Offshore wind power dc collection system single-ended protection method based on transient current rate of change

Abstract

The present application relates to a kind of offshore wind power dc collection system single-end protection method based on transient current rate of change, the transient fault current of each collection line of dc collection system is calculated, the transient fault current is the difference between current value and steady-state current value before fault;The transient current rate of change of each line positive and negative is calculated;If the inter-pole unbalance voltage is greater than the first voltage threshold, then start monopolar ground fault protection process, according to the polarity and amplitude relationship of the transient current rate of change of each line positive and negative, determine fault line and fault pole;If the inter-pole measurement voltage is less than the second voltage threshold, then start bipolar short-circuit fault protection process, according to the polarity and amplitude relationship of the transient current rate of change of each line positive and negative, determine fault line and fault pole.Compared with prior art, the present application has the advantages of high accuracy, high adaptability and strong reliability.

Description

Technical Field

[0001] This invention relates to train signal control systems, and more particularly to a single-ended protection method for offshore wind power DC collector systems based on transient current change rate. Background Technology

[0002] As the installed capacity of offshore wind power continues to increase and development scenarios gradually extend to deep-sea areas, the application of traditional AC wind farms is significantly restricted due to reactive power voltage issues, cable charging current limitations, and overvoltage risks. All-DC offshore wind farms, employing DC collection and transmission architectures, have become an important technological direction for solving these problems due to their significant advantages in long-distance, large-capacity power transmission, demonstrating broad application prospects.

[0003] Currently, research on all-DC offshore wind farms mainly focuses on converter topology design, system stability analysis, and operation control strategies. However, in practical engineering applications, relay protection remains a critical challenge that urgently needs to be addressed. DC system faults develop rapidly, fault current rises at extremely high rates, and the system contains a large number of power electronic devices with limited current-carrying capacity. If faults cannot be quickly and accurately identified and isolated, they can easily lead to equipment damage or even system collapse.

[0004] In terms of DC collection network protection, existing technologies mainly include the following categories: First, protection methods based on current change rate or waveform curvature. Although these methods are not affected by transition resistance to a certain extent, they require extremely high sampling frequency, increasing hardware costs and implementation complexity. Second, single-ended or double-ended protection schemes based on boundary elements (such as smoothing reactors) distinguish between internal and external faults by identifying the difference in high-frequency energy during fault transients. However, in offshore wind power DC systems, such boundary elements are usually not installed to save platform space and weight, which limits the applicability of this type of method. Third, protection schemes based on the current differential principle. Although they have strong fault discrimination capabilities, they rely on communication channels to achieve double-ended data synchronization, which is susceptible to communication delays and interruptions, resulting in decreased reliability in complex multi-ended DC networks.

[0005] In summary, existing protection methods, when applied to deep-sea all-DC wind power collection systems, generally suffer from high hardware requirements, reliance on boundary components or communication systems, and difficulty in adapting to complex multi-branch fault scenarios. Therefore, how to enable single-ended protection methods to be independent of communication, require no additional boundary components, and quickly and accurately identify fault types and locations to ensure the safe and stable operation of the system is a technical problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the existing technology and provide a single-ended protection method for offshore wind power DC collection systems based on transient current change rate. By integrating a series of synergistic technical means such as transient power factor secondary confirmation, transient current change rate accurate algorithm, extreme value ratio comparison line selection, and bus fault identification, a complete, reliable and fast-responding single-ended protection scheme is constructed.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] According to one aspect of the present invention, a single-ended protection method for an offshore wind power DC collector system based on transient current change rate is provided, the specific steps of which include: S1, collecting the positive and negative currents at the outlets of each collecting line of the DC collector system; calculating the transient fault current of each line, wherein the transient fault current is the difference between the current value and the steady-state current value before the fault; S2, calculating the transient current change rate of the positive and negative poles of each line based on the transient fault current; S3, if the inter-pole unbalanced voltage is detected to be greater than a first voltage threshold, then a single-pole grounding fault protection process is initiated, and the faulty line and faulty pole are determined according to the polarity and amplitude relationship of the transient current change rate of the positive and negative poles of each line; if the inter-pole measured voltage is detected to be less than a second voltage threshold, then a bipolar short-circuit fault protection process is initiated, and the faulty line and faulty pole are determined according to the polarity and amplitude relationship of the transient current change rate of the positive and negative poles of each line; before initiating the single-pole or bipolar fault protection process, a secondary confirmation step is also included, calculating the transient power factor; if the transient power factor is greater than zero, then the existence of the fault is confirmed, and the protection process continues to be executed; otherwise, the protection process is stopped.

[0009] Furthermore, the transient power factor The calculation expression is:

[0010] ,

[0011] in, This is the current of the non-fault line. This is the DC bus voltage. To collect the voltage at the beginning of the line;

[0012] When the fault is a single-pole ground fault, the non-faulty line current is:

[0013] ,

[0014] in, This refers to the non-faulty line current during a single-pole ground fault. This is the component in the equivalent grounding capacitance current. The impedance ratio, k There are 8 branches for collecting data from corresponding wind farms;

[0015] When the fault is a bipolar short circuit, the non-faulty line current is:

[0016] ,

[0017] in, This refers to the non-faulty line current during a bipolar short-circuit fault. This is the equivalent grounding capacitance current.

[0018] Furthermore, the transient current change rate is obtained by using the transient fault current values ​​at three consecutive sampling points, and is expressed as:

[0019] ,

[0020] in, It is the transient current, and its value is the total current. Current before the fault The difference; The sampling period; , and The first n Fault current at +1 sampling point, the first n +2 sampling points of fault current and the first n Fault current at each sampling point.

[0021] Furthermore, the specific steps for determining the faulty line and faulty pole in the single-pole grounding fault protection process include:

[0022] Calculate the maximum rate of change of the positive transient current in each line. The minimum value of the negative electrode transient current change rate. The maximum rate of change of the positive electrode was obtained. and the minimum rate of change of the negative electrode maximum ratio K The expression is:

[0023] ,

[0024] ,

[0025] in, The rate of change of the transient current at the positive electrode. The rate of change of the transient current at the negative electrode;

[0026] Compare the ratio K with the preset threshold M. If the rate of change of the transient current at the positive pole of the corresponding line is greater than the rate of change of the transient current at the negative pole, the fault occurs at the positive pole of the line corresponding to the maximum rate of change of the positive pole; otherwise, the fault occurs at the negative pole of the line corresponding to the minimum rate of change of the negative pole.

[0027] Furthermore, the steps for determining the faulty line and faulty pole in the bipolar short-circuit fault protection process are consistent with those in the unipolar ground fault protection process.

[0028] Furthermore, before initiating the single-pole or double-pole fault protection process, bus fault judgment is also included. If the transient current change rate of all lines is positive and the transient current change rate of the negative lines is negative, then the fault is determined to occur on the bus.

[0029] Furthermore, the first voltage threshold is 0.1 times the rated inter-electrode voltage.

[0030] Furthermore, the second voltage threshold is 0.9 times the rated inter-electrode voltage.

[0031] According to a second aspect of the present invention, an electronic device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the program to implement the method described thereon.

[0032] According to a third aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the method described thereon.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) By introducing a two-level confirmation step based on transient power factor and combining it with a precisely set voltage start criterion, the protection false start caused by normal system fluctuations or interference is effectively avoided, the reliability and accuracy of the protection system are improved, and the protection action is ensured to be triggered only when a real fault occurs, thereby reducing the risk of misoperation and improving the stability and safety of offshore wind power DC collection system operation.

[0035] (2) It provides specific formulas for the discretization of transient current change rate and fault line selection and pole selection method based on extreme value ratio comparison, which can quickly and accurately capture the transient characteristics of the initial stage of fault, and use the characteristics of the algorithm itself to amplify the characteristic differences between the fault line and the healthy line, thereby realizing the rapid location and type identification of faults, reducing the excessive requirements on hardware sampling frequency, and improving the adaptability to different fault locations and transition resistances.

[0036] (3) By setting a bus fault criterion, it is possible to effectively distinguish whether the fault occurs on the line or on the bus. This criterion is based on the consistency of the electrical quantity change characteristics of all outgoing lines when a bus fault occurs, which prevents the protection device from tripping the line circuit breaker incorrectly due to a bus fault, making the protection strategy more complete, avoiding the expansion of the fault range, ensuring the continuous power supply of non-faulty lines, and improving the reliability of the system power supply. Attached Figure Description

[0037] Figure 1 The flowchart shows a single-ended protection method for offshore wind power DC collector systems based on transient current change rate.

[0038] Figure 2 This is a topology diagram of an offshore wind power DC system. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0040] Example 1

[0041] like Figure 1 As shown, this paper presents a single-ended protection method for offshore wind power DC collector systems based on transient current change rate. By integrating a series of synergistic technologies, including two-level transient power factor verification, precise transient current change rate algorithm, extreme value ratio comparison for line selection, and bus fault identification, a complete, reliable, and fast-responding single-ended protection scheme is constructed. This scheme can accurately identify the fault type and location in the early stages of a fault, effectively avoiding false trips and failures to trip. It improves the speed, selectivity, and reliability of offshore wind power DC collector system protection, providing key technical support for the safe and stable operation of deep-sea DC wind power.

[0042] Specifically, the single-ended protection method provided in this application effectively filters out normal system fluctuation interference by introducing a transient power factor as a secondary confirmation step, reducing the risk of false start-up of the protection system and improving the reliability of the protection system. By using a discretized calculation formula based on three consecutive sampling points to accurately calculate the transient current change rate, the excessive dependence on hardware sampling frequency is reduced, enhancing the convenience and adaptability of engineering implementation. Furthermore, by constructing a line selection criterion based on the ratio of the extreme values ​​of the positive and negative transient current change rates, the difference in transient characteristics between faulty lines and healthy lines is amplified, thereby improving the sensitivity and accuracy of line selection for identifying faults at the end of the line and high-resistance grounding faults. Moreover, because a ratio form is used, it eliminates the need to set multiple sets of thresholds for lines of different lengths, simplifying engineering settings. The synergistic effect of technologies such as transient power factor secondary confirmation, accurate algorithm for transient current change rate, extreme value ratio comparison for line selection, and bus fault identification ultimately enables this protection scheme to achieve a comprehensive improvement in speed, selectivity, and reliability: it can quickly locate and isolate faults in a very short time before the converter is blocked, effectively preventing the expansion of the fault range; it accurately distinguishes between line faults and bus faults, avoiding false tripping of healthy lines due to bus faults, and ensuring continuous power supply to non-faulty areas; at the same time, this scheme does not rely on communication channels or additional boundary components, providing a complete, economical, and easy-to-implement safe operation guarantee for deep-sea all-DC wind power collection systems.

[0043] The specific steps of the single-ended protection method for offshore wind power DC collector systems based on transient current change rate include:

[0044] S1. Collect the positive and negative currents at the outlets of each collecting line of the DC collector system; calculate the transient fault current of each line, which is the difference between the current value and the steady-state current value before the fault.

[0045] S2. Based on the transient fault current, calculate the rate of change of transient current at the positive and negative poles of each line;

[0046] S3. If the inter-electrode unbalanced voltage is detected to be greater than the first voltage threshold, the single-pole grounding fault protection procedure is initiated. The faulty line and faulty pole are determined based on the polarity and amplitude relationship of the transient current change rate of each line's positive and negative poles. If the inter-electrode measured voltage is detected to be less than the second voltage threshold, the double-pole short-circuit fault protection procedure is initiated. The faulty line and faulty pole are determined based on the polarity and amplitude relationship of the transient current change rate of each line's positive and negative poles. Before initiating the single-pole or double-pole fault protection procedure, a secondary confirmation step is also included to calculate the transient power factor. If the transient power factor is greater than zero, the existence of the fault is confirmed, and the protection procedure continues to be executed; otherwise, the protection procedure is stopped.

[0047] This embodiment employs a single-ended protection method based on transient current change rate, avoiding the communication synchronization issues of dual-ended protection. The protection method is independent of boundary elements and is suitable for DC offshore wind farm structures. Furthermore, it eliminates the dimensional and amplitude differences in the transient current change rate between internal and external faults by using a ratio form, eliminating the need for multiple threshold values ​​for lines of different lengths. In addition, the protection method of this embodiment has the ability to withstand grounding resistance, improving the reliability of the protection.

[0048] Offshore wind power DC systems employ a parallel two-stage boost topology, such as... Figure 2 As shown, the system comprises eight collection branches, namely voltage transformation chains, converter structures, and grounding designs. Each branch is connected to a 50MW equivalent wind turbine unit via submarine cables of varying lengths. At the turbine outlet, the voltage is converted from 6.6kV via an AC / DC converter, then stepped up to ±33kV via an input-parallel-output series DC / DC / DC converter before being connected to the collection line. At the wind farm outlet, a back-to-back modular multilevel converter (FTF-MMC) is used, which includes multiple half-bridge sub-modules and three-phase voltage transformers in star / star configurations. The FTF-MMC boosts the voltage to ±200kV, and finally transmits it to the onshore modular multilevel converter (MMC) via a high-voltage DC line. Referring to the DC distribution network grounding model, the primary winding of the three-phase transformer connected to the onshore grid uses a delta connection, while the secondary winding uses a star connection with a neutral point grounded. The grounding design considers the effects of harmonics and fault currents to ensure system stability.

[0049] In the event of a ground fault, if the transient current change rates of all collecting lines (positive and negative poles) have the same sign, it is determined to be a single-pole ground fault on the busbar. For single-pole ground faults, the fault current mainly originates from the charging and discharging process of the cable capacitance, and its characteristics are reflected by the transient current change rate. If the positive current direction is from the busbar to the line, the transient current change rate of the faulty branch is initially positive, and that of the non-faulty branch is negative, and the fault line current satisfies... Non-fault line current Where k represents the corresponding wind farm collection branch, of which there are 8; p and n represent the positive and negative electrodes, respectively; For converter current; This is the equivalent grounding capacitance current; This is the impedance ratio. Since the equivalent impedance of the line is less than the equivalent impedance of the MMC, we can obtain... and That is, the rate of change of transient current at the faulty electrode is greater than that at the non-faulty electrode.

[0050] In the single-pole fault protection scheme of a DC offshore wind farm, when the system is in steady-state operation, the positive and negative voltages of the collector line are equal in magnitude and opposite in direction, and their phasor sum is zero. However, when a single-pole ground fault occurs, the voltage of the grounded electrode drops rapidly to zero, and the voltage of the non-faulty electrode rises to twice the rated voltage due to coupling effects. At this point, the phasor sum of the positive and negative voltages is no longer zero. Therefore, the activation criterion for single-pole fault protection is: if the detected inter-electrode unbalanced voltage is greater than a first voltage threshold, the single-pole ground fault protection procedure is initiated. The first voltage threshold is 0.1 times the rated inter-electrode voltage.

[0051] If the transient current change rate of all collecting lines is negative at the positive terminal or positive at the negative terminal, it is determined to be a bipolar short-circuit fault on the bus. When a bipolar short-circuit fault occurs, the voltage at the fault terminal drops sharply to 0, and both the converter parallel capacitor and the MMC submodule capacitor participate in the discharge. This characteristic is also reflected in the transient current change rate. The transient current change rate of the faulty line is significantly greater than that of the non-faulty line. The transient current change rate of the faulty line is positive at the positive terminal and negative at the negative terminal, while the non-faulty line is the opposite. Non-fault line current Total fault current This reflects the superposition effect of multi-source capacitor discharge. Among them, This refers to the capacitor current on the MMC side.

[0052] Fault line and pole selection are achieved by starting with unbalanced voltage and combining ROCOTC polarity and amplitude. In the bipolar fault protection scheme, a bipolar short-circuit fault causes a rapid drop in the inter-electrode voltage, and this characteristic can be used as the starting criterion for bipolar fault protection. Therefore, the starting criterion for bipolar short-circuit fault protection is: if the measured inter-electrode voltage is detected to be less than a second voltage threshold, the bipolar short-circuit fault protection process is initiated, where the second voltage threshold is 0.9 times the rated inter-electrode voltage.

[0053] The secondary verification process after startup confirms whether the fault truly occurs within the protected fault line and whether activating the protection is meaningful. If the transient power factor is greater than 0, the fault location is confirmed, and the protection is officially activated. If the transient power factor is less than 0, it indicates no fault, and operation is stopped. This secondary verification effectively filters out interference such as voltage fluctuations, preventing false tripping.

[0054] Transient power factor The calculation expression is:

[0055] ,

[0056] in, This is the current of the non-fault line. This is the DC bus voltage. To collect the voltage at the beginning of the line. Transient power factor. It is a dimensionless transient energy flow index, used only to determine faults.

[0057] When the fault is a single-pole ground fault, the current in the non-faulty line is:

[0058] ,

[0059] in, This refers to the non-faulty line current during a single-pole ground fault. This is the component in the equivalent grounding capacitance current. The impedance ratio, k There are 8 branches for collecting data from corresponding wind farms;

[0060] When the fault is a bipolar short circuit, the current in the non-faulty line is:

[0061] ,

[0062] in, This refers to the non-faulty line current during a bipolar short-circuit fault. This is the equivalent grounding capacitance current.

[0063] The rate of change of transient current is obtained by taking the transient fault current values ​​at three consecutive sampling points, and its expression is:

[0064] ,

[0065] in, It is the transient current, and its value is the total current. Current before the fault The difference; The sampling period; , and The first n Fault current at +1 sampling point, the first n +2 sampling points of fault current and the first n Fault current at each sampling point.

[0066] The specific steps for determining the faulty line and faulty pole in the single-pole grounding fault protection process include:

[0067] Calculate the maximum rate of change of the positive transient current in each line. The minimum value of the negative electrode transient current change rate. The maximum rate of change of the positive electrode was obtained. and the minimum rate of change of the negative electrode maximum ratio K The expression is:

[0068] ,

[0069] ,

[0070] in, The rate of change of the transient current at the positive electrode. The rate of change of the transient current at the negative electrode;

[0071] Compare the ratio K with the preset threshold M. If the transient current change rate at the positive terminal of the corresponding line is greater than that at the negative terminal, the fault occurs at the positive terminal corresponding to the maximum rate of change at the positive terminal; otherwise, the fault occurs at the negative terminal corresponding to the minimum rate of change at the negative terminal. A value of M of 0.2 is sufficient to ensure reliability and sensitivity. By amplifying the characteristics of the faulty line, the accuracy and sensitivity of line selection are improved, especially in the case of high-resistance faults or faults at the end of the line, enabling more reliable identification of the faulty line. In addition, the ratio form eliminates the difference in the amplitude of the transient current change rate caused by the inherent capacitance of lines of different lengths, making a single threshold preset value M applicable to lines of all lengths in the system, greatly reducing the complexity of engineering tuning.

[0072] The steps for determining the faulty line and faulty pole in the bipolar short-circuit fault protection process are the same as those in the unipolar ground fault protection process.

[0073] To prevent maloperation of protection systems due to single-pole grounding faults on the busbar, a busbar fault criterion has been added. Before initiating the single-pole or double-pole fault protection procedure, a busbar fault determination is included. If the transient current change rate of all lines' positive poles is also positive, and the transient current change rate of all lines' negative poles is also negative, then the fault is determined to occur on the busbar. That is, the determination... and Is the product of and greater than 0? If the product is greater than 0, that is... A value greater than 0 indicates that the ROCOTC values ​​of all collector lines are either both positive or both negative, suggesting that the fault occurred on the busbar. Single-pole fault protection first determines whether to activate the protection based on activation criteria. If activated, it then performs a series of calculations and judgments to determine the faulty line and pole. The busbar fault criterion can quickly and accurately distinguish between busbar faults and line faults, preventing the false tripping of all healthy lines due to a busbar fault, minimizing the fault isolation range, and ensuring the continuity of power supply to the system.

[0074] This embodiment analyzes the fault characteristics of different fault types in offshore wind farm DC collection systems, such as single-pole grounding and double-pole short circuit, including current variation patterns and polarity differences. The fault characteristic analysis quantifies the polarity-amplitude combination law, providing a theoretical basis for single-end protection of boundaryless components and promoting the practical application of DC grids for deep-sea wind power.

[0075] In addition, a single-ended protection method based on transient current change rate is proposed. The method uses the difference in polarity and amplitude of transient current change rate between internal and external faults to quickly identify faults. A two-level start-up criterion is designed to avoid system collapse caused by communication failures and signal delays. This effectively improves the efficiency of offshore wind power system protection while ensuring that there is no misoperation.

[0076] By simplifying the judgment by using a ratio in the line selection criterion stage, the complementary polarity information of bipolar transient currents is fully utilized, eliminating the need to set multiple thresholds for lines of different lengths. This reduces time costs and improves efficiency.

[0077] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the described module can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0078] Example 2

[0079] The electronic device of this invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in read-only memory (ROM) or loaded from a storage unit into random access memory (RAM). The RAM may also store various programs and data required for device operation. The CPU, ROM, and RAM are interconnected via a bus. Input / output (I / O) interfaces are also connected to the bus.

[0080] Multiple components in the device are connected to an I / O interface, including: input units such as a keyboard, mouse, etc.; output units such as various types of displays, speakers, etc.; storage units such as disks, optical disks, etc.; and communication units such as network interface cards, modems, wireless transceivers, etc. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks. The processing unit performs the various methods and processes described above, such as the method of the present invention. For example, in some embodiments, the method of the present invention may be implemented as a computer software program tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via ROM and / or the communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of the method of the present invention described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute the method of the present invention by any other suitable means (e.g., by means of firmware).

[0081] The functions described above in this document can be performed, at least in part, by one or more hardware logic components. For example, exemplary types of hardware logic components that can be used, without limitation, include: Field Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application Standard Products (ASSPs), System-on-Chip (SoCs), Complex Programmable Logic Devices (CPLDs), and so on.

[0082] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0083] In the context of this invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A single-ended protection method for offshore wind power DC collector systems based on transient current change rate, characterized in that, The specific steps include: S1, collecting the positive and negative currents at the outlets of each collecting line of the DC collector system; calculating the transient fault current of each line, wherein the transient fault current is the difference between the current value and the steady-state current value before the fault; S2, calculating the transient current change rate of each line's positive and negative poles based on the transient fault current; S3, if the inter-pole unbalanced voltage is detected to be greater than the first voltage threshold, then the single-pole grounding fault protection process is initiated, and the faulty line and faulty pole are determined according to the polarity and amplitude relationship of the transient current change rate of each line's positive and negative poles; if the inter-pole measured voltage is detected to be less than the second voltage threshold, then the bipolar short-circuit fault protection process is initiated, and the faulty line and faulty pole are determined according to the polarity and amplitude relationship of the transient current change rate of each line's positive and negative poles; before initiating the single-pole grounding or bipolar short-circuit fault protection process, a secondary confirmation step is also included, calculating the transient power factor; if the transient power factor is greater than zero, then the existence of the fault is confirmed, and the protection process continues to be executed; otherwise, the protection process is stopped. The transient power factor The calculation expression is: ， in, This is the current of the non-fault line. This is the DC bus voltage. To collect the voltage at the beginning of the line; When the fault is a single-pole ground fault, the non-faulty line current is: ， in, This refers to the non-faulty line current during a single-pole ground fault. This is the component of the equivalent grounding capacitance current. The impedance ratio, k There are 8 branches for collecting data from corresponding wind farms; When the fault is a bipolar short circuit, the non-faulty line current is: ， in, This refers to the non-faulty line current during a bipolar short-circuit fault. This is the equivalent grounding capacitance current.

2. The single-ended protection method for an offshore wind power DC collector system based on transient current change rate according to claim 1, characterized in that, The transient current change rate is obtained from the transient fault current values ​​at three consecutive sampling points, and is expressed as: ， in, It is the transient current, and its value is the total current. Current before the fault The difference; The sampling period; , and The first n Fault current at +1 sampling point, the first n +2 sampling points of fault current and the first n Fault current at each sampling point.

3. The single-ended protection method for an offshore wind power DC collector system based on transient current change rate according to claim 1, characterized in that, The specific steps for determining the faulty line and faulty pole in the single-pole grounding fault protection process include: Calculate the maximum rate of change of the positive transient current in each line. The minimum value of the negative electrode transient current change rate. The maximum rate of change of the positive electrode was obtained. and the minimum rate of change of the negative electrode maximum ratio K The expression is: ， ， in, The rate of change of the transient current at the positive electrode. The rate of change of the transient current at the negative electrode; Compare the ratio K with the preset threshold M. If the rate of change of the transient current at the positive pole of the corresponding line is greater than the rate of change of the transient current at the negative pole, the fault occurs at the positive pole of the line corresponding to the maximum rate of change of the positive pole; otherwise, the fault occurs at the negative pole of the line corresponding to the minimum rate of change of the negative pole.

4. The single-ended protection method for an offshore wind power DC collector system based on transient current change rate according to claim 1, characterized in that, The steps for determining the faulty line and faulty pole in the bipolar short-circuit fault protection process are the same as those in the unipolar ground fault protection process.

5. A single-ended protection method for an offshore wind power DC collector system based on transient current change rate according to claim 1, characterized in that, Before initiating the single-pole or double-pole fault protection process, bus fault judgment is also included. If the transient current change rate of all lines is positive and the transient current change rate of the negative lines is negative, then the fault is determined to occur on the bus.

6. The single-ended protection method for an offshore wind power DC collector system based on transient current change rate according to claim 1, characterized in that, The first voltage threshold is 0.1 times the rated inter-electrode voltage.

7. The single-ended protection method for an offshore wind power DC collector system based on transient current change rate according to claim 1, characterized in that, The second voltage threshold is 0.9 times the rated inter-electrode voltage.

8. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the program, it implements the method as described in any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 7.

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