A method for correcting PMU phase frequency measurement values ​​in transient process after fault

Abstract

The present invention discloses a method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault, and belongs to the technical field of frequency measurement in a power system. The method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault includes the following steps: performing a fast Fourier transform on the sampling value of the power signal, taking its amplitude to obtain a spectrum, calculating the power spectrum according to the spectrum and performing normalization calculation; calculating the power spectrum information entropy according to the normalized power spectrum, and calculating the confidence factor; if the confidence factor is lower than a preset threshold, using an exponentially decaying sliding weighted correction model to correct the phasor and frequency measurement values ​​to obtain the final measurement result; if the confidence factor is higher than the preset threshold, the current measurement result is the final measurement result; and uploading the final measurement result. The PMU phasor frequency measurement value correction method described in the present invention can realize real-time judgment of the confidence of the PMU measurement result, and smooth transition of the phasor frequency measurement value during the transient period when the system frequency offsets before and after the fault.

Description

Technical Field

[0001] The present invention relates to the technical field of power system frequency measurement, and in particular to a method for correcting a PMU phasor frequency measurement value in a transient process after a fault. Background Art

[0002] With the access of large-scale new energy and power electronic equipment, the dynamic response characteristics and control strategies of power systems have become more complex, resulting in serious waveform distortion of electrical quantities in electromagnetic transient processes after faults. Traditional characterization and measurement methods based on steady-state Fourier basis face significant measurement errors, affecting the reliability of applications such as preventive control or emergency control based on real-time measurement data.

[0003] However, the discrete sampling sequence of the electrical quantity waveform in the transient process after a fault has many mutation points, random mutation moments, severe interference, and short duration, making it difficult to achieve efficient and non-redundant decomposition and characterization in a short time scale. Therefore, it is urgent to study the characterization and measurement methods of transient electrical quantities in power systems after faults and explore the application potential of synchronous measurement data during transient periods.

[0004] Patent CN202410707549.8 now discloses a method and device for correcting electromagnetic transient frequency based on frequency domain information entropy, by designing two bandpass filters with amplitude-frequency responses symmetrical about 50Hz in the measurement frequency band; calculating the ratio RH of the amplitude-frequency responses of the two bandpass filters in the measurement frequency band, constructing a function of frequency about RH, establishing a frequency calculation model and a correction frequency calculation model; performing fast Fourier transform on the signal sampling value sequence, and calculating the frequency domain information entropy and its mutation amount of the electrical quantity according to the spectrum; using two bandpass filters to filter and calculate the signal sampling value sequence to obtain two phasors; judging whether the frequency domain information entropy and its mutation amount exceed the preset threshold; and performing frequency correction calculation or frequency calculation according to the judgment result. The present invention adopts the above-mentioned electromagnetic transient frequency correction method and device based on frequency domain information entropy, which can realize the correction of electromagnetic transient frequency measurement data of the power system. The above-mentioned patent only involves frequency correction, and the correction target value is the rated frequency. It is suitable for large power grids and strong systems where the frequency will not shift significantly before and after the fault, and is not suitable for weak systems where the system frequency is prone to shift before and after the fault. Summary of the invention

[0005] The purpose of the present invention is to provide a method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault, which can realize real-time judgment of the confidence of PMU measurement results and smooth transition of phasor frequency measurement values ​​in a transient period when the system frequency offsets before and after the fault, and realize real-time correction of phasor frequency measurement values ​​of voltage or current in a transient process after a power system fault.

[0006] To achieve the above object, the present invention provides a method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault, comprising the following steps:

[0007] S1. Perform fast Fourier transform on the sampling value of the power signal, take its amplitude to obtain the spectrum, calculate the power spectrum according to the spectrum, and perform normalization calculation to obtain the normalized power spectrum;

[0008] S2. Calculate the power spectrum information entropy according to the normalized power spectrum, calculate the confidence factor of the measurement result according to the power spectrum information entropy, and determine whether the confidence factor is lower than a preset threshold;

[0009] S3. If the confidence factor is lower than the preset threshold, the current measurement result is determined to be unreliable, and the phasor and frequency measurement values ​​are corrected using an exponential decay sliding weighted correction model to obtain the final measurement result;

[0010] S4. If the confidence factor is higher than the preset threshold, the current measurement result is determined to be reliable, and the current measurement result is the final measurement result;

[0011] S5. Upload the final measurement results.

[0012] Preferably, in S1, the specific calculation process of the spectrum is:

[0013] The fundamental signal model of voltage and current in the power system is:

[0014] ;

[0015] in, Indicates the sampling value of voltage and current signals, X m ( t） express t Moment amplitude, φ ( t )express t Moment phase angle, represents the fundamental frequency, Indicates noise;

[0016] Perform fast Fourier transform on the voltage and current signals and calculate the spectrum. The result is:

[0017] ;

[0018] in, Indicates frequency components The spectrum amplitude of N Indicates the number of sampling points in the time window, Indicates the sampling value sequence number, j Represents the imaginary part.

[0019] Preferably, in S1, the normalized power spectrum is:

[0020] ;

[0021] in, Indicates the signal The power spectrum amplitude of the components, The normalized signal The power spectrum amplitude of the components.

[0022] Preferably, in S2, the power spectrum information entropy is:

[0023]

[0024] in, Indicates signal The power spectrum information entropy of .

[0025] Preferably, in S2, the confidence factor is:

[0026] ;

[0027] in, L ( t k )express t k The confidence factor of the moment phasor calculation, α represents the attenuation coefficient of the confidence factor, H ( t k ) indicates t k is the power spectrum information entropy of the signal in the measurement time window at the center moment.

[0028] Preferably, in S3,

[0029] The phasor amplitude correction model is:

[0030] ;

[0031] in, X c ( t k )express t k The phasor amplitude correction value at time instant, M represents the weighted average model order, Indicates An exponential decay weight coefficient, represents the phasor calculation frequency, X m (·) represents the calculated value of the phasor amplitude;

[0032] The exponential decay weight coefficient is:

[0033] ;

[0034] in, Indicates The weights correspond to the confidence factors of the phasors, β Represents the attenuation coefficient.

[0035] Preferably, in S3,

[0036] The correction model of the phase angle is:

[0037] ;

[0038] The frequency correction model is:

[0039] ;

[0040] in, φ c ( t k )express t k Phase angle correction value at the moment, φ (·) represents the calculated phase angle value, express t k The moment frequency correction value, Indicates the frequency correction value.

[0041] The advantages and positive effects of the method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault described in the present invention are:

[0042] 1. The present invention defines the power spectrum information entropy of discrete sampling signals, which is used to characterize the degree of distortion starting from the waveform and provide a basis for calculating the confidence factor.

[0043] 2. The present invention defines the confidence factor of the PMU measurement result, quantifies the reliability of the real-time measurement result, monitors when the transient process starts and ends, and provides a criterion for starting the correction algorithm.

[0044] 3. The present invention proposes an exponentially decaying sliding weighted measurement result correction model. When the measurement result is unreliable during the transient period after a fault, the measurement result is adaptively corrected in real time to improve the accuracy of the measurement result.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1It is a flow chart of the method for correcting the PMU phase frequency measurement value in the transient process after a fault of the present invention;

[0047] Figure 2 is the calculated value of the confidence factor in the embodiment of the present invention;

[0048] Figure 3 4 is a comparison diagram of the correction effect of the frequency measurement result of the field fault signal in the embodiment of the present invention. DETAILED DESCRIPTION

[0049] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0050] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0051] like Figure 1 A method for correcting PMU phase frequency measurement values ​​in a transient process after a fault, comprising the following steps:

[0052] S1. Perform fast Fourier transform on the sampling value of the power signal, take its amplitude to obtain the spectrum, calculate the power spectrum according to the spectrum, and perform normalization calculation to obtain the normalized power spectrum.

[0053] The specific calculation process of the spectrum is:

[0054] The fundamental signal model of voltage and current in the power system is:

[0055] ;

[0056] in, Indicates the sampling value of voltage and current signals, X m ( t )express t Moment amplitude, φ ( t )express t Moment phase angle, represents the fundamental frequency, Indicates noise;

[0057] Perform fast Fourier transform on the voltage and current signals and calculate the spectrum. The result is:

[0058] ;

[0059] in, Indicates frequency components The spectrum amplitude of N Indicates the number of sampling points in the time window, Indicates the sampling value sequence number, jRepresents the imaginary part.

[0060] The normalized power spectrum is:

[0061] ;

[0062] in, Indicates the signal The power spectrum amplitude of the components, The normalized signal The power spectrum amplitude of the components.

[0063] S2. Calculate the power spectrum information entropy according to the normalized power spectrum, calculate the confidence factor of the measurement result according to the power spectrum information entropy, and determine whether the confidence factor is lower than a preset threshold.

[0064] The power spectrum information entropy is:

[0065] ;

[0066] in, Indicates signal The power spectrum information entropy of .

[0067] The confidence factor is:

[0068] ;

[0069] in, L ( t k )express t k The confidence factor of the moment phasor calculation, α represents the attenuation coefficient of the confidence factor, H ( t k ) indicates t k is the power spectrum information entropy of the signal in the measurement time window at the center moment.

[0070] S3. If the confidence factor is lower than the preset threshold, the current measurement result is determined to be unreliable and needs to be corrected. The exponential decay sliding weighted correction model is used to correct the phase and frequency measurement values ​​to obtain the final measurement result.

[0071] Assumptions t k The calculated value of the phasor at this moment is:

[0072] ;

[0073] In the formula, X ( t k )express tk The calculated value of the phasor at the moment, X m ( t k )express t k The calculated value of the phasor amplitude at time φ ( t k )express t k The calculated value of the phasor phase angle at the moment.

[0074] The phasor amplitude correction model is:

[0075] ;

[0076] in, X c ( t k )express t k The phasor amplitude correction value at time instant, M represents the weighted average model order, Indicates An exponential decay weight coefficient, Indicates the phase calculation frequency;

[0077] The exponential decay weight coefficient is:

[0078] ;

[0079] in, Indicates The weights correspond to the confidence factors of the phasors, β Represents the attenuation coefficient.

[0080] The correction model of the phase angle is:

[0081] ;

[0082] The frequency correction model is:

[0083] ;

[0084] in, φ c ( t k )express t k Phase angle correction value at the moment, φ (·) represents the calculated phase angle value, express t k The moment frequency correction value, Indicates the frequency correction value.

[0085] S4. If the confidence factor is higher than the preset threshold, the current measurement result is determined to be reliable and no correction is required. The current measurement result is the final measurement result.

[0086] S5. Upload the final measurement results.

[0087] Example

[0088] In order to verify the effect of the proposed method, a section of ultra-high voltage line voltage fault signal was selected as the analysis object. The signal sampling rate was 9600Hz, and the fault occurred at 50ms. The confidence factor threshold was set to 80%. Three frequency estimation methods, phase angle difference method (M1), differential geometry method (M2), and dual complex bandpass filter method (M3), were used for comparative testing. The data window length was set to 2 cycles, and the upload frequency was 100Hz. Since the frequency measurement is obtained by phasor amplitude ratio or phase angle difference calculation, the frequency calculation can also reflect the phasor amplitude and phase angle measurement effect to a certain extent. Therefore, this paper takes the correction result of frequency measurement as an example to demonstrate the effect of the proposed method.

[0089] The confidence factor of the proposed method is Figure 2 As shown. Figure 2 It can be seen that before the fault occurred, the waveform was stable and the confidence factor of the measurement result was close to 100%. However, during the fault process, the waveform was severely distorted within the time window and the confidence factor dropped to a lower level. Figure 2 It can be seen that the proposed confidence factor can better reflect the confidence of the measurement results.

[0090] The frequency measurement results of each method are as follows Figure 3 As shown. Figure 3 It can be seen that in the initial electromagnetic transient after the fault, M3 has the largest frequency offset, followed by M1 and M2. The maximum frequency offset of the method described in the present invention is less than one tenth of that of the control method, which significantly reduces the frequency and frequency change rate calculation offset in the electromagnetic transient process.

[0091] For electromechanical transients after the waveform is restored to stability, the method of the present invention, M1 and M3 have similar measurement effects, and the calculation effect of M2 is slightly different from that of other methods. This is because M2 has a short window length and is difficult to filter out harmonic components in electromechanical transient electrical quantities, and is easily interfered with. The method of the present invention and M1 and M3 can suppress these interferences and thus present similar measurement effects.

[0092] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field.

[0093] Therefore, by adopting the method for correcting the PMU phasor frequency measurement value in the transient process after a fault described in the present invention, real-time correction of the phasor frequency measurement value of the voltage or current in the transient process after a fault in the power system can be achieved.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for correcting PMU phase frequency measurement values ​​in a transient process after a fault, characterized in that: The following steps are involved: S1. Perform fast Fourier transform on the sampling value of the power signal, take its amplitude to obtain the spectrum, calculate the power spectrum according to the spectrum, and perform normalization calculation to obtain the normalized power spectrum; S2. Calculate the power spectrum information entropy according to the normalized power spectrum, calculate the confidence factor of the measurement result according to the power spectrum information entropy, and determine whether the confidence factor is lower than a preset threshold; S3. If the confidence factor is lower than the preset threshold, the current measurement result is determined to be unreliable, and the phasor and frequency measurement values ​​are corrected using an exponential decay sliding weighted correction model to obtain the final measurement result; S4. If the confidence factor is higher than the preset threshold, the current measurement result is determined to be reliable, and the current measurement result is the final measurement result; S5. Upload the final measurement results.

2. A method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault according to claim 1, characterized in that: In S1, the specific calculation process of the spectrum is: The fundamental signal model of voltage and current in the power system is: ； in, Indicates the sampling value of voltage and current signals, X m ( t )express t Moment amplitude, φ ( t )express t Moment phase angle, represents the fundamental frequency, Indicates noise; Perform fast Fourier transform on the voltage and current signals and calculate the spectrum. The result is: ； in, Indicates frequency components The spectrum amplitude of N Indicates the number of sampling points in the time window, Indicates the sampling value sequence number, j Represents the imaginary part.

3. A method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault according to claim 2, characterized in that: In S1, the normalized power spectrum is: ； in, Indicates the signal The power spectrum amplitude of the components, The normalized signal The power spectrum amplitude of the components.

4. A method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault according to claim 3, characterized in that: In S2, the power spectrum information entropy is: ； in, Indicates signal The power spectrum information entropy of .

5. A method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault according to claim 4, characterized in that: In S2, the confidence factor is: ； in, L ( t k )express t k The confidence factor of the moment phasor calculation, α represents the attenuation coefficient of the confidence factor, H ( t k ) indicates t k is the power spectrum information entropy of the signal in the measurement time window at the center moment.

6. A method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault according to claim 5, characterized in that: In S3, The phasor amplitude correction model is: ； in, X c ( t k )express t k The phasor amplitude correction value at time instant, M represents the weighted average model order, Indicates An exponential decay weight coefficient, represents the phasor calculation frequency, X m (·) represents the calculated value of the phasor amplitude; The exponential decay weight coefficient is: ； in, Indicates The weights correspond to the confidence factors of the phasors, β Represents the attenuation coefficient.

7. A method for correcting PMU phasor frequency measurement values ​​in a transient process after a fault according to claim 6, characterized in that: In S3, The correction model of the phase angle is: ； The frequency correction model is: ； in, φ c ( t k )express t k Phase angle correction value at the moment, φ (·) represents the calculated phase angle value, express t k The moment frequency correction value, Indicates the frequency correction value.

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