Abstract:
Provided are an electric automobile to which a power supply device supplies power, and an electricity supply system capable of accurately associating the power supply device and the electric automobile carrying out communication therewith. A power supply-side control unit ( 24 ) controls such that electricity that a power supply unit ( 21 ) supplies reaches a first electricity quantity Pa before a power supply-side communications unit ( 23 ) receives a request signal from a vehicle-side communications unit ( 43 ), and controls such that electricity that the power supply unit ( 21 ) supplies reaches a second electricity quantity Pb, which is greater than the first electricity quantity Pa, after the power supply-side communications unit ( 23 ) receives the request signal from the vehicle-side communications unit ( 43 ). The vehicle-side communications unit ( 43 ) activates on the basis of the first electricity quantity Pa received from the power supply unit ( 21 ) of a power supply device ( 2 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a power supply system for an electric vehicle which supplies power from a power supply apparatus to an electric vehicle in a non-contact manner, and an electric vehicle and a power supply apparatus which are used for the power supply system. 
       BACKGROUND ART 
       [0002]    A power supply system for an electric vehicle is known which includes an electric vehicle and a power supply apparatus that supplies power to the electric vehicle in a non-contact manner. 
         [0003]    An electric vehicle includes a communication section that transmits a signal (hereinafter, referred to as a “request signal”) for requesting for a supply of power and a power receiving section (power receiving coil) that can be supplied with power in a non-contact manner. A power supply apparatus includes a power supply section (power supply coil) that can supply power in a non-contact manner and a control section that controls the supply of power to the power supply coil in response to a request signal transmitted from an electric vehicle. For example, PTL 1 is known as a related art document. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1 
         Japanese Patent Application Laid-Open No. 2005-73313 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    In a conventional power supply system, it is not considered that multiple electric vehicles are present around a power supply apparatus. 
         [0007]    Accordingly, an electric vehicle located above the power supply coil may be different from an electric vehicle having transmitted a request signal. 
         [0008]    For example, there is a possibility that the power supply apparatus receives a request signal from an electric vehicle not located above the power supply coil and supplies power to an electric vehicle located above the power supply coil in response to the received request signal. 
         [0009]    At this time, when it is necessary to charge the rechargeable battery of the electric vehicle having transmitted the request signal and the rechargeable battery of the electric vehicle located above the power supply coil is fully charged, the rechargeable battery of the electric vehicle located above the power supply coil may be overcharged, thereby causing problems such as destruction and overheating of the rechargeable battery. 
         [0010]    In a system in which an electric vehicle supplied with power is specified through communications between the electric vehicle and a power supply apparatus to bill the electric vehicle, when an electric vehicle located above the power supply coil is different from an electric vehicle having transmitted a request signal, there is a problem in that an electric vehicle not supplied with power is erroneously billed. 
         [0011]    An object of the present invention is to provide a power supply system which can accurately associate an electric vehicle supplied with power from a power supply apparatus, with an electric vehicle communicating with the power supply apparatus. 
       Solution to Problem 
       [0012]    According to an aspect of the present invention, there is provided a power supply system for an electric vehicle that supplies power from a power supply apparatus to an electric vehicle in a non-contact manner, wherein the electric vehicle includes a vehicle-side communication section that wirelessly communicates with the power supply apparatus, a power receiving section that is supplied with power from the power supply apparatus in a non-contact manner, and a power storage section that stores power received by the power receiving section, wherein the power supply apparatus includes a vehicle detecting section that detects the entrance of the electric vehicle to a predetermined area, a power supply-side communication section that wirelessly communicates with the vehicle-side communication section of the electric vehicle, a power supply section that supplies power to the power receiving section of the electric vehicle in a non-contact manner, and a power supply-side control section that controls the power supply section, and wherein the power supply-side control section performs a control for causing the power supply section to supply power of a first power value when the vehicle detecting section detects the entrance of the electric vehicle to the predetermined area, and performs a control for causing the power supply section to supply power of a second power value greater than the first power value when it is determined that a communication is set up between the power supply-side communication section and the vehicle-side communication section in a state where the power supply section is supplying power of the first power value. 
         [0013]    According to another aspect of the present invention, there is provided an electric vehicle that is supplied with power from a power supply apparatus in a non-contact manner, including: a vehicle-side communication section that wirelessly communicates with the power supply apparatus; a power receiving section that is supplied with power from the power supply apparatus in a non-contact manner; and a power storage section that stores power received by the power receiving section, wherein the vehicle-side communication section transmits a request signal to the power supply apparatus in a state where the power receiving section is being supplied with power of a first power value from the power supply apparatus, and wherein the power storage section stores power of a second power value which is greater than the first power value and which is supplied from the power supply apparatus to the power receiving section after transmitting the request signal. 
         [0014]    According to still another aspect of the present invention, there is provided a power supply apparatus that supplies power to an electric vehicle in a non-contact manner, including: a vehicle detecting section that detects the entrance of the electric vehicle to a predetermined area; a power supply-side communication section that wirelessly communicates with the electric vehicle; a power supply section that supplies power to the electric vehicle in a non-contact manner; and a power supply-side control section that controls the power supply section, wherein the power supply-side control section performs a control for causing the power supply section to supply power of a first power value when the vehicle detecting section detects the entrance of the electric vehicle to the predetermined area, and performs a control for causing the power supply section to supply power of a second power value greater than the first power value when the power supply-side communication section receives a request signal from the electric vehicle in a state where the power supply section is supplying power of the first power value. 
       Advantageous Effects of Invention 
       [0015]    According to the aspects of the present invention, since the vehicle-side communication section is started up with the first power value supplied from the power supply section of the power supply apparatus and transmits a request signal to the power supply apparatus, it is possible to accurately associate an electric vehicle supplied with power from the power supply section of the power supply apparatus, with an electric vehicle communicating with the power supply apparatus. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a diagram illustrating the configuration of a power supply system for an electric vehicle according to Embodiment 1 of the present invention; 
           [0017]      FIG. 2  is a block diagram illustrating the configuration of the power supply system for an electric vehicle according to Embodiment 1 of the present invention; 
           [0018]      FIG. 3  is a diagram illustrating the operation of a power supply apparatus according to Embodiment 1 of the present invention; 
           [0019]      FIG. 4  is a diagram illustrating the operation of a power receiving apparatus according to Embodiment 1 of the present invention; 
           [0020]      FIG. 5  is a diagram illustrating a communication setup process according to Embodiment 1 of the present invention; 
           [0021]      FIG. 6  is a timing diagram in Embodiment 1 of the present invention; 
           [0022]      FIG. 7  is a diagram illustrating a communication setup process according to Embodiment 2 of the present invention; 
           [0023]      FIG. 8  is a block diagram illustrating the configuration of a power supply system for an electric vehicle according to Embodiment 3 of the present invention; 
           [0024]      FIG. 9  is a diagram illustrating the configuration of a power supply system for an electric vehicle according to Embodiment 4 of the present invention; and 
           [0025]      FIG. 10  is a diagram illustrating a communication setup process according to Embodiment 4 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
       [0026]    Hereinafter, a power supply system for an electric vehicle according to an embodiment of the present invention will be described with reference to  FIGS. 1 and 2 .  FIG. 1  is a diagram illustrating the configuration of a power supply system for an electric vehicle according to Embodiment 1 of the present invention.  FIG. 2  is a block diagram illustrating the configuration of the power supply system for an electric vehicle. In  FIG. 2 , a solid arrow represents the flow of signals and a dotted arrow represents the flow of power. 
         [0027]    As shown in  FIG. 1 , the power supply system for an electric vehicle according to an embodiment of the present invention includes power supply apparatus  2  installed in a road and electric vehicle  3  supplied with power from power supply apparatus  2 . More specifically, electric vehicle  3  is charged with power supplied from power supply apparatus  2  through the use of power receiving apparatus  4 . 
         [0028]    Electric vehicle  3  in Embodiment 1 of the present invention is a vehicle obtaining a thrust by electricity and includes an electric motor that generates, with power, a driving force transmitted to wheels. The electric motor is driven with power of power storage section  42  (see  FIG. 2 ). The power stored in the power storage section  42  is supplied from the outside of electric vehicle  3 . 
         [0029]    Examples of electric vehicle  3  in the present invention include an EV (Electric Vehicle) that is driven using only an electric motor and a plug-in hybrid vehicle that is driven using an engine and an electric motor and that enables power storage section  42  to be supplied with power from a power supply outside electric vehicle  3 . 
         [0030]    Detailed configurations of power supply apparatus  2  and power receiving apparatus  4  will be described below. 
         [0031]    Power supply apparatus  2  includes power supply section  21  that supplies power to power receiving section  41  of electric vehicle  3  in a non-contact manner, vehicle detecting section  22  that detects the entrance of electric vehicle  3  to a predetermined range on a road, power supply-side communication section  23  that communicates with electric vehicle  3 , and power supply-side control section  24  that controls sections of power supply apparatus  2 . 
         [0032]    Electric vehicle  3  can be charged in a non-contact manner by stopping in a predetermined range (hereinafter, referred to as “chargeable area B”) on road surface A in  FIG. 1 .  FIG. 1  shows an example where electric vehicle  3   a  is going to enter chargeable area B and electric vehicle  3   b  stops in the vicinity of electric vehicle  3   a.    
         [0033]    When electric vehicle  3   a  enters chargeable area B, power supply apparatus  2  sets up a communication with electric vehicle  3   a  and supplies power to electric vehicle  3   a . At this time, it is necessary for power supply apparatus  2  to control a communication not to be set up with electric vehicle  3   b  stopping in the vicinity thereof. The sections of power supply apparatus  2  will be described in detail below. 
         [0034]    Power supply section  21  generates power and supplies the generated power to electric vehicle  3  in a non-contact manner. It is preferable that power supply section  21  be installed in the vicinity of the road surface of a road. 
         [0035]    Power supply section  21  includes a power supply coil and a coil driving circuit that drives the power supply coil. The coil driving circuit drives the power supply coil by applying a pulse of a predetermined frequency to the power supply coil. The predetermined frequency (chopper frequency) of the pulse is controlled by power supply-side control section  24 . A magnetic field proportional to the current is generated in the power supply coil using the pulse as excitation current. An electromotive force is generated in the power receiving coil of power receiving section  41  by the magnetic field, and power is supplied from power supply section  21  to power receiving section  41 . 
         [0036]    Here, it is assumed that the magnitude of power supplied from power supply section  21  when electric vehicle  3  enters chargeable area B is defined as first power value Pa and the magnitude of power supplied from power supply section  21  after a communication between power supply apparatus  2  and electric vehicle  3  is set up is defined as second power value Pb. First power value Pa is such power as to have no influence on a human body. Here, the “such power as to have no influence on a human body” means such a small magnitude of power to have no influence on animals or the like present around power supply section  21 . Second power value Pb means a magnitude which is larger than first power value Pa and which enables power receiving section  41  to charge power storage section  42 . For example, first power value Pa is about several W to several tens W, and second power value Pb is about several kW to several tens kW. 
         [0037]    Vehicle detecting section  22  is a sensor used to determine whether electric vehicle  3  enters chargeable area B. Vehicle detecting section  22  transmits the determination result on whether electric vehicle  3  enters chargeable area B to power supply-side control section  24 . 
         [0038]    Vehicle detecting section  22  includes, for example, an infrared sensor that detects whether an object is present within a predetermined distance. A plurality of the infrared sensors are disposed at facing positions on the boundary of chargeable area B. Vehicle detecting section  22  determines that electric vehicle  3  enters chargeable area B, when all the infrared sensors detect an object. In another example of vehicle detecting section  22 , an imaging camera imaging a vehicle may be installed around the road and may detect that electric vehicle  3  enters or leaves chargeable area B by the use of an image captured with the imaging camera. 
         [0039]    Power supply-side communication section  23  wirelessly communicates with vehicle-side communication section  43  of electric vehicle  3  to be described later. Power supply-side communication section  23  is controlled by power supply-side control section  24 . 
         [0040]    Power supply-side communication section  23  includes an antenna receiving RF waves and a modulation and demodulation section modulating or demodulating a received signal. Power supply-side communication section  23  is always supplied with power. It is preferable that power supply-side communication section  23  be installed around a surface of a road. 
         [0041]    In the present invention, the communication method is not particularly limited, but a communication method of performing a short-distance communication of which the communication distance is several meters can be preferably used. This is because power supply-side communication section  23  needs only to be able to communicate with vehicle-side communication section  43  of electric vehicle  3  (electric vehicle  3  entering chargeable area B) to be supplied with power from power supply section  21 , and needs to prevent a communication with electric vehicle  3   b  stopping in the vicinity of electric vehicle  3   a  to be supplied with power, for example, as shown in  FIG. 1 . Examples of the communication method applicable to the present invention include ZigBee (registered trademark), wireless LAN, and communications using specified low power bands. 
         [0042]    Power supply-side control section  24  controls power supply section  21  on the basis of the detection result from vehicle detecting section  22  and information received by power supply-side communication section  23 . 
         [0043]    Specifically, when vehicle detecting section  22  detects that electric vehicle  3  enters chargeable area B, power supply-side control section  24  sets the magnitude of power to be supplied from power supply section  21  to first power value Pa. Power supply-side control section  24  then causes power supply-side communication section  23  to transmit and receive data in order to set up a communication between power supply-side communication section  23  and vehicle-side communication section  43 . When the communication is set up, power supply-side control section  24  sets the magnitude of power to be supplied from power supply section  21  to second power value Pb. Details of the control performed by power supply-side control section  24  will be described later. 
         [0044]    Power receiving apparatus  4  includes power receiving section  41  that receives power supplied from power supply section  21  of power supply apparatus  2 , power storage section  42  that stores power received by power receiving section  41 , vehicle-side communication section  43  that communicates with power supply-side communication section  23 , and vehicle-side control section  44  that controls power receiving section  41  and vehicle-side communication section  43 . The sections of power receiving apparatus  4  will be described in detail below. 
         [0045]    Power receiving section  41  is installed on the bottom surface of the vehicle body of electric vehicle  3  and includes a power receiving coil and a rectifier circuit. It is preferable that power receiving section  41  is installed on the bottom surface of electric vehicle  3  facing the road. 
         [0046]    The surface of the power receiving coil is covered with a synthetic resin or the like. The power receiving coil is a coil formed, for example, in a coplanar shape and can receive power from power supply section  21  through electromagnetic induction. The power received through electromagnetic induction is input to the rectifier circuit, is converted into DC current therein, and is output to power storage section  42 . 
         [0047]    Power storage section  42  stores power received by power receiving section  41 . A secondary battery (such as a nickel-hydrogen secondary battery or a lithium ion secondary battery) having a high energy density or a capacitor having large capacity is used as power storage section  42 . The power stored in power storage section  42  serves as a power source for driving the wheels of electric vehicle  3  and is used to operate an electric motor. The power stored in power storage section  42  is used as power for operating accessories such as a car navigation apparatus and a car audio apparatus, electrical components such as power windows, an ETC (registered trademark), and an ECU (Electronic Control Unit), and the like, in addition to the electric motor. 
         [0048]    Vehicle-side communication section  43  wirelessly communicates with power supply-side communication section  23  of power supply apparatus  2 . Vehicle-side communication section  43  is controlled by vehicle-side control section  44 . 
         [0049]    Vehicle-side communication section  43  includes an antenna for receiving RF waves and a modulation and demodulation section for modulating or demodulating a received signal. It is preferable that vehicle-side communication section  43  be installed on the bottom surface of electric vehicle  3  facing the road. Accordingly, the antenna is preferably a planar antenna not protruding from the bottom surface of electric vehicle  3 . 
         [0050]    In the present invention, the communication method is not particularly limited, but a communication method of performing a short-distance communication of which the communication distance is about several meters can be preferably used. 
         [0051]    Vehicle-side communication section  43  is started up on the basis of power received by power receiving section  41 . Specifically, vehicle-side communication section  43  is started when power of first power value Pa or more is supplied from power supply section  21  to power receiving section  41 , and operates with the power output from power receiving section  41 . 
         [0052]    After being started up, vehicle-side communication section  43  performs a process of setting up a communication with power supply-side communication section  23 . Vehicle-side communication section  43  operates with power received by power receiving section  41  until the communication is set up, and operates with power of power storage section  42  after the communication is set up. 
         [0053]    Vehicle-side communication section  43  is in a communication standby state after the communication is set up. Since vehicle-side communication section  43  operates with power received by power receiving section  41  until the communication is set up, it is possible to start the communication without using the power of power storage section  42 . 
         [0054]    Vehicle-side control section  44  controls vehicle-side communication section  43  and power receiving section  41  of power receiving apparatus  4 . Specifically, vehicle-side control section  44  controls power receiving section  41  to prepare reception of power and causes vehicle-side communication section  43  to transmit and receive data so as to set up a communication between power supply-side communication section  23  and vehicle-side communication section  43 . Details of the control performed by vehicle-side control section  44  will be described later. 
         [0055]    Vehicle-side control section  44  and power supply-side control section  24  include a CPU, a ROM, and a RAM. The CPU performs various operations, outputting of control signals, and the like by executing a program stored in the ROM. The CPU uses the RAM as a work area during execution of the program. 
         [0056]    The processing operations of the power supply system for an electric vehicle having the above-mentioned configuration will be described below with reference to  FIG. 3  to  FIG. 5 .  FIG. 3  is a diagram illustrating the operation of the power supply apparatus.  FIG. 4  is a diagram illustrating the operation of the power receiving apparatus.  FIG. 5  is a diagram illustrating a communication setup process. 
         [0057]    First, the operation of the power supply apparatus will be described with reference to  FIG. 3 . In “start” of  FIG. 3 , power supply section  21  does not supply power. 
         [0058]    Power supply-side control section  24  first determines whether electric vehicle  3  enters chargeable area B on the basis of the detection result from vehicle detecting section  22  (S 10 ). When electric vehicle  3  does not enter chargeable area B (NO in S 10 ), power supply-side control section  24  performs the process of S 10  again. 
         [0059]    When electric vehicle  3  enters chargeable area B (YES in S 10 ), power supply-side control section  24  controls power supply section  21  so that power supply section  21  supplies power of first power value Pa (S 11 ). 
         [0060]    Power supply-side communication section  23  performs a process of setting up a communication with vehicle-side communication section  43  of electric vehicle  3  entering chargeable area B (S 12 ). Details of this process will be described later. 
         [0061]    After the communication is set up in S 12 , power supply-side control section  24  controls power supply section  21  so that power supply section  21  supplies power of second power value Pb (S 13 ). When power supply section  21  supplies power of second power value Pb in S 13 , electric vehicle  3  starts receiving power. 
         [0062]    After the supply of power is started in S 13 , power supply-side control section  24  determines whether electric vehicle  3  leaves chargeable area B (S 14 ). When the electric vehicle leaves chargeable area B (YES in S 14 ), power supply-side control section  24  causes power supply section  21  to stop the supply of power (S 16 ). This process is performed regardless of whether the charging of electric vehicle  3  is ended. This is because when electric vehicle  3  is being charged but electric vehicle  3  moves for a certain reason, power supply section  21  supplying power of second power value Pb is exposed, which is dangerous. 
         [0063]    When electric vehicle  3  does not leave chargeable area B (NO in S 14 ), power supply-side control section  24  determines whether power supply-side communication section  23  receives a power supply stop signal from vehicle-side communication section  43  (S 15 ). When the power supply stop signal is received (YES in S 15 ), power supply-side control section  24  causes power supply section  21  to stop the supply of power (S 16 ). On the other hand, when the power supply stop signal is not received (NO in S 15 ), power supply-side control section  24  performs the process of S 14  again. When the process of S 16  is ended, the same state as “START” of  FIG. 3  is obtained. 
         [0064]    The operation of power receiving apparatus  4  will be described below with reference to  FIG. 4 . 
         [0065]    First, vehicle-side control section  44  prepares power receiving section  41  to receive power of first power value Pa (S 20 ). This preparation is a process for enabling power receiving section  41  to receive power. This preparation is started, for example, when the speed of a vehicle becomes lower than or equal to a predetermined speed. This is because the charging operation when a vehicle travels at a high speed cannot be normally considered. 
         [0066]    When the process of S 20  is ended, vehicle-side control section  44  determines whether vehicle-side communication section  43  is started up (S 21 ). Vehicle-side communication section  43  is started up when power receiving section  41  receives power of first power value Pa. When vehicle-side communication section  43  is not started up (NO in S 21 ), vehicle-side control section  44  repeatedly performs the process of S 21 . 
         [0067]    After power receiving section  41  receives power of first power value Pa to start up vehicle-side communication section  43  (YES in S 21 ), vehicle-side communication section  43  performs a process of setting up a communication with power supply-side communication section  23  of power supply apparatus  2  (S 22 ). Details of this process will be described later. 
         [0068]    When power receiving section  41  receives power of first power value Pa in S 21  and S 22 , vehicle-side communication section  43  operates with power output from power receiving section  41 . 
         [0069]    After the communication is set up in S 22 , vehicle-side control section  44  prepares power receiving section  41  to receive power of second power value Pb (S 23 ). This preparation includes, for example, a process of turning on a relay (not shown) connecting power receiving section  41  and power storage section  42 . 
         [0070]    After the communication is set up in S 22 , vehicle-side control section  44  switches the power source for vehicle-side communication section  43  so that vehicle-side communication section  43  operates with power supplied from power storage section  42  as a power source. This is because after the communication is set up once, it is preferable that the power source be switched to power storage section  42  which can stably supply power, to stabilize the communication. 
         [0071]    When the process of S 23  is ended, power receiving section  41  starts receiving power from power supply section  21 . Vehicle-side control section  44  determines whether power storage section  42  is fully charged during the reception of power (S 24 ). 
         [0072]    When it is determined that power storage section  42  is not fully charged (NO in S 24 ), vehicle-side control section  44  performs the process of S 24  again after a predetermined time passes, in order for power receiving section  41  to consecutively receive power. 
         [0073]    When it is determined that power storage section  42  is fully charged (YES in S 24 ), vehicle-side control section  44  causes vehicle-side communication section  43  to transmit a power supply stop signal (S 25 ). The power supply stop signal is a signal used for causing power supply section  2  to stop the supply of power of second power value Pb from power supply section  21 . When the charging is continuously performed even after power storage section  42  is fully charged, overcharging occurs to cause overheating of power storage section  42  and degradation in lifetime. Therefore, the supply of power is stopped by the use of the power supply stop signal. 
         [0074]    After transmitting the power supply stop signal, vehicle-side control section  44  performs a power reception ending process. Here, the power reception ending process includes, for example, a process of turning off a relay (not shown) connecting power receiving section  41  and power storage section  42 . 
         [0075]    The communication setup process will be described below with reference to  FIG. 5 . The left flowchart in  FIG. 5  represents the power supply-side process (S 12 ) and the right flowchart represents the vehicle-side process (S 22 ). 
         [0076]    After vehicle-side communication section  43  is started up in S 21 , vehicle-side control section  44  generates a random number (S 221 ). Then, vehicle-side control section  44  generates predetermined time Ttest and predetermined power value Ptest on the basis of the random number (S 222 ). 
         [0077]    Predetermined time Ttest and predetermined power value Ptest are values to be set for power supply apparatus  2 . Vehicle-side control section  44  determines that the communication with power supply apparatus  2  is set up when power supply section  21  provides power of predetermined power value Ptest after predetermined time Ttest passes. 
         [0078]    Here, predetermined time Ttest is a time of about several seconds. When this time is excessively long, it takes a lot of time to start the supply of power. On the other hand, when this time is excessively short, power supply apparatus  2  cannot respond. 
         [0079]    Predetermined power value Ptest is a value greater than first power value Pa and smaller than second power value Pb and is about several W to several tens kW. When power value Ptest is excessively great, the periphery of power supply section  21  is affected. When the power value is excessively small, vehicle-side communication section  43  cannot be started up. 
         [0080]    For example, when it is assumed that vehicle-side control section  44  generates a random number of 8 bits (0 to 255) in S 221 , vehicle-side control section  44  can divide the above-mentioned preferable ranges of predetermined time Ttest and predetermined power value Ptest into 256 equal parts and select a numerical value corresponding to the generated random number. It is assumed that multiple power supply apparatuses  2  are installed in parallel and electric vehicles  3  stops on respective power supply apparatuses  2  and are charged. Then, when predetermined time Ttest and predetermined power value Ptest of neighboring vehicles are set to the same value, the correspondence between power supply apparatuses  2  and electric vehicles  3  may be erroneously determined. By using the random number, it is possible to actively avoid the state where predetermined time Ttest and predetermined power value Ptest of neighboring vehicles have the same values. 
         [0081]    Vehicle-side control section  44  then generates a request signal including predetermined time Ttest and predetermined power value Ptest and causes vehicle-side communication section  43  to transmit the request signal (S 223 ). 
         [0082]    The request signal transmitted from vehicle-side communication section  43  is received by power supply-side communication section  23 . Power supply-side control section  24  determines whether power supply-side communication section  23  receives the request signal within predetermined time Tlimit after power supply section  21  starts the supply of power of first power value Pa in S 11  (S 121 ). Predetermined time Tlimit is, for example, about several seconds. 
         [0083]    When the request signal is not received within predetermined time Tlimit (NO in S 121 ), power supply-side control section  24  causes power supply section  21  to stop the supply of power (S 16 ). When it is considered that a vehicle passes through chargeable area B after the supply of power of first power value Pa is started, the subsequent supply of power of first power value Pa causes power waste. Therefore, when a response is not received within a predetermined time, it is preferable to determine that there is no power supply target and stop the supply of power. 
         [0084]    When the request signal is received within predetermined time Tlimit (YES in S 121 ), power supply-side control section  24  controls power supply section  21  on the basis of predetermined time Ttest and predetermined power value Ptest included in the request signal. Specifically, after predetermined time Ttest passes from when power supply-side communication section  23  receives the request signal, the power supplied from power supply section  21  is controlled to be predetermined power value Ptest (S 122 ). 
         [0085]    Vehicle-side control section  44  determines whether the power received by power receiving section  41  is predetermined power value Ptest after predetermined time Ttest passes from when transmitting the request signal (S 224 ). 
         [0086]    When the power is not power value Ptest (NO in S 224 ), vehicle-side control section  44  determines that a communication with power supply apparatus  2  is not set up, and returns the process flow to START of  FIG. 4 . 
         [0087]    On the other hand, when the power is predetermined power value Ptest (YES in S 224 ), vehicle-side control section  44  determines that a communication between power supply-side communication section  23  and vehicle-side communication section  43  is set up, and performs a control for causing vehicle-side communication section  43  to transmit a power supply start signal (S 225 ). Then, vehicle-side control section  44  performs the process of S 23 . 
         [0088]    The power supply start signal transmitted from vehicle-side communication section  43  in S 225  is received by power supply-side communication section  23 . Power supply-side control section  24  determines whether the power supply start signal is received within predetermined time Tlimit after the supply of power in S 122  is started (S 123 ). When the power supply start signal is not received within predetermined time Tlimit (NO in S 123 ), power supply-side control section  24  causes power supply section  21  to stop the supply of power (S 16 ). 
         [0089]    On the other hand, when the power supply start signal is received within predetermined time Tlimit (YES in S 123 ), power supply-side control section  24  determines that a communication between power supply-side communication section  23  and vehicle-side communication section  43  is setup up, and performs a control for causing power supply section  21  to supply power of second power value Pb in the process of S 13 . The reason of determining whether the power supply start signal is received within predetermined time Tlimit is the same as described in S 121 . 
         [0090]    When the request signal is received within predetermined time Tlimit in S 121  (YES in S 121 ), power supply-side control section  24  may determine that a communication between power supply-side communication section  23  and vehicle-side communication section  43  is set up. In this case, the calculation of predetermined power value Ptest in S 222  and the transmission of predetermined power value Ptest in S 223  become unnecessary. Power supply-side control section  24  performs a control such that power supplied from power supply section  21  becomes second power value Pb after predetermined time Ttest passes from when the request signal is received in S 122 . When the supplied power is second power value Pb in S 224 , vehicle-side control section  44  determines that a communication between power supply-side communication section  23  and vehicle-side communication section  43  is set up. The processes of S 225  and S 123  are unnecessary. 
         [0091]    A variation in power value supplied from power supply section  21  will be described below with reference to  FIG. 6 .  FIG. 6  is a timing diagram in Embodiment 1 of the present invention. Time T 0  represents the “START” state of  FIG. 3 , and the power value supplied from power supply section  21  is zero at this time. Time T 1  represents a state where a vehicle enters chargeable area B (YES in S 10 ), and the magnitude of the power supplied from power supply section  21  is first power value Pa. 
         [0092]    Since the magnitude of the power supplied from power supply section  21  is first power value Pa, vehicle-side communication section  43  is started up (YES in S 21 ) and vehicle-side communication section  43  transmits a request signal (S 223 ). 
         [0093]    When power supply-side communication section  23  receives the request signal within predetermined time Tlimit after a vehicle enters chargeable area B at time T 2  (S 121 ), power supply-side control section  24  controls power supply section  21  so that the supplied power is set to predetermined power value Ptest included in the request signal at the time point where predetermined time Ttest included in the request signal passes from T 2  to T 3  (S 122 ). 
         [0094]    When it is confirmed that the supplied power is set to predetermined power value Ptest at the time point where predetermined time Ttest passes after the transmission of the request signal at time T 3  (YES in S 224 ), vehicle-side control section  44  transmits a power supply start signal (S 225 ). Power supply-side control section  24  controls power supply section  21  so that the supplied power is set to second power value Pb from T 3  to T 4  (S 123 ). 
         [0095]    When the vehicle leaves chargeable area B (YES in S 14 ), or when power storage section  42  is fully charged, power supply-side control section  24  causes power supply section  21  to stop the supply of power (after T 4 ). 
         [0096]    In this way, in the power supply system according to this embodiment, power supply-side control section  24  performs a control for causing power supply section  21  to supply power of first power value Pa when vehicle detecting section  22  detects that electric vehicle  3  enters chargeable area B. In this state, when it is determined that a communication between power supply-side communication section  23  and vehicle-side communication section  43  is set up, the system performs a control for causing power supply section  21  to supply power of second power value Pb. 
         [0097]    Accordingly, it is possible to accurately associate electric vehicle  3  supplied with power from power supply apparatus  2 , with electric vehicle  3  communicating with power supply apparatus  2 . 
         [0098]    Additionally, since vehicle-side communication section  43  of electric vehicle  3  is started up on the basis of first power value Pa smaller than second power value Pb for supplying power to electric vehicle  3 , it is possible to improve safety without discharging high power to the periphery of power supply section  21  of power supply apparatus  2 . 
         [0099]    It has been stated in this embodiment that vehicle-side communication section  43  is operated with the power supplied to power receiving section  41  until a communication is set up and is operated with the power of power storage section  42  after the communication is set up. However, the present invention is not limited to this example, but vehicle-side communication section  43  may be always operated with power supplied from power storage section  42  as a power source. At this time, vehicle-side communication section  43  is started up with a signal indicating reception of power of first power value Pa or larger output from power receiving section  41  as a trigger. Accordingly, since vehicle-side communication section  43  can be always in a communication standby state, it is possible to shorten the time until a communication is started, compared with the case where vehicle-side communication section  43  is started up with power supplied from power receiving section  41 . 
         [0100]    It has been stated in this embodiment that in S 223 , vehicle-side control section  44  generates a request signal including predetermined time Ttest and predetermined power value Ptest generated in S 222  and causes vehicle-side communication section  43  to transmit the generated request signal. However, the present invention is not limited to this example, but only any one of predetermined time Ttest and predetermined power value Ptest may be transmitted. 
         [0101]    When only predetermined time Ttest is transmitted, the processes of S 122  and S 224  of  FIG. 5  can be performed without any change by causing power supply apparatus  2  and power receiving apparatus  4  to share a predetermined value of predetermined power value Ptest. 
         [0102]    When only predetermined power value Ptest is transmitted, power supply-side control section  24  controls power supply section  21  on the basis of predetermined power value Ptest included in the request signal just after receiving the request signal. Vehicle-side control section  44  determines whether the power received by power receiving section  41  is predetermined power value Ptest in S 224 , just after transmitting the request signal. 
         [0103]    It is preferable that power receiving section  41  and vehicle-side communication section  43  be installed on the bottom surface of electric vehicle  3  facing the road, and power supply section  21  and power supply-side communication section  23  be installed in the vicinity of the road surface of the road. 
         [0104]    Accordingly, only by locating electric vehicle  3  on the road surface in which power supply section  21  and power supply-side communication section  23  are installed, vehicle-side communication section  43  can be easily started up. Since electric vehicle  3  serves as a shielding member, it is possible to prevent a communication with a different electric vehicle. 
       Embodiment 2 
       [0105]    Hereinafter, a power supply system for an electric vehicle according to Embodiment 2 of the present invention will be described with reference to  FIG. 7 .  FIG. 7  is a diagram illustrating a communication setup process in Embodiment 2 of the present invention. In  FIG. 7 , the same steps as described with reference to  FIG. 5  in Embodiment 1 will be referenced by the same reference numerals and description thereof will not be repeated. 
         [0106]    Embodiment 2 is different from Embodiment 1, in that it is determined whether a communication is set up on the basis of chopper frequency Ftest instead of power value Ptest in Embodiment 1. 
         [0107]    The chopper frequency is an ON-OFF cycle of current when AC current is generated from a DC power source by repeating ON-OFF of current. Vehicle-side control section  44  can acquire chopper frequency Ftest by measuring the output of power receiving section  41  through the use of a dedicated measuring circuit. 
         [0108]    As shown in  FIG. 7 , vehicle-side control section  44  calculates time Ttest and chopper frequency Ftest on the basis of a random number (S 216 ) subsequently to S 211  as described above, and causes vehicle-side communication section  43  to transmit a request signal including time Ttest and chopper frequency Ftest (S 217 ). 
         [0109]    Power supply-side control section  24  performs a control for causing power supply section  21  to supply power so as to achieve chopper frequency Ftest after time Ttest passes, in response to the request signal received by power supply-side communication section  23  (S 124 ). 
         [0110]    Vehicle-side control section  44  determines whether the power received by power receiving section  41  in time Ttest after the transmission of the request signal has chopper frequency Ftest (S 218 ). When it is determined that the power has chopper frequency Ftest (YES in S 218 ), vehicle-side control section  44  determines that a communication is set up and causes vehicle-side communication section  43  to transmit a power supply start signal (S 215 ). 
         [0111]    As described above, the power supply system according to this embodiment determines whether a communication is set up on the basis of chopper frequency Ftest. When power value Ptest is measured as described in Embodiment 1, the absolute value of power is measured and an error may therefore be included in the power due to attenuation dependent on the distance. On the other hand, the measured value of chopper frequency Ftest does not depend on the distance but is constant. Accordingly, it is possible to reduce the measurement error in comparison with the case where power value Ptest is used, by using chopper frequency Ftest. 
         [0112]    It has been stated in this embodiment that vehicle-side control section  44  generates the request signal including predetermined time Ttest and chopper frequency Ftest generated in S 216  and causes vehicle-side communication section  43  to transmit the generated request signal in S 217 . However, the present invention is not limited to this example, but only any one of predetermined time Ttest and chopper frequency Ftest may be transmitted. 
         [0113]    When only predetermined time Ttest is transmitted, the processes of S 124  and S 218  of  FIG. 7  can be performed without any change by causing power supply apparatus  2  and power receiving apparatus  4  to share a predetermined value of chopper frequency Ftest. 
         [0114]    When only chopper frequency Ftest is transmitted, power supply-side control section  24  controls power supply section  21  on the basis of chopper frequency Ftest included in the request signal just after receiving the request signal. Vehicle-side control section  44  determines whether the power received by power receiving section  41  has chopper frequency Ftest in S 218 , just after transmitting the request signal. 
       Embodiment 3 
       [0115]    Hereinafter, a power supply system for an electric vehicle according to Embodiment 3 of the present invention will be described with reference to  FIG. 8 .  FIG. 8  is a block diagram illustrating the configuration of the power supply system for an electric vehicle according to Embodiment 3 of the present invention. In  FIG. 8 , solid arrows represent the flow of signals and dotted arrows represent the flow of power. In  FIG. 8 , the same elements as described with reference to  FIG. 2  in Embodiment 1 will be referenced by the same reference numerals and description thereof will not be repeated. 
         [0116]    It has been stated in Embodiment 1 that vehicle-side communication section  43  is operated with power received by power receiving section  41  until a communication is set up between vehicle-side communication section  43  and power supply-side communication section  23 , and is operated with power stored in power storage section  42  as a power source after the communication is set up. On the contrary, in Embodiment 3, vehicle-side communication section  43  is always operated with power received by power receiving section  41  as a power source. Accordingly, in  FIG. 8 , the supply of power from power storage section  42  to vehicle-side communication section  43  in  FIG. 2  is deleted. 
         [0117]    In Embodiment 1, vehicle-side communication section  43  is operated with power of power storage section  42  after a communication is set up. This means that the power which is first received by power receiving section  41  and then stored in power storage section  42  is used. When power is once stored in power storage section  42  and the power is used, loss is necessarily caused in the power. 
         [0118]    In Embodiment 3, since power is directly supplied from power receiving section  41  to vehicle-side communication section  43  without storing the power in power storage section  42  after a communication is set up, it is possible to operate vehicle-side communication section  43  with small power loss. 
       Embodiment 4 
       [0119]    In Embodiment 4, an example where multiple power supply apparatuses supply power of first power values pa different from one another will be described. Hereinafter, a power supply system for an electric vehicle according to Embodiment 4 of the present invention will be described with reference to  FIG. 9  and  FIG. 10 .  FIG. 9  is a diagram illustrating the configuration of the power supply system for an electric vehicle according to Embodiment 4 of the present invention.  FIG. 10  is a diagram illustrating a communication setup process in Embodiment 4 of the present invention. The configurations of power supply apparatus  2  and power receiving apparatus  4  in this embodiment are the same as described with reference to  FIG. 2  in Embodiment 1. 
         [0120]    In  FIG. 9 , three power supply apparatuses  2   a ,  2   b , and  2   c  are shown. Power supply section  21   a  of power supply apparatus  2   a  supplies power of first power value Pa 1  to electric vehicle  3   a  when electric vehicle  3   a  enters chargeable area B 1 . Power supply section  21   b  of power supply apparatus  2   b  supplies power of first power value Pa 2  to electric vehicle  3   b  when electric vehicle  3   b  enters chargeable area B 2 . Power supply section  21   c  of power supply apparatus  2   c  supplies power of first power value Pa 3  to electric vehicle  3   c  when electric vehicle  3   c  enters chargeable area B 3 . First power values Pa 1 , Pa 2 , and Pa 3  are about several W to several tens W and are different from each other. 
         [0121]    The communication setup process will be described below with reference to  FIG. 10 . The left flowchart in  FIG. 10  represents a power supply-side process (S 12 ) and the right flowchart represents a vehicle-side process (S 22 ). 
         [0122]    After vehicle-side communication section  43  is started up in S 21 , vehicle-side control section  44  generates a request signal including the power value received by power receiving section  41  and a vehicle identification number and causes vehicle-side communication section  43  to transmit the generated request signal (S 41 ). 
         [0123]    The request signal transmitted from vehicle-side communication section  43  is received by power supply-side communication section  23 . Power supply-side control section  24  determines whether the power value included in the request signal is substantially equal to first power value pa supplied from power supply section  21  in S 11  (S 31 ). The term “substantially equal” means that the power value included in the request signal belongs to a predetermined range including first power value Pa. 
         [0124]    When the power value included in the request signal is not equal to first power value pa supplied from power supply section  21  (NO in S 31 ), power supply-side control section  24  causes power supply section  21  to stop the supply of power (S 16 ). This is because it is thought in this case that electric vehicle  3  supplied with power from power supply apparatus  2  is not matched with electric vehicle  3  communicating with power supply apparatus  2 . 
         [0125]    When the power value included in the request signal is substantially equal to first power value Pa supplied from power supply section  21  (YES in S 31 ), power supply-side control section  24  generates a response signal including the vehicle identification number included in the request signal and causes power supply-side communication section  23  to transmit the generated response signal (S 32 ). In this case, it is thought that the electric vehicle supplied with power from the power supply apparatus is matched with the electric vehicle communicating with the power supply apparatus. 
         [0126]    Vehicle-side control section  44  determines whether vehicle-side communication section  43  receives the response signal including its own vehicle identification number before predetermined time Ttest passes from when transmitting the request signal (S 42 ). 
         [0127]    When the response signal is not received (NO in S 42 ), vehicle-side control section  44  determines that a communication with power supply apparatus  2  is not set up and returns the flow of processes to START of  FIG. 4 . 
         [0128]    When the response signal is received (YES in S 42 ), vehicle-side control section  44  determines that a communication is set up between power supply-side communication section  23  and vehicle-side communication section  43 , and performs a control for causing vehicle-side communication section  43  to transmit a power supply start signal (S 43 ). Then, vehicle-side control section  44  performs the process of S 23 . 
         [0129]    The power supply start signal transmitted from vehicle-side communication section  43  in S 43  is received by power supply-side communication section  23 . Power supply-side control section  24  determines whether the power supply start signal is received within predetermined time Tlimit after the supply of power in S 11  is started (S 33 ). When the power supply start signal is not received within predetermined time Tlimit (NO in S 33 ), power supply-side control section  24  causes power supply section  21  to stop the supply of power (S 16 ). 
         [0130]    When the power supply start signal is received within predetermined time Tlimit (YES in S 33 ), power supply-side control section  24  determines that a communication is set up between power supply-side communication section  23  and vehicle-side communication section  43 , moves the flow of processes to S 13 , and performs a control for causing power supply section  21  to supply power of second power value Pb. 
         [0131]    As described above, in the power supply system according to this embodiment, power supply-side control section  24  performs a control for causing power supply section  21  to supply power of first power value Pa when vehicle detecting section  22  detects that electric vehicle  3  enters chargeable area B. At this time, power supply sections  21   a ,  21   b , and  21   c  supply power of first power values Pa (Pa 1 , Pa 2 , and Pa 3 ) different from each other. In this state, when determining that a communication is set up between power supply-side communication section  23  and vehicle-side communication section  43 , power supply-side control section  24  performs a control for causing power supply section  21  to supply power of second power value Pb. 
         [0132]    Accordingly, it is possible to accurately associate electric vehicle  3  supplied with power from power supply apparatus  2 , with electric vehicle  3  communicating with power supply apparatus  2 . 
         [0133]    In this embodiment, first power values Pa (Pa 1 , Pa 2 , and Pa 3 ) may be fixedly assigned to power supply apparatuses  2  ( 2   a ,  2 B, and  2 C), respectively, or may be assigned to power supply apparatuses  2  ( 2   a ,  2 B, and  2 C) in patterns determined depending on the time for supplying power, respectively. The patterns of first power values Pa differ depending on power supply apparatuses  2 . 
         [0134]    In this case, vehicle-side control section  44  generates a request signal including the pattern of first power value Pa received by power receiving section  41  instead of generating the request signal including the power value received by power receiving section  41  in S 41 . When the pattern of first power value Pa included in the request signal is substantially equal to the pattern of first power value pa supplied from power supply section  21  of power supply apparatus  2  in S 32 , power supply-side control section  24  generates a response signal including the vehicle identification number included in the request signal and causes power supply-side communication section  23  to transmit the generated response signal. 
         [0135]    First power values Pa (Pa 1 , Pa 2 , and Pa 3 ) may vary in power receiving section  41  due to positional mismatch between power supply section  21  and power receiving section  41 . By causing the first power value Pa to temporally vary in patterns different depending on power supply apparatuses  2 , it is possible to accurately associate therewith electric vehicle  3  communicating with power supply apparatus  2  with temporal variation of the power value, even when variation occurs in the absolute value of first power value Pa received by power receiving section  41 . 
         [0136]    The disclosure of Japanese Patent Application No. 2010-223759, filed on Oct. 1, 2010, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0137]    The present invention can be suitably used for a power supply system for an electric vehicle that supplies power from a power supply apparatus to an electric vehicle in a non-contact manner, and an electric vehicle and a power supply apparatus that are used for the system. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Power supply system for electric vehicle 
           2  Power supply apparatus 
           21  Power supply section 
           22  Vehicle detecting section 
           23  Power supply-side communication section 
           24  Power supply-side control section 
           3  Electric vehicle 
           4  Power receiving apparatus 
           41  Power receiving section 
           42  Power storage section 
           43  Vehicle-side communication section 
           44  Vehicle-side control section