Fault detection method, device, medium and equipment for multi-terminal flexible direct current transmission system

Abstract

The present application discloses a multi-terminal flexible direct current transmission system fault detection method, device, medium and equipment. The method described in the present application monitors whether an abnormal situation occurs in the multi-terminal flexible direct current transmission system in real time through the direct current voltage change rate of the direct current line to ensure the continuous and stable operation of the system, and judges whether the abnormal situation occurs on the direct current line side according to the magnitude relationship between the direct current voltage change rate and the preset start threshold, so as to ensure that the fault on the direct current line side can be effectively identified; further, the present application determines the fault pole at the abnormal situation according to the single-ended differential current, and comprehensively considers the time domain and frequency domain information characteristics of the voltage data, performs a generalized S transform on the voltage data at the abnormal situation to obtain the first-order derivative sequence of energy, captures the energy change of the fault voltage in the frequency domain, and judges whether the abnormal situation is a direct current line side fault inside the system, thereby combining the fault pole to quickly and reliably determine the fault type and specific location of the system fault.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to a method, device, medium and equipment for fault detection of a multi-terminal flexible direct current transmission system. Background Art

[0002] With the transformation of energy structure and the upgrading of power system, multi-terminal flexible DC transmission system is becoming more and more widely used in power system due to its advantages such as large transmission capacity, high controllability and suitability for long-distance transmission. However, how to ensure the stable operation of the system has become the focus of the industry.

[0003] In the prior art, traditional HVDC transmission protection includes traveling wave protection, voltage differential protection, current differential protection, undervoltage protection and other protections. However, the multi-terminal flexible DC transmission system includes a large number of sensitive power electronic devices that cannot withstand high fault currents for a long time. Therefore, it is necessary to quickly and accurately identify faults in the system. The faulty line must trip before the converter is blocked, but traditional HVDC transmission protection cannot meet this high requirement.

[0004] However, most of the current detection methods for multi-terminal flexible DC transmission system faults only identify which category the fault belongs to, such as DC line side fault, converter fault or AC system side fault, but are unable to further detect the specific location of the fault and accurately identify the specific type of fault, which affects the reliability and speed of subsequent system protection measures and is difficult to meet the complex requirements for the protection of multi-terminal flexible DC transmission systems in actual application scenarios. Summary of the invention

[0005] In view of this, the present application provides a multi-terminal flexible direct current transmission system fault detection method, device, medium and equipment, which can quickly and accurately identify the fault location and fault type, and increase the reliability and speed of fault detection.

[0006] According to one aspect of the present application, a multi-terminal flexible direct current transmission system fault detection method is provided, comprising: determining a DC voltage change rate of a DC line according to voltage data of the DC line; if the DC voltage change rate is greater than a preset starting threshold, determining a current in a local differential zone according to current data of the DC line, and determining a fault type of a system fault according to the current in the local differential zone; wherein the local differential zone comprises a first converter and a triangle side of a transformer connected to three phases of the first converter, the first converter being a converter corresponding to the DC voltage change rate greater than the preset starting threshold; if the If the DC voltage change rate is less than or equal to the preset starting threshold, the single-ended differential current of the second converter is determined according to the current data of the DC line, wherein the second converter is the converter corresponding to the DC voltage change rate that is less than or equal to the preset starting threshold; the fault pole is determined according to the single-ended differential current; the voltage data corresponding to the second converter located in the preset frequency band is subjected to a generalized S transform to obtain a time-frequency matrix; according to the time-frequency matrix, the energy first-order derivative sequence of the voltage transient energy and the preset frequency band is determined; according to the fault pole and the energy first-order derivative sequence, the fault type of the system fault is determined.

[0007] Optionally, the current in the local differential zone is determined based on the positive current in the local differential zone, the negative current in the local differential zone and the neutral current in the local differential zone; and the single-ended differential current is determined based on the difference between the positive current and the negative current at the same end of the second target converter.

[0008] Optionally, determining the fault type of the system fault based on the current of the local differential zone specifically includes: determining a first current sum of the currents of the local differential zone at different sampling times; if the absolute value of the first current sum is greater than a preset fault threshold, determining that the fault type is a converter fault.

[0009] Optionally, determining the fault pole according to the single-ended differential current specifically includes: determining a second current sum of the single-ended differential current at different sampling times; if the second current sum is greater than a preset fault pole threshold, determining that the fault pole is a positive pole; if the absolute value of the second current sum is less than or equal to the preset fault pole threshold, determining that the fault pole is an inter-pole pole; if the second current sum is less than the opposite of the preset fault pole threshold, determining that the fault pole is a negative pole.

[0010] Optionally, the fault type of the system fault is determined according to the fault pole and the first-order derivative sequence of energy, specifically including: if the fault pole is a positive pole, when the absolute values ​​of at least a preset number of consecutive elements in the first-order derivative sequence of energy are greater than a preset positive pole energy threshold, the fault type is determined to be a positive pole grounding short circuit fault on the DC line side; if the fault pole is inter-pole, when the absolute values ​​of at least a preset number of consecutive elements in the first-order derivative sequence of energy are greater than a preset inter-pole energy threshold, the fault type is determined to be an inter-pole short circuit fault on the DC line side; if the fault pole is a negative pole, when the absolute values ​​of at least a preset number of consecutive elements in the first-order derivative sequence of energy are greater than a preset negative pole energy threshold, the fault type is determined to be a negative pole grounding short circuit fault on the DC line side.

[0011] Optionally, determining the energy first-order derivative sequence of the voltage transient energy sum in the preset frequency band according to the time-frequency matrix specifically includes: determining a spectrum energy matrix according to the time-frequency matrix; calculating the spectrum energy sum according to the spectrum energy matrix; determining a voltage transient energy sum sequence according to the spectrum energy sum at different sampling moments; and calculating an energy first-order derivative sequence according to the voltage transient energy sum sequence.

[0012] Optionally, the spectrum energy matrix is ​​expressed as: E i(j,a) =[abs(SU[j,a])] 2 ;

[0013] The spectrum energy and is expressed as:

[0014] The energy first-order derivative sequence is expressed as:

[0015] Among them, E i(j,a) is the spectrum energy matrix, E ipq is the spectrum energy sum, i is the sampling time, SU[j,a] is the time-frequency matrix, j is the row of the time-frequency matrix, a is the column of the time-frequency matrix, p is the upper limit of the preset frequency band, q is the lower limit of the preset frequency band, N is the total number of columns of the time-frequency matrix, DE pq (i) is the energy first-order derivative sequence, E pq (i) E pq (i-1) is the voltage transient energy and two adjacent elements in the sequence, E pq (i) = E ipq , Δt is the sampling interval.

[0016] According to another aspect of the present application, a multi-terminal flexible direct current transmission system fault detection device is provided, comprising:

[0017] An acquisition module, used to determine a DC voltage change rate of the DC line according to voltage data of the DC line;

[0018] A first judgment module is used to determine the current of the local differential area according to the current data of the DC line if the DC voltage change rate is greater than a preset start threshold, and determine the fault type of the system fault according to the current of the local differential area; wherein the local differential area includes a first converter and a delta side of a transformer connected to the three phases of the first converter, and the first converter is a converter corresponding to the DC voltage change rate greater than the preset start threshold;

[0019] a second judgment module, configured to determine the single-ended differential current of a second converter according to the current data of the DC line if the DC voltage change rate is less than or equal to a preset start threshold, wherein the second converter is a converter corresponding to the DC voltage change rate that is less than or equal to the preset start threshold; and

[0020] A fault pole determination module, used for determining a fault pole according to the single-ended differential current;

[0021] A first calculation module, configured to perform a generalized S transform on the voltage data corresponding to the second converter in a preset frequency band to obtain a time-frequency matrix;

[0022] A second calculation module, used to determine the energy first-order derivative sequence of the voltage transient energy sum in the preset frequency band according to the time-frequency matrix;

[0023] The fault type determination module is used to determine the fault type of the system fault according to the fault pole and the energy first-order derivative sequence.

[0024] Optionally, the multi-terminal flexible direct current transmission system fault detection device further includes:

[0025] The third calculation module is used to determine the current in the local differential area according to the positive current in the local differential area, the negative current in the local differential area and the neutral current in the local differential area; and determine the single-ended differential current according to the difference between the positive current and the negative current at the same end of the second target converter.

[0026] Optionally, the first judgment module is specifically used to determine a first current sum of the currents of the local differential area at different sampling times; if the absolute value of the first current sum is greater than a preset fault threshold, the fault type is determined to be a converter fault.

[0027] Optionally, the fault pole determination module is specifically used to determine the second current sum of the single-ended differential current at different sampling times; if the second current sum is greater than a preset fault pole threshold, the fault pole is determined to be a positive pole; if the absolute value of the second current sum is less than or equal to the preset fault pole threshold, the fault pole is determined to be an inter-pole pole; if the second current sum is less than the opposite of the preset fault pole threshold, the fault pole is determined to be a negative pole.

[0028] Optionally, the fault type determination module is specifically used to determine that if the fault is at the positive pole, when the absolute value of at least a preset number of consecutive elements in the first-order derivative sequence of energy is greater than a preset positive pole energy threshold, the fault type is determined to be a positive pole ground short circuit fault on the DC line side; if the fault is at the inter-pole pole, when the absolute value of at least a preset number of consecutive elements in the first-order derivative sequence of energy is greater than a preset inter-pole energy threshold, the fault type is determined to be an inter-pole short circuit fault on the DC line side; if the fault is at the negative pole, when the absolute value of at least a preset number of consecutive elements in the first-order derivative sequence of energy is greater than a preset negative pole energy threshold, the fault type is determined to be a negative pole ground short circuit fault on the DC line side.

[0029] Optionally, the second calculation module is specifically used to determine the spectral energy matrix based on the time-frequency matrix; calculate the spectral energy sum based on the spectral energy matrix; determine the voltage transient energy and sequence based on the spectral energy sum at different sampling times; and calculate the energy first-order derivative sequence based on the voltage transient energy and sequence.

[0030] According to another aspect of the present application, a readable storage medium is provided, on which a program or instruction is stored. When the program or instruction is executed by a processor, the steps of the above-mentioned multi-terminal flexible direct current transmission system fault detection method are implemented.

[0031] According to another aspect of the present application, a computer device is provided, including a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, and the processor implements the steps of the above-mentioned multi-terminal flexible direct current transmission system fault detection method when executing the program.

[0032] By means of the above technical solution, the present application has the following beneficial effects compared with the prior art:

[0033] The multi-terminal flexible direct current transmission system fault detection method, device, medium and equipment described in the present application monitors whether the multi-terminal flexible direct current transmission system has abnormal conditions in real time through the direct current voltage change rate of the direct current line to ensure the continuous and stable operation of the system. And judge whether the abnormal condition occurs on the direct current line side inside the system according to the magnitude relationship between the direct current voltage change rate and the preset start threshold, so as to ensure that any fault occurring in the direct current line inside the system can be effectively identified; when the abnormal condition occurs on the non-direct current line side, the fault type of the system fault is determined according to the current in the local differential area, and when the abnormal condition occurs on the direct current line side inside the system, the fault pole causing the abnormal condition is determined according to the single-ended differential current, and the voltage data at the abnormal condition is subjected to a generalized S transformation to obtain the first-order derivative sequence of energy by combining the time domain and frequency domain information characteristics of the voltage data, capturing the energy change of the fault voltage signal in the preset frequency band, and judging whether the abnormal condition is a fault occurring on the direct current line side inside the system in combination with the fault pole and determining the direct current line where the fault occurs, so as to quickly and reliably determine the fault type and specific location of the system fault. The present application makes full use of the characteristics of current data and voltage data at the time of fault, and effectively captures the frequency changes of voltage signals in the short time domain through generalized S transform, which can better adapt to voltage signals with local frequency changes and non-stationary voltage signals, improve the ability to identify faulty voltage signals, and obtain more accurate energy changes, thereby quickly and accurately detecting and locating faults on the DC line side, effectively avoiding misjudgment, increasing the reliability and rapidity of fault detection and the effectiveness of subsequent relay protection of circuit breakers and other equipment, and facilitating the long-term and stable operation of multi-terminal flexible DC transmission systems.

[0034] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1 A schematic diagram of a multi-terminal flexible direct current transmission system fault detection method provided in an embodiment of the present application is shown;

[0037] Figure 2 A topological diagram of a multi-terminal flexible direct current transmission system model provided in an embodiment of the present application;

[0038] Figure 3A topological diagram of a local difference zone provided in an embodiment of the present application;

[0039] Figure 4 A graph showing a change in DC voltage conversion rate over time provided in an embodiment of the present application;

[0040] Figure 5 A graph showing a change in the second current sum over time provided in an embodiment of the present application;

[0041] Figure 6 A graph showing the change of the first-order derivative of energy over time provided in an embodiment of the present application;

[0042] Figure 7 Another graph of the change of DC voltage conversion rate over time provided in an embodiment of the present application;

[0043] Figure 8 Another graph of the change of the second current sum over time provided in an embodiment of the present application;

[0044] Fig. 9 Another graph of the change of the first-order derivative of energy over time provided in an embodiment of the present application;

[0045] Fig.10 A graph showing a change in DC voltage conversion rate over time provided in another embodiment of the present application;

[0046] Fig.11 A graph showing a change in the second current sum over time provided in an embodiment of the present application;

[0047] Fig.12 A graph showing the change of the first-order derivative of energy over time provided in an embodiment of the present application;

[0048] Fig.13 A graph showing a change in DC voltage conversion rate over time provided in another embodiment of the present application;

[0049] Fig.14 A graph showing a change in the second current sum over time provided in an embodiment of the present application;

[0050] Fig.15 A graph showing the change of the first-order derivative of energy over time provided in an embodiment of the present application;

[0051] Fig.16 A graph showing a change in DC voltage conversion rate over time provided in another embodiment of the present application;

[0052] Fig.17 A graph showing a change in the first current sum over time provided in an embodiment of the present application;

[0053] Fig.18A graph showing a change in DC voltage conversion rate over time provided in another embodiment of the present application;

[0054] Fig.19 A graph showing a change in the second current sum over time provided in an embodiment of the present application;

[0055] Fig. 20 A graph showing the change of the first-order derivative of energy over time provided in an embodiment of the present application;

[0056] Fig.21 A structural block diagram of a multi-terminal flexible direct current transmission system fault detection device provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0057] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0058] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present application.

[0059] Those skilled in the art will appreciate that, unless expressly stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, or there may be intermediate elements. In addition, the "connection" or "connection" used herein may include wireless connection or wireless fusion. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0060] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in a variety of different forms and should not be interpreted as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art.

[0061] In this embodiment, a multi-terminal flexible direct current transmission system fault detection method is provided. Figure 1 As shown, the method includes:

[0062] S101, determining a DC voltage change rate of the DC line according to voltage data of the DC line.

[0063] Specifically, when a multi-terminal flexible DC transmission system fails, the voltage on the DC line side will fluctuate significantly. ef_L / dt) to monitor in real time whether the multi-terminal flexible DC transmission system has any abnormal situation.

[0064] Among them, the DC voltage change rate is expressed as: du ef_L / dt, d is the derivative operation, u ef_L is the voltage data on the DC line L between the converter e and the converter f, and t is the unit time.

[0065] For the sake of ease of expression, the multi-terminal flexible DC transmission system will be referred to as the “system” in the following text.

[0066] In this embodiment, the voltage and current are sampled in real time through the voltage transformer and the current transformer connected to the converter, and the voltage data and the current data at various locations in the DC line are obtained to monitor the system in real time.

[0067] Exemplarily, the sampling parameters of the voltage data may be 20,000 samples per 1 second, a sampling interval of 50 μs, and a sampling frequency of 20 kHz.

[0068] It should be noted that the fault types of the multi-terminal flexible DC transmission system include: intra-regional faults and extra-regional faults. Intra-regional faults are DC line side faults (faults occurring in the DC line within the system), and extra-regional faults are faults occurring outside the DC line within the system, such as converter faults and AC side faults. In the system, DC line side faults may cause large-scale power outages in the system and even cause safety accidents, so this application focuses on DC line side faults.

[0069] S102: If the DC voltage change rate is greater than a preset start threshold, determine the current of the local differential area according to the current data of the DC line, and determine the fault type of the system fault according to the current of the local differential area.

[0070] The local differential area includes the first converter and the transformer delta side connected to the three phases of the first converter, and the first converter is greater than the preset start threshold DV set The DC voltage change rate du ef_L / dt corresponding to the converter.

[0071] Specifically, the DC voltage change rate du when a DC line fault occurs ef_L / dt and the DC voltage change rate du when a fault occurs outside the DC line ef_L / dt value range is different, and the DC voltage change rate du when a DC line fault occurs ef_L / dt is less than the DC voltage change rate du when a fault occurs outside the DC line ef_L / dt. In order to ensure that the DC line side fault can be accurately identified when it occurs, and to avoid misjudgment when the DC line side fault does not occur, this application sets the DC voltage change rate du ef_L / dt corresponding to the preset start threshold DV set , by presetting the start threshold DV set Determine whether the fault occurs on the DC line side.

[0072] Among them, the preset start threshold DV set The critical value can be determined based on the most serious fault occurring outside the DC line and the least serious fault occurring on the DC line side, so as to set a specific value to accurately identify the fault type, thereby improving the sensitivity of the method described in the present application.

[0073] In this embodiment, when the DC voltage change rate du at a certain point on the DC line side is detected ef_L / dt is greater than the preset start threshold DV set When a fault occurs in the area outside the DC line of the system, it indicates that an abnormal situation has occurred there, and the cause of the abnormal situation is in the area outside the DC line of the system. When a fault occurs in the area outside the DC line of the system, the current size of the local differential area will change differently depending on the type of fault. Based on this, the present application further judges the abnormal situation according to the current of the local differential area.

[0074] For example, Figure 3 As shown, the local differential area includes the first converter which is closest to the location where the abnormal situation occurs and the delta side of the transformer connected to the three phases of the first converter.

[0075] Among them, the current i in the local differential region LDZC is the difference between the positive current, negative current and neutral current in the local differential region. The current in the local differential region is expressed as i LDZC =i p1 +i n1 +i g1 , where i p1 is the positive current in the local differential region, i n1 is the negative current in the local differential region, i g1 It is the neutral current in the local differential zone. The neutral current is the current generated in a three-phase AC system due to unbalanced three-phase voltage or unbalanced load.

[0076] Further, as a refinement and extension of the specific implementation method of the above-mentioned embodiment, in order to fully illustrate the specific implementation process of this embodiment, the step of determining the fault type of the system fault according to the current of the local differential zone in step S102 specifically includes: determining the first current sum of the currents of the local differential zone at different sampling times; if the absolute value of the first current sum is greater than the preset fault threshold, determining that the fault type is a converter fault.

[0077] In this embodiment, when a converter fault occurs, the current i LDZC The value of is not 0 and belongs to a certain value range, so the current i of the local differential area is set in this application LDZC The corresponding preset fault threshold I set.2 To judge the fault type. In order to improve the accuracy of the judgment, the present application calculates the current i of the local differential area at different sampling moments i within the preset sampling time. LDZC The sum of the first current I LDZC ), and the first current sum I LDZC With the preset fault threshold I set.2 Compare them to get the fault type of the system fault.

[0078] Among them, the first current sum I LDZC Expressed as

[0079] Specifically, when the first current sum I LDZC The absolute value of the fault is less than or equal to the preset fault threshold I set.2 When the first current sum I LDZC The absolute value of the fault is greater than the preset fault threshold I set.2 When the abnormal situation is determined to be a converter fault, the circuit breaker and other equipment in the system start the corresponding relay protection according to the obtained fault type, thereby effectively protecting the stable operation of the system.

[0080] S103: If the DC voltage change rate is less than or equal to a preset start threshold, determining a single-ended differential current of the second converter according to current data of the DC line.

[0081] The second converter is a converter corresponding to a DC voltage change rate that is less than or equal to a preset starting threshold.

[0082] In this embodiment, when the DC voltage change rate du at a certain point on the DC line side is detected ef_L / dt is less than or equal to the preset start threshold DV setWhen a fault occurs on the DC line side, the single-ended differential current i SEDC Different fault poles will produce different changes. This application sets the single-ended differential current i accordingly. SEDC The corresponding preset fault threshold I set.1 , to distinguish different fault poles, so as to locate the fault pole and fault position through single-ended differential current.

[0083] Among them, the single-ended differential current i SEDC is the difference between the positive current and the negative current at the same end of the second converter, the single-ended differential current i SEDC Represented as i SEDC =i p2 +i n2 ,i p2 、i n2 are respectively the positive current and the negative current at the same end of the second converter. Exemplarily, the second converter is the converter closest to the location where the abnormal situation occurs.

[0084] S104, determining the fault pole according to the single-ended differential current.

[0085] In this embodiment, when a fault occurs on the DC line side of the system, the submodule capacitor of the faulty pole discharges through paths such as the AC side grounding point and the DC line side grounding point. When the positive pole is grounded and short-circuited, the current flowing through the neutral point grounding resistors on both sides is negative, and there is i SEDC >0, when a negative grounding short circuit fault occurs, the current flowing through the neutral grounding resistors on both sides is positive, and i SEDC <0; when an AC system failure occurs, i SEDC =0.

[0086] Due to the different fault poles, the corresponding single-ended differential current i SEDC The numerical range is different. This application is based on the single-ended differential current i corresponding to the abnormal situation. SEDC To further determine the fault pole at the abnormal situation, so as to clearly and accurately locate the fault point, avoid unnecessary maintenance scope and waste of time, and help improve the efficiency and speed of fault handling.

[0087] Further, as a refinement and expansion of the specific implementation of the above embodiment, in order to fully illustrate the specific implementation process of this embodiment, step S104, that is, the step of determining the fault pole according to the single-ended differential current, specifically includes: determining the second current sum of the single-ended differential current at different sampling times; if the second current sum is greater than the preset fault pole threshold, determining that the fault pole is the positive pole; if the absolute value of the second current sum is less than or equal to the preset fault pole threshold, determining that the fault pole is the inter-pole pole; if the second current sum is less than the opposite of the preset fault pole threshold, determining that the fault pole is the negative pole.

[0088] In this embodiment, in order to improve the accuracy of the judgment, the present application calculates the single-ended differential current i at different sampling times i within the preset sampling time. SEDC The sum of the second current I SEDC ), and the second current sum I SEDC With the preset fault threshold I set.1 Compare them and get the fault pole.

[0089] Among them, the second current sum I SEDC Expressed as

[0090] Specifically, when the second current sum I SEDC Greater than the preset fault threshold I set.1 When the second current sum I SEDC The absolute value of the fault threshold I is less than or equal to the preset fault threshold I set.1 When the second current sum I SEDC Less than the preset fault threshold I set.1 When it is the opposite number of , it means that the fault pole causing the abnormal situation is negative.

[0091] S105, performing a generalized S transform on the voltage data corresponding to the second converter located in the preset frequency band to obtain a time-frequency matrix.

[0092] In this embodiment, when a DC line fault occurs, a high-frequency transient signal is generated. The current-limiting inductors installed at both ends of the DC line can be regarded as high impedance to the high-frequency signal, so that the DC line voltage undergoes obvious energy changes in a certain frequency domain. Therefore, the present application determines whether the abnormal situation is a DC line fault by the energy change of the DC line voltage. The generalized S (Stockwell) transform is used to process the voltage data, thereby improving the reliability of fault identification.

[0093] It is worth mentioning that the generalized S transform in this application adds a width parameter α of the Gaussian function on the basis of the S transform, which can solve the problem of spectrum leakage when the S transform processes non-stationary signals. When the value of α is small, the standard deviation of the Gaussian function is small, the main lobe width is narrow, and the distinction between adjacent frequency components is high. The higher the frequency domain resolution, the lower the time resolution. When the value of α is large, the related characteristics are opposite. At the same time, the generalized S transform also has the advantages of the S transform. Its window function is adaptive in frequency, can better adapt to the local frequency changes of the signal, adapt to non-stationary signals, and can obtain a more accurate time-frequency representation. It can effectively capture the frequency changes of the signal in the short time domain, improve the recognition ability of fault signals, reduce errors, and increase the accuracy of the calculation results. Among them, the result of the generalized S transform is a time-frequency spectrum matrix, and each element in the time-frequency spectrum matrix represents the energy distribution of the signal at a specific time and frequency.

[0094] Exemplarily, a generalized S transform is performed on the voltage data in the preset frequency band [p, q] at the abnormal situation to obtain the time-frequency matrix SU(k, a) at the sampling time i, where j is the row of the time-frequency matrix SU(k, a) and a is the column of the time-frequency matrix SU(j, a).

[0095] S106, determining a first-order derivative sequence of the voltage transient energy sum in a preset frequency band according to the time-frequency matrix.

[0096] Specifically, the absolute value of each element of the time-frequency matrix SU(j, a) is squared to obtain the corresponding spectrum energy matrix E i(j,a) , the spectrum energy and E in the preset frequency band [p, q] ipq is the spectrum energy matrix E i(j,a) Therefore, each sampling time i can correspond to a spectrum energy and E in the preset frequency band. ipq , according to the spectrum energy and E at different sampling times ipq Determine the voltage transient energy and sequence E pq , voltage transient energy and sequence E pq Each element in corresponds to the energy value spectral energy and E in the preset frequency band [p, q] at a certain sampling time. ipq , specifically expressed as E pq (i) = E ipq , and according to the voltage transient energy and sequence E pq Determine the voltage transient energy and sequence E pq The energy first-order derivative sequence DE pq (i) is used to represent the energy change of the voltage signal in the preset frequency band [p, q] under abnormal conditions.

[0097] In this embodiment, the voltage energy fluctuation in the preset frequency band is larger and has more obvious characteristics, which is conducive to quickly capturing the energy changes of the voltage signal when a fault occurs. On this basis, the abnormal fluctuation of the voltage signal is accurately detected according to the first-order derivative sequence of energy, so as to more reliably locate the fault type of the system fault.

[0098] Where p is the upper limit of the preset frequency band [p, q], q is the lower limit of the preset frequency band [p, q], and the spectrum energy matrix is ​​expressed as: E i(j,a) =[abs(SU[j,a])] 2 , the spectrum energy and is expressed as: N is the total number of columns of the time-frequency matrix SU(j, a), the energy first-order derivative sequence DE pq (i) is expressed as: E pq (i) E pq (i-1) is the voltage transient energy and sequence E pq Two adjacent elements in , Δt is the sampling interval.

[0099] In actual application scenarios, the preset frequency band can be reasonably set according to parameters such as circuit structure and voltage energy, and this application does not make specific restrictions. For example, when the voltage signal is in the frequency band [50Hz, 70Hz], the energy fluctuation is large and the characteristics are obvious, which is conducive to reflecting the energy change of the voltage signal when a fault occurs. Therefore, in this embodiment, the preset frequency band is set to [50Hz, 70Hz].

[0100] S107, determining the fault type of the system fault according to the fault pole and the first-order derivative sequence of energy.

[0101] In this embodiment, when a DC line fault occurs, the energy change of the voltage in the preset frequency band at the abnormal situation is within a certain value range, and different fault poles have different effects on the energy change of the voltage. Therefore, the present application sets the preset positive pole energy threshold DE according to the three situations that the fault pole is positive pole, inter-pole and negative pole. set，1，i , preset inter-electrode energy threshold DE set，2，i and preset negative electrode energy threshold DE set，3，i Three different energy thresholds DE, and the energy first-order derivative sequence DE pq (i) Compare with the corresponding energy threshold DE to accurately determine whether the abnormal situation is a DC line side fault.

[0102] The fault detection method provided in the embodiment of the present application combines the characteristics of current and voltage when a fault occurs and uses the DC voltage change rate du ef_L / dt detects in real time whether there is any abnormality in the system; on the one hand, according to the DC voltage change rate du ef_L / dt determines whether the abnormal situation occurs on the DC line side of the system, and based on the single-ended differential current i SEDC Further determine the fault pole and use the energy first-order derivative sequence DE pq (i) Determine whether the abnormal situation is a DC line fault, and determine the DC line side where the fault occurs based on the abnormal situation, thereby determining the fault type and specific location of the system fault; on the other hand, use the current i in the local differential area LDZC Detect whether the converter is faulty, so as to achieve comprehensive and accurate identification of converter faults and DC line-side faults in the multi-terminal flexible DC transmission system, and improve the reliability and rapidity of fault detection.

[0103] Further, as a refinement and extension of the specific implementation of the above embodiment, in order to fully illustrate the specific implementation process of this embodiment, step S107, that is, determining the fault type of the system fault according to the fault pole and the first-order derivative sequence of energy, can be performed in the following manner:

[0104] Method 1: If the fault is positive, when the energy first-order derivative sequence DE pq (i) The absolute values ​​of at least a preset number of consecutive elements are greater than the preset positive electrode energy threshold DE set，1，i When the fault type is determined to be a positive grounding short circuit fault on the DC line side, that is, a positive grounding short circuit fault occurs on the DC line side where the abnormal situation inside the system is located;

[0105] Method 2: If the fault is between poles, when the energy first-order derivative sequence DE pq (i) The absolute value of at least a preset number of consecutive elements is greater than the preset inter-electrode energy threshold DE set，2，i When the fault type is determined to be an inter-pole short-circuit fault on the DC line side, that is, an inter-pole short-circuit fault occurs on the DC line side where the abnormal situation occurs inside the system;

[0106] Method 3: If the fault is extremely negative, when the energy first-order derivative sequence DE pq (i) The absolute values ​​of at least a preset number of consecutive elements are greater than the preset negative electrode energy threshold DE set，3，i When the fault type is determined to be a negative pole grounding short circuit fault on the DC line side, that is, a negative pole grounding short circuit fault occurs on the DC line side where the abnormal situation inside the system is located.

[0107] The preset number can be configured as any value between 1 and 10, such as 5, 8, etc.

[0108] Specifically, for example, the present application constructs the following in the simulation program PSCAD / EMTDC: Figure 2The multi-terminal flexible DC transmission system model of the modular multi-level converter is shown in the figure. In the multi-terminal flexible DC transmission system model, T1, T2, T3 and T4 are four converters, L12, L24, L43 and L31 are four DC lines, f1, f2, f3, f4, f 12 、f 21 、f 24 、f 42 、f 43 、f 34 、f 31 、f 13 、f T1 、f T2 、f T3 、f T4 All are fault locations, u1, u2, u3, u4, u 12 、u 21 、u 24 、u 42 、u 43 、u 34 、u 31 、u 13 They are f1, f2, f3, f4, f 12 、f 21 、f 24 、f 42 、f 43 、f 34 、f 31 、f 13 The system parameters of the multi-terminal flexible direct current transmission system model are shown in Table 1.

[0109] Table 1

[0110]

[0111] like Figure 2 As shown in the figure, the faults f3, f4, and f 43 、f 34 Table 2 shows f3, f4, f 43 、f 34 The preset start threshold DV is measured when different types of faults occur in the set When a fault occurs on the DC line side, the measured DC voltage change rate du ef_L / dt should be less than the preset start threshold DV set Considering the most serious fault outside the DC line (inter-pole short circuit fault) and the least serious DC line side fault (positive pole grounding short circuit fault, transition resistance is 200Ω), based on the concept of focusing on the DC line side fault in this application, the startup threshold DV is preset. setWhen it is set between -886.75 and -1295 kV / ms, a DC line fault can be identified by the method described in this application, but a DC line fault will not be identified. set Setting it to -800 kV / ms can ensure that both converter faults and DC line side faults can be accurately identified by the present application.

[0112] Table 2

[0113]

[0114] Table 3 and Table 4 are f3, f4, f 43 、f 34 The second current sum I corresponding to different types of faults occurring at the same place SEDC Calculation results. The data in the second column of Table 3 and Table 4 are the calculation results under normal conditions when no fault occurs, and the data starting from the third column are the calculation results when the transition resistance is 0Ω or 200Ω. set.1 As can be seen from Table 3, the preset fault threshold I set.1 The value of can be set between 0.02kA and 0.40kA. In this embodiment, I set.1 The value of is set to 0.2 kA. As can be seen from Table 3, the present application can reliably protect the system under different short-circuit faults and over-resistance conditions.

[0115] Table 3

[0116]

[0117] Table 4

[0118]

[0119]

[0120] Tables 5 and 6 show f3, f4, and f 43 、f 34 The energy first-order derivative sequence DE in 20 time windows after different types of faults occur at the same place pq (i) is the value with the largest absolute value of the element. The data in the second column of Table 5 and Table 6 are the calculation results under normal conditions when no fault occurs, and the data starting from the third column are the calculation results when the transition resistance is 0Ω or 200Ω. In this embodiment, for the setting of the three energy thresholds DE, considering that the minimum value of DE is -6.61 when a positive ground short circuit fault occurs outside the DC line, and the maximum value of DE is -16.44 when a positive ground short circuit fault occurs on the DC line side, the positive energy threshold DE is preset. set，1 ,i Between 6.61-16.44, this embodiment uses 10. In addition, the negative electrode grounding short circuit fault is similar to the positive electrode grounding short circuit fault, so the negative electrode energy threshold DE is preset set，3，i is also set to 10. Similarly, as shown in the third row of Table 4, the inter-electrode energy threshold DE is preset set，2，i The absolute value can be set between -36.77 and -50.52, and is set to 40 in this embodiment.

[0121] Table 5

[0122]

[0123] Table 6

[0124]

[0125] Reference Figures 4 to 6 As shown in FIG. 1 , in this embodiment, a positive grounding short circuit fault occurs on the DC line L43 side 125 km away from the converter T3. Figure 4 As shown, the method described in this application detects that the fault occurs at 2s, and the DC voltage change rate changes rapidly when the fault occurs. Since the fault location is near the converter T4, f 43 The voltage u 43 The DC voltage change rate changes first, from Figure 4 It can be seen that the application detects the abnormal situation very quickly. Figure 5 The response curve shown is based on the single-ended differential current i corresponding to the converter T4. SEDC.4 Calculate the second current sum I of the converter T4 within the preset sampling time 1ms SEDC.4 To identify the fault pole, the result is 0.7775kA, which is greater than the preset fault pole threshold I set.1 , so the fault pole is determined to be the positive pole; further, calculate f 43 The energy first-order derivative sequence DE at 43 , determine whether it is a DC line side fault, such as Figure 6 As shown, at a preset number of consecutive sampling points, its absolute value is greater than the preset positive electrode energy threshold DE set，1，i It is determined that a positive grounding short circuit fault occurs on the DC line L43 side, which is consistent with the known fault type and specific fault location, thereby verifying that the present application can quickly and accurately detect faults.

[0126] It should be noted that in actual application scenarios, in addition to calculating and determining the fault pole by using the difference between the positive current and the negative current at the same end of the second converter closest to the abnormal situation as described in S103, the present application can also calculate and determine the fault pole according to the difference between the positive current and the negative current at the same end of the converter in the same DC line as the abnormal situation. For example, 0.4ms after the fault occurs, f 43 The voltage u 43 The DC voltage change rate changes. Then, refer to Figure 5 As shown, according to the single-ended differential current i corresponding to the converter T3 SEDC.3 Calculate the second current sum I of the converter T3 within the preset sampling time 1ms SEDC.3 The result is 0.7796kA, which is greater than the preset fault threshold I set.1 , determine that the fault pole is the positive pole, and further calculate f according to the fault pole 43 The energy first-order derivative sequence DE at 43 The absolute value of each element in is greater than the preset positive electrode energy threshold DE at a preset number of consecutive sampling points. set，1，i , so this application in f 43 A positive grounding short circuit fault is detected on the DC line L43 side. Therefore, this implementation can also detect the fault quickly and accurately.

[0127] Reference Figures 7 to 9 As shown in FIG. 1 , in this embodiment, a negative grounding short circuit fault occurs on the DC line L43 side 125 km away from the converter T3. Figure 7 As shown, the method described in this application detects that the fault occurs at 2s, in which case there is a 200Ω transition resistance. The fault identification process of this embodiment is similar to the positive grounding fault described above. Figure 7 It can be seen from the response curve in that the DC voltage change rate changes very quickly when the fault occurs, and the present application also detects the abnormal situation very quickly. 43 The voltage u 43 The DC voltage change rate changes first, according to Figure 8 The response curve shown in FIG. 1 is used to calculate the second current sum I of the converter T4 within the preset sampling time 1 ms. SEDC..4 To identify the fault pole, the result is -0.40kA, which is a negative number and less than the preset fault pole threshold I set.1 The opposite number of f, so the fault pole is negative; further, calculate f 43 The energy first-order derivative sequence DE at 43 , determine whether it is a DC line side fault, such as Fig. 9 As shown, at a preset number of consecutive sampling points, f 43 The energy first-order derivative sequence DE at43 The absolute value of the negative electrode energy threshold DE is greater than the preset negative electrode energy threshold DE set，3，i It is determined that a negative grounding short circuit fault occurs on the DC line L43 side, which is consistent with the known fault type and specific fault location, thereby verifying that the present application can quickly and accurately detect the fault.

[0128] Reference Figure 10-12 As shown in FIG. 1 , in this embodiment, a short circuit fault occurs between poles on the DC line L43 side, which is 125 km away from the converter T3. Fig.10 It can be seen from the response curve that the DC voltage change rate changes rapidly when a fault occurs. Since the fault location is close to the converter T4, the method described in this application detects f 43 The DC voltage change rate at the position changes first, which shows that the detection speed of the present application is very fast. Fig.11 The response curve shown in FIG. 1 is used to calculate the second current sum I of the converter T4. SEDC.4 To determine the fault pole, the result is 4.75×10 -4 kA, whose absolute value is less than the preset fault threshold I set.1 , then the fault pole is determined to be between poles, and f is further calculated based on the fault pole 43 The energy first-order derivative sequence DE at 43 , and determine whether it is a DC line side fault, such as Fig.12 As shown, at a preset number of consecutive sampling points, f 43 The energy first-order derivative sequence DE at 43 The absolute value of is greater than the preset inter-electrode energy threshold DE set，2，i It was determined that a DC line side inter-pole short circuit fault occurred on the DC line L43 side, which was consistent with the known fault type and specific fault location.

[0129] Reference Figures 13 to 15 As shown, in this embodiment, a single-pole metallic ground fault occurs in the DC bus outside the system. The method described in this application detects u 31 and u 34 The changes of f are almost the same because they are connected to the same bus. Since the fault location is close to converter T3, f 34 The DC voltage change rate at 1 changes first. Fig.14 The response curve shown in FIG. 1 is used to calculate the second current sum I of the converter T3 within the preset sampling time 1 ms. SEDC.3 To identify the fault pole, the result is 1.13×10 -3 kA, whose absolute value is less than the preset fault threshold I set.1 , then the fault pole is determined to be between poles. Fig.12 The response curve shown in Figure 2 shows the calculation of f 34 The energy first-order derivative sequence DE at34 , to determine whether it is a DC line side fault, such as Fig.15 As shown, f 34 The energy first-order derivative sequence DE at 34 There is no continuous preset number of sampling points where the absolute value is greater than the preset inter-electrode energy threshold DE set，2，i , it is determined to be a fault outside the DC line side, which is consistent with the known fault type, thereby verifying that even if the fault type is very similar to the DC side fault inside the system, the method described in the present application will not make a misjudgment.

[0130] Reference Fig.16 , Fig.17 As shown, in this embodiment, the method described in this application is based on Fig.16 The DC voltage change rate and Fig.17 The first current sum shown detects that the converter T4 has a fault, the fault occurs for 2 seconds and lasts for 50 ms. This shows that the converter fault can also be detected quickly and reliably by the present application.

[0131] Reference Figures 18 to 20 As shown, in this embodiment, the metal positive pole on the DC line L43 side (125km from T3) is faulted to the ground, and the fault occurs at 2s. Noise will cause fluctuations in the measured data. In order to test whether the application is effective when noise exists, this embodiment adds white noise with a signal-to-noise ratio of 35db to the measured voltage and current. The test results are shown in Figures 18 to 20 As shown, in the case of noise interference, the present application Fig.18 The DC voltage change rate shown, Fig.19 The second current sum shown and Fig. 20 The energy first-order derivative sequence shown can still detect the fault quickly and accurately, indicating that the present invention has the ability to correct low-frequency drift, can effectively suppress sidelobe leakage, is not affected by noise, helps to reduce error introduction, reduces interference, and improves the accuracy and reliability of fault detection.

[0132] Based on the analysis of fault voltage and current signal characteristics, the present application considers the influence of noise, determines the fault pole according to the single-ended single-ended differential current, uses the generalized S transform to obtain the first-order derivative sequence of energy, and selects the DC line where the fault occurs according to the energy change reflected in the first-order derivative sequence of energy, so as to quickly and reliably determine the fault type and specific location of the system fault, which is beneficial to the implementation of subsequent relay protection and effectively protects the long-term stable operation of the system.

[0133] It should be noted that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0134] Furthermore, if Fig.21 As shown, as a specific implementation of the above-mentioned multi-terminal flexible direct current transmission system fault detection method, an embodiment of the present application provides a multi-terminal flexible direct current transmission system fault detection device 300, and the multi-terminal flexible direct current transmission system fault detection device 300 includes: an acquisition module 301, a first judgment module 302, a second judgment module 303, a fault pole determination module 304, a first calculation module 305, a second calculation module 306 and a fault type determination module 307.

[0135] An acquisition module 301 is used to determine a DC voltage change rate of the DC line according to voltage data of the DC line;

[0136] The first judgment module 302 is used to determine the current of the local differential area according to the current data of the DC line if the DC voltage change rate is greater than the preset starting threshold, and determine the fault type of the system fault according to the current of the local differential area; wherein the local differential area includes the first converter corresponding to the DC voltage change rate greater than the preset starting threshold and the delta side of the transformer connected to the three phases of the first converter;

[0137] The second judgment module 303 is used to determine the single-ended differential current of the second converter according to the current data of the DC line if the DC voltage change rate is less than or equal to the preset start threshold, wherein the second converter is a converter corresponding to the DC voltage change rate that is less than or equal to the preset start threshold;

[0138] A fault pole determination module 304, configured to determine a fault pole according to a single-ended differential current;

[0139] The first calculation module 305 is used to perform a generalized S transform on the voltage data corresponding to the DC voltage change rate that is less than or equal to the preset start threshold in the preset frequency band to obtain a time-frequency matrix;

[0140] A second calculation module 306 is used to determine the energy first-order derivative sequence of the voltage transient energy sum in a preset frequency band according to the time-frequency matrix;

[0141] The fault type determination module 307 is used to determine the fault type of the system fault according to the fault pole and the energy first-order derivative sequence.

[0142] Optionally, the multi-terminal flexible direct current transmission system fault detection device 300 further includes:

[0143] The third calculation module is used to determine the current in the local differential area according to the positive current in the local differential area, the negative current in the local differential area and the neutral current in the local differential area; and determine the single-ended differential current according to the difference between the positive current and the negative current at the same end of the second target converter.

[0144] Optionally, the first judgment module is specifically used to determine a first current sum of currents in the local differential area at different sampling moments; if the absolute value of the first current sum is greater than a preset fault threshold, the fault type is determined to be a converter fault.

[0145] Optionally, the fault pole determination module is specifically used to determine the second current sum of the single-ended differential current at different sampling times; if the second current sum is greater than a preset fault pole threshold, the fault pole is determined to be a positive pole; if the absolute value of the second current sum is less than or equal to the preset fault pole threshold, the fault pole is determined to be an inter-pole pole; if the second current sum is less than the opposite of the preset fault pole threshold, the fault pole is determined to be a negative pole.

[0146] Optionally, the fault type determination module is specifically used to determine that if the fault is at the positive pole, when the absolute value of at least a preset number of consecutive elements in the first-order derivative sequence of energy is greater than a preset positive pole energy threshold, the fault type is determined to be a positive pole ground short circuit fault on the DC line side; if the fault is at the inter-pole pole, when the absolute value of at least a preset number of consecutive elements in the first-order derivative sequence of energy is greater than a preset inter-pole energy threshold, the fault type is determined to be an inter-pole short circuit fault on the DC line side; if the fault is at the negative pole, when the absolute value of at least a preset number of consecutive elements in the first-order derivative sequence of energy is greater than a preset negative pole energy threshold, the fault type is determined to be a negative pole ground short circuit fault on the DC line side.

[0147] Optionally, the second calculation module is specifically used to determine the spectrum energy matrix according to the time-frequency matrix; calculate the spectrum energy sum according to the spectrum energy matrix; determine the voltage transient energy sum sequence according to the spectrum energy sum at different sampling moments; and calculate the energy first-order derivative sequence according to the voltage transient energy sum sequence.

[0148] For the specific definition of the multi-terminal flexible direct current transmission system fault detection device, please refer to the definition of the multi-terminal flexible direct current transmission system fault detection method mentioned above, which will not be repeated here. Each module in the above-mentioned multi-terminal flexible direct current transmission system fault detection device can be implemented in whole or in part by software, hardware and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0149] Based on the above Figure 1 The method shown in the embodiment of the present application accordingly provides a readable storage medium on which a computer program is stored, and when the program is executed by a processor, the above-mentioned Figure 1 The multi-terminal flexible direct current transmission system fault detection method is shown.

[0150] Based on this understanding, the technical solution of the present application can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.), and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each implementation scenario of the present application.

[0151] Based on the above Figure 1 The method shown, and Fig.21 In order to achieve the above-mentioned purpose, the embodiment of the present application further provides a computer device, which can be a personal computer, a server, a network device, etc. The computer device includes a storage medium and a processor; the storage medium is used to store a computer program; the processor is used to execute the computer program to achieve the above-mentioned Figure 1 The multi-terminal flexible direct current transmission system fault detection method is shown.

[0152] Optionally, the computer device may further include a user interface, a network interface, a camera, a radio frequency (RF) circuit, a sensor, an audio circuit, a WI-FI module, etc. The user interface may include a display, an input unit such as a keyboard, etc., and the optional user interface may also include a USB interface, a card reader interface, etc. The network interface may optionally include a standard wired interface, a wireless interface (such as a Bluetooth interface, a WI-FI interface), etc.

[0153] Those skilled in the art will appreciate that the computer device structure provided in this embodiment does not limit the computer device, and may include more or fewer components, or a combination of certain components, or different component arrangements.

[0154] The storage medium may also include an operating system and a network communication module. The operating system is a program that manages and saves the hardware and software resources of the computer device, and supports the operation of information processing programs and other software and / or programs. The network communication module is used to realize communication between the components inside the storage medium, and communication with other hardware and software in the physical device.

[0155] Through the description of the above implementation methods, those skilled in the art can clearly understand that the present application can be implemented by means of software plus a necessary general hardware platform, or the embodiments of the present application can be implemented by hardware.

[0156] Those skilled in the art will appreciate that the accompanying drawings are only schematic diagrams of a preferred implementation scenario, and the modules or processes in the accompanying drawings are not necessarily necessary for implementing the present application. Those skilled in the art will appreciate that the modules in the devices in the implementation scenario can be distributed in the devices of the implementation scenario according to the description of the implementation scenario, or can be changed accordingly and located in one or more devices different from the present implementation scenario. The modules of the above-mentioned implementation scenario can be combined into one module, or can be further split into multiple submodules.

[0157] The above serial numbers of this application are only for description and do not represent the advantages and disadvantages of the implementation scenarios. The above disclosure is only a few specific implementation scenarios of this application, but this application is not limited to them, and any changes that can be thought of by technicians in this field should fall within the scope of protection of this application.

Claims

1. A multi-terminal flexible direct current transmission system fault detection method, characterized in that: The method comprises: Determining a DC voltage change rate of the DC line according to voltage data of the DC line; If the DC voltage change rate is greater than a preset start threshold, the current of the local differential area is determined according to the current data of the DC line, and the fault type of the system fault is determined according to the current of the local differential area; wherein the local differential area includes a first converter and a delta side of a transformer connected to the three phases of the first converter, and the first converter is a converter corresponding to the DC voltage change rate greater than the preset start threshold; If the DC voltage change rate is less than or equal to the preset start threshold, determining the single-ended differential current of the second converter according to the current data of the DC line, wherein the second converter is a converter corresponding to the DC voltage change rate that is less than or equal to the preset start threshold; determining a fault pole according to the single-ended differential current; Performing a generalized S transform on the voltage data corresponding to the second converter located in a preset frequency band to obtain a time-frequency matrix; Determining, according to the time-frequency matrix, a first-order derivative sequence of the energy of the voltage transient energy sum in the preset frequency band; The fault type of the system fault is determined according to the fault pole and the energy first-order derivative sequence.

2. The multi-terminal flexible direct current transmission system fault detection method according to claim 1, characterized in that: The method further comprises: Determining a current in the local differential region according to a positive current in the local differential region, a negative current in the local differential region, and a neutral current in the local differential region; The single-ended differential current is determined according to the difference between the positive current and the negative current at the same end of the second converter.

3. The multi-terminal flexible direct current transmission system fault detection method according to claim 1, characterized in that: The determining the fault type of the system fault according to the current in the local differential area specifically includes: Determine a first current sum of the currents of the local differential region at different sampling moments; If the absolute value of the first current sum is greater than a preset fault threshold, it is determined that the fault type is a converter fault.

4. The multi-terminal flexible direct current transmission system fault detection method according to claim 1, characterized in that: Determining the fault pole according to the single-ended differential current specifically includes: Determine a second current sum of the single-ended differential current at different sampling moments; If the second current sum is greater than a preset fault pole threshold, determining that the fault pole is a positive pole; If the absolute value of the second current sum is less than or equal to the preset fault pole threshold, determining that the fault pole is inter-pole; If the second current sum is less than the negative number of the preset fault pole threshold, it is determined that the fault pole is a negative pole.

5. The multi-terminal flexible direct current transmission system fault detection method according to claim 1, characterized in that: Determining the fault type of the system fault according to the fault pole and the first-order derivative sequence of energy, specifically includes: If the fault pole is a positive pole, when the absolute values ​​of at least a preset number of consecutive elements in the energy first-order derivative sequence are greater than a preset positive pole energy threshold, the fault type is determined to be a positive pole grounding short circuit fault on the DC line side; If the fault pole is between poles, when the absolute values ​​of at least a preset number of consecutive elements in the energy first-order derivative sequence are greater than a preset pole energy threshold, the fault type is determined to be a DC line side pole short circuit fault; If the fault pole is a negative pole, when the absolute values ​​of at least a preset number of consecutive elements in the energy first-order derivative sequence are greater than a preset negative pole energy threshold, the fault type is determined to be a negative pole grounding short circuit fault on the DC line side.

6. According to the multi-terminal flexible direct current transmission system fault detection method as described in claim 1, the step of determining the energy first-order derivative sequence of the voltage transient energy and the voltage transient energy in the preset frequency band according to the time-frequency matrix specifically comprises: Determine a spectrum energy matrix according to the time-frequency matrix; Calculate the spectrum energy sum according to the spectrum energy matrix; Determining voltage transient energy and sequence according to the spectrum energy at different sampling moments; The energy first-order derivative sequence is calculated according to the voltage transient energy and sequence.

7. The multi-terminal flexible direct current transmission system fault detection method according to claim 6, characterized in that: The spectrum energy matrix is ​​expressed as: E i(j,a) =[abs(SU[j,a])] 2 ; The spectrum energy and is expressed as: The energy first-order derivative sequence is expressed as: Among them, E i(j,a) is the spectrum energy matrix, E ipq is the spectrum energy sum, i is the sampling time, SU[j,a] is the time-frequency matrix, j is the row of the time-frequency matrix, a is the column of the time-frequency matrix, p is the upper limit of the preset frequency band, q is the lower limit of the preset frequency band, N is the total number of columns of the time-frequency matrix, DE pq (i) is the energy first-order derivative sequence, E pq (i) E pq (i-1) is the voltage transient energy and two adjacent elements in the sequence, E pq (i) = E ipq , Δt is the sampling interval.

8. A multi-terminal flexible direct current transmission system fault detection device, characterized in that: The device comprises: An acquisition module, used to determine a DC voltage change rate of the DC line according to voltage data of the DC line; A first judgment module is used to determine the current of the local differential area according to the current data of the DC line if the DC voltage change rate is greater than a preset start threshold, and determine the fault type of the system fault according to the current of the local differential area; wherein the local differential area includes a first converter and a delta side of a transformer connected to the three phases of the first converter, and the first converter is a converter corresponding to the DC voltage change rate greater than the preset start threshold; A second judgment module is used to determine the single-ended differential current of the second converter according to the current data of the DC line if the DC voltage change rate is less than or equal to the preset start threshold, wherein the second converter is a converter corresponding to the DC voltage change rate that is less than or equal to the preset start threshold; A fault pole determination module, used for determining a fault pole according to the single-ended differential current; A first calculation module, configured to perform a generalized S transform on the voltage data corresponding to the second converter in a preset frequency band to obtain a time-frequency matrix; A second calculation module, used to determine the energy first-order derivative sequence of the voltage transient energy sum in the preset frequency band according to the time-frequency matrix; The fault type determination module is used to determine the fault type of the system fault according to the fault pole and the energy first-order derivative sequence.

9. A readable storage medium having a program or instruction stored thereon, characterized in that: When the program or instruction is executed by the processor, the steps of the multi-terminal flexible direct current transmission system fault detection method as described in any one of claims 1 to 7 are implemented.

10. A computer device comprising a storage medium, a processor, and a computer program stored in the storage medium and executable on the processor, characterized in that: When the processor executes the program, the multi-terminal flexible direct current transmission system fault detection method according to any one of claims 1 to 7 is implemented.

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