Method for detecting broadband transmission characteristics of capacitor voltage transformer

Abstract

The invention discloses a method for detecting broadband transmission characteristics of a capacitor voltage transformer (CVT), which comprises the following steps of: inputting a uniform white noise signal into a test system without a tested CVT, and calculating a transfer function H (f) of the test system and a corresponding compensation function A (f); a reference test voltage is constructed by superimposing multiple harmonic waves on the fundamental wave voltage, a reference spectrum Y (f) is obtained through Fourier transform, and a driving spectrum X (f) and a driving signal x (t) are obtained by combining the compensation function A (f); a driving signal x (t) is applied to a test system provided with a tested CVT, a test voltage ui (t) applied between a primary side medium voltage end of the tested CVT and the ground is collected, a response signal measurement spectrum Ui (f) of the test system is obtained through Fourier transform, and then the driving signal x (t) is corrected according to an error spectrum of the response signal measurement spectrum Ui (f) and a reference spectrum Y (f), so that the voltage signal ui (t) meets design requirements; and collecting the test voltage uo (t) output by the secondary side of the tested CVT at the moment, and calculating the transmission characteristic parameters of the tested CVT by combining the test voltage ui (t) and the test current ii (t) of the medium-voltage end of the tested CVT at the moment.

Description

Technical Field

[0001] The invention relates to the technical field of automatic control, and in particular to a method for detecting broadband transmission characteristics of a capacitive voltage transformer. Background Art

[0002] With the large-scale grid connection of new energy represented by wind power and photovoltaic power, the continuous increase of nonlinear loads and impact loads, and the continuous increase of new energy vehicles, rail transit, high-speed rail and other loads characterized by power electronics technology, the power quality in traditional power grids, especially the harmonic problem, has attracted more and more attention and concern. The power quality problems caused by this have had a huge impact on the normal operation of the power system itself and user equipment, so there are higher requirements for the accuracy of harmonic detection in power electronics systems.

[0003] Research on capacitive voltage transformers (CVTs) mainly focuses on their transient characteristics and measurement accuracy and error characteristics at rated power. Many research reports at home and abroad have shown that CVTs cannot fully transmit harmonic signals. Most conclusions are that CVTs will produce distortion in harmonic measurements and are no longer able to characterize the actual harmonic content in the system. Existing harmonic testing methods cannot accurately reflect the harmonic proportion in the power grid. Therefore, CVTs currently do not have the ability to accurately measure the harmonic content in the power grid and cannot be used to measure harmonics.

[0004] The transmission ratio of capacitive voltage transformers at different frequencies varies greatly, and the harmonic content is complex under actual operating conditions. The existing CVT broadband transmission characteristic test methods basically focus on reducing the test voltage level while ensuring a small measurement error. There is not much research on the harmonic sources applied to the CVT. In actual tests, the existing methods use a single harmonic injection method, which leads to low test efficiency. The method of controlling the harmonic source in the time domain cannot control multiple harmonics well, and the control accuracy is limited by the calculation of each harmonic impedance. In fact, the impedance will be affected by the ambient temperature and it is difficult to calculate accurately. Summary of the invention

[0005] The invention provides a method for detecting broadband transmission characteristics of a capacitive voltage transformer, which solves the technical problems of low testing efficiency and harmonic control accuracy in the existing method.

[0006] The present invention can be achieved through the following technical solutions:

[0007] A method for detecting broadband transmission characteristics of a capacitive voltage transformer comprises the following steps:

[0008] Step 1: Input a uniform white noise signal into a test system without a capacitive voltage transformer to be tested, and calculate the transfer function of the test system as H(f) and its corresponding compensation function A(f);

[0009] Step 2: construct a reference test voltage by superimposing multiple harmonics with the fundamental voltage, obtain the reference spectrum Y(f) through Fourier transform, and then combine the compensation function A(f) to obtain the driving spectrum X(f) and the driving signal x(t);

[0010] Step 3: Apply the driving signal x(t) to the test system equipped with the capacitive voltage transformer under test, and collect the test voltage u applied between the medium voltage terminal of the primary side of the CVT under test and the ground. i (t), the measured spectrum U of the test system response signal is obtained by Fourier transform i (f) Then the spectrum U is measured with the response signal i The error spectrum of the reference spectrum Y(f) and the driving signal x(t) is corrected so that the voltage signal u i (t) meet the design requirements;

[0011] Step 4: Collect the test voltage u output by the secondary side of the capacitive voltage transformer under test o (t), combined with the test voltage u at the medium voltage end of the CVT under test i (t) and test current i i (t), calculate the transmission characteristic parameters of the capacitive voltage transformer under test.

[0012] Further, in step 3, the current driving signal, the current test voltage at the medium voltage end, and the current test system response signal measurement spectrum are recorded as x and k (t),u ik (t), U ik (f);

[0013] The current response signal measurement spectrum U is calculated using the following formula: ik The current error spectrum E between (f) and the reference spectrum Y(f) k (f)

[0014] E k (f) = U ik (f)-Y(f)

[0015] Using the compensation function A(f) and the current error spectrum E k (f) Calculate the corrected spectrum △X of the current driving signal k (f):

[0016] △X k (f) = A(f)E k (f)

[0017] Using the corrected spectrum △X k (f) Correct the current drive spectrum X k (f), derive the corrected driving spectrum X k+1 (f):

[0018] X k+1 (f) = X k (f)-ε△X k (f)

[0019] Among them, ε is the modified weighting coefficient, ε>0;

[0020] Use inverse Fourier transform to transform the modified driving spectrum X k+1 (f) Transformed into the corrected driving signal x k+1 (t):

[0021] x k+1 (t) = F -1 [X k+1 (f)].

[0022] Further, in step 2, the following formula is used to calculate the driving spectrum X(f) using the compensation function A(f) and the reference spectrum Y(f), and the driving signal x(t) is obtained by inverse Fourier transform:

[0023] x(t)=F -1 [X(f)] = F -1 [A(f)·Y(f)].

[0024] Furthermore, the driving signal x(t) is converted into an analog signal by digital-to-analog conversion, and then a preset test voltage that meets the requirements, i.e., the test voltage u, is generated by a power amplifier and a step-up transformer. i (t), and applying the preset test voltage between the medium voltage terminal of the capacitive voltage transformer under test and the ground.

[0025] Furthermore, the amplitude of the fundamental voltage of the reference test voltage is U 11 The following conditions must be met:

[0026]

[0027] Wherein, C1, C2, and U represent the high-voltage capacitance, medium-voltage capacitance, and primary-side rated voltage of the capacitive voltage transformer under test, respectively;

[0028] Choose uniform white noise signal as the superimposed nth harmonic signal, that is, the power frequency f1 to frequency f n The integer harmonics between 1n Subject to the following constraints:

[0029]

[0030] Further, the step 4 of calculating the transmission characteristic parameters of the capacitive voltage transformer under test includes the following steps:

[0031] (1) Collect the test voltage u input between the medium voltage terminal and ground of the capacitive voltage transformer under test i (t), the test current i on the medium voltage capacitor C2 i (t), test voltage u output on the secondary side o (t), and Fourier transform is performed to obtain the corresponding amplitude-frequency characteristic and phase-frequency characteristic, that is, the test voltage u i (t) After Fourier transformation, the nth harmonic test voltage is obtained Specifically expressed as Among them U in for The amplitude of θ uin for The phase angle of

[0032] Test current i i (t) After Fourier transformation, the nth harmonic test current is obtained Specifically expressed as

[0033] Test voltage u of secondary output o (t) After Fourier transformation, the n-th secondary output voltage is obtained Specifically expressed as

[0034] (2) Calculate the primary input voltage of the capacitive voltage transformer under test

[0035] Calculation of equivalent impedance of medium voltage unit under nth harmonic

[0036] The impedance between the high-voltage terminal and the medium-voltage terminal under the nth harmonic can be obtained according to the high-voltage capacitance of the capacitive voltage transformer under test.

[0037] According to the impedance and equivalent impedance Calculate the voltage between the high voltage terminal and the ground, that is, the primary input voltage

[0038]

[0039] (3) Use the following equation to calculate the ratio of the secondary side output voltage amplitude to the primary side input voltage amplitude, that is, the amplitude-frequency characteristic A at each frequency point: n , calculate the difference between the secondary output voltage phase angle and the primary input voltage phase angle, that is, the phase-frequency characteristic △φ of each frequency point n.

[0040]

[0041] △φ n =θ u2n -θ un

[0042] Furthermore, the transfer function of the test system without the tested voltage transformer is denoted as H(f), and a uniform white noise signal is injected into the test system without the tested capacitive voltage transformer while collecting the system response signal u i ′(t), the amplitude-frequency characteristic of the transfer function H(f) is calculated using the H1 estimation method of the frequency response function |H(f) 2 An unbiased estimate of

[0043]

[0044] Among them, G xx (f) is the autospectral density of the driving signal x(t), G xy (f) is the driving signal x(t) and the system response signal u i The cross-spectral density of ′(t).

[0045] The compensation function A(f) is calculated using the equation A(f)=1 / H(f).

[0046] Furthermore, the uniform white noise signal is realized in the host computer by using a Wichmann-Hill generator to generate a pseudo-random sequence, and the frequency range is obtained by a narrow-band bandpass filter with adjustable gain. The corresponding probability density function f(x) is set as follows:

[0047]

[0048] Where a is the absolute value of the uniform white noise signal amplitude.

[0049] The beneficial technical effects of the present invention are:

[0050] 1. The harmonics applied to the CVT under test are generated by a uniform white noise signal with a uniform spectrum. The transfer function of all integer harmonics of the CVT within a given frequency range can be obtained in one test, thereby improving the test efficiency.

[0051] 2. By performing FFT on the system response signal and the reference input signal, the time domain signal is transferred to the frequency domain. After error correction of each frequency harmonic in the drive signal spectrum, it is output after IFFT conversion, so that the harmonic amplitude and phase applied to the CVT under test can be completely controlled in the frequency domain, avoiding the influence of the time delay between signals that may be affected during control in the time domain, and improving the control accuracy of the harmonic current amplitude and phase.

[0052] 3. Collect the voltage, current and secondary voltage of the CVT primary side medium voltage terminal, obtain the harmonic voltage of the primary side high voltage end by capacitor voltage division, and calculate the harmonic transfer function of the voltage transformer CVT under test, that is, the amplitude-frequency / phase-frequency transfer function. The calculation process is simple; by applying multiple harmonics to the medium voltage end instead of the high voltage end, the voltage level required for the test is reduced, the measurement error is reduced, and the safety factor is improved. The test plan is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0054] Figure 2 It is a schematic diagram of the overall structure of the test system of the present invention;

[0055] Figure 3 This is a block diagram of the driving signal control principle of the present invention;

[0056] Figure 4 It is a structural diagram of an equivalent circuit of a capacitive voltage transformer of the present invention. DETAILED DESCRIPTION

[0057] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] See attached Figure 1 The present invention provides a method for detecting the broadband transmission characteristics of a capacitor voltage transformer, which can realize accurate and comprehensive detection of the broadband transmission characteristics of a capacitor voltage transformer CVT. The corresponding test system structure is as shown in the attached figure. Figure 2 As shown, the system mainly includes the following parts:

[0059] (1) Host computer: It realizes the setting of the system multi-harmonic signal x(t) and its correction in the frequency domain, and analyzes the harmonic transmission characteristics of each frequency point of the CVT;

[0060] (2) Low-voltage harmonic source: including a high-speed digital-to-analog converter and a power amplifier. The high-speed digital-to-analog converter converts the given multi-harmonic time domain signal into an analog signal. The power amplifier ensures that the output meets the requirements through real-time control of voltage and current.

[0061] (3) Boost transformer: to boost the voltage of injected multi-harmonic signals;

[0062] (4) Data acquisition device: collects the primary side harmonic voltage u of the CVT medium voltage side of the device under test i and harmonic current i i , harmonic voltage u on the secondary side o , and then transmitted to the host computer after analog-to-digital conversion.

[0063] The specific detection methods are as follows:

[0064] Step 1: Input a uniform white noise signal into a test system without a CVT under test, and calculate the transfer function of the test system as H(f) and its corresponding compensation function A(f).

[0065] In order to control the harmonic signal in the frequency domain, it is necessary to estimate the transfer function of the test system first. The system transfer function is defined as H(f), as shown in the attached figure. Figure 2 As shown in the figure (excluding the CVT under test), the system transfer function H(f) is the system response signal, that is, the test voltage u applied to the CVT of the device under test i ′(t) and the system drive signal x′(t), which is the ratio of the multi-harmonic time domain signal given by the host computer. The details are as follows:

[0066] (1) Estimate the system transfer function H(f) and use a broadband random signal to test the system transfer function. Only the amplitude-frequency characteristic of the system transfer function |H(f)| or |H(f)| needs to be considered. 2 .

[0067] In the frequency range required for testing, a uniform white noise signal with limited bandwidth and small amplitude is injected into the system. The uniform white noise can be achieved by generating a uniformly distributed pseudo-random waveform. For example, a Wichmann-Hill generator is used to generate a pseudo-random sequence. The pseudo-random number generator uses a three-seed linear congruential algorithm. The probability density function f(x) of the uniformly distributed uniform white noise signal is:

[0068]

[0069] Where a is the absolute value of the specified white noise amplitude.

[0070] When estimating the system transfer function, a uniform white noise signal with a small amplitude should be given, and the frequency range of the signal is intercepted by a bandpass filter.

[0071] Inject a uniform white noise signal into the system and collect the system response signal u i ′(t), using the H1 estimation method of the frequency response function gives |H(f)| 2 An unbiased estimate of The specific reference is Wang Shuai, Xia Yilin, Rong Kelin. Vibration Environment Test [M]. National Defense Industry Press: 2021.1. The corresponding calculation formula is as follows:

[0072]

[0073] Among them, G xx (f) is the autospectral density of the driving signal x′(t), G xy (f) is the driving signal x′(t) and the system response signal u i The cross-spectral density of ′(t).

[0074] (2) Using the equation A(f) = 1 / H(f), calculate the compensation function A(f).

[0075] Step 2: construct a reference test voltage by superimposing multiple harmonics on the fundamental voltage, obtain the reference spectrum Y(f) through Fourier transform, and then combine the compensation function A(f) to obtain the drive spectrum X(f) and the drive signal x(t).

[0076] The reference test voltage is a voltage composed of the fundamental wave (50Hz / 60Hz) and multiple harmonics within a certain frequency range. 11 It is approximately equal to the rated voltage of the medium voltage transformer on the primary side of the CVT, which can be estimated based on the rated voltage U of the primary side of the CVT, the high voltage capacitor C1, and the medium voltage capacitor C2:

[0077]

[0078] In order to obtain the CVT in a frequency range (i.e. power frequency f1 and integer harmonic frequencies f2 to f n ) under each frequency point, uniform white noise is selected as the superimposed harmonic signal. The uniform white noise can be realized by generating a uniformly distributed pseudo-random waveform, and the frequencies f1 to f in the white noise are obtained by a narrow-band bandpass filter with adjustable gain. n The integer harmonics between the two, for the amplitude U of the nth harmonic in the white noise 1n , can be set to 0.2% to 3% of the fundamental voltage, subject to the following constraints:

[0079]

[0080] The details are as follows:

[0081] (1) Given a reference test voltage, i.e., a multi-harmonic time domain signal y(t), which is a superposition of a fundamental wave and multiple harmonics constructed by filtered uniform white noise, the reference test voltage y(t) is subjected to Fourier transform to obtain frequency domain data, i.e., the reference spectrum Y(f):

[0082]

[0083] In the formula, t is time, h is frequency, and e is -iht is a complex function, and F[y(t)] represents the Fourier transform operation.

[0084] (2) Use the compensation function A(f) and the reference spectrum Y(f) to calculate the driving spectrum X(f), and use the inverse Fourier transform FFT to obtain the time history x(t) corresponding to the driving signal:

[0085] x(t)=F -1 [X(f)] = F -1 [A(f)·Y(f)] (7)

[0086] (3) The time history x(t) of the driving signal is converted into an analog signal through digital-to-analog conversion, and then a preset test voltage that meets the requirements is generated through a power amplifier and a step-up transformer, and the preset test voltage is applied between the CVT medium voltage terminal and the ground.

[0087] Step 3: Apply the drive signal x(t) to the test system equipped with the CVT under test, and collect the test voltage u applied between the medium voltage terminal of the primary side of the CVT under test and the ground. i (t), the measured spectrum U of the test system response signal is obtained by Fourier transform i (f) Then the spectrum U is measured with the response signal i The error spectrum of the reference spectrum Y(f) and the driving signal x(t) is corrected so that the voltage signal u i (t)Meet the design requirements.

[0088] As attached Figure 3 As shown, in order to accurately control the test voltage applied to the device under test, the test voltage amplitude and phase are corrected in the frequency domain according to the system response signal. The specific steps include:

[0089] (1) When the drive signal is used to stimulate the CVT under test, the test voltage applied to the CVT under test is synchronously collected, and the time history u of the current voltage signal is obtained after analog-to-digital conversion. ik (t), k = 0, 1, 2, 3..., and use Fourier transform to get the current system response signal measurement spectrum U ik (f):

[0090] U ik (f) = F[u ik (t)] (8)

[0091] (2) Spectrum U measured by the current system response signal ik The difference between (f) and the reference spectrum Y(f) is used to calculate the current error spectrum E k (f):

[0092] E k (f) = R k (f)-Y(f) (9)

[0093] (3) Using the compensation function A(f) and the current error spectrum E k (f) Calculate the current corrected spectrum △X corresponding to the driving signal k (f):

[0094] △X k (f) = A(f)E k (f) (10)

[0095] (4) Use the current corrected spectrum △X k (f) Correct the current drive spectrum X k (f), derive the corrected driving spectrum X k+1 (f):

[0096] X k+1 (f) = X k (f)-ε△X k (f) (11)

[0097] Where ε is the correction weighting coefficient, which is used to consider the convergence stability of the control process, ε>0; the selection of the correction weighting coefficient should usually ensure that the overshoot of the control process does not exceed 1dB.

[0098] (5) Use inverse Fourier transform to transform the corrected driving spectrum X k+1 (f) is transformed into the time history x of the corresponding driving signal k+1 (t):

[0099] x k+1 (t) = F -1 [X k+1 (f)] (12)

[0100] Among them, x k+1 (t) is the time history of the corrected drive signal, which is injected into the medium voltage terminal of the primary side of the CVT under test through the DAC, power amplifier and step-up transformer.

[0101] Step 4: Collect the test voltage u output by the secondary side of the CVT under test o (t), combined with the test voltage u input to the medium voltage terminal of the CVT under test i (t) and test current i i (t), calculate the transmission characteristic parameters of the CVT under test.

[0102] As attached Figure 4 As shown in the figure, a test voltage u is applied between the CVT medium voltage terminal and the ground. i(t), the high voltage capacitor is C1, the medium voltage capacitor is C2, i i (t) is the test current on the medium voltage capacitor C2, u o (t) is the test voltage of the output measured on the secondary side of the CVT. The amplitude-frequency characteristic and phase-frequency characteristic of the CVT are calculated. The specific steps include:

[0103] (1) Collect the multi-harmonic test voltage u input between the CVT medium voltage terminal and the ground i (t), harmonic test current i on medium voltage capacitor C2 i (t), harmonic test voltage u at the secondary output o (t).

[0104] (2) The collected u i (t), i i (t),u o (t) The three time history quantities are Fourier transformed to obtain the corresponding amplitude-frequency characteristics and phase-frequency characteristics;

[0105] That is, the test voltage u i (t) After Fourier transformation, the nth harmonic test voltage is obtained Specifically expressed as Among them U in for The amplitude of θ uin for The phase angle of

[0106] Test current i i (t) After Fourier transformation, the nth harmonic test current is obtained Specifically expressed as

[0107] Test voltage u of secondary output o (t) After Fourier transformation, the n-th secondary output voltage is obtained Specifically expressed as

[0108] (3) Based on the impedance of the high-voltage capacitor and the medium-voltage unit under each frequency harmonic voltage, the primary input voltage corresponding to the high-voltage side of the CVT is calculated.

[0109] Calculation of equivalent impedance of medium voltage unit under nth harmonic

[0110]

[0111] According to the high-voltage capacitor value of the CVT under test, the impedance between the high-voltage terminal and the medium-voltage terminal under the nth harmonic is obtained.

[0112] According to the impedance and equivalent impedance Calculate the voltage between the high voltage terminal and the ground, that is, the primary input voltage

[0113]

[0114] It should be noted that in the test, the high-voltage terminal should be suspended, the high-voltage capacitor is not connected to the loop, and the primary input voltage between the high-voltage terminal and the ground is calculated by applying the voltage between the medium-voltage terminal and the ground and the harmonic equivalent impedance of the high-voltage capacitor and the medium-voltage unit, which does not actually exist.

[0115] (4) Calculate the ratio of the amplitude of the secondary side output voltage to the amplitude of the primary side input voltage, that is, the amplitude-frequency characteristic of each frequency point, and calculate the difference between the phase angle of the secondary side output voltage and the phase angle of the primary side input voltage, that is, the phase-frequency characteristic of each frequency point.

[0116] According to the CVT primary input voltage Secondary output voltage The amplitude-frequency transfer characteristic A of CVT is calculated n :

[0117]

[0118] Phase-frequency transfer characteristic △φ n :

[0119] △φ n =θ uon -θ un (16)

[0120] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is limited by the appended claims.

Claims

1. A method for detecting broadband transmission characteristics of a capacitive voltage transformer, characterized in that The following steps are involved: Step 1: Input a uniform white noise signal into a test system without a capacitive voltage transformer to be tested, and calculate the transfer function of the test system as H(f) and its corresponding compensation function A(f); Step 2: construct a reference test voltage by superimposing multiple harmonics with the fundamental voltage, obtain the reference spectrum Y(f) through Fourier transform, and then combine the compensation function A(f) to obtain the driving spectrum X(f) and the driving signal x(t); Step 3: Apply the driving signal x(t) to the test system equipped with the tested capacitive voltage transformer, and collect the test voltage u applied between the medium voltage terminal of the primary side of the tested capacitive voltage transformer and the ground. i (t), the measured spectrum U of the test system response signal is obtained by Fourier transform i (f) Then the spectrum U is measured with the response signal i The error spectrum of the reference spectrum Y(f) and the driving signal x(t) is corrected so that the voltage signal u i (t) meet the design requirements; Step 4: Collect the test voltage u output by the secondary side of the capacitive voltage transformer under test o (t), combined with the test voltage u at the medium voltage end of the capacitive voltage transformer under test i (t) and test current i i (t), calculate the transmission characteristic parameters of the capacitive voltage transformer under test.

2. The method for detecting the broadband transmission characteristics of a capacitive voltage transformer according to claim 1, characterized in that: In step 3, the current driving signal, the current test voltage at the medium voltage end, and the current test system response signal measurement spectrum are recorded as x k (t),u ik (t), U ik (f); The current response signal measurement spectrum U is calculated using the following formula: ik The current error spectrum E between (f) and the reference spectrum Y(f) k (f) E k (f)=U ik (f)-Y(f) Using the compensation function A(f) and the current error spectrum E k (f) Calculate the corrected spectrum △X of the current driving signal k (f): △X k (f)=A(f)E k (f) Using the corrected spectrum △X k (f) Correct the current drive spectrum X k (f), derive the corrected driving spectrum X k+1 (f): X k+1 (f)=X k (f)-ε△X k (f) Among them, ε is the modified weighting coefficient, ε>0; Use inverse Fourier transform to transform the modified driving spectrum X k+1 (f) Transformed into the corrected driving signal x k+1 (t): x k+1 (t)=F -1 [X k+1 (f)]。 3. The method for detecting the broadband transmission characteristics of a capacitive voltage transformer according to claim 2, characterized in that: In step 2, the following formula is used to calculate the driving spectrum X(f) using the compensation function A(f) and the reference spectrum Y(f), and the driving signal x(t) is obtained by inverse Fourier transform: x(t)=F -1 [X(f)]=F -1 [A(f)·Y(f)]。 4. The method for detecting broadband transmission characteristics of a capacitive voltage transformer according to claim 1, characterized in that: The driving signal x(t) is converted into an analog signal through a digital-to-analog conversion, and then a preset test voltage that meets the requirements, i.e., the test voltage u, is generated through a power amplifier and a step-up transformer. i (t), and applying the preset test voltage between the medium voltage terminal of the capacitive voltage transformer under test and the ground.

5. The method for detecting the broadband transmission characteristics of a capacitive voltage transformer according to claim 4, characterized in that: The amplitude of the fundamental voltage of the reference test voltage is U 11 The following conditions must be met: Wherein, C1, C2, and U represent the high-voltage capacitance, medium-voltage capacitance, and primary-side rated voltage of the capacitive voltage transformer under test, respectively; Choose uniform white noise signal as the superimposed nth harmonic signal, that is, the power frequency f1 to frequency f n The integer harmonics between 1n Subject to the following constraints:

6. The method for detecting the broadband transmission characteristics of a capacitive voltage transformer according to claim 5, characterized in that Calculating the transmission characteristic parameters of the capacitive voltage transformer under test in step 4 includes the following steps: (1) Collect the test voltage u input between the medium voltage terminal and ground of the capacitive voltage transformer under test i (t), the test current i on the medium voltage capacitor C2 i (t), test voltage u output on the secondary side o (t), and Fourier transform is performed to obtain the corresponding amplitude-frequency characteristic and phase-frequency characteristic, that is, the test voltage u i (t) After Fourier transformation, the nth harmonic test voltage is obtained Specifically expressed as Among them U in for The amplitude of θ uin for The phase angle of The test current ii(t) is transformed by Fourier transform to obtain the nth harmonic test current Specifically expressed as Test voltage u of secondary output o (t) After Fourier transformation, the n-th secondary output voltage is obtained Specifically expressed as (2) Calculate the primary input voltage of the capacitive voltage transformer under test Calculation of equivalent impedance of medium voltage unit under nth harmonic The impedance between the high-voltage terminal and the medium-voltage terminal under the nth harmonic can be obtained according to the high-voltage capacitance of the capacitive voltage transformer under test. According to the impedance and equivalent impedance Calculate the voltage between the high voltage terminal and the ground, that is, the primary input voltage (3) Use the following equation to calculate the ratio of the secondary side output voltage amplitude to the primary side input voltage amplitude, that is, the amplitude-frequency characteristic A at each frequency point: n , calculate the difference between the secondary output voltage phase angle and the primary input voltage phase angle, that is, the phase-frequency characteristic △φ of each frequency point n . △φ n =θ u2n -θ un 。 7. The method for detecting broadband transmission characteristics of a capacitive voltage transformer according to claim 1, characterized in that: The transfer function of the test system without the tested capacitive voltage transformer is denoted as H(f). A uniform white noise signal is injected into the test system without the tested capacitive voltage transformer while the system response signal u is collected. i ′(t), the amplitude-frequency characteristic of the transfer function H(f) is calculated using the H1 estimation method of the frequency response function |H(f)| 2 An unbiased estimate of Among them, G xx (f) is the autospectral density of the driving signal x(t), G xy (f) is the driving signal x(t) and the system response signal u i The cross-spectral density of ′(t). The compensation function A(f) is calculated using the equation A(f)=1 / H(f).

8. The method for detecting broadband transmission characteristics of a capacitive voltage transformer according to claim 7, characterized in that: The uniform white noise signal is realized in the host computer by using the Wichmann-Hill generator to generate a pseudo-random sequence, and the frequency range is obtained by a narrow-band bandpass filter with adjustable gain. The corresponding probability density function f(x) is set as follows: Where a is the absolute value of the uniform white noise signal amplitude.

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