Method for measuring frequency of power grid

Abstract

The method for measuring the frequency of the power grid comprises the following steps: executing zero-crossing detection on the voltage of the power grid to obtain a zero-crossing time point of the voltage of the power grid; calculating and recording a time interval between N adjacent two zero-crossing time points, wherein N is a positive integer; the N time intervals are ranked from small to large, an interval formed by the maximum time interval and the minimum time interval is divided into M equal parts, the number of the time intervals in each interval is counted, and M is a positive integer and is smaller than N; selecting an interval with the maximum time interval number, and calculating a first time interval average value; and calculating the power grid frequency based on the first time interval average value.

Description

Technical Field

[0001] The invention relates to the field of circuit measurement, and in particular to a method for measuring power grid frequency. Background Art

[0002] Circuit breakers in low-voltage distribution networks generally have a frequency measurement function, which measures the grid frequency through zero-crossing detection. When the circuit breaker samples and measures the grid frequency in a complex electromagnetic environment, it is susceptible to electromagnetic interference, resulting in false detection or missed detection, which leads to inaccurate grid frequency measurement and frequency distortion. Circuit breakers with frequency protection functions may cause false tripping due to frequency measurement errors. Summary of the invention

[0003] Based on the above problems in the prior art, the present invention provides a method for measuring power grid frequency, comprising:

[0004] Perform zero-crossing detection on the grid voltage to obtain the zero-crossing time point of the grid voltage;

[0005] Calculate and record the time interval between N adjacent zero-crossing time points, where N is a positive integer;

[0006] Sort the N time intervals from small to large, divide the interval formed by the maximum time interval and the minimum time interval into M equal parts, and count the number of time intervals that fall into each interval, where M is a positive integer and is less than N;

[0007] Select the interval with the largest number of time intervals and calculate the average value of the first time interval;

[0008] The grid frequency is calculated based on the first time interval average value.

[0009] In one embodiment, N time intervals are recorded in the form of an array.

[0010] In one embodiment, the recorded N time intervals are updated in a rolling manner, in a first-in-first-out manner, and only the N time interval data are retained.

[0011] In one embodiment, after sorting the N time intervals from small to large, the largest p values ​​and the smallest q values ​​are first eliminated, and then the interval formed by the largest time interval and the smallest time interval is divided into M equal parts, and the number of time intervals falling into each interval is counted, where p and q are positive integers, and p+q <N。

[0012] In one embodiment, after the step of selecting the interval with the largest number of time intervals and calculating the first time interval average value, the following steps are also included:

[0013] In the next sampling period, update the data, record a new time interval data, and delete the oldest time interval data;

[0014] Sort the new N time intervals from small to large, divide the interval formed by the maximum time interval and the minimum time interval into L equal parts, and count the number of time intervals that fall into each interval, where L is a positive integer and is less than N;

[0015] Select the interval with the largest number of time intervals among the L intervals, and calculate the average value of the second time interval;

[0016] The grid frequency is calculated based on the first time interval average value and the second time interval average value.

[0017] In one embodiment, the step of calculating the grid frequency based on the first time interval average value and the second time interval average value further comprises:

[0018] The third time interval average is calculated as the first time interval average * t + the second time interval average * (1-t), where 0 <t<1;

[0019] The grid frequency is calculated based on the third time interval average value.

[0020] In one embodiment, the grid voltage is a voltage regulated by a grid voltage regulating component in a circuit breaker.

[0021] In one embodiment, L=M.

[0022] The present invention also provides a computer-readable storage medium, characterized in that a computer program is contained thereon, and the computer program can be executed by a processor to implement the steps of the above method.

[0023] The present invention also provides a circuit breaker, comprising:

[0024] one or more processors; and

[0025] A memory for storing one or more executable instructions;

[0026] The one or more processors are configured to implement the steps of the above method by executing the one or more executable instructions.

[0027] The method for measuring the power grid frequency of the present invention selects data in the interval with the largest number of time intervals to obtain an average value, thereby improving the concentration of time interval data, eliminating abnormal points to the greatest extent, and improving the accuracy of frequency measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart of a method for measuring grid frequency according to an embodiment of the present invention is shown.

[0029] Figure 2A flow chart of a method for measuring grid frequency according to another embodiment of the present invention is shown.

[0030] Figure 3 A flow chart of a method for measuring grid frequency according to yet another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be noted that the embodiments given in the present invention are only for illustration and do not limit the scope of protection of the present invention.

[0032] The inventors have found that if there is a problem with the grid frequency, it is usually continuous, while interference in frequency measurement is usually sporadic. Therefore, if the sudden abnormal points in the grid frequency measurement can be filtered out, the accuracy of the frequency measurement can be greatly improved.

[0033] Figure 1 A flow chart of a method for measuring power grid frequency according to an embodiment of the present invention is shown. The method comprises:

[0034] Step S101: performing zero-crossing detection on the grid voltage to obtain a grid voltage zero-crossing time point.

[0035] Zero-crossing detection refers to detecting the "zero-crossing" point when the grid voltage is 0 (or very small). A zero-crossing detection method or circuit known in the art can be used to detect the grid voltage zero-crossing time point.

[0036] In an embodiment of measuring grid frequency by a circuit breaker, the circuit breaker generally includes a grid voltage conditioning component for converting a large voltage (eg, 220V) from the grid into a small voltage (eg, 5V), and can perform zero-crossing detection on the conditioned grid voltage.

[0037] In one embodiment, the zero-crossing detection circuit includes a voltage comparator, which converts the conditioned grid voltage into a square wave, and the microprocessor obtains the grid voltage zero-crossing time point by capturing the rising edge of the square wave. The grid voltage is usually a sine wave, and a zero-crossing time point can be obtained within a sampling period.

[0038] In one embodiment, the zero-crossing detection circuit includes a voltage comparator, which receives the conditioned grid voltage and compares it with a reference level (eg, 0V). When the conditioned grid voltage passes through the zero point, the output signal will jump, and this jump is the zero-crossing point.

[0039] Step S102: Calculate and record the time interval Δti (i=1, 2, ...N, N is a positive integer) between two N adjacent zero-crossing time points.

[0040] In one embodiment, the time interval Δti is stored in the memory or register of the circuit breaker. In one embodiment, N time intervals Δt are recorded in the form of an array.

[0041] In one embodiment, N = 10.

[0042] In one embodiment, the consecutive time intervals Δt are calculated and recorded. In one sampling period, one time interval data can be obtained.

[0043] Step S103: Perform a rolling update on the recorded N time intervals Δt, first in first out, and only keep N data.

[0044] Step S104: Sort the N time intervals from small to large, eliminate the largest p (p < N and p is a positive integer) values and the smallest q (q < N and q is a positive integer, p + q < N) values, and calculate the average value of the remaining time intervals.

[0045] In one embodiment, p = 2 and q = 2.

[0046] Step S105: Calculate the power grid frequency based on the average value of the time intervals.

[0047] Average value of time intervals Has a reciprocal relationship with the power grid frequency f.

[0048] In this embodiment, the influence of interference terms on the power grid frequency can be removed. However, if the interference terms are not completely removed, or the remaining time intervals vary greatly, the power grid frequency calculated by taking the average value still has problems of low accuracy and poor anti-interference ability.

[0049] Figure 2 Fig. shows a flowchart of a method for measuring the power grid frequency according to another embodiment of the present invention. The method includes:

[0050] Step S201: Perform zero-crossing detection on the power grid voltage to obtain the zero-crossing time points of the power grid voltage.

[0051] Step S202: Calculate and record the time intervals Δti (i = 1, 2,..., N, N is a positive integer) between two adjacent zero-crossing time points.

[0052] Among them, a rolling update is performed on the N time intervals Δt, first in first out, and only keep N time interval data. In one embodiment, N time intervals Δt are recorded in the form of an array. Initially, there is no data in the array, and the newly recorded time intervals will be saved in the array in sequence. When there are N time intervals Δt in the array, after the new time interval data arrives, the first time interval data in the array will be erased, and so on, keeping only N time interval data in the array.

[0053] Step S203: Sort the N time intervals in ascending order, divide the interval formed by the maximum time interval and the minimum time interval into M equal parts (M is a positive integer and less than N), and then count the number of time intervals falling into each interval, which are respectively recorded as M 1 , M 2 , M 3 , …, M M . Where M is an adjustable parameter and can be set according to actual needs.

[0054] In one embodiment, after sorting the N time intervals in ascending order, first eliminate the largest p (p is a positive integer) values and the smallest q (q < N and is a positive integer, p + q < N) values, then divide the interval formed by the maximum time interval and the minimum time interval into M equal parts (M is a positive integer and less than N), and then count the number of time intervals falling into each interval.

[0055] Step S204: Select the interval with the largest number of time intervals and calculate the average value P of the time intervals.

[0056] Step S205: Calculate the grid frequency based on the average value P of the time intervals.

[0057] In this embodiment, by calculating the average value of the data in the interval with the largest number of time intervals, the concentration of the time interval data is improved, abnormal points can be excluded to the greatest extent, and the accuracy of frequency measurement is improved.

[0058] Figure 3 FIG. shows a flowchart of a method for measuring grid frequency according to another embodiment of the present invention.

[0059] Where steps S301 - S304 are the same as those in the Figure 2 illustrated embodiment.

[0060] Step S301: Perform zero-crossing detection on the grid voltage to obtain the zero-crossing time points of the grid voltage.

[0061] Step S302: Calculate and record the time intervals Δti (i = 1, 2, … N, N is a positive integer) between N adjacent zero-crossing time points.

[0062] Step S303: Sort the N time intervals in ascending order, divide the interval formed by the maximum time interval and the minimum time interval into M equal parts (M is a positive integer and less than N), and then count the number of time intervals falling into each interval, which are respectively recorded as M 1 , M 2 , M 3 , …, M M .

[0063] Step S304: Select the interval with the largest number of time intervals, and calculate the average value P of the time intervals.

[0064] Step S305: In the next sampling period, update the data, record a new time interval data, delete the oldest time interval data, and only retain N data.

[0065] Step S306: Sort the new N time intervals from smallest to largest, divide the interval formed by the largest time interval and the smallest time interval into L equal parts (L is a positive integer and less than N), and then count the number of time intervals falling into each interval, and record them as L 1 ,L 2 ,L 3 ,…,L L 。Among them, L is an adjustable parameter and can be set according to actual needs.

[0066] In one embodiment, L = M.

[0067] Step S307: Select the interval with the largest number of time intervals in Step S306, and calculate the average value Y of the time intervals.

[0068] Step S308: Calculate the grid frequency based on the average value P and the average value Y.

[0069] In one embodiment, calculate the average value Z = P * t + Y * (1 - t), where 0 < t < 1, and t is an adjustable weight and the value of t can be set according to actual needs.

[0070] In other embodiments, more average values can also be used to calculate the grid frequency. Calculating the grid frequency based on multiple time interval average values makes the calculation result of the grid frequency smoother, more accurate, and the adjustment more flexible.

[0071] The method for measuring the grid frequency of the present invention can be applied to a circuit breaker, and can also be applied to other circuits and devices that need to measure the grid frequency.

[0072] The method for measuring the grid frequency of the present invention, by obtaining the average value from the data in the interval with the largest number of time intervals, improves the concentration of the time interval data, can exclude abnormal points to the greatest extent, and improves the accuracy of frequency measurement.

[0073] The circuit breaker using the method for measuring the grid frequency of the present invention can suppress electromagnetic interference in a complex electromagnetic environment, and solves the problem of false tripping of frequency protection of the circuit breaker in a complex electromagnetic environment.

[0074] Although the present invention has been described through preferred embodiments, the present invention is not limited to the embodiments described herein, and various changes and variations made without departing from the scope of the present invention are also included.

Claims

1. A method for measuring power grid frequency, comprising: Perform zero-crossing detection on the grid voltage to obtain the zero-crossing time point of the grid voltage; Calculate and record the time interval between N adjacent zero-crossing time points, where N is a positive integer; Sort the N time intervals from small to large, divide the interval formed by the maximum time interval and the minimum time interval into M equal parts, and count the number of time intervals that fall into each interval, where M is a positive integer and is less than N; Select the interval with the largest number of time intervals and calculate the average value of the first time interval; The grid frequency is calculated based on the first time interval average value.

2. The method for measuring power grid frequency according to claim 1, wherein: Record N time intervals in the form of an array.

3. The method for measuring power grid frequency according to claim 2, wherein: The recorded N time intervals are updated in a rolling manner, first in first out, and only the data of N time intervals are retained.

4. The method for measuring power grid frequency according to claim 1, wherein: After sorting the N time intervals from small to large, first remove the largest p values ​​and the smallest q values, then divide the interval formed by the largest time interval and the smallest time interval into M equal parts, and count the number of time intervals falling into each interval, where p and q are positive integers, and p+q <N。 5. The method for measuring power grid frequency according to claim 1, wherein: After the step of selecting the interval with the largest number of time intervals and calculating the first time interval average value, the following steps are also included: In the next sampling period, update the data, record a new time interval data, and delete the oldest time interval data; Sort the new N time intervals from small to large, divide the interval formed by the maximum time interval and the minimum time interval into L equal parts, and count the number of time intervals that fall into each interval, where L is a positive integer and is less than N; Select the interval with the largest number of time intervals among the L intervals, and calculate the average value of the second time interval; The grid frequency is calculated based on the first time interval average value and the second time interval average value.

6. The method for measuring power grid frequency according to claim 5, wherein: The step of calculating the grid frequency based on the first time interval average value and the second time interval average value also includes: The third time interval average is calculated as the first time interval average * t + the second time interval average * (1-t), where 0 <t<1; The grid frequency is calculated based on the third time interval average value.

7. The method for measuring power grid frequency according to claim 1, wherein: The grid voltage is a voltage regulated by a grid voltage regulating component in the circuit breaker.

8. The method for measuring power grid frequency according to claim 5, wherein: L=M.

9. A computer-readable storage medium, characterized in that: A computer program is included thereon, and the computer program can be executed by a processor to implement the steps of the method according to any one of claims 1 to 8.

10. A circuit breaker comprising: one or more processors; as well as A memory for storing one or more executable instructions; The one or more processors are configured to implement the steps of the method of any one of claims 1-8 by executing the one or more executable instructions.

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