JP2969192B2 - Current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device.

[0002]

2. Description of the Related Art Normally, a current detection method for detecting a current flowing through a conducting wire involves taking a current to be detected into a primary winding of a current transformer and connecting a resistor to a secondary winding of the current transformer. A current detection method of detecting the terminal voltage of the resistor as a detection signal of a primary current, and a current detection method of detecting a current flowing through a conductor by a Hall effect element are used.

[0003]

By the way, one of the current transformers is
A current detection method in which a current to be detected flows through the secondary winding, a resistor is connected to the secondary winding of the current transformer, and the terminal voltage of the resistor is detected as a primary current detection signal is a current detection method. If the current to be detected flowing in the primary winding is a current having a positive / negative asymmetric waveform such as a distorted wave current, the current transformer causes a DC bias, and the exciting current of the current transformer is a current including a DC component. Becomes According to the current transformer theory, since the secondary current of the current transformer is the difference between the primary current and the exciting current, the primary current and the secondary current of the current transformer do not have similar waveforms and are accurate. There is a problem that a primary current detection signal cannot be obtained.

A current detection method for detecting a current flowing through a conducting wire by a Hall effect element is similar to the current to be detected even when the current to be detected is a current having a positive or negative asymmetric waveform such as a distorted wave current. A detection signal is obtained,
There is a problem in that the Hall effect element is expensive, so that the current detector is also expensive and uneconomical.

The present invention has been made in view of the above circumstances, and has as its object to accurately detect not only a sinusoidal current but also a current having a positive / negative asymmetric waveform such as a distorted wave current, and is economical. An object of the present invention is to provide an excellent current detection device.

[0006]

In order to achieve the above object, a first aspect of the present invention is to provide a current transformer and the current transformer.
A resistor connected to the secondary winding to convert a secondary current to a secondary voltage;
And a first amplifier for amplifying the terminal voltage of the resistor as an input with an inverse gain of the resistance value of the resistor, and a leakage inductance of a secondary winding of the current transformer for outputting an output signal of the first amplifier. A second amplifier for amplifying the gain as a gain,
A differentiator for differentiating the output signal of the amplifier, a third amplifier for amplifying the output signal of the first amplifier using a secondary winding resistance of the current transformer as a gain, an output signal of the differentiator, A first adder for adding an output signal of a third amplifier; and a second adder for adding a terminal voltage of the resistor and an output signal of the first adder. A secondary induced voltage calculator for calculating a secondary induced voltage, and an output signal of the secondary induced voltage calculator being obtained by dividing the number of turns of a primary winding of the current transformer by a winding of a secondary winding. fourth amplifier which amplifies a gain to be, and the number of turns of the secondary winding of the reciprocal and the current transformer of the resistance value of the terminal voltage of the resistor the resistor
A primary load current calculator comprising a fifth amplifier for amplifying with a gain obtained by multiplying a value obtained by dividing the value by the number of turns of the primary winding, and
An integrator for integrating the output signal of the fine said fourth amplifier, and a sixth amplifier for amplifying the output signal of the integrator the inverse of the mutual inductance of the current transformer as the gain, the fourth
A seventh amplifier that amplifies the output signal of the first amplifier using the reciprocal of the iron loss resistance of the current transformer as a gain, and a third amplifier that adds the output signal of the sixth amplifier and the output signal of the seventh amplifier. A first excitation current calculator configured by an adder to calculate an excitation current of the current transformer; and an output signal of the first excitation current calculator and an output signal of the primary load current calculator. A first exciting current compensator including a fourth adder, wherein an output signal of the first exciting current compensator is used as a detection signal of a current flowing through a primary winding of the current transformer, and And outputting a detection signal having a waveform similar to the current flowing through the primary winding of the detector.

According to a second aspect of the present invention, in the current detecting device according to the first aspect, instead of the first exciting current compensator, an iron loss resistance of the current transformer and a leakage inductance of a secondary winding are used. By replacing the secondary winding resistance with approximately zero, the first amplifier, the second amplifier, the third amplifier, the differentiator, the first adder, the second adder, and the seventh amplifier A second exciting current compensator without a third adder;
Wherein the configuration of the amplifier inside the exciting current compensator is simplified.

[0008]

First, the principle of the current detecting device according to the present invention will be described with reference to FIGS. 8 is a current detection circuit diagram, FIG. 9 is a T-type equivalent circuit diagram of the current detection circuit of FIG. 8, and FIG.
FIG. 3 is a block diagram in which ₁ is input and i ₀ is output.

In FIGS. 8 and 9, reference numeral 30 denotes a current transformer;
1 is a resistor, i ₁ is a primary current of the current transformer 30, i ₂ is a secondary current of the current transformer 30, v ₂ is a terminal voltage of the resistor 31, 40
Is a primary winding resistance of the current transformer 30, 41 is a leakage inductance of a primary winding of the current transformer 30, 42 is an exciting resistance such as an iron loss of the current transformer 30, and 43 is a mutual inductance of the current transformer 30. , 44 is a primary conversion resistance of the secondary winding resistance of the current transformer 30, 45 is a primary conversion inductance of the leakage inductance of the secondary winding of the current transformer 30, and 46 is a primary conversion resistance of the resistor 31. The resistance, i ′ ₁ is the primary conversion current of the secondary current of the current transformer 30, that is, the primary load current, v ′ ₂ is the primary conversion voltage of the terminal voltage of the resistor 31, and i ₀ is the current transformer 30 Excitation current,
i _ow is the iron loss current of the current transformer 30, and i _ol is the magnetizing current of the current transformer 30.

In the block diagram of FIG. 10, blocks 50, 51, 52, 54, 55, 57 and 58 are gains, 53 is a differentiator, 56 is an integrator, 59 is a subtractor, 6
0, 61, and 62 are adders.

Accordingly, the subtractor 59 calculates were primary load current i _'1 subtracts the exciting current i ₀ from the primary current i _1. Gain 50 primary load current i 'ratio of turns N ₁ of the primary winding for the number of turns N ₂ of the secondary winding of current transformer 30 to _1, i.e. N _1/2 by multiplying the N ₂ primary current i Calculate ₂ and
Gain 51 calculates a terminal voltage v ₂ of the resistor 31 by multiplying the resistance value of the resistor 31 to the secondary current i _2, the gain 52 secondary winding of the current transformer 30 to the secondary current i ₂ multiplied by the leakage inductance, differentiator 53 differentiates the output signal of the gain 52, the gain 54 multiplies the resistance of the secondary winding resistance of transformer secondary current i _2. The adder 60 calculates the voltage drop inside the secondary winding of the current transformer 30 by adding the output signal of the differentiator 53 and the output signal of the gain 54, and
1 calculates the secondary induced voltage e ₂ of the current transformer 30 by adding the output signal v ₂ of the gain 51 and the voltage drop inside the secondary winding which is the output signal of the adder 60.

The gain 55 is obtained by multiplying the secondary induced voltage e ₂ by the ratio of the number of turns N ₁ of the primary winding to the number of turns N ₂ of the secondary winding of the current transformer 30, ie, N ₁ / N _2. The primary induced voltage e ₁ of the current transformer 30 is calculated, and the integrator 56 calculates the primary winding interlink main magnetic flux number ψ ₁ of the current transformer 30 by integrating the primary induced voltage e ₁ , gain 57 computes the magnetization current i _0l the current transformer 30 by multiplying the inverse of the mutual inductance of the current transformer 30 to [psi _1. The gain 58 is 1
By multiplying the next induced voltage e ₁ by the reciprocal of the iron loss resistance of the current transformer 30, the iron loss current i _0w of the current transformer 30 is calculated, and the adder 62 adds the magnetizing current i ₀₁ and the iron loss current i _0w . Thus, the excitation current i ₀ is calculated.

When the current i _{1 to} be detected is a current having an asymmetrical positive and negative waveform such as a distorted wave current, the exciting current i ₀ contains a DC component because the current transformer 30 causes a DC bias. Since the primary load current i ′ ₁ has a waveform obtained by subtracting the exciting current i ₀ from the current i ₁ to be detected, the primary load current i ′ ₁ has a waveform biased by the DC amount of the exciting current i ₀ , not a current i _1, similar to a waveform. Since the secondary current i ₂ of the current transformer 30 is similar to the primary load current i ′ ₁ , the terminal voltage v ₂ of the resistor 31 also does not have a waveform similar to the detection target current i ₁ .

Therefore, in the current detector shown in FIG. 8 which uses the terminal voltage v ₂ as a detection signal of the current i ₁ to be detected, the current to be detected is a current having a positive / negative asymmetric waveform such as a distorted wave current. , An accurate detection signal cannot be obtained.

[0015] Therefore, current transformer with respect to the detection signal v ₂ 30
It is considered that a detection signal similar to the current to be detected i ₁ is obtained by compensating the amount of the exciting current of. That is, FIG.
, It can be seen that the primary load current i ′ _{1 of the} current transformer 30 can be calculated by multiplying the detection signal v ₂ by the reciprocal of the gain 51 and the reciprocal of the gain 50. Also looking at the block diagram of the detection signal v ₂ until the exciting current i ₀ of the current transformer 30, found to be capable of calculating an exciting current i _0, further detected current i ₁ is the primary load current i _'1 and strange Sink 30
It can be seen that the excitation current i ₀ is added. Depending, the terminal voltage v ₂ from the primary load current i of the resistor 31 '
It is understood that the detected symmetric current i ₁ can be calculated by calculating ₁ and the exciting current i ₀ and adding the both.

Based on the above, an amount corresponding to the exciting current of the current transformer 30 is compensated for the terminal voltage v ₂ of the resistor 31 in the circuit shown in FIG. 8 and flows through the primary winding of the current transformer. the principle diagram of the excitation current compensator for calculating a detected current i ₁ is shown in FIG. 11.

In the block diagram of FIG. 11, 80 is an exciting current compensator, 81 is a secondary induced voltage calculator, 82 is an exciting current calculator, 83 is a primary load current calculator, 70 and 71 are gains, 72 Is an adder, and the other reference numerals are the same as those in FIG. That is, 52, 54, 55,
57 and 58 are gains, 53 is a differentiator, 56 is an integrator, 6
0, 61, and 62 are adders.

As shown in FIG. 11, the excitation current compensator 80
Is the terminal voltage v _{2 of} the resistor connected to the secondary winding of the current transformer.
To calculate the primary winding current i ₁ of the current transformer from
The secondary induced voltage calculator 81 calculates the secondary induced voltage e ₂ of the current transformer from the terminal voltage v ₂ , and the exciting current calculator 82 calculates the excitation of the current transformer from the primary induced voltage e ₁ of the current transformer. It shows that the current i ₀ is calculated, and that the primary load current calculator 83 calculates the primary load current i ′ ₁ of the current transformer from the terminal voltage v ₂ . The gains 52, 54, 55, 57, 58, the differentiator 53, the integrator 56, and the adders 60, 61, 62 operate in the same manner as the gain, differentiator, integrator, and adder in FIG.

Accordingly, the gain 70 calculates the secondary current i ₂ of the current transformer 30 by multiplying the terminal voltage v ₂ by the reciprocal of the resistance value of the resistor 31, and the gain 71 calculates the output signal i ₂ of the gain 70. 2 for the number of turns N ₁ of the primary winding of the current transformer 30
The ratio of the number of turns N ₂ follows the windings, i.e. calculates a primary load current i _'1 current transformers by multiplying the N ₂ / N _1, the adder 72 and the output signal i ₀ of the exciting current calculator 82 it can be seen that computing the primary winding current i ₁ flowing through the primary winding of the current transformer by adding the output signal i _'1 of the primary load current calculator 83.

Here, the principle of the current detecting device according to the first embodiment (corresponding to claim 1) of the present invention will be described with reference to the circuit diagram of FIG. 30 is a current transformer, 31 is a resistor, 8
0 is a first exciting current compensator.

As shown in the figure, in the first embodiment, the terminal voltage of the resistor 31 connected to the secondary side of the current transformer 30 is input to the first exciting current compensator 80, and the first The operation shown in FIG. 11 is performed in the exciting current compensator to compensate the amount of exciting current for the input signal. As a result, the output signal of the first exciting current compensator is similar to the primary current of the current transformer 30. Waveform. Therefore, even if the primary current of the current transformer 30 is a non-sinusoidal wave, it can be correctly detected.

Next, the principle of an exciting current compensator according to a second embodiment of the present invention (corresponding to claim 2) will be described with reference to the block diagram of FIG.

As shown in the drawing, in the exciting current compensator 90 of the second embodiment , the leakage inductance, winding resistance and iron loss resistance of the secondary winding of the current transformer in the block diagram shown in FIG. Is very small and can be approximated to zero, and the secondary induced voltage calculator 81 and the gain 58 are omitted. The number of each block in FIG. 13 indicates the same element as in FIG. Therefore, the second exciting current compensator 90 is the first exciting current compensator.
With less than 80 components, a more economical second current sensing device can be provided. As shown in FIG.
Also receives the terminal voltage of the resistor 31 connected to the secondary side of the current transformer 30, and as a result of the calculation,
And outputs a detection signal having the same waveform as the primary current.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a first embodiment (corresponding to claim 1) of the present invention. In the figure, 1 is a current detector, 2 is a current transformer, 3 is a resistor, and 4 is an exciting current compensator. The exciting current compensator 4 is implemented using an electric circuit element such as an operational amplifier, a resistor, and a capacitor, or a microcomputer.

The function of the exciting current compensator 4 is shown in the block diagram of FIG. In the figure, 5 is the secondary induced voltage calculator 6 is the ratio of number of turns N ₁ of the primary winding for the number of turns N ₂ of the secondary winding, namely the N ₁ / N ₂ amplification of current transformer 2 amplifiers, 7 exciting current calculator, 8 the ratio of number of turns N ₂ of the secondary winding for the number of turns N ₁ of the primary winding of the current transformer 2, i.e. N ₂ / N ₁ and the resistance value of the resistor 3 Is a primary load current calculator that multiplies the input signal by a gain obtained by multiplying the reciprocal of the input signal, and 9 is an adder. The secondary induced voltage calculator 5, the amplifier 6, the exciting current calculator 7, the primary load current calculator 8, and the adder 9 are implemented using electric circuit elements such as an operational amplifier, a resistor, and a capacitor, or a microcomputer. Is done.

FIG. 3 is a block diagram of the secondary induced voltage calculator 5 of FIG. In the figure, reference numeral 10 denotes an amplifier whose amplification is the reciprocal of the resistance value of the resistor 3, reference numeral 11 denotes an amplifier whose amplification is based on the leakage inductance of the secondary winding of the current transformer 2, reference numeral 12 denotes a differentiator, and reference numeral 13 denotes a current transformer. Amplifiers which use the resistance value of the secondary winding resistance of the amplifier 2 as an amplification degree, and 14 and 15 are adders. Amplifier 1
0 and amplifier 11 and differentiator 12 and amplifier 13
The adders 14 and 15 are implemented using an electric circuit element such as an operational amplifier, a resistor and a capacitor, or a microcomputer.

FIG. 4 is a block diagram of the exciting current calculator 7 of FIG. In the figure, 16 is an integrator, 17 is an amplifier whose amplification is the reciprocal of the mutual inductance of the current transformer 2, 18 is an amplifier whose amplification is the excitation conductance of the current transformer 2, and 19 is an adder. The integrator 16, the amplifier 17, the amplifier 18, and the adder 19 are implemented using an electric circuit element such as an operational amplifier, a resistor, and a capacitor, or a microcomputer.

Next, the operation of the present embodiment will be described with reference to FIGS. In the circuit diagram of FIG. 1, and outputs a detection signal I _{1, p} of the current detector 1 has a detection Target current I _1, similar to a waveform. Detection Target current I current transformer 2 through the primary winding
₁ and a secondary current I ₂ is supplied to the secondary winding. Resistor 3
Represents the secondary current I ₂ flowing through the secondary winding of the current transformer ₂ by the voltage V ₂
Convert to At this time, the resistance value of the resistor 3 is set to a value sufficiently smaller than the input impedance of the exciting current compensator 4. Excitation current compensator 4 compensates the amount corresponding to the exciting current of the current transformer 2 with respect to the terminal voltage V ₂ of the resistor 3, the detection Target <br/> current I ₁ and the detection signal having a similar waveform Output I _{1, p} . The details will be described later.

FIG. 2 is a block diagram showing the structure of the element 4 in FIG. The secondary induced voltage calculator 5 receives the terminal voltage V ₂ of the resistor 3 as an input, calculates the secondary induced voltage E ₂ of the current transformer 2 based on the theory of the current transformer, and outputs the result. Details will be described later. Amplifier 6 as input signal E ₂ to the output of the secondary induced voltage calculator 5, the number of turns N ₂ of the secondary winding of the E ₂ transformer 2
, The ratio of the number of turns of the primary winding N ₁ to N ₁ / N ₂
The by amplifying as amplification degree, and outputs a primary induced voltage E ₁ current transformer 2. The exciting current calculator 7 receives the signal E ₁ output from the amplifier 6 as an input, calculates the exciting current I ₀ of the current transformer 2 based on the theory of the current transformer, and outputs the result. Details will be described later. Primary load current computing unit 8 inputs the terminal voltage V ₂ of the resistor 3, the V ₂ of a current transformer 2 of the primary winding turns N
The ratio of the number of turns N ₂ of the secondary winding relative to _1, i.e. N ₂ / N
By amplifying the value obtained by multiplying the reciprocal of the resistance value of ₁ and the resistor 3 as the amplification degree, and outputs the calculation of the primary load current I _'1 current transformer 2. The adder 9 adds the signal I ₀ output from the exciting current calculator 7 and the signal I ′ ₁ output from the primary load current calculator 8 to form a waveform similar to the primary current I _{1 of the} current transformer 2. And outputs a detection signal I _{1, p} having the same.

FIG. 3 shows the secondary induced voltage calculator 5 shown in FIG.
Is shown. The amplifier 10 receives the terminal voltage V ₂ of the resistor 3 as an input, amplifies V ₂ as the reciprocal of the resistance value of the resistor 3 as an amplification degree, calculates and outputs a secondary current I ₂ of the current transformer 2. . The amplifier 11 amplifies and outputs the output signal I ₂ of the amplifier 10 with the leakage inductance of the secondary winding of the current transformer 2 as an amplification factor, and the differentiator 12 differentiates and outputs the output signal of the amplifier 11. 13 and amplifies the output signal I ₂ of the amplifier 10 the resistance of the secondary winding resistance of transformer 2 as the amplification degree of the adder 15 is the output signal of the output signal and the amplifier 13 of the differentiator 12 Current transformer 2 by adding
_Is calculated and output. The adder 14 calculates and outputs the secondary induced voltage E ₂ of the current transformer 2 by adding the terminal voltage V ₂ of the resistor 3 and the output signal V _{2, s} of the adder 15.

FIG. 4 is a block diagram showing the configuration of the exciting current calculator 7 shown in FIG. The integrator 16 receives the output signal E ₁ of the amplifier 6 as an input, calculates the primary flux main flux number ψ ₁ of the current transformer 2 by integrating E ₁ , and outputs the result. Amplifier 17 receives the output signal [psi ₁ integrator 18 calculates and outputs the magnetizing current I _0l current transformer 2 by amplifying the [psi ₁ the inverse of the mutual inductance of the current transformer 2 as an amplification degree . Amplifier 18 receives the output E ₁ of the amplifier 6 calculates and outputs an iron loss current I _ow current transformer 2 by amplifying the excitation conductance of the current transformer 2 as an amplification degree. The adder 19 calculates and outputs the exciting current I ₀ of the current transformer 2 by adding the output signal I _ol of the amplifier 17 and the output signal I _ow of the amplifier 18.

As described above, according to the present embodiment, the excitation current compensator 4 compensates the secondary winding voltage of the current transformer for the amount corresponding to the excitation current, thereby detecting the current to be detected. Is a current having an asymmetrical positive and negative waveform such as a distorted wave current, it is possible to obtain a detection signal having a waveform similar to the current to be detected without being affected by the DC bias of the current transformer, and A current detector excellent in cost efficiency can be provided by being constituted by an electric circuit element such as a current transformer and a resistor, an operational amplifier and a capacitor, or a microcomputer.

FIG. 5 is a circuit diagram of a second embodiment (corresponding to claim 2) of the present invention. In the figure, 23 is a current detecting device, 2 is a current transformer, 3 is a resistor, and 22 is an exciting current compensator. The exciting current compensator 22 is implemented using an electric circuit element such as an operational amplifier, a resistor, and a capacitor, or a microcomputer.

FIG. 6 is a block diagram of the exciting current compensator 22 of FIG. In the figure, the ratio of number of turns N ₁ of the primary winding for the number of turns N ₂ of the secondary winding of the current transformer 2 6, i.e. an amplifier to amplify the degree of N ₁ / N _2, 20 is the exciting current calculator , 8 the ratio of number of turns N ₂ of the secondary winding for the number of turns N ₁ of the primary winding of the current transformer 2, i.e. a value obtained by multiplying the reciprocal of the resistance value of the N ₂ / N ₁ and the resistor 3 A primary load current calculator that amplifies the amplification degree, and 21 is an adder. The amplifier 6, the excitation current calculator 20, the primary load current calculator 8, and the adder 21 are implemented using, for example, an electric circuit element such as an operational amplifier, a resistor, and a capacitor, or a microcomputer.

FIG. 7 is a block diagram of the exciting current calculator 20 of FIG. In the figure, reference numeral 16 denotes an integrator, and 17 denotes an amplifier whose amplification factor is the reciprocal of the mutual inductance of the current transformer 2. The integrator 16 and the amplifier 17 are implemented using an electric circuit element such as an operational amplifier, a resistor, and a capacitor, or a microcomputer.

Next, the operation of this embodiment will be described with reference to FIGS. In the circuit diagram of FIG.
Is a detection signal I _{1, p} having a waveform similar to the detection target current I _1.
Is output. The current transformer 2 transforms the current to be detected I ₁ flowing through the primary winding, and causes the secondary current I ₂ to flow through the secondary winding. The resistor 3 converts the secondary current I ₂ flowing through the secondary winding of the current transformer ₂ into a current V.
Convert to ₂ . At this time, the resistance value of the resistor 3 is set to a value sufficiently smaller than the input impedance of the exciting current compensator 22. The exciting current compensator 22 compensates for the terminal voltage V ₂ of the resistor 3 by an amount corresponding to the exciting current of the current transformer ₂ , and generates a detection signal I _{1, p} having a waveform similar to the detection target current I _1. Is output. The details will be described later.

FIG. 6 is a block diagram showing the configuration of the exciting current compensator 22 shown in FIG. The amplifier 6 receives the terminal voltage V ₂ of the resistor 3 as an input by approximating the secondary induced voltage of the current transformer _2, and uses V ₂ of the primary winding with respect to the number of turns N ₂ of the secondary winding of the current transformer 2. The primary induced voltage E ₁ of the current transformer 2 is output by amplifying the ratio of the number of turns N ₁ , that is, N ₁ / N ₂ as the amplification degree. The exciting current calculator 20 receives the signal E ₁ output from the amplifier 6 as an input, calculates the exciting current I ₀ of the current transformer 2 and outputs the result. Details will be described later. Primary load current computing unit 8 inputs the terminal voltage V ₂ of the resistor 3, 1 V ₂ of the current transformer 2
The ratio of the number of turns N ₂ of the secondary winding for the number of turns N ₁ of the next winding, i.e. by amplifying the value obtained as an amplification degree multiplied by the reciprocal of the resistance value of the N ₂ / N ₁ and the resistor 3, variable Sink 2
The primary load current I _'1 and calculates and outputs. Adder 21
Is a signal having a waveform similar to the primary winding current I _{1 of the} transformer 2 by adding the signal I ₀ output from the exciting current calculator 20 and the signal I ′ ₁ output from the primary load current calculator 8. The signal I'1 _{, p} is output.

FIG. 7 is a block diagram showing the configuration of the exciting current calculator 20 shown in FIG. The integrator 16 receives the output signal E ₁ of the amplifier 6 as an input, calculates the primary magnetic flux linkage ψ ₁ of the current transformer 2 by integrating E ₁ , and outputs the result.
Amplifier 17 receives the output signal [psi ₁ integrator 16 calculates the magnetizing current of the current transformers 2 by amplifying the output signal [psi ₁ the inverse of the mutual inductance of the current transformer 2 as the amplification degree of magnetizing current Is output as a signal approximating the exciting current I ₀ of the current transformer 2.

As described above, according to the present embodiment, the structure of the device is simplified by approximating the iron loss resistance, the secondary winding leakage inductance and the secondary winding resistance of the current transformer to zero.
At the same time, it is possible to provide a means for obtaining a detection signal having a similar waveform with a small error even when the primary current of the current transformer is a non-sinusoidal current.

[0040]

As described above, according to the present invention,
It is possible to provide a current detecting device that accurately detects not only a sine wave current but also a current having a positive / negative asymmetric waveform such as a distorted wave current and is excellent in economy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a current detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an exciting current compensator of FIG. 1;

FIG. 3 is a block diagram of a secondary induced voltage calculator of FIG. 1;

FIG. 4 is a block diagram of an exciting current calculator of FIG. 1;

FIG. 5 is a circuit diagram of a current detection device according to a second embodiment of the present invention.

FIG. 6 is a block diagram of the exciting current compensator of FIG. 5;

FIG. 7 is a block diagram of an exciting current calculator of FIG. 5;

FIG. 8 is a diagram of a conventional current detection circuit.

9 is a T-type equivalent circuit diagram of FIG.

FIG. 10 is a block diagram of the circuit shown in FIGS. 8 and 9;

FIG. 11 is a block diagram for explaining the principle of the excitation current compensator of the current detection device according to the first embodiment of the present invention.

FIG. 12 is a circuit diagram for explaining the principle of the current detection device in FIG. 11;

FIG. 13 is a block diagram for explaining the principle of the exciting current compensator of the current detecting device according to the second embodiment of the present invention.

FIG. 14 is a circuit diagram for explaining the principle of the current detection device in FIG. 13;

[Explanation of symbols]

1, 23 ... current detection device, 2 ... current transformer, 3 ... resistor,
4, 22 ... exciting current compensator, 5 ... secondary induced voltage calculator,
6: Amplifier, 7, 20: Excitation current calculator, 8: Primary load current calculator, 9: Adder.

Claims (2)

(57) [Claims] 1. A current transformer, and the current transformer resistor for converting the secondary voltage secondary current is connected to the secondary windings, and the resistor of the resistor terminal voltage of the resistor as input A first amplifier for amplifying the output signal with a reciprocal gain of a value, a second amplifier for amplifying an output signal of the first amplifier as a gain with a leakage inductance of a secondary winding of the current transformer; A differentiator for differentiating the output signal of the amplifier, a third amplifier for amplifying the output signal of the first amplifier using a secondary winding resistance of the current transformer as a gain, an output signal of the differentiator, And a second adder for adding the terminal voltage of the resistor and the output signal of the first adder. A secondary induced voltage calculator for calculating a secondary induced voltage, and an output signal of the secondary induced voltage calculator. A fourth amplifier for amplifying a gain obtained by dividing the number of turns of the primary winding of the current transformer by the number of windings of the secondary winding, and a reciprocal of a resistance value of the resistor for a terminal voltage of the resistor fifth it is amplified with the gain obtained by multiplying the value obtained by dividing the number of turns of the secondary winding the turns of the primary winding of the current transformer and
A primary load current calculator composed of the amplifiers described above, an integrator integrating the output signal of the fourth amplifier, and a sixth amplifying the output signal of the integrator using a reciprocal of a mutual inductance of the current transformer as a gain. , An amplifier that amplifies the output signal of the fourth amplifier using the reciprocal of the iron loss resistance of the current transformer as a gain, an output signal of the sixth amplifier, and an output of the seventh amplifier A first exciting current calculator configured to calculate an exciting current of the current transformer, comprising a third adder for adding a signal; and an output signal of the first exciting current calculator and the primary load current calculation. A first exciting current compensator comprising a fourth adder for adding the output signal of the first exciter.
The output signal of the exciting current compensator of (1) as a detection signal of the current flowing in the primary winding of the current transformer, and outputting a detection signal having a waveform similar to the current flowing in the primary winding of the current transformer. A current detection device characterized by the above-mentioned. 2. The current detection device according to claim 1, wherein
Instead of the first exciting current compensator, the iron loss resistance of the current transformer, the leakage inductance of the secondary winding, and the secondary winding resistance are approximately replaced with zero, so that the first amplifier and the second amplifier are replaced. The second amplifier, the second amplifier, the third amplifier, the differentiator, the first adder, the second adder, the seventh amplifier, and the third adder.
A current detecting device comprising the exciting current compensator of (1), wherein the configuration of the amplifier inside the first exciting current compensator is simplified.