Grid voltage frequency calculation method and device based on recursive Fourier series

Abstract

The present invention discloses a method and device for calculating the voltage frequency of a power grid based on a recursive Fourier series, wherein the calculation method comprises the following steps: S1: initializing a gain matrix; S2: sampling to obtain a discrete signal; S3: obtaining the Fourier transform phasor of a sampling point in the first cycle; S4: using a recursive Fourier transform formula to obtain the Fourier transform phasor of the sampling points in the remaining cycles; S5: obtaining a phase angle sequence; S6: performing least squares polynomial fitting on the phase angle sequence; S7: calculating and obtaining a first frequency estimation deviation value and a first frequency estimation value; S8: correcting a triangular basis function set, solving a Fourier series, and correcting the discrete signal based on the Fourier series to obtain a corrected sampling sequence; S9: repeating S3-S7 on the corrected sampling sequence to obtain a second frequency estimation offset; S10: calculating the voltage frequency. The present invention improves the calculation efficiency and accuracy, and has high robustness and frequency calculation accuracy.

Description

Technical Field

[0001] The present invention relates to the field of power grid voltage frequency calculation, and in particular to a power grid voltage frequency calculation method and device based on recursive Fourier series. Background Art

[0002] In the power system, frequency is one of the most important indicators of power energy quality and plays a very important role in the system's dynamic detection, feedback control, and relay protection. Due to the imbalance between power generation and load in the actual power generation process, the grid voltage frequency often deviates from its rated value, endangering the safe and stable operation of the grid. Therefore, accurate grid voltage and frequency calculation is very important for the power system.

[0003] The voltage frequency calculation of the power grid originates from the frequency estimation method of digital signal processing, which can be generally divided into time domain method and frequency domain method. The time domain algorithm is based on the signal model, such as Prony, Music and Esprit, and has extremely high calculation accuracy under the premise of known model order. Due to the high computational complexity of the determination of the model order and the analytical process, this method is greatly limited in the application of real-time online power grid voltage frequency calculation. The frequency domain algorithm is a discrete Fourier transform implemented by the fast Fourier transform, which is not only not restricted by the parameterization of the signal model, but also can effectively reduce the computational complexity, so that the frequency domain algorithm is widely used in the calculation of power grid voltage frequency. However, in the case of actual asynchronous sampling, the spectrum leakage and fence effect caused by the time domain window length and the discrete interval sampling in the frequency domain make the direct use of the discrete Fourier transform result have a large estimation error. Therefore, it is particularly important to design a method for calculating the power grid voltage frequency that can obtain high accuracy with less calculation. Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method and device for calculating the voltage frequency of a power grid based on recursive Fourier series, which solves the problems of spectrum leakage and fence effect existing in the existing frequency domain algorithms.

[0005] The present invention is achieved through the following technical solutions:

[0006] According to one aspect of the present invention, a method for calculating a power grid voltage frequency based on a recursive Fourier series is provided, comprising the following steps:

[0007] S1: Set the sampling frequency, calculate the number of sampling points, and initialize the gain matrix to obtain the coefficient matrix;

[0008] S2: sampling the voltage signal to be measured to obtain a discrete signal;

[0009] S3: Perform Fourier transform on the sampling point signal in the first cycle to obtain the Fourier transform phasor of the sampling point in the first cycle;

[0010] S4: Based on the Fourier transform phasor of the sampling point in the first period, a recursive Fourier transform formula is used to obtain the Fourier transform phasor of the sampling point in the remaining periods;

[0011] S5: Calculate the inverse tangent of the ratio of the imaginary part to the real part of each phase quantity to obtain a phase angle sequence, and untwist the phase angle sequence;

[0012] S6: performing least squares polynomial fitting on the phase angle sequence to obtain an updated coefficient matrix;

[0013] S7: Calculate a first frequency estimation deviation value based on the updated coefficient matrix, and calculate a first frequency estimation value based on the first frequency estimation deviation value;

[0014] S8: modifying the triangular basis function set according to the first frequency estimation value, solving the Fourier series using an improved quasi-synchronous iterative algorithm, and modifying the discrete signal in step S2 based on the Fourier series to obtain a modified sampling sequence;

[0015] S9: repeat S3-S7 for the modified sampling sequence to obtain a second frequency estimation offset;

[0016] S10: Calculating the voltage frequency based on the first frequency estimation deviation value, the second frequency estimation offset and the rated frequency of the system.

[0017] In the above technical scheme, a recursive Fourier transform is performed on the collected voltage signal, and a first frequency estimation is performed on the voltage signal to obtain a first frequency estimation deviation value and a first frequency estimation value. A Fourier series is calculated based on the first frequency estimation value. The voltage signal is corrected according to the Fourier series to obtain a corrected voltage signal sequence, and a second frequency estimation deviation value of the corrected voltage signal sequence is calculated. The first frequency estimation deviation value and the second frequency estimation deviation value are substituted into the calculation to obtain the grid voltage frequency.

[0018] Furthermore, the step S1 specifically includes: calculating the number of sampling points according to the set sampling frequency and the rated frequency of the system; initializing the gain matrix according to the number of phase angle sequences to obtain a coefficient matrix, and the number of phase angle sequences is equal to the number of sampling points; wherein:

[0019] Set the sampling frequency f s , and obtain the rated frequency f0 of the system, then the expression of the number of sampling points N is:

[0020]

[0021] Furthermore, the step S4 specifically includes:

[0022] S401: Introduce the rotation coordinates and construct the functional relationship between the Fourier transform phasors of adjacent sampling points;

[0023] S402: Substitute the Fourier transform phasor of the sampling point in the first cycle into the functional relationship obtained in S401, and use recursive Fourier transform to sequentially calculate the Fourier transform phasors of the sampling points in the remaining cycles.

[0024] Furthermore, the step S6 specifically includes: defining a polynomial function, converting the polynomial function to obtain a phase angle sequence matrix, and updating a coefficient matrix based on the phase angle sequence matrix to obtain an updated coefficient matrix.

[0025] Furthermore, the step S8 comprises:

[0026] S801: Obtaining a grid voltage signal characterization function based on the polynomial coefficient matrix;

[0027] S802: Obtaining a discrete sampling data sequence based on the grid voltage characterization function and the number of sampling points;

[0028] S803: Based on the principle of signal orthogonal decomposition, a discrete Fourier series in the form of a trigonometric function is obtained on the basis of the discrete sampling data sequence;

[0029] S804: Modify the triangular basis function set;

[0030] S805: using a weighted window function instead of an iterative operation to calculate a Fourier series;

[0031] S806: Correct the discrete model in step S2 based on the Fourier series in step S805 to obtain a corrected sampling sequence.

[0032] Furthermore, the method of correcting the triangular basis function set in step S8 is:

[0033]

[0034] in is the triangular basis function before correction, is the modified triangular basis function, where: N is the number of sampling points, f0 is the rated frequency of the system, f1 is the first frequency estimation value, m is the harmonic order, n=1, 2, 3...N.

[0035] According to another aspect of the present invention, a grid voltage frequency calculation device based on recursive Fourier series is provided, comprising a capacitive coupling sensor, a controller and a host computer, wherein the capacitive coupling sensor is used to detect the voltage of a winding under test and transmit the voltage signal to the controller; the controller is used to calculate the voltage frequency based on a grid voltage frequency calculation method based on recursive Fourier series, and transmit the voltage frequency to the host computer, and the host computer is used to display the received voltage frequency in real time.

[0036] In the above technical solution, the voltage of the measured winding is detected by a capacitive coupling sensor, and the voltage signal is transmitted to the controller. The controller has a built-in grid voltage frequency calculation method based on the recursive Fourier series. The controller uses this method to calculate the voltage frequency based on the received voltage signal, and transmits the calculated voltage frequency to the upper display, so that the management personnel can check the voltage frequency.

[0037] Furthermore, the controller includes a control chip and a sampling and conditioning circuit, the sampling and conditioning circuit is used to obtain and adjust the voltage signal, and transmit the voltage signal to the control chip; the control chip is used to calculate the voltage frequency according to the received voltage signal, and transmit the calculated voltage frequency to the host computer for display.

[0038] Furthermore, the sampling and conditioning circuit includes a first operational amplifier, the input end of the first operational amplifier is connected to the output end of the capacitive coupling sensor, and the output end of the first operational amplifier is connected to the input end of the second operational amplifier through a resistor; the output end of the second operational amplifier is connected to the control chip through a resistor, the output end of the second operational amplifier is also connected to a voltage clamping diode, and the output end of the second operational amplifier is grounded through a capacitor; the positive power supply pin of the first operational amplifier is connected to a +15VVCC power supply, and the negative power supply pin of the first operational amplifier is connected to a -15VVDD power supply; the positive power supply pin of the second operational amplifier is connected to a 3.3VVCC power supply, and the negative power supply pin of the second operational amplifier is grounded.

[0039] Furthermore, the controller also includes a protection circuit, the input end of the protection circuit is connected to the capacitive coupling sensor, and the output end of the protection circuit is connected to the sampling and conditioning circuit. The protection circuit can prevent the sampling and conditioning circuit from overvoltage, thereby protecting the sampling and conditioning circuit.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The present invention provides a method for calculating the voltage frequency of a power grid based on a recursive Fourier series. The method performs a recursive Fourier transform on the collected voltage signal and performs a rough frequency estimation on the voltage signal to obtain a rough frequency estimation deviation value and a rough frequency estimation value. The Fourier series is calculated based on the rough frequency estimation value. The voltage signal is corrected according to the Fourier series to obtain a corrected voltage signal sequence. The secondary frequency estimation deviation value of the corrected voltage signal sequence is calculated, and the rough frequency estimation deviation value and the secondary frequency estimation deviation value are substituted into the calculation to obtain the voltage frequency of the power grid. The calculation method provided by the present invention is based on a recursive Fourier transform. By improving the shortcomings of the quasi-synchronous iterative operation to compensate for the frequency domain calculation method, the calculation efficiency and calculation accuracy are improved, and the method has high robustness and frequency calculation accuracy.

[0042] (2) The present invention provides a grid voltage frequency calculation device based on recursive Fourier series, which detects the voltage of the winding under test through a capacitive coupling sensor and transmits the voltage signal to a controller. The controller is equipped with a grid voltage frequency calculation method based on recursive Fourier series. The controller uses this method to calculate the voltage frequency based on the received voltage signal and transmits the calculated voltage frequency to a host display, so that the management personnel can view the voltage frequency. The on-chip resources of TMS320F28377D are fully utilized to quickly calculate the above algorithm, and the voltage conditioning circuit can perform preliminary filtering, thereby improving the calculation accuracy and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a flow chart of a method according to an embodiment of the present invention;

[0044] Figure 2 is a schematic diagram of the structure of a computing device according to an embodiment of the present invention;

[0045] Figure 3 4 is a schematic diagram of a sampling and conditioning circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions of various embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] Example 1

[0048] like Figure 1 As shown, this embodiment provides a method for calculating the voltage frequency of a power grid based on a recursive Fourier series, comprising the following steps:

[0049] S1: Set the sampling frequency, calculate the number of sampling points, and initialize the gain matrix to obtain the coefficient matrix; specifically:

[0050] Set the sampling frequency f s , and obtain the rated frequency f0 of the system, then the expression of the number of sampling points N is:

[0051]

[0052] S2: Sampling the measured voltage signal to obtain a discrete signal, and constructing a sine equation corresponding to the discrete signal. The sine equation is:

[0053]

[0054] Where: A is the amplitude, is the initial phase angle, N is the number of sampling points, and k is the sampling point sequence number.

[0055] S3: Perform Fourier transform on the sampling point signal in the first cycle to obtain the Fourier transform phasor of the sampling point in the first cycle; specifically:

[0056] By performing discrete Fourier transform on equation (1), the Fourier transform phasor can be obtained. The expression of the Fourier transform phasor is:

[0057]

[0058] In order to facilitate analysis, the real and imaginary parts of the phasor are defined as W c and W s :

[0059]

[0060]

[0061] Substituting equation (3) and equation (4) into equation (2), we can obtain:

[0062]

[0063] S4: Based on the Fourier transform phasor of the sampling point in the first period, a recursive Fourier transform formula is used to obtain the Fourier transform phasor of the sampling point in the remaining periods, which specifically includes the following steps:

[0064] S401: Introduce rotating coordinates and construct a functional relationship between Fourier transform phasors of adjacent sampling points; introduce rotating coordinates and use rotating coordinates to represent Fourier transform phasor formulas of two adjacent sampling points respectively; for example: introduce rotating coordinates to represent the rth phasor:

[0065]

[0066] Where: the subscript r+1+n represents the r+1+nth sampling point in the sampling sequence;

[0067] Similarly, the r+1th phasor can be expressed as:

[0068]

[0069] Expanding equation (6) and equation (7), we can get W (r) and W (r+1) The relationship is:

[0070]

[0071] At this time, equation (3) and equation (4) can be rewritten as:

[0072]

[0073]

[0074] S402: Substitute the Fourier transform phasor of the sampling point in the first cycle into the functional relationship obtained in S401, and use recursive Fourier transform to sequentially calculate the Fourier transform phasors of the sampling points in the remaining cycles.

[0075] S5: Calculate the inverse tangent of the ratio of the imaginary part to the real part of each phase quantity to obtain a phase angle sequence, and unwind the phase angle sequence; the calculation method of the phase angle is shown in the following formula:

[0076]

[0077] In actual calculation, in order to prevent the phase angle from jumping between 0 and 2π, it is necessary to perform unwrapping processing on the integer multiples of plus or minus 2π in equation (11) so as to be used for polynomial fitting of the phase angle sequence.

[0078] S6: Perform least squares polynomial fitting on the phase angle sequence to obtain an updated coefficient matrix; specifically including:

[0079] Define a polynomial function; the polynomial function defined in this embodiment is:

[0080] θ (g) =α0+α1g+…+α p g p (12)

[0081] Where p is the number of polynomial fitting; α0, α1…α p is the coefficient of the polynomial function; g is the sampling point pointer, and its expression is:

[0082] g=Nf0t (13)

[0083] Where t is the sampling time.

[0084] Transforming the polynomial function to obtain a phase angle sequence matrix;

[0085] Convert equation (12) into matrix form, expressed as:

[0086] θ=αM (14)

[0087] Among them, the phase angle sequence matrix θ=[θ (1) ,θ (2) …θ (h) ]; coefficient matrix α = [α0, α1…α p ]; The sampling point pointer constant matrix M satisfies:

[0088]

[0089] Where h is the number of phase angle sequences used to calculate the frequency.

[0090] The updated coefficient matrix derived from the phase angle sequence matrix is:

[0091] α=[M T M] -1 M T θ (16)

[0092] S7: Calculate a first frequency estimation deviation value based on the updated coefficient matrix, and calculate a first frequency estimation value based on the first frequency estimation deviation value;

[0093] The voltage signal frequency is defined as:

[0094] f=f0+Δf (17)

[0095] Where Δf is the grid voltage frequency offset.

[0096] From the phase angle characteristics of the recursive Fourier transform, we can get:

[0097]

[0098] Combining equations (12), (13), (17), and (18), we can obtain the first frequency estimation deviation Δf1 and the first frequency estimation value f1 respectively:

[0099]

[0100] f1=f0+Δf1 (20)

[0101] S8: correcting the triangular basis function set according to the first frequency estimation value, solving the Fourier series using an improved quasi-synchronous iterative algorithm, and correcting the discrete signal in step S2 based on the Fourier series to obtain a corrected sampling sequence; specifically comprising:

[0102] S801: Obtaining a grid voltage signal characterization function based on the polynomial coefficient matrix;

[0103]

[0104] m represents the harmonic order; A m is the amplitude of the mth harmonic component in the voltage signal; is the phase angle of the mth harmonic component in the voltage signal.

[0105] S802: Obtain a discrete sampling data sequence based on the grid voltage characterization function and the number of sampling points; perform synchronous sampling with the number of sampling points in each fundamental wave cycle being N, and the obtained discrete sampling data sequence is:

[0106]

[0107] In the formula, Indicates rounding down.

[0108] S803: Based on the principle of signal orthogonal decomposition, a discrete Fourier series b in the form of a trigonometric function is obtained based on the discrete sampling data sequence. x (m);

[0109]

[0110] In the formula, represents the dot product of two discrete sequences, n = 1, 2, 3, ... N.

[0111] S804: Modify the triangular basis functions in the discrete Fourier series function in the trigonometric function form to obtain modified triangular basis functions, and substitute the modified triangular basis functions into the discrete Fourier series function in the trigonometric function form; the method for modifying the triangular basis function set is:

[0112]

[0113] in is the set of triangular basis functions before correction, is the corrected triangular basis function set, where N is the number of sampling points, f0 is the rated frequency of the system, f1 is the rough frequency estimate, m is the harmonic order, and n=1, 2, 3…N.

[0114] S805: Using a weighted window function to replace the iterative operation, the Fourier series is calculated; in order to reduce the amount of algorithm calculation, the weighted window function is used to replace the iterative operation, and the weighted window function is ζ=[δ1,δ2,…δ LN+1 ], we get:

[0115]

[0116] Where L is the number of iterations.

[0117] S806: Correct the discrete model in step S2 based on the Fourier series in step S805 to obtain a corrected sampling sequence.

[0118] S9: Repeat S3-S7 for the modified sampling sequence to obtain a second frequency estimation offset Δf2;

[0119] S10: Calculate the voltage frequency f2 based on the first frequency estimation deviation value, the second frequency estimation offset and the rated frequency of the system, and output the result. The method for calculating the secondary frequency estimation value f2 is as follows:

[0120] f2=f0+Δf1+Δf2 (26).

[0121] Example 2

[0122] like Figure 2 As shown, this embodiment provides a grid voltage frequency calculation device based on recursive Fourier series, including a capacitive coupling sensor, a controller and a host computer, wherein the capacitive coupling sensor is used to detect the voltage of the winding under test, and convert the voltage into a voltage signal and transmit it to the controller; the controller is used to calculate the voltage frequency based on the grid voltage frequency calculation method based on the recursive Fourier series, and transmit the voltage frequency to the host computer, and the host computer is used to display the received voltage frequency in real time. .

[0123] The controller includes a TMS320F28377D control chip and a sampling and conditioning circuit, wherein the sampling and conditioning circuit is used to collect a grid voltage signal and transmit the grid voltage signal to the TMS320F28377D control chip; the TMS320F28377D control chip is used to calculate the grid voltage frequency according to the received grid voltage signal and transmit the calculated grid voltage frequency to a host computer for display. The on-chip resources of the TMS320F28377D control chip perform fast calculations on the above algorithm, and the voltage conditioning circuit can perform preliminary filtering, thereby improving the efficiency and accuracy of frequency calculation.

[0124] The schematic diagram of the conditioning circuit is as follows Figure 3As shown, the conditioning circuit includes an operational amplifier U25B, the model of which is TL074ACD, an operational amplifier U24A, the model of which is OPA4377AIPWR, and a voltage clamping diode U23, the model of which is BAT54S. The input of U25B is connected to the voltage signal input by the capacitive coupling sensor, and the output is connected to U24A through resistor R61 as a voltage follower; the output of U24A is directly output to the control chip through resistor R60, and the output of U24A is also connected to the voltage clamping diode U23 to clamp the voltage at the input of the control chip. Resistors R60 and C14 together form an RC filter with a filtering bandwidth of 5KHz. The positive power pin of U25B is connected to the +15VVCC power supply, the negative power pin is connected to the -15VVDD power supply, the positive power pin of U24A is connected to the 3.3VVCC power supply, and the negative power pin is grounded.

[0125] The controller also includes a protection circuit, the input end of the protection circuit is connected to the capacitive coupling sensor, and the output end of the protection circuit is connected to the sampling and conditioning circuit. The protection circuit can prevent the sampling and conditioning circuit from overvoltage, thereby protecting the sampling and conditioning circuit.

[0126] The voltage of the winding under test is detected by a capacitive coupling sensor, and the voltage signal is transmitted to the controller. The controller has a built-in grid voltage frequency calculation method based on recursive Fourier series. The controller uses this method to calculate the voltage frequency based on the received voltage signal and transmits the calculated voltage frequency to the upper display, making it convenient for managers to view the voltage frequency.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating power grid voltage frequency based on recursive Fourier series, characterized in that: The following steps are involved: S1: Set the sampling frequency, calculate the number of sampling points, and initialize the gain matrix to obtain the coefficient matrix; S2: sampling the voltage signal to be measured to obtain a discrete signal; S3: Perform Fourier transform on the sampling point signal in the first cycle to obtain the Fourier transform phasor of the sampling point in the first cycle; S4: Based on the Fourier transform phasor of the sampling point in the first period, a recursive Fourier transform formula is used to obtain the Fourier transform phasor of the sampling point in the remaining periods; S5: Calculate the inverse tangent of the ratio of the imaginary part to the real part of each phase quantity to obtain a phase angle sequence, and untwist the phase angle sequence; S6: performing least squares polynomial fitting on the phase angle sequence to obtain an updated coefficient matrix; S7: Calculate a first frequency estimation deviation value based on the updated coefficient matrix, and calculate a first frequency estimation value based on the first frequency estimation deviation value; S8: modifying the triangular basis function set according to the first frequency estimation value, solving the Fourier series using an improved quasi-synchronous iterative algorithm, and modifying the discrete signal in step S2 based on the Fourier series to obtain a modified sampling sequence; S9: repeat S3-S7 for the modified sampling sequence to obtain a second frequency estimation offset; S10: Calculating the voltage frequency based on the first frequency estimation deviation value, the second frequency estimation offset and the rated frequency of the system.

2. The method for calculating the voltage and frequency of a power grid based on recursive Fourier series according to claim 1, characterized in that: The S1 specifically includes: calculating the number of sampling points according to the set sampling frequency and the rated frequency of the system; initializing the gain matrix according to the number of phase angle sequences to obtain a coefficient matrix, and the number of phase angle sequences is equal to the number of sampling points.

3. The method for calculating the voltage frequency of a power grid based on recursive Fourier series according to claim 2, characterized in that: The S4 specifically includes: S401: Introduce the rotation coordinates and construct the functional relationship between the Fourier transform phasors of adjacent sampling points; S402: Substitute the Fourier transform phasor of the sampling point in the first cycle into the functional relationship obtained in S401, and use recursive Fourier transform to sequentially calculate the Fourier transform phasors of the sampling points in the remaining cycles.

4. The method for calculating the voltage frequency of a power grid based on recursive Fourier series according to claim 3, characterized in that: The S6 specifically includes: defining a polynomial function, converting the polynomial function to obtain a phase angle sequence matrix, and updating a coefficient matrix based on the phase angle sequence matrix to obtain an updated sequence matrix.

5. The method for calculating the voltage frequency of a power grid based on recursive Fourier series according to claim 4, characterized in that: The S8 includes: S801: Obtaining a grid voltage signal characterization function based on the updated sequence matrix; S802: Obtaining a discrete sampling data sequence based on the grid voltage signal characterization function and the number of sampling points; S803: Based on the principle of signal orthogonal decomposition, a discrete Fourier series in the form of a trigonometric function is obtained on the basis of the discrete sampling data sequence; S804: Modify the triangular basis function set; S805: using a weighted window function instead of an iterative operation to calculate a Fourier series; S806: Correct the discrete model in step S2 based on the Fourier series in S805 to obtain a corrected sampling sequence.

6. The method for calculating the voltage frequency of a power grid based on recursive Fourier series according to claim 4, characterized in that: The method of S8 correcting the triangular basis function set is: ， in is the triangular basis function before correction, is the modified triangular basis function, where: N is the number of sampling points, f 0 is the rated frequency of the system, f 1 is the first frequency estimation value, m is the harmonic number, n=1, 2, 3...N.

7. A grid voltage frequency calculation device based on recursive Fourier series, used to implement the grid voltage frequency calculation method based on recursive Fourier series in any one of claims 1 to 6, characterized in that: It includes a capacitive coupling sensor, a controller and a host computer. The capacitive coupling sensor is used to detect the voltage of the winding under test and transmit the voltage signal to the controller; the controller is used to calculate the voltage frequency based on the grid voltage frequency calculation method of the recursive Fourier series, and transmit the voltage frequency to the host computer, and the host computer is used to display the received voltage frequency in real time.

8. The grid voltage frequency calculation device based on recursive Fourier series according to claim 7, characterized in that: The controller includes a control chip and a sampling and conditioning circuit. The sampling and conditioning circuit is used to adjust the voltage signal and transmit the voltage signal to the control chip; the control chip is used to calculate the voltage frequency according to the received voltage signal and transmit the calculated voltage frequency to the host computer for display.

9. The grid voltage frequency calculation device based on recursive Fourier series according to claim 8, characterized in that: The sampling and conditioning circuit includes a first operational amplifier, the input end of the first operational amplifier is connected to the output end of the capacitive coupling sensor, and the output end of the first operational amplifier is connected to the input end of the second operational amplifier through a resistor; the output end of the second operational amplifier is connected to the control chip through a resistor, the output end of the second operational amplifier is also connected to a voltage clamping diode, and the output end of the second operational amplifier is grounded through a capacitor; the positive power supply pin of the first operational amplifier is connected to a +15V VCC power supply, and the negative power supply pin of the first operational amplifier is connected to a -15V VDD power supply; the positive power supply pin of the second operational amplifier is connected to a 3.3V VCC power supply, and the negative power supply pin of the second operational amplifier is grounded.

10. The grid voltage frequency calculation device based on recursive Fourier series according to claim 8, characterized in that: The controller further comprises a protection circuit, an input end of the protection circuit is connected to the capacitive coupling sensor, and an output end of the protection circuit is connected to the sampling and conditioning circuit.

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