JP3001238B2 - Watt hour meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a watt-hour meter, and more particularly to a watt-hour meter that calculates an integrated power amount using an electronic circuit.

[Conventional technology]

The watt hour meter outputs a pulse proportional to the measured power amount for verification. In a conventional watt-hour meter, a pulse proportional to the measured power is output as a compression wave as shown in FIG. 5 (d), even if the voltage and current are constant within one cycle of the commercial frequency.

[Problems to be Solved by the Invention] As described above, in the conventional watt-hour meter, the pulse output for verification is a compression wave in one cycle. Therefore, when the test is performed in a short time, the number of pulse outputs within a certain period varies depending on whether the test start or end timing is close or close to the pulse output. As a result, there is a problem that the test accuracy is deteriorated.

Accordingly, an object of the present invention is to provide a watt-hour meter with high verification accuracy.

[Means for solving the problem]

A watt hour meter according to the present invention is a watt hour meter for obtaining an integrated power signal representing an integrated power amount using an input voltage signal and an input current signal, wherein the first analog converting the input voltage signal into a digital voltage signal / Digital converter, a second analog / digital converter for converting the input current signal into a digital current signal, and a digital multiplier for multiplying the digital voltage signal by the digital current signal and outputting a multiplication result signal And a digital filter that filters the multiplication result signal and outputs a smoothed signal; and an integrator that integrates the filtered signal and outputs the integrated power signal.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, a watt hour meter according to one embodiment of the present invention obtains an integrated power signal representing an integrated power amount using an input voltage signal 1 and an input current signal 2.

The input voltage signal 1 and the input current signal 2 represent an analog voltage value (V) and an analog current value (I), respectively. The input voltage signal 1 and the input current signal 2 are the first
Analog / digital converter 3 and a second analog / digital converter
It is supplied to the digital converter 4. The first analog / digital converter 3 converts the input voltage signal 1 into a digital voltage signal 5. Similarly, the second analog / digital converter 4 converts the input current signal 2 into a digital current signal 6. The digital voltage signal 5 and the digital current signal 6 represent a digital voltage value and a digital current value, respectively.

The digital voltage signal 5 and the digital current signal 6 are supplied to a digital multiplier 7. Digital multiplier 7 multiplies digital voltage signal 5 by digital current signal 6 and outputs multiplication result signal 8. The multiplication result signal 8 represents a digital power value.

In the following, the input voltage signal 1 and the input current signal 2 are respectively expressed as shown in FIGS. 5 (a) and 5 (b).
The case of a sine wave signal of Hz will be described. At this time, the multiplication result signal 8 output from the digital multiplier 7
Is a DC component proportional to the product of the amplitudes of the input voltage signal 1 and the input current signal 2 and 100 Hz, as shown in FIG.
Sine wave signal.

In the present embodiment, the multiplication result signal 8 is supplied to the digital band suppression filter 9 in order to remove a 100 Hz sine wave signal from the sum signal.

FIG. 2 shows the frequency characteristic of the suppression amount of the digital band suppression filter 9 used in the power meter of FIG. As apparent from FIG. 2, the digital band suppression filter 9 has a characteristic of passing a DC component and sufficiently suppressing an AC component of 100 Hz. The smoothed signal 10 output from the digital band suppression filter 9 is
As shown in FIG. 7E, the signal is a signal obtained by smoothing the multiplication result signal 8.

The smoothed signal 10 is supplied to a digital integrator 11. The digital integrator 11 integrates the smoothed signal 10 and outputs an integrated signal 12. The integrated signal 12 is an integrated power signal representing the digital integrated power amount.

In this embodiment, the integrated power signal 12 is supplied to the power / pulse conversion circuit 13. The electric energy / pulse conversion circuit 13 converts the integrated electric power signal 12 into electric energy / pulse, and the electric power / pulse conversion circuit 13 shown in FIG.
The power pulse output signal 14 is output as shown in FIG.

FIG. 3 is a block diagram of a watt hour meter according to a second embodiment of the present invention. It has the same configuration as that shown in FIG. 1 except that a low-pass filter 9a is used instead of the digital band-pass filter 9 as a digital filter.

Analog / digital converter 3 used in this embodiment
And 4 are the frequencies of the input voltage signal 1 and the input current signal 2
It is assumed that the sampling frequency fs0 is sufficiently higher than 50 Hz. In this example, the sampling frequency fs0 is 102.4 kHz.
Let it be z.

In the present embodiment, the low-pass filter 9a is composed of ten digital low-pass filters 91 connected in series, and nine decimators 92 inserted between two adjacent digital low-pass filters 91. Consists of

Each of the digital low-pass filters 91 has transfer characteristics represented by the following transfer function H (z).

H (z) = (1−z ⁻¹ ) / 2 (1) Here, the digital low-pass filter 91 having the transfer function H (z) represented by the equation (1) is shown in FIG. Pass the DC component and
Has the characteristic of suppressing the frequency component of

The output of the first-stage digital low-pass filter 91 is subjected to sampling by a decimator 92 connected to the output. The sampling frequency fs is a first sampling frequency fs1 of 51.2 kHz, which is 1/2 of the sampling frequency fs0 of the analog / digital converters 3 and 4.

Thereafter, by repeating the same processing, the 100 Hz signal component is suppressed by the digital low-pass filter 91 at the final stage where the sampling frequency fs is 200 Hz of the ninth sampling frequency fs9. Thereby, a smoothed signal 10 as shown in FIG. 5E is obtained from the output of the digital low-pass filter 91 at the last stage.

As described above, the case of 50 Hz has been described as an example.
Obviously, the same method can be applied to other frequencies including Hz.

〔The invention's effect〕

As described above, according to the present invention, a digital filter is provided in the output of the digital multiplier, so that the power pulse output is an equally-spaced pulse with no sparse / dense. Therefore,
Even when the test is performed in a short time, the number of pulse outputs within a certain period is stabilized, so that there is an effect that the test accuracy is increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a watt hour meter according to a first embodiment of the present invention, FIG. 2 is a diagram showing frequency characteristics of a suppression amount of a digital band suppression filter used in the watt hour meter of FIG. 1, FIG. 3 is a block diagram showing a watt-hour meter according to a second embodiment of the present invention, FIG. 4 is a diagram showing frequency characteristics of loss of a digital low-pass filter used in the watt-hour meter of FIG. 3, FIG. 5 is a diagram showing a waveform example of each part of the watt hour meter according to the present invention and a power pulse output waveform example without a digital filter. 3,4 ... A / D converter, 7 ... Digital multiplier, 9 ... Digital band suppression filter, 9a ...
Low-pass filter, 11 ... Digital integrator, 13 ... Power / pulse conversion circuit.

Continuation of the front page (72) Inventor Masatoshi Komatsu 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Toshio Takagi 1-3-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Company (56) References JP-A-3-92771 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 21/00-22/04 G01R 11/00-11/66

Claims (3)

(57) [Claims] 1. A watt hour meter for obtaining an integrated power signal representing an integrated power amount using an input voltage signal and an input current signal, wherein the input voltage signal is converted into a digital voltage signal.
And a second converter for converting the input current signal into a digital current signal.
An analog-to-digital converter, a digital multiplier that multiplies the digital voltage signal and the digital current signal to output a multiplication result signal, and outputs a filtered signal obtained by filtering the multiplication result signal. A watt hour meter, comprising: a digital filter; and an integrator that integrates the smoothed signal and outputs the integrated power signal. 2. The watt hour meter according to claim 1, wherein said digital filter is a band suppression filter. 3. The watt hour meter according to claim 1, wherein said digital filter is a low-pass filter.