U.S. patent application number 15/281745 was filed with the patent office on 2017-03-30 for power transmission device and wireless power transmission system including the same.
The applicant listed for this patent is Semiconductor Energy Laboratory Co., LTD.. Invention is credited to Koichiro KAMATA.
Application Number | 20170093221 15/281745 |
Document ID | / |
Family ID | 46126124 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170093221 |
Kind Code |
A1 |
KAMATA; Koichiro |
March 30, 2017 |
POWER TRANSMISSION DEVICE AND WIRELESS POWER TRANSMISSION SYSTEM
INCLUDING THE SAME
Abstract
Not a structure in which a resonance frequency of a power
transmission device is set after a resonance frequency of a power
receiving device is directly measured but a structure in which the
resonance frequencies of the power receiving device and the power
transmission device are estimated after reflection of an
electromagnetic field for transmitting electric power to the power
receiving device is monitored by the power transmission device is
employed. After a capacitance value of a variable capacitor in a
resonance coil of the power receiving device is once set to 0, an
S11 parameter is detected while a frequency of an electromagnetic
wave is changed, and the resonance frequency of the power
transmission device is estimated on the basis of the S11
parameter.
Inventors: |
KAMATA; Koichiro; (lsehara,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Semiconductor Energy Laboratory Co., LTD. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
46126124 |
Appl. No.: |
15/281745 |
Filed: |
September 30, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13300049 |
Nov 18, 2011 |
9461476 |
|
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15281745 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 50/20 20160201;
H01F 38/14 20130101; H02J 50/12 20160201; H02J 7/025 20130101; H02J
5/005 20130101 |
International
Class: |
H02J 50/12 20060101
H02J050/12; H01F 38/14 20060101 H01F038/14 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 2010 |
JP |
2010-263048 |
Claims
1. (canceled)
2. A power transmission device comprising: a first coil; a first
resonance coil; a high-frequency power source; a coupler; a
variable capacitor; a detector; and a control device, wherein the
first coil is connected to the high-frequency power source through
the coupler, wherein the first coil is configured to be
electromagnetically coupled with the first resonance coil, wherein
the variable capacitor is connected to the first resonance coil and
the control device, wherein the detector is connected to the
coupler and the control device, and wherein the first coil is
configured to transmit a signal to a power receiving device under a
condition that a capacitance value of the variable capacitor is set
to 0.
3. The power transmission device according to claim 2, further
comprising a memory circuit in which the capacitance value of the
variable capacitor for setting a resonance frequency of the first
resonance coil on the basis of a resonance frequency of a second
resonance coil is stored, wherein the memory circuit is connected
to the control device.
4. A power transmission device comprising: a first coil; a first
resonance coil; a high-frequency power source; a coupler; a
variable capacitor; a detector; and a control device, wherein the
first coil is connected to the high-frequency power source through
the coupler, wherein the first resonance coil is connected to the
variable capacitor and is configured to be electromagnetically
coupled with the first coil, and electromagnetic resonance occurs
between the first resonance coil and a second resonance coil
electromagnetically coupled with a second coil in a power receiving
device, wherein the detector is configured to detect intensity of
an S11 parameter output from the coupler, and wherein the control
device is configured to change a capacitance value of the variable
capacitor and an oscillation frequency of a signal output from the
high-frequency power source, wherein the control device is
configured to set the capacitance value of the variable capacitor
to 0, wherein the control device is configured to set a frequency
at which the intensity of the S11 parameter which is an indication
of loss due to reflection of electromagnetic wave between the first
coil and the second resonance coil is changed at the time when the
oscillation frequency of the signal output from the high-frequency
power source is changed under a condition that the capacitance
value of the variable capacitor is 0, as a resonance frequency of
the second resonance coil, wherein the control device is configured
to set a resonance frequency of the first resonance coil after the
capacitance value of the variable capacitor is set in accordance
with the resonance frequency of the second resonance coil, and
wherein the control device is configured to set the oscillation
frequency of the signal output from the high-frequency power source
as the resonance frequencies of the first resonance coil and the
second resonance coil.
5. The power transmission device according to claim 4, further
comprising a memory circuit in which the capacitance value of the
variable capacitor for setting the resonance frequency of the first
resonance coil on the basis of the resonance frequency of the
second resonance coil is stored, wherein the memory circuit is
connected to the control device.
6. A wireless power transmission system comprising a power
transmission device and a power receiving device, wherein the power
transmission device comprising: a first coil; a first resonance
coil; a high-frequency power source; a coupler; a variable
capacitor; a detector; and a control device, wherein the first coil
is connected to the high-frequency power source through the
coupler, wherein the first resonance coil is configured to be
electromagnetically coupled with the first coil and is connected to
the variable capacitor, wherein the detector configured to detect
intensity of an S11 parameter output from the coupler, wherein the
control device is configured to change a capacitance value of the
variable capacitor and an oscillation frequency of a signal output
from the high-frequency power source, wherein the control device is
configured to set the capacitance value of the variable capacitor
to 0, wherein the control device sets a frequency at which the
intensity of the S11 parameter which is an indication of loss due
to reflection of electromagnetic wave between the first coil and a
second resonance coil in the power receiving device is changed at
the time when the oscillation frequency of the signal output from
the high-frequency power source is changed under a condition that
the capacitance value of the variable capacitor is 0, as a
resonance frequency of the second resonance coil, wherein the
control device is configured to set a resonance frequency of the
first resonance coil after the capacitance value of the variable
capacitor is set in accordance with the resonance frequency of the
second resonance coil, and wherein the control device is configured
to set a frequency at which the intensity of the S11 parameter is
changed at the time when the oscillation frequency of the signal
output from the high-frequency power source is changed under a
condition that the capacitance value of the variable capacitor is
set to a capacitance value based on the resonance frequency of the
second resonance coil, as the oscillation frequency of the signal
output from the high-frequency power source, and wherein the power
receiving device includes the second resonance coil which is
configured to cause electromagnetic resonance with the first
resonance coil and is connected to a capacitor and a second coil
which is configured to be electromagnetically coupled with the
second resonance coil and is connected to a load.
7. The wireless power transmission system according to claim 6,
wherein the power transmission device includes a memory circuit in
which the capacitance value of the variable capacitor for setting
the resonance frequency of the first resonance coil on the basis of
the resonance frequency of the second resonance coil is stored, and
wherein the memory circuit is connected to the control device.
8. A wireless power transmission system comprising a power
transmission device and a power receiving device, wherein the power
transmission device comprising: a first coil; a first resonance
coil; a high-frequency power source; a coupler; a variable
capacitor; a detector; and a control device, wherein the first coil
is connected to the high-frequency power source through the
coupler, wherein the first coil is electromagnetically coupled with
the first resonance coil, wherein the variable capacitor is
connected to the first resonance coil and the control device, and
wherein the detector is connected to the coupler and the control
device, wherein the power receiving device includes a second
resonance coil which is configured to cause electromagnetic
resonance with the first resonance coil and is connected to a
capacitor and a second coil which is configured to be
electromagnetically coupled with the second resonance coil and is
connected to a load, and wherein the first coil transmits a signal
to the power receiving device under a condition that the
capacitance value of the variable capacitor is set to 0.
9. The wireless power transmission system according to claim 8,
wherein the power transmission device includes a memory circuit in
which a capacitance value of the variable capacitor for setting a
resonance frequency of the first resonance coil on the basis of a
resonance frequency of the second resonance coil is stored, and
wherein the memory circuit is connected to the control device.
Description
TECHNICAL FIELD
[0001] The present invention relates to power transmission devices
and wireless power transmission systems including the power
transmission devices.
BACKGROUND ART
[0002] Various kinds of electronic devices have spread, and a wide
variety of products have been shipped to the market. In recent
years, portable electronic devices such as cellular phones and
digital video cameras have widely spread. Further, electric
propulsion moving vehicles that are powered by electric power, such
as electric cars, appear on the market as products.
[0003] Cellular phones, digital video cameras, and electric
propulsion moving vehicles include batteries that are energy
storage means. The batteries are charged while being in direct
contact with home AC sources that are power transmission means in
many cases. In a structure without a battery or a structure where
electric power stored in a battery is not used, electric power is
directly transmitted to an electronic device from a home AC source
through a wiring or the like so that the electronic device
operates.
[0004] On the other hand, methods by which batteries are charged
wirelessly or electric power is transmitted to loads wirelessly
have been researched and developed. Typical methods are an
electromagnetic coupling method (also referred to as an
electromagnetic induction method), a radio wave method (also
referred to as a microwave method), and a resonance method. As
electronic devices such as small household electrical appliances,
devices utilizing the electromagnetic coupling method have
spread.
[0005] Resonant wireless power transmission systems have been
developed in order to increase the efficiency of electric power
transmission as disclosed in References 1 to 3.
REFERENCE
[0006] Reference 1: Japanese Published Patent Application No.
2010-193598
[0007] Reference 2: Japanese Published Patent Application No.
2010-239690
[0008] Reference 3: Japanese Published Patent Application No.
2010-252468
DISCLOSURE OF INVENTION
[0009] In a resonant wireless power transmission system, as
disclosed in Reference 1, it is important that the resonance
frequency of a device that receives electric power (hereinafter
such a device is referred to as a power receiving device) be
consistent with the resonance frequency of a device that transmits
electric power (hereinafter such a device is referred to as a power
transmission device) in increasing the efficiency of electric power
transmission.
[0010] In particular, the resonance frequency of the power
receiving device is changed depending on arrangement or the like of
the power receiving device. Thus, it is important to monitor a
change in resonance frequency of the power receiving device by the
power transmission device.
[0011] However, in the case where the resonance frequency of the
power receiving device is measured, the measured value of the
resonance frequency is fed back to the power transmission device,
and the resonance frequency of the power transmission device is
changed, a structure is complex. Reference 3 discloses a specific
example in which a structure is complex. In Reference 3, a
structure is disclosed in which a circuit for monitoring a change
in resonance frequency is provided in each power receiving device.
The structure is unfavorable because additional provision of a
circuit in each power receiving device leads to an increase in
cost. In particular, in transmission using four elements in which
electric power is transmitted wirelessly between a first coil (also
referred to as a power transmission coil) of a power transmission
device and a second coil (also referred to as a power receiving
coil) of a power receiving device through a first resonance coil
and a second resonance coil by a resonance method, it is
unfavorable to provide a means for measuring a resonance frequency
in the power receiving device because the size of the power
receiving device is further increased.
[0012] Thus, it is an object of one embodiment of the present
invention to provide a resonant power transmission device with
which resonance frequency matching can be performed between
resonance coils of the power transmission device and a power
receiving device only by a change in design of the structure of the
power transmission device and the efficiency of electric power
transmission can be increased and a wireless power transmission
system including the power transmission device.
[0013] One embodiment of the present invention is not a structure
in which the resonance frequency of a power transmission device is
set after the resonance frequency of a power receiving device is
directly measured but a structure in which the resonance
frequencies of a power receiving device and a power transmission
device are estimated after reflection of an electromagnetic field
for transmitting electric power to the power receiving device is
monitored by the power transmission device. In particular, in one
embodiment of the present invention, the resonance frequency of a
power transmission device is estimated under the condition that a
capacitance component in a resonance coil of the power transmission
device is controlled so as not to influence monitoring of
reflection of an electromagnetic wave when the reflection of the
electromagnetic wave is monitored. Specifically, after the
capacitance value of a variable capacitor in a resonance coil of
the power receiving device is once set to 0, an S11 parameter that
gives an indication in a scattering matrix (hereinafter referred to
as an S parameter) at the time when reflection of an
electromagnetic wave for transmitting electric power is monitored
is detected while the frequency of the electromagnetic wave is
changed, and the resonance frequency of the power transmission
device is estimated on the basis of the S11 parameter.
[0014] One embodiment of the present invention is a power
transmission device that includes a first coil, a first resonance
coil, a detector, and a control device. The first coil is connected
to a high-frequency power source through a coupler. The first
resonance coil is connected to a variable capacitor and is
electromagnetically coupled with the first coil, and
electromagnetic resonance occurs between the first resonance coil
and a second resonance coil that is electromagnetically coupled
with a second coil in a power receiving device. The detector
detects the intensity of an S11 parameter output from the coupler.
The control device has a function of changing the capacitance value
of the variable capacitor and the oscillation frequency of a signal
output from the high-frequency power source, sets the capacitance
value of the variable capacitor to 0, sets a frequency at which the
intensity of the S11 parameter is changed at the time when the
oscillation frequency of the signal output from the high-frequency
power source is changed under the condition that the capacitance
value of the variable capacitor is 0, as the resonance frequency of
the second resonance coil, sets the resonance frequency of the
first resonance coil after the capacitance value of the variable
capacitor is set in accordance with the resonance frequency of the
second resonance coil, and sets the oscillation frequency of the
signal output from the high-frequency power source as the resonance
frequencies of the first resonance coil and the second resonance
coil.
[0015] One embodiment of the present invention is a power
transmission device that includes a first coil, a first resonance
coil, a detector, and a control device. The first coil is connected
to a high-frequency power source through a coupler. The first
resonance coil is connected to a variable capacitor and is
electromagnetically coupled with the first coil, and
electromagnetic resonance occurs between the first resonance coil
and a second resonance coil that is electromagnetically coupled
with a second coil in a power receiving device. The detector
detects the intensity of an S11 parameter output from the coupler.
The control device has a function of changing the capacitance value
of the variable capacitor and the oscillation frequency of a signal
output from the high-frequency power source, sets the capacitance
value of the variable capacitor to 0, sets a frequency at which the
intensity of the S11 parameter is changed at the time when the
oscillation frequency of the signal output from the high-frequency
power source is changed under the condition that the capacitance
value of the variable capacitor is 0, as the resonance frequency of
the second resonance coil, sets the resonance frequency of the
first resonance coil after the capacitance value of the variable
capacitor is set in accordance with the resonance frequency of the
second resonance coil, and sets a frequency at which the intensity
of the S11 parameter is changed at the time when the oscillation
frequency of the signal output from the high-frequency power source
is changed under the condition that the capacitance value of the
variable capacitor is set to a capacitance value based on the
resonant frequency of the second resonance coil, as the oscillation
frequency of the signal output from the high-frequency power
source.
[0016] In one embodiment of the present invention, the power
transmission device may include a memory circuit in which the
capacitance value of the variable capacitor for setting the
resonance frequency of the first resonance coil on the basis of the
resonance frequency of the second resonance coil is stored, and the
memory circuit may be connected to the control device.
[0017] One embodiment of the present invention is a wireless power
transmission system that includes a power transmission device and a
power receiving device. The power transmission device includes a
first coil, a first resonance coil, a detector, and a control
device. The first coil is connected to a high-frequency power
source through a coupler. The first resonance coil is
electromagnetically coupled with the first coil and is connected to
a variable capacitor. The detector detects the intensity of an S11
parameter output from the coupler. The control device has a
function of changing the capacitance value of the variable
capacitor and the oscillation frequency of a signal output from the
high-frequency power source, sets the capacitance value of the
variable capacitor to 0, sets a frequency at which the intensity of
the S11 parameter is changed at the time when the oscillation
frequency of the signal output from the high-frequency power source
is changed under the condition that the capacitance value of the
variable capacitor is 0, as the resonance frequency of the second
resonance coil, sets the resonance frequency of the first resonance
coil after the capacitance value of the variable capacitor is set
in accordance with the resonance frequency of the second resonance
coil, and sets the oscillation frequency of the signal output from
the high-frequency power source as the resonance frequencies of the
first resonance coil and the second resonance coil. The power
receiving device includes the second resonance coil which causes
electromagnetic resonance with the first resonance coil and is
connected to a capacitor and a second coil which is
electromagnetically coupled with the second resonance coil and is
connected to a load.
[0018] One embodiment of the present invention is a wireless power
transmission system that includes a power transmission device and a
power receiving device. The power transmission device includes a
first coil, a first resonance coil, a detector, and a control
device. The first coil is connected to a high-frequency power
source through a coupler. The first resonance coil is
electromagnetically coupled with the first coil and is connected to
a variable capacitor. The detector detects the intensity of an S11
parameter output from the coupler. The control device has a
function of changing the capacitance value of the variable
capacitor and the oscillation frequency of a signal output from the
high-frequency power source, sets the capacitance value of the
variable capacitor to 0, sets a frequency at which the intensity of
the S11 parameter is changed at the time when the oscillation
frequency of the signal output from the high-frequency power source
is changed under the condition that the capacitance value of the
variable capacitor is 0, as the resonance frequency of the second
resonance coil, sets the resonance frequency of the first resonance
coil after the capacitance value of the variable capacitor is set
in accordance with the resonance frequency of the second resonance
coil, and sets a frequency at which the intensity of the S11
parameter is changed at the time when the oscillation frequency of
the signal output from the high-frequency power source is changed
under the condition that the capacitance value of the variable
capacitor is set to a capacitance value based on the resonant
frequency of the second resonance coil, as the oscillation
frequency of the signal output from the high-frequency power
source. The power receiving device includes the second resonance
coil which causes electromagnetic resonance with the first
resonance coil and is connected to a capacitor and a second coil
which is electromagnetically coupled with the second resonance coil
and is connected to a load.
[0019] In one embodiment of the present invention, in the wireless
power transmission system, the power transmission device may
include a memory circuit in which the capacitance value of the
variable capacitor for setting the resonance frequency of the first
resonance coil on the basis of the resonance frequency of the
second resonance coil is stored, and the memory circuit may be
connected to the control device.
[0020] According to one embodiment of the present invention, it is
possible to provide a resonant power transmission device with which
resonance frequency matching can be performed between resonance
coils of the power transmission device and a power receiving device
only by a change in design of the structure of the power
transmission device and the efficiency of electric power
transmission can be increased and a wireless power transmission
system including the power transmission device.
BRIEF DESCRIPTION OF DRAWINGS
[0021] In the accompanying drawings:
[0022] FIG. 1 illustrates a structure in Embodiment 1;
[0023] FIG. 2 shows a structure in Embodiment 1;
[0024] FIG. 3 shows a structure in Embodiment 1;
[0025] FIG. 4 illustrates a structure in Embodiment 1;
[0026] FIGS. 5A to 5C illustrate structures in Embodiment 1;
[0027] FIG. 6 illustrates a structure in Embodiment 2; and
[0028] FIGS. 7A and 7B illustrate structures in Embodiment 3.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] Embodiments of the present invention will be described below
with reference to the drawings. Note that the present invention can
be implemented in various different ways, and it will be readily
appreciated by those skilled in the art that modes and details of
the present invention can be modified in various ways without
departing from the spirit and scope of the present invention. The
present invention therefore should not be construed as being
limited to the description of the embodiments. Note that in
structures of the invention described below, reference numerals
denoting the same portions are used in common in different
drawings.
[0030] Note that the size, the layer thickness, or the signal
waveform of each component illustrated in drawings and the like in
embodiments is exaggerated for clarity in some cases. Thus,
embodiments of the present invention are not limited to such
scales.
[0031] Note that in this specification, terms such as "first",
"second", "third", and "n-th" (n is a natural number) are used in
order to avoid confusion among components and do not limit the
number of components.
Embodiment 1
[0032] In this embodiment, a resonant wireless power transmission
device and a resonant wireless power transmission system in one
embodiment of the present invention are described.
[0033] FIG. 1 is a block diagram of a power transmission device and
a power receiving device. FIG. 1 illustrates electric power
transmission with an electromagnetic wave by resonance of a first
resonance coil in the power transmission device and a second
resonance coil in the power receiving device.
[0034] FIG. 1 illustrates a power transmission device 101 and a
power receiving device 102. The power transmission device 101
includes a first coil 103 (also referred to as a power transmission
coil), a high-frequency power source 104, a coupler 105 (also
referred to as a directional coupler), a first resonance coil 107,
a variable capacitor 106, a detector 108, a control device 109, and
a memory circuit 110.
[0035] The power receiving device 102 includes a second resonance
coil 111, a capacitor 112, a second coil 113 (also referred to as a
power receiving coil), and a load 114.
[0036] In FIG. 1, the first coil 103 is connected to the
high-frequency power source 104 through the coupler 105. A coil
formed by winding of a wire may be used as the first coil 103. The
first coil 103 in the power transmission device 101 has higher
design flexibility than the second coil 113 in the power receiving
device 102 because the position of the power transmission device
101 is not particularly limited in comparison with the position of
the power receiving device 102.
[0037] Note that when it is explicitly described that "A is
connected to B", the case where A is electrically connected to B,
the case where A is functionally connected to B, and the case where
A is directly connected to B are included.
[0038] In FIG. 1, the high-frequency power source 104 is a power
supply circuit for outputting a signal whose frequency is
successively changed in accordance with control by the control
device 109.
[0039] Note that the high-frequency power source 104 may include a
voltage controlled oscillator (VCO) or the like so that the
frequency of an output signal is changed in accordance with voltage
input from the control device 109.
[0040] There is no particular limitation on a frequency which is
oscillated with an AC signal output from the high-frequency power
source 104 in the power transmission device 101 in this embodiment
(such a frequency is referred to as an oscillation frequency), and
an oscillation frequency at which electric power can be transmitted
by a resonance method may be used. The oscillation frequency of a
power transmission electromagnetic wave can be used, for example,
in the frequency range of several kilohertz to several gigahertz.
In particular, in this embodiment, in terms of transmission
efficiency, the frequency range of several megahertz is preferable
because resonance (magnetic resonance) can be caused.
[0041] In FIG. 1, the coupler 105 (the directional coupler) is a
circuit for detecting an S parameter in the circuit including the
high-frequency power source. In this embodiment, the coupler 105
detects an S11 parameter that gives an indication of loss due to
reflection between a two-terminal port of the first coil 103 and a
two-terminal port of the second resonance coil 111.
[0042] In FIG. 1, the first resonance coil 107 is connected to the
variable capacitor 106. A coil formed by winding of a wire may be
used as the first resonance coil 107. There is no particular
limitation on the shape of the first resonance coil 107; however,
the first resonance coil 107 in the power transmission device 101
has higher design flexibility than the second resonance coil 111 in
the power receiving device 102 because the position of the power
transmission device 101 is not particularly limited in comparison
with the position of the power receiving device 102. Note that
signals for supplying electric power wirelessly are transmitted and
received between the first coil 103 and the first resonance coil
107 by electromagnetic coupling. In addition, signals for supplying
electric power wirelessly are transmitted and received between the
first resonance coil 107 and the second resonance coil 111 by
electromagnetic resonance. Electromagnetic resonance is used in
resonant wireless power transmission. By electromagnetic resonance,
electric power which is higher than electric power generated by
electromagnetic coupling can be transmitted within a distance of 1
m or less from an electric field or a magnetic field.
[0043] In FIG. 1, the variable capacitor 106 may be, for example, a
variable capacitance diode utilizing the spread of a depletion
layer due to a semiconductor material so that capacitance is
changed by voltage applied from the outside. Alternatively, the
variable capacitor 106 may be micro electro mechanical systems
(MEMS) so that capacitance is changed by voltage applied from the
outside.
[0044] In FIG. 1, the detector 108 detects the intensity of the S11
parameter obtained in the coupler 105. Specifically, the detector
108 is a circuit which converts the intensity of the S11 parameter
that is an analog value into a digital value and transmits the
intensity of the S11 parameter that is the digital value to the
control device 109.
[0045] In FIG. 1, the control device 109 has a function of changing
the capacitance value of the variable capacitor 106 and the
oscillation frequency of a signal output from the high-frequency
power source 104. The control device 109 performs a plurality of
different operations.
[0046] Specifically, the control device 109 has a function of
adjusting the capacitance value of the variable capacitor 106 to 0.
Further, the control device 109 has a function of adjusting voltage
to be applied to the high-frequency power source 104 so that the
oscillation frequency of the high-frequency power source 104 is
successively changed under the condition that the capacitance value
of the variable capacitor 106 is 0.
[0047] Note that in this specification, the expression "the
capacitance value of the variable capacitor 106 is set to 0" means
that the capacitance value of the variable capacitor 106 is set
such that the first resonance coil 107 does not influence signals
transmitted and received between the first coil 103 and the second
resonance coil 111.
[0048] Note that when the oscillation frequency of the
high-frequency power source 104 is successively changed under the
condition that the capacitance value of the variable capacitor 106
is 0, the S11 parameter obtained in the coupler 105 is changed in
accordance with a change in oscillation frequency of the
high-frequency power source 104. In the following description, a
peak frequency at which the S11 parameter obtained by a successive
change in oscillation frequency of the high-frequency power source
104 under the condition that the capacitance value of the variable
capacitor 106 is 0 is changed is referred to as f0. Note that the
frequency f0 detected by the control device 109 can be estimated as
the resonance frequency of the second resonance coil 111.
[0049] FIG. 2 is a graph in which the horizontal axis represents
the oscillation frequency of the high-frequency power source 104
and the vertical axis represents the intensity of the S11 parameter
that is obtained in the detector 108. Specifically, a frequency f
represents the intensity (dB) of a magnetic field that indicates
the intensity of the S11 parameter while the frequency f is changed
from 2.0 to 4.0 MHz.
[0050] In FIG. 2, the peak frequency f0 at the time when the
intensity of the S11 parameter that is obtained in the detector 108
is changed is estimated at 3 MHz. In other words, when the
oscillation frequency is 3 MHz, the intensity of the S11 parameter
is low and power loss due to reflection between the first coil 103
and the second resonance coil 111 is low.
[0051] Note that in this specification, "the peak frequency at the
time when the intensity of the S11 parameter is changed" is a
frequency at the time when the intensity of the S11 parameter is
markedly decreased in successively changing the oscillation
frequency and then is rapidly returned to the original intensity,
as illustrated in FIG. 2. Note that the peak frequency at the time
when the intensity of the S11 parameter is changed might be
referred to as "a frequency at which the intensity of the S11
parameter is changed".
[0052] Note that FIG. 3 is a graph in which the horizontal axis
represents the oscillation frequency of the high-frequency power
source 104 and the vertical axis represents the intensity of
magnetic fields of the S11 parameter and an S21 parameter that are
obtained in the coupler 105 in the case where electromagnetic
resonance occurs between the first resonance coil 107 and the
second resonance coil 111. The S21 parameter gives an indication of
the efficiency of electric power transmission in the S
parameter.
[0053] As is clear from FIG. 3, the frequencies f0 at which the S11
parameter obtained in the detector 108 is changed are estimated at
around 2.6 MHz and 3.6 MHz. In other words, power loss due to
reflection is low when the oscillation frequencies are 2.6 MHz and
3.6 MHz. Similarly, the frequencies f0 at which the S21 parameter
is changed are estimated at around 2.6 MHz and 3.6 MHz. FIG. 3
shows that the peak of the S11 parameter is consistent with the
peak of the S21 parameter. That is, the efficiency of electric
power transmission is high when the oscillation frequencies are 2.6
MHz and 3.6 MHz. In other words, when the frequency f0 is obtained
by monitoring of a change in oscillation frequency of the S11
parameter, a frequency with high efficiency of electric power
transmission, i.e., the resonance frequency of the second resonance
coil 111 can be estimated.
[0054] Further, the control device 109 has a function of changing
the capacitance value of the variable capacitor 106 into a value
based on the frequency f0 after the frequency f0 is detected.
Furthermore, the control device 109 has a function of fixing the
oscillation frequency of the high-frequency power source 104 to the
frequency f0 while the capacitance value of the variable capacitor
106 is set to the value based on the frequency f0.
[0055] In FIG. 1, the memory circuit 110 stores a look-up table in
which voltage for adjusting the capacitance of the variable
capacitor 106 by the control device 109 is estimated in advance in
order that the control device 109 adjust the resonance frequency of
the first resonance coil 107 in accordance with the frequency f0
that is the resonance frequency of the second resonance coil
111.
[0056] In FIG. 1, a coil formed by winding of a wire may be used as
the second resonance coil 111. There is no particular limitation on
the shape of the second resonance coil 111; however, the second
resonance coil 111 in the power receiving device 102 is preferably
designed such that it is smaller than the first resonance coil 107
in the power transmission device 101 because the power receiving
device 102 needs to be smaller than the power transmission device
101. In particular, the Q-value of the second resonance coil 111 is
preferably high. Specifically, the Q-value of the second resonance
coil 111 is preferably 1000 or more. Note that signals for
supplying electric power wirelessly are transmitted and received
between the second resonance coil 111 and the first resonance coil
107 by electromagnetic resonance.
[0057] Although FIG. 1 illustrates the capacitor 112, the capacitor
112 may be parasitic capacitance generated at the time of formation
of the second resonance coil 111. Alternatively, the capacitor 112
may be a capacitor provided in advance independently of the second
resonance coil 111.
[0058] In FIG. 1, a coil formed by winding of a wire may be used as
the second coil 113. There is no particular limitation on the shape
of the second coil 113; however, the second coil 113 in the power
receiving device 102 is preferably designed such that it is smaller
than the first coil 103 in the power transmission device 101
because the power receiving device 102 needs to be smaller than the
power transmission device 101. Note that signals for supplying
electric power wirelessly are transmitted and received between the
second coil 113 and the second resonance coil 111 by
electromagnetic coupling.
[0059] In FIG. 1, the load 114 needs to operate by wireless power
transmission. For example, a battery, an electric motor, or the
like can be used. Specifically, an electronic device which operates
by a battery, such as a cellular phone, or an electric propulsion
moving vehicle can be used. Note that in the power receiving device
102, a circuit such as a DCDC converter or a rectifier circuit for
converting AC voltage transmitted to the second coil 113 into DC
voltage used in the load 114 may be provided between the load 114
and the second coil 113.
[0060] FIG. 4 is a flow chart of a wireless power transmission
system in the present invention. FIGS. 5A to 5C are schematic
diagrams in the flow chart in FIG. 4.
[0061] In Step 201 in FIG. 4, in the power transmission device 101,
the capacitance value of the variable capacitor 106 is adjusted to
0 by control with the control device 109. In other words, in Step
201 in FIG. 4, as illustrated in the schematic diagram in FIG. 5A,
the variable capacitor 106 and the first resonance coil 107 (dotted
lines in the diagram) are not to be influenced by a signal output
from the first coil 103.
[0062] In Step 202 in FIG. 4, in the power transmission device 101,
the oscillation frequency of the high-frequency power source 104 is
scanned by control with the control device 109 so that the
oscillation frequency of the high-frequency power source 104 is
changed successively.
[0063] In Step 203 in FIG. 4, in the power transmission device 101,
whether the frequency f0 at which the intensity of the S11
parameter is changed is detected in the control device 109 when the
oscillation frequency of the high-frequency power source 104 is
changed successively is determined. In Step 203, if the frequency
f0 is not detected, rearrangement of a power receiving device or
the like by a user is required, and the steps are performed again
from Step 201. In other words, in Steps 202 and 203 in FIG. 4, as
illustrated in the schematic diagram in FIG. 5B, a frequency at
which power loss due to reflection between the first coil 103 and
the second resonance coil 111 is decreased is determined while the
variable capacitor 106 and the first resonance coil 107 (dotted
lines in the diagram) are not influenced by a signal output from
the first coil 103. Through the series of steps, the frequency f0
is detected.
[0064] In Step 204 in FIG. 4, if the frequency f0 is detected in
Step 203, the capacitance value of the variable capacitor is
adjusted in accordance with the frequency M. The capacitance value
of the variable capacitor 106 may be adjusted referring to the
look-up table stored in the memory circuit 110. The look-up table
stores application voltage based on the capacitance value of the
variable capacitor 106 adjusted in accordance with the frequency f0
that is a resonance frequency estimated in advance.
[0065] In Step 205 in FIG. 4, in the power transmission device 101,
voltage to be applied to the high-frequency power source 104 is
adjusted by control with the control device 109 so that the
frequency f0 is set as the oscillation frequency of the
high-frequency power source 104. In other words, in Steps 204 and
205 in FIG. 4, as illustrated in the schematic diagram in FIG. 5C,
resonance frequency matching is performed so that resonance occurs
between the first resonance coil 107 and the second resonance coil
111 by application of voltage to the variable capacitor 106, and
output from the high-frequency power source 104 whose oscillation
frequency is the frequency f0 is obtained.
[0066] According to one embodiment of the present invention, it is
possible to provide a resonant power transmission device with which
resonance frequency matching can be performed between resonance
coils of the power transmission device and a power receiving device
only by a change in design of the structure of the power
transmission device and the efficiency of electric power
transmission can be increased and a resonant wireless power
transmission system.
[0067] This embodiment can be combined with any of the structures
described in the other embodiments as appropriate.
Embodiment 2
[0068] In this embodiment, the case where different steps are added
to the flow chart in FIG. 4 in Embodiment 1 is described.
[0069] Note that the control device 109 in FIG. 1 in Embodiment 1
that is described in this embodiment has a function of changing the
capacitance value of a variable capacitor and the oscillation
frequency of a signal output from a high-frequency power source.
Specifically, the control device 109 has a function of adjusting
the capacitance value of the variable capacitor 106 to 0. Further,
the control device 109 has a function of adjusting voltage to be
applied to the high-frequency power source 104 so that the
oscillation frequency of the high-frequency power source 104 is
successively changed under the condition that the capacitance value
of the variable capacitor 106 is 0. Further, the control device 109
has a function of changing the capacitance value of the variable
capacitor 106 into a value based on the frequency f0 in accordance
with the frequency f0 after the frequency f0 is detected.
Furthermore, the control device 109 has a function of setting a
frequency at which the intensity of the S11 parameter is changed at
the time when the oscillation frequency of the signal output from
the high-frequency power source is changed while the capacitance
value of the variable capacitor 106 is set to the value based on
the frequency f0, as the oscillation frequency of the signal output
from the high-frequency power source.
[0070] Note that Steps 201 to 204 in FIG. 6 are similar to those of
the flow chart in FIG. 4 in Embodiment 1.
[0071] In Step 301 in FIG. 6, in the power transmission device 101,
while the capacitance value of the variable capacitor 106 is fixed
to the value adjusted in accordance with the frequency f0 that is
the resonance frequency, the oscillation frequency of the
high-frequency power source 104 is scanned by control with the
control device 109 so that the oscillation frequency of the
high-frequency power source 104 is changed successively.
[0072] In Step 302 in FIG. 6, in the power transmission device 101,
whether the peak of a frequency at which the intensity of the S11
parameter is changed is detected in the control device 109 when the
oscillation frequency of the high-frequency power source 104 is
changed successively is determined. In Step 302, if the peak of the
frequency is not detected, rearrangement of a power receiving
device or the like by a user is required, and the steps are
performed again from Step 201.
[0073] In Step 303 in FIG. 6, whether the peak of the frequency in
Step 302 corresponds to two peaks of (f0+.DELTA.f) and
(f0-.DELTA.f) that are separated from the frequency f0 detected in
Step 203 is determined.
[0074] In Step 304 in FIG. 6, in the case where the number of peaks
of the frequency is determined to be two in Step 303, in the power
transmission device 101, voltage to be applied to the
high-frequency power source 104 is adjusted by control with the
control device 109 so that the frequency (f0+.DELTA.f) or the
frequency (f0-.DELTA.f) is set as the oscillation frequency of the
high-frequency power source 104. Note that one of the frequency
(f0+.DELTA.f) and the frequency (f0-.DELTA.f) at which the
intensity of the S11 parameter detected by a detector is lower is
preferably used as the oscillation frequency.
[0075] In Step 305 in FIG. 6, in the case where the peak of the
frequency is determined to be f0 in Step 303, in the power
transmission device 101, voltage to be applied to the
high-frequency power source 104 is adjusted by control with the
control device 109 so that the frequency f0 is set as the
oscillation frequency of the high-frequency power source 104.
[0076] According to one embodiment of the present invention, it is
possible to provide a resonant wireless power transmission device
in which resonance frequency matching can be performed between
resonance coils of the power transmission device and a power
receiving device only by a change in design of the structure of the
power transmission device and the efficiency of electric power
transmission can be increased and a resonant wireless power
transmission system. In particular, in the structure of this
embodiment, a decrease in efficiency of electric power transmission
that is caused by separation of the peaks of frequency due to
reduction in distance between a receiving device and a power
transmission device can be suppressed while the resonance
frequencies of resonance coils match each other.
[0077] This embodiment can be combined with any of the structures
described in the other embodiments as appropriate.
Embodiment 3
[0078] In this embodiment, applications of the wireless power
transmission system in the above embodiment are described. Note
that as applications of a wireless power transmission system in the
present invention, for example, portable electronic devices such as
a cellular phone, a digital video camera, a computer, a portable
information terminal (e.g., a mobile computer, a portable game
machine, or an e-book reader), and an image reproducing device
including a recording medium (specifically a digital versatile disc
(DVD)) can be given. In addition, an electric propulsion moving
vehicle that is powered by electric power, such as an electric car,
can be given. Examples of such electronic devices are described
below with reference to drawings.
[0079] FIG. 7A illustrates an application of a wireless power
transmission system to a cellular phone and a portable information
terminal, and a power transmission device 701, a cellular phone
702A including a power receiving device 703A, and a cellular phone
702B including a power receiving device 703B are included. The
wireless power transmission system in the above embodiment can be
provided between the power transmission device 701 and the power
receiving device 703A and between the power transmission device 701
and the power receiving device 703B. Thus, it is possible to
provide a resonant wireless power transmission device in which
resonance frequency matching can be performed between resonance
coils of the power transmission device and a power receiving device
only by a change in design of the structure of the power
transmission device and the efficiency of electric power
transmission can be increased and a resonant wireless power
transmission system.
[0080] FIG. 7B illustrates an application of a wireless power
transmission system to an electric car that is an electric
propulsion moving vehicle, and a power transmission device 711 and
an electric car 712 including a power receiving device 713 are
included. The wireless power transmission system in the above
embodiment can be provided between the power transmission device
711 and the power receiving device 713. Thus, it is possible to
provide a resonant wireless power transmission device in which
resonance frequency matching can be performed between resonance
coils of the power transmission device and a power receiving device
only by a change in design of the structure of the power
transmission device and the efficiency of electric power
transmission can be increased and a resonant wireless power
transmission system.
[0081] As described above, the wireless power transmission system
in the above embodiment can be used in any object that is driven
with power.
[0082] This embodiment can be combined with any of the structures
described in the other embodiments as appropriate.
REFERENCE NUMERALS
[0083] 101: power transmission device, 102: power receiving device,
103: first coil, 104: high-frequency power source, 105: coupler,
106: variable capacitor, 107: first resonance coil, 108: detector,
109: control device, 110: memory circuit, 111: second resonance
coil, 112: capacitor, 113: second coil, 114: load, 201: step, 202:
step, 203: step, 204: step, 205: step, 301: step, 302: step, 303:
step, 304: step, 305: step, 701: power transmission device, 702A:
cellular phone, 702B: cellular phone, 703A: power receiving device,
703B: power receiving device, 711: power transmission device, 712:
electric car, and 713: power receiving device.
[0084] This application is based on Japanese Patent Application
serial No. 2010-263048 filed with Japan Patent Office on Nov. 26,
2010, the entire contents of which are hereby incorporated by
reference.
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