JPH02187669A - Frequency detecting device - Google Patents

Abstract

PURPOSE:To detect the frequency at a high speed without finding an impossible solution of an arithmetic output by bringing five pieces of amplitude value of an AC electricity quantity of an electric power system to sampling in a prescribed period, and executing a prescribed operation after the A/D conversion. CONSTITUTION:Five pieces of voltage values are brought to sampling in a sampling period T, and thereafter, brought to A/D conversion. Subsequently, a third sample value is squared by a square device 7, a first and a fifth sample values are multiplied by a multiplier 6, and by a subtracter 9, {V(2T)<2>-V(0).V(4 T)} is derived. Also, by a subtracter 10, a multiplied value of a second and a fourth sample values derived by a subtracter 8 is subtracted from an output of the square device 7, and {V(2T)<2>-V(T).V(3T)} is derived. Next, by a divider 11, an output of the subtracter 9 is divided by an output of the subtracter 10, and an output Y=4cos<2>T is derived. From this output Y, a frequency (f) is derived by an inverse trigonometric function arithmetic means. In this case, since it does not occur that a denominator of the output Y becomes '0', the frequency is detected at a high speed and with satisfactory reliability.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a frequency detection device that samples an alternating current amount of electricity in a power system at a constant cycle, executes an amount of electricity calculation processing based on the sampling array after digital conversion, and detects the frequency of the alternating current amount of electricity. be.

[Conventional technology]

FIG. 4 is a block connection diagram of a conventional frequency detection device disclosed in, for example, Japanese Patent Laid-Open No. 57-133362. In the figure, 1 is the first sampled at a constant period T.
2 is a first subtractor that subtracts the fourth sampling value from the first sampling value, and 3 is a subtracter that subtracts the third sampling value from the second sampling value. 2 is a subtracter; 4 is a divider that divides the output of the first subtracter 2 by the output of the second subtracter 3; 14 is an arithmetic processing means composed of each of the above-mentioned arithmetic devices; 15 is the arithmetic processing means; This is an inverse trigonometric function calculation means that outputs the absolute value of the frequency based on the inverse trigonometric function of the final output of No. 14. Next, the operation will be explained. For convenience of explanation, the amount of AC electricity is assumed to be AC voltage, and the maximum value is
, the instantaneous value is 73, the frequency is f, and the sampling period is T. In addition, the sampling value of each voltage when t-nT (n-0, 1, 2, = 1) is set at each sampling time t-nT (n-0, 1, 2, = 1) at a period T apart from the predetermined time t is v (nT) (n = 0.1 ,2
．． ...). Here, the four sampling values 1 that are input to the arithmetic processing means 14 are expressed at times t, t -T, t-3Tt-4
At T, v (0), v (T), v
(3T) and V (4T), the output of the first subtractor 2 is (V (0) - V (4T)) and the output of the second subtractor 3 is (v (T) - v (3T) )l, and the output Y of the arithmetic processing means 14 is determined by the divider 4, and the inverse trigonometric function arithmetic means 15, which calculates the electric quantity Y at each sampling time and solves its inverse trigonometric function, calculates the frequency f.
can be found.

[Problem to be solved by the invention]

Since the conventional frequency detection device is configured as described above, the arithmetic processing means determines the output of the second subtracter, that is, the output, based on the relationship between the frequency of the voltage, its sampling time, and sampling period. The denominator term of Y (v
(T) -v (3T) 1 may become 0, and as a result, a problem occurs in which the magnitude of the output Y becomes infinite. Therefore, in the arithmetic processing means of the conventional frequency detection device, the determination at the sampling time is ignored as unsolvable, and the determination at one sampling time before the sampling time is used. Here, if the denominator term of the output Y of the arithmetic processing means is D, then D = V (T) -v (3T) -V-sin(θ-T) -V-sin(θ-3T)
= 2 V ・5in(T) ・cos(θ-27)
...-(2), which is 2 V -5in (
It is a periodic function of cosine whose amplitude value is T), and from the relationship among the frequency of the voltage, the sampling time of the voltage, and the sampling period, D=O. Therefore, if the denominator term is 0, the time to determine the frequency will be delayed, and in extreme cases, due to the relationship between the frequency of the voltage, the sampling time of the voltage, and the sampling period, calculation at each sampling time will be delayed. In the worst case where the denominator term becomes 0 in the process, there is a possibility that there will be a significant delay in detection, which poses a problem in that it will have an adverse effect on the frequency detection of the amount of alternating current electricity in the power system. This invention was made in order to solve the above-mentioned problems, and uses an arithmetic expression in which the denominator term of the output Y does not become 0 in the electrical quantity arithmetic processing means, thereby reducing the time delay in determination. The purpose is to obtain a highly reliable frequency detection device that was lost.

[Means to solve the problem]

In the frequency detection device according to the present invention, in the arithmetic processing means, five sampling values from the first to the fifth are input, the second sampling value is squared by a squarer, and the first and fifth sampling values are squared. The output of the first subtracter is subtracted by the output obtained by multiplying the sampling value by the first multiplier, and the output of the second multiplier is multiplied by the first and third sampling values from the output of the squarer. The frequency is divided by the output of the second subtracter to be subtracted, and the frequency of the alternating current quantity of electricity is further detected by means of inverse trigonometric function calculation means.

[Function] The arithmetic processing means of the frequency detection device according to the present invention obtains a calculation output at high speed by using five sampling values of the alternating current quantity of electricity, and the denominator term of the output of the arithmetic processing means is 0. This increases reliability by preventing impossible solutions from appearing in the calculation output.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a block connection diagram showing the arithmetic processing means and the inverse trigonometric function arithmetic means of the frequency detection device of the present invention. In the figure, 5 indicates the sampling value of the AC voltage at the time t.
(0), the sampling values at periods T, 2T, 3T, and 4T before the said time are v (T) and v (2T), respectively.
), v (3T), v (4T) are the five sampling values from the first to the fifth, and 6 is the first and fifth sampling values.
7 is a squaring device that multiplies the third sampling value, 8 is a second multiplier that multiplies the second and fourth sampling values, and 9 is the second A first subtracter that subtracts the output of the multiplier 7 by the output of the first multiplier 6, 1° is a second subtracter that subtracts the output of the squaring device 7 by a second multiplier 8, 11 1 is a divider that divides the output of the first subtracter 9 by the output of the second subtracter 10; 12 is an inverse trigonometric function calculation means that detects a frequency from the inverse trigonometric function of the output of the divider 11; and 13 is 5 This is an arithmetic processing means that receives the sampled values 5 as input. Next, the operation will be explained. The output V (
2T) 2 by the output of the first multiplier 6 which multiplies the first and fifth sampling values. The output of the first subtractor 9 is (v(2T)2-v(θ)・v( 4T)), a second subtractor 1 that subtracts the output of the squarer 7 by the output of a second multiplier 8 that multiplies the first and fourth sampling values;
The output of 0 is (v (2T)2- v (T)・V (3
T) l. Furthermore, the output Y of the arithmetic processing means 13 is the output of the divider 11 that divides the output of the first subtractor 9 by the output of the second subtractor 10, and is expanded by the following formula of the diagonal function. , ν”・5in2(θ−2T)−V”・5in(θ)
・5in(θ-4T)ν2・5in2(θ-2T)-
V2・5in(θ-7)-5in(θ-37)1-co
s(4T) 1-cos(2T) sin"(2T) sin2(T) -Acos"(T) ・ ・ ・ ・ ・ ・ ・
. . . . (4) From the output Y (4th equation) of the calculation processing means 13, the frequency f can be determined by the inverse trigonometric function calculation means 12. The fourth equation has no relation to the magnitude of the voltage V and is a function of the sampling period T. Here, the sampling period T is expressed in units of angle, and is generally the fundamental frequency f of the voltage V. For 1/(
12f, ) (In the field of power systems, it is called 30 degree sampling. 30 degrees - π/6 radians.) Therefore, T-(2・π・f)/(12・ro)
The frequency f is expressed in radians, and the frequency f to be determined is determined by the inverse trigonometric function calculation means as shown in Equation 5. Next, regarding the denominator term of the fourth equation, assuming this as D, D −v (2T)2− v (T) ・v (3T)
-V 2・5in2(θ-2T) -V'sin (
θ-T) ・5in(θ=V 2・5in2(T) π −V2・5in2(・m)・・・(6) However, m
= f / f 0 , and this sixth equation does not become 0 in the range of 0<m<5. The sampling period T is 30 degrees (π/6 radians) sampling, 60 degrees (π/3 radians) sampling, 9
When changing to 0 degree (π/2 radian) sampling, the value of the denominator term of the fourth equation is shown in the range of Q<m<2 (frequency f is twice the fundamental frequency f.): Figure 2 shows this. FIG. 3 is an example of a hardware configuration diagram of the frequency detection device 20 of the present invention. In the figure, 21 is the power system, 22
23 is a current transformer, 23 is a voltage transformer, 24 is a human power converter that converts the current and voltage of the power system into values that are easy to process, 25
26 is a filter that removes frequency components of 1 to 2 or more of the sampling frequency among harmonics contained in the current and voltage; 26 is a sample hold that holds the sampled value until the next sampling period; 27 is a sample hold 26
The output of analog/digital converter 2 is switched sequentially.
8, and 29 is a microprocessor that executes the arithmetic processing means and the inverse trigonometric function calculation means using the program stored in advance in the memo IJ30, and outputs the output from the output circuit 31 to the terminal 32. The frequency detecting device 20 is constituted by the respective parts denoted by the numerals 24 to 32. In addition, in the above embodiment, as means for determining the frequency f,
From the electrical quantity output of the arithmetic processing means, it is calculated by calculating the inverse trigonometric function (cos-') using the fifth inverse trigonometric function arithmetic means, but the output of the commonly used electrical quantity arithmetic processing means Alternatively, a table of inverse trigonometric functions may be referenced by using the address as an address. Furthermore, in the above embodiment, the voltage is sampled, and the arithmetic processing means inputting the sampled value outputs the quantity of electricity, and the frequency is determined by the inverse trigonometric function arithmetic means. Even if there is, the same effect will be achieved.

【Effect of the invention】

As described above, according to the present invention, five sampling values are used as input for the calculation process of the amplitude value of the alternating current quantity of electricity, so even if the frequency varies over a wide range, the output of the calculation processing means Since the denominator of Y does not become O, a calculation output can be obtained at high speed and the reliability of the calculation output can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the arithmetic processing means of the frequency detection device of the present invention, FIG. 2 is a diagram showing the existence range of the denominator term of the output Y of the arithmetic processing means of the invention, and FIG. 3 is a block diagram showing the arithmetic processing means of the invention. Figure 4 is a block diagram showing the hardware configuration of a frequency detection device that implements the processing means. Figure 4 is a block diagram showing the arithmetic processing means of the conventional frequency detection device. , 6 is a first multiplier, 7 is a squarer, 8 is a second multiplier, 9 is a first subtractor, 10 is a second subtractor, 11 is a divider, 12 is an inverse trigonometric function operation The means and 13 are arithmetic processing means. In the figures, the same reference numerals indicate the same or corresponding parts. Patent applicant: Mitsubishi Electric Corporation -48゜U'') ■ L-1111 ” Procedural amendment (voluntary) - 1st year, 1st year, 30th year

Claims (1)

[Claims] sampling means for sampling the amount of alternating current electricity in the power system at a constant period T; analog/digital conversion means for converting the sampled analog value into a digital value; and arithmetic processing based on the digitally converted sampling value. , a frequency detection device having an arithmetic processing means for detecting the frequency of the alternating current quantity of electricity, wherein five sampling values sampled by the sampling means, from the first to the fifth, are input, and the first and fifth sampling values are inputted to the sampling means. a first multiplier that multiplies the sampling value; a squaring device that squares the third sampling value; a second multiplier that multiplies the second and fourth sampling values; and an output of the squaring device. a first subtractor for subtracting the output of the first multiplier from the squarer; and a second subtracter for subtracting the output of the second multiplier from the output of the squarer.
a subtracter, an arithmetic processing means comprising a divider that divides the output of the first subtracter by the output of the second subtracter, and an inverse trigonometric function of the output of the arithmetic processing means. 1. A frequency detection device comprising: inverse trigonometric function calculation means for detecting the absolute value of the frequency of an electrical quantity.