JPH0712860A - Frequency detector - Google Patents

Abstract

(57) [Summary] [Object] To provide an inexpensive frequency detection device with a simple configuration. A sampling frequency means 301 samples an alternating current input for each predetermined sampling frequency, and outputs the sampling value to a polarity change detecting means 302 and a frequency calculating means 303. Sampling value x ₁ ,
Assuming that the polarities of x ₂ are negative and positive, respectively, at this time, the means 302 outputs a polarity change detection signal to the means 303, and then the polarities of the sampling values x _n and x _{n + 1} are positive and negative, respectively. Even when there is, the means 302 outputs the polarity change detection signal to the means 303. The means 303 receives the sampling value x based on the input of the detection signal from the means 302.
₁ , x ₂ , x _n are read and the fluctuation value f of the rated frequency f ₀ is calculated using a predetermined calculation formula.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency detecting device used for a control device of a power system.

[0002]

2. Description of the Related Art When the frequency of a power system fluctuates greatly,
On the power plant side, stable and economical operation is hindered, while
On the consumer side, various types of equipment will be seriously affected.

Therefore, control for suppressing the frequency fluctuation of the power system within a certain range is performed, but a frequency detection device is required for this control.

A so-called pulse counter method has been widely used as such a frequency detecting apparatus. This is a method of sampling the value of the AC input for each predetermined sampling frequency, detecting the polarity change, and calculating the frequency based on the pulse count number from a certain polarity change detection time point to the next polarity change detection time point. It is a thing.

[0005]

However, in the case of the pulse counter type frequency detecting device, a pulse oscillating circuit is required in addition to the sampling circuit. Further, in order to improve the detection accuracy, a high frequency of this pulse oscillating circuit is required. A device capable of outputting a pulse is required. Therefore, the conventional frequency detection device has a complicated circuit configuration and is disadvantageous in terms of cost.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an inexpensive frequency detection device having a simple structure.

[0007]

As a means for solving the above problems, the present invention provides a frequency detecting device for detecting a variation value (f) of a rated frequency (f ₀ ) of an AC input, wherein the AC sampling means for sampling the value of the input at every predetermined sampling frequency (f _s), the alternating two consecutive sampling values of the input (x _1, x ₂₎ when the polarity changes from positive to negative or positive from negative , And two consecutive sampling values (x
_n , x _{n + 1} ) polarity change detection means for outputting a polarity change detection signal when the polarity changes from positive to negative or from negative to positive, and the following equation is used when the polarity change detection signal is input. And a frequency calculating means for calculating the fluctuation value (f).

[0008]

[Equation 2]

[0009]

In the above-mentioned structure, the frequency calculating means is configured so that the sampling value before and after the polarity change,
And the rated frequency fluctuation value is calculated using only the rated frequency value. And sampling means, polarity change detection means,
Both the frequency calculation means and the frequency calculation means can be configured by a microcomputer, and a high frequency pulse oscillator or the like is not required. Therefore, it is possible to realize an inexpensive frequency detection device with a simple configuration.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 2 is a block diagram showing a schematic configuration of the frequency detection device according to this embodiment.

In FIG. 2, the rated frequency f from the power supply system
AC input of ₀ (for example, 50 Hz) is 1 of the instrument transformer 1
It is sent to the secondary side, and from the secondary side of the instrument transformer 1, an analog signal with a reduced AC input signal level is sent to the analog input device 2. The analog input device 2 converts the input analog signal into a digital signal and outputs the digital signal to the microprocessor 3.

The microprocessor 3 obtains a fluctuation value f of the rated frequency f ₀ by performing a predetermined calculation on the input digital signal. The digital output device 4 is
The calculated fluctuation value f is output to the numerical display 5, and the numerical display 5 displays the fluctuation value f.

FIG. 1 shows the microprocessor 3 in FIG.
3 is a block diagram showing the configuration of FIG. Sampling means 30
Reference numeral 1 denotes a digital value of an AC input sent from the analog input device 2 at a predetermined frequency f _s (for example, 1200 Hz)
It is designed to sample each time. Then, the sampling means 301 outputs continuous sampling values (x ₁ , x ₂ , ..., X _n , x _{n + 1} , ...) Of the AC input to the polarity change detecting means 302 and the frequency calculating means 303. Has become.

Next, FIG. 3 will be described. The waveform diagram of FIG. 3 illustrates the principle of the present invention. The AC input (solid line part) of the rated frequency f ₀ is the sampling period t _{1 to} t ₂ and t
_It is assumed that the polarity changes from _{n to} t _{n + 1} , and the time point when the voltage value becomes zero, that is, the zero cross point is 0 ₁ and 0 ₂ . The relationship between the rated frequency f ₀ and the fluctuation value f is f
The waveforms in the case of <f ₀ , f = f ₀ , f> f ₀ are shown by a one-dot chain line, a solid line, and a two-dot chain line. If the sampling period is T _s , then 1 / f _s = T _s = t ₂ −t ₁ =
There is a relationship of t _{n + 1} −t _n .

[0015] The value of x ₁ in the example of FIG. 3 is negative, the value of x _n so becomes positive, depending on the magnitude relationship between f and f ₀ (x
_It can be seen that the value of ₁ + x _n ) changes as follows.

When f <f ₀ | x ₁ | <| x _n | ∴x ₁ + x _n > 0 When f = f ₀ | x ₁ | = | x _n | ∴x ₁ + x _n = 0 f> f _{When 0} | x ₁ |> | x _n | ∴x ₁ + x _n <0 These are the values of (x ₁ + x _n ) corresponding to the fluctuation value f when the rated frequency f ₀ fluctuates. It means fluctuating.

The waveform of the AC input shown in FIG. 3 is a sine wave curve, but the portions near the zero crossing points 0 ₁ and 0 _{2 of} this curve can be approximately viewed as straight lines. Then, two triangles before and after the zero-cross point 0 ₁ △ 0 ₁ t ₁
It can be seen that x ₁ and Δ0 ₁ t ₂ x ₂ are equal to the triangles Δ0 ₂ t _n x _n and Δ0 ₂ t _{n + 1} x _{n + 1} , respectively, when f = f ₀ .

Even if the rated frequency f ₀ changes from the state of f = f _{0 to} the state of f <f ₀ or f> f ₀ , the triangles Δ0 ₂ t _n x _n and Δ0 ₂ t _{n +} The total area of ₁ x _{n + 1} is always the triangles △ 0 ₁ t ₁ x ₁ and △ 0 ₁ t ₂ x ₂
Is equal to the total area of. That is, the triangle △ 0 ₂
It can be seen that the degree of increase or decrease in the area of each of t _n x _n and Δ0 ₂ t _{n + 1} x _{n + 1} corresponds to the degree of fluctuation of the rated frequency f ₀ .

From these, it can be derived that the following relational expression holds between the rated frequency f ₀ and the fluctuation value f.

[0020]

[Equation 3] The frequency calculation means 303 in FIG. 1 calculates the fluctuation value f using such a relational expression. However, m
By setting = (f _s / f ₀ ) · 1/2, the above relational expression can be expressed as the following expression.

[0021]

[Equation 4] M in this equation can be calculated in advance as a constant.

Next, the operation of FIG. 1 will be described with reference to the waveform chart of FIG. 3 and the flowchart of FIG.

The sampling means 301 has a predetermined frequency f _s.
Polarity change detection means 3 detects the sampling value every (50 Hz)
02 and the frequency calculation means 303. As shown in FIG. 3, since the polarity of the AC input changes from negative to positive between the sampling values x ₁ and x ₂ , the polarity change detecting means 302 inputs x ₁ and then inputs x ₂ . At that time, the polarity change detection signal is output to the frequency calculating means 303 (step 1). The frequency calculation means 303 reads the values of x ₁ and x ₂ based on the input of this signal and stores them (step 2).

After that, since the polarity of the AC input changes from positive to negative between the sampling values x _n and x _{n + 1} , the polarity change detecting means 302 inputs x _n and then changes x _{n + 1} . When the polarity change detection signal is input, the frequency calculation means 303
(Step 1). The frequency calculation means 303 is
The value of x _n is read based on the input of this signal and stored (step 2). And the frequency calculation means 303
Calculates the fluctuation value f using the above-mentioned relational expression, and outputs the calculation result to the digital output device 4 (step 3).

According to the above-mentioned structure, the fluctuation value of the rated frequency can be easily and surely obtained without using the high-frequency pulse oscillator and with the simple structure of only the microcomputer. That is, in the prior art, a pulse oscillator capable of oscillating a high-frequency pulse of several megahertz or higher was required, whereas according to the present invention, sampling can be performed only at low frequencies of 1200 Hz.

As is clear from the waveform diagram of FIG.
When the fluctuation range of the AC input is very large, that is, when the zero-cross point 0 ₂ is shifted to the right of t _{n + 1} or to the left of t _n , the frequency is changed by the method according to the present invention. It cannot be calculated. However, when the rated frequency is 50 Hz, the zero crossing point 0 is set in the section from t _{n to} t _{n + 1.}
The range of the fluctuation value in which ₂ falls is about 40 Hz to 60 Hz, while the range in which the rated frequency actually changes is about 45 Hz to 55 Hz. Therefore, theoretically, even if the present invention cannot be applied when the variation value is large, there is almost no problem in practical use.

[0027]

As described above, according to the present invention, since the fluctuation value of the rated frequency is obtained by a predetermined arithmetic expression using only the sampling values before and after the polarity change point, a simple structure using a microcomputer is provided. Thus, an inexpensive frequency detection device can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining the principle of the present invention.

FIG. 4 is a flowchart for explaining the operation of FIG.

[Explanation of symbols]

301 Sampling means 302 Polarity change detecting means 303 Frequency calculating means f ₀ Rated frequency f Fluctuation value f _s Sampling frequency x ₁ , x ₂ , x _n , x _{n + 1} sampling value

Claims (1)

[Claims] 1. A rated frequency (f ₀ ) of an AC input,
In the frequency detection device for detecting the variation value (f), said sampling means for sampling the value of the AC input to the predetermined sampling frequency (f _s), two consecutive sampling values of the AC input (x _1,
x ₂ ) when the polarity changes from negative to positive or from positive to negative, two subsequent sampling values (x _n , x
_{(n + 1} ) polarity change detection means for outputting a polarity change detection signal when the polarity changes from positive to negative or from negative to positive; and when the polarity change detection signal is input, the fluctuation using the following formula A frequency detecting device for calculating a value (f). [Equation 1]