Patent Description:
Wireless power transfer is becoming increasingly popular. Wireless power transfer involves transmitting power from a primary pad located on a stationary wireless power transfer device, such as a charging station, to a secondary pad on a mobile device, such as an electric vehicle, over a significant gap. The gap typically includes an air gap and can be significant. For example, the air gap may be from ground level to a secondary pad located under a vehicle. An air gap in the range of six inches to <NUM> inches is not uncommon. As the amount of power transferred over an air gap increases, voltages for transmission and reception systems has increased. One method of wireless power transfer includes using a resonant tank, which often boosts voltages of a wireless power transfer pad, which increases voltage ratings of components used for the equipment.

<CIT> discloses an electric power supply device for supplying electric power to an electric power-receiving device using an electromagnetic field resonant coupling. The device is provided with an inverter for converting inputted direct-current voltage to alternating-current voltage and an (LC) serial resonance circuit which is connected to the output side of the inverter and has the same resonance frequency as an external resonance circuit provided with an electric power-receiving device. In the LC serial resonance circuit, a plurality of inductance components (L1 to L5) and a plurality of capacitors (C1 to C5) are alternatingly connected to each other in series.

<CIT> discloses a transmission coil which is set up for inductive energy transmission, comprising a carrier, a coil arrangement with a plurality of turns and a capacitance. The capacitance is formed by a large number of capacitors, each capacitor being assigned to a single turn or a group of at least two turns of the coil arrangement and the capacitors are arranged together with the coil arrangement on the carrier.

<CIT> discloses a power reception device and a power transmission device that include a coil unit containing a coil and capacitors provided at both the ends of the coil unit.

<CIT> discloses an installation for the non-contact transfer of energy includes at least one primary conductor system and a pick-up. The pick-up includes at least one secondary winding inductively coupled to the primary conductor system, the secondary winding including at least one flat ribbon cable, which has at least two electrical conductors extending in parallel, that are held at a distance from each other and are insulated with respect to each other, the secondary winding being made up of part windings, which in each case are formed from one of the electrical conductors, each of the part windings, together with an associated capacitance, forming a series resonant circuit, whose resonant frequency corresponds substantially to the medium frequency of the primary current.

A wireless power transfer ("WPT") pad includes a plurality of capacitors and a winding shaped for wireless power transfer. The winding is divided into a plurality of winding sections. The plurality of winding sections are connected in series with one or more capacitors of the plurality of capacitors connected in series between winding sections.

Another WPT pad includes a plurality of capacitors, where one or more capacitors of the plurality of capacitors form a capacitor group, and where the plurality of capacitors form a plurality of capacitor groups, and a winding shaped for wireless power transfer. The winding is divided into a plurality of winding sections. The winding sections and the capacitor groups are connected in series forming a series-connected winding that include the winding sections and the capacitor groups and a capacitor group of the plurality of capacitor groups is connected in series between two winding sections. A WPT system includes a rectification circuit that receives alternating current ("AC") power and produces direct current ("DC") power, a resonant converter that receives the DC power, and a WPT pad connected to the resonant converter that transfers power wirelessly to a secondary WPT pad. The WPT pad includes a plurality of capacitors. One or more capacitors of the plurality of capacitors form a capacitor group. The plurality of capacitors form a plurality of capacitor groups, and each capacitor group is identical. The WPT pad includes a winding shaped for wireless power transfer. The winding is divided into a plurality of winding sections. The winding sections and the capacitor groups are connected in series forming a series-connected winding that include the winding sections and the capacitor groups. A capacitor group of the plurality of capacitor groups is connected in series between two winding sections.

In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:.

The terms "including," "comprising," "having," and variations thereof mean "including but not limited to" unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise.

Furthermore, the described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

The schematic flow chart diagrams included herein are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one embodiment of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown.

In some embodiments, the winding inlcudes a pad inductance and the capacitors of the plurality of capacitors connected in series form a pad capacitance and the pad inductance and the pad capacitance form a resonant frequency, where an alternating current ("AC") in the WPT pad resonates with respect to the resonant frequency to transfer power wirelessly through the WPT pad. In other embodiments, two or more capacitors of the plurality of capacitors are connected between winding sections and form a desired capacitance. In a further embodiment, the two or more capacitors connected between winding sections have an overall current rating above a specified current value.

In embodiments of the present invention, the winding sections are wound in a spiral pattern that expands away from a center starting point. In embodiments of the present invention, the winding sections are wound in parallel. In some embodiments, each capacitor of the plurality of capacitors is located in a container adjacent to the winding sections. In other embodiments, the winding sections are wound around a center section and each capacitor of the plurality of capacitors is located in the center section.

In some embodiments, a first winding section of the plurality of winding sections is connected to a first terminal and a last section of the plurality of winding sections is connected to a second terminal, where the first and second terminals form an input to the WPT pad. In other embodiments, an end of the first winding section and the last winding section not connected to the first and second terminals are connected to one or more capacitors of the plurality of capacitors. In other embodiments, one or more capacitors of the plurality of capacitors which are connected between winding sections form a capacitor group. In other embodiments, the WPT pad includes a capacitor group that includes one or more capacitors of the plurality of capacitors connected between a winding section and a terminal.

Another WPT pad includes a plurality of capacitors, where one or more capacitors of the plurality of capacitors form a capacitor group, and where the plurality of capacitors form a plurality of capacitor groups, and a winding shaped for wireless power transfer. The winding is divided into a plurality of winding sections. The winding sections and the capacitor groups are connected in series forming a series -connected winding that include the winding sections and the capacitor groups and a capacitor group of the plurality of capacitor groups is connected in series between two winding sections.

In some embodiments, the winding includes a pad inductance and the capacitors of the plurality of capacitors form a pad capacitance and the pad inductance and the pad capacitance form a resonant frequency where an alternating current ("AC") in the WPT pad resonates with respect to the resonant frequency to transfer power wirelessly through the WPT pad. In other embodiments, each capacitor group is identical. In other embodiments, each capacitor group includes two or more capacitors and an overall current rating of each capacitor group is greater than or equal to a current rating of a winding section. According to the invention, the winding sections are wound in a spiral pattern that expands away from a center starting point and the winding sections are wound in parallel. In other embodiments, a first winding section of the plurality of winding sections is connected to a first terminal and a last section of the plurality of winding sections is connected to a second terminal. The first and second terminals form an input to the WPT pad and an end of the first winding section and the last winding section not connected to the first and second terminals are connected to a capacitance group of the plurality of capacitance groups.

A WPT system includes a rectification circuit that receives alternating current ("AC") power and produces direct current ("DC") power, a resonant converter that receives the DC power, and a WPT pad connected to the resonant converter that transfers power wirelessly to a secondary WPT pad. The WPT pad includes a plurality of capacitors. One or more capacitors of the plurality of capacitors form a capacitor group. The plurality of capacitors form a plurality of capacitor groups, and each capacitor group is identical. The WPT pad includes a winding shaped for wireless power transfer. The winding is divided into a plurality of winding sections. The winding sections and the capacitor groups are connected in series forming a series-connected winding that include the winding sections and the capacitor groups. A capacitor group of the plurality of capacitor groups is connected in series between two winding sections.

<FIG> is a schematic block diagram illustrating one embodiment of a wireless power transfer ("WPT") system <NUM> with a low voltage WPT pad. The WPT system <NUM> includes a power converter apparatus <NUM> and a secondary receiver apparatus <NUM> separated by a gap <NUM>, and a load <NUM>, which are described below.

The WPT system <NUM> includes a power converter apparatus <NUM> that receives power from a power source <NUM> and transmits power over a gap <NUM> to a secondary receiver apparatus <NUM>, which transfers power to a load <NUM>. The power converter apparatus <NUM>, in one embodiment, includes a resonant converter <NUM> that receives DC voltage from a DC bus <NUM>. In one embodiment, the power source <NUM> provides DC power to the DC bus <NUM>. In another embodiment, the power source <NUM> is an alternating current ("AC") power source, for example from a building power system, from a utility, from a generator, etc. and the power converter apparatus <NUM> includes a form of rectification to provide DC power to the DC bus <NUM>. For example, the rectification may be in the form of a power factor correction and rectification circuit <NUM>. In the embodiment, the power factor correction and rectification circuit <NUM> may include an active power factor correction circuit, such as a switching power converter. The power factor correction and rectification circuit <NUM> may also include a full-bridge, a half-bridge rectifier, or other rectification circuit that may include diodes, capacitors, surge suppression, etc..

The resonant converter <NUM> may be controlled by a primary controller <NUM>, which may vary parameters within the resonant converter <NUM>, such as conduction time, conduction angle, duty cycle, switching, etc. The primary controller <NUM> may receive information from sensors and position detection <NUM> within or associated with the power converter apparatus <NUM>. The primary controller <NUM> may also receive information wirelessly from the secondary receiver apparatus <NUM>.

The power converter apparatus <NUM> includes a primary WPT pad <NUM> that receives power from the resonant converter <NUM>. In one embodiment, portions of the resonant converter <NUM> and primary WPT pad <NUM> form a resonant circuit that enables efficient wireless power transfer across the gap <NUM>. The gap <NUM>, in some embodiments includes an air gap, but may also may partially or totally include other substances. For example, where the primary WPT pad <NUM> is in a roadway, the gap <NUM> may include a resin, asphalt, concrete or other material just over the windings of the primary WPT pad <NUM> in addition to air, snow, water, etc. between the primary WPT pad <NUM> and a secondary WPT pad <NUM> located in the secondary receiver apparatus <NUM>. As used herein, a WPT pad may be a primary WPT pad <NUM> or a secondary WPT pad <NUM>.

The secondary receiver apparatus <NUM> includes a secondary WPT pad <NUM> connected to a secondary circuit <NUM> that delivers power to the load <NUM>. The secondary receiver apparatus <NUM> may also include a secondary decoupling controller <NUM> that controls the secondary circuit <NUM> and may also be in communication with sensors and/or position detection <NUM> and wireless communications <NUM> coupled to the power converter apparatus <NUM>.

In one embodiment, the secondary receiver apparatus <NUM> and load <NUM> are part of a vehicle <NUM> that receives power from the power converter apparatus <NUM>. The load <NUM> may include a battery <NUM>, a motor, a resistive load, a circuit or other electrical load. For example, the WPT system <NUM> may transfer power to a portable computer, a consumer electronic device, to an industrial load, or other load that would benefit from receiving power wirelessly.

In one embodiment, the secondary circuit <NUM> includes a portion of resonant circuit that interacts with the secondary WPT pad <NUM> and that is designed to receive power at a resonant frequency. The secondary circuit <NUM> may also include a rectification circuit, such as a full-bridge rectifier, a half-bridge rectifier, and the like. In another embodiment, the secondary circuit <NUM> includes a power converter of some type that receives power from the resonant circuit/rectifier and actively controls power to the load <NUM>. For example, the secondary circuit <NUM> may include a switching power converter. In another embodiment, the secondary circuit <NUM> includes passive components and power to the load <NUM> is controlled by adjusting power in the power converter apparatus <NUM>. In another embodiment, the secondary circuit <NUM> includes an active rectifier circuit that may receive and transmit power. One of skill in the art will recognize other forms of a secondary circuit <NUM> appropriate for receiving power from the secondary WPT pad <NUM> and delivering power to the load <NUM>.

The resonant converter <NUM>, in one embodiment, includes an active switching section coupled to a resonant circuit formed with components of the resonant converter <NUM> and the primary WPT pad <NUM>. The resonant converter <NUM> is described in more detail with regard to <FIG>.

<FIG> is a schematic block diagram illustrating one embodiment of a power converter apparatus <NUM>. The power converter apparatus <NUM> is connected to a power source <NUM> and includes a power factor correction and rectification circuit <NUM> connected to a DC bus <NUM> feeding a resonant converter <NUM> connected to a primary WPT pad <NUM> as described with regard to the WPT system <NUM> of <FIG>.

The resonant converter <NUM> includes a switching module <NUM> and a tuning section <NUM>. The switching module <NUM>, includes four switches configured to connect the DC bus <NUM> and to ground. Typically, switches S1 and S3 close while switches S2 and S4 are open and vice-versa. When switches S1 and S3 are closed, the DC bus <NUM> is connected to a positive connection of the tuning section <NUM> through inductor L1a and the ground is connected to the negative connection of the tuning section <NUM> through inductor L1b while switches S2 and S4 are open. When switches S2 and S4 are closed, the ground is connected to the positive terminal of the tuning section <NUM> and the DC bus <NUM> is connected to the positive connection of the tuning section <NUM>. Thus, the switching module alternates connection of the DC bus <NUM> and ground to the tuning section simulating an AC waveform. The AC waveform typically imperfect due to harmonics.

Typically switches S1-S4 are semiconductor switches, such as a metal-oxide-semiconductor field-effect transistor ("MOSFET"), a junction gate field-effect transistor ("JFET"), a bipolar junction transistor ("BJT"), an insulated-gate bipolar transistor ("IGBT") or the like. Often the switches S1-S4 include a body diode that conducts when a negative voltage is applied. In some embodiments, the timing of opening and closing switches S1-S4 are varied to achieve various modes of operations and switching loss reduction, such as zero-voltage switching. In other embodiments, snubbers and other components are used to reduce switching losses.

The tuning section <NUM> of the resonant converter <NUM> and the primary WPT pad <NUM> are designed based on a chosen topology. For example, the resonant converter <NUM> and primary WPT pad <NUM> may form an inductor-capacitor-inductor ("LCL") load resonant converter, a series resonant converter, a parallel resonant converter, and the like. The embodiment depicted in <FIG> includes an LCL load resonant converter.

Resonant converters include an inductance and capacitance that form a resonant frequency. When a switching frequency of the tuning section <NUM> is at or close to the resonant frequency, voltage with the tuning section <NUM> and primary WPT pad <NUM> often increases to voltages levels higher than the voltage of the DC bus <NUM>. For example, if the voltage of the DC bus <NUM> is <NUM> kilovolt ("kV"), voltage in the tuning section <NUM> and resonant converter <NUM> may be <NUM> kV or higher. The high voltages require component ratings, insulation ratings, etc. to be high enough for expected voltages.

The primary WPT pad <NUM> includes capacitor C3 and inductor Lp while the tuning section <NUM> includes series capacitor C2. Capacitors C2 and C3 add to provide a particular capacitance that forms a resonant frequency with inductor Lp. <FIG> is a graph indicating voltage changes within a typical prior art WPT pad, such as the primary WPT pad <NUM> depicted in <FIG>. Assuming that capacitors C2 and C3 are combined to form capacitor Cs, the voltage at the input to the primary WPT pad <NUM>, which is the left side of the Cs capacitor is <NUM> kV in this example. For example, an AC waveform may be applied to the WPT pad with a peak voltage of <NUM> kV. The voltage at the junction between the Cs capacitor and the Lp inductor is <NUM> kV when the input voltage is <NUM> kV and the voltage at the other end of the Lp inductor is zero volts, ignoring any voltage drop across inductor L1b. Components of the WPT pad must then be rated for the expected <NUM> kV, which may dictate using expensive components.

While the <FIG> is focused on the resonant converter <NUM> and primary WPT pad <NUM>, the secondary receiver apparatus <NUM> includes a secondary WPT pad <NUM> and a secondary circuit <NUM> that typically includes a tuning section where the inductance of the secondary WPT pad <NUM> and capacitance of the tuning section of the secondary circuit <NUM> form a resonant frequency and the secondary WPT pad <NUM> and secondary circuit <NUM> have voltage issues similar to the primary WPT pad <NUM> and resonant converter <NUM>.

<FIG> is a schematic block diagram illustrating one embodiment of a low voltage WPT pad. As used herein, a low voltage WPT pad means that voltage of the low voltage WPT pad is lower than voltage across a typical WPT pad and the term "low voltage" does not refer to a particular voltage limit or voltage standard. In the embodiment, the capacitance Cs has been distributed in three capacitors, Cs1, Cs2 and Cs3. The winding of the primary WPT pad <NUM>, which forms an inductance, is divided into four winding sections, Lp1, Lp2, Lp3, Lp4. The capacitors Cs1, Cs2 and Cs3 are distributed between winding sections as depicted. While three capacitors and four winding sections are depicted, one of skill in the art will recognize that other numbers of capacitors and winding sections may be used. While the WPT pad of <FIG> is depicted as a primary WPT pad <NUM>, the topology depicted in <FIG> may also be used on a secondary WPT pad <NUM>. The embodiment depicted in <FIG> includes one more inductor section (e.g. four inductors Lp1-<NUM>) than the number of capacitors (e.g. Cs1-<NUM>). In other embodiments, a WPT pad may include a same number of capacitors and inductance sections where one capacitor (e.g. a Cs4 capacitor) is connected between a terminal and a last inductance section Lp4.

<FIG> is a graph indicating voltage changes within one embodiment of a low voltage WPT pad, for example in the low voltage WPT pad of <FIG>. The voltage at the input, which is the left side of inductor Lp1 is <NUM> kV, which is the same as for <FIG>. Voltage is dropped across inductor Lp1 so that at the LP1/Cs1 junction the voltage is zero. Voltage at the Cs1/Lp2 is again at <NUM> kV and is again at zero at the Lp2/Cs2 junction. Voltage at the Cs2/Lp3 is again at <NUM> kV and is again at zero at the Lp3/Cs3 junction. Voltage at the Cs3/Lp4 is again at <NUM> kV and is again at zero at the return (again ignoring any voltage drop across inductor L1b if provided). Thus, voltage in the primary WPT pad <NUM> depicted in <FIG> is reduced, which increases safety and allows components to have a lower voltage rating.

Note that the inductance Lp and capacitance Cs of the primary WPT pad <NUM>, in one embodiment, are a result of the design of the primary WPT pad <NUM>, a desired resonant frequency, and other factors. The number of winding sections and capacitors are chosen based on factors, such as physical dimensions of the primary WPT pad <NUM>, conductor size, etc. The low voltage primary WPT pad <NUM> depicted in <FIG> may also be used for the secondary WPT pad <NUM> and the principles discussed with regard to the low voltage WPT pad of <FIG> are equally applicable to the secondary receiver apparatus <NUM>.

<FIG> is a schematic block diagram of one embodiment of a layout of a WPT pad with capacitors Cs1, Cs2 and Cs3 in a junction box <NUM> to the side of winding sections <NUM>. The winding sections <NUM> are wound in a spiral pattern that expands away from a center starting point. Note that each winding section (e.g. Lp1-<NUM>) are depicted with two turns for clarity, but one of skill in the art will recognize that a WPT winding may include any number of turns. The winding sections <NUM> includes a first winding section Lp1, a second winding section Lp2, a third winding section Lp3 and a fourth winding section Lp4 wound in parallel with connections to capacitors Cs1, Cs2 and Cs3. The capacitors Cs1, Cs2 and Cs3 are located to the side of the winding sections <NUM> in a junction box <NUM>. Having the capacitors in a junction box is convenient for replacement of the capacitors and is a convenient place for making connections, which may be configured to be water resistant. The junction box <NUM> may include lid on top that may be removed to gain access to the capacitors Cs1, Cs2 and Cs3. The junction box <NUM> may include grommets or similar penetrations for conductors entering and leaving the junction box <NUM>. While an input conductor <NUM> and a return conductor <NUM> are depicted leaving the junction box <NUM> at separate locations, typically the conductors <NUM>, <NUM> would be in a conduit that runs to the resonant converter <NUM>.

<FIG> is a schematic block diagram of an embodiment of a layout of a WPT pad with capacitors Cs1, Cs2 and Cs3 in a center of winding sections <NUM>. As in <FIG>, the winding sections <NUM> includes a first winding section Lp1, a second winding section Lp2, a third winding section Lp3 and a fourth winding section Lp4 wound in parallel with connections to capacitors Cs1, Cs2 and Cs3. The capacitors Cs1, Cs2 and Cs3 are located in the center of the winding sections <NUM>. Typically, the winding sections <NUM> have a center section that is open due to the physical geometry of the conductors, magnetics, etc. The center of the winding sections <NUM> is typically an unused space. Placing the capacitors Cs1, Cs2 and Cs3 in the center of the winding sections <NUM> reduces the overall size of the primary WPT pad <NUM>. In one embodiment, the capacitors Cs1, Cs2 and Cs3 are molded into the center of the winding sections <NUM> and are surrounded by a resin or other material. In another embodiment, the capacitors Cs1, Cs2 and Cs3 are accessible. For example, the capacitors Cs1, Cs2 and Cs3 may be located in a junction box or other structure within the center of the winding sections <NUM>. In other embodiments, some capacitors are located in a center section and some capacitors are located elsewhere.

<FIG> is a schematic block diagram illustrating one configuration of capacitors that make up one of the capacitors (e.g. Cs1) depicted in the embodiments of <FIG>, <FIG> and <FIG>. In one embodiment, the capacitors (e.g. Cs1) depicted in the embodiments of <FIG>, <FIG> and <FIG> may each be a capacitor group. A capacitor group, such as Cs1 may be made up of multiple capacitors, i.e. Csla, Cslb, Cslc, Csld, Csle and Csld to meet current requirements, voltage requirements, etc. A capacitor group as used herein, refers to a group of capacitors (e.g. Cs1) connected between two winding sections (e.g. Lp1, Lp2). For example, a single capacitor Cs1 may not be capable of handling current requirements based on size considerations, capacitors that are commercially available, voltage ratings, etc. While six capacitors Cs1a-d are depicted in <FIG>, one of skill in the art will recognize other capacitor configurations, with more capacitors in parallel, more or less capacitors in series, etc..

Claim 1:
A wireless power transfer, WPT, pad (<NUM>) comprising:
a plurality of capacitors (Cs1, Cs2, Cs3); and
a winding shaped in a spiral pattern for wireless power transfer, the winding divided into a plurality of winding sections (<NUM>, Lp1, Lp2, Lp3, Lp4),
wherein the plurality of winding sections are connected in series with one or more capacitors of the plurality of capacitors connected in series between winding sections, and
wherein each of the plurality of winding sections is wound in a spiral pattern that expands from a central starting point to an outer ending point, wherein the plurality of spiral patterns are arranged in parallel and characterized in that the plurality of winding sections lie next to each other in a plane such that the spiral patterns are interleaved.