JPH112647A - Direct current sensor and method for preventing flowing-out of direct current - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a direct current sensor which can measure a very small direct current mixed in an alternating current flowing through a conductor to be detected for forming a transformerless type inverter which can substantially prevent the flowing-out of the direct current by detecting a relatively small direct current which flows in and is mixed with a large alternating current on the output side of the inverter and making the direct current zero by applying negative feedback based on the detected data. SOLUTION: A direct current sensor detects a direct current by reducing an alternating current component generated in an alternating current component detecting sensor by passively canceling the greater part of the alternating current component with a constitution in which a short-circuited coil 26 for reducing alternating current is extendedly wound around three cores in a toroidal core-like state and actively canceling the alternating current component with a coil 22 for feedback current which is extendedly wound around detecting cores 10 and 20 and through which a feedback current is made to flow so that the electromotive force generated in an alternating current detecting coil 21 by an alternating current may become zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct current mixed in an alternating current, which is used in the field of facilities for converting a direct current into an alternating current, such as a photovoltaic power generation system, an uninterruptible power supply, and various home appliances. The present invention relates to a DC current sensor for detecting a current, particularly, a DC current sensor having a simple structure and capable of detecting a small DC current superimposed on an AC current of a relatively large current with high sensitivity, and using the same in an AC current. The present invention relates to a DC current outflow prevention method for preventing a DC current from flowing out.

[0002]

2. Description of the Related Art Conventionally, in a device such as a photovoltaic power generation system or an uninterruptible power supply, a direct current is converted into an alternating current through an inverter. When a small DC current flows out and DC current flows into electrical equipment using an AC power supply used on the load side, the inductance of the power transformer, reactor, motor, etc. built in the equipment decreases due to DC bias, In order to cause a problem such as burning due to overcurrent, a configuration in which a transformer is arranged on the inverter output side has been adopted.

In a device such as a photovoltaic power generation system or an uninterruptible power supply, there is a configuration in which the inverter output is several hundreds of amps.
Since a small amount of direct current flows out, it is necessary to arrange a large transformer.

However, in this configuration, since the insulating transformer is expensive, large, and heavy, the inverter can be reduced in size and weight.
It is a factor that hinders cost reduction, and the use of a so-called transformerless inverter without a transformer has been considered.

[0005]

Although the above-mentioned transformerless inverter has advantages such as small size, light weight and low cost, it has a problem from the viewpoint of preventing DC current from flowing to the inverter output side as described above. It remains.

In order to put a transformerless inverter into practical use, it is indispensable to propose an inexpensive DC current outflow prevention means having a relatively simple structure as compared with the conventional transformer arrangement. However, until now, no specific DC current outflow prevention means has been proposed, and at present, it has not been put to practical use as a transformerless inverter.

In order to prevent a DC current from flowing out to the inverter output side when realizing a transformerless inverter, the inventor firstly uses a DC current sensor to detect a small DC current flowing out and mixed into an AC current. It has been found that by applying a negative feedback based on the detected data and setting the DC current to zero, it is possible to substantially prevent DC current from flowing out.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a DC current sensor suitable for realizing a substantial DC current outflow prevention method which solves the above problems.
It is an object of the present invention to provide a DC current sensor having a simple structure and capable of detecting a relatively small DC current superimposed on an AC current with high sensitivity, and to provide a DC current outflow prevention method using the same.

[0009]

SUMMARY OF THE INVENTION The inventor has previously made various measurements used in a wide range of fields, such as current measurement for maintaining and managing a switchboard control circuit signal and current measurement for controlling various DC devices. (Japanese Patent Application Laid-Open Nos. 6-74978 and 6-1943) have been proposed.
No. 89, JP-A-6-281674, JP-A-7-493
No. 57, JP-A-7-55846, JP-A-7-1103
No. 43, JP-A-7-128373, JP-A-7-198
754, JP-A-9-5361, etc.).

[0010] In order to achieve the above object, the present inventors have studied a configuration that can effectively utilize the DC current sensors having various configurations proposed above. The inventor provided a sensor for detecting a DC component flowing in the detected wire and a sensor for detecting an AC component flowing in the detected wire, and further arranged a coil for a feedback current extending over each of these sensors. It has been found that the above object can be achieved by adopting the configuration.

That is, once the AC component detection sensor detects only the AC component and applies a feedback current to the feedback current coil so that the output of the AC component detection sensor becomes zero, the AC component detection sensor In addition to making the effect of the AC component substantially zero, the effect of the AC component in the DC component detection sensor can also be made substantially zero at the same time. It has been found that it can be used effectively and that DC current mixed in AC current can be detected.

Particularly, in the DC current sensors proposed by the inventor, a detection core made of an annular soft magnetic material is disposed in each case, and the detection core is formed based on a magnetic flux in the detection core generated by a DC current flowing in a detected wire. This configuration detects the absolute value of the DC current, and when the AC current and the DC current simultaneously flow through the detected wire, the magnetic flux in the detection core generated by the AC current and the magnetic flux in the detection core generated by the DC current are superimposed. As a result, it becomes impossible to detect the absolute value of only the DC current.

However, the inventor of the present invention provided the above-described AC component detection sensor and the feedback current coil together, and became able to perform active cancellation in which the magnetic flux in the detection core generated by the AC current was made substantially zero. We have found that the superior characteristics of the DC current sensor proposed earlier can be used effectively, and that the absolute value of only DC current can be detected with high sensitivity.

Further, in some devices such as a photovoltaic power generation system and an uninterruptible power supply, the output of the inverter is several hundred A, and a DC current of at least several A is superimposed on the output side, and an AC component In the configuration where the detection sensor and the feedback current coil are installed together, the output of the detection sensor becomes large, and there is a problem that an amplifier or the like for active cancellation needs a large output, but the DC component detection sensor and the AC component detection sensor are used. And, by arranging the AC current reduction core and arranging the AC current reduction coil around both sensors and this AC current reduction core, most of the AC component generated in the AC component detection sensor is passively canceled. Completed the present invention by finding that a small amplifier can be used for the active cancellation amplifier. It was.

That is, according to the present invention, a DC component detection sensor, an AC component detection sensor, and a conductor to be detected through which a DC current and an AC current flow are arranged inside each of the AC current reduction cores, and the winding is wound over both the sensors. A coil having a return current coil to be arranged and an alternating current reduction coil arranged to be wound around both sensors and an alternating current reduction core, and has an AC component current generated by an alternating current flowing through the detected wire. The return current is passed through the return current coil so that the output of the AC component detection sensor, which has been reduced to a required value in advance by the AC current reduction coil, becomes zero, and the DC component is detected by the AC current flowing through the detected wire. Is a DC current sensor in which a DC component detection sensor detects a DC current flowing through the detected conductor by substantially eliminating the influence of.

Further, the inventor has set forth that in the DC current sensor having the above-described configuration, the AC component detection sensor includes an AC component detection core made of an annular soft magnetic material and an AC detection coil wound around the core in a toroidal shape. A DC component detection sensor comprising a ring-shaped soft magnetic material and a DC component detection sensor wound around the core in a toroidal manner. A configuration consisting of a coil and a DC detection coil is also proposed.

Further, the inventor has set forth that, in the DC current sensor having the above-described configuration, the DC component detection sensor causes the excitation coil to generate a triangular wave-like excitation current for generating a magnetic field exceeding the coercive force of the core in the DC component detection core. Flowing, detecting the timing at which the direction of the magnetic flux in the DC component detection core is reversed with a pulse-like voltage generated in the detection coil, and comparing and measuring the interval between the pulses to detect the DC current,
A DC component detection sensor causes a DC component detection core to flow through the excitation coil alternately with a positive / negative pulse current having a magnetically saturable peak value. The sampled and held values are individually measured, and the average output of the peak value is measured to detect a DC current. Also proposed is a DC current sensor configured to periodically switch the magnetic flux in the DC component detection core generated based on the DC current flowing through the DC current sensor.

Further, as described above, the inventor needs to detect a minute DC current flowing out and mixed in an AC current in order to prevent the DC current from flowing out to the inverter output side. It has been found that by applying a negative feedback based on the detected data and setting the DC current to zero, it is possible to substantially prevent the DC current from flowing out.

According to the present invention, a DC current is detected by a DC current sensor, and the DC current flowing out of the AC current on the output side of the inverter, which is obtained by converting the DC current into an AC current via an inverter, is detected. In the DC current outflow prevention method of applying the negative feedback based on the DC current to make the leaked DC current substantially zero, the DC current detection sensor, the AC component detection sensor, and the DC current The coil has a return current coil that is wound around both sensors and an AC current reduction coil that is wound around both sensors and the AC current reduction core. The AC component current generated by the AC current flowing through the detected wire is reduced to a required value in advance by the AC current reducing coil. A return current is caused to flow through the return current coil so that the output of the AC component detection sensor becomes zero, and the effect of the AC current flowing through the detected wire on the DC component detection sensor is substantially reduced to zero. This is a method for preventing direct current outflow using a direct current sensor in which a direct current flowing through the detected conductor is detected by a sensor.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the DC current sensor according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic explanatory view showing an embodiment of a DC current sensor according to the present invention. FIG. 1 shows a core made of three annular soft magnetic materials. From above, an AC current reducing core 25 for reducing an AC component current, an AC component detection core 20 constituting the AC component detection sensor 3, A DC component detection core 10 constituting the DC component detection sensor 2. Inside each of these cores 25, 20, and 10, a detected conducting wire 1 through which a direct current flowing out together with an alternating current flows is arranged.

The DC component detecting core 10 includes an exciting coil 11
And the DC detection coil 12 is wound and disposed in a toroidal shape,
An AC detection coil 21 is wound around the AC component detection core 20 in a toroidal shape. A return current coil 22 is wound around the DC component detection core 10 and the AC component detection core 20 in a toroidal manner, and a phase correction is provided between the AC detection coil 21 and the return current coil 22. The circuit 30 and the amplifier 31 are connected. The AC current reduction core 25, the AC component detection core 20, and the DC component detection core 1
The AC current reducing coil 26 is wound around the three cores 0 in a toroidal manner and short-circuited.

In the DC current sensor having the above structure, the DC component detection sensor 2 has the structure proposed by the inventor, and the excitation coil 11 has the DC component detection core 10 attached thereto.
A triangular wave-like exciting current for generating a magnetic field exceeding the coercive force of the core 10 flows therein, and the timing at which the direction of the magnetic flux in the DC component detecting core 10 is reversed is determined by a pulse voltage generated in the DC detecting coil 12. The basic structure is a configuration for detecting and comparing and measuring the interval between the pulses (Japanese Patent Laid-Open No. 7-128373).

In this configuration, as shown in the figure, the structure of the DC component detection core is extremely simple, and the attached electronic circuit is also simple.
It is possible to provide the most effective DC current sensor at a small size and at a low price.

Further, these configurations will be described in detail with reference to FIGS. 4, 5 and 6. FIG. 4 shows a DC component detection sensor 2
FIG. 5 is a conceptual explanatory diagram illustrating the principle of operation of detecting a DC component. Here, in order to explain the principle of detection and operation of DC current, it is assumed that AC current does not flow through the detected conducting wire 1, and only DC current detection will be described.

The excitation coil 11 has a DC component detection core 10
5 in which a magnetic field exceeding the coercive force of the core 10 is generated.
A triangular waveform exciting current i as shown by the solid line of A flows. That is, the peak value of the exciting current and i _p, the exciting coil 1
1, the number of turns is N, the coercive force of the DC component detection core 10 is Hc,
Assuming that the magnetic path length of the DC component detection core 10 is l, Hc <N
so that i _p / l the peak value of the triangular waveform exciting current i to set a i _p.

When the DC current I is not flowing through the detected conductor 1 (I = 0), the exciting current i increases and Ni / l = Hc
, The exciting current i decreases and Ni / l = −
At the time of Hc, the direction of the magnetic flux in the DC component detection core 10 rapidly reverses as shown by the solid line in FIG. 5B, and the reverse direction pulse voltage as shown by the solid line in FIG. I do.

By passing this pulse voltage through a predetermined electric circuit, it is possible to finally obtain an analog output as shown in FIG. 5D. Here, if the coercive force Hc of the DC component detection core 10 is positive / negative symmetric, the pulse intervals T ₁ and T ₂ generated on the peak side and the valley side of the triangular excitation current i are independent of the magnitude of the coercive force Hc. Become equal.

When the DC current I is flowing through the detected conductor 1 (I = I ₀ ), the DC component detection core 10 has a magnetic field other than the magnetic field generated by the increase and decrease of the exciting current i as described above.
The direct current I flowing through the detection target wire 1 causes the magnetic field I
_{Since 0/1} is formed, these magnetic fields are superimposed and change as shown by broken lines in FIGS. 5A to 5C, respectively, and finally, an analog output as shown in FIG. 5E is obtained.

In this case, even if the coercive force Hc of the DC component detection core 10 is positive / negative symmetric, the difference (T ₂ <) between the pulse intervals T ₁ , T ₂ generated on the peak side and the valley side of the triangular excitation current i.
T ₁ ) will occur.

However, when the change per unit time of the triangular-wave excitation current i is constant and the absolute values of the gradients at the time of increase and decrease are equal, the DC current I flowing through the detected wire 1 becomes
Proportional to _{{(T 1 -T 2) /} (T 1 ten T _2)}.

Therefore, by previously measuring the correlation between the difference between these pulse intervals T ₁ and T ₂ and the DC current I flowing through the wire 1 to be detected, the respective pulse intervals T ₁ and T ₂ are electrically determined. Thus, the absolute value of the DC current I flowing through the detected conductor 1 can be detected.

Next, means for making the magnetic flux in the detection core generated by the alternating current substantially zero will be described with reference to FIG. FIG. 6 is an explanatory perspective view of the AC component detection sensor 3, and shows a configuration in which an AC detection coil 21 and a return current coil 22 are wound around an AC component detection core 20.

The alternating current flowing through the detected wire 1 causes
A magnetic flux φ is generated in the AC component detection core 20, and further,
An electromotive force is generated in the AC detection coil 21 based on the temporal change of the magnetic flux φ. Here, when a predetermined return current is passed through the return current coil 22 so that the electromotive force generated in the AC detection coil 21 becomes zero, the magnetic flux in the AC component detection core 20 can be substantially reduced to zero. it can.

Therefore, as shown in FIG. 1, the return current coil 22 is connected not only to the AC component detection sensor 3 and the DC component detection sensor 2, that is, the AC component detection core 20, but also to the DC component detection core 10. If it is wound and arranged, the magnetic flux generated by the alternating current flowing through the detected wire 1 generated in the DC component detection core 10 can be substantially reduced to zero. The DC detection coil 12 can detect only the DC current based on the above-described operation principle of the active cancellation without being affected by the AC current.

In short, the alternating current component detecting sensor 3 and the direct current component detecting sensor 2 and the return current coil 22 wound around both of them detect the magnetic flux in the detecting core 20 generated by the alternating current flowing through the conductor 1 to be detected. By substantially setting the magnetic flux generated by the AC current generated in the DC component detection core 10 to substantially zero, the DC detection coil 12 can be connected to the DC detection coil 12 without being affected by the AC current. Although it is possible to detect only the current, if the AC current flowing through the detection target wire 1 is, for example, several hundred A, the magnetic flux in the AC component detection core 20 naturally increases, and the return current The current flowing through the coil 22 also needs to be much larger, so that the phase correction circuit 30 and the amplifier 31 connected between the AC detection coil 21 and the return current coil 22 have a large current. It must be in the corresponding configuration.

Therefore, in order to reduce the magnetic flux generated in the AC component detecting core 20, as shown in FIG. 1, the AC current reducing core 25 is similarly detected adjacent to the AC component detecting core 20 inside the core. The conducting wire 1 is penetrated, and the AC current reducing coil 26 is toroidally formed over the three cores of the AC component detection core 20 and the DC component detection core 10.
Are wound, and the AC current applied to the AC component detection core 20 is passively canceled and reduced.

The passive canceling mechanism using the AC current reducing core 25 and the AC current reducing coil 26 will be described in detail. As shown in FIG. 2A, when the AC current flowing through the detected conductor 1 is I ₀ , Due to the alternating current flowing through the conducting wire 1, the magnetic flux φ ₀
Is generated, and an electromotive force is generated in the alternating current reducing coil 26 based on the temporal change of the magnetic flux φ ₀ , and the phase of the coil 26 of the alternating current reducing core 25 is shifted as shown in FIG. 2B. AC current i (= I _A / N, N is the coil 26
Turns).

The AC current I ₀ flowing through the detected conductor 1 also acts on the AC component detection core 20, but the magnetomotive force generated by the current i flowing through the AC current reducing coil 26 is generated by the through current I _0. is magnetomotive force applied to the AC component detecting core 20 acts on the magnetomotive force in the opposite direction is reduced by I _A min, as shown in FIG. 2c, the AC component detecting core 20 I _B (= I ₀ -I _A ) Magnetomotive force is applied.

[0039] AC component detecting core 20 wound Kikan current coil 22 are wound are current flows to cancel the I _B in an active cancellation described above, not only the AC component detecting core 20, Similarly, the DC component detection core 10 is also substantially zero, so that only the DC component remains in the DC component detection core 10 as shown in FIG. 2D, and detection of only the DC current can be realized. That is, the magnetic flux due to the AC magnetomotive force I _B of the AC component detecting core 20, substantially cancel in the magnetic flux due Kikan current from the amplifier 31 to flow in Kikan current coil 22, coil 22 for Kikan current AC Since the winding is arranged so as to extend over the component detection core 20 and the DC component detection core 10, only the DC component remains in the DC component detection core 10, and detection of only the DC current can be realized.

When the passive canceling amount is reduced as shown by a broken line in FIG. 2B when the AC current reducing core 25 generates heat during operation, the AC component appearing in the AC component detecting core 20 increases. It is advisable to increase the return current in anticipation.

In FIG. 1, the alternating current reducing coil 25, the alternating current detecting coil 20 and the direct current component detecting core
Is shown, a one-turn configuration made of a wide material may be used. Further, as shown in FIG. 3, the AC current reducing coil 26a is wound around the AC current reducing core 25 in a toroidal shape. And the AC component detection core 2
It is also possible to adopt a configuration in which the AC current reducing coil 26b is wound around the 0 and the DC component detection core 10 and connected to form one AC current reducing coil 26. However, it is necessary to set the turns ratio of the AC current reducing coils 26a and 26b to be larger on the AC component detection core 20 side and on the DC component detection core 10 side.

The inductance of the alternating current reducing coil 26 is L ₁ , and the inductance of the return current coil 22 is L ₂
In both cases, the value depends on the number of turns of each of the coils 22 and 26 and the cross-sectional areas of the AC component detection core 20 and the DC component detection core 10. It is necessary to appropriately select various conditions such as the number of turns and the core cross-sectional area according to characteristics required for the sensor, such as a current and a range of a DC current to be detected.

The inductance of the AC detection coil 21 and the feedback current coil 22 due to the DC bias occurs in the AC component detection core 20, and if the phase correction in the return circuit becomes inappropriate, the system becomes unstable. Oscillate. In order to prevent this, it is desirable to form a gap at at least one location in the circumferential direction for the purpose of stabilizing the inductance. In particular, from the viewpoint of electrical balance and manufacturability,
As shown in FIG. 6, it is desirable to form gaps 23a and 23b at two locations in the circumferential direction that are symmetrical. It is desirable to appropriately select the gap size according to the magnetic characteristics of the detection core and the magnitude of the DC current to be measured.

Known soft magnetic materials such as a Ni—Fe alloy (permalloy), a silicon steel plate, and a soft ferrite can be used for the DC component detection core, the AC component detection core, and the AC current reduction core. However, as can be seen from the above description, a material having a high magnetic permeability and a small coercive force is more preferable for the DC component detection core, and a material having good AC magnetic characteristics is used for the AC component detection core and the AC current reduction core. Because it is more preferable, the DC component detection core is Ni-
It is desirable that the AC component detecting core and the AC current reducing core are made of Mn-Zn soft ferrite in an Fe-based alloy. In addition, the AC current reducing core has a low Br
(Residual magnetic flux density) and high Bm (saturated magnetic flux density) can be used to achieve gapless operation.

Note that the excitation coil and the DC detection coil wound around the DC component detection core are not limited to the configuration provided independently as shown in the figure, but may be one coil sharing each function. Is also possible. That is, the excitation coil and the DC detection coil are wound substantially in the same direction and at the same position, and the pulse-like voltage is also generated in the excitation coil. Is added, the exciting coil can share the function of the DC detection coil.

The DC current sensor of the present invention having the structure shown in FIG. 1 has the advantages that the whole structure of the sensor is simple, and that it can be reduced in size and inexpensive. It has been found that the use of the exciting current inevitably limits the response speed. That is, when the frequency of the triangular excitation current is increased, the AC magnetic characteristic of the soft magnetic material constituting the DC component detection core becomes a loop shape unlike the DC magnetic characteristic, and a clear zero crossing and a pulse are generated from the detection coil. Therefore, a triangular current of up to about several tens of Hz is usually used.

When a triangular wave current having such a frequency is used, the response speed of the sensor is about 2 seconds.
Application to a photovoltaic power generation system that requires a high response speed within 0.5 seconds is difficult. The inventor
As a result of studying a configuration that enables a high response speed while maintaining the advantages of the DC current sensor having the configuration shown in FIG. 1, it was found that, in the configuration shown in FIG. No, DC component detection core 10
It was confirmed that high responsiveness can be realized by alternately passing positive and negative pulse currents having peak values that can be magnetically saturated.

The mechanism for generating an electromotive force to the detection coil shown in FIG. 14 will be further described in detail. In the DC current sensor having the configuration shown in FIG. 1, in a state where no DC current is flowing through the detection target wire, the excitation coil 11 has a positive / negative value having a peak value capable of magnetically saturating the DC component detection core 10. When a pulse current (the absolute value of the peak value is the same) is alternately passed, the detection core 10 changes to O → a → O, and further changes to O → b → O on the BH curve as shown in FIG. 14A. A corresponding magnetic flux is generated, and as shown in FIG. 14B, an electromotive force proportional to the amount of change in the generated magnetic flux is detected by the detection coil 12 as outputs V ₁ and V ₂ .

In the state where no DC current is flowing through the conductor to be detected, V ₁ = V ₂ as shown in the figure, and the average output of the peak value becomes zero. Here, for example, when a DC current on the + side flows through the detected wire, the DC component is detected by the DC current.
There is magnetized, moved by + [Delta] H in O point + side on the B-H curve of FIG. 14A, the position of O ₁ of FIG 14C. In such a state, when the same positive / negative pulse current as described above is applied to the exciting coil 11, the detection core 10
As shown in FIG. 14D, a magnetic flux is generated according to the change of O ₁ -a ₁ -O ₁ on the BH curve, and further, the change of O ₁ → b ₁ → O ₁ , and FIG.
As described above, the electromotive force proportional to the amount of change in the generated magnetic flux is detected by the detection coil 12 as V ₁₁ and V ₁₂ .

In the display of A, C, and E in FIG. 14, the positions a and b change in the H direction according to the DC current flowing through the conductor to be detected at the required BH position. For convenience, the moving position is shortened and schematically displayed.

As is apparent from the figure, the amount of change of the magnetic flux based on the change of O ₁ -a ₁ -O ₁ is small. That is, the O point is +
This is because, by moving to the side by + ΔH, the saturation region on the + side is reached with a slight change in current, and the amount of magnetic flux generated substantially does not change even if the current increases thereafter. Also, O
₁ the amount of change in magnetic flux based on the change in the -b ₁ -O ₁ is large. That is, when the point O moves to the + side by + ΔH, the amount of change in magnetic flux until reaching the saturation region on the − side increases. Therefore, the electromotive forces V ₁₁ and V ₁₂ also satisfy V ₁₁ <V ₁₂ according to the change.

Similarly, when a negative DC current flows through the conductor to be detected, the DC component magnetizes the DC component detection core 10, and the O point on the BH curve in FIG.
Only moves, the position of the O ₂ in FIG. 14E. In such a state, when the same positive / negative pulse current as described above is applied to the exciting coil 11, the detection core 10 receives O ₂ → a ₂ → O ₂ on the BH curve as shown in FIG. Furthermore, O ₂ → b
A magnetic flux corresponding to the change of ₂ → O ₂ is generated, and as shown in FIG. 14F, electromotive forces proportional to the amount of change of the generated magnetic flux are detected by the detection coil 12 as V ₂₁ and V ₂₂ (V ₂₁ > V _22). ).

As described with reference to FIGS. 14C and 14E,
According to the DC current flowing through the detected wire, the detection coil 12
Different peak values (V ₁₁ <
V ₁₂ , V ₂₁ > V ₂₂ ) are obtained, these positive and negative peak values are individually sampled and held, and the average output of the peak values is measured to obtain the average output and the absolute value of the DC current. Is confirmed in advance, the absolute value and direction of the DC current flowing through the detected conductor can be confirmed. Note that V ₁ + V ₂ , V ₁₁ + V ₁₂ , and V ₂₁ + V ₂₂ have substantially the same value.

In order to obtain the above effects, the positive and negative pulse currents flowing through the exciting coil 11 must be large enough to sufficiently saturate the detection core 10. That is, by the DC current flowing through the detected wire,
Even after the point O on the BH curve has moved, the saturation region on the BH curve (a,
It is clear from the above description that changes up to b, a ₁ , b ₁ , a ₂ , b ₂ ) need to be made.

Therefore, the required response speed, the detection core 1
It is desirable to set the frequency and the peak value of the pulse current flowing through the exciting coil 11 according to the material of 0 or the like. In addition,
According to the experiment of the inventor, in the configuration shown in FIG. 13, a pulse current having a frequency of 2 kHz and a positive and negative peak value of 25 V was passed through the exciting coil 11 and measured. A measurement result with the same linearity as the measurement is obtained, and the response speed is about 0.1 second, which enables measurement at a response speed that is at least an order of magnitude faster than when a triangular wave current is applied. Was confirmed. In the above experiment, the excitation coil 11 was formed by winding an enamel wire having an outer diameter of 0.1 mm for 50 turns, and the detection coil 12 was formed by winding an enamel wire having an outer diameter of 0.1 mm for 500 turns.

In the configuration in which a predetermined pulse current is applied to the exciting coil 11, the AC magnetic characteristics (BH)
If the waveform of the pulse current is sharp (short time) without being affected by the curve, the electromotive force generated in the detection coil 12 inevitably becomes sharp (short time), and the response speed can be greatly improved. Becomes

Although the principle of detecting a direct current has been described in detail above, the alternating current component detecting core 20, the alternating current detecting coil 21, and the feedback current coil 22 constituting the alternating current component detecting sensor 3 also adopt the same arrangement as in FIG. Therefore, only a minute DC current flowing together with an AC current in the detected conductor can be measured with high sensitivity based on the same principle as that of the configuration in which a triangular wave current flows through the exciting coil 11.

Since any of the above-described configurations can employ a very simple configuration as the DC component detection core, it has already been described that the entire configuration as the DC current sensor can be simplified, miniaturized, and inexpensive. As described above, by selecting the current to be supplied to the exciting coil according to the required response speed, the use thereof can be further expanded.
However, when the detection current becomes an eddy current and scales out, the operation as a sensor becomes unstable, so that the measurement range is relatively narrow (usually about 0.1 to 20 A).

In order to remedy such a drawback, the inventor arranged DC current sensors having various configurations as proposed above as a DC component detection sensor in the DC current sensor of the present invention. In addition, it has been confirmed that various configurations according to various required characteristics can be provided. For example, it has been confirmed that the adoption of the configuration as shown in FIG. 11 enables not only expansion of the measurement range but also improvement of the response speed.

That is, as the DC component detection sensor 2, a pair of DC detection coils 33 electrically connected
a and 33b are wound in a toroidal shape on the short side of the rectangular frame-shaped soft magnetic material opposite to the DC component detection core 32, and flow out together with the AC current into the DC component detection core 32. The detecting conductor 1 through which a minute DC current flows flows through the detecting conductor 1. Further, as means for switching the magnetic flux Φ ₀ in the DC component detecting core 32 generated based on the DC current I flowing through the detecting conductor 1, A pair of exciting cores 34 made of a soft magnetic material forming a quadrangular cylindrical shape on the long sides at positions opposing the detection core 32
a, 34b and the DC component detection core 32
A configuration in which the exciting coil 35 is wound around the outer circumference (Japanese Patent Laid-Open No. 6-74978) can be employed.

In the DC component detection sensor 2 having such a configuration, when the DC current I flows through the detected conductor 1, a magnetic flux Φ ₀ is generated in the DC component detection core 32. When an alternating current (frequency f ₀ ) flows, an alternating magnetic flux is generated in the excitation cores 34a and 34b in the α direction in the figure, and the alternating magnetic flux causes the DC component detecting core 32 to rotate.
And the excitation cores 34a and 34b are magnetically saturated, and the magnetic flux Φ ₀ in the DC component detection core 32 is switched, so that the frequency of the alternating magnetic flux is twice (2f ₀ ) the excitation frequency. Is modulated. With the change of the magnetic flux Φ ₀ , an electromotive force (V _DET ) having a frequency of 2f ₀ proportional to the DC current I flowing through the wire 1 to be detected is applied to the DC detection coils 33 a, 3.
3b, and as a result, the absolute value of the DC current I flowing through the detected conductor 1 can be known.

Further, as the AC component detection sensor 3,
Rectangular component AC component detection core 40 made of soft magnetic material
By arranging a return current coil 42 so as to straddle the DC component detection core 32 and the AC component detection core 40 while arranging an AC detection coil 41 in the same manner as in FIG. The magnetic flux generated in the DC component detection core 32 due to the AC current flowing through the detected conductor I can be made substantially zero. Therefore, the DC component detection sensor 2 can realize detection of only the DC current based on the operation principle described above. In the drawings, 43a and 43b are gaps for preventing a change in inductance.

In the drawing, the configuration in which the feedback current coil 42 is arranged at only one location is shown. However, considering the electromagnetic balance, each side of the DC component detection core 32 and the AC component detection core 40 is provided. It is most preferable to dispose them at four locations. Further, although the AC component detection core 40 is shown as a rectangular plate-shaped configuration, the shape is not limited to the shape, and a disk-shaped or the like may be used in consideration of required measurement accuracy, winding workability of various coils, and the like. It is also possible to adopt the configuration described above.

According to the configuration of FIG. 11, it is not necessary to use a triangular excitation current, and the responsiveness can be greatly improved as compared with the configuration of FIG. Further, although the structure of the DC component detection core 32 is slightly more complicated than that of the configuration of FIG. 1, the detection current becomes an eddy current, and the operation as a sensor is relatively stable even when scaled out. Since high-sensitivity and high-accuracy measurement can be performed, the measurement range is also as wide as about 1 mA to 100 A. In addition, since noise can be easily removed on an electronic circuit, noise resistance is improved.

In the configuration shown in FIG. 12, characteristics equal to or higher than the configuration shown in FIG. 11 can be obtained. The DC component detection sensor 2 constituting the DC current sensor shown in FIG. 12 simplifies the configuration of the DC component detection core and enables the S / N ratio to be improved, and the DC detection coil 53 is formed in a toroidal shape. The DC component detection core 52 made of an annular soft magnetic material to be wound and arranged is formed in a tubular shape.
(See Japanese Patent Application Laid-Open No. 7-198754) in which an exciting coil 55 is wound around a hollow portion communicating in the circumferential direction.

In such a configuration, when the DC current I flows through the conductive wire 1 to be detected, the magnetic flux Φ
₀ occurs, but this time, alternating magnetic flux in the figure α direction is generated and flow excitation coil 55 in a predetermined excitation current (AC current) in the DC component detecting core 52, the DC component detecting core by the alternating magnetic flux Almost the entire region 52 is periodically magnetically saturated, and the magnetic flux Φ ₀ in the DC component detection core 52 is switched. In this configuration, the DC component detection core 52 also serves as the excitation core in the DC component detection sensor described with reference to FIG. 11, but is basically covered in the same manner as the operation principle of the DC current sensor in FIG. It is possible to know the absolute value of the DC current I flowing through the detection conductor 1.

In the figure, 3 is an AC component detection sensor 3
The configuration is substantially the same as that of the DC current sensor of FIG. That is, in the figure, reference numeral 60 denotes an AC component detection core made of a ring-shaped soft magnetic material, 61 denotes an AC detection coil, 62 denotes a feedback current coil, and 63a and 63b.
Is a gap for preventing inductance change. Therefore,
The operating principle similar to that of FIG. 1 makes it possible to make the magnetic flux generated in the DC component detection core 52 by the AC current flowing through the detected wire substantially zero, and the DC component detection sensor 2 described earlier. Based on the working principle
Detection of only DC current can be realized.

Also in the DC current sensor having this configuration,
As in the configuration shown in FIG. 11, high-speed response, high sensitivity, and high accuracy can be realized, but in particular, the manufacture of the DC component detection core 52 is easy to mechanize, and a lower price can be realized. Further, if a ferrite core is used for the DC component detection core 52, the AC magnetic characteristics are originally good, so that a higher speed response can be further improved. Further, although the electronic circuit is slightly complicated, the noise resistance characteristics are also shown in FIGS.
With the above configuration, excellent characteristics can be obtained.

The DC component detection sensor constituting the DC current sensor having the configuration shown in FIGS. 11 and 12 described above has a magnetic flux Φ ₀ in the DC component detection core generated based on the DC current I flowing through the conductor 1 to be detected. Is configured to form a magnetically saturated region due to the alternating magnetic flux in a part or all of the DC component detection core 52 in the circumferential direction to periodically cut off the magnetic flux Φ _0. The DC component detection sensor having the configuration shown in FIG. 13 differs in the means for switching the magnetic flux Φ ₀ .

The DC component detection sensor 2 constituting the DC current sensor shown in FIG. 13 is applied to a circumferential magnetic field in the DC component detection core 72 generated based on the DC current I flowing through the detected wire 1. By applying a magnetic field whose direction changes periodically orthogonal to the magnetic field, the magnetization direction in the DC component detection core 72 based on these synthetic magnetic fields is rotated,
The magnetic flux Φ ₀ in the DC component detection core 72 generated based on the DC current I flowing through the detected conductor 1 is modulated to perform magnetic switching. Also in this configuration, the mechanism of generating an electromotive force to the DC detection coil 73 is substantially the same as that of the DC current sensor of FIG. 11 except for the switching means (Japanese Patent Application No. Hei 7-180721).
issue).

More specifically, the DC component detection core 72 includes:
A plurality of through holes 7 formed on the side surface of the detection core 72
8 (shown in a rectangular shape in the figure, but may be a circular shape, etc.) so that the direction of the current in the same through-hole is the same and the direction of the current in the adjacent through-hole is opposite.
a, 75b are wound and the DC detection coil 73 is wound around the outer periphery in a toroidal shape. By applying a predetermined exciting current (AC current) to the exciting coils 75a and 75b, the DC component detecting core 7
2, the absolute value of the DC current I flowing through the target wire 1 to be detected can be known as described above.

In the figure, reference numeral 3 denotes an AC component detection sensor 3, which has substantially the same configuration as that of the DC current sensor of FIG. That is, in the drawing, reference numeral 80 denotes an AC component detection core made of a ring-shaped soft magnetic material, 81 denotes an AC detection coil, 82 denotes a feedback current coil, and 83a and 83b denote inductance change preventing gaps. Therefore, the magnetic flux generated in the DC component detection core 72 due to the AC current flowing through the detected wire can be made substantially zero by the operation principle similar to that of FIG. Based on the operation principle described above, detection of only DC current can be realized.

Although the DC current sensor having this configuration can obtain substantially the same characteristics as the configuration shown in FIG. 11, when the detected current becomes an eddy current and scales out, the DC component detection core 72 Although the rotation of the magnetization direction in the inside is not performed smoothly and the operation as a sensor becomes unstable, the measurement range is slightly narrowed, but it is usually 1 m.
Within the range of about A to 10 A, high-speed response, high sensitivity, and high accuracy can be realized. Further, since the structure of the DC component detection core 72 is very simple, it is an effective configuration from the viewpoint of size reduction and cost reduction.

As described above, FIGS. 11 to 15 show a DC component detection sensor in which a predetermined AC current is supplied to an exciting coil to generate a DC component generated based on the DC current mixed in the AC current flowing in the conductor to be detected. Although the example has been described in which the configuration is such that the magnetic flux in the component detection core is switched synchronously, the present invention is not limited to the illustrated example.For example, the magnetic flux Φ ₀ in the detection core generated based on the DC current flowing in the detected wire is detected. substantially blocking the magnetic flux [Phi ₀ periodically by changing the repulsion between the direction of the alternating magnetic flux perpendicular to a direction with respect to magnetic flux [Phi _0, switching the magnetic flux [Phi ₀ as a result configuration (JP-a-7 It is possible to use sensors of various configurations proposed earlier, such as US Pat.

Further, as a DC component detection sensor,
It is also possible to adopt a configuration in which a gap is formed in a part of a DC component detection core made of an annular soft magnetic material, and a Hall element is arranged in the gap.

Further, as a configuration of a DC component detecting sensor having excellent zero point accuracy and temperature characteristics and capable of measuring a wide range of DC current from a small current to a large current, an annular soft coil having a detection coil wound in a toroidal shape is provided. A direct current sensor having a means for switching a magnetic flux in a detection core generated based on a direct current flowing through the detected conductor, wherein the detected conductor through which a direct current flows is disposed through a detection core made of a magnetic material, A feedback coil that generates a magnetic flux in a direction to cancel the magnetic flux in the detection core generated based on the DC current flowing through the detected wire and makes the output of the detection coil substantially zero is disposed in a toroidal shape around the detection core. A configuration for detecting a direct current flowing through a detection target wire by measuring an applied current to the feedback coil (Japanese Patent Application No. Hei 8 54454 No.) can be adopted.

Further, as a configuration of a similar DC component detection sensor, a detection core made of an annular or polygonal annular soft magnetic material through which a detected wire through which a DC current flows is disposed, and an outer peripheral portion of the detection core are provided. An exciting core made of a soft magnetic material connected at right angles to the circumferential direction of the detecting core at a position symmetrical with respect to the axial center of the detecting core at least at four or more locations to form an annular shape; A detection coil wound around the detection core, an excitation coil wound around the detection core in the circumferential direction, and a toroidal winding around the detection core, which is generated based on a DC current flowing through the detected conductor. A feedback coil that generates a magnetic flux in a direction to cancel the magnetic flux in the detection core and makes the output of the detection coil substantially zero (Japanese Patent Application No. 8-35445).
No. 3) can be adopted.

In the DC current sensor of the present invention, the feedback current coil includes a DC component detection sensor (DC component detection core) and an AC component detection sensor (AC component detection core).
The configuration in which the coils are wound and arranged means that the winding is such that the same magnetomotive force (ampere turn) is applied to each of the two sensors (cores). Instead, it is possible to employ a configuration in which each sensor (core) is independently wound and arranged, and then connected in series with each other.

In the present invention, the ring-shaped soft magnetic material is not limited to the soft magnetic material having a so-called ring shape, but may be any other material as long as the soft magnetic material can form an electromagnetic closed circuit. Various configurations such as an annular shape, a rectangular frame shape and the like can be adopted as shown in the figure, and the DC component detection core and the AC component detection core do not necessarily have to have the same shape and the same dimensions.

[0080]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The direct current component detection core is a permalloy C (78% Ni-5% Mo-4% C) made of a thin plate having a thickness of 0.5 mm.
u-balFe) was punched into an outer diameter of 45 mm and an inner diameter of 33 mm, and was subjected to a predetermined heat treatment to complete it.

The AC component detecting core and the AC current reducing core are formed by stacking ten permalloy C punched products having the same material and the same dimensions as those of the DC component detecting core, and then halving the symmetrical shape. After each of the core pieces is cut into a substantially C-shape and subjected to a predetermined heat treatment, the pair of core pieces are formed with a gap spacer having a thickness of 50 μm so that gaps for preventing inductance change are formed at two places in the circumferential direction. It was integrated into a ring and completed.

After each of the DC component detection core, the AC component detection core, and the AC current reduction core are placed in an insulating case, as shown in FIG. 1, an excitation coil, a DC detection coil, an AC detection coil, a return current coil, The alternating current reducing coil was wound and arranged in a toroidal shape at a predetermined position. The excitation coil, the DC detection coil, the AC detection coil, and the return current coil are each provided with an enameled wire having an outer diameter of 0.2 mm.
Turn wound. AC current reduction coil is 0.2m in outer diameter
The m enameled wire was wound 1000 turns.

Further, the electronic circuit shown in FIG. 7 was connected to each coil, and the characteristics of the DC current sensor of the present invention were measured. The results are shown in FIGS. L ₂₁ is the alternating-current detection coil in FIG. 7A, L ₂₂ is Kikan current coil, L ₁₂ in FIG. 7B
DC detection coil, Aout the sensor output, L ₁₁ in FIG 7C illustrates the excitation coil.

The detected conductor penetrating through the DC component detecting core, the AC component detecting core, and the AC current reducing core is a vinyl-coated wire having an outer diameter of 15 mm, and the AC current is 3 mm.
00A, the triangular excitation current flowing through the excitation coil is 90H
z, l _p = ± 15 mA.

First, the influence of the AC current of 300 A flowing through the wire to be detected was passively canceled to 15 A by the AC component detecting core by the AC current reducing core and the AC current reducing coil. FIG. 8 shows the input / output characteristics when only the DC current is applied to the detected conductor while no AC current is applied. FIG. 9 shows the case where the AC current of the detected conductor acting on the AC component detection core is 15 A. Input current measured DC current in
FIG. 10 shows the output characteristics.
Are the input / output characteristics in which the measurement results are shown on the same graph. In FIG. 10, black circles indicate input / output characteristics corresponding to FIG. 8, and circles indicate input / output characteristics corresponding to FIG.

FIG. 10 shows that the DC current sensor according to the present invention can measure a minute DC current with high sensitivity regardless of the presence or absence of an AC current flowing through the conductor to be detected. In other words, the passive cancellation and active cancellation mechanisms make it possible to measure with relatively high sensitivity the relatively small DC current flowing into and out of the 300 A AC current, realizing the objective of achieving the practical use of a transformerless inverter. It is possible.

Since the AC component detection core forms a gap for stabilizing inductance as described above, the magnetic resistance increases and the amount of magnetic flux generated substantially decreases. Output cannot be obtained. For this reason, a plurality of punched permalloy thin sheets as in the embodiment are laminated on the AC component detection core, and by increasing the cross-sectional area of the detection core, the substantial amount of magnetic flux generated is increased and good AC magnetic field is obtained. Characteristics can be secured.

Since the use of the Mn-Zn ferrite essentially has good AC magnetic properties, the C
Since it can be made into a mold integrated product, it is easy to assemble and has a preferable configuration in terms of productivity and the like.

Further, it was confirmed that substantially the same results can be obtained with respect to the measurement sensitivity and the like of the entire DC current sensor as well as the configuration using the above-described integrated product of the permalloy laminate and the Mn—Zn-based ferrite.

Further, in the configurations shown in FIGS. 11, 12, and 13, it is possible to measure a small or relatively large DC current flowing out or mixed into the AC current with high sensitivity, similarly to the previous embodiment. It was confirmed that the transformer-less inverter could be put to practical use.

[0091]

The direct current sensor according to the present invention can cancel an alternating current component acting on the sensor core by a passive canceling and active canceling mechanism, and flows out to a large current alternating current in the detected wire. ,
It is possible to measure the relatively small DC current mixed in with high sensitivity without contact.For example, in a transformerless inverter, etc., a minute DC current flowing out and mixed into the AC current on the inverter output side can be measured. By detecting, applying a negative feedback based on the detected data, and making the DC current zero, it is possible to substantially prevent the DC current from flowing out.

Therefore, the DC current sensor and the DC current outflow prevention method using the same according to the present invention can prevent DC current from flowing into AC electric equipment on the load side of the inverter, and connect a transformer to the conventional inverter output side. A transformerless inverter having a simpler configuration and a lower cost can be put into practical use without causing a problem such as burnout of the inverter as compared with the configuration in which the inverters are arranged.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing one embodiment of a DC current sensor of the present invention.

FIGS. 2A and 2B are conceptual explanatory views illustrating the operation principle of passive cancellation of a DC current sensor according to the present invention. FIG. 2A illustrates an AC component current of a detected wire, and FIG. 2B illustrates an AC current reduction coil in an AC current reduction core. The generated AC component current, c represents the AC component current in the AC component detection core, and d represents the DC current.

FIG. 3 is a perspective explanatory view showing an example of a winding arrangement of an alternating current reducing coil of the direct current sensor of the present invention.

FIG. 4 is a perspective explanatory view of a DC component detection sensor of the DC current sensor according to the present invention.

FIG. 5 is a conceptual explanatory view illustrating the operation principle of the DC component detection sensor of the DC current sensor according to the present invention, wherein A is a triangular excitation current, B is the direction of magnetic flux, C is a pulse voltage,
D represents an analog output, and E represents an analog output.

FIG. 6 is an explanatory perspective view of an AC component detection sensor of the DC current sensor according to the present invention.

FIGS. 7A, 7B, and 7C are circuit diagrams of electronic circuits connected to the DC current sensor of the present invention.

FIG. 8 is a graph showing a relationship between a through DC current and an output voltage in the embodiment, and shows input / output characteristics when only a DC current is passed in a state where an AC current is not passed through a detected conductor.

FIG. 9 is a graph showing a relationship between a through DC current and an output voltage in the example, and shows input / output characteristics obtained by measuring a DC current in a state where a 15 A AC current is superimposed on a conductive wire to be detected.

FIG. 10 is a graph showing input / output characteristics in which the measurement results of FIGS. 6 and 7 are described on the same graph.

FIG. 11 is an explanatory perspective view showing a combination of an AC component detection sensor and a DC component detection sensor that constitute another DC current sensor according to the present invention.

FIG. 12 is a perspective explanatory view showing a combination of an AC component detection sensor and a DC component detection sensor that constitute another DC current sensor according to the present invention.

FIG. 13 is an explanatory perspective view showing a combination of an AC component detection sensor and a DC component detection sensor that constitute another DC current sensor according to the present invention.

FIG. 14 shows an electromotive force generation mechanism for a detection coil when a positive / negative pulse current having a peak value that magnetically saturates a DC component detection core is alternately supplied to an excitation coil of the DC current sensor of FIG. 1; To explain, A,
C and D are BH curves, and B, D and F are graphs showing the electromotive force output to the detection coil.

[Explanation of symbols]

DESCRIPTION OF REFERENCE NUMERALS 1 detected conductor 2 DC component detection sensor 3 AC component detection sensor 10, 32, 52, 72 DC component detection core 11, 35, 55, 75a, 75b Exciting coil 12, 33a, 33b, 53, 73 DC detection coil 20, 40, 60, 80 AC component detection cores 21, 41, 61, 81 AC detection coils 22, 42, 62, 82 Return current coils 23a, 23b, 43a, 43b, 63a, 63b, 8
3a, 83b Gap 25 AC current reducing core 26, 26a, 26b AC current reducing coil 30 Phase correction circuit 31 Amplifier 34a, 34b Exciting core 36 Orthogonal section 78 Through hole L ₁₁ Exciting coil L ₁₂ DC detecting coil L ₂₁ AC detecting coil L ₂₂ Kikan current for the coil

Claims (8)

[Claims] 1. A return ring in which a detection target wire through which a DC current and an AC current flow is penetrated inside each of a DC component detection sensor, an AC component detection sensor, and an AC current reduction core, and is wound around both sensors. A current coil and an alternating current reducing coil arranged to be wound over both sensors and an alternating current reducing core, and configured to reduce an alternating current component generated by an alternating current flowing through the detected wire to reduce the alternating current. A return current is passed through the return current coil so that the output of the AC component detection sensor, which has been reduced to a required value in advance by the coil, becomes zero, and the effect of the AC current flowing through the detected wire on the DC component detection sensor is substantially reduced. A direct current sensor for detecting a direct current flowing through the detected conductor with a direct current component detection sensor by setting the current to zero. 2. The direct current sensor according to claim 1, wherein the alternating current component detecting sensor comprises an alternating current component detecting core made of an annular soft magnetic material and an alternating current detecting coil wound around the core in a toroidal shape. 3. The direct current sensor according to claim 2, wherein a gap is formed in at least one circumferential position of the alternating current component detection core. 4. A DC current sensor according to claim 2, wherein the DC component detection sensor comprises a DC component detection core made of an annular soft magnetic material, an excitation coil wound around the core in a toroidal shape, and a DC detection coil. . 5. The DC component detection sensor according to claim 4, wherein the DC component detection sensor supplies a triangular wave-like exciting current for generating a magnetic field exceeding a coercive force of the DC component detection core to the excitation coil. A DC current sensor having a configuration in which a timing at which the direction of a magnetic flux is reversed is detected by a pulse-like voltage generated in a detection coil, and an interval between the pulses is compared and measured to detect a DC current. 6. The DC component detecting sensor according to claim 4, wherein the DC component detecting core flows through the exciting coil alternately a positive / negative pulse current having a peak value which can be magnetically saturated, and is generated in the detecting coil. A direct current sensor comprising a configuration in which the peak value of each of positive and negative pulse-shaped outputs is individually sampled and held, and an average output of the peak values is measured to detect a direct current. 7. A DC component detecting sensor according to claim 4, wherein the DC component detecting sensor periodically generates a magnetic flux in the DC component detecting core based on the DC current flowing through the detected conductor by flowing a predetermined AC current through the exciting coil. DC current sensor consisting of a switching device. 8. A DC current, which is obtained by converting a DC current into an AC current via an inverter and flowing out into the AC current on the output side of the inverter, is detected by a DC current sensor, and based on data detected by the DC current sensor. In the DC current outflow prevention method of applying the negative feedback to make the outflowing DC current substantially zero, the DC current and the AC component are detected inside each of the DC component detecting sensor and the AC component detecting sensor and the AC current reducing core. Arrange the lead wire through which the current flows,
It has a configuration having a coil for a return current that is wound and disposed over both sensors and a coil for AC current reduction that is wound and disposed over both sensors and an AC current reduction core,
An AC component current generated by the AC current flowing through the detected wire is passed through the return current coil so that the output of the AC component detection sensor reduced to a required value by the AC current reduction coil in advance becomes zero. A DC current flowing using a DC current sensor for detecting the DC current flowing through the detected conductor by the DC component detection sensor with substantially zero effect of the AC current flowing through the detected conductor on the DC component detection sensor. Prevention method.