Wireless power receiver

An automatic tuning assist circuit is coupled in series with a transmission antenna. A first switch and a second switch are arranged in series between a first terminal and a second terminal of the automatic tuning assist circuit. Furthermore, a third switch and a fourth switch are arranged in series between the first terminal and the second terminal. A first auxiliary capacitor is arranged between a connection node that connects the first switch and the second switch and a connection node that connects the third switch and the fourth switch. A control unit switches the first switch through the fourth switch with the same frequency as that of the driving voltage, and with a predetermined phase difference with respect to the driving voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless power supply technique.

2. Description of the Related Art

In recent years, wireless (contactless) power transmission has been receiving attention as a power supply technique for electronic devices such as cellular phone terminals, laptop computers, etc., or for electric vehicles. Wireless power transmission can be classified into three principal methods using an electromagnetic induction, an electromagnetic wave reception, and an electric field/magnetic field resonance.

The electromagnetic induction method is employed to supply electric power at a short range (several cm or less), which enables electric power of several hundred watts to be transmitted in a band that is equal to or lower than several hundred kHz. The power use efficiency thereof is on the order of 60% to 98%. In a case in which electric power is to be supplied over a relatively long range of several meters or more, the electromagnetic wave reception method is employed. The electromagnetic wave reception method allows electric power of several watts or less to be transmitted in a band between medium waves and microwaves. However, the power use efficiency thereof is small. The electric field/magnetic field resonance method has been receiving attention as a method for supplying electric power with relatively high efficiency at a middle range on the order of several meters (A. Karalis, J. D. Joannopoulos, M. Soljacic, “Efficient wireless non-radiative mid-range energy transfer” ANNALS of PHYSICS Vol. 323, January 2008, pp. 34-48)

FIG. 1is a diagram showing a wireless power transmission system according to a comparison technique. The wireless power transmission system1rincludes a wireless power transmitting apparatuspower transmitting apparatus2rand a wireless power receiving apparatus4r. The wireless power transmitting apparatuspower transmitting apparatus2rincludes a transmission coil LTX, a resonance capacitor CTX, and an AC power supply10r. The wireless power receiving apparatus4rincludes a reception coil LRX, a resonance capacitor CRX, and a load70.

The resonance frequency is an important factor in magnetic field (electric field) resonance power transmission. The resonance frequency of the transmitter side LC resonance circuit is represented by fTX=1/(2π√(LTX·CTX)). The resonance frequency of the receiver side LC resonance circuit is represented by fRX=1/(2π√(LRX·CRX)). Thus, in order to provide high-efficiency electric power transmission, there is a need to appropriately adjust the transmitter-side and receiver-side resonance frequencies and the frequency of the AC power supply10r. However, in actuality, such resonance frequencies fluctuate depending on various kinds of factors. It is difficult for the power receiving apparatus side to tune the fluctuating resonance frequency based on the magnetic field (or electric field) itself as it has been transmitted from the power transmitting apparatuspower transmitting apparatus. This is because, in some cases, the resonance frequency detected by the power receiving apparatus side further changes depending on the resonance frequency and the phase conditions of the power receiving apparatus side.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve such a problem. Accordingly, it is an exemplary purpose of an embodiment of the present invention to provide a wireless power transmitting apparatus, a wireless power receiving apparatus, and a wireless power supply system, which are capable of automatically tuning the resonance frequency.

An embodiment of the present invention relates to a wireless power transmitting apparatus configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field to a wireless power receiving apparatus. The wireless power transmitting apparatus comprises: multiple channels of transmission antennas each comprising a transmission coil; an automatic tuning assist circuit coupled in series with the transmission antenna of a tuning channel which is one from among the multiple channels; and a power supply configured to apply an AC driving voltage across a series circuit comprising the transmission antenna and the automatic tuning assist circuit for the tuning channel, and across the transmission antenna for the other channels. The automatic tuning assist circuit comprises: a first terminal; a second terminal; N (N represents an integer) auxiliary capacitors each comprising a first electrode and a second electrode; multiple switches each of which is arranged between two terminals from among the first terminal and the second terminal, and from among the first electrode and the second electrode of the N auxiliary capacitors; and a first control unit configured to switch on and off the multiple switches in synchronization with the driving voltage.

Another embodiment of the present invention also relates to a wireless power transmitting apparatus. The wireless power transmitting apparatus comprises: multiple channels of transmission antennas each comprising a transmission coil; an automatic tuning assist circuit coupled in series with the transmission antenna of a tuning channel which is one from among the multiple channels; and a power supply configured to apply an AC driving voltage across a series circuit comprising the transmission antenna and the automatic tuning assist circuit for the tuning channel, and across the transmission antenna for the other channels. The automatic tuning assist circuit comprises: at least one auxiliary capacitor; multiple switches configured to charge and discharge at least the aforementioned one auxiliary capacitor using a current that flows through the transmission coil; and a first control unit configured to switch on and off the multiple switches so as to generate a capacitor voltage across at least the aforementioned one auxiliary capacitor, and to apply a correction voltage that corresponds to the capacitor voltage across at least the aforementioned one auxiliary capacitor to the transmission coil.

When the frequency of the driving voltage does not match the resonance frequency of the resonance circuit including the transmission antenna, the resonance circuit functions as a capacitor circuit or otherwise an inductor circuit. In this case, in the transmission antenna, a resonance current is induced with a phase that is delayed or otherwise advanced with respect to the phase of the driving voltage. In this state, in a case in which the multiple switches are switched on and off with a predetermined phase difference with respect to the driving voltage, each auxiliary capacitor is charged or otherwise discharged so as to provide phase matching between the resonance current and the driving voltage. By applying the correction voltage that develops across each auxiliary capacitor to the transmission antenna, such an arrangement provides a quasi-resonant state. Such an embodiment is capable of automatically tuning the transmission antenna with respect to the driving voltage even without an operation such as adjusting the capacitance of the resonance capacitor. It should be noted that, in the present specification, the “phase difference” may be set to zero. That is to say, examples of the “phase difference” state include a phase matching state.

With such an arrangement, the multiple channels of transmission antennas are provided. This allows the voltage applied to a coil and/or a capacitor of the transmission antenna of each channel to be reduced, as compared with a power transmitting apparatus configured to transmit electric power via a single coil and a single capacitor. This allows the automatic tuning assist circuit to be configured using switches or capacitors having a low breakdown voltage. Such an arrangement provides a reduced cost or otherwise provides an improved degree of circuit design freedom.

In this case, by magnetically coupling the multiple channels of transmission coils with each other, and by providing the automatic tuning assist circuit for only a single tuning channel, such an arrangement provides a quasi-resonant state to the overall operation of the multiple channels of transmission antennas without a need to provide such an automatic tuning assist circuit to all the multiple channels.

Also, multiple channels from among the aforementioned multiple channels may be configured as the tuning channels. Also, the tuning assist circuit may be provided for each tuning channel. Also, all of the multiple channels may each be configured as the tuning channel.

By increasing the number of tuning channels, such an arrangement provides a quasi-resonant state with higher precision and with higher flexibility, as compared with an arrangement including a single tuning channel.

Also, the first control unit may be configured to switch on and off each of the multiple switches with the same frequency as that of the driving voltage, or otherwise with a frequency obtained by multiplying or dividing the frequency of the driving voltage by an odd number.

Also, the automatic tuning assist circuit may comprise: a first switch and a first auxiliary capacitor arranged in series between the first terminal and the second terminal; and a second switch arranged between the first terminal and the second terminal such that it is arranged in parallel with the first switch and the first auxiliary capacitor.

Also, the automatic tuning assist circuit may further comprise a second auxiliary capacitor between the first terminal and the second terminal such that it is arranged in series with the second switch.

Also, the automatic tuning assist circuit may comprise: a first switch and a second switch arranged in series between the first terminal and the second terminal; a third switch and a fourth switch sequentially arranged in series between the first terminal and the second terminal such that they are configured as a path in parallel with the first switch and the second switch; and a first auxiliary capacitor arranged between a connection node that connects the first switch and the second switch and a connection node that connects the third switch and the fourth switch.

Yet another embodiment of the present invention relates to a wireless power receiving apparatus configured to receive an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field, transmitted from a wireless power transmitting apparatus. The wireless power receiving apparatus comprises: multiple channels of reception antennas each comprising a reception coil configured to supply the electric power thus received to a common load; and an automatic tuning assist circuit coupled in series with the reception antenna of a tuning channel which is one from among the multiple channels. The automatic tuning assist circuit comprises: a first terminal; a second terminal; N (N represents an integer) auxiliary capacitors each comprising a first electrode and a second electrode; multiple switches each of which is arranged between two terminals from among the first terminal and the second terminal, and from among the first electrode and the second electrode of the N auxiliary capacitors; and a second control unit configured to switch on and off the multiple switches.

Yet another embodiment of the present invention also relates to a wireless power receiving apparatus. The wireless power receiving apparatus comprises: multiple channels of reception antennas each comprising a reception coil, and configured to supply received electric power to a common load; and an automatic tuning assist circuit coupled in series with the reception antenna of a tuning channel which is one from among the multiple channels. The automatic tuning assist circuit comprises: at least one auxiliary capacitor; multiple switches configured to charge and discharge the aforementioned at least one auxiliary capacitor using a current that flows through the reception coil; and a second control unit configured to switch on and off the multiple switches so as to generate a capacitor voltage across the aforementioned at least one auxiliary capacitor, and to apply, to the reception coil, a correction voltage that corresponds to the capacitor voltage across the aforementioned at least one auxiliary capacitor.

When the frequency of the electric power signal does not match the resonance frequency of the resonance circuit including the reception antenna, the resonance circuit functions as a capacitor circuit or otherwise an inductor circuit. In this case, phase lag or otherwise phase lead occurs between the resonance current that flows through the resonance circuit and the resonance voltage that develops at the resonance circuit. In this state, in a case in which the multiple switches are switched on and off with the same frequency as that of the electric power signal, each auxiliary capacitor is charged or otherwise discharged so as to provide phase matching between the resonance current and the resonance voltage. By applying the correction voltage that develops across each auxiliary capacitor to the reception antenna, such an arrangement provides a quasi-resonant state. Such an embodiment is capable of automatically tuning the reception antenna with respect to the electric power signal without an operation such as adjusting the capacitance of the resonance capacitor.

With such an arrangement, the multiple channels of reception antennas are provided. This allows the voltage applied to a coil and/or a capacitor of each channel to be reduced, as compared with a power receiving apparatus configured to receive electric power via a single coil and a single capacitor. This allows the circuit parameters to be adjusted using an electric mechanism employing electronic circuit components. Thus, such an arrangement allows the control operation with higher flexibility and with a low cost, as compared with conventional techniques.

In this case, by magnetically coupling the multiple channels of reception coils with each other, and by providing the automatic tuning assist circuit for only a single tuning channel, such an arrangement provides a quasi-resonant state to the overall operation of the multiple channels of reception antennas without a need to provide such an automatic tuning assist circuit to all the multiple channels.

Also, multiple channels from among the aforementioned multiple channels may be configured as the tuning channels. Also, the tuning assist circuit may be provided for each tuning channel. Also, all of the multiple channels may each be configured as the tuning channel.

By increasing the number of tuning channels, such an arrangement provides a quasi-resonant state with higher precision and with higher flexibility, as compared with an arrangement including a single tuning channel.

Also, the second control unit is configured to switch on and off each of the multiple switches with the same frequency as that of the electric power signal, or otherwise with a frequency obtained by multiplying or dividing the frequency of the electric power signal by an odd number.

Also, the automatic tuning assist circuit may comprise: a third switch and a third auxiliary capacitor arranged in series between the first terminal and the second terminal; and a fourth switch arranged between the first terminal and the second terminal such that it is arranged in parallel with the third switch and the third auxiliary capacitor.

Also, the automatic tuning assist circuit may further comprise a fourth auxiliary capacitor between the first terminal and the second terminal such that it is arranged in series with the fourth switch.

Also, the automatic tuning assist circuit may comprise: a fifth switch and a sixth switch arranged in series between the first terminal and the second terminal; a seventh switch and an eighth switch sequentially arranged in series between the first terminal and the second terminal such that they are configured as a path in parallel with the fifth switch and the sixth switch; and a second auxiliary capacitor arranged between a connection node that connects the fifth switch and the sixth switch and a connection node that connects the seventh switch and the eighth switch.

Yet another embodiment of the present invention relates to a wireless power supply system. The wireless power supply system comprises: the wireless power transmitting apparatus according to any one of the aforementioned embodiments, and/or a wireless power receiving apparatus according to any one of the aforementioned embodiments.

DETAILED DESCRIPTION OF THE INVENTION

In the present specification, the state represented by the phrase “the member A is connected to the member B” includes a state in which the member A is indirectly connected to the member B via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is physically and directly connected to the member B.

Similarly, the state represented by the phrase “the member C is provided between the member A and the member B” includes a state in which the member A is indirectly connected to the member C, or the member B is indirectly connected to the member C via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is directly connected to the member C, or the member B is directly connected to the member C.

First Embodiment

Wireless Power Transmitting Apparatus

FIG. 2is a circuit diagram showing a configuration of a wireless power transmitting apparatus2according to a first embodiment. The wireless power transmitting apparatus2is configured to transmit an electric power signal S1to a wireless power receiving apparatus (not shown). As such an electric power signal S1, the wireless power transmitting apparatus2uses the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power transmitting apparatus2includes a power supply10, a transmission antenna20, an automatic tuning assist circuit30, and a first control unit40.

The transmission antenna20includes a transmission coil LTXarranged between its first terminal21and its second terminal22. A resonance capacitor CTXis arranged in series with the transmission coil LTX. The resonance capacitor CTXand the transmission coil LTXmay also be mutually exchanged.

The automatic tuning assist circuit30is coupled in series with the transmission antenna20. The power supply is configured to apply an AC driving voltage VDRVhaving a predetermined transmission frequency fTXacross a series circuit comprising the transmission antenna20and the automatic tuning assist circuit30. The driving voltage VDRVmay be configured to have a desired AC waveform, examples of which include a rectangular waveform, a trapezoidal waveform, a sine waveform, and the like. With the present embodiment, the driving voltage VDRVis configured as a rectangular wave signal which swings between a first voltage level (power supply voltage VDD) and a second voltage level (ground voltage VGND=0 V).

The power supply10includes a DC power supply12, a first high-side switch SWH1, and a first low-side switch SWL1. The DC power supply12is configured to generate a DC power supply voltage VDD. The first high-side switch SWH1and the first low-side switch SWL1are sequentially connected in series between the output terminal of the DC power supply12and a fixed voltage terminal (ground terminal). The first control unit40is configured to switch on and off the first high-side switch SWH1and the first low-side switch SWL1in a complementary manner, with a transmission frequency fTX.

The automatic tuning assist circuit30includes a first terminal31, a second terminal32, a first switch SW1, a second switch SW2, and a first auxiliary capacitor CA1.

The first switch SW1and the first auxiliary capacitor CA1are arranged in series between the first terminal and the second terminal32. The first switch SW1and the first auxiliary capacitor CA1may also be mutually exchanged. The second switch SW2is arranged in parallel with the first switch SW1and the first auxiliary capacitor CA1between the first terminal31and the second terminal32. The first auxiliary capacitor CA1is preferably configured to have a sufficiently greater capacitance than that of the resonance capacitor CTX.

The first control unit40is configured to switch on and off the first switch SW1and the second switch SW2in a complementary manner, with the same frequency fTXas that of the driving voltage VDRV, and with a predetermined phase difference θTXwith respect to the driving voltage VDRV. The phase difference θTXmay preferably be set to a value in the vicinity of +90 degrees or otherwise −90 degrees (270 degrees). That is to say, a part of the first control unit40functions as a component of the automatic tuning assist circuit30.

The first switch SW1and the second switch SW2are each configured employing a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), bipolar transistor, or the like.FIGS. 3A and 3Bare diagrams each showing an example configuration of a switch employing a MOSFET.

FIG. 3Ashows a configuration of the switch employing an N-channel MOSFET.FIG. 3Bshows a configuration of the switch employing a P-channel MOSFET. In a case in which the back gate of the MOSFET is connected to its source, the body diode that forms between the back gate and the drain is in the connection state regardless of the gate voltage. Thus, such a switch configured as a single MOSFET is not capable of blocking a current that flows in one particular direction. In the present specification, such a switch will be referred to as a “uni-directional switch”.

The switches shown inFIGS. 3C through 3Feach comprise two N-channel MOSFETs or otherwise two P-channel MOSFETs connected such that their body diodes are connected in reverse directions (back-to-back connection). With the switches shown inFIGS. 3C through 3F, in the off state, no current flows in either direction. In the present specification, such a switch will be referred to as a “bi-directional switch”.

With the present embodiment, the switches SW1and SW2may each be configured as a uni-directional switch or otherwise a bi-directional switch. It should be noted that, in a case in which the switches SW1and SW2are each configured as a uni-directional switch, there is a need to pay attention to their switching phases. Detailed description thereof will be made later.

The above is the configuration of the wireless power transmitting apparatus2. Next, description will be made regarding the operation thereof.

Let us consider an arrangement in which the switches SW1and SW2are each configured as a bi-directional switch which is capable of blocking a current in both directions in the off state.

FIG. 4shows waveform diagrams each showing the operation of the wireless power transmitting apparatus2shown inFIG. 2.FIG. 4shows, in the following order beginning from the top, the voltage at the first high-side switch SWH1, the voltage at the first low-side switch SWL1, the driving voltage VDRV, the voltage at the first switch SW1, the voltage at the second switch SW2, the voltage VCA1at the first auxiliary capacitor CA1, the voltage VAat the first terminal31, the resonance current ITXthat flows through the transmission antenna20, and the resonance voltage VTXthat develops across the transmission coil LTXand the resonance capacitor CTX. In the waveform diagram for each switch, the high level represents the on state, and the low level represents the off state. It should be noted thatFIG. 4shows the waveforms of the resonance current ITXand the resonance voltage VTXobtained after a sufficient time has elapsed after the automatic tuning assist circuit30starts to operate.

As shown inFIG. 4, by switching on and off the first high-side switch SWH1and the first low-side switch SWL1in a complementary manner, such an arrangement is capable of generating the driving voltage VDRVhaving a rectangular waveform. The driving voltage VDRVthus generated is applied across the transmission antenna20and the automatic tuning assist circuit30. The first control unit40is configured to switch on and off the first switch SW1and the second switch SW2in a complementary manner, with the same frequency as that of the driving voltage VDRV, and with a phase that is delayed by θTX(=90 degrees) with respect to the driving voltage VDRV. The resonance current ITXflows to the first auxiliary capacitor CA1during the on time TON1of the first switch SW1, and flows to the ground via the second switch SW2during the on time TON2of the second switch SW2. That is to say, the first auxiliary capacitor CA1is charged and discharged by means of the resonance current ITX. As a result, the capacitor voltage VCA1develops at the first auxiliary capacitor CA1.

The automatic tuning assist circuit30is configured to apply a correction voltage VAto the second terminal22of the transmission antenna20. During the on time TON1of the first switch SW1, the first auxiliary capacitor voltage VCA1is used as the correction voltage VA. On the other hand, during the on time TON2of the second switch SW2, the ground voltage VGNDis used as the correction voltage VA. The automatic tuning assist circuit30can be regarded as a correction power supply configured to apply the correction voltage VAto the transmission antenna20.FIG. 5is an equivalent circuit diagram showing an equivalent circuit of the wireless power transmitting apparatus2shown inFIG. 2.

FIG. 6Ais a waveform diagram showing a state in which the automatic tuning assist circuit30does not operate, andFIG. 6Bis a waveform diagram showing a state in which the automatic tuning assist circuit30operates.

First, description will be made with reference toFIG. 6Aregarding the state in which the automatic tuning assist circuit30does not operate, i.e., a state in which the first switch SW1is fixed to the off state, and the second switch SW2is fixed to the on state. In this state, the correction voltage VAis fixed to the ground voltage VGND.

The impedance Z of the transmission antenna20is represented by the following Expression (1). The resonance frequency fcof the transmission antenna20is represented by the following Expression (2). The following Expressions (1) and (2) represent the impedance and the resonance frequency assuming that the resistance component is negligible. However, it is needless to say that, in actual circuits, the resistance component connected in series contributes to the circuit impedance.
Z=jωLTX+1/(jωCTX)  (1)
fc=1/2π√(LTX·CTX)  (2)

In a case in which the frequency fTXof the driving voltage VDRVis higher than the resonance frequency fc(fTX>fc), the transmission antenna20functions as an inductor. In this case, the resonance current ITXthat flows through the transmission antenna20has a phase which is delayed with respect to the phase of the driving voltage VDRV. Conversely, in a case in which the frequency fTXof the driving voltage VDRVis lower than the resonance frequency fc(fTX<fc), the transmission antenna20functions as a capacitor. In this case, the resonance current ITXhas a phase which is advanced with respect to the driving voltage VDRV.

FIG. 6Ashows a state in which fc>fTX. In this state, the resonance current ITXhas a phase which is advanced by the phase difference φ with respect to the driving voltage VDRV. It should be noted that the phase difference φ is not 90 degrees. This is because the resonance circuit includes a non-negligible resistance component (not shown) connected in series. In the non-resonant state, the impedance Z exhibits a high value, leading to a reduced amplitude of the resonance current ITX. In this state, such an arrangement is not capable of transmitting a large amount of electric power.

Next, description will be made with reference toFIG. 6Bregarding a case in which the automatic tuning assist circuit30operates.

In a case in which the automatic tuning assist circuit30operates, the correction voltage VAis applied to the transmission antenna20with a phase that is delayed by θTX=90 degrees with respect to the driving voltage VDRV. As a result, phase matching is obtained between the resonance current ITXand the driving voltage VDRV, thereby providing a quasi-resonant state. In this state, the resonance current ITXhas a greater amplitude than that in the non-resonant state.

FIG. 7is a phasor diagram (vector diagram) for describing the quasi-resonant state provided by the automatic tuning assist circuit30.

The phase of the driving voltage VDRVis 0 degrees. The phase of the correction voltage VAis θTX=90 degrees. In a case in which fc<fTX, the current has a phase that is delayed by the phase difference φ with respect to the voltage. Thus, the phase difference φ exists between the driving voltage VDRVand the current component IDRV. Furthermore, the phase difference φ exists between the correction voltage VAand the current component VA.

Based on the “principle of superposition”, the resonance current ITXis configured as the sum of the current component IDRVinduced by the driving voltage VDRVand the current component IAinduced by the correction voltage VA. There is a phase difference of θTX(=90 degrees) between the driving voltage VDRVand the correction voltage VA. Accordingly, there is a phase difference of 90 degrees between the current components IDRVand IA. Thus, by optimizing the amplitude of the correction voltage VA, i.e., by optimizing the amplitude of the current component IA, such an arrangement is capable of providing phase matching between the driving voltage VDRV(having a phase of 0 degrees) and a resultant current obtained by combining the two current components IDRVand IA, i.e., the resonance current ITX. That is to say, it can be clearly understood that such an arrangement provides a quasi-resonant state.

The wireless power transmitting apparatus2according to the embodiment is capable of automatically generating the correction voltage VAwhich provides the quasi-resonant state, which is an important excellent advantage of the wireless power transmitting apparatus2according to the embodiment.

FIG. 8is a diagram showing the resonance current ITXin the non-resonant state and in the resonance state. The waveform (I) represents the resonance current ITXin the non-resonant state. In the on time TON1in which the switch SW1is on, the first auxiliary capacitor CAis charged and discharged by means of the resonance current ITX. Specifically, the first auxiliary capacitor CA1is charged during a period in which the resonance current ITXis positive, and is discharged during a period in which the resonance current ITXis negative. As a result, in a case in which the period in which the resonance current ITXis positive is longer than the period in which the resonance current ITXis negative, the capacitor voltage VCA1rises. Otherwise, the capacitor voltage VCA1drops.

Let us say that the capacitor voltage VCA1rises in the on time TON1of a certain cycle. In this case, the correction voltage VAis applied to the transmission antenna20according to the rising capacitor voltage VCA1. This advances the phase of the resonance current ITXwith respect to the resonance current ITXof the previous cycle. By repeatedly performing this processing, the capacitor voltage VCA1rises in increments of cycles, which gradually advances the phase of the resonance current ITX. Eventually, the phase of the resonance current ITXshifts until it matches the phase of the driving voltage VDRV(resonance point). When the phase of the resonance current ITXexceeds the resonance point, the discharge current of the first auxiliary capacitor CA1becomes greater than its charging current, thereby providing a feedback control operation in the reverse direction. This reduces the capacitor voltage VCA1, thereby returning the phase of the resonance current ITXto the resonance point. At the resonance point, such an arrangement provides a balance between the charging current and the discharging current of the first auxiliary capacitor CA1for each cycle, thereby providing an equilibrium state of the capacitor voltage VCA1. In this state, a quasi-resonant state is maintained. As described above, with the wireless power transmitting apparatus2shown inFIG. 2, such an arrangement is capable of automatically generating the correction voltage VAthat is required to provide the quasi-resonant state.

The above is the operation of the wireless power transmitting apparatus2.

As described above, without adjusting the resonance frequency fcof the transmission antenna20, the wireless power transmitting apparatus2is capable of automatically tuning the circuit state so as to provide the quasi-resonant state. In the wireless power transmission, the resonance frequency changes over time according to the position relation between the wireless power transmitting apparatus2and the wireless power receiving apparatus4. The wireless power transmitting apparatus2is capable of following the change in the resonance frequency with high speed, thereby providing high-efficiency electric power transmission.

Furthermore, in a case in which a large amount of electric power is transmitted by means of wireless power transmission, a very high voltage develops between both ends of the resonance capacitor CTX, which limits the use of a variable capacitor. With the wireless power transmitting apparatus2, there is no need to adjust the capacitance of the resonance capacitor CTX. Thus, such an arrangement does not require such a variable capacitor or the like, which is another advantage.

Description has been made above regarding a case in which the first switch SW1is switched on and off with a phase that is delayed by θTX(=90 degrees) with respect to the phase of the switching of the first high-side switch SWH1. However, the phase difference θTXbetween the first switch SW1and the first high-side switch SWH1is not restricted to 90 degrees. Also, an arrangement may be made in which the phase difference θTXbetween the first switch SW1and the first high-side switch SWH1is set to 270 degrees (−90 degrees). In this case, the capacitor voltage VCA1is automatically adjusted such that it becomes a negative voltage.

That is to say, in a case in which fc<fTX, by setting the phase difference θTXto 90 degrees or otherwise 270 degrees, such an arrangement provides a quasi-resonant state.

Also, the phase difference θTXmay be moved away from 90 degrees or 270 degrees. In this case, the phase difference θTXbetween the current components IDRVand IAdoes not match 90 degrees. However, even in such a case, the capacitor voltage VCA1is automatically adjusted such that the resultant resonance current ITXhas a phase of 0 degrees. It should be noted that, as the phase difference θTXbecomes closer to 90 degrees or otherwise 270 degrees, the required value of the amplitude of the current component IA, i.e., the required absolute value of the capacitor voltage VCA1, becomes smaller. This is an advantage in employing an arrangement in which the phase difference θTXis set to 90 degrees or otherwise 270 degrees.

It should be noted that, in a case in which fc<fTX, such an arrangement is capable of supporting the quasi-resonant state in which the phase difference θTXis set to 270 degrees only in a case in which the first switch SW1and the second switch SW2are each configured as a bi-directional switch. In other words, in a case in which the first switch SW1and the second switch SW2are each configured as a uni-directional switch, such an arrangement is not capable of supporting the quasi-resonant state in which the phase difference θTXis set to degrees. This is because the current flows through the body diode. Thus, in a case in which the first switch SW1and the second switch SW2are each configured as a uni-directional switch, there is a need to switch on and off the first switch SW1and the second switch SW2with a phase such that no current flows through the body diodes which each function as an inversely conducting element.

The wireless power transmitting apparatus2automatically provides a quasi-resonant state not only in a case in which fc<fTX, but also in a case in which fc>fTX. In this case, the phase difference θTXis preferably set to 270 degrees (−90 degrees).

FIG. 9is a phasor diagram for describing a quasi-resonant state provided by the automatic tuning assist circuit in a case in which fc>fTX. Description will be made below assuming that the driving voltage VDRVhas a phase of 0 degrees, and the correction voltage VAhas a phase θTXof 270 degrees (−90 degrees). In a case in which fc>fTX, the current has a phase which is advanced with respect to that of the voltage. Such an arrangement also provides a quasi-resonant state even in such a case.

It should be noted that, in a case in which fc>fTX, the phase difference θTXmay be set to a value in the vicinity of 90 degrees. In this case, the capacitor voltage VCA1is automatically adjusted such that it becomes a negative voltage so as to provide a quasi-resonant state.

It should be noted that, in a case in which fc<fTX, such an arrangement is capable of supporting the quasi-resonant state in which the phase difference θTXis set to 90 degrees only in a case in which the first switch SW1and the second switch SW2are each configured as a bi-directional switch. In other words, in a case in which the first switch SW1and the second switch SW2are each configured as a uni-directional switch, such an arrangement is not capable of supporting the quasi-resonant state in which the phase difference θTXis set to degrees. This is because the current flows through the body diode.

Next, description will be made regarding modifications of the wireless power transmitting apparatus2. Each modification may be combined with any one of the other modifications, which is encompassed within the scope of the present invention.

FIG. 10is a circuit diagram showing a configuration of a wireless power transmitting apparatus2aaccording to a first modification. An automatic tuning assist circuit30aincludes a second auxiliary capacitor CA2between the first terminal31and the second terminal32such that it is connected in series with the second switch SW2.

With such a modification, during the on time TON1of the first switch SW1, the correction voltage VAis set to the capacitor voltage VCA1. During the on time TON2of the second switch SW2, the correction voltage VAis set to the capacitor voltage VCA2.

With the wireless power transmitting apparatus2a, by optimizing the capacitor voltages VCA1and VCA2, such an arrangement provides a quasi-resonant state both in the case in which VTX>fcand in the case in which VTX<fc.

FIG. 11is a circuit diagram showing a configuration of a wireless power transmitting apparatus2baccording to a second modification. An automatic tuning assist circuit30bincludes a charger circuit34and a detection resistor Rs. The detection resistor Rs is arranged on a path of the resonance current ITX. A detection voltage VSdevelops at the detection resistor Rs in proportion to the resonance current ITX. The charger circuit34is configured to charge the first auxiliary capacitor CA1based on the detection voltage VSso as to provide a quasi-resonant state. As described above, the capacitor voltage VCA1automatically becomes the optimum level. In addition, by providing the charger circuit34, such an arrangement provides a quasi-resonant state in a shorter period of time.

FIG. 12is a circuit diagram showing a configuration of a wireless power transmitting apparatus2caccording to a third modification. Description has been made in which the power supply is configured as a half-bridge circuit. In contrast, a power supply10cshown inFIG. 12is configured as an H-bridge circuit. A second high-side switch SWH2and a second low-side switch SWL2are sequentially connected in series between the output terminal of the power supply12and a fixed voltage terminal (ground terminal).

The first control unit40cis configured to repeatedly switch states between a state in which the pair of the high-side switch SWH1and the second low-side switch SWL2are turned on and a state in which the pair of the second high-side switch SWH2and the first low-side switch SWL1are turned on.

A driving voltage VDRVthat develop at a connection node (first output terminal) OUT1that connects the first high-side switch SWH1and the first low-side switch SWL1has a phase that is the reverse of the phase of a driving voltage #VDRVthat develops at a connection node (second output terminal) OUT2that connects the second high-side switch SWH2and the second low-side switch SWL2. The transmission antenna20and an automatic tuning assist circuit30care coupled in series between the first output terminal OUT1and the second output terminal OUT2.

With the wireless power transmitting apparatus2cshown inFIG. 12, such an arrangement provides the same advantages as those provided by the wireless power transmitting apparatus described above.

FIGS. 13A and 13Bare circuit diagrams showing the configurations of wireless power transmitting apparatuses2dand2eaccording to a fourth modification and a fifth modification. The first control unit40is omitted from the diagrams.

With the wireless power transmitting apparatus2dshown inFIG. 13A, an automatic tuning assist circuit30dis coupled in series with the transmission antenna20via a first transformer T1. Specifically, a secondary winding W2of the first transformer T1is arranged between the first terminal31and the second terminal32, and a primary winding W1of the first transformer T1is arranged in series with the transmission antenna20. The power supply10is configured to apply a driving voltage across a series circuit comprising the transmission antenna20and the primary winding W1.

With the wireless power transmitting apparatus2d, energy is transmitted and received between the transmission antenna20and the automatic tuning assist circuit30dvia the transformer T1. Such an arrangement provides the same advantages as those provided by the wireless power transmitting apparatuses described above.

With an arrangement shown inFIG. 13B, the power supply10is configured to apply the driving voltage VDRVacross the transmission antenna20and the automatic tuning assist circuit30dvia the second transformer T2. Specifically, the secondary winding W2of the second transformer T2is arranged in series with the transmission antenna20. The power supply is configured to apply the driving voltage VDRVbetween both ends of the primary winding W1of the second transformer T2.

With the wireless power transmitting apparatus2e, the driving voltage VDRVis applied across the transmission antenna20and the automatic tuning assist circuit30dvia the second transformer T2. Such an arrangement also provides the same advantages as those of the wireless power transmitting apparatuses described above. With the wireless power transmitting apparatus2e, the first transformer T1may be omitted. The power supply10shown inFIGS. 13A and 13Bmay be configured as an H-bridge circuit, a half-bridge circuit, or any other kind of power supply.

The automatic tuning assist circuit described above may also be employed in the wireless power receiving apparatus. Description will be made below regarding such a wireless power receiving apparatus.

FIG. 14is a circuit diagram showing a configuration of a wireless power receiving apparatus4according to the first embodiment. The wireless power receiving apparatus4is configured to receive the electric power signal S1transmitted from the aforementioned wireless power transmitting apparatus or otherwise a wireless power transmitting apparatus having an entirely different configuration. The electric power signal S1is configured using the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power receiving apparatus4includes a reception antenna50, an automatic tuning assist circuit60, and a load70to be supplied with electric power. The load70may include an unshown rectifier circuit, detector circuit, or the like, as a built-in component.

The reception antenna50includes a reception coil LRXand a resonance capacitor CRXarranged in series between a first terminal51and a second terminal52.

The automatic tuning assist circuit60has the same configuration as that of the automatic tuning assist circuit30described above. Specifically, a third switch SW3and a third auxiliary capacitor CA3are arranged between a first terminal and a second terminal62. Furthermore, a fourth switch SW4is arranged between the first terminal61and the second terminal62such that it is connected in parallel with the third switch SW3and the third auxiliary capacitor CA3.

The second control unit64is configured to switch on and off the third switch SW3and the fourth switch SW4in a complementary manner, with the same frequency as that of the electric power signal S1and with a phase difference θRXwith respect to the driving voltage (VDRV) which is applied to the transmitter-side antenna. For example, the phase difference θRXis set to 180 degrees or otherwise 0 degrees.

The automatic tuning assist circuit60is coupled in series with the reception antenna50. Furthermore, the load to be supplied with electric power is connected to the third auxiliary capacitor CA3.

The above is the configuration of the wireless power receiving apparatus4. Next, description will be made regarding the operation thereof.FIG. 15is an equivalent circuit diagram showing an equivalent circuit configuration of the wireless power receiving apparatus4shown inFIG. 14. As with the automatic tuning assist circuit30of the wireless power transmitting apparatus2, the automatic tuning assist circuit60can be regarded as a correction power supply configured to apply a correction voltage VAto the reception antenna50. During the on time TON3in which the third switch SW3is turned on, the correction voltage VAis set to the voltage VCA3that develops at the third auxiliary capacitor CA3. During the on time TON4of the fourth switch SW4, the correction voltage VAis set to the ground voltage.

FIG. 16is a waveform diagram showing the operation of the wireless power receiving apparatus4shown inFIG. 14.FIG. 16shows, in the following order beginning from the top, the voltages applied to the third switch SW3and the fourth switch SW4, the correction voltage VA, the resonance current IRXthat flows through the reception antenna50, and the resonance voltage VRXthat develops across the reception coil LRXand the resonance capacitor CRX. In the waveform diagrams showing the voltages applied to the respective switches, the high-level state represents the on state, and the low-level state represents the off state. In the waveform diagrams showing the resonance current IRXand the resonance voltage VRX, the solid line represents the waveform of a steady state (quasi-resonant state) after a sufficient period of time elapses after the automatic tuning assist circuit60starts to operate, and the broken line represents the waveform of a non-resonant state when the automatic tuning assist circuit60does not operate.

By switching on and off the third switch SW3and the fourth switch SW4in a complementary manner, with a phase θRXwhich is shifted by 180 degrees or otherwise 0 degrees with respect to the driving voltage VDRVof the wireless power transmitting apparatus side, such an arrangement charges or otherwise discharges the third auxiliary capacitor CA3. Furthermore, by applying the correction voltage VAto the reception antenna50, such an arrangement allows the resonance current IAto have a phase matching the phase of the driving voltage VDRVof the transmission side, thereby providing a quasi-resonant state.

In order to provide a quasi-resonant state, there is a need to switch on and off the third switch SW3and the fourth switch SW4with a suitable frequency fTXand with a suitable phase θRX. In order to meet this requirement, the wireless power transmitting apparatus2may be configured to transmit the data which represents the frequency fTXand the phase θRXto the wireless power receiving apparatus4. Also, the wireless power receiving apparatus4may be configured to sweep the phase θRXso as to detect the optimum phase θRX.

The above is the operation of the wireless power receiving apparatus4.

As described above, with the wireless power receiving apparatus4shown inFIG. 14, such an arrangement automatically provides a resonant state without a need to adjust the capacitance of the resonance capacitor CRX.

Next, description will be made regarding modifications of the wireless power receiving apparatus4.

Description has been made with reference toFIG. 14regarding an arrangement in which the load70is connected to the third auxiliary capacitor CA3. Also, the load70may be connected to a different position.FIGS. 17A and 17Bare circuit diagrams showing the configurations of wireless power receiving apparatuses according to a first modification and a second modification. With a wireless power receiving apparatus4ashown inFIG. 17A, a load70ais arranged in series with the reception antenna50and the automatic tuning assist circuit60. Specifically, the load70ais connected to a first terminal51of the reception antenna50.

A wireless power reception apparatus4bshown inFIG. 17Bincludes a third transformer T3by means of which a load70bis insulated from the reception antenna50. The primary winding W1of the third transformer T3is connected in series with the reception antenna50. The load70bis connected to the secondary winding W2of the third transformer T3.

In a case in which the load is connected in series with the reception antenna50as shown inFIGS. 17A and 17B, and in a case in which the load has a low impedance, such an arrangement has an advantage of a certain level of acquisition of electric power even without the adjustment by means of the automatic tuning assist circuit60. However, such an arrangement has a disadvantage of a reduction of the Q-value of the reception antenna50due to the resistance component of the load. Thus, it is difficult for such an arrangement to acquire a large amount of electric power.

Conversely, in a case in which electric power is acquired from the automatic tuning assist circuit60as shown inFIG. 14, the Q-value of the reception antenna50is not reduced due to the load70. Thus, such an arrangement is capable of acquiring a large amount of electric power even in a case in which the load70has a high impedance. However, in a case in which the load70has a very low impedance, such an arrangement has a problem of a reduction in the efficiency of the operation of the automatic tuning assist circuit60.

Thus, the position of the load in the circuit is preferably determined giving consideration to the electric power to be transmitted, the impedance of the load, and so forth.

FIG. 18is a circuit diagram showing a configuration of a wireless power receiving apparatus4caccording to a third modification. An automatic tuning assist circuit60cfurther includes a fourth auxiliary capacitor CA4between the first terminal61and the second terminal62such that it is connected in series with the fourth switch SW4. The position of the load70is not restricted in particular.

With such a modification, during the on time TON3of the third switch SW3, the correction voltage VAis set to the capacitor voltage VCA3, and during the on time TON4of the fourth switch SW4, the correction voltage VAis set to the capacitor voltage VCA4. With the wireless power receiving apparatus4c, the capacitor voltages VCA1and VCA2can be optimized so as to provide a quasi-resonant state in both the state in which fTX>fcand the state in which fTX<fc.

With such a wireless power receiving apparatus, the third switch SW3and the fourth switch SW4may each be configured as a uni-directional switch or otherwise a bi-directional switch. In a case in which the third switch SW3and the fourth switch SW4are each configured as a uni-directional switch, there is a need to switch on and off the third switch SW3and the fourth switch SW4with a phase such that no current flows through each of the inversely conducting elements.

FIGS. 19A and 19Bare circuit diagrams showing the configurations of wireless power receiving apparatuses according to a fourth modification and a fifth modification, respectively. The second control unit64is omitted from the diagrams.

With a wireless power receiving apparatus4dshown inFIG. 19A, an automatic tuning assist circuit60dis coupled in series with the reception antenna50via a fourth transformer T4. Specifically, the secondary winding W2of the fourth transformer T4is arranged between the first terminal61and the second terminal62. The primary winding W1of the fourth transformer T4is arranged in series with the reception antenna50.

With the wireless power receiving apparatus4d, energy is transmitted and received between the reception antenna50and the automatic tuning assist circuit60dvia the fourth transformer T4. Such an arrangement provides the same advantages as those provided by the wireless power receiving apparatuses described above.

FIG. 19Bshows an arrangement in which the load70is coupled with the reception antenna50and the automatic tuning assist circuit60dvia a fifth transformer T5. Specifically, the primary winding W1of the fifth transformer T5is connected in series with the reception antenna50. The load70is connected between both ends of the secondary winding W2of the fifth transformer T5.

Such an arrangement also provides the same advantages as those provided by the wireless power receiving apparatuses described above. With such a wireless power receiving apparatus4e, the fourth transformer T4may be omitted. With such an arrangement shown inFIG. 19A, the load may be coupled with the third auxiliary capacitor CA3. Also, with such an arrangement shown inFIG. 19B, the load70may be coupled with the third capacitor CA3via a fifth transformer T5.

By combining the wireless power transmission apparatus and the wireless power receiving apparatus described above, such an arrangement provides a wireless power transmission system.

FIG. 20is a circuit diagram showing an example configuration of a wireless power transmission system according to the first embodiment. The wireless power transmission system1includes the wireless power transmission apparatus2and the wireless power receiving apparatus4.

The load70includes a rectifier circuit72and a switching regulator74, in addition to a load circuit76. The rectifier circuit72is configured as a synchronous detector circuit, and includes a smoothing capacitor C3, a third high-side switch SWH3, and a third low-side switch SWL3.

The switching regulator74is configured as a step-up converter, and controlled so as to be capable of supplying the load circuit76with the maximum electric power. The configuration and the operation of the switching regulator74are known, and accordingly, description thereof will be omitted.

The above is the configuration of the wireless power transmission system1.FIG. 21is a waveform diagram showing the operation of the wireless power transmission system shown inFIG. 20.

With the wireless power transmission apparatus2, the first switch SW1and the second switch SW2are driven with a phase that is delayed by θTX=90 degrees with respect to the driving voltage VDRV. As a result, the wireless power transmitting apparatus2provides a quasi-resonant state.

With the wireless power receiving apparatus4, the third switch SW3and the fourth switch SW4are driven with a phase that is delayed by θRX=180 degrees with respect to the driving voltage VDRVemployed on the wireless power transmitting apparatus2side. The third switch SW3is driven with a phase that is delayed by 90 degrees with respect to the first switch SW1. As a result, the wireless power receiving apparatus4also provides a quasi-resonant state.

The third high-side switch SWH3and the third low-side switch SWL3of the rectifier circuit72are driven with a phase that is delayed by 90 degrees with respect to the third switch SW3and the fourth switch SW4. As a result, a DC voltage is generated at the smoothing capacitor C3. The switching regulator74is configured to convert the DC voltage thus generated into an optimum voltage level for the load circuit76.

The above is the operation of the wireless power transmission system1. As described above, with the wireless power transmission system1, the wireless power transmission apparatus2and the wireless power receiving apparatus4each include an automatic tuning assist circuit. Thus, such an arrangement allows the maximum electric power to be transmitted to the load70.

It is needless to say that any of the aforementioned wireless power transmitting apparatuses2including the modifications may be combined with any of the aforementioned wireless power receiving apparatuses4including the modifications.

Description has been made with reference toFIG. 20regarding an arrangement in which an automatic tuning assist circuit is mounted on both the wireless power transmitting apparatus2and the wireless power receiving apparatus4. However, the present invention is not restricted to such an arrangement.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus2, and the wireless power receiving apparatus is configured to adjust the resonance capacitor CRXin the same way as with conventional techniques.

Conversely, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus4, and the wireless power transmitting apparatus2is configured to adjust the resonance capacitor CTXin the same way as with conventional techniques.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus2, and the wireless power receiving apparatus4has no adjustment mechanism. Alternatively, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus4, and the wireless power transmitting apparatus2has no adjustment mechanism.

With such arrangements, tuning is performed by means of a single automatic tuning assist circuit so as to provide impedance matching between the power supply10and the load70, thereby providing high-efficiency electric power transmission. It is needless to say that, with such arrangements, the optimum value of the phase θTX(θRX) of the switching of the automatic tuning assist circuit does not match the aforementioned values, i.e., 90 degrees or otherwise 270 degrees (180 degrees or otherwise 0 degrees).

Description has been made regarding the present invention with reference to the first embodiment. The above-described embodiment has been described for exemplary purposes only, and is by no means intended to be interpreted restrictively. Rather, it can be readily conceived by those skilled in this art that various modifications may be made by making various combinations of the aforementioned components or processes, which are also encompassed in the technical scope of the present invention. Description will be made below regarding such modifications.

With the wireless power transmitting apparatus2including the automatic tuning assist circuit30, in some cases, such an arrangement is capable of providing a quasi-resonant state even without including the resonance capacitor CTX. In this case, such a resonance capacitor CTXmay be omitted. In the same way, an arrangement may be made in which the wireless power receiving apparatus4including the automatic tuning assist circuit60does not include the resonance capacitor CRX.

The wireless power transmitting apparatus2is configured to encrypt the electric power signal S1by changing at least one of the frequency fTXand the phase of the driving voltage VDRVaccording to a predetermined rule (encryption code). In a case in which the wireless power receiving apparatus4knows the encryption code, the wireless power receiving apparatus4controls the switching frequency and phase of the automatic tuning assist circuit60based on the encryption code. As a result, even if the electric power signal S1is encrypted, such an arrangement is capable of decrypting the electric power signal S1and receiving the power supply. In a case in which a wireless power receiving apparatus does not know the encryption code, the wireless power receiving apparatus cannot appropriately control the switching operation of the automatic tuning assist circuit60. Thus, such a wireless power receiving apparatus cannot receive electric power. With wireless power transmission, there is a problem of potential power theft by malicious users. However, by employing such an automatic tuning assist circuit, such a problem can be solved.

Also, in a case in which a single wireless power transmitting apparatus2supplies electric power to multiple wireless power receiving apparatuses4, by employing such an automatic tuning assist circuit, such an arrangement is capable of controlling the amount of electric power to be supplied to each terminal.

Second Embodiment

Description has been made in the first embodiment regarding the automatic tuning assist circuit including the two switches SW1and SW2. An automatic tuning assist circuit according to a second embodiment has a configuration including four switches. The automatic tuning assist circuit according to the second embodiment has the same block configuration as that of the first embodiment except for the automatic tuning assist circuit80. Also, various kinds of modifications as described in the first embodiment may effectively be made for the second embodiment.

FIG. 22is a circuit diagram showing a configuration of a wireless power receiving apparatus6according to a second embodiment. The wireless power receiving apparatus6is configured to transmit an electric power signal S1to a wireless power receiving apparatus (not shown). The electric power signal S1is configured using the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power transmitting apparatus6includes a power supply10, a transmission antenna20, an automatic tuning assist circuit80, and a first control unit40.

The transmission antenna20includes a transmission coil LTXarranged between its first terminal21and its second terminal22. A resonance capacitor CTXis arranged in series with the transmission coil LTX. The resonance capacitor CTXand the transmission coil LTXmay also be mutually exchanged.

The automatic tuning assist circuit80is coupled in series with the transmission antenna20. The power supply is configured as a half-bridge circuit in the same way as shown inFIG. 2. The power supply10is configured to apply an AC driving voltage VDRVhaving a predetermined transmission frequency fTXbetween the respective terminals of the circuit that comprises the transmission antenna20and the automatic tuning assist circuit80. The driving voltage VDRVmay be configured to have a desired AC waveform, examples of which include a rectangular waveform, a trapezoidal waveform, a sine waveform, and the like. With the present embodiment, the driving voltage VDRVis configured as a rectangular wave signal which swings between a first voltage level (power supply voltage VDD) and a second voltage level (ground voltage VGND0 V).

The power supply10is configured as a half-bridge circuit, as with the power supply10shown inFIG. 2. The first control unit40is configured to switch on and off the first high-side switch SWH1and the first low-side switch SWL1in a complementary manner, with a transmission frequency fTX.

With the second embodiment, the automatic tuning assist circuit80includes a first terminal81, a second terminal82, a first switch SWc1through a fourth switch SWc4, and a first auxiliary capacitor CA5.

The first switch SWc1and the second switch SWc2are sequentially arranged in series between the first terminal and the second terminal82. The third switch SWc3and the fourth switch SWc4are sequentially arranged between the first terminal81and the second terminal82, and are arranged in parallel with the first switch SWc1and the second switch SWc2. The first auxiliary capacitor CA5is arranged between a connection node N1that connects the first switch SWc1and the second switch SWc2and a connection node N2that connects the third switch SWc3and the fourth switch SWc4. The first auxiliary capacitor CA5is preferably configured to have a capacitance that is sufficiently greater than that of the resonance capacitor CTX.

The first control unit40is configured to switch on and off the first switch SWc1through the fourth switch SWc4in a complementary manner, with the same frequency fTXas that of the driving voltage VDRV, and with a predetermined phase difference θTXwith respect to the driving voltage VDRV. The phase difference θTXis preferably set to a value in the vicinity of +90 degrees or otherwise −90 degrees (270 degrees). That is to say, a part of the first control unit40functions as a component of the automatic tuning assist circuit80.

In the same way as with the first embodiment, the first switch SWc1through the fourth switch SWc4may each be configured as a uni-directional switch or otherwise a bi-directional switch. In a case in which the first switch SWc1through the fourth switch SWc4are each configured as a uni-directional switch, there is a need to pay attention to their switching phases, as described above in the first embodiment.

The above is the configuration of the wireless power transmitting apparatus6. Next, description will be made regarding the operation thereof.

FIG. 23is a waveform diagram showing the operation of the wireless power transmitting apparatus6shown inFIG. 22.FIG. 23shows, in the following order beginning from the top, the voltage at the first high-side switch SWH1, the voltage at the first low-side switch SWL1, the driving voltage VDRV, the voltage at the first switch SWc1, the voltage at the second switch SWc2, the voltage at the third switch SWc3, the voltage at the fourth switch SWc4, the correction voltage VAgenerated at the first terminal81, the resonance current ITXthat flows through the transmission antenna20, and the resonance voltage VTXthat develops across the transmission coil LTXand the resonance capacitor CTX. In the waveform diagram for each switch, the high level represents the on state, and the low level represents the off state. It should be noted that FIG. shows the waveforms of the resonance current ITXand the resonance voltage VTXobtained after a sufficient time has elapsed after the automatic tuning assist circuit80starts to operate.

As shown inFIG. 23, by switching on and off the first high-side switch SWH1and the first low-side switch SWL1in a complementary manner, such an arrangement is capable of generating the driving voltage VDRVhaving a rectangular waveform. The driving voltage VDRVthus generated is applied across the transmission antenna20and the automatic tuning assist circuit80. The first control unit40is configured to drive a first pair P1comprising the first switch SWc1and the fourth switch SWc4with the same frequency as that of the driving voltage VDRV, and with a phase that is delayed by θTX(=degrees) with respect to the driving voltage VDRV. Furthermore, the first control unit40is configured to drive a second pair P2comprising the second switch SWc2and the third switch SWc3in a complementary manner with respect to the first pair P1, i.e., with a phase that is shifted by 180 degrees with respect to that of the first pair P1.

During the on time TON1of the first pair P1, the resonance current ITXflows through a path including the first switch SWc1, the first auxiliary capacitor CA5, and the fourth switch SWc4. During the on time TON2of the second pair P2, the resonance current ITXflows through a path including the third switch SWc3, the first auxiliary capacitor CA5, and the second switch SWc2.

That is to say, the first auxiliary capacitor CA5is charged and discharged by means of the resonance current ITX. As a result, the capacitor voltage VCA5develops at the first auxiliary capacitor CA5.

The automatic tuning assist circuit80is configured to apply a correction voltage VAto the second terminal22of the transmission antenna20. During the on time TON1of the first pair P1, the correction voltage VAis set to a first polarity. During the on time TON2of the second pair P2, the correction voltage VAis set to a second polarity. The automatic tuning assist circuit80can be regarded as a correction power supply configured to apply the correction voltage VAto the transmission antenna20. That is to say, it can be clearly understood that the wireless power transmitting apparatus6can be represented by the same equivalent circuit as that shown inFIG. 5, and is configured to operate according to the same operation mechanism.

That is to say, in a case in which the automatic tuning assist circuit80operates, the correction voltage VAis applied to the transmission antenna20with a phase that is delayed by θTX=90 degrees with respect to the driving voltage VDRV. As a result, phase matching is obtained between the resonance current ITXand the driving voltage VDRV, thereby providing a quasi-resonant state. In this state, the resonance current ITXhas a greater amplitude than that in the non-resonant state. This is as shown in the phasor diagrams inFIGS. 7 and 9.

The operation of the automatic tuning assist circuit80according to the second embodiment is the same as described in the first embodiment with reference toFIG. 8. Thus, such an arrangement is capable of automatically generating the correction voltage VAwhich provides a quasi-resonant state.

The above is the operation of the wireless power transmitting apparatus6.

As described above, without adjusting the resonance frequency fcof the transmission antenna20, the wireless power transmitting apparatus6is capable of automatically tuning the circuit state so as to provide the quasi-resonant state. In the wireless power transmission, the resonance frequency changes over time according to the position relation between the wireless power transmitting apparatus and the wireless power receiving apparatus. The wireless power transmitting apparatus6is capable of following the change in the resonance frequency with high speed, thereby providing high-efficiency electric power transmission.

Furthermore, in a case in which a large amount of electric power is transmitted by means of wireless power transmission, a very high voltage develops between both ends of the resonance capacitor CTX, which limits the use of a variable capacitor. With the wireless power transmitting apparatus6, there is no need to adjust the capacitance of the resonance capacitor CTX. Thus, such an arrangement does not require such a variable capacitor or the like, which is another advantage.

Description has been made above regarding an arrangement in which the first pair comprising the first switch SWc1and the fourth switch SWc4is switched on and off with a phase that is delayed by θTX(=90 degrees) with respect to the phase of the switching of the first high-side switch SWH1(driving voltage VDRV). However, the phase difference θTXbetween the first pair and the first high-side switch SWH1is not restricted to 90 degrees. Also, an arrangement may be made in which the phase difference θTXbetween the first pair and the first high-side switch SWH1is set to 270 degrees (−90 degrees) In this case, the capacitor voltage VCA1is automatically adjusted such that the polarity reverses. In a case in which the first switch SWc1through the fourth switch SWc4are each configured as a uni-directional switch, there is a need to switch on and off the first switch SWc1through the fourth switch SWc4with a phase such that no current flows through each of the inversely conducting elements. Specifically, in a case in which fc<fTX, the phase difference θTXis preferably set to 90 degrees. Conversely, in a case in which fc>fTX, the phase difference θTXis preferably set to 270 degrees.

Also, the phase difference θTXmay be moved away from 90 degrees or 270 degrees, as described in the first embodiment.

Next, description will be made regarding modifications of the wireless power transmitting apparatus6. Each modification may be combined with any one of the other modifications, which is encompassed within the scope of the present invention.

FIG. 24is a circuit diagram showing a configuration of a wireless power transmitting apparatus6aaccording to a first modification. A power supply10cshown inFIG. 24is configured as an H-bridge circuit. A transmission antenna20and an automatic tuning assist circuit80aare arranged in series between a first output terminal OUT1and a second output terminal OUT2of a power supply10c. Furthermore, a capacitor C2configured to block DC current is arranged in series with the transmission antenna20and the automatic tuning assist circuit80a. With the automatic tuning assist circuit80a, one end (N2) of a first auxiliary capacitor CA5is grounded.

With the wireless power transmitting apparatus6ashown inFIG. 24, such an arrangement provides the same advantages as those provided by the wireless power transmitting apparatuses described above.

As described in the first embodiment, the power supply, the automatic tuning assist circuit, or otherwise both of them, may be coupled with the transmission antenna20via a transformer.FIGS. 25A through 25Care circuit diagrams respectively showing the configurations of wireless power transmitting apparatuses6bthrough6daccording to second through fourth modifications. The first control unit40is not shown.

With the wireless power transmitting apparatus6bshown inFIG. 25A, the automatic tuning assist circuit80ais coupled in series with the transmission antenna20via a sixth transformer T6. Specifically, the sixth transformer T6is configured to have a primary winding W1connected in series with the transmission antenna20, and to have a secondary winding W2connected between the first terminal61and the second terminal62of the automatic tuning assist circuit80a. The power supply10cis configured to apply a driving voltage across a series circuit that comprises the transmission antenna and the primary winding W1of the sixth transformer T6.

With a wireless power transmitting apparatus6cshown inFIG. 25B, the power supply10cis coupled with the transmission antenna20and the automatic tuning assist circuit80avia a seventh transformer T7. The power supply10cis configured to apply a driving voltage across the primary winding W1of the seventh transformer T7. The transmission antenna20and the automatic tuning assist circuit80aare arranged in series with the secondary winding W2.

With a wireless power transmitting apparatus6dshown inFIG. 25C, the power supply10having a half-bridge configuration is coupled with the transmission antenna20and the automatic tuning assist circuit80avia the seventh transformer T7. A capacitor C3configured to block DC current is arranged between the output terminal of the power supply10and the first winding W1of the seventh transformer T7.

Also, the modifications shown inFIGS. 25A through 25Cmay be combined. That is to say, both the power supply and the automatic tuning assist circuit may be coupled with the transmission antenna via a transformer.

Such modifications also provide the same advantages provided by the wireless power transmitting apparatuses described above.

The automatic tuning assist circuit according to the second embodiment described above may be employed in a wireless power receiving apparatus. Description will be made below regarding such a wireless power receiving apparatus.

FIG. 26is a circuit diagram showing a wireless power receiving apparatus8according to the second embodiment. The wireless power receiving apparatus8is configured to receive the electric power signal S1transmitted from the aforementioned wireless power transmitting apparatus or otherwise a wireless power transmitting apparatus having an entirely different configuration. The electric power signal S1is configured using the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power receiving apparatus8includes a reception antenna50, an automatic tuning assist circuit90, and a load70to be supplied with electric power. The load70may include an unshown rectifier circuit, detector circuit, or the like, as a built-in component.

The reception antenna50includes a reception coil LRXand a resonance capacitor CRXarranged in series between a first terminal51and a second terminal52.

The automatic tuning assist circuit90has the same configuration as that of the automatic tuning assist circuit80shown inFIG. 22. Specifically, the automatic turning assist circuit90includes a first terminal91, a fifth switch SWc5through an eighth switch SWc8, and a second auxiliary capacitor CA6.

The fifth switch SWc5and the sixth switch SWc6are arranged in series between the first terminal91and the second terminal92. The seventh switch SWc7and the eighth switch SWc8are sequentially arranged in series between the first terminal91and the second terminal92. Furthermore, the seventh switch SWc7and the eighth switch SWc8are arranged in parallel with the fifth switch SWc5and the sixth switch SWc6. The second auxiliary capacitor CA6is arranged between a connection node N3that connects the fifth switch SWc5and the sixth switch SWc6and a connection node N4that connects the seventh switch SWc7and the eighth switch SWc8. The second auxiliary capacitor CA6is preferably configured to have a sufficiently great capacitance as compared with the resonance capacitance CRX.

A second control unit94is configured to switch on and off the fifth switch SWc5through the eighth switch SWc8with the same frequency as that of the electric power signal S1, and with a phase difference θRXwith respect to the driving voltage (VDRV) which is applied to the transmitter-side antenna. For example, the phase difference θRXis preferably set to 180 degrees or otherwise 0 degrees.

The automatic tuning assist circuit90is coupled in series with the reception antenna50. Furthermore, the load to be supplied with electric power is directly connected with the reception antenna50and the automatic tuning assist circuit90.

The above is the configuration of the wireless power receiving apparatus8. Next, description will be made regarding the operation thereof. The wireless power receiving apparatus8can be represented by the same equivalent circuit diagram as that which represents the wireless power receiving apparatus4shown inFIG. 15. As with the automatic tuning assist circuit80of the wireless power transmitting apparatus6, the automatic tuning assist circuit90can be regarded as a correction power supply configured to apply a correction voltage VAto the reception antenna50.

FIG. 27is a waveform diagram showing the operation of the wireless power receiving apparatus8shown inFIG. 26.FIG. 27shows the voltages applied to the fifth switch SWc5through the eighth switch SWc8, the correction voltage VA, the resonance current IRXthat flows through the reception antenna50, and the resonance voltage VRXthat develops across the reception coil LRXand the resonance capacitor CRX. In the waveform diagrams showing the voltages applied to the respective switches, the high-level state represents the on state, and the low-level state represents the off state.

A first pair comprising the fifth switch SWc5and the eighth switch SWc8is switched on and off with a phase θRXwhich is shifted by 180 degrees or otherwise 0 degrees with respect to the driving voltage VDRVof the wireless power transmitting apparatus side. A second pair comprising the sixth switch SWc6and the seventh switch SWc7is switched on and off in a complementary manner with respect to the first pair. During the on time TON1of the first pair, the resonance current IRXflows through a path comprising the fifth switch SWc5, the second auxiliary capacitor CA6, and the eighth switch SWc8. During the on time TON2of the second pair, the resonance current IRXflows through a path comprising the sixth switch SWc6, the second auxiliary capacitor CA6, and the seventh switch SWc7.

The second auxiliary capacitor CA6is charged and discharged by means of the resonance current IRX. As a result, a capacitor voltage VCA6develops at the capacitor CA6. With such an arrangement, the correction voltage VAthat corresponds to the capacitor voltage VCA6is applied to the reception antenna50. Thus, such an arrangement allows the resonance current IAto have a phase that matches the phase of the driving voltage VDRVthat is used in the transmitter side, thereby providing a quasi-resonant state.

In order to provide a quasi-resonant state, there is a need to switch on and off the fifth switch SWc5and the eighth switch SWc8with a suitable frequency fTXand with a suitable phase θRX. In order to meet this requirement, the wireless power transmitting apparatus may be configured to transmit the data which represents the frequency fTXand the phase θRXto the wireless power receiving apparatus8. Also, the wireless power receiving apparatus8may be configured to sweep the phase θRXso as to detect the optimum phase θRX.

The above is the operation of the wireless power receiving apparatus8.

As described above, with the wireless power receiving apparatus8shown inFIG. 26, such an arrangement automatically provides a resonant state without a need to adjust the capacitance of the resonance capacitor CRX.

Next, description will be made regarding modifications of the wireless power receiving apparatus8.

Description has been made with reference toFIG. 26regarding an arrangement in which one terminal of the load70is grounded, and the ground potential is used as the reference potential. Also, instead of such an arrangement in which one terminal of the load70is grounded, one terminal of the second auxiliary capacitor CA6of the automatic tuning assist circuit90, i.e., either the connection node N3or N4, may be grounded.

FIGS. 28A and 28Bare circuit diagrams showing the configurations of wireless power receiving apparatuses according to a second modification and a third modification.

Description has been made with reference toFIG. 26regarding an arrangement in which the load70is connected in series with the reception antenna50. Also, the load70may be arranged at a different position.

With a wireless power receiving apparatus8aaccording to a first modification shown inFIG. 28A, the connection node N4of the automatic tuning assist circuit90ais grounded. A load70ais arranged in parallel with the second auxiliary capacitor CA6. That is to say, the load70ais supplied with a capacitor voltage VCA6that develops at the second auxiliary capacitor CA6.

With a wireless power receiving apparatus8baccording to a second modification shown inFIG. 28B, a load70bis coupled via an eighth transformer T8with a series circuit comprising the reception antenna50and the automatic tuning assist circuit90a.

FIGS. 28C and 28Dare circuit diagrams each showing an example configuration of such a load. A load70cshown inFIG. 28Cincludes a diode rectifier circuit72cand a load circuit76. A load70dshown inFIG. 28Dincludes a synchronous detector circuit72dand the load circuit76. Such a load circuit may further include a switching regulator74as shown inFIG. 20.

Such an automatic tuning assist circuit90may be coupled in series with the reception antenna50via a transformer.FIG. 29is a circuit diagram showing a configuration of a wireless power receiving apparatus8caccording to a third modification. The automatic tuning assist circuit90ais coupled in series with the reception antenna50via a ninth transformer T9. A load may be arranged in series with the reception antenna50and the primary winding W1. Also, such a load may be arranged in parallel with the second auxiliary capacitor CA6.

Such modifications also provide the same advantages as those provided by the wireless power receiving apparatus8shown inFIG. 26.

In a case in which the load is connected in series with the reception antenna50as shown inFIG. 26, and in a case in which the load has a low impedance, such an arrangement has an advantage of a certain level of acquisition of electric power even without the adjustment by means of the automatic tuning assist circuit90. However, such an arrangement has a disadvantage of a reduction of the Q-value of the reception antenna50due to the resistance component of the load. Thus, it is difficult for such an arrangement to acquire a large amount of electric power.

Conversely, in a case in which electric power is acquired from the automatic tuning assist circuit90aas shown inFIG. 28A, the Q-value of the reception antenna50is not reduced due to the load70. Thus, such an arrangement is capable of acquiring a large amount of electric power even in a case in which the load70ahas a high impedance. However, in a case in which the load70ahas a very low impedance, such an arrangement has a problem of a reduction in the efficiency of the operation of the automatic tuning assist circuit60.

Thus, the position of the load in the circuit is preferably determined giving consideration to the electric power to be transmitted, the impedance of the load, and so forth.

The fifth switch SWc5through the eighth switch SWc8may each be configured as a uni-directional switch or otherwise a bi-directional switch. As described above, in a case in which these switches are each configured as a uni-directional switch, there is a need to pay attention to their switching phases.

By combining the wireless power transmitting apparatus6and the wireless power receiving apparatus8described in the second embodiment, such an arrangement provides a wireless power transmission system.

Description has been made regarding an arrangement in which an automatic tuning assist circuit is mounted on each of the wireless power transmitting apparatus6and the wireless power receiving apparatus8. However, the present invention is not restricted to such an arrangement.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus6, and the wireless power receiving apparatus adjusts the resonance capacitor CRXin the same way as with conventional techniques. Conversely, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus8, and the wireless power transmitting apparatus6adjusts the resonance capacitor CTXin the same way as with conventional techniques.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus6, and the wireless power receiving apparatus8has no adjustment mechanism. Alternatively, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus8, and the wireless power transmitting apparatus6has no adjustment mechanism.

With such arrangements, tuning is performed by means of a single automatic tuning assist circuit so as to provide impedance matching between the power supply10and the load70, thereby providing high-efficiency electric power transmission. It should be noted that, with such arrangements, the optimum value of the phase θTX(θRX) of the switching of the automatic tuning assist circuit does not match the aforementioned values, i.e., 90 degrees or otherwise 270 degrees (180 degrees or otherwise 0 degrees).

Also, the wireless power transmitting apparatus2according to the first embodiment may be combined with the wireless power receiving apparatus8according to the second embodiment. Also, the wireless power receiving apparatus4according to the first embodiment may be combined with the wireless power transmitting apparatus6according to the second embodiment.

Description has been made regarding the present invention with reference to the second embodiment. The above-described embodiment has been described for exemplary purposes only, and is by no means intended to be interpreted restrictively. Rather, it can be readily conceived by those skilled in this art that various modifications may be made by making various combinations of the aforementioned components or processes, which are also encompassed in the technical scope of the present invention. Description will be made below regarding such modifications.

With the wireless power transmitting apparatus6including the automatic tuning assist circuit80, in some cases, such an arrangement is capable of providing a quasi-resonant state even while omitting the resonance capacitor CTX. In this case, such a resonance capacitor CTXmay be omitted. In the same way, an arrangement may be made in which the wireless power receiving apparatus8including the automatic tuning assist circuit90does not include the resonance capacitor CRX.

The wireless power transmitting apparatus6is configured to encrypt the electric power signal S1by changing at least one of the frequency fTXand the phase of the driving voltage VDRVaccording to a predetermined rule (encryption code). In a case in which the wireless power receiving apparatus8knows the encryption code, the wireless power receiving apparatus8controls the switching frequency and phase of the automatic tuning assist circuit90based on the encryption code. As a result, even if the electric power signal S1is encrypted, such an arrangement is capable of decrypting the electric power signal S1and receiving the power supply. In a case in which the wireless power receiving apparatus does not know the encryption code, the wireless power receiving apparatus cannot appropriately control the switching operation of the automatic tuning assist circuit90. Thus, such a wireless power receiving apparatus cannot receive electric power. With wireless power transmission, there is a problem of potential power theft by malicious users. However, by employing such an automatic tuning assist circuit, such a problem can be solved.

Also, in a case in which a single wireless power transmitting apparatus6supplies electric power to multiple wireless power receiving apparatuses8, by employing such an automatic tuning assist circuit, such an arrangement is capable of controlling the amount of electric power to be supplied to each terminal.

The usage of the automatic tuning assist circuit30is not restricted to such wireless power transmission. Rather, the present invention is applicable to various kinds of applications which require tuning.

Third Embodiment

Description has been made in the first and second embodiments regarding an arrangement including a single transmission coil LTXor otherwise a single reception coil LRX. In contrast, description will be made in the third embodiment regarding an arrangement including multiple transmission coils LTXor multiple reception coils LRX.

FIG. 30is a circuit diagram showing a configuration of a wireless power transmitting apparatus3according to a third embodiment. The wireless power transmitting apparatus3includes multiple, i.e., n (n represents an integer of 2 or more) channels of transmission antennas20_1through20_n. Each transmission antenna20includes a resonance capacitor CTXand a transmission coil LTXconnected in series. Such a third embodiment includes multiple transmission coils LTX, which can be regarded as a configuration obtained by dividing a single transmission coil described in the first and second embodiment. In the present embodiment, such a configuration will be referred to as the “divided coil configuration”. The transmission coil of each channel is wound around a shared magnetic member (core), thereby magnetically coupling the transmission coils with each other. The multiple transmission coils LTXmay each be configured as an air-core coil. Such an arrangement provides a reduced degree of coupling, as compared with an arrangement employing a core. However, by reducing the distance between the adjacent air-core coils to a certain extent, the multiple transmission coils LTXare magnetically coupled with each other.

One of the multiple channels (which corresponds to the n-th channel inFIG. 30) is configured as a tuning channel. For the tuning channel, the transmission antenna20_nis coupled in series with the automatic tuning assist circuit30or80described in any one of the aforementioned embodiments or otherwise the modifications thereof.

For the tuning channel, a power supply10applies an AC driving voltage VDRVacross a series circuit comprising the transmission antenna20_nand the automatic tuning assist circuit30(80). For each of the other channels, the power supply10applies the AC driving voltage VDRVbetween both ends of the transmission antenna20.

The power supply10includes power supplies10_1through10_nprovided for the respective channels. The power supplies10_1through10_n−1 respectively apply the driving voltage VDRVto the corresponding transmission antennas20_1through20_n−1. The power supply10_napplies the driving voltage VDRVacross a series circuit comprising the transmission antenna20_nand the automatic tuning assist circuit30(80). As described above, the driving voltage VDRVmay be configured to have a desired AC waveform, examples of which include a rectangular waveform, a trapezoidal waveform, a sine waveform, and the like.

FIG. 31is a circuit diagram showing a configuration of a wireless power transmitting apparatus3aaccording to a first modification of the third embodiment. With the modification, the terminals of the transmission antennas20_1through20_n, each of which is configured to receive the driving voltage VDRV, are connected in common. Such an arrangement allows the transmission antennas20_1through20_nto be driven using a single power supply.

Next, description will be made regarding the principle of the coil dividing.FIG. 32Ais a diagram showing a wireless power transmitting apparatus2rincluding a single coil.FIGS. 32B and 32Care diagrams each showing a wireless power transmitting apparatus having a divided coil configuration obtained by dividing a single coil into two coils.FIG. 32Dis a diagram showing a wireless power transmitting apparatus3having a divided coil configuration obtained by dividing a single coil into N coils.

The wireless power transmitting apparatus shown inFIG. 32Aincludes a single transmission coil L1and a resonance capacitor C1, which corresponds to the wireless power transmitting apparatus2rshown inFIG. 1. The transmission coils L11and L12shown inFIG. 32Bcan be regarded as a configuration obtained by dividing the transmission coil L1shown inFIG. 32Ainto two coils. With the inductance of the transmission coil L1before the coil division as L, the inductance of each of the coils L11and L12after the coil division is represented by L/2, which can be immediately understood. Furthermore, the resonance capacitors C11and C12shown inFIG. 32Bcan be regarded as a configuration obtained by dividing the capacitor C1shown inFIG. 32Ainto two capacitors. With the capacitance of the capacitor C1as C, the capacitance of each of the resonance capacitors C11and C12is represented by (2×C), which can be immediately understood.

With such an arrangement, the impedance of the transmission antenna (resonance circuit14) as viewed from the AC power supply10does not change even if the sequence of the coils L11and L12and the resonance capacitors C11and C12is changed in any arbitrary order. Thus, the current that flows through the transmission coils L11and L12does not change. Furthermore, the magnitude of the generated electric power signal S1is maintained at the same level. That is to say, even in a case in which the divided transmission coils L1and the divided resonance capacitors C1are arranged in an alternating manner, such an arrangement is capable of generating a magnetic field having the same magnitude as that provided by an arrangement shown inFIG. 32A. Generalizing the number of divisions as an integer N which is greater than 2, the configuration of the wireless power transmitting apparatus shown inFIG. 32Dis derived. In this case, the inductance of each of the divided coils L11through L1nis represented by L/n. The capacitance of each of the divided resonance capacitors C11through C1nis represented by (n×C).

InFIG. 32A, with the amplitude of the voltage across the transmission coil L1as VL, and with the amplitude of the voltage across the resonance capacitor C1as VC, when the conditions for resonance are satisfied, the relation VL=VCholds true. With the wireless power transmitting apparatus shown inFIG. 32D, the voltage across each divided transmission coil L1iis represented by VL/n. The voltage across each divided resonance capacitor C1iis represented by VC/n.

The advantage of the wireless power transmitting apparatus3shown inFIG. 32Dis clearly understood in comparison with the wireless power transmitting apparatus2rshown inFIG. 1. In order to supply large electric power by means of the wireless power transmitting apparatus2rshown inFIG. 1, there is a need to supply a large current such that it flows through the transmission coil L1. With such an arrangement, the resonance voltage VCor VLcan become several hundreds of V or more.

From the viewpoint of the practical usage of the wireless power transmitting apparatus, in order to adjust the resonance frequency or in order to change the Q value, there is a need to configure the resonance capacitor C1to have an adjustable capacitance and/or to configure the transmission coil L1to have an adjustable inductance. However, in a case in which the resonance voltage VCor VLbecomes several hundreds of V, it is difficult to employ electric circuit elements such as transistor elements or diode elements because they have a low breakdown voltage. Thus, such an arrangement requires mechanical components.

In contrast, with the wireless power transmitting apparatus3shown inFIG. 32D, the number of coils n is increased. Thus, such an arrangement allows the resonance voltage VCiof each divided resonance capacitor C1and the resonance voltage VLiof each divided transmission coil L1to have a reduced amplitude. This allows the resonance frequency and the Q value to be adjusted using an electronic component employing electronic circuit components such as transistor elements, diode elements, etc. In other words, the number of divisions n may preferably be determined such that the resonance voltages VC1and VL1are each reduced to a level at which such electronic circuit elements can be used. With such an electric adjustment mechanism, such an arrangement is capable of adjusting the resonance frequency or the Q value with high speed as compared with a mechanical adjustment mechanism employing a motor-driven variable capacitor, which is another advantage.

With such an arrangement, the resonance voltages VCand VLare reduced as compared with conventional techniques, thereby allowing an implementation to be configured employing transistor elements. Furthermore, by reducing the voltage to be applied to each transistor element to a voltage level on the order of several V, such an arrangement can be configured on a semiconductor substrate using a CMOS process. That is to say, such an arrangement allows multiple AC power supplies10to be integrated as a single IC. Also, such an arrangement allows multiple switch elements to be integrated as a single IC, which allows the constant of the resonance capacitor C1or the constant of the transmission coil L1to be changed.

From the following consideration, it can be clearly understood that the wireless power transmitting apparatus3shown inFIG. 30can be derived from the wireless power transmitting apparatus3shown inFIG. 32D.

With the wireless power transmitting apparatus3shown inFIG. 32D, a pair of the divided transmission coil L1iand the divided resonance coil C1iarranged adjacent to each other can be regarded as forming a resonance circuit14i. With such an arrangement, with the voltage amplitude of the electric signal S2generated by the AC power supply10shown inFIG. 32Das VDRV, the voltage equally applied to each of the resonance circuits141through14nis represented by VDRV/n. This is because the resonance circuits141through14nare each configured to have the same impedance.

Thus, in a case in which the driving voltage generated by each of the AC power supplies10_1through10_nshown inFIG. 30is 1/n times the driving voltage VDRVgenerated by the AC power supply10shown inFIG. 32D, and in a case in which the degree of coupling K between the divided transmission coils L11through L1nas shown inFIG. 30is equal to the degree of coupling K between the divided transmission coils L11through L1nas shown inFIG. 32D, the wireless power transmitting apparatus3shown inFIG. 30is capable of generating the electric signal S2having the same magnitude as that provided by the wireless power transmitting apparatus3shown inFIG. 32D.

The above is the configuration of the wireless power transmitting apparatus3.

With the first and second embodiments, a resonance voltage that occurs at the transmission antenna20exceeds several tens through several hundreds of V. Thus, there is a need to configure each switch and each auxiliary capacitor that form the automatic tuning assist circuit30(80) using a high breakdown voltage element.

In contrast, the third embodiment provides a reduced voltage applied to the automatic tuning assist circuit30(80). Thus, such an arrangement allows the automatic tuning assist circuit30(80) to be configured using a low breakdown voltage element. Such an arrangement provides a reduced cost, or otherwise provides an improved degree of circuit design freedom.

Furthermore, in a case in which the multiple transmission coils LTXare coupled via a magnetic member, and in a case in which the circuit state of a given channel is controlled, the effect of the control operation extends to the other channels. In other words, the automatic tuning assist circuit30(80) of the tuning channel operates so as to provide the quasi-resonance state to the overall operation of the wireless power transmitting apparatus3. Thus, there is no need to provide such an automatic tuning assist circuit30(80) to all the channels, thereby allowing such an arrangement to have a simple circuit configuration.

Moreover, with such an arrangement, the number of transmission coils is increased, which allows the magnetic flux generated by each separate transmission coil to be reduced. Such an arrangement is capable of suppressing spatial concentration of the magnetic field. This is another advantage from the viewpoint of protecting the human body.

FIG. 33is a circuit diagram showing a configuration of a wireless power receiving apparatus5according to a fourth embodiment. The wireless power receiving apparatus5includes multiple, i.e., n (n represents an integer of 2 or more) channels of reception antennas50_1through50_n. Each reception antenna50includes a resonance capacitor CRXand a reception coil LRXconnected in series. The reception coil LRXof each channel is wound around a shared magnetic member (core), thereby magnetically coupling the reception coils LRXwith each other. The multiple reception coils LRXmay each be configured as an air-core coil. Such an arrangement provides a reduced degree of coupling, as compared with an arrangement employing a core. However, by reducing the distance between the adjacent air-core coils to a certain extent, the multiple reception coils LRXare magnetically coupled with each other.

The electric power received by the multiple reception antennas50is supplied to a common load70. The connection configuration between the load70and the reception antennas50is not restricted in particular. Specifically, any one of the aforementioned embodiments may be applied to the connection configuration. One of the multiple channels (which corresponds to the n-th channel inFIG. 33) is configured as a tuning channel. For the tuning channel, the reception antenna n is coupled in series with the automatic tuning assist circuit60or90described in any one of the aforementioned embodiments or otherwise the modifications thereof.

The above is the configuration of the wireless power receiving apparatus5.

With the wireless power receiving apparatus5, as the number of reception antennas50, i.e., n, becomes greater, the amplitude of the resonance voltage that occurs at each of the resonance capacitors CRXand the reception coils LRXbecomes smaller.

With the first and second embodiments, a resonance voltage that occurs at the reception antenna50exceeds several tens through several hundreds of V. Thus, there is a need to configure each switch and each auxiliary capacitor that form the automatic tuning assist circuit60(90) using a high breakdown voltage element.

In contrast, the third embodiment provides a reduced voltage applied to the automatic tuning assist circuit60(90). Thus, such an arrangement allows the automatic tuning assist circuit60(90) to be configured using a low breakdown voltage element. Such an arrangement provides a reduced cost, or otherwise provides an improved degree of circuit design freedom.

Furthermore, in a case in which the multiple reception coils LRXare coupled via a magnetic member, and in a case in which the circuit state of a given channel is controlled, the effect of the control operation extends to the other channels. In other words, the automatic tuning assist circuit60(90) of the tuning channel operates so as to provide the quasi-resonance state to the overall operation of the wireless power receiving apparatus5. Thus, there is no need to provide such an automatic tuning assist circuit60(90) to all the channels, thereby allowing such an arrangement to have a simple circuit configuration.

Moreover, with such an arrangement, the number of reception coils is increased, which allows the magnetic flux generated by each separate reception coil to be reduced. Such an arrangement is capable of suppressing spatial concentration of the magnetic field. This is another advantage from the viewpoint of protecting the human body.

Fourth Embodiment

Wireless Power Transmitting Apparatus

FIG. 34is a circuit diagram showing a configuration of a wireless power transmitting apparatus3baccording to a fourth embodiment. As described in the third embodiment, in a case in which multiple transmission coils are coupled with each other with a certain degree of strength, by providing the automatic tuning assist circuit30(80) for only a single channel, such an arrangement provides the quasi-resonant state for all the channels. However, the third embodiment requires the multiple coils to be coupled with each other. Thus, the layout of the coils is restricted.

The wireless power transmitting apparatus3baccording to the fourth embodiment described below can be employed in a case in which the coupling of the multiple coils is weak.

The wireless power transmitting apparatus3described with reference toFIG. 30has a single tuning channel. With the present embodiment, multiple tuning channels are provided, and the automatic tuning assist circuit30(80) is provided for each tuning channel.FIG. 34shows an arrangement in which all the channels are each provided with the automatic tuning assist circuit30(80).

Next, description will be made regarding the operation of the wireless power transmitting apparatus3bshown inFIG. 34. With the wireless power transmitting apparatus3b, the power supplies10of the respective channels each apply a driving voltage with the same phase between both terminals of the corresponding circuit comprising the transmission antenna and the automatic tuning assist circuit30(80). Furthermore, the automatic tuning assist circuits30(80) of the respective channels each perform a switching operation with a phase that is shifted by the same angle with respect to the driving voltage.

The advantage of the wireless power transmitting apparatus3bis clearly understood in comparison with the wireless power transmitting apparatus3shown inFIG. 30. Here, description will be made regarding a problem that can occur in the wireless power transmitting apparatus3shown inFIG. 30. For ease of understanding, description will be made regarding an arrangement in which n=2, and the coupling of the transmission coils of the two channels is very weak.

Let us consider a case in which a wireless power receiving apparatus approaches the coils of the two channels. In this case, the power transmitting apparatus and the power receiving apparatus exert mutual effects on each other. That is to say, when the wireless power receiving apparatus approaches the wireless power transmitting apparatus, this leads to a change in the conditions for resonance of each channel. In this case, in the tuning channel provided with the automatic tuning assist circuit30(80), the phase of the coil current is shifted so as to provide a quasi-resonant state. In contrast, in the other channel, i.e., in the non-tuning channel, a coil current flows with a phase that corresponds to the resultant impedance of the transmission antenna20of the non-tuning channel and the wireless power receiving apparatus.

In this case, such an arrangement does not provide phase matching between the currents that flow through the transmission coils of the two channels. Thus, the electric power signals (electromagnetic field signals) generated by the transmission coils of the two channels cancel each other out. Such an arrangement is not capable of transmitting large electric power to the wireless power receiving apparatus, which is a problem.

In contrast, with the wireless power transmitting apparatus3bshown inFIG. 34, such an arrangement provides a quasi-resonant state for all the multiple channels. That is to say, such an arrangement provides a state in which the coil current flows through each of all the channels with a uniform phase shifted by 90 degrees with respect to the driving voltage.

Thus, such an arrangement solves a problem of the electric power signals (electromagnetic field signals) generated by the transmission coils of the two channels canceling each other out. This allows the wireless power transmitting apparatus to transmit large electric power to a wireless power receiving apparatus.

FIG. 35is a circuit diagram showing a configuration of a wireless power receiving apparatus5aaccording to the fourth embodiment. As described in the third embodiment, in a case in which multiple reception coils are coupled with each other with a certain degree of strength, by providing the automatic tuning assist circuit60(90) for only a single channel, such an arrangement provides the quasi-resonant state for all the channels. However, the third embodiment requires the multiple coils to be coupled with each other. Thus, the layout of the coils is restricted.

The wireless power receiving apparatus5aaccording to the fourth embodiment described below can be employed in a case in which the coupling of the multiple coils is weak.

The wireless power receiving apparatus5described with reference toFIG. 33has a single tuning channel. With the fifth embodiment, multiple tuning channels are provided, and the automatic tuning assist circuit60(90) is provided for each tuning channel.FIG. 35shows an arrangement in which all the channels are each provided with the automatic tuning assist circuit60(90).

Next, description will be made regarding the operation of a wireless power receiving apparatus5ashown inFIG. 35. With the wireless power receiving apparatus5a, the automatic tuning assist circuits60(90) of the respective channels each perform a switching operation with the same phase.

With the wireless power receiving apparatus5ashown inFIG. 35, even in a case in which the coupling between the multiple reception coils LRXis weak, such an arrangement is capable of receiving large electric power, thereby being capable of supplying the large electric power thus received to the load70.

FIGS. 36A and 36Bare diagrams each showing an example layout of the multiple transmission coils or otherwise the multiple reception coils according to the fourth embodiment.FIG. 36Ashows an example layout in which the multiple transmission coils (or reception coils) are arranged on the same plane.

FIG. 36Bshows an example layout in which the multiple transmission coils (or reception coils) are arranged on different planes. More specifically, the coils are arranged on different respective planes that are orthogonal to one another. In some cases, the layout shown inFIG. 36Ahas a problem of the occurrence of null points at which the magnitude of the electric power is very weak. In contrast, the layout shown inFIG. 36Bhas an advantage of reducing the number of such null points.

As described with reference toFIGS. 36A and 36B, with the fourth embodiment, the multiple channels are each provided with an automatic tuning assist circuit. Such an arrangement operates normally even if the degree of coupling of the multiple transmission coils or otherwise the multiple reception coils is low. This enables flexible design of the layout.