JPH03158770A - Watthourmeter circuit - Google Patents

Abstract

PURPOSE:To make an offset adjustment easy and to always maintain a good performance by providing a means to invert polarities in the manner of synchronizing the polarity of either an AC voltage or current and the polarity of the product of digital voltage/current at the time interval settled beforehand. CONSTITUTION:A voltage signal is amplified by an amplifier 3 through a switch 2 for polarity changeover of a transformer PT1 and converted to the voltage digital signal by an A/D converter 4. On the other hand, a current flowing to a load is converted to the signal by a current transformer CT5 then converted to the current digital signal by an A/D converter 7 after amplifier by an amplifier 6. These voltage and current digital signals are multiplied by a multiplier 8 to calculate an instantaneous power which is a product of them, and this value is integrated by an integrator 10 through a polarity changeover circuit 9 to obtain the electric energy. By this arrangement, an error caused by the offset is eliminated and the accurate watthourmeter circuit can be realized with a simple constitution.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power meter circuit, and particularly to a power meter circuit that converts voltage and current into digital voltage data and digital current data, respectively, and integrates the product of these voltage and current data. The present invention relates to a power meter circuit that obtains integrated power data.

[Conventional technology]

Conventionally, this type of power meter circuit samples analog voltage and current signals proportional to the respective instantaneous values of AC voltage and current supplied to the load at a predetermined period to generate digital voltage data and digital current. Convert to data and integrate the multiplication results of these voltage data and current data.

Obtaining integrated power data.

Here, a conventional power meter circuit will be outlined with reference to FIG.

The signal source 11 has a voltage input signal V, n=4E, casω
t, and a voltage input signal generator of 12 signal sources i n =4
I , -ω is generated (ψ). vo2, 14. voF
212 is the input offset generated in the amplifier and analog-to-digital converter, Vo, 315 is the multiplier 16
is the output offset of The output of the multiplier, that is, the power W, is integrated in an integrator 17 and output as the power amount Wh.

Now, considering the above-mentioned offset, calculate the power W.

W=(v1n+Vo21)(T1n+Vo, 2)+Vo
F3=2Er Cursing the bunch ω (ωt-ψ) e 1y'E“V ・Ko Mei (ω one ψ) OFI
e + 2vOF2 * v, Qlii (ωt)-4
−v −v +v・・・・・・
・(1)071 0)"2 0F5Here, when formula (1) is integrated for one period, 2π (however, ω=-) + (V,, 1° VOF2 + VOF5) t ) 0This result.

Wh, = T (EeIeccsψ+C”op+・v
oy2+voF3)) -(2) (the second term indicates the error due to the offset).

[Problem to be solved by the invention]

By the way, 1. Normally, the voltage amplitude of a voltage signal is almost constant, but the current amplitude of a current signal varies depending on the load, so the current amplitude is required to cover a wide range. However, as mentioned above, conventional 1 vOF1~
"The offset of OF3 causes an error in the amount of power obtained by multiplication and integration. Therefore, in order to reduce the measurement error near the lower limit of the current amplitude, it is necessary to The DCC offset adjustment must be made as small as possible.Therefore, in order to adjust the offsets of amplifiers, sample hold circuits, and analog-to-digital converters used in power meter circuits, many offset adjustment volumes are required. It requires a long time to adjust.

Furthermore, even if offset adjustment is performed, the offset will shift due to temperature changes and aging, making it difficult to maintain good characteristics. For this reason, there is a culmination of the need to use expensive parts with high performance.

An object of the present invention is to provide a power meter circuit that allows easy offset adjustment and always maintains good characteristics.

[Means to solve the problem]

According to the present invention, an alternating voltage and an alternating current are each converted to predetermined signal levels, analog-to-digital conversion is performed to obtain digital voltage data and digital current data, and the product of the digital voltage data and the digital current data is integrated. In the power meter circuit for obtaining integrated power data, the power meter circuit includes an inverting means for synchronizing the polarity of either the alternating current voltage or the alternating current with the polarity of the product at a predetermined time interval to invert the polarity. Features: Power meter circuit power 2 obtained.

〔Example〕

The present invention will be explained below with reference to Examples.

Referring to Figure 1, the voltage signal is transferred to the transformer (P-T-1).
.

Amplifier 3 through first polarity switch 2
The signal is amplified to a predetermined signal level and converted into a voltage digital signal by an analog-to-digital converter 4. On the other hand, the current flowing through the load is converted into a current signal by a current transformer (C, T) 5,
After the signal is amplified to a predetermined signal level by amplifier f6, it is converted into a current digital signal by analog/digital converter 7. These voltage digital signals and current digital signals are multiplied by a multiplier 8.

That is, the instantaneous power, which is the product of the two, is calculated, and the instantaneous power is integrated in the integrator 10 through the entire polarity switching circuit 9 to obtain the electric energy.

In FIG. 1, the polarity of the voltage input signal E, is inverted, but the polarity of the current input signal 1. The polarity of In may be reversed. It is only necessary to invert one of the sums fi, E, and . For example, if the polarity of the current input signal 'in is inverted, then in the above equation (1).

All you have to do is to substitute w→−W, and the result is In.

Lying down - XV = -2E r c + zωtoys (ωt -
ψ)−l”i v.Fl・IeCGS(鴫−ψ)+l'
iV. , −E−ωt+vo,・VOF2 +VOF
'3 Integrating this over the next period (in other words, integrating from 9T to 2T) gives -wh□ri (-W)at = T (-EeIeccsψ+("OFl・VOF2
+vOF3) ) −(3) Here, the equation (2) and the equation (
3) From the formula, find the average 1 of pw and -Wh2, and get Whl-wh2=TE I cm (?
e e This TE I casψ is the accurate power for one cycle. That is, by integrating the polarity voltage power and the reversed power over a predetermined time period, it is possible to accurately measure the amount of power.

By the way, as shown in FIG.
8 and 19, the voltage data and current data are stored in memories 22 and 23, respectively, through an analog-to-digital converter (A/D) 20, and multiplied by a multiplier 24. You can also do this. Note that when an oversample encoder is used in the analog-to-digital converter 20, two encoders may be used.

Furthermore, in the embodiment shown in FIG. 1, regardless of the type of analog-to-digital converter, the square multiplier 8. Polarity switch9. and the integrator 1O may be configured by hardware such as an IC, or may be realized by software such as a microcomputer.

Further, the period (time) of polarity switching may be longer or shorter than the - period as long as the polarity switching period is the same time for forward and reverse polarity.

〔Effect of the invention〕

As explained above, in the present invention, the voltage or current signal and the integrated output of the voltage signal and current signal are synchronized, the polarity is inverted, and the integration is performed for a predetermined time, so it is possible to eliminate errors caused by offsets that occur in analog circuits. This has the effect of realizing a highly accurate power meter circuit with a simple configuration.

[Brief explanation of the drawing]

1 is a diagram showing one embodiment of the power meter circuit according to the present invention, FIG. 2 is a diagram showing an equivalent circuit for explaining the operation of a conventional power meter circuit, and FIG. 3 is a diagram showing an example of the power meter circuit according to the present invention. FIG. 3 is a diagram showing main parts of an example. l...Converter (P, T,), 2...Polarity changeover switch, 3゜6...Amplifier (Anlp), 4, 7
, 20-...Analog-digital converter (A/D)
, 5... Current transformer (C, T,), 8... Denotal multiplier, 9... Polarity switch, 10... Integrator. 11, 1.3... signal source, 12.14... input signal source. 15...output offset), 16...multiplier. Foil 3 figure 9 5 2

Claims (1)

[Claims] 1. Convert the AC voltage and AC current to predetermined signal levels, perform analog-to-digital conversion to obtain digital voltage data and digital current data, and calculate the product of the digital voltage data and the digital current data. A power meter circuit for obtaining integrated power data by integrating, comprising an inverting means for synchronizing and inverting the polarity of either the alternating current voltage or the alternating current and the polarity of the product at predetermined time intervals. A power meter circuit characterized by: 2. The power meter circuit according to claim 1, wherein the analog-to-digital conversion is performed by an oversampling A/D converter.