U.S. patent application number 14/379068 was filed with the patent office on 2015-08-20 for multiple coil flux pad.
The applicant listed for this patent is Auckland UniServices Limited. Invention is credited to John Talbot Boys, Grant Anthony Covic.
Application Number | 20150236513 14/379068 |
Document ID | / |
Family ID | 48984495 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150236513 |
Kind Code |
A1 |
Covic; Grant Anthony ; et
al. |
August 20, 2015 |
MULTIPLE COIL FLUX PAD
Abstract
The present invention provides a magnetic flux pad for
generating or receiving magnetic flux, comprising at least three
coils positioned such that the windings thereof are in
substantially the same plane, and a power supply or pickup
controller operable to selectively energise or receive power from
two or more of the coils such that a magnetic field is produced or
received by at least one of a plurality of pairs of the at least
three coils. In preferred embodiments, the three or more coils are
substantially mutually decoupled, overlapping, and/or equidistantly
spaced from one another.
Inventors: |
Covic; Grant Anthony; (Mount
Albert, NZ) ; Boys; John Talbot; (Takapuna,
NZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Auckland UniServices Limited |
Auckland City, Auckland |
|
NZ |
|
|
Family ID: |
48984495 |
Appl. No.: |
14/379068 |
Filed: |
February 15, 2013 |
PCT Filed: |
February 15, 2013 |
PCT NO: |
PCT/NZ2013/000016 |
371 Date: |
August 15, 2014 |
Current U.S.
Class: |
307/104 |
Current CPC
Class: |
H02J 50/70 20160201;
H02J 50/10 20160201; H02J 2310/48 20200101; Y02T 10/70 20130101;
Y02T 10/7072 20130101; H01F 27/2871 20130101; H02J 50/40 20160201;
Y02T 90/14 20130101; H02J 7/0044 20130101; H02J 7/025 20130101;
H02J 50/12 20160201; H01F 38/14 20130101 |
International
Class: |
H02J 5/00 20060101
H02J005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2012 |
NZ |
598253 |
Claims
1. A magnetic flux pad for generating or receiving magnetic flux,
the pad comprising: at least three coils positioned such that the
windings thereof are in substantially the same plane; and a power
supply or pickup controller operable to selectively conduct with
two or more of the coils such that a magnetic field is produced or
power is received by at least one of a plurality of pairs of the at
least three coils.
2. The magnetic flux pad of claim 1 wherein the power supply or
pickup controller is operable to selectively conduct with the coils
to energise or receive power from any one or more of the coils.
3. The magnetic flux pad of claim 1, wherein the power supply or
pickup controller is operable to sequentially energise or receive
power from the at least three coils.
4. The magnetic flux pad of claim 1, wherein the power supply or
pickup controller is operable to independently control the phase,
magnitude and/or frequency of current in each of the at least three
coils.
5. The magnetic flux pad of claim 1, wherein the at least three
coils are substantially mutually decoupled from one another.
6.-8. (canceled)
9. The magnetic flux pad of claim 1, wherein the power supply is
operable in a plurality of modes comprising at least two of:
single-phase modes, wherein one or more of the coils are energised
in phase with each other; two-phase modes, wherein one or more of
the coils are simultaneously energised out of phase with one or
more other coils; and a multiphase mode, wherein three or more of
the coils are simultaneously energised out of phase with each
other.
10. The magnetic flux pad of claim 1, further comprising a
magnetically permeable material, wherein the at least three coils
are magnetically associated with the permeable material.
11. The magnetic flux pad of claim 1, further comprising a further
coil disposed substantially centrally and encircling or partially
overlapping the at least three coils.
12. The magnetic flux pad of claim 11, wherein the further coil is
substantially mutually decoupled from the at least three coils in
at least one mode of operation.
13. The magnetic flux pad of claim 1, comprising: three overlapping
and substantially mutually decoupled coils each spaced
substantially equidistantly from one another, and a magnetically
permeable material providing a low reluctance magnetic path between
poles of the three coils.
14.-15. (canceled)
16. A magnetic flux pad for generating magnetic flux, the magnetic
flux pad being configured to be operable in a plurality of modes so
as to control the magnetic flux generated thereby, and comprising
three or more coils capable of being selectively energised to
enable said control to be effected.
17.-19. (canceled)
20. The magnetic flux pad of claim 16, wherein the plurality of
modes comprises at least two of: single-phase modes, wherein one or
more of the coils are energised in phase with each other; two-phase
modes, wherein one or more of the coils are simultaneously
energised out of phase with one or more other coils; and a
multiphase mode, wherein three or more of the coils are
simultaneously energised out of phase with each other.
21.-22. (canceled)
23. The magnetic flux pad of claim 20, comprising a further
substantially central coil.
24. A power supply apparatus for an inductive power transfer
system, the power supply apparatus comprising: a magnetic flux pad
for generating magnetic flux, comprising at least three coils
positioned such that the windings thereof are in substantially the
same plane; and a power supply adapted to provide a current in one
coil which has a different phase to a current in the other
coils.
25. The power supply apparatus of claim 24 wherein the magnetic
flux pad further comprises a magnetically permeable material and
the at least three coils are magnetically associated with the
permeable material.
26. The power supply apparatus of claim 24, wherein the power
supply is adapted to provide a current in any one coil so as to
have a different phase to a current in all respective other coils
in use.
27. The power supply apparatus of claim 24, wherein the power
supply is adapted to adjust the phase to produce a field that
varies with time and with spatial position on the pad.
28. The power supply apparatus of claim 24, wherein the apparatus
comprises means to detect where a field is or is not required in
the vicinity of the pad and adjust the phase and/or amplitude of
the current in at least one of said coils in response thereto.
29. The power supply apparatus of claim 28, wherein the means to
detect is adapted to adjust a relative phase between at least a
first of said coils and at least a second of said coils.
30. The power supply apparatus of claim 24, wherein the power
supply comprises an inverter for each coil.
31.-36. (canceled)
Description
FIELD OF THE INVENTION
[0001] This invention relates to apparatus for generating or
receiving magnetic flux. The invention has particular, but not
sole, application to a low profile, substantially flat device such
as a pad for power transfer using an inductive power transfer (IPT)
system.
BACKGROUND
[0002] IPT systems, and the use of a pad which includes one or more
windings which may comprise the primary or secondary windings for
inductive power transfer, are reproduced in our International
Patent Publication No. WO 2008/14033, the contents of which are
incorporated herein by reference.
[0003] One particular example application of IPT power transfer
pads is electric vehicle charging, and that application is
discussed in this section to provide the background to one
application of the invention. However, electric vehicle charging is
an example of only one application, and the invention has
application to inductive power transfer in general. Electric
vehicle charging may occur while the vehicle is stationary, or
alternatively while the vehicle is moving along a roadway, for
example. IPT power transfer pads can be used both in the vehicle as
a power "pickup" (i.e. the secondary side winding of the IPT
system), and at a stationary location such as a garage floor or a
roadway for example as the "charging pad" (i.e. the primary side
winding) from which power is sourced.
[0004] The purpose of an IPT roadway system is to wirelessly
transfer power to a stationary or moving vehicle without physical
contact to the vehicle. The transmitting part of the system
consists of a power supply supplying a lumped coil (for example a
pad as described above) or a track with many similar lumped coils
where such a system is tuned for operation at a suitable frequency,
usually anywhere from 10 kHz to 150 kHz. Where the receiver is
placed underneath a vehicle and coupled to receive power either
when the vehicle is stationary above or near (in sufficiently close
proximity to couple power) to the primary transmitter. The pickup
receiver also typically comprises a lumped coil (such as a pad
described above) which is connected to a converter and appropriate
controller within the vehicle to regulate power. For convenience,
the part of a roadway from which power may be received inductively
is referred to herein as a track.
[0005] The track may be formed by placing a plurality of pads along
the centre of a lane in a roadway.
[0006] This results in the possibility of an essentially continuous
supply of power to the vehicle as it moves along the roadway in the
immediate vicinity of the track.
[0007] In recent years such systems have received increasing
attention due to their potential to allow sustainable wireless
powered personal transportation. For such a system to be useful it
should not only be able to transfer sufficient power over an airgap
of reasonable size (e.g. 100-300 mm) it should also prove tolerant
to any displacements between track and pickup, to avoid dependency
on a vehicle-to-track guidance system. In a roadway system such
displacement will most likely occur in the lateral direction
(orthogonal to both vertical and the direction of movement) for
moving vehicles. For stationary vehicle charging the ability to
transfer acceptable levels of power with suitable longitudinal
displacement is of particular concern in order to ensure ease of
parking. The power transfer profile in the pick-up pad is ideally a
smooth power profile which is essentially constant (and sufficient)
over as wide as possible a distance laterally, with smooth
drop-offs at each end. Such a power transfer profile eases the
demands on the electronic (primary and secondary) regulators in the
system, enabling improved operating performance for a comparable
coupling over a system where during operation significant
variations are experienced in the coupling between the primary and
receiver pads.
[0008] A further problem to be solved is the need to be able to
couple to vehicles or appliances with varying ground clearances,
which largely determines the distance between the charging pad on
the ground or as part of a primary structure (such as a mat or
other surface) and the secondary pad of a particular vehicle or
other device. In such applications there will be significant
changes in coupling between the two pads that may require the
primary inductive apparatus to operate with substantially increased
VA to meet the power demand. This operation will also increase the
magnetic field leakage present in the system, which may exceed
allowable limits defined by regulations.
[0009] A further problem may occur if the primary and secondary
inductive pads are polarised but oriented at an angle of 90 degrees
to each other such that there is no coupling, and thus no
possibility of power transfer.
[0010] Yet a further problem arises due to the many different
possible pad designs and operation methods, and the potential
mismatch between the charging and pickup pads. For example, the pad
on the ground may have a completely different structure to the
vehicle pickup, and/or may be operated as a single phase, two phase
or multiphase system to produce substantially different field flux
shapes within the space between the two coupled pads under time
varying conditions. Under such conditions the ability of a fixed
magnetic structure to capture power is limited.
[0011] An inductive power transfer apparatus which goes at least
some way to addressing some of the above problems was described in
our International Patent Publication No. WO 2011/16737, the
contents of which are incorporated herein by reference. Embodiments
of WO 2011/16737 provide a magnetic flux pad for generating or
receiving magnetic flux, the pad including a magnetically permeable
core, two substantially flat overlapping coils magnetically
associated with the core whereby there is substantially no mutual
coupling between the coils.
OBJECT OF THE INVENTION
[0012] It is an object of the present invention to provide an
improved apparatus for generating and/or receiving magnetic flux
for the purposes of inductive power transfer, or to at least
provide the public or the industry with a useful choice.
SUMMARY OF THE INVENTION
[0013] In a first aspect the invention broadly provides a magnetic
flux pad for generating or receiving magnetic flux, the pad
comprising: [0014] a magnetically permeable core, and [0015] at
least three overlapping coils magnetically associated with the
core, the at least three coils all being positioned such that the
windings thereof are in substantially the same plane, [0016]
whereby there is substantially no mutual coupling between the coils
in use.
[0017] The coils are preferably positioned proximate to or to abut
the core such that the surface of the coils that abuts the core is
substantially flat. For the avoidance of doubt, the coils may have
a thickness such that the coils do not lie entirely within a single
plane. Further, as will be appreciated, at least in the region
where the coils overlap, there will be some deviation out-of-plane.
References to being "in substantially the same plane" are to be
interpreted subject to these limitations throughout the
specification.
[0018] Preferably each coil in use is substantially decoupled from
all other coils of the at least three coils.
[0019] Preferably the coils are substantially completely
magnetically decoupled in use.
[0020] Preferably the coils partially overlap.
[0021] Preferably the coils are substantially coplanar.
[0022] Preferably the coils are provided on one side of the said
permeable core, and a shielding means is provided on the other side
of the core.
[0023] Preferably the shielding means comprises a shielding plate
made of a suitable material such as aluminium.
[0024] Preferably a dielectric cover is provided on the side of the
coils opposite the magnetic core.
[0025] Preferably the flux pad is adapted to receive currents from
a power supply which are out of phase with each other to produce a
time varying magnetic field which also varies spatially.
[0026] Preferably the field produced by the out-of-phase currents
in the coils produces a time varying magnetic field which moves
spatially and ultimately between poles of the magnetic field.
[0027] In a second aspect, there is provided a magnetic flux pad
for generating magnetic flux, the magnetic flux pad being
configured to be operable in a plurality of modes so as to control
the magnetic flux generated thereby.
[0028] Preferably the magnetic flux pad includes three or more
coils, any one or more of the coils capable of being selectively
energised, thereby enabling said control to be effected.
[0029] Preferably, the coils are substantially magnetically
decoupled from one another.
[0030] Any one or combination (including all) of the coils may be
selectively energised as desired and depending on the particular
implementation.
[0031] Note that when used herein, "mode" or the like is to be
interpreted broadly as not only meaning that, say, the pad is
capable of switching between two coils being energised and three
coils being energised, but additionally or alternatively that
different ones of the coils (but the same number), may be
energised. For example, different ones or different pairs of a
three coil pad may be selectively energised.
[0032] According to presently preferred embodiments, the flux pad
includes three said coils. The provision of three coils strikes a
balance between the additional performance and flexibility
(provided by the adaptability of the flux) and the additional
componentry and complexity thereof (particularly in positioning of
the multiple coils).
[0033] Further features of the second aspect may be taken from the
features set out in relation to the first aspect.
[0034] According to a third aspect, there is provided a ferrite
arrangement for a magnetic flux pad having at least three coils,
the ferrite arrangement comprising a plurality of elongate ferrite
elements configured such that the elements are co-aligned with
and/or parallel to an imaginary line extending between the centres
of at least two of said coils.
[0035] Preferably a plurality of arrays of elements are provided,
each array being aligned with the imaginary line between a
different pair of coils. As will be appreciated, the imaginary
lines between different coil centres may be parallel in some
arrangements (see, for example, FIG. 5). Consequently, the same
array (but extended perpendicular to the orientation of the ferrite
element lengths) may be used for different pairs of coils.
[0036] According to some embodiments, the arrangement comprises (or
when assembled forms) one or more raised and/or recessed portions
provided on the surface of the ferrites configured to receive the
coils. For example, for ease of reference, consider an arrangement
where coils are positioned on the upper surface of a ferrite
arrangement, raised ferrite portion(s) may be provided at an outer
edge of one or more of the coils. Additionally or alternatively, a
raised portion may be provided at a centre of one or more the
coils. Other positions of raised portions are also possible, as are
recessed portions. The provision of raised and/or recessed portions
can be used to further adapt the flux to conform to a desired
pattern.
[0037] According to one embodiment, the extent or combined
operating area of the ferrite arrangement is commensurate with that
of the coils.
[0038] According to one embodiment, the ferrite material extends
beyond the extent of the coils. Preferably the increased extent of
the provision of ferrites is provided at edges of the coils that
cross the imaginary line (or are proximate thereto) but that are at
the outer extremities of the coil/ferrite arrangement. Elsewhere,
the coils may extend beyond the extent of the ferrites. Such
arrangements of the ferrites and coils can improve efficiency and
reduce the amount of ferrite material required because it is
believed that only ferrite provided substantially along the
imaginary lines will add to mutual inductance, ferrite material
elsewhere simply adding to inductance. Extending the ferrite
material beyond the extent of the coils along the imaginary lines
can serve to capture flux spill out or over. This aspect of the
invention may comprise only two coils and is not to be limited as
requiring three or more coils.
[0039] Preferably the ferrite arrangement is configured for use in
the magnetic flux pad of the first and second aspects.
[0040] In a fourth aspect the invention provides power supply
apparatus for an inductive power transfer system, the power supply
apparatus comprising: [0041] a magnetic flux pad for generating
magnetic flux, the pad comprising: [0042] a magnetically permeable
core, and [0043] at least three overlapping coils magnetically
associated with the core, the at least three coils all being
positioned such that the windings thereof are in substantially the
same plane; and [0044] a power supply adapted to provide a current
in one coil which has a different phase to a current in the other
coils.
[0045] Preferably, the power supply is adapted to provide a current
in any one coil so as to have a different phase to a current in all
respective other coils in use.
[0046] Providing currents with different phases in each coil and
adjusting the overlap between the coils, enables each coil to be
substantially decoupled from all other coils.
[0047] Preferably the power supply is adapted to adjust the phase
to produce a field that varies with time and with spatial position
on the pad.
[0048] Preferably the apparatus comprises means to detect where a
field is or is not required in the vicinity of the pad and adjust
the phase and/or amplitude of the current in at least one of said
coils in response thereto.
[0049] More preferably, the means to detect is adapted to adjust a
relative phase between at least a first of said coils and at least
a second of said coils.
[0050] Preferably the power supply comprises an inverter for each
coil.
[0051] According to one embodiment, the power supply operates two
of three inverters to be synchronised with each other such that in
one mode of operation the power supply produces a current in a
first one of said coils (preferably any one said coils) which is
90.degree. out of phase with the current in a second one of said
coils.
[0052] According to another embodiment, the power supply operates
one of three inverters to produce a current in one of said coils,
preferably any one said coils. Where different ones of said coils
may be driven independently of the other coils, preferably the
current is produced in the coil that is in closest proximity to a
coil on a vehicle.
[0053] Preferably the magnetic flux pad produces a sliding time
varying magnetic field.
[0054] According to one embodiment, the power supply operates at
least one pair of the at least three coils 180.degree. out of phase
with each other. In this embodiment a common inverter may be used,
or two inverters, one driving each coil.
[0055] Thus, the present invention provides all of the flexibility
and functionality described in WO 2011/16737 but provides
additional functionality and flexibility by enabling additional
single coils or pairs of coils that may be energised, as well as
enabling higher numbers of coils to be energised, thereby enabling
the flux to be better tailored and improve power transfer. For
example, the coils energised may be selected at least in part on
the required rate of power transfer or the relative position
between the pickup and the charging pad.
[0056] In a fifth aspect, the invention provides power supply
apparatus for an inductive power transfer system, the power supply
apparatus comprising: [0057] a magnetic flux pad for generating
magnetic flux, the magnetic flux pad being configured to be
operable in a plurality of modes so as to control the magnetic flux
generated thereby; and [0058] a power supply adapted to provide a
current to the magnetic flux pad.
[0059] Other features of the fifth aspect are readily derivable
from features of the first through fourth aspects without invention
in light of the disclosure herein. For the avoidance of doubt, the
magnetic flux pad may be configured to be operable in the plurality
of modes by selectively energising any one or combination of at
least three coils of the magnetic flux pad. Further, the particular
coils energised may be varied.
[0060] In a sixth aspect the invention broadly provides a method
for providing an IPT magnetic flux pad having at least three coils
in which there is no mutual magnetic coupling between the coils,
the method comprising the steps of: [0061] overlapping the coils;
and [0062] varying the overlap between the coils such that an
overlap position is achieved whereby there is substantially no
mutual coupling between the coils.
[0063] Preferably the absence of mutual coupling is detected by
detecting when an open circuit voltage induced in a first one of
the coils by energisation of at least one (but preferably all) of
the other coils is minimised.
[0064] Energisation of the other coils may comprise energising each
coil in turn and/or energising multiple coils simultaneously and/or
energising each coil as they would be energised in normal use,
including with varying phases between the coils.
[0065] According to one embodiment, overlap determination is
achieved by considering pairs of said at least three coils in turn
(i.e., for an arrangement having three coils, evaluating coil 1
against coil 2, coil 2 against coil 3, and coil 3 against coil
1).
[0066] According to one embodiment, the method comprises detecting
an open circuit voltage induced in a second one of the coils
substantially simultaneously (or at least subject to the same
operating conditions) as when the open circuit voltage is detected
for the first coil. This may similarly be performed for the third
(and more) of said plurality of coils.
[0067] In a seventh aspect, the invention provides a method of
generating magnetic flux, the method comprising: [0068] selectively
energising one or more coils of at least three coils of a magnetic
flux pad.
[0069] For the avoidance of doubt, said selectively energising may
comprise energising any subset of the coils, or all of the
coils.
[0070] Preferably said selectively energising comprises switching
between energising a first subset of coil(s) and a second subset of
coil(s).
[0071] The first and second subsets may comprise the same or a
different number of coils. Further, one or more coils may be common
to both subsets.
[0072] Additional or alternative subsets of coils may additionally
or alternatively be energised. Further, one or more of said subsets
may comprise all said coils.
[0073] Further features of the method of the seventh aspect may be
derived from analogous features of the first through sixth
aspects.
[0074] In an eighth aspect the invention may broadly be said to
consist in a magnetic flux pad for generating or receiving magnetic
flux, the pad comprising: [0075] at least three coils positioned
such that the windings thereof are in substantially the same plane;
and [0076] a power supply or pickup controller operable to
selectively conduct with two or more of the coils such that a
magnetic field is produced or power is received by at least one of
a plurality of pairs of the at least three coils.
[0077] Preferably the power supply or pickup controller is operable
to operable to selectively conduct with the coils to energise or
receive power from any one or more of the coils.
[0078] Preferably the power supply or pickup controller is operable
to sequentially energise or receive power from the at least three
coils.
[0079] Preferably the power supply or pickup controller is operable
to independently control the phase, magnitude and/or frequency of
current in each of the at least three coils.
[0080] Preferably the at least three coils are substantially
mutually decoupled from one another.
[0081] Preferably the at least three coils partially overlap.
[0082] Preferably the at least three coils are spaced substantially
equidistantly from one another.
[0083] Preferably the magnetic flux pad comprises three
substantially mutually decoupled coils.
[0084] Preferably the magnetic flux pad is operable in a plurality
of modes comprising at least two of: [0085] single-phase modes,
wherein one or more of the coils are energised in phase with each
other; [0086] two-phase modes, wherein one or more of the coils are
simultaneously energised out of phase with one or more other coils;
and [0087] a multiphase mode, wherein three or more of the coils
are simultaneously energised out of phase with each other.
[0088] Preferably the magnetic flux pad further comprises a
magnetically permeable core, wherein the at least three coils are
magnetically associated with the core.
[0089] Preferably the magnetic flux pad comprises a further coil
disposed substantially centrally and encircling or partially
overlapping the at least three coils.
[0090] Preferably the further coil is substantially mutually
decoupled from the at least three coils in at least one mode of
operation.
[0091] Preferably the magnetic flux pad comprises: [0092] three
overlapping and substantially mutually decoupled coils each spaced
substantially equidistantly from one another, and [0093] a
magnetically permeable core providing a low reluctance magnetic
path between poles of the three coils.
[0094] Preferably the power supply or pickup controller is operable
to independently control the magnitude, phase, and/or frequency of
current in each coil.
[0095] Preferably the flux pad is operable in at least a
three-phase mode.
[0096] In a ninth aspect the invention may broadly be said to
consist in a magnetic flux pad for receiving magnetic flux and
supplying power to a load, the magnetic flux pad being configured
to be operable in a plurality of modes so as to control the
magnetic flux received thereby, and comprising three or more coils
capable of being selectively operated to enable said control to be
effected.
[0097] In a ninth aspect the invention may broadly be said to
consist in a pickup apparatus for an inductive power transfer
system, the pickup apparatus comprising: [0098] a magnetic flux pad
for receiving magnetic flux, comprising at least three coils
positioned such that the windings thereof are in substantially the
same plane; and [0099] a pickup controller adapted to operate one
coil with a different phase to the other coils.
[0100] Further aspects of the invention will become apparent from
the following description.
DRAWING DESCRIPTION
[0101] One or more embodiments of the invention will be described
with reference to the accompanying drawings in which:
[0102] FIG. 1 is a side view and a plan view respectively of a
magnetic flux pad;
[0103] FIG. 2: is a side view and plan view respectively of the pad
of FIG. 1 including a quadrature coil;
[0104] FIG. 3: is a side view and plan view respectively of an
alternative form of magnetic flux pad;
[0105] FIG. 4: (a) is a plan view of a magnetic flux pad according
to a first embodiment of the invention; and (b) is a plan view of a
variation of the first embodiment;
[0106] FIG. 5: is a plan view of a magnetic flux pad according to a
second embodiment of the invention;
[0107] FIG. 6: is a schematic power supply circuit for a known 2
coil pad with mutually decoupled coils;
[0108] FIG. 7: is a schematic power supply circuit for a three coil
mutually decoupled pad;
[0109] FIG. 8: is a schematic receiver circuit for a three coil pad
with mutually decoupled coils which can both receive and reverse
power flow to and from the load;
[0110] FIG. 9: is a schematic circuit for a three coil pad with
mutually decoupled coils which can independently decouple any of
the coils and control power flow to the load;
[0111] FIG. 10: is a plan view of a magnetic flux pad according to
a third embodiment of the invention;
[0112] FIG. 11: is a plan view of a magnetic flux pad according to
a fourth embodiment of the invention;
[0113] FIG. 12: shows plan views of two further embodiments of
magnetic flux pads according to the invention;
[0114] FIG. 13: shows plan views of five further embodiments of
magnetic flux pads according to the invention, comprising
variations of the embodiments of FIG. 4; and
[0115] FIG. 14: shows plan views of four further embodiments of
magnetic flux pads according to the invention, comprising
sub-optimal variations of the embodiments of FIG. 4.
DETAILED DESCRIPTION
[0116] FIGS. 1 to 3 are prior art arrangements taken from the
aforementioned International Patent Publication No. WO
2011/16737.
[0117] Referring to FIG. 1, a prior art magnetic flux pad
construction is shown. For convenience, this general construction
is referred to herein as a DDP pad, and is generally referenced DDP
in the relevant drawing figures.
[0118] The DDP pad shown in FIG. 1 generally comprises two
substantially coplanar coils referenced 2 and 3 which are
magnetically associated with, and sit on top of, a core 4. As can
be seen, the core 4 may consist of a plurality of individual
lengths of permeable material such as ferrite strips or bars 5
which are arranged parallel to each other but spaced apart. The pad
construction may include a spacer 6 on which the core is located,
and a plate 7 below the spacer. A cover 8 may be provided on the
other surface of the flat coils 2 and 3. Padding 9 may be provided
about the periphery of the pad. As can be seen, the coils 2 and 3
each define a pole area 10 and 11 respectively. This DDP pad
construction shows very good characteristics suitable for IPT power
transfer applications such as vehicle charging. The coils 2, 3 may
be connected out of phase and driven by a single inverter to
produce a stationary time varying magnetic field to couple to a
receiver (which may for example be of substantially the same
magnetic design) at distances suitable for electric vehicle power
transfer with good coupling.
[0119] Turning to FIG. 2, the DDP construction of FIG. 1 is shown
but further including a quadrature coil 12 (referred to herein as a
DDPQ pad). The quadrature coil extends the power transfer profile
when there is lateral movement of the construction shown in FIG. 2
with respect to a flux generator such as the DDP pad of FIG. 1 when
energised by an appropriate inverter. The quadrature coil allows
power to be extracted from the "vertical" component of the magnetic
field that the receiver pad intercepts while the other coils 2, 3
facilitate power extraction from the "horizontal" component of the
flux intercepted. Therefore, the construction of FIG. 2 is suited
as a flux receiver.
[0120] Turning to FIG. 3, another construction is shown which is
referred to in this document as a bi-polar pad or, alternatively,
as a BPP pad. The BPP pad has a similar construction to the DDP pad
discussed with respect to FIGS. 1 and 2 above as it enables
excellent coupling to secondary receivers at distances suitable for
charging and powering of electric vehicles.
[0121] The BPP pad consists, from bottom up, of an aluminium plate
7, a dielectric spacer 6, a core 4 comprising four rows of ferrite
bars 5 (referred to herein as ferrites), two flat substantially
coplanar, yet overlapping and ideally "rectangular" shaped coils 2,
3 (although in practice these are more oval due to the ease in
winding Litz wire) spread out in the lateral direction, and a
dielectric cover 8. The core 4 acts as a shield so that ideally all
flux is directed away form the core 4 through the top of the pad.
The plate 7 merely acts to a) eliminate any small stray or spurious
fields that may be present beneath the core 4 in certain
environments, and b) provide additional structural strength. Table
A1 provides example dimensions of a working prototype of a BPP pad.
Tables A2 and A3 provide example dimensions of the DPP pad of FIG.
1 and the DDPQ pad of FIG. 3, respectively.
[0122] The magnetic structure of the BPP of FIG. 3 is designed so
that there is substantially no mutual coupling between either of
the coils 2, 3 in the primary, as described later. This allows the
coils to be driven independently at any magnitude or phase without
coupling voltage into each other which if present would oppose the
power output of such a coil.
[0123] In one mode of operation, the two coils within the BPP can
be driven using two separate but synchronised inverters operating
with known current magnitude and phase difference as shown
conceptually in FIG. 6. The switches in the H-bridge inverter of
FIG. 6 are shown as FETs. In practice these switches may comprise
an IGBT with a suitable inverse parallel diode, or SiC JFET and SiC
diode or other suitable arrangement as desired. The power supply
tuning arrangement of FIG. 6 uses a known LCL topology (see, for
example, WO 2007/100265) at the output of the each inverter's
H-bridge. The inductances in each of the coils of FIG. 3 are
assumed to be identical based on them having the same shape and
turns ratio. This inductance (as seen by the supply and including
lead lengths and any other compensation elements such as a series
capacitor which may be required to limit voltage across the power
supply tuning capacitor C.sub.p) is given a value of L.sub.1. The
primary inductor (L.sub.p) is chosen to be identical to L.sub.1,
and the tuning capacitor C.sub.p has an identical reactance at the
designed frequency of the supply. Subscripts 2 and 3 represent the
circuit attached to coils labelled 2 and 3 in the BPP of FIG. 3. If
the coils are completely magnetically decoupled, ideally there will
be no power transfer between the primary inverters to limit power
transfer to the secondary receiver, although due to small loading
differences on the coils from a receiver there may be some small
mutual coupling which may cause a small residual current to flow
between the inverters. Because the DC bus of each inverter is
common, this residual current simply circulates between the
inverters and does not cause any issue or loss of performance
during operation.
[0124] The two inverters shown in FIG. 6 may be synchronised but
operated so as to produce currents with the same RMS magnitude, but
operating 90 degrees out of phase in each of the coils 2, 3. By
having a 90.degree. phase separation between the currents in the
coils 2, 3, a spatially varying and time varying magnetic field is
created rather than the stationary time varying magnetic field of
the DDP. The spatial variation in the field of the BPP may appear
as a sliding movement in alternate directions between the poles of
the coils 2, 3.
[0125] Other relative phase and/or magnitude variations between the
currents in the coils could be used to shape the field if there is
a need to reduce the field emissions on one side of the transmitter
to avoid leakage during operation due to an offset nature of the
coupled receiver, for example to meet ICNIRP regulations. Thus the
field may be directed in response to the output of a sensor for
example which may sense where greater field strength is required,
or where the field strength should be reduced. Also, the field
strength may be time varying but spatially stationary dependent on
where across the pad the field is required.
[0126] It is also possible to operate the coils 2, 3 180 degrees
out of phase using the circuit of FIG. 6, or they could be simply
connected to one inverter (as in the DDP operation). This
particular single phase operating mode is a second possible mode of
operation to simplify the electronic control and power conversion
that will produce a stationary time varying field as for the
DDP.
[0127] WO 2011/16737 further provides guidance on preferred
configurations of the ferrite strips 5 above which the coils 2, 3
are placed in the BPP pad. The ferrite strips 5 are used to enhance
power transfer and ensure that a predominately single sided flux
field is created to best couple to the secondary power receiver,
while ensuring that a minimal amount of ferrite is used to keep
weight to a minimum and restrict the inductance of the pad. In such
a sliding field it is shown that the ferrite strips should
preferably extend under the winding coils otherwise the field may
not be forced upwards towards the receiver.
[0128] When the two primary coils 2, 3 of the BPP are placed with
an arbitrary overlap (or substantially adjacent with no overlap)
with respect to each other, there will be a mutual coupling between
the coils. However for a certain ratio of overlap to coil width,
denoted r.sub.0, this mutual coupling is almost zero. The ideal
overlap required to ensure no mutual coupling exists between each
primary coil is not simple due to the presence of the ferrite but
can be determined by simply fixing one coil and energising this
with a predetermined current at fixed frequency (either via a
suitable 3D simulator or using a suitable experimental setup, for
example). The open circuit voltage induced in the second primary
coil can then be measured. If the second coil is moved so as to
change the overlap there will be a change in coupled voltage. When
this is minimised (ideally zero) the ideal configuration can be
set. The optimal overlap is dependent on the length of the ferrite
strips underneath the coils.
[0129] In WO 2011/16737 it was noted that there was a significant
increase in power when the ferrite under the coils was extended,
and it was clear that the ferrite should extend at least under the
entire extent of coils 2, 3 for the BPP pad arrangement of FIG. 3.
The reason for this is that the field close to the BPP pad can best
be described as a sliding wave across the surface.
[0130] FIG. 4(a) shows a plan view of a variation of the FIG. 3
arrangement according to an embodiment of the invention. The
magnetic flux pad of FIG. 4(a) includes three coils 2, 3, 3a and a
modified ferrite 5 arrangement. Otherwise, the construction of the
pad of FIG. 4(a) is generally in accordance with that of the BPP
pad of FIG. 3, including, from the bottom upwards (when comparing
with the upper drawing of FIG. 3), base plate 7 (preferably
aluminium), spacer 6 (preferably dielectric), a core 4 comprising
ferrite material 5, substantially co-planar coils 2, 3, 3a and a
cover 8 (preferably dielectric). The key difference is that an
additional coil 3a is placed above or below coil 2 or above coil 3
such that the centres or poles of all three coils are spaced
substantially equidistantly from one another in a triangular
arrangement. Furthermore, the configuration of the core 4 has been
adapted and includes three sets of ferrites 5 arranged with an
offset of or substantially of 60.degree. between each set, wherein
each the three ferrite sets extends substantially parallel with an
axis extending between the centre of respective pairs of coils 2, 3
and 3a.
[0131] FIG. 4(b) illustrates a variation of the embodiment of FIG.
4(a), in which the core comprises a single ferrite strip or bar 5
along each of the imaginary lines between the centres of the coils,
forming at equilateral triangle in the centre. The plate 7 in this
embodiment has a shape corresponding substantially with the outer
perimeter of overlapping coils 2, 3 and 3a, including padding.
[0132] FIG. 5 shows a plan view of another embodiment of the
invention. The arrangement of FIG. 5 is substantially the same as
those of FIG. 4 but includes four coils 2, 3, 3a, 3b and a modified
ferrite 5 arrangement within the core 4. The additional coil 3b may
be placed above, below or between coils 2, 3 and 3a. In the
arrangement shown, a ferrite lattice is used with one set of
ferrites offset from the other by or substantially by 90.degree. to
form a grid.
[0133] As with the arrangement of FIG. 3, the extent of overlap
between the coils may be varied to obtain the desired decoupling.
More particularly, one or more of the at least three coils may be
energised with a predetermined current at a fixed or respective
fixed frequency and the overlap with the other or other ones of the
at least three coils varied so as to minimise the voltage in the
other or other ones of the at least three coils. To achieve such an
overlap in practice, preferably the ferrites 5 should first be
fixed in place (since any change to the position and shape of
ferrites 5 will impact on the overlap required between the coils
necessary to ensure mutual coupling is minimised). The shape and
size of each of coils 2, 3 and 3A should preferably be identical
(although the invention is not limited thereto). If coil 2 is fixed
in position, then coil 3 can be moved into the relative position
shown while energising coil 2. The open circuit voltage coupled
into coil 3 from the energisation of coil 2 can be easily measured
and with suitable movement of coil 3 relative to coil 2 can be
reduced to a minimum (ideally zero), to determine the ideal
relative position of both coils. Once the position of coils 2 and 3
have been fixed, then coil 3a can be added generally in the
position shown on FIG. 4(a). Coil 3a can now be energised and the
voltages coupled into coils 2 and 3 monitored. By adjusting the
position of coil 3a relative to both coils 2 and 3 the coupled
voltages should be reduced to a minimum (ideally zero), at which
point its position is fixed.
[0134] While circular coils are shown in FIGS. 4 and 5, the
invention is not limited to coils of that shape. By way of example
only, the coils may alternatively have a generally oval, square or
rectangular configuration. Further, different coils within the same
pad may have different configurations. For example, referring to
the FIG. 4(a) arrangement, coil 2 may be oval and coils 3, 3a
circular. Furthermore, while the lateral spacing of the circular
coils of the Figures may be substantially equidistant such that
imaginary lines or axes extending between the centres of adjacent
coils may form a substantially equilateral triangle or square
shape, this need not necessarily be the case.
[0135] Further, while particular ferrite 5 arrangements have been
shown in FIGS. 4 and 5, the invention is not limited thereto. Other
arrangements may be devised to direct the field in a desired
manner, or more particularly to provide a path of low magnetic
reluctance between the poles of the three or more mutually
decoupled coils, including a single sheet of ferrite material of
sufficient size. However, it has been found that the use of ferrite
strips as opposed to a sheet of ferrite material provides similar
performance in terms of controlling the flux and so appropriately
configured strips may be favoured to reduce the cost and weight
thereof. On the other hand, a core comprising a sheet of ferrite
material may be thinner and preferred in other applications, and
may be shaped to ensure that it provides a path of low magnetic
reluctance only between the poles.
[0136] As shown in FIGS. 4 and 5, where ferrite strips are used, it
is preferable that these are arranged to pass through or be
parallel to an imaginary line or axis extending between the centres
of adjacent coils. Thus, arrays of ferrite strips may be provided,
each array being configured to be so aligned with one or more pairs
of said coils (i.e., with the imaginary lines or axes extending
between coil centres).
[0137] Generally, it is preferable for the ferrite material to
extend beyond the edges of the coils (as shown in at least FIGS. 4
and 5). However, the invention is not limited thereto and may be
configured differently depending on the particular application and
the coils may in fact extend over a larger area than the ferrite
material.
[0138] According to one embodiment, the ferrite material extends
beyond the outer extremity of the coils in selected regions of the
coils only, the selected regions being at or proximate to where
said imaginary lines cross said coils (see FIG. 3). Additionally or
alternatively, one or more of the coils may extend beyond the
extent of the ferrites, preferably outside of said previously
mentioned selected regions (again, see FIG. 3).
[0139] Referring to FIGS. 4 and 5, while it is possible for the
ferrites to include arrays of strips one above the other as shown,
preferably, the ferrites are configured to form the desired pattern
in a single layer. For example, referring to FIG. 5, the ferrites
may be arranged such that the ferrites extending up and down the
page (the vertical ferrites) are as shown and the left to right
ferrites (the horizontal ferrites) are then each formed by a
plurality of shorter ferrites that extend across the gap between
the vertical ferrites, preferably such that the ends of the
horizontal elements abut or substantially abut the adjacent
vertical ferrites.
[0140] Forming the ferrites in this manner reduces the thickness
and weight of the core.
[0141] It will be appreciated that the ferrites may be otherwise
configured. For example, referring again to the FIG. 5 example, the
strips may have a varying thickness such that they are thinner at
the regions of overlap. Reducing the thickness as a step enables
the different ferrite elements to interlock.
[0142] The examples of ferrite arrangements described in relation
to FIG. 5 in the preceding three paragraphs are not intended to be
limited to the FIG. 5 arrangement and may be adapted without
invention to other required ferrite arrangements such as those
similar to the FIG. 4 arrangement or those requiring a more
complicated ferrite arrangement where additional coils are
added.
[0143] Further, each strip of ferrite may be formed from more than
one piece of ferrite material. Thus, smaller strips or pieces of
ferrite material may abut or substantially abut one another to form
each larger piece.
[0144] Additionally or alternatively, the degree of integration
between adjacent ferrite portions may be increased. For example, a
ferrite arrangement may be formed from one or more sheets of
ferrite material with portions thereof removed as desired.
[0145] Further coils may also be added, as desired.
[0146] FIG. 7 shows a possible power supply arrangement necessary
for driving the pad shown in FIG. 4. As shown subscripts 2, 3 and
3A represent the inverter topology connection to coils 2, 3 and 3A
in FIG. 4.
[0147] An advantage of using at least three coils of the present
invention is that the pad may be used in multiple modes. For
example, for a stationary vehicle charging application, a single
coil of at least three coils of a charging pad may be activated to
couple power to a small receiver on a small utility vehicle, where
the chosen coil to be activated depends on the coil which is best
coupled (i.e. best aligned) to the receiver on the vehicle.
Alternatively, all coils may be energised in phase with each other,
creating a larger stationary time varying field to power a large
vehicle or one requiring faster charge. Further, said coils
(preferably three) may be used in a three phase system (i.e. each
120 degrees out of phase) to create a sliding spatially varying and
time varying field or multiple selected coils may be energised in a
single phase system (i.e., to create a stationary time varying
field).
[0148] In another mode, coils of the charging pad may be energised
dependent on the orientation and/or alignment of the pick-up (e.g.
on the vehicle to be charged). In this mode, all or a subset of the
coils may be energised in use. For example, pairs of coils may be
energised, per the BPP pad arrangement of FIG. 3, to produce a
field most effectively received by a pickup. The pair of coils
energised may be varied, for example, to modify the field to
compensate for movement of the pickup. According to one embodiment,
pairs of coils of a pad containing at least three coils may be
selectively energised (including sequentially) if that produces the
most effective field.
[0149] The presence of at least three coils further enables
improved steering of the field generated by the charging pad. In
addition or as an alternative to energising only selected coils of
the plurality of coils, different coils may be energised to
different levels, thereby "steering" the field in a selected
direction to, say, accommodate misalignment of a pickup with a
charging pad, such as due to variations in parking of vehicles to
which a charge is to be provided.
[0150] The use of at least three coils can additionally or
alternatively assist in sensing a location of a vehicle pickup so
that an appropriate (ideally optimal) charging regime can be
implemented, depending at least in part on the detected location.
While this is achievable to some extent using the arrangements
described in WO 2011/16737, the inclusion of additional coils
provides greater accuracy of detected position and enables position
to be determined in at least two dimensions.
[0151] Thus the use of additional, decoupled coils provides for
increased flexibility in the manners in which the apparatus of the
invention may be used by enabling all or a subset of the coils to
be used and further provides for improved power transfer by varying
the mode of operation and/or through the improved
steering/positioning of the field achieved (improved in terms of
being controllable in multiple dimensions and/or across a larger
area and/or better determination of pickup position and/or
adaptation of the field as a result thereof).
[0152] Operating the triangular arrangements of FIG. 4 in a
three-phase mode is particularly useful, as it is capable of high
power transfer, possesses the ability to cope with variable
secondary alignments, and has inherent field cancellation (i.e.
low/no leakage) in the far field.
[0153] It will be noted from the foregoing that embodiments of the
invention have particular application for use as a "charging pad"
(i.e., the primary side winding) but the same or similar
arrangements may be used for the pickup, again with improved power
transfer characteristics as a result of the decoupling between
coils of the pickup. In such embodiments, the coils would be
electrically coupled to and controlled by a pick-up controller,
rather than a power supply, the pickup controller being operable to
deliver power received from the pickup coils to a load. The
controller would typically comprise a controllable rectifier or
rectifiers, rather than the inverters of a power supply.
[0154] For example, the circuit of FIG. 8 which is essentially
identical to the that of FIG. 7, could also be used at the output
of a pad to enable power transfer to a load connected across the DC
capacitor which in such a case could also be across the battery of
an electric vehicle. The power available from each receiver coil
can be monitored, and if small, the bottom switches in each
inverter bridge can be closed to decouple that receiver coil and
remove any losses which would otherwise occur from its
operation.
[0155] In yet other embodiments of the invention, the primary
and/or secondary pads may be reversible, wherein the pad may be
operated to selectively conduct with the coils to receive or
deliver power from/to another pad. The circuit of FIG. 8 could
easily be used to reverse the power flow back to the primary but in
order to synchronise this power flow back into mains utility
supply, the three phase rectifier of FIG. 7 would need to be
replaced with a suitable reversible rectifier.
[0156] Where reversible power flow is unnecessary, a simpler
secondary circuit can be used, an example of which is shown in FIG.
9. At the output of each coil a tuning capacitor can be used either
in series or parallel or both to bring each AC circuit to
resonance. Here a parallel resonant circuit is shown with optional
series capacitance to boost the current from each coil if required
at design. The output of each of these tuned circuits is then
rectified, filtered (using the common L.sub.dc and C.sub.dc) and
regulated using switch S to the load. If the coupled power to any
of the coils is determined to be low, then the two switches at the
base of each rectifier can be turned on and used to decouple that
coil from the circuit without affecting the power transfer in
either of the remaining coils, thereby substantially removing any
loss associated with that circuit. This power transfer from each
coil can be easily determined by measuring the magnitude of the AC
current in each of the rectifiers. The output diode ensures that
the energy in C.sub.dc is not discharged undesirably through any of
the switches in the circuit when these switches are turned on.
Switch S is used to both regulate the total power flow and decouple
all three coils if and when required.
[0157] In any embodiment where the IPT pad of the present invention
is configured as a primary side magnetic apparatus generating a
magnetic field, it preferably couples power to the secondary or
receiving pad as effectively as possible, irrespective of the
secondary pad's magnetic configuration, orientation, and
displacement (lateral or otherwise). The secondary pad may be
integrated within a vehicle, mobile telephone, laptop or other such
electrical device, providing little if any control over these
variable factors. That is, the primary pad is preferably designed
to be universal or near-universal in that it is adapted to transfer
power to a range of possible secondary pads and/or under a wide
range of conditions which could be reasonably anticipated in a
particular application.
[0158] When a device with a circular secondary pad is in proximity
with varying ground clearance or displacement with respect to the
primary, for example, there will be a need to configure the system
to best couple power from the primary to the secondary. If the
device is in close proximity to the ground, then the coil which is
in best alignment might be selected, whereas if the secondary is
further away a group of coils may be energised either together in
phase or as a multiphase system to produce a better coupling
between the primary and secondary. Another important consideration
is limiting or minimising magnetic field leakage at distances of
concern, such as where there are foreign objects which may heat up
or humans or animals which may be subjected to these leakage
fields.
[0159] For secondary devices which have polarised magnetics such as
those disclosed in International Patent Publication Nos. WO
2010/090539 or WO 2010/090538, then the orientation of this device
is of equal concern. In such situations the primary coils may be
energised to ensure best coupling and in the case where the coils
are separately controlled either a single phase polarised coil with
best orientation can be energised, or multiphase operation can be
used to transfer power while ensuring greatest coupling and power
transfer with minimal leakage for the designated application.
Variations in ground clearance, alignment and rotation may all
affect the choice of which coils are selected under what
conditions. Preferably the coils in the primary ground side have
minimal mutual coupling between them, so that any configuration is
acceptable and can be used without detrimental effects such as
coupled voltages from the energising of neighbouring coils
appearing in nearby coils and disrupting power flow and the
generation of the desired flux shape. However some mutual
cross-coupling may be allowable in certain configurations if is
sufficiently small, provided the power coupling between the
apparatus is controllable and leakage is contained as required for
the application.
[0160] It will be appreciated that numerous other embodiments or
variations of the coil arrangements of FIGS. 4 and 5 are possible
without departing from the scope of the present invention. A number
of such embodiments and variations are briefly described below by
way of example.
[0161] While a backing comprising the core and/or conductive plate
is useful to ensure that the fields are single sided and can be
oriented in space such that they enhance the coupling to a
secondary magnetic device, the ferrite strips 5 are not essential
to the present invention, and may in particular be omitted where a
double-sided flux field may be tolerable or even desirable.
[0162] FIGS. 10 and 11 show variations of the embodiments of FIGS.
4 and 5, respectively, in which the ferrite strips 5 are omitted.
Without the core a backplate made of a conductive material such as
aluminium or copper provided a suitable distance from the coils may
act as a shield while minimising losses. The plate 7 may therefore
comprise a ferrite loaded printed circuit board (PCB) and/or an
aluminium plate, for example. Alternatively there may be
applications where there is a desire to have fields in both
directions, such as in a primary pad which may need to couple to
two or more secondary's which are situated both above and below the
coils. In such cases the ferrite or shields can be removed entirely
to enable such coupling. In other cases, the fields below the
structure may not be able to couple undesirably to any structure,
and therefore will not cause any losses. While having fields
present on both sides of the primary reduces coupling to a
secondary device, it does not produce any significant loss and may
therefore be preferred in some circumstances to minimise the cost
of producing the primary pad.
[0163] FIGS. 12(a) and 12(b) show two variations of a further
embodiment of an IPT pad according to the present invention, with
and without ferrite strips 5. The pad according to this embodiment
comprises four coils 2, 3, 3a and 3b with a quadrature coil 12. If
the four circular coils 2, 3, 3a and 3b are thought of as each
having a centre collectively defining the vertices of a square,
diagonally opposing coils of the square abut each other without
overlapping to form two orthogonal DDP pairs (as described above
with respect to FIGS. 1 and 2) operating as dipoles. Each coil of
the DDP pairs overlaps both the coils of the orthogonal DDP pair,
and the two DDP pairs are accordingly mutually decoupled. The
quadrature coil 12 is also mutually decoupled from both of the DDP
pairs. As a primary structure the DDP pairs and the quadrature coil
are all independent and may also be operated with different
magnitude, phase or frequency without interfering with each other,
to shape the field as required. As a secondary structure the DDP or
quadrature coils can be separately tuned at different or similar
frequencies and power can be extracted as and when desired based on
the application.
[0164] In one possible mode of operation of the embodiments of FIG.
12, the DDP pairs may be operated in phase with each other,
generating a stationary time varying magnetic field. In another
mode, one pair of diagonally opposing DDP coils may be energised
out of phase with the other pair. In yet another mode, only one DDP
may be energised. In yet further modes, the quadrature coil 12 may
be energised simultaneously with either or both of the DDP pairs.
The mode of operation and, where appropriate, coils energised are
preferably chosen to produce a field most effectively received by a
pickup. The IPT system is preferably capable of switching between
any such mode as required to operate in the most efficient way, but
may be limited to a single mode or a selection of modes to simplify
the power supply design and/or control.
[0165] FIGS. 12(c)-(e) show further variations of the embodiments
of FIGS. 12(a) and (b). The embodiment of FIG. 12(c) omits the
quadrature coil. FIG. 12(d) illustrates that the coils of each DDP
pair need not necessarily be the same size, yet are still capable
of being mutually decoupled. A quadrature coil 12 can also be added
to this embodiment as shown in FIG. 12(e). Because the DDP pairs of
coils are operated as dipoles, the quadrature coil 12 is mutually
decoupled from both DDP pairs in this embodiment.
[0166] While the coils of an IPT pad according to various
embodiments of the present invention are ideally completely
decoupled from one another, some nominal coupling may be
inevitable. The IPT pad of FIG. 4(b), with the dimensions listed in
Table A4, under testing was shown to have an optimum mutual
coupling or coupling coefficient k of 0.15% between coils 2 and 3,
and 0.08% between coils 2 and 3a, for example. However, any
significant mutual coupling between coils will severely impact the
efficiency of the system and the mutual coupling should ideally be
as close to zero as practically possible. It should be noted that
the mutual coupling measured between coils will generally increase
under load or in the presence of an external ferrite material. An
IPT pad according to the present invention is thus preferably
designed to have a mutual coupling of less than about 10% in the
absence of a load or external ferrite material, and more
particularly less than about 2% or even 1%. For the purpose of the
description and claims, the phrases "mutually decoupled", "no
mutual coupling" and the like are intended to encompass such mutual
couplings.
[0167] For such apparatuses to have coils which are mutually
decoupled requires proper spacing of the coils relative to each
other so that the flux generated from one device enters and exits
in approximately equal proportion with neighbouring coils in the
primary (or secondary), wherein the net flux through neighbouring
coils is approximately zero.
[0168] Nevertheless, a higher level of coupling between the coils,
such as up to about 20%, may be acceptable in at least some
applications without departing from the scope of the invention.
Even higher levels of mutual decoupling may be tolerable for some
applications, in particular where the spacing between the primary
and secondary pads is low. FIGS. 13 and 14 show embodiments of the
invention in which there may be a low level of mutual coupling, of
up to about 20% for example.
[0169] FIGS. 13(a)-13(e) show embodiments comprising further
variations of the three-coil IPT pad of FIG. 4.
[0170] The IPT pad of FIG. 13(a) further comprises a further coil
13 which is not ideally mutually decoupled, in this case entirely
encircling coils 2, 3 and 3a. The further coil 13 in this
embodiment is preferably disposed such that its centre or pole is
substantially central with respect to coils 2, 3 and 3a which are,
preferably, mutually decoupled from one another. Although the
central coil 13 in this embodiment encircles the other coils, in
other embodiments the substantially central coil 13 may
circumscribe or partially overlap the three or more other coils, as
described below.
[0171] As the central coil 13 encircles or partially overlaps all
of the other coils, it will not be mutually decoupled from those
coils in all possible modes of operation. In particular, the
central coil 13 of FIG. 13(a) will be substantially mutually
decoupled from coils 2, 3 and 3a when all three of those coils are
energised, but will not typically be mutually decoupled when only
coils 2 and 3 are energised, for example,
[0172] The IPT pad of FIG. 13(a) also omits the core or ferrite
strips 5 of the embodiment of FIG. 4. The square shape of the plate
7 can also be seen to differ from the triangular plate 7 of FIG. 4
to accommodate the central coil 13.
[0173] The embodiment of FIG. 13(b) is similar to that of FIG.
13(a), but comprises a lattice or grid of substantially orthogonal
ferrite strips 5. It will be apparent that the ferrite strips 5
thus need not necessarily extend parallel to imaginary lines
between the centres of coils 2, 3 and 3a as shown in FIG. 4. As
previously described, the core may alternatively comprise a sheet
of ferrite material.
[0174] The embodiment of FIG. 13(c) comprises a further
modification with respect to FIG. 13(b), in that the ferrite strips
5 extend beyond the outer circumference of central coil 13. If the
ferrite strips 5 terminate within the central coil 13 then the
field will radiate, and the elongated ferrite strips 5 of this
embodiment will thus generally be preferred.
[0175] FIGS. 13(d) and 13(e) show further variations of the
three-coil pad of FIG. 4, further comprising a central coil 13
which partially encircles coils 2, 3 and 3a. FIG. 13(d) shows an
embodiment of an IPT pad without ferrite strips 5, while FIG. 13(e)
comprises a lattice of ferrite strips 5 extending to, or slightly
beyond, the outer circumference of coils 2, 3 and 3a.
[0176] FIGS. 14(a) to 14(d) illustrate some sub-optimal variations
of the three-coil embodiments of FIG. 4, by way of example. In
these embodiments, the coils 2, 3 and 3a do not overlap, and will
therefore have mutual coupling.
[0177] In the case where the multi-coil structure of the present
invention is used as a secondary pad to receive power, ideally the
coils will all be mutually decoupled from each other to ensure that
each coil can be easily tuned to receive power at a selected
frequency, and that power transfer is maximised. Under such
conditions, when a coil is not receiving power it can be switched
off without impacting the operation of the other coils, to reduce
any operating loss. Nevertheless, if the secondary coils are not
perfectly mutually coupled (independent), then provided the
operating circuit tuning Q (reactance of the coil divided by the
load of the circuit) is low, then nominal tuning can be achieved
and operation can still arise despite there being some mutual
coupling between neighbouring coils. Such coils can also be
switched out and while this may slightly impact the power transfer
in adjacent coils, this can be compensated for by operation of the
primary ground coils increasing or decreasing its driving VA or by
adjusting a secondary regulator to modify the power to the
load.
[0178] In a further embodiment of the present invention comprising
three or more mutually decoupled coils, it may in some applications
be desirable to tune one or more of the various coils to different
frequencies to enable coupled operation with secondary devices
which have different tunings. For example, for high power transfer
some of the coils may be designed and tuned for operation at 40 kHz
while others may be tuned at 80 kHz, enabling coupling to different
magnetic structures at different tuned frequencies. Alternatively,
for lower power transfer some coils may be tuned at 800 MHz while
others may be tuned to 2.4 GHz (both unlicensed bands) to achieve
the same for smaller appliances or mobile consumer electronics
devices, for example.
TABLE-US-00001 TABLE A1 Dimensions of the BPP Common Dimensions
Winding width 80 mm Ferrite spacing 32 mm Ferrite width 28 mm Y
coil spacing 50 mm Y padding 46 mm Cover thickness 6 mm Coil height
4 mm Ferrite height 16 mm Spacer thickness 6 mm Plate thickness 4
mm Variations based on number of ferrites A: BBP6: using 6 ferrite
slabs to make each ferrite strip (BPP6) Ferrite length 558 mm
(BBP6) Overlap 156 mm X coil spacing 10 mm X padding 10 mm B: BBP8:
using 8 ferrite slabs to make each ferrite strip Ferrite length 774
mm Overlap 74 mm X coil spacing -83 mm (-represents an overlap) X
padding 10 mm C: BBP10: using 10 ferrite slabs to make each ferrite
strip Ferrite length 930 mm Overlap 39 mm X coil spacing -174 mm
(-represents an overlap) X padding 110 mm (nb: 200 mm added overall
to padding to fit extra ferrites)
TABLE-US-00002 TABLE A2 Dimensions of the DDP Winding width 80 mm
Inner winding width 120 mm Ferrite spacing 32 mm Ferrite width 28
mm Y coil spacing 10 mm Y padding 46 mm Cover thickness 6 mm Coil
height 4 mm Ferrite height 16 mm Spacer thickness 6 mm Plate
thickness 4 mm Ferrite length 558 mm X coil spacing 10 mm X padding
10 mm
TABLE-US-00003 TABLE A3 Dimensions of the DDQP Winding width 80 mm
Inner winding width 120 mm Ferrite spacing 32 mm Ferrite width 28
mm Y coil spacing 10 mm Y padding 46 mm Cover thickness 6 mm Coil
height 4 mm Ferrite height 16 mm Spacer thickness 6 mm Plate
thickness 4 mm Ferrite length 558 mm X coil spacing 10 mm X padding
10 mm Quadrature coil length 534 mm
TABLE-US-00004 TABLE A4 Dimensions of the IPT Pad of FIG. 12
Ferrite length 520 mm Ferrite width 28 mm Ferrite height 16 mm Each
side of the equilateral triangle formed 200 mm by ferrite structure
Inner diameter of each coil 130 mm Outer diameter of each coil 150
mm Optimum distance from centre point of 172 mm one coil to the
other Mutual coupling k between coils 2 and 3 0.15% Mutual coupling
k between coils 2 and 3a 0.08%
[0179] While the invention has been described primarily with
reference to applications in powering or charging electric
vehicles, it is to be noted that the invention has application to
inductive power transfer in general, and may therefore be applied
in a range of industrial or consumer applications including, but
not limited to, wirelessly powering or charging high- or low-power
appliances or consumer electronics such as mobile telephones,
computer devices, and/or computer peripherals. By way of example
with reference to a human interface device (HID), a primary
magnetic flux pad according to the present invention may be
provided in a mouse pad to power or charge a wireless mouse, or may
be integrated in the mouse to receive power from a known primary
pad.
[0180] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise", "comprising",
and the like, are to be construed in an inclusive sense as opposed
to an exclusive or exhaustive sense, that is to say, in the sense
of "including, but not limited to".
[0181] Reference to any prior art in this specification is not, and
should not be taken as, an acknowledgement or any form of
suggestion that that prior art forms part of the common general
knowledge in the field of endeavour in any country in the
world.
[0182] The invention 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, in
any or all combinations of two or more of said parts, elements or
features.
[0183] Where in the foregoing description, reference has been made
to specific components or integers of the invention having known
equivalents then such equivalents are herein incorporated as if
individually set forth.
[0184] Although this invention has been described by way of example
and with reference to possible embodiments thereof, it is to be
understood that modifications or improvements may be made thereto
without departing from the scope or spirit of the invention.
* * * * *