JPH02190769A - Wattmeter - Google Patents

Abstract

PURPOSE:To measure an electric power with high accuracy over the wide range in the manner of obtaining a true phase angle by calculating a phase rotation angle at the device side measured with each frequency of each range and an apparent phase angle calculated from the actually measured value. CONSTITUTION:Values of the phase rotation angles theta of each range corresponding to the measuring frequencies are held on a phase angle table 11, and the value of the rotation angle corresponding to the frequency in the necessary range is read into an arithmetic means 12 for phase angle when the actual measurement is made. Then, the calculations of the phase angle phi for voltage E, current I and of the electric power W are made as follows; that is, as to the output Pa of a filter 5, Pa=EIcos(phidivided by theta). To the equation phi=cos<-1>(Pa/EI)-theta which is modified from the above, the measured value Pa, voltage E, current I and rotation angle theta read-out from the table 11 are interposed to calculate 12 the phase angle phi, then the true power Pt for an electric circuit 1 is calculated in arithmetic means 13 for electric power by using the phase angle phi, power Pa, rotation angle theta, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wattmeter, and more particularly to a wattmeter equipped with means for correcting measurement errors based on phase rotation within the device.

[Conventional example]

The effective power (hereinafter referred to as "power") w of the electric circuit is, if the voltage and current of the electric circuit are sinusoidal waves, the effective values are E and I, respectively, and the phase angle between the voltage and current is φ, as follows. It is expressed as W=E1 cos φ.

In this case, if there is a phase rotation of, for example, 100 degrees inside the wattmeter, the power factor will appear to be cog (φ10), which will cause a measurement error. It grows and becomes impossible to ignore. Therefore, a phase correction circuit or the like is generally provided to prevent the occurrence of errors.

An example of this is shown in FIG. 3, for example, the voltage E of the electrical circuit 1 to be measured. Electric current flowing with sinωt. Each component of 5 inches (ω is 10φ) is taken out by the sensor 2, and 1E and sinωt are added to the voltage component to the multiplier 4.

In addition, the current component is I, 5in (ωt+φ+θ),
For example, it is applied to a multiplier 4 via a phase corrector 3 that corrects the internal phase rotator 〇 including the sensor 2 described above. Here, k
,,k,represent appropriate constants.

This is because the output P' of the multiplier 4 is the product of the two inputs.

P'=1E, sinωt Xk, 1.5in(ωt+
φ)=(kx kiEa Ia/2)(cog(2(
II t + φ゛) 0 cos φ) If this output P' is added to, for example, the filter 5 and the first term AC component is removed, the output P of the same filter 5 becomes P=(k,
E, I, /2) cogφ=to, (E, /v'2) (
1,/v'2) cosφ=, EIeosφ=kW, and an output proportional to the electric power W of the electric circuit is obtained.

However, it is assumed that ni=ni, ・k2.

If W=P/k is determined from the above equation, the power W can be read on the display 6.

[Problem to be solved by the invention]

The method for preventing errors in the conventional device described above is relatively simple, and is suitable for a 50/60 Hz wattmeter.

By the way, the phase rotation angle θ is 1. For example, if the resistance component in the device as seen from the electric circuit side is R, and the reactance component is ωX, then θ=tan'((II X/R), where ω=
It is expressed as 2πf, and changes depending on the frequency f, as is well known.

Therefore, there is a problem that conventional analog phase correction circuits cannot cope with electrical circuits that use an inverter or the like to supply power at a frequency different from that of a general commercial power source.

Furthermore, when a multi-range configuration is used to widen the measurement range, the phase rotation angle θ on the device side in each range is generally not equal. Therefore, a separate phase corrector is required for each range, which complicates the measurement system.

This invention was made in consideration of the above points.

The purpose is to measure the phase rotation angle θ on the device side at each frequency in each required range in advance.

During actual power measurement, the apparent phase angle φ' (=φ10) calculated from the measured value is subjected to a digital calculation such as φ=φ'-〇 using the phase rotation angle θ at the frequency at that time. The object of the present invention is to provide a power meter that can determine the true phase angle φ and measure power over a wide band and with high accuracy.

[Explanation of correction principle]

If Pa is the power value measured without correcting the phase rotation angle θ inside power measurement of a single-phase electric circuit, then Pa=EIcos φ' −...
-(1) = EIcog (φ10) = E I (cosφcos 0-sinφsin
O).

Here, if θ is very small, cos 041,
Since sin θ valve θ can be set, from the above formula, P a = E
I (eosφ−B sinφ) −・−・
−・(2)”EIcosφ(l−θtanφ)
−・・−・(3) is obtained. However, it is assumed that cosφ≠0.

The first term in the above equations (2) and (3) represents the true power value, and the second term represents the error based on the internal phase rotation angle.

Now, if the true power value is pt, then Pt=EIcosφ
Therefore, equations (2) and (3) are Pt=Pa+θEI
sinφ (2a)-=Pa/(1-θt
anφ) (3a).

In equation (2a) or (3a), if θ is known, φ=φ
φ can be found from '−〇. Since Pa is a known measured value that includes an error, the true power value pt can be determined by calculation.

How to find the internal phase rotation angle Now, apply to this device voltages and currents E and I whose phase angles φ differ by +90°, and voltages and currents E and I which differ by -90°, and calculate the respective electric power (zero power factor power). , and the measured value at that time is P a (gzx) * P a (-Kzzl). In equation (2), when φ = π/2, e08φ = O, sinφ; 1 φ = -π/2. Since cosφ=Q, sinφ#-1, P a t x is ) = −E Iθ(g/1)
Pa (z, 2) = EIθ (-1Ci2). In this case, it should be θ (π72) 20 (-π7m), but it does not match due to the calibration signal generator, measurement conditions, etc. In this case, for example, it is desirable to take the average value of both and set it as θ=(θ(π7100(−π/2))/2.

For example, the value of θ is calculated from the lowest operating frequency f1 to the highest frequency fn for each measurement range, as shown by the solid line in
If measurements are taken at the required frequency intervals, the power of the circuit under test can be easily calculated.

[Means to solve the problem]

Referring to FIG. 2, in which an embodiment of the invention is shown, 1
For example, sensor 21 multiplier 4. The filter 5 and the display 6 are almost the same units as the conventional device shown in FIG.
Therefore, the same reference numerals are given.

Furthermore, in this example, in order to solve the above problem,
For example, the following means A to E are provided.

B. Effective value detectors 7 and 8° for detecting the effective values E and I of the voltage and current components taken from the electrical circuit under test 1, including the error due to the above effective values E and I and the internal phase rotation angle θ. An A/D converter 9 and a measuring section 10 C digitally convert and measure the apparent power Pa of the electrical circuit to be measured, respectively, and a phase rotation angle θ that holds data on the phase rotation angle θ illustrated in FIG. 1 above. Angle table 11゜2, Phase angle calculation means 12゜ for calculating the phase angle φ between the voltage and current in the electric circuit 1 from the above effective value E, 1, the power Pa and the phase rotation angle 0; this calculated φ and the above Power calculation means 13 for calculating the true effective power p t (w) of the electric line 1 from the power Pa and the phase rotation angle 0 [Operation] By providing the above means, the phase rotation angle θ generated on the device side can be digitally calculated. is corrected to enable wideband power measurement.

[Example] Referring again to FIG. 2, the phase rotation angle θ generated on the device side is measured using a calibration signal generator or the like for each predetermined frequency within the operating frequency band of each range, and This phase rotation angle table 11 is inputted in advance into the phase rotation angle table 11 which is composed of:
For example, the measurement frequency fl#f2m in Fig. 1 above...
The value of the phase rotation angle θ of each range corresponding to .

In actual measurement, when a measurement range and frequency are specified using, for example, a switch on a control board (not shown), data of θ at that frequency in that range is read into the phase angle calculating means 12. Below, electric line 1
Calculation of phase angle φ of voltage and current at (φ=φ′±θ)
, and the calculation of the power W (W = E I cosφ) is as follows.

In FIG. 2 above, the output Pa of the filter 5 is P a
=E Icos(φ+θ) where φ represents the phase angle of the electric circuit 1 and θ represents the phase rotation angle inside the device.

When the above formula is transformed, φ=cos-1(P a / E I )-〇 becomes 0
The phase angle calculation means 12 adds measured values Pa, E, I,
Then, the phase angle φ is determined by substituting the data 0 read from the table.

The power calculation means 13 calculates the obtained phase angle φ and the power Pa,
Using data θ etc., Pt=Pa/(1
-8tanφ) to calculate the true power p t (=w) of the electric line 1.

Alternatively, it may be calculated using the phase angle φ, the power Pa, the voltage and the currents E and I, and using the formula (2a), Pt=Pa+θEIsinφ.

The above explanation was made regarding the correction of a single-phase electric circuit, but in the case of a three-phase electric circuit, the power can be measured by the well-known two-wattmeter method. Therefore, the correction is made for each phase in the same way as above.

Two powers after correction pt1. By calculating the algebraic sum of pt, the true power value Pt of the three-phase circuit can be obtained.

In the above example, the phase rotation table is stored in the memory on the main body side of the apparatus, but it is also possible to provide a memory on the sensor side, store it there, and read out the data on the main body side.

〔effect〕

As explained above in detail, in this embodiment, the internal phase rotation angle of the measurement system is measured in advance for a predetermined frequency in the operating frequency range of each range of the device, and the data is stored in the memory as a table. ing. When actually measuring power, the internal phase rotation angle data at the frequency of the range used is read from the above memory, and the apparent power including errors due to voltage and current detected from the electrical circuit and internal phase rotation is read from the above table. The original phase angle φ of the electrical circuit is calculated from the phase rotation angle data, and the true power of the electrical circuit is determined based on the calculated phase angle data.

Therefore, the power meter according to the present invention eliminates the need for an analog phase correction circuit, etc., and enables highly accurate power measurement over a wide frequency band.

[Brief explanation of the drawing]

1 and 2 relate to an embodiment of the present invention, FIG. 1 is an explanatory diagram of the internal phase rotation angle of the measurement system, FIG. 2 is a block diagram showing an example of the device configuration, and FIG. 3 is a conventional device. FIG. In the figure, ■ is the electric circuit to be measured, 2 is the sensor, 9 is the A/D converter, 10 is the measurement section, 11 is the phase rotation angle table, 12
13 is a phase angle calculation means, and 13 is a power calculation means.

Claims (1)

[Claims] (1) In a wattmeter that measures the power of a circuit under test by detecting voltage, current, and their phase angle, the internal phase rotation of the measurement system including the sensor at a predetermined frequency in the operating frequency range of the wattmeter data holding means for measuring the angle in advance for each measurement range and holding the measurement data; apparent power including voltage, current, and internal phase rotation angle detected from the electrical circuit to be measured; and the measurement frequency for the measurement range. phase angle calculation means for calculating the original phase angle data of the electric circuit using the internal phase rotation angle data in the calculation means; and electric power for calculating the true power of the electric circuit based on the phase angle data calculated by the calculation means. A wattmeter comprising a measuring means.