JP2000340437A - Noise filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a noise reducing effect while miniaturizing the whole part of this noise filter. SOLUTION: This noise filter 3 is constituted of ground capacitors 5a, 5b, and 5c for connecting each phase of power source lines 7a, 7b, and 7c with ground, a first common mode choke coil 8 connected with the load side of the ground capacitors 5a, 5b, and 5c which is provided with a magnetic core whose initial magnetic permeability is 3000 or less, a second common mode choke coil 9 connected with the power source side of the ground capacitors which is provided with a magnetic core whose initial magnetic permeability is 5000 or more, and capacitors 6a, 6b, and 6c for absorbing a noise connected among the power source lines for reducing a normal mode noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise filter using a common mode choke coil.

[0002]

2. Description of the Related Art As shown in FIG.
A noise filter 3 provided between the power electronics device 2 serving as an electrical device includes a common mode choke coil 4 for reducing common mode noise, and a noise absorbing device for reducing ground mode capacitors 5a, 5b, 5c and normal mode noise. Capacitor between phases 6 which is a capacitor
a, 6b and 6c.

The common mode choke coil 4 has a large impedance with respect to common mode noise flowing through the power supply lines 7a, 7b, 7c, and functions to prevent common mode noise generated from the power electronic device 2 from flowing out to the power supply side. do.

[0004] The impedance of the common mode choke coil 4 is mainly determined by the magnetic permeability of the core material and the number of turns of the coil. The greater the impedance, the greater the noise reduction effect. Generally common mode choke coil 4
Inexpensive ferrite is used for the core, but a material with a higher magnetic permeability than ferrite, such as a nanocrystalline soft magnetic material, is used for the purpose of obtaining higher impedance or miniaturization. In some cases.

The ground capacitors 5a, 5b, and 5c function as a bypass for returning common mode noise leaking from the power electronic device 2 to the power electronic device 2 without flowing the power to the power supply. Similarly, the inter-phase capacitors 6a, 6b, and 6c function as bypasses for returning normal mode noise to the power electronics device without flowing to the power supply.

[0006]

By the way, power electronic equipment generates conduction noise of all frequencies, and a limit value is set for noise over a wide band from 150 kHz to 30 MHz.
In this noise filter for reducing broadband noise, when one common mode choke coil is used, a core material having a high initial permeability is generally used to reduce low frequency noise having a high noise terminal voltage. When a ferrite core exhibiting high inductance in a low frequency band is used, the inductance sharply decreases in a high frequency band, so that the effect of the noise filter for reducing high frequency noise is reduced. On the other hand, although measures such as increasing the size of the common mode choke coil are taken, sufficient impedance for high frequency noise cannot be obtained because the number of turns of the coil increases and the stray capacitance between lines increases. On the other hand, the present situation is that the common mode choke coil is over-specified with respect to low frequency noise.

Although a common mode choke coil using a nanocrystalline soft magnetic material or the like that maintains a high magnetic permeability between high frequency bands as a core material is also used, it is more expensive than ferrite, and furthermore has high frequency noise. On the other hand, since a common mode choke coil is attached to the power supply side of the ground capacitor, which is not so effective, the effect of reducing high frequency noise as expected is not obtained at present. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a noise filter that can improve a noise reduction effect while reducing the size of the entire device.

[0008]

In order to achieve the above object, a noise filter according to the present invention comprises a grounding capacitor for connecting each phase of a power supply line to ground, and an initial magnetic permeability connected to the load side of the grounding capacitor. A first common mode choke coil having a magnetic core of 3000 or less, and a first magnetic permeability connected to the power supply side of the grounding capacitor and having an initial permeability of 5000
A second common mode choke coil having the above-described magnetic core and a noise absorbing capacitor connected between the power supply lines to reduce normal mode noise are provided.

[0009] According to the noise filter configured as described above, the common mode choke coil located on the side of the electric device shows a sufficiently high impedance with respect to high frequency noise of about 1 MHz or more, and further, the connection position is changed to the load side of the grounding capacitor. Therefore, high frequency noise can be reduced most effectively.

On the other hand, the common mode choke coil located on the power supply side has a noise frequency band of about 1M.
Since the band is limited to a narrow band of not more than Hz, it is possible to optimally design the common mode choke coil having the highest impedance in this band.

Further, the core material of the two common mode choke coils is made of ferrite. According to this configuration, since the ferrite is inexpensive, the cost of the common mode choke coil can be significantly reduced.

According to a third aspect of the present invention, at least one of the two common mode choke coils is provided.
On the other hand, a configuration in which a plurality of common mode choke coils are connected in parallel can be adopted.

According to this configuration, since the filter is composed of the common mode choke coils each occupying a small volume, the size of the entire filter can be reduced by optimally arranging the components.

According to a fourth aspect of the present invention, the number of turns of the common mode choke coil on the load side may be set to be not more than １ ／ of the number of turns of the common mode choke coil on the power supply side.

According to this configuration, the stray capacitance existing between the wires of the common mode choke coil on the load side becomes sufficiently small due to the decrease in the number of turns, so that it is possible to prevent a decrease in impedance with respect to high-frequency noise of 1 MHz or more. Thereby, the high-frequency noise reduction effect of the common mode choke coil on the load side is further increased. At the same time, the size of the coil can be reduced, and the total amount of common mode noise flowing through the center of the core is reduced, so that the amount of heat generated by the core is reduced and deterioration of material properties can be prevented.

Further, as in the fifth aspect of the present invention, instead of the common mode choke coil on the load side, a configuration may be adopted in which all phases of the power supply line pass through one ferrite core.

According to this configuration, since a ferrite core having no winding is used, the material cost can be greatly reduced, and the manufacturability can be reduced due to a simple structure in which the ferrite core is simply passed through the power supply line. Dramatically improved.

The ferrite core may be a split core. According to this configuration, further improvement in manufacturability can be realized.

Further, the noise absorbing capacitor may be connected to the load side with respect to the power supply side common mode choke coil. According to this configuration, the inductance of the parallel circuit formed between the ground capacitor and the noise absorbing capacitor is reduced, and resonance that hinders noise reduction occurs on the high frequency side where the amount of noise generation is small. , Noise can be reduced more effectively.

[0020]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 shows the overall configuration of a noise filter provided between a three-phase AC source 1 and a power electronic device 2 which is an electric device, and the inter-phase capacitors 6a and 6 which are noise absorbing capacitors located closest to the power supply.
b and 6c reduce normal mode noise mainly generated from the power electronic device 2.

Also, ground capacitors 5a, 5b, 5c
And two common mode choke coils 8, 9 provided in series with the power supply lines 7a, 7b, 7c so as to sandwich these ground capacitors 5a, 5b, 5c reduce common mode noise mainly leaking to the power supply side. Works effectively.

The common mode choke coil 9 employs a magnetic core having an initial magnetic permeability of 3,000 or less so that the impedance is high in a high frequency band.
It has a great effect on reducing high-frequency noises of not less than Hz. Further, by disposing the common mode choke coil 9 on the load side of the ground capacitors 5a, 5b, 5c, a greater effect of reducing high frequency noise can be obtained as compared with the case where the common mode choke coil 9 is disposed on the power supply side.

On the other hand, the noise borne by the common mode choke coil 8 on the power supply side is limited to a narrow band of 1 MHz or less. For this reason, by using a magnetic core having an initial permeability of 5,000 or more that exhibits high inductance only in the low-frequency band, it is possible to design a common-mode choke coil 8 that is optimal for reducing low-frequency noise.
Can be miniaturized.

FIG. 2 shows a second embodiment of the present invention.
The cores of the common mode choke coil 10 and the common mode choke coil 11 both employ ferrite. In this case, since the most common and inexpensive ferrite is used as the magnetic core, the two common mode choke coils 10 and 11 can be significantly reduced in cost.

FIG. 3 shows a third embodiment of the present invention.
On the power supply side of the ground capacitors 5a, 5b, 5c, two identical common mode choke coils 12, 13 are provided.
Two identical common mode choke coils 1 on the load side
4 and 15 are connected in parallel.

In such a configuration, the current flowing through each of the common mode choke coils 12, 13, 14, and 15 is halved, so that the current capacity of the coil can be small and the occupied volume of each coil is small. Become. Therefore, by optimizing the arrangement with other components, the noise filter 3
Is reduced in size. Further, when a filter is built in the power electronics device 2, the common mode choke coils 12, 13, 14, and 15 can be separately mounted by utilizing the vacant space in the device. In addition, the degree of freedom of the design can be increased and the size of the equipment can be prevented.

FIG. 4 shows a fourth embodiment of the present invention.
The number of turns of the common mode choke coil 17 mounted on the load side is reduced to 以下 or less as compared with the common mode choke coil 16 on the power supply side.

According to this configuration, the number of turns of the common mode choke coil 17 is reduced, so that the stray capacitance existing between the windings is sufficiently reduced. For this reason, it is possible to prevent a decrease in impedance particularly against high-frequency noise of 1 MHz or more. As a result, the high-frequency noise reduction effect of the common mode choke coil 17 on the load side is further increased. Further, since the core size largely limited by the winding is suppressed, the common mode choke coil 17 is sufficiently smaller than the common mode choke coil 16. Further, the common mode choke coil 17 mounted on the load side of the ground capacitors 5a, 5b, and 5c allows all the common mode noise generated from the power electronic device 2 to pass therethrough. There is a problem that the characteristics of the core are deteriorated, but this problem can be solved by reducing the number of turns.

FIG. 5 shows a fifth embodiment of the present invention.
Power supply lines 7a, 7b, 7c extending to the load side of the ground capacitors 5a, 5b, 5c pass through the ferrite core 19.

With this configuration, the price of the ferrite core 19 having no winding is significantly lower than that of the common mode choke coil, and the noise filter 3 can be reduced in price. Further, when a common mode choke coil is used, there is a problem in manufacturability, such as the necessity of attachment to a substrate. However, when a ferrite core 19 is used, the power supply lines 7a, 7b, 7c are connected to the core. Manufacturability is greatly improved because only simple work is required.

FIG. 6 shows a sixth embodiment of the present invention.
A split core 20 is attached to the power supply lines 7a, 7b, 7c extending to the load side of the ground capacitors 5a, 5b, 5c.

According to this, the power supply lines 7a, 7
Manufacturability is further improved as compared with the case where cores are attached to b and 7c. FIG. 7 shows a seventh embodiment of the present invention, in which the inter-phase capacitors 21a, 21b, 21c are located between the two common mode choke coils 10, 11 like the ground capacitors 5a, 5b, 5c. Inter-phase capacitors 21a, 21b, 21c and ground capacitor 5
The wiring connecting a, 5b, and 5c is connected in the shortest.

In such a structure, the inter-phase capacitors 21a, 21b and 21c and the ground capacitors 5a and 5a
The inductance is reduced in the parallel circuit formed between b and 5c.

In general, in a parallel circuit formed by an inductance L and a capacitance C, the impedance becomes high near the resonance frequency. This is because the inter-phase capacitors 21a, 21 and 21c and the ground capacitors 5a and 5a
The same applies to the parallel circuit formed between b and 5c.
In the vicinity of the resonance frequency, the impedance between the power supply lines 7a, 7b, 7c that bypass common mode noise and the ground increases, and the effect of reducing noise is reduced by half.

On the other hand, the level of noise generated from the power electronics device 2 generally decreases as the frequency increases. Therefore, the inter-phase capacitors 21a, 21
By lowering the inductance of the parallel circuit formed by b, 15c and the ground capacitors 5a, 5b, 5c and shifting the parallel resonance frequency to a higher frequency side, the noise can be easily reduced. Further, when the resonance frequency shifts to 30 MHz or more outside the noise regulation band, it is possible to cope with the smaller common mode choke coils 10 and 11, and further downsizing can be realized.

[0036]

As is apparent from the above description, the following effects can be obtained according to the present invention. Claim 1
According to the described noise filter, the common mode choke coil located on the side of the electric device has a sufficiently high impedance against high-frequency noise of about 1 MHz or more, and the connection position is on the load side of the grounding capacitor. High frequency noise can be reduced.

On the other hand, the common mode choke coil located on the power supply side has a noise frequency band of about 1M.
Since the band is limited to a narrow band of not more than Hz, it is possible to optimally design the common mode choke coil having the highest impedance in this band.

According to the noise filter of the second aspect,
Since ferrite is inexpensive, the cost of the common mode choke coil can be significantly reduced. According to the noise filter of the third aspect, since the filter is constituted by the common mode choke coils each occupying a small volume, the size of the entire filter can be reduced by optimally disposing the components.

According to the noise filter of the fourth aspect,
The stray capacitance existing between the lines of the load-side common mode choke coil becomes sufficiently small due to the decrease in the number of turns.
It is possible to prevent a decrease in impedance with respect to high frequency noise of MHz or more. Thereby, the high-frequency noise reduction effect of the common mode choke coil on the load side is further increased. At the same time, the size of the coil can be reduced, and the total amount of common mode noise flowing through the center of the core is reduced, so that the amount of heat generated by the core is reduced and deterioration of material properties can be prevented.

According to the noise filter of the fifth aspect,
Since a ferrite core with no winding is used, material costs can be greatly reduced, and manufacturability is greatly improved because of a simple structure in which a ferrite core is simply passed through a power supply line.

According to the noise filter of the sixth aspect,
Further improvement in manufacturability can be realized. According to the noise filter of the seventh aspect, the inductance of the parallel circuit formed between the noise filter and the noise absorbing capacitor is reduced, and resonance that hinders noise reduction occurs on the high frequency side where the amount of noise generation is small. , Noise can be reduced more effectively.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a noise filter and a peripheral circuit according to a first embodiment of the present invention;

FIG. 2 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 3 is a view corresponding to FIG. 1, showing a third embodiment of the present invention;

FIG. 4 is a view corresponding to FIG. 1, showing a fourth embodiment of the present invention;

FIG. 5 is a view corresponding to FIG. 1, showing a fifth embodiment of the present invention.

FIG. 6 is a view corresponding to FIG. 1, showing a sixth embodiment of the present invention;

FIG. 7 is a view corresponding to FIG. 1, showing a seventh embodiment of the present invention.

FIG. 8 is a diagram corresponding to FIG. 1 showing a conventional example.

[Explanation of symbols]

1 is a three-phase AC power supply, 2 is a power electronics device (electric device), 3 is a noise filter, 5a, 5b, 5c
Is a ground capacitor, 6a, 6b, 6c are inter-phase capacitors (noise absorbing capacitors), 7a, 7b, 7c are power lines, 8, 10, 11, 12, 13, 14, 15, 15, 1
6, 17, 18 are common mode choke coils, 19 is ferrite, 20 is a split core, 21a, 21b, 21c
Indicates an interphase capacitor.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01F 17/04 H03H 7/075 A H03H 7/075 7/09 A 7/09 H01F 15/00 D

Claims (7)

[Claims] 1. A noise filter interposed in a power supply line connecting a power supply and an electric device, comprising: a grounding capacitor connecting each phase of the power supply line to ground; and a grounding capacitor connected to a load side of the grounding capacitor. A first common mode choke coil having a magnetic core having a magnetic permeability of 3000 or less, a second common mode choke coil having a magnetic core having an initial magnetic permeability of 5000 or more connected to the power supply side of the grounding capacitor, A noise filter comprising: a noise absorbing capacitor connected between the power supply lines to reduce normal mode noise. 2. The noise filter according to claim 1, wherein the core material of the two common mode choke coils is ferrite. 3. The noise filter according to claim 1, wherein at least one of the two common mode choke coils has a plurality of common mode choke coils connected in parallel. 4. The number of turns of the common mode choke coil on the load side is one of the number of turns of the common mode choke coil on the power supply side.
The noise filter according to any one of claims 1 to 3, wherein the ratio is equal to or less than / 2. 5. The noise filter according to claim 1, wherein all phases of the power supply line are passed through one ferrite core instead of the common mode choke coil on the load side. 6. The noise filter according to claim 5, wherein the ferrite core is a split core. 7. The noise filter according to claim 1, wherein the noise absorbing capacitor is connected to the load side with respect to the common mode choke coil on the power supply side.