JPH0493772A - Dc current detector - Google Patents

Abstract

PURPOSE:To make it possible to follow up even a sudden change in a detected current without generating noise, by adding up an output from a magnetoelectric conversion element and a detected value of a current outputted from a coil. CONSTITUTION:A magnetoelectric conversion element 2 and an input end of an amplifier 4 are connected, an output end of the amplifier 4, one end of a coil 3 wound by the number of winds N2 on a magnetic body 1, and one end of a resistor 5 of resistance R, are connected together, and further the other end of the coil 3 and the other end of the resistor 5 are connected. An output from the element 2 is amplified by the amplifier 4, and an output V1 thereof and an output V2 obtained by converting an output current i2 from the coil 3 into a voltage by the resistor 5 are added up. Thereby an output voltage Vout is obtained and a current i1 is detected. The output Vout is in a proportional relation with the detected current i1 and a magnetic flux phi turns to be in a relation of primary delay with the detected current i1. Since dphi/dt becomes small, in other words, generation of noise is prevented substantially and a hyster esis loss and an eddy current loss in the magnetic body 1 which increase in accordance with the frequency of the magnetic flux can be reduced to be small.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a DC current detector for detecting DC current of an inverter circuit for driving a motor, etc. (Prior art) Fig. 5 shows a conventional DC current detector. FIG. 2 is a plan view showing an example of a current detector, in which a 6n electric conversion element 2 is arranged in the cap of a ring-shaped magnetic body 1, and a current Il is passed through the ring of the magnetic body 1 so that the current Il is proportional to the current I. By forming a magnetic flux φ (the following equation (1)), an output V+ (the following equation (2)
), that is, an output V1 (the following equation (3)) proportional to the current 11 is obtained from the magnetoelectric conversion element 2 to detect the electric current 1ffiil.

φ-, ・II (kl constant of proportionality)...(1)
V, -2.
...(3) Also, FIG. 6 is a plan view showing another example of a conventional DC current detector corresponding to FIG. 5, and bH
Connect the N conversion element 2 and the input terminal of the amplifier 4,
Connect the output end of the coil 3 wound on the magnetic material 1 with a number of turns N, and further connect the other end of the coil 3 to one end of the resistor 5 having a resistance r. The end is grounded, and the output from the electric conversion element 2 is amplified by the amplifier 4 to provide negative feedback in the direction of canceling the magnetic flux φ, and the magnetic flux φ is always kept at zero and a negative feedback current 13 (proportional to the current i) is generated. The following formula (4), (
5) ) is obtained, and the negative feedback current 13 is converted into voltage by resistor M5 and output. (the following equation (6)) is obtained, and the current 1. It is designed to detect.

+ to φ- (11-N1・13) ...(
4) From φ~O in the above equation (4)! 3-1+/N+・
...(5) From the above equation (5), νor-r・13-r・
j+/N+ = 15) (Problem to be Solved by the Invention) In the conventional DC current voltage detector shown in FIG.
The output from the filter tends to generate noise when the di/dt is high, so it is necessary to insert a filter, resulting in a slow response. In addition, when the detection current 11 changes at a high frequency, the magnetic flux φ, which is proportional to the detection current l, also changes at a high frequency as shown in the above equation (1). There was a problem that the product became sharper depending on the frequency of change in the magnetic flux φ, and the ifl body 1 generated heat.

In addition, in the DC current voltage detector shown in Fig. 6, when detecting a large current, a large number of negative feedback currents 1. As a result, there was a lot of unnecessary electricity.

In addition, to reduce the negative feedback current i, the t number N1 of the coil 3 is
The problem is that it requires a lot of repeating (usually several thousand times) and is expensive.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to be able to follow sudden changes in detection current without generating noise, to suppress heat generation of the magnetic material, and to reduce consumption. An object of the present invention is to provide an inexpensive direct current detector with reduced current.

(Means for Solving the Problems) The present invention relates to a DC current detector that detects a DC current of an inverter circuit for driving a motor, etc. A magnetoelectric conversion element that generates an output according to a detected current, and a coil wound around the magnetic material, and the output from the magnetoelectric conversion element and the detected value of the current output from the coil are added. achieved by.

(Function) The DC current detector according to the present invention is configured so that the output of the magnetoelectric conversion element has a first-order lag with respect to changes in the detected current, so noise is less likely to occur and the magnetic material generates less heat. In addition, because the current from the coil is directly converted into voltage using a low-impedance resistor, high-speed response with little noise is possible.

(Example) FIG. 1 is a plan view showing an example of the DC current detector of the present invention in correspondence with FIG. One end of the coil 3 wound around the magnetic body 1 with a number of turns N2 and a resistor 5 with a resistance R
The other end of the coil 3 is roughly connected to the other end of the resistor 5, and the output from the magnetoelectric conversion element 2 is sent to the amplifier 4.
The output Vl (& Equation (7)) and the output current 12 from the coil 3 are converted into voltage by the resistor 5.
2 (the following equation (8)), the output voltage V. u
The current 1 is detected by obtaining t (the following equation (9)).

The magnetic conversion element 2 and the amplifier 4 are realized with a circuit configuration as shown in FIG.
By passing the output through the RC filter 6, it is possible to further strengthen the noise resistance.

V, -k2 ・φ V2− R・l2 vaut+v, "V2 ... (7) ... (8) ... (9) Here, a current 12 is applied to the coil 3 in the direction that prevents the change of the magnetic flux φ. Since a voltage ν2 is generated across the resistor 5, the magnetic flux φ can be expressed by the following equations (10) and (1).

φ −k+ (i+ −N2 ・12)
...(lO)+1! ' - (1/N2)
・I v2・dt −(II) Above formula (1
0) to i2+ (i, -φ/to 1)/N2...
・(12) In addition, 1) φ-0 cutoff V, ・0 Therefore, the above formula (8), (9), (12+ to V
out-R・i+/N2- (13)2) dφ/d
t-077) when V2・0. Therefore, from the above equations (7), (9), (10), Vout-k+
・k2・i+ −(14) Output V for both conditions 1) and 2). The above formula (1
3) The number of turns N2 of the coil can be determined from (1, 4) and expressed as the following equation (15).

N2- R/(k+・k2)...(Is) Above formula (7), (8), (9), (+),
Based on (12) and (Is), the transfer function can be expressed by the following equations (16) and (17) using the block diagram shown in FIG. 3 after Laplace transform.

Vout[S] −+ ・k2・i+ [S]・
(16) From the above equations (16) and (17), the output Vout has a proportional relationship with the detection current 11, and the magnetic flux φ has a next-order lag relationship with the detection current 11. In other words, since dφ/dt is smaller, noise is less likely to occur, and the hysteresis loss and eddy current product within the magnetic body 1, which increase depending on the frequency of the magnetic flux, can be kept low, so the heat generation of the magnetic body 1 is also reduced. few.

In addition, since the current 12 flowing through the coil 3 due to the action of the detection current 11 is directly converted into the output V2 by the low impedance resistor 5, as shown in FIG. Either the output V2 changes greatly or the output v1 changes slowly, making it possible to provide a very high-speed response with little noise.

(Effects of the Invention) As described above, the DC current detector of the present invention is capable of following the occurrence of noise due to sudden changes in the detected current, and also has the advantage of being able to Due to the action of the wound coil, the magnetic flux has a first-order lag and 1. Since no sudden changes occur, heat generation in the magnetic material can be suppressed. Furthermore, since there is no need to supply negative feedback current to the coil, current consumption can be reduced, and there is no need to increase the number of turns of the coil (11! can.

Therefore, the range of application of the DC current detector can be expanded.

FIG. 5 shows an example of the output waveform of the DC current detector of the invention.
6 are plan views showing an example of a conventional DC current detector.

1... 6f1 element, 2... Magnetoelectric conversion element, 3...
Coil, 4. Amplifier, 5.. Resistor, 6.. Filter.

Claims (1)

[Claims] 1. A magnetoelectric transducer disposed in a magnetic material that generates an output according to a detected current, and a coil wound around the magnetic material, the output from the magnetoelectric transducer and the coil being wound around the magnetic material. A DC current detector characterized in that the detected value of the current output from the coil is added. 2. The DC current detector according to claim 1, further comprising a filter for removing high frequency components of the output from the magnetoelectric conversion element.