CN113468474B - Power grid frequency estimation method based on root Mini-Norm - Google Patents
Power grid frequency estimation method based on root Mini-Norm Download PDFInfo
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- CN113468474B CN113468474B CN202111035426.7A CN202111035426A CN113468474B CN 113468474 B CN113468474 B CN 113468474B CN 202111035426 A CN202111035426 A CN 202111035426A CN 113468474 B CN113468474 B CN 113468474B
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Abstract
The invention discloses a power grid frequency estimation method based on a root Mini-norm.A complex exponential model of sampled data is designed aiming at steady-state power grid sampled data of an additive Gaussian noise background, then asymptotic unbiased autocorrelation processing is carried out on the sampled data, then the data after autocorrelation processing is decomposed into a multidimensional signal subspace and a multidimensional noise subspace by adopting an MUSIC algorithm in spectrum decomposition, then the multidimensional noise subspace is mapped into a one-dimensional vector, and finally, a polynomial root solving method is adopted aiming at the characteristics that the power grid center frequency is one and the corresponding complex exponential model is two, so that the power grid center frequency is calculated; according to the method, the Mini-Norm method is utilized to map the multidimensional matrix operation into the one-dimensional vector operation, so that the calculated amount is reduced, the power grid frequency estimation performance of the multidimensional noise subspace can be achieved, and the calculated amount can be reduced; the method not only considers the performance precision of the power grid frequency estimation, but also reduces the requirement on calculated amount.
Description
Technical Field
The invention relates to a power grid frequency estimation method based on a root Mini-Norm, which is used for estimating the frequency of a power system and belongs to the technical field of operation and control of the power system.
Background
With the wide application of nonlinear loads such as power electronic semiconductor devices and the like in a power grid, a large amount of higher harmonics are injected into a power system, so that the voltage and current waveforms of the power grid are distorted, and serious influence is brought to the accurate measurement and harmonic analysis of the power grid frequency. The frequency is the most basic parameter for the operation of the power system, and accurate and rapid frequency estimation has important application value for the operation, monitoring and control of the power system.
At present, a frequency estimation method of a power system mainly uses Fast Fourier Transform (FFT), and performs two-point or three-point interpolation on a spectral line to obtain a frequency estimation value of a signal. The classic FFT transform belongs to the frequency domain method, which has a high requirement on the requirement of the sample data volume.
Music (multiple Signal classification), a class of spatial spectrum estimation algorithms, is characterized by using covariance matrix (Rx) of received data to perform feature decomposition, separating Signal subspace and noise subspace, using orthogonality of Signal direction vector and noise subspace to form spatial scanning spectrum, and performing global search spectrum peak, thereby implementing parameter estimation of Signal. However, the classical MUSIC algorithm is computationally intensive.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a power grid frequency estimation method based on a root Mini-Norm, which not only retains the estimation precision of the spectrum estimation method on the power grid frequency, but also reduces the operation amount compared with the classical MUSIC algorithm.
In order to solve the technical problem, the power grid frequency estimation method based on the root Mini-Norm is characterized in that a complex exponential model of sampled data is designed aiming at steady-state power grid sampled data of an additive Gaussian noise background, then asymptotic unbiased autocorrelation processing is carried out on the sampled data, then the data after autocorrelation processing is decomposed into a multidimensional signal subspace and a multidimensional noise subspace by adopting a MUSIC algorithm in spectrum decomposition, then the multidimensional noise subspace is mapped into a one-dimensional vector, and finally a polynomial root solving method is adopted aiming at the characteristics that the power grid center frequency is one and the corresponding complex exponential model is two, so that the power grid center frequency is calculated.
The Mini-Norm algorithm belongs to a time domain method. The time domain method can greatly reduce the requirement for the amount of sampled data relative to the frequency domain method. The time domain method utilizes an Euler formula and Hilbert transformation to transform a sinusoidal signal into a complex exponential sinusoidal signal, then utilizes the uniqueness of spectral decomposition, can intuitively and quickly estimate the frequency of a power grid, and theoretically, the estimation precision can reach the lower boundary of Clarmero.
Specifically, the power grid frequency estimation method based on the root Mini-Norm comprises the following steps:
step 1: selecting a section of sine signal sampling sequence sampled at equal intervalsWherein, in the step (A),represents a vector of a sequence of samples representing the sequence of samples,represents the firstThe number of sequential samples of the data is,,representing the total number of sampled data;
step 2: to the sampling sequence vectorPerforming asymptotic unbiased autocorrelation operation to obtain autocorrelation vector,The expression of (a) is:
wherein the content of the first and second substances,representative pairThe conjugation is taken out and the reaction is carried out,,representing the number of autocorrelation vectors;
and step 3: according to a given autocorrelation vectorWill beRewriting is in the form of Toeplitz matrix, set to(ii) a To pairSingular value decomposition is carried out, and the expression is as follows:
wherein the content of the first and second substances,、andrespectively corresponding to a left singular vector, a singular value and a right singular vector of the signal subspace;、andrespectively corresponding to a right singular vector, a singular value and a right singular vector of the noise subspace;
and 4, step 4: for step 3Mapping to Mini-Norm form: for a complex exponential type grid frequency estimation,is composed ofDimension matrix, letIs composed ofThe Mini-Norm form (1), wherein,the expression of (a) is:
solving a polynomial byThe mode is a positive value closest to 1, and the grid frequency estimation value isIs that(ii) a Wherein the content of the first and second substances,representative pairTaking the imaginary part of the signal to be processed,representative pairTaking a real part of the signal,represents the function of the inverse tangent of the line,representing a sequence of acquired samplesThe sampling frequency of the time.
Under the background of power grid frequency estimation based on the existing MUSIC spectrum estimation, according to the dividing mode of a signal subspace and a noise subspace of the power grid frequency estimation in the MUSIC spectrum estimation method, the power grid frequency estimation calculation amount based on the multidimensional noise subspace method is in direct proportion to the dimension of the subspace. And the multidimensional noise subspace is converted into a one-dimensional vector, so that the power grid frequency estimation performance of the multidimensional noise subspace can be achieved, and the calculated amount can be reduced.
The invention utilizes the Mini-Norm method to map the multidimensional matrix operation into the one-dimensional vector operation, thereby reducing the calculated amount, achieving the power grid frequency estimation performance of the multidimensional noise subspace and reducing the calculated amount. Compared with the prior art, the method not only considers the power grid frequency estimation performance precision, but also reduces the requirement on calculated amount.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a flow chart of a method for estimating grid frequency based on root Mini-Norm.
Fig. 2 shows a sample sequence with a signal-to-noise ratio of 10 dB.
FIG. 3 is a graph of the mean estimate of the grid frequency for signal-to-noise ratios from 0dB to 20 dB.
Fig. 4 is a plot of the power grid frequency estimated variance from 0dB to 20dB signal-to-noise ratio.
Detailed Description
In the power grid frequency estimation method based on the root Mini-Norm according to the embodiment, as shown in fig. 1 to 4, for steady-state power grid sampling data of a section of additive gaussian noise background, a complex exponential model of the sampling data is designed, then, the sampling data is subjected to asymptotic and unbiased autocorrelation processing, then, the data subjected to autocorrelation processing is decomposed into a multidimensional signal subspace and a multidimensional noise subspace by using a MUSIC classification algorithm in spectrum decomposition, the multidimensional noise subspace is mapped into a one-dimensional vector, and finally, for the characteristic that the power grid center frequency is one and the corresponding complex exponential model is two, a polynomial root-finding method is adopted to calculate the power grid center frequency.
As shown in fig. 1, the method specifically comprises the following steps:
step 1: selecting a section of power grid voltage signal sampling sequence sampled at equal intervals
Order sampling sequenceWherein, in the step (A),represents a vector of a sequence of samples representing the sequence of samples,represents the firstThe number of sequential samples of the data is,representing the total number of sample data.
Step 2: obtaining a self-correlation vector
And step 3: for the autocorrelation vectorPerforming singular value decomposition in the form of Toeplitz matrix
Order toIs an autocorrelation vectorIn the form of Toeplitz matrix. To pairSingular value decomposition is carried out, and the expression is as follows:
wherein the content of the first and second substances,、andrespectively corresponding to a left singular vector, a singular value and a right singular vector of the signal subspace;、andcorresponding to the right singular vector, singular value and right singular vector of the noise subspace, respectively.
And 4, step 4: mapping noise subspaces to Mini-Norm form
For a complex exponential type grid frequency estimation,is composed ofDimension matrix, letIs composed ofThe Mini-Norm form (1), wherein,the expression of (a) is:
and 5: solving the polynomial to obtain the estimated value of the frequency
solving a polynomial byThe mode is a positive value closest to 1, and the grid frequency estimation value isIs that. Wherein the content of the first and second substances,representative pairTaking the imaginary part of the signal to be processed,representative pairTaking a real part of the signal,represents the function of the inverse tangent of the line,representing a sequence of acquired samplesThe sampling frequency of the time.
Step 6: simulation result
The invention aims at power grid frequency estimation method simulation based on a root Mini-Norm. In the simulation, the assumption is made,,. A sample sequence at a signal-to-noise ratio of 10dB, as shown in fig. 2. From fig. 3 and 4, it can be seen that the power grid frequency estimation performance based on the root Mini-Norm is substantially consistent with the estimation performance of the MUSIC method.
According to the simulation result, the data are decomposed into the multi-dimensional signal subspace and the multi-dimensional noise subspace by adopting the MUSIC algorithm in the spectrum decomposition, then the multi-dimensional noise subspace is mapped into the one-dimensional vector, and finally, the power grid center frequency is calculated by adopting a polynomial root-finding method according to the characteristic that the power grid center frequency is one and the corresponding complex exponential model is two. The method can not only achieve the power grid frequency estimation performance of the multidimensional noise subspace, but also reduce the calculated amount.
The above embodiments do not limit the present invention in any way, and all technical solutions obtained by means of equivalent substitution or equivalent transformation fall within the protection scope of the present invention.
Claims (1)
1. A power grid frequency estimation method based on a root Mini-Norm is characterized by comprising the following steps: aiming at steady-state power grid sampling data of an additive Gaussian noise background, designing a complex index model of the sampling data, then performing asymptotic unbiased autocorrelation processing on the sampling data, then decomposing the data after autocorrelation processing into a multi-dimensional signal subspace and a multi-dimensional noise subspace by adopting an MUSIC algorithm in spectrum decomposition, mapping the multi-dimensional noise subspace into a one-dimensional vector, and finally calculating the power grid center frequency by adopting a polynomial root-solving method aiming at the characteristics that the power grid center frequency is one and the corresponding complex index model is two; which comprises the following steps:
step 1: selecting a section of sine signal sampling sequence sampled at equal intervalsWherein, in the step (A),represents a vector of a sequence of samples representing the sequence of samples,represents the firstThe number of sequential samples of the data is,,representing the total number of sampled data;
step 2: to the sampling sequence vectorPerforming asymptotic unbiased autocorrelation operation to obtain autocorrelation vector,The expression of (a) is:
wherein the content of the first and second substances,representative pairThe conjugation is taken out and the reaction is carried out,,representing the number of autocorrelation vectors;
and step 3: according to a given autocorrelation vectorWill beRewriting is in the form of Toeplitz matrix, set to(ii) a To pairSingular value decomposition is carried out, and the expression is as follows:
wherein the content of the first and second substances,、andrespectively corresponding to a left singular vector, a singular value and a right singular vector of the signal subspace;、andrespectively corresponding to a right singular vector, a singular value and a right singular vector of the noise subspace;
and 4, step 4: for step 3Mapping to Mini-Norm form: for a complex exponential type grid frequency estimation,is composed ofDimension matrix, letIs composed ofThe Mini-Norm form (1), wherein,the expression of (a) is:
solving a polynomial byThe mode is a positive value closest to 1, and the grid frequency estimation value isIs that(ii) a Wherein the content of the first and second substances,representative pairTaking the imaginary part of the signal to be processed,representative pairTaking a real part of the signal,represents the function of the inverse tangent of the line,representing a sequence of acquired samplesThe sampling frequency of the time.
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