JP2014235086A - Current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detector capable of reproducing a state that a current is conducted through a current line to be measured, in a flux gate type current sensor, and to provide a current detector capable of detecting a current to be measured with high accuracy by correcting sensor sensitivity, even in a situation where the working environment temperature of the sensor changes.SOLUTION: A current detector comprises: a flux gate type current sensor 51 having a magnetic substance core 2 forming a closed magnetic circuit, an excitation coil 3 wound around the magnetic substance core 2, and a detection coil 4 wound around the magnetic substance core 2, a current line 1 to be measured passing through the magnetic substance core 2; an excitation processing unit 61 for generating an excitation magnetic field by conducting an AC excitation signal 38 through the excitation coil 3; a detection processing unit 62 for extracting only a second harmonic component of the excitation magnetic field from an output voltage waveform of the detection coil 4 and performing signal processing on it; and an offset control circuit 22 or the like for superposing an offset signal on the AC excitation signal 38 at a predetermined timing.

Description

  The present invention relates to a current detection device using a fluxgate type current sensor.

  The fluxgate type current sensor is an application of a fluxgate type magnetic sensor. In general, fluxgate type magnetic sensors have higher magnetic field detection sensitivity than Hall elements and magnetoresistive elements, which are magnetic sensors, and are suitable for detecting minute magnetic fields such as geomagnetism. Also, they are more temperature dependent than Hall elements and magnetoresistive elements. It has excellent properties. For this reason, commercially available current sensors using Hall elements and magnetoresistive elements are widely used for A (ampere) order current detection, whereas fluxgate current sensors are in the order of mA (milliampere). Currently, it is widely used for current detection.

  A conventional fluxgate type current sensor has a structure in which an excitation winding and a detection winding are wound around a magnetic ring core made of a high permeability material, as shown in FIG. 2 of Patent Document 1, for example. The conductor through which the current to be measured flows is passed through the ring core.

  Next, the operation principle will be described. An AC exciting current is applied to the exciting winding to periodically magnetically saturate the magnetic ring core. When the measured current value is zero, the magnetic field change generated by the excitation current is symmetric with respect to the origin of the BH curve of the magnetic ring core material. In accordance with Faraday's electromagnetic induction law, an output voltage is generated in the detection winding as the amount of magnetic flux in the magnetic ring core around which the detection winding is wound changes. Therefore, the output voltage becomes zero in the magnetic field region where the magnetic ring core is sufficiently saturated. That is, when the BH curve is symmetrical with respect to the origin, and the magnetic ring core is excited with a certain period, the time and period when the output voltage is zero are constant, and the period is symmetric with respect to the origin of the BH curve. Therefore, it becomes twice the excitation frequency.

  On the other hand, when the measured current value is not zero, the magnetic field generated by the measured current is superimposed in addition to the exciting magnetic field generated by the exciting current. In this case, since the change in the magnetic field is not symmetrical with respect to the origin of the BH curve of the magnetic ring core material, the time during which the output voltage is zero is constant even when the magnetic ring core is excited with an excitation magnetic field having a certain period. It becomes different when the change in the magnetic field changes to the positive side or the negative side, not the interval. Since the measured current value can be obtained from the difference between the time intervals when the output voltage is zero, the flux gate type current sensor can measure the measured current value without contact with the measured current line.

  Further, in recent years, in order to improve the detection accuracy of the fluxgate type current sensor, a structure that removes the influence of the excitation magnetic field with respect to the magnetic field change interlinking the detection winding, for example, as shown in FIG. As described above, a structure in which the excitation magnetic field and the direction of the magnetic field generated by the current to be measured are orthogonal to each other has been proposed. Further, as shown in FIG. 2 of Patent Document 3, a structure for applying differential excitation magnetic fields to two magnetic ring cores, winding a detection winding integrally, and performing differential detection has been proposed. . Further, as shown in FIG. 1 of Patent Document 4, in a structure in which detection windings are wound around two magnetic ring cores and differential processing is performed in a subsequent circuit, only a magnetic field component generated from a current line to be measured is obtained. Can be detected. Furthermore, the current value to be measured can be measured with high accuracy by performing closed loop control in which a current flows through the feedback coil in the magnetic ring core so as to cancel the detected magnetic field. In addition, differential and closed-loop control can offset changes in the magnetic characteristics of the magnetic ring core and hysteresis characteristics of the magnetic ring core due to changes in the operating environment temperature, and is robust against changes in the operating environment temperature. In addition, a highly accurate current sensor can be constructed.

Japanese Utility Model Publication No. 59-92532 (1 page, FIG. 1) Japanese Patent Laid-Open No. 6-281684 (paragraph [0016], FIG. 1) JP 2001-228181 A (paragraph [0017], FIG. 2) JP 2002-22774 A (paragraph [0017], FIG. 1)

  The fluxgate type current sensor is a sensor that utilizes the non-linear magnetic characteristics of a magnetic core. For this reason, there is a problem that the magnetic characteristics of the magnetic core change due to a change in the ambient temperature of the sensor, resulting in a change in sensor sensitivity. When the ambient temperature of the sensor is constant, there is no particular problem because the sensor sensitivity is constant. However, when the fluxgate type current sensor is applied to automobiles and industrial equipment having a large temperature change, it is necessary to correct the temperature characteristics of the sensor sensitivity. In the conventional method of correcting the temperature characteristics, the differential processing is performed using two magnetic cores, or the closed loop control in which the current is fed to the feedback coil through the magnetic ring core so as to cancel the detected magnetic field. This cancels the temperature characteristics.

  However, when two magnetic cores are used, the size of the sensor is increased and the member cost is increased. Therefore, downsizing and reduction of the member cost are problems. In addition, when using feedback control, the current required to cancel the detected magnetic field causes an increase in power consumption, and reducing power consumption is a problem.

  An object of the present invention is to provide a current detection device capable of reproducing a state in which a current is supplied to a current line to be measured in a fluxgate type current sensor.

  Another object of the present invention is to provide a current detection device capable of correcting the sensor sensitivity and detecting the current to be measured with high accuracy even under a situation where the use environment temperature of the sensor changes.

In order to achieve the above object, a current detection device according to the present invention comprises a magnetic core forming a closed magnetic circuit, an excitation winding wound around the magnetic core, and a detection wound around the magnetic core. A fluxgate type current sensor having a winding and a current wire to be measured penetrating the magnetic core;
An excitation processing unit for generating an excitation magnetic field by energizing an AC excitation signal to the excitation winding;
A detection processing unit that performs signal processing by extracting only the second harmonic component of the excitation magnetic field from the output voltage waveform of the detection winding;
An offset control unit that superimposes an offset signal on the AC excitation signal at a predetermined timing.

  According to the present invention, it is possible to reproduce a state in which a current is supplied to the current line to be measured by superimposing an offset signal at a predetermined timing on the AC excitation signal. For this reason, the output signal waveform from the detection processing unit changes depending on the presence or absence of the offset signal, and it becomes possible to calculate the sensor sensitivity of the fluxgate current sensor. Based on the calculated sensor sensitivity, the fluxgate current It becomes possible to correct the output from the sensor. As a result, the current to be measured can be detected with high accuracy even under conditions where the ambient temperature of the sensor changes.

It is a block diagram which shows Embodiment 1 of this invention. FIGS. 2A and 2B are explanatory diagrams showing a relationship between an excitation magnetic field and a magnetic flux density. FIG. 2A shows a case where the measured current value is zero, and FIG. 2B shows a case where the measured current value is not zero. 3A shows the output voltage waveform of the filter circuit, and FIG. 3B shows the output voltage waveform of the rectifier circuit. It is a graph which shows the relationship between a to-be-measured current value and the output voltage value of a rectifier circuit. It is a graph which shows an example of the magnetic characteristic with respect to the exciting magnetic field of a magnetic body core at the time of changing use environment temperature. FIGS. 6A and 6B are explanatory diagrams showing the relationship between the excitation magnetic field and the magnetic flux density when the use environment temperature is changed. FIG. 6A shows a case where the measured current value is zero, and FIG. 6B shows the measured current. Indicates the case where the value is not zero. FIGS. 7A and 7B are explanatory diagrams showing output voltage waveforms of the detection winding when the use environment temperature is changed. FIG. 7A shows a case where the measured current value is zero, and FIG. 7B shows a measured current value. Indicates that is not zero. It is a graph which shows the relationship between a to-be-measured current value and the effective value of the 2nd harmonic component of a detection coil | winding at the time of changing use environment temperature. FIG. 9A shows the output waveform of the offset power supply, and FIG. 9B shows the output waveform of the offset control circuit. It is a graph which shows an example of the waveform which superimposed the offset current on the alternating current excitation current. It is a graph which shows an example of the output voltage waveform of a filter circuit and a rectifier circuit when an offset current is superimposed on an alternating current excitation current. It is a graph which shows an example of the waveform which superimposed the offset current on the alternating current excitation current. It is a graph which shows an example of the output voltage waveform of a filter circuit and a rectifier circuit when an offset current is superimposed on an alternating current excitation current. It is explanatory drawing of the aspect which penetrates two to-be-measured current lines in a magnetic body core, and uses it as a zero phase current sensor. It is a block diagram which shows Embodiment 2 of this invention. It is a graph which shows an example of the waveform which superimposed the offset current on the alternating current excitation current. It is a graph which shows an example of the output voltage waveform of a filter circuit and a rectifier circuit when an offset current is superimposed on an alternating current excitation current. It is a block diagram which shows Embodiment 3 of this invention.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing Embodiment 1 of the present invention. The current detection device 101 includes a fluxgate type current sensor 51 and a sensor sensitivity calculation processing unit 71.

  The flux gate type current sensor 51 includes an annular magnetic core 2, an excitation winding 3 and a detection winding 4 wound around the magnetic core 2, an excitation processing unit 61, and a detection processing unit 62. The current wire 1 to be measured is used in a state of passing through the magnetic core 2. The magnetic core 2 is made of a high magnetic permeability material such as a silicon steel plate, an amorphous magnetic body, or PC permalloy. In addition, the magnetic body core 2 should just be a shape which forms a closed magnetic circuit, and is not limited to an annular | circular shape.

  The excitation processing unit 61 includes an AC excitation power source 5 that generates an AC excitation signal, an amplifier circuit 6 that amplifies the output from the AC excitation power source 5, and an excitation for converting an excitation current supplied to the excitation winding 3 into a voltage. And a current-voltage conversion circuit 7.

  The detection processing unit 62 rectifies, preferably full-wave rectifies, the output of the filter circuit 8 that extracts a signal component that is twice the frequency of the excitation current with respect to the output voltage of the detection winding 4, A smoothing rectifier circuit 9, a sensor sensitivity storage circuit 10, and a sensor sensitivity correction circuit 11 are provided. The sensor sensitivity storage circuit 10 has a function of storing sensor sensitivity information of the fluxgate type current sensor 51. The sensor sensitivity correction circuit 11 has a function of correcting the sensor sensitivity of the fluxgate type current sensor 51 by correcting the output of the rectifier circuit 9 based on sensor sensitivity information stored in advance in the sensor sensitivity storage circuit 10.

  The sensor sensitivity calculation processing unit 71 includes an offset power supply 21, an offset control circuit 22, a synchronization circuit 23, and a sensor sensitivity calculation circuit 24. The offset power supply 21 has a function of supplying a predetermined offset current. The offset control circuit 22 has a function of superimposing the offset current on the AC excitation signal from the AC excitation power supply 5 at a predetermined timing in synchronization with the AC excitation signal.

  The synchronization circuit 23 has a function of extracting a signal component synchronized with the offset current of the offset control circuit 22 from the output of the rectifier circuit 9. The sensor sensitivity calculation circuit 24 has a function of calculating the sensor sensitivity based on the output of the synchronization circuit 23 and overwriting the obtained sensor sensitivity with the sensor sensitivity stored in the sensor sensitivity storage circuit 10.

  The current detection device 101 applies the technology of a fluxgate type magnetic sensor that can detect a magnetic field generated near the current line 1 to be measured without contact. It is known that the fluxgate type magnetic sensor can detect a minute magnetic field and has a good temperature dependency as compared with a magnetic sensor such as a Hall element or a magnetoresistive element (MR element or GMR element). The operation principle of the fluxgate type current sensor 51 to which the fluxgate type magnetic sensor is applied will be described with reference to FIGS.

  First, consider the case where the current flowing through the measured current line 1 is zero. By applying a triangular wave-shaped excitation current to the excitation winding 3, a positive and negative symmetrical excitation magnetic field 31 is applied to the magnetic core 2 as shown in FIG. The excitation magnetic field H can be expressed by the formula (1).

Here, N ₁ is the number of turns of the excitation winding 3, I is the excitation current, and r is the average radius of the magnetic core.

  Since the magnetic core 2 has a magnetic characteristic (BH characteristic) 32 in which the magnetic flux density does not increase with respect to a certain or higher magnetic field, the magnetic flux density in the magnetic core 2 is higher than the excitation magnetic field 31. A saturated magnetic saturation phenomenon is obtained. On the other hand, when the cross-sectional area of the magnetic core 2 is S and the magnetic flux density of the magnetic core 2 is B, the magnetic flux φ penetrating the magnetic core 2 can be expressed as φ = B × S. The detection winding 4 is wound around the magnetic core 2. Therefore, the output voltage expressed by the equation (2) can be obtained according to Faraday's electromagnetic induction law.

Where N ₂ is the number of turns of the detection winding 4, μ is the magnetic permeability of the magnetic core 2, μ ₀ is the vacuum magnetic permeability (4π × 10 ⁻⁷ H / m), and μ _r is the relative permeability of the magnetic core 2. The magnetic susceptibility, S is the cross-sectional area of the magnetic core 2, f is the frequency of the exciting magnetic field, and H is the exciting magnetic field.

  Since the cross-sectional area S of the magnetic core 2 is a constant, an output voltage corresponding to the time change 33 of the magnetic flux density B of the magnetic core 2 is obtained at the detection winding 4. In the output voltage waveform 34 of the detection winding 4, as shown in FIG. 2A, the time change of the magnetic flux is zero when the magnetic core 2 is magnetically saturated. Therefore, during that period, the output voltage of the detection winding 4 becomes zero according to the equation (2). Since the magnetic characteristic 32 of the magnetic core 2 is symmetrical with respect to the excitation magnetic field, the zero voltage is repeated at a cycle twice that of the excitation magnetic field.

Next, let us consider a case where the current flowing through the measured current line 1 is not zero. A magnetic field is generated in the vicinity of the current line 1 to be measured according to Ampere's law. Note that the generated magnetic field H _d can be expressed by Equation (3).

Here, I _d represents the current to be measured, and r represents the average radius of the magnetic core 2.

  When the current flowing through the current line 1 to be measured is a direct current, the magnetic field generated by the current is superimposed on the excitation magnetic field as a direct current bias magnetic field and applied to the magnetic core 2 as shown in FIG. Will be. For this reason, the output voltage of the detection winding 4 has a waveform 35 in which the time interval of the zero voltage varies depending on the magnetic field pole applied to the magnetic core 2, one of which increases the time interval of the zero voltage and the other decreases. It becomes.

This change is obtained with a period twice that of the exciting magnetic field. Therefore, only the component (second harmonic component) V _2f corresponding to twice the frequency of the excitation magnetic field is extracted from the output voltage waveform of the detection winding 4 using the filter circuit 8.

The change of the effective value V _2f of the second harmonic component of the detection winding 4 with respect to the measured current value I _d is, for example, when I _d is a (a is an arbitrary value), 2a, 3a, as shown in FIG. ) Can be obtained. Specifically, the relationship between the measured current value _Id and the output voltage of the detection winding 4 will be described using mathematical expressions. When Fourier series expansion is performed on the output voltage waveform V _c 35 of the detection winding 4 shown in FIG. 2B, Expression (4) is obtained.

Where N ₂ is the number of turns of the detection winding 4, μ is the magnetic permeability of the magnetic core 2, μ ₀ is the vacuum magnetic permeability (4π × 10 ⁻⁷ H / m), and μ _r is the relative permeability of the magnetic core 2. permeability, S is the cross-sectional area of the magnetic core 2, f is the frequency of the excitation field, the H _m maximum of the excitation magnetic field, H _d is the magnetic field generated by the current to be measured, H _s represents the saturation magnetic field of the magnetic core 2 .

  Furthermore, when the amplitude value of the second harmonic component is obtained from Expression (4), Expression (5) is obtained.

Note that the generated magnetic field H _d by the current to be measured is as shown in equation (3), by substituting equation (3) into equation (5), proportional to the measured current I _d of the formula (6) Relational expressions can be derived.

From equation (6), the amplitude b ₂ of the second harmonic component in the output voltage of the detection winding 4, that is, V _2f is the frequency f of the excitation magnetic field, the number of turns N ₂ of the detection winding 4, and the maximum value H of the excitation magnetic field. _It can be seen that this depends on _m 2, the saturation magnetic field H _{s of} the magnetic core 2, the relative permeability μ _{r of} the magnetic core 2, the cross-sectional area S of the magnetic core 2, and the like.

Subsequently, the rectifier circuit 9 performs full-wave rectification and smoothing on the output of the detection winding 4, whereby a voltage V _d as shown in FIG. 3B can be obtained. Furthermore, the output voltage V _d of the rectifier circuit 9 is corrected by the sensor sensitivity correction circuit 11 based on the sensor sensitivity stored in the sensor sensitivity storage circuit 10 in advance, whereby the measured current value I _d. Can be requested. In the present specification, “sensor sensitivity” means a change in the output voltage V _d of the rectifier circuit 9 with respect to the measured current value I _d .

By the excitation magnetic field waveform is a triangular wave, and when the magnetic core is a relative magnetic permeability mu _r up to the magnetic saturation constant, from equation (2), the amplitude value of the output voltage V of the detection winding 4 is a constant value Show. Therefore, only the time interval of zero voltage is affected by the current to be measured. That is, since the time interval of the zero voltage increases or decreases in proportion to the measured current value I _d , the change in the output voltage V _d of the rectifier circuit 9 can obtain a linear characteristic as shown in FIG. Further, the same thing can be explained from the equations (5) and (6), and the measured current value I _d can be obtained by using this linearity.

  Next, the influence on the output of the fluxgate type current sensor 51 when the magnetic characteristics of the magnetic core 2 change due to the change in the use environment temperature will be described.

FIG. 5 is a graph showing an example of the magnetic characteristics with respect to the excitation magnetic field of the magnetic core when the use environment temperature is changed. The magnetic permeability μ, which is the product of the vacuum magnetic permeability μ ₀ and the relative magnetic permeability μ _r , is represented by the ratio between the magnetic flux density B and the magnetic field strength H. Thus in Figure 5, low temperature is compared with at high temperatures, the value of the relative permeability mu _r of the magnetic core 2 and it can be seen that the value of saturation magnetic flux density is increased. When the current flowing through the measured current line 1 is zero, as shown in FIG. 6A, the change in the magnetic flux density in the magnetic core 2 with respect to the excitation magnetic field 31 varies depending on the use environment temperature. As a result, as shown in FIG. 7A, output voltages having different peak values depending on the use environment temperature are obtained. This is because the relative permeability μ _r of the magnetic core of the formula (2) is changed depending on the use environment temperature.

When the current flowing through the current line 1 to be measured is not zero, the change in the magnetic flux density in the magnetic core 2 and the waveform of the output voltage are as shown in FIGS. 6B and 7B. Since the time interval of zero voltage increases or decreases in proportion to the current to be measured, the change in the output voltage V _d of the rectifier circuit 9 with respect to the current value to be measured I _d varies depending on the use environment temperature as shown in FIG. That is, the sensor sensitivity varies depending on the operating temperature environment. In Figure 5, when the environmental temperature rises than when room temperature, the value of the relative permeability mu _r becomes smaller, the sensor sensitivity is also reduced. The rate of change of the sensor sensitivity to changes in ambient temperature can be explained by the rate of change of the relative magnetic permeability mu _r of the magnetic core 2 from the equation (6). For example, if the value of the relative permeability mu _r of the magnetic core 2 is reduced by 10%, the sensor sensitivity is reduced by 10%. That is, the fluxgate type current sensor has a temperature characteristic that the sensor output changes depending on the use environment temperature.

  Therefore, in the current detection device 101 according to the present embodiment, the sensor sensitivity calculation processing unit 71 is provided in the flux gate type current sensor 51, and the sensor sensitivity in the use environment even when the flux gate type current sensor 51 has temperature characteristics. Is calculated step by step to correct the sensor sensitivity.

First, the roles of the offset power supply 21 and the offset control circuit 22 will be described. For example, as shown in FIG. 9A, the offset power supply 21 functions as a power supply that continuously outputs an offset current 36 having a current value _Io . For example, as shown in FIG. 9B, the offset control circuit 22 periodically switches the offset current between on and off and outputs a switching waveform 37 of the offset current. Subsequently, the switching waveform 37 obtained by the offset control circuit 22 is superimposed as an offset signal of the AC excitation power supply 5. Specifically, for example, as shown in FIG. 10, the switching waveform 37 is superimposed on the AC excitation current waveform 38. In FIG. 10, for convenience of explanation, the ON / OFF state of the switching waveform is synchronized every period of the excitation current. As described above, with respect to the phenomenon that occurs when the current obtained by superimposing the switching waveform 37 of the offset current on the AC excitation current waveform 38 is supplied to the excitation winding 3 of the fluxgate type current sensor 51, the time sequence t1 shown in FIG. A description will be given for each of t2, t3, and t4. FIG. 11 shows the output voltage V _2f of the filter circuit 8 and the output voltage V _d of the rectifier circuit 9 in time sequences t1, t2, t3, and t4, respectively.

As shown in FIG. 11, when the offset current switching waveform 37 is superimposed, it can be seen that the output voltage V _d of the rectifier circuit 9 is also a switched waveform 40. Superimposing the DC offset component on the excitation signal means that it is equivalent to measuring a certain DC magnetic field.

  Therefore, the output voltage waveform 40 of the rectifier circuit 9 is synchronized with the signal of the offset control circuit 22 by the synchronization circuit 23, and sensor sensitivity calculation is performed from information when the offset current is off and when the offset current is on. The circuit 24 can determine the sensor sensitivity. Therefore, even when the operating environment temperature is changed, the sensor sensitivity can be obtained every two periods of the excitation current, and the information on the sensor sensitivity stored in the sensor sensitivity storage circuit 10 is overwritten every two periods of the excitation current. By doing so, it is possible to realize a current detection device capable of detecting the current to be measured with high accuracy even under a situation where the temperature of the environment in which the sensor is used changes.

  Specifically, when the sensor output changes due to a change in the usage environment temperature, the sensor sensitivity can be detected by the configuration of the present invention, for example, by 10%. When the sensor sensitivity at a certain ambient temperature is 10% lower than that at room temperature, the output voltage of the rectifier circuit 8 is obtained by multiplying the output voltage of the rectifier circuit 8 by 100/90. Can do.

  1 illustrates the case where the excitation winding 3 and the detection winding 4 are locally wound around the annular magnetic core 2, the excitation winding 3 and / or the detection winding are illustrated. 4 may be wound uniformly around the entire circumference. The magnetic core 2 does not necessarily have an annular shape, and any shape such as a triangle, a square, or a polygon is acceptable as long as a fluxgate type current sensor can be configured.

  When the annular magnetic core 2 is used, the leakage magnetic flux from the magnetic core 2 becomes small. In this case, a transformer is formed at the voltage across the excitation winding 3 and the detection winding 4, and when the number of turns of the excitation winding 3 and the detection winding 4 is the same, the output voltage of the detection winding 4 is the excitation winding. Can be considered equivalent to the input voltage. Therefore, the excitation winding 3 and the detection winding 4 can be shared as a single winding, and the role of the detection winding 4 can be replaced by the excitation winding 3.

  The second harmonic component may be extracted using a lock-in amplifier synchronized with the excitation magnetic field control. Further, in the present embodiment, the filter circuit 8 has a form using a bandpass filter constructed by an analog circuit or a digital filter constructed by a digital circuit, a form in which only a specific frequency component is extracted by Fourier calculation using a microcomputer, and the like. In addition, a form that can extract only a signal having a period twice the period of the excitation magnetic field from the output voltage waveform of the detection winding 4 is included. Further, the rectifier circuit 9, the sensor sensitivity memory circuit 10, and the sensor sensitivity correction circuit 11 are not limited to analog circuits as long as the functions described above can be realized, and digital circuits or my computers are used. Can be configured.

  The offset current 37 is controlled to be turned on and off every cycle of the AC excitation current. However, there is no problem if the on period and the off period are each one period or more, for example, nine periods are continuously off, It is also possible to perform control such that only one cycle is on. In this case, the frequency of correcting the temperature characteristic is less than that in the case of once every two cycles, but the frequency of superimposing the offset current on the AC excitation current is also reduced, so the power consumption required for correcting the temperature characteristic is reduced. For example, it is convenient in a place where there is little change in the use environment temperature.

Furthermore, in the present embodiment, for the sake of convenience of explanation, the case where no current flows through the measured wire 1 has been described. However, in the output voltages of the filter circuit 8 and the rectifier circuit 9, the signal component amount corresponding to the offset current is offset control. Needless to say, the correction of the sensor sensitivity as described above operates correctly even if a current flows through the measured wire 1 because it can be calculated backward from the set value of the circuit 22 and the like. Therefore, the offset current is not limited to a binary combination of non-zero and zero values such as on and off, but may be a combination of different binary values other than zero as shown in FIG. In this case, the output voltage V _2f of the filter circuit 8 and the output voltage V _d of the rectifier circuit 9 have the waveforms shown in FIG. 13, and the sensor sensitivity can be calculated as in FIG.

  Further, as shown in FIG. 14, a plurality of current wires 1 to be measured may be passed through the magnetic core 2 and used as a zero-phase current sensor. In this case, it can be used as a leakage detection sensor. Note that the current line to be measured penetrating the magnetic core 2 is not limited to two as long as it forms a zero-phase state, and there is no problem with three, four, or more.

  Further, in the graphs of FIGS. 2, 5, and 6, the hysteresis characteristic and the nonlinear characteristic near the origin are omitted for convenience of explanation, but this does not affect the extraction of the second harmonic component. For convenience of explanation, the excitation magnetic field is described using a triangular wave. However, even when the excitation magnetic field is a sine wave, only the output voltage waveform of the detection winding 4 is slightly different, and the same effect can be obtained. it can. The same applies to the following description. Further, in this specification, the current-based mode in which the offset current is superimposed on the AC excitation current has been described. However, the same applies to the voltage-based mode in which the offset voltage is superimposed on the AC excitation voltage.

  In addition, for convenience of explanation, the offset current rise and fall timings are shown as synchronized with the zero crossing timing of the AC excitation current, but the timings of the two do not necessarily coincide with each other. It may be shifted by (phase difference).

  As described above, in this embodiment, the sensor sensitivity can be calculated from the output voltage waveform obtained by the rectifier circuit 9 by superimposing the switched offset current waveform on the AC excitation current waveform. Even if it changes, the sensor sensitivity can be corrected. As a result, highly accurate current detection is possible with stable sensor sensitivity.

  Furthermore, since the configuration of the present embodiment does not have the conventional closed loop control configuration and differential configuration, the current consumption of the sensor does not increase and the size of the sensor does not increase. In particular, in the case of closed-loop control, the current required for closed-loop control increases as the current measurement range increases, but with the method of this embodiment, only the minimum offset current that can be measured by the sensor is superimposed on the AC excitation current. Therefore, less current is required than the current required for closed-loop control. The same applies to the following embodiments.

Embodiment 2. FIG.
FIG. 15 is a block diagram showing Embodiment 2 of the present invention. The current detection device 102 includes a fluxgate sensor 51 and a sensor sensitivity calculation processing unit 72, and has the same configuration as the current detection device 101 according to the first embodiment as a whole. The difference is that a positive / negative sensitivity calculation circuit 25 is used instead of the sensor sensitivity calculation circuit 24.

In the present embodiment, the offset current 37 superimposed on the AC excitation current is set to three different values including positive and negative as shown in FIG. In this case, the output voltage V _2f of the filter circuit 8 and the output voltage V _d of the rectifier circuit 9 are shown in FIG. Similar to FIGS. 11 and 13, it is possible to calculate the sensor sensitivity in FIG.

  The flux gate type current sensor has a sensor output that is zero even when the current to be measured is zero, due to the magnetic characteristics of the magnetic core 2 and the direct current component slightly different from the alternating current excitation current (different from the offset current component). In some cases, the sensor output does not become zero and an offset occurs in the sensor output, or the sensor sensitivity varies depending on whether the current is positive or negative. In such a case, this embodiment shows an effect.

Specifically, the offset control circuit 22 superimposes different ternary offset currents 37 including positive and negative on the AC excitation current 38, so that the positive / negative sensitivity calculation circuit 25 sets the positive side sensor sensitivity and the negative side sensor sensitivity, respectively. Can be sought. For example, when superimposing the positive and negative different offset currents of the same value, if the sensor sensitivity of the positive side of the sensor sensitivity and the negative side are the same, the magnitude of the output voltage V _d of the rectifier circuit 9 should match. Further, different magnitude of the output voltage V _d of the rectifier circuit 9, will be the sensor sensitivity of the positive side of the sensor sensitivity and the negative side are different, or when the measured current is zero even at the sensor output is zero It becomes clear that there is no offset, that is, there is an offset in the sensor output. Whether the positive and negative sensor sensitivities are different or whether there is an offset in the sensor output should be clarified by superimposing more different values of offset current on the AC excitation current. Can do.

  As described above, in the present embodiment, the presence or absence of an offset in the sensor output is determined by superimposing different three-value offset currents including positive and negative values, or more, on the AC excitation current, and the positive-side sensor sensitivity and Since both negative sensor sensitivities can be calculated, the sensor sensitivity can be corrected with higher accuracy.

Embodiment 3 FIG.
FIG. 18 is a block diagram showing Embodiment 3 of the present invention. The current detection device 103 includes a fluxgate type sensor 51 and a sensor sensitivity calculation processing unit 73, and has the same configuration as the current detection device 101 according to the first embodiment as a whole. The difference is that the offset power supply 21 is provided with a test switch 26 and that the two measured current lines 1 penetrate the magnetic core 2. When the test switch 26 is manually activated, the offset control circuit 22 can forcibly superimpose the above-described offset signal on the AC excitation signal from the AC excitation power supply 5.

  For example, an earth leakage circuit breaker that detects an electric leakage in an electric circuit and interrupts the electric circuit may be provided with a test button for testing whether the interruption operation and the electric leakage sensor operate correctly after being installed in the electric circuit. When performing such a conventional test, a test current simulating a leakage is applied to the tertiary winding that is passed through or wound around the magnetic core of the leakage sensor by pressing a test button provided on the breaker body. Is actually energized. In this case, a tertiary winding for supplying a test current to the earth leakage sensor is required separately, which complicates apparatus assembly work and increases manufacturing costs.

  In the present embodiment, in view of such a situation, when the user presses the test switch 26, the offset current 37 can be forcibly superimposed on the AC excitation current 38 as shown in the first embodiment. It is configured. When the offset current is superimposed, the flux gate type current sensor 51 is in the same state as measuring the DC magnetic field. In other words, the test current simulating the above leakage can be substituted with the offset current superimposed on the AC excitation current, so that the test operation can be performed without using a conventional tertiary winding. it can.

  As described above, in this embodiment, it is possible to detect whether or not the flux gate type current sensor 51 is operating correctly by providing a function of superimposing the offset current on the AC excitation current when the test switch is pressed. .

1 current wire to be measured, 2 magnetic core, 3 excitation winding, 4 detection winding,
5 AC excitation power supply 6 Amplification circuit 7 Excitation current-voltage conversion circuit
8 Filter circuit, 9 Rectifier circuit, 10 Sensor sensitivity memory circuit,
11 Sensor sensitivity correction circuit, 21 Offset power supply, 22 Offset control circuit,
23 synchronization circuit, 24 sensor sensitivity calculation circuit, 25 positive / negative sensitivity calculation circuit,
26 test switch, 31 exciting magnetic field, 32 magnetic characteristics,
33 Magnetic flux time change, 34, 35 Output voltage waveform, 36 Offset current,
37 Offset current switching waveform, 38 AC excitation current waveform,
40 output voltage waveform, 51 fluxgate type current sensor, 61 excitation processing unit,
62 detection processing unit, 71, 72, 73 sensor sensitivity calculation processing unit,
101, 102, 103 Current detection device.

Claims (8)

A magnetic core that forms a closed magnetic path; an excitation winding wound around the magnetic core; and a detection winding wound around the magnetic core, and the current wire to be measured passes through the magnetic core. A fluxgate current sensor,
An excitation processing unit for generating an excitation magnetic field by energizing an AC excitation signal to the excitation winding;
A detection processing unit that performs signal processing by extracting only the second harmonic component of the excitation magnetic field from the output voltage waveform of the detection winding;
And an offset control unit that superimposes an offset signal on the AC excitation signal at a predetermined timing.   2. The current detection device according to claim 1, wherein the offset control unit superimposes offset signals having at least two different values on the AC excitation signal for a period of one or more periods of the excitation magnetic field. A synchronization processing unit that synchronizes the output signal waveform from the detection processing unit and the offset signal waveform;
The current detection device according to claim 2, further comprising: a sensor sensitivity calculation unit that calculates the sensor sensitivity of the fluxgate type current sensor based on an output signal waveform obtained when the offset signal is superimposed. The offset controller superimposes an offset signal having a value including at least three different positive and negative values on the AC excitation signal for a period of one or more periods of the excitation magnetic field,
The current detection device includes a synchronization processing unit that synchronizes the output signal waveform from the detection processing unit and the offset signal waveform,
And a positive / negative sensor sensitivity calculation unit for calculating the positive and negative sensor sensitivities of the fluxgate type current sensor for positive and negative currents based on the output signal waveform obtained when the offset signal is superimposed. The current detection device according to claim 2.   The current detection apparatus according to claim 4, wherein the positive / negative sensor sensitivity calculation unit determines the presence or absence of an offset of the fluxgate type current sensor based on an output signal waveform obtained when the offset signal is superimposed.   The current detection device according to claim 3, further comprising a sensor sensitivity correction unit that corrects an output from the fluxgate type current sensor based on the calculated sensor sensitivity.   2. The current detection device according to claim 1, wherein a test switch is provided in the offset control unit, and an offset signal is superimposed on the AC excitation signal when the test switch is activated.   The current detection device according to claim 1, wherein the excitation winding and the detection winding are shared as a single winding.

Images