RESONANT FREQUENCY CONTROL METHOD, ELECTRIC POWER TRANSMITTING
DEVICE, ELECTRIC POWER RECEIVING DEVICE IN MAGNETIC RESONANT
TYPE POWER TRANSMISSION SYSTEM
Background of the Invention
[0001] The present invention relates to a resonant frequency
control method, an power transmitting device and a power
receiving device in a magnetic resonant coupling type power
transmission system.
Description of the Related Art
[0002] In a so-called Wireless Power Transmission or Wireless
Power Supply (WPS) to transmit power wirelessly, power (energy)
is transmitted and received between two points that are apart
spatially, without using any cables. There are two types of
wireless power transmission systems: one type of systems uses
electromagnetic induction and another type of systems uses radio
waves . A system that uses magnetic resonant coupling (also called
magnetic field resonant coupling, magnetic resonance, magnetic
field resonant mode) has also been proposed (Patent Document
1) .
[Patent Document 1] International Publication Pamphlet No. WO
98/34319
Summary of the Invention
[0003] An objective of the present invention is to make it
possible to control the resonant frequency of a coil at a high
speed and with a high accuracy in real time.
[0004] A magnetic resonant coupling type power transmission
system to which the present invention is applied will be
explained.
[0005] The systems that use magnetic resonance (magnetic
resonant coupling type) has advantages such as that a larger
power may be transmitted compared with the systems that use radio
wave, that the transmission distance may be longer, and/or that
the coil f or power transmiss ion/ receptionmay be smaller compared
with the electromagnetic induction coupling type systems.
[0006] In the systems that use magnetic resonance, it becomes
possible to transmit energy with a high efficiency by setting
the resonant frequency of the power transmitting coil and the
power receiving coil at the same value with each other and
transmitting power at a frequency around to it.
[0007] In order to increase the efficiency of power
transmission in the magnetic resonant coupling type power
transmission systems, there is one in which a higher frequency
compared with the frequency of the oscillation signal at the
primary coil side is set as the resonant frequency for the
secondary coil side (Patent Document 1) . According to this, it
is said that the capacitance may be smaller and the coupling
coefficient of the primary coil and the secondary coil may be
seemingly increased.
[0008] By increasing the degree of coupling between coils,
the efficiency of power transmiss ionmay be increased to a certain
degree.
[0009] In addition, in order to increase the efficiency of
power transmission, it may be considered to make the resonant
peak of each coil as sharp as possible. In order to do so, the.
design may be made such that the Q value of each coil becomes
high, for example.
[0010] However, there is a problem in which, when the Q value
is high, the sensitivity to the difference between the resonant
frequencies of the coils becomes high, that is, the influence
of the difference between the resonant frequencies of the both
coils on the decrease of the efficiency of power transmission
becomes large.
[0011] For example, due to a change in the environmental
factors such as the temperature, a change in the inductance or
the capacitance by the approach of a conducting body or a magnetic
body, or the like, the resonant frequency of a coil may change.
In addition, the frequency may also be shifted due to variation
at the time of manufacturing.
[0012] For this reason, in order to take advantages of its
merits in the magnetic field resonant coupling type power
transmission system with a high Q value, a mechanism to adjust
the resonant frequency of the coil according to the change in
the environment and the like is needed.
[0013] In order to match the resonant frequency of the coil
to a target frequency, the L (inductance) of the coil or the
C (capacitance) of the capacitor needs to be adjusted.
[0014] In a method of an embodiment described herein, a
resonant frequency control method in a magnetic resonant coupling
type power transmission system transmitting an electric power
from a power transmitting coil to a power receiving coil using
magnetic field resonance, includes : a phase of a voltage supplied
to the power transmitting coil and a phase of a current that
flows in the power transmitting coil or the power receiving coil
is detected, and a resonant frequency of the power transmitting
coil or the power receiving coil is varied such that phase
difference between them becomes a target value.
[0015] .It is also possible to vary the resonant frequency
of the power transmitting coil or the power receiving coil such
that the current peak appears at the frequency of the
alternating-current power supply when the degree of coupling
between the power transmitting coil and the power receiving coil
increases and a diphasic property appears.
[0016] Meanwhile, in a device of an embodiment described
herein, a magnetic resonant coupling type power transmission
system transmitting an electric power from a power transmitting
coil to a power receiving coil using magnetic field resonance
includes : a phase detection unit configured to detect a phase
of a voltage supplied to the power transmitting coil and a phase
of a current that flows in the power transmitting coil or the
power receiving coil; and a resonant frequency control unit
configured to vary a resonant frequency of the power transmitting
coil or the power receiving coil such that a phase difference
between the detected phases becomes a target value.
Brief Description of the Drawings
[0017] FIG. 1 is a diagram illustrating a magnetic field
resonant coupling type power transmission method.
FIG. 2 is a diagram illustrating an outline of a magnetic
field resonant coupling type power transmission method.
FIG. 3 is a diagram illustrating an example of the
configuration of a control unit of a power transmission system
of the present embodiment.
FIG. 4 is a diagram illustrating the state of the current
and phase in resonant frequency control.
FIG. 5 is a diagram illustrating the state of the current
and phase in resonant frequency control.
FIG. 6 is a diagram illustrating the state of the current
and phase when the diphasic property appears.
FIG. 7 is a diagram illustrating the state of the current
and phase in resonant frequency control when the diphasic
property appears.
FIG. 8 is a diagram illustrating the change of transmission
power when resonant frequency control according to the diphasic
property is performed.
FIG. 9 is a diagram illustrating the frequency dependence
of the power transmission system.
FIG. 10 is a diagram illustrating a method to sweep the
resonant frequency of the coil.
FIG. 11 is a diagram illustrating an example of the
configuration to switch between resonant frequency control and
diphasic resonant control.
FIG. 12 is a flowchart illustrating an outline process
procedure of resonant frequency control.
FIG. 13 is a flowchart illustrating an outline process
procedure of resonant frequency control.
Description of the Preferred Embodiments
[0018] In the power transmission system (power transmission
device) 1 of the embodiments described below, based on the phase
difference ?? between phases of the voltage of the
alternating-current power source (drive voltage) and the current
flowing in the coil, real-time resonant frequency control is
performed for L or C of the coil (resonant circuit).
[0019] In addition, when a diphasic property (split) appears
as the coupling between the power transmitting coil and the power
receiving coil increases, in order to suppress the decrease of
the efficiency in power transmission, the resonant frequency
of the frequencies of the power transmitting coil and the power
receiving coil is shifted such that the peak (split peak) appears
in the frequency of the alternating-current power source. The
resonant frequency control in this case may be referred to as
"diphasic resonant control" to distinguish it from the resonant
frequency control in the case without the appearance of the
diphasic property.
[0020] In addition, the resonant frequency control in the
case in which the "diphasic resonant control" is not included
may be referred to as "normal rescnant frequency control". When
described simply as "resonant frequency control", it includes
"diphasic resonant control" in principle.
[0021] In FIG. 1 and FIG. 2, the power transmission system
1 has a power transmitting coil SC, a power receiving coil JC,
an alternating-current power supply 11, power-transmitting side
control unit 14, a device 21 to be a load, and a power-transmitting
side control unit 24.
[0022] In FIG. 2, the power transmitting coil SC has a power
supplying coil 12 and a power transmitting resonant coil 13.
The power supplying coil 12 is made by winding multiple turns
of a metal wire such as a copper wire or an aluminum wire in
a circumferential manner, and an alternating-current voltage
(high frequency voltage) is applied to both ends of it.
[0023] The power transmitting resonant coil 13 consists of
a coil 131 made by winding multiple turns of a metal wire such
as a copper wire or an aluminum wire in a circumferential manner
and a capacitor 132 connected to the both ends of the coil 131,
and forms a resonant circuit of them. The resonant frequency
fO is expressed in the following (1) formula.
[0024] [Formula 1]
where L is the inductance of the coil 131, and C is the capacitance
of the capacitor 132.
[0025] The coil 131 of the power transmitting resonant coil
13 is a one turn coil for example. As the capacitor 132, various
types of capacitors can be used, but one with the smallest possible
loss and the sufficient pressure resistance is preferable. In
this embodiment, in order to make the resonant frequency variable,
a variable capacitor is used as the capacitor 132 . As the variable
capacitor, for example, a variable capacity device made using
the MEMS technology is used. It may also be a variable capacity
device (varactor) using a semiconductor.
[0026] The power supplying coil 12 and the power transmitting
resonant coil 13 are placed to be electromagnetically coupled
closely to each other. For example, they are placed on the same
plane and concentrically. That is, for example, they are placed
in a state in which the power supplying coil 12 is fit in the
inner circumference side of the power transmitting resonant coil
13. Alternatively, they may be placed coaxially with a suitable
distance.
[0027] In this state, when an alternating current voltage
is supplied from the alternating-current power supply 11 to the
power supplying coil 12, a resonant current flows in the power
transmitting resonant coil 13 by the electromagnetic induction
by the alternating magnetic field generated in the power
supplying coil 12. That is, electric power is supplied from the
power supplying coil 12 to the power transmitting resonant coil
13 by electromagnetic induction.
[0028] The power receiving coil JC has a power drawing coil
23. The power receiving resonant coil 22 consists of a coil 221
made by winding multiple turns of a metal wire such as a copper
wire or an aluminum wire in a circumferential manner and a
capacitor 222 connected to the both ends of the coil 221. The
resonant frequency fO is expressed in the following (1) formula.
[0029] The coil 221 of the power receiving resonant coil 22
is a one turn coil for example. As the capacitor 222, various
types of capacitors are used as described above. In this
embodiment, in order to make the resonant frequency variable,
a variable capacitor is used as the capacitor 222 . As the variable
capacitor, for example, a variable capacity device made using
the MEMS technology is used. It may also be a variable capacity
device (varactor) using a semiconductor.
[0030] The power drawing coil 23 is made by winding multiple
turns of a metal wire such as a copper wire or an aluminum wire
in a circumferential manner and a device 21 being a load is
connected to the both ends of the coil 221.
[0031] The power receiving resonant coil 22 and the power
drawing coil 23 are placed to be electromagneticalry coupled
closely to each other. For example, they are placed on the same
plane and concentrically. That is, for example, they are placed
in a state in which the power drawing coil 23 is fit in the inner
circumference side of the power receiving resonant coil 22.
Alternatively, they may be placed coaxially with a suitable
distance.
[0032] In this state, when a resonant current flows in the ,
power receiving resonant coil 22 with generating the alternating
magnetic field, the electromagnetic induction causes a current
to flow in the power drawing coil 23 . That is, the electromagnetic
induction causes electric power to sent from the power receiving
resonant coil 22 to the power drawing coil 23.
[0033] In oreder to transmit electric power wirelessly by
the magnetic field resonance, the power transmitting coil SC
and the power receiving coil JC are placed within a range of
a suitable distance with each other such that their coil planes
are parallel to each other and their coil axis centers correspond
with each other or does not shift from each other so much, as
illustrated in FIG. 2. For example, when the diameter of the
power transmitting resonant coil 13 and the power receiving
resonant coil 22 is about 100mm, they are placed within a range
of about several hundred mm distance.
[0034] In the power transmission system 1 illustrated in FIG.
2, the direction along the coil axis center KS is the mainradiation
direction of the magnetic field KK, and the direction from the
power transmitting coil SC to the power receiving coil JC is
the power transmitting direction SH.
[0035] Here, when both the resonant frequency fs of the power
transmitting resonant coil 13 and the resonant frequency fj of
the power receiving resonant coil 22 coincide with the frequency
fd of the alternating-current power supply 11, the maximum power
is transmitted. However, if those resonant frequencies fs, fj
deviate from each other, or they deviate from the frequency fd
of the alternating-current power supply 11, the transmitted power
decreases, and the efficiency decreases.
[0036] That is, in FIG. 9, the horizontal axis is the frequency
fd[MHz] of the alternating-current power supply 11, and the
vertical axis is the magnitude of the transmitted power [dB] .
The curve CVl represents the case in which the resonant frequency
fs of the power transmitting resonant coil 13 and the resonant
frequency fj of the power receiving resonant coil 22 coincide
with each other. In this case, according to FIG. 9, the resonant
frequencies fs, fj is 13.56MHz.
[0037] Meanwhile, the curves CV2, CV3 represents the cases
in which the resonant frequency f j of the power receiving resonant
coil 22 is higher than the resonant frequency fs of the power
transmitting resonant coil 13 by 5% and 10%, respectively.
[0038] In FIG. 9, when the frequency fd of the
alternating-current power supply 11 is 13.56MHz, the maximum
power is transmitted the case shown in the curve CVl, but in
the case shown in the curves CV2, CV3, it sequentially decreases .
Meanwhile, when the frequency fdof the alternating-current power
supply 11 shifts from 13 . 56MHz, the transmitted power decreases
in all of the curves CV1-CV3 except when it slightly shifts upward.
[0039] Therefore, there is a need for matching the resonant
frequencies fs, fj of the power transmitting resonant coil 13
and the power receiving resonant coil 22 to the frequency fd
of the alternating-current power supply 11 as much as possible.
[0040] In FIG. 10, the horizontal axis is the frequency [MHz]
and the vertical axis is the magnitude [dB] of the current that
flows in the coil. The curve CV4 represents the case in which
the resonant frequency of the coil corresponds to the frequency
fd of the alternating-current power supply 11. In this case,
in FIG. 10, the resonant frequency is 10MHz.
[0041] In addition, the curves CV5, CV6 represents the cases
in which the resonant frequency of the coil becomes higher or
lower with respect to the frequency fd of the alternating current
power supply 11.
[0042] In FIG. 10, the maximum current flows in the case shown
in the curve CV4, but the current decreases in both cases shown
in the curves CV5, CV6. Meanwhile, if the Q value of the coil
is high, the influence of the deviation of the resonant frequency
on the decrease in the current or the transmitted power is lc. *"ge.
[0043] Therefore, in the power transmission system 1,
resonanc frequency control is per formed by the power transmitting
side control unit 14 and the power transmitting side control
unit 24, using the phase <|>vs of the alternating-current power
supply 11 and the phases <(>is, (|>ij of the current flowing in the
power transmitting resonant coil 13 and the power receiving
resonant coil 22.
[0044] Here, the power-transmitting side control unit 14
detects the phase (|>vs of the voltage Vs supplied to the power
transmitting coil SC and the phase <|>is of the current Is that
flows in the power transmitting coil SC, and varies the resonant
frequency fs of the power transmitting coil SC such that the
phase difference A<|)s between them becomes a predetermined target
value (|>ms .
[0045] That is, the power-transmitting side control unit 14
has a current detection sensor SE1, a phase detection units 141,
142, a target value setting unitl43, a feedback control unit
144, and a phase transmission unit 145.
[0046] The current detection sensor SE1 detects the current
Is that flows in the power transmitting resonant coil 13. As
the current detection sensor SEl, a hole element, a magnetic
resistant element or a detection coil or the like may be used.
The current detection sensor SEl outputs a voltage signal
according to the waveform of the current Is for example.
[0047] The phase detection unit 14 detects the phase <|>vs of
the voltage Vs supplied to the power supplying coil 12. The phase
detection unit 141 outputs, for example, a voltage signal
according to the voltage Vs. In this case, the voltage Vs may
be output without any changes, or may be divided by a suitable
resistor. Therefore, the phase detection unit 141 may be
constituted by a simple electric wire, or by one or more resistors .
[0048] The phase detection unit 142 detects the phase (|>is
of a current Is that flows in the power transmitting resonant
coil 13, based on the output from the current detection sensor
SEl. The phase detection unit 142 outputs, for example, a voltage
signal according to the waveform of the current Is. in this case,
the phase detecLion unit 142 may output the output of the current
detection sensor SEl without any changes. Therefore, it is
possible to configure the current detection sensor SEl to act
as the phase detection unit 142.
[0049] The target value setting unit 143 sets and stores the
target value (|>ms of the phase difference A<|)s. Therefore, a memory
for storing the target value <|)ms is provided in the target value
setting unit 143. As the target value ms, as described later,
for example, "-n" or "a value in which a suitable correction
value a is added to -n" is set.
[0050] Meanwhile, the setting of the s between the phase tyvs of the voltage
Vs of the alternating-current power supply 11 and the phase <|>is
of the current Is of the power transmitting resonant coil 13
becomes the target value <|>ms.
[0052] The phase transmission unit 145 transmits information
about the phase <|)vs of the voltage Vs supplied to the power
supplying coil 12 to the power-transmitting side control unit
24 wirelessly for example. The phase transmission unit 145
transmits, for example a voltage signal according to the waveform
of the voltage Vs to as an analog signal or a digital signal.
In this case, in order to improve the S/N ratio, the voltage
signal according to the waveform of the voltage Vs may be
multiplied by an integer and transmitted.
[0053] . The power-transmitting side control unit 24 detects
the phase <|>vs of the voltage VS supplied to the power transmitting
coil SC and the phase j
between them becomes a predetermined target value ij
of the current Ij that flows in the power receiving resonant
coil 22, based on the output from the current detection sensor
SE2. The phase detection unit 242. outputs, for example, a voltage
signal according to the waveform of the current Ij . In this case,
the phase detection unit 242 may output the output of the current
detection sensor SE2 without any changes. Therefore, it is
possible to configure the current detection sensor SE2 to act
as the phase detection unit 142.
[0058] The target value setting unit 243 sets and stores the
target value mj of the phase difference Amj , as described later, for example, a value in which "-7t/2"
is added to the target value tyms in the power-transmitting side
control unit 14 is set. That is, as the target value <|>mj , "-3tc/2"
is set. Alternatively, a value in which a suitable correction
volue b is added is set. Meanwhile, the setting method of the
target value <|>mj and the like may be similar to the case of the
target value <|>ms.
[0059] The feedback control unit 24 4 varies the resonant
frequency f j of the power receiving resonant coil 22 such that
the phase difference Atjij between the phase <|>vs of the voltage
Vs of the alternating-current power supply 11 and the phase (|>ij
of the current Ij of the power receiving resonant coil 22 becomes
the target value <|)mj .
[0060] Meanwhile, the target value setting unit 143 and the
feedback control unit 144 in the power-transmitting side control
unitl4 , the target value setting unit 243 and the feedback control
unit 244 in the power-transmitting side control unit 24 are
examples of the resonant frequency control unit.
[0061] Hereinafter, more detail explanation will be provided
referring to FIG. 3. In FIG. 3, the same numerals are assigned
to the elements having the same function as the elements
illustrated in FIG. 2, and explanation for them may be omitted
or simplified.
[0062] In FIG. 3, the power transmission system (power
transmission device IB) has a transmitting device 3 and a power
receiving device 4.
[0063] The power transmitting device 3 has a power
transmitting coil SC consisting of an alternating-current power
supply 11, a power supplying coil 12 and a power transmitting
resonant coil 13, and a resonant frequency control unit CTs and
the like.
[0064] The power receiving device 4 has a power receiving
coil consisting of a power receiving resonant coil 22 and a
power drawing coil 23, a resonant frequency control unit CTj,
and the like.
[0065] The resonant frequency control unit CTs at the power
transmitting side has a target value setting unitl43, phase
comparison unit 151, an addition unit 152, gain adjustment units
153, 154, a compensation unit 155, and a driver 156.
[0066] The phase comparison unit 151 compares the vs of the voltage Vs of the alternating-current power
supply 11, and outputs the phase difference As being the
difference between them.
[0067] The addition unit 152 adds the phase difference A([>s
that the phase comparison unit 151 outputs and the target value
ms set by the target value setting unit 143. Since the target
value <|)ms is set to have an opposite positive/negative sign with
respect to the target phase difference At(>s in this embodiment,
when the absolute values of the phase difference A(j)s and the
target value ((ims are coincided with each other, the output of
the addition unit 152 becomes 0.
[0068] The gain adjustment units 153, 154 adjusts the gain
with respect to the input value or to data, or performs conversion
of data and the like.
[0069] The compensation unit 155 for example determines me
gain with respect to the low frequency component. The resonant
frequency control unit CTs in the present embodiment may be viewed
as a component of a servo system that performs feedback control
with respect to the MEMS variable capacity device being the
capacitor 132. Therefore, for the compensation unit 155, a
suitable servo filter for making the servo system more stable
with a higher speed and a higher accuracy may be used. In addition,
a filter circuit or a differentiation integration circuit for
the PID operation to be performed in such a servo system is used
as needed.
[0070] The driver 156 drives the MEMS variable capacity device
being the capacitor 132 and outputs drive KSs to the capacitor
132 for variable control of its capacitance.
[0071] In the MEMS variable capacity device (MEMS variable
capacitor) , a lower part electrode and an upper part electrode
?re provided on a glass substrate, and the space between them
changes by the bend due to electro static attraction force
generated by the applied voltage between them, thereby the
capacitance between them varies. An electrode for the capacitor
and an electrode for driving may also be provided separately.
Since the relationship between the voltage applied to the
electrode for driving and the variation amount of the capacitance
is not linear, a calculation or table conversion is also performed
as needed in the driver 156 for the conversion.
[0072] The power receiving side resonant frequency control
unit CTj has a target value setting unit 243, a phase comparison
unit 251, an addition unit 252, gain adjustment units 253, 254,
a compensation unit 255, and a driver 256 and the like. The
configuration and the operation of each unit of the power
receiving side resonant frequency control unit CTj are similar
to the configuration and the operation of each unit of the resonant
frequency control unit CTs.
[0073] Meanwhile, the power-transmit ting side control unitl4 ,
power-transmitti ng side control unit 24, the resonant frequency
control units CTs, CTj and the like may be realized by software
or hardware, or their combination. For example, the CPU may
perform a suitable computer program using a computer consisting
of a CPU, a memory such as ROM and RAM and other peripheral devices
and the like. In that case, a suitable hardware circuit may be
used together.
[0074] Next, referring to FIG. 4-FIG. 7, the operation of
the resonant frequency control in the power transmission system
IB will be explained.
[0075] ' In FIG. 4-FIG. 7, in each FIG (A) , the horizontal axis
represents the frequency f [MHz] of the alternating-current power
supply 11, and the vertical axis represents the magnitude [dB]
of the current I that flows in each coil. In each FIG. (B) , the
horizontal axis represents the frequency f[MHz] of the
alternating-current power supply 11, and the vertical axis
represents the phase (|> [radian] of the current I that flows in
each coil. In each of FIG. 4-FIG. 7, FIG. (A) and FIG. (B) are
corresponding.
[0076] Meanwhile, the phase represents the phase difference
Avs.
[0077] In the symbols CAA1-4, CAB1-4, CBAl-4, CBB1-4, CCAl-4,
CCBl-4, CDA1-4, CDB1-4, the numbers 1, 2, 3, 4 of the suffixes
indicates correspondence with the power supplying coil 12, the
power transmitting resonant coil 13, the power receiving resonant
coil 22, the power drawing coil 23, respectively.
[0078] Then, in the resonant frequency control, the power
transmitting resonant coil 13, or power transmitting resonant
coil 13 and the power receiving resonant coil 22 are controlled
such that their resonant frequencies fs, fj becomes 10MHz.
[0079] TheseEIG. 4-FIG. 7 illustrate the result of simulation
by a computer under these conditions.
[0080] FIG. 4 represents a case in which the resonant frequency
control is performed by only one of the power-transmitting side
control unitl4 and the power transmitting device 3, and FIG.
5 represents a case in which the resonant frequency control is
performed by both the power-transmitting side control unit14
or the power transmitting device 3 and the power-transmitting
side control unit 24or the power receiving device 4.
[0081] In FIG. 4, for the power transmitting resonant coil
13, the resonant frequency control is performed such that its
resonant frequency fs becomes 10MHz. In this case, the frequency
fd of the alternating-current power supply 11 is set to 10MHz,
and "-rc" is set as the target value <|»ms in the target value setting
unit 143.
[0082] As illustrated in the curve CAA2m the current Is of
the power transmitting resonant coil 13 peaks at 10MHz that
coincides with the frequency f d of the alternating-current power
supply 11.
[0083] As illustrated in FIG. CAB2, the phase <|>is of the power
transmitting resonant coil 13 is -n at 10MHz being the resonant
frequency fs. That is, it coincides with the target value (juris.
[0084] Meanwhile, the power transmitting resonant coil 13
may be considered as a serial resonant circuit viewed from thr:
power supplying coil 12. Therefore, at the frequency fd that
is lower tnan the resonant frequency fs, it becomes capacitive
and approaches tt/2, and at the higher frequency fd, it becomes
inductive and approaches -3n/2,
[0085] As described above, the phase is of the current Is
that flows in the power transmitting resonant coil 13
significantly varies around the resonant frequency fs. By
performing control under which the phase is, that is, the phase
difference Ams, and "~3rc/2" is set as the target value <|)mj .
[0088] That is, as the target value §mj, the value "ms-rc/2"
in which -n/2 is added to the target value ijims, that is, a phase
that is behind the target value ms by n/2 is set.
[0089] The curve CBA2 and the curve CBB2 are almost similar
to the curve CAA2 and the CAB2 in FIG. 4.
[0090] As illustrated in the curve CBA3, the current Ij of
the power receiving resonant coil 22 peaks at 10MHz that coincides
with the frequency fd of the alternating-current power supply
11.
[0091] As illustrated in the curve CBB3, the phase increases and approaches -bn/2, that is, -n/2.
[0092] Thus, the phases <(>is, of the
coil current with respective to the voltage Vs of the
alternating-current power supply, an accurate control may be
performed without any influences from the variation in the
amplitude of the current as in the case of the sweep search method.
[0097] Meanwhile, in the sweep search method, for example,
L or C in the power transmitting coil SC or the power receiving
coil is swept and the position at which the current value of
the coil peaks is searched in a trial-and-error-like manner.
[0098] However, there may be following problems in the case
of the sweep search method described above. That is,
(1) Since the current value of the coil constantly varies
depending on the usage state, a detection error occurs due to
the variation (amplitude variation) of the current value of the
coil, and it is not easy to perform an accurate adjustment.
(2) , A round-trip sweep operation is needed for the adjustment
and time is required for the adjustment, and high-speed real-time
control is difficult. In addition, even if the adjustment is
performed once, the adjustment needs to be performed again when
the usage environment changes, and the usage needs to be stopped
at each time.
[0099] However, according to the resonant frequency control
method according to the present embodiment, since the control
is performed in real time, correction is performed constantly
for the variation of the frequency fd of the alternating-current
power supply 11 and the variation in the environmental factor
and the like, there is no need for re-adjustment and stop and
the like as in the case of the sweep search method.
[0100] In addition, in the power transmission system 1, IB
of the present embodiment, when the Q values of the power
transmitting resonant coil 13 and the power receiving resonant
coil 22 are high, the sensitivity to the shift between the resonant
frequencies of the both coils becomes high.
[0101] However, according to the resonant frequency control
method of the present embodiment, as the Q value becomes high,
the rate of variation around the resonant frequencies of the
phases <}>is, ±j increases, and because ot this, the sensitivity
of the control also becomes high. As a result, the phase
differences A(|>s, Aj may be matched with the target values mj with a higher accuracy, and che power transmission with a
higher efficiency may be performed with the increase in the Q
value.
[0102] Next, the resonant frequency control (diphasic
resonant control) when the coupling between the power
transmitting coil SC and the power receiving coil increases a
diphasic property appears will be explained.
[0103] FIG. 6 illustrates the state of the currents Is, Ij
and the phases <|>is, <|>ij in a case in which the diphasic property
appears and the diphasic resonant control is not performed.
[0104] That is, the state illustrated in FIG. 6 appears, for
example, when operating in the state illustrated in FIG. 5, the
coupling increases as the power receiving coil comes closer to
the power transmitting coil SC.
[0105] The single peak as illustrated in the curves CBA2,
CBA3 in FIG. 5 is diphasic as illustrated in the curves CCA2,
CCA3 in FIG. 6 . Accordingly, at 10MHz being the resonant frequency,
as illustrated in the curve CCA4, the current taken from the
power drawing coil 23 becomes lower, and the transmitted power
decreases.
[0106] Therefore, in the diphasic resonant control, the
resonant frequency of the power transmitting coil SC and the
power receiving coil are shifted such that one peak of the two
peaks appear at 10MHz being the resonant frequency fs.
[0107] For that reason, while "-3tc/2" is set as the target
value <|>mj , in the diphasic resonant control, as the target value
<|»mj, a phase in which -7t/2 is further added, that is, "-2n" that
is further behind by n/2 is set. That is, the target value <|)mj
is switched from "-3tc/2" to "-2n".
[0108] As described above, in the diphasic resonant control,
w-2tc" is set as the target value ^ for the target value setting
unit 243.
[0109] The target value <|»ms for the target vaiue setting unit
143 is unchanged w-7t". Therefore, the difference between the
target value <|>ms and the target value <(>mj is switched from -7t/2
to -7i with the shift to the diphasic resonant control.
[0110] In FIG. 7, as illustrated by the curve CDB2, the phase
<|)is ot the current Is of the power transmitting resonant coil
13 is -tc at 10MHz that is the resonant frequency fs. In addition,
as illustrated by the curve CDB3, the phase (|>ij of the currnet
Ij of the power receiving coil 22 is -2nat 10MHz being the resonant
frequency fs.
[0111] As illustrated by the curves CDA2, CDA3, CDA4, the
current I of all increases by the diphasic resonant control.
For example, in the curve CDA4, the current is about -30dB with
the normal resonant frequency control, but is about -20dB with
the diphasic resonant control, increasing by about lOdB.
[0112] FIG. 8 illustrates the state of change of the power
drawn from the power drawing coil 23 in a case in which hthe
distance ^ptween the power transmitting resonant coil 13 and
the power receiving resonant coil 22 is changed between 200mm
and 100mm.
[0113] Meanwhile, FIG. 8 is the result of a simulation
performed with the coil diameter 100mm, a 50mm the space between
the power supplying coil 12 and the power transmitting resonant
coil 13, and a 40mm space between the power receiving resonant
coil 22 and the power drawing coil 23. As the device 21 being
the load for the power drawing coil 23, a 10 O resistor was
connected.
[0114] In FIG. 8, the curve CUl and the curve CU2 illustrate
a case of switching between the normal resonant frequency control
and the diphasic resonant control and a case in which the diphasic
resonant control was not performed, respectively.
[0115] When the diphasic resonant control is not performed,
as illustrated by the curve CU2, the power decreases as the
distance between coils becomes closer. By contrast, as
illustrated by the curve CUl, when switched to the diphasic
resonant control when the distance between the coil becomes
closer around 140mm, the power does not decrease but increases
instead. .
[0116] Meanwhile, various methods are possible for the method
to automatically switch between the normal resonant frequency
control and the diphasic resonant control.
[0117] For example, as illustrated in FIG. 11, a target value
?mj 1 for the normal resonant frequency control and the target
value ?mj2 for the diphasic resonant control are stored in the
target value setting unit 243C. Then, a double-peak detection
unit 245 for detecting the appearance of the diphasic property
is provided.
[0118] The target value setting unit 243C outputs the target
value ?mj 1 as the target value ?mj in the normal resonant frequency
control, but if the double-peak detection unit 245 detects a
detection signal S1,- outputs the target value ?mj2 as the target
value ?mj . Accordingly, the normal resonant frequency control
and the diphasic resonant control are automatically switched.
[0119] Meanwhile, the double-peak detection unit 245 may also
detect, for example, the decrease of the transmitted power below
a predetermined amount, or, the distance of the power receiving
coil becoming closer than predetermined. Alternatively, the two
target values ?mj 1, ?mj2 may be switched and output at a suitable
timing, and the target value (?m with a larger power may be selected.
[0120] Next, the resonant frequency control in the power
transmission system 1, 1B of the present embodiment will be
explained with reference to a flowchart.
[0121] In FIG. 12, the phase ?vs of the alternating-current
power supply 11, the phase ?vs of the alternating-current power
supply 11 is detected (#11) , and the phases ?is, ?ij of the power
transmitting resonant coil 13 and the power receiving resonant
coil 22 are detected (#12) , to obtain the phase differences ??s,
??j (#13).
[0122] Then, feedback control is performed such that the phase
differencec ??s, ??j coincides with the target values ?ms, ?mj .
[0123] In FIG. 13, in the feedback control, depending on
whether or not the diphasic property has appeared (#21), the
target values ?mh2, ?mj 1 are switched (#22, 23).
[0124] As described above, by performing the dlphasic
resonant control when the diphasic property appears, decrease
in the transmitted power may be suppressed, and the efficiency
of the power transmission may be increased.
[0125] Therefore, by switching and performing the normal
resonant frequency control and the diphasic resonant control
for the case in which the diphasic property appears, the maximum
power may be transmitted to the power receiving device 4
constantly, and the energy transmission may be performed with
a high efficiency.
[0126] In each embodiment described above, -n is set as the
target value ?mj , and -3p/2 or -2p is set as the target value
?mj . The value "-p" set as the target value ?mj is an example
of the target value "ß" . The values "-3p/2" and "-2p" is an example
of the target values "ß-p/2" and "ß-p", respectively.
[0127] These target values ?ms, ?mj may be changed variously
according to the configuration of the power-transmitting side
control unit 14, the power-transmitting side control unit 24,
the feedback control units 144,24 4, the resonant frequency
control units CTs, CTj.
[0128] Meanwhile, in this embodiment, the phase and the phase
difference are expressed in radian. Assuming a phase or a phase
difference as a [radian] , this is equivalent to (a+2p) [radian] ,
where n is an arbitrary integer. In addition, the phase and the
phase difference may be expressed in degrees instead of radian.
[0129] In addition, it has been mentioned that in setting
the target values ?ms, ?ms, the correction values a, b may be
added to those values. Such correction values a, b may be
determined such that the maximum power is obtained actually.
[0130] In the embodiment described above, the configuration
of the phase detection units 141,142 may be changed variously.
That is, either the voltage waveform or the current waveform
is fine, and a value or data indicating a phase is also fine.
That is, a signal or data including phase information about the
voltage Vs or the current Is is fine.
[0131] In the embodiment described above, the addition unit
152 and the gain adjustment unit 153, and the addition unit 252
and the gain adjustment unit 253 are respectively an example
of a calculation unit. While the MEMS variable capacity device
being the capacitors 132, 222 are driven by the drivers 156,
256, other types of capacitors maybe driven. Inaddition, driving
may be performed by the driver 156 such that the inductance of
the coil instead of the capacitor is varied.
[0132] In the embodiment described above, the configuration,
structure, circuit, shape, number, placement of each part or
the entirety of the power transmitting coil SC, the power
receiving coil, the power-transmitting side control unit 14,
the power-transmit ting side control unit 24 , the feedback control
units 144, 244, the resonant frequency control units CTs, CTj,
the power transmitting device 3, the power receiving device 4,
the power transmission system 1, 1B may be changed as needed
according to the gist of the present invention.
[0133] The power transmission system (power transmission
device) 1, 1B of the embodiment described above may be applied
to charging of a secondary battery built in a mobile device such
as a mobile phone, a mobile computer, a portable music player,
or, charging of a secondary battery of a transportation machine
such as an automobile.
We Claim:
1. A resonant frequency control method in a magnetic field
resonant coupling type power transmission system transmitting
an electric power from a power transmitting coil to a power
receiving coil using magnetic field resonance, comprising:
detecting a phase of a voltage supplied to the power
transmitting coil and a phase of a current that flows in the
power transmitting coil or the power receiving coil, and varying
a resonant frequency of the power transmitting coil or the power
receiving coil such that phase difference between them becomes
a target value.
2 . The resonant frequency control method in the magnetic field
resonant coupling type power transmission system according to
claim 1, wherein:
the power transmitting coil comprises a power supplying
coil to which an alternating-current power supply is connected,
and a power transmitting resonant coil closely coupled
electromagnetically with tne power supplying coil;
the power receiving coil comprises a power receiving
resonant coil, and a power drawing coil closely coupled
electromagnetically with the power receiving resonant coil;
a resonant frequency of the power transmitting resonant
coil is varied such that a phase difference between a voltage
of the alternating-current power supply and a current of the
power transmitting resonant coil becomes a target value (3; and
a resonant frequency of the power receiving coil is varied
such that a phase difference between the voltage of the
alternating-current power supply and a current of the power
receiving resonant coil becomes a target value (ß-p/2).
3 . The resonant frequency control method in the magnetic field
resonant coupling type power transmission system according to
claim 2, wherein:
the target value ß is -p.
4 . The resonant frequency control method in the magnetic field
resonant coupling type power transmission system according to
claim 1, wherein:
when a degree of coupling between the power transmitting
coil and the power receiving coil increases and a diphasic
property appears, a resonant frequency of the power transmitting
coil or the power receiving coil is varied such that a peak of
a current appears at a frequency of the alternating-current power
supply.
5. The resonant frequency control method in the magnetic field
resonant coupling type power transmission system according to
claim 1, wherein:
the power transmitting coil comprises a power supplying
coil to which an alternating-current power supply is connected,
and a power transmitting resonant coil closely coupled
electromagnetically with the power supplying coil;
the power receiving coil comprises a power receiving
resonant coil, and a power drawing coil closely coupled
electromagnetically with the power receiving resonant coil;
when a degree of coupling between the power transmitting
coil and the power receiving coil increases and a diphasic
property appears,
a resonant frequency of the power transmitting resonant
coil is varied such that a phase difference between a voltage
of the alternating-current power supply and a current of the
power transmitting resonant coil becomes a target value ß; and
a resonant frequency of the power receiving coil is varied
such, that a phase difference between the voltage of the
alternating-current power supply and a current of the power
receiving resonant coil becomes a target value (ß-p) .
6. A magnetic field resonant type power transmission device
transmitting an electric power from a power transmitting coil
to a power receiving coil using magnetic field resonance,
comprising:
a phase detection unit configured to detect a phase of
a voltage supplied to the power transmitting coil and a phase
of a current that flows in the power transmitting coil or the
power receiving coil; and
a resonant frequency control unit configured to vary a
resonant frequency of the power transmitting coil or the power
receiving coil such that a phase difference between the detected
phases becomes a target value.
7 . Amagnetic field resonant coupling type power transmission
device transmitting an electric power from a power transmitting
coil to a power receiving coil using magnetic field resonant,
comprising:
a power transmitting phase detection unit configured to
detect a phase of a voltage supplied to the power transmitting
coil and a phase of a current that flows in the power transmitting
coil;
a power transmitting resonant frequency control unit
configured to vary a resonant frequency of the power transmitting
coil such that a phase difference between the detected phases
becomes a target value.
8. The power transmission device in the magnetic field
resonant coupling type power transmission device according to
claim 7, wherein:
the power transmitting coil comprises a power supplying
coil to which an alternating-current power supply is connected,
and a power transmitting resonant coil closely coupled
electromagnetically with the power supplying coil;
and
the power transmitting resonant frequency control unit
comprises a target value setting unit configured to set and store
the target value; and
a feedback control unit configured to vary a resonant
frequency of the power transmitting resonant coil such that a
phase difference between a voltage of the alternating-current
power supply and a current of the power transmitting resonant
coil becomes the set target value.
9. The power transmission device in the magnetic field
resonant coupling type power transmission device according to
claim 8, wherein:
the feedback control unit comprises:
a phase comparison unit configured to compare the phase
of the voltage and the phase of the current, and to output a
phase difference being a difference between them;
a calculation unit configured to calculate a phase
difference that the phase comparison unit outputs and a target
value set by the target value setting unit; and
a driver configured to drive to as to vary an inductance
or a capacitance in the power transmitting resonant coil.
10. The power transmission device in the magnetic field
resonant coupling type power transmission device according to
claim 8 or 9, wherein:
the target value setting unit sets -p as the target value.
11. The power transmission device in the magnetic field
resonant coupling type power transmission device according to
one of claims 7 through 10, comprising:
a phase information transmission unit configured to
transmit information about a phase of a voltage supplied to the
power transmitting coil wirelessly.
12. A power receiving device in a magnetic field resonant
coupling type power transmission device transmitting an electric
power from a power transmitting coil to a power receiving coil
using magnetic field resonance, comprising:
a phase information reception unit configured to receive
information about a phase of a voltage supplied to the power
transmitting coil;
a power receiving phase detection unit configured to detect
a phase of a current that flows in the power receiving coil;
and
a power receiving resonant frequency control unit
configured to vary a resonant frequency of the power receiving
coil such that a phase difference between a phase of a voltage
received by the phase information reception unit and a detected
phase of the current becomes a target value.
13. The power receiving device in the magnetic field resonant
coupling type power transmission device according to claim 12,
wherein
the power receiving coil comprises a power drawing coil,
and a power drawing coil closely coupled electromagnetically
with the power drawing coil;
and
the power receiving resonant frequency control unit
comprises
a target value setting unit configured to set and store
the target value; and
a feedback control unit configured to vary a resonant
frequency of the power receiving resonant coil such that a phase
difference between a phase of a voltage received by the phase
information reception unit and a detected phase of the current
becomes the target value.
14 . , The power receiving device in the magnetic field resonant
coupling type power transmission device according to claim 13,
wherein:
the feedback control unit comprises:
a phase comparison unit configured to compare the phase
of the voltage and the phase of the current, and to output a
phase difference being the difference between them;
a calculation unit configured to calculate a phase
difference that the phase comparison unit outputs and a target
value set by the target value setting unit; and
a driver configured to drive to as to vary an inductance
or a capacitance in the power receiving resonant coil.
15. The power receiving device in the magnetic field resonant
coupling type power transmission device according to claim 13
or 14, wherein:
the target value setting unit sets -3p/2 as the target
value.
16. The power receiving device in the magnetic field resonant
coupling type power transmission device according to claim 13,
wherein:
the target value setting unit switches and sets the target
value to -2p when a degree of coupling between the power
transmitting coil and the power receiving coil increases and
a diphasic property appears.