JP3097375B2 - Three-phase current detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase current detection circuit for protecting three-phase devices such as three-phase power converters from overcurrent or ground faults.

[0002]

2. Description of the Related Art As a conventional three-phase current detection circuit of this type, there are known those shown in the respective circuit diagrams of FIGS. First, FIG. 4 is a main circuit diagram of a three-phase inverter as an example of a three-phase power converter, wherein 1 is a DC power supply, 2 is an inverter whose switching element is a transistor having an anti-parallel diode, and U, V, and W are each U-phase of the inverter 2, V-phase, the output terminals of the W-phase, 31 current transformer for outputting the detected current ^* I _u from the secondary side to the U-phase output current of the inverter 2 and the primary input current, Similarly 41 is a current transformer that outputs a detection current ^* I _w inverter W-phase output current.

[0003] In the following, in the following description, the vector display is performed by using an asterisk ( ^*) attached to the left shoulder of the target amount display character. Shall be performed. Therefore, for example, ^* _Iu indicates a vector of current _Iu . FIG. 5 is a current operation circuit diagram corresponding to FIG. 4 and performing operation estimation of the required V-phase current using the detected currents ^* _Iu and ^* _Iw .

[0004] In FIG. 5, and 1 the gain and amplifier AM ₃ and three resistors R ₃ of the same resistance value, and the operational amplifier which forms the phase reversal between its input and output signals based on the zero potential at point G It constitutes a circuit and performs the operation of equation (2) derived from equation (1) below. ^{_{* I u + * I v +}} * I w = * I z .................. (1) ∴ * I v - * I z = - (* I u + * I w) ......... (2) here The ^* I _z has a value three times the ground fault current ^* I ₀ when a ground fault occurs in the three-phase circuit.

That is, when a ground fault occurs in the three-phase circuit, there are four types of currents having a vector relationship forming a quadrilateral as shown in equation (1).
The detection current ^* I _u and ^* I _w of the sum of the phase-inverted signal as obtained ^* I _v accordance - ^* with a I _z in which form the desired V-phase current. When the three-phase circuit is normal, ^* I _z =
0, and the vector relationship represented by equation (1) forms a closed triangle irrespective of whether the three-phase circuit is balanced or unbalanced. The equation (2) is represented by the following equation (3). Become.

^* I _v = − ( ^* I _u + ^* I _w ) (3) FIG. 6 shows that a current transformer 51 is provided in the V phase in the main circuit diagram shown in FIG. This directly detects the V-phase current without using the operational amplifier circuit shown in FIG.

[0007]

FIG. 4 is a diagram showing the purpose of protecting an overcurrent or a ground fault of a three-phase device such as a three-phase power converter.
And the currents ^* I _u , obtained by the circuit configuration shown in FIG.
^{When *} _Iv- ^* _Iz and ^* _Iw are used, if there is no ground fault in the three-phase circuit, ^* _Iz = 0 and normal overcurrent protection is possible.

However, if when a ground fault occurs in the three-phase circuit ^* I _z ≠ 0, and this ^* the V-phase operation currents related to I _z ^* I _v - absolute value of ^* I _z is ground Depending on the accident occurrence phase, it becomes smaller than that of ^* _Iv itself, and there is a possibility that ground fault detection via overcurrent detection and overcurrent detection for the V phase may become impossible. Therefore, when reliable protection is required to avoid the danger of unprotection as described above, current transformers are conventionally inserted in all phases of a three-phase circuit as shown in FIG. Direct detection was performed.

That is, in the current detection for the purpose of protection as described above, when the current of each of the three phases is performed using two current transformers according to the circuit configurations of FIGS. 4 and 5, the reliability of the protection operation is ensured. In addition, if three current transformers are used as shown in FIG. 6 in order to maintain the reliability of the protection operation, it is inevitable that the device as a whole becomes larger and more expensive. In view of the above, the present invention detects two-phase currents of three phases each for the purpose of overcurrent protection or ground fault protection of three-phase equipment such as a three-phase power converter, while maintaining the reliability of protection. It is an object of the present invention to provide a three-phase current detection circuit that can be performed by the current transformer.

[0010]

In order to achieve the above object, a three-phase current detection circuit according to the present invention comprises a three-phase current detection circuit.
A first current transformer having both of the two phases of the current as its primary inputs, and the remaining one of the three phases and the two selected as described above.
A second current transformer having one phase current as its primary input, and a second output of the first current transformer having a phase inversion characteristic between its input and output signals. A second operational amplifier having as its input the secondary output of the second current transformer and having the same characteristics as the first operational amplifier with respect to its phase characteristics and gain; And a third operational amplifier having as its input the sum of the outputs of the first and second operational amplifiers and having the same characteristics as the first operational amplifier in terms of its phase characteristics and gain. Are used as the required detection values of the three-phase currents.

[0011]

In general, the current or voltage vector of each phase of a three-phase circuit is represented by a triangle when the circuit is normal without a ground fault,
When a ground fault occurs, a quadrilateral is formed. FIG. 3 is a current vector diagram generally showing the mutual relationship of each phase current vector in a three-phase circuit including the time of occurrence of a ground fault. If the three phases are U, V, and W, sides AO to form a quadrilateral OABC, BA, CB, CO, respectively the respective current vector ^{_{* I u, * I v,}} * I w, * will correspond to I _z, respectively by the above formula (1) Be correlated.

When the three-phase circuit is normal, ^* I _z = 0
And the quadrilateral OABC changes to a triangle ABC.
Now, the currents of two phases of the three phases, for example, U and V phases, the remaining one phase of the three phases, and the currents of one phase, for example, both W and V phases of the two phases selected as described above, are obtained. 1 for each primary input
Using two sets of current transformers of the following two-input type,
From the next output, two sets of current composite vectors ^* _Iu + ^* _Iv and ^*
If _Iv + ^* _Iw is detected, it is possible to perform calculations by the following equations (4) to (6) derived from the above equation (1) using both detected values.

^* I _u − ^* I _z = − ( ^* I _v + ^* I _w ) (4) ^* I _v + ^* I _z = − [( ^* I _u − ^* I _z ) + ( ^* _Iw− ^* _Iz )] (5) ^* _Iw− ^* _Iz = − ( ^* _Iu + ^* _Iv ) (6) FIG. 3 shows the interrelationship between the currents. As a result, the following expressions (7) to (9) hold in the absolute value comparison of each current vector.

| ^* _Iu− ^* _Iz | ≧ | ^* _Iu | (7) | ^* _Iv + ^* _Iz | ≧ | ^* _Iv |...... _{^{(8) | * I w -}} * I z | ≧ | * I w | ..................... (9) the magnitude relation shown in the expression (7) to (9), ground fault in the three-phase circuit Although the phase varies depending on the phase in which the accident occurs, the magnitude relationship shown in Equations (7) to (9) is established in at least two sets of phases regardless of the phase in which the ground fault accident occurs.

That is, as described above, the two sets of currents consisting of the two-phase currents having one phase common among the three-phase currents are applied to each of the two current transformers, and the detected currents obtained by the equations (4) are used. )-(6)
Assuming that the required detection current for the protection operation in each of the three phases of V and W is the overcurrent detection when the three-phase circuit is normal, the ground fault detection can be reliably performed regardless of the ground fault occurrence phase. It becomes possible.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the main circuit diagram of the three-phase inverter of FIG. 1 and the current calculation circuit diagram of FIG. In FIGS. 1 and 2, components having the same functions as those of the embodiment of the prior art shown in FIGS. 4 and 5 are denoted by the same reference numerals.

First, FIG. 1 shows both current transformers 31 and 4 shown in FIG.
1 is provided with current transformers 3 and 4 of a primary two-input type, and the primary side of the current transformer 3 receives the current of both U and V phases of the inverter 2 and the current transformer 1 The currents of both the V and W phases of the inverter 2 are supplied to the secondary side, and the detected currents ^* I _u + ^* I _v
And ^* I _v + ^* is obtained by the circuit constructed as to output and I _w.

FIG. 2 shows three sets of operational amplifier circuits having the same characteristics with respect to the phase inversion characteristic and the gain, and
₁ and No the current ^* I _u + ^* I _v and its input to the first operational amplifier circuit consisting of three resistors R ₁ Tokyo, consisting amplifier AM ₂ and three resistors R ₂ Metropolitan for the second operational amplifier circuit without the current ^* I _v + ^* I _w and the input for the third operational amplifier circuit further comprising an amplifier AM ₃ and three resistors R ₃ Metropolitan 9 shows a current operation circuit configured so that the sum of the operation outputs of the first and second operation amplifier circuits is used as an input.

Accordingly, the three-phase currents determined by the above equations (4), (5) and (6) and shown in FIG. 3 are supplied to the second, third and first operational amplifier circuits, respectively. , And each of these phase currents is expressed as U, V, W
By using the required detection current for the protection operation in each of the three phases, the overcurrent detection and the ground fault detection can be reliably performed.

[0020]

According to the present invention, the three-phase circuit
A first current transformer having both primary currents of two phase currents (for example, both U and V phases); and a remaining one phase among the three phases and a current among the two phases selected as described above. The current of one phase (for example, W
And V-phase currents), and a second current transformer whose primary input is both, and a second current transformer having a phase inversion characteristic between its input and output signals and having a secondary output of the first current transformer as its input. An operational amplifier, a second operational amplifier having a secondary output of the second current transformer as an input, and a second operational amplifier having the same characteristics as the first operational amplifier with respect to its phase characteristics and gain; And a third operational amplifier having as its input the sum of the outputs of the two operational amplifiers and having the same characteristics as the first operational amplifier in terms of its phase characteristics and gain. With the required detection value of each three-phase current for the purpose of overcurrent protection or ground fault protection of three-phase equipment such as a three-phase power converter that constitutes the three-phase circuit, To ensure that ground faults are detected together with overcurrent detection in a three-phase circuit. Ukoto can, it is possible to maintain the reliability of the protection with small cost reduction of the entire device, such as the conversion device.

[Brief description of the drawings]

FIG. 1 is a main circuit diagram of a three-phase inverter showing an embodiment of the present invention.

FIG. 2 is a current operation circuit diagram corresponding to FIG.

FIG. 3 is a current vector diagram in a three-phase circuit.

FIG. 4 is a main circuit diagram of a three-phase inverter showing an embodiment of the prior art (part 1);

FIG. 5 is a current calculation circuit diagram corresponding to FIG.

FIG. 6 is a main circuit diagram of a three-phase inverter showing an embodiment of the prior art (part 2).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Inverter 3 Current transformer (two-input type of U and V dual phase current) 4 Current transformer (two-input type of V and W dual phase current) 31 Current transformer (one input type of U phase current) 41 current transformer (1 input type of W-phase current) 51 current transformer (V-phase 1 input type of the current) AM amplifier _{(AM 1, AM 2, AM} 3) R resistor _{(R 1, R 2, R} 3)

Claims (1)

(57) [Claims] 1. A first current transformer having two primary currents of three phases in a three-phase circuit as primary inputs, and a remaining one phase of the three phases and a two phase selected as described above. A second current transformer having the primary current therein as its primary input, and a secondary output of the first current transformer having phase inversion characteristics between its input and output signals. A first operational amplifier, a second operational amplifier having as its input a secondary output of the second current transformer, and having the same characteristics as the first operational amplifier in terms of its phase characteristics and gain; A third operational amplifier having as its input the sum of the outputs of the first and second operational amplifiers and having the same characteristics as the first operational amplifier in terms of its phase characteristics and gain; The output of the operational amplifier is used as a required detection value for each of the three-phase currents. Current detection circuit.