JP2006084381A - Three-phase power measurement method and three-phase power measurement device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a three phase electric power measurement method, and a three phase electric power measurement device capable of carrying out highly accurate electric power measurement, and capable of minimizing a measurement error when impedances of three phase loads are not equal in measuring electric power of a three phase three wire connection. <P>SOLUTION: In measuring the electric power of the three phase three wire connection, it is characterized by that it includes a step of measuring phase currents of three phases, a step of measuring a voltage between the first phase and the second phase, and a voltage between the first phase and the third phase, a step of calculating the electric power of the three phase three wire connection on the basis of two voltage measurement outputs and a current measurement output of the third phase, and a step of calculating an electric power error correction portion on the basis of the two voltage measurement outputs and three current measurement outputs. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a three-phase power measurement method and a three-phase power measurement device, and more particularly to reduction of errors in power measurement of a three-phase three-wire connection.

Patent Document 1 relates to a digital wattmeter including a plurality of power measuring units, and discloses that not only single-phase power but also three-phase three-wire three-phase power can be measured.
Specifically, there is disclosed a configuration for obtaining a correct addition result regardless of the combination of the power range setting states of each power measurement unit. There is no description about reducing the measurement error when the impedances of the phase loads are not equal.

JP-A-6-50002

FIG. 3 is an explanatory diagram showing an example of a connection relationship of a conventional three-phase power measuring apparatus. In FIG. 3, three-phase power sources R, S, and T generate voltages U _R , U _S , and U _T , respectively, and supply currents IR, IS, and IT to loads L1 to L3 corresponding to the respective phases. One end of each of these power sources R, S, and T is connected to one end of a corresponding load L1 to L3 via a power line, and each other end is commonly connected as a connection midpoint. The other ends of the loads L1 to L3 are also commonly connected as connection midpoints.

Current measuring unit I1 to power line R-phase of measuring the phase currents I _R flowing from the power source R to load L1 is connected in series, measuring the phase current I _R flowing from the power source S to the load L2 in the power line of the S-phase A current measuring unit I2 is connected in series. A voltage measuring unit U1 that measures the voltage between the R-phase power line and the T-phase power line is connected, and a voltage measuring unit U2 that measures the voltage between the lines between the S-phase power line and the T-phase power line. Is connected. The current measuring unit I1 and the voltage measuring unit U1 constitute a first power measuring unit P1, and the current measuring unit I2 and the voltage measuring unit U2 constitute a second power measuring unit P2.

Here, _assuming that the power measured by the first power measurement unit P1 is P1, and the power measured by the second power measurement unit P2 is P2, the power P _2WATTS of the three-phase three-wire connection is obtained by Blondel's theorem. It can be obtained by equation (1).
P _2WATTS = P1 + P2 (1)

FIG. 4 is a functional block diagram illustrating the configuration example of FIG. The DSP (digital signal processor) 1 includes instantaneous voltage values u ₁ (n) and u ₂ (n) from the voltage measuring units U1 and U2 and instantaneous current values i ₁ (n) and i from the current measuring units I1 and I2. Based on ₂ (n), the powers P1 and P2 are obtained by performing the calculations of the following formulas (2) and (3), and the power _P2WATTS of the three-phase three-wire connection is calculated by the formula (1).

The power P _2WATTS of the three-phase three-wire connection calculated by the equation (1) in this way is displayed on the display 3 via the CPU 2.

  By the way, the condition under which Blondel's theorem holds is the equation (4).

  However, the stray capacitance C1 exists between the connection midpoint of the power sources R, S, and T and the ground, and the stray capacitance C2 exists between the connection midpoint of the loads L1 to L3 and the ground. If L1 = L2 = L3 does not hold between the impedances L1, L2, and L3 of L3, equation (4) does not hold and a measurement error occurs.

If the measurement error due to the fact that the equation (4) does not hold is expressed by a vector, the equation (5) is obtained. If the measured power value in the connection of FIG. 3 is P 2 _WATTS ,

On the other hand, assuming that the true value of the three-phase power in FIG. 3 is P _TRUE , P _TRUE is expressed by equation (6).

Therefore, the measurement error P _ERROR when Expression (4) does not hold becomes Expression (7).

  As a method for eliminating such measurement errors, for example, three voltage measuring units and three current measuring units may be used, and the voltage measuring unit may be connected to the three-phase midpoint and the power sources S, R, and T. However, it cannot be used if the midpoint is inside the device and cannot be removed.

  The present invention solves these conventional problems, and its purpose is to reduce the measurement error when the impedance of the three-phase load is not equal in measuring the power of the three-phase three-wire connection. An object of the present invention is to realize a three-phase power measurement method and a three-phase power measurement apparatus that can perform power measurement with high accuracy.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
A three-phase power measurement method for measuring the power of a three-phase three-wire connection,
Measuring a three-phase phase current;
Measuring the voltage between the first phase and the second phase and the voltage between the first phase and the third phase;
Calculating the power of the three-phase three-wire connection based on the two voltage measurement outputs and the current measurement outputs of the second phase and the third phase;
The method includes a step of calculating a power error correction based on two voltage measurement outputs and three current measurement outputs.

Of the present invention, the invention according to claim 2
A three-phase power measuring device for measuring the power of a three-phase three-wire connection,
Three current measuring means for measuring three-phase phase currents;
Two voltage measuring means for measuring the voltage between the first phase and the second phase and the voltage between the first phase and the third phase, respectively;
Based on the measurement output of the two voltage measurement means and the measurement output of the second and third phase current measurement means, the power of the three-phase three-wire connection is calculated, the measurement output of the two voltage measurement means and the three current measurements An arithmetic means for calculating an electric power error correction amount based on the measurement output of the means is provided.

The invention according to claim 3 is the three-phase power measuring device according to claim 2,
The computing means is a digital computing unit.

The invention according to claim 4 is the three-phase power measuring device according to claim 2,
The computing means is an analog computing unit.

  According to the present invention, in measuring the power of a three-phase three-wire connection, a three-phase power measurement method and a three-phase power measurement method capable of reducing the measurement error when the impedances of the three-phase loads are not equal can be reduced and performing high-precision power measurement. A phase power measuring device can be realized.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing an example of a connection relationship of a three-phase power measuring apparatus according to the present invention, and the same reference numerals are given to the parts common to FIG. Point 1 differs from FIG. 3 is that the current measurement unit I3 also to the power line of the T-phase measuring the phase current I _T flows from the power source T to a load L3 are connected in series. That is, in FIG. 1, a current measuring unit for measuring a phase current is connected in series with each phase power line.

FIG. 2 is a functional block diagram showing a configuration example of FIG. The DSP 4 includes instantaneous voltage values u ₁ (n) and u ₂ (n) input from the voltage measuring units U1 and U2 and instantaneous current values i ₁ (n) and u2 (n) input from the current measuring units I1, I2 and I3. Based on i ₂ (n) and i ₃ (n), the calculation of equations (1), (2) and (3) is performed in the same manner as the DSP 1 in FIG. Power _P2WATTS is calculated, and an error correction amount P ′ is calculated by performing the calculation of the following equation (8).

Then, based on the power P 2 _WATTS obtained by the equation (1) and the error correction P ′ obtained by the equation (8), the calculation of the equation (9) is performed to calculate the power P ′ _2WATTS of the three-phase three-wire connection. To do.
_P'2WATTS = _P2WATTS + P '(9)
The power P ′ _2WATTS of the three-phase three-wire connection calculated by the equation (9) in this way is displayed on the display 6 via the CPU 5.

  When equation (8) is expressed as a vector, equation (10) is obtained.

From these equations (5) and (11), the measurement error P ′ _ERROR according to the present invention becomes equation (12).

From these, the measurement error P _{ERROR in} equation (7) is compared with the measurement error P ' _ERROR in equation (12).
P ' _ERROR <P _ERROR . That is, with the configuration of the present invention, the measurement error is reduced, and power measurement can be performed with high accuracy.

  In the embodiment, the power is calculated using the DSP 4, but an analog calculator may be used instead of the DSP 4.

  In the embodiment, the voltage between R and T and the voltage between S and T are measured. However, the voltage between R and S and the voltage between T and S may be measured. The voltage between and the voltage between T and R may be measured. In this case, the power calculation may be changed according to the measurement location.

It is explanatory drawing which shows an example of the connection relation of the three-phase electric power measuring apparatus based on this invention. It is a functional block diagram which shows the structural example of FIG. It is explanatory drawing which shows an example of the connection relation of the conventional three-phase electric power measuring apparatus. It is a functional block diagram which shows the structural example of FIG.

Explanation of symbols

4 Calculation means (DSP)
5 CPU
6 Display

Claims (4)

A three-phase power measurement method for measuring the power of a three-phase three-wire connection,
Measuring a three-phase phase current;
Measuring the voltage between the first phase and the second phase and the voltage between the first phase and the third phase;
Calculating the power of the three-phase three-wire connection based on the two voltage measurement outputs and the current measurement outputs of the second phase and the third phase;
A three-phase power measurement method comprising a step of calculating a power error correction based on two voltage measurement outputs and three current measurement outputs. A three-phase power measuring device for measuring the power of a three-phase three-wire connection,
Three current measuring means for measuring three-phase phase currents;
Two voltage measuring means for measuring the voltage between the first phase and the second phase and the voltage between the first phase and the third phase, respectively;
Based on the measurement output of the two voltage measurement means and the measurement output of the second and third phase current measurement means, the power of the three-phase three-wire connection is calculated, the measurement output of the two voltage measurement means and the three current measurements A three-phase power measuring apparatus, comprising a calculating means for calculating a power error correction based on a measurement output of the means.   3. The three-phase power measuring apparatus according to claim 2, wherein the computing means is a digital computing unit. 3. The three-phase power measuring apparatus according to claim 2, wherein the computing means is an analog computing unit.

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