U.S. patent application number 17/086282 was filed with the patent office on 2021-02-18 for inductive coupling gap compensation.
The applicant listed for this patent is Evatran Group, Inc.. Invention is credited to James Brian Normann, Thomas Gattan Stout.
Application Number | 20210046832 17/086282 |
Document ID | / |
Family ID | 1000005190818 |
Filed Date | 2021-02-18 |
United States Patent
Application |
20210046832 |
Kind Code |
A1 |
Stout; Thomas Gattan ; et
al. |
February 18, 2021 |
INDUCTIVE COUPLING GAP COMPENSATION
Abstract
A first inductive element including a plurality of first
subcoils, each first subcoil characterized at least in part by a
geometry that comprises a winding direction and a physical size is
provided. The plurality of first subcoils are in electrical
communication with each other, and the geometry of each first
subcoil is selected to reduce a variation in an inductive coupling
between the first inductive element and a second inductive element
when a gap between the first inductive element and the second
inductive element varies. A method of vehicle wireless power
charging using the above system is also provided.
Inventors: |
Stout; Thomas Gattan;
(Morrisville, NC) ; Normann; James Brian; (Holy
Springs, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Evatran Group, Inc. |
Richmond |
VA |
US |
|
|
Family ID: |
1000005190818 |
Appl. No.: |
17/086282 |
Filed: |
October 30, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15674091 |
Aug 10, 2017 |
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17086282 |
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62373856 |
Aug 11, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60L 53/12 20190201;
H01F 38/14 20130101; H02J 50/12 20160201; H02J 7/0042 20130101;
H02J 50/10 20160201; H01F 27/38 20130101 |
International
Class: |
B60L 53/12 20060101
B60L053/12; H02J 50/12 20060101 H02J050/12; H01F 27/38 20060101
H01F027/38; H02J 7/00 20060101 H02J007/00; H02J 50/10 20060101
H02J050/10; H01F 38/14 20060101 H01F038/14 |
Claims
1. A vehicle wireless power charging system, comprising: a
controller configured to execute instructions on a non-transitory
computer-readable data storage medium; a transfer coil apparatus,
wherein the transfer coil apparatus has minimal coupling variation
over a wide variation of a gap due to a combination of the coupling
of a plurality of subcoils without adjusting current settings in an
electric inverter supplying AC power; wherein the transfer coil
apparatus comprises: two inductive elements magnetically coupled
together, the two inductive elements comprising (i) a first
inductive element that is a wireless power transmitter, and (ii) a
second inductive element that is a wireless power receiver; wherein
the first inductive element is comprised of a plurality of first
subcoils in electrical communication with each other, each first
subcoil characterized at least in part by a geometry comprising a
winding direction, a number of turns, and a physical size; wherein
at least one first subcoil is wound in a first direction
(clockwise), at least one first subcoil is wound in a second
direction that is opposite to the first direction
(counter-clockwise), the locations of the plurality of first
subcoils are fixed relative to each other, the physical size of the
plurality of first subcoils are fixed, the physical size of the
plurality of first subcoils are substantially different; wherein
the second inductive element is comprised of a plurality of second
subcoils in electrical communication with each other, each second
subcoil characterized at least in part by a geometry comprising a
winding direction, a number of turns, and a physical size; wherein
the geometries of the first subcoils of the first inductive element
are selected to reduce the variation in coupling between the first
inductive element and the second inductive element as a function of
a gap between each of the first subcoils and the second inductive
element, the coupling defined as
k(G,.phi.)=C.sub.ak.sub.a(G,.phi.)+C.sub.bk.sub.b(G,.phi.); where
C.sub.a and C.sub.b are constants whose values depend on intrinsic
properties of each subcoil when planes on which the first and
second inductive elements lie are substantially parallel; and the
centers of the first and second inductive elements in X and Y
directions are at a fixed distance smaller than the largest
physical size of either inductive element; and a Z direction gap
between the first and second inductive elements varies over a large
distance; and wherein the controller is in communication with first
inductive element and with second inductive element.
2. A vehicle wireless power charging method, comprising the steps
of: executing instructions, by a controller, on a non-transitory
computer-readable data storage medium; statically optimizing
inductive coupling between two inductive elements over a wide range
of gaps in a wireless power transfer system without adjusting a
current settings in an electric inverter supplying AC power;
forming a plurality of first subcoils, each first subcoil
characterized at least in part by an original geometry that
comprises a winding direction, number of turns, and a physical
size; providing a second inductive element; determining the
couplings between each of the first sub coils individually and the
second inductive element as a function of a gap between each of the
first subcoils and the second inductive element; the coupling
defined as
k(G,.phi.)=C.sub.ak.sub.a(G,.phi.)+C.sub.bk.sub.b(G,.phi.); where
C.sub.a and C.sub.b are constants whose values depend on intrinsic
properties of each subcoil; adjusting the geometry of at least one
of the first subcoils to a modified geometry, based on the coupling
functions; electrically interconnecting the plurality of first
subcoils to form a first inductive element, wherein the winding
directions of at least two of the plurality of first subcoils are
opposite; communicating, by the controller, with the first
inductive element and with the second inductive element and;
achieving a reduced variation in coupling between the first
inductive element and the second inductive element when the gap
varies, by using the first subcoil modified geometry in place of
the original geometry through the entire range of gaps.
3. A vehicle wireless inductive power charging system, comprising:
a controller configured to execute instructions on a non-transitory
computer-readable data storage medium; two inductive elements
magnetically coupled together, the two inductive elements
comprising (i) a first inductive element that is a wireless power
transmitter, and (ii) a second inductive element that is a wireless
power receiver; wherein the first inductive element is comprised of
a plurality of first subcoils in electrical communication with each
other, each first subcoil characterized at least in part by a
geometry comprising a winding direction, a number of turns, and a
physical size; wherein at least one first subcoil is wound in a
first direction (clockwise), at least one first subcoil is wound in
a second direction that is opposite to the first direction
(counter-clockwise), the locations of the plurality of first
subcoils are fixed relative to each other; the physical size of the
plurality of first subcoils are fixed; the physical size of the
plurality of first subcoils are substantially different; wherein
the second inductive element is comprised of a plurality of second
subcoils in electrical communication with each other, each second
subcoil characterized at least in part by a geometry comprising a
winding direction, a number of turns, and a physical size; wherein
the controller is in communication with first inductive element and
with second inductive element; wherein the geometries of the first
subcoils of the first inductive element are selected to reduce the
variation in coupling between the first inductive element and the
second inductive element when the planes on which the first and
second inductive elements lie are substantially parallel and the
centers of the first and second inductive element in X and Y
directions are at a fixed distance smaller than the largest
physical size of either inductive element, and a Z direction gap
between the first and second inductive elements varies over a large
distance; and wherein a power source is connected to the input of
an electric inverter, the wireless power transmitter is connected
to the output of the electric inverter, the wireless power receiver
is connected to the input of a rectifier; a load is connected to
the output of the rectifier; and power from the source is
transferred through the inverter, magnetic coupling, and rectifier,
to the load, and current settings of the electric inverter are not
adjusted.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present disclosure is related and claims priority to
U.S. Provisional Pat. Appl. No. 62/373,856, filed on Aug. 11, 2016,
and U.S. patent application Ser. No. 15/674,091, filed on Aug. 10,
2017, the contents of which are hereby incorporated by reference in
their entirety, for all purposes.
BACKGROUND
Field of Disclosure
[0002] Embodiments described herein are generally related to the
field of wireless powering of electronic devices. More
specifically, embodiments described herein are related to systems
and methods for compensating an inductive coupling variation with
respect to a gap variation between a primary inductor and a
secondary inductor in a wireless powering configuration. One or
more of these embodiments may be employed to transfer power to a
vehicle from a base charging system.
Related Art
[0003] Current systems for wireless power transfer into mobile
electronic appliances have wide variability in total power
efficiency over the charging configuration geometry. For example,
the inductive coupling between two inductive elements, each having
a single coil, may vary by a factor of two or more over a span of
about two inches for the gap between the two inductive elements.
This inductive coupling variability is compensated by adjusting the
current settings in the electric inverter supplying AC power for
the primary inductive element, typically resulting in higher losses
when the inductive coupling is reduced with distance.
SUMMARY
[0004] In one embodiment, a first inductive element includes a
plurality of first subcoils, each first subcoil characterized at
least in part by a geometry that comprises a winding direction and
a physical size. The plurality of first subcoils are in electrical
communication with each other, and the geometry of each first
subcoil is selected to reduce a variation in an inductive coupling
between the first inductive element and a second inductive element
when a gap between the first inductive element and the second
inductive element varies.
[0005] In another embodiment, a method of optimizing inductive
coupling includes forming a plurality of first subcoils, each first
subcoil characterized at least in part by a geometry that comprises
a winding direction and a physical size. The method includes
electrically interconnecting the plurality of first subcoils to
form a first inductive element, providing a second inductive
element, and determining a variation of an inductive coupling
between the first inductive element and the second inductive
element as a function of a gap between the first inductive element
and the second inductive element. The method also includes
adjusting the geometry of at least one of the first subcoils to
reduce the variation of the inductive coupling when the gap
varies.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates an inductive wireless charging system
including a first inductive element and a second inductive element
having a mutual inductance M there between, according to some
embodiments.
[0007] FIG. 2 illustrates a configuration between a first inductive
element and a second inductive element, according to some
embodiments.
[0008] FIG. 3 illustrates a chart with graphs describing a magnetic
coupling as a function of a gap between the first inductive element
and the second inductive element, according to some
embodiments.
[0009] FIG. 4 is a flow chart illustrating steps in a method for
inductive coupling, according to some embodiments.
[0010] In the figures, elements and steps denoted by the same or
similar reference numerals are associated with the same or similar
elements and steps, unless indicated otherwise.
DETAILED DESCRIPTION
[0011] The detailed description set forth below is intended as a
description of various implementations and is not intended to
represent the only implementations in which the subject technology
may be practiced. As those skilled in the art would realize, the
described implementations may be modified in various different
ways, all without departing from the scope of the present
disclosure. Accordingly, the drawings and description are to be
regarded as illustrative in nature and not restrictive.
[0012] A wireless inductively coupled power transfer system
typically includes a primary coil and a secondary coil. A
traditional coil in the system is wound as a single spiral of wire,
with each turn being concentric and each turn going in the same
direction (e.g. clockwise or counterclockwise). In some embodiments
consistent with the present disclosure, a single coil can be
constructed from what is conceptually a plurality of subcoils where
the winding directions are not all the same. A small diameter coil
couples well at small gaps, but the inductive coupling with the
primary inductor that wirelessly provides an AC power typically
drops off quickly as the gap is increased. A larger diameter coil
couples better across the full range (i.e. the inductive coupling
does not fall off as quickly with increased gap), but will have a
lower coupling coefficient at small gaps. Subcoils comprising the
primary coil that are described as "large" are larger than the
secondary coil. Conversely, subcoils comprising the primary coil
that are described as "small" are smaller than the secondary coil.
Similarly, subcoils comprising the secondary that are described as
"large" or "small" are larger or smaller, respectively, than the
primary coil.
[0013] FIG. 1 illustrates an inductive wireless charging system 100
including a first inductive element 101, having inductance,
L.sub.1, and a second inductive element 102, having inductance,
L.sub.2. First inductive element 101 and second inductive element
102 may electromagnetically interact through a mutual inductance,
M, therebetween, according to some embodiments. Charging system 100
may include a configuration where a source 140, coupled to second
inductive element 102 (e.g., via an inverter circuit), would
typically provide power to a remote electronic device, e.g., charge
a battery for an electric vehicle that includes first inductive
element 101 at a voltage, V.sub.1, and generating a current,
I.sub.1.
[0014] First inductive element 101 includes subcoils 111a and 111b
(hereinafter, collectively referred to as "subcoils 111"). Subcoils
111 are in electrical communication with each other. Subcoil 111a
may be associated with an inductance, L.sub.1a, and subcoil 111b
may be associated with an inductance, L.sub.1b, so that, in some
embodiments, L.sub.1=L.sub.1a+L.sub.1b (e.g., when subcoils 111 are
interconnected in series as in system 100). In some embodiments,
L.sub.1 and L.sub.1a, and L.sub.1b are related as:
1/L.sub.1=1/L.sub.1a+1/L.sub.1b (e.g., when subcoils 111 are
interconnected in parallel). More generally, the relation between
L.sub.1, L.sub.1a, L.sub.1b, and any other inductance from an
additional subcoil 111 in first inductive element 101 may depend on
the specific electric coupling between subcoils 111, and also on a
fixed, relative angle .theta. 115 formed between axis W.sub.a of
subcoil 111a and axis W.sub.b of subcoil 111b, respectively.
[0015] Subcoils 111 may include a plurality of substantially
concentric loops of an electrically conductive material (e.g., a
conductive wire). In some embodiments, subcoils 111 are
interconnected in series. In some embodiments, subcoils 111 are
interconnected in parallel. Subcoils 111 also have a physical size
that may be defined by a diameter 110a and 110b (hereinafter,
collectively referred to as "diameter 110") and a thickness 112a
and 112b (hereinafter, collectively referred to as "thickness
112"). Further, each subcoil 111 may be characterized by a geometry
that comprises a winding direction 114a and 114b (e.g.,
counterclockwise or clockwise) and a physical size such as diameter
110 or thickness 112. The geometry of subcoils 111 may include a
number of loops, N.sub.a, and N.sub.b, in each subcoil.
[0016] In some embodiments, second inductive element 102 includes a
plurality of subcoils characterized in a similar manner as subcoils
111 in first inductive element 101. Source 140 generates a voltage
V.sub.2, and a current I.sub.2 flowing through second inductive
element 102, at a frequency, .omega.. Voltage V.sub.2 and current
I.sub.2 generate AC voltage V.sub.1 and AC current I.sub.1 through
first inductive element 101, due to the mutual inductance factor,
M. Accordingly, voltages V.sub.1 and V.sub.2 may satisfy the
following expressions:
V.sub.1=j.omega.(L.sub.1I.sub.1+MI.sub.2) (1.1)
V.sub.2=j.omega.(MI.sub.1+L.sub.2I.sub.2) (1.2)
System 100 may include a capacitor 155 that introduces a resonant
behavior in the inductive coupling of second inductive element 102
and first inductive element 101. Accordingly, for high .omega.
relative to 1/C (where the impedance is 1/.omega.C), primary coil
101 is substantially shorted down to ground voltage, V.sub.g (e.g.,
zero). Assuming V.sub.g=0, under high frequency conditions, then,
V.sub.2 is shorted down to zero and the following is true:
I 2 = - M I 1 L 2 ( 2 ) ##EQU00001##
[0017] And using Eq. (2) into Eq. 1.1:
V 1 = j .omega. ( L 1 I 1 - M 2 I 1 L 2 ) = I 1 j .omega. ( L 1 - M
2 L 2 ) ( 3 ) ##EQU00002##
[0018] By analogy with Eqs. 1.1 and 1.2, an effective inductance
L.sub.s may be defined as:
L s = L 1 - M 2 L 2 Wherein ( 4 ) V 1 = I 1 j .omega. L s ( 5 )
##EQU00003##
[0019] Accordingly, L.sub.s may be interpreted as the inductance
measured across L.sub.1 when second inductor 102 is shorted (e.g.,
at high frequencies, .omega.). From Eq. 4, the value of the mutual
inductance, M, may be found as:
M= {square root over (L.sub.2(L.sub.1-L.sub.s))} (6)
[0020] A unit-less coupling coefficient, k, may be further defined
as:
k = M L 1 L 2 = ( 1 - L s L 1 ) ( 7 ) ##EQU00004##
[0021] Measurement of L.sub.s when second inductive element 102 is
shorted, together with prior knowledge of L.sub.2 and L.sub.1,
gives a measure of coupling coefficient, k. The coupling
coefficient, k, is a unit-less value between 0 and 1, which is
dependent on the geometry of each of subcoils 111, the
configuration between subcoils 111 themselves, and the
configuration of each subcoil 111 relative to second inductive
element 102. In some embodiments, the geometry of subcoils 111 may
include a size (e.g., diameter 110 and thickness 112). The
configuration between subcoils 111 themselves may include a
relative winding direction between the subcoils (e.g., coil 111-1
wound clockwise, and coil 111-2 wound counter-clockwise) and the
value of fixed angle .theta. 115. The configuration between
subcoils 111 relative to second inductive element 102 includes the
value of gap 150 (G) and the value of an angle .PHI. 125 between
the axes of first conductive element 101 and second conductive
element 102 (W.sub.a and W.sub.2, respectively). In some
embodiments, the geometry of subcoils 111 is selected to reduce a
variation in the coupling coefficient, k, between first inductive
element 101 and second inductive element 102 when G 150 varies, or
when .PHI. 125 varies. Likewise, in embodiments where second
inductive element 102 includes a plurality of subcoils, the
geometry of each subcoil in the second inductive element 102 may be
selected to reduce the variation in the inductive coupling between
the first inductive element and the second inductive element when G
150 or .PHI. 125 vary.
[0022] In some embodiments, and to a first order approximation, it
is desirable to express the inductive coupling, k, between first
inductive element 101 and second inductive element 102 as a linear
combination of two inductive coupling coefficients k.sub.a and
k.sub.b. Accordingly, inductive coupling k.sub.a may be an
inductive coupling between subcoil 111a and second inductive
element 102. Likewise, inductive coupling k.sub.b may be an
inductive coupling between subcoil 111b and second inductive
element 102. In such embodiments, an expression for inductive
coupling, k, between first inductive element 101 and second
inductive element 102 may be given by the following mathematical
equation
k(G,.phi.)=C.sub.ak.sub.a(G,.phi.)+C.sub.bk.sub.b(G,.phi.) (8)
Where C.sub.a and C.sub.b are constants whose value depends on
intrinsic properties of each of subcoils 111a and 111b,
respectively, and their relative configuration (e.g., angle .theta.
115). In some embodiments, the intrinsic properties of each of
subcoils 111a and 111b may include the inductance of each subcoil
111, separately (e.g., L.sub.a and L.sub.b). For example, the value
of constants C.sub.a and C.sub.b may depend on at least one of the
diameter, the length, and the number of loops of each of the
subcoils 111. Further, the relative ratio between constants C.sub.a
and C.sub.b may depend on the relative configuration between
subcoils 111. For example, the parity between constants C.sub.a and
C.sub.b (C.sub.a, C.sub.b=+,+; +, -; -,+; -,-) may depend on the
relative winding orientation between the subcoils (e.g.,
clockwise-clockwise, clockwise-counterclockwise,
counterclockwise-clockwise, counterclockwise-counterclockwise). In
some embodiments, an expression similar to Eq. 8 applies for any
number of subcoils 111 in first inductive element 101, and a
constant C.sub.i is associated with each subcoil, 111i.
[0023] As Eq. 8 indicates, coupling coefficients k, k.sub.a, and
k.sub.b may be functions of G 150, and of .PHI. 125. More
generally, k.sub.a and k.sub.b may be different functions of G 150
and of .PHI. 125. The variation in the coupling coefficient, k, as
a function of G 150 may be expressed from Eq. 8 as:
.DELTA.k(G,.phi.)=(C.sub.ak'.sub.a(G,.phi.)+C.sub.bk'.sub.b(G,.phi.)).DE-
LTA.G (9)
Where k'.sub.a and k'.sub.b are first derivatives of functions
k.sub.a and k.sub.b with respect to G 150. In some embodiments, it
is desirable to choose the intrinsic properties (e.g., geometry and
relative configuration, including .theta. 115) of subcoils 111 so
that the values of constants C.sub.a and C.sub.b are such that
.DELTA.k(G,.PHI.) is minimized for a selected range of values of
gap 150 (G) and of angle .PHI. 125 (cf. Eq. 9).
[0024] When G 150 changes (e.g., first inductive element 101 is
displaced relative to second inductive element 102), inductive
coupling, k, changes as well by an amount .DELTA.k (cf. Eq. 9). The
value of .DELTA.k leads to a change in the induced voltage V.sub.1,
which may induce a reduction in voltage V.sub.2 (e.g., when
.DELTA.G>0). However, reducing V.sub.2 may be compensated by an
increase the current I.sub.2 to maintain a constant output power,
P.sub.out=V.sub.2I.sub.2, provided by source 140. However, current
I.sub.2 is typically supplied by an inverter circuit having losses
that are proportional to the square of the current, I.sub.2.
Embodiments as disclosed herein include specially designed first
inductive element 101 having a plurality of subcoils 111, each with
a geometry and a winding direction 114 that minimizes the variation
ink over a wide range of values of G 150 and of .PHI. 125.
[0025] Accordingly, in some embodiments consistent with the present
disclosure, the inductive coupling, k, between inductive elements
101 and 102 may vary by a factor of about two or less, over a G 150
span of five inches, or more (e.g., a variability at least half or
less of what would be expected between two traditional, single-coil
inductive elements). This prevents the need to over-design the
inverter coupled to source 140 to operate at high values of k, and
allows for the system to run at a more consistent operating point
over a broader range of configurations between first inductive
element 101 and second inductive element 102. Accordingly,
embodiments as disclosed herein reduce the power losses in the
circuitry providing current I.sub.2 to second inductive element 102
(e.g., source 140).
[0026] Wireless charging system 100 may further include a
controller 160 having a processor 161 configured to execute
instructions from, and receive and store data in, a memory 162.
Controller 160 may communicate (e.g., wirelessly or via a wire)
with first inductive element 101 and with second inductive element
102, so that when processor 161 executes instructions from memory
162, controller 160 may cause wireless charging system 100 to
perform steps in a method consistent with the present disclosure.
In some embodiments, controller 160 causes a charge start in
wireless charging system 100 according to a detected value of G 150
or .PHI. 125 (e.g., when G 150 is smaller than a first threshold,
or when .PHI. 125 is smaller than a second threshold), or a
combination of a value of G 150 and a value of .PHI. 125. Further,
in some embodiments controller 160 may cause a charge stop in
wireless charging system 100 according to a detected value of G 150
or .PHI. 125 (e.g., when G 150 is larger than a third threshold, or
when .PHI. 125 is larger than a fourth threshold), or a combination
of both. Further, in some embodiments controller 160 may cause
wireless charging system 100 to start or stop charging according to
a value of V.sub.1, V.sub.2, I.sub.1, I.sub.2, or a combination of
the above. In some embodiments, processor 161 may be configured to
determine a value of k, a value of .DELTA.k, or a combination of
both (cf. Eqs. 8-9). Accordingly, controller 160 may cause wireless
charging system 100 to start or stop charging according to the
value of k, of .DELTA.k, or a combination of the two.
[0027] FIG. 2 illustrates a configuration 200 between a first
inductive element 201 and a second inductive element 202 separated
by a gap G (e.g., along the Z axis) 250, according to some
embodiments. In some embodiments, second inductive element 202 is
configured as a primary inductor in a wireless power transfer
system, receiving an alternating current (AC), I.sub.2, to induce
an AC voltage in first inductive element 201, which acts as a
secondary inductor configured to receive power from the primary
inductor (e.g., in a wirelessly re-chargeable electric appliance).
First inductive element 201 includes a smaller subcoil 211a and a
larger subcoil 211b (hereinafter, collectively referred to as
"subcoils 211"). Subcoil 211a has an inner diameter 210ia, an outer
diameter 210oa (hereinafter, collectively referred to as "diameters
210a"), a thickness 212a, and is wound in a clockwise direction
214a. Likewise, subcoil 211b has an inner diameter 210ib
(hereinafter, collectively referred to as "diameters 210b"), an
outer diameter 210ob, a thickness 212b, and is wound in a
counter-clockwise direction 214b.
[0028] For example, in some embodiments subcoil 211a may include 25
turns with an inner diameter 210ia of about 2.5 inches, an outer
diameter 210oa of about 4.25 inches, and a thickness 212a of about
0.25 inches. Further, in some embodiments subcoil 211b may include
25 turns with an inner diameter 210ib of about 9.5 inches, an outer
diameter 210ob of about 11.25 inches, and a thickness 212b of about
0.25 inches.
[0029] By winding subcoils 211 in opposite directions, the combined
effective inductive coupling, k, between first inductive element
201 and second inductive element 202, is associated with a
difference between the inductive coupling between subcoil 211a and
second inductive element 202, k.sub.a, and the inductive coupling
between subcoil 211b and second inductive element 202, k.sub.b.
Furthermore, by adjusting the number of turns in each coil the
ratio Ca/Cb of inductive coupling coefficients of each of subcoils
211 with second inductive element 202 can be controlled.
Accordingly, an effective inductive coupling, k, may be
approximately: k=k.sub.b-0.5*k.sub.a (cf. Eqs. 8-9, with
C.sub.a=-0.5, and C.sub.b=1), wherein k.sub.a is the inductive
coupling between subcoil 211a and second inductive element 202, and
k.sub.b is the inductive coupling between subcoil 211b and second
inductive element 202.
[0030] Tables 1-3 below list the results for mutual inductance (M)
and inductive coupling, k(G), as a function of G 150 for the
inductive coupling system illustrated in configuration 200. Without
limitation, and for illustrative purposes only, the variation of G
150 in Tables 1-3 is from zero (0), to seven (7) inches.
[0031] Note that the configuration of subcoils 211 in first
inductive element 201 includes a fixed gap 251 (G.sub.2) between
subcoil 211a and subcoil 211b, and coplanar subcoils 211 (along an
XY plane). Accordingly, in some embodiments the value of G.sub.2
251 may also be adjusted to modify coefficients C.sub.a and C.sub.b
(and their relative value). For example, while subcoils 211 are
shown to be concentric, some embodiments may include non-concentric
subcoils 211, so that G.sub.2 251 may in fact be different around
the circumference of either one of subcoils 211. Moreover, in some
embodiments, subcoils 211, in addition to have different diameters
210a/210b, and different winding directions 214, may be placed in
different planes.
TABLE-US-00001 TABLE 1 Total inductive coupling, k Mutual Primary
Secondary Inductance Inductance Inductance (H) Inductive Z
.times.10.sup.-5 (H) .times.10.sup.-4 (H) .times.10.sup.-5 Coupling
(inches) (201) (202) (M) (k) 7 2.02 6.94 0.895 0.075467 6 2.02 6.94
1.02 0.085772 5 2.02 6.94 1.14 0.096533 4 2.02 6.94 1.27 0.106769 3
2.02 6.94 1.37 0.115187 2 2.02 6.94 1.42 0.119404 1 2.02 6.94 1.39
0.117647 0 2.02 6.94 1.32 0.1117
TABLE-US-00002 TABLE 2 Small subcoil 211a Primary Secondary Mutual
Inductance Inductance Inductance Inductive Z .times.10.sup.-5 (H)
.times.10.sup.-4 (H) .times.10.sup.-5 (H) Coupling (inches) (201)
(202) (M) (k) 7 2.02 1.34 0.297 0.057098 6 2.02 1.34 0.380 0.073057
5 2.02 1.34 0.491 0.09437 4 2.02 1.34 0.639 0.122869 3 2.02 1.34
0.834 0.160482 2 2.02 1.34 1.08 0.208506 1 2.02 1.34 1.37 0.264079
0 2.02 1.34 1.62 0.312451
TABLE-US-00003 TABLE 3 Large subcoil 211b Primary Secondary Mutual
Inductance Inductance Inductance Inductive Z .times.10.sup.-5 (H)
.times.10.sup.-4 (H) .times.10.sup.-5 (H) Coupling (inches) (201)
(202) (M) (k) 7 2.02 6.34 1.19 0.10521 6 2.02 6.34 1.40 0.123324 5
2.02 6.34 1.63 0.144373 4 2.02 6.34 1.90 0.168171 3 2.02 6.34 2.20
0.19425 2 2.02 6.34 2.50 0.220711 1 2.02 6.34 2.77 0.244385 0 2.02
6.34 2.95 0.260366
[0032] FIG. 3 illustrates a chart 300 with graphs describing the
inductive coupling results of configuration 200 as a function of G
150 (cf. FIG. 2 and Tables 1-3). Curve 310a corresponds to total
inductive coupling, k, (cf. Table 1). Curve 310b corresponds to
inductive coupling, k.sub.a, (small subcoil 211a, cf. Table 2),
dropping fast as a function of G 150 from a large value at G=0.
Curve 310c corresponds to inductive coupling, k.sub.b, (large
subcoil 211b, cf. Table 3), dropping at a lower rate than the small
inductive coupling, from a lower inductive coupling at G=0.
Further, the variation of k for first inductive element 201 over a
large range (e.g., 7 inches) is reduced compared to either subcoil
211a (small, k.sub.a) and 211b (large, k.sub.b), independently.
[0033] FIGS. 2 and 3 illustrate embodiments were the secondary
inductor (e.g., first inductive elements 101 or 201) includes a
plurality of subcoils. Furthermore, embodiments consistent with the
present disclosure may include using a plurality of opposite wound
coils on second inductive elements 102 or 202 (e.g., the primary
inductor that supplies power), or on both the primary and secondary
sides. A precise control over the coupling variance (.DELTA.k,
e.g., Eq. 9) is achieved by adjusting geometries (e.g., inner/outer
diameter, thickness, and relative angles) and number of turns in
the subcoils. In some embodiments, a certain degree of variation
.DELTA.k.noteq.0 is allowed in the system. For example, in some
embodiments it may be desirable to design an inverter circuit that
operates over a range of current, I.sub.2, from X to 2X. In this
case, a first inductive element 101, or 201 may include subcoils
111 or 211 designed and arranged so that .DELTA.k/k is less than
two (2) over a pre-selected desired gap range (.DELTA.G). In some
embodiments, inductive coupling, k, generally decreases as
inductive elements 101 and 102 (201 and 202, likewise) move farther
away (.DELTA.G>0). The results (cf. FIG. 3 and Table 1) verify
that .DELTA.k is substantially reduced over a wide variation in gap
(no power was transferred), and that k may decrease below a certain
gap value G 350.
[0034] FIG. 4 is a flow chart illustrating steps in a method 400 of
optimizing inductive coupling between a first inductive element and
a second inductive element, according to some embodiments. The
first inductive element may be separated by a variable gap from the
second inductive element, and form a variable angle between the
axis of the two inductive elements (e.g., G 150, G 250, and .PHI.
125, cf. FIGS. 1-2). Further, at least one, or both, of the first
and second inductive elements may include a plurality of subcoils,
each subcoil having a geometry, and a relative configuration to
each other (e.g., subcoils 111 and 211). In some embodiments, the
geometry of each subcoil may include a thickness, an inner
diameter, an outer diameter, and a number of loops. Moreover, a
relative configuration between the subcoils may include a fixed
angle and a fixed gap between any two of the subcoils, and a
clockwise, counter-clockwise winding direction (e.g., angle 115,
gap G.sub.2 251, thickness 110, diameter 112, winding direction
114, cf. FIGS. 1 and 2).
[0035] Methods consistent with method 400 may include at least one,
but not all of the steps in method 400. At least some of the steps
in method 400 may be performed by a processor circuit in a
controller, wherein the processor circuit is configured to execute
instructions and commands stored in a memory (e.g., controller 160,
processor 161, and memory 162, cf. FIG. 1). Further, methods
consistent with the present disclosure may include at least some of
the steps in method 400 performed in a different sequence. For
example, in some embodiments a method may include at least some of
the steps in method 400 performed in parallel, simultaneously,
almost simultaneously, or overlapping in time.
[0036] Step 402 includes forming a plurality of first subcoils,
each first subcoil characterized by a geometry that comprises a
winding direction and a physical size. In some embodiments, step
402 includes winding a plurality of substantially concentric loops
of an electrically conductive material for each first subcoil.
[0037] Step 404 includes electrically interconnecting the plurality
of first sub-coils to form the first inductive element. In some
embodiments, step 404 includes connecting at least two of the first
subcoils in series. In some embodiments, step 404 includes
connecting at least two of the first subcoils in parallel.
[0038] Step 406 includes providing the second inductive element. In
some embodiments, step 406 includes forming a plurality of second
subcoils. In some embodiments, step 406 includes winding a
plurality of substantially concentric loops of an electrically
conductive material for each second subcoil. Accordingly, in some
embodiments step 406 includes electrically interconnecting the
plurality of second subcoils. In some embodiments, step 406
includes electrically interconnecting at least two of the plurality
of second subcoils in series. In some embodiments, step 406
includes connecting at least two of the plurality of second
subcoils in parallel.
[0039] Step 408 includes determining a variation of an inductive
coupling between the first inductive element and the second
inductive element as a function of a gap between the first
inductive element and the second inductive element.
[0040] Step 410 includes adjusting the geometry of at least one of
the first subcoils to reduce the variation of the inductive
coupling when the gap varies.
[0041] To the extent that the term "include," "have," or the like
is used in the description or the claims, such term is intended to
be inclusive in a manner similar to the term "comprise" as
"comprise" is interpreted when employed as a transitional word in a
claim.
[0042] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment described
herein as "exemplary" is not necessarily to be construed as
preferred or advantageous over other embodiments. Phrases such as
an aspect, the aspect, another aspect, some aspects, one or more
aspects, an implementation, the implementation, another
implementation, some implementations, one or more implementations,
an embodiment, the embodiment, another embodiment, some
embodiments, one or more embodiments, a configuration, the
configuration, another configuration, some configurations, one or
more configurations, the subject technology, the disclosure, the
present disclosure, other variations thereof and alike are for
convenience and do not imply that a disclosure relating to such
phrase(s) is essential to the subject technology or that such
disclosure applies to all configurations of the subject technology.
A disclosure relating to such phrase(s) may apply to all
configurations, or one or more configurations. A disclosure
relating to such phrase(s) may provide one or more examples. A
phrase such as an aspect or some aspects may refer to one or more
aspects and vice versa, and this applies similarly to other
foregoing phrases.
[0043] A reference to an element in the singular is not intended to
mean "one and only one" unless specifically stated, but rather "one
or more." The term "some" refers to one or more. Underlined and/or
italicized headings and subheadings are used for convenience only,
do not limit the subject technology, and are not referred to in
connection with the interpretation of the description of the
subject technology. Relational terms such as first and second and
the like may be used to distinguish one entity or action from
another without necessarily requiring or implying any actual such
relationship or order between such entities or actions. All
structural and functional equivalents to the elements of the
various configurations described throughout this disclosure that
are known or later come to be known to those of ordinary skill in
the art are expressly incorporated herein by reference and intended
to be encompassed by the subject technology. Moreover, nothing
disclosed herein is intended to be dedicated to the public
regardless of whether such disclosure is explicitly recited in the
above description. No claim element is to be construed under the
provisions of 35 U.S.C. .sctn. 112(f), unless the element is
expressly recited using the phrase "means for" or, in the case of a
method claim, the element is recited using the phrase "step
for."
[0044] While this specification contains many specifics, these
should not be construed as limitations on the scope of what may be
claimed, but rather as descriptions of particular implementations
of the subject matter. Certain features that are described in this
specification in the context of separate embodiments can also be
implemented in combination in a single embodiment. Conversely,
various features that are described in the context of a single
embodiment can also be implemented in multiple embodiments
separately or in any suitable subcombination. Moreover, although
features may be described above as acting in certain combinations
and even initially claimed as such, one or more features from a
claimed combination can in some cases be excised from the
combination, and the claimed combination may be directed to a
subcombination or variation of a subcombination.
[0045] The subject matter of this specification has been described
in terms of particular aspects, but other aspects can be
implemented and are within the scope of the following claims. For
example, while operations are depicted in the drawings in a
particular order, this should not be understood as requiring that
such operations be performed in the particular order shown or in
sequential order, or that all illustrated operations be performed,
to achieve desirable results. The actions recited in the claims can
be performed in a different order and still achieve desirable
results. As one example, the processes depicted in the accompanying
figures do not necessarily require the particular order shown, or
sequential order, to achieve desirable results. In certain
circumstances, multitasking and parallel processing may be
advantageous. Moreover, the separation of various system components
in the aspects described above should not be understood as
requiring such separation in all aspects, and it should be
understood that the described program components and systems can
generally be integrated together in a single software product or
packaged into multiple software products.
[0046] The title, background, brief description of the drawings,
abstract, and drawings are hereby incorporated into the disclosure
and are provided as illustrative examples of the disclosure, not as
restrictive descriptions. It is submitted with the understanding
that they will not be used to limit the scope or meaning of the
claims. In addition, in the detailed description, it can be seen
that the description provides illustrative examples and the various
features are grouped together in various implementations for the
purpose of streamlining the disclosure. The method of disclosure is
not to be interpreted as reflecting an intention that the claimed
subject matter requires more features than are expressly recited in
each claim. Rather, as the claims reflect, inventive subject matter
lies in less than all features of a single disclosed configuration
or operation. The claims are hereby incorporated into the detailed
description, with each claim standing on its own as a separately
claimed subject matter.
[0047] The claims are not intended to be limited to the aspects
described herein, but are to be accorded the full scope consistent
with the language claims and to encompass all legal equivalents.
Notwithstanding, none of the claims are intended to embrace subject
matter that fails to satisfy the requirements of the applicable
patent law, nor should they be interpreted in such a way.
* * * * *