JPH01239475A - Electronic watthour meter - Google Patents

Abstract

PURPOSE:To simplify a computation and to make a microcomputer, etc., usable by taking signals proportional to a load voltage and a load current of a feeder into an arithmetic part after they are rectified with a half-wave and converted to the digital values, and making the computation on the data in the most common with an adding. CONSTITUTION:By an auxiliary transformer 1, the signal proportional to the load voltage of the feeder is supplied to an input terminal 9a on a rectifier circuit 9, and by an auxiliary current transformer 2, the signal proportional to the load current of the feeder is supplied to the input terminal 10a on the rectifier circuit 10. In each rectifier circuit 9, 10, the inputted signals are rectified with the half-wave and inputted to 1st and 2nd channels 15a, 15b of an A/D converter circuit 15. In this converter circuit 15, each signal inputted by means of receiving a channel number and a command from the arithmetic part 17 are converted to digital values, and these converted data are supplied to the arithmetic part 17. Then in the arithmetic part 17, the data written are made to compute in the most common with the adding, and the computed results are displayed on a display part 8.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an improvement in an electronic watt-hour meter employing a microcomputer.

"Prior Art" FIG. 8 is a block diagram of a conventional electronic watt-hour meter employing a microcomputer. In the same figure, 1
2 is an auxiliary transformer, and 2 is an auxiliary current transformer, which respectively supply a signal proportional to the load voltage of the power supply line and a signal proportional to the load current of the power supply line to the sample and hold circuit 3.4. The sample and hold circuit 3.4 samples and holds the instantaneous value of the input signal at a cycle faster than the cycle of the input signal.

The sampled and held input signal is sent to an A/D conversion circuit 5.
After each of the signals is converted into a digital value in step 6, it is taken into a calculation section 7, subjected to predetermined calculation processing, and displayed on a display section 8.

"Problem to be Solved by the Invention" In the prior art as described above, the A/D conversion circuit 5.
Since the data digitally converted in step 6 and taken into the calculation unit 7 is AC instantaneous value data, the electric energy can be obtained by repeating the multiplication of the voltage data and the current data and the addition of the results a certain number of times. Therefore, the arithmetic unit 7 is required to perform complex arithmetic processing mainly consisting of high-speed multiplication.

In view of this point, the present invention is designed to allow simple arithmetic processing.

"Means for Solving the Problem" A signal proportional to the load voltage of the power supply line and a signal proportional to the load current of the power supply line are half-wave rectified and then converted into digital values.

"Operation" According to the present invention, the amount of electric power can be calculated by performing calculations mainly based on addition from data converted to digital values and taken into the calculation section, and high-speed multiplication is not required, so it is inexpensive. A microcomputer can be used.

"Example" Embodiments of the present invention will be described in detail below based on the drawings.

Note that the same parts as those in the above embodiment are given the same numbers, and the explanation thereof will be omitted.

FIG. 1 is a block diagram of an electronic watt-hour meter showing one embodiment of the present invention. In this figure, 9 is a rectifier circuit that half-wave rectifies the signal supplied from the auxiliary transformer 1 to the input terminal 9a, and 10 is a rectifier circuit that half-wave rectifies the signal supplied from the auxiliary transformer 2 to the input terminal 10a. It is. Further, reference numeral 15 denotes an A/R which supplies the signals from the rectifying circuits 9 and 10 to the first channel 15a and the second channel 15b, respectively.
The D conversion circuit 17 is a calculation section that performs predetermined calculation processing on the digital data taken in from the A/D conversion circuit 15 to calculate the amount of electric power.

Next, the operation of the above embodiment will be explained.

The auxiliary transformer 1 supplies a signal proportional to the load voltage of the power supply line to the rectifier circuit 90 input terminal 9a. The auxiliary current transformer 2 supplies a signal proportional to the load current of the power supply line to the input terminal 10a of the rectifier circuit 10.

Rectifier circuits 9 and 10 half-wave rectify the signals supplied to input terminals 9a and 1Qa, respectively, and supply them to first channel 15a and second channel 15b of A/D conversion circuit 15, respectively.

The A/D conversion circuit 15 receives a channel number and a command from the calculation section 17 through a control line (not shown), and sequentially A/D converts the signals supplied to the input terminals 15a and 15b, and the data is sent to the calculation section 17. be taken in.

The arithmetic unit 17 performs predetermined arithmetic processing on the captured data to calculate the amount of power and displays it on the display unit 8 .

Here, the content of the calculation process performed by the calculation unit 17 will be explained.

FIG. 2 shows general AC waveforms shown to explain the calculation principle, 11 shows the voltage waveform, 12 shows the current waveform, and the current waveform 12 has a phase angle φ from the voltage waveform 11.
This indicates that there is a delay. If the half-cycle time of the voltage waveform 11 and the current waveform 12 is T, and the voltage waveform 11 is ysrnωt, then the average value of the half-cycle valve is , and a value proportional to the magnitude V of the voltage waveform 11 is obtained. Also, regarding the current waveform 12, the average value of the half-period valve is proportional to the effective component (directly is obtained.In addition, (1)
, (2), where K is a proportionality constant.

The meaning of equation (2) is from the average half-cycle of the area of the part surrounded by the code 03 A204 of the current waveform 12 in FIG. l! The value after subtracting l02h2 is IC0
This shows that it is proportional to 6φ.

Since the current waveform 12 is a sine wave, the area of the waveform portion surrounded by 02A103 is 04A? It is equal to the area of the part surrounded by 0. Therefore, by subtracting the area of the waveform portion surrounded by the symbol 04A205 from the area of the waveform portion surrounded by the symbol 03A204, a value proportional to ICO3φ is obtained. Further, by adding the area of the waveform portion surrounded by the symbol @03A204 and the area of the waveform portion surrounded by the symbol 04A205, a value proportional to the magnitude I of the current is obtained.

FIG. 3 shows a case where the current waveform 12 leads the voltage waveform 11 by a phase angle φ. Regarding current waveform 12, code 03A is obtained from the area of the waveform portion surrounded by code o2A103.
By subtracting the area of the waveform surrounded by 204, lCo5φ
Since the area of the waveform surrounded by the code 03A204 is equal to the area of the waveform surrounded by the code 05A306, the value proportional to lCo8φ is obtained by the sign @0
Code 05A3 from the area of the waveform surrounded by 2A103
It is obtained by subtracting the area of the waveform portion surrounded by o6. Further, by adding the area of the waveform portion surrounded by the symbol 05A306 to the area of the waveform portion surrounded by the symbol 02A1Q3, a value proportional to the magnitude of the current ■ can be obtained.

FIG. 4 is also an explanatory diagram of the calculation principle, and shows how sampling is performed by dividing a half period of an AC waveform into n sections, and n pieces of data are obtained in the order of al, a2, . . . a. By adding the n1ljil data obtained in this way, a value proportional to the size of the AC waveform is given, as is well known as an algorithm called the area method.

Using this method, the code OAO2 of the alternating current waves in Fig. 4 is
To find the area of the waveform surrounded by , simply al, a
Although it would be impossible to add data of ak to ak, the error would be large, but it would be impossible to add data of ak to ak, but it would be impossible to add data of ak to ak. , an-1 . . . an+ and take the average value, the error can be reduced.

The size difference of the AC waveform in Fig. 4 is assumed to be 1, and the phase angles for a1 to aH are expressed based on 01. Let θ be the phase angle of the sampling interval, and θ0 be the sampling phase angle within each sampling interval. If, a1=s:00g,
a2=s! n(θ+θ0), a3=S1n(2
It is expressed as θ100)..., +1 for an-, -arl-
Expressing the phase angle based on 01, a,=sin
(θ-θ), a n-1=s i n (2θ〇1θ.)...so, al +82 +""+aH+an 10 an-1+'
・+1 to 10 an- (4), and the error is θ. Since it can be seen that this is caused by fluctuations in the range of O to θ/2, it is clear that the error can be reduced by increasing the number of half-cycle divisions n.

FIG. 5 is an explanatory diagram when the area method algorithm is applied to calculation of phase information. FIG. 5 shows that the AC waveform first changes from negative to positive at mark @03 within the sampling interval,
This shows a case where positive sampling data ak in the same interval is obtained. When the area of the part surrounded by the code Q and A204 is calculated using the above method, the actual waveform is the code 03.
Although it changes from negative to positive at , the same result as when it changes from negative to positive at code O-3, which is the start of the second interval, is obtained, and the negative waveform part surrounded by code 02A103 The area will be underestimated to the area surrounded by the symbol Q2A10'3. As a result, even though the actual phase information is φ, φ
It will be evaluated as −. The maximum difference between ψ and φ- may be the phase angle θ of the sampling interval. Although this phase difference is a value that can be ignored when only determining the magnitude of the AC waveform, it can cause a large error in calculations that include phase information. In other words, by increasing the sampling frequency, it is possible to reduce the phase error and perform calculations with high accuracy.

Now, FIG. 6 and FIG. 7 show the signal 11 proportional to the load voltage of the feeder line taken into the calculation unit 17 in consideration as described above.
This shows data for each period of the signal 12 which is proportional to the load current of the power supply line.

6 shows that the current phase is delayed φ, and FIG. 7 shows that the current phase is advanced φ.

In Fig. 6, the value obtained by the area method of the voltage waveform 11 is ΣV, the value obtained by the area method of the waveform portion of the current waveform 12 surrounded by the symbol 02AO3 is Σ■6, and the value surrounded by the symbol @03AO4. If the value similarly obtained for the waveform part is ΣIB, then the power consumption of the feeder line - is Σ■(ΣIA n1B)...
...(5) (Here, K is a proportionality constant) What can be obtained is as described above.

In addition, in FIG. 7, the code 02A1 of the current waveform 12 is
The value obtained by the area method of the waveform part surrounded by 03 is ΣIA,
As mentioned above, if the similarly obtained value of the waveform portion surrounded by the symbol 04A205 is ΣIB, the power consumption of the feeder line can be obtained by equation (5).

A predetermined calculation is performed on the power of the feeder line obtained in this manner to calculate the amount of power, and the amount of power is displayed on the display unit 8.

"Effects of the Invention" As detailed above, according to the present invention, it is possible to provide an electronic watt-hour meter that can calculate the amount of power by performing simple calculations mainly consisting of addition.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an electronic watt-hour meter showing an embodiment of the present invention; FIGS. 2, 3, 4, and 5 are AC waveform diagrams for explaining the principle; FIG. 7 is a relationship diagram of data taken into the calculation section, and FIG. 8 is a block diagram of an electronic wattmeter according to the prior art. In the figure, 9.10 indicates the rectifier circuit 15 and the A/D conversion circuit 17 as an arithmetic unit.

Claims (1)

[Claims] A rectifier circuit that separately performs half-wave rectification of a signal proportional to the load voltage of the power supply line and a signal proportional to the load current of the power supply line, and an A/D conversion circuit that digitally converts the signal output from the rectification circuit. An electronic watt-hour meter comprising: a calculation unit that performs predetermined calculation processing on the digital data taken in from the A/D conversion circuit to calculate the amount of electric power.