JPH07253443A - Frequency measuring circuit - Google Patents

Abstract

PURPOSE:To obtain a frequency measuring circuit in which a period counter can be formed of one counter, and a frequency measurement of a polyphase type power system can be realized without using a control of switching an input destination of an input port of a microcomputer. CONSTITUTION:An inverting adder 3 adds two-phase electromotive forces. A comparator 4 compares an output of the adder 3 with a reference signal, and binarizes it. A counter 6 counts a reference clock while a binary signal rises, and outputs a counted value corresponding to a period of the electromotive force. A microcomputer 8 calculates a frequency of a power system with the counted value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency measuring circuit for measuring the frequency of a transmission voltage or a distribution voltage in a polyphase power system.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a configuration of a frequency measuring circuit applied to a conventional multi-phase power system.
In the figure, 1 is a distribution line that is a part of the power system, 2
A and 2B are voltage transformers for extracting voltages of different phases in the distribution line 1, 4A is a first comparator for converting the A-phase input voltage from the voltage transformer 2A into a rectangular wave, and 4B is a voltage meter Second comparator for converting the B-phase input voltage from the transformer 2B into a rectangular wave, 6A is a counter for counting the time of one cycle of the rectangular wave output from the first comparator 4A, 6B Is a counter for counting the time of one cycle of the rectangular wave output from the second comparator 4B, and 7 is a counter 6A, 6B
This is a microcomputer that calculates the frequency based on the count value of.

Next, the operation will be described with reference to the timing chart of FIG. The phase of the A phase and the phase of the B phase are deviated by 60 °, for example. The frequency measuring circuit measures the frequency of one phase, for example, the A phase. That is, the input port of the microcomputer 7 is connected to the counter 6A so that the count value of the counter 6A is input. The A-phase input voltage, which is a sine wave voltage as shown in FIG. 6A, is supplied from the meter transformer 2A to one input terminal of the first comparator 4A. At the other input terminal of the first comparator 4A,
A reference voltage is supplied. The reference voltage is, for example, a voltage corresponding to the voltage at the zero cross point of the input voltage. The first comparator 4A will be described as an output of high level as shown in FIG. 6H when the instantaneous value of the A-phase input voltage is larger than the reference voltage.

The counter 6A counts the reference clock. Then, the count value in the period from the rising of the output of the first comparator 4A to the next rising is supplied to the microcomputer 7. That is, the count value corresponds to the cycle of the A-phase input voltage. The microcomputer 7
The period of the A-phase input voltage is obtained from the count value from the counter 6A and the frequency of the reference clock given to the counter 6A. Then, the reciprocal thereof is taken to obtain the frequency of the A-phase input voltage.

When the voltage of the A phase disappears due to the occurrence of an accident or the like, if the other phase is sound, it is necessary to continue the frequency measurement of the system for that phase. Therefore, in such a case, the input destination of the input port of the microcomputer 7 is switched to the counter 6B on the B phase side. The second comparator 4B operates similarly to the first comparator 4A and outputs a rectangular wave having a frequency corresponding to the frequency of the B-phase input voltage. The counter 6B operates similarly to the counter 6A, and outputs a count value corresponding to the cycle of the B-phase input voltage. Therefore,
The microcomputer 7 can continue frequency measurement for the B-phase input voltage. As described above, the frequency measurement circuit measures the frequency by duplicating the inputs of the microcomputer 7 and switching the measurement target to the sound phase side at the time of an accident. In addition, as a method for measuring a frequency after binarizing an input voltage with a comparator, Japanese Patent Laid-Open No. 5-27 is known.
There is one described in Japanese Patent No. 3265.

[0006]

Since the conventional frequency measuring circuit is constructed as described above, the counters 6A and 6B corresponding to each phase are required. In addition, there is a problem that it is necessary to detect that the voltage of the phase currently being measured is exhausted and perform control to switch the input destination of the input port of the microcomputer 7. The present invention has been made in order to solve the above problems, and the counting portion constituting the frequency calculating means can be constituted by one counter, and the input port of the microcomputer constituting the frequency calculating means can be constituted. An object of the present invention is to obtain a frequency measurement circuit that can continue frequency measurement control without performing control to switch the input destination.

[0007]

According to a first aspect of the present invention, there is provided a frequency measuring circuit which indicates a cycle start point of a signal corresponding to a combination of electromotive forces of arbitrary two phases of a polyphase power system. It is provided with a periodic signal generating means for generating a signal and a frequency calculating means for calculating the frequency of the power system using the signal generated by the periodic signal generating means.

Further, in the frequency measuring circuit according to the second aspect of the present invention, the periodic signal generating means compares the output of the adder with an adder for adding electromotive forces of arbitrary two phases, and compares the output with a reference signal. It is configured to include a comparator for digitizing the signal and supplying the binarized signal to the frequency calculating means.

In the frequency measuring circuit according to the third aspect of the present invention, the periodic signal generating means compares the electromotive force of one of the arbitrary two phases with the reference signal and binarizes it. Of the output of the first comparator and the output of the second comparator, and a second comparator for binarizing the electromotive force of the other of the arbitrary two phases with the reference signal It has a configuration including a logical sum circuit for taking a sum and supplying a logical sum signal to the frequency calculating means.

[0010]

According to the first aspect of the present invention, the periodic signal generating means adds and binarizes the electromotive force of any two phases and binarizes the electromotive force of any two phases. Then, a signal indicating the cycle start point of a signal corresponding to a combination of electromotive forces of arbitrary two phases is generated.

The periodic signal generating means in the invention according to claim 2 generates a signal indicating a period start point of a signal corresponding to a combination of electromotive forces of arbitrary two phases,
First, two-phase electromotive forces are added, and then the added signal is compared with the reference signal to be binarized.

The periodic signal generating means in the third aspect of the present invention first generates each signal in order to generate a signal indicating a period start point of a signal corresponding to a combination of electromotive forces of arbitrary two phases. The power is compared with the reference signal and binarized, and then the two binary signals are ORed.

[0013]

【Example】

Example 1. 1 is a block diagram showing the configuration of a frequency measuring circuit according to a first embodiment of the present invention. In the figure,
Reference numeral 1 is a distribution line, 2A and 2B are instrument transformers for extracting voltages of different phases in the distribution line 1, 3 is an inverting adder for adding the A-phase input voltage and B-phase input voltage, and 4 is an inverting adder 3 Comparator for converting the output of the to a square wave, 6
Is a counter that counts the time of one cycle of the rectangular wave output from the comparator 4, and 8 is a microcomputer that calculates the frequency based on the count value of the counter 6. Since the microcomputer 8 inputs only the count value of the counter 6,
Does not control to switch the input port. The inverting adder 3 is an example of an adder. The periodic signal generating means is realized by the inverting adder 3 and the comparator 4. The frequency calculating means is realized by the counter 6 and the microcomputer 8.

Next, the operation will be described with reference to the timing chart of FIG. The phase of the A phase and the phase of the B phase are deviated by 60 °, for example. The inverting adder 3 outputs the inverted value of the added value of the A-phase input voltage and the B-phase input voltage, as shown in the left half of FIG. Due to the phase relationship between the A phase and the B phase, the frequency of the added value signal is also equal to the frequencies of the A phase and the B phase. That is, when both the A phase and the B phase are sound, the phase of the inverting adder 3 is different from the A phase and the B phase, but the output frequency is equal to the A phase and B phase frequencies. .

The output of the inverting adder 3 is supplied to one input terminal of the comparator 4. A reference voltage is supplied to the other input terminal of the comparator 4. The reference voltage is, for example, a voltage corresponding to the voltage at the zero cross point of the input voltage. When the instantaneous value of the input signal is larger than the reference voltage, the comparator 4 outputs a high level as shown in FIG. 2 (D).

The counter 6 counts the reference clock. Then, the count value in the period from the rising of the output of the comparator 4 to the next rising is supplied to the microcomputer 8. That is, the count value corresponds to the cycle of the input signal of the counter 6. Here, the counter 6 is the comparator 4
The count value in the period from the fall of the output of to the next fall may be supplied to the microcomputer 8. The microcomputer 8 obtains the cycle of the input signal from the count value from the counter 6 and the frequency of the reference clock given to the counter 6. Then, the reciprocal thereof is taken to obtain the frequency of the input signal. Since the frequency of the input signal of the counter 6 corresponds to the frequencies of the A phase and the B phase, the microcomputer 8 can eventually obtain the frequency of the power system.

When the A-phase voltage disappears due to an accident or the like, the output of the inverting adder 3 becomes the inverted value of the B-phase input voltage. Therefore, the comparator 4 outputs a rectangular wave having a frequency corresponding to the frequency of the B-phase input voltage. Counter 6
Outputs a count value corresponding to the cycle of the B-phase input voltage.
Therefore, the microcomputer 8 can continue the frequency measurement for the B-phase input voltage. As described above, the microcomputer 8 in the frequency measuring circuit according to this embodiment can continue the frequency measurement without switching the input when an accident occurs. Also, the number of counters 6 may be one.

It should be noted that when the A-phase voltage is exhausted, the rising cycle provided to the counter 6 is slightly shifted. Therefore, the cycle recognized by the microcomputer 8 is deviated, and a frequency measurement error occurs. The microcomputer 8 measures the frequency for a plurality of consecutive cycles in order to reduce such a frequency measurement error.
Then, a filtering process of removing the maximum value and the minimum value of each frequency value and averaging the rest is performed. It should be noted that this processing was also executed in the conventional frequency measurement circuit.

Example 2. FIG. 3 is a block diagram showing the configuration of a frequency measuring circuit according to the third embodiment of the present invention.
In the figure, 4A is a first comparator for converting the A-phase input voltage from the instrument transformer 2A into a rectangular wave, and 4B is a converter for converting the B-phase input voltage from the instrument transformer 2B into a rectangular wave. Second comparator 5 of the output of the first comparator 4A and the second comparator
Is a logical sum circuit that takes the logical sum with the output of the comparator 4B. The other components are the same as those shown in FIG. Incidentally, the periodic signal generating means is composed of the first comparator 4A,
It is realized by the second comparator 4B and the OR circuit 5.

Next, the operation will be described with reference to the timing chart of FIG. The phase of the A phase and the phase of the B phase are deviated by 60 °, for example. The A-phase input voltage that is a sine wave voltage as shown in FIG.
Is supplied to one input terminal of the comparator 4A. A reference voltage is supplied to the other input terminal of the first comparator 4A. The first comparator 4A outputs a high level as shown in FIG. 4E when the instantaneous value of the A-phase input voltage is larger than the reference voltage. Similarly, the second comparator 4B
When the instantaneous value of the B-phase input voltage as shown in FIG. 4 (B) is larger than the reference voltage, a high level is output as shown in FIG. 4 (F).

The logical sum circuit 5 corresponds to the logical sum of the output of the first comparator 4A and the output of the second comparator 4B.
A signal as shown in (G) is output. The period between the two rising points in the signal is the same as the period of the A phase and the B phase. The counter 6 and the microcomputer 8 calculate the frequency as in the case of the first embodiment.

When the voltage of the phase A disappears due to the occurrence of an accident or the like, the OR circuit 5 is supplied with only the output of the second comparator 4B. That is, the rectangular wave corresponding to only the B-phase input voltage is input to the second comparator 4B. Therefore, the microcomputer 8 can continue the frequency measurement for the B-phase input voltage. As described above, the microcomputer 8 in the frequency measuring circuit according to this embodiment can also continue the frequency measurement without switching the input when an accident occurs.

[0023]

As described above, according to the first aspect of the present invention, the frequency measuring circuit is a signal indicating the cycle start point of a signal corresponding to a combination of electromotive forces of arbitrary two phases of the power system. Is configured to be supplied to the frequency calculation means,
It is only necessary to provide one counter, and it is not necessary to control the switching of the input port in the microcomputer that constitutes the frequency calculating means, and there is an effect that the frequency of the power system can be obtained at low cost.

According to the second aspect of the present invention, the frequency measuring circuit binarizes the output of the adder for adding the electromotive force of any two phases, and the rising portion of the binarized signal or Since the configuration is provided with the periodic signal generating means having the comparator that outputs the falling portion as the signal indicating the period start point, the above-described effect is achieved and 2
There is an effect that it is possible to easily obtain a signal indicating the cycle start point of a signal corresponding to a combination of the electromotive forces of the phases.

According to the invention described in claim 3, the frequency measuring circuit sets the electromotive force of one of the two phases to 2
A first comparator that digitizes, a second comparator that binarizes the other electromotive force, and a logical sum that outputs a logical sum of the output of the first comparator and the output of the second comparator A signal having a period start point of a signal corresponding to a combination of electromotive forces of two phases, as well as having the effect of the invention according to claim 1, since it is configured to include a periodic signal generating means having a circuit. There is an effect that what can be easily generated is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a frequency measuring circuit according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing signal waveforms of respective parts in the frequency measuring circuit according to the first embodiment.

FIG. 3 is a block diagram showing a configuration of a frequency measuring circuit according to a second embodiment of the present invention.

FIG. 4 is a timing chart showing signal waveforms of respective parts in the frequency measuring circuit according to the second embodiment.

FIG. 5 is a block diagram showing a configuration of a conventional frequency measurement circuit.

FIG. 6 is a timing diagram showing signal waveforms of various parts in the conventional frequency measurement circuit.

[Explanation of symbols]

 3 Inverting Adder (Adder, Periodic Signal Generating Means) 4 Comparator (Periodic Signal Generating Means) 4A First Comparator (Periodic Signal Generating Means) 4B Second Comparator (Periodic Signal Generating Means) 5 Logical OR Circuit (Period signal generation means) 6 Counter (frequency calculation means) 8 Microcomputer (frequency calculation means)

Claims (3)

[Claims] 1. A frequency measuring circuit for measuring a frequency in a multi-phase power system in which a plurality of electromotive forces having the same frequency but different phases are present in one circuit system. A periodic signal generating means for generating a signal indicating a period start point of a signal corresponding to the synthesized signal, and a frequency calculating means for calculating the frequency of the power system using the signal generated by the periodic signal generating means. A frequency measurement circuit characterized in that 2. The periodic signal generating means adds an arbitrary two-phase electromotive force and compares the output of the adder with a reference signal to binarize it, to binarize or rise the binarized signal. The frequency measuring circuit according to claim 1, further comprising a comparator that outputs the falling portion as a signal indicating a cycle start point. 3. The periodic signal generating means comprises a first comparator for binarizing an electromotive force of one of arbitrary two phases with a reference signal and binarizing the other of the arbitrary two phases. A second comparator for binarizing electric power by comparing it with a reference signal and a logical sum of the output of the first comparator and the output of the second comparator to obtain a rising portion in the logical sum signal. The frequency measuring circuit according to claim 1, further comprising an OR circuit that outputs the falling portion as a signal indicating a cycle start point.