JP2012233718A - Current detection device - Google Patents

Abstract

Provided is a current detection device capable of reducing cost and reducing current consumption while minimizing the influence of hysteresis characteristics of a magnetic core.
The present invention supplies an excitation coil 3 wound around a magnetic core 2 surrounding a conducting wire 1 through which a measurement current flows, and an excitation current whose polarity is reversed to the excitation coil 3, and a signal corresponding to a change in the excitation current. And a detection circuit 5 that detects a current flowing through the conductor 1 based on an output signal from the oscillation circuit 4. The exciting current supplied from the oscillation circuit 4 to the exciting coil 3 is such that the magnetic flux density of the magnetic core 2 is equal to or higher than the residual magnetic flux density.
[Selection] Figure 1

Description

  The present invention uses a zero-phase current transformer (ZCT) using a magnetic material, is used in various leakage current detectors, etc., and utilizes a magnetic phenomenon of a magnetic core to make an electrical contactless and direct current. The present invention relates to a current detection device for detecting a current.

As this type of current detection device, devices having various configurations have been proposed and implemented, but a flux gate type current sensor is known as a device that is structurally simple and capable of detecting a minute current. (For example, see Patent Document 1).
The conventional example described in Patent Document 1 has a configuration shown in FIG. That is, the same shape and isometrically formed cores 101 and 102 made of a soft magnetic material, the exciting coil 103 wound around the cores 101 and 102, and the cores 101 and 102 in a lump. And a wound detection coil 104.

An AC power supply (not shown) is connected to the excitation coil 103, and a detection circuit (not shown) is connected to the detection coil 104. And the to-be-measured conducting wire 105 which is an object which measures an electric current is inserted in the center of both the cores 101 and 102.
The exciting coil 103 is wound around the cores 101 and 102 so that the magnetic fields generated in the cores 101 and 102 are opposite in phase when they are energized and cancel each other.
When the exciting current iex is supplied to the exciting coil 103, the change with time of the magnetic flux density B generated in each of the cores 101 and 102 is as shown in FIG. The magnetic characteristics of the soft magnetic cores 101 and 102 have a linear relationship between the magnetic field magnitude H and the magnetic flux density B when the magnetic field magnitude H is within a predetermined range.

However, when the magnitude H of the magnetic field exceeds a predetermined value, the magnetic flux density B does not change and the magnetic saturation state is established. Therefore, when the exciting current iex is supplied to the exciting coil 103, it is generated in each of the cores 101 and 102. The magnetic flux density B to be changed changes to a vertically symmetric trapezoidal wave shape as shown by the solid line, and the phases are 180 ° out of phase with each other.
Assuming that a direct current value I is energized downward as shown by an arrow in the lead 105 to be measured, a magnetic flux density corresponding to this direct current component is superimposed. As a result, the magnetic flux density B is as shown in FIG. As indicated by the broken line, the upper trapezoidal wave has an enlarged width while the lower trapezoidal wave has a reduced width.

  Here, when the change in the magnetic flux density B generated in both the cores 101 and 102 is expressed by a sine wave (corresponding to the electromotive force), it is as shown in FIG. In FIG. 5 (c), a sine wave (electromotive force) having a frequency f shifted by 180 ° as shown in the solid line corresponding to the trapezoidal wave shown in the solid line in FIG. 5 (b) is shown. Are offset by 180 °, so they cancel each other. On the other hand, corresponding to the trapezoidal wave shown by the broken line in FIG. 5B, the second harmonic of the double frequency 2f as shown by the broken line appears in FIG. 5C. Since the second harmonics are 180 ° out of phase, when they are superimposed on each other, a sine wave signal as shown in the lowermost stage of FIG. 5C is obtained, and this is detected by the detection coil 104.

The detection signal captured by the detection coil 104 corresponds to the direct current value I flowing through the conductor 105 to be measured, and the current value I can be detected by processing this.
Further, as another conventional example, a primary winding for passing a current to be detected, and a secondary winding electrically insulated from the primary winding and magnetically coupled to the primary winding by a magnetic core For periodically driving the magnetic core to saturation, including one or more first sensing transformers comprising: and means for detecting saturation and reversing the direction of the magnetization current accordingly Proposed is a current sensor comprising sensing means comprising means for alternately supplying magnetizing currents in opposite directions to the secondary winding and processing means for outputting an output signal substantially proportional to the sensed current. (For example, refer to Patent Document 2).

  The current sensor further includes a low-pass filter that separates a low frequency or direct current component of the magnetizing current generated in the secondary winding by a current sensed by being connected to the secondary winding of the first sensing transformer. And a primary winding through which a sensed current passes, and a secondary winding, the input side of the secondary winding being coupled to the output of the low-pass filter, the output side of which is the device And a second sensing transformer installed by a resistor from which an output signal is generated.

  However, in the conventional example described in Patent Document 1, since the two cores 101 and 102 are used, it is actually difficult to completely match the magnetic characteristics of the cores 101 and 102. Due to the difference in magnetic characteristics, the voltage generated by the exciting current iex is generated without being completely canceled out. This deteriorates the S / N ratio of the detection voltage corresponding to the second harmonic component, and there is an unsolved problem that it is difficult to detect a minute current.

  Further, the second harmonic corresponding to the current value I output from the detection coil 104 has a trapezoidal wave shape distorted as shown by the broken line in FIG. 5C when the current value I becomes too large. In addition, the relationship between the current I and the second harmonic component is not proportional. Accordingly, since the detection range of the current value I is limited, there is an unsolved problem that a wide range of current cannot be detected. Furthermore, since at least two cores are used, there is also an unsolved problem that it is difficult to realize miniaturization and cost reduction.

Further, even in the conventional example described in Patent Document 2, it is necessary to provide the first detection transformer and the second detection transformer, and it is not possible to detect a wide range of current by one magnetic core. There is a problem to be solved.
In order to solve these problems, an improved invention as shown in FIG. 6 can be considered.
The improved invention shown in FIG. 6 is made of a soft magnetic material and is electrically insulated and wound around a magnetic core 2 surrounding a conducting wire 1 through which a measurement current flows, and an excitation current is supplied to the excitation coil 3. A circuit including an oscillation circuit 6 that performs the detection and a detection circuit 7 that is connected to the oscillation circuit 6 is conceivable.

  In such an improved invention, it is conceivable that the oscillation circuit 6 supplies the exciting current to the exciting coil and changes the duty of the rectangular wave voltage output according to the current flowing through the conducting wire 1. The oscillation circuit 6 needs to oscillate such that an excitation current in a state in which the magnetic core 2 is magnetically saturated or close to the magnetic saturation is supplied. The detection circuit 7 detects a current flowing through the conducting wire 1 by detecting a change in duty of the rectangular wave voltage.

JP 2000-162244 A Japanese Patent No. 2923307

However, in the above-described improved invention, there is a problem that the magnetic core 2 requires an iron core with good squareness of magnetic hysteresis, and generally requires an expensive magnetic material.
In addition, since the oscillation circuit 6 needs to supply an excitation current to the magnetic core 2 so that the magnetic core 2 is in the state of magnetic saturation or near the magnetic saturation, the current consumption of the circuit increases. There is.
Therefore, the present invention has been made paying attention to the above-described problems, and a current detection device that achieves cost reduction and low current consumption while minimizing the influence of the hysteresis characteristics of the magnetic core. The purpose is to provide.

  In order to achieve the above object, the current detection device of the present invention supplies an excitation coil wound around a magnetic core surrounding a conducting wire through which a measurement current flows, an excitation current whose polarity is reversed to the excitation coil, and the excitation coil Excitation means for outputting a signal corresponding to a change in current and current detection means for detecting the measurement current based on an output signal from the excitation means, the excitation means supplied to the excitation coil by the excitation means The current was such that the magnetic core had a magnetic flux density greater than or equal to the residual magnetic flux density.

The exciting means divides an operational amplifier, an output voltage of the operational amplifier, a threshold voltage setter for supplying the divided voltage to the first input terminal of the operational amplifier, and a second input terminal of the operational amplifier. A resistor to which one end is connected, and the exciting coil is connected between a second input terminal and an output terminal of the operational amplifier.
Further, the threshold voltage setting device sets the exciting current that is equal to or higher than the residual magnetic flux density of the magnetic core to an arbitrary value.

  In the present invention, the exciting means supplies an exciting current whose polarity is reversed to the exciting coil, and the magnitude of the exciting current is such that the magnetic flux density of the magnetic core is equal to or higher than the residual magnetic flux density. Therefore, according to the present invention, it is possible to reduce the cost and reduce the current consumption while minimizing the influence of the hysteresis characteristic of the magnetic core.

It is a block diagram which shows embodiment of the current detection apparatus which concerns on this invention. FIG. 2 is a circuit diagram illustrating an example of the oscillation circuit of FIG. 1. It is a wave form diagram which shows an example of the output waveform of an oscillation circuit. It is a figure explaining the relationship between the BH curve of a magnetic core, and the amplitude of the exciting current of an exciting coil. It is explanatory drawing which shows a prior art example, (a) is a block diagram of a sensor part, (b) is a figure which shows the magnetic flux density of each magnetic core when energizing an exciting current to an exciting coil, (c) is each magnetic It is the figure which expressed the magnetic flux density of the core with the sine wave. It is a block diagram which shows schematic structure of improved invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Configuration of the embodiment)
FIG. 1 is a configuration diagram showing a configuration of an embodiment of a current detection device according to the present invention.
In this embodiment of the current detection device, a current Io flowing through the conducting wire 1 is detected, and a ring-shaped magnetic core 2 is disposed around the conducting wire 1. That is, the conducting wire 1 is inserted into the magnetic core 2.
In this embodiment, as shown in FIG. 1, an excitation coil 3, an oscillation circuit 4 as excitation means, and a detection circuit 5 as current detection means are provided.

The exciting coil 3 is wound around the magnetic core 2 with a predetermined number of turns, and an exciting current is supplied to the exciting coil 3 from the oscillation circuit 4.
The oscillation circuit 4 supplies an excitation current whose polarity is inverted to the excitation coil 3 and outputs a voltage corresponding to a change in the excitation current as an output voltage. The oscillation circuit 4 supplies an exciting current to the exciting coil 3, and the magnitude of the exciting current is configured such that the magnetic flux density of the magnetic core 2 is equal to or higher than the residual magnetic flux density (see FIG. 4).

Therefore, as shown in FIG. 2, the oscillation circuit 4 includes an operational amplifier 41 that operates as a comparator. The exciting coil 3 is connected between the output terminal and the inverting input terminal of the operational amplifier 41.
A voltage dividing resistor 43 is connected between the output terminal and the non-inverting input terminal of the operational amplifier 41, and a voltage dividing resistor 44 is connected between the non-inverting input terminal of the operational amplifier 41 and the ground. Therefore, the voltage dividing resistors 43 and 44 constitute a threshold voltage setting unit that sets a divided voltage obtained by dividing the output voltage of the operational amplifier 41 as a threshold voltage Vth at the non-inverting input terminal of the operational amplifier 41.

A resistor 42 and a resistor 45 are connected in series between the inverting input terminal of the operational amplifier 41 and the output terminal 47. A capacitor 46 is connected between the output terminal 47 and the output terminal 48, and the output terminal 48 is connected to the ground.
Based on the output voltage of the oscillation circuit 4, the detection circuit 5 detects the amount of change in the current Io flowing through the conducting wire 1 and the current value at that time.

(Operation of the embodiment)
Next, an operation example of this embodiment will be described with reference to FIGS.
In this embodiment, as shown in FIG. 2, the divided voltage obtained by dividing the output voltage Va of the operational amplifier 41 by the voltage dividing resistors 43 and 44 is supplied to the non-inverting input terminal of the operational amplifier 41 as the threshold voltage Vth. Therefore, the operational amplifier 41 compares the threshold voltage Vth with the voltage Vd at the connection point between the exciting coil 3 and the resistor 42, and outputs the comparison output as a rectangular wave from the output side.

Now, when the output voltage Va on the output side of the operational amplifier 41 becomes a high level, this is applied to one end of the exciting coil 3. For this reason, the exciting coil 3 is excited by the exciting current Ib corresponding to the output voltage Va and the resistance values of the resistors 42 and 45. The exciting current Ib increases according to the inductance value of the exciting coil 3.
At this time, a relatively large threshold voltage Vth obtained by dividing the output voltage Va by the voltage dividing resistors 43 and 44 is input to the non-inverting input terminal of the operational amplifier 41. On the other hand, the voltage Vd at the connection point between the exciting coil 3 and the resistor 42 of the inverting input terminal of the operational amplifier 41 increases as the exciting current Ib of the exciting coil 3 increases, and this voltage Vd becomes the threshold voltage Vth of the non-inverting input terminal. Is exceeded, the output voltage Va of the operational amplifier 41 is inverted to a low level.

In response to this, the polarity of the excitation current Ib flowing through the excitation coil 3 is reversed, and the excitation current Ib decreases.
At this time, since the threshold voltage Vth is at a low level, the threshold voltage Vth is also low. Then, the voltage Vd at the connection point between the exciting coil 3 and the resistor 42 of the inverting input terminal of the operational amplifier 41 decreases with a decrease in the exciting current Ib of the exciting coil 3, and this voltage Vd is the threshold voltage Vth of the non-inverting input terminal. Is less than, the output voltage Va of the operational amplifier 41 is inverted to a high level.

For this reason, the output voltage Va of the operational amplifier 41 is a rectangular wave voltage that repeats a high level and a low level. The exciting current Ib of the exciting coil 3 is a sawtooth wave current that repeatedly increases and decreases.
With such an operation, as described above, the voltage Vd at the connection point between the exciting coil 3 of the inverting input terminal of the operational amplifier 41 and the resistor 42 changes, so that the output voltage Vo of the oscillation circuit 4 is as shown in FIG. Becomes a waveform including a vibration component (sine wave). The magnitude (amplitude) of the vibration component of the output voltage Vo changes up and down in accordance with the change in the current Io flowing through the conducting wire 1.
When the output voltage Vo of the oscillation circuit 4 is input, the detection circuit 5 obtains, for example, a change amount (difference) of the vibration component, and the change amount of the current Io of the conductor 1 and the current value at that time from the obtained change amount. Etc. are detected.

(Excitation current of excitation coil)
The oscillation circuit 4 of this embodiment supplies an exciting current to the exciting coil 3 as described above. The magnitude (amplitude) of the exciting current is such that the magnetic flux density of the magnetic core 2 is equal to or higher than the residual magnetic flux density Br. (See FIG. 4). The reason for this will be described below.
The magnetic core 2 has, for example, a BH characteristic (BH curve) as shown in FIG. The BH characteristic of the magnetic core 2 shows the relationship between the magnitude of the magnetic field H generated by the excitation current flowing through the exciting coil 3 and the magnitude of the magnetic flux density B, and is determined by the material of the magnetic core 2. Is done.

When a magnetic field is applied to the magnetic core 2, the magnetic flux density changes. However, when the magnitude of the magnetic field reaches a certain value, the magnetic flux density does not change, and this maximum magnetic flux density is the saturation magnetic flux density Bs. Further, once a magnetic field is applied to the magnetic core 2, even if the magnitude of the magnetic field is H = 0, a magnetic flux remains inside, and this is the residual magnetic flux density Br.
The BH characteristics of the magnetic core 2 are different between a case of using a general magnetic material and a case of a square made of a high magnetic permeability material. In order to suppress the current consumption of the oscillation circuit 4 when supplying an exciting current to the exciting coil 3 of the magnetic core 2, a rectangular core made of a high permeability material can be used as the magnetic core 2. In this case, the cost required for production increases. Therefore, in this embodiment, the magnetic core 2 using a general magnetic material capable of suppressing an increase in production cost is used.

When a general magnetic material is used as the magnetic core 2, it is necessary to suppress the amplitude of the excitation current supplied to the excitation coil 3 in order to suppress the current consumption of the oscillation circuit 4.
However, if the amplitude of the excitation current is suppressed, the BH characteristic of the magnetic core 2 draws a small hysteresis loop. In the case of a small hysteresis loop, there is a possibility of affecting the change in impedance of the magnetic core 2. Moreover, since the change of the electric current Io which flows into the conducting wire 1 is measured by the change of the impedance, there is a possibility that the measurement accuracy may be affected.

  Therefore, in this embodiment, as shown in FIG. 4, the magnitude (amplitude) of the exciting current supplied from the oscillation circuit 4 to the exciting coil 3 is such that the magnetic flux density of the magnetic core 2 is equal to or higher than the residual magnetic flux density Br. It is configured as follows. Such a configuration can be realized by presetting the threshold voltage Vth of the comparator 41 divided by the voltage dividing resistors 43 and 44 in accordance with the characteristics of the magnetic core 2.

(Effect of embodiment)
As described above, in this embodiment, the exciting current supplied to the exciting coil by the oscillation circuit is supplied, and the magnitude of the exciting current is set so that the magnetic flux density of the magnetic core is equal to or higher than the residual magnetic flux density. For this reason, according to this embodiment, even if an inexpensive magnetic core is used, it is possible to suppress the supply of exciting current that saturates the magnetic core, and to reduce the current consumption of the circuit. .

(Other embodiments)
(1) In the above embodiment, one conductor 1 is inserted into the magnetic core 2, but instead of this, two conductors through which a reciprocating current flows are inserted into the magnetic core 2. Also good.
In this case, the sum of the currents flowing through the two conductors is zero in a healthy state, but the difference current flows because the sum of the currents does not become zero in case of leakage or ground fault. can do.

(2) In the above embodiment, the threshold voltage setter is configured by the voltage dividing resistors 43 and 44, and the voltage dividing resistors 43 and 44 are configured by fixed resistors.
However, the threshold voltage setting device may be configured such that at least one of the voltage dividing resistors 43 and 44 is a variable resistor or a semi-fixed resistor. With this configuration, the magnitude of the excitation current that satisfies the above conditions can be set to an arbitrary value, and the magnitude of the excitation current can be set to an arbitrary value according to the difference in the BH characteristics of the magnetic core. it can.

  DESCRIPTION OF SYMBOLS 1 ... Conductive wire, 2 ... Magnetic core, 3 ... Excitation coil, 4 ... Oscillation circuit, 5 ... Detection circuit, 41 ... Operational amplifier, 42-45 ... Resistance, 46 ... Capacitor

Claims (3)

An exciting coil wound around a magnetic core surrounding a conducting wire through which a measurement current flows;
Excitation means for supplying an excitation current whose polarity is reversed to the excitation coil and outputting a signal corresponding to a change in the excitation current;
Current detection means for detecting the measurement current based on an output signal from the excitation means,
The current detection device according to claim 1, wherein the exciting current supplied to the exciting coil by the exciting means is such that a magnetic flux density of the magnetic core is equal to or higher than a residual magnetic flux density. The excitation means includes
An operational amplifier,
A threshold voltage setter that divides the output voltage of the operational amplifier and supplies the divided voltage to the first input terminal of the operational amplifier;
A resistor having one end connected to the second input terminal of the operational amplifier.
The current detection device according to claim 1, wherein the exciting coil is connected between a second input terminal and an output terminal of the operational amplifier.   The current detection device according to claim 2, wherein the threshold voltage setting unit sets the exciting current that is equal to or higher than a residual magnetic flux density of the magnetic core to an arbitrary value.

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