Patent Application
20200027652
The present disclosure relates to a noise filter and a power conversion apparatus that includes the noise filter.
An inverter device is provided with an electro-magnetic compatibility (EMC) filter that reduces noise generated by an inverter. In an EMC filter unit disclosed in Patent Literature 1, cables for each phase are wound around a ring core composed of ring-shaped ferrite cores. High-frequency noise current flowing through the cables produces a magnetic field that is concentrated into the ferrite cores, and high frequency loss attenuates noise by converting the magnetic field into heat.
Patent Literature 1: Japanese Patent No. 5499795
Even if high-frequency noise current does not flow through a conductor, a steady-state current produces a magnetic field around the conductor. In the EMC filter unit disclosed in Patent Literature 1, the ring core concentrates not only a magnetic field produced by high-frequency noise current but also the magnetic field produced by the steady-state current. Consequently, magnetic saturation in the ring core occurs and noise removal efficiency may decrease.
In order to solve the aforementioned circumstances, an objective of the present disclosure is to improve noise removal efficiency.
In order to achieve the aforementioned objective, a noise filter of the present disclosure includes a center conductor, at least one outer conductor, and a core. The at least one outer conductor is cylindrical in shape and has an interior through which the center conductor is inserted. The core is a cylindrical magnetic body and has an interior through which the center conductor and the at least one outer conductor are inserted. The center conductor and the at least one outer conductor are insulated from each other. Phase currents of symmetrical polyphase alternating current flow through the center conductor and the at least one outer conductor.
According to the present disclosure, the noise filter is provided with the at least one cylindrical outer conductor that is inserted through the interior of the cylindrical core and the center conductor that is inserted through the interior of the at least one outer conductor, thereby enabling the noise filter to improve noise removal efficiency.
Embodiments of the present disclosure are described below in detail with reference to the drawings. Throughout the drawings, components that are the same or equivalent are assigned the same reference signs.
The outer peripheral surface of the center conductor 20 is covered with an insulating member 30. The outer peripheral surface of the first outer conductor 21 is covered with an insulating member 31. The outer peripheral surface of the second outer conductor 22 is covered with an insulating member 32. The insulating members 30, 31, and 32 are, for example, heat-shrinkable tubing with insulation properties. A gap 40 is provided between the outer peripheral surface of the insulating member 30 and the inner peripheral surface of the first outer conductor 21. A gap 41 is provided between the outer peripheral surface of the insulating member 31 and the inner peripheral surface of the second outer conductor 22. Also, a gap 42 is provided between the outer peripheral surface of the insulating member 32 and the inner peripheral surface of the core 10. The providing of the insulating members 30, 31, and 32 is unnecessary as long as the center conductor 20, the first outer conductor 21, and the second outer conductor 22 are insulated from one another by the gaps 40, 41, and 42.
A centroid of the cross-section of the center conductor 20 perpendicular to the central axis of the core 10 and a centroid of the cross section of each of the at least one outer conductor perpendicular to the central axis can be treated as being the same by setting the distance between the centroid of the cross section of the center conductor 20 and the centroid of the cross section of the at least one outer conductor to a sufficiently small value. In the steady state, the total sum of the phase currents is 0. Since the centroid of the cross section of the center conductor 20 and the centroid of each of the at least one outer conductor can be treated as being the same, the magnetic fields produced by the phase currents, in the steady state, is canceled out on the outer peripheral side of the outer conductor in the outermost position. Since the magnetic fields are canceled out on the outer peripheral side of the outer conductor in the outermost position, the core 10, in the steady state, does not concentrate the magnetic field. Conversely, in a case, for example, in which common mode noise that is high-frequency noise current is produced, the core 10 concentrates the magnetic field produced by the common mode noise, and high frequency loss attenuates noise by converting the magnetic field into heat. According to the noise filter 1, the core 10, in the steady state, concentrates the magnetic field produced by the phase currents, and thus magnetic saturation in the core 10 can be suppressed and noise removal efficiency can be improved. The result of the noise filter 1 is similar in the case in which round-trip current flows.
In the example of
Moreover, the centroid of the cross section of the center conductor 20 perpendicular to the central axis of the core 10 and the centroid of the cross section of the core 10 perpendicular to the central axis can be treated as being the same by setting the distance between the centroid of the cross section of the center conductor 20 and the centroid of the cross section of the core 10 to a sufficiently small value. Also, as previously described, by setting the distance between the centroid of the cross section of the center conductor 20 and the centroid of the cross section of the at least one outer conductor to a sufficiently small value, the centroid of the cross section of the center conductor 20, the centroid of the cross section of the first outer conductor 21, and the centroid of the cross section of the second outer conductor 22, can be treated as being coincident with one another. With this configuration, noise removal efficiency improves when high-frequency noise flows through.
In the noise filter 1 according to Embodiment 1, magnetic saturation in the core 10 is less likely to occur in comparison to that in the noise filter 6, and thus noise removal efficiency is high. Also, the interior of the core 60 in the configuration of the noise filter 6 has dead space 64 because the column-shaped conductors 61, 62, and 63 whose cross sections are circular are individually inserted through the interior of the core 60. The noise filter 1 according to Embodiment 1 does not have dead space on the interior of the core 10 as both the cylindrical outer conductors and the center conductor 20 are inserted through the interior of the core 10. In a case in which the surface area of the cross section perpendicular to the central axis of the core 10 and the surface area of the cross section perpendicular to the cross section perpendicular to the central axis of the core 60 are the same, the inner diameter of the core 10 is smaller than the inner diameter of the core 60. Also, the outer diameter of the core 10 is smaller than the outer diameter of the core 60. That is to say, the size of the cross section perpendicular to the central axis of the noise filter 1 is small compared to the cross section perpendicular to the central axis of the noise filter 6.
The cross-sectional surface area of the core 10 can be made larger than cross-sectional surface area of the core 60 by making the inner diameter of the core 10 smaller while also maintaining an outer diameter of the core 10 similar to the outer diameter of core 60. This greater cross-sectional surface area of the core 10 improves noise removal efficiency and suppresses a rise in temperature in the core 10. In the noise filter 6, the Mum-shaped conductors 61, 62, and 63 ought to be twisted in order to suppress magnetic field bias. Contrary to this, in the noise filter 1 according to Embodiment 1, twisting of the center conductor 20 and the outer conductors is unnecessary as the cylindrical outer conductors and the center conductor 20 are inserted through the interior of the core 10. Since bending work is unnecessary in the case of the noise filter 1, it is easy to pull components through in comparison to the noise filter 6 through which the twisted column-shaped conductors 61, 62, and 63 are inserted.
The length of the center conductor 20 in the longitudinal direction is longer than the length of each of the at least one outer conductor in the longitudinal direction. The longitudinal direction is the direction in which the current flows. In the example of
After the center conductor 20, the first outer conductor 21, and the second outer conductor 22 are inserted through the interior of the core 10, the terminals 50, 51, and 52 may be respectively crimped-on. In such a case, the inner diameter of the core 10 may be made smaller because passing of the terminals 50, 51, and 52 through the interior of the core 10 is unnecessary. In other words, the inner diameter of the core 10 can be made smaller because the terminals are provided on the outer portion of the core 10. As the inner diameter of the core 10 can be made smaller in the aforementioned manner, the outer diameter of the core 10 can be made smaller, and thus the noise filter 1 can be made more compact. Moreover, by making the inner diameter of the core 10 smaller, noise removal efficiency can be improved. Also, the conductors 20, 21, and 22 may be bended and the bended portions may respectively serve as the terminals 50, 51, and 52.
In the example of
As described above, the noise filter 1 according to Embodiment 1 of the present disclosure includes the at least one cylindrical outer conductor inserted through the interior of the cylindrical core 10 and the center conductor 20 inserted through the interior of the at least one outer conductor, thereby enabling the noise filter 1 to improve noise removal efficiency.
There is an amplitude of steady-state current flowing (individually) through the center 20, the first outer conductor 23, and the second outer conductor 24 that is greater than or equal to a threshold. The threshold is, for example, greater than or equal to 10 A. Since current greater than or equal to 10 A flows through, the noise filter 1 can be used for noise removal in a main circuit.
The surface area of a cross section of the center conductor 20 perpendicular to the central axis of the core 10 and the surface area of the at least one outer conductor perpendicular to the central axis may be the same or may be different. By assigning the same value to the surface area of the cross section of the center conductor 20 and the surface area of the cross section of the outer conductor, the current density in the center conductor 20 and the current density in the outer conductor can be made the same.
As described above, the noise filter 1 according to Embodiment 2 of the present disclosure includes the at least one cylindrical outer conductor that is inserted through the interior of the cylindrical core 10 and the center conductor 20 that is inserted through the interior of the at least one outer conductor, thereby enabling improvement to noise removal efficiency. Moreover, by making at least one of the center conductor 20 or the outer conductor a braided wire conductor having a plurality of braided conducting wires, the manufacturing cost can be reduced.
The present disclosure is not limited to the above embodiments. The shape of the cross-sections of the center conductor 20, the at least one outer conductor, and the core 10 that are perpendicular to the central axis of the core 10 is not limited to the examples described above. The shape may be polygonal.
The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/013581 | 3/31/2017 | WO | 00 |
