Multi-terminal flexible DC power transmission fault diagnosis method for extracting high-frequency power based on HHT (Hilbert-Huang Transform)

Abstract

The invention belongs to the technical field of high-voltage direct-current power transmission, and particularly relates to a multi-terminal flexible direct-current power transmission fault diagnosis method for extracting high-frequency power based on HHT transformation. The method comprises the following steps: acquiring voltage and current data at protection mounting positions on two sides of positive and negative cables; voltage change rates are calculated, and when the positive and negative voltage change rates both exceed a threshold value, voltage and current data before and after a fault occurs are obtained; performing Hilbert-Huang transform (HHT) to calculate the high-frequency power of any side of the positive and negative electrode cables, judging whether the amplitude of the high-frequency power of any side of the line meets fault identification, and performing fault identification criteria to determine whether a fault occurs; calculating high-frequency power correlation coefficients at the protection parts on the two sides of the positive and negative cables; fault type judgment is carried out; and performing fault isolation according to the fault type. According to the method, various fault types can be distinguished, meanwhile, high reliability, selectivity and sensitivity are achieved, fault recognition is efficiently completed within a short time, and the excellent transition resistance and noise interference resisting capacity is achieved.

Description

Technical Field

[0001] This invention belongs to the field of high voltage direct current transmission technology, and particularly relates to a fault diagnosis method for multi-terminal flexible DC transmission based on HHT transformation to extract high-frequency power, and more specifically, a fault diagnosis method for multi-terminal flexible DC transmission system based on HHT transformation to extract high-frequency power. Background Technology

[0002] With the formulation of national strategic goals, promoting energy revolution and achieving "clean energy substitution" has become an urgent need. New energy sources such as wind and solar power have the potential to compete at par with traditional energy sources like coal power. However, due to the geographically opposite distribution of large-scale centralized wind and photovoltaic power plants on land to load centers, ultra-high voltage direct current (UHVDC) or alternating current (AC) transmission technologies are required for power transfer. Therefore, flexible direct current (DC) transmission technology, due to its advantages such as strong controllability, fast power regulation speed, and flexible operation, is widely used in the asynchronous interconnection of AC power grids and the large-capacity, long-distance transmission of renewable energy.

[0003] The fault characteristics of flexible DC transmission differ significantly from those of traditional power grids. After a fault occurs, the fault current increases rapidly, the voltage drops rapidly, and the development speed is extremely fast. If the fault is not cleared in time, it can cause fluctuations throughout the entire DC grid, resulting in device damage. Therefore, it is necessary to identify the fault type and location within 3ms. Currently, the protection methods for flexible DC transmission lines are mainly divided into single-ended and double-ended protection. Single-ended protection has better speed and is mostly used as the main protection, but its selectivity is weak and it cannot accurately determine the fault type. Double-ended protection, although having better selectivity, requires a transmission channel to transmit fault information, thus incurring a certain delay, and is usually used as backup protection.

[0004] In addition, protection methods can be divided into electrical quantity protection, distance protection, traveling wave protection, and longitudinal connection protection.

[0005] Electrical quantity protection identifies faults by the changes in the amplitude of voltage and current or the derivative of electrical quantities during a fault, and completes fault clearing by setting a specific threshold. However, electrical quantity protection is susceptible to lightning and noise signals, has low tolerance to transition resistance, and poor ability to identify high-resistivity faults.

[0006] Distance protection refers to using relevant grid parameters to calculate and analyze the transient characteristics of faults and estimate the location of the fault point to achieve accurate fault location. However, when a fault occurs in a flexible DC distribution network, its transient parameters are difficult to identify, resulting in long calculation time and low protection sensitivity of this method.

[0007] Traveling wave protection identifies faults by analyzing the information reflected back and forth between the fault point and the monitoring point by the traveling waves of voltage and current generated during a distribution network fault. This method relies on the information of the traveling wave front to achieve accurate fault location. However, the traveling waves in flexible DC distribution networks are weak, wave front identification is difficult, and this method requires a high sampling frequency, making it difficult to apply in practical engineering.

[0008] Longitudinal protection identifies faulty lines by utilizing the specific relationship between electrical quantities at both ends of the line. This method, based on information from both ends, offers high reliability. Although it also suffers from information delay, the impact of this delay on protection performance can be effectively reduced by adjusting the data window and optimizing the algorithm.

[0009] In summary, given the numerous problems existing in flexible DC transmission fault identification technology, those skilled in the art need to continuously update and improve the existing technology. Summary of the Invention

[0010] To address the shortcomings of the existing technologies, this invention provides a multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation to extract high-frequency power. Its purpose is to utilize the correlation coefficient of high-frequency power on both sides of the positive and negative cables during a fault to construct a fault type identification criterion, enabling the differentiation of multiple fault types. It also possesses high reliability, selectivity, and sensitivity, allowing for efficient fault identification in a short time, and exhibits excellent resistance to transition resistance and noise interference under various conditions.

[0011] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0012] A fault diagnosis method for multi-terminal flexible DC transmission based on HHT transform for extracting high-frequency power includes:

[0013] Collect voltage and current data at the protective installation points on both sides of the positive and negative cables;

[0014] The voltage change rate is calculated based on the voltage and current data at the protection installation points on both sides of the cable. When the voltage change rate of both the positive and negative poles exceeds the threshold, the voltage and current data at the protection installation points on both sides of the cable are used to calculate the voltage change rate.

[0015] Based on the voltage and current data before and after the fault, the Hilbert-Huang transform (HHT) is used to calculate the high-frequency power on either side of the positive and negative cables; it is then determined whether the high-frequency power amplitude on either side of the line meets the fault identification criteria to confirm whether a fault has occurred.

[0016] After the fault occurs, calculate the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables;

[0017] Fault type determination using high-frequency power correlation coefficient;

[0018] Based on the fault type, a signal is sent to the DC circuit breaker in the fault-prone area to isolate the fault.

[0019] Furthermore, the voltage change rate is calculated by acquiring voltage and current data before and after the fault occurs. The criterion is as follows: when the voltage change rate of the positive or negative terminal exceeds a threshold, voltage and current data before and after the fault occurs are acquired; the fault judgment module is activated, and the formula is as follows:

[0020]

[0021] In the above formula, This is the voltage at the positive protection point. This is the voltage at the negative protection point. The threshold for fault initiation criteria is 'start', which indicates that the fault detection module is started.

[0022] Furthermore, the voltage and current data before and after the fault occurred are obtained, and the high-frequency power on either side of the positive and negative cables is calculated using the Hilbert-Huang Transform (HHT) based on the voltage and current data before and after the fault. The specific calculation process is as follows:

[0023] Empirical Mode Transform (EMT) is applied to the data to decompose the voltage and current signals into a series of Intrinsic Mode Functions (IMFs). Hilbert Transform is then applied to the voltage and current to construct analytical signals, and their instantaneous amplitude and phase angle are calculated. Based on this, the high-frequency power of the IMF components in the corresponding frequency range is calculated. The formula for calculating the high-frequency power at the protection points on both sides of the positive and negative cables using the IMF components in the corresponding frequency band is as follows:

[0024]

[0025] In the above formula, The instantaneous high-frequency power of the positive or negative cable. This represents the instantaneous amplitude of the voltage IMF component within the corresponding frequency range. This represents the instantaneous amplitude of the IMF component of the current in the corresponding frequency range. For the instantaneous phase of the voltage IMF component in the corresponding frequency range, This represents the instantaneous phase of the IMF component of the current in the corresponding frequency range.

[0026] Furthermore, the high-frequency power amplitude on either side of the line is determined to see if it meets the fault identification criteria, thus confirming whether a fault has occurred; the formula is as follows:

[0027]

[0028] In the above formula, This represents the absolute value of the instantaneous high-frequency power of the positive or negative cable. The threshold is used for fault identification criteria.

[0029] Furthermore, the formula for calculating the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables is as follows:

[0030]

[0031] In the above formula, This represents the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables. and The two sides of the cable represent the high-frequency power at the corresponding frequency sequence. and These are the average high-frequency power values ​​for all serial numbers on both sides of the cable; The total number of frequency bands required; For a specific sampling frequency, .

[0032] Furthermore, the fault type is determined using a high-frequency power correlation coefficient; wherein, when the high-frequency power on both sides of the cable has the same sign, the correlation coefficient is positive; when the high-frequency power on both sides of the cable has opposite signs, the correlation coefficient is negative; including:

[0033] When the fault type is a bipolar short-circuit fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0034] When the fault type is a positive grounding fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0035] When the fault type is a negative pole grounding fault within the zone, the correlation coefficient of the positive pole cable is negative, and the correlation coefficient of the negative pole cable is positive.

[0036] When the fault type is an external fault, the correlation coefficient of the positive cable is negative, and the correlation coefficient of the negative cable is also negative.

[0037] A multi-terminal flexible DC transmission fault diagnosis device based on HHT conversion for extracting high-frequency power includes:

[0038] The voltage and current acquisition module is used to acquire voltage and current data at the protective installation points on both sides of the positive and negative cables;

[0039] The voltage change rate calculation module is used to calculate the voltage change rate based on the voltage and current data at the protection installation points on both sides of the cable. When the voltage change rate of both the positive and negative poles exceeds the threshold, the voltage and current data before and after the fault occurs are obtained.

[0040] The high-frequency power calculation module includes an HHT transformation module and a fault identification module. It is used to calculate the high-frequency power on either side of the positive and negative cables by performing HHT transformation based on the voltage and current data before and after the fault occurs; and to determine whether the high-frequency power amplitude on either side of the line meets the fault identification criteria to confirm whether a fault has occurred.

[0041] The high-frequency power correlation coefficient calculation module is used to calculate the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables after a fault occurs.

[0042] The fault type determination module is used to determine the fault type using the high-frequency power correlation coefficient.

[0043] The fault isolation module is used to send signals to the DC circuit breakers in the fault range according to the fault type to isolate the fault.

[0044] Furthermore, the fault type determination module is used to determine the fault type using a high-frequency power correlation coefficient; wherein, when the high-frequency power on both sides of the cable has the same sign, the correlation coefficient is positive; when the high-frequency power on both sides of the cable has different signs, the correlation coefficient is negative; including:

[0045] When the fault type is a bipolar short-circuit fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0046] When the fault type is a positive grounding fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0047] When the fault type is a negative pole grounding fault within the zone, the correlation coefficient of the positive pole cable is negative, and the correlation coefficient of the negative pole cable is positive.

[0048] When the fault type is an external fault, the correlation coefficient of the positive cable is negative, and the correlation coefficient of the negative cable is also negative.

[0049] A computer device includes a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor. When the processor executes the computer program, it implements the steps of the multi-terminal flexible DC transmission fault diagnosis method based on HHT conversion for extracting high-frequency power as described in any one of the claims.

[0050] A computer storage medium storing a computer program, wherein when the computer program is executed by a processor, it implements the steps of any of the methods for fault diagnosis of multi-terminal flexible DC transmission based on HHT conversion to extract high-frequency power.

[0051] The present invention has the following beneficial effects and advantages:

[0052] This invention proposes a method for fault identification by extracting high-frequency power on both sides of a line using HHT transform. This method utilizes the Hilbert-Huang Transform (HHT) to distinguish various fault types, while possessing high reliability, selectivity, and sensitivity. It can efficiently complete fault identification in a short time and has excellent resistance to transition resistance and noise interference under different conditions. It is beneficial to solve the technical problem of fault identification in the process of offshore wind power transmission via flexible DC transmission, and provides a new solution.

[0053] This invention solves the difficulties in threshold setting and protection coordination for DC fault identification during offshore wind power transmission via flexible DC transmission, as well as the shortcomings in speed and stability, and the technical challenges of fault type identification and area selection in offshore wind power transmission via flexible DC transmission distribution networks.

[0054] Compared with existing technologies, this invention uses high-frequency power correlation coefficient as the identification criterion for fault type and region. The correlation coefficient of faulty cables is positive, while that of non-faulty cables is negative. The threshold is easy to adjust, and the fault identification discrimination is good. This invention employs a high-frequency power feature extraction and correlation coefficient calculation step based on HHT transform in the fault signal processing process. By adaptively decomposing the collected voltage and current signals, high-frequency components within the frequency range are extracted, and high-frequency power and its correlation coefficient are calculated as criteria for fault occurrence, region, and type. The introduction of this step makes faulty cables and non-faulty cables show a significant difference in correlation coefficients, enabling not only fast and accurate region positioning but also fault pole selection without the need for additional independent pole selection criteria. Furthermore, in terms of high-frequency information extraction from fault signals, compared to using short-time Fourier transform to extract specific frequency features of fault signals, this invention uses HHT transform to simultaneously extract high-frequency information within a frequency range. The calculation speed is fast, avoiding the disadvantage of misjudgment caused by background noise in the environment when only identifying a specific single frequency information. Compared to wavelet transform methods, the adaptive nature of the invented HHT transform enables this method to extract information from non-stationary signals during fault processes, and it has better resistance to noise interference and lightning strike interference, making it a promising candidate for engineering applications. Attached Figure Description

[0055] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0056] Figure 1 This is a flowchart of the fault diagnosis method of the present invention;

[0057] Figure 2 This is a schematic diagram of the four-terminal flexible DC power grid structure of the present invention;

[0058] Figure 3 This is a schematic diagram of the fault identification device of the present invention. Detailed Implementation

[0059] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0060] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0061] The following reference Figures 1-3 The technical solutions of some embodiments of the present invention are described below.

[0062] Example 1

[0063] This invention provides an embodiment of a multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation for extracting high-frequency power. For example... Figure 1 As shown, Figure 1 This is a flowchart of the fault diagnosis method of the present invention.

[0064] Step 1. Collect voltage and current data at the protection installation points on both sides of the positive and negative cables using current transformer equipment;

[0065] Step 2. Calculate the voltage change rate based on the voltage and current data at the protection installation points on both sides of the cable. When the voltage change rate of the positive or negative pole exceeds the threshold, obtain the voltage and current data before and after the fault occurs; the fault judgment module is activated, using the following formula:

[0066]

[0067] In the above formula, This is the voltage at the positive protection point. This is the voltage at the negative protection point. The threshold for fault initiation criteria is 'start', which indicates that the fault detection module is started.

[0068] Step 3. Once the fault initiation criterion is activated, first acquire the voltage and current data within 1ms before and after the fault occurs. Then, perform a Hilbert-Huang transform (HHT transform) on the voltage and current data before and after the fault occurs to extract the instantaneous amplitude and instantaneous phase angle of the voltage and current within a specific frequency band. Calculate the high-frequency power on both sides of the positive and negative cables. The specific calculation process is as follows:

[0069] Empirical Mode Transform (EMT) is used to decompose voltage and current signals into a series of Intrinsic Mode Functions (IMFs). The decomposition process is as follows: Taking a voltage signal as an example, firstly, all local maxima and minima in the original signal are identified. Cubic spline interpolation is then performed on all local maxima and minima to obtain the upper and lower envelopes of the voltage signal, and the mean of the envelopes is calculated. The mean of the envelopes is subtracted from the original voltage signal to obtain an intermediate function. It is then determined whether the intermediate function meets the IMF conditions. If it does, the next step is performed; otherwise, the intermediate function replaces the initial signal, and the above steps are repeated until the conditions are met. Finally, the first IMF component of the voltage signal EMD decomposition is obtained. The first IMF component is subtracted from the original signal to obtain the residual component. The residual component is used as the new original signal, and the above steps are repeated to sequentially obtain the IMF components of each order until the final residual component is obtained.

[0070] An analytical signal is constructed by performing a Hilbert transform on the voltage and current, and its instantaneous amplitude and instantaneous phase angle are obtained. Based on this, the high-frequency power of the IMF component in the corresponding frequency range is calculated. The formula for calculating the high-frequency power is shown below:

[0071]

[0072] In the above formula, The instantaneous high-frequency power of the positive or negative cable. This represents the instantaneous amplitude of the voltage IMF component within the corresponding frequency range. This represents the instantaneous amplitude of the IMF component of the current in the corresponding frequency range. For the instantaneous phase of the voltage IMF component in the corresponding frequency range, This represents the instantaneous phase of the IMF component of the current in the corresponding frequency range.

[0073] Secondly, by analyzing the high-frequency power amplitude on any side of the line, it is determined whether it meets the fault identification criteria to determine whether a fault has occurred. The formula is as follows:

[0074]

[0075] In the above formula, This represents the absolute value of the instantaneous high-frequency power of the positive or negative cable. The threshold is used for fault identification criteria.

[0076] Step 4. After the fault identification criterion is triggered, the occurrence of the fault is confirmed, and the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables is calculated. The formula is as follows:

[0077]

[0078] In the above formula, This represents the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables. and The two sides of the cable represent the high-frequency power at the corresponding frequency sequence. and These are the average high-frequency power values ​​for all serial numbers on both sides of the cable. The total number of frequency bands required; For a specific sampling frequency, .

[0079] Step 5. Use the high-frequency power correlation coefficient to determine the fault type.

[0080] High-frequency power correlation coefficient relationships include:

[0081] When the high-frequency power on both sides of the cable has the same sign, the correlation coefficient is positive.

[0082] When the high-frequency power signals on both sides of the cable are opposite, the correlation coefficient is negative.

[0083] Significant differences in the high-frequency power coefficients on both sides of the cable can occur under different fault types, as detailed below:

[0084] When the fault type is a bipolar short-circuit fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0085] When the fault type is a positive grounding fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0086] When the fault type is a negative pole grounding fault within the zone, the correlation coefficient of the positive pole cable is negative, and the correlation coefficient of the negative pole cable is positive.

[0087] When the fault type is an external fault, the correlation coefficient of the positive cable is negative, and the correlation coefficient of the negative cable is also negative.

[0088] Step 6. Send an interruption signal to the DC circuit breaker in the fault range according to the fault type to isolate the fault.

[0089] Specifically, the circuit breaker control unit sends an interruption signal to the DC circuit breaker in the fault range based on the result obtained by the fault type discrimination unit in step 6, thereby isolating the fault and protecting the normal operation of the power grid.

[0090] Example 2

[0091] This invention provides another embodiment, which is a method for fault diagnosis of multi-terminal flexible DC transmission based on HHT transformation to extract high-frequency power. For example... Figure 2 As shown, Figure 2 This is a schematic diagram of a four-terminal flexible DC power grid structure in an embodiment of the present invention.

[0092] The method described in this embodiment is applied to a four-terminal offshore wind power flexible DC transmission and distribution network structure. Voltage transformers and current transformers are installed on the line side of the DC output circuit breaker at each converter station, adjacent to the positive and negative busbars, to collect voltage and current signals flowing into the DC cable in real time. The fault identification device is centrally deployed in the converter station control and protection room, connected to the transformers via cables to form a data acquisition loop, and outputs commands to the circuit breaker control unit.

[0093] As attached Figure 3 As shown, Figure 3 This is a schematic diagram of the fault identification device of the present invention. The raw signals collected by the current transformer are sent in parallel to the voltage change rate calculation unit and the high-frequency power calculation unit; the voltage change rate calculation unit calculates the voltage change rate and controls whether the latter is activated; the high-frequency power calculation unit calculates the high-frequency power through HHT transformation and identifies whether a fault has actually occurred; if a fault occurs, the information is transmitted to the fault type discrimination unit, which distinguishes the fault type based on the correlation coefficient characteristics and drives the circuit breaker control unit to perform the corresponding tripping or blocking operation.

[0094] This invention discloses a fault diagnosis method for multi-terminal flexible DC transmission based on HHT transformation for extracting high-frequency power, which specifically includes the following steps:

[0095] Step 1. Collect voltage and current data at the protection installation points on both sides of the positive and negative cables using current transformer equipment;

[0096] Step 2. Calculate the voltage change rate. When the voltage change rate of the positive or negative terminal exceeds the threshold, the fault diagnosis module is activated, and the process proceeds to the next step. The formula is as follows:

[0097]

[0098] In the above formula, where , These are the voltages at the positive and negative protection points, respectively. The threshold for fault initiation criteria is 'start', which indicates that the fault detection module is started.

[0099] Step 3. Obtain voltage and current data within 1ms before and after the fault occurs, perform HHT transformation calculations to select the amplitude and phase angle of the high-frequency IMF component voltage and current. The entire process is as follows:

[0100] Taking the data processing at the right positive terminal protection point as an example, the data processing at the right negative terminal, left positive terminal, and left negative terminal is similar. Empirical Mode Transform (EMT) is performed on the data at the right positive terminal to decompose the voltage and current signals into a series of Intrinsic Mode Functions (IMFs). Taking the voltage signal as an example: First, all local maxima and minima in the signal are determined. Cubic spline interpolation is then performed on all local maxima and minima to obtain the upper and lower voltage envelopes. The mean of the envelopes is calculated as follows:

[0101]

[0102] In the above formula: The mean value of the voltage signal envelope. The upper envelope of the current signal. The lower envelope of the current signal. These represent the sampling signals at various time points.

[0103] The intermediate function is obtained by subtracting the mean from the original voltage signal, as shown in the following formula. The same applies to the current signal:

[0104]

[0105] in, For intermediate functions, The original voltage signal, This represents the mean value of the voltage signal envelope.

[0106] Determine if the intermediate function meets the criteria for inclusion in the IMF:

[0107] ① The number of poles in the original signal differs from the number of zeros by one, or the two numbers are the same;

[0108] ②At each time point, the average value of the upper envelope formed by the local maxima and the lower envelope formed by the local minima is 0.

[0109] If the condition is met, proceed to the next step; if not, replace the initial signal with an intermediate function and repeat the above steps until the condition is met, thereby obtaining the first IMF component.

[0110] Step 4. Subtract the first IMF component from the original signal to obtain the residual component. Repeat the above steps for the residual component to obtain the IMF components of each order in turn until the final residual component is obtained. The final residual component is characterized by the signal being monotonic or having only one pole. At this point, the EMD decomposition is complete, and the original signal can be expressed as follows:

[0111]

[0112] In the above formula: The original voltage signal, For each IMF component, The final residual component is n, where n is the number of IMF components and s is the IMF component index.

[0113] Step 5. Perform Hilbert transform on the voltage and current signals to construct analytic signals and obtain the instantaneous amplitude and instantaneous phase angle of the original IMF component signals. The voltage transformation formula is as follows, and the current transformation formula is similar:

[0114]

[0115] In the above formula, The "orthogonal components" are obtained by performing a Hilbert transform on the IMF components. Represents Cauchy's principal value. For the selected IMF components, For the selected original signal in the integral variable The following form, For integration, the virtual time variable is used, where 's' represents the IMF component index. Instantaneous amplitude, For instantaneous phase:

[0116] Step 6. Calculate the high-frequency power on both sides of the positive and negative cables, using the following formula:

[0117]

[0118] In the above formula, The instantaneous high-frequency power of the positive or negative cable. This represents the instantaneous amplitude of the voltage IMF component within the corresponding frequency range. This represents the instantaneous amplitude of the IMF component of the current in the corresponding frequency range. For the instantaneous phase of the voltage IMF component in the corresponding frequency range, This represents the instantaneous phase of the IMF component of the current in the corresponding frequency range.

[0119] Step 7. Analyze the high-frequency power amplitude on any side of the line to determine whether it meets the fault identification criteria, in order to determine whether a fault has occurred. The formula is as follows:

[0120]

[0121] In the above formula, This represents the absolute value of the instantaneous high-frequency power of the positive or negative cable. The threshold is used for fault identification criteria.

[0122] Step 8. Calculate the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables, using the following formula:

[0123]

[0124] In the above formula, This represents the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables. and The two sides of the cable represent the high-frequency power at the corresponding frequency sequence. and These represent the average high-frequency power of all serial numbers on both sides of the cable. The total number of frequency bands required; For a specific sampling frequency, .

[0125] Step 9. The high-frequency power correlation coefficient is positive when the high-frequency power on both sides of the cable has the same sign, and negative when the high-frequency power on both sides of the cable has opposite signs. The ratio of the high-frequency power on both sides of the cable can be expressed by the following formula:

[0126]

[0127] in, , This indicates the high-frequency power at the busbar protection installation points on both sides of the cable. and These represent the high-frequency impedances of the cable at the distances from the fault point to the busbars on both sides of the cable, respectively. and These represent the equivalent high-frequency impedances on the back side of the busbars on both sides of the cable. and These represent the high-frequency voltages of the busbars on both sides of the cable. and These represent the high-frequency currents on both sides of the cable busbars.

[0128] in, When different fault types, The values ​​are different. Taking an intra-zone fault as an example, when an intra-zone fault occurs... and At this point, the proportionality coefficient is positive, while it is negative during faults outside the fault zone. When a single-pole fault occurs, because of the coupling between the positive and negative cables, high-frequency power will also appear in the non-faulty cable. However, the non-faulty cable does not contain a high-frequency voltage source, therefore the ratio of high-frequency power on both sides of the non-faulty cable is negative. This is the ratio of the power factors at both ends of the cable. and These are the power factors on one side, respectively.

[0129] To better identify fault types and prevent false positives, the following formulas are set for different fault type identification conditions:

[0130]

[0131] In the above formula: and These are the high-frequency power correlation coefficients on both sides of the positive and negative cables, respectively.

[0132] Step 10. Based on the result obtained by the fault type discrimination unit, the circuit breaker control unit sends a disconnection signal to the DC circuit breaker in the fault range to isolate the fault and protect the normal operation of the power grid.

[0133] Example 3

[0134] This invention provides another embodiment, which is a fault diagnosis device for multi-terminal flexible DC transmission systems based on HHT transformation to extract high-frequency power. This device implements the steps of the fault diagnosis method for multi-terminal flexible DC transmission systems based on HHT transformation to extract high-frequency power described in embodiments 1-2, specifically including:

[0135] The voltage and current acquisition module is used to acquire voltage and current data at the protective installation points on both sides of the positive and negative cables;

[0136] The voltage change rate calculation module is used to calculate the voltage change rate based on the voltage and current data before and after the fault occurs. When the voltage change rate of both the positive and negative poles exceeds the threshold, the voltage and current data before and after the fault occurs are obtained.

[0137] The high-frequency power calculation module includes an HHT transformation module and a fault identification module. The HHT transformation module extracts the instantaneous amplitude and phase angle of the IMF component and the corresponding frequency band components of voltage and current, and uses this to calculate the high-frequency power. The fault identification module performs HHT transformation on the voltage and current data before and after the fault to calculate the high-frequency power on either side of the positive and negative cables; it then determines whether the high-frequency power amplitude on either side of the line meets the fault identification criteria to confirm whether a fault has occurred. Specifically, it acquires the voltage and current data before and after the fault, performs HHT transformation to calculate the high-frequency power on both sides of the positive and negative cables, analyzes the high-frequency power amplitude on either side of the line, and determines whether it meets the fault identification criteria to confirm whether a fault has occurred.

[0138] The high-frequency power correlation coefficient calculation module is used to calculate the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables after a fault occurs.

[0139] The fault type determination module is used to determine the fault type using the high-frequency power correlation coefficient.

[0140] The fault isolation module is used to send signals to the DC circuit breakers in the fault range according to the fault type to isolate the fault.

[0141] The fault type determination module described in this embodiment is used to determine the fault type using a high-frequency power correlation coefficient; wherein, when the high-frequency power on both sides of the cable has the same sign, the correlation coefficient is positive; when the high-frequency power on both sides of the cable has opposite signs, the correlation coefficient is negative; including:

[0142] When the fault type is a bipolar short-circuit fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0143] When the fault type is a positive grounding fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive.

[0144] When the fault type is a negative pole grounding fault within the zone, the correlation coefficient of the positive pole cable is negative, and the correlation coefficient of the negative pole cable is positive.

[0145] When the fault type is an external fault, the correlation coefficient of the positive cable is negative, and the correlation coefficient of the negative cable is also negative.

[0146] Example 4

[0147] Based on the same inventive concept, embodiments of the present invention also provide a computer device, including a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor. When the processor executes the computer program, it implements the steps of any of the methods described in Embodiment 1 or 2 for diagnosing faults in multi-terminal flexible DC transmission based on HHT transformation for extracting high-frequency power.

[0148] Example 5

[0149] Based on the same inventive concept, this embodiment of the invention also provides a computer storage medium storing a computer program, which, when executed by a processor, implements the steps of any one of the methods for diagnosing faults in multi-terminal flexible DC transmission based on HHT transformation for extracting high-frequency power as described in Embodiment 1 or 2.

[0150] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0151] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0152] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0153] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A fault diagnosis method for multi-terminal flexible DC transmission based on HHT transform for extracting high-frequency power, characterized by: include: Collect voltage and current data at the protective installation points on both sides of the positive and negative cables; The voltage change rate is calculated based on the voltage and current data at the protection installation points on both sides of the cable. When the voltage change rate of both the positive and negative poles exceeds the threshold, the voltage and current data before and after the fault occurs are obtained. Based on the voltage and current data before and after the fault, the Hilbert-Huang transform (HHT) is used to calculate the high-frequency power on either side of the positive and negative cables; it is then determined whether the high-frequency power amplitude on either side of the line meets the fault identification criteria to confirm whether a fault has occurred. After confirming the fault, calculate the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables; Fault type determination using high-frequency power correlation coefficient; Based on the fault type, a signal is sent to the DC circuit breaker in the fault-prone area to isolate the fault.

2. The multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation for extracting high-frequency power according to claim 1, characterized in that: The voltage change rate is calculated based on the voltage and current data at the protective installation points on both sides of the cable. The criterion is as follows: when the voltage change rate of the positive or negative pole exceeds a threshold, voltage and current data before and after the fault occurs are obtained; the fault judgment module is activated, and the formula is as follows: ； In the above formula, This is the voltage at the positive protection point. This is the voltage at the negative protection point. The threshold for fault initiation criteria is 'start', which indicates that the fault detection module is started.

3. The multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation for extracting high-frequency power according to claim 1, characterized in that: The process involves acquiring voltage and current data before and after the fault, and then performing a Hilbert-Huang Transform (HHT) calculation on either side of the positive and negative cables based on this data. The specific calculation process is as follows: Empirical Mode Transform (EMT) is applied to the data to decompose the voltage and current signals into a series of Intrinsic Mode Functions (IMFs). Hilbert Transform is then applied to the voltage and current to construct analytical signals, and their instantaneous amplitude and phase angle are calculated. Based on this, the high-frequency power of the IMF components in the corresponding frequency range is calculated. The formula for calculating the high-frequency power at the protection points on both sides of the positive and negative cables using the IMF components in the corresponding frequency band is as follows: ； In the above formula, The instantaneous high-frequency power of the positive or negative cable. This represents the instantaneous amplitude of the voltage IMF component within the corresponding frequency range. This represents the instantaneous amplitude of the IMF component of the current in the corresponding frequency range. For the instantaneous phase of the voltage IMF component in the corresponding frequency range, This represents the instantaneous phase of the IMF component of the current in the corresponding frequency range.

4. The multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation for extracting high-frequency power according to claim 1, characterized in that: The method involves determining whether the high-frequency power amplitude on either side of the line meets the fault identification criterion to confirm whether a fault has occurred; the formula is as follows: ； In the above formula, This represents the absolute value of the instantaneous high-frequency power of the positive or negative cable. The threshold is used for fault identification criteria.

5. The multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation for extracting high-frequency power according to claim 1, characterized in that: The formula for calculating the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables is as follows: ； In the above formula, This represents the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables. and The two sides of the cable represent the high-frequency power at the corresponding frequency sequence. and These are the average high-frequency power values ​​for all serial numbers on both sides of the cable; The total number of frequency bands required; For a specific sampling frequency, .

6. The multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation for extracting high-frequency power according to claim 1, characterized in that: The method of using high-frequency power correlation coefficient to determine fault type includes: when the high-frequency power on both sides of the cable has the same sign, the correlation coefficient is positive; when the high-frequency power on both sides of the cable has different signs, the correlation coefficient is negative; including: When the fault type is a bipolar short-circuit fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive. When the fault type is a positive grounding fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive. When the fault type is a negative pole grounding fault within the zone, the correlation coefficient of the positive pole cable is negative, and the correlation coefficient of the negative pole cable is positive. When the fault type is an external fault, the correlation coefficient of the positive cable is negative, and the correlation coefficient of the negative cable is also negative.

7. A multi-terminal flexible DC transmission fault diagnosis device based on HHT transformation for extracting high-frequency power, characterized by: include: The voltage and current acquisition module is used to acquire voltage and current data at the protective installation points on both sides of the positive and negative cables; The voltage change rate calculation module is used to calculate the voltage change rate based on the voltage and current data at the protection installation points on both sides of the cable. When the voltage change rate of both the positive and negative poles exceeds the threshold, the voltage and current data before and after the fault occurs are obtained. The high-frequency power calculation module includes an HHT transformation module and a fault identification module. It is used to calculate the high-frequency power on either side of the positive and negative cables by performing HHT transformation based on the voltage and current data before and after the fault occurs; and to determine whether the high-frequency power amplitude on either side of the line meets the fault identification criteria to confirm whether a fault has occurred. The high-frequency power correlation coefficient calculation module is used to calculate the high-frequency power correlation coefficient at the protection points on both sides of the positive and negative cables after a fault occurs. The fault type determination module is used to determine the fault type using the high-frequency power correlation coefficient. The fault isolation module is used to send signals to the DC circuit breakers in the fault range according to the fault type to isolate the fault.

8. The multi-terminal flexible DC transmission fault diagnosis device based on HHT conversion for extracting high-frequency power according to claim 7, characterized in that: The fault type determination module is used to determine the fault type using a high-frequency power correlation coefficient; wherein, when the high-frequency power on both sides of the cable has the same sign, the correlation coefficient is positive; when the high-frequency power on both sides of the cable has opposite signs, the correlation coefficient is negative; including: When the fault type is a bipolar short-circuit fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive. When the fault type is a positive grounding fault within the zone, the correlation coefficient of the positive cable is positive and the correlation coefficient of the negative cable is positive. When the fault type is a negative pole grounding fault within the zone, the correlation coefficient of the positive pole cable is negative, and the correlation coefficient of the negative pole cable is positive. When the fault type is an external fault, the correlation coefficient of the positive cable is negative, and the correlation coefficient of the negative cable is also negative.

9. A computer device, comprising a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation to extract high-frequency power as described in any one of claims 1-6.

10. A computer storage medium, characterized in that: The computer storage medium contains a computer program, which, when executed by a processor, implements the steps of the multi-terminal flexible DC transmission fault diagnosis method based on HHT transformation for extracting high-frequency power as described in any one of claims 1-6.

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