Patent ID: 12191682

DETAILED DESCRIPTION

A power feeding station according to one or more embodiments will now be described with reference to the drawings. The power feeding station includes a feeder for supplying power to a two-wheeler in a housing to transmit power to the two-wheeler through a feeder coil in the feeder and a receiver coil in a receiver included in the two-wheeler being parked. The frequency of alternating current (AC) power supplied to the feeder coil is set to a predetermined frequency corresponding to the degree of coupling between the feeder coil and the receiver coil. The feeder in the power feeding station and the receiver in the two-wheeler can thus perform a constant voltage output operation in which the receiver outputs a constant voltage independently of the resistance of a load connected to the receiver. The power feeding station identifies the frequency of AC power supplied to the feeder coil that allows the feeder and the receiver to perform a constant voltage output operation, and provides, based on the identified frequency, a notification to guide the two-wheeler to a position at which higher power transmission efficiency is achieved.

FIG.1is a schematic diagram of a contactless power feeding system including a power feeding station and a two-wheeler according to the present embodiment.

As shown inFIG.1, the contactless power feeding system1includes a power feeding station2and a two-wheeler3. The power feeding station2can feed power to the two-wheeler3. The power feeding station2includes a housing10, a feeder11, and a display12. The feeder11includes a feeder coil32in the housing10.

The two-wheeler3is an example of an electric mobility vehicle. The two-wheeler3includes a receiver21including a receiver coil41, and a battery22for storing power received by the receiver21. The two-wheeler3includes a front basket24above its front wheel23, and a box25attached to the bottom surface of the front basket24. The box25is formed from an insulating material such as a resin. The box25accommodates the receiver21. The receiver coil41in the receiver21between the front wheel23and the front basket24of the two-wheeler3is attached to the two-wheeler3with its winding axis extending ahead of the two-wheeler3. The battery22is installed on a rack located above the rear wheel of the two-wheeler3and is charged with power received through the receiver21. The power charged in the battery22is used to drive a motor (not shown) that provides auxiliary power for the two-wheeler3or is used to turn on a headlight26. When the parked two-wheeler3satisfies a predetermined positional relationship with the power feeding station2, the feeder coil32in the feeder11feeds power contactlessly to the receiver coil41in the receiver21.

FIG.2is a schematic front view of the power feeding station2as viewed from the two-wheeler3to be parked.FIG.3is a schematic side view of the power feeding station2.FIG.4is a schematic perspective view of the power feeding station2with the two-wheeler3parked at the power feeding station2.FIG.5is a partially enlarged view of the power feeding station2and the two-wheeler3describing power feeding from the power feeding station2to the two-wheeler3parked at the power feeding station2. A surface of the housing10facing the two-wheeler3parked at the power feeding station2may hereafter be referred to as a front surface of the housing10.

The housing10in the power feeding station2defines a predetermined parking position for the two-wheeler3. In the present embodiment, as shown inFIGS.2to4, the front surface of the housing10has an inverted U shape as a whole. The housing10includes two substantially quadrangular prism-shaped pillars13and14, which extend substantially vertically to a road surface on which the power feeding station2is installed, and an upper end15connecting upper portions of the two pillars13and14. When the two-wheeler3is parked at the power feeding station2, the front wheel of the two-wheeler3is placed in a space between the two pillars13and14of the housing10. More specifically, the space between the two pillars13and14corresponds to the position of the front wheel of the two-wheeler3to be parked.

Each of the pillars13and14and the upper end15is hollow and is formed from a metal such as aluminum or stainless steel, a resin, or a combination of these materials. One of the pillars13or14internally accommodates a power cable (not shown) for transmitting power from a utility or direct current (DC) power source to the feeder11. A board (not shown) is attached inside the pillar13, the pillar14, or the upper end15. A power supply circuit in the feeder11is located on the board. The pillar13may have a groove13aon its surface facing the pillar14. The pillar14may have a groove14aon its surface facing the pillar13. The grooves13aand14amay be engageable with the hub shaft of the front wheel of the two-wheeler3when the two-wheeler3is parked. Each of the grooves13aand14amay be gradually narrower from its portion near the front surface to its portion near a surface opposite to the front surface (hereafter referred to as a back surface).

To allow the receiver coil41in the receiver21in the two-wheeler3parked at the power feeding station2to face the feeder coil32in the feeder11, the upper end15of the housing10includes, on its front surface, a substantially rectangular compartment16protruding toward the parked two-wheeler3. The compartment16internally accommodates the feeder coil32. The feeder coil32is installed with its winding axis orthogonal to a surface16aat the front (hereafter also referred to as a front surface) of the compartment16. The compartment16is formed from an insulating material, such as a resin, to avoid being affected by power fed from the feeder11to the receiver21.

The compartment16may have a cover17protruding further toward the two-wheeler3than the front surface16aof the compartment16. The cover17may surround at least a part of the outer periphery of the compartment16including its upper end.

The upper end15includes the display12on its front surface. The display12is located lateral to the compartment16. The display12is an example of a notification source and may be, for example, a liquid crystal display or an organic electroluminescent (EL) display. The display12displays a message for guidance about the parking position (or stop position) of the two-wheeler3received from the feeder11. The position of the display12is not limited to the present example. The display12may be located on the top surface of the upper end15.

The feeder11and the receiver21will now be described in detail.

In the present embodiment, the feeder11and the receiver21are included in a contactless power feeding apparatus that uses no resonance in the power feeder but uses a series resonance between the receiver coil41and the resonant capacitor42in the power receiver (an NS configuration). The feeder11and the receiver21are not limited to the present example and may be, for example, a contactless power feeding apparatus including primary series-secondary series resonant capacitors (an SS configuration) or primary series-secondary parallel resonant capacitors (an SP configuration). In another example, the feeder11and the receiver21may be included in a contactless power feeding apparatus that uses no resonance in the power feeder but uses a parallel resonance between the receiver coil41and the resonant capacitor42in the power feeder (an NP configuration).

The feeder11included in the power feeding station2will now be described.FIG.6is a schematic diagram of the feeder11. The feeder11includes a power supply circuit31, the feeder coil32, a communicator33, and a control circuit34.

The power supply circuit31supplies AC power with an adjustable frequency and an adjustable voltage to the feeder coil32. The power supply circuit31includes a full-wave rectifying circuit311that converts the AC power supplied from a utility power source to pulsed current power, a power factor correction circuit312, and an inverter circuit313.

The full-wave rectifying circuit311is connected between the utility power source and the power factor correction circuit312, and converts the AC power supplied from the utility power source to pulsed current power. The full-wave rectifying circuit311includes four bridge-connected diodes. The full-wave rectifying circuit311outputs pulsed current power to the power factor correction circuit312.

The power factor correction circuit312is connected between the full-wave rectifying circuit311and the inverter circuit313, and improves the power factor of the pulsed current power output from the full-wave rectifying circuit311to convert the pulsed current power to DC power with a boosted voltage. The power factor correction circuit312includes, for example, a coil L and a diode D connected in series in the described order from the positive electrode output terminal of the full-wave rectifying circuit311, a switching element SW, which is an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET) having a drain terminal connected between the coil L and the diode D and a source terminal connected to the negative electrode output terminal of the full-wave rectifying circuit311, and a smoothing capacitor C connected in parallel to the switching element SW across the diode D. The switching element SW has a gate terminal connected to the control circuit34. The power factor correction circuit312includes two resistors R1and R2connected in series between the positive electrode output terminal and the negative electrode output terminal of the full-wave rectifying circuit311. The resistors R1and R2are connected in parallel to the smoothing capacitor C between the diode D and the smoothing capacitor C. The voltage across the resistors R1and R2is measured by the control circuit34as a voltage output from the diode D.

The control circuit34controls the on-off state of the switching element SW in accordance with the duty cycle indicated by the control circuit34to allow the waveform of the current output from the diode D to have the same waveform as the voltage of the pulsed current power supplied from the full-wave rectifying circuit311. The power factor correction circuit312thus performs power factor correction. As the duty cycle in which the switching element SW is on is higher, the diode D outputs a higher voltage.

The power output from the diode D is smoothed by the smoothing capacitor C into DC power and is output to the inverter circuit313.

The power factor correction circuit312is not limited to the above structure and may have another structure to output a voltage adjustable as controlled by the control circuit34.

The inverter circuit313connected between the power factor correction circuit312and the feeder coil32converts the DC power supplied from the power factor correction circuit312to AC power with a predetermined frequency and supplies the AC power to the feeder coil32. The inverter circuit313may be a full-bridge inverter with four switching elements (e.g., n-channel MOSFETs) forming a full-bridge connection. The inverter circuit313may be a half-bridge inverter with two switching elements forming a half-bridge connection. With the control circuit34controlling on-off switching of each switching element in accordance with the predetermined frequency, the inverter circuit313converts the DC power supplied from the power factor correction circuit312to AC power with a predetermined frequency. The predetermined frequency allows the feeder11and the receiver21to perform a constant voltage output operation and is determined in accordance with the degree of coupling between the feeder coil32and the receiver coil41. The predetermined frequency is hereafter referred to as a constant voltage frequency for ease of explanation.

The power supply circuit31may further include, between the power factor correction circuit312and the inverter circuit313, a DC-DC converter that increases or decreases the voltage of the DC power output from the power factor correction circuit312. The power supply circuit31may include an AC-DC converter that converts AC power supplied from a utility AC power source to DC power, instead of the full-wave rectifying circuit311and the power factor correction circuit312. The power supply circuit31may include a DC power source, such as a lithium-ion secondary battery or a lead-acid storage battery, to supply DC power and a DC-DC converter that increases or decreases the voltage of the DC power supplied from the DC power source, instead of the full-wave rectifying circuit311and the power factor correction circuit312.

The feeder coil32transmits, through a space, AC power supplied from the power supply circuit31to the receiver coil41in the receiver21. The feeder11may include a capacitor connected in series to the feeder coil32between the feeder coil32and the inverter circuit in the power supply circuit31. The capacitor may be used to cut DC power or to form a resonant circuit that resonates with the feeder coil32at the frequency of the AC power supplied to the feeder coil32.

The communicator33extracts, from every radio signal received from a communicator in the receiver21, a signal indicating the power reception state of the receiver21, and outputs the signal to the control circuit34. The communicator33includes, for example, an antenna that receives a radio signal in accordance with a predetermined wireless communication standard and a communication circuit that demodulates the radio signal. The predetermined wireless communication standard is, for example, ISO/IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

The control circuit34includes, for example, nonvolatile and volatile memory circuits, an arithmetic circuit, and an interface circuit for connection to another circuit.

Based on the signal received from the receiver21through the communicator33indicating the power reception state of the receiver21, the control circuit34controls on-off switching of each switching element included in the inverter circuit313to allow the feeder11and the receiver21to perform a constant voltage output operation. More specifically, the control circuit34controls on-off switching of each switching element included in the inverter circuit313to cause the AC power supplied to the feeder coil32to have a constant voltage frequency. The control circuit34may control the on-off state of the switching element SW in the power factor correction circuit312to adjust the voltage of the DC power supplied to the inverter circuit313to retain a constant voltage of the power received by the receiver21.

The control circuit34determines whether the two-wheeler3is at an appropriate parking position by referring to the constant voltage frequency. When determining that the parking position is inappropriate, the control circuit34causes the display12to display a message prompting movement of the two-wheeler3to an appropriate parking position.

The operation of the control circuit34will be described in detail later.

The receiver21included in the two-wheeler3will now be described.FIG.7is a schematic diagram of the receiver21. The receiver21includes the receiver coil41, a resonant capacitor42, a power receiver circuit43, and a communicator44. The receiver coil41forms a resonant circuit with the resonant capacitor42.

The receiver coil41forming the resonant circuit with the resonant capacitor42resonates with the AC flowing through the feeder coil32in the feeder11to receive power from the feeder coil32. The resonant capacitor42is connected in series to the receiver coil41. The resonant capacitor42may be connected in parallel to the receiver coil41. The resonant circuit including the receiver coil41and the resonant capacitor42outputs AC power, which is output to the power receiver circuit43. The receiver coil41and the feeder coil32may have the same number or different numbers of turns.

The power receiver circuit43converts the AC power from the resonant circuit including the receiver coil41and the resonant capacitor42to DC power. The DC power is output to the battery22that is connected to the power receiver circuit43through a power cable (not shown) and a charger (not shown) and is located above the rear wheel. The power receiver circuit43determines the state of power reception from the feeder11, or more specifically, determines whether the output voltage from the power receiver circuit43is constant. The power receiver circuit43includes a rectifier-smoothing circuit431, a voltage detection circuit432, a switching element433, and a determination circuit434.

The rectifier-smoothing circuit431, which is an example of a rectifier circuit, includes a full-wave rectifying circuit including four bridge-connected diodes or switching elements (e.g., MOSFETs), and a smoothing capacitor. The rectifier-smoothing circuit431rectifies and smooths the power received through the receiver coil41to convert the power to DC power. The rectifier-smoothing circuit431outputs the resultant DC power to the battery22through the charger.

The voltage detection circuit432measures an output voltage across the rectifier-smoothing circuit431(specifically, an output voltage from the power receiver circuit43, hereafter simply referred to as an output voltage) at predetermined intervals. The output voltage across the rectifier-smoothing circuit431corresponds one-to-one to the output voltage from the resonant circuit including the receiver coil41and the resonant capacitor42. The measurement value of the output voltage across the rectifier-smoothing circuit431thus indirectly represents the measurement value of the output voltage from the resonant circuit. The voltage detection circuit432may be any known voltage detection circuit that can detect, for example, a DC voltage. The voltage detection circuit432outputs a voltage detection signal representing the measurement value of the output voltage to the determination circuit434.

The switching element433is, for example, a MOSFET and is connected between the rectifier-smoothing circuit431and the battery22. The switching element433does not allow a current to flow from the rectifier-smoothing circuit431to the battery22in the off state (specifically, the AC equivalent resistance of the battery22and the charger Rac=00) and allows a current to flow from the rectifier-smoothing circuit431to the battery22in the on state.

The determination circuit434determines, based on the measurement value of the output voltage received from the voltage detection circuit432, whether the feeder11and the receiver21are performing a constant voltage output operation and whether the measurement value of the output voltage is within the range of allowable voltages. The determination circuit434provides the determination result to the communicator44. The determination circuit434includes, for example, a memory circuit that stores the allowable range of voltages, an arithmetic circuit that compares the measurement value of the output voltage with the allowable range of voltages, and the control circuit that controls the on-off state of the switching element433.

The determination circuit434turns on and off the switching element433at predetermined intervals while the measurement value of the output voltage is out of the allowable range of voltages, which changes the resistance of the entire circuit including the battery22connected to the rectifier-smoothing circuit431at predetermined intervals. The determination circuit434can thus determine whether the feeder11and the receiver21are performing a constant voltage output operation by determining whether the measurement value of the output voltage is substantially constant while turning on and off the switching element433. The determination circuit434notifies the communicator44that the feeder11and the receiver21are performing a constant voltage output operation when the measurement value of the output voltage remains substantially constant while the switching element433is being turned on and off at predetermined intervals.

When the measurement value of the output voltage indicates that the feeder11and the receiver21are performing a constant voltage output operation for a predetermined period longer than the predetermined interval, the determination circuit434stops turning on and off the switching element433and retains the on state. The determination circuit434determines whether the measurement value of the output voltage is within the allowable range of voltages and provides the determination result to the communicator44.

When the measurement value of the output voltage is within the allowable range of voltages for the predetermined period longer than the predetermined interval, the determination circuit434provides the communicator44with the determination result indicating that the feeder11and the receiver21are performing a constant voltage output operation and the measurement value of the output voltage is within the allowable range of voltages.

In one modification, the power receiver circuit43may include a resistor connected in parallel to the battery22to the rectifier-smoothing circuit431. Accordingly, the switching element433may be connected in series to the resistor and in parallel to the battery22. The determination circuit434turns off the switching element433while the measurement value of the output voltage is within the allowable range of voltages. When the measurement value of the output voltage is out of the allowable range of voltages, the determination circuit434may turn on and off the switching element433at predetermined intervals in the same manner as in the above embodiment. In the present modification, the battery22continuously receives power while the feeder11and the receiver21are not performing a constant voltage output operation.

In another modification, a second switching element, such as a MOSFET, may be connected in parallel to the above resistor and in series to the battery22. Accordingly, while the measurement value of the output voltage is within the allowable range of voltages, the determination circuit434retains the on state of the second switching element to supply power to the battery22. When the measurement value of the output voltage is out of the allowable range of voltages, the determination circuit434may turn off the second switching element to stop supplying power to the battery22. The above described structure prevents an unexpectedly high voltage from being applied to the battery22, although the voltage of received power rises unexpectedly during adjustment of the frequency of the AC power applied to the feeder coil32in the feeder11.

The communicator44generates, at predetermined transmission intervals, a signal indicating the power reception state based on the determination result received from the determination circuit434. The signal indicating the power reception state includes determination information indicating whether the feeder11and the receiver21are performing a constant voltage output operation and whether the measurement value of the output voltage is within the allowable range of voltages. The communicator44then generates a radio signal including the signal indicating the power reception state and transmits the radio signal to the communicator33in the feeder11. The communicator44includes, for example, a communication circuit that generates a radio signal in accordance with a predetermined wireless communication standard and an antenna that outputs the radio signal. As in the communicator33, the predetermined wireless communication standard is, for example, ISO/IEC 15693, ZigBee (registered trademark), or Bluetooth (registered trademark).

The operation of the control circuit34in the feeder11will be described in detail. A constant voltage output operation will be described first.

FIG.8is an equivalent circuit diagram of the feeder11and the receiver21. In an equivalent circuit100, the feeder coil32is coupled with the receiver coil41to form an ideal transformer of n:1. In the equivalent circuit100, Lr is the leakage inductance of the feeder coil32, and Lm is the magnetizing inductance of the feeder coil32. An inductance Lp of the feeder coil32is equal to (Lm+Lr), and Lr=(1−k)Lp and Lm=kLp, where k is the degree of coupling between the feeder coil32and the receiver coil41. Ri is the coil resistance in the feeder11, and Ris is the coil resistance in the receiver21. Cp is the capacitance of the resonant capacitor42in the receiver21. Rac is the AC equivalent resistance of a resistance Ro of the battery22and the charger, and Rac=(8/π2)×Ro.

FIG.9is a graph showing example simulation results of the frequency response of an output voltage from the receiver21calculated in accordance with the output gain from the equivalent circuit. InFIG.9, the horizontal axis indicates the frequency of AC power applied to the feeder coil32, and the vertical axis indicates an output voltage from the receiver21. A line901represents the frequency response of an output voltage for the degree of coupling k=0.15, and the AC equivalent resistance of the battery22and the charger being Rac. A line902represents the frequency response of an output voltage for the degree of coupling k=0.15, and the AC equivalent resistance of the battery22and the charger being (10*Rac). A line903represents the frequency response of an output voltage for the degree of coupling k=0.3, and the AC equivalent resistance of the battery22and the charger being Rac. A line904represents the frequency response of an output voltage for the degree of coupling k=0.3, and the AC equivalent resistance of the battery22and the charger being (10*Rac). A line905represents the frequency response of an output voltage for the degree of coupling k=0.6, and the AC equivalent resistance of the battery22and the charger being Rac. A line906represents the frequency response of an output voltage for the degree of coupling k=0.6, and the AC equivalent resistance of the battery22and the charger being (10*Rac). In the simulation, Lp=174 pH, Cp=20 nF, Ri=Ris=0.1Ω, n=1, Vin=300 V, and Ro=10Ω(Rac 8.1Ω).

As indicated with the points911to913inFIG.9, the graph includes, for each degree of coupling k, the combination of the frequency and the output voltage that causes an output voltage to be substantially constant against a varying AC equivalent resistance of the battery22under a constant degree of coupling k (or to be a constant voltage output under a constant degree of coupling k). Accordingly, it becomes apparent that appropriately adjusting the frequency of the AC power applied to the feeder coil32allows the feeder11and the receiver21to perform a constant voltage output operation independently of the varying resistance of the battery22and the charger. Further, although the output voltage, which is constant against a varying resistance of the battery22and the charger, differs depending on the degree of coupling as indicated at the points911to913, adjusting the voltage applied to the feeder coil32can eliminate the difference in the output voltage. The output voltage thus can be substantially constant at any degree of coupling.

FIG.10is a graph showing example simulation results of the frequency response of an output voltage at varying voltages applied to the feeder coil32in accordance with the degree of coupling in the simulation shown inFIG.9. InFIG.10, the horizontal axis indicates the frequency of the AC power applied to the feeder coil32, and the vertical axis indicates an output voltage from the receiver21. A line1001represents the frequency response of an output voltage for the degree of coupling k=0.15, the AC equivalent resistance of the battery22and the charger being Rac, and a voltage applied to the feeder coil32being Vin. A line1002represents the frequency response of an output voltage for the degree of coupling k=0.15, the AC equivalent resistance of the battery22and the charger being (10*Rac), and a voltage applied to the feeder coil32being Vin. A line1003represents the frequency response of an output voltage for the degree of coupling k=0.3, the AC equivalent resistance of the battery22and the charger being Rac, and a voltage applied to the feeder coil32being (0.5*Vin). A line1004represents the frequency response of an output voltage for the degree of coupling k=0.3, the AC equivalent resistance of the battery22and the charger being (10*Rac), and a voltage applied to the feeder coil32being (0.5*Vin). A line1005represents the frequency response of an output voltage for the degree of coupling k=0.6, the AC equivalent resistance of the battery22and the charger being Rac, and a voltage applied to the feeder coil32being (0.25*Vin). A line1006represents the frequency response of an output voltage for the degree of coupling k=0.6, the AC equivalent resistance of the battery22and the charger being (10*Rac), and a voltage applied to the feeder coil32being (0.25*Vin).

The combinations of the frequency and the output voltage at three points1011to1013correspond to the combinations at the three points911to913shown inFIG.9that cause an output voltage to be substantially constant (or to be a constant voltage output) against a varying AC equivalent resistance of the battery22and the charger under the constant degree of coupling k. The output voltages at the points1011to1013are substantially equal to one another.

Accordingly, it becomes apparent that appropriately adjusting the frequency and the voltage of the AC power applied to the feeder coil32allows the output voltage to remain substantially constant independently of the varying resistance of the battery22and the charger or the varying degree of coupling.

The control circuit34thus controls the frequency of the AC power applied to the feeder coil32(hereafter, simply referred to as a frequency) and the voltage of the AC power applied to the feeder coil32in the manner described below to perform a constant voltage output operation.

When the determination information included in the signal indicating the power reception state received from the receiver21through the communicator33indicates that the feeder11and the receiver21are not performing a constant voltage output operation, the control circuit34increases the frequency from the lowest limit within a predetermined frequency range to the highest limit within the frequency range.

To allow the determination circuit434in the receiver21to determine whether the output voltage is substantially constant, the control circuit34may change the frequency in a stepwise manner to retain a constant frequency for a period longer than the interval at which the determination circuit434turns on and off the switching element433.

The control circuit34may lower the voltage applied to the feeder coil32to the lowest value while adjusting the frequency. Lowering the voltage, while adjusting the frequency reduces the likelihood that power with an unexpectedly high voltage is supplied to the receiver21.

When the determination information included in the signal indicating the power reception state received from the receiver21through the communicator33indicates that the measurement value of the output voltage is out of the allowable range of voltages but remains substantially constant against a varying resistance of the battery22, or more specifically, a constant voltage output operation is being performed, the control circuit34subsequently retains a constant frequency. The control circuit34selects the duty cycle by referring to a reference table indicating the correspondence between each frequency and the duty cycle that controls the on-off state of the switching element SW in the power factor correction circuit312to perform a constant voltage output at the corresponding frequency at any degree of coupling. The control circuit34turns on and off the switching element SW in the power factor correction circuit312in accordance with the duty cycle. Thus, the voltage to be applied to the feeder coil32is adjusted to allow an output voltage from the receiver21to be within the allowable range of voltages, or more specifically, to allow a constant voltage to be output at any degree of coupling. When the determination information included in the signal indicating the power reception state received from the receiver21through the communicator33indicates that the measurement value of the output voltage is within the allowable range of voltages, the control circuit34retains a constant frequency and a constant voltage of AC power supplied to the feeder coil32.

The control circuit34may gradually change the duty cycle until the determination information indicates that the measurement value of the output voltage is within the allowable range of voltages, instead of referring to the above reference table to select the duty cycle.

The control circuit34detects the frequency (constant voltage frequency) of the AC power applied to the feeder coil32that allows the feeder11and the receiver21to perform a constant voltage output operation and determines whether the parking position of the two-wheeler3is to be changed based on the frequency. Based on the determination result, the control circuit34provides a notification of guidance about the stop position of the two-wheeler3relative to the housing10through the display12.

Referring back toFIG.9, when the AC power applied to the feeder coil32has a constant voltage, the output voltage with the feeder11and the receiver21performing a constant voltage output operation varies depending on the degree of coupling between the feeder coil32and the receiver coil41. More specifically, the output voltage increases as the degree of coupling between the feeder coil32and the receiver coil41increases. The power transmission efficiency thus increases as the degree of coupling increases. The degree of coupling between the feeder coil32and the receiver coil41changes in accordance with the positional relationship between the feeder coil32and the receiver coil41. With the structure of the housing10in the power feeding station2in the present embodiment, the two-wheeler3parked at the power feeding station2moves to cause the receiver coil41to approach the front of the feeder coil32. More specifically, when the two-wheeler3is parked, the distance between the feeder coil32and the receiver coil41changes in the direction parallel to the winding axis of the feeder coil32, but the feeder coil32and the receiver coil41remain in mostly the same positional relationship in the direction orthogonal to the winding axis of the feeder coil32. In the present embodiment, the distance between the feeder coil32and the receiver coil41is smaller when the two-wheeler3is nearer the housing10, thus increasing the degree of coupling between the feeder coil32and the receiver coil41.

The control circuit34thus compares the constant voltage frequency with a predetermined frequency threshold. As shown inFIG.9, the feeder11and the receiver21in the present embodiment have higher power transmission efficiency when the constant voltage frequency is higher. The predetermined frequency threshold is thus set as a minimum constant voltage frequency with which the power transmission efficiency from the feeder11to the receiver21satisfies a predetermined power efficiency condition. When the constant voltage frequency is lower than the predetermined frequency threshold, the control circuit34determines that the feeder coil32is farther than intended from the receiver coil41. The control circuit34then causes the display12to display a message prompting movement of the two-wheeler3further toward the power feeding station2.

When the constant voltage frequency is higher than or equal to the predetermined frequency threshold, the control circuit34determines that the feeder coil32is sufficiently near the receiver coil41to achieve sufficiently high power transmission efficiency. The control circuit34then causes the display12to display a message prompting stopping of the two-wheeler3at the current position.

FIGS.11A and11Bare diagrams each showing an example positional relationship between the feeder coil32in the power feeding station2and the receiver coil41in the two-wheeler3and an example message appearing on the display12in the positional relationship.

In the example shown inFIG.11A, the receiver coil41is not sufficiently near the feeder coil32. The constant voltage frequency is thus lower than the frequency threshold. The display12displays a message such as “Please move your vehicle a little forward.” prompting movement of the two-wheeler3further toward the power feeding station2.

In the example shown inFIG.11B, the receiver coil41is sufficiently near the feeder coil32. The constant voltage frequency is thus higher than or equal to the frequency threshold. The display12displays a message such as “Please park here.” prompting stopping of the two-wheeler3at the current position.

As described above, the power feeding station includes the feeder for feeding power to a two-wheeler and transmits power to the two-wheeler through the feeder coil in the feeder and the receiver coil in the receiver included in the parked two-wheeler. The power feeding station detects the frequency of AC power supplied to the feeder coil that allows the feeder and the receiver to perform a constant voltage output operation and provides, based on the frequency, a notification to guide the two-wheeler to a position at which higher power transmission efficiency is achieved. The power feeding station thus can feed power contactlessly to the two-wheeler through the feeder coil and can also provide guidance about the parking position of the two-wheeler to increase the power transmission efficiency.

In one modification, the control circuit34in the feeder11may determine whether a parking position of a two-wheeler is appropriate based on the voltage of the AC power applied to the feeder coil32with which the receiver21outputs a constant voltage.

Referring back toFIGS.9and10, each constant voltage frequency corresponds one-to-one to the voltage of the AC power applied to the feeder coil32to allow the receiver21to output a predetermined voltage. When the feeder coil32and the receiver coil41have a higher degree of coupling, the AC power applied to the feeder coil32is set to have a lower voltage. The control circuit34thus compares the voltage of the AC power applied to the feeder coil32, which allows the receiver21to output the predetermined voltage when the feeder11and the receiver21are performing a constant voltage output operation, with a predetermined voltage threshold. When the voltage of the AC power applied to the feeder coil32is higher than the predetermined voltage threshold, the control circuit34causes the display12to display a message prompting movement of the two-wheeler3further toward the power feeding station2. When the voltage of the AC power applied to the feeder coil32is lower than or equal to the predetermined voltage threshold, the control circuit34causes the display12to display a message prompting stopping of the two-wheeler3at the current position.

In the present modification, the power feeding station can feed power contactlessly to a two-wheeler through the feeder coil and can provide guidance about the parking position of the two-wheeler to increase the power transmission efficiency.

In another modification, the receiver coil41included in the receiver21in the two-wheeler3may be attached to the two-wheeler3with its winding axis extending in the lateral direction of the two-wheeler3. For example, the receiver coil41may be installed lateral to the front wheel23of the two-wheeler3with its winding axis orthogonal to the surface of rotation of the front wheel23of the two-wheeler3. Accordingly, the feeder coil32included in the feeder11in the power feeding station2may be installed to face the receiver coil41when the two-wheeler3is parked at an appropriate position for power transmission. For example, in the above embodiment, the feeder coil32may be installed in one of the pillars13or14in the housing10to be adjacent to the front wheel23of the parked two-wheeler3. Accordingly, the feeder coil32is installed with its winding axis orthogonal to the surface of the pillar in the housing10that faces the front wheel23of the two-wheeler3.

The above-described structure may cause insufficient power transmission efficiency when the two-wheeler3is parked to have its receiver coil41located beyond the feeder coil32or before the feeder coil32. To place the receiver coil41near the feeder coil32, the two-wheeler3is to be moved in a different direction depending on whether the receiver coil41is located beyond the feeder coil32or before the feeder coil32.

In the present modification, the control circuit34records temporal changes in the constant voltage frequency in a memory included in the control circuit34. The control circuit34then refers to the temporal changes in the constant voltage frequency to determine the direction in which the two-wheeler3is to be moved.

For example, the receiver coil41located beyond the feeder coil32passes a position nearest the feeder coil32. The constant voltage frequency changes to be high and then to be low again. In contrast, the receiver coil41located before the feeder coil32does not reach the position nearest the feeder coil32. Thus, the constant voltage frequency is not very high. The control circuit34causes the display12to display a message prompting movement of the two-wheeler3rearward from the power feeding station2when the temporal changes in the constant voltage frequency for a latest predetermined period include a maximum value that is higher than or equal to a predetermined frequency threshold and the current constant voltage frequency is lower than the frequency threshold. In contrast, the control circuit34causes the display12to display a message prompting movement of the two-wheeler3further toward the power feeding station2when the temporal changes in the constant voltage frequency for the latest predetermined period do not include reaching the predetermined frequency threshold or higher. When the current constant voltage frequency is higher than or equal to the frequency threshold, the control circuit34causes the display12to display a message prompting stopping of the two-wheeler3at the current position.

Similarly, the control circuit34may record, in a memory included in the control circuit34, the temporal changes in the voltage of AC power applied to the feeder coil32that allows an output voltage from the receiver21to be a predetermined voltage while the feeder11and the receiver21are performing a constant voltage output operation. The control circuit34may thus determine the direction in which the two-wheeler3is to be moved by referring to the temporal changes in the voltage of the AC power. Accordingly, the control circuit34causes the display12to display a message prompting movement of the two-wheeler3rearward from the power feeding station2when the temporal changes in the voltage of the AC power for the latest predetermined period include a minimum voltage that is lower than or equal to a predetermined voltage threshold and the current voltage of the AC power is higher than the voltage threshold. In contrast, the control circuit34causes the display12to display a message prompting movement of the two-wheeler3further toward the power feeding station2when the temporal changes in the voltage of the AC power for the latest predetermined period do not include reaching the predetermined voltage threshold or lower. When the current voltage of the AC power is lower than or equal to the voltage threshold, the control circuit34causes the display12to display a message prompting stopping of the two-wheeler3at the current position.

In the present modification, the power feeding station can appropriately determine the direction in which the two-wheeler is to be moved relative to the power feeding station to increase the power transmission efficiency.

In the embodiment or the modifications described above, the power feeding station2may include one or more light sources instead of the display12. Accordingly, the light source is another example of the notification source. The control circuit34changes the lighting state of the light source depending on whether the constant voltage frequency is lower than the predetermined frequency threshold or the constant voltage frequency is higher than or equal to the predetermined threshold. For example, when the constant voltage frequency is lower than the predetermined frequency threshold, the control circuit34may cause the light source to flash or to emit red light to prompt movement of the two-wheeler3further forward. When the constant voltage frequency is higher than or equal to the predetermined frequency threshold, the control circuit34may cause the light source to light continuously or to emit blue or green light to prompt parking of the two-wheeler3at the current position. In some embodiments, the power feeding station2may include a speaker instead of the display12or in addition to the display12. The speaker is still another example of the notification source. The control circuit34may use a sound from the speaker to provide a notification of guidance about the parking position of the two-wheeler3.

In still another modification, the display12may be installed on the two-wheeler3. For example, the display12may be installed on the handle of the two-wheeler3to face upward. Accordingly, the control circuit34in the feeder11transmits a signal including a notification of guidance about the stop position of the two-wheeler3through the communicator33to the communicator44in the receiver21installed on the two-wheeler3. Upon receiving the signal from the communicator33, the communicator44outputs a notification of guidance about the stop position of the two-wheeler3included in the signal to the display12. The display12may display the notification. The power feeding station2and the two-wheeler3may each include the display12. The display12in the power feeding station2and the display12in the two-wheeler3may each output a notification of guidance about the stop position of the two-wheeler3. Similarly to the above modification, instead of the display12, or in addition to the display12, the two-wheeler3may include a light source or a speaker. The light source or the speaker may output a notification of guidance about the stop position of the two-wheeler3included in the signal received through the communicator44. The present modification also allows the power feeding station2to achieve the advantageous effects similar to the above embodiment.

In still another modification, the control circuit34in the feeder11may detect the constant voltage frequency by monitoring a current flowing through the feeder coil32as described in Japanese Unexamined Patent Application Publication No. 2018-207764. Accordingly, the feeder11includes a current detection circuit (not shown) that detects a current flowing through the feeder coil32. The power receiver circuit43in the receiver21includes a constant load circuit (not shown). The constant load circuit provides a constant load connected to the resonant circuit including the receiver coil41and the resonant capacitor42. The current detection circuit measures a current flowing through the feeder coil32. The control circuit34may determine, as the constant voltage frequency, the frequency of the AC power applied to the feeder coil32and causing a maximum current to flow through the feeder coil32.

In still another modification, the power feeding station may feed power to an object other than a two-wheeler. For example, the power feeding station may feed power to an electric scooter. The electric scooter is another example of an electric mobility vehicle. When the electric scooter is placed at the power feeding station with the receiver coil installed on the electric scooter approaching the feeder coil in a predetermined direction, the power feeding station can guide the electric scooter to a position at which higher power transmission efficiency is achieved as in the embodiments or the modifications described above.

As described above, those skilled in the art can make various changes in accordance with embodiments implemented within the scope of the present invention.