KR20100058251A - A method for temperature compensation of digital power meter - Google Patents

Abstract

PURPOSE: A method for correcting the temperature variation of a digital watt-hour meter is provided to correct a temperature error of all additional elements by correcting the measured electric energy using the coefficient of a fitting error curve. CONSTITUTION: An error of a measurement value about an input current is obtained in a plurality of watt-hour meters. Error data is secured. The error data is the mean value of the errors of the plurality of watt-hour meters. A fitting error function is obtained using a temperature variable. The coefficient of the fitting error function is inputted to the watt-hour meter. The temperature correction coefficient is obtained. The temperature correction coefficient is the difference between a real temperature and a temperature measured by the watt-hour meter. The fitting error of the output electric energy of the watt-hour meter is obtained using the temperature correction coefficient. A predicted input value is obtained. The predicted input value is the corrected error of the output electric energy.

Description

A method for temperature compensation of digital power meter according to temperature change of an electronic power meter

The present invention relates to a method for compensating a power amount according to a temperature change of an electronic watt-hour meter, and more particularly, to correct an error of a measured power amount value for an operation error of internal elements generated by a temperature change of an electronic digital watt-hour meter. The present invention relates to a power amount correction method according to a temperature change of an electronic watt-hour meter that is corrected for the entire device, not an element.

In general, the electronic digital electricity meter (hereinafter also referred to as an electricity meter), which is widely used in the industry, is composed of various electric and electronic devices, and converts analog data of voltage and current into digital data, calculates power using digital data, and calculates time. The amount of power is measured by accumulating the power change according to the flow.

The process of converting voltage analog data into digital data is performed by using a voltage divider circuit using a resistor to step down several tens or hundreds of volts into a few volts that can be converted digitally. Current transformers are used to convert high currents into low currents, resistances are converted to voltages, and the signals are digitally converted to analog / digital converters.

Internal devices for such operation have an error condition according to each driving condition, and an error occurs in temperature. Due to the temperature dependence of each of the internal devices, the amount of power measured by the wattmeter also has a temperature dependency corresponding to the sum of the errors of these devices, and an error occurs accordingly.

Accordingly, when the temperature increases or decreases during the digital conversion process, the characteristics of the resistor change, and the analog / digital converter also has a change characteristic according to temperature.

Since the change of the data conversion characteristic is due to the material and physical characteristics of the electronic digital watt-hour meter, it is not a problem that is easily overcome. Therefore, it is necessary to predict the change of the data conversion characteristic to correct the current weighing value.

That is, the electricity meter is required to find the cause of the error and correct it because the accuracy of the measured value can be reduced when the measurement error is out of a certain range and the value as a measuring device can be lost.

As a conventional method of compensating the error of a watt-hour meter, a method of compensating an error of a device temperature such as an A / D converter inside an internal CPU has been proposed, and an error of temperature dependence of all devices of a watt-hour meter is corrected. There is no suggestion how to do this.

However, the general electronic digital watt-hour meter has a larger error caused by additional devices such as a current transformer than a device inside the CPU, so the error of the additional devices takes up a large portion of the total errors. In particular, current transformers used in current measurement react sensitively to temperature, which causes errors in temperature change.

If only the error of some devices, not the error of the entire meter, is corrected, a full error correction is not performed, which leads to a problem that the desired accuracy is not obtained.

The present invention has been invented to solve the above problems, in order to minimize the error of the electronic digital electricity meter to a certain range, the second approximation function (fitting error) fitting the error between the input value and the meter value of the electricity meter in advance It provides a power amount correction method according to the temperature change of the electronic watt-hour meter that stores the coefficient of the curve) and corrects the actual measured power value by using the same. The purpose is.

In order to achieve the above object, the present invention provides a power amount correction method according to a temperature change of an electronic power meter,

(a) obtaining an error E of the measured value Po with respect to the input current in the plurality of electricity meters, and obtaining error data E1 which is an average value of the errors E of the plurality of electricity meters; (b) obtaining the fitting error function (y = ax ² + bx + c) using the temperature as a variable by obtaining the error data E1 at a predetermined interval with respect to the actual temperature and then fitting the least squares method; (c) obtaining the fitting error function for each input current (i) and inputting coefficients (a (i), b (i), c (i)) to the wattmeter; (d) obtaining a temperature correction coefficient according to the difference between the temperature read by the electricity meter and the actual temperature; (e) obtaining a fitting error (Efit) that the output power value of the watt-hour meter has at the actual temperature at the time of measurement by using the temperature correction coefficient; (f) calculating the predicted input value Pfit by correcting the error of the output power amount value using Pfit ≒ Po / (1-Efit) as the measured power amount value as the measured value Po. Provided is a power amount correction method according to a temperature change of an electronic power meter, characterized in that the power amount correction method according to the temperature change of the electronic power meter.

Preferably, the error E of the measured value Po with respect to the input current in step (a) is obtained by multiplying the input current by a fixed voltage value to obtain the input value Pi, and E = (Pi-Po). It is characterized by obtaining using / Pi.

Also, in the step (e), the current value of the output power amount value is compared with a plurality of input currents (or power value data) to obtain two input currents closest to the current value of the output power amount value. Using the coefficients of the fitting error function corresponding to the two input currents, the fitting error function values at the actual temperature are obtained, and then the two fitting error function values are interpolated into internal components, thereby fitting the fitting error of the output power value (Efit). ) To be obtained.

Or preferably, in step (e), when the current value of the output power amount value is the same value as the input current (or power amount data), fitting error at the actual temperature by using the coefficient of the fitting error function corresponding to the input current A function value is obtained, and the fitting error function value is determined as a fitting error Efit of the output power amount value.

The power amount correction method according to the temperature change of the electronic power meter according to the present invention can obtain the effect of improving the accuracy of the measured power value by correcting the overall error of the electronic digital power meter represented by the sum of the errors of the internal devices due to the temperature. have.

In other words, by storing the coefficients of the fitting error curve of the electronic digital electricity meter calculated in advance, the measured power value is corrected using this to correct the temperature error of all the additional elements such as the current transformer and not only the CPU element, and reduce the temperature dependence. By improving the accuracy and precision of the electricity meter, the error of the electricity value can be minimized within a certain range.

In the case of power meters designed using the same devices, one can expect the temperature compensation coefficient to be reduced within a certain range by obtaining a temperature correction coefficient in one measurement.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present disclosure, and the singular forms “a”, “an” and “the” include plural forms unless the context clearly indicates otherwise.

There may be a plurality of embodiments of the present invention, and overlapping descriptions of the same parts as in the prior art may be omitted.

There are many causes of error of weighing value of general electronic digital wattmeter (hereinafter also referred to as wattmeter). Among them, the error due to temperature is due to the temperature dependence of each internal device. Current transformers (CTs) are sensitive to temperature, resulting in large temperature errors.

In order for the electricity meter to be operated with high precision due to seasonal temperature difference, the temperature error must be minimized or the error due to temperature must be corrected.

The present invention improves the metering accuracy of the electronic digital watt-hour meter by correcting and minimizing the error caused by the temperature change of the measured watt-hour value in order to use with precision.

To do this, the error is measured and corrected for the entire system, rather than just one or two devices, to minimize the error between the input power and the measured power.

Accordingly, the source of error is reduced by using elements with less temperature dependence firstly, and the input value (actual power value) input to the electricity meter and the measured value (measurement) output by the electricity meter are measured secondly by correcting the error. By reducing the error between power values, the value close to the actual power can be measured within a certain range error.

Hereinafter, with reference to the accompanying drawings will be described in detail the power amount correction method according to the temperature change of the power meter.

The present invention fits between the input value Pi and the metered value Po of the electricity meter in advance in order to minimize and correct the error of the electricity meter in which an error occurs in the measured energy value according to the temperature change within a predetermined range. Calculate and store the coefficient of the temperature compensation curve (fitting error curve or error curve) to obtain the calculated error (E1), using this to minimize the error according to the temperature of the power value measured in the meter.

1 is a graph showing a measurement value Po of a wattmeter with respect to an input value Pi according to the present invention, and data Po 'fitting an approximation function of this measurement value Po.

Normally, the metered output Po of the electricity meter has a temperature dependence that can be approximated as a quadratic or cubic function of temperature, and thus the temperature compensation curve can be used to obtain the fitted error E1 using this characteristic. Find the coefficient.

First, the process of correcting the error of the electronic digital electricity meter using the fitting error (Efit) will be described.

FIG. 2 is a graph showing an error E1 of the wattmeter according to the present invention and a fitting error Efit represented as an approximation function by fitting the error E1.

The power amount value input to the electricity meter is called an input value Pi, and the power amount value outputted by inputting the input value Pi to the electricity meter is called a weighing value Po.

The input value Pi is an ideal value that is unknown when measuring the output power value of the actual power meter. The input value Pi is power amount data input to the power meter in order to obtain a fitting error of the corresponding power meter in advance.

The error E1 between the input value Pi and the measured value Po may be calculated as in Equation 1 below, and the input value Pi may be collectively represented as in Equation 2 below.

E1 = (Pi-Po) / Pi = 1- (Po / Pi)

Pi = Po / (1-E1)

The input value Pi may be fitted to a predictive input value Pfit, which is a second order approximation function for temperature, using a least square method.

When the error E1 data is regarded as actual data, it may be represented as a second-order approximation function fitted as shown in FIG. 2, and a large number of fitting error data that fits the error E1 data as an approximation function are numerous. Assuming that the data are averaged using the data, it can be said that the fitting error Efit has an accurate temperature dependency, and this fitting error Efit represents the temperature dependency of the wattmeter.

In addition, the fitting error Efit is closer to the error E1 value as the error E1 data is collected and calculated, and the error between the error E1 data and the fitting error data may be reduced.

Therefore, it is assumed that the fitting error Efit is a function approximated by collecting a large amount of data that can ignore the difference from the error E1, and the prediction input value Pfit is very close to the input value Pi. Assuming a value, the following Equation 3 can be derived using Equation 2.

Pfit ≒ Po / (1-Efit)

The error E2 between the predicted input value Pfit and the input value Pi calculated by Equation 3 may be expressed as Equation 4 below.

E2 = (Pi-Pfit) / Pi = 1-Pfit / Pi = 1- (1-E1) / (1-Efit) = (E1-Efit) / (1-Efit)

3 is a graph showing an error E1 between the input value Pi and the weighing value Po according to the present invention in terms of a percentage of the error E2 between the input value Pi and the predicted input value Pfit.

The error E1 between the input value Pi and the weighing value Po and the error E2 between the input value Pi and the predicted input value Pfit may be compared with Equation 5 below.

E1 / E2 = E1 / [(E1-Efit) / (1-Efit)] = E1 (1-Efit) / (E1-Efit)

Table 1 below summarizes the meter value Po and other data of the electricity meter according to the input value Pi, and FIG. 2 is shown based on the data of Table 1. FIG.

Therefore, since it is assumed that the predicted input value Pfit is very close to the input value Pi, when the predicted input value Pfit is calculated instead of the input value Pi for the metered value Po of the electricity meter, The error that the measured value Po has with respect to the predicted input value Pfit can be regarded as the fitting error Efit, and when the measured value Po is corrected using the fitting error Efit according to Equation 3, the power meter The overall error of is corrected to improve the accuracy of the meter.

As shown in the graph of FIG. 3, the error E2 between the predicted input value Pfit and the input value Pi is greatly reduced compared to the error E1 between the input value Pi and the measured value Po. It can be seen that the change has been changed to an error irrelevant to the temperature change, and it can also be seen that the magnitude of the total error of the electricity meter occurs within a certain range.

Accordingly, the predicted input value Pfit is closer to the input value Pi than the measured value Po, and the predicted input value Pfit is closer to the temperature change than the measured value Po with respect to the input value Pi. It can be seen that the resulting error is small.

According to the result, it can be seen that the predicted input value Pfit calculated by correcting the weighing value Po with fitting error data is a power amount value in which an error caused by temperature change in the electricity meter is reduced.

Hereinafter, a process of correcting the output power value by minimizing an error with respect to the temperature change by using the power amount correction method according to the temperature change of the electronic power meter according to the present invention will be described.

Figure 4 shows a three-dimensional temperature compensation curve showing the fitting error curve (Efit, error curve) according to the temperature change of the power amount value (also called current value, voltage value is fixed) input to the electricity meter according to the present invention It is a graph.

In order to prepare fitting error data (error curve) as shown in FIG. 4, an experiment is performed to secure error data E1 of the watt-hour meter.

The experiment for securing the error data (E1) is carried out in a temperature control chamber in which the temperature is adjusted according to the set temperature data, and the measured value Po while changing the input value Pi of the plurality of wattmeters input to the temperature control chamber. Is measured and the error E between the input value Pi and the measured value Po is obtained.

In this case, since the input value Pi is a power value with a fixed voltage value, the input value Pi changes according to the input current, so that the error E can be regarded as an error of the wattmeter having the input current according to the temperature change. have.

Since the error E shows a slight difference for each electricity meter, the average value E1 of the error E of the electricity meters is calculated to minimize dispersion. In this case, each of the electricity meters are devices designed in the same manner, and the electricity meters that deviate much from the average value give accuracy to the average value by excluding from the error data E1.

As described above, a process of obtaining the error data E1 according to the temperature of the input current using a plurality of wattmeters is performed for each temperature data at a predetermined interval, thereby obtaining error data E1 in which each input current changes according to the temperature data. .

By fitting the error data (E1) obtained from the average values of the multimeters by the least-square method for each input current (or input value (Pi)), a second approximation function (y = ax ² + bx + c) is used as a variable. Obtain

Then, the function value y of the quadratic approximation function becomes a fitting error Efit, and the fitting error Efit can be obtained using an external computer.

The temperature compensation curve as shown in FIG. 4 can be obtained by calculating the coefficients of the quadratic approximation function obtained in this way by a (i), b (i), and c (i) matrices according to the input current (i). The coefficient of the quadratic approximation function is input and thus the fitting error (Efit) for temperature and current can be determined.

That is, the second approximation function is a function of an error curve (temperature compensation curve) indicating a fitting error (Efit), and a function value y fitting the error data E1 that each power amount data has according to temperature change. Becomes

Accordingly, if the coefficient of the temperature compensation curve corresponding to each input current is known, the fitting error according to the temperature change of the measured power amount value can be known, and a large number of fitting errors according to the temperature data (actual temperature) of a certain unit ) Can be calculated as shown in FIG.

All electricity meters go through a calibration procedure after assembly. In this process, other errors are corrected and the temperature calculated by correcting the difference between the actual temperature and the temperature read by the central processing unit of the electricity meter. When measuring the output power value using the correction factor, convert the temperature of the power meter to the actual temperature, and fit it using the coefficients of the fitting error curve (a (i), b (i), c (i)) obtained at the actual temperature. The Efit is calculated.

The process of correcting the amount of power measured using the temperature compensation curve (fitting error data) obtained as described above is as follows.

The power meter measures the output power amount value with respect to the power amount value input to the actual power meter, and converts the temperature at the time of measuring the output power amount value into the actual temperature using a temperature correction coefficient.

When the current value of the output power amount value (voltage value is usually fixed and can be viewed as a current value) is equal to the input current of the fitting error data, the corresponding fitting error is determined using the coefficient of the fitting error curve of the input current of the fitting error data. The curve is obtained, and the function value of the fitting error curve at the actual temperature is the fitting error Efit.

However, the output power amount value is generally different from the input current of the fitting error data, in which case the output power amount value is positioned between the two input current data.

Accordingly, by comparing the current value of the output power amount value with the input current of the fitting error data, finding two input current data closest to the current value of the output power amount value, and then calculating the coefficient of the fitting error function corresponding to the two input current data. The fitting error curve is obtained by using, and the first fitting error Efit1 and the second fitting error Efit2 of the actual temperature are obtained from the fitting error curve.

By interpolating the first fitting error (Efit1) and the second fitting error (Efit2) thus obtained, the fitting error value for the output power amount of the watt-hour meter at the actual temperature is calculated, and the output power amount is applied by applying Equation 3. If the value is a measured value Po, the predicted input value Pfit, which is a corrected power amount value, may be calculated.

Example

Assuming that an error curve (or fitting error curve) as shown in FIG. 2 is obtained according to the present invention, 12 fitting error functions in units of 0.5 A current (fixed voltage 110 V) are in the form of coefficients of a second approximation function whose temperature is a variable. Stored.

Assuming that the power meter under the condition corresponding to one point (blue dot, 14 ° C, near 1.8A) on the temperature compensation curve is measured as shown in FIG. 4, the temperature compensation procedure will be described first. Since the input current data of 1.5A is between the corresponding error curve and the input current data of 2.0A, the fitting error data corresponding to the temperature of 14 degrees is read from the two error curves.

In addition, the fitting error value at 1.8A can be obtained by applying the equation to each fitting error value at 1.5A and 2.0A.

After calculating the fitting error value at the output power value 1.8A, and substituting the fitting error value into the fitting error Efit and substituting the output power value into the weighing value Po, Equation 3 (Pfit = Po / (1 -Efit)) to obtain the predicted input value Pfit that is close to the input value Pi (ideal power amount value).

Although the present invention has been shown and described with respect to specific preferred experimental examples, the present invention is not limited to these examples, and the technical features of the present invention which are claimed in the claims by those skilled in the art to which the present invention pertains. It includes all the various forms that can be implemented without departing from the spirit.

1 is a graph showing the measured value Po of a watt-hour meter according to the present invention and the data Po 'fitting the measured value Po to an approximation function.

2 is a graph showing an error E1 of the watt-hour meter according to the present invention and an fitting error Efit represented as an approximation function by fitting the error E1.

FIG. 3 is a graph showing an error E1 between the input value Pi and the measured value Po and the error E2 between the input value Pi and the predicted input value Pfit in terms of percentages according to the present invention.

4 is a graph showing a three-dimensional temperature compensation curve showing an fitting error (error curve) according to a temperature change of a power amount value (current value, voltage value is fixed) input to the electricity meter according to the present invention.

Claims (4)

In the power amount correction method according to the temperature change of the electronic power meter, (a) obtaining an error E of the measured value Po with respect to the input current in the plurality of electricity meters, and obtaining error data E1 which is an average value of the errors E of the plurality of electricity meters; (b) obtaining the fitting error function (y = ax ² + bx + c) using the temperature as a variable by obtaining the error data E1 at a predetermined interval with respect to the actual temperature and then fitting the least squares method; (c) obtaining the fitting error function for each input current (i) and inputting coefficients (a (i), b (i), c (i)) to the wattmeter; (d) obtaining a temperature correction coefficient according to the difference between the temperature read by the electricity meter and the actual temperature; (e) obtaining a fitting error (Efit) that the output power value of the watt-hour meter has at the actual temperature at the time of measurement by using the temperature correction coefficient; (f) obtaining the predicted input value Pfit by correcting the error of the output power amount value by using the output power amount value as a measured value Po and using Pfit 값 Po / (1-Efit); Power amount correction method according to the temperature change of the electronic watt-hour meter comprising a. The method according to claim 1, The error E of the measured value Po with respect to the input current in step (a) is obtained by multiplying the input current by a fixed voltage value to obtain an input value Pi, and E = (Pi-Po) / Pi. Power amount correction method according to the temperature change of the electronic electricity meter, characterized in that obtained by using. The method according to claim 1, In the step (e), the current value of the output power amount value is compared with a plurality of input currents (or power value data) to obtain two input currents closest to the current value of the output power amount value, and then two input currents. After calculating the fitting error function value at the actual temperature by using the coefficient of the fitting error function corresponding to the interpolation of the two fitting error function values by the internal components, the fitting error (Efit) of the output power amount value is obtained. Power amount correction method according to the temperature change of the electronic power meter. The method according to claim 1, In the step (e), if the current value of the output power value is the same value as the input current (or power value data), the fitting error function value at the actual temperature is obtained by using the coefficient of the fitting error function corresponding to the input current. And adjusting the fitting error function value as a fitting error (Efit) of the output amount of power.

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