Power reception device and method

Abstract

To accurately detect an object different from a power reception device.SOLUTION: A power transmission device that wirelessly transmits power to a power reception device via a power transmission antenna controls whether to configure a resonance circuit including the power transmission antenna and a resonance capacitor connected to the power transmission antenna, and detects an object different from the power reception device based on characteristics of voltage or current in the resonance circuit in at least two frequencies including a frequency corresponding to a resonance frequency of the resonance circuit.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an object detection technique in wireless power transmission. [Background technology]

[0002] Technical development of wireless power transmission systems has been widely conducted, and the standard (WPC standard) established by the standardization organization Wireless Power Consortium (WPC) as a wireless charging standard is widely known. In such wireless power transmission, when a foreign object exists within a range where a power transmitting device can transmit power, it is essential to detect the foreign object and control power transmission and reception. The foreign object is an object different from the power receiving device. Patent Document 1 describes a method of detecting a foreign object and restricting power transmission and reception when a foreign object exists near a power transmitting and receiving device conforming to the WPC standard. Patent Document 2 describes a method of a power transmitting device transmitting a signal for detecting a foreign object to a power receiving device and determining the presence or absence of a foreign object using an echo signal from the power receiving device. Patent Document 3 describes a technology for detecting a foreign object by shorting a coil of a wireless power transmission system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-070074 A [Patent Document 2] JP 2015-027172 A [Patent Document 3] JP 2017-034972 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a technique for accurately detecting an object other than a power receiving device. [Means for solving the problem]

[0005] A power transmission device according to one embodiment of the present invention comprises a power transmission means for wirelessly transmitting power to a power receiving device via a power transmission antenna, a control means for controlling whether or not to form a resonant circuit including the power transmission antenna and a resonant capacitor connected to the power transmission antenna, and a detection means for detecting an object other than the power receiving device based on characteristics of the voltage or current in the resonant circuit at at least two frequencies including a frequency corresponding to the resonant frequency of the resonant circuit. Effect of the Invention

[0006] According to the present invention, it is possible to detect an object other than a power receiving device with high accuracy. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating a configuration example of a wireless power transmission system. [Diagram 2] FIG. 2 is a diagram illustrating a configuration example of a power transmitting device. [Diagram 3] FIG. 2 illustrates an example of the configuration of a power receiving device. [Figure 4] 4 is a diagram illustrating an example of a functional configuration of a control unit of the power transmitting device. FIG. [Diagram 5] FIG. 1 is a diagram showing an example of a processing flow of power transmission according to the WPC standard. [Figure 6] 1A to 1C are diagrams illustrating the principle of foreign object detection using a waveform attenuation method. [Figure 7] 10A and 10B are diagrams for explaining a method of detecting a foreign object using radio wave transmission during power transmission. [Figure 8] FIG. 13 is a diagram for explaining a method for detecting a foreign object. [Figure 9] FIG. 13 is a diagram for explaining a method for detecting a foreign object. [Figure 10] 11 is a diagram for explaining a method of setting a foreign object detection threshold value by a power loss method. FIG. [Figure 11] FIG. 11 is a diagram illustrating an example of a flow of processing executed by a power transmitting device. [Figure 12] FIG. 11 is a diagram illustrating an example of a flow of processing executed by a power receiving device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0009] (Configuration of wireless power transmission system) FIG. 1 shows a configuration example of a wireless power transmission system according to the present embodiment. This system is, for example, a wireless charging system. This system includes a power transmitting device 101 and a power receiving device 102. Hereinafter, the power transmitting device 101 may be referred to as TX, and the power receiving device 102 may be referred to as RX. The RX is an electronic device that has a built-in battery and charges the built-in battery with power received from the TX. The TX is an electronic device that wirelessly transmits power to the RX placed on a charging stand 103 prepared as a part of the housing of the TX, for example. Since the charging stand 103 is a part of the TX, hereinafter, "placed on the charging stand 103" may be referred to as "placed on the TX (power transmitting device 101)". The range 104 indicated by the dashed line is a range in which the RX can receive power from the TX. The TX and the RX may have a function of executing applications other than wireless charging. The RX is, for example, a smartphone, and the TX is, for example, an accessory device for charging the smartphone. In addition, TX and RX may be storage devices such as a tablet, a hard disk device, or a memory device, or may be information processing devices such as a personal computer (PC). In addition, TX and RX may be image input devices such as an imaging device (camera, video camera, etc.) or a scanner, or may be image output devices such as a printer, a copier, or a projector. In addition, RX may be a vehicle such as an automobile, and TX may be a charger installed in the console of the automobile.

[0010] In this system, wireless power transmission is performed using an electromagnetic induction method for wireless charging based on the WPC standard. That is, TX and RX perform wireless power transmission for wireless charging based on the WPC standard between the power transmitting antenna of TX and the power receiving antenna of RX. In this system, the method specified by the WPC standard is used as the wireless power transmission method, but is not limited to this, and other methods may be used. For example, an electromagnetic induction method, a magnetic field resonance method, an electric field resonance method, a microwave method, a method using a laser, etc. may be used. In this embodiment, wireless power transmission is used for wireless charging, but wireless power transmission may be performed for purposes other than wireless charging.

[0011] In the WPC standard, the magnitude of power guaranteed when the power receiving device 102 receives power from the power transmitting device 101 is specified by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates a power value that is guaranteed to be output to a load (e.g., a charging circuit, a battery, etc.) of the power receiving device 102 even if the positional relationship between the power receiving device 102 and the power transmitting device 101 changes and the power transmission efficiency between the power receiving antenna and the power transmitting antenna decreases. For example, when the GP is 5 watts, the power transmitting device 101 performs control to transmit power so as to output 5 watts to the load in the power receiving device 102, even if the positional relationship between the power receiving antenna and the power transmitting antenna changes and the power transmission efficiency decreases.

[0012] Furthermore, when transmitting power from the power transmitting device 101 to the power receiving device 102, if a foreign object, which is an object other than a power receiving device, is present near the power transmitting device 101, the electromagnetic waves for transmitting power may affect the foreign object, raising the temperature of the foreign object and possibly destroying the foreign object. In order to take measures such as stopping power transmission when a foreign object is present, the WPC standard prescribes a method for the power transmitting device 101 to detect the presence of a foreign object on, for example, the charging stand 103. Specifically, the WPC standard prescribes a power loss method for detecting a foreign object based on the relationship between the transmitted power in the power transmitting device 101 and the received power in the power receiving device 102. In addition, the WPC standard prescribes a Q-factor measurement method for detecting a foreign object based on a change in the quality factor (Q-factor) of the power transmitting antenna (power transmitting coil) in the power transmitting device 101. The power transmitting device 101 may not only detect an object present on the charging stand 103 as a foreign object, but may also detect a foreign object located near the power transmitting device 101. For example, the power transmitting device 101 may detect a foreign object present within the power transmitting range 104.

[0013] Here, foreign object detection based on the power loss method defined in the WPC standard will be described with reference to Fig. 10. The horizontal axis of Fig. 10 is the transmitted power of the power transmitting device 101, and the vertical axis is the received power of the power receiving device 102. Note that a foreign object is an object other than the power receiving device 102 that may affect the power transmission from the power transmitting device 101 to the power receiving device 102, such as an object such as a metal piece having electrical conductivity.

[0014] First, the power transmitting device 101 transmits power to the power receiving device 102 at a first transmission power value Pt1, and the power receiving device 102 receives power at a first reception power value Pr1. This state may be called a light load state. The power transmitting device 101 stores the first transmission power value Pt1. Here, the first transmission power value Pt1 or the first reception power value Pr1 is a predetermined minimum transmission power or reception power. At this time, the power receiving device 102 controls the load so that the received power becomes the minimum power. For example, the power receiving device 102 may disconnect the load from the power receiving antenna so that the received power is not supplied to the load (such as a charging circuit and a battery). The power receiving device 102 reports the first reception power value Pr1 to the power transmitting device 101. When the power transmitting device 101 receives the first received power value Pr1 from the power receiving device 102, it calculates the power loss between the power transmitting device 101 and the power receiving device 102 to be Pt1-Pr1 (Ploss1), and creates a calibration point 1000 indicating the correspondence between Pt1 and Pr1.

[0015] Next, the power transmitting device 101 changes the transmission power value to the second transmission power value Pt2 and transmits power to the power receiving device 102, and the power receiving device 102 obtains the received power of the second received power value Pr2. This state may be called a connected load state. The power transmitting device 101 stores the second transmission power value Pt2. Here, the second transmission power value Pt2 or the second received power value Pr2 is a predetermined maximum transmission power or received power. At this time, the power receiving device 102 controls the load so that the received power becomes the maximum power. For example, the power receiving device 102 connects the receiving antenna and the load so that the received power is supplied to the load. The power receiving device 102 reports the second transmission power value Pr2 to the power transmitting device 101. When the power transmitting device 101 receives the second transmission power value Pr2 from the power receiving device 102, it calculates the power loss between the power transmitting device 101 and the power receiving device 102 to be Pt2-Pr2 (Ploss2), and creates a calibration point 1001 indicating the correspondence between Pt2 and Pr2.

[0016] Then, the power transmitting device 101 creates a straight line 1002 that linearly interpolates between the calibration point 1000 and the calibration point 1001. The straight line 1002 indicates the relationship between the transmitted power and the received power in a state where no foreign object is present near the power transmitting device 101 and the power receiving device 102. Based on the straight line 1002, the power transmitting device 101 can predict the power value received by the power receiving device 102 when transmitting power at a predetermined transmitted power in a state where no foreign object is present. For example, when the power transmitting device 101 transmits power at a third transmitted power value Pt3, the third received power value Pr3 received by the power receiving device 102 can be estimated from a point 1003 on the straight line 1002 that corresponds to Pt3.

[0017] As described above, it is possible to identify the power loss between the power transmitting device 101 and the power receiving device 102 according to the load, based on multiple combinations of the transmission power value of the power transmitting device 101 and the reception power value of the power receiving device 102 measured while changing the load. In addition, it is possible to estimate the power loss between the power transmitting device 101 and the power receiving device 102 according to the load, by interpolation based on multiple combinations. In this way, the calibration process performed by the power transmitting device 101 and the power receiving device 102 to obtain a combination of the transmission power value and the reception power value by the power transmitting device 101 is hereinafter referred to as "calibration process (CAL process) of the power loss method."

[0018] Assume that after the calibration, the power transmitting device 101 actually transmits power to the power receiving device 102 at Pt3, and the power transmitting device 101 receives a received power value Pr3' from the power receiving device 102. The power transmitting device 101 calculates a value Pr3-Pr3' (=Ploss_FO) by subtracting the received power value Pr3' actually received from the power receiving device 102 from the received power value Pr3 in a state where no foreign object is present. This Ploss_FO can be considered as a power loss due to power consumed by a foreign object when a foreign object is present near the power transmitting device 101 and the power receiving device 102. Therefore, the power transmitting device 101 can determine that a foreign object is present when the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold value. In addition, the power transmitting device 101 calculates the power loss Pt3-Pr3 (Ploss3) between the power transmitting device 101 and the power receiving device 102 in advance from the received power value Pr3 in a state where no foreign object is present. Then, the power transmitting device 101 calculates the power loss Pt3-Pr3' (Ploss3') between the power transmitting device 101 and the power receiving device 102 using the received power value Pr3' received from the power receiving device 102. Then, the power transmitting device 101 may estimate the power Ploss_FO that would have been consumed by the foreign object using Ploss3'-Ploss3 (=Ploss_FO).

[0019] As described above, the power Ploss_FO that would have been consumed by the foreign object may be calculated based on the received power as Pr3-Pr3', or based on the magnitude of the power loss as Ploss3'-Ploss3. Note that, although Ploss_FO is calculated by Ploss3'-Ploss3 in the following description, Ploss_FO may also be calculated by Pr3-Pr3'.

[0020] Foreign object detection using the Power Loss method is performed during power transmission (during the Power Transfer phase described below) based on data obtained in the Calibration phase described below. Foreign object detection using the Q-value measurement method is performed before power transmission (before sending a Digital Ping, during the Negotiation phase or Renegotiation phase described below).

[0021] In this embodiment, RX and TX perform communication for power transmission and reception control based on the WPC standard. In the WPC standard, multiple phases are defined, including a power transfer phase in which power transmission is performed and one or more phases before the actual power transmission, and in each phase, communication required for power transmission and reception control is performed. The phase before power transmission may include a selection phase, a ping phase, an identification and configuration phase, a negotiation phase, and a calibration phase. In the following, the identification and configuration phase is called an I&C phase. The processing of each phase will be described below.

[0022] In the Selection phase, the TX transmits Analog Pings intermittently to detect that an object has been placed on the charging base of the TX (for example, that the RX or a conductor piece has been placed on the charging base). The TX detects at least one of the voltage value and current value of the power transmitting antenna when the Analog Ping is transmitted, and if the voltage value is below a certain threshold or the current value exceeds a certain threshold, it determines that an object is present and transitions to the Ping phase.

[0023] In the Ping phase, the TX transmits a Digital Ping with a higher power than the Analog Ping. The power of the Digital Ping is sufficient to start the control unit of the RX placed on the TX. The RX notifies the TX of the magnitude of the received voltage. In this way, the TX recognizes that the object detected in the Selection phase is the RX by receiving a response from the RX that received the Digital Ping transmitted by the TX. When the TX is notified of the received voltage value, it transitions to the I&C phase. In addition, the TX measures the Q-factor of the power transmitting antenna before transmitting the Digital Ping. This measurement result is used when executing a foreign object detection process using the Q-factor measurement method.

[0024] In the I&C phase, TX identifies RX and obtains device configuration information (capability information) from RX. RX transmits an ID packet and a configuration packet. The ID packet contains the identifier information of RX, and the configuration packet contains the device configuration information (capability information) of RX. When TX receives the ID packet and the configuration packet, it responds with an acknowledgement (ACK, positive response). Then, the I&C phase ends.

[0025] In the negotiation phase, the GP value is determined based on the GP value requested by RX and the power transmission capability of TX. In addition, TX performs foreign object detection processing using the Q-factor measurement method, for example, according to a request from RX. In addition, the WPC standard specifies that after transitioning to the power transfer phase once, if there is a request from RX, processing similar to that in the negotiation phase is performed again. The phase in which this processing is performed again after transitioning to the power transfer phase is called the renegotiation phase.

[0026] In the calibration phase, calibration is performed based on the WPC standard. In addition, RX notifies TX of a predetermined received power value (received power value in a light load state / received power value in a maximum load state), and TX performs adjustments to transmit power efficiently. The received power value notified to TX can be used for foreign object detection processing using the Power Loss method.

[0027] In the power transfer phase, control is performed to start and continue power transmission, and to stop power transmission due to an error or full charge. For these power transmission and reception control, TX and RX communicate by superimposing a signal on the electromagnetic waves transmitted from the power transmitting antenna or the power receiving antenna, using the power transmitting antenna and the power receiving antenna used when performing wireless power transmission based on the WPC standard. The range in which communication based on the WPC standard between TX and RX is possible is almost the same as the power transmission range of TX.

[0028] (Configuration of power transmitting device 101 and power receiving device 102) Next, a configuration example of the power transmitting device 101 (TX) and the power receiving device 102 (RX) of this embodiment will be described. Note that the configuration described below is merely an example, and a part (in some cases, the whole) of the configuration described may be replaced with another configuration having a similar function or omitted, and further configuration may be added. Furthermore, one block shown in the following description may be divided into multiple blocks, or multiple blocks may be integrated into one block. Also, each of the functional blocks shown below may be realized by one or more processors executing software instructions, but some or all of the functions included in each functional block may be realized by hardware.

[0029] Fig. 2 shows a configuration example of a power transmitting device 101 (TX) according to this embodiment. The TX includes, for example, a control unit 201, a power supply unit 202, a power transmitting unit 203, a communication unit 204, a power transmitting antenna 205, a memory 206, resonant capacitors 207 and 212-213, and switches 208-211. Note that, in Fig. 2, the control unit 201, the power supply unit 202, the power transmitting unit 203, the communication unit 204, and the memory 206 are illustrated as separate functional blocks, but two or more or all of these functional blocks may be implemented in the same chip.

[0030] The control unit 201 executes the control program stored in the memory 206, for example, to control the entire TX. That is, the control unit 201 executes the control of each functional unit shown in FIG. 2. The control unit 201 further executes control related to power transmission control including communication for device authentication in the TX. The control unit 201 may also perform control for executing applications other than wireless power transmission. The control unit 201 includes one or more processors, such as a central processing unit (CPU) or a micro processor unit (MPU). The control unit 201 may be configured with hardware such as an application specific integrated circuit (ASIC). The control unit 201 may also be configured with an array circuit such as a field programmable gate array (FPGA) compiled to execute a predetermined process. The control unit 201 stores information to be stored in the memory 206 while executing various processes. The control unit 201 may measure time using a timer (not shown).

[0031] The power supply unit 202 supplies power to each functional block. The power supply unit 202 is, for example, a commercial power supply or a battery. The battery stores power supplied from the commercial power supply.

[0032] The power transmitting unit 203 converts the DC or AC power input from the power supply unit 202 into AC frequency power in the frequency band used for wireless power transmission, and inputs the power to the power transmitting antenna 205 to generate electromagnetic waves for receiving power at the RX. The power transmitting unit 203 converts the DC voltage supplied by the power supply unit 202 into an AC voltage using a switching circuit in a half-bridge or full-bridge configuration using a FET (Field Effect Transistor). In this case, the power transmitting unit 203 includes a gate driver that controls ON / OFF of the FET. The power transmitting unit 203 further controls the intensity of the electromagnetic waves to be output by adjusting the voltage (power transmitting voltage) or current (power transmitting current) input to the power transmitting antenna 205, or both. Increasing the power transmitting voltage or power transmitting current increases the intensity of the electromagnetic waves, and decreasing the power transmitting voltage or power transmitting current decreases the intensity of the electromagnetic waves. Moreover, the power transmitting unit 203 performs power output control so as to start or stop power transmission from the power transmitting antenna 205 based on an instruction from the control unit 201. Moreover, the power transmitting unit 203 is assumed to have a capacity to supply power sufficient to output 15 watts (W) to a charging unit of the power receiving device 102 (RX) that complies with the WPC standard.

[0033] The communication unit 204 performs communication with the RX for power transmission control based on the WPC standard as described above. The communication unit 204 modulates the electromagnetic waves output from the power transmitting antenna 205 and transmits information to the RX to perform communication. The communication unit 204 also demodulates the electromagnetic waves transmitted from the power transmitting antenna 205 and modulated by the RX to acquire information transmitted by the RX. That is, the communication performed by the communication unit 204 is performed by superimposing a signal on the electromagnetic waves transmitted from the power transmitting antenna 205. The communication unit 204 may also perform communication with the RX by communication based on a standard other than the WPC standard using an antenna other than the power transmitting antenna 205, or may perform communication with the RX by selectively using multiple communications.

[0034] The memory 206 stores a control program executed by the control unit 201. The memory 206 can also store TX and RX states (transmitted power value, received power value, etc.). For example, the TX state is acquired by the control unit 201, and the RX state is information acquired by the RX control unit 301 and received via the communication unit 204.

[0035] The switches 208 to 211 are each controlled by the control unit 201, and switch between open and short circuits to switch the configuration of the TX circuit. When the switch 208 is turned off and opened, the power transmitting antenna 205 and the resonant capacitor 207 connected to the power transmitting antenna 205 are disconnected from the power transmitting unit 203. When the switch 208 is turned on and short-circuited, the power transmitting antenna 205 and the resonant capacitor 207 are connected to the power transmitting unit 203.

[0036] The switches 209 to 211 are switches that can configure a series resonant circuit including the corresponding resonant capacitor. When the switch 209 is turned on and short-circuited, the power transmitting antenna 205 and the resonant capacitor 207 become a series resonant circuit. This series resonant circuit is configured to resonate at a specific frequency f1. At this time, a current flows through a closed circuit formed by the power transmitting antenna 205, the resonant capacitor 207, and the switch 209. The switch 210 is connected to the resonant capacitor 212, and when the switch 210 is turned on and short-circuited, it configures a series resonant circuit including the power transmitting antenna 205, the resonant capacitor 207, and the resonant capacitor 212. This series resonant circuit is configured to resonate at a specific frequency f2. At this time, a current flows through a closed circuit formed by the power transmitting antenna 205, the resonant capacitor 207, the resonant capacitor 212, and the switch 210. When the switch 211 is connected to the resonant capacitor 213 and is turned on and short-circuited, it can form a series resonant circuit including the power transmitting antenna 205, the resonant capacitor 207, and the resonant capacitor 213. This series resonant circuit is configured to resonate at a specific frequency f3. At this time, a current flows through a closed circuit formed by the power transmitting antenna 205, the resonant capacitor 207, the resonant capacitor 213, and the switch 211.

[0037] When the switch 208 is turned on and short-circuited, and the switches 209 to 211 are turned off and opened, power is supplied from the power transmitting unit 203 to the power transmitting antenna 205 and the resonant capacitor 207 .

[0038] Fig. 3 is a block diagram showing a configuration example of the power receiving device 102 (RX) according to this embodiment. The RX includes, for example, a control unit 301, a UI (user interface) unit 302, a power receiving unit 303, a communication unit 304, a power receiving antenna 305, a charging unit 306, a battery 307, a memory 308, switches 309 to 311 and 315, and resonance capacitors 312 to 314. Two or more or all of the function blocks shown separately in Fig. 3 may be implemented in the same chip. Furthermore, the multiple function blocks shown in Fig. 3 may be realized by one hardware module.

[0039] The control unit 301 executes the control program stored in the memory 308, for example, to control the entire RX. That is, the control unit 301 executes the control of each functional unit shown in FIG. 3. The control unit 301 may also perform control for executing applications other than wireless power transmission. The control unit 301 includes one or more processors, such as a CPU or an MPU. The control unit 301 may control the entire RX (when the RX is a smartphone, the entire smartphone) in cooperation with an operating system (OS) being executed. The control unit 301 may also be configured with hardware such as an ASIC. The control unit 301 may also be configured with an array circuit such as an FPGA compiled to execute a predetermined process. The control unit 301 stores information to be stored in the memory 308 while executing various processes. The control unit 301 may also measure time using a timer (not shown).

[0040] The UI unit 302 performs various outputs to the user. The various outputs include, for example, screen display, blinking or color change of an LED (Light Emitting Diode), audio output by a speaker, vibration of the RX main body, and other operations. For this reason, the UI unit 302 includes, for example, a liquid crystal panel, a speaker, a vibration motor, and the like. The UI unit 302 may have, for example, an input mechanism for receiving operations from the user.

[0041] The power receiving unit 303 acquires AC power (AC voltage and AC current) generated by electromagnetic induction based on electromagnetic waves radiated from the power transmitting antenna 205 of TX through the power receiving antenna 305. Then, the power receiving unit 303 converts the AC power into DC power or AC power of a predetermined frequency, and outputs the converted power to the charging unit 306 that performs processing for charging the battery 307. For this purpose, the power receiving unit 303 includes, for example, a rectification unit and a voltage control unit required for supplying power to a load in RX. The above-mentioned GP is the amount of power guaranteed to be output from the power receiving unit 303. It is assumed that the power receiving unit 303 has a power supply capacity sufficient to supply power for the charging unit 306 to charge the battery 307 and output 15 watts of power to the charging unit 306.

[0042] The communication unit 304 performs communication for power reception control based on the WPC standard with the communication unit 204 of the TX as described above. The communication unit 304 demodulates the electromagnetic wave input from the power receiving antenna 305 to obtain information transmitted from the TX. The communication unit 304 also transmits information to the TX by superimposing a signal related to information to be transmitted to the TX on the electromagnetic wave through load modulation of the input electromagnetic wave. The communication unit 304 may communicate with the TX by communication based on a standard other than the WPC standard using an antenna other than the power receiving antenna 305, or may selectively use multiple communications to communicate with the TX.

[0043] The memory 308 stores a control program executed by the control unit 301. The memory 308 also stores the TX and RX states. For example, the RX state is acquired by the control unit 301, and the TX state is information acquired by the TX control unit 201 and received via the communication unit 304.

[0044] The switches 309 to 311 and 315 are each controlled by the control unit 301, and switch between open and short circuits to switch the configuration of the RX circuit.

[0045] When the switch 309 is turned on and short-circuited, the power receiving antenna 305 and the resonant capacitor 312 connected to the power receiving antenna 305 form a series resonant circuit. This series resonant circuit is configured to resonate at a specific frequency f4. At this time, a current flows through the closed circuit formed by the power receiving antenna 305, the resonant capacitor 312, and the switch 309. The switch 310 is connected to the resonant capacitor 313, and when the switch 310 is turned on and short-circuited, the power receiving antenna 305, the resonant capacitor 312, and the resonant capacitor 313 form a series resonant circuit. This series resonant circuit is configured to resonate at a specific frequency f5. At this time, a current flows through the closed circuit formed by the power receiving antenna 305, the resonant capacitor 312, the resonant capacitor 313, and the switch 310. The switch 311 is connected to the resonant capacitor 314, and when the switch 311 is turned on and short-circuited, the power receiving antenna 305, the resonant capacitor 312, and the resonant capacitor 314 form a series resonant circuit. This series resonant circuit is configured to resonate at a specific frequency f6. At this time, a current flows through a closed circuit formed by the power receiving antenna 305, the resonant capacitor 312, the resonant capacitor 314, and the switch 311.

[0046] When switches 309 to 311 are turned off and opened, the power received by power receiving antenna 305 and resonant capacitor 312 is supplied to power receiving unit 303 .

[0047] The switch 315 is used to control whether or not the received power is supplied to the battery, which is a load. The switch 315 also has a function of controlling the value of the load. When the switch 315 is turned on and short-circuited, the power received by the power receiving antenna 305 is supplied to the battery 307 via the charging unit 306. When the switch 315 is turned off and opened, the power received by the power receiving antenna 305 is not supplied to the battery 307. Although the switch 315 is disposed between the resonant capacitor 312 and the power receiving unit 303 in FIG. 3, it may be disposed between the power receiving unit 303 and the charging unit 306. Furthermore, the switch 315 may be disposed between the charging unit 306 and the battery 307. Furthermore, the switch 315 is shown as one block in FIG. 3, but the switch 315 may be realized as a part of the charging unit 306 or a part of the power receiving unit 303.

[0048] Next, the function of the control unit 201 of the TX will be described with reference to FIG. 4. The control unit 201 includes, for example, a communication control unit 401, a power transmission control unit 402, a measurement unit 403, a setting unit 404, and a foreign object detection unit 405. The communication control unit 401 performs control communication with the RX based on the WPC standard via the communication unit 204. The power transmission control unit 402 controls the power transmission unit 203 and controls power transmission to the RX. The measurement unit 403 measures a waveform attenuation index, which will be described later. In addition, the measurement unit 403 measures the power transmitted to the RX via the power transmission unit 203 and measures the average transmission power per unit time. In addition, the measurement unit 403 measures the Q value of the power transmission antenna 205. The setting unit 404 sets a threshold value used for foreign object detection, for example, by a calculation process, based on the waveform attenuation index measured by the measurement unit 403. The foreign object detection unit 405 has a foreign object detection function using a power loss method, a foreign object detection function using a Q value measurement method, and a foreign object detection process using a waveform attenuation method. The foreign object detection unit 405 may also have a function of performing foreign object detection processing using other methods. For example, the foreign object detection unit 405 in the TX having an NFC (Near Field Communication) communication function may perform foreign object detection processing using a detection function of a partner device according to the NFC standard. The foreign object detection unit 405 can also detect a change in the state on the TX as a function other than detecting a foreign object. For example, the TX can detect an increase or decrease in the number of power receiving devices 102 on the TX.

[0049] The setting unit 404 sets a threshold value that is a reference for determining the presence or absence of a foreign object when the TX detects a foreign object using the power loss method, the Q value measurement method, or the waveform attenuation method. The setting unit 404 may also have a function of setting a threshold value that is a reference for determining the presence or absence of a foreign object, which is necessary when performing foreign object detection processing using other methods. The foreign object detection unit 405 can perform foreign object detection processing based on the threshold value set by the setting unit 404 and the waveform attenuation index, transmission power, and Q value measured by the measurement unit 403.

[0050] The functions of the communication control unit 401, the power transmission control unit 402, the measurement unit 403, the setting unit 404, and the foreign object detection unit 405 are realized as programs that run in the control unit 201. Each functional unit may be configured by an independent program. Each functional unit may operate in parallel while establishing synchronization between the programs by event processing or the like. However, two or more of these processing units may be realized by one program.

[0051] (Process flow for power transmission according to WPC standards) As described above, the WPC standard specifies a Selection phase, a Ping phase, an I&C phase, a Negotiation phase, a Calibration phase, and a Power Transfer phase. The operations of the power transmitting device 101 and the power receiving device 102 in these phases will be described below with reference to FIG.

[0052] The TX repeatedly and intermittently transmits Analog Ping of the WPC standard in order to detect an object present within the power transmission range (F501). Then, the TX executes processes defined as the Selection phase and Ping phase of the WPC standard, and waits for the RX to be placed. The user of the RX brings the RX (e.g., a smartphone) close to the TX for charging (F502). For example, the user places the RX on the TX, thereby bringing the RX close to the TX. When the TX detects that an object exists within the power transmission range (F503, F504), it transmits Digital Ping of the WPC standard (F505). When the RX receives the Digital Ping, it can grasp that the TX has detected the RX (F506). Furthermore, when there is a predetermined response to the Digital Ping, the TX can determine that the detected object is the RX and that the RX has been placed on the charging stand 103.

[0053] When the TX detects that the RX is placed, the TX acquires the identification information and capability information from the RX through communication in the I&C phase defined by the WPC standard (F507). Here, the identification information of the RX includes a Manufacturer Code and a Basic Device ID. The capability information of the RX includes an information element capable of identifying the version of the WPC standard supported, a Maximum Power Value that is a value that identifies the maximum power that the RX can supply to a load, and information indicating whether the RX has a negotiation function of the WPC standard. The TX may acquire the identification information and capability information of the RX through a method other than communication in the I&C phase of the WPC standard. The identification information may be any other identification information capable of identifying an individual RX, such as a Wireless Power ID. The capability information may include information other than the above-mentioned information.

[0054] Next, the TX determines the value of GP with the RX through communication in the negotiation phase defined by the WPC standard (F508). Note that in F508, other procedures for determining GP may be executed, not limited to communication in the negotiation phase of the WPC standard. In addition, when the TX acquires information indicating that the RX does not support the negotiation phase (for example, in F507), the TX may not perform communication in the negotiation phase and may set the GP value to a small value (for example, predefined in the WPC standard). In this embodiment, it is assumed that the GP is determined to be 5 watts in F508.

[0055] After determining the GP, the TX executes calibration based on the GP. In the calibration process, first, the RX transmits information (hereinafter, this information is called "first reference received power information") including the received power in a light load state (load disconnected state, load state in which the transmitted power is equal to or less than the first threshold) to the TX (F509). In this embodiment, the first reference received power information is the received power information of the RX when the transmitted power of the TX is 250 milliwatts. The first reference received power information is notified using a Received Power Packet (mode 1) defined in the WPC standard, but other messages may be used for notification. The TX judges whether or not to accept the first reference received power information based on the power transmission state of its own device. If the TX accepts, the TX transmits an acknowledgement (ACK) to the RX, and if not, the TX transmits a negative acknowledgement (NAK).

[0056] When RX receives an ACK from TX (F510), it performs processing for transmitting information including the received power in a load connection state (maximum load state, a load state in which the transmitted power is equal to or greater than the second threshold) to TX (hereinafter, this information is referred to as "second reference received power information"). In this embodiment, since GP is 5 watts, the second reference received power information is, for example, the received power information of RX when the transmitted power of TX is 5 watts. Here, the second reference received power information is notified using a Received Power Packet (mode 2) defined in the WPC standard, but this notification may be performed using another message. In order to increase the transmitted power from TX to 5 watts, RX transmits a transmitted power output change instruction including a value (positive value) corresponding to the transmitted power increase (F511). When TX receives this transmitted power output change instruction, if it is possible to increase the transmitted power, it responds to RX with an ACK and increases the transmitted power (F512, F513). The second reference received power information is received power information when the transmission power of TX is 5 watts. Therefore, when TX receives a power increase request exceeding 5 watts from RX, TX responds with NAK to the transmission output change instruction to notify RX that the transmission output cannot be changed (F514). This makes it possible to prevent power above the specified level from being transmitted. By receiving a NAK from TX, RX determines that the default transmission power has been reached, and transmits to TX second reference received power information regarding the received power in the load connected state (F516). TX can calculate the amount of power loss between TX-RX in the load disconnected state and the load connected state based on the received power values ​​indicated by the first reference received power information and the second reference received power information, and the transmission power values ​​of TX when those received power values ​​are obtained, respectively. Furthermore, the TX can estimate the power loss value between TX and RX for all possible transmission powers of the TX (here, from 250 milliwatts to 5 watts) by interpolation based on the relationship between the amounts of power loss (F517). The TX transmits an ACK in response to the second reference received power information from the RX (F518) and completes the calibration process. Then, when the TX determines that the charging process of the RX can be started, it starts the power transmission process to the RX, and charging of the RX starts.

[0057] Before the start of the power transmission process, the TX and RX perform device authentication process (F519), and when it is determined that they can support a larger GP, the GP may be reset to a larger value such as 15 watts (F520). In this case, the RX and TX increase the power transmission output of the TX using a power transmission output change instruction, ACK, and NAK to increase the power transmission output of the TX to 15 watts (F521 to F524). Then, the TX and RX perform calibration process again in response to the fact that the GP has become 15 watts. That is, the RX transmits information including the received power in the load connection state of the RX when the power transmission power of the TX is 15 watts (hereinafter, this information is referred to as "third reference received power information") (F525). The TX performs calibration based on the received power indicated by the first reference received power information, the second reference received power information, and the third reference received power information, and the transmitted power when each received power was obtained. This enables the TX to estimate the amount of power loss between TX and RX for all possible transmission powers of the TX (here, 250 milliwatts to 15 watts) (F526). Then, the TX transmits an ACK in response to the third reference received power information from the RX (F527) and completes the calibration process. After that, the TX starts the power transmission process to the RX when it determines that the charging process of the RX can be started, and the charging of the RX starts (F528).

[0058] In the power transfer phase, the TX transmits power to the RX. In addition, in the power transfer phase, foreign object detection is performed by the above-mentioned power loss method. Here, foreign object detection by the power loss method can maintain high power transmission efficiency because foreign object detection can be performed while continuing power transmission, but when the power transmitting device 102 transmits large power, the accuracy of foreign object detection may decrease. For this reason, foreign object detection only by the power loss method may have the possibility of erroneous detection of a foreign object or erroneous determination that a foreign object is not present even though a foreign object is present. In particular, the power transfer phase is a phase in which the TX transmits power, and if a foreign object is present near the TX and RX during power transmission, the heat generation from the foreign object increases, so it is required to improve the accuracy of foreign object detection in this phase. Therefore, in this embodiment, in order to improve the accuracy of foreign object detection, the following waveform attenuation method is used as a foreign object detection method different from the power loss method to perform further foreign object detection.

[0059] (Foreign object detection method using waveform attenuation method) In the power transfer phase, the power transmitting device 101 transmits power to the power receiving device 102. If foreign object detection can be performed using a power transmission waveform (voltage waveform or current waveform) related to this power transmission, it becomes possible to detect a foreign object without defining and using a new signal for foreign object detection or the like. As such a method, in this embodiment, a method of detecting a foreign object based on the attenuation state of a transmitted wave (this method is called the "waveform attenuation method") is used. The principle of foreign object detection using this waveform attenuation method will be described with reference to FIG. 6. Here, foreign object detection using a power transmission waveform related to power transmission from the power transmitting device 101 (TX) to the power receiving device 102 (RX) will be described as an example.

[0060] In FIG. 6, the waveform shows the change over time of the voltage value 600 (hereinafter simply referred to as the voltage value) of the high frequency voltage applied to the power transmitting antenna 205 of the TX. The horizontal axis of FIG. 6 represents time, and the vertical axis represents the voltage value. The TX stops transmitting power at time T0 from a state in which the TX is transmitting power to the RX via the power transmitting antenna 205. That is, at time T0, the power supply for power transmission from the power supply unit 202 is stopped. The frequency of the transmission wave related to the power transmission from the TX is a predetermined frequency, for example, a fixed frequency between 85 kHz and 205 kHz used in the WPC standard. Point 601 is a point on the envelope of the high frequency voltage, and is the voltage value at time T1. (T1, A1) in the figure indicates that the voltage value at time T1 is A1. Similarly, point 602 is a point on the envelope of the high frequency voltage, and is the voltage value at time T2. (T2, A2) in the figure indicates that the voltage value at time T2 is A2. The quality factor (Q value) of the power transmitting antenna 205 can be determined based on the time change in the voltage value after time T0. For example, the Q value is calculated by Equation 1 based on the time, the voltage value, and the frequency f of the high-frequency voltage at points 601 and 602 on the envelope of the voltage value. Q = πf(T2-T1) / ln(A1 / A2) (Equation 1) This Q value decreases when a foreign object is present near TX and RX. This is because a foreign object causes energy loss when the foreign object is present. Therefore, when focusing on the slope of the attenuation of the voltage value, the slope of the line connecting points 601 and 602 becomes steeper and the attenuation rate of the waveform amplitude becomes higher when a foreign object is present than when no foreign object is present, because energy loss occurs due to the foreign object. That is, the waveform attenuation method judges the presence or absence of a foreign object based on the attenuation state of the voltage value between points 601 and 602. In the waveform attenuation method, the presence or absence of an actual foreign object can be judged by comparing any numerical value corresponding to this attenuation state. For example, the judgment can be made using the above-mentioned Q value. In this case, a lower Q value means a higher waveform attenuation rate (degree of reduction in the waveform amplitude per unit time). In addition, the judgment can be made using the slope of the line connecting points 601 and 602, calculated by (A1-A2) / (T2-T1). Furthermore, when the time (T1 and T2) for observing the attenuation state of the voltage values ​​is fixed, the judgment may be made using a value (A1-A2) representing the difference in the voltage values ​​or a value (A1 / A2) representing the ratio of the voltage values. Furthermore, when the voltage value A1 immediately after the power transmission is stopped is constant, the judgment may be made using the value of the voltage value A2 after a predetermined time has elapsed. Furthermore, the judgment may be made using the value of the time (T2-T1) until the voltage value A1 reaches the predetermined voltage value A2.

[0061] As described above, the presence or absence of a foreign object can be determined by the attenuation state of the voltage value during the power transmission stop period, and there are multiple values ​​that represent the attenuation state. In this embodiment, the values ​​that represent these attenuation states are called "waveform attenuation indexes." For example, as described above, the Q value calculated by Equation 1 is a value that represents the attenuation state of the voltage value related to power transmission and is included in the "waveform attenuation index." All waveform attenuation indexes are values ​​that correspond to the waveform attenuation rate. Note that in the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation index." The following description will focus on the case where the waveform attenuation rate is used as the waveform attenuation index, but the contents of this embodiment can be applied to the case where other waveform attenuation indexes are used.

[0062] In addition, even if the vertical axis of FIG. 6 is the current value flowing through the power transmitting antenna 205, the attenuation state of the current value during the power transmission stop period changes depending on the presence or absence of a foreign object, as in the case of the voltage value. When a foreign object is present, the waveform attenuation rate is higher than when a foreign object is not present. For this reason, a foreign object can also be detected by applying the above-mentioned method to the time change of the current value flowing through the power transmitting antenna 205. That is, the presence or absence of a foreign object can be determined and a foreign object can be detected by using the Q value obtained from the current waveform, the slope of the attenuation of the current value, the difference in the current value, the ratio of the current value, the absolute value of the current value, and the time until a predetermined current value is reached as the waveform attenuation index. In addition, foreign object detection may be performed based on both the attenuation state of the voltage value and the attenuation state of the current value, such as determining the presence or absence of a foreign object using an evaluation value calculated from the waveform attenuation index of the voltage value and the waveform attenuation index of the current value. In the above example, the waveform attenuation index is measured during the period when the TX temporarily stops power transmission, but the waveform attenuation index may be measured during the period when the TX temporarily reduces the power supplied from the power supply unit 202 from a predetermined power level to a power level lower than that.

[0063] A method of detecting a foreign object based on a transmission waveform during power transmission by the waveform attenuation method will be described with reference to FIG. 7. FIG. 7 shows a transmission waveform when detecting a foreign object by the waveform attenuation method, with the horizontal axis representing time and the vertical axis representing the voltage value of the power transmission antenna 205. As in FIG. 6, the vertical axis may represent the current value of the current flowing through the power transmission antenna 205. It is assumed that the transmission waveform is not stable during the transient response period immediately after the TX starts transmitting power. For this reason, during this transient response period, the RX controls the TX not to communicate (communication by load modulation). Also, the TX controls the RX not to communicate (communication by frequency shift keying). When it is time to detect a foreign object, the TX suspends power transmission. Since the amplitude of the transmission wave attenuates due to the stop of this power transmission, the TX calculates the waveform attenuation rate of this attenuated waveform. Then, the TX determines that a foreign object is present when the calculated waveform attenuation rate exceeds a predetermined threshold value. If no foreign object is detected during a predetermined foreign object detection period, the TX resumes power transmission after the period. After resuming power transmission, the TX repeatedly executes the above-mentioned waiting for the transient response period, identifying the timing of foreign object detection, stopping power transmission, and foreign object detection processing. In this way, in the power transfer phase, foreign object detection can be performed using the waveform attenuation method in addition to the power loss method.

[0064] (Treatment of power transmission equipment when applying the waveform attenuation method to the WPC standard) Next, a process executed by the power transmitting device 101 when detecting a foreign object by applying this waveform attenuation method to the WPC standard will be described. When detecting a foreign object using the waveform attenuation method, the power transmitting device 101 measures in advance the waveform attenuation rate when no foreign object is present, and calculates a threshold value based on the measured waveform attenuation rate. After that, the power transmitting device 101 executes foreign object detection using the waveform attenuation method, and if the measured waveform attenuation rate is greater than the threshold value, it determines that "a foreign object is present" or "there is a possibility that a foreign object is present." On the other hand, if the measured waveform attenuation rate is less than the threshold value, the power transmitting device 101 determines that "no foreign object is present" or "there is a high possibility that a foreign object is not present."

[0065] In the waveform attenuation method, the power transmitting device 101 temporarily stops power transmission and observes the attenuation rate of the transmitted radio wave to detect a foreign object, which may result in a decrease in power transmission efficiency due to the temporary suspension of power transmission. On the other hand, the waveform attenuation method is capable of detecting a foreign object with high accuracy even when a large amount of power is being transmitted. In other words, even in a situation where it is difficult to detect a foreign object with high accuracy using the power loss method, the waveform attenuation method can be used to detect a foreign object with high accuracy.

[0066] In the above example, when foreign object detection is performed using the waveform attenuation method, the waveform attenuation rate in a state where no foreign object exists is measured before the start of power transmission, and the threshold value is calculated based on the measured waveform attenuation rate. For this reason, foreign object detection may be performed using a threshold value calculated from the waveform attenuation rate measured at a timing when it is estimated that no foreign object exists after the start of power transmission. For example, the TX confirms that no foreign object exists using the power loss method during power transmission, performs a first waveform attenuation rate measurement, and calculates a threshold value based on the measured waveform attenuation rate. Since this first waveform attenuation rate measurement is performed immediately after it has been confirmed in advance that no foreign object exists using the power loss method, the measured waveform attenuation rate can be considered to be the waveform attenuation rate in a state where no foreign object exists. Next, the TX resumes power transmission, and performs a second waveform attenuation rate measurement at a timing when it is determined that foreign object detection should be performed. Then, the presence or absence of a foreign object can be determined by comparing the measurement result of the second waveform attenuation rate measurement with the measurement result of the first waveform attenuation rate measurement or a threshold value calculated based on the first waveform attenuation rate measurement. That is, when foreign object detection is performed using the waveform attenuation method, the waveform attenuation rate measured at that point in time may be compared with the waveform attenuation rate measured previously in the absence of a foreign object and with a corresponding threshold value.

[0067] In the above example, the frequency of the transmission wave for power transmission from the power transmitting device 101 is a fixed frequency. However, the above-mentioned processing for foreign object detection may be executed at each of a plurality of frequencies, and the presence or absence of a foreign object may be determined by combining the results. By detecting a foreign object using not only the waveform attenuation rate at one frequency, but also the waveform attenuation rate at a plurality of frequencies, it becomes possible to perform foreign object detection with higher accuracy. This will be described later.

[0068] In this embodiment, immediately after the power transmitting device 101 stops transmitting power or immediately after it starts transmitting power, the transmitting power waveform becomes unstable due to a transient response, so a waiting time is provided before moving to each operation. In this way, instability in the transmitting wave waveform is caused by a sudden start or stop of power transmission. For this reason, in order to alleviate such instability in the transmitting wave waveform, the power transmitting device 101 may perform control so as to gradually increase the transmitting power when starting power transmission and to gradually decrease the transmitting power when stopping power transmission. Note that the power transmitting device 101 may perform only one of increasing and decreasing the transmitting power in a stepwise manner, or may perform both in a stepwise manner.

[0069] (Foreign object detection method using waveform attenuation method with multiple frequencies) A foreign object that gets between the power transmitting device 101 and the power receiving device 102 may generate heat during power transmission, and therefore the power transmitting device 101 must detect the foreign object early when the foreign object gets in and control the power transmission, such as stopping the power transmission or reducing the power transmission. The foreign object that gets in between the power transmitting device 101 and the power receiving device 102 may have various sizes and shapes. In the waveform attenuation method described in FIG. 6 and FIG. 7, the power transmitting device 101 transmits power at a predetermined frequency, temporarily stops the power transmission, and detects the foreign object from the waveform attenuation rate of the transmitted wave. However, the energy consumed by the foreign object may differ depending on the frequency. That is, when the foreign object A exists, the waveform attenuation rate of the waveform of frequency X is large but the waveform attenuation rate of the waveform of frequency Y is small, and when the foreign object B exists, the waveform attenuation rate of the waveform of frequency X is small but the waveform attenuation rate of the waveform of frequency Y is large. This is because the frequency characteristics of the energy consumed by the foreign object differ depending on the size and shape of the foreign object. In the above example, if frequency Y is used for the waveform, the waveform attenuation rate is small even if foreign object A exists, and it may be erroneously determined that "no foreign object exists" even though foreign object A exists. In order to prevent such erroneous determination, it is effective to perform foreign object detection using the waveform attenuation rate of the waveform of frequency X as well as the waveform attenuation rate of the waveform of frequency Y for foreign object A. That is, by measuring the attenuation rates of the waveforms of multiple frequencies and performing foreign object detection, the probability of erroneous determination can be reduced. In the following, the process performed by the power transmitting device 101 and the process performed by the power receiving device 102 when performing such foreign object detection will be described with reference to FIG. 11 and FIG. 12. FIG. 11 shows an example of the flow of the process performed by the power transmitting device 101, and FIG. 12 shows an example of the flow of the process performed by the power receiving device 102.

[0070] While transmitting power to the power receiving device 102, the power transmitting device 101 notifies the power receiving device 102 by using a predetermined packet through communication that the power receiving device 102 should perform foreign object detection using a waveform attenuation method (S1101, S1102). When the power receiving device 102 receives the packet, the power transmitting device 101 transmits a command requesting the power transmitting device 101 to perform foreign object detection. This command may include time information for notifying the power transmitting device 101 of the time (timing) at which foreign object detection should be performed. The time at which foreign object detection should be performed may be notified to the power receiving device 102 from the power transmitting device 101 by the above-mentioned packet. In this manner, the power transmitting device 101 and the power receiving device 102 share information on the timing at which foreign object detection should be performed (S1102, S1202). The power transmitting device 101 stops power transmission at the time at which foreign object detection should be performed (S1103). Then, the power transmitting device 101 turns on the switch 209 to short-circuit and forms a closed loop circuit formed by the power transmitting antenna 205, the resonant capacitor 207, and the switch 209, which resonates at a frequency f1 (S1104). Note that the power transmitting device 101 may stop power transmission after turning on the switch 209 to short-circuit. Also, the power transmitting device 101 may stop power transmission at the same time as turning on the switch 209 to short-circuit. Meanwhile, the power receiving device 102 turns on the switch 309 to short-circuit and forms a closed loop circuit formed by the power receiving antenna 305, the resonant capacitor 312, and the switch 309, which resonates at a frequency f2, during the time when foreign object detection is performed (S1203). As a result, an attenuated waveform of frequency f1 is observed at the power transmitting antenna 205 and resonant capacitor 207 of the power transmitting device 101 (S1105), and an attenuated waveform of frequency f2 is observed at the power receiving antenna 305 and resonant capacitor 312 of the power receiving device 102 (S1204).

[0071] Here, the power transmitting antenna 205 and the power receiving antenna 305 are electromagnetically coupled to each other so that wireless power transmission and wireless communication are performed by them. Therefore, an attenuated waveform of frequency f2 can be observed in a circuit formed by the power transmitting antenna 205 and the resonant capacitor 207 present in the power transmitting device 101 (S1106). Also, an attenuated waveform of frequency f1 can be observed in a circuit formed by the power receiving antenna 305 and the resonant capacitor 312 present in the power receiving device 102 (S1205). Here, the attenuated waveform observed in the circuit formed by the power transmitting antenna 205 and the resonant capacitor 207 of the power transmitting device 101, or the attenuated waveform observed in the circuit formed by the power receiving antenna 305 and the resonant capacitor 312 of the power receiving device 102 is shown in FIG. 8 as a schematic diagram. When the power transmitting device 101 stops power transmission and turns on the switch 209 to short-circuit, and the power receiving device 102 turns on the switch 309 to short-circuit, a mixed waveform of the frequencies f1 and f2 can be observed during the foreign object detection period as shown in Fig. 8. Then, the power transmitting device 101 and the power receiving device 102 can detect the presence or absence of a foreign object from this waveform attenuation index, as described with reference to Figs. 6 and 7 (S1107, S1206). By performing the above-mentioned operation, the power transmitting device 101 and the power receiving device 102 can observe the waveform attenuation of a mixed wave of two frequencies, not one frequency. Then, the power transmitting device 101 and the power receiving device 102 can improve the accuracy of foreign object detection by observing the waveform attenuation index of this mixed wave.

[0072] A method for detecting a foreign object from a mixed wave of two frequencies will be described. As shown in FIG. 8, a waveform in which two frequencies are mixed is observed during a foreign object detection period. By observing the time waveform of the attenuation waveform of the mixed wave, the attenuation rates of the waveforms of f1 and f2 can be identified. For example, as shown in FIG. 8, the attenuation state of the waveform of frequency f1 and the attenuation state of the waveform of frequency f2 can be identified. The method for identifying the waveform attenuation index from the attenuation waveforms of frequencies f1 and f2 is as described above with reference to FIG. 6 and FIG. 7.

[0073] The power transmitting device 101 or the power receiving device 102 calculates in advance waveform attenuation indexes for frequencies f1 and f2 in a state where no foreign object is present. Then, the power transmitting device 101 or the power receiving device 102 calculates a threshold value for frequency f1 based on the waveform attenuation index for frequency f1 in a state where no foreign object is present, and calculates a threshold value for frequency f2 based on the waveform attenuation index for frequency f2 in a state where no foreign object is present. The power transmitting device 101 or the power receiving device 102 compares the waveform attenuation index identified from the observed attenuation waveform of frequency f1 with the threshold value calculated for frequency f1. Also, the power transmitting device 101 or the power receiving device 102 compares the waveform attenuation index identified from the observed attenuation waveform of frequency f2 with the threshold value calculated for frequency f2. Then, the power transmitting device 101 or the power receiving device 102 determines that "a foreign object exists" or "there is a high possibility that a foreign object exists" when the waveform attenuation index for frequency f1 exceeds a threshold and the waveform attenuation index for frequency f2 exceeds a threshold. The power transmitting device 101 or the power receiving device 102 may also determine that "a foreign object exists" or "there is a high possibility that a foreign object exists" when the waveform attenuation index for frequency f1 exceeds a threshold or when the waveform attenuation index for frequency f2 exceeds a threshold. In other words, the power transmitting device 101 or the power receiving device 102 may determine that "a foreign object exists" or "there is a high possibility that a foreign object exists" when the waveform attenuation index for either frequency f1 or f2 exceeds a threshold. This makes it possible to more reliably detect a foreign object.

[0074] As described above, the mixed wave of the frequency f1 and the frequency f2 can be observed by both the power transmitting device 101 and the power receiving device 102. Therefore, the above-mentioned "method of detecting a foreign object from a mixed wave of two frequencies" can be performed by both the power transmitting device 101 and the power receiving device 102. In addition, in the above-mentioned embodiment, an example in which the threshold value of the frequency f1 and the threshold value of the frequency f2 are set separately from each other has been described. However, this is not limited to this, and the same value may be set as these threshold values. In addition, when the switch 209 is turned ON, the power transmitting device 101 may turn the switch 208 OFF to disconnect the power transmitting antenna 205 and the resonant capacitor 207 from the power transmitting unit 203. This makes it possible to eliminate the influence of the power transmitting unit when detecting a foreign object by the waveform attenuation method, and to detect a foreign object with higher accuracy. Furthermore, when the switch 309 is turned ON, the power receiving device 102 may turn the switch 315 OFF to disconnect the power receiving antenna 305 and the resonant capacitor 312 from the power receiving unit 303. This makes it possible to eliminate the influence of the power transmitting unit when detecting a foreign object using the waveform attenuation method, and thus makes it possible to detect a foreign object with higher accuracy.

[0075] By having at least one of the power transmitting device 101 and the power receiving device 102 operate as described above and performing foreign object detection based on the voltage or current characteristics at multiple frequencies (here, the waveform attenuation index of the attenuated waveform), it becomes possible to detect foreign objects with higher accuracy.

[0076] (Modification 1 of the foreign object detection method using the waveform attenuation method with multiple frequencies) In the above example, a method for detecting a foreign object based on a time waveform (attenuation waveform) of frequency f1 and a time waveform (attenuation waveform) of frequency f2 has been described. In this modification, a foreign object is detected from the signal spectrum of frequencies f1 and f2, rather than the time waveforms of frequencies f1 and f2. That is, when foreign object detection is performed based on the time waveform, if noise is mixed in and the time waveform is disturbed, it may not be easy to identify the waveform attenuation index. In contrast, in this modification, arithmetic processing is performed on the time waveform to identify the signal spectrum (signal intensity, frequency spectrum) for each frequency, and a foreign object is detected based on the signal spectrum, making it possible to perform foreign object detection that is robust against disturbances in the time waveform.

[0077] In this modification, for example, the power transmitting device 101 or the power receiving device 102 performs arithmetic processing on the waveform of the analysis target section as shown in Fig. 8 to convert at least the components of frequencies f1 and f2 in the frequency domain into an identifiable format. The power transmitting device 101 or the power receiving device 102 can identify the signal spectrum (signal strength, frequency spectrum) for each frequency of the analysis target section, for example, by performing a Fourier transform on the waveform of the analysis target section. The signal spectrum (signal strength, frequency spectrum) for each frequency of the analysis target section is identified, for example, as shown in Fig. 9. If a foreign object is present between the power transmitting device 101 and the power receiving device 102, energy is consumed in the foreign object, and the intensity of the signal spectrum as shown in Fig. 9 is also weakened.

[0078] Therefore, the power transmitting device 101 or the power receiving device 102 performs foreign object detection by utilizing this characteristic. For example, the power transmitting device 101 or the power receiving device 102 specifies the signal spectrum of each of the frequencies f1 and f2 in a state where no foreign object is present. Then, the power transmitting device 101 or the power receiving device 102 calculates a threshold value for the frequency f1 based on the signal spectrum of the frequency f1 in a state where no foreign object is present. Also, the power transmitting device 101 or the power receiving device 102 calculates a threshold value for the frequency f2 based on the signal spectrum of the frequency f2 in a state where no foreign object is present. Then, the power transmitting device 101 or the power receiving device 102 compares the signal spectrum specified from the observed attenuation waveform of the frequency f1 with the threshold value for the frequency f1. Also, the power transmitting device 101 or the power receiving device 102 compares the signal spectrum specified from the observed attenuation waveform of the frequency f2 with the threshold value for the frequency f2. Then, when the signal spectrum of frequency f1 exceeds the threshold and the signal spectrum of frequency f2 exceeds the threshold, the power transmitting device 101 or the power receiving device 102 determines that "a foreign object exists" or "it is highly likely that a foreign object exists." Furthermore, when the signal spectrum of frequency f1 exceeds the threshold or when the signal spectrum of frequency f2 exceeds the threshold, the power transmitting device 101 or the power receiving device 102 determines that "a foreign object exists" or "it is highly likely that a foreign object exists." In other words, the power transmitting device 101 or the power receiving device 102 determines that "a foreign object exists" or "it is highly likely that a foreign object exists" when at least one of the signal spectra of frequency f1 and frequency f2 exceeds the threshold.

[0079] This makes it possible to perform foreign object detection more reliably. As described above, the mixed wave of frequency f1 and frequency f2 can be observed in both the power transmitting device 101 and the power receiving device 102. Therefore, the foreign object detection method according to this modification can also be performed in both the power transmitting device 101 and the power receiving device 102. Also, in this modification, the threshold value of frequency f1 and the threshold value of frequency f2 may be set separately or may be set to the same value.

[0080] In this way, at least one of the power transmitting device 101 and the power receiving device 102 operates as described above to perform foreign object detection based on signal spectra of a plurality of frequencies, thereby making it possible to detect a foreign object with higher accuracy.

[0081] (Modification 2 of the foreign object detection method using the waveform attenuation method with multiple frequencies) In the above configuration, a method for detecting a foreign object based on the time waveform of a mixed wave of frequencies f1 and f2 or the signal spectrum of the time waveform at frequencies f1 and f2 has been described. In this case, in the above configuration, if the frequencies f1 and f2 are very close to each other, the correlation between the energy consumption of the foreign object at these frequencies is high, and the advantage of detecting a foreign object using multiple frequencies is reduced. In addition, if the difference between the frequencies f1 and f2 is small, a "beat" occurs in the composite wave, making it difficult to detect a foreign object as described above. For this reason, in this modified example, foreign objects are detected by using a frequency different from the frequencies f1 and f2 instead of these frequencies, or by using an additional frequency in addition to the frequencies f1 and f2.

[0082] For example, a frequency f1 determined by the power transmitting antenna 205 and the resonant capacitor 207 of the power transmitting device 101, and a frequency f2 determined by the power receiving antenna 305 and the resonant capacitor 312 of the power receiving device 102 are specified to be included within a predetermined frequency range. Here, the predetermined frequency ranges are specified such that the frequency f1 and the frequency f2 are separated from each other by a predetermined frequency width. Then, the inductance and capacitance values ​​of the power transmitting antenna 205 and the resonant capacitor 207 of the power transmitting device 101 and the power receiving antenna 305 and the resonant capacitor 312 of the power receiving device 102 are determined so that the frequencies f1 and f2 are included in the respective frequency ranges. This makes it possible to separate the frequency f1 and the frequency f2 by a predetermined frequency width, enabling more accurate foreign object detection.

[0083] 2 and 3, the power transmitting device 101 or the power receiving device 102 may have a plurality of resonant capacitors, and may switch between them to set the resonant frequency in the power transmitting device 101 and the resonant frequency in the power receiving device 102 to be separated by a predetermined frequency width in advance. The power transmitting device 101 and the power receiving device 102 communicate with each other to determine a first resonant frequency in the power transmitting device 101 and a second resonant frequency in the power receiving device 102. At this time, the first resonant frequency and the second resonant frequency are set to be separated by a predetermined frequency width. In order to realize the first resonant frequency determined between the power transmitting device 101 and the power receiving device 102, the power transmitting device 101 controls, for example, the switch 210 connected to the resonant capacitor 212 and the switch 211 connected to the resonant capacitor 213. The power transmitting device 101 executes control to turn on at least one of the switches 209 to 211 so as to obtain a circuit configuration that can obtain the determined first resonant frequency. Further, in order to realize the second resonant frequency determined between the power transmitting device 101 and the power receiving device 102, the power receiving device 102 controls, for example, the switch 310 connected to the resonant capacitor 313 and the switch 311 connected to the resonant capacitor 314. The power receiving device 102 executes control to turn on at least one of the switches 309 to 311 so as to obtain a circuit configuration that can obtain the determined second resonant frequency. In this way, the power transmitting device 101 and the power receiving device 102 have a plurality of resonant capacitors and switches, and by appropriately controlling them based on information determined between the power transmitting device 101 and the power receiving device 102, the respective resonant frequencies are separated from each other. This makes it possible to perform more accurate foreign object detection. Note that the resonant capacitors of the power transmitting device 101 and the power receiving device 102 and the switches to which they are connected may be provided in greater numbers than those shown in FIG. 2 and FIG. 3. This makes it possible to perform more precise control of the resonant frequency, and to further improve the accuracy of foreign object detection.

[0084] As described above, foreign object detection can be performed based on the characteristics (e.g., attenuation rate of a time waveform) of the voltage or current in the resonant circuit at three or more frequencies. At this time, it may be determined that a foreign object is present when the characteristics at one of the three or more frequencies exceed a threshold value. It may also be determined that a foreign object is present when the characteristics at two or more (e.g., all) of the three or more frequencies exceed a threshold value.

[0085] Also, the frequency f1 determined by the power transmitting antenna 205 and the resonant capacitor 207 of the power transmitting device 101 may be controlled to be 13.56 MHz or its vicinity, which is a frequency band used in NFC (Near Field Communication). Alternatively or in addition to this, the frequency f2 determined by the power receiving antenna 305 and the resonant capacitor 312 of the power receiving device 102 may be controlled to be 13.56 MHz or its vicinity, which is a frequency band used in NFC. For this purpose, the power transmitting device 101 or the power receiving device 102 appropriately sets at least one of the inductance and the capacitance as described above, or controls the switch to control the resonant frequency to be 13.56 MHz. This makes it possible to detect an NFC-using device or an NFC tag, which is not the power receiving device 102, placed on the power transmitting device 101. Note that NFC is just an example, and a frequency used in another wireless standard may be set as the resonant frequency in the power transmitting device 101 or the power receiving device 102. This enables the power transmitting apparatus 101 or the power receiving apparatus 102 to detect that a device conforming to that wireless standard has been placed on the power transmitting apparatus or the power receiving apparatus 102 .

[0086] In the above embodiment, the timing for measuring the waveform attenuation index and the signal spectrum in advance in a state where no foreign object exists will be described. In the WPC standard, foreign object detection is performed by the Q-value measurement method in the negotiation phase as described above. Then, when it is determined that no foreign object exists as a result of the foreign object detection, the phase transitions to the calibration phase and the power transfer phase. That is, the transition to a phase after the negotiation phase means that it is determined that no foreign object exists by the Q-value measurement method. Therefore, by measuring the waveform attenuation rate in any of the negotiation phase, calibration phase, and power transfer phase, it is highly likely that the waveform attenuation rate in a state where no foreign object exists can be measured. Therefore, the timing for measuring the waveform attenuation rate in a state where no foreign object exists can be any of the negotiation phase, calibration phase, and power transfer phase.

[0087] On the other hand, a foreign object may be introduced between the power transmitting device 101 and the power receiving device 102 during the period from when it is confirmed by the Q-value measurement method that no foreign object is present in the negotiation phase until the measurement of the waveform attenuation rate in the absence of the foreign object is performed. In such a case, it is expected that the waveform attenuation rate in the absence of the foreign object cannot be measured with high accuracy. For this reason, it is useful to measure the waveform attenuation rate immediately after it is confirmed that no foreign object is present.

[0088] For this purpose, for example, the power receiving device 102 detects a change in the state of the power transmitting device 101 or the power receiving device 102, and determines whether or not it is necessary to update or add a threshold value used for foreign object detection using the waveform attenuation method. If it is determined that it is necessary to update or add a threshold value, the power receiving device 102 transmits a command to the power transmitting device 101 to execute foreign object detection using the power loss method. In response to receiving this command, the power transmitting device 101 executes foreign object detection using the power loss method and determines whether or not a foreign object exists. If it is determined that no foreign object exists or that there is a high possibility that no foreign object exists, the power receiving device 102 notifies the power receiving device 102 that no foreign object exists. The power receiving device 102 executes an operation to set a threshold value used for foreign object detection using the waveform attenuation method and to update or add a threshold value. That is, if it is notified that no foreign object exists, the power receiving device 102 transmits a command to the power transmitting device 101 to request execution of a measurement for setting a threshold value for foreign object detection using the waveform attenuation method. In response to receiving this command, the power transmitting device 101 suspends power transmission. Furthermore, the power transmitting device 101 and the power receiving device 102 control the circuits as described above to measure the waveform attenuation index and the signal spectrum of the frequencies f1 and f2. Then, the power transmitting device 101 uses the measured waveform attenuation index and the signal spectrum to calculate a threshold value for foreign object detection using the waveform attenuation method, and sets the calculated threshold value.

[0089] In this way, when the power receiving device 102 determines to update / change the threshold value of the waveform attenuation method, it causes the power transmitting device 101 to confirm that no foreign object is present by the power loss method immediately before performing the operation for updating / changing the threshold value of the waveform attenuation method. Then, in response to confirmation that no foreign object is present, the power receiving device 102 executes the operation for updating / changing the threshold value of the waveform attenuation method. This makes it possible to sufficiently increase the probability that no foreign object is present when performing a measurement for setting the threshold value for foreign object detection using the waveform attenuation method, and to set the foreign object detection threshold value with greater accuracy.

[0090] In the above example, a method for confirming that no foreign object exists by the power loss method immediately before performing an operation for updating or changing the threshold value of the waveform attenuation method has been described. However, the power loss method also has a threshold value for determining the presence or absence of a foreign object. Then, as with the waveform attenuation method, it may be necessary to update or add the threshold value of this power loss method when the state of the power transmitting device 101 or the power receiving device 102 changes. This updating or adding of the threshold value can be performed in the power transfer phase. That is, as with the above method, when the power receiving device 102 determines to set, update, or change the threshold value of the power loss method, it executes a process for confirming that no foreign object exists by the waveform attenuation method immediately before performing the operation for that purpose. Then, in response to confirmation that no foreign object exists by the waveform attenuation method, the power receiving device 102 may execute an operation for updating or changing the threshold value of the power loss method. For example, when the power receiving device 102 determines that it is necessary to update or add the threshold value used for foreign object detection by the power loss method, it transmits a command to the power transmitting device 101 to execute foreign object detection by the waveform attenuation method. In response to receiving this command, the power transmitting device 101 executes foreign object detection using the waveform attenuation method to determine the presence or absence of a foreign object. Then, when the power transmitting device 101 determines that no foreign object is present or that there is a high possibility that no foreign object is present, it notifies the power receiving device 102 that no foreign object is present. When notified that no foreign object is present, the power receiving device 102 executes an operation for updating or adding a threshold value used for foreign object detection using the power loss method. That is, in order to update or add a threshold value used for foreign object detection, the power receiving device 102 transmits to the power transmitting device 101 a command requesting execution of a measurement for setting a threshold value for foreign object detection using the power loss method. Then, the power receiving device 102 controls the load so that the load is configured to correspond to the transmission power of the threshold value (point) to be updated or added. When the power transmitting device 101 receives the command, it calculates and sets a threshold value for foreign object detection using the power loss method.This makes it possible to sufficiently increase the probability that no foreign object is present when performing measurements for setting the foreign object detection threshold by the power loss method, and to set the foreign object detection threshold with greater accuracy. In the above embodiment, power transmission is stopped in order to detect a foreign object, but instead of completely stopping power transmission, the power may be reduced to, for example, close to zero.

[0091] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0092] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0093] 101: power transmitting device, 201: control unit, 203: power transmitting unit, 205: power transmitting antenna, 207, 212-213: resonance capacitors

Claims

1. A power transmitting means for wirelessly transmitting power to a power receiving device via a power transmitting antenna; a control means for controlling whether or not a resonant circuit including the power transmitting antenna and a resonant capacitor connected to the power transmitting antenna is formed; a detection means for detecting an object other than the power receiving device based on a characteristic of a voltage or a current in the resonant circuit at at least two frequencies including a frequency corresponding to a resonant frequency of the resonant circuit; A power transmitting device comprising:

2. The power transmitting device according to claim 1 , wherein the at least two frequencies include a frequency corresponding to a resonant frequency of a resonant circuit configured in the power receiving device.

3. The power transmitting means stops or suppresses the supply of power to be transmitted to the power receiving device when the resonant circuit is formed, The power transmission device according to claim 1 or 2, characterized in that the characteristic is a state of attenuation of a time waveform of a voltage or current in the resonant circuit at each of the at least two frequencies after the supply of the power is stopped or suppressed.

4. the state of attenuation is indicated by a value corresponding to an attenuation rate, which is a ratio of the magnitude of attenuation of the time waveform to time; The power transmitting device according to claim 3 , wherein the detection means detects the presence of the object when the attenuation rate corresponding to the value at any one of the at least two frequencies exceeds a threshold value.

5. the state of attenuation is indicated by a value corresponding to an attenuation rate, which is a ratio of the magnitude of attenuation of the time waveform to time; The power transmitting device according to claim 3 , wherein the detection means detects the presence of the object when the attenuation rate corresponding to the value at two or more frequencies among the at least two frequencies exceeds a threshold value.

6. The power transmitting means stops or suppresses the supply of power to be transmitted to the power receiving device when the resonant circuit is formed, 3. The power transmitting device according to claim 1, wherein the characteristic is a spectral magnitude of a voltage or a current in the resonant circuit at each of the at least two frequencies after the supply of the power is stopped or suppressed.

7. The power transmitting device according to claim 6 , wherein the detection means detects the presence of the object when the spectrum at any one of the at least two frequencies is lower than a threshold value.

8. The power transmitting device according to claim 6 , wherein the detection means detects the presence of the object when the spectrum at two or more frequencies among the at least two frequencies is lower than a threshold value.

9. 9. The power transmitting device according to claim 1, wherein the control means performs control to change a resonant frequency of the resonant circuit by changing a configuration of the resonant circuit.

10. The power transmitting device according to claim 1 , wherein the at least two frequencies include a frequency used in a wireless standard different from a standard related to wireless power transmission.

11. a power receiving means for wirelessly receiving power from a power transmitting device via a power receiving antenna; a control means for controlling whether or not a resonant circuit including the power receiving antenna and a resonant capacitor connected to the power receiving antenna is formed; a detection means for detecting an object other than the power transmitting device based on a characteristic of a voltage or a current in the resonant circuit at at least two frequencies including a frequency corresponding to a resonant frequency of the resonant circuit; A power receiving device comprising:

12. The power receiving device according to claim 11 , wherein the at least two frequencies include a frequency corresponding to a resonant frequency of a resonant circuit configured in the power transmitting device.

13. the power transmitting device stops or suppresses a supply of power to be transmitted to the power receiving device when the resonant circuit is configured; The power receiving device according to claim 11 or 12, characterized in that the characteristic is a state of attenuation of a time waveform of a voltage or current in the resonant circuit at each of the at least two frequencies after the supply of the power is stopped or suppressed.

14. the state of attenuation is indicated by a value corresponding to an attenuation rate, which is a ratio of the magnitude of attenuation of the time waveform to time; The power receiving device according to claim 13 , wherein the detection means detects the presence of the object when the attenuation rate corresponding to the value at any one of the at least two frequencies exceeds a threshold value.

15. the state of attenuation is indicated by a value corresponding to an attenuation rate, which is a ratio of the magnitude of attenuation of the time waveform to time; The power receiving device according to claim 13, characterized in that the detection means detects the presence of the object when the attenuation rate corresponding to the value at two or more frequencies among the at least two frequencies exceeds a threshold value.

16. the power transmitting device stops or suppresses a supply of power to be transmitted to the power receiving device when the resonant circuit is configured; The power receiving device according to claim 11 or 12, characterized in that the characteristic is a spectral magnitude of a voltage or a current in the resonant circuit at each of the at least two frequencies after the supply of the power is stopped or suppressed.

17. 17. The power receiving device according to claim 16, wherein the detection means detects the presence of the object when the spectrum at any of the at least two frequencies is lower than a threshold value.

18. 17. The power receiving device according to claim 16, wherein the detection means detects the presence of the object when the spectrum at two or more frequencies among the at least two frequencies is lower than a threshold value.

19. 19. The power receiving device according to claim 11, wherein the control means performs control to change a resonant frequency of the resonant circuit by changing a configuration of the resonant circuit.

20. 20. The power receiving device according to claim 11, wherein the at least two frequencies include a frequency used in a wireless standard different from a standard related to wireless power reception.

21. A control method executed by a power transmitting device that wirelessly transmits power to a power receiving device via a power transmitting antenna, comprising: Controlling whether or not to configure a resonant circuit including the power transmitting antenna and a resonant capacitor connected to the power transmitting antenna; Detecting an object other than the power receiving device based on characteristics of a voltage or a current in the resonant circuit at at least two frequencies including a frequency corresponding to a resonant frequency of the resonant circuit; A control method comprising:

22. A control method executed by a power receiving device that wirelessly receives power from a power transmitting device via a power receiving antenna, comprising: Controlling whether or not to configure a resonant circuit including the power receiving antenna and a resonant capacitor connected to the power receiving antenna; Detecting an object other than the power transmitting device based on characteristics of a voltage or a current in the resonant circuit at at least two frequencies including a frequency corresponding to a resonant frequency of the resonant circuit; A control method comprising:

23. A program for causing a computer to execute the control method according to claim 21 or 22.

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