Power reception device, contactless power supply system, and method for searching for resonance frequency

Abstract

The present invention achieves a power reception device capable of identifying its own resonance frequency without a power transmission device.　This power reception device (3) comprises: a resonance circuit (31); an application unit (52) that applies a search voltage to the resonance circuit from inside the power reception device and changes the frequency of the search voltage; a measurement unit (53) that measures a change in the impedance of the resonance circuit due to the change in the frequency of the search voltage, without power transmission from a power transmission device; and a determination unit (54) that determines the resonance frequency of the resonance circuit on the basis of the change in the impedance.

Description

Power receiving device, non-contact power supply system, and resonance frequency search method

[0001] The present invention relates to a power receiving device and a non-contact power supply system.

[0002] Patent Document 1 discloses a power transmission and reception system that wirelessly transmits power. The power transmission device of this power transmission and reception system searches for the resonance frequency when transmitting power.

[0003] Japanese Patent Laid-Open No. 2014-135851

[0004] The resonance circuit of the power receiving device includes a coil and a capacitor. The characteristic values of commercially available coils and capacitors can have an error of about 10% with respect to the nominal value. Therefore, the resonance frequency of the resonance circuit including those coils and capacitors can also have a certain degree of error. That is, the resonance frequency varies within a certain range for each power receiving device.

[0005] In the configuration described in Patent Document 1, in order to search for the resonance frequency in the power transmission device, it is necessary to transmit power from the power transmission device to the power receiving device. Therefore, it takes time until power transmission starts at the resonance frequency. In the configuration described in Patent Document 1, the resonance frequency cannot be searched in advance on the power receiving device side without power transmission from the power transmission device.

[0006] One aspect of the present invention aims to realize a power receiving device that can identify its own resonance frequency without power transmission from a power transmission device.

[0007] The power receiving device for non-contact power supply according to Aspect 1 of the present invention includes a resonance circuit, an application circuit that applies a search voltage from inside the power receiving device to the resonance circuit and changes the frequency of the search voltage, a measurement unit that measures the change in impedance of the resonance circuit according to the change in the frequency of the search voltage without power transmission from the power transmission device, and a determination unit that determines the resonance frequency of the resonance circuit based on the change in impedance.

[0008] According to the above configuration, the power receiving device can identify its own resonance frequency without receiving power transmission from the power transmission device.

[0009] The power receiving device according to embodiment 2 of the present invention may be configured to include a storage unit that stores the specified resonant frequency in embodiment 1 described above.

[0010] The power receiving device according to embodiment 3 of the present invention may be configured to include a power receiving communication unit that transmits information indicating the resonant frequency to the power transmitting device, as in embodiment 2 described above.

[0011] With the above configuration, the power transmission equipment can start supplying power at the appropriate frequency. Therefore, power can be supplied quickly.

[0012] The power receiving device according to embodiment 4 of the present invention may be configured to include a notification unit that notifies of an abnormality in the resonant frequency based on the specified resonant frequency in embodiment 1 described above.

[0013] With the above configuration, abnormalities such as the presence of foreign objects can be notified to external devices or users.

[0014] The power receiving device according to embodiment 5 of the present invention may be configured to include a notification unit that notifies of an abnormality in the resonant frequency based on the difference between the newly identified resonant frequency and the past resonant frequency, as described in embodiment 2 above.

[0015] The power receiving device according to embodiment 6 of the present invention may be configured to include a notification unit that notifies of an abnormality based on the impedance of the resonant circuit at the resonant frequency, as described in embodiment 1 above.

[0016] The power receiving device according to embodiment 7 of the present invention, in embodiment 1 described above, when power is supplied, the resonant circuit is in series resonance and is connected to the resonant circuit and includes a first switching circuit that changes the resonant circuit to parallel resonance by being in a short-circuit state, and the application circuit may be configured to change the frequency of the search voltage applied to the resonant circuit without power being supplied from the power transmitting device when the resonant circuit is in parallel resonance.

[0017] With the above configuration, the resonant frequency can be searched while the resonant circuit is in a parallel resonant state, allowing the resonant frequency to be accurately identified with a small current.

[0018] In the power receiving device according to embodiment 8 of the present invention, in embodiment 7 described above, the determination unit may be configured to determine that the frequency at which the impedance is maximum is the resonant frequency of the resonant circuit.

[0019] In the power receiving device according to embodiment 9 of the present invention, in embodiment 7 described above, the first switching circuit may be configured to constitute a part of a rectifier circuit that rectifies the AC power receiving voltage during power supply.

[0020] With the above configuration, a portion of the rectifier circuit used during power supply can be utilized to change the resonant circuit to a parallel resonance during the search. Therefore, the number of additional elements required for searching the resonant frequency can be reduced.

[0021] A power receiving device according to embodiment 10 of the present invention may be configured such that, in embodiment 1 above, it comprises a transformer having a primary coil connected to the resonant circuit and a secondary coil with fewer turns than the primary coil, and the measuring unit measures the change in impedance of the resonant circuit by measuring the voltage on the secondary side of the transformer.

[0022] With the above configuration, it is possible to avoid applying high voltages that may occur in the resonant circuit during power supply to the measurement section.

[0023] The power receiving device according to embodiment 11 of the present invention includes, in embodiment 10 above, a second switching circuit connected between both ends of the secondary coil and capable of short-circuiting the two ends of the secondary coil, wherein the second switching circuit has a first switching element and a second switching element connected in series with each other, the node between the first switching element and the second switching element is connected to ground, and the application circuit may be configured to change the frequency of the search voltage applied to the resonant circuit without power being supplied from the power transmission device, with the first switching element in an off state and the second switching element in an open state.

[0024] According to the above configuration, the second switching circuit can prevent overvoltage during power supply, and the second switching circuit can be used to configure the current path during searching.

[0025] A contactless power supply system according to embodiment 12 of the present invention may be configured in any one of embodiments 1 to 11 above, comprising the power receiving device and the power transmission device equipped with a power transmission coil that supplies power to the power receiving device.

[0026] In the contactless power supply system according to embodiment 13 of the present invention, the power transmission device may be configured to include a power transmission communication unit that receives information indicating the resonant frequency from the power receiving device, and a power transmission control unit that initiates power supply to the power transmission coil at the resonant frequency when power supply is started.

[0027] With the above configuration, the power transmission equipment can start supplying power at the appropriate frequency. Therefore, power can be supplied quickly.

[0028] A contactless power supply system according to embodiment 14 of the present invention comprises, in embodiment 4 or 5 above, the power receiving device and the power transmitting device equipped with a power transmitting coil that supplies power to the power receiving device, wherein the power transmitting device may be configured not to supply power when an abnormality is notified from the power receiving device.

[0029] According to the above configuration, it is possible to avoid supplying power in undesirable situations.

[0030] A method for searching for a resonant frequency according to embodiment 15 of the present invention is a method for searching for a resonant frequency in a power receiving device for contactless power supply equipped with a resonant circuit, comprising: an application step of applying a search voltage to the resonant circuit from inside the power receiving device and changing the frequency of the search voltage; a measurement step of measuring the change in impedance of the resonant circuit in accordance with the change in frequency of the search voltage without power transmission from a power transmitting device; and a determination step of determining the resonant frequency of the resonant circuit based on the change in impedance.

[0031] According to one aspect of the present invention, a power receiving device can determine its own resonant frequency without power transmission from a power transmitting device.

[0032] This is a block diagram illustrating the schematic configuration of a contactless power supply system according to one embodiment of the present invention. This is a circuit diagram showing an example of a more detailed configuration of a contactless power supply system according to one embodiment of the present invention. This is a circuit diagram showing the equivalent circuit of the power receiving device during the search for the resonant frequency. This is a circuit diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention. This is a circuit diagram showing the configuration of a contactless power supply system according to one embodiment of the present invention.

[0033] [Embodiment 1] Hereinafter, an embodiment relating to one aspect of the present invention (hereinafter also referred to as "this embodiment") will be described based on the drawings.

[0034] §1 Application Example Figure 1 is a block diagram showing the schematic configuration of the contactless power supply system 1 of this embodiment. The contactless power supply system 1 comprises a power transmission device 2 and a power receiving device 3. The power transmission device 2 supplies power to the power receiving device 3 in a contactless manner.

[0035] The power transmission device 2 comprises a power transmission communication unit 21, a power transmission control unit 22, an inverter 24, and a power transmission coil 28. During power supply, the power transmission coil 28 generates an alternating magnetic field to supply power to the power receiving device 3 in a non-contact manner. During the search for the resonant frequency, the power transmission device 2 does not need to be near the power receiving device 3 and does not perform power supply operations or operations related to the search for the resonant frequency.

[0036] The power receiving device 3 includes a resonant circuit 31, a first rectifier circuit 34, a smoothing capacitor 35, a load 90, a specific unit 50, a storage unit 55, a notification unit 56, and a power receiving communication unit 57.

[0037] During power supply, the resonant circuit 31 outputs the AC receiving voltage generated by the AC magnetic field from the power transmission coil 28 to the first rectifier circuit 34. The first rectifier circuit 34 rectifies the receiving voltage from the resonant circuit 31 into DC and outputs it to the smoothing capacitor 35. The smoothing capacitor 35 outputs the smoothed output voltage to the load 90.

[0038] During the search for the resonant frequency, the identification unit 50 generates a periodically changing search voltage for the resonant circuit 31 using the internal power supply of the power receiving device 3, without power being supplied from the power transmission device 2. The identification unit 50 applies the search voltage to the resonant circuit 31. The identification unit 50 identifies the resonant frequency of the resonant circuit 31 by changing the frequency of the search voltage. When the frequency of the search voltage changes, the impedance of the resonant circuit 31 changes. By measuring the voltage or current that changes in response to the change in impedance, the identification unit 50 can identify the resonant frequency of the resonant circuit 31.

[0039] The memory unit 55 stores the identified resonant frequency. The notification unit 56 notifies the power transmission device 2 of the resonant frequency information, which indicates the resonant frequency, via the power receiving communication unit 57.

[0040] The power receiving device 3 can determine the resonant frequency of its own resonant circuit 31 without receiving power from the power transmitting device 2. Therefore, the power receiving device 3 can determine the resonant frequency before power is supplied from the power transmitting device 2. By notifying the power transmitting device 2 of the resonant frequency determined by the power receiving device 3, the power transmitting device 2 can quickly transmit power at the appropriate frequency from the start of power supply. Thus, the contactless power supply system 1 can suppress power supply losses and provide power quickly.

[0041] §2 Configuration Example (Configuration of Power Transmission Device 2) Figure 2 is a circuit diagram showing a more detailed example of the configuration of the contactless power supply system 1 of this embodiment. The power transmission device 2 comprises a power transmission communication unit 21, a power transmission control unit 22, a power supply 23, an inverter 24, a coil 25, a first capacitor 26, a second capacitor 27, and a power transmission coil 28. The power supply 23 is a DC power supply. The inverter 24 is connected to the power supply 23 and converts the DC voltage to an AC voltage. The inverter 24 includes a plurality of switching elements 24a to 24d.

[0042] One end of the coil 25 is connected to one output terminal of the inverter 24. One end of the first capacitor 26 is connected to the other end of the coil 25, and the other end of the first capacitor 26 is connected to the other output terminal of the inverter 24. One end of the second capacitor 27 is connected to the other end of the coil 25.

[0043] One end of the power transmission coil 28 is connected to the other end of the second capacitor 27, and the other end of the power transmission coil 28 is connected to the other output terminal of the inverter 24. The power transmission coil 28 supplies power to the power receiving device 3 in a non-contact manner by generating an alternating magnetic field.

[0044] The power transmission communication unit 21 performs wireless communication with the power receiving communication unit 57 of the power receiving device 3. The power transmission communication unit 21 receives the resonance frequency information and operation information of the power receiving device 3 from the power receiving device 3. The power transmission communication unit 21 outputs the resonance frequency information and operation information received from the power receiving device 3 to the power transmission control unit 22.

[0045] The power transmission control unit 22 controls the frequency or power, or both, of the alternating voltage output by the inverter 24 by controlling a plurality of switching elements 24a to 24d. The power transmission control unit 22 stores the resonance frequency information of the power receiving device 3. At the start of power supply, the power transmission control unit 22 sets the frequency of the alternating voltage to the resonance frequency of the resonance circuit 31 of the power receiving device 3 based on the resonance frequency information of the power receiving device 3. During power supply, the power transmission control unit 22 controls the frequency or power, or both, of the alternating voltage based on the operation information of the power receiving device 3. For example, the power transmission control unit 22 controls the average voltage applied to the power transmission coil 28 by performing phase shift control. Thereby, the power transmission control unit 22 controls the power supplied from the power transmission coil 28 to the power receiving device 3.

[0046] (Configuration of the power receiving device 3) The power receiving device 3 includes a resonance circuit 31, a first rectifying circuit 34 (first switching circuit), a smoothing capacitor 35, a transformer 36, a second rectifying circuit 39, a second switching circuit 40, a specifying unit 50, a storage unit 55, a notification unit 56, a power receiving communication unit 57, and a load 90. The specifying unit 50 includes a resistance element 37, a diode 38, a constant voltage source 43, a third switching circuit 44, a power receiving control unit 51, an applying unit 52, a measuring unit 53, and a determining unit 54.

[0047] The resonance circuit 31 has a resonance coil 32 and a resonance capacitor 33. The resonance coil 32 receives power from the power transmission coil 28 of the power transmission device 2. The resonance capacitor 33 is connected in series with the resonance coil 32.

[0048] The first rectifying circuit 34 rectifies the AC voltage generated in the resonance circuit 31 into a DC voltage during power supply. The first rectifying circuit 34 outputs a full-wave rectified DC (pulsating) voltage. The first rectifying circuit 34 includes first to fourth switching elements 34a to 34d, which are transistors. The first switching element 34a and the second switching element 34b are connected in series with each other. The third switching element 34c and the fourth switching element 34d are connected in series with each other. The resonance circuit 31 is connected between the node (input terminal) between the first switching element 34a and the second switching element 34b and the node (input terminal) between the third switching element 34c and the fourth switching element 34d.

[0049] The smoothing capacitor 35 smooths the voltage output from the first rectifying circuit 34. The smoothing capacitor 35 outputs the smoothed output voltage to the load 90. The smoothing capacitor 35 is connected between the output terminals of the first rectifying circuit 34. Specifically, the smoothing capacitor 35 is connected in parallel with the first switching element 34a and the second switching element 34b, and in parallel with the third switching element 34c and the fourth switching element 34d. One end of the smoothing capacitor 35 is connected to the first switching element 34a and the third switching element 34c. The other end of the smoothing capacitor 35 is connected to the second switching element 34b and the fourth switching element 34d. The other end of the smoothing capacitor 35 is connected to the ground.

[0050] The transformer 36 has a primary coil and a secondary coil. The primary coil is connected between one end and the other end of the resonance coil 32 in the resonance circuit 31. The number of turns of the secondary coil is less than the number of turns of the primary coil. The transformer 36 is a transformer that steps down the voltage input to the primary side and outputs it to the secondary side.

[0051] The second rectifier circuit 39 rectifies the AC voltage on the secondary side of the transformer 36 into a DC voltage. The second rectifier circuit 39 is connected to the secondary coil of the transformer 36. Here, the second rectifier circuit 39 is a bridge circuit with multiple diodes, but it is not limited to this and may be a circuit with multiple switching elements. The second rectifier circuit 39 has a first AC terminal 39a connected to one end of the secondary coil of the transformer 36, a second AC terminal 39b connected to the other end of the secondary coil of the transformer 36, a positive terminal 39c, and a negative terminal 39d. The positive terminal 39c is connected to one end of the smoothing capacitor 35. The negative terminal 39d is connected to the other end of the smoothing capacitor 35. The second rectifier circuit 39 outputs a full-wave rectified DC (pulsating) voltage from the positive terminal 39c and the negative terminal 39d to the smoothing capacitor 35.

[0052] The second switching circuit 40 is connected between the ends of the secondary coil of the transformer 36. The second switching circuit 40 can switch between a closed state (non-conductive) and a short-circuit state (conductive) between the ends of the secondary coil of the transformer 36. For example, the second switching circuit 40 has a fifth switching element 40a and a sixth switching element 40b, which are transistors. The fifth switching element 40a and the sixth switching element 40b are connected in series with each other. One end of the fifth switching element 40a is connected to one end of the secondary coil of the transformer 36. The other end of the fifth switching element 40a is connected to one end of the sixth switching element 40b. The other end of the sixth switching element 40b is connected to the other end of the secondary coil of the transformer 36. The node between the fifth switching element 40a and the sixth switching element 40b is connected to ground.

[0053] One end of the resistive element 37 is connected to one end of the secondary coil of the transformer 36.

[0054] The cathode of diode 38 is connected to the other end of resistor 37.

[0055] The third switching circuit 44 generates a periodically changing search voltage. The third switching circuit 44 has a seventh switching element 44a and an eighth switching element 44b, which are transistors. One end of the seventh switching element 44a is connected to a constant voltage source 43. The other end of the seventh switching element 44a is connected to one end of the eighth switching element 44b. The other end of the eighth switching element 44b is connected to ground. The node between the seventh switching element 44a and the eighth switching element 44b is connected to the anode of the diode 38.

[0056] The power receiving control unit 51 controls the first switching element 34a, the second switching element 34b, the third switching element 34c, and the fourth switching element 34d of the first rectifier circuit 34. The power receiving control unit 51 also controls the fifth switching element 40a and the sixth switching element 40b of the second switching circuit 40.

[0057] During power supply, the power receiving control unit 51 short-circuits (conducts) the second switching circuit 40 based on the output voltage output by the smoothing capacitor 35 to the load 90. For example, during power supply, if the output voltage is above a voltage threshold, the power receiving control unit 51 switches the fifth switching element 40a and the sixth switching element 40b to a conductive state. During power supply, if the output voltage is below a voltage threshold, the power receiving control unit 51 sets the fifth switching element 40a and the sixth switching element 40b to a non-conductive state.

[0058] The application unit 52 controls the seventh switching element 44a and the eighth switching element 44b of the third switching circuit 44. The application unit 52 outputs information indicating the frequency of the search voltage to the measurement unit 53.

[0059] The measurement unit 53 measures the change in impedance of the resonant circuit 31 by measuring the voltage on the secondary side of the transformer 36. The measurement unit 53 measures the voltage between the secondary coil of the transformer 36 and the resistive element 37. The measurement unit 53 outputs impedance information for each frequency of the search voltage to the determination unit 54. The measurement unit 53 also measures the output voltage of the smoothing capacitor 35. The measurement unit 53 outputs output voltage information to the determination unit 54.

[0060] The determination unit 54 determines (specifies) the resonant frequency of the resonant circuit 31 based on the change in impedance. The determination unit 54 outputs information of the specified resonant frequency to the storage unit 55 and the notification unit 56. The determination unit 54 also generates operation information of the power receiving device 3 indicating whether or not an overvoltage is occurring in the power receiving device 3 based on the output voltage information. If the output voltage is below the voltage threshold, the determination unit 54 generates operation information indicating that no overvoltage is occurring. If the output voltage is above the voltage threshold, the determination unit 54 generates operation information indicating that an overvoltage is occurring. The operation information may include information indicating the output voltage. The determination unit 54 outputs the operation information to the notification unit 56. The determination unit 54 notifies the power receiving control unit 51 whether the output voltage is below or above the voltage threshold.

[0061] The memory unit 55 stores the identified resonant frequency.

[0062] The notification unit 56 notifies the power transmission device 2 of resonant frequency information indicating the resonant frequency via the power receiving communication unit 57. The notification unit 56 notifies the power transmission device 2 of an abnormality in the resonant frequency based on the difference between past resonant frequencies stored in the memory unit 55 and the resonant frequency newly identified by the determination unit 54. The notification unit 56 may also notify another device of the resonant frequency information or abnormality via the power receiving communication unit 57. The notification unit 56 may also notify the user of the resonant frequency information or abnormality via a display device or speaker provided by the power receiving device 3. The notification unit 56 notifies the power transmission device 2 of operation information via the power receiving communication unit 57 during power supply.

[0063] The power receiving communication unit 57 communicates wirelessly with the power transmission communication unit 21 of the power transmission device 2. The power receiving communication unit 57 transmits resonant frequency information, operation information, and information indicating an abnormality in the resonant frequency to the power transmission device 2.

[0064] (Power Supply Operation) The operation of the contactless power supply system 1 during power supply is described below. Before power supply begins, the power receiving device 3 has already identified the resonant frequency of the resonant circuit 31 and notifies the power transmitting device 2 of the identified resonant frequency. The power transmitting device 2 starts supplying power at the identified resonant frequency of the resonant circuit 31. The power transmission control unit 22 causes the power transmission coil 28 to start supplying power at the identified resonant frequency.

[0065] During power supply, the power receiving control unit 51 controls the first switching element 34a, the second switching element 34b, the third switching element 34c, and the fourth switching element 34d so that the first rectifier circuit 34 performs full-wave rectification. For example, the first period and the second period are repeated alternately in accordance with the power supply frequency. In the first period, the first switching element 34a and the fourth switching element 34d are in a conductive state, and the second switching element 34b and the third switching element 34c are in a non-conductive state. In the second period, the first switching element 34a and the fourth switching element 34d are in a non-conductive state, and the second switching element 34b and the third switching element 34c are in a conductive state.

[0066] During power supply, the application unit 52 causes the seventh switching element 44a and the eighth switching element 44b of the third switching circuit 44 to be in a non-conductive state.

[0067] Before power supply begins, the smoothing capacitor 35 of the power receiving device 3 is not charged. As power supply begins, charging of the smoothing capacitor 35 begins, and the output voltage rises. Therefore, immediately after power supply begins, the current from the first rectifier circuit 34 flows into the smoothing capacitor 35, so the load resistance as seen from the resonant circuit 31 is close to zero. During power supply, the resonant coil 32 and the resonant capacitor 33 are connected in series, forming a series resonance. In this case, the smaller the load resistance of the resonant circuit, the larger the Q value, which represents the sharpness of the resonance peak. When power is supplied from the power transmitting device 2 at the resonant frequency of the resonant circuit 31 while the load resistance of the power receiving device 3 is close to zero, very large voltages are generated across the resonant coil 32 and the resonant capacitor 33 due to resonance. To prevent the occurrence of overvoltage immediately after power supply begins, the power receiving device 3 is equipped with a transformer 36 and a second rectifier circuit 39. Furthermore, in order to prevent the occurrence of overvoltage, the power transmission device 2 may control the phase shift amount at the start of power supply and gradually increase the voltage applied to the power transmission coil 28.

[0068] In the contactless power supply system 1 of this embodiment, when power supply is started from the power transmission device 2, a voltage is generated across the resonant coil 32. The same voltage as across the resonant coil 32 is applied to the primary coil of the transformer 36. The voltage of the primary coil is stepped down according to the turns ratio of the transformer 36 and output from the secondary coil. The second rectifier circuit 39 outputs the stepped-down voltage to the smoothing capacitor 35. When the smoothing capacitor 35 is not sufficiently charged immediately after power supply is started, the voltage output from the second rectifier circuit 39 is higher than the output voltage of the smoothing capacitor 35. Therefore, current flows from the secondary coil of the transformer 36 to the smoothing capacitor 35 via the second rectifier circuit 39. That is, a current corresponding to the current flowing in the secondary coil also flows from the resonant coil 32 to the primary coil of the transformer 36. In this state, the paths of the transformer 36 and the second rectifier circuit 39 are added to the resonant circuit 31, so the resonant frequency of the power receiving device 3, including the resonant circuit 31, the transformer 36, and the second rectifier circuit 39, deviates from the resonant frequency of the resonant circuit 31 itself. Therefore, even if the power transmitting device 2 supplies power at the resonant frequency of the resonant circuit 31 when the smoothing capacitor 35 is not sufficiently charged, resonance will not occur in the resonant circuit 31. Thus, the contactless power supply system 1 can appropriately suppress an excessive rise in the voltage across the resonant coil 32.

[0069] Adjusting the power supply via communication involves a delay due to the communication (for example, about 10 ms). In the contactless power supply system 1, even though the power transmission device 2 controls the amount of power supplied, overvoltage can be prevented by the control on the power receiving device 3 side without waiting for the power transmission device 2 to adjust the power supply. Therefore, the occurrence of failures due to overvoltage can be reduced.

[0070] After a certain period of time has elapsed since power supply began, the smoothing capacitor 35 is sufficiently charged, and the power receiving device 3 performs normal constant voltage output operation to the load 90. When the smoothing capacitor 35 is sufficiently charged, the winding ratio of the transformer 36 is set so that the secondary voltage stepped down by the transformer 36 is lower than the output voltage of the smoothing capacitor 35. Therefore, during constant voltage output operation, power is not supplied from the second rectifier circuit 39 to the smoothing capacitor 35, and power is supplied to the smoothing capacitor 35 only from the first rectifier circuit 34. Consequently, no current flows through the secondary coil of the transformer 36. At this time, if the inductance of the primary coil of the transformer 36 is sufficiently larger than the inductance of the resonant coil 32, the transformer 36 hardly affects the resonant frequency of the resonant circuit 31. The inductance of the primary coil of the transformer 36 may be 10 times or more the inductance of the resonant coil 32. More preferably, the inductance of the primary coil of the transformer 36 may be 100 times or more the inductance of the resonant coil 32.

[0071] The power receiving control unit 51 shuts off the fifth switching element 40a and the sixth switching element 40b when the output voltage of the smoothing capacitor 35 is below the voltage threshold. In other words, the second switching circuit 40 remains shut off while normal constant voltage output operation is being performed immediately after the start of power supply.

[0072] On the other hand, changes in the relative position between the power transmission coil 28 and the resonant coil 32 may increase the output of the resonant circuit 31, potentially causing an overvoltage in the smoothing capacitor 35. The power receiving control unit 51 switches the fifth switching element 40a and the sixth switching element 40b to a conductive state when the output voltage is above a voltage threshold. This allows the second switching circuit 40 to short-circuit the terminals of the secondary coil of the transformer 36. The voltage threshold is set to a value higher than the output voltage during constant voltage output operation.

[0073] When the terminals of the secondary coil of the transformer 36 are short-circuited, the resonant frequency of the power receiving device 3, which includes the resonant circuit 31, the transformer 36, and the second switching circuit 40, changes. As a result, the power received by the power receiving device 3 from the power transmitting device 2 decreases, and the voltage output from the resonant circuit 31 to the smoothing capacitor 35 also decreases. Therefore, the output voltage of the smoothing capacitor 35 can be reduced, and overvoltage can be suppressed.

[0074] Furthermore, if the output voltage of the smoothing capacitor 35 is above a voltage threshold, the power receiving communication unit 57 transmits operational information to the power transmitting device 2 indicating that an overvoltage has occurred in the power receiving device 3.

[0075] When the power transmission communication unit 21 receives operational information indicating that an overvoltage has occurred, the power transmission control unit 22 reduces the voltage applied to the power transmission coil 28 or shifts its frequency from the resonant frequency. As a result, the power transmission control unit 22 reduces the power supplied to the power receiving device 3. This prevents an overvoltage from occurring again when the power receiving control unit 51 of the power receiving device 3 returns the second switching circuit 40 to the off state.

[0076] (Resonance Frequency Search Operation) The operation of the non-contact power supply system 1 during resonance frequency search is described below. During the search, the power transmission device 2 does not need to be within the range where it can supply power or communicate, and does not perform any power supply operations or operations related to resonance frequency search. The power receiving device 3 performs the resonance frequency search independently.

[0077] During the search phase, the power receiving control unit 51 turns off the first switching element 34a and the third switching element 34c of the first rectifier circuit 34, and turns on the second switching element 34b and the fourth switching element 34d (short circuit). As a result, the first rectifier circuit 34 (first switching circuit) short-circuits the terminals of the resonant coil 32 and the resonant capacitor 33 that are not connected to each other to ground. As a result, the first rectifier circuit 34 changes the resonant circuit 31 from series resonance to parallel resonance. The second switching element 34b and the fourth switching element 34d constitute the first switching circuit that changes the resonant circuit 31 from series resonance to parallel resonance by being in a short-circuit state.

[0078] During the search, the power receiving control unit 51 turns off the fifth switching element 40a of the second switching circuit 40 and turns on the sixth switching element 40b. This creates a path for current to flow from the constant voltage source 43 and the third switching circuit 44 through the secondary coil of the transformer 36 to ground.

[0079] Figure 3 is a circuit diagram showing the equivalent circuit of the power receiving device 3 during the search for the resonant frequency. During the search, the first rectifier circuit 34 and the second switching circuit 40 in Figure 2 are omitted, resulting in Figure 3. In Figure 3, some blocks are also omitted from the illustration. During the search, the resonant coil 32 and resonant capacitor 33 of the resonant circuit 31 are connected in parallel between the low potential (ground) and the high potential.

[0080] The application unit 52 generates a periodically changing search voltage from the constant voltage source 43 by alternately making the seventh switching element 44a and the eighth switching element 44b conduct at a certain frequency. Here, the search voltage is a square wave. The third switching circuit 44 outputs the search voltage from the node between the seventh switching element 44a and the eighth switching element 44b. The search voltage is voltage-dropped across the resistor element 37 and applied to the secondary coil of the transformer 36. The transformer 36 boosts the voltage of the secondary coil according to the turns ratio and outputs it from the primary coil. The search voltage output from the primary coil is applied to the resonant circuit 31, which is a parallel resonant circuit.

[0081] Furthermore, the maximum value of the search voltage dropped across the resistor 37 is set to be smaller than the forward voltage drop of the diode in the second rectifier circuit 39. This prevents current from flowing through the diode in the second rectifier circuit 39 during the search. Therefore, the influence of the second rectifier circuit 39 and the smoothing capacitor 35 connected to it can be ignored during the search.

[0082] The measuring unit 53 measures the voltage between the resistive element 37 and the secondary coil of the transformer 36. The measured voltage is the voltage across the secondary coil of the transformer 36, which has been divided by the resistive element 37. The voltage across the secondary coil of the transformer 36 is proportional to the voltage across the primary coil. The voltage across the primary coil is the voltage across the resonant circuit 31. If the impedance of the resonant circuit 31 increases, the voltage across the resonant circuit 31 also increases. The resonant circuit 31 has impedance as a parallel resonant circuit. In the case of a parallel resonant circuit, the impedance is maximum at the resonant frequency. Since the search voltage changes periodically, the peak of the measured voltage is maximum when the impedance is maximum. Therefore, when the frequency of the search voltage is varied, the frequency at which the peak of the voltage measured by the measuring unit 53 is maximum is the resonant frequency.

[0083] The application unit 52 changes the frequency of the search voltage within the search frequency range. The third switching circuit 44 applies the search voltage to the resonant circuit 31. The application unit 52 and the third switching circuit 44 constitute an application circuit that applies the search voltage to the resonant circuit 31 from inside the power receiving device 3 and changes the frequency of the search voltage.

[0084] The measuring unit 53 measures the change in voltage applied to the secondary coil of the transformer 36 in accordance with the change in the frequency of the search voltage. The measured voltage changes in accordance with the voltage applied to the resonant circuit 31. Therefore, by measuring the change in voltage, the measuring unit 53 measures the change in impedance of the resonant circuit 31.

[0085] The determination unit 54 determines that the frequency of the search voltage when the impedance of the resonant circuit 31 is at its maximum is the resonant frequency of the resonant circuit 31. The determination unit 54 stores the identified resonant frequency of the resonant circuit 31 in the storage unit 55. In this way, the identification unit 50 of the power receiving device 3 identifies the resonant frequency of the resonant circuit 31 by changing the frequency of the search voltage applied to the resonant circuit 31, without power being supplied from the power transmitting device 2.

[0086] The power receiving device 3 performs the above-described resonant frequency search operation independently at a predetermined timing before power supply begins. For example, the power receiving device 3 may perform the resonant frequency search operation during post-manufacturing quality inspection, when power is turned on, when it receives a search instruction from an external device or user, or at predetermined intervals. Once the power receiving device 3 becomes able to communicate with the power transmitting device 2 before power supply begins, it notifies the power transmitting device 2 of the identified resonant frequency. This allows the power transmitting device 2 to quickly transmit power at the appropriate frequency from the start of power supply.

[0087] The first switching circuit (second switching element 34b and fourth switching element 34d) constitutes part of the first rectifier circuit 34, which rectifies the AC power receiving voltage during power supply. The power receiving device 3 uses the first rectifier circuit 34 to change the resonant circuit 31 from series resonance to parallel resonance during search.

[0088] The second switching circuit 40 plays a role in preventing overvoltage during power supply and in creating a current path from the application circuit through the secondary coil of the transformer 36 during search.

[0089] Similarly, the transformer 36 plays a role in preventing overvoltage during power supply. During exploration, the measurement unit 53 measures voltage at the secondary side of the transformer 36. This prevents the high voltage generated in the resonant circuit 31 during power supply from being directly applied to the measurement unit 53 or the third switching circuit 44.

[0090] Therefore, the power receiving device 3 can efficiently utilize the elements for power supply operation during the search, thereby reducing the number of elements added for the search.

[0091] For example, the resonant coil 32 and resonant capacitor 33 may be configured to be connected in series during the search, with the search voltage applied across both ends. In a series resonant circuit, the impedance is minimal at the resonant frequency. Since the winding resistance of the resonant coil 32 is very small, the minimum value of the impedance is very small. Therefore, in order to accurately identify the frequency at which the impedance is minimal, an internal power supply capable of supplying a reasonably large current to the resonant circuit 31 is required.

[0092] On the other hand, the power receiving device 3 changes the resonant circuit 31 to a parallel resonance during the search and searches for the frequency at which the impedance is maximum. Because the winding resistance is very small, the Q value becomes large, and the impedance (i.e., the measured voltage) changes sharply and significantly near the maximum. Therefore, the power receiving device 3 can accurately identify the frequency at which the impedance is maximum with a small current.

[0093] (Determination of abnormal resonant frequency) Foreign objects such as metal present near the resonant coil 32 affect the characteristics of the resonant coil 32. Therefore, if foreign objects are present, the resonant frequency of the resonant circuit 31 changes. It is not advisable to supply power in this state.

[0094] In the power receiving device 3, the search for the resonant frequency may be performed multiple times with intervals in between. When a new resonant frequency is identified, the notification unit 56 compares the newly identified resonant frequency with the previously identified resonant frequencies (most recent normal resonant frequencies) stored in the memory unit 55. The notification unit 56 determines whether there is an abnormality based on the difference (difference or ratio, etc.) between the new resonant frequency and the past resonant frequency. For example, if the new resonant frequency is within the normal range including the past resonant frequency, the notification unit 56 determines that the resonant frequency is normal.

[0095] If the new resonant frequency is outside the normal range, the notification unit 56 determines that there is an abnormality in the resonant frequency. If there is an abnormality, the notification unit 56 notifies the power transmission device 2 of the abnormality in the resonant frequency.

[0096] If the power receiving device 3 notifies the power receiving device of an abnormal resonant frequency, the power transmitting device 2 will not supply power to the power receiving device 3. This allows the contactless power supply system 1 to avoid supplying power under undesirable circumstances.

[0097] The determination unit 54 may store the peak value of the measured voltage when the impedance (measured voltage) is at its maximum in the storage unit 55. When foreign matter is present, the impedance of the resonant circuit 31 changes. Therefore, the peak value of the measured voltage when the impedance is at its maximum during the search also changes. The notification unit 56 may determine whether or not there is an abnormality based on the difference between the new peak value of the measured voltage when the impedance is at its maximum and the peak value of the measured voltage in the past. The peak value of the measured voltage when the impedance is at its maximum corresponds to the resonant frequency. Therefore, the peak value of the measured voltage when the impedance is at its maximum indicates the resonant frequency. Thus, observing the change in the peak value of the measured voltage means observing the change in the resonant frequency. Therefore, making a determination based on the peak value of the measured voltage at the resonant frequency means making a determination based on the resonant frequency.

[0098] Furthermore, depending on the type (material) of foreign matter present around the resonant circuit 31, the resonant frequency may not change, but only the loss may change. In this case, the foreign matter lowers the impedance when the resonant frequency search voltage is applied to the resonant circuit 31, which appears as a change in the measured voltage value. The notification unit 56 may notify of an abnormality based on the peak value (or impedance) of the measured voltage when the resonant frequency search voltage is applied. For example, the notification unit 56 may determine the presence or absence of an abnormality based on the difference between the new peak value (or impedance) of the measured voltage when the specified resonant frequency search voltage is applied and the peak value (or impedance) of the measured voltage in the past. The peak value of the measured voltage corresponds to the impedance, and looking at the peak value of the measured voltage means looking at the impedance. This makes it possible to determine the presence or absence of foreign matter even if the resonant frequency does not change due to the foreign matter.

[0099] Furthermore, the normal range for the resonant frequency or the normal range for the peak value of the measured voltage may be predetermined, regardless of past measurement results. Even if there are variations in the characteristics of the components, an expected normal range can be set. The notification unit 56 may determine an abnormality in the resonant frequency based on the newly identified resonant frequency or the peak value of the measured voltage, regardless of past measurement results. In this case, the storage unit 55 does not need to store the identified resonant frequency.

[0100] According to the contactless power supply system 1 of this embodiment, the resonant frequency can be notified to the power transmission device 2 before the power receiving device 3 reaches a position where power can be supplied. Therefore, power supply can be started quickly and efficiently in environments where the relative position of the power receiving device 3 with respect to the power transmission device 2 changes. For this reason, the contactless power supply system 1 can also be used for wireless power supply while driving (DWPT), etc.

[0101] (Variation) The search voltage can be any voltage that changes periodically, such as a sine wave or a triangular wave.

[0102] The second switching circuit 40 may have a relay instead of a transistor switching element.

[0103] The second rectifier circuit 39 may be omitted. In this case, the fifth switching element 40a may also be omitted. Alternatively, the transformer 36 may be omitted, and the resistor 37 may be connected to the node between the resonant coil 32 and the resonant capacitor 33. The position of the resistor 37 and the position of the secondary coil of the transformer 36 may be swapped. In this case, it is necessary to ensure that the search voltage does not flow through the second rectifier circuit 39.

[0104] Instead of load 90, a battery may be connected to the power receiving device.

[0105] The power receiving device 3 does not necessarily have a memory unit 55. For example, before shipment, at the manufacturing plant, multiple power receiving devices 3 may notify the power transmitting device 2 of the identified resonant frequencies, and the power transmitting device 2 may store the resonant frequencies of each power receiving device 3. The power receiving device 3 may also notify the power transmitting device 2 of the identified resonant frequencies via another external device. For example, the external device may store the resonant frequencies of each of the multiple power receiving devices 3 and notify the power transmitting device 2 of the resonant frequencies of each power receiving device 3 at any time.

[0106] [Embodiment 2] Another embodiment of the present invention will be described below. For the sake of convenience of explanation, components having the same function as those described in the above embodiment will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0107] Figure 4 is a circuit diagram showing the configuration of the contactless power supply system 1a of this embodiment. The contactless power supply system 1a comprises a power transmission device 2 and a power receiving device 3a. The power receiving device 3a differs from the power receiving device 3 of Embodiment 1 in that its specific section 50a includes an operation switching circuit 47 and does not include a diode 38.

[0108] The power receiving device 3a includes a resonant circuit 31, a first rectifier circuit 34 (first switching circuit), a smoothing capacitor 35, a transformer 36, a second rectifier circuit 39, a second switching circuit 40, a specific unit 50a, a storage unit 55, a notification unit 56, a power receiving communication unit 57, and a load 90. The specific unit 50a includes a resistive element 37, a constant voltage source 43, a third switching circuit 44, an operation switching circuit 47, a power receiving control unit 51, an application unit 52, a measurement unit 53, and a determination unit 54.

[0109] The operation switching circuit 47 comprises a plurality of relays (switching elements). Here, the operation switching circuit 47 comprises a first relay 47a, a second relay 47b, a third relay 47c, and a fourth relay 47d. The first relay 47a and the second relay 47b are connected to the resonant circuit 31. The first relay 47a can short-circuit both ends of the second switching element 34b. The second relay 47b can short-circuit both ends of the fourth switching element 34d. The third relay 47c can short-circuit both ends of the sixth switching element 40b. The fourth relay 47d is positioned between the secondary coil of the transformer 36 and the resistive element 37, and can short-circuit the secondary coil of the transformer 36 and the resistive element 37. The power receiving control unit 51 controls the operation switching circuit 47.

[0110] During power supply, the power receiving control unit 51 turns off the first relay 47a, the second relay 47b, the third relay 47c, and the fourth relay 47d. The operation of the first rectifier circuit 34 and the second switching circuit 40 during power supply is the same as in Embodiment 1. Because the fourth relay 47d is in the off state, it is possible to prevent the voltage generated in the secondary coil of the transformer 36 from being applied to the third switching circuit 44 and the measuring unit 53.

[0111] During the search phase, the power receiving control unit 51 short-circuits the first relay 47a, the second relay 47b, the third relay 47c, and the fourth relay 47d. Meanwhile, the power receiving control unit 51 shuts off the first switching element 34a, the second switching element 34b, the third switching element 34c, and the fourth switching element 34d of the first rectifier circuit 34. The power receiving control unit 51 also shuts off the fifth switching element 40a and the sixth switching element 40b of the second switching circuit 40. The operation switching circuit 47 connects both ends of the resonant circuit 31 to ground and the secondary coil of the transformer 36 to ground, instead of the first rectifier circuit 34 and the second switching circuit 40. The first relay 47a and the second relay 47b of the operation switching circuit 47 function as the first switching circuit, and the third relay 47c functions as the second switching circuit. This allows the operation switching circuit 47 to change the resonant circuit 31 to a parallel resonance. The operation of the power application unit 52 to the power receiving communication unit 57 is the same as in Embodiment 1.

[0112] In the power receiving device 3a of this embodiment, the operation switching circuit 47 allows the circuit of the power receiving device 3a to be switched between power supply operation and search operation. For example, the circuit that controls the first rectifier circuit 34 in the power receiving control unit 51 is optimized for rectification operation. With the power receiving device 3a, the operation can be easily switched to search operation by the operation switching circuit 47 using a relay without affecting the circuit that controls the first rectifier circuit 34. In other words, the function of search operation can be easily added without affecting the rectification operation.

[0113] Alternatively, instead of the fourth relay 47d, a diode 38 may be provided as in Embodiment 1. In the power receiving device 3a, the second switching circuit 40 may be omitted.

[0114] [Embodiment 3] Another embodiment of the present invention will be described below. For the sake of convenience of explanation, components having the same function as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0115] Figure 5 is a circuit diagram showing the configuration of the contactless power supply system 1b of this embodiment. The contactless power supply system 1b comprises a power transmission device 2 and a power receiving device 3b. The power receiving device 3b differs from the power receiving device 3 of Embodiment 1 in that it includes an auxiliary coil 41 instead of a transformer 36.

[0116] The power receiving device 3b includes a resonant circuit 31, a first rectifier circuit 34 (first switching circuit), a smoothing capacitor 35, an auxiliary coil 41, a second rectifier circuit 39, a second switching circuit 40, a specific unit 50, a storage unit 55, a notification unit 56, a power receiving communication unit 57, and a load 90.

[0117] The auxiliary coil 41 is electromagnetically coupled to the resonant coil 32. For example, the auxiliary coil 41 and the resonant coil 32 share a core and are electromagnetically coupled with a high degree of coupling. The number of turns of the auxiliary coil 41 is less than the number of turns of the resonant coil 32. One end of the auxiliary coil 41 is connected to the resistive element 37. The other end of the auxiliary coil 41 is connected to the second AC terminal 39b of the second rectifier circuit 39.

[0118] During power supply, resonance in the resonant circuit 31 generates an AC voltage in the resonant coil 32, and an AC voltage is also generated in the auxiliary coil 41, corresponding to the degree of coupling with the resonant coil 32 and the turns ratio. Therefore, the auxiliary coil 41 functions in the same way as the transformer 36 in Embodiment 1.

[0119] During the search phase, the search voltage output from the third switching circuit 44 is applied to the auxiliary coil 41. As the magnetic flux in the auxiliary coil 41 changes, the search voltage is also applied to the electromagnetically coupled resonant coil 32. During the search phase, both ends of the resonant circuit 31 are connected to ground, as in Embodiment 1. Therefore, during the search phase, the resonant circuit 31 functions as a parallel resonant circuit. During the search phase, the auxiliary coil 41 functions in the same way as the transformer 36 in Embodiment 1.

[0120] Therefore, the power receiving device 3b of this embodiment can appropriately identify the resonant frequency of the resonant circuit 31.

[0121] [Example of implementation by software] The functions of the contactless power supply systems 1, 1a, and 1b (hereinafter referred to as "devices") can be realized by programs that cause a computer to function as the device, and these programs cause a computer to function as each control block of the device (particularly the power receiving control unit 51, the application unit 52, the measurement unit 53, the determination unit 54, the notification unit 56, and the power receiving communication unit 57).

[0122] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., memory) as hardware for executing the program. By executing the program using this control device and storage device, the functions described in each of the embodiments are realized.

[0123] The above program may be recorded on one or more computer-readable recording media, not temporary ones. These recording media may or may not be provided by the above device. In the latter case, the program may be supplied to the above device via any wired or wireless transmission medium.

[0124] Furthermore, some or all of the functions of each of the above control blocks can also be realized by analog circuits or logic circuits. For example, an integrated circuit in which logic circuits that function as each of the above control blocks are formed is also included in the scope of the present invention. In addition, it is also possible to realize the functions of each of the above control blocks by, for example, a quantum computer.

[0125] [Summary] The power receiving device for contactless power supply according to Embodiment 1 of the present invention comprises a resonant circuit, an application circuit that applies a search voltage to the resonant circuit from inside the power receiving device and changes the frequency of the search voltage, a measurement unit that measures the change in impedance of the resonant circuit in accordance with the change in frequency of the search voltage without power transmission from a power transmitting device, and a determination unit that determines the resonant frequency of the resonant circuit based on the change in impedance.

[0126] The power receiving device according to embodiment 2 of the present invention may be configured to include a storage unit that stores the specified resonant frequency in embodiment 1 described above.

[0127] The power receiving device according to embodiment 3 of the present invention may be configured to include a power receiving communication unit that transmits information indicating the resonant frequency to the power transmitting device, in embodiment 1 or 2 described above.

[0128] The power receiving device according to embodiment 4 of the present invention may be configured to include a notification unit that notifies of an abnormality in the resonant frequency based on the identified resonant frequency, in any of embodiments 1 to 3 described above.

[0129] The power receiving device according to embodiment 5 of the present invention may be configured to include a notification unit that notifies of an abnormality in the resonant frequency based on the difference between the newly identified resonant frequency and the past resonant frequency, as described in embodiment 2 above.

[0130] The power receiving device according to embodiment 6 of the present invention may be configured to include a notification unit that notifies of an abnormality based on the impedance of the resonant circuit at the resonant frequency, in any of embodiments 1 to 3 described above.

[0131] The power receiving device according to embodiment 7 of the present invention, in embodiment 1 described above, when power is supplied, the resonant circuit is in series resonance and is connected to the resonant circuit and includes a first switching circuit that changes the resonant circuit to parallel resonance by being in a short-circuit state, and the application circuit may be configured to change the frequency of the search voltage applied to the resonant circuit without power being supplied from the power transmitting device when the resonant circuit is in parallel resonance.

[0132] In the power receiving device according to embodiment 8 of the present invention, in embodiment 7 described above, the determination unit may be configured to determine that the frequency at which the impedance is maximum is the resonant frequency of the resonant circuit.

[0133] In the power receiving device according to embodiment 9 of the present invention, in embodiment 7 or 8 described above, the first switching circuit may be configured to constitute a part of a rectifier circuit that rectifies the AC power receiving voltage during power supply.

[0134] A power receiving device according to embodiment 10 of the present invention may be configured such that, in any of embodiments 1 to 9 above, it comprises a transformer having a primary coil connected to the resonant circuit and a secondary coil with fewer turns than the primary coil, and the measuring unit measures the change in impedance of the resonant circuit by measuring the voltage on the secondary side of the transformer.

[0135] The power receiving device according to embodiment 11 of the present invention includes, in embodiment 10 above, a second switching circuit connected between both ends of the secondary coil and capable of short-circuiting the two ends of the secondary coil, wherein the second switching circuit has a first switching element and a second switching element connected in series with each other, the node between the first switching element and the second switching element is connected to ground, and the application circuit may be configured to change the frequency of the search voltage applied to the resonant circuit without power being supplied from the power transmission device, with the first switching element in an off state and the second switching element in an open state.

[0136] A contactless power supply system according to embodiment 12 of the present invention may be configured to include, in any of embodiments 1 to 11 above, the power receiving device and the power transmission device equipped with a power transmission coil that supplies power to the power receiving device.

[0137] In the contactless power supply system according to embodiment 13 of the present invention, the power transmission device may be configured to include a power transmission communication unit that receives information indicating the resonant frequency from the power receiving device, and a power transmission control unit that initiates power supply to the power transmission coil at the resonant frequency when power supply is started.

[0138] A contactless power supply system according to embodiment 14 of the present invention, in any of embodiments 4 to 6 above, comprises a power receiving device and a power transmission device equipped with a power transmission coil that supplies power to the power receiving device, wherein the power transmission device may be configured not to supply power when an abnormality is notified from the power receiving device.

[0139] A method for searching for a resonant frequency according to embodiment 15 of the present invention is a method for searching for a resonant frequency in a power receiving device for contactless power supply equipped with a resonant circuit, comprising: an application step of applying a search voltage to the resonant circuit from inside the power receiving device and changing the frequency of the search voltage; a measurement step of measuring the change in impedance of the resonant circuit in accordance with the change in frequency of the search voltage without power transmission from a power transmitting device; and a determination step of determining the resonant frequency of the resonant circuit based on the change in impedance.

[0140] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0141] 1, 1a, 1b Contactless power supply system 2 Power transmission device 3, 3a, 3b Power receiving device 21 Power transmission communication unit 22 Power transmission control unit 28 Power transmission coil 31 Resonant circuit 32 Resonant coil 33 Resonant capacitor 34 First rectifier circuit (first switching circuit) 35 Smoothing capacitor 36 Transformer 39 Second rectifier circuit 40 Second switching circuit 41 Auxiliary coil 43 Constant voltage source 44 Third switching circuit 47 Operation switching circuit (first switching circuit, second switching circuit) 50, 50a Specific unit 51 Power receiving control unit 52 Application unit 53 Measurement unit 54 Judgment unit 55 Storage unit 56 Notification unit 57 Power receiving communication unit 90 Load

Claims

1. A power receiving device for contactless power supply, comprising: a resonant circuit; an application circuit that applies a search voltage to the resonant circuit from inside the power receiving device and changes the frequency of the search voltage; a measurement unit that measures the change in impedance of the resonant circuit in accordance with the change in frequency of the search voltage without power transmission from a power transmitting device; and a determination unit that determines the resonant frequency of the resonant circuit based on the change in impedance.

2. The power receiving device according to claim 1, further comprising a storage unit for storing the identified resonant frequency.

3. The power receiving device according to claim 1, further comprising a power receiving communication unit that transmits information indicating the resonant frequency to the power transmitting device.

4. The power receiving device according to claim 1, further comprising a notification unit that notifies of an abnormality in the resonant frequency based on the identified resonant frequency.

5. The power receiving device according to claim 2, further comprising a notification unit that notifies of an abnormality in the resonant frequency based on the difference between the newly identified resonant frequency and the past resonant frequency.

6. The power receiving device according to claim 1, further comprising a notification unit that notifies of an abnormality based on the impedance of the resonant circuit at the resonant frequency.

7. The power receiving device according to claim 1, wherein, during power supply, the resonant circuit is in series resonance, and is connected to the resonant circuit and includes a first switching circuit that changes the resonant circuit to parallel resonance by being in a short-circuit state, and the application circuit changes the frequency of the search voltage applied to the resonant circuit without power being supplied from the power transmitting device when the resonant circuit is in parallel resonance.

8. The power receiving device according to claim 7, wherein the determination unit determines that the frequency at which the impedance is maximum is the resonant frequency of the resonant circuit.

9. The power receiving device according to claim 7, wherein the first switching circuit constitutes part of a rectifier circuit that rectifies the AC power receiving voltage during power supply.

10. The power receiving device according to claim 1, comprising a transformer having a primary coil connected to the resonant circuit and a secondary coil with fewer turns than the primary coil, wherein the measuring unit measures the change in impedance of the resonant circuit by measuring the voltage on the secondary side of the transformer.

11. The power receiving device according to claim 10, comprising a second switching circuit connected between both ends of the secondary coil and capable of short-circuiting the two ends of the secondary coil, wherein the second switching circuit has a first switching element and a second switching element connected in series with each other, the node between the first switching element and the second switching element is connected to ground, and the application circuit changes the frequency of the search voltage applied to the resonant circuit without power being supplied from the power transmission device, with the first switching element in an off state and the second switching element in an open state.

12. A contactless power supply system comprising: a power receiving device according to any one of claims 1 to 11; and a power transmission device equipped with a power transmission coil for supplying power to the power receiving device.

13. The contactless power supply system according to claim 12, wherein the power transmission device comprises a power transmission communication unit that receives information indicating the resonant frequency from the power receiving device, and a power transmission control unit that initiates power supply to the power transmission coil at the resonant frequency when power supply is initiated.

14. A contactless power supply system comprising: a power receiving device according to claim 4 or 5; and a power transmitting device equipped with a power transmitting coil for supplying power to the power receiving device, wherein the power transmitting device does not supply power when an abnormality is notified from the power receiving device.

15. A method for searching for a resonant frequency in a power receiving device for contactless power supply equipped with a resonant circuit, comprising: an application step of applying a search voltage to the resonant circuit from inside the power receiving device and changing the frequency of the search voltage; a measurement step of measuring a change in the impedance of the resonant circuit in response to the change in the frequency of the search voltage without power transmission from a power transmitting device; and a determination step of determining the resonant frequency of the resonant circuit based on the change in impedance.

Images