DESCRIPTION
TITLE OF INVENTION: POWER TRANSMISSION DEVICE AND
POWER TRANSMISSION-RECEPTION SYSTEM
TECHNICAL FIELD
[0001] The present invention relates to a power
transmission device and a power transmission-
reception system.
BACKGROUND ART
[0002] Non-contact power supply technology
represented by electromagnetic induction has been
studied. The non-contact power supply technology is
used in, for example, a shaver or an electric tooth
brush. In recent years, with introduction of
magnetic field resonance technology as a cue, non-
contact power supply is actively developed again.
[0003] Further, there has been known a wireless
power supply system transmitting power to a power
reception antenna from a power transmission antenna
by wireless method, the wireless power supply system
having a detection unit detecting information related
to a disposition state of the power reception antenna,
plural driving units separately driving plural power
transmission coils of the power reception antennas,
and a control unit controlling current flowing
through the power transmission coils via the driving
units based on at least the information related to
the disposition state of the power reception antenna
(see, for example, Patent Literature 1).

[0004] Further, there has been known a non-contact
power transmission device having N (N is an integer
of 2 or larger) power transmission circuits and a
control means controlling this N power transmission
circuits, in which the power transmission circuits
have a power transmission side LC tank circuit
constituted of serially connected capacitors and a
power transmission coil, and an oscillation circuit
supplying power to this power transmission side LC
tank circuit, the power transmission coils of the N-
power transmission circuits are disposed in a matrix
form, and the control means controls a phase of a
signal generated by each oscillation circuit of the N
power transmission circuits so that phases of changes
of magnetic fields coming from at least two power
transmission coils among the power transmission coils
of the N power transmission circuits align in a power
reception coil of a power reception circuit (see, for
example, Patent Literature 2) .
CITATION LIST
PATENT LITERATURE
[0005] Patent Literature 1: Japanese Laid-open
Patent Publication No. 2008-283789
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2011-199975
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0006] An object of the present invention is to
provide a power transmission device and a power

transmission-reception system which are capable of
controlling power of wireless transmission according
to the number of power reception devices.
SOLUTION TO PROBLEM
[0007] A power transmission device has: a power
transmission unit configured to perform wireless
power transmission; a communication unit configured
to perform wireless communication within a range
wider than a power transmission possible range of the
power transmission unit; and a power transmission
control circuit configured to control power of
wireless power transmission of the power transmission
unit, wherein the power transmission control circuit
controls the power of wireless power transmission of
the power transmission unit according to a number of
power reception devices for which the communication
unit received a response indicating that power
reception is performed from power reception devices
receiving power equal to or more than a threshold
when the power transmission unit performs power
transmission by first power, and a number of power
reception devices for which the communication unit
received a response indicating that power reception
is performed from power reception devices receiving
power equal to or more than the threshold when the
power transmission unit does not perform power
transmission or performs power transmission by second
power smaller than the first power.
ADVANTAGEOUS EFFECTS OF INVENTION

[0008] The number of power reception devices inside
a power transmission possible range can be detected,
and wireless power transmission can be performed by
appropriate power according to this number.
BRIEF DESCRIPTION OF DRAWINGS
[0009] [Fig. 1] Fig. 1 is a diagram illustrating a
structural example of a power transmission-reception
system according to a first embodiment.
[Fig. 2] Fig. 2 is a diagram illustrating a
structural example of a power transmission device and
a power reception device.
[Fig. 3] Fig. 3 is a diagram illustrating a
structural example of a power transmission-reception
system having two power transmission devices> and two
power reception devices.
[Fig. 4A] Fig. 4A is a diagram for describing
a method of detecting the number of power reception
devices existing inside the power transmission
possible range of a second power transmission device.
[Fig. 4B] Fig. 4B is a diagram for describing
a method of detecting the number of power reception
devices existing inside the power transmission
possible range of. the second power transmission
device.
[Fig. 4C] Fig. 4C is a diagram for describing
a method of detecting the number of power reception
devices existing inside the power transmission
possible range of the second power transmission
device.

[Fig. 5] Fig. 5 is a flowchart illustrating a
processing example of the second power transmission'
device.
[Fig. 6] Fig. 6 is a diagram illustrating a
structural example of a power transmission-reception
system according to a second embodiment.
[Fig. 7] Fig. 7 is a sequence flow diagram
illustrating a processing example of the power
transmission-reception system of Fig. 6.
[Fig. 8] Fig. 8 is a sequence flow diagram
illustrating a processing example of the power
transmission-reception system of Fig. 6.
[Fig. 9] Fig. 9 is a sequence flow diagram
illustrating a processing example of the power
transmission-reception system of Fig. 6.
[Fig. 10] Fig. 10 is a sequence flow diagram
illustrating a processing example of the power
transmission-reception system of Fig. 6.
[Fig. 11] Fig. 11 is a time chart
illustrating a power transmission example of a first
power transmission device according to a third
embodiment.
[Fig. 12] Fig. 12 is a time chart
illustrating a power transmission example of the
first power transmission device and the second power
transmission device according to a fourth embodiment.
[Fig. 13A] Fig. 13A is a diagram illustrating
a processing example of the first power transmission
device and the second power transmission device

according to a fifth embodiment.
[Fig. 13B] Fig. 13B is a diagram illustrating
a processing example of the first power transmission
device and the second power transmission device
according to the fifth embodiment.
[Fig. 14A] Fig. 14A is a diagram illustrating
a processing example of the first power transmission
device and the second power transmission device
according to a fifth embodiment.
[Fig. 14B] Fig. 14B is a diagram illustrating
a processing example of the first power transmission
device and the second power transmission device
according to the fifth embodiment.
DESCRIPTION OF EMBODIMENTS
[0010] (First Embodiment)
Fig. 1 is a diagram illustrating a structural
example of a power transmission-reception system
according to a first embodiment. The power
transmission-reception system has, for example, one
power transmission device 101 and plural power
reception devices 102. The plural power transmission
device 101 can wirelessly transmit power to plural
power reception devices 102. The plural power
reception devices 102 are a personal computer, a
mobile terminal or mobile phone, and the like for
example, and can wirelessly receive power from the
power transmission device 101 to charge an internal
battery. Thus, the power transmission device 101 can
simultaneously charge the plural power reception

devices 102. At this time, the power transmission
device 101 needs to perform wireless transmission by
relatively small power when the number of power
reception devices 102 receiving power is small, and
to perform wireless transmission by relatively large
power when the number of power reception devices 102
receiving power is large. If the power transmission
device 101 performs wireless transmission by power
larger than necessary when the number of power
reception devices 102 is small, there occurs a
problem that the power reception devices 102 receives
power excessively and heat exceeding a tolerance
value occurs. Therefore, the power transmission
device 101 needs to control power of wireless
transmission according to the number of power
reception devices existing in a power transmission
possible range.
[0011] Fig. 2 is a diagram illustrating a structural
example of the power transmission device 101 and the
power reception device 102. The power transmission
device 101 has a high-frequency power supply circuit
201, a power transmission coil 202, a power
transmission LC resonator 203, a power transmission
control circuit 204, and a communication unit 205.
The power reception devices 102 has a power reception
LC resonator 211, a power reception coil 212, a power
reception circuit 213, a battery 214, a communication
unit 215, and a power reception control circuit 216.
The LC resonators 203 and 211 are serially connected

circuits of coils (inductors) and capacitors, and a
resonance frequency thereof is 1/{2 × π × √ (L ×
C)}. Here, L is inductance and C is capacitance
value. The power transmission device 101 can perform
wireless power transmission to the power reception
device 102. The high-frequency power supply circuit
201 has an oscillator, an amplifier, and a matching
circuit, and applies high-frequency voltage to the
power transmission coil 202. Then, a magnetic field
occurs in the power transmission coil 202, and
current flows through the power transmission LC
resonator 203 by electromagnetic induction 221
Since the frequency of voltage applied by the high-
frequency power supply circuit 201 is the resonance
frequency of 1/{2 × π × √ (L ×C)},the power
transmission LC resonator 203 becomes a resonance
state. A magnetic field occurs in the power
transmission LC resonator 203, current flows through
the power reception LC resonator 211 by magnetic
field resonance 222 of the resonance frequency of
1/{2 × π × √ (L ×C)}, and the power reception LC
resonator 211 becomes a resonance state. Then, a
magnetic field occurs in the power reception LC
resonator 211, and current flows through the power
reception coil 212 by electromagnetic induction 223.
The power reception circuit 213 has a rectifying
circuit, rectifies voltage occurring in the power
reception coil 212, and supplies the rectified
voltage to the battery 214. The battery 214 is

charged by the supplied voltage. The power
transmission device 101 can perform wireless power
transmission to the power reception device 102 by the
magnetic field resonance 222, to thereby charge the
battery 214 of the power reception device 102.
[0012] The communication unit 205 of the power
transmission device 101 and the communication unit
215 of the power reception device 102 are
communication units for performing wireless
communication by a method different from power
transmission and reception by the coils 202, 212 and
the LC resonators 203, 211 and can mutually perform
transmission and reception. The power transmission
control circuit 204 is connected to the communication
unit 205 and controls the high-frequency power supply
circuit 201. The power reception control circuit 216
is connected to the communication unit 215 and
controls the power reception circuit 213.
[0013] Here, the power transmission coil 202
performs wireless power transmission to the power
transmission LC resonator 203 by the electromagnetic
induction 221. Next, the power transmission LC
resonator 203 performs wireless power transmission to
the power reception LC resonator 211 by magnetic
field resonance 222. Next, the power reception LC
resonator 211 performs wireless power transmission to
the power reception coil 212 by electromagnetic
induction 223. Thus, the power transmission device
101 can perform wireless transmission to the power

reception device 102 by the magnetic field resonance
222.
[0014] Note that, not limited to the magnetic field
resonance 222, the power transmission device 101 can
perform various types of wireless power transmission
to the power reception device 102. The wireless
transmission includes electromagnetic induction,
electric field induction, electric field resonance,
microwave power transmission, or laser power
transmission besides the above magnetic field
resonance 222. In the case of the electromagnetic
induction, for example, the LC resonators 203 and 211
may be deleted. In this case, the power transmission
coil 202 of the power transmission device 101 can
perform wireless power transmission to the power
reception coil 212 of the power reception device 102
by electromagnetic induction. Further, in the case
of the electric field induction or the electric field
resonance, wireless power transmission can be
performed from the power transmission device 101 to
the power reception device 102 by using an antenna or
the like. Hereinafter, the case where the power
transmission device 101 performs wireless
transmission to the power reception device 102 by the
magnetic field resonance 222 will be described as an
example.
[0015] Fig. 3 is a diagram illustrating a structural
example of a power transmission-reception system
having two power transmission devices 101a, 101b and

two power reception devices 102a, 102b. The power
transmission devices 101a and 101b have the same
structure as the power transmission device 101 of Fig.
2. The power reception devices 102a and 102b have
the same structure as the power reception device 102
of Fig. 2.
[0016] A first power transmission possible range
301a is a range in which a power transmission unit
(including the power transmission coil 202 and the
power transmission LC resonator 203) of the first
power transmission device 101a can perform wireless
power transmission. A first transmission possible
range 302a is a range in which the communication unit
205 of the first power transmission device 101a can
perform wireless transmission and is wider than the
first power transmission possible range 301a.
[0017] A second power transmission possible range
301b is a range in which a power transmission unit
( inc 1 u'ding the power transmission coil 202 and the
power transmission LC resonator 203) of the second
power transmission device 101b can perform wireless
power transmission. A second transmission possible
range 302b is a range in which the communication unit
205 of the second power transmission device 101b can
perform wireless transmission and is wider than the
second power transmission possible range 301b.
[0018], For example, when the power transmission
units of the power transmission devices 101a and 101b
are power transmission units of magnetic field

resonance method, the power transmission possible
ranges 301a and 301b are about several tens of
centimeters. Further, when the communication units
205 of the power transmission devices 101a and 101b
are of communication method of Bluetooth (registered
trademark), the transmission possible ranges 302a and
302b are several meters.
[0019] The first power transmission device 101a can
perform power transmission to the first power
reception device 102a located inside the first power
transmission possible range 301a, but cannot perform
power transmission to the second power reception
device 102b located .outside the first power
transmission possible range 301a. The second power
transmission device 101b can perform power
transmission to the second power reception device
102b located inside the second power transmission
possible range 301b, but cannot perform power
transmission to the first power reception device 102a
located outside the second power transmission
possible range 301b.
[0020] Further, the first power transmission device
101a can perform transmission to the first power
reception device 102a and the second power reception
device 102b located inside the first transmission
possible range 302a, but cannot perform transmission
to a power reception device located outside the first
transmission possible range 302a. The second power
transmission device 101b can perform transmission to

the first power reception device 102a and the second
power reception device 102b located inside the second
transmission possible range 302b, but cannot perform
transmission to a power reception device located
outside the second transmission possible range 302b.
[0021] As described above, a power transmission
target of the first power transmission device 101a is
only the first power reception device 102a, and a
power transmission target of the second power
transmission device 101b is only the second power
reception device 102b.
[0022] On the other hand, transmission targets of
the first power transmission device 101a are the
first power reception device 102a and the second
power reception device 102b, and transmission targets
of the second power transmission device 101b are the
first power reception device 102a and the second
power reception device 102b.
[0023] The first transmission possible range 302a is
wider than the first power transmission possible
range 301a, and the second transmission possible
range 302b is wider than the second power
transmission possible range 301b. Accordingly, the
number of power reception devices 102 as the power
transmission target of the power transmission device
101 and the number of power reception devices 102 as
the transmission targets of the power transmission
device 101 do not match. Therefore, it is uneasy for
the power transmission devices 101a and 101b to

dete.ct the number of power reception devices located
inside the power transmission possible ranges 301a
and 301b by only wireless communication of the
communication units 205. A method will be described
below by which the power transmission devices 101a
and 101b detects the number of power reception
devices 102 located inside the power transmission
possible ranges 301a and 3 01b and perform
transmission of appropriate power according to the
number of detected power reception devices 102.
[0024] Fig. 4A to Fig. 4C are diagrams for
describing a method of detecting the number of power
reception devices existing inside the power
transmission possible range of the second power
transmission device 101b, and Fig. 5 is a flowchart
illustrating a processing example of the second power
transmission device 101b. In Fig. 4A to Fig. 4C, a
method will be described by which the second power
transmission device 101b detects the number of power
reception devices existing inside the second power
transmission possible range 301b when the first power
transmission device 101a performs power transmission
to the first power reception device 102a. Note that
. the first power reception de.vice 102a and the second
power reception device 102b exist inside the second
transmission possible range 302b of the second power
transmission device 101b.
[0025] First, in step S501, as illustrated in Fig.
4A, by control of the power transmission control

circuit 204, the power transmission unit (including
the power transmission coil 202 and the power
transmission LC resonator 203) of the second power
transmission device 101b starts test power
transmission by first power, before regular power
transmission is performed.
[0026] Next, in step S502, the second power
transmission device 101b detects a power reception
device receiving power during the test power
transmission. Specifically, the communication unit
'205 of the second power transmission device 101b
transmits a power reception device detection notice
for detecting the power reception device receiving
power. The second power reception device 102b exists
inside the second power transmission possible range
301b of the second power transmission device 101b,
and thus it receives power from the second power
transmission device 101b. The communication unit 215
of the second power reception device 102b receives
power equal to or more than a threshold, and thus
upon receipt of the aforementioned power reception
device detection notice from the second-power
transmission device 101b it transmits an indication
of receiving power to the second power transmission
device 101b.
[0027] On the other hand, the first power reception
device 102a is located outside the second power
transmission possible range 301b of the second power
transmission device 101b, and thus it does not

receive power from the second power transmission
device 101b but receives power from the first power
transmission device 101a. Accordingly, also the
communication unit 215 of the first power reception
device 102a receives power equal to or more than, the
threshold, and thus upon receipt of the
aforementioned power reception device detection
notice from the second power transmission device 101b
it transmits an indication of receiving power to the
second power transmission device 101b.
[0028] Therefore, the second power transmission
device 101b receives the indications of receiving
power from the first power reception device 102a and
the second power reception device 102b, and detects
that the power reception devices receiving power are
two power reception devices 102a and 102b.
[0029] Next, in step S503, the second power
transmission device 101b proceeds to step S504 when
it receives one. or more indications of receiving
power from the power reception devices, or when it
receives no indication of receiving power from the
power reception devices, no power reception device
receiving power exists and thus it proceeds to step
S511.
[0030] .Next, in step S504, as illustrated in Fig. 4B,
the power transmission unit (including the power
transmission coil 202 and the power transmission LC
resonator 203) of the second power transmission
device l'Olb stops the aforementioned test power

transmission by control of the power transmission
control circuit 204, thereby changing it to a state
of not performing power transmission.
[0031] Next, in step S505, the second power
transmission device 101b detects the power reception
devices receiving power after the test power
transmission is stopped. Specifically, the
communication unit 205 of the second power
transmission device 101b transmits the power
reception device detection notice for detecting a
power reception device receiving power. The second
power reception device 102b becomes a state of not
receiving power and is not receiving power equal to
or more than the threshold, and thus does not
transmit the indication of receiving power when the
aforementioned power reception device detection
notice is transmitted.
[0032] On the other hand, the first power reception
device 102a receives power from the first power
transmission device 101a and receives power equal to
or more than the threshold, and thus upon receipt of
the aforementioned power reception device detection
notice it transmits the indication of receiving power
to the second power transmission device 101b.
[0033] Therefore, the second power transmission
device 101b receives the indication of receiving
power from only the first power reception device 102a,
and detects that the power reception device receiving
power is one power re.ception device 102a.

[0034] Next, in step S506, the second power,
transmission device 101b checks whether the number of
power reception devices detected in step S502 and the
number of power reception devices detected in step
S505 are the same or not. When they are not the same,
it proceeds to step S507-, or when they are the same,
it means that no power reception device receiving
power exists inside the second power transmission
possible range 301b of the second power transmission
device 101b, and thus it proceeds to step S511.
[0035] Next, in step S507, as illustrated in Fig. 4C,
the.second power transmission device 101b subtracts
the number of power reception devices from which
there is a response in step S502 from the number of
power reception devices from which there is a
response in step S505, to thereby detect the number
of power reception devices which changed to a state
of no response. That is, by subtracting the number
of power reception devices 102a detected in step S505,
which is one, from the number of power reception
devices 102a and 102b detected in step S502, which is
two, the power transmission control circuit 204 of
the second power transmission device 101b can detect
that the number of power reception devices existing
inside its own second power transmission possible
range 301b is one, the second power reception device
102b.
[0036] Next, in steps S508 and S509, the power
transmission unit (including the power transmission

coil 202 and the power transmission LC resonator 203)
.of the second power transmission device 101b performs
power transmission by appropriate power to the number
of power reception devices 102b detected in step S507,
which is one, by that the power transmission control
circuit 204 controls gain of the amplifier in the
high-frequency power supply circuit 201. Thus,
appropriate power is transmitted from the second
power transmission device 101b to the second power
reception device 102b, which can prevent excessive
power reception of the second power reception device
102b and prevent abnormal heat generation.
[0037] Next, in step S510, when the communication
unit 215 of the second power reception device 102b
completes charging, it transmits a power reception
completion notice to the second power transmission
device 101b. Upon receipt of the power reception
completion notice from the second power reception
device 102b, the communication unit 205 of the second
power transmission device 101b proceeds to step S511.
. [0038] In step S511, the power transmission unit
(including the power transmission coil 202 and the
power transmission LC resonator 203) of the second
power transmission device 101b stops power
transmission by control of the power transmission
control circuit 2 04.
[0039] The example of processing of the second power
transmission device 101b has been described above,
but processing of all the power transmission devices

101 including another power transmission device 101a
is similar to the processing of the second power
transmission device 101b.
[0040] As above, first, in step S502, the power
transmission control circuit 204 of the power
transmission device 101 detects the number of power
reception devices 102 for which the communication
unit 205 received the response indicating that power
reception is performed from the power reception
devices 102 receiving power'equal to or more than the
threshold when the power transmission unit performs
power transmission by the first power. Thereafter,
in step S505, the power transmission control circuit
204 of the power transmission device 101 detects the
number of power reception devices 102 for- which the
communication unit 205 received the response
indicating that power reception is performed from the
power reception devices 102 receiving power equal to
or more than the threshold when the power
transmission unit does not perform power transmission.
Thereafter in step S507, the power transmission
control circuit 204 of the power transmission device
101 detects the number of power reception devices 102
existing inside the power transmission possible range
of the power transmission unit according to the
number of power reception devices 102 detected in
step S502 and the number of power reception devices
detected in step S505. Thereafter, in step S508, the
power transmission control circuit 204 of the power

transmission device 101 controls the power of
wireless power transmission of the power transmission
unit according to the number of power reception
devices 102 detected in step S 5 0 7 ..
[0041] Note that the order of the processing of
steps S501 and S502 and the processing of steps S504
and S505 may be reversed. Specifically, the order
may be such that first the processing of step S504 is
performed, then the processing of step S505 is
performed, then the processing of step S501 is
performed, then the processing of step S502 is
performed, and thereafter the processing of step S507
and so on is performed.
[0042] Specifically, first, as in' step S505, the
power transmission control circuit 204 of the power
transmission device 101 detects the number of power
reception devices 102 for which the communication
unit 205 received the response indicating that power
reception is performed from the power reception
devices 102 receiving power equal to or more than the
.threshold when the power transmission unit does not
perform power transmission. Thereafter, as in step
S502, the power transmission control circuit 204 of
the power transmission device 101 detects the number
of power reception devices 102 for which the
communication unit 205 received the response
indicating that power reception is performed from the
power reception devices 102 receiving power equal to
or more than the threshold when the power

transmission unit performs power transmission by the
first power. Thereafter, in step S507, the power
transmission control circuit 204 of the power
transmission device 101 detects the number of power
reception devices 102 existing inside the power
transmission possible range of the., power transmission
unit according to the number of power reception
devices 102 detected in step.S502 and the number of
power reception devices detected in step S505.
Thereafter, in step S508, the power transmission
control circuit 204 of the power transmission device
101 controls the power of wireless power transmission
of the power transmission unit according to the
number of the power reception devices 102 detected in
step S507.
[0043] Further, in step S504, the example of
stopping power transmission is described, but power
transmission may be performed by second power
(including minimum power) smaller than the first
power of test transmission of step S501.
[0044] Specifically, in step S502, the power
transmission, control circuit 204 of the power
transmission device 101 detects the number of power
reception devices for which the communication unit
205 received the response indicating that power
reception is performed from the power reception
devices 102 receiving power equal to or more than the
threshold when the power transmission unit performs
power transmission by the first power. Further,

similarly to steps S504 and S505, the power
transmission control circuit 204 of the power
transmission device 101 detects the number of power
reception devices 102 for which the communication
unit 205 received the response indicating that power
reception is performed from the power reception
devices 102 receiving power equal to or more than the
threshold when the power transmission unit performs
power transmission by the second power smaller than
the first power. Thereafter, in step S508, the power
transmission control circuit 204 of the power
transmission device 101 controls the power of
wireless power transmission of the power transmission
unit according to the number of power reception
devices detected in step S507. Also in this case,
the order of the processing of steps S502 and S505
may be reversed as described above.
[0045] As described above, when the power reception
devices 102 is a laptop personal computer, a mobile
terminal, or the like, the power reception devices
102 are movable. According to this embodiment, when
the number of the power reception devices 102 inside
the power transmission possible range of the power
transmission device 101 changes, the number of the
power reception devices 102 inside its own power
transmission possible range is detected, and wireless
power transmission can be performed by appropriate
power according to the number thereof.
[0046] (Second Embodiment)

Fig. 6 is a diagram illustrating a structural
example of a power transmission-reception system
according to a second embodiment. The power
transmission-reception system has two power
transmission devices 101a, 101b and four power
reception devices 102a, 102b, 102c, 102d. A first
power transmission possible range 301a is a range in
which a power transmission unit of the first power
transmission device 101a can perform power
transmission, and the first power reception device
102a and the second power reception device 102b exist. ■
A second power transmission possible range 301b is a
range in which a power transmission unit of the
second power transmission device 101b can perform
power transmission, and the third power reception
device 102c and the fourth power reception device
102d exist.
[0047] The first transmission possible range 302a is
a range in which the communication unit 205 of the
first power transmission device 101a can perform
transmission and is wider than the first power
transmission possible range 301a, and the first power
reception device 102a, the second power reception
device 102b, the third power reception device 102c,
and the fourth power reception device 102d exist
therein. The second transmission possible range 302b
is a range in which the communication unit 205 of the
second power transmission device 101b can perform
transmission and is wider than the second power

transmission possible range 301b, and the first power
reception device 102a, the second power reception
device 102b, the third power reception device 102c,
and the fourth power reception device 102d exist
therein.
[0048] Fig. 7 to Fig. 10 are sequence flow diagrams
illustrating a processing example of the power
transmission-reception system of Fig. 6. First, in
Fig. 7, in step 701, the first power transmission
device 101a instructs a start of charge processing.
[0049] Next, in step 702, which corresponds to step
5501 of Fig. 5, the power transmission unit of the
first power transmission device 101a starts test
power transmission by first power. Since the first
power reception device 102a and the second power
reception device 102b are located inside the first
power transmission possible range 301a of the first
power transmission device 101a, they start power
reception from the first power transmission device
101a in steps 703 and 704, and their power is turned
on by this power reception.
[0050] On the other hand, since the third power
reception device 102c and the fourth power reception
device 102d are located outside first power
transmission possible range 301a of the first power
transmission device 101a, they do not perform power
re'ception and their power is not tu.rned on.
[0051] Next, in step 705, which corresponds to step
5502 of Fig. 5, the communication unit 205 of the

first power transmission device 101a transmits a
power reception device detection notice for detecting
a power reception device receiving power.
[0052] Then, in step 706, since the first power
reception device 102a is receiving power, upon
receipt of the aforementioned power reception device
detection notice from the first power transmission
device 101a, it transmits an indication of receiving
power as a response to the first power transmission
device 101a. In step 707, since also the second
power reception device 102b is receiving power, upon
receipt of the aforementioned power reception device
detection notice from the first power transmission
device 101a, it transmits an indication of receiving
power as a response to the first power transmission
device 101a.
[0053] On the other hand, in step 708, since the
third power reception device 102c is not receiving
power, it does not respond when the aforementioned
power reception device detection notice is
transmitted. In step 709, since also the fourth
power reception device 102d is not receiving power,
it does not respond when the aforementioned power
reception device detection notice is transmitted.
[0054] Next, in step 710, the power transmission
control circuit 204- of the first power transmission
device 101a stores in a storage unit 711 information
of the first power reception device 102a and the
second power reception device 102b from which there

is a response in steps 706 and 707.
[0055] Next, in step 712, which corresponds to step
5504 of Fig. 5, the power transmission unit of the
first power transmission device 101a stops the test
power transmission. Then, in step 713, the first
power reception device 102a stops power reception and
the power is cut off. In step 714, also the second
power reception device 102b stops power reception and
the power is cut off.
[0056] Next, in step 715, which corresponds to step
5505 of Fig. 5, the communication unit 2 0.5 of the
first power transmission device 101a transmits the
power reception device detection notice for detecting
a power reception device receiving power.
[0057] Then, as illustrated in Fig. 8, in step 801,
since the first power reception device 102a is not
receiving power, it does not respond when the
aforementioned power reception device detection
notice is transmitted. In step 802, since also the
second power reception device 102b is not receiving
power, it does hot respond when the aforementioned
power reception device detection notice is
transmitted. In step 803, since also the third power
reception device 102c is not receiving power, it does
not.respond when the aforementioned power reception
device detection notice is transmitted. In step 804,
also the fourth power reception device 102d is not
receiving power, it does not respond when the
aforementioned power reception device detection

notice is transmitted.
[0058] Next, in step 805, the power transmission
control circuit 204 of the first power transmission
device 101a performs processing'of deleting from the
storage unit 711 information of power reception
devices which responded. However, in step 805, since
there exists no power reception device which
responded, the power transmission control circuit 204
of the first power transmission device l'Ola does not
delete the information of the storage unit 711.
[0059] Next, in step 806, which corresponds to step
5507 of Fig. 5, the power transmission control
circuit 204 of the first power transmission device
101a detects that two power reception devices, the
first power reception device 102a and the second
power reception device 102b, stored in the storage
unit 711 exist in its own first power transmission
possible range 301a.
[0060] Next, in step 807, which corresponds to step
5508 of Fig. 5, the power transmission control
circuit 204 of the first power transmission device
101a sets gain of the amplifier in the high-frequency
power supply circuit 201 so that it becomes power
appropriate for the number of power reception devices
detected in step 806.
[0061] Next, in step 808, which corresponds to step
5509 of Fig. 5, the power transmission unit of the
first power transmission device 101a starts power
transmission by the aforementioned set appropriate

power. Then, in step 809, the first power reception
device 102a receives power by the appropriate power,
and its power is turned on. In step 810, also the
second power reception device 102b receives power by
the appropriate power, and its power is turned on.
[0062] On the other hand, since the third power
reception device 102c and the fourth power reception
device 102d are located outside the first power
transmission possible range 301a of the first power
transmission device 101a, they do not receive power.
[0063] Next, as illustrated in Fig. 9, in step 901,
the second power transmission device 101b instructs
start of charge processing.
[0064] Next, in step 902, which corresponds to step
5501 of Fig. 5, the power transmission unit of the
second power transmission device 101b starts test
transmission by the first power. Since the third
power reception device 102c and the fourth power
reception device 102d are. located inside the second
power transmission possible range 301b of the second
power transmission device 101b, they start power
reception from the second power transmission device
101b in steps 903 and 904, and power is turned on by
this power reception.
[0065] Next, in step 905, which corresponds to step
5502 of Fig. 5, the communication unit 205 of the
second power transmission device 101b transmits the
power reception device detection notice for detecting
a power reception device receiving power.

[0066] Then, in step 906, since the first power
reception device 102a is receiving power from the
first power transmission device 101a, upon receipt of
the aforementioned power reception device detection
notice from the second power transmission device 101b,
it transmits an indication of receiving power as a
response to the second power transmission device 101b.
In step 907, since also the second power reception
device 102b is receiving power from the first power
transmission device 101a, upon receipt of the
aforementioned power reception device detection
notice from the second power transmission device 101b,
it transmits an indication of receiving power as a
response to the second power transmission device 101b.
[0067] On the other hand, in step 908, since the
third power reception device 102c is receiving power
from the second power transmission device 101b, upon
receipt of the aforementioned power reception device
detection notice from the second power transmission
device 101b, it transmits an indication of receiving
power as a response to the second power transmission
device 101b. In step 909, since also the fourth
power reception device 102d is receiving power from
' the second power transmission device 101b, upon
receipt of the aforementioned power reception device
detection notice from the second power transmission
device 101b, it transmits an indication of receiving
power as a response to the second power transmission
device 101b.

[0068] Next, in step 910, the power transmission
control circuit 204 of the second power transmission
device 101b stores in a storage unit 911 information
of the first power reception device 102a to the
fourth power reception device 102d from which there
is a response in steps 906 to 909.
[0069] Next, in step 912, which corresponds to step
5504 of Fig. 5, the power transmission unit of the
second power transmission device 101b stops test
power transmission. Then, in step 913, the third
power reception device 102c stops power reception,
and the power is cut off. In step 914, also the-
fourth powe.r reception device 102d stops power
reception, and the power is cut off.
[0070] Then, in step 915, which corresponds to step
5505 of Fig. '5, the communication unit 205 of the
second power transmission device 101b transmits the
power reception device detection notice for detecting
a power reception device receiving power.
[0071] Then, as illustrated in Fig. 10, in step 1001,
since the first power reception device 102a is
receiving power from the first power transmission
device 101a, upon receipt of the aforementioned power
reception device detection notice from the second
power transmission device 101b, it transmits an
indication of receiving power as a response to the
second power transmission device 101b. In step 1002,
since also the second power reception device 102b is
receiving power from the first power transmission

device 101a, upon receipt of the aforementioned power
reception device detection notice from the second
power transmission device 101b, it transmits an
indication of receiving power as a response to the
second power transmission device 101b.
[0072] On the other hand, in step 1003, since the
third power reception device 102c is not receiving
power, it does not respond upon receipt of the
■ aforementioned power reception device detection
notice. In step 1004, since also the fourth power
reception device 102d is not receiving power, it does
not respond when the aforementioned power reception
device • detect ion notice is transmitted.
[0073] Next, in step 1005, the power transmission
control circuit 204 of the second power transmission
device 101b deletes information of the first power
reception device 102a and the second power reception
device 102b which responded in steps 1001 and 1002
from the storage unit 911. Thus, information of the
third power reception device 102c and the fourth
power reception device 102d remains in the storage
unit 911.
[0074] Next, in step 1006, which corresponds to step
S507 of Fig. 5, the power transmission control
circuit 204 of the second power transmission device
101b detects that two power reception devices, the
third power reception device 102c and the fourth
power reception device 102d stored in the storage
unit 911, exist in its own second power transmission

possible range 301b. N
[0075] Next, in step 1007, which corresponds to step
5508 of Fig. 5, the power transmission control
circuit 204 of the second power transmission device
101b sets gain of the amplifier in the high-frequency
power supply circuit 201 so that it becomes power
appropriate for the number of power reception devices
detected in step 1006.
[0076] Next, in step 1008, which corresponds to step
5509 of Fig. 5, the power transmission unit of the
second power transmission device 101b starts power
transmission by the aforementioned set appropriate
power. Then in step 1009, the third power reception
device 102c receives power by the appropriate power,
and its power is turned on. In step 1010, also the
fourth power reception device 102d receives power by
the appropriate power, and its power is turned on.
[0077] As described above, according to this
embodiment, the first power transmission device 101a
can perform power transmission by power appropriate
for the two power reception devices -102a and 102b
inside the first power transmission possible range
301a. The second power transmission device 101b can
perform power transmission by power appropriate for
the two power reception devices 102c and 102d inside
the second power transmission possible range 301b.
[0078] (Third Embodiment)
Fig. 11 is a time chart illustrating a power
transmission example of the first power transmission

device 101a according to a third embodiment.
Differences of this embodiment from the first and
second embodiments will be described below. The
first power transmission device 101a regularly
performs the processing of steps S501' to S509 of Fig.
5 at certain cycles. Thus, as illustrated in Fig. .11,
in the first power transmission device 101a, the
power transmission stoppage of step S504 is performed
regularly.
[0079] Specifically, the power transmission control
circuit 204 of the first power transmission device
101a regularly performs the processing of controlling
the power of wireless power transmission of the power
transmission unit in step S508 according to the
number of power reception devices 102 received by the
communication unit 205 in step S502 when the power
transmission unit performs power transmission by
■ first power in step S501 and the number of power
reception devices 102 received by the communication
unit 205 in step S505 when the power transmission
unit does not perform power transmission in step S504.
[0080] It can be expected that the power reception
device 102 is moved or increased in number while
being charged. In this embodiment, the first power
transmission device 101a regularly detects the number
of power reception devices 102 existing inside the
first power transmission possible range 301a and
controls the transmitted power, and thus when the
number of power reception devices 102 inside the

first power transmission possible range 301a changes,
power transmission can be performed by appropriate
power.
[0081] Note that when the first power transmission
device 101a and the second power transmission device
101b which are contingently located closely starts
charging processing simultaneously, ifthefirst
power transmission device 101a and the second power
transmission device 101b perform the aforementioned
power control processing.regularly at the same cycles,
the first power transmission device 101a erroneously
detects that the first power reception device 102a to
the fourth power reception device 102d exist inside
the first power transmission possible range 301a, and
also the second power transmission device 101b
erroneously detects that the first power reception
device 102a to the fourth power reception device 102d
exist in the second power transmission possible range
301b. Accordingly, an embodiment which can respond
to such contingent cases will be described in a
fourth embodiment below.
[0082] (Fourth Embodiment)
Fig. 12 is a time chart illustrating a power
transmission example of the first power transmission
device 101a and the second power transmission device
101b according to a fourth embodiment. Differences
of this embodiment from the third embodiment will be
described below. The second power transmission
*
device 101b regularly performs the processing of

steps S501 to S509 of Fig. 5 at certain cycles
similarly to the first power transmission device 101a
of the third embodiment. Thus, as illustrated in Fig.
12, in the second power transmission device 101b, the
power transmission stoppage of step S504 is performed
regularly at certain cycles.
[0083] On the other hand, the first power
transmission device 101a performs the processing of
steps S501 to S509 of Fig. 5 plural times at random
cycles. Thus, as illustrated in Fig. 12, in the
first power transmission device 101a, the power
transmission stoppage of step S504 is performed
plural times at random cycles.
[0084] That is, the power transmission control
circuit 204 of the first power transmission device
101a performs, plural times at random cycles, the
processing of controlling the power of wireless power
transmission of the power transmission unit in step
S508 according to the number of power reception
devices 102 received by the communication unit 205 in
step S502 when the power transmission unit performs
power transmission by first power in step S501 and
the number of power reception devices 102 received by
the communication unit 205 in step S505 when the
power transmission unit does not perform power
transmission in step S504.
[0085] According to this embodiment, even when the
first power transmission device 101a and the second
power transmission device 101b which are contingently

located closely start the charging processing
simultaneously, the first power transmission device
101a and the second power transmission device 101b
can perform correct power control because they
perform the power transmission control processing of
the second time and so on at different timings.
Specifically, the first power transmission device
101a performs correct detection when the first power
reception device 102a and the second power reception
device 102b exist inside the first power transmission
possible range 301a, and also the second power
transmission device 101b performs correct detection
when the third power reception device 102c and the
fourth power reception device 102d exist inside the
second power transmission possible range 3.01b,
thereby making it possible to perform transmission by
appropriate power.
[0086] (Fifth Embodiment)
Fig. 13A, Fig. 13B, Fig. 14A, and Fig. 14B are
diagrams illustrating a processing example of the
first power transmission device 101a. and the second
•power transmission device 101b according to a fifth
embodiment.
[0087] In Fig. 13A, the first power transmission
device 101a is located outside the second
transmission possible range 302b of the second power
transmission device 101b, and the second power
transmission device 101b is located outside the first
transmission possible range 302a of the first power

transmission device 101a.
[0088] When the communication unit 205 of the first
power transmission device 101a transmits a power
transmission device detection notice, since the
second power transmission device 101b does not exist
inside the first transmission possible range 302a,
the communication unit 205 of the second power
transmission device 101b is unable to receive the
power transmission device detection notice from the
first power transmission device 101a, and hence does
not respond thereto. Since the communication unit
205 does not receive the aforementioned response, the
power transmission control circuit 204 of the first
power transmission device 101a can detect that the
second power transmission device 101b does not exist
in the first transmission possible range 302a.
[0089] Similarly, when the communication unit 205 of
the second power transmission device 101b transmits
the power transmission device detection notice, since
the first power transmission device 101a' does not
exist in the second transmission possible range 302b,
the communication unit 205 of the first power
transmission device 101a is unable to receive the
power transmission device detection notice from the
second power transmission device 101b, and hence does
not respond thereto. Since the communication unit
205 does not receive the aforementioned response, the
power transmission control circuit 204 of the second
power transmission device 101b can detect that the

first power transmission device 101a does not exist
in the second transmission possible range 302b.
[0090] Fig. 13B is a time chart illustrating a power
transmission example of the first power transmission
device 101a and the second power transmission device
101b in the state of Fig. 13A. In the case of Fig.
13A, the first power transmission device 101a does
not exist inside the second transmission possible
range 302b and thus of course does not exist inside
the second power transmission possible range ,301b.
Similarly, the second power transmission device 101b
does not exist inside the first transmission possible
range 302a and thus of course does not exist inside
the first power transmission possible range 301a.
[0091] In this case, the first power transmission
device 101a and the second power transmission device
101b regularly perform power control processing
similarly to Fig. 11, and thus periodic power
transmission 1301 is performed. Since the first
power transmission device 101a and the second power
transmission device 101b are separated from each
other, they can perform correct power control
processing even when they perform the power control
processing at the same timing.
[0092] In Fig. 14A, the first power transmission
device 101a is located inside the second transmission
possible range 302b of the second power transmission
device 101b, and the second power transmission device
101b is located inside the first transmission

possible range 302a of the first power transmission
device 101a.
[0093] When the communication unit 205 of the first
power transmission device 101a transmits the power
transmission device detection notice, since the
second power transmission device 101b exists inside
the first transmission possible range 302a, the
communication unit 205 of the second power
transmission device 101b receives the power
transmission device detection notice from the first
power transmission device 101a, and transmits a
response thereof. The communication unit 205
receives the aforementioned response, and thus the
power transmission control circuit 204 of the first
power transmission device 101a can detect that the
second power transmission device 101b exists inside'
the first transmission possible range 302a.
[0094] Similarly, when the communication unit 205 of
the second power transmission device 101b transmits
the power transmission device detection notice, since
the first power transmission device 101a exists
inside the second transmission possible range 302b,
the communication unit 205 of the first power
transmission device 101a receives the power
transmission device detection notice from the second
power transmission device 101b, and transmits a
response thereof. The communication unit 205
receives the aforementioned response, and thus the
power transmission control circuit 204 of the second

power transmission device 101b can detect that the
first power transmission device 101a exists inside
the second transmission possible range 302b.
[0095] Fig. 14B is a time chart illustrating a power
transmission example of the first power transmission
device 101a and the second power transmission device
101b in the state of Fig. 14A. In the case of Fig.
14A, the first power transmission device 101a exists
inside the second transmission possible range 302b
and thus there is a possibility that it also exists
inside the second power transmission possible range
301b. Similarly, the second power transmission
device 1,01b exists inside the first transmission
•possible range 302a and thus there is a' possibility
that it also exists inside the first power
transmission possible range 301a.
[0096] In this case, the first power transmission
device 101a periodically performs the power control
processing at first cycles similarly to Fig. 11, and
thus periodic power transmission 1301 at the first
cycles is performed. The second power transmission
device 101b periodically performs the power control
processing at second cycles different from the first
cycles similarly to Fig.. 11, and thus periodic power
transmission 1302 at the second cycles is performed.
[0097] Specifically, when the communication unit 205
receives an indication of existence of another power
transmission device 101 inside the transmission
possible range of the communication unit 205, the

power transmission control circuit 204 of the power
transmission device 101 makes the cycles of the
regularly performed power transmission control
processing be different from the power transmission
control processing regularly performed by the
aforementio.ned other power transmission device 101.
[0098] Since the first power transmission device
101a and the second power transmission device 101b
are located close to each other, timings of at least
the second power control processing and thereafter
are shifted by making the cycles of performing the
processing periodically be different, thereby making
it possible to perform correct power control
process ing.
[0099] According to.the first to fifth embodiments,
the power transmission device 101 can detect the
number of power reception devices 102 existing inside
the power transmission possible range, and perform
wireless power transmission by appropriate power
according to this number. Thus, it is possible to
prevent a problem that the power transmission device
101 transmits excessive power and abnormal heating
occurs in the power reception device 102, and thereby
prevent unnecessary power transmission loss.
[0100] It should be noted that the above embodiments
merely illustrate concrete examples of implementing
the present invention, and the technical scope of the
present invention is not to be construed in a
restrictive manner by these embodiments. That is,

the present invention may be implemented in various
forms without departing from the technical spirit or
main features thereof.
INDUSTRIAL APPLICABILITY
[0101] The number of power reception devices inside
a power transmission possible range can be detected,
and wireless power transmission can be performed by
appropriate power according to this number.

We Claim:
[Claim 1] A power transmission device, comprising:
a power transmission unit configured to perform
wireless power transmission;
a communication unit configured to perform
wireless communication within a range wider than a
power transmission possible range of the power
transmission unit; and
a power transmission control circuit configured
to control power of wireless power transmission of
the power transmission unit, wherein .
the power transmission control circuit controls
the power of wireless power transmission of the power
transmission unit according to a number of power
reception devices for which the communication unit
received a response indicating that power reception
is performed from power reception devices receiving
power equal to or more than a threshold when the
power transmission unit performs power transmission
by first power, and a number of power reception
devices for which the communication unit received a
response indicating that power reception is performed
from power reception devices receiving power equal to
or more than the threshold when the power
transmission unit does not perform power transmission
or performs power transmission by second power
smaller than the first power.
[Claim 2] The power transmission device according to
claim 1, wherein the power transmission control

circuit detects a number of power reception devices
existing in the power transmission possible range of
the power transmission unit according to the number
of power reception devices for which the
communication unit received a response indicating
that power reception is performed from power
reception devices receiving power equal to or more
than the threshold when the power transmission unit
performs power transmission by the first power, and
the number of power reception devices for which the
communication unit received a response indicating
that power reception is performed from power
reception devices receiving power equal to or more
than the. threshold when the power transmission unit
does not perform power transmission or performs power
transmission by the second power, and controls the
power of wireless power transmission of the power
transmission unit according to the number of detected
power reception devices.
[Claim 3] The power transmission device according to
claim 1, wherein the power transmission control
circuit controls the power of wireless power
transmission of the power transmission unit according
to the number of power reception devices for which
the communication unit received a response indicating
that power reception is performed from power
reception devices receiving power equal to or more
than the threshold when the power transmission unit
performs power transmission by the first power, and

the number of power reception devices for which the
communication unit received a response indicating
that power reception is performed from power
reception devices receiving power equal to or more
than the threshold when the power transmission unit
does not perform power transmission.
[Claim 4] The power transmission device according to
claim 1, wherein the power transmission control
circuit controls the power of wireless power,
transmission of the power transmission unit according
to the number of power reception devices for which
the communication unit received, a response indicating
that power reception is performed from power
reception devices receiving power equal to or more
than the threshold when the power transmission unit
performs power transmission by the first power, and
the number of power reception devices for which the
communication unit received a response indicating
that power reception is performed from power
reception devices receiving power equal.to or more
than the threshold when the power transmission unit
performs power transmission by the second power.
[Claim 5] The power transmission device according to
claim 1, wherein the power transmission control
circuit first detects the number of power reception
devices for which the communication unit received a
response indicating that power reception is performed
from power reception devices receiving power equal to
or more than the threshold when the power

transmission unit performs power transmission by the
first power, thereafter detects the number of power
reception devices for which the communication unit
received a response indicating that power reception
is performed from power reception devices receiving
power equal to or more than the threshold when the
power transmission unit does not perform power
transmission or performs power transmission by the
second power, and controls the power of wireless
power transmission of the power transmission unit
according to a result of the detection.
[Claim 6] The power transmission device according to
claim 1, wherein the power transmission control
circuit first detects the number of power reception
devices for which the communication unit received a
response indicating that power reception is performed
from power reception devices receiving power equal to
or more than the threshold when the power
transmission unit does not perform power transmission
or performs power transmission by the second power,
thereafter detects the number of power reception
devices for which the communication unit received a
response indicating that power reception is performed
from power reception devices receiving power equal to
or more than the threshold when the power
transmission unit performs power transmission by the
first power, and.controls the power of wireless power
transmission of the power transmission unit according
to a result of the detection.

[Claim 7] The power transmission device according to
claim 1, wherein the power transmission control
circuit regularly performs processing to control the
power of wireless power transmission of the power
transmission unit according to the number of power
reception devices received by the communication unit
when the power transmission unit performs power
transmission by the first power, and the number of
power reception devices received by the communication
unit when the power transmission unit does not
perform power transmission or performs power
transmission by the second power.
[Claim 8] The power transmission device according to
claim 1, wherein the power transmission control
circuit performs, several times at random cycles,
processing to control the power of wireless power
transmission of the power transmission unit according
to the number of power reception devices received by
the communication unit when the power transmission
unit performs power transmission by the first power,
and the number of power reception devices received by
the communication unit when the power transmission
unit does not perform power transmission or performs
power transmission by the second power.
[Claim 9] The power transmission device according to
claim 7, wherein when the communication unit receives
an indication of existence of another power
transmission device inside the transmission possible
range of the communication unit, the power

transmission control circuit makes the cycles of the
periodically performed processing be different from
cycles of processing periodically performed by the
other power transmission device.
[Claim 10] A power transmission-reception system,
compris ing:
a power transmission device; and
a power reception device, wherein
the power transmission device comprises:
a power transmission.unit configured to perform
wireless power transmission;
a communication unit configured to perform
wireless communication within a range wider than a
power transmission possible range of the power
transmission unit; and
a power transmission control circuit configured
to control the power of wireless power transmission
of the power transmission unit, wherein
the power transmission control circuit controls
the power of wireless power transmission of the power
transmission unit according to a number of power
reception devices for which the communication unit
received a response indicating that power reception
is performed from power reception devices receiving
power equal to or more than a threshold when the
power transmission unit performs power transmission
by first power, and a number of power reception
devices for which the communication unit received a
response indicating that power reception is performed

from power reception devices receiving power equal to
or more than the threshold when the power
transmission unit does not perform power transmission
or performs power transmission by second power
smaller than the first power, and
the power reception device has a communication
unit transmitting to the power transmission device an
indication of receiving power when power equal to or
more than the threshold is received.