Magnetic coupling structure

Abstract

The present disclosure generally relates to structures for magnetic coupling used in wireless power charging, in particular for loosely coupled or resonant wireless power transfer. In part it relates to a magnetic coupling structure with reflection coils and methods of use of the reflection coils to affect magnetic coupling. In particular it may relate to A magnetic coupling structure comprising: two or more coupled main coils; and two or more reflection coils; wherein the two or more reflection coils are configured to substantially decouple the two or more coupled main coils and / or a method for designing a multi-phase magnetic coupling structure comprising a plurality of main coils; and a plurality of reflection coils.

Description

Magnetic coupling structureTECHNICAL FIELD

[0001] The present disclosure generally relates to structures for magnetic coupling used in wireless power charging, in particular for loosely coupled or resonant wireless power transfer. In part it relates to a magnetic coupling structure with reflection coils and methods of use of the reflection coils to affect magnetic coupling.BACKGROUND

[0002] Magnetic coupling structures improve coupling profiles for wireless power transfer. By designing a magnetic coupling structure (also referred to as a pad) the efficiency and / or ease of wireless power transfer can be improved.

[0003] Mutual decoupling removes all or substantially all coupling between the coils. This allows the coils to act independently, with the current and / or voltage in one coil not affecting the other coils on the pad. However, it is difficult to mutually decouple coils. US11581124 teaches how to decouple two, three, and four coil systems with circular coils. For example, a bipolar pad uses the overlap between two neighbouring coils to offset flux transfer to and from the neighbouring coils. By adjusting the overlap carefully, the flux into and out of each coil is balanced such that the coils are decoupled. In some cases, the overlap is adjusted with consideration the presence of magnetically permeable material (such as ferrite). This is because the magnetically permeable material will affect the coupling and decoupling. Similarly, the presence of a second magnetic coupling structure (i.e., a corresponding transmitter or receiver) may require a change in the overlap to reduce coupling.

[0004] US11031826B2 shows example arrangements of primary coils with reflection coils. A single-phase structure is shown with two coils operated in a complementary manner. Reflection coils are shown to shape the field in the flux coupling region above the structure and / or reduce the field that would otherwise be present behind or below the structure. A three-phase single-sided pad is shown where the primary coils are independently decoupled to remove all or substantially all coupling between the coils. A two-phase track structure is also shown with decoupled coils due to the spatial overlap. Reflection coils are proposed to provide a single-sided field structure.

[0005] It is the intention of the present invention to describe a magnetic coupling structure that substantially mitigates the above limitations, or at least provide the public with a choice.SUMMARY

[0006] In an aspect the disclosure may broadly be said to consist in a multi-phase magnetic coupling structure for a wireless charging system comprising: two or more coupled main coils; and two or more reflection coils; wherein the two or more reflection coils are configured to substantially decouple the two or more coupled main coils.

[0007] Reflection coils are used for reducing leakage fields. However, previously reflection coils have been configured to substantially mirror the main coils and / or only control leakage field. The present disclosure explains that the reflection coils may also be tuned to decouple the main coils. This means that the main coils can be designed as (or provided as) coupled coils, with the reflection coils acting to remove or reduce this coupling between main coils. This may be achieved by determining one or more of a geometry, size, orientation and / or shape of the reflection coils to result in the required mutual couplings between the main coils becoming substantially zero. Typically, the reflection coils are thereby also decoupled. By this method a system is created which has decoupled coils, but where removal of the reflection coils would result in coupled main coils. This can simplify the creation of magnetic coupling structures because there is greater freedom of choice in the arrangement of main coils. This can include main coils arranged in positions where they cannot be decoupled without the reflection coils. For example, a linear arrangement for transferring power along a direction of movement is not decoupled using the main coils alone but can be decoupled with the reflection coils.

[0008] Optionally the main coils and reflection coils form a primary structure, which may be referred to as a ground assembly. A ground assembly contains the coils present for the primary of a wireless power transfer system. The ground assembly comprises the main and reflection coils. In some cases, such as for car charging the ground assembly is built into a lower surface such as a floor or a road. In some cases, all of the main coils in the ground assembly are substantially decoupled. The main coils may be alternatively referred to as driving coils, secondary coils or primary coils. This is because they are configured to transfer power, in use, or are located in a primary or secondary structure. If the magnetic coupling structure is a primary magnetic coupling structure it may be configured to transfer power to an associated secondary. However, it is also possible for the magnetic coupling structure to be a secondary magnetic coupling structure. A secondary magnetic coupling structure maybe configured to receive power from a primary magnetic coupling structure. A magnetic coupling structure may be configured to both transmit and receive power.

[0009] Optionally the main coils and reflection coils form a secondary structure. The secondary structure contains the coils present for the secondary of a wireless power transfer system and / or is configured to receive power. The secondary structure comprises the main and reflection coils. In some cases, such as for car charging the secondary structure is built into the floor of a vehicle, such as a car. The secondary structure may form a surface, such as a surface of an electronic device. In some cases, all of the main coils in the secondary structure are substantially decoupled. The main coils may be alternatively referred to as secondary coils or receiving coils. This is because they are configured to receive power from an associated main structure, in use. In some cases, a magnetic coupling system comprises the described magnetic coupling structures for both primary and secondary coupling structures.

[0010] Unless otherwise specified the described magnetic coupling structures should be understood to be suitable as either or both of primary or secondary coupling structures.

[0011] The main coils and reflection coils may form a unitary structure, or they may be separate structures. The main and reflection coils may be configured within a housing. The housing may be a frame or one or more supports. The frame or supports may be configured to to secure or mount the coils in a desired position relative to one another and / or the housing.

[0012] Although described herein with respect to vehicle charging, and in particular, dynamic vehicle charging on a roadway, it will be understood that the applications of the described examples are applicable to other wireless charging examples. For example, the magnetic coupling structure could be applied to stationary charging. This would enable a common coupling structure (for example on a vehicle) to charge or couple with both stationary and dynamic chargers. For example, the magnetic coupling structure could be used with electronic devices. The reflection coils may remove the need for a magnetically permeable material (e.g. ferrite) layer, providing a lighter electronic device. The magnetic coupling structure may be ferrite-less. For example, the main and reflection coils may be arranged in layers of a printed circuit board (PCB), optionally opposing layers or opposing surfaces of a PCB.

[0013] Optionally the reflection coils are smaller than the main coils. Optionally the reflection coils have a smaller length and / or width than the main coils. Optionally the reflection coils are larger than the main coils. Optionally the reflection coils have a greater length and / or width than the main coils. Optionally the combined area of the reflection coils is smaller than the combined area of the main coils.

[0014] The length and width of the coils are expressed relative to the direction of the poles (or the direction of the centers of the coils) where the length is parallel to the poles and the width is perpendicular to the poles. In some cases, this may result in the respective widths of the main and reflection coils being perpendicular.

[0015] The present examples show smaller reflection coils than main coils. However, the reflection coils may be larger than the main coils. For example, where more space is available for the reflection coils, or larger reflection coils improves control of flux leakage.

[0016] Optionally one or more, or each of the coupled main coils is associated with a corresponding one of the reflection coils. Optionally the magnetic coupling structure comprises a plurality of pairs of main and reflection coil. Pairs of main coils and reflection coils may be referred to as associated main and reflection coils. Optionally the magnetic coupling structure comprises one or more main coils without an associated reflection coils.

[0017] Arranging the main and reflection coils in pairs, or associating main and reflection coils, simplifies the decoupling of the main coils because the connected or associated main and reflection coils are coupled. This coupling, for example by electrical connection means that the coils work in combination. Therefore the magnetic coupling structure comprises coupled associated main and reflection coils, while the main coils are decoupled from one another. In some cases, each associated main and reflection coil forms a phase of the multi-phase system. The decoupling may referred to as interphase decoupling. In some cases, only a portion of the phases have associated reflection coils. Optionally associated main and reflection coils are configured in the same order relative to the other coils. In some cases each associated main and reflection coil at least partially overlap. Optionally each main and reflection coil pair at least partially overlap.

[0018] Optionally one or more of the main coils and the associated reflection coils are configured to have an inverted current polarity. Optionally each of the main coil and reflection coil pairs are configured to have an inverted current polarity. Optionally the coils are configured to have an inverted current polarity by being electrically connected andwound in opposite directions. Optionally two or more of the reflection coils are configured to have reversed current polarities relative to their associated main coils.

[0019] The reversed current polarities in the reflection coil may improve decoupling because the reversed polarity increases the opposition of the reflection coil flux to the main coil flux. This means that interphase couplings between the main and reflection coil oppose the interphase couplings of the main coil only. Only a portion of the reflection coils being out of phase with the main coils may lead to improved flux cancellation. In a three-phase example, having at least two of the reflection coils configured with reversed current polarity compared to the main coils configures the fields produced by the reflection coils to cancel those fields produced by the main coil.

[0020] The opposition of the interphase couplings of only the main coils allows, in some cases, the reflection coil depth (e.g.. a distance of the reflection coils from the main coils) to be configured to control the couplings between the main coils and the reflection coils. Finally, the coupling between the reflection coils can be controlled independently. For example, by considering the overlap between the reflection coils. Considering a multi-phase system with N coils decoupling may be assisted if there are reflection coils with opposite polarities relative to their associated main coils (e.g. at least one reflection coil with an opposite polarity to its associated main coils). The flux generated by the reflection coil(s) with opposite polarity may help to counteract the coupling flux of the main coils.

[0021] Optionally a central main coil (for example, a third main coil) is configured to have an offset, or reversed, current polarity compared to the outer main coils. The outer main coils may be second and first main coils.

[0022] Optionally the main coils have balanced coupling (i.e. the coupling is the same between each of the respective coils). Optionally the main coils are configured to have asymmetric coupling. Optionally the main coils are arranged linearly. Optionally the poles of the main coils are arranged in a line. Optionally the line is configured to be in a direction of movement of a secondary coil.

[0023] One advantage of the described system is that it allows coupled main coils to be decoupled. This may improve performance of, for example, balanced coils. This is because the use of the reflection coils either avoids additional work to decouple main coils by rearrangement and / or overlap or allow geometries in which main coils could not otherwise be decoupled t.

[0024] One example is a magnetic coupling structure configured to transfer wireless power to a moving secondary coupling structure. Advantageously, the magnetic coupling structure extends along the direction of movement to increase the length of charging time. However, this means that it is difficult to use a symmetric magnetic coupling structure. One solution is to provide a linear arrangement of main coils. The main coils are therefore asymmetrically coupled, as, in a three-coil example, the central coil is completely overlapped, while the outer two coils have portions which do not overlap with any other coil. The design of suitable reflection coils allows this arrangement to be decoupled. In some cases, this is referred to as interphase decoupling, as each phase coil in the multi-phase system is decoupled from one another.

[0025] Optionally comprising a three-phase system or being a three-phase system. Optionally the reflection coils are associated with at least two of the phases. Optionally comprising at least three phases. Optionally the reflection coils are associated with main coils of at least two of the phases. In some cases, the magnetic coupling structure does not require reflection coils for each phase. In one example a three-phase arrangement (such as a linear three phase arrangement) does not require a reflection coil for the central coil or phase. Optionally at least one main coil does not have an associated reflection coil. Optionally this is the central coil. The central coil or phase may refer to a coil or phase arranged between at least two other coils. The central coil may completely overlap with the combined other coils.

[0026] Optionally the magnetic coupling structure comprises or is configured with a charging direction. The charging direction may refer to a direction of movement, or an expected direction of movement of a secondary. Optionally the direction of movement is substantially parallel to a roadway. Optionally the direction of movement is substantially parallel to a track or path of a corresponding magnetic coupling structure.

[0027] Optionally the magnetic coupling structure is configured to couple to a moving magnetic coupling structure. For example, the magnetic coupling structure may be a primary configured to couple to a moving secondary, or vice versa. The coupling may allow power transfer from a primary wireless power charging device or pad to a secondary wireless power charging device or pad.

[0028] Optionally the poles of the main coils are configured to align parallel to an expected direction of movement of main coils of the secondary. Optionally the poles of themain coils are configured to align perpendicular to with an expected direction of movement of the main coils associated with the secondary.

[0029] Optionally the plurality of main coils comprise coil centers aligned parallel to the charging direction. Optionally the plurality of main coils comprise coil centers aligned perpendicular to the charging direction. Optionally the plurality of reflection coils comprise coil centers aligned perpendicular to the charging direction. Optionally the plurality of reflection coils comprise coil centers aligned parallel to the charging direction. Optionally the charging direction is substantially parallel and / or perpendicular to the poles of the main and / or reflection coils. Optionally the main and / or reflection coils comprise coil centers aligned parallel or perpendicular to the charging direction.

[0030] Poles refer to the areas of the coils in which magnetic flux enters and leaves the coils. Poles may refer to the substantially center of highest flux region of the entering or leaving of the coils. Pole locations can be calculated or determined in a magnetic coupling structure.

[0031] Optionally the main coils comprise a first and a second main coil extending in a first direction (the charging direction or the direction of movement), and a third main coil is arranged between (and optionally overlapping) the first and second main coils. Optionally the magnetic coupling structure comprises first and second reflection coils, wherein the reflection coils are associated with the second and third main coils respectively. Optionally the first and second main coils are configured to have a reversed current polarity compared to the third main coil. In one example this structure is used for a dynamic (i.e. charging while moving) roadway application.

[0032] Optionally the third main coil is smaller than each of the first and second main coils. Optionally the third main coil has a length (i.e. parallel to the direction of movement) less than each of the first and second coils. Optionally the third main coil has a width (i.e. perpendicular to the direction of movement) less than the first and second main coils. Optionally the main coils have substantially the same width and / or length. Optionally the third main coil, or a dimension of the third primary coil, is approximately 80% the size of the first and second main coils. Optionally the third main coil is between 30% and 95% the size of the first and second main coils. Optionally the third main coil is between 50% and 95% the size of the first and second main coils. Optionally the third main coils is between 50% and100% the size of the first and second main coils. Optionally the third main coil is less than 99%, less than 95%, less than 90% or less than 80% the size of the first and second main coils.

[0033] Reducing the size of the- third main coil reduces the mutual inductances with the first and second main coils. This may simplify the decoupling and / or allow smaller reflection coils. However, reducing the size of the main coil may also reduce the power delivery to the secondary. Therefore, the size of the third main coil is a balance between the power transfer and inductance with the other coils (phases). In symmetrical systems it may be preferable not to reduce the size of any of the main coils to balance the coupling between the coils. In some cases the main coils are substantially similar to one another, or substantially identical. In some case the reflection coils are substantially similar to one another, or substantially identical.

[0034] Optionally the reflection coils and the main coils are parallel or aligned in parallel. Optionally the reflection coils are perpendicular or aligned perpendicularly to the main coils. Optionally the poles of the reflection coils are aligned substantially perpendicular to the poles of the main coils. Optionally the poles of the reflection coils are aligned substantially parallel to the poles of the main coils. Optionally axis of the centers of the reflection coils is aligned substantially parallel and / or perpendicular to a an axis the centers of the main coils. Optionally the center of the reflection coils is aligned substantially below the center of the main coils. Optionally the center of each of the reflection coils is aligned substantially below the center of a corresponding and / or associated main coil.

[0035] The reflection coils may decouple the main coils independently of their relative orientation. In some cases, the orientation of the reflection coils is selected to improve control of the magnetic field leakage. For example, where the magnetic coupling structure is configured to supply power along a roadway the reflection coils may be arranged perpendicularly to the roadway to reduce leakage flux off the roadway.

[0036] In some cases the magnetic coupling structure comprises a loop of main coils (e.g. the main coils are arranged or evenly distributed on the circumference of a loop, such as a circle). The reflection coils may be aligned with each of the main coils, such that a centre of each the main coil is aligned with a centre of a respective or associated reflection coil. In some cases each reflection coil overlaps with a respective or associated the main coil. In some cases the arrangement of the main and reflection coils are substantially similar. Substantially similar arrangements provide balanced inductances between main and reflection coils. Thissimplifies the practical building of the magnetic coupling structure. Balanced inductances also reduce the VA (e.g. the reactive power) in the magnetic coupling structure, or at least mean substantially constant VA, so easier to maintain the VA below a threshold.

[0037] Optionally the coils are configured to be powered by one or more inverters. Optionally each main and reflection coil is configured to be powered by a separate inverter. Optionally each main coil and associated reflection coil is configured to be powered by a separate inverter. Optionally the winding direction of the main coil and its associated reflection coil is reversed. Optionally the reversed winding direction is configured to provide a reversed current polarity between the main and reflection coil. Optionally a multi-phase inverter is configured to power all or a plurality of the main and reflection coils. Optionally the magnetic coupling structure comprises the one or more inverters. Optionally the inverters and associated coils are arranged in a wye-connection and / or a delta connection.

[0038] Optionally the inverters are configured to selectively power any one or more of the main coils and / or any one or more of the associated main and reflection coils and / or any one or more of the phases. In a multi-phase system each main coil is associated with a phase. In the described system each phase may also have a reflection coil. Optionally the inverters are configured to selectively power either all or a subset of the coils and / or phases. Optionally the inverters are configured to selectively power a plurality of the main coils and / or phases in phase. Optionally the inverters are configured to power the plurality of main coils and / or phases offset. Optionally the offset phases are at 360 / n degrees offset, where n is the number of phases. Optionally the inverters are configured to operate two of the main coils as a double D coil. Because the main coils are decoupled they can be operated in one or more selective power arrangements in which a first subset of coils are operated while a second subset of coils are turned off.

[0039] In a coupled system independent operation of the main coils would cause reduced performance due to coupling between the coils causing power loss. Typically, the off period is substantially longer than the frequency of power transfer. For example, the system may identify a type of associated magnetic coupling structure which is, or is to, couple to the magnetic coupling structure. Optionally, based on the type of associated magnetic coupling structure the system is configured to select which main coils to operate and / or the relative phase of those main coils. If a different type of associated magnetic coupling structure (e.g. a secondary) is detected a different selection of main coils may be used. Optionally any one ormore of the main coils is configured to operate independently. Optionally comprising a controller configured to selectively operate any one or more of the main coils (and associated reflection coil) independently of the remaining coils.

[0040] Optionally the magnetic coupling structure comprises first, second and third main coils, and first and second reflection coils. Optionally the first and second main coils are associated with the first and second reflection coils. Optionally comprising a third reflection coil associated with the third main coil. Optionally the third reflection coil is configured to have the same current polarity as the third main coil. Optionally the first and second reflection coils are configured to have a reversed current polarity. Optionally the third reflection coil is arranged between (including optionally overlapping) the first and second reflection coils, the third main coil is arranged between (including optionally overlapping) the first and second main coils

[0041] The third reflection coil may be configured to balance voltages in each phase. The third reflection coil also introduces additional magnetic couplings, which can help to decouple the main coils, therefore reducing the reflection coil sizes.

[0042] Optionally the reflection coils are arranged on the opposite side of the main coils than an expected associated magnetic coupling structure, or an expected direction of power transfer. Optionally the reflection coils are arranged below the main coils. Optionally the reflection coils are buried beneath the main coils. Optionally the reflection coils are arranged on the opposite side of the main coils to a charging surface. Optionally the reflection coils are arranged on, or towards, the bottom of a ground structure or secondary structure.

[0043] Optionally the reflection coils are substantially planar. Optionally the main coils are substantially planar, (e.g. the coils are arranged in a single plane or layer, except for coil overlaps or tolerances etc.). Optionally the reflection coils and main coils are arranged in separated planes and / or the planes are spaced apart. Optionally the main coils are arranged substantially in a first plane and the reflection coils are arranged substantially in a second plane. Optionally the planes are separated by a distance less than 10% of the width of the coils. Optionally the planes are separated by a distance greater than 2% of the width of the coils.

[0044] A planar coil, which may also be referred to as a flat coil extends in substantially one layer. The use of planar coils also has the advantage that a more robuststructure can be provided and is simpler to construct. The planar or pancake like coils may be easily embedded in a casing, for example suitable for a road structure. One or more electrical connections may need to pass under the coils, resulting in the coil not being completely flat. The coil may be formed by Litz wire. Planar coils may be arranged in layers.

[0045] Optionally the main coils are arranged in a first layer and the reflection coils are arranged in a second layer. Optionally the first layer and second layer are spaced apart. Optionally the first layer and second layer are spaced apart by a gap. Optionally the spacing is vertical. Optionally the first and second layer are substantially planar.

[0046] The use of two spaced apart layers reduces coupling between the different phases of reflection and main coils making decoupling with the reflection coils easier, as well as reducing magnetic flux leakage from the back of the magnetic coupling structure.

[0047] Optionally one or more of the coils are substantially circular or substantially rectangular. Optionally one or more of the coils are substantially rotationally symmetrical. Optionally the reflection coils are centered relative to the main coils. Optionally the reflection coils have substantially the same shape as the main coils. Optionally substantially no magnetically permeable material is located between the main coils and the reflection coils. Optionally each of the main coils overlap at least one, optionally all, of the other main coils. Optionally each of the reflection coils overlap at least one, optionally all, of the other reflection coils. Optionally comprising one or more blocks of magnetically permeable materials. Optionally the magnetic coupling structure is configured for vehicle charging. Optionally the magnetic coupling structure is configured for dynamic charging. Optionally the magnetic coupling structure is configured to charge a battery.

[0048] Optionally comprising a primary, secondary or ground structure comprising the magnetic coupling structure.

[0049] In a further aspect the disclosure may broadly be said to consist in a method of designing a multi-phase magnetic coupling structure comprising a plurality of main coils; and a plurality of reflection coils, the method comprising the steps of: Selecting a pole orientation of the main coils and the reflection coils; Optimising one or more, or a plurality, of geometric parameters of the main coils and the reflection coils, Wherein the optimisation requires decoupling of the main and reflection coils and the optimisation objective comprise one or more of: a coupling parameter with the secondary, and a leakage parameter.

[0050] Optionally the main coils are arranged in a first layer and the reflection coils are arranged in a second layer.

[0051] Optionally the plurality of geometric parameters comprise one or more of: A reflection coil distance from the main coils; A reflection coil length; A reflection coil width; An overlap between two or more reflection coils; Any one of the main coil lengths; A main coil width; An overlap between two or more main coils; A spacing between turns of the reflection and / or main coils; A number of turns of the reflection and / or main coils; A distance between the inner surface and outer surface of the main and / or reflective coils; A shape of the main and / or reflection coils, A winding pattern of the main and / or reflection coils.

[0052] Optionally one or more of the geometric parameters are common between each, or a subset of the main and / or reflection coils. Common parameters between at least some of the reflection and / or main coils may provide a more balanced coupling structure and / or simplify construction. Optionally at least two, or each, of the main coils may be substantially the same as one another. Optionally at least two, or each, of the reflection coils may be substantially the same as one another. Optionally, each of the main coils have the same length, or at least the outer main coils have the same length. Optionally, two or more of the coils, or all of the coils, the reflection coils or the main coils, may have the same width so as to span the charging path or roadway.

[0053] Optionally the step of optimising the plurality of geometric parameters comprises selecting geometric parameters for one or more, or all, of the main coils and optimising the geometric parameters of the reflection coils based on the selected reflection coils. Optionally the step of optimising the plurality of geometric parameters comprises selecting geometric parameters for one or more, or all, of the reflection coils and optimising the geometric parameters of the main coils based on the selected reflection coils. In some cases the main coil (or reflection coil) may be of a known or fixed type and the optimization to decouple the main coils may be focused on only reflection coils (or main coils). This may be helpful to retrofit reflection coils to known coupled main coils or magnetic coupling structures.

[0054] Optionally comprising the step of configuring one or more electrical characteristics of each of the main coils and an associated reflection coil. This may introduce opposing magnetic fields. For example, configured a direction of a current in the main and an associated reflection coil.

[0055] Optionally comprising selecting an orientation of the main coils. Optionally comprising selecting an orientation of the reflection coils. Optionally the orientation of the reflection coils is parallel or perpendicular to the main coils. Optionally the orientation of the reflection coils is configured to reduce magnetic field leakage.

[0056] In a further aspect the disclosure may broadly be said to consist in a magnetic coupling structure designed and / or constructed through the above method.

[0057] In a further aspect the disclosure may broadly be said to consist in a plurality of reflection coils configured to substantially decouple an arrangement of main coils when placed a specified distance beneath the main coil. Optionally the reflection coils are arranged in a housing and / or support structure. The housing or support structure may support the relative position of the reflection coils.

[0058] In a further aspect the disclosure may broadly be said to consist in a multiphase magnetic coupling structure comprising a three overlapping main coils and two or more reflection coils. Optionally the two or more reflection coils are each associated with one of the main coils.

[0059] In a further aspect the disclosure may broadly be said to consist in a multiphase magnetic coupling structure comprising a three overlapping main coils.

[0060] In a further aspect the disclosure may broadly be said to consist in a combination of the features of the magnetic coupling structures described herein.

[0061] Features from one or more embodiments or configurations may be combined with features of one or more other embodiments or configurations. Additionally, more than one embodiment or configuration may be used together in a structure or system.

[0062] As used herein the term "(s)" following a noun means the plural and / or singular form of that noun.

[0063] As used herein the term "and / or" means "and" or "or", or where the context allows both.

[0064] The term "comprising" as used in this specification means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0065] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (forexample, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

[0066] This disclosure may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features.

[0067] Where specific integers are mentioned herein which have known equivalents in the art to which this disclosure relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0068] The disclosure consists in the foregoing and also envisages constructions of which the following gives examples only.BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Specific embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein having reference to the figures that follow, of which:

[0070] Figure 1 shows a dynamic vehicle charging system.

[0071] Figure 2 shows an example magnetic charging system with a magnetic charging structure.

[0072] Figure 3 shows example electrical connections of the magnetic charging structure of Figure 2.

[0073] Figure 4a, 4b, 4c and 4d show coupling between two coils.

[0074] Figures 5a and 5b show an example of reflection coils used for decoupling.

[0075] Figures 6a and 6b show an example of reflection coils used for decoupling in a three-phase system.

[0076] Figures 7a and 7b show an example of reflection coils used for decoupling in a two-phase track system

[0077] Figure 8 shows an example circuit diagram of a wireless power system comprising a magnetic charging structure.

[0078] Figure 9 shows example arrangements to drive the main and reflection coils.

[0079] Figure 10 shows an example magnetic coupling system with a magnetic coupling structure.

[0080] Figure 11 shows an example arrangement of main coils for a magnetic coupling structure.

[0081] Figure 12 shows example field shaping of in-road coils which are 12a a rectangular coil, 12b 1 c|> poles along the road, 12c 2c|> poles along the road, and 12d 3c|> poles along the road.

[0082] Figure 13 shows example arrangements of the coils in a ground assembly relative to the charging direction 13a show perpendicular main coil / perpendicular reflection coil; 13b shows perpendicular main coil / parallel reflection coil; 13c shows parallel main coil / perpendicular reflection coil; and 13d shows parallel main coil / parallel reflection coils

[0083] Figure 14 shows an example flowchart for determining an arrangement of main 9main) and reflection (ref) coils.

[0084] Figure 15a, 15b, 15c and 15d show example optimization performance for each of the arrangements of Figure 13.

[0085] Figure 16 shows an example optimized magnetic coupling structure design.

[0086] Figure 17 shows an example optimized magnetic coupling structure design, with a) the main coil highlights and b) the reflection coil highlighted.

[0087] Figure 18 shows example changes in magnetic fields when an example reflection coil is introduced.

[0088] Figure 19 shows a plan view example of a magnetic coupling structure as built.

[0089] Figure 20 shows a side view example of a magnetic coupling structure as built.DETAILED DESCRIPTION

[0090] This description relates to magnetic coupling structures. Magnetic coupling structure may be referred to as pads. In wireless power transfer power is transmitted from a transmitter to a receiver. In some cases, this is reversible, or one or both may be transceivers. Each of the transmitter and receiver has a magnetic coupling structure to improve or assist the power transfer. The magnetic coupling structures comprise one of more coils of wire. The transmitters or transceivers may be referred to as a primary and secondary. Where primary typically refers to a transmitter and a secondary is a receiver. In some cases the magnetic coupling structures may operate as either transmitter or receiver depending on the powertransfer requirements. This may be the case even if they are considered a primary or secondary.

[0091] Wireless power transfer refers to the ability to use magnetic fields to transfer power over a distance. The coils of the magnetic coupling structure are typically driven by resonant circuits to increase the distance that power can be transferred efficiently. Wireless power transfer may also be referred to as inductive power transfer (IPT) or resonant power transfer (RPT). Because of the distances (e.g. an air gap or other space) between the transmitter (also referred to as a primary) and the receiver (also referred to as a secondary) the structures are loosely coupled. This makes the design more complex than, for example, transformers.

[0092] A coil may refer to a loop of wire, such as Litz wire, which is formed into a loop or spiral. Current passing through the coil creates a magnetic field which is used to transmit power to a transmitter coils. Similarly, a coil placed in a magnetic field will have an induced current and act as a receiver coil. Where coils are shown by block representations herein it will be understood this is to simplify the drawing and that the skilled person will be able to construct a suitable winding pattern for the coil based on these drawings. A main coil refers to a coil configured to transmit power to and / or receive power from an coil of an associated magnetic coupling structure. Magnetic coupling structures may be formed from coils arranged in layers. Each layer may be substantially planar, extending substantially further in two dimensions than a third dimensions. The spacing between coils within a layer, and spacing between layers of coils effects coupling.

[0093] A reflection coil is typically used to reduce leakage flux from the main coil, although as described herein the reflection coil is used to decouple the main coils or to ameliorate inter-phase coupling. The main coil may refer to the driving coil (also referred to as a main coil or power transmitting coil) of either a main or a secondary magnetic coupling structure. A coil may alternatively be referred to as a winding or loop.

[0094] The presence of multiple coils on one structure means that the coils typically interact and transfer power between themselves. This reduces the efficiency of and / or maximum power transfer from the structure to an associated structure. In one example, controlling an overlap between coils can balance the transmitted and received magnetic flux between the coils. This can be understood based on Faraday's law of induction and Lenz's law. The change in magnetic flux of time induces a change in magnetic field over the coilarea. The reactive mutual inductance can be minimized when the net magnetic flux into and out of one coil due to anther coil is zero. This is achieved by offsetting magnetic flux into the coil and out of the coil (i.e., magnetic flux perpendicular to the coil) from the other coil. Because the coils receive as much flux as they transmit there is no effect due to the presence of the other coil. In this way the effective coupling can be ameliorated, ideally to zero. This is termed decoupling. However, it is not always possible to decouple coils by controlling an overlap, especially with multi-phase coils and coils arranged linearly.

[0095] To determine if two coils are mutual decoupled simulations or experiments may be used. This may be helpful, particularly where magnetically permeable material or complex geometries are present. However, identifying areas in which the magnetic flux can be offset provides an indication of likely decoupled coils for pads. In many cases, it is difficult to fully decouple coils.

[0096] References to no mutual coupling (or decoupled) herein may therefore be understood as substantially no mutual coupling, or negligible mutual coupling. Therefore, mutually decoupled coils may have a low level of coupling compared to the coupling of the coils with an associated coil for power transfer. For example the coupling between the decoupled coils may be less than 5%, less than 2% or less than 1% of the coupling with an associated coil for power transfer. For example a primary structure may be associated with a secondary structure for power transfer (or vice versa). In this disclosure a bi-polar secondary is described receiving power from a primary magnetic coupling structure. However, other secondaries may be used (or, if reversed other primaries). The secondary is loosely coupled to the main coils of the primary, so as the presence of the secondary is typically not sufficiently to substantially effect the decoupling. In some applications, for example at lower powers, a greater amount of coupling may be acceptable (the coupling still be reduced by the reflection coils). For example, the reflection coils may reduce the coupling to below 15% or below 10% of the expected coupling.

[0097] Some magnetic coupling structures use a magnetically permeable material to enhance or encourage magnetic flux to flow in the magnetic coupling structure. An example magnetically permeable material is ferrite, but any material which has a high permeability to magnetic flux may be used. A suitable magnetic permeability may have a relative permeability of at least 2, at least 3, at least 5, at least 10, at least 50, or at least 100, for example. The magnetically permeable material may be formed by one or more sections (i.e.,bars or blocks) which may have spacing between them. In some cases, a shield layer, such as aluminum, or other metal, is placed behind the magnetic coupling structure, to reduce flux leaving the back of the magnetic coupling structure. However magnetically permeable materials may be difficult to use and / or incorporate in some magnetic coupling structures, and there may sometimes be advantages in avoiding the use of magnetic permeable materials. In some cases magnetic coupling structures are described which are ferriteless.

[0098] Figure 1 shows a dynamic charging situation in which a car 100 with a secondary structure 102 is associated with a primary structure 101. The primary structure 101 may be referred to as a ground assembly as it is located in or on the ground. The primary structure 101 has coil(s) 111. The power electronics 110 may also form part of the primary structure 101. Alternatively, the power electronics 110 is separate to the primary structure 101. The primary structure is connected to a power source 140. The secondary structure 102 may be the same as the primary structure 101. The secondary structure has coil(s) 121 and may have power electronics 120. Alternatively, the power electronics 120 is separate to the primary structure 101. The secondary structure 102 is connected to a load 130, such as the vehicle 100 battery 130 or motor. A similar system may be applied to a different electrical or electronic device, such as any battery powered device.

[0099] Power electronics 110, 120 may comprise one or more inverters configured to convert the power from the power source 140 into a suitable waveform to drive the coil(s) 111. Inverters should be understood to refer to any power electronics configured to produce drive signals for the coils. These include DC-AC converters, or an AC to AC converters, although other systems may be used. Typically the inverters are configured to output a higher frequency output provide a power waveform with a frequency suitable for wireless power transfer. This may be several kHz tens of kHz, or higher. Inverters may power single coils, or may power multiple coils with a magnetic coupling structure 101.

[0100] Coupling k is shown between the coils 111 of the main structure 101 and the coils 121 of the secondary structure. As the vehicle 100 moves along the road (e.g. moving in the x direction as shown) the coupling k may change. Designing coupling structures 101, 102 to reduce this change, or increase the length of road able to transfer power is advantageous. The coupling k may be referred to as the effective coupling (Keff) of the system.

[0101] Figure 2 shows an example magnetic coupling structure 101. The magnetic coupling structure 101 is illustrated as a primary coupling structure 101, but could similarlybe used as a secondary if required. The primary coupling structure 101 is shown coupled to a secondary coupling structure 102. A bipolar secondary is shown but other secondary coupling structures 102 may be used. Figure 2 shows a primary coupling structure 101 with three main coils 200, individual labelled as coils 201, 202, 203. The main coils 200 each partially overlap one another. However, because they extend along a movement or driving direction the overlap between the coils 200 is different. This results in coupling between the coils 200. The coupling between the coils 200 causes the current in one coil 201, 202, 203 to effect the current in the other coils 202, 203, 201, and therefore the power transfer. This can reduce coupling structure 101 performance, particularly with a moving secondary.

[0102] The present disclosure describes how reflection coils 300, shown with individual coils 301, 302 can ameliorate this coupling. The reflection coils 300 are designed to decouple the main coils 200. Advantageously, the reflection coils 300 may also reduce the leakage flux of the system. The reflection coils 300 are arranged below the main coils 200. This is on the opposite side of the main coils 200 to the direction of power transfer or the secondary structure 102. If power is being transferred downward the reflection coils 300 would be in above the main coils 200. Figure 2 shows the reflection coils 200 arranged perpendicular to the main coils 200 (i.e. the axis of the centers of the reflection coils 300 are perpendicular), but they may also be arranged in parallel. Two reflection coils 301, 302 are shown. This is one less than the number of main coils 201, 202, 203. In some cases each main coils 201, 202, 203 has an associated reflection coil 301, 302.

[0103] Figure 3 shows example electrical connections of the magnetic charging structure 101 of Figure 2. A three-phase inverter 115 is used to drive the coils 200, 300. The main coils 200 may be driven with a 120 degree phase shift in a 3-phase system. Although, once decoupled a specific phase shift may not required. As shown, the a-phase coil 202 does not have an associated reflection coil. However, a third reflection coil may be used. The b phase has main 201 and reflection 301 coils and the c-phase has main 203 and reflection 302 coils. The reflection coils 301, 302 are each associated with a single main coil 201, 203, such that each phase has a main and optionally a reflection coil. This coupled arrangement between the associated main and reflection coils assists the decoupling between the main coils. The decoupling may be referred to as inter-phase decoupling because it allows independent operation of each of the phased. As will be described later alternative inverter arrangements may be used..

[0104] Figure 4 illustrates the coupling between two overlapping, planar, circularcoils 401 and 402. Figure 4a shows how current passing clockwise through first coil 401 generates flux 403, 404 entering the centre of the coil 401 in the -z direction. Figure 4b shows how current passing clockwise through second coil 402 generates flux 405, 406 entering the centre of the coil 402 in the -z direction. Figure 4c shows how, by controlling the distance (overlap) between the two coils 401, 402 the flux generated by coil 401 passing into 407 and out of 408 the second coil 402 can be balanced or offset. This means there is equal flux passing into and out of the coil 401. If this flux is balanced the coil 402 is decoupled from coil 401 because coil 401 causes no change in flux in coil 402. Similarly Figure 4d shows the same distance can allow the flux in 405 and out 406 of coil 401 to be balanced when coil 402 is operated. Therefore all the coils are decoupled. However, it is not always possible or convenient to overlap two coils 401, 402. It is also not possible to overlap many desired arrangements of three or more coils. For example, coils extending linearly, or where there are different amounts of overlap of the three or more coils.

[0105] Figure 5 illustrates how reflection coils 503, 504 may be used to decouple coupled main coils 501, 502. The main coils 501, 502 are not overlapped, so current in coil 501 will cause flux (i.e. coupling), epi, in coil 502. However, reflection coil 503 is associated with coil 501 and has inverted phase (a phase shift of 180 degrees). Similarly, reflection coil 504 is associated with coil 502 and has inverted phase. Therefore, there is also coupling rpM1 between coils 501 and 503 and cp2 between coils 501 and 504. If we consider current flowing counterclockwise in reflection coil 503 there is coupling cp4 with reflection coil 504, cp3 with main coil 502 and rpM2 with main coil 501. Similar relationships can be shown starting from coils 502 and 504. Main coil 501 and reflection coil 503 are associated, with an inverted current relationship. Therefore, it can be shown that the main coils can be decoupled if the system is designed so that:rp1 + rp2+ rp3+ cp4 = 0This is achievable by changing the geometric parameters of the main and / or reflection coils. Once achieved this is independent of the driving signals of the main coils 501, 502. Therefore, previously coupled main coils 501, 502 can be decoupled by the appropriate selection of reflection coils 503, 504, or a decoupled system can be designed with main coils 501, 502 that, but for the presence of the reflection coils 503, 504, would be coupled.

[0106] The decoupling with reflection coils can be extended to further phases. A three-phase system is shown in Figure 6. More phases may be added, but additional phases introduce more components to align and arrange so it may be difficult to improve performance further. Figure 6a shows three main coils 510, 520, 530 arranged circularly. Again, because there is no overlap the coils are coupled. Even if the coils 510, 520, 530 did overlap, unless specifically designed as described above, coupling would be present between the coils. Three reflection coils 511, 521, 521 are shown. Each reflection coil 511, 521, 531 is associated with a corresponding main coil 510, 520 530 respectively. In the illustrated case the reflection coils are shown aligned with the associated main coils - i.e., the centers are aligned along the z-axis. The currents in the reflection coils are shown as inverted relative to the associated main coils. Although all six coils are shown with similar shape and size it will be understood that the variation of geometries to decouple the system may cause variation, at least between the main and reflection coils. In some cases the decoupling may use main coils of a first size and reflection coils of a second size, the second size different to the first size.

[0107] Figure 6b shows the same arrangement with a current in reflection coil 531. Again the coupling between the associated main and reflection coils (e.g., 530, 531) cancels. The system allows decoupling of coils 530 and 531 from the other coils by solving:cp 11 + cp21 + cp31 + cp41 = 0 (no coupling between 530, 531, 520 and 521), and cp12+ rp22+ rp32+ cp42 = 0 (no coupling between 530, 531, 510 ad 511).A corresponding equation can be solved to ensure the 520 and 510 coils are also decoupled. Additional phases would require solving for additional couplings between main coils. The increase in phases results in more couplings to ameliorate, although also provides additional variables in which to optimize the coils to decouple them.

[0108] As shown by comparing Figure 6a and Figure 2 the technique is applicable to a range of main coil arrangements. Figure 6 shows a rotationally symmetric 3-phase system, where the coils are arranged in a loop. Figure 2 shows a linear arrangement. Further arrangements may also be used, depending, for example, on the use case of the wireless power system.

[0109] Figure 7, for example shows a two-phase track application. Again, the reflection coils 551, 561 are 180 degrees out of phase with their respective associated main coils 550, 560. The coils 550, 551, 560, 561 are each tracks which extend along the y-axis. Thelength of extension may depend on the use case. The position and / or size and / or structure of the coils is used to create a decoupled system. Two inverters 115 are shown, each inverter 115 driving one of the associated pairs of main 550, 560 and reflection 551, 561 coils. Alternative track shapes and power electronics may be implemented.

[0110] Figure 8 shows a circuit diagram of a wireless power system comprising a magnetic coupling structure as in Figure 6. A multi-phase inverter 115 is used to drive the primary structure 101 comprising the main coils 510, 520, 530 and reflection coils 511, 521, 531. Each main coil is associated with a reflection coil. In this example they are shown electrically connected. Two of the phases (520, 530) are shown with the reflection coils (521, 531) reverse wound, to create and inverse current polarity. Note the dots indicating winding direction. The remaining phase has the same polarity in main 510 and reflection 511 coil. This is optional, and may suit a linear coil rather than the circular arrangement of Figure 6. The inverter 115 has compensation networks 704 to generate the appropriate resonant frequency for wireless power transfer. A bipolar style secondary 102 is shown coupling to the primary structure 101. The two bipolar coils have rectification 701 to provide an output to a load, such as a battery 700.

[0111] Figure 9 shows alternative styles of driving or powering the coils. Although inverters 115 are shown any device suitable for powering wireless power circuits may be used. Typically this requires high-frequency AC power inputs. Figure 9a shows individual inverters 115 driving each associated pair of main coils 202, 201, 203 and reflection coils 302, 301, 303. Figure 9b shows a single inverter driving all three pairs of coils. The coupling M shows that the associated coils are coupled. However, based on the described systems there is no coupling between the phases. In a further example each reflection coil and main coil could be driven separately, with the power electronics controlled to provide inverted current polarities to associated main and reflection coils. However, this requires further control to ensure the current polarity remains consistent so that the coupling between the associated main and reflection coils remains constant. Where individual inverters are used for a subset of the coils, such as each phase or each coil, the inverters may control the current magnitudes and / or phases between the coils. In one example this is used to further control leakage flux and / or depending on the nature of the secondary coil.

[0112] The coils relationships can be applied to the coils 200, 300 shown in Figure 2. In figure 2 there are three main coils 201, 202, 203 and two reflection coils 301, 302. The tworeflection coils 301, 302 are electrically connected (i.e., directly coupled) to the outer main coils 201, 203 with reverses current polarity. The reflection coils form a bipolar overlap. We can consider the inductance matrix (Lp) of the five coils to understand the decoupling mechanism:As we define lr=lPand lrc=lpc because of the electrical connection (although this may also be achieved by suitable power control) these relationships may be simplified:The conditions for inter-phase decoupling (i.e. decoupling of each main coil 200and (if present) the associated reflection coil 300) can be identified as:1) Mpa + Mparb = 0,’2) Mpac + Mparc = 0,’3) Mpbc + Mrbc + Mpbrc + M pcrb — OfBecause these reduce the relationships to a diagonal matrix.

[0113] The reduced relationships simplify the decoupling by making the conditions more straightforward. However, if required, the decoupling the original induction matrix could be considered, for instance if there were limitations on the currents available. The reversed current polarity of the reflection coil benefits inter-phase decoupling because interphase couplings across the main and reflection coils oppose the inter-phase couplings of the main coils only. This means that the reflection coil depth ZR can be adjusted to tune the opposing coupling terms (Mparb, Mparc , MPbrc , MpCTb ). Therefore, Mrbc can be tuned independently by changing the bipolar overlap of the reflection coils. The main-to-secondary mutual inductance matrix Mps gives the induced secondary voltages:Hence, the effective system coupling keff can be found to a bipolar secondary.

[0114] Figure 10 shows an example magnetic charging system. The arrangement is similar to Figure 2, but an additional reflection coil 303 is now present. This reflection coil 303 is associated with the central main coil 202. The size of the central main coil 202 has also been reduced relative to the remaining main coils 202, 203. Considering the decoupling of Figures 5 and 6, it is understood that full overlap and / or alignment of the reflection 300 and main coils 200 is not required. The reflection coils 300 are configured to provide opposing flux or coupling with the main coils 200 to decouple the main coils 200. This is possible based on similar equations as described for figure 6 as three phases and six coils 200, 300 are involved.

[0115] The shape or type of coils 200, 300 may be selected depending on the application. For example, a circular or symmetrical arrangement as in Figure 6 may be useful for stationary charging, or when an orientation of charging is not known, whereas linear coils as in Figure 10 may be useful when dynamic or moving charging is required. In some cases, the pole arrangement, or other selected geometrical parameters, of the main 200 and / or reflection coils 300 may be specified and the remaining geometrical parameters may be adjusted to decouple the phases. In some cases, the main 200 and / or reflection 300 coils may be of a known or fixed type and the remaining reflection 300 or main coils 200 may be used to decouple the phases. This may be useful, for example, to retrofit reflection coils 300 to a wireless power system with main coils.

[0116] Figure 10 shows the central coil 202 is smaller than the remaining main coils 201, 203. As shown, the central coil 202 is 80% the size of the remaining two coils, but a range of reduced sizes may be acceptable. Reducing the size of the main coil reduces the mutual inductances with the first and second main coils. This may simplify the decoupling and / or allow smaller reflection coils because there is less coupling between the phases. However, reducing the size of the main coil may also reduce the coupling to a secondary structure 102, reducing overall performance of the magnetic coupling structure 101. A size(e.g. width or length) of the reduced size central coil 202 may be selected based on the difficulty of decoupling a magnetic coupling structure and the importance of the effective coupling with the secondary 102, for example. Figure 10 shows central coil 202 completely overlapped by the combination of the remaining main coils 201, 202 and / or is positioned between the coils 201, 202 in the direction of charging.

[0117] The additional reflection coil 303 in Figure 10, compared to Figure 2, provides additional degrees of freedom for decoupling the system. The additional reflection coil 303 is associated with the central coil 202. In some cases, as shown in the electrical circuit of Figure 8 (which is suitable for driving Figure 10), the additional reflection coil 303 may have the same polarity as its associated main coil 202. This produces more counteracting-flux than if the current polarity was reversed, as with the other reflection coils. The additional reflection coil 303 may also improve voltage balancing in each phase.

[0118] Figure 11 shows a plan view of only the main coils 200, showing individual coils 201, 202 and 203. The dimensions are shown with outer coils 201, 203 having a width 'w' and central coil 202 having a width 'wa'. As shown only the width 'wa' is reduced relative to the outer coils (i.e., the central coil 202 length is the same as the outer coils 201, 203. Therefore, a main coil with reduced size may refer to a reduction in one or more dimensions, and in some cases in coil width only. It is possible to also reduce the length. The length the main coils is defined relative to the direction of the poles (or the alignment of the centers of the coils). In figure 11 the length (I) is therefore across the page, while the width (w, wa) is vertical on the page. Figure 11 shows the length of all three coils is the same. This can improve power transfer characteristics, but in some examples could be modified for decoupling.

[0119] Figure 12 shows example field shaping of in-road coils which are 12a a rectangular coil, 12b single phase DoubleD poles along the road, 12c two-phase DoubleD+Quadrature poles along the road, and 12d three-phase poles along the road. Each arrangement causes different time-varying magnetic fields to be generated. Poles along the road coils can extend pole pitch in the driving direction, provide increase length of power transfer. Increasing the number of poles (e.g., by using higher phase systems) introduces further coils that will splice the coil geometry, reducing the fundamental flux height. While this can reduce system coupling, the dynamic power profile is improved significantly by removing null power points. Furthermore, the presence of additional coils will distribute thecoil voltages across multiple terminations when pushing higher power. In dynamic charging cases, balanced three-phase coils like Figure 12d may be used for heavy-duty charging. Balanced three-phase magnetic design can be achieved through reduced sequence interaction of symmetric components. However, this forces an uneven spacing of track conductors. In other cases, a front-end toroidal cancellation matrix may enable phase decoupling for an evenly spaced track conductor layout. However, this increases system cost and complexity. The present disclosure describes how the benefit of a multi-phase system can be achieved through the use of reflection coils configured to decouple the main coils. Additionally, the reflection coils may act as active leakage shield to reduce flux on the back of the magnetic coupling structure. Optimizing the design of the reflection coils also reduces any reduction in the main-to-secondary coupling. This may avoid more complex arrangements or decoupling techniques used previously.

[0120] Figure 13a-d shows how the coils three-phase systems can be aligned with the charging direction. Similar alignments could be made for relevant two phase or multiphase systems. This alignment of coils 200, 300 will change the fields produced, as shown in Figure 12. The alignment of the reflection coils 300 will also change the flux leakage control. The selection of arrangement may depend on an expected secondary orientation, the important direction for leakage control and / or physical limitations. For example, on a roadway it may be advantageous to prevent flux leakage off the roadway in priority to leakage along the roadway. Figure 13 shows the secondary coils 250 parallel to the alignment of the main (main) coils 200. Figure 13 shows designs which have been optimized for effective coupling between the main magnetic coupling structure and the secondary magnetic coupling structure. By the method described below the following values were achieved:

[0121] Figure 13 shows parallel coils where their centers are aligned with the driving direction x, which may be a charging direction in other applications. The centers are also aligned with the poles of the coils when parallel. In a perpendicular arrangement the centersand / or poles are aligned perpendicular to the direction of charging. Although rectangular coils are shown these are illustrative only, as real coils would have a width and likely curvature at the corners. Alternative arrangements of circular or other loop shapes may be used.

[0122] As can also be seen in Figures 13a-d, but as described throughout the disclosure, the main coils 200 and reflection coils 300are substantially planar, or flat. This may refer to having a height substantially the same as the height of the coil wire. In some cases a coil must pass under itself, for instance to make an electrical connection to a power source. In such cases the height of the flat coil may increase, for example to twice the height of the coil wire. In other cases tolerances in the manufacture of the magnetic coupling structure may cause an increase in height. However, the coils maintain a width and length substantially greater than their height. For example, the length and width may be at least 10, at least 20, at least 50 or at least 100 times the height of the coil. The use of planar coils reduced the space required for the coil and / or spreads the charging field.

[0123] Figure 14 shows an example method to determine the characteristics of the main and / or reflection coils to enable decoupling. In this case there are two reflection coils, although similar approaches will work for other systems. Although a specific method is described it will be clear that different optimization approaches and / or optimization targets may be used if required. In some cases, the optimized characteristics may be a subset of the possible characteristics. For example, based on preference or preset characteristics.

[0124] At start 800 a decision is made on the optimization or determination algorithm and which characteristics to control. In the example of Figure 14 effective system coupling (keff - between the primary magnetic coupling structure and a nominal secondary magnetic coupling structure, such as a bipolar) and the normalised leakage field (Bmax / Su (i.e. the leakage flux is normalised with respect to the uncompensated secondary apparent power, Su)) are chosen. Su may be selected as 1VA at maximum keff. The nominal secondary may be chosen by reference to a wireless charging standard. For example, SAE-J2954 / 2 has a standard mounting area for heavy-duty EVs of 1.5*0.7m (length by width). This example positions the secondary at x = 0 : 200 : 400mm, y = 0 : 200 : 200mm. The leakage may be calculated at a position of concern, for example at the lane edge for road usage. This example uses lane edge - 1.75m either side of the center of the lane. In some cases, only one of these values, or an alternative value may be used. The process may generate design with an NSGA-II optimisation-based approach. Design values may be resolved analytically whereno ferrite is present. A genetic algorithm approach may be used, but other optimization techniques are possible.

[0125] Figure 14 shows the steps of determining the main coil poles (801) and choosing the reflection coil poles (802). As mentioned, these can be generated by an algorithm, such as a genetic algorithm, optionally based in part on the previous results. In some cases, these may be determined by system requirements (e.g., a current main coil design, or power transmission requirements. Step 803 then generates designs for the coils based on one or more geometric variable of the coils. As shown in step 803 these variables may include the length and / or width of the main and / or reflection coil, the overlap between the reflection coils, and the spacing between the main and the reflection coils (or between the plane of the main and reflection coils). The geometric characteristics may be constrained, for example the design parameters may be provided, an example of parameters is:

[0126] Step 804 calculates the optimization parameters to determine the performance of each generated design. Step 805 determines which designs to discard, in this case designs with coupling between the phases are discarded in step 806. This may use a coupling threshold, such as the decoupling limits discussed above. In this example a threshold of 2.5% was used. Step 807 produces updated designs by selecting / mutating / crossing over of the generated designs. Step 808 determines if a sufficient number of steps is performed. The number of steps may be 50, with 100 individuals, for example. Alternatively, a different threshold, such as a required effective coupling and / or leakage could be used. The algorithm may repeat until this threshold is met. The final design is then provided based on the best performance against the algorithm targets.

[0127] Figure 15 shows an example performance of this algorithm for the four magnetic coupling structure arrangements of Figure 13. In each case the algorithm improves the effective coupling with small increase in the leakage flux. The shading of the figures shows the size of the reflection coil area changing as the coil parameters change. For example, Figure 15d shows the reflection coil area increasing the most in a parallel / parallel arrangement. Figures 15a-d show that, for this example there is a balance between the increase in coupling and reducing leakage. The optimization may be controlled to balance these depending on application and / or priority. Figure 15c shows the best performance of this example system, with a parallel main coil and perpendicular reflection coil.

[0128] Figure 16 shows an example primary magnetic coupling structure coils 200, 300, with shaded secondary 102 with secondary coils 250 arranged above. The dimensions shown were determined by the algorithm of Figure 14 for the arrangement of Figure 15c. For example, the distance between the main 200 and reflection 300 coils was determined to be 39mm, with the main coils 200 have a length of 1859mm and a width of 683mm. Each of the main coils 200 is similar - i.e., has the same width and length. However, in some cases this is not the case, in particular where the central coil is varied, as discussed above. This design was tested with a ferrite containing secondary with coils 250 to check the robustness of the decoupling. The large secondary ferrite plane changed the inter-phase couplings slightly but these remained beneath 2.5%. If the reflection coil 300 was removed the inter-phase couplings would be 44%, 45% and 16% respectively. In some cases the optimization step is performed with a ferrite containing secondary to provide improved decoupling in the presence of ferrite. This example, with the ferrite bipolar secondary, has simulated values for centred keff and Bmax / SU of 15.2% and 0.050 pT / VA respectively. Comparatively, the design values without the reflection coil are 19.6% and 0.059 pT / VA respectively. Despite this reduction in coupling, this example reflection coils 300 manage to achieve leakage field reduction of 18% when transferring rated, uncompensated, apparent power.

[0129] The same design process can be used for reflection coils with a third coil. Figure 17a and Figure 17b show a determined primary magnetic coupling structure 101. Figure 17a highlights and dimensions the main coils 201, 202, 203, while Figure 17b highlights and dimensions the reflection coils 301, 302, 303. Again the main and secondary coils are parallel the direction of charging while the reflection coils are perpendicular to the direction of charging. In the case of Figure 17a the size of 2m x 1 m was selected for the maincoils 201, 202, 203, with the length of 2m parallel to the roadway and the width of 1m perpendicular to the roadway. The secondary 102 was again a bipolar with poles along the road and 1.5mx0.7m. This choice trades off a simpler design procedure with the ability to receive rotating magnetic fields. As discussed above, this example uses a reduced size of the central main coil 202. The central coil 202 has a width 80% of the size of the other main coils 201, 202. This allows for a smaller reflection coils 301, 302, 303 with less interference to kps. Trade-offs exist between the different design parameters. Parameters of the reflection coil(s) 301, 302, 303 that may be determined include the vertical spacing of the reflection and main coils, the length of each of the reflection coils, the width of each of the reflection coils and the overlap between the outer two reflection coils. Figure 17b shows the central reflection coil 303 having a much narrower width than the remaining coils (240mm). The combined length of the reflection coils is 840mm, which is arranged parallel to the width of the main coils (1000mm). All reflection coils 301, 302, 303 have a width of 700mm, although this may also be varied.

[0130] A small reflection coil (LR X WR) reduces both the impact on kpsand additional copper usage. However, increasing W towards the lane edge is beneficial in terms of leakage field cancellation, Z also reduces kpsif the reflection coils is not far enough away from the main coils and secondary coils or magnetically permeable material. Simultaneously, larger distance from the main coils also increases the main coil phase self-inductance. As discussed in the flow chart an example approach is a numerical approach which is applied by trialing numerous solutions. Where possible analytical equations may be used to determine inductances, or other possible values to increase the speed of the method. Additional coil parameters may be used. This example selects coil which use two filars in each turn, with each turn separated by 40mm. Other numbers of turns and / or numbers of filars in each turn and / or turn spacings may also be used.

[0131] In one example a magnetic coupling structure is determined without a central reflection phase self-inductance. However, Figure 17a and 17b show the presence of the central reflection coil 303, as introduced in Figure 10. The central reflection coil 303 may have different geometric parameters from the outer reflection coils 301, 302. For examplethe reflection coil is shown with a reduced length. Therefore, additional geometric parameters of the length and / or width of the central reflection coil 303 may be optimized. In this example the central reflection coil 303 is associated with the central main coil 202 and has the samecurrent polarity. The central reflection coil 303 may have a self-inductance will balance the voltages across each phase; introduced additional decoupling terms through Mrab and Mrac which can reduce reflection coil size, amd additional main / secondary coupling is contributed through Mrasa and Mrasb, increasing kps. This adds an additional row to the inductance matrix, which is now:This can be reduced in a similar method to the previous inductance matrix.

[0132] Figure 17a and Figure 17b shows a determined arrangement to decouple the main coils 201, 202, 203. The dimensions are shown as:[zR, IR, WR, Woveriap.R, h.a, wR a] = [0.06, 0.84, 0.70, 0.10, 0.70, 0.24] m.The reflection coil has reduced in area by 27% from the geometry in without the central reflection coil. This leads to a 14% increase in kps(coupling between the primary and secondary) to 0.16. The reflection coils 301, 302, 303 are designed to decouple the main coils 201, 202, 203. However, an additional advantage is that the reflection coils 301, 302, 303 can improve magnetic field leakage cancellation beneath the magnetic coupling structure. This can improve safety or magnetic performance of the coupling structure. The leakage may be normalised to power transfer for fair comparison. In these examples, based on the context of dynamic wireless power transfer (DWPT), leakage is measured at the lane edge (y = 1.75m).

[0133] The magnetic coupling structure may be interoperable with different magnetic topologies (circular pads, bipolar pads and DD pads), as well as with different power class magnetics (e.g., WPT3 to WPT6 pads). In some cases, the same system design is used for each arrangement, making interoperability easier. Considering the performance of the central reflection coil, this increases per-amp leakage (B / lp) by operating in phase with the main / main coil. B / lp is calculated as 0.033 pi and 0.028 pi for the design examples with and without the a-phase reflection coil respectively. However, accounting for the improvement in kps, both primaries end up with the same B / VSU of 0.083 pi. From these results, adding the a-phase reflection coil has improved kpsand the self-inductance balancing across phases. At thesame time, the leakage reduction benefit of the described topology of magnetic coupling structures has not been compromised.

[0134] Comparing the magnetic coupling structures of Figures 17a and 17b to a rectangular coil primary of equivalent surface area (2x1 m) provides insight into the ability to improve performance. B / lp is similar at 0.033 pi and 0.034 pi for the three-phase and rectangular coil primary systems respectively. This is despite the summative coil apparent power Spbeing nearly three times higher for a three-phase system under equal lp. The kpsto a ferrite-less bipolar secondary increases slightly to 0.17 with the rectangular main compared to 0.16 for the three-phase main. However, the B / VSU remains significantly lower for the three-phase main at 0.083 pi compared to 0.126 pi for the rectangular coil primary . In these examples the three- phase coil has three turns, while the rectangular coil has four turns and the secondary is a bipolar with three turns, but these can be varied. A comparison of Max RMS leakage was calculated, including with changes in secondary position. This used a 10kW charging region, with the secondary operated at 79.0A with the phase angles of the induced voltage phasors. This assumes resistive loading of perfectly tuned coils. In the worst-case leakage position (y = 100mm), the full system leakage of the 3-phase system is 26% lower than the rectangular system.:position relative io primary. 4-^ axis faces secondary pad.

[0135] Figure 18 shows example magnetic field lines without (Figure 18a) and with (Figure 18b) reflection coils 300 present. As can be seen in Figure 18a the magnetic field is symmetrical, with flux leakage shown at the back of the main coils 200, so in the opposite direction to the desired power transfer. Figure 18b shows how the introduction of the reflection coils 300 modifies the magnetic field lines to reduce the field below the reflection coils 300. The actual change in magnetic field will depend on the geometrical characteristics discussed herein.

[0136] Figure 19 shows an example magnetic coupling structure 101 as built. For ease of construction and testing the reflection coils 300 are arranged above the main coils 200. This would typically be reversed in a primary coupling structure so the main coils provide the charging surface (e.g. the ground in a ground structure). This example is a 10kW system with three-phases. The coils 200, 300 are wound with three turns of 3200 x 0.1mm Litz wire in single filar onto acrylic backing sheets. A secondary (not shown) was constructed with a core made of TDK N95 ferrite plates of 5mm thickness.

[0137] The coupling structure is powered by a circuit according to Figure 8. The three-phase inverter is switched at 85 kHz with conduction angle QCA = 120 degrees. A dead time of 150ns is included to avoid inverter shoot-through. LCL tuning is implemented on the main for its bandpass filter characteristic with inclusion of the DC blocking capacitor Cb. The secondary is parallel tuned for constant current characteristics. The bipolar coils of the secondary are independently rectified through full-diode bridges. The output filter is formed by a split filter inductor and common filter capacitor. The DC source and load used in this experiment are separate Regatron G5.RSS bi-directional power supplies. The values for system parameters are:The difference in L a, L and L c has no significance, being the result of the available bridge inductor values. They are compensated down to the same effective impedance by C a, C and Cbc respectively (10). Although a specific system is described it will be appreciated that a system may have any one or more of these characteristics or may used known alternatives to provide the same functionality.

[0138] The system parameters showed a close matching of mutual inductance terms. This validated the decoupling design procedure. The self-inductances have slightly more difference with simulation as the coil lead lengths are changed. The system is able to soft-switch. For each phase, the bridge current may be slightly negative at the rising edge of the bridge voltage.

[0139] Figure 19 shows how the reflection coils 300 (two are shown) are formed by three turns of wire 206, separated by a spacing distance. The number of turns, spacing distance and shape may be varied. The reflection coils 300 are smaller than the main (main) coils 200 to increase coupling between the main 200 and secondary coils, but this is not required for all cases. Figure 19 shows cables 207 connected to the ends of the coils 200, 300 and how these cables typically run over or under the coils. Although Figure 19 shows the coils 200, 300 fixed in position using adhesion to a support structure (plastic sheets are used) in other cases a housing or frame may provide this support, or the magnetic coupling structure may be formed into a substantially unitary object. The coils may be otherwise secured to the housing, frame or sheet. For example, the coils may be buried in the road with reading material, such as concrete, securing them in place.

[0140] Figure 20 shows a side view of the arrangement of Figure 19. This shows the vertical spacing between the main 200 and reflection 300 coils and the support surfaces 208 used for this example. For this demonstration the dimensions of the system were reduced by half, for ease of construction. Provided all ratios are maintained, the system characteristics do not change significantly. This means that system could be designed to be scaled depending on expected use. This side view shows that the spacing of the main coils 200 from the reflection coils 300 may be greater than the width of the coils, optionally substantially greater than the width of the coils.

[0141] The systems described here may be understood to use reflection coils which in summary generate magnetic flux which opposes the main (main) coils. Careful determination allows selection of reflection coils geometries which cancel coupling between the main coils. Therefore, the system is able to use reflection windings to both decouple the main coils and reduce magnetic flux leakage.

[0142] Although certain embodiments and examples are disclosed herein, inventive subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments and / or uses, and to modifications and equivalents thereof. Thus, the scope of the claims or embodiments appended hereto is not limited by any of the particular embodiments described herein. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence andare not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain embodiments; however, the order of description should not be construed to imply that these operations are order dependent. Additionally, some structures described herein may be embodied as integrated components or as separate components. For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein.

[0143] It should be emphasized that many variations and modifications may be made to the embodiments described herein, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. Further, nothing in the foregoing disclosure is intended to imply that any particular component, characteristic or process step is necessary or essential.

Claims

CLAIMS1. A magnetic coupling structure comprising:two or more coupled main coils; andtwo or more reflection coils;wherein the two or more reflection coils are configured to substantially decouple the two or more coupled main coils.

2. The magnetic coupling structure as claimed in claim 1 wherein the main coils and reflection coils form a primary magnetic coupling structure or a secondary magnetic coupling structure.

3. The magnetic coupling structure as claimed in any one of claims 1 or 2 wherein the reflection coils have a smaller length and / or width than the main coils.

4. The magnetic coupling structure as claimed in any one of claims 1 to 3 wherein one or more of the coupled main coils is associated with a corresponding one of the reflection coils.

5. The magnetic coupling structure as claimed in any claim 4 wherein the magnetic coupling structure comprises a plurality of pairs of main and reflection coil.

6. The magnetic coupling structure as claimed in claims 4 or 5 wherein one or more main coils do not have an associated reflection coil.

7. The magnetic coupling structure as claimed in any one of claims 4 to 6 wherein one or more of the main coils and the associated reflection coils are configured to have an inverted current polarity.

8. The magnetic coupling structure as claimed in any one of claims 1 to 7 wherein the main coils are arranged linearly.

9. The magnetic coupling structure as claimed in any one of claims 1 to 8 wherein the magnetic coupling structure is configured to transfer wireless power to a moving secondary coupling structure.

10. The magnetic coupling structure as claimed in any one of claims 1 to 9 wherein the magnetic coupling structure is a three-phase magnetic coupling structure.

11. The magnetic coupling structure as claimed in any claim 10 wherein the reflection coils are associated main coils of at least two of the phases.

12. The magnetic coupling structure as claimed in claims 10 or 11 wherein a central main coil does not have an associated reflection coil.

13. The magnetic coupling structure as claimed in any one of claims 1 to 12 wherein the magnetic coupling structure comprises or is configured with a charging direction.

14. The magnetic coupling structure as claimed in claim 13 wherein the main coils comprise coil centres are aligned parallel to or perpendicular to the charging direction.

15. The magnetic coupling structure as claimed in claim 13 or 14 wherein the reflection coils comprise coil centres aligned parallel or perpendicular to the charging direction.

16. The magnetic coupling structure as claimed in any one of claims 1 to 15 wherein the main coils comprise a first and a second main coil extending in a first direction, and a third main coil is arranged between the first and second main coils.

17. The magnetic coupling structure as claimed in claim 16 wherein the reflection coils are associated with the second and third main coils respectively.

18. The magnetic coupling structure as claimed in claim 16 or 17 wherein the third main coil is smaller than each of the first and second main coils.

19. The magnetic coupling structure as claimed in claim 18 wherein the third main coil has a length smaller than each of the first and second main coils.

20. The magnetic coupling structure as claimed in claims 18 or 19 wherein the third main coil is between 50% and 95% the size of the first and second main coils.

21. The magnetic coupling structure as claimed in any one of claims 1 to 20 wherein the reflection coils and the main coils are aligned in parallel and / or are aligned perpendicularly.

22. The magnetic coupling structure as claimed in any one of claims 1 to 21 comprising a loop of main coils.

23. The magnetic coupling structure as claimed in any one of claims 1 to 22 wherein the coils are configured to be powered by one or more inverters.

24. The magnetic coupling structure as claimed in claim 23 wherein the one or more inverters are configured to selectively power any one or more of the main coils or subsets of the main coils.

25. The magnetic coupling structure as claimed in any one of claims 1 to 24 wherein the magnetic coupling structure comprises first, second and third main coils, and first andsecond reflection coils, the first and second reflection coils associated with the first and second main coils.

26. The magnetic coupling structure as claimed in claim 25 comprising a third reflection coil associated with the third main coil.

27. The magnetic coupling structure as claimed in claim 26 wherein the third reflection coil is configured to have the same current polarity as the third main coil.

28. The magnetic coupling structure as claimed in claims 26 or 27 wherein the third main coil is arranged between the first and second main coils and / or the third reflection coil is arranged between the first and second reflection coils.

29. The magnetic coupling structure as claimed in any one of claims 1 to 28 wherein the reflection coils are arranged on the opposite side of the main coils to an expected direction of power transfer.

30. The magnetic coupling structure as claimed in any one of claims 1 to 29 wherein one or more of:the reflection coils are substantially planar;the main coils are substantially planar;the reflection coils and main coils are arranged in separated planes, the planes spaced apart.

31. The magnetic coupling structure as claimed in any one of claims 1 to 30 wherein one or more of the coils are substantially circular or substantially rectangular.

32. The magnetic coupling structure as claimed in any one of claims 1 to 31 wherein the magnetic coupling structure is ferrite-less.

33. The magnetic coupling structure as claimed in any one of claims 1 to 32 wherein the magnetic coupling structure is configured for vehicle charging and / or is configured to charge a battery.

34. A primary or secondary structure comprising the magnetic coupling structure of claims 1 to 33.

35. A method of designing a multi-phase magnetic coupling structure comprising a plurality of main coils; and a plurality of reflection coils, the method comprising the steps of:Selecting a pole orientation of the main coils and the reflection coils;Optimising one or more of geometric parameters of the main coils and the reflection coils,Wherein the optimisation requires decoupling of the main and reflection coils and the optimisation objective comprise one or more of:a coupling parameter with the secondary, anda leakage parameter.

36. The method of claim 35 wherein the plurality of geometric parameters comprise one or more of:A reflection coil distance from the main coils;A reflection coil length any one of the reflection coil lengths;A reflection coil width or any one of the reflection coil width;An overlap between two or more reflection coils;A main coil length or any one of the main coil lengths;A main coil width, or any one of the main coil width;An overlap between two or more main coils;A spacing between turns of the reflection and / or main coils;A number of turns of the reflection and / or main coils;A distance between the inner surface and outer surface of the main and / or reflective coils;A shape of the main and / or reflection coils,A winding pattern of the main and / or reflection coils.

37. The method of any one of claims 35 or 36 wherein one or more of the geometric parameters are common between each, or a subset of, the main and / or reflection coils.

38. The method of claim 37 wherein each of the main coils have the same length, or at least the outer main coils may have the same length.

39. The method of any one of claims 37 or 38 wherein the two or more of the coils have the same width.

40. The method of any one of claims 35 to 39 wherein the step of optimising the plurality of geometric parameters comprises:selecting geometric parameters for one or more, or all, of the main coils, andoptimising the geometric parameters of the reflection coils based on the selected reflection coils.

41. The method of any one of claims 35 to 39 wherein the step of optimising the plurality of geometric parameters comprises:selecting geometric parameters for one or more, or all, of the reflection coils andoptimising the geometric parameters of the main coils based on the selected reflection coils.

42. The method of any one of claims 35 to 41 comprising the step of configuring one or more electrical characteristics of each of the main coils and an associated reflection coils.

43. The method of any one of claims 35 to 42 comprising selecting an orientation of the main coils and / or the reflection coils.

44. A magnetic coupling structure designed by the method of claims 35 to 43.

45. A plurality of reflection coils configured to substantially decouple an arrangement of main coils when placed a specified distance beneath the main coil.

46. A three-phase magnetic coupling structure comprising three overlapping main coils and two or more reflection coils.

47. A multiphase magnetic coupling structure comprising three overlapping main coils.

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