JP4156412B2 - Current sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a current sensor using an air-core coil as a detection unit.
[0002]
[Prior art]
As this type of current sensor, there is a current sensor described in Non-Patent Document 1. This current sensor uses a Rogowski coil (an example of an air-core coil) as a current detector. A Rogowski coil uses an insulator instead of an iron core as a winding core, and a secondary winding is wound on the winding core. Furthermore, in order to return the output voltage proportional to the time change of the primary current obtained from the Rogowski coil to the signal proportional to the primary current via the A / D converter, the DC offset removal circuit and the incomplete integrator are digitally converted. A configuration that uses computation is employed. The discharge time constant of this incomplete integration is 1 second.
[0003]
When the value of the primary current is the maximum value (phase 90 degrees), the air core coil output is 0, and the sign of the output is inverted thereafter. The primary current waveform is restored by integrating this.
[0004]
[Non-Patent Document 1]
Mitsubishi Electric Technical Journal, Vol.75, No.8, 2001 (pages 31-36)
[0005]
[Problems to be solved by the invention]
Normally, when a DC component is included in the input signal of the integrator, this component is continuously added by the integrator, so the value in the integrator increases or decreases monotonically, and the integrator is saturated. It becomes impossible to perform current measurement. Note that there are two types of DC components here: the DC component of the input signal and the DC component accumulated in the integrator in accordance with ON / OFF of the primary current, phase change, and the like.
[0006]
The DC component of the input signal is caused by a deviation in the ground potential of the input signal due to the influence of the power supply circuit, peripheral devices, etc., the influence of the analog circuit from the air-core coil output to the A / D converter, etc. Is attributed.
[0007]
The DC component accumulated in the integrator occurs when the phase of the primary current changes abruptly. For example, the phase of the primary current changes abruptly when the load having a large capacity is turned on and off. As an example, when the primary current becomes the maximum value, the value in the integrator becomes the maximum value. In this state, the case where the phase of the primary current changes by 180 degrees and becomes the minimum value will be described.
[0008]
Originally, the sign of the air core coil output is inverted, and the value in the integrator should fluctuate around 0 by subtracting, but the sign of the air core coil output is not inverted by changing the current phase of the measurement target, The value in the integrator increases. That is, the fluctuation is based on the value in the integrator when the phase of the primary current changes. This is equivalent to the accumulation of DC components in the integrator, and the margin until saturation (difference between the range of the integrator and the DC component) becomes small, and may be saturated depending on the value of the primary current.
[0009]
In the prior art, in order to deal with the DC component, the DC component included in the input signal is removed using a DC offset removal circuit. However, when the DC component of the input signal changes, the DC component passes through the DC offset circuit and is input to the incomplete integration circuit until the DC offset circuit converges. In order to remove this DC component, in the prior art, incomplete integration is performed, and the input signal is designed to decay with time and become zero after one second. As described above, a two-stage processing circuit is required as a countermeasure against the saturation of the integrator.
[0010]
In addition, since the integrator discharges with a time constant (because of incomplete integration), the integration process cannot be performed accurately, and a signal proportional to the primary current cannot be obtained with high accuracy. The output waveform obtained by continuously digitally integrating the output from the A / D converter advances in phase with respect to the primary current. However, the above-described conventional technique does not take any measures.
[0011]
The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a current sensor that can quickly follow a change in primary current. It is another object of the present invention to obtain a current sensor with a small phase shift with respect to the primary current.
[0012]
[Means for Solving the Problems]
The current sensor according to the present invention is:
Air-core coil, A / D converter for quantizing the output signal of the air-core coil for detecting a measurement target current, the integrator, the high range of the output data of said integrator for integrating the quantized data of the A / D converter It passes only frequency components, the high-pass filter for outputting the electrical quantity which is proportional to the measured current from the input signal and the output signal of said high pass filter, a difference detecting means for taking the difference of the two signals, said difference detected A coefficient multiplication means for multiplying the difference value obtained by the means by a constant coefficient , and an addition means for adding the output of the coefficient multiplication means to the input side of the integrator .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 shows a configuration of a current sensor according to Embodiment 1 of the present invention. An output signal of an air-core coil 1 that detects a primary current as a measurement target and outputs a voltage proportional to a temporal change amount thereof. Are quantized by sampling by the A / D converter 2 and added to the digital processing unit 20 that digitally processes the quantized data.
[0014]
The digital processing unit 20 includes a high-pass filter 3 that removes a DC component, an integrator 4 that continuously integrates a signal, and a difference detection unit that has a function of calculating a difference between an input signal and an output signal of the high-pass filter 3. 5. Coefficient multiplying means 6 having a function of multiplying the difference value output from the difference detecting means 5 by a constant coefficient, and adding means having a function of adding the difference calculation result to the input of the integrator 4 7.
[0015]
Specifically, the amount of change in the primary current is detected by the air-core coil 1 with the above configuration. The analog voltage signal from the air-core coil 1 is input to the A / D converter 2 to be converted into a digital value. The converted digital data is processed by the digital processing unit 20, and an electric quantity proportional to the primary current to be measured is obtained as an output.
[0016]
The A / D converter 2 and later are digital processing by software. The flow of processing will be described with reference to FIG. The air core coil 1 detects an amount of electricity proportional to the primary current (S1), and the A / D converter 2 quantizes the analog signal by sampling and converts it into a digital signal (S2). At this time, when the DC component is superimposed on the analog signal output, if the continuous integration is simply performed as it is, the range that can be handled by the integrator 4 is exceeded (saturated), and an accurate signal cannot be obtained. In order to remove this DC component from the integrator 4, a process of feeding back the difference value between the input signal and the output signal of the high-pass filter 3 is performed (S6). The initial value of the difference value to be fed back is set to 0, and this value and the signal from the A / D converter 2 are added by the adding means 7 (S3).
[0017]
Next, the coefficient multiplication means 6 performs a process of multiplying the difference value between the input signal and the output signal of the high-pass filter 3 by a constant coefficient. As a result, the DC component in the integrator 4 is gradually removed, and the DC component is converged to zero.
[0018]
Next, integration processing is continuously performed by the integrator 4 (S4). Specifically, the initial value of the integrator is set to 0, and input data (measurement data + difference data) is sequentially added for each sampling to obtain an output.
[0019]
Next, the output of the integrator 4 is held, and the difference between the output and the output of the high-pass filter 3 is calculated (S6).
[0020]
Next, the DC component is removed from the output (integration result) of the integrator 4 by applying the high-pass filter 3 (S5).
[0021]
Next, the value held as the output of the integrator 4 is subtracted from the result obtained through the high-pass filter 3. A value obtained by multiplying the difference result by a constant coefficient (S7) is added to the output of the preceding A / D converter 2 by the addition processing function 7 (S3).
[0022]
However, the constant coefficient to be multiplied by the difference value is set to a value smaller than 1. It is preferable to use a value of 0.5 or less. By using a numerical value of 1 or less for the coefficient, the DC component in the integrator 4 gradually converges to 0.
[0023]
When this coefficient is small, it takes time until the DC component in the integrator 4 converges to zero. Conversely, when it is close to 1, it converges quickly, but if it is too large (a number very close to 1), the DC component in the integrator 4 oscillates without converging to 0.
[0024]
The current sensor output in the present invention is a value obtained by applying the high-pass filter 3 to the output of the integrator 4 or a value obtained by performing some processing.
[0025]
The present invention shown in the first embodiment is characterized in that all processes subsequent to the A / D converter 2 are performed by digital processing by the digital processing unit 20 , but all functions other than this are analog. Processing with a circuit is also conceivable. It is also conceivable to change the position where the A / D converter 2 is inserted, and to perform pre-processing up to the A / D converter 2 with an analog circuit and digitally process the subsequent stage of the A / D converter 2. .
[0026]
The high-pass filter 3 may have any configuration as long as it has a function of removing a DC component.
[0027]
According to the present invention, it is possible to remove the high-pass filter in the previous stage of the integrator 4 that was necessary in the prior art, but of course, there is no problem even if the high-pass filter is installed in the previous stage of the integrator 4.
[0028]
In this embodiment, the output of the air-core coil 1 is directly input to the A / D converter, but a low-pass filter for surge countermeasures may be inserted between them. That is, the first embodiment does not limit the scope of the present invention, and various modifications other than the use of the air-core coil 1 for the detection unit and the functions after the A / D converter 2 are considered. It is done.
[0029]
Embodiment 2. FIG.
The second embodiment is a technique for matching the phase of the primary current waveform with the result of integration by the integrator 4 by devising a sampling method in the current sensor shown in the first embodiment.
[0030]
FIG. 3 shows a main part of the current sensor according to the second embodiment. The A / D converter 2 quantizes the analog voltage signal proportional to the change amount of the primary current, and the desired timing from the quantized data. From the selection processing means 8 having the function of selecting only the data of the data or calculating the data at the desired timing and the sampling cycle performed by the A / D converter 2, the processing such as approximation is performed to perform the desired processing. Downsampling means 9 having a function of changing to a sampling period is provided. FIG. 3 shows the minimum function that can achieve the effect of the present invention. Actually, the air-core coil 1 is connected to the front stage of the A / D converter 2, and the digital processing unit 20 is connected to the rear stage of the downsampling means 9. The digital processing unit may be between the A / D converter and the selection processing means.
[0031]
More specifically, referring to FIG. 4, when the voltage signal V proportional to the amount of change in the primary current signal I to be measured is Euler integrated by the integrator 4, the waveform of the integration result R is the primary current signal I. The phase advances with respect to the waveform. The amount D by which the phase advances depends on the sampling period, and always advances by ½ sampling period. The measurement accuracy is improved by correcting the amount of phase advance.
[0032]
First, so-called oversampling is performed in the A / D converter 2 at a sampling period that is twice or more the sampling period required for the current sensor output. From the sampled data, the selection processing means 8 is used to select data at a desired timing. Since the integration result data is data whose phase is advanced by 1/2 sampling period compared to the primary current, the data to be extracted is delayed by 1/2 sampling from the desired sampling. To do. Only the previously selected data is extracted by the downsampling means 9, and the data is transferred to the next function at the same timing as the sampling period of the current sensor output.
[0033]
When the sampling frequency of the A / D converter 2 is 2N times the current sensor output frequency (N is an integer), the data after ½ sampling simply exists and is selected.
[0034]
When the sampling frequency of the A / D converter 2 is other than 2N times the current sensor output frequency, approximation such as linear interpolation or fitting by a primary voltage waveform function is performed, and the current sensor output is delayed by 1/2 sampling. Calculate the timing output and extract it.
[0035]
Only the previously selected data is extracted by the down-sampling means 9, and the data is transferred to the next function at the same timing as the current sensor output cycle.
[0036]
The above processing is equivalent to delaying the sampling timing by a 1/2 sampling period of the current sensor.
[0037]
In the present embodiment, the sampling frequency of the A / D converter 2 is set to be twice or more of the current sensor output. However, even when the sampling frequency is lower than that, the phase can be similarly corrected and high-precision measurement can be performed. However, when the sampling frequency of the A / D converter 2 is twice or less, the high frequency component is deteriorated by downsampling, and the measurement accuracy in this high frequency region is lowered.
[0038]
By delaying the sampling waveform, the phase of the output waveform of the integrator can be matched with the phase of the current waveform to be measured, and a more accurate current sensor can be configured.
[0039]
Embodiment 3 FIG.
The third embodiment is a technique for matching the integration result of the integrator with the phase of the primary current waveform by devising the integration procedure in the current sensor described in the first embodiment. As shown in FIG. 5, the current sensor includes an A / D converter 2 that quantizes an analog voltage signal proportional to the amount of change in primary current, and a trapezoidal integrator 10 that trapezoidally integrates quantized data. FIG. 5 shows a minimum function capable of obtaining the effect of the present invention. Actually, the air-core coil 1 is connected to the front stage of the A / D converter 2, the adding means 7 is connected to the input side of the trapezoidal integrator 10, and the high-pass filter or the like is connected to the output side.
[0040]
As described in the second embodiment, the waveform of the integration result always advances in phase by ½ sampling period compared to the waveform of the primary current waveform. In order to correct this phase, a trapezoidal integrator 10 that delays the phase of the waveform of the integration result by 1/2 sampling period is employed. The trapezoidal integrator 10 includes the integrator 4 in the first embodiment, held data, and averaged data.
[0041]
A specific processing flow is shown in FIG. First, the held data (1) is initialized with 0 (S10). The retained data (1) is data for averaging the sampling data by the A / D converter 2. Next, the sampling data sampled (S11) by the A / D converter 2 is stored in the retained data (2) (S12).
[0042]
Next, the sum of the sampling data and the held data (1) is taken and further halved (averaged) (S13). The averaged data (averaged data) is sequentially added by the integrator 4 in the trapezoidal integrator 10. However, the initial value of the integrator 4 is 0. The retained data (2) is copied to the retained data (1) (S14). Thereafter, trapezoidal integration is performed by repeating the same procedure.
[0043]
In the present embodiment, the retained data (1) and the retained data (2) are distinguished. The retained data (2) is a means for substituting sampling data into the retained data (1), and any other type. A method may be used.
[0044]
In the present embodiment, the averaging process is performed before the integrator 4 as a trapezoidal integration, but the same effect can be obtained even if the averaging process is performed after the integrator 4.
[0045]
By averaging the pre-sampling data and the current sampling data, or by averaging the pre-integrator output and the current integrator output, the phase of the integrator output waveform and the primary current waveform can be matched, and more accurate A high current sensor can be constructed.
[0046]
As shown in the first to third embodiments, the current sensor of the present invention using the air-core coil in the detection unit can prevent the saturation phenomenon of the primary current and can detect the instantaneous value, so it is used as a current sensor. In particular, it is suitable for a circuit or device that calculates power (including reactive power and harmonic power) affected by the phase of current and voltage and power amount (including reactive power and harmonic power).
[0047]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
Since the DC component is gently removed by adding an amount obtained by multiplying the difference value of the input / output signal of the high-pass filter by a constant coefficient to the integrator, if the output signal of the air-core coil contains an excessive DC component, the primary current will be When ON / OFF, even when the phase of the primary current changes, the saturation phenomenon can be avoided and accurate current measurement can be performed.
[0048]
In addition, the configuration of the present invention can be realized simply by adding a function for feeding back the difference value of the input / output signal of the high-pass filter to the integrator in the basic configuration (integrator and high-pass filter). Saturation countermeasures can be realized.
[0049]
Furthermore, since the DC removal circuit configuration can be simplified, a current sensor having a simple and inexpensive air core coil in the detection unit can be configured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a current sensor according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing a flow of processing in the first embodiment.
FIG. 3 is a diagram showing a configuration of a main part of a current sensor according to Embodiment 2 of the present invention.
FIG. 4 is a diagram showing a relationship between a primary current phase and a phase after integration in the second embodiment.
FIG. 5 is a diagram showing a configuration of a main part of a current sensor according to Embodiment 3 of the present invention.
FIG. 6 is a diagram showing a flow of processing in the third embodiment.
[Explanation of symbols]
1 air core coil, 2 A / D converter,
3 high-pass filter, 4 integrator,
5 difference detection means, 6 coefficient multiplication means,
7 addition means, 8 selection processing means,
9 down-sampling means, 10 trapezoidal integrator,
20 Digital processing unit.

Claims (3)

Air-core coil, A / D converter for quantizing the output signal of the air-core coil for detecting a measurement target current, the integrator, the high range of the output data of said integrator for integrating the quantized data of the A / D converter It passes only frequency components, the high-pass filter for outputting the electrical quantity which is proportional to the measured current from the input signal and the output signal of said high pass filter, a difference detecting means for taking the difference of the two signals, said difference detected A current sensor comprising coefficient multiplication means for multiplying the difference value obtained by the means by a constant coefficient , and addition means for adding the output of the coefficient multiplication means to the input side of the integrator . 2. The current sensor according to claim 1, wherein only data having a desired timing is selected from the data quantized by oversampling by the A / D converter, or a desired timing is provided after the A / D converter. Selection processing means having a function of calculating the data of the data, and downsampling means for extracting only the data selected by the selection processing means and changing the oversampling period to a desired sampling period. By means of downsampling with a certain amount of delay with respect to the sampling result oversampled by the A / D converter by the means and the downsampling means , the phase of the current to be measured and the output of the integrator are matched. A current sensor characterized by that.   2. The current sensor according to claim 1, wherein the integrator is a trapezoidal integrator.

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