Directional pilot protection method and device for DC line

Abstract

The present disclosure provides a method and device for longitudinal protection of a DC line direction, which can be applied to the fields of new energy technology and power system relay protection technology. The method includes: in response to protection initiation, obtaining sampling data corresponding to each protection moment, wherein the sampling data includes current sampling data and voltage sampling data; obtaining mutation data corresponding to the sampling data based on the sampling data; processing the mutation data to obtain transient high-frequency power corresponding to the mutation data; determining the direction of the fault according to the maximum amplitude in the transient high-frequency power; determining the fault polarity according to the fault direction and the mutation data; generating a local-end discrimination signal according to the fault direction and the fault polarity; obtaining a peer-end discrimination signal based on the local-end discrimination signal; determining a fault section according to the logical operation result of the local-end discrimination signal and the peer-end discrimination signal, so as to confirm the protection scheme corresponding to the fault according to the fault section.

Description

Technical Field

[0001] The present disclosure relates to the fields of new energy technology and power system relay protection technology, and more specifically to a longitudinal protection method for a DC line direction. Background Art

[0002] Longitudinal protection of DC lines is one of the key technologies in the development of multi-terminal DC systems and DC grids. It minimizes the impact of faults on the system through accurate fault identification and rapid protection action.

[0003] In the process of realizing the concept of the present invention, the inventors discovered that the existing longitudinal protection method for DC lines is too dependent on precise line parameters or boundary elements at both ends of the line. Summary of the Invention

[0004] In view of the above problems, the present disclosure provides a method and device for longitudinal protection in the DC line direction.

[0005] According to a first aspect of the present disclosure, a method for longitudinal protection of a DC line is provided, comprising:

[0006] In response to protection initiation, sampling data corresponding to each protection moment is obtained, wherein the sampling data includes current sampling data and voltage sampling data; mutation data corresponding to the sampling data is obtained based on the sampling data; the mutation data is processed to obtain transient high-frequency power corresponding to the mutation data; the direction of the fault is determined based on the maximum amplitude in the transient high-frequency power; the fault polarity is determined based on the fault direction and the mutation data; a local-end discrimination signal is generated based on the fault direction and the fault polarity; a peer-end discrimination signal is obtained based on the local-end discrimination signal; a fault occurrence section is determined based on the logical operation result of the local-end discrimination signal and the peer-end discrimination signal, so as to confirm the protection scheme corresponding to the fault based on the fault occurrence section.

[0007] According to an embodiment of the present disclosure, the local-end discrimination signal corresponds to the local-end protection device, and the opposite-end discrimination signal corresponds to the opposite-end protection device. According to the local-end discrimination signal, obtaining the opposite-end discrimination signal includes: sending the local-end discrimination signal to the opposite-end protection device to obtain the opposite-end discrimination signal.

[0008] According to an embodiment of the present disclosure, the mutation data includes current mutation data and voltage mutation data, wherein the current mutation data includes modulus current mutation data, and the voltage mutation data includes modulus voltage mutation data; processing the mutation data to obtain transient high-frequency power corresponding to each protection moment includes: performing wavelet transform on the current mutation data and the voltage mutation data to obtain high-frequency components of the current mutation data and the voltage mutation data, wherein the high-frequency components of the current mutation data and the voltage mutation data are the second-layer detail coefficients of the wavelet transform; and obtaining the transient high-frequency power corresponding to each protection moment based on the high-frequency components of the current mutation data and the voltage mutation data.

[0009] According to an embodiment of the present disclosure, the direction of fault occurrence is determined based on the maximum amplitude of the transient high-frequency power, including: determining the polarity of the transient high-frequency power based on the maximum amplitude of the transient high-frequency power; when the polarity of the transient high-frequency power is positive, determining that the direction of fault occurrence is in the reverse direction; when the polarity of the transient high-frequency power is negative, determining that the direction of fault occurrence is in the positive direction.

[0010] According to an embodiment of the present disclosure, the fault polarity is determined according to the fault occurrence direction and mutation data, including: when the fault occurrence direction is the positive direction, determining the fault polarity criterion according to the maximum amplitude in the high-frequency component of the current mutation data; when the fault polarity criterion meets the first judgment condition, determining it as a positive pole fault, wherein the first judgment condition is that the fault polarity criterion is greater than the fault forward threshold; when the fault polarity criterion meets the second judgment condition, determining it as a negative pole fault, wherein the second judgment condition is that the fault polarity criterion is less than the fault reverse threshold; when the fault polarity criterion meets the third judgment condition, determining it as a bipolar fault, wherein the third judgment condition is that the fault polarity criterion is between the fault forward threshold and the fault reverse threshold.

[0011] According to an embodiment of the present disclosure, the local-end judgment signal includes a first local-end judgment signal and a second local-end judgment signal; the local-end judgment signal is generated according to the fault direction and the fault polarity, including: when the fault direction is the reverse direction, determining that the first local-end judgment signal and the second local-end judgment signal are both the first signal predetermined data; when the fault direction is the positive direction and the fault polarity is positive, determining that the first local-end judgment signal is the second signal predetermined data, and the second local-end judgment signal is the first signal predetermined data; when the fault direction is the positive direction and the fault polarity is negative, determining that the first local-end judgment signal is the first signal predetermined data, and the second local-end judgment signal is the second signal predetermined data; when the fault direction is the positive direction and the fault polarity is bipolar, determining that the first local-end judgment signal and the second local-end judgment signal are both the second signal predetermined data.

[0012] According to an embodiment of the present disclosure, the opposite-end discrimination signal includes a first opposite-end discrimination signal and a second opposite-end discrimination signal; the fault occurrence section is determined based on the logical operation result of the local-end discrimination signal and the opposite-end discrimination signal, including: generating a first criterion and a second criterion based on the logical operation result between the local-end protection discrimination signal and the opposite-end protection discrimination signal; and determining the fault occurrence section based on the first criterion and the second criterion.

[0013] According to an embodiment of the present disclosure, the first criterion represents that the logical AND result of the first local protection judgment signal and the first opposite-end protection judgment signal is a second predetermined signal, and the second criterion represents that the logical AND result of the second local protection judgment signal and the second opposite-end protection judgment signal is the first signal predetermined data; according to the first criterion and the second criterion, the fault occurrence section is determined, including: when the first criterion is met and the second criterion is not met, it is determined to be a positive pole fault within the zone; when the second criterion is met and the first criterion is not met, it is determined to be a negative pole fault within the zone; when the first criterion and the second criterion are met at the same time, it is determined to be a bipolar fault within the zone; when the first criterion and the second criterion are not met at the same time, it is determined to be an out-of-zone fault.

[0014] According to an embodiment of the present disclosure, obtaining mutation data corresponding to the sampled data based on the sampled data includes: obtaining a modulus component of the sampled data based on the sampled data; and obtaining mutation data corresponding to the sampled data based on the modulus component.

[0015] A second aspect of the present disclosure provides a longitudinal protection device for a DC line, comprising:

[0016] A first acquisition module is configured to acquire sampling data corresponding to each protection moment in response to protection startup, wherein the sampling data includes current sampling data and voltage sampling data;

[0017] An obtaining module is used to obtain mutation data corresponding to the sampled data based on the sampled data;

[0018] A processing module is used to process mutation data to obtain transient high-frequency power corresponding to each protection moment;

[0019] A first determination module is used to determine the direction of the fault according to the maximum amplitude of the transient high-frequency power;

[0020] The second determination module is used to determine the fault polarity according to the fault occurrence direction and mutation data;

[0021] A generation module is used to generate a local identification signal based on the fault direction and fault polarity;

[0022] A second acquisition module is used to obtain the opposite end discrimination signal based on the local end discrimination signal;

[0023] The third determination module is used to determine the fault occurrence section according to the logic operation result of the local end discrimination signal and the opposite end discrimination signal, so as to confirm the protection scheme corresponding to the fault according to the fault occurrence section.

[0024] According to the embodiments of the present disclosure, when protection is activated, mutation data is calculated based on sampled data and its modulus component. The transient high-frequency power corresponding to each protection moment is calculated based on the mutation data. The fault direction and polarity are determined based on the mutation data and the transient high-frequency power. Local and peer-end discrimination signals are generated. These signals are combined to determine the fault-occurring section, allowing protection to be implemented according to the corresponding protection scheme. Because the fault direction can be quickly identified based on the polarity of the transient high-frequency power, no tuning is required, and there is no reliance on line parameters or boundary elements at the line terminals. This system exhibits high engineering practicality and robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above contents and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0026] Figure 1 A flow chart schematically illustrates a method for longitudinal protection of a DC line according to an embodiment of the present disclosure;

[0027] Figure 2 A schematic diagram schematically shows a strain gauge located at a junction of a passivation layer and an electrical insulation layer according to an embodiment of the present disclosure;

[0028] Figure 3 The schematic diagram shows the structure of a four-terminal flexible DC grid according to an embodiment of the present disclosure;

[0029] Figure 4 Schematically shows a structural diagram of a four-terminal flexible DC grid according to another embodiment of the present disclosure; and

[0030] Figure 5 The structural block diagram of the longitudinal protection device in the DC line direction according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0032] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0033] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0034] When expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0035] In the technical solution of the present invention, the user information involved (including but not limited to user personal information, user image information, user device information, such as location information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) are all information and data authorized by the user or fully authorized by all parties, and the collection, storage, use, processing, transmission, provision, disclosure and application of the relevant data comply with relevant laws, regulations and standards, take necessary confidentiality measures, do not violate public order and good morals, and provide corresponding operation entrances for users to choose to authorize or refuse.

[0036] In scenarios where personal information is used for automated decision-making, the methods, devices, and systems provided by embodiments of the present invention provide users with corresponding operational portals, allowing them to choose to agree or reject the automated decision-making results; if the user chooses to reject, the expert decision-making process will be entered. The term "automated decision-making" herein refers to the activity of automatically analyzing and evaluating an individual's behavioral habits, interests, or economic, health, or credit status through computer programs and making decisions. The term "expert decision-making" herein refers to the activity of decision-making by individuals who specialize in a particular field, possess specialized experience, knowledge, and skills, and have reached a certain level of professional expertise.

[0037] For circuits where a DC bus connects multiple DC lines, DC line pilot protection can identify and protect against both internal and external faults. Existing HVDC line pilot protection methods are generally highly dependent on precise line parameters or on boundary elements at both ends of the line. However, pilot protection methods that rely on line parameters are sensitive to the frequency-varying characteristics of these parameters, and when these parameters are difficult to accurately obtain, the sensitivity and reliability of the protection device cannot be guaranteed. Furthermore, pilot protection methods based on the characteristics of line boundary elements are not applicable to DC grid topologies without boundary elements. Therefore, their engineering applicability needs to be improved.

[0038] It can be seen from this that there is still much room for improvement in terms of DC pilot protection methods that reduce dependence on boundary elements and line parameters to enhance the universality and robustness of DC pilot protection projects.

[0039] In order to at least partially solve the technical problems existing in the related art, an embodiment of the present disclosure provides a method for longitudinal protection in a DC line direction, the method comprising:

[0040] In response to protection initiation, sampling data corresponding to each protection moment is obtained, wherein the sampling data includes current sampling data and voltage sampling data; mutation data corresponding to the sampling data is obtained based on the sampling data; the mutation data is processed to obtain transient high-frequency power corresponding to the mutation data; the direction of the fault is determined based on the maximum amplitude in the transient high-frequency power; the fault polarity is determined based on the fault direction and the mutation data; a local-end discrimination signal is generated based on the fault direction and the fault polarity; a peer-end discrimination signal is obtained based on the local-end discrimination signal; a fault occurrence section is determined based on the logical operation result of the local-end discrimination signal and the peer-end discrimination signal, so as to confirm the protection scheme corresponding to the fault based on the fault occurrence section.

[0041] The following will be passed Figures 1 to 4 The longitudinal protection method for the DC line direction according to the embodiment of the present disclosure is described in detail.

[0042] Figure 1 The flowchart of the method for longitudinal protection in the DC line direction according to an embodiment of the present disclosure is schematically shown.

[0043] like Figure 1 As described above, the embodiment 100 includes operations S110 to S180.

[0044] In operation S110 , in response to protection being initiated, sampling data corresponding to each protection moment is acquired.

[0045] According to the embodiments of the present disclosure, when protection is activated, electrical quantity sampling data is collected in real time at each moment to ensure that protection faults can be accurately analyzed and judged through the sampling data. The sampling data includes current sampling data and voltage sampling data.

[0046] According to an embodiment of the present disclosure, the current sampling data reflects the magnitude and direction of the current flowing through the line, and the current sampling data includes positive current sampling data and negative current sampling data.

[0047] According to an embodiment of the present disclosure, the voltage sampling data reflects the voltage level of the circuit. The voltage sampling data includes positive voltage sampling data and negative voltage sampling data.

[0048] In operation S120 , mutation data corresponding to the sampled data is obtained according to the sampled data.

[0049] According to an embodiment of the present disclosure, the mutation data may include current mutation data and voltage mutation data.

[0050] According to embodiments of the present disclosure, current mutation data can represent the change in current between two consecutive sampling points or within a certain time period, which can be an increase or decrease in current. When the difference between the circuit sampling data corresponding to two different moments exceeds a preset threshold, a current mutation has occurred, indicating a fault in the circuit. The current mutation data can trigger a corresponding action of the protection device.

[0051] According to embodiments of the present disclosure, voltage mutation data can represent the amount of voltage change between two consecutive sampling points or within a certain time period, which can be an increase or decrease in voltage. When the difference between circuit sampling data corresponding to two different times exceeds a preset threshold, a voltage mutation has occurred, indicating a fault in the circuit. The voltage mutation data can trigger a corresponding action of the protection device.

[0052] In operation S130 , the mutation data is processed to obtain transient high-frequency power corresponding to the mutation data.

[0053] According to embodiments of the present disclosure, transient high-frequency power can represent the power of high-frequency components generated during transient processes caused by a power system fault. Detecting transient high-frequency power typically requires the use of broadband sensors and high-speed data acquisition systems to capture the transient process following a fault. Signal processing techniques, such as fast Fourier transforms (FFTs) or wavelet transforms, are then used to analyze the high-frequency components of the power signal.

[0054] According to embodiments of the present disclosure, the nature and location of a fault can be inferred by analyzing the data information contained in transient high-frequency power. Different fault types may generate transient high-frequency power with different characteristics. Since high-frequency power caused by a fault typically propagates from the fault point to both ends, the fault section can be determined based on transient high-frequency power.

[0055] In operation S140 , a fault occurrence direction is determined according to the maximum amplitude of the transient high-frequency power.

[0056] According to an embodiment of the present disclosure, within a data window, the transient high-frequency power signal may vary with time, wherein the maximum amplitude of the transient high-frequency power may represent the maximum positive peak value and the maximum negative peak value at an instant.

[0057] According to an embodiment of the present disclosure, the fault occurrence direction may include a positive direction and a negative direction.

[0058] In operation S150 , the fault polarity is determined according to the fault occurrence direction and the mutation data.

[0059] According to an embodiment of the present disclosure, the fault polarity may include a positive polarity fault and a negative polarity fault.

[0060] In operation S160 , a local-end discrimination signal is generated according to the fault occurrence direction and the fault polarity.

[0061] According to an embodiment of the present disclosure, the local-end discrimination signal may represent a signal of a customized local-end protection device, and is used to reflect the direction of occurrence and polarity of a fault.

[0062] In operation S170, a peer-end determination signal is acquired according to the local-end determination signal.

[0063] According to an embodiment of the present disclosure, the opposite-end discrimination signal may represent a signal of a customized opposite-end protection device, and is used to reflect the direction of occurrence and polarity of the fault.

[0064] According to the embodiments of the present disclosure, the fault occurrence section can be accurately determined by combining the local end judgment signal and the opposite end judgment signal.

[0065] In operation S180 , the fault occurrence section is determined according to the logic operation result of the local end determination signal and the peer end determination signal, so as to confirm a protection scheme corresponding to the fault according to the fault occurrence section.

[0066] According to the embodiments of the present disclosure, the fault-occurring section may include both internal faults and external faults. In the case of an internal fault, the local protection device in the line implements the internal protection scheme, i.e., tripping to isolate the fault-occurring section. In the case of an external fault, the local protection device in the line implements the external protection scheme, i.e., issuing an alarm signal to inform personnel of the fault.

[0067] According to the embodiments of the present disclosure, when protection is activated, mutation data is calculated based on sampled data and its modulus component. The transient high-frequency power corresponding to each protection moment is calculated based on the mutation data. The fault direction and polarity are determined based on the mutation data and the transient high-frequency power. Local and peer-end discrimination signals are generated. These signals are combined to determine the fault-occurring section, allowing protection to be implemented according to the corresponding protection scheme. Because the fault direction can be quickly identified based on the polarity of the transient high-frequency power, no tuning is required, and there is no reliance on line parameters or boundary elements at the line terminals. This system exhibits high engineering practicality and robustness.

[0068] According to an embodiment of the present disclosure, the local-end discrimination signal corresponds to the local-end protection device, and the opposite-end discrimination signal corresponds to the opposite-end protection device. According to the local-end discrimination signal, obtaining the opposite-end discrimination signal includes: sending the local-end discrimination signal to the opposite-end protection device to obtain the opposite-end discrimination signal.

[0069] According to an embodiment of the present disclosure, after receiving the local-end discrimination signal, the opposite-end protection device generates an opposite-end discrimination signal according to the fault polarity and the fault occurrence direction.

[0070] According to the embodiments of the present disclosure, the local end discrimination signal and the peer end discrimination signal need to work together to ensure the accuracy of fault detection and the correctness of protection action. The fault occurrence section can be determined by the logical calculation results of the two.

[0071] According to the embodiments of the present disclosure, by combining the local end discrimination signal and the opposite end discrimination signal, the accuracy of fault judgment can be improved, so that corresponding protection actions can be implemented according to the nature of the fault to ensure the safety and stability of the line.

[0072] According to the embodiments of the present disclosure, the fault judgment is based on the activation of the protection device. Therefore, it is necessary to judge whether the protection device is activated. The activation judgment of the protection device will be described in detail below through formulas (1) to (6).

[0073] According to an embodiment of the present disclosure, in the line operation state, the positive current sampling data i corresponding to the sampling point k is obtained in real time. p (k), negative electrode current sampling data i n (k), positive electrode voltage sampling data u p (k), negative electrode voltage sampling data u n (k).

[0074] According to an embodiment of the present disclosure, the 1-mode component u1(k) of the voltage sampling data, the 0-mode component u0(k) of the voltage sampling data, the 1-mode component i1(k) of the current sampling data, and the 0-mode component u0(k) of the current sampling data can be calculated according to the following formula (1).

[0075] (1)

[0076] According to the embodiment of the present disclosure, the differential mode current data i can be obtained according to the positive current sampling data and the negative current sampling data by the following formula (2): d (k).

[0077] (2)

[0078] According to the embodiment of the present disclosure, the common mode current data 2i can be obtained according to the positive current sampling data and the negative current sampling data by the following formula (3): c (k).

[0079] (3)

[0080] According to the embodiment of the present disclosure, it is possible to p (k),u n (k), i p (k), i n (k) Calculate the differential mode current i d (k) Mutation data Δi d (k), common mode current 2i c (k) Mutation data Δ2i c (k) Positive electrode voltage mutation data Δu p (k) and negative electrode voltage mutation data Δu n (k).

[0081] For example, the mutation data of the differential mode current can be calculated by the following formula (4). The mutation data calculated by the algorithm in formula (4) has a certain inhibitory effect on the errors caused by common mode interference and power grid fluctuations, and has high sensitivity.

[0082] (4)

[0083] Where N is used to represent the number of sampling points corresponding to 20ms, which can be calculated using the following formula (5).

[0084] (5)

[0085] Among them, f s Used to indicate the sampling frequency.

[0086] According to an embodiment of the present disclosure, the common mode current 2i c (k) Mutation data Δ2i c (k) Positive electrode voltage mutation data Δu p (k) and negative electrode voltage mutation data Δu n The calculation of (k) is similar to the above formula (4) and will not be repeated here.

[0087] According to an embodiment of the present disclosure, the protection start-up condition may be determined by the protection start-up criterion in formula (6).

[0088] (6)

[0089] Among them, I QD The starting value of the current mutation data can be calculated as 0.05*I N Setting. QD The starting value of voltage mutation data can be calculated as 0.05*U N Adjustment. Among them, I N Indicates the unipolar current of the protected DC line under rated operating conditions, U N Indicates the single-pole voltage of the protected DC line under rated operating conditions.

[0090] According to an embodiment of the present disclosure, if any mutation data in the protection start criterion of formula (6) exceeds the start set value three times in a row, the protection is started. The sampling point n_Str corresponding to the moment when the mutation data corresponding to the start protection first exceeds the start set value is recorded.

[0091] According to an embodiment of the present disclosure, mutation data is processed to obtain transient high-frequency power corresponding to the mutation data, including: performing wavelet transform on current mutation data and voltage mutation data to obtain high-frequency components of the current mutation data and voltage mutation data, wherein the high-frequency components of the current mutation data and voltage mutation data are the second-layer detail coefficients of the wavelet transform; and obtaining transient high-frequency power corresponding to the mutation data based on the high-frequency components of the current mutation data and voltage mutation data.

[0092] According to an embodiment of the present disclosure, the modulus current mutation data includes 1-modulus component current mutation data and 0-modulus component current mutation data, and the modulus voltage mutation data includes 1-modulus component voltage mutation data.

[0093] According to an embodiment of the present disclosure, the voltage mutation data Δu1(k) of the first mode component can be calculated according to the following formula (7).

[0094] (7)

[0095] According to the embodiment of the present disclosure, wavelet transform is performed on Δu1(k), Δi1(k), and Δi0(k), and the detail coefficients of each layer of the wavelet transform are obtained, and the second layer detail coefficients of the wavelet transform are used as the high-frequency components Δu of Δu1(k), Δi1(k), and Δi0(k). 1H (k), Δi 1H (k), Δi 0H (k). The starting point of the wavelet transform data window can be t before the protection starts. tw1 Time period, where t tw1 It can be 1~3ms. The data window of wavelet transform can focus on t after protection is started. tw2 Time period, where t tw2 It can be 1~3ms. The data window length can be expressed as [n_Str–f s *t tw1 , n_Str+f s *t tw2 ].

[0096] According to an embodiment of the present disclosure, the transient high-frequency power corresponding to the mutation data may be calculated according to the following formula (8).

[0097] (8)

[0098] According to the embodiments of the present disclosure, high-frequency components of the modulus current mutation data and the modulus voltage mutation data are extracted through wavelet transform and the high-frequency transient power is calculated so that the direction of the fault occurrence can be judged based on the high-frequency transient power. Since the wavelet transform has good denoising performance and the advantages of rapid analysis, it is more efficient and accurate for fault judgment in the line.

[0099] According to an embodiment of the present disclosure, the direction of fault occurrence is determined based on the maximum amplitude of the transient high-frequency power, including: determining the polarity of the transient high-frequency power based on the maximum amplitude of the transient high-frequency power; when the polarity of the transient high-frequency power is positive, determining that the direction of fault occurrence is in the reverse direction; when the polarity of the transient high-frequency power is negative, determining that the direction of fault occurrence is in the positive direction.

[0100] According to an embodiment of the present disclosure, the maximum amplitude p of the transient high-frequency power in the data window is 1H (k max ) can be positive or negative, so the polarity of transient high-frequency power K can be determined by the following formula (9): dr .

[0101] (9)

[0102] According to an embodiment of the present disclosure, when the polarity of the transient high-frequency power is positive, that is, K dr=1, it is determined that the fault direction is the reverse direction; when the polarity of the transient high-frequency power is negative, that is, K dr =−1, the fault direction is determined to be positive.

[0103] According to the embodiments of the present disclosure, the polarity of transient high-frequency power refers to the direction of power. In a DC system, power flows from the source to the load; however, in the event of a fault, the direction of transient high-frequency power may change. Therefore, the polarity can be determined based on the maximum magnitude of the transient high-frequency power, thereby preliminarily determining the direction of the fault.

[0104] According to an embodiment of the present disclosure, the fault polarity is determined according to the fault occurrence direction and mutation data, including: when the fault occurrence direction is the positive direction, determining the fault polarity criterion according to the maximum amplitude in the high-frequency component of the current mutation data; when the fault polarity criterion meets the first judgment condition, determining it as a positive pole fault, wherein the first judgment condition is that the fault polarity criterion is greater than the fault forward threshold; when the fault polarity criterion meets the second judgment condition, determining it as a negative pole fault, wherein the second judgment condition is that the fault polarity criterion is less than the fault reverse threshold; when the fault polarity criterion meets the third judgment condition, determining it as a bipolar fault, wherein the third judgment condition is that the fault polarity criterion is between the fault forward threshold and the fault reverse threshold.

[0105] According to an embodiment of the present disclosure, fault polarity is used to characterize the direction of fault current flow. In a DC line, a fault may flow from the positive pole to the negative pole, or vice versa. Fault polarity includes unipolar fault and bipolar fault.

[0106] According to an embodiment of the present disclosure, when the fault direction is the positive direction, that is, when the fault occurs at the location of the current protection device, it is necessary to further determine the fault polarity to determine the specific location where the fault occurs.

[0107] According to an embodiment of the present disclosure, the maximum amplitude Δi of the high frequency components of Δi1(k) and Δi0(k) obtained by wavelet transform is converted to 1H-max and Δi 0H-max Process and determine the fault polarity criterion.

[0108] According to the embodiment of the present disclosure, the fault polarity criterion K can be obtained according to the following formula (10): ap .

[0109] (10)

[0110] According to an embodiment of the present disclosure, the fault threshold includes a positive fault threshold λ and a negative fault threshold −λ, wherein the value range of λ may be 0.05 to 0.2.

[0111] According to the embodiment of the present disclosure, in the fault polarity criterion K ap When the fault polarity is greater than the fault forward threshold λ, the fault polarity is determined to be a single-pole positive fault; when the fault polarity criterion K ap If the fault polarity is less than the fault reverse threshold -λ, the fault polarity is determined to be a single-pole negative fault; ap When the fault polarity is between the fault forward threshold λ and the fault reverse threshold –λ, the fault polarity is determined to be a bipolar fault.

[0112] According to the embodiments of the present disclosure, the polarity of the fault is determined by the fault polarity criterion, which helps to determine which part of the line the fault occurs in, thereby locating the fault location more accurately.

[0113] According to an embodiment of the present disclosure, the local-end judgment signal includes a first local-end judgment signal and a second local-end judgment signal; the local-end judgment signal is generated according to the fault direction and the fault polarity, including: when the fault direction is the reverse direction, determining that the first local-end judgment signal and the second local-end judgment signal are both the first signal predetermined data; when the fault direction is the positive direction and the fault polarity is positive, determining that the first local-end judgment signal is the second signal predetermined data, and the second local-end judgment signal is the first signal predetermined data; when the fault direction is the positive direction and the fault polarity is negative, determining that the first local-end judgment signal is the first signal predetermined data, and the second local-end judgment signal is the second signal predetermined data; when the fault direction is the positive direction and the fault polarity is bipolar, determining that the first local-end judgment signal and the second local-end judgment signal are both the second signal predetermined data.

[0114] According to an embodiment of the present disclosure, the local end determination signal includes a first local end determination signal DR Locp and the second local determination signal DR Locn , the local discrimination signal is the self-defined discrimination signal of the fault occurrence section.

[0115] According to an embodiment of the present disclosure, the first predetermined data is used to indicate that the result is 1, and the second predetermined data is used to indicate that the result is 0.

[0116] According to an embodiment of the present disclosure, when the fault direction is the reverse direction, the first local end judgment signal satisfies DR Locp =0 and the second local judgment signal meets DR Locn =0; when the fault direction is positive and the fault polarity is positive, the first local end judgment signal is determined to meet DR Locp =1, the second signal predetermined data meets DR Locn =0; when the fault direction is positive and the fault polarity is negative, the first local judgment signal satisfies DR Locp=0, the second local end determines that the signal meets DR Locn =1; when the fault direction is positive and the fault polarity is bipolar, the first local judgment signal satisfies DR Locp =1 and the second local judgment signal satisfies DR Locn =1.

[0117] According to an embodiment of the present disclosure, the opposite-end discrimination signal includes a first opposite-end discrimination signal and a second opposite-end discrimination signal; the fault occurrence section is determined based on the logical operation result of the local-end discrimination signal and the opposite-end discrimination signal, including: generating a first criterion and a second criterion based on the logical operation result between the local-end protection discrimination signal and the opposite-end protection discrimination signal; and determining the fault occurrence section based on the first criterion and the second criterion.

[0118] According to an embodiment of the present disclosure, the peer identification signal includes a first peer identification signal DR Rmtp and the second peer discrimination signal DR Rmtn .

[0119] According to an embodiment of the present disclosure, a first criterion and a second criterion are generated according to a logical operation result between the local protection judgment signal and the opposite protection judgment signal.

[0120] According to an embodiment of the present disclosure, the logical operation may include logical operations such as AND, OR, and NOT.

[0121] According to an embodiment of the present disclosure, the first criterion can be expressed as the following formula (11).

[0122] (11)

[0123] According to an embodiment of the present disclosure, the second criterion can be expressed as the following formula (12).

[0124] (12)

[0125] According to an embodiment of the present disclosure, the fault occurrence section is determined based on the first criterion and the second criterion, including: when the first criterion is met and the second criterion is not met, it is determined to be a positive pole fault within the zone; when the second criterion is met and the first criterion is not met, it is determined to be a negative pole fault within the zone; when the first criterion and the second criterion are met at the same time, it is determined to be a bipolar fault within the zone; when the first criterion and the second criterion are not met at the same time, it is determined to be an out-of-zone fault.

[0126] According to an embodiment of the present disclosure, the first criterion represents that the logical AND result of the first local protection judgment signal and the first opposite-end protection judgment signal is the second predetermined signal, and the second criterion represents that the logical AND result of the second local protection judgment signal and the second opposite-end protection judgment signal is the first signal predetermined data.

[0127] According to the embodiments of the present disclosure, in combination with the local-end judgment signal and the opposite-end judgment signal, when the local-end judgment signal indicates that the fault is in the local-end direction, and the opposite-end judgment signal indicates that the fault is in the opposite-end direction, it can be determined that the fault occurs in the section between the current local-end protection device and the opposite-end protection device, without relying on line parameters or boundary elements, effectively overcoming the technical problems existing in the prior art to be solved by the present disclosure.

[0128] According to an embodiment of the present disclosure, obtaining mutation data corresponding to the sampled data based on the sampled data includes: obtaining a modulus component of the sampled data based on the sampled data; and obtaining mutation data corresponding to the sampled data based on the modulus component.

[0129] According to an embodiment of the present disclosure, the modulus components of the sampling data include a 0-modulus component and a 1-modulus component of the current sampling data and a 0-modulus component and a 1-modulus component of the voltage sampling data.

[0130] According to the embodiments of the present disclosure, the zero-mode component is often caused by asymmetrical loads, system faults, or grounding problems, and has a wide range of applications in power system protection, control, and fault analysis. The zero-mode component helps better understand and manage imbalances in power systems.

[0131] According to an embodiment of the present disclosure, the 1-mode component helps to determine whether the line is in a normal operating state. If an asymmetric fault exists, the 1-mode component may be affected.

[0132] According to an embodiment of the present disclosure, by performing differential processing on the modulus component data, mutation data is obtained, so that the location information of the fault can be determined through the mutation data.

[0133] According to the embodiments of the present disclosure, in order to better understand the embodiments of the present disclosure, the following will be based on Figure 2 The overall process of longitudinal protection in the DC line direction is explained.

[0134] Figure 2 The flowchart schematically shows the process of starting the longitudinal protection and fault judgment in the DC line direction according to an embodiment of the present disclosure.

[0135] like Figure 2 As described above, the embodiment 200 includes operations S210 to S260.

[0136] In operation S210 , a modulus component of the sampled data is calculated, and mutation data is obtained according to the modulus component.

[0137] In operation S220 , the mutation data is processed to generate a protection start criterion.

[0138] In operation S230 , it is determined whether the protection device is activated according to the protection activation criterion.

[0139] When protection is enabled, the following operation S240 is performed.

[0140] In operation S240 , the fault occurrence direction and the fault polarity are determined based on the transient high-frequency power.

[0141] In operation S250 , a local end identification signal and a peer end identification signal are generated according to the fault occurrence direction and the fault polarity.

[0142] In operation S260 , the fault occurrence section is identified through the local end identification signal and the peer end identification signal, and a protection action corresponding to the fault occurrence section is implemented.

[0143] Figure 3 The structural diagram of a four-terminal flexible DC power grid according to an embodiment of the present disclosure is schematically shown.

[0144] like Figure 3 As shown, in this structure 300, Line 1 to Line 4 are DC transmission lines, S1 to S4 are DC converter stations, and M and N represent the protection devices on both sides of Line 1, respectively.

[0145] According to the embodiment of the present disclosure, when a fault occurs on line Line 1, the current local protection device M and the current opposite-end protection device N determine that the fault direction is the positive direction based on the polarity of the transient high-frequency power. The discrimination signals of M and N are used to determine that it is an intra-zone fault. The protection scheme implemented is to protect both M and N to operate to cut off the faulty line, thereby achieving a certain isolation effect and protecting the non-faulty part to a certain extent.

[0146] Figure 4 The schematic diagram shows the structure of a four-terminal flexible DC grid according to another embodiment of the present disclosure.

[0147] like Figure 4 As shown, in the structure 400, when a fault occurs on line Line2, the local-end discrimination signal of the current local-end protection device M reflects that the fault direction is a forward fault, and the opposite-end discrimination signal of the current opposite-end protection device N reflects that the fault direction is a reverse fault. After communication, it is determined that it is an out-of-zone fault, and both protection devices M and N do not operate.

[0148] Based on the above-mentioned longitudinal protection method for DC line direction, the present disclosure also provides a longitudinal protection device for DC line direction. Figure 5 The device is described in detail.

[0149] Figure 5 The structural block diagram of the longitudinal protection device in the DC line direction according to an embodiment of the present disclosure is schematically shown.

[0150] like Figure 5 As shown, the embodiment 500 includes a first acquisition module 510 , an obtaining module 520 , a processing module 530 , a first determination module 540 , a second determination module 550 , a generating module 560 , a second acquisition module 570 , and a third determination module 580 .

[0151] The first acquisition module 510 is configured to acquire sampling data corresponding to each protection moment in response to protection activation, wherein the sampling data includes current sampling data and voltage sampling data. In one embodiment, the first acquisition module 510 may be configured to perform the operation S110 described above, which will not be described in detail here.

[0152] The obtaining module 520 is configured to obtain mutation data corresponding to the sampled data based on the sampled data. In one embodiment, the obtaining module 520 may be configured to perform the operation S120 described above, which will not be described in detail herein.

[0153] The processing module 530 is configured to process the mutation data to obtain the transient high-frequency power corresponding to each protection moment. In one embodiment, the processing module 530 may be configured to execute the operation S130 described above, which will not be described in detail here.

[0154] The first determination module 540 is configured to determine the fault direction according to the maximum amplitude of the transient high-frequency power. In one embodiment, the first determination module 540 may be configured to execute the operation S140 described above, which will not be described in detail here.

[0155] The second determining module 550 is configured to determine the fault polarity according to the fault occurrence direction and the mutation data. In one embodiment, the second determining module 550 may be configured to execute the operation S150 described above, which will not be described in detail here.

[0156] The generating module 560 is configured to generate a local-end discrimination signal according to the fault direction and fault polarity. In one embodiment, the generating module 560 may be configured to execute the operation S160 described above, which will not be described in detail here.

[0157] The second acquisition module 570 is configured to acquire the peer end determination signal based on the local end determination signal. In one embodiment, the second acquisition module 570 may be configured to execute the operation S170 described above, which will not be described in detail herein.

[0158] The third determination module 580 is configured to determine the fault occurrence section based on the logical operation result of the local-end discrimination signal and the peer-end discrimination signal, so as to determine a protection scheme corresponding to the fault based on the fault occurrence section. In one embodiment, the third determination module 580 can be configured to perform operation S180 described above, and will not be further described here.

[0159] According to an embodiment of the present disclosure, the second acquisition module 570 includes an acquisition submodule.

[0160] The acquisition submodule is used to send the local end discrimination signal to the opposite end protection device and obtain the opposite end discrimination signal

[0161] According to an embodiment of the present disclosure, the processing module 530 includes an acquisition submodule and a obtaining submodule.

[0162] The acquisition submodule is used to perform wavelet transform on the current mutation data and the voltage mutation data to obtain high-frequency components of the current mutation data and the voltage mutation data.

[0163] The obtaining submodule is used to obtain the transient high-frequency power corresponding to each protection moment according to the high-frequency components of the current mutation data and the voltage mutation data.

[0164] According to an embodiment of the present disclosure, the first determining module 540 includes a first determining submodule, a second determining submodule, and a third determining submodule.

[0165] A first determining submodule, configured to determine the polarity of the transient high-frequency power according to the maximum amplitude of the transient high-frequency power;

[0166] The second determining submodule is configured to determine that the fault direction is the reverse direction when the polarity of the transient high-frequency power is positive;

[0167] The third determining submodule is configured to determine that the fault direction is a positive direction when the polarity of the transient high-frequency power is negative.

[0168] According to an embodiment of the present disclosure, the second determining module 550 includes a first determining submodule, a second determining submodule, a third determining submodule, and a fourth determining submodule.

[0169] The first determination submodule is configured to determine a fault polarity criterion based on a maximum amplitude of a high-frequency component of current mutation data when the fault direction is positive.

[0170] The second determining submodule is configured to determine that the fault is a positive pole fault when the fault polarity criterion satisfies a first judgment condition.

[0171] The third determining submodule is configured to determine that the fault is a negative pole fault when the fault polarity criterion satisfies a second judgment condition.

[0172] and a fourth determining submodule, configured to determine that the fault is a bipolar fault when the fault polarity criterion satisfies a third judgment condition.

[0173] According to an embodiment of the present disclosure, the generation module 560 includes a first determination submodule, a second determination submodule, a third determination submodule, and a fourth determination submodule.

[0174] The first determining submodule is configured to determine that both the first local end discrimination signal and the second local end discrimination signal are first signal predetermined data when the fault occurs in the reverse direction.

[0175] The second determination submodule is configured to determine, when the fault direction is positive and the fault polarity is positive, that the first local end determination signal is the second signal predetermined data and the second local end determination signal is the first signal predetermined data.

[0176] The third determination submodule is used to determine that the first local end discrimination signal is the first signal predetermined data and the second local end discrimination signal is the second signal predetermined data when the fault direction is the positive direction and the fault polarity is the negative polarity.

[0177] The fourth determining submodule is configured to determine that both the first local end discrimination signal and the second local end discrimination signal are second signal predetermined data when the fault direction is positive and the fault polarity is bipolar.

[0178] According to an embodiment of the present disclosure, the third determining module 580 includes a generating submodule and a determining submodule.

[0179] The generating submodule is used to generate a first criterion and a second criterion according to a logic operation result between the local end protection judgment signal and the opposite end protection judgment signal.

[0180] The determination submodule is used to determine the fault occurrence section according to the first criterion and the second criterion.

[0181] According to an embodiment of the present disclosure, the determining submodule includes a first determining unit, a second determining unit, a third determining unit, and a fourth determining unit.

[0182] The first determining unit is configured to determine that the fault is an intra-zone positive electrode fault when the first criterion is met and the second criterion is not met.

[0183] The second determining unit is configured to determine that the fault is an intra-zone negative electrode fault when the second criterion is met and the first criterion is not met.

[0184] The third determining unit is configured to determine that the fault is an intra-zone bipolar fault when the first criterion and the second criterion are simultaneously met.

[0185] The fourth determining unit is configured to determine that the fault is an out-of-zone fault when both the first criterion and the second criterion are not satisfied.

[0186] According to an embodiment of the present disclosure, the obtaining module 520 includes a first obtaining submodule and a second obtaining submodule.

[0187] The first obtaining submodule is used to obtain the modulus component of the sampling data according to the sampling data.

[0188] The second obtaining submodule is used to obtain mutation data corresponding to the sampled data according to the modulus component.

[0189] The flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram can represent a module, program segment, or a part of code, and the above-mentioned module, program segment, or a part of code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flowchart, and the combination of boxes in the block diagram or flowchart, can be implemented with a dedicated hardware-based system that performs the specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0190] Those skilled in the art will appreciate that the features described in the various embodiments and / or claims of this disclosure may be combined and / or coupled in various ways, even if such combinations and / or couplings are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure may be combined and / or coupled in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or couplings are intended to fall within the scope of this disclosure.

[0191] The embodiments of the present disclosure are described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be used in combination to advantage. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A method for longitudinal protection of a DC line, characterized in that: The method includes: in response to protection startup, obtaining sampling data corresponding to each protection moment, wherein the sampling data includes current sampling data and voltage sampling data; obtaining mutation data corresponding to the sampling data based on the sampling data; processing the mutation data to obtain transient high-frequency power corresponding to the mutation data; determining the direction of fault occurrence based on the maximum amplitude of the transient high-frequency power; determining the fault polarity based on the fault direction and the mutation data; generating a local-end discrimination signal based on the fault direction and the fault polarity; obtaining a peer-end discrimination signal based on the local-end discrimination signal; and determining a fault occurrence section based on a logical operation result of the local-end discrimination signal and the peer-end discrimination signal, so as to confirm a protection scheme corresponding to the fault based on the fault occurrence section.

2. The method according to claim 1, characterized in that The local-end discrimination signal corresponds to the local-end protection device, and the opposite-end discrimination signal corresponds to the opposite-end protection device. Acquiring the opposite-end discrimination signal based on the local-end discrimination signal includes: sending the local-end discrimination signal to the opposite-end protection device to acquire the opposite-end discrimination signal.

3. The method according to claim 1, characterized in that The mutation data includes current mutation data and voltage mutation data, wherein the current mutation data includes modulus current mutation data, and the voltage mutation data includes modulus voltage mutation data; processing the mutation data to obtain transient high-frequency power corresponding to the mutation data includes: performing wavelet transform on the current mutation data and the voltage mutation data to obtain high-frequency components of the current mutation data and the voltage mutation data, wherein the high-frequency components of the current mutation data and the voltage mutation data are the second-layer detail coefficients of the wavelet transform; and obtaining the transient high-frequency power corresponding to the mutation data based on the high-frequency components of the current mutation data and the voltage mutation data.

4. The method according to claim 1, wherein Determining the direction of the fault occurrence based on the maximum amplitude of the transient high-frequency power includes: determining the polarity of the transient high-frequency power based on the maximum amplitude of the transient high-frequency power; when the polarity of the transient high-frequency power is positive, determining that the direction of the fault occurrence is the reverse direction; when the polarity of the transient high-frequency power is negative, determining that the direction of the fault occurrence is the positive direction.

5. The method according to claim 3, characterized in that The determining of the fault polarity based on the fault occurrence direction and the mutation data includes: when the fault occurrence direction is the positive direction, determining the fault polarity criterion based on the maximum amplitude in the high-frequency component of the current mutation data; when the fault polarity criterion satisfies a first judgment condition, determining it as a positive pole fault, wherein the first judgment condition is that the fault polarity criterion is greater than a fault forward threshold; when the fault polarity criterion satisfies a second judgment condition, determining it as a negative pole fault, wherein the second judgment condition is that the fault polarity criterion is less than a fault reverse threshold; when the fault polarity criterion satisfies a third judgment condition, determining it as a bipolar fault, wherein the third judgment condition is that the fault polarity criterion is between the fault forward threshold and the fault reverse threshold.

6. The method according to claim 2, characterized in that The local-end discrimination signal includes a first local-end discrimination signal and a second local-end discrimination signal; the local-end discrimination signal is generated according to the fault direction and the fault polarity, including: when the fault direction is a reverse direction, determining that the first local-end discrimination signal and the second local-end discrimination signal are both first signal predetermined data; when the fault direction is a positive direction and the fault polarity is positive, determining that the first local-end discrimination signal is second signal predetermined data, and the second local-end discrimination signal is first signal predetermined data; when the fault direction is a positive direction and the fault polarity is negative, determining that the first local-end discrimination signal is first signal predetermined data, and the second local-end discrimination signal is second signal predetermined data; when the fault direction is a positive direction and the fault polarity is bipolar, determining that the first local-end discrimination signal and the second local-end discrimination signal are both second signal predetermined data.

7. The method according to claim 6, characterized in that The opposite-end discrimination signal includes a first opposite-end discrimination signal and a second opposite-end discrimination signal; determining the fault occurrence section based on the logical operation result of the local-end discrimination signal and the opposite-end discrimination signal includes: generating a first criterion and a second criterion based on the logical operation result between the local-end discrimination signal and the opposite-end discrimination signal; and determining the fault occurrence section based on the first criterion and the second criterion.

8. The method according to claim 7, characterized in that The first criterion represents that the logical AND result of the first local-end judgment signal and the first opposite-end judgment signal is the second signal predetermined data, and the second criterion represents that the logical AND result of the second local-end judgment signal and the second opposite-end judgment signal is the first signal predetermined data; the fault occurrence section is determined according to the first criterion and the second criterion, including: when the first criterion is met and the second criterion is not met, it is determined to be a positive pole fault in the zone; when the second criterion is met and the first criterion is not met, it is determined to be a negative pole fault in the zone; when the first criterion and the second criterion are met at the same time, it is determined to be a bipolar fault in the zone; when the first criterion and the second criterion are not met at the same time, it is determined to be an out-of-zone fault.

9. The method according to claim 1, characterized in that The obtaining, based on the sampled data, mutation data corresponding to the sampled data, includes: obtaining, based on the sampled data, a modulus component of the sampled data; and obtaining, based on the modulus component, mutation data corresponding to the sampled data.

10. A longitudinal protection device for a DC line, comprising: The first acquisition module is used to obtain sampling data corresponding to each protection moment in response to protection startup, wherein the sampling data includes current sampling data and voltage sampling data; the acquisition module is used to obtain mutation data corresponding to the sampling data based on the sampling data; the processing module is used to process the mutation data to obtain transient high-frequency power corresponding to the mutation data; the first determination module is used to determine the direction of fault occurrence based on the maximum amplitude in the transient high-frequency power; the second determination module is used to determine the fault polarity based on the fault direction and the mutation data; the generation module is used to generate a local-end discrimination signal based on the fault direction and the fault polarity; the second acquisition module is used to obtain a peer-end discrimination signal based on the local-end discrimination signal; the third determination module is used to determine the fault occurrence section based on the logical operation result of the local-end discrimination signal and the peer-end discrimination signal, so as to confirm the protection scheme corresponding to the fault based on the fault occurrence section.

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