JPH02173576A - Digital watthour meter - Google Patents

Abstract

PURPOSE:To miniaturize a circuit scale by using analog-ditital encoding devices of oversampling type. CONSTITUTION:Analog filters 21a and 21b, oversampling type encoding devices 23a and 23b, digital filters 24a and 24b, a multiplier 25, and a digital adding device 28 are provided. An analog voltage value at the measuring point is inputted to the filter 21a, wherein frequency components higher than Nyquist frequency are removed, then supplied to the encoding device 23a and outputted as a digital voltage signal therefrom. In the same manner, a digital current signal is outputted from the encoding device 23b, then both signals are multiplied by the multiplier 25 and cumulated by the adding device to obtain the electric energy. With this arrangement, the circuit scale for the digital watthour meter can be integrated in miniature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a watt-hour meter, and more particularly to a digital watt-hour meter using an oversampled encoder.

[Prior Art] Power meters using digital technology have been known as power meters, and for example, there is a power meter having the configuration shown in FIG. 5 as this type of power meter.

Referring to FIG. 5, when measuring the amount of electric power, an analog voltage signal (analog voltage value) is input to an analog filter 7a, and the analog voltage signal has frequency components higher than the Nyquist frequency removed by the analog filter 7a. It is applied to the sample and hold circuit 8a as a filtered analog voltage signal. The sample and hold circuit 8a samples and holds this filtered analog voltage signal. In other words, it samples and sends out a sampled voltage signal. This sampled voltage signal is then quantized by the analog-to-digital converter 9a and converted into a digital voltage signal.

On the other hand, the analog current signal corresponding to the analog voltage signal (
analog current value) is input to the analog filter 7b,
Thereafter, the signal is similarly converted into a digital current signal via the sample-and-hold circuit 8b and the analog-to-digital converter 9b. These digital voltage signals and digital current signals are input to a digital multiplier 10, where they are multiplied and a digital multiplied signal is sent out. This digital multiplication (No. 4) is cumulatively added by a digital accumulator consisting of an adder 11 and a memory 12, thereby obtaining the electric energy.

[Problem to be solved by the invention] By the way, in the case of the above-mentioned conventional power consumption of 51゛, the =
In order to increase the single-layer viscosity, it is necessary to increase the accuracy of the analog/digital converter5, and as a result, the circuit scale of the analog circuit used in the analog/digital converter increases, and moreover, the circuit size of the analog circuit used in the analog/digital converter increases. The precision of the element must be increased.

However, with current device technology, it is extremely difficult to realize an analog-to-digital converter with a resolution of 12 bits or more without trimming the elements. In other words, there is a limit to the miniaturization of analog circuits.

On the other hand, since the Nyquist frequency of the analog filter is close to the highest frequencies of the analog voltage signal and analog current signal, there is a problem that the circuit scale of the analog filter increases.

Therefore, there is a problem that a digital watt-hour meter cannot be realized in one integrated circuit by integrating an analog filter, a sample-and-hold circuit, an analog-to-digital converter, a digital multiplier, and a digital accumulator.

An object of the present invention is to provide digital power that can be realized in one integrated circuit. In other words, the objective is to provide a digital watt-hour meter with a small circuit scale.

[Means for Solving the Problems] According to the present invention, analog voltage values and analog current values at points where electric energy is measured are manually input, and frequency components higher than a predetermined Nyquist frequency are removed. , an analog filter means for outputting a first voltage value and a first current value, and sampling the first voltage value and the first current value respectively based on a sampling frequency and converting them into digital voltage values and digital current values. A digital device characterized in that the digital current value and the digital voltage value are multiplied (17) to obtain digital power, and the digital power is accumulated to obtain the amount of power. A power meter is obtained.

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

First, referring to Fig. 1, this digital watt-hour meter is:
Analog filters 21a and 21b, oversample encoders 23a and 23b, digital filter 24a
and 24b1 multiplier 25 and adder 26 and memory 27
A digital adder 28 is provided.

The analog voltage signal (analog voltage value) at the point where the electric energy is measured is input to the analog filter 21a, where frequency components higher than the vicinity of the Nyquist frequency are removed, and a filtered analog voltage signal is output. This filtered analog voltage signal is then sent to an oversampling encoder 23.
given to a.

Ru. As shown in FIG. 2, the output of the local digital-to-analog converter 36 is subtracted from the filtered analog voltage signal by an analog subtracter 31, and a difference voltage signal is output. This differential voltage signal is then successively integrated by an analog integrator 32 and output as an integrated voltage signal. This integrated voltage signal is quantized by a quantizer 33 and becomes a digital voltage signal. This digital voltage signal is processed by a digital delay device 34.
Given a delay of one sampling time, the signal is integrated by the digital integrator 35 and becomes the output digital voltage signal of the oversampled analog/digital encoder 23B.

On the other hand, the output of the digital delay device 34 and the output of the digital integrator 35 are added by a digital adder 37, and the addition result is input to the local digital-to-analog converter 36. The output of the local digital-to-analog converter is then given to an analog subtracter 31.

Here, the filtered analog voltage signal is x, the quantization noise is q,
Let the output digital voltage signal be y and X.

Let the zt transformations of q and y be X, Q, and Y, respectively.1.
If the delay of one sampling time is Z-1, the output of the oversampling encoder is Y-[X0(1-Z-')Ql Z-'...
...(1) gives lj. Therefore, the output digital voltage signal has the form of a hollow wave analog voltage signal component plus a quantization noise component.

FIG. 3 shows the frequency spectrum of the output digital voltage signal. Here, normalized angular frequency ~ 2 x π x (sampling frequency)...
・(2) It is.

In an oversampled analog-digital encoder, the scale of its analog circuitry can be reduced. By removing quantization noise under the condition of a 7-bit digital-to-analog converter, 13-bit precision can be obtained. This quantization noise is filtered by digital filter 2.
Analog-to-digital conversion can be performed by removing the signal in step 4a.

Similarly, an analog current signal (analog current value) is input to an analog filter 21b, and an oversampled analog/digital encoder 23b.

It is output as a digital current signal via the digital filter 24b. Note that the configuration of the oversampled analog/digital encoder 23b is similar to that of the oversampled analog/digital encoder 23a.

The digital voltage signal from the digital filter 24a and the digital voltage signal from the digital filter 24b are multiplied by a multiplier 25 and accumulated by a digital accumulator 28 to obtain the amount of power.

Next, other embodiments of the present invention will be described.

Referring to FIG. 4, this embodiment differs from the embodiment shown in FIG. 1 in that digital filters 24a and 24b are removed, and the other configurations are the same as in the embodiment shown in FIG.

By the way, if the output digital voltage signal of the oversampling encoder 23a is y, the filtered analog voltage signal is X, and the quantization noise is q, then the vth
From the v(]) formula, y −x +Q ・・・・・・
(3) It is expressed as v v ■. Similarly, the oversample encoder 23b
The output digital current signal of y, the filtered analog current f
Summer where A゛ is x, g quantization noise is ql, and yi ""i + qi...
... is expressed as (4).

Therefore, the power P is P=Vv "yl - (x + q) - (x + q,)v v
1 ■X X ” X q +X q +
qv Q 1vl vi iv (5). Here, Q and J are random (No. 8 ν), and between X and Q +X' and q, and between q and J
l+v
v There is no correlation. Therefore, for the electric energy that is the time integral of P, term 2.3.4 in equation (5) becomes 0, so PdL”
Y 'Y dL" Xv X1dt・
...(6) becomes.

As a result, the digital low-pass filters 24a and 24b for removing quantization noise, which are normally required when using an oversampled analog-digital encoder, are not required, resulting in the configuration shown in FIG. 4.

Note that the operation for determining the amount of power is the same as that in the embodiment shown in FIG. 1, so a description thereof will be omitted.

[Effects of the Invention] As explained above, since the present invention uses an oversampling type analog-digital encoder, the sampling frequency can be made sufficiently higher than the highest frequency of the human input signal, and therefore the analog filter can be reduced in scale. As a result, the scale of the analog circuit can be reduced, the required element precision can be reduced, and trimming is not necessary.

Further, a digital low-pass filter normally required in an oversampled analog-to-digital converter can be omitted, and a digital watt-hour meter with a small circuit scale can be obtained. In other words, a digital watt-hour meter can be integrated with a small circuit scale.

23a, 23b... Oversample A/D encoder, 24a, 24b... Digital filter, 25...
- Multiplier, 28...digital cumulative adder.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the digital watt-hour meter according to the present invention, FIG. 2 is a block diagram showing the configuration of the oversampled analog digital encoder shown in FIG. 1, and FIG. 3 is the oversampled analog digital encoder shown in FIG. FIG. 4 is a block diagram showing another embodiment of the digital watt-hour meter according to the present invention, and FIG. 5 is a block diagram showing a conventional digital watt-hour meter. . 21a, 21b...Analog low-pass filter, second
Figure input No. 1 Figure input OdB

Claims (1)

[Claims] 1. The analog voltage value and analog current value at the point where the electric energy is measured are input, and the first voltage value and the first current value are obtained by removing frequency components higher than a predetermined Nyquist frequency vicinity. It has analog filter means for outputting, and oversampling encoding means for sampling the first voltage value and the first current value based on a sampling frequency and converting them into digital voltage values and digital current values, A digital watt-hour meter characterized in that digital power is determined by multiplying a digital current value and a digital voltage value, and the amount of power is determined by accumulating the digital power.