JPH0126029B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power measuring device for a three-phase AC power supply, which is necessary for grasping various characteristics of the three-phase AC power supply.

Figures 1 to 3 are circuit diagrams for explaining the principle of conventional measurement circuits. Figure 1 is an active power measurement circuit that measures active power, and Figure 2 is a reactive power measurement circuit that measures reactive power. Circuit FIG. 3 is a power factor measuring circuit that measures the power factor.

In the figure, numerals 1 and 2 indicate wattmeter elements, which are composed of a current coil (fixed coil) 3 and a voltage coil (movable coil) 4, and the wattmeter elements 1 and 2 are attached to the same axis.

5 is a power factor element, and 6 is a three-phase load.

Next, the operation will be explained.

In the active power measurement circuit shown in FIG. 1, when a U-phase current I _U corresponding to a three-phase load 6 flows in the direction of the arrow, a torque corresponding to a line voltage E _EV and a U-phase current I _U is applied to the voltage coil 4. Occur.

The same applies to the W phase, where torque is generated in the wattmeter element 2, and the amount of active power is indicated by the amount of torque applied to the shaft to which the wattmeter elements 1 and 2 are attached.

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 I _U , and the U-phase voltage E _U
Torque is generated in the voltage coil 4 by the line voltage E VW delayed by π/2 from the line voltage E _VW . Due to the action of this torque, an amount deviated from active power by π/2, that is, reactive power is measured.

However, reactive power can only be obtained in a three-phase balanced state.

Figure 3 shows a power factor measuring circuit, in which the power factor element 5 consists of two sets of coils mechanically positioned at an angle of 60 degrees to each other, namely voltage coils 4A and 4B connected to line voltages E _UV and E _UW . and two sets of current coils 3A and 3B connected to the U-phase current _IU , and the torque corresponding to the power factor is applied to each voltage coil 4.
It acts on A and 4B and indicates the power factor.

Note that although each measurement circuit is shown in which the wattmeter elements 1 and 2 and the power factor element 5 are constructed from the respective coils 3, 3A, 3B, 4, 4A, and 4B, there are also measurement circuits constructed from Hall elements.

The conventional power measurement device for three-phase AC power supply is configured as described above, so it can measure active power, reactive power,
When attempting to measure power factor, etc., individual measuring instruments are required.

In addition, since a moving coil or a Hall element was used to detect power, it was only possible to measure frequencies as low as commercial frequencies. It was impossible to measure.

Furthermore, there were other problems such as the inability to measure in the case of three-phase unbalance.

This invention was made in order to solve the above-mentioned problems.As measurement sample values, instantaneous voltage values and instantaneous current values are given to an arithmetic circuit based on the d,q conversion theory. An object of the present invention is to obtain a power measuring device for a three-phase AC power supply that can measure the power, instantaneous power factor, or three-phase unbalanced power.

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

In Fig. 4, 7 is a d- and q-axis conversion circuit that converts three-phase AC voltage and current values into d- and q-axis voltage and current values based on the d- and q-axis conversion theory, and 8A.
~8D is a multiplication circuit that multiplies the voltage value and current value of the d-axis and q-axis, 9A is an addition circuit that adds the calculation results of multiplication circuits 8A and 8D, and 10 is a multiplication circuit that adds the calculation results of multiplication circuit 8C to the calculation result of multiplication circuit 8B. 11 is a subtraction circuit that subtracts the calculation results; 8E and 8F are multiplication circuits; 9B is an addition circuit that adds the calculation results of the multiplication circuits 8E and 8F;
Reference numeral 12 indicates a root arithmetic circuit that performs a square root calculation of the arithmetic result of the adder circuit 9B, and 12 a division circuit as a power factor arithmetic circuit, which divides the arithmetic result of the adder circuit 9A by the arithmetic result of the root arithmetic circuit 11. .

Note that the d and q axis conversion circuit 7 has two phases, for example, U,
From the W-phase currents I _U , I _W and the line voltages E _UV , E _WV , the d-axis and q-axis currents I _d , I _q and the voltages E _d ,
E _q and the analog arithmetic circuit or central processing unit
Calculations are performed using a digital arithmetic circuit using a CPU.

Id=√32・I _U Iq=−√2/2(I _U +2I _W ) Ed=√23(V _UV −0.5V _WV ) Eq=−√2・V _WV /2 Next, I will explain the operation. ,Before that, I will explain the principle.

The effective values of the phase voltage and phase current of three-phase AC are V,
When I is the phase difference and θ is the phase difference, the active power W and the reactive power Q are expressed by the following equations 1.1 and 2.2.

W=3VIcosθ...1.1 Q=3VIsinθ...1.2 Furthermore, when the angular frequency is ω, the instantaneous values of each phase voltage and phase current are expressed by the following equations 2.1 to 3.3.

V _U =√2Vcosωt ……2.1 V _V =√2Vcos(ωt−2π/3) ……2.2 V _W =√2Vcos(ωt+2π/3) ……2.3 I _U =√2Icos(ωt−θ) ……3.1 I _V = √2Iccs (ωt−θ−2π/3) …3.2 I _W =√2Icos (ωt−θ+2π/3) …3.3 Here, the instantaneous voltage and instantaneous current expressed by Equations 2.1 to 3.3 above When converted into d-axis and q-axis voltages and currents based on the d- and q-axis conversion theory, the following equations 4.1 to 5.2 are obtained.

V _d = √3Vcosωt …4.1 V _q =√3Vsinωt …4.2 I _d =√3Icos (ωt−θ) …5.1 I _p =√3Isin (ωt−θ) …5.2 Therefore, the d and q axes When calculating the active power and reactive power using voltage and current, the following equation is obtained.
Equations 6.1 and 6.2 are obtained.

W=V _d・I _d +V _q・I _q ……6.1 Q=−V _d・I _q +V _q・I _d ……6.2 In addition, the power factor cos θ is the active power W and the reactive power in equations 1.1 and 1.2. It can be expressed by the following equation 7 using the power Q.

cosθ=W/√ ² + ² (7) Therefore, by configuring the circuit formula from the above logical formula, it becomes possible to obtain the instantaneous values of active power, reactive power, and power factor.

FIG. 4 shows an example embodying the above logical formula. In order to convert phase currents and line voltages into d-axis and q-axis currents and voltages, a d- and q-axis conversion circuit 7 is used.
Calculate I _d , I _q , V _d , and V _q using .

Next, the converted voltage and current values are multiplied by a multiplication circuit 8.
A to 8D, addition circuit 9A, subtraction circuit 10, No. 6.1
The active power W and reactive power Q shown in Equation 6.2 are calculated.

Then, when the active power W and the reactive power Q are obtained, the multiplication circuit 8E,
8F, an addition circuit 9B, and a route calculation circuit 11 perform various calculation processes, and finally a division circuit 12 calculates the power factor.

In addition, although the above embodiment has been explained using an example in which power is taken into account when the three phases are balanced, the present invention is not limited to this example, and the same applies even when the power is when the three phases are unbalanced. To establish.

Further, although the arithmetic circuit has been shown to be configured with an analog circuit, by configuring it with 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, if the power and power factor of a three-phase AC power source are converted by an arithmetic circuit based on the d- and q-axis conversion theory, the configuration is such that the electrical four arithmetic arithmetic circuits perform arithmetic processing. Therefore, there is an excellent effect that the instantaneous values of active power, reactive power, and power factor can be measured at high speed and with high accuracy regardless of whether the three-phase alternating current is balanced or unbalanced.

[Brief explanation of drawings]

Figure 1 shows a conventional active power measurement circuit that measures active power, Figure 2 shows a conventional reactive power measurement circuit that measures reactive power, Figure 3 shows a conventional power factor measurement circuit that measures power factor, and Figure 4 shows a conventional power factor measurement circuit that measures power factor. The figure is a block diagram showing a power measuring device for a three-phase AC power supply according to an embodiment of the present invention. In the figure, 1 and 2 are wattmeter elements, 3 and 3A,
3B is a current coil, 4, 4A, 44B are voltage coils, 5 is a power factor element, 6 is a 3-phase load, 7 is d, q
Axis conversion circuit, 8A to 8F are multiplication circuits, 9A, 9B
10 is an addition circuit, 10 is a subtraction circuit, 11 is a root calculation circuit, and 12 is a division circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A 3-phase/2-phase conversion circuit that converts the line voltage and phase current of a 3-phase AC power supply into 2-phase voltage and current as input, and the d-axis converted by this 3-phase/2-phase conversion circuit. an active power calculation circuit that adds the multiplication result of the voltage and the d-axis current to the multiplication result of the q-axis voltage and the q-axis current converted by the 3-phase/2-phase conversion circuit; From the multiplication result of the q-axis voltage and d-axis current converted by the 2-phase conversion circuit, the multiplication result of the d-axis voltage and q-axis current converted by the 3-phase/2-phase conversion circuit is calculated. A reactive power calculation circuit to subtract, and a power to divide the above active power by the square root of the value obtained by squaring the active power obtained by the above active power calculation circuit and the value obtained by squaring the reactive power obtained by the above reactive power calculation circuit. A power measurement device for a three-phase AC power supply, which is equipped with a rate calculation circuit.