Metal neutral line protection method and system suitable for flexible direct current topology

Abstract

The invention discloses a metal neutral line protection method and system suitable for a flexible direct current topology, and is applied to the technical field of flexible direct current power transmission of a power system. Performing fault analysis processing on the fault data to obtain an equivalent circuit model; processing the system parameter data and the operation state data by using a fault distance measurement technology to obtain a fault point position; a neutral line protection strategy model is constructed through the equivalent circuit model and the fault point position, and the neutral line protection strategy model is configured to process the neutral line protection strategy model through the mode conversion technology and process the operation state data based on the obtained current ratio data to obtain a fault processing state; processing the fault processing state by using a constant value determination technology to obtain a metal neutral line protection parameter; and protecting the metal center line based on the metal center line protection parameters. According to the method provided by the invention, accurate isolation of a fault area and continuous power supply of a non-fault area can be realized.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology in power systems, and in particular to a method and system for protecting the metallic neutral line of a flexible DC topology. Background Technology

[0002] With the widespread application of flexible DC transmission technology in new power systems, the topology with a metal neutral wire has become a key technology for overseas projects because it can effectively solve the problems of grounding electrode construction and ground current corrosion in areas with high soil resistivity.

[0003] Considering that metallic neutral line faults include various types such as single-pole grounding, open circuit, and high-resistance grounding, and because it is impossible to distinguish the fault type, in the existing technology, the system is generally directly blocked and tripped when there is a metallic neutral line fault. This can easily lead to the normal shutdown of the non-faulty parts of the system and reduce the reliability of power supply. Summary of the Invention

[0004] This invention provides a method and system for protecting a metallic neutral line suitable for flexible DC topologies, in order to solve the technical problem in the prior art where the system trips due to the inability to distinguish the fault type, resulting in the normal shutdown of the non-faulty parts of the system, so as to achieve accurate isolation of the faulty area and continuous power supply to the non-faulty area.

[0005] To address the aforementioned technical problems, this invention provides a method for protecting a metallic neutral line in a flexible DC topology, the method comprising: Acquire system parameter data and operating status data of the target flexible DC topology, and acquire fault data of the metal centerline in the target flexible DC topology; Fault analysis and processing are performed on the fault data of the metal centerline to obtain the equivalent circuit model of the target flexible DC topology; The system parameter data and the operating status data are processed using fault location technology to obtain the location of the fault point in the metal centerline; A neutral protection strategy model is constructed based on the equivalent circuit model and the fault location. The neutral protection strategy model is configured to process the neutral protection strategy model using mode conversion technology and process the operating status data based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology. The fault handling state is processed using a fixed value determination technique to obtain the metal neutral protection parameters of the target flexible DC topology; Based on the metal neutral protection parameters, the metal neutral of the target flexible DC topology is protected.

[0006] As one preferred embodiment, the step of processing the system parameter data and the operating status data using fault location technology to obtain the location of the fault point in the metal centerline includes: The operating status data includes at least the metal neutral wire sending end current, the metal neutral wire receiving end current, and the metal return line loop current. Based on the equivalent circuit model, the current at the sending end of the metal neutral line, the current at the receiving end of the metal neutral line, and the current in the loop of the metal return line are processed to obtain the parallel loop current-resistance relationship and resistance ratio relationship in the equivalent circuit model. Based on the current-resistance relationship of the parallel circuit and the resistance ratio relationship, the location of the fault point of the metal neutral line is obtained.

[0007] As one preferred embodiment, the construction of the neutral protection strategy model based on the equivalent circuit model and the fault location includes: Based on the equivalent circuit model and the location of the fault point, the fault type, fault severity, and protection activation conditions of the target flexible DC topology are determined. Based on the fault type and severity of the metal neutral line and the protection activation conditions of the target flexible DC topology, the neutral line protection strategy model is constructed.

[0008] As one preferred embodiment, the conversion process of the mode conversion technology includes at least establishing a parallel path of metal neutral-metal return loop, transferring current, and fault isolation. The method conversion technology is used to process the neutral protection strategy model, and the operating status data is processed based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology, including: The neutral line protection strategy model is processed using mode conversion technology to obtain the current ratio data; Based on the current ratio data and the operating status data, the fault handling status of the target flexible DC topology is obtained.

[0009] As one preferred embodiment, the process of using a fixed-value determination technique to process the fault handling state and obtain the metallic neutral protection parameters of the target flexible DC topology includes: The fault handling status is analyzed to obtain key operating parameters. The key operating parameters are processed using a setpoint determination technique to obtain the metal neutral protection parameters of the target flexible DC topology. The metal neutral protection parameters include at least the current reduction setpoint, the protection blocking time setpoint, and the operation sequence time coordination parameter.

[0010] The present invention also provides a metallic neutral protection system suitable for flexible DC topologies, the system comprising: The acquisition module is used to acquire system parameter data and operating status data of the target flexible DC topology, and to acquire fault data of the metal centerline in the target flexible DC topology; The analysis module is used to perform fault analysis processing on the fault data of the metal centerline to obtain the equivalent circuit model of the target flexible DC topology; The processing module is used to process the system parameter data and the operating status data using fault location technology to obtain the location of the fault point of the metal centerline; A construction module is used to construct a neutral protection strategy model based on the equivalent circuit model and the fault point location. The neutral protection strategy model is configured to process the neutral protection strategy model using mode conversion technology and process the operating status data based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology. The determination module is used to process the fault handling state using a fixed value determination technique to obtain the metal neutral protection parameters of the target flexible DC topology; The protection module is used to protect the metal neutral line of the target flexible DC topology based on the metal neutral line protection parameters.

[0011] As one preferred embodiment, the step of processing the system parameter data and the operating status data using fault location technology to obtain the location of the fault point in the metal centerline includes: The operating status data includes at least the metal neutral wire sending end current, the metal neutral wire receiving end current, and the metal return line loop current. Based on the equivalent circuit model, the current at the sending end of the metal neutral line, the current at the receiving end of the metal neutral line, and the current in the loop of the metal return line are processed to obtain the parallel loop current-resistance relationship and resistance ratio relationship in the equivalent circuit model. Based on the current-resistance relationship of the parallel circuit and the resistance ratio relationship, the location of the fault point of the metal neutral line is obtained.

[0012] As one preferred embodiment, the construction of the neutral protection strategy model based on the equivalent circuit model and the fault location includes: Based on the equivalent circuit model and the location of the fault point, the fault type, fault severity, and protection activation conditions of the target flexible DC topology are determined. Based on the fault type and severity of the metal neutral line and the protection activation conditions of the target flexible DC topology, the neutral line protection strategy model is constructed.

[0013] As one preferred embodiment, the conversion process of the mode conversion technology includes at least establishing a parallel path of metal neutral-metal return loop, transferring current, and fault isolation. The method conversion technology is used to process the neutral protection strategy model, and the operating status data is processed based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology, including: The neutral line protection strategy model is processed using mode conversion technology to obtain the current ratio data; Based on the current ratio data and the operating status data, the fault handling status of the target flexible DC topology is obtained.

[0014] As one preferred embodiment, the process of using a fixed-value determination technique to process the fault handling state and obtain the metallic neutral protection parameters of the target flexible DC topology includes: The fault handling status is analyzed to obtain key operating parameters. The key operating parameters are processed using a setpoint determination technique to obtain the metal neutral protection parameters of the target flexible DC topology. The metal neutral protection parameters include at least the current reduction setpoint, the protection blocking time setpoint, and the operation sequence time coordination parameter.

[0015] Compared with the prior art, the beneficial effects of the present invention are at least one of the following: This invention acquires system parameter data and operational status data of a target flexible DC topology, and obtains fault data of the metal neutral line in the target flexible DC topology; performs fault analysis processing on the metal neutral line fault data to obtain an equivalent circuit model of the target flexible DC topology; processes the system parameter data and operational status data using fault location technology to obtain the fault location of the metal neutral line; constructs a neutral line protection strategy model based on the equivalent circuit model and the fault location, wherein the neutral line protection strategy model is configured to process the neutral line protection strategy model using mode conversion technology, and processes the operational status data based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology; processes the fault handling status using setpoint determination technology to obtain the metal neutral line protection parameters of the target flexible DC topology; and protects the metal neutral line of the target flexible DC topology based on the metal neutral line protection parameters.

[0016] Compared with existing technologies, this invention collects parameters, operating status, and metallic neutral fault data of flexible DC systems to construct an equivalent circuit model that can distinguish fault types such as single-pole grounding, open circuit, and high-resistance grounding. Combined with fault location technology, it accurately locates the fault point and dynamically configures protection strategies using mode conversion and setting optimization technologies. Ultimately, it achieves precise isolation of the metallic neutral fault area and continuous power supply to non-faulty areas. In this process, the closed-loop mechanism of fault type identification, fault point location, and dynamic strategy adaptation significantly improves the power supply reliability and operational flexibility of the flexible DC system, preventing outages in non-faulty areas due to over-protection, and effectively ensuring the safe and efficient application of flexible DC transmission technology in new power systems. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a method for protecting a metal neutral line in a flexible DC topology according to one embodiment of the present invention. Figure 2 This is an equivalent circuit model in one embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a metal neutral protection system suitable for flexible DC topology in one embodiment of the present invention; Figure label: The module consists of: 11. Acquisition module; 12. Analysis module; 13. Processing module; 14. Construction module; 15. Determination module; and 16. Protection module. Detailed Implementation

[0018] 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 purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] One embodiment of the present invention provides a method for protecting the metallic neutral line in a flexible DC topology. For details, please refer to [link to relevant documentation]. Figure 1 , Figure 1The diagram shown is a flowchart illustrating a metal neutral protection method for flexible DC topologies according to one embodiment of the present invention. The method includes: S1: Obtain system parameter data and operating status data of the target flexible DC topology, and obtain fault data of the metal neutral line in the target flexible DC topology; S2: Perform fault analysis processing on the fault data of the metal centerline to obtain the equivalent circuit model of the target flexible DC topology; S3: The system parameter data and the operating status data are processed using fault location technology to obtain the location of the fault point of the metal centerline; S4: Construct a neutral protection strategy model based on the equivalent circuit model and the fault location, wherein the neutral protection strategy model is configured to process the neutral protection strategy model using mode conversion technology, and process the operating status data based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology; S5: The fault handling state is processed using the fixed value determination technology to obtain the metal neutral protection parameters of the target flexible DC topology; S6: Based on the metal neutral protection parameters, protect the metal neutral of the target flexible DC topology.

[0021] Specifically, the fault data for the metallic neutral line includes the measured current at the sending and receiving ends of the metallic neutral line (DMR) during the fault, the current in the metallic return line (PMR) loop, and the fault characteristics, of which the fault characteristics are at least the change in grounding resistance; the system parameter data includes at least the target flexible DC topology, the DMR resistance, the PMR resistance, and the total line length; the operating status data includes at least the current operating mode of the system, whether the other pole line is under maintenance, and whether it is in a switching state.

[0022] The system's current operating modes mainly include unipolar operation and bipolar operation.

[0023] It should be noted that the difference between a metallic neutral line and a metallic return line is that a metallic neutral line is a fixed component in a flexible DC transmission system and the main return path during normal operation, as part of the system's inherent topology; while a metallic return line is a backup path and an emergency path in case of a fault in the system.

[0024] The fault data of the metal centerline is processed by fault analysis to obtain the equivalent circuit model of the target flexible DC topology. Specifically, based on the fault data, the current distribution and resistance relationship are analyzed. Through fault current path analysis, the system is simplified into a resistor network to quantify the fault impact, and then the fault equivalent model is constructed.

[0025] Furthermore, the system parameter data and the operating status data are processed using fault location technology to obtain the location of the fault point of the metal neutral line, including: processing the sending current of the metal neutral line, the receiving current of the metal neutral line, and the loop current of the metal return line based on the equivalent circuit model to obtain the parallel loop current-resistance relationship and resistance ratio relationship in the equivalent circuit model; and obtaining the location of the fault point of the metal neutral line based on the parallel loop current-resistance relationship and the resistance ratio relationship.

[0026] Specifically, based on the previously constructed equivalent circuit model, these three sets of current data are substituted into the model. Kirchhoff's current law and voltage law are used to analyze the circuit loop under fault conditions. By decomposing the positive sequence, negative sequence and zero sequence components of the fault current, the current components related to the fault are separated, the interference of normal operating current is eliminated, and then the current distribution law of the parallel loop in the equivalent circuit model is derived. The correspondence between current and resistance in different loops is clarified. At the same time, by calculating the amplitude change and phase difference of each current before and after the fault, the resistance ratio relationship between the parallel loops is established.

[0027] After converting the original current data into key parameters that reflect the characteristics of the lines on both sides of the fault point, the derivation is carried out by combining the known total length of the metal neutral line and the resistance per unit length using the linear correspondence between resistance and length.

[0028] Since the resistance of the metal neutral line is proportional to the length of the line, the fault point will divide the metal neutral line into two segments. The resistance ratio of the two segments is the length ratio. By using this ratio and the total length data, the specific distance from the fault point to the sending or receiving end can be calculated, thereby achieving accurate location of the fault point.

[0029] Specifically, taking unipolar operation as an example, the location of the fault point can be calculated through the resistance and current relationship of the fault model. The calculation process is as follows.

[0030] in R DMR Let the resistance be the resistance of the metal neutral line, then: in R’ This refers to the resistance of the metal neutral line after the fault. R 3 The resistance from the fault point to the grounding point. R 1 and R 2 These are the resistance values ​​of the two resistors on the metal neutral line, such as... Figure 2 As shown, Figure 2 This is the equivalent circuit model.

[0031] Furthermore, since the currents on both sides of the DMR's transmitting and receiving ends can be measured by current transformers, they are respectively... I DEL1 and I DEL2 Therefore: The PMR return current can also be measured by a current transformer. I DME Therefore: Solving the above four formulas, we get: Therefore, we can obtain Assuming the line length is S and the distance from the fault point to the receiving station is S', then: Therefore, the distance S' between the fault point and the receiving station can be calculated by the following formula: Furthermore, the step of constructing a neutral protection strategy model based on the equivalent circuit model and the fault location includes: determining the fault type, fault severity, and protection activation conditions of the target flexible DC topology of the metallic neutral line based on the equivalent circuit model and the fault location; and constructing the neutral protection strategy model based on the fault type, fault severity, and protection activation conditions of the target flexible DC topology of the metallic neutral line.

[0032] Specifically, based on the constructed equivalent circuit model and the precisely located fault point, in-depth analysis of fault characteristics is carried out.

[0033] In practical operation, the current and voltage distribution patterns corresponding to different fault types in the equivalent circuit model are combined with the amplitude changes, phase relationships, and dynamic adjustments of the equivalent resistance of the current at the sending and receiving ends of the metal neutral line and the return loop current before and after the fault, so as to distinguish fault types such as single-pole grounding disconnection and high-resistance grounding.

[0034] For example, a single-pole grounding fault will show a significant zero-sequence current component and an imbalance in the resistance ratio on both sides of the fault point. A broken wire fault will show a sudden change in the loop current and the current in a certain section of the line will approach zero. A high-resistance grounding fault will show a small fault current amplitude but a persistent voltage distortion.

[0035] In determining the severity of a fault, the fault is classified into three levels: minor, moderate, and severe by quantifying indicators such as the ratio of fault current to rated current, voltage drop amplitude, and distance of the fault point from key equipment such as the converter. The determination of protection activation conditions is based on a combination of equipment tolerance threshold, line rated capacity, and fault characteristic quantification indicators in the system parameters, and a clear activation threshold is set.

[0036] Based on this, a targeted midline protection strategy model is constructed.

[0037] The conversion process of mode conversion technology includes at least establishing a parallel path for the metal neutral-metal return loop, transferring current, and fault isolation; Furthermore, the neutral protection strategy model is processed using mode conversion technology, and the operating status data is processed based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology. This includes: processing the neutral protection strategy model using mode conversion technology to obtain the current ratio data; and obtaining the fault handling status of the target flexible DC topology based on the current ratio data and the operating status data.

[0038] In practice, differentiated protection action logic and execution paths are designed based on different fault types, fault severity, and protection activation conditions.

[0039] For severe single-pole ground faults, the model is set to quickly activate the DC circuit breaker to isolate the line segment where the fault point is located. At the same time, it triggers the system mode switching technology to switch the bipolar operation mode to the single-pole metallic return operation mode to ensure that the non-faulty pole continues to transmit power. For medium-severity open-circuit faults, if the fault point is located in a non-critical section, the model formulates a strategy to adjust the converter control parameters. By optimizing the modulation ratio and firing angle, it compensates for the power imbalance caused by the open circuit. There is no need to activate the whole system blockade; only the faulty line segment needs to be isolated.

[0040] For minor high-resistance grounding faults, the model adopts an adaptive setpoint protection method, appropriately increases the protection action threshold and extends the observation delay to avoid false operation due to instantaneous interference, and continuously monitors the fault status. If the fault worsens, the protection action is automatically upgraded.

[0041] In addition, the model will integrate a feedback mechanism for real-time operating status data to ensure that the protection strategy can be dynamically adjusted according to the fault development trend. For example, if the fault current gradually increases during the observation period of a minor fault, it can automatically switch to the protection action logic corresponding to a moderate severity fault.

[0042] First, based on the fault type and location, the standby interconnection switch between the metal neutral line and the metal return line is closed by controlling the opening and closing status of the DC switching equipment to establish a new current transmission path and ensure that the current in the non-faulty area has a reliable flow path.

[0043] Next, the control parameters of the converter, including the modulation ratio and firing angle, are adjusted. Through precise control, the current that originally flowed through the metal neutral line of the fault section is smoothly transferred to the newly established interconnection path. During the transfer process, the rate of change of current is strictly controlled to avoid system voltage fluctuations or equipment impacts caused by sudden current changes.

[0044] Simultaneously, based on the fault location results, the DC circuit breakers at both ends of the faulty section are triggered to disconnect the faulty area from the normal line, achieving physical isolation of the faulty area and preventing the fault from spreading to non-faulty parts. Throughout the entire conversion process, the sending and receiving currents of the new connection path, as well as the current data before and after fault isolation, are collected in real time. Combined with the current distribution pattern under normal operating conditions in the equivalent circuit model, the current ratio data between different circuits are calculated.

[0045] When obtaining fault handling status based on current ratio data and operating status data, the real-time operating status data of the target flexible DC topology is first continuously collected, including key parameters such as converter output voltage, power transmission value in non-fault areas, and equipment operating temperature.

[0046] The current ratio data is compared with the preset normal operating threshold range in the neutral protection strategy model to determine whether the current distribution after the transfer meets the requirements for safe operation. For example, whether the current ratio of the new connection path is within the equipment's tolerance range and whether the residual current ratio after fault isolation is close to zero.

[0047] Simultaneously, a comprehensive analysis is conducted based on voltage stability indicators and power balance data from the operational status data. If the current ratio is within the preset threshold, and system voltage fluctuations are controlled within the allowable range, power transmission remains stable, and equipment operating parameters in non-faulty areas are normal, it indicates that fault isolation and current transfer have been successful. If the current ratio exceeds the threshold, or the operational status data shows excessive voltage drops and power imbalance, it indicates that there are oversights in fault handling, possibly due to incomplete fault isolation or incomplete current transfer. If the current ratio approaches zero and the operational status data returns to normal levels, it indicates that the fault has been completely cleared and the system can operate stably.

[0048] Through such comprehensive judgment, the fault handling status of the target flexible DC topology is finally clarified, including types such as successful fault isolation, stable system operation, incomplete fault handling requiring secondary adjustment, and complete fault clearance allowing restoration to the original operating mode.

[0049] The process of using a setpoint determination technique to process the fault handling state and obtain the metal neutral protection parameters of the target flexible DC topology includes: performing state feature analysis on the fault handling state to obtain key operating parameters; and using the setpoint determination technique to process the key operating parameters to obtain the metal neutral protection parameters of the target flexible DC topology. The metal neutral protection parameters include at least a current reduction setpoint, a protection blocking time setpoint, and an operation sequence time coordination parameter.

[0050] The specific types of fault handling status include different scenarios such as successful fault isolation, incomplete fault handling, and complete fault clearance, and targeted feature extraction is carried out for each scenario.

[0051] For cases where fault isolation is successful, the focus is on collecting stable operating data from non-faulty areas, including real-time current and voltage amplitudes of the non-faulty section's metal neutral line, converter output power and modulation ratio, system frequency and voltage stability, etc. For cases where fault handling is incomplete, the focus is on residual fault-related characteristics, extracting residual fault current amplitude and rate of change, voltage distortion coefficient, electric field distribution data near the fault point, etc. For cases where the fault is completely cleared, the reference current and voltage values, power transmission balance, and steady-state values ​​of converter control parameters after the system returns to normal operation are recorded.

[0052] At the same time, the inherent parameters of the system, such as the resistance and inductance per unit length of the metal neutral line, the action response time of the DC circuit breaker, and the maximum withstand current and voltage threshold of the converter, are integrated. These scattered data are classified, filtered, denoised, and normalized and integrated to finally extract key operating parameters that can reflect the current operating conditions of the system, the residual impact of faults, and the equipment's tolerance.

[0053] An adaptive setpoint calculation algorithm is adopted, and three types of core protection parameters are derived by combining key operating parameters and system design requirements.

[0054] For the current reduction setting, the core basis is the system rated current, the maximum peak fault current during a fault, and the equipment withstand current threshold. The calculation weight is adjusted according to the severity of the fault. For example, in a severe fault scenario, the current reduction setting should be set to 80% lower than the equipment withstand threshold, while in a minor fault scenario, it can be close to the rated current to ensure that the current can be quickly limited to a safe range when a fault occurs, thus avoiding equipment damage.

[0055] For the protection blocking time setting, based on the transient characteristics of the fault handling state, combined with the decay rate of the residual fault current, the voltage recovery time, and the duration of the transient disturbance, a reasonable blocking time is calculated through a time series analysis model. It is necessary to prevent the protection from malfunctioning due to the blocking time being too short, and to avoid the fault from expanding due to the blocking time being too long. For example, the blocking time for instantaneous disturbances can be set to 5-10 milliseconds, while for continuous faults, it is necessary to match the total time consumed by fault isolation and current transfer.

[0056] For the timing parameters of the operation sequence, focusing on key operations such as DC circuit breaker operation, converter mode switching, and current transfer, the time interval between each operation is determined by a timing coordination algorithm based on parameters such as the response time of each operation and the equipment action delay. For example, the faulty section circuit breaker is triggered to open first, the converter mode switching is started after an interval of 20-30 milliseconds, and the current distribution is adjusted after an interval of 15-20 milliseconds. This ensures that each operation is connected in an orderly manner without conflict, and avoids system fluctuations caused by timing chaos.

[0057] Based on the metal neutral protection parameters, the metal neutral of the target flexible DC topology is protected.

[0058] After the protection action is executed, the system's operating status is continuously monitored, tracking in real time whether the current and voltage are stable within the safe range corresponding to the reduced current setting, whether fault isolation is complete, and whether power transmission in non-fault areas is normal. Simultaneously, protection parameters are dynamically adjusted based on the monitoring results. If the residual fault current gradually decreases to a safe range and the system operates smoothly, the reduced current setting can be gradually increased, and the protection blocking time setting shortened to prepare for the system to return to normal operation. If the fault is found to be worsening, such as the current continuously exceeding the reduced current setting or the voltage distortion increasing, the reduced current setting is immediately decreased, the protection blocking time setting extended, and secondary protection actions are initiated according to the operation sequence time and parameters to further enhance the fault isolation effect. When the fault is completely cleared and the system returns to normal operation, the protection parameters are adjusted to normal operating values ​​according to preset benchmark parameters to ensure the power supply reliability and equipment safety of the system under normal operating conditions.

[0059] Specifically, the above protection methods all address faults in the metallic neutral line during unipolar operation. For the protection of the metallic neutral line in a bipolar DC system, if a fault occurs, the traditional protection action is to perform polar balancing. If the protection action signal does not return after polar balancing, meaning the fault still exists, then bipolar operation is blocked. Analogous to unipolar operation, the new strategy, in the case where the protection action still does not return after polar balancing, cancels the blocking of bipolar operation. Instead, it first blocks and isolates one unipolar line, then performs a DMR / PMR metallic return mode conversion, the conversion process being the same as in unipolar operation. Since the operating condition changes from bipolar operation before the fault to unipolar operation, after the mode conversion, the above protection methods should be followed.

[0060] In another embodiment, under single-pole operation, if a fault occurs in the metallic neutral DMR line, and the protection action still fails to return after the current reduction restart, i.e., the fault still exists, then, provided that the other pole line is not under maintenance, the metallic return mode is automatically switched. First, the relevant disconnect switches and metallic neutral control switches are closed, and the other pole line is used as the metallic return PMR, establishing a parallel line with the faulty metallic neutral return DMR. At the same time, the total current is reduced to below the switch current transfer capacity and the grounding grid bearing capacity, and then the switch that can be opened is opened, and the metallic neutral return DMR is isolated, transferring all current to the metallic return PMR.

[0061] Another embodiment of the present invention provides a metallic neutral protection system suitable for flexible DC topologies. For details, please refer to [link to relevant documentation]. Figure 3 , Figure 3 The diagram shown illustrates the structure of a metal neutral protection system suitable for flexible DC topologies according to one embodiment of the present invention. The system includes: The acquisition module 11 is used to acquire system parameter data and operating status data of the target flexible DC topology, and to acquire fault data of the metal centerline in the target flexible DC topology; Analysis module 12 is used to perform fault analysis processing on the fault data of the metal centerline to obtain the equivalent circuit model of the target flexible DC topology; Processing module 13 is used to process the system parameter data and the operating status data using fault location technology to obtain the location of the fault point of the metal centerline; The construction module 14 is used to construct a neutral line protection strategy model based on the equivalent circuit model and the fault point location. The neutral line protection strategy model is configured to process the neutral line protection strategy model using mode conversion technology and process the operating status data based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology. The determination module 15 is used to process the fault handling state using the fixed value determination technology to obtain the metal neutral protection parameters of the target flexible DC topology; The protection module 16 is used to protect the metal neutral line of the target flexible DC topology based on the metal neutral line protection parameters.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for protecting a metallic neutral line suitable for flexible DC topologies, characterized in that, include: Acquire system parameter data and operating status data of the target flexible DC topology, and acquire fault data of the metal centerline in the target flexible DC topology; Fault analysis and processing are performed on the fault data of the metal centerline to obtain the equivalent circuit model of the target flexible DC topology; The system parameter data and the operating status data are processed using fault location technology to obtain the location of the fault point in the metal centerline; A neutral protection strategy model is constructed based on the equivalent circuit model and the fault location. The neutral protection strategy model is configured to process the neutral protection strategy model using mode conversion technology and process the operating status data based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology. The fault handling state is processed using a fixed value determination technique to obtain the metal neutral protection parameters of the target flexible DC topology; Based on the metal neutral protection parameters, the metal neutral of the target flexible DC topology is protected.

2. The method for protecting the metallic neutral line in a flexible DC topology as described in claim 1, characterized in that, The process of using fault location technology to process the system parameter data and the operating status data to obtain the location of the fault point in the metal centerline includes: The operating status data includes at least the metal neutral wire sending end current, the metal neutral wire receiving end current, and the metal return line loop current. Based on the equivalent circuit model, the current at the sending end of the metal neutral line, the current at the receiving end of the metal neutral line, and the current in the loop of the metal return line are processed to obtain the parallel loop current-resistance relationship and resistance ratio relationship in the equivalent circuit model. Based on the current-resistance relationship of the parallel circuit and the resistance ratio relationship, the location of the fault point of the metal neutral line is obtained.

3. The method for protecting the metallic neutral line of a flexible DC topology as described in claim 1, characterized in that, The construction of the neutral protection strategy model based on the equivalent circuit model and the fault location includes: Based on the equivalent circuit model and the location of the fault point, the fault type, fault severity, and protection activation conditions of the target flexible DC topology are determined. Based on the fault type and severity of the metal neutral line and the protection activation conditions of the target flexible DC topology, the neutral line protection strategy model is constructed.

4. The method for protecting the metallic neutral line in a flexible DC topology as described in claim 1, characterized in that, The conversion process of the aforementioned conversion technology includes at least establishing a parallel path for the metal neutral-metal return loop, transferring current, and fault isolation. The method conversion technology is used to process the neutral protection strategy model, and the operating status data is processed based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology, including: The neutral line protection strategy model is processed using mode conversion technology to obtain the current ratio data; Based on the current ratio data and the operating status data, the fault handling status of the target flexible DC topology is obtained.

5. The method for protecting the metallic neutral line in a flexible DC topology as described in claim 1, characterized in that, The process of using a fixed-value determination technique to handle the fault state and obtain the metallic neutral protection parameters of the target flexible DC topology includes: The fault handling status is analyzed to obtain key operating parameters. The key operating parameters are processed using a setpoint determination technique to obtain the metal neutral protection parameters of the target flexible DC topology. The metal neutral protection parameters include at least the current reduction setpoint, the protection blocking time setpoint, and the operation sequence time coordination parameter.

6. A metallic neutral protection system suitable for flexible DC topologies, characterized in that, include: The acquisition module is used to acquire system parameter data and operating status data of the target flexible DC topology, and to acquire fault data of the metal centerline in the target flexible DC topology; The analysis module is used to perform fault analysis processing on the fault data of the metal centerline to obtain the equivalent circuit model of the target flexible DC topology; The processing module is used to process the system parameter data and the operating status data using fault location technology to obtain the location of the fault point of the metal centerline; A construction module is used to construct a neutral protection strategy model based on the equivalent circuit model and the fault point location. The neutral protection strategy model is configured to process the neutral protection strategy model using mode conversion technology and process the operating status data based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology. The determination module is used to process the fault handling state using a fixed value determination technique to obtain the metal neutral protection parameters of the target flexible DC topology; The protection module is used to protect the metal neutral line of the target flexible DC topology based on the metal neutral line protection parameters.

7. The metallic neutral protection system for flexible DC topologies as described in claim 6, characterized in that, The process of using fault location technology to process the system parameter data and the operating status data to obtain the location of the fault point in the metal centerline includes: The operating status data includes at least the metal neutral wire sending end current, the metal neutral wire receiving end current, and the metal return line loop current. Based on the equivalent circuit model, the current at the sending end of the metal neutral line, the current at the receiving end of the metal neutral line, and the current in the loop of the metal return line are processed to obtain the parallel loop current-resistance relationship and resistance ratio relationship in the equivalent circuit model. Based on the current-resistance relationship of the parallel circuit and the resistance ratio relationship, the location of the fault point of the metal neutral line is obtained.

8. The metallic neutral protection system for flexible DC topology as described in claim 6, characterized in that, The construction of the neutral protection strategy model based on the equivalent circuit model and the fault location includes: Based on the equivalent circuit model and the location of the fault point, the fault type, fault severity, and protection activation conditions of the target flexible DC topology are determined. Based on the fault type and severity of the metal neutral line and the protection activation conditions of the target flexible DC topology, the neutral line protection strategy model is constructed.

9. The metallic neutral protection system for flexible DC topologies as described in claim 6, characterized in that, The conversion process of the aforementioned conversion technology includes at least establishing a parallel path for the metal neutral-metal return loop, transferring current, and fault isolation. The method conversion technology is used to process the neutral protection strategy model, and the operating status data is processed based on the obtained current ratio data to obtain the fault handling status of the target flexible DC topology, including: The neutral line protection strategy model is processed using mode conversion technology to obtain the current ratio data; Based on the current ratio data and the operating status data, the fault handling status of the target flexible DC topology is obtained.

10. The metallic neutral protection system for flexible DC topologies as described in claim 6, characterized in that, The process of using a fixed-value determination technique to handle the fault state and obtain the metallic neutral protection parameters of the target flexible DC topology includes: The fault handling status is analyzed to obtain key operating parameters. The key operating parameters are processed using a setpoint determination technique to obtain the metal neutral protection parameters of the target flexible DC topology. The metal neutral protection parameters include at least the current reduction setpoint, the protection blocking time setpoint, and the operation sequence time coordination parameter.

Images