A multi-branch area protection method for an extreme scenario direct current power supply system

Abstract

This invention discloses a multi-branch area protection method for a DC power supply system in extreme scenarios, comprising: S1: determining the main branch unit from each branch unit in the submarine DC power supply network, deploying a measuring device on the main branch unit, and defining the area between every two adjacent main branch units as the protection area; S2: after determining that a fault has occurred, collecting data after the fault. T w Internal main branch unit m and n Initial fault current IFC: i mn and i nm ,in i mn express m Flow direction n The initial fault current, i nm express n Flow direction m The initial fault current was calculated separately. i mn and i nm 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 i mn and i nm The trend of the derivative, and according to i mn and i nm 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.

Description

Technical Field

[0001] This invention relates to the field of power supply system technology, and specifically to a multi-branch area protection method for a DC power supply system in extreme scenarios. Background Technology

[0002] Submarine DC power supply systems serve as critical infrastructure supporting long-term, continuous, and real-time ocean observation. They provide stable power to various underwater sensors and scientific instruments via cables and enable data transmission. These systems typically employ a multi-branch structure, connecting numerous distributed loads through LLC resonant converters. However, the harsh underwater environment makes cable insulation susceptible to damage, resulting in a high probability of failure. Furthermore, the fault current characteristics are complicated by the multi-branch structure. In addition, limitations in underwater deployment and equipment costs make it difficult to configure measurement and communication units at every node, leading to multiple challenges for system protection, including insufficient measurement coverage and limited communication bandwidth.

[0003] Currently, DC system protection schemes are mainly divided into two categories: single-ended measurement protection and multi-ended measurement protection. Single-ended measurement schemes rely on the comparison of local electrical characteristics with preset thresholds. Although they have a fast response speed, they cannot achieve full-line protection and lack sensitivity under high-resistance faults. Some schemes introduce inverse-time characteristics or direction discrimination to improve selectivity, but this may sacrifice operating speed. Another type of protection scheme based on boundary effects relies on specific physical boundary components such as series inductors and parallel capacitors, which are often difficult to implement in compact and constrained submarine systems. Multi-ended measurement schemes can achieve high selectivity through multi-end information comparison, such as by comparing the waveform similarity, difference, and polarity of the currents at both ends of the line. However, they usually have strict requirements for data synchronization and real-time communication, limiting their applicability in long-distance, multi-branch, and low-bandwidth submarine DC power supply. In addition, existing centralized protection schemes mostly rely on wide-area measurement information, and their reliability is still unclear in complex topologies where some nodes lack measurement and communication links are limited. Summary of the Invention

[0004] In view of this, the present invention provides a multi-branch area protection method for DC power supply systems in extreme scenarios, which at least solves the problem that the existing technology is difficult to adapt to the structural characteristics of submarine DC power supply systems with multiple branches, few measurement points, and limited communication.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for protecting multi-branch areas of a DC power supply system in extreme scenarios includes the following steps:

[0007] 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.

[0008] S2: After determining that a fault has occurred, collect the fault data. Internal main branch unit and Initial fault current IFC: and ,in express Flow direction The initial fault current, express Flow direction 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.

[0009] 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.

[0010] Preferably, the specific method for determining the main branch unit in S1 includes:

[0011] A branch unit is defined as one that meets any of the following criteria:

[0012] (1) Connecting three or more submarine cables;

[0013] (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;

[0014] (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.

[0015] Preferably, the specific methods for determining that a fault has occurred in S2 include:

[0016] Each main branch unit continuously collects the outgoing current of its respective lines. and calculate derivative ;

[0017] 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.

[0018] Preferably, after fault is collected in S2 Internal main branch unit and The specific content of calculating the initial fault current IFC and the average value of the derivative of IFC includes:

[0019] After data acquisition failure Internal main branch unit and Initial fault current IFC: and ;

[0020] Calculate separately and The corresponding derivative average is calculated as follows:

[0021] ;

[0022] 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 .

[0023] Preferably, the specific content of determining the protection area where the fault is located based on the preset average threshold in S2 includes:

[0024] 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.

[0025] 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:

[0026] Sequentially divide the main branch units To the main branch unit The four lines between them are denoted as , , and ;

[0027] If the derivative of IFC shows a decreasing trend, that is... and The faulty line is near Side line ;

[0028] If the derivative of IFC shows a decreasing trend, that is... and The fault line is near Side line ;

[0029] If the derivative of IFC shows an upward trend, that is... and Then calculate arrive Line failure probability and arrive Line failure probability ,like Then the faulty line is the circuit. Otherwise, it's a line. .

[0030] 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:

[0031] like and Then the closest The line at the end is faulty;

[0032] like and Then the closest The line at the end is the faulty line; otherwise, the line in the middle of the protected area is the faulty line.

[0033] Preferably, calculation is performed in S3. and The specific method for understanding the changing trend of the derivative is as follows:

[0034] ;

[0035] in, express Trend of derivative or Trend of derivative , for and Sampling point index, For the length of the data window, The sampling interval is denoted as .

[0036] 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:

[0037] Get them respectively and Initial rise time of the derivative and and the magnitude of the increase and Obtain from the following formulas respectively and Corresponding failure probability:

[0038] ;

[0039] In the formula, Representing an interval Inside or The probability of failure, For position parameters, Here, is the scale parameter; express or The initial rise time, express or The rate of increase It is an integral variable, representing an interval. and The value in.

[0040] 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:

[0041] 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.

[0042] 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

[0043] 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.

[0044] Figure 1 A flowchart of a multi-branch area protection method for a DC power supply system in extreme scenarios provided by the present invention;

[0045] 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.

[0046] 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.

[0047] Figure 4 A topology diagram of a mesh-like submarine DC power supply system provided in an embodiment of the present invention;

[0048] 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

[0049] 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.

[0050] 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:

[0051] 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.

[0052] S2: After determining that a fault has occurred, collect the fault data. Internal main branch unit and Initial fault current IFC: and ,in express Flow direction The initial fault current, express Flow direction 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.

[0053] 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.

[0054] It should be noted that:

[0055] 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).

[0056] 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.

[0057] To further implement the above technical solution, the specific methods for determining the main branch units in S1 include:

[0058] A branch unit is defined as one that meets any of the following criteria:

[0059] (1) Connecting three or more submarine cables;

[0060] (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;

[0061] (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.

[0062] To further implement the above technical solution, the specific methods for determining the occurrence of a fault in S2 include:

[0063] Each main branch unit continuously collects the outgoing current of its respective lines. and calculate derivative ;

[0064] 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.

[0065] To further implement the above technical solution, fault data is collected in S2. Internal main branch unit and The specific content of calculating the initial fault current IFC and the average value of the derivative of IFC includes:

[0066] After data acquisition failure Internal main branch unit and Initial fault current IFC: and ;

[0067] Calculate separately and The corresponding derivative average is calculated as follows:

[0068] ;

[0069] 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 .

[0070] 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:

[0071] 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.

[0072] 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 line where the fault occurs in S3 based on the changing trend and fault probability include:

[0073] Sequentially divide the main branch units To the main branch unit The four lines between them are denoted as , , and ;

[0074] If the derivative of IFC shows a decreasing trend, that is... and The faulty line is near Side line ;

[0075] If the derivative of IFC shows a decreasing trend, that is... and The fault line is near Side line ;

[0076] If the derivative of IFC shows an upward trend, that is... and Then calculate arrive Line failure probability and arrive Line failure probability ,like Then the faulty line is the circuit. Otherwise, it's a line. .

[0077] 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:

[0078] like and Then the closest The line at the end is faulty;

[0079] like and Then the closest The line at the end is the faulty line; otherwise, the line in the middle of the protected area is the faulty line.

[0080] It should be noted that:

[0081] The specific judgment logic is as follows: Figure 3 As shown.

[0082] 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:

[0083] ;

[0084] in, express Trend of derivative or Trend of derivative , for and Sampling point index, For the length of the data window, The sampling interval is denoted as .

[0085] It should be noted that:

[0086] 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.

[0087] 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:

[0088] Get them respectively and Initial rise time of the derivative and and the magnitude of the increase and Obtain from the following formulas respectively and Corresponding failure probability:

[0089] ;

[0090] In the formula, Representing an interval Inside or The probability of failure, For position parameters, Here, is the scale parameter; express or The initial rise time, express or The rate of increase It is an integral variable, representing an interval. and The value in.

[0091] It should be noted that:

[0092] The Laplace distribution is a double exponential distribution. If a random variable... Following a Laplace distribution, for a given location parameter and scale parameters Cumulative distribution function It can be defined as,

[0093] ;

[0094] CDF F(y) can be regarded as Belongs to the interval The probability. To integrate the two waveform characteristics of the IFC derivative. and ,Will Set as , Set as .like Figure 2 As shown, when Increase or 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.

[0095] The invention will be further illustrated below through specific examples:

[0096] 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.

[0097] Table 1 Parameters of the research system

[0098] ;

[0099] (1) Fault line identification results at different fault locations

[0100] 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 29 All values ​​are greater than 100. Therefore, the area where the fault is located can be correctly identified.

[0101] Table 2 shows the average value, trend, and probability of IFC derivatives in the identified fault regions.

[0102] Table 2. Fault line identification results of the proposed solutions under different fault scenarios.

[0103] ;

[0104] 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 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.

[0105] This demonstrates that the solution is effective for regions with varying numbers of lines.

[0106] 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 and Initial fault current IFC: and ,in express Flow direction The initial fault current, express Flow direction 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... or( Within the range of -1) / 2 lines, 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 and 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 and 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 .

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 To the main branch unit The four lines between them are denoted as , , and ; If the derivative of IFC shows a decreasing trend, that is... and The faulty line is near Side line ; express The trend of the derivative; If the derivative of IFC shows a decreasing trend, that is... and The fault line is near Side line ; express The trend of the derivative; If the derivative of IFC shows an upward trend, that is... and Then calculate arrive Line failure probability and arrive Line failure probability ,like Then the faulty line is the circuit. Otherwise, it's a line. .

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 The line at the end is faulty; express The trend of the derivative; like and Then the closest The line at the end of the protection zone is the faulty line; otherwise, the line in the middle of the protection zone is the faulty line. express The trend of the derivative.

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 , for and Sampling point index, For the length of the data window, The sampling interval is denoted as .

9. The 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 and and the magnitude of the increase and Obtain from the following formulas respectively and Corresponding failure probability: ； In the formula, Representing an interval Inside or The probability of failure, For position parameters, Here, is the scale parameter; express or The initial rise time, express or The rate of increase It is an integral variable, representing an interval. The value in.

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