JPH05126870A - Detector for current of inverter - Google Patents

Abstract

PURPOSE:To make the constitution simple and small, and to reduce the detected level of a ground current much more, by making possible the detection of an inverter input direct current and the ground fault current by a set of detectors for current including a current transformer. CONSTITUTION:A current detecting circuit 3 consists of a current transformer, and a current detector for receiving the output voltage of the Hall element 3a of the transformer to discriminate between an input direct current and a ground current and to detect the magnitude of each current. In the transformer, currents I1, I2 are allowed to flow on the same iron core having the element 3a inserted into its opening part, and the predetermined turn difference eta is provided between the first and second coils the numbers of turns of which are N1, N2 respectively. The directions of magnetic fluxes phi1, phi2 generated through both coils become opposite to each other. The ground fault current I3 flows into the ground through a virtual switch 6. By such a circuit constitution, the discrimination of currents I1 and I2 by polarity and the detection of each magnitude can be made by using a set of detected signals of the transformer, and the reduction of the detection level can be made together with the sharp detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection circuit for detecting an input DC current of an inverter and a ground fault current via a current transformer provided on the DC input side of an inverter.

[0002]

2. Description of the Related Art As a conventional current detecting circuit for an inverter of this type, as shown in a circuit diagram of an inverter device of FIG.
It is known to provide a separate current detection circuit for each of the input DC current and the ground fault current of the inverter. FIG. 3 shows an example of an inverter device having a three-phase circuit configuration for both input and output, 1 is a three-phase rectifier circuit having a diode bridge configuration, 2 is a smoothing capacitor, and 4 is an antiparallel diode. A three-phase inverter having a bridge structure in which a switching transistor having a switch is used as an arm element, 5 is a three-phase AC electric motor serving as a load of the inverter, and 6 is a ground fault at the output side of the inverter, for example, in the T phase It is a virtual switch for indicating a case where it occurs.

Reference numeral 8 is a ground fault current detection circuit, and the current detector whose input voltage is the output voltage of the current transformer is not shown. Here, the current transformer is provided with two sets of windings having the same number of turns on an iron core having a hole element inserted in its void portion,
A configuration in which a reciprocating current of a positive polarity current and a negative polarity current of the input DC current of the inverter are respectively passed through the both windings, and the directions of magnetic flux generated through the both windings are opposite to each other. Is. Further, 9 is a DC input current detection circuit, which comprises a DC current transformer (not shown) and its current detector.

Assuming that the inverter is operating normally, the positive current and the negative current are equal in magnitude, and therefore both currents can flow through the two sets of windings. The two sets of magnetic flux generated by are equal in magnitude and opposite in direction to each other, and the combined magnetic flux value is always zero irrespective of the magnitudes of the two currents, so that the output voltage of the hall element is also zero. If a ground fault occurs in the inverter and a ground fault current occurs as a difference between the two currents, the current difference, that is, the magnitude of the ground fault current, is proportional to the polarity corresponding to the polarity. A synthetic magnetic flux is generated in the iron core, and a voltage having a polarity proportional to the magnitude of the synthetic magnetic flux and corresponding to the polarity is output from the hall element. That is, the required ground fault current detection is performed.

[0005]

However, the conventional current detecting circuit for the inverter as described above requires separate current detecting circuits for detecting the input DC current and the ground fault current of the inverter. did. This complicates the circuit configuration of the inverter device and causes its size to increase. Further, from the viewpoint of protecting the human body, it is desired that the detection of the ground fault current is performed at a lower level. In view of this, the present invention enables detection of the input DC current and the ground fault current by a set of current transformers, simplifies and downsizes the circuit configuration of the entire inverter device, and further detects the ground fault current. It is an object of the present invention to provide a current detection circuit for an inverter that can further reduce the level.

[0006]

To achieve the above object, an inverter current detection circuit of the present invention is a detection circuit for detecting an input DC current of the inverter and a ground fault current in the event of a ground fault. On the iron core having a hole element inserted in the void, there are first and second windings that share the iron core and pass a reciprocating current of a positive polarity current and a negative polarity current of the input DC current, respectively. The magnetic fluxes generated through the both windings are provided so that the directions thereof are opposite to each other, and the difference between the two magnetic fluxes causes the positive and negative polarities thereof to be reversed with the increase of the difference current between the positive and negative currents and the difference current. A current transformer having a configuration in which the number of turns of each of the windings and the difference in the number of turns between the windings are appropriately selected so that the rate of change of the magnetic flux difference with respect to Proportional to the polarity corresponding to the magnetic flux difference and the magnitude of the magnetic flux difference A current detection for receiving the output voltage of the hall element having a value and discriminating the input DC current and the ground fault current from the magnitude and polarity of the output voltage and detecting the magnitude of each of the two currents. It shall consist of a container and a container.

[0007]

Operation: Two sets of windings for passing a forward current and a return current of a reciprocating current passing through a load are provided on the same iron core so that the directions of the magnetic flux due to the magnetomotive force in the two windings are opposite to each other. If the two sets of windings have the same number of turns, the combined magnetic flux in the iron core becomes zero when the forward current and the return current are the same, and if for some reason, there is a difference between the two currents. Occurs, the composite magnetic flux has a value proportional to the current difference and a polarity corresponding to the current difference. On the other hand, if an appropriate difference is given to the number of turns of the two sets of windings, and if the number of turns of the windings on which the current on the side that is supposed to decrease due to some reason flows is large, the two currents will be the same. In the case of, the combined magnetic flux is generated according to the difference in the magnetomotive forces in the two windings, and when the current difference between the two currents is generated due to the decrease in the one current as described above, the combined magnetic flux increases its value with the increase in the current difference. Is reduced to zero, the polarity is inverted, and then the value is increased again. The current change as described above can be detected by a hole element inserted in the void of the iron core through the magnetic flux in the iron core.

According to the present invention, the reciprocating current is used as the input DC current of the inverter, the inflow current and the outflow current of the input DC current are passed through the two sets of windings, respectively, and the outflow current passing winding is passed. The number of turns of the inflow current carrying winding is greater than the number of turns of the inflow current carrying winding,
The current difference is made to correspond to the ground fault current on the assumption that the inflow current decreases due to the ground fault of the input circuit. Therefore,
Since the combined magnetic flux in the iron core changes as described above including the polarity reversal as the ground fault current increases, it corresponds to the magnitude of the input DC current with the maximum value of the combined magnetic flux when the ground fault current is zero. Can be set to a value corresponding to the magnitude of the ground fault current by using the combined magnetic flux value after polarity reversal. However, the range from zero of the ground fault current to the value at the time of reversal of the composite magnetic flux polarity needs to be processed as an uncertain region of the ground fault current. Therefore, in the present invention as well, in order to reduce the uncertain region of the ground fault current and decrease the ground fault current detectable level due to the increase of the synthetic magnetic flux value corresponding to the expected maximum ground fault current, the two windings are connected to each other. A difference in the number of turns is selected.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the inverter device circuit diagram of FIG. 1 and the current transformer basic configuration diagram of FIG. In FIG. 1, constituent elements having the same functions as those in the embodiment of the prior art shown in FIG. 3 are designated by the same reference numerals. First, the basic operation of the present invention will be described below with reference to FIG. 2 showing the basic configuration of the current transformer. As shown in the figure, in the current transformer, currents I ₁ and I _{2 in the} directions of the arrows shown in the drawing are respectively passed on the same iron core having a hole element inserted in the gap, and the number of turns is N ₁ and N ₂ . The certain first and second windings are provided such that the directions of the magnetic fluxes Φ ₁ and Φ ₂ generated through the both windings are opposite to each other. Therefore, the magnetic flux of the iron core cavity passing through the hole element becomes the difference ΔΦ between the _two magnetic fluxes Φ ₁ and Φ _2, and the output voltage V _H of the hole element proportional to the difference ΔΦ. The formulas are as follows. Here, R is the magnetic resistance of the magnetic path of the iron core, and k is a proportional constant. Note that the currents I ₁ and I
_The numeral ₂ corresponds to a positive polarity current and a negative polarity current which form a round trip current of the input DC current in the inverter. Formula 1; ΔΦ = Φ ₁ −Φ ₂ = (N ₁ · I ₁ −N ₂ · I ₂ ) / R Formula 2; V _H = k · ΔΦ

Incidentally, in the conventional current detection system, N ₁
= N ₂ , and the current difference ΔI corresponding to the ground fault current is ΔI =
The following formula 3 is obtained as I ₁ -I ₂ . Formula 3; V _H = k · N ₁ · ΔI / R Therefore, when ΔI = 0, that is, I ₁ = I _{2, the} inverter operates normally and no ground fault occurs, V _H = 0. Further, when a ground fault accident occurs, that is, when I ₁ > I ₂ is usually satisfied, the detection voltage V _H of the ground fault current is expressed by the equation (3). However, the current I ₁ or I ₂ itself is not detected.

On the other hand, the present invention relates to the winding configuration of the current transformer, wherein the magnetic flux difference ΔΦ reverses its positive / negative polarity as the current difference ΔI increases, and the rate of change of the magnetic flux difference with respect to the difference current ΔΦ / ΔI. Is a predetermined large value,
The number of turns of each of the two windings and the difference in the number of turns between the two windings are appropriately selected. Now, assuming that the number of turns is n, for example, N ₂ = N ₁ + n (where n is 1 or more). Equation (1) is changed to Equation 4 below. Formula 4; ΔΦ = (N ₂ · ΔI−n · I ₁ ) / R If I ₁ = I _{2 is} satisfied, V _H is represented by the following formula 5. Formula 5: V _H = −k · n · I ₁ / R = −k · n · I ₂ / R That is, it is possible to detect the input DC current during normal operation of the inverter.

Further, when a ground fault accident in which I ₁ > I _{2 as} described above usually occurs, the above ΔΦ and V
_H has its polarity inverted from negative to positive at the boundary of ΔI = (n / N ₂ ) I ₁ . Also, the V _H is ΔI = 0
When that is, the inverter - generated ΔI from the value -k · n · I ₁ / R when no = value corresponding to the complete ground fault of I ₁ k · N ₁ · I else ground fault to operate normally It will change drastically up to ₁ / R.

Therefore, regarding the detection of the input DC current I ₁ and the ground fault current ΔI, the ratio of the current to the current ratio of 0 to (n / N ₂ ) I ₁ is detected by using the detection signals of the set of current transformers. It is possible to discriminate the input DC current I ₁ and the ground fault current ΔI based on the polarities and detect the respective magnitudes with the interval defined as an indeterminate region. If, for example, n = 1 and N ₂ = 100, the uncertain region is 1% of the current I ₁ , which is a value that causes no practical problems. Further, the ground fault current detection value at the time of a complete ground fault of ΔI = I ₁ is N ₁ / n times the current detection value at the time of normal operation of the inverter of ΔI = 0, 99 times in the above example, It is possible to detect extremely sharply and reduce the detection level.

Next, FIG. 1 shows a configuration in which the DC input and ground fault current detection circuit 3 is provided in place of the ground fault current detection circuit 8 in FIG. 3 and the DC input current detection circuit 9 is removed. Here, the current detection circuit 3 receives the output voltage of the current transformer shown in FIG. 2 and the hall element of the transformer, and distinguishes between the DC input current and the ground fault current and the magnitude of each current. And a current detector (not shown) that performs the detection of the current transformer, and in terms of the current transformer, it is the same as the first winding of the number of turns N ₁ through which the positive polarity current I ₁ of the DC input current is conducted. A predetermined winding number difference n as described above is provided for the second winding having the number of windings N ₂ through which the negative polarity current I ₂ is passed. In FIG. 1, the ground fault current ΔI in the above description
Is indicated by I ₃ as indicated by the dotted line in the figure, and the current flows into the ground via the virtual switch 6. With such a circuit configuration, it is possible to discriminate between the DC input current and the ground fault current and detect the magnitude of each current by only one set of the current transformers 3 as described above.

[0015]

According to the present invention, the detection circuit for detecting the input DC current of the inverter and the ground fault current at the time of the ground fault is shared by the core on which the hole element is inserted in the void portion. Then, the directions of the magnetic fluxes generated through the first and second windings, through which the positive and negative currents of the input DC current and the negative current are respectively passed, are opposite to each other. And the difference between the two magnetic fluxes is such that the positive and negative polarities thereof are reversed as the difference current between the positive and negative currents increases and the rate of change of the magnetic flux difference with respect to the difference current becomes a predetermined large value. A current transformer having a configuration in which the number of turns of each of the two windings and the number of turns between the two windings are appropriately selected; a polarity corresponding to the magnetic flux difference; and a value proportional to the magnitude of the magnetic flux difference. Receiving the output voltage of the hall element having To a current detector for discriminating between the input DC current and the ground-fault current and detecting the magnitude of each of the two currents, thereby forming a set of currents including one current transformer as described above. The detection circuit enables detection of the inverter input DC current and the ground fault current, which simplifies and downsizes the circuit configuration of the inverter device as a whole.
Furthermore, the ground fault current detection level can be further reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an inverter device showing an embodiment of the present invention.

FIG. 2 is a basic configuration diagram of a current transformer showing an embodiment of the present invention.

FIG. 3 is a circuit diagram of an inverter device showing an example of a conventional technique.

[Explanation of symbols]

 1 Three-Phase Rectifier Circuit 2 Smoothing Capacitor 3 DC Input and Ground Fault Current Detection Circuit 3a Hall Element 4 Three Phase Inverter 5 Three Phase AC Motor 6 Virtual Switch 8 Ground Fault Current Detection Circuit 9 DC Input Current Detection Circuit

Claims (1)

[Claims] 1. A detection circuit for detecting an input direct current of an inverter and a ground fault current in the event of a ground fault, wherein the core is shared on an iron core in which a hole element is inserted in the void. A first winding and a second winding for passing a round trip current of a positive current and a negative current of a direct current are provided so that the directions of magnetic flux generated through the both windings are opposite to each other. And so that the difference between the two magnetic fluxes reverses the positive and negative polarities with an increase in the difference current between the positive and negative currents, and the rate of change of the magnetic flux difference with respect to the difference current becomes a predetermined large value,
A current transformer having a configuration in which the number of turns of each of the two windings and the number of turns between the two windings are appropriately selected; a polarity corresponding to the magnetic flux difference; and a value proportional to the magnitude of the magnetic flux difference. A current detector for receiving the output voltage of the hall element having the above-mentioned, and discriminating the input DC current and the ground fault current from the magnitude and polarity of the output voltage and detecting the magnitude of each of the both currents. An inverter current detection circuit comprising: