JP5794864B2 - Three-phase power measuring device - Google Patents

Description

  The present invention relates to a three-phase power measuring device, and more particularly to multi-functional measurement.

  FIG. 6 is a block diagram showing an example of a conventional three-phase AC power measuring device described in Patent Document 1. In FIG. In FIG. 6, the A / D converter 1 receives the R phase voltage uR, the A / D converter 2 receives the R phase current iR, and the A / D converter 3 receives the S phase S u. A phase voltage uS is input to the A / D converter 4, an S-phase phase current iS is input to the A / D converter 4, and a T-phase phase voltage uT is input to the A / D converter 6. Is supplied with a T-phase phase current iT. Here, R, S, and T represent each phase of a three-phase alternating current, u represents a voltage, and i represents a current.

  The outputs of the A / D converters 1 and 2 are input to the multiplier 7, and the R phase instantaneous power is calculated by multiplying them. The outputs of the A / D converters 3 and 4 are input to the multiplier 8, and the instantaneous power of the S phase is calculated by multiplying them. The outputs of the A / D converters 5 and 6 are input to the multiplier 9, and the T phase instantaneous power is calculated by multiplying them.

  The adder 10 receives the outputs of the multipliers 7, 8, and 9 and adds them to output three-phase instantaneous active power.

  The output of the adder 10 is input to the low-pass filter 11 and smoothed, and three-phase active power is output.

  According to the description of Patent Document 1, in such a configuration, the amplitudes of the three-phase voltages uR, uS, uT are equal and the phases are shifted from each other by 120 °, and the three-phase currents iR, iS, iT also have an amplitude. In the balanced three-phase state where the phases are equal and shifted by 120 °, the output of the adder 10 becomes active power without the low-pass filter 11. That is, in the balanced three-phase, the active power of the three-phase alternating current can be measured without the low-pass filter 11 by eliminating the low-pass filter 11 (paragraph 0034).

JP2004-170097

  By the way, the operation description of the conventional block diagram shown in FIG. 6 described in Patent Document 1 is only the measurement of the active power in the three-phase four-wire connection in a balanced three-phase state that does not require the low-pass filter 11.

  However, the measurement function necessary as a three-phase power measuring device is not limited to the active power in the three-phase four-wire connection as described above, but can be obtained from the apparent power obtained from the voltage / current and the voltage / current / active power. It is required to measure power factor and reactive power at the same time.

  Further, three-phase three-wire connection measurement is also required, and it is desirable that the average phase voltage (effective value) and average phase current (effective value) of the R phase, S phase, and T phase can be measured.

  The present invention solves these problems, and an object of the present invention is to realize a three-phase power measuring apparatus capable of measuring various items related to three-phase alternating current without using a low-pass filter.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
A plurality of A / D converters to which three-phase voltages uR, uS, uT and phase currents iR, iS, iT are respectively input;
A plurality of multipliers for calculating instantaneous power by multiplying voltage and current for each phase;
A power adder for adding the outputs of these multipliers;
A power low-pass filter configured to be set on / off and to which the output of the power adder is input;
A plurality of square units that square the conversion output of the A / D converter;
A voltage adding unit that adds the phase voltages uR, uS, uT squared by these square units;
A voltage averaging unit for averaging the addition output of the voltage adding unit;
A voltage low-pass filter configured to be set on / off and to which an average output of the voltage average unit is input,
The voltage square root part to which the output of this voltage low-pass filter is input,
A current addition unit for adding the phase currents iR, iS, iT squared by the square unit;
A current averaging unit that averages the addition output of the current addition unit;
A current low-pass filter configured to be set on / off and to which an average output of the current average unit is input;
The current square root part to which the output of this current low-pass filter is input,
Is a three-phase power measuring device.

The invention of claim 2
A plurality of A / D converters to which three-phase interphase voltages uRT, uST, uRS and respective phase currents iR, iS, iT are respectively input;
Two multipliers for multiplying two interphase voltages and currents to calculate two instantaneous powers;
A power adder for adding the outputs of these two multipliers;
A power low-pass filter configured to be set on / off and to which the output of the power adder is input;
A plurality of square units that square the conversion output of the A / D converter;
An interphase voltage adder for adding the interphase voltages uRT, uST, uRS squared by these squares;
An interphase voltage averaging unit that averages the addition output of the interphase voltage addition unit;
An interphase voltage low-pass filter configured to be able to be turned on / off and to which an average output of the interphase voltage average unit is input,
An interphase voltage square root to which an output of the interphase voltage low-pass filter is input,
A current addition unit for adding the phase currents iR, iS, iT squared by the square unit;
A current averaging unit that averages the addition output of the current addition unit;
A current low-pass filter configured to be set on / off and to which an average output of the current average unit is input;
The current square root part to which the output of this current low-pass filter is input,
Is a three-phase power measuring device.

  With these configurations, various items related to three-phase alternating current can be measured without using a low-pass filter.

It is a block diagram which shows one Example of this invention. It is an example of an operation waveform of the apparatus of FIG. It is a block diagram which shows the other Example of this invention. FIG. 4 is an operation waveform example diagram of the apparatus of FIG. 3. FIG. 4 is another operational waveform diagram of the apparatus of FIG. 3. It is a block diagram which shows an example of the conventional three-phase alternating current power measuring apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, and the same reference numerals are given to portions common to FIG. In FIG. 1, square units 12, 13, and 14 are connected to A / D converters 1, 3, and 5 to which phase voltages uR, uS, and uT, respectively, and phase currents iR, iS, and iT are input. Square units 19, 20, and 21 are connected to the A / D converters 2, 4, and 6, respectively.

  The square outputs of the square units 12, 13, and 14 related to the phase voltages uR, uS, and uT are input to the adder unit 15 and added, and the output of the adder unit 15 is input to the average unit 16 and divided by “3”. Averaged. The output of the average unit 16 is input to the square root unit 18 through a low-pass filter 17 configured to be turned on / off. The square root portion 18 performs an operation for obtaining a square root of 1/3 of the square sum of each phase voltage uR, uS, uT as expressed by the equation (1), and calculates an average phase voltage (effective value) U.

  In the balanced three-phase state where the amplitudes of the three-phase voltages uR, uS, and uT are equal and the phases are shifted from each other by 120 °, the output of the square root portion 18 is the same as in FIG. As shown in the operation waveform example diagram, a constant value is obtained, and an average phase voltage (effective value) U is obtained.

  The low-pass filter 17 is configured so that the cutoff frequency can be set to an arbitrary value when it is on. As a result, the fluctuation of the output of the averaging unit 16 that occurs when the three-phase alternating current is not balanced three-phase is smoothed based on the characteristics of the cutoff frequency set in the low-pass filter 17 by turning on the low-pass filter 17. Can be

  The square outputs of the square units 19, 20, and 21 related to the phase currents iR, iS, and iT are input to and added to the adder unit 22, and the output of the adder unit 22 is input to the average unit 23 and divided by “3”. Averaged. The output of the average unit 23 is input to the square root unit 25 through a low-pass filter 24 configured to be turned on / off. The square root portion 25 performs an operation for obtaining a square root of 1/3 of the square sum of each phase current iR, iS, iT as expressed by the equation (2), and calculates an average phase current (effective value) I.

  The low-pass filter 24 is configured so that the cutoff frequency can be set to an arbitrary value when it is on. As a result, the fluctuation of the output of the averaging unit 23 that occurs when the three-phase alternating current is not balanced three-phase is smoothed based on the characteristics of the cutoff frequency set in the low-pass filter 24 by turning on the low-pass filter 24. Can be

  FIG. 3 is a block diagram showing another embodiment of the present invention, which enables measurement of effective power, average line voltage (effective value), and average phase current (effective value) at the time of three-phase three-wire connection. Therefore, the same reference numerals are given to the parts common to FIG. In FIG. 3, the A / D converter 1 receives the line voltage uRT between the R phase and the T phase, and the A / D converter 3 receives the line voltage uST between the S phase and the T phase. The line voltage uRS between the R phase and the S phase is input to the device 5. Then, the multiplication unit 9 provided in FIG. 1 is deleted, and the outputs of the multiplication units 7 and 8 are input to the addition unit 10.

  When attention is paid to the output of the adder 10 in FIG. 3, three-phase instantaneous power is output based on the Blondel theorem. The low-pass filter 11 smoothes the three-phase instantaneous power and outputs the three-phase active power P. The low-pass filter 11 may be configured to be able to be turned on / off similarly to the other low-pass filters 14 and 24 so that the cutoff frequency can be set to an arbitrary value when turned on.

  Accordingly, the balanced three-phase state in which the phase voltages uR, uS, and uT have the same amplitude and the phases are shifted from each other by 120 °, and the phase currents iR, iS, and iT have the same amplitude and the phases are shifted from each other by 120 °. In this case, even when the low-pass filter 11 is off, the output of the adder 10 becomes a constant value and becomes active power P as shown in the operation waveform example diagram of FIG. This active power P is expressed by equation (3).

  When the phase is not balanced three-phase, fluctuation occurs in the output of the adding unit 10, but a stable measurement value can be obtained by turning on and smoothing the low-pass filter 11.

  For the average line voltage (effective value) of the three-phase three-wire connection, the low-pass filter 17 is turned off in the case of balanced three-phase by measuring three line voltages between RT, ST, and RS. Even so, as shown in the operation waveform example diagram of FIG. 5, the output of the square root portion 18 becomes a constant value without delay, and becomes an average line voltage (effective value) U. The average line voltage (effective value) U is expressed by equation (4).

  When the phase is not balanced three-phase, fluctuation occurs in the output of the square root portion 18, but a stable measurement value can be obtained by turning on and smoothing the low-pass filter 17.

  Furthermore, by using the voltage U, the current I, and the active power P obtained by the present invention, the apparent power S, the power factor λ, and the reactive power Q can also be measured based on the following arithmetic expression.

Apparent power S = U × I (5)
Power factor = P / (U x I) (6)

  As described above, according to the present invention, it is possible to realize a three-phase power measuring device that can measure various items related to three-phase AC power without using a low-pass filter, and a measurement device in the field that uses three-phase AC. It is suitable as.

1-6 A / D converter 7-9 Multiplier 10, 15, 22 Adder 11, 17, 24 Low pass filter 12-14, 19-21 Squared 16, 23 Average 18, 25 Square root

Claims (2)

A plurality of A / D converters to which three-phase voltages uR, uS, uT and phase currents iR, iS, iT are respectively input;
A plurality of multipliers for calculating instantaneous power by multiplying voltage and current for each phase;
A power adder for adding the outputs of these multipliers;
A power low-pass filter configured to be set on / off and to which the output of the power adder is input;
A plurality of square units that square the conversion output of the A / D converter;
A voltage adding unit that adds the phase voltages uR, uS, uT squared by these square units;
A voltage averaging unit for averaging the addition output of the voltage adding unit;
A voltage low-pass filter configured to be set on / off and to which an average output of the voltage average unit is input,
The voltage square root part to which the output of this voltage low-pass filter is input,
A current addition unit for adding the phase currents iR, iS, iT squared by the square unit;
A current averaging unit that averages the addition output of the current addition unit;
A current low-pass filter configured to be set on / off and to which an average output of the current average unit is input;
The current square root part to which the output of this current low-pass filter is input,
A three-phase power measuring device characterized by comprising: A plurality of A / D converters to which three-phase interphase voltages uRT, uST, uRS and respective phase currents iR, iS, iT are respectively input;
Two multipliers for multiplying two interphase voltages and currents to calculate two instantaneous powers;
A power adder for adding the outputs of these two multipliers;
A power low-pass filter configured to be set on / off and to which the output of the power adder is input;
A plurality of square units that square the conversion output of the A / D converter;
An interphase voltage adder for adding the interphase voltages uRT, uST, uRS squared by these squares;
An interphase voltage averaging unit that averages the addition output of the interphase voltage addition unit;
An interphase voltage low-pass filter configured to be able to be turned on / off and to which an average output of the interphase voltage average unit is input,
An interphase voltage square root to which an output of the interphase voltage low-pass filter is input,
A current addition unit for adding the phase currents iR, iS, iT squared by the square unit;
A current averaging unit that averages the addition output of the current addition unit;
A current low-pass filter configured to be set on / off and to which an average output of the current average unit is input;
The current square root part to which the output of this current low-pass filter is input,
A three-phase power measuring device characterized by comprising:

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