阅读说明：本技术 一种新能源柔性直流并网暂态谐波检测方法及系统 (New energy flexible direct-current grid-connected transient harmonic detection method and system ) 是由 李清泉 刘超 迟永宁 李琰 王良凯 王文欣 于 2019-12-02 设计创作，主要内容包括：本公开提出了一种新能源柔性直流并网暂态谐波检测方法及系统,采用皮尔逊相关系数法确定VMD分解模态分量个数K,利用奇异值分解(Singular Value Decomposition,SVD)精确定位信号扰动起止时刻,最后通过Hilbert变换及最小二乘拟合提取瞬时幅值频率信息,在实现暂态谐波信号的高精度检测和扰动定位的同时,提高了算法自适应性和计算效率。本公开提高了谐波检测的效率和准确性,有利于根据检测结果对谐波进行治理,减少了电网功率损耗,减少暂态扰动对电网稳态运行产生冲击,提高电网运行的稳定性。(The method and the system for detecting the transient harmonic wave of the new energy flexible direct current grid connection are characterized in that a Pearson correlation coefficient method is adopted to determine the number K of VMD Decomposition modal components, Singular Value Decomposition (SVD) is utilized to accurately position the signal disturbance starting and stopping time, and instantaneous amplitude frequency information is extracted through Hilbert transformation and least square fitting, so that the algorithm adaptability and the calculation efficiency are improved while the high-precision detection and disturbance positioning of the transient harmonic wave signal are realized. The harmonic detection method and the harmonic detection device improve the efficiency and accuracy of harmonic detection, are beneficial to treating harmonic according to detection results, reduce power consumption of a power grid, reduce the impact of transient disturbance on steady-state operation of the power grid, and improve the stability of operation of the power grid.)

1. A new energy flexible direct current grid-connected transient harmonic detection method is characterized by comprising the following steps:

acquiring a power signal of a flexible direct current grid-connected system to be detected;

setting VMD decomposition parameters, and adaptively searching and obtaining the VMD modal decomposition number by adopting a Pearson correlation coefficient method;

performing VMD decomposition on the electric power signal according to the set VMD decomposition parameters and the obtained VMD modal decomposition number K to obtain K modal components;

and distinguishing a steady state harmonic wave and a transient state harmonic wave according to the obtained harmonic wave modes, carrying out singular value decomposition on a modal component corresponding to the transient state harmonic wave to position the transient state harmonic wave disturbance starting and stopping time, and solving the instantaneous amplitude and frequency of each modal component of the transient state harmonic wave, namely obtaining the disturbance time and amplitude frequency of a transient state harmonic wave signal.

2. The method for detecting the transient harmonic waves of the new energy flexible direct-current grid connection as claimed in claim 1, wherein the method comprises the following steps: the method adopts a Pearson correlation coefficient method to adaptively find the VMD modal decomposition number, and comprises the following steps:

step 2-1: initializing an initial modal decomposition number K to 2;

step 2-2: performing VMD decomposition according to the decomposition number to obtain K modal components;

step 2-3: calculating the correlation coefficient between each modal component and the original signal by using a Pearson correlation coefficient method;

step 2-4: calculating residual errors of the modal components and the original signal to obtain residual errors of the modal components, and calculating a correlation coefficient of the residual errors and the original signal by using a Pearson correlation coefficient method;

step 2-5: if the modal component residual error is related to the correlation coefficient r of the original signal_2kLess than or equal to the minimum value of the correlation coefficient between each mode and the original signal, and not more than the residual error and the original signal phase1/10 of the maximum value of the correlation coefficient, wherein the modal decomposition number of the current cycle is the optimal modal decomposition number, and a K value is output; otherwise, let K be K +1 and execute step 2-2.

3. The method for detecting the transient harmonic waves of the new energy flexible direct-current grid connection as claimed in claim 2, wherein the method comprises the following steps: the calculation formula for calculating the correlation coefficient between each modal component and the original signal and the correlation coefficient between the residual error and the original signal by using the pearson correlation coefficient method is as follows:

wherein r is_1kFor each modal component with respect to the original signal_k(t) is the residual of the modal component from the original signal, r_2kIs the correlation coefficient between the modal residual and the original signal, and f (t) is the original signal.

4. The method for detecting the transient harmonic waves of the new energy flexible direct-current grid connection as claimed in claim 1 or 2, wherein the method comprises the following steps: the method for performing VMD decomposition on the power signal to obtain K modal components comprises the following steps:

step 3-1, setting VMD decomposition parameter values;

step 3-2, initializing a K-th modal component decomposed in the first cycle, and a central frequency and a Lagrangian multiplication operator corresponding to the K-th modal component in the first cycle;

and 3-3, updating the Kth modal component and the corresponding central frequency and Lagrange multiplication operator thereof by adopting a multiplication operator alternating direction method according to the set VMD decomposition parameter.

3-4, judging whether the obtained modal components tend to be stable or not, if so, finishing the cycle and outputting K modal components; otherwise, step 3-3 is performed.

5. The method for detecting the transient harmonic waves of the new energy flexible direct-current grid connection as claimed in claim 1, wherein the method comprises the following steps: singular value decomposition is carried out on modal components corresponding to the transient harmonics to position the transient harmonic disturbance starting and stopping time, and the steps are as follows:

constructing a reconstructed attractor track matrix H of the power signal;

performing singular value decomposition on the reconstructed attractor trajectory matrix H;

and determining the transient harmonic disturbance start-stop time information through the mode maximum value of the decomposed mode component signal.

6. The method for detecting the transient harmonic waves of the new energy flexible direct-current grid connection as claimed in claim 1, wherein the method comprises the following steps: and (3) solving the instantaneous amplitude and frequency of each modal component of the transient harmonic: the instantaneous amplitude and frequency of each modal component are obtained by employing a Hilbert transform.

7. The method for detecting the transient harmonic waves of the new energy flexible direct-current grid connection as claimed in claim 6, wherein the method comprises the following steps: after the instantaneous amplitude and the frequency of each modal component of the transient harmonic are obtained, the method further comprises the following steps: and fitting the instantaneous amplitude and the frequency of each modal component of the transient harmonic by adopting a least square method to obtain the final instantaneous amplitude and frequency.

8. The utility model provides a flexible direct current of new forms of energy and is incorporated into power networks transient state harmonic detecting system which characterized in that, including setting up electric transformer and the harmonic detection treater that once inclines to detect electric power signal at the electric wire netting, the harmonic detection treater includes:

a signal acquisition module: the method comprises the steps of acquiring a power signal of a flexible direct current grid-connected system to be detected;

a mode number determination module: the method is used for setting VMD decomposition parameters and adaptively searching and obtaining the VMD modal decomposition number by adopting a Pearson correlation coefficient method;

a decomposition module: the VMD decomposition device is used for performing VMD decomposition on the electric power signal according to the set VMD decomposition parameters and the obtained VMD modal decomposition number K to obtain K modal components;

a detection module: the method is used for distinguishing the steady-state harmonic waves and the transient-state harmonic waves according to the obtained harmonic wave modes, carrying out singular value decomposition on the modal components corresponding to the transient-state harmonic waves to locate the transient-state harmonic wave disturbance starting and stopping time, and solving the instantaneous amplitude and frequency of each modal component of the transient-state harmonic waves, namely obtaining the disturbance time and amplitude frequency of a transient-state harmonic wave signal.

9. An electronic device comprising a memory and a processor and computer instructions stored on the memory and executable on the processor, the computer instructions when executed by the processor performing the steps of the method of any of claims 1 to 7.

10. A computer-readable storage medium storing computer instructions which, when executed by a processor, perform the steps of the method of any one of claims 1 to 7.

Technical Field

The disclosure relates to the technical field of power grid harmonic detection, in particular to a new energy flexible direct current grid-connected transient harmonic detection method and system.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

In recent years, with the continuous development of smart power grids in China, new energy power generation represented by wind power and photoelectricity is continuously connected to the power grids, and a large number of nonlinear electrical devices and impact loads are put into use to bring serious power quality pollution problems to the power grids, wherein harmonic pollution is the main problem. Due to the existence of harmonic waves, the power loss of a power grid is increased, the randomness of transient disturbance generates impact on the steady-state operation of the power grid, and more challenges are brought to the detection of the harmonic waves of the system especially in a new scene that a new energy station transmits electricity through flexible direct current in a long distance, so that research on a high-precision power grid harmonic wave and disturbance detection method is necessary.

The harmonic waves of the power system are divided into steady-state harmonic waves and transient-state harmonic waves, and domestic and foreign experts carry out deep research on steady-state harmonic wave detection, but have less research on transient-state harmonic wave/inter-harmonic wave detection methods. The existing harmonic detection method mainly comprises Fourier transform, an instantaneous reactive power theory, wavelet transform, Hilbert-Huang transform (HHT) and the like, under asynchronous sampling, the harmonic detected by the Fourier transform has frequency spectrum leakage and fence effect, and transient harmonic cannot be detected; the instantaneous reactive power theory has the advantages of high calculation speed, small calculation amount and good real-time performance, but requires no distortion of signal waveforms; the wavelet transform time-frequency local analysis effect is good, but the decomposition excessively depends on the selection of wavelet bases and decomposition layer numbers; the HHT can self-adaptively decompose nonlinear and non-stationary signals, has analysis capability on stationary harmonic waves, and is easy to have the problem of mode aliasing when harmonic signals with similar frequencies are decomposed.

In the variational problem framework, a Variational Modal Decomposition (VMD) continuously updates each mode and its center frequency by using an alternating direction penalty factor, but the VMD generally determines the number K of components in an original signal in advance by fast fourier transform, and needs to manually observe the center frequency of a frequency spectrum, so that the method has low adaptivity and low calculation efficiency. Transient harmonics generated by the new energy flexible direct current grid connection need to be detected in terms of instantaneous amplitude and frequency, disturbance starting and stopping moments need to be positioned, higher detection precision and noise robustness are needed, and the current detection method cannot meet the requirements of transient harmonic detection.

Disclosure of Invention

The method and the system for detecting the transient harmonic wave of the new energy flexible direct current grid connection are used for solving the problems, the number K of VMD Decomposition modal components is determined by adopting a Pearson correlation coefficient method, the signal disturbance starting and stopping time is accurately positioned by utilizing Singular Value Decomposition (SVD), and finally instantaneous amplitude frequency information is extracted through Hilbert transformation and least square fitting, so that the algorithm adaptivity and the calculation efficiency are improved while the high-precision detection and disturbance positioning of the transient harmonic wave signal are realized.

In order to achieve the purpose, the following technical scheme is adopted in the disclosure:

one or more embodiments provide a new energy flexible direct current grid-connected transient harmonic detection method, which includes the following steps:

acquiring a power signal of a flexible direct current grid-connected system to be detected;

setting VMD decomposition parameters, and adaptively searching and obtaining the VMD modal decomposition number by adopting a Pearson correlation coefficient method;

performing VMD decomposition on the electric power signal according to the set VMD decomposition parameters and the obtained VMD modal decomposition number K to obtain K modal components;

and distinguishing a steady state harmonic wave and a transient state harmonic wave according to the obtained harmonic wave modes, carrying out singular value decomposition on a modal component corresponding to the transient state harmonic wave to position the transient state harmonic wave disturbance starting and stopping time, and solving the instantaneous amplitude and frequency of each modal component of the transient state harmonic wave, namely obtaining the disturbance time and amplitude frequency of a transient state harmonic wave signal.

One or more embodiments provide a new energy flexible direct current grid-connected transient harmonic detection system, which includes a power transformer and a harmonic detection processor, the power transformer and the harmonic detection processor being disposed on a primary side of a power grid to detect a power signal, and the harmonic detection processor includes:

a signal acquisition module: the method comprises the steps of acquiring a power signal of a flexible direct current grid-connected system to be detected;

a mode number determination module: the method is used for setting VMD decomposition parameters and adaptively searching and obtaining the VMD modal decomposition number by adopting a Pearson correlation coefficient method;

a decomposition module: the VMD decomposition device is used for performing VMD decomposition on the electric power signal according to the set VMD decomposition parameters and the obtained VMD modal decomposition number K to obtain K modal components;

a detection module: the method is used for distinguishing the steady-state harmonic waves and the transient-state harmonic waves according to the obtained harmonic wave modes, carrying out singular value decomposition on the modal components corresponding to the transient-state harmonic waves to locate the transient-state harmonic wave disturbance starting and stopping time, and solving the instantaneous amplitude and frequency of each modal component of the transient-state harmonic waves, namely obtaining the disturbance time and amplitude frequency of a transient-state harmonic wave signal.

An electronic device comprising a memory and a processor and computer instructions stored on the memory and executed on the processor, the computer instructions, when executed by the processor, performing the steps of the above method.

A computer readable storage medium storing computer instructions which, when executed by a processor, perform the steps of the above method.

Compared with the prior art, the beneficial effect of this disclosure is:

the method utilizes the Pearson correlation coefficient method to realize self-adaptive acquisition of the VMD modal decomposition number K, improves the self-adaptability of the transient harmonic detection method, and simultaneously improves the detection efficiency. The method combines the VMD and the Hilbert transform, has good dividing capability on similar frequency components by virtue of a VMD algorithm and the accurate analysis capability on signals by the Hilbert transform, introduces singular value decomposition to realize disturbance positioning and amplitude frequency detection on transient harmonic signals, solves the problems of mode mixing and noise interference of the traditional signal decomposition, and improves the adaptability and the universality of the algorithm. The simulation example verifies the effectiveness, accuracy and noise robustness of the algorithm in detecting transient harmonic signals, and has important significance for detecting and managing the harmonic/inter-harmonic of a system after new energy flexible direct current grid connection. The harmonic detection method and the harmonic detection device improve the efficiency and accuracy of harmonic detection, are beneficial to treating harmonic according to detection results, reduce power consumption of a power grid, reduce the impact of transient disturbance on steady-state operation of the power grid, and improve the stability of operation of the power grid.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and not to limit the disclosure.

FIG. 1 is an overall flow diagram of a transient harmonic detection method in accordance with one or more embodiments;

fig. 2 is a flowchart of determining the number of VMD modalities of embodiment 1 of the present disclosure;

fig. 3 is a schematic time domain waveform of an original signal containing transient harmonics in an example of embodiment 1 of the present disclosure;

fig. 4 is a raw signal VMD decomposition result in an example of embodiment 1 of the present disclosure;

fig. 5 is a layer 4 component signal of the harmonic component IMF3 of fig. 4 after singular value decomposition.

The specific implementation mode is as follows:

the present disclosure is further described with reference to the following drawings and examples.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise. It should be noted that, in the case of no conflict, the embodiments and features in the embodiments in the present disclosure may be combined with each other. The embodiments will be described in detail below with reference to the accompanying drawings.

Technical term interpretation:

VMD: variational modal decomposition, called as variational modedecomposition, abbreviated as VMD.

Hilbert transform: is a hilbert transform.

SVD: singular Value Decomposition (Singular Value Decomposition) is an important matrix Decomposition in linear algebra, and is a generalization of unitary diagonalization of a normal matrix in matrix analysis.

In the technical solutions disclosed in one or more embodiments, as shown in fig. 1, a new energy flexible direct current grid-connected transient harmonic detection method includes the following steps:

step 1: acquiring a power signal to be detected;

optionally, the signals are collected through a power transformer, a current transformer can be adopted to convert primary side current of new energy after grid connection through the flexible direct current transmission system into a secondary side measurable current signal, and a power signal f (t) containing transient harmonic is obtained through sampling.

Step 2: setting VMD decomposition parameters which comprise a penalty factor alpha and a noise tolerance degree tau, and adaptively searching and obtaining the VMD modal decomposition number by adopting a Pearson correlation coefficient method;

parameters such as a VMD penalty factor alpha and a noise tolerance degree tau are set, and the VMD modal decomposition number K is searched in a self-adaptive mode.

And step 3: performing VMD decomposition on the electric power signal f (t) containing the transient harmonic according to the set VMD decomposition parameters and the obtained VMD modal decomposition number to obtain K modal components u_k(t); each mode is an am/fm function, corresponding to a harmonic component.

And 4, step 4: distinguishing a steady state harmonic wave and a transient state harmonic wave according to the obtained harmonic wave mode, carrying out singular value decomposition on a modal component corresponding to the transient state harmonic wave to position the transient state harmonic wave disturbance starting and stopping time, and solving the instantaneous amplitude and frequency of each modal component of the transient state harmonic wave, namely obtaining the disturbance time and amplitude frequency of a transient state harmonic wave signal; and disturbance positioning and detection of the transient harmonic signals are realized.

In step 1, the expression of the power signal f (t) containing the transient harmonic may be:

wherein H is the highest harmonic order, A_hAnd

the amplitude and phase of the h harmonic, respectively.

In step 2, variational modal decomposition: VariationMododecomposition, abbreviated VMD; the larger the VMD parameter penalty factor alpha is, the smaller the bandwidth of each component signal obtained by decomposition is, otherwise, the larger the bandwidth is, alpha can be set to 2000; the noise tolerance tau represents the tolerance degree of noise, and the smaller tau is, the stronger noise tolerance capability is, and the smaller tau can be set as a smaller value empirically;

optionally, in step 2, the number K of modal decompositions is determined according to a pearson correlation coefficient method, which may be shown in fig. 2, and the steps may include:

step 2-1: initializing an initial modal decomposition number K to 2;

step 2-2: performing VMD decomposition on the power signal f (t) according to the decomposition number to obtain K modal components u_k(t)；

Step 2-3: calculating each modal component u by using Pearson correlation coefficient method_k(t) correlation coefficient r with original signal f (t)_1k；

Step 2-4: calculating each modal component u_k(t) residual error with original signal f (t) to obtain residual error epsilon_k(t) calculating the residual ε by Pearson's correlation coefficient method_k(t) correlation coefficient r with original signal f (t)_2k；

Step 2-5: setting the cycle end condition as r_2k≤min(r_1k)，And r is_2k≤max(r_2k)/10；

If the modal component residual error is related to the correlation coefficient r of the original signal_2kLess than or equal to the minimum value of the correlation coefficient between each mode and the original signal and not more than 1/10 (r) of the maximum value of the correlation coefficient between the residual error and the original signal_2k≤min(r_1k) And r is_2k≤max(r_2k) 10, the modal decomposition number of the current cycle is the optimal modal decomposition number, and a K value is output; otherwise, making K equal to K +1, and executing the step 2-2;

wherein, the termination condition r_2k≤min(r_1k) In order to avoid the occurrence of modal aliasing and ensure the full VMD decomposition; end condition r_2k≤max(r_2k) The/10 is to prevent the VMD from over-decomposing, creating spurious components.

Calculating each modal component u by using Pearson correlation coefficient method_k(t) correlation coefficient with original signal f (t) and residual ε_k(t) the correlation coefficient with the original signal f (t) is calculated as follows:

wherein r is_1kFor each modal component with respect to the original signal_k(t) is the residual of the modal component from the original signal, r_2kIs the correlation coefficient between the modal residual and the original signal, and f (t) is the original signal.

In step 3 and step 2-2, VMD decomposition is performed on the power signal f (t) containing the transient harmonic, specifically including the steps of:

step 3-1, setting parameter values; setting VMD decomposition parameters comprising a penalty factor alpha and a noise tolerance degree tau;

step 3-2, initializing a K-th modal component decomposed in the first cycle, and a central frequency and a Lagrangian multiplication operator corresponding to the K-th modal component in the first cycle;

initialization

And n, wherein

Representing the k-th modal component decomposed in the first cycle,

indicating the first cycle

The center frequency of the corresponding frequency is set,

indicating the first cycle

A corresponding Lagrangian multiplier;

and 3-3, updating the Kth modal component and the corresponding center frequency and Lagrange multiplication operator thereof by adopting a multiplication operator alternating direction method.

The method for the alternative direction of the multiplicative operator is concretely as follows:

updating the Kth modal component u according to the formula (4) and the formula (5)_kCenter frequency ω corresponding to the Kth modal component_k；

Wherein

Is the fourier transform of the power signal f (t), and α is a penalty factor.

Updating the Lagrangian multiplier lambda according to the formula (6);

where τ is the noise tolerance level.

And 3-4, judging whether an iteration termination condition is met, namely whether the obtained modal components tend to be stable, if not, executing the step 3-3, otherwise, finishing the cycle and outputting K modal components.

Whether the obtained modal component tends to be stable may specifically be: the change rate of each modal component when the current cycle is compared with the modal component obtained in the previous cycle is smaller than the set determination accuracy, and can be expressed as follows:

where e is a given decision accuracy.

In step 4, whether the time domain characteristics of the multiple different frequency components obtained by VMD decomposition are steady state or transient state harmonic is judged, wherein the noise component can not be considered.

Singular value decomposition is carried out on modal components corresponding to the transient harmonics to position the transient harmonic disturbance start-stop moment, and the steps can be as follows:

step 4-1, constructing a reconstructed attractor trajectory matrix H of the modal component u (t);

constructing a reconstructed attractor trajectory matrix H for the modal component u (t) according to equation (8):

wherein, 1< N < N, N is the total sampling point number of u (t).

Step 4-2, performing singular value decomposition on the reconstructed attractor trajectory matrix H;

optionally, singular value decomposition may be performed on the reconstructed attractor trajectory matrix H by using formula (9):

wherein U ═ U (U)₁,u₂,…,u_q) And V ═ V (V)₁,v₂,…,v_q) Is an orthogonal matrix, S ═ diag (σ)₁,σ₂,…,σ_q),o)^TFor diagonal matrix, q ═ min (N-N, N), 1<n<N, N is the total number of sampling points of x (t), then sigma_iAre the singular values of the matrix a.

And 4-3, determining the transient harmonic disturbance start-stop time information through the modulus maximum value of the decomposed component signal.

The modal component u (t) signal is decomposed into a plurality of singular value decomposition component signals, which may be as follows:

order to

Then there is

Let s_i＝[u_i(1),u_i(2),…,u_i(n)]，h_i＝[u_i(n+1),u_i(n+2),…,u_i(N)]^TThus, an i-th layer singular value decomposition component signal P is constructed_i＝[s_i,h_i]And the primary harmonic component signal

Singular value component signal P_iThe mutation information of u (t) is reflected.

As a further improvement, the instantaneous amplitude and frequency of each modal component of the transient harmonic are obtained, a Hilbert transform may be used to obtain the instantaneous amplitude and frequency of each modal component, and the Hilbert transform for a certain modal component u (t) is:

inverse transformation to

Then u (t) and y (t) form the analytic signal:

y(t)＝u(t)+jy(t)＝a(t)e^jθ(t)

in the formula

The calculation formula of the amplitude A and the frequency F of the modal component is as follows:

as a further improvement, for convenience of overall analysis, the obtained curves of the amplitude a and the frequency F of each modal component may be processed, and optionally, the instantaneous amplitude and the frequency of each modal component may be determined by a total least squares fitting, and the method may specifically be as follows:

the instantaneous amplitude frequency calculated by equations (11) and (12) has slight fluctuation, and the final instantaneous amplitude and frequency can be further determined by least square fitting, as follows:

in the graph of the change of the amplitude a (t) along with the time, an average straight line is obtained according to a least square fitting method to approximately replace the change relation of the amplitude a along with the time t, the average value of the average straight line in the interval is calculated, and the instantaneous amplitude A can be predicted through the average value of the straight line.

In the graph of the change of the phase angle theta (t) along with the time, an average straight line is obtained according to a least square fitting method to approximately replace the change relation of the phase angle theta along with the time t, and the instantaneous frequency F can be predicted by fitting the slope of the straight line.

A simulation experiment is performed on the method for explaining the effect of the method of the embodiment, which specifically includes the following steps:

the power signal containing transient harmonics in this example is:

f(t)＝f₁(t)+f₂(t)+f₃(t)

wherein the content of the first and second substances,

the power signal is composed of fundamental, short-time 8 th harmonic and 525Hz inter-harmonic, and is superimposed with 30dB Gaussian white noise. The transient starts at 0.01s and ends at 0.03 s. As shown in fig. 3, is a time domain waveform of the transient harmonic signal.

Referring to fig. 2, the number of mode components of VMD decomposition obtained by pearson's correlation coefficient method satisfies the loop termination condition when K is 3, and it is determined that the optimum number of mode decompositions of the harmonic signal is 3.

Setting K to 3, α to 2000, and τ to 0.5, VMD decomposition is performed on the original signal, and the result is shown in fig. 4. Under the condition of 30dB noise, the VMD method can completely separate fundamental wave, short-time 8-order harmonic wave and 525Hz inter-harmonic wave, and the accurate extraction and decomposition capacity of the method on transient harmonic signals is verified.

Fig. 5 shows a layer 4 component signal obtained by singular value decomposition of IMF3, and it can be seen that the start time of the 8 th harmonic is 0.0098s, and the end time is 0.0304s, which are basically consistent with the theoretical value.

TABLE 1 transient disturbance harmonic detection results

Hilbert transformation is carried out on each modal component, harmonic amplitude and frequency of each component under 30dB noise are calculated, least square fitting is carried out on amplitude frequency values of each modal component, and finally, accurate harmonic parameter detection results are obtained and are shown in table 1. The average detection error of the amplitude is 0.275%, the average detection error of the frequency is 0.117%, the detection precision is high, the effectiveness of the method in transient harmonic detection is verified, and the method has anti-noise capability and good robustness.