JPH06258354A - Three-phase current detection circuit - Google Patents

Abstract

PURPOSE:To detect by means of two current transformers a current of each phase for protecting over-current and ground fault in a three-phase circuit. CONSTITUTION:In an inverter 2 that is an example of three-phase equipment forming three-phase circuit, primary-side-two-input type current transformers 3, 4 having a U, V phase output current and a V, W phase output current as primary inputs respectively, is provided. A circuit is so constituted that by using both secondary detection currents *Iu+*Iv and *Iv+*Iw, each current *Iu-*Iz, *Iv+*Iz, *Iw-*Iz including ground current *Iz is outputted as a protection current in the respective U, V and W phases via three computing circuits so that detection of over-current in the three phase circuit and detection of ground fault regardless of the phase that the ground fault happened thereto, are securely carried out.

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 three-phase power converters and other three-phase equipment for overcurrent protection or ground fault protection.

[0002]

2. Description of the Related Art As a conventional three-phase current detection circuit of this type, there are known ones illustrated in the 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 conversion device. 1 is a DC power supply, 2 is an inverter having a transistor having an antiparallel diode as its switching element, U, V, W are U-phase, V-phase, and W-phase output terminals of the inverter 2, 31 are current transformers that use the U-phase output current of the inverter 2 as the primary-side input current and output the detected current ^* I _u from the secondary side, Similarly, reference numeral 41 is a current transformer that outputs a detection current ^* I _w of the inverter W-phase output current.

In the following, in this sentence, the vector display is made by using the ^* mark attached to the left shoulder of the target amount display character, and in the related drawings, the vector display is made by using the ^* mark attached above the display character. Shall be performed. Therefore, for example, the above ^* I _u indicates the vector of the current I _u . 5 is a current operation circuit diagram corresponding to FIG. 4 for performing operation estimation of the V-phase required current using the detected currents ^* I _u and ^* I _w .

[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 the equation (2) derived from the following equation (1). ^{_{* I u + * I v +}} * I w = * I z .................. (1) ∴ * I v - * I z = - (* I u + * I w) ......... (2) here In addition, ^* I _z has a value three times as large as the ground fault current ^* I ₀ when the 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 electric currents having a vector relationship that forms a quadrangle as shown in equation (1), and equation (2)
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 above three-phase circuit is normal, ^* I _z =
The vector relation of 0 becomes a closed triangle regardless of whether the three-phase circuit is balanced or unbalanced, and the equation (2) is expressed by the following equation (3). Become.

^* _Iv =-( ^* _Iu + ^* _Iw ) (3) Further, FIG. 6 shows a current transformer 51 provided in the V phase of the main circuit diagram shown in FIG. The V-phase current is directly detected without using the operational amplifier circuit shown in FIG.

[0007]

For the purpose of overcurrent protection or ground fault protection of three-phase equipment such as a three-phase power converter, FIG.
And each current ^* I _u obtained by the circuit configuration shown in FIG.
^{When *} I _v − ^* I _z and ^* I _w are used, if there is no ground fault in the three-phase circuit, ^* I _z = 0 and normal overcurrent protection is possible.

However, if a ground fault occurs in the three-phase circuit, ^* I _z ≠ 0, and the absolute value of the V-phase operation current ^* I _v − ^* I _z related to this ^* I _z is the ground fault. Depending on the accident occurrence phase, it becomes smaller than that of ^* I _v itself, and there is a risk that the overcurrent protection for the V phase and the ground fault detection via overcurrent detection may be disabled. Therefore, when reliable protection is required to avoid the risk of being unable to protect as described above, conventionally, as shown in FIG. 6, a current transformer is inserted in all phases of the three-phase circuit, and the required current is calculated without making an estimation by calculation. The detection was done directly.

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 by 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 size and cost of the entire device will be increased. In view of the above, the present invention detects three-phase currents for the purpose of overcurrent protection or ground-fault protection of three-phase equipment such as three-phase power converters, while maintaining the reliability of protection, and 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, the three-phase current detection circuit of the present invention is a three-phase current detection circuit.
A first current transformer that uses both of the two phase currents as its primary inputs, the remaining one phase of the three phases, and the two selected as described above.
A second current transformer which has as its primary input both the currents of one of the phases, and a secondary output of the first current transformer having its phase inversion characteristic between its input and output signals as its input And a second operational amplifier having the secondary output of the second current transformer as its input and having the same characteristics as the first operational amplifier with respect to its phase characteristics and gain. Of the first and second operational amplifiers as an input, and a third operational amplifier having the same characteristics as the first operational amplifier with respect to its phase characteristic and gain, and the three sets The output of the operational amplifier is used as a required detection value for each of the three-phase currents.

[0011]

In general, the current or voltage vector of each phase of a three-phase circuit is a triangle when the circuit is normal without a ground fault,
It also forms a quadrilateral when a ground fault occurs. FIG. 3 is a current vector diagram that generally shows the mutual relation of the phase current vectors in the three-phase circuit, including when a ground fault occurs. If the three-phase phases are U, V, W, then Each side AO, BA, CB, CO forming the quadrangle OABC corresponds to each of the current vectors ^* I _u , ^* I _v , ^* I _w , ^* I _z , respectively, according to the above equation (1). Be related to each other.

When the three-phase circuit is normal, ^* I _z = 0
Then, the quadrangle OABC changes into 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 of the two phases selected as described above, for example, W and V phases. 1 for each primary input
Next, two sets of current transformers with two inputs are used.
From the next output, two sets of current composition vectors ^* I _u + ^* I _v and ^*
If I _v + ^* I _w is detected, it is possible to perform the calculation by the following formulas (4) to (6) derived from the above formula (1) using these detected values.

^* _Iu- ^* _Iz =-( ^* _Iv + ^* _Iw ) (4) ^* _Iv + ^* _Iz =-[( ^* _Iu- ^* _Iz ) + ( ^* _Iw− ^* _Iz )] (5) ^* _Iw− ^* _Iz = − ( ^* _Iu + ^* _Iv ) (6) The mutual relationship between the currents is shown in FIG. As a result, the following equations (7) to (9) are established in the absolute value comparison of the respective current vectors.

│ ^* I _u − ^* I _z │ ≧ │ ^* I _u │ ……………… (7) ｜ ^* I _v + ^* I _z │ ≧ │ ^* I _v │ …………………… (8) | ^* I _w − ^* I _z | ≧ | ^* I _w | ………………………………………………………………………………………………………………………………… (9) Although the phase changes depending on the occurrence of the accident, the magnitude relationship shown in Expressions (7) to (9) is established in at least two phases regardless of which phase the ground fault accident occurs.

That is, as described above, the equation (4) is used by using the detected current obtained by passing two sets of currents, each of which is a two-phase current having a common one phase among the three-phase currents, to each of the two current transformers. ) To Eq. (6), the U,
If the required detection current for the protection operation in each of the three phases of V and W is used, it is possible to surely detect the ground fault regardless of the phase in which the ground fault occurs, as well as the overcurrent when the three-phase circuit is normal. It will be possible.

[0016]

Embodiments of the present invention will be described below with reference to the main circuit diagram of the three-phase inverter shown in FIG. 1 and the current operation circuit diagram shown in FIG. 1 and 2, components having the same functions as those in the embodiment of the prior art shown in FIGS. 4 and 5 are designated by the same reference numerals.

First, FIG. 1 shows both current transformers 31 and 4 shown in FIG.
In place of 1, the primary and secondary input type current transformers 3 and 4 are provided. On the primary side of the current transformer 3, currents of both U and V phases of the inverter 2 and 1 of the current transformer 4 are provided. The V and W phase currents of the inverter 2 are passed to the next side, and the detected currents ^* I _u + ^* I _v
And ^* I _v + ^* I _w are output.

Next, in FIG. 2, three sets of operational amplifier circuits having the same characteristics with respect to the phase inversion characteristic and the gain are provided, and the amplifier AM is provided.
_For the first operational amplifier circuit consisting of ₁ and 3 resistors R ₁ , the current ^* I _u + ^* I _v is used as its input and consists of an amplifier AM ₂ and 3 resistors R _2. For the second operational amplifier circuit, the current ^* _Iv + ^* _Iw is used as its input, and for the third operational amplifier circuit consisting of the amplifier AM ₃ and the three resistors R _3. 1 shows a current operation circuit configured so that a sum of operation outputs of both the first and second operational amplifier circuits is used as an input.

Therefore, the respective three-phase currents determined by the equations (4), (5), and (6) as shown in FIG. 3 are supplied to the second, third, and first operational amplifier circuits, respectively. Can be obtained as the output of U, V, W
By setting the required detection current for the protection operation in each of the three phases, it is possible to ensure overcurrent detection and ground fault detection.

[0020]

According to the present invention, the three-phase circuit is used.
A first current transformer having currents of two phases (for example, both U and V phases) as its primary inputs, a remaining one phase of the three phases, and two phases selected as described above. 1-phase current (for example, W
And V both-phase current) both have their primary inputs as the second current transformer, and a second current transformer having the phase inversion characteristic between its input and output signals and having the secondary output of the first current transformer as its input. One operational amplifier, a second operational amplifier having the secondary output of the second current transformer as its input and having the same phase characteristics and gains as the first operational amplifier; And a third operational amplifier having the sum of the outputs of both the second operational amplifiers as its input and having the same phase characteristics and gains as the first operational amplifier, and the outputs of the three sets of operational amplifiers. A required current transformer is obtained by setting a required detection value of each three-phase current for the purpose of overcurrent protection or ground fault protection of a three-phase device such as a three-phase power converter that constitutes the three-phase circuit. Assures overcurrent detection and ground fault detection in a three-phase circuit with two 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 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 a prior art embodiment (No. 1).

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

FIG. 6 is a main circuit diagram of a three-phase inverter showing an example of a conventional technique (part 2).

[Explanation of symbols]

1 DC power supply 2 Inverter 3 Current transformer (2 input type of both U and V phase current) 4 Current transformer (2 input type of both V and W phase current) 31 Current transformer (1 input type of U phase current) 41 Current transformer (W-phase current 1-input type) 51 Current transformer (V-phase current 1-input type) AM amplifier (AM _1, AM _2, AM ₃ ) R resistance (R _1, R _2, R ₃ )

Claims (1)

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