A dc fault ride-through method for a wind power flexible direct current transmission system without centralized energy consumption

Abstract

The application discloses a DC fault ride-through method of a wind power flexible HVDC transmission system without centralized energy consumption, which makes the converter enter a fault ride-through mode based on network construction voltage reduction control after a DC single-pole grounding fault of the wind power flexible HVDC transmission system, establishes a three-node equivalent network of a sending-end converter AC bus node, a wind farm collection node and a wind turbine port node; solves current constraints of wind power generators under a low-voltage ride-through mode in advance, and obtains a one-to-one correspondence between the converter AC bus voltage and the wind turbine port voltage through point-by-point iteration; then, a nonlinear mapping relationship between the converter AC bus voltage amplitude and active current is established, and a voltage reference value of the voltage reduction control is determined by taking the converter overcurrent threshold as a safety boundary. The method makes the converter transmit the maximum active power under the condition of not overcurrent, relieves the shortage of active power of the system during the fault, and reduces the land occupation area and cost of the converter without centralized energy consumption devices.

Description

Technical Field

[0001] This invention belongs to the field of power system protection and control technology, specifically relating to a DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption. Background Technology

[0002] High-voltage direct current (HVDC) transmission systems based on MMC (Modular Multilevel Converter) have the advantages of large transmission capacity, flexible control, and suitability for long-distance transmission of new energy, making them an important technical route for large-scale wind power transmission. For bipolar flexible HVDC transmission systems using overhead DC lines, the probability of DC single-pole grounding faults is relatively high. After a fault occurs, the faulty pole needs to suppress the fault current, while the healthy pole still has the ability to maintain power transmission. However, the continuous active power input from the wind power side will cause system power imbalance during fault ride-through, leading to converter overcurrent and power deficit in the receiving-end grid.

[0003] Among existing fault ride-through schemes, one type relies on remote communication to issue rapid load reduction commands to wind turbines, as in the literature [S. Jiang, Y. Xu, G. Li, Y. Xin and L. Wang, Coordinated Control Strategy for Receiving-End Fault Ride-through in Large-Scale Wind Power Connected to DC Grids, IEEE Transactions on Electric Power Transmission, Vol. 37, No. 4, pp. 2673-2683, August 2022]. This alleviates power surplus by reducing the active power output of the wind turbines, but communication delays and lag in wind turbine power regulation can cause significant transient overcurrents on the converter side. Another type of scheme configures centralized energy dissipation devices on the AC bus side of the converter station, as in the literature [S. Wu et al., Modular Multilevel Converter for Integrated Energy Dissipation Devices in Offshore Wind Power VSC-HVDC Systems, IEEE Transactions on Sustainable Energy, Vol. 13, No. 1, pp. 353-362, January 2022]. This absorbs excess power through resistive energy dissipation, but such devices bring additional land occupation, investment, and thermal design pressure. Another type of active voltage reduction scheme reduces the AC voltage of the converter to put the wind turbine into a low-voltage ride-through state, as in the literature [U. Karaagac, J. Mahseredjian, L. Cai and H. Saad, Accuracy and efficiency of offshore wind farm modeling in multi-terminal HVDC transmission access based on MMC, IEEE Transactions on Electric Power Transmission, Vol. 32, No. 2, pp. 617-627, April 2017]. This scheme utilizes the wind turbine's built-in chopper to consume excess energy. However, when the AC voltage is fixed and reduced to a low level, the active power output of the wind turbine decreases significantly. The healthy pole converter cannot transmit active power during fault ride-through, and the receiving-end grid suffers a large power deficit.

[0004] The shortcomings of the above scheme are that the AC voltage reduction command during fault ride-through is usually a fixed voltage value, and it does not take into account the low-voltage ride-through current injection characteristics of the wind turbine, the electrical coupling relationship of the wind farm collector network, and the overcurrent safety boundary of the converter. Therefore, if the voltage reduction is too large, it will cause unnecessary active power loss, while if the voltage reduction is too small, it will cause overcurrent in the healthy pole converter, making it difficult to form a calculable boundary trade-off between power maintenance and equipment safety. Summary of the Invention

[0005] In view of the above, the present invention provides a DC fault ride-through method for wind power flexible DC transmission systems without centralized energy consumption. During a DC unipolar ground fault, the wind power transmission system via a bipolar modular multilevel converter (HVDC) determines a reference value for the step-down control voltage that satisfies the converter's overcurrent safety boundary by iteratively solving the candidate converter AC bus voltage, the wind turbine port voltage prediction initial value, the low-voltage ride-through current constraint, and the three-node network admittance matrix. This allows the converter to transmit maximum active power under non-overcurrent conditions, alleviating the active power deficit of the system during the fault period. Simultaneously, it eliminates the need for centralized energy consumption devices, reducing the converter's footprint and cost.

[0006] A DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption includes: After a DC single-pole grounding fault occurs in the wind power flexible DC transmission system, the MMC enters the fault ride-through mode based on grid-connected step-down control. Construct a three-node network admittance matrix based on the parameters of the wind power AC aggregation network; Based on the current constraint in the low voltage ride-through mode of the wind turbine, the point-by-point solution is performed within the search range of the AC bus voltage amplitude of the MMC to obtain the wind turbine port voltage amplitude that corresponds one-to-one with the AC bus voltage amplitude. The active current of the MMC is calculated point by point based on the voltage amplitude of the wind turbine port, and the nonlinear mapping relationship curve between the active current of the MMC and the AC bus voltage is obtained. Based on the nonlinear mapping curve, the AC bus voltage amplitude corresponding to when the MMC active current reaches the allowable overcurrent threshold is used as the voltage reference value for buck control during fault ride-through, and is sent to the AC voltage control loop of the MMC to maximize the active power transmitted by the MMC under the allowable overcurrent threshold.

[0007] Furthermore, the specific implementation of the three-node network admittance matrix is ​​as follows: First, the MMC AC bus is taken as the first node, the wind farm collection point as the second node, and the wind turbine AC port as the third node. The wind power AC collection line between the first and second nodes is represented by a π-type equivalent circuit, and the connection between the second and third nodes is represented by the wind turbine transformer impedance. Then, the three-node network admittance matrix... Y The expression is as follows: , in: y 1g and y 2g These are the ground capacitance admittances of the first node and the second node, respectively. y 12 Let be the admittance of the series branch between the first node and the second node. y 23 The admittance of the series branch between the second and third nodes. C π This refers to the equivalent capacitance to ground of the wind power AC collection line. R π and L π These are the equivalent resistance and equivalent inductance of the wind power AC collection line, respectively. R T,WT and L T,WT These are the equivalent resistance and equivalent inductance of the wind turbine transformer, respectively. ω For AC angular frequency, G 12 and B 12 These are the series branch admittances. y 12 The real and imaginary parts, G 23 and B 23 These are the series branch admittances. y 23 The real and imaginary parts, j It is the imaginary unit.

[0008] Furthermore, the current constraint expression for the low-voltage ride-through mode of the wind turbine is as follows: in: For the first k The active current component of the wind turbine in the next iteration. For the first k The reactive current component of the wind turbine in the next iteration. k v This refers to the dynamic reactive current injection coefficient. I N,WT This is the rated current of the fan. For the first k The amplitude of the wind turbine port voltage in the next iteration. k It is a natural number.

[0009] Furthermore, for any AC bus voltage amplitude within the MMC AC bus voltage amplitude search range...V m,MMC We take this as the initial value of the wind turbine port voltage amplitude, and iteratively solve the wind turbine port voltage amplitude using the following quadratic equation; , in: For the first k +1 iteration of the wind turbine port voltage amplitude a , b , c Let be the coefficients of the quadratic equation in one variable. G eq and B eq Y represents the real and imaginary parts of the equivalent admittance after elimination. 21 Y is the value of the element in the 2nd row and 1st column of the admittance matrix of a three-node network. 22 Y is the value of the element in the 2nd row and 2nd column of the admittance matrix of a three-node network. 23 Y is the value of the element in the 2nd row and 3rd column of the admittance matrix of a three-node network. 32 Y is the value of the element in the 3rd row and 2nd column of the admittance matrix of a three-node network. 33 This is the value of the element in the 3rd row and 3rd column of the admittance matrix of the three-node network.

[0010] Furthermore, the nonlinear mapping relationship curve between MMC active current and AC bus voltage is expressed as follows: in: I d,MMC Let Re be the active current in the MMC, and let Re() denote the real part. I MMC This refers to the AC side current of the MMC. V 1 represents the voltage phasor of the first node, and its magnitude is... V m,MMC , V 2 represents the voltage phasor of the second node. V 3 is the voltage phasor of the third node, and its amplitude is V m,WT , V m,WT Y is the amplitude of the wind turbine port voltage obtained through iterative convergence. 11 Y is the value of the element in the first row and first column of the admittance matrix of a three-node network. 12 This is the value of the element in the first row and second column of the admittance matrix of the three-node network.

[0011] Furthermore, when there is no MMC active current discrete point corresponding to the allowable overcurrent threshold in the nonlinear mapping curve, interpolation calculation is performed between two adjacent discrete points that cross the allowable overcurrent threshold, and the MMC AC bus voltage amplitude obtained by interpolation calculation is used as the voltage reference value for step-down control during fault ride-through.

[0012] Furthermore, after implementing grid-based voltage reduction control for the MMC using the voltage reference value, the wind turbine detects the decrease in the AC bus voltage of the MMC and automatically enters the low voltage ride-through control mode. In turn, the wind turbine's built-in chopper absorbs the remaining power that cannot be transmitted by the MMC, reducing the dependence on centralized energy-consuming devices.

[0013] A computer device includes a memory and a processor, wherein the memory stores a computer program and the processor executes the computer program to implement the above-described method for DC fault ride-through of a wind power flexible DC transmission system without centralized energy consumption.

[0014] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the aforementioned method for DC fault ride-through of a wind power flexible DC transmission system without centralized energy consumption.

[0015] Based on the above technical solution, the present invention has the following beneficial technical effects: 1. This invention introduces the low-voltage ride-through current constraint of the wind power AC collection network and wind turbine into the generation process of the MMC grid step-down reference value, so that the step-down control is transformed from a fixed value setting to a boundary optimization process determined by electrical mapping relationship.

[0016] 2. This invention uses the converter's allowable overcurrent threshold as the optimization boundary, so that the active power transmission capacity of the converter can be fully utilized during fault ride-through.

[0017] 3. This invention utilizes a built-in chopper in the wind turbine to absorb residual power that cannot be transmitted through the healthy pole, thereby reducing reliance on centralized energy-consuming devices.

[0018] 4. This invention reduces DC power deficit during fault ride-through, enhances the transient power support capability of the receiving-end power grid, and reduces the converter footprint and cost by eliminating the need for centralized energy consumption devices. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption, as described in this invention.

[0020] Figure 2 This is a topology diagram of a wind power transmission system via a bipolar MMC high-voltage direct current system.

[0021] Figure 3This is a schematic diagram of the topology of the three-node network system constructed in this invention.

[0022] Figure 4 This is a schematic diagram illustrating the nonlinear mapping relationship between the AC bus voltage amplitude and the MMC active current in this invention, where (a) corresponds to 1.5≤ k v The three-dimensional mapping relationship diagram when ≤2.5, (b) corresponds to k v Two-dimensional mapping relationship diagram when =2.

[0023] Figure 5 This is a schematic diagram comparing the simulation results of the method of the present invention and the traditional method. In the figure, (a) corresponds to the traditional method and (b) corresponds to the method of the present invention. Detailed Implementation

[0024] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] This invention provides a DC fault ride-through method for wind power flexible DC transmission systems without centralized energy consumption, applicable to wind power transmission systems via true bipolar MMC high-voltage DC transmission. During steady-state operation, the bipolar converters jointly handle wind power transmission. When a single-pole ground fault occurs on either the positive or negative DC line, the faulty pole converter enters fault current suppression control, while the healthy pole converter maintains AC voltage grid control and handles active power transmission during the fault. To prevent overcurrent in the healthy pole converter due to insufficient voltage reduction and to avoid significant loss of active power output from the wind turbine due to excessive voltage reduction, this implementation employs overcurrent boundary optimization-based voltage reduction control. The specific implementation process is as follows: Figure 1 As shown: Step S1: After a DC single-pole grounding fault occurs in the high-voltage DC transmission system of the wind power through the bipolar modular multilevel converter, the converter is put into a fault ride-through mode based on grid-connected step-down control, and the parameters required for step-down optimization are obtained. Figure 2 The system topology of the wind power flexible direct transmission system is shown. MMC1 is the fault-pole converter, and MMC2 is the healthy-pole converter. Required parameters include the AC bus voltage amplitude search range of the converters, the low-voltage ride-through current injection parameters of the wind turbines, the parameters of the wind power AC collection network, and the allowable overcurrent threshold of the converters. The wind power AC collection network parameters include the collector line resistance, collector line inductance, capacitance to ground, and the wind turbine transformer impedance. The allowable overcurrent threshold of the converters is determined by the allowable fault ride-through current multiple of the converters. In this embodiment, the allowable overcurrent threshold of the converters is 1.5 pu, the lower limit of the voltage search is 0.35 pu, the upper limit of the voltage search is 0.9 pu, and the search step size is 0.001 pu.

[0026] Step S2: Construct a three-node network admittance matrix based on the wind power AC aggregation network parameters, consisting of the converter AC bus node, the wind farm aggregation node, and the wind turbine port node. For example... Figure 2 As shown, the converter AC bus is designated as the first node, the wind farm collection point as the second node, and the wind turbine AC port as the third node. The wind power AC collection line between the first and second nodes is characterized by a π-type equivalent circuit consisting of resistance, inductance, and capacitance to ground. The connection between the second and third nodes utilizes the impedance of the wind turbine transformer. Z T,WT Characteristic, such as Figure 3 As shown. The admittance of the collector line to ground and the admittances of the two series branches are determined by the following formula: in: C π This refers to the equivalent capacitance to ground of the wind power AC collection line. R π and L π These are the equivalent resistance and inductance of the wind power AC collection line, respectively. R T,WT and L T,WT These are the equivalent resistance and inductance of the wind turbine transformer, respectively. ω For AC angular frequency, G 12 , B 12 , G 23 and B 23 These are the real and imaginary parts of the admittance of the corresponding branch, respectively.

[0027] The three-node admittance matrix is ​​formed from the above branch admittances, and the relationship between the nodal injected current column vector and the nodal voltage column vector is established: in: V MMC This refers to the AC bus voltage phasor of the converter. V 2 represents the voltage phasor of the wind farm's collection node. V WT This is the phasor of the fan port voltage. I MMC For the AC side current phasor of the converter, I WT Inject current phasors into the wind turbine; Y11 to Y 33 These are the elements of a three-node admittance matrix.

[0028] Step S3: Within the AC bus voltage amplitude search range of the converter, pre-solve the current constraints of the iteration process. First, assign the AC bus voltage amplitude of the converter to the predicted value of the AC voltage amplitude at the wind turbine end as the initial value for iteration. Based on the AC voltage amplitude at the wind turbine end, solve the current constraints of the corresponding wind turbine low-voltage ride-through mode. Specifically: S31: For each candidate converter AC bus voltage amplitude within the voltage search interval, use the candidate converter AC bus voltage amplitude as the initial prediction value of the corresponding wind turbine port voltage amplitude, that is, set the initial prediction value of the wind turbine port voltage amplitude equal to the current candidate converter AC bus voltage amplitude: S32: Based on the predicted initial values, calculate the d-axis and q-axis current constraints of the wind turbine according to the wind turbine low-voltage ride-through criterion: in: I d,WT This represents the active current component of the wind turbine. I q,WT This represents the reactive current component of the wind turbine. k v This refers to the dynamic reactive current injection coefficient. I N,WT δ is the rated current of the fan. WT 0.9 is the phase angle of the fan end current relative to the MMC side current; 0.9 is the per-unit voltage threshold for the fan to enter the low-voltage ride-through current injection range.

[0029] Step S4: Within the AC bus voltage amplitude search range of the converter, iteratively solve the turbine port voltage amplitude point by point based on current constraints to obtain the turbine port voltage amplitude that corresponds one-to-one with the AC bus voltage of the converter. Specifically: S41: For each candidate converter AC bus voltage magnitude, eliminate it using the condition that the injected current at the second node is zero. V 2. Obtain the reduced-order network relationship between the fan port current, fan port voltage, and converter AC bus voltage: in: A = G eq + jBeq The equivalent admittance after elimination, B This is the equivalent transfer coefficient for the equation from the AC bus voltage of the converter to the fan port.

[0030] S42: Substituting the low-voltage ride-through current model of the wind turbine into the reduced-order network relationship, and taking the square of the modulus of the complex equation, the first... k The next iteration transforms into a quadratic equation concerning the amplitude of the wind turbine port voltage in the next iteration: S43: Utilize first in each iteration renew and Then, find the non-negative real roots of the quadratic equation within the stable operating voltage range of the wind turbine as... Iteration stops when two consecutive iterations satisfy the following equation: Where: ε is the preset convergence threshold; if the quadratic equation has multiple mathematical roots, the root that is located in the low voltage crossing operation range of the wind turbine and is continuous with the previous iteration value is retained, so as to exclude solutions that do not meet the operation constraints.

[0031] Step S5: Calculate the active current of the converter corresponding to the AC bus voltage amplitude of the candidate converter point by point based on the obtained wind turbine port voltage amplitude, and obtain the nonlinear mapping relationship between the AC bus voltage and the active current of the converter.

[0032] Based on the convergence V m,WT Obtained by back substitution of nodal equations V 2. Calculate the AC side current of the converter using the three-node network admittance matrix. I MMC And projected onto V m,MMC A directional, synchronously rotating coordinate system is used to obtain, as follows: Figure 4 The nonlinear mapping relationship between the AC bus voltage and active current of the converter is shown in Figure (a): in, I d,MMC The active current of the converter; the reactive current of a healthy pole converter, after being suppressed by current control. I d,MMC As a criterion for determining the current capacity occupancy of a healthy polarity converter.

[0033] Step S6: The amplitude of the candidate converter AC bus voltage corresponding to when the converter active current reaches the converter's allowable overcurrent threshold is determined as the voltage reference value for fault ride-through buck control. For example... Figure 4 As shown in (b), a nonlinear mapping curve is constructed by plotting the AC bus voltage amplitude of all candidate converters and their corresponding active currents, using the converter's allowable overcurrent threshold. I max,MMC Define safety boundaries; determine the voltage reference value for fault ride-through buck control as the candidate converter AC bus voltage amplitude corresponding to when the converter active current reaches the allowable overcurrent threshold. When the discrete calculation point does not fall directly on the overcurrent threshold, the adjacent discrete points that cross the overcurrent threshold ( V a , I a )and( V b , I b The boundary voltage between them is calculated using the following formula: From this, we obtain V mref It simultaneously satisfies network constraints, wind turbine low-voltage ride-through current constraints, and converter overcurrent constraints, avoiding excessive active power loss caused by fixed-depth voltage reduction.

[0034] Step S7: The fault ride-through buck control voltage reference value is sent to the AC voltage control loop of the healthy pole modular multilevel converter, while maximizing the active power transmission of the healthy pole converter within the allowable overcurrent threshold. In this embodiment, the fault ride-through buck control voltage reference value obtained by the above method is 0.54 pu, the healthy pole converter transmits 0.82 pu of active power, the converter overcurrent is limited to within 1.5 pu, and the wind turbine chopper absorbs 0.58 pu of surplus power.

[0035] Step S8: After the converter grid-connected voltage reduction control is implemented, the wind turbine detects the decrease in AC voltage, automatically enters the low voltage ride-through control mode, and uses the wind turbine's built-in chopper to absorb the remaining power that cannot be transmitted by the sending-end converter. P ch This reduces reliance on centralized energy-consuming devices.

[0036] Figure 5The paper presents a comparison of system simulation results under the methods of this invention and traditional methods. In the traditional fault ride-through method, the voltage reference value for the sending-end MMC grid-based voltage reduction control is a fixed low voltage. Under this low voltage, the wind turbine provides maximum reactive power support and no longer outputs active power. Under the same DC unipolar ground fault and fault clearance conditions, the traditional fault ride-through method... Figure 5 As shown in (a), the AC bus voltage of the converter V MMC The reactive power handled by the positive and negative converters drops to 0.38 pu. Q MMCp , Q MMCn Both are 0.4 pu, while the active power of the positive and negative converters... P MMCp , P MMCn Both decreased to 0, and the AC current of phase a of the positive and negative converters decreased. I ap , I an The amplitude reached 1.6 pu, and the wind turbine chopper absorbed the surplus power. P ch The voltage reaches 1.0 pu. When using the optimization method provided by this invention, based on the nonlinear mapping relationship between the converter active current and the AC bus voltage, the voltage reference value for buck control is determined to be 0.54 pu; during a fault, if... Figure 5 As shown in (b) above, the reactive power of a healthy polarity converter Q MMCn It drops to 0 and transmits 0.82 pu of active power. P MMCn Active power of the faulty converter P MMCp Reduced to 0 and bears 0.75 pu of reactive power. Q MMCp The converter's AC current is limited to within the allowable overcurrent threshold of 1.5 pu, and the wind turbine chopper absorbs power. P ch The voltage drop is reduced to 0.58 pu. The simulation results above show that, compared with the traditional method, the present invention improves the AC bus voltage and the active power transmission capability of the healthy pole during the fault while satisfying the converter overcurrent constraint, and reduces the surplus power borne by the wind turbine chopper by 0.42 pu, thereby reducing the power transmission deficit and energy consumption pressure during the fault.

[0037] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption, characterized in that, include: After a DC single-pole grounding fault occurs in the wind power flexible DC transmission system, the MMC enters the fault ride-through mode based on grid-connected step-down control. Construct a three-node network admittance matrix based on the parameters of the wind power AC aggregation network; Based on the current constraint in the low voltage ride-through mode of the wind turbine, the point-by-point solution is performed within the search range of the AC bus voltage amplitude of the MMC to obtain the wind turbine port voltage amplitude that corresponds one-to-one with the AC bus voltage amplitude. The active current of the MMC is calculated point by point based on the voltage amplitude of the wind turbine port, and the nonlinear mapping relationship curve between the active current of the MMC and the AC bus voltage is obtained. Based on the nonlinear mapping curve, the AC bus voltage amplitude corresponding to when the MMC active current reaches the allowable overcurrent threshold is used as the voltage reference value for buck control during fault ride-through, and is sent to the AC voltage control loop of the MMC to maximize the active power transmitted by the MMC under the allowable overcurrent threshold.

2. The DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption as described in claim 1, characterized in that, The specific implementation of the three-node network admittance matrix is ​​as follows: First, the MMC AC bus is taken as the first node, the wind farm collection point as the second node, and the wind turbine AC port as the third node. The wind power AC collection line between the first and second nodes is represented by a π-type equivalent circuit, and the connection between the second and third nodes is represented by the wind turbine transformer impedance. Therefore, the three-node network admittance matrix... Y The expression is as follows: ， in: y 1g and y 2g These are the ground capacitance admittances of the first node and the second node, respectively. y 12 This is the admittance of the series branch between the first node and the second node. y 23 The admittance of the series branch between the second and third nodes. C π This refers to the equivalent capacitance to ground of the wind power AC collection line. R π and L π These are the equivalent resistance and equivalent inductance of the wind power AC collection line, respectively. R T,WT and L T,WT These are the equivalent resistance and equivalent inductance of the wind turbine transformer, respectively. ω For AC angular frequency, G 12 and B 12 These are the admittances of the series branches. y 12 The real and imaginary parts, G 23 and B 23 These are the admittances of the series branches. y 23 The real and imaginary parts, j It is the imaginary unit.

3. The DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption as described in claim 1, characterized in that, The current constraint expression for the low-voltage ride-through mode of the wind turbine is as follows: in: For the first k The active current component of the wind turbine in the next iteration. For the first k The reactive current component of the wind turbine in the next iteration. k v This refers to the dynamic reactive current injection coefficient. I N,WT This is the rated current of the fan. For the first k The amplitude of the wind turbine port voltage in the next iteration. k It is a natural number.

4. The DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption as described in claim 3, characterized in that, For any AC bus voltage amplitude within the MMC AC bus voltage amplitude search range V m,MMC We take this as the initial value of the wind turbine port voltage amplitude, and iteratively solve the wind turbine port voltage amplitude using the following quadratic equation; ， in: For the first k +1 iteration of the wind turbine port voltage amplitude a , b , c Let be the coefficients of the quadratic equation in one variable. G eq and B eq Y represents the real and imaginary parts of the equivalent admittance after elimination. 21 Y is the value of the element in the 2nd row and 1st column of the admittance matrix of a three-node network. 22 Y is the value of the element in the 2nd row and 2nd column of the admittance matrix of a three-node network. 23 Y is the value of the element in the 2nd row and 3rd column of the admittance matrix of a three-node network. 32 Y is the value of the element in the 3rd row and 2nd column of the admittance matrix of a three-node network. 33 This is the value of the element in the 3rd row and 3rd column of the admittance matrix of the three-node network.

5. The DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption according to claim 4, characterized in that, The nonlinear mapping relationship curve between MMC active current and AC bus voltage is expressed as follows: in: I d,MMC Let Re be the active current in the MMC, and let Re() denote the real part. I MMC This refers to the AC side current of the MMC. V 1 represents the voltage phasor of the first node, and its magnitude is... V m,MMC , V 2 represents the voltage phasor of the second node. V 3 is the voltage phasor of the third node, and its amplitude is V m,WT , V m,WT Y is the amplitude of the wind turbine port voltage obtained through iterative convergence. 11 Y is the value of the element in the first row and first column of the admittance matrix of a three-node network. 12 This is the value of the element in the first row and second column of the admittance matrix of the three-node network.

6. The DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption according to claim 1, characterized in that: When there is no MMC active current discrete point corresponding to the allowable overcurrent threshold in the nonlinear mapping curve, interpolation calculation is performed between two adjacent discrete points that cross the allowable overcurrent threshold, and the MMC AC bus voltage amplitude obtained by interpolation calculation is used as the voltage reference value for step-down control during fault ride-through.

7. The DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption according to claim 1, characterized in that: After implementing grid-based voltage reduction control for the MMC using the voltage reference value, the wind turbine detects the decrease in the AC bus voltage of the MMC and automatically enters the low voltage ride-through control mode. Then, the wind turbine's built-in chopper absorbs the remaining power that cannot be transmitted by the MMC, reducing the dependence on centralized energy-consuming devices.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: The processor is used to execute the computer program to implement the DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption as described in any one of claims 1 to 7.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by the processor, it implements the DC fault ride-through method for a wind power flexible DC transmission system without centralized energy consumption as described in any one of claims 1 to 7.

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