CN110888020B - Synchronous and asynchronous alternating current mixed sampling method based on threshold value - Google Patents
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Abstract
A threshold-based synchronous and asynchronous alternating current hybrid sampling method solves the problem that sampled data are inaccurate after system frequency changes sharply when a power system fails. The method comprises the following steps: determining a frequency threshold value for switching two sampling modes; collecting real-time data of the power, wherein the data are known as follows: [ (t)1,y1)、(t2,y2)、……、(ti,yi)、……(tn,yn)]And the frequency corresponding to the above-mentioned acquisition point is (f)1,f2,……fi……fn) Wherein t isi(i-1 to n) are time points acquired in time series, yi(i is 1 to n) is the amplitude of the acquired data; verifying a frequency change point; determining a sampling pattern at tiThe former time acquisition mode is a synchronous sampling method, at tiThe later time acquisition mode is an asynchronous sampling method; at tpThe former time acquisition mode is an asynchronous sampling method, at tpThe later time acquisition mode is a synchronous sampling method.
Description
Technical Field
The invention relates to the technical field of power system automation, in particular to a synchronous and asynchronous alternating current hybrid sampling method based on a threshold value.
Background
At present, the inside of a power grid is more and more intelligent, and a plurality of high-level application software exist in the power grid, so that the requirement on the precision of power data is higher and higher. Accurate power data enables monitoring to be more accurate and scheduling decisions to be more correct. At present, in a power system, a lot of research is performed on collected data processing, such as data processing by using a quasi-simultaneous compensation algorithm, a windowing method, a software compensation algorithm, and the like. In the aspect of data acquisition, alternating current sampling is generally adopted in microcomputer measurement of periodic electrical signals, and sampling modes are divided into synchronous sampling and asynchronous sampling.
The synchronous sampling is subdivided into software synchronous sampling and hardware synchronous sampling, and most of the software synchronous sampling methods are used, namely, a software method is used for determining the sampling time. In the synchronous sampling of software, because the CPU can not measure the current period of the alternating current power information, only the previous period can be used for replacing the current period, if the variation range of the power frequency signal is not large, the CPU can measure the previous period; however, if the power system fails (power grid short-circuit fault, power grid low-frequency oscillation, and power grid high-frequency oscillation, as shown in fig. 2-4), the frequency of the power frequency signal changes rapidly, and the CPU may not measure the previous period accurately or cannot measure the previous period, so that the sampling points are not uniformly distributed in the signal period, the sampling time intervals are not completely consistent, and a synchronization error exists, which increases the asynchronous sampling error of the system, and the subsequent analysis of the power data requires uniform distribution of the sampling points, thereby limiting the application of the sampling points in high-precision measurement.
Asynchronous sampling is to assume that the power grid frequency is a certain fixed value, and the timing value of a timer is determined according to the certain fixed value and the number of sampling points in each cycle, so as to realize synchronization. Because the asynchronous sampling is simple to realize and the hardware requirement is low, the method is widely applied to microcomputer protection or measurement with low precision requirement. When the frequency of the power grid does not accord with the certain value or changes, the synchronous error of asynchronous sampling is quite large, so that the method is not suitable for occasions with higher precision requirements. But when the power grid operation fails, the sampling speed is faster than synchronous sampling.
Disclosure of Invention
The invention provides a threshold-based synchronous and asynchronous alternating current mixed sampling method, which aims to solve the technical defect of the conventional acquisition mode that when a power system fails, the frequency fluctuation of a power grid is large, synchronous sampling is used for acquisition, the sampling frequency of the next sampling period is determined by calculating the previous sampling period, so that a processor processes data slowly, and the asynchronous sampling frequency is a fixed value and does not need pre-calculation.
The technical solution of the invention is as follows:
the synchronous and asynchronous alternating current mixed sampling method based on the threshold comprises the following steps:
step 1: determining frequency threshold for switching two sampling modes
Step 1.1: collecting real-time data of the power, wherein the data are known as follows:
[(t1，y1)、(t2，y2)、……、(ti，yi)、……(tn，yn)]and the frequency corresponding to the above-mentioned acquisition point is (f)1，f2，……fi……fn) Wherein t isi(i-1 to n) are time points acquired in time series, yi(i is 1 to n) is the amplitude of the acquired data;
step 1.2: verifying frequency variation point
Step 1.2.1: setting a frequency threshold
f N50; according to the GB/T15945 Standard of allowable deviation of frequency of electric energy quality electric power system: the frequency of the power grid in China is normally 50 +/-0.2 HZ;
step 1.2.2: after the power system breaks down in operation, searching a frequency change point:
step 1.2.3: after the power system recovers normal operation, searching a frequency change point:
step 2: determining a sampling pattern
Step 2.1: from step 1.2.2.1 to step 1.2.2.2, t is knowniThe frequency crosses the threshold, so at tiThe former time acquisition mode is a synchronous sampling method, at tiThe later time acquisition mode is an asynchronous sampling method;
step 2.2: from step 1.2.3.1 to step 1.2.3.2, t is knownpWithin a frequency regression threshold, so at tpThe former time acquisition mode is an asynchronous sampling method, at tpThe later time acquisition mode is a synchronous sampling method.
Further, after the power system fails in operation in step 1.2.2, the process of searching for a frequency change point is as follows:
suppose a frequency transition point (t)i，yi) I.e. (1 to n), known from step 1.1 (t)i-2，yi-2)、(ti-1，yi-1)、(ti+1，yi+1)、(ti+2，yi+2)；
Step 1.2.2.1: and (3) judging the frequency change point by using a formula (1) and a formula (2):
wherein
The frequency interval acquired at the moment before the frequency change,
a frequency interval acquired at a moment after the frequency change; wherein f isNAt power frequency, fi-1A point before the frequency change point, fi+1A point after the frequency change point;
if it is
This point frequency crosses the threshold;
step 1.2.2.2: determining whether the frequency variation point is correct;
wherein
The frequency difference values collected at the two moments before the frequency change,
the frequency difference value is acquired at two moments after the frequency changes; f. ofi-2The second acquisition point before the frequency variation point, fi+2A second acquisition point after the frequency transition point;
if it is
Then explain tiThe fault is not an abnormal point, but a normal frequency change point in the fault.
Further, step 1.2.3: after the power system recovers normal operation, searching a frequency change point:
suppose a frequency transition point (t)p，yp) P.epsilon. (1. about.n), known from step 1.1 (t)p-2，yp-2)、(tp-1，yp-1)、(tp+1，yp+1)、(tp+2，yp+2)；
Step 1.2.3.1: judging a frequency change point; judging by using the formula (1) and the formula (2):
wherein
For the frequency interpolation acquired at the moment before the frequency variation,
interpolating the frequency acquired at a moment after the frequency changes; f. ofp-11 acquisition point before the frequency variation point, fp+11 acquisition point behind the frequency change point;
if it is
It indicates that the frequency at this point does not cross the threshold;
step 1.2.3.2: determining whether the frequency variation point is correct;
if it is
Then explain tpIs not an abnormal point but a normal frequency variation point, wherein fp-22 acquisition points before the frequency variation point, fP+22 acquisition points after the frequency variation point.
According to the technical scheme, the invention has the beneficial effects that: the invention provides a power data acquisition method, which is characterized in that when a power system has a fault, the frequency change is large, and after formula judgment, the acquisition mode is determined to be switched from synchronous acquisition to asynchronous acquisition. When the power system recovers to normal operation, the frequency returns to the normal threshold value, and after formula judgment, the acquisition mode is determined to be switched from asynchronous acquisition to synchronous acquisition. Therefore, the accuracy of data acquisition when the power system fails in operation is improved, and a more reliable basis is provided for subsequent data processing.
Drawings
Fig. 1 is a flowchart of a method conversion of an ac hybrid sampling technique according to an embodiment of the present invention;
fig. 2 is a current collection diagram of a power grid during operation short-circuit fault according to an embodiment of the present invention;
fig. 3 is a current collection diagram of the power grid during operation low-frequency oscillation fault according to the embodiment of the present invention;
fig. 4 is a current collection diagram of the power grid during operation of a high-frequency oscillation fault according to the embodiment of the present invention;
FIG. 5 is a frequency variation graph of a steady-state to transient-state process of the grid operation according to an embodiment of the present invention;
fig. 6 is a frequency variation graph of the transient-state to steady-state process of the power grid operation according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
The invention takes the collected data of the power grid operation as an example, and switches the sampling mode when the power grid frequency fluctuates by using the alternating current synchronous sampling and asynchronous sampling method, as shown in figure 1.
Step 1: and determining a frequency threshold method for switching two sampling modes.
Step 1.1: as shown in fig. 4, the synchronous sampling device detects the occurrence of a fluctuation in frequency at point C. Transition from steady state to transient state, transition from transient state to steady state at point H. 2 points in front of the frequency variation point are selected and analyzed with 2 points in the back, as shown in fig. 5 and 6, and specific detection values are shown in tables 1 and 2.
Table 1: steady state-transient state data
| Sampling point | Sampling time | Amplitude value | Frequency of |
| A | 0.022222 | 15.32089 | 49.9HZ |
| B | 0.022278 | 15.09419 | 49.8HZ |
| C | 0.022333 | 14.8629 | 50.1HZ |
| D | 0.022389 | 13.97095 | 53.1HZ |
| E | 0.022444 | 12.78903 | 52.4HZ |
Table 2: transient-steady state data
Step 1.2: and verifying the frequency change point.
Step 1.2.1: setting a frequency threshold
According to the GB/T15945 Standard of allowable deviation of frequency of electric energy quality electric power system: the frequency of the power grid in China is normally 50 +/-0.2 HZ, and the frequency threshold value of the embodiment
Step 1.2.2: and searching a frequency change point after the power system fails in operation. From step 1.1, it is known that the frequency change point is point C through sampling analysis by a sampling system.
Step 1.2.2.1: and judging a frequency change point. The point data according to B, D is determined by using the formulas (1) and (2):
0.2＝|49.8-50|
3.1＝|53.1-50|
since 0.2 ≦ 0.2, 3.1 > 0.2, indicating that this point frequency crossed the threshold, point C should be the frequency crossing point.
Step 1.2.2.2: whether the frequency variation point is correct or not is determined, and the judgment is performed according to A, E point data by using formulas (3), (4) and (5).
0.1＝|49.9-50|
2.4＝|52.4-50|
Because 0.1 is less than or equal to 0.2 and 2.4 is more than 0.2, t is indicatediThe fault is not an abnormal point, but a normal frequency change point in the fault.
Step 1.2.3: and after the power system recovers to normal operation, searching a frequency change point. From step 1.1, it is known that the frequency change point is the H point through sampling analysis by the sampling system.
Step 1.2.3.1: and judging a frequency change point. Judging by using the formulas (1) and (2):
0.8＝|49.2-50|
0＝|50-50|
since 0.8 ≧ 0.2, 0 < 0.2, this indicates that the H-point frequency has not crossed the threshold.
Step 1.2.3.2: it is determined whether the frequency change point is correct.
1.5＝|48.5-50|
0.1＝|50.1-50|
Since 1.5 is more than or equal to 0.2 and 0.1 is less than 0.2, t is shownpThe abnormal point is not the abnormal point, but the normal frequency variation point.
Step 2: determining a sampling pattern
Step 2.1: from step 1.2.2.1 to step 1.2.2.2, it can be known that the frequency at C crosses the threshold, so the time acquisition mode before 0.022333s is a synchronous sampling method, and the time acquisition mode after 0.022333s is an asynchronous sampling method.
Step 2.2: from step 1.2.3.1 to step 1.2.3.2, it can be known that the frequency at H is within the regression threshold, so the time acquisition mode before 0.044056s is asynchronous sampling method, and the time acquisition mode after 0.044056s is synchronous sampling method.
The above description is only exemplary of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. The synchronous and asynchronous alternating current mixed sampling method based on the threshold value is characterized by comprising the following steps of:
step 1: determining frequency threshold for switching two sampling modes
Step 1.1: the collected real-time data of the electric power is known as follows:
[(t1,y1)、(t2,y2)、……、(ti,yi)、……(tn,yn)]and the frequency corresponding to the above-mentioned acquisition point is (f)1,f2,……fi……fn) Wherein t isi(i-1 to n) are time points acquired in time series, yi(i is 1 to n) is the amplitude of the acquired data;
step 1.2: verifying frequency variation point
Step 1.2.1: setting a frequency threshold
fN50; according to the GB/T15945 Standard of allowable deviation of frequency of electric energy quality electric power system: the frequency of the power grid in China is normally 50 +/-0.2 HZ;
step 1.2.2: after the power system breaks down in operation, searching a frequency change point:
suppose a frequency transition point (t)i,yi) I.e. (1 to n), known from step 1.1 (t)i-2,yi-2)、(ti-1,yi-1)、(ti+1,yi+1)、(ti+2,yi+2)；
Step 1.2.2.1, judging the frequency change point, and judging by using a formula (1) and a formula (2):
wherein
The frequency interval acquired at the moment before the frequency change,
a frequency interval acquired at a moment after the frequency change; wherein f isNAt power frequency, fi-1A point before the frequency change point, fi+1A point after the frequency change point;
if it is
This point frequency crosses the threshold;
step 1.2.2.2: determining whether the frequency variation point is correct;
wherein
The frequency difference values collected at the two moments before the frequency change,
the frequency difference value is acquired at two moments after the frequency changes; f. ofi-2The second acquisition point before the frequency variation point, fi+2A second acquisition point after the frequency transition point;
if it is
Then explain tiThe fault is not an abnormal point and is a normal frequency change point in fault;
step 1.2.3: after the power system recovers normal operation, searching a frequency change point:
suppose a frequency transition point (t)p,yp) P.epsilon. (1. about.n), known from step 1.1 (t)p-2,yp-2)、(tp-1,yp-1)、(tp+1,yp+1)、(tp+2,yp+2)；
Step 1.2.3.1, judging a frequency change point; judging by using the formula (1) and the formula (2):
wherein
For the frequency interpolation acquired at the moment before the frequency variation,
interpolating the frequency acquired at a moment after the frequency changes; f. ofp-11 acquisition point before the frequency variation point, fp+11 acquisition point behind the frequency change point;
if it is
It indicates that the frequency at this point does not cross the threshold;
step 1.2.3.2: determining whether the frequency variation point is correct;
if it is
Then explain tpIs not an abnormal point but a normal frequency variation point, wherein fp－22 acquisition points before the frequency variation point, fP+22 acquisition points behind the frequency variation point;
step 2: determining a sampling pattern
Step 2.1: from step 1.2.2.1 to step 1.2.2.2, t is knowniThe frequency crosses the threshold, so at tiThe former time acquisition mode is a synchronous sampling method, at tiThe later time acquisition mode is an asynchronous sampling method;
step 2.2: from step 1.2.3.1 to step 1.2.3.2, t is knownpWithin a frequency regression threshold, so at tpThe former time acquisition mode is an asynchronous sampling method, at tpThe later time acquisition mode is a synchronous sampling method.
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