JPS5836741B2 - Peak value detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a device for detecting the peak value of an alternating current waveform.

It is necessary to narrow the peak value of the positive or current waveform for the operation of the protective relay power type in the power system.

On the other hand, the use of digital computers in the protection relay power formula has recently been considered, and along with this, it has become necessary to calculate the peak value digitally, and the configuration for this has already been proposed separately. However, these existing proposals sample the AC waveform at regular time intervals,
The sampled value is held and converted into digital data by an AD converter, and required calculations are performed using the digital value.

However, this configuration requires an A-D converter, but this type of converter is expensive, and data near the zero point of the AC waveform is greatly affected by the bit error of the converter. , it has the disadvantage of lowering the spermatozoa.

In view of the above points, it is an object of the present invention to detect the peak value of an alternating current waveform with high precision using a simple method.

This invention basically defines the time at which an AC waveform crosses a set level when the AC waveform has a positive or negative slope, and the time at which it crosses the level again when the slope is reversed. The time difference is determined, and the peak value of the AC waveform is determined according to an arithmetic expression that uses the time difference as a function.

The principle of peak value detection according to this invention will be explained based on FIG. 1. In the same figure, the AC waveform to be detected is
It can be expressed as inωt (where ■ is the peak value,
ω is the angular frequency), and K is the set level.

When this AC waveform is in its positive slope state, time t1
, and if this slope crosses level K at time t2 when it is next inverted, then the following holds true.

If the time difference between current time 11.12 is T, then T=12-1
1, so by substituting this into equation (2), we get K=VmSmω(T+t1).If we expand this, we get? is a set level and is known, and if ω is constant, the peak value ■ can be found by detecting the time difference T and substituting it into equation (4) for calculation.

Since equation (4) is an extremely simple functional equation, the configuration for its calculation is extremely simple.

In Figure 1, it is determined from the time difference between the times when level K is passed during the positive half-wave period, but this can also be set as the negative half-wave period, in which case the negative level (for example, 1 K) is determined.
, and find it from the time difference between passing times.

Furthermore, the time when the negative slope state passes through level K,
Subsequently, it can be detected using exactly the same method by calculating the time difference between the time when the force passes through the negative half-wave and reaches the positive slope state.

In all of the above explanations, the peak value was determined with ω constant; however, ω may not necessarily be constant, and if ω changes, an error may occur depending on equation (4).

In other words, as shown in Figure 2, the AC waveform ■ is at time 11.12.
Due to the change in ω, there will naturally be a difference between the time difference T when it crosses level K at time t and the time difference T when it crosses level K at times t3 and t4 in the next half-wave period. , even if the peak value does not change in each half-wave, (
4) The wave height values obtained from equation (4) will be different values.

This invention is designed to obtain accurate peak values even when ω is not constant.

In other words, as shown in FIG. 2, when the AC waveform has a positive slope and crosses the level K at time t1, then again has a positive slope and crosses the level K at time t3, then the time difference T
1=t3-11 (see FIG. 2A) corresponds to one period of the AC waveform (■).

Therefore, at this time, ω can be expressed as a force). Substituting this into equation (4), we get You will be able to seek higher prices.

In this case, the time difference T1 is from when the level K is crossed at time t2 with a negative slope, and then the level K is crossed again with a negative slope.
The time difference until crossing at time t4, that is, T1 = t4-
It may also be determined as t2 (see FIG. 2).

Furthermore, as shown in FIG. 2C, the time difference T2 from time t2 to t3 may be determined and the time difference T1 may be determined.

In this case, equation (5) becomes.

Furthermore, as shown in FIG. 2D, the time difference T3 from time t1 to time t4 may be determined and the time difference T1 may be used.

This misplaced formula 5) is becomes.

In any case, by finding the time difference between the times when adjacent half waves of the same polarity cross level K, the peak value can be found regardless of ω.

FIG. 4 shows an embodiment of this invention.

Before explaining FIG. 4, a detection device based on the above-mentioned equation (4) will be explained with reference to FIG.

Figure 3 shows the configuration for determining the peak value of the alternating current waveform of electric power E (or current) in a single power system, where 1 is the voltage transformer (or current transformer) of the power system, and 2 is the electric power transformer 1. 3 is a level detector that insulates the output of the output and converts it into an appropriate amount. 3 is a level detector that rises immediately after the input amount exceeds a set level K, and also rises immediately after falling below level K. A falling pulse P (see FIGS. 1 and 2) is emitted.

A pulse counter 4 counts clock pulses from an oscillator 5 that generates clock pulses only during the period in which the pulse P is being generated.

Therefore, its output value becomes a digital value corresponding to the time difference T explained earlier.

This digital output is given to the arithmetic circuit 6.

The level K and the angular frequency ω are stored in advance in the calculation circuit 6, and the calculation shown in equation (4) is performed using these and the digital output from the pulse counter 4.

Therefore, the calculation result is nothing but a digital value corresponding to the peak value of the voltage waveform of the system.

Note that a commercially available central processing unit can be used as the pulse counter 4, oscillator 5, and arithmetic circuit 6.

FIG. 4 shows an embodiment of the present invention for detecting the peak value without being affected by changes in ω.

This can be done by adding a pulse counter 11 for detecting the time difference T1 (or T2, T3) and a storage circuit 12 for storing each time difference to the configuration shown in FIG.

When trying to detect the time difference T1 as shown in FIG. Count clock pulses.

This count value is a digital value corresponding to the time difference T1.

During this time, as in the case of Fig. 1, the pulse counter 4)
A digital value corresponding to the time difference T between them is stored in the memory circuit 14, and when the digital value from the pulse counter 11 is given to the arithmetic circuit 6, this is read out from the memory circuit 12 (output), and (5) Perform the calculation shown in the formula.

In this case, there is no need to store ω in the arithmetic circuit 6; it is sufficient to simply store the level K. Also, the peak value obtained as a result of the calculation is an accurate value that is not related to the fluctuation of ω. becomes.

When determining the peak value based on FIG. 2B, the pulse counter 11 may count the clock pulses during the period from the falling edge of the pulse P to the next falling edge.

When determining the peak value based on FIG. 2C, the pulse counter 11 counts clock pulses during the period from when the pulse P falls to when it rises next.

On the other hand, the pulse counter 4 counts the clock pulses only during the period when the pulse P is being generated.

The count f of the pulse counter 4 and the count value of the pulse counter 11 during the period when the first pulse P is being emitted are respectively stored in the memory circuit 12, and the pulse counter is stored only during the period when the second pulse P is being emitted. 1
After 1 has been counted, the arithmetic circuit 6 performs the calculation shown in equation (6) using the count value and the count value read from the memory circuit 12.

When determining the peak value based on FIG. 2D, the pulse counter 11 counts clock pulses during the period from the rise of the first pulse P to the fall of the next pulse P,
Using this count value and the count value of the pulse counter 4 counted during the generation period of each pulse P, the calculation shown in equation (7) is performed.

Note that as the level detector 3, a Schmitt circuit Zener diode, a 1-bit AD converter, or the like can be used.

As described above, according to the present invention, the peak value of the AC waveform to be detected can be determined by simply determining the time difference between the times when the AC waveform to be detected passes through a preset level, and calculations and calculations for that purpose can be performed. The configuration for the calculation is extremely simple, and the angular frequency of the AC waveform is not used in any way to detect the peak value, so even if the angular frequency fluctuates, the peak value can be accurately detected. There is an effect that can be done.

[Brief explanation of the drawing]

1 and 2 are waveform diagrams for explaining the operating principle of this invention, and FIGS. 3 and 4 are block diagrams showing this invention. 3... Level detector, 4.11... Counter, 6... Arithmetic circuit.

Claims (1)

[Claims] 1. A level detector that receives an AC waveform to be detected as input and detects when the AC waveform passes a positive or negative level K; ), a first counter outputs a digital value corresponding to a time difference T until the slope of the AC waveform is reversed and the level K is detected again; When level K is detected within a negative half cycle, a digital value corresponding to the time difference T1 from when level K is detected again within the next positive (or negative) half cycle of the AC waveform is output. a second counter; and a second counter;
and the digital output of the second counter as input? However, ■ is a peak value detection device consisting of an arithmetic unit that calculates the peak value of an AC waveform and a power). 2. When the second counter first detects the level K within the positive (or negative) half cycle of the AC waveform, the second counter detects the level K again within the next positive (or negative) half cycle of the AC waveform. 2. The peak value detection device according to claim 1, which outputs a digital value corresponding to a time difference T1 until K is first detected. 3. The second counter detects level K within the next positive (or negative) half cycle of the AC waveform from the time when level K is detected for the second time within the positive (or negative) half cycle of the AC waveform. The peak value detection device according to claim 1, which outputs a digital value corresponding to the time difference T1 until the second detection. 4 The second counter detects the level K within the next positive (or negative) half cycle of the AC waveform from the time when the level K is detected for the second time within the first positive (or negative) half cycle of the AC waveform. output a digital value corresponding to the time difference T2 until the first detection of 2. The peak value detecting device according to claim 1, wherein the output is a time difference T1. 5 The second counter measures the level within the next positive (or negative) half cycle of the AC waveform from when level K is first detected within the first positive (or negative) half cycle of the AC waveform. A digital value corresponding to the time difference T3 until the second detection is output, and a digital output corresponding to the time difference T and T' within the first and next half cycles output from the first counter. With that,
Wave height value detection according to claim 1, where the time difference T1 is taken as? Device.