Power receiving 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 object detection technology in wireless power transmission.

Background Art

[0002] The technological development of wireless power transmission systems has been widely carried out, and the standard (WPC standard) formulated by the standardization organization Wireless Power Consortium (WPC) as a wireless charging standard is widely known. In such wireless power transmission, when there is a foreign object within the range where the power transmission device can transmit power, it is essential to detect the foreign object and control power transmission and reception. A 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 transmission and reception device compliant with the WPC standard. Patent Document 2 describes a method in which the power transmission device transmits a signal for foreign object detection to the power receiving device and determines the presence or absence of a foreign object using the echo signal from the power receiving device. Patent Document 3 describes a technique for detecting a foreign object by short-circuiting the coil of a wireless power transmission system.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention provides a technique for accurately detecting an object different from the power receiving device.

Means for Solving the Problems

[0005] A power receiving device according to one aspect of the present invention includes power receiving means for wirelessly receiving power from a power transmitting device, communication means for communicating with the power transmitting device, determination means for determining a frequency based on communication with the power transmitting device, Determined the frequency During power reception at measurement means for measuring voltage, and processing using the measured voltage different processing means for performing processing related to foreign object detection, and has different, wherein the frequency is a frequency related to processing related to the foreign object detection .

Effects of the Invention

[0006] According to the present invention, it is possible to accurately detect an object different from the power receiving device.

Brief Description of the Drawings

[0007]

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Figure 12

Best Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0009] (Configuration of Wireless Power Transmission System) FIG. 1 shows a configuration example of the wireless power transmission system according to this embodiment. This system is, for example, a wireless charging system. This system includes a power transmission device 101 and a power reception device 102. Hereinafter, the power transmission device 101 may be referred to as TX, and the power reception device 102 may be referred to as RX. RX is an electronic device that has a built-in battery and charges the built-in battery with the power received from TX. TX is an electronic device that wirelessly transmits power to RX placed on a charging stand 103 prepared as a part of the housing of TX, for example. Since the charging stand 103 is a part of TX, hereinafter, "placed on the charging stand 103" may be referred to as "placed on TX (power transmission device 101)". The range 104 indicated by the broken line is the range in which RX can receive power from TX. Note that TX and RX may have functions for executing applications other than wireless charging. RX is, for example, a smartphone, and TX is, for example, an accessory device for charging the smartphone. Note that TX and RX may be storage devices such as tablets, hard disk devices, and memory devices, or information processing devices such as personal computers (PCs). Further, TX and RX may be, for example, image input devices such as imaging devices (cameras, video cameras, etc.) and scanners, or image output devices such as printers, copiers, and projectors. Further, RX may be, for example, a vehicle such as an automobile, and TX may be a charger installed in a console of an automobile.

[0010] In this system, wireless power transmission using the electromagnetic induction method for wireless charging is performed based on the WPC standard. That is, the TX and RX perform wireless power transmission for wireless charging based on the WPC standard between the power transmission antenna of the TX and the power reception antenna of the RX. Note that in this system, although the method defined by the WPC standard is used as the wireless power transmission method, it is not limited to this, and other methods may be used. For example, methods using electromagnetic induction, magnetic field resonance, electric field resonance, microwave, laser, etc. may be used. Also, in this embodiment, it is assumed that wireless power transmission is used for wireless charging, but wireless power transmission may be performed for applications other than wireless charging.

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

[0012] Also, when power is transmitted from the power transmission device 101 to the power reception device 102, if there is a foreign object, which is an object other than the power reception device, near the power transmission device 101, the electromagnetic wave for power transmission may affect the foreign object and increase the temperature of the foreign object, and in some cases, the foreign object may be destroyed. Therefore, in the WPC standard, in order to take measures such as stopping power transmission when a foreign object exists, a method for the power transmission device 101 to detect, for example, the presence of a foreign object on the charging stand 103 is specified. Specifically, a Power Loss method for detecting a foreign object based on the relationship between the power transmission power in the power transmission device 101 and the power reception power in the power reception device 102 is specified. Also, a Q-value measurement method for detecting a foreign object based on a change in the quality factor (Q-value) of the power transmission antenna (power transmission coil) in the power transmission device 101 is specified. Note that the power transmission device 101 can not only detect an object existing on the charging stand 103 as a foreign object, but also detect a foreign object located near the power transmission device 101. For example, the power transmission device 101 may detect a foreign object existing in the power transmission possible range 104.

[0013] Here, foreign object detection based on the Power Loss method specified in the WPC standard will be described with reference to FIG. 10. The horizontal axis in FIG. 10 is the power transmission power of the power transmission device 101, and the vertical axis is the power reception power of the power reception device 102. Note that a foreign object is an object other than the power reception device 102 that can affect the power transmission from the power transmission device 101 to the power reception device 102, and is, for example, an object such as a metal piece having conductivity.

[0014] First, the power transmission device 101 transmits power to the power receiving device 102 at the first power transmission power value Pt1, and it is assumed that the power receiving device 102 obtains the received power of the first received power value Pr1. Note that this state can be called the Light Load state (light load state). Then, the power transmission device 101 stores the first power transmission power value Pt1. Here, the first power transmission power value Pt1 or the first received power value Pr1 is a predetermined minimum power transmission or received 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 can 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 received power value Pr1 to the power transmission device 101. When the power transmission device 101 receives the first received power value Pr1 from the power receiving device 102, it calculates that the power loss between the power transmission device 101 and the power receiving device 102 is Pt1 - Pr1 (Ploss1), and creates a calibration point 1000 indicating the correspondence between Pt1 and Pr1.

[0015] Subsequently, the power transmission device 101 changes the power transmission power value to the second power transmission power value Pt2, transmits power to the power receiving device 102, and it is assumed that the power receiving device 102 obtains the received power of the second received power value Pr2. Note that this state can be called the Connected Load state (load connection state). Then, the power transmission device 101 stores the second power transmission power value Pt2. Here, the second power transmission power value Pt2 or the second received power value Pr2 is a predetermined maximum power transmission 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 power receiving antenna and the load so that the received power is supplied to the load. The power receiving device 102 reports the second received power value Pr2 to the power transmission device 101. When the power transmission device 101 receives the second received power value Pr2 from the power receiving device 102, it calculates that the power loss between the power transmission device 101 and the power receiving device 102 is Pt2 - Pr2 (Ploss2), and creates a calibration point 1001 indicating the correspondence between Pt2 and Pr2.

[0016] Then, the power transmission device 101 creates a straight line 1002 that linearly interpolates between the calibration point 1000 and the calibration point 1001. The straight line 1002 shows the relationship between the transmitted power and the received power when there is no foreign object in the vicinity of the power transmission device 101 and the power reception device 102. Based on the straight line 1002, the power transmission device 101 can predict the power value received by the power reception device 102 when transmitting power at a predetermined transmitted power in a state without foreign objects. For example, when the power transmission device 101 transmits power at the third transmitted power value Pt3, the third received power value Pr3 received by the power reception device 102 can be estimated from the point 1003 corresponding to Pt3 on the straight line 1002.

[0017] As described above, based on a plurality of combinations of the transmitted power value of the power transmission device 101 and the received power value of the power reception device 102 measured while changing the load, the power loss between the power transmission device 101 and the power reception device 102 according to the load can be specified. Also, by interpolation based on the plurality of combinations, it becomes possible to estimate the power loss between the power transmission device 101 and the power reception device 102 according to the load. In this way, the calibration process performed by the power transmission device 101 and the power reception device 102 to obtain a combination of the transmitted power value and the received power value is hereinafter referred to as "Calibration process of Power Loss method (CAL process)".

[0018] After calibration, when the power transmission device 101 actually transmits power to the power reception device 102 at Pt3, assume that the power transmission device 101 receives a value of the received power value Pr3' from the power reception device 102. The power transmission device 101 calculates a value Pr3 - Pr3' (= Ploss_FO) obtained by subtracting the received power value Pr3' actually received from the power reception device 102 from the received power value Pr3 in a state where there is no foreign object. This Ploss_FO can be considered as the power loss due to the power consumed by the foreign object when there is a foreign object near the power transmission device 101 and the power reception device 102. Therefore, when the power Ploss_FO consumed by the foreign object exceeds a predetermined threshold value, the power transmission device 101 can determine that there is a foreign object. Also, the power transmission device 101 calculates in advance the power loss Pt3 - Pr3 (Ploss3) between the power transmission device 101 and the power reception device 102 from the received power value Pr3 in a state where there is no foreign object. Then, the power transmission device 101 calculates the power loss Pt3 - Pr3' (Ploss3') between the power transmission device 101 and the power reception device 102 using the received power value Pr3' received from the power reception device 102. Then, the power transmission device 101 may estimate the power Ploss_FO that would be consumed by the foreign object using Ploss3' - Ploss3 (= Ploss_FO).

[0019] As described above, the power Ploss_FO that would be consumed by the foreign object may be calculated as Pr3 - Pr3' based on the received power, or may be calculated as Ploss3' - Ploss3 based on the magnitude of the power loss. In the following, it is assumed that Ploss_FO is calculated by Ploss3' - Ploss3, but Ploss_FO may also be calculated by Pr3 - Pr3'.

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

[0021] The RX and TX in this embodiment perform communication for power transmission and reception control based on the WPC standard. The WPC standard defines a plurality of phases including a Power Transfer phase in which power transmission is executed and one or more phases before actual power transmission. In each phase, necessary communication for power transmission and reception control is performed. The phases before power transmission may include a Selection phase, a Ping phase, an Identification and Configuration phase, a Negotiation phase, and a Calibration phase. Hereinafter, the Identification and Configuration phase is referred to as the I&C phase. Hereinafter, the processing of each phase will be described.

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

[0023] In the Ping phase, the TX transmits a Digital Ping with higher power than the Analog Ping. The power level of the Digital Ping is sufficient to activate the control unit of the RX placed on the TX. The RX notifies the TX of the magnitude of the received power voltage. In this way, the TX recognizes that the object detected in the Selection phase is the RX by receiving the response from the RX that has received the Digital Ping transmitted by the self-device. When the TX receives the notification of the received power voltage value, it transitions to the I&C phase. Also, before transmitting the Digital Ping, the TX measures the Q value (Q-Factor) of the power transmission antenna. This measurement result is used when performing foreign object detection processing using the Q value measurement method.

[0024] In the I&C phase, the TX identifies the RX and acquires device configuration information (capability information) from the RX. The RX transmits an ID Packet and a Configuration Packet. The ID Packet contains the RX's identifier information, and the Configuration Packet contains the RX's device configuration information (capability information). When the TX receives the ID Packet and the Configuration Packet, it responds with an acknowledge (ACK, positive response). Then, the I&C phase ends.

[0025] In the Negotiation phase, the value of GP is determined based on the value of GP required by the RX and the power transmission capability of the TX, etc. Also, the TX executes foreign object detection processing using the Q-value measurement method, for example, in accordance with a request from the RX. Further, in the WPC standard, it is stipulated that once the Power Transfer phase is entered, if there is a request from the RX, the same processing as in the Negotiation phase is performed again. The phase in which this processing is executed again after entering the Power Transfer phase is called the Renegotiation phase.

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

[0027] In the Power Transfer phase, control is performed for starting, continuing power transmission, and stopping power transmission due to errors or full charge, etc. The TX and the RX perform communication by superimposing a signal on the electromagnetic wave transmitted from the power transmission antenna or the receiving antenna using the power transmission antenna and the receiving antenna used when performing wireless power transmission based on the WPC standard for these power transmission and reception controls. Note that the range in which communication based on the WPC standard is possible between the TX and the RX is almost the same as the power transmission range of the TX.

[0028] (Configuration of Power Transmission Device 101 and Power Reception Device 102) Next, a configuration example of the power transmission device 101 (TX) and the power reception device 102 (RX) of the present embodiment will be described. Note that the configuration described below is merely an example, and part (or all in some cases) of the described configuration may be replaced with or omitted by other configurations having similar functions, and further configurations may be added. Furthermore, one block shown in the following description may be divided into a plurality of blocks, or a plurality of blocks may be integrated into one block. Also, each of the functional blocks shown below can be realized by one or more processors executing software instructions, but part or all of the functions included in each functional block may be realized by hardware.

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

[0030] The control unit 201 executes the overall control of the TX by, for example, executing a control program stored in the memory 206. 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. Also, the control unit 201 may perform control for executing applications other than wireless power transmission. The control unit 201 is configured to include one or more processors such as a CPU (Central Processing Unit) or an MPU (Micro Processor Unit), for example. Note that the control unit 201 may be configured by hardware such as an application specific integrated circuit (ASIC). Also, the control unit 201 may be configured to include an array circuit such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processing. The control unit 201 stores information to be stored in the memory 206 while executing various processes. Also, the control unit 201 can 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. Electric power supplied from the commercial power supply is stored in the battery.

[0032] The power transmission unit 203 converts the DC or AC power input from the power supply unit 202 into AC power of a frequency band used for wireless power transmission, and generates an electromagnetic wave for power reception by the RX by inputting the power to the power transmission antenna 205. For example, the power transmission unit 203 converts the DC voltage supplied by the power supply unit 202 into an AC voltage using a switching circuit with a half-bridge or full-bridge configuration using FETs (Field Effect Transistors). In this case, the power transmission unit 203 includes a gate driver that controls the ON / OFF of the FETs. The power transmission unit 203 further controls the intensity of the output electromagnetic wave by adjusting the voltage (transmission voltage) or current (transmission current), or both, input to the power transmission antenna 205. Increasing the transmission voltage or transmission current increases the intensity of the electromagnetic wave, and decreasing the transmission voltage or transmission current decreases the intensity of the electromagnetic wave. Also, the power transmission unit 203 performs power output control so that power transmission from the power transmission antenna 205 is started or stopped based on an instruction from the control unit 201. Also, it is assumed that the power transmission unit 203 has the ability to supply power sufficient to output 15 watts (W) of power to the charging unit of the power receiving device 102 (RX) compliant with the WPC standard.

[0033] The communication unit 204 communicates with the RX for power transmission control based on the WPC standard as described above. The communication unit 204 modulates the electromagnetic wave output from the power transmission antenna 205, transmits information to the RX, and performs communication. Also, the communication unit 204 demodulates the electromagnetic wave transmitted from the power transmission antenna 205 and modulated by the RX, and acquires the information transmitted by the RX. That is, the communication performed by the communication unit 204 is performed with a signal superimposed on the electromagnetic wave transmitted from the power transmission antenna 205. Also, the communication unit 204 may communicate with the RX using a communication standard different from the WPC standard using an antenna different from the power transmission antenna 205, or may communicate with the RX by selectively using a plurality of communications.

[0034] The memory 206 stores a control program executed by the control unit 201. The memory 206 can also store the states of TX and RX (such as transmission power value, reception power value, etc.). For example, the state of TX can be acquired by the control unit 201, and the state of RX can be the information acquired by the control unit 301 of RX 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 transmission antenna 205 and the resonance capacitor 207 connected to the power transmission antenna 205 are disconnected from the power transmission unit 203. When the switch 208 is turned on and short-circuited, the power transmission antenna 205 and the resonance capacitor 207 are connected to the power transmission unit 203.

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

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

[0038] FIG. 3 is a block diagram showing a configuration example of a power receiving device 102 (RX) according to the present 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. Note that two or more or all of the functional blocks separately shown in FIG. 3 may be implemented in the same chip. Also, a plurality of functional blocks shown in FIG. 3 may be realized by one hardware module.

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

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

[0041] The power receiving unit 303 obtains alternating current power (alternating current voltage and alternating current) generated by electromagnetic induction based on the electromagnetic wave radiated from the transmission antenna 205 of the TX via the power receiving antenna 305. Then, the power receiving unit 303 converts the alternating current power into direct current power or alternating current power of a predetermined frequency, and outputs the converted power to the charging unit 306 that performs a process for charging the battery 307. For this purpose, the power receiving unit 303 includes, for example, a rectifying unit and a voltage control unit necessary for supplying power to the load in the RX. The above-described GP is the amount of power guaranteed to be output from the power receiving unit 303. Assume that the power receiving unit 303 has a power supply capacity to supply the 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 as described above with the communication unit 204 of the TX. The communication unit 304 demodulates the electromagnetic wave input from the power receiving antenna 305 to obtain the information transmitted from the TX. In addition, the communication unit 304 transmits information to the TX by superimposing a signal regarding the information to be transmitted to the TX on the electromagnetic wave by load-modulating the input electromagnetic wave. Note that the communication unit 304 may communicate with the TX by a standard different from the WPC standard using an antenna different from the power receiving antenna 305, or may communicate with the TX by selectively using a plurality of communications.

[0043] The memory 308 stores the control program executed by the control unit 301. The memory 308 also stores the states of the TX and RX, etc. For example, the state of the RX is obtained by the control unit 301, and the state of the TX can be received via the communication unit 304 with the information obtained by the control unit 201 of the TX.

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

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

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

[0048] Next, with reference to FIG. 4, the functions of the control unit 201 of the TX will be described. 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 the power transmission to the RX. The measurement unit 403 measures the waveform attenuation index described later. Also, it measures the power transmitted to the RX via the power transmission unit 203 and measures the average power transmission per unit time. Further, 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 calculation processing, based on the waveform attenuation index measured by the measurement unit 403. The foreign object detection unit 405 has a function of performing foreign object detection processing by the Power Loss method, the Q value measurement method, or the waveform attenuation method. Also, the foreign object detection unit 405 may have a function of performing foreign object detection processing using other methods. For example, the foreign object detection unit 405 in a TX having an NFC (Near Feald Communication) communication function may perform foreign object detection processing using the detection function of the counterpart device according to the NFC standard. Also, the foreign object detection unit 405 can detect that the state on the TX has changed as a function other than detecting foreign objects. 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 serves as a criterion for determining the presence or absence of a foreign object when the TX performs foreign object detection by the Power Loss method, the Q value measurement method, or the waveform attenuation method. Also, the setting unit 404 may have a function of setting a threshold value that serves as a criterion for determining the presence or absence of a foreign object, which is required 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, power transmission power, or Q value measured by the measurement unit 403.

[0050] 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 realize their functions as programs operating in the control unit 201. Each functional unit can be constituted by an independent program. Each functional unit can operate in parallel while establishing synchronization between programs by event processing or the like. However, two or more of these processing units may be realized by one program.

[0051] (Flow of processing for power transmission according to the WPC standard) In the WPC standard, as described above, the Selection phase, the Ping phase, the I&C phase, the Negotiation phase, the Calibration phase, and the Power Transfer phase are defined. Hereinafter, the operations of the power transmission device 101 and the power reception device 102 in these phases will be described with reference to FIG. 5.

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

[0053] When TX detects the placement of RX, it acquires identification information and capability information from RX through communication in the I&C phase defined by the WPC standard (F507). Here, the identification information of RX includes Manufacturer Code and Basic Device ID. The capability information of RX includes information elements that can identify the corresponding WPC standard version, a Maximum Power Value which is a value specifying the maximum power that RX can supply to the load, and information indicating whether the RX has the Negotiation function of the WPC standard. Note that TX may acquire the identification information and capability information of RX by methods other than communication in the I&C phase of the WPC standard. Also, the identification information may be any other identification information that can identify the individual RX, such as Wireless Power ID. As the capability information, information other than the above-mentioned information may be included.

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

[0055] After the GP's decision, TX performs Calibration based on that GP. In the Calibration process, first, RX transmits information including the received power in a light load state (load cut-off state, load state where the transmitted power is equal to or less than the first threshold) of TX (hereinafter, this information is referred to as "first reference received power information"). (F509). In this embodiment, the first reference received power information is the received power information of RX when the transmitted power of TX is 250 milliwatts. The first reference received power information is notified using the Received Power Packet (mode1) defined in the WPC standard, but other messages may be used for the notification. TX determines whether to accept the first reference received power information based on its own transmission state. If TX accepts it, it transmits an affirmative response (ACK) to RX; if it does not accept it, it transmits a negative response (NAK) to RX.

[0056] When RX receives an ACK from TX (F510), it performs a process to transmit information including the received power in the load connection state (maximum load state, load state where the transmission 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 transmission power of TX is 5 watts. Here, the second reference received power information is notified using the Received Power Packet (mode2) defined in the WPC standard, but this notification may be performed using other messages. RX transmits a transmission output change instruction including a value (positive value) corresponding to the increase in transmission power in order to increase the transmission power from TX to 5 watts (F511). When TX receives this transmission output change instruction, if it is possible to increase the transmission power, it responds to RX with an ACK and increases the transmission power (F512, F513). The second reference received power information is the 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, it responds to the transmission output change instruction with a NAK and notifies RX that the transmission output cannot be changed (F514). Thereby, it is possible to prevent power above the specified value from being transmitted. When RX receives a NAK from TX, it determines that the predetermined transmission power has been reached, and transmits the second reference received power information regarding the received power in the load connection state to TX (F516). TX can calculate the power loss amount between TX and RX in the load disconnection state and the load connection 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. Also, TX can estimate the power loss value between TX and RX at all transmission powers that TX can obtain (here, from 250 milliwatts to 5 watts) by interpolation based on the relationship of those power loss amounts (F517). TX transmits an ACK to the second reference received power information from RX (F518) and completes the Calibration process. Then, in a state where TX determines that it can start the charging process of RX, it starts the power transmission process to RX, and the charging of RX is started.

[0057] Before the start of the power transmission process, if the TX and RX perform device authentication processing (F519) and determine that they can support each other for 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 transmission power output of the TX using a transmission power output change instruction, ACK, and NAK to increase the transmission power of the TX to 15 watts (F521 - F524). Then, the TX and RX execute the Calibration process again in response to GP = 15 watts. That is, the RX transmits information including the received power in the load connection state of the RX when the transmission power of the TX is 15 watts (hereinafter, this information is referred to as "third reference received power information") (F525). The TX executes 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 transmission power at which each received power was obtained. Thereby, the TX can estimate the power loss amount between the TX - RX at all possible transmission powers of the TX (here, from 250 milliwatts to 15 watts) (F526). Then, the TX transmits an ACK to the third reference received power information from the RX (F527) and completes the Calibration process. After that, the power transmission process to the RX is started in a state where the TX determines that the charging process of the RX can be started, and the charging of the RX is started (F528).

[0058] In the Power Transfer phase, the TX transmits power to the RX. Also, in the Power Transfer phase, foreign object detection is performed by the above-described Power Loss method. Here, since foreign object detection by the Power Loss method can be performed while continuing power transmission, the power transmission efficiency can be kept high. However, when the power transmission device 102 is transmitting a large amount of power, the accuracy of foreign object detection may decrease. For this reason, with only foreign object detection by the Power Loss method, there is a possibility of false detection of foreign objects and a possibility of false determination that no foreign object exists even though a foreign object is present. In particular, the Power Transfer phase is the phase in which the TX transmits power. If a foreign object exists near the TX and RX during power transmission, heat generation from the foreign object increases, so it is required to improve the accuracy of foreign object detection in this phase. Therefore, in the present embodiment, in order to improve the accuracy of foreign object detection, as a foreign object detection method different from the Power Loss method, the following waveform attenuation method is used to perform further foreign object detection.

[0059] (Foreign Object Detection Method by Waveform Attenuation Method) In the Power Transfer phase, the power transmission device 101 is transmitting power to the power reception device 102. At this time, if foreign object detection can be performed using the power transmission waveform (voltage waveform or current waveform) related to this power transmission, it becomes possible to detect foreign objects without newly defining and using a foreign object detection signal or the like. As such a method, in the present embodiment, a method of performing foreign object detection based on the attenuation state of the power transmission waveform (this method is called the "waveform attenuation method") is used. The principle of foreign object detection by this waveform attenuation method will be described with reference to FIG. 6. Here, foreign object detection using the power transmission waveform related to power transmission from the power transmission device 101 (TX) to the power reception device 102 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 transmission antenna 205 of TX. The horizontal axis in FIG. 6 represents time, and the vertical axis represents the voltage value. TX stops power transmission at time T0 from the state of transmitting power to RX via the transmission 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 waveform related to the transmission from 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 this transmission antenna 205 can be specified based on the time change of the voltage value after time T0. For example, the Q value is calculated by Equation 1 based on the time, 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 there is a foreign object in the vicinity of the TX and RX. This is because when a foreign object exists, energy loss occurs due to the foreign object. Therefore, focusing on the slope of the attenuation of the voltage value, when a foreign object exists, compared to when there is no foreign object, energy loss due to the foreign object occurs, so the slope of the straight line connecting point 601 and point 602 becomes steeper, and the attenuation rate of the waveform amplitude increases. That is, the waveform attenuation method determines the presence or absence of a foreign object based on the attenuation state of the voltage value between this point 601 and point 602. In the waveform attenuation method, the presence or absence of an actual foreign object can be determined by comparing any numerical value corresponding to this attenuation state. For example, the determination can be made using the above-mentioned Q value. In this case, the decrease in the Q value means that the waveform attenuation rate (the degree of decrease in the amplitude of the waveform per unit time) increases. Also, the determination may be made using the slope of the straight line connecting point 601 and point 602 calculated by (A1 - A2) / (T2 - T1). Also, when the observation times (T1 and T2) of the attenuation state of the voltage value are fixed, the determination may be made using a value (A1 - A2) representing the voltage value difference or a value (A1 / A2) representing the voltage value ratio. Also, when the voltage value A1 immediately after power transmission stops is constant, the determination can also be made using the value of the voltage value A2 after a predetermined time has elapsed. Also, the determination may be made using the value of the time (T2 - T1) until the voltage value A1 becomes a predetermined voltage value A2.

[0061] As described above, it is possible to determine the presence or absence of a foreign object based on the attenuation state of the voltage value during the power transmission stop period, and there are a plurality of values representing the attenuation state. In the present embodiment, the values representing these attenuation states are called "waveform attenuation indicators". For example, as described above, the Q value calculated by Equation 1 is a value representing the attenuation state of the voltage value related to power transmission and is included in the "waveform attenuation indicator". All waveform attenuation indicators are values corresponding to the waveform attenuation rate. Note that in the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation indicator". Hereinafter, the case where the waveform attenuation rate is used as the waveform attenuation indicator will be mainly described, but the content of the present embodiment can be similarly applied when other waveform attenuation indicators are used.

[0062] Note that, regarding the vertical axis in FIG. 6, even when the current value flowing through the power transmission antenna 205 is used, similar to the case of the voltage value, the attenuation state of the current value during the power transmission stop period changes depending on the presence or absence of a foreign object. And when a foreign object is present, the waveform attenuation rate is higher than when no foreign object is present. Therefore, a foreign object can also be detected by applying the above-described method to the time change of the current value flowing through the power transmission antenna 205. That is, the Q value obtained from the current waveform, the slope of the attenuation of the current value, the difference in current values, the ratio of current values, the absolute value of the current value, and the time until a predetermined current value is reached are used as waveform attenuation indicators to determine the presence or absence of a foreign object, and a foreign object can be detected. Further, foreign object detection based on both the attenuation state of the voltage value and the attenuation state of the current value may be performed, such as determining the presence or absence of a foreign object using an evaluation value calculated from the waveform attenuation indicator of the voltage value and the waveform attenuation indicator of the current value. In the above example, the waveform attenuation indicator during the period when TX temporarily stops power transmission is measured. However, TX may measure the waveform attenuation indicator during the period when the power supplied from the power supply unit 202 is temporarily decreased from a predetermined power level to a lower power level.

[0063] A method for detecting foreign objects based on the power transmission waveform during power transmission by the waveform attenuation method will be described with reference to FIG. 7. In FIG. 7, the power transmission waveform when detecting foreign objects by the waveform attenuation method is shown. The horizontal axis represents time, and the vertical axis represents the voltage value of the power transmission antenna 205. Similar to FIG. 6, the vertical axis may represent the current value of the current flowing through the power transmission antenna 205. Note that during the transient response period immediately after TX starts power transmission, it is assumed that the power transmission waveform is not stable. Therefore, during this transient response period, RX is controlled not to communicate with TX (communication by load modulation). Also, TX is controlled not to communicate with RX (communication by frequency shift modulation). When it is time to detect foreign objects, TX temporarily stops power transmission. Since the amplitude of the power transmission waveform attenuates due to this power transmission stop, TX calculates the waveform attenuation rate of this attenuated waveform. Then, TX determines that a foreign object exists when the calculated waveform attenuation rate exceeds a predetermined threshold. If no foreign object is detected during a predetermined foreign object detection period, TX resumes power transmission after that period. After resuming power transmission, TX repeatedly executes the above-described standby during the transient response period, identification of the foreign object detection timing, power transmission stop, and foreign object detection process. In this way, in the Power Transfer phase, in addition to the Power Loss method, foreign object detection by the waveform attenuation method can be performed.

[0064] (Processing of the power transmission device when applying the waveform attenuation method to the WPC standard) Subsequently, the processing executed by the power transmission device 101 when applying this waveform attenuation method to the WPC standard for foreign object detection will be described. When performing foreign object detection by the waveform attenuation method, the power transmission device 101 measures in advance the waveform attenuation rate in a state where no foreign object exists and calculates a threshold based on that. Thereafter, the power transmission device 101 executes foreign object detection by the waveform attenuation method and determines that "a foreign object exists" or "there may be a foreign object" when the measured waveform attenuation rate is greater than that threshold. On the other hand, the power transmission device 101 determines that "no foreign object exists" or "it is highly likely that no foreign object exists" when the measured waveform attenuation rate is less than that threshold.

[0065] Note that in the waveform attenuation method, since the power transmission device 101 temporarily stops power transmission and observes the attenuation rate of the power transmission waveform to detect foreign objects, it may cause a decrease in power transmission efficiency due to the temporary stop of power transmission. On the other hand, the waveform attenuation method can detect foreign objects with high precision even while transmitting a large amount of power. That is, even in a situation where it is difficult to accurately detect foreign objects by the Power Loss method, by using the waveform attenuation method, foreign objects can be detected with higher precision.

[0066] In the above example, when performing foreign object detection by the waveform attenuation method, it was explained that the attenuation rate of the waveform in a state where no foreign object exists is measured before power transmission starts, and a threshold value is calculated based on this. For this purpose, foreign object detection may be performed using the threshold value obtained from the attenuation rate of the waveform measured at the timing when it is estimated that no foreign object exists after power transmission starts. For example, the TX confirms that no foreign object exists by the Power Loss method during power transmission, performs the first measurement of the waveform attenuation rate, and calculates a threshold value based on the measured waveform attenuation rate. Since the first measurement of the waveform attenuation rate is performed immediately after it has been confirmed in advance by the Power Loss method that no foreign object exists, the measured waveform attenuation rate can be regarded as the attenuation rate of the waveform in a state where no foreign object exists. Next, the TX resumes power transmission and performs a second measurement of the waveform attenuation rate at the 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 measurement of the waveform attenuation rate with the measurement result of the first measurement of the waveform attenuation rate or the threshold value calculated based on it. That is, when performing foreign object detection by the waveform attenuation method, the attenuation rate of the waveform measured at that time may be compared with the attenuation rate of the waveform measured in a state where no foreign object existed before or the corresponding threshold value.

[0067] Also, in the above example, it is assumed that the frequency of the power transmission waveform related to the power transmission from the power transmission device 101 is a fixed frequency. However, the presence or absence of a foreign object may be determined by performing the above-described processing for foreign object detection at each of a plurality of frequencies and combining the results. By performing foreign object detection using not only the waveform attenuation rate at one frequency but also the waveform attenuation rates at a plurality of frequencies, it becomes possible to perform more accurate foreign object detection. This will be described later.

[0068] Also, in this embodiment, immediately after the power transmission device 101 stops power transmission or immediately after starting power transmission, the power transmission waveform becomes unstable due to the transient response. Therefore, a standby time is provided before shifting to each operation. Thus, the instability of the power transmission waveform is caused by a sudden start or sudden stop of power transmission. For this reason, in order to mitigate such instability of the power transmission waveform, the power transmission device 101 may perform control so that the power transmission power is increased step by step when starting power transmission and the power transmission power is decreased step by step when stopping power transmission. Note that the power transmission device 101 may perform stepwise increase or decrease of only one of the increase and decrease of the power transmission power, or may perform both stepwise.

[0069] (Foreign Object Detection Method Using Waveform Attenuation Method with Multiple Frequencies) Foreign objects mixed between the power transmission device 101 and the power reception device 102 cause heat generation and the like during power transmission. Therefore, when a foreign object is mixed, the power transmission device 101 needs to detect the foreign object at an early stage and perform power transmission control such as stopping power transmission or reducing the power transmission power. Foreign objects mixed between the power transmission device 101 and the power reception device 102 can have various sizes and shapes. In the waveform attenuation method described with reference to FIGS. 6 and 7, the power transmission device 101 transmits power at a predetermined frequency, temporarily stops the power transmission, and detects a foreign object from the waveform attenuation rate of the power transmission waveform. However, the energy consumed by the foreign object can vary depending on the frequency. That is, when foreign object A is present, the waveform attenuation rate of the waveform at frequency X is large, but the waveform attenuation rate of the waveform at frequency Y is small. When foreign object B is present, the waveform attenuation rate of the waveform at frequency X is small, but the waveform attenuation rate of the waveform at frequency Y is large, and so on. 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, when frequency Y is used for the waveform, even if foreign object A is present, the waveform attenuation rate is small, and there is a possibility of misjudgment that "no foreign object is present" despite the presence of foreign object A. To prevent such misjudgment, it is effective to perform foreign object detection not only using the waveform attenuation rate of the waveform at frequency Y for foreign object A but also using the waveform attenuation rate of the waveform at frequency X. That is, by measuring the attenuation rates of waveforms at a plurality of frequencies and performing foreign object detection, the probability of misjudgment can be reduced. Hereinafter, the processing executed by the power transmission device 101 and the processing executed by the power reception device 101 when performing such foreign object detection will be described with reference to FIGS. 11 and 12. FIG. 11 shows an example of the flow of processing executed by the power transmission device 101, and FIG. 12 shows an example of the flow of processing executed by the power reception device 102.

[0070] While the power transmission device 101 is transmitting power to the power reception device 102, it should communicate with the power reception device 102 using a predetermined packet to convey that foreign object detection by the waveform attenuation method should be executed (S1101, S1102). When the power reception device 102 receives the packet, it transmits a command for requesting the execution of foreign object detection to the power transmission device 101. This command may include time information for conveying the time (timing) at which the power transmission device 101 executes foreign object detection. Note that the time at which foreign object detection should be executed may also be notified from the power transmission device 101 to the power reception device 102 by the above-mentioned packet. In this way, the power transmission device 101 and the power reception device 102 share information on the timing for executing foreign object detection (S1102, S1202). The power transmission device 101 stops power transmission at the time of executing foreign object detection (S1103). Then, the power transmission device 101 turns on and shorts the switch 209 to form a closed-loop circuit formed by the power transmission antenna 205 that resonates at the frequency f1, the resonance capacitor 207, and the switch 209 (S1104). Note that the power transmission device 101 may stop power transmission after turning on and shorting the switch 209. Also, the power transmission device 101 may stop power transmission simultaneously with turning on and shorting the switch 209. On the other hand, the power reception device 102 turns on and shorts the switch 309 at the time of executing foreign object detection to form a closed-loop circuit formed by the power reception antenna 305 that resonates at the frequency f2, the resonance capacitor 312, and the switch 309 (S1203). As a result, an attenuation waveform of the frequency f1 is observed in the power transmission antenna 205 and the resonance capacitor 207 of the power transmission device 101 (S1105), and an attenuation waveform of the frequency f2 is observed in the power reception antenna 305 and the resonance capacitor 312 of the power reception device 102 (S1204).

[0071] Here, the power transmission antenna 205 and the power reception antenna 305 are electromagnetically coupled to each other so as to be supported by the fact that wireless power transmission and wireless communication are performed thereby. Therefore, even in the circuit formed by the power transmission antenna 205 and the resonance capacitor 207 existing in the power transmission device 101, the attenuation waveform of the frequency f2 can be observed (S1106). Also, even in the circuit formed by the power reception antenna 305 and the resonance capacitor 312 existing in the power reception device 102, the attenuation waveform of the frequency f1 is observable (S1205). Here, the attenuation waveform observed in the circuit formed by the power transmission antenna 205 and the resonance capacitor 207 of the power transmission device 101, or the attenuation waveform observed in the circuit formed by the power reception antenna 305 and the resonance capacitor 312 of the power reception device 102 is schematically shown in FIG. 8. When the power transmission device 101 stops power transmission and turns on and shorts the switch 209, and the power reception device 102 turns on and shorts the switch 309, as shown in FIG. 8, a mixed waveform of the frequencies f1 and f2 can be observed during the foreign object detection period. Then, as described with reference to FIGS. 6 and 7, the power transmission device 101 and the power reception device 102 can detect the presence or absence of a foreign object from this waveform attenuation index (S1107, S1206). By performing the operations as described above, the power transmission device 101 and the power reception device 102 can observe the waveform attenuation of a mixed wave of two frequencies instead of one frequency. Then, by observing the waveform attenuation index of this mixed wave, the power transmission device 101 and the power reception device 102 can improve the accuracy of foreign object detection.

[0072] A method for detecting a foreign object from a mixed wave of two frequencies will be described. As shown in FIG. 8, during the foreign object detection period, a waveform in which two frequencies are mixed is observed. By observing the time waveform of the attenuation waveform of the mixed wave, the attenuation rate of each waveform of f1 and f2 can be specified. For example, as shown in FIG. 8, the attenuation state of the waveform of the frequency f1 and the attenuation state of the waveform of the frequency f2 can be specified respectively. The method for specifying the waveform attenuation index from the respective attenuation waveforms of these frequencies f1 and f2 is as described above in relation to FIGS. 6 and 7.

[0073] The power transmission device 101 or the power reception device 102 calculates in advance the waveform attenuation indexes in the state where there are no foreign objects at frequencies f1 and f2, respectively. Then, the power transmission device 101 or the power reception device 102 calculates the threshold value for frequency f1 based on the waveform attenuation index in the state where there is no foreign object at frequency f1, and calculates the threshold value for frequency f2 based on the waveform attenuation index in the state where there is no foreign object at frequency f2. The power transmission device 101 or the power reception device 102 compares the waveform attenuation index specified from the observed attenuation waveform of frequency f1 with the threshold value calculated for frequency f1. Also, the power transmission device 101 or the power reception device 102 compares the waveform attenuation index specified from the observed attenuation waveform of frequency f2 with the threshold value calculated for frequency f2. Then, when the waveform attenuation index of frequency f1 exceeds the threshold value and the waveform attenuation index of frequency f2 exceeds the threshold value, the power transmission device 101 or the power reception device 102 determines that "a foreign object exists" or "there is a high possibility that a foreign object exists". Also, the power transmission device 101 or the power reception 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 of frequency f1 exceeds the threshold value, or when the waveform attenuation index of frequency f2 exceeds the threshold value. That is, the power transmission device 101 or the power reception device 102 can determine that "a foreign object exists" or "there is a high possibility that a foreign object exists" when the waveform attenuation index of either one of frequencies f1 and f2 exceeds the threshold value. Thereby, it becomes possible to more reliably detect a foreign object.

[0074] Note that, as described above, the mixed wave of the frequency f1 and the frequency f2 can be observed in both the power transmission device 101 and the power reception device 102. Therefore, the above-described "method for detecting a foreign object from a mixed wave of two frequencies" can be executed in either the power transmission device 101 or the power reception device 102. Further, in the above-described embodiment, an example in which the threshold value of the frequency f1 and the threshold value of the frequency f2 are set separately has been described. However, the present invention is not limited to this, and the same value may be set as these threshold values. Further, when the switch 209 is turned on, the power transmission device 101 may turn off the switch 208 to disconnect the power transmission antenna 205 and the resonance capacitor 207 from the power transmission unit 203. Thereby, when detecting a foreign object by the waveform attenuation method, it is possible to exclude the influence of the power transmission unit, and it is possible to detect a foreign object with higher accuracy. Further, when the switch 309 is turned on, the power reception device 102 may turn off the switch 315 to disconnect the power reception antenna 305 and the resonance capacitor 312 from the power reception unit 303. Thereby, when detecting a foreign object by the waveform attenuation method, it is possible to exclude the influence of the power transmission unit, and it is possible to detect a foreign object with higher accuracy.

[0075] When at least one of the power transmission device 101 and the power reception device 102 operates as described above and detects a foreign object based on the characteristics of the voltage or current at a plurality of frequencies (here, the waveform attenuation index of the attenuation waveform), it becomes possible to detect the foreign object with higher accuracy.

[0076] (Modification Example 1 of the Foreign Object Detection Method by the Waveform Attenuation Method Using a Plurality of Frequencies) In the above example, a method for detecting a foreign object based on the time waveforms (attenuation waveforms) of frequencies f1 and f2 was described. In this modification example, instead of the time waveforms of frequencies f1 and f2, a foreign object is detected from the signal spectra of frequencies f1 and f2. That is, when foreign object detection is performed based on a time waveform, if noise is mixed in and the time waveform is disturbed, it may become difficult to specify a waveform attenuation index. In contrast, in this modification example, arithmetic processing is executed on the time waveform to specify the signal spectrum (signal intensity, frequency spectrum) for each frequency, and a foreign object is detected based on the signal spectrum, thereby enabling robust foreign object detection against disturbances in the time waveform.

[0077] In this modification example, for example, the power transmission device 101 or the power reception device 102 executes arithmetic processing on the waveform of the analysis target section as shown in FIG. 8, and converts it into a form capable of specifying at least the components of frequencies f1 and f2 in the frequency domain. The power transmission device 101 or the power reception device 102 can specify the signal spectrum (signal intensity, 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 intensity, frequency spectrum) for each frequency of the analysis target section is specified as shown in FIG. 9, for example. When a foreign object exists between the power transmission device 101 and the power reception device 102, energy is consumed by the foreign object, so the intensity of the signal spectrum as shown in FIG. 9 also weakens.

[0078] Therefore, the power transmission device 101 or the power reception device 102 performs foreign object detection by utilizing this characteristic. For example, the power transmission device 101 or the power reception device 102 specifies the signal spectra of the frequencies f1 and f2 in the state where no foreign object is present. Then, the power transmission device 101 or the power reception device 102 calculates the threshold value of the frequency f1 based on the signal spectrum of the frequency f1 in the state where no foreign object is present. Also, the power transmission device 101 or the power reception device 102 calculates the threshold value of the frequency f2 based on the signal spectrum of the frequency f2 in the state where no foreign object is present. Then, the power transmission device 101 or the power reception device 102 compares the signal spectrum specified from the observed attenuation waveform of the frequency f1 with the threshold value of the frequency f1. Also, the power transmission device 101 or the power reception device 102 compares the signal spectrum specified from the observed attenuation waveform of the frequency f2 with the threshold value of the frequency f2. And, when the signal spectrum of the frequency f1 exceeds the threshold value and the signal spectrum of the frequency f2 exceeds the threshold value, the power transmission device 101 or the power reception device 102 determines that "a foreign object is present" or "there is a high possibility that a foreign object is present". Also, when the signal spectrum of the frequency f1 exceeds the threshold value, or when the signal spectrum of the frequency f2 exceeds the threshold value, the power transmission device 101 or the power reception device 102 determines that "a foreign object is present" or "there is a high possibility that a foreign object is present". That is, when the signal spectrum of at least one of the frequency f1 and the frequency f2 exceeds the threshold value, the power transmission device 101 or the power reception device 102 determines that "a foreign object is present" or "there is a high possibility that a foreign object is present".

[0079] Thereby, it becomes possible to perform foreign object detection more reliably. As described above, the mixed wave of the frequencies f1 and f2 can be observed in both the power transmission device 101 and the power reception device 102. Therefore, the foreign object detection method according to this modified example can also be executed in either the power transmission device 101 or the power reception device 102. Also, in this modified example as well, the threshold value of the frequency f1 and the threshold value of the frequency f2 may be set separately or may be set to the same value.

[0080] In this way, by at least one of the power transmission device 101 and the power reception device 102 operating as described above and performing foreign object detection based on the signal spectra of a plurality of frequencies, it becomes possible to detect foreign objects with higher accuracy.

[0081] (Modification Example 2 of the Foreign Object Detection Method Using the Waveform Attenuation Method with a Plurality of Frequencies) In the above-described configuration, a method of detecting a foreign object based on the time waveform of the mixed wave of frequencies f1 and f2 or the signal spectra at frequencies f1 and f2 of the time waveform has been described. At this time, in the configuration as described above, when frequencies f1 and f2 are very close frequencies, the correlation of energy consumption by foreign objects at these frequencies is high, and the merit of performing foreign object detection using a plurality of frequencies is reduced. Also, when the difference between frequency f1 and frequency f2 is slight, "beats" occur in the composite wave, and foreign object detection as described above may become difficult. For this reason, in this modification example, frequencies different from these frequencies are used instead of frequencies f1 and f2, or additional frequencies are used in addition to frequencies f1 and f2 to detect foreign objects.

[0082] For example, it is stipulated that the frequency f1 determined by the power transmission antenna 205 and the resonance capacitor 207 of the power transmission device 101 and the frequency f2 determined by the power reception antenna 305 and the resonance capacitor 312 of the power reception device 102 are each included within a predetermined frequency range. Here, the predetermined frequency ranges are each stipulated so that frequency f1 and frequency f2 are separated by a predetermined frequency width in advance. Then, the values of the inductance and capacitance in the power transmission antenna 205 and the resonance capacitor 207 of the power transmission device 101 and the power reception antenna 305 and the resonance capacitor 312 of the power reception device 102 are determined so as to be included in their respective frequency ranges. Thereby, it becomes possible to separate frequency f1 and frequency f2 by a predetermined frequency width, and more accurate foreign object detection becomes possible.

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

[0084] Note that, as described above, foreign object detection can be performed based on the characteristics (such as the attenuation rate of the time waveform, etc.) of the voltage or current in the resonant circuit at three or more frequencies. At this time, when the characteristic at one of the three or more frequencies exceeds the threshold value, it can be determined that a foreign object is present. Also, when the characteristics at two or more (for example, all) of the three or more frequencies exceed the threshold value, it may be determined that a foreign object is present.

[0085] Also, the frequency f1 determined by the power transmission antenna 205 and the resonant capacitor 207 of the power transmission device 101 may be controlled to be 13.56 MHz or in the vicinity thereof, which is the frequency band used in NFC (Near Field Communication). Instead of this, or in addition to this, the frequency f2 determined by the power reception antenna 305 and the resonant capacitor 312 of the power reception device 102 may be controlled to be 13.56 MHz or in the vicinity thereof, which is the frequency band used in NFC. For this purpose, the power transmission device 101 or the power reception device 102 appropriately sets at least one of the inductance and the capacitance as described above, or controls the resonant frequency to be 13.56 MHz by controlling the switch. Thereby, even if a device using NFC or an NFC tag, which is not the power reception device 102, is placed on the power transmission device 101, it is possible to detect it. Note that NFC is an example, and the frequency used in other wireless standards may be used as the resonant frequency in the power transmission device 101 or the power reception device 102. Thereby, the power transmission device 101 or the power reception device 102 can detect that a device conforming to the wireless standard is placed.

[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 that the state of the power transmitting device 101 or the power receiving device 102 has changed, and determines whether it is necessary to update or add a threshold value used for foreign object detection by the waveform attenuation method. Then, when the power receiving device 102 determines that it is necessary to update or add the threshold value, it transmits a command for executing foreign object detection by the Power Loss method to the power transmitting device 101. In response to receiving this command, the power transmitting device 101 executes foreign object detection by the Power Loss method and determines the presence or absence of a foreign object. Then, when the power transmitting device 101 determines that no foreign object exists or the possibility of no foreign object existing is high, it notifies the power receiving device 102 that there is no foreign object. The power receiving device 102 executes operations for setting the threshold value used for foreign object detection by the waveform attenuation method and for updating or adding the threshold value. That is, when notified that there is no foreign object, the power receiving device 102 transmits a command to the power transmitting device 101 requesting the execution of measurements for setting the threshold value of foreign object detection by the waveform attenuation method. Then, in response to receiving this command, the power transmitting device 101 temporarily stops power transmission. Also, the power transmitting device 101 and the power receiving device 102 control the circuit as described above to measure the waveform attenuation index and signal spectrum of frequencies f1 and f2. Then, the power transmitting device 101 calculates the threshold value of foreign object detection by the waveform attenuation method using the measured waveform attenuation index and signal spectrum and sets it as the threshold value.

[0089] As described above, when the power receiving device 102 determines that it is necessary to update or change the threshold value of the waveform attenuation method, immediately before performing the operations therefor, it causes the power transmitting device 101 to confirm that no foreign object exists by the Power Loss method. Then, in response to the confirmation that no foreign object exists, the power receiving device 102 executes operations for updating or changing the threshold value of the waveform attenuation method. Thereby, when measuring for setting the threshold value of foreign object detection by the waveform attenuation method, the probability of the state of no foreign object existing can be made sufficiently high, and it becomes possible to set the foreign object detection threshold value more accurately.

[0090] In the above example, before performing the operation for updating and changing the threshold value of the waveform attenuation method, a method for confirming the absence of foreign matter by the Power Loss method was described. However, even in the Power Loss method, there is a threshold value for determining the presence or absence of foreign matter. And regarding this threshold value of the Power Loss method, similar to the waveform attenuation method, when the state of the power transmission device 101 or the power reception device 102 changes, it may be necessary to update or add the threshold value. This update or addition of the threshold value can be performed in the Power Transfer phase. That is, similar to the above method, when the power reception device 102 determines that it will perform the operation for setting, updating, or changing the threshold value of the Power Loss method, immediately before performing the operation therefor, it executes the process for confirming the absence of foreign matter by the waveform attenuation method. Then, the power reception device 102 can execute the operation for updating or changing the threshold value of the Power Loss method in response to the confirmation that no foreign matter is present by the waveform attenuation method. For example, when the power reception device 102 determines that it is necessary to update or add the threshold value used for foreign matter detection by the Power Loss method, it transmits a command for executing foreign matter detection by the waveform attenuation method to the power transmission device 101. In response to receiving this command, the power transmission device 101 executes foreign matter detection by the waveform attenuation method and determines the presence or absence of foreign matter. Then, when the power transmission device 101 determines that no foreign matter is present or that the possibility of the presence of foreign matter is low, it notifies the power reception device 102 that there is no foreign matter. When notified that no foreign matter is present, the power reception device 102 executes the operation for updating or adding the threshold value used for foreign matter detection by the Power Loss method. That is, the power reception device 102 transmits a command to the power transmission device 101 requesting the execution of measurement for setting the threshold value of foreign matter detection by the Power Loss method in order to update or add the threshold value used for foreign matter detection. Then, the power reception device 102 controls the load so that it has a configuration corresponding to the power transmission power of the threshold value (point) to be updated or added. When receiving the command, the power transmission device 101 calculates and sets the threshold value of foreign matter detection by the Power Loss method.As a result, when performing measurements for setting the threshold for foreign object detection by the Power Loss method, the probability that there is no foreign object can be made sufficiently high, and the foreign object detection threshold can be set more accurately. Also, in the above embodiments, power transmission is stopped for foreign object detection, but instead of completely stopping the power transmission, for example, the power may be suppressed to a power close to zero.

[0091] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and having one or more processors in a computer of the system or apparatus read and execute the program. Further, it can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.

[0092] The invention is not limited to the above embodiments, and various changes and modifications are possible without departing from the spirit and scope of the invention. Therefore, the claims are attached to disclose the scope of the invention.

Explanation of Reference Numerals

[0093] 101: Power transmission device, 201: Control unit, 203: Power transmission unit, 205: Power transmission antenna, 207, 212 to 213: Resonance capacitor

Claims

1. Power receiving means for wirelessly receiving power from a power transmission device, Communication means for communicating with the power transmission device, Determination means for determining a frequency based on communication with the power transmission device, Measurement means for measuring a voltage during power reception at the determined frequency, Processing means for performing processing related to foreign object detection using the measured voltage, comprising: The power receiving device, wherein the frequency is a frequency related to the processing related to foreign object detection.

2. The power receiving device according to claim 1, wherein the measurement means measures the voltage during a period in which power transmission is restricted.

3. The determination means determines a first frequency and a second frequency based on communication with the power transmission device, The measurement means measures a voltage for the first frequency and a voltage for the second frequency, The power receiving device according to claim 1 or 2, wherein the processing means performs the processing based on the voltage for the first frequency and the voltage for the second frequency.

4. A method performed by a power receiving device, determining a frequency based on communication with a power transmission device, measuring a voltage during power reception at the determined frequency, performing processing related to foreign object detection using the measured voltage, The method, wherein the frequency is a frequency related to the processing related to foreign object detection.

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