The invention relates to a winding structure of a system for inductive power transfer, in particular to a vehicle. Further, the invention relates to a method of operating a winding structure of a system for inductive power transfer and such a system for inductive power transfer.

Electric vehicles, in particular a track-bound vehicle, and/or a road automobile, can be operated by electric energy which is transferred by means of an inductive power transfer. Such a vehicle may comprise a circuit arrangement, which can be a traction system or a part of a traction system of the vehicle, comprising a receiving device adapted to receive an alternating electromagnetic field and to produce an alternating electric current by electromagnetic induction. Furthermore, such a vehicle can comprise a rectifier adapted to convert an alternating current (AC) to a direct current (DC). The DC can be used to

charge a traction battery or to operate an electric machine. In the latter case, the DC can be converted into an AC by means of an inverter.

The inductive power transfer is performed using two sets of windings, in particular single- phase windings. A first set is installed on the ground (primary windings) and can be fed by a wayside power converter (WPC). The second set of windings is installed on the vehicle. For example, the second set of windings can be attached underneath the vehicle, in the case of trams under some of its wagons. For an automobile it can be attached to the vehicle chassis. The second set of windings or, generally, the secondary side is often referred to as pick-up-arrangement or receiver. The first set of windings and the second set of windings form a high frequency transformer to transfer electric energy to the

vehicle. This can be done in a static state (when there is no movement of the vehicle) and in a dynamic state (when the vehicle moves). In particular in the case of road automobiles, a stationary primary unit comprises a plurality of elements which are often arranged spatially or separated.

GB 2522851 A and GB 2522852 A disclose that a signal transmitted via a communication link is used to determine a correct position and/or orientation of the secondary winding structure relative to the primary winding structure of the primary unit.

It is an object of the invention to improve the inductive power transfer from a way-sided primary winding structure to a vehicle-sided secondary winding structure if said winding structures are misaligned. A further object of the invention is to provide a method of operating such a winding structure, wherein an amount of transferred energy is maximized. It is a further object of the invention to provide a corresponding system for inductive power transfer.

The solution is provided by the subject-matter with the characteristics of claims 1 , 12 and 15. Further embodiments of the invention are provided by the subject-matter with the characteristics of the subclaims.

It is a main idea of the invention to provide at least one additional winding structure, preferably at least one additional winding structure per pole of a primary or secondary winding structure, wherein the additional winding structure refines the electromagnetic field generated by said pole or received by said pole.

A winding structure of a system for inductive power transfer is proposed. The present invention can be applied in particular to the field of energy transfer to any land vehicle, for example track bound vehicles, such a rail vehicles (e.g. trams). Further, the invention relates to the field of energy transfer to road automobiles, such as individual (private) passenger cars or public transport vehicles (e.g. buses). The winding structure can provide a primary winding structure or a secondary winding structure of the system for inductive power transfer. This will be explained later in more detail.

The winding structure comprises a main winding structure with a first sub-winding and at least another sub-winding. The first and the at least one other sub-winding of the main winding structure are electrically connected. The main winding structure can provide a primary winding structure. In this case, the main winding structure generates a main electromagnetic field if it is energized. In this case, the first sub-winding generates a first portion of a main electromagnetic field if the winding structure is energized. Accordingly, the at least one other sub-winding generates another portion of the main electromagnetic field if the winding structure is energized.

Alternatively, the main winding structure can provide a secondary winding structure. In this case, the main winding structure receives the main electromagnetic field and provides an induced output voltage. In this case, the first sub-winding receives a first portion of a main electromagnetic field and the at least one other sub-winding receives another portion of the main electromagnetic field if the winding structure is exposed to such a main electromagnetic field. Each sub-winding can provide a pole of the main electromagnetic field or the electromagnetic field generated by the induced current (induced

electromagnetic field).

A sub-winding can comprise one or more section(s) of a phase line of the main winding structure. The main winding structure can comprise one or more phase lines for carrying an electric current, e.g. three phase lines. A sub-winding can enclose a predetermined area. Also, a sub-winding can provide or form a coil, e.g. with a predetermined number of turns.

The at least one phase line of the primary winding structure can be designed such that a course of the phase line provides an even or uneven number of sub-windings which are arranged adjacent to each other. In this context, a sub-winding can denote a, preferably complete, conductor loop which encloses a predetermined area. The conductor loop can provide or comprise one turn or multiple turns of the respective sub-winding. Adjacent to each other means that central axes of the sub-windings, in particular the axes of symmetry, are spaced apart from one another, e.g. with the predetermined distance, along the common straight line. The common straight line can be parallel to a longitudinal axis of a reference coordinate system and can correspond to a direction of extension of the primary winding structure. This means that a phase line of the primary winding structure can extend in a direction of extension, wherein a predetermined number of sub- windings is provided along said direction of extension. Neighboring or adjacent sub-windings can be counter-oriented. In this context, counter- oriented can mean that a current flow in a first sub-winding is oriented clockwise, wherein the current flow in the neighboring or adjacent second sub-winding is oriented counterclockwise. The clockwise direction can be defined with respect to the parallel central axes which point into the same direction. If a current flows through the said of sub-windings, adjacent sub-windings can generate a magnetic field of the same magnitude but oriented in opposite directions.

Preferably, the primary winding structure can be 8-shaped. This can mean that a course of the at least one phase line is 8-shaped. In this case, the phase line can comprise two e.g. circular-shaped or rectangular-shaped sub-windings which are arranged adjacent to each other along the direction of extension according to the aforementioned explanation.

Preferably, the primary winding structure can comprise three phase lines, wherein each phase line can comprise or provide multiple, in particular two, sub-windings which extend along a common direction of extension.

Alternatively, a phase line of a primary winding structure can have a meandering course. In this context "meandering" means that the phase line of the primary winding structure extends along a track or route in a meandering manner, i.e. sections of an electric line which provides the phase line which extend in a longitudinal direction of the primary winding structure are followed in the course of the conductor by section which extends transversely to the longitudinal direction (i.e. in a lateral direction of the primary winding structure). In the case of a multiphase system with at least two electric phase lines, this preferably applies to all the phase lines.

In other words, the first sub-winding can provide a first pole of the main electromagnetic field and the at least one other sub-winding can provide another pole of the main or induced electromagnetic field, wherein field lines of the main electromagnetic field extend at least partially from the first to the other pole. So, the first and the at least one other sub- winding can provide a pair of sub-windings, wherein said pair of sub-windings provides a pole pair.

It is, of course, possible that the main winding structure comprises more than two sub- windings. In this case, each sub-winding can provide a pole of an electromagnetic field if the main winding structure is energized or receives a portion of a main electromagnetic field if the main winding structure is exposed to said main electromagnetic field.

Preferably, the main winding structure comprises a first sub-winding and a second sub-winding. In this case, the main winding structure can also be referred to as double D-winding structure.

The sub-windings of the main winding structure can be arranged and/or electrically connected such that the main electromagnetic field generated by the first sub-winding is oriented along a first direction and the electromagnetic field generated by the other sub- winding is oriented against the first direction, wherein the main electromagnetic field is generated if the main winding structure is energized by a current. The directions can be directions of the electromagnetic field in a geometric centre of each sub-winding. The electromagnetic fields or portion thereof generated by each sub-winding can have an opposite directions but the same magnitude.

In the context of this invention, the following reference coordinate system can be used. A first axis, which can also be referred to as longitudinal axis, can extend parallel to a longitudinal axis of the primary winding structure, e.g. the aforementioned direction of extension. A second axis, which can also be referred to as lateral axis, can be oriented parallel to a lateral axis of the primary winding structure. A third axis, which can also be referred to as vertical axis, can be oriented parallel to a main direction of propagation of the electromagnetic field generated by a primary winding structure, i.e. oriented from the primary winding structure towards a secondary winding structure. The first, the second and the third axis can provide a right-handed Cartesian coordinate system.

It is possible, that the third axis is oriented perpendicular to a surface of the route, in particular if the primary unit is integrated into a route and/or arranged under the surface of the route. Alternatively, the third axis can be oriented perpendicular to an upper surface of the primary unit, in particular if the primary unit is installed on the surface of the route, e.g. as an elevated charging pad.

Terms referring to a direction such as "above", "under", "ahead", "beside", can be related to the aforementioned longitudinal, lateral and vertical axes. According to the invention, the winding structure comprises at least one additional winding structure, wherein the at least one additional winding structure is arranged asymmetric, in particular magnetically asymmetric, with respect to the first and the other sub-winding.

In the context of this invention, asymmetric or magnetically asymmetric can mean that a mutual coupling between the first sub-winding and the additional winding structure is different from the mutual coupling between the other sub-winding and the additional winding structure. In the context of the invention, the term "mutual coupling" can refer to a strength of the mutual coupling, wherein the strength of the mutual coupling can e.g. be provided by an absolute value of the coupling coefficient of said mutual coupling.

Asymmetric can also mean that the at least one additional winding structure is arranged asymmetrically with respect to one or multiple, in particular all, magnetic centre(s) of the main winding structure. A magnetic center can be a defined as a point of symmetry, a line of symmetry or a plane of symmetry of the mutual coupling or the spatial distribution of the mutual coupling, in particular the strength of the mutual coupling, of the main winding structure to a secondary winding structure for different relative displacements of the main winding structure and the secondary winding structure. Depending on the design of the main winding structure and/or the secondary winding structure, a magnetic center can correspond to a geometric center or comprise the geometric center.

Thus, asymmetric can mean that a strength of the mutual coupling between the first sub- winding and the additional winding structure is different from the strength of the mutual coupling between the other sub-winding and the additional winding structure. In particular, an absolute value of a coupling coefficient of the magnetic coupling between the first sub- winding and the additional winding structure can be higher or lower than the absolute value of the coupling coefficient of the magnetic coupling between the other sub-winding and the additional winding structure.

The additional winding structure can be designed and/or arranged such that an additional electromagnetic field can be generated if the additional winding structure is energized. In addition or alternatively, the additional winding structure can be arranged and/or designed such that a portion of the main electromagnetic field can be received by the additional winding structure, wherein a voltage can be induced in the additional winding structure by said portion of the main electromagnetic field. The asymmetric arrangement can also mean that, if the first sub-winding and the at least one other sub-winding receive or generate portions of a main electromagnetic field, in particular with an equal magnitude, the at least one additional winding structure is designed and/or arranged such that the at least one additional winding structure receives at least a portion of said main electromagnetic field, wherein a first portion of the electromagnetic field received by the additional winding structure is (also) received by the first sub-winding or generated by the first sub-winding, wherein another portion of the electromagnetic field received by the additional winding structure is (also) received by the other sub-winding or generated by the other sub-winding, wherein the first portion of the electromagnetic field received by the additional winding structure is different from, e.g. higher or lower than, the other portion of the electromagnetic field received by the additional winding structure. This can especially be the case if the first sub-winding, the at least one other sub-winding and the at least one additional winding are part of a winding structure of a primary unit of the inductive power transfer system and a receiving winding structure and, if applicable, an arrangement of magnetically conductive material of a secondary unit of the inductive power transfer system is placed centrally over the winding structure, in particular of the winding structure provided by the first and the at least one other subwinding.

The asymmetric arrangement can also mean that the at least one additional winding structure is arranged such that, if the at least one additional winding structure generates an additional electromagnetic field, the first sub-winding receives a first portion of the additional electromagnetic field and the at least one other sub-winding receives another portion of the additional electromagnetic field, wherein the first portion of the additional electromagnetic field is different from, e.g. higher or lower than, the other portion.

In particular in the case that the main winding structure provides a primary winding structure of the system for inductive power transfer, the asymmetric arrangement can also mean that, if the first sub-winding generates a first portion of a main electromagnetic field and the at least one other sub-winding generates another portion of the main

electromagnetic field which has the same magnitude but in opposite direction of the first portion, the at least one additional winding structure is arranged such that a first portion of the additional electromagnetic field generated by the additional winding structure is superposed upon the first portion of the main electromagnetic field and another portion of the additional electromagnetic field is superposed upon the other portion of the main electromagnetic field, wherein the first portion of the additional electromagnetic field is different from, e.g. higher or lower than, the other portion of the additional electromagnetic field.

The case that the main winding structure provides a primary winding structure, the additional winding structure advantageously allows a spatially targeted variation, e.g. a spatially targeted augmentation or attenuation, of the main electromagnetic field, in particular of a flux density of the main electromagnetic field. This can mean that the electromagnetic field is varied only locally. This, in turn, advantageously allows improving a magnetic coupling between a primary winding structure and a secondary winding structure if these winding structures are not perfectly aligned.

In particular in the case that a winding structure provides a secondary structure of the system for inductive power transfer, the at least one additional winding structure advantageously allows generating an additionally induced voltage which is induced by a spatially selected portion of the main electromagnetic field. This, in turn, also allows adjusting, e.g. increasing or decreasing, a voltage induced in the secondary winding structure if the primary winding structure and the secondary winding structure are not perfectly aligned.

An imperfect alignment can e.g. be given if a position and/or an orientation of the secondary winding structure relative to the primary winding structure is not within a predetermined position interval and/or orientation interval, i.e. differs more than a predetermined amount from a desired position and/or desired orientation.

A position of the secondary winding structure can e.g. be provided by a position of a centre point of the secondary winding structure, in particular a geometric centre point. A position of the primary winding structure can also be provided by, in particular geometric, centre point of the primary winding structure. It is, however, possible to use any reference point with a known spatial relation to the primary winding structure or secondary winding structure.

An orientation of the secondary winding structure can be provided by an orientation of a longitudinal axis of the secondary winding structure. This longitudinal axis can e.g. correspond to a longitudinal axis of the vehicle which can also be denoted as roll axis. In particular, the longitudinal axis can point into direction of travel if the vehicle moves forward on a flat driving surface.

With respect to the aforementioned reference coordinate system, an imperfect alignment can e.g. be given if a displacement between the secondary winding structure and the primary winding structure, e.g. a displacement between their respective geometric centres, along the longitudinal axis and/or the lateral axis is higher than a predetermined threshold value.

In another embodiment, the winding structure comprises at least one additional winding structure per sub-winding of a winding structure, wherein at least one additional winding structure is assigned to each sub-winding. As stated before, a sub-winding can denote one or more section(s) of a phase line which provides a pole of the electromagnetic field.

In this context, the term "assign" means that the coupling between the additional winding structure assigned and a selected sub-winding, e.g. the coupling coefficient or the absolute value of the coupling coefficient of the coupling between said windings, is higher than the coupling between the additional winding structure and each of the remaining sub- windings. In other words, the winding structure comprises at least one additional winding structure per sub-winding of the main winding structure, wherein each of the additional winding structures is arranged such that a mutual coupling between the additional winding structure and one of the sub-windings is higher than the mutual coupling between the additional winding structure and each of the remaining sub-windings.

The feature that at least one additional winding structure is assigned to each sub-winding can also mean that the first portion, in particular the aforementioned first portion received by the additional winding structure or the aforementioned first portion received by the first sub-winding or the aforementioned first portion of the additional electromagnetic field, is higher than the other portion.

In particular, the main winding structure can comprise an even number of sub-windings, preferably two sub-windings. In this case, the electromagnetic field generated by the main winding structure can have two poles. In this case, the proposed winding structure comprises an even number of additional winding structures, wherein an even number of additional winding structures can be assigned to each sub-winding.

In particular in the case of two sub-windings, the winding structure can comprise an even number of additional winding structures, wherein a first half of the additional winding structures is assigned to the first sub-winding and the other half of the additional winding structures is assigned to the other sub-winding. If each sub-winding provides a pole of the electromagnetic field, at least one additional winding structure per pole is provided.

In summary, this advantageously allows to spatially refine, e.g. to increase or decrease, the main electromagnetic field such that a desired power transfer efficiency is provided.

A current flow within an additional winding structure can have an orientation which is equal to or opposite the orientation of a current flow in the sub-winding to which the additional winding structure is assigned. In the first case, the electromagnetic field generated by the sub-winding can be locally increased, wherein in the second case, the electromagnetic field generated by the sub-winding can be locally decreased.

In a preferred embodiment, a mutual coupling, e.g. a coupling coefficient between the first sub-winding and a first additional winding structure is equal to a mutual coupling, e.g. a coupling coefficient, between the other sub-winding and another additional winding structure. In this case, the first additional winding structure can be assigned to the first sub-winding and the other additional winding structure can be assigned to the other sub- winding.

In another embodiment, assignments of an additional winding structure to a sub-winding are symmetrical, in particular coupling-symmetrical. This can mean that a mutual coupling between the first sub-winding and the other additional winding structure can be equal to the mutual coupling between the other sub-winding and the first additional winding structure. In summary, a coupling-symmetric arrangement of additional winding structures with respect to the main winding structure is provided. This can e.g. be the case if the arrangement of the first sub-winding and the first additional winding structure is designed similar to the arrangement of the other sub-winding and the other additional winding structure, wherein the arrangements are arranged mirror symmetric. In other words, assignments of an additional winding structure to a sub-winding are mirror symmetrical.

This advantageously provides an identical or symmetrical coupling for positive and negative misalignment.

In another embodiment, the main winding structure comprises two sub-windings, wherein a first and another additional winding structure are arranged and/or designed

symmetrically with respect to a mirror plane, wherein the mirror plane is oriented perpendicular to a longitudinal axis of the main winding structure and a geometric centre of the main winding structure is arranged in the mirror plane. This advantageously provides a simple design of the proposed winding structure.

In a preferred embodiment, an additional winding structure which is assigned to a sub- winding is fully arranged within an area enclosed by the sub-winding in a common plane of projection. The common plane of projection can be oriented perpendicular to the main direction of propagation of the electromagnetic field generated by the sub-winding in a geometric centre of the sub-winding, e.g. perpendicular to the aforementioned vertical axis.

This means, that dimensions, in particular a length and/or a width, of the additional winding structure are chosen smaller than corresponding dimensions of the sub-winding to which the additional winding structure is assigned.

Thus, a winding structure can be provided which comprises two sub-windings and two additional winding structures, wherein the first additional winding structure is fully arranged within an area enclosed by the first sub-winding in the common plane of projection and another additional winding structure is fully arranged within an area enclosed by the other sub-winding in the common plane of projection.

This advantageously simplifies a mechanical design of the winding structure and the corresponding primary or secondary unit. Further, a weight of the proposed winding structure can be reduced as the additional winding structures feature small geometric dimensions. In a preferred embodiment, a geometric centre of an additional winding structure assigned to a sub-winding is arranged with a predetermined distance from a geometric centre of the sub-winding along a lateral axis in a common plane of projection, wherein the

predetermined distance is larger than zero. This means that the additional winding structure is laterally displaced with respect to the sub-winding to which the additional winding structure is assigned in the aforementioned reference coordinate system.

Alternatively or in addition, the geometric centre of the additional winding structure assigned to the sub-winding is arranged with another predetermined distance from the geometric centre of the sub-winding along a longitudinal axis of the main winding structure in the common plane of projection, wherein the predetermined displacement is larger than zero. The proposed embodiment does not exclude the case that the geometric centre of the additional winding structures is arranged with the predetermined displacement along the vertical axis from the geometric centre of the sub-winding, wherein the predetermined displacement is larger than zero. This means that the additional winding structure can be arranged under or above the sub-winding to which the additional winding structure is assigned.

The predetermined distance can be chosen such that a desired special refinement, i.e. augmentation or attenuation, of the main electromagnetic field can be provided.

It is for instance possible to arrange the additional winding structure in a front half or a rear half of the sub-winding, wherein the term "front" and "rear" relate to the longitudinal axis of the reference coordinate system. It is also possible to arrange the additional winding structure in a left or a right half of the sub-winding, wherein the terms "right" and ""left" relate to the lateral axis of the coordinate system. It is further possible to arrange an additional winding structure in each of the four quadrants of the sub-winding, in particular if the sub-winding has a rectangular shape.

In another embodiment, the additional winding structure has a rectangular shape. It is, of course, possible that the additional winding structure can have another geometric shape, e.g. a circular shape, a hexagonal shape or an oval shape or any other geometric shape.

In another embodiment, the main winding structure is a winding structure of a primary unit of the system for inductive power transfer. In this case, the spatial or local refinement of the main electromagnetic field can be provided by an adequate operation, e.g.

energization, of the additional winding structure (s) assigned to the primary winding structure. This, in turn, eliminates the need of providing additional winding structures assigned to a secondary winding which in turn, ensures a light-weight secondary unit or receiving device. In summary, a desired refinement of the main electromagnetic field is achievable without increasing a weight of the secondary unit and of the vehicle.

Such a configuration is preferably chosen if ad least one dimension, e.g. a length and/or a width, of the primary winding structure is larger than the corresponding dimension of the secondary winding structure, in particular the secondary structure which is expected to be used for inductive power transfer.

Alternatively, the main winding structure is a winding structure of a secondary unit of the system for inductive power transfer. Such a configuration is preferably chosen if at least one dimension, e.g. a length and/or a width, of the secondary winding structure is larger than the corresponding dimension of the primary winding structure, in particular the primary winding structure which is expected to be used for inductive power transfer.

In a preferred embodiment, the additional winding structure is operable independent from the main winding structure.

This means that the additional winding structure can be energized independent of the energization of the main winding structure. Thus, it is possible to energize the additional winding structure with a current having an amplitude (RMS value) and/or frequency and/or phase different from the current which is energizing the main winding structure. In particular, the additional winding structure can be energized such that a desired refinement of the main electromagnetic field generated by the main winding structure is achieved.

The term "operable", however, also includes that a desired portion of the additional voltage induced in the additional winding structure by the main electromagnetic field can be added to or subtracted from the voltage induced in the main winding structure upon reception of the main electromagnetic field.

In another embodiment, the at least one additional winding structure can be operated or is operable depending on a position and/or orientation of a primary winding structure relative to a secondary winding structure. In this case, the position and/or orientation of the primary winding structure, in particular of a geometric centre of the primary winding structure, relative to the secondary winding structure, in particular relative to a geometric centre of the secondary winding structure, can be determined. This can e.g. be done by adequate positioning detection means for determining a position and/or orientation of the primary winding structure relative to the secondary winding structure. Such positioning detection means are e.g. disclosed by GB 1401957.4 and GB 1401960.8, which are hereby fully incorporated by reference.

The position and/or orientation of the primary winding structure relative to the secondary winding structure can e.g. be determined as a displacement between the respective geometric centres along the longitudinal and/or the lateral axis of the aforementioned reference coordinate system.

It is, for instance, possible that the at least one additional winding structure is not operated if the position and/or orientation of the secondary winding structure relative to the primary winding structure is within a predetermined position interval and/or orientation interval, i.e. differs not more than a predetermined amount from a desired position and/or desired orientation. In this case, the winding structures can be aligned (aligned state or status).

If, however, the position and/or orientation of the secondary winding structure relative to the primary winding structure is not within a predetermined position interval and/or orientation interval (misaligned state or status), the at least one additional winding structure can be operated. It is possible that at least one characteristic, e.g. a direction of current flow, a RMS value, a frequency and/or a phase, of the operating current which is used to energize the at least one additional winding structure is adjusted depending on the position and/or orientation of the secondary winding structure relative to the primary winding structure.

If more than one additional winding structure is provided, it is possible to operate only selected but not all additional winding structures. The selected additional winding structures can be chosen depending on the position and/or orientation of the secondary winding structure relative to the primary winding structure. If, for instance, the secondary winding structure is displaced along the lateral axis relative to the primary winding structure, only additional winding structures can be operated whose geometric centres are also displaced along the lateral axis relative to the geometric centre of the primary winding structure.

Further proposed is a method of operating a winding structure of a system for inductive power transfer, wherein sub-windings and at least one additional winding structure of a winding structure according to one of embodiments described in this invention are energized in a field generating operating mode.

Alternatively or in addition, an induced voltage provided by the sub-windings and at least a portion of an induced voltage provided by at least one additional winding structure are fused, e.g. added or subtracted, in a field receiving operating mode. The induced voltage denotes a voltage which is provided by the respective winding structure upon exposure to a main electromagnetic field.

This advantageously allows a local and asymmetric refinement of a main electromagnetic field or a desired variation of the induced voltage.

In another embodiment, the main winding structure is operated independent of the at least one additional winding structure. This has been explained previously.

In another embodiment, a position and/or orientation of a primary winding structure relative to a position and/or orientation of a secondary winding structure is determined, wherein at least one additional winding structure is operated depending on the position and/or orientation of a primary winding structure relative to the position and/or orientation of the secondary winding structure. In other words, the at least one additional winding structure can be operated depending on an alignment status.

It is, for instance, possible to select the least one additional winding structure to be operated from a number of more than one additional winding structure depending on the position and/or orientation of a primary winding structure relative to the position and/or orientation of the secondary winding structure. Further, it is possible to adapt or adjust at least one current characteristic of an operation current depending on the position and/or orientation of a primary winding structure relative to the position and/or orientation of the secondary winding structure, in particular if the additional winding structure is used to generate an additional electromagnetic field.

Alternatively, it is also possible to determine a portion of a voltage induced in the additional winding structure which is to be added to or subtracted from a voltage induced in the main winding structure, in particular if the additional winding structure is used to receive the main electromagnetic field.

This has also been explained previously.

Further proposed is a system for inductive power transfer comprising a winding structure according to one of the embodiments described in this invention. The main winding structure of a winding structure is a winding structure of a primary unit or a secondary unit.

In summary, the proposed winding structure advantageously allows increasing or decreasing a flux density of a main electromagnetic field locally, in particular by the asymmetrical arranged additional winding structure(s). However, the increase or decrease of the flux density is non-symmetrical with respect to the main electromagnetic field. This means, an additional winding structure can change the symmetry of the main

electromagnetic field by locally increasing or decreasing the flux density. The flux density can e.g. be increased if a current flows through the additional winding structure, e.g. a current for generating an electromagnetic field or a current generated by receiving an electromagnetic field.

The invention will be described with reference to the attached figures. The figures show:

Fig. 1 a a schematic top view on a primary and secondary winding structure in a first configuration,

Fig. 1 b a schematic top view on a primary and secondary winding structure in another configuration,

Fig. 2 a winding structure according to a first embodiment of the invention and Fig. 3 a winding structure according to another embodiment of the invention. Fig. 1 a shows a schematic top view on a primary winding structure 1 and a secondary winding structure 3. The primary winding structure 1 comprises a first sub-winding 2a and a second sub-winding 2b which are electrically connected. The first and the second sub- winding 2a, 2b have a rectangular shape. This is, however, not a mandatory design. Each of the first and the second subwinding 2a, 2b provides a coil, wherein a number of turns is equal to one or higher.

Further shown is a longitudinal axis x which is oriented parallel to a longitudinal axis of the primary winding structure 1 . The longitudinal axis x connects geometric centres of each sub-winding 2a, 2b. A vertical axis (not shown) is oriented perpendicular to the plane of projection and points towards an observer. Further indicated is a lateral axis y which is oriented perpendicular to the longitudinal axis x and the vertical axis. The lateral axis y can be oriented parallel to a lateral axis of the primary winding structure 1.

Shown is also a geometric centre Op of the primary winding structure 1 . A first magnetic centre of the primary winding structure 1 can be a plane which is spanned by an axis parallel to the longitudinal axis and an axis parallel to the vertical axis, wherein the axes intersect in the geometric centre Op of the primary winding structure 1 . Another magnetic centre of the primary winding structure 1 can be a plane spanned by an axis parallel to the lateral axis y and an axis parallel to the vertical axis, wherein the axes intersect in the geometric centre Op of the primary winding structure 1. The magnetic centres can comprise to the geometric centre Op of the primary winding structure 1 , in particular if the sub-windings 2a, 2b of the primary winding structure 1 are designed identically.

If the primary winding structure 1 is energized, the first sub-winding 2a will generate first portion of a main electromagnetic field and the second sub-winding 2b will generate another portion of the main electromagnetic field. In the geometric centres of each sub- winding 2a, 2b, the main electromagnetic field will have the same magnitude but an opposite direction. In particular, a direction of the main electromagnetic field in the geometric centre of the first sub-winding 2a can be equal to the vertical direction, wherein the direction of the main electromagnetic field in the geometric centre of the second sub- winding 2b is oriented against the vertical direction.

Further shown is a secondary winding structure 3 with a geometric centre Os of the secondary winding structure 3. A first magnetic centre of the secondary winding structure 3 can be a plane which is spanned by an axis parallel to the longitudinal axis x and an axis parallel to the vertical axis, wherein the axes intersect in the geometric centre Os of the secondary winding structure 3. Another magnetic centre of the secondary winding structure 3 can be a plane spanned by an axis parallel to the lateral axis y and an axis parallel to the vertical axis, wherein the axes intersect in the geometric centre Os of the secondary winding structure 3. The magnetic centres can comprise to the geometric centre Os of the secondary winding structure 3, in particular if the sub-windings 4a, 4b of the secondary winding structure 3 are designed identically.

The secondary winding structure 3 comprises a first sub-winding 4a and a second sub- winding 4b which are electrically connected. Each of the first and the second subwinding 4a, 4b provides a coil, wherein a number of turns is equal to one or higher. The secondary winding structure 3 is arranged above the primary winding structure 1. However, the secondary winding structure 3 and the primary winding structure 1 are misaligned. This means that there is a displacement between the centres Op, Os along the longitudinal axis x and the lateral axis y of the primary structure 1.

In the configuration shown in Fig. 1 a, a magnetic coupling of the first sub-winding 4a to the primary winding structure 1 is nullified. In particular, the first sub-winding 4a is arranged symmetric with respect to the aforementioned other magnetic centre of the primary winding structure 1 . This means that if the primary winding structure 1 is energized, no voltage will be induced within the first sub-winding 4a of the secondary winding structure. The second sub-winding 4b of the secondary winding structure 3, however, has a non-zero coupling to the primary winding structure 1 and will thus provide an induced voltage upon reception of the main electromagnetic field. In particular, the second sub-winding 4b is arranged symmetric with respect to the aforementioned other magnetic centre of the primary winding structure 1 .

Fig. 1 b shows a schematic top view on a primary winding structure 1 in another configuration. In contrast to the configuration shown in Fig. 1 a, both sub-windings 4a, 4b have a non-zero coupling with a primary winding structure 1. In comparison with the configuration shown in Fig. 1 a, the configuration shown in Fig. 1 b will provide twice the induced output voltage as configuration shown in Fig. 1 a upon reception of the main electromagnetic field. However, in the configuration shown in Fig. 1 b, the secondary winding structure 3 is still laterally displaced with respect to the primary winding structure 1.

Simulation and experience have shown that the magnetic coupling between the winding structures 1 , 3 decreases with increasing displacement along the longitudinal axis x and the lateral axis y of the primary winding structure 1. It has further been shown that the coupling decreases faster with an increasing displacement along the longitudinal axis x as with an increasing displacement along the lateral axis y.

It is a main idea of the invention to compensate the decreased coupling by means of at least one additional winding structure 5a, 5b, 5c, 5d.

Fig. 2 shows a schematic top view on a winding structure 6 according to the first embodiment of the invention. The winding structure 6 comprises a main winding structure 1 with a first sub-winding 2a and a second sub-winding 2b. The main winding structure 1 is a primary winding structure 1 of the system for inductive power transfer shown in Fig. 1 a.

Further, the winding structure 6 comprises an even number, namely four, additional winding structures 5a, 5b, 5c, 5d. Each of the additional winding structures 5a, 5d provides a coil, wherein a number of turns is equal to one or higher than one. In particular, the winding structure 6 comprises two pairs of additional winding structures 5a, 5d, wherein a first pair is provided by a first additional winding structure 5a and a second additional winding structure 5b and a second pair is provided by a third additional winding structure 5c and fourth additional winding structure 5d. All additional winding structures 5a, 5b, 5c, 5d are arranged asymmetric with respect to the first and the second sub- winding 2a, 2b. In particular, each of the additional winding structures 5a, 5b, 5c, 5d is arranged asymmetric with respect to the aforementioned first and other magnetic centres of the main winding structure 1 .

Fig. 2 shows that all additional winding structures 5a, 5d are fully arranged within a sub-winding 2a, 2b in a common plane of projection with is oriented perpendicular to the aforementioned vertical axis. In particular, the first and the third additional winding structure 5a, 5c are fully arranged within the first sub-winding 2a, wherein the second and the fourth sub-winding 5b, 5d are fully arranged in the second sub-winding 2b. All additional winding structures 5a, 5d have a rectangular shape. This, however, is not a mandatory design.

The first and the third sub-winding 5a, 5c are assigned to the first sub-winding 2a. This means that a mutual coupling coefficient of the coupling between the first additional winding structure 5a is higher than the coupling coefficient of the mutual coupling of the first additional winding structure 5a to all remaining sub-windings 2b. Correspondingly, the third additional winding structure 5c is assigned to the first sub-winding 2a and the second and the fourth additional winding structure 5b, 5d are assigned to the second sub-winding 2b.

Further, pairs of additional winding structures 5a, 5b, 5c, 5d are arranged in a coupling- symmetric arrangement. This means that the coupling coefficient of the coupling between the first additional winding structure 5a and the first sub-winding 2a is equal to the coupling coefficient of the magnetic coupling between the second additional winding structure 5b and the second sub-winding 2b. Further, the coupling of the coupling between the first additional winding structure 5a and the second sub-winding 2b can be equal to the coupling coefficient of the coupling between the second additional winding structure 5b and the first sub-winding 2a. The same coupling-symmetric arrangement is provided by the second pair of additional winding structures 5c, 5d.

Moreover, it can be seen from Fig. 2, that additional winding structures 5a, 5b, 5c, 5d of a pair of additional winding structures 5a, 5d are arranged mirror symmetric with respect to a mirror plane which is oriented orthogonal to a longitudinal axis x of the primary winding structure 1 and comprises the geometric center Op of the primary winding structure 1 .

With respect to a geometric center of the first sub-winding 2a and the longitudinal and lateral axis x, y, the geometric center of the first additional winding structure 5a is arranged in the front left corner of an area/volume enclosed by the first sub-winding 2a. Correspondingly, a geometric center of the third additional winding structure 5c is arranged in a front right corner. With respect to the second sub-winding 2b and the longitudinal and lateral axis x, y, the geometric center of the second additional winding structure 5b is arranged in a rear left quarter of an area/volume enclosed by the second sub-winding 2b. Correspondingly, a geometric center of the fourth additional winding structure 5d is arranged in a rear right corner.

If the primary winding structure is energized, a current 11 will flow through the primary winding structure 1 and generate a main electromagnetic field. A direction of current flow is indicated by arrow heads the current 11 .

In order to refine the main electromagnetic field locally, the first additional winding structure 5a can be energized by a first additional current I5a. With respect to a vertical axis which is oriented towards the observer, the current flow in the first additional winding structure 5a has the same orientation as the current flow in the first sub-winding 2a.

Correspondingly, the third additional winding structure 5c can be energized by a third additional current I5c, wherein a current flow of the third additional current I5c in a third additional winding structure 5c has the same orientation as the current flow in the first sub-winding 2b. Further, the second and the fourth additional winding structure 5b, 5d can be energized by a second and a fourth additional current I5b, I5d, respectively. A current flow of these additional currents I5b, I5d can have the same orientation as the current flow in the second sub-winding 2b. In summary, the shown arrangement of the windings 5a, 5d allows compensating a decrease of the magnetic coupling if a secondary winding structure is displaced laterally. In particular, the first pair of additional winding structures 5a, 5b allows compensating for the decrease of the magnetic coupling if the secondary winding structure is displaced to the left of the primary winding structure 1 , i.e. with a displacement along the lateral direction, wherein the lateral direction is indicated by an arrowhead of the lateral axis y. The second pair of additional winding structures 5c, 5d allows compensating for the decrease of magnetic coupling if the secondary winding structure is displaced to the right, i.e. a displacement against the lateral direction.

Fig. 3 shows a schematic top view on a winding structure 6 according to another embodiment of the invention. In contrast to the embodiment shown in Fig. 2, the winding structure 6 comprises only two additional winding structures 5a, 5b which provide a pair of additional winding structures 5a, 5b. With respect to the first sub-winding 2a of the primary winding structure 1 , the first additional winding structure 5a is fully arranged within an area/volume enclosed by the first sub-winding 2a. Further, the second additional winding structure 5b is fully arranged in an area/volume enclosed by the second sub-winding 2b of the primary winding structure 1. Each of the additional winding structures 5a, 5b is arranged asymmetric with respect to the first and the second sub-winding 2a, 2b. In particular, all additional winding structures 5a, 5b are arranged asymmetric with respect to the aforementioned first and other magnetic centres of the main winding structure 1.

Moreover, with respect to the shown longitudinal axis x and lateral axis y, the first additional winding structure 5a is arranged in a rear half of the area/volume enclosed by the first sub-winding, wherein the second additional winding structure 5b is arranged in a front of the area/volume enclosed by the second sub-winding 2b.

It shown, however, that a geometric center of the additional winding structures 5a, 5b are not laterally displaced with respect to a geometric center of the respective sub-winding 2a, 2b, respectively. Further, each additional winding structure extends along the full width with the respective sub-winding 2a, 2b.

Further shown are additional currents I5a, I5b flowing through the additional winding structures 5a, 5b respectively, wherein the additional currents I5a, I5b have the same orientation as the current flow of the primary current in the sub-winding 2a, 2b to which the respective additional winding structure 5a, 5b is assigned.

The configuration shown in Fig. 3 advantageously allows compensating the decrease of the magnetic coupling between a secondary winding structure (not shown) and the primary winding structure 1 if the secondary winding structure is displaced with respect to the primary winding structure 1 along or against a longitudinal direction which is indicated by an arrowhead of the longitudinal axis x.