Residual Current Fault Detection Method and System

Abstract

The present application relates to a method for detecting residual current faults, including: obtaining a bus single-pole current signal; filtering and feature reconstructing the bus single-pole current signal using preset wavelet parameters to obtain a wavelet analysis signal; performing a rate-of-change analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal; comparing the periodic change amount with a preset threshold to obtain a residual current fault result; wherein the preset wavelet parameters and the preset threshold are obtained through residual current simulation analysis. This solution simplifies the hardware design of existing residual current protectors that need to obtain signals from both ends of the bus, greatly reduces the volume of the measurement hardware of traditional DC residual current protectors, and improves the accuracy of residual current fault detection by applying signal processing means to the bus single-pole signal for detection.

Description

Technical Field

[0001] This application relates to the technical field of electric shock protection, and particularly to a method and system for detecting residual current faults. Background Art

[0002] With the improvement of economic and technological levels, the rapid development of the power industry has greatly facilitated people's lives. However, with the significant increase in power consumption and the intensity of electrical equipment, fire accidents and personal electric shock accidents often occur. The reasons are, on the one hand, that the overloaded operation of equipment generates a large amount of heat, causing a fire in the event of a short circuit; on the other hand, the line is damaged during the operation of the equipment, and the insulating outer skin falls off, resulting in leakage of electrical equipment or lines, and thus a residual current in the system. Therefore, it is very necessary to detect the change of the residual current in the line to determine whether an electric shock or other grounding leakage accident has occurred.

[0003] Currently, in order to cope with such accidents, the existing method is to use a leakage protector to detect the leakage current in the line, and timely disconnect the threatening leakage line to protect the safety of the power system line, equipment and personnel. However, most of the existing residual current protectors are for AC systems and cannot effectively protect the residual current faults in DC systems. Moreover, with the significant increase in power consumption and the intensity of electrical equipment, the current level in the DC system increases, and the accuracy of residual current detection gradually decreases. Summary of the Invention

[0004] Based on this, in view of the above technical problems, it is necessary to provide a method and system for detecting residual current faults that can accurately determine whether a residual current fault has occurred.

[0005] A method for detecting residual current faults, the method comprising:

[0006] Obtaining a bus single-pole current signal;

[0007] Filtering and feature reconstructing the bus single-pole current signal with preset wavelet parameters to obtain a wavelet analysis signal;

[0008] Performing a rate-of-change analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal;

[0009] Comparing the periodic change amount with a preset threshold value to obtain a residual current fault result;

[0010] Wherein, the preset wavelet parameters and the preset threshold value are obtained through residual current simulation analysis.

[0011] In one embodiment, the process of obtaining the preset wavelet parameters and the preset threshold value through residual current simulation analysis includes:

[0012] Obtain a bus monopole current signal including a simulated residual current; wherein, the simulated residual current is obtained by simulation under different bus voltage levels, bus current levels, and residual current levels;

[0013] Based on the bus monopole current signal including the simulated residual current, and two or more wavelet parameters and thresholds, determine two or more simulated residual current fault results;

[0014] Based on two or more simulated residual current fault results, statistically obtain the residual current fault accuracy corresponding to each wavelet parameter and threshold;

[0015] Select the wavelet parameter and threshold with the highest residual current fault accuracy as the preset wavelet parameter and preset threshold.

[0016] In one embodiment, the preset wavelet parameter includes a preset wavelet basis, a preset decomposition level, and a preset frequency band. Filtering and feature reconstruction of the bus monopole current signal using the preset wavelet parameter to obtain a wavelet analysis signal includes:

[0017] Perform filtering processing on the bus monopole current signal to obtain a filtered bus monopole current signal;

[0018] Perform wavelet transform on the filtered bus monopole current signal using the preset wavelet basis and the preset decomposition level, and extract the decomposed low-frequency band wavelet coefficients according to the preset frequency band;

[0019] Perform feature construction on the low-frequency band wavelet coefficients to obtain a wavelet analysis signal.

[0020] In one embodiment, the obtaining of the bus monopole current signal includes:

[0021] Sample the bus monopole current signal according to the sampling frequency and time window.

[0022] In one embodiment, the periodic change amount includes a first periodic change amount and a second periodic change amount. Performing a change rate analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal includes:

[0023] Obtain the amplitude change amount and the maximum amplitude of the wavelet analysis signal corresponding to the current time window;

[0024] Take the amplitude change amount as the first periodic change amount of the current period; take the difference between the maximum amplitude and the maximum amplitude of the wavelet analysis signal corresponding to the previous time window as the second periodic change amount of the current period.

[0025] In one embodiment, the preset threshold includes a preset pulse threshold and a preset attenuation threshold. Comparing the periodic change amount with the preset threshold to obtain a residual current fault result includes:

[0026] When the first periodic change amount in the current period is less than the preset pulse threshold, the residual current fault result is no fault;

[0027] When the first periodic change amount in the current period is greater than the preset pulse threshold, the residual current fault result is obtained according to the second periodic change amount after the current period and the preset attenuation threshold.

[0028] In one embodiment, obtaining the residual current fault result according to the second periodic change amount after the current period and the preset attenuation threshold includes:

[0029] When the second periodic change amounts in a continuous preset number of periods after the current period are all less than the preset attenuation threshold, the residual current fault result is a fault; otherwise, the residual current fault result is no fault.

[0030] In one embodiment, a residual current fault detection system is provided. The system includes a current acquisition device and a host computer. The current acquisition device is connected to the positive / negative pole of the bus, and the current acquisition device is also connected to the host computer;

[0031] The current acquisition device is used to acquire a single-pole current signal of the bus;

[0032] The host computer is used to filter and perform feature reconstruction on the single-pole current signal of the bus using preset wavelet parameters to obtain a wavelet analysis signal; it is also used to perform a change rate analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal; it is also used to compare the periodic change amount with a preset threshold to obtain a residual current fault result.

[0033] In one embodiment, the above residual current fault detection system further includes a residual current simulation device, and the residual current simulation device is connected to the current acquisition device;

[0034] The residual current simulation device is used to simulate and obtain simulation residual currents under different bus voltage levels, bus current levels, and residual current levels;

[0035] The current acquisition device is further used to acquire a single-pole current signal of the bus including the simulation residual current;

[0036] The host computer is further configured to determine two or more simulation residual current fault results based on the bus monopole current signal including the simulation residual current, as well as two or more wavelet parameters and thresholds; statistically obtain the residual current fault accuracy rates corresponding to the respective wavelet parameters and thresholds according to the two or more simulation residual current fault results; and select the wavelet parameter and threshold with the highest residual current fault accuracy rate as the preset wavelet parameter and preset threshold.

[0037] In one embodiment, the residual current simulation device includes a DC power supply module, a variable resistor R1, a variable resistor R2, a resistor R+, a resistor R-, a timing conduction module, and a current detection module. The variable resistor R1 is connected between the positive and negative output terminals of the DC power supply module. One end of the resistor R+ is connected to the positive output terminal of the DC power supply module. One end of the resistor R- is connected to the negative output terminal of the DC power supply module. The variable resistor R2 and the timing conduction module are connected in series, and one end is connected to the other end of the resistor R+, and the other end is connected to the other end of the resistor R-. The current detection module is connected to both ends after the variable resistor R2 and the timing conduction module are connected in series.

[0038] When the timing conduction module conducts, the resistance values of the variable resistor R1 and the variable resistor R2 are adjusted to simulate the simulation residual current under different bus voltage levels, bus current levels, and residual current levels.

[0039] The above-mentioned residual current fault detection method and system obtain a monopole bus current signal, perform wavelet transform analysis, extract the periodic change amount of its wavelet analysis signal, and then compare it with a preset threshold to determine whether a residual current fault occurs. This simplifies the hardware design of the existing residual current protector that needs to obtain signals from both ends of the bus, greatly reduces the volume of the measurement hardware of the traditional DC residual current protector, and improves the accuracy of residual current detection by using signal processing means for the bus monopole signal. Description of the Drawings

[0040] Figure 1 It is a schematic flowchart of the residual current fault detection method in one embodiment;

[0041] Figure 2 It is a current waveform diagram when a residual current fault of 80 mA occurs with a bus voltage of 200 V and no load;

[0042] Figure 3 It is a current waveform diagram when a residual current fault of 80 mA occurs with a bus voltage of 200 V and a bus current of 5 A;

[0043] Figure 4Current waveform diagram of a 300 mA residual current fault occurring when the busbar voltage is 200 V and the busbar current is 10 A;

[0044] Figure 5 Variation trend diagram of the residual current with the busbar current from 0 - 10 A when the busbar voltage is 200 V and 400 V and the residual current is 300 mA;

[0045] Figure 6 Flow schematic diagram of the residual current fault detection method in another embodiment;

[0046] Figure 7 Wavelet analysis signal diagram of the busbar single - pole current signal of an 80 mA residual current fault occurring when the busbar voltage is 200 V and the busbar current is 5 A;

[0047] Figure 8 Wavelet analysis signal diagram of the busbar single - pole current signal of an 80 mA residual current fault occurring when the busbar voltage is 400 V and the busbar current is 5 A;

[0048] Figure 9 Wavelet analysis signal diagram of the busbar single - pole current signal of an 80 mA residual current fault occurring when the busbar voltage is 400 V and the busbar current is 10 A;

[0049] Figure 10 Flow schematic diagram of the residual current fault detection method in another embodiment;

[0050] Figure 11 Flow schematic diagram of the residual current fault detection method in another embodiment;

[0051] Figure 12 Flow schematic diagram of the residual current fault detection method in another embodiment;

[0052] Figure 13 Structure schematic diagram of the residual current simulation device in one embodiment;

[0053] Figure 14 Current waveform diagram with an 80 mA simulated residual current added when the busbar voltage is 200 V and the busbar current is 10 A;

[0054] Figure 15 Current waveform diagram with a 300 mA simulated residual current added when the busbar voltage is 200 V and the busbar current is 10 A;

[0055] Figure 16 Current waveform diagram with a 300 mA simulated residual current added when the busbar voltage is 400 V and the busbar current is 10 A;

[0056] Figure 17The current waveform diagram when the bus voltage is 400V, the bus current is 20A, and a simulated residual current of 80mA is added;

[0057] Figure 18 The current waveform diagram when the bus voltage is 400V, the bus current is 20A, and a simulated residual current of 300mA is added;

[0058] Figure 19 The change trend diagram of the residual current with the bus current varying from 0 to 20A when the bus voltage is 200V and the residual current is 300mA. Detailed implementation manners

[0059] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0061] It can be understood that the terms "first", "second", etc. used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, the first resistor may be referred to as the second resistor, and similarly, the second resistor may be referred to as the first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0062] It can be understood that in the following embodiments, "connection", if there is an electrical signal or data transmission between the connected circuits, modules, units, etc., should be understood as "electrical connection", "communication connection", etc.

[0063] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprises / include" or "has" etc. specify the presence of the stated features, wholes, steps, operations, components, parts or combinations thereof, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof.

[0064] At present, existing DC residual current detection methods and protectors mainly use multiple hardware such as DC bridges, Hall sensors, and magnetic modulation sensors to connect the positive and negative poles of the bus respectively. By calculating the current value after the phase cancellation of the positive and negative bus currents, the residual current is obtained, and then the fault or accident situation is determined by judging the change of the residual current. This method not only has high requirements for hardware, but also as the power consumption and the intensity of electrical equipment increase significantly, when the bus current level in the DC system increases, the weak amplitude of the residual current is relatively larger compared to the bus current difference, and the detection accuracy gradually decreases.

[0065] In view of this situation, this application proposes a residual current fault detection method and system from the perspective of bus current signal analysis. However, in a DC system with a large bus current level, the significant change degree of the DC bus current is weakened, which poses a huge obstacle to the effective detection of DC residual current. Therefore, this application effectively clarifies the evolution law of DC residual current under the conditions of the change trends of DC system voltage and current, and guides the DC residual current protection under various DC system power influence conditions.

[0066] In one embodiment, as Figure 1 shown, a residual current fault detection method is provided, including:

[0067] Step 102: Obtain the bus single-pole current signal.

[0068] Specifically, the bus single-pole current signal is the current signal obtained by connecting only the positive or negative pole of the bus. It can be understood that the bus single-pole current signal can be the bus positive-pole current signal or the bus negative-pole current signal. In one embodiment, step 102 of obtaining the bus single-pole current signal includes sampling the bus single-pole current signal according to the sampling frequency and time window. Specifically, the values of the sampling frequency f and the time window T are not fixed and can be set according to the actual bus current signal situation. For example, the following explanations are all based on the sampling frequency f of 1 MHz and the time window T of 8 ms. In one embodiment, the sampling frequency f and the time window T can also be obtained through residual current simulation analysis.

[0069] Among them, by simulating the real residual current fault current occurring in the DC system, it can be obtained that the method of identifying the residual current fault by measuring and analyzing the bus current is feasible. As Figure 2 shown, when the bus voltage is 200 V and an 80 mA residual current fault occurs under no-load conditions, the bus current changes significantly during the fault occurrence, and the average value of the DC residual current after the change is 84.7148 mA.

[0070] However, after increasing the load, as Figure 3As shown, when the busbar current rises to 5 A, the connected residual current branch remains unchanged (with an average value of 79.7468 mA). From the measured true residual current fault current in the DC system, it can be seen that the busbar current does not change significantly before and after the occurrence of the residual current fault, which increases the difficulty of accurately detecting DC residual current. That is to say, when the busbar current becomes larger, simply relying on the change of the busbar current cannot effectively detect the DC residual current fault in the line. In addition, by increasing the residual current to about 300 mA (average value of 299.082 mA), when the corresponding Figure 3 busbar current in Figure 4 is 5 A, there will be a certain degree of change. But as

[0071] shown, after further increasing the system busbar current to 10 A, from the measured true residual current fault current in the DC system, it can be seen that the change of the busbar current before and after the occurrence of the residual current fault will decrease. Figure 5 Therefore, according to the research on the residual current law under various busbar current and voltage levels in the actual DC power supply system, as

[0072] shown, keeping the busbar voltage of 200 V and the residual current condition of 300 mA unchanged, changing the busbar current from 0 to 10 A, the residual current shown by the dotted line shows a downward trend. This is also because the line voltage division is larger when the busbar current becomes larger, correspondingly reducing the DC residual current amplitude. Then, when the busbar voltage is further increased to 400 V, the residual current shown by the solid line also keeps showing a downward trend, but when the voltage increases, the amplitude of the residual current will increase. In view of this situation, this scheme considers using the wavelet transform method to analyze the busbar current and identify the residual current fault therein.

[0073] Step 104: Filter and reconstruct the features of the busbar monopole current signal using preset wavelet parameters to obtain the wavelet analysis signal.

[0074]

[0075] Among them, wavelet transform is a time-scale analysis method, which is very suitable for processing non-stationary signals and can change the sizes of the time window and frequency window to analyze the signal in multiple resolutions from the time and frequency domains. Specifically, for the busbar monopole current signal f(t), the wavelet transform result of the residual current signal is solved according to the following formula:

[0076] Specifically, first, the obtained busbar monopole current signal is filtered to obtain the filtered busbar monopole current signal. Then, the filtered busbar monopole current signal is subjected to wavelet transform using a preset wavelet basis and a preset decomposition level, and the decomposed low-frequency band wavelet coefficients are extracted according to the frequency band. Finally, feature construction is performed on the low-frequency band wavelet coefficients to obtain the wavelet analysis signal.

[0077] Step 106: Perform a rate-of-change analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal.

[0078] Among them, the periodic change amount includes a first periodic change amount and a second periodic change amount. Specifically, take the amplitude change amount and the maximum amplitude of the wavelet analysis signal corresponding to the current time window. Then, take the amplitude change amount as the first periodic change amount of the current period; take the difference between the maximum amplitude and the maximum amplitude of the wavelet analysis signal corresponding to the previous time window as the second periodic change amount of the current period.

[0079] Step 108: Compare the periodic change amount with a preset threshold to obtain the residual current fault result.

[0080] Among them, the preset threshold includes a preset pulse threshold and a preset attenuation threshold. Specifically, when the first periodic change amount of the current period is less than the preset pulse threshold, the residual current fault result is no fault. When the first periodic change amount of the current period is greater than the preset pulse threshold, the residual current fault result is obtained according to the second periodic change amount after the current period and the preset attenuation threshold.

[0081] Among them, the preset wavelet parameters and the preset threshold are obtained through residual current simulation analysis. Specifically, the simulation analysis process includes: first, use the residual current simulation model to generate busbar monopole current signals under different busbar voltage levels, busbar current levels, and residual current levels. According to the busbar monopole current signal including the simulated residual current, and two or more wavelet parameters and thresholds, two or more simulated residual current fault results are judged. Then, according to the two or more simulated residual current fault results, the residual current fault accuracy corresponding to each wavelet parameter and threshold is statistically obtained. Finally, select the wavelet parameters and thresholds with the highest residual current fault accuracy as the preset wavelet parameters and the preset threshold.

[0082] The above residual current fault detection method and system, by obtaining the busbar current signal of a single pole, performing wavelet transform analysis, extracting the periodic change amount of its wavelet analysis signal, and then comparing it with a preset threshold to judge whether there is a residual current fault, simplifies the hardware design of the existing residual current protector that needs to obtain signals from both ends of the busbar, greatly reduces the volume of the measurement hardware of the traditional DC residual current protector, and improves the accuracy of residual current detection by using signal processing means for the busbar monopole signal.

[0083] In one embodiment, as Figure 6 shown, the process of obtaining the preset wavelet parameters and the preset threshold through residual current simulation analysis includes:

[0084] Step 202: Obtain a bus monopole current signal including simulated residual current.

[0085] Among them, the simulated residual current is simulated under different bus voltage levels, bus current levels, and residual current levels. Specifically, the bus voltage level, bus current level, and residual current level can be set according to actual situations. For example, the bus voltage can vary within the range of 0 - 1000V, the bus current can vary within the range of 0 - 20A, and the residual current can vary within the range of 0 - 300mA. In addition, the method of simulating the simulated residual current is not fixed. It can be generated by a residual current simulation model or other methods recognized by those skilled in the art. Through the combination of multiple voltage and current levels, the effectiveness of the residual current fault characteristics used in the detection method is ensured at the physical simulation level, and the effective application range of the detection method in various system voltage levels, current levels, and residual current level forms is expanded.

[0086] Step 204: Based on the bus monopole current signal including simulated residual current, and two or more wavelet parameters and thresholds, obtain two or more simulated residual current fault results.

[0087] Among them, the wavelet parameters include necessary parameters for implementing the wavelet transform process, such as wavelet basis, decomposition level, and frequency band. Among them, the wavelet basis can be 15 common wavelet bases including spline wavelet, Daubechies wavelet, and ReverseBior wavelet. The decomposition level is used to divide the frequency range of the target signal to a certain extent and can be an integer from 1 to 10.

[0088] Among them, the thresholds include a pulse threshold and an attenuation threshold. The pulse threshold is used to determine whether there is a pulse in the wavelet analysis result. If there is a pulse, it is considered that a DC residual current fault may have occurred. The attenuation threshold is used to determine whether there is a continuous attenuation situation after a pulse appears in the wavelet analysis result. If so, it is confirmed that a residual current fault has occurred. In one embodiment, the evolution law of the bus current when the above-mentioned residual current fault occurs is also obtained through residual current simulation analysis. Specifically, under the condition that the DC residual current is 80mA, after performing wavelet transform on the bus monopole current signal measured under the conditions of a bus voltage of 200V and a bus current of 5A, the obtained wavelet analysis signal is as Figure 7 shown. When the voltage level is increased to 400V and the system current of 5A remains unchanged, the wavelet transform graph of the collected bus monopole current signal is as Figure 8As shown in the figure. When the system current level is increased to 10 A and the system voltage of 400 V remains unchanged, the wavelet transform graph of the single-pole bus current signal collected is as Figure 9 shown. It can be seen that when a residual current fault occurs, a large-amplitude pulse appears in the wavelet analysis signal of the bus current, accurately indicating the fault phenomenon of the residual current occurring in the DC power supply system. At the same time, during the continuous occurrence of the DC residual current phenomenon, the amplitude of the wavelet analysis signal has always been in a relatively small amplitude state, and thus it is extracted as a basis for detecting DC residual current faults.

[0089] Specifically, the above optional wavelet parameters and thresholds are respectively used to determine whether there is a residual current fault in the single-pole bus current signal including the simulated residual current, and two or more simulated residual current fault results are obtained. Among them, the process of determining whether there is a residual current fault is similar to the above steps 102 - 108 and will not be elaborated here.

[0090] Step 206: According to two or more simulated residual current fault results, statistically obtain the residual current fault accuracy corresponding to each wavelet parameter and threshold.

[0091] It can be understood that the above single-pole bus current signals including simulated residual current are all samples with residual current faults. Then, by statistically calculating the detection rates of the simulated residual current fault results corresponding to the above wavelet parameters and thresholds, the residual current fault accuracy corresponding to each wavelet parameter and threshold can be obtained.

[0092] In another embodiment, in addition to the single-pole bus current signal including simulated residual current, the single-pole bus current signal without residual current faults can also be used to detect each wavelet parameter and threshold, and the corresponding residual current fault accuracy is obtained. By adding the single-pole bus current signal without residual current faults to detect each wavelet parameter and threshold, the final detection method can have stronger recognition ability.

[0093] Step 208: Select the wavelet parameter and threshold with the highest residual current fault accuracy as the preset wavelet parameter and preset threshold.

[0094] Specifically, selecting the wavelet parameter and threshold with the highest residual current fault accuracy as the preset wavelet parameter and preset threshold can ensure the highest recognition accuracy of the final detection method for residual current faults during the actual operation of the power grid.

[0095] In one embodiment, the preset wavelet parameters include a preset wavelet basis, a preset decomposition level, and a preset frequency band. Then, as Figure 10 shown, in step 104, the single-pole bus current signal and the preset wavelet parameters are filtered and feature-reconstructed to obtain a wavelet analysis signal, including:

[0096] Step 302: Filter the busbar monopole current signal to obtain the filtered busbar monopole current signal.

[0097] Specifically, filter the obtained busbar monopole current signal to obtain high-frequency components and low-frequency components. Among them, the low-frequency component is used as the filtered busbar monopole current signal. For example, when the sampling frequency f is 1 mHz, the filtered busbar monopole current signal is the busbar monopole current signal of 0 - 500 kHz.

[0098] Step 304: Perform wavelet transform on the filtered busbar monopole current signal using a preset wavelet basis and a preset decomposition level, and extract the decomposed low-frequency band wavelet coefficients according to a preset frequency band.

[0099] Specifically, according to the results of the residual current simulation analysis, in this embodiment, the Rbio3.1 wavelet is selected as the preset wavelet basis, and the preset decomposition level is selected as 2-layer decomposition to perform wavelet transform on the filtered busbar monopole current signal. Then, the low-frequency band wavelet coefficients after wavelet transform are selected as the high-frequency band component h20 of the second layer as the basis for subsequent feature construction, that is, the wavelet coefficients in the frequency band of 125 kHz to 250 kHz.

[0100] Step 306: Construct features from the low-frequency band wavelet coefficients to obtain a wavelet analysis signal.

[0101] Specifically, construct features from the wavelet coefficients in the frequency band of 125 kHz to 250 kHz to obtain the wavelet analysis result. Among them, the feature form is the sum of squares calculation method.

[0102] In one embodiment, the periodic variation includes a first periodic variation and a second periodic variation. As Figure 11 shown, perform a rate of change analysis on the wavelet analysis signal in step 106, and extract the periodic variation of the wavelet analysis signal, including:

[0103] Step 402: Take the amplitude change amount and the maximum amplitude of the wavelet analysis signal corresponding to the current time window.

[0104] Among them, the amplitude change amount is the difference between the maximum amplitude and the minimum amplitude, and the time window T is taken as 8 ms for example. Specifically, the wavelet analysis signal is obtained by performing wavelet transform on the busbar monopole current signal after being trimmed by the time window, and it is a continuous signal. Therefore, calculate the amplitude change amount and the maximum amplitude of the wavelet analysis signal corresponding to the current time window.

[0105] Step 404: Take the amplitude change amount as the first periodic variation of the current period; take the difference between the maximum amplitude and the maximum amplitude of the wavelet analysis signal corresponding to the previous time window as the second periodic variation of the current period.

[0106] Specifically, the wavelet analysis signal of each time window length is regarded as a period. Then, the amplitude change amount thereof can be used as the first period change amount of the current period, which can characterize the change of the wavelet analysis signal within the current period. Further, the difference between the maximum amplitude of the wavelet analysis signal in the current period and the maximum amplitude of the wavelet analysis signal in the previous period is used as the second period change amount of the current period, which can characterize the change of the wavelet analysis signal in the current period relative to the wavelet analysis signal in the previous period.

[0107] In one embodiment, the preset threshold includes a preset pulse threshold and a preset attenuation threshold. As Figure 12 shown, comparing the period change amount with the preset threshold in step 108 to obtain the residual current fault result includes:

[0108] Step 502: When the first period change amount in the current period is less than the preset pulse threshold, the residual current fault result is no fault.

[0109] Specifically, when the first period change amount in the current period is less than the preset pulse threshold, it indicates that there is no mutation in the wavelet analysis signal within the current period, and it can be analyzed that no residual current fault occurs. The preset pulse threshold is obtained by analyzing the residual current simulation and can also be adjusted according to the situation during the subsequent actual detection process.

[0110] Step 504: When the first period change amount in the current period is greater than the preset pulse threshold, obtain the residual current fault result according to the second period change amount after the current period and the preset attenuation threshold.

[0111] Specifically, when the first period change amount in the current period is greater than the preset pulse threshold, it indicates that there is a pulse signal situation in the wavelet analysis signal within the current period, and a residual current fault may have occurred. According to the evolution law obtained above, it is necessary to continue to compare the second period change amount after the current period with the preset attenuation threshold to obtain the finally determined residual current fault result. Among them, the means of comparing the second period change amount with the preset attenuation threshold can be that there is a preset proportion of the second period change amounts less than the preset attenuation threshold among the continuous preset number of second period change amounts after the current period; it can also be that the continuous preset number of second period change amounts after the current period are all less than the preset attenuation threshold; it can also be other forms under the evolution law of the single-pole bus current signal under the residual current fault.

[0112] In one embodiment, obtaining the residual current fault result according to the second period change amount after the current period and the preset attenuation threshold in step 504 includes: when the second period change amounts of the continuous preset number of periods after the current period are all less than the preset attenuation threshold, the residual current fault result is a fault; otherwise, the residual current fault result is no fault.

[0113] Specifically, according to the evolution law obtained above, after a large-amplitude pulse indication occurs in the single-pole current signal of the bus after a residual current fault, a small-amplitude state will be maintained during the continuous occurrence process. Therefore, when the change amount in the second cycle in a continuous preset number of cycles after the current cycle is less than the preset attenuation threshold, the result of the residual current fault is a fault. Among them, the preset number can be set according to the actual situation. For example, in this embodiment, the preset number is 5.

[0114] In this embodiment, by checking the pulse point of the wavelet analysis waveform of the single-pole current signal of the bus, the time point when the DC residual current is generated in the line can be determined, and then the fault situation can be accurately judged through the continuously occurring decreasing residual current characteristic trend, thereby greatly reducing the volume of the measurement hardware of the traditional DC residual current protector.

[0115] It should be understood that although the steps in the flowcharts involved in the above-described embodiments are shown in sequence according to the indication of the arrows, these steps do not necessarily need to be executed in the order indicated by the arrows. Unless there is a clear indication in this article, the execution of these steps does not have a strict order limit, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-described embodiments may include multiple steps or multiple stages. These steps or stages do not necessarily need to be executed at the same moment, but can be executed at different moments. The execution order of these steps or stages does not necessarily need to be sequential, but can be executed alternately or alternately with at least a part of other steps or steps or stages in other steps.

[0116] Based on the same inventive concept, the embodiment of the present application also provides a residual current fault detection system for implementing the above-mentioned residual current fault detection method. The implementation solution provided by this system to solve the problem is similar to the implementation solution described in the above method. Therefore, the specific limitations in one or more embodiments of the following residual current fault detection system can refer to the limitations on the residual current fault detection method in the above text, and will not be repeated here.

[0117] In one embodiment, a residual current fault detection system is provided. The system includes a current acquisition device and a host computer. The current acquisition device is connected to the positive / negative pole of the bus, and the current acquisition device is also connected to the host computer. The current acquisition device is used to acquire the single-pole current signal of the bus; the host computer is used to filter and reconstruct the features of the single-pole current signal of the bus to obtain a wavelet analysis signal; it is also used to perform a change rate analysis on the wavelet analysis signal to extract the period change amount of the wavelet analysis signal; it is also used to compare the period change amount with a preset threshold to obtain the result of the residual current fault.

[0118] Specifically, the bus monopole current signal is the current signal obtained by connecting only the positive or negative pole of the bus. In one embodiment, the bus monopole current signal is sampled according to the sampling frequency and the time window. Specifically, the values of the sampling frequency f and the time window T are not fixed and can be set according to the actual bus current signal situation. For example, the sampling frequency f is 1 MHz and the time window T is 8 ms.

[0119] Furthermore, by simulating the real residual current fault current occurring in the DC system, it can be obtained that the method of identifying the residual current fault by measuring and analyzing the bus current is feasible. However, after further increasing the system bus current, it is found that the change in the bus current before and after the occurrence of the residual current fault will decrease. Therefore, this solution considers using the wavelet transform method to analyze the bus current and identify the residual current fault therein.

[0120] Specifically, first, the obtained bus monopole current signal is filtered to obtain the filtered bus monopole current signal. Then, the filtered bus monopole current signal is subjected to wavelet transform using a preset wavelet basis and a preset decomposition level, and the decomposed low-frequency band wavelet coefficients are extracted according to the frequency band. Finally, feature construction is performed on the low-frequency band wavelet coefficients to obtain the wavelet analysis signal.

[0121] Specifically, the periodic variation includes a first periodic variation and a second periodic variation. The amplitude variation and the maximum amplitude of the wavelet analysis signal corresponding to the current time window are taken. Then, the amplitude variation is used as the first periodic variation of the current period; the difference between the maximum amplitude and the maximum amplitude of the wavelet analysis signal corresponding to the previous time window is used as the second periodic variation of the current period.

[0122] In one embodiment, the above-mentioned residual current fault detection system further includes a residual current simulation device, and the residual current simulation device is connected to the current acquisition device; the residual current simulation device is used to simulate the simulated residual current under different bus voltage levels, bus current levels, and residual current levels; the current acquisition device is further used to obtain the bus monopole current signal including the simulated residual current; the upper computer is further used to judge two or more simulated residual current fault results according to the bus monopole current signal including the simulated residual current, and two or more wavelet parameters and thresholds; according to the two or more simulated residual current fault results, the residual current fault accuracy corresponding to each wavelet parameter and threshold is statistically obtained; the wavelet parameters and thresholds with the highest residual current fault accuracy are selected as the preset wavelet parameters and preset thresholds.

[0123] In one embodiment, as Figure 13As shown, the residual current simulation device includes a DC power supply module, variable resistors R1 and R2, resistors R+ and R-, a timing conduction module, and a current detection module. The variable resistor R1 is connected between the positive and negative output terminals of the DC power supply module. One end of the resistor R+ is connected to the positive output terminal of the DC power supply module, and one end of the resistor R- is connected to the negative output terminal of the DC power supply module. The variable resistor R2 and the timing conduction module are connected in series, and one end is connected to the other end of the resistor R+, and the other end is connected to the other end of the resistor R-. The current detection module is connected to both ends of the series connection of the variable resistor R2 and the timing conduction module. When the timing conduction module conducts, the resistance values of the variable resistor R1 and the variable resistor R2 are adjusted to simulate the simulated residual current under different bus voltage levels, bus current levels, and residual current levels.

[0124] Specifically, the resistors R+ and R- respectively represent the line resistances of the positive and negative poles of the DC bus. The magnitude of the loop bus current can be controlled by the variable resistor R1, and the current difference generated at both ends of the bus can be controlled by the variable resistor R2, so as to achieve the purpose of simulating the generation of DC residual current. Among them, the points IPV2 at point A and IPV3 at point B are the current detection points. When the timing conduction module conducts in the experiment, the variable resistor R2 is connected, and at the same time, the current values at points A and B are detected. It is found that the sum of the current values at points A and B is not zero, which means that DC residual current is generated in the line. The magnitude of the required detected DC residual current is the sum of the currents at points A and B. Since the residual current obtained by directly measuring the currents at points A and B and then summing them is inaccurate, the current simulated and measured at the IPV4 of the variable resistor R2 in the present invention is used as the final DC residual current amplitude.

[0125] Furthermore, the timing conduction module includes a timer and a switching element. The timer is connected to the control part of the switching element, and the controlled part of the switching element is connected in series with the variable resistor R2. After the controlled part of the switching element conducts, the variable resistor R2 is connected to the bus loop, so that a current difference is generated at both ends of the bus, simulating the generation of DC residual current. By adjusting the resistance value of the variable resistor R2, the magnitude of the simulated DC residual current can be changed. Among them, the switching element can specifically be a relay. The timer is used to output a conduction signal to the control part of the switching element after timing, conducting the variable resistor R2, and the purpose of adding residual current to the bus monopole current signal at a specific moment can be achieved.

[0126] As Figure 14As shown, set the resistance values of variable resistors R1 and R2 in the simulation model to simulate an 80 mA residual current fault when the bus voltage is 200 V and the bus current is 10 A. The DC residual current is generated at 0.5 s of timing. The DC residual current changes significantly, but the amplitude of this residual current is much smaller than the bus current. Therefore, no change in the bus current can be observed throughout the entire time period, and the simulation process also confirms the existence of the weak DC residual current phenomenon, verifying the necessity of accurately detecting this fault condition. Further, keeping the bus voltage and current unchanged, adjust the residual current branch fault simulator to increase the residual current to about 300 mA. The DC residual current obtained from the simulation is as Figure 15 shown. Keeping the DC residual current and the bus current unchanged, adjust the bus voltage to increase to about 400 V. The DC residual current obtained from the simulation is as Figure 16 shown. As can be seen from the figure, the increased residual current makes the change in the bus current relatively obvious, and the influence of the DC residual current amplitude on the current form is greater than that of the bus voltage. With the support of the DC residual current simulation device, the DC residual current fault condition under a larger bus current can be realized. Considering the bus current waveforms under the conditions of a 400 V bus voltage and a 20 A bus current, when the DC residual currents are 80 mA and 300 mA respectively, are as Figure 17 and 18 shown. It can be seen more clearly that the weak DC residual current phenomenon occurs frequently under the condition of a significantly increased bus current, and there is an urgent need for an effective method for detecting weak DC residual current.

[0127] Further, keeping the system voltage at 200 V and the residual current at 300 mA unchanged, change the system current within the range of 0 - 20 A. The DC system residual current shows a downward trend as Figure 19 shown. This means that as the types and quantities of loads connected increase, the bus current is large, and the DC residual current will show a decreasing trend as the bus current increases, verifying the correctness of the DC residual current change trend obtained under the previous experimental analysis conditions. At the same time, the simulation range of the DC residual current can realize the influence of system voltage and current levels outside the reach of experimental conditions on the form and characteristics of the DC residual current.

[0128] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0129] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A residual current fault detection method, characterized in that, The method includes: Obtaining a bus single-pole current signal, where the bus single-pole current signal is a current signal obtained by connecting only the positive or negative pole of the bus; Filtering and feature reconstructing the bus single-pole current signal with preset wavelet parameters to obtain a wavelet analysis signal; Performing a rate-of-change analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal; Comparing the periodic change amount with a preset threshold to obtain a residual current fault result; Wherein, the preset wavelet parameters and the preset threshold are obtained through residual current simulation analysis, and are the wavelet parameters and threshold with the highest residual current fault accuracy; The periodic change amount includes a first periodic change amount and a second periodic change amount. The performing a rate-of-change analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal includes: Obtaining the amplitude change amount and the maximum amplitude of the wavelet analysis signal corresponding to the current time window; Taking the amplitude change amount as the first periodic change amount of the current period; Taking the difference between the maximum amplitude and the maximum amplitude of the wavelet analysis signal corresponding to the previous time window as the second periodic change amount of the current period.

2. The residual current fault detection method according to claim 1, wherein The process of obtaining the preset wavelet parameters and the preset threshold through residual current simulation analysis includes: Obtaining a bus single-pole current signal including simulated residual current; wherein, the simulated residual current is simulated under different bus voltage levels, bus current levels, and residual current levels; Judging two or more simulated residual current fault results according to the bus single-pole current signal including simulated residual current and two or more wavelet parameters and thresholds; Statistically obtaining the residual current fault accuracy corresponding to each wavelet parameter and threshold according to two or more simulated residual current fault results; Selecting the wavelet parameters and threshold with the highest residual current fault accuracy as the preset wavelet parameters and preset threshold.

3. The method according to claim 1, wherein The preset wavelet parameters include a preset wavelet basis, a preset decomposition level, and a preset frequency band. The filtering and feature reconstructing the bus single-pole current signal with preset wavelet parameters to obtain a wavelet analysis signal includes: Performing filtering processing on the bus single-pole current signal to obtain a filtered bus single-pole current signal; Performing wavelet transform on the filtered bus single-pole current signal with the preset wavelet basis and the preset decomposition level, and extracting the decomposed low-frequency band wavelet coefficients according to the preset frequency band; Performing feature construction on the low-frequency band wavelet coefficients to obtain a wavelet analysis signal.

4. The method according to claim 1, wherein The obtaining the bus single-pole current signal includes: Sampling the bus single-pole current signal according to the sampling frequency and the time window.

5. The method according to claim 4, wherein The preset threshold includes a preset pulse threshold and a preset attenuation threshold. The comparing the periodic change amount with the preset threshold to obtain a residual current fault result includes: When the first periodic change amount of the current period is less than the preset pulse threshold, the residual current fault result is no fault; When the first periodic change amount of the current period is greater than the preset pulse threshold, the residual current fault result is obtained according to the second periodic change amount after the current period and the preset attenuation threshold.

6. The method according to claim 5, characterized in that, Obtaining a residual current fault result based on a second cycle change amount after the current cycle and the preset attenuation threshold includes: When the second cycle change amounts in a continuous preset number of cycles after the current cycle are all less than the preset attenuation threshold, the residual current fault result is that there is a fault; otherwise, the residual current fault result is that there is no fault.

7. A residual current fault detection system, characterized in that, The system includes a current acquisition device and a host computer. The current acquisition device is connected to the positive / negative pole of the bus, and the current acquisition device is also connected to the host computer; The current acquisition device is used to obtain a single-pole bus current signal, and the single-pole bus current signal is a current signal obtained by connecting only the positive or negative pole of the bus; The host computer is used to filter and perform feature reconstruction on the single-pole bus current signal using preset wavelet parameters to obtain a wavelet analysis signal; it is also used to perform a rate-of-change analysis on the wavelet analysis signal to extract the periodic change amount of the wavelet analysis signal; it is also used to compare the periodic change amount with a preset threshold to obtain a residual current fault result; wherein, the preset wavelet parameters and the preset threshold are obtained through residual current simulation analysis and are the wavelet parameters and threshold with the highest residual current fault accuracy rate; The periodic change amount includes a first periodic change amount and a second periodic change amount. The host computer is also used to obtain the amplitude change amount and the maximum amplitude of the wavelet analysis signal corresponding to the current time window; use the amplitude change amount as the first periodic change amount of the current cycle; use the difference between the maximum amplitude and the maximum amplitude of the wavelet analysis signal corresponding to the previous time window as the second periodic change amount of the current cycle.

8. The residual current fault detection system according to claim 7, characterized in that, It further includes a residual current simulation device, and the residual current simulation device is connected to the current acquisition device; The residual current simulation device is used to simulate and obtain simulation residual currents under different bus voltage levels, bus current levels, and residual current levels; The current acquisition device is also used to obtain a single-pole bus current signal including the simulation residual current; The host computer is also used to judge and obtain two or more simulation residual current fault results based on the single-pole bus current signal including the simulation residual current and two or more wavelet parameters and thresholds; according to the two or more simulation residual current fault results, statistically obtain the residual current fault accuracy rates corresponding to each wavelet parameter and threshold; select the wavelet parameters and threshold with the highest residual current fault accuracy rate as the preset wavelet parameters and preset threshold.

9. The residual current fault detection system according to claim 8, wherein The residual current simulation device includes a DC power supply module, a variable resistor R1, a variable resistor R2, a resistor R+, a resistor R-, a timing conduction module, and a current detection module. The variable resistor R1 is connected between the positive and negative output terminals of the DC power supply module. One end of the resistor R+ is connected to the positive output terminal of the DC power supply module. One end of the resistor R- is connected to the negative output terminal of the DC power supply module. The variable resistor R2 and the timing conduction module are connected in series, and one end is connected to the other end of the resistor R+, and the other end is connected to the other end of the resistor R-. The current detection module is connected to both ends of the series connection of the variable resistor R2 and the timing conduction module; When the timing conduction module conducts, adjust the resistance values of the variable resistor R1 and the variable resistor R2, and simulate the residual current under different bus voltage levels, bus current levels, and residual current levels.

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