DC side fault detection protection method and system based on MMC-HVDC

Abstract

The invention discloses a DC side fault detection protection method and system based on MMC-HVDC, and the method directly judges whether a fault occurs or not through the ratio of the voltage of the voltage source side of a current-limiting inductor at two ends of a DC line to the voltage of the line side, thereby avoiding the transient quantity which depends on the voltage differential or the wave head of a traveling wave and is liable to be affected by noise. The anti-interference capability and reliability of protection are improved, when it is determined that a fault occurs, the specific type of the fault and the fault polar line are gradually judged in a progressive mode, a reliable basis is provided for subsequent selective isolation, judgment is conducted from fault starting to final polar line determination based on the obtained electrical quantity, and the reliability of the fault is improved. And the data anti-interference is low, the fault can be accurately identified and rapidly isolated, and the problem that the traditional DC power grid protection is low in reliability and speed is solved.

Description

Technical Field

[0001] This invention belongs to the field of high voltage DC power grid protection, and relates to a DC side fault detection and protection method and system based on MMC-HVDC. Background Technology

[0002] Flexible DC grids, with their excellent control capabilities, rapid power regulation response, and highly flexible operating modes, significantly improve the operational flexibility and power supply reliability of power systems. Considering factors such as reducing the probability of DC faults, transmission distance, and voltage levels, overhead line transmission is widely used as one of the main methods for large-scale power transmission in MMC-HVDC projects. Grid protection has stringent requirements in terms of speed; currently, DC grid fault protection still faces technical challenges such as slow response speed and low reliability.

[0003] Currently, domestic and international literature on protection based on the characteristic quantities of current-limiting inductors combines differential undervoltage and directional longitudinal protection to achieve rapid isolation. Differential undervoltage protection achieves millisecond-level action by detecting the voltage drop rate, while directional longitudinal protection utilizes communication channels to ensure accurate fault location. The synergy of these two methods significantly improves the fault response capability of the renewable energy grid. However, differential undervoltage is susceptible to system disturbances and noise interference, leading to false tripping. Directional longitudinal protection relies on communication channels, and delays or interruptions will affect reliability. The synergy of both methods may exacerbate the risk of transient overvoltage or power angle instability. Using the high-frequency transient components of voltage traveling waves offers high reliability and anti-interference capabilities, making it particularly suitable for UHV and long-distance transmission lines. However, this method has limitations: capturing the wavefront is difficult, leading to errors and decreased sensitivity; high-frequency noise interference requires complex algorithms such as wavelet transform, increasing implementation difficulty. In summary, existing research on the voltage characteristic quantities of current-limiting reactors still has shortcomings in terms of speed and sensitivity in DC fault protection. Summary of the Invention The purpose of this invention is to solve the problems of insufficient speed, limited reliability and weak anti-interference ability in the DC grid protection of the prior art due to reliance on complex signal processing or external communication, and to provide a DC side fault detection and protection method and system based on MMC-HVDC.

[0004] To achieve the above objectives, the present invention employs the following technical solution: A DC-side fault detection and protection method based on MMC-HVDC includes the following steps: Obtain the ratio of the voltage source side to the voltage line side of the current-limiting inductor at both ends of the DC line, and compare the ratio with the preset fault initiation threshold to determine whether a fault has occurred. If a fault occurs, calculate the magnitude of the voltage change in the current-limiting inductor, compare the magnitude of the change with the preset fault type identification threshold, and confirm whether the fault type is a single-pole grounding fault or a bipolar short-circuit fault. If the fault type is a bipolar short circuit fault, select the corresponding fault isolation measures. If the fault type is a bipolar short circuit fault, calculate the voltage change difference of the current limiting inductor, compare the voltage change difference of the current limiting inductor with the preset fault pole identification threshold, and confirm whether the fault is a positive short circuit fault or a negative short circuit fault. Select the corresponding fault isolation measures based on the detected fault.

[0005] A further improvement of the present invention is that: After confirming the occurrence of a fault, the fault is determined to be either a line fault or a bus fault based on the sub-thresholds in the fault initiation threshold.

[0006] After confirming a fault has occurred, the process of determining whether the fault is a line fault or a bus fault based on a sub-threshold in the fault initiation threshold includes: When the ratio of the voltage on the source side of the current-limiting inductor to the voltage on the line side satisfies the following formula, the fault is confirmed as a line fault:

[0007] When the ratio of the voltage on the current-limiting inductor voltage source side to the voltage on the line side satisfies the following formula, the fault is confirmed as a bus fault:

[0008] in, U dc Voltage on the voltage source side, U L Indicates the line-side voltage. U c This represents the ratio of the voltages across the current-limiting inductor. U n The voltage ratio during normal operation is set to 1. U 1 indicates the line fault initiation threshold and margin of increase. r 1. Take 30%; U st This represents the ratio of the maximum theoretical voltage to the busbar grounding fault. U 2 represents the bus fault initiation threshold, a proportional coefficient. r 2. Take 30%.

[0009] If a fault occurs, the amplitude of the voltage change in the current-limiting inductor is calculated, and the amplitude is compared with a preset fault type identification threshold to confirm whether the fault type is a single-pole ground fault or a bipolar short-circuit fault, including: Calculate the amplitude of voltage changes at the positive and negative terminals of the current-limiting inductor, and compare the calculation results with the fault type identification threshold. U 3. Comparison:

[0010] in, u P and u N These are the positive and negative voltages of the current-limiting inductor, respectively. t Indicates time, U 3. Fault type identification threshold U m This represents the maximum difference in voltage change between the positive and negative poles after a single-pole grounding fault. r 3 represents a growth margin of 25%; when U s > U At 3 o'clock, the current fault is determined to be a single-pole ground fault; when U s ≤ U At time 3, the current fault is determined to be a bipolar short-circuit fault.

[0011] If the fault type is a bipolar short-circuit fault, the difference in voltage change of the current-limiting inductor is calculated, and the difference in voltage change of the current-limiting inductor is compared with a preset fault polarity identification threshold to confirm whether the fault is a positive short-circuit fault or a negative short-circuit fault, including: Determine whether a single-pole grounding fault occurs on the positive or negative pole using the following formula:

[0012] in, u P and u N These are the positive and negative voltages of the current-limiting inductor, respectively. t Indicates time, U 4 represents the fault identification threshold. U a The voltage variation difference during normal operation, representing the fluctuation margin. r 4. Take 10%; like U f > U At 4 o'clock, the current fault is determined to be a negative ground fault; like U f ≤ U At 4 o'clock, the current fault is determined to be a positive ground fault.

[0013] The step of selecting corresponding fault isolation measures based on the detected fault includes: Based on the detected fault, the fault current is interrupted using a hybrid DC circuit breaker.

[0014] A DC-side fault detection and protection system based on MMC-HVDC includes: The fault confirmation module is used to obtain the ratio of the voltage source side of the current-limiting inductor voltage and the voltage line side at both ends of the DC line, and compare the ratio with the preset fault initiation threshold to determine whether a fault has occurred. The fault type confirmation module is used to calculate the voltage change amplitude of the current-limiting inductor if a fault occurs, compare the change amplitude with the preset fault type identification threshold, and confirm whether the fault type is a single-pole grounding fault or a double-pole short-circuit fault. The fault pole identification and confirmation module is used to select the corresponding fault isolation measures if the fault type is a bipolar short circuit fault. If the fault type is a bipolar short circuit fault, it calculates the difference in the voltage change of the current limiting inductor, compares the difference in the voltage change of the current limiting inductor with the preset fault pole identification threshold, and confirms whether the fault is a positive short circuit fault or a negative short circuit fault. The circuit protection module is used to select the corresponding fault isolation measures based on the detected fault.

[0015] A computer program product includes a computer program that, when executed by a processor, implements the method described in any one of the present invention.

[0016] A terminal device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of any of the methods described in this invention.

[0017] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of any of the methods described in this invention.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a DC-side fault detection and protection method based on MMC-HVDC. It directly determines whether a fault has occurred by the ratio of the voltage source side voltage and the line side voltage of the current-limiting inductor at both ends of the DC line. This avoids relying on transient quantities such as voltage differential or traveling wave front, which are susceptible to noise, thus improving the anti-interference capability and reliability of the protection. When a fault is determined, the specific type of fault and the fault pole are gradually determined in a progressive manner, providing a reliable basis for subsequent selective isolation. From fault initiation to final pole determination, this invention is based on the acquired electrical quantities for judgment. The data has low anti-interference capability and can accurately identify and quickly isolate faults, solving the problems of low reliability and speed of traditional DC grid protection. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the fault detection process disclosed in an embodiment of the present invention; Figure 2 This is the four-segment MMC-HVDC system topology disclosed in the embodiments of the present invention; Figure 3a This is a simulation waveform diagram of the operating current of a single-pole line grounding fault circuit interrupter disclosed in an embodiment of the present invention; Figure 3b This is a simulation waveform diagram of the fault line voltage in a single-pole line grounding fault disclosed in an embodiment of the present invention; Figure 4a This is a simulation waveform diagram of the operating current of a single-pole line grounding fault circuit interrupter disclosed in an embodiment of the present invention; Figure 4b This is a simulation waveform diagram of the fault line voltage in a single-pole line grounding fault disclosed in an embodiment of the present invention; Figure 5a This is a simulation waveform diagram of the operating current of the circuit breaker during a bus grounding fault, as disclosed in an embodiment of the present invention. Figure 5b This is a simulation waveform diagram of the fault line voltage during a bus grounding fault as disclosed in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0025] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0026] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 This invention discloses a DC-side fault detection and protection method based on MMC-HVDC, which has the advantages of quickly blocking fault current and accurately locating fault points. Specifically, it includes the following steps: Step 1: Fault start-up; The fault initiation is determined by the ratio of the voltage source side to the voltage on the line side of the current-limiting inductor at both ends of the DC line.

[0028] In step 1, the fault initiation step selects to monitor the voltage parameters on both sides of the current-limiting inductor, and when the voltage ratio between the voltage source side and the line side of the current-limiting inductor is detected to be greater than 1.3 or less than 0.5, it is determined that a system fault has occurred.

[0029] Furthermore, based on the fault voltage and current characteristics, if the voltage ratio is greater than 1.3, it is judged as a line fault; if the voltage ratio is less than 0.5, it is judged as a bus fault.

[0030] Specifically, in this step, the main protection identification step includes: When the system is running, it collects the voltage ratio data of the current-limiting inductor voltage source side and the line side at both ends of the DC line; When this ratio satisfies the condition of equation (1), the protection is activated and the line fault is identified. If the ratio satisfies the condition of equation (2), the protection will be activated and the fault will be judged as a bus fault. (1) (2) in, U dc Voltage on the voltage source side, U L Indicates the line-side voltage. U c This represents the ratio of the voltages across the current-limiting inductor. U n The voltage ratio during normal operation is set to 1. U 1 indicates the line fault initiation threshold and margin of increase. r 1. Take 30%; U st This represents the ratio of the maximum theoretical voltage to the busbar grounding fault. U 2 represents the bus fault initiation threshold, a proportional coefficient. r 2 take 30% Step 2: Type identification; In this step, type identification is achieved by using the amplitude of the voltage change of the current-limiting inductor to distinguish between single-pole and double-pole short-circuit faults.

[0031] After determining that a line fault has occurred in step 1, the fault type identification step selects the rate of change of the current-limiting inductor voltage amplitude and the setting threshold of 500kV / ms for judgment to determine the fault type.

[0032] If the rate of change of voltage amplitude is greater than the set threshold of 500kV / ms, it is determined to be a single-pole grounding fault. If the rate of change of voltage amplitude is less than the set threshold of 500kV / ms, it is determined to be a bipolar short-circuit fault. Specifically, the type identification step in this process includes: Measure the voltage change across the current-limiting inductor in the DC circuit, calculate the amplitude of the voltage change between the positive and negative terminals of the current-limiting inductor, and distinguish between single-pole and double-pole short-circuit faults. The specific criteria are as follows: (3) in, u P and u N These are the positive and negative voltages of the current-limiting inductor, respectively. t Indicates time, U 3. Fault type identification threshold Um This represents the maximum difference in voltage change between the positive and negative poles after a single-pole grounding fault. r 3 represents a growth margin of 25%; when the conditions of equation (3) are met, it is judged as a single-pole ground fault, and polarity selection is also required to determine the circuit breaker's operation; otherwise, it is a double-pole short-circuit fault, that is, when U s ≤ U At 3 o'clock, the current fault is determined to be a bipolar short circuit fault, and the DC circuit breakers at both ends of the positive and negative lines are activated.

[0033] Step 3: Fault polarity selection; Fault pole selection uses the difference in voltage change of the current-limiting inductor to determine whether a positive or negative short-circuit fault has occurred in the system. In step 3, the fault selection step selects the current-limiting inductor voltage change rate and the setting threshold 10. 3 The fault location is determined by measuring kV / ms to pinpoint the fault pole and obtain the accurate fault location.

[0034] If the voltage change rate is greater than the setting threshold 10 3 kV / ms, determined to be a grounding fault on the negative line; If the voltage change rate is less than the setting threshold of 10 3 The value was measured in kV / ms, indicating a grounding fault on the positive line.

[0035] Specifically, the fault selection step in this process includes: To further determine whether a unipolar ground fault occurs on the positive or negative pole, the fault pole selection criterion is set as follows: (4) in, u P and u N These are the positive and negative voltages of the current-limiting inductor, respectively. t Indicates time, U 4 represents the fault identification threshold. U a The voltage variation difference during normal operation, representing the fluctuation margin. r 4. Take 10%; if the condition of equation (4) is met, a negative grounding fault occurs, and the DC circuit breaker at both ends of the negative line will operate; otherwise, a positive grounding fault occurs, and the DC circuit breaker at both ends of the positive line will operate.

[0036] Step 4: Fault Isolation Once the corresponding fault is detected, the fast-acting characteristics of the hybrid DC circuit breaker are used for isolation. The fault isolation process can quickly cut off the fault current and isolate the faulty line from other parts of the system. Finally, the feasibility of the scheme is verified through various performance indicators.

[0037] Furthermore, the hybrid DC circuit breaker structure consists of a main branch, a transfer branch, and an energy consumption branch, which can compensate for the lack of fault self-clearing capability in half-bridge type MMCs and has the advantages of fast breaking speed and low conduction loss. Example 2 This invention discloses a DC-side fault detection and protection method based on MMC-HVDC, comprising the following steps: First, determine whether the fault initiation conditions are met based on the voltage ratio across the current-limiting inductor, and then determine whether the fault is a line fault or a bus fault based on the initiation criteria. Among them, the line fault types include single-pole grounding faults and double-pole short-circuit faults. The fault type is determined based on the rate of change of the voltage amplitude of the current-limiting inductor. When the fault type is a single-pole grounding fault, the specific location of the fault point on which line needs to be further determined. Among them, the single-pole grounding fault type is further subdivided into positive pole grounding fault and negative pole grounding fault, and the location of the fault pole is determined according to the voltage change rate of the current-limiting inductor criterion. like Figure 1 As shown, the fault detection method includes the following steps: Step 1: Data Processing and Fault Protection Activation Criteria: First, the ratio of the voltages across the current-limiting inductor on each line was calculated. Comparisons were made under three scenarios: normal system operation, line faults, and bus grounding faults. Significant differences in the voltage ratios were observed across these scenarios. Through multiple verifications, the voltage ratio across the current-limiting inductor was determined. U c It can serve as a fault start criterion and ensure the stability of the system during normal operation. U c The value after reserving the interference margin range is set as the fault initiation threshold. U 1 = 1.3 and U 2 = 0.5.

[0038] Based on the voltage mechanism and current flow direction, it's easy to understand that the voltage at the fault point will suddenly drop to zero, indicating that during the instant of a line fault, the voltage on the line side is much smaller than the voltage on the voltage source side; similarly, during the instant of a bus fault, the voltage on the voltage source side is much smaller than the voltage on the line side. Therefore, the fault initiation criteria for both types of faults are derived: the line fault criterion is greater than... U 1. Busbar Fault Judgment Criteria U 2.

[0039] Line faults are common in power grid systems. In order to more accurately locate the fault point, line faults are then analyzed in detail according to single / double grounding and positive / negative grounding types.

[0040] Step 2, Criteria for Determining Single / Bipolar Fault Types: During a single-pole short circuit, the fault current is mainly concentrated at the faulty pole, and the voltage at the fault point drops rapidly, while the voltage change at the non-faulty poles is relatively small. During a double-pole short circuit, the fault current forms a closed short-circuit path through the positive and negative poles and the fault path, and the voltages at both poles drop significantly. Therefore, the difference in the voltage amplitude change of the current-limiting inductor is used as a criterion for fault type determination.

[0041] The voltage difference between the positive and negative poles caused by a single-pole grounding fault is more significant. Therefore, the maximum voltage difference between the positive and negative poles after a single-pole grounding fault, i.e., the voltage difference when a fault occurs at the far end of the line, is selected as the threshold. After allowing for interference margin, the following is applied: U 3 = 500kV / ms was determined as the fault type discrimination threshold.

[0042] Step 3, Positive and Negative Pole Fault Identification: Because the voltage difference between the fault point and ground drops abruptly at the moment a ground fault occurs, the rate of voltage drop on the voltage source side is significantly higher than that on the line side when the fault is positive; while the rate of voltage drop on the line side is significantly higher than that on the voltage source side when the fault is negative. Therefore, the occurrence of positive or negative ground faults can be distinguished based on the voltage difference across the current-limiting inductor.

[0043] When a positive-to-ground fault occurs, the voltage at the negative terminal of the current-limiting inductor decreases more slowly than the voltage at the faulty positive terminal, and the difference in the rate of change of the positive and negative voltages is calculated as a negative value. Similarly, when a negative-to-ground fault occurs, the voltage changes at the faulty and non-faulty terminals are opposite. Under normal operation, the voltage difference across the inductor is approximately zero. However, the actual trend of this value is very pronounced, reaching several thousand values. Considering the fluctuation margin, [the following is omitted as it is not directly related to the voltage calculation]. U 4=10 3 kV / ms is used as the fault pole identification threshold.

[0044] Specifically, the embodiments of the present invention also disclose the process of verifying the effectiveness and reliability of the above-mentioned fault detection scheme: This invention is based on a four-terminal flexible DC transmission system, which includes a converter, a DC line, and a hybrid DC circuit breaker. The converter adopts a modular multilevel converter (MMC), such as... Figure 2 As shown.

[0045] S1-S4 represent the AC system; MMC1-MMC4 are converters; Bus1-Bus4 are DC buses; 12, 14, 21, 23, 32, 34, 41, and 43 represent the DC circuit breaker and current-limiting inductor numbers, respectively; Line12, Line24, Line34, and Line13 are DC transmission lines; F1-F3 are fault points, where F1 occurs on Line12, F2 occurs on Line34, and F3 occurs on the Bus3 DC bus. The DC circuit breaker is installed at the DC bus outlet, and the current-limiting inductor is installed between the DC circuit breaker and the DC transmission line. Each transmission line includes two lines, one positive and one negative.

[0046] The fault detection scheme includes fault initiation, type identification, and fault polarity selection criteria. Based on these steps, the fault point can be accurately located. When the corresponding fault is detected, a trip signal is issued. The corresponding hybrid DC circuit breaker at the location of the fault point will immediately disconnect after receiving the fault detection pulse signal, thereby achieving rapid fault isolation.

[0047] Protection strategy verification was conducted for single-pole grounding faults, double-pole short-circuit faults, and bus grounding faults, such as... Figures 3a-5b As shown. After each type of fault is detected, the corresponding circuit breaker's main branch disconnects upon receiving the fault signal. Current flows to the transfer branch, and then to the energy-dissipating branch to complete the current interruption. The total operating time does not exceed 4ms, and the voltage of the line where the fault point is located rapidly drops from its rated value under steady-state conditions within a short period. After the circuit breaker operates, the voltage on that line gradually decreases and stabilizes at a value close to zero. These signals indicate that the fault on that line has been completely disconnected, meeting the requirements for speed and reliability of fault protection.

[0048] This invention discloses a DC-side fault detection and protection method based on MMC-HVDC, comprising: The fault confirmation module is used to obtain the ratio of the voltage source side of the current-limiting inductor voltage and the voltage line side at both ends of the DC line, and compare the ratio with the preset fault initiation threshold to determine whether a fault has occurred. The fault type confirmation module is used to calculate the voltage change amplitude of the current-limiting inductor if a fault occurs, compare the change amplitude with the preset fault type identification threshold, and confirm whether the fault type is a single-pole grounding fault or a double-pole short-circuit fault. The fault pole identification and confirmation module is used to select the corresponding fault isolation measures if the fault type is a bipolar short circuit fault. If the fault type is a bipolar short circuit fault, it calculates the difference in the voltage change of the current limiting inductor, compares the difference in the voltage change of the current limiting inductor with the preset fault pole identification threshold, and confirms whether the fault is a positive short circuit fault or a negative short circuit fault. The circuit protection module is used to select the corresponding fault isolation measures based on the detected fault.

[0049] A schematic diagram of a terminal device according to an embodiment of the present invention. The terminal device of this embodiment includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps in the various method embodiments described above. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the various device embodiments described above.

[0050] The computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention.

[0051] The terminal device can be a desktop computer, laptop computer, cloud server, or other device with strong computing power. The terminal device may include, but is not limited to, a processor and memory.

[0052] The optimal choice for the processor is a multi-core high-speed central processing unit (CPU).

[0053] The memory can be used to store the computer program and / or module. The processor implements various functions of the terminal device by running or executing the computer program and / or module stored in the memory and calling the data stored in the memory.

[0054] If the modules / units integrated into the terminal device are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0055] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A DC-side fault detection and protection method based on MMC-HVDC, characterized in that, Includes the following steps: Obtain the ratio of the voltage source side to the voltage line side of the current-limiting inductor at both ends of the DC line, and compare the ratio with the preset fault initiation threshold to determine whether a fault has occurred. If a fault occurs, calculate the magnitude of the voltage change in the current-limiting inductor, compare the magnitude of the change with the preset fault type identification threshold, and confirm whether the fault type is a single-pole grounding fault or a bipolar short-circuit fault. If the fault type is a bipolar short circuit fault, select the corresponding fault isolation measures. If the fault type is a bipolar short circuit fault, calculate the voltage change difference of the current limiting inductor, compare the voltage change difference of the current limiting inductor with the preset fault pole identification threshold, and confirm whether the fault is a positive short circuit fault or a negative short circuit fault. Select the corresponding fault isolation measures based on the detected fault.

2. The DC-side fault detection and protection method based on MMC-HVDC according to claim 1, characterized in that, After confirming the occurrence of a fault, the fault is determined to be either a line fault or a bus fault based on the sub-thresholds in the fault initiation threshold.

3. The DC-side fault detection and protection method based on MMC-HVDC according to claim 1, characterized in that, After confirming a fault has occurred, the process of determining whether the fault is a line fault or a bus fault based on a sub-threshold in the fault initiation threshold includes: When the ratio of the voltage on the source side of the current-limiting inductor to the voltage on the line side satisfies the following formula, the fault is confirmed as a line fault: When the ratio of the voltage on the current-limiting inductor voltage source side to the voltage on the line side satisfies the following formula, the fault is confirmed as a bus fault: in, U dc Voltage on the voltage source side, U L Indicates the line-side voltage. U c This represents the ratio of the voltages across the current-limiting inductor. U n The voltage ratio during normal operation is set to 1. U 1 indicates the line fault initiation threshold and margin of increase. r 1. Take 30%; U st This represents the ratio of the maximum theoretical voltage to the busbar grounding fault. U 2 represents the bus fault initiation threshold, a proportional coefficient. r 2. Take 30%.

4. The DC-side fault detection and protection method based on MMC-HVDC according to claim 1, characterized in that, If a fault occurs, the amplitude of the voltage change in the current-limiting inductor is calculated, and the amplitude is compared with a preset fault type identification threshold to confirm whether the fault type is a single-pole ground fault or a bipolar short-circuit fault, including: Calculate the amplitude of voltage changes at the positive and negative terminals of the current-limiting inductor, and compare the calculation results with the fault type identification threshold. U 3. Comparison: in, u P and u N These are the positive and negative voltages of the current-limiting inductor, respectively. t Indicates time, U 3. Fault type identification threshold U m This represents the maximum difference in voltage change between the positive and negative poles after a single-pole grounding fault. r 3 represents a growth margin of 25%; when U s > U At 3 o'clock, the current fault is determined to be a single-pole ground fault; when U s ≤ U At time 3, the current fault is determined to be a bipolar short-circuit fault.

5. The DC-side fault detection and protection method based on MMC-HVDC according to claim 1, characterized in that, If the fault type is a bipolar short-circuit fault, the difference in voltage change of the current-limiting inductor is calculated, and the difference in voltage change of the current-limiting inductor is compared with a preset fault polarity identification threshold to confirm whether the fault is a positive short-circuit fault or a negative short-circuit fault, including: Determine whether a single-pole grounding fault occurs on the positive or negative pole using the following formula: in, u P and u N These are the positive and negative voltages of the current-limiting inductor, respectively. t Indicates time, U 4 represents the fault identification threshold. U a The voltage variation difference during normal operation, representing the fluctuation margin. r 4. Take 10%; like U f > U At 4 o'clock, the current fault is determined to be a negative ground fault; like U f ≤ U At 4 o'clock, the current fault is determined to be a positive ground fault.

6. The DC-side fault detection and protection method based on MMC-HVDC according to claim 1, characterized in that, The step of selecting corresponding fault isolation measures based on the detected fault includes: Based on the detected fault, the fault current is interrupted using a hybrid DC circuit breaker.

7. A DC-side fault detection and protection system based on MMC-HVDC, characterized in that, include: The fault confirmation module is used to obtain the ratio of the voltage source side of the current-limiting inductor voltage and the voltage line side at both ends of the DC line, and compare the ratio with the preset fault initiation threshold to determine whether a fault has occurred. The fault type confirmation module is used to calculate the voltage change amplitude of the current-limiting inductor if a fault occurs, compare the change amplitude with the preset fault type identification threshold, and confirm whether the fault type is a single-pole grounding fault or a double-pole short-circuit fault. The fault pole identification and confirmation module is used to select the corresponding fault isolation measures if the fault type is a bipolar short circuit fault. If the fault type is a bipolar short circuit fault, it calculates the difference in the voltage change of the current limiting inductor, compares the difference in the voltage change of the current limiting inductor with the preset fault pole identification threshold, and confirms whether the fault is a positive short circuit fault or a negative short circuit fault. The circuit protection module is used to select the corresponding fault isolation measures based on the detected fault.

8. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-6.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1-6.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1-6.

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