a theoretical minimum value of the toughness index, and a fourth difference between the theoretical maximum value of the toughness index and the theoretical minimum value of the toughness index; A recovery index value corresponding to the initial recovery solution is calculated according to the standardized rapidity index value and the standardized toughness index value.

[0011] In a possible implementation, calculating the recovery index value corresponding to the initial recovery solution according to the standardized rapidity index value and the standardized toughness index value includes: Calculating a first distance between a normalized index point and an optimal index point and a second distance between the normalized index point and a worst index point; The standardized index point refers to a coordinate point composed of the standardized rapidity index value and the standardized toughness index value; the optimal index point refers to a coordinate point composed of the theoretical maximum value of the rapidity index and the theoretical minimum value of the toughness index; the worst index point refers to a coordinate point composed of the theoretical minimum value of the rapidity index and the theoretical maximum value of the toughness index; A recovery index value corresponding to the initial recovery solution is calculated according to the first distance and the second distance.

[0012] In a second aspect, the embodiments of the present application also provide a multi-direct-current receiving-end system recovery device under secondary faults, the device comprising: a generating module configured to generate, for a receiving-end system, an initial recovery scheme that satisfies all network topology corresponding constraints in a preset time step; different network topologies correspond to different constraints; the network topologies include each first network topology in which each secondary fault occurs in the receiving-end system, each second network topology in which a current source is separately set at each converter bus in the receiving-end system, and a third network topology in which a current source equal to a corresponding direct-current transmission power unit value is set at all converter buses in the receiving-end system; a calculating module configured to, for each initial recovery scheme, calculate a recovery index value corresponding to the initial recovery scheme according to a first difference between a predicted rapidity index value corresponding to the initial recovery scheme and a theoretical maximum value of a rapidity index, and a second difference between a predicted resilience index value corresponding to the initial recovery scheme and a theoretical minimum value of a resilience index; wherein the smaller the predicted resilience index value, the higher the resilience level of the receiving-end system; a determining module configured to determine the initial recovery scheme with the smallest recovery index value as a target recovery scheme of the receiving-end system.

[0013] In a possible implementation, the calculating module is specifically configured to calculate the predicted resilience index value corresponding to each initial recovery scheme by the following formula: ; wherein, the predicted resilience index value corresponding to the initial recovery scheme is, the resilience index value under the first network topology s at the kth time step in the recovery process; p is the pth time step in a preset recovery time domain, i.e., the first time step in the current rolling window in the preset recovery time domain; the predicted resilience index value corresponding to the initial recovery scheme is calculated by the following formula: ; ; ; ; ; wherein, the high-risk function value is, the load loss of the system under the secondary fault scenario w is, the expectation is, the set of secondary fault scenarios is, ​a probability of occurrence of a secondary failure scenario w, a high-risk flag factor, a medium-risk function value, a medium-risk flag factor, a high-risk urgency factor, a high-conformity loss split point, a low-load loss split point.

[0014] In a possible implementation, the calculating module is specifically configured to calculate a standardized rapidity index value according to a first difference between a predicted rapidity index value corresponding to the initial recovery scheme and a theoretical maximum value of the rapidity index, and a third difference between the theoretical maximum value of the rapidity index and a theoretical minimum value of the rapidity index; calculate a standardized tenacity index value according to a second difference between a predicted tenacity index value corresponding to the initial recovery scheme and the theoretical minimum value of the tenacity index, and a fourth difference between a theoretical maximum value of the tenacity index and the theoretical minimum value of the tenacity index; and calculate a recovery index value corresponding to the initial recovery scheme according to the standardized rapidity index value and the standardized tenacity index value.

[0015] In a possible implementation, the calculating module is specifically configured to calculate a first distance between a standardized index point and an optimal index point, and a second distance between the standardized index point and a worst index point; the standardized index point refers to a coordinate point composed of the standardized rapidity index value and the standardized tenacity index value; the optimal index point refers to a coordinate point composed of the theoretical maximum value of the rapidity index and the theoretical minimum value of the tenacity index; the worst index point refers to a coordinate point composed of the theoretical minimum value of the rapidity index and the theoretical maximum value of the tenacity index; and calculate a recovery index value corresponding to the initial recovery scheme according to the first distance and the second distance.

[0016] In a third aspect, an electronic device is provided, including a processor, a storage medium, and a bus. The storage medium stores machine readable instructions executable by the processor. When the electronic device is running, the processor communicates with the storage medium through the bus. The processor executes the machine readable instructions to perform the steps of the method for recovery of a multi-direct-current receiving end system under a secondary failure according to any one of the first aspect.

[0017] In a fourth aspect, a computer readable storage medium is provided, which stores a computer program. When the computer program is run by a processor, the steps of the method for recovery of a multi-direct-current receiving end system under a secondary failure according to any one of the first aspect are performed.

[0018] The embodiment of the present application provides a multi-direct-current receiving end system recovery method and device under secondary faults, which comprises the following steps: generating an initial recovery scheme for a receiving end system, which satisfies all network topology corresponding constraints; the network topology comprises each first network topology in which each secondary fault occurs in the receiving end system, each second network topology in which a current source is separately arranged at each converter bus in the receiving end system, and a third network topology in which a current source with a corresponding direct-current transmission power unit value is arranged at all converter buses in the receiving end system; calculating a recovery index value corresponding to the initial recovery scheme according to a first difference value between a predicted rapidity index value corresponding to the initial recovery scheme and a theoretical maximum value of the rapidity index, and a second difference value between a predicted resilience index value corresponding to the initial recovery scheme and a theoretical minimum value of the resilience index; and determining the initial recovery scheme with the minimum recovery index value as a target recovery scheme of the receiving end system. Through the method of the present application, the resilience of the receiving end system under secondary faults is significantly improved, the system adaptability and stability are enhanced, the risk of system lockout failure or collapse again in the recovery process is effectively avoided, and the recovery efficiency and reliability are improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0020] Figure 1 A flow chart of a multi-direct-current receiving end system recovery method under secondary faults provided by the embodiment of the present application is shown; Figure 2 A framework diagram of a rolling recovery provided by the embodiment of the present application is shown; Figure 3 A recovery scheme solving framework based on a 2S+n+1 network topology provided by the embodiment of the present application is shown; Figure 4 A structural schematic diagram of a multi-direct-current receiving end system recovery device under secondary faults provided by the embodiment of the present application is shown; Figure 5 A structural schematic diagram of an electronic device provided by the embodiment of the present application is shown. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. It should be understood that the drawings in the present application serve only the purpose of description and illustration, and do not serve to limit the scope of protection of the present application. In addition, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in the present application show the operations implemented according to some embodiments of the present application. It should be understood that the operations of the flowcharts can not be implemented in sequence, and the steps without logical context relationship can be reversed in sequence or implemented simultaneously. In addition, one or more other operations can be added to the flowcharts or one or more operations can be removed from the flowcharts under the guidance of the content of the present application.

[0022] In addition, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0023] In order to enable those skilled in the art to use the content of the present application, the following implementation is given in combination with a specific application scenario "electric power system and its automation field". For those skilled in the art, the general principles defined herein can be applied to other embodiments and application scenarios without departing from the spirit and scope of the present application. Although the present application is mainly described in relation to the "electric power system and its automation field", it should be understood that this is only an exemplary embodiment.

[0024] It should be noted that the term "comprising" will be used in the embodiments of the present application to indicate the presence of the features declared thereafter, but does not exclude the addition of other features.

[0025] A multi-direct-current receiving-end system recovery method under secondary failure provided by an embodiment of the present application will be described in detail below.

[0026] Referring to Figure 1 FIG. 1 shows a flowchart of a multi-direct-current receiving-end system recovery method under secondary failure provided by an embodiment of the present application, and the exemplary steps of the embodiments of the present application will be described below: S101, generate an initial recovery scheme that satisfies all network topology corresponding constraints in a current rolling window for the receiving-end system according to a preset time step.

[0027] In the embodiment of the present application, the grid reconstruction phase of the power system is a complex process with multiple variables and multiple time periods, and is a continuous dynamic process. On the one hand, the large-scale decision variables limit the solution speed of the model. On the other hand, the grid in the recovery state is at risk of a secondary power outage, and the started generators may also stop running, causing the reconstruction process to not be carried out completely according to the pre-planned plan. Therefore, the embodiment of the present application establishes a rolling recovery plan. Specifically, referring to Figure 2 As shown in the figure, it is a framework diagram of rolling recovery provided by an embodiment of the present application, which divides the recovery process within the preset recovery time domain into multiple windows, and each window contains q Preset time steps , then the scroll window W The time step set contained in 1 is [1, q]. Then, the rolling window W p The time step set is [ p , p+q-1 ]. In each rolling window W p Solve within, but only each rolling window W p The first One The decision of the pth time step (i.e., the pth time step in the preset recovery time domain) is incorporated into the final recovery plan. In other words, the initial recovery plan refers to the local recovery plan for the first preset time step in the current rolling window that satisfies all network topology constraints. It is not necessary for all preset time steps in the initial recovery plan to satisfy all network topology constraints, which saves the recovery speed of the receiving system.

[0028] Among them, different network topologies correspond to different constraints; the network topology includes each first network topology in which each secondary fault occurs in the receiving system, each second network topology after a current source is separately set at each commutation busbar in the receiving system, and a third network topology after a current source equal to the corresponding DC transmission power per unit value is set at all commutation buses in the receiving system. Specifically, the secondary fault scenario refers to the scenario after the secondary fault occurs; the number of first network topologies is the same as the number of secondary fault scenarios, and each first network topology corresponds to one secondary fault scenario; the number of second network topologies is the same as the number of commutation buses in the receiving system, and only one commutation busbar in a second network topology has a current source separately set at it; the number of third network topologies is 1, and all commutation buses in the third network topology have a current source equal to the corresponding DC transmission power per unit value set at them.

[0029] Here, refer to Figure 3As shown, the recovery scheme solving framework based on the 2S+n+1 network topology provided by the embodiment of the application. In the first aspect, in order to depict the recovery risk of the receiving end system under the network structure of the secondary fault scene, s first network topologies can be established for the fault scene set containing s secondary fault scenes. The s first network topologies are completely the same as the network topologies after the secondary fault occurs, the change of the unit direct current output power and the node load conforms to the system control constraint, to represent the steady-state operation state of the receiving end system after the secondary fault occurs, which is called "fault layer network". In addition, in order to represent the bearing capacity of the receiving end system to the direct current under the secondary fault scene, an accompanying network is constructed for each first network topology, to linearize the output power nonlinear constraint of the direct current transmission system under the secondary fault. These network topologies are completely the same as the fault layer network topologies, only injecting a current source with the same size as the direct current transmission power at the direct current input point, which is called "fault layer operation network".

[0030] In the second aspect, the start and operation of the direct current need to meet certain constraints. In order to linearize the safe start constraint of the direct current, it is judged whether the direct current meets the start condition under the current network state of the receiving end system. For the receiving end system containing n direct current feed-ins, n different third network topologies are established by setting current sources at the commutation bus, to realize the linear expression of the respective short-circuit capacity constraint, which is called "decision layer start network". In addition, the safe operation of the direct current should meet the response constraint. For the nonlinear model linearization caused by the product of the direct current power and the node impedance in the multi-feed-in short-circuit ratio calculation, in order to meet the response constraint, only an accompanying network of the network architecture of the current network state of the receiving end system needs to be constructed in the recovery process, which is called "decision layer operation network".

[0031] From the above analysis of the recovery scheme solving framework, for the recovery process of the receiving end system, s fault layer network topologies and s fault operation layer network topologies are constructed, to evaluate the bearing capacity of the receiving end system to the direct current transmission power under the secondary fault and the recovery risk of the receiving end system. At the same time, in order to ensure the safe operation of the receiving end system in the recovery process of the n direct current feed-ins, n decision layer start network topologies and 1 decision layer operation network topology are needed to assist the decision scheme formulation of the direct current recovery time and operation output.

[0032] In summary, the network topologies include the fault layer network topology, the fault layer operation network topology, the decision layer start network topology and the decision layer operation network topology; the fault layer network topology and the fault layer operation network topology both include all the first network topologies; the decision layer start network topology includes all the second network topologies; the decision layer operation network topology includes the third network topology; The first network topology in the fault layer network topology corresponds to constraints for meeting system regulation constraints on unit DC output power and node load changes after each secondary fault occurs in the receiving end system to represent the steady-state operating state of the receiving end system after the secondary fault occurs; the first network topology in the fault layer operating network topology corresponds to constraints for linearizing the nonlinear constraints of the DC power transmission system under secondary faults and using multi-infeed short circuit ratio as a quantitative index to evaluate the safe and stable operation capability of the DC under the secondary fault scenario; the second network topology in the decision layer startup network topology corresponds to constraints for linearizing the nonlinear conditions of DC safe startup and determining whether the DC meets the startup requirements based on the current operating state of the system; and the third network topology in the decision layer operating network topology corresponds to constraints for linearizing the nonlinear model caused by the product of DC power and node impedance in multi-infeed short circuit ratio calculation to meet the response constraints.

[0033] Further, the secondary fault risk assessment in the AC / DC receiving end system recovery. The application assesses the impact of different secondary faults on the receiving end system by quantifying the loss of load. Under the influence of a pre-set secondary fault set, the receiving end system may need to perform load shedding measures to meet a series of safe operating constraints of the system. For a system containing multiple DC feeder lines, the operating state of the DC system and its potential impact on the AC system must be considered when assessing the resilience of the secondary fault set. In particular, during the recovery process, the transmission power of the DC tie line needs to be carefully managed to avoid exceeding the stability boundary of the system, which may trigger a larger-scale power outage event. Therefore, the application proposes a method to adjust the DC transmission power to ensure the stability of the system while minimizing load loss, thereby effectively guiding the recovery process of the receiving end system when facing secondary faults. This method helps to improve the recovery efficiency and reliability of the receiving end system after experiencing faults, reducing the impact on users and power grid operations. Therefore, the application constructs the first network topology corresponding constraints in the fault layer network topology and the first network topology corresponding constraints in the fault layer operating network topology.

[0034] Specifically, the risk of load loss in the receiving system is quantitatively assessed. If a preset line failure (i.e., a secondary failure) occurs during the recovery process of the receiving system, the network flow will transition from the original steady state to the new steady state as the system topology changes. During this transition process, key adjustments include the redistribution of DC transmission power and conventional unit output, as well as the reduction of node load. These adjustments are necessary because secondary failures may force the restored load to be cut off again. This application evaluates the specific impact of different secondary failures on the receiving system by quantifying the amount of load loss. In order to more accurately guide the recovery process, this application proposes a model that associates the resilience measure of the receiving system with the recovery state. The model aims to calculate the expected load loss of the receiving system when a secondary failure occurs and the system operation constraints are met. This quantitative indicator not only helps to evaluate the system's recovery capability, but also has important significance for optimizing recovery strategies and improving the overall resilience of the system. Through this model, recovery measures can be planned and implemented more effectively to reduce the impact of the failure on system operation and speed up recovery. Therefore, the first network topology corresponding constraints in the fault layer network topology include: (1); (2); (3); (4); (5); (6); (7); (8); in, is the transmission power of DC i in the first network topology s at the kth time step, is the set of generators connected to node i, is the active power output of unit g in the first network topology s at time step k, The kth time step in the first network topology s Middle Line j-i-c The meritorious trend on For the k Time step in the first network topology s Middle Line i-j-c Active power flow on the line j-i-c in j is the first end node of the line, j-i-c in i Number the end node of the line. j-i-c in c is the circuit number of the line, For the k Time step in the first network topology s midpoint i The load, For the k Time step in the first network topology s Medium unit g The startup status of the 0-1 variable (1 if the unit is started, otherwise 0), For the crew g Required starting power, N is a collection of nodes, S is a set of first network topologies, L is the line set that does not include the generator grounding branch, For the line i-j-c The reactance, For the k Time step in the first network topology s midpoint i and nodes j The phase angle difference between For the k Time-step route i-j-c A 0-1 variable indicating the operational status (1 if the line is operational, 0 otherwise), For the first network topology s Middle Line i-j-c A 0-1 variable indicating whether the system is shut down (1 if shut down, 0 otherwise). is an integer, For the line i-j-c The upper limit of active power flow, For the k Time step unit g The meritorious contribution, For the crew g The upper limit of the downward climbing rate, For the crew g The upper limit of the climbing rate for upward climbing, is the duration corresponding to one time step, is the collection of units, For the k Time step unit g In the first network topology s 0-1 variable indicating the grid connection status (1 if connected to the grid, 0 otherwise), For the k Time step unit g 0-1 variable of the grid connection status (1 if connected to the grid, 0 otherwise), For the k Time step in the first network topology s midpoint ia 0-1 variable whether load shedding (1 if load shedding, otherwise 0), the load amount of the first network topology s at the nth time step, k the load amount of the first network topology s at the nth time step, i the load amount of the first network topology s at the nth time step, the total load loss amount of the receiving end system in the first network topology s at the nth time step. k It should be noted that the parameters without the s superscript correspond to the parameter values in the normal operation state, and the parameters with the s superscript correspond to the parameter values in the first network topology (corresponding to the secondary fault scenario).

[0035] s Here, formula (1) is the power balance constraint of the node in the first network topology s. Formula (2) and formula (3) are the active power flow constraints of the line in the first network topology s, which ensures that the active power flow is 0 when the line is not restored and faulted. Formula (4) is the phase angle difference constraint of the node in the first network topology s. Formula (5) is the upper and lower limit constraint of the unit output adjustment. Formula (6) indicates that the online unit in the first network topology s can be tripped. Formula (7) and formula (8) are the load shedding constraint in the first network topology s and the total load loss amount of the receiving end system.

[0036] s

[0037] ​​​Specifically, the receiving system's DC support capability under secondary faults is modeled. During the grid restoration process, the occurrence of secondary faults may weaken the strength of the system grid, thereby reducing the AC grid's ability to support the stable operation of the DC system. This situation may lead to a reduction in DC transmission power or even a shutdown. Therefore, for hybrid power systems containing DC feed-in, when evaluating secondary fault scenarios, it is necessary to consider whether the DC output power meets the safe operation conditions. For a receiving grid containing n DC feed-ins, in the sth secondary fault scenario, this application constructs a companion grid model that is completely consistent with the topology of the secondary fault scenario. In this model, only the corresponding DC transmission power is injected into the nodes where each DC feed-in is located, and the current sources of other nodes are set to zero. The purpose of constructing this companion grid model is to evaluate the safe and stable operation of the DC system through the multi-feed short-circuit ratio when a secondary fault occurs. That is, for each secondary fault scenario, this application constructs a corresponding first network topology s. This type of network topology helps accurately assess the impact of reduced grid strength on the DC system's ability to support stable operation if a secondary fault occurs during the recovery process, and adjust the DC output power accordingly to ensure the safe operation of the DC system. This approach can more effectively guide the grid's recovery process and reduce the impact of secondary faults on grid stability and reliability. Based on the above analysis and modeling ideas, the following model can be obtained to evaluate the receiving-end AC system's ability to withstand DC transmission power when a predicted fault scenario occurs during the recovery process. That is, the corresponding constraints of the first network topology in the fault layer operating network topology include: (9); (10); (11); (12); (13); (14); (15); (16); in, For the k Time step in the first network topology s Medium DC i The transmission power, For the k Time step in the first network topology s Middle Line j-i-c The current value on the line j-i-c in j is the first end node of the line,j-i-c i is the end node number of the line, the line j-i-c c is the loop number of the line, is the first k time step on the line s in the first network topology, i-j-c is the current value on the line in the first network topology, is the set of nodes where the DC is located, is the set of lines including the generator grounding branch, is the set of nodes, is the first k time step on the line i- j-c is the 0-1 variable of the operation state, is the 0-1 variable of whether the line s is out of operation in the first network topology, i-j-c is an integer, is the reactance of the line i-j-c is the voltage value of the node in the first network topology k at the first s time step, i is the voltage value of the node in the first network topology k at the first s time step, j is the minimum starting power of the DC i is the rated capacity of the DC i is the 0-1 variable of the start state of the DC k at the first i time step (1 if the DC is started, otherwise 0), is the 0-1 variable of the start state of the DC k s in the first network topology i at the first time step (1 if the DC is started, otherwise 0), k is the multi-infeed short-circuit ratio index of the DC s i in the first network topology at the first

[0038] ​​​​​​​​Here, equation (9) is the KCL law of the DC node, which ensures that each DC node injects a current source of the size of the DC transmission power. Equation (10) is the KCL law of the remaining nodes, that is, the current source of the node is set to 0. Equations (11) and (12) are the ohm laws of the lines, which ensure that there is only a current flowing through the line when the line is restored and not faulty. Equation (13) is the voltage constraint of each node, which ensures that only when there is transmission power in a certain DC start, there is a current source injected in the first network topology, and then the voltage value of each node is non-negative. Equation (14) indicates that if the DC can still operate normally under the fault scenario, its transmission power should meet the upper and lower limit constraints. Equation (15) indicates that the started DC may also be blocked due to the fault, and equation (16) is the multi-infeed short-circuit ratio constraint of each return DC under the secondary fault scenario.

[0039] Further, a multi-infeed DC receiving-end system network reconfiguration optimization model considering secondary fault impact is considered. The task of network reconfiguration decision aims to develop a recovery scheme for the target backbone network of the receiving-end system. This scheme focuses on achieving the rapid start of the main unit and the efficient reconstruction of the system network, and the key problems involved include: (1) unit start sequence optimization: determine the optimal unit start sequence to speed up the recovery of the power grid; (2) power transmission path optimization: select the most efficient power transmission route to improve the operation efficiency of the power grid; (3) target network structure determination: determine the optimal structure of the recovered power grid to ensure the stability and reliability of the power grid. In particular, for a receiving-end system containing multiple DC infeed lines, this application emphasizes the timely start of the DC system during the recovery process to promote the acceleration of the recovery process. In addition, this application also fully utilizes the regulation potential of the power grid structure for DC power enhancement to enhance the recovery capability of the system. In the model construction, this application comprehensively considers the key safety constraints of the DC system participating in the recovery process and the system resilience measure constraints under the secondary fault condition. Such comprehensive consideration ensures that while pursuing rapid recovery, the proposed decision scheme is not only feasible, but also has sufficient robustness to cope with possible secondary fault risks. Therefore, this application carries out linear modeling of the stable operation of multi-infeed DC, and constructs a network reconfiguration optimization model considering secondary faults.

[0040] Here, the multi-infeed DC system is linearized and modeled. In the initial stage of power system restoration, the strength of the AC system is relatively weak. In order to balance the reactive power generated by the DC transmission system, the extinction angle of the inverter station is usually reduced. However, when the extinction angle is reduced to a certain critical value, it may cause the problem of commutation failure. Given that the network of the AC system in the initial stage of restoration is relatively fragile and its ability to resist external shocks is limited, the principle to be followed in order to ensure the safety and stability of the entire power grid is to minimize the active power impact on the AC system and promote the reactive power balance of the system. Based on this principle, appropriate starting mode and control strategy should be selected for the DC system. In order to reduce the reactive power generated during DC operation, the method commonly adopted is to increase the trigger angle, thereby absorbing more reactive power. Therefore, step-down starting is a common practice. At the same time, considering the requirements of the DC system itself, the minimum current during starting is usually set to 10% of the rated current. According to the simulation results, under the condition of minimum current, 70% step-down starting can achieve the best effect. During the starting process of the DC system, the transient power frequency overvoltage needs to be strictly controlled, which generally should not exceed 1.4 times of the rated value, while the steady-state power frequency voltage should not exceed 1.1 times of the rated value. When the inverter station starts, it usually needs to put in two sets of filters and adopt the control strategy of constant current on the rectifier side and constant voltage on the inverter side, in order to ensure the smooth starting and safe operation of the DC system. Therefore, the application constructs the second network topology corresponding constraint in the decision layer starting network topology and the third network topology corresponding constraint in the decision layer running network topology.

[0041] Specifically, the second network topology corresponding constraint in the decision layer starting network topology is used for safety constraint during DC starting, which mainly includes two aspects: system frequency regulation capability constraint and network voltage support capability constraint.

[0042] Specifically, the system frequency regulation capability constraint. At the moment of DC starting, the governor has not started to act, at which time the mechanical rotational inertia of the AC system maintains the frequency stability. For simplicity of analysis, n generators are combined into an equivalent machine, and the inertia constant of the equivalent machine is the sum of the inertia time constants of each generator calculated to the same reference power . Therefore, the system frequency regulation capability constraint includes: (17); (18); (19); wherein, n is the number of units, is the inertia time constant of unit g, is the grid-connected state of unit g, is the installed capacity of unit g, For DC i Transient frequency deviation at startup, is the minimum power per unit value when DC i starts, is the receiving system frequency (take 50Hz), is the equivalent inertia time constant of the system, is the duration of unbalanced power action.

[0043] After a frequency modulation action is completed, the frequency fluctuation is mainly reduced by the speed regulator, and the frequency deviation is estimated using the following formula.

[0044] (20); in, is the rated capacity of unit g, is the transient frequency response value of unit g, Take 0.5Hz, is the rated power of the i-th DC circuit.

[0045] Here, since 10% rated voltage and 70% reduced voltage starting is used, the injected power at starting is Frequency regulation capacity is solely dependent on the generator set; the commissioning or decommissioning of lines does not affect the equation. Frequency regulation capacity only changes when new generators are connected to the grid. Furthermore, as more generators are connected to the grid, the system's frequency regulation capacity increases. Therefore, connecting more generators to the grid can increase system strength and facilitate DC startup.

[0046] Specifically, the grid voltage support capacity constraint. Short-circuit capacity is an important indicator to measure the voltage support capacity of the AC grid. According to the reactive power of the DC starting injection system and the short-circuit capacity of the commutation bus, the voltage offset of the bus where DC i is located at the kth time step can be calculated. Further combining the intrinsic relationship between short-circuit capacity and node self-impedance elements, the short-circuit capacity constraint can be transformed into an upper limit constraint on the commutation bus node self-impedance.

[0047] (twenty one); (twenty two); (twenty three); in, For the i The reactive power injected into the receiving system by DC startup is is the short-circuit capacity index of the commutation bus where DC i is located at the kth time step; is the rated voltage of the commutation bus; is the per-unit self-impedance value of the commutation bus where DC i is located at the kth time step; the reactive power available for the single group filter of the inverter station at the DC node i, the upper limit of the self-impedance of the i-th DC safe start node; the base capacity of the system.

[0048] According to formula (23), the short-circuit capacity constraint can be converted into a node self-impedance constraint, and therefore the key problem is how to realize the explicit expression of the impedance element in the system restoration process. The research on the linear relationship between the node impedance and the branch state is that, for an n-feed-in receiving end system, an accompanying network is constructed, which has the same network topology as the n topologies in the restoration process. Since the network is constructed to ensure the safe and stable start of the DC, it can be called the "start layer accompanying network".

[0049] (24); (25); (26); (27); (28); (29); In the formula, is the 0-1 variable of the charged state of the bus where the DC i is located at the k time step (charged is 1, otherwise is 0); is the current value on the line j-i-c in the second network topology d about the start of the DC i at the k time step, is the current value on the line i-j-c in the second network topology d about the start of the DC i at the k time step, is the voltage value of node i in the second network topology d about the start of the DC i at the k time step, is the voltage value of node j in the second network topology d about the start of the DC j at the k time step.

[0050] Specifically, the DC safe operation constraint (corresponding constraint of the third network topology). In the operation process, the coupling between the AC and DC systems depends largely on the relative size of the two system capacities, i.e., the short-circuit ratio. For a multi-feed-in system, if the electrical distance between DC landing points is small, the strength of the AC system is poor, etc., which will lead to commutation failure. According to the standard of IEEE, the short-circuit ratio greater than 3 is selected as the constraint of the DC operation. The linearization model of the multi-feed-in short-circuit ratio constraint for the stable operation of the DC in the normal restoration process is similar to formula (9)-(16), and the main difference is that the state of the line is only determined by the restoration operation, and does not involve the preset secondary fault scenario.

[0051] Further, a network framework reconstruction optimization model considering secondary faults is considered. Specifically, it is described from two aspects of objective function and basic constraint condition: Firstly, the objective function. In the recovery process, the rapidity index of recovery should be considered first. Generally, the optimization objective of power system recovery is to maximize the power generation of the system. For the network framework reconstruction optimization with the participation of DC, the output of conventional units and the power support of DC need to be considered. Secondly, the robustness index of recovery should also be considered, that is, the recovery scheme is optimized before the occurrence of the secondary fault set constructed, so as to improve the system resilience in the recovery process. Therefore, the double optimization objectives are constructed as follows: (30); (31); In the formula, is the objective function of the rapidity index in the system recovery process, and represents the cumulative recovery power of the receiving end system in the current rolling window. is the robustness objective function in the recovery process of the receiving end system, and is specifically based on the modeling method of PMRM to represent the resilience level of the receiving end system. is the active power output of the unit g at the k-th time step in the normal recovery process, is the actual transmission power of the DC i at the k-th time step in the normal recovery process, is the resilience index value under the first network topology s at the k-th time step in the recovery process, is the system state at the k-th time step (k=p) in the rolling window Wp, and p is the p-th time step in the preset recovery time domain, that is, the first time step in the current rolling window in the preset recovery time domain.

[0052] Here, the modeling method based on PMRM represents the resilience level of the receiving end system. In the risk assessment research of power system, the fault with high probability and low loss has high probability but small loss to the system, and the fault with low probability and high loss has low probability but serious consequences and is easy to cause chain accidents, which is the object of strict prevention and control by power system operators. PMRM is a risk analysis method, which divides the loss into several different risk ranges and highlights the influence of high loss events by conditional expectation. This method distinguishes between events with high occurrence probability and low serious consequences and events with low occurrence probability and high serious consequences. Therefore, the PMRM is introduced in this application to analyze the risk and resilience of the system, and the influence of medium and high loss faults is reduced by optimizing the network framework reconstruction recovery scheme, so as to ensure the stable recovery of the system.

[0053] In PMRM, the exceeding probability e x is often used to measure the sum of the probabilities of all events whose losses are greater than a given value p . The loss segmentation point , The load loss of the system is divided into three different risk intervals: [0, Three conditional risk functions and are introduced to represent the high, medium and low loss conditional risks, respectively, and their calculation formulas are as follows: (32) (33) (34) (35) (36) (37) (38) wherein is the high risk function value, is the load loss of the system under the secondary failure scenario w, is the expectation, is the set of secondary failure scenarios, is the occurrence probability of the secondary failure scenario w, is the high risk indicator factor, is the medium risk function value, is the medium risk indicator factor, is the high risk urgency factor, is the high consistent loss split point, is the low load loss split point.

[0054] During the system recovery process, a smaller failure loss may be within the system's bearing range, while a larger degree of loss may cause the system in a low redundancy recovery state to collapse again, greatly delaying the system recovery process. To highlight the importance of high-risk secondary failures, a high-risk urgency factor λ is introduced, and different severity of failures are treated differently. The resilience level indicator R is shown in formula (36), The smaller the value of R is, the higher the resilience level of the system is.

[0055] In the second aspect, the basic constraint condition. In the system network reconstruction process participated by the DC, in addition to the certain safety constraints on the start and output power of the DC tie line, the AC receiving end system itself should also meet certain constraint conditions, mainly including unit start and climbing constraint, power flow constraint, connectivity constraint, etc.​​​​​​

[0056] (1) Output power constraints of DC and conventional units. During the system recovery process with DC participation, if the DC transmission power is adjusted or a predicted failure occurs, the flexible ramping capability of the conventional units will ensure the continuous power supply of the load. Therefore, a flexible ramping model of the units is constructed, and the unit output function is discretized.

[0057] (39); (40); (41); in, is a 0-1 variable of the grid-connected state of unit g at the kth time step, is the 0-1 variable of the steady state of unit g at the kth time step, is the minimum technical output of unit g, is the rated power of unit g, is the starting time of unit g, is the time required for unit g to start up and connect to the grid, is the total duration of the system recovery process, is the k-1th time step unit g The meritorious contribution.

[0058] Here, Equation (39) ensures that the unit output is 0 before grid connection and ramps up to the minimum technical output at the maximum ramp rate after grid connection. Equation (40) indicates that the ramp rate can be flexibly adjusted after the unit stabilizes combustion. Equation (41) is the upper and lower limit constraints for the output adjustment after the unit stabilizes combustion. The linearization process of the intermediate variables is shown in the Appendix.

[0059] In addition, unlike traditional units that require ramping, DC transmission has the advantage of fast and reliable regulation. Therefore, compared with traditional units, the DC ramping time can be ignored, and the DC transmission power can be approximated as a step function. The linearized model of the DC transmission power function can be obtained as follows: (42); (43); (44); in, For the i The node self-impedance upper limit for DC safety startup, For DC i The per-unit value of the node self-impedance of the commutation bus, No. k Time step in the first network topology s Medium DC i The transmission power, For the first i The minimum starting power of the DC return, For the first i The rated capacity of the DC return.

[0060] Here, equation (42) and equation (43) represent the DC starting constraint, and equation (44) represents the upper and lower limit constraints of the DC transmission power.

[0061] (2) The power flow constraint: (45); (46); (47); (48).

[0062] (3) The reactive power self-excitation constraint. In the early stage of system restoration, the amount of load recovery is small, and the operation of no-load lines will generate charging reactive power, which needs to be absorbed by the grid-connected unit to maintain voltage stability. Therefore, the reactive power and self-excitation constraints are: (49) In the formula, is the maximum reactive power that the unit g can absorb when operating in phase; is the charging capacity of the line i-j-c. (4) System connectivity constraint. During the system restoration process, it is necessary to ensure that the restored parts are connected to each other. In this paper, based on the network flow theory, the connectivity constraint of the network is established by taking the black-start unit node as the source point and the remaining restored nodes as the sink point.

[0063] (5) Other constraints During the restoration process, the operation sequence of lines and nodes needs to be considered. Only when any line connected to the node is operated will the node be electrified. The line and node relationship constraints are established. In a time step, the number of operations that the operator can complete is limited, and the difficulty of closing the loop operation is high, the risk is high, and it takes a long time. The line operation number constraint is established; considering that in the system restoration, the restored lines and loads will not be actively shut down in the next time step, the time step boundary constraint is established.

[0064] Further, the method needs to construct a preset secondary fault scenario set before S101. After a very regular event occurs (such as extreme weather, deliberate attack, etc.), secondary faults often occur. Since power transmission elements are widely distributed and are often exposed to the external environment, the probability of being affected by secondary faults is much higher than in normal conditions. In addition, during the recovery process, the working conditions of the system are very different from the normal state, and the network topology, system power flow changes frequently, the parameters of the control and protection devices do not match and are not coordinated, or the operation of the operating personnel is not coordinated, which may cause the line and other elements to trip again. For the above reasons, the present application focuses on the line breakage fault and studies the multi-infeed DC receiving-end system reconstruction decision optimization under the influence of secondary faults. Take typhoon disaster as an example to construct a preset secondary fault set: on the one hand, the continuous damage of typhoon disaster to the conductor and tower is accumulated, and on the other hand, the soil structure near the transmission tower will be softened under the soaking action of heavy rain. Even if some transmission lines and towers survive the typhoon, there is still a potential risk of failure during the subsequent recovery process due to the influence of secondary disasters.

[0065] S102, for each initial recovery scheme, calculating a recovery index value corresponding to the initial recovery scheme according to a first difference between a predicted rapidity index value corresponding to the initial recovery scheme and a theoretical maximum value of the rapidity index, and a second difference between the predicted resilience index value corresponding to the initial recovery scheme and a theoretical minimum value of the resilience index; wherein the smaller the predicted resilience index value, the higher the resilience level of the receiving-end system.

[0066] In the embodiment of the present application, the predicted rapidity index value (i.e. the value of the objective function of the rapidity index) is calculated by formula (30). The predicted resilience index value (i.e. the value of ) is calculated by formula (31)-(36).

[0067] Specifically, the recovery index value corresponding to the initial recovery scheme is calculated by the following steps: Step one, calculating a standardized rapidity index value according to the first difference between the predicted rapidity index value corresponding to the initial recovery scheme and the theoretical maximum value of the rapidity index, and the third difference between the theoretical maximum value of the rapidity index and the theoretical minimum value of the rapidity index.

[0068] In the embodiment of the present application, the ratio of the first difference to the second difference is taken as the standardized rapidity index value.

[0069] Step two, calculating a standardized resilience index value according to the second difference between the predicted resilience index value corresponding to the initial recovery scheme and the theoretical minimum value of the resilience index, and the fourth difference between the theoretical maximum value of the resilience index and the theoretical minimum value of the resilience index.

[0070] In the embodiment of the present application, the ratio of the second difference to the fourth difference is used as the normalized toughness index value.

[0071] Step 3: Calculate the recovery index value corresponding to the initial recovery plan based on the standardized rapidity index value and the standardized toughness index value.

[0072] i. Calculating a first distance between the normalized index point and the optimal index point and a second distance between the normalized index point and the worst index point; Among them, the standardized index point refers to the coordinate point composed of the standardized rapidity index value and the standardized toughness index value; the optimal index point refers to the coordinate point composed of the theoretical maximum value of the rapidity index and the theoretical minimum value of the toughness index; the worst index point refers to the coordinate point composed of the theoretical minimum value of the rapidity index and the theoretical maximum value of the toughness index.

[0073] Specifically, the first distance is calculated by the following formula: : ; in, is the weight value of the i-th standardized index value (including the standardized rapidity index value and the standardized toughness index value), is the ith standardized index value.

[0074] Specifically, the first distance is calculated by the following formula: : .

[0075] ii. Calculate a recovery index value corresponding to the initial recovery solution based on the first distance and the second distance.

[0076] In the embodiment of the present application, the first distance and the second distance are substituted into the following formula to obtain the recovery index value corresponding to the initial recovery solution: .

[0077] .

[0078] S103: Determine the initial recovery solution with the smallest recovery index value as the target recovery solution of the receiving system.

[0079] It should be noted that the goal f P The utilization of the cumulative output of the units takes into account the rapidity of system recovery, so its theoretical maximum value is determined by the traditional recovery scheme that only considers the rapidity of recovery. The theoretical minimum value is that the system does not take any recovery operation, that is, during the recovery window, the generator maintains the output state before the recovery decision.

[0080] In addition, the goal fR The resilience index is used to evaluate the recovery risk, and the greater the value represents the higher the recovery risk of the system, and therefore the theoretical maximum value should also be determined by the traditional recovery scheme considering only the recovery speed. The corresponding time step in the traditional recovery state is evaluated, and the maximum loss of load under the preset secondary fault set is set as the theoretical maximum value of the time step, and the theoretical minimum value is set to 0, which is considered to eliminate the risk of loss of load under the preset secondary fault set through the formulation of the recovery decision.

[0081] Here, the present application introduces the target positive and negative ideal point to construct the relative target proximity optimization model, and based on this, the multi-objective problem is transformed into the target problem. Considering the weight factor, the weighted distance between the standardized target vector of the feasible solution and the standardized vector between the ideal point and the negative ideal point is defined to objectively and efficiently handle the relationship between the recovery speed and the robustness of the system.

[0082] By the method, the recovery resilience of the receiving end system under the secondary fault is significantly improved, the adaptability and stability of the system are enhanced, the risk of system lockout failure or collapse again in the recovery process is effectively avoided, and the recovery efficiency and reliability are improved.

[0083] Based on the same inventive concept, the present application embodiment also provides a multi-direct current receiving end system recovery device under secondary fault corresponding to the multi-direct current receiving end system recovery method under secondary fault. Since the principle of solving problems in the device of the present application embodiment is similar to the above-mentioned multi-direct current receiving end system recovery method under secondary fault in the present application embodiment, the implementation of the device can be referred to the implementation of the method, and the repeated parts will not be described here.

[0084] Referring to Figure 4 Fig. 1 is a schematic diagram of a multi-direct current receiving end system recovery device under secondary fault provided by an embodiment of the present application, the device comprises: The generating module 401 is configured to generate, for the receiving end system, an initial recovery scheme satisfying all network topology corresponding constraints in a current rolling window according to a preset time step; different network topologies correspond to different constraints; the network topologies include a first network topology constructed under a current network state of the receiving end system, each second network topology under each secondary fault, and each third network topology after setting a current source at each converter bus in the receiving end system; The computing module 402 is configured to, for each initial recovery scheme, calculate a recovery index value corresponding to the initial recovery scheme according to a first difference between a predicted speed index value corresponding to the initial recovery scheme and a theoretical maximum value of the speed index, and a second difference between a predicted resilience index value corresponding to the initial recovery scheme and a theoretical minimum value of the resilience index; wherein the smaller the predicted resilience index value, the higher the resilience level of the receiving end system. The determination module 403 is configured to determine the initial recovery solution with the smallest recovery index value as the target recovery solution of the receiving system.

[0085] This device significantly improves the recovery resilience of the receiving system under secondary faults, enhances the system adaptability and stability, effectively avoids the risk of system lockout failure or re-collapse during the recovery process, and improves recovery efficiency and reliability.

[0086] like Figure 5 As shown, an electronic device 500 provided in an embodiment of the present application includes: a processor 501, a memory 502 and a bus, wherein the memory 502 stores machine-readable instructions executable by the processor 501. When the electronic device is running, the processor 501 communicates with the memory 502 via the bus, and the processor 501 executes the machine-readable instructions to perform the steps of the multi-DC receiving end system recovery method under the secondary fault as described above.

[0087] Specifically, the memory 502 and processor 501 can be general-purpose memories and processors, which are not specifically limited here. When the processor 501 runs the computer program stored in the memory 502, it can execute the multi-DC receiving system recovery method under the secondary fault.

[0088] Corresponding to the above-mentioned method for restoring a multi-DC receiving-end system under a secondary fault, an embodiment of the present application further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned method for restoring a multi-DC receiving-end system under a secondary fault are executed.

[0089] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the system and device described above can refer to the corresponding process in the method embodiment, and will not be repeated in this application. In the several embodiments provided in this application, it should be understood that the disclosed system, device and method can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the modules is only a logical function division. There may be other division methods in actual implementation. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0090] The modules described as separate components may or may not be physically separate, and the components displayed as modules may or may not be physical units, i.e., may be located in one place, or may be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0091] In addition, the functional units in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit.

[0092] If the functions are realized in the form of software functional units and sold or used as independent products, they can be stored in a non-volatile computer readable storage medium executable by a processor. Based on this understanding, the technical solutions of the present application or the part of the present application that essentially contributes to the prior art or the part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the information processing method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, ROM, RAM, magnetic disk or optical disk, and various program code storage media.

[0093] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for restoring a multi-DC receiving-end system under a secondary fault, characterized in that: The method comprises: generating, for the receiving system, an initial restoration plan satisfying corresponding constraints of all network topologies within a current rolling window according to a preset time step; different network topologies corresponding to different constraints; the network topologies including first network topologies in which respective secondary faults occur in the receiving system, second network topologies in which current sources are individually provided at respective commutation buses in the receiving system, and third network topologies in which current sources equal to per-unit values ​​of corresponding direct current transmission powers are provided at all commutation buses in the receiving system; For each initial recovery plan, a recovery index value corresponding to the initial recovery plan is calculated based on a first difference between a predicted rapidity index value corresponding to the initial recovery plan and a theoretical maximum value of the rapidity index, and a second difference between a predicted resilience index value corresponding to the initial recovery plan and a theoretical minimum value of the resilience index; wherein the smaller the predicted resilience index value, the higher the resilience level of the receiving system; The initial recovery solution with the smallest recovery index value is determined as the target recovery solution of the receiving system.

2. The method for restoring a multi-DC receiving-end system under a secondary fault according to claim 1, characterized in that: The network topology includes a fault layer network topology, a fault layer operation network topology, a decision layer startup network topology and a decision layer operation network topology; The fault layer network topology and the fault layer operating network topology both include all first network topologies; the decision layer startup network topology includes all second network topologies; and the decision layer operating network topology includes the third network topology; Among them, the first network topology corresponding constraint in the fault layer network topology is used to ensure that the changes in the unit's DC output power and node load comply with the system control constraints after each secondary fault occurs in the receiving system, so as to characterize the steady-state operating state of the receiving system after the secondary fault occurs; the first network topology corresponding constraint in the fault layer operating network topology is used to linearize the nonlinear constraint of the DC transmission system's output power under secondary faults, and use the multi-infeed short-circuit ratio as a quantitative indicator to evaluate the safe and stable operation capability of the DC under secondary fault scenarios; the second network topology corresponding constraint in the decision layer startup network topology is used to linearize the nonlinear conditions for DC safe startup, and determine whether the DC meets the startup requirements based on the current operating state of the system; the third network topology corresponding constraint in the decision layer operating network topology is used to linearize the nonlinear model caused by the product of DC power and node impedance in the calculation of the multi-infeed short-circuit ratio, so as to meet the response constraint.

3. The method for restoring a multi-DC receiving-end system under a secondary fault according to claim 2, characterized in that: The first network topology in the fault layer network topology corresponds to a constraint including: ； ； ； ； ； ； ； ； in, is the transmission power of DC i in the first network topology s at the kth time step, is the set of generators connected to node i, is the active power output of unit g in the first network topology s at time step k, The kth time step in the first network topology s Middle Line jic The meritorious trend on For the k Time step in the first network topology s Middle Line ijc Active power flow on the line jic in j is the first end node of the line, jic in i Number the end node of the line. jic in c is the circuit number of the line, For the k Time step in the first network topology s midpoint i The load, For the k Time step in the first network topology s Medium unit g A 0-1 variable for the startup state, For the crew g Required starting power, N is a collection of nodes, S is a set of first network topologies, L is the line set that does not include the generator grounding branch, For the line ijc The reactance, For the k Time step in the first network topology s midpoint i and nodes j The phase angle difference between For the k Time-step route ijc 0-1 variable of commissioning status, For the first network topology s Middle Line ijc A 0-1 variable indicating whether the system is shut down. is an integer, For the line ijc The upper limit of active power flow, For the k Time step unit g The meritorious contribution, For the crew g The upper limit of the downward climbing rate, For the crew g The upper limit of the climbing rate for upward climbing, is the duration corresponding to one time step, For the collection of units, For the k Time step unit g In the first network topology s 0-1 variable of the grid connection status, For the k Time step unit g 0-1 variable of the grid connection status, For the k Time step in the first network topology s midpoint i 0-1 variable to indicate whether to cut the load. For the k Time step node i The load, For the k The total load loss of the receiving system in the first network topology s at the time step.

4. The method for restoring a multi-DC receiving-end system under a secondary fault according to claim 2, characterized in that: The first network topology corresponding constraint in the fault layer operation network topology includes: ； ； ； ； ； ； ； ； in, For the k Time step in the first network topology s Medium DC i The transmission power, For the k Time step in the first network topology s Middle Line jic The current value on the line jic in j is the first end node of the line, jic in i Number the end node of the line. jic in c is the circuit number of the line, For the k Time step in the first network topology s Middle Line ijc The current value on is the node set where the DC is located, is a set of first network topologies, is the set of lines including the generator grounding branch, is a collection of nodes, For the k Time-step route ijc 0-1 variable of commissioning status, For the first network topology s Middle Line ijc A 0-1 variable indicating whether the system is shut down. is an integer, For the line ijc The reactance, For the k Time step in the first network topology s midpoint i The voltage value, For the k Time step in the first network topology s midpoint j The voltage value, For the i Minimum starting power of DC back to For the i Rated capacity of DC backhaul, No. k Time-step DC i 0-1 variables for the start-up state before and after, For the k Time step in the first network topology s Medium DC i 0-1 variables for the start-up state before and after, For the k Time step in the first network topology s Medium DC i The multi-infeed short-circuit ratio indicator, To ensure the minimum short-circuit ratio under the premise of stable operation of the receiving system.

5. The method for restoring a multi-DC receiving-end system under a secondary fault according to claim 1, characterized in that: The predicted resilience index value corresponding to each initial recovery plan is calculated using the following formula: ； in, is the predicted resilience index value corresponding to the initial recovery plan, is the resilience index value of the first network topology s at the kth time step in the recovery process; p is the pth time step in the preset recovery time domain, that is, the first time step in the current rolling window in the preset recovery time domain; Calculated by the following formula : ； ； ； ； ； in, is the high risk function value, is the load loss of the system under the secondary fault scenario w, For expectations, is the set of secondary failure scenarios, is the probability of occurrence of secondary failure scenario w, High-risk markers, is the medium risk function value, is a medium-risk marker factor, is a high-risk urgency factor, is a high-conformity loss cutoff point. It is the low load loss cut-off point.

6. The method for restoring a multi-DC receiving-end system under a secondary fault according to claim 1, characterized in that: Calculating the recovery index value corresponding to the initial recovery scheme according to a first difference between the predicted rapidity index value corresponding to the initial recovery scheme and the theoretical maximum value of the rapidity index and a second difference between the predicted toughness index value corresponding to the initial recovery scheme and the theoretical minimum value of the toughness index includes: Calculating a standardized rapidity index value according to a first difference between the predicted rapidity index value corresponding to the initial recovery plan and a theoretical maximum value of the rapidity index, and a third difference between the theoretical maximum value of the rapidity index and a theoretical minimum value of the rapidity index; Calculating a normalized toughness index value according to a second difference between the predicted toughness index value corresponding to the initial recovery plan and a theoretical minimum value of the toughness index, and a fourth difference between the theoretical maximum value of the toughness index and the theoretical minimum value of the toughness index; A recovery index value corresponding to the initial recovery solution is calculated according to the standardized rapidity index value and the standardized toughness index value.

7. The method for restoring a multi-DC receiving-end system under a secondary fault according to claim 6, characterized in that: The calculating, according to the standardized rapidity index value and the standardized toughness index value, a recovery index value corresponding to the initial recovery solution includes: Calculating a first distance between a normalized index point and an optimal index point and a second distance between the normalized index point and a worst index point; The standardized index point refers to a coordinate point composed of the standardized rapidity index value and the standardized toughness index value; the optimal index point refers to a coordinate point composed of the theoretical maximum value of the rapidity index and the theoretical minimum value of the toughness index; the worst index point refers to a coordinate point composed of the theoretical minimum value of the rapidity index and the theoretical maximum value of the toughness index; A recovery index value corresponding to the initial recovery solution is calculated according to the first distance and the second distance.

8. A multi-DC receiving-end system restoration device under secondary fault, characterized in that: The device comprises: A generation module is configured to generate, for the receiving system, an initial restoration plan that satisfies constraints corresponding to all network topologies within a current rolling window according to a preset time step; different network topologies correspond to different constraints; the network topologies include first network topologies in which respective secondary faults occur in the receiving system, second network topologies in which current sources are individually provided at respective commutation buses in the receiving system, and third network topologies in which current sources equal to the per-unit values ​​of the corresponding DC transmission powers are provided at all commutation buses in the receiving system; a calculation module configured to calculate, for each initial recovery plan, a recovery index value corresponding to the initial recovery plan based on a first difference between a predicted rapidity index value corresponding to the initial recovery plan and a theoretical maximum value of the rapidity index, and a second difference between a predicted resilience index value corresponding to the initial recovery plan and a theoretical minimum value of the resilience index; wherein the smaller the predicted resilience index value, the higher the resilience level of the receiving system; The determination module is configured to determine the initial recovery solution with the smallest recovery index value as the target recovery solution of the receiving system.

9. An electronic device, characterized in that: include: A processor, a storage medium, and a bus, wherein the storage medium stores machine-readable instructions executable by the processor. When the electronic device is running, the processor and the storage medium communicate via the bus, and the processor executes the machine-readable instructions to perform the steps of the method for restoring a multi-DC receiving-end system under a secondary fault according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the computer program executes the steps of the method for restoring a multi-DC receiving-end system under a secondary fault according to any one of claims 1 to 7.

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