Power transmission device and method to be performed by the same

Abstract

To appropriately control the detection process in a case where multiple detection methods can be executed for detecting an object different from a receiving device when performing wireless power transmission.SOLUTION: A wireless power transmission system transmits power from a power transmission device to a power receiving device via wireless transmission. The system periodically executes detection processing using a first detection method for detecting an object different from the receiving device. The system also determines whether a predetermined condition regarding the status of at least one of the power transmission device and the power receiving device has been satisfied. The system then executes detection processing of the object using a second detection method that differs from the first detection method in accordance with the results of the predetermined condition determination.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to wireless power transmission technology. [Background technology]

[0002] In recent years, technological development of wireless power transmission systems has been widely carried out. Patent Document 1 discloses a foreign object detection method in accordance with the Wireless Power Consortium (WPC) standard. Patent Document 2 discloses a foreign object detection method in which a power transmitting device transmits a foreign object detection signal to a power receiving device and determines the presence or absence of a foreign object using an echo signal from the power receiving device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-70074 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-27172 Summary of the Invention [Problem to be solved by the invention]

[0004] The foreign object detection method (power loss method) disclosed in Patent Document 1 detects a foreign object, which is an object other than a power receiving device, based on the measurement results of power loss that occurs between a power transmitting device and a power receiving device during power transmission from the power transmitting device to the power receiving device. On the other hand, the foreign object detection method disclosed in Patent Document 2 detects a foreign object based on the measurement results of the attenuation state of a signal transmitted by the power transmitting device. As described above, there are several possible methods for detecting a foreign object when wireless power transmission is performed, but no method has been established for appropriately controlling the detection process when these several detection methods are feasible.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to appropriately control the detection process when multiple detection methods for detecting an object other than a power receiving device can be implemented when performing wireless power transmission. [Means for solving the problem]

[0006] As one means for solving the above problem, the power transmission device of the present invention has the following configuration: That is, the power transmission device has a power transmission means that wirelessly transmits power to a power receiving device, a first detection means that periodically executes a detection process by a first detection method that detects an object different from the power receiving device based on a power loss related to power transmission by the power transmission means, a determination means that determines whether a predetermined condition related to the state of at least one of the power transmission device and the power receiving device is satisfied, and a second detection means that executes a detection process by a second detection method that detects the object based on at least one of a voltage attenuation state and a current attenuation state related to power transmission by the power transmission means, depending on the result of the determination by the determination means. [Effects of the Invention]

[0007] According to the present invention, when a plurality of detection methods for detecting an object other than a power receiving device can be implemented for wireless power transmission, the detection process can be appropriately controlled. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram illustrating an example of the configuration of a power transmission device. [Figure 2] FIG. 2 is a diagram illustrating a configuration example of a power receiving device. [Figure 3] FIG. 2 is a block diagram illustrating an example of a functional configuration of a control unit of the power transmitting device. [Figure 4] FIG. 1 is a diagram illustrating a configuration example of a wireless power transmission system. [Figure 5] FIG. 10 is a sequence diagram illustrating an example of a process for wireless power transmission. [Figure 6] 10A and 10B are diagrams for explaining foreign object detection using a waveform attenuation method. [Figure 7]10A and 10B are diagrams for explaining a method for detecting a foreign object based on a power transmission waveform during power transmission. [Figure 8] 10 is a flowchart illustrating an example of processing in a power transfer phase of a power transmitting device. [Figure 9] 10 is a flowchart illustrating an example of processing in a power transfer phase of a power receiving device. [Figure 10] 10A and 10B are diagrams for explaining a method for setting a threshold value in foreign matter detection using the Power Loss method. [Figure 11] 10A and 10B are diagrams for explaining a method for setting a threshold value in detecting foreign matter using a waveform attenuation method. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Although the embodiments describe a plurality of features, not all of these features are necessarily essential to the invention, and the plurality of features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components.

[0010] [Wireless power transmission system configuration] 4 shows an example of the configuration of a wireless power transmission system (wireless charging system) according to this embodiment. In one example, this system includes a power receiving device 401 and a power transmitting device 402. Detailed configurations of the power receiving device 401 and the power transmitting device 402 will be described later with reference to FIGS. 2 and 1. Hereinafter, the power receiving device 401 may be referred to as RX, and the power transmitting device 402 may be referred to as TX. The RX is an electronic device that receives power from the TX and charges its built-in battery. The TX is an electronic device that wirelessly transmits power to the RX placed on a charging stand 403, which is part of the TX. Hereinafter, since the charging stand 403 is part of the TX, "placed on the charging stand 403" may be referred to as "placed on the TX (power transmitting device 402)." The area 404 enclosed by the dotted line is the range in which the RX can receive power from the TX. The RX and TX may have a function to execute applications other than wireless charging. An example of the RX is a smartphone, and an example of the TX is an accessory device for charging the smartphone. The RX and TX may be a tablet, a storage device such as a hard disk drive or a memory device, or an information processing device such as a personal computer (PC). Furthermore, RX and TX may be, for example, an imaging device (such as a camera or video camera), an automobile, a robot, a medical device, a printer, or the like.

[0011] In this system, wireless power transmission is performed using an electromagnetic induction method for wireless charging based on the WPC standard. That is, the RX and TX perform wireless power transmission for wireless charging based on the WPC standard between the RX power receiving antenna 205 and the TX power transmitting antenna 105. Note that the wireless power transmission method applied to this system is not limited to the method specified by the WPC standard, and may be other methods such as electromagnetic induction, magnetic field resonance, electric field resonance, microwave, or laser. In addition, in this embodiment, wireless power transmission is used for wireless charging, but wireless power transmission may also be performed for purposes other than wireless charging.

[0012] In the WPC standard, the amount of power guaranteed when power receiving device 401 receives power from power transmitting device 402 is defined by a value called guaranteed power (hereinafter referred to as "GP"). GP indicates a power value that is guaranteed to be output to a load (e.g., a charging circuit, a battery, etc.) of power receiving device 401, even if the positional relationship between power receiving device 401 and power transmitting device 402 fluctuates and the power transmission efficiency between power receiving antenna 205 and power transmitting antenna 105 decreases. For example, if GP is 5 watts, power transmitting device 402 transmits power by controlling so as to be able to output 5 watts to the load in power receiving device 401, even if the positional relationship between power receiving antenna 205 and power transmitting antenna 105 fluctuates and the power transmission efficiency decreases.

[0013] Furthermore, when transmitting power from power transmitting device 402 to power receiving device 401, if a foreign object other than power receiving device 401 is present near power transmitting device 402, the electromagnetic waves used for power transmission may affect the foreign object, raising its temperature or even destroying it. Therefore, the WPC standard specifies a method for power transmitting device 402 to detect the presence of a foreign object on charging stand 403, so that the power transmitting device can prevent the foreign object from heating up or being destroyed by stopping power transmission if a foreign object is present. Specifically, the WPC standard specifies a power loss method for detecting a foreign object based on the difference between the transmitted power in power transmitting device 402 and the received power in power receiving device 401. Also, a Q-factor measurement method is defined for detecting foreign objects based on changes in the quality factor (Q-factor) of the power transmitting antenna 105 (power transmitting coil) in the power transmitting device 402. Note that the foreign object detected by the power transmitting device 402 in this embodiment is not limited to an object present on the charging stand 403. The power transmitting device 402 only needs to detect a foreign object located near the power transmitting device 402, and may detect a foreign object located within a range where the power transmitting device 402 can transmit power, for example.

[0014] Foreign object detection based on the power loss method defined in the WPC standard will be described with reference to Fig. 10. The horizontal axis of Fig. 10 represents the transmitted power of power transmitting device 402, and the vertical axis represents the received power of power receiving device 401. Note that a foreign object is an object other than power receiving device 401 that may affect power transmission from power transmitting device 402 to power receiving device 401, such as an object such as a conductive metal piece.

[0015] First, the power transmitting device 402 transmits power to the power receiving device 401 at a first transmission power value Pt1. The power receiving device 401 receives power at a first reception power value Pr1 (this state is called a light load state). Then, the power transmitting device 402 stores the first transmission power value Pt1. Here, the first transmission power value Pt1 or the first reception power value Pr1 is a predetermined minimum transmission power or reception power. At this time, the power receiving device 401 controls the load so that the received power is minimum power. For example, the power receiving device 401 may disconnect the load from the power receiving antenna 205 so that the received power is not supplied to the load (such as a charging circuit and a battery). Next, the power receiving device 401 reports the power value Pr1 of the first reception power to the power transmitting device 402. The power transmitting device 402, which receives Pr1 from the power receiving device 401, calculates that the power loss between the power transmitting device 402 and the power receiving device 401 is Pt1-Pr1 (=Ploss1), and can create a calibration point 1000 that shows the correspondence between Pt1 and Pr1.

[0016] Next, the power transmitting device 402 changes the transmission power value to the second transmission power value Pt2 and transmits power to the power receiving device 401. The power receiving device 401 receives power at the second reception power value Pr2 (this state is called a connected load state). The power transmitting device 402 then stores the second transmission power value Pt2. Here, the second transmission power value Pt2 or the second reception power value Pr2 is a predetermined maximum transmission power or reception power. At this time, the power receiving device 401 controls the load so that the received power is the maximum power. For example, the power receiving device 401 connects the power receiving antenna 205 to the load so that the received power is supplied to the load. Next, the power receiving device 401 reports Pr2 to the power transmitting device 402. The power transmitting device 402, which receives Pr2 from the power receiving device 401, calculates that the power loss between the power transmitting device 402 and the power receiving device 401 is Pt2-Pr2 (=Ploss2), and can create a calibration point 1001 showing the correspondence between Pt2 and Pr2.

[0017] The power transmitting device 402 then creates a straight line 1002 that linearly interpolates between the calibration point 1000 and the calibration point 1001. The straight line 1002 represents the relationship between the transmitted power and the received power in a state where no foreign object is present near the power transmitting device 402 and the power receiving device 401. Based on the straight line 1002, the power transmitting device 402 can predict the power value that the power receiving device 401 will receive when transmitting power at a predetermined transmitted power in a state where no foreign object is present. For example, if the power transmitting device 402 transmits power at a third transmitted power value Pt3, it can estimate from point 1003 on the straight line 1002 that corresponds to Pt3 that the third received power value that the power receiving device 401 will receive will be Pr3.

[0018] As described above, the power loss between the power transmitting device 402 and the power receiving device 401 corresponding to the load can be determined based on multiple combinations of the transmitted power value of the power transmitting device 402 and the received power value of the power receiving device 401 measured while changing the load. Furthermore, the power loss between the power transmitting device 402 and the power receiving device 401 corresponding to all loads can be estimated by interpolating from multiple combinations. In this way, the calibration process performed by the power transmitting device 402 and the power receiving device 401 so that the power transmitting device 402 acquires combinations of transmitted power values ​​and received power values ​​will be referred to below as "calibration process (CAL process) using the power loss method."

[0019] Assume that after calibration, when power transmitting device 402 actually transmits power to power receiving device 401 at Pt3, power transmitting device 402 receives a received power value Pr3' from power receiving device 401. Power transmitting device 402 calculates a value Pr3-Pr3' (=Ploss_FO) by subtracting the received power value Pr3' actually received from power receiving device 401 from the received power value Pr3 in a state where no foreign object is present. This Ploss_FO can be considered to be the power loss due to power consumed by a foreign object when a foreign object is present near power transmitting device 402 and power receiving device 401. Therefore, when power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold, it can be determined that a foreign object is present. Alternatively, power transmitting device 402 may calculate in advance the power loss Pt3-Pr3 (=Ploss3) between power transmitting device 402 and power receiving device 401 from the received power value Pr3 in a state where no foreign object is present. Next, the power loss Pt3-Pr3' (=Ploss3') between the power transmitting device 402 and the power receiving device 401 in the presence of the foreign object is calculated from the received power value Pr3' received from the power receiving device 401 in the presence of the foreign object. Then, the power Ploss_FO that would have been consumed by the foreign object may be estimated using Ploss3'-Ploss3 (==Ploss_FO).

[0020] As described above, the power Ploss_FO that would have been consumed by a foreign object may be calculated as Pr3-Pr3' (=Ploss_FO) or as Ploss3'-Ploss3 (=Ploss_FO). In the following description, the method of calculating Ploss3'-Ploss3 (=Ploss_FO) will be basically described, but the contents of this embodiment can also be applied to the method of calculating Pr3-Pr3' (=Ploss_FO). This concludes the description of foreign object detection based on the Power Loss method.

[0021] Foreign object detection using the Power Loss method is performed during power transmission (the Power Transfer phase, described later) based on data obtained in the Calibration phase, described later. Foreign object detection using the Q-factor measurement method is performed before power transmission (before sending a Digital Ping, the Negotiation phase, or the Renegotiation phase, described later).

[0022] In this embodiment, the RX and TX communicate for power transmission and reception control based on the WPC standard. The WPC standard defines multiple phases, including a power transfer phase in which power transmission is performed and one or more phases before the actual power transmission, and communication for the necessary power transmission and reception control is performed in each phase. 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. Note that the identification and configuration phase will be referred to as the I&C phase below. The processing in each phase will be described below.

[0023] In the Selection phase, the TX intermittently transmits Analog Pings to detect that an object has been placed on the charging base of the TX (for example, that the RX or a conductor piece has been placed on the charging base). The TX detects at least one of the voltage value and current value of the power transmitting antenna 105 when the Analog Ping is transmitted, and if the voltage value is below a certain threshold or the current value exceeds a certain threshold, it determines that an object is present and transitions to the Ping phase.

[0024] In the Ping phase, the TX transmits a Digital Ping with higher power than the Analog Ping. The power of the Digital Ping is sufficient to start the control unit of the RX placed on the TX. The RX notifies the TX of the magnitude of the received voltage. In this way, the TX recognizes that the object detected in the Selection phase is the RX by receiving a response from the RX that received the Digital Ping. Upon receiving notification of the received voltage value, the TX transitions to the I&C phase. Furthermore, before transmitting the Digital Ping, the TX measures the Q-factor of the power transmitting antenna 105. This measurement result is used when performing foreign object detection processing using the Q-factor measurement method.

[0025] In the I&C phase, the TX identifies the RX and obtains 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). Upon receiving the ID packet and configuration packet, the TX responds with an acknowledgement (ACK, positive response). Then the I&C phase ends.

[0026] In the Negotiation phase, the GP value is determined based on the GP value requested by the RX and the power transmission capability of the TX. The TX also performs foreign object detection processing using the Q-factor measurement method in response to a request from the RX. The WPC standard also specifies a method in which, after transitioning to the Power Transfer phase, the same processing as in the Negotiation phase is performed again at the request of the RX. The phase in which these processing steps are performed after transitioning from the Power Transfer phase is called the Renegotiation phase.

[0027] In the calibration phase, calibration is performed based on the WPC standard. In addition, RX notifies TX of the specified received power value (received power value under light load / full load), and TX adjusts the power for efficient transmission. The received power value notified to the TX can be used for foreign object detection processing using the Power Loss method.

[0028] In the power transfer phase, control is performed to start and continue power transmission, and to stop power transmission due to an error or full charge. For this power transmission and reception control, TX and RX use the power transmitting antenna 105 and power receiving antenna 205 used when performing wireless power transmission based on the WPC standard to communicate by superimposing a signal on the electromagnetic waves transmitted from the power transmitting antenna 105 or power receiving antenna 205. The range in which communication based on the WPC standard between TX and RX is possible is approximately the same as the power transmission range of TX.

[0029] [Configuration of power transmitting device 402 and power receiving device 401] Next, the configurations of the power transmitting device 402 (TX) and the power receiving device 401 (RX) in this embodiment will be described. Note that the configurations described below are merely examples, and part (or in some cases the whole) of the described configurations may be replaced with other configurations that perform similar functions or may be omitted, or additional configurations may be added to the described configurations. Furthermore, one block described below may be divided into multiple blocks, or multiple blocks may be integrated into one block. Furthermore, although the functions of each functional block described below are implemented as a software program, some or all of the components included in this functional block may be implemented in hardware.

[0030] Fig. 1 is a functional block diagram showing an example of the configuration of a power transmitting device 402 (TX) according to this embodiment. The TX has a control unit 101, a power supply unit 102, a power transmitting unit 103, a communication unit 104, a power transmitting antenna 105, a memory 106, a resonant capacitor 107, and a switch 108. In Fig. 1, the control unit 101, the power supply unit 102, the power transmitting unit 103, the communication unit 104, and the memory 106 are depicted as separate entities, but any two or more of these functional blocks may be implemented on the same chip.

[0031] The control unit 101 controls the entire TX by executing a control program stored in the memory 106, for example. The control unit 101 also controls power transmission control, including communication for device authentication in the TX. The control unit 101 may also control the execution of applications other than wireless power transmission. The control unit 101 includes one or more processors, such as a CPU (Central Processing Unit) or an MPU (Microprocessor Unit). The control unit 101 may also be configured with hardware, such as an Application Specific Integrated Circuit (ASIC). The control unit 101 may also be configured with an array circuit, such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processes. The control unit 101 stores information to be stored during the execution of various processes in the memory 106. The control unit 101 may also measure time using a timer (not shown).

[0032] The power supply unit 102 supplies power to each functional block. The power supply unit 102 is, for example, a commercial power supply or a battery. The battery stores power supplied from the commercial power supply.

[0033] The power transmitting unit 103 converts DC or AC power input from the power supply unit 102 into AC power in a frequency band used for wireless power transmission, and inputs the AC power to the power transmitting antenna 105 to generate electromagnetic waves for receiving power at the RX. For example, the power transmitting unit 103 converts the DC voltage supplied by the power supply unit 102 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 transmitting unit 103 includes a gate driver that controls the ON / OFF of the FETs.

[0034] The power transmitting unit 103 controls the intensity of the electromagnetic waves to be output by adjusting the voltage (power transmission voltage) or current (power transmission current), or both, input to the power transmitting antenna 105. Increasing the power transmission voltage or power transmission current increases the intensity of the electromagnetic waves, and decreasing the power transmission voltage or power transmission current decreases the intensity of the electromagnetic waves. Furthermore, the power transmitting unit 103 controls the output of AC power so as to start or stop power transmission from the power transmitting antenna 105 based on instructions from the control unit 101. Furthermore, the power transmitting unit 103 is assumed to be capable of supplying enough power to output 15 watts (W) to the charging unit 206 of the power receiving device 401 (RX) that complies with the WPC standard.

[0035] The communication unit 104 communicates with the RX for power transmission control based on the WPC standard as described above. The communication unit 104 modulates electromagnetic waves output from the power transmitting antenna 105 and transmits information to the RX to perform communication. The communication unit 104 also demodulates the electromagnetic waves modulated by the RX and transmitted from the power transmitting antenna 105 to acquire information transmitted by the RX. That is, the communication performed by the communication unit 104 is performed by superimposing a signal on the electromagnetic waves transmitted from the power transmitting antenna 105. The communication unit 104 may also communicate with the RX using an antenna different from the power transmitting antenna 105 and based on a standard different from the WPC standard, or may communicate with the RX by selectively using multiple communication methods.

[0036] The memory 106 can store the control program as well as the TX and RX states (transmitted power value, received power value, etc.). For example, the TX state is acquired by the control unit 101, and the RX state is acquired by the RX control unit 201, and can be received via the communication unit 104.

[0037] The switch 108 is controlled by the control unit 101. The power transmitting antenna 105 is connected to a resonant capacitor 107, and when the switch 108 is turned on and short-circuited, the power transmitting antenna 105 and the resonant capacitor 107 form a series resonant circuit that resonates at a specific frequency f1. At this time, a current flows through a closed circuit formed by the power transmitting antenna 105, the resonant capacitor 107, and the switch 108. When the switch 108 is turned off and opened, power is supplied from the power transmitting unit 103 to the power transmitting antenna 105 and the resonant capacitor 107.

[0038] 2 is a block diagram showing an example of the configuration of a power receiving device 401 (RX) according to this embodiment. The RX includes a control unit 201, a UI (user interface) unit 202, a power receiving unit 203, a communication unit 204, a power receiving antenna 205, a charging unit 206, a battery 207, a memory 208, a first switch unit 209, a second switch unit 210, and a resonant capacitor 211. Note that the multiple functional blocks shown in FIG. 2 may be realized as one hardware module.

[0039] The control unit 201 controls the entire RX by executing a control program stored in, for example, the memory 208. That is, the control unit 201 controls each of the functional units shown in FIG. Furthermore, the control unit 201 may perform control for executing applications other than wireless power transmission. An example of the control unit 201 is configured to include one or more processors such as a CPU or an MPU. Note that the control unit 201 may control the entire RX (if the RX is a smartphone, the entire smartphone) in cooperation with an OS (Operating System) that it is running.

[0040] The control unit 201 may also be configured with hardware such as an ASIC. The control unit 201 may also be configured to include an array circuit such as an FPGA compiled to execute predetermined processes. The control unit 201 stores information to be stored while executing various processes in the memory 208. The control unit 201 may also measure time using a timer (not shown).

[0041] The UI unit 202 performs various outputs to the user. The various outputs referred to here include screen display, blinking or color changes of LEDs (Light Emitting Diodes), audio output from a speaker, vibration of the RX main unit, etc. The UI unit 202 is realized by a liquid crystal panel, speaker, vibration motor, etc.

[0042] The power receiving unit 203 acquires, via the power receiving antenna 205, AC power (AC voltage and AC current) generated by electromagnetic induction based on electromagnetic waves radiated from the power transmitting antenna 105 of the TX. Then, power receiving unit 203 converts AC power into DC power or AC power of a predetermined frequency, and outputs the power to charging unit 206, which performs processing to charge battery 207. That is, power receiving unit 203 includes a rectification unit and a voltage control unit necessary for supplying power to the load in RX. The above-mentioned GP is the amount of power guaranteed to be output from power receiving unit 203. It is assumed that power receiving unit 203 has the capacity to supply power for charging unit 206 to charge battery 207 and to output 15 watts of power to charging unit 206.

[0043] The communication unit 204 communicates with the communication unit 104 of the TX for power receiving control based on the WPC standard as described above. The communication unit 204 demodulates the electromagnetic waves input from the power receiving antenna 205 to acquire information transmitted from the TX. The communication unit 204 then performs load modulation on the input electromagnetic waves to superimpose a signal related to information to be transmitted to the TX onto the electromagnetic waves, thereby communicating with the TX. Note that the communication unit 204 may communicate with the TX using a standard other than the WPC standard using an antenna other than the power receiving antenna 205, or may communicate with the TX by selectively using multiple communication methods.

[0044] The memory 208 stores the control program and also stores the TX and RX states. For example, the RX state is acquired by the control unit 201, and the TX state is acquired by the TX control unit 101 and can be received via the communication unit 204.

[0045] The first switch unit 209 and the second switch unit 210 are controlled by the control unit 201 . The power receiving antenna 205 is connected to the resonant capacitor 211, and when the second switch unit 210 is turned on and short-circuited, the power receiving antenna 205 and the resonant capacitor 211 form a series resonant circuit that resonates at a specific frequency f2. At this time, current flows through the closed circuit formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210, and no current flows through the power receiving unit. When the second switch unit 210 is turned off and opened, the power received by the power receiving antenna 205 and the resonant capacitor 211 is supplied to the power receiving unit 203.

[0046] First switch unit 209 controls whether or not to supply the received power to a battery, which is a load. It also has a function of controlling the load value. When first switch unit 209 connects charging unit 206 and battery 207, the received power is supplied to battery 207. When first switch unit 209 disconnects the connection between charging unit 206 and battery 207, the received power is not supplied to battery 207. Note that, although first switch unit 209 is arranged between charging unit 206 and battery 207 in FIG. 2 , it may also be arranged between power receiving unit 203 and charging unit 206. Alternatively, it may be arranged between power receiving unit 203 and a closed circuit formed by power receiving antenna 205, resonant capacitor 211, and second switch unit 210. In other words, first switch unit 209 may control whether or not to supply the received power to power receiving unit 203. Furthermore, while first switch unit 209 is depicted as one block in FIG. 2, first switch unit 209 can also be realized as part of charging unit 206 or as part of power receiving unit 203 .

[0047] Next, the function of the control unit 101 of the TX will be described with reference to Fig. 3. Fig. 3 is a block diagram showing an example of the functional configuration of the control unit 101 of the power transmitting device 402 (TX). The control unit 101 has a communication control unit 301, a power transmission control unit 302, a measurement unit 303, a setting unit 304, and a foreign object detection unit 305. The communication control unit 301 performs control communication with the RX based on the WPC standard via the communication unit 104. The power transmission control unit 302 controls the power transmitting unit 103 and controls power transmission to the RX. The measurement unit 303 measures a waveform attenuation index, which will be described later. The measurement unit 303 also measures the power transmitted to the RX via the power transmission unit 103, and measures the average transmitted power per unit time. The measurement unit 303 also measures the Q value of the power transmitting antenna 105. The setting unit 304 sets a threshold value used for foreign object detection based on the waveform attenuation index measured by the measurement unit 303, for example, by calculation processing.

[0048] The foreign object detection unit 305 can realize a foreign object detection function using a power loss method, a foreign object detection function using a Q-value measurement method, or a foreign object detection function using a waveform attenuation method. The foreign object detection unit 305 may also have a function for performing foreign object detection processing using other methods. For example, in a TX equipped with an NFC (Near Field Communication) communication function, the foreign object detection unit 305 may perform foreign object detection processing using an opposite device detection function according to the NFC standard. The foreign object detection unit 305 can also detect changes in the state of the TX, in addition to detecting foreign objects. For example, the TX can detect an increase or decrease in the number of power receiving devices 401 on the TX. The setting unit 304 sets a threshold value that serves as a reference for determining the presence or absence of a foreign object when the TX performs foreign object detection using the power loss method, the Q-value measurement method, or the waveform attenuation method. The setting unit 304 may also have a function for setting a threshold value that serves as a reference for determining the presence or absence of a foreign object, which is necessary when performing foreign object detection processing using other methods. Furthermore, the foreign object detection unit 305 can perform foreign object detection processing based on the threshold value set by the setting unit 304 and the waveform attenuation index, transmission power, and Q value measured by the measurement unit 303.

[0049] The functions of the communication control unit 301, power transmission control unit 302, measurement unit 303, setting unit 304, and foreign object detection unit 305 are realized as programs that run in the control unit 101. Each processing unit is configured as an independent program, and can run in parallel while maintaining synchronization between the programs through event processing or the like. However, two or more of these processing units may be incorporated into a single program.

[0050] [Process flow for power transmission according to WPC standards] The WPC standard defines a selection phase, a ping phase, an I&C phase, a negotiation phase, a calibration phase, and a power transfer phase. The operations of the power transmitting device 402 and the power receiving device 401 in these phases will be described below with reference to the sequence diagram of FIG. 5 is a sequence diagram for power transmission according to the WPC standard. Here, a power transmitting device 402 (TX) and a power receiving device 401 (RX) will be described as an example.

[0051] The TX repeatedly and intermittently transmits Analog Pings conforming to the WPC standard to detect objects within its power transmission range (F501). The TX executes the processes defined as the Selection phase and Ping phase of the WPC standard, and waits for the RX to be placed on it. The user of the RX brings the RX (e.g., a smartphone) close to the TX to charge it (F502). For example, the RX is brought close to the TX by placing it on the TX. When the TX detects the presence of an object within its power transmission range (F503, F504), it transmits Digital Pings conforming to the WPC standard (F505). When the RX receives the Digital Ping, it knows that the TX has detected the RX (F506). Furthermore, when the TX receives a predetermined response to the Digital Ping, it determines that the detected object is the RX and that the RX has been placed on the charging stand 403. When the TX detects that the RX has been placed, it acquires identification information and capability information from the RX through communication in the I&C phase specified in the WPC standard (F507). The identification information of the RX includes a Manufacturer Code and a Basic Device ID. The capability information of the RX includes information elements that can identify the version of the WPC standard that the RX supports, a Maximum Power Value that specifies the maximum power that the RX can supply to a load, and information indicating whether the RX has the negotiation function of the WPC standard. The TX may acquire the identification information and capability information of the RX through a method other than communication in the I&C phase of the WPC standard. The identification information may also be any other identification information that can identify an individual RX, such as a Wireless Power ID. The capability information may include information other than the above.

[0052] Next, TX determines the GP value with RX through communication in the negotiation phase defined by the WPC standard (F508). Note that in F508, other procedures for determining GP may be executed, not limited to communication in the negotiation phase defined by the WPC standard. Furthermore, if TX acquires information indicating that RX does not support the negotiation phase (for example, in F507), it may not execute communication in the negotiation phase and may set the GP value to a small value (for example, defined in advance in the WPC standard). In this embodiment, GP = 5 watts.

[0053] After determining the GP, the TX performs calibration based on the GP. In the calibration process, first, the RX transmits information (hereinafter referred to as first reference received power information) including the received power in a light load state (load disconnected state, load state in which the transmitted power is equal to or less than the first threshold) to the TX (F509). In this embodiment, the first reference received power information is the received power information of the RX when the transmitted power of the TX is 250 milliwatts. The first reference received power information is the Received Power Packet (mode 1) specified in the WPC standard, but other messages may also be used. The TX determines whether to accept the first reference received power information based on the power transmission state of its own device. If the TX accepts, it transmits an acknowledgment (ACK) to the RX, and if not, it transmits a negative acknowledgment (NAK).

[0054] Next, when RX receives an ACK from TX (F510), it performs processing to transmit information (hereinafter referred to as second reference received power information) including the received power in a load connection state (maximum load state, a load state in which the transmitted power is equal to or greater than the second threshold) to TX. In this embodiment, since GP is 5 watts, the second reference received power information is the received power information of RX when the transmitted power of TX is 5 watts. Here, the second reference received power information is the Received Power Packet (mode 2) specified in the WPC standard, but other messages may also be used. RX transmits a transmitted power output change instruction including a positive value to increase the transmitted power from TX to 5 watts (F511).

[0055] TX receives the above-mentioned instruction to change the transmission power output, and if it is possible to increase the transmission power, it responds with an ACK and increases the transmission power (F512, F513). Since the second reference received power information is the received power information when the transmission power of TX is 5 watts, if TX receives a power increase request exceeding 5 watts from RX (F514), it responds with a NAK to the instruction to change the transmission power output. This prevents power transmission above the specified level (F515).

[0056] When the RX determines that the predetermined transmission power has been reached by receiving a NAK from the TX, it transmits information including the received power in the load-connected state to the TX as second reference received power information (F516). The TX can calculate the amount of power loss between the TX and RX in the light-load state and the load-connected state based on the TX's transmission power value and the received power values ​​included in the first and second reference received power information. In addition, by interpolating between these power loss amounts, it is possible to calculate the power loss value between the TX and RX for all possible transmission powers of the TX (in this case, 250 milliwatts to 5 watts) (F517). The TX transmits an ACK in response to the second reference received power information from the RX (F518), completing the calibration process. If the TX determines that charging can be started and starts power transmission to the RX, charging of the RX begins. Before starting the power transmission process, TX and RX perform device authentication processing (F519), and if it is determined that each device can support a larger GP, the GP may be reset to a larger value, for example, 15 watts (F520).

[0057] In this case, the RX and TX increase the transmission power output using a transmission power output change command, ACK, and NAK to increase the TX's transmission power to 15 watts (F521-F524). Then, the TX and RX perform calibration again for GP = 15 watts. Specifically, the RX transmits information including the received power in the RX load-connected state when the TX's transmission power is 15 watts (hereinafter referred to as third reference received power information) (F525). The TX performs calibration based on the received power included in the first, second, and third reference received power information, and can calculate the amount of power loss between the TX and RX for all possible transmission powers of the TX (in this case, from 250 milliwatts to 15 watts) (F526). The TX transmits an ACK in response to the third reference received power information from the RX (F527), completing the calibration process. Having determined that charging can be started, the TX starts power transmission to the RX and transitions to the Power Transfer phase (F528).

[0058] In the power transfer phase, the TX transmits power to the RX. Foreign object detection is also performed using the power loss method. In the power loss method, the TX first uses the calibration described above to calculate the amount of power loss between the TX and RX in a state where there is no foreign object, based on the difference between the power transmitted by the TX and the power received by the RX. This calculated value corresponds to the reference amount of power loss in a normal state (a state where there is no foreign object) during power transmission processing. Then, if the amount of power loss between the TX and RX measured during power transmission after calibration deviates from the amount of power loss in the normal state by more than a threshold, the TX determines that there is a "foreign object" or that there is a "possible presence of a foreign object."

[0059] This concludes the explanation of the power loss method, which performs foreign object detection based on the results of measuring power loss while power is being transmitted from power transmitting device 402 to power receiving device 401. Foreign object detection using the power loss method has the disadvantage that the accuracy of foreign object detection decreases when power transmitting device 402 is transmitting a large amount of power, but has the advantage that foreign object detection can be performed while power transmission is continuing, thereby maintaining high power transmission efficiency.

[0060] In this way, foreign object detection can be performed using the power loss method during the power transfer phase. However, foreign object detection using only the power loss method may result in erroneous detection of a foreign object or in a false determination that a foreign object is not present when a foreign object is actually present. In particular, the power transfer phase is the phase in which the TX transmits power, and if a foreign object is present near the TX and RX during power transmission, heat generation from the foreign object increases, so it is necessary to improve the accuracy of foreign object detection during this phase. Therefore, in this embodiment, a foreign object detection method other than the power loss method is considered to be implemented in order to improve the accuracy of foreign object detection.

[0061] [Foreign object detection method using waveform attenuation method] In the power transfer phase, the power transmitting device 402 transmits power to the power receiving device 401. Therefore, if foreign object detection can be performed using the transmission waveform (voltage waveform or current waveform) related to this power transmission, foreign object detection becomes possible without using a newly defined foreign object detection signal or the like. A method of foreign object detection based on the attenuation state of the transmitted wave (hereinafter referred to as the waveform attenuation method) will be described with reference to FIG. 6. FIG. 6 is a diagram illustrating the principle of foreign object detection using the waveform attenuation method. Here, foreign object detection using the transmission waveform related to power transmission from the power transmitting device 402 (TX) to the power receiving device 401 (RX) will be described as an example.

[0062] In FIG. 6, the waveform shows the change over time in the voltage value 600 (hereinafter simply referred to as the voltage value) of the high-frequency voltage applied to the power transmitting antenna 105 of the TX. The horizontal axis of FIG. 6 represents time, and the vertical axis represents the voltage value. The TX, which is transmitting power to the RX via the power transmitting antenna 105, stops transmitting power at time T0. That is, at time T0, the power supply for power transmission from the power supply unit 102 is stopped. The frequency of the transmitting wave for power transmission from the TX is a predetermined frequency, for example, a fixed frequency between 85 kHz and 205 kHz used in the WPC standard. Point 601 is a point on the envelope of the high-frequency voltage and is the voltage value at time T1. (T1, A1) in the figure indicates that the voltage value at time T1 is A1. Similarly, point 602 is a point on the envelope of the high-frequency voltage and is the voltage value at time T2. (T2, A2) in the figure indicates that the voltage value at time T2 is A2. The quality factor (Q value) of this power transmitting antenna 105 can be calculated based on the change in the voltage value over time after time T0. For example, the Q value is calculated using Equation 1 based on the time, voltage value, and frequency f of the high-frequency voltage at points 601 and 602 on the voltage value envelope. Q=πf(T2-T1) / ln(A1 / A2) (Equation 1) If a foreign object is present near TX and RX, the Q factor decreases. This is because the presence of a foreign object causes energy loss. Therefore, focusing on the slope of the voltage attenuation, the presence of a foreign object causes more energy loss due to the foreign object than the absence of a foreign object. Therefore, the slope of the line connecting points 601 and 602 becomes steeper, and the attenuation rate of the waveform amplitude increases. In other words, the waveform attenuation method determines the presence or absence of a foreign object based on the attenuation state of the voltage value between points 601 and 602. The actual presence or absence of a foreign object can be determined by comparing some numerical value representing this attenuation state. For example, the determination can be made using the above-mentioned Q factor. A lower Q factor means a higher waveform attenuation rate (the degree of decrease in waveform amplitude per unit time). Alternatively, the determination can be made using the slope of the line connecting points 601 and 602, calculated from (A1-A2) / (T2-T1). Alternatively, if the times (T1 and T2) for observing the attenuation state of the voltage values ​​are fixed, the determination can be made using the value (A1-A2) representing the difference in the voltage values ​​or the value of the voltage value ratio (A1 / A2). Alternatively, if the voltage value A1 immediately after power transmission is stopped is constant, the determination can be made using the value of the voltage value A2 after a predetermined time has elapsed. Alternatively, the determination can be made using the value of the time (T2-T1) until the voltage value A1 reaches the predetermined voltage value A2.

[0063] As described above, the presence or absence of a foreign object can be determined based on the attenuation state of the voltage value during the power transmission outage period, and there are multiple values ​​that represent this attenuation state. In this embodiment, these values ​​representing the attenuation state are referred to as "waveform attenuation indexes." For example, as described above, the Q value calculated by Equation 1 is a value that represents the attenuation state of the voltage value related to power transmission, and is included in the "waveform attenuation index." All waveform attenuation indexes correspond to the waveform attenuation rate. Note that in the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation index." The following description will focus on the case where the waveform attenuation rate is used as the waveform attenuation index, but the contents of this embodiment can also be applied to cases where other waveform attenuation indexes are used.

[0064] Even if the vertical axis of FIG. 6 represents the current value flowing through the power transmitting antenna 105, the attenuation state of the current value during the power transmission suspension period changes depending on the presence or absence of a foreign object, as in the case of the voltage value. Furthermore, the waveform attenuation rate is higher when a foreign object is present than when a foreign object is not present. Therefore, foreign objects can be detected by applying the above-described method to the temporal change in the current value flowing through the power transmitting antenna 105. That is, the presence or absence of a foreign object can be determined and foreign objects can be detected using the Q value obtained from the current waveform, the slope of the current value attenuation, the difference between the current values, the ratio of the current values, the absolute value of the current values, and the time until the current value reaches a predetermined value as waveform attenuation indicators. Furthermore, foreign object detection may be performed based on both the attenuation state of the voltage value and the attenuation state of the current value, such as determining the presence or absence of a foreign object using an evaluation value calculated from the waveform attenuation indicator of the voltage value and the waveform attenuation indicator of the current value. In the above example, the waveform attenuation indicator is measured during the period when the TX temporarily suspends power transmission. However, the waveform attenuation indicator may also be measured during the period when the TX temporarily reduces the power supplied from the power supply unit 102 from a predetermined power level to a lower power level.

[0065] A method for detecting a foreign object based on the transmission waveform during power transmission using the waveform attenuation method will be described with reference to Fig. 7. Fig. 7 shows the transmission waveform when detecting a foreign object using the waveform attenuation method, with the horizontal axis representing time and the vertical axis representing the voltage value applied to the power transmitting antenna 105 or the resonant capacitor 107. Note that, as with Fig. 6, the vertical axis may represent the current value of the current flowing through the power transmitting antenna 105. During the transient response period immediately after the TX starts transmitting power, the transmission waveform is unstable. Therefore, during this transient response period when the transmission waveform is unstable, the RX is controlled not to communicate with the TX (communication by load modulation). Furthermore, the TX is controlled not to communicate with the RX (communication by frequency shift keying).

[0066] When it is time to detect a foreign object, the TX temporarily suspends power transmission. Then, since the amplitude of the transmitted wave attenuates during the foreign object detection period when power transmission is halted, the TX calculates the waveform attenuation rate of this attenuated waveform. If the calculated waveform attenuation rate exceeds a predetermined threshold, the TX determines that a foreign object is present. If no foreign object is detected after the predetermined foreign object detection period has elapsed, the TX resumes power transmission. After resuming power transmission, the TX repeatedly executes the above-mentioned waiting for the transient response period, determining the timing of foreign object detection, halting power transmission, and foreign object detection processing. The above is the basic process of foreign object detection using the waveform attenuation method.

[0067] When measuring the waveform attenuation rate of a transmitted wave, if elements such as the power receiving unit 203, the charging unit 206, and the battery 207 are connected to the power receiving antenna 205 and the resonant capacitor 211 of the power receiving device 401, the waveform attenuation rate of the attenuated waveform is affected by the loads of these elements. That is, the waveform attenuation rate changes depending on the states of the power receiving unit 203, the charging unit 206, and the battery 207. Therefore, even if the waveform attenuation rate is large, it is difficult to distinguish whether it is due to the influence of a foreign object or a change in the state of the power receiving unit 203, the charging unit 206, the battery 207, etc. Therefore, when observing the waveform attenuation rate to detect a foreign object, the first switch unit 209 may be turned off. This makes it possible to eliminate the influence of the battery 207. Alternatively, the second switch unit 210 may be turned on to short-circuit the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210, allowing a current to flow through a closed loop formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210. This makes it possible to eliminate the influence of power receiving unit 203, charging unit 206, and battery 207. As described above, highly accurate foreign object detection is possible by performing foreign object detection with first switch unit 209 disconnected or with second switch unit 210 turned on and short-circuited (connected). Highly accurate foreign object detection is also possible by performing both disconnection of first switch unit 209 and short-circuiting (connection) of second switch unit 210.

[0068] Furthermore, when measuring the waveform attenuation rate of a transmitting wave, if elements such as the power transmitting unit 103, the communication unit 104, and the power supply unit 102 are connected to the power transmitting antenna 105 and the resonant capacitor 107 of the power transmitting device 402, the waveform attenuation rate of the attenuated waveform is affected by the loads of these elements. That is, the waveform attenuation rate changes depending on the states of the power transmitting unit 103, the communication unit 104, and the power supply unit 102. Therefore, even if the waveform attenuation rate is large, it is difficult to distinguish whether it is due to the influence of a foreign object or the influence of the power transmitting unit 103, the communication unit 104, and the power supply unit 102. Therefore, when measuring the waveform attenuation rate, the switch 108 may be turned on to short-circuit the power transmitting antenna 105, the resonant capacitor 107, and the switch 108, allowing current to flow through the closed loop formed by the power transmitting antenna 105, the resonant capacitor 107, and the switch 108. This makes it possible to eliminate the influence of the power transmitting unit 103, the communication unit 104, and the power supply unit 102. Alternatively, a switch may be provided between the power transmitting unit 103 and a closed loop circuit formed by the power transmitting antenna 105, resonant capacitor 107, and switch 108. Then, when foreign object detection is performed, the switch is used to disconnect the closed loop circuit from the power transmitting unit, thereby eliminating the influence of the power transmitting unit 103, the communication unit 104, and the power supply unit 102. As described above, highly accurate foreign object detection is possible by performing foreign object detection with the switch 108 turned on to create a short-circuit (connection) state, or with the closed loop circuit and the power transmitting unit 103 disconnected by the switch. Furthermore, highly accurate foreign object detection is also possible by performing both the short-circuit (connection) state by turning on the switch 108 and the disconnection state between the closed loop circuit and the power transmitting unit 103 by the switch.

[0069] [How to set the foreign object detection threshold in the waveform attenuation method] FIG. 11 is a diagram illustrating a method for setting a foreign object detection threshold in the waveform attenuation method. First, when power is transmitted from TX, RX controls the load of RX to be in a light load state so that no power or only very little power is supplied to the load of RX. The transmitted power of TX at this time is defined as Pt1. Then, TX stops transmitting power in this state and measures the waveform attenuation factor. The waveform attenuation factor at this time is defined as δ1. At this time, TX recognizes the transmitted power Pt1 that TX is transmitting and stores in its memory a calibration point 1100 that associates the transmitted power Pt1 with the waveform attenuation factor δ1. Next, RX controls the load of RX to be in a load-connected state so that when power is transmitted from TX, maximum power or power equal to or greater than a predetermined threshold is supplied to the load of RX. The transmitted power of TX at this time is defined as Pt2. Then, TX stops transmitting power in this state and measures the waveform attenuation factor. At this time, the TX stores in its memory a calibration point 1101 that associates the transmission power Pt2 with the waveform attenuation rate δ2. Next, the TX performs linear interpolation between the calibration points 1100 and 1101 to create a line 1102. The line 1102 represents the relationship between the transmission power and the waveform attenuation rate of the transmission wave when no foreign object is present around the TX and RX. Therefore, the TX can estimate the waveform attenuation rate of the transmission wave for each transmission power value when no foreign object is present, from the line 1102. For example, if the transmission power value is Pt3, the waveform attenuation rate can be estimated to be δ3 from the point 1103 on the line 1102 that corresponds to the transmission power value Pt3. Based on the above estimation results, the TX can then calculate a threshold value for each transmission power value to be used to determine the presence or absence of a foreign object. For example, a waveform attenuation rate that is greater by a predetermined value (a value corresponding to a measurement error) than the estimated waveform attenuation rate when there is no foreign object at a certain transmitted power value may be set as the threshold for determining the presence or absence of a foreign object. The calibration process performed by the power transmitting device 402 and the power receiving device 401 so that the power transmitting device 402 acquires a combination of the transmitted power value and the waveform attenuation rate is hereinafter referred to as "calibration process of the waveform attenuation method (CAL process)."

[0070] Note that RX may perform the control to put the load into a no-power / light-load state and the control to put the load into a connected state after notifying TX of the control to be performed. Also, either of the two controls may be performed first.

[0071] Note that the operation for calculating the threshold value used to determine the presence or absence of a foreign object for each load (each transmitted power value) described in this embodiment may be performed in the calibration phase. As described above, in the calibration phase, the TX acquires data required for foreign object detection using the power loss method. At that time, the TX acquires data related to power loss when the load state of the RX is a light load state and when a load is connected. Therefore, measurements of the calibration points 1100 and 1101 in FIG. 11 may be performed together with the power loss measurements when the RX is in a light load state and a loaded state in the calibration phase described above. That is, when the TX receives first reference received power information from the RX, it measures the calibration point 1100 in addition to the predetermined processing to be performed in the calibration phase. Furthermore, when the TX receives second reference received power information from the RX, it measures the calibration point 1101 in addition to the predetermined processing to be performed in the calibration phase. This eliminates the need to provide a separate period for measuring the calibration points 1100 and 1101, and therefore allows the calibration points 1100 and 1101 to be measured in a shorter time.

[0072] [Treatment of power transmission equipment when applying the waveform attenuation method to the WPC standard] Next, we will explain the processing of the power transmitting device 402 when foreign object detection is performed by applying this waveform attenuation method to the WPC standard. When performing foreign object detection using the waveform attenuation method, the power transmitting device 402 measures in advance the waveform attenuation rate when there is no foreign object and calculates a threshold value based on that. The power transmitting device 402 then performs foreign object detection using the waveform attenuation method, and if the measured waveform attenuation rate is greater than the threshold value, it determines that "foreign object is present" or "there is a possibility that there is a foreign object," and if it is smaller than the threshold value, it determines that "foreign object is not present" or "there is a high possibility that there is no foreign object."

[0073] The timing for measuring the waveform attenuation rate in advance when there is no foreign object will be described. In the WPC standard, foreign object detection is performed using the Q-factor measurement method in the negotiation phase as described above. If it is determined that no foreign object is present as a result of foreign object detection, the system proceeds to the calibration phase and power transfer phase. In other words, proceeding to the negotiation phase or later means that the Q-factor measurement method determined that no foreign object is present as a result of foreign object detection. Therefore, if the waveform attenuation rate is measured in either the negotiation phase, calibration phase, or power transfer phase, there is a high possibility that the waveform attenuation rate in a foreign object-free state can be measured. Therefore, the timing for measuring the waveform attenuation rate in a foreign object-free state may be any of the negotiation phase, calibration phase, or power transfer phase.

[0074] In this embodiment, the timing for measuring the waveform attenuation rate in the absence of a foreign object is set to the first stage of the power transfer phase. The reason for this is that the longer the time that passes after it is determined by the Q-value measurement method that no foreign object is present, the higher the probability that a foreign object will be placed near the power transmitting device 402 and the power receiving device 401. Then, at the timing for foreign object detection designated by the power receiving device 401 or the power transmitting device 402, the power transmitting device 402 measures the waveform attenuation rate of the transmitted wave. The power transmitting device 402 then compares the measured waveform attenuation rate with a threshold calculated from the waveform attenuation rate in the absence of the foreign object described above, and determines whether a foreign object is present.

[0075] The waveform attenuation method has the disadvantage of reducing power transmission efficiency due to the temporary suspension of power transmission, since the power transmitting device 402 temporarily stops power transmission and observes the attenuation rate of the transmitted radio wave to detect a foreign object. On the other hand, it has the advantage of being able to detect a foreign object with high accuracy even when the foreign object detection process is performed while transmitting a large amount of power. In other words, even in situations where it is difficult to accurately detect a foreign object using the power loss method, the waveform attenuation method can be used to detect a foreign object.

[0076] In the above-described embodiment, when foreign object detection is performed using the waveform attenuation method, the waveform attenuation rate in a state where no foreign object is present is measured before the start of power transmission, and a threshold value is calculated based on that measurement. Then, if the waveform attenuation rate measured when performing foreign object detection using the waveform attenuation method is greater than the threshold value, it is determined that a foreign object is present or that there is a possibility that a foreign object is present. If the waveform attenuation rate is smaller than the threshold value, it is determined that no foreign object is present or that there is a high possibility that a foreign object is absent. However, foreign object detection may also be performed using a threshold value calculated from a waveform attenuation rate measured at a timing when it is estimated that no foreign object is present after the start of power transmission. For example, while the TX is transmitting power, the TX confirms the absence of a foreign object using the power loss method. Next, the TX performs a first waveform attenuation rate measurement and calculates a threshold value based on the measured waveform attenuation rate. This first waveform attenuation rate measurement is performed immediately after the absence of a foreign object is confirmed using the power loss method, so the measured waveform attenuation rate is estimated to be the waveform attenuation rate in a state where no foreign object is present. Next, the TX resumes power transmission and performs a second waveform attenuation rate measurement at a timing when it is determined that foreign object detection should be performed. The presence or absence of a foreign object can be determined by comparing the result of the second waveform attenuation measurement with the result of the first waveform attenuation measurement or with a threshold value calculated based on that result. In other words, when detecting foreign objects using the waveform attenuation method, the waveform attenuation measured at that time may be compared with a waveform attenuation measured previously when no foreign object was present, or with a threshold value.

[0077] In the above-described embodiment, the frequency of the transmission wave for power transmission from the power transmitting device 402 is a fixed frequency. However, the foreign object detection process described in this embodiment may be performed at each of multiple frequencies, and the presence or absence of a foreign object may be determined by combining the results. Performing foreign object detection using waveform attenuation rates at multiple frequencies, rather than just one frequency, enables more accurate foreign object detection.

[0078] In this embodiment, a waiting time is provided before transitioning to each operation because the transmission waveform is unstable due to a transient response immediately after the power transmitting device 402 stops or starts power transmission. However, this instability in the transmission waveform is caused by a sudden start or stop of power transmission. Therefore, to alleviate this, the power transmitting device 402 may be controlled to increase the transmission power in stages when starting power transmission. Alternatively, the transmission power may be controlled to decrease in stages when stopping power transmission.

[0079] [Foreign object detection process in response to communication errors] As described above, the power transmitting device 402 and the power receiving device 401 communicate for power transmission and reception control based on the WPC standard. This communication is performed wirelessly via the power transmitting antenna 105 of the power transmitting device 402 and the power receiving antenna 205 of the power receiving device 401. Therefore, if a foreign object is present near the power transmitting device 402 and the power receiving device 401 (for example, between the power transmitting device 402 and the power receiving device 401), the foreign object may interfere with wireless communication between the power transmitting device 402 and the power receiving device 401, causing a communication error. Therefore, in this embodiment, if a communication error occurs, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401, and therefore the power transmitting device 402 and the power receiving device 401 perform control to detect the foreign object.

[0080] As described above, methods for detecting a foreign object during power transmission from the power transmitting apparatus 402 to the power receiving apparatus 401 include the power loss method and the waveform attenuation method. In the power loss method, as described with reference to FIG. 10 , the power receiving apparatus 401 notifies the power transmitting apparatus 402 of the received power value Pr3′ measured by the power receiving apparatus 401. The power transmitting apparatus 402 calculates Pr3−Pr3′ (=Ploss_FO), which is the value obtained by subtracting the received power value Pr3′ actually received from the power receiving apparatus 401 from the received power value Pr3 in a state in which no foreign object is present. This Ploss_FO can be considered to be the power loss due to power consumed by a foreign object when a foreign object is present near the power transmitting apparatus 402 and the power receiving apparatus 401. Therefore, the power transmitting apparatus 402 can determine the presence of a foreign object when the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold. That is, in the power loss method, when foreign object detection is performed, communication is performed between the power transmitting device 402 and the power receiving device 401 to notify the power transmitting device 402 of the received power value Pr3' as described above. A communication error has already occurred between the power transmitting device 402 and the power receiving device 401, and there is a possibility that an error will occur in the communication for foreign object detection due to the same cause.

[0081] On the other hand, the waveform attenuation method determines whether or not a foreign object is present by stopping power transmission from the power transmitting device 402 and comparing the waveform attenuation rate at that time with a pre-measured waveform attenuation rate when no foreign object is present. Therefore, foreign object detection can be performed without communication between the power transmitting device 402 and the power receiving device 401. Therefore, when a communication error occurs, the power transmitting device 402 performs foreign object detection using the waveform attenuation method, which does not require communication. This increases the chances of successful foreign object detection.

[0082] Furthermore, even if a foreign object is present near the power transmitting device 402 and the power receiving device 401 during power transmission, a communication error may not occur. However, even if a communication error does not occur, the presence of a foreign object may cause problems such as a large power loss or heat generation due to the foreign object. Therefore, the power transmitting device 402 periodically performs a foreign object detection process during the power transfer phase in which wireless power transmission is performed to check whether a foreign object is present near the power transmitting device 402 and the power receiving device 401. If the waveform attenuation method is used for this periodic foreign object detection, power transmission from the power transmitting device 402 is temporarily stopped each time foreign object detection is performed, resulting in a decrease in power transmission efficiency. On the other hand, if the power loss method is used, it is possible to detect a foreign object while continuing to transmit power from the power transmitting device 402 to the power receiving device 401. Therefore, when a communication error does not occur, the power transmitting device 402 and the power receiving device 401 periodically perform foreign object detection using the power loss method during the power transfer phase. This allows for early detection of a foreign object while maintaining high power transfer efficiency.

[0083] The operation of the power transmitting device 402 and the power receiving device 401 using the above-described multiple foreign object detection methods will now be described. Fig. 8 shows an example of the operation of the power transmitting device 402 in the Power Transfer phase. The process in Fig. 8 starts when the power transmitting device 402 detects the power receiving device 401 placed on the charging stand 403, performs communication, and completes the processing of each phase defined by the WPC standard. Phases that are executed before the process in Fig. 8 starts include a Selection phase, a Ping phase, an I&C phase, a Negotiation phase, and a Calibration phase. However, the process in Fig. 8 may start without performing at least some of the above phases.

[0084] In S801, the power transmitting device 402 starts power transmission in the power transfer phase. In S802, the power transmitting device 402 determines whether a command to execute foreign object detection using the power loss method has been received from the power receiving device 401. This command includes the received power value measured by the power receiving device 401. If this command has been received, in S803 the power transmitting device 402 executes foreign object detection using the power loss method based on the received power value received from the power receiving device 401 and the transmitted power value measured by the power transmitting device 402.

[0085] In S804, the power transmitting device 402 determines whether or not a foreign object is present near the power transmitting device 402 based on the result of the foreign object detection process. If it is determined that a foreign object is present, in S805 the power transmitting device 402 transmits a negative acknowledgement (NAK) that is information indicating the presence of a foreign object to the power receiving device 401. In S806, the power transmitting device 402 performs control to stop power transmission or reduce the transmitted power. On the other hand, if it is determined that no foreign object is present in S804, the power transmitting device 402 transmits an affirmative acknowledgement (ACK) that is information indicating the absence of a foreign object to the power receiving device 401, continues power transmission, and returns to S802.

[0086] If the power transmitting device 402 does not receive a foreign object detection execution command using the Power Loss method in S802, the power transmitting device 402 determines in S808 whether a communication error has occurred in communication between the power transmitting device 402 and the power receiving device 401. If the power transmitting device 402 does not receive a command that should be transmitted from the power receiving device 401, the power transmitting device 402 determines that a communication error has occurred (i.e., detects a communication error). For example, in order to periodically execute foreign object detection using the Power Loss method described above, the power receiving device 401 periodically transmits a foreign object detection execution command using the Power Loss method to the power transmitting device 402. If the power transmitting device 402 does not receive the command that should be received periodically, or if it receives a command including an invalid packet, it determines that a communication error has occurred. However, the method for detecting a communication error by the power transmitting device 402 is not limited to this.

[0087] If a communication error is detected in S808, there is a possibility that a foreign object is present, so in S809, the power transmitting device 402 performs foreign object detection using the waveform attenuation method. Then, the power transmitting device 402 performs the processes from S804 to S807 based on the result of foreign object detection, similar to when foreign object detection is performed using the power loss method.

[0088] If no communication error is detected in S808, the power transmitting device 402 determines in S810 whether a command to execute foreign object detection using the waveform attenuation method has been received from the power receiving device 401. The power receiving device 401 transmits this command when, for example, the power receiving device 401 detects a communication error, as will be described later. If the power transmitting device 402 receives this command, it executes foreign object detection using the waveform attenuation method in S809. Then, the power transmitting device 402 performs the processes from S804 to S807 based on the result of foreign object detection.

[0089] 9 shows an example of the operation of the power receiving device 401 in the power transfer phase. The processing in FIG. 9 starts at the same timing as the processing in FIG. 8. In S901, the power receiving device 401 starts receiving power in the power transfer phase. In S902, the power receiving device 401 transmits a command to execute foreign object detection using the power loss method, which is a command to be periodically transmitted to the power transmitting device 402. This command is a notification from the power receiving device 401 requesting the power transmitting device 402 to execute foreign object detection processing using the power loss method.

[0090] In S903, the power receiving apparatus 401 determines whether a communication error has occurred in communication between the power transmitting apparatus 402 and the power receiving apparatus 401. The power receiving apparatus 401 determines whether a communication error has occurred as follows: In accordance with the WPC standard, the power receiving apparatus 401 transmits various commands to the power transmitting apparatus 402. Then, upon receiving a command from the power receiving apparatus 401, the power transmitting apparatus 402 responds to the power receiving apparatus 401 (such as an affirmative response or a negative response). For example, to periodically perform foreign object detection using the above-described power loss method, the power receiving device 401 periodically transmits a foreign object detection execution command using the power loss method to the power transmitting device 402. Upon receiving the command, the power transmitting device 402 responds to the power receiving device 401. Therefore, if the power receiving device 401 transmits the foreign object detection execution command using the power loss method to the power transmitting device 402 but does not receive a response from the power transmitting device 402, the power receiving device 401 determines that a communication error has occurred (i.e., detects a communication error). Furthermore, even if the power receiving device 401 receives a response from the power transmitting device 402, the power receiving device 401 determines that a communication error has occurred if the response includes an invalid packet. However, the method for detecting a communication error by the power receiving device 401 is not limited to this.

[0091] If a communication error is detected in S903, there is a possibility that a foreign object is present and that foreign object detection using the power loss method has not been performed normally. Therefore, in S904, the power receiving device 401 transmits a command to execute foreign object detection using the waveform attenuation method to the power transmitting device 402. This command is a notification from the power receiving device 401 requesting the power transmitting device 402 to perform foreign object detection processing using the waveform attenuation method. The power receiving device 401 then waits for a response from the power transmitting device 402 in accordance with the result of foreign object detection execution using the waveform attenuation method. Note that if a communication error is not detected in S903, the power receiving device 401 waits for a response from the power transmitting device 402 in accordance with the result of foreign object detection execution using the power loss method.

[0092] In S905, the power receiving apparatus 401 determines whether a negative response, which is information indicating the presence of a foreign object, has been received from the power transmitting apparatus 402. If a negative response has been received, in S906 the power receiving apparatus 401 transmits an EPT (End Power Transfer) command, which is a command for terminating power transmission, to the power transmitting apparatus 402, and transitions to a state in which power is not received. On the other hand, if a negative response is not received in S905, for example, if a positive response is received, the power receiving apparatus 401 continues receiving power and returns to S902.

[0093] The above is a description of an example of the operation of the power transmitting device 402 and the power receiving device 401. In this way, when a communication error is detected in communication between the power transmitting device 402 and the power receiving device 401, the power transmitting device 402 and the power receiving device 401 perform control so that foreign object detection is performed using the waveform attenuation method. This makes it possible to detect a foreign object early and stop power transmission (or reduce the transmitted power) when a foreign object is present near the power transmitting device 402 and the power receiving device 401, thereby increasing the likelihood of preventing an extreme temperature rise or destruction of the foreign object. Note that, although the above description assumes that both the power transmitting device 402 and the power receiving device 401 perform error detection, it is also possible for either the power transmitting device 402 or the power receiving device 401 to perform error detection.

[0094] As already described, the power transmitting device 402 may short-circuit the switch 108 or disconnect the switch between the power transmitting unit 103 and the closed loop circuit including the power transmitting antenna 105 at the timing when foreign object detection using the waveform attenuation method is performed. This eliminates the influence of the power transmitting unit 103, the communication unit 104, and the power supply unit 102 on the attenuated waveform, enabling more accurate foreign object detection. Similarly, the power receiving device 401 may short-circuit the second switch unit 210 or disconnect the first switch unit 209 at the timing when foreign object detection using the waveform attenuation method is performed. This eliminates the influence of the power receiving unit 203, the charging unit 206, and the battery 207 on the attenuated waveform, enabling more accurate foreign object detection. In this case, the power transmitting device 402 and the power receiving device 401 communicate to identify the timing when foreign object detection is performed.

[0095] Furthermore, in the above-described embodiment, when foreign object detection is performed using the waveform attenuation method, the power transmitting device 402 measures the attenuation rate of the voltage applied to the power transmitting antenna 105 or the current flowing through the power transmitting antenna 105 as the attenuation state of the transmitted wave related to wireless power transmission. However, because the power transmitting antenna 105 and the power receiving antenna 205 are opposed to each other and electromagnetically coupled, the electromagnetic energy of the power transmitting antenna 105 is also excited in the power receiving antenna 205. Therefore, foreign object detection using the waveform attenuation method can also be achieved by the power receiving device 401 measuring the attenuation rate of the voltage applied to the power receiving antenna 205 or the current flowing through the power receiving antenna 205 as the attenuation state of the received wave related to wireless power transmission.

[0096] Furthermore, when the power transmitting device 402 measures the waveform attenuation factor, it may notify the power receiving device 401 of the measurement result of the waveform attenuation factor or a threshold value calculated from the measurement result. This allows the power receiving device 401 to determine the presence or absence of a foreign object based on the measurement result, etc. received from the power transmitting device 402. Similarly, when the power receiving device 401 measures the waveform attenuation factor, it may notify the power transmitting device 402 of the measurement result of the waveform attenuation factor or a threshold value calculated from the measurement result. This allows the power transmitting device 402 to determine the presence or absence of a foreign object based on the measurement result, etc. received from the power receiving device 401.

[0097] In the above description using FIGS. 8 and 9, the waveform attenuation method is adopted to perform foreign object detection with high accuracy when a communication error is detected. As a result, even if a foreign object is not detected in the periodic foreign object detection process using the power loss method, the foreign object can be detected by performing the foreign object detection process using the waveform attenuation method in response to the communication error, and power transmission can be stopped (or the transmitted power can be reduced). However, if it is desired to avoid a decrease in power transmission efficiency, the power transmitting device 402 and the power receiving device 401 may perform foreign object detection using the power loss method in response to the detection of a communication error. In this case, the power transmitting device 402 that detected a communication error in S808 of FIG. 8 may perform foreign object detection using the power loss method instead of performing foreign object detection using the waveform attenuation method in S809. Furthermore, the power receiving device 401 that detected a communication error in S903 of FIG. 9 may transmit a foreign object detection execution command using the power loss method instead of transmitting a foreign object detection execution command using the waveform attenuation method in S904. When foreign object detection is performed using the power loss method in S809, the power transmitting device 402 requests the power receiving device 401 to send a command including a received power value, and detects a foreign object based on the received power value received in response to the request and the transmitted power value measured by the power transmitting device 402. When the power receiving device 402 sends a command to perform foreign object detection using the power loss method in S903, the power transmitting device 401, upon receiving the command, performs foreign object detection using the power loss method. With this processing, even if a foreign object fails to be detected during periodic foreign object detection processing using the power loss method, the probability of detecting a foreign object increases by performing the foreign object detection processing again in response to a communication error.

[0098] When foreign object detection is performed using the power loss method in response to the detection of a communication error, communication for foreign object detection is performed between the power transmitting device 402 and the power receiving device 401. However, there is a possibility that a communication error will occur again in this communication, causing the power transmitting device 402 or the power receiving device 401 to be unable to receive data from the other device, or to receive data containing an invalid packet. If the foreign object detection execution command sent by the power receiving device 401 to the power transmitting device 402 is lost due to a communication error, the power transmitting device 402 will not recognize that foreign object detection is being requested, and will not perform foreign object detection. Therefore, no response to the foreign object detection execution command will be sent from the power transmitting device 402 to the power receiving device 401.

[0099] Therefore, when it is considered that such a communication error has occurred again, the power receiving device 401 may transmit an EPT command to the power transmitting device 402, which is a command to terminate power transmission, and transition to a state in which power is not received. If the power transmitting device 402 receives the EPT, it stops power transmission. Even if the power transmitting device 402 does not receive the EPT, the power transmitting device 402 may detect that the power receiving device 401 has transitioned to a state in which power is not received, stop power transmission, and transition to the Selection phase. If a communication error occurs again in communication for performing foreign object detection in response to the detection of a communication error, the frequency of communication errors is high, so it is likely that a foreign object is present, or that there is a factor other than a foreign object that is interfering with communication. Therefore, by stopping power transmission or controlling the power transmission to be reduced as described above in such cases, it is possible to suppress the occurrence of problems caused by power transmission.

[0100] Furthermore, when foreign object detection is performed using the power loss method or the waveform attenuation method described above, foreign object detection may fail. For example, if the power receiving device 401 placed on the power transmitting device 402 moves during the foreign object detection process, the measurement value used for foreign object detection may become abnormal, causing foreign object detection to fail. In this case, too, since the state may be inappropriate for wireless power transmission, the power transmitting device 402 and the power receiving device 401 may stop power transmission or reduce the power transmission. This can prevent problems caused by power transmission.

[0101] [Foreign object detection process in response to power drop] 8 and 9, the process of detecting a foreign object when the power transmitting device 402 and the power receiving device 401 detect a communication error has been described. Next, the process of detecting a foreign object when the power receiving device 401 detects a decrease in the received power will be described.

[0102] If a foreign object is present near the power transmitting device 402 and the power receiving device 401, the foreign object may interfere with wireless power transmission between the power transmitting device 402 and the power receiving device 401, possibly causing a decrease in the received power of the power receiving device 401. Therefore, when a decrease in the received power of the power receiving device 401 occurs, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401, and therefore the power transmitting device 402 and the power receiving device 401 perform control to detect the foreign object.

[0103] The following describes the operations of the power transmitting device 402 and the power receiving device 401 when foreign object detection is performed in response to the power transmitting device 402 detecting a decrease in the received power of the power receiving device 401. The power transmitting device 402 periodically receives the received power value Pr3' from the power receiving device 401 to perform foreign object detection using the power loss method during the power transfer phase. The power transmitting device 402 then determines whether the received power of the power receiving device 401 has decreased based on the received power value Pr3' received from the power receiving device 401 or Ploss_FO, which is the difference between Pr3 and Pr3' determined in advance. If the received power value Pr3' received from the power receiving device 401 falls below a certain threshold or if Ploss_FO exceeds a certain threshold, the power transmitting device 402 determines that the received power of the power receiving device 401 has decreased and performs foreign object detection using the waveform attenuation method.

[0104] That is, the power transmitting device 402 periodically performs foreign object detection using the power loss method, which can maintain high power transmission efficiency, and performs foreign object detection using the waveform attenuation method, which has higher foreign object detection accuracy, depending on the received power received from the power receiving device 401 for foreign object detection. For example, the power transmitting device 402 may set a first threshold for determining the possibility of the presence of a foreign object and a second threshold for determining the presence of a foreign object, with respect to the value of Pr3' or Ploss_FO. Then, when Pr3' or Ploss_FO exceeds the second threshold, the power transmitting device 402 determines that a foreign object has been detected using the power loss method and controls to stop power transmission or reduce the transmitted power. Furthermore, when Pr3' or Ploss_FO exceeds the first threshold but does not exceed the second threshold, the power transmitting device 402 performs foreign object detection using the waveform attenuation method. As a result, even if a foreign object cannot be detected using the power loss method, it is possible to detect a foreign object by using the more accurate waveform attenuation method in response to a decrease in received power. The above-mentioned threshold values ​​may be set based on data obtained by calibration processing using the power loss method (straight line 1002 in FIG. 10).

[0105] Furthermore, in the above description, the power transmitting device 402 performs foreign object detection in response to a decrease in the received power of the power receiving device 401. However, the power transmitting device 402 may also perform foreign object detection in response to a change in the transmitted power of the power transmitting device 402. The power transmitting device 402 is capable of measuring the transmitted power value of the power transmitting device 402. If the difference between this transmitted power value and a predetermined reference value is greater than a certain threshold, the power transmitting device 402 may determine that a foreign object may be present and perform foreign object detection using a waveform attenuation method. This configuration also provides the same effect as when foreign object detection is performed in response to a decrease in received power.

[0106] Next, the operation of the power transmitting device 402 and the power receiving device 401 when foreign object detection is performed in response to the power receiving device 401 detecting a decrease in the received power of the power receiving device 401 will be described. The power receiving device 401 periodically measures the power received from the power transmitting device 402 during the power transfer phase. The power receiving device 401 then determines whether the received power of the power receiving device 401 has decreased based on the periodically measured received power value. If the calculated received power value falls below a certain threshold, or if the difference between the calculated received power value and a reference value exceeds a certain threshold, the power receiving device 401 determines that the received power of the power receiving device 401 has decreased, and requests the power transmitting device 402 to perform foreign object detection using the waveform attenuation method.

[0107] That is, the power receiving device 401 periodically measures the received power value and, depending on the measurement results, requests the power transmitting device 402 to perform foreign object detection using the waveform attenuation method, which has high foreign object detection accuracy. For example, the power receiving device 401 may transmit a foreign object detection execution command using the power loss method when the difference between the measured received power and the reference value is equal to or less than a predetermined threshold. On the other hand, the power receiving device 401 may transmit a foreign object detection execution command using the waveform attenuation method when the difference between the measured received power and the reference value exceeds the predetermined threshold. With this configuration, when there is a high possibility of the presence of a foreign object (when the received power is low), foreign objects are detected using the highly accurate waveform attenuation method, and when this is not the case, foreign object detection can be performed using the power loss method while maintaining high power transmission efficiency.

[0108] Note that, when the decrease in the received power value exceeds a threshold, the power receiving device 401 may determine that a foreign object is present and may request the power transmitting device 402 to stop power transmission or reduce the transmitted power. The power receiving device 401 may also set a first threshold for determining that a foreign object may be present based on the decrease in the received power value and a second threshold for determining that a foreign object is present. When the decrease in the received power exceeds the first threshold but does not exceed the second threshold, the power receiving device 401 requests the power transmitting device 402 to perform foreign object detection using a waveform attenuation method. When the decrease in the received power exceeds the second threshold, the power receiving device 401 may request the power transmitting device 402 to stop power transmission by transmitting an EPT command to the power transmitting device 402. Alternatively, the power receiving device 401 may send a command to the power transmitting device 402 requesting that the transmitted power be reduced.

[0109] As described above, when the power transmitting device 402 and the power receiving device 401 detect a drop in the received power of the power receiving device 401, they control the devices so that foreign object detection is performed using the waveform attenuation method. This makes it possible to detect a foreign object early when there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401.

[0110] [Foreign object detection processing according to calibration data] Next, a process for detecting foreign matter based on data obtained by calibration processing using the power loss method or data obtained by calibration processing using the waveform attenuation method will be described.

[0111] As described above, in foreign object detection using the power loss method and foreign object detection using the waveform attenuation method, a calibration process is performed to set a reference threshold value used to determine the presence or absence of a foreign object. The reference data obtained by these calibration processes is expected to indicate the relationship between the transmitted power value and the received power value, or the relationship between the transmitted power value and the waveform attenuation rate, in a state in which no foreign object is present. Therefore, if the reference data obtained by the calibration process does not indicate the expected relationship between the transmitted power value and the received power value or between the transmitted power value and the waveform attenuation rate, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401. Therefore, the power transmitting device 402 and the power receiving device 401 perform control to perform foreign object detection.

[0112] First, the operation of the power transmitting device 402 and the power receiving device 401 when foreign object detection is performed based on data obtained by calibration processing using the power loss method will be described. The power transmitting device 402 and the power receiving device 401 perform a calibration process using the power loss method, which is a process for determining a threshold value used in the power loss method. The data obtained by this calibration process using the power loss method should represent the relationship between transmitted power and received power in a state where there is no foreign object, and it is possible to predict in advance the range of the received power value corresponding to the transmitted power value. Therefore, when the power transmitting device 402 obtains data through the calibration process using the power loss method, it determines whether the received power value included in the data is within a predetermined range corresponding to the transmitted power value. If the received power value is outside the range, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401, and the power transmitting device 402 performs foreign object detection using the waveform attenuation method. If it is determined that a foreign object is present through foreign object detection using the waveform attenuation method, the power transmitting device 402 stops transmitting power or reduces the transmitted power. On the other hand, if it is determined by the waveform attenuation method that no foreign object is present, the power transmitting device 402 executes the calibration process by the power loss method again and updates the data.

[0113] That is, the power transmitting device 402 performs foreign object detection using a waveform attenuation method different from the power loss method, depending on the data values ​​obtained by the calibration process using the power loss method. With this configuration, if the calibration process using the power loss method determines that there is a possibility of a foreign object being present, foreign object detection using the waveform attenuation method can be performed to detect the foreign object early. Furthermore, if the accuracy of foreign object detection using the power loss method is reduced due to inaccurate calibration data, foreign objects can be detected with high accuracy using the waveform attenuation method. Note that the power receiving device 401 may determine whether to detect a foreign object based on the data obtained by the calibration process.

[0114] Next, we will describe the operation of the power transmitting device 402 and the power receiving device 401 when foreign object detection is performed based on data obtained through calibration processing using the waveform attenuation method. The power transmitting device 402 and the power receiving device 401 perform calibration processing using the waveform attenuation method, which is processing to determine the threshold value used in the waveform attenuation method. The reference data obtained through this calibration processing using the waveform attenuation method should be data that represents the relationship between the transmitted power and the waveform attenuation rate in a state where there is no foreign object, and it is possible to predict in advance the range of values ​​that the data can take. Therefore, the power transmitting device 402 determines whether the waveform attenuation rate indicated by the reference data obtained through calibration processing using the waveform attenuation method is within a predetermined range. If the waveform attenuation rate is not within the predetermined range, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401, and the power transmitting device 402 performs foreign object detection using the power loss method. More specifically, the power transmitting device 402 transmits a command to the power receiving device 401 to notify it of the execution of the power loss method. Upon receiving the command, the power receiving apparatus 401 transmits to the power transmitting apparatus 402 a foreign object detection execution command using the power loss method, including the received power value measured by the power receiving apparatus 401. Upon receiving the command from the power receiving apparatus 401, the power transmitting apparatus 402 executes foreign object detection using the power loss method.

[0115] If the power loss method determines that a foreign object is present, the power transmitting device 402 stops power transmission or controls the power transmission to be reduced. If the power loss method determines that no foreign object is present, the power transmitting device 402 executes the calibration process using the waveform attenuation method again and updates the data. In this way, the power transmitting device 402 executes foreign object detection using the power loss method, which is different from the waveform attenuation method, according to the data values ​​obtained by the calibration process using the waveform attenuation method. With this configuration, if the calibration process using the waveform attenuation method determines that a foreign object may be present, foreign object detection using the power loss method can be executed, thereby enabling early detection of the foreign object. Note that the power receiving device 401 may determine whether a foreign object has been detected according to the data obtained by the calibration process.

[0116] [Foreign object detection process according to temperature rise] The following describes processing performed when foreign object detection is performed in response to detection of a temperature rise in the power transmitting device 402 or the power receiving device 401. Possible causes of a temperature rise in the power transmitting device 402 or the power receiving device 401 include heat generation from electrical circuits, including antennas, that the power transmitting device 402 and the power receiving device 401 have, and heat generation from the CPU due to various processes. Furthermore, if a foreign object is present near the power transmitting device 402 or the power receiving device 401, the foreign object may consume part of the energy of the transmitted power, generating heat, which may in turn increase the temperature of the power transmitting device 402 or the power receiving device 401 that is in contact with the foreign object. Therefore, if the temperature of the power transmitting device 402 or the power receiving device 401 rises above a predetermined threshold, there is a possibility that a foreign object is present near the power transmitting device 402 or the power receiving device 401, and therefore the power transmitting device 402 and the power receiving device 401 perform control to detect a foreign object.

[0117] First, the operation of the power transmitting device 402 and the power receiving device 401 when the power transmitting device 402 detects a temperature rise will be described. The power transmitting device 402 has a temperature sensor, and when the temperature sensor detects that the temperature of the power transmitting device 402 has exceeded a predetermined threshold, the power transmitting device 402 performs foreign object detection using a waveform attenuation method. If it is determined that a foreign object is present, the power transmitting device 402 stops power transmission or controls the power transmission to be reduced.

[0118] The reason why foreign object detection is performed using the waveform attenuation method rather than the power loss method is as follows. In other words, the power loss method requires the power transmitting device 402 to receive a received power value from the power receiving device 401, whereas the waveform attenuation method does not require the power transmitting device 402 to receive information from the power receiving device 401, thereby enabling foreign object detection to be performed in a short time. Furthermore, the waveform attenuation method can perform foreign object detection with higher accuracy than the power loss method. In other words, when the temperature of the power transmitting device 402 is high and there is a possibility that a foreign object may be present, the waveform attenuation method can detect the foreign object quickly and with high accuracy. However, foreign object detection may also be performed using the power loss method. In this case, the power transmitting device 402 notifies the power receiving device 401 that foreign object detection will be performed using the power loss method. Upon receiving this notification, the power receiving device 401 transmits to the power transmitting device 402 a foreign object detection execution command using the power loss method, including the received power value measured by the power receiving device 401.

[0119] Next, the operation of the power transmitting device 402 and the power receiving device 401 when the power receiving device 401 detects a temperature rise will be described. The power receiving device 401 has a temperature sensor, and when the temperature sensor detects that the temperature of the power receiving device 401 has exceeded a predetermined threshold, the power receiving device 401 transmits a command to the power transmitting device 402 to perform foreign object detection using the waveform attenuation method. The power transmitting device 402 then performs foreign object detection using the waveform attenuation method, and when it determines that a foreign object is present, it stops power transmission or controls the power transmission so as to reduce the transmitted power. Note that foreign object detection may be performed using a power loss method instead of the waveform attenuation method. In this case, the power receiving device 401 transmits a command to the power transmitting device 402 to perform foreign object detection using the power loss method in response to temperature information detected by the temperature sensor.

[0120] Note that the allowable temperature of power transmitting or receiving devices may be subject to certain standards or national laws. Therefore, by setting the threshold for determining whether to perform foreign object detection lower than these standards, even if a temperature rise occurs due to a foreign object, it is possible to detect the foreign object early, before the temperature reaches the specified value.

[0121] [Foreign object detection processing according to transmission power] Next, a process will be described for when foreign object detection is performed using a method selected according to the transmission power transmitted from the power transmitting device 402. As described above, the power loss method performs foreign object detection based on the loss of power during power transmission from the power transmitting device 402 to the power receiving device 401. This method has the disadvantage that the accuracy of foreign object detection decreases when the power transmitting device 402 is transmitting large amounts of power. On the other hand, it has the advantage that foreign object detection can be performed while power transmission is continuing, thereby maintaining high power transmission efficiency. On the other hand, the waveform attenuation method performs foreign object detection by observing the attenuation rate of the transmitted wave when the power transmitting device 402 temporarily stops transmitting power. This method has the disadvantage that power transmission efficiency decreases when power transmission is temporarily stopped. On the other hand, it has the advantage that foreign object detection can be performed with high accuracy even during high power transmission.

[0122] Therefore, when the transmitted power value from the power transmitting device 402 is below a predetermined threshold, the power transmitting device 402 and the power receiving device 401 are controlled to perform foreign object detection only using the power loss method. This is because, when the transmitted power is low, the power loss method also has high foreign object detection accuracy, making the power loss method advantageous for maintaining high power transmission efficiency. On the other hand, when the transmitted power from the power transmitting device 402 is equal to or greater than a predetermined threshold, the power transmitting device 402 and the power receiving device 401 are controlled to perform foreign object detection using both the power loss method and the waveform attenuation method, or to perform foreign object detection only using the waveform attenuation method. This is because, when the transmitted power is high, the accuracy of foreign object detection using the power loss method decreases, making it effective to use the waveform attenuation method, which has high foreign object detection accuracy. In this way, by selectively using multiple foreign object detection methods depending on the transmitted power, it is possible to improve foreign object detection accuracy while maintaining high power transmission efficiency.

[0123] The above-described foreign object detection processes in response to communication errors, power drop, calibration data, and temperature information have been described with a focus on cases where both the power loss method and the waveform attenuation method are used. However, when the transmitted power is lower than a predetermined threshold, foreign object detection may be performed using the power loss method at the timing when the waveform attenuation method was used in these embodiments. Furthermore, when the transmitted power is equal to or greater than a predetermined threshold, both the power loss method and the waveform attenuation method may be used, or foreign object detection may be performed using the waveform attenuation method at the timing when the power loss method was used in the above-described embodiments.

[0124] In the present embodiment, the wireless power transmission system determines whether a predetermined condition related to the state of at least one of the power transmitting device 402 and the power receiving device 401 is satisfied, and selectively uses the power loss method or the waveform attenuation method depending on the determination result. However, this is not limiting, and at least one of the power transmitting device 402 and the power receiving device 401 may selectively use a plurality of foreign object detection methods, including foreign object detection methods other than those described above, depending on the conditions. Furthermore, the wireless power transmission system may select a foreign object detection method or control foreign object detection processing by combining a plurality of conditions, including the various conditions described above and other conditions.

[0125] 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 device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. The program may also be provided by recording it on a computer-readable storage medium. [Explanation of symbols]

[0126] 401 Power receiving device 402 Power transmission equipment

Claims

[Claim 1] A power transmission device, power transmission means for wirelessly transmitting power to a power receiving device; a first detection means for periodically executing a detection process using a first detection method for detecting an object other than the power receiving device based on a power loss related to power transmission by the power transmitting means; a determination means for determining whether a predetermined condition regarding the state of at least one of the power transmitting device and the power receiving device is satisfied; A power transmission device characterized by having a second detection means that executes a detection process using a second detection method that detects the object based on at least one of the voltage attenuation state and the current attenuation state related to power transmission by the power transmission means, in accordance with the result of the judgment by the judgment means.

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