A time-frequency domain fusion synchronous measurement method suitable for transient and steady state of power system

Abstract

The invention discloses a time-frequency domain fusion synchronous measurement method suitable for transient and steady states of power systems, and relates to the technical field of synchronous waveform measurement of power systems, comprising S1, obtaining a signal sampling value sequence with a time stamp through a signal sampling module, filtering and calculating the obtained signal sampling value sequence through a bandpass filter to obtain a synchronous phasor; S2, reconstructing a time domain signal according to the synchronous phasor, subtracting the reconstructed time domain signal from the original signal to obtain a residual signal, and judging whether the residual signal energy exceeds a starting threshold; S3, if the residual signal energy does not exceed the starting threshold, judging that no electromagnetic transient process occurs, calculating the frequency and the frequency change rate according to the phasor measurement result, and uploading the synchronous phasor, the frequency and the frequency change rate; S4, if the residual signal energy exceeds the starting threshold, judging that an electromagnetic transient process occurs, performing adaptive Fourier decomposition on the residual signal to obtain a TM phasor, uploading the synchronous phasor and the TM phasor, and reconstructing the transient waveform at a master station.

Description

Technical Field

[0001] The present invention relates to the technical field of synchronous waveform measurement of electric power systems, and in particular to a time-frequency domain fusion synchronous measurement method suitable for transient steady states of electric power systems. Background Art

[0002] Synchronous measurement devices can measure and upload phasor, frequency, waveform and other data with a unified time scale in real time to realize dynamic monitoring of the power system. Therefore, they have been widely deployed in transmission networks and have begun to be deployed in distribution networks and new energy stations. They are of great significance to power system state estimation, stability control, fault identification and location.

[0003] However, traditional synchronized phasors are only applicable to steady-state or quasi-steady-state processes of power systems, and are not applicable to electromagnetic transient processes after faults. During power system faults, the waveform of electrical quantities is severely distorted. The traditional Fourier transform-based phasor characterization method uses a base with both amplitude and frequency being static, which cannot accurately and efficiently decompose the distorted signal. The synchronized phasor and frequency measurement results during transients are meaningless. Therefore, synchronized waveform measurement is of great significance during transients. However, although synchronized waveform measurement can provide complete transient process recording results, its intermediate characterization quantity is a simple algorithm compression result and has no physical meaning, which means that the data it provides needs to be reprocessed to achieve other application purposes. In addition, the existing synchronized waveform measurement is separated from the synchronized phasor measurement, and the two measurement systems are incompatible with each other, which increases the device development cost and system operation and maintenance cost.

[0004] Therefore, it is urgent to study the phasor waveform fusion measurement method suitable for steady-state and transient power system, scientifically combine phasor measurement and waveform measurement, and support steady-state and transient applications of power system. Summary of the invention

[0005] The purpose of the present invention is to provide a time-frequency domain fusion synchronous measurement method suitable for transient and steady states of power systems, so as to solve the problems existing in the prior art of separation of synchronous waveform measurement and synchronous phasor measurement, incompatibility of measurement systems, high device development cost and system operation and maintenance cost, and difficulty in accurate measurement of distorted signals.

[0006] To achieve the above object, the present invention provides a time-frequency domain fusion synchronous measurement method suitable for transient steady state of power system, comprising the following steps:

[0007] S1. Obtain a signal sampling value sequence with a time stamp through a signal sampling module, and filter and calculate the obtained signal sampling value sequence through a bandpass filter to obtain a synchronized phasor;

[0008] S2, reconstructing the time domain signal according to the synchronized phasor, subtracting the reconstructed time domain signal from the original signal to obtain a residual signal, and determining whether the residual signal energy exceeds the start threshold;

[0009] S3. If the residual signal energy does not exceed the start threshold, it is determined that no electromagnetic transient process occurs, and the frequency and frequency change rate are calculated based on the phasor measurement results, and the synchronous phasor, frequency and frequency change rate are uploaded;

[0010] S4. If the residual signal energy exceeds the starting threshold, it is determined that an electromagnetic transient process has occurred. The residual signal is adaptively decomposed by Fourier to obtain the TM phasor. The synchronous phasor and TM phasor are uploaded, and the transient waveform is reconstructed at the master station.

[0011] Preferably, the length of the bandpass filter in S1 is not greater than two cycles.

[0012] Preferably, the calculation expression of the synchronized phasor in S1 is as follows:

[0013] ;

[0014] In the formula, represents the nth sampling value in the original power signal sampling value sequence, express The synchronized phasor value at time, Represents the nth filter coefficient, and N represents the total number of sample values ​​in the time window.

[0015] Preferably, the expression for reconstructing the time domain signal according to the synchronized phasor in S2 is as follows:

[0016] ;

[0017] in, represents the signal reconstruction value, express The phase angle of the synchronized phasor at time Indicates the rated frequency of the power system, Represents the signal sampling frequency, and n represents the sequence number of the signal sampling value in the time window.

[0018] Preferably, the calculation expression of the residual signal in S2 is as follows:

[0019] ;

[0020] In the formula, Represents the nth value in the residual signal sequence.

[0021] Preferably, the calculation expression of the residual signal energy in S2 is as follows:

[0022] ;

[0023] Where E represents the residual signal energy.

[0024] Preferably, the start threshold is 10% of the original signal energy, and the original signal energy calculation expression is as follows:

[0025] ;

[0026] In the formula, Represents the original signal energy.

[0027] Preferably, the adaptive Fourier decomposition process in S4 is as follows:

[0028] Adaptive Fourier decomposition uses a set of rational orthogonal dynamic bases based on the Takenaka-Malmquist system with strict mathematical expression to decompose and characterize the signal. The basis used is called the improved Blaschke basis, which is expressed as follows:

[0029] ;

[0030] ;

[0031] ;

[0032] In the formula, i represents the i-th decomposition, M represents the total number of decompositions, represents the basis of the i-th decomposition, represents the value of the free variable a at the i-th decomposition, a is a complex number with a modulus less than 1, z represents a variable related to the signal phase, t represents the signal phase, N represents the number of sampling points in the data window, express The conjugate of represents the value of the free variable a during the k-th decomposition, express The conjugate of represents the value set of the free variable a, represents a complex number, j represents the imaginary part;

[0033] Calculate the energy evaluation operator , energy evaluation operator The signal to be decomposed and The calculation expression is as follows:

[0034] ;

[0035] In the formula, Indicates the signal to be decomposed at the i-th decomposition, specifically a set of sampling points, obtained by subtracting the previous i-1 decomposition amount from the original signal; Represents the calculation weight array, which is set to 1 in this article; corresponding to Each of Correspondingly, the largest value The corresponding is selected, the expression is as follows:

[0036] ;

[0037] In the formula, Indicates for finding The maximum value corresponds to Function of

[0038] According to the determined , calculate the basis of the i-th decomposition And the characterization quantity, the expression is as follows:

[0039] ;

[0040] ;

[0041] In the formula, Indicates the TM phase to be uploaded.

[0042] Preferably, the expression for waveform reconstruction in S4 is as follows:

[0043] ;

[0044] ;

[0045] ;

[0046] In the formula, represents the intermediate component during the i-th reconstruction, represents the real signal reconstructed for the i-th time, Sum represents the matrix column summation function, Re represents the function of taking the real part, Represents the final reconstructed waveform signal.

[0047] Therefore, the present invention adopts the above-mentioned time-frequency domain fusion synchronous measurement method suitable for transient steady state of power system, which has the following beneficial effects:

[0048] (1) Accurately identify transient processes and severe interharmonic interference based on residual signal energy levels;

[0049] (2) The TM phasor is calculated by adaptive Fourier decomposition. The TM phasor has physical meaning and has a similar representation form to the traditional synchronized phasor.

[0050] (3) High-precision waveform reconstruction can be achieved based on the TM phasor.

[0051] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is an overall flow chart of a time-frequency domain fusion synchronous measurement method applicable to transient and steady states of power systems according to the present invention;

[0053] Figure 2 This is a waveform reconstruction effect diagram of the TM method proposed by the present invention in an embodiment of the present invention;

[0054] Figure 3 This is a waveform reconstruction effect diagram of the FFT method in the embodiment of the present invention;

[0055] Figure 4 This is a comparison diagram of waveform reconstruction errors between the TM method and the FFT method in an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] See also Figure 1-Figure 4 A time-frequency domain fusion synchronous measurement method suitable for transient and steady states of power systems comprises the following steps:

[0058] S1. Obtain a signal sampling value sequence with a time stamp through a signal sampling module, and filter and calculate the obtained signal sampling value sequence through a bandpass filter to obtain a synchronized phasor; wherein the length of the bandpass filter is not greater than two cycles; specifically: design a bandpass filter with a length equal to two cycles, a passband center at 48Hz, a passband width greater than 4Hz, a passband ripple less than 0.05dB, a gain less than -100dB at -50Hz and each harmonic frequency, and an order less than 2 cycle sampling points. ;in, The coefficients of the bandpass filter are coefficients, Represents the total number of sampled values ​​in the time window; the calculation expression of the synchronized phasor is as follows:

[0059] ;

[0060] In the formula, represents the nth sampling value in the original power signal sampling value sequence, express The synchronized phasor value at time, Represents the nth filter coefficient, and N represents the total number of sample values ​​in the time window.

[0061] S2. Reconstruct the time domain signal according to the synchronized phasor, subtract the reconstructed time domain signal from the original signal to obtain the residual signal, and determine whether the residual signal energy exceeds the start threshold; wherein, the expression of reconstructing the time domain signal according to the synchronized phasor is as follows:

[0062] ;

[0063] in, represents the signal reconstruction value, express The phase angle of the synchronized phasor at time Indicates the rated frequency of the power system, Represents the signal sampling frequency, and n represents the sequence number of the signal sampling value in the time window.

[0064] The calculation expression of the residual signal is as follows:

[0065] ;

[0066] In the formula, Represents the nth sample value in the residual signal.

[0067] The calculation expression of residual signal energy is as follows:

[0068] ;

[0069] Where E represents the residual signal energy.

[0070] The start threshold is 10% of the original signal energy. The original signal energy calculation expression is as follows:

[0071] ;

[0072] In the formula, Represents the original signal energy.

[0073] S3. If the residual signal energy does not exceed the start threshold, it is determined that no electromagnetic transient process occurs, and the frequency and frequency change rate are calculated based on the phasor measurement results, and the synchronous phasor, frequency and frequency change rate are uploaded;

[0074] S4. If the residual signal energy exceeds the starting threshold, it is determined that an electromagnetic transient process has occurred, and the residual signal is adaptively decomposed by Fourier to obtain the TM phasor. The synchronous phasor and TM phasor are uploaded, and the transient waveform is reconstructed at the master station. The adaptive Fourier decomposition process is as follows:

[0075] Adaptive Fourier decomposition uses a set of rational orthogonal dynamic bases based on the Takenaka-Malmquist system with strict mathematical expression to decompose and characterize the signal. The basis used is called the improved Blaschke basis, which is expressed as follows:

[0076] ;

[0077] ;

[0078] ;

[0079] In the formula, i represents the i-th decomposition, M represents the total number of decompositions, represents the basis of the i-th decomposition, represents the value of the free variable a at the i-th decomposition, a is a complex number with a modulus less than 1, z represents a variable related to the signal phase, t represents the signal phase, N represents the number of sampling points in the data window, express The conjugate of represents the value of the free variable a during the k-th decomposition, express The conjugate of represents the value set of the free variable a, represents a complex number, j represents the imaginary part;

[0080] Easy to know, Only Influence, in each calculation of AFD, the free variables are also calculated first Then calculate the basis , and then calculate the decomposition amount. Because is a complex number with a modulus less than 1, so the AFD algorithm first generates a dictionary with a certain resolution, including All possible values ​​of .

[0081] Calculate the energy evaluation operator , energy evaluation operator The signal to be decomposed and The calculation expression is as follows:

[0082] ;

[0083] In the formula, Indicates the signal to be decomposed at the i-th decomposition, specifically a set of sampling points, obtained by subtracting the previous i-1 decomposition amount from the original signal; Represents the calculation weight array, which is set to 1 in this article; corresponding to each , each has one Correspondingly, the largest value The corresponding is selected, the expression is as follows:

[0084] ;

[0085] In the formula, Indicates for finding The maximum value corresponds to Function of

[0086] According to the determined , calculate the basis of the i-th decomposition And the characterization quantity, the expression is as follows:

[0087] ;

[0088] ;

[0089] In the formula, Indicates the TM phase to be uploaded.

[0090] The expression of waveform reconstruction is as follows:

[0091] ;

[0092] ;

[0093] ;

[0094] In the formula, represents the intermediate component during the i-th reconstruction, represents the real signal reconstructed for the i-th time, Sum represents the matrix column summation function, Re represents the function of taking the real part, Represents the final reconstructed waveform signal.

[0095] Among them, frequency domain measurement refers to calculating and uploading synchronous phasors and frequencies; time domain measurement refers to calculating and uploading TM phasors, and reconstructing time domain waveforms based on TM phasors at the master station.

[0096] 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 0.5s. The TM method proposed in this invention and the ordinary FFT method were used for experiments. The decomposition effects of the two methods are shown in Figure 2. Figure 2 and Figure 3 As shown in the figure, the waveform reconstruction error comparison is as follows Figure 4 shown.

[0097] Figure 4The maximum error of the waveform reconstruction of the proposed method is 0.68%, and the maximum error of the comparison method is 9.48%. Figure 2 and Figure 3 It can be seen that the reconstructed waveform of the proposed method almost coincides with the original signal, while the reconstructed waveform of the FFT method has a larger offset compared to the original signal. One reason for this phenomenon is the sudden change of the signal, and another reason is the large number of non-integer harmonics in the signal after the fault. Because the short-window FFT is limited by the frequency resolution, it is difficult to distinguish these interharmonics. If the window length is increased, it will be difficult to track the signal changes within the time window. The traditional method based on the Fourier basis is difficult to take into account both frequency resolution and dynamic performance. The method proposed in the present invention uses a series of dynamic Blaschke bases, which is no longer limited by concepts such as frequency resolution in the frequency domain, and has good fitting and characterization effects.

[0098] Therefore, the present invention adopts the above-mentioned time-frequency domain fusion synchronous measurement method suitable for the transient and steady state of the power system, and selects different processing methods by judging whether the residual signal energy exceeds the starting threshold, so as to realize the steady-state phasor measurement and transient waveform measurement of the power system.

[0099] 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 time-frequency domain fusion synchronous measurement method suitable for transient and steady states of power systems, characterized in that: The following steps are involved: S1. Obtain a signal sampling value sequence with a time stamp through a signal sampling module, and filter and calculate the obtained signal sampling value sequence through a bandpass filter to obtain a synchronized phasor; S2, reconstructing the time domain signal according to the synchronized phasor, subtracting the reconstructed time domain signal from the original signal to obtain a residual signal, and determining whether the residual signal energy exceeds the start threshold; S3. If the residual signal energy does not exceed the start threshold, it is determined that no electromagnetic transient process occurs, and the frequency and frequency change rate are calculated based on the phasor measurement results, and the synchronous phasor, frequency and frequency change rate are uploaded; S4. If the residual signal energy exceeds the starting threshold, it is determined that an electromagnetic transient process has occurred, and the residual signal is adaptively decomposed by Fourier to obtain the TM phasor. The synchronous phasor and the TM phasor are uploaded, and the transient waveform is reconstructed at the master station. The adaptive Fourier decomposition process in S4 is as follows: Adaptive Fourier decomposition uses a set of dynamic bases based on the Takenaka-Malmquist system to decompose and characterize the signal. The base used is called the improved Blaschke base, which is expressed as follows: ； ； ； In the formula, i represents the i-th decomposition, M represents the total number of decompositions, represents the basis of the i-th decomposition, represents the value of the free variable a at the i-th decomposition, a is a complex number with a modulus less than 1, z represents a variable related to the signal phase, t represents the signal phase, N represents the number of sampling points in the data window, express The conjugate of represents the value of the free variable a during the k-th decomposition, express The conjugate of represents the value set of the free variable a, represents a complex number, j represents the imaginary part; Calculate the energy evaluation operator , energy evaluation operator The signal to be decomposed and The calculation expression is as follows: ； In the formula, Indicates the signal to be decomposed at the i-th decomposition, specifically a set of sampling points, obtained by subtracting the previous i-1 decomposition amount from the original signal; Represents the calculation weight array, which is set to 1 in this article; corresponding to Each of Correspondingly, the largest value The corresponding is selected, the expression is as follows: ； In the formula, Indicates for finding The maximum value corresponds to Function of According to the determined , calculate the basis of the i-th decomposition And the characterization quantity, the expression is as follows: ； ； In the formula, Indicates the TM phase to be uploaded.

2. The time-frequency domain fusion synchronous measurement method applicable to transient steady state of power system according to claim 1 is characterized in that: The length of the bandpass filter in S1 is no more than two cycles.

3. The time-frequency domain fusion synchronous measurement method applicable to transient and steady states of power systems according to claim 2, characterized in that: The calculation expression of the synchronized phasor in S1 is as follows: ； In the formula, represents the nth sampling value in the original power signal sampling value sequence, express The synchronized phasor value at time, Represents the nth filter coefficient, and N represents the total number of sample values ​​in the time window.

4. The time-frequency domain fusion synchronous measurement method applicable to transient steady state of power system according to claim 3 is characterized in that: The expression of reconstructing the time domain signal according to the synchronized phasor in S2 is as follows: ； in, represents the signal reconstruction value, express The synchronized phase angle at time, Indicates the rated frequency of the power system, Represents the signal sampling frequency, and n represents the sequence number of the signal sampling value in the time window.

5. The time-frequency domain fusion synchronous measurement method applicable to transient steady state of power system according to claim 4, characterized in that: The calculation expression of the residual signal in S2 is as follows: ； In the formula, Represents the nth value in the residual signal sequence.

6. The time-frequency domain fusion synchronous measurement method applicable to transient steady state of power system according to claim 5, characterized in that: The calculation expression of the residual signal energy in S2 is as follows: ； Where E represents the residual signal energy.

7. The time-frequency domain fusion synchronous measurement method applicable to transient steady state of power system according to claim 6, characterized in that: The start threshold is 10% of the original signal energy. The original signal energy calculation expression is as follows: ； In the formula, Represents the original signal energy.

8. The time-frequency domain fusion synchronous measurement method applicable to transient and steady states of power systems according to claim 7, characterized in that: The expression for waveform reconstruction in S4 is as follows: ； ； ； In the formula, represents the intermediate component during the i-th reconstruction, represents the real signal reconstructed for the i-th time, Sum represents the matrix column summation function, Re represents the function of taking the real part, Represents the final reconstructed waveform signal.

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