Method, circuit and device for detecting poor contact of smart meter terminal blocks

Abstract

The present invention discloses a method, circuit and device for detecting poor contact of the wiring terminals of a smart meter. The circuit includes a current sampling circuit, which is arranged between the incoming and outgoing wiring terminals of the live wire and the neutral wire, and is respectively connected to a pre-detection circuit and a signal conditioning circuit to collect the live wire current signal and the neutral wire current signal; the pre-detection circuit is connected to a detection chip to obtain a first high-frequency signal from the neutral wire current signal and a second high-frequency signal from the live wire current signal; the signal conditioning circuit is connected to the detection chip to adjust the live wire current signal and the neutral wire current signal to obtain the corresponding first adjustment signal and second adjustment signal; the detection chip determines whether there is a suspected arc according to the first high-frequency signal and the second high-frequency signal, and when there is a suspected arc, the first adjustment signal and the second adjustment signal are sampled to determine whether the wiring terminals are in poor contact, so that whether the terminals are loose can be found at an early stage, thereby improving the detection sensitivity and safety.

Description

Technical Field

[0001] The present invention relates to the field of electrical detection technology, and in particular to a method, circuit and device for detecting poor contact of connection terminals of a smart meter. Background Art

[0002] Cable terminals are generally made of metal materials. During use, they are subject to factors such as climate change, processing technology, and oxidation, which can easily cause loose crimping, insufficient pressure, or changes in the contact part between the contacts, causing increased contact resistance, and easily cause arcing, etc., resulting in local temperature increases during equipment operation, and even fires and burning of equipment. Daily inspections cannot frequently open the wire box to detect whether the terminal is loose offline. Therefore, loose contact of the cable head has become a loophole in power protection.

[0003] At present, the industry's online detection method for loose terminal blocks mainly uses the characteristic that the contact resistance between the loose terminal and the cable is too large, which can easily cause the contact part to heat up. The terminal temperature is detected to determine whether the terminal is loose. This method is technically difficult and cost-effective to implement, but it is necessary to arrange infrared or thermistor detection elements under the cable terminal. The processing and assembly process requirements are relatively complex, and the insulation must be strictly guaranteed. If the ceramic insulation shell of the thermistor is damaged by stress, it will cause systematic insulation damage and easily cause electric shock hazards. Secondly, the temperature measurement method is achieved by setting a terminal over-temperature threshold, which is a threshold that may cause the terminal to melt or cause a fire. It reflects long-term looseness and heating under high current. It is not easy to detect in the early stage of terminal loosening or when the line current is not large, and the sensitivity is not high.

[0004] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The main purpose of the present invention is to provide a method, circuit and device for detecting poor contact of connection terminals of a smart meter, aiming to solve the technical problem of low sensitivity and safety of online detection of connection terminals in the prior art.

[0006] To achieve the above object, the present invention provides a smart meter terminal poor contact detection circuit, the circuit comprising a current sampling circuit, a pre-detection circuit, a signal conditioning circuit and a detection chip; wherein,

[0007] The current sampling circuit is arranged between the incoming and outgoing wiring terminals of the live line and between the incoming and outgoing wiring terminals of the neutral line, and is respectively connected to the pre-detection circuit and the signal conditioning circuit, and the current sampling circuit is used to collect the live line current signal and the neutral line current signal, and send the live line current signal and the neutral line current signal to the pre-detection circuit and the signal conditioning circuit;

[0008] The pre-detection circuit is connected to the detection chip, and is used to receive the live line current signal and the neutral line current signal, and respectively obtain a first high-frequency signal with a frequency not less than a first preset threshold from the neutral line current signal and obtain a second high-frequency signal with a frequency not less than a first preset threshold from the live line current signal, so as to send the first high-frequency signal and the second high-frequency signal to the detection chip;

[0009] The signal conditioning circuit is connected to the detection chip, and is used to adjust the live line current signal and the neutral line current signal respectively, obtain the corresponding first adjustment signal and second adjustment signal, and send the first adjustment signal and the second adjustment signal to the detection chip;

[0010] The detection chip is used to determine whether there is a suspected arc based on the first high-frequency signal and the second high-frequency signal. When there is a suspected arc, the first adjustment signal and the second adjustment signal are sampled respectively to obtain the first current signal to be detected and the second current signal to be detected accordingly, and obtain the characteristic vector group in each current signal to be detected, and judge whether the connection terminal has poor contact based on the characteristic vector group.

[0011] Preferably, the current sampling circuit includes a first current sampling unit and a second current sampling unit, the pre-detection circuit includes a first pre-detection unit and a second pre-detection unit, the signal conditioning circuit includes a first signal conditioning unit and a second signal conditioning unit, and the detection chip includes a first analog-to-digital converter, a first counter, a second analog-to-digital converter, a second counter, an OR gate, and a microcontroller; wherein,

[0012] The first current sampling unit is arranged between the input and output wiring terminals of the neutral line, and is respectively connected to the first pre-detection unit and the first signal conditioning unit;

[0013] The first pre-check unit is connected to the first analog-to-digital converter;

[0014] The first signal conditioning unit is connected to the first counter;

[0015] The second current sampling unit is arranged between the incoming and outgoing wiring terminals of the live wire, and is respectively connected to the second pre-detection unit and the second signal conditioning unit;

[0016] The second pre-check unit is connected to the second analog-to-digital converter;

[0017] The second signal conditioning unit is connected to the second counter;

[0018] The first analog-to-digital converter is connected to the output end of the OR gate and the microcontroller respectively;

[0019] The second analog-to-digital converter is connected to the output end of the OR gate and the microcontroller respectively;

[0020] The first counter and the second counter are respectively connected to the input end of the OR gate.

[0021] Preferably, the first pre-check unit includes a first high-pass filter and a first comparator, and the second pre-check unit includes a second high-pass filter and a second comparator; the first high-pass filter is respectively connected to the first sampling unit, the first signal conditioning unit and the first comparator, and the first comparator is connected to the first counter; the second high-pass filter is respectively connected to the second sampling unit, the second signal conditioning unit and the second comparator, and the second comparator is connected to the second counter.

[0022] The present invention also provides a method for detecting poor contact of a smart meter terminal. The method comprises the following steps:

[0023] Obtaining neutral line current signal and live line current signal;

[0024] respectively obtaining a first high-frequency signal having a frequency not less than a first preset threshold from the neutral current signal and obtaining a second high-frequency signal having a frequency not less than a first preset threshold from the live current signal;

[0025] respectively detecting whether there is a suspected arc in the first high-frequency signal and the second high-frequency signal;

[0026] When a suspected electric arc is detected, obtaining a first current signal to be detected and a second current signal to be detected corresponding to the live line current signal and the neutral line current signal;

[0027] Obtaining a set of characteristic vectors in each current signal to be detected;

[0028] It is determined whether the connection terminal has poor contact according to the feature vector group.

[0029] Preferably, the step of respectively detecting whether there is a suspected arc in the first high-frequency signal and the second high-frequency signal comprises:

[0030] Counting the number of first high-frequency pulses in the first high-frequency signal and the number of second high-frequency pulses in the second high-frequency signal within a first preset time period;

[0031] When the first high-frequency pulse number or the second high-frequency pulse number is greater than a second preset threshold, it is determined that there is a suspected arc.

[0032] Preferably, the step of obtaining a characteristic vector group in each current signal to be detected includes:

[0033] Performing a fast Fourier transform on the first current signal to be detected and the second current signal to be detected within a second preset time, respectively, to obtain first data and second data having frequency spectrum information;

[0034] Respectively acquiring a first amplitude value and a second amplitude value corresponding to a preset frequency from the first data and the second data;

[0035] The first amplitude value and the second amplitude value are respectively vectorized to form a first feature vector group and a second feature vector group respectively.

[0036] Preferably, the step of judging whether the connection terminal has poor contact according to the characteristic vector comprises:

[0037] Calculate the square sum of the first eigenvector group and the second eigenvector group according to a preset formula;

[0038] When the square sum value is not less than the third preset threshold value, it is determined that the connection terminal has poor contact; wherein the preset formula is:

[0039]

[0040] Wherein, α is the first square sum value, n is the number of frequency points in the preset frequency, FD1 is the first eigenvector group, and FD2 is the second eigenvector group;

[0041] Or, the preset formula is:

[0042]

[0043] Wherein, α' is the second square sum value, n is the number of frequency points in the preset frequency, FD1 is the first eigenvector group, FD2 is the second eigenvector group, and K(i) is the first weighting coefficient corresponding to the i-th frequency point.

[0044] Preferably, the step of obtaining the characteristic vector in the current signal to be detected includes:

[0045] respectively performing digital bandpass filtering on the first current signal to be detected and the second current signal to be detected, and obtaining filtered third data and fourth data accordingly;

[0046] respectively calculating the effective value of the third data and the effective value of the fourth data within the second preset time;

[0047] The effective value of the third data and the effective value of the fourth data are respectively vectorized to form a third eigenvector group and a fourth eigenvector group respectively.

[0048] Preferably, the step of judging whether the connection terminal has poor contact according to the characteristic vector comprises:

[0049] Calculate the sum of squares of the third eigenvector group and the fourth eigenvector group according to a preset formula;

[0050] When the square sum value is not less than the third preset threshold value, it is determined that the connection terminal has poor contact; wherein the preset formula is:

[0051]

[0052] Wherein, β is the third square sum value, n is the number of frequency points in the preset frequency, UD1 is the third eigenvector group, and UD2 is the fourth eigenvector group;

[0053] Or, the preset formula is:

[0054]

[0055] Wherein, β' is the fourth square sum value, n is the number of frequency points in the preset frequency, UD1 is the third eigenvector group, UD2 is the fourth eigenvector group, and H(i) is the second weighting coefficient corresponding to the i-th frequency point.

[0056] The present invention also provides a smart meter terminal poor contact detection device, which includes the smart meter terminal poor contact detection circuit as described above or applies the smart meter terminal poor contact detection method as described above.

[0057] The present invention arranges a current sampling circuit between the incoming and outgoing wiring terminals of the live wire and the neutral wire, and is respectively connected to a pre-detection circuit and a signal conditioning circuit to collect the live wire current signal and the neutral wire current signal; the pre-detection circuit is connected to a detection chip to obtain a first high-frequency signal from the neutral wire current signal and a second high-frequency signal from the live wire current signal; the signal conditioning circuit is connected to the detection chip to adjust the live wire current signal and the neutral wire current signal to obtain corresponding first adjustment signals and second adjustment signals; the detection chip determines whether there is a suspected arc according to the first high-frequency signal and the second high-frequency signal, and samples the first adjustment signal and the second adjustment signal respectively when there is a suspected arc, and obtains a first current signal to be detected and a second current signal to be detected, and obtains a characteristic vector group in each current signal to be detected, and judges whether the wiring terminal has poor contact according to the characteristic vector group, so that it can be found at an early stage whether the terminal is loose, thereby improving the detection sensitivity and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0059] Figure 1 It is a functional module diagram of an embodiment of a poor contact detection circuit for smart meter terminals of the present invention;

[0060] Figure 2 This is a schematic diagram of an application scenario of an embodiment of a poor contact detection circuit for smart meter terminals of the present invention;

[0061] Figure 3 It is a structural schematic diagram of an embodiment of a poor contact detection circuit for smart meter terminals of the present invention;

[0062] Figure 4 It is a schematic diagram of the arrangement of the smart meter terminal poor contact detection circuit of the present invention applied to the smart meter;

[0063] Figure 5 It is a flow chart of an embodiment of a method for detecting poor contact of a smart meter terminal according to the present invention;

[0064] Figure 6 It is the distribution of arc high frequency characteristics with frequency when there is impedance suppression or not.

[0065] Description of Figure Numbers:

[0066] Label name Label name 100 Current sampling circuit 1 Live line L incoming line 200 Pre-check circuit 2 Live wire L outgoing line (house entrance line) 300 Signal conditioning circuit 3 Neutral line N incoming line IC Detection chip 4 Neutral line N outgoing line (household line) 110 The first current sampling unit 5 Live wire L (entry line) current sensor 120 The second current sampling unit 6 Neutral line N (entry line) current sensor 210 First pre-check unit 7 Relay 220 Second pre-check unit 8 Case

[0067] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0068] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0070] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0071] The invention provides a poor contact detection circuit for connection terminals of an intelligent electric meter.

[0072] Reference Figure 1 In one embodiment, the circuit includes a current sampling circuit 100, a pre-detection circuit 200, a signal conditioning circuit 300 and a detection chip IC; wherein the current sampling circuit 100 is arranged between the input and output wiring terminals of the live line L and between the input and output wiring terminals of the neutral line N, and is respectively connected to the pre-detection circuit 200 and the signal conditioning circuit 300, and the current sampling circuit 100 is used to collect the live line current signal and the neutral line current signal, and send the live line current signal and the neutral line current signal to the pre-detection circuit 200 and the signal conditioning circuit 300; the pre-detection circuit 200 is connected to the detection chip IC, and is used to receive the live line current signal and the neutral line current signal, and respectively obtain a first high frequency signal with a frequency not less than a first preset threshold from the neutral line current signal and a first high frequency signal from the live line current signal. A second high-frequency signal having a frequency not less than a first preset threshold is obtained to send the first high-frequency signal and the second high-frequency signal to the detection chip IC; the signal conditioning circuit 300 is connected to the detection chip IC, and is used to adjust the live current signal and the neutral current signal respectively, obtain the corresponding first adjustment signal and second adjustment signal, and send the first adjustment signal and the second adjustment signal to the detection chip IC; the detection chip IC is used to determine whether there is a suspected arc according to the first high-frequency signal and the second high-frequency signal, and when there is a suspected arc, the first adjustment signal and the second adjustment signal are sampled respectively, and the first current signal to be detected and the second current signal to be detected are correspondingly obtained, and the characteristic vector group in each current signal to be detected is obtained, and whether the connection terminal is in poor contact is determined according to the characteristic vector group.

[0073] It should be noted that there are two scenarios for loose terminals of electric meters: one is that the terminals are loose, and arcs are formed between the terminals and the cables through the air gap; the other is that the contact resistance is too large, especially in the case of point contact, which easily melts the contact points under high current, forming an air gap and thus generating arcs. This embodiment uses whether there is a suspected arc in the line as a prerequisite for judging whether the terminals are loose.

[0074] It is easy to understand that suspected arcs can be divided into three categories and appear in five locations: arcs at the meter (meter live wire L terminal, meter neutral wire N terminal), indoor arcs (indoor lines, indoor equipment wiring terminals), and indoor harmonic interference (no arc). Among them, the incoming line from the meter to the indoor house is very long. Although arcs may occur, there are strict requirements on the material and layout of the incoming line, and the probability of causing an arc is extremely low, so it is not considered here.

[0075] The effective means of detecting arcs is to use the characteristics of the high-frequency part of the current. Since arcs are not necessarily generated on the meter terminals, any loose point on the user's line may generate arcs and superimpose on the entire circuit, how to distinguish them becomes a difficult problem.

[0076] The circuit for online detection of loose terminals in this embodiment does not need to use a thermistor in the circuit, which can avoid the risk of electric shock caused by damage to the thermistor housing. At the same time, according to the inhibitory effect of line impedance on high frequency, this embodiment uses the principle that the farther the fault point is, the more serious the attenuation of the high-frequency characteristics of the arc is, and the fault point is on the meter terminal, and the high-frequency characteristics of the arc are highly complete. A current sampling circuit 100 is arranged on a group of loop start and end terminals (for example, L and N for a single-phase meter). If an arc occurs on a certain terminal, the high-frequency signals in the live wire current signal and the neutral wire current signal will be completely different. The detection chip IC determines whether the terminal is in poor contact based on the characteristics of the current signal. This method does not require a high-precision time measurement module, has good accuracy for positioning of lines of several hundred meters (it should be clarified that this positioning only refers to the ability to distinguish between arcs at the meter and arcs in the user's room), can detect loose events at an early stage, and has important practical significance.

[0077] Specifically, a pair of current sensors with the same characteristics can be arranged at the meter terminals (taking a single-phase meter as an example, the live wire L and the neutral wire N), and the high-frequency characteristics of the current can be used to determine whether there is an arc on the line. The high-frequency energy of the arc current can then be divided according to the frequency range, and a set of characteristic vectors can be obtained for the live wire L and the neutral wire N respectively. Further analysis of the characteristic vectors can be used to identify whether there is a terminal arc, that is, to determine whether the terminal has become loose.

[0078] This embodiment Figure 2The specific scenario shown can achieve better results, namely: the device equipped with the circuit is installed on the main loop of the line, and the incoming line of the device is long. Since the possibility of an arc occurring in the incoming line is extremely small, once an arc is detected, it generally occurs at the meter and in the resident's room. Due to the inhibitory effect of the line impedance on the high-frequency signal, this embodiment uses the different reactions of the high-frequency characteristics of the current when an arc occurs in the resident's room and at the meter as a basis for judgment.

[0079] The circuit described in this embodiment includes a current sampling circuit, which is arranged between the incoming and outgoing wiring terminals of the live wire and the neutral wire, and is respectively connected to the pre-detection circuit and the signal conditioning circuit to collect the live wire current signal and the neutral wire current signal; the pre-detection circuit is connected to the detection chip to obtain a first high-frequency signal from the neutral wire current signal and a second high-frequency signal from the live wire current signal; the signal conditioning circuit is connected to the detection chip to adjust the live wire current signal and the neutral wire current signal to obtain corresponding first adjustment signals and second adjustment signals; the detection chip determines whether there is a suspected arc based on the first high-frequency signal and the second high-frequency signal, and samples the first adjustment signal and the second adjustment signal when there is a suspected arc, and obtains a first current signal to be detected and a second current signal to be detected, and obtains a characteristic vector group in each current signal to be detected, and judges whether the wiring terminals are in poor contact based on the characteristic vector group, so that it can be discovered at an early stage whether the terminals are loose, thereby improving the detection sensitivity and safety.

[0080] Please refer to Figure 1 and Figure 3 Although some components in the figure are not numbered, Figure 3 The connection relationship between each component can be determined accurately and without doubt.

[0081] In this embodiment, the current sampling circuit 100 includes a first current sampling unit 110 and a second current sampling unit 120, the pre-detection circuit 200 includes a first pre-detection unit 210 and a second pre-detection unit 220, and the signal conditioning circuit 300 includes a first signal conditioning unit (not labeled) and a second signal conditioning unit (not labeled); wherein the first current sampling unit 110 is arranged between the input and output wiring terminals of the neutral line N, and is respectively connected to the first pre-detection unit 210 and the first signal conditioning unit; the first pre-detection unit 210 and the first signal conditioning unit are respectively connected to the detection chip IC; the second current sampling unit 120 is arranged between the input and output wiring terminals of the live line L, and is respectively connected to the second pre-detection unit 220 and the second signal conditioning unit; the second pre-detection unit 220 and the second signal conditioning unit are respectively connected to the detection chip IC.

[0082] In a specific implementation, the first current sampling unit 110 and the second current sampling unit 120 are a pair of current sensors with the same characteristics. The arrangement diagram of the two current sensors in the electric meter can refer to Figure 4 , the live wire L (household entry line) current sensor 5 and the neutral wire N (household entry line) current sensor are respectively arranged between the live wire L incoming line 1 and the live wire L outgoing line 2 and between the neutral wire N incoming line 3 and the neutral wire N outgoing line 4. The current sensor requires a wide measurement bandwidth and is not easy to saturate under large currents. It is preferred to use a Rogowski coil because the Rogowski coil only needs to be passed through the live wire and the neutral wire and does not need to be electrically connected to the live wire and the neutral wire, thereby achieving electrical isolation and being safer. Of course, in addition to the Rogowski coil, a sampling resistor, such as a manganese copper resistor, can also be used. Specifically, when a sampling resistor is used for current sampling, the first current sampling unit 110 is a first sampling resistor, and the second current sampling unit 120 is a second sampling resistor. The first sampling resistor is connected to the neutral wire N, and the second sampling resistor is connected to the live wire L.

[0083] Furthermore, the detection chip IC includes a first analog-to-digital converter (not marked), a first counter (not marked), a second analog-to-digital converter (not marked), a second counter (not marked), an OR gate (not marked) and a microcontroller (not marked); wherein the first analog-to-digital converter is respectively connected to the first signal conditioning unit, the output end of the OR gate and the microcontroller; the first counter is respectively connected to the first pre-detection unit 210 and the input end of the OR gate; the second analog-to-digital converter is respectively connected to the second signal conditioning unit, the output end of the OR gate and the microcontroller; the second counter is respectively connected to the second pre-detection unit 220 and the input end of the OR gate.

[0084] It should be understood that the first counter and the second counter can respectively count the number of first high-frequency pulses in the first high-frequency signal and the number of second high-frequency pulses in the second high-frequency signal within the first preset time; when the number of the first high-frequency pulses or the second high-frequency pulses is greater than the second preset threshold, it is determined that there is a suspected arc.

[0085] It should be noted that the bandwidth of the current sensor can be selected between 10 and 20 MHz, preferably 20 MHz, to capture more high-frequency components of the arc. The sampling rate of the first analog-to-digital converter and the second analog-to-digital converter is at least twice the bandwidth, that is, 20 to 40 MSPS (MSPS is one million samples per second). Since the probability of a fault arc is low, the first analog-to-digital converter and the second analog-to-digital converter continue to work at a high speed, which is a very large expense for memory resources and processor power consumption. Therefore, this embodiment designs a pre-check circuit 200 to determine whether an arc is suspected to occur in the line. At the same time, the counter outputs a control signal to the analog-to-digital converter, and the analog-to-digital converter starts sampling to reduce resource consumption.

[0086] It is easy to understand that when at least one of the live line current signal or the neutral line current signal detects a suspected arc, the first analog-to-digital converter and the second analog-to-digital converter will be started simultaneously for sampling.

[0087] It is particularly important to note that the present embodiment has a gain effect: after a suspected arc is detected, there is no need to further verify whether an arc has actually occurred (i.e., there is no need to distinguish between the interference caused by the arc and the indoor impact load, which requires additional hardware and software resource expenditures). After positioning and analyzing by the microcontroller, if the suspected arc is on the meter side, it is determined that an arc has occurred and was caused by loose terminals.

[0088] When a Rogowski coil is used, the first signal conditioning circuit includes a first auxiliary integration unit (not labeled) and a first signal amplifying unit (not labeled), and the second signal conditioning circuit includes a second auxiliary integration unit (not labeled) and a second signal amplifying unit (not labeled); wherein the first auxiliary integration unit is respectively connected to the first Rogowski coil and the first auxiliary integration unit; the first signal amplifying unit is respectively connected to the first auxiliary integration unit and the first analog-to-digital converter; the second auxiliary integration unit is respectively connected to the second Rogowski coil and the second auxiliary integration unit; and the second signal amplifying unit is respectively connected to the second auxiliary integration unit and the second analog-to-digital converter.

[0089] As another embodiment, when a sampling resistor is used, the first signal conditioning circuit includes a first boost amplifier unit (not labeled), and the second signal conditioning circuit includes a second boost amplifier unit (not labeled); wherein the first boost amplifier unit is respectively connected to the first sampling resistor and the first analog-to-digital converter; and the second boost amplifier unit is respectively connected to the second sampling resistor and the second analog-to-digital converter.

[0090] Furthermore, the first pre-check unit 210 includes a first high-pass filter (not labeled) and a first comparator (not labeled); the first high-pass filter is respectively connected to the first sampling unit, the first signal conditioning unit and the first comparator, and the first comparator is connected to the first counter. The second pre-check unit 220 includes a second high-pass filter (not labeled) and a second comparator (not labeled); the second high-pass filter is respectively connected to the second sampling unit, the second signal conditioning unit and the second comparator, and the second comparator is connected to the second counter.

[0091] This embodiment does not require a high-precision time measurement module and has good accuracy in locating lines of several hundred meters, thereby solving the positioning accuracy and application cost problems of the prior art time domain reflection fault arc locating method in the electric meter scenario.

[0092] Please refer to Figure 5 , Figure 5 It is a flow chart of an embodiment of a method for detecting poor contact of smart meter connection terminals proposed based on the poor contact detection circuit of the smart meter connection terminals of the present invention.

[0093] In this embodiment, the method for detecting poor contact of the smart meter terminal includes the following steps:

[0094] S10: Obtaining a neutral line current signal and a live line current signal;

[0095] S20: respectively obtaining a first high-frequency signal having a frequency not less than a first preset threshold from the neutral line current signal and obtaining a second high-frequency signal having a frequency not less than a first preset threshold from the live line current signal;

[0096] S30: Detecting whether there is a suspected arc in the first high-frequency signal and the second high-frequency signal respectively;

[0097] S40: acquiring a first to-be-detected current signal and a second to-be-detected current signal corresponding to the live line current signal and the neutral line current signal when a suspected arc is detected;

[0098] S50: Acquire a characteristic vector group in each current signal to be detected;

[0099] S60: Determine whether the connection terminal has poor contact according to the feature vector group.

[0100] It should be understood that since the smart meter terminal poor contact detection method of this embodiment is based on the technical solution of the above-mentioned smart meter terminal poor contact detection circuit, the smart meter terminal poor contact detection method has all the above-mentioned beneficial effects, which will not be repeated here.

[0101] Furthermore, the number of first high-frequency pulses in the first high-frequency signal and the number of second high-frequency pulses in the second high-frequency signal are counted respectively within a first preset time; when the number of the first high-frequency pulses or the number of the second high-frequency pulses is greater than a second preset threshold, it is determined that there is a suspected arc.

[0102] In a specific implementation, by counting the number of high-frequency pulses exceeding the limit (set by the counter threshold) in the first high-frequency signal and the second high-frequency signal every half power frequency cycle (such as 10ms), as long as the number of high-frequency pulses in one of the lines is greater than the second preset threshold, it can be determined that a suspected arc occurs in the line. As long as there is a suspected arc in one of the lines, the first counter and the second counter simultaneously output control signals to the first analog-to-digital converter and the second analog-to-digital converter to start sampling and obtain the first current signal to be detected and the second current signal to be detected.

[0103] By performing frequency domain analysis and positioning analysis on the first current signal to be detected and the second current signal to be detected, the location of the suspected arc can be located, thereby determining whether the arc occurs at the meter or in the resident's room, thereby determining whether the meter terminals have poor contact.

[0104] Furthermore, there are two optional ways to perform frequency domain analysis: frequency domain analysis 1-fast Fourier transform (hereinafter referred to as FFT), frequency domain analysis 2-digital bandpass filter bank.

[0105] If the FFT method is adopted, the amplitude values ​​of different frequency components can be obtained according to the results of FFT; a group of frequency points f1, f2, f3...fn are selected to form a group of characteristic vectors, with n=10 being the preferred embodiment, and f1 being the amplitude value of the 1MHz frequency point, f2 being the amplitude value of the 2MHz frequency point, and so on, and f10 being the amplitude value at 10MHz.

[0106] If the digital bandpass filter group method is selected, f1, f2, f3...fn are used as the cutoff frequencies of the digital bandpass filter, such as the upper and lower cutoff frequencies of the digital bandpass filter are f1 and f2 respectively; the upper and lower cutoff frequencies of the digital bandpass filter 2 are f2 and f3 respectively, and so on. Assuming that the analog-to-digital converter samples data once every 10ms, the effective value is calculated in units of 10ms; thus, a set of characteristic vectors can be formed, preferably n=10, and U1 is the effective value calculated every 10ms after passing through the digital bandpass filter 1 (upper cutoff frequency 2MHz, lower cutoff frequency 1MHz), and so on.

[0107] The positioning analysis is performed using the results of frequency domain analysis 1 and frequency domain analysis 2; the core idea is the suppression effect of line impedance on high frequencies. Figure 6 As shown, 1 is an ideal condition - when there is no line impedance, the arc high-frequency feature content decreases approximately linearly with increasing frequency. 2 shows that when there is line impedance, especially in the meter scenario, there is a long household line, and the arc high-frequency feature is suppressed by the impedance and decreases rapidly. That is, the distance of the fault point will affect the distribution characteristics of the high-frequency feature of the receiving end current. The farther the fault point is (arc not at the meter terminal), the more serious the attenuation of the high-frequency part. The fault point is on the meter terminal, and the integrity of the arc high-frequency feature is high. According to the different methods used in the frequency domain analysis (FFT analysis method, digital bandpass filter group method), the methods used for positioning analysis are different.

[0108] For the FFT analysis method, FFT transformation is performed on the first current signal to be detected and the second current signal to be detected within a second preset time, respectively, to obtain first data and second data with spectrum information; a first amplitude value and a second amplitude value corresponding to a preset frequency are obtained from the first data and the second data, respectively; the first amplitude value and the second amplitude value are vectorized, respectively, to form a first feature vector group FD1 and a second feature vector group FD2.

[0109] The location analysis takes the sum of the squares of the difference between the feature vectors FD1 and FD2. That is:

[0110]

[0111] Among them, α first is the square sum value, n is the number of frequency points in the preset frequency, FD1 is the first eigenvector group, and FD2 is the second eigenvector group.

[0112] By comparing α with the third preset threshold α0, if α≥α0, it means that the arc occurs at a certain terminal of the meter (live wire L or neutral wire N), that is, the terminal is loose and causes the arc.

[0113] For the sampling digital bandpass filter group method, the first current signal to be detected and the second current signal to be detected are respectively subjected to digital bandpass filtering to obtain the filtered third data and the fourth data; the effective value of the third data and the effective value of the fourth data within the second preset time are respectively calculated; the effective value of the third data and the effective value of the fourth data are respectively vectorized to form a third eigenvector group UD1 and a fourth eigenvector group UD2 accordingly.

[0114] The positioning analysis takes the sum of the squares of the differences between the feature vectors UD1 and UD2. That is:

[0115]

[0116] Wherein, β is the third square sum value, n is the number of frequency points in the preset frequency, UD1 is the third eigenvector group, and UD2 is the fourth eigenvector group.

[0117] By comparing β with the third preset threshold α0, if β≥α0, it means that the arc occurs at a certain terminal of the meter (live wire L or neutral wire N), that is, the terminal is loose and causes the arc.

[0118] There is another extended form of the above two positioning analysis methods. That is, considering that in the high-frequency characteristic components of the arc, the higher the frequency part, the less the content and the more easily it is suppressed by impedance and annihilated. Therefore, a set of weighting coefficients K = {k1, k2,... kn} (for the FFT method) and H = {h1, h2,... hn} (for the digital band-pass filter method) can be introduced. In the first weighting coefficient K, k1 < k2 <... < kn; in the second weighting coefficient H, h1 < h2 <... < hn; so that the formulas become respectively:

[0119]

[0120] Where α' is the second sum of squares value, n is the number of frequency points in the preset frequency, FD1 is the first eigenvector group, FD2 is the second eigenvector group, and K(i) is the first weighting coefficient corresponding to the i-th frequency point.

[0121]

[0122] Where β' is the fourth sum of squares value, n is the number of frequency points in the preset frequency, UD1 is the third eigenvector group, UD2 is the fourth eigenvector group, and H(i) is the second weighting coefficient corresponding to the i-th frequency point.

[0123] It should be understood that the above extended form of adding weighting coefficients or other equivalent forms also belong to the scope of this embodiment.

[0124] In this embodiment, a pair of current sensors with the same characteristics are arranged at the starting and ending positions of the electric meter loop. First, it is detected whether there is a suspected arc on the line, and then the arc is located by the difference in the high-frequency characteristic distribution of the current obtained by the two current sensors. The principle is to utilize the suppression effect of the line impedance on the high frequency, that is, the distance of the fault point will affect the distribution characteristics of the high-frequency characteristics of the current at the receiving end. When the fault point is farther away (arc at non-electric meter terminal), the high-frequency part attenuates more severely. When the fault point is on the electric meter terminal, the integrity of the arc high-frequency characteristics is high. In the existing positioning technology, it not only avoids using a high-precision timing module but also can achieve a good positioning effect in a specific environment, timely discovers the looseness of the electric meter wiring terminal, and improves the detection sensitivity and safety.

[0125] The present invention also proposes an intelligent electric meter wiring terminal poor contact detection device. The intelligent electric meter wiring terminal poor contact detection device includes the above-mentioned intelligent electric meter wiring terminal poor contact detection circuit or applies the above-mentioned intelligent electric meter wiring terminal poor contact detection method; it can be understood that since the intelligent electric meter wiring terminal poor contact detection device in this embodiment adopts the technical solutions of the above-mentioned intelligent electric meter wiring terminal poor contact detection circuit or intelligent electric meter wiring terminal poor contact detection method, the intelligent electric meter wiring terminal poor contact detection device has all the above beneficial effects.

[0126] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A smart meter terminal poor contact detection circuit, characterized in that: It includes a current sampling circuit, a pre-detection circuit, a signal conditioning circuit and a detection chip; wherein, The current sampling circuit is arranged between the incoming and outgoing wiring terminals of the live line and between the incoming and outgoing wiring terminals of the neutral line, and is respectively connected to the pre-detection circuit and the signal conditioning circuit, and the current sampling circuit is used to collect the live line current signal and the neutral line current signal, and send the live line current signal and the neutral line current signal to the pre-detection circuit and the signal conditioning circuit; The pre-detection circuit is connected to the detection chip, and is used to receive the live line current signal and the neutral line current signal, and respectively obtain a first high-frequency signal with a frequency not less than a first preset threshold from the neutral line current signal and a second high-frequency signal with a frequency not less than a first preset threshold from the live line current signal, so as to send the first high-frequency signal and the second high-frequency signal to the detection chip; The signal conditioning circuit is connected to the detection chip, and is used to adjust the live line current signal and the neutral line current signal respectively, obtain the corresponding first adjustment signal and second adjustment signal, and send the first adjustment signal and the second adjustment signal to the detection chip; The detection chip is used to determine whether there is a suspected arc according to the first high-frequency signal and the second high-frequency signal, and when there is a suspected arc, the first adjustment signal and the second adjustment signal are sampled respectively to obtain a first current signal to be detected and a second current signal to be detected, and obtain a characteristic vector group in each current signal to be detected, and judge whether the connection terminal has poor contact according to the characteristic vector group; The current sampling circuit includes a first current sampling unit and a second current sampling unit, the pre-detection circuit includes a first pre-detection unit and a second pre-detection unit, the signal conditioning circuit includes a first signal conditioning unit and a second signal conditioning unit, and the detection chip includes a first analog-to-digital converter, a first counter, a second analog-to-digital converter, a second counter, an OR gate, and a microcontroller; wherein, The first current sampling unit is arranged between the input and output wiring terminals of the neutral line, and is respectively connected to the first pre-detection unit and the first signal conditioning unit; The first pre-check unit is connected to the first analog-to-digital converter; The first signal conditioning unit is connected to the first counter; The second current sampling unit is arranged between the incoming and outgoing wiring terminals of the live wire, and is respectively connected to the second pre-detection unit and the second signal conditioning unit; The second pre-check unit is connected to the second analog-to-digital converter; The second signal conditioning unit is connected to the second counter; The first analog-to-digital converter is connected to the output end of the OR gate and the microcontroller respectively; The second analog-to-digital converter is connected to the output end of the OR gate and the microcontroller respectively; The first counter and the second counter are respectively connected to the input end of the OR gate.

2. The smart meter terminal poor contact detection circuit according to claim 1, characterized in that: The first pre-check unit includes a first high-pass filter and a first comparator, and the second pre-check unit includes a second high-pass filter and a second comparator; the first high-pass filter is respectively connected to the first sampling unit, the first signal conditioning unit and the first comparator, and the first comparator is connected to the first counter; the second high-pass filter is respectively connected to the second sampling unit, the second signal conditioning unit and the second comparator, and the second comparator is connected to the second counter.

3. A method for detecting poor contact of smart meter terminals, characterized in that: The method comprises the following steps: Obtaining neutral line current signal and live line current signal; respectively obtaining a first high-frequency signal having a frequency not less than a first preset threshold from the neutral current signal and obtaining a second high-frequency signal having a frequency not less than a first preset threshold from the live current signal; respectively detecting whether there is a suspected arc in the first high-frequency signal and the second high-frequency signal; When a suspected electric arc is detected, obtaining a first current signal to be detected and a second current signal to be detected corresponding to the live line current signal and the neutral line current signal; Obtaining a set of characteristic vectors in each current signal to be detected; It is determined whether the connection terminal has poor contact according to the feature vector group.

4. The method for detecting poor contact of smart meter terminals according to claim 3, characterized in that: The step of respectively detecting whether there is a suspected arc in the first high-frequency signal and the second high-frequency signal comprises: Counting the number of first high-frequency pulses in the first high-frequency signal and the number of second high-frequency pulses in the second high-frequency signal within a first preset time period; When the first high-frequency pulse number or the second high-frequency pulse number is greater than a second preset threshold, it is determined that there is a suspected arc.

5. The method for detecting poor contact of smart meter terminals according to claim 4, characterized in that: The step of obtaining the characteristic vector group in each current signal to be detected includes: Performing a fast Fourier transform on the first current signal to be detected and the second current signal to be detected within a second preset time, respectively, to obtain first data and second data having frequency spectrum information; Respectively acquiring a first amplitude value and a second amplitude value corresponding to a preset frequency from the first data and the second data; The first amplitude value and the second amplitude value are respectively vectorized to form a first feature vector group and a second feature vector group respectively.

6. The method for detecting poor contact of smart meter terminals according to claim 5, characterized in that: The step of judging whether the connection terminal has poor contact according to the characteristic vector comprises: Calculate the square sum of the first eigenvector group and the second eigenvector group according to a preset formula; When the square sum value is not less than the third preset threshold value, it is determined that the connection terminal has poor contact; wherein the preset formula is: ； in, is the first square sum value, n is the number of frequency points in the preset frequency, FD1 is the first eigenvector group, and FD2 is the second eigenvector group; Or, the preset formula is: ； in, is the second square sum value, n is the number of frequency points in the preset frequency, FD1 is the first eigenvector group, FD2 is the second eigenvector group, and K(i) is the first weighting coefficient corresponding to the i-th frequency point.

7. The method for detecting poor contact of smart meter terminals according to claim 4, characterized in that: The step of obtaining the characteristic vector in the current signal to be detected includes: respectively performing digital bandpass filtering on the first current signal to be detected and the second current signal to be detected, and obtaining filtered third data and fourth data accordingly; respectively calculating the effective value of the third data and the effective value of the fourth data within the second preset time; The effective value of the third data and the effective value of the fourth data are respectively vectorized to form a third eigenvector group and a fourth eigenvector group respectively.

8. The method for detecting poor contact of smart meter terminals according to claim 7, characterized in that: The step of judging whether the connection terminal has poor contact according to the characteristic vector comprises: Calculate the sum of squares of the third eigenvector group and the fourth eigenvector group according to a preset formula; When the square sum value is not less than the third preset threshold, it is determined that the connection terminal has poor contact; wherein, The preset formula is: ； in, is the third square sum value, n is the number of frequency points in the preset frequency, UD1 is the third eigenvector group, and UD2 is the fourth eigenvector group; Or, the preset formula is: ； in, is the fourth square sum value, n is the number of frequency points in the preset frequency, UD1 is the third eigenvector group, UD2 is the fourth eigenvector group, and H(i) is the second weighting coefficient corresponding to the i-th frequency point.

9. A device for detecting poor contact of smart meter terminals, characterized in that: The invention comprises a smart meter terminal poor contact detection circuit as claimed in any one of claims 1 to 2, or applies a smart meter terminal poor contact detection method as claimed in any one of claims 3 to 8.

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