A method for detecting wideband transmission characteristics of a capacitive voltage transformer

Abstract

The application discloses a kind of detection methods of wideband transmission characteristic of capacitive voltage transformer, including the test system without being measured CVT is input in with uniform white noise signal, the transfer function of test system is calculated as H (f) And its corresponding compensation function A (f) ;With fundamental voltage superimposed multiple harmonic to build reference test voltage, reference spectrum Y (f) Is obtained by Fourier transform, then combined with compensation function A (f) Further obtain drive spectrum X (f) And drive signal x (t) ;Drive signal x (t) Is applied to the test system with measured CVT, the test voltage u i (t) Between the measured CVT primary side medium voltage end to ground is collected, the test system response signal measurement spectrum U i (f) Is obtained by Fourier transform, then with the error spectrum of response signal measurement spectrum U i (f) And reference spectrum Y (f) Drive signal x (t) Is corrected, so that voltage signal u i (t) Meet design requirements;The test voltage u o (t) Output by measured CVT secondary side is collected, then combined with the test voltage u i (t) And test current i i (t) of measured CVT medium voltage end at this time, the transmission characteristic parameter of measured CVT is calculated.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of automatic control, in particular to a detection method for wide-frequency transmission characteristics of a capacitive voltage transformer. BACKGROUND

[0002] With large-scale new energy represented by wind energy and photovoltaic being connected to the grid, non-linear loads and impact loads are increasing, and loads such as new energy vehicles, rail transit and high-speed rail characterized by power electronic technology are increasing. More and more people pay attention to power quality, especially harmonic problems in traditional power grids. The power quality problems caused thereby have a great impact on the normal operation of the power system itself and user equipment, so there is a higher requirement for the accuracy of harmonic detection of power electronic systems.

[0003] Research on capacitive voltage transformers (CVT) mainly focuses on the transient characteristics and measurement accuracy and error characteristics under rated power. Many research reports at home and abroad show that CVT cannot completely transmit harmonic signals, and most conclusions are that CVT will distort harmonic measurement and cannot represent the actual harmonic content in the system. The existing harmonic test method cannot accurately reflect the harmonic proportion in the power grid, so the CVT does 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 the capacitive voltage transformer is quite different at different frequencies, and the harmonic content is complex in actual operation conditions. The existing CVT wide-frequency transmission characteristic test method basically focuses on reducing the test voltage level while ensuring small measurement error. There is no much research on the harmonic source applied to the CVT. In actual testing, the existing method uses single harmonic injection, which leads to low test efficiency. The time-domain control of the harmonic source cannot well control multiple harmonics, and the control accuracy is limited by the calculation of each harmonic impedance. In fact, the impedance is affected by the environmental temperature, and it is difficult to calculate accurately. SUMMARY

[0005] The application provides a detection method for wide-frequency transmission characteristics of a capacitive voltage transformer, which solves the technical problems of low test efficiency and harmonic control accuracy of the existing method.

[0006] The application can be implemented by the following technical solutions:

[0007] A detection method for wide-frequency transmission characteristics of a capacitive voltage transformer, comprising the following steps:

[0008] Step one, input uniform white noise signal into the test system without the measured capacitive voltage transformer, calculate the transfer function of the test system as H(f) and its corresponding compensation function A(f);

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

[0010] Step three, apply the drive signal x(t) to the test system with the measured capacitive voltage transformer, collect the test voltage u i (t) applied between the medium voltage end of the primary side of the measured CVT and the ground, obtain the test system response signal measurement spectrum U i (f) through Fourier transform, then correct the drive signal x(t) with the error spectrum between the response signal measurement spectrum U i (f) and the reference spectrum Y(f), so that the voltage signal u i (t) meets the design requirements;

[0011] Step four, collect the test voltage u o (t) output by the secondary side of the measured capacitive voltage transformer at this time, then combine the test voltage u i (t) of the medium voltage end of the measured CVT at this time and the test current i i (t), calculate the transmission characteristic parameters of the measured capacitive voltage transformer.

[0012] Further, in the step three, record the current drive signal, the current test voltage of the medium voltage end and the current test system response signal measurement spectrum as x k (t), u ik (t), U ik (f) respectively;

[0013] Calculate the current error spectrum E k (f) between the current response signal measurement spectrum U ik (f) and the reference spectrum Y(f) by using the following formula,

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

[0015] Calculate the correction spectrum △X k (f) of the current drive signal using the compensation function A(f) and the current error spectrum E k (f):

[0016] △X k (f) = A(f)E k (f)

[0017] Using the corrected spectrum ΔX k (f) correcting the current drive spectrum X k (f), deriving the corrected drive spectrum X k+1 (f):

[0018] X k+1 (f) = X k (f) - ε ΔX k (f)

[0019] where ε is a correction weighting factor, ε > 0;

[0020] Using the inverse Fourier transform, the corrected drive spectrum X k+1 (f) is transformed into the corrected drive signal x k+1 (t):

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

[0022] Further, in the step two, the drive spectrum X(f) is calculated using the compensation function A(f) and the reference spectrum Y(f) by the following formula, and the drive signal x(t) is obtained using the inverse Fourier transform,

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

[0024] Further, the drive signal x(t) is converted into an analog signal through digital-to-analog conversion, and then is amplified through a power amplifier and a step-up transformer to generate a preset test voltage, i.e., a test voltage u i (t) that meets the requirements, and the preset test voltage is applied between the medium voltage end and the ground of the measured capacitive voltage transformer.

[0025] Further, the amplitude U 11 of the fundamental wave voltage of the test voltage meets the following condition:

[0026]

[0027] where C1, C2, and U respectively represent the high voltage capacitor, the medium voltage capacitor, and the primary side rated voltage of the measured capacitive voltage transformer.

[0028] The uniform white noise signal is selected as the superimposed n-th harmonic signal, i.e., the integer multiple harmonic wave between the power frequency f1 and the frequency f n , and the amplitude U 1n is constrained by the following formula:

[0029]

[0030] Further, the step four of calculating the transmission characteristic parameters of the measured capacitive voltage transformer comprises the following steps:

[0031] (1) Collecting the test voltage u i (t) input between the medium voltage end and the ground of the measured capacitive voltage transformer, the test current i i (t) on the medium voltage capacitor C2, and the test voltage u o (t) output on the secondary side, respectively performing Fourier transform to obtain the corresponding amplitude-frequency characteristic and phase-frequency characteristic, i.e. the amplitude-frequency characteristic A i (t) of the test voltage u Specifically expressed as Wherein U in is the amplitude of A , and θ uin is the phase angle of A ;

[0032] The test current i i (t) is Fourier transformed to obtain the n-th harmonic test current i Specifically expressed as

[0033] The test voltage u o (t) output on the secondary side is Fourier transformed to obtain the n-th secondary side output voltage u Specifically expressed as

[0034] (2) Calculating the primary side input voltage u

[0035] Calculating the equivalent impedance Z

[0036] According to the high voltage capacitor value of the measured capacitive voltage transformer, the impedance between the high voltage terminal and the medium voltage terminal under the n-th harmonic is obtained

[0037] According to the impedance Z and the equivalent impedance Z , the voltage between the high voltage terminal and the ground, i.e. the primary side input voltage u

[0038]

[0039] (3) Using the following equations, the ratio of the secondary side output voltage amplitude and the primary side input voltage amplitude, i.e. the amplitude-frequency characteristic A n of each frequency point, is calculated, and the difference between the phase angle of the secondary side output voltage and the phase angle of the primary side input voltage, i.e. the phase-frequency characteristic Δφ n.

[0040]

[0041] △φ n =θ u2n -θ un

[0042] Further, the transfer function of the test system without the measured capacitive voltage transformer is recorded as H(f), the uniform white noise signal is injected into the test system without the measured capacitive voltage transformer while the system response signal u i '(t) is collected, the amplitude-frequency characteristic |H(f)| of the transfer function H(f) is calculated by using the H1 estimation method of the frequency response function 2 The unbiased estimation of the amplitude-frequency characteristic |H(f)|

[0043]

[0044] Wherein, G xx (f) is the self-spectrum density of the driving signal x(t), G xy (f) is the cross-spectrum density of the driving signal x(t) and the system response signal u i '(t).

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

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

[0047]

[0048] In the formula, a is the absolute value of the amplitude of the uniform white noise signal.

[0049] The beneficial technical effects of the present application are as follows:

[0050] 1. The uniform white noise signal containing uniform spectrum is used to generate the harmonic applied to the measured CVT, so that the transfer functions of all integer harmonics of the CVT in a given frequency range can be obtained in one test, and the test efficiency is improved.

[0051] 2. By doing FFT to the system response signal and the reference input signal, the time domain signal is converted into the frequency domain, the error of each frequency harmonic in the frequency spectrum of the driving signal is corrected, and then the output is converted by IFFT, realizing the complete control of the harmonic amplitude and phase of the measured CVT in the frequency domain, avoiding the influence of time delay between signals when controlling in the time domain, and improving the control accuracy of the harmonic current amplitude and phase.

[0052] 3. The voltage and current of the medium voltage terminal of the CVT on the primary side, the voltage of the secondary side, and the harmonic voltage of the high voltage terminal of the primary side obtained by the capacitor voltage division are collected, the harmonic transfer function of the measured voltage transformer CVT, i.e. the amplitude-frequency / phase-frequency transfer function, is calculated, and the calculation process is simple; by applying multiple harmonics to the medium voltage terminal instead of the high voltage terminal, the required voltage level of the test is reduced, the measurement error is reduced, the safety factor is improved, and the test scheme is simple and easy to implement. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

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

[0057] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0058] Referring to the drawings Figure 1 , the present application provides a detection method for the wideband transmission characteristics of a capacitive voltage transformer, which realizes accurate and comprehensive detection of the wideband transmission characteristics of the capacitive voltage transformer CVT, and the corresponding test system structure is shown in the accompanying Figure 2 , the system mainly includes the following parts:

[0059] (1) Host computer: realizes the given and correction of the multi-harmonic signal x(t) in the frequency domain, and realizes the analysis of the harmonic transmission characteristics of the CVT at each frequency point;

[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, and the power amplifier realizes real-time control of voltage and current to ensure that the output meets the requirements;

[0061] (3) Step-up transformer: realizes the step-up of the injected multi-harmonic signal;

[0062] (4) Data acquisition device: collect the measured device CVT in the primary side of the harmonic voltage u i and harmonic current i i , the secondary side of the harmonic voltage u o , after analog-to-digital conversion to the host computer.

[0063] The specific detection method is as follows:

[0064] Step one, input the uniform white noise signal into the test system without the measured CVT, calculate the transfer function of the test system H(f) and its corresponding compensation function A(f).

[0065] In order to control the harmonic signal in the frequency domain, first, the transfer function of the test system needs to be estimated, define the system transfer function as H(f), as shown in the attached Figure 2 The system transfer function H(f) is the ratio of the system response signal, that is, the test voltage u i ′(t) applied to the measured device CVT, and the system driving signal x′(t), that is, the multi-harmonic time domain signal given by the host computer. Specifically as follows:

[0066] (1) Estimate the system transfer function H(f), use wideband random signal to test the system transfer function, and only consider the amplitude-frequency characteristic |H(f)| or |H(f)| 2 .

[0067] In the required frequency range, inject a uniform white noise signal with limited bandwidth and small amplitude into the system. The uniform white noise can be realized by generating a uniformly distributed pseudo-random waveform, for example, using Wichmann-Hill generator to generate pseudo-random sequence. The pseudo-random number generator uses three seed linear congruence algorithm, and 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 small amplitude should be given, and the frequency range of the signal is intercepted by a band-pass filter.

[0071] At the same time, the system response signal u i ′(t) is collected, and the unbiased estimate of |H(f)| 2 is given by using the H1 estimation method of frequency response function. The specific reference is Wang Shuai, Xia Yilin, and Rong Kelin. Vibration Environment Test [M]. National Defense Industry Press: 2021.1. The corresponding calculation formula is as follows:

[0072]

[0073] Where, G xx (f) is the autocorrelation density of the driving signal x'(t), G xy (f) is the cross-correlation density of the driving signal x'(t) and the system response signal u i '(t).

[0074] (2) Calculate the compensation function A(f) using the equation A(f) = 1 / H(f).

[0075] Step two, construct the reference test voltage by superimposing the fundamental voltage and multiple harmonics, obtain the reference spectrum Y(f) by Fourier transform, and then obtain the driving spectrum X(f) and the driving signal x(t) by combining the compensation function A(f).

[0076] The reference test voltage is the voltage superimposed by the fundamental (50Hz / 60Hz) and multiple harmonics in a certain frequency range, where the fundamental voltage amplitude U 11 is approximately equal to the rated voltage of the CVT primary side medium voltage transformer. It can be estimated according to the CVT primary side rated voltage U, high voltage capacitor C1, and medium voltage capacitor C2:

[0077]

[0078] In order to obtain the response characteristics of CVT at each frequency point in a certain frequency range (i.e. power frequency f1 and integer harmonic frequencies f2 to f n ) in one test, uniform white noise is selected as the superimposed harmonic signal. Uniform white noise can be realized by generating a uniformly distributed pseudo-random waveform, and the integer harmonics between f1 and f n in the white noise can be obtained by a gain-adjustable narrow-band band-pass filter. For the amplitude U 1n of the n-th harmonic in the white noise, it can be set to 0.2% to 3% of the fundamental voltage, which is subject to the following constraint:

[0079]

[0080] Specifically as follows:

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

[0082]

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

[0084] (2) The driving spectrum X(f) is calculated using the compensation function A(f) and the reference spectrum Y(f), and the time history x(t) corresponding to the driving signal is obtained using the inverse Fourier transform FFT:

[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 through a power amplifier and a step-up transformer to generate a preset test voltage that meets the requirements, and the preset test voltage is applied between the medium voltage terminal of the CVT and the ground.

[0087] Step three, the driving signal x(t) is applied to the test system equipped with the measured CVT, and the test voltage u i (t) applied between the medium voltage terminal of the measured CVT on the primary side and the ground is collected, and the measurement spectrum U i (f) of the test system response signal is obtained through Fourier transform, and then the driving signal x(t) is corrected with the error spectrum of the response signal measurement spectrum U i (f) and the reference spectrum Y(f), so that the voltage signal u i (t) meets the design requirements.

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

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

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

[0091] (2) The current error spectrum E k (f) is calculated from the difference between the current system response signal measurement spectrum U ik (f) and the reference spectrum Y(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 correction spectrum ΔX corresponding to the driving signal. k (f):

[0094] △X k (f)=A(f)E k (f) (10)

[0095] (4) Using the current corrected spectrum ΔX k (f) Correct the current driving 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] In the formula, ε is the modified weighting coefficient, which is used to consider the convergence stability of the control process, and ε>0; the selection of the modified 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) Time history of transformation into the corresponding driving signal x k+1 (t):

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

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

[0101] Step 4: Collect the test voltage u output from the secondary side of the CVT under test at this time. o (t), and then combined with the test voltage u input at the voltage terminal of the CVT under test at this time. 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, a test voltage u was applied between the voltage terminal and ground in the CVT. i(t), the high-voltage capacitor is C1, and the medium-voltage capacitor is C2, i i (t) is a test current on the medium-voltage capacitor C2, u o (t) is a test voltage of the output of the secondary side of the CVT, the amplitude-frequency characteristic and the phase-frequency characteristic of the CVT are calculated, and the specific steps include:

[0103] (1) Collecting the input test voltage u i (t) of the multi-harmonic type on the medium-voltage capacitor C2 i (t), the test voltage u o (t) of the harmonic type output by the secondary side

[0104] (2) Collecting the three time history quantities u i (t), i i (t), u o (t), respectively, and performing Fourier transform to obtain the corresponding amplitude-frequency characteristic and phase-frequency characteristic;

[0105] that is, the test voltage u i (t) after Fourier transform is the n-th harmonic test voltage The specific expression is where U in is the amplitude of , and θ uin is the phase angle of ;

[0106] The test current i i (t) after Fourier transform is the n-th harmonic test current The specific expression is

[0107] The test voltage u o (t) output by the secondary side after Fourier transform is the n-th secondary side output voltage The specific expression is

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

[0109] The equivalent impedance of the medium-voltage unit under the n-th harmonic is calculated

[0110]

[0111] According to the capacitance value of the high-voltage capacitor of the measured CVT, the impedance between the high-voltage terminal and the medium-voltage terminal under the n-th harmonic is obtained

[0112] According to the impedance and equivalent impedance Calculate the voltage between high voltage terminal and ground, i.e. primary side 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 circuit, the primary side input voltage between the high voltage terminal and the ground is calculated by the voltage applied 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 and the amplitude of the primary side input voltage, i.e. the amplitude-frequency characteristic of each frequency point, and the difference between the phase angle of the secondary side output voltage and the phase angle of the primary side input voltage, i.e. the phase-frequency characteristic of each frequency point.

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

[0117]

[0118] Phase-frequency transfer characteristic Δφ n :

[0119] Δφ n = θ uon - θ un (16)

[0120] Although the specific embodiments of the present application are described above, those skilled in the art should understand that these are only illustrative, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present application, therefore, the protection scope of the present application is defined by the appended claims.

Claims

1. A method for detecting wideband transmission characteristics of a capacitive voltage transformer, characterized in that The method comprises the following steps: Step one, input uniform white noise signal into the test system without the measured capacitive voltage transformer, calculate the transfer function of the test system as And its corresponding compensation function ; Step two, construct the reference test voltage by superimposing fundamental voltage and multiple harmonics, and obtain the reference spectrum by Fourier transform , combined with the compensation function , and obtain the driving spectrum , and the driving signal ; Step 3: Drive signal The test voltage applied to the test system containing the capacitive voltage transformer under test is collected between the intermediate voltage terminal of the primary side of the capacitive voltage transformer under test and ground. The measurement spectrum of the test system response signal was obtained by Fourier transform. Then the spectrum is measured using the response signal. and reference spectrum The error spectrum of the driving signal Make corrections to ensure the test voltage is correct. Meets design requirements; Step four, collect the test voltage of the secondary side output of the measured capacitive voltage transformer at this time , combined with the test voltage of the medium voltage end of the measured capacitive voltage transformer at this time and test current , calculate the transmission characteristic parameters of the measured capacitive voltage transformer.

2. The method of claim 1, wherein the method further comprises: In the step three, record the current driving signal, the current test voltage of the middle voltage terminal and the current test system response signal measurement spectrum respectively as , , ; The current error spectrum between the current response signal measurement spectrum and the reference spectrum is calculated using the equation ,​​ Using a compensation function and a current error spectrum calculating a correction spectrum for the current drive signal : Using the corrected spectrum correcting the current drive spectrum deriving the corrected drive spectrum : wherein to correct the weighting coefficients, ; using an inverse Fourier transform to transform the modified drive spectrum into a modified drive signal : 。 3. The method of claim 2, wherein the method further comprises: In said step two, the driving spectrum is calculated using the compensation function and the reference spectrum and using the inverse Fourier transform to obtain the driving signal ,​ 。 4. The method of claim 1, wherein the method further comprises: The driving signal An analog signal is generated by digital-to-analog conversion, and a preset test voltage satisfying a requirement is generated by a power amplifier and a step-up transformer , and the preset test voltage is applied between a medium voltage end of the capacitor voltage transformer under test and the ground.

5. The method of claim 4, wherein the method further comprises: an amplitude of a fundamental wave voltage of the reference test voltage satisfies the following condition: wherein, , , respectively represent the high-voltage capacitor, the medium-voltage capacitor, and the primary-side rated voltage of the measured capacitor voltage transformer. A uniform white noise signal is chosen as the superimposed n-th harmonic signal, i.e. the power frequency to the frequency between the integer harmonics, whose amplitude is subject to the following constraint: 。 6. The method of claim 5, wherein the method further comprises: The step four comprises the following steps: (1) Collecting the input test voltage between the medium voltage end and the ground of the measured capacitor voltage transformer , the test current on the medium voltage capacitor , the test voltage output on the secondary side , respectively, Fourier transform is carried out to obtain the corresponding amplitude-frequency characteristic and phase-frequency characteristic, that is, the test voltage After Fourier transform, the n-th harmonic test voltage is obtained , which is specifically expressed as , wherein is the amplitude of , and is the phase angle of ;​ test current after Fourier transformation, the n-th harmonic test current is obtained , which is specifically expressed as ; Test voltage of secondary side output After Fourier transform, n times secondary side output voltage is obtained , which is specifically expressed as ; The step four comprises the following steps: Calculating the equivalent impedance under the n-th harmonic of the medium voltage unit ; According to the high voltage capacitor value of the measured capacitor voltage transformer, the impedance between the high voltage terminal and the medium voltage terminal under n times harmonic is obtained ; According to the impedance and the equivalent impedance , the voltage between the high voltage end and the ground, i.e. the primary side input voltage is calculated; (3) The ratio of the secondary output voltage amplitude to the primary input voltage amplitude, i.e. the amplitude-frequency characteristic of each frequency point, is calculated using the following equation The difference between the secondary output voltage phase angle and the primary input voltage phase angle, i.e. the phase-frequency characteristic of each frequency point, is calculated ; 。 7. The method of claim 1, wherein the method further comprises: The transfer function of the test system without the tested capacitive voltage transformer is , uniform white noise signal is injected into the test system without the tested capacitive voltage transformer while collecting the system response signal , the transfer function is calculated by using the H1 estimation method of the frequency response function , the amplitude-frequency characteristic , the unbiased estimation , wherein, the auto-spectral density of the drive signal the cross-spectral density of the drive signal and the system response signal ​​ Using the equation , the compensation function is calculated.

8. The method of claim 7, wherein the method further comprises: 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 gain-adjustable narrow-band band-pass filter, and the corresponding probability density function is The following settings are made (2) calculating the primary side input voltage of the measured capacitive voltage transformer In the formula, a is the absolute value of the uniform white noise signal amplitude.

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