Wireless power transfer systems containing foil-type transmitter and receiver coils

Wireless power transfer systems include at least one foil-type transmitter/receiver coil with a plurality of turns, which is configured to reduce eddy current losses therein when energized to conduct an alternating current that supports inductive power transfer including coil-to-coil power electrical transfer, inductive heating, etc. The plurality of turns includes at least an outermost turn with a first arcuate-shaped corner having a concave inner surface, which faces an immediately adjacent one of the plurality of turns. The immediately adjacent one of the plurality of turns may also have a second arcuate-shaped corner with a concave inner surface facing an innermost one of the plurality of turns. The first arcuate-shaped corner may have a non-uniform radius of curvature and/or an innermost one of the plurality of turns may have an arcuate-shaped corner, which is a mirror image of the first arcuate-shaped corner when the coil is view in transverse cross-section.

FIELD OF THE INVENTION

The present invention relates to power transfer systems and, more particularly, to wireless power transfer systems and methods of operating same.

BACKGROUND OF THE INVENTION

Wireless power transfer systems have been receiving increased attention in response to expanding popularity and availability of battery-powered handheld electronic devices. Some wireless power transfer systems use near-field electromagnetic coupling (e.g., mutual inductance) to charge electronic devices by transferring power from a transmitter winding (“primary winding”) located external to a device to a receiver winding (“secondary winding”) within the device. Wireless connections can provide a number of advantages over conventional hardwired connections, including a high degree of electrical isolation between the transmitter and receiver circuits. Nonetheless, relatively reduced levels of power transfer efficiency have often limited inductive power transfer systems to niche applications. One effort to improve power transfer efficiency is disclosed in U.S. Pat. No. 7,411,479 to Baarman et al., entitled “Inductive Coil Assembly.”

As will be understood by those skilled in the art, because a resonant tank circuit within the power transfer system may operate at relatively high frequency, the skin effects of winding conductors should be minimized; otherwise, eddy current losses may be unacceptably high and power transfer efficiency may be unacceptably low. Various techniques have been developed to reduce eddy current losses in high frequency applications. These techniques can include using Litz wire, which consists of thin wire strands that are individually insulated and twisted or woven together, and reduced-thickness copper foil. In addition to increasing power transfer efficiency, the configuration and layout of the primary and secondary windings should also be sufficient to comply with the International commission on Non-Ionizing Radiation Protection Guidelines (ICNIRP) in order to limit human exposure to time-varying EMFs.

SUMMARY OF THE INVENTION

Wireless power transfer systems according to embodiments of the invention include at least one foil-type transmitter/receiver coil configured to reduce eddy current losses therein when energized to conduct an alternating current that supports inductive power transfer. According to some of these embodiments of the invention, a wireless power transfer system can include a foil-type transmitter coil having a plurality of turns therein. This plurality of turns includes at least an outermost turn with a first arcuate-shaped corner having a concave inner surface, which faces an immediately adjacent one of the plurality of turns. This immediately adjacent one of the plurality of turns may also have a second arcuate-shaped corner with a concave inner surface facing an innermost one of the plurality of turns. In some embodiments of the invention, a length of the second arcuate-shaped corner is greater than a length of the first arcuate-shaped corner. In other embodiments of the invention, the first arcuate-shaped corner is sharper than the second arcuate-shaped corner. In still further embodiments of the invention, the first arcuate-shaped corner has a non-uniform radius of curvature and/or an innermost one of the plurality of turns has an arcuate-shaped corner, which is a mirror image of the first arcuate-shaped corner when the coil is view in transverse cross-section. A middle one of the plurality of turns may also have a rectangular-shaped cross-section, with flat inner and outer surfaces. Similarly, a next-to-innermost one of the plurality of turns can have an arcuate-shaped corner that is a mirror image of the second arcuate-shaped corner.

According to still further embodiments of the invention, a wireless power transfer system may include a foil-type coil having N turns, where N is an odd integer greater than one. These N turns include an outermost turn having an at least partially concave inner surface and an innermost turn having an at least partially concave outer surface, which may be a mirror image of the at least partially concave inner surface of the outermost turn. According to still further embodiments of the invention, first and second opposing edges (e.g., top and bottom edges) of the outermost turn can have unequal shape when viewed in transverse cross-section. For example, the first edge may be arcuate-shaped and the second edge may be flat. A ferrite shielding cover may also be provided, which extends adjacent the second edge of the outermost turn. A middle one of the plurality of turns may also have flat inner and outer surfaces. In some further embodiments of the invention, N is an odd integer greater than three, and the outermost turn and a next-to-outermost turn have nonequivalent concave shapes when viewed in transverse cross-section. Alternatively, the outermost turn and a next-to-outermost one of the N turns may have equivalent concave shapes when viewed in transverse cross-section.

According to still further embodiments of the invention, a wireless power transfer system can include a foil-type transmitter coil having N turns, where N is an odd integer greater than one, and a foil-type receiver coil, which is inductively coupled to the foil-type transmitter coil. The N turns includes an outermost turn having an at least partially concave inner surface and an innermost turn having an at least partially concave outer surface. These transmitter and receiver coils may have equivalent dimensions.

Wireless power transfer systems according to still further embodiments of the invention can include a foil-type transmitter coil having a plurality of turns, including an outermost turn having an outer surface that is substantially parallel with magnetic flux lines extending immediately adjacent the outer surface when the transmitter coil is energized to conduct an alternating current therein. In some of these embodiments of the invention, a wireless transmitter for inductive power transfer can include a foil-type coil having an innermost turn and an outermost turn. The outermost turn can have an at least partially curved outer surface that is substantially parallel with magnetic flux lines extending immediately adjacent the curved outer surface when the transmitter coil is energized to conduct an alternating current therein.

DETAILED DESCRIPTION OF EMBODIMENTS

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprising”, “including”, “having” and variants thereof, when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. In contrast, the term “consisting of” when used in this specification, specifies the stated features, steps, operations, elements, and/or components, and precludes additional features, steps, operations, elements and/or components.

Referring now toFIGS. 1A-1B, one example of a foil-type transmitter/receiver coil10according to an embodiment of the invention is illustrated as including a plurality of turns10a-10e, including at least an outermost turn10ewith at least a first arcuate-shaped corner(s)12ehaving a concave inner surface facing an immediately adjacent one of the plurality of turns10d. This immediately adjacent one of the plurality of turns10dhas at least a second arcuate-shaped corner(s)12dwith a concave inner surface facing an innermost one of the plurality of turns10a. The plurality of turns may include N turns, where N is an odd integer greater than one. As illustrated byFIG. 1A, a length of the second arcuate-shaped corner12dis greater than a length of the first arcuate-shaped corner12eand concomitantly, the first arcuate-shaped corner12eis sharper than the second arcuate-shaped corner12d. As further illustrated byFIG. 1A, the first arcuate-shaped corner12emay have a non-uniform radius of curvature. In addition, an innermost one of the plurality of turns10acan have an arcuate-shaped corner12athat is a mirror image of the first arcuate-shaped corner12e.FIG. 1Aalso illustrates that a middle one of the plurality of turns10chas a rectangular-shaped (e.g., flat) cross-section with flat inner and outer surfaces. Furthermore, a next-to-innermost one of the plurality of turns10bcan have an arcuate-shaped corner12bthat is a mirror image of the second arcuate-shaped corner12d, as illustrated.

Referring now toFIG. 1B, a cross-sectional view of a left-side portion of the five-turn foil-type transmitter/receiver coil ofFIG. 1Ais provided with a plot of magnetic flux lines associated with a variable excitation current (e.g., AC current) passing through the coil10. As illustrated, the magnetic flux lines that are immediately adjacent the innermost turn10aand the outermost turn10eare curved in a manner that extends closely parallel to the arcuate-shaped corners12aand12e, which achieves reduced eddy current losses because the flux lines do not operate to “cut” the foil turns as in a conventional foil-type coil having flat innermost and outermost turns.

Referring now toFIGS. 2A-2B, another example of a foil-type transmitter/receiver coil10′ according to an embodiment of the invention is illustrated as including a plurality of turns10a′-10e′, which are similar to the turns10a-10eofFIGS. 1A-1B, but include one-sided curved ends and one-sided flat ends that may be positioned closely adjacent a ferrite shielding cover14as illustrated byFIG. 2B. This ferrite shielding cover14operates to terminate the magnetic flux lines associated with a variable excitation current passing through the coil. The many novel aspects of these coils10and10′ ofFIGS. 1A-1Band2A-2B are further highlighted by additional embodiments of the invention in examples (3) through (7) ofFIG. 3A(without shielding cover14) andFIG. 3B(with ferrite (Fe3O4) shielding cover14), which show differing degrees and shapes of curvature in the outermost and innermost coils relative to a conventional coil with flat turns (example (1)) and a coil having exclusively convex-shaped turns (example (2)).

The eddy current losses for the seven (7) examples ofFIGS. 3A-3Bare illustrated byFIG. 4, for a 5-turn copper coil excited with a 20 ampere current at 60 kHz (sine waveform). The dimensions of the coil include an inner diameter of 21.2 cm, with a spacing of 8 mm between each turn having a cross-section of 1 mm×10 mm. As shown, the coil embodiments ofFIGS. 1A-1BandFIG. 4(example 5, without ferrite shielding cover) offer the lowest eddy current losses of 56.791 Watts, whereas the coil configurations of Examples 1 and 2 demonstrate the worst eddy current losses. Moreover, when a ferrite shielding cover is required for a particular application, such as one requiring a relative high degree of magnetic isolation from a surrounding environment, the coil embodiments ofFIGS. 2A-2BandFIG. 4(example 7) offer the lowest eddy current losses of 63.009 Watts. In the illustrated examples, the ferrite shielding cover may have a diameter of 60 cm with a thickness of 8 mm, may be spaced from the coil by 4 mm and may have a permeability of 1000, for example.