EFFICIENCY GAINS THROUGH MAGNETIC FIELD MANAGEMENT

Abstract

A resonant induction wireless power transfer coil assembly designed for low loss includes a wireless power transfer coil, an unsaturated backing core layer adjacent to the wireless power transfer coil, eddy current shielding, a separation layer between the backing core layer and the eddy current shielding, and a housing enclosing the wireless power transfer coil, backing core layer, separation layer, and eddy current shielding. The separation layer has a thickness within a range for a given thickness of the backing core layer where the eddy current loss in the eddy current shielding is substantially flat across that thickness range.A thickness of the backup core layer and a thickness of the separation layer are selected so as to substantially minimize a total power loss comprising power loss in the backup core layer plus eddy current loss through the separation layer.

Description

[0001] This application claims the benefit of United States Patent Application No. 16 / 940,658, filed July 28, 2020, and entitled “EFFICIENCY GAINS THROUGH MAGNETIC FIELD MANAGEMENT”, which is incorporated herein by reference in its entirety. CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This patent application is related to U.S. Patent Application No. 16 / 615,290, filed November 20, 2019, entitled “Wireless Power Transfer Thin Profile Coil Assembly”, which is a national phase entry of document PCT / US2018 / 035060, filed May 30, 2018, which claims priority to U.S. Provisional Patent Application No. 62 / 512,544, filed May 30, 2017. The contents of these patent applications are incorporated herein by reference. FIELD OF INVENTION

[0003] This patent application describes a wireless power transfer coil assembly for wireless charging using magnetic resonance induction. The wireless power transfer coil assembly described herein may be used as part of the wireless power transfer apparatus for sending and / or receiving. BACKGROUND OF THE INVENTION

[0004] Wireless charging by resonant induction utilizes an air-core transformer consisting of two concentric coils offset along a common coil axis. Electrical energy is sent from the sending device to the receiving device by means of a magnetic flux link between the two transfer coils. As explained by Faraday's law of induction, the first coil, the primary or transmitting coil, creates the time-varying magnetic field. The corresponding secondary or receiving coil converts the received magnetic flux into an electrical signal for use in powering electrical systems such as an electric vehicle or a charging system for electrical storage (e.g., a battery).Such air-core transformers use individual cores (nominally made of ferrite) located behind the primary and secondary coils instead of core(s) positioned to make a complete magnetic circuit between the coils as is normal for air-coreless transformers. ML / a / ZUZ J / UUl 1 ou BRIEF DESCRIPTION OF THE INVENTION

[0005] Several examples are now provided to introduce a selection of concepts in a simplified manner, which are further described in the Detailed Description below. The Brief Description is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0006] In exemplary embodiments, a resonant induction wireless power transfer coil assembly designed for low power loss is provided. The assembly includes a wireless power transfer coil, an unsaturated backup core layer adjacent to the wireless power transfer coil, eddy current shielding, a separation layer between the backup core layer and the eddy current shielding, and a housing enclosing the wireless power transfer coil, backup core layer, separation layer, and eddy current shielding. The separation layer has a thickness within a range of thicknesses for a given thickness of the backup core layer where the eddy current loss in the eddy current shielding is substantially flat across the separation layer thickness range.The thickness of the backing core layer and the thickness of the separation layer are selected to substantially minimize the total power loss, which comprises power loss in the backing core layer plus eddy current loss in the eddy current shielding. The backing core layer may comprise backing core, layered metal sheets, powdered oxides, sintered powdered oxides, and / or amorphous metals.

[0007] In exemplary embodiments, the separation layer may comprise an air space, a non-magnetic filler, a non-magnetic structural support element, at least one non-magnetic conduit, and / or a non-magnetic coolant. A cooling / heating fluid, which may be air or a liquid, may circulate in said at least one conduit. Said at least one conduit may comprise a non-conductive, non-magnetic material positioned immediately against the backing core layer and / or immediately against the eddy current shielding. A thermal management device may also be provided for circulating the cooling / heating fluid in said at least one conduit to thermally manage the backing core layer to substantially minimize power loss due to hysteresis heating and / or to thermally manage the wireless power transfer (WPT) coil assembly.

[0008] In other exemplary embodiments, eddy current shielding may comprise one or more temperature sensors that provide temperature readings to the thermal management device. In turn, the thermal management device may control the circulation of the cooling / heating fluid to maintain the backup core layer at a predetermined temperature to minimize energy loss. The thermal management device may provide an inlet air temperature and backup core layer temperature readings so that a predictive model can anticipate heating / cooling requirements. When cooling or heating requirements are predicted to exceed passive cooling or passive heating capacities, the circulation of the cooling / heating fluid is controlled to adjust the backup core layer temperature. A reservoir of MA.a.ZUZÓ / UU 11 or cooling / heating fluid may be provided with at least one valve that is controlled by the thermal management system to provide cooling / heating fluid to the separation layer through said at least one conduit.

[0009] In accordance with other aspects, a method is provided for assembling a wireless power transfer assembly of a wireless power transfer system. The method includes providing an unsaturated backing core layer adjacent to a wireless power transfer coil; providing eddy current shielding separated by a separation layer from the backing core layer, the separation layer having a separation layer thickness within a separation layer thickness range for a given thickness of the backing core layer where the eddy current loss in the eddy current shielding is substantially flat across the separation layer thickness range; and enclosing the wireless power transfer coil, backing core layer, separation layer, and eddy current shielding in a housing.The method further includes selecting a thickness of the backing core layer versus a thickness of the separation layer such that the total energy loss, comprising energy loss in the backing core layer plus eddy current loss through the separation layer, is substantially minimized. In exemplary embodiments, the method includes a total constrained thickness, C, where C = dg + df, df is the thickness of the backing core layer, and dg is the thickness of the separation layer.

[0010] In exemplary embodiments, the method includes circulating cooling / heating fluid through at least one conduit in the separation layer. This at least one conduit may be positioned directly against the backup core layer. A thermal management device may thermally manage the backup core layer to minimize energy loss by maintaining circulation of the cooling / heating fluid through this at least one conduit. The thermal management device may further provide an inlet fluid temperature and backup core layer temperature readings to enable a predictive model to anticipate heating / cooling requirements. When cooling or heating requirements are anticipated to exceed passive cooling or passive heating capacities, the circulation of the cooling / heating fluid is controlled to adjust the backup core layer temperature.The method may further include providing at least one cooling / heating fluid reservoir with at least one valve. The thermal management system may control this at least one valve to supply cooling / heating fluid to the separation layer through this at least one conduit to provide heating or cooling to the backup core layer in order to substantially minimize energy loss.

[0011] It will be appreciated that any of the above examples can be combined with any or more of the other examples above to create a new modality within the scope of this disclosure BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In drawings, which are not necessarily drawn to scale, similar numbers may describe similar components in different views. The drawings generally illustrate, by way of example, but not MA.a.ZUZÓ / UU I Ί ou as a limitation, different modalities that are discussed in this document.

[0013] Figure 1 shows the main components of a vehicle assembly in a wireless power transfer system.

[0014] Figure 2 shows the main components of a grounding assembly in a wireless power transfer system.

[0015] Figure 3 represents the eddy currents induced due to a magnetic field applied in conductive housings that act as shields against eddy currents.

[0016] Figure 4 illustrates the effect of increasing the thickness of the separation layer between the backing core and the backing plate on energy loss in a magnetic energy transfer system

[0017] Figure 5 shows the expected energy losses for different thicknesses of backing core and expanding separation layer.

[0018] Figure 6 illustrates the relative relationship between the thickness of the backing core layer versus the thickness of the separation layer and the energy losses in a magnetic energy transfer system.

[0019] Figure 7A shows the expected energy losses for a fixed layer where different thicknesses of backing core are progressively thinned to increase the thickness of the separation layer.

[0020] Figure 7B shows the substantially optimized ratio range of backing core thicknesses to separation layer thicknesses for an exemplary range of total thickness (sum of backing core and separation layer).

[0021] Figure 8 illustrates a convenient use of the backup core layer spacing in a grounding assembly.

[0022] Figure 9 illustrates a convenient use of the backing core layer spacing in a vehicle assembly.

[0023] Figure 10 schematically details a wireless power transfer system for vehicular use.

[0024] Figure 11A illustrates, at a high level, an exemplary passive or active air-cooled vehicle assembly.

[0025] Figure 11B illustrates, at a high level, an exemplary liquid-cooled vehicle assembly.

[0026] Figure 12 shows the temperature sensitivity of the efficiency of a backup core expressed as energy loss density versus the temperature of the backup core. DETAILED DESCRIPTION OF THE INVENTION

[0027] The wireless power transfer coil assembly, housing, accessories, and associated method described herein can be more easily understood by referring to the following detailed description taken in conjunction with the accompanying figures and examples, which form a part of this disclosure. It should be understood that this description is not limited to the specific products, methods, conditions, or parameters described and / or MA.a.ZUZÓ / UU I Ί ou shown in this document, and that the terminology used herein is for the purpose of describing particular modalities by way of example only and is not intended to be limiting of any subject matter claimed. Similarly, any description as to a possible mechanism, mode of action, or reason for improvement is intended to be illustrative only, and the subject matter described herein shall not be restricted by the accuracy or inaccuracy of any such mechanism, mode of action, or reason for improvement suggested. Throughout this text, it is acknowledged that the descriptions refer to both methods and systems / software for implementing such methods.

[0028] A detailed description of illustrative modalities will now be given with reference to Figures 1 to 12. Although this description provides a detailed example of possible implementations, it should be noted that these details are intended to be exemplary and in no way limit the scope of the inventive matter in question.

[0029] As previously taught in PCT application PCT / US2018 / 035060, “WIRELESS POWER TRANSFER THIN PROFILE COIL ASSEMBLY”, thinning the ferrite core layer is desirable as a means of reducing the weight and cost of the transfer coil. As described herein, the thickness and positioning of the backing core layers (e.g., ferrite) can also be used to control and optimize (nominally minimize) power loss due to heating and induced eddy currents.

[0030] The examples and terminology in the figures are directed toward the stationary charging of conventional electric vehicles (EVs) such as cars, trucks, and buses. Other uses (e.g., charging rail motors, ships, dynamically charged roads, or railways) are not excluded by these descriptions. In addition to EV charging, the wireless power transfer (WPT) system described herein is symmetrical and may allow the discharge of EV energy storage (e.g., a battery, capacitor bank, reversible fuel cell) for use in powering secondary electronic components (e.g., such as a home or grid-based power reserve management system).

[0031] Although the examples show simple ground assembly (GA) and vehicle assembly (VA) systems, each consisting of a single coil, they also contemplate higher energy systems that use a modular approach, where multiple GA coils are geometrically placed in groups and corresponding VA coil groups are installed in the EVs.

[0032] The terms “backup core” and “ferrite” are used to describe materials used to guide magnetic flux and are not intended to limit the selection of such materials. Both terms are used herein as a generic term for any high-permeability magnetic material construction, where high permeability refers to a relative permeability substantially greater than 1 (nominally >100). The term ferrite is not intended to exclude this usage from other similar or compatible materials that could be used in the construction of a backup core and may include layered metal foils, powder oxides, sintered powder oxides, and / or amorphous metals. MA.a.ZUZÓ / UU I Ί ou ω 6 N CN Figure 1

[0033] Figure 1 illustrates the main components of a vehicle assembly (VA) 101 for managing the magnetic field required for wireless power transfer. In this exploded view, the relative thicknesses of the different layers are not shown, and the spacing between layers is exaggerated for illustrative purposes. Structural support elements, galvanic isolation, weatherproofing, and associated circuitry are omitted from the figure, all of which do not materially affect the magnetic flux distribution.

[0034] The VA 101 is normally mounted to the underside of an electric vehicle (EV), but side or rear mounting is possible in some EV applications. As shown here, the underside of the vehicle chassis 102 provides the attachment for the conductive metal backing plate 103. The backing plate 103 acts as an eddy current shield, protecting the EV chassis and conductive components from stray magnetic flux. A separation layer 104 separates the backing plate 103 from the backing core 105. The secondary coil 106 can be a circular or rectangular coil of windings contained or embedded in a nonmagnetic substrate to maintain spacing, galvanic isolation, and heat transfer. The secondary coil 106 is the bottommost layer of the VA 101's magnetic components. Figure 2

[0035] Figure 2 shows the main components of a grounding assembly (GA) 201 for managing the magnetic field required for wireless power transfer. In this exploded view, the relative thicknesses of the different layers are not shown, and the spacing between layers is exaggerated for illustrative purposes. Structural support elements, galvanic isolation, waterproofing, coatings, and associated circuitry are omitted from the figure, all of which do not materially affect the magnetic flux distribution.

[0036] The GA 201 is nominally laid flat on (or within) the pavement 202, which may be grounded 203. The primary coil 204 that produces the magnetic field may be a circular coil or a rectangular coil of windings embedded in a non-magnetic substrate to maintain spacing, galvanic isolation, and heat transfer. The primary coil 204 is the outermost layer of the magnetic components of the GA 201. The backing core 205 is positioned beneath the primary coil 204 and serves to guide the magnetic flux produced not only by the primary coil 204 but also by the secondary coil 106 of the VA (see Figure 1). The separation layer 206 is immediately beneath the backing core 205. The conductive metal backing plate 207 between the separation layer 206 and the floor 202 serves not only to mechanically support the GA 201 but can also provide an electrical ground connection to the unit.In some installations, this grounding is provided locally, provided remotely through the incoming power connections (not shown), or is optional. Figure 3

[0037] Figure 3 shows the magnetic flux behavior caused by eddy currents and, therefore, the energy loss due to Joule heating in the eddy current shield. In this example, the eddy current shield is formed by the conductive metal backing plates 303, 304 of the assembly.

[0038] In an air-core transformer, the primary coil uses an oscillating electric current to generate a time-varying magnetic field. Some of the uncontained magnetic flux can impinge on surrounding metal housings and external conductive objects.

[0039] Figure 3 shows this uncontained magnetic flux 301 causing eddy currents 302 in the eddy current shields (e.g., metal housings) 303 and 304. These eddy currents 302 are created almost entirely on the inside of the metal housings 303 and 304 near the parallel primary and secondary windings of an open transformer (not shown) because the oscillating magnetic flux 301 must not penetrate deeply into the conductive metal of the housings 303, 304. These eddy currents 302 are a significant source of Joule effect loss. Figures 4 to 7B

[0040] Figures 4 through 7B are graphics used to illustrate the effect of a separation layer between a specific thickness of backing core (e.g., a ferrite sheet) and the metal backing plate of the vehicle assembly (VA) or grounding assembly (GA). The use of a ferrite backing core sheet of uniform thickness is contemplated in Figures 4 through 7B for the sake of simplicity. The use of continuous sheets (or sheets comprised of interlaced or overlapping strips of backing core material) is desirable both from the perspective of preventing magnetic flux leakage and from the economic benefit of lower material costs.

[0041] The magnetic flux distribution in the thin backing core creates an upper limit for the scenarios shown in Figures 4 to 7B. When a backing core layer is dimensioned so that the magnetic flux density (in the prescribed externally applied magnetic field (H)) is uniform throughout its thickness, it is a thin core. Saturation in thin cores presents a lower limit on the backing core thickness in the scenario shown in Figure 5. In a thin backing core, saturation is reached when the backing core becomes too thin, to the point that the magnetic flux cannot be fully redirected to the externally applied magnetic field strength (H). The backing core thicknesses shown in Figures 4 to B7 were selected to avoid backing core thicknesses small enough to cause saturation effects.

[0042] Shaping or contouring a backup core (i.e., increasing thickness in areas of high magnetic flux and thinning in areas of low magnetic flux while avoiding saturation of the backup core) can be combined with any of the scenarios described in Figures 4 to 7B to reduce the overall weight of the backup core, which is very important in mobile applications (e.g., in a vehicle assembly) since the vehicle's weight directly affects its range and therefore its charging time. Increasing range and decreasing charging times are critical factors in expanding the acceptance of electric vehicles compared to those using internal combustion engines.

[0043] In an air-core transformer as illustrated in Figure 1 and Figure 2, the currents of MA.a.ZUZÓ / UU I Ί ou Eddy currents are induced by the magnetic flux incident on the conductive backing plates. The tangential component of the magnetic field strength has a discontinuity at the interface of the conductive surface equal to the magnitude of the induced eddy current. The magnetic field strength is high in the backing core and drops to zero with skin decay at the conductive backing plate.

[0044] Introducing a separation layer between the backing core (e.g., ferrite layer) and the conductive backing plate reduces the change in magnetic field strength across the edge of the conductive backing plate. This reduces the magnitude of eddy currents and their associated energy loss. Further increasing the size of the separation layer may have a minimal effect on energy loss because the change in magnetic field strength across the interface of the conductive backing plate has already been significantly reduced.

[0045] Another influence on the design is that the thickness (and mass) of the backup core also affects heat transfer from the coil and heat retention of the backup core.

[0046] Mathematically, the losses incurred by the backing core (i.e., ferrite) and the induced eddy currents can be expressed as: Ptctal_Pnicleo+PFoicault EQUaCÍÓn (1) where; “Ptotai” = total energy loss, “PnUcieo = magnetic loss (e.g., from backup core), and “PFojsauit = eddy current loss in the conductive backup plate.

[0047] The backup core loss is calculated using a modified version of the Steinmetz equation (energy loss per area W / m2) where: MA.a.ZUZÓ / UU I Ί ou \ i—b -I (d^ Equation (2) W / where the variables are k, a, b = material-dependent “Steinmetz coefficients” with 1 < a < 2 and 2 < b < 3, f = frequency, φ = total magnetic flux, w = effective backing core width (dimension perpendicular to the plane of the coil), and df = backing core thickness. The backing core loss is mainly due to hysteresis heating in the backing core caused by the oscillating magnetic flux.

[0048] In the modified Steinmetz equation, because ab > 2, this equation shows that Pnucieo decreases as the thickness of the backing core increases, even though more backing core (in an attempt to better redirect the flow) is being added, which is a lossy material. The reduction in flux density from adding a 30 layer of separation between the backing core and the backing plate more than compensates for the addition of more backing core material.

[0049] The energy loss due to eddy currents (energy loss per area W / m2) can also be calculated for an AC magnetic field incident on a large conductor more than a few depths thick, as follows ^Eddy currents Equation (3) where dg = thickness of the separation layer, B(dg) = magnetic flux density on the surface of a conductive backing plate as a function of the thickness of the separation layer. When the thickness of the separation layer is 0, B(dg) = Bnudeo. As the thickness of the separation layer increases, B(dg) decreases. μο = magnetic constant (4n x 107H / m); f = frequency in Hz, and σ = conductivity of the conductive backing plate in siemens / meter.

[0050] In some embodiments, a non-conductive backing plate (approximating the case where σ = 0) may be used. Since the backing plate acts as the eddy current shield, such implementations include grounding assemblies (GAs) embedded in pavement, as the flux extending past the backing core layer (e.g., ferrite) will not impinge on or affect people or equipment on the surface. GAs embedded in parking garage floors will use eddy current shields to manage the flux so that it does not impinge on the floor below. Surface-mounted GAs (permanently or temporarily mounted on the pavement surface) may use eddy current shields with the appropriate separation layer to reduce the overall installation height. Figure 4

[0051] In Figure 4, the position of the fixed-thickness backing core layer (e.g., the ferrite layer) is displaced from the metallic backing plate by the progressive addition of a separation layer. The separation layer may consist of air space(s), a nonmagnetic filler, nonmagnetic structural support elements and ducts, nonmagnetic coolant, or any mixture thereof. In the example shown in Figure 4, the WPT system is transferring 60 kilowatts.

[0052] In Figure 4, the X-axis 401 is used to show the increase in separation layer thickness (in mm) and therefore the displacement of the backing core from the backing plate. The Y-axis 402 is used to show the power losses (in watts). The eddy current loss is shown in curve 404. As noted, the eddy current losses shown in curve 404 are highest when the backing core is almost in contact with the metal backing plate, i.e., when the separation layer is thinnest. The backing core power loss component curve 405 shows that the backing core loss is nearly constant in the useful regions of 409, 410, and beyond. In the second region 410, the increased separation layer thickness shows diminished gains compared to the first region 409.After introducing a separation layer thickness 403 with lower eddy current losses, both the eddy current losses shown in curve 404 and the backup core energy losses shown in the backup core energy loss component curve 405 remain unchanged. Increasing the separation layer thickness 403 therefore introduces additional, undesirable thickness while producing virtually no improvement in efficiency.

[0053] The total energy loss curve 406 shows that an optimum energy loss point 407 can be determined. This optimum energy loss point 407 will vary with the thickness of the backing core used, MA.a.ZUZÓ / UU 11 ou < tu 10 N c N but the relationship between the backing core losses and the backing plate eddy current losses will follow the same pattern for thin backing cores. As the separation layer becomes thicker, the backing core losses increase the Y-axis value at the crossover point 408 where the backing core losses in the backing core power loss component curve 405 dominate. The eddy current loss curve 404 shows a sharp reduction that continues to decrease through an initial region 409 before flattening substantially in a second region 410. Although the separation layer thicknesses through the second region 410 show small reductions in eddy current power losses, the addition of the separation layer thickness can be beneficial for the introduction of cooling apparatus and media.Continuing to increase the thickness of the separation layer through 403 has little or no effect on eddy current losses but is available to increase cooling flow at lower pressures.

[0054] In some applications, the increased energy losses due to eddy currents in the backing plate before the optimum (i.e., minimum) energy loss point 407 may be acceptable (e.g., to decrease the overall assembly thickness by limiting the thickness of the backing core plus separation layer). Introducing additional backing layer thickness 403 does not show any efficiency increase, but it could be used to create additional cooling volume, albeit at the cost of additional thickness in the WPT assembly (GA or VA).In applications where the assembly is required to be at or below a specific thickness (e.g., when the GA is mounted on the surface over pavement, or the VA must adhere to limited vehicle body restrictions), the separation layer can be reduced with little impact on efficiency in the separation layer thickness region beyond the separation layer thickness where eddy current losses are minimized. 403 Additionally, if the addition of losses and heating can be tolerated, lower efficiencies are possible in the layer thickness region. 410The 409 separation layer thickness region exhibits a markedly asymptotic behavior towards eddy current losses as the separation layer thickness is reduced, and while it is possible to construct an assembly in this range, reductions to the thickness of the backing core may be favorable to further decrease the thickness of the separation stage. Figure 5

[0055] Figure 5 shows the modeled power losses for a wireless power assembly (either primary or secondary). Figure 5 illustrates graphs for power losses for multiple backing core thicknesses across a progressive range of additional separation layer thickness inserted between the backing core and the backing plate.

[0056] The X-axis 501 shows the addition of a separation layer from zero to 5 mm. The Y-axis 502 shows the power loss in watts.

[0057] For a 5 mm thick backup core, the total power loss line 503 is the sum of the backup core loss line 506 and the backup plate induced eddy current loss line 509 as shown.

[0058] For a 6.35 mm thick backup core, the total power loss line 504 is the sum of the backup core loss line 507 and the backup plate induced eddy current loss line 510 as shown.

[0059] For a 9.5 mm thick backup core, the total power loss line 505 is the sum of the backup core loss line 508 and the backup plate induced eddy current loss line 511 as shown.

[0060] For each of the backing core thicknesses, the same behavior is observed in the total power loss in 503, 504, and 505, with the highest power losses occurring in the separation layer thicknesses. As the separation layer thickness increases (moving to the right on the X-axis 501), the increased thickness reduces eddy current losses in 509, 510, and 511, while the backing core losses in 506, 507, and 508 remain constant. For each backing core thickness, the addition of the separation layer shows a decreasing gain in power loss savings until they become fairly static. Figures 6 and 7A

[0061] Figure 6 illustrates the energy losses incurred at different thicknesses of the backing core when introducing a separation layer between the backing core and the backing plate. As illustrated in Figure 5, the overall thickness of the assembly increases as the thickness of the backing core increases, and therefore the potential thicknesses of the separation layer also increase.

[0062] Since in Figures 6 and 7A the total allowable thickness is restricted as described above with respect to Equations (1) to (3), the thickness of the separation layer and the thickness of the backing core are restricted, generating dg + df = C, where C = restricted thickness, df = thickness of the backing core, and dg = thickness of the separation layer. In both Figures 6 and 7A, as we move to the right along the X-axis, dg increases while C remains constant. Figure 6

[0063] Figure 6 shows the replacement (thinning) of the backing core (e.g., a ferrite sheet) with the addition (thickening) of the separation layer. Since, especially on the receiving side (e.g., the vehicle-mounted assembly), the assembly thickness may be limited by the availability of installation space (e.g., to maintain vehicle-to-ground clearance), minimizing the assembly thickness is vital. As such, the thickness of the magnetic flux control layer (i.e., the backing core layer and the separation layer as described in Figure 6) may be restricted by the overall thickness design goal. The separation layer may consist of air space(s), a nonmagnetic filler, nonmagnetic structural support elements and conduits, nonmagnetic coolant, or any mixture thereof.

[0064] As illustrated in Figure 6, the X-axis 601 is used to show the separation layer thickness when the total thickness of the separation layer and the backing core sheet is held constant. The Y-axis 602 is used to show the power level loss (in watts). Three curves 603, 604, and 605 are plotted. The eddy current loss is shown on curve 605. The eddy current loss curve 605 indicates that the MA.a.ZUZÓ / UU I Ί The power loss is highest when the backing core is both the thickest and almost in contact with the metal backing plate. The power loss component curve for backing core 604 shows that the power loss increases as the backing core thins and the thickness of the resulting separation layer increases. As the backing core layer thins, the losses in the backing core increase. At crossover point 606, the power losses due to backing core 604 dominate, but the power losses due to eddy currents 605 continue to decrease.

[0065] The total energy loss curve 603 shows that an optimum (substantially minimal) energy loss point 607 can be determined. In Figure 6, the energy loss is substantially minimized through the introduced thicknesses of the backing layer (and resulting thinning of the backing core layer) from approximately 0.25 mm to 1.0 mm.

[0066] The eddy current loss curve 605 shows a sharp reduction that continues to decrease through an initial region 608 before flattening substantially in a second region 609. Continuing decreases in backing core sheet thickness and the resulting addition of the separation layer have little or no effect on the eddy current losses through region 609.

[0067] In some applications, increasing the power losses per backup core beyond the optimum loss point 607 may be acceptable (e.g., to decrease the overall thickness of the assembly, to achieve a reduction in cost or weight by thinning the backup core, or to provide additional cooling / coolant volume). Figure 7A

[0068] Figure 5 illustrates the power losses incurred at different backing core thicknesses when introducing a separation layer between the backing core and the backing plate, while Figure 7A illustrates that the overall assembly thicknesses cannot increase as the separation layer is introduced and backing core thickness is removed. The X-axis 701 shows the replacement of the backing core with the separation layer, while the Y-axis 702 shows the power loss in watts.

[0069] The sum of the total power loss from the backup core loss and eddy current losses is shown for three backup core thicknesses. Each of these backup core thicknesses decreases as separation layer is added. The total power loss line for a 5 mm backup core 703 is the sum of the backup core losses 706 and the eddy current losses 709. The power loss line 704 for the 6.35 mm backup core shown is the sum of the 6.35 mm backup core losses 707 and the eddy current losses 710. The total loss line 705 for the 9.5 mm backup core scenario is the sum of the backup core losses 708 and the eddy current loss 711.

[0070] For all initial backing core thicknesses, the backing core losses 706, 707, and 708 increase proportionally as the backing core thickness decreases. The eddy current losses 709, 710, and 711 show the expected improvements in power losses as the backing core layer MA.a.ZUZÓ / UU 11 or additional separation replaces the backup core. In Figure 7A, power loss is substantially minimized for each backup core through replacement separation layer thicknesses of approximately 0.25 mm to approximately 0.75 mm for the 5 mm backup core 703 to approximately 0.25 mm to approximately 2.0 mm for the 9.5 mm backup core. Figure 7B

[0071] Figure 7B shows the substantially optimized ratio range of backing core thicknesses to separation layer thicknesses for an exemplary range of total thickness (sum of backing core and separation layer). Using these ratios, the separation layer thickness can be selected where the total energy loss is substantially minimized for a given backing core layer thickness, given the constraints of a thin backing core.

[0072] The X-axis 712 shows the total thickness in millimeters. The Y-axis 713 shows the ratio of the thickness of the backing core layer to the thickness of the separating layer. The upper limit 714 and lower limit 715 show the upper and lower limits, respectively, of the ratios for a given backing core thickness. Between the limits 714 and 715, the total power loss due to backing core losses and eddy current losses is substantially minimized, i.e., within 5% of the absolute minimum. Due to the properties of different backing cores, the exact point of backing core saturation 716 may vary. For the same reason, the exact point 717 where the magnetic flux density in the backing core becomes non-uniform may also vary. Figure 8

[0073] Figure 8 shows an exploded view of GA 801. Using this view, the relative thicknesses of the different layers are not shown, and the spacing between layers is exaggerated for illustrative purposes. Structural support elements, galvanic isolation, waterproofing, and associated circuitry are omitted from the figure, all of which do not materially affect the magnetic flux distribution. In this illustrative example, the GA is surface-mounted to a pavement surface 802.

[0074] As illustrated in Figure 8, the GA 801 comprises a metal backing plate 803 that functions as an eddy current shield, a separation layer 804, a backing core layer 807, and a primary coil 808. In exemplary embodiments, the spacing of the backing core can be set to optimize for the lowest power loss as described with reference to Figures 4 and 7A-7B. As illustrated in Figure 8, the resulting separation layer 804 can be used for cooling (and heating) the coil assembly using refrigerant tubes 806. Ideally, the GA 801 would have a high utilization rate with nearly constant waste heat generation and limited cooling periods between load / use sessions. The external inlet and outlet connections 809 to the refrigerant resource supplies can be located above or below the floor.A local or remote ground connection can be provided, if necessary, to provide grounding.

[0075] In exemplary embodiments, the separation layer 804 is filled with a non-magnetic material, for example air space(s), an active or passive cooling / heating system (liquid- or air-based), ducts, MA.a.ZUZÓ / UU I Ί or structural support members, or a mixture of the aforementioned. In one example, coolant tubes 806 made of non-conductive, non-magnetic material are placed directly against the backup core layer 807 or the eddy current shield 803, both of which generate heat and conduct heat from the primary coil 808 during a wireless power-up. Since the backup core operates best within specific temperature ranges, the coolant can provide both cooling and heating as required. The separation layer 804 not used for piping or heat-conducting surfaces can be filled with a non-magnetic, heat-conducting material 805 with mechanical support structures.In one example, an idle GA (or group of GAs) receives waste heat from co-located power electronics and / or charging stations to maintain an efficient backup core temperature. Figure 9

[0076] Figure 9 provides an exploded view of the vehicle assembly (VA) 901. In Figure 9, the relative thicknesses of the different layers are not shown, and the spacing between layers is exaggerated for illustrative purposes. Structural support elements, galvanic isolation, waterproofing, and associated circuitry are omitted from the figure, all of which do not materially affect the magnetic flux distribution.

[0077] The VA 901 operates under different environmental and mechanical constraints than the GA 801, but it can utilize a separation layer. A primary constraint is that the VA 901, in some installations, must be as thin as possible to fit better beneath the vehicle chassis. Weight reduction is another constraint, as is limited charging time. The VA 901 is nominally attached to the vehicle body 902 mechanically by means of connections to the metal backing plate 903, which acts as an eddy current shield. The separation layer 904 is filled with a non-magnetic material, for example, an active or passive cooling / heating system (liquid- or air-based), ductwork, structural support members, air space, or a combination thereof, as shown, for example, with respect to the separation layer 804 of the GA 801.The backup core layer 905 is supported by structures spanning the separation layer 904. Attached to the backup core layer 905, the secondary coil 906 receives the magnetic flux generated by the primary coil 808 of the corresponding GA. The heat generated within the secondary coil 906 is conducted through the attached backup core layer 905 and to the environment through the VA cover and housing (not shown) via the matched inlet and outlet piping 907. Signaling and control of distributed sensors 909 (e.g., thermocouple) are achieved via a bidirectional or unidirectional data link 908, as required. One or more temperature sensors 909 can be conveniently located on the VA stack. In exemplary configurations, the backup core spacing is set to optimize for the lowest power loss, as described with reference to Figures 6 and 7. Figure 10

[0078] Figure 10 illustrates a high-power wireless energy transfer system for electric vehicles with battery storage. In this system, the ground-side electronic components 1001 provide a conditioned power signal to the primary assembly 1002. As is preferred in high-power systems MA.a.ZUZÓ / UU I Ί ou power, the primary assembly 1002 can have a balanced series-series configuration with the primary windings 1003 with coupled capacitors 1004 and 1005. Through an air gap 1010, the coil of the secondary assembly 1006 is used to receive the magnetic signal generated by the primary assembly 1002. The secondary coil 1006 can also have a balanced series-series configuration with the secondary windings 1007 with coupled capacitors 1008 and 1009. The level, frequency, and phase of the AC energy (i.e., AC signal data) generated by the secondary coil 1006 are measured by a sensor 1011, which reports these measurements via the digital data link 1012 to the active rectifier controller (ARC) 1013. The ARC 1013 uses the AC signal data to predictively model the signal to determine zero crossings in order to optimize active rectification.The rectification control signals are passed through control links 1017 to the active rectifier 1016, which takes the AC signal inputs 1015 and converts them to a DC power output 1019. Temperature sensors in the rectifier module use digital data links 1018 to report to the ARC 1013. The power conditioner 1020 takes the DC output 1019 from the rectifier 1016 and removes ripple and noise in filter 1021 to charge the battery pack 1024. The conditioned DC signal characteristics are monitored by a sensor 1022 and reported back to the ARC 1013 via digital data link 1023. The ARC 1013 reports both AC and DC power characteristics to a network controller 1014 for storage and reporting. Figures 11A and 11B

[0079] Figure 11A and Figure 11B illustrate examples of cooling modes for the assembly (nominally the vehicle assembly (VA)) containing the secondary windings of an open-core magnetic resonance-based wireless power transfer (WPT) system. The VA is expected to be used intermittently, with aperiodic charging sessions and long cooling periods following charging sessions. Figure 11A

[0080] Figure 11A illustrates an air-cooling system for a movable secondary winding in a wireless power transfer (WPT) system. Using the secondary winding (not shown) in the magnetic resonance-based WPT, the VA 1101 receives power from the GA 1102 shown here embedded in the pavement 1103, although above-ground installations are contemplated. The magnetic flux (not shown) crosses the gap 1104 between the primary and secondary coils.

[0081] The vehicle-mounted assembly (the VA) 1101 is structurally connected to the vehicle (not shown) by means of a heat-conducting backing plate 1105. The backing plate 1105 also serves as a passive heat sink for the VA 1101. The backing plate 1105 may be equipped with one or more temperature sensors (not shown) on the VA and on the front and / or rear surfaces of the backing plate 1105 that provide readings to the thermal management system (TMS) 1106 through a bidirectional or unidirectional data link 1107 (for example, a CAN bus interface). The temperature sensors may be located on the VA assembly 1101 wherever elevated temperatures are expected or have historically been encountered.

[0082] The TMS 1106 uses the inlet air temperature 1108 and various temperature readings from VA 1101 in a predictive model to anticipate cooling requirements. When the requirements of ML / a / ZUZÓ / UU 11 ou < you If the cooling capacity exceeds that of passive cooling, the active air-cooling components at the inlet 1108 and outlet 1109 are activated as needed via control links through the bidirectional data link 1107. The resulting inlet 1110 and exhaust 1111 airflow serve to cool the VA 1101. Internal structures 1112 within the VA 1101 are used to direct airflow and channel heat. Examples of internal structures include heat pipes, cooling fins, directional vanes, and ducts sized to provide uniform airflow to deliver cooling for the expected thermal load.Cooling structures comprised of non-magnetic material may hang from or be otherwise attached to the backing core layer and / or backing plate and provide a degree of structural support through the separation layer between the backing core and the backing plate. Figure 11B

[0083] Figure 11B illustrates a liquid-cooling system for a movable secondary winding in a wireless power transfer (WPT) system. Using the secondary winding (not shown) in the magnetic resonance-based WPT, the VA 1101 receives power from the GA 1102 through the primary winding (not shown) embedded in the pavement 1103, although above-ground installations are contemplated. The magnetic flux (not shown) crosses the gap 1104 between the primary and secondary coils.

[0084] The vehicle-mounted assembly (the VA) 1101 is structurally connected to the vehicle (not shown) by means of a heat-conducting backing plate 1105. The backing plate 1105 also serves as a passive heat sink for the VA 1101. The backing plate 1105 is equipped with one or more temperature sensors on the VA 1101 and backing plate 1105 that provide readings to the thermal management system (TMS) 1106 through a unidirectional or bidirectional data link 1107 (for example, a CAN bus interface). The temperature sensors (not shown) can be located on the VA 1101 assembly wherever elevated temperatures are expected or have historically been encountered.

[0085] The TMS 1106 uses air temperature and various temperature readings from the VA 1101 in a predictive model to anticipate cooling requirements. When cooling requirements are predicted to exceed passive cooling capabilities, active liquid cooling is activated via control links through the bidirectional or unidirectional data link network 1107. A vehicle-based coolant reservoir 1118 supplies liquid coolant to the VA 1101. The inlet flow 1113 of the liquid is controlled by an inlet valve 1114, and the outlet flow 1115 is controlled by an outlet valve 1116, which serves to cool the VA 1101. Internal structures 1117 within the VA 1101 are used to direct airflow and channel heat.Examples of internal structures include heat exchangers, cooling loops, heat pipes, and through-ducts to provide cooling for the expected thermal load. In this way, the TMS 1106 can circulate the cooling / heating fluid through one or more ducts to thermally manage the WPT coil assembly. Figure 12

[0086] Figure 12 shows an example of energy loss density versus characteristic temperature for a representative high-permeability magnetic material, e.g., a backing core consisting of manganese zinc iron (MnZnFe). Further information regarding the magnetic material can be found in the data sheet “Material M25, Revi” provided by National Magnetics Group, Inc. of Bethlehem, Pennsylvania, the contents of which are incorporated by reference. In the example in Figure 12, the energy loss is substantially minimized between approximately 60°C and approximately 80°C, which may be a desired optimum range in an exemplary mode 5.

[0087] Although different implementations have been described above, it should be understood that they have been presented as examples only, and not as a limitation. For example, any of the elements associated with the systems and methods described above may employ any of the functionalities established above. Therefore, the breadth and scope of a preferred implementation should not be limited by any of the exemplary implementations described above.

Claims

1. An assembly for a wireless power transfer system, the assembly comprising: a wireless power transfer coil; an unsaturated backup core layer adjacent to the wireless power transfer coil; an eddy current shield; a separation layer between the backup core layer and the eddy current shield, the separation layer having a separation layer thickness in a separation layer thickness range for a given thickness of the backup core layer where the eddy current loss in the eddy current shield is substantially flat across the separation layer thickness range; and a housing enclosing the wireless power transfer coil, backup core layer, separation layer, and eddy current shield.

2. The assembly according to claim 1, wherein a thickness of the backing core layer and a thickness of the separation layer are selected so as to substantially minimize a total power loss comprising power loss in the backing core layer plus eddy current loss in the eddy current shield.

3. The assembly according to claim 1, wherein the separation layer comprises at least one of an air space, a non-magnetic filling agent, a non-magnetic structural support element, at least one non-magnetic conduit, or a non-magnetic coolant.

4. The assembly according to claim 3, wherein a cooling / heating fluid circulates through said at least one conduit.

5. The assembly according to claim 4, wherein the fluid is a liquid.

6. The assembly according to claim 3, wherein said at least one conduit comprises a non-conductive, non-magnetic material positioned immediately against the backing core layer.

7. The assembly according to claim 3, wherein said at least one non-magnetic conduit comprises a non-conductive, non-magnetic material positioned immediately against the eddy current shield.

8. The assembly according to claim 4, further comprising a thermal management device that circulates the cooling / heating fluid in said at least one conduit to thermally manage the backing core layer to substantially minimize energy loss due to hysteresis heating.

9. The assembly according to claim 4, further comprising a thermal management device that circulates the cooling / heating fluid in said at least one conduit to thermally manage the wireless power transfer coil assembly.

10. The assembly according to claim 8, wherein the eddy current shield comprises one or more temperature sensors that provide temperature readings to the MA.a.ZUZÓ / UU I Ί ou < tu 19N c N thermal management device, which controls the circulation of the cooling / heating fluid to maintain the backup core layer at a predetermined temperature to minimize energy loss.

11. The assembly according to claim 10, wherein the thermal management device provides an inlet air temperature and backup core temperature readings to a predictive model to anticipate heating / cooling requirements, and when the cooling or heating requirements are expected to exceed the passive cooling or passive heating capacities, the circulation of the cooling / heating fluid is controlled by means of the thermal management device to adjust a backup core layer temperature.

12. The assembly according to claim 11, further comprising a cooling / heating fluid reservoir with at least one valve that is controlled by the thermal management system to provide cooling / heating fluid to the separation layer through said at least one conduit.

13. The assembly according to claim 1, wherein the backing core layer comprises at least one of ferrite, layered metal sheets, powder oxides, sintered powder oxides, or amorphous metals.

14. A method for assembling a wireless power transfer assembly of a wireless power transfer system, comprising: providing an unsaturated backup core layer adjacent to a wireless power transfer coil; providing eddy current shielding separated by a separation layer from the backup core layer, the separation layer having a separation layer thickness in a separation layer thickness range for a given thickness of the backup core layer where the eddy current loss in the eddy current shielding is substantially flat across the separation layer thickness range; and enclosing the wireless power transfer coil, backup core layer, separation layer, and eddy current shielding in a housing.

15. The method according to claim 14, further comprising selecting a thickness of the backing core layer against a thickness of the separation layer so as to substantially minimize a total power loss comprising power loss in the backing core layer plus eddy current loss through the separation layer.

16. The method according to claim 15, further comprising restricting a total thickness C = dg + df where df is a thickness of the backing core layer and dg is the thickness of the separation layer.

17. The method according to claim 14, further comprising circulating a cooling / heating fluid through at least one conduit in the separation layer that is placed immediately against the backing core layer.

18. The method according to claim 14, further comprising a thermal management device that thermally manages the backing core layer to minimize energy loss by maintaining circulation of the cooling / heating fluid through said at least one conduit.

19. The method according to claim 18, further comprising the thermal management device that provides an inlet air temperature and backup core temperature readings to a predictive model to anticipate heating / cooling requirements, and when cooling or heating requirements are expected to exceed passive cooling or passive heating capabilities, controlling the circulation of the cooling / heating fluid to adjust a backup core layer temperature.

20. The method according to claim 19, further comprising providing at least one cooling / heating fluid reservoir with at least one valve and the thermal management system controlling said at least one valve to provide cooling / heating fluid to the separation layer through said at least one conduit to provide heating or cooling to the backup core to substantially minimize energy loss.

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