Noise filter and power supply device

A noise filter includes: a first bus bar that is electrical wiring of a flat plate, the first bus bar including a first extending wiring portion extending in a first direction, a second extending wiring portion extending in a second direction that is a direction opposite to the first direction, and a first coupling wiring portion connecting the first extending wiring portion and the second extending wiring portion; a first lead conductor having a first end connected with the first coupling wiring portion; a first capacitor having a first end connected with a second end of the first lead conductor and a second end connected with a ground; and a magnetic core having an opening in a central portion, the magnetic core disposed in such a manner that the first coupling wiring portion passes through the opening.

TECHNICAL FIELD

The present invention relates to a noise filter including a capacitor and a power supply device.

BACKGROUND ART

Patent Literature 1 below discloses a printed board on which a noise filter that reduces electromagnetic noise that leaks to a power supply side is mounted.

In the printed board disclosed in Patent Literature 1, four or more conductor layers including a conductor layer in which a power supply line connected to a power supply terminal of a circuit element is disposed and a conductor layer in which a ground plane is formed are stacked.

In a first layer, which is one of the conductor layers included in the printed board disclosed in Patent Literature 1, a reactor is formed by deformation of a power supply line.

Also in a second layer, which is one of the conductor layers included in the printed board disclosed in Patent Literature 1, a reactor is formed by deformation of the power supply line. The reactor formed in the first layer and the reactor formed in the second layer are connected in series.

One end of a capacitor is connected with wiring drawn out from between the reactor formed in the first layer and the reactor formed in the second layer, and the other end of the capacitor is connected to the ground plane.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2016-031965 A

SUMMARY OF INVENTION

Technical Problem

For example, in a power supply device that handles a large current, such as an inverter device for driving a motor, there are cases that a bus bar is used as a power supply line.

In a case where a structure like the printed board disclosed in Patent Literature 1 is applied to a power supply device using a bus bar as a power supply line in order to reduce electromagnetic noise that leaks to the power supply side, it is necessary to form each of a reactor formed in a first layer and a reactor formed in a second layer by the bus bar. In addition, a lead wire drawn from between the reactor formed in the first layer and the reactor formed in the second layer also needs to be formed by the bus bar.

The bus bar is typically manufactured by punching or pressing a metal plate or the like, and it is difficult to manufacture a bus bar having a complicated three-dimensional shape. That is, even if it is attempted to apply a structure like the printed board disclosed in Patent Literature 1 to a power supply device using a bus bar, a three-dimensional bus bar, in which two reactors having a loop-like shape are formed in mutually different layers and are connected in series, does not have a planar structure, and thus there is a problem that it is difficult to manufacture the bus bar by punching or pressing a metal plate or the like.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a noise filter and a power supply device using a bus bar having a planar structure that can be manufactured by punching, pressing, or the like.

Solution to Problem

A noise filter according to the present invention includes: a first bus bar that is electrical wiring of a flat plate, the first bus bar including a first extending wiring portion extending in a first direction, a second extending wiring portion extending in a second direction that is a direction opposite to the first direction, and a first coupling wiring portion connecting the first extending wiring portion and the second extending wiring portion; a first lead conductor having a first end connected with the first coupling wiring portion; a first capacitor having a first end connected with a second end of the first lead conductor and a second end connected with a ground; and a magnetic core having an opening in a central portion, the magnetic core disposed in such a manner that the first coupling wiring portion passes through the opening.

Advantageous Effects of Invention

According to the present invention, it is possible to implement a noise filter using a first bus bar having a planar structure that can be manufactured by punching, pressing, or the like.

DESCRIPTION OF EMBODIMENTS

In order to describe the present invention further in detail, embodiments for carrying out the invention will be described below by referring to the accompanying drawings.

First Embodiment

FIG.1is a configuration diagram illustrating a power supply device including a noise filter1according to a first embodiment.

The power supply device is, for example, a power electronics device that handles a large current, such as an inverter device for driving a motor. Note that, the power supply device is not limited to the inverter device for driving a motor and may be, for example, a DC-DC converter such as a switching regulator.

The power supply device uses a first bus bar11as a power supply line, and a noise filter1is inserted in the first bus bar11.

The noise filter1is inserted in the first bus bar11in order to suppress electromagnetic noise propagated in the first bus bar11, and the noise filter1includes a part of the first bus bar11.

FIG.2is a perspective view illustrating the noise filter1according to the first embodiment.

FIG.3is a top view of the noise filter1illustrated inFIG.2as viewed from +Z direction.

FIG.4is a cross-sectional view of cross section A1-A2illustrated inFIG.3as viewed from −Y direction.

FIG.5is a Y-Z plane view of the noise filter1illustrated inFIG.2as viewed from +X direction.

FIG.6Ais a perspective view illustrating the structure of a magnetic core18in the noise filter1illustrated inFIG.2.

FIG.6Bis a perspective view illustrating the structure of the first bus bar11in the noise filter1illustrated inFIG.2.

InFIGS.2to6, the noise filter1is installed on a certain plane parallel to a plane including the X axis and the Y axis in a three-dimensional space defined by the X axis, the Y axis, and the Z axis. Hereinafter, this plane is referred to as an X-Y plane.

A direction parallel to the X axis is referred to as the X direction, a direction parallel to the Y axis is referred to as the Y direction, and a direction parallel to the Z axis is referred to as the Z direction.

The Z direction is a direction parallel to a normal line with respect to the surface of a printed board13.

The X direction is a direction parallel to the surface of the printed board13. The Y direction is a direction parallel to the surface of printed board13and orthogonal to the X direction.

The first bus bar11is installed on an X-Y plane.

The first bus bar11is electrical wiring of a flat plate having one end connected with, for example, a connector connected with a voltage output terminal in a power supply and the other end connected with, for example, a motor driving circuit.

The first bus bar11includes a first extending wiring portion11aextending in a first direction and a second extending wiring portion11bextending in a second direction that is a direction opposite to the first direction.

As illustrated inFIG.3, the first direction is a clockwise direction starting from the side connected with the connector when the first bus bar11is viewed from the +Z direction. As illustrated inFIG.3, the second direction is a counterclockwise direction starting from the side connected with the connector when the first bus bar11is viewed from the +Z direction.

In addition, the first bus bar11includes a first coupling wiring portion11cthat coupling the first extending wiring portion11aand the second extending wiring portion11b.

In the noise filter1illustrated inFIG.2, the first extending wiring portion11a, the second extending wiring portion11b, and the first coupling wiring portion11care integrally formed.

In the noise filter1illustrated inFIG.2, the first direction is the clockwise direction, and the second direction is the counterclockwise direction. However, this is merely an example, and the first direction may be the counterclockwise direction, and the second direction may be the clockwise direction. That is, the first bus bar11may have a first extending wiring portion11aextending counterclockwise and a second extending wiring portion11bextending clockwise.

A first lead conductor12is electrical wiring of a flat plate having one end connected with the first coupling wiring portion11cand the other end connected with a wiring pattern13bformed on the printed board13.

The printed board13is installed on an X-Y plane.

A first capacitor14is mounted on the printed board13.

An insulator13ais an insulating layer of the printed board13.

The wiring pattern13bis conductive electric wiring and is connected with each of the other end of the first lead conductor12and one end of the first capacitor14.

A ground pattern13cis conductive electric wiring and is connected with the other end of the first capacitor14.

The one end of the first capacitor14is connected with the other end of the first lead conductor12via the wiring pattern13b.

The other end of the first capacitor14is connected with the ground pattern13c.

A screw15is formed of a conductive member.

The screw15fixes the printed board13to a spacer16in order to electrically connect the ground pattern13cformed on the printed board13and the spacer16.

The spacer16is formed of a conductive member.

The spacer16is secured to a housing17and is electrically connected with each of the ground pattern13cand the housing17.

The housing17is formed of a conductive member and is connected with a ground (not illustrated).

The magnetic core18is formed of a magnetic material and has an opening18din the central portion.

The magnetic core18is disposed in such a manner that the first coupling wiring portion11cpasses through the opening18d.

The magnetic core18includes a first core18a, a second core18b, and a third core18c.

The first core18ais formed by molding a magnetic material into a three-sided frame shape.

As illustrated inFIG.6A, one end18b1of the first core18ais connected with each of one end18b1of the second core18band one end18c1of the third core18c. Likewise, the other end18a2of the first core18ais connected with each of the other end18b2of the second core18band the other end18c2of the third core18c.

The second core18bis formed by molding a magnetic material into a rectangular column.

The one end18b1of the second core18bis connected with the one end18a1of the first core18a, and the other end18b2of the second core18bis connected with the other end18a2of the first core18a.

The third core18cis formed by molding a magnetic material into a rectangular column.

One end18c1of the third core18cis connected with the one end18a1of the first core18a, and the other end18c2of the third core18cis connected with the other end18a2of the first core18a.

The opening18dis a space surrounded by the first core18a, the second core18b, and the third core18c, and the first coupling wiring portion11cis inserted in the opening18d.

FIG.7is an explanatory diagram illustrating a manufacturing process of the first lead conductor12in the noise filter1illustrated inFIG.2.

The first bus bar11and the first lead conductor12having a planar shape as illustrated inFIG.7are integrally formed by punching, pressing, or the like of a sheet metal.

A bent portion19indicates a position where the first lead conductor12is bent after the first bus bar11and the first lead conductor12are integrally formed.

The first lead conductor12is bent at the bent portion19to form the first bus bar11and the first lead conductor12having the shape as illustrated inFIG.6B.

At the time of assembling the noise filter1, the first core18ais, for example, brought downward in the −Z direction from the +Z direction of the first bus bar11so that the first coupling wiring portion11cof the first bus bar11illustrated inFIG.6Bis positioned in the opening18dof the magnetic core18.

Next, for example, the second core18bis moved in the +Y direction from the −Y direction of the first bus bar11. Then, the second core18bis secured to the first core18aat a position where the one end18b1of the second core18bis in contact with the one end18a1of the first core18aand the other end18b2of the second core18bis in contact with the other end18a2of the first core18a.

Next, for example, the third core18cis moved in the +Y direction from the −Y direction of the first bus bar11. Then, the third core18cis secured to the first core18aat a position where the one end18c1of the third core18cis in contact with the one end18a1of the first core18aand the other end18c2of the third core18cis in contact with the other end18a2of the first core18a.

At this time, in cross section A1-A2illustrated inFIG.3, as illustrated inFIG.4, the second core18bis positioned on the left side of the first lead conductor12in the drawing, and the third core18cis located on the right side of the first lead conductor12in the drawing.

Next, the operation of the noise filter1illustrated inFIG.2will be described.

FIG.8Ais an explanatory diagram illustrating noise current Inoiseflowing through the first bus bar11.

FIG.8Bis an explanatory diagram illustrating magnetic fluxes Φaand Φbgenerated by the noise current Inoiseflowing through the first bus bar11.

The first extending wiring portion11aof the first bus bar11extends clockwise and forms a reactor L1as illustrated inFIG.9.

The second extending wiring portion11bof the first bus bar11extends counterclockwise and forms a reactor L2as illustrated inFIG.9.

InFIG.8A, an example is illustrated in which the noise current Inoiseflows through the first bus bar11from the circuit side toward the connector side.

As the noise current Inoiseflows through the first bus bar11from the circuit side toward the connector side, a magnetic flux Φadirected in the +Z direction is generated in the magnetic core18present inside the reactor L1formed by the first extending wiring portion11aas illustrated inFIG.8A.

In addition, as the noise current Inoiseflows through the first bus bar11from the circuit side toward the connector side, a magnetic flux Φbdirected in the −Z direction is generated in the magnetic core18present inside the reactor L2formed by the second extending wiring portion11bas illustrated inFIG.8A.

At this point, in the magnetic core18, the directions in which the magnetic flux Φaand the magnetic flux Φbare directed are the same as illustrated inFIG.8B, and the magnetic flux Φaand the magnetic flux Φbintensify each other.

Since the magnetic flux Φaand the magnetic flux Φbshare a magnetic path, there is a mutual inductance M between the reactor L1and the reactor L2.

FIG.9is an equivalent circuit of the noise filter1illustrated inFIG.2.

InFIG.9, Lwiredenotes an inductance component of the first lead conductor12, C denotes a capacitance of the first capacitor14, Lcdenotes an inductance component of the first capacitor14, and Lpatterndenotes a sum of an inductance component of the wiring pattern13band an inductance component of the ground pattern13c.

Lspacerdenotes an inductance component of the spacer16, and M denotes a mutual inductance between the reactor L1and the reactor L2.

FIG.10is a diagram illustrating a circuit obtained by converting the equivalent circuit illustrated inFIG.9into an equivalent circuit.

InFIG.10, ESL denotes the sum of the inductance component Lwire, the inductance component Lc, the inductance component Lpattern, and the inductance component Lspacer.

In the noise filter1illustrated inFIG.2, as illustrated inFIG.10, ESL is connected in series with the capacitance C of the first capacitor14, and an inductance component of −M is connected in series with the capacitance C.

An inductance component in which ESL and the inductance component of −M are connected in series is expressed as ESL−M. Therefore, in the noise filter1illustrated inFIG.2, ESL can be canceled by the amount of the mutual inductance M.

In a case where there is inductance, the impedance generally increases as the frequency increases. Therefore, also in a case where the ESL illustrated inFIG.10is present, the impedance increases as the frequency increases.

Accordingly, ESL illustrated inFIG.10acts to prevent the noise current Inoiseof a high frequency flowing through the first bus bar11from flowing through the housing17. Since ESL acts to prevent the noise current Inoisefrom flowing through the housing17, ESL deteriorates the effect of suppressing the high frequency noise.

In the noise filter1illustrated inFIG.2, since ESL can be canceled by the amount of mutual inductance M, the effect of suppressing high frequency noise can be improved by the amount of mutual inductance M.

In the noise filter1illustrated inFIG.2, the effect of suppressing the high frequency noise is optimized by determining the dimension of each of the first extending wiring portion11a, the second extending wiring portion11b, and the first coupling wiring portion11c, the magnetic material of the magnetic core18, and the dimension of the magnetic core18so as to obtain the mutual inductance M that satisfies ESL−M=0. The dimension of each of the first extending wiring portion11a, the second extending wiring portion11b, and the first coupling wiring portion11care mainly the inner diameter of the reactor L1and the inner diameter of the reactor L2.

The value of ESL to be canceled can be obtained by performing electromagnetic field analysis or the like based on the respective structures of the first lead conductor12, the wiring pattern13b, and the spacer16.

Therefore, it is important to select the dimensions and the magnetic material that allows the mutual inductance M to be as close to ESL as possible by performing electromagnetic field analysis or the like.

FIG.11is an explanatory diagram illustrating a noise suppression effect of the noise filter1according to the first embodiment.

In the graph illustrated inFIG.11, the horizontal axis represents the frequency, and the vertical axis represents the noise transmission amount between the circuit side and the connector side. As the noise transmission amount is lower, the noise suppression effect of the noise filter1is higher.

InFIG.11, a noise filter “with structure” corresponds to the noise filter1illustrated inFIG.2whose dimensions and the like are determined so that M=ESL holds.

As illustrated inFIG.12, the “no structure” noise filter is a noise filter having a structure in which a linear bus bar11′ is used instead of the first bus bar11and the magnetic core18is not disposed.

FIG.12is a perspective view illustrating a noise filter in which the linear bus bar11′ is used instead of the first bus bar11and the magnetic core18is not disposed.

Around a frequency fr that is determined by the values of ESL and the capacitance C of the first capacitor14, a noise filter “without structure” has a higher noise suppression effect than the noise filter “with structure”.

However, at frequencies higher than the frequency fr to some extent, the noise suppression effect of the noise filter “without structure” decreases. Therefore, at frequencies higher than the frequency fr to some extent, the noise suppression effect is higher in the noise filter “with structure” than in the noise filter “without structure”.

Note that, even if the mutual inductance M of the noise filter “with structure” does not match ESL, if the noise filter “with structure” has the mutual inductance M satisfying 0<M<2×ESL, the noise suppression effect becomes higher at frequencies higher than the frequency fr to some extent than that of the noise filter “without structure”. The noise transmission amount at a frequency higher than the frequency fr to some extent is between the noise transmission amount of the noise filter “without structure” and the noise transmission amount of the noise filter in which M=ESL holds.

In the first embodiment described above, the noise filter1includes: the first bus bar11that is electrical wiring of a flat plate, the first bus bar11including the first extending wiring portion11aextending in the first direction, the second extending wiring portion11bextending in the second direction that is a direction opposite to the first direction, and the first coupling wiring portion11cconnecting the first extending wiring portion11aand the second extending wiring portion11b; the first lead conductor12having the one end connected with the first coupling wiring portion11c; the first capacitor14having the one end connected with the other end of the first lead conductor12and the other end connected with the ground; and the magnetic core18having the opening18din the central portion, the magnetic core18disposed in such a manner that the first coupling wiring portion11cpasses through the opening18d. Therefore, it is possible to implement the noise filter1using the first bus bar11having a planar structure that can be manufactured by punching, pressing, or the like.

In the noise filter1illustrated inFIG.2, the first extending wiring portion11aextends clockwise, and the second extending wiring portion11bextends counterclockwise.

In order to obtain a desired magnetic flux Φa, it is sufficient that the portion of the first bus bar11having the first extending wiring portion11aand the first coupling wiring portion11ccircumferentially surrounds the magnetic core18by about three quarters or more. In addition, in order to obtain a desired magnetic flux Φb, it is sufficient that the portion of the first bus bar11having the second extending wiring portion11band the first coupling wiring portion11ccircumferentially surrounds the magnetic core18by about three quarters or more.

FIG.13is an explanatory diagram illustrating an example in which a portion having the first extending wiring portion11aand the first coupling wiring portion11ccircumferentially surrounds the magnetic core18by three quarters, and a portion having the second extending wiring portion11band the first coupling wiring portion11ccircumferentially surrounds the magnetic core18by three quarters.

In the noise filter1illustrated inFIG.2, the one end of the first bus bar11is connected with the connector, and the other end of the first bus bar11is connected with the motor driving circuit. However, this is merely an example, and the one end of the first bus bar11may be connected with the motor driving circuit, and the other end of the first bus bar11may be connected with the connector.

In the noise filter1illustrated inFIG.2, the first bus bar11and the first lead conductor12are integrally formed, and then the first lead conductor12is bent at the bent portion19.

However, this is merely an example, and for example, a cable may be used as the first lead conductor12, and one end of the cable may be connected with the first coupling wiring portion11c, and the other end of the cable may be connected with the wiring pattern13b.

The connection between the one end of the cable and the first coupling wiring portion11cand the connection between the other end of the cable and the wiring pattern13bmay be each achieved by soldering or screwing. Alternatively, the connection between the one end of the cable and the first coupling wiring portion11cmay be achieved by soldering, and the connection between the other end of the cable and the wiring pattern13bmay be achieved by screwing, or the connection between one end of the cable and the first coupling wiring portion11cmay be achieved by screwing, and the connection between the other end of the cable and the wiring pattern13bmay be achieved by soldering.

Furthermore, as the first lead conductor12, for example, a conductive material having a spring property may be used.

Note that the first lead conductor12and the wiring pattern13bonly need to be electrically connected, and the connection may be achieved by screwing, contact by a conductive material having a spring property, adhesion by a conductive adhesive, welding, or the like.

In the noise filter1illustrated inFIG.2, each of the first core18a, the second core18b, and the third core18cis made of a magnetic material. Each of the first core18a, the second core18b, and the third core18conly needs to be a magnetic body and may be made of iron, ferrite, an amorphous-based alloy, or the like.

In the noise filter1illustrated inFIG.2, the second core18band the third core18care each secured to the first core18aat the time of assembly.

However, it is sufficient that the magnetic core18can be disposed in such a manner that the first coupling wiring portion11cpasses through the opening18d, and the first core18a, the second core18b, and the third core18cmay be integrally molded in whole or in part.

In the noise filter1illustrated inFIG.2, the first core18ais formed by molding into a three-sided frame shape, and each of the second core18band the third core18cis molded in a rectangular column shape.

However, it is sufficient that the magnetic core18can be disposed in such a manner that the first coupling wiring portion11cpasses through the opening18d, and the first core18amay have, for example, a curved shape, and the second core18band the third core18cmay each have, for example, a curved shape.

In the noise filter1illustrated inFIG.2, each of the first core18a, the second core18b, and the third core18cis held by some member. At this time, it is sufficient that the magnetic core18can be disposed in such a manner that the first coupling wiring portion11cpasses through the opening18d, and it is assumed that each of the first core18a, the second core18b, and the third core18cis held by a non-conductive member such as resin.

Specifically, it is assumed that each of the first core18a, the second core18b, and the third core18cis held by a non-conductive support member having one end secured to the first bus bar11.

In the noise filter1illustrated inFIG.2, each of the wiring pattern13band the ground pattern13cis formed on the printed board13.

However, this is merely an example, and the printed board13may be a multilayer substrate, and the wiring pattern13band the ground pattern13cmay be formed on different layers of the multilayer substrate.

In the noise filter1illustrated inFIG.2, the first capacitor14is mounted on the printed board13. The first capacitor14only needs to have the capacitance C and may be a surface-mounting-type capacitor or a lead-type capacitor.

In the noise filter1illustrated inFIG.2, the screw15electrically connects the ground pattern13cand the spacer. However, this is merely an example, and the ground pattern13cand the spacer may be electrically connected by soldering, welding, or fitting by a spring member.

In the noise filter1illustrated inFIG.2, the spacer16electrically connects the ground pattern13cand the housing17. However, this is merely an example, and the housing17may be formed into a spacer shape, and the housing17formed in the spacer shape may be electrically connected with the ground pattern13c.

In the noise filter1illustrated inFIG.2, the spacer16is connected with the housing17connected with the ground (not illustrated). However, this is merely an example, and the spacer16may be connected with the ground (not illustrated).

Second Embodiment

In a second embodiment, a noise filter1including a first bus bar11and a second bus bar21will be described.

FIG.14is a perspective view illustrating the noise filter1according to the second embodiment.

FIG.15is a Y-Z plane view of the noise filter1illustrated inFIG.14as viewed from +X direction.

InFIGS.14and15, the same symbol as that inFIGS.2to6represents the same or a corresponding part, and thus description thereof is omitted.

A second bus bar21is installed on an X-Y plane.

The second bus bar21is electrical wiring of a flat plate having the same shape as that of the first bus bar11. Here, the same shape is not limited to shapes that are exactly the same, and the shapes of the first bus bar11and the second bus bar21may be different in a range where there is no practical problem.

The one end of the second bus bar21is connected with, for example, a connector connected with a voltage output terminal of an electrode in a DC power supply, and the other end of the second bus bar21is connected with, for example, a motor driving circuit.

In the noise filter1illustrated inFIG.14, the one end of the first bus bar11is connected with, for example, a connector connected with a voltage output terminal of a +electrode in a DC power supply.

The first bus bar11and the second bus bar21are arranged in parallel with each other in a state where electrical insulation is maintained. Note that, the arrangement of the first bus bar11and the second bus bar21is not limited to being strictly parallel and may be substantially parallel in a range where there is no practical problem.

The second bus bar21includes a third extending wiring portion21aextending in a first direction and a fourth extending wiring portion21bextending in a second direction.

The first direction is a clockwise direction starting from the side connected with the connector when the second bus bar21is viewed from the +Z direction. The second direction is a counterclockwise direction starting from the side connected with the connector when the second bus bar21is viewed from the +Z direction.

In addition, the second bus bar21includes a second coupling wiring portion21cconnecting the third extending wiring portion21aand the fourth extending wiring portion21b.

In the noise filter1illustrated inFIG.14, the third extending wiring portion21a, the fourth extending wiring portion21b, and the second coupling wiring portion21care integrally formed.

In the noise filter1illustrated inFIG.14, the first direction is the clockwise direction, and the second direction is the counterclockwise direction. However, this is merely an example, and the first direction may be the counterclockwise direction, and the second direction may be the clockwise direction. That is, the first bus bar11may have a first extending wiring portion11aextending counterclockwise and a second extending wiring portion11bextending clockwise, and the second bus bar21may have a third extending wiring portion21aextending counterclockwise and a fourth extending wiring portion21bextending clockwise.

A second lead conductor22is electrical wiring of a flat plate having one end connected with the second coupling wiring portion21cand the other end connected with a wiring pattern13dformed on the printed board13.

The second lead conductor22is manufactured in a similar manner to that of the first lead conductor12.

The first capacitor14and the second capacitor23are each mounted on the printed board13.

The wiring pattern13dis conductive electric wiring and is connected with each of the other end of the second lead conductor22and one end of the second capacitor23.

A ground pattern13eis conductive electric wiring and is connected with each of the other end of the first capacitor14and the other end of the second capacitor23.

The one end of the second capacitor23is connected with the other end of the second lead conductor22via the wiring pattern13d.

The other end of the second capacitor23is connected with the ground pattern13e.

A magnetic core18is disposed in such a manner that each of the first coupling wiring portion11cand the second coupling wiring portion21cpasses through an opening18d.

FIG.16is an equivalent circuit of the noise filter1illustrated inFIG.14. InFIG.16, ESL and mutual inductance M are omitted for simplicity of description.

The third extending wiring portion21aof the second bus bar21extends clockwise and forms a reactor L3.

The fourth extending wiring portion21bof the second bus bar21extends counterclockwise and forms a reactor L4.

InFIG.16, a solid line indicated by B indicates that the reactors L1and L2and the reactors L3and L4are magnetically coupled by the magnetic core18.

Next, the operation of the noise filter1illustrated inFIG.14will be described.

As the noise current that flows through each of the first bus bar11and the second bus bar21, there are a normal mode current and a common mode current.

In the normal mode current, the direction in which the current flows through the first bus bar11is opposite to the direction in which the current flows through the second bus bar21.

In the common mode current, the direction in which the current flows through the first bus bar11is the same as the direction in which the current flows through the second bus bar21.

In both the normal mode current and the common mode current, the amount of a current flowing through the first bus bar11is the same as the amount of a current flowing through the second bus bar21.

In a device using a bus bar such as an inverter device for driving a motor, a normal mode current is often a large current greater than or equal to several tens of amperes. When a magnetic flux generated by a large current greater than or equal to several tens of amperes passes through the magnetic body, the magnetic body may cause magnetic saturation. In the state of magnetic saturation, the relative permeability of the magnetic body is close to 1, and the magnetic body almost does not serve as a core.

In the noise filter1illustrated inFIG.14, even when a normal mode current flows through each of the first bus bar11and the second bus bar21, the current flowing through the first bus bar11and the current flowing through the second bus bar21have the same amount in opposite directions.

Since the current flowing through the first bus bar11and the current flowing through the second bus bar21have the same amount in opposite directions, the magnetic flux Φagenerated by the normal mode current flowing through the first bus bar11and the magnetic flux Φa′ generated by the normal mode current flowing through the second bus bar21cancel each other. In addition, the magnetic flux Φbgenerated by the normal mode current flowing through the first bus bar11and the magnetic flux Φb′ generated by the normal mode current flowing through the second bus bar21cancel each other.

Therefore, in the noise filter1illustrated inFIG.14, even if the normal mode current flows through each of the first bus bar11and the second bus bar21, the magnetic core18hardly causes magnetic saturation.

In the common mode current, as described above, the current flowing through the first bus bar11and the current flowing through the second bus bar21have the same direction and the same amount.

Therefore, magnetic flux Φagenerated by the common mode current flowing through the first bus bar11and magnetic flux Φa′ generated by the common mode current flowing through the second bus bar21do not cancel each other. Likewise, the magnetic flux Φbgenerated by the common mode current flowing through the first bus bar11and the magnetic flux Φb′ generated by the common mode current flowing through the second bus bar21do not cancel each other.

When the common mode current flows through each of the first bus bar11and the second bus bar21, the magnetic flux Φaand the magnetic flux Φa′ are not canceled, and the magnetic flux Φband the magnetic flux Φb′ are not canceled either, and thus the mutual inductance M is generated.

In the noise filter1illustrated inFIG.14, the mutual inductance M is used to cancel ESL that is a factor of deteriorating the effect of suppressing high frequency noise (hereinafter, referred to as “common mode noise”) due to the common mode current.

In the noise filter1illustrated inFIG.14, the dimensions of the first extending wiring portion11a, the second extending wiring portion11b, and the first coupling wiring portion11care determined so that the mutual inductance M satisfying ESL−M=0 is obtained. In addition, the dimensions of the third extending wiring portion21a, the fourth extending wiring portion21b, and the second coupling wiring portion21c, the magnetic material of the magnetic core18, and the dimensions of the magnetic core18are determined.

As described above, by determining the dimensions and the magnetic material, the effect of suppressing the common mode noise is optimized.

The dimension of each of the first extending wiring portion11a, the second extending wiring portion11b, and the first coupling wiring portion11care mainly the inner diameter of the reactor L1and the inner diameter of the reactor L2. The dimension of each of the third extending wiring portion21a, the fourth extending wiring portion21b, and the second coupling wiring portion21care mainly the inner diameter of the reactor L3and the inner diameter of the reactor L4.

Note that the value of ESL to be canceled can be obtained by performing electromagnetic field analysis or the like based on the respective structures of the first lead conductor12, the second lead conductor22, the wiring patterns13band13d, and the spacer16.

Therefore, it is important to select the dimensions and the magnetic material that allows the mutual inductance M to be as close to ESL as possible by performing electromagnetic field analysis or the like.

FIG.17is an explanatory diagram illustrating a noise reduction effect of the noise filter1according to the second embodiment.

In the graph illustrated inFIG.17, the horizontal axis represents the frequency, and the vertical axis represents the noise transmission amount between the circuit side and the connector side. As the noise transmission amount is lower, the noise suppression effect of the noise filter1is higher.

InFIG.17, a noise filter “with structure” corresponds to the noise filter1illustrated inFIG.14whose dimensions and the like are determined so that M=ESL holds.

As illustrated inFIG.18, the noise filter “without structure” has a structure in which the linear bus bar11′ is used instead of the first bus bar11, the linear bus bar21′ is used instead of the second bus bar21, and the magnetic core18is not disposed.

FIG.18is a perspective view illustrating the noise filter in which the linear bus bar11′ is used instead of the first bus bar11, the linear bus bar21′ is used instead of the second bus bar21, and the magnetic core18is not disposed.

Around a frequency fr′ that is determined by the values of ESL, the capacitance C of the first capacitor14, and the capacitance C of the second capacitor23, a noise filter “without structure” has a higher noise suppression effect than the noise filter “with structure”.

However, at frequencies higher than the frequency fr′ to some extent, the noise suppression effect of the noise filter “without structure” decreases. Therefore, at frequencies higher than the frequency fr′ to some extent, the noise suppression effect is higher in the noise filter “with structure” than in the noise filter “without structure”.

Note that, even if the mutual inductance M of the noise filter “with structure” does not match ESL, if the noise filter “with structure” has the mutual inductance M satisfying 0<M<2×ESL, the noise suppression effect becomes higher at frequencies higher than the frequency fr′ to some extent than that of the noise filter “without structure”. The noise transmission amount at a frequency higher than the frequency fr′ to some extent is between the noise transmission amount of the noise filter “without structure” and the noise transmission amount of the noise filter in which M=ESL holds.

In the second embodiment described above, the noise filter1includes: the second bus bar21that is electrical wiring of a flat plate shape same as that of the first bus bar11, the second bus bar21including the third extending wiring portion21aextending in the first direction, the fourth extending wiring portion21bextending in the second direction that is a direction opposite to the first direction, and the second coupling wiring portion21cconnecting the third extending wiring portion21aand the fourth extending wiring portion21b; the second lead conductor22having the one end connected with the second coupling wiring portion21c; and the second capacitor23having the one end connected with the other end of the second lead conductor22and the other end connected with the ground. In addition, in the noise filter1, the first bus bar11and the second bus bar21are arranged in parallel with each other in a state where electrical insulation is maintained, and the magnetic core18is disposed in such a manner that the first coupling wiring portion11cand the second coupling wiring portion21ceach pass through the opening18d. Therefore, it is possible to implement the noise filter1using each of the first bus bar11and the second bus bar21having a planar structure that can be manufactured by punching, pressing, or the like. Furthermore, the noise filter1can prevent occurrence of magnetic saturation due to the normal mode current.

In the noise filter1illustrated inFIG.14, the first extending wiring portion11aextends clockwise, and the second extending wiring portion11bextends counterclockwise. Moreover, the third extending wiring portion21aextends clockwise, and the fourth extending wiring portion21bextends counterclockwise.

In order to obtain a desired magnetic flux Φa, it is sufficient that the portion of the first bus bar11having the first extending wiring portion11aand the first coupling wiring portion11ccircumferentially surrounds the magnetic core18by about three quarters or more. In addition, in order to obtain a desired magnetic flux Φb, it is sufficient that the portion of the first bus bar11having the second extending wiring portion11band the first coupling wiring portion11ccircumferentially surrounds the magnetic core18by about three quarters or more.

In order to obtain a desired magnetic flux Φa′, it is sufficient that the portion of the second bus bar21having the third extending wiring portion21aand the second coupling wiring portion21ccircumferentially surrounds the magnetic core18by about three quarters or more. In addition, in order to obtain a desired magnetic flux Φb′, it is sufficient that the portion of the second bus bar21having the fourth extending wiring portion21band the second coupling wiring portion21ccircumferentially surrounds the magnetic core18by about three quarters or more.

In the noise filter1illustrated inFIG.14, the one end of the first bus bar11is connected with the connector connected with the voltage output terminal of the +electrode in the DC power supply, and the one end of the second bus bar21is connected with the connector connected with the voltage output terminal of the −electrode in the DC power supply. However, this is merely an example, and the one end of the first bus bar11may be connected with a connector connected with a voltage output terminal of a −electrode in the DC power supply, and the one end of the second bus bar21may be connected with a connector connected with a voltage output terminal of a +electrode in the DC power supply.

Alternatively, the one end of the first bus bar11may be connected with a connector connected with one of two lines of a single-phase AC, and the one end of the second bus bar21may be connected with a connector connected with the other of the two lines of the single-phase AC.

Further alternatively, one end of each of a plurality of bus bars may be connected with one of three lines of three-phase alternating current or one of four lines of three-phase alternating current. In a case where the one end of each of the plurality of bus bars is connected with one of three lines of three-phase alternating current, there are three sets of a bus bar, a lead conductor, and a capacitor. Alternatively, in a case where the one end of each of the plurality of bus bars is connected with one of four lines of three-phase alternating current, there are four sets of a bus bar, a lead conductor, and a capacitor.

Third Embodiment

In a third embodiment, a noise filter1including a magnetic core18in which non-magnetic spacers40are inserted in a part of a magnetic body will be described.

FIG.19is a Y-Z plane view of the noise filter1according to the third embodiment as viewed from +X direction. InFIG.19, the same symbol as that inFIGS.2and5represents the same or a corresponding part, and thus description thereof is omitted.

Spacers40are formed of a non-magnetic material.

A spacer40is sandwiched between the one end18a1of the first core18aand each of the one end18b1of the second core18band the one end18c1of the third core18c.

Likewise, a spacer40is sandwiched between the other end18a2of the first core18aand each of the other end18b2of the second core18band the other end18c2of the third core18c.

Note that the spacers40are only required to be a non-magnetic body and may be formed of resin or metal. Alternatively, the spacers40may be the air.

Next, the operation of the noise filter1illustrated inFIG.19will be described.

In the noise filter1illustrated inFIG.2, the magnetic core18does not include the spacers40, and no gap is formed between the first core18aand each of the second core18band the third core18c.

When there is no gap, as illustrated inFIG.8B, there is almost no leakage of the magnetic flux Φafrom the magnetic core18nor a leakage of the magnetic flux Φbfrom the magnetic core18.

In the noise filter1illustrated inFIG.19, the magnetic core18includes the spacers40, and there are gaps between the first core18aand each of the second core18band the third core18c.

Since there are gaps, a part of the magnetic flux Φaleaks from the gap, and a part of the magnetic flux Φbleaks from the gap. Therefore, in a case where there are gaps, the magnetic coupling between the reactor L1and the reactor L2is weaker and the mutual inductance M decreases as compared with a case where there are no gaps.

In addition, the larger the size of the gaps is, the larger the reduction amount of the mutual inductance M is.

In the noise filter1illustrated inFIG.19, the size of the gaps can be modified by adjusting the thickness of the spacers40, thereby allowing the mutual inductance M to be adjusted.

Therefore, the thickness of the spacers40is one of adjustment parameters of the mutual inductance M when dimensions and a magnetic material that allows the mutual inductance M to be as close to ESL as possible are selected by performing electromagnetic field analysis or the like.

FIG.20Ais an explanatory diagram illustrating a correspondence relationship between the size of the gaps and the mutual inductance M.

FIG.20Bis an explanatory graph illustrating a correspondence relationship between a frequency f and the noise transmission amount.

FIG.20Cis an explanatory graph illustrating a correspondence relationship between the size of the gaps and the noise transmission amount at a frequency f.

As illustrated inFIG.20A, the mutual inductance M decreases as the size of the gaps increases.

When the frequency of the noise current Inoiseis high and the frequency of the noise current Inoiseequals f, as illustrated inFIGS.20B and20C, the noise transmission amount decreases, and the noise suppression effect becomes higher in a case where M=ESL than cases where M<ESL and M>ESL.

In the third embodiment described above, the noise filter1illustrated inFIG.19includes the magnetic core18in which the spacer40of the non-magnetic body is inserted in a part of the magnetic body. Therefore, the noise filter1illustrated inFIG.19can be implemented using the first bus bar11having a planar structure that can be manufactured by punching, pressing, or the like, similarly to the noise filter1illustrated inFIG.2. In addition, the noise filter1illustrated inFIG.19can adjust the noise suppression effect without changing the dimensions of the first bus bar11or the dimensions and the material of the magnetic core18.

In the noise filter1illustrated inFIG.19, the spacer40is sandwiched between the first core18aand the second core18b, and the spacer40is sandwiched between the first core18aand the third core18c.

However, this is merely an example, and the spacer40may be sandwiched only between the first core18aand the second core18b, or the spacer40may be sandwiched only between the first core18aand the third core18c.

Furthermore, the thickness of the spacer40sandwiched between the first core18aand the second core18bmay be different from the thickness of the spacer40sandwiched between the first core18aand the third core18c.

Note that the present invention may include a flexible combination of the embodiments, a modification of any component of the embodiments, or an omission of any component in the embodiments within the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is suitable for a noise filter including a capacitor and a power supply device.

REFERENCE SIGNS LIST