Wireless power transmission system and power transmission apparatus

In an embodiment, a wireless power transmission system includes at least one of the following combinations: i) a transmission-side series resonance circuit including the first coil and a first capacitor disposed between the first coil and a power transmission circuit, and ii) a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and a combination of i) a reception-side parallel resonance circuit including a third coil and a third capacitor disposed between the third coil and two power reception electrodes, and ii) a reception-side series resonance circuit including a fourth coil and a fourth capacitor disposed between the fourth coil and a power reception circuit.

BACKGROUND

1. Technical Field

The present disclosure relates to a wireless power transmission system and a power transmission apparatus that wirelessly transmit electric power.

2. Description of the Related Art

In recent years, activities have been made to develop a wireless (contactless) electric power transmission technique for wirelessly (contactlessly) transmitting electric power to a mobile apparatus such as a portable telephone device, an electric vehicle, or the like. The wireless power transmission technique is classified into an electromagnetic induction type, an electric field coupling type, etc. Of these types, in the electric field coupling type, a pair of power transmission electrodes and a pair of power reception electrodes are disposed opposing each other, and AC power is supplied to the pair of power transmission electrode thereby contactlessly transmitting electric power to a reception-electrode side. The electric field coupling type may be preferably used to transmit electric power to a load (for example, a mobile robot or the like) from a pair of power transmission electrodes disposed, for example, on a floor surface. Japanese Unexamined Patent Application Publication No. 2010-193692 discloses an example of a wireless power transmission system using such an electric field coupling type.

SUMMARY

In the related technique described above, in a case where power transmission electrodes and power reception electrodes are located close to each other or in a case where a dielectric material with high relative permittivity is provided between the power transmission electrodes and the power reception electrodes, it is possible to achieve high-efficiency contactless power transmission. However, in a case where the distance between the power transmission electrodes and the power reception electrodes is large or in a case where a dielectric material with high relative permittivity is not provided between the power transmission electrodes and the power reception electrodes, it is impossible to achieve high-efficiency power transmission.

In one general aspect, the techniques disclosed here feature a wireless power transmission system including a power transmission apparatus and a power reception apparatus, the power transmission apparatus including a power transmission circuit that converts DC power of an external DC power supply to AC power, a first coil connected to the power transmission circuit, a second coil inductively coupled to the first coil, and two power transmission electrodes that are connected to the second coil and that transmit the AC power, the power reception apparatus including two power reception electrodes disposed opposing the two power transmission electrodes so as to be capacitively coupled with the two power transmission electrodes to contactlessly receive the transmitted AC power, a third coil connected to the two power reception electrodes, a fourth coil connected to the third coil, and a power reception circuit that is connected to the fourth coil and that converts the received AC power to DC power, the wireless power transmission system having at least one of the following combinations: a combination of i) a transmission-side series resonance circuit including the first coil and a first capacitor disposed between the first coil and the power transmission circuit, and ii) a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and a combination of i) a reception-side parallel resonance circuit including the third coil and a third capacitor disposed between the third coil and the two power reception electrodes, and ii) a reception-side series resonance circuit including the fourth coil and a fourth capacitor disposed between the fourth coil and the power reception circuit.

These general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, or a storage medium, or as an arbitrary combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a storage medium.

According to one aspect of the present disclosure, it is possible to transmit electric power with a higher efficiency than is conventionally achieved, even in the case where the distance between the power transmission electrodes and the power reception electrodes is long or even in a case where no dielectric material with high relative permittivity is provided.

DETAILED DESCRIPTION

Before embodiments of the present disclosure are described, underlying knowledge forming basis of the present disclosure is described.

The inventors of the present disclosure have found that the known wireless power transmission system described in “Background Art” has problems described below.

FIG. 13is a diagram illustrating an example (a comparative example) of a circuit configuration of a wireless power transmission system similar to the power supply system disclosed in Japanese Unexamined Patent Application Publication No. 2010-193692. This system includes a power transmission apparatus100that transmits electric power and a power reception apparatus200that receives the transmitted electric power. Electric power is contactlessly transmitted between two power transmission electrodes120possessed by the power transmission apparatus100and two power reception electrodes220possessed by the power reception apparatus200.

The power transmission apparatus100includes a power transmission circuit110that converts DC power supplied from an external DC power supply310to AC power and outputs the resultant AC power, a first parallel resonance circuit130connected to the power transmission circuit110, a second parallel resonance circuit140magnetically coupled to the first parallel resonance circuit130, and two power transmission electrodes120connected to the second parallel resonance circuit140. The first parallel resonance circuit130includes a coil L1and a capacitor C1that are connected to each other in parallel. The second parallel resonance circuit140includes a coil L2and a capacitor C2that are connected to each other in parallel. The coil L1and the coil L2from a transformer in which the coil L1and the coil L2are coupled to each other with a coupling coefficient k1. The turn ratio (1:N1) between the coil L1and the coil L2is set to a value so as to achieve a desired voltage transformation ratio.

The power reception apparatus200includes the pair of power reception electrodes220that receives AC power transmitted from the pair of power transmission electrodes120, a third parallel resonance circuit230connected to the pair of power reception electrodes220, a fourth parallel resonance circuit240magnetically coupled to the third parallel resonance circuit230, and a power reception circuit210that converts AC power output from the fourth parallel resonance circuit240to DC power and supplies the resultant DC power to a load330. The third parallel resonance circuit230is configured such that a coil L3and a capacitor C3are connected in parallel. The fourth parallel resonance circuit240is configured such that a coil L4and a capacitor C4are connected in parallel. The coil L3and the coil L4from a transformer in which the coil L3and the coil L4are coupled to each other with a coupling coefficient k2. The turn ratio (N2:1) between the coil L3and the coil L4is set to a value so as to achieve a desired voltage transformation ratio.

The first parallel resonance circuit130, the second parallel resonance circuit140, the third parallel resonance circuit230, and the fourth parallel resonance circuit240are all equal in terms of the resonance frequency, and the power transmission circuit110outputs AC power with the frequency equal to this resonance frequency. This makes it possible for each parallel resonance circuit to be in a resonant state and be high in impedance when electric power is transmitted.

The power transmission electrode120and the power reception electrode220are disposed close to each other such that they oppose each other. A dielectric material320(for example, a floor surface) with a high relative permittivity is disposed between the power transmission electrode120and the power reception electrode220. In the related technique configured in the above-described manner, electric power is transmitted in a state in which the capacitance Cm1and the capacitance Cm2between the two power transmission electrodes120and the two power reception electrodes220are set to be as high as possible so as to make it possible to stably transmit electric power even when a deviation occurs in a relative position between the power transmission electrodes120and the power reception electrodes220. By setting the capacitance Cm1and the capacitance Cm2to be as large as possible, the power transmission electrode120and the power reception electrode220are made to have extremely low impedance compared with the impedance of the third parallel resonance circuit230and the fourth parallel resonance circuit240in the resonant state. Therefore, even in a case where a deviation in relative position occurs between the power transmission electrodes120and the power reception electrodes220and thus a change occurs in the capacitance Cm1or Cm2, it is possible to reduce a change in voltage applied to the load330.

In the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2010-193692, as described above, it is necessary to set the capacitance Cm1and the capacitance Cm2to be large in order to reduce the impedance of the electrodes. To achieve this necessity, the distance between the electrodes is set to be as small as possible, and the high-permittivity dielectric material320is disposed between the electrodes.

However, in this wireless power transmission system configured in the above-described manner, there is a restriction on the relative position between the power transmission apparatus100and the power reception apparatus200. To make it possible to use the wireless power transmission system in a wide variety of applications, it is desirable that a high transmission efficiency can be maintained even in a case where the dielectric material between the electrodes is replaced by an air gap or in a case where the distance between the electrodes is relatively large (for example, 10 mm to several ten mm).

The inventors of the present application have found that in the configuration shown inFIG. 13, when the dielectric material320is removed or the distance between the electrodes is increased, an increase occurs n impedance between the electrodes and it becomes difficult to achieve impedance matching. This problem is described further referring toFIG. 14AandFIG. 14B.

FIG. 14Aillustrates a relationship in terms of impedance between units in the configuration shown inFIG. 13.FIG. 14Billustrates a relationship in terms of impedance between units for a case where the dielectric material320is removed from the configuration shown inFIG. 13and the distance between the electrodes is increased. As shown inFIG. 14A, in the case where the dielectric material320exists between the electrodes and the distance between the electrodes is small, the impedance between the electrode has a small value, for example, several Ω. In this case, it is relatively easy to achieve impedance matching between the impedance Z1of the power transmission circuit110and the impedance Z2of the power transmission electrode120, and it is also relatively easy to achieve impedance matching between the impedance Z3of the power reception electrode220and the impedance Z4of the load side.

However, as shown inFIG. 14B, in the case where the dielectric material320is removed and the distance between the electrodes is increased to, for example, about 10 mm, the capacitance becomes very small. When the angular frequency of the AC power transmitted is denoted by co, a relation of Z=1/(ωC) holds between the impedance Z and the capacitance C. Therefore, when the capacitance becomes very small, the impedance between the electrodes becomes very large (for example, the impedance may be several kΩ). In this case, the impedance Z2and the impedance Z3on the electrode side become too large compared with the impedance Z1of the power transmission circuit110and the impedance Z4(for example, several Ω) of the power reception circuit, and thus it becomes difficult to achieve impedance matching. As a result, it becomes impossible to achieve a high electric power transmission efficiency.

The problem described above arises from the configuration shown inFIG. 13in which each of the power transmission apparatus100and the power reception apparatus200has a combination of two parallel resonance circuits. The inventors of the present application have found that it is possible to solve the problem described above by configuring at least one of the power transmission apparatus100and the power reception apparatus200such that the two resonance circuits thereof are formed so as to have a combination of a series resonance circuit and a parallel resonance circuit. This configuration is described below with reference toFIG. 15AandFIG. 15B.

FIG. 15Aillustrates a resonator configuration in the power transmission apparatus100according to the related technique.FIG. 15Billustrates a configuration obtained by replacing the resonance circuit on the power-supply side (left side inFIG. 15A) in the configuration shown inFIG. 15Aby a series resonance circuit. In the configuration according to the related technique shown inFIG. 15A, the resonators located on both the power-supply side and the electrode side (the right-hand side inFIG. 15A) are configured in the parallel resonance circuit, and thus both resonators have infinite impedance in the resonant state (in which the frequency f becomes equal to the resonance frequency f0). Therefore, it is difficult to achieve impedance matching between the low impedance on the power-supply side and the high impedance on the electrode side.

In contrast, in the configuration shown inFIG. 15B, the resonance circuit on the power-supply side is formed in the series resonance circuit, and thus it is possible to achieve impedance matching between the low impedance on the power-supply side and the high impedance on the electrode side. In the series resonance circuit, the impedance becomes zero (0) in the resonant state, and thus the series resonance circuit is suitable for achieving matching with low impedance. On the other hand, in the parallel resonance circuit, the impedance becomes infinite in the resonant state, and thus the parallel resonance circuit is suitable for achieving matching with high impedance. Thus, it is possible to easily achieve impedance matching by disposing a series resonance circuit on the power-supply side with low impedance and a parallel resonance circuit on the electrode side with high impedance as in the configuration shown inFIG. 15B.

The technique described above can be applied not only to the power transmission apparatus100but also to the power reception apparatus200. That is, it is possible to preferably achieve impedance matching in the power reception apparatus200by disposing a parallel resonance circuit on the electrode side and a series resonance circuit on the load side.

Based on the knowledge described above, the present inventors have got ideas of various aspects of the present disclosure as described below.

In an aspect, the present disclosure provides a wireless power transmission system including a power transmission apparatus and a power reception apparatus, the power transmission apparatus including: a power transmission circuit that converts DC power of an external DC power supply to AC power, a first coil connected to the power transmission circuit, a second coil inductively coupled to the first coil, and two power transmission electrodes that are connected to the second coil and that transmit the AC power, the power reception apparatus including two power reception electrodes disposed opposing the two power transmission electrodes so as to be capacitively coupled with the two power transmission electrodes to contactlessly receive the transmitted AC power, a third coil connected to the two power reception electrodes, a fourth coil connected to the third coil, and a power reception circuit that is connected to the fourth coil and that converts the received AC power to DC power, the wireless power transmission system having at least one of the following combinations: a combination of i) a transmission-side series resonance circuit including the first coil and a first capacitor disposed between the first coil and the power transmission circuit, and ii) a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and a combination of i) a reception-side parallel resonance circuit including the third coil and a third capacitor disposed between the third coil and the two power reception electrodes, and ii) a reception-side series resonance circuit including the fourth coil and a fourth capacitor disposed between the fourth coil and the power reception circuit.

In this aspect described above, the wireless power transmission system has at least one of the following combinations: the combination of i) a transmission-side series resonance circuit including the first coil and a first capacitor disposed between the first coil and the power transmission circuit, ii) a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and the combination of i) a reception-side parallel resonance circuit including the third coil and a third capacitor disposed between the third coil and the two power reception electrodes, and ii) a reception-side series resonance circuit including the fourth coil and a fourth capacitor disposed between the fourth coil and the power reception circuit.

Thus, a parallel resonance circuit is disposed on a side close to electrodes at least in one of the power transmission apparatus and the power reception apparatus, and a series resonance circuit is disposed on a side far from the electrodes. This makes it possible to preferably achieve impedance matching even in a case where the impedance between electrodes is high.

Specific embodiments of the present disclosure are described below. Note that a description in unnecessary detail may be omitted. For example, a detailed description of an already well known fact or item, or a duplicated description of substantially the same element may be omitted in order to prevent the following description from being unnecessarily redundant thereby making it possible for those skilled in the art to easily understand the description. It should be noted that the present inventors provide accompanying drawing and the following description in order to allow those skilled in the art to well understand the present disclosure but not to limit the subject matter of the present disclosure to the scope described in claims. In the following description, the same or similar constituent elements are denoted by the same reference symbols.

First Embodiment

First, a first embodiment of the present disclosure is described.

FIG. 1is a diagram schematically illustrating a wireless power transmission system according to the present embodiment. In this example, electric power is wirelessly transmitted from a power transmission apparatus having a pair of power transmission electrodes120embedded below a floor surface30to a transport robot10having a pair of power reception electrodes. In this system, the wireless power transmission is performed using the electric field coupling technique described above. The pair of power transmission electrodes120extends in parallel along the floor surface30over which the transport robot10is capable of conveying an object while receiving electric power.

FIG. 2is a block diagram illustrating an outline of a configuration of the wireless power transmission system according to the present embodiment. This system includes a power transmission apparatus100, and a transport robot10. The power transmission apparatus100includes a power transmission circuit110that converts DC power supplied from an external DC power supply310to AC power, a transmission-side series resonance circuit130sconnected to the power transmission circuit110, a transmission-side parallel resonance circuit140pinductive coupled with the transmission-side series resonance circuit130s, and two power transmission electrodes120that are connected to the transmission-side parallel resonance circuit140pand transmit AC power. The transport robot10includes a power reception apparatus200and a load330. The power reception apparatus200includes two power reception electrodes220that are capacitively coupled with the two power transmission electrodes120and contactlessly receive the transmitted AC power, a reception-side parallel resonance circuit230pconnected to the two power reception electrodes220, a reception-side series resonance circuit240sinductively coupled with the reception-side parallel resonance circuit230p, and a power reception circuit210that are connected to the reception-side series resonance circuit240sand that converts the received AC power to DC power and outputs the resultant DC power. The load330includes, for example, a secondary battery and a motor, and is charged or driven by the DC power output from the power reception circuit210.

FIG. 3is a circuit diagram illustrating an outline of a configuration of the wireless power transmission system according to the present embodiment. As shown inFIG. 3, the transmission-side series resonance circuit130sin the power transmission apparatus100is configured such that a first coil L1and a first capacitor C1are connected in series. The transmission-side parallel resonance circuit140pin the power transmission apparatus100is configured such that a second coil L2and a second capacitor C2are connected in parallel. The first coil L1and the second coil L2from a transformer in which the coil L1and the coil L2are coupled to each other with a coupling coefficient k1. The turn ratio (1:N1) between the first coil L1and the second coil L2is set to a value so as to achieve a desired voltage transformation ratio.

The reception-side parallel resonance circuit230pin the power reception apparatus200is configured such that a third coil L3and a third capacitor C3are connected in parallel. The reception-side series resonance circuit240sin the power reception apparatus200is configured such that a fourth coil L4and a fourth capacitor C4are connected in series. The third coil and the fourth coil from a transformer in which the coil L3and the coil L4are coupled to each other with a coupling coefficient k2. The turn ratio (N2:1) between the third coil L3and the fourth coil L4is set to a value so as to achieve a desired voltage transformation ratio (a step-up ratio or a step-down ratio).

As described above, the wireless power transmission system according to the present embodiment includes both of the following combinations: the combination of transmission-side series resonance circuit130sand the transmission-side parallel resonance circuit140p, and the combination of the reception-side parallel resonance circuit230pand the reception-side series resonance circuit240s.

Each constituent element is described in further detail below. Note that in the present description, reference symbols L1, L2, L3, and L4used to denote inductors are also used to denote inductance values of the corresponding inductors. Similarly, reference symbols C1, C2, C3, and C4used to denote capacitors are also used to denote capacitance values of the corresponding capacitors.

FIG. 4is a diagram schematically illustrating an example of a configuration of the power transmission circuit110. In this example, the power transmission circuit110includes a full-bridge inverter circuit including four switching elements (for example, transistors such as IGBTs, MOSFETs, or the like) and a control circuit112. The control circuit112includes a gate driver that outputs a control signal to control an on-state (conduction state) and an off-state (non-conduction state) of each switching element, and a processor such as a microcontroller or the like for controlling the gate driver to output the control signal. Alternatively, instead of the full-bridge inverter circuit shown in the figure, a half-bridge inverter circuit or another type of oscillation circuit such as an E-class oscillation circuit may be used. The power transmission circuit110may include a modulation-demodulation circuit for communication, and various sensors for measuring a voltage, a current, or the like.

FIG. 5is a diagram schematically illustrating an example of a configuration of the power reception circuit210. In this example, the power reception circuit210is a full-wave rectifying circuit including a diode bride and a smoothing capacitor. However, the power reception circuit210may be configured in the form of another type of rectifier. The power reception circuit210may include, in addition to the rectification circuit, other various circuits such as a constant voltage/constant current control circuit, a modulation-demodulation circuit for communication, or the like. The power reception circuit210converts the received AC energy to DC energy usable by the load330. The power reception circuit210may further include various sensors for measuring a voltage, a current, or the like output from the reception-side series resonance circuit240s.

In the transmission-side series resonance circuit130sthe transmission-side parallel resonance circuit140p, the reception-side parallel resonance circuit230p, and the reception-side series resonance circuit240s, each coil used therein may be, for example, a planar coil or a multilayer coil formed on a circuit board, or a winding coil using a copper wire, a litz wire, or a twisted wire. In the transmission-side series resonance circuit130s, the transmission-side parallel resonance circuit140p, the reception-side parallel resonance circuit230p, and the reception-side series resonance circuit240s, each capacitor may be a capacitor of any type, for example, a capacitor having a chip shape or a lead shape. Capacitance formed between two wirings via air may be used as each capacitor. Instead of using capacitors, a self-resonance characteristic possessed by each coil may be used.

The DC power supply310may be an arbitrary power supply such as a commercial power supply, a primary battery, a secondary battery, a solar battery, a fuel battery, a USB (Universal Serial Bus) power supply, a high-capacitance capacitor (for example, an electric double-layer capacitor), a voltage transformer connected to a commercial power supply, or the like.

In the transmission-side series resonance circuit130s, the transmission-side parallel resonance circuit140p, the reception-side parallel resonance circuit230p, and the reception-side series resonance circuit240s, the resonance frequency f0thereof is set to be equal to the transmission frequency fin the electric power transmission state. Note that the resonance frequency f0of each of the transmission-side series resonance circuit130s, the transmission-side parallel resonance circuit140p, the reception-side parallel resonance circuit230p, and the reception-side series resonance circuit240sdoes not need to be exactly equal to the transmission frequency f0. Each resonance frequency f0may be set, for example, in a range of 50% to 150% of the transmission frequency f. The frequency fin the electric power transmission may be set, for example, in a range from 50 Hz to 300 GHz and more preferably from 20 kHz to 10 GHz, still more preferably from 20 kHz to 20 MHz, and still more preferably from 20 kHz to 1 MHz.

In the present embodiment, there is an air gap between the power transmission electrode120and the power reception electrode220, and the distance between them is set to be relatively large (for example, about 10 mm). Therefore, the capacitance Cm1and the capacitance Cm2between the electrodes are very small, and the impedance of the power transmission electrode120and the impedance of the power reception electrode220is very high (for example, about several kΩ). In contrast, the impedances of the power transmission circuit110and the power reception circuit210are as small as, for example, several Ω. Therefore, in the present embodiment, the transmission-side parallel resonance circuit140pand the reception-side parallel resonance circuit230pare respectively disposed on sides close to the power transmission electrode120and the power reception electrode220, and the transmission-side series resonance circuit130sand the reception-side series resonance circuit240sare respectively disposed on sides close to the power transmission circuit110and the power reception circuit210.

This configuration makes it possible to easily achieve the impedance matching. As a result, it becomes possible to transmit electric power with a higher efficiency than is conventionally achieved as described later.

Second Embodiment

Next, a second embodiment of the present disclosure is described.

FIG. 6is a circuit diagram illustrating an outline of a configuration of the wireless power transmission system according to the present embodiment. The present embodiment is different from the first embodiment in that the power reception apparatus200includes a circuit230cincluding a third coil L3instead of the reception-side parallel resonance circuit230pin the first embodiment. In this configuration, the inductance value L4of the fourth coil L4is smaller than the inductance value L3of the third coil L3. Except for the above, the present embodiment is similar to the first embodiment.

That is, in the wireless power transmission system according to the present embodiment, the power transmission apparatus100has a combination of i) a transmission-side series resonance circuit130sincluding a first coil and a first capacitor disposed between the first coil and a power transmission circuit110, and ii) a transmission-side parallel resonance circuit140pincluding a second coil and a second capacitor disposed between the second coil and two power transmission electrodes120. On the other hand, the power reception apparatus200has a combination of i) the third coil with the inductance value L3and ii) a reception-side series resonance circuit240sincluding a fourth coil with an inductance value L4lower than the inductance value L3and a fourth capacitor disposed between the fourth coil and the power reception circuit210.

In the present embodiment, the power transmission apparatus100has a combination of a series resonance circuit and a parallel resonance circuit although the power reception apparatus200does not have a combination of a series resonance circuit and a parallel resonance circuit. This configuration makes it possible to easily achieve impedance matching in the power transmission apparatus100. Thus, also in the configuration according to the present embodiment, it is possible to achieve a higher transmission efficiency than is conventionally achieved as described later.

Third Embodiment

Next, a third embodiment of the present disclosure is described.

FIG. 7is a circuit diagram illustrating an outline of a configuration of the wireless power transmission system according to the present embodiment. The present embodiment is different from the first embodiment in that the power transmission apparatus100includes a circuit140cincluding a second coil L2instead of the transmission-side parallel resonance circuit140pin the first embodiment. In this embodiment, the inductance value L2of the second coil L2is greater than the inductance value L1of the first coil L1. Except for the above, the present embodiment is similar to the first embodiment.

That is, the power transmission apparatus100according to the present embodiment has a combination of i) a transmission-side series resonance circuit130sincluding the first coil with the inductance value L1and a first capacitor disposed between the first coil and a power transmission circuit110, and ii) the second coil with the inductance value L2higher than the inductance value L1. On the other hand, the power reception apparatus200has a combination of i) a reception-side parallel resonance circuit230pincluding a third coil and a third capacitor disposed between the third coil and two power reception electrodes220, and ii) a reception-side series resonance circuit240sincluding the fourth coil and a fourth capacitor disposed between the fourth coil and a power reception circuit210.

In the present embodiment, the power reception apparatus200has a combination of a series resonance circuit and a parallel resonance circuit although the power transmission apparatus100does not have a combination of a series resonance circuit and a parallel resonance circuit. This configuration makes it possible to easily achieve impedance matching in the power reception apparatus200. Thus, also in the configuration according to the present embodiment, it is possible to achieve a higher transmission efficiency than is conventionally achieved as described later.

Fourth Embodiment

Next, a fourth embodiment of the present disclosure is described.

FIG. 8is a circuit diagram illustrating an outline of a configuration of the wireless power transmission system according to the present embodiment. The present embodiment is different from the first embodiment in that the power transmission apparatus100includes a parallel resonance circuit130pinstead of the transmission-side series resonance circuit130sin the first embodiment. Except for the above, the present embodiment is similar to the first embodiment.

In the present embodiment, the power reception apparatus200has a combination of a series resonance circuit and a parallel resonance circuit although the power transmission apparatus100does not have a combination of a series resonance circuit and a parallel resonance circuit. This configuration makes it possible to easily achieve impedance matching in the power reception apparatus200. Thus, also in the configuration according to the present embodiment, it is possible to achieve a higher transmission efficiency than is conventionally achieved as described later.

Fifth Embodiment

Next, a fifth embodiment of the present disclosure is described.

FIG. 9is a circuit diagram illustrating an outline of a configuration of the wireless power transmission system according to the present embodiment. The present embodiment is different from the first embodiment in that the power reception apparatus200includes a reception-side parallel resonance circuit230pinstead of the reception-side series resonance circuit240sin the first embodiment. Except for the above, the present embodiment is similar to the first embodiment.

In the present embodiment, the power transmission apparatus100has a combination of a series resonance circuit and a parallel resonance circuit although the power reception apparatus200does not have a combination of a series resonance circuit and a parallel resonance circuit. This configuration makes it possible to easily achieve impedance matching in the power transmission apparatus100. Thus, also in the configuration according to the present embodiment, it is possible to achieve a higher transmission efficiency than is conventionally achieved as described later.

EXAMPLES

Next, examples of the present disclosure are described.

The inventors of the present disclosure performed circuit simulations for wireless power transmission systems configured according to the first to fifth embodiments, and made comparisons with the configuration of the comparative example shown inFIG. 13thereby verifying the advantageous effects of the embodiments of the present disclosure.

FIG. 10is a diagram schematically illustrating a positional relationship between a pair of power transmission electrodes120and a pair of power reception electrodes220in an example and the comparative example. The two power transmission electrodes120are disposed in parallel via a gap of 100 mm, and the two power reception electrodes220are disposed opposing the two power transmission electrodes120. The size of each power transmission electrode120was set to 100 mm×1000 mm2, and the size of each power reception electrode220was set to 100 mm×400 mm2. The distance between the power transmission electrode120and the power reception electrode220was set to 10 mm.

FIG. 11is a diagram illustrating an equivalent circuit of the power transmission electrodes120and the power reception electrodes220. Let Cm1and Cm2denote the capacitances of two capacitors formed by the two power transmission electrodes120and the two power reception electrodes220. Let C22denote the capacitance between the two power transmission electrodes120, and let C33denote the capacitance between the two power reception electrodes220. In this example and the comparative example, the capacitances were set such that Cm1=Cm2=93.2 pF, C22=44.5 pF, and C33=9.89 pF. In a case where a parallel resonance circuit is formed using C22or C33, C2or C3may be omitted. Other parameters were set such that the inductance value L2of the second coil and the inductance value L3of the third coil were both set to 100 μH. The Q-value of a matching transformer formed by a combination of a series resonance circuit and a parallel resonance circuit was to 300. Herein, the ratio, L2/L1, of the inductance value L2of the second coil to the inductance value L1of the first coil is denoted by an inductance ratio N1. Similarly, the ratio, L3/L4, of the inductance value L3of the third coil to the inductance value L4of the fourth coil is denoted by an inductance ratio N2. Note that the inductance ratio equal to a turn ratio. The transmission frequency f was set to 480 kHz.

As for each coil, a spiral coil with a diameter of 80 mm was used which was formed in two layers using a litz wire including 375 element wires each having a diameter of 40 μm. A magnetic shield was disposed at each location 20 mm above and 20 mm below each coil. The inductance L2of the second coil and the inductance L3of the third coil on the high-impedance side were fixed to 100 μH, and the inductance L1of the first coil and the inductance L4of the fourth coil on the low-impedance side were adjusted so as to achieve as good impedance matching as possible.

Table 1 shows the inductance ratios (turn ratios) N1and N2, the coupling coefficients k1and k2, and electric power transmission efficiencies for the configurations according to the first to fifth embodiments and the comparative example. Table 2 shows capacitance values C1to C4for the respective configurations.

Each parameter shown in Tables 1 and 2 was set in each configuration so as to minimize the reduction in efficiency caused by impedance mismatching. As shown in Table 1, in the configurations having at least one combination of a series resonance circuit and a parallel resonance circuit according to the first to fifth embodiments, it has been confirmed that a higher efficiency is achieved than is achieved in the configuration of the comparative example. Note that in the configuration of the comparative example, to minimize the impedance mismatching, the turn ratios N1and N2were set to as very large a value as20. Such a large turn ratio is not usually used because a reduction in Q-value occurs. In a case where the turn ratio is set to a usually-used value in the configuration of the comparative example, impedance matching is not achieved, which results in a further reduction in transmission efficiency from the values shown in Table 1.

The effects of the embodiments of the present disclosure are greater as the impedance between the two power transmission electrodes120and the two power reception electrodes220increases. When the capacitance between the electrodes is denoted by C and the angular frequency of the transmitted electric power is denoted by ω, the impedance between the electrodes is represented as 1/(ωC), where the capacitance between the electrodes is one of the capacitance Cm1and the capacitance Cm2or the average value thereof. In a case where the impedance between the electrodes is higher, for example, than the impedance ωL2of the second coil, it is possible to achieve further enhanced effects in the embodiments of the present disclosure. Therefore, it is preferable to satisfy ωL2<1/(ωC). More preferably, each constituent element is designed such that 10 ωL2<1/(ωC) is satisfied.

Next, a description is given as to a relationship between the inductance ratio N and the Q-value in a matching transformer configured by a combination of a series resonance circuit and a parallel resonance circuit. Herein, the inductance ratio N is the ratio N1(=L2/L1) of the inductance value L2to the inductance value L1or the ratio N2(=L3/L4) of the inductance value L3to the inductance value L4. The Q-value is an index indicating the degree to which the loss is low. The loss decreases as the Q-value increases. Therefore, it is desirable to set the Q-value of the matching transformer to be as high as possible.

FIG. 12is a graph representing a relationship between the inductance ratio N and the Q-value of the matching transformer. Herein, when the Q-value of the coil (the second coil or the third coil) on the high-impedance side is denoted by QLhi, and the Q-value of the coil (the first coil or the fourth coil) on the low-impedance side is denoted by QLlo, the Q-value of the matching transformer is represented as √(QLhi*QLlo). Herein, a condition similar to that used in the verification described above was used, that is, the inductance Lhi of the coil on the high-impedance side was fixed to 100 μH, and the number of turns of the coil on the low-impedance side was changed within a range from 3 to 50 thereby changing the impedance ratio N.

As can be seen fromFIG. 12, when 1<N<15 was satisfied, the Q-value was as high as 70% or more of the peak value. Furthermore, when 3<N<8 was satisfied, the Q-value was as very high as 90% or more of the peak value. Therefore, the inductance ratio N, that is, the ratio of the inductance value L2to the inductance value L1or the ratio of the inductance value L3to the inductance value L4is designed such that 1<N<15 is preferably satisfied, and more preferably 3<N<8 is satisfied.

As described above, the present disclosure includes wireless power transmission systems and power transmission apparatuses described below in the following items.

A wireless power transmission system includes a power transmission apparatus and a power reception apparatus, the power transmission apparatus including a power transmission circuit that converts DC power of an external DC power supply to AC power, a first coil connected to the power transmission circuit, a second coil inductively coupled to the first coil, and two power transmission electrodes that are connected to the second coil and that transmit the AC power, the power reception apparatus including two power reception electrodes disposed opposing the two power transmission electrodes so as to be capacitively coupled with the two power transmission electrodes to contactlessly receive the transmitted AC power, a third coil connected to the two power reception electrodes, a fourth coil connected to the third coil, and a power reception circuit that is connected to the fourth coil and that converts the received AC power to DC power, the wireless power transmission system having at least one of the following combinations: a combination of i) a transmission-side series resonance circuit including the first coil and a first capacitor disposed between the first coil and the power transmission circuit, and ii) a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and a combination of i) a reception-side parallel resonance circuit including the third coil and a third capacitor disposed between the third coil and the two power reception electrodes, and ii) a reception-side series resonance circuit including the fourth coil and a fourth capacitor disposed between the fourth coil and the power reception circuit.

In this aspect, the wireless power transmission system has at least one of the following combinations: the combination of i) the transmission-side series resonance circuit including the first coil and the first capacitor disposed between the first coil and the power transmission circuit, and ii) the transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and the combination of i) a reception-side parallel resonance circuit including the third coil and a third capacitor disposed between the third coil and the two power reception electrodes, and ii) a reception-side series resonance circuit including the fourth coil and a fourth capacitor disposed between the fourth coil and the power reception circuit.

That is, in at least one of the power transmission apparatus and the power reception apparatus, a parallel resonance circuit is disposed on a side close to an electrode, and a series resonance circuit is disposed on a side far from the electrode, and thus it is possible to preferably achieve impedance matching even in a case where the impedance between electrodes is high.

The wireless power transmission system described in item 1 may have a combination of i) a transmission-side series resonance circuit including the first coil and the first capacitor disposed between the first coil and the power transmission circuit, and ii) a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and a combination of i) a reception-side parallel resonance circuit including the third coil and the third capacitor disposed between the third coil and the two power reception electrodes, and ii) a reception-side series resonance circuit including the fourth coil and a fourth capacitor disposed between the fourth coil and the power reception circuit.

In this aspect, in both of the power transmission apparatus and the power reception apparatus, a parallel resonance circuit is disposed on a side close to an electrode, and a series resonance circuit is disposed on a side far from electrodes, and thus it is possible to more preferably achieve impedance matching.

The wireless power transmission system described in item 1 may have a combination of i) a transmission-side series resonance circuit including the first coil and a first capacitor disposed between the first coil and the power transmission circuit, and ii) a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes, and a combination of i) the third coil with an inductance value L3and ii) a reception-side series resonance circuit including the fourth coil with an inductance value L4lower than the inductance value L3and a fourth capacitor disposed between the fourth coil and the power reception circuit.

In the aspect described above, in the power transmission apparatus, a parallel resonance circuit is disposed on a side close to an electrode, and a series resonance circuit is disposed on a side far from electrodes. Thus, it is possible to preferably achieve impedance matching.

The wireless power transmission system described in item 1 may have a combination of i) a transmission-side series resonance circuit including the first coil with an inductance value L1and the first capacitor disposed between the first coil and the power transmission circuit, and ii) the second coil with an inductance value L2higher than the inductance value L1, and a combination of i) a reception-side parallel resonance circuit including the third coil and the third capacitor disposed between the third coil and the two power reception electrodes, and ii) a reception-side series resonance circuit including the fourth coil and a fourth capacitor disposed between the fourth coil and the power reception circuit.

In the aspect described above, in the power reception apparatus, a parallel resonance circuit is disposed on a side close to an electrode, and a series resonance circuit is disposed on a side far from electrodes. Thus, it is possible to preferably achieve impedance matching.

In the wireless power transmission system described in one of items 1 to 4, an air gap may be provided between the two power transmission electrodes and the two power reception electrodes disposed opposing the two power transmission electrodes.

In the aspect described above, the electrodes are spaced apart via the air gap, and it is not necessary to provide a dielectric material with high relative permittivity, which makes it possible to simplify the configuration between electrodes.

In the wireless power transmission system described in one of items 1 to 5, when the AC power has an angular frequency co, the second coil has an inductance value L2, and the capacitance between the two power transmission electrodes and the two power reception electrodes has a capacitance value C, a condition described in the following mathematical expression (1) may be satisfied:
ωL2<1/(ωC)  (1).

In the aspect described above, the impedance between the electrodes is higher than the impedance of the second coil, and thus it is possible to achieve further enhanced effects of the impedance matching.

In the wireless power transmission system described in one of items 1 to 5, when the AC power has an angular frequency co, the second coil has an inductance value L2, and the capacitance between the two power transmission electrodes and the two power reception electrodes has a capacitance value C, a condition described in the following mathematical expression (3) may be satisfied:
10 ωL2<1/(ωC)  (3)

In the aspect described above, the impedance between the electrodes is extremely higher than the impedance of the second coil, and thus it is possible to achieve further extremely enhanced effects of the impedance matching.

In the wireless power transmission system described in one of items 1 to 7, when the first coil has an inductance value L1, and the second coil has an inductance value L2, an inductance ratio N(=L2/L1) of the inductance value L2to the inductance value L1may satisfy a condition described in the following mathematical expression:
1<N<15.

In the aspect described above, it is possible to achieve the Q-value being as high as, for example, 70% or more of the peak value.

In the wireless power transmission system described in one of items 1 to 8, when the first coil has an inductance value L1, and the second coil has an inductance value L2, an inductance ratio N(=L2/L1) of the inductance value L2to the inductance value L1may satisfy a condition described in the following mathematical expression:
3<N<8.

In the aspect described above, it is possible to achieve the Q-value being as high as, for example, 90% or more of the peak value.

In the wireless power transmission system described in one of items 1 to 9, when the third coil has an inductance value L3, and the fourth coil has an inductance value L4, an inductance ratio N(=L3/L4) of the inductance value L3to the inductance value L4may satisfy a condition described in the following mathematical expression:
1<N<15.

In the aspect described above, it is possible to achieve the Q-value being as high as, for example, 70% or more of the peak value.

In the wireless power transmission system described in one of items 1 to 9, when the third coil has an inductance value L3, and the fourth coil has an inductance value L4, an inductance ratio N(=L3/L4) of the inductance value L3to the inductance value L4may satisfy a condition described in the following mathematical expression:
3<N<8.

In the aspect described above, it is possible to achieve the Q-value being as high as, for example, 90% or more of the peak value.

A power transmission apparatus in a wireless power transmission system includes the power transmission apparatus and a power reception apparatus, the power transmission apparatus including a power transmission circuit that converts DC power of an external DC power supply to AC power, a first coil connected to the power transmission circuit, a second coil inductively coupled to the first coil, two power transmission electrodes that are connected to the second coil and that transmit the AC power, the power reception apparatus including two power reception electrodes disposed opposing the two power transmission electrodes so as to be capacitively coupled with the two power transmission electrodes to contactlessly receive the transmitted AC power, a third coil connected to the two power reception electrodes, a fourth coil connected to the third coil, and a power reception circuit that is connected to the fourth coil and that converts the received AC power to DC power, the power transmission apparatus having a combination of a transmission-side series resonance circuit including the first coil and a first capacitor disposed between the first coil and the power transmission circuit, and a transmission-side parallel resonance circuit including the second coil and a second capacitor disposed between the second coil and the two power transmission electrodes.

In the aspect described above, the power transmission apparatus has the combination of the transmission-side series resonance circuit including the first coil and the first capacitor disposed between the first coil and the power transmission circuit, and the transmission-side parallel resonance circuit including the second coil and the second capacitor disposed between the second coil and the two power transmission electrodes. In this configuration, in the power transmission apparatus, a parallel resonance circuit is disposed on a side close to an electrode, and a series resonance circuit is disposed on a side far from the electrode. This makes it possible to advantageously achieve impedance matching even in a case where the impedance between electrodes is high.

In the power transmission apparatus described in item 12, wherein an air gap may be provided between the two power transmission electrodes and the two power reception electrodes disposed opposing the two power transmission electrodes.

In the aspect described above, the electrodes are spaced apart via the air gap, and it is not necessary to provide a dielectric material with high relative permittivity, which makes it possible to simplify the configuration between electrodes.

In the power transmission apparatus described in item 12 or 13, when the AC power has an angular frequency ω, the second coil has an inductance value L2, and the capacitance between the electrodes has a capacitance value C, a condition described in the following mathematical expression (4) may be satisfied:
ωL2<1/(ωC)  (4).

In the aspect described above, the impedance between the electrodes is higher than the impedance of the second coil, and thus it is possible to achieve further enhanced effects of the impedance matching.

In the power transmission apparatus described in item 12 or 13, when the AC power has an angular frequency ω, the second coil has an inductance value L2, and the capacitance between the two power transmission electrodes and the two power reception electrodes has a capacitance value C, a condition described in the following mathematical expression (5) may be satisfied:
10ωL2<1/(ωC)  (5).

In the aspect described above, the impedance between the electrodes is extremely higher than the impedance of the second coil, and thus it is possible to achieve further extremely enhanced effects of the impedance matching.

In the wireless power transmission system described in one of items 12 to 15, when the first coil has an inductance value L1, and the second coil has an inductance value L2, an inductance ratio N(=L2/L1) of the inductance value L2to the inductance value L1may satisfy a condition described in the following mathematical expression:
1<N<15.

In the aspect described above, it is possible to achieve the Q-value being as high as, for example, 70% or more of the peak value.

In the wireless power transmission system described in one of items 12 to 15, when the first coil has an inductance value L1, and the second coil has an inductance value L2, an inductance ratio N(=L2/L1) of the inductance value L2to the inductance value L1may satisfy a condition described in the following mathematical expression:
3<N<8.

In the aspect described above, it is possible to achieve the Q-value being as high as, for example, 90% or more of the peak value.

The technique of the present disclosure may be used in an apparatus such as a surveillance camera, a robot, or the like in which, in addition to electric power transmission, real-time bidirectional transmission of data is necessary. According to embodiments of the present disclosure, it is possible to perform full-duplex bidirectional data transmission between a power transmission apparatus and a power reception apparatus.