POSITION DETECTION SYSTEM AND ELECTRIC POWER TRANSMISSION SYSTEM

An antenna is provided in one device from among a power transmission device and a power reception device. A transmission circuit drives the antenna. A plurality of antennas is provided in the other device from among the power transmission device and the power reception device. A radio wave detection circuit detects intensity of a radio wave received by the plurality of antennas. A position detector detects a relative position between the power transmission coil and the power reception coil, based on the intensity detected by the radio wave detection circuit. A transmission circuit drives at least one antenna. The radio wave detection circuit detects intensity of a radio wave being transmitted from an antenna driven by the transmission circuit and being received by an antenna other than the antenna driven by the transmission circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No. 2021-11687, filed on Jan. 28, 2021, the entire disclosure of which is incorporated by reference herein.

FIELD

This application relates generally to a position detection system and an electric power transmission system.

BACKGROUND

A wireless electric power transmission technology for wirelessly transmitting electric power has been receiving attention. The wireless electric power transmission technology can wirelessly transmit electric power from a power transmission device to a power reception device, and therefore application of the technology to various products such as transportation equipment such as an electric train and an electric vehicle, a home appliance, wireless communication equipment, and a toy is expected. A power transmission coil and a power reception coil coupled to each other by magnetic flux are used for transmission of electric power in the wireless electric power transmission technology.

In order to efficiently transmit electric power, a coil axis of the power transmission coil needs to be precisely aligned with a coil axis of the power reception coil. In order to precisely align the coil axes, a relative position between the power transmission coil and the power reception coil needs to be precisely detected. Unexamined Japanese Patent Application Publication No. 2020-198689 describes a technology for detecting a relative position between a power transmission coil and a power reception coil by using a radio wave in the low frequency (LF) band.

In the technology described in Unexamined Japanese Patent Application Publication No. 2020-198689, a relative position between the power transmission coil and the power reception coil is detected based on intensity of a radio wave acquired for each combination of a transmission antenna and a reception antenna at the time of detection of the relative position and predetermined reference data. The reference data are data indicating, for each combination of a transmission antenna and a reception antenna, a reference of a correspondence between a relative position between the power transmission coil and the power reception coil, and intensity of a radio wave received by the reception antenna. For example, the reference data are acquired by using a reference position detection system before executing detection of a relative position. The reference position detection system is basically a position detection system similar to a position detection system used for detection of a relative position.

SUMMARY

In order to precisely detect a relative position by using the reference data, a difference in the antenna characteristics of antennas including the transmission antenna and the reception antenna is required not to exist between the time of acquisition of the reference data and the time of detection of the relative position. However, the antenna characteristic of an antenna used when the reference data are acquired may differ from the antenna characteristic of an antenna used for detection of a relative position due to individual differences between antenna characteristics caused in a manufacturing process of antennas, a change in an environment around the antennas, and the like.

Therefore, calibration is preferably executed when a relative position is detected, in order to align the antenna characteristic of the antenna used for detection of the relative position with the antenna characteristic of the antenna used when the reference data are acquired. However, the technology described in Unexamined Japanese Patent Application Publication No. 2020-198689 does not have a mechanism for achieving such calibration and therefore may not precisely detect a relative position. Therefore, a position detection system precisely detecting a relative position between a power transmission coil and a power reception coil in wireless electric power transmission is desired.

The present disclosure has been made in view of the aforementioned problem, and an objective of the present disclosure is to precisely detect a relative position between a power transmission coil and a power reception coil in wireless electric power transmission.

In order to solve the aforementioned problem, a position detection system according to an embodiment of the present disclosure

is a position detection system for an electric power transmission system wirelessly transmitting electric power from a power transmission coil included in a power transmission device to a power reception coil included in a power reception device and includes:

at least one first antenna provided in one device from among the power transmission device and the power reception device;

a first transmission circuit driving the at least one first antenna;

a plurality of second antennas provided in the other device from among the power transmission device and the power reception device;

a radio wave detection circuit detecting intensity of a radio wave received by the plurality of second antennas;

a position detector detecting a relative position between the power transmission coil and the power reception coil, based on the intensity detected by the radio wave detection circuit; and

a second transmission circuit driving at least one second antenna from among the plurality of second antennas,

wherein the radio wave detection circuit detects intensity of a radio wave being transmitted from a second antenna driven by the second transmission circuit from among the plurality of second antennas and being received by another second antenna being a second antenna other than the second antenna driven by the second transmission circuit from among the plurality of second antennas.

The aforementioned configuration can precisely detect a relative position between a power transmission coil and a power reception coil in wireless electric power transmission.

DETAILED DESCRIPTION

Electric power transmission systems according to embodiments of a technology according to the present disclosure will be described below referring to drawings. Note that, in the following embodiments, the same components are given the same sign. Further, the ratio in size between components and the shapes of the components that are illustrated in each diagram are not necessarily the same as those in implementation.

An electric power transmission system according to the present embodiment can be used for charging secondary batteries in various devices such as an electric vehicle (EV), mobile equipment such as a smartphone, and industrial equipment. An example of the electric power transmission system executing charging of a storage battery in an EV will be described below.

FIG. 1is a diagram illustrating a schematic configuration of an electric power transmission system1000used for charging of a storage battery500included in an electric vehicle700. The electric vehicle700travels with a motor driven by electric power charged in the storage battery500such as a lithium-ion battery or a lead storage battery as a power source. The electric vehicle700is an example of a movable body.

As illustrated inFIG. 1, the electric power transmission system1000is a system wirelessly transmitting electric power from a power transmission device200to a power reception device300by magnetic coupling. The electric power transmission system1000includes a position detection system100detecting a relative position between a power transmission coil and a power reception coil, a power transmission device200wirelessly transmitting electric power of an alternating-current (AC) or direct-current (DC) commercial power source400to the electric vehicle700, and a power reception device300receiving the electric power transmitted by the power transmission device200and charging the storage battery500. Note that the commercial power source400is an AC power source in the following description. Further, details of the position detection system100will be described later.

The power transmission device200is a device wirelessly transmitting electric power to the power reception device300by magnetic coupling. The power transmission device200includes a power transmission coil unit210transmitting AC power to the electric vehicle700and an electric power supply device220supplying AC power to the power transmission coil unit210.

FIG. 2illustrates main parts of the power transmission coil unit210and main parts of a power reception coil unit310. As illustrated inFIG. 2, the power transmission coil unit210includes a power transmission coil211being supplied with AC power from the electric power supply device220and inducing alternating magnetic flux1, and a magnetic body plate212provided for improving the inductance value of the power transmission coil211. The power transmission coil211is formed by spirally winding a conducting wire around a coil axis213on the magnetic body plate212. The power transmission coil211and a capacitor provided at each of two ends of the power transmission coil211form a resonant circuit and induce alternating magnetic flux Φ by AC current flowing according to application of AC voltage. InFIG. 2, an axis in an upward vertical direction is a Z-axis, an axis orthogonal to the Z-axis is an X-axis, and an axis orthogonal to the Z-axis and the X-axis is a Y-axis.

The magnetic body plate212has a plate shape with a hole in the central part and is formed of a magnetic body. For example, the magnetic body plate212is a plate-shaped member formed of ferrite being a composite oxide of iron oxide and metal. The magnetic body plate212may be formed of an aggregate of a plurality of segmented magnetic bodies, and the plurality of segmented magnetic bodies may be placed in a frame shape having an opening in the central part.

The electric power supply device220includes a power factor improvement circuit improving the power factor of commercial AC power supplied by the commercial power source400and an inverter circuit generating AC power to be supplied to the power transmission coil211. The power factor improvement circuit rectifies and boosts AC power generated by the commercial power source400and converts the power into DC power having a predetermined voltage value. The inverter circuit converts DC power generated by electric power conversion by the power factor improvement circuit into AC power at a predetermined frequency. For example, the power transmission device200is fixed on the floor surface of a parking lot.

The power reception device300is a device wirelessly receiving electric power from the power transmission device200by magnetic coupling. The power reception device300includes the power reception coil unit310receiving AC power transmitted by the power transmission device200and a power rectifier circuit320converting AC power supplied from the reception coil unit310into DC power and supplying the DC power to the storage battery500.

As illustrated inFIG. 2, the power reception coil unit310includes a power reception coil311inducing an electromotive force according to a change in the alternating magnetic flux1induced by the power transmission coil211, and a magnetic body plate312provided for improving the inductance value of the power reception coil311. The power reception coil311is formed by spirally winding a conducting wire around a coil axis313on the magnetic body plate312. The power reception coil311and a capacitor provided at each of two ends of the power reception coil311forms a resonant circuit.

The power reception coil311faces the power transmission coil211when the electric vehicle700is at a standstill at a preset position. When the power transmission coil211induces the alternating magnetic flux1by receiving electric power from the electric power supply device220, an induced electromotive force is induced at the power reception coil311by interlinkage of the alternating magnetic flux1with the power reception coil311.

The magnetic body plate312is a plate-shaped member with a hole in the central part and is formed of a magnetic body. For example, the magnetic body plate312is a plate-shaped member formed of ferrite being a composite oxide of iron oxide and metal. The magnetic body plate312may be formed of an aggregate of a plurality of segmented magnetic bodies, and the plurality of segmented magnetic bodies may be placed in a frame shape having an opening in the central part.

The rectifier circuit320generates DC power by rectifying an electromotive force induced at the power reception coil311. The DC power generated by the rectifier circuit320is supplied to the storage battery500. The power reception device300may include, between the rectifier circuit320and the storage battery500, a charging circuit converting DC power supplied from the rectifier circuit320into DC power suitable for charging the storage battery500. For example, the power reception device300is fixed to the chassis of the electric vehicle700.

The position detection system100is a system detecting a relative position between the power transmission coil211included in the power transmission device200and the power reception coil311included in the power reception device300. The position detection system100is incorporated into the electric power transmission system1000and is used for alignment of a coil axis of the power transmission coil211with a coil axis of the power reception coil311. The position detection system100detects a relative position between the power transmission coil211and the power reception coil311by using a radio wave in the LF band. The position detection system100is placed in such a way as to be split between the power transmission device200and the power reception device300.

For example, part of components of the position detection system100are placed in the power transmission coil unit210and the other components of the position detection system100are placed in the power reception coil unit310, as illustrated inFIG. 3. Specifically, an antenna110and a transmission circuit120are placed in the power reception coil unit310; and four antennas150, a transmission circuit160, and a radio wave detection circuit170are placed in the power transmission coil unit210. The four antennas150are placed at four corners of the power transmission coil unit210having an almost rectangular shape in a plan view. The antenna150is a general name for an antenna150A, an antenna150B, an antenna150C, and an antenna150D. Note thatFIG. 3illustrates only main components from among the components included in the position detection system100.

The antenna110is an antenna emitting a radio wave in the LF band. The antenna110converts a high-frequency signal supplied from the transmission circuit120into a radio wave and emits the radio wave. The antenna110according to the present embodiment is a coil formed by winding a conducting wire around a bar-shaped magnetic body. While the impedance of the antenna110includes resistance, inductive reactance, and capacitive reactance, inductive reactance is dominant. The antenna110may be hereinafter referred to as a transmission antenna. The antenna110is an example of a first antenna.

The transmission circuit120is a circuit feeding electric power to at least one antenna110and driving at least one antenna110. The transmission circuit120according to the present embodiment drives one antenna110. The transmission circuit120generates a high-frequency signal from power source voltage and supplies the generated high-frequency signal to the antenna110. The transmission circuit120includes an inverter circuit converting DC power into AC power and is pulse width modulation (PWM) controllable. The transmission circuit120includes a capacitive element forming an LC resonant circuit with the antenna110. The LC resonant circuit according to the present embodiment is an LC series resonant circuit. The frequency characteristic of the LC series resonant circuit may be hereinafter referred to as an antenna characteristic of the antenna110. The transmission circuit120is an example of a first transmission circuit.

The antenna150is an antenna for receiving a radio wave in the LF band. The antenna150captures a radio wave emitted by the antenna110, converts the captured radio wave into a high-frequency signal, and supplies the signal to the radio wave detection circuit170. The antenna150is basically formed similarly to the antenna110. In other words, the antenna150is a coil formed by winding a conducting wire around a bar-shaped magnetic body. Further, while the impedance of the antenna150includes resistance, inductive reactance, and capacitive reactance, inductive reactance is dominant. The antenna150may be hereinafter referred to as a reception antenna. The antenna150is an example of a second antenna.

The radio wave detection circuit170is a circuit detecting intensity of a radio wave received by a plurality of antennas150. The radio wave detection circuit170outputs voltage related to the amplitude of a high-frequency signal related to a radio wave received by each of the plurality of antennas150. The radio wave detection circuit170includes a second capacitive element and a first resistor forming an RLC resonant circuit with the antenna150. The RLC resonant circuit according to the present embodiment is an RLC parallel resonant circuit. The frequency characteristic of the RLC parallel resonant circuit may be hereinafter referred to as an antenna characteristic of the antenna150.

The position detection system100detects a relative position between the power transmission coil211and the power reception coil311, based on intensity detected by the radio wave detection circuit170and predetermined reference data. The reference data are data indicating, for each combination of the antenna110and the antenna150, a reference of a correspondence between a relative position between the power transmission coil211and the power reception coil311, and intensity of a radio wave received by the antenna150. For example, the reference data are acquired before detection of a relative position is executed. The reference data are data indicating a map of reference intensity and therefore may be referred to as map data.

In order to precisely detect a relative position by using the reference data, a difference in the antenna characteristics of the antenna110and the antenna150between the time of acquisition of the reference data and the time of detection of the relative position is required to be nonexistent. However, the antenna characteristics of the antenna110and the antenna150used when the reference data are acquired may differ from the antenna characteristics of the antenna110and the antenna150used for detection of the relative position due to individual differences between the antenna characteristics caused in a manufacturing process of the antenna110and the antenna150, a change in an environment around the antenna110and the antenna150, and the like.

Therefore, calibration is executed when a relative position is detected, in order to align the antenna characteristics of the antenna110and the antenna150used for detection of the relative position with the antenna characteristics of the antenna110and the antenna150used when the reference data are acquired, according to the present embodiment. In order to achieve such calibration, at least one antenna150from among a plurality of antennas150being reception antennas can not only receive a radio wave but also transmit a radio wave, according to the present embodiment. Specifically, the position detection system100according to the present embodiment includes the transmission circuit160driving the at least one antenna150.

The transmission circuit160is a circuit feeding electric power to at least one antenna150and driving at least one antenna150. Antennas150driven by the transmission circuit160according to the present embodiment are two antennas being the antenna150A and the antenna150B. The transmission circuit160generates a high-frequency signal from power source voltage and supplies the generated high-frequency signal to the antenna150. The transmission circuit160includes an inverter circuit converting DC power into AC power and is PWM controllable. The transmission circuit160includes a first capacitive element forming an LC resonant circuit with the antenna150. The LC resonant circuit according to the present embodiment is an LC series resonant circuit. The frequency characteristic of the LC series resonant circuit may be hereinafter referred to as an antenna characteristic of the antenna150. The transmission circuit160is an example of a second transmission circuit.

The radio wave detection circuit170detects intensity of a radio wave being transmitted from an antenna150driven by the transmission circuit160from among a plurality of antennas150and being received by another antenna150being an antenna150other than the antenna150driven by the transmission circuit160from among the plurality of antennas150. For example, a case of the antenna150A being driven by the transmission circuit160and the antenna150D receiving a radio wave emitted by the antenna150A is assumed. In this case, the radio wave detection circuit170detects intensity of the radio wave received by the antenna150D.

The position detection system100detects the difference between the intensity of the radio wave received by the antenna150D and predetermined reference intensity. The reference intensity is intensity to be detected by the radio wave detection circuit170when the antenna150D receives a radio wave emitted by the antenna150A in a case of the antenna characteristic of the antenna150A and the antenna characteristic of the antenna150D being suitable. For example, the reference intensity is acquired when the reference data are acquired, for each combination of an antenna150capable of transmitting a radio wave and an antenna150capable of receiving the radio wave. Since there are two antennas150capable of transmitting a radio wave and three antennas150capable of receiving a radio wave, there are six combinations, according to the present embodiment.

A relative position between the four antennas150is the same between the time of acquisition of the reference intensity and the time of detection of the relative position. Accordingly, intensity acquired when the relative position is detected is the same as the reference intensity as long as the antenna characteristic of the antenna150transmitting a radio wave and the antenna characteristic of the antenna150receiving the radio wave are the same between the time of acquisition of the reference intensity and the time of detection of the relative position. In other words, the antenna characteristics at the time of acquisition of the reference intensity are considered to be reproduced by adjusting the antenna characteristic of the antenna150transmitting a radio wave and the antenna characteristic of the antenna150receiving the radio wave in such a way that intensity acquired when the relative position is detected is the same as the reference intensity.

Therefore, the antenna characteristic of the antenna150transmitting a radio wave and the antenna characteristic of the antenna150receiving the radio wave are adjusted in such a way that the antenna characteristics at the time of acquisition of the reference intensity are reproduced, according to the present embodiment. Specifically, the frequency characteristic of an LC series resonant circuit including the antenna150transmitting a radio wave and the frequency characteristic of an RLC parallel resonant circuit including the antenna150receiving the radio wave are adjusted. Details of the adjustment method will be described later.

Next, connections between the antenna150, the transmission circuit160, and the radio wave detection circuit170will be described with reference to a circuit diagram of the position detection system100illustrated inFIG. 4. Note thatFIG. 4illustrates a circuit diagram of part of the components included in the position detection system100. As illustrated inFIG. 4, the position detection system100includes two switches151and four switches152. The switch151is a general name for a switch151A and a switch151B. The switch152is a general name for a switch152A, a switch152B, a switch152C, and a switch152D.

The switches151are switches changing a connection between at least one antenna150from among a plurality of antennas150and the transmission circuit160. The switch151A is a switch changing a connection between the antenna150A and the transmission circuit160. When the switch151A is turned on, an LC series resonant circuit is formed by the antenna150A and a capacitive element161A included in the transmission circuit160. The switch151B is a switch changing a connection between the antenna150B and the transmission circuit160. When the switch151B is turned on, an LC series resonant circuit is formed by the antenna150B and a capacitive element161B included in the transmission circuit160. Each of the capacitive element161A and the capacitive element161B is a variable capacitance element having a variable capacitance value. A capacitive element161is a general name for the capacitive element161A and the capacitive element161B. The capacitive element161A and the capacitive element161B are examples of the first capacitive element. The switch151is an example of a first switch.

The switches152are switches changing connections between a plurality of antennas150and the radio wave detection circuit170. The switch152A is a switch changing a connection between the antenna150A and the radio wave detection circuit170. When the switch152A is turned on, an RLC parallel resonant circuit is formed by the antenna150A, and a capacitive element171A and a resistor172A that are included in the radio wave detection circuit170. The switch152B is a switch changing a connection between the antenna150B and the radio wave detection circuit170. When the switch152B is turned on, an RLC parallel resonant circuit is formed by the antenna150B, and a capacitive element171B and a resistor172B that are included in the radio wave detection circuit170.

The switch152C is a switch changing a connection between the antenna150C and the radio wave detection circuit170. When the switch152C is turned on, an RLC parallel resonant circuit is formed by the antenna150C, and a capacitive element171C and a resistor172C that are included in the radio wave detection circuit170. The switch152D is a switch changing a connection between the antenna150D and the radio wave detection circuit170. When the switch152D is turned on, an RLC parallel resonant circuit is formed by the antenna150D, and a capacitive element171D and a resistor172D that are included in the radio wave detection circuit170. The switch152is an example of a second switch.

Each of the capacitive element171A, the capacitive element171B, the capacitive element171C, and the capacitive element171D is a variable capacitance element having a variable capacitance value. Each of the resistor172A, the resistor172B, the resistor172C, and the resistor172D is a variable resistance element having a variable resistance value. A capacitive element171is a general name for the capacitive element171A, the capacitive element171B, the capacitive element171C, and the capacitive element171D. A resistor172is a general name for the resistor172A, the resistor172B, the resistor172C, and the resistor172D. The capacitive element171A, the capacitive element171B, the capacitive element171C, and the capacitive element171D are examples of the second capacitive element. The resistor172A, the resistor172B, the resistor172C, and the resistor172D are examples of the first resistor.

The antenna110and the transmission circuit120are always connected. Accordingly, an LC series resonant circuit is always formed by the antenna110and a capacitive element121C included in the transmission circuit120. The capacitive element121C is a capacitive element having a fixed capacitance value.

When the antenna150A is connected to the transmission circuit160, one of the antenna150B, the antenna150C, and the antenna150D is connected to the radio wave detection circuit170. When the antenna150B is connected to the transmission circuit160, one of the antenna150A, the antenna150C, and the antenna150D is connected to the radio wave detection circuit170. The antenna150C and the antenna150D are not connected to the transmission circuit160. The antenna150A and the antenna150B are not simultaneously connected to the transmission circuit160. The antenna150A and the antenna150B are not simultaneously connected to the radio wave detection circuit170. Each of the antenna150A and the antenna150B is not simultaneously connected to both the transmission circuit160and the radio wave detection circuit170.

Next, the configuration of the position detection system100will be described in detail with reference toFIG. 5. Note that description of a component that has been already described is omitted or simplified. The position detection system100includes the antenna110, the transmission circuit120, a power source circuit125, a controller135, a storage141, a communicator142, the antennas150, the switches151, the switches152, the transmission circuit160, a power source circuit165, the radio wave detection circuit170, a controller180, a storage191, and a communicator192.

The antenna110emits a radio wave related to a high-frequency signal supplied from the transmission circuit120. The transmission circuit120supplies a high-frequency signal generated from power source voltage to the antenna110. The power source circuit125supplies power source voltage to the transmission circuit120. The controller135controls operation of components placed in the power reception device300from among the components included in the position detection system100. For example, the controller135causes the transmission circuit120to emit a radio wave from the antenna110by controlling the transmission circuit120. The controller135includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), a real time clock (RTC), an analog/digital (A/D) converter, and the like.

The storage141stores various types of information used by the controller135or various types of information acquired through operation of the controller135. For example, the storage141includes a flash memory. The communicator142communicates with the communicator192in accordance with control by the controller135. The communicator142includes a communication interface conforming to a well-known wireless communication standard such as Wi-Fi (registered trademark), Bluetooth (registered trademark), Long Term Evolution (LTE), the 4th Generation (4G), or the 5th Generation (5G).

The antenna150receives a radio wave emitted by the antenna110. The switch151changes the connection between the antenna150and the transmission circuit160. The switch152changes the connection between the antenna150and the radio wave detection circuit170. The transmission circuit160supplies a high-frequency signal generated from power source voltage to the antenna150. The power source circuit165supplies power source voltage to the transmission circuit160. The radio wave detection circuit170detects intensity of a radio wave received by the antenna150.

The controller180controls operation of components placed in the power transmission device200from among the components included in the position detection system100. For example, the controller180adjusts the antenna characteristic of the antenna150, based on intensity detected by the radio wave detection circuit170. The controller180includes a CPU, a ROM, a RAM, an RTC, an A/D converter, and the like. Details of the controller180will be described later.

The storage191stores various types of information used by the controller180or various types of information acquired through operation of the controller180. For example, the storage191stores the reference data used for detection of a relative position and the reference intensity used for adjustment of an antenna characteristic. For example, the storage191includes a flash memory. The communicator192communicates with the communicator142in accordance with control by the controller180. The communicator192includes a communication interface conforming to a well-known wireless communication standard, similarly to the communicator142.

Next, the function of the controller180will be described in detail. The controller180functionally includes a switch controller181, a position detector182, a difference detector183, and an adjuster184. For example, the functional units included in the controller180are provided by the CPU executing an operation program stored in the ROM.

The switch controller181controls the switches151and the switches152. The switch controller181controls the switches152in such a way as to connect the radio wave detection circuit170to an antenna150other than an antenna150connected to the transmission circuit160by the switch151from among a plurality of antennas150.

The position detector182detects a relative position between the power transmission coil211and the power reception coil311, based on intensity detected by the radio wave detection circuit170. For example, the position detector182estimates a relative position, based on reference data previously acquired for each of four combinations of one antenna110being a transmission antenna and four antennas150being reception antennas, and intensity detected by the radio wave detection circuit170for each of the four combinations. For example, for each of the four combinations, the position detector182specifies a relative position where the difference between intensity based on an intensity distribution indicated by the reference data and detected intensity is small as a candidate position. Then, the position detector182specifies a relative position repeatedly specified as a candidate position for each of the four combinations. Alternatively, the position detector182retrieves similar coordinates from statistics by using four detected intensity values, based on the reference data. Alternatively, the position detector182generates a function acquiring an output for an input from compressed reference data and calculates a relative position by using the function. In the power transmission device200, positions where the power transmission coil211and the antenna150are installed, respectively, are predetermined, and a positional relation between the power transmission coil211and the antenna150is predetermined. Further, in the power reception device300, positions where the power reception coil311and the antenna110are installed, respectively, are predetermined, and a positional relation between the power reception coil311and the antenna110is predetermined. Therefore, when a positional relation between the antenna110and the antenna150can be specified from detected intensity values, a positional relation between the power transmission device200and the power reception device300can also be specified.

The difference detector183detects the difference between intensity of a radio wave received by another antenna150and predetermined reference intensity. The another antenna150is an antenna150other than an antenna150driven by the transmission circuit160from among the four antennas150. The antenna150driven by the transmission circuit160is the antenna150A, and the another antenna150is the antenna150D. For example, the reference intensity is intensity of a radio wave being emitted from an antenna150placed at the same position as the antenna150A and being received by an antenna150placed at the same position as the antenna150D when the reference data are acquired. A larger difference detected by the difference detector183indicates a larger difference in the antenna characteristic between the time of acquisition of the reference intensity and the time of execution of calibration.

The adjuster184adjusts each element in such a way that the difference detected by the difference detector183decreases. For example, the adjuster184adjusts the frequency characteristic of an RLC parallel resonant circuit including an antenna150receiving a radio wave. For example, the adjuster184adjusts the capacitance value of a capacitive element171included in the RLC parallel resonant circuit in such a way that the aforementioned difference decreases. Further, the adjuster184adjusts the resistance value of a resistor172included in the RLC parallel resonant circuit in such a way that the aforementioned difference decreases.

Further, for example, the adjuster184adjusts the frequency characteristic of an LC series resonant circuit including an antenna150transmitting a radio wave. For example, the adjuster184adjusts the capacitance value of a capacitive element161included in the LC series resonant circuit in such a way that the aforementioned difference decreases. Further, the adjuster184adjusts a duty ratio in PWM control of the transmission circuit160in such a way that the aforementioned difference decreases. PWM information indicating the duty ratio is transmitted from the communicator192to the communicator142. Then, when a relative position is detected, PWM control of the transmission circuit120is executed at the duty ratio indicated by the PWM information in accordance with control by the controller135.

FIG. 6illustrates a frequency characteristic of an RLC parallel resonant circuit including an antenna150receiving a radio wave. InFIG. 6, VCr denotes a capacitance value of a capacitive element171included in the RLC parallel resonant circuit, and VRr denotes a resistance value of a resistor172included in the RLC parallel resonant circuit. As illustrated inFIG. 6, the resonance frequency of the RLC parallel resonant circuit is adjusted by adjusting the capacitance value of the capacitive element171. Further, a peak value at the resonance frequency of the RLC parallel resonant circuit is adjusted by adjusting the resistance value of the resistor172. Intensity of a radio wave received by the antenna150is adjusted by adjustment of the resonance frequency of the RLC parallel resonant circuit or the peak value at the resonance frequency of the RLC parallel resonant circuit.

FIG. 7illustrates a frequency characteristic of an LC series resonant circuit including an antenna150transmitting a radio wave. InFIG. 7, VCt denotes a capacitance value of a capacitive element161included in the LC series resonant circuit, and Wt denotes a duty ratio in PWM control of the transmission circuit160. As illustrated inFIG. 7, the resonance frequency of the LC series resonant circuit is adjusted by adjusting the capacitance value of the capacitive element161. Further, a peak value at the resonance frequency of the LC series resonant circuit is adjusted by adjusting the duty ratio. Intensity of a radio wave transmitted by the antenna150is adjusted by adjustment of the resonance frequency of the LC series resonant circuit or the peak value at the resonance frequency of the LC series resonant circuit.

Next, a method of adjusting each element by the adjuster184will be described with reference toFIG. 8,FIG. 9, andFIG. 10.FIG. 8is a first graph illustrating a correspondence between difference voltage and VCr.FIG. 9is a second graph illustrating a correspondence between difference voltage and VCr.FIG. 10is a graph illustrating a correspondence between difference voltage and VRr. A main objective of the present embodiment is basically adjustment of the antenna characteristic of an antenna150receiving a radio wave. Accordingly, the adjuster184mainly adjusts the frequency characteristic of the RLC parallel resonant circuit including the antenna150receiving a radio wave.

However, when the antenna characteristic of an antenna150transmitting a radio wave is not suitably adjusted, the antenna characteristic of an antenna150receiving the radio wave may not be suitably adjusted. Therefore, the adjuster184additionally adjusts the frequency characteristic of the LC series resonant circuit including the antenna150transmitting a radio wave. Further, the frequency characteristic of an RLC parallel resonant circuit heavily depends on the capacitance value of the capacitive element171rather than the resistance value of the resistor172. Therefore, the adjuster184adjusts the resistance value of the resistor172after precisely adjusting the capacitance value of the capacitive element171.

Difference voltage is voltage related to the difference between the reference intensity and intensity detected by the radio wave detection circuit170and is voltage related to the difference detected by the difference detector183. V1denotes a first threshold value, and V2denotes a second threshold value. The first threshold value is an upper limit of allowable difference voltage. In other words, when the difference voltage is adjusted to the first threshold value or less, calibration is considered to be suitably executed. The second threshold value is an upper limit of the difference voltage at which a big-step search is changed to a small-step search in a search for VCr minimizing the difference voltage. The second threshold value is a value larger than the first threshold value.

A big-step search has a larger step width being a shift amount of VCr compared with a small-step search. In a big-step search, speed of bringing VCr close to C0being VCr minimizing the difference voltage is high but precision is low. In a small-step search, speed of bringing VCr close to C0is low but precision is high. Therefore, the adjuster184rapidly brings VCr close to C0by a big-step search and then precisely brings VCr close to C0by a small-step search.

FIG. 8illustrates a scene in which VCr is rapidly brought close to C0by a big-step search. C1is the current value of VCr. C2is a value less than C1by one first step width being a large step width. C3a value less than C1by two first step widths. C4is a value greater than C1by one first step width. C5is a value greater than C1by two first step widths. The adjuster184acquires difference voltage while changing VCr on a per first step width basis with the current value of VCr as a reference. Then, the adjuster184employs a value of VCr minimizing the acquired difference voltage as a new value of VCr. The adjuster184repeats the big-step search with a newly employed value of VCr as a current value of VCr. When the difference voltage is equal to or less than the second threshold value, the adjuster184completes the big-step search. For example, the big-step search is completed at the time point when the value of VCr becomes C5.

FIG. 9illustrates a scene in which VCr is precisely brought close to C0by a small-step search. C6is a value less than C5by one second step width. The second step width is smaller than the first step width. C7is a value less than C5by two second step widths. C8is a value greater than C5by one second step width. C9is a value greater than C5by two second step widths. The adjuster184acquires difference voltage while changing VCr on a per second step width basis with the current value of VCr as a reference. Then, the adjuster184employs a value of VCr minimizing the acquired difference voltage as a new value of VCr. The adjuster184repeats the small-step search with a newly employed value of VCr as a current value of VCr. When the difference voltage is equal to or less than the first threshold value, the adjuster184completes the small-step search. For example, the small-step search is completed at the time point when the value of VCr becomes C9.

FIG. 10illustrates a scene in which VRr is brought close to R0by a step search. R0is VRr minimizing difference voltage when the value of VCr is C9. R1is a value of VRr after completion of a small-step search. R2is a value less than R1by one third step width. The third step width is a shift amount of VRr. R3is a value less than R1by two third step widths. R4is a value greater than R1by one third step width. R5is a value greater than R1by two third step widths. The adjuster184acquires difference voltage while changing VRr on a per third step width basis with the current value of VRr as a reference. Then, the adjuster184employs a value of VRr minimizing the acquired difference voltage as a new value of VRr. The adjuster184repeats the step search with a newly employed value of VRr as a current value of VRr. When the difference voltage becomes a minimum value, the adjuster184completes the step search.

When adjustment of the antenna characteristic of the antenna150receiving a radio wave is completed, the adjuster184adjusts the antenna characteristic of the antenna150transmitting a radio wave. In other words, the adjuster184adjusts the frequency characteristic of the LC series resonant circuit including the antenna150transmitting a radio wave. The adjuster184adjusts the frequency characteristic of the LC series resonant circuit by a procedure similar to that for adjustment of the frequency characteristic of the RLC parallel resonant circuit.

Specifically, the adjuster184repeats processing of rapidly adjusting VCt by a big-step search until the difference voltage becomes equal to or less than the second threshold value. Then, when the difference voltage becomes equal to or less than the second threshold value, the adjuster184repeats processing of precisely adjusting VCt by a small-step search until the difference voltage becomes equal to or less than the first threshold value. When the difference voltage becomes equal to or less than the first threshold value, the adjuster184repeats processing of adjusting Wt by a step search until the difference voltage becomes a minimum value.

Next, antenna calibration processing executed by the position detection system100will be described with reference toFIG. 11. For example, when receiving a start instruction for position detection processing from the power transmission device200, the position detection system100executes the antenna calibration processing prior to the position detection processing. The position detection processing is processing of detecting a relative position between the power transmission coil211and the power reception coil311.

First, the controller180included in the position detection system100selects a reception antenna capable of transmission (Step S101). For example, the controller180selects either antenna150of the antenna150A and the antenna150B. When completing the processing in Step S101, the controller180selects a reception antenna (Step S102). For example, the controller180selects one antenna150other than the antenna150selected in Step S101from among the four antennas150.

When completing the processing in Step S102, the controller180executes first calibration processing (Step S103). The first calibration processing will be described in detail with reference to a flowchart illustrated inFIG. 12. The first calibration processing is processing of adjusting the antenna characteristic of an antenna150receiving a radio wave.

First, the controller180zeros n (Step S201). Note that n denotes a counter variable for counting the number of repetitions of search processing. When completing the processing in Step S201, the controller180acquires reception intensity (Step S202). For example, the controller180causes the antenna150selected in Step S101to emit a radio wave and causes the antenna150selected in Step S102to receive the radio wave. The controller180acquires reception intensity being intensity of the radio wave received by the antenna150from the radio wave detection circuit170.

When completing the processing in Step S202, the controller180determines whether an intensity difference is equal to or less than the first threshold value (Step S203). The intensity difference is the difference between reference intensity being previously acquired and being stored in the storage191and the reception intensity acquired in Step S202. When determining that the intensity difference is not equal to or less than the first threshold value (Step S203: NO), the controller180determines whether the intensity difference is equal to or less than the second threshold value (Step S204). When determining that the intensity difference is not equal to or less than the second threshold value (Step S203: NO), the controller180executes a big-step search on VCr (Step S205). Specifically, the controller180searches for VCr minimizing the intensity difference while adjusting VCr on a per first step width basis.

When determining that the intensity difference is equal to or less than the second threshold value (Step S203: YES), the controller180executes a small-step search on VCr (Step S206). Specifically, the controller180searches for VCr minimizing the intensity difference while adjusting VCr on a per second step width basis. When completing the processing in Step S206, the controller180executes a step search on VRr (Step S207). Specifically, the controller180searches for VRr minimizing the intensity difference while adjusting VRr on a per third step width basis.

When completing the processing in Step S205or Step S207, the controller180increments n by one (Step S208). When completing the processing in Step S208, the controller180determines whether n exceeds N (Step S209). When determining that n does not exceed N (Step S209: NO), the controller180returns the processing to Step S202. When determining that the intensity difference is equal to or less than the first threshold value (Step S203: YES) or determining that n exceeds N (Step S209: YES), the controller180completes the first calibration processing.

When completing the first calibration processing in Step S103, the controller180executes second calibration processing (Step S104). The second calibration processing will be described in detail with reference to a flowchart illustrated inFIG. 13. The second calibration processing is processing of adjusting the antenna characteristic of an antenna150transmitting a radio wave.

First, the controller180zeros n (Step S301). When completing the processing in Step S301, the controller180acquires reception intensity (Step S302). When completing the processing in Step S302, the controller180determines whether an intensity difference is equal to or less than the first threshold value (Step S303). When determining that the intensity difference is not equal to or less than the first threshold value (Step S303: NO), the controller180determines whether the intensity difference is equal to or less than the second threshold value (Step S304). When determining that the intensity difference is not equal to or less than the second threshold value (Step S303: NO), the controller180executes a big-step search on VCt (Step S305). When determining that the intensity difference is equal to or less than the second threshold value (Step S303: YES), the controller180executes a small-step search on VCt (Step S306). When completing the processing in Step S306, the controller180executes a step search on Wt (Step S307).

When completing the processing in Step S305or Step S307, the controller180increments n by one (Step S308). When completing the processing in Step S308, the controller180determines whether n exceeds N (Step S309). When determining that n does not exceed N (Step S309: NO), the controller180returns the processing to Step S302. When determining that the intensity difference is equal to or less than the first threshold value (Step S303: YES) or determining that n exceeds N (Step S309: YES), the controller180completes the second calibration processing.

When completing the second calibration processing in Step S104, the controller180determines whether an unselected reception antenna exists (Step S105). Specifically, the controller180determines whether an antenna150not being selected in Step S102and being an antenna150other than the antenna150selected in Step S101from among the four antennas150exists. When determining that an unselected reception antenna exists (Step S105: YES), the controller180returns the processing to Step S102and selects the unselected reception antenna.

When determining that an unselected reception antenna does not exist (Step S105: NO), the controller180determines whether an unselected reception antenna capable of transmission exists (Step S106). Specifically, the controller180determines whether an antenna150not selected in Step S101from among the antenna150A and the antenna150B exists. When determining that an unselected reception antenna capable of transmission exists (Step S106: YES), the controller180returns the processing to Step S101and selects the unselected reception antenna capable of transmission.

When determining that an unselected reception antenna capable of transmission does not exist (Step S106: NO), the controller180transmits PWM information (Step S107). For example, the controller180transmits PWM information including Wt finally acquired by the second calibration processing to the communicator142through the communicator192. On the other hand, the controller135acquires the PWM information from the communicator142. In the position detection processing, the controller135controls the transmission circuit120in such a way that PWM at a duty ratio indicated by the PWM information is executed. When completing the processing in Step S107, the controller180completes the antenna calibration processing.

As described above, the transmission circuit160driving the antenna150being a reception antenna is provided, and intensity of a radio wave being transmitted from a driven antenna150and being received by another antenna150is detected by the radio wave detection circuit170, according to the present embodiment. Accordingly, a basis for determination of whether the antenna characteristic of the another antenna150is suitable can be acquired, according to the present embodiment. Further, the difference between the intensity of the radio wave received by the another antenna150and the predetermined reference intensity is detected, according to the present embodiment. Accordingly, whether the antenna characteristic of the another antenna150is suitable can be determined, according to the present embodiment.

Further, the frequency characteristic of an RLC parallel resonant circuit including the another antenna150is suitably adjusted by adjustment of the capacitance value of the capacitive element171and adjustment of the resistance value of the resistor172, according to the present embodiment. Accordingly, the antenna characteristic of the another antenna150is suitably adjusted, and a relative position between the power transmission coil211and the power reception coil311can be precisely detected in wireless electric power transmission, according to the present embodiment.

Further, the frequency characteristic of an LC series resonant circuit including the antenna150transmitting a radio wave is suitably adjusted by adjustment of the capacitance value of the capacitive element161and adjustment of a duty ratio in PWM control, according to the present embodiment. Accordingly, the antenna characteristic of the another antenna150is precisely adjusted even when the antenna characteristic of the antenna150transmitting a radio wave changes from that at the time of acquisition of the reference data and the reference intensity, according to the present embodiment.

Further, PWM control of the transmission circuit120is executed at a duty ratio adjusted in PWM control of the transmission circuit160, according to the present embodiment. Accordingly, the antenna characteristic of an antenna110being a transmission antenna can be suitably adjusted without providing a function of detecting suitability of the antenna characteristic of the antenna110on the power reception device300side where the antenna110is placed, according to the present embodiment.

Further, transmission circuit160according to the present embodiment drives two or more antennas150from among the four antennas150. Accordingly, the antenna characteristic of every antenna150can be adjusted, according to the present embodiment.

An example of providing the function of transmitting a radio wave for a reception antenna and adjusting antenna characteristics between reception antennas has been described in Embodiment 1. An example of providing a function of receiving a radio wave for a transmission antenna and adjusting antenna characteristics between transmission antennas will be described in the present embodiment. Note that description of a configuration and processing similar to those according to Embodiment 1 is omitted or simplified.

According to the present embodiment, a part of components of a position detection system101are placed in a power transmission coil unit210and the other components of the position detection system101are placed in a power reception coil unit310, as illustrated inFIG. 14. Specifically, two antennas110, a transmission circuit120, and a radio wave detection circuit130are placed in the power reception coil unit310, and an antenna150and a radio wave detection circuit170are placed in the power transmission coil unit210. The two antennas110are placed at positions distant from each other on the power reception coil unit310. The antenna110is a general name for an antenna110A and an antenna110B. Note thatFIG. 14illustrates only main components from among the components included in the position detection system101.

The antenna110is an antenna emitting a radio wave in the LF band. There are two antennas110, according to the present embodiment. The antenna110may be hereinafter referred to as a transmission antenna. The antenna110is an example of a second antenna. The transmission circuit120is a circuit driving a plurality of antennas110. The transmission circuit120is an example of a transmission circuit. The transmission circuit120includes a first capacitive element forming an LC resonant circuit with the antenna110. The LC resonant circuit according to the present embodiment is an LC series resonant circuit. The frequency characteristic of the LC series resonant circuit may be hereinafter referred to as an antenna characteristic of the antenna110.

According to the present embodiment, calibration is executed when a relative position is detected, in order to align the antenna characteristic of an antenna110used for detection of the relative position with the antenna characteristic of an antenna110used when reference data are acquired. In order to achieve such calibration, at least one antenna110from among a plurality of antennas110being transmission antennas is capable of not only transmitting a radio wave but also receiving a radio wave, according to the present embodiment. Specifically, the position detection system100according to the present embodiment includes the radio wave detection circuit130detecting intensity of a radio wave received by the at least one antenna110.

The radio wave detection circuit130is a circuit detecting intensity of a radio wave received by at least one antenna110. For example, the radio wave detection circuit130detects intensity of a radio wave being transmitted from the antenna110A and being received by the antenna110B. The radio wave detection circuit130includes a second capacitive element and a first resistor forming an RLC resonant circuit with the antenna110. The RLC resonant circuit according to the present embodiment is an RLC parallel resonant circuit. The frequency characteristic of the RLC parallel resonant circuit may be hereinafter referred to as an antenna characteristic of the antenna110. The radio wave detection circuit130is an example of a second radio wave detection circuit.

The position detection system101detects the difference between intensity of a radio wave received by the antenna110B and predetermined reference intensity. The reference intensity is intensity to be detected by the radio wave detection circuit130when the antenna110B receives a radio wave emitted by the antenna110A in a case of the antenna characteristic of the antenna110A and the antenna characteristic of the antenna110B being suitable. For example, the reference intensity is acquired for each combination of a plurality of antennas110transmitting a radio wave and an antenna110capable of receiving a radio wave when the reference data are acquired. Since there are two antennas110transmitting a radio wave and one antenna110capable of receiving the radio wave, there are two combinations, according to the present embodiment.

A relative position between the two antennas110when the reference intensity is acquired and that when the relative position is detected are the same. Accordingly, intensity acquired when the relative position is detected is the same as the reference intensity as long as the antenna characteristic of the antenna110transmitting a radio wave and the antenna characteristic of the antenna110receiving the radio wave at the time of acquisition of the reference intensity and those at the time of detection of the relative position are the same. In other words, the antenna characteristic at the time of acquisition of the reference intensity is considered to be reproduced by adjusting the antenna characteristic of the antenna110transmitting a radio wave and the antenna characteristic of the antenna110receiving the radio wave in such a way that intensity acquired when the relative position is detected and the reference intensity are the same.

Therefore, the antenna characteristic of the antenna110transmitting a radio wave and the antenna characteristic of the antenna110receiving the radio wave are adjusted in such a way that the antenna characteristics at the time of acquisition of the reference intensity is reproduced, according to the present embodiment. Specifically, the frequency characteristic of an LC series resonant circuit including the antenna110transmitting a radio wave and the frequency characteristic of an RLC parallel resonant circuit including the antenna110receiving the radio wave are adjusted. Details of the adjustment method will be described later.

The antenna150is an antenna receiving a radio wave in the LF band. There is one antenna150in the present embodiment. The antenna150may be hereinafter referred to as a reception antenna. The antenna150is an example of a first antenna. The radio wave detection circuit170is a circuit detecting intensity of a radio wave received by at least one antenna150. The radio wave detection circuit170detects intensity of a radio wave received by the antenna150.

Next, connections between the antenna110, the transmission circuit120, and the radio wave detection circuit130will be described with reference to a circuit diagram of the position detection system101illustrated inFIG. 15. Note thatFIG. 15illustrates a circuit diagram of part of components included in the position detection system101. As illustrated inFIG. 15, the position detection system101includes two switches111and two switches112. The switch111is a general name for a switch111A and a switch111B. The switch112is a general name for a switch112A and a switch112B.

The switches111are switches changing a connection between at least one antenna110from among a plurality of antennas110and the transmission circuit120. The switch111A is a switch changing a connection between the antenna110A and the transmission circuit120. When the switch111A is turned on, an LC series resonant circuit is formed by the antenna110A and a capacitive element121A included in the transmission circuit120. The switch111B is a switch changing a connection between the antenna110B and the transmission circuit120. When the switch111B is turned on, an LC series resonant circuit is formed by the antenna110B and a capacitive element121B included in the transmission circuit120. Each of the capacitive element121A and the capacitive element121B is a variable capacitance element having a variable capacitance value. The capacitive element121A and the capacitive element121B are examples of the first capacitive element.

The switches112are switches changing connections between a plurality of antennas110and the radio wave detection circuit130. The switch112A is a switch changing a connection between the antenna110A and the radio wave detection circuit130. When the switch112A is turned on, an RLC parallel resonant circuit is formed by the antenna110A, and a capacitive element131A and a resistor132A that are included in the radio wave detection circuit130. The switch112B is a switch changing a connection between the antenna110B and the radio wave detection circuit130. When the switch112B is turned on, an RLC parallel resonant circuit is formed by the antenna110B, and a capacitive element131B and a resistor132B that are included in the radio wave detection circuit130.

Each of the capacitive element131A and the capacitive element131B is a variable capacitance element having a variable capacitance value. Each of the resistor132A and the resistor132B is a variable resistance element having a variable resistance value. A capacitive element131is a general name for the capacitive element131A and the capacitive element131B. A resistor132is a general name for the resistor132A and the resistor132B. The capacitive element131A and the capacitive element131B are examples of the second capacitive element. The resistor132A and the resistor132B are examples of the first resistor.

The antenna150and the radio wave detection circuit170are always connected. Accordingly, an RLC parallel resonant circuit is always formed by the antenna150, and a capacitive element171E and a resistor172E that are included in the radio wave detection circuit170. The capacitive element171E is a capacitive element having a fixed capacitance value. The resistor172E is a resistance element having a fixed resistance value.

When the antenna110A is connected to the transmission circuit120, the antenna110B is connected to the radio wave detection circuit130. When the antenna110B is connected to the transmission circuit120, the antenna110A is connected to the radio wave detection circuit130. The antenna110A and the antenna110B are not simultaneously connected to the transmission circuit120. The antenna110A and the antenna110B are not simultaneously connected to the radio wave detection circuit130. Each of the antenna110A and the antenna110B is not simultaneously connected to both the transmission circuit120and the radio wave detection circuit130.

Next, components of the position detection system101will be described in detail with reference toFIG. 16. Note that description of a component that has been already described is omitted or simplified. The position detection system101includes the antennas110, the switches111, the switches112, the transmission circuit120, a power source circuit125, the radio wave detection circuit130, a controller135, a storage141, a communicator142, the antenna150, the radio wave detection circuit170, a controller180, a storage191, and a communicator192.

The antenna110emits a radio wave related to a high-frequency signal supplied by the transmission circuit120. The switch111changes the connection between the antenna110and the transmission circuit120. The switch112changes the connection between the antenna110and the transmission circuit120. The transmission circuit120supplies a high-frequency signal generated from power source voltage to the antenna110. The power source circuit125supplies power source voltage to the transmission circuit120. The radio wave detection circuit130detects intensity of a radio wave received by the antenna110. The radio wave detection circuit130is an example of the second radio wave detection circuit.

The controller135controls operation of components placed in a power reception device300from among the components included in the position detection system101. For example, the controller135causes the antenna110to emit a radio wave by controlling the transmission circuit120. For example, the controller135adjusts the antenna characteristic of the antenna110, based on intensity detected by the radio wave detection circuit130. The controller135includes a CPU, a ROM, a RAM, an RTC, an A/D converter, and the like. Details of the controller135will be described later.

The storage141stores various types of information used by the controller135or various types of information acquired through operation of the controller135. For example, the storage141stores reference data used for detection of a relative position and reference intensity used for adjustment of an antenna characteristic. For example, the storage141includes a flash memory. The communicator142communicates with the communicator192in accordance with control by the controller135. The communicator142includes a communication interface conforming to a well-known wireless communication standard.

The antenna150receives a radio wave emitted by the antenna110. The radio wave detection circuit170detects intensity of a radio wave received by the antenna150. The radio wave detection circuit170is an example of a first radio wave detection circuit. The controller180controls operation of components placed in a power transmission device200from among the components included in the position detection system100. The controller180functionally includes a position detector182. The position detector182detects a relative position between a power transmission coil211and a power reception coil311, based on intensity detected by the radio wave detection circuit170. The controller180includes a CPU, a ROM, a RAM, an RTC, an A/D converter, and the like.

The storage191stores various types of information used by the controller180and various types of information acquired through operation of the controller180. For example, the storage191includes a flash memory. The communicator192communicates with the communicator142in accordance with control by the controller180. The communicator192includes a communication interface conforming to a well-known wireless communication standard, similarly to the communicator142.

Next, the function of the controller135will be described in detail. The controller135functionally includes a switch controller136, a difference detector137, and an adjuster138. For example, the functional units included in the controller135are provided by the CPU executing an operation program stored in the ROM.

The switch controller136controls the switches111and the switches112. The switch controller136controls the switches112in such a way as to connect the radio wave detection circuit130to an antenna110other than an antenna110connected to the transmission circuit120by a switch111from among a plurality of antennas110.

The difference detector137detects the difference between intensity of a radio wave received by another antenna110and predetermined reference intensity. The another antenna110is an antenna110other than an antenna110driven by the transmission circuit120from among the two antennas110. The antenna110driven by the transmission circuit120here is the antenna110A, and the another antenna110is the antenna110B. For example, the reference intensity is intensity of a radio wave being emitted from an antenna110placed at the same position as the antenna110A and being received by an antenna110placed at the same position as the antenna110B when the reference data are acquired. A larger difference detected by the difference detector137indicates a larger difference in the antenna characteristic between the time of acquisition of the reference intensity and the time of execution of calibration.

The adjuster138adjusts each element in such a way that the difference detected by the difference detector137decreases. For example, the adjuster138adjusts the frequency characteristic of an LC series resonant circuit including an antenna110transmitting a radio wave. For example, the adjuster138adjusts the capacitance value of a capacitive element121included in the LC series resonant circuit in such a way that the aforementioned difference decreases. Further, the adjuster138adjusts a duty ratio in PWM control of the transmission circuit120in such a way that the aforementioned difference decreases.

Further, for example, the adjuster138adjusts the frequency characteristic of an RLC parallel resonant circuit including an antenna110receiving a radio wave. For example, the adjuster138adjusts the capacitance value of a capacitive element131included in the RLC parallel resonant circuit in such a way that the aforementioned difference decreases. Further, the adjuster138adjusts the resistance value of a resistor132included in the RLC parallel resonant circuit in such a way that the aforementioned difference decreases.

Next, antenna calibration processing executed by the position detection system101will be described with reference toFIG. 17. For example, when receiving a start instruction for position detection processing from the power transmission device200, the position detection system101executes the antenna calibration processing prior to the position detection processing.

First, the controller135included in the position detection system101selects a transmission antenna capable of reception (Step S401). For example, the controller135selects either antenna110of the antenna110A and the antenna110B. When completing the processing in Step S401, the controller135selects a transmission antenna (Step S402). For example, the controller135selects an antenna110other than the antenna110selected in Step S401from among the two antennas110.

When completing the processing in Step S402, the controller135executes third calibration processing (Step S403). The third calibration processing will be described in detail with reference to a flowchart illustrated inFIG. 18. The third calibration processing is processing of adjusting the antenna characteristic of an antenna110transmitting a radio wave.

First, the controller135zeros n (Step S501). When completing the processing in Step S501, the controller135acquires reception intensity (Step S502). For example, the controller135causes the antenna110selected in Step S402to emit a radio wave and causes the antenna110selected in Step S401to receive the radio wave. The controller135acquires reception intensity being intensity of the radio wave received by the antenna110from the radio wave detection circuit130.

When completing the processing in Step S502, the controller135determines whether an intensity difference is equal to or less than a first threshold value (Step S503). The intensity difference is the difference between reference intensity being previously acquired and being stored in the storage191, and the reception intensity acquired in Step S502. When determining that the intensity difference is not equal to or less than the first threshold value (Step S503: NO), the controller135determines whether the intensity difference is equal to or less than a second threshold value (Step S504). When determining that the intensity difference is not equal to or less than the second threshold value (Step S504: NO), the controller135executes a big-step search on VCt (Step S505). Specifically, the controller135searches for VCt minimizing the intensity difference while adjusting VCt on a per first step width basis.

When determining that the intensity difference is equal to or less than the second threshold value (Step S504: YES), the controller135executes a small-step search on VCt (Step S506). Specifically, the controller135searches for VCt minimizing the intensity difference while adjusting VCt on a per second step width basis. When completing the processing in Step S506, the controller135executes a step search on VRt (Step S507). Specifically, the controller135searches for VRt minimizing the intensity difference while adjusting VRt on a per third step width basis.

When completing the processing in Step S505or Step S507, the controller135increments n by one (Step S508). When completing the processing in Step S508, the controller135determines whether n exceeds N (Step S509). When determining that n does not exceed N (Step S509: NO), the controller135returns the processing to Step S502. When determining that the intensity difference is equal to or less than the first threshold value (Step S503: YES) or determining that n exceeds N (Step S509: YES), the controller135completes the third calibration processing.

When completing the third calibration processing in Step S403, the controller135executes fourth calibration processing (Step S404). The fourth calibration processing will be described in detail with reference to a flowchart illustrated inFIG. 19. The fourth calibration processing is processing of adjusting the antenna characteristic of an antenna110receiving a radio wave.

First, the controller135zeros n (Step S601). When completing the processing in Step S601, the controller135acquires reception intensity (Step S602). When completing the processing in Step S602, the controller135determines whether the intensity difference is equal to or less than the first threshold value (Step S603). When determining that the intensity difference is not equal to or less than the first threshold value (Step S603: NO), the controller135determines whether the intensity difference is equal to or less than the second threshold value (Step S604). When determining that the intensity difference is not equal to or less than the second threshold value (Step S604: NO), the controller135executes a big-step search on VCr (Step S605). When determining that the intensity difference is equal to or less than the second threshold value (Step S604: YES), the controller135executes a small-step search on VCr (Step S606). When completing the processing in Step S606, the controller135executes a step search on VRr (Step S607).

When completing the processing in Step S605or Step S607, the controller135increments n by one (Step S608). When completing the processing in Step S608, the controller135determines whether n exceeds N (Step S609). When determining that n does not exceed N (Step S609: NO), the controller135returns the processing to Step S602. When determining that the intensity difference is equal to or less than the first threshold value (Step S603: YES) or determining that n exceeds N (Step S609: YES), the controller135completes the fourth calibration processing.

When completing the fourth calibration processing in Step S404, the controller135determines whether an unselected transmission antenna exists (Step S405). Specifically, the controller135determines whether an antenna110being not selected in Step S402and being an antenna110other than the antenna110selected in Step S401from among the two antennas110exists. When determining that an unselected transmission antenna exists (Step S405: YES), the controller135returns the processing to Step S402and selects the unselected transmission antenna.

When determining that an unselected transmission antenna does not exist (Step S405: NO), the controller135determines whether an unselected transmission antenna capable of reception exists (Step S406). Specifically, the controller135determines whether an antenna110not selected in Step S401from among the antenna110A and the antenna110B exists. When determining that an unselected transmission antenna capable of reception exists (Step S406: YES), the controller135returns the processing to Step S401and selects the unselected transmission antenna capable of reception. When determining that an unselected transmission antenna capable of reception does not exist (Step S406: NO), the controller135completes the antenna calibration processing.

As described above, the radio wave detection circuit130detecting intensity of a radio wave received by an antenna110being a transmission antenna is provided, and intensity of a radio wave being transmitted from a driven antenna110and being received by another antenna110is detected by the radio wave detection circuit130, according to the present embodiment. Accordingly, a basis for determination of whether the antenna characteristic of the antenna110transmitting the radio wave is suitable can be acquired, according to the present embodiment. Further, the difference between the intensity of the radio wave received by the another antenna110and the predetermined reference intensity is detected, according to the present embodiment. Accordingly, whether the antenna characteristic of the antenna110transmitting the radio wave is suitable can be determined, according to the present embodiment.

Further, the frequency characteristic an LC series resonant circuit including an antenna110transmitting a radio wave is suitably adjusted by adjustment of the capacitance value of the capacitive element121and adjustment of a duty ratio in PWM control, according to the present embodiment. Accordingly, the antenna characteristic of the antenna110transmitting the radio wave is suitably adjusted, and a relative position between the power transmission coil211and the power reception coil311can be precisely detected in wireless electric power transmission, according to the present embodiment.

Further, the frequency characteristic of an RLC parallel resonant circuit including the another antenna110is suitably adjusted by adjustment of the capacitance value of the capacitive element131and adjustment of the resistance value of the resistor132, according to the present embodiment. Accordingly, the antenna characteristic of the antenna110transmitting a radio wave is precisely adjusted even when the antenna characteristic of the antenna110receiving the radio wave changes from that at the time of acquisition of the reference data and the reference intensity, according to the present embodiment.

Further, the radio wave detection circuit130according to the present embodiment detects intensity of a radio wave received by two or more antennas110from among a plurality of antennas110. Accordingly, the antenna characteristic of every antenna110can be adjusted, according to the present embodiment.

Modified Examples

While the embodiments of the present disclosure have been described above, modifications and applications in various forms can be made in implementation of the present disclosure. In the present disclosure, any part of the configurations, functions, and operations described in the aforementioned embodiments can be employed. Further, in the present disclosure, further configurations, functions, and operations may be employed in addition to the aforementioned configurations, functions, and operations. Further, the aforementioned embodiments may be combined in any way as appropriate. Further, the number of components described in the aforementioned embodiments may be adjusted as appropriate. Further, it is apparent that materials, sizes, electric characteristics, and the like employable in the present disclosure are not limited to those described in the aforementioned embodiments.

An example of providing the function of transmitting a radio wave for a reception antenna and adjusting the antenna characteristics of reception antennas between the reception antennas has been described in Embodiment 1. Further, an example of providing the function of receiving a radio wave for a transmission antenna and adjusting the antenna characteristics of transmission antennas between the transmission antennas has been described in Embodiment 2. The antenna characteristics of reception antennas may be adjusted between the reception antennas by providing the function of transmitting a radio wave for a reception antenna, and the antenna characteristics of transmission antennas may be adjusted between the transmission antennas by providing the function of receiving a radio wave for a transmission antenna.

An example of automatically adjusting the antenna characteristic of a reception antenna or a transmission antenna when the antenna characteristic differs from a predetermined antenna characteristic has been described in Embodiments 1 and 2. The antenna characteristic of a reception antenna or a transmission antenna may not be adjusted and an error notification may be made when the antenna characteristic differs from the predetermined antenna characteristic.

An example of adjusting a duty ratio in PWM control when adjusting the frequency characteristic of an LC series resonant circuit has been described in Embodiments 1 and 2. Power source voltage of a high-frequency signal in PWM control may be adjusted when adjusting the frequency characteristic of the LC series resonant circuit. In this case, output voltage of the inverter included in the transmission circuit120or the transmission circuit160is adjusted.

An example of not only adjusting the frequency characteristic of an RLC parallel resonant circuit including a reception antenna receiving a radio wave but also adjusting the frequency characteristic of an LC series resonant circuit including a reception antenna transmitting a radio wave has been described in Embodiment 1. The frequency characteristic of the LC series resonant circuit including the reception antenna transmitting a radio wave may not be adjusted. Further, an example of not only adjusting the frequency characteristic of an LC series resonant circuit including a transmission antenna transmitting a radio wave but also adjusting the frequency characteristic of an RLC parallel resonant circuit including a transmission antenna receiving a radio wave has been described in Embodiment 2. The frequency characteristic of the RLC parallel resonant circuit including the transmission antenna receiving a radio wave may not be adjusted.

An example of placing a reception antenna in the power transmission device200and placing a transmission antenna in the power reception device300has been described in Embodiments 1 and 2. A transmission antenna may be placed in the power transmission device200, and a reception antenna may be placed in the power reception device300.

Applying an operation program defining the operation of the position detection system100or101according to the present disclosure to a computer such as an existing personal computer or an information terminal device may cause the computer to also function as the position detection system100or101according to the present disclosure. Further, any method may be employed as a distribution method of such a program, and for example, the program may be stored and distributed in a non-transitory computer-readable recording medium such as a compact disk ROM (CD-ROM), a digital versatile disk (DVD), a magneto optical disk (MO), or a memory card and may be distributed through a communication network such as the Internet.