JPH063384A - Electronic watthour meter - Google Patents

Abstract

PURPOSE:To obtain an accurate measurement value where influence of DC offset and light load characteristics is eliminated. CONSTITUTION:An adder 12 integrates an instantaneous value data output from an A/D converter 2 at each time indicated by an addition time setter 11 and then gives the result for each unit integration time and the integration count to an arithmetic unit 13. The arithmetic unit 13 divides the integration time by the integration count to calculate the DC offset per instantaneous value, thus generating a compensation data. An adder/subtractor 5 adds or subtracts the compensation data content to and from the output data of the A/D converter 2, thus eliminating the DC offset from the output data of the A/D converter 2. An adder 14 and an arithmetic unit 15 perform a similar processing to an adder/subtractor 6. A light load characteristic compensation data for compensating an error when a power feeder line is lightly loaded is set in a light load compensation value setter 16, the adders/subtractors 5 and 6 add or subtract the output data of the A/Ds 2 and 4 even for a light load compensation data, thus compensating the light load error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic watt hour meter for determining load power on a power feeding line based on a digital signal obtained by analog-digital conversion of a signal proportional to the power of the power feeding line. is there.

[0002]

2. Description of the Related Art With the development of electronic equipment, in the field of watt-hour meters, electronic watt-hour meters that measure digitally are about to replace conventional inductive watt-hour meters in recent years.

This electronic watt-hour meter converts a voltage signal and a current signal proportional to a voltage and a current on a power feeding line into a digital signal and multiplies and converts them to obtain power data.
The amount of power is calculated by accumulating this power data, and now that the development of semiconductor devices is remarkable, it is operating in a form suitable for the times, and it is possible to improve the performance as the capabilities of the device improve. Has sex.

A voltage signal obtained by analog-digital conversion of a voltage signal whose instantaneous value and effective value are proportional to the load voltage is represented by V, and a current signal whose instantaneous value and effective value are proportional to the load current is analogized. -The digitally converted current signal is represented by I, and the DC offsets on the voltage circuit side and the current circuit side of the analog circuit from the power supply line to the analog-digital converter are Δdcv and Δdci, respectively, and the load current is more in phase than the load voltage. If it is delayed by the angle θ, then eR = 2 ^(1/2) VR sin ωt + Δdcv (1) iR = 2 ^(1/2) IR sin (ωt−θ) + Δdci (2), and the instantaneous power pR is , PR = VR IR (cos θ-cos (2ωt-θ)) +2 ^(1/2) VR sin ωt Δdci +2 ^(1/2) IR sin ωt Δdcv + Δdcv Δdci (3) where ω is each frequency , T represents time).

The electric energy corresponds to the integral of pR in the equation (3). That is, a certain time T in the equation (3)
The integrated value of

[0006]

[Equation 1] And this is the amount of power.

[0007]

However, there are still unsolved problems in the electronic power meter described above.

One is the problem of DC offset from the power feed line to the analog-to-digital converter.

As is clear from the equation (4), (3)
The second and third terms in the equation become zero, but the influence of the fourth term on the DC offset remains. Therefore, the measured power amount includes an error due to the DC offset. This DC offset is constant over the entire range of load current, and the smaller the load current, the greater the influence on power. That is, the lighter the load on the watthour meter, the greater the error amount included in the measured power amount.

Another problem is the influence of characteristic changes of constituent elements of instrument circuits, such as transformers and analog-digital converters, depending on the load condition. The error amount in the negative direction increases due to the characteristic of.

An object of the present invention is to provide an electronic watt-hour meter with improved measurement accuracy by solving the above problems.

[0012]

The electronic watt hour meter of the present invention is a power data generator for generating power data based on a result of a signal proportional to voltage and current on a power feeder being adjusted by a correction signal value. Means and the data proportional to the voltage and current on the power feed line are accumulated for a preset time, and then the DC offset per unit time included in the voltage and current on the power feed line is calculated, and the influence thereof is calculated. DC offset compensation data generating means for generating DC offset compensation data for compensation and giving this to the power data generating means as the correction signal is provided.

Further, in the electronic watt-hour meter of the present invention, light load characteristic compensation data for compensating an error when the power feeder is in a specific light load state is given to the power data generating means as a correction signal. It is desirable to have a compensation data generating means.

[0014]

According to the present invention, when the AC signal having no DC offset is integrated for at least one cycle and an integral multiple of the time, the integrated value becomes zero, and therefore the DC offset compensation data generating means By counting the actual power data proportional to the actual power on the power supply line, the AC component is canceled and becomes zero, and only the DC offset component is left as a value larger than zero. The offset is detected, DC offset compensation data is generated based on the result, and the power data generating means corrects the actual power digital signal based on this DC offset compensation data. It is possible to obtain a highly accurate measurement result in which the influence of the DC offset included in the power is removed.

Furthermore, by compensating for the error that occurs in the integrated value when the power supply line is in a light load state, a more accurate measurement result can be obtained.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an electronic watt hour meter according to an embodiment of the present invention.

In this figure, 1 is a transformer and 2 is an analog-digital (hereinafter referred to as AD) converter.
The primary side of the transformer 1 is connected to the power feeding line, the voltage of this power feeding line is stepped down to a value that can be handled by the AD converter 2 in the subsequent stage, and the voltage of the power feeding line is instantaneously supplied to the secondary side. It outputs a voltage signal whose value and effective value are proportional. AD
The converter 2 samples the instantaneous value of the secondary voltage signal of the transformer 1 and outputs code data indicating each sampled value.

Reference numeral 3 is a current transformer, and 4 is an AD converter. The primary side of the current transformer 3 is connected to a power feed line, and the current of the power feed line is converted into a small current to a value that can be handled by the AD converter 4 in the subsequent stage, and the secondary side is connected to the power feed line. It outputs a current signal whose instantaneous value and effective value are proportional to the current.
The AD converter 4 samples the instantaneous value of the secondary current pressure signal of the current transformer 3 and outputs code data indicating each sampled value.

Reference numerals 5 and 6 are adder / subtractors, and these adder / subtractors 5 and 6 are for compensating the output code data of the AD converters 2 and 4. The adder / subtractor 5 adjusts the code data from the AD converter 2 by a correction signal value (that is, DC offset compensation data and light load compensation data described later). The adder / subtractor 6 corrects the code data from the AD converter 4 with a correction signal value (that is, DC offset compensation data and light load compensation data described later).
The amount is adjusted.

Reference numeral 7 is a multiplier, 8 is an integrator, 9 is a pulse generator, and 10 is a display. The output data of the adders / subtractors 5 and 6 are multiplied by the multiplier 7 and converted into power data. The integrator 8 integrates this power data for a fixed time and supplies the integrated value to the pulse generator 9. Then,
This pulse generator 9 outputs the pulse train of the number according to the input value. The output pulse is given to the display unit 10, and the display unit 10 adds the pulse number to the present integrated value and displays the electric energy every moment. The output pulse of the pulse generator 9 is also output to the external output terminal, and the test of the power meter can be performed using this external output terminal.

Reference numeral 11 is an addition time controller, reference numerals 12 and 14 are adders, and reference numerals 13 and 15 are direct-current offset calculators, which generate the direct-current offset compensation data. Here, the principle will be described before describing those functions.

First, when the voltage signal and the current signal shown in the above equations (1) and (2) are respectively integrated and the respective average values of the times are obtained, if the integration time is sufficiently long, the AC component becomes almost zero. Therefore, only the DC offset remains. By subtracting the DC offset component from each of the voltage signal and the current signal, only the AC component can be extracted.

The addition time setter 11 is set with a time corresponding to the integration time, and outputs a control signal indicating the set time.

The adder 12 adds the instantaneous value code data output from the AD converter 2 every moment to the addition time setter 11.
Of the time control signal, and the result and the number of times of integration are given to the DC offset calculator 13. The DC offset calculator 13 divides the input integrated value by the number of input integrations to calculate the DC offset per instantaneous value, and generates the DC offset compensation data by inverting the sign of the calculated DC offset. The output of the DC offset calculator 13 is input to the adder / subtractor 5, and operates to reduce or add the output data value of the DC offset calculator 13 to the output data value of the AD converter 2. As a result, the DC offset component is removed from the output data of the AD converter 2.

Adder 14 and DC offset calculator 15
Performs the same processing on the adder / subtractor 6. This allows
The DC offset component will be removed from the output data of the AD converter 4.

FIG. 2 shows a current characteristic in which the DC offset is not compensated and a current characteristic in which the DC offset is compensated for in comparison.

As described above, as is clear from this figure, the error due to the DC offset component has a greater effect on the electric power as the load current becomes smaller. That is, the lighter the load on the watthour meter, the greater the error amount included in the measured power amount. In the present invention, since the DC offset component that causes this error is compensated for, a highly accurate measurement value can be obtained. It should be noted that FIG. 2 shows the characteristics in a state in which an error due to a light load described below is ignored.

Next, the light load compensation value setting device 16 is set with light load characteristic compensation data for compensating for an error that occurs in the integrated value when the power supply line is in a specific light load state. This data is set based on the actual test data of the power meter. In the adder / subtractors 5 and 6, the output data of the corresponding AD converters 2 and 4 is also adjusted by the data of the light load compensation value setting device 16.

FIG. 3 shows a current characteristic in which the light load is not compensated and a current characteristic in which the light load is compensated.

As shown in this figure, as the load of the watt hour meter becomes lighter, the error amount in the negative direction increases due to the characteristics of the circuit constituent elements. In the present invention, since the offset amount due to this light load is also compensated,
When the load is light, the added / subtracted value is effective, and the power measurement value with higher accuracy can be obtained. In addition, in order to compensate for the error caused by the light load, in other words, the compensation value of the DC offset is adjusted by the light load compensation value, and the influence of the DC offset is used in reverse.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above.

For example, in the above embodiment, the conversion of the current signal into digital data is performed in the current mode, but
It may be performed after converting to the voltage mode.

In the above embodiment, the offset compensation operation is performed during the generation of the power data, that is, at the stage of the voltage or current data of the AD converters 2 and 4, but it is multiplied and converted into the power data. The offset compensation operation may be performed later.

Further, in the above embodiment, the AD converters 2 and 4 are configured to output the code data of the instantaneous value, but they may be configured to be the counting type. In this case, the adders 12 and 14 are configured to integrate the pulse trains according to the format, and the DC offset calculator 1
In 5, the integrated value is divided by the integrated time to calculate a DC offset per unit time, and an add / subtract pulse train corresponding to the calculated DC offset is output to the adder / subtractors 5 and 6.
Further, the light load compensation value setting device 16 that outputs a pulse train is also used. The multiplier 7 or both adders / subtractors 5 and 6 may be converted into data indicating the number of pulses, and may be multiplied and converted to generate power data.

[0036]

As described above, according to the present invention, if an AC signal having no DC offset is integrated for at least one period and an integral multiple of the time, the integrated value becomes zero. By counting the actual power data proportional to the actual power on the power feed line in the DC offset compensation data generating means, the AC component is canceled and becomes zero, and only the DC offset component is left as a value larger than zero. The DC offset is detected using the integration result, the DC offset compensation data is generated based on the result, and the power data generating means corrects the actual power digital signal based on the DC offset compensation data. Therefore, it is possible to obtain a highly accurate measurement result in which the influence of the DC offset contained in the power on the power supply line is removed.

Furthermore, by compensating for the error that occurs in the integrated value when the power feed line is in a light load state, a more accurate measurement result can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an electronic watt hour meter according to an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram showing current characteristics not compensated for DC offset and current characteristics compensated for DC offset in comparison.

FIG. 3 is a characteristic curve diagram showing current characteristics in which the light load characteristics are not compensated and current characteristics in which the light load characteristics are compensated.

[Explanation of symbols]

 1 Transformer 2 Digital-analog converter of voltage signal 3 Current transformer 4 Digital-analog converter of current signal 5 Adder / subtractor of voltage data 6 Adder / subtractor of current data 7 Multiplier 11 Addition time setter 12 Addition of voltage data Unit 13 DC offset calculator for voltage data 14 Adder for current data 15 DC offset calculator for current data 16 Light load compensation value setter

Claims (2)

[Claims] 1. A power data generating means for generating power data based on a result of a signal proportional to a voltage and a current on a power feeding line being adjusted by a correction signal value, and a power data generating means proportional to a voltage and a current on the power feeding line. After integrating the data for a preset time, the DC offset per unit time included in the voltage and current on the power supply line is obtained, and DC offset compensation data for compensating for the influence is generated, and this is generated. An electronic watt-hour meter, comprising: a DC offset compensation data generating unit that supplies the electric power data generating unit with the correction signal. 2. A light load characteristic compensation data generating means for giving to the power data generating means light load characteristic compensation data for compensating an error when the power supply line is in a specific light load state. The electronic watt hour meter described in 1.