JPH0687069B2 - Watt meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power meter, and more particularly to a power meter including a correction unit for a measurement error due to phase rotation in a device.

[Conventional example]

If the voltage and current of the electric path are sinusoidal waves, the effective power of the electric path (hereinafter, referred to as “electric power”) W is E, I, and the phase angle between the voltage and the current is φ. It is represented by W = EI _cos φ.

In this case, if there is a phase rotation of + θ inside the wattmeter, the power factor will be apparently cos (φ + θ) and a measurement error will occur. The effect of this θ will be greater as the power factor of the circuit is lower. Can not be ignored. Therefore, generally, a phase correction circuit or the like is provided to prevent an error from occurring.

Although an example of which is shown in Figure 3, for example, each component of the current I ₀ flowing voltage E ₀ sin .omega.t of the measured circuit 1 sin (ωt + φ) was removed by the sensor 2, the voltage component k ₁ E ₀ sinω
Add t to multiplier 4. In addition, the current component k ₂ I ₀ sin (ωt
+ Φ + θ) is added to the multiplier 4 via the phase corrector 3 that corrects the internal phase rotation + θ including the sensor 2, for example. Here, k ₁ and k ₂ represent appropriate constants.

'Since the product of the two inputs, P' output P of the multiplier _{4 = k 1 E 0 sinωt ×} k 2 I 0 sin (ωt + φ) = (k 1 k 2 E 0 I 0/2) {cos ( 2ωt + φ) + cosφ} excluding the AC component of the first term by adding the output P ', for example, in the filter 5, the output P of the filter 5 is _{P = (k 1 k 2 E} 0 I 0/2) cosφ = k 1 k ₂ (E ₀ / √2) (I ₀ / √2) cosφ = k ₁ k ₂ EIcosφ = kW, and an output proportional to the electric power W of the electric line is obtained. However, k = k ₁ · k ₂ .

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

[Problems to be Solved by the Invention]

The error occurrence prevention method in the above conventional device is relatively simple, and is suitable for a 50/60 Hz power meter.

By the way, the phase rotation angle θ is expressed by θ = tan ⁻¹ (ωX / R), where ω = 2πf, where R is the resistance component and ωX is the reactance component in the device viewed from the electric path side. As is known, it varies with frequency f.

Therefore, there is a problem that the conventional analog phase correction circuit cannot handle the electric line that supplies electric power of a frequency different from that of the general commercial power source using an inverter or the like.

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

This invention has been made in consideration of the above points, and its purpose is to measure the phase rotation angle θ on the device side at each frequency of each required range in advance, and from the measured value at the time of actual power measurement. Calculated apparent phase angle φ '(= φ +
θ), for example, the true phase angle φ is obtained by performing a digital operation of φ = φ′−θ from the phase rotation angle θ at the frequency at that time, and it is possible to measure the power in a wide band and with high accuracy. The purpose is to provide an electric power meter.

[Explanation of correction principle]

Power measurement of single-phase circuit If the power value measured without correcting the internal phase rotation angle θ is Pa, Pa = EIcosφ ′ …… (1) = EIcos (φ + θ) = EI (cosφcosθ-sinφsinθ) .

If θ is very small, cos θ ≈ 1, sin θ ≈
From the above equation, Pa = EI (cosφ−θsinφ) (2) = EIcosφ (1-θtanφ) (3) However, 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, assuming that the true power value is Pt, Pt = EIcosφ, so equations (2) and (3) can be transformed into Pt = Pa + θEIsinφ (2a) = Pa / (1-θtanφ) (3a) .

In the formula (2a) or (3a), if θ is known, φ = φ′−
φ can be found from θ. Since Pa is a measurement value including an error and is known, the true power value Pt can be calculated.

How to obtain the internal phase rotation angle Now, in this device, for example, the phase angle φ is + 90 °
The electric current (zero power factor electric power) is measured by applying the current E and I and the voltage and current E and I that differ by −90 °, and the measured value at that time is Pa.
If (π _{/ 2} ), Pa (−π _{/ 2} ), then in equation (2) cosφ = 0, sinφ = 1 when φ = π / 2, cosφ = 0, sinφ = − when φ = −π / 2 Since it is 1, Pa (π _{/ 2} ) = − EIθ (π _{/ 2} ) Pa (−π _{/ 2} ) = − EIθ (−π _{/ 2} ). In this case, originally, θ (π _{/ 2} ) = θ (−
π _{/ 2} ), but if they do not match due to the calibration signal generator and measurement conditions, take the average value of the two, and θ = (θ (π _{/ 2} ) + θ (-π _{/ 2} ) It is desirable to set it to / 2.

If the value of this θ is measured at required frequency intervals from the minimum operating frequency f ₁ to the maximum operating frequency f _n for each measurement range, as shown by the solid line in FIG. It can be easily calculated.

[Means for Solving the Problems]

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

Further, in order to solve the above problems in this embodiment,
For example, the following means (a) to (e) are provided.

I. Effective value detectors 7 and 8 that detect the effective values E and I of the voltage and current components taken from the measured circuit 1.

B. The A / D converter 9 and the measuring unit 1 for digitally measuring the effective values E and I and the apparent electric power Pa of the measured electric path including the error due to the internal phase rotation angle θ, respectively.
0.

C. A phase rotation angle table 11 that holds the data of the phase rotation angle θ illustrated in FIG. 1 above.

D. From the effective values E, I and the power Pa and the phase rotation angle θ,
Phase angle calculation means 12 for obtaining the phase angle φ between the voltage and the current in the electric circuit 1.

E. Power calculating means 1 for calculating the true effective power Pt (W) of the electric circuit 1 from the calculated φ, the power Pa and the phase rotation angle θ.
3.

[Action]

By including the above means, the phase rotation angle θ generated on the device side is digitally corrected, and the wide band power measurement becomes possible.

〔Example〕

Referring to FIG. 2 again, the position rotation angle θ generated on the device side is measured by using a calibration signal generator or the like for each predetermined frequency within the operating frequency band of each range, and the phase configured in the memory is measured. It is entered in the rotation angle table 11 in advance. The phase rotation angle table 11 holds the value of the phase rotation angle θ of each range corresponding to the measurement frequencies f ₁ , f ₂ , ... Of FIG. 1, for example.

In the actual measurement, for example, when the measurement range and frequency are designated by the switch of the control board (not shown), the data of θ at that frequency in the range is read into the phase angle calculation means 12. Hereinafter, the calculation of the phase angle φ of the voltage and current in the electric path 1 (φ = φ ′ ± θ),
And the calculation of the electric power W (W = EIcosφ) is as follows.

In FIG. 2, the output Pa of the filter 5 is Pa = EIcos (φ + θ). Here, φ represents the phase angle of the electric circuit 1, and θ represents the phase rotation angle inside the device.

If the above equation is transformed, φ = cos ⁻¹ (Pa / EI) −θ. The phase angle calculation means 12 has the measured values Pa, E, I, and
And the phase angle φ is obtained by substituting the data θ read from the table.

The power calculation means 13 uses the calculated phase angle φ, the power Pa, the data θ, etc., and uses Pt = Pa / (1-θtanφ) of the equation (3a) to obtain the true power Pt (= W) is calculated.

Alternatively, the phase angle φ, the electric power Pa, the voltage and the current E, I may be used to calculate using Pt = Pa + θEIsinφ in the equation (2a).

Although the above description has been made on the correction of the single-phase electric circuit, the electric power can be measured by the two-power meter method as is well known in the case of the three-phase electric circuit. Therefore, the correction is also performed for each phase as described above, and the two corrected powers Pt ₁ , Pt
If the algebraic sum of t ₂ is calculated, the true power value Pt ₃ of the three-phase circuit can be obtained.

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

〔effect〕

As described 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 in each range of the device, and the data is stored as a table on the memory. ing. At the time of actual power measurement, the internal position rotation angle data at the frequency of the operating range is read from the memory, and the apparent power including the error due to the voltage, current and internal phase rotation detected from the circuit, and the phase rotation read from the table above. The original phase angle φ of the electric circuit is calculated from the angle data, and the true electric power of the electric circuit is obtained based on the calculated phase angle data.

Therefore, according to the power meter of the present invention, an analog phase correction circuit or the like is not required, and highly accurate power measurement can be performed over a wide frequency band.

[Brief description of drawings]

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

Claims (1)

[Claims] 1. A power meter for measuring voltage and current of a circuit to be measured and its phase angle to measure electric power of the circuit, the inside of a measuring system including a sensor for a predetermined frequency in an operating frequency region of the power meter. Data holding means for preliminarily measuring the phase rotation angle for each measurement range and holding the measurement data, apparent power including the voltage, current, and internal phase rotation angle detected from the measured circuit, and 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 at the measurement frequency, and true power of the electric circuit based on the phase angle data calculated by the calculation means. An electric power meter comprising: a required electric power measuring means.