A power inductor assembly includes and multiple coil sections disposed upon a mounting frame. Multiple winding sections each encircle one of the multiple core sections and a portion of the mounting frame. Air gap spacers separate adjacent core sections. The arrangement facilitates removal of thermal energy from the magnetic core. Lamination build direction normal to inductor mounting surface minimizes eddy current losses.

BACKGROUND OF THE INVENTION

The present invention relates generally to an inductor and, more particularly, to an inductor with multiple air gaps for thermal management.

High power motor controllers typically require inductors exhibiting stable inductance at both high magnitude currents and at frequencies ranging from DC to tens of kilohertz. Parameters for one such inductor, typical of aerospace applications, operates at: 35 μH rated for 260 A at 1,400 Hz continuous. An inductor designed to these parameters should retain 90% inductance at DC currents up to 880 amps. These inductors, specifically power quality filter inductors, should be lightweight and be configured for conduction cooling. Use in aerospace applications heightens the need for lightweight inductors.

Many conventional inductor permutations attempt to meet desired performance parameters yet minimize inductor weight. One such inductor is a gapped tape-wound cut core inductor. This type of inductor contains a magnetic core and typically exhibits high losses around the air gaps due to magnetic core eddy currents which are caused by flex fringing near the air gaps in the magnetic core. As a result, the heat generated by the inductor may most noticeably increase in the areas adjacent the air gaps. In addition, high temperatures may be realized in inductor portions proximate the air gaps. Air gaps in the magnetic path create a high reluctance path, avoiding saturation of the magnetic field at lower frequencies.

Powder magnetic core materials have been used in an attempt to reduce the high temperatures. The powder core materials inherently contain distributed air gaps, which minimize flux fringing and eddy current losses. However, as the DC magnetizing force of the inductor increases, the effective permeability of the powder core drops significantly which thereby limits the effectiveness of the powder magnetic core material to reduce inductor temperatures, especially in inductors producing high magnetizing forces.

Reducing the number of coil turns increases the current with which the permeability of the powder core drop becomes unacceptable. However, to maintain the desired inductance, the cross-sectional area of the powder core must increase substantially in response to a decrease in the number of coil turns, such that the overall weight of the inductor increases, with disadvantageous results for aerospace applications.

Other attempts to minimize the high temperatures generated by the inductors include eliminating entirely the ferromagnetic core. This approach results in an air core inductor with no air gaps or gap losses but requires a significant number of turns and relatively large diameter inductors coils to generate sufficient inductance. Eliminating the ferromagnetic core also induces high magnetic fields outside of the area enclosed by the coil windings, which may heat metal surfaces near the inductor and may interfere with the fields of other inductors in the area. Thus, the elimination of the ferromagnetic core results in a relatively large mounting footprint and stray magnetic fields, which may have disadvantageous results in aerospace applications.

Accordingly, it is desirable to provide an inductor for aerospace applications that minimizes eddy current losses and effectively facilitates inductor heat conduction.

SUMMARY OF THE INVENTION

A cut core inductor assembly having a magnetic core disposed in a winding. An electric current travels through the inductor assembly generating a magnetic field and thermal energy.

The magnetic core includes magnetic core sections on a mounting frame. The winding includes winding sections each encircling one of the magnetic core sections and the mounting frame. Multiple air gap spacers separate adjacent magnetic core sections of the magnetic core. Thermal energy removed from the magnetic core is communicated to the mounting frame.

The magnetic core section includes substantially rectangular profiled magnetic laminations arranged in a stack upon a planar mounting surface of the mounting frame. The stack of magnetic laminations extends from the mounting frame and perpendicular to the planar mounting surface. Upturned flanges on the mounting frame partially secure the magnetic laminations.

The present invention therefore provides a power inductor assembly which efficiently conducts heat from the magnetic core while minimizing eddy current losses and maintaining a desired inductance level.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1illustrates an isometric view of a typical cut core inductor assembly10having a magnetic core18disposed in a winding26. The magnetic core18includes a multitude of magnetic core sections22arranged on a mounting frame14. The winding26includes a multitude of winding sections28each encircling a portion of one of the magnetic core sections22and a portion of the mounting frame14. Multiple air gap spacers30separate adjacent magnetic core sections22of the magnetic core18. An electric current travels through the inductor assembly10generating a magnetic field and thermal energy.

The inductor assembly10may include magnetic core sections22of varying sizes. For example, the inductor assembly10may include larger magnetic core sections22near the ends of the inductor assembly10. It should be understood that although a rectangular inductor assembly10is described, various other geometries or arrangements of magnetic core sections22are included within the scope of this invention, including, toroidal or polygonal geometries.

Referring toFIG. 2, magnetic core section22includes a multitude of substantially rectangular profiled magnetic laminations34arranged in a stack upon a planar mounting surface16defined by the mounting frame14. The stack of magnetic laminations34extends from the mounting frame14and perpendicular to the planar mounting surface16. Arranging the magnetic laminations34in this way creates a coplanar path for the magnetic field traveling through the magnetic core section22. The horizontal stack of magnetic laminations34results in lower induction heating losses than other arrangements of magnetic laminations34, e.g., vertical arrangements. Upturned flanges42on the mounting frame14partially secure the magnetic laminations34upon the planer mounting surface16.

The winding section28surrounds a segment of the magnetic core section22and a portion of the mounting frame14, further securing the magnetic laminations34upon the planer mounting surface16of the mounting frame14. The winding section28contacts both the mounting frame14and a portion of the magnetic core section22to facilitate thermal energy transfer to the mounting frame14. The coil windings26are typically copper or other highly conductive material. In addition, the coil windings26and the magnetic core sections22may include a thermally conductive encapsulating material for reducing thermal impedance. The coil winding26arrangements and the encapsulating material result in reduced operating temperatures of the inductor assembly10.

The air gap spacer30is disposed between adjacent magnetic core sections22. The winding section28encircles the magnetic core section22but need not encircle the air gap spacer30. Segregating the air gap spacer30in this manner optimizes the air gaps in the inductor assembly10. In addition, flux fringe induced eddy current losses typically peak in the central portion of the magnetic core section22and at the perimeter of the magnetic core section22which may create a build-up of thermal energy in those portions of the magnetic core section22. The position of the air gap spacer30facilitates removal of thermal energy from the perimeter of the magnetic core section22while the position of the winding section28facilitates removal of thermal energy from the central portion of the magnetic core section22.

The air gap spacer30extends past the stacks of magnetic laminations34to contact a mounting foot50of the mounting frame14. The mounting foot50provides an attachment surface to secure the inductor assembly10to a desired location. Thermal energy is thereby readily transferred from the magnetic core18to the mounting frame14. Preferably, the air gap spacer30is made of a material having a high thermal conductivity and high electrical resistivity, such as aluminum nitride.

As the inductor assembly10utilizes multiple air gap spacers30, the eddy current effect is dispersed around the magnetic core18such that losses in inductance due to eddy currents in the magnetic core18are reduced. The air gap spacer30creates a high reluctance path in the magnetic core18, avoiding saturation at low frequencies. The multiple air gap spacers30provide multiple paths for thermal energy from the magnetic core18, facilitating rapid conduction of thermal energy from the magnetic core18. It should be understood that an increase in the number of air gap spacers30or the thickness of the existing air gap spacer30will modify the inductance of the inductor assembly10.

Referring toFIG. 3, thermal energy removed from the magnetic core section22is communicated to the mounting frame14whereupon the heat sink plate58removes thermal energy from the mounting frame14. Threaded fasteners60, such as bolts, extend from the mounting frame14through access holes56in the heat sink plate58to secure the heat sink plate58to the mounting frame14. Similar threaded fasteners60, extend through mounting foot50to secure the mounting frame14to a surface upon which the inductor assembly10is mounted.

Threaded tie-rods62, or other such fasteners, extend through endplates54on opposing sides of the inductor assembly10. Tightening the threaded tie-rods62draws the end plates54together securing the stacks of the magnetic laminations34and the air gap spacers30between them. The threaded tie-rods62and the end plates54effectively clamp multiple air gap spacers30between multiple magnetic core sections22.

Referring toFIG. 4, adjustment to the length and the arrangement of the magnetic core sections22enables the current invention to be applied to a three-phase inductor. As shown, the threaded tie-rods62extend through end plates54securing the three rows of magnetic core sections22between two larger magnetic core sections22. The air gap spacers30are maintained between the magnetic core sections22and proximate the winding sections28in the three-phase inductor.

It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.