Patent Application
20150130583
The present invention relates to power transfer systems and, more particularly, to wireless power transfer systems and methods of operating same.
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.
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.
The present invention now will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.
It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
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.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
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In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.
