CN108334822B - Kalman and modified wavelet transform filtering method based on electric vehicle charging nonlinear load characteristics - Google Patents
Kalman and modified wavelet transform filtering method based on electric vehicle charging nonlinear load characteristics Download PDFInfo
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Abstract
The invention discloses a Kalman and correction wavelet transform filtering method based on charging nonlinear load characteristics of an electric automobile, which comprises the following steps of: reasonably correcting threshold parameters and layering parameters of a traditional wavelet transformation algorithm according to the signal characteristics of direct current fundamental waves and unsteady state waves in the charging nonlinear load of the electric automobile; filtering unsteady state waves and higher harmonics by using modified wavelet transform; filtering low-order harmonic waves by using a Kalman filtering algorithm; detecting a signal mutation point; smoothing at a signal mutation point of a Kalman filtering algorithm; after the signal break point is detected in the last step, the fundamental wave signal at the signal break point is obtained by adopting modified wavelet transform decomposition instead of Kalman filtering algorithm decomposition at the subsequent time L. The method can improve the identification accuracy of the Kalman filtering algorithm, and avoids the phenomenon of 'climbing delay' of the Kalman filtering algorithm at a signal mutation position.
Description
Technical Field
The invention relates to the technical field of charging nonlinear load filtering of electric automobiles, in particular to a Kalman and correction wavelet transform filtering method based on charging nonlinear load characteristics of electric automobiles.
Background
The new energy automobile mainly comprises an electric automobile, and the large-scale development of the ultra-conventional electric automobile needs a large number of matched charging station supports. A charger of an electric vehicle charging station belongs to novel high-power nonlinear equipment, 150-600A of large current can be formed in the charging process, and excessive intensive centralized charging can cause excessive instantaneous load of the charging station. And the charging of the storage battery of the electric automobile belongs to capacitive load, the load power factor is lower, and the charging load shows nonlinear characteristics. Due to the complexity of the charging process, a large amount of harmonic waves and unsteady waves are generated in the charging process, and influence is generated on electric energy metering and power grid operation of the charging station.
At present, the most common method is to filter nonlinear loads in the charging process of the electric vehicle by adopting a fourier algorithm, decompose periodic signals into a superposition form of different frequency components according to a fourier series mode, have the advantages of high response speed, high data processing capacity, high calculation precision, good real-time performance and the like, and are suitable for detecting harmonic waves. The Short Time Fourier Transform (STFT) of the sliding window function used can improve this limitation, but its frequency resolution is fixed and it has no adaptive capability. The widths of a time window and a frequency window of the wavelet transformation algorithm can be adjusted, the sampling density is automatically adjusted to process the mutation signal according to the frequency components of the signal, the method is suitable for reflecting the sudden change and time-varying tracking of the signal, and is particularly suitable for analyzing the fluctuation harmonic wave, the fast change harmonic wave, the mutation signal and the non-stationary signal, but the signal characteristics of the fundamental wave and the multiple harmonic wave cannot be analyzed and calculated. In the field, a separate kalman filter algorithm is used for carrying out nonlinear load in the charging process of the electric vehicle, which can well identify and decompose each harmonic wave, but the existing data is used for prediction, when the signal changes rapidly, a certain buffer time is needed, unstable waves cannot be identified accurately, and the identification of signal components at the sudden change position of the signal has serious 'climbing delay'. The three methods cannot meet the requirements of real application on filtering.
Disclosure of Invention
The invention aims to solve the technical problem of providing a Kalman and modified wavelet transform filtering method based on the charging nonlinear load characteristics of an electric automobile, which can improve the identification accuracy of a Kalman filtering algorithm and avoid the phenomenon of 'climbing delay' of the Kalman filtering algorithm at a signal mutation position.
In order to solve the technical problem, the invention provides a Kalman and modified wavelet transform filtering method based on charging nonlinear load characteristics of an electric vehicle, which comprises the following steps:
(1) reasonably correcting threshold parameters and layering parameters of a traditional wavelet transformation algorithm according to the signal characteristics of direct current fundamental waves and unsteady state waves in the charging nonlinear load of the electric automobile;
(2) filtering unsteady state waves and higher harmonics by using modified wavelet transform;
(3) filtering low-order harmonic waves by using a Kalman filtering algorithm;
(4) detecting a signal mutation point;
(5) smoothing at a signal mutation point of a Kalman filtering algorithm; and (4) after the signal break point is detected in the step (4), decomposing by adopting modified wavelet transform decomposition to replace a Kalman filtering algorithm at the subsequent time L to obtain a fundamental wave signal at the signal break point.
Preferably, in the step (1), the modifying of the layering parameter specifically comprises: the frequency of a wave is 0Hz when the electric automobile is charged by direct current, n layers are added on the original basis when the number of decomposition layers is calculated, and the formula of the number of decomposition layers is as follows:
wherein f issTo sample frequency, f0The greatest common divisor of the ripple signal frequency, mu is 2;
the threshold parameter is modified specifically as follows: averaging the two thresholds;
wherein Ds is the processed data, D is the collected data, beta is the correction weight, and epsilon is the selected threshold; equation (2) is smoothed using a linear interpolation function.
Preferably, in the step (2), the filtering of the unsteady state waves and the higher harmonics by using the modified wavelet transform specifically comprises: the fundamental wave signal is positioned at the bottom layer part of the charging nonlinear load frequency of the electric automobile, and unsteady state waves and higher harmonics are filtered by utilizing modified wavelet transform;
wherein f (t) is a low-frequency signal of the charging nonlinear load of the electric automobile; χ () is a scale space function;
filtering unsteady state waves and higher harmonics for projection on a scale; e.g. of the typer,k、er,mIs an approximation parameter on the r scale; j is the sequence number of the fundamental wave, 1 is taken: m is a power series of scale discretization; and S () is a scale space filtering function and embodies the low-pass characteristic of the signal.
Preferably, in the step (3), filtering the low-order harmonic by using a kalman filter algorithm specifically includes the following steps:
(31) selecting an observation State
Wherein y is1,z,y2,zAs a group, orthogonal decomposition waveforms of fundamental wave and each harmonic; w is aiIs the amplitude of the ith harmonic; thetaiPhase angle of the ith harmonic;
(32) selecting system dynamic equations and measurement equations
Wherein W (K) is an observation matrix, YKIs an observation vector, ω, related to W (K)kFor process noise random sequence, vkIn order to observe the noise, it is,
to shift the matrix, xK+1A system dynamic matrix, wherein N is the harmonic (ripple) frequency in the charging nonlinear load of the electric automobile;
(33) identifying and tracking the amplitude and phase angle of the fundamental wave;
preferably, in the step (4), the detecting the signal mutation point specifically comprises the following steps:
(41) for the direct current charging of the electric automobile, data D at the current moment is collected0Data D before time intervals T, 2T, 3T1、D2、D3If, if
Are all formed intoImmediately, this time is the signal discontinuity, where σ1Is a determined threshold;
(42) for alternating current charging of the electric automobile, collecting amplitude delta w calculated by Kalman algorithm at the current moment0Time interval T1、2T1、3T1Amplitude of front Δ w1、Δw2、Δw3If, if
All hold true, then this moment is the signal discontinuity, where σ2Is a determined threshold.
The invention has the beneficial effects that: reasonably correcting threshold parameters and layering parameters of a traditional wavelet transformation algorithm according to the signal characteristics of direct current fundamental waves and unsteady state waves in the charging nonlinear load of the electric automobile, wherein the obtained corrected wavelet algorithm is more accurate in layering of the acquired alternating current and direct current charging signals of the electric automobile, and the filtered unsteady state waves are more accurate; after the influence of unsteady waves is eliminated by correcting wavelet transformation, fundamental wave signals are identified by using a Kalman filtering algorithm, so that the identification accuracy of the Kalman filtering algorithm is improved; and the signal mutation is detected, and the wavelet change algorithm is used for replacing the signal obtained by decomposition of the Kalman filtering algorithm, so that the phenomenon of 'climbing delay' of the Kalman filtering algorithm at the signal mutation position is avoided.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention.
Detailed Description
As shown in fig. 1, a kalman and modified wavelet transform filtering method based on nonlinear load characteristics of electric vehicle charging includes the following steps:
step 1: reasonably correcting threshold parameters and layering parameters of a traditional wavelet transformation algorithm according to the signal characteristics of direct current fundamental waves and unsteady state waves in the charging nonlinear load of the electric automobile;
(11) modifying the layering parameters;
the direct current charging time base wave frequency of the electric automobile is 0Hz, the meterWhen the number of decomposition layers is counted, f0Cannot be calculated at the fundamental frequency. In addition, the direct current has a form of a primary function and a secondary function, which greatly interferes with the wavelet decomposition level, so that n layers need to be added on the original basis, and the formula of the decomposition layer number is as follows:
wherein f issTo sample frequency, f0μ is 2, which is the greatest common divisor of the ripple signal frequency.
(12) Determination of threshold values
The invention reasonably corrects the classic soft threshold value method and the hard threshold value method, and adopts the discontinuity of the smooth change of the linear interpolation function, and the specific method is as follows:
firstly, averaging two thresholds;
wherein Ds is the processed data, D is the collected data, beta is the correction weight, and epsilon is the selected threshold.
And secondly, smoothing the equation (2) by utilizing a linear interpolation function.
Step 2: filtering unsteady state waves and higher harmonics by using modified wavelet transform;
the fundamental wave signal is positioned at the bottommost part of the charging nonlinear load frequency of the electric automobile, and unsteady state waves and higher harmonics can be filtered out by utilizing the modified wavelet transform.
Wherein f (t) is a low-frequency signal of the charging nonlinear load of the electric automobile; χ () is a scale space function;
for projection on a scale, realizing non-steady stateFiltering waves and higher harmonics; e.g. of the typer,k、er,mIs an approximation parameter on the r scale; j is the sequence number of the fundamental wave, 1 is taken: m is a power series of scale discretization; and S () is a scale space filtering function and embodies the low-pass characteristic of the signal.
And step 3: filtering low order harmonic wave by Kalman filtering algorithm
Selecting observation state
Wherein y is1,z,y2,zAs a group, orthogonal decomposition waveforms of fundamental wave and each harmonic; w is aiIs the amplitude of the ith harmonic; thetaiPhase angle of the ith harmonic.
Selecting system dynamic equation and measuring equation
Wherein W (K) is an observation matrix, YKIs an observation vector, ω, related to W (K)kFor process noise random sequence, vkIn order to observe the noise, it is,
to shift the matrix, xK+1And (3) a system dynamic matrix, wherein N is the harmonic (ripple) frequency in the charging nonlinear load of the electric automobile.
Identifying and tracing fundamental wave amplitude and phase angle
And 4, step 4: detecting signal discontinuities
Firstly, for the direct current charging of the electric automobile, the data D at the current moment is collected0Data D before time intervals T, 2T, 3T1、D2、D3If, if
All hold true, then this moment is the signal discontinuity, where σ1Is a determined threshold.
Secondly, for alternating current charging of the electric automobile, collecting the amplitude delta w calculated by the Kalman algorithm at the current moment0Time interval T1、2T1、3T1Amplitude of front Δ w1、Δw2、Δw3If, if
All hold true, then this moment is the signal discontinuity, where σ2Is a determined threshold.
And 5: smoothing of Kalman filtering algorithm signal discontinuities
And (4) after the signal break point is detected in the step (4), decomposing by adopting modified wavelet change decomposition to replace a Kalman filtering algorithm at the subsequent time L to obtain a fundamental wave signal at the signal break point.
According to the invention, the threshold parameter and the layering parameter of the traditional wavelet transform algorithm are reasonably corrected according to the signal characteristics of direct current fundamental wave and unsteady state wave in the charging nonlinear load of the electric automobile, the obtained corrected wavelet algorithm more accurately layers the acquired alternating current and direct current charging signals of the electric automobile, and the filtered unsteady state wave is more accurate; after the influence of unsteady waves is eliminated by correcting wavelet transformation, fundamental wave signals are identified by using a Kalman filtering algorithm, so that the identification accuracy of the Kalman filtering algorithm is improved; and the signal mutation is detected, and the wavelet change algorithm is used for replacing the signal obtained by decomposition of the Kalman filtering algorithm, so that the phenomenon of 'climbing delay' of the Kalman filtering algorithm at the signal mutation position is avoided.
Claims (3)
1. The Kalman and correction wavelet transform filtering method based on the charging nonlinear load characteristics of the electric automobile is characterized by comprising the following steps of:
(1) reasonably correcting threshold parameters and layering parameters of a traditional wavelet transformation algorithm according to the signal characteristics of direct current fundamental waves and unsteady state waves in the charging nonlinear load of the electric automobile;
(2) filtering unsteady state waves and higher harmonics by using modified wavelet transform; the fundamental wave signal is positioned at the bottom layer part of the charging nonlinear load frequency of the electric automobile, and unsteady state waves and higher harmonics are filtered by utilizing modified wavelet transform;
wherein f (t) is a low-frequency signal of the charging nonlinear load of the electric automobile; χ () is a scale space function;
filtering unsteady state waves and higher harmonics for projection on a scale; e.g. of the typer,k、er,mIs an approximation parameter on the r scale; j is the sequence number of the fundamental wave, and 1 is taken; m is a power series of scale discretization; s () is a scale space filtering function and embodies the low-pass characteristic of a signal;
(3) filtering low-order harmonic waves by using a Kalman filtering algorithm; the method specifically comprises the following steps:
(31) selecting an observation State
Wherein y is1,z,y2,zAs a group, orthogonal decomposition waveforms of fundamental wave and each harmonic; w is aiIs the amplitude of the ith harmonic; thetaiPhase angle of the ith harmonic;
(32) selecting system dynamic equations and measurement equations
Wherein W (K) is an observation matrix, YKIs an observation vector, ω, related to W (K)kFor process noise random sequence, vkIn order to observe the noise, it is,
to shift the matrix, xK+1System dynamic matrix, fNCharging the electric vehicle with harmonic frequency in the nonlinear load;
(33) identifying and tracking the amplitude and phase angle of the fundamental wave;
(4) detecting a signal mutation point;
(5) smoothing at a signal mutation point of a Kalman filtering algorithm; and (4) after the signal break point is detected in the step (4), decomposing by adopting modified wavelet transform decomposition to replace a Kalman filtering algorithm at the subsequent time L to obtain a fundamental wave signal at the signal break point.
2. The Kalman and modified wavelet transform filtering method based on nonlinear load characteristics for electric vehicle charging according to claim 1, characterized in that in step (1), the modification of the hierarchical parameters specifically comprises: the frequency of a wave is 0Hz when the electric automobile is charged by direct current, n layers are added on the original basis when the number of decomposition layers is calculated, and the formula of the number of decomposition layers is as follows:
wherein f issTo sample frequency, f0The greatest common divisor of the ripple signal frequency, mu is 2;
the threshold parameter is modified specifically as follows: averaging the two thresholds;
wherein Ds is the processed data, D is the collected data, beta is the correction weight, and epsilon is the selected threshold; equation (2) is smoothed using a linear interpolation function.
3. The Kalman and modified wavelet transform filtering method based on nonlinear load characteristics for electric vehicle charging according to claim 1, wherein in the step (4), the step of detecting the signal discontinuity specifically comprises the following steps:
(41) for the direct current charging of the electric automobile, data D at the current moment is collected0Data D before time intervals T, 2T, 3T1、D2、D3If, if
All hold true, then this moment is the signal discontinuity, where σ1Is a determined threshold;
(42) for alternating current charging of the electric automobile, collecting amplitude delta w calculated by Kalman algorithm at the current moment0Time interval T1、2T1、3T1Amplitude of front Δ w1、Δw2、Δw3If, if
All hold true, then this moment is the signal discontinuity, where σ2Is a determined threshold.
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