Vehicle, power transmission device, and power feeding system

A vehicle includes a power receiving unit and an RFID tag. The power receiving unit contactlessly receives electric power output from a power transmission unit. The RFID tag preliminarily stores information which is identification information for identifying the vehicle in the power transmission device and can be contactlessly read by the power transmission device. Here, the RFID tag is arranged at a vehicle body front end (a vehicle body trailing end) in a vehicle traveling direction when the vehicle is guided into a parking frame.

TECHNICAL FIELD

The present invention relates to a vehicle, a power transmission device, and a power feeding system, and particularly to a pairing technique between a power transmission device and a vehicle in a power feeding system configured to supply electric power from the power transmission device to the vehicle contactlessly.

BACKGROUND ART

A contactless wireless power transmission without a power cord or a power transmission cable has been attracting attention, and its application to an electric vehicle, which receives a supply of power from a power supply outside of a vehicle (hereinafter, also referred to as “external power supply”), a hybrid vehicle, or the like has been proposed. In such a contactless power feeding system, it is necessary to suitably perform identification (pairing) between a power transmission device and a power receiving device (vehicle).

Japanese Patent Laying-Open No. 2007-19719 (PTD 1) discloses a technique that, in a system including a mobile terminal device and a portable wireless communication unit for identifying a user of the mobile terminal device for the purpose of theft prevention, the presence of a mobile terminal device subjected to authentication in a specified area is determined based on a signal from an RFID provided in the wireless communication unit (refer to PTD 1).

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

An RFID (Radio Frequency IDentification) is a technique of performing an object recognition with use of an RFID tag, which stores ID information, and an RFID reader, which reads the information from the RFID tag through a wireless communication with the RFID tag. When such an RFID technique is applied to the pairing between a power transmission device and a vehicle in a contactless power feeding system, the following problem arises.

In other words, since a communicable distance of an RFID is generally small, a situation may occur in which, before a pairing between a power transmission device and a vehicle is established, parking to a parking frame provided with a power transmission unit of the power transmission device is completed. In such a case, since the pairing between the power transmission device and the vehicle is established after the completion of the parking, and determination on whether or not parking is made at an appropriate position can be performed after the pairing, it would be necessary to perform the parking operation again when the parking is not made at the appropriate position, thus it lacks convenience.

The present invention was achieved to solve the problem described above, and its object is to enable establishment of the pairing between the power transmission device and the vehicle at an early stage in the power feeding system for supplying electric power from the power transmission device to the vehicle contactlessly.

Solution to Problem

According to the present invention, a vehicle is a vehicle which receives electric power from a power transmission device, and the includes a power receiving unit and an ID tag. The power receiving unit contactlessly receives electric power output from the power transmission device. The ID tag preliminarily stores information which is identification information for the power transmission device to identify the vehicle and can be contactlessly read by the power transmission device. Here, the ID tag is arranged at a vehicle body front end in a vehicle traveling direction of the vehicle being guided into a parking frame in which the vehicle receives electric power from the power transmission device.

Preferably, the vehicle further includes another ID tag. The another ID tag is arranged at a vehicle body end on a side opposite to the ID tag in vehicle body forward and backward directions and preliminarily stores the identification information which can be contactlessly read by the power transmission device.

Preferably, the vehicle further includes another ID tag. This yet another ID tag is arranged close to the power receiving unit and preliminarily stores the identification information which can be contactlessly read by the power transmission device.

More preferably, the power receiving unit is provided at a vehicle body underneath part. The another ID tag is arranged close to the power receiving unit on a vehicle body end side having a larger distance among a distance from the power receiving unit to a vehicle body leading end and a distance from the power receiving unit to a vehicle body trailing end.

With such an arrangement, when the ID tag is arranged on the vehicle body end side having a larger distance among the distance from the power receiving unit to the vehicle body leading end and the distance from the power receiving unit to the vehicle body trailing end, a distance between the ID tag and the another ID tag can be reduced. Accordingly, even when the reading range of the ID tag and the another ID tag is narrow, the range of reading any one of the ID tag and the another ID tag can be increased. Therefore, the pairing between the power transmission device and the vehicle becomes less likely to be interrupted when the vehicle enters into the parking frame.

Preferably, the ID tag is arranged substantially at a center in vehicle body leftward and rightward directions.

Preferably, the vehicle further includes a communication unit which performs a wireless communication with the power transmission device. When the vehicle information indicated in the identification information read by the power transmission device corresponds to the vehicle information indicated in the information transmitted from the communication unit to the power transmission device, the vehicle is identified as a vehicle which should be supplied with electric power from the power transmission device.

More preferably, a communicable distance between the ID tag and the power transmission device is smaller than a communicable distance between the communication unit and the power transmission device.

Preferably, a difference between a natural frequency of the power receiving unit and a natural frequency of the power transmission device is less than or equal to ±10% of the natural frequency of the power receiving unit or the natural frequency of the power transmission unit.

Preferably, a coupling coefficient between the power receiving unit and a power transmission unit of the power transmission device is less than or equal to 0.3.

Preferably, the power receiving unit receives electric power from the power transmission unit through at least one of a magnetic field and an electric field. The magnetic field is formed between the power receiving unit and a power transmission unit of the power transmission device. The electric field is formed between the power receiving unit and the power transmission unit. The magnetic field and the electric field are formed between the power receiving unit and the power transmission unit and oscillate at a particular frequency.

Moreover, according to the present invention, the power transmission device is a power transmission device which supplies electric power to a vehicle and includes a power transmission unit and a reading unit. The power transmission unit contactlessly outputs electric power to the vehicle. The reading unit contactlessly reads identification information from an ID tag. The ID tag preliminarily stores the identification information and is provided in the vehicle to identify the vehicle. Here, the reading unit is arranged in a parking frame and close to a vehicle entering end of the parking frame, electric power is supplied to the vehicle in the parking frame.

Preferably, the power transmission device further includes another reading unit. This another reading unit is arranged close to the power transmission unit and contactlessly reads from the ID tag the identification information preliminarily stored in the ID tag.

Moreover, according to the present invention, the power feeding system is a power feeding system which contactlessly supplies electric power from a power transmission device to a vehicle. The vehicle includes a power receiving unit and an ID tag. The power receiving unit contactlessly receives electric power output from the power transmission device. The ID tag preliminarily stores identification information for identifying the vehicle in the power transmission device. The power transmission device includes a power transmission unit and a reading unit. The power transmission unit contactlessly outputs electric power to the power receiving unit. The reading unit contactlessly reads the identification information from the ID tag. Here, the ID tag is arranged at a vehicle body front end in a vehicle traveling direction when the vehicle is guided into a parking frame in which electric power is supplied from the power transmission device to the vehicle.

Preferably, the reading unit is arranged in the parking frame and close to a vehicle entering end of the parking frame.

Advantageous Effects of Invention

According to the present invention, an ID tag is arranged at a vehicle body front end in a vehicle traveling direction when the vehicle is guided into a parking frame in which the vehicle receives electric power from the power transmission device. Therefore, the vehicle identification information stored in the ID tag can be read by the power transmission device at an early stage. Thus, according to the present invention, the pairing between the power transmission device and the vehicle can be established at an early stage. Consequently, it allows for the alignment or the like during the parking operation.

DESCRIPTION OF EMBODIMENT

In the following, the embodiment of the present invention will be described with reference to the drawings. It should be noted that the same or corresponding parts have the same reference numerals allotted, and description thereof will not be repeated.

(Configuration of Power Feeding System)

FIG. 1represents an entire configuration of a power feeding system10according to the embodiment of the present invention. Referring toFIG. 1, power feeding system10includes a vehicle100and a power transmission device200. Power transmission device200includes a power supply device210, a power transmission unit220, and an RFID reader270.

Power supply device210generates alternating current power having a predetermined frequency. As one example, power supply device210receives electric power from a commercial power supply400to generate high-frequency alternating current power, and supplies the generated alternating current power to power transmission unit220. Power transmission unit220contactlessly supplies electric power to power receiving unit110of vehicle100through an electromagnetic field generated around power transmission unit220.

Power supply device210includes a communication unit230, a power transmission ECU (Electronic Control Unit)240, a power supply unit250, and a matching device260. Power transmission unit220includes a coil221(hereinafter, also referred to as “resonant coil” or may be suitably referred to as “resonance coil” or the like), a capacitor222, and a coil223(hereinafter, also referred to as “electromagnetic induction coil”).

Power supply unit250is controlled by a control signal MOD from power transmission ECU240, and converts electric power received from an alternating current power supply such as commercial power supply400or the like into high-frequency electric power. Power supply unit250supplies the converted high-frequency electric power to electromagnetic induction coil223through matching device260. Moreover, power supply unit250outputs each detection value of a power transmission voltage Vtr and a power transmission current Itr respectively detected by a voltage sensor and a current sensor, which are not illustrated, to power transmission ECU240.

Matching device260is configured to adjust an impedance of power transmission unit220, and is typically constituted of a circuit including a reactor and a capacitor. The impedance adjustment by matching device260may be fixed or variable. When matching device260is variable, the impedance is adjusted based on a control signal SE10from power transmission ECU240. It should be noted that power supply unit250may be configured to include a function of matching device260.

Electromagnetic induction coil223can be magnetically coupled to resonant coil221by electromagnetic induction. Electromagnetic induction coil223transmits the high-frequency power supplied from power supply unit250to resonant coil221by electromagnetic induction.

Resonant coil221contactlessly transfers the electric power transmitted from electromagnetic induction coil223to a resonant coil111included in power receiving unit110of vehicle100. It should be noted that the contactless power transmission between power receiving unit110and power transmission unit220will be described later in detail.

Communication unit230is a communication interface configured to perform a wireless communication between power transmission device200and vehicle100, and performs transmission and reception of information INFO with a communication unit160of vehicle100. Communication unit230receives vehicle information, a signal for commanding starting and stopping of power transmission, and the like transmitted from communication unit160of vehicle100, and outputs the received information, signal, and the like to power transmission ECU240. Moreover, communication unit230transmits information of power transmission voltage Vtr, power transmission current Itr, and the like received from power transmission ECU240, to vehicle100.

RFID reader270is a reading unit configured to contactlessly read information of an RFID tag155provided at vehicle100. RFID reader270includes an antenna which is not illustrated in the drawing, and uses this antenna to, for example, transmit electric power to RFID tag155of vehicle100by electromagnetic induction and receives information transmitted from RFID tag155in response to the transmission of power. The communication with use of the RFID has a smaller communicable distance as compared to the communication by communication unit230. Then, RFID reader270outputs information SIG10received from RFID tag155to power transmission ECU240.

Power transmission ECU240includes a CPU (Central Processing Unit), a storage device, an input-output buffer, and the like (none of these are illustrated), performs input of a signal from each sensor or the like and output of a control signal to each equipment, and performs a control of each device in power transmission device200. It should be noted that these controls are not limited to the processing by software but can be processed with a dedicated hardware (electronic circuit).

On the other hand, vehicle100includes, in addition to RFID tag155described above, power receiving unit110, matching device170, a rectifier180, a charging relay (hereinafter, also referred to as “CHR (CHarging Relay)”)185, and a power storage device190. Moreover, vehicle100further includes a system main relay (hereinafter, also referred to as “SMR (System Main Relay)”)115, a power control unit (hereinafter, also referred to as “PCU (Power Control Unit)”)120, a motor generator130, a drive power transmission gear140, drive wheels150, a communication unit160, a voltage sensor195, a current sensor196, and a vehicle ECU300. Power receiving unit110includes a coil111(hereinafter, also referred to as “resonant coil” and may be suitable referred to as “resonance coil” or the like), a capacitor112, and a coil113(hereinafter, also referred to as “electromagnetic induction coil”).

It should be noted that, although vehicle100is described as an electric vehicle representatively in the present embodiment, the configuration of vehicle100is not limited to this as long as it is a vehicle which can travel with use of electric power stored in power storage device190. Another examples of vehicle100include a hybrid vehicle having an engine, a fuel cell vehicle having a fuel cell, and the like.

Resonant coil111contactlessly receives electric power from resonant coil221of power transmission device200. Electromagnetic induction coil113can be magnetically coupled to resonant coil111by electromagnetic induction. Electromagnetic induction coil113extracts by electromagnetic induction the electric power received by resonant coil111and outputs the electric power to rectifier180through matching device170.

Matching device170is configured to adjust an input impedance of a load which receives the electric power received by resonant coil111, and has for example a circuit (not illustrated) including a capacitor and a reactor as with matching device260of power transmission device200.

Rectifier180rectifies alternating current power received from electromagnetic induction coil113through matching device170, and outputs the rectified direct current power to power storage device190. Rectifier180may have a static circuit configuration including for example a diode bridge and a smoothing capacitor (none of these are illustrated). As rectifier180, so-called switching regulator can be used which performs rectification by means of a switching control. When rectifier180is included in power receiving unit110, it is preferable to have a static rectifier such as a diode bridge to prevent an incorrect operation of the switching element due to an electromagnetic field.

CHR185is electrically connected between rectifier180and power storage device190. CHR185is controlled by a control signal SE2from vehicle ECU300and switches supplying and cutting of electric power from rectifier180to power storage device190.

Power storage device190is a power storage element configured to be rechargeable. Power storage device190is configured to include, for example, a rechargeable battery such as a lithium-ion battery, a nickel hydride battery, or a lead battery, or a storage element such as an electric double layer capacitor.

Power storage device190stores electric power received by power receiving unit110and rectified by rectifier180. Moreover, power storage device190is connected also to PCU120through SMR115. Then, power storage device190supplies electric power for generating a vehicle driving force to PCU120. Further, power storage device190receives electric power generated by motor generator130from PCU120and stores the electric power.

Moreover, power storage device190is provided with a voltage sensor and a current sensor (neither illustrated in the drawing) for detecting a voltage VB and a current IB of power storage device190respectively. A detection value of each of these sensors is outputted to vehicle ECU300. Vehicle ECU300calculates a state of charge (also referred to as “SOC (State Of Charge)” and expressed as 0% to 100% with a fully charged state of 100%) of power storage device190based on each detection value of voltage VB and current IB.

SMR115is electrically connected between power storage device190and PCU120. SMR115is controlled by a control signal SE1from vehicle ECU300and switches supplying and cutting of electric power between power storage device190and PCU120.

PCU120includes a converter and an inverter (neither illustrated in the drawing). The converter is controlled by a control signal PWC from vehicle ECU300and performs a voltage conversion between power storage device190and the inverter. The inverter is controlled by a control signal PWI from vehicle ECU300and uses the electric power having a voltage converted by the converter to drive motor generator130.

Motor generator130is an alternating-current rotating electrical machine and is constituted of, for example, a permanent-magnet type synchronous motor including a rotor having a permanent magnet buried therein. Output torque of motor generator130is transmitted to drive wheels150through drive power transmission gear140. Vehicle100travels with use of this torque. Motor generator130can generate electric power by a rotational force of drive wheels150during the regenerative braking of vehicle100. Then, the voltage of the electric power generated by motor generator130is converted by PCU120, and the electric power is then stored in power storage device190.

It should be noted that, in a hybrid vehicle having an engine (not illustrated) in addition to motor generator130, the engine and motor generator130are operated cooperatively to generate a required vehicle driving force. In this case, power storage device190can be charged by generating electric power with use of power of the engine.

Communication unit160is a communication interface for performing a wireless communication between vehicle100and power transmission device200and performs transmission and reception of information INFO with communication unit230of power transmission device200. Information INFO outputted from communication unit160to power transmission device200includes vehicle information from vehicle ECU300and a signal commanding starting and stopping of power transmission.

RFID tag155includes an antenna and a storage unit preliminarily storing the vehicle information (neither illustrated in the drawing). When electric power is supplied from RFID reader270of power transmission device200through the antenna, RFID tag155transmits information stored in the storage unit through the antenna. It should be noted that, in the present embodiment, a plurality of RFID tags155are provided, and the RFID tags are arranged at a leading end and a trailing end of vehicle100as well as close to power receiving unit220. The arrangement configuration of RFID tags155and RFID reader270of power transmission device200will be described later in detail.

Vehicle ECU300includes a CPU, a storage device, an input-output buffer, and the like (none of these are illustrated in the drawing), performs input of a signal from each sensor and output of a control signal to each device, and performs a control of each device in vehicle100. These controls are not limited to the processing by software but can be processed with a dedicated hardware (electronic circuit).

Voltage sensor195detects a receiving voltage Vre of power receiving unit110. Current sensor196detects a receiving current Ire of power receiving unit110. Each detection value of receiving voltage Vre and receiving current Ire is transmitted to vehicle ECU300and used for calculation of a power transfer efficiency.

It should be noted that, althoughFIG. 1shows the configuration in which power receiving unit110and power transmission unit220respectively have electromagnetic induction cols113,223, it is also possible to employ another configuration like a power feeding system10A shown inFIG. 2in which a power receiving unit110A and a power transmission unit220A do not include electromagnetic induction coils. In this case, resonant coil221is connected to matching device260in power transmission unit220A, and resonant coil111is connected to rectifier180in power receiving unit110A.

It should be noted that, although capacitor224is connected to resonant coil221in series to form an LC resonant circuit with resonant coil221in power transmission unit220A, capacitor224may be connected to resonant coil221in parallel. Moreover, although capacitor114is connected to resonant coil111in series to form an LC resonant circuit with resonant coil111also in power receiving unit110A, capacitor114may be connected to resonant coil111in parallel.

Moreover, as shown inFIG. 2, as impedance adjustment means in the vehicle, a DC/DC converter170A for converting the direct current voltage rectified by rectifier180may be provided in place of matching device170inFIG. 1.

(Principle of Power Transfer)

FIG. 3is an equivalent circuit diagram representing the power transfer from power transmission device200to vehicle100. Referring toFIG. 3, in power transmission device200, electromagnetic induction coil223of power transmission unit220is provided, for example, substantially coaxially with resonant coil221and is spaced apart by a predetermined gap from resonant coil221. Electromagnetic induction coil223magnetically couples with resonant coil221by electromagnetic induction, and supplies high-frequency electric power supplied from power supply device210to resonant coil221by electromagnetic induction.

Resonant coil221forms an LC resonant circuit with capacitor222. It should be noted that, as will be described later, an LC resonant circuit is formed also in power receiving unit110of vehicle100. A difference between the natural frequency of the LC resonant circuit formed by resonant coil221and capacitor222and the natural frequency of the LC resonant circuit of power receiving unit110is less than or equal to ±10% of the natural frequency of the former or the natural frequency of the latter. Resonant coil221receives electric power from electromagnetic induction coil223by electromagnetic induction and contactlessly transmits the electric power to power receiving unit110of vehicle100.

It should be noted that electromagnetic induction coil223is provided so as to facilitate a supply of power from power supply device210to resonant coil221and that, as shown inFIG. 2, power supply device210may be directly connected to resonant coil221without providing electromagnetic induction coil223. Moreover, since capacitor222is provided to adjust the natural frequency of the resonant circuit, the configuration without capacitor222may be employed when a desired natural frequency can be obtained with use of a stray capacity of resonant coil221.

On the other hand, in vehicle100, resonant coil111of power receiving unit110forms an LC resonant circuit with capacitor112. As described above, the difference between the natural frequency of the LC resonant circuit formed by resonant coil111and capacitor112and the natural frequency of the LC resonant circuit formed by resonant coil221and capacitor222in power transmission unit220of power transmission device200is ±10% of the natural frequency of the former or the natural frequency of the latter. Then, resonant coil111contactlessly receives electric power from power transmission unit220of power transmission device200.

Electromagnetic induction coil113is provided, for example, substantially coaxially with resonant coil111and spaced apart by a predetermined gap from resonant coil111. Electromagnetic induction coil113is magnetically coupled with resonant coil111by electromagnetic induction, extracts by electromagnetic induction the electric power received by resonant coil111, and outputs the electric power to an electric load118. It should be noted that electric load118is electric equipment using the electric power received by power receiving unit110. Specifically, electric load118collectively represents electric equipment provided subsequently to matching device170(FIG. 1).

It should be noted that electromagnetic induction coil113is provided to facilitate the extraction of the electric power from resonant coil111, and resonant coil111may be directly connected to electric load118without providing electromagnetic induction coil113as shown inFIG. 2. Moreover, since capacitor112is provided to adjust the natural frequency of the resonant circuit, the configuration without capacitor112may be employed when a desired natural frequency can be obtained by using the stray capacity of resonant coil111.

In power transmission device200, the high-frequency alternating-current power is supplied from power supply device210to electromagnetic induction coil223, and the electric power is supplied to resonant coil221with use of electromagnetic induction coil223. Then, energy (electric power) is transferred from resonant coil221to resonant coil111through a magnetic field formed between resonant coil221and resonant coil111of vehicle100. The energy (electric power) transferred to resonant coil111is extracted with use of electromagnetic induction coil113and transferred to electric load118of vehicle100.

As described above, in this power transfer system, the difference between the natural frequency of power transmission unit220of power transmission device200and the natural frequency of power receiving unit110of vehicle100is less than or equal to ±10% of the natural frequency of power transmission unit220or the natural frequency of power receiving unit110. Setting the natural frequencies of power transmission unit220and power receiving unit110to be within such a range can improve the power transfer efficiency. On the other hand, when the difference between the natural frequencies described above becomes greater than ±10%, the power transfer efficiency becomes less than 10%, so that there is a possibility that the negative effect such as lengthening of the power transfer time may occur.

It should be noted that the natural frequency of power transmission unit220(power receiving unit110) means the oscillation frequency which is provided when the electrical circuit (resonant circuit) constituting power transmission unit220(power receiving unit110) oscillates. It should be noted that, in the electrical circuit (resonant circuit) constituting power transmission unit220(power receiving unit110), the natural frequency which is provided when the damping force or electric resistance is substantially zero is also referred to as a resonant frequency of power transmission unit220(power receiving unit110).

Referring toFIGS. 4 and 5, a simulation result of analyzing the relationship between the difference in the natural frequencies and the power transfer efficiency will be described.FIG. 4represents a simulation model of the power transfer system. Moreover,FIG. 5represents a relationship between the deviation in the natural frequencies of the power transmission unit and power receiving unit and the power transfer efficiency.

Referring toFIG. 4, a power transfer system89includes a power transmission unit90and a power receiving unit91. Power transmission unit90includes a first coil92and a second coil93. Second coil93includes a resonant coil94and a capacitor95provided in resonant coil94. Power receiving unit91includes a third coil96and a fourth coil97. Third coil96includes a resonant coil99and a capacitor98connected to this resonant coil99.

It is defined that an inductance of resonant coil94is an inductance Lt, and a capacitance of capacitor95is a capacitance C1. Moreover, it is defined that an inductance of resonant coil99is an inductance Lt, and a capacitance of capacitor98is a capacitance C2. With such a setting of each parameter, a natural frequency f1of second coil93is expressed by the following formula (1), and a natural frequency f2of third coil96is expressed by the following formula (2).
f1=1/{2π(Lt×C1)1/2}  (1)
f2=1/{2π(Lr×C2)1/2}  (2)

Here, in the case where inductance Lr and capacitance C1, C2are fixed, and only inductance Lt is changed, the relationship between the deviation in the natural frequencies of second coil93and third coil96and the power transfer efficiency is shown inFIG. 5. It should be noted that, in this simulation, the relative positional relationship between resonant coil94and resonant coil99is fixed, and the frequency of the current supplied to second coil93is constant.

In the graph shown inFIG. 5, the horizontal axis denotes the deviation in the natural frequencies (%), and the vertical axis denotes the power transfer efficiency (%) in the current of the constant frequency (%). The deviation in the natural frequencies (%) is expressed by the following formula (3).
(deviation in natural frequencies)={(f1−f2)/f2}×100(%)  (3)

As is apparent fromFIG. 5, when the deviation in the natural frequencies (%) is 0%, the power transfer efficiency is close to 100%. When the deviation in the natural frequencies (%) is ±5%, the power transfer efficiency is about 40%. When the deviation in the natural frequencies (%) is ±10%, the power transfer efficiency is about 10%. When the deviation in the natural frequencies (%) is ±15%, the power transfer efficiency is about 5%. In other words, it can be understood that the power transfer efficiency can be enhanced to a practical level by setting the natural frequencies of second coil93and third coil96so that an absolute value of the deviation in the natural frequencies (%) (the difference between the natural frequencies) falls within the range of less than or equal to 10% of the natural frequency of third coil96. Further, it is more preferable to set the natural frequencies of second coil93and third coil96so that the absolute value of the deviation in the natural frequencies (%) becomes less than or equal to 5% of the natural frequency of third coil96since the power transfer efficiency can be further enhanced. It should be noted that electromagnetic field analyzing software (JMAG (registered trademark) manufactured by JSOL Corporation) is employed as simulation software.

Referring back toFIG. 3, power transmission unit220and power receiving unit110contactlessly transmit and receive electric power through at least one of a magnetic field and an electric field formed between power transmission unit220and power receiving unit110. The magnetic field and/or electric field formed between power transmission unit220and power receiving unit110oscillates at a particular frequency. Then, by allowing power transmission unit220and power receiving unit110to resonate by the electromagnetic field, electric power is transferred from power transmission unit220to power receiving unit110.

Here, the magnetic field having the particular frequency formed around power transmission unit220will be described. The “magnetic field having the particular frequency” typically has a relevance between the power transfer efficiency and the frequency of the current supplied to power transmission unit220. Therefore, firstly, the relationship between the power transfer efficiency and the frequency of the current supplied to power transmission unit220will be described. The power transfer efficiency which is provided when the electric power is transferred from power transmission unit220to power receiving unit110changes due to various factors such as a distance between power transmission unit220and power receiving unit110. For example, the natural frequencies (resonant frequencies) of power transmission unit220and power receiving unit110are f0, and the frequency of the current supplied to power transmission unit220is f3, and an air gap between power transmission unit220and power receiving unit110is an air gap AG.

FIG. 6is a graph representing a relationship between the power transfer efficiency and frequency f3of a current supplied to power transmission unit220when air gap AG is changed in the state where a natural frequency f0is fixed. Referring toFIG. 6, the horizontal axis denotes frequency f3of the current supplied to power transmission unit220, and the vertical axis denotes the power transfer efficiency (%). An efficiency curve L1schematically represents a relationship between the power transfer efficiency and frequency f3of the current supplied to power transmission unit220when air gap AG is small. As indicated by this efficiency curve L1, when air gap AG is small, peaks of the power transfer efficiency occur at frequencies f4, f5(f4<f5). When air gap is set larger, the two peaks of high power transfer efficiency are changed so as to come close to each other. Then, as indicated by an efficiency curve L2, when air gap AG is set larger than a predetermined distance, one peak of the power transfer efficiency is provided, and the power transfer efficiency reaches a peak when the frequency of the current supplied to power transmission unit220is at frequency f6. When air gap AG is set larger than the state of efficiency curve L2, the peak of the power transfer efficiency becomes small as indicated by efficiency curve L3.

For example, the following approaches can be considered as approaches for improving the power transfer efficiency. As a first approach, it can be considered to fix the frequency of the current supplied to power transmission unit220in accordance with air gap AG and change the capacitance of capacitor222and capacitor112to thereby change the characteristics of the power transfer efficiency between power transmission unit220and power receiving unit110. Specifically, the capacitance of capacitor222and capacitor112is adjusted so that the power transfer efficiency reaches a peak in the state where the frequency of the current supplied to power transmission unit220is fixed. In this approach, the frequency of the current flowing to power transmission unit220and power receiving unit110is fixed regardless of the size of air gap AG.

Moreover, as a second approach, the frequency of the current supplied to power transmission unit220is adjusted based on the size of air gap AG. For example, in the state where the power transfer characteristics takes efficiency curve L1, the current of frequency f4or f5is supplied to power transmission unit220. When the frequency characteristic takes efficiency curves L2, L3, the current of frequency f6is supplied to power transmission unit220. In this case, the frequency of the current flowing to power transmission unit220and power receiving unit110is changed in accordance with the size of air gap AG.

In the first approach, the frequency of the current flowing to power transmission unit220has a fixed constant frequency. In the second approach, the frequency flowing to power transmission unit220is suitably changed in accordance with air gap AG. With the first approach and the second approach, a current having a particular frequency set so as to raise the power transfer efficiency is supplied to power transmission unit220. With a flow of the current having a particular frequency to power transmission unit220, a magnetic field (electromagnetic field) oscillating at a particular frequency is formed around power transmission unit220. Power receiving unit110receives electric power from power transmission unit220through a magnetic field which is formed between power receiving unit110and power transmission unit220and oscillates at a particular frequency. Thus, the “magnetic field oscillating at a particular frequency” is not necessarily a magnetic field having a fixed frequency. It should be noted that, although the frequency of the current supplied to power transmission220is set by focusing on air gap AG in the example described above, the power transfer efficiency is changed due to other factors such as the deviation of power transmission unit220and power receiving unit110in the horizontal direction, thus there is a case where the frequency of the current supplied to power transmission unit220is adjusted based on the other factors.

It should be noted that, although the coil (for example, a helical coil) is employed in power transmission unit220and power receiving unit110in the description above, an antenna such as a meander line may be employed in place of the coil. In the case where an antenna such as a meander line is employed, a flow of the current having a particular frequency to power transmission unit220forms an electric field having a particular frequency around power transmission unit220. Then, the power transfer is performed between power transmission unit220and power receiving unit110through this electric field.

In this power transfer system, the improvement in the power transmission and power reception efficiency is attempted by using a near field (evanescent field) in which a “static magnetic field” of an electromagnetic field is dominant.

FIG. 7represents a relationship between a distance from a current source or magnetic current source and an intensity of the electromagnetic field. Referring toFIG. 7, the electromagnetic field is constituted of three components. A curve k1is a component which is inversely proportional to a wave source, and it is referred to as a “radiation electromagnetic field.” A curve k2is a component which is inversely proportional to a square of the distance from the wave source, and it is referred to as an “induction electromagnetic field.” Moreover, a curve k3is a component which is inversely proportional to a cube of the distance from the wave source, and it is referred to as a “static electromagnetic field.” It should be noted that, when a wavelength of the magnetic field is provided as “λ,” a distance at which the intensities of the “radiation electromagnetic field,” “induction electromagnetic field,” and “static electromagnetic field” are substantially equal can be expressed by λ/2π.

The “static electromagnetic field” is a region in which the intensity of the electromagnetic wave is drastically reduced with a distance form the wave source. In the power transfer system of the present embodiment, the transfer of energy (electric power) is performed with use of a near field (evanescent field) in which this “static electromagnetic field” is dominant. In other words, in the near field in which the “static electromagnetic field” is dominant, power transmission unit220and power receiving unit110(for example, a pair of LC resonant coils) having a close natural frequency are resonated to transfer energy (electric power) from power transmission unit220to power receiving unit110. Since this “static electromagnetic field” does not propagate energy to a distant place, the resonance method can transmit electric power with a less energy loss as compared to the electromagnetic wave which transfers energy (electric power) by means of “radiation electromagnetic field” propagating energy to a distant place.

As described above, in this power transfer system, power transmission unit220and power receiving unit110are resonated by means of the electromagnetic field to contactlessly transfer electric power between power transmission unit220and power receiving unit110. Such an electromagnetic field formed between power transmission unit220and power receiving unit110is sometimes referred to as a near field resonant (resonance) coupling field. A coupling coefficient (κ) between power transmission unit220and power receiving unit110is, for example, about less than or equal to 0.3, preferably less than or equal to 0.1. As a matter of course, a coupling coefficient (κ) within the range of about 0.1 to 0.3 can be employed. Coupling coefficient (κ) is not limited to such values, and it may take various values providing a favorable power transfer.

It should be noted that, the coupling of power transmission unit220and power receiving unit110described above in the power transfer is referred to as, for example, “magnetic resonance coupling,” “magnetic field resonance coupling,” “magnetic field resonant (resonance) coupling,” “near field resonant (resonance) coupling,” “electromagnetic field resonant coupling,” “electric field resonant coupling,” or the like. The “electromagnetic field resonant coupling” means coupling including any of “magnetic resonance coupling,” “magnetic field resonance coupling,” and “electric field resonant coupling.”

When power transmission unit220and power receiving unit110are formed in the manner described above, power transmission unit220and power receiving unit110are coupled mainly by the magnetic field, and “magnetic resonance coupling” or “magnetic field resonance coupling” is formed. It should be noted that, for example, an antenna such as a meander line can be employed for power transmission unit220and power receiving unit110, and in this case power transmission unit220and power receiving unit110are coupled mainly by an electric field to form “electric field resonance coupling.”

(Description of Authentication Processing between Power Transmission Device and Vehicle)

In the power feeding system described above, the power transfer is contactlessly performed. Therefore, the transmission of various information between the power transmission device and the vehicle is also generally performed by a wireless communication by the communication unit. The wireless communication with use of the communication unit is generally designed to have a relatively wide range of a communicable range to notify a plurality of vehicles that the power transmission device can be used or to allow a vehicle to search a power transmission device which can be used among a plurality of power transmission devices.

However, the wide communicable range may cause a mismatch between a vehicle identified by the power transmission device as a subject to be supplied with power and a vehicle which is about to be parked in a parking frame provided with the power transmission unit of the power transmission device and receive a supply of power. Specifically, the power transmission device may identify a vehicle which is parked in an adjacent parking frame provided with other power transmission device as a subject to the supply of power. When such a mismatch occurs, a specification of a vehicle and a state of charge of a power storage device actually receiving a supply of power from the power transmission device cannot be grasped appropriately, so that the charging operation is not performed correctly.

Or, in the case where the parking operation to the parking frame provided with the power transmission device is started, and thereafter the parking operation is stopped for some reason and the vehicle is moved from the parking frame, the wide range of the communicable range of the wireless communication with use of the communication unit causes unnecessary identification (pairing) to be continued between the power transmission device and the vehicle, and may reduce the opportunity for other vehicle to use the power transmission device.

Thus, in such a power feeding system, it would be necessary to appropriately set pairing between the power transmission device and the vehicle and a timing of setting and releasing. Therefore, in the present embodiment, as shown inFIGS. 1 and 2, a communication with use of an RFID tag155and an RFID reader270having a narrower communicable range than the communication with use of communication units160,230is used together with the communication with use of communication unit160,230to improve a reliability of the pairing between power transmission device200and vehicle100.

On the other hand, in the communication with use of the RFID, the narrow communicable range may cause the situation where parking into the parking frame provided with power transmission unit220of power transmission device200is completed before the pairing between power transmission device200and vehicle100is established. In such a case, pairing between power transmission device200and vehicle100is established after the completion of the parking, and the determination on whether or not the parking is performed at an appropriate position can be made after the pairing is established. Therefore, it would be necessary to perform the parking operation again when the parking is not performed at an appropriate position.

Therefore, in the present embodiment, to allow the pairing between power transmission device200and vehicle100to be established at an early stage, RFID tag155is arranged at a vehicle body front end in the vehicle traveling direction when vehicle100is guided to the parking frame provided with power transmission unit220. Specifically, in the present embodiment, RFID tag155is provided at each of a vehicle body leading end and a vehicle body trailing end of vehicle100, assuming the case where vehicle100is parked forward in the parking frame and the case where vehicle100is parked backward in the parking frame.

It should be noted that the “front end” of the vehicle body does not mean only the most front end of the vehicle body, and in the vehicle body leading end it means, for example, the portion of the vehicle body on a more front side than front wheels, and in the vehicle body trailing end it means the portion on a more rear side than the rear wheels.

Moreover, in the present embodiment, RFID tag155is provided also near power receiving unit110to detect a position of power receiving unit110of vehicle100with a high accuracy. In other words, the communication with use of the RFID uses a known distance estimating approach to detect a distance between the RFID reader and the RFID tag. Thus, a distance of the RFID tag provided close to power receiving unit110is detected from, for example, three RFID readers to allow detection of a position of power receiving unit110through a principle of trilateration.

It should be noted that RFID tags155arranged at the vehicle body leading end, the vehicle body trailing end, and the location close to the power receiving unit are preferably arranged substantially at a center in the vehicle body leftward and rightward directions to avoid incorrect pairing with a power transmission device associated with an adjacent parking frame.

FIG. 8represents an arrangement example of RFID tags155and RFID readers270. It should be noted that, in thisFIG. 8, the case where vehicle100is parked backward to parking frame280will be described representatively.

Referring toFIG. 8, vehicle100includes power receiving unit110and three RFID tags155-1to155-3. RFID tag155-1is arranged at the vehicle body trailing end. In other words, RFID tag155-1is arranged at a vehicle body front end in the vehicle traveling direction when vehicle100is guided to a parking frame280provided with power transmission unit220. RFID tag155-2is arranged at the vehicle body leading end. If vehicle100is parked forward into the parking frame, RFID tag155-2is an RFID tag arranged at the vehicle body front end in the vehicle traveling direction.

In the present embodiment, power receiving unit110is arranged in a vehicle body lower part and closer to the rear part of the vehicle body. RFID tag155-3is arranged on a side of power receiving unit110closer to the vehicle body front end. In other words, RFID tag155-3is arranged close to power receiving unit110on the vehicle body front side having a longer distance among a distance from power receiving unit110to the vehicle body leading end and a distance from power receiving unit110to the vehicle body trailing end. Accordingly, the interruption of the communication of the RFID due to an excessively large gap between RFID tag155-2and RFID tag155-3is avoided.

On the other hand, power transmission device200includes power transmission unit220and RFID readers270-1to270-6. Power transmission unit220is arranged at an appropriate location in parking frame280correspondingly to the arrangement of power receiving unit110of vehicle100. RFID reader270-1is arranged on a side closer to the vehicle entering end of parking frame280than power transmission unit220. In the present embodiment, RFID reader270-1is arranged near the vehicle entering end of parking frame280. As described above, while RFID tag155-1is arranged at the vehicle body trailing end in vehicle100so that the pairing between power transmission device200and vehicle100during the parking operation can be completed at an early stage, RFID reader270-1is further arranged near the vehicle entering end of parking frames280, thus the pairing between power transmission device200and vehicle100can be completed at an earliest stage. It should be noted that arranging RFID reader270-1outside of parking frame280is not preferable since it may raise the possibility of detection of a vehicle parked in other parking frame.

RFID readers270-2,270-3are arranged relatively close to RFID reader270-1, and these are respectively arranged on left and right sides of RFID reader270-1. RFID readers270-2,270-3are provided to calculate a vehicle height (a height of power receiving unit110from the ground) by means of RFID readers270-1to270-3when RFID tag155-3arranged at an end of power receiving unit110comes close. In other words, a distance of RFID tag155-3is detected from each of RFID readers270-1to270-3, so that a position (height) of RFID tag155-3can be calculated with use of the principle of trilateration, and a vehicle height (a height of power receiving unit110from the ground) can be calculated with use of the calculation result.

It should be noted that the vehicle height affects an impedance between power transmission unit220and power receiving unit110, assuming a distance between power transmission unit220and power receiving unit110. Therefore, in the present embodiment, the impedance is adjusted by adjusting matching device170(it may be matching device260of power transmission device200) in accordance with the vehicle height, so that improvement of the power transfer efficiency between power transmission unit220and power receiving unit110can be made.

RFID readers270-4to270-6are arranged close to power transmission unit220, and provided to detect a relative positional relationship of power receiving unit110with respect to power transmission unit220. As one example, RFID reader270-4is arranged at an end of power transmission unit220, and RFID readers270-5,270-6are arranged respectively on left and right of RFID reader270-4relatively close to RFID reader270-1. As with the principle of the position detection of the RFID tag by means of RFID readers270-1to270-3, RFID readers270-4to270-6detect the relative positions of power receiving unit110with respect to power transmission unit220, and an alignment processing of power receiving unit110with respect to power transmission unit220is executed based on the detection result.

It should be noted that the alignment with use of the communication by the RFID cannot find out the position at which the power transfer efficiency between power transmission unit220and power receiving unit110is actually appropriate. Therefore, in the present embodiment, a test power transmission (power transmission smaller than the transmission of power for actually charging power storage device190) from power transmission unit220to power receiving unit110is performed during the parking operation to supplement the alignment processing based on the power transfer efficiency during the test power transmission.

FIGS. 9 and 10represent flowcharts for explanation of an authentication processing executed in vehicle100and power transmission device200. Each step in the flowcharts can be achieved by calling a program preliminarily stored mainly in vehicle ECU300and power transmission ECU240from the main routine and executing the program at predetermined cycles or in response to meeting a predetermined condition. Alternatively, processing of all or some of the steps can be achieved by constructing a dedicated hardware (electronic circuit).

Referring toFIGS. 1 and 8withFIG. 9, the processing in vehicle100will be described. Vehicle100starts searching for a power transmission device (in the following, also referred to as a “charging stand” or “stand”) by a wireless communication with use of communication unit160(Step S100). Specifically, vehicle100transmits, for example, continuously at predetermined intervals, response request information including a vehicle ID for identifying the vehicle without specifying a mate stand.

Then, vehicle100is operated by a user to start a parking operation to a parking frame of a particular stand to perform contactless charging (Step S105). It should be noted that vehicle100is parked backward into parking frame280also herein as shown inFIG. 8. During the parking operation, RFID reader270of power transmission device200(specifically, RFID reader270-1arranged at the vehicle entering end of parking frame280) reads tag information stored in RFID tag155-1provided at the vehicle body trailing end of vehicle100(Step S125). This tag information includes a vehicle ID of vehicle100and ID information of RFID tag155-1.

It should be noted that, as will be described later, in power transmission device200, when the vehicle information wirelessly transmitted from vehicle100and vehicle information read from RFID tag155-1correspond to each other and it is identified as the same vehicle, a wireless transmission (polling) of connection request information, which specifies a mate vehicle for example by adding a vehicle ID of the vehicle and a stand ID of the stand itself, is executed (Steps S205, S210).

Next, vehicle100determines whether or not the connection request information specifying the vehicle itself is received from the stand (Step S110). When the connection request information is not received (NO in Step S110), the process returns to Step S100, and vehicle100continues the parking operation while transmitting response request information to the stand.

When the connection request information is received (YES in Step S110), vehicle100determines that the vehicle itself is a vehicle subjected to a supply of electric power in the stand where the parking is currently performed, and transmits a connection completion notification to the stand (Step S115). Then, vehicle100starts a wireless communication specifying the mate stand. Accordingly, one-to-one communication between power transmission device200and vehicle100is started (Step S120).

On the other hand, when the response request information is received from vehicle100, power transmission device200starts searching for RFID tag155by means of RFID reader270(specifically, RFID reader270-1arranged at the vehicle entering end of parking frame280) (step S200). When RFID tag155-1provided at a near end of vehicle100(a rear end of the vehicle) receives electric power from RFID reader270-1, RFID tag155-1transmits tag information stored therein (Step S125).

After searching for RFID tag155is started, power transmission device200determines whether or not tag information is received which includes a vehicle ID matching with a vehicle ID included in the response request information from vehicle100(Step S205). When such tag information is not received (NO in Step S205), the process returns to step S200, and power transmission device200continues searching for the RFID tag.

When the tag information including the vehicle ID included in the response request information is received (YES in Step S205), power transmission device200transmits connection request information having the stand ID of the stand itself and the received vehicle ID through a wireless communication (Step S210). When vehicle100receives the connection request information, a connection completion notification is transmitted from vehicle100through a wireless communication (Step S115). Then, when the connection completion notification is received at power transmission device200(YES in Step S215), power transmission device200starts a wireless communication specifying the vehicle. Accordingly, one-to-one communication between vehicle100and power transmission device200is established (Step S220).

Referring toFIG. 10, the description as to power transmission device200will be continued. Even after RFID tag155-1provided at the near end of vehicle100(the rear end of the vehicle) is detected, and the one-to-one communication with vehicle100is started, power transmission device200continuously executes the searching for RFID tag155(Step S225). Then, as the parking operation proceeds, and when RFID tag155-3provided close to power receiving unit110receives electric power from RFID reader270-1subsequently to RFID tag155-1, RFID tag155-3transmits tag information stored therein (Step S155). It should be noted that the tag information includes, in addition to vehicle ID of vehicle100, the ID information for specifying RFID tag155-3.

When the tag information of RFID tag155-3is received (YES in Step S230), power transmission device200calculates a vehicle height of vehicle100(a height of power receiving unit110from the ground) (Step S235). In the present embodiment, as shown inFIG. 8, RFID readers270-2,270-3are provided at positions relatively close to RFID reader270-1, and a distance of RFID tag155-3from each of RFID readers270-1to270-3is detected, so that a position of RFID tag155-3(a height from the ground) is calculated with use of the principle of trilateration. Then, a vehicle height (a height of power receiving unit110from the ground) is calculated with use of the calculation result. The calculation result of the vehicle height is transmitted to vehicle100, and matching device170is adjusted in vehicle100in accordance with the vehicle height. It should be noted that, although it is not illustrated in the drawing, matching device260of power transmission device200may be adjusted in accordance with the vehicle height.

Next, power transmission device200starts test power transmission for supporting the alignment process of power receiving unit110with respect to power transmission unit220(Step S240). Next, power transmission device200detects a relative position of power receiving unit110with respect to power transmission unit220(Step S245). In the present embodiment, as shown inFIG. 8, RFID reader270-4is provided close to power transmission unit220, and RFID readers270-5,270-6are further provided at positions relatively close to RFID reader270-4. Then, a distance from each of RFID readers270-4to270-6to RFID tag155-3provided close to power receiving unit110is detected, so that the position of RFID tag155-3is calculated with use of the principle of trilateration, and the relative position of power receiving unit110with respect to power transmission unit220is detected based on the calculation result.

The result of detecting the position of power receiving unit110is transmitted to vehicle100, and the alignment processing of power receiving unit110with respect to power transmission unit220is executed based on the result of detection of the position (Step S135). It should be noted that, since the position detection with use of the communication by means of the RFID cannot find out the position at which the power transfer efficiency between power transmission unit220and power receiving unit110actually becomes optimum as described above, the alignment processing between power transmission unit220and power receiving unit110is supplemented based on the power transfer efficiency involved in the test power transmission started in step S240.

Power transmission device200continuously executes searching for RFID tag155(Step S250). Then, as the parking operation proceeds, and when RFID tag155-2arranged at a far end of vehicle100(the vehicle leading end) receives electric power from RFID reader270-1subsequently to RFID tag155-3, RFID tag155-2transmits tag information stored therein (Step S160). It should be noted that this tag information also includes, in addition to the vehicle ID of vehicle100, the ID information for specifying RFID tag155-2.

Then, when the tag information of RFID tag155-2is received (YES in Step S255), and further the parking of vehicle100is completed (YES in step S260), power transmission device200stops the test power transmission (Step S265) and executes the power transmission processing for charging power storage device190of vehicle100(Step S270).

On the other hand, in vehicle100, matching device170is adjusted based on the calculation result of the vehicle height (Step S130). It should be noted that the adjustment of matching device170can be made by, for example, preliminarily obtaining a relationship between a vehicle height and an adjusted value, preparing a map or the like, and adjusting matching device170based on the calculation result of the vehicle height with use of the map.

Moreover, vehicle100executes the alignment processing of power receiving unit110with respect to power transmission unit220based on the detection result of the position of power receiving unit110(Step S135). It should be noted that, in vehicle100, the test power transmission is received from power transmission device200, and the alignment processing is supplemented based on the power transmission efficiency in the test power transmission (it may be simply the received power).

Next, vehicle100determines whether or not the parking position of vehicle100in parking frame280is appropriate (Step S140). For example, when the deviation amount in the relative position between power transmission unit220and power receiving unit110is within a predetermined range, and the power transfer efficiency by the test power transmission exceeds a predetermined value, it is determined that the parking position is appropriate.

When the parking position is not appropriate (NO in Step S140), the process returns to Step S135, and the alignment processing is executed continuously. On the other hand, when the parking position is appropriate (YES in Step S140), vehicle100transmits a completion notification of the parking operation to power transmission device200(Step S145). After that, the process proceeds to Step S150, and the power receiving processing is executed in vehicle100with the execution of the power transmission processing in power transmission device200(Step S150).

As described above, in the present embodiment, since RFID tag155(RFID tag155-1) is arranged at the vehicle body front end (the vehicle body trailing end) in vehicle100in the vehicle traveling direction when the vehicle is guided to parking frame280, the vehicle ID stored in RFID tag155can be read by power transmission device200at an early stage. Thus, according to the present embodiment, the pairing between power transmission device200and vehicle100can be established at an early stage. Consequently, it allows for the alignment during the parking operation.

Moreover, in the present embodiment, since RFID tag155(RFID tag155-2) is provided also at the vehicle body leading end, the pairing between power transmission device200and vehicle100can be established at an early stage also during the forward parking.

Further, in the present embodiment, since RFID tag155(RFID tag155-3) is further provided close to power receiving unit110, a height of power receiving unit110from the ground and the relative position between power transmission unit220and power receiving unit110can be detected with a high accuracy by detecting a distance from the RFID reader to RFID tag155-3.

Further, RFID tag155-3is provided close to power receiving unit110on the vehicle body end side having a larger distance (in the present embodiment, it is the vehicle front side) among a distance from power receiving unit110to the vehicle body leading end and a distance from power receiving unit110to the vehicle body trailing end. Accordingly, the interruption of communication of the RFID due to excessively large gap between RFID tag155-3and RFID tag155-2during the parking operation can be avoided.

Moreover, in the present embodiment, each of RFID tags155-1to155-3is arranged substantially at a center in the vehicle body leftward and rightward directions, incorrect pairing with the power transmission device corresponding to the adjacent parking frame can be avoided.

Further, according to the present embodiment, a wide area communication with use of the communication unit and the narrow area communication with use of the RFID are used together to perform the pairing between power transmission device200and vehicle100, so that a highly reliable pairing can be achieved.

Moreover, in the present embodiment, RFID reader270-1is arranged near the vehicle entering end of parking frame280in parking frame280also in power transmission device200. Accordingly, the pairing between power transmission device200and vehicle100can be completed at an earliest stage.

It should be noted that, in the present embodiment, RFID tag155-1corresponds to one example of the “ID tag” in the present invention, and each of RFID tags155-2,155-3corresponds to one example of “another ID tag” in the present invention. Moreover, RFID reader270-1corresponds to one example of the “reading unit” in the present invention, and RFID reader270-4corresponds to one example of “another reading unit” in the present invention.

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