DESCRIPTION
POWER RECEPTION APPARATUS AND POWER RECEIVING METHOD
Technical Field
[0001] The present invention relates to a power
reception apparatus and a power receiving method.
Background Art
[0002] In the related art, techniques of supplying power
in a wireless manner by using electromagnetic induction or
electromagnetic wave have been considered. Recently,
techniques of supplying power in a wireless manner by using
magnetic field resonance have been considered. The
magnetic field resonance is a phenomenon where two
resonating coils are coupled with each other through a
magnetic field, so that energy transfer occurs. The
magnetic field resonance is referred to as the resonance of
a magnetic field.
Citation List
Patent Literature
[0003]
Patent Document 1: Japanese Laid-open Patent
Publication No. 2009-106136
Patent Document 2: Japanese National Publication of
International Patent Application No. 2009-501510
Patent Document 3: Japanese National Publication of
International Patent Application No. 2002-544756
Patent Document 4: Japanese Laid-open Patent
Publication No. 2008-301918
Patent Document 5: Japanese Laid-open Patent
Publication No. 2008-160312
Patent Document 6: Japanese Laid-open Patent

Publication No. 2006-230129
Summary of Invention
Technical Problem
[0004] Energy is transferred between coils, and a load
is connected to the coil at an energy extraction side, so
that power can be supplied to the load. Power supply
efficiency depends on impedance of the load.
[0005] In the case where a battery is connected as the
load, the impedance of the load is sequentially changed
according to a charging state of the battery. Therefore,
in the related art, there is a situation that the power
supply efficiency is deteriorated in the period from the
discharged state of the battery to the fully-charged state
thereof.
[0006] The technique disclosed in the present
application is contrived by taking into consideration the
above situation, and it is an object of the technique
disclosed to provide a' power reception apparatus and power
receiving method capable of improving power supply
efficiency with respect to a battery.
Solution to Problem
[0007] According to a power reception apparatus and a
power receiving method disclosed in the present application,
the power reception apparatus includes a plurality of power
extraction coils which extract power from a coil which is a
power supply source and allows a switch to select one of
the plurality of the power extraction coils and to connect
the selected power extraction coil to a battery. The
plurality of the power extraction coils are different from
each other in terms of a diameter, a distance from the
power extraction coil, or the number of turns (the number

of windings). In the power reception apparatus and the
power receiving method disclosed in the present application,
a charging state of the battery is sensed, so that the
switch is changed over.
[0008] According to. a power reception apparatus and a
power receiving method disclosed in the present application,
the power reception apparatus includes: a power extraction
coil which extracts power from a coil which is a power
supply source and charges a battery; and a position control
mechanism which controls a positional relation between the
coil which is the power supply source and the power
extraction coil. In the power reception apparatus and
power receiving method disclosed in the present application,
a charging state of the battery is sensed, so that the
position control mechanism is controlled.
Advantageous Effects of Invention
[0009] According to the power reception apparatus and
the power receiving method disclosed in the present
application, it is possible to improve power supply
efficiency with respect to a battery.
Brief Description of Drawings
[0010] FIG. 1 is a diagram illustrating a configuration
of a power reception/transmission system including a power
reception apparatus according to an embodiment.
FIG. 2 is an equivalent circuit diagram illustrating a
magnetic field resonance type power reception/transmission
system including four coils illustrated in FIG. 1.
FIG. 3 is a diagram for explaining a sequence of
charging a lithium ion battery.
FIG. 4 is a diagram for explaining deterioration in
power transmission efficiency according to variation of

load.
FIG. 5 is a diagram for explaining power transmission
efficiency with respect to a power reception apparatus 3.
FIG, 6 is a diagram for explaining a specified example
of a power extraction coil (first example thereof).
FIG. 7 is a diagram for explaining a specified example
of a power extraction coil (second example thereof).
FIG. 8 is a diagram illustrating a circuit
configuration of a power reception apparatus 3.
FIG. 9 is a flowchart for explaining a process
operation of a control circuit 35.
FIG. 10 is a diagram for explaining a modified example
of a power reception/transmission system (first example
thereof).
FIG. 11 is a diagram for explaining a modified example
of a power reception/transmission system (second example
thereof).
Description of Embodiments
[0011] Preferred embodiments of the present invention
will be explained with reference to accompanying drawings.
In addition, the embodiments do not limit the technique
disclosed herein.
[Embodiment]
[0012] FIG. 1 is a diagram illustrating a configuration
of a power reception/transmission system including a power
reception apparatus according to an embodiment. FIG. 2 is
an equivalent circuit diagram illustrating a magnetic field
resonance type power reception/transmission system
including four coils illustrated in FIG. 1. The power
reception/transmission system 1 illustrated in FIG. 1
includes a power transmission apparatus 2 and a power
reception apparatus 3. The power transmission apparatus 2

includes an AC power supply 21, a power supply coil 11, and
a power transmission coil 12 in an inner portion of the
power transmission apparatus 2. In addition, the power
reception apparatus 3 includes a power reception coil 13,
four power extraction coils 14-1 to 14-4, a switch 31, a
rectification circuit 32, a DC-to-DC (DD) converter 33, a
battery (rechargeable battery) 34, and a control circuit 35.
[0013] The power transmission coil 12 and the power
reception coil 13 form an LC resonance circuit. A
condenser component of the LC resonance circuit may be
implemented with an element. Otherwise, the condenser
component may be implemented with floating capacitance
formed by opening the two ends of the coil. In the LC
resonance circuit, when inductance and condenser
capacitance are denoted by L and C, respectively, a
resonance frequency f is defined as follows.

[0014] In the case where the resonance frequency of the
power transmission coil 12 and the resonance frequency of
the power reception coil 13 are sufficiently close to each
other and a distance between the power transmission coil 12
and the power reception coil 13 is sufficiently small,
magnetic field resonance may occur between the power
transmission coil 12 and the power reception coil 13.
[0015] Therefore, when the magnetic field resonance
occurs in the state where the power transmission coil 12 is
resonating, magnetic field energy may be transferred from
the power transmission coil 12 to the power reception coil
13. In the magnetic field resonance type, there are
advantages in that large power can be transmitted in
comparison with the case using electromagnetic wave and a
long transfer distance can be obtained in comparison with

the electromagnetic induction type.
[0016] The power supply coil 11 supplies the power,
which is acquired from the AC power supply 21, to the power
transmission coil 12 according to electromagnetic induction.
In the arrangement of the power supply coil 11 and the
power transmission coil 12, the distance and arrangement
are configured so that the electromagnetic induction can
occur. Since the power transmission coil 12 is allowed to
resonate through the power supply coil 11 according to the
electromagnetic induction, there is no need to electrically
connect the power transmission coil 12 and other circuits.
Therefore, the resonance frequency of the power
transmission coil 12 can be designed to be an arbitrary
value with high accuracy.
[0017] The power extraction coils 14-1 to 14-4 are
disposed at positions where electromagnetic induction
occurs with respect to the power reception coil 13. The
switch 31 selects one of the power extraction coils 14-1 to
14-4 and connects the selected power extraction coil to the
rectification circuit 32. When the power reception coil 13
resonates according to the magnetic field resonance, energy
is transferred due to the electromagnetic induction from
the power reception coil 13 to the power extraction coil
selected by the switch 31 among the power extraction coils
14-1 to 14-4. The energy transferred to the power
extraction coil selected by the switch 31 is extracted as
power, and the power is supplied through the switch 31, the
rectification circuit 32, and the DD converter 33 to the
battery 34.
[0018] In this manner, since the power is extracted from
the power reception coil 13 through the power extraction
coils 14-1 to 14-4 according to the electromagnetic
induction, there is no need to electrically connect the

power reception coil 13 and other circuits. Therefore, the
resonance frequency of the power reception coil 13 can be
designed to be an arbitrary value at high accuracy.
[0019] The AC power supply 21 outputs an AC current
having a predetermined frequency and amplitude.
Hereinafter, the frequency of the AC power supply 21 is
referred to as a driving frequency. A power supply coil 11
electrically connected to the AC power supply 21 is allowed
to vibrate at the driving frequency. Therefore, the power
transmission coil 12 is allowed to resonate at the driving
frequency. Similarly, the power reception coil 13 is also
allowed to resonate at the driving frequency.
[0020] In this manner, in the power
reception/transmission system 1, the power of the AC power
supply 21 is extracted as power according to the
electromagnetic induction between the power supply coil 11
and the power transmission coil 12, the magnetic field
resonance between the power transmission coil 12 and the
power reception coil 13, and the electromagnetic induction
between the power reception coil 13 and the power
extraction coils 14-1 to 14-4. The extracted power is
converted into DC power by the rectification circuit 32 and
converted into a voltage by the DD converter 33 to be used
for charging the battery 34.
[0021] As performance required for wireless power
transmission, there is power transmission efficiency from a
power transmission portion to a power reception portion.
In the example illustrated in FIGS. 1 and 2, the power
transmission efficiency is defined as a ratio of power
consumed by a load resistor connected to a power extraction
coil 14 to an effective power input to a power supply coil
11.
[0022] In the case where power is supplied to a mobile

apparatus such as a mobile phone or an electric vehicle
(EV), a load resistor portion is configured to include a
rectification circuit 32, a DD converter 33, and a battery
34. In general, as illustrated in FIG. 3, in a sequence of
charging a lithium ion battery, constant-current charging
is performed when the battery is close to a discharged
state, and constant-voltage charging is performed when a
charged amount reaches a certain amount. In this case, as
seen from a magnetic field resonance type wireless power
transmission system, the impedance of the load portion is
sequentially changed. Therefore, in the configuration that
a single power extraction coil is fixed, it is difficult to
always accomplish good power transmission efficiency as
illustrated in FIG. 4.
[0023] In the example illustrated in FIG. 4, if the load
resistance is about 10 ohm, it is possible to obtain good
power transmission efficiency of 0.8 or more. However, if
the load resistance is 100 ohm, the power transmission
efficiency becomes about 0.55; and if the load resistance
is 1000 ohm, the power transmission efficiency becomes
about 0.1.
[0024] Therefore, in the power reception apparatus 3
illustrated in Fig. 1, in order to suppress deterioration
or variation in power transmission efficiency according to
a change in charged amount of the battery 34, that is, a
change in load impedance, changing-over of the power
extraction coils 14-1 to 14-4 is controlled according to
the charging state of the battery 34.
[0025] The power extraction coils 14-1 to 14-4
correspond to a change in load impedance and are different
in terms of a diameter. For example, if the power
extraction coils 14-1 to 14-4 are arrayed in a concentric
shape, there is no need to newly secure additional space.

[0026] The switch 31 installed between the power
extraction coils 14-1 to 14-4 and the rectification circuit
32 selectively changes over the connection therebetween
according to a command from the control circuit 35.
Information used for sensing the load impedance seen from
the magnetic field resonance system such as a voltage or a
charging current of the battery 34 is input to the control
circuit 35. The control circuit 35 selects a coil which is
optimized with respect to the load impedance and stored in
advance from the power extraction coils 14-1 to 14-4 based
on the aforementioned information and issues a changing-
over signal to the switch 31. According to the operations
hereinbefore, even in the case where the load impedance is
greatly changed as the charging of the battery 34 proceeds,
it is possible to suppress deterioration or variation of
the power transmission efficiency.
[0027] FIG. 5 is a diagram for explaining power
transmission efficiency with respect to the power reception
apparatus 3. In the case where the power extraction coil
14-1 having the smallest diameter is used, the power
transmission efficiency E1 is higher than 0.8 at the load
resistance of 10 ohm, and the power transmission efficiency
E1 is lower than 0.6 from a load resistance higher than 100
ohm. Next, in the case where the power extraction coil 14-
2 having a second smallest diameter is used, the power
transmission efficiency E2 is higher than 0.8 at the load
resistance of 10 ohm, and the power transmission efficiency
E2 is lower than 0.8 from a load resistance higher than 100
ohm. Next, in the case where the power extraction coil 14-
3 having a third smallest diameter is used, the power
transmission efficiency E3 is higher than 0.8 at the load
resistance of 100 ohm, and the power transmission
efficiency E3 is lower than 0.5 from a load resistance

higher than 1000 ohm. In the case where the power
extraction coil 14-4 having the largest diameter is used,
the power transmission efficiency E4 is about 0.8 at the
load resistance of 100 ohm, and the power transmission
efficiency E4 is maintained to be equal to or higher than
0.7 in a load resistance from 100 ohm to 1000 ohm.
[0028] Therefore, in the case where the power extraction
coils 14-1 to 14-4 are changed over according to the load
resistance, the power transmission efficiency E5 can be
maintained to be equal to or higher than 0.7 in the range
of a load resistance up to 1000 ohm.
[0029] FIGS. 6 and 7 are diagrams for explaining
specified examples of the power extraction coil. In FIGS.
6 and 7, in order to simplify the description, three power
extraction coils 14-1 to 14-3 are illustrated.
[0030] In a coil substrate 14a illustrated in FIG. 6,
rectangular wire lines having the same center and different
sizes are disposed on the first layer which is one surface
of the substrate, so that the power extraction coils 14-1
to 14-3 are formed. In each rectangle, the wire line is
disconnected at one of the four corners, and the end
portion is connected to the through-hole. In the example
illustrated in FIG. 6, among the through-holes, a through-
hole H11 is provided at the one end of the wire line
corresponding to the power extraction coil 14-3.
[0031] In the coil substrate 14a, a wire line connected
from the through-hole to an outer portion of the substrate
is disposed on the other surface of the substrate, that is,
the rear surface thereof. The wire line is a connection
wire line used for connection to a load side. In addition,
on the rear surface of the coil substrate 14a, the one end
portion of the two end portions of each of the three
rectangular wire lines is connected to the same connection

wire line. In this manner, the connection wire line shared
by the three rectangular wire lines is always connected to
the load side, and one of the remaining three wire lines is
selected, so that the changing-over of the power extraction
coils 14-1 to 14-3 is performed.
[0032] In a coil substrate 14b illustrated in FIG. 7, a
spiral rectangular wire line is disposed on the first layer
which is one surface of the substrate. Two end portions of
the spiral wire line are connected to through-holes. Among
the through-holes, the end portion of the outer
circumference side is the through-hole H12. In addition,
on the coil substrate 14b, two through-holes are disposed
at two end portions in the path of the spiral wire line.
[0033] In addition, in the coil substrate 14b, a wire
line connected from the through-hole to an outer portion of
the substrate is disposed on the other surface of the
substrate, that is, the rear surface thereof. The wire
line is a connection wire line used for connection to a
load side. On the coil substrate 14b, the connection wire
line connected to the through-hole H12 is always connected
to the load side, and one of the remaining three through-
holes is selected, so that the power extraction coils 14-1
to 14-3 are changed over. Therefore, the number of turns
of the power extraction coil is changed.
[0034] FIG. 8 is a diagram illustrating a circuit
configuration of the power reception apparatus 3. FIG. 8
illustrates a circuit diagram in the case where the coil
substrate 14a is used. The connection wire line shared by
the three rectangular wire lines is connected to the
rectification circuit 32. The remaining three connection
wire lines are connected to the switch 31.
[0035] The switch 31 changes over three connection wire
lines in response to a command of the control circuit 35.

The output of the rectification circuit 32 is input to the
DD converter 33. A resistor (sense resistor) Rs for
current detection is installed to one of two wire lines
between the DD converter 33 and the battery 34.
[0036] The control circuit 35 acquires a voltage which
is to be supplied to the battery 34 and acquires voltages
before and after the sense resistor Rs to calculate a
current value. In addition, the control circuit 35
acquires a remaining amount from the battery 34. The
control circuit 35 selects the to-be-used power extraction
coil based on the supplied voltage, the current, and the
remaining amount of the battery and outputs a change-over
command to the switch 31, if necessary,
[0037] FIG. 9 is a flowchart for explaining a process
operation of the control circuit 35. In the process starts,
the control circuit 35 detects a supply voltage, a current,
and a remaining amount of a battery as a charging state
(S101). Next, the control circuit 35 selects a to-be-used
power extraction coil based on the charging state (S102).
If necessary, the control circuit 35 outputs a change-over
command of the power extraction coil to the switch 31
(S103), and the process ends. In addition, the process
operations are repetitively performed by the control
circuit 35 during the charging of the battery 34.
[0038] FIG. 10 is a diagram for explaining a modified
example of the power reception/transmission system. In a
power reception/transmission system la illustrated in FIG.
10, a power reception apparatus 3a includes a power
reception coil 13, one power extraction coil 15, a
rectification circuit 32, a DD converter 33, a battery 34,
a control circuit 35a, and a position control mechanism 36.
[0039] The power reception apparatus 3a can adjust a
distance between the power reception coil 13 and the power

extraction coil 15 by changing the position of the power
extraction coil 15 through the position control mechanism
36. The control circuit 35a controls the position control
mechanism 36 based on the charging state of the battery 34,
so that the power transmission efficiency can be maintained
according to a change in load resistance. Other
configurations and operations are similar to those of the
power reception/transmission system 1 illustrated in FIG. 1.
The same components are denoted by the same reference
numerals, and the description thereof is not provided.
[0040] FIG. 11 is a diagram for explaining a modified
example of the power reception/transmission system. A
power reception/transmission system lb illustrated in FIG.
11 includes a power transmission apparatus 2b and a power
reception apparatus 3b. The power transmission apparatus
2b includes an AC power supply 21b and a power supply coil
16 in an inner portion thereof the power transmission
apparatus 2b. In addition, the power reception apparatus 3
includes a power extraction coil 17, four power extraction
coils 17, a switch 31, a rectification circuit 32, a DD
converter 33, a battery 34, and a control circuit 35b.
[0041] In the power reception/transmission system lb,
energy transfer using electromagnetic induction is
performed from the power supply coil 16 of the power
transmission apparatus 2b to the power extraction coils 17
of the power reception apparatus 3b. Therefore, the
control circuit 35b controls the switch 31 based on the
charging state of the battery 34 to select one of the power
extraction coils 17 so that energy transfer using
electromagnetic induction is efficiently performed. In
this manner, the disclosed technique can be also applied to
wireless power transmission using electromagnetic induction.
Other configurations and operations are similar to those of

the power reception/transmission system 1 illustrated in
FIG. 1. The same components are denoted by the same
reference numerals, and the description thereof is not
provided.
[0042] As described above, in the power
reception/transmission system 1 according to the embodiment,
since the power reception apparatus 3 controls a diameter
or position of the power extraction coil according to the
charging state of the battery 34, so that it is possible to
improve power supply efficiency in wireless power
transmission using magnetic field resonance or
electromagnetic induction.
[0043] In addition, the embodiment is exemplary one, and
thus, the configurations and operations may be
appropriately modified. For example, the battery 34 may be
disposed outside the power reception apparatus 3. In
addition, the battery 34 may be detachable.
[0044] In addition, in a configuration, a plurality of
power extraction coils having the same diameter and
different distances from the power reception coil 13 or the
power supply coil 16 may be disposed, and the power
extraction coil is changed over according to the charging
state. In addition, in another configuration, a plurality
of the power extraction coils having different diameters
and different distances may be disposed. In addition, in
still another configuration, the position of the power
extraction coil is fixed, and the position of the power
reception coil is controlled, so that the distance between
the power extraction coil and the power reception coil is
changed.
Reference Signs List
[0045] 1, la: power reception/transmission system

2, 2b: power transmission apparatus
3, 3b: power reception apparatus
11, 16: power supply coil
12: power transmission coil
13: power reception coil
14_1 to 14_4, 15, 17: power extraction coil
14a, 14b: coil substrate
21, 21b: AC power supply
31: switch
32: rectification circuit
33: DD converter
34: battery
35, 35a, 35b: control circuit
36: position control mechanism

W
e Claim:
1. A power reception apparatus comprising:
a plurality of power extraction coils that extract
power from a coil being a power supply source;
a switch that selects one of the plurality of the
power extraction coils and connects the selected power
extraction coil to a battery; and
a controller that senses a charging state of the
battery and changes over the switch,
wherein the plurality of the power extraction coils
are different from each other in terms of a diameter, the
number of turns, or a distance from the power extraction
coil.
2. A power reception apparatus comprising:
a power extraction coil that extracts power from a
coil being a power supply source and charges a battery;
a position control mechanism that controls a
positional relation between the coil being the power supply
source and the power extraction coil; and
a controller that senses a charging state of the
battery and controls the position control mechanism.
3. The power reception apparatus according to claim 1 or
2, wherein the coil being the power supply source is
installed in an inner portion of the power reception
apparatus, and the coil being the power supply source
receives power from a coil outside the power reception
apparatus using magnetic field resonance.
4. A power receiving method comprising the steps of:
sensing a charging state of a battery connected to one

of a plurality of power extraction coils that extract power
from a coil being a power supply source;
selecting one of the plurality of the power extraction
coils based on the charging state of the battery; and
changing over a connection relation between the
plurality of the power extraction coils and the battery
based on a result of the selecting.
5. A power receiving method comprising the steps of:
sensing a charging state of a battery connected to a
power extraction coil that extracts power from a coil being
a power supply source;
determining a distance between the coil being the
power supply source and the power extraction coil based on
the charging state of the battery; and
controlling a positional relation between the coil
being the power supply source and the power extraction coil
based on the determined distance.