Power receiving device, power transmitting device, wireless power transmission method, and program

Abstract

To make it possible to more quickly perform re-detection processing, according to a result of detection processing for detecting an object different from a power transmitting device and a power receiving device.SOLUTION: A power receiving device 401 includes: a coil 205 that wirelessly receives power from a power transmitting device; a communication unit 204 that transmits at predetermined intervals a signal for executing detection processing for detecting an object different from the power transmitting device and the power receiving device, based on values of voltage or current at at least two time points during a predetermined time period during which the power transmitting device restricts transmission, and receives, from the power transmitting device, a response signal that includes a detection result based on the detection processing executed according to the transmitted signal; and a control unit 201 that performs control so that the signal is transmitted at intervals shorter than the predetermined intervals when the detection result included in the received response signal satisfies a predetermined condition.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, technological developments in wireless power transmission systems have been widely conducted. Patent Document 1 discloses a foreign object detection method in accordance with the Wireless Power Consortium standard (WPC standard). Patent Document 2 discloses a foreign object detection method for detecting the presence of an object (hereinafter referred to as a foreign object) different from a power receiving device and a power transmitting device based on a change in energy attenuation or a change in resonant frequency of a power transmitting coil and a resonant circuit integrated with or coupled to the power transmitting coil. Patent Document 3 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] Special Publication No. 2018-512036 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-27172 Summary of the Invention [Problem to be solved by the invention]

[0004] In wireless power transmission, if a foreign object is determined to be present, the power transmitting device stops power transmission, thereby reducing the possibility of the foreign object generating heat due to power transmission to the foreign object. Furthermore, the foreign object detection process is assumed to be performed in response to a predetermined signal received by the power transmitting device from the power receiving device. However, depending on the result of the foreign object detection process, there may be cases where the presence or absence of a foreign object is not clearly indicated. In such cases, there is a risk that power transmission will continue, increasing the possibility of the foreign object generating heat, or that power transmission will be stopped even when no foreign object is present, resulting in reduced power transmission efficiency.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to enable a re-detection process to be performed more quickly depending on the results of a detection process for detecting an object other than a power transmitting device and a power receiving device. [Means for solving the problem]

[0006] The power receiving device of the present disclosure includes a power receiving unit that wirelessly receives power from a power transmitting device, and a packet including information on the received power in the power transfer phase. Send a transmitting means for receiving a response from the power transmitting device in response to the packet regarding the presence of a foreign object; and a control means for switching to a second mode in which the packet is transmitted at a second time interval longer than the first time interval when a response indicating that no foreign object is present in response to the packet is received after the packet has been transmitted in a first mode in which the packet is transmitted at a first time interval. [Effects of the Invention]

[0007] According to the present disclosure, a detection process is performed again more quickly depending on the result of the detection process for detecting an object different from the power transmitting device and the power receiving device. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram illustrating an example of the configuration of a power transmitting device. [Figure 2]FIG. 2 illustrates an example of the configuration 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 diagram illustrating an example of a process for performing 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] 4 is a flowchart for explaining the operation of the power receiving device in the first embodiment. [Figure 9] 4 is a diagram for explaining the operation of the power receiving device and the power transmitting device in the first embodiment. FIG. [Figure 10] 10 is a flowchart illustrating the operation of the power receiving device according to the second embodiment. [Figure 11] 10 is a diagram for explaining the operation of a power receiving device and a power transmitting device in the second embodiment. FIG. [Figure 12] 10A and 10B are diagrams for explaining a method for setting a threshold value in foreign matter detection using the Power Loss method. [Figure 13] 10A and 10B are diagrams for explaining a method for setting a threshold value in detecting foreign matter using a waveform attenuation method. [Figure 14] FIG. 10 is a diagram for explaining a process when a plurality of waveform attenuation methods are performed. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Embodiment 1> 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 configurations, 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 configurations.

[0010] (Configuration of wireless power transmission system) FIG. 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 RX401, and the power transmitting device 402 may be referred to as TX402. The RX401 is an electronic device that receives power from the TX402 and charges its built-in battery. The TX402 is an electronic device that wirelessly transmits power to the RX401 placed on a charging stand 403, which is part of the TX402. Hereinafter, since the charging stand 403 is part of the TX402, "placed on the charging stand 403" may be referred to as "placed on the TX402 (power transmitting device 402)." An area 404 surrounded by a dotted line is an area within which the RX401 can receive power from the TX402. Furthermore, the state of being "placed" does not necessarily mean that the RX 401 and the TX 402 are in contact with each other, but refers to a state in which the RX 401 is included in the range 404.

[0011] Note that the RX401 and the TX402 may have a function for executing applications other than wireless charging. An example of the RX401 is an information processing terminal such as a smartphone, and an example of the TX402 is an accessory device for charging the information processing terminal. For example, the information terminal device has a display unit (display) that displays information to a user and receives power from a receiving coil (antenna). The power received from the receiving coil is stored in a power storage unit (battery), and power is supplied from the battery to the display unit. In this case, the RX401 may have a communication unit that communicates with another device different from the TX402. The communication unit may be compatible with communication standards such as NFC communication or the fifth-generation mobile communication system (5G). In this case, the communication unit may perform communication by receiving power from the battery. The RX401 may also have a function for notifying the remaining battery level. The RX401 may also be a tablet terminal, a storage device such as a hard disk drive or a memory device, or an information processing device such as a personal computer (PC). The RX 401 may be, for example, an imaging device (such as a camera or video camera). The RX 401 may be an image input device such as a scanner, or an image output device such as a printer, a copier, or a projector. The RX 401 may be a robot, a medical device, or the like. The TX 402 may be a device for charging the above-mentioned devices.

[0012] TX402 may be a smartphone, in which case RX401 may be another smartphone or a wireless earphone.

[0013] Furthermore, the RX401 in this embodiment may be a vehicle such as an automobile. For example, the automobile serving as the RX401 may receive power from a charger (TX402) via a power transmitting antenna installed in a parking lot. Alternatively, the automobile serving as the RX401 may receive power from the charger (TX402) via a power transmitting coil (antenna) embedded in the road. In such an automobile, the received power is supplied to a battery. The battery power may be supplied to a driving unit (motor, electric unit) that drives the wheels, or may be used to drive a sensor used for driving assistance or a communication unit that communicates with an external device. In other words, in this case, the RX401 may have, in addition to the wheels, a battery, a motor or sensor that is driven using the received power, and even a communication unit that communicates with devices other than the TX402.

[0014] Furthermore, RX401 may have a storage unit for storing a person. For example, the sensor may be a sensor used to measure the distance between vehicles or the distance to other obstacles. The communication unit may be compatible with the Global Positioning System (Global Positioning Satellite, GPS). The communication unit may also be compatible with communication standards such as the fifth generation mobile communication system (5G). The vehicle may also be a bicycle or a motorcycle. RX401 is not limited to a vehicle, and may also be a mobile object or an aircraft having a power source that is powered by power stored in a battery. TX402 may also be a charger installed in a console or the like inside a vehicle, or a charging device that charges an electric vehicle. RX102 does not necessarily have to have a built-in battery.

[0015] In addition, the RX 401 and TX 402 in this embodiment perform processing based on the Wireless Power Consortium standard (WPC standard). Details of the processing will be described later.

[0016] (Configuration of power transmitting device 402 and power receiving device 401) Next, the configurations of the power transmitting device 402 (TX402) and the power receiving device 401 (RX401) in this embodiment will be described. Note that the configurations described below are merely examples, and part (or in some cases all) 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.

[0017] Fig. 1 is a functional block diagram showing an example configuration of a TX 402 according to this embodiment. The TX 402 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.

[0018] The control unit 101 controls the entire TX 402 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 402. 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 central processing unit (CPU) or a microprocessor unit (MPU). 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 a field programmable gate array (FPGA), 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).

[0019] 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.

[0020] The power transmitting unit 103 converts DC or AC power input from the power supply unit 102 into AC frequency power in a frequency band used for wireless power transmission, and inputs the AC frequency power to the power transmitting antenna (coil) 105 to generate electromagnetic waves for receiving power in the RX 401. 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.

[0021] 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 frequency 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 (RX401) that complies with the WPC standard.

[0022] The communication unit 104 communicates with the RX 401 for power transmission control based on the WPC standard. The communication unit 104 performs frequency shift keying on the electromagnetic waves output from the power transmitting antenna 105 and transmits information to the RX 401 to perform communication. The communication unit 104 also acquires information transmitted by the RX 401 by demodulating the electromagnetic waves transmitted from the power transmitting antenna 105 that have been amplitude-modulated or load-modulated by the RX 401. 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 401 using a standard other than the WPC standard that uses an antenna other than the power transmitting antenna 105, or may communicate with the RX 401 by selectively using multiple communication standards. Examples of such communication standards include Bluetooth (registered trademark) Low Energy (BLE) and NFC (Near Field Communication).

[0023] The memory 106 stores the control program and also stores the states (transmitted power value, received power value, etc.) of the TX 402 and the RX 401. For example, the state of the TX 402 is acquired by the control unit 101, and the state of the RX 401 is acquired by the control unit 201 of the RX 401, and can be received via the communication unit 104.

[0024] 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, 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.

[0025] 2 is a block diagram showing an example of the configuration of a power receiving device 401 (RX401) according to this embodiment. The RX401 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 implemented as a single hardware module.

[0026] The control unit 201 controls the entire RX401 by executing a control program stored in the memory 208, for example. That is, the control unit 201 controls each functional unit shown in FIG. 2. 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 RX401 (or the entire smartphone if the RX401 is a smartphone) in cooperation with an OS (Operating System) that it is running.

[0027] 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).

[0028] 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 RX401 main body, and other operations. The UI unit 202 is realized by a liquid crystal panel, speaker, vibration motor, etc.

[0029] The power receiving unit 203 acquires, via the power receiving antenna (coil) 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 402. The power receiving unit 203 then converts the AC power into DC power or AC power of a predetermined frequency, and outputs the power to the charging unit 206, which performs processing to charge the battery 207. That is, the power receiving unit 203 includes a rectifier unit and a voltage control unit required to supply power to the load in the RX 401. The above-mentioned GP is the amount of power guaranteed to be output from the power receiving unit 203. The power receiving unit 203 is assumed to have the capacity to supply power for the charging unit 206 to charge the battery 207 and to output 15 watts of power to the charging unit 206.

[0030] The communication unit 204 communicates with the communication unit 104 of the TX 402 for power reception control based on the WPC standard. The communication unit 204 demodulates electromagnetic waves input from the power receiving antenna 205 to acquire information transmitted from the TX 402. The communication unit 204 then performs amplitude modulation or load modulation on the input electromagnetic waves to superimpose a signal related to information to be transmitted to the TX 402 onto the electromagnetic waves, thereby communicating with the TX 402. Note that the communication unit 204 may communicate with the TX 402 using a standard other than the WPC standard and using an antenna other than the power receiving antenna 205, or may selectively use multiple communication standards to communicate with the TX 402. Examples of such communication standards include Bluetooth (registered trademark) Low Energy (BLE) and NFC (Near Field Communication).

[0031] The memory 208 stores the control program and also stores the status of the TX 402 and the RX 401. For example, the status of the RX 401 is acquired by the control unit 201, and the status of the TX 402 is acquired by the control unit 101 of the TX 402, and can be received via the communication unit 204.

[0032] First switch unit 209 and second switch unit 210 are controlled by control unit 201. Power receiving antenna 205 is connected to resonant capacitor 211, and when second switch unit 210 is turned on and short-circuited, power receiving antenna 205 and 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 power receiving antenna 205, resonant capacitor 211, and second switch unit 210, but no current flows through the power receiving unit. When second switch unit 210 is turned off and opened, power received by power receiving antenna 205 and resonant capacitor 211 is supplied to power receiving unit 203.

[0033] 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 .

[0034] Next, the function of the control unit 101 of the TX 402 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 402). 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.

[0035] The communication control unit 301 performs control communication with the RX 401 based on the WPC standard via the communication unit 104. The power transmission control unit 302 controls the power transmitting unit 103 to control power transmission to the RX 401. The measurement unit 303 measures a waveform attenuation index, which will be described later. It also measures the power transmitted to the RX 401 via the power transmitting unit 103 and measures the average transmitted power per unit time. It 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.

[0036] The foreign object detection unit 305 performs processing to detect a foreign object within the power transmission range of the TX 402. Here, in this embodiment, a foreign object refers to an object other than a power receiving device and a power transmitting device. 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, and a foreign object detection function using a waveform attenuation method, which will be described later. 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 402 equipped with an NFC (Near Field Communication) communication function, the foreign object detection unit 305 may perform foreign object detection processing using an opposing device detection function according to the NFC standard. In addition to detecting foreign objects, the foreign object detection unit 305 can also detect changes in the state of the TX 402. For example, the TX 402 can detect an increase or decrease in the number of RXs 401 on the TX 402.

[0037] 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 402 performs foreign object detection using the power loss method, the Q-factor 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. 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-factor measured by the measurement unit 303.

[0038] 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.

[0039] In this embodiment, the RX401 and TX402 perform wireless power transmission using an electromagnetic induction method for wireless charging based on the WPC standard. That is, the RX401 and TX402 perform wireless power transmission for wireless charging based on the WPC standard between the power receiving antenna 205 of the RX401 and the power transmitting antenna 105 of the TX402. Note that the wireless power transmission method applied to this system is not limited to the method defined by the WPC standard, and may be other methods such as electromagnetic induction, magnetic field resonance, electric field resonance, microwave, or laser. Furthermore, 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.

[0040] In the WPC standard, the amount of power guaranteed to be output to a load (battery) of a power receiving device when the power receiving device receives power from a power transmitting device is specified by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates a power value that is guaranteed to be output to a load (e.g., a charging circuit, battery, etc.) of the RX401 even if, for example, the positional relationship between the RX401 and the TX402 fluctuates and the power transmission efficiency between the power receiving antenna 205 and the power transmitting antenna 105 decreases. For example, if the GP is 5 watts, the TX402 transmits power by controlling so as to be able to output 5 watts to the load in the RX401, even if the positional relationship between the power receiving antenna 205 and the power transmitting antenna 105 fluctuates and the power transmission efficiency decreases.

[0041] Furthermore, when transmitting power from the TX402 to the RX401, if a foreign object other than the RX401 is present near the TX402, 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 the TX402 to detect the presence of a foreign object on the charging base 403, so that power transmission can be stopped if a foreign object is present, thereby preventing the foreign object from overheating or being destroyed. Specifically, the WPC standard specifies a power loss method for detecting a foreign object based on the difference between the power transmitted by the TX402 and the power received by the RX401. The standard also specifies a Q-factor measurement method for detecting a foreign object based on a change in the quality factor (Q-factor) of the power transmitting antenna 105 in the TX402. Note that the foreign object detected by the TX402 in this embodiment is not limited to an object present on the charging base 403. The TX402 may detect a foreign object located near the TX402, for example, within a range to which the TX402 can transmit power.

[0042] (Processing based on WPC standards) The following describes processing based on the WPC standard performed by the RX401 and TX402 according to this embodiment. The WPC standard defines multiple phases, including a power transfer phase in which power transfer is performed and one or more phases before the actual power transfer, and in each phase, communication is performed for necessary power transmission and reception control. Phases before power transfer 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.

[0043] In the Selection phase, the TX402 transmits Analog Pings intermittently to detect that an object has been placed on the charging base of the TX402 (for example, that the RX401 or a conductor piece has been placed on the charging base). The TX402 detects at least one of the voltage value and current value of the power transmitting antenna 105 when the Analog Ping is transmitted, and determines that an object is present if the voltage value is below a certain threshold or the current value exceeds a certain threshold, and transitions to the Ping phase.

[0044] In the Ping phase, the TX402 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 RX401 placed on the TX402. The RX401 notifies the TX402 of the magnitude of the received voltage. In this way, the TX402 recognizes that the object detected in the Selection phase is the RX401 by receiving a response from the RX401 that received the Digital Ping. Upon receiving notification of the received voltage value, the TX402 transitions to the I&C phase. Furthermore, before transmitting the Digital Ping, the TX402 measures the Q-factor of the power transmitting antenna 105. This measurement result is used when executing foreign object detection processing using the Q-factor measurement method.

[0045] In the I&C phase, the TX402 identifies the RX401 and acquires device configuration information (capability information) from the RX401. The RX401 transmits an ID packet and a configuration packet. The ID packet contains the identifier information of the RX401, and the configuration packet contains the device configuration information (capability information) of the RX401. Upon receiving the ID packet and configuration packet, the TX402 responds with an acknowledgement (ACK, positive response). Then the I&C phase ends.

[0046] In the Negotiation phase, the GP value is determined based on the GP value requested by RX401 and the power transmission capability of TX402. TX402 also receives an FOD Status Packet containing Reference Quality Factor Value information from RX401, and adjusts and determines the threshold value for the Q-factor measurement method. TX402 then performs foreign object detection processing using the Q-factor measurement method in accordance with the request from RX401. The WPC standard also stipulates a method in which, after transitioning to the Power Transfer phase, processing similar to that of the Negotiation phase is performed again at the request of RX401. The phase in which these processing operations are performed after transitioning from the Power Transfer phase is called the Renegotiation phase.

[0047] In the calibration phase, calibration is performed based on the WPC standard. The RX 401 also notifies the TX 402 of a predetermined received power value (received power value under light load / received power value under maximum load), and the TX 402 adjusts the power transmission for efficient power transmission. The received power value notified to the TX 402 can be used for foreign object detection processing using the Power Loss method.

[0048] 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, the TX402 and RX401 communicate using the power transmitting antenna 105 and the power receiving antenna 205 by superimposing a signal on the electromagnetic waves transmitted from the power transmitting antenna 105 or the power receiving antenna 205. The range in which communication based on the WPC standard is possible between the TX402 and RX401 is approximately the same as the power transmission range of the TX402.

[0049] The above is an explanation of the processing performed by the RX401 and TX402 in this embodiment. Below, the operations of the RX401 and TX402 in each of the above-mentioned phases will be explained using the sequence diagram in Fig. 5. Fig. 5 is a sequence diagram for power transmission in accordance with the WPC standard. Here, the explanation will be given using the power transmitting device 402 (TX402) and the power receiving device 401 (RX401) as examples.

[0050] The TX402 repeatedly and intermittently transmits Analog Pings according to the WPC standard to detect objects within its power transmission range (F501). The TX402 executes the processes defined as the Selection phase and Ping phase of the WPC standard, and waits for the RX401 to be placed on it. The user of the RX401 brings the RX401 (e.g., a smartphone) close to the TX402 to charge it (F502). For example, the user places the RX401 on the TX402, bringing the RX401 closer to the TX402.

[0051] When the TX402 detects the presence of an object within its power transmission range using Analog Ping (F503, F504), it transmits a Digital Ping according to the WPC standard (F505). When the RX401 receives the Digital Ping, it knows that the TX402 has detected the RX401 (F506). Furthermore, when the TX402 receives a predetermined response to the Digital Ping, it determines that the detected object is the RX401 and that the RX401 has been placed on the charging stand 403. When the TX402 detects that the RX401 has been placed, it acquires identification information and capability information from the RX401 through I&C phase communication defined in the WPC standard (F507). Here, the RX401 identification information includes the Manufacturer Code and Basic Device ID. The RX401 capability information includes the following information: That is, it includes information elements capable of identifying the supported version of the WPC standard, a Maximum Power Value that specifies the maximum power that the RX401 can supply to a load, and information indicating whether the RX402 has the negotiation function of the WPC standard. Note that the TX402 may acquire the identification information and capability information of the RX401 by a method other than communication in the I&C phase of the WPC standard. The identification information may also be any other identification information capable of identifying the individual RX401, such as a Wireless Power ID. The capability information may also include information other than the above.

[0052] Next, the TX402 determines the GP value with the RX401 through communication in the negotiation phase defined by the WPC standard (F508). Note that in F508, other procedures for determining the GP may be executed, not limited to communication in the negotiation phase defined by the WPC standard. Furthermore, if the TX402 acquires information indicating that the RX401 does not support the negotiation phase (for example, in F507), the TX402 may not perform communication in the negotiation phase. In this case, the TX402 may set the GP value to a small value (for example, predefined in the WPC standard). In this embodiment, GP=5 watts.

[0053] After determining the GP, the TX402 performs calibration based on the GP. In the calibration process, first, the RX401 transmits information (hereinafter referred to as first reference received power information) including the received power in a light load state (a load disconnected state or a load state in which the transmitted power is equal to or less than a first threshold) to the TX402 (F509). In this embodiment, the first reference received power information is the received power information of the RX401 when the transmitted power of the TX402 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. Note that Received Power Packet (mode 1) will also be referred to as "RP1" below. The TX402 determines whether to accept the first reference received power information based on the power transmission state of its own device. If the TX402 accepts the information, it transmits an acknowledgement (ACK) to the RX401, and if not, it transmits a negative acknowledgement (NAK) to the RX401.

[0054] Next, when the RX401 receives an ACK from the TX402 (F510), it performs processing to transmit to the TX402 information (hereinafter referred to as second reference received power information) including the received power in a load connection state (a maximum load state or a load state in which the transmitted power is equal to or greater than the second threshold). In this embodiment, since the GP is 5 watts, the second reference received power information is the received power information of the RX401 when the transmitted power of the TX402 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. Note that Received Power Packet (mode 2) will also be referred to as "RP2" below. The RX401 transmits a transmitted power output change request including a positive value to increase the transmitted power from the TX402 to 5 watts (F511).

[0055] The TX402 receives the above-mentioned transmission power output change request, 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 the TX402 is 5 watts, if the TX402 receives a power increase request exceeding 5 watts from the RX401 (F514), it responds with an NAK to the transmission power output change request. This prevents power transmission above the specified level (F515).

[0056] When RX401 determines that the predetermined transmission power has been reached by receiving a NAK from TX402, it transmits information including the received power in the load-connected state to TX402 as second reference received power information (F516). TX402 can calculate the amount of power loss between TX402 and RX401 in the load-disconnected state and the load-connected state based on the TX402 transmission power value and the received power values ​​included in the first and second reference received power information. Furthermore, by interpolating between these power loss amounts, it is possible to calculate an estimate of the power loss between TX402 and RX401 for all possible transmission power values ​​of TX402 (between 250 milliwatts and 5 watts in this case) (F517). TX402 transmits an ACK in response to the second reference received power information from RX401 (F518), completing the calibration process.

[0057] When the TX 402 determines that charging processing can be started, it starts power transmission processing to the RX 401, which starts charging the RX 401. Before starting power transmission processing, the TX 402 and RX 401 perform device authentication processing (F519), and if it is determined that the other device can support a higher GP, the GP may be reset to a higher value, for example, 15 watts (F520).

[0058] In this case, RX401 and RX402 increase the transmission power using a transmission power change request, ACK, and NAK to increase the transmission power of TX402 to 15 watts (F521 to F524). Then, TX402 and RX401 perform calibration processing again for GP=15 watts. Specifically, RX401 transmits information including the received power in the RX401 load-connected state when the TX402 transmission power is 15 watts (hereinafter referred to as third reference received power information) (F525). TX402 performs calibration based on the received power included in the first, second, and third reference received power information. This allows TX402 to calculate the amount of power loss between TX402 and RX401 for all possible transmission powers of TX402 (in this case, from 250 milliwatts to 15 watts) (F526). The TX402 sends an ACK in response to the third reference received power information from the RX401 (F527) and completes the calibration process. When the TX402 determines that charging can begin, it starts transmitting power to the RX401 and moves to the power transfer phase (F528). Note that the processes from F519 to F527 are not essential.

[0059] In the power transfer phase, the TX402 transmits power to the RX401. Foreign object detection is also performed using the power loss method. In the power loss method, the TX402 first calculates the amount of power loss between the TX402 and RX401 in a state where no foreign object is present, based on the difference between the power transmitted by the TX402 and the power received by the RX401, using the calibration described above. The calculated value corresponds to the reference amount of power loss in a normal state (a state where no foreign object is present) during power transmission processing. The TX402 then determines that a foreign object is present if the amount of power loss between the TX402 and RX401 measured during power transmission after calibration deviates from the amount of power loss in a normal state by more than a threshold value. A more detailed explanation of the power loss method will be given later.

[0060] The power loss method detects foreign objects based on the results of measuring power loss while power is being transmitted from the TX402 to the RX401. While the power loss method of foreign object detection has the disadvantage that the accuracy of foreign object detection decreases when the TX402 is transmitting a large amount of power, it has the advantage that foreign object detection can be performed while power transmission is continuing, thereby maintaining high power transmission efficiency.

[0061] The above is the flow of processing based on the WPC standard. In the F528 power transmission processing, when power transmission is to be terminated because the battery of RX401 is fully charged, a foreign object is detected, or the like, RX401 transmits a power transmission stop request command to TX402 requesting that power transmission be stopped. In this embodiment, the power transmission stop request command is an EPT (End Power Transfer) command (packet). This terminates the power transmission processing.

[0062] (Power Loss Method) Foreign object detection based on the power loss method defined in the WPC standard will be explained using Fig. 12. The horizontal axis of Fig. 12 represents the transmitted power of the TX 402, and the vertical axis represents the received power of the RX 401. A foreign object is an object other than the RX 401 that may affect the power transmission from the TX 402 to the RX 401, such as a conductive metal piece.

[0063] First, the TX 402 transmits power to the RX 401 at a first transmission power value Pt1. The RX 401 receives power at a first reception power value Pr1 (this state is called a light load state). Then, the TX 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 RX 401 controls the received power to be minimum power. For example, the RX 401 may control the first switch unit 209 to disconnect the power receiving antenna 205 from the load (such as a charging circuit and a battery) so that the received power is not supplied to the load. Next, the RX 401 notifies the TX 402 of the power value Pr1 of the first reception power. TX402, which has received Pr1 from RX401, calculates that the power loss between TX402 and RX401 is Pt1-Pr1 (Ploss1), and can create a calibration point 1200 (which indicates the correspondence between Pt1 and Pr1).

[0064] Next, the TX402 changes the transmission power value to the second transmission power value Pt2 and transmits power to the RX401. The RX401 receives power at the second received power value Pr2 (this state is called a connected load state). The TX402 then stores the second transmission power value Pt2. Here, the second transmission power value Pt2 or the second received power value Pr2 is a predetermined maximum transmission power or received power. At this time, the RX401 controls the received power to be the maximum power. For example, the RX401 controls the first switch unit 209 to connect the power receiving antenna 205 and the load so that the received power is supplied to the load. Next, the RX401 notifies the TX402 of Pr2. Upon receiving Pr2 from RX401, TX402 calculates that the power loss between TX402 and RX401 is Pt2-Pr2 (Ploss2), and can create a calibration point 1001 that indicates the correspondence between Pt2 and Pr2.

[0065] Then, the TX402 creates a straight line 1202 that linearly interpolates between the calibration point 1200 and the calibration point 1201. The straight line 1202 shows the relationship between the transmitted power and the received power in a state where there is no foreign object near the TX402 and the RX401. Based on the straight line 1202, the TX402 can predict the power value that the RX401 will receive when transmitting power at a predetermined transmitted power in a state where there is no foreign object. For example, if the TX402 transmits power at a third transmitted power value Pt3, it can be inferred from the point 1203 on the straight line 1202 that corresponds to Pt3 that the third received power value that the RX401 will receive will be Pr3.

[0066] As described above, the power loss between the TX402 and RX401 corresponding to the load can be calculated based on multiple combinations of the transmitted power value of the TX402 and the received power value of the RX401 measured while changing the load. Furthermore, the power loss between the TX402 and RX401 corresponding to all loads can be estimated by interpolating from multiple combinations. In this way, the calibration process performed by the TX402 and RX401 to allow the TX402 to obtain combinations of transmitted power values ​​and received power values ​​is hereinafter referred to as "calibration process (CAL process) using the power loss method."

[0067] Assume that after calibration, when the TX402 actually transmits power to the RX401 at Pt3, the TX402 receives a received power value Pr3' from the RX401. The TX402 calculates Pr3-Pr3' (=Ploss_FO) by subtracting the received power value Pr3' actually received from the RX401 from the received power value Pr3 when no foreign object is present. This Ploss_FO can be considered to be the power loss due to the power consumed by a foreign object when a foreign object is present near the TX402 and RX401. Therefore, if the 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, the TX402 may calculate the power loss Pt3-Pr3 (Ploss3) between the TX402 and RX401 in advance from the received power value Pr3 when no foreign object is present. Next, the power loss Pt3-Pr3' (Ploss3') between TX402 and RX401 when a foreign object is present is calculated from the received power value Pr3' received from RX401 when a foreign object is present. Then, the power Ploss_FO that would have been consumed by the foreign object may be estimated using Ploss3'-Ploss3 (=Ploss_FO).

[0068] 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 described as a basic method, 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.

[0069] After the straight line 1002 is acquired by the calibration process, the foreign object detection unit 305 of the TX 402 periodically receives the current received power value (for example, the above-mentioned Pr3') from the RX 401 via the communication unit 104. The current received power value periodically transmitted by the RX 401 is transmitted to the TX 402 as a Received Power Packet (mode 0). The foreign object detection unit 305 of the TX 402 performs foreign object detection based on the received power value stored in the Received Power Packet (mode 0) and the straight line 1002. Note that Received Power Packet (mode 0) will be referred to as "RP0" below.

[0070] 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).

[0071] During the power transfer phase in the WPC standard, foreign object detection is performed using the power loss method. 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 one is actually present. In particular, the power transfer phase is the phase in which the TX402 transmits power. If a foreign object is present near the TX402 and RX401 during power transmission, heat generation from the foreign object increases. Therefore, 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 implemented to improve the accuracy of foreign object detection.

[0072] (Foreign object detection method using waveform attenuation method) In the power transfer phase, the TX402 transmits power to the RX401. 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 will be possible without using a newly defined foreign object detection signal, etc. A method of foreign object detection based on the attenuation state of the transmission wave (hereinafter referred to as the waveform attenuation method) will be explained using FIG. 6. FIG. 6 is a diagram explaining 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 TX402 (TX402) to the RX401 (RX401) will be explained as an example.

[0073] In Figure 6, the waveform shows the change over time in the voltage value 600 (hereinafter simply referred to as voltage value) of the high-frequency voltage applied to the power transmitting antenna 105 of the TX402. The horizontal axis of Figure 6 represents time, and the vertical axis represents voltage value. The TX402, which is transmitting power to the RX401 via the power transmitting antenna 105, limits its power transmission at time T0. That is, at time T0, the power supply for power transmission from the power supply unit 102 is limited. Note that limiting the power means stopping the power or reducing the power to a predetermined value or below.

[0074] The frequency of the transmitting wave for power transmission from the TX 402 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 can be calculated using Equation 1 based on the time, voltage values ​​at points 601 and 602 on the voltage value envelope and the frequency f of the high-frequency voltage. Q=πf(T2-T1) / ln(A1 / A2) (Equation 1)

[0075] If a foreign object is present near the TX402 and RX401, the Q value 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 value. A lower Q value 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.

[0076] 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.

[0077] 6, the attenuation of the current value flowing through the power transmitting antenna 105 during the power transmission stop period changes depending on the presence or absence of a foreign object, just as in the case of the voltage value. The waveform attenuation rate is higher when a foreign object is present than when no foreign object is present. Therefore, a foreign object can be detected by applying the above-described method to the temporal change in the current value flowing through the power transmitting antenna 105. Specifically, the Q value obtained from the current waveform, the slope of the attenuation of the current value, the difference in the current values, the ratio of the current values, the absolute value of the current values, the time it takes to reach a predetermined current value, and the like can be used as waveform attenuation indicators to determine the presence or absence of a foreign object and detect the foreign object.

[0078] 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 index of the voltage value and the waveform attenuation index of the current value. In the above example, the waveform attenuation index is measured during a period in which the TX402 temporarily stops power transmission, but this is not limiting. For example, the waveform attenuation index may be measured during a period in which the TX402 temporarily reduces the power supplied from the power supply unit 102 from a predetermined power level to a lower power level. In the above example, the voltage or current values ​​are measured at two points in time during a period in which the TX402 limits power transmission, but measurements may be performed at three or more points in time.

[0079] A method for detecting a foreign object based on a power transmission waveform during power transmission using the waveform attenuation method will be described with reference to Fig. 7. Fig. 7 shows a power 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 of the power transmitting antenna 105. Note that, similar to Fig. 6, the vertical axis may represent the voltage value of the power transmitting antenna 105.

[0080] During the transient response period immediately after TX402 starts transmitting power, the transmitted power waveform is not stable. Therefore, during this transient response period when the transmitted power waveform is not stable, RX401 controls TX402 not to communicate (communication by amplitude modulation or load modulation). Also, TX402 controls RX401 not to communicate (communication by frequency shift keying) with RX401. Hereinafter, this period is referred to as the communication prohibited period. Note that during this communication prohibited period, TX402 transmits power to RX401. After the communication prohibited period has elapsed, TX402 transmits power to RX401. Hereinafter, this period is referred to as the power transmission period. When TX402 receives a foreign object detection execution request (command) from RX401, it suspends power transmission after a predetermined period has elapsed. Alternatively, it temporarily reduces the transmitted power. Hereinafter, this predetermined period is referred to as the preparation period. Note that this foreign object detection execution request may be the above-mentioned Received Power Packet (mode 0), Received Power Packet (mode 1), or Received Power Packet (mode 2). Then, the power transmission control unit 302 of the TX 402 stops power transmission or temporarily reduces the transmission power. As a result, the amplitude of the transmitted wave attenuates. The period from when the TX 402 temporarily suspends or temporarily reduces the transmission power until it resumes power transmission is hereinafter referred to as the transmission power control period. The TX 402 calculates a waveform attenuation index of this attenuated waveform, and compares the calculated waveform attenuation index with a predetermined threshold to determine the presence or absence of a foreign object or the possibility (probability of presence) of a foreign object. The determination may be performed during the transmission power control period, a communication prohibited period, or a power transmission period.

[0081] If no foreign object is detected after the transmission power control period has elapsed, the TX402 resumes power transmission. During the transient response period immediately after power transmission resumes, the transmission waveform is not stable, and communication is prohibited again. The TX402 then transitions to a power transmission period in which stable power transmission is possible from the TX402 to the RX401.

[0082] As described above, the TX402 repeatedly executes the power transmission start, communication prohibition period, power transmission period, and transmission power control period. The TX402 then calculates the waveform attenuation index of the attenuated waveform at a predetermined timing, compares the calculated waveform attenuation index with a predetermined threshold, and determines the presence or absence of a foreign object, or the possibility (probability) of the presence of a foreign object. In other words, the waveform attenuation method determines the presence or absence of a foreign object based on the voltage or current values ​​at at least two points in time during the predetermined period during which the TX402 restricts power transmission. This completes the basic process of foreign object detection using the waveform attenuation method.

[0083] During the transmission power control period, 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 RX 401, the waveform attenuation index of the attenuated waveform is affected by the loads of these elements. That is, the waveform attenuation index 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 index is large, it is difficult to distinguish whether this 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 index to detect a foreign object, the RX 401 may turn off the first switch unit 209 during the preparation period. 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 the power receiving unit 203, the charging unit 206, and the battery 207. The RX 401 performs the above process when it transmits a foreign object detection execution request (command) to the TX 402. This enables highly accurate foreign object detection by detecting a foreign object based on the waveform attenuation index of the waveform observed when the first switch unit 209 or the second switch unit 210 is turned on and short-circuited (connected). Alternatively, the RX 401 may transition to a low power consumption mode or control power consumption to be constant during the above preparation period when the first switch unit 209 is turned on and short-circuited, and the second switch unit 210 is turned off and disconnected. In other words, if the power consumed by the RX 401 is not constant or if a large amount of power is consumed, the waveform attenuation index of the attenuated waveform will be affected by the fluctuations in power consumption. Therefore, the following process can be performed to eliminate this effect. That is, the power consumed by the RX401 is controlled by limiting or stopping the operation of software applications running on the RX401, putting the hardware function blocks of the RX401 into low power consumption mode or into operation stop mode, etc. Highly accurate foreign object detection is possible by detecting foreign objects based on the waveform attenuation index of the waveform observed under such conditions.

[0084] Similarly, the TX 402 may be configured to turn on the switch unit 108 to short-circuit it during the preparation period upon receiving a foreign object detection execution request (command) from the RX 401. That is, the TX 402 may be configured to allow current to flow through a closed loop formed by the power transmitting antenna 105, the resonant capacitor 107, and the switch unit 108. This makes it possible to eliminate the influence of the power supply unit 102, the power transmitting unit 103, and the communication unit 104. Alternatively, a switch (not shown) may be provided between the power transmitting antenna and the power transmitting unit, and the influence of the power supply unit 102, the power transmitting unit 103, and the communication unit 104 may be eliminated by turning off the switch during the preparation period.

[0085] (Method for setting the foreign object detection threshold in the waveform attenuation method) This section describes a method for setting a threshold value for determining the presence or absence of a foreign object or the possibility (probability) of the presence of a foreign object when detecting a foreign object using the waveform attenuation method. As described above, the waveform attenuation method detects a foreign object based on a "waveform attenuation index." The measured "waveform attenuation index" is compared with a predetermined threshold, and the presence or possibility of a foreign object is determined based on the result. There are several methods for setting this threshold. The first method is for the TX402 to store a predetermined value as the threshold value, which is a common value independent of the RX401 to which power is transmitted. Note that this value may be the same in all cases, or it may be a value determined by the TX402 depending on the situation. As described above, the presence of a foreign object increases the waveform attenuation rate of the transmission waveform during the transmission power control period. Therefore, a "waveform attenuation index" that is considered to be "absent" is stored as a predetermined value, and this is used as a threshold value to compare with the measured "waveform attenuation index." If the measured waveform attenuation index results in a waveform attenuation rate greater than the threshold, it is determined that "a foreign object is present" or "there is a high possibility that a foreign object is present." For example, if the "waveform attenuation index" is the Q value, the Q value measured by the TX402 is compared with a predetermined Q value (threshold) at which it is considered that no foreign object is present. If the measured Q value is smaller than the threshold Q value, it is determined that "foreign object is present" or "there is a high possibility that a foreign object is present." If the measured Q value is larger than or approximately equal to the threshold Q value, it is determined that "foreign object is not present" or "there is a low possibility that a foreign object is present." By doing as described above, foreign object detection using the waveform attenuation method can be achieved using the first method.

[0086] The second method is for the TX402 to adjust and determine the threshold value based on information transmitted from the RX401. As described above, the presence of a foreign object increases the waveform attenuation rate of the transmission waveform during the transmission power control period. Therefore, a "waveform attenuation index" that is considered to be "no foreign object present" is stored as a predetermined value in advance, and this is used as a threshold value to compare with the measured "waveform attenuation index." If the measured waveform attenuation index shows a waveform attenuation rate greater than the threshold value, it is determined that "foreign object is present" or "there is a high possibility that a foreign object is present." Here, the value of the "waveform attenuation index" may differ depending on the RX401 that is the power transmission target mounted on the TX402. This is because the electrical characteristics of the RX401, which is coupled via the TX402's power transmission coil, affect the value of the waveform attenuation index.

[0087] For example, if the "waveform attenuation index" is a Q-value, the Q-value measured by the TX402 when no foreign object is present may differ depending on the RX401 placed on the TX402. Therefore, the RX401 stores, for each TX402, Q-value information when the RX401 is placed on the TX402 when no foreign object is present, and communicates this Q-value to the TX402. The TX402 then adjusts and determines the threshold based on the Q-value information received from the RX401. More specifically, in the negotiation phase, the TX402 receives an FOD Status Packet containing information about the Reference Quality Factor Value, and adjusts and determines the threshold for the Q-value measurement method. This Reference Quality Factor Value corresponds to "Q-value information when the RX401 is placed on the TX402 when no foreign object is present." Therefore, the TX402 also adjusts and determines the threshold for foreign object detection using the waveform attenuation method based on this Reference Quality Factor Value. The Reference Quality Factor Value transmitted from RX401 to TX402 during the negotiation phase is information used for foreign object detection in the Q-factor measurement method, which originally measures the Q-factor in the frequency domain. However, when the "waveform attenuation index" is the Q-factor, the Q-factor is derived in a different way, but even with the waveform attenuation method, which measures the Q-factor in the time domain, for example, from the waveform in Figure 6, Q=πf(T2-T1) / ln(A1 / A2) Since it is possible to calculate the Q value in this way, it is possible to set the Q value threshold for the waveform attenuation method based on the Reference Quality Factor Value. In this way, the TX402 sets the Q value threshold for the waveform attenuation method based on the information already sent from the RX401 to the TX402 in the negotiation phase, eliminating the need for new measurements or other processing to set the threshold. As a result, it is possible to set the threshold in a shorter time.

[0088] The TX402 compares the measured Q value with the threshold determined by the above method, and if the measured Q value is smaller than the threshold Q value, it determines that "foreign matter is present" or "there is a possibility that a foreign matter is present." If the measured Q value is larger than or approximately equal to the threshold Q value, it determines that "foreign matter is not present" or "there is a low possibility that a foreign matter is present."

[0089] By doing as described above, foreign objects can be detected by the waveform attenuation method using the second method.

[0090] The third method is for the TX402 to measure the waveform attenuation index when there is no foreign object, and then adjust and determine the threshold value based on the information from the measurement results. The value of the "waveform attenuation index" may vary depending on the power transmitted by the TX402. This is because the amount of heat generated and the characteristics of the TX402's electrical circuitry change depending on the power transmitted by the TX402, which in turn affect the value of the "waveform attenuation index." Therefore, by having the TX402 measure the waveform attenuation index for each power transmitted and then adjust and determine the threshold value based on the results, more accurate foreign object detection becomes possible.

[0091] FIG. 13 is a diagram illustrating a method for setting a foreign object detection threshold for each transmission power of the TX402 in the waveform attenuation method. First, when power is transmitted from the TX402, the RX401 controls the load of the RX401 to be in a light load state so that no power or only very small power is supplied to the load of the RX401. The transmission power of the TX402 at this time is defined as Pt1. Then, the TX402 stops power transmission in this state and measures the waveform attenuation index. The waveform attenuation index at this time is defined as δ1. At this time, the TX402 recognizes the transmission power Pt1 that the TX402 is transmitting, and stores in memory a calibration point 1300 that associates the transmission power Pt1 with the waveform attenuation index δ1. Next, the RX401 controls the load of the RX401 to be in a load-connected state so that, when power is transmitted from the TX402, maximum power or power equal to or greater than a predetermined threshold is supplied to the load of the RX401. The transmission power of the TX402 at this time is Pt2. The TX402 then stops power transmission in this state and measures the waveform attenuation index. At this time, the TX402 stores in memory a calibration point 1301 that associates the transmission power Pt2 with the waveform attenuation index δ2. Next, the TX402 performs linear interpolation between the calibration point 1300 and the calibration point 1301 to create a line 1302. The line 1302 represents the relationship between the transmission power and the waveform attenuation index of the transmission wave when no foreign object is present around the TX402 and the RX401. Therefore, the TX402 can estimate the waveform attenuation index of the transmission wave for each transmission power value when no foreign object is present, from the line 1302. For example, if the transmission power value is Pt3, the waveform attenuation index can be estimated to be δ3 from the point 1303 on the line 1302 that corresponds to the transmission power value Pt3. Based on the above estimation results, the TX 402 can calculate a threshold value for each transmission power value to be used for determining whether or not a foreign object is present. For example, a waveform attenuation index that is larger by a predetermined value (a value corresponding to a measurement error) than the estimated result of the waveform attenuation index when there is no foreign object at a certain transmission power value may be set as the threshold value for determining whether or not a foreign object is present.The calibration process performed by the TX402 and the RX401 in order for the TX402 to acquire a combination of the transmission power value and the waveform attenuation index is hereinafter referred to as the “calibration process of the waveform attenuation index (CAL process).” Note that in the above example, measurements were performed at two points, Pt1 and Pt2, of the transmission power of the TX402, but to improve accuracy, measurements may be performed at three or more points to calculate the waveform attenuation index for each transmission power.

[0092] The RX401 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 the TX402 of the control to be performed. Also, either of the two controls may be performed first.

[0093] 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 TX402 acquires data required for foreign object detection using the power loss method. At that time, the TX402 acquires data related to power loss when the load state of the RX401 is a light load state and when a load is connected. Therefore, measurements of the calibration point 1300 and the calibration point 1301 in FIG. 13 may be performed in the calibration phase described above when the RX401 is in a light load state and when a load is connected. That is, when the TX402 receives first reference received power information from the RX401, it measures the calibration point 1300 in addition to the predetermined processing to be performed in the calibration phase. Furthermore, when the TX402 receives second reference received power information from the RX401, it measures the calibration point 1301 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 1300 and 1301, and therefore allows the calibration points 1300 and 1301 to be measured in a shorter time.

[0094] In this way, based on the waveform attenuation index information measured by the TX402 at each transmission power, the TX402 adjusts and sets the threshold value of the waveform attenuation index for the waveform attenuation method for each transmission power. For example, if the waveform attenuation index is a Q value, the TX402 compares the measured Q value with the threshold determined by the above method, and if the measured Q value is smaller than the threshold Q value, it determines that "foreign object is present" or "there is a possibility that a foreign object exists." If the measured Q value is greater than or approximately equal to the threshold Q value, it determines that "foreign object is not present" or "there is a low possibility that a foreign object exists." By doing the above, it becomes possible to set the threshold value for each transmission power of the TX402, enabling more accurate foreign object detection.

[0095] By doing as described above, foreign objects can be detected by the waveform attenuation method using the third method.

[0096] Furthermore, when foreign object detection is performed, there is a possibility that accurate foreign object detection cannot be achieved by performing the foreign object detection process only once. For example, when performing foreign object detection using the waveform attenuation method, if a single transmission power control is performed and the presence or absence of a foreign object or the possibility (probability of presence) of a foreign object is determined based on the waveform attenuation index, there is a possibility that the transmission waveform may be disturbed during the transmission power control period. Possible causes of disturbance in the transmission waveform during the transmission power control period include the inclusion of other noise during the transmission power control period or the displacement of the RX401 mounted on the TX402 for some reason. Furthermore, the waveform attenuation index calculated from the transmission waveform during a single transmission power control period may not be accurate due to the disturbance in the conductive waveform, which may result in an erroneous determination of foreign object detection. To prevent this, it is possible to perform transmission power control multiple times, measure the waveform attenuation index from the transmission waveform during multiple transmission power control periods, and perform foreign object detection based on the results.

[0097] (Foreign object detection using multiple waveform attenuation method) In the waveform attenuation method described above, the TX402 is configured to perform a single Q-value measurement and then perform foreign object detection processing based on the results. However, there may be cases where the TX402 performs Q-value measurement multiple times and then performs foreign object detection processing based on the results. Processing for detecting foreign objects based on the results of multiple Q-value measurements will be explained using FIG. 14. Note that in FIG. 14, the TX402 performs Q-value measurement using the waveform attenuation method twice and then performs foreign object detection processing based on the results.

[0098] First, RX401 sends RP0 to TX (F636). When TX402 receives RP0, it performs a Q-factor measurement using the waveform attenuation method (F637). Here, it is clear that the Q-factor measurement performed by TX402 (F637) is the first of two that will be performed. Therefore, in response to RP0 (F636), TX402 sends to RX401 a packet indicating that it is "not determining" whether or not a foreign object is present (F638).

[0099] RX401 sends CE(0) to TX402 (F639). Here, CE stands for Control Error Packet, which requests TX402 to increase or decrease the receiving voltage (or receiving current, receiving power). CE can contain a positive integer to increase the receiving voltage, a negative integer to decrease the receiving voltage, or 0 to leave the receiving voltage unchanged. CE(0) is a packet that requests that the receiving voltage be maintained.

[0100] The RX 401 transmits RP0 again (F640). When the TX 402 receives RP0, it measures the Q value using the waveform attenuation method (F641).

[0101] Here, it can be seen that the Q value measurement (F641) performed on TX402 was the second of two measurements. window Assume that the transmission power value during this period is stable and that the third foreign object detection determines that there is a high possibility that there is no foreign object. In this case, the TX402 determines whether there is a foreign object, and based on the determination result, transmits a response signal including the possibility (probability) of the presence of a foreign object to the RX401 (F642).

[0102] Here, an example of a method for deriving the possibility (existence probability) of a foreign object's presence using multiple waveform attenuation methods will be described. For example, the possibility (existence probability) of a foreign object's presence is derived based on the difference between the Q value obtained by one waveform attenuation method and a threshold value. This process is performed for multiple waveform attenuation methods, and the average value of the existence probability is derived. In this way, the possibility (existence probability) of a foreign object is obtained based on the results of multiple waveform attenuation methods. A second example is a method in which weighting is performed based on the total value of the possibility (existence probability) of a foreign object's presence obtained by multiple waveform attenuation methods. A third example is a method in which the number of waveform attenuation methods in which a possibility (existence probability) of a foreign object's presence equal to or greater than a certain value is counted. In this embodiment, when the possibility (existence probability) of a foreign object's presence is notified to the RX401, "no foreign object" is replaced with the value 0 and "foreign object present" is replaced with the value 10, and the average value of the multiple existence probability values ​​is notified to the RX401. In addition, a process of rounding up the decimal point of the average value may be performed.

[0103] Furthermore, in this embodiment, the RX401 controls the interval at which RP0, which is a foreign object detection execution request, is transmitted in order to control the timing at which the TX402 limits power transmission related to the waveform attenuation method multiple times. When the RX401 transmits RP0 multiple times as a foreign object detection execution request to the TX402, the RX401 waits a predetermined interval after transmitting RP0 before transmitting the next RP0. However, if the possibility of the presence of a foreign object (probability of presence) satisfies a predetermined condition, the RX401 controls the timing from transmitting RP0 to transmitting the next RP0. This processing will be described later.

[0104] (Processing of power receiving device 401 and power transmitting device 402) The flow of processing by the power receiving device 401 (RX401) in this embodiment will be described with reference to the flowchart in Fig. 8. Fig. 8 is a flowchart illustrating the operation of the RX401 that is executed after the start of power transmission processing in F528 in Fig. 5.

[0105] The RX 401 starts receiving power transmitted from the TX 402 (S801). After starting power reception, the RX 401 determines a threshold value for the presence probability (S802). Here, the threshold value for the presence probability is a threshold value for determining whether or not there is a possibility that a foreign object exists. For example, if the presence probability obtained by the foreign object detection process is greater than the threshold value for the presence probability, it is determined that there is a "high possibility that a foreign object exists." Alternatively, if the presence probability obtained by the foreign object detection process is smaller than the threshold value for the presence probability, it is determined that there is a "low possibility that a foreign object exists." The threshold value for the presence probability is a value for determining whether or not to adjust the interval at which the RX 401 waits to transmit a foreign object detection execution request, which will be described later. The threshold value for the presence probability may be determined using a value determined in advance for each RX 401 or a value determined based on the power transmission output from the TX 402.

[0106] The RX401 waits a predetermined interval before transmitting a foreign object detection execution request to the TX402 (S803). In this embodiment, the TX402 performs foreign object detection based on the waveform attenuation method multiple times, so as described above, the RX401 waits a predetermined interval (predetermined time length) after transmitting a foreign object detection execution request until transmitting the next foreign object detection execution request. If this predetermined interval is short, the TX402 will execute transmission power control in a short period of time, and the RX401 will also be burdened with increased processing related to the foreign object detection execution request. Therefore, it is desirable to set the waiting time long. After waiting the predetermined interval in S803, the RX401 transmits a foreign object detection execution request to the TX402 (S804). This foreign object detection execution request may be the above-mentioned Received Power Packet (mode 0), Received Power Packet (mode 1), or Received Power Packet (mode 2). After transmitting the foreign object detection execution request in S804, RX401 determines whether the response packet from TX402 includes the possibility of the presence of a foreign object (probability of presence) (S805). The determination in S805 corresponds to the process of determining the possibility of the presence of a foreign object (probability of presence) from a predetermined number of transmission power control attempts. If the predetermined number of transmission power control attempts has not been reached, the response from TX402 does not include the probability of the presence of a foreign object. This is achieved by TX402 transmitting an ND (Not-Defined) packet, indicating "no determination," as a response to RX401. RX401 determines whether the predetermined number of transmission power control attempts has been completed based on the ND packet. If the ND packet is received, RX401 determines that the predetermined number of transmission power control attempts has not been completed (NO in S805), returns to S803, and waits a predetermined interval for another transmission of a foreign object detection execution request. If the response from TX402 includes the possibility of the presence of a foreign object (probability of presence) (YES in S805), it is determined whether the notified possibility of the presence of a foreign object (probability of presence) is equal to or greater than the threshold value of the probability of presence (S806). If it is not equal to or greater than the threshold value of the probability of presence (NO in S806), the process returns to S803 and waits for a predetermined interval until a foreign object detection execution request is sent again.

[0107] If the presence probability is equal to or greater than the threshold (YES in S806), a determination is made as to whether the notified possibility of the presence of a foreign object (presence probability) is clearly "foreign object present" (S807). In this embodiment, the presence probability is expressed as a value of 0 for "no foreign object" and 10 for "foreign object present." Therefore, if the presence probability value is 10, it is clearly determined that "foreign object present," and if it is not 10, it is not clearly determined that "foreign object present." Note that this is not limited to this, and a value of 8, for example, may be set as the threshold used to clearly determine whether "foreign object present." In this case, if the presence probability value is greater than 8, it is clearly determined that "foreign object present," and if it is less than or equal to 8, it is not clearly determined that "foreign object present." In this case, the threshold used to clearly determine whether "foreign object present" is a threshold greater than the presence probability threshold. Furthermore, the way in which the presence probability is expressed is not limited to the above, and values ​​or ranges other than 0 to 10 may be used.

[0108] If the determination result clearly indicates that a foreign object is present (YES in S807), power reception is stopped (S808). Note that S808 can be achieved by the RX 401 transmitting an EPT (End Power Transfer) command (packet), which is a power transmission stop request command requesting the TX 402 to stop power transmission.

[0109] If the result of the determination in S807 is not a clear determination that "foreign object presence" exists, the current standby interval is determined in order to adjust the standby interval for transmitting the foreign object detection execution request (S809). Specifically, it is determined whether the standby time until the next foreign object detection execution request is transmitted can be shortened from the current time. If the standby time for transmitting the foreign object detection execution request is not the shortest time that the RX401 can achieve (NO in S809), the standby time for transmitting the foreign object detection execution request is shortened (S810), and the transmission of the foreign object detection execution request is postponed until the shortened time has elapsed (S811). On the other hand, if the standby time for transmitting the foreign object detection execution request is already the shortest time (YES in S809), the standby time for transmitting the foreign object detection execution request is not shortened, and the transmission of the foreign object detection execution request is postponed until the current standby time has elapsed (S811).

[0110] The predetermined interval (length of standby time) for transmitting a foreign object detection request may be determined using a value determined in advance for at least one of the RX401 and TX402. Alternatively, the predetermined interval (length of standby time) may be determined using a value determined based on the power transmission output from the TX402. The shortest length of time may be determined based on, for example, the shortest length of time in which the TX402 can perform the waveform attenuation method or the shortest length of time in which the RX401 can transmit a foreign object detection request. For example, the predetermined interval may be determined through negotiation between the RX401 and TX402. This negotiation may be performed in the negotiation phase.

[0111] In addition, the method of shortening the time length may include shortening it by a predetermined time length, shortening it to the shortest time length in one processing, or shortening it by a time length corresponding to the transmission power output from TX402.

[0112] The processing from S811 to S813 is the same as the processing from S803 to S805, and therefore a description thereof will be omitted. If the response from TX402 includes the possibility of the presence of a foreign object (probability of presence) (YES in S813), RX401 determines whether the notified possibility of the presence of a foreign object (probability of presence) clearly indicates "foreign object present" (S814). If the determination result clearly indicates "foreign object present" (YES in S814), power reception is stopped (S808).

[0113] On the other hand, if the result of the determination is not clearly "foreign object present" (NO in S814), the RX 401 determines whether there is clearly "no foreign object" (S815). Here, "no foreign object present" is defined as when the value of the presence probability is 0. If there is clearly "no foreign object" (YES in S815), the RX 401 restores the shortened waiting time for transmitting a foreign object detection execution request to the previous length, returns to S803, and continues receiving power (S816). On the other hand, if there is not clearly "no foreign object" (NO in S815), the RX 401 determines whether transmission of a foreign object detection execution request with a shortened waiting time for transmitting a foreign object detection execution request has been performed a predetermined number of times in succession (S817). If the transmission has been performed a predetermined number of times in succession (YES in S817), there is a possibility that a device malfunction or the like may be suspected, and the RX 401 stops receiving power (S808). If the predetermined number of times has not been executed consecutively (NO in S817), the process returns to S809, and the current waiting interval is determined in order to adjust the length of the waiting time for sending the foreign object detection execution request. Here, the predetermined number of times can be determined by using a value determined in advance for each RX 401, or by using a value determined based on the power transmission output from the TX 402, or the like.

[0114] As described above, when the possibility of the presence of a foreign object (probability of presence) is higher than the threshold for the probability of presence and lower than the threshold for clearly determining whether a foreign object is present, RX401 controls the transmission of requests to perform foreign object detection at shorter intervals.

[0115] It is also possible to configure the system so that, without making the determination in S807, if the presence probability is equal to or greater than the threshold in S806, the processing from S809 onwards is performed. With this configuration, if the presence probability is equal to or greater than the threshold, the transmission of the foreign object detection execution request is expedited and foreign object detection is performed again, thereby making it possible to quickly and reliably confirm the presence or absence of a foreign object.

[0116] Next, the flow of processing in this embodiment of the power receiving device 401 (RX401) and the TX402 (TX402) will be explained using the sequence diagram in Fig. 9. Fig. 9 shows processing that is executed after the start of power transmission processing in F528 in Fig. 5. As an example of processing, the processing that is performed when foreign matter is mixed in between transmission power control in the waveform attenuation method when the TX402 performs the waveform attenuation method three times will be explained.

[0117] The TX402 and RX401 start power transmission processing (F901). After starting power reception, the RX401 determines the threshold value for the presence probability (F902). Here, it is assumed that the 15 watts of power transmission determined in F527 is being performed, and the RX401, which has determined that the received power is high, determines the threshold value so as to adjust the length of time to wait before transmitting a foreign object detection execution request, even if the "possibility of the presence of a foreign object is low."

[0118] After determining the threshold value in F902, RX401 waits for the waiting interval for transmitting a foreign object detection execution request (F903). Here, the default waiting time for RX401 is 2 seconds. The shortest waiting time for transmitting a foreign object detection execution request is 0.5 seconds. After the waiting time in F903 has elapsed, RX401 transmits a foreign object detection execution request to TX402 (F904). Having received the foreign object detection execution request from RX401 in F904, TX402 controls the transmission power and executes foreign object detection (F905). Here, three times is the predetermined number of times that TX402 will perform transmission power control to detect the possibility (probability) of the presence of a foreign object.

[0119] In the transmission power control of F905, since no foreign object is present, the possibility of the presence of a foreign object (probability of presence) is clearly determined to be "no foreign object." In the transmission power control of F905, since the predetermined number of transmission power control attempts has not been reached, TX402 notifies RX401 of an ND packet (F906). Upon receiving the notification of F906, RX401 waits until the waiting time has elapsed before sending the next foreign object detection execution request (F907). The processing from F908 to F911 is the same as the processing from F904 to F907, and therefore a description thereof will be omitted.

[0120] Here, assume that a foreign object has entered the power transmission range of TX402 while it is waiting in F911 (F912). After the waiting time in F911 has elapsed, RX401 transmits a foreign object detection execution request to TX402 (F913). TX402, which has received the foreign object detection execution request from RX401 in F913, performs transmission power control and executes foreign object detection (F914). In the transmission power control in F914, because a foreign object is present, the possibility of foreign object presence (probability of presence) is clearly detected as "foreign object present."

[0121] Because the transmission power control in F914 has reached the predetermined number of waveform attenuation methods (=3), TX402 determines the possibility of foreign object presence (presence probability) to notify RX401 from the results of transmission power control in F905, F909, and F914 (F915). TX402 notifies RX401 of the possibility of foreign object presence (presence probability) determined in F915 (F916). Upon receiving the notification in F916, RX401 determines whether the notified possibility of foreign object presence (presence probability) is equal to or greater than the presence probability threshold determined in F902 (F917). Here, RX401 compares the notified possibility of foreign object presence (presence probability) with the threshold and determines that the presence probability is equal to or greater than the threshold.

[0122] Based on the result of the determination in F917, the RX401 checks the current waiting time for sending a foreign object detection execution request in order to shorten the waiting time for sending a foreign object detection execution request (F918). As a result of F918, the current waiting time for sending a foreign object detection execution request is 2 seconds, which is longer than the shortest waiting time of 0.5 seconds for sending a foreign object detection execution request, so the RX401 shortens the waiting time for sending a foreign object detection execution request (F919). Here, the RX401 determines the waiting time to be 0.5 seconds, which is the shortest waiting time. Note that, although the waiting time is shortened to the shortest value in one go in this embodiment, it may also be configured to be gradually shortened.

[0123] The RX401 waits for the waiting time determined in F919 before sending a foreign object detection request (F920). After the shortened waiting time in F920 has elapsed, the RX401 sends a foreign object detection request to the TX402 (F921). As a result, if the possibility of a foreign object being present (probability of presence) based on foreign object detection is higher than the threshold and a clear determination that a foreign object is present is not made, the TX402 will receive the next foreign object detection request at an earlier timing than when these conditions are not met. Upon receiving the foreign object detection request sent in F921, the TX402 performs transmission power control and executes foreign object detection (F922). Here, the same as in F905, the number of times that the TX402 will perform transmission power control to detect the possibility of a foreign object being present (probability of presence) is set to three.

[0124] In the transmission power control of F922, because a foreign object is present, the possibility of a foreign object being present (probability of presence) is clearly determined to be "foreign object present." In the transmission power control of F922, because the predetermined number of transmission power controls has not been reached, TX402 notifies RX401 of an ND packet (F923). Upon receiving the notification of F923, RX401 waits again for the waiting interval for sending a foreign object detection execution request (F924). The processing from F925 to F930 is the same as the processing from F921 to F926, and therefore a description thereof will be omitted.

[0125] Because the transmission power control of F930 has reached a predetermined number of transmission power control attempts, TX402 determines the possibility of the presence of a foreign object (presence probability) to notify RX401 from the results of the transmission power controls of F922, F926, and F930 (F931). Here, TX402 determines to notify the presence probability indicating "foreign object present" from the results of "foreign object present" of F922, "foreign object present" of F926, and "foreign object present" of F930. TX402 notifies RX401 of the possibility of the presence of a foreign object (presence probability) determined in F931 (F932). Upon receiving the notification from F932, RX401 confirms that the notified possibility of the presence of a foreign object (presence probability) is "foreign object present," and transmits an EPT (End Power Transfer) command (packet) to TX402 to stop power reception (F933). The above is an example of processing when a foreign object is detected based on the multiple waveform attenuation method.

[0126] In this embodiment, there are two types of intervals to adjust for waiting for transmission of a foreign object detection execution request: the "interval until the first foreign object detection execution" represented by F903, and the "interval between multiple transmission power control attempts" represented by F907. In this embodiment, a method of adjusting both at the same time is described, but it is also possible to adjust only one of them.

[0127] With the above configuration, when the RX401 is notified by the TX402 that "there is a high possibility that a foreign object is present," the RX401 can shorten the interval between transmissions of foreign object detection execution requests. This allows the RX401 to shorten the time until it performs foreign object detection processing again when there is a high possibility that a foreign object is present. As a result, the RX401 can quickly determine whether or not a foreign object is present. Furthermore, when there is no foreign object present or when it is notified that there is a clear "no foreign object," the RX401 sets the transmission time of the foreign object detection execution request to be longer than the shortest time length. This reduces the processing load related to the waveform attenuation method, and realizes a safer and more efficient wireless power transmission system.

[0128] <Embodiment 2> In the first embodiment, an example of applying foreign object detection using the multiple waveform attenuation method in accordance with the WPC standard was described. In the present embodiment, a method for achieving safer power transmission using the method described in the first embodiment will be described.

[0129] (Processing of power transmitting device 402 and power receiving device 401) The flow of processing by the power receiving device 401 (RX401) in this embodiment will be described with reference to the flowchart in Fig. 10. Fig. 10 is a flowchart showing the operation of the RX401 that is executed after the start of power transmission processing in F528 in Fig. 5. Note that a description of the same processing content as in the first embodiment will be omitted.

[0130] The processing from S1001 to S1015 is the same as the processing from S801 to S815, and therefore description thereof will be omitted. If it is not clear that "no foreign object is present" (NO in S1015), it is determined whether transmission of a foreign object detection execution request with a shortened wait time for transmission of the foreign object detection execution request has been executed a predetermined number of times in succession (S1017). If it has not been executed a predetermined number of times in succession (NO in S1016), the process returns to S1009, and the RX401 determines the current wait time in order to adjust the wait time for transmission of the foreign object detection execution request. The method for determining the predetermined number of times is the same as in the first embodiment.

[0131] On the other hand, if the detection has been performed a predetermined number of times in succession (YES in S1016), the RX401 determines whether the current transmission power from the TX402 is the lowest possible value between the TX402 and the RX401 (S1017). If the transmission power from the TX402 is the lowest possible value (YES in S1017), the process returns to S1009, and the RX401 determines the current waiting time in order to adjust the waiting time for sending a foreign object detection execution request. If the transmission power from the TX402 is not the lowest possible value (NO in S1017), the RX401 sends a transmission power change request to the TX402 to lower the transmission power (S1018).

[0132] After the transmission power change process in S1018 is completed, the process returns to S1009, and the RX401 determines the current waiting time in order to adjust the waiting time for transmitting a foreign object detection execution request.

[0133] Furthermore, if it is clearly determined in S1015 that "no foreign object is present" (YES in S1015), the shortened waiting time for sending a foreign object detection execution request is returned to the length of time before the shortening (S1019), and it is determined whether the transmission power has been changed in S1018 (S1020). If the transmission power output has not been changed (NO in S1020), the process returns to S803, and RX401 continues receiving power. On the other hand, if the transmission power has been changed (YES in S1020), RX401 transmits a transmission power output change request to TX402 to return the changed transmission power to the transmission power before the change (S1021), and the process returns to S803, and continues receiving power.

[0134] The above-described processing has the following advantages. Specifically, by reducing the transmission power when there is a high possibility that a foreign object is present, it is possible to avoid the risk of transmitting power to the foreign object and raising its temperature. Furthermore, the higher the transmission power, the greater the impact of noise related to the power transmission. Therefore, when foreign object detection is performed using the waveform attenuation method, there is a higher possibility of false detection, such as a determination that a foreign object is present when no foreign object is present, or a determination that a foreign object is absent when a foreign object is present. Therefore, when it is determined that there is a high possibility that a foreign object is present, the presence or absence of a foreign object can be confirmed with greater accuracy by reducing the transmission power and performing foreign object detection again.

[0135] Next, the flow of processing in the power receiving device 401 (RX401) and the power transmitting device 402 (TX402) according to this embodiment will be described with reference to the sequence diagram of Fig. 11. Fig. 11 shows processing that is executed after the start of power transmission processing in F528. As an example of processing, processing will be described here when temporary noise causes disturbance in the transmission waveform during the transmission power control period when performing transmission power control using the waveform attenuation method. The processing from F1101 to F1104 is the same as the processing from S901 to S904, and therefore description thereof will be omitted.

[0136] Upon receiving the foreign object detection execution request from RX401 in F1104, TX402 performs transmission power control and executes foreign object detection (F1105). Here, one time is defined as the number of times that TX402 performs transmission power control to detect the possibility of the presence of a foreign object (existence probability). In the transmission power control in F1105, even though no foreign object is present, it is assumed that the possibility of the presence of a foreign object (existence probability) is detected as "low possibility of the presence of a foreign object" due to disturbance of the transmission wave pattern during the transmission power control period caused by noise. TX402 notifies RX401 of the detection result in F1105 (F1106). Upon receiving the notification in F1106, RX401 determines whether the notified possibility of the presence of a foreign object (existence probability) is equal to or greater than the existence probability threshold determined in F1102 (F1107). Here, RX401 compares the notified possibility of the presence of a foreign object (existence probability) with a threshold and determines that it is equal to or greater than the existence probability threshold.

[0137] The processing from F1108 to F1111 is similar to the processing from F918 to F921, and therefore a description thereof will be omitted. The processing from F1112 and F1113 is similar to the processing from F1105 and F1106, and therefore a description thereof will be omitted. While foreign object detection is repeatedly performed using the same processing from F1110 to F1113, with the transmission standby interval for the foreign object detection execution request shortened, the RX401 determines whether a predetermined number of repetitions has been reached (F1114). After determining in F1114 that the predetermined number of repetitions has been reached, the RX401 determines whether the current transmission power is set to a lower limit (F1115). In this embodiment, the lower limit of the transmission power is set to 5 watts, and the current transmission power output is set to 15 watts. Therefore, in the determination at F1115, it is determined that the current transmission power is not the lower limit, and the RX401 transmits a transmission power change request to the TX402 to set the transmission power to the lower limit of 5 watts (F1116).

[0138] Upon receiving the transmission power output change request of F1116, TX402 changes the transmission power to 5 watts (F1117) and notifies RX401 that the change in transmission power output has been completed by sending an ACK (F1118). Note that in this embodiment, RX401 changes the transmission power to the lower limit value in one change, but the transmission power may be gradually reduced.

[0139] By changing the transmission power to the lower limit, the noise affecting the transmission waveform disappears (F1119). After the noise disappears in F1119, RX401 transmits a foreign object detection execution request to TX402 (F1120). TX402, having received the foreign object detection execution request from RX401 in F1120, performs transmission power control using the waveform attenuation method and executes foreign object detection (F1121). Here, since the noise affecting the disturbance of the transmission wave waveform during the transmission power control period in S1119 has disappeared, the possibility of the presence of a foreign object (probability of presence) is clearly determined to be "no foreign object." TX402 notifies RX401 of the presence probability based on the determination result of F1121 (F1122).

[0140] Upon receiving the notification of F1122, the RX401 repeats the foreign object detection process similar to that of F1120 to F1122 and determines that no foreign object is present (F1123). In this embodiment, since the transmission power control was performed only once, the RX401 makes the determination in F1123 based on the results of multiple foreign object detection attempts in consideration of the effects of noise, etc. However, the determination may also be based on the results of a single foreign object detection attempt. Having determined that no foreign object is present in F1123, the RX401 returns the shortened waiting time for transmission of a foreign object detection execution request to the previous time length (S1124) and determines whether the transmission power has been changed (S1125). In this embodiment, since the transmission power has been changed from 15 watts to 5 watts, the RX401 transmits a transmission power change request to the TX402 to return the transmission power to 15 watts (S1126). Upon receiving the transmission power output change request of F1126, TX402 changes the transmission power to 15 watts (F1127) and notifies RX401 that the change in transmission power has been completed by sending an ACK (F1128).

[0141] In this way, when the RX401 is notified by the TX402 that a foreign object may be present, the RX401 shortens the time to send a foreign object detection request and reduces the transmitted power. This allows the RX401 and TX402 to reduce the possibility of heat generation by a foreign object, prevent power transmission from being stopped due to erroneous detection, and continue transmitting power. Furthermore, by continuing to shorten the time to send a foreign object detection request, it is possible to quickly detect the presence of a foreign object, thereby achieving a safer and more efficient wireless power transmission system.

[0142] <Other embodiments> The contents of the above-described first and second embodiments may be combined as appropriate. In the above-described embodiments, the TX402 controls the transmission power and detects foreign objects based on the waveform attenuation index. The following method can be considered as another method for measuring the Q value, which is one of the waveform attenuation indexes. That is, there is also a method for measuring the Q value by transmitting a signal (e.g., a pulse wave) having multiple frequency components, measuring the amplitude or attenuation state of the waveform, and performing arithmetic processing (e.g., Fourier transform) on the results, and this method can also be applied to the above-described embodiments.

[0143] The present disclosure can also be realized by providing 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 recording medium. [Explanation of symbols]

[0144] 401 Power receiving device 201 Control Unit 204 Communications Department 205 Coil

Claims

1. power receiving means for wirelessly receiving power from a power transmitting device; a transmitting means for transmitting a packet including information on received power in a power transfer phase; a receiving means for receiving a response regarding the presence of a foreign object in response to the packet from the power transmitting device; a control means for switching to a second mode in which the packets are transmitted at a second time interval longer than the first time interval when a response indicating that no foreign object is present in response to the packet is received after the packet is transmitted in a first mode in which the packets are transmitted at a first time interval.

2. A power receiving device as described in claim 1, wherein the time interval for transmitting the packets is determined by negotiation between the power receiving device and the power transmitting device.

3. 2. The power receiving device according to claim 1, wherein the power is reduced when the receiving means receives a response indicating the presence of a foreign object.

4. The power receiving device according to claim 1 , wherein the transmitting means transmits a request to stop power transmission when a response indicating that the probability of the presence of a foreign object is higher than a threshold value is received.

5. A method performed by a power receiving device, a transmitting step of transmitting a packet including information on received power in a power transfer phase; a receiving step of receiving a response regarding the presence of a foreign object in response to the packet from the power transmitting device; a control step of switching to a second mode in which the packets are transmitted at a second time interval longer than the first time interval when a response indicating that no foreign object is present in response to the packet is received after the packet is transmitted in a first mode in which the packets are transmitted at a first time interval.

Images