U.S. patent application number 17/066093 was filed with the patent office on 2021-04-01 for inductive power transmitter.
The applicant listed for this patent is Apple Inc.. Invention is credited to Ali Abdolkhani.
Application Number | 20210099021 17/066093 |
Document ID | / |
Family ID | 1000005273771 |
Filed Date | 2021-04-01 |
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United States Patent
Application |
20210099021 |
Kind Code |
A1 |
Abdolkhani; Ali |
April 1, 2021 |
Inductive Power Transmitter
Abstract
An inductive power transmitter comprising: at least one power
transmitting coil configured to generate an inductive power
transfer (IPT) field; and an object detection system configured to
detect objects in or adjacent a space occupied by the IPT field
when generated; wherein the object detection system is configured
to detect a receiver object based on a tag associated with the
receiver object.
Inventors: |
Abdolkhani; Ali; (Freemans
Bay, NZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Family ID: |
1000005273771 |
Appl. No.: |
17/066093 |
Filed: |
October 8, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15554938 |
Aug 31, 2017 |
10840744 |
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PCT/NZ2016/050034 |
Mar 4, 2016 |
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17066093 |
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62128263 |
Mar 4, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 50/60 20160201;
H01F 7/02 20130101; H02J 50/10 20160201; G06K 19/07758 20130101;
H02J 50/12 20160201; H02J 50/90 20160201; H02J 50/40 20160201 |
International
Class: |
H02J 50/60 20060101
H02J050/60; H02J 50/10 20060101 H02J050/10; H02J 50/12 20060101
H02J050/12; G06K 19/077 20060101 G06K019/077 |
Claims
1. An inductive power transmitter comprising: a power transmitting
coil configured to generate an inductive power transfer (IPT)
field; and an object detection system configured to detect objects
in or adjacent a space occupied by the IPT field when generated;
wherein the inductive power transmitter is configured to: perform
detection of a potential receiver object using the object detection
system by correlating a shape of a voltage versus time waveform or
a current versus time waveform with a reference waveform shape,
wherein the voltage versus time or current versus time waveform is
magnetically induced by the potential receiver object; in response
to detecting the potential receiver object, attempt to communicate
with the potential receiver object; and in response to a failure to
communicate with the potential receiver object, perform further
detection of a potential receiver object.
2. The inductive power transmitter of claim 1 wherein the inductive
power transmitter is further configured to energize the power
transmitting coil in response to a successful attempt to
communicate with the potential receiver object.
3. The inductive power transmitter of claim 2 wherein the inductive
power transmitter is further configured to energize the power
transmitting coil in response to a detection of the potential
receiver object.
4. The inductive power transmitter of claim 2 or 3 wherein the
inductive power transmitter is further configured to de-energize
the power transmitting coil in response to a failure to communicate
with the potential receiver object.
5. The inductive power transmitter in claim 1, wherein the object
detection system comprises at least one magnetic switch.
6. The inductive power transmitter in claim 5, wherein the at least
one magnetic switch comprises a component selected from the group
consisting of: a Hall Effect switch, a Reed switch, and a 3D hall
effect sensor.
7. The inductive power transmitter in claim 1, comprising a
plurality of power transmitting coils, wherein the object detection
system is located about each power transmitting coil, and the
inductive power transmitter is configured to energise the
respective power transmitting coil based on activation of the
respective object detector through interaction with the potential
receiver object.
8. The inductive power transmitter in claim 7, wherein a plurality
of object detectors are located between respective power
transmitting coils, and the inductive power transmitter is
configured to energise one or more of the power transmitting coils
based on activation of the respective detectors through interaction
with the potential receiver object.
9. The inductive power transmitter in claim 8, wherein all the
object detectors for a respective power transmitting coil are
connected in parallel.
10. The inductive power transmitter in claim 7, wherein the power
transmitting coils are not energised unless a potential receiver
object is detected by the object detectors associated therewith
under control of a controller of the inductive power
transmitter.
11. The inductive power transmitter in claim 1 wherein the object
detection system is configured to detect an adjacent non receiver
object simultaneously with a receiver object.
12. The inductive power transmitter of claim 1, wherein the object
detection system is configured to determine whether a response of
the object detection system to detecting an object has a
correlation with a reference response which is less than a
threshold.
Description
FIELD
[0001] This invention relates generally to an inductive power
transmitter, particularly, but not exclusively, for an inductive
power transfer system.
BACKGROUND
[0002] IPT systems are a well-known area of established technology
(for example, wireless charging of electric toothbrushes) and
developing technology (for example, wireless charging of handheld
devices on a `charging mat`). Typically, a power transmitter
generates a time-varying magnetic field from a transmitting coil or
coils. This magnetic field induces an alternating current in a
suitable receiving coil in a power receiver that can then be used
to charge a battery, or power a device or other load.
[0003] Regarding IPT systems for wireless charging of handheld
devices in particular it is important that the wireless power is
transferred to the receiver device only and not to so-called
foreign objects, which can be defined as any object that is
positioned on the charging mat (e.g., interface surface), but is
not part of a receiver device. Typical examples of such foreign
objects are parasitic elements containing metals such as coins,
keys, paperclips, etc. For example if a parasitic metal is close to
the active IPT area it could heat up during power transfer due to
eddy currents that result from the oscillating magnetic field. In
order to prevent the temperature of such parasitic metal from
rising to unacceptable levels, the power transmitter should be able
to discriminate between power receivers and foreign objects and
timely abort the power transfer.
[0004] A conventional manner of detecting heating of foreign
objects on an interface surface uses a power loss method. In this
method the received power P.sub.PR is used to indicate the total
amount of power that is dissipated within the power receiver
contained in the handheld device due to the magnetic field produced
by the power transmitter. The received power equals the power that
is available from the output of the power receiver plus any power
that is lost in producing that output power. The power receiver
communicates its P.sub.PR to the power transmitter so that the
power transmitter can determine whether the power loss is within
acceptable set limits, and if not, the power transmitter determines
anomalous behaviour which may indicate presence of a foreign object
and aborts power transmission. However, this power loss accounting
method does not in itself provide actual detection of a foreign
object, only the occurrence of non-expected behaviour.
[0005] International patent publication number WO2014/095722, by
contrast, proposes a method of foreign object detection which uses
excitation and detection coils within the transmitter, separate
from the primary IPT transmitter coil(s). In that case either
changes in the output voltage in the detection winding, or changes
in the inductance of the detection winding are used to determine
possible presence of an object. However this system requires a
complex calibration to determine the base inductance. It is also
insensitive to metal objects versus ferrous or magnetic objects,
and therefore does not provide a means to discriminate between
foreign objects and friendly objects, e.g., a receiver device which
typically include ferrite for magnetic flux control. Any
undesirable effects of operation of the primary IPT field on the
detection is also not considered or characterised, such that the
proposed method may be unreliable.
[0006] Existing methods may also need to continuously monitor for
the presence of anything that is placed on the charging pad. This
may increase power consumption of the system and adds complexity to
the processing needed.
[0007] It is an object of the invention to provide the public with
a useful choice.
SUMMARY
[0008] According to one example embodiment there is provided an
inductive power transmitter comprising: [0009] at least one power
transmitting coil configured to generate an inductive power
transfer (IPT) field; and [0010] an object detection system
configured to detect objects in or adjacent a space occupied by the
IPT field when generated; [0011] wherein the object detection
system is configured to detect a receiver object based on a tag
associated with the receiver object.
[0012] It is acknowledged that the terms "comprise", "comprises"
and "comprising" may, under varying jurisdictions, be attributed
with either an exclusive or an inclusive meaning. For the purpose
of this specification, and unless otherwise noted, these terms are
intended to have an inclusive meaning--i.e., they will be taken to
mean an inclusion of the listed components which the use directly
references, and possibly also of other non-specified components or
elements.
[0013] Reference to any document in this specification does not
constitute an admission that it is prior art or that it forms part
of the common general knowledge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings which are incorporated in and
constitute part of the specification, illustrate embodiments of the
invention and, together with the general description of the
invention given above, and the detailed description of embodiments
given below, serve to explain the principles of the invention.
[0015] FIG. 1 is a schematic diagram of an inductive power transfer
system;
[0016] FIG. 2 is a schematic diagram of an inductive power
transmitter and adjacent receiving coil;
[0017] FIG. 3 is a circuit diagram of an inverter and an object
detection system;
[0018] FIG. 4 is a schematic diagram of an array of transmitting
coils;
[0019] FIG. 5 is a circuit diagram of an object detection system of
a transmitting coil of FIG. 4;
[0020] FIG. 6 is a circuit diagram of a receiver circuit where the
receiver coil is used to generate a magnet;
[0021] FIG. 7 is a graph of circuit waveforms used to correlate the
presence of foreign magnets; and
[0022] FIGS. 8a-e are schematic diagrams of an alternative receiver
configuration.
DETAILED DESCRIPTION
[0023] An inductive power transfer (IPT) system 1 is shown
generally in FIG. 1. The IPT system includes an inductive power
transmitter 2 and an inductive power receiver 3. The inductive
power transmitter 2 is connected to an appropriate power supply 4
(such as mains power or a battery). The inductive power transmitter
2 may include transmitter circuitry having one or more of a
converter 5, e.g., an AC-DC converter (depending on the type of
power supply used) and an inverter 6, e.g., connected to the
converter 5 (if present). The inverter 6 supplies a transmitting
coil o or coils 7 with an AC signal so that the transmitting coil
or coils 7 generate an alternating magnetic field. In some
configurations, the transmitting coil(s) 7 may also be considered
to be separate from the inverter 5. The transmitting coil or coils
7 may be connected to capacitors (not shown) either in parallel or
series to create a resonant circuit.
[0024] A controller 8 may be connected to each part of the
inductive power transmitter 2. The controller 8 to receives inputs
from each part of the inductive power transmitter 2 and produces
outputs that control the operation of each part. The controller 8
may be implemented as a single unit or separate units, configured
to control various aspects of the inductive power transmitter 2
depending on its capabilities, including for example: power flow,
tuning, selectively energising transmitting coils, inductive power
receiver detection and/or communications.
[0025] The inductive power receiver 3 includes a receiving coil or
coils 9 connected to receiver circuitry which may include power
conditioning circuitry 10 that in turn supplies power to a load 11.
When the coils of the inductive power transmitter 2 and the
inductive power receiver 3 are suitably coupled, the alternating
magnetic field generated by the transmitting coil or coils 7
induces an alternating current in the receiving coil or coils 9.
The power conditioning circuitry 10 is configured to convert the
induced current into a form that is appropriate for the load 11,
and may include for example a power rectifier, a power regulation
circuit, or a combination of both. The receiving coil or coils 9
may be connected to capacitors (not shown) either in parallel or
series to create a resonant circuit. In some inductive power
receivers, the receiver may include a controller 12 which may
control tuning of the receiving coil or coils 9, operation of the
power conditioning circuitry 10 and/or communications.
[0026] The term "coil" may include an electrically conductive
structure where an electrical current generates a magnetic field.
For example inductive "coils" may be electrically conductive wire
in three dimensional shapes or two dimensional planar shapes,
electrically conductive material fabricated using printed circuit
board (PCB) techniques into three dimensional shapes over plural
PCB `layers`, and other coil-like shapes. The use of the term
"coil", in either singular or plural, is not meant to be
restrictive in this sense. Other configurations may be used
depending on the application.
[0027] It may be desirable in certain applications for the IPT
transmitter to selectively provide power to associated receiver
devices (e.g., mobile phones, remote controls, etc.) and not to
foreign objects (e.g., paperclips, coins, etc.). To this end, the
IPT transmitter may include an Object Detection (OD) system. The OD
system may detect receiver devices that are in proximity to the
transmitter and activate, or cause to be activated, a transmitting
coil only when there is an adjacent receiver device. In situations
where there is a plurality of transmitting coils, such as an array
of coils (e.g., on a charging mat), the OD system may only
activate, or cause to be activated, the subset of coil/s which are
adjacent to one or more receiver devices.
[0028] Receiver devices may include "receiver tags". The receiver
tags may include one or more unique properties or characteristics
which are detectable by the OD system and are not generally present
in foreign objects. The OD system may include one or more object
detectors or sensors which detect the presence and/or proximity of
receiver tags (or more precisely, they detect certain properties or
characteristics of the receiver tags) through interaction with the
tags. These sensors may be provided as part of the OD system as
specialised elements or the transmitter circuitry itself may be
used as these sensors. Similarly, the controller of the transmitter
may form part or all of the OD system. In this way, the receiver
tags act as identification elements which enable a power
transmitter to identify when a power receiver is in proximity of
the power transmitter, more particularly, when the receiver tags,
and therefore receiver device, is within the space that an IPT
field generated by one or more of the transmitter coils will occupy
when the transmitter coils are operated. As explained in detail
later, these identification elements can be configured so that just
the presence of a receiver device can be sensed or so that the type
of receiver device present can be ascertained, which can assist in
the power transmitter enacting modes of power transfer specific to
different receiver types, such as, for example, may be the case in
a multi-mode IPT system.
[0029] The sensors of the OD system may be connected to one or more
transmitting coils of the charging mat. When foreign objects that
may be otherwise be energised by the magnetic flux produced by the
power transmitter (e.g. metal objects such as paper clips, coins,
etc.) are placed on the transmitter, the transmitting coil or coils
of the charging mat will not be activated as such foreign objects
lack "receiver tags". Conversely, when receiver devices are placed
on the charging mat, the OD system detects the nearby receiver tags
of the receiver objects, and activates, or causes to be activated,
the transmitting coil or coils of the charging mat either on that
basis or in conjunction with other condition settings.
[0030] FIG. 2 shows an example of an OD system detecting an
adjacent receiver object. The transmitting coil(s) 7 is associated
with an object detection (OD) system or element 202 of the power
transmitter 2 which is configured to detect objects in or adjacent
to the IPT field.
[0031] The receiving coil 9 is associated with or adjacent to a
receiver tag or element 204. The receiving coil 9 may be part of
any suitable receiver, such as a mobile phone, remote control,
tablet, etc. The receiver tag 204 may include one or more unique
properties or characteristics which are detectable by the OD system
202 and are not generally present in foreign objects.
[0032] Non-limiting examples of receiver tags and corresponding OD
systems include: [0033] A receiver tag including a permanent magnet
and an OD system including magnetic sensors configured to respond
to the permanent magnet and not necessarily to other magnets.
[0034] A receiver tag including a non-permanent magnet, e.g., an
electromagnet, and an OD system or transmitter control which causes
the non-permanent magnet to be activated when the receiver tag is
brought into proximity of the transmitter, for example, through
some communicated signal from the transmitter to the receiver,
e.g., a modulated IPT signal, or through receipt of magnetic flux
from the IPT coil(s) of the transmitter or other magnet of the OD
system, for example. This may be implemented using the receiver
coil energised with a DC voltage. Once the receiver has been
identified using this, the receiver coil is de-energised so that it
can begin receiving power, and the OD system 202 stays in the
receiver identified mode until a disconnect is determined. The
receiver disconnect may be determined by measuring power transfer,
a time period or other communication channels. [0035] A receiver
tag including a coded reflective surface 208 and an OD system
including photodetectors 210 configured to measure reflected light
patterns.
[0036] As mentioned earlier, the characteristics of the receiver
tag can be configured so that the type of receiver device, as well
as the presence, can be ascertained by the OD system. For example,
the magnetic material of the permanent or non-permanent magnet of
the above examples can be configured so that a unique magnetic flux
(e.g., of a certain strength, quality or other characteristic) is
induced in the OD system sensors or the reflective surface of the
other example is uniquely coded based on the receiver type. For
example, different receiver types may be those that require
different power levels for effective powering/charging of the
receiver-side load, that rely on protocols of a particular industry
standard or different versions of an industry standard, or are
different devices, e.g., a cellular phone, wearable device, etc. In
such case, the OD system may be provided with sensor(s) or control
that is able to discern between these different characteristics, or
with individual sensors for individual receiver types.
[0037] FIG. 6 shows an example of the circuit 600 that could be
used to implement the receiver coil based "magnet". The available
DC power in the battery 602 of the device can be used to drive the
Rx coil 604 and generate static magnetic field to activate the
sensor. The required static flux density to activate the sensor can
be deliberately chosen as very low (.about.few milli Tesla), to
minimise the amount of DC power required to generate the
magnet.
[0038] In FIG. 6, when the battery is used to provide static
magnetic field (electromagnet) the switches S.sub.1, S.sub.2 are
closed and the switches S.sub.3 and S.sub.4 are open to isolate the
coil from the receiver circuitry. It may operate in the
electromagnetic mode intermittently or when a user manually selects
wireless charge mode. Likewise when the Rx coil 604 is in its
receiving power mode, the switches S.sub.3 and S.sub.4 are closed
and the upper switches S.sub.1 and S.sub.2 are open. This may have
the advantage that it saves the spaces and cost of including a
magnet and any interference caused or shielding required as a
result.
[0039] Returning to FIG. 2, the receiving coil 9 of the receiver
device is illustrated as having a receiver tag 204 which contains
or consists of a permanent magnet. The receiver tag 204 is
substantially located in the centre of the receiving coil 9.
Alternatively, if the receiver coil does not have space within for
the placement of the receiver tag, e.g., due to the receiver coil
being a fully wound spiral or having ferrite material located
within the coil, or otherwise, the receiver tag 204 maybe located
outside of the receiving coil 9 in a relative location that still
enables detection. Alternatively, a plurality of tags could be
provided located within or without of the receiver coil (or coils
if multiple coils are present in the receiver) or a combination of
both of these locations. The tag(s) may be positioned in the plane
of the receiver coil or in a different plane, or may project out of
the plane dependent on the relative dimensions of the tag and
coil.
[0040] Being a permanent magnet, the receiver tag 204 has a
magnetic field 206. The magnetic field of the permanent magnet of
the receiver tag may adapted according to the requirements of the
OD system 202 and the application. For example, the density of
magnetic material of the permanent magnet can be selected to
provide a magnetic field of a certain strength or volume.
[0041] In order to not cause significant coupling with the IPT
coils of the power transmitter, which could otherwise effect the
wireless power transfer, the magnetic field of the associated
magnet 204 is lower than the magnetic field of the transmitting
coil(s) 7. For example it may be at least 100 times lower.
Alternatively, in embodiments of the OD system in which the
receiver tag is a non-permanent magnet, the IPT coil(s) of the
power transmitter can be used as at least part of the object sensor
if the non-permanent magnet is temporarily activated to provide
identification, in which case the magnetic field strength of the
non-permanent magnetic is sufficient to cause coupling with the
transmitter coil(s).
[0042] The OD system 202 of the transmitter 2 may include one or
more magnetic switches, sensors or relays which detect the magnetic
flux 206 caused therein by the magnetic field 206 of the receiver
tag 204.
[0043] In the example of FIG. 2, the OD system 202 is illustrated
as a separate component connected to the controller 8 of the
transmitter 2, accordingly when the OD system 202 detects a
receiver tag, it causes the controller 8 to activate the inverter
6, thereby supplying power to the transmitting coil(s) 7.
Alternatively, the OD system may be an integral part of the
controller 8. In either case, the OD system 202 may include any
suitable switch, sensor or relay which is responsive to receipt of
magnetic flux. In some embodiments, this may be a magnetic switch,
such as a Hall Effect switch, a Reed switch or a combination of
these or other types. Magnetic switches may be normally open
(closing when a magnetic field is present), or normally closed
(opening when a magnetic field is present). Selection of the type
of detection mechanism of the OD system may be governed by many
factors, but in the case of a typical wireless power transfer
system it is desirable that the OD system, and therefore the sensor
mechanism, is able to withstand a wide range of operating
temperatures (e.g., about -40 degrees Celsius to about 150 degrees
Celsius). Like the receiver tag 204, the OD system sensor may be
located within or without the respective transmitting coil 7. It
may be beneficial, for example, to have the OD sensor located
within the transmitter coil (considering that the transmitter coil
is not a fully wound spiral or has ferrite material therein
preventing such placement) if the receiver tag is within the
associated receiver coil, or if the receiver tag is offset, to have
the OD sensor correspondingly offset from the transmitter coil.
This relative placement of the tag and sensors depends on the
actual configuration of the IPT system and the need or otherwise to
have the transmitter and receiver coils aligned for power transfer.
Further, multiple sensors may be used for the or each transmitter
coil, which may be arranged within or without of the coils, or in a
combination of these relative positions, to provide detection
independent of the receiver devices position relative to the
transmitter.
[0044] The OD system will advantageously be activated only by the
permanent or non-permanent magnet of the receiver tag 204, and not
by non-magnetic metal objects. Further, the OD system may be highly
tuned such that it is activated by only certain magnetic flux
strengths, ensuring that it selectively detects a receiver object
with a corresponding associated magnet rather than just any magnet.
However a high degree of tuning may cause non-detection in certain
circumstances. In a given application a particular distance between
the magnet and the magnetic switch would be identified according to
design considerations at which the switch changes state. For
example the transmitter and receiver coils should be significantly
coupled before being energised, but equally perfect alignment may
not be desired or necessary. The distance may be in terms of z
height, in terms of x/y distance or a combination, and may be
adjusted by selecting the sensitivity of the switch and/or the
strength of the magnet.
[0045] On the other hand, if the OD system is not tuned it may
disadvantageously be activated by a foreign permanent magnet which
is not part of the receiver. Nonetheless, if a transmitter is
activated by a foreign magnet, this is under no load conditions, so
minimum power is wasted. Further, under no load conditions, a
magnet on an operating transmitter does not heat up as may occur
with foreign metal objects on an operating transmitter. Thus the
consequence associated with foreign o magnets may be negligible.
Further, in IPT systems where communications between the
transmitter and receivers are used to establish and maintain
so-called `power contracts` actual power transfer would only occur
when an actual receiver is present. In other words if a foreign
magnet activated the transmitter, the transmitter tries to
communicate with the object/device that caused this activation. If
the object is a foreign magnet it would not respond, then in that
case the transmitter terminates charging.
[0046] It is possible that a transmitting coil may be activated by
a receiver even if a metal object is positioned between the
receiver and the transmitter, a so-called `intervening` or
`overlapping` foreign object. This may result in heating of the
metal foreign object causing a reduction of power transfer
efficiency through losses into the parasitic foreign object and
possible safety issues. Possible solutions to this include a
correlation method in which the voltage or current waveforms of the
sensor when it is activated by a magnet alone are compared to those
for a magnet+a metal object. It has been observed that the response
of the sensor when it is activated by only a magnet is different
from the case when activated by a magnet+a metal object. Such
information can be modelled and programmed into the OD system or
transmitter controller through hardware, firmware or software
means, e.g., as a lookup table in memory associated with controller
or OD system, with the controller or OD system configured to enable
measurement of the detection waveforms or signals. The actual
waveforms measured in operation are then correlated to one of the
example/known waveforms to distinguish such non-powering events.
Other solutions may include combining the permanent magnet option
with other FOD method (i.e. such as power loss accounting, etc.) to
overcome the overlapping FO/receiver scenario.
[0047] For example, when monitoring the voltage and/or current of
the sensor, when a magnet from a receiver is placed on the
transmitter, a characteristic V.sub.s or I.sub.s verses time
waveform is observed as shown in FIG. 7. An Rx with a valid magnet
is placed on the Tx, with the first waveform 702 for an Rx magnet
aligned with the Tx sensor and the second waveform 704 with the Rx
magnet offset. The second waveform 704 is the same characteristic
shape as the first waveform 702, but with a lower amplitude due to
the Rx magnet being further from the Tx sensor. The third waveform
706 with a foreign object such as a coin present is distorted or
has a different shape compared to the waveforms 702 and 704 without
a foreign object. This different shape can be detected by
correlating the detected shape with a reference waveform shape (702
or 704), and is a sufficiently different the presence of a foreign
objection can be declared and the power delivery prevented or
interrupted. The reference waveform shape may be determined
experimentally and included in a lookup table of the Tx for
example. Various statistical methods may be used to correlate the
shape of a detected waveform (702, 704, 706) with the reference
waveform, and if a difference above a predetermined threshold is
calculated then the presence of a foreign object is declared to the
power transfer control process.
[0048] An example statistical method for correlating a detected
waveform with a reference waveform is cross-correlation. By
normalising the detected waveform average amplitude then applying a
cross-correlation function, the shapes of the two waveforms can be
compared. The cross correlation of two discrete sequences x[n] and
y[n] could be represented mathematically as shown in Equation
(1).
R.sub.xy[l]=.SIGMA..sub.n=-.infin..sup..infin.x[n].times.y[n-l]
where l=0, +1, +2, +3, . . . . (1)
[0049] For example a reference (normalised) voltage or the current
waveform of the sensor when it is activated by an Rx only waveform
(say one of 702 or 704 shown in FIG. 7) is represented by the
discrete sequence x[n]. And y[n] represents the detected waveform
when the sensor is activated by the Rx and a metal object placed in
between (706).
[0050] The sequence x[n] (the reference voltage/current of the
sensor activation by Rx only) is cross-correlated with the
normalised voltage/current of the sensor y[n]. when a metal is
placed in between. This will result in a cross-correlation product
Rxy[1] below a threshold, indicating the presence of a foreign
object. On the other hand, when a waveform is detected without a
foreign object, the normalised cross-correlation product will be
above the threshold and therefore indicate the presence of an Rx
only. The skilled person will appreciate that other statistical or
pattern recognition methods could alternatively be used.
[0051] It has also been observed using a digital Hall Effect sensor
that the placement of an Rx with metal foreign object causes a
measurable distortion of the normal output response of such a
sensor when a minimum magnetic field strength is detected. In this
implementation no normalisation is required and only a
cross-correlation calculation is required. Again a
cross-correlation above a threshold indicates the presence of an Rx
only, whereas below the threshold indicates the presence of an Rx
and metal foreign object.
[0052] FIG. 3 shows an example implementation of the inverter 5 and
object detection system. The OD system includes two Hall-Effect
switches 302 and 304, each connected to a transmitting coil (306
and 308 respectively) via associated power switches S of the
transmitting coil circuits and connected to the inverter 5 through
junction 310, thereby providing closed loop control. The power
switches S are used to selective allow power from the inverter 5 to
flow within the transmitting coils (smoothing capacitors are also
shown in each circuit), thereby selecting which of the transmitting
coils are used to transfer power to a coupled receiver. Each
Hall-Effect switch is used to control the operation of an
associated power switch S. The power switches may be, for example,
transistors, such as bipolar junction transistors (BJT), field
effect transistors (FETs), etc., and any variations thereof. In
such examples, the Hall-Effect switches are connected to the
control terminal of the respective power switch transistor, e.g.,
to the gate of the FET.
[0053] By default, the Hall-Effect switches 302 and 304 are
normally open, accordingly the power switches S are open and the
inverter 5 does not supply any power to the transmitting coils 306
and 308. When a switch 302 or 304 is activated by a receiver tag of
a proximate receiver, that switch closes, thereby closing the
associated power switch S and allowing current from the inverter 5
to flow to the corresponding transmitting coil 306 or 308. This
circuit design may reduce the need for communication or control
circuitry to supply power to the appropriate transmitting coil. In
the illustrated example, the inverter 5 is depicted in a
half-bridge configuration, however one of ordinary skill in the art
understands that a full-bridge, configuration is also applicable.
Further, in the illustrated example, the magnetic switches of the
OD system are not directly connected to the transmitting coils, as
typical magnetic switches are unable to cope with the relatively
high current from the inverter. Accordingly, the power switches,
which are rated for such high current, are used and the magnetic
switches are able to control the power switches with relatively low
current. Depending on application however, if the power levels
being transferred by the wireless power system are relatively low,
the power switches could be omitted and the magnetic switches used
to directly connect the transmitting coils.
[0054] An example of an array of transmitting coils is shown in
FIG. 4. Each transmitting or IPT coil 402, 404, 406, 408, 410, 412,
414 and 416 may include a number of systematically arranged IPT
ferrite elements (not shown) within the coils to enhance/shape the
magnetic field induced by the AC signal from the one or more
inverters of the transmitter. The IPT coils 402-416 may be arranged
in a rectangular array structure and may be linear (2D),
overlapping (as in FIG. 4) or 3 dimensionally (3D) arranged.
[0055] The IPT coils 402-416 are interleaved with magnetic switches
(A1-H1) in an example configuration. In the example overlapped
transmitter coil arrangement of FIG. 4, each transmitting coil
402-412 in the `lower` layer (i.e., the coils 402-412 are
overlapped by the coils 414 and 416 in the `upper` layer) is
associated with a number or group of magnetic-switches, arranged at
the centre of and on each side of the transmitting coil 502,
whereas the transmitting coils 414 and 414 in the `upper` layer are
each associated with a magnetic-switch. In this description the
terms `lower` and `upper` are used relative to the interface
surface of the charging mat of the power transmitter in which power
receivers may be placed to be charged/powered, where "upper" is
closer to the interface surface than "lower".
[0056] Further, as the coils 406 and 408 are between the coils 402
and 410 and 404 and 412, respectively, these `inner` coils 406 and
408 are each associated with a larger group of magnetic switches
than the `outer` coils 402, 402, 410 and 412. Accordingly, as
illustrated in FIG. 4, in the lower layer, the coil 402 is
associated with three magnetic switches Al-A3, the coil 404 is
associated with three magnetic switches B1-B3, the coil 406 is
associated with four magnetic-switches C1-C4, the coil 408 is
associated with four magnetic switches D1-D4, the coil 410 is
associated with three magnetic switches E1-E3, and the coil 412 is
associated with three magnetic switches F1-F3, and in the upper
layer, the coil 414 is associated with one magnetic-switch G1, and
the coil 416 is associated with one magnetic switch H1. This
arrangement ensures reasonably fine detection by the OD system
whilst maximising the number of transmitting coils that can be
powered to provide an expanded area over which the IPT field can be
generated by the transmitting coils to power the receiving coil(s)
when a receiver is in the proximity of the transmitting
coil(s).
[0057] In particular, in the arrangement of the transmitting coil
402 and the associated three magnetic switches A1, A2 and A3,
magnetic switch A1 is within (illustrated as substantially at the
centre of) the coil 402, magnetic switch A2 is on a first `inner`
side (illustrated as the right side in FIG. 4) of the coil 402 with
respect to the adjacent coil 404, and magnetic switch A3 is on a
second `inner` side (illustrated as the bottom side in FIG. 4) of
the coil 402 with respect to the adjacent coil 406. Similar
arrangements are used for the other outer coils 404, 410 and 412
and associated magnetic switches B1-B3, E1-E3 and F1-F3, such that
the magnetic switches are either within the associated transmitter
coil or between that coil and o the adjacent coil of the array (or
coils within a larger array). With this configuration, a receiver
object including a receiver tag may activate the transmitting coil
402 if it is placed in the vicinity of any of the associated
magnetic switches.
[0058] A receiver (which includes a receiver tag) placed between
the coils 402 and 404 may activate both of the magnetic switches A2
(associated with coil 402) and B2 (associated with coil 404). In
this case, the receiver coil may be coupled to both of the
transmitting coils 402 and 404. Such coupling can be used by the
controller of the transmitter to decide whether one or both of the
coils are energised to enact power transfer (e.g., using more than
one transmitter coil can increase the amount of power transferred
meeting power requirements of the receiver and/or speeding up
charging of a rechargeable load of the power receiver).
[0059] Further, in the arrangement of the transmitting coil 406 and
the associated four magnetic switches, C1, C2, C3 and C4, magnetic
switch C1 is within (illustrated as located substantially at the
centre of) the coil 406, magnetic switch C2 is on a first `inner`
side (illustrated as the upper side in FIG. 4) of the coil 406,
magnetic switch C3 is on a second `inner` side (illustrated as the
right side in FIG. 4) of the coil 406, and magnetic switch C4 is on
a third `inner` side (illustrated as the lower side in FIG. 4) of
the coil 406. A similar arrangement is used for the other inner
coils 408 and associated magnetic switches Dl-B4, such that the
magnetic switches are either within the associated transmitter coil
or between that coil and the adjacent coils of the array. A
receiver including a receiver tag placed on the charging pad above
any of these magnetic switches will activate the transmitting coil
406.
[0060] Any number of transmitting coils may be associated with any
suitable number of magnetic switches, in any suitable
configuration.
[0061] FIG. 5 shows an example circuit diagram for transmitting
coil 404 (similar arrangements apply with respect to the other
outer coils and like arrangements apply with respect to the inner
coils). The three Hall-Effect switches B1-B3 are arranged in
parallel, and are connected in series between the transmitting coil
404 and the inverter. If one or more of the switches B1-B3 are
activated (by the proximity of a suitable permanent or activated
non-permanent magnet), the inverter energises the transmitting coil
404.
[0062] Alternatively 3D type hall effect devices may be used to
approximately determine the location of a receiver relative to an
array of transmitter coils, and energise the most appropriate
combination of transmitter coils to couple to the receiver. Such
devices may be used to reduce the number of switches shown in FIG.
4, for a similar level of location sensitivity.
[0063] In a further alternative shown in FIGS. 8(a)-(e), each
receiver could be provided with multiple tags or permanent magnets.
In this case only one sensor (magnetic switch) is provided in the
centre of each Tx coil. To enable detection at different Rx
locations, several permanent magnets are distributed over the Rx
instead. In this way the sensor can be activated either by the
central magnet or the side magnets when it not positioned
centre-to-centre with the Tx coil. This approach may have the
advantage of reducing the number of required sensors, the number of
required Tx coils or layers of Tx coils, complexity and cost.
[0064] For example the receiver is shown in FIG. 8a with 7 magnets
802 distributed across its charging surface, within the receiver
coil 804. The transmitter is configured with 6 coils 806 in a
rectangular array, each with a permanent magnet 808 in the
respective centre. In the Rx location in FIG. 8a no coils would be
activated. In FIG. 8b only coil 2 would be activated. In FIG. 8c
coils 1 and 2 would be activated. In FIG. 8d coils 1 and 3 would be
activated. In FIG. 8e coils 1 and 4 would be activated. In a
further alternative, a ribbon of magnetic material can be placed
around the lower surface of the Rx.
[0065] The IPT system may avoid unnecessary powering of the
transmitter, since by default the transmitter remains off as a
standby power source when there is no load present. Where the
transmitter has an array of transmitting coils, only the
transmitting coil or coils of the array positioned relative the
detected receiver device is or are powered on, thereby minimising
wasted power and or exposure of users or other objects to magnetic
fields. Further, activation of the transmitting coils due to the
presence of foreign objects (including metals) on or near the
charging pad may be obviated. Further, receivers receiving power
from the transmitter may still receive that power even if foreign
or other objects are placed on other parts of the transmitter
interface surface. These factors may increase the life-span of the
IPT system relative to conventional OD systems.
[0066] While the present invention has been illustrated by the
description of the embodiments thereof, and while the embodiments
have been described in detail, it is not the intention of the
Applicant to restrict or in any way limit the scope of the appended
claims to such detail. Additional advantages and modifications will
readily appear to those skilled in the art. Therefore, the
invention in its broader aspects is not limited to the specific
details, representative apparatus and method, and illustrative
examples shown and described. Accordingly, departures may be made
from such details without departure from the spirit or scope of the
Applicant's general inventive concept.
* * * * *