D.C. reactor

Details D.C. reactor D.C. reactor

1996-08-05

1998-10-13

Kozma, Thomas J.

Inductor devices

With permanent magnet

336178, 336212, H01F 1704, H01F 2724

Patent

active

058218440

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a D.C. reactor in which flux generated by the D.C. reactor does not pass inside a permanent magnet so that an eddy current loss is decreased, and even when a large current abruptly flows through a coil of the D.C. reactor, the permanent magnet is not demagnetized. The reactors are capable of using low-cost permanent magnets of lower coercive force than the SmCo-system, such as the Nd-Fe-B system. The invention also relates to D.C. reactors capable of decreasing the core cross-sectional area suitable for downsizing, wherein the magnetic flux is decreased inside the core due to mutual cancellation of a bias magnetic flux formed by permanent magnets and a magnetic flux formed by the coil which are in opposite directions.
Conventional, so-called D.C. reactors make use of permanent magnets to provide magnetic biassing. As one such reactor, there is proposed a D.C. reactor employing an E-shaped core and an I-shaped core, wherein the E-shaped core has a center leg on which a coil is wound and which is lower than side legs, and wherein the side legs are bridged by the I-shaped core while permanent magnets provide magnetic bias and are disposed in a magnetic gap between the center leg of E-shaped core and the I-shaped core. Such an arrangement has been disclosed in, for example, Japanese Patent Publication No. Sho 46-37128. However, with this type of D.C. reactor, since the magnets are inserted into the gap, a specific magnetic material must be employed which will exhibit no demagnetization upon application of the magnetic flux formed by the coil. Also, while the inductance of the D.C. reactor becomes greater as the gap is reduced, a reduced gap renders the magnet thinner, impeding fabrication and causing demagnetization to occur more frequently. Accordingly, it should be strictly required that the magnet be thicker as long as there is some possibility of a large current. This may increase the resulting gap, also increasing the cross-sectional area of the core, and necessitating a larger reactor. Another disadvantage encountered with the prior art reactors is that, when high coercive-force magnets such as rare earth magnets are used to eliminate demagnetization, an increased eddy current may take place inside the magnet due to the small inherent resistance thereof.
One improved D.C. reactor is disclosed in Unexamined Japanese Patent Publication No. Sho 50-30047, wherein the permanent magnet of the aforesaid D.C. reactor consists of a plurality of permanent magnets. With this D.C. reactor, however, while the problem concerning the eddy current loss may be solved, the demagnetization problem remains unsolved, thus increasing manufacturing costs due to the assembly of the plurality of permanent magnets.
A further improved D.C. reactor has been disclosed in Unexamined Japanese Patent Publication No. Hei 4-84405. This reactor comes with an energizing coil provided on the center leg of an E-shaped core of an EI-shaped core, a gap defined between respective tip portions of the center leg and both legs of the E-shaped eve and an I-shaped core, magnetically biased permanent magnets which are arranged at respective outer surfaces of the E-shaped core and magnetized along the thickness thereof in such a manner that their opposed portions are of opposed polarity, and a yoke provided on the outer surface of each permanent magnet to be in contact with a corresponding edge of the I-shaped core. With this kind of D.C. reactor, since the magnetic flux formed by the coil does not flow inside the permanent magnets, demagnetization will no longer take place. However, the reactor suffers from another problem in that the magnetic flux formed by the permanent magnets and the magnetic flux formed by the coil are such that they extend in the same direction on either the right or left side of the E-shaped core while they extend in opposite directions on the other side, thus causing the nearby core in the same direction to be easily saturated.


SUMMARY OF THE INVENTION

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