Multi-branch area protection method for direct current power supply system in extreme scene

Abstract

The invention discloses a multi-branch area protection method for a direct-current power supply system in an extreme scene, and the method comprises the steps: S1, determining a main branch unit from each branch unit in a submarine direct-current power supply network, deploying a measurement device on the main branch unit, and enabling an area between every two adjacent main branch units to be called as a protection area; s2, after it is judged that a fault occurs, initial fault currents IFC: imn and imn between trunk branch units m and n in Tw after the fault are collected, imn represents the initial fault current flowing from m to n, imn represents the initial fault current flowing from n to m, and imn represents the initial fault current flowing from n to m, average values of derivatives of imn and imn are calculated respectively, and a protection area where the fault is located is determined according to a preset average value threshold value; and S3, calculating the change trend of the imn and imn derivatives, calculating the fault probability according to the initial rise time and rise amplitude of the imn and imn derivatives, and determining the line where the fault is located according to the change trend and the fault probability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power supply systems, in particular to a multi-branch regional protection method for an extreme scenario DC power supply system. BACKGROUND

[0002] As a key infrastructure supporting long-term, continuous and real-time ocean observation, the submarine DC power supply system provides stable power for various underwater sensors and scientific instruments through cables and realizes data backhaul. This kind of system usually adopts a multi-branch structure and accesses a large number of distributed loads through LLC resonant converters. However, the underwater environment is harsh, the cable insulation is easy to be damaged, the probability of failure is high, and the fault current characteristics are complicated due to the multi-branch structure. In addition, due to the limitations of underwater deployment conditions and equipment costs, it is difficult to configure measurement and communication units at each node, resulting in multiple challenges such as insufficient measurement coverage and limited communication bandwidth for system protection.

[0003] At present, the DC system protection scheme mainly includes single-end measurement protection and multi-end measurement protection. The single-end measurement scheme relies on the comparison of local electrical characteristics and preset thresholds, although it has fast response speed, but it cannot realize full-line protection, and the sensitivity is insufficient under high resistance fault; some schemes introduce anti-time limit characteristics or direction discrimination to improve selectivity, but may sacrifice the action speed. Another type of protection scheme based on boundary effect needs to rely on specific physical boundary elements such as series inductors and parallel capacitors, which are often difficult to implement in compact and limited deployment submarine systems. The multi-end measurement scheme can achieve high selectivity through multi-end information comparison, such as using waveform similarity, difference, polarity comparison and other methods of line current at both ends, which usually requires strict data synchronization and real-time communication, and has limited applicability in long-distance, multi-branch and low-bandwidth submarine DC power supply systems. In addition, the existing centralized protection scheme relies on wide-area measurement information, and its reliability is not clear in complex topologies with limited measurement and communication links at some nodes. SUMMARY

[0004] Therefore, the present application provides a multi-branch regional protection method for an extreme scenario DC power supply system, which at least solves the problem that the prior art is difficult to adapt to the structural characteristics of the multi-branch, few measurement points and communication limited submarine DC power supply system.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme: A multi-branch regional protection method for an extreme scenario DC power supply system, comprising the following steps: S1: determining a trunk branch unit from each branch unit in the submarine DC power supply network, and deploying a measurement device on the trunk branch unit, and regarding the region between each two adjacent trunk branch units as a protection region; S2: After determining that a fault has occurred, collect the fault data. Internal main branch unit m and n Initial fault current IFC: and ,in express m Flow direction n The initial fault current, express n Flow direction m The initial fault current was calculated separately. and The average value of the derivative is used to determine the protection zone where the fault is located based on a preset average value threshold. S3: Calculation and The trend of the derivative, and according to and The initial rise time and rise amplitude of the derivative are used to calculate the fault probability, and the fault location is determined based on the trend and fault probability.

[0006] Preferably, the specific method for determining the main branch unit in S1 includes: A branch unit is defined as one that meets any of the following criteria: (1) Connecting three or more submarine cables; (2) It is located within a single loop and the loop contains more than 8 branch units, and the distance between it and the adjacent main branch unit does not exceed four lines; (3) Located within a single loop containing fewer than 8 branch units, and the distance from adjacent trunk branch units is within... N / 2 or ( N Within the range of -1) / 2 lines, N This represents the number of branch units.

[0007] Preferably, the specific methods for determining that a fault has occurred in S2 include: Each main branch unit continuously collects the outgoing current of its respective lines. and calculate derivative ; When any one Exceeding the preset threshold If this occurs, it is determined that a fault has occurred in the power supply system, further triggering the detection of the area where the fault is located.

[0008] Preferably, after fault is collected in S2 Internal main branch unit m and nThe specific content of calculating the initial fault current IFC and the average value of the derivative of IFC includes: After data acquisition failure Internal main branch unit m and n Initial fault current IFC: and ; Calculate separately and The corresponding derivative average is calculated as follows: ; Where A represents or The average value of the derivative for and Sampling point index, For the length of the data window, The sampling interval is denoted as .

[0009] Preferably, the specific content of determining the protection area where the fault is located based on the preset average threshold in S2 includes: When the condition is met and When this occurs, the protected area is determined to be the area where the fault is located. This indicates the preset average threshold. It depends on the line impedance, LLC branch capacitance, and the voltage before the fault.

[0010] Preferably, for a protection zone containing four lines in two adjacent main branch units, the specific details of determining the line where the fault occurs in S3 based on the changing trend and fault probability include: Sequentially divide the main branch units m To the main branch unit n The four lines between them are denoted as l 1. l 2. l 3 and l 4; If the derivative of IFC shows a decreasing trend, that is... and The faulty line is near m Side line l 1; If the derivative of IFC shows a decreasing trend, that is... and The fault line is near n Side line l 4; If the derivative of IFC shows an upward trend, that is... and Then calculate m arrive n Line failure probability and n arrive m Line failure probability ,like Then the faulty line is the circuit. l 2, otherwise it's a line. l 3.

[0011] Preferably, for protection zones containing two or three lines in two adjacent main branch units, the specific details in S3 for determining the line where the fault occurs based on the trend and fault probability include: like and Then the closest m The line at the end is faulty; like and Then the closest n The line at the end is the faulty line; otherwise, the line in the middle of the protected area is the faulty line.

[0012] Preferably, calculation is performed in S3. and The specific method for understanding the changing trend of the derivative is as follows: ; in, express Trend of derivative or Trend of derivative , q for and Sampling point index, N w1 For the length of the data window, The sampling interval is denoted as .

[0013] Preferably, in S3 according to and The specific details of calculating the failure probability using the initial rise time and rise amplitude of the derivative include: Get them respectively and Initial rise time of the derivative T smn and T snm and the magnitude of the increase D rmn and D rmn Obtain from the following formulas respectively and Corresponding failure probability: ; In the formula, F Representing an interval Inside or The probability of failure, For position parameters, Here, is the scale parameter; T s express or The initial rise time, D r express or The rate of increase It is an integral variable, representing an interval. and The value in.

[0014] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a multi-branch area protection method for DC power supply systems in extreme scenarios, which has the following beneficial effects: 1. Effectively Reduce System Construction and Maintenance Costs: This invention, through an innovative regionalized protection architecture, integrates multiple lines under a unified protection unit, significantly reducing the number of underwater measurement and communication equipment required. This not only reduces the direct costs of equipment procurement, installation, and maintenance for the subsea system but also alleviates the dependence on limited communication bandwidth, making it possible to achieve economical and reliable comprehensive protection in harsh underwater environments.

[0015] 2. Significantly improves the adaptability and reliability of the protection system: The method proposed in this invention identifies and locates fault currents based on their inherent characteristics, without relying on a single fixed threshold or specific boundary element. Therefore, it has good adaptability to complex operating conditions such as environmental interference, load fluctuations, and high-resistance faults. This solution effectively avoids the problems of false tripping or failure to trip that traditional protection systems are prone to in similar scenarios, thus improving the overall stability and safety of the submarine power distribution system. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1A flowchart of a multi-branch area protection method for a DC power supply system in extreme scenarios provided by the present invention; Figure 2 A schematic diagram illustrating the fault probability calculation for line fault location in a multi-branch area protection method for an extreme scenario DC power supply system provided by the present invention. Figure 3 The present invention provides a fault line identification logic diagram for different types of protection areas in a multi-branch area protection method for a DC power supply system in extreme scenarios. Figure 4 A topology diagram of a mesh-like submarine DC power supply system provided in an embodiment of the present invention; Figure 5 The following is a schematic diagram of the average value of the IFC derivative of the current at both ends of the regions (regions 23, 34, 45, 56, 67, 89, 92, 69, 35, 12 and 810 in sequence) under different fault scenarios provided in the embodiments of the present invention: (a) the maximum value of the IFC derivative at both ends; (b) the minimum value of the IFC derivative at both ends. 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a method for protecting multi-branch areas of a DC power supply system in extreme scenarios, such as... Figure 1 As shown, it includes the following steps: S1: Determine the main branch unit from each branch unit in the submarine DC power supply network, and deploy measuring devices on the main branch unit. The area between every two adjacent main branch units is called the protection area. S2: After determining that a fault has occurred, collect the fault data. Internal main branch unit m and n Initial fault current IFC: and ,in express m Flow direction n The initial fault current, express n Flow direction m The initial fault current was calculated separately. and The average value of the derivative is used to determine the protection zone where the fault is located based on a preset average value threshold. S3: Calculation and The trend of the derivative, and according to and The initial rise time and rise amplitude of the derivative are used to calculate the fault probability, and the fault location is determined based on the trend and fault probability.

[0020] It should be noted that: To adapt to the structural characteristics of submarine DC power supply systems—multiple branches, few measurement points, and limited communication—and to achieve reliable and rapid fault isolation, this invention proposes a protection zone division and identification mechanism based on the derivative characteristics of the initial fault current (IFC). The core principle is that the IFC derivatives of faulty and non-faulty lines have distinctly different time-domain characteristics, and the characteristic amplitude of non-faulty lines significantly decreases with increasing electrical distance from the fault point (measured by the number of branch units, which consist of an LLC resonant converter and its connected load).

[0021] In this embodiment, after the initial fault current (IFC) is acquired, the signal is filtered by a Savitzky-Golay filter, which can suppress noise while preserving the IFC waveform characteristics.

[0022] To further implement the above technical solution, the specific methods for determining the main branch units in S1 include: A branch unit is defined as one that meets any of the following criteria: (1) Connecting three or more submarine cables; (2) It is located within a single loop and the loop contains more than 8 branch units, and the distance between it and the adjacent main branch unit does not exceed four lines; (3) Located within a single loop containing fewer than 8 branch units, and the distance from adjacent trunk branch units is within... N / 2 or ( N Within the range of -1) / 2 lines, N This represents the number of branch units.

[0023] To further implement the above technical solution, the specific methods for determining the occurrence of a fault in S2 include: Each main branch unit continuously collects the outgoing current of its respective lines. and calculate derivative ; When any one Exceeding the preset threshold If this occurs, it is determined that a fault has occurred in the power supply system, further triggering the detection of the area where the fault is located.

[0024] To further implement the above technical solution, fault data is collected in S2. Internal main branch unit m and n The specific content of calculating the initial fault current IFC and the average value of the derivative of IFC includes: After data acquisition failure Internal main branch unit m and n Initial fault current IFC: and ; Calculate separately and The corresponding derivative average is calculated as follows: ; Where A represents or The average value of the derivative for and Sampling point index, For the length of the data window, The sampling interval is denoted as .

[0025] To further implement the above technical solution, the specific content of S2 for determining the protection area where the fault is located based on a preset average threshold includes: When the condition is met and When this occurs, the protected area is determined to be the area where the fault is located. This indicates the preset average threshold.

[0026] To further implement the above technical solution, for protection zones with four lines in two adjacent main branch units, the specific details of determining the faulty line in S3 based on the changing trend and fault probability include: Sequentially divide the main branch units m To the main branch unit n The four lines between them are denoted as l 1. l 2. l 3 and l 4; If the derivative of IFC shows a decreasing trend, that is... and The faulty line is near m Side line l 1; If the derivative of IFC shows a decreasing trend, that is... and The fault line is near n Side line l4; If the derivative of IFC shows an upward trend, that is... and Then calculate m arrive n Line failure probability and n arrive m Line failure probability ,like Then the faulty line is the circuit. l 2, otherwise it's a line. l 3.

[0027] To further implement the above technical solution, for protection zones with two or three lines in two adjacent main branch units, the specific details of determining the line where the fault occurs in S3 based on the changing trend and fault probability include: like and Then the closest m The line at the end is faulty; like and Then the closest n The line at the end is the faulty line; otherwise, the line in the middle of the protected area is the faulty line.

[0028] It should be noted that: The specific judgment logic is as follows: Figure 3 As shown.

[0029] To further implement the above technical solution, calculations are performed in S3. and The specific method for understanding the changing trend of the derivative is as follows: ; in, express Trend of derivative or Trend of derivative , q for and Sampling point index, N w1 For the length of the data window, The sampling interval is denoted as .

[0030] It should be noted that: The trend ΔA of IFC derivatives was quantified by comparing the average values ​​of two consecutive time windows. A positive difference ΔA indicates an upward trend, while a negative difference ΔA indicates a downward trend.

[0031] To further implement the above technical solution, S3 is based on... and The specific details of calculating the failure probability using the initial rise time and rise amplitude of the derivative include: Get them respectively and Initial rise time of the derivative T smn and T snm and the magnitude of the increase D rmn and D rmn Obtain from the following formulas respectively and Corresponding failure probability: ; In the formula, F Representing an interval Inside or The probability of failure, For position parameters, Here, is the scale parameter; T s express or The initial rise time, D r express or The rate of increase It is an integral variable, representing an interval. and The value in.

[0032] It should be noted that: The Laplace distribution is a double exponential distribution. If a random variable... y Following a Laplace distribution, for a given location parameter and scale parameters Cumulative distribution function It can be defined as, ; CDF F(y) can be regarded as y Belongs to the interval [ y 1, y The probability of 2]. To integrate the two waveform features of the IFC derivative. T s and D r ,Will y 1 set as , y 2 set as .like Figure 2 As shown, when D r Increase or T s When the capacitance of the LLC branch between the measurement point and the fault point is reduced (i.e., the less LLC capacitance between the measurement point and the fault point), the closer the measurement point is to the fault point, the greater the corresponding fault probability.

[0033] The invention will be further illustrated below through specific examples: Build such in PSCAD / EMTDC Figure 4 The system simulation model shown is illustrated in Table 1, with detailed system parameters. It includes a modular multilevel converter for the shore base station, an LLC resonant converter in the primary junction box, and submarine cables. All cables are set to be 10 kilometers long. The simulation uses a sampling frequency of 50 kHz, equivalent to a sampling interval of 0.02 milliseconds. This invention will... set Set to 100.

[0034] Table 1 Parameters of the research system ; (1) Fault line identification results at different fault locations To verify the effectiveness of the proposed solution, six failure scenarios, F1 to F6, were simulated. The faults occurred on line L7 in area 45, line L22 in area 69, lines L12 and L13 in area 67, line L15 in area 78, and line L20 in area 91. Figure 5 The average IFC derivatives at both ends of all protected areas under fault scenarios F1 to F6 are given. It can be seen that only the average IFC derivatives for regions 45, 69, 67, 78, and 92 satisfy min{A}. 45 A 54}, min{A 69 A 96}, min{A 67 A 76}, min{A 78 A 87} and min{A 92 A 29} are all greater than zero, and max{A 45 A 54}, max{A 69 A 96}, max{A 67 A 76}, max{A 78 A 87} and max{A 92 A 29All values ​​are greater than 100. Therefore, the area where the fault is located can be correctly identified.

[0035] Table 2 shows the average value, trend, and fault probability of the IFC derivative in the identified fault regions.

[0036] Table 2. Fault line identification results of the proposed solutions under different fault scenarios. ; For region 45, which contains two lines, the IFC derivative... di 45 / dt and di 54 / dt Trend of change ∆A 45 >0 and ∆A 54 The value is less than 0, therefore L7 is determined to be a faulty line. For area 69, which contains three lines... di 69 / dt and di 96 / dt ∆A 69 With ∆A 96 All are greater than zero, therefore lines L21 and L23 are non-faulty lines, meaning line L22 is the faulty line. For area 67, which contains four lines, under fault scenario F3, di 67 / dt and di 76 / dt ∆A 67 >0 and ∆A 76 >0, and di 67 / dt Failure probability F 67 Greater than di 76 / dt di dt of F 76 Therefore, line L12 was correctly identified as the fault line. In fault scenario F4, ∆A 67 >0 and ∆A 76 Since <0 is true, line L13 is the faulty line. For areas 78 and 92, which contain only one line, ∆A 78 <0 and ∆A 87 <0, ∆A 92 <0 and ∆A 29 A value less than 0 indicates that the faulty area can be correctly detected.

[0037] This demonstrates that the solution is effective for regions with varying numbers of lines.

[0038] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for protecting multi-branch areas of a DC power supply system in extreme scenarios, characterized in that, Includes the following steps: S1: Determine the main branch unit from each branch unit in the submarine DC power supply network, and deploy measuring devices on the main branch unit. The area between every two adjacent main branch units is called the protection area. S2: After determining that a fault has occurred, collect the fault data. Internal main branch unit m and n Initial fault current IFC: and ,in express m Flow direction n The initial fault current, express n Flow direction m The initial fault current was calculated separately. and The average value of the derivative is used to determine the protection zone where the fault is located based on a preset average value threshold. S3: Calculation and The trend of the derivative, and according to and The initial rise time and rise amplitude of the derivative are used to calculate the fault probability, and the fault location is determined based on the trend and fault probability.

2. The multi-branch area protection method for a DC power supply system in extreme scenarios according to claim 1, characterized in that, The specific methods for determining the main branch units in S1 include: A branch unit is defined as one that meets any of the following criteria: (1) Connecting three or more submarine cables; (2) It is located within a single loop and the loop contains more than 8 branch units, and the distance to the adjacent main branch unit does not exceed four lines; (3) Located within a single loop containing fewer than 8 branch units, and the distance from adjacent trunk branch units is within... N / 2 or ( N Within the range of -1) / 2 lines, N This represents the number of branch units.

3. The multi-branch area protection method for a DC power supply system in extreme scenarios according to claim 1, characterized in that, The specific methods for determining whether a fault has occurred in S2 include: Each main branch unit continuously collects the outgoing current of its respective lines. and calculate derivative ; When any one Exceeding the preset threshold If this occurs, it is determined that a fault has occurred in the power supply system, further triggering the detection of the area where the fault is located.

4. The multi-branch area protection method for a DC power supply system in extreme scenarios according to claim 1, characterized in that, After collecting fault data in S2 Internal main branch unit m and n The specific content of calculating the initial fault current IFC and the average value of the derivative of IFC includes: After data acquisition failure Internal main branch unit m and n Initial fault current IFC: and ; And calculate separately and The corresponding derivative average is calculated as follows: ； Where A represents or The average value of the derivative for and Sampling point index, For the length of the data window, The sampling interval is denoted as .

5. A multi-branch area protection method for an extreme scenario DC power supply system according to claim 4, characterized in that, The specific details of determining the protection zone where the fault is located based on a preset average threshold in S2 include: When the condition is met and When this occurs, the protected area is determined to be the area where the fault is located. This indicates the preset average threshold.

6. The multi-branch area protection method for a DC power supply system in extreme scenarios according to claim 1, characterized in that, For a protection zone containing four lines in two adjacent main branch units, the specific details in S3 for determining the line where the fault occurs based on the trend and fault probability include: Sequentially divide the main branch units m To the main branch unit n The four lines between them are denoted as l 1. l 2. l 3 and l 4; If the derivative of IFC shows a decreasing trend, that is... and The faulty line is near m Side line l 1; If the derivative of IFC shows a decreasing trend, that is... and The fault line is near n Side line l 4; If the derivative of IFC shows an upward trend, that is... and Then calculate m arrive n Line failure probability and n arrive m Line failure probability ,like Then the faulty line is the circuit. l 2, otherwise it's a line. l 3.

7. The multi-branch area protection method for an extreme scenario DC power supply system according to claim 1, characterized in that, For protection zones containing two or three lines in two adjacent main branch units, the specific details in S3 for determining the line where the fault occurs based on the trend and fault probability include: like and Then the closest m The line at the end is faulty; like and Then the closest n The line at the end is the faulty line; otherwise, the line in the middle of the protected area is the faulty line.

8. The multi-branch area protection method for a DC power supply system in extreme scenarios according to claim 1, characterized in that, Calculation in S3 and The specific method for understanding the changing trend of the derivative is as follows: ； in, express Trend of derivative or Trend of derivative , q for and Sampling point index, N w1 For the length of the data window, The sampling interval is denoted as .

9. A multi-branch area protection method for a DC power supply system in extreme scenarios according to claim 1, characterized in that, According to S3 and The specific details of calculating the failure probability using the initial rise time and rise amplitude of the derivative include: Get them respectively and Initial rise time of the derivative T smn and T snm and the magnitude of the increase D rmn and D rmn Obtain from the following formulas respectively and Corresponding failure probability: ； In the formula, F Representing an interval Inside or The probability of failure, For position parameters, Here, is the scale parameter; T s express or The initial rise time, D r express or The rate of increase It is an integral variable, representing an interval. and The value in.

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