CN111562533B - Method for testing attenuation time constant of integration loop of acquisition unit - Google Patents
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Abstract
The embodiment of the application provides a method for testing the attenuation time constant of an integration loop of an acquisition unit, which comprises the steps of generating an alternating current and direct current superposition test waveform at an upper computer, and processing data of the alternating current and direct current superposition test waveform to obtain a small-voltage analog signal; acquiring an optical fiber digital signal output by an integration loop of the acquisition unit, and testing by combining a small-voltage analog signal to obtain an alternating current-direct current transmission ratio; and calculating the attenuation time constant based on the AC/DC transmission/transformation ratio. The test is carried out by adopting the alternating current and direct current superposition synchronous output mode, so that the influence of discrete test errors on the accuracy of the test result can be avoided while the test result is obtained.
Description
Technical Field
The application belongs to the field of electronic transformer detection, and particularly relates to a method for testing an attenuation time constant of an integration loop of a collecting unit.
Background
At present, an intelligent transformer substation or a digital transformer substation is mainly used for power grid construction, and the main technical characteristic of the intelligent transformer substation or the digital transformer substation is primary equipment intellectualization, so that an electronic transformer is a main intelligent primary equipment for future intelligent transformer substation construction.
The transient state transmission error current of the electronic transformer is mainly determined by a system attenuation constant and an integral loop attenuation constant, and only when T is b ＞＞T a The transient error caused by the integration loop can be ignored. So the decay time constant T of the integration loop b Is a main index for determining the transient characteristic of the electronic current transformer based on the Rogowski coil principle. But the integration loop is designed inside the acquisition unit and cannot be obtained through a separate test.
Disclosure of Invention
In order to solve the defects and shortcomings in the prior art, the method for testing the attenuation time constant of the integration loop of the acquisition unit is provided, the test is carried out in an alternating current-direct current superposition synchronous output mode, the test result is obtained, and meanwhile the influence of discrete test errors on the accuracy of the test result can be avoided.
Specifically, the method for testing the decay time constant of the integration loop of the acquisition unit provided by this embodiment includes:
generating an alternating current and direct current superposition test waveform at an upper computer, and processing data of the alternating current and direct current superposition test waveform to obtain a small-voltage analog signal;
acquiring an optical fiber digital signal output by an integration loop of the acquisition unit, and testing by combining a small-voltage analog signal to obtain an alternating current-direct current transmission ratio;
and calculating the attenuation time constant based on the AC/DC transmission/transformation ratio.
Optionally, an alternating current-direct current superposition test waveform is generated at the upper computer, and data of the alternating current-direct current superposition test waveform are processed to obtain a small-voltage analog signal, including:
setting preset parameters of alternating current amplitude, angular frequency and direct current voltage value at the upper computer, and generating an alternating current and direct current superposition test waveform based on the preset parameters;
and carrying out discretization processing on the data of the alternating current-direct current superposition test waveform, and carrying out D/A conversion to obtain a small-voltage analog signal.
Optionally, the host computer department sets up the preset parameter of alternating current amplitude, angular frequency and direct current voltage value, generates the alternating current-direct current stack test waveform based on preset parameter, includes:
based on a formula, generating a function expression of the AC/DC superposed test waveform,
v(t)＝U m sin(ωt)+U 0 according to the formula I, the first step is that,
in the formula, v (t) is the output amplitude of the AC/DC superimposed test waveform, U m Is an alternating current amplitude, omega is an angular frequency, the calculation expression is omega =2 pi f, f is an alternating current frequency, U 0 Is a DC value, and U is used for testing to prevent testing error caused by DC overflow after integration 0 Less than 10mV.
Optionally, the discretization processing is performed on the data of the alternating current-direct current superposition test waveform, and a small-voltage analog signal is obtained after the D/a conversion, including:
the data of the alternating current-direct current superposition test waveform is subjected to discretization processing as shown in a formula II,
v(n)＝v(nT s )＝U m sin(ωnT s )+U 0 in the formula II, the first step is carried out,
where v (n) is the discretized output result, T s For discretized sampling isolation time, the value range of n is a positive integer, U m Is the AC amplitude, omega is the angular frequency, U 0 Is a dc value.
Optionally, acquiring the optical fiber digital signal output by the acquisition unit integrating loop, combining with the small voltage analog signal to test, and obtaining the ac/dc transmission/transformation ratio includes:
collecting a small-voltage analog signal and an optical fiber digital signal from a test sample by adopting an FPGA chip;
respectively extracting alternating current and direct current signals from a standard signal and a signal to be detected comprising the acquired optical fiber digital signal and the small voltage analog signal;
respectively calculating the transmission ratio k of the DC signals according to the extraction results 1 Transmission ratio k to AC signal 2 。
Optionally, the method further includes:
after the FPGA chip is adopted to collect the small-voltage analog signal and the optical fiber digital signal from the test article, the alternating current frequency f is calculated by a fundamental wave frequency measurement method based on an FFT algorithm.
Optionally, respectively, performing ac/dc signal extraction on the standard signal and the signal to be measured including the collected optical fiber digital signal and the small voltage analog signal includes:
after frequency measurement, hanning window processing is respectively carried out on the standard signal and the signal to be measured, fourier transform is carried out on a windowing sequence, and the amplitude and the phase of an alternating current signal are obtained;
and extracting time window data of the direct current component based on the alternating current signal, and adopting generalized polynomial fitting to calculate the amplitude of the direct current component to eliminate harmonic signals and noise influence.
Optionally, the transmission ratio k of the dc signal is calculated according to the extraction result 1 Transmission ratio k to AC signal 2 The method comprises the following steps:
obtaining a transmission calculation formula on a direct current frequency domain and an alternating current frequency domain:
direct current transmission ratio k 1 ，k 1 ＝R 2 /R 1 ，
Ratio k of AC transmission 2 ，k 2 ≈1/ωC/R 1 ≈1/ωCR 1 ，
Where C is the capacitance of the integrating output capacitor and R 1 For the resistance value, R, connected to the integrating output capacitor in a lossy integrator circuit 2 The resistance value of the lossy integrator circuit connected in parallel to the integrating output capacitor is ω, which is the angular frequency.
Optionally, the calculating a decay time constant based on the ac/dc transmission/transformation ratio includes:
transmission ratio k based on direct current signal 1 Transmission ratio k to AC signal 2 Calculating the decay time constant by combining the formula III,
T b ＝RC≈k 1 /ωk 2 ≈k 1 /2πfk 2 in the formula three, the first step is to use,
in the formula, T b Is the decay time constant of the integration loop, C is the capacitance of the loop integration capacitor, k 1 Is a direct current transformation ratio, k 2 The ratio of the AC transmission to the transformation, f is the AC frequency, and omega is the angular frequency.
The beneficial effect that technical scheme that this application provided brought is:
the test is carried out by adopting an alternating current and direct current superposition synchronous output mode, so that the influence of discrete test errors on the accuracy of a test result is avoided. Meanwhile, the test waveform is generated and then discretized, so that discrete errors in the waveform superposition process are avoided.
Drawings
In order to more clearly illustrate the technical solutions of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic circuit diagram of a lossy integrator according to an embodiment of the present application;
fig. 2 is a schematic flowchart of a method for testing an integration loop decay time constant of an acquisition unit according to an embodiment of the present disclosure.
Detailed Description
To make the structure and advantages of the present application clearer, the structure of the present application will be further described with reference to the accompanying drawings.
Example one
At present, electronic transformers mainly use electronic transformers, and the electronic transformers are used for electronic transformers of a relay protection circuit based on the principle of Rogowski coil. The basic principle of Rogowski coil for measuring current is Faraday's law of electromagnetic induction and ampere's loop law, the Rogowski coil is an air-core coil formed by using non-magnetic material as skeleton, and in the air-core coil, it is wound on the non-magnetic skeleton for the second time, and the non-ferromagnetic material can make the linearity of said sensor good, and its unsaturation and hysteresis-free are used, so that the air-core coil possesses excellent frequency response capability.
However, the voltage v (t) output by the rogowski coil in the second time and the primary current Ip (t) are in a differential relation, and the electronic transformer based on the rogowski coil principle needs to be restored through an integral link because the output is a signal after differentiation. In order to eliminate the influence of an ideal integrator on infinite integration of a direct current signal, a lossy integrator is generally adopted, that is, a resistor R2 is connected in parallel to an integration output capacitor to form a direct current attenuation loop so as to suppress an interference signal output by a rogowski coil.
The circuit structure of the lossy integrator is shown in fig. 1, and the output voltage signal of the rogowski coil is:
in the formula, the proportionality coefficient M is a mutual inductance coefficient between the Rogowski coil and the current-carrying conductor, and is a constant related to the structure of the Rogowski coil only, and i (t) is a measured current.
When the system has a short-circuit fault, the final transient fault current of the electronic transformer is reduced through the differential and integral loops of the rogowski coil as follows:
in the formula I m Is the magnitude of the periodic component of the fault current,
alpha is fault voltage phase; phi is the impedance angle, is greater than>
T a Time constant, T, of short-circuit loop a L/R, L and R are short circuit loop inductance and resistance, T b The integral of the decay time constant of the integral loop is the product T of the integral capacitance and the decay resistance of the loop b ＝RC 2 . In high voltage networks, the inductance value of the fault loop is typically much larger than the resistance value, which can be considered approximately as φ ≈ 90 °, so its transient error current is approximately equal to: />
From the above formula, the transient state transmission error current of the electronic transformer is mainly determined by the attenuation constant of the system and the attenuation constant of the integral loop, and only when T is b ＞＞T a The transient error caused by the integration loop can be ignored. So the decay time constant T of the integrating loop b Is a main index for determining the transient characteristic of the electronic current transformer based on the Rogowski coil principle. But the integration loop is designed inside the acquisition unit and cannot be obtained through a separate test.
In order to solve the influence of the transient characteristics of the electronic transformer based on the rogowski coil principle, the embodiment of the application provides a method for testing the attenuation time constant of an integration loop of an acquisition unit, as shown in fig. 1, the method comprises the following steps:
11. generating an alternating current and direct current superposition test waveform at an upper computer, and processing data of the alternating current and direct current superposition test waveform to obtain a small-voltage analog signal;
12. acquiring an optical fiber digital signal output by an integration loop of the acquisition unit, and testing by combining a small-voltage analog signal to obtain an alternating current-direct current transmission ratio;
13. and calculating the attenuation time constant based on the AC/DC transmission/transformation ratio.
In implementation, an alternating current-direct current superposition test waveform is generated through an upper computer, test data are discretized and then converted into a small-voltage analog signal through a D/A conversion module, then the test system is constructed by acquiring the analog signal and simultaneously acquiring an optical fiber digital signal output by an acquisition unit, an alternating current-direct current input-output ratio is obtained through testing, a test result is uploaded to the upper computer, and an integral loop of the test result is calculated by the upper computer to obtain an attenuation time constant.
Specifically, the specific content executed in step 11 includes:
111. setting preset parameters of alternating current amplitude, angular frequency and direct current voltage value at the upper computer, and generating an alternating current and direct current superposition test waveform based on the preset parameters;
112. and carrying out discretization processing on the data of the alternating current-direct current superposition test waveform, and carrying out D/A conversion to obtain a small-voltage analog signal.
In implementation, generating an ac-dc superimposed test waveform includes:
based on a formula, generating a function expression of the AC/DC superposition test waveform,
v(t)＝U m sin(ωt)+U 0 the formula I is shown in the specification,
in the formula, v (t) is the output amplitude of the AC/DC superimposed test waveform, U m Is an alternating current amplitude, omega is an angular frequency, the calculation expression is omega =2 pi f, f is an alternating current frequency, U 0 Is a DC value, and U is used for testing to prevent testing error caused by DC overflow after integration 0 Less than 10mV.
The data of alternating current-direct current stack test waveform is discretized, and a small-voltage analog signal is obtained after D/A conversion, and the method comprises the following steps:
the data of the alternating current-direct current superposition test waveform is subjected to discretization processing as shown in a formula II,
v(n)＝v(nT s )＝U m sin(ωnT s )+U 0 in the formula II, the first step is carried out,
where v (n) is the discretized output result, T s For discretized sampling isolation time, the value range of n is a positive integer, U m Is the AC amplitude, omega is the angular frequency, U 0 Is a dc value.
In the implementation, the D/A conversion chip adopts AD5683R of ADI company, which is a 16-bit single-channel converter, the relative accuracy of the converter is +/-2 LSB INL, and a 2 ppm/DEG C2.5V reference voltage source is arranged in the converter; the space-saving 2mm x 2mm 8-pin LFCSP and 10-pin MSOP packaging is adopted, so that more functions can be realized in a smaller circuit board space; 2mV total non-adjustment error, without initial calibration or adjustment; and 4kV HBM ESD rating value is adopted, and system robustness is realized.
The step of obtaining the transmission ratio of alternating current to direct current provided in step 12 includes:
121. collecting a small-voltage analog signal and an optical fiber digital signal from a test sample by adopting an FPGA chip;
122. respectively extracting alternating current and direct current signals from the standard signals and the signals to be detected comprising the collected optical fiber digital signals and the collected small-voltage analog signals;
123. respectively calculating the transmission ratio k of the DC signals according to the extraction results 1 Transmission ratio k to AC signal 2 。
In implementation, step 121 specifically includes: after the FPGA chip is adopted to collect the small-voltage analog signal and the optical fiber digital signal from the test article, the alternating current frequency f is calculated by a fundamental wave frequency measuring method based on an FFT algorithm.
In addition to alternating current-direct current signal extraction, still include:
1221. hanning window processing is respectively carried out on the standard signal and the signal to be detected, fourier transform is carried out on a window sequence, and the amplitude and the phase of the alternating current signal are obtained;
1222. and extracting time window data of the direct current component based on the alternating current signal, and adopting generalized polynomial fitting to calculate the amplitude of the direct current component to eliminate harmonic signals and noise influence.
Combining the steps, the step of finally obtaining the transmission ratio comprises the following steps:
1223. obtaining a transmission calculation formula on a frequency domain:
direct current transmission ratio k 1 ，k 1 ＝R 2 /R 1 ，
AC transmission ratio k 2 ，k 2 ≈1/ωC/R 1 ≈1/ωCR 1 ，
Where C is the capacitance of the integrating output capacitor and R 1 For the resistance value, R, connected to the integrating output capacitor in a lossy integrator circuit 2 The lossy integrator circuit has a resistance value connected in parallel across the integrating output capacitance.
Finally, the step 13 of calculating the decay time constant based on the ac/dc transfer ratio includes:
transmission ratio k based on direct current signal 1 Transmission ratio k to AC signal 2 Calculating the decay time constant by combining the formula III,
T b ＝RC≈k 1 /ωk 2 ≈k 1 /2πfk 2 in the formula three, the first step is,
in the formula, T b Is the decay time constant of the integration loop, C is the capacitance of the loop integration capacitor, k 1 Is a direct current transformation ratio, k 2 Is the AC transmission ratio, f is the AC frequency, and ω is the angular frequency.
In practice, the decay time constant T is obtained in order to obtain an integration loop b ＝RC 2 The method comprises the following steps of constructing a function derivation formula, wherein an integral loop is formed by an integral resistor, an integral capacitor, a direct current attenuation resistor and an operational amplifier, and the ideal integral formula is as follows:
in the formula: i (0) is the initial value of i (t)
However, in the amplitude-frequency domain, the characteristic of the integral loop is that the transmission of the fundamental wave cannot be changed due to the direct current attenuation, so R 2 > 1/ω C. Therefore, the following two transformation equations are obtained in the dc and ac frequency domains:
ratio of direct current transmission to transformation of k 1 ＝R 2 /R 1 K is the ratio of AC transmission to transformation 2 ≈1/ωC/R 1 ≈1/ωCR 1 ，
Two formulas are divided: k is a radical of formula 1 /k 2 ≈(R 2 /R 1 )/(1/ωCR 1 )≈ωCR 2 The decay time constant can be obtained: t is a unit of b ＝RC 2 ≈k 1 /ωk 2 ≈k 1 /2πfk 2 。
The invention relates to a test scheme for an integral loop attenuation time constant of an electronic transformer based on the Rogowski coil principle for an intelligent substation and a digital substation, aiming at improving the transient capability of the electronic transformer and providing guarantee for the safe and stable operation of a power grid. Therefore, the invention has the following technical characteristics:
1. and the alternating current and direct current superposition test is carried out by adopting an alternating current and direct current superposition synchronous output mode, so that the influence of discrete test errors on the accuracy of a test result is avoided.
2. Discretization processing is carried out, and discretization processing is carried out after test waveforms are generated, so that discrete errors in the waveform overlapping process are avoided.
3. Compatibility, because the output protocol of the collector of the electronic transformer manufacturer is basically a proprietary protocol, the self-adaptive analysis of the protocols of multiple manufacturers is supported.
4. And (4) standard source recovery, wherein the standard source is recovered in order to ensure the test precision of the whole test system, so that the precision problem possibly existing in the data source is avoided.
5. Adaptability, the coefficients of the digital quantity and the analog quantity in the acquisition units of various manufacturers are inconsistent, and the input-output ratio is adopted for calculation without concerning the setting of the coefficients in the acquisition units of the manufacturers.
6. The method is easy to realize, the attenuation time constant is a transient index, the testing precision is greatly improved by calculation after the transient index is tested by adopting a steady state method, the accurate measurement of the attenuation time constant can be realized, and the testing method is simple and easy to realize.
The sequence numbers in the above embodiments are merely for description, and do not represent the sequence of the assembly or the use of the components.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (4)
1. A method for testing an attenuation time constant of an integration loop of an acquisition unit is characterized by comprising the following steps:
generating an alternating current and direct current superposition test waveform at an upper computer, and processing data of the alternating current and direct current superposition test waveform to obtain a small-voltage analog signal;
acquiring an optical fiber digital signal output by an integration loop of the acquisition unit, and testing by combining a small-voltage analog signal to obtain an alternating current-direct current transmission ratio;
calculating an attenuation time constant based on the AC/DC transmission/transformation ratio;
wherein, acquire the optic fibre digital signal of collection unit integral loop output, combine little voltage analog signal to test, obtain the alternating current-direct current transmission and transformation ratio, include:
collecting a small-voltage analog signal and an optical fiber digital signal from a test sample by adopting an FPGA chip;
respectively extracting alternating current and direct current signals from the standard signals and the signals to be detected comprising the collected optical fiber digital signals and the collected small-voltage analog signals;
respectively calculating the transmission ratio k of the DC signals according to the extraction results 1 Transmission ratio k to AC signal 2 ；
The method for calculating the attenuation time constant based on the AC/DC transmission/transformation ratio comprises the following steps:
transmission ratio k based on direct current signal 1 Transmission ratio k to AC signal 2 Calculating the decay time constant by combining the formula III,
T b ＝RC≈k 1 /ωk 2 ≈k 1 /2πfk 2 in the formula three, the first step is,
in the formula, T b Is the decay time constant of the integration loop, C is the capacitance of the loop integration capacitor, k 1 Is a direct current transfer ratio, k 2 Is the AC transmission ratio, f is the AC frequency, and omega is the angular frequency; generating alternating current-direct current stack test waveform at host computer department, handle the data that obtains little voltage analog signal to alternating current-direct current stack test waveform, include:
setting preset parameters of alternating current amplitude, angular frequency and direct current voltage value at the upper computer, and generating an alternating current and direct current superposition test waveform based on the preset parameters;
carrying out discretization processing on the data of the alternating current-direct current superposition test waveform, and carrying out D/A conversion to obtain a small-voltage analog signal;
respectively calculating the transmission ratio k of the direct current signals according to the extraction result 1 Transmission ratio k to AC signal 2 The method comprises the following steps:
obtaining a transmission calculation formula on a direct current frequency domain and an alternating current frequency domain:
direct current transmission ratio k 1 ，k 1 ＝R 2 /R 1 ，
AC transmission ratio k 2 ，k 2 ≈1/ωC/R 1 ≈1/ωCR 1 ，
Wherein C is the capacitance of the loop integrating capacitor, R 1 For resistance values, R, connected to loop integrating capacitors in lossy integrator circuits 2 For the resistance value of the lossy integrator circuit connected in parallel to the loop integrating capacitor, ω is the angular frequency.
2. The method for testing the decay time constant of the integration loop of the acquisition unit according to claim 1, wherein preset parameters of the alternating current amplitude, the angular frequency and the direct current voltage value are set at the upper computer, and the alternating current-direct current superposition test waveform is generated based on the preset parameters, and comprises the following steps:
based on a formula, generating a function expression of the AC/DC superposition test waveform,
v(t)＝U m sin(ωt)+U 0 the formula I is shown in the specification,
in the formula, v (t) is the output amplitude of the AC/DC superimposed test waveform, U m Is an alternating current amplitude, omega is an angular frequency, the calculation expression is omega =2 pi f, f is an alternating current frequency, U 0 Is a DC voltage value, and is used for preventing test error caused by DC overflow after integration 0 Less than 10mV.
3. The method for testing the decay time constant of the integration loop of the acquisition unit according to claim 1, wherein the discretization of the data of the AC/DC superposition test waveform and the D/A conversion are performed to obtain a small-voltage analog signal, comprising the following steps:
the data of the alternating current and direct current superposition test waveform is subjected to discretization treatment as shown in a formula II,
v(n)＝v(nT s )＝U m sin(ωnT s )+U 0 in the formula II, the first step is carried out,
wherein v (n) is the discretization output result, T s For discretized sampling isolation time, the value range of n is a positive integer, U m Is the ac amplitude, ω is the angular frequency,U 0 is a dc voltage value.
4. The acquisition unit integration loop decay time constant test method of claim 1, further comprising:
after the FPGA chip is adopted to collect the small-voltage analog signal and the optical fiber digital signal from the test article, the alternating current frequency f is calculated by a fundamental wave frequency measurement method based on an FFT algorithm.
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Effective date of registration: 20201217 Address after: 310000, No. 219, Jianguo Middle Road, Shangcheng District, Zhejiang, Hangzhou Applicant after: HANGZHOU POWER SUPPLY COMPANY, STATE GRID ZHEJIANG ELECTRIC POWER Co.,Ltd. Applicant after: Innovation and entrepreneurship center of State Grid Zhejiang Electric Power Co.,Ltd. Address before: 310000, No. 219, Jianguo Middle Road, Shangcheng District, Zhejiang, Hangzhou Applicant before: HANGZHOU POWER SUPPLY COMPANY, STATE GRID ZHEJIANG ELECTRIC POWER Co.,Ltd. Applicant before: JIANGSU LINGCHUANG ELECTRIC AUTOMATION Co.,Ltd. |
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