CN113341224A - Method and device for measuring low-frequency oscillation signal of power system - Google Patents
Method and device for measuring low-frequency oscillation signal of power system Download PDFInfo
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Abstract
The invention discloses a method and a device for measuring low-frequency oscillation signals of a power system, wherein the method comprises the following steps: s1, acquiring three-phase voltage signals in an acquired power system, and converting the acquired three-phase voltage signals into a complex signal sequence based on a pre-constructed low-frequency oscillation three-phase signal model; s2, performing discrete Fourier transform on the complex signal sequence obtained by conversion in the step S1 to obtain a complex frequency spectrum, performing parameter estimation on the obtained complex frequency spectrum by adopting an interpolation method, estimating dynamic parameters in the complex frequency spectrum, and obtaining final low-frequency oscillation signal output. The invention has the advantages of simple realization method, low cost, high measurement precision and test efficiency, strong anti-interference performance and the like.
Description
Technical Field
The invention relates to the technical field of power system parameter measurement, in particular to a method and a device for measuring a low-frequency oscillation signal of a power system.
Background
Accurate estimation of power grid parameters is an important basis for electric energy metering, electric energy quality detection and relay protection. Disturbances in the power system, such as faults, large loads being switched on/off, disconnections of the generators, line switches, etc., can cause the rotor angle between the generators to oscillate, resulting in low frequency oscillations in the grid. How to realize accurate and rapid measurement of power grid parameters under the condition of low-frequency oscillation plays a crucial role in maintaining stable operation of a power system.
The currently common measurement methods for power grid parameters mainly include: 1. a detection algorithm based on a sinusoidal signal model; 2. the periodic method and the improved algorithm thereof mainly comprise a zero-crossing detection method, a horizontal intersection point method, a high-order correction function method, a least square polynomial curve fitting method and the like; 3. the random model algorithm mainly comprises a least square method, a minimum absolute value approximation method, a Newton iteration algorithm, a linear filtering algorithm and the like. The detection algorithm based on the periodic signal model is most widely applied, and mainly includes Discrete Fourier Transform (DFT) and fast Fourier transform (fft) algorithms and improved algorithms thereof.
Ideally, the power grid signal is a standard sinusoidal signal, and a power grid frequency measurement method based on a sinusoidal signal model is widely applied, wherein the most widely applied method is a parameter estimation method based on discrete fourier transform. In the case of synchronous sampling, accurate estimation of the parameters can be achieved with only one cycle of sampling information. The conventional measurement method is based on the measurement of the grid signal in the ideal case. However, in the case of asynchronous sampling, the accuracy is affected by spectral leakage and the barrier effect, and methods such as windowing interpolation and the like are required for optimization. When the power grid signal is in dynamic change, the related dynamic parameters cannot be accurately estimated due to the limitation of the DFT method.
Power system faults, line switching, generator disconnection and connection, and disconnection or connection of a large number of loads can cause fluctuations in the power system, which in turn can cause voltage or current low frequency oscillations. The low-frequency oscillation is a balance phenomenon in a three-phase power system, and under the low-frequency oscillation scene, voltage and current signals in a power grid are no longer stable signals, and the amplitude of the voltage and current signals can generate periodic fluctuation, so that if the monitoring and the control are not timely carried out, power oscillation is further generated among systems, a transmission line and electric equipment are adversely affected, and the safety and the stability of the system are damaged, so that how to accurately and quickly estimate parameters of oscillation signals is very important for estimating the severity of the low-frequency oscillation, and the traditional measurement method cannot timely and accurately realize the measurement of the low-frequency oscillation signals.
In order to realize timely and accurate measurement of low-frequency oscillation signals, the prior art mainly adopts the following methods: 1. the Prony method is combined with digital filtering, so that the noise resistance is improved compared with the traditional Prony method; 2. the measurement method based on the Kalman filtering has better tracking effect on the dynamic signal due to the Kalman filtering algorithm, so that better noise immunity and measurement precision can be achieved; 3. the iterative filtering algorithm can realize high-precision measurement under the condition that the frequency is close to the power frequency, but has larger error under the conditions of larger frequency deviation and dynamic change of amplitude; 4. although the wavelet transformation method can be suitable for dynamic signal analysis, the calculation amount is large, and the problem of insufficient real-time performance exists; 5. the Taylor Fourier method simplifies calculation through Taylor series expansion, and has high precision under the steady state condition, strong harmonic suppression capability and high response speed under the dynamic condition.
However, in the above various measuring methods for low-frequency oscillation signals, single-phase signals are used to achieve parameter estimation, and three phases are generally considered as a whole in the power system, and the balance characteristics of a three-phase system need to be considered, so that the above various measuring methods for low-frequency oscillation signals still cannot accurately achieve measurement of three-phase signals in the power system, and especially when the number of sampling points is small, not only is the measurement accuracy not high, but also the anti-noise performance and the anti-interference performance are poor, and even under the condition of a large amount of noise interference, it is difficult to measure three-phase low-frequency oscillation signals in the system.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems in the prior art, the invention provides the method and the device for measuring the low-frequency oscillation signal of the power system, which have the advantages of simple implementation method, low cost, high measurement precision and strong anti-interference performance.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a method for measuring a low-frequency oscillation signal of a power system comprises the following steps:
s1, acquiring a three-phase signal in an acquired power system, and converting the acquired three-phase signal into a complex signal sequence based on a pre-constructed low-frequency oscillation three-phase signal model;
s2, performing discrete Fourier transform on the complex signal sequence obtained by conversion in the step S1 to obtain a complex frequency spectrum, performing parameter estimation on the complex frequency spectrum by adopting an interpolation method, estimating dynamic parameters in the complex frequency spectrum, and obtaining final low-frequency oscillation signal output.
Further, in the low-frequency oscillation three-phase signal model, the low-frequency oscillation three-phase signals are respectively modeled into a group of symmetrical exponentially decaying sinusoidal signals based on amplitude, attenuation coefficient, phase and angular frequency parameters.
Further, the low-frequency oscillation three-phase signal model specifically includes:
wherein, ya、yb、ycRepresenting the three phases of the acquired signal, respectively, A, T, phi and omega representing the amplitude, attenuation coefficient, phase and angular frequency, respectively, fsIs the sampling rate of the signal and n is the sampling point.
Further, in step S1, the three-phase signal obtained is converted into a complex signal sequence in the form of orthogonal components by using clarke transform.
Further, after the clarke transform is adopted to convert the obtained three-phase signal into a complex signal in an orthogonal component form, the method further comprises the step of obtaining a complex signal y in an orthogonal component formαAnd yβSignal reconstruction is performed as follows:
wherein, ycomplexFor the reconstructed signal, TsIs the sampling period.
Further, when the parameter estimation is performed by using an interpolation method in step S2, the two spectral lines with the largest amplitude are screened first, and then the dynamic parameters in the complex spectrum are estimated by using the two screened spectral lines.
Further, the step S2 includes:
s201, using a rectangular window with the length of N to pair the complex signal sequence y obtained by the conversion in the step S1complex(N) weighting, and performing N-point discrete Fourier transform on the sequence to obtain a complex frequency spectrum;
s202, converting the complex frequency spectrum into a linear combination formed by using parameters lambda and rho, wherein lambda is e(τTs+jω)，ρ＝Aejφ(1-e(τTs+jω)N)，TsFor the sampling period, τ, φ, and ω represent the attenuation coefficient, phase, and angular frequency, respectively;
s203, solving the parameters lambda and rho, and screening out two spectral lines k with the maximum amplitude1And k2And using the selected spectral line k1And k2Constructing and forming a linear equation system:
wherein, Y (k)1)、Y(k2) Are respectively corresponding spectral lines k1And k2A post-discrete Fourier transform sequence at a location;
obtaining the relationship between the parameters lambda and rho and the amplitude frequency phase as follows:
τTs＝ln|λ| ω＝angle(λ)
wherein a represents amplitude.
Further, the screening out two spectral lines with the largest amplitude includes: firstly, a spectral line k with the maximum amplitude is taken1Then, the spectral line k with the second largest amplitude is selected according to the following formula2：
Wherein Re represents a real part;
when delta--Δ+When > 0, k2＝k1+1,Δ--Δ+<At 0, k2＝k1-1。
A power system low-frequency oscillation signal measuring device comprises:
the complex signal conversion module is used for acquiring three-phase signals in the collected power system and converting the acquired three-phase signals into complex signal sequences based on a pre-constructed low-frequency oscillation three-phase signal model;
and the parameter estimation module is used for performing discrete Fourier transform on the complex signal sequence obtained by the conversion of the complex signal conversion module to obtain a complex frequency spectrum, performing parameter estimation on the complex frequency spectrum by adopting an interpolation method, estimating dynamic parameters in the complex frequency spectrum, and obtaining the final low-frequency oscillation signal output.
A computer apparatus comprising a processor and a memory, the memory being adapted to store a computer program, the processor being adapted to execute the computer program to perform the above method.
Compared with the prior art, the invention has the advantages that:
1. the invention considers the three-phase signal in the power system as a whole, converts the parameter estimation problem in the three-phase system into the parameter estimation of the complex exponential signal, and simultaneously realizes the measurement of the low-frequency oscillation signal based on the DFT mode of complex spectrum interpolation, thereby reducing the difficulty of dynamic parameter estimation, improving the precision of dynamic parameter estimation and realizing the accurate measurement of the frequency amplitude of the three-phase signal.
2. The method realizes the measurement of the low-frequency oscillation signal based on the DFT mode of complex frequency spectrum interpolation, can realize the accurate measurement of the frequency amplitude under the condition of less sampling points, has good anti-noise performance, and can accurately estimate the three-phase signal parameters under the low-frequency oscillation state under the conditions of less sampling points and noise interference.
3. The method realizes the measurement of the low-frequency oscillation signal based on the DFT mode of complex frequency spectrum interpolation, has high dynamic response speed, can accurately realize the measurement of the low-frequency oscillation signal before the fault occurs, when the fault occurs and after the fault is cleared, and can also realize the rapid and accurate tracking of the voltage dip when the fault occurs.
Drawings
Fig. 1 is a schematic flow chart of an implementation of the method for measuring a low-frequency oscillation signal of a power system in this embodiment.
Fig. 2 is a graph comparing the frequency and amplitude estimation errors with the signal to noise ratio obtained in the specific embodiment.
Fig. 3 is a comparison diagram of amplitude and phase estimation results obtained in an embodiment.
FIG. 4 is a comparison of the results of the integrated vector errors obtained in the specific example.
FIG. 5 is a schematic diagram of a three-machine nine-node system architecture employed in a particular embodiment.
Fig. 6 is a schematic waveform diagram of an a-phase voltage signal acquired in a specific embodiment.
FIG. 7 is a comparison of amplitude estimation results obtained in the specific example.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
As shown in fig. 1, the method for measuring a low-frequency oscillation signal of a power system of the present embodiment includes the steps of:
s1, acquiring a three-phase signal in an acquired power system, and converting the acquired three-phase signal into a complex signal sequence based on a pre-constructed low-frequency oscillation three-phase signal model;
s2, performing discrete Fourier transform on the complex signal sequence obtained by conversion in the step S1 to obtain a complex frequency spectrum, performing parameter estimation on the complex frequency spectrum by adopting an interpolation method, estimating dynamic parameters in the complex frequency spectrum, and obtaining final low-frequency oscillation signal output.
In the embodiment, the balance characteristic of a three-phase system is considered, the three-phase signal in the power system is considered as a whole, after the three-phase signal in the power system is obtained, the three-phase signal is converted into a complex signal sequence, then the complex signal sequence is subjected to discrete Fourier transform, and the parameter estimation problem in the three-phase system is converted into the parameter estimation of a complex exponential signal, so that the difficulty of dynamic parameter estimation can be reduced, the accurate measurement of the frequency amplitude of the three-phase signal can be realized under the condition of less sampling points, the noise-resistant performance is good, the three-phase signal parameter in the low-frequency oscillation state can be accurately estimated under the condition of noise interference, the dynamic response speed is high, and the voltage change can be accurately tracked when a fault occurs.
The three-phase signal is specifically a three-phase voltage, and other types of signals, such as a three-phase current signal, may be adopted according to actual requirements.
The exponentially decaying sinusoidal signal can be used to approximately fit low frequency oscillations and symmetric faults, considering the fluctuations of the power system due to power system faults, line switching, generator disconnection and connection, and disconnection or connection of a large number of loads, which in turn cause low frequency oscillations of the voltage or current, i.e. in the case of low frequency oscillations or symmetric faults, the power system still maintains symmetric characteristics. By utilizing the characteristics, the low-frequency oscillation three-phase signal model respectively models the low-frequency oscillation three-phase signals into a group of symmetrical exponentially decaying sinusoidal signals based on amplitude, attenuation coefficient, phase and angular frequency parameters so as to accurately represent the characteristics of the three-phase signals in the low-frequency oscillation scene in the power system.
The low-frequency oscillation three-phase signal model in the embodiment specifically comprises:
wherein, ya、yb、ycRepresenting the three phases of the voltage signal, respectively, A, T, phi and omega representing the amplitude, attenuation coefficient, phase and angular frequency, respectively, fsBeing the sampling rate of the signal, Ts＝1/fsAnd n is a sampling point.
It can be understood that the low-frequency oscillation three-phase signal model may also adopt other models according to actual requirements, may simply add an adjustment coefficient and the like on the basis of the above models, and may further add other required dynamic parameters and the like in the models.
In step S1 of this embodiment, the three-phase signal obtained is converted into a complex signal sequence in the form of orthogonal components by specifically using clarke transform. After the three-phase signal is subjected to Clark transformation, the three-phase signal can be converted into a complex signal sequence in an orthogonal component form, and the complex signal sequence comprises dynamic parameters such as amplitude, attenuation coefficient, phase, angular frequency and the like, so that the parameter estimation problem in a three-phase system is converted into the parameter estimation problem of a complex exponential signal. Compared with the parameter estimation problem in a three-phase system, the parameter estimation of the complex exponential signal is simpler and is easier to realize accurate estimation.
Specifically, the clark transformation may be a constant amplitude clark transformation method. For a three-phase three-wire system, three-phase current and three-phase voltage with any point as a voltage reference point are subjected to Clark conversion to obtain alpha and beta two-phase instantaneous voltage uα、uβAnd instantaneous current iα、iβThe three-phase three-wire system can be completely characterized, and the three-phase signal model given by the above formula (1) is subjected to constant-amplitude clark transformation to obtain:
y obtained by the above-mentioned constant-amplitude Clark transformation in a symmetrical three-phase systemαAnd yβHas the property of orthogonality, i.e. a phase difference of 90 °.
In this embodiment, after converting the obtained three-phase signal into a complex signal in an orthogonal component form by clark conversion, the method further includes obtaining a complex signal y in an orthogonal component formαAnd yβSignal reconstruction is performed as follows:
wherein, ycomplexFor the reconstructed signal, TsIs the sampling period.
Thereby, canTo obtain a new complex signal sequence having the same frequency, amplitude and phase as the three-phase system according to the nature of clarke transformation, so that the parameter estimation problem of the three-phase system is converted into the complex signal ycomplexWherein, A, tau, phi and omega are dynamic parameters to be solved.
In this embodiment, when the complex spectrum is specifically estimated by using an interpolation method in step S2, specifically, two spectral lines with the largest amplitude, that is, two spectral lines with the largest amplitude and two spectral lines with the largest amplitude are screened first, and then the two screened spectral lines are used to estimate the dynamic parameters in the complex spectrum, so that not only can accurate parameter estimation be effectively implemented, but also the estimation calculation amount can be greatly reduced, and the parameter estimation efficiency is improved.
The detailed step of step S2 in this embodiment includes:
s201, using a rectangular window with the length of N to pair the complex signal sequence y obtained by the conversion in the step S1complexAnd (N) weighting, and performing N-point discrete Fourier transform on the sequence to obtain a complex frequency spectrum as shown in a formula (4).
Wherein, WN＝e-j2π/N，k is 0,1, …, N-1, let λ be e(τTs+jω)，ρ＝Aejφ(1-e(τTs+jω)N)；
The above expression (4) can be further simplified as:
s202, converting the complex frequency spectrum into a linear combination formed by using parameters lambda and rho, wherein lambda is e(τTs+jω)，ρ＝Aejφ(1-e(τTs+jω)N)，TsFor the sampling period, τ, φ, and ω represent the attenuation coefficient, phase, and angular frequency, respectively.
As can be seen from equation (5), λ and ρ contain the parameters of amplitude, phase and frequency by these two unknowns, so that all the target parameters can be obtained by solving λ and ρ for constipation. Further rewriting equation (5) to a matrix form can be obtained:
the DFT sequence y (k) may be represented by a linear combination of the unknown parameters λ and ρ, in case N >2 there are two unknown parameters and N available equations, then the values of the unknown parameters λ and ρ may be solved by solving the linear equations, and then the parameters λ and ρ are further solved.
S203, solving the parameters lambda and rho, and screening out two spectral lines k with the maximum amplitude1And k2And using the selected spectral line k1And k2Constructing and forming a linear equation system:
wherein, Y (k)1)、Y(k2) Are respectively corresponding spectral lines k1And k2A complex spectrum at the location;
using the selected spectral line k1And k2Solving the linear equation set to obtain unknown parameters lambda and rho, wherein the relation between the parameters lambda and rho and the amplitude frequency phase is specifically obtained as follows:
τTs＝ln|λ| ω＝angle(λ)
wherein a represents amplitude.
Normally, the two spectral lines with the maximum amplitude and the second largest amplitude are selected simply, but if the signal frequency is very close to the power frequency, the spectral lines on the left and right sides of the peak spectral line have very small amplitudes and the second largest amplitude spectral line (k) has very small amplitudes2) The selection of (b) may cause misjudgment due to the influence of noise, thereby affecting the estimation accuracy.
Suppose the actual angular frequency of the signal is denoted as ω and the maximum amplitude spectral line position is denoted as k1And then:
from equations (5) and (9):
then any spectral line is associated with Y (k)1) The following relationships exist:
memory k2＝k1+1，k3＝k1-1, as δ approaches 0, as can be derived from equation (12):
|Y(k3)|2≈|Y(k1)|2[δ(1-|δ|)]2
≈|Y(k2)2[1-4δ2|δ|)] (13)
as can be seen from the formulas (13) and (14), when δ approaches 0, the spectral lines at both sides of the maximum amplitude spectral line have very close amplitudes, and directly comparing the amplitudes is likely to cause erroneous judgment of selection of the second-order maximum spectral line under the influence of noise.
In this embodiment, two spectral lines with the largest amplitude are screened out specifically by the following method: firstly, a spectral line k with the maximum amplitude is taken1Then, the next largest spectral line k is selected according to the following formula2：
Wherein Re represents a real part;
when delta--Δ+When > 0, k2＝k1+1,Δ--Δ+<At 0, k2＝k1-1。
The embodiment selects the next largest spectral line k by the above method2Even when the signal frequency is very close to the power frequency, the next largest spectral line can be accurately selected under the noise interference, and misjudgment when the next largest spectral line is selected is avoided, so that the parameter estimation precision is further improved.
In a specific application embodiment, the detailed steps of measuring the low-frequency oscillation signal in the power system by adopting the method provided by the invention are as follows:
step 1) setting sampling parameters and synchronously acquiring three-phase voltage signals ya，yb，yc，。
Step 2) converting the collected three-phase voltage signal sequence into a complex signal sequence y through Clark conversioncomplex。
Step 3) intercepting complex signal sequence y by using rectangular window with length of NcomplexAnd performing N-point DFT to obtain DFT sequence Y (k).
Step 4) screening maximum and secondary large spectral lines, and marking the serial number as k1And k2And solving the unknown parameters lambda and rho according to the formula (7).
And 5) solving amplitude, frequency and phase parameters according to the obtained lambda and rho and a formula (8).
In this embodiment, by using the symmetry characteristic of the three-phase system, the three-phase real signal in the power system is converted into the complex signal in the form of an orthogonal component through clark transformation, then discrete fourier transform is performed on the complex signal, and meanwhile, by using a complex frequency spectrum interpolation method, each dynamic parameter is estimated by using two spectral line samples with the largest amplitude, so that the measurement accuracy and the measurement efficiency of the low-frequency oscillation signal in the power system can be effectively realized, and meanwhile, the anti-interference performance of measurement is improved.
In order to verify the effectiveness of the method, the method is subjected to simulation verification. Firstly, simulation verification is carried out under the steady state condition, the parameter estimation precision is evaluated under the conditions of different signal-to-noise ratios (SNR), meanwhile, the traditional windowing interpolation method and the Keze window are adopted for comparison, wherein the windowing types are respectively a maximum sidelobe attenuation window and a Hanning window. The simulation parameters are set as follows: fundamental frequency f of three-phase signal is 49.5Hz, sampling rate fs1.6kHz, amplitude A1, initial phase
The sampling window length is set to N-64, the SNR varies in the range of 10dB to 60dB, and the root mean square error of the obtained frequency and amplitude estimation is specifically shown in fig. 2, where fig. 2(a) corresponds to the frequency estimation error and fig. 2(b) corresponds to the amplitude estimation error.
As can be seen from the result of frequency estimation in fig. 2(a), under the influence of white noise, as the signal-to-noise ratio increases, the root mean square error of the frequency and the amplitude decreases, the method of the present invention is significantly better than the conventional method, and as can be seen from the result of amplitude estimation in fig. 2(b), the error rapidly decreases as the signal-to-noise ratio increases, and both are smaller than the result of the conventional method.
The embodiment further performs simulation analysis under the condition of low-frequency oscillation. In the case of low-frequency oscillation, parameters of the power grid signal are dynamically changed, and in this embodiment, a typical low-frequency oscillation signal is simulated through an amplitude-phase modulation signal to evaluate the method of the present invention, and a conventional taylor fourier TFT method is used for comparison.
Considering the balanced characteristics of a three-phase system, the simulation signal settings are specifically as follows:
ya(t)＝A(t)cos(2πft+φ(t))
wherein:
A0＝1,φ0＝0.5,A1＝0.1,φ1＝0.05
fa＝fφ＝5,τ1＝0.5，τ2＝0.4
fundamental frequency f is 50Hz, sampling frequency fsThe SNR of the signal is set to 60dB at 1kHz, and considering the real-time nature of the measurement in the case of low frequency oscillations, the delay of the parameter estimation preferably does not exceed one cycle, so the sampling window length is set to N16. The simulation process takes the form of a sliding window, 1 point is slid each time, and the amplitude and phase parameters at each moment are estimated.
The obtained parameter estimation result is shown in fig. 3, in which the middle solid line corresponds to the true value, the gray scale region formed around the middle solid line corresponds to the result of the method of the present invention, and the outermost triangular mark region corresponds to the result of the conventional TFT method. From the results of fig. 3, it is obvious that the results obtained by the method of the present invention have better consistency with the true values, whereas the estimation results of the frequency and amplitude of the conventional TFT method have larger fluctuation due to the influence of noise.
The TVE obtained by the method and the TFT method is shown in figure 4, the maximum comprehensive vector error within 50 power frequency cycles is reflected in the figure, the TVE of the method is kept below 0.5 percent, and the TVE of the TFT method can reach 12 percent maximally, so that the method has higher and more stable estimation precision in a low-frequency oscillation scene.
The embodiment further applies the method of the invention to a three-machine nine-node system for simulation and sub-simulation. The three-machine nine-node system is shown in fig. 5, and is specifically simulated by adopting PSCAD software. The simulation conditions were set as follows: the relay protection device R is located in the line between the bus nos. 7 and 5. In order to generate low frequency oscillations in the system, a three-phase earth fault is introduced in the line between the bus 7 and the bus 8, the fault starts when t is 1s and is cleared after 0.2s by opening the circuit breakers at both ends of the line, at which time the system generates low frequency oscillations and a low frequency oscillation signal can be observed at the relay protection device R.
The sampling rate of the relay protection device is set to 2kHz, and the sampling window length is set to 0.5 power frequency cycles, so that there are 20 sampling points in each sampling window (N ═ 20). In this embodiment, three-phase voltage signals collected by the relay protection device R are specifically collected and analyzed, all data are processed in MATLAB, and the signal-to-noise ratio SNR is 40dB, where a-phase voltage signals are shown in fig. 6.
The amplitude estimation results obtained by the method of the present invention and the TFT method, respectively, are shown in fig. 7, where the middle solid line corresponds to the true value, the gray scale region formed around the middle solid line corresponds to the result of the method of the present invention, and the outermost square mark region corresponds to the result of the conventional TFT method. The comparison shows that the amplitude estimation can be accurately realized under three conditions of before fault occurrence, when fault occurrence and after fault clearing, the voltage dip can be quickly and accurately tracked when fault occurrence, the TFT method is more easily influenced by noise, the estimation result has larger deviation under the condition of less sampling points, and the result has larger fluctuation when fault occurrence, so that the voltage change cannot be accurately tracked.
The low-frequency oscillation signal measuring device of the power system comprises:
the complex signal conversion module is used for acquiring the collected three-phase voltage signals in the power system and converting the acquired three-phase voltage signals into a complex signal sequence based on a pre-constructed low-frequency oscillation three-phase signal model;
and the parameter estimation module is used for performing discrete Fourier transform on the complex signal sequence obtained by the conversion of the complex signal conversion module to obtain a complex frequency spectrum, performing parameter estimation on the complex frequency spectrum by adopting an interpolation method, estimating dynamic parameters in the complex frequency spectrum, and obtaining the final low-frequency oscillation signal output.
The low-frequency oscillation signal measuring device of the power system of the embodiment corresponds to the low-frequency oscillation signal measuring method of the power system one by one, and the two have the same principle and effect, and are not described in detail herein.
The embodiment also provides a computer device, comprising a processor and a memory, wherein the memory is used for storing the computer program, the processor is used for executing the computer program, and the processor is used for executing the computer program to execute the method.
The foregoing is considered as illustrative of the preferred embodiments of the invention and is not to be construed as limiting the invention in any way. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention should fall within the protection scope of the technical scheme of the present invention, unless the technical spirit of the present invention departs from the content of the technical scheme of the present invention.
Claims (10)
1. A method for measuring a low-frequency oscillation signal of a power system is characterized by comprising the following steps:
s1, acquiring a three-phase signal in an acquired power system, and converting the acquired three-phase signal into a complex signal sequence based on a pre-constructed low-frequency oscillation three-phase signal model;
s2, performing discrete Fourier transform on the complex signal sequence obtained by conversion in the step S1 to obtain a complex frequency spectrum, performing parameter estimation on the complex frequency spectrum by adopting an interpolation method, estimating dynamic parameters in the complex frequency spectrum, and obtaining final low-frequency oscillation signal output.
2. The method for measuring a low-frequency oscillation signal of a power system according to claim 1, wherein in step S1: in the low-frequency oscillation three-phase signal model, low-frequency oscillation three-phase signals are respectively modeled into a group of symmetrical exponential decay sinusoidal signals based on amplitude, attenuation coefficient, phase and angular frequency parameters.
3. The method for measuring the low-frequency oscillation signal of the power system according to claim 2, wherein the low-frequency oscillation three-phase signal model is specifically:
wherein, ya、yb、ycRepresenting the three phases of the acquired signal, respectively, A, T, phi and omega representing the amplitude, attenuation coefficient, phase and angular frequency, respectively, fsIs the sampling rate of the signal and n is the sampling point.
4. The method according to claim 1, wherein in step S1, the three-phase signals obtained are converted into complex signal sequences in the form of orthogonal components by using clarke transformation.
5. The method for measuring the low-frequency oscillation signal of the power system according to claim 4, wherein after the obtained three-phase signal is converted into the complex signal in the form of the orthogonal component by using Clark conversion, the method further comprises obtaining the complex signal y in the form of the orthogonal componentαAnd yβSignal reconstruction is performed as follows:
wherein, ycomplexFor the reconstructed signal, TsIs the sampling period.
6. The method for measuring the low-frequency oscillation signal of the power system according to any one of claims 1 to 5, wherein when the parameter estimation is performed by using an interpolation method in the step S2, two spectral lines with the largest amplitude are screened out first, and then the dynamic parameter in the complex spectrum is estimated by using the two screened out spectral lines.
7. The method for measuring the low-frequency oscillation signal of the power system according to any one of claims 1 to 5, wherein the step S2 includes:
s201, using a rectangular window with the length of N to pair the complex signal sequence y obtained by the conversion in the step S1complex(N) weighting, and performing N-point discrete Fourier transform on the sequence to obtain a complex frequency spectrum;
s202, converting the complex frequency spectrum into a linear combination formed by using parameters lambda and rho, wherein
TsFor the sampling period, τ, φ, and ω represent the attenuation coefficient, phase, and angular frequency, respectively;
s203, solving the parameters lambda and rho, and screening out two spectral lines k with the maximum amplitude1And k2And using the selected spectral line k1And k2Constructing and forming a linear equation system:
wherein, Y (k)1)、Y(k2) Are respectively corresponding spectral lines k1And k2A post-discrete Fourier transform sequence at a location;
obtaining the relationship between the parameters lambda and rho and the amplitude frequency phase as follows:
τTs＝ln|λ| ω＝angle(λ)
wherein a represents amplitude.
8. The method for measuring the low-frequency oscillation signal of the power system according to claim 7, wherein: the screening of the two spectral lines with the maximum amplitude comprises the following steps: firstly, a spectral line k with the maximum amplitude is taken1Then, the spectral line k with the second largest amplitude is selected according to the following formula2：
Wherein Re represents a real part;
when delta--Δ+When > 0, k2＝k1+1,Δ--Δ+<At 0, k2＝k1-1。
9. A low-frequency oscillation signal measuring device of a power system is characterized by comprising:
the complex signal conversion module is used for acquiring three-phase signals in the collected power system and converting the acquired three-phase signals into complex signal sequences based on a pre-constructed low-frequency oscillation three-phase signal model;
and the parameter estimation module is used for performing discrete Fourier transform on the complex signal sequence obtained by the conversion of the complex signal conversion module to obtain a complex frequency spectrum, performing parameter estimation on the complex frequency spectrum by adopting an interpolation method, estimating dynamic parameters in the complex frequency spectrum, and obtaining the final low-frequency oscillation signal output.
10. A computer arrangement comprising a processor and a memory, the memory being adapted to store a computer program, the processor being adapted to execute the computer program, wherein the processor is adapted to execute the computer program to perform the method according to any of claims 1-8.
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