WO2019227213A1

WO2019227213A1 - Apparatus, methods, and systems for wireless power transfer

Info

Publication number: WO2019227213A1
Application number: PCT/CA2019/050732
Authority: WO
Inventors: Hirokazu Matsumoto; Olivier Trescases; Nameer Ahmed KHAN
Original assignee: The Governing Council Of The University Of Toronto
Priority date: 2018-05-29
Filing date: 2019-05-29
Publication date: 2019-12-05
Also published as: WO2019227213A8; CN112912271A

Abstract

The present disclosure describes apparatuses, methods, and systems for wireless power transfer. Each of transmission and reception apparatuses have an alignment coil (DC coil) in addition to a wireless power 5 transmitter/receiver coil (AC coil). At least one of the transmission and reception apparatuses is movably coupled to a support frame that allows the respective transmission and reception apparatus to move there-along to align itself with the other of the transmission and reception apparatus. Transmission and reception apparatuses are thus configured to perform self-0 position-correction.

Description

APPARATUS. METHODS, AND SYSTEMS FOR WIRELESS

POWER TRANSFER

TECHNICAL FIELD

[0001] The present disclosure relates to electric charging, and in particular to wireless power transfer.

BACKGROUND

[0002] In recent years, Electric Vehicles (EV) have been rising in popularity with 40-70 million EVs expected on the road by 2025. Wireless Power Transfer (WPT) systems are gaining traction in EVs, primarily as an enabling technology for autonomous vehicles. With 85 million autonomous vehicles expected to be deployed by 2035, there is a need to establish a charging infrastructure that eliminates the need for driver intervention. WPT systems enable fully automated charging for short periods of time when EVs are parked; reducing the battery size requirements. WPT systems are also much safer than wired systems by eliminating electrical shock and cable tripping hazards.

[0003] However, the inevitable misalignment between the transmitter and receiver, which degrades charger efficiency, is a major impediment to the adoption of WPT systems. The predominant reason is the diminishing mutual inductance between the transmitter and receiver coils with respect to coil misalignment. Several different coil structures have been proposed in literature to improve misalignment tolerance. However, when the misaligned distance approaches the dimension of the coil, even these structures cannot mitigate the drop in efficiency. Hence, large transmitter coils are typically used in WPT systems, which are impractical in EV applications.

[0004] WPT research has mainly been focused on accommodating a large gap between the charging pad and the underside of passenger EVs, while also improving the misalignment tolerance. However, existing systems that have been developed to date are impractical due to EV design constraints and high costs. [0005] Accordingly, apparatuses, methods, and/or systems that enable additional, alternative, and/or improved wireless power transfer remains highly desirable.

SUMMARY

[0006] In accordance with one aspect of the disclosure, a wireless charging system for charging a battery of an electric vehicle (EV) is disclosed, the system comprising: a support frame; a wireless power transmission apparatus movably coupled to the support frame, the wireless power transmission apparatus having a transmitter alternating current (AC) transmitter coil and a transmitter direct current (DC) alignment coil; and a transmission controller coupled to the wireless power transmission apparatus, the transmission controller configured to power the DC alignment coil to align the AC transmitter coil with a wireless power receiving apparatus on the EV, to charge the battery of the EV.

[0007] In a further aspect of the above system the DC alignment coil aligns the power transmission apparatus with a receiver DC alignment coil of the wireless power receiving apparatus of the EV.

[0008] In a further aspect of the above system the transmission controller initiates a current to the transmitter DC alignment coil to magnetize the transmitter DC alignment coil to a first polarity opposite a secondary polarity of a receiver DC alignment coil of the EV.

[0009] In a further aspect of the above system a magnetic force is generated between the transmitter DC alignment coil and the receiver DC alignment coil that causes movement of the wireless power transmission apparatus in at least one direction along the support frame to align the transmitter AC coil and a receiver AC coil.

[0010] In a further aspect of the above system when the transmission controller determines that the transmitter AC coil of the wireless power transmission apparatus and a receiver AC coil of the EV are aligned, a supply of power to the AC transmitter coil induces a current in the AC receiver coil to charge the battery of the EV. [001 1] In a further aspect of the above system the transmission controller initiates a supply of current to the transmitter DC alignment coil upon detection of the EV.

[0012] In a further aspect of the above system detection of the EV comprises receiving an instruction wirelessly at the transmission controller from a receiver controller of the EV.

[0013] In a further aspect of the above system when the transmitter DC alignment coil and the receiver DC alignment coil are aligned, the supply of the current is stopped to the transmitter DC alignment coil.

[0014] In a further aspect of the above system alignment of the transmitter DC alignment coil and the receiver DC alignment coil is determined by measuring a perturbation current in the transmitter AC coil or the receiver AC coil.

[0015] In a further aspect of the above system a perturbation frequency of the perturbation current is swept across a frequency range to determine a gap distance between the transmitter AC coil and the receiver AC coil.

[0016] In a further aspect of the above system a peak current of the perturbation current from the frequency sweep determines a minimum gap separation between the AC transmitter coil and the receiver AC coil.

[0017] In a further aspect of the above system the transmission controller provides an indicator to the controller to move the vehicle closer to the wireless power transmission apparatus if the minimum gap separation is larger than a threshold value.

[0018] In a further aspect of the above system the transmitter DC alignment coil and the transmitter AC coil are arranged perpendicular to each other.

[0019] In a further aspect of the above system the transmitter AC coil is any one of: a spiral-type coil, a DD-type coil, and a solenoid-type coil. [0020] In a further aspect of the above system the transmitter DC alignment coil comprises a DC core and the AC transmitter coil comprises an AC core.

[0021] In a further aspect of the above system the DC core is made of steel.

[0022] In a further aspect of the above system the AC core is made of ferrite.

[0023] In a further aspect of the above system the transmitter AC coil is made of Litz wire.

[0024] In a further aspect of the above system the transmitter DC alignment coil is made of enamel wire or copper wire.

[0025] In a further aspect of the above system the support frame is any one of: a linear slider, a ball screw arrangement, a pulley and belt arrangement, and a wheel and guide arrangement.

[0026] In a further aspect of the above system the support frame comprises two linear sliders configured to allow for movement in two directions.

[0027] In a further aspect of the above system the transmitter AC coil comprises a plurality of ferrite bars.

[0028] In a further aspect of the above system the plurality of ferrite bars have non-uniform spacing.

[0029] In a further aspect of the above system the wireless power transmission apparatus further comprises a copper shield made of a continuous sheet.

[0030] In a further aspect of the above system the wireless power transmission apparatus moves horizontally along the support frame.

[0031] In accordance with another aspect of the disclosure, a wireless charging system for charging of a battery of an electric vehicle (EV) is disclosed, comprising: a wireless power receiver apparatus mounted on the EV, the wireless power receiver apparatus having a receiver alternating current (AC) coil and a receiver direct current (DC) alignment coil coupled to the battery of the EV; and a controller coupled to the wireless power receiver apparatus, the controller configured to power the receiver DC alignment coil to allow a transmitter DC coil of a wireless power transmission apparatus to align with the wireless power receiver.

[0032] In a further aspect of the above system a DC alignment coil of the wireless power transmission apparatus moves horizontal by a magnetic field of the transmitter DC alignment coil and the receiver DC alignment coil coupled to the battery of the EV.

[0033] In a further aspect of the above system upon alignment of the DC receiver alignment coil with the transmitter DC alignment coil the receiver AC coil inductively receives power from a transmitter AC coil of the wireless power transmission apparatus to charge the battery of the EV.

[0034] In a further aspect of the above system the receiver AC coil can provide power from the battery of the EV to the transmitter AC coil.

[0035] In a further aspect of the above system the controller initiates a current to the transmitter DC alignment coil to magnetize the transmitter DC alignment coil to a first polarity opposite a secondary polarity of a receiver DC alignment coil of the EV.

[0036] In a further aspect of the above system the controller wirelessly sends and instruction to wireless power transmission apparatus to initiate alignment and charging of the battery of the EV.

[0037] In a further aspect of the above system when the transmitter DC alignment coil and the receiver DC alignment coil are aligned, a supply of the current is stopped to the receiver DC alignment coil and the transmitter DC alignment coil.

[0038] In a further aspect of the above system alignment of the transmitter DC alignment coil and the receiver DC alignment coil is determined by measuring a perturbation current in the transmitter AC coil or the receiver AC coil.

[0039] In a further aspect of the above system a perturbation frequency of the perturbation current is swept across a frequency range to determine a gap distance between the transmitter AC coil and the receiver AC coil. [0040] In a further aspect of the above system a peak current of the perturbation current from the frequency sweep is utilized to determine a minimum gap separation between the transmitter AC coil and the receiver AC coil.

[0041] In a further aspect of the above system an indicator is provided to the controller to move the EV closer to the wireless power transmission apparatus if the minimum gap separation is larger than a threshold value.

[0042] In a further aspect of the above system the receiver DC alignment coil and the receiver AC coil are arranged perpendicular to each other.

[0043] In accordance with still a further aspect of the disclosure, a kit is disclosed comprising transmitter side and receiver side wireless charging systems for charging a battery of an electric vehicle (EV) in accordance with the above aspects.

[0044] In accordance with yet another aspect of the disclosure, a method of wireless charging of a battery of an electric vehicle (EV) is disclosed, the method comprising: receiving an indicator to commence alignment of a transmitter DC alignment coil of a wireless power transmission apparatus with a receiver DC alignment coil coupled to the EV; supplying current to the transmitter DC alignment coil; verifying alignment of the transmitter DC alignment coil with the receiver DC alignment coil; and supplying current to a transmitter AC coil to inductively charge a battery of the EV through a receiver AC coil when the alignment has been verified.

[0045] In a further aspect of the above method verifying the alignment of the transmitter DC alignment coil with the receiver DC alignment coil comprises measuring the AC self-inductance of a perturbation current of the transmitter AC alignment coil.

[0046] In a further aspect of the above method the method further comprises changing a frequency of a perturbation current across a defined frequency range to determine a distance between the transmitter DC alignment coil and the receiver DC alignment coil.

[0047] In a further aspect of the above method power to the transmitter DC alignment coil is stopped when alignment is verified. [0048] In a further aspect of the above method the transmitter DC alignment coil is coupled to the transmitter AC coil comprising a wireless power transmission apparatus, wherein the wireless transmission apparatus is horizontally movable along a support frame.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

FIGs. 1 (a) to (c) show three types of commonly used wireless power transfer coils;

FIGs. 2(a) and 2(b) show the normalized mutual inductance of the spiral-type, DD- type, and solenoid-type coils at an alignment as a function of normalized misaligned distance in the x- and z- directions, respectively;

FIG. 3 shows transmitter and receiver apparatuses of the wireless power transfer system;

FIGs. 4(a) to (c) show parts for alignment that may be used for the transmission and reception apparatuses;

FIG. 5 shows the wireless power transfer system and apparatus used for charging an electric vehicle;

FIG. 6 shows an overview of a wireless transfer power system for charging a battery of an electric vehicle;

FIG. 7A shows the electrical architecture of the wireless power transfer system;

FIG. 7B shows a control block diagram of transmission and receiver controllers;

FIG. 8A shows an operation of self-position-correction and wireless power transfer of the wireless power transfer system for charging a vehicle battery;

FIG. 8B shows a timing diagram of the position-correcting control sequence; FIG. 9 shows a simulated self-inductance of the ac coil for varying horizontal misalignment;

FIG. 10(a) shows typical waveforms of fixed duty Vperturb, ipenurb , and Ztank, and, FIG. 10(b) shows typical waveforms of Pl-controlled Vpenurb, regulated ipenurb , and resulting Ztank,

FIG. 1 1 shows a simulated self-inductance of the ac coil for varying separation gap;

FIG. 12(a) shows typical waveforms of Pl-controlled Vpenurb, iperiurb, ipenurb pk , and Ztank with large Ay, and, FIG. 12(b) shows typical waveforms of Pl-controlled Vperturb, iperturb, iperturb.pk , and Ztan with Ay = 50 mm; FIG. 13 shows a WPT setup consisting of (a) a secondary electro-magnetic based coil, (b) a solenoid coil mounted inside the electro-magnetic based coil with non- uniform spacing of ferrite bars, and (c) a solenoid coil mounted inside the electromagnetic based coil with uniform spacing of ferrite bars;

FIG. 14A shows simulated Fmag.x versus d with he t = 25 mm and I_dc = 30 A, and FIG. 14B shows simulated Fmag x versus dc core extension, hex t, with d = 8 mm and /dc = 30

A;

FIGs. 15A and 15B respectively show simulated mutual inductance versus (a) misalignment in x-direction, Dc and (b) separation gap, Ay;

FIG. 16 shows normalized mutual inductance of spiral-type, DD-type, and solenoid- type coils as a function of normalized misalignment in the z- direction;

FIGs. 17A and 17B respectively show simulated system efficiency for varying horizontal misalignment, Ax, and loss breakdown of dual-coil apparatus at 5kW WPT;

FIGs. 18A and 18B respectively show magnetic field simulation of 5kW WPT with (a) Ax = 0mm and (b) Ax = 80 mm, before misalignment correction; FIGs. 19A and 19B respectively show simulated F_mag._x versus Ax with l_dc = 30 A, and simulated F_mag_,z versus Az with I_dc = 30 A; 8

RECTIFIED SHEET (RULE 91.1) FIG. 20 shows a representation of a magnetic flux density distribution of the solenoid coil; the increase of flux density at the edges of the solenoid results in higher core loss;

FIGs. 21 A and 21 B respectively show simulated magnetic flux density at 5kW WPT with (a) 10 mm spacing, and (b) optimally spaced ferrite bars;

FIG. 22 shows simulated eddy current loss versus shield thickness at 5kW WPT;

FIG. 23 shows eddy current distribution in (a) a continuous sheet of copper and (b) multiple isolated pieces of copper;

FIG. 24 shows simulated current density distribution at 5kW WPT of the shield when composed of (a) multiple isolated pieces of copper, (b) multiple isolated pieces connected with thin copper tape, and (c) a continuous sheet of copper;

FIG. 25 shows (a) an experimental setup of a charger, and (b) power electronics PCB for the WPT charger;

FIG. 26 shows measured current waveforms of the dc coils; FIG. 27 shows measured magnetic force versus misalignment in x-direction, Dc;

FIG. 28 shows position measurement of dc coils for varying ld_C;

FIG. 29 shows position measurement of dc coils for varying separation gap, Ay;

FIG. 30 shows position measurement of dc coils for varying vertical misalignment, Dz;

FIG. 31 shows measured current and voltage waveform of the 5kW WPT converter; FIG. 32 shows thermal images of (a) WPT coil system at 5kW WPT, (b) transmitter and (c) receiver MOSFETs;

FIG. 33 shows measured efficiency versus P_bat for varying V_bat, \4us is manually adjusted to achieve desired P_bat;

FIG. 34 shows measured efficiency versus Ay, V_bUS is manually adjusted to achieve desired Pbat;

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RECTIFIED SHEET (RULE 91.1) FIG. 35 shows measured efficiency versus Dz, V_bUS is manually adjusted to achieve desired Pbat;

FIG. 36 shows (a) measured waveforms of uniformly spaced ferrite bars at 3.7kW WPT as a comparative example, and (b) image of damaged uniformly spaced ferrite bars after attempted operation at 5kW WPT; and

FIG. 37 shows measured waveforms of non-uniformly spaced ferrite bars at (a) 3.7kW and (b) 5kW WPT.

[0050] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

[0051] The present disclosure describes apparatuses, methods, and systems for wireless power transfer. In accordance with the present disclosure, transmission and reception apparatuses are configured to perform self-position-correction to align themselves, thus enabling improved power transfer efficiency. The reception apparatus may be provided in an electric vehicle and electrically coupled to a vehicle battery for charging the battery. An electric vehicle as referred to herein may be anything that is electrically powered and is displaceable (including but not limited to autonomous vehicles, drones, robots, etc., for the sake of example). The transmission apparatus may be provided as part of a vehicle charging system. The transmission and reception apparatuses may also be provided as part of a kit.

[0052] As described herein, each of transmission and reception apparatuses have an alignment coil (DC coil) in addition to a wireless power transmitter/receiver coil (AC coil). At least one of the transmission and reception apparatuses is movably coupled to a support frame that allows the respective transmission and reception apparatus to move there-along to align itself with the other of the transmission and reception apparatus. When the DC alignment coils of both apparatuses are magnetized with different poles, these attract each other. Hence, the transmitter or receiver apparatus, depending on which one is mounted on the support frame, or both if they are each mounted on a support frame, can move to in front of the other apparatus that was set at a misalignment. 10

RECTIFIED SHEET (RULE 91.1) [0053] During the position correction operation, the AC coil(s) may be used for detecting the misalignment distance to assess whether the transmitter and receiver apparatuses are aligned. The wireless power transfer system comprises a transmission controller that can assess misalignment by applying a perturbation to the AC transmitter coil. The transmission controller can then adjust the DC current supplied to the DC alignment coil to facilitate alignment. If the misalignment distance is too large to be overcome by movement of the transmission apparatus, the transmission controller may send a notification to a receiver controller of the electric vehicle instructing the vehicle to be moved. The transmission controller may also send a notification to the receiver controller once alignment is complete.

[0054] After the self-position-correcting operation has finished, current supply to the DC alignment coils may be stopped and wireless power transfer is performed using the AC coils. The wireless power transfer is performed at higher efficiencies as a result of the improved alignment. Additionally, the receiver controller may calculate power that is being received at the AC receiver coils, and communicate the power being received to the transmission controller so that the transmission controller can adjust the magnitude/frequency of the AC voltage supplied to the AC transmission coils.

[0055] Embodiments are described below, by way of example only, with reference to FIGs. 1-37.

[0056] FIGs. 1 (a) to (c) show three types of wireless power transfer coils disposed on a receiver side 102 and a transmitter side 104. FIG. 1 (a) shows a spiral- type coil 106, FIG. 1 (b) shows a DD-type coil 108, and FIG. 1 (c) shows a solenoid- type coil 1 10. A ferrite core 1 12 is shown as the back yoke. [0057] A spiral-type coil 106 is popular for use in wireless power transfer because of its simple structure. A DD-type coil 108 consists of two spiral coils, which are arranged side by side. A spiral-type and DD-type have coils with linkage area facing the counter apparatus. Alternatively, a solenoid-type coil 1 10 has coils with linkage area facing in the perpendicular direction to the counter apparatus.

- 1 1

RECTIFIED SHEET (RULE 91.1) [0058] As previously described, in wireless power transfer systems the degradation of power transfer and efficiency due to the misalignments between a transmitter coil and a receiver coil is a critical issue. The predominant reason for this is that mutual inductance between the transmitter coil and receiver coil shrinks with the misaligned distance.

[0059] FIGs. 2(a) and 2(b) show the mutual inductance of the spiral-type, DD- type, and solenoid-type coils normalized to mutual inductance at an alignment as a function of misaligned distance in the x- and z- directions, respectively. The misaligned distance is also normalized to the widths of the transmitter and the receiver with the same width. In FIGs. 2(a) and 2(b), the mutual inductance of the spiral-type coil is represented with lines 202a and 202b, respectively, the mutual inductance of the DD-type coil is represented with lines 204a and 204b, respectively, and the mutual inductance of the solenoid-type coil is represented with lines 206a and 206b, respectively.

[0060] With the spiral-type coil, a distance of roughly 0.7, which is normalized to the widths of the transmitter and the receiver, reduces the mutual inductances to zero, where wireless power transfer is infeasible. At this distance, although there are a few magnetic fluxes linking with the receiver coil, magnetic fluxes of two kinds with opposite directions absolutely cancels each other. Temporarily beyond this distance, the mutual inductance increases but eventually decrease toward zero.

[0061 ] The solenoid-type coil has a similar trend with the distance in the x- direction. Flowever, in the z-direction, the solenoid-type has a trend that the mutual inductance gradually decreases without crossing zero.

[0062] The mutual inductance of the DD-type coil, regardless of the direction, does not cross zero; especially the characteristics in the z-direction is realised by changing the direction of the current thorough the coils depending on the distance_.

[0063] These results, however, show that the mutual inductances of every coil type decreases to levels less than a half at a normalised distance of 1.0 in the x- and z-directions; in particular, misalignments in the x-direction cause significant degradation. The reduction in mutual inductance causes larger current to transfer the 12

RECTIFIED SHEET (RULE 91.1) same power and therefore causes the decrease in the efficiency or, in worse cases, shortage of power.

[0064] In the wireless power transfer systems and apparatuses described herein, in addition to the receiver and transmitter apparatuses having an AC coil for wireless power transfer, each of the receiver and transmitter apparatuses also have a DC alignment coil that is used for position correction. At least one of the transmitter and receiver apparatuses are arranged on a support frame that allows for movement of the respective receiver or transmitter apparatus in one or more directions. When the DC alignment coils are provided with a direct current and magnetized with opposite poles, an electromagnetic force is generated, which enables the respective receiver or transmitter apparatus to move in front of the other apparatus. As a result, the wireless power transfer system, method, and apparatuses disclosed herein provide for self-position-correction between the transmitter and receiver coils.

[0065] FIG. 3 shows transmitter and receiver apparatuses of the wireless power transfer system. On each of the transmitter apparatus 302 and the receiver apparatus 304 there are two coils: an AC transmitter/receiver coil, which enables wireless power transfer between the transmitter and receiver apparatuses, and a DC alignment coil, which causes movement of at least one of the apparatuses to perform self-position-correction. It is noted that while the AC coil and DC coil are depicted in FIG. 3 as a solid object, these are coil structures with a number of windings. The wireless power transmitter/receiver apparatuses may be substantially symmetrical to one another, which may facilitate bi-directional power transfer.

[0066] In the exemplary transmitter and receiver apparatuses shown in FIG. 3, the AC coil includes AC yokes. The AC coil may be arbitrary in structure and may be any of the types of coils described with reference to FIGs. 1 (a) to (c). In the depicted configuration, a solenoid-type coil is employed. The AC coil may be made from litz wire and the AC core made of ferrite because these materials can suppress losses under high frequency operation. Litz wire is effective for suppressing loss caused by a high-frequency current.

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RECTIFIED SHEET (RULE 91.1) [0067] The DC coil may consist of normal electric wire. The kind of the cable of the dc coil is not critical (due to low frequency). Enamel wire is much cheaper than litz wire and therefore may be used for the DC coil. A copper coil may also be used as the DC coil. Steel may be used for the DC core because steel is cheap, has high mechanical strength and magnetic field saturation of high, all of which are advantageous characteristics for the material of the DC core.

[0068] The AC coil may be mounted inside of a DC yoke with U-formed structure. This DC yoke can serve as a case for the AC coil. The DC core and coil may be covered by a copper shield to prevent the AC magnetic fluxes from penetrating these and to avoid hysteresis loss.

[0069] At least one of the transmitter and receiver apparatuses is movably coupled (i.e. directly or indirectly connected) to a support frame such as a linear slider (not shown in FIG. 3). As described with reference to FIG. 5, the support frame allows for movement of the respective receiver or transmitter apparatus. The support frame may allow for movement in one or more directions. For example, when the transmitter and receiver apparatuses are vertically mounted (separated by a distance in the y- direction in FIG. 3), the support frame may allow for movement in the x- and z- directions. The apparatus may also be coupled to the support frame in a configuration that allows for some movement in the y-direction (e.g. via a spring).

[0070] When the DC alignment coils in both apparatuses are magnetized with different poles, the DC coils attract each other and facilitates alignment of the transmitter apparatus and receiver apparatus. The DC core is a path of magnetic fluxes that induce a force for alignment.

[0071] FIGs. 4(a) to (c) show parts for alignment that may be used for the transmission and reception apparatuses. One of the configurations shown in FIGs. 4(a) to (c) may replace the DC coil and DC core depicted in FIG. 3. In both or either of the transmitter and the receiver apparatuses, a set of permanent magnets (PMs) as shown in FIG. 4(b) may replace the DC coils. This structure with PMs is thinner than the structure with the DC coil. The structure of FIG. 4(a) consists of core, coils and PMs, the magnetic field of which is enhanced by PMs and controlled by the coils.

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RECTIFIED SHEET (RULE 91.1) Either the transmitter apparatus or the receiver apparatus might employ just a DC core in FIG. 4(c), which has the simplest and lightest structure although it generates the smallest electromagnetic force. However, at least one of the transmitter/receiver apparatuses may comprise a structure with the DC coils in order to perform/control alignment.

[0072] FIG. 5 shows the wireless power transfer system and apparatus used for charging an electric vehicle 510. As depicted in FIG. 5, the WPT system can be implemented at the front or rear of the EV; resulting in a separation gap constrained by the vehicle parking (e.g. as a result of a human driver or a computer of an autonomous vehicle controlling the motion of the car) rather than the EV suspension. The smaller gap leads to better magnetic coupling and enabling a much more compact design. However, the configuration depicted in FIG 5 is not limited to such an arrangement, and could also be arranged at an underside of the electric vehicle 510 as well.

[0073] The wireless power transfer system comprises an electric transmission apparatus 502, an electric reception apparatus 504, and a support frame 506. The transmission apparatus 502 and the reception apparatus 504 may be the same as those depicted in FIG. 3, for example. In the wireless power transfer system of FIG. 5, the receiver apparatus 504 is mounted on the back side of the vehicle 510 and coupled with a rechargeable battery or other electrical storage device (e.g. a supercapacitor) (not shown) of the vehicle 510, and the transmission apparatus 502 is arranged on the support frame 506 that is mounted on a stand or wall facing the vehicle^’s rear and coupled with a power source (not shown). In some instances, the receiver apparatus 504 mounted on the vehicle 510 may be arranged on a support frame on the vehicle 510 (not shown), in addition to or alternatively to the transmitter apparatus 502 being mounted on the support frame 506. In some instances, the receiver apparatus 504 may be mounted for example on a trailer hitch bracket of a vehicle, which may provide standard heights. The receiver apparatus 504 and/or the transmitter apparatus may be removable. A wireless charging system for charging a battery of an electric vehicle comprises the electric transmission apparatus 502 and the support frame 506. The system for wireless power transfer may be installed at a

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RECTIFIED SHEET (RULE 91.1) vehicle owner’s home (i.e. garage), a parking garage, a commercial facility, an industrial facility, a charging station, etc.

[0074] The wireless power transfer system may be set-up vertically (i.e. the transmitter and receiver apparatuses are vertically mounted), as depicted in FIG. 5. Vertical mounting like this allows the shorter gap length between the receiver and transmitter in comparison with horizontal mounting, for example if the receiver apparatus 504 were mounted on the underside of the vehicle 510 and the transmitter apparatus 502 and support frame 506 were mounted on the floor.

[0075] As depicted in FIG. 5, with vertical mounting of the transmitter and receiver apparatuses the support frame 506 may be configured to allow the transmitter apparatus 502 to move horizontally to adjust to the position of the vehicle / receiver apparatus 504, which may change each time the vehicle stops. In this case, a linear slider may be used for the support frame 506. Alternative support frames 506 such as a ball screw arrangement, a pulley and belt arrangement, and a wheel and guide arrangement are also possible, as would be appreciated by a person skilled in the art without departing from the scope of this disclosure.

[0076] A change of the vertical position of the receiver apparatus 504 may occur when the body of the vehicle 510 declines due to loads, or based on different vehicle heights. A vertical distance caused by loads, however, which may for example be 5-10 cm, which is much less in comparison with the distance of the horizontal position. Therefore, the employment of a solenoid-type power transfer coil for the transmitter and receiver apparatuses, which has tolerance over the distance in the z- direction (see FIG. 2(b)), may allow for the system to deal with vertical alignments without additional mechanism.

[0077] Additionally or alternatively, the support frame 506 may allow for the transmitter apparatus 502 to move in more than one direction. For example, using two linear sliders the transmitter apparatus 502 may be able to move in both the x- and z- directions.

[0078] FIG. 6 shows an overview of a wireless transfer power system for charging a battery of an electric vehicle 650. The wireless transfer power system

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RECTIFIED SHEET (RULE 91.1) depicted in FIG. 6 may be bi-directional and can also be used to supply power from the electric vehicle to ground or other devices. The wireless transfer power system includes a system for wirelessly transmitting power to the electric vehicle that comprises a wireless power transmission apparatus 602 movably coupled to a support frame 610. The wireless power transmission apparatus 602 comprises an AC transmitter coil 604 and a transmitter DC alignment coil 606. The system for wirelessly transmitting power further comprises a transmission controller 620. As depicted, the transmission controller 620 comprises a central processing unit, a non- transitory computer readable memory, non-volatile storage, a communication module, and an input-output (I/O) interface. The non-transitory computer readable memory may store instructions which, when executed by the CPU, configures the transmission controller to perform certain functionality as for example further described with reference to FIG. 8A.

[0079] The transmission controller is coupled with a power converter 630, for example through the I/O interface. The power converted 630 in FIG. 6 is able to supply both DC and AC power from a mains line 632 to/from the transmitter AC coil 604 and transmitter DC alignment coil 606. The power converter 630 is configured to supply power thereto in accordance with control from the transmission controller 620. Still further, one or more measurement devices 608 (e.g. sensors, voltmeters, ammeters, etc.) may be arranged at the electric transmission apparatus, whose measurement values are provided to the transmission controller 620. In this manner, the transmission controller may adjust control of the power converter 630 based on measurement values received from the measurement devices 608 to optimize power transfer.

[0080] An electric vehicle 650 is also depicted in FIG. 6 for receiving electric power from the wireless power transmission system (or transferring power from the electric vehicle to the wireless power transmission apparatus 602). The electric vehicle comprises a battery 660 or other electrical energy storage device (e.g. a supercapacitor), a wireless power receiver apparatus 652 that is electrically coupled with the battery 660, and a power converter 680 between the battery 660 and the wireless power receiver apparatus 652. The wireless power receiver apparatus 652

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RECTIFIED SHEET (RULE 91.1) comprises a receiver AC coil 654 and a receiver DC alignment coil 656. The electric vehicle also comprises a receiver controller 670. As depicted, the receiver controller 670 comprises a central processing unit, a non-transitory computer readable memory, non-volatile storage, a communication module, and an input-output (I/O) interface. The non-transitory computer readable memory may store instructions which, when executed by the CPU, configures the transmission controller to perform certain functionality as for example further described with reference to FIG. 8A. One or more measurement devices 658 may be arranged at the wireless power receiver apparatus 652, whose measurement values are provided to the receiver controller 670. In this manner, the receiver controller may be able to perform calculations of how much power is being received at the wireless power receiver apparatus 652 based on measurement values received from the measurement devices 658 and communicate this information to facilitate optimizing power transfer. The I/O interface of the receiver controller 670 may also receive measurement readings from a battery management system the battery 660, such as the state of charge, etc.

[0081] Among other things, the receiver controller 670 may be configured to initiate a charging operation with the wireless power transfer system by sending an indicator to the transmission controller 620, via the communication interface, to initiate charging. The receiver controller 670 is configured to initiate a supply of direct current from the battery 660 to the receiver DC alignment coil 656 to magnetize the receiver DC alignment coil 656 to a second polarity opposite a first polarity of the transmitter DC alignment coil 606. The transmission controller is configured to initiate a supply of direct current from the power supply 630 to magnetize the transmitter DC alignment coil 606 to the first polarity. The transmission controller 620 may also be able to determine whether the transmitter DC alignment coil 606 and the receiver DC alignment coil 656 are aligned (thereby indicating that the transmitter AC coil 604 and the receiver AC coil 654 are in alignment for optimal power transfer). When the transmitter DC alignment coil 606 and the receiver DC alignment coil 656 are determined to be aligned, the transmission controller is configured to initiate a supply of alternating current from the power converter 630 to the wireless power transmission coil 604 generate an inductance between the transmitter AC coil 604 and the receiver

- 18 -

RECTIFIED SHEET (RULE 91.1) AC coil 654. The alternating current induced in the wireless power reception coil 654 is used for charging the battery 660.

[0082] The transmitter and receiver controllers may be configured to wirelessly communicate with one another. For example, each of the transmitter and receiver controllers may comprise communication interfaces that allow for communication using protocols of standards such as IEEE 802.11 (Wi-Fi™), IEEE 802.15.1 (Bluetooth™), and IEEE 802.15.4 (ZigBee™).

[0083] FIG. 7 shows the electrical architecture of the wireless power transfer system. Both of the transmitter and receiver apparatuses may have the same configuration and each may have three legs. One leg is used for supplying to the DC coil and the others are for the AC coil. The transmitter controller 620 and receiver controller 670 are configured to control switches (M1-M6 and M7-M12, respectively).

[0084] The electrical architecture shown in Fig. 7A comprises a full-bridge converter being used to drive the AC coil for WPT and a half-bridge driving the DC coil during misalignment correction. In the transmitter apparatus, the full-bridge inverter converts the bus voltage, ½_us, to an 85 kHz square waveform with 50% duty cycle, for example. The Series-Series (SS) capacitor compensation, shown in Fig. 7A, was chosen for resonance operation at 85 kHz due to its size and form factor. On the receiver apparatus, the full-bridge converter, as shown in Fig. 7A, acts as a synchronous rectifier to supply current to the EV battery. The symmetric nature of the system architecture allows for bi-directional power transfer; enabling Vehicle-to-Grid (V2G) operation in the proposed WPT system. An increasing number of bi-directional EV chargers are adopting V2G operation. V2G operation allows the EV battery to transfer energy to the grid during peak demand hours and provide grid-support functions.

[0085] FIG. 7B show a control block diagram of the transmitter apparatus and the receiver apparatus, respectively. The field-programmable gate array (FPGA) executes main control and generates switching signals for M1-M12. Microcontroller unit (MCU) manages modes, which indicate whether position correction or wireless power transfer is being executed, and interfaces with the FPGA with a communication

- 19 -

RECTIFIED SHEET (RULE 91.1) interface. Based on data from the other apparatus, the MCU provides references to the controller in FPGA and MCU transfers data obtained in FPGA to the other apparatus via wireless communication.

[0086] FIG. 8A shows an operation of self-position-correction and wireless power transfer of the wireless power transfer system for charging a vehicle battery. Once the EV is stopped/parked (802), the receiver controller may initiate a charging operation (804) by communicating wirelessly to the transmitter controller to indicate that the EV is ready for charging. The transmission controller initializes in preparation for charging (806). [0087] Position correction is performed to align the transmitter apparatus and the receiver apparatus. Controlled DC currents are supplied to the DC coils from the DC leg to magnetize them with different poles (808, 810). To ensure misalignment correction under all operating conditions, the DC coils can be enabled for a sufficiently long time to account for weaker magnetic force. However, while enabling the DC coil for a sufficient time is one option, it results in a wastage of time and energy in addition to increased device stress over the lifetime of the charger. To optimize this process, a real-time impedance detection technique may be performed. Furthermore, by placing the charger on the front/rear of the EV, a much smaller gap can be achieved for more efficient WPT. However, the variation in the gap is also increased as it depends highly on the driver. To minimize the variation in the separation gap, a real time resonant frequency tracking method may also be performed.

[0088] To optimally disable the dc coils and minimize alignment time, the distance between the transmitter and receiver apparatuses must be estimated. The AC legs of the transmitter apparatus supply a small AC current to the AC coil to estimate the misaligned distance, based on the sensed current and voltage (812). The

AC legs of the transmitter apparatus may estimate the misaligned distance with several techniques.

[0089] With reference concurrently to FIG. 7A as well as FIG. 7B, estimating a misaligned distance may be performed by one or more of the following: 20

RECTIFIED SHEET (RULE 91.1) 1) While the switches M7-M10 are in the off-state (this operation is commanded by 732b), the transmitter apparatus inputs low current pulses controlled by 732a into the primary coil (the transmitter AC coil) to estimate input impedances at 736a. The transmitter controller may estimate misaligned distances based on a lookup table 734a (stored in memory) of misaligned distance vs. the impedance.

2) While the switches M7-M 10 are in the off-state (this operation is commanded by 732b), the transmitter apparatus inputs a large AC current controlled by 732a into the primary coil (the transmitter AC coil) and the receiver apparatus measures transferred power at 734b. The receiver controller may estimate misaligned distances based on a lookup table 734a (stored in memory) of misaligned distance vs. power, or the receiver controller may transmit the measured power to the transmitter controller for estimation of the misaligned distance.

3) While either the switches M7 and M8 or the switches M9 and M10 are in the on-state (this operation is commanded by 732b), the transmitter apparatus inputs low current pulses controlled by 732a into the primary coil (the transmitter AC coil) to estimate input impedance at 736a. The transmitter controller may estimate misaligned distances based on a lookup table 734a (stored in memory) of misaligned distance vs. impedance.

4) While either the switches M6 and M7 or the switches M8 and M9 are in the on-state (this operation is commanded by 732b), the transmitter apparatus inputs low current pulses controlled by 732a into the primary coil (transmitter coil) and the receiver apparatus measures the current through secondary coil (the receiver coil). The receiver controller may estimate misaligned distances based on a lookup table 734a of misaligned distance vs. the secondary current.

[0090] Another technique is to measure the resonant tank impedance, Ztank, which refers to the series capacitor C1 and the self-inductance of the AC coil. The resonant tank impedance, Ztank , is a function of the pad position as the ac coil self inductance, L i, varies with DC, as shown in FIG. 9, which shows a simulated self-

- 21

RECTIFIED SHEET (RULE 91.1) inductance of the ac coil for varying horizontal misalignment. The method perturbs the voltage such that the current is regulated and the duty cycle of the voltage becomes a measure of the resonant tank impedance. Thus, the self-alignment time can be optimized by observing the duty cycle.

[0091] Ztank can be approximated by applying a small perturbation, Vpenurb, as shown in FIG. 10(a), to the resonant tank. By setting the perturbation frequency, f_s, near the resonant frequency, f_r, the tank current, iperturb_, will be sinusoidal with the higher-order harmonics being attenuated due to the high-Q of the resonant tank. As the pads begin to align, i perturb increases and peaks when the compensation capacitor, C , resonants with the nominal value of L·. By setting a threshold, ith, the pads can be considered aligned once i perturb > ith\ allowing the dc coils to be disabled in a timely manner. However, by applying a fixed vpenurb , i penurb increases significantly near alignment due to the high-Q of Ztank. Thus, it is desirable to regulate i pe urb and set a threshold on Ztank which can be estimated by adjusting Vperturb.

[0092] To determine how to control vpenurb, its rms value is calculated according to

[0093] After integrating and average Vpenurb over the perturbation period, T_s, the rms value of Vpe urb is given by

[0094] According to Eq. 2,

can be controlled with the duty cycle, D. By extension, Zm,,_k can then be estimated according to the following equation

[0095] As the transmitter aligns with the receiver pad, i_perturb increases for constant D due to the increase in L·. Therefore, the duty cycle, D, is controlled with a 22

RECTIFIED SHEET (RULE 91.1) PI controller to regulate i_pen_urb as shown in Fig. 10(b). Once Z_ta„k drops below a threshold, Zm, alignment is achieved and the dc coils can be disabled.

[0096] An important aspect of the proposed technique is the selection of perturbation frequency, f_s. Once the dc coils are enabled, Zonk transitions from a capacitive to an inductive impedance. If f_s~ fr, the threshold limit for D could potentially occur earlier than alignment due to variation in the self-inductance; resulting in a significant Dc. To prevent this scenario, fs « fr, causing ZtanAo monotonically decrease since its impedance is primarily capacitive, as shown in Fig. 10(b). Doing so allows the alignment time to be minimized using the condition: D < Dm, where if the condition is true, alignment has been achieved. Having presented an impedance-based detection technique for optimizing misalignment correction, the high-level controller also uses a resonant frequency tracker to minimize gap variation which is presented below.

[0097] For the dc coils to correct misalignment, the system requires that the EV is parked such that the separation gap is approximately 50 mm. However, gap variations occur due to the driver’s parking which results in a weaker F mag. If Fmag is not able overcome the linear slider friction force, Fmction, for larger DC the proposed impedance-based detection technique will never achieve the alignment condition, D < Dm. Therefore, the driver must reduce the gap to improve alignment and efficiency. Along with F_mag, L1 also diminishes with a larger gap, as shown in Fig. 1 1 , which lead to variations in the resonant frequency, f_r.

[0098] By estimating f_r in real time, the driver can adjust the separation gap to a much higher degree. One solution to estimate f_r is to sweep the perturbation frequency, f_s and measure ipenurb Once ipenurb > im, the ac coil self-inductance begins resonating with the compensation capacitor and f_s ~ fr. The disadvantage with this approach is the peak of i perturb will vary depending on Li which can potentially lead to scenarios where \m \s never met or met too early. Therefore, a more robust method is required to determine f_r.

[0099] While the magnitude of i _pe urb will vary depending on the self-inductance, ipe urb peaks at fr as Ztank . is minimized when Zu cancels Zci. By tracking the peak of

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RECTIFIED SHEET (RULE 91.1) iperturb during frequency sweep as shown in Fig. 12(a), the resonant frequency can be determined regardless of the variation in Li during alignment. Having estimated f_r, the system utilizes f_r to minimize the separation gap.

[00100] If there is a large Dc due to weak F_mag after dc coil operation, Li < Li ,_n0m which translates to f_r > fr.nom, as shown in Fig. 12(b). As the driver adjusts the EV to minimize the gap, Li will increase due to stronger coupling and f_r will approach its nominal value. By setting a threshold, f_r.th, on the resonant frequency, the driver has an accurate measure of the gap. Once f_r = fr.th, the impedance-based detection technique can be applied again to reduce x as F_mag is larger with a smaller gap.

[00101] Based on the above, and with reference again to FIG. 8, a determination is made if the transmitter and receiver apparatuses are aligned (814). The controller may determine if the estimated distance between the transmitter and receiver apparatuses is less than a threshold distance to determine alignment. If the transmitter and receiver apparatuses are not aligned (No at 814), a determination is made if there is a large misalignment gap (820), which may be determined based on the iac _pk detector (816) and performing an fac sweep (818). In particular, the frequency f_ac sweep may be performed and the peak current i_ac _pk, detected, which is indicative of the gap between the coils. If there is a large gap (Yes at 820), a communication may be sent from the transmission controller to the receiver controller that the vehicle needs to move position. If there is not a large gap (NO at 820), the transmission controller continues performing the DC current control (808). In some configurations, performing the frequency sweep and determining the peak current may only be performed after the transmitter DC alignment coil is as close to the receiver AC alignment coil as possible, in which case if a sufficient alignment is still not achieved, the transmitter/receiver apparatuses may simply be too far apart.

[00102] A timing diagram of the position-correcting control sequence is shown in FIG. 8A. The diagram demonstrates the scenario where the separation gap Ay is large, which is why alignment cannot be achieved on the initial attempt. By correcting for Ay, the horizontal misalignment can be further reduced which leads to efficient WPT.

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RECTIFIED SHEET (RULE 91.1) [00103] At the receiver apparatus, the position correction operation may determine if the transmitter and receiver apparatuses are aligned (822) based on communication received from the transmitter apparatus. The receiver controller determines if there is a large gap (824), and if so (YES at 824), the car adjusts (826). If there is not a large gap (NO at 824) the receiver apparatus may continue to repeat the position correction operation by repeating DC current control (810) until an affirmative indication is received from the transmitter controller that the transmitter and receiver apparatuses are aligned. When the transmitter apparatus determines that the transmitter and receiver apparatuses are aligned (Yes at 814), the transmitter controller may communicate this determination to the receiver controller by sending a notification to the receiver controller. The receiver controller determines that the transmitter and receiver apparatuses are aligned (Yes at 822).

[00104] Once aligned, the WPT is commenced. The DC alignment coils may become idle and the AC coil starts transferring power from the transmitter apparatus to the receiver apparatus. The AC coil legs in the transmitter apparatus operate as an inverter and supply high-frequency power to the AC coil. The AC coil legs in the receiver apparatus operates as a rectifier. Reverse power flow (for example, vehicle to grid) can be achieved by replacing roles of these legs.

[00105] Aside from rectifying the ac current from the receiver apparatus, the receiver controller communicates with a battery management system (BMS) of the battery which sends commands to the receiver controller to control the charging process. The output power data may be sent to the transmission controller which regulates power by adjusting the bus voltage. Once the battery is charged, the receiver signals the transmitter to stop power transfer.

[00106] The receiver apparatus performs a power calculation (826). The power calculation may be executed using sensed voltage Vout and current lac_rx to calculate the power P during cycle periods as P=average(Vout*lac_rx) with the power calculation unit 722b. The receiver controller is configured to send the result of the power calculation to the transmission controller. The transmission controller performs power control (828). The power control block include generating switching signals for M1 -M4 for the actual transferred power to follow the reference (desired) power level.

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RECTIFIED SHEET (RULE 91.1) The generation of the switching signals may be based on the received power calculation. During power transfer the efficiency may be continuously tracked (i.e. by comparing the transmitted and received power); if the two are seen to diverge (i.e.: something is going wrong, for example an objective is introduced between the plates), for safety the system can shut down and re-attempt after some pre-determined delay, or simply create a warning for the system.

[00107] A determination is made at the receiver controller if the vehicle battery is charged (830). If the battery is not charged (No at 830), the wireless power transfer continues and the power calculation is executed (826). If the battery is charged (Yes at 830), the receiver controller communicates to the transmission controller that the charging is complete. The transmission controller makes a determination if the charging is complete (832). If the charging is not complete (No at 832), the transmission controller continues to transmit power to the receiver apparatus and power control is executed (828). If the charging is complete (Yes at 832), the transmission controller stops transmitting power to the receiver apparatus and the transmission apparatus becomes idle (834). The car may leave the power transmission system (836), or may remain parked.

[00108] The operation described with reference to FIG. 8 is provided for the sake of example and modifications to this method can be made without departing from the scope of this disclosure. For example, the transmitter apparatus may initialize the charging operation with the receiver apparatus instead of the other way around; the receiver apparatus may be configured to determine alignment instead of the transmitter apparatus; the receiver apparatus may instead supply electric power to the transmitter apparatus, etc.

[00109] Simulation and experimental results of an exemplary wireless power transmission system is now described.

[001 10] FIG. 13 shows a WPT setup consisting of (a) a secondary electro magnetic based coil and (b) a solenoid coil mounted inside the electro-magnetic based coil. The WPT setup in FIG. 13 comprises a transmission apparatus 1302 mounted on a support frame 1320, and a reception apparatus 1330. The transmission

- 26 -

RECTIFIED SHEET (RULE 91.1) apparatus 1302 comprises a steel core 1304 and copper windings 1306 as seen in FIG. 13(a). As further seen in FIG. 13(b), the transmission apparatus further comprises a power transmission coil 1308 comprising Litz wire, for example, a copper shield 1310, and a plurality of ferrite bars 1312. [001 1 1] Misalignment correction is performed by an electro-magnetic coil, denoted as the dc coil, which is activated by applying dc current, creating a magnetic force, Fmag as shown in Fig. 13(a), between the apparatuses. Self-alignment is possible due to the transmitter pad being movably mounted on the support frame such as a low-friction linear slider which enables horizontal motion. The power transfer coil, denoted as the ac coil, as shown in Fig. 13(b), performs WPT once alignment is achieved.

[001 12] The dimensions for both the transmitter apparatus and receiver apparatus depicted in Fig. 13 are given in Table I. These dimensions can be scaled for different power levels, or different gap distances. To achieve a compact design, the dc coil serves as a structural case for the ac coil with both being integrated perpendicular to each other. The chosen orientation of the coils reduces the circulation of the ac coil magnetic flux density in the dc core. Nevertheless, there is still leakage flux from the ac coil during WPT that induces eddy currents in the dc core, causing shielding to become critical for this apparatus which leads to lower dc core loss and improves the efficiency.

Table I: Dimensions of Dual-Coil Charging Pads

[001 13] The core of the dc coil is constructed with low-cost carbon steel. The dc coil is implemented with standard copper windings, as there is no need for Litz wire.

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RECTIFIED SHEET (RULE 91.1) As the transmission and reception apparatuses align, the magnitude of Fma_g increases due to stronger magnetic coupling. However, the direction of the F_mag vector shifts from along the linear slider towards the receiver, causing a decrease in F_mag,x, as shown in Fig. 13(a), that directly contributes to self-alignment. Thus, to achieve a wide misalignment correction range, F_mag.x must be sufficiently large to overcome the linear-slider friction force for misalignments that are comparable to the width of the transmission apparatus, which is 200 mm in this design.

[00114] The thickness of the steel core, d, which impacts the cost and weight of the charger system, was selected to generate sufficient F_mag,x, as shown in FIG. 14A. For d < 4 mm, F_mag.x diminishes significantly while only a marginal increase in F_mag,x is observed for d > 6 mm. Hence, d was chosen to be 8 mm to overcome the slider friction force over a wide range of x. While a lighter core results in lower friction force and core loss during WPT, F_mag also diminishes with smaller d; allowing for optimizations.

[001 15] To increase F_mag further, the dc steel core was extended by a height, hext, as shown in FIG. 13B. By increasing the surface area of the steel core, the magnetic flux linkage between the two coils increases; allowing for larger F_mag for a given idc, as shown in FIG. 14B. By increasing h_ext from 10 mm to 25 mm, F_mag,x increases from 3.99 N to 5.04 N; a 26.3% increase. In this way, F_mag.x is increased independently of d, hence with a minimal impact on the dc core mass.

[001 16] The ac coil includes ferrite bars to improve the magnetic coupling, while Litz wire is used for the windings to minimize skin effect losses. The ferrite bars were designed to optimize the inductance and coupling of the coils for WPT. The ferrite bars are housed within a custom 3D printed case capable of withstanding high temperatures while remaining lightweight. The height of the ac coil, /?soi is determined by: h-soi h-pad 2/l ext (1 )

[001 17] where h_{P ad} = 210 mm and he t = 25 mm. The ferrite bars are spatially distributed across the ac coil. The nominal ac coil design parameters are provided in Table II. Due to the rear placement of the charger pad, the separation gap is not

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RECTIFIED SHEET (RULE 91.1) limited by the vehicle suspension, where 120 mm is typically needed. A nominal separation gap of 50 mm is feasible; resulting in a coupling coefficient, k, of 0.41 ; an 87.9% increase as compared to conventional coil designs.

TABLE II: Ac Coil Design Parameters

Designed parameters meter V Unit

Self-Inductance, L_a 129 ( ll Mutual Inductance. A I 53.3

Coupling Coefficient, k 0.41

Switching Frequency, / 85 kHz

Resonant Capacitor, C_\ 27.17 nF

[001 18] The simulated mutual inductance versus horizontal misalignment, Dc, is shown in FIG. 15A. The mutual inductance begins to decrease rapidly for Dc > 20 mm. At Dc = 100 mm, there is zero coupling between the apparatuses due to the symmetric positioning of the coils canceling the magnetic field. However, the self-alignment of the dc coils ensures a small Dc; resulting in high mutual inductance during WPT. The impact of the separation gap, y, is much more significant for the charger operation as the dual-coil charging apparatus cannot correct for any y. The mutual inductance varies almost linearly with the separation gap, as shown in FIG. 15B. However, by leveraging the rear placement of the system, the gap can be directly adjusted by the driver to maintain high mutual inductance as described herein. [001 19] Since one possible application of the proposed charger is fleet vehicles, the payload of the EV could create variations in the compression of shock absorbers; resulting in vertical misalignment, z, between the transmitter and receiver pads. Given that the dc coil self-corrects for horizontal misalignment, x, the ac coil structure was selected based on its tolerance against z. Three coil structures shown in Fig. 1 , Spiral, DD, and solenoid, were simulated to compare their mutual inductances versus vertical misalignment, as shown in Fig. 16 (DD-type coil represented by line 1602, solenoid- type coil represented by line 1604, spiral-type coil represented by line 1606). Based on Fig. 16, the solenoid coil structure was selected since it maintains 18% of its

- 29 -

RECTIFIED SHEET (RULE 91.1) nominal mutual inductance despite a 150% increase in vertical misalignment which normalized to a coil width of 200 mm.

[00120] The simulated magnetic field distribution of the coil system during misalignment correction and WPT were examined. To prevent interference of magnetic fields, the dc and ac coils are physically integrated perpendicular to each other. Doing so prevents the magnetic field from causing additional core losses in the steel core of the dc coil. During WPT, the magnetic field in the dc coil is nearly zero due to the copper shield.

[00121] The simulated efficiency versus misaligned distance, Dc, at 5 kW WPT is shown in FIG. 17A. The efficiency was determined by extracting the lumped element model of the coil structure using Finite Element Analysis (FEA) simulation tools and then running a circuit-level simulation including non-ideal switches in PLECs. Losses due to magnetic fields such as core loss and eddy current loss are also included by using FEA tools. A maximum efficiency of 96.5% is achieved when the pads are perfectly aligned. The system maintains high efficiency up to x = 20 mm. the loss breakdown of the dual-coil charging pad is shown in FIG. 17B at Vout = 400 V and 5kW WPT. The eddy current loss in the shield is approximately equal to the loss in the ferrite cores which is due to the usage of a solenoid coil structure. However, the superior tolerance over vertical misalignment, as shown in Fig. 15, exhibited by the solenoid coil is important due to the EV payload.

[00122] The simulated magnetic field distribution of the coil system at 5kW WPT is shown in Fig. 18 under two conditions; x = 0 and 80 mm. The magnetic field is well contained within the coil system at x = 0, as shown in Fig. 18(a). At x = 80 mm, the magnetic field dramatically increases to 15 mT and the transmitter current increases from 13.5 rms to 59.1 Arms due to the magnetic field linkage between the ac coils diminishing. This corresponds to the steep efficiency drop in Fig. 17A around x = 80 mm. Note that the efficiency at x = 100 mm is not presented, since WPT is not feasible due to the excessive current required. The operation of the proposed charger is not affected by low-efficiency operating conditions caused by horizontal misalignment as WPT only occurs after the position correction process is performed.

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RECTIFIED SHEET (RULE 91.1) [00123] FIG. 19A shows the simulated magnetic force in the x-direction, Fmag.x , with respect to horizontal misalignment, Dc. With z = 0 mm, Fmag.x peaks at 5 N and is able to overcome the friction force from Dc = 20 mm to Dc > 200 mm, which is the coil width in this design. Similarly, even Dz = 60 mm, Fmag x \s able to overcome the friction force over range of x. Assuming Idc = 30 A, the minimum self-alignment time for x = 200 mm is 359 ms at Dz = 0 mm and 730 ms at Dz = 60 mm, which is too short of a time for the temperature of the do coils to saturate. Therefore, the winding thickness of the DC coils can be smaller. The vertical magnetic force, Fmag.z, versus vertical misalignment, z is shown in FIG. 19B. If z is significantly large, the vertical misalignment in the z-direction can be resolved by the DC coils as well by using an additional linear slider and installing counter weights.

[00124] To achieve a charging time comparable to traditional on-board wired chargers, the WPT system was designed for Level-2 AC charging ports with a power rating of 5 kW. However at relatively high power transfer, it becomes necessary to increase the magnetic coupling of the coils to reduce leakage flux. To accomplish this, separate ferrite bars are used in solenoid coils as their low reluctance channels the magnetic flux through the bars from transmitter to receiver. Due to the high cost of ferromagnetic material, the minimum amount of ferrite volume is used. The custom fabricated bars are distributed across the solenoid coil to distribute the magnetic flux. The spacing is necessary, otherwise the temperature of the ferrite bars increases due to the high core loss associated with high magnetic flux density. To understand the effect of ferrite bar spacing on power transfer, an analysis of the magnetic flux density, B, in the solenoid coil is required. FIG. 20 shows a representation of a magnetic flux density distribution of the solenoid coil; the increase of flux density at the edges of the solenoid results in higher core loss.

[00125] Assuming steady-state sinusoidal current flow in an infinitely long straight wire, a steady-state sinusoidal flux density, B wire, is generated around the wire according to:

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RECTIFIED SHEET (RULE 91.1) [00126] where mo is the magnetic permeability, I is the current through the wire, and r is the distance away from the wire.

[00127] The magnetic flux density distribution of the solenoid coil is shown in Fig. 20. Ferrite bars placed near the center of the coil are exposed to the Litz wire on the front and back sides; causing them to experience a magnetic flux density of 2 c Bwire. Approximating the Litz wire at the top of the solenoid as a straight wire, the ferrite bars placed at the solenoid edges are exposed to the Litz wire on three sides; resulting in a magnetic flux density of 3 x Bw^. The higher B results in a higher core loss in the ferrite bars near the edges as compared to the ferrite bars near the center. The high core loss limits the maximum power transfer since the resulting increase in core temperature cannot be reduced by convection cooling.

[00128] A potential solution is to use a uniform block of ferrite as opposed to multiple bars, which results in a lower reluctance. This distributes the magnetic flux such that lower B is experienced at the solenoid edges at the expense of increased ferrite volume and cost. Another approach, which may be used in accordance with some embodiments, is to use ferrite bars with non-uniform spacing near the solenoid edges, where higher B is expected. Electromagnetic simulations of the ac coil were performed at 5kW WPT as the spacing of the ferrite bars was varied to determine its effect on the magnetic flux density distribution, as shown in Fig. 21. By increasing the concentration of ferrite bars near the edges of the ac coil as shown in Fig. 21 B, the peak magnetic flux density decreases from 260 mT to 208.2 mT; a 20% reduction without increasing the total volume of ferrite material.

[00129] Although ferrite bars increase the magnetic coupling, the solenoid coil structure still suffers from significant leakage flux that induces eddy currents in the dc core, causing core loss according to:

Pr = * /" B^b. (6)

[00130] where P_v is the time average power per unit volume in mW/cm³, f is the frequency in kHz, and k, b, and a are empirically determined coefficients based on the B-H curve of the material. To mitigate this effect, a copper shield is placed between

- 32 -

RECTIFIED SHEET (RULE 91.1) the ac coil and dc coil, as shown in Fig. 13(b). While a shield reduces losses in the steel core, eddy currents are generated in the shield which results in ohmic losses as well. Due to the skin effect, the high-frequency eddy currents circulate primarily within a penetration depth of 0.224 mm which is calculated according to:

[00131] where d is the penetration depth, p is the resistivity of copper, f is the frequency, and m is the magnetic permeability of copper. To account for the skin effect, the shield thickness was varied in simulation to reduce the eddy current losses, as shown in Fig. 22. As expected, the eddy current loss, P_e, increases significantly below a shield thickness of 0.3 mm as the thickness approaches the penetration depth. A shield thickness of 0.5 mm was selected to achieve a low eddy current loss of 49.3 W without increasing the total mass of the pad significantly.

[00132] To optimize the copper shield design, the effect of implementing a shield with a continuous sheet versus multiple isolated pieces of copper was compared. Due to the U-shaped steel core, a continuous sheet of copper must be bent to properly shield the steel core from leakage flux. Due to manufacturing imperfections, air gaps between the shield and core exist when the copper sheet is bent to cover the corners of the steel core, which leads to dc core loss. Hence, an alternative solution is to create a shield from multiple isolated pieces of copper that have no gaps. Since eddy currents are induced in the shield, the distribution of eddy currents in shields composed of both a continuous sheet and multiple isolated pieces of copper are investigated.

[00133] A copper shield exposed to a time-varying magnetic flux density, Bsoienoi_d, is shown in Fig. 23(a). By Faraday’s law of induction, an opposing electromotive force (EMF), E, is generated according to:

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RECTIFIED SHEET (RULE 91.1) [00134] where cpsoienoi_d is the magnetic flux due to Bsoiemi_d over a certain area, A. The EMF results in circulating eddy currents which generate an opposing magnetic flux density. To understand the current distribution of theshield composed of multiple isolated copper pieces, the continuous sheet is split into three pieces, as shown in Fig. 23(b). By doing so, the eddy currents are constrained to each individual piece of copper which causes the current density around the boundary to increase. In the case of the continuous sheet of copper, the eddy current is lower near the center since the current circulates along the edges of the sheet. Thus, a shield composed of multiple isolated pieces of copper incurs more eddy current losses than a shield composed of a continuous sheet.

[00135] Electromagnetic simulations were performed to observe the current density distribution in the copper shield, as shown in Fig. 24. As expected, the current density increases significantly along the boundaries of copper pieces, as shown in Fig. 24(a), due to the eddy currents being constrained to each piece. To reduce the eddy currents, a copper tape of 88.9 pm thickness is used to electrically connect the multiple isolated pieces of copper which allow the eddy currents to circulate around the entire shield.

[00136] To account for the resistance of the copper tape in the simulation, each piece of the shield is connected with an 88.9 pm strip of copper. The copper tape reduces eddy currents significantly, as shown in Fig. 24(b), with the peak current density decreasing from 1.08x10⁹ A/m² to 8.13x10⁸ A/m². This translates to a decrease in eddy current losses from P_e = 238.4 W to P_e = 69.6 W; a 71 % reduction. While copper tape does reduce eddy current circulation, the main limitation of copper tape is its thickness which is much smaller than the penetration depth of copper at 85 kHz. Thus, due to the skin effect, the current density is still relatively higher along the boundaries, as shown in Fig. 24(b).

[00137] To mitigate this effect, a shield composed of a continuous sheet of copper was simulated to observe the eddy current density, as shown in Fig. 24(c). The current density is much smaller in the continuous sheet of copper, as shown in Fig. 24(c), with a peak of 5.74x107 A/m² as compared to 8.13x108 A/m² in the shield with copper tape. The current density peaks around the boundaries of each copper

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RECTIFIED SHEET (RULE 91.1) piece in Fig. 24(a) and (b), whereas it stays relatively uniform for the continuous sheet of copper, as shown in Fig. 24(c). This is primarily due to a thicker connection at each bend in the continuous sheet of copper which reduces the current density. In terms of eddy current loss, the continuous sheet of copper performs much better with Pe = 49.3 W as compared to Pe = 69.6 W for the copper tape shield; a 29% reduction.

[00138] A prototype of the proposed charger composed of the coil system and power electronics was fabricated, as shown in Fig. 25(a). The efficiency and alignment time of the dual coil system was measured against different parameters such as separation gap, vertical misalignment, and EV battery voltages to characterize its performance in real-world charging scenarios.

[00139] All switches in the converter are implemented with Silicon Carbide (SiC) MOSFETs with forced air cooling, as shown in Fig. 25(b). The system could also be liquid or air cooled on either the transmitter or receiver side. Additionally, alternative power semiconductor technologies, such as silicon and gallium nitride, are also suitable. To achieve synchronous rectification, the ac coil current is sensed using a high-bandwidth hall-effect current sensor whose output is sampled using a parallel 10-bit Analog-to-Digital Converter (ADC). The digital controller, which is implemented on a Field Programmable Gate Array (FPGA), commutates the MOSFETs whenever the ac current switches polarity using a Zero Cross Detection (ZCD) circuit.

[00140] For misalignment correction, a pulse of current is applied to generate a magnetic force. The dc coil current is regulated using Average Current Mode Control (ACMC), as shown in Fig. 26. The battery voltage, V_bat, is also sensed to prevent overcharging of the EV battery. A Zigbee™ module coordinates the power flow between the transmitter and the receiver.

[00141] The dc coil magnetic force versus DC for varying Lc is shown in Fig. 27. The static and dynamic friction forces of the linear guide were measured to be 0.76 N. Based on this measured friction, the magnetic force of the dc coil can overcome the friction force when 20 mm < DC < 240 mm at 1* = 30 A. The prototype is capable of correcting horizontal misalignment ranging from DC = 240 mm which is 20% larger than the apparatus width.

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RECTIFIED SHEET (RULE 91.1) [00142] The position of the WPT pads during the alignment process was measured for varying Idc, as shown in Fig. 28, using a 240 frames per second (FPS) video camera. With a 1.5x increase in Idc, from 20 A to 30 A, the alignment time is reduced by 3.1 x, from 6.2 s to 2 s. Overshoot occurs during the alignment process when Idc = 30 A with the pad settling to Dc = -1 1.5 mm. Based on Fig. 17, this overshoot should not degrade the efficiency, which remains relatively constant for Dc < 20 mm.

[00143] The position-correcting process was performed for varying separation gap, Ay, as shown in Fig. 29. The system aligns well for small separation gaps with the coil overshooting and settling to Dc = -1 1.5 mm due to the large magnetic force at Ay = 50 mm. Due to this overshoot, the alignment time decreases from 2 s to 1.75 s, a 12.5% decrease, when Ay is increased to 60 mm. However, as Ay is increased from 50 mm to 80 mm, the magnetic force diminishes significantly such that the alignment time increases from 2 s to 2.5 s, a 25% increase, while the alignment error increases from Dc = -1 1.5 mm to Dc = 25 mm.

[00144] The position of the dc coil during self-alignment for varying vertical misalignments, Dz, was also measured, as shown in Fig. 30. The alignment time varies by 6.25% for Dz < 25 mm; approximately 12.5% of the coil width. Slight overshoot occurs due to the large magnetic force at Dz = 0 mm which results in a slightly larger alignment time under perfect conditions. The system is capable of mitigating horizontal misalignments up to Dz = 43 mm with the charging pad settling to within 15 mm of perfect alignment. Beyond this, an increase of 25% was observed in the alignment time when Dz = 68 mm was applied. The apparatuses settle with a large D^c with an increase from 5 mm to 78 mm being observed when D_z = 68 mm.

[00145] The voltage and current waveforms of the converters at 5kW WPT are shown in Fig. 31. \A, _Swas adjusted manually to achieve the desired Ri, . The system efficiency, including the inverter, rectifier, and coil losses, was 90.1 % at 5kW WPT. The square wave ac voltages, v_acJX and v«r__rY were applied to the transmitter and receiver ac coils, respectively. The resulting sinusoidal ac currents, ^and i„c ; verify that the SS compensation capacitors, G and C2, resonate with the ac coil.

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RECTIFIED SHEET (RULE 91.1) [00146] The proposed WPT charger was operated at 5 kW for three minutes to determine its preliminary thermal performance, as shown in Fig. 32. The copper shield appears to mitigate core losses in the dc steel core. The peak temperature of the charging pad is 87.7° C, as shown in Fig. 32(a), which occurs on the receiver copper shield. The inverter/rectifier PCBs utilize fan-mounted heatsinks with forced-air cooling for the full-bridge converter. This results in the transmitter and receiver MOSFETs reaching a peak temperature of 47.6° C and 49.7° C, respectively, as shown in Fig. 32(b) and (c).

[00147] The efficiency was measured for varying V , as shown in Fig. 33. For Pbat > 2.5 kW, the efficiency remains relatively flat with only variations of 2%. The efficiency degrades significantly at low Pbat due to the large iacjx required for the magnetic field linkage between the ac coils.

[00148] With modern parking sensors and on-board cameras, it is reasonable to expect that the EV should be capable of parking within 50 mm of the transmitter pad. However, to account for variations in the parking sensors, the efficiency was measured for varying separation gap, as shown in Fig. 34. The efficiency degrades linearly with the separation gap; justifying the importance of minimizing the gap by placing the charger on the rear of the EV. The charger is less susceptible to gap variations at rated Pbat with only a 4.9% drop at 5 kW as compared to a 10.3% drop at 2 kW; incentivizing charging at high P_bat.

[00149] Given that one possible application of this charger is fleet vehicles, the charger pads will inevitably be subjected to vertical misalignment depending on the payload of the EV. The efficiency was measured against vertical misalignment for varying Pout, as shown in Fig. 35. The efficiency varies by only 1.4% for DZ < 36 mm, approximately 18% of the pad width, which indicates good tolerance against small vertical misalignment. This correlates to the performance of the position-correcting coil which also tolerated vertical misalignment up to 25% of the coil width. However, the efficiency significantly degrades as DZ approaches 90 mm, approximately 45% of the pad width. Also note that the overall degradation in efficiency is much smaller at 5 kW, 7.7%, as compared to 14.5% at 2 kW.

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RECTIFIED SHEET (RULE 91.1) [00150] Two custom-made 3D-printed cases were manufactured to vary the spacing of the ferrite bars of the ac coils; one with uniform 10 mm spacing such as depicted in Fig. 13(c) and another with non-uniform spacing as shown in Fig. 13(b). The uniformly spaced ferrite bars were first operated at a power level of 3.7 kW successfully, as shown in Fig. 36(a). However, the coil with uniformly spaced ferrite bars failed when 5kW WPT was attempted with the resulting ferrite damage shown in Fig. 36(b). As the bus voltage, Vbus, was gradually increased to achieve higher power transfer, the uniformly spaced ferrite bars were unable to operate beyond 4kW WPT. It is interesting to note that the visible damage to the ferrite is done in the area directly below the Litz wire, as shown in Fig. 36(b). This validates the simulation results in Fig. 21A, where the peak B was observed directly below the ac coil windings in the top and bottom ferrite bars.

[00151] The non-uniformly spaced ferrite bars were then operated at a power level of 3.7 kW successfully, as shown in Fig. 37(a). WPT was then increased to 5 kW and the coil with non-uniformly spaced ferrite bars achieved successful steady-state operation, as shown in Fig. 37(b), with a dc-dc efficiency of 90.1 %.

[00152] In view of the foregoing, the wireless power transfer system, method, and apparatus disclosed herein are capable of self-position-correction and improve the efficiency of wireless power transfer. Compared to other types of charging systems, such as conventional wireless charging with no alignment mechanism, and wired charging using a robotic arm, efficient wireless power transfer can be achieved with systems/apparatuses that are smaller, lighter, and more cost-effective while maintaining scalability.

[00153] Table III provides a comparison between wireless charging with the wireless power transfer system, method, and apparatus of the present disclosure when vertically mounted, conventional wireless charging with no alignment mechanism, and wired charging using a robotic arm.

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RECTIFIED SHEET (RULE 91.1) [00154] Table III - Comparison of Autonomous Charging Methods

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RECTIFIED SHEET (RULE 91.1)

[00155] It would be appreciated by one of ordinary skill in the art that the system and components shown in the Figures may include components not shown in the drawings. For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, are only schematic and are non-limiting of the elements structures. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described herein.

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RECTIFIED SHEET (RULE 91.1)

Claims

CLAIMS:

1 . A wireless charging system for charging a battery of an electric vehicle (EV), the system comprising:

a support frame;

a wireless power transmission apparatus movably coupled to the support frame, the wireless power transmission apparatus having a transmitter alternating current (AC) transmitter coil and a transmitter direct current (DC) alignment coil; and

a transmission controller coupled to the wireless power transmission apparatus, the transmission controller configured to power the DC alignment coil to align the AC transmitter coil with a wireless power receiving apparatus on the EV, to charge the battery of the EV.

2. The system of claim 1 wherein the DC alignment coil aligns the power transmission apparatus with a receiver DC alignment coil of the wireless power receiving apparatus of the EV.

3. The system of claims 1 or 2 wherein the transmission controller initiates a current to the transmitter DC alignment coil to magnetize the transmitter DC alignment coil to a first polarity opposite a secondary polarity of a receiver DC alignment coil of the EV.

4. The system of claim 3 wherein a magnetic force is generated between the transmitter DC alignment coil and the receiver DC alignment coil that causes movement of the wireless power transmission apparatus in at least one direction along the support frame to align the transmitter AC coil and a receiver AC coil.

5. The system of any one of claims 1 to 4 wherein when the transmission controller determines that the transmitter AC coil of the wireless power transmission apparatus and a receiver AC coil of the EV are aligned, a supply of power to the AC transmitter coil induces a current in the AC receiver coil to charge the battery of the EV.

6. The system of any one of claims 1 to 5 wherein the transmission controller initiates a supply of current to the transmitter DC alignment coil upon detection of the EV.

7. The system of any one of claims 1 to 6, wherein detection of the EV comprises receiving an instruction wirelessly at the transmission controller from a receiver controller of the EV.

8. The system of any one of claims 1 to 7, wherein when the transmitter DC alignment coil and the receiver DC alignment coil are aligned, the supply of the current is stopped to the transmitter DC alignment coil.

9. The system of any one of claims 1 to 8, wherein alignment of the transmitter DC alignment coil and the receiver DC alignment coil is determined by measuring a perturbation current in the transmitter AC coil or the receiver AC coil.

10. The system of claim 9 wherein a perturbation frequency of the perturbation current is swept across a frequency range to determine a gap distance between the transmitter AC coil and the receiver AC coil.

1 1. The system of claim 10 wherein a peak current of the perturbation current from the frequency sweep determines a minimum gap separation between the AC transmitter coil and the receiver AC coil.

12. The system of claim 1 1 wherein the transmission controller provides an indicator to the controller to move the vehicle closer to the wireless power transmission apparatus if the minimum gap separation is larger than a threshold value.

13. The system of any one of claims 1 to 12, wherein the transmitter DC alignment coil and the transmitter AC coil are arranged perpendicular to each other.

14. The system of any one of claims 1 to 13, wherein the transmitter AC coil is any one of: a spiral-type coil, a DD-type coil, and a solenoid-type coil.

15. The system of any one of claims 1 to 14, wherein the transmitter DC alignment coil comprises a DC core and the AC transmitter coil comprises an AC core.

16. The system of claim 15, wherein the DC core is made of steel.

17. The system of claim 15, wherein the AC core is made of ferrite.

18. The system of any one of claims 1 to 17, wherein the transmitter AC coil is made of Litz wire.

19. The system of any one of claims 1 to 18, wherein the transmitter DC alignment coil is made of enamel wire or copper wire.

20. The system of any one of claims 1 to 19, wherein the support frame is any one of: a linear slider, a ball screw arrangement, a pulley and belt arrangement, and a wheel and guide arrangement.

21. The system of any one of claims 1 to 20, wherein the support frame comprises two linear sliders configured to allow for movement in two directions.

22. The system of any one of claims 1 to 21 , wherein the transmitter AC coil comprises a plurality of ferrite bars.

23. The system of claim 22, wherein the plurality of ferrite bars have non-uniform spacing.

24. The system of any one of claims 1 to 23, wherein the wireless power transmission apparatus further comprises a copper shield made of a continuous sheet.

25. The system of any one of claims 1 to 24 wherein the wireless power transmission apparatus moves horizontally along the support frame.

26. A wireless charging system for charging of a battery of an electric vehicle (EV), comprising: a wireless power receiver apparatus mounted on the EV, the wireless power receiver apparatus having a receiver alternating current (AC) coil and a receiver direct current (DC) alignment coil coupled to the battery of the EV; and

a controller coupled to the wireless power receiver apparatus, the controller configured to power the receiver DC alignment coil to allow a transmitter DC coil of a wireless power transmission apparatus to align with the wireless power receiver.

27. The system of claim 26 wherein a DC alignment coil of the wireless power transmission apparatus moves horizontal by a magnetic field of the transmitter DC alignment coil and the receiver DC alignment coil coupled to the battery of the EV.

28. The system of claims 26 or 27 wherein upon alignment of the DC receiver alignment coil with the transmitter DC alignment coil the receiver AC coil inductively receives power from a transmitter AC coil of the wireless power transmission apparatus to charge the battery of the EV.

29. The system of any one of claims 26 to 28 wherein the receiver AC coil can provide power from the battery of the EV to the transmitter AC coil.

30. The system of any one of claims 26 to 29 wherein the controller initiates a current to the transmitter DC alignment coil to magnetize the transmitter DC alignment coil to a first polarity opposite a secondary polarity of a receiver DC alignment coil of the EV.

31. The system of any one of claims 26 to 30, wherein the controller wirelessly sends and instruction to wireless power transmission apparatus to initiate alignment and charging of the battery of the EV.

32. The system of any one of claims 26 to 31 , wherein when the transmitter DC alignment coil and the receiver DC alignment coil are aligned, a supply of the current is stopped to the receiver DC alignment coil and the transmitter DC alignment coil.

33. The system of any one of claims 26 to 32, wherein alignment of the transmitter DC alignment coil and the receiver DC alignment coil is determined by measuring a perturbation current in the transmitter AC coil or the receiver AC coil.

34. The system of claim 33 wherein a perturbation frequency of the perturbation current is swept across a frequency range to determine a gap distance between the transmitter AC coil and the receiver AC coil.

35. The system of claim 34 wherein a peak current of the perturbation current from the frequency sweep is utilized to determine a minimum gap separation between the transmitter AC coil and the receiver AC coil.

36. The system of claim 35 wherein an indicator is provided to the controller to move the EV closer to the wireless power transmission apparatus if the minimum gap separation is larger than a threshold value.

37. The system of any one of claims 26 to 36, wherein the receiver DC alignment coil and the receiver AC coil are arranged perpendicular to each other.

38. A method of wireless charging of a battery of an electric vehicle (EV), the method comprising:

receiving an indicator to commence alignment of a transmitter DC alignment coil of a wireless power transmission apparatus with a receiver DC alignment coil coupled to the EV;

supplying current to the transmitter DC alignment coil;

verifying alignment of the transmitter DC alignment coil with the receiver DC alignment coil; and

supplying current to a transmitter AC coil to inductively charge a battery of the EV through a receiver AC coil when the alignment has been verified.

39. The method of claim 38 wherein verifying the alignment of the transmitter DC alignment coil with the receiver DC alignment coil comprises measuring the AC self-inductance of a perturbation current of the transmitter AC alignment coil.

40. The method of claim 39 further comprising changing a frequency of a perturbation current across a defined frequency range to determine a distance between the transmitter DC alignment coil and the receiver DC alignment coil.

41. The method of claim 38 wherein power to the transmitter DC alignment coil is stopped when alignment is verified.

42. The method of claim 38 wherein the transmitter DC alignment coil is coupled to the transmitter AC coil comprising a wireless power transmission apparatus, wherein the wireless transmission apparatus is horizontally movable along a support frame.

43. A kit, comprising:

the wireless charging system of claim 1 ; and

the wireless charging system of claim 26.