JP3060723B2 - Meter adjustment device for electric power - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power meter using digital technology, and more particularly to a power meter adjusting device for correcting a phase error between an input voltage and an input current generated in an input transformer.

[0002]

2. Description of the Related Art FIG. 6 shows a configuration diagram of a conventional example. FIG.
FIG. 6A shows a power meter constituted by only an analog circuit, and FIG. 6B shows a power meter using a digital technique for an operation part. In FIG. 6A, the signal line to be measured is often a high-voltage, large-current power supply line, and the input signal is insulated and stepped down by the transformer 1a and input to the analog operation circuit 2. The power of the output of the analog operation circuit 2 is displayed by the display means 3a. On the other hand, FIG.
, The input signal is insulated and stepped down by the transformer 1b, input to the A / D converters 4a and 4b, and converted into a digital value. The outputs of the A / D converters 4a and 4b are input to a programmable digital calculator 5. The digital arithmetic unit 5 converts the calculation result into a PWM (Pulse Width Modu).
lation) After converting the signal into a signal such as a signal, the power is sent to the display means 3b, the voltage value, the current effective value, the reactive power, the apparent power,
Displays phase angle, power factor, frequency, etc.

Here, the transformers 1a and 1b are:
It acts as a phase lead element between the primary side input and the secondary side output, and since the phase advance differs between voltage conversion and current conversion, a phase error occurs between the input voltage and the input current. Furthermore, this phase error is a function of the input frequency,
This phase error causes a reduction in the accuracy of the entire power meter.

In a power meter using an analog circuit shown in FIG. 6A, a complicated circuit and a large number of adjustment steps are required to accurately correct a phase error. Instruments are the majority. On the other hand, FIG.
In the power meter using the digital technique shown in FIG. 1B, the circuit operation can be specified by an internal program, and the phase error can be corrected by a correction function.

As a method of correcting a phase error by a correction function, there is a power meter adjusting method disclosed in Japanese Patent Application No. 4-51411. In this method, a low distortion sine wave is input and A
The digital output from the / D converter is directly extracted as serial data, the input waveform is estimated by the least squares method, and a correction coefficient is obtained so as to correct the estimated waveform.

[0006]

SUMMARY OF THE INVENTION However, Japanese Patent Application No. Hei.
The power meter adjusting method according to No. 1411 requires a low distortion sine wave generator for estimating an input waveform with high accuracy and an interface for capturing the serial data. In addition, in order to estimate the input waveform with high accuracy by the least square method, it is necessary to acquire a large amount of data, and since the amount of computation is enormous, the acquisition time and the computation time of the acquired data are increased, The adjustment time of the power meter increases. Therefore, an object of the present invention is to reduce the number of measuring instruments such as a low-distortion sine wave generator and the like, and realize a power meter adjusting device which does not need to take in a large amount of data and has a short adjusting time of the power meter.

[0007]

According to the present invention, there is provided a power meter adjusting apparatus for correcting a phase error of a meter using a correction function stored in a storage element of the power meter. A power supply that supplies a power supply voltage to the power meter, a signal source that applies a sine wave signal of an arbitrary input frequency to a voltage input terminal of the power meter, and a phase shift of the sine wave signal of the signal source. A phase shifter applied to a current input terminal of the power meter, a voltmeter that measures a power value calculation output of the power meter, a writer that writes the correction coefficient to a storage element of the power meter, A signal source is controlled to apply a sine wave signal of two types of input frequencies to the power meter, and the phase shifter is controlled to control a voltage input and a current input for each sine wave signal of the two types of input frequencies. Phase difference of 90 ° Then, three kinds of sine wave signals are sequentially applied to the power meter, and a power value calculation output including a phase error characteristic of the power meter at each input measured by the voltmeter is taken in. From this power value calculation output, A phase error between the voltage input and the current input is calculated, and a correction coefficient of a correction function, which is a linear expression of the input frequency, is calculated from the phase error and the two types of input frequencies, and the calculation is performed by controlling the writer. Calculation control means for storing the correction coefficient of the corrected function in the storage element of the power meter.

[0008]

[Function] For two kinds of frequencies in the power meter adjustment device,
By obtaining the correction coefficient of the phase error correction function only from the measurement outputs at three points having different phase differences, the number of measuring devices is reduced, so that a large amount of data acquisition processing is not required, and the adjustment time of the power meter is shortened. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.
FIG. 1 is a configuration block diagram showing an embodiment of a power meter adjusting device according to the present invention. 6 is a signal source that supplies a sine wave to the voltage input terminal of the power meter 50, 7 is a phase shifter that changes the phase of the signal source 6 and supplies the current input terminal of the power meter 50, and 8 is a power meter. Power value calculation output signal 10 of 50
A voltmeter for detecting 0, a power supply 9 for supplying to the power meter 50, a signal source 6, and other workstations as operation control means for controlling the measuring instrument. The power meter 50 includes a storage element 11 for storing a correction coefficient of a correction function, and an ASIC (Application / Application Control Unit) for converting an input signal from analog to digital, and calculating and controlling display or output.
specific integrated circuit: hereinafter referred to as an ASIC circuit). 13 is a storage element 11
Is a writer for writing the correction coefficient of the correction function into the writer. Here, since the workstation 10 does not perform much arithmetic processing, a low-speed workstation is sufficient.

The power meter 50 has an A in the ASIC circuit 12.
/ D converter, microprocessor and the like. In the normal operation, the acquired voltage and current are A / D-converted, corrected by the correction coefficient of the correction function stored in the storage element 11, and the result is output after calculating the power or the like.

The operation of FIG. 1 will be described with reference to the flowchart of FIG. As a step, the power meter 50 is brought into a normal operation state. Workstation 7 as a step
Applies a sine wave to the current and voltage input terminals of the power meter 50. As a step, the frequency is changed by the signal source 6, and the phase shifter 7 changes the phase of the sine wave applied to the current input terminal with respect to the sine wave applied to the voltage input terminal of the power meter 50. As a step, the power value calculation output signal 100 of the power meter 50 in this state is measured by the voltmeter 8. As steps, the phase differences “−90 °”, “0 °”, and “+90” for the two frequencies
Check whether the measurement of the single-phase power output of “°” has been completed. If not completed, repeat the steps and the steps.
Find phase errors at different frequencies. As a step, a correction coefficient is obtained from two kinds of frequencies and a phase error at the frequency, and the obtained coefficient of the correction function is written into the storage element 11 of the power meter 50 by the writer 13.

Further, the correction function will be described with reference to characteristic curve diagrams shown in FIGS. FIG. 3 is a characteristic curve diagram showing a change in voltage or current with time. "A" in FIG.
Is a voltage or current waveform actually captured, and "b" is a voltage or current waveform when there is no phase error between the voltage input and the current input. In FIG. 3, "d" denotes a phase error "ΔΦ" between a voltage input and a current input, and "c" denotes an ASIC circuit 1.
2 A / D converter equivalent to one sampling cycle phase "
Φ _sampling ”.

Here, since the single-phase power is affected by the phase error “ΔΦ” between the voltage input and the current input, the phase of the voltage input is corrected to match the phase of the current input, or The phase error may be corrected to match the phase of the voltage input or the phase error “ΔΦ” may be set to zero. That is, the n-th sampling data of the voltage input or the current input is “S (n)”, and the immediately preceding data, that is, the (n−1) -th sampling data is “S (n−
1) ", the corrected n-th sampling
The data "S _comp (n)" is obtained by linear interpolation as follows. S _comp (n) = S (n) − [{S (n) −S (n−1)} / Φ _sampling ] · ΔΦ = ΔΦ / Φ _sampling · S (n−1) + (1−ΔΦ / Φ _sampling ) ・ S (n) (1)

Further, the phase error “ΔΦ” is obtained from the single-phase power output of the phase difference “−90 °”, “0 °” and “+ 90 °” by the phase shifter 7. FIG. 4 is a characteristic curve diagram showing the relationship between the phase difference by the phase shifter 7 and the single-phase power. In FIG. 4, “A” indicates the characteristic when the phase error is “0”, and “B” indicates the characteristic when the phase error “ΔΦ” indicated by “C” exists. Here, "d", "e", and "f" in FIG. 4 indicate single-phase power outputs when the phase difference by the phase shifter 7 is "-90", "0", and "+90", respectively. "P".

When the phase difference by the phase shifter 7 is "Φ", and the voltage input value and the current input value are "V ₀ " and "I ₀ ", respectively, the single-phase power output "P (Φ)" is as follows. It is expressed by an equation. P (Φ) = phase difference due to _{(V 0 · I 0/2} ) cos (Φ + ΔΦ) (2) phase shifter 7 "-90 °", "0 °" and "
Since a + 90 ° ", the formula (2) is, P (-90 °) = ( V 0 · I 0/2) cos (-90 ° + ΔΦ) = - (V 0 · I 0/2) sinΔΦ (3 ) P (0 °) = ( V 0 · I 0/2) cos (0 ° + ΔΦ) = (V 0 · I 0/2) cos (ΔΦ) (4) P (90 °) = (V 0 · I _{0/2) cos (90 °} + ΔΦ) = become _{(V 0 · I 0/2} ) sinΔΦ (5).

From equations (3) to (5), the phase error "ΔΦ"
Is obtained by ΔΦ = tan ⁻¹ {−P (−90 °) / P (0 °)} = tan ⁻¹ {P (90 °) / P (0 °)} (6) However, since the phase error “ΔΦ” is a function of the frequency of the input waveform as described above, “
Let ΔΦ / Φ _{sampling be} “δ” and let this “δ” be a linear expression of frequency as follows: δ = Gf + H (7) where “G” and “H” are correction coefficients, and “f” "" Is the frequency of the input waveform.

Accordingly, two types of frequencies "f ₁ ", "f"
_From equation (6), two types of phase errors “Δ
Φ ₁ ”,“ ΔΦ ₂ ”, ie,“ δ ₁ ”,“ δ ₂ ”, and the following simultaneous equations obtained by substituting into equation (7): δ ₁ = Gf ₁ + H δ ₂ = By solving Gf ₂ + H, the correction coefficients “G” and “H” are obtained as follows: G = (δ ₂ −δ ₁ ) / (f ₂ −f ₁ ) H = (f ₂ δ ₁ − f ₁ δ ₂ ) / (f ₂ −f ₁ )

FIGS. 5A and 5B are characteristic curve diagrams showing simulation results of the power meter adjusted by the power meter adjusting device described above. FIG. 5 (A) is 50-60 Hz
In (B), the correction coefficient is obtained in the range of 40 to 70 Hz, and the phase difference between the voltage input and the current input is “Φ = + 90 °” using a single-phase wattmeter having a phase error “ΔΦ ≦ 0.36 °”.
3 shows a reading error of the single-phase wattmeter in the case of. However, "a" and "c" in FIG. 5 indicate a case without correction, and "b" and "d" indicate a case with correction. Here, in FIG. 5A, the reading error is improved to about 1/1000 in the range of 50 to 60 Hz, and in FIG. 5B, the reading error is improved to about １ ／ in the range of 40 to 70 Hz.

As a result, the low-distortion sine wave generator, interface, and the like used in the conventional adjustment method become unnecessary, and the data to be taken in becomes six types, and only "tan ^-1 " and several arithmetic operations are required. Therefore, the acquisition time and the calculation time are also reduced. In addition, it is easy to construct an adjustment system for readjustment in a production line or a customer where it is generally difficult to use an expensive low distortion sine wave generator or high-speed workstation.

In equation (6), the phase error "ΔΦ"
When computing is not required, the expression (6)
Is used, and the average value of both is used when calculation accuracy is required. The phase difference by the phase shifter 7 is "-90.
° ”,“ 0 ° ”and“ + 90 ° ”instead of“
0 ° ”,“ + 90 ° ”, and“ + 180 ° ”.

Further, when performing the non-linearity correction together with the phase error correction, the power meter adjusting apparatus according to the present invention is combined with the power meter adjusting method according to Japanese Patent Application No. 4-51411. Can be realized.

[0022]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. By obtaining the correction coefficient of the phase error correction function using only three measurement outputs having different phase differences with respect to two kinds of frequencies, the number of measuring devices such as a low distortion sine wave generator as in the conventional example is reduced. This eliminates the need for data fetching processing, thereby realizing a power meter adjustment device that requires a short time to adjust the power meter.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram showing an embodiment of a power meter adjusting device according to the present invention.

FIG. 2 is a flowchart illustrating the operation of the apparatus of FIG.

FIG. 3 is a characteristic curve diagram showing a time change of a voltage or a current.

FIG. 4 is a characteristic curve diagram showing a relationship between a phase difference and single-phase power.

FIG. 5 is a characteristic curve diagram showing a simulation result of the power meter adjusted in the embodiment of FIG. 1;

FIG. 6 is a configuration block diagram illustrating an example of a conventional power meter.

[Explanation of symbols]

 1a, 1b Transformer 2 Analog operation circuit 3a, 3b Display means 4a, 4b A / D converter 5 Digital operation unit 6 Signal source 7 Phase shifter 8 Voltmeter 9 Power supply 10 Workstation 11 Storage element 12 ASIC circuit 13 Writer 50 Power meter 100 Power value calculation output signal

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenji Fujino 2-9-132 Nakamachi, Musashino City, Tokyo Inside Yokogawa Electric Corporation (56) References JP-A-3-108674 (JP, A) JP-A Sho 63-173973 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 21/00-22/04 G01R 11/00-11/66

Claims (1)

(57) [Claims] 1. A power meter adjusting device for correcting a phase error of a meter by a correction function stored in a storage element of the power meter, a power source for supplying a power voltage to the power meter, and a power meter. A signal source for applying a sine wave signal having an arbitrary input frequency to a voltage input terminal of the power source; a phase shifter for applying a sine wave signal of the signal source to a current input terminal of the power meter by shifting the phase; A voltmeter that measures the power value calculation output of the power meter; a writer that writes the correction coefficient into a storage element of the power meter; and a sine wave signal having two types of input frequencies by controlling the signal source. The three types of sine wave signals are sequentially applied by controlling the phase shifter to shift the phase difference between the voltage input and the current input by 90 ° for each of the two types of sine wave signals. Apply to the power meter and A power value calculation output including a phase error characteristic of the power meter at each input measured by a voltmeter is taken in, and a phase error between a voltage input and a current input is calculated from the power value calculation output. Calculating a correction coefficient of a correction function, which is a linear expression of the input frequency, from the input frequency of the type and controlling the writer to store the correction coefficient of the calculated correction function in a storage element of the power meter; A power meter adjusting device, comprising: a control unit.