U.S. patent application number 16/994060 was filed with the patent office on 2020-11-26 for wireless power transmission device, wireless power transmission system, and wireless power transmission method.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Toshiya MITOMO, Kentaro MURATA, Kohei ONIZUKA.
Application Number | 20200373661 16/994060 |
Document ID | / |
Family ID | 1000005019847 |
Filed Date | 2020-11-26 |
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United States Patent
Application |
20200373661 |
Kind Code |
A1 |
MURATA; Kentaro ; et
al. |
November 26, 2020 |
WIRELESS POWER TRANSMISSION DEVICE, WIRELESS POWER TRANSMISSION
SYSTEM, AND WIRELESS POWER TRANSMISSION METHOD
Abstract
A wireless power transmission device includes a power
transmitter to transmit a wireless power signal through a plurality
of first antennas, a propagation path estimation unit to estimate
first propagation path information characterizing a propagation
path between the plurality of first antennas and a predetermined
antenna, a propagation path extraction unit to extract second
propagation path information characterizing a propagation path
passing through a moving body, based on at least one of a
difference on a time axis of a plurality of pieces of the first
propagation path information each acquired at different times, and
filtering on a frequency axis, a weight calculator to calculate a
weight vector that determines a directivity of a combined power
transmission beam formed by the plurality of first antennas, and a
controller to control an amplitude and a phase of the wireless
power signal inputted to each of the plurality of first
antennas.
Inventors: |
MURATA; Kentaro; (Ota,
JP) ; ONIZUKA; Kohei; (Shinagawa, JP) ;
MITOMO; Toshiya; (Yokahama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Minato-ku |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Minato-ku
JP
|
Family ID: |
1000005019847 |
Appl. No.: |
16/994060 |
Filed: |
August 14, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16290403 |
Mar 1, 2019 |
10777886 |
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16994060 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 50/40 20160201;
H01Q 3/2623 20130101; H01Q 3/28 20130101; H02J 50/90 20160201; H01Q
3/2611 20130101; H01Q 3/36 20130101; H02J 50/60 20160201; H02J
50/23 20160201; H02J 50/20 20160201 |
International
Class: |
H01Q 3/26 20060101
H01Q003/26; H01Q 3/28 20060101 H01Q003/28; H02J 50/60 20060101
H02J050/60; H02J 50/20 20060101 H02J050/20; H02J 50/40 20060101
H02J050/40; H01Q 3/36 20060101 H01Q003/36; H02J 50/23 20060101
H02J050/23; H02J 50/90 20060101 H02J050/90 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2018 |
JP |
2018-173761 |
Claims
1. An electronic device comprising a power transmitter to transmit
a wireless power signal through a plurality of first antennas; and
a propagation path estimation unit to estimate first propagation
path information characterizing a propagation path between the
plurality of first antennas and a predetermined antenna, based on a
propagation path estimation signal having a same frequency as a
frequency of the wireless power signal and being transmitted from
the predetermined antenna.
2. The electronic device according to claim 1, further comprising:
a controller to control an amplitude and a phase of the wireless
power signal inputted to each of the plurality of first antennas,
based on the first propagation path information.
3. The electronic device according to claim 2, further comprising:
a propagation path extraction unit to extract second propagation
path information characterizing a propagation path passing through
a moving body, based on at least one of a difference on a time axis
of a plurality of pieces of the first propagation path information
each acquired at different times, and filtering on a frequency
axis, wherein the controller controls the amplitude and the phase
of the wireless power signal inputted to each of the plurality of
first antennas, based on at least one of the first propagation path
information and the second propagation path information.
4. The electronic device according to claim 3, further comprising:
a weight calculator to calculate a weight vector that determines a
directivity of a combined power transmission beam formed by the
plurality of first antennas, based on at least one of the first
propagation path information and the second propagation path
information, wherein the controller controls the amplitude and the
phase of the wireless power signal inputted to each of the
plurality of first antennas, based on the weight vector.
5. The electronic device according to claim 1, wherein the
predetermined antenna is a second antenna of a power receiving
device to receive the wireless power signal transmitted from the
power transmitter; and the propagation path estimation unit
estimates first propagation path information characterizing a
propagation path between the plurality of first antennas and the
second antenna, based on the propagation path estimation signal
transmitted from the power receiving device through the second
antenna.
6. The electronic device according to claim 1, wherein the
predetermined antenna is a third antenna provided in the power
transmitter; and the propagation path estimation unit estimates
first propagation path information characterizing a propagation
path between the plurality of first antennas and the third antenna,
based on the propagation path estimation signal transmitted by the
third antenna.
7. The electronic device according to claim 6, wherein the third
antenna is a part of a first antenna among the plurality of first
antennas provided in the power transmitter; and the power
transmitter comprises a signal source to generate the wireless
power signal and the propagation path estimation signal.
8. The electronic device according to claim 1, wherein the
predetermined antenna is a fourth antenna of a moving-body
detection device provided separately from the electronic device and
a power receiving device to receive the wireless power signal
transmitted from the power transmitter; and the propagation path
estimation unit estimates first propagation path information
characterizing a propagation path between the plurality of first
antennas and the fourth antenna, based on the propagation path
estimation signal transmitted by the fourth antenna.
9. The electronic device according to claim 4, wherein the
predetermined antenna is a second antenna of a power receiving
device to receive the wireless power signal transmitted from the
power transmitter, the propagation path estimation unit estimates
first propagation path information characterizing a propagation
path between the plurality of first antennas and the second
antenna, based on the propagation path estimation signal
transmitted by the second antenna from the power receiving device,
and the weight calculator calculates the weight vector so that a
power transmission beam at a position of the moving body becomes a
null and transmission of wireless power to the power receiving
device is performed.
10. A system comprising: a power transmission device to transmit a
wireless power signal through a plurality of first antennas; and a
power receiving device to receive the wireless power signal through
a second antenna, the power transmission device comprising: a
propagation path estimation unit to estimate first propagation path
information characterizing a propagation path between the plurality
of first antennas and a predetermined antenna, based on a
propagation path estimation signal having a same frequency as a
frequency of the wireless power signal transmitted from the
predetermined antenna.
11. The system according to claim 10, wherein the power
transmission device further comprises a controller to control an
amplitude and a phase of the wireless power signal inputted to each
of the plurality of first antennas, based on the first propagation
path information.
12. The system according to claim 11, wherein the power
transmission device comprises a propagation path extraction unit to
extract second propagation path information characterizing a
propagation path passing through a moving body, based on at least
one of a difference on a time axis of a plurality of pieces of the
first propagation path information each acquired at different
times, and filtering on a frequency axis, wherein the controller
controls the amplitude and the phase of the wireless power signal
inputted to each of the plurality of first antennas, based on at
least one of the first propagation path information and the second
propagation path information.
13. The system according to claim 12, wherein the power
transmission device further comprises a weight calculator to
calculate a weight vector that determines a directivity of a
combined power transmission beam formed by the plurality of first
antennas, based on at least one of the first propagation path
information and the second propagation path information, wherein
the controller controls the amplitude and the phase of the wireless
power signal inputted to each of the plurality of first antennas,
based on the weight vector.
14. The system according to claim 10, wherein the predetermined
antenna is a second antenna of a power receiving device to receive
the wireless power signal transmitted from the power transmitter;
and the propagation path estimation unit estimates first
propagation path information characterizing a propagation path
between the plurality of first antennas and the second antenna,
based on the propagation path estimation signal transmitted from
the power receiving device through the second antenna.
15. The system according to claim 10, wherein the predetermined
antenna is a third antenna provided in the power transmitter; and
the propagation path estimation unit estimates first propagation
path information characterizing a propagation path between the
plurality of first antennas and the third antenna, based on the
propagation path estimation signal transmitted by the third
antenna.
16. The system according to claim 15, wherein the third antenna is
a part of a first antenna among the plurality of first antennas
provided in the power transmitter; and the power transmitter
comprises a signal source to generate the wireless power signal and
the propagation path estimation signal.
17. The system according to claim 10, wherein the predetermined
antenna is a fourth antenna of a moving-body detection device
provided separately from the system and a power receiving device to
receive the wireless power signal transmitted from the power
transmitter; and the propagation path estimation unit estimates
first propagation path information characterizing a propagation
path between the plurality of first antennas and the fourth
antenna, based on the propagation path estimation signal
transmitted by the fourth antenna.
18. The system according to claim 13, wherein the predetermined
antenna is a second antenna of a power receiving device to receive
the wireless power signal transmitted from the power transmitter,
the propagation path estimation unit estimates first propagation
path information characterizing a propagation path between the
plurality of first antennas and the second antenna, based on the
propagation path estimation signal transmitted by the second
antenna from the power receiving device, and the weight calculator
calculates the weight vector so that a power transmission beam at a
position of the moving body becomes a null and transmission of
wireless power to the power receiving device is performed.
19. A method for performing electronic between a power transmission
device to transmit a wireless power signal through a plurality of
first antennas, and a power receiving device to receive the
wireless power signal through a second antenna, the power
transmission device comprising: estimating first propagation path
information characterizing a propagation path between the plurality
of first antennas and a predetermined antenna, based on a
propagation path estimation signal having a same frequency as that
of the wireless power signal and being transmitted from the
predetermined antenna.
20. The method according to claim 19, wherein the power
transmission device controls an amplitude and a phase of the
wireless power signal inputted to each of the plurality of first
antennas, based on the first propagation path information.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/290,403, filed Mar. 1, 2019, which is based upon and claims
the benefit of priority from the prior Japanese Patent Application
No. 2018-173761, filed on Sep. 18, 2018, the entire contents of
which are incorporated herein by reference.
FIELD
[0002] Embodiments of the present invention relate to a wireless
power transmission device, a wireless power transmission system,
and a wireless power transmission method.
BACKGROUND
[0003] Wireless power transmission is attracting attention. Since a
radio wave with a high power density is transmitted in wireless
power transmission using radio waves, in particular, it is required
not to cause radio disturbance on wireless devices other than a
power receiving device, and a power density of radio waves
irradiated to a human body is required to be reduced to a
predetermined value or less specified by international non-ionizing
radiation protection committee (ICNIRP) or the like.
[0004] There has been proposed a technique of detecting an obstacle
existing in a power transmission section from a power transmission
device to a power receiving device, and changing a direction in
which a radio wave is transmitted by the power transmission device
so as not to irradiate the obstacle (person or animal).
[0005] However, estimation of a direction and a position of the
obstacle requires hardware and software to realize a function for
the estimation. In addition, since hardware and software of this
type are affected by antennas, feeder lines, and peripheral
components, regular or irregular calibration is required. Further,
in estimating a direction and a position of the obstacle, an error
occurs due to environmental conditions and the like. Furthermore,
even if a main beam that maximizes the radiation of the radio wave
is controlled such that the radio wave is not radiated at a
position or in a direction of the obstacle, a radio wave is
irradiated on a human body by a sub-beam generated secondarily, and
a part of the human body is exposed to the radio wave if a range
not radiated with the radio wave is too narrow, since the human
body has a width.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a block diagram showing a schematic configuration
of a wireless power transmission device according to a first
embodiment;
[0007] FIG. 2 is a block diagram showing a schematic configuration
of a power receiving device according to the first embodiment;
[0008] FIG. 3 is a view schematically showing a signal flow of a
wireless power transmission system according to the first
embodiment;
[0009] FIG. 4 is a flowchart showing a processing operation of the
wireless power transmission system;
[0010] FIG. 5A is a view conceptually plotting a trajectory of
first propagation path information in polar coordinates, FIG. 5B is
a view conceptually plotting a point of a pseudo static propagation
path after averaging the first propagation path information in
polar coordinates, and FIG. 5C is a view conceptually plotting a
trajectory of a pseudo dynamic propagation path in polar
coordinates;
[0011] FIG. 6A is a view showing a position for each time of a
moving body that makes vibration movement on a line, FIG. 6B is a
view showing a state where a null is formed for the vicinity of a
center of a trajectory in which the moving body makes vibration
movement, and FIG. 6C shows a view showing a state where a
plurality of nulls are connected to form a null in a wide
range;
[0012] FIG. 7A is a view conceptually showing first propagation
path information in a time domain, and FIG. 7B is a view
conceptually showing first propagation path information in a
frequency domain;
[0013] FIG. 8 is a view showing an example in which the power
receiving device is arranged in a direction of an angle .theta.
from a y axis with respect to an array of a plurality of first
antennas arranged linearly at equal element intervals on an x
axis;
[0014] FIG. 9 is a block diagram showing a schematic configuration
of a wireless power transmission device according to a second
embodiment;
[0015] FIG. 10 is a block diagram showing a schematic configuration
of a power receiving device according to the second embodiment;
[0016] FIG. 11 is a view schematically showing a signal flow of a
wireless power transmission system according to the second
embodiment;
[0017] FIG. 12 is a view showing a schematic configuration of a
wireless power transmission system according to a third
embodiment;
[0018] FIG. 13 is a block diagram showing a schematic configuration
of a moving-body detection device according to a fourth embodiment;
and
[0019] FIG. 14 is a view schematically showing a signal flow of the
wireless power transmission system according to the fourth
embodiment.
DETAILED DESCRIPTION
[0020] In the present embodiment, there is provided a wireless
power transmission device including a power transmitter to transmit
a wireless power signal through a plurality of first antennas;
[0021] a propagation path estimation unit to estimate first
propagation path information characterizing a propagation path
between the plurality of first antennas and a predetermined
antenna, on the basis of a propagation path estimation signal
having a same frequency as a frequency of the wireless power signal
and being transmitted from the predetermined antenna;
[0022] a propagation path extraction unit to extract second
propagation path information characterizing a propagation path
passing through a moving body, on the basis of at least one of a
difference on a time axis of a plurality of pieces of the first
propagation path information each acquired at different times, and
filtering on a frequency axis;
[0023] a weight calculator to calculate a weight vector that
determines a directivity of a combined power transmission beam
formed by the plurality of first antennas, on the basis of at least
one of the first propagation path information and the second
propagation path information; and
[0024] a controller to control an amplitude and a phase of the
wireless power signal inputted to each of the plurality of first
antennas, on the basis of the weight vector.
[0025] Embodiments of the present invention is described below with
reference to drawings. In the following embodiments, a
characteristic configuration and an operation of a wireless power
transmission device and a wireless power transmission system will
be mainly described. However, the wireless power transmission
device and the wireless power transmission system may have
configurations and operations omitted in the following
description.
First Embodiment
[0026] FIG. 1 is a block diagram showing a schematic configuration
of a wireless power transmission device 1 according to a first
embodiment.
[0027] Note that the wireless power transmission device 1 in this
specification transmits a wireless power signal to a power
receiving device 2 in FIG. 2 to be described later, and is also
referred to as a power transmission device.
[0028] The wireless power transmission device 1 of FIG. 1 includes
a plurality of first antennas 3, a first transmission/reception
switch 4, a power transmitter 6 having a plurality of power
transmission units 5, a plurality of propagation path estimation
units 7, a propagation path extraction unit 8, a weight calculator
9, and a control unit 10.
[0029] The plurality of first antennas 3 are active phased array
antennas, for example, and can control a combined power
transmission beam formed by the plurality of first antennas 3, by
controlling an amplitude and a phase of a wireless power signal
inputted to each of the first antennas 3. The plurality of first
antennas 3 can also receive a propagation path estimation signal
from the power receiving device 2, in addition to transmitting the
wireless power signal. The first transmission/reception switch 4
switches whether to transmit a wireless power signal or to receive
a propagation path estimation signal from the power receiving
device 2, through the plurality of first antennas 3.
[0030] The plurality of power transmission units 5 transmit a
wireless power signal via the plurality of first antennas 3. A
variable phase shifter and a variable amplifier are provided in
each power transmission unit 5, and the controls of a phase value
and an amplitude value set in the variable phase shifter and the
variable amplifier enables control of a direction of the combined
power transmission beam formed by the plurality of first antennas
3.
[0031] The propagation path estimation unit 7 estimates first
propagation path information characterizing a propagation path
between the plurality of first antennas 3 and a predetermined
antenna, on the basis of a propagation path estimation signal
having the same frequency as that of the wireless power signal
received by the predetermined antenna.
[0032] In the present embodiment, the predetermined antenna is a
second antenna 21 of the power receiving device 2. As will be
described later, the power receiving device 2 transmits a
propagation path estimation signal from the second antenna 21 in
response to a request from the wireless power transmission device
1. Consequently, the propagation path estimation unit 7 according
to the present embodiment estimates the first propagation path
information characterizing the propagation path between the
plurality of first antennas 3 and the second antenna 21, on the
basis of the propagation path estimation signal transmitted from
the power receiving device 2 through the second antenna 21.
[0033] The propagation path extraction unit 8 extracts second
propagation path information characterizing a propagation path
passing through a moving body, on the basis of at least one of a
difference on a time axis of a plurality of pieces of the first
propagation path information each acquired at different times, and
filtering on a frequency axis. The moving body is, for example, a
human body.
[0034] On the basis of at least one of the first propagation path
information and the second propagation path information, the weight
calculator 9 calculates a weight vector that determines a
directivity of the plurality of first antennas 3.
[0035] The control unit 10 controls an amplitude and a phase of a
wireless power signal inputted to each of the plurality of first
antennas 3, on the basis of the weight vector.
[0036] The wireless power transmission device 1 of FIG. 1 may
include a storage unit 11, a first signal source 12, and a first
communication unit 13 in addition to the units described above.
[0037] The storage unit 11 stores a plurality of pieces of first
propagation path information each acquired at different times. The
propagation path extraction unit 8 reads out the plurality of
pieces of first propagation path information stored in the storage
unit 11, and extracts the second propagation path information
characterizing a propagation path passing through the moving
body.
[0038] The first signal source 12 generates a wireless power
signal. The first communication unit 13 performs wireless
communication with a second communication unit 25 in the power
receiving device 2 to be described later. This wireless
communication may conform to an existing wireless standard such as
a radio frequency identifier (RFID), Bluetooth, or a wireless local
area network (LAN), or may be other wireless systems. The first
communication unit 13 transmits a transmission request for a
propagation path estimation signal and the like, to the second
communication unit 25.
[0039] FIG. 2 is a block diagram showing a schematic configuration
of the power receiving device 2 according to the first embodiment.
The power receiving device 2 in FIG. 2 includes the second antenna
21, a power receiving unit 22, a second transmission/reception
switch 23, a second signal source 24, and the second communication
unit 25. When a wireless power signal transmitted from the wireless
power transmission device 1 is received by the second antenna 21,
the power receiving unit 22 acquires the wireless power signal.
[0040] Upon receiving the transmission request for the propagation
path estimation signal from the transmission unit, The second
signal source 24 transmits a propagation path estimation signal via
the second antenna 21.
[0041] FIG. 3 is a view schematically showing a signal flow of a
wireless power transmission system 31 according to the first
embodiment, and FIG. 4 is a flowchart showing a processing
operation of the wireless power transmission system 31. First, the
wireless power transmission device 1 requests the second
communication unit 25 in the power receiving device 2 to transmit a
propagation path estimation signal, from the first communication
unit 13 (step S1). Here, the propagation path estimation signal is
a non-modulated continuous wave signal having the same frequency as
that of the wireless power signal.
[0042] Upon receiving this request, the power receiving device 2
transmits a propagation path estimation signal generated by the
second signal source 24 via the second antenna 21 (step S2).
Meanwhile, when the power receiving device 2 transmits the
propagation path estimation signal, the second
transmission/reception switch 23 is connected to the second signal
source 24 side.
[0043] The wireless power transmission device 1 receives the
propagation path estimation signal through the plurality of first
antennas 3 (step S3). Meanwhile, when the propagation path
estimation signal is received, the first transmission/reception
switch 4 is connected to the propagation path estimation unit 7
side. The propagation path estimation unit 7 acquires propagation
path information of an electromagnetic wave propagation path
included in the received propagation path estimation signal. Here,
the propagation path information indicates a complex transfer
function of the propagation path. In the present specification,
propagation path information included in the propagation path
estimation signal and passing through a first propagation path 33
between the plurality of first antennas 3 and the second antenna 21
is referred to as first propagation path information. For example,
assuming that the number of the plurality of first antennas 3 is
NT, first propagation path information h1 (t) characterizing the
first propagation path 33 between the NT pieces of the first
antenna 3 and the second antenna 21 at a certain time t is
expressed by the following Expression (1). Note that, in this
specification, symbols representing matrices and vectors are
underlined, and the underlined symbols correspond to matrices or
vectors with the same symbols in boldface in expressions captured
as an image.
h.sub.1(t)=[h.sub.1,11(t) . . . h.sub.1,1N.sub.T(t)] (1)
[0044] In Expression (1), h1 (t) is a complex vector of one row and
NT columns, and a first row n-th column element h1,1n (t) is a
complex number indicating propagation path information between an
n-th antenna among the plurality of first antennas 3 and the second
antenna 21. Meanwhile, the propagation path information includes
any form in which a complex vector given by Expression (1) is
deformed/transformed.
[0045] Here, focusing on FIG. 3, the first propagation path
information contains: (i) a static propagation path h0 representing
a propagation path of a direct wave or a scattered wave from a
fixed propagation environment; (ii) dynamic second propagation path
information h2 (t) characterizing a second propagation path 34 of a
scattered wave passing through a moving body 32; and (iii) other
noise components hnoise (t). The first propagation path information
can be expressed as in Expression (2).
h.sub.1(t)=h.sub.0+h.sub.2(t)+h.sub.noise(t) (2)
[0046] In Expression (2), h0 corresponds to the static propagation
path information described above, and does not depend on the time
t. Whereas, h2 (t) corresponds to the dynamic second propagation
path information described above, and depends on a behavior of the
moving body 32 and varies with time. The hnoise (t) is a noise
component. Meanwhile, each of the above three components is a
complex vector having the same size as h1 (t) of Expression
(1).
[0047] The wireless power transmission device 1 receives a
propagation path estimation signal for a plurality of times at
different times, acquires a plurality of pieces of first
propagation path information given by Expression (1), and stores
the first propagation path information in the storage unit 11 in
the wireless power transmission device 1 (step S4).
[0048] Next, the propagation path extraction unit 8 extracts second
propagation path information required for forming a null 35 for the
moving body 32 and passing through the moving body 32, from the
first propagation path information given by Expression (1) (step
S5).
[0049] Next, on the basis of the first propagation path information
and the second propagation path information, the weight calculator
9 calculates a weight vector of an active phased array antenna of
the wireless power transmission device 1, such that the null 35 can
be formed for the moving body 32 while a power transmission beam 36
can be formed for the power receiving device 2 (step S6). The
weight vector is a set of a phase value and an amplitude value that
are set in the variable phase shifter and the variable amplifier
provided in each power transmission unit 5 of the first antenna
3.
[0050] Here, the weight vector can be calculated by one of the
following two methods.
[0051] [First Weight Calculation Method]
[0052] A first method is to extract second propagation path
information through a difference between a plurality of pieces of
first propagation path information in a time domain. As a
prerequisite, firstly, assumptions are given as follows in
Expression (1).
[0053] 1) Static propagation path information h0 is to be constant
without depending on a time t.
[0054] 2) The moving body 32 makes vibration movement at a constant
period T, and each element of dynamic second propagation path
information h2 (t) passing through the moving body 32 is a complex
exponential function of the period T. Note that the period T of the
vibration movement of the moving body 32 is predictable or
measurable in advance.
[0055] 3) Each element of a noise component hnoise (t) is additive
white Gaussian noise with variance .sigma..sup.2noise, and is to be
sufficiently small as compared with levels of the static
propagation path and the dynamic propagation path.
[0056] FIG. 5A is a view conceptually plotting a trajectory of a
certain element of first propagation path information h1 (t) in
polar coordinates under the above assumptions. Here, it is assumed
that a sampling period Tsample for acquiring the first propagation
path information h1 (t) is Tsample<T/2 on the basis of a
sampling theorem, and a total of Nsample pieces of first
propagation path information are acquired. Here, a plurality of the
pieces of first propagation path information are averaged as in the
following expression.
h 0 ' = 1 N sample n = 1 N ? h 1 ( t 0 + ( n - 1 ) T sample )
.apprxeq. h 0 ? indicates text missing or illegible when filed ( 3
) ##EQU00001##
[0057] In Expression (3), t0 is a time at which a first piece of
the first propagation path information is acquired. Here, when
Nsample is set to a large value, in the first propagation path
information h1 (t) shown in Expression (2), an average value of the
dynamic second propagation path information h2 (t) passing through
the moving body 32 can be approximated to zero by periodicity
thereof. Further, since the noise component hnoise (t) follows
circularly symmetric complex Gaussian distribution with an average
of zero, an average value thereof can also be approximated to zero.
Whereas, since the static propagation path information h0 does not
depend on the time t, a time average thereof is h0 itself. As a
result, when an average value h'0 of the first propagation path
information h1 (t) is calculated, the static propagation path
information h0 alone remains, and h0 can be approximately
extracted.
[0058] FIG. 5B is a view conceptually plotting a certain element of
a pseudo static propagation path h'0 after averaging the first
propagation path information h1 (t) of Expression (3), in polar
coordinates.
[0059] Expression (4) is obtained by subtracting Expression (3)
from Expression (2).
h'.sub.2(t)=h.sub.1(t)-h'.sub.0
.apprxeq.h.sub.2(t) (4)
[0060] In Expression (4), assuming that the average value h'can be
approximated to the static propagation path information h0, and the
noise component hnoise (t) in the first propagation path
information h1 (t) shown in Expression (2) is sufficiently small
and can be ignored, the dynamic second propagation path information
h2 (t) can be approximately extracted by obtaining h'2 (t) of
Expression (4).
[0061] FIG. 5C is a view conceptually plotting a trajectory of a
certain element of pseudo dynamic propagation path information h'2
(t) obtained by Expression (4), in polar coordinates. For the
pseudo dynamic propagation path information h'2 (t) obtained in
Expression (4), a transmission correlation matrix R2 thereof is
obtained by Expression (5).
R.sub.2=E[h'.sub.2(t).sup.Hh'.sub.2(t)] (5)
[0062] Here, H represents the Hermitian transpose of a complex
matrix, and E [ ] means a time average. Meanwhile, it is obvious
that a rank of the pseudo dynamic propagation path information h'2
(t) at a specific time is 1, but a rank of the transmission
correlation matrix R2 is 1 or more by taking a time average of the
correlation matrix.
[0063] Further, the correlation matrix R2 on the transmission side
may be obtained as follows. First, a virtual propagation path
matrix H'2 having the pseudo dynamic propagation path information
h'2 (t) acquired at different times in each row vector is defined
as in Expression (6).
H 2 ' = [ h 2 ' ( t 0 ) h 2 ' ( t 0 + ( N sample - 1 ) T sample ) ]
( 6 ) ##EQU00002##
[0064] Here, a size of the virtual propagation path matrix H'2 is
Nsample rows and NT columns. However, for convenience of forming
the null 35, Nsample is set to be smaller than NT. Then, from the
virtual propagation path matrix H'2 of Expression (6), the
transmission correlation matrix R2 can be obtained as in Expression
(7).
R.sub.2=H'.sub.2.sup.HH'.sub.2 (7)
[0065] Meanwhile, the rank of the transmission correlation matrix
R2 is Nsample at maximum. However, in a case where there are ones
highly correlated with each other among a plurality pieces of the
pseudo dynamic propagation path information h'2 (t) acquired at
different times, (e.g., in a case where two or more pieces of
propagation path information are acquired at different times but
when the moving body 32 is present at the same point or in the
vicinity thereof), the rank of the transmission correlation matrix
R2 is equal to or less than Nsample.
[0066] Here, all the transmission correlation matrices R2 obtained
by Expressions (5) and (7) are Hermitian matrices. Therefore,
Expression (5) and Expression (7) can be eigenvalue decomposed as
follows.
R.sub.2=V.sub.2.LAMBDA..sub.2V.sub.2.sup.n (8)
[0067] In Expression (8), V2 is an eigenvector matrix of the
transmission correlation matrix R2, and is given as follows.
V.sub.2=[v.sub.2,1 . . . v.sub.2,N.sub.T] (9)
[0068] The n-th vector v2,n of Expression (9) is an eigenvector of
an n-th eigenmode. Whereas, .LAMBDA.2 is a diagonal matrix having
an eigenvalue of the transmission correlation matrix R2 as a
diagonal element, and is given as in the following expression.
.LAMBDA..sub.2=diag(.lamda..sub.2,1 . . . .lamda..sub.2,N.sub.T)
(10)
[0069] Here, .lamda.2,n of an n-th diagonal line is an eigenvalue
of the n-th eigenmode, a largest eigenvalue is set as a first
eigenvalue, and each eigenvalue is defined in descending order as
follows.
.lamda..sub.2,1.gtoreq. . . .
.gtoreq..lamda..sub.2,N.sub.rank.gtoreq..lamda..sub.2,N.sub.rank.sub.+1.a-
pprxeq. . . .
.apprxeq..lamda..sub.2,N.sub.T.apprxeq..sigma..sub.noise.sup.2
(11)
[0070] In Expression (11), Nrank represents the rank of the
transmission correlation matrix R2, and shows a value approximately
equal to the variance .sigma..sup.2noise of each element of the
noise component hnoise (t), for eigenvalues after the Nrank.
[0071] Here, the eigenmode conceptually represents an equivalent
propagation path between the wireless power transmission device 1
and the power receiving device 2, in a case where a certain
eigenvector of Expression (9) is used as a weight vector of the
active phased array antenna of the wireless power transmission
device 1. The eigenvalue represents a strength of the equivalent
propagation path. In particular, the eigenmode of the second
propagation path information h2 (t) represents an equivalent
propagation path passing through the moving body 32. An eigenmode
having a larger eigenvalue means that scattering in the moving body
32 is more conspicuous, that is, the moving body 32 is irradiated
with more electromagnetic waves.
[0072] Therefore, from the viewpoint of reducing the exposure of
the moving body 32 with electromagnetic waves, it is desirable to
use an eigenvector having a small corresponding eigenvalue (that
is, small irradiation of the moving body 32 with electromagnetic
waves) among the eigenvectors of V2 in Expression (9), for the
weight of the active phased array antenna of the wireless power
transmission device 1. Particularly, in Expression (11),
eigenvalues after the Nrank have approximately equal values as the
variance .sigma..sup.2noise of each element of the noise component
hnoise (t), indicating that irradiation of the moving body 32 with
electromagnetic waves is particularly small for the eigenmodes
corresponding to these eigenvalues. Consequently, among the
eigenvectors of V2 in Expression (9), eigenvectors after the Nrank
are defined as in the following expression as a pre-weight matrix
of the active phased array antenna of the wireless power
transmission device 1.
W.sub.NS=[v.sub.2,N.sub.rank.sub.+1 . . . v.sub.2,N.sub.T] (12)
[0073] Here, each column vector (weight) included in Expression
(12) conceptually forms a directivity that directs the null 35 to
the moving body 32.
[0074] FIGS. 6A to 6C show conceptual views of a directivity formed
by the pre-weight matrix that is of Expression (12) and obtained
from the transmission correlation matrix R2 of Expressions (5) and
(7). FIG. 6A is a view showing a position for each time of the
moving body 32 that makes vibration movement on a line.
[0075] First, in Expression (5), a time average of a correlation
matrix of the pseudo dynamic propagation path information h'2 (t)
is defined as the transmission correlation matrix R2. In this case,
a principal eigenmode of the transmission correlation matrix R2
corresponds to a propagation path for the vicinity of a center of a
trajectory of the moving body 32 making vibration movement (that
is, a position with a high existence probability of the moving body
32). Consequently, the directivity formed by the pre-weight matrix
obtained on the basis of Expression (5) forms the null 35 for the
vicinity of the center of the trajectory of the moving body 32
making vibration movement (that is, a position with a high
existence probability of the moving body 32). (See FIG. 6B)
[0076] Whereas, in Expression (7), a correlation matrix of the
virtual propagation path matrix H'2 having the pseudo dynamic
propagation path information h'2 (t) acquired at different times in
each row vector is defined as the transmission correlation matrix
R2. In this case, a rank of the transmission correlation matrix R2
is to be Nsample at maximum, and at this time, the first to
Nsample-th eigenmodes represent equivalent propagation paths
corresponding to individual positions where the moving body 32 is
present at different times. Therefore, the directivity formed by
the pre-weight matrix obtained on the basis of Expression (7) forms
the null 35 for each position where the moving body 32 is present
at different times, causing the plurality of nulls 35 to be
connected and forming the null 35 in a wide range. (See FIG.
6C)
[0077] Subsequently, a weight vector for forming the power
transmission beam 36 is derived for the power receiving device 2,
while the pre-weight matrix of Expression (12) is used. First, the
following expression is obtained by multiplying the pseudo static
propagation path h'0 obtained in Expression (3) by a pre-weight
matrix W.sub.NS obtained by Expression (12).
h''.sub.0=h'.sub.0W.sub.NS (13)
[0078] That is, h''0 in Expression (13) indicates a pseudo static
propagation path in a case where the null 35 is formed for the
moving body 32. Here, a size of h''0 in Expression (13) is one row
and (NT-Nrank) columns.
[0079] In Expression (13), a post-weight vector that maximizes
power transmission efficiency for the power receiving device 2 is
given as in the following expression.
w.sub.BF=h''.sub.0.sup.H/.parallel.h'.sub.0.parallel..sub.2
(14)
[0080] In Expression (14), .parallel. .parallel.2 represents an L2
norm of a complex vector. Here, an n-th element of w.sub.BF
represents a weighting coefficient multiplied by an n-th column
vector of W.sub.NS given by Expression (12). In a case of w.sub.BF
given by Expression (14), in particular, a directivity in using
each column vector of W.sub.NS as a weight is combined so as to
intensify in the same phase at a point of the second antenna 21 of
the power receiving device 2, resulting in formation of the power
transmission beam 36 for the power receiving device 2.
[0081] Finally, the following Expression (15) gives a weight vector
for forming the power transmission beam 36 for the power receiving
device 2, while the null 35 is formed for the moving body 32 from
Expressions (12) and (14). In the Expression (15), W.sub.NS is a
formation of null for moving body, and w.sub.BF is a formation of
beam for power receiving device.
.omega.=W.sub.NS.omega..sub.BF (15)
[0082] Here, a weight vector w of Expression (15) is a complex
vector of NT rows and one column, and an amplitude and a phase of
an n-th element thereof correspond to a gain and a phase component
that are set in the amplifier and the variable phase shifter of the
power transmission unit 5 of an n-th antenna among the plurality of
first antennas 3.
[0083] [Second Weight Calculation Method]
[0084] A second method is to extract second propagation path
information by converting a plurality of pieces of first
propagation path information in a time domain into first
propagation path information in a frequency domain, and filtering
first propagation path information in a frequency band including a
frequency derived from a behavior of the moving body 32. Note that,
in the following derivation, assumptions similar to those of [first
weight calculation method] are used.
[0085] Here, similarly to [first weight calculation method], it is
assumed that a sampling period Tsample for acquiring first
propagation path information h1 (t) is Tsample<T/2 on the basis
of a sampling theorem, and a total of Nsample pieces of first
propagation path information are acquired.
[0086] FIG. 7A conceptually illustrates a certain element of the
first propagation path information h1 (t) in a time domain given by
Expression (2). The first propagation path information h1 (t)
contains: static propagation path information h0 not depending on a
time; dynamic second propagation path information h2 (t) passing
through the moving body 32 making vibration movement at the period
T; and a noise component hnoise (t).
[0087] By applying the discrete Fourier transformation to the
Nsample pieces of first propagation path information h1 (t) in a
time domain acquired with the sampling period Tsample, first
propagation path information g1 (f) in a frequency domain given by
the following expression is obtained.
g.sub.1(f)=[g.sub.1,11(f) . . . g.sub.1,1N.sub.T(f)] (16)
[0088] FIG. 7B is a view conceptually showing first propagation
path information g1 (f) in a frequency domain. First, a noise
component gnoise (f) in a frequency domain ideally exists at the
same level in all frequencies due to a property of additive white
Gaussian noise. Next, static propagation path information g0
appears as a DC component (f=0) of the first propagation path
information g1 (f) in a frequency domain, and is given as in the
following expression.
g.sub.0=g.sub.1(0) (17)
[0089] Whereas, dynamic second propagation path information g2 in a
frequency domain appears as a component of a frequency F of the
vibration movement of the moving body 32 out of the first
propagation path information g1 (f) in a frequency domain, and is
given as in the following expression.
g.sub.2=g.sub.1(F) (18)
[0090] Note that there is a relationship of F=1/T between the
period T and the frequency F of the vibration movement of the
moving body 32. Therefore, the pre-weight matrix W.sub.NS for
forming the null 35 for the moving body 32 can be obtained
similarly to the [first weight calculation method], from the
dynamic second propagation path information g2 in a frequency
domain out of the first propagation path information g1 (f) in a
frequency domain.
[0091] However, in the above description, it is assumed that the
dynamic second propagation path information g2 in a frequency
domain is included in a component of f=F out of the first
propagation path information g1 (f) in a frequency domain, and the
dynamic second propagation path information g2 does not necessarily
appear in the component of f=F in a case where there is an error in
the frequency (period) of the vibration movement of the moving body
32 predicted or measured in advance, or where the vibrating
movement of the moving body 32 includes a different frequency
component. Therefore, by defining a range of the vibration
frequency that may be included in the vibration movement of the
moving body 32 and using the plurality of pieces of the first
propagation path information g1 (f) in a frequency domain in that
range, it is possible to more reliably extract the dynamic second
propagation path information.
[0092] For example, the transmission correlation matrix R2 can be
obtained by obtaining each correlation matrix of the plurality of
pieces of first propagation path information g1 (f) in a frequency
domain as in Expression (5) of [First weight calculation method] in
a time domain and averaging on a frequency axis, or by rearranging
the first propagation path information g1 (f) at each frequency
point as in Expressions (6) and (7) to construct a virtual
propagation path matrix and obtaining the correlation matrix.
[0093] The pre-weight matrix W.sub.NS for forming the null 35 for
the moving body 32 can be obtained by the eigenvalue decomposition
of the transmission correlation matrix R2 as in Expressions (8) to
(12). Subsequently, a post-weight vector w.sub.BF for forming the
power transmission beam 36 for the power receiving device 2 is
calculated from the static propagation path information g0 in a
frequency domain and the obtained pre-weight matrix W.sub.NS, as in
Expressions (13) and (14). Finally, the weight vector w for forming
the power transmission beam 36 for the power receiving device 2 is
obtained, while the null 35 is formed for the moving body 32, by
multiplying the pre-weight matrix W.sub.NS and the post-weight
vector w.sub.BF similarly to Expression (15).
[0094] After calculating the weight vector w by the above-described
first or second weight calculation method, the control unit 10 in
the wireless power transmission device 1 sets a gain of the
variable amplifier and a phase value of the variable phase shifter
in the power transmission unit 5 connected to the plurality of
first antennas 3, on the basis of the amplitude and phase
information of the weight vector w (step S7).
[0095] Here, in practice, it may not possible to precisely realize
an amplitude ratio of the weight vector w, depending on a dynamic
range (a settable gain range) of the variable amplifier. In this
case, out of the weight vector w, the gain of the variable
amplifier of the power transmission unit 5 of the first antenna 3
corresponding to an element having a maximum amplitude is set as an
upper limit value of the dynamic range. Then, out of the weight
vector w, the gain of the variable amplifier of the power
transmission unit 5 of the first antenna 3 corresponding to an
element having an amplitude equal to or less than a lower limit
value of the dynamic range can be clipped with the lower limit
value of the dynamic range.
[0096] Further, in a case where the gain of the variable amplifier
and the phase of the variable phase shifter are discretely
controlled, an amplitude and a phase of each element of the weight
vector w may be rounded to a value close to a discrete value of a
settable gain of the variable amplifier and a settable phase of the
variable phase shifter.
[0097] Thereafter, a power transmission signal transmitted from the
first signal source 12 is transmitted to the power receiving device
2 via the power transmission unit 5 and the plurality of first
antennas 3 (step S8). In the power receiving device 2, the power
transmission signal is received via the second antenna 21 (step
S9), and the DC power is generated in the power receiving unit 22.
At this time, a first transmission/reception switch 4 is connected
to the power transmission unit 5 side, and the second
transmission/reception switch 23 is connected to the power
receiving unit 22.
[0098] As described above, in the first embodiment, the first
propagation path information between the plurality of first
antennas 3 in the wireless power transmission device 1 and the
second antenna 21 is estimated on the basis of the propagation path
estimation signal transmitted from the power receiving device 2;
the second propagation path information passing through the moving
body 32 is extracted on the basis of the first propagation path
information; the weight vector of the plurality of first antennas 3
is determined on the basis of the first propagation path
information and the second propagation path information; and the
amplitude and the phase of the wireless power signal inputted to
the plurality of first antennas 3 are controlled on the basis of
the weight vector. This makes it possible to transmit power to the
power receiving device 2 with high efficiency while reducing the
exposure of the moving body 32 with the electromagnetic waves,
without requiring a direction or position information of the moving
body 32.
Second Embodiment
[0099] In the above-described first embodiment, the example has
been described in which the first propagation path information and
the second propagation path information are acquired on the basis
of the propagation path estimation signal transmitted from the
power receiving device 2, and power is transmitted to the power
receiving device 2 with high efficiency while the null 35 is formed
for the moving body 32. However, from the viewpoint of power saving
and downsizing of the power receiving device 2, it is desirable
that the propagation path information can be estimated between the
wireless power transmission device 1 and the power receiving device
2 without transmission of the propagation path estimation signal
from the power receiving device 2.
[0100] As an alternative to the propagation path estimation signal,
a communication signal may be transmitted via the second antenna 21
of the power receiving device 2, and on the basis of this
communication signal, a relative direction or position information
of the power receiving device 2 with respect to the wireless power
transmission device 1 may be estimated, rather than the exact
propagation path information.
[0101] For example, as shown in FIG. 8, in a case where the power
receiving device 2 is arranged in a direction of an angle .theta.
from a y axis with respect to an array of a plurality of the first
antennas 3 arranged linearly at equal element intervals d on an x
axis, an array response vector (that is, first propagation path
information h1 considering a direct wave component alone) is given
by the following expression. Meanwhile, it is also possible to
define an array response vector of any array shape, with a similar
way of thinking.
h.sub.1=[1e.sup.jkd sin .theta. . . . e.sup.jk(N.sup.T.sup.-1)d sin
.theta.] (19)
[0102] In Expression (19), k represents a wave number at a
frequency of a power transmission signal. Here, when the power
receiving device 2 exists in a line-of-sight environment, first
propagation path information calculated on the basis of a
propagation path estimation signal from the power receiving device
2 and propagation path information given by Expression (19) are
substantially equivalent. Further, since a level of a scattered
wave component generally becomes smaller than a direct wave
component even in a scattering environment, it is possible to
obtain a power transmission efficiency equal to a power
transmission efficiency in a case where power is transmitted on the
basis of the exact first propagation path information substantially
by calculating a weight vector so as to form a power transmission
beam 36 on the basis of Expression (19). Further, since the formed
power transmission beam 36 has a constant width, a possibility that
the power transmission efficiency is extremely degraded is low even
if there is an estimation error in a direction or position
information of the power receiving device 2.
[0103] Whereas, as described above, it is difficult to form an
appropriate null 35 for the moving body 32 on the basis of the
direction or the position information. Therefore, it is necessary
to acquire propagation path information between the wireless power
transmission device 1 and the moving body 32 through some
means.
[0104] Accordingly, in the present embodiment, a wireless power
transmission device 1 transmits a propagation path estimation
signal, and a scattered wave from a moving body 32 is received by a
plurality of first antennas 3 of the wireless power transmission
device 1, thereby acquiring propagation path information between
the wireless power transmission device 1 and the moving body 32,
and forming a null 35 for the moving body 32 on the basis of the
propagation path information.
[0105] FIG. 9 is a block diagram showing a schematic configuration
of the wireless power transmission device 1 according to a second
embodiment.
[0106] Unlike the wireless power transmission device 1 shown in
FIG. 1, there are provided a third antenna 14 to transmit a
propagation path estimation signal, and a third signal source 15 to
generate a propagation path estimation signal.
[0107] FIG. 10 is a block diagram showing a schematic configuration
of a power receiving device 2 according to the second embodiment.
Unlike the power receiving device 2 shown in FIG. 2, the second
transmission/reception switch 23 to switch to a mode for
transmitting the propagation path estimation signal and the second
signal source 24 to generate the propagation path estimation signal
are unnecessary.
[0108] FIG. 11 is a view schematically showing a signal flow of a
wireless power transmission system 31 according to the second
embodiment. In the wireless power transmission system 31 of FIG.
11, the wireless power transmission device 1 transmits a power
transmission signal via a power transmission unit 5, and a power
receiving unit 22 in the power receiving device 2 receives the
power transmission signal, whereby power transmission is carried
out.
[0109] Note that a control flow in the second embodiment is the
same as the wireless power transmission control flow in the first
embodiment shown in FIG. 4, except that "direction estimation
processing of the power receiving device 2 is performed in advance"
and "transmission of the propagation path estimation signal is
performed by the wireless power transmission device 1 itself". For
example, in the first embodiment, the dynamic second propagation
path information between the first antenna 3 and the moving body 32
is extracted from the propagation path estimation signal that is
transmitted by the power receiving device 2, is scattered by the
moving body 32, and arrives at the plurality of first antennas 3.
Whereas, in the second embodiment, third propagation path
information between the third antenna 14 and the plurality of first
antennas 3 is acquired by transmitting a propagation path
estimation signal from the third signal source 15 in the wireless
power transmission device 1 into an environment via the third
antenna 14, and receiving the signal scattered in the environment
by the plurality of first antennas 3. Here, similarly to Expression
(2), the third propagation path information contains: (i) a static
propagation path representing a propagation path of a direct wave
or a scattered wave from a fixed propagation environment; (ii)
dynamic fourth propagation path information characterizing a fourth
propagation path 38 of a scattered wave passing through the moving
body 32; and (iii) other noise components.
[0110] Among them, the fourth propagation path information passing
through the moving body 32 is extracted by either or both of a
difference on a time axis or filtering on a frequency axis
similarly to that of the first embodiment, and a pre-weight matrix
for forming the null 35 for the moving body 32 is calculated, on
the basis of the fourth propagation path information. Thereafter, a
post-weight vector for forming the power transmission beam 36 for
the power receiving device 2 is calculated from the pre-weight
matrix and the first propagation path information between the
wireless power transmission device 1 and the power receiving device
2, the information being given by Expression (19). Then, by
multiplying the pre-weight matrix and the post-weight vector, the
null 35 is formed for the moving body 32, and the weight vector for
forming the power transmission beam 36 for the power receiving
device 2 is obtained.
[0111] As described above, in the second embodiment, a function for
transmitting the propagation path estimation signal is given to the
wireless power transmission device 1 side, which has relatively
less power constraints and implementation constraints. This can
simplify an internal configuration of the power receiving device 2,
reduce a load of the power receiving device 2, and also suppress
the power consumption of the power receiving device 2.
Third Embodiment
[0112] In the above-described second embodiment, the example has
been described in which the fourth propagation path information
between the wireless power transmission device 1 and the moving
body 32 is acquired on the basis of the propagation path estimation
signal transmitted from the third signal source 15 included in the
wireless power transmission device 1 via the third antenna 14, and
a beam corresponding to the direction or the position information
of the power receiving device 2 is transmitted while the null 35
for the moving body 32 is formed.
[0113] However, in the wireless power transmission device 1 of FIG.
9, the third antenna 14 and the third signal source 15 are
additionally required, an internal configuration of the wireless
power transmission device 1 becomes complicated, and a device cost
also increases.
[0114] Accordingly, in the present embodiment, a part or all of a
plurality of first antennas 3 included in a wireless power
transmission device 1 are used as one or more third antennas 14.
That is, among the plurality of first antennas 3, at least a part
of the first antennas 3 transmits a propagation path estimation
signal.
[0115] For example, as an alternative to the third antenna 14 used
for transmission of a propagation path estimation signal, the
plurality of first antennas 3 are grouped into a plurality of
subarrays, a part of subarrays is used for transmission of a
wireless power signal and reception of a propagation path
estimation signal, and the remaining subarrays are used for
transmission of a propagation path estimation signal. Note that
both the wireless power signal and the propagation path estimation
signal are non-modulated continuous wave signals having the same
frequency. Therefore, the wireless power signal generated by a
first signal source 12 and reduced in its output level may
alternatively be used as the propagation path estimation
signal.
[0116] FIG. 12 is a view showing a schematic configuration of a
wireless power transmission system 31 according to a third
embodiment, and shows an example in which the wireless power
transmission device 1 is divided into two blocks in order to
distinguish the plurality of first antennas 3 divided into the
plurality of subarrays. Note that the wireless power transmission
device 1 divided into a plurality of blocks may be regarded as a
network including a plurality of wireless power transmission
devices 1, and the plurality of wireless power transmission devices
1 may be wired or wirelessly connected with each other. A control
flow of the third embodiment is the same as that of the second
embodiment, in which the wireless power transmission device 1
transmits a propagation path estimation signal in a third
propagation path 37 by using a part of the first antennas 3; and on
the basis of the propagation path information between the
subarrays, the information including the propagation path
information scattered by the moving body 32 and reaching the first
antenna 3 via a fourth propagation path 38, a null 35 is formed for
the moving body 32, and a weight vector for forming a power
transmission beam 36 for a power receiving device 2 is
calculated.
[0117] As described above, in the third embodiment, since a part of
the plurality of first antennas 3 used for transmission of the
wireless power signal is used for transmission of the propagation
path estimation signal, it is unnecessary to provide a dedicated
antenna for transmission of the propagation path estimation signal
in the wireless power transmission device 1. Further, by
alternatively using the wireless power signal generated by the
first signal source 12 having a reduced output level as the
propagation path estimation signal, it is not necessary to provide
a dedicated signal source for generation of the propagation path
estimation signal. Therefore, it is possible to downsize the
wireless power transmission device 1 and to reduce the
manufacturing cost.
Fourth Embodiment
[0118] In the above-described third embodiment, a part or all of
the plurality of first antennas 3 included in the wireless power
transmission device 1 is used as the third antenna 14 for
transmission of the propagation path estimation signal, which
eliminates necessity of a dedicated antenna for transmission of the
propagation path estimation signal, and simplifies the system
configuration.
[0119] However, coupling between the first antenna 3 and the third
antenna 14 that are arranged in a limited space in the same
wireless power transmission device 1 is not negligible. As compared
with a radio wave intensity of the propagation path estimation
signal that is transmitted from the third antenna 14, scattered
within a propagation environment, and received by the first antenna
3, a radio wave intensity of the propagation path estimation signal
reaching the first antenna 3 directly from the third antenna 14 is
extremely large. Therefore, there is a possibility that an input
signal level of the propagation path estimation unit 7 is saturated
or the propagation path estimation unit 7 is damaged due to the
radio wave intensity of the propagation path estimation signal
reaching the first antenna 3 directly from the third antenna 14.
This phenomenon is called self interference. A simple measure to
improve the self interference includes: setting a large distance
between the first antenna 3 and the third antenna 14; directing the
first antenna 3 and the third antenna 14 in opposite directions;
and providing a decoupling mechanism between the first antenna 3
and the third antenna 14 (absorber, shield, or the like). However,
this becomes a big restriction on implementation.
[0120] Accordingly, in the present embodiment, the problem of the
self interference is solved by using a moving-body detection device
provided separately from a wireless power transmission device 1 and
a power receiving device 2.
[0121] FIG. 13 is a block diagram showing a schematic configuration
of a moving-body detection device 41 according to a fourth
embodiment.
[0122] The moving-body detection device 41 of FIG. 13 includes a
fourth antenna 42, a fourth signal source 43, and a third
communication unit 44. The fourth antenna 42 transmits a
propagation path estimation signal in response to a transmission
request from the wireless power transmission device 1. The fourth
signal source 43 generates a propagation path estimation signal by
using electric power from an external power supply device 45 that
is externally attached to the moving-body detection device 41. The
third communication unit 44 performs wireless communication between
a second communication unit 25 in the wireless power transmission
device 1 and the third communication unit 44 in the power receiving
device 2.
[0123] In addition to this, the moving-body detection device 41 of
FIG. 13 may include a moving-body detection sensor (e.g., a camera,
a pyroelectric sensor, or a human sensor such as a sonar). For
example, the moving-body detection device 41 may transmit the
propagation path estimation signal after detecting the presence of
a moving body 32 with the moving-body detection sensor. Since there
is no particular limitation on an arrangement location of the
moving-body detection device 41, it is possible to arrange the
wireless power transmission device 1 and a moving body detection
signal transmission device at a relatively large distance, and to
avoid self interference.
[0124] FIG. 14 is a view schematically showing a signal flow of a
wireless power transmission system 31 according to the fourth
embodiment. A control flow is the same as the control flow of the
first to third embodiments, except that "the moving-body detection
device 41 transmits the propagation path estimation signal via a
fifth propagation path 39". For example, when the propagation path
estimation signal is first transmitted via the fourth antenna 42 of
the moving-body detection device 41, a first antenna 3 in the
wireless power transmission device 1 receives the propagation path
estimation signal scattered in a propagation environment. On the
basis of the received propagation path estimation signal, a
propagation path estimation unit 7 estimates fifth propagation path
information characterizing the fifth propagation path 39 between a
plurality of first antennas 3 and the fourth antenna 42. A
propagation path extraction unit 8 extracts sixth propagation path
information characterizing a sixth propagation path 40 passing
through the moving body 32. On the basis of the fifth propagation
path information and the sixth propagation path information, a
weight calculator 9 obtains a pre-weight matrix for forming a null
35 for the moving body 32, and calculates a post-weight vector for
forming a power transmission beam 36 for the power receiving device
2, from the pre-weight matrix and the first propagation path
between the wireless power transmission device 1 and the power
receiving device 2, the path being given by Expression (19). Then,
by multiplying the pre-weight matrix and the post-weight vector,
the null 35 is formed for the moving body 32, and the weight vector
for forming the power transmission beam 36 for the power receiving
device 2 is generated.
[0125] As described above, in the fourth embodiment, since the
moving-body detection device 41 to transmit the propagation path
estimation signal is provided separately from the wireless power
transmission device 1 and the power receiving device 2, it is
possible to simplify the configuration of the power receiving
device 2, and to eliminate self interference that becomes a problem
in transmitting the propagation path estimation signal from the
wireless power transmission device 1.
[0126] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
methods and systems described herein may be embodied in a variety
of other forms; furthermore, various omissions, substitutions and
changes in the form of the methods and systems described herein may
be made without departing from the spirit of the inventions. The
accompanying claims and their equivalents are intended to cover
such forms or modifications as would fall within the scope and
spirit of the inventions.
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