JPS5819068B2 - Denshiki Denryokuriyokei - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a watt-hour meter, and particularly to an electronic watt-hour meter that can perform highly accurate measurements with a simple configuration.

Currently, inductive type and other integrated wattmeters are often used to measure the amount of commercial power, but they have problems in terms of lifespan.
Instruments had to be replaced periodically.

Therefore, in response to the demand for longer lifespan, electronic watt-hour meters are being considered.

One possible method for this electronic watt-hour meter is a method in which a voltage waveform and a current waveform are multiplied in an analog manner, converted into digits, and integrated.

However, this method has the disadvantage that it cannot be put to practical use because it cannot provide a highly accurate analog multiplier.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an electronic watt-hour meter that is inexpensive and capable of calculating the amount of electric power with high accuracy.

First, the principle of the present invention will be described.

When the voltage is V and the current is I, the electric power P is P=VI, and the electric energy Q is expressed by its time integral value as shown in the following equation.

Here, the frequencies fV and fI of the voltage waveform and current waveform include the following components, where f is the fundamental frequency.

However, mf and nf are voltage waveforms. and the highest frequency of the current waveform.

On the other hand, the frequency f of the power waveform is fp:f, 2f, 3f,...,(m10)f...(
4).

According to the sampling theorem, in order to completely obtain information about a certain waveform, sampling should be performed at a frequency higher than twice the highest order frequency included in the waveform.

Therefore, it is sufficient to sample the power waveform at a frequency higher than 2(m+n)f, but an analog multiplier is required as described above to obtain the power waveform.

To avoid this, the present invention samples the voltage and current waveforms individually.

In order to obtain the power amount Q shown in equation (1), it is sufficient to multiply the sample value of the voltage waveform obtained by the above sampling by the sample value of the current waveform, and then integrate the multiplied values.

Note that if this multiplication were to be performed directly, an analog multiplier would be required, so in reality, each sample value is converted into a digital value before multiplication is performed.

This calculation is expressed as follows. Q-ΣVI・Δ
T2ΔTΣVI (5) Here, ΔT is the sampling period.

Hereinafter, ΔT will be expressed as follows. However, b is a number larger than 2 (does not have to be an integer).

A of the sample value of the voltage waveform and the sample value of the current waveform
The DD conversion and multiplication operations must be completed before the next sample is taken.

In other words, it must be completed within a time shorter than ΔT.

Here, b (m+n) in the force equation is at least larger than 4, so for example, when f = 50 Hz, ΔT is shorter than 5 ms.

Therefore, A/D conversion speed and multiplication speed are required to be very fast.

In particular, multipliers are expensive even if they are digital, so when measuring three-phase power, for example, it is desirable to use a multiplier in common for measuring the power amount of each phase. In that case, the A/D conversion speed and multiplication speed need to be three times faster than in the single-phase case.

Furthermore, in order to share the multiplier when calculating the electric energy of a large number of power systems separately, it is necessary to use a multiplier with a correspondingly high speed.

Converters and multipliers that operate at such high speeds are difficult to implement with current technology, and even if they could be implemented, they would be extremely expensive.

The present invention attempts to reduce the operating speed required of A/D converters and multipliers by sampling voltage and current waveforms at specific time intervals longer than the intervals shown in the equation. be.

That is, in a power system, it can be considered that voltage and current waveforms are almost always the same and repeated within a relatively short period of time.

In this case, the sampling time interval can be chosen as follows.

However, a is an integer of 1 or more.

be. Here, when a-1, sampling is performed once per cycle of the fundamental wave frequency f, and the positions are sequentially ΔT
It means to shift by increments.

Further, when a = 2 or more, it means that sampling is performed 11 times every two cycles or more, and similarly, the positions are sequentially shifted by ΔT.

In this case, the electric energy Q is Q-ΣVI(-+ΔT)-(-+Δ
T) ΣVI... (9) f This is expressed as f, which is substantially the same as the equation (5), just by reducing the number of samplings.

Comparing equation (7) with equation (8), (-+ΔT)=(ab(m+n)+1)ΔT, and the sampling time interval is (ab(m+0)+1) times larger.

Since b (m 10 units) is larger than 4 as mentioned above, a-
1, the sampling time interval will be at least 5 times larger.

That is, the operating speed of the A/D converter and multiplier can be lowered.

Of course, the operating speed can be further reduced by increasing the values of a and b.

The sampling time interval is It is also possible to do this.

In this case, the sampling position is ΔT for each sampling.
It will gradually shift forward.

Similar effects can also be obtained in this manner. An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is a voltage detector that detects the voltage in the desired power system or the voltage obtained by dividing it.
Generates a voltage waveform signal as shown in .

Reference numeral 2 denotes a current detector which detects the current in the power system or a current obtained by branching it as a voltage, and generates a current waveform signal as shown in FIG.

The outputs of voltage detector 1 and current detector 2 are led to sampling and hold circuits 3 and 4, respectively.

Reference numeral 5 denotes a sampling pulse generation circuit which generates sampling pulses at time intervals shown in equation (8) and supplies them to sampling and hold circuits 3 and 4.

For example, if a == 1 in equation (8), the sample/7'' pulse will be as shown in FIG. 2 SP.

Sampling and holding circuits 3 and 4 receive this sampling pulse, sample the voltage waveform signal and current waveform signal from detectors 1 and 2, and hold them for a certain period of time until the conversion operation of the next stage VD converter is completed. .

The outputs of the sample and hold circuits 3.4, ie, the samplings, are converted into digital values by NΦ converters 6 and 7, respectively, and then multiplied by a multiplier 8.

The multiplied value calculated by this multiplier 8 represents the instantaneous power P.

Therefore, by integrating this multiplication value with an integrator 9, a digital value corresponding to the amount of electric power Q can be obtained.

The output value of this integrator 9 is displayed on a digital display 10.

With this configuration, since a digital multiplier is used as the multiplier 8, the electric power amount can be determined with higher precision than in a method in which the voltage waveform and the current waveform are directly multiplied in an analog manner.

Further, since the voltage waveform and current waveform are sampled at long time intervals, there is an advantage that inexpensive A/D converters 6, 7 and multiplier 8 that operate at low speeds can be used.

Note that it goes without saying that the sampling time interval can be changed in various ways within the range that satisfies equation (8) or equation (10).

Furthermore, the present invention can be applied not only to single-phase power but also to measurement of three-phase power or the amount of power in multiple power systems, and as described above, the multiplier can be shared in this case.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing one embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of FIG. 1. 1... Voltage detector, 2... Current detector, 3, 4... Sampling hold circuit, 5.
...Sampling pulse generation circuit, 6, 7...
...VD converter, 8...Digicle multiplier,
9... Totalizer, 10... Digicle display.

Claims (1)

[Claims] 1 Voltage waveform and current waveform, respectively, are the fundamental wave frequencies of the voltage waveform and current waveform, mf is the highest frequency of the stain pressure waveform, nf is the highest frequency of the current waveform, and a is an integer of 1 or more. , b is a number larger than 2), means for converting each sample value of the voltage waveform and current waveform obtained by this means into a digital value, and An electronic system characterized by comprising means for multiplying a digital value corresponding to a voltage waveform by a digital value corresponding to a current waveform, and a means for calculating electric energy by integrating the multiplied values obtained by this means. Electric energy meter.