A high-precision and fast calculation method for power grid frequency

Abstract

The present invention discloses a method for high-precision and rapid calculation of power grid frequency, which comprises the following steps: a high-speed acquisition card acquires a secondary voltage signal of the power grid; the voltage signal is subjected to high-precision analog-to-digital conversion; the converted signal is subjected to a high sampling rate to acquire a voltage signal; the voltage signal is resampled; the resampled signal is subjected to frequency calculation; the position of the sampling point where the primary threshold is located is obtained by verifying the resampling period using a threshold and a secondary threshold in sequence; the resampled signal is restored to the original signal and high-precision frequency calculation is performed again; and the actual frequency of the power grid is obtained. The present invention greatly reduces the amount of calculation without changing the frequency calculation accuracy, saves calculation time, and ensures the accuracy and real-time performance of the power grid frequency calculation. At the same time, the secondary threshold introduced in the method eliminates the influence of interference signals, avoiding calculation errors caused thereby.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid frequency calculation, and in particular to a high-precision and fast calculation method for power grid frequency. Background Art

[0002] With the increasing demand for power supply reliability, new requirements have been put forward for the real-time and accuracy of grid parameter calculations. To obtain more accurate parameters, the data sampling rate must be increased. For example, a Chinese patent application (application number 202010221855.2) discloses a new method for real-time, high-precision measurement of grid frequency. In this method, the sampling rate reaches 100Ms / s. While high-speed sampling brings higher accuracy, it also puts huge pressure on the calculation, which greatly affects the real-time performance of grid parameters. At the same time, since grid parameters require real-time calculation, if the computing power or memory is insufficient, long-term operation will inevitably cause the computer to crash or even freeze. In addition, this method calculates the area representative value at different frequencies based on the frequency range and compensation, and determines the grid frequency by finding the minimum area representative value. It can obtain a higher-precision frequency, but due to its large amount of calculation, it fails to meet the requirements of fast calculation. A Chinese patent application (application number 201310689682.7) discloses a large-dynamic, high-precision synchronous continuous frequency measurement method. The measured signal in this method is a pulse signal. Since the grid voltage signal is a sine wave signal, it is different from the grid voltage signal and cannot be used for grid frequency calculation. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a high-precision and fast calculation method for power grid frequency to solve the technical problems existing in the prior art and to achieve fast and accurate calculation of the current power grid frequency under high-speed sampling conditions.

[0004] The technical solution adopted by the present invention is: a high-precision and fast calculation method for power grid frequency, which comprises the following steps: a high-speed acquisition card acquires a secondary voltage signal of the power grid; the voltage signal is subjected to high-precision analog-to-digital conversion; the converted signal is subjected to a high sampling rate to acquire a voltage signal; the voltage signal is resampled and processed; the frequency of the resampled signal is calculated; the position of the sampling point where the primary threshold is located is obtained by verifying the resampling period through the threshold and the secondary threshold in sequence; the resampled signal is restored to the original signal and the high-precision frequency calculation is performed again; and the actual frequency of the power grid is obtained.

[0005] A high-precision and fast calculation method for power grid frequency, the specific steps of the method are as follows:

[0006] A) Through the principle of electromagnetic induction, the primary voltage of the power grid is converted into a secondary voltage signal. The secondary voltage signal has the same frequency as the primary voltage signal, and its amplitude is proportional to the primary voltage. The data acquisition channel of the high-speed acquisition card is connected to the secondary voltage signal.

[0007] B) The secondary voltage signal is converted into a digital signal through analog-to-digital conversion by a high-speed data acquisition card;

[0008] C) reading the digital signal data obtained in step 2) into a data processing device through acquisition software;

[0009] D) resampling the read digital signal according to the set resampling coefficient (software implementation) with the resampling coefficient being k to reduce the data volume;

[0010] E) performing a primary threshold judgment and a secondary threshold judgment on the resampled signal to determine the position of the sampling point where the primary threshold is located;

[0011] F) Marking the sampling point position of the threshold in the resampled signal in the original signal;

[0012] G) Re-search the threshold value within the range of the marked point [-k, k] in the original signal and confirm the sampling point position of the original signal corresponding to the threshold value in the original signal;

[0013] H) Confirm the voltage frequency and period through the sampling point position corresponding to the primary threshold.

[0014] In step C), the original data is resampled, and the resampling sequence is V r , and its calculation process is:

[0015] V r ={v0,v 1k ,v 2k ,…,v mk}

[0016] Where, v mk V r The last element where mk <= x.

[0017] The signal sequence V after the secondary voltage signal is converted into a digital signal in step B) o , which is expressed as:

[0018] V o ={v0,v1,v2,…,v n …,v x}

[0019] Where, v x V o The last element in .

[0020] In step E, a threshold judgment is performed on the resampled signal, and the process is as follows:

[0021] vik ≤U0

[0022] v (i+1)k ≤U0

[0023] Where i ranges from 0 to m-1. If all the above equations are true, the first i that is true is recorded as i0, the second that is true is recorded as i1, and so on, to obtain the sequence I:

[0024] I={i0,i1,i2,…,i z}

[0025] i z is the last element of sequence I;

[0026] Where, U0 is the primary threshold, U0=0 in the grid frequency calculation; i is the sequence V r The sampling point position corresponding to the threshold.

[0027] The process of performing secondary threshold judgment on the resampled signal in step E is as follows:

[0028]

[0029] v r ≥U1

[0030] Where, v r For sequence V r Sampling point i j with i j+1 Medium V r The maximum value, U1 is the second threshold, U1=(0.3~0.9)U f , where U f is the original signal V r The amplitude of

[0031] j ranges from 0 to z-1. If the above equations are all true, the first j that is true is recorded as j0, the second one that is true is recorded as j1, and so on, to obtain the sequence J:

[0032] J={j0,j1,j2,…,j y}

[0033] Where y≤z; sequence J is the resampled signal V r The sampling point location of the primary threshold.

[0034] For step F), the position of the sampling point where the threshold value in the resampled signal is located in the original signal is identified, and the process is as follows:

[0035] H={j0k,j1k,j2k,…,j y k}.

[0036] For step F), the threshold is searched again within the range of [-k, k] of the marked points in the original signal and the sampling point position of the original signal corresponding to the threshold is confirmed in the original signal. The process is as follows:

[0037]

[0038]

[0039] g∈[-k,k-1]

[0040] Among them, g ranges from -k to k-1, and h ranges from 0 to y. If the above equations are all true, the first sampling point that is true is (j0k)+g0, the second sampling point that is true is (j1k)+g1, and so on. The sequence is recorded as:

[0041] E={j0k+g0,j1k+g1,…,j y k+g y ,}={e1,e2,…,e y}

[0042] Sequence E is the original signal V o Confirm the sampling point position of the original signal corresponding to the threshold.

[0043] The grid voltage cycle and frequency are confirmed by the sampling point position corresponding to the threshold in step H. The frequency cycle sequence T o and sequence F o They are:

[0044] T o ={(e1-e0)*Δt,(e2-e1)*Δt,…,(e y -e y-1 )*Δt}={t1,t2,…,t y}

[0045] F o ={1 / t1,1 / t2,…,1 / t y}={f1,f2,…,f3}

[0046] Where Δt is the original signal sequence V o The time interval between two sampling points.

[0047] The resampling coefficient k in step D) is:

[0048]

[0049] Where S is the number of sampling points per unit period. If the sampling rate is P, for a grid with a rated frequency of 50 Hz, S is:

[0050] S=P / 20.

[0051] Beneficial effects of the present invention: Compared with the prior art, the present invention processes the original signal by resampling, and then uses the resampled data to perform a threshold judgment to determine the position of the threshold in the resampling, and also obtains the approximate position of the threshold in the original signal, and then searches near the threshold of the original signal to determine the exact position of the threshold sampling point in the original signal, and calculates the period and frequency of the original signal by the difference between the sampling points corresponding to adjacent thresholds; this calculation method greatly reduces the amount of calculation without changing the frequency calculation accuracy, saves calculation time, and ensures the accuracy and real-time performance of the power grid frequency calculation. At the same time, the secondary threshold introduced by this method eliminates the influence of interference signals and avoids the calculation errors caused thereby. The calculation method of the present invention can also be used in the calculation of apparent power, active power, and reactive power of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is the system flow chart;

[0053] Figure 2 Schematic diagram of the original waveform and resampling. DETAILED DESCRIPTION

[0054] The present invention will be further described below with reference to specific embodiments.

[0055] Example 1: Figure 1-2 As shown, a method for high-precision and rapid calculation of power grid frequency is shown, which comprises: acquiring a secondary voltage signal of the power grid with a high-speed acquisition card; performing high-precision analog-to-digital conversion on the voltage signal; obtaining a voltage signal at a high sampling rate from the converted signal; resampling the voltage signal; performing frequency calculation on the resampled signal; verifying the resampling period by sequentially performing a threshold and a secondary threshold to obtain the position of the sampling point where the primary threshold is located; restoring the resampled signal to the original signal and re-performing high-precision frequency calculation; and obtaining the actual frequency of the power grid. The specific steps of the method are as follows:

[0056] A) Through the principle of electromagnetic induction, the primary voltage of the power grid is converted into a secondary voltage signal. The secondary voltage signal has the same frequency as the primary voltage signal, and its amplitude is proportional to the primary voltage. The data acquisition channel of the high-speed acquisition card is connected to the secondary voltage signal.

[0057] B) The secondary voltage signal is converted into a digital signal through analog-to-digital conversion by a high-speed data acquisition card; the signal sequence V after the secondary voltage signal is converted into a digital signal o , which is expressed as:

[0058] V o ={v0,v1,v2,…,v n…,v x}

[0059] Where, v x V o The last element in the data acquisition card is 50k / s in analog-to-digital conversion rate and 16-bit in resolution.

[0060] C) reading the digital signal data obtained in step 2) into a data processing device through acquisition software;

[0061] Resample the original data, the resampling sequence is V r , and its calculation process is:

[0062] V r ={v0,v 1k ,v 2k ,…,v mk}

[0063] Where, v mk V r The last element where mk <= x;

[0064] D) resampling the read digital signal according to the set resampling coefficient (software implementation) with the resampling coefficient being k to reduce the data volume;

[0065] The resampling coefficient k is:

[0066]

[0067] Where S is the number of sampling points per unit period. If the sampling rate is P, for a grid with a rated frequency of 50 Hz, S is:

[0068] S = P / 20;

[0069] E) Perform a primary threshold judgment and a secondary threshold judgment on the resampled signal to determine the position of the sampling point where the primary threshold is located; perform a primary threshold judgment on the resampled signal, and the process is as follows:

[0070] v ik ≤U0

[0071] v (i+1)k ≤U0

[0072] Where i ranges from 0 to m-1. If all the above equations are true, the first i that is true is recorded as i0, the second that is true is recorded as i1, and so on, to obtain the sequence I:

[0073] I={i0,i1,i2,…,i z}

[0074] i zis the last element of sequence I;

[0075] Where, U0 is the primary threshold, U0=0 in the grid frequency calculation; i is the sequence V r The sampling point position corresponding to the threshold;

[0076] The process of performing secondary threshold judgment on the resampled signal is as follows:

[0077]

[0078] v r ≥U1

[0079] Where, v r For sequence V r Sampling point i j with i j+1 Medium V r The maximum value, U1 is the second threshold, U1=(0.3~0.9)U f , where U f is the original signal V r The amplitude of

[0080] j ranges from 0 to z-1. If the above equations are all true, the first j that is true is recorded as j0, the second one that is true is recorded as j1, and so on, to obtain the sequence J:

[0081] J={j0,j1,j2,…,j y}

[0082] Where y≤z; sequence J is the resampled signal V r The sampling point location of the primary threshold;

[0083] F) Marking the sampling point position of the threshold in the resampled signal in the original signal;

[0084] The sampling point where the threshold value in the resampled signal is located is identified in the original signal. The process is as follows:

[0085] H={j0k,j1k,j2k,…,j y k}

[0086] G) Re-search the threshold value within the range of the marked point [-k, k] in the original signal and confirm the sampling point position of the original signal corresponding to the threshold value in the original signal;

[0087] Re-search the threshold within the range of [-k, k] in the original signal and confirm the sampling point position of the original signal corresponding to the threshold in the original signal. The process is as follows:

[0088]

[0089]

[0090] g∈[-k,k-1]

[0091] Among them, g ranges from -k to k-1, and h ranges from 0 to y. If the above equations are all true, the first sampling point that is true is (j0k)+g0, the second sampling point that is true is (j1k)+g1, and so on. The sequence is recorded as:

[0092] E={j0k+g0,j1k+g1,…,j y k+g y ,}={e1,e2,…,e y}

[0093] Sequence E is the original signal V o Confirm the sampling point position of the original signal corresponding to the threshold value;

[0094] H) Confirm the voltage frequency and period through the sampling point position corresponding to the primary threshold.

[0095] The grid voltage cycle and frequency are confirmed by the sampling point position corresponding to the primary threshold, and its frequency cycle sequence T o and sequence F o They are:

[0096] T o ={(e1-e0)*Δt,(e2-e1)*Δt,…,(e y -e y-1 )*Δt}={t1,t2,…,t y}

[0097] F o ={1 / t1,1 / t2,…,1 / t y}={f1,f2,…,f3}

[0098] Where Δt is the original signal sequence V o The time interval between two sampling points.

[0099] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A high-precision and fast calculation method for power grid frequency, characterized by: The specific steps of this method are as follows: A) Through the principle of electromagnetic induction, the primary voltage of the power grid is converted into a secondary voltage signal. The secondary voltage signal has the same frequency as the primary voltage signal, and its amplitude is proportional to the primary voltage. The data acquisition channel of the high-speed acquisition card is connected to the secondary voltage signal. B) The secondary voltage signal is converted into a digital signal through analog-to-digital conversion by a high-speed data acquisition card; C) reading the digital signal data obtained in step B) into a data processing device through acquisition software; D) resampling the read digital signal according to the set resampling coefficient, the resampling coefficient is k'; E) performing a primary threshold judgment and a secondary threshold judgment on the resampled signal to determine the position of the sampling point where the primary threshold is located; F) Marking the sampling point position of the threshold in the resampled signal in the original signal; G) Re-search the threshold value within the range of the marked point [-k, k] in the original signal and confirm the sampling point position of the original signal corresponding to the threshold value in the original signal; H) confirm the voltage frequency and period through the sampling point position corresponding to the primary threshold; The signal sequence V after the secondary voltage signal is converted into a digital signal in step B) o , which is expressed as: V o ={v0,v1,v2,…,v n …,v x } Where, v x V o The last element in In step D), the original data is resampled, and the resampling sequence is V r , and its calculation process is: V r ={v0,v 1k ,v 2k ,…,v mk } Where, v mk V r The last element where mk≤x; In step E), a threshold value judgment is performed on the resampled signal, and the process is as follows: in ik ≤U0 in (i+1)k ≥U0 Where i ranges from 0 to m-1. If all the above equations are true, the first i that is true is recorded as i0, the second that is true is recorded as i1, and so on, to obtain the sequence I: I={i0,i1,i2,…,i z } i z is the last element of sequence I; Where, U0 is the primary threshold, U0=0 in the grid frequency calculation; i is the sequence V r The sampling point position corresponding to the threshold; The process of performing secondary threshold judgment on the resampled signal in step E is as follows: in r ≥U1 Where, v r For sequence V r Sampling point i j with i j+1 Medium V r The maximum value of U1 is the second threshold, U1=(0.3~0.9)U f , where U f is the original signal V r The amplitude of j ranges from 0 to z-1. If the above equations are all true, the first j that is true is recorded as j0, the second one that is true is recorded as j1, and so on, to obtain the sequence J: J={j0,j1,j2,…,j y } Where y≤z; sequence J is the resampled signal V r The sampling point location of the primary threshold; For step F), the position of the sampling point where the threshold value in the resampled signal is located in the original signal is identified, and the process is as follows: H={j0k,j1k,j2k,…,j y k}; For step G), the threshold is searched again within the range of [-k, k] of the marked points in the original signal and the sampling point position of the original signal corresponding to the threshold is confirmed in the original signal. The process is as follows: g∈[-k,k-1] Among them, g ranges from -k to k-1, and h ranges from 0 to y. If the above equations are all true, the first sampling point that is true is (j0k)+g0, the second sampling point that is true is (j1k+g1), and so on. The sequence is recorded as: And={j0k+g0,j1k+g1,…,j y k+g y ,}={e1,e2,…,e y } Sequence E is the original signal V o Confirm the sampling point position of the original signal corresponding to the threshold value; The grid voltage cycle and frequency are confirmed by the sampling point position corresponding to the threshold in step H. The frequency cycle sequence T o and sequence F o They are: T o ={(e1-e0)*Δt,(e2-e1)*Δt,…,(e y -e y-1 )*Δt}={t1,t2,…,t y } <h2 style=";text-align:left;direction:ltr">F<h2 style=";text-align:left;direction:ltr"> o <h2 style=";text-align:left;direction:ltr"> ={1 / t1,1 / t2,…,1 / t<h2 style=";text-align:left;direction:ltr"> y <h2 style=";text-align:left;direction:ltr">}={f1,f2,…,f3} Where Δt is the original signal sequence V o The time interval between two sampling points.

2. A high-precision and fast calculation method for power grid frequency according to claim 1, characterized in that: The resampling coefficient k' in step D) is: Where S is the number of sampling points per unit period. If the sampling rate is P, for a grid with a rated frequency of 50 Hz, S is: S=P / 20.

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