Multi-terminal flexible direct current power transmission system direct current line single-end protection method and device

Abstract

A multi-terminal flexible DC power transmission system DC line single-end protection method and device and a storage medium thereof. The method comprises: after protection is started, obtaining DC line single-end positive and negative electrode voltage instantaneous values; calculating fault components of line mode voltage and ground mode voltage; calculating wave front integration of the ground mode voltage fault component to identify a fault type and adaptively match a protection threshold value; constructing a full-time window customized wavelet transform and using the same to calculate wavelet coefficients and high-frequency transient energy of the line mode voltage fault component; comparing the high-frequency transient energy with the matched protection threshold value to determine a fault occurrence area. The application solves the problems of insufficient frequency resolution in a high-frequency band and weak anti-noise interference ability of a traditional method, realizes accurate extraction of a fault traveling wave characteristic, and, in combination with an adaptive threshold matching strategy based on wave front integration, significantly enhances the transition resistance resistance, effectively balances the speed, sensitivity and reliability of single-end protection.

Description

Technical Field

[0001] This invention relates to a method, device, and storage medium for single-end protection of DC lines in a multi-terminal flexible DC transmission system, belonging to the field of transmission line protection in relay protection. Background Technology

[0002] Multi-terminal flexible DC transmission systems, with their advantages of power mutual assistance, ability to mitigate fluctuations in renewable energy transmission, and enhanced reliability of DC power supply, are gradually becoming an important form of DC transmission. However, multi-terminal flexible DC systems exhibit low-damping characteristics, resulting in extremely rapid transient current rise after a fault. This necessitates that protection devices rapidly output action signals within an extremely short protection time window (e.g., within 3ms). Single-terminal quantity protection utilizes only the transient electrical quantities at its own end, eliminating the need for communication channels and possessing extremely high speed. However, in actual engineering electromagnetic interference environments, accurately extracting high-frequency transient characteristics of faults within an extremely short data window and making reliable fault area identification based on this is currently the core bottleneck restricting the performance of single-terminal protection.

[0003] Currently, high-frequency feature extraction mainly relies on algorithms such as empirical mode decomposition (EMD), variational mode decomposition (VMD), and various traditional wavelet transforms. However, EMD and VMD are computationally complex and easily affected by preset parameters, making it difficult to meet the stringent real-time requirements of protection systems. Traditional wavelet transforms have extremely short analysis time windows in the high-frequency band, resulting in severely insufficient frequency resolution, and weak fault features are easily submerged by random noise. Furthermore, the selection of the mother wavelet relies excessively on human experience, further restricting the accurate extraction of high-frequency transient features of faults. Meanwhile, existing single-ended protection systems generally use fixed protection action thresholds when identifying fault zones. Due to the significant difference in high-frequency transient energy between inter-pole short-circuit faults and single-pole grounding faults on flexible DC lines, setting a single fixed threshold faces a dilemma: a threshold that is too high may cause failure to operate under high-resistivity single-pole grounding faults within the zone, while a threshold that is too low may cause false operation due to interference from inter-pole short-circuit faults on lines outside the zone. These limitations in high-frequency feature extraction and the defects in the fixed threshold criteria fundamentally make it difficult to balance the sensitivity and reliability of existing single-ended protection systems. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, the present invention aims to provide a method, device, and storage medium for single-end protection of DC lines in a multi-terminal flexible DC transmission system. This overcomes the shortcomings of existing high-frequency feature extraction algorithms such as wavelet transform in terms of insufficient frequency resolution when processing short time windows and noisy signals, and solves the technical problem that traditional fixed protection action thresholds cannot balance sensitivity and reliability.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention proposes a single-ended protection method for DC lines in a multi-terminal flexible DC transmission system based on full-time window customized wavelet transform, characterized by comprising the following steps: Step 1: Obtain the instantaneous values ​​of the positive and negative voltages at one end of the DC line, determine the start of the protection, and record the start time of the protection. Step 2: Calculate the fault components of the line-mode voltage and the ground-mode voltage based on the instantaneous values ​​of the single-ended voltage of the DC line. Step 3: Calculate the fault type judgment factor based on the fault component of the ground mode voltage and the preset fault type identification time window, identify the fault type, and adaptively match the protection threshold. Step 4: Calculate the wavelet coefficients and high-frequency transient energy of the fault component of the line-mode voltage based on the full-time-window customized wavelet transform; Step 5: Compare the high-frequency transient energy with the adaptive matching protection threshold to determine the fault location.

[0006] More preferably, In step 2, the line-mode voltage and ground-mode voltage are calculated according to the following formula:

[0007] in, Line-mode voltage, Ground mode voltage, This represents the instantaneous value of the positive voltage at one end of a DC line. This represents the instantaneous value of the negative pole voltage at one end of a DC line. It is a time variable; The fault components of the line-mode voltage and the ground-mode voltage are calculated using the following formula:

[0008]

[0009] in, The fault component of the line-mode voltage. The fault component of the ground mode voltage. This represents the steady-state value of the line-mode voltage before the fault. This represents the steady-state value of the ground mode voltage before the fault.

[0010] More preferably, In step 3, the fault type judgment factor is calculated according to the following formula. :

[0011] in, To protect the startup time; For the preset fault type identification time window The number of sampling points within the range, and satisfying the constraints. , This indicates the floor operator. Time window for fault type identification Length; To obtain the sampling time interval for the instantaneous values ​​of the positive and negative voltages at one end of a DC line, It represents the ground mode voltage fault component at the nth sampling point from the moment the protection is activated.

[0012] More preferably, In step 3, the fault type judgment factor is used. Identify fault types and adaptively match protection action thresholds Specifically, it includes: like If so, it is identified as a positive ground fault, and the protection action threshold is matched. ; like If so, it is identified as a negative ground fault, and the protection action threshold is matched. ; like If so, it is identified as a short circuit between poles of the line, and the protection action threshold is matched. ; in, The preset polarity determination threshold, The preset single-pole grounding fault threshold, The preset inter-electrode short-circuit fault threshold; where, .

[0013] More preferably, The range of values ​​is ,in This is the rated voltage of the DC line; Single-pole grounding fault threshold It is less than the minimum high-frequency transient energy of a single-pole grounding fault within the zone and greater than the maximum high-frequency transient energy of a single-pole grounding fault outside the zone. Inter-electrode short-circuit fault threshold It is less than the minimum high-frequency transient energy of inter-electrode short-circuit faults within the zone and greater than the maximum high-frequency transient energy of inter-electrode short-circuit faults outside the zone.

[0014] More preferably, The formula for calculating the wavelet coefficients for full-time window customization is as follows:

[0015] in, This represents the custom wavelet coefficients for the entire time window. For the first The scaling parameters of the full-time-window custom wavelet corresponding to each characteristic frequency. To protect the startup time, To obtain the sampling time interval for the instantaneous values ​​of the positive and negative voltages at one end of a DC line, This refers to the line-mode voltage fault component at the nth sampling point from the moment the protection is activated. The conjugate function of the mother wavelet of the custom wavelet for the full-time window; For wavelet computation time windows of the corresponding scale The number of internal sampling points, and satisfying the constraints. , This indicates the floor operator. For the first Each characteristic frequency corresponds to a specific wavelet computation time window. The length.

[0016] More preferably, Based on the high-frequency band distribution characteristics of DC line fault traveling waves, a discrete characteristic frequency sequence is determined. ,in Indicates the first Each characteristic frequency, The total number of characteristic frequencies; For characteristic frequency sequences any characteristic frequency in Calculate the scaling parameters of the corresponding full-time window customized wavelet. ,in, The center frequency of the mother wavelet is customized for the entire time window; Based on the scale parameter Calculate the wavelet computation time window corresponding to each characteristic frequency. length The specific calculation formula is as follows:

[0017] in, The effective time-domain length of the mother wavelet of the wavelet is customized for the full time window.

[0018] More preferably, The full-time-window customized wavelet is an asymmetric flat-top attenuated complex wavelet, whose mother wavelet is composed of a time-domain envelope function and a complex exponential modulation term, and its specific definition is as follows:

[0019] in, The mother wavelet analytical expression for the wavelet is customized for the full-time window; The duration of the flat-top interval is such that the flat-top interval includes the wavefront portion of the initial traveling wave of the fault. The attenuation bandwidth parameter, whose value allows the time-domain envelope function to... Rapid attenuation at the tail end to meet protection speed requirements; It is the time-domain envelope function; The range of values ​​is ,in It is the Nyquist frequency.

[0020] More preferably, The time-domain envelope function The piecewise construction design is adopted, and its specific expression is: ; Based on the exponential decay characteristic of the envelope function, the effective time-domain length of this mother wavelet is... The principle for determining the effective length of the wavelet is as follows: when the amplitude of the attenuation interval drops to less than 10% of the constant amplitude of the flat-top interval, it is considered to be the cutoff point that has reached the effective length of the wavelet.

[0021] More preferably, The high-frequency transient energy of the line-mode voltage fault component is calculated based on the full-time window customized wavelet coefficients. The specific formula is as follows: ; in, This represents the custom wavelet coefficients for the entire time window. This refers to the total number of discrete characteristic frequencies determined based on the high-frequency band distribution characteristics of the traveling wave during a DC line fault.

[0022] More preferably, Step 5 specifically includes: like If the fault occurs in the area, it is determined that the fault is within the zone, and a protection action signal is output. like If so, the fault location is determined to be an external fault. in, To calculate the high-frequency transient energy based on wavelet coefficients tailored to the full-time window of the line-mode voltage fault component. The adaptive matching protection threshold obtained in step 3.

[0023] Secondly, the present invention provides a single-ended protection device for a multi-terminal flexible DC transmission system DC line based on full-time window customized wavelet transform, the protection device comprising: The data acquisition and protection start-up module is used to acquire the instantaneous values ​​of the positive and negative voltages at one end of the DC line, determine the protection start-up, and record the protection start-up time. The fault component calculation module is used to calculate the fault component of the line-mode voltage and the fault component of the ground-mode voltage based on the instantaneous value of the single-ended voltage of the DC line. The fault identification and threshold matching module is used to calculate the fault type judgment factor based on the fault component of the ground mode voltage to identify the fault type and adaptively match the protection threshold. The full-time-window customized wavelet transform and energy calculation module is used to calculate the wavelet coefficients and high-frequency transient energy of the line-mode voltage based on the fault component of the line-mode voltage using the full-time-window customized wavelet transform. The fault area discrimination module is used to compare the high-frequency transient energy with the matched protection threshold to determine the fault occurrence area; Thirdly, the present invention provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method described in the first aspect.

[0024] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method as described in the first aspect.

[0025] This invention proposes a method, device, and storage medium for single-ended protection of DC lines in multi-terminal flexible DC transmission systems. Compared to traditional signal processing methods such as wavelet transform, this invention, by constructing a full-time-window customized wavelet transform, not only solves the problem of insufficient frequency resolution in the high-frequency band under DC line faults, enabling more accurate extraction of the high-frequency transient features of the fault traveling wave, but also possesses advantages such as low computational complexity and strong anti-noise interference capability. Simultaneously, this invention employs an adaptive threshold matching strategy based on fault type judgment factors, matching protection settings according to the fault type, effectively addressing the difficulty in balancing sensitivity and reliability faced by existing single-ended quantitative protection methods using fixed thresholds. When determining the fault location, this invention, through the accurate extraction of fault features via full-time-window customized wavelet transform, combined with adaptively matched protection thresholds, significantly enhances the protection's ability to withstand high transition resistance, effectively balancing the protection's speed, sensitivity, and reliability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the multi-terminal flexible DC transmission system in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the steps of the single-end protection method for a multi-terminal flexible DC transmission system of the present invention. Figure 3 This is a flowchart of a single-ended protection method for a multi-terminal flexible DC transmission system based on full-time window customized wavelet transform, according to an embodiment of the present invention. Figure 4The mother wavelet time-domain waveform diagram of the custom wavelet for the full time window of this invention; Figure 5 This is a schematic diagram of the structure of a single-ended protection device for a multi-terminal flexible DC transmission system based on full-time window customized wavelet transform according to the present invention.

[0027] Among them, 1 is a DC transmission line, 2 is a DC protection device, 3 is a DC reactor, and 4 is a circuit breaker. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0029] Figure 1 This is a schematic diagram of a multi-terminal flexible DC transmission system according to an embodiment of the present invention. The transmission system includes multiple voltage source converter stations ( Figure 1 The diagram shows the first, second, third, and fourth converter stations. These multiple converter stations are interconnected via DC lines, forming a closed-loop four-terminal (multi-terminal) flexible DC transmission network. The AC side of each converter station is connected to the AC power grid via a transformer. Specifically, the transformers of the first and fourth converter stations connected to the power grid use Y / D connections, while the transformers of the second and third converter stations connected to the power grid use D / Y connections. Figure 1 In the diagram, 1 represents a DC transmission line, 2 represents a DC protection device, 3 represents a DC reactor, and 4 represents a circuit breaker.

[0030] like Figure 2 As shown, this invention proposes a single-end protection method for DC lines in a multi-terminal flexible DC transmission system, comprising the following steps: Step 1: Obtain the instantaneous values ​​of the positive and negative voltages at one end of the DC line, determine the start of the protection, and record the start time of the protection. With a fixed discrete sampling time interval Real-time acquisition of instantaneous positive voltage at one end of a DC line. and instantaneous value of negative electrode voltage Set the protection start-up voltage threshold to be [value]. When the instantaneous value of the positive or negative voltage is detected to be lower than the voltage start-up threshold, the system is determined to meet the protection start-up conditions.

[0031] Record the current sampling time as the protection start time. .

[0032] Step 2: Calculate the fault components of the line-mode voltage and the ground-mode voltage based on the instantaneous values ​​of the single-ended voltage of the DC line. Calculate the line-mode voltage and ground-mode voltage using the following formula:

[0033] in, Line-mode voltage, Ground mode voltage, This represents the instantaneous value of the positive voltage at one end of a DC line. This represents the instantaneous value of the negative pole voltage at one end of a DC line. It is a time variable; The fault components of the line-mode voltage and the ground-mode voltage are calculated using the following formula:

[0034]

[0035] in, The fault component of the line-mode voltage. The fault component of the ground mode voltage. This represents the steady-state value of the line-mode voltage before the fault. This represents the steady-state value of the ground mode voltage before the fault.

[0036] Step 3: Calculate the fault type judgment factor based on the fault component of the ground mode voltage and the preset fault type identification time window, identify the fault type, and adaptively match the protection threshold. In step 3, the fault type judgment factor is calculated according to the following formula. :

[0037] in, To protect the startup time; For the preset fault type identification time window The number of sampling points within the range, and satisfying the constraints. , This indicates the floor operator. Time window for fault type identification Length; To obtain the sampling time interval for the instantaneous values ​​of the positive and negative voltages at one end of a DC line, This refers to the ground mode voltage fault component at the nth sampling point since the protection activation time. The fault type identification time window length. The principle for determining the value is: Not greater than the length of the time window for each wavelet calculation .

[0038] Based on the fault type judgment factor Identify fault types and adaptively match protection action thresholds Specifically, it includes: like If so, it is identified as a positive ground fault, and the protection action threshold is matched. ; like If so, it is identified as a negative ground fault, and the protection action threshold is matched. ; like If so, it is identified as a short circuit between poles of the line, and the protection action threshold is matched. ; in, The preset polarity determination threshold, The preset single-pole grounding fault threshold, Set the preset inter-pole short-circuit fault threshold; . The range of values ​​is ,in This is the rated voltage of the DC line. The principle for determining the value is: less than the high-frequency transient energy of a single-pole grounding fault within the area. The minimum value is greater than the high-frequency transient energy of a single-pole grounding fault outside the zone. Maximum value. The principle for determining the value is: less than the high-frequency transient energy of the inter-electrode short-circuit fault within the region. The minimum value is greater than the high-frequency transient energy of an inter-electrode short-circuit fault outside the region. Maximum value.

[0039] Step 4: Calculate the wavelet coefficients and high-frequency transient energy of the fault component of the line-mode voltage based on the full-time-window customized wavelet transform; Based on the high-frequency band distribution characteristics of DC line fault traveling waves, a discrete characteristic frequency sequence is determined. ,in Indicates the first Each characteristic frequency, The total number of characteristic frequencies; For characteristic frequency sequences any characteristic frequency in Calculate the scaling parameters of the corresponding full-time window customized wavelet. ,in, The center frequency of the mother wavelet is customized for the entire time window; Based on the scale parameter Calculate the wavelet computation time window corresponding to each characteristic frequency. length The specific calculation formula is as follows:

[0040] in, The effective time-domain length of the mother wavelet of the wavelet is customized for the full time window.

[0041] Then, calculate the full-time window customized wavelet coefficients according to the following formula:

[0042] in, This represents the custom wavelet coefficients for the entire time window. For the first The scaling parameters of the full-time-window custom wavelet corresponding to each characteristic frequency. To protect the startup time, To obtain the sampling time interval for the instantaneous values ​​of the positive and negative voltages at one end of a DC line, This refers to the line-mode voltage fault component at the nth sampling point from the moment the protection is activated. The conjugate function of the mother wavelet of the custom wavelet for the full-time window; For wavelet computation time windows of the corresponding scale The number of internal sampling points, and satisfying the constraints. , This indicates the floor operator. For the first Each characteristic frequency corresponds to a specific wavelet computation time window. The length.

[0043] The high-frequency transient energy of the line-mode voltage fault component is calculated based on the full-time window customized wavelet coefficients. The specific formula is as follows: ; in, This represents the custom wavelet coefficients for the entire time window. This refers to the total number of discrete characteristic frequencies determined based on the high-frequency band distribution characteristics of the traveling wave during a DC line fault.

[0044] Step 5: Compare the high-frequency transient energy with the adaptive matching protection threshold to determine the fault location; like If the fault occurs in the area, it is determined that the fault is within the zone, and a protection action signal is output. like If so, the fault location is determined to be an external fault. in, To calculate the high-frequency transient energy based on wavelet coefficients tailored to the full-time window of the line-mode voltage fault component. The adaptive matching protection threshold obtained in step 3.

[0045] Example: Combined with Appendix Figure 1 As attached Figure 3 As shown in the figure, this invention proposes a single-ended protection method for DC lines in a multi-terminal flexible DC transmission system based on full-time window customized wavelet transform, which specifically includes the following steps: Step 1: Obtain the instantaneous values ​​of the positive and negative voltages at one end of the DC line, determine the protection activation time, and record the protection activation moment. With a fixed discrete sampling time interval Real-time acquisition of instantaneous positive voltage at one end of a DC line. and instantaneous value of negative electrode voltage The corresponding positive discrete voltage sampling sequence is obtained. and negative discrete voltage sampling sequence ,in This is the discrete time index of the current sampling point.

[0046] Set the protection start-up voltage threshold to be: When the positive voltage discrete sampling sequence is detected Or negative electrode voltage discrete sampling sequence The absolute value of continuous When a sampling point drops to or below the voltage trigger threshold, the system is determined to meet the protection activation conditions. In this embodiment... Take 5. The specific protection activation criteria are as follows:

[0047] When the above criterion is met for the first time, a suspected fault is detected in the system, triggering protection, and the system will continuously activate protection if the voltage drop condition is met. The first sampling point in the nth sampling point (i.e., the first sampling point) The time corresponding to each sampling point is recorded as the protection start time. The corresponding formula is:

[0048] Step 2: Calculate the fault components of the line-mode voltage and the ground-mode voltage based on the instantaneous values ​​of the single-ended voltage of the DC line. The specific operation is as follows: Step 201: Perform pole-mode transformation to decouple the coupled positive and negative lines, and calculate the line-mode voltage and ground-mode voltage. The specific calculation formula is as follows:

[0049] in, Line-mode voltage, Ground mode voltage, It is a time variable; Step 202: Calculate the fault components of the line-mode voltage and the ground-mode voltage. The specific calculation formulas are as follows:

[0050]

[0051] in, The fault component of the line-mode voltage. The fault component of the ground mode voltage. This represents the steady-state value of the line-mode voltage before the fault. This represents the steady-state value of the ground mode voltage before the fault.

[0052] Step 3: Calculate the wavefront integral based on the fault component of the ground mode voltage to identify the fault type, and adaptively match the protection threshold. The specific operation is as follows: Step 301: Calculate the protection start time based on the fault component of the ground mode voltage. Post-preset fault type identification time window Fault type judgment factor within ,calculate The specific formula is:

[0053] in Time window for fault type identification The number of sampling points within the range, and satisfying the constraints. , This indicates the floor operator. Time window for fault type identification The length of the fault type identification time window. The principle for determining the value is: Not greater than the length of the time window for each wavelet calculation This ensures that fault type identification is completed before fault identification within or outside the zone. In this embodiment... Select 1ms.

[0054] Step 302: Determine the factor based on the fault type. The fault type is identified as positive ground fault, negative ground fault, or inter-pole short circuit. Based on the identified fault type, the corresponding protection action threshold is adaptively matched for subsequent faults within the judgment zone. The specific logic includes: like If so, it is identified as a positive ground fault, and the protection action threshold is matched. ; like If so, it is identified as a negative ground fault, and the protection action threshold is matched. ; like If so, it is identified as a short circuit between poles of the line, and the protection action threshold is matched. ; in, The preset polarity determination threshold, The preset single-pole grounding fault threshold, This is the preset threshold for inter-electrode short-circuit faults. Because the high-frequency transient energy generated by inter-electrode short-circuit faults is significantly greater than that of single-electrode grounding faults, this threshold is set to improve the reliability of the protection. . The range of values ​​is ,in The rated voltage of the DC line is used in this embodiment. The voltage is set to 10kV. The principle for determining the value is: less than the high-frequency transient energy of the weakest single-pole grounding fault in the area. (i.e., the minimum high-frequency transient energy among all single-pole grounding faults within the zone) and greater than the high-frequency transient energy of the most severe single-pole grounding fault outside the zone. (That is, the maximum value among all high-frequency transient energies caused by single-pole grounding faults outside the zone). The principle for determining the value is: less than the high-frequency transient energy of the weakest inter-electrode short-circuit fault in the region. (i.e., the minimum high-frequency transient energy among all intra-region inter-electrode short-circuit faults) and greater than the high-frequency transient energy of inter-electrode short-circuit faults outside the region. (That is, the maximum value among all high-frequency transient energies caused by inter-electrode short-circuit faults outside the region). In this embodiment... Set it to 2. Set it to 10.

[0055] Step 4: Calculate the wavelet coefficients and high-frequency transient energy of the fault component of the line-mode voltage based on the full-time-window customized wavelet transform. This includes the following steps: Step 401: Select a set of discrete feature frequency sequences to generate the scaling parameters and wavelet calculation time windows corresponding to each feature frequency. The specific operations are as follows: First, based on the high-frequency band distribution characteristics of DC line fault traveling waves, a set of characteristic frequency sequences is selected. ,in Indicates the first Each characteristic frequency, This represents the total number of characteristic frequencies.

[0056] Secondly, for the characteristic frequency sequence any characteristic frequency in Calculate the scaling parameters of the corresponding full-time window customized wavelet. Scale parameters With characteristic frequency It is inversely proportional, and the specific calculation formula is as follows:

[0057] in, The center frequency of the mother wavelet is customized for the full-time window wavelet.

[0058] Finally, based on the scale parameters Calculate the wavelet computation time window corresponding to each characteristic frequency. length The specific calculation formula is as follows:

[0059] in, The effective time-domain length of the mother wavelet of the wavelet is customized for the full time window.

[0060] To accurately extract the high-frequency components at the initial moment of fault occurrence, the wavelet calculation time window is... The starting point is uniformly fixed at the protection start time. At the same time, the length of the time window for each wavelet calculation is limited. Not less than the fault type identification time window length This ensures that the fault type is identified before the high-frequency component extraction operation; furthermore, to improve frequency resolution and meet speed requirements, the length of each wavelet calculation time window is... The value should not exceed the set protection action time window. (i.e., the length of the time from protection activation to protection action exit) .

[0061] Step 402: Use the full-time window customized wavelet to transform the fault component of the line mode voltage and calculate the full-time window customized wavelet coefficients corresponding to each characteristic frequency.

[0062] The full-time-window customized wavelet used is an asymmetric flat-top decaying complex wavelet, whose mother wavelet consists of a time-domain envelope function and a complex exponential modulation term. The time-domain envelope function is always zero before the flat-top interval and consists of a flat-top interval that maintains a constant amplitude, followed by a decay interval. Its specific definition is as follows:

[0063] in, The mother wavelet analytical expression for the custom wavelet of the full-time window is given. The center frequency of the mother wavelet. The duration of the flat-topped interval. For attenuation bandwidth parameters, This is the time-domain envelope function. To avoid excessive compression of wavelets at various scales in the time domain when extracting high-frequency components, and to ensure that the transformed wavelets can basically cover the entire protection action time window. To ensure the complete extraction of fault information, The range of values ​​is ,in It is the Nyquist frequency. The principle for selecting the value is to ensure that the flat-top interval includes the wavefront portion of the initial traveling wave of the fault. The principle for choosing the value of is to make the time-domain envelope function Rapid decay at the tail end meets the protection speed requirements. In this embodiment, Pick , Take 1ms, Pick .

[0064] The time-domain envelope function The piecewise construction design is adopted, and its specific expression is: .

[0065] Based on the exponential decay characteristic of the envelope function, the effective time-domain length of this mother wavelet is... The principle for determining the effective wavelet length is as follows: when the amplitude of the attenuation interval drops below 10% of the constant amplitude of the flat-top interval, it is considered to have reached the cutoff point. In this embodiment, The length is 1.5ms.

[0066] The formula for calculating the wavelet coefficients for full-time window customization is as follows:

[0067] in, This represents the custom wavelet coefficients for the entire time window. The conjugate function of the mother wavelet of the custom wavelet for the full-time window; For wavelet computation time windows of the corresponding scale The number of internal sampling points, and satisfying the constraints. , This represents the floor operator.

[0068] Step 403: Calculate the high-frequency transient energy of the line-mode voltage fault component based on the full-time window customized wavelet coefficients. The specific formula is as follows:

[0069] Step 5: Compare the high-frequency transient energy with the matched protection threshold to determine the fault location, specifically including: like If the fault occurs in the area, it is determined that the fault is within the zone, and a protection action signal is output. like If so, the fault location is determined to be an external fault.

[0070] It should be noted that there are multiple DC lines in a multi-terminal flexible DC system. One line can be selected as the DC line to be protected, or several lines can be selected as the DC lines to be protected at the same time. If several lines are selected as the DC lines to be protected, each DC line to be protected will be protected according to the above process.

[0071] To further verify the effectiveness and superiority of the protection method proposed in this invention, a detailed explanation is provided below in conjunction with specific simulation model parameters and test data.

[0072] This embodiment is based on PSCAD / EMTDC and has been built as follows: Figure 1 The simulation model of the multi-terminal flexible DC transmission system is shown. The main topology of the simulation system is consistent with the actual engineering, and its core parameters are shown in Table 1.

[0073] Table 1. Main parameters of the simulation model of the multi-terminal flexible DC transmission system

[0074] For the aforementioned multi-terminal flexible DC transmission system, to ensure the selectivity, speed, sensitivity, and reliability of the single-terminal protection method, this embodiment provides detailed tuning of the core calculation and discrimination parameters of the protection method. The specific tuning principles are explained below: characteristic frequency sequence The sampling rate is selected to satisfy the Nyquist sampling theorem; the mother wavelet correlation parameters are set based on the time-domain attenuation characteristics of the mother wavelet and the system's speed performance index; each discrimination threshold is set based on a large amount of simulation data to ensure that external faults do not cause false triggering and internal faults are identified with high sensitivity. It should be noted that the specific values ​​in Table 2 are only one example of implementing the technical solution of this invention and are not the only limitation on the parameter range. The specific parameter tuning results are shown in Table 2.

[0075] Table 2. Core parameter setting table for the single-end protection method of the present invention.

[0076] To more intuitively demonstrate the wavelet characteristics constructed in this invention, based on the core parameters selected in Table 2, the time-domain waveform of the mother wavelet of the full-time-window customized wavelet generated in this embodiment is as follows: Figure 4 As shown. Combined with Figure 4 It can be seen that, Figure 4 The upper curve represents the oscillation waveform of the mother wavelet in the real and imaginary parts of the time domain, while the lower curve represents its time-domain envelope function. .Depend on Figure 4It can be seen that the envelope function maintains a constant amplitude (i.e., a flat-topped interval) in the 0~1ms interval. This ensures that the high-frequency transient characteristics of the system are given the maximum and constant extraction weight in the critical initial stage of the fault, effectively avoiding information loss caused by the energy decay at the edge of the traditional window function. After 1ms, it enters the exponential decay interval, which effectively suppresses the spectral leakage problem caused by direct truncation through smooth transition. Its amplitude has smoothly decayed to a minimum value at 1.5ms, so it is reasonably truncated at 1.5ms.

[0077] Based on the above system parameters and protection settings, further simulation tests were conducted for different fault locations, fault types and transition resistance conditions to verify the sensitivity and reliability of the protection method. The simulation results are shown in Table 3.

[0078] Table 3 Simulation results under different faults

[0079] In Table 3, PTG represents a positive ground fault, NTG represents a negative ground fault, and PTP represents a line-to-pole fault. express Figure 1 A busbar fault occurred at the first converter station. express Figure 1 A busbar fault occurred at the second converter station. express Figure 1 A fault occurred in the DC line connecting the first and second converter stations. This represents the percentage of the distance from the fault location to the first converter station relative to the total length of the line. Indicates the magnitude of the transition resistance, in units of .

[0080] Based on the simulation test data in Table 3, it can be seen that as the fault transition resistance gradually increases, the high-frequency components of the fault traveling wave are significantly weakened, and the extracted high-frequency transient energy... It exhibits an inevitable downward trend. However, thanks to the precise extraction of high-frequency energy from weak signals by the full-time window customized wavelet transform, and the wavefront integral... protection action threshold Adaptive matching, even when the transition resistance is as high as Even under extreme working conditions, it can still meet the requirements. The fault determination conditions within the zone are well-defined, and the protection action time window is only 1.5ms long, which fully balances extremely high speed and sensitivity.

[0081] This invention also provides a single-ended protection device for DC lines in a multi-terminal flexible DC transmission system based on full-time-window customized wavelet transform, such as... Figure 5As shown, the system includes a data acquisition and protection activation module, a fault component calculation module, a fault identification and threshold matching module, a full-time-window customized wavelet transform and energy calculation module, and a fault area discrimination module. Specifically, the data acquisition and protection activation module acquires the instantaneous values ​​of the positive and negative voltages at one end of the DC line, determines the protection activation time, and records the activation moment. The fault component calculation module calculates the fault components of the line-mode voltage and the ground-mode voltage based on the instantaneous values ​​of the single-end voltages of the DC line. The fault identification and threshold matching module calculates the wavefront integral based on the fault component of the ground-mode voltage to identify the fault type and adaptively matches the protection threshold. The full-time-window customized wavelet transform and energy calculation module calculates the wavelet coefficients and high-frequency transient energy of the line-mode voltage based on the fault component using a full-time-window customized wavelet transform. The fault area discrimination module compares the high-frequency transient energy with the matched protection threshold to determine the fault location.

[0082] The present invention also provides a single-end protection device for a multi-terminal flexible DC transmission system based on full-time window customized wavelet transform, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the single-end protection method for a multi-terminal flexible DC transmission system based on full-time window customized wavelet transform of the present invention.

[0083] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of a single-ended protection method for a multi-terminal flexible DC transmission system based on full-time-window customized wavelet transform according to the present invention.

[0084] Compared with existing technologies, this invention has the following advantages: 1. It constructs a full-time-window customized wavelet transform, which, compared with traditional wavelet transform and other signal processing methods, breaks through the technical bottleneck of insufficient frequency resolution in the high-frequency band under DC line faults, and can extract the high-frequency transient features of the fault traveling wave more accurately; 2. The full-time-window calculation mechanism effectively suppresses the influence of random noise, making the protection system more resistant to noise interference and further ensuring the reliability of high-frequency feature extraction in complex electromagnetic environments; 3. It selects a set of discrete feature frequency sequences for wavelet transform calculation, effectively reducing the amount of data processing and significantly reducing... 4. The computational complexity of the algorithm is reduced, thus ensuring that the single-ended protection scheme can meet the stringent real-time calculation requirements; 5. An adaptive threshold matching strategy based on fault type judgment factors is adopted, which can adaptively match the protection setting value according to the identified fault type, effectively solving the problem of difficulty in balancing sensitivity and reliability when the existing single-ended quantity protection uses a fixed threshold; 6. When judging the fault occurrence area, the criterion proposed in this invention fully combines high-frequency transient energy and adaptive matching threshold, significantly enhancing the protection's ability to withstand high transition resistance, and effectively balancing the speed, sensitivity and reliability of single-ended line protection.

[0085] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0086] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0087] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0088] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0089] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A method for single-end protection of DC lines in a multi-terminal flexible DC transmission system, characterized in that, Includes the following steps: Step 1: Obtain the instantaneous values ​​of the positive and negative voltages at one end of the DC line, determine the start of the protection, and record the start time of the protection. Step 2: Calculate the fault components of the line-mode voltage and the ground-mode voltage based on the instantaneous values ​​of the single-ended voltage of the DC line. Step 3: Calculate the fault type judgment factor based on the fault component of the ground mode voltage and the preset fault type identification time window, identify the fault type, and adaptively match the protection threshold. Step 4: Calculate the wavelet coefficients and high-frequency transient energy of the fault component of the line-mode voltage based on the full-time-window customized wavelet transform; Step 5: Compare the high-frequency transient energy with the adaptive matching protection threshold to determine the fault location.

2. The single-ended protection method for DC lines according to claim 1, characterized in that, In step 2, the line-mode voltage and ground-mode voltage are calculated according to the following formula: in, Line-mode voltage, Ground mode voltage, This represents the instantaneous value of the positive voltage at one end of a DC line. This represents the instantaneous value of the negative pole voltage at one end of a DC line. It is a time variable; The fault components of the line-mode voltage and the ground-mode voltage are calculated using the following formula: in, The fault component of the line-mode voltage. The fault component of the ground mode voltage. This represents the steady-state value of the line-mode voltage before the fault. This represents the steady-state value of the ground mode voltage before the fault.

3. The single-ended protection method for DC lines according to claim 1, characterized in that, In step 3, the fault type judgment factor is calculated according to the following formula. : in, To protect the startup time; For the preset fault type identification time window The number of sampling points within the range, and satisfying the constraints. , This indicates the floor operator. Time window for fault type identification Length; To obtain the sampling time interval for the instantaneous values ​​of the positive and negative voltages at one end of a DC line, It represents the ground mode voltage fault component at the nth sampling point from the moment the protection is activated.

4. The single-ended protection method for DC lines according to claim 3, characterized in that, In step 3, the fault type judgment factor is used. Identify fault types and adaptively match protection action thresholds Specifically, it includes: like If so, it is identified as a positive ground fault, and the protection action threshold is matched. ; like If so, it is identified as a negative ground fault, and the protection action threshold is matched. ; like If so, it is identified as a short circuit between poles of the line, and the protection action threshold is matched. ; in, The preset polarity determination threshold, The preset single-pole grounding fault threshold, The preset inter-electrode short-circuit fault threshold; where, .

5. The single-ended protection method for DC lines according to claim 4, characterized in that, The range of values ​​is ,in This is the rated voltage of the DC line; Single-pole grounding fault threshold It is less than the minimum high-frequency transient energy of a single-pole grounding fault within the zone and greater than the maximum high-frequency transient energy of a single-pole grounding fault outside the zone. Inter-electrode short-circuit fault threshold It is less than the minimum high-frequency transient energy of inter-electrode short-circuit faults within the zone and greater than the maximum high-frequency transient energy of inter-electrode short-circuit faults outside the zone.

6. The single-ended protection method for DC lines according to claim 1, characterized in that, The formula for calculating the wavelet coefficients for full-time window customization is as follows: in, This represents the custom wavelet coefficients for the entire time window. For the first The scaling parameters of the full-time-window custom wavelet corresponding to each characteristic frequency. To protect the startup time, To obtain the sampling time interval for the instantaneous values ​​of the positive and negative voltages at one end of a DC line, This refers to the line-mode voltage fault component at the nth sampling point from the moment the protection is activated. The conjugate function of the mother wavelet of the custom wavelet for the full-time window; For wavelet computation time windows of the corresponding scale The number of internal sampling points, and satisfying the constraints. , This indicates the floor operator. For the first Each characteristic frequency corresponds to a specific wavelet computation time window. The length.

7. The single-ended protection method for DC lines according to claim 6, characterized in that, Based on the high-frequency band distribution characteristics of DC line fault traveling waves, a discrete characteristic frequency sequence is determined. ,in Indicates the first Each characteristic frequency, The total number of characteristic frequencies; For characteristic frequency sequences any characteristic frequency in Calculate the scaling parameters of the corresponding full-time window customized wavelet. ,in, The center frequency of the mother wavelet is customized for the entire time window; Based on the scale parameter Calculate the wavelet computation time window corresponding to each characteristic frequency. length The specific calculation formula is as follows: in, The effective time-domain length of the mother wavelet of the wavelet is customized for the full time window.

8. The single-ended protection method for DC lines according to claim 6 or 7, characterized in that, The full-time-window customized wavelet is an asymmetric flat-top attenuated complex wavelet, whose mother wavelet is composed of a time-domain envelope function and a complex exponential modulation term, and its specific definition is as follows: in, The mother wavelet analytical expression for the wavelet is customized for the full-time window; The duration of the flat-top interval is such that the flat-top interval includes the wavefront portion of the initial traveling wave of the fault. The attenuation bandwidth parameter, whose value allows the time-domain envelope function to... Rapid attenuation at the tail end to meet protection speed requirements; It is the time-domain envelope function; The range of values ​​is ,in It is the Nyquist frequency.

9. The single-ended protection method for DC lines according to claim 8, characterized in that, The time-domain envelope function The piecewise construction design is adopted, and its specific expression is: ； Based on the exponential decay characteristic of the envelope function, the effective time-domain length of this mother wavelet is... The principle for determining the effective length of the wavelet is as follows: when the amplitude of the attenuation interval drops to less than 10% of the constant amplitude of the flat-top interval, it is considered to be the cutoff point that has reached the effective length of the wavelet.

10. The single-ended protection method for DC lines according to claim 6 or 9, characterized in that, The high-frequency transient energy of the line-mode voltage fault component is calculated based on the full-time window customized wavelet coefficients. The specific formula is as follows: ； in, This represents the custom wavelet coefficients for the entire time window. This refers to the total number of discrete characteristic frequencies determined based on the high-frequency band distribution characteristics of the traveling wave during a DC line fault.

11. The single-ended protection method for DC lines according to claim 10, characterized in that, Step 5 specifically includes: like If the fault occurs in the area, it is determined that the fault is within the zone, and a protection action signal is output. like If so, the fault location is determined to be an external fault. in, To calculate the high-frequency transient energy based on wavelet coefficients tailored to the full-time window of the line-mode voltage fault component. The adaptive matching protection threshold obtained in step 3.

12. A single-ended protection device for a multi-terminal flexible DC transmission system DC line based on the method of any one of claims 1-11, characterized in that, The protective device includes: The data acquisition and protection start-up module is used to acquire the instantaneous values ​​of the positive and negative voltages at one end of the DC line, determine the protection start-up, and record the protection start-up time. The fault component calculation module is used to calculate the fault component of the line-mode voltage and the fault component of the ground-mode voltage based on the instantaneous value of the single-ended voltage of the DC line. The fault identification and threshold matching module is used to calculate the fault type judgment factor based on the fault component of the ground mode voltage to identify the fault type and adaptively match the protection threshold. The full-time-window customized wavelet transform and energy calculation module is used to calculate the wavelet coefficients and high-frequency transient energy of the line-mode voltage based on the fault component of the line-mode voltage using the full-time-window customized wavelet transform. The fault area identification module is used to compare the high-frequency transient energy with the matched protection threshold to determine the fault location.

13. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1-11.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1-11.

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