A wind farm fault voltage recovery method based on topology reconfiguration

Abstract

This invention discloses a wind farm fault voltage recovery method based on topology reconstruction. The proposed method utilizes a radial network for both normal operation and fault isolation of the wind farm. Topology-level optimization calculations enable the wind farm to achieve both the low redundancy and high reliability of traditional radial and ring networks. Compared to the traditional radial network approach where circuit breakers directly disconnect during internal faults, the proposed topology reconstruction method ensures both the recovery of voltage at the wind turbine generator terminals and the continued power supply from downstream wind turbines without disconnecting from the grid.

Description

Technical Field

[0001] This invention relates to the field of wind power fault recovery technology, specifically to a wind farm fault voltage recovery method based on topology reconstruction. Background Technology

[0002] Currently, common AC topologies for wind farm power collection systems include radial network topologies and ring network topologies. Radial networks are characterized by poor reliability and low resilience, while ring network wind turbines are characterized by low utilization rates and relatively complex control schemes.

[0003] Typically, radial wind farm networks only have switches at the booster station. When a fault occurs on the line, all wind turbines on the entire feeder will go offline. Even with fully equipped switch systems, which have higher investment costs, an upstream line fault can cause all downstream wind turbines to disconnect from the grid. If wind turbines disconnect from the grid, fault clearing and reconnection become complex and time-consuming, resulting in significant economic losses for the wind farm. Furthermore, as the grid penetration rate of wind power continues to increase, large-scale disconnections of wind turbines can cause substantial energy shortages and severely impact the external power grid, leading to incalculable losses. In traditional radial wind farm networks, when an internal fault occurs, the circuit breaker will directly trip, causing downstream wind turbines to disconnect from the grid at the fault point. Summary of the Invention

[0004] The main objective of this invention is to provide a method for restoring fault voltage in wind farms based on topology reconstruction, which aims to solve the problem that downstream wind turbines will disconnect from the grid when an internal fault occurs in a traditional radial wind farm network.

[0005] The technical solution proposed in this invention is as follows:

[0006] A wind farm fault voltage recovery method based on topology reconstruction includes:

[0007] Multiple potential fault points are set on the collector lines of the wind farm;

[0008] Generating a wind farm impedance parameter matrix based on wind farm topology information;

[0009] The loop current is calculated based on the wind farm impedance parameter matrix, thereby removing the interconnecting lines in the wind farm interconnecting line matrix where the loop current exceeds the limit.

[0010] The optimal connecting lines corresponding to each fault point that meet the constraints are obtained and constructed based on integer second-order cone calculations.

[0011] When a fault occurs on the collector line of a wind farm, the fault point is marked as the target point. Based on the optimized calculation of the wind farm's interconnection lines, the preferred interconnection line corresponding to the target point is connected, and the circuit breakers at both ends of the target point are tripped to cut off the fault and enable the downstream wind turbines of the target point to continue supplying power without disconnecting from the grid.

[0012] Preferably, the step of calculating the optimal interconnection lines corresponding to each fault point that satisfies the constraints based on integer second-order cones, and the step of marking the fault point as the target point when a fault occurs on the wind farm's collector line, connecting the optimized interconnection lines of the wind farm to the optimal interconnection line corresponding to the target point, and tripping the circuit breakers at both ends of the target point to clear the fault, further includes:

[0013] The preferred interconnection lines corresponding to each fault point are updated in the wind farm topology information to obtain the updated wind farm topology information.

[0014] The optimized interconnection lines of the wind farm are constructed based on the updated wind farm topology information.

[0015] Preferably, the wind farm topology information includes: the correlation matrix between all interconnecting lines and transformer nodes of the wind farm, the electrical parameters of the wind turbines, the voltage level, current carrying capacity and impedance parameters of the collector lines, the voltage level, current carrying capacity and impedance parameters of the transmission lines, and the impedance parameters of the step-up transformers at the substation.

[0016] Preferably, the step of calculating the loop current based on the wind farm impedance parameter matrix to remove interconnecting lines in the wind farm interconnecting line matrix whose loop current exceeds the limit includes:

[0017] A closed-loop steady-state model after a wind farm fault is established. Based on the closed-loop steady-state model, Thevenin's theorem, and the superposition theorem, the closed-loop steady-state current and feeder current are calculated.

[0018] The impulse current is obtained based on the steady-state current, and the tie lines in the wind farm's tie line matrix with a loop current greater than the impulse current are removed.

[0019] Preferably, the step of calculating the preferred connecting lines corresponding to each fault point that satisfy the constraints based on the integer second-order cone includes:

[0020] Obtain the first objective function that considers the cost of adding new lines;

[0021] Obtain a second objective function that considers voltage recovery capability;

[0022] Construct a third objective function based on the first and second objective functions;

[0023] Integer second-order cone calculations are performed based on the third objective function to obtain the preferred connecting lines corresponding to each fault point that satisfy the constraints.

[0024] Preferably, the first objective function is:

[0025] f1 = x ij δΔL ij ,

[0026]

[0027] In the formula: f1 is the first objective function; xij takes any term of 0 or 1, x ij =1 indicates that a new connection has been established between node i and node j, x ij =0 indicates that no new connecting lines have been built between nodes i and j; δ is the cost per unit length of the line; N is the total number of nodes on the transformer's lower collector line; L N It is the total number of all possible communication lines; L ave It is the average of all possible tie line lengths; ΔL is the tie line length offset; L is the tie line length; L i,j It is the length of the link between node i and node j; ΔL i,j It is the length offset of the connection line between node i and node j.

[0028] Preferably, the second objective function is:

[0029]

[0030]

[0031] In the formula: f2 is the second objective function; ΔV is the rated voltage of node j; ΔV is the voltage deviation; ΔV ave This represents the average voltage deviation. It is the square of the average voltage deviation, used to eliminate non-differentiable points in the function; V j It is the voltage at node j.

[0032] Preferably, the third objective function is:

[0033] min f(x) = αf1 + βf2,

[0034] In the formula, α and β are both weighting coefficients.

[0035] Preferably, the step of performing integer second-order cone calculations based on a third objective function to obtain the preferred connecting lines corresponding to each fault point that satisfy the constraints includes:

[0036] Obtain the constraints for the integer second-order cone algorithm:

[0037]

[0038] In the formula, P ij Q is the active power flowing from node i to node j. ij This represents the reactive power flowing from node i to node j; v i It is the square of the voltage at node i; i ij The square of the current flowing from node i to node j;

[0039] Constraints for obtaining the location of the connecting line:

[0040]

[0041] In the formula, T represents any medium-voltage transformer; it means that interconnection lines are not allowed between feeders under different transformers.

[0042] Obtain the active power balance constraints and reactive power balance constraints for each node:

[0043]

[0044] In the formula, P gen,i Q is the active power injected into node i by the wind turbine; gen,i P is the reactive power injected into node i by the wind turbine; ki Q is the active power flowing from node k to node i. ki It is the reactive power flowing from node k to node i, i ki R is the square of the current flowing from node k to node i; ki Let X be the resistance of the branch between node k and node i. ki P represents the reactance of the branch between node k and node i; load,i Q is the active power consumed by the load at node i. load,i P is the reactive power consumed by the load at node i; ij Q is the active power flowing from node i to node j. ij It is the reactive power flowing from node i to node j;

[0045] Obtain Ohm's law constraints for each branch:

[0046]

[0047] In the formula, v i It is the square of the voltage at node i, v j It is the square of the voltage at node j; M is a positive integer; y ij Take either 0 or 1, y ij =1 indicates that there is a line between node i and node j, y ij=0 means there is no line between node i and node j; R ij The resistance between node i and node j, X ij Reactance between node i and node j, i ij The square of the current flowing from node i to node j.

[0048] The above technical solution can achieve the following beneficial effects:

[0049] The wind farm fault voltage recovery method proposed in this invention, based on topology reconstruction, is a radial network for both normal operation and after fault isolation. The topology-level optimization calculation enables the wind farm to achieve both the low redundancy and high reliability of traditional radial and ring networks. Compared with the traditional radial network scheme where the circuit breaker is directly disconnected when an internal fault occurs, the wind farm fault voltage recovery method proposed in this invention can not only ensure the recovery voltage of the wind turbine generators in the wind farm, but also ensure that the downstream wind turbine generators do not disconnect from the grid and continue to supply power. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0051] Figure 1 This is a flowchart of the first embodiment of a wind farm fault voltage recovery method based on topology reconstruction proposed in this invention;

[0052] Figure 2 This is a wind farm topology diagram used in the tenth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention.

[0053] Figure 3 This is a schematic diagram of the superposition theorem solution for the closed loop current in the tenth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention.

[0054] Figure 4 This is a line current waveform diagram obtained after implementing the tenth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention.

[0055] Figure 5 This is a node voltage waveform diagram obtained after implementing the tenth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention.

[0056] Figure 6This is a comparison diagram of the voltage waveforms of wind turbine generator 3 using a wind farm fault voltage recovery method based on topology reconstruction proposed in this invention and a traditional method.

[0057] Figure 7 The diagram shows a comparison of the active power output waveforms of a wind farm using a topology reconstruction-based wind farm fault voltage recovery method proposed in this invention and a traditional method.

[0058] Figure 8 This is a comparison of the reactive power output waveforms of a wind farm based on topology reconstruction proposed in this invention and the traditional method.

[0059] Figure 9 This is a comparison chart showing the number of calculations required for a wind farm fault voltage recovery method based on topology reconstruction and an enumeration method proposed in this invention. Detailed Implementation

[0060] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0061] This invention proposes a method for restoring fault voltage in wind farms based on topology reconstruction.

[0062] As attached Figure 1 As shown, in the first embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, the location of the interconnecting lines is calculated and constructed in advance. Faults in different sections of the collector lines may correspond to different optimal voltage recovery paths. To avoid excessive economic costs and cable (submarine cable) crossing problems caused by too many interconnecting lines, this embodiment includes the following steps:

[0063] Step S110: Set up multiple potential fault points on the collector lines of the wind farm.

[0064] Step S120: Generate the wind farm impedance parameter matrix based on the wind farm topology information.

[0065] Step S130: Calculate the loop current based on the wind farm impedance parameter matrix, thereby removing the interconnecting lines in the wind farm interconnecting line matrix where the loop current exceeds the limit.

[0066] Step S140: Calculate and construct the preferred connection lines corresponding to each fault point that satisfy the constraints based on integer second-order cones.

[0067] Specifically, considering that wind turbines have a certain voltage ride-through capability, and ensuring that the turbine terminal voltage does not exceed the limit, tie lines are activated to boost the turbine voltage on the faulty line. The optimal voltage recovery tie line after a fault in the wind farm's collector line is studied, relaxing the secondary non-convex power balance constraints and Ohm's law constraints into convex constraints to improve computational efficiency.

[0068] Step S150: When a fault occurs on the collector line of the wind farm, the fault point is marked as the target point. Based on the optimized calculation of the wind farm's interconnection line, the preferred interconnection line corresponding to the target point is connected, and the circuit breakers at both ends of the target point are tripped to cut off the fault and enable the downstream wind turbines of the target point to continue supplying power without disconnecting from the grid.

[0069] The wind farm fault voltage recovery method proposed in this invention, based on topology reconstruction, utilizes a radial network for both normal operation and fault isolation. Topology-level optimization calculations enable the wind farm to achieve both the low redundancy and high reliability of traditional radial and ring networks. Compared to the traditional radial network approach where circuit breakers directly disconnect during internal faults, the proposed topology reconstruction method ensures both the restored voltage at the wind turbine generator terminals and the continuous power supply from downstream wind turbines without disconnecting from the grid. This enables downstream turbines to operate continuously without disconnecting from the grid, avoiding energy waste during fault clearing and turbine restart.

[0070] This method involves switching on and off lines and circuit breakers to restore voltage to all wind turbines without shutting them down, provided that the wind turbines have a certain voltage ride-through capability.

[0071] Compared to traditional ring networks that only build connecting lines at the feeder ends, this method offers flexibility and variability in the number and location of connecting lines, addressing the economic and voltage recovery capabilities of complex asymmetric wind farms. With the increasing number of wind turbines and wind power penetration, this method's integer second-order cone optimization solution avoids the computational inefficiency caused by multiple iterations, compared to heuristic algorithms or enumeration methods.

[0072] In the second embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the first embodiment, the following steps are further included between steps S140 and S150:

[0073] Step S210: Update the preferred interconnection lines corresponding to each fault point to the wind farm topology information to obtain the updated wind farm topology information.

[0074] Specifically, during the loop closing process of wind farm topology reconfiguration, the current impact of connecting lines on the wind farm is considered, and loop closing current constraints are set based on the impact current capacity that the collector lines can withstand. During the loop unclosing process of wind farm topology reconfiguration, in order to ensure that the wind farm after loop unclosing is a radial network, all wind turbines are connected to the collector lines. There are no three-point constraints on connecting lines between feeders under different medium-voltage transformers, but constraints on the location of connecting line construction are set.

[0075] Step S220: Based on the updated wind farm topology information, construct the optimized wind farm connection lines.

[0076] Specifically, during the construction of interconnection lines for wind farm voltage restoration, there may be instances of cable (submarine cable) crossing. To avoid these issues, cross-crossing constraints on interconnection lines have been implemented.

[0077] Under normal operating conditions of a wind farm, the interconnection lines are redundant and not put into use. In order to reduce line costs, the updated interconnection lines should be used as a backup plan for other fault points.

[0078] In the third embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the first embodiment, the wind farm topology information includes: the correlation matrix between all interconnecting lines and transformer nodes of the wind farm, the electrical parameters of the wind turbine, the voltage level, current carrying capacity and impedance parameters of the collector lines, the voltage level, current carrying capacity and impedance parameters of the transmission lines, and the impedance parameters of the step-up transformer of the step-up substation.

[0079] In the fourth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the first embodiment, the step of calculating the loop current based on the wind farm impedance parameter matrix to remove the interconnecting lines in the wind farm interconnecting line matrix with loop current exceeding the limit includes the following steps:

[0080] Step S410: Establish a closed-loop steady-state model after a wind farm fault, and calculate the closed-loop steady-state current and feeder current based on the closed-loop steady-state model, Thevenin's theorem and the superposition theorem.

[0081] Step S420: Obtain the impact current based on the steady-state current (1.8 times the steady-state current is the impact current), and remove the interconnection lines in the wind farm interconnection line matrix whose loop current is greater than the impact current, as a prerequisite for selecting interconnection lines in the wind farm fault recovery scheme based on topology reconstruction.

[0082] Specifically, wind turbines have a certain voltage fault ride-through capability. Within the allowable voltage range at the wind turbine terminals, they can be connected to the tie line with a fault, and perform switching operations of first closing the loop and then isolating the fault.

[0083] Whether the feeder current exceeds the limit is a prerequisite for determining whether the loop can be closed. The loop current is usually calculated approximately using the superposition theorem. The specific calculation method is as follows:

[0084]

[0085] In the formula, and Z represents the voltage vectors on the left and right sides of the closed loop, respectively. eq The equivalent impedance of the loop. This is the circulating current caused by the voltage difference on both sides of the loop closure point.

[0086]

[0087] In the formula, and These are the current vectors on the left and right feeders before the loop is closed, respectively. and These are the current vectors on the left and right feeders after the loop is closed.

[0088] In the fifth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the first embodiment, step S140 includes the following steps:

[0089] Step S510: Obtain the first objective function that takes into account the cost of the new line.

[0090] Step S520: Obtain the second objective function that takes into account voltage recovery capability.

[0091] Step S530: Construct a third objective function based on the first objective function and the second objective function.

[0092] Step S540: Perform integer second-order cone calculations based on the third objective function to obtain the preferred connecting lines corresponding to each fault point that satisfy the constraints.

[0093] Specifically, this embodiment provides a specific scheme for obtaining the preferred connecting lines corresponding to each fault point that meet the constraints based on integer second-order cone calculations.

[0094] In traditional radial networks, interconnection lines are built as fault voltage recovery lines. Two objective functions are considered: interconnection line cost and voltage recovery capability. The two different index elements are first standardized, and then weight coefficients are assigned to transform the multi-objective problem into a single equation for solution.

[0095] In the sixth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the fifth embodiment, the first objective function is:

[0096] f1 = xij δΔL ij ,

[0097]

[0098] In the formula: f1 is the first objective function; xij takes any term of 0 or 1, x ij =1 indicates that a new connection has been established between node i and node j, x ij =0 indicates that no new connecting lines have been built between nodes i and j; δ is the cost per unit length of the line; N is the total number of nodes on the collector line under the transformer (e.g., a 33 / 155kV transformer); L N It is the total number of all possible communication lines; L ave It is the average of all possible tie line lengths; ΔL is the tie line length offset; L is the tie line length; L i,j It is the length of the link between node i and node j; ΔL i,j It is the length offset of the connection line between node i and node j.

[0099] In the seventh embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the sixth embodiment, the second objective function is:

[0100]

[0101]

[0102] In the formula: f2 is the second objective function; ΔV is the rated voltage of node j; ΔV is the voltage deviation; ΔV ave This represents the average voltage deviation. It is the square of the average voltage deviation, used to eliminate non-differentiable points in the function; V j It is the voltage at node j.

[0103] In the eighth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the seventh embodiment, the third objective function is:

[0104] min f(x) = αf1 + βf2,

[0105] In the formula, α and β are both weighting coefficients.

[0106] In the ninth embodiment of the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the eighth embodiment, step S540 includes the following steps:

[0107] Step S910: Obtain the constraints of the integer second-order cone algorithm:

[0108]

[0109] In the formula, P ij Q is the active power flowing from node i to node j. ij This represents the reactive power flowing from node i to node j; v i It is the square of the voltage at node i; i ij The square of the current flowing from node i to node j.

[0110] Specifically, the second-order cone constraint is derived from the power flow equation through convex relaxation. It transforms the original non-convex quadratic equality constraint into a convex second-order cone constraint, making it easier to obtain the optimal solution of the objective function.

[0111] Step S920: Obtain the constraints for the integer second-order cone algorithm:

[0112]

[0113] In the formula, T represents any medium-voltage transformer; it means that interconnection lines are not allowed between feeders under different transformers.

[0114] Step S930: Obtain the active power balance constraints and reactive power balance constraints for each node:

[0115]

[0116] In the formula, P gen,i Q is the active power injected into node i by the wind turbine; gen,i P is the reactive power injected into node i by the wind turbine; ki Q is the active power flowing from node k to node i. ki It is the reactive power flowing from node k to node i, i ki R is the square of the current flowing from node k to node i; ki Let X be the resistance of the branch between node k and node i. ki P represents the reactance of the branch between node k and node i; load,i Q is the active power consumed by the load at node i. load,i P is the reactive power consumed by the load at node i; ij Q is the active power flowing from node i to node j. ij It is the reactive power flowing from node i to node j.

[0117] Step S940: Obtain Ohm's law constraints for each branch:

[0118]

[0119] In the formula, v i It is the square of the voltage at node i, v jIt is the square of the voltage at node j; M is a large positive integer (100 in this patent); y ij Take either 0 or 1, y ij =1 indicates that there is a line between node i and node j, y ij =0 means there is no line between nodes i and j; please add R. ij The resistance between node i and node j, X ij Reactance between node i and node j, i ij The square of the current flowing from node i to node j.

[0120] In the wind farm fault voltage recovery method based on topology reconstruction proposed in this invention, based on the ninth embodiment, after step S940, the following steps are further included:

[0121] Step S1010: For the wind power system to operate stably, the following conditions must be met: (Considering that branch power, current, and node voltage are within safe ranges)

[0122]

[0123] In the formula, P max Q represents the maximum active power. max V represents the maximum reactive power. max I represents the maximum voltage. max P represents the maximum value of the current. min Q represents the minimum active power. min V represents the minimum reactive power. min Indicates the minimum voltage value; i loop This represents the square of the effective value of the steady-state current in the loop. This indicates the maximum value of the loop inrush current.

[0124] To ensure that the network after fault isolation is a radial network, and that each wind turbine is connected to the wind farm's collection line, the following constraints are imposed on the location of the interconnection lines:

[0125]

[0126] In the formula, dnsteam represents the downstream, and l represents the faulty collector line; the above formula indicates that there is only one tie line built between the faulty downstream node and the healthy line.

[0127] Specifically, in the second embodiment described above, the obtained interconnection lines are updated in the wind farm topology information. Considering the non-crossing constraints of cables (submarine cables), steps S120-S140 are repeated. The calculation is performed using an integer second-order cone optimization method. If a fault condition is set later, the pre-set interconnection lines can be used, meaning no new interconnection lines are needed, i.e., x ij=0; x ij =1 indicates that an additional connecting line is needed as the optimal voltage recovery strategy; the non-crossing constraint of the cable (submarine cable) is:

[0128] (i1-i2)×(j1-j2)≥0,

[0129] In the formula, i1 and j1 are connection lines. The node coordinates, i2 and j2 are the connecting lines. The node coordinates, where i1 and i2, j1 and j2 are on the same feeder.

[0130] As attached Figure 3 As shown, according to the superposition principle, the feeder current after loop closing consists of two parts. One part is the initial current on both feeders before loop closing, and the other part is the circulating current caused by the voltage difference across the loop closing point. and These are the voltage vectors on the left and right sides of the closed loop, respectively. The circulating current is caused by the voltage difference across the loop closure point. and These are the current vectors on the left and right feeders before the loop is closed, respectively. and These are the current vectors on the left and right feeders after the loop is closed.

[0131] In this embodiment, as shown in the appendix Figure 2 As shown, there are 16 wind turbines, each numbered. Taking the failure of wind turbine 3 as an example (i.e., wind turbine 3 as the target point), the connecting lines from node 8 to node 12 are obtained. Figure 4 To the attached Figure 8 This is a simulation diagram showing that after a 10-second fault in wind turbine generator 3, the loop closes at 10.5 seconds, the interconnection line is put into operation, and the loop closes at 11 seconds, thus isolating the fault.

[0132] Appendix Figure 4 The diagram shows the line current waveform obtained after implementing this method, where I 7,6 This is the current flowing from node 7 to node 6. After the fault occurs, the current I... 7,6 and I 8,7 The amplitude increases. After loop closure, I 7,6 I 8,7 and I 11,12 Conversely, the current amplitude increases. The fault point becomes an energy dissipation point for the wind farm; the closer to the fault point, the greater the branch current. After the loop is broken, the current amplitude basically returns to its initial state, but the current direction in some branches changes due to the change in topology.

[0133] Appendix Figure 5The diagram shows the node voltage waveforms obtained after implementing this method. After loop closing, the terminal voltages of wind turbine generators 2 and 3 rise to approximately 0.8 pU. After loop unclosing, the terminal voltages of the wind turbine generators gradually recover to 1 pU.

[0134] Appendix Figure 6 The diagram shows a comparison of the voltage waveforms of the wind turbine generator 3 using the method proposed in this invention and the conventional method. Compared with the droop control scheme, this scheme and the enumeration method are more effective in restoring the voltage of the wind turbine generator 3. The voltage of WT3 using the droop control scheme remains around 0.7 pu, while the voltage using the proposed method gradually increases, and after 17 seconds, the voltage of the proposed method returns to normal.

[0135] Appendix Figure 7 and attached Figure 8 The figures show a comparison of the active and reactive power output waveforms of the wind farm using the proposed method and the traditional method, respectively. The direct fault isolation strategy responds rapidly, with the wind farm outputting power to the external grid after 10.5 seconds. The droop control reduces the active power output of the wind farm (WF) to ensure the voltage at the wind turbine (WT) terminals. An enumeration method was used to calculate all possible loop closure scenarios. After 13.1 seconds, the active power output under both the proposed scheme and the enumeration method was higher than that under direct fault isolation. After 17 seconds, the active power output using the proposed scheme returned to a steady state. The reactive power output waveform of the wind farm is similar to that of the active power output.

[0136] Appendix Figure 9 This diagram compares the computational complexity of the proposed method and the enumeration method. The number of wind turbines on the two feeders under the medium-voltage transformer is equal. The diagram shows the computational complexity as the number of wind turbines on one feeder increases from 1 to 4. When the number of wind turbines reaches 4, the enumeration method increases to 80 computations, while the integer second-order cone method only requires 8 computations.

[0137] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0138] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), including several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0139] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for fault voltage recovery of a wind farm based on topology reconfiguration, characterized in that, include: Multiple potential fault points are set on the collector lines of the wind farm; Generating a wind farm impedance parameter matrix based on wind farm topology information; The loop current is calculated based on the wind farm impedance parameter matrix, thereby removing the interconnecting lines in the wind farm interconnecting line matrix where the loop current exceeds the limit. The optimal connecting lines corresponding to each fault point that meet the constraints are obtained and constructed based on integer second-order cone calculations. When a fault occurs on the collector line of a wind farm, the fault point is marked as the target point. Based on the optimized calculation of the wind farm's interconnection line, the preferred interconnection line corresponding to the target point is connected, and the circuit breakers at both ends of the target point are tripped to cut off the fault and enable the downstream wind turbines of the target point to continue to supply power without disconnecting from the grid. The preferred connecting lines corresponding to each fault point satisfying the constraints, obtained based on integer second-order cone calculations, include: Obtain the first objective function that considers the cost of adding new lines; Obtain a second objective function that considers voltage recovery capability; Construct a third objective function based on the first and second objective functions; Integer second-order cone calculations are performed based on the third objective function to obtain the preferred connecting lines corresponding to each fault point that satisfy the constraints. The first objective function is: ， ， In the formula: Let the first objective function be ; Choose either 0 or 1. Time Representative Node i and nodes j A new connection line was built between them. Time Representative Node i and nodes j No new connecting lines were built; It is the cost per unit length of the line; N This is the total number of nodes on the collector line of the medium-voltage transformer. It is the total number of all possible communication lines; It is the average length of all possible connection lines; It is an offset in the length of the connecting line; It is the length of the connecting line; It is a node i and nodes j The length of the connecting lines between them; It is a node i and nodes j The length offset of the connecting lines between them; The second objective function is: ， ， In the formula: The second objective function; yes j The rated voltage of the node; For voltage deviation; This represents the average voltage deviation. It is the square of the average voltage deviation, used to eliminate non-differentiable points in the function; yes j The voltage at the node; The third objective function is: ， In the formula, and All are weighting coefficients.

2. The wind farm fault voltage recovery method based on topology reconstruction according to claim 1, characterized in that, Between the steps of calculating the optimal interconnection lines corresponding to each fault point that satisfies the constraints based on integer second-order cones, and the steps of marking the fault point as the target point when a fault occurs on the wind farm's collector line, activating the optimal interconnection line corresponding to the target point based on the optimized calculation of the wind farm's interconnection lines, and tripping the circuit breakers at both ends of the target point to clear the fault, the method further includes: The preferred interconnection lines corresponding to each fault point are updated in the wind farm topology information to obtain the updated wind farm topology information. The optimized interconnection lines of the wind farm are constructed based on the updated wind farm topology information.

3. The wind farm fault voltage recovery method based on topology reconstruction according to claim 1, characterized in that, The wind farm topology information includes: the correlation matrix between all interconnecting lines and transformer nodes of the wind farm, the electrical parameters of the wind turbines, the voltage level, current carrying capacity and impedance parameters of the collector lines, the voltage level, current carrying capacity and impedance parameters of the transmission lines, and the impedance parameters of the step-up transformers at the step-up substation.

4. The wind farm fault voltage recovery method based on topology reconstruction according to claim 1, characterized in that, The method of calculating the loop current based on the wind farm impedance parameter matrix, thereby removing interconnecting lines in the wind farm interconnecting line matrix whose loop current exceeds the limit, includes: A closed-loop steady-state model after a wind farm fault is established. Based on the closed-loop steady-state model, Thevenin's theorem, and the superposition theorem, the closed-loop steady-state current and feeder current are calculated. The impulse current is obtained based on the steady-state current, and the tie lines in the wind farm's tie line matrix with a loop current greater than the impulse current are removed.

5. The wind farm fault voltage recovery method based on topology reconstruction according to claim 1, characterized in that, The calculation of integer second-order cones based on the third objective function to obtain the preferred connecting lines corresponding to each fault point that satisfies the constraints includes: Obtain the constraints for the integer second-order cone algorithm: In the formula, From node i Flow to Node j active power, From node i Flow to Node j reactive power; From node i The square of the voltage; From node i Flow to Node j The square of the current; Constraints for obtaining the location of the connecting line: ， In the formula, T This indicates any medium-voltage transformer; it also indicates that interconnecting lines between feeders from different transformers are not permitted. Obtain the active power balance constraints and reactive power balance constraints for each node: ， In the formula, It is the injection node of the wind turbine. i The active power; It is the injection node of the wind turbine. i reactive power; From node k Flow to Node i active power, From node k Flow to Node i reactive power, From node k Flow to Node i The square of the current; For nodes k and nodes i The resistance of the branch between, For nodes k and nodes i Reactance of the branch circuit; It is a node i The active power consumed by the load. It is a node i The reactive power consumed by the load; From node i Flow to Node j active power, From node i Flow to Node j reactive power; Obtain Ohm's law constraints for each branch: ， In the formula, From node i The square of the voltage, From node j The square of the voltage; M It is a positive integer; Choose either 0 or 1. Time Representative Node i and nodes j There is a line. Representative node i and nodes j No line exists; node i and nodes j resistance between node i and nodes j Between reactance, From node i Flow to Node j The square of the current.

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