JPS59195165A - Electric power measuring device for three-phase ac power source - Google Patents

Abstract

PURPOSE:To measure an instantaneous value at a high speed with high accuracy irrespectively of balance and inbalance by converting the electric power and power factor of a 3-phase AC power source in accordance with d, q conversion theory, then processing arithmetically the same in a four rules arithmetic circuit. CONSTITUTION:Phase current and line voltage are calculated by a d-, q-axis converting circuit 7 in order to convert respectively said current and voltage to the current and voltage of d-axis and q-axis, by which the respectively converted current and voltage values are obtd. The resulted current and voltage values are fed to multipliers 8A and 8D, adders 9A, 9B and a substractor 10, by which available power W and reactive power Q are calculated. When the available power and reactive power are respectively obtd., the calculation by the multiplier 8A and adder 9 and the various arithmetic processing by a route calculating circuit 11 and a divider 12 are accomplished in accordance with the arithmetic equations used for said calculation, and finally the power factor is calculated by a power factor arithmetic circuit. The above-mentioned arithmetic processing holds irrespectively of the balance and inbalance of the 3-phase AC power source.

Description

[Detailed Description of the Invention] The present invention provides three
The present invention relates to a power measuring device for a phase AC power supply.

Conventionally, there have been measuring devices of this type that individually measure active power, reactive power, power factor, etc., and a composite power measuring device as intended by the present invention has been desired. Figures 1 to 3 show measurement circuits with four individual configurations for the purpose of explaining the principles. Figure 1 is an active power measurement circuit, Figure 2 is a reactive power measurement circuit, and Figure 3 is a power factor measurement circuit. This is a power factor measurement circuit for measurement. In the figure, reference numerals 1 and 2 denote wattmeter elements, each of which is composed of a current coil 3 (fixed coil) and a voltage coil 4 (movable coil). Further, 5 is a power factor element, and 6 is a three-phase load.

Next, the operation will be explained. The wattmeter elements 1 and 2 in the active power measuring circuit shown in FIG. A torque commensurate with the line voltage Euv and the U-phase current Iu is generated in the coil 4. Similarly, for the W phase, torque is generated in the wattmeter element 2, and the wattmeter elements 1 and 2 are mounted on the same axis, and a circuit is constructed so that the amount of active power is indicated by the degree of torque applied to the axis. It consists of In the reactive power measurement circuit shown in FIG. 2, a magnetic field is generated in the current coil 3 by the U-phase current Iu, and a torque is generated in the voltage coil 4 by the Evw voltage delayed by π/2 from the U-phase voltage Eu. This action causes the second
In the reactive power measurement circuit shown in the figure, an amount deviated from active power by π/2, that is, reactive power is measured. However, the reactive power can only be obtained in a three-phase balanced state. In addition, FIG. 3 shows a power factor measuring circuit in which the power factor elements 5 are mechanically connected to each other by six points.
Two sets of coils positioned at an angle of 0 degrees, namely voltage coils 4A, 4 connected to line voltages Euv and Euw.
B and two sets of current coils 3A, 3 connected to the U-phase current.
A torque commensurate with the power factor acts on each voltage coil 4A, 4B to indicate the power factor. In addition, in the figure, l, 2
．． Although each power rate meter element in 5 is shown as a measurement circuit composed of a coil, there is also a circuit composed of a Hall element.
Since conventional power measuring devices were configured as described above, individual measuring instruments were required to measure active power, reactive power, power factor, etc., and a moving coil, Alternatively, since a Hall element was used, it was only possible to measure frequencies as low as the commercial frequency, and it was impossible to measure instantaneous power, instantaneous power factor, etc. of current, voltage waveform, etc. at the inverter frequency. Furthermore, there were also drawbacks such as the inability to measure even in the case of three-phase unbalance.

The present invention was made in order to eliminate the drawbacks of the conventional ones as described above.As a measurement sample, instantaneous voltage and current values are based on the d and q conversion theory (by feeding them to an arithmetic circuit, instantaneous It is an object of the present invention to provide a power measuring device for a three-phase AC power supply that can measure power, power factor, three-phase unbalanced power, etc.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 4, the same parts as in FIGS. 1 to 3 are shown with the same reference numerals. In FIG. ctq-axis conversion circuit that calculates q-axis voltage and current values, 8 people or 8D
is a multiplication circuit that multiplies the voltage and current values of the d-axis and q-axis,
9A, 9B and H1O are addition circuits and subtraction circuits that add or subtract the calculation results of the multiplication circuits 8A to 8D, 8E and 8F are also multiplication circuits, 11 is a root calculation circuit that performs factor calculations, and 12 is a division circuit. It is a calculation circuit.

Next, the operation of the present invention shown in FIG. 4 will be explained below. When the effective values of the phase voltage and phase current of the three-phase alternating current are {circle around (1)} and {circle around (2)}, and the phase difference is θ, the active power W and the reactive power Q are expressed by equation (1).

Further, when the angular frequency is ω, the instantaneous values of each phase voltage and phase current are expressed by equations (2) and (3).

Here, based on the instantaneous voltage and current d, q conversion theory expressed by equations (2) and (3) above, the d-axis and q-axis voltages,
When converted to current, the following equations (4) and (5) are obtained1.
Therefore, when the active power and the reactive power are determined using the voltage and current on the d and q axes, equation (6) is obtained.

Further, the power factor cos θ can be expressed using active power and reactive power from equation (1), and is given by equation (7).

Therefore, by configuring a circuit using the above theoretical formula, it becomes possible to obtain instantaneous values of active power, reactive power, and power factor.

That is, FIG. 4 shows an example embodying the above theoretical formula, in which calculations are performed by the d- and q-axis conversion circuit 7 to convert the phase current and line voltage into d-axis and q-axis currents and voltages, respectively. , I
Obtain d, ■q, vd, and Vq.

Next, the voltage and current values converted to the d-q axes are applied to multiplication circuits 8A and 8D, addition circuits 9A and 9B, and subtraction circuit 10.
The active power W and reactive power Q shown in equation (6) above are calculated. Then, when the effective power and reactive power are obtained, the multiplication circuits 8 to 8D and the addition circuit 9 perform calculations according to the equation (7), and then the root calculation circuit 11
, the division circuit 12 performs various arithmetic operations, and finally the power factor cos θ is calculated by the power factor calculation circuit.

Although the above explanation has considered power in a three-phase balanced state for convenience, it is not limited to this example (the same holds true even in the case of power in a three-phase unbalanced state).

Furthermore, although the arithmetic circuit is shown as an analog circuit in the above embodiment, by configuring the circuit as a digital circuit, it is also possible to configure a highly accurate measurement circuit that is free from the effects of temperature drift and the like.

As described above, according to the present invention, the circuit is configured such that the power and power factor of a three-phase AC power source are converted by an arithmetic circuit based on d, q conversion theory, and then subjected to arithmetic processing by an electrical arithmetic operation circuit. This method has the advantage of being able to measure instantaneous values at high speed and with high precision, regardless of whether the AC is balanced or unbalanced.

[Brief explanation of the drawing]

Fig. 1 is a conventional active power measurement circuit diagram, Fig. 2 is a conventional reactive power measurement circuit diagram, Fig. 3 is a conventional power factor measurement circuit diagram, and Fig. 4 is an instantaneous power according to an embodiment of the present invention. It is a calculation circuit block diagram of a power factor reduction measuring device. 1, 2... Wattmeter element 3... Current coil 4, 4A, 4B... Voltage coil 5... Power factor element 6... 3-phase load 7... d, q @ conversion circuit 8 people to 8F...Multiplication circuits 9A, 9B...Addition circuit 10...Subtraction circuit 11...Root calculation circuit 12...Divide circuit Note that the same reference numerals in the drawings indicate the same or equivalent parts. Agent Masuo Oiwa Figure No. 35゜Procedural Amendment - (Indication) Commissioner of the Japan Patent Office 1. Case description Patent Application No. 58-71596 2. Name of the invention Power measurement device for 3-phase AC power supply 3. Amendment Relation to the case of the person who filed the patent Ichikatayama, the representative of the patent author I 4i'1J of Explanation (Drawing 31, Contents of Amendment (1) The claims are amended as per the attached sheet. (2) Page 3 of the specification, lines 12 to 13 K "Famous Power Rate Meter System" ＋31 Figure 4 is amended as shown in the attached sheet. 7. List of markings (1 + document stating the scope of claims after amendment 1 copy 1
2+ The document described in Figure 4 after amendment and a d- and q-axis conversion circuit that converts the voltage into d-axis and q-axis voltage and current, respectively. lf'L'fcd is converted by modifying the d and q axis exchange circuit.
shaft. q-axis ゛ Turtle pressure current area instantaneous effective reactive power, history [A power measuring device for a 3rd main flow power source, which is equipped with four arithmetic operations and a power factor calculation circuit for calculating the power factor of the instantaneous value. □Do

Claims (1)

[Claims] The two-phase voltage and two-phase current of a three-phase AC power source are input, and the two-phase voltage and two-phase current are respectively converted into d411 (d and q-axis conversion circuits into 1-axis voltage and current, and the d , a plurality of multiplication circuits that calculate instantaneous values of active power, reactive power, etc. from the d-axis and q-axis voltage and current converted by the q-axis conversion circuit, and instantaneous values of active power and reactive power based on the calculation outputs of the multiplication circuits, A power measuring device for a three-phase AC power supply further comprising four arithmetic operations and a power factor calculation circuit for calculating the power factor of an instantaneous value.