A small-signal direct current leakage detection method and system

Abstract

The application discloses a small-signal DC leakage current detection method and system, relates to the technical field of leakage current detection, and comprises the following steps: firstly, collecting AC-DC mixed frequency signals and performing pretreatment; secondly, separating AC mixed frequency interference signals and DC leakage current signals from the pretreated data; finally, performing AC filtering and quantization processing on the AC mixed frequency interference signals to obtain AC mixed frequency interference standard signals, and performing DC filtering and quantization processing on the DC leakage current signals to obtain DC leakage current standard signals; the scheme is based on the magnetic flux gate technology to realize AC-DC mixed frequency signal collection, and then uses digital filtering technology to extract the measured AC-DC signals respectively, finally, converts the extracted DC pulse width signals into analog voltage signals through a DAC conversion circuit to output, and realizes mA-level DC small-signal leakage current detection.

Description

Technical Field

[0001] This invention relates to the field of leakage current detection technology, specifically to a small-signal DC leakage current detection method and system. Background Technology

[0002] Currently, there are many mA-level DC leakage current detection technologies on the market, but the signal bandwidth can generally only reach about 2kHz. When there are A-level AC harmonic interference signals on the signal line, the accuracy of DC leakage current detection will drop significantly, eventually leading to false alarms in the DC leakage current detection system. Summary of the Invention

[0003] The technical problem to be solved by this invention is that interference from AC mixed current signals in the field leads to inaccurate detection of DC leakage current signals, and the signal bandwidth is limited. The purpose of this invention is to provide a method and system for detecting small-signal DC leakage current. It is based on fluxgate technology to acquire AC and DC mixed signals, then uses digital filtering technology to extract the AC and DC signals to be measured, and finally converts the extracted DC pulse width signal into an analog voltage signal output through a DAC conversion circuit to achieve mA-level DC small-signal leakage current detection.

[0004] This invention is achieved through the following technical solution:

[0005] This solution provides a small-signal DC leakage current detection method, including:

[0006] Step 1: Acquire AC / DC mixing signals and perform preprocessing; the AC / DC mixing signals are AC mixing interference current signals and DC leakage current signals;

[0007] Step 2: Separate the AC mixing interference signal and the DC leakage signal from the preprocessed data;

[0008] Step 3: Perform AC filtering and quantization processing on the AC mixing interference signal to obtain the AC mixing interference standard signal, and perform DC filtering and quantization processing on the DC leakage current signal to obtain the DC leakage current standard signal.

[0009] The working principle of this solution is as follows: Interference from the AC mixing current signal in the field leads to inaccurate detection of the DC leakage current signal, and the signal bandwidth is limited. The purpose of this invention is to provide a small-signal DC leakage current detection method and system. It uses fluxgate technology to acquire AC / DC mixing signals, then employs digital filtering technology to extract the AC / DC signals to be measured, and finally converts the extracted DC pulse width signal into an analog voltage signal output via a DAC conversion circuit, achieving mA-level DC small-signal leakage current detection.

[0010] This scheme utilizes fluxgate technology to acquire the output AC / DC mixed voltage signal, which is then sampled at high speed by the CPU's internal ADC mechanism. The sampled raw data undergoes spectral leakage compensation, and then enters the IIR's elliptic filter for digital filtering. After that, it is processed by the DC and AC branches respectively to obtain the DC leakage standard signal and the AC mixing interference standard signal.

[0011] To eliminate interference from AC mixing current signals and improve the accuracy of DC leakage current signal detection, the acquisition equipment uses fluxgate technology to acquire AC and DC mixing signals. Digital filtering technology is then used to extract the measured AC and DC signals separately. Finally, a DAC conversion circuit converts the extracted DC pulse width signal into an analog voltage signal for output. Testing personnel determine the magnitude of DC leakage current (i.e., AC mixing interference) based on the DC leakage current standard signal and the AC mixing interference standard signal.

[0012] Traditional DC leakage current detection methods cannot achieve detection with a wide bandwidth (such as 25kHz). This solution proposes a new technical concept: to achieve detection with a bandwidth of more than 25kHz by high-speed sampling and AC / DC separation processing, laying the foundation for small signal DC leakage current detection methods.

[0013] A further optimized solution involves acquiring AC / DC mixed signals based on fluxgate magnetometer technology. Electromagnetic induction technology is used to detect the presence of leakage current in the circuit, eliminating the need to apply the detection device directly to the operating circuit and simplifying the detection process.

[0014] A further optimized solution is that the preprocessing includes the following steps:

[0015] The original data is obtained by high-speed sampling of the AC / DC mixed signal;

[0016] The original data is compensated for spectral leakage, and the compensated original data is then input into the elliptic filter of the IIR for digital filtering.

[0017] A further optimized solution is that both the DC leakage current standard signal and the AC mixing interference standard signal are analog voltage signals of 0-5V.

[0018] A further optimization solution is to use a high-speed Cortex-M7 core CPU for system sampling, and to use a high-speed ADC inside the CPU.

[0019] A further optimized solution is that the DC filter quantization processing includes the following steps:

[0020] T1 sequentially applies a Sinc4 filter, a first RC low-pass filter, a second elliptic filter, and a second RC low-pass filter to obtain the DC signal L. The Sinc4 filter can obtain the signal required by the DC channel under complex mixed signal input conditions. The first RC low-pass filter removes high-frequency noise from the modulator output.

[0021] T2, the DC signal L is normalized to obtain the DC leakage current standard signal.

[0022] A further optimized solution is that the filtering in step T1 follows the following:

[0023] y[k]=a×(y[k-1]-x[k])+x[k]

[0024] a is the filtering coefficient, k is the filtering position, x[k] is the original value of the input signal, y[k] is the filtered output value, and y[k-1] is the output value after the previous filtering.

[0025] The further optimized solution includes the following process for AC filtering and quantization:

[0026] AC mixing interference signal The fundamental and harmonic values ​​were separated by FFT radix-4 calculation: The results after FFT calculation are as follows:

[0027]

[0028] in,

[0029]

[0030] k represents the harmonic order, and N represents the number of sampling points in one period of the signal. a represents the DC component of the signal. k This represents the formula for calculating the real part of a complex number using the radix-4 FFT, b. k This represents the formula for calculating the imaginary part of the complex number in the radix-4 FFT, where u represents the signal phase.

[0031] The amplitude of the AC signal is calculated based on the fundamental and harmonic values:

[0032] The amplitude of the AC mixing interference signal is normalized to obtain the AC mixing interference standard signal.

[0033] A further optimized solution is to output the standard signal for AC mixing interference as follows:

[0034] PWM_I AC =(I AC_SAMPLE -I AC_CALIB_ZERO )*10000 / (I AC_CALIB_FULL -IAC_CALIB_ZERO )

[0035] in:

[0036] PWM_I AC This indicates the output value of AC mixing interference current, with a resolution of 0.01%.

[0037] I AC_SAMPLE This represents the real-time sampled per-unit value of the AC mixing interference current;

[0038] I AC_CALIB_FULL This indicates the positive full-scale calibration value of the AC mixing interference current signal;

[0039] I AC_CALIB_ZERO This indicates the zero-point calibration value of the AC mixing interference current signal;

[0040] The standard DC leakage current signal output is:

[0041] PWM_I DC =(I DC_SAMPLE -I DC_CALIB_ZERO )*10000 / (I DC_CALIB_FULL -I DC_CALIB_ZERO )

[0042] in:

[0043] PWM_I DC DC leakage current output value, resolution 0.01%;

[0044] I DC_SAMPLE Real-time sampling of DC leakage current at per-unit values;

[0045] I DC_CALIB_FULL DC leakage current signal positive full-scale calibration value;

[0046] I DC_CALIB_ZERO DC leakage current signal zero-point calibration value.

[0047] This solution also provides a small-signal DC leakage current detection system for implementing the small-signal DC leakage current detection method described above, including:

[0048] The acquisition module acquires and preprocesses AC / DC mixed signals; the AC / DC mixed signals are AC mixing interference current signals and DC leakage current signals; the acquisition module is a fluxgate acquisition device.

[0049] The preprocessing module is used to separate the AC mixing interference signal and the DC leakage signal from the preprocessed data;

[0050] The detection module is used to perform AC filtering and quantization processing on the AC mixing interference signal to obtain the AC mixing interference standard signal, and to perform DC filtering and quantization processing on the DC leakage current signal to obtain the DC leakage current standard signal.

[0051] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0052] This invention provides a method and system for detecting small-signal DC leakage current. It uses fluxgate technology to acquire AC / DC mixed signals, then employs digital filtering technology to extract the AC / DC signals to be measured. Finally, a DAC conversion circuit converts the extracted DC pulse width signal into an analog voltage signal for output, achieving mA-level small-signal DC leakage current detection. Traditional DC leakage current detection methods cannot achieve detection with a wide bandwidth (e.g., 25kHz). This solution proposes a new technical concept: achieving detection with a bandwidth exceeding 25kHz through high-speed sampling and AC / DC separation processing, laying the foundation for small-signal DC leakage current detection methods. Attached Figure Description

[0053] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0054] In the attached diagram:

[0055] Figure 1 This is a schematic diagram of a small-signal DC leakage current detection method.

[0056] Figure 2 Here is a block diagram of the overall scheme for a small-signal DC leakage current detection system;

[0057] Figure 3 A digital filtering processing scheme;

[0058] Figure 4 A high-speed sampling scheme for a small-signal DC leakage current detection system;

[0059] Figure 5 To simulate interference signal waveforms;

[0060] Figure 6 This is the output waveform after simulation. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0062] The interference of AC mixing current signals in the field leads to inaccurate detection of DC leakage current signals, and also limits the signal bandwidth. To eliminate this interference and improve the accuracy of DC leakage current signal detection, this invention provides the following embodiments:

[0063] This solution uses fluxgate technology to acquire AC / DC mixed signals, then uses digital filtering technology to extract the measured AC / DC signals, and finally uses a DAC conversion circuit to convert the extracted DC pulse width signal into an analog voltage signal for output.

[0064] Example 1

[0065] This embodiment provides a method for detecting small-signal DC leakage current, such as... Figure 1 As shown, it includes:

[0066] Step 1: Acquire AC / DC mixed signals and perform preprocessing;

[0067] Step 2: Separate the AC mixing interference signal and the DC leakage signal from the preprocessed data;

[0068] Step 3: Perform AC filtering and quantization processing on the AC mixing interference signal to obtain the AC mixing interference standard signal, and perform DC filtering and quantization processing on the DC leakage current signal to obtain the DC leakage current standard signal.

[0069] The acquisition of AC / DC mixed signals is achieved based on fluxgate technology.

[0070] The preprocessing includes the following steps:

[0071] The original data is obtained by high-speed sampling of the AC / DC mixed signal;

[0072] The original data is compensated for spectral leakage, and the compensated original data is then input into the elliptic filter of the IIR for digital filtering.

[0073] Both the DC leakage current standard signal and the AC mixing interference standard signal are analog voltage signals of 0-5V.

[0074] The system samples from a high-speed Cortex-M7 core CPU, and the ADC uses an internal high-speed ADC within the CPU.

[0075] The DC filtering quantization process includes the following steps:

[0076] T1, the DC signal is obtained by sequentially applying a Sinc4 filter, a first RC low-pass filter, a second elliptic filter, and a second RC low-pass filter to the DC signal;

[0077] T2, the DC signal L is normalized to obtain the DC leakage current standard signal.

[0078] The filtering in step T1 follows the following:

[0079] y[k]=a×(y[k-1]-x[k])+x[k]

[0080] a is the filtering coefficient, k is the filtering position, x[k] is the original value of the input signal, y[k] is the filtered output value, and y[k-1] is the output value after the previous filtering.

[0081] The AC filtering and quantization process includes the following steps:

[0082] AC mixing interference signal The fundamental and harmonic values ​​were separated by FFT radix-4 calculation: The results after FFT calculation are as follows:

[0083]

[0084] in,

[0085]

[0086] k represents the harmonic order, and N represents the number of sampling points in one period of the signal. a represents the DC component of the signal. k This represents the formula for calculating the real part of a complex number using the radix-4 FFT, b. k This represents the formula for calculating the imaginary part of the complex number in the radix-4 FFT, where u represents the signal phase.

[0087] The amplitude of the AC signal is calculated based on the fundamental and harmonic values:

[0088] The amplitude of the AC mixing interference signal is normalized to obtain the AC mixing interference standard signal.

[0089] The standard signal output for AC mixing interference is:

[0090] PWM_I AC =(I AC_SAMPLE -I AC_CALIB_ZERO )*10000 / (I AC_CALIB_FULL -I AC_CALIB_ZERO )

[0091] in:

[0092] PWM_I AC The output value is the AC mixing interference current, with a resolution of 0.01%.

[0093] I AC_SAMPLE The per-unit value is used for real-time sampling of AC mixing interference current;

[0094] I AC_CALIB_FULL This is the positive full-value calibration value for the AC mixing interference current signal;

[0095] I AC_CALIB_ZERO This is the zero-point calibration value for the AC mixing interference current signal;

[0096] The standard DC leakage current signal output is:

[0097] PWM_I DC =(I DC_SAMPLE -I DC_CALIB_ZERO )*10000 / (I DC_CALIB_FULL -I DC_CALIB_ZERO );

[0098] in:

[0099] PWM_I DC DC leakage current output value, resolution 0.01%;

[0100] I DC_SAMPLE Real-time sampling of DC leakage current at per-unit values;

[0101] I DC_CALIB_FULL DC leakage current signal positive full-scale calibration value;

[0102] I DC_CALIB_ZERO DC leakage current signal zero-point calibration value.

[0103] This embodiment first acquires and preprocesses AC / DC mixed signals; then, it separates AC mixed interference signals and DC leakage signals from the preprocessed data; finally, it performs AC filtering and quantization on the AC mixed interference signals to obtain AC mixed interference standard signals, and performs DC filtering and quantization on the DC leakage signals to obtain DC leakage current standard signals. This scheme uses fluxgate technology to acquire AC / DC mixed signals, then uses digital filtering technology to extract the AC and DC signals to be measured, and finally converts the extracted DC pulse width signals into analog voltage signals for output via a DAC conversion circuit, realizing mA-level DC small signal leakage current detection.

[0104] Example 2

[0105] This embodiment provides a small-signal DC leakage current detection system for implementing the small-signal DC leakage current detection method described in Embodiment 1, including:

[0106] The acquisition module is used to acquire AC / DC mixed signals and perform preprocessing; the acquisition module is a fluxgate acquisition device.

[0107] The preprocessing module is used to separate the AC mixing interference signal and the DC leakage signal from the preprocessed data;

[0108] The detection module performs AC filtering and quantization on the AC mixing interference signal to obtain the AC mixing interference standard signal, and performs DC filtering and quantization on the DC leakage current signal to obtain the DC leakage current standard signal. The workflow of the small-signal DC leakage current detection system is as follows: Figure 2 As shown. In order to eliminate the interference of AC mixed current signal on site and improve the detection accuracy of DC leakage current signal, the sensor adopts fluxgate technology to realize the acquisition of AC and DC mixed signals, and then uses digital filtering technology to extract the measured AC and DC signals respectively. Finally, the extracted DC pulse width signal is converted into an analog voltage signal output by a DAC conversion circuit.

[0109] Digital filtering technology is used to extract AC / DC mixed signals separately, such as... Figure 3 As shown, the AC / DC mixed voltage signal acquired using fluxgate technology is sampled at high speed by the CPU's internal ADC (>50kHz). The raw data is then compensated for spectral leakage and digitally filtered by the IIR elliptic filter before being processed by the DC and AC branches respectively.

[0110] The system samples from a high-speed Cortex-M7 core CPU, and the ADC uses the CPU's internal high-speed ADC to achieve a 25kHz bandwidth. Figure 4 As shown, the original signal is sampled at high speed using a 16-bit high-speed ADC (16-bit ADC: 3.6 MSPS). The ADC sampling frequency is 50 * 1024 = 51.2 kHz. This reduces the noise in the sampled data. Each original data is oversampled by 256 times. Based on the original signal sampling period, 1024 original data (AC mixing interference signal and DC leakage signal) are obtained.

[0111] DC current shunting:

[0112] The raw data (DC signal) is filtered by IIR data filtering, and then filtered by a Sinc4 filter. This allows the DC channel to obtain the signal required under complex mixed signal input conditions. Then, the data is subjected to a first RC low-pass filter to remove high-frequency noise from the modulator output. The data is then subjected to a second elliptic filter, followed by a second RC low-pass filter to obtain the DC signal. The obtained data is then normalized and finally output as a PWM signal.

[0113] LPC filtering formula:

[0114] y[k]=a×(y[k-1]-x[k])+x[k].

[0115] AC current shunting: After the raw data is filtered by IIR, the filtered data is processed by FFT radix-4 (1024 points) to separate the fundamental and harmonic values ​​of the signal. Further calculations are then performed, and the obtained data is normalized before final PWM output. This technology can accurately detect small-signal DC leakage current under Class A AC mixing interference conditions with a signal bandwidth of 25kHz and an order of 512.

[0116] Alternating current shunting:

[0117] The on-site mixing interference current signal can be expressed as:

[0118]

[0119] The signal is sampled at high speed by an ADC, and the original data (AC signal) can be represented by FFT after processing:

[0120]

[0121] in, AC mixing interference signal amplitude:

[0122]

[0123] The final output DC leakage current standard signal and AC mixing interference standard signal are both 0-5V analog voltage signals.

[0124] Example 4

[0125] This embodiment uses MATLAB to simulate the original DC 150mA signal and the AC mixing interference signal as a fundamental frequency of 1000mA with each harmonic content of 100mA. The frequency points of the original signal are as follows: The unit of the data in TABLE is Hz. The design distribution of the interference signal frequency points is shown below:

[0126] TABLE=[50,100,150,200,250,300,350,400,450,500,550,600,650,700,

[0127] 4000, 4050, 4100, 4150, 4200, 4250, 4300, 4350, 4400, 4450, 4500, 4550, 4600, 4650, 4700, 4750, 4800, 4850, 4900, 4950, 5000, 5050]

[0128] The waveform of the simulated AC mixing interference signal is shown below. Figure 5 The waveform is close to the interference waveform at the scene.

[0129] The waveform after digital filtering is shown below. Figure 6 The output is approximately 146.4 mA, with an actual error of less than 3%.

[0130] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. Those skilled in the art will understand that all or part of the steps in the above-described facts and methods can be implemented by a program instructing related hardware, and the program involved, or the program described, can be stored in a computer-readable storage medium. When executed, the program includes the following steps: [The text then describes the corresponding method steps, and the storage medium can be ROM / RAM, magnetic disk, optical disk, etc.].

[0131] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0132] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting small-signal DC leakage current, characterized in that, include: Step 1: Acquire AC / DC mixed signals and perform preprocessing; The AC / DC mixing signal consists of an AC mixing interference current signal and a DC leakage current signal; the preprocessing includes the following steps: The original data is obtained by high-speed sampling of the AC / DC mixed signal; Spectral leakage compensation is performed on the original data, and the compensated original data is then input into the elliptic filter of the IIR for digital filtering. Step 2: Separate the AC mixing interference signal and the DC leakage signal from the preprocessed data; Step 3: Perform AC filtering and quantization processing on the AC mixing interference signal to obtain the AC mixing interference standard signal, and perform DC filtering and quantization processing on the DC leakage current signal to obtain the DC leakage current standard signal; The DC filtering quantization process includes the following steps: T1, the DC signal is obtained by sequentially applying a Sinc4 filter, a first RC low-pass filter, a second elliptic filter, and a second RC low-pass filter to the DC signal; T2, the DC signal L is normalized to obtain the DC leakage current standard signal; The AC filtering quantization process includes the following steps: AC mixing interference signal The fundamental and harmonic values ​​were separated by FFT radix-4 calculation: After FFT calculation, the following results were obtained: ； in, ， ； k represents the harmonic order, and N represents the number of sampling points in one period of the signal. Represents the DC component of the signal. This represents the formula for calculating the real part of a complex number using the radix-4 FFT. This represents the formula for calculating the imaginary part of the complex number in the radix-4 FFT, where u represents the signal phase; The amplitude of the AC signal is calculated based on the fundamental and harmonic values: ; The amplitude of the AC mixing interference signal is normalized to obtain the AC mixing interference standard signal.

2. The small-signal DC leakage current detection method according to claim 1, characterized in that, The acquisition of AC / DC mixed signals is achieved based on fluxgate technology.

3. The small-signal DC leakage current detection method according to claim 1, characterized in that, The DC leakage current standard signal and the AC mixing interference signal output are both analog voltage signals of 0-5V.

4. The small-signal DC leakage current detection method according to claim 1, characterized in that, The system samples from a high-speed Cortex-M7 core CPU, and the ADC uses a high-speed ADC built into the CPU.

5. The method for detecting small-signal DC leakage current according to claim 1, characterized in that, The filtering in T1 follows: Where a is the filtering coefficient, k is the filtering position, x[k] is the original value of the input signal, y[k] is the filtered output value, and y[k-1] is the output value after the previous filtering.

6. The small-signal DC leakage current detection method according to claim 1, characterized in that, The AC mixing interference signal output is: ； in: The output value is the AC mixing interference current, with a resolution of 0.01%. Real-time sampling of the per-unit value of AC mixing interference current; This is the positive full-value calibration value for the AC mixing interference current signal; This is the zero-point calibration value for the AC mixing interference current signal; The standard DC leakage current signal output is: ； in: DC leakage current output value, resolution 0.01%; Real-time sampling of DC leakage current at per-unit values; DC leakage current signal positive full-scale calibration value; DC leakage current signal zero-point calibration value.

7. A small-signal DC leakage current detection system, characterized in that, The method for implementing the small-signal DC leakage current detection method according to any one of claims 1-6 includes: The acquisition module is used to acquire AC / DC mixed signals and perform preprocessing; the AC / DC mixed signals are AC mixing interference current signals and DC leakage current signals; the acquisition module is a fluxgate acquisition device; The preprocessing module is used to separate the AC mixing interference signal and the DC leakage signal from the preprocessed data; The detection module is used to perform AC filtering and quantization processing on the AC mixing interference signal to obtain the AC mixing interference standard signal, and to perform DC filtering and quantization processing on the DC leakage current signal to obtain the DC leakage current standard signal.

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