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 Art

[0002] In recent years, the technical development of wireless power transmission systems has been widely carried out. Patent Document 1 discloses a method for detecting foreign objects in the Wireless Power Consortium standard (WPC standard). Further, Patent Document 2 discloses a method for detecting the presence of an object different from a power receiving device and a power transmitting device (hereinafter referred to as a foreign object) based on a change in energy attenuation or a change in resonance frequency of a power transmitting coil and a resonance circuit integrated with or coupled to the power transmitting coil. Further, Patent Document 3 discloses a method for detecting foreign objects, in which a power transmitting device transmits a signal for detecting foreign objects to a power receiving device and determines the presence or absence of foreign objects using an echo signal from the power receiving device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In wireless power transmission, when it is determined that a foreign object is present, the power transmission device stops power transmission, thereby suppressing the possibility of heat generation of the foreign object due to power transmission to the foreign object. Further, it is assumed that the foreign object detection process is configured such that the power transmission device receives a predetermined signal from the power receiving device and executes the process accordingly. However, depending on the result of the foreign object detection process, it may not be clearly indicated whether a foreign object is present or not. In this case, there are problems such as an increased possibility that power transmission continues and the foreign object generates heat, or power transmission stops even though no foreign object is present, resulting in a decrease in power transmission efficiency.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to enable a re-detection process to be performed more quickly according to the result of a detection process for detecting an object different from the power transmission device and the power receiving device.

Means for Solving the Problems

[0006] The power receiving device of the present disclosure includes power receiving means for wirelessly receiving power from a power transmission device, transmission means for transmitting at predetermined intervals a signal for executing a detection process for detecting an object different from the power transmission device and the power receiving device based on voltage or current values at at least two time points within a predetermined period during which the power transmission device restricts power transmission, reception means for receiving, from the power transmission device, a response signal including a detection result based on the detection process executed in response to the signal transmitted by the transmission means, and control means for controlling the transmission means to transmit the signal at an interval shorter than the predetermined interval when the detection result included in the response signal received by the reception means satisfies a predetermined condition.

Advantages of the Invention

[0007] According to the present disclosure, a re-detection process is performed more quickly according to the result of a detection process for detecting an object different from the power transmission device and the power receiving device.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

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Embodiments for Carrying Out the Invention

[0009] <Embodiment 1> Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential configurations, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are given the same reference numerals.

[0010] (Configuration of Wireless Power Transmission System) FIG. 4 shows a configuration example of a wireless power transmission system (wireless charging system) according to the present embodiment. In one example, this system includes a power receiving device 401 and a power transmitting device 402. The 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. RX401 is an electronic device that receives power from TX402 and charges a built-in battery. TX402 is an electronic device that wirelessly transmits power to RX401 placed on a charging stand 403 that is part of TX402. Hereinafter, since the charging stand 403 is part of TX402, the phrase "placed on the charging stand 403" may be referred to as "placed on TX402 (power transmitting device 402)". The range 404 surrounded by the dotted line is the range within which RX401 can receive power from TX402. Also, the state of being "placed" does not necessarily mean that RX401 and TX402 are in contact with each other, and refers to a state where RX401 is included in the range 404.

[0011] Note that RX401 and TX402 may have functions to execute applications other than wireless charging. An example of RX401 is an information processing terminal such as a smartphone, and an example of 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 the user, to which power received from a power receiving coil (antenna) is supplied. Further, the power received from the power receiving coil is stored in a power storage unit (battery), and power is supplied from the battery to the display unit. In this case, RX401 may have a communication unit that communicates with another device different from TX402. The communication unit may conform to communication standards such as NFC communication or the fifth generation mobile communication system (5G). Also in this case, the communication unit may communicate by being supplied with power from the battery. Further, RX401 may have a function to notify the remaining amount of the battery. Also, RX401 may be a tablet terminal, or a storage device such as a hard disk device and a memory device, or an information processing device such as a personal computer (PC). Also, RX401 may be, for example, an imaging device (such as a camera or a video camera). Also, RX401 may be an image input device such as a scanner, or an image output device such as a printer, a copier, or a projector. Also, RX401 may be a robot, a medical device, or the like. TX402 may be a device for charging the above-described devices.

[0012] Also, TX402 may be a smartphone. In this case, RX401 may be another smartphone or a wireless earphone.

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

[0014] Furthermore, RX401 may have an accommodation part for accommodating a person. For example, as sensors, there are sensors used for measuring the distance between vehicles and the distance to other obstacles. The communication unit may, for example, be compatible with the Global Positioning System (GPS). Further, the communication unit may be compatible with a communication standard such as the 5th generation mobile communication system (5G). Also, as the vehicle, it may be a bicycle or a motorcycle. Further, RX401 is not limited to a vehicle, and may be a moving body, a flying body, etc. having a driving unit that is driven using the power stored in a battery. Also, TX402 may be a charger installed in a console or the like inside a vehicle, or may be a charging device for charging an electric vehicle. Also, RX102 may not have a built-in battery.

[0015] In addition, RX401 and TX402 in the present embodiment shall perform processing based on the Wireless Power Consortium standard (WPC standard). Details of the processing will be described later.

[0016] (Configuration of Power Transmission Device 402 and Power Reception Device 401) Next, the configurations of the power transmission device 402 (TX402) and the power reception device 401 (RX401) in the present embodiment will be described. Note that the configurations described below are merely examples, and some (or in some cases, all) of the described configurations may be replaced with other configurations that perform the same functions or omitted, and further configurations may be added to the described configurations. Furthermore, one block shown in the following description may be divided into a plurality of blocks, or a plurality of blocks may be integrated into one block. Also, each of the functional blocks shown below is assumed to have its functions implemented as a software program, but some or all of the functional blocks included in this functional block may be implemented in hardware.

[0017] FIG. 1 is a functional block diagram showing a configuration example of TX402 according to the present embodiment. TX402 includes a control unit 101, a power supply unit 102, a power transmission unit 103, a communication unit 104, a power transmission 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 transmission unit 103, the communication unit 104, and the memory 106 are shown as separate entities, but any plurality of these functional blocks may be implemented on the same chip.

[0018] The control unit 101 controls the entire TX402 by executing, for example, a control program stored in the memory 106. Further, the control unit 101 performs control related to power transmission control including communication for device authentication in the TX402. Furthermore, the control unit 101 may perform control for executing applications other than wireless power transmission. The control unit 101 includes one or more processors such as, for example, a CPU (Central Processing Unit) or an MPU (MicroProcessor Unit). Note that the control unit 101 may be configured by hardware such as an application specific integrated circuit (ASIC). Also, the control unit 101 may be configured to include an array circuit such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processing. The control unit 101 stores in the memory 106 information to be stored during the execution of various processes. Also, the control unit 101 can 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. Electric power supplied from the commercial power supply is stored in the battery.

[0020] The power transmission unit 103 converts the 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 generates an electromagnetic wave for causing power reception in the RX401 by inputting the AC frequency power to the power transmission antenna (coil) 105. For example, the power transmission unit 103 converts the DC voltage supplied by the power supply unit 102 into an AC voltage using a switching circuit having a half-bridge or full-bridge configuration using FETs (Field Effect Transisters). In this case, the power transmission unit 103 includes a gate driver that controls the ON / OFF of the FETs.

[0021] The power transmission unit 103 controls the intensity of the electromagnetic wave to be output by adjusting the voltage (transmission voltage) or current (transmission current), or both, input to the power transmission antenna 105. When the transmission voltage or transmission current is increased, the intensity of the electromagnetic wave becomes stronger, and when the transmission voltage or transmission current is decreased, the intensity of the electromagnetic wave becomes weaker. Also, the power transmission unit 103 performs output control of AC frequency power so that power transmission from the power transmission antenna 105 is started or stopped based on an instruction from the control unit 101. Further, it is assumed that the power transmission unit 103 has the ability to supply power sufficient to output 15 watts (W) of power to the charging unit 206 of the power receiving device 401 (RX401) compliant with the WPC standard.

[0022] The communication unit 104 communicates with the RX401 for power transmission control based on the WPC standard. The communication unit 104 frequency-shift modulates the electromagnetic wave output from the power transmission antenna 105 and transmits information to the RX401 to perform communication. Also, the communication unit 104 demodulates the electromagnetic wave transmitted from the power transmission antenna 105 amplitude-modulated or load-modulated by the RX401 to acquire the information transmitted by the RX401. That is, the communication performed by the communication unit 104 is performed with a signal superimposed on the electromagnetic wave transmitted from the power transmission antenna 105. Further, the communication unit 104 may communicate with the RX401 by a standard different from the WPC standard using an antenna different from the power transmission antenna 105, or may communicate with the RX401 by selectively using a plurality of communications. Examples of this communication standard include Bluetooth (registered trademark) Low Energy (BLE) and NFC (Near Field Communication).

[0023] In addition to storing the control program, the memory 106 can also store the states of the TX402 and RX401 (such as the power transmission power value, power reception power value, etc.). For example, the state of the TX402 is acquired by the control unit 101, and the state of the RX401 is acquired by the control unit 201 of the RX401 and can be received via the communication unit 104.

[0024] Switch 108 is controlled by control unit 101. Power transmission antenna 105 is connected to resonance capacitor 107. When switch 108 is turned on and short-circuited, power transmission antenna 105 and resonance capacitor 107 form a series resonance circuit and resonate at a specific frequency f1. At this time, current flows through the closed circuit formed by power transmission antenna 105, resonance capacitor 107, and switch 108. When switch 108 is turned off and opened, power is supplied from power transmission unit 103 to power transmission antenna 105 and resonance capacitor 107.

[0025] FIG. 2 is a block diagram showing a configuration example of power receiving device 401 (RX401) according to the present embodiment. RX401 includes control unit 201, UI (user interface) unit 202, power receiving unit 203, communication unit 204, power receiving antenna 205, charging unit 206, battery 207, memory 208, first switch unit 209, second switch unit 210, and resonance capacitor 211. Note that a plurality of functional blocks shown in FIG. 2 may be realized as one hardware module.

[0026] Control unit 201 controls the entire RX401 by executing, for example, a control program stored in memory 208. That is, control unit 201 controls each functional unit shown in FIG. 2. Further, control unit 201 may perform control for executing applications other than wireless power transmission. An example of control unit 201 includes one or more processors such as a CPU or MPU. Note that the entire RX401 (the entire smartphone when RX401 is a smartphone) may be controlled in cooperation with the OS (Operating System) executed by control unit 201.

[0027] Further, control unit 201 may be configured by hardware such as an ASIC. Also, control unit 201 may include an array circuit such as an FPGA compiled to execute predetermined processing. Control unit 201 stores information to be stored during execution of various processes in memory 208. Also, control unit 201 can measure time using a timer (not shown).

[0028] The UI unit 202 performs various outputs to the user. The various outputs here refer to operations such as screen display, blinking and color change of an LED (Light Emitting Diode), voice output by a speaker, and vibration of the RX401 main body. The UI unit 202 is realized by a liquid crystal panel, a speaker, a vibration motor, etc.

[0029] The power receiving unit 203 obtains alternating current power (alternating current voltage and alternating current) generated by electromagnetic induction based on the electromagnetic wave radiated from the power transmitting antenna 105 of the TX402 via the power receiving antenna (coil) 205. Then, the power receiving unit 203 converts the alternating current power into direct current or alternating current power of a predetermined frequency, and outputs the power to a charging unit 206 that performs processing for charging the battery 207. That is, the power receiving unit 203 includes a rectifying unit and a voltage control unit necessary for supplying power to the load in the RX401. The above-mentioned GP is the amount of electric power guaranteed to be output from the power receiving unit 203. It is assumed that the power receiving unit 203 has the ability to supply the power required for the charging unit 206 to charge the battery 207 and supply 15 watts of power to the charging unit 206.

[0030] The communication unit 204 performs communication for power receiving control based on the WPC standard with the communication unit 104 of the TX402. The communication unit 204 demodulates the electromagnetic wave input from the power receiving antenna 205 to obtain the information transmitted from the TX402. Then, the communication unit 204 performs communication with the TX402 by superimposing a signal regarding the information to be transmitted to the TX402 on the electromagnetic wave by amplitude modulation or load modulation of the input electromagnetic wave. Note that the communication unit 204 may communicate with the TX402 by a communication based on a standard different from the WPC standard using an antenna different from the power receiving antenna 205, or may communicate with the TX402 by selectively using a plurality of communications. Examples of this communication standard include Bluetooth (registered trademark) Low Energy (BLE) and NFC (Near Field Communication).

[0031] In addition to storing the control program, the memory 208 also stores the states of TX402 and RX401, etc. For example, the state of RX401 is acquired by the control unit 201, and the state of TX402 is acquired by the control unit 101 of TX402 and can be received via the communication unit 204.

[0032] The first switch unit 209 and the second switch unit 210 are controlled by the control unit 201. The power receiving antenna 205 is connected to the resonant capacitor 211. When the second switch unit 210 is in the ON state and short-circuited, the power receiving antenna 205 and the resonant capacitor 211 form a series resonance circuit and resonate at a specific frequency f2. At this time, a current flows through the closed circuit formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210, and no current flows through the power receiving unit. When the second switch unit 210 is in the OFF state and open, the power received by the power receiving antenna 205 and the resonant capacitor 211 is supplied to the power receiving unit 203.

[0033] The first switch unit 209 is for controlling whether to supply the received power to the battery which is the load. It also has a function of controlling the value of the load. If the first switch unit 209 connects the charging unit 206 and the battery 207, the received power is supplied to the battery 207. If the first switch unit 209 disconnects the connection between the charging unit 206 and the battery 207, the received power is not supplied to the battery 207. In FIG. 2, the first switch unit 209 is arranged between the charging unit 206 and the battery 207, but it may also be arranged between the power receiving unit 203 and the charging unit 206. Alternatively, it may be arranged between the closed circuit formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210 and the power receiving unit 203. That is, the first switch unit 209 may be for controlling whether to supply the received power to the power receiving unit 203. Also, in FIG. 2, the first switch unit 209 is described as one block, but it is also possible to realize the first switch unit 209 as a part of the charging unit 206 or a part of the power receiving unit 203.

[0034] Next, with reference to FIG. 3, the functions of the control unit 101 of TX402 will be described. FIG. 3 is a block diagram showing a functional configuration example of the control unit 101 of the power transmission device 402 (TX402). The control unit 101 includes 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 RX401 based on the WPC standard via the communication unit 104. The power transmission control unit 302 controls the power transmission unit 103 and controls the power transmission to RX401. The measurement unit 303 measures a waveform attenuation index described later. Also, it measures the power transmitted to RX401 via the power transmission unit 103 and measures the average power transmission power per unit time. Further, the measurement unit 303 measures the Q value of the power transmission 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 a calculation process.

[0036] The foreign object detection unit 305 performs processing for detecting foreign objects included in the power transmission range of TX402. Here, the foreign object in this embodiment refers to an object different from the power receiving device and the power transmission device. The foreign object detection unit 305 can implement a foreign object detection function by the Power Loss method described later, a foreign object detection function by the Q value measurement method, and a foreign object detection function by the waveform attenuation method. Also, the foreign object detection unit 305 may have a function for performing foreign object detection processing using other methods. For example, in TX402 equipped with an NFC (Near Feald Communication) communication function, the foreign object detection unit 305 may perform foreign object detection processing using the opposing device detection function according to the NFC standard. Also, as a function other than detecting foreign objects, the foreign object detection unit 305 can detect that the state on TX402 has changed. For example, TX402 can also detect an increase or decrease in the number of RX401s on TX402.

[0037] The setting unit 304 sets a threshold value that serves as a criterion for determining the presence or absence of a foreign object when the TX 402 performs foreign object detection by the Power Loss method, the Q-value measurement method, or the waveform attenuation method. Further, the setting unit 304 may have a function of setting a threshold value that serves as a criterion for determining the presence or absence of a foreign object, which is necessary for performing foreign object detection processing using other methods. Also, 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, transmitted power, or Q-value measured by the measurement unit 303.

[0038] The communication control unit 301, the power transmission control unit 302, the measurement unit 303, the setting unit 304, and the foreign object detection unit 305 have their functions realized as programs operating in the control unit 101. Each processing unit is configured as an independent program and can operate in parallel while synchronizing between programs through event processing and the like. However, two or more of these processing units may be incorporated into one program.

[0039] The RX 401 and TX 402 in the present embodiment perform wireless power transmission using the electromagnetic induction method for wireless charging based on the WPC standard. That is, the RX 401 and the TX 402 perform wireless power transmission for wireless charging based on the WPC standard between the power receiving antenna 205 of the RX 401 and the power transmitting antenna 105 of the TX 402. Note that the wireless power transmission method applied to this system is not limited to the method defined by the WPC standard, and other electromagnetic induction methods, magnetic field resonance methods, electric field resonance methods, microwave methods, methods using lasers, etc. may also be used. Also, in the present embodiment, it is assumed that wireless power transmission is used for wireless charging, but wireless power transmission may be performed for purposes other than wireless charging.

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

[0041] Also, when power is transmitted from TX402 to RX401, if there is a foreign object, which is an object other than RX401, near TX402, there is a risk that the electromagnetic wave for power transmission will affect the foreign object and increase the temperature of the foreign object or damage the foreign object. Therefore, in the WPC standard, a method for TX402 to detect the presence of a foreign object on the charging stand 403 is defined so that the temperature rise or destruction of the foreign object can be prevented by stopping power transmission when a foreign object is present. Specifically, the Power Loss method for detecting a foreign object based on the difference between the power transmitted by TX402 and the power received by RX401 is defined. Also, the Q-value measurement method for detecting a foreign object based on the change in the quality factor (Quality-Factor, Q-value) of the power transmitting antenna 105 in TX402 is defined. Note that the foreign object detected by TX402 in this embodiment is not limited to an object existing on the charging stand 403. TX402 only needs to detect a foreign object located near TX402, and for example, it may detect a foreign object located within the range where TX402 can transmit power.

[0042] (Processing Based on WPC Standard) The processing based on the WPC standard performed by RX401 and TX402 according to this embodiment will be described. In the WPC standard, a plurality of phases are defined, including a Power Transfer phase in which power transmission is executed and one or more phases before the actual power transmission. Communication for power transmission and reception control required in each phase is performed. The phases before power transmission may include a Selection phase, a Ping phase, an Identification and Configuration phase, a Negotiation phase, and a Calibration phase. Hereinafter, the Identification and Configuration phase will be referred to as the I&C phase. The processing of each phase will be described below.

[0043] In the Selection phase, TX402 intermittently transmits an Analog Ping to detect that an object is placed on the charging stand of TX402 (for example, RX401, a conductor piece, etc. are placed on the charging stand). TX402 detects at least one of the voltage value and the current value of the power transmission antenna 105 when transmitting the Analog Ping, and determines that an object exists when the voltage value is lower than a certain threshold or the current value exceeds a certain threshold, and then transitions to the Ping phase.

[0044] In the Ping phase, TX402 transmits a Digital Ping with higher power than the Analog Ping. The power of the Digital Ping is sufficient to activate the control unit of RX401 placed on TX402. RX401 notifies TX402 of the magnitude of the received power voltage. In this way, TX402 recognizes that the object detected in the Selection phase is RX401 by receiving the response from RX401 that has received the Digital Ping. When receiving the notification of the received power voltage value, TX402 transitions to the I&C phase. Also, before transmitting the Digital Ping, TX402 measures the Q value of the power transmission antenna 105. This measurement result is used when performing foreign object detection processing using the Q value measurement method.

[0045] In the I&C phase, TX402 identifies RX401 and obtains device configuration information (capability information) from RX401. RX401 transmits an ID Packet and a Configuration Packet. The ID Packet contains the identifier information of RX401, and the Configuration Packet contains the device configuration information (capability information) of RX401. TX402 that has received the ID Packet and the Configuration Packet responds with an acknowledge (ACK, positive response). Then, the I&C phase ends.

[0046] In the Negotiation phase, the value of GP is determined based on the value of GP requested by RX401 and the power transmission capability of TX402, etc. Also, TX402 receives a FOD Status Packet containing information on the Reference Quality Factor Value from RX401, adjusts and determines the threshold value in the Q-value measurement method. Then, TX402 executes foreign object detection processing using the Q-value measurement method according to the request from RX401. Also, in the WPC standard, after once transitioning to the Power Transfer phase, a method of performing the same processing as in the Negotiation phase again according to the request of RX401 is defined. The phase of performing these processes 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. Also, RX401 notifies TX402 of a predetermined received power value (received power value in the light load state / received power value in the maximum load state), and TX402 performs adjustments for efficient power transmission. The received power value notified to TX402 can be used for foreign object detection processing by the Power Loss method.

[0048] In the Power Transfer phase, control is performed for starting power transmission, continuing power transmission, and stopping power transmission due to errors or full charge. TX402 and RX401 perform communication by superimposing signals on the electromagnetic waves transmitted from the power transmission antenna 105 or the power reception antenna 205 using the power transmission antenna 105 and the power reception antenna 205 for these power transmission and reception controls. Note that the range within which communication is possible between TX402 and RX401 based on the WPC standard is almost the same as the power transmission range of TX402.

[0049] The above is the description of the processing performed by RX401 and TX402 in this embodiment. Hereinafter, the operations of RX401 and TX402 in each of the above-described phases will be described with reference to the sequence diagram of FIG. 5. FIG. 5 is a sequence diagram for power transmission according to the WPC standard. Here, the power transmission device 402 (TX402) and the power reception device 401 (RX401) will be described as an example.

[0050] TX402 repeatedly transmits Analog Ping of the WPC standard intermittently in order to detect an object existing within the power transmission range (F501). TX402 executes the processing defined as the Selection phase and the Ping phase of the WPC standard and waits for RX401 to be placed. The user of RX401 brings RX401 closer to TX402 to charge RX401 (for example, a smartphone) (F502). For example, by placing RX401 on TX402, RX401 is brought closer to TX402.

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

[0052] Subsequently, TX402 determines the value of GP with RX401 through communication in the Negotiation phase defined by the WPC standard (F508). Note that in F508, not only communication in the Negotiation phase of the WPC standard but also other procedures for determining GP may be executed. Also, when TX402 acquires information indicating that RX401 does not support the Negotiation phase (for example, in F507), the communication in the Negotiation phase may not be performed. In this case, TX402 may set the value of GP to a small value (for example, predefined by the WPC standard). In this embodiment, GP = 5 watts.

[0053] After the determination of the GP, TX402 performs calibration based on the GP. In the calibration process, first, RX401 transmits information including the received power in the light load state (load cut-off state or load state where the transmitted power is equal to or less than the first threshold value) of TX402 (hereinafter referred to as the first reference received power information) (F509). The first reference received power information in this embodiment is the received power information of RX401 when the transmitted power of TX402 is 250 milliwatts. The first reference received power information is Received Power Packet (mode1) defined by the WPC standard, but other messages may be used. Hereinafter, Received Power Packet (mode1) is also referred to as "RP1". TX402 determines whether to accept the first reference received power information based on its own transmission state. TX402 transmits an affirmative response (ACK) to RX401 if it accepts, and a negative response (NAK) if it does not accept.

[0054] Next, when RX401 receives an ACK from TX402 (F510), it performs processing to transmit information including the received power in the load connection state (maximum load state or load state where the transmitted power is equal to or greater than the second threshold value) of TX402 (hereinafter referred to as the second reference received power information). In this embodiment, since the GP is 5 watts, the second reference received power information is the received power information of RX401 when the transmitted power of TX402 is 5 watts. Here, the second reference received power information is Received Power Packet (mode2) defined by the WPC standard, but other messages may be used. Hereinafter, Received Power Packet (mode2) is also referred to as "RP2". RX401 transmits a transmission output change request including a positive value to increase the transmitted power of TX402 up to 5 watts (F511).

[0055] TX402 receives the power transmission output change request described above. When it is possible to increase the power transmission, it responds with an ACK and increases the power transmission (F512, F513). Since the second reference received power information is the received power information when the power transmission of TX402 is 5 watts, when TX402 receives a power increase request exceeding 5 watts from RX401 (F514), it responds with a NAK to the power transmission output change request. This suppresses power transmission above the specified level (F515).

[0056] When RX401 determines that the default power transmission has been reached by receiving a NAK from TX402, it transmits information including the received power in the load connection state to TX402 as the second reference received power information (F516). TX402 can calculate the power loss amount between TX402 - RX401 in the load disconnection state and the load connection state based on the power transmission value of TX402 and the received power values included in the first and second reference received power information. Also, by interpolating between those power loss amounts, it is possible to calculate an estimated value of the power loss between TX402 - RX401 at all possible power transmission levels of TX402 (in this case, between 250 milliwatts and 5 watts) (F517). TX402 transmits an ACK to the second reference received power information from RX401 (F518) and completes the Calibration process.

[0057] When TX402, which has determined that it can start the charging process, starts the power transmission process to RX401, the charging of RX401 starts. Before starting the power transmission process, if TX402 and RX401 perform device authentication processing (F519) and determine that the mutual devices can support a larger GP, the GP may be reset to a larger value, for example, 15 watts (F520).

[0058] In this case, RX401 and TX402 increase the transmission output by using a transmission output change request, ACK, and NAK to increase the transmission power of TX402 up to 15 watts (F521 - F524). Then, TX402 and RX401 perform the Calibration process again for GP = 15 watts. Specifically, RX401 transmits information including the received power in the load connection state of RX401 when the transmission power of TX402 is 15 watts (hereinafter referred to as the 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. Thereby, TX402 can calculate the power loss amount between TX402 - RX401 at all possible transmission powers of TX402 (in this case, from 250 milliwatts to 15 watts) (F526). TX402 transmits an ACK to the third reference received power information from RX401 (F527) and completes the Calibration process. TX402, having determined that the charging process can be started, starts the transmission process to RX401 and shifts to the Power Transfer phase (F528). Note that the processes from F519 to F527 are not essential processes.

[0059] In the Power Transfer phase, TX402 transmits power to RX401. Also, foreign object detection is performed by the Power Loss method. In the Power Loss method, first, TX402 calculates the power loss amount between TX402 - RX401 in a state without foreign objects from the difference between the transmission power by TX402 and the received power by RX401 through the above-described Calibration. The calculated value corresponds to the reference power loss amount in the normal state (state without foreign objects) during the power transmission process. Then, TX402 determines that there is a "foreign object" when the power loss amount between TX402 - RX401 measured during the power transmission after Calibration exceeds the threshold value from the power loss amount in the normal state. A more detailed explanation of the Power Loss method will be described later.

[0060] The Power Loss method performs foreign object detection based on the measurement results of power loss during power transmission from TX402 to RX401. While foreign object detection using the Power Loss method has the drawback that the accuracy of foreign object detection decreases when TX402 is transmitting a large amount of power, it has the advantage that power transmission efficiency can be kept high because foreign object detection can be performed while power transmission continues.

[0061] The above is the processing flow based on the WPC standard. In the power transmission process of F528, when power transmission ends due to the battery of RX401 being fully charged, a foreign object being detected, etc., RX401 transmits a power transmission stop request command to request TX402 to stop power transmission. The power transmission stop request command in this embodiment is an EPT (End Power Transfer) command (packet). Thereby, the power transmission process is terminated.

[0062] (Power Loss method) Regarding foreign object detection based on the Power Loss method defined in the WPC standard, it will be described with reference to FIG. 12. The horizontal axis in FIG. 12 is the power transmitted by TX402, and the vertical axis is the power received by RX401. A foreign object is an object other than RX401 that can affect power transmission from TX402 to RX401, and can be, for example, an object such as a metal piece having conductivity.

[0063] First, TX402 transmits power to RX401 at the first transmission power value Pt1. RX401 receives power at the first received power value Pr1 (this state is called the Light Load state (light load state)). Then, TX402 stores the first transmission power value Pt1. Here, the first transmission power value Pt1 or the first received power value Pr1 is a predetermined minimum transmission power or received power. At this time, RX401 controls so that the received power becomes the minimum power. For example, RX401 may control the first switch unit 209 to disconnect the receiving antenna 205 from the load so that the received power is not supplied to the load (charging circuit, battery, etc.). Subsequently, RX401 notifies TX402 of the power value Pr1 of the first received power. TX402 that has received Pr1 from RX401 can calculate that the power loss between TX402 and RX401 is Pt1 - Pr1 (Ploss1), and create a calibration point 1200 indicating the correspondence between Pt1 and Pr1.

[0064] Subsequently, TX402 changes the transmission power value to the second transmission power value Pt2 and transmits power to RX401. RX401 receives power at the second received power value Pr2 (this state is called the Connected Load state (load connection state)). Then, TX402 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, RX401 controls so that the received power becomes the maximum power. For example, RX401 controls the first switch unit 209 to connect the receiving antenna 205 to the load so that the received power is supplied to the load. Subsequently, RX401 notifies TX402 of Pr2. TX402 that has received Pr2 from RX401 can calculate that the power loss between TX402 and RX401 is Pt2 - Pr2 (Ploss2), and create a calibration point 1001 indicating the correspondence between Pt2 and Pr2.

[0065] Then, TX402 creates a straight line 1202 that linearly interpolates between calibration point 1200 and calibration point 1201. Straight line 1202 shows the relationship between the transmitted power and the received power when there is no foreign object in the vicinity of TX402 and RX401. Based on straight line 1202, TX402 can predict the power value received by RX401 when transmitting power at a predetermined transmitted power in the absence of a foreign object. For example, when TX402 transmits power at the third transmitted power value Pt3, it can be inferred from point 1203 corresponding to Pt3 on straight line 1202 that the third received power value received by RX401 is Pr3.

[0066] As described above, based on a plurality of combinations of the transmitted power value of TX402 and the received power value of RX401 measured while changing the load, the power loss between TX402 and RX401 according to the load can be obtained. Further, by interpolation from a plurality of combinations, the power loss between TX402 and RX401 corresponding to all loads can be estimated. In this way, the calibration process performed by TX402 and RX401 to obtain a combination of the transmitted power value and the received power value is hereinafter referred to as "Calibration Process (CAL Process) of Power Loss Method".

[0067] After calibration, assume that when TX402 actually transmits power to RX401 at Pt3, TX402 receives a received power value Pr3' from RX401. TX402 calculates a value Pr3 - Pr3' (= Ploss_FO), which is the difference between the received power value Pr3 in the state where there is no foreign object and the actually received power value Pr3' from RX401. This Ploss_FO can be considered as the power loss due to the power consumed by the foreign object when a foreign object exists near TX402 and RX401. Therefore, when the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold value, it can be determined that a foreign object exists. Alternatively, TX402 previously obtains the power loss Pt3 - Pr3 (Ploss3) between TX402 and RX401 from the received power value Pr3 in the state where there is no foreign object. Then, next, from the received power value Pr3' received from RX401 in the state where a foreign object exists, the power loss Pt3 - Pr3' (Ploss3') between TX402 and RX401 in the state where a foreign object exists is obtained. And 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, as a method for obtaining the power Ploss_FO that would have been consumed by the foreign object, it may be obtained as Pr3 - Pr3' (= Ploss_FO), or it may be obtained as Ploss3' - Ploss3 (= Ploss_FO). In the following description of this specification, basically, the method of obtaining it as Ploss3' - Ploss3 (= Ploss_FO) will be described, but the content of this embodiment is also applicable to the method of obtaining it as Pr3 - Pr3' (= Ploss_FO). The above is the description of foreign object detection based on the Power Loss method.

[0069] After the straight line 1002 is obtained by the calibration process, the foreign object detection unit 305 of TX402 periodically receives the current power reception value (e.g., the above Pr3') from RX401 via the communication unit 104. The current power reception value periodically transmitted by RX401 is transmitted to TX402 as a Received Power Packet (mode0). The foreign object detection unit 305 of TX402 performs foreign object detection based on the power reception value stored in the Received Power Packet (mode0) and the straight line 1002. Hereinafter, the Received Power Packet (mode0) will be referred to as "RP0".

[0070] Foreign object detection by the Power Loss method is performed during power transmission (power sending) (Power Transfer phase described later) based on the data obtained by the Calibration phase described later. Also, foreign object detection by the Q-value measurement method is performed before power transmission (before Digital Ping transmission, Negotiation phase or Renegotiation phase described later).

[0071] Note that during the Power Transfer phase in the WPC standard, foreign object detection by the Power Loss method is performed. However, with only foreign object detection by the Power Loss method, there is a possibility of false detection of foreign objects and a possibility of false determination that there are no foreign objects even though there are foreign objects. In particular, the Power Transfer phase is a phase in which TX402 performs power transmission. If a foreign object exists near TX402 and RX401 during power transmission, heat generation from the foreign object increases, so it is required to improve the foreign object detection accuracy in this phase. Therefore, in the present embodiment, in order to improve the foreign object detection accuracy, it is considered to implement a foreign object detection method different from the Power Loss method.

[0072] (Foreign object detection method using the waveform attenuation method) In the Power Transfer phase, TX402 is performing power transmission to RX401. Therefore, if foreign object detection can be performed using the power transmission waveform (voltage waveform or current waveform) related to this power transmission, foreign object detection can be achieved without using newly defined signals for foreign object detection or the like. A method of performing foreign object detection based on the attenuation state of the power transmission waveform (hereinafter referred to as the waveform attenuation method) will be described with reference to FIG. 6. FIG. 6 is a diagram for explaining the principle of foreign object detection by the waveform attenuation method. Here, foreign object detection using the power transmission waveform related to the power transmission from TX402 to RX401 will be described as an example.

[0073] In FIG. 6, the waveform shows the change over time of the voltage value 600 of the high-frequency voltage applied to the power transmission antenna 105 of TX402 (hereinafter simply referred to as the voltage value). The horizontal axis in FIG. 6 represents time, and the vertical axis represents the voltage value. TX402, which is performing power transmission to RX401 via the power transmission antenna 105, restricts power transmission at time T0. That is, at time T0, the power supply for power transmission from the power supply unit 102 is restricted. Note that the restriction of power means stopping the power or reducing it so that the power becomes less than or equal to a predetermined value.

[0074] The frequency of the power transmission waveform related to the power transmission from TX402 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 T 1 . In the figure, (T 1 , A 1 ) indicates that the voltage value at time T 1 is A1. Similarly, point 602 is a point on the envelope of the high-frequency voltage and is the voltage value at time T 2 . In the figure, (T 2 , A 2 ) indicates that the voltage value at time T 2 is A 2indicates that. The quality factor (Q value) of this power transmission antenna 105 can be obtained based on the time change of the voltage value after time T0. For example, the Q value is calculated by Equation 1 based on the time, voltage value, and frequency f of the high-frequency voltage at points 601 and 602 on the envelope of the voltage value. Q = πf(T 2 -T 1 ) / ln(A 1 / A 2 ) (Equation 1)

[0075] When a foreign object exists near TX402 and RX401, this Q value decreases. This is because when a foreign object exists, energy loss occurs due to the foreign object. Therefore, focusing on the attenuation slope of the voltage value, when there is a foreign object, energy loss due to the foreign object occurs more than when there is no foreign object, so the slope of the straight line connecting point 601 and point 602 becomes steeper and the attenuation rate of the waveform amplitude becomes higher. That is, the waveform attenuation method determines the presence or absence of a foreign object based on the attenuation state of the voltage value between point 601 and point 602. In actually determining the presence or absence of a foreign object, it is possible to make a determination by comparing some numerical value representing this attenuation state. For example, a determination can be made using the Q value described above. A decrease in the Q value means that the waveform attenuation rate (the degree of decrease in the amplitude of the waveform per unit time) increases. Or, (A 1 -A 2 ) / (T 2 -T 1 ) can be used to make a determination using the slope of the straight line connecting point 601 and point 602 obtained therefrom. Or, if the time (T 1 and T 2 ) for observing the attenuation state of the voltage value is fixed, a determination can also be made using the value of the voltage difference (A 1 -A 2 ) or the ratio of the voltage values (A 1 / A 2 ). Or, if the voltage value A 1 immediately after power transmission stops is constant, a determination can also be made using the value of the voltage value A 2 after a predetermined time has elapsed. Or, using the voltage value A 1until it reaches a predetermined voltage value A 2 The time (T 2 - T 1 ) may be used for determination.

[0076] As described above, the presence or absence of foreign matter can be determined based on the attenuation state of the voltage value during the power transmission stop period, and there are a plurality of values representing the attenuation state. In this embodiment, the values representing these attenuation states are referred to as "waveform attenuation indicators". For example, as described above, the Q value calculated by Equation 1 is a value representing the attenuation state of the voltage value related to power transmission and is included in the "waveform attenuation indicator". All waveform attenuation indicators are values corresponding to the waveform attenuation rate. In the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation indicator". Hereinafter, the case where the waveform attenuation rate is used as the waveform attenuation indicator will be mainly described, but the content of this embodiment can be similarly applied when other waveform attenuation indicators are used.

[0077] Note that even if the vertical axis of FIG. 6 is the current value flowing through the power transmission antenna 105, the attenuation state of the current value during the power transmission stop period changes depending on the presence or absence of foreign matter, similar to the case of the voltage value. And when there is foreign matter, the waveform attenuation rate is higher than when there is no foreign matter. Therefore, even if the above-described method is applied to the time change of the current value flowing through the power transmission antenna 105, foreign matter can be detected. That is, using the Q value obtained from the current waveform, the inclination of the attenuation of the current value, the difference of the current value, the ratio of the current values, the absolute value of the current value, and the time until it reaches a predetermined current value as waveform attenuation indicators, the presence or absence of foreign matter can be determined and foreign matter can be detected.

[0078] Further, foreign object detection based on both the attenuation state of the voltage value and the attenuation state of the current value may be performed, such as determining the presence or absence of a foreign object using an evaluation value calculated from the waveform attenuation index of the voltage value and the waveform attenuation index of the current value. In the above example, the waveform attenuation index during the period when TX402 temporarily stopped power transmission was measured, but it is not limited to this. For example, the waveform attenuation index during the period when TX402 temporarily reduces the power supplied from the power supply unit 102 from a predetermined power level to a lower power level may be measured. Also, in the above example, the voltage or current values at two time points during the period when TX402 restricts power transmission are measured, but the measurement may be performed at three or more time points.

[0079] A method for detecting a foreign object based on a power transmission waveform during power transmission by the waveform attenuation method will be described with reference to FIG. 7. FIG. 7 shows a power transmission waveform when detecting a foreign object by the waveform attenuation method, where the horizontal axis represents time and the vertical axis represents the voltage value of the power transmission antenna 105. Similar to FIG. 6, the vertical axis may represent the voltage value of the power transmission antenna 105.

[0080] In the transient response period immediately after TX402 starts power transmission, the power transmission waveform is not stable. Therefore, during this transient response period when the power transmission waveform is not stable, RX401 controls not to communicate with TX402 (communication by amplitude modulation or load modulation). Also, TX402 controls not to communicate with RX401 (communication by frequency shift keying modulation). Hereinafter, this period is called the communication prohibition period. During this communication prohibition period, TX402 performs power transmission to RX401. After passing through the communication prohibition period, TX402 performs power transmission to RX401. Hereinafter, this period is called the power transmission period. When TX402 receives a foreign object detection execution request (command) from RX401, it temporarily stops power transmission after a predetermined period has elapsed. Or it temporarily reduces the power transmission power. This predetermined period is hereinafter called the preparation period. Note that this foreign object detection execution request may be the above-mentioned Received Power Packet (mode0), Received Power Packet (mode1), or Received Power Packet (mode2). Then, the power transmission control unit 302 of TX402 stops power transmission or temporarily reduces the power transmission power. Then, the amplitude of the power transmission waveform attenuates. The period from when TX402 temporarily stops or reduces the power transmission power until it starts resuming power transmission is hereinafter called the power transmission power control period. TX402 calculates the waveform attenuation index of this attenuated waveform, compares the calculated waveform attenuation index with a predetermined threshold value, and determines the presence or absence of a foreign object or the possibility (probability of existence) that a foreign object exists. The determination may be performed during the power transmission power control period, or during the communication prohibition period or the power transmission period.

[0081] After the elapse of the power transmission power control period, if no foreign object is detected, TX402 resumes power transmission. In the transient response period immediately after resuming power transmission, since the power transmission waveform is not stable, it becomes the communication prohibition period again. Then, it shifts to the power transmission period in which TX402 stably performs power transmission to RX401.

[0082] As described above, TX402 repeatedly executes power transmission start, communication prohibition period, power transmission period, and power transmission power control period. Then, TX402 calculates a waveform attenuation index of the attenuation waveform at a predetermined timing, compares the calculated waveform attenuation index with a predetermined threshold value, and determines the presence or absence of a foreign object or the possibility (probability of existence) that a foreign object exists. That is, in the waveform attenuation method, the presence or absence of a foreign object is determined based on the voltage or current values at at least two time points during a predetermined period in which TX402 restricts power transmission. The above is the basic process of foreign object detection by the waveform attenuation method.

[0083] During the power transmission 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 RX401, the waveform attenuation index of the attenuation waveform is affected by the load of these elements. That is, the waveform attenuation index will change depending on the states of the power receiving unit 203, the charging unit 206, and the battery 207. Therefore, for example, even if the waveform attenuation index is large, it becomes difficult to distinguish whether it is due to the influence of a foreign object or due to changes in the states of the power receiving unit 203, the charging unit 206, the battery 207, etc. Thus, when performing foreign object detection by observing the waveform attenuation index, the RX401 may disconnect the first switch unit 209 during the above 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, so that a current flows in the 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. When the RX401 transmits a foreign object detection execution request (command) to the TX402, the above processing is performed. Thus, by performing foreign object detection based on the waveform attenuation index of the waveform observed with the first switch unit 209 or the second switch unit 210 turned ON to short-circuit (connect), highly accurate foreign object detection becomes possible. Alternatively, during the above preparation period, the RX401 may shift to the low power consumption mode or control the power consumption to be constant in a state where the first switch unit 209 is turned ON to short-circuit and the second switch unit 210 is turned OFF to disconnect. That is, when the power consumed by the RX401 is not constant or a large amount of power is consumed, the waveform attenuation index of the attenuation waveform is affected by the fluctuations of these power consumptions. Therefore, in order to eliminate that, the following processing can be executed. That is, the operation of the software application operating in the RX401 is restricted or stopped, the hardware function block of the RX401 is set to the low power consumption mode or the operation stop mode, etc., so that the power consumed by the RX401 is controlled. By performing foreign object detection based on the waveform attenuation index of the waveform observed in such a state, highly accurate foreign object detection becomes possible.

[0084] Also, similarly to TX402, when receiving a foreign object detection execution request (command) from RX401, during the above preparation period, the switch unit 108 may be turned ON to short-circuit. That is, TX402 may be in a state where current flows through a closed loop formed by the power transmission antenna 105, the resonance capacitor 107, and the switch unit 108. Thereby, it becomes possible to eliminate the influence of the power supply unit 102, the power transmission unit 103, and the communication unit 104. Alternatively, a switch (not shown) may be provided between the power transmission antenna and the power transmission unit, and by disconnecting the switch during the above preparation period, it becomes possible to eliminate the influence of the power supply unit 102, the power transmission unit 103, and the communication unit 104.

[0085] (Method for setting the foreign object detection threshold value in the waveform attenuation method) A method for setting a threshold value for determining the presence or absence of a foreign object, or the possibility (probability of existence) of the presence of a foreign object, when detecting a foreign object by the waveform attenuation method will be described. As described above, in the waveform attenuation method, foreign object detection is performed based on the "waveform attenuation index". The measured "waveform attenuation index" is compared with a predetermined threshold value, and based on the result, the presence or absence of a foreign object, or the possibility of the presence of a foreign object is determined. As a method for setting this threshold value, there are the following methods. First, one method is that the threshold value is a common value that does not depend on RX401 to be powered, and TX402 holds a predetermined value determined in advance. Note that this may be the same value in any case, or it may be a value determined by TX402 according to the situation. As described above, during the power transmission control period, the power transmission waveform has a higher waveform attenuation rate when a foreign object is present. Therefore, the "waveform attenuation index" when it is considered that "there is no foreign object" is held in advance as a predetermined value, and this is used as the threshold value and compared with the result of the measured "waveform attenuation index". When the measured waveform attenuation index has a result with a larger waveform attenuation rate than the threshold value, it is determined that "there is a foreign object" or "the possibility of the presence of a foreign object is high". For example, when the "waveform attenuation index" is the Q value, the Q value measured by TX402 is compared with the Q value (threshold value) when it is considered that there is no foreign object determined in advance. When the measured Q value is smaller than the Q value of the threshold value, it is determined that "there is a foreign object" or "the possibility of the presence of a foreign object is high". When the measured Q value is larger than or approximately equal to the Q value of the threshold value, it is determined that "there is no foreign object" or "the possibility of the presence of a foreign object is low". By doing the above, foreign object detection by the waveform attenuation method becomes possible using the first method.

[0086] The second is a method in which TX402 adjusts and determines a threshold value based on the information transmitted from RX401. As described above, during the power transmission control period, the waveform of the transmitted power has a higher waveform attenuation rate when a foreign object is present. Therefore, the "waveform attenuation index" when it is considered that "there is no foreign object" is retained in advance as a predetermined value, and this is used as a threshold value to be compared with the result of the measured "waveform attenuation index". When the measured waveform attenuation index has a result with a waveform attenuation rate greater than the threshold value, it is determined that "there is a foreign object" or "there is a high possibility that a foreign object is present". Here, the value of the "waveform attenuation index" may vary depending on the RX401 to be powered, which is placed on TX402. This is because the electrical characteristics of RX401 coupled via the power transmission coil of TX402 affect the value of the waveform attenuation index.

[0087] For example, when the "waveform attenuation index" is the Q value, the Q value measured by TX402 when there is no foreign object may vary depending on RX401 placed on TX402. Therefore, RX401 holds the Q value information for each TX402 when RX401 is placed on TX402 with no foreign object present, and communicates and notifies that Q value to TX402. Then, TX402 adjusts and determines the threshold value based on the Q value information received from RX401. More specifically, in the Negotiation phase, TX402 receives a FOD Status Packet containing information on the Reference Quality Factor Value, and adjusts and determines the threshold value in the Q value measurement method. This Reference Quality Factor Value corresponds to the "Q value information when RX401 is placed on TX402 with no foreign object present". Therefore, the threshold value in foreign object detection by the waveform attenuation method is also adjusted and determined by TX402 based on this Reference Quality Factor Value. Note that the Reference Quality Factor Value transmitted from RX401 to TX402 in the Negotiation phase is information used for foreign object detection in the Q value measurement method that originally measures the Q value in the frequency domain. However, when the "waveform attenuation index" is the Q value, although the method for deriving the Q value is different, even in the waveform attenuation method that measures the Q value in the time domain, for example, from the waveform in FIG. 6, Q = πf(T 2 -T 1 ) / ln(A 1 / A 2 ) it is possible to obtain the Q value as shown above. Therefore, it is possible to set the threshold value of the Q value of the waveform attenuation method based on the Reference Quality Factor Value. By setting the threshold value of the Q value of the waveform attenuation method by TX402 based on the information already transmitted from RX401 to TX402 in the Negotiation phase in this way, processes such as new measurements for threshold value setting become unnecessary. As a result, it becomes possible to set the threshold value in a shorter time.

[0088] Compare the Q value measured by TX402 with the threshold value determined by the above method. If the measured Q value is smaller than the Q value of the threshold, determine that "there is foreign matter" or "there may be foreign matter". If the measured Q value is larger than or approximately equal to the Q value of the threshold, determine that "there is no foreign matter" or "the possibility of foreign matter existing is low".

[0089] By doing as above, foreign matter detection by the waveform attenuation method becomes possible using the second method.

[0090] The third one is a method in which TX402 measures the waveform attenuation index in a state without foreign matter, and based on the information of the measurement result, TX402 adjusts and determines the threshold value. The value of the "waveform attenuation index" may vary depending on the transmission power of TX402. This is because the calorific value, various characteristics of the electric circuit of TX402, etc. change depending on the magnitude of the transmission power of TX402, and they affect the value of the "waveform attenuation index". Therefore, by TX402 measuring the waveform attenuation index for each transmission power, adjusting the threshold value based on the result, and making a determination, more accurate foreign matter detection becomes possible.

[0091] FIG. 13 is a diagram for explaining a method of setting a foreign object detection threshold for each transmission power in the waveform attenuation method. First, when power is transmitted from TX402, RX401 controls the load of RX401 to be in a light load state so that no power is supplied to the load of RX401 or only a very small amount of power is supplied. Let the transmission power of TX402 at this time be Pt1. Then, TX402 stops power transmission in that state and measures the waveform attenuation index. Let the waveform attenuation index at this time be δ1. At this time, TX402 recognizes the transmission power Pt1 at which it is transmitting power, and stores a calibration point 1300 associating the transmission power Pt1 and the waveform attenuation index δ1 in the memory. Next, when power is transmitted from TX402, RX401 controls the load of RX401 to be in a load connection state so that the maximum power is supplied to the load of RX401 or a power equal to or greater than a predetermined threshold is supplied. Let the transmission power of TX402 at this time be Pt2. Then, TX402 stops power transmission in that state and measures the waveform attenuation index. At this time, TX402 stores a calibration point 1301 associating the transmission power Pt2 and the waveform attenuation index δ2 in the memory. Subsequently, TX402 linearly interpolates between the calibration point 1300 and the calibration point 1301 to create a straight line 1302. The straight line 1302 shows the relationship between the transmission power and the waveform attenuation index of the transmission waveform in a state where no foreign object exists around TX402 and RX401. Therefore, TX402 can estimate the waveform attenuation index of the transmission waveform for each transmission power value in a state without foreign objects from the straight line 1302. For example, when the transmission power value is Pt3, it can be estimated that the waveform attenuation index is δ3 from the point 1303 on the straight line 1302 corresponding to the transmission power value Pt3. Then, based on the above estimation result, TX402 can calculate a threshold value for determining the presence or absence of a foreign object for each transmission power value. For example, a waveform attenuation index that is larger than the estimation result of the waveform attenuation index in the case of no foreign object at a certain transmission power value by a predetermined value (a value corresponding to the measurement error) may be set as the threshold value for determining the presence or absence of a foreign object.The calibration process performed by TX402 and RX401 for TX402 to obtain a combination of transmitted power value and waveform attenuation index is hereinafter referred to as "Calibration process of waveform attenuation index (CAL process)". In the above example, the transmitted powers Pt1 and Pt2 of TX402 were measured at two points. However, in order to improve the accuracy, the measurement may be carried out at three or more points to calculate the waveform attenuation index of each transmitted power.

[0092] Note that RX401 may perform control to make the state such that no power is supplied to the load / light load state and control to make the load connection state, respectively, after notifying TX402 of performing the control. 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 foreign matter for each load (for each power transmission power value) described in this embodiment may be performed in the Calibration phase. As described above, in the Calibration phase, TX402 acquires the data necessary for foreign matter detection by the Power Loss method. At that time, TX402 acquires the data related to power loss when the load state of RX401 is a light load state and when it is a load connection state. Therefore, the measurement of calibration point 1300 and calibration point 1301 in FIG. 13 may be performed when RX401 becomes a light load state and when it becomes a load connection state in the above-described Calibration phase. That is, when TX402 receives the first reference received power information from RX401, in addition to the predetermined processing to be performed in the Calibration phase, TX402 measures calibration point 1300. Also, when TX402 receives the second reference received power information from RX401, in addition to the predetermined processing to be performed in the Calibration phase, TX402 measures calibration point 1301. As a result, there is no need to separately provide a period for measuring calibration point 1300 and calibration point 1301, so calibration point 1300 and calibration point 1301 can be measured in a shorter time.

[0094] Based on the information on the waveform attenuation index measured by TX402 at each power transmission power in this way, TX402 adjusts and sets the threshold value of the waveform attenuation index of the waveform attenuation method for each power transmission power. For example, when the waveform attenuation index is the Q value, the Q value measured by TX402 is compared with the threshold value determined by the above method. If the measured Q value is smaller than the Q value of the threshold value, it is determined that "there is foreign matter" or "there is a possibility of foreign matter existing". If the measured Q value is larger than or substantially equal to the Q value of the threshold value, it is determined that "there is no foreign matter" or "the possibility of foreign matter existing is low". By doing the above, it becomes possible to set the threshold value at each power transmission power of TX402, and more accurate foreign matter detection becomes possible.

[0095] By doing the above, it becomes possible to detect foreign objects by the waveform attenuation method using the third method.

[0096] Also, when performing foreign object detection, it may not be possible to accurately detect foreign objects by simply executing the process for foreign object detection once. For example, when performing foreign object detection by the waveform attenuation method, if power transmission control is performed once and the presence or absence of foreign objects, or the possibility (probability of existence) of foreign object presence is determined from the waveform attenuation index, there is a possibility that the power transmission waveform during the power transmission control period will be disturbed. What can be considered as a possibility of disturbance in the power transmission waveform during the power transmission control period is that other noise is mixed in during the power transmission control period, or the position of the RX401 placed on the TX402 is displaced for some reason. And the waveform attenuation index obtained from the power transmission waveform during one power transmission control period will not be the correct value due to the disturbance of the conductive waveform, and as a result, there is a possibility of making an incorrect determination in foreign object detection. To prevent this, it is conceivable to perform power transmission control multiple times, measure the waveform attenuation index from the power transmission waveforms during multiple power transmission control periods, and perform foreign object detection from the results.

[0097] (Foreign object detection by the waveform attenuation method multiple times) In the above-described waveform attenuation method, the TX402 was configured to perform Q-value measurement once and perform foreign object detection processing based on the result. Here, the TX402 may perform Q-value measurement multiple times and perform foreign object detection processing based on the results. The process of performing foreign object detection based on the results of multiple Q-value measurements will be described with reference to FIG. 14. In FIG. 14, it is assumed that the TX402 performs Q-value measurement by the waveform attenuation method twice and performs foreign object detection processing based on the results.

[0098] First, RX401 transmits RP0 to TX (F636). When TX402 receives RP0, it performs Q-value measurement by the waveform attenuation method (F637). Here, it can be seen that the Q-value measurement (F637) performed by TX402 is the first of two times. Therefore, as a response to RP0 (F636), TX402 transmits a packet indicating "not judge" the presence or absence of foreign matter at the current time to RX401 (F638).

[0099] RX401 transmits CE(0) to TX402 (F639). Here, CE is an abbreviation for Control Error Packet that requests an increase or decrease in the received voltage (or received current, received power) for TX402. CE may include a positive integer to increase the received voltage, a negative integer to decrease the received voltage, or 0 to not change the received voltage. CE(0) is a packet that requests to maintain the received voltage.

[0100] RX401 transmits RP0 again (F640). When TX402 receives RP0, it performs Q-value measurement by the waveform attenuation method (F641).

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

[0102] Here, an example of a method for deriving the possibility (probability of existence) of foreign matter by the waveform attenuation method multiple times will be described. For example, based on the difference between the Q value obtained by the waveform attenuation method once and the threshold value, the possibility (probability of existence) of foreign matter is derived. This process is performed for the waveform attenuation method multiple times, and the average value of the probability of existence is derived. Thereby, the possibility (probability of existence) of foreign matter based on the results of the waveform attenuation method multiple times is obtained. The second example is a method of weighting from the total value of the possibility (probability of existence) of foreign matter for multiple times. The third is a method of measuring the number of times of the waveform attenuation method in which the possibility (probability of existence) of foreign matter equal to or greater than a certain value is detected. In the present embodiment, when notifying the possibility (probability of existence) of foreign matter to RX401, "no foreign matter" is replaced with the value 0, "there is foreign matter" is replaced with the value 10, and the average value of the values of the probability of existence for multiple times is notified to RX401. Also, a process of rounding up the decimal part of the average value may be performed.

[0103] Also, in the present embodiment, 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 TX402 restricts power transmission related to the waveform attenuation method multiple times. When RX401 transmits a plurality of RP0s as foreign object detection execution requests to TX402, after transmitting RP0, it waits for a predetermined interval and then transmits the next RP0. However, when the possibility (probability of existence) of foreign matter satisfies a predetermined condition, the timing from the transmission of RP0 to the transmission of the next RP0 is controlled. This process will be described later.

[0104] (Processing of the power receiving device 401 and the power transmitting device 402) The flow of the processing of the power receiving device 401 (RX401) in the present embodiment will be described using the flowchart of FIG. 8. FIG. 8 is a flowchart showing the operation of RX401 executed after the start of the power transmission process of F528 in FIG. 5.

[0105] RX401 starts receiving the power transmitted from TX402 (S801). RX401 that has started receiving power determines a threshold value for the presence probability (S802). Here, the threshold value for the presence probability is a threshold value for determining whether there may be a foreign object present. For example, when 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 is present". Also, for example, when the presence probability obtained by the foreign object detection process is less than the threshold value for the presence probability, it is determined that "there is a low possibility that a foreign object is present". Further, the threshold value for the presence probability is a value for determining whether to adjust the interval during which RX401, which will be described later, waits for the transmission of a foreign object detection execution request. As a method for determining the threshold value for the presence probability, a method using a value determined in advance for each RX401 or a method using a value determined by the power transmission output from TX402 may be used.

[0106] RX401 waits for a predetermined interval to send a foreign object detection execution request to TX402 (S803). In this embodiment, since TX402 performs foreign object detection based on the waveform attenuation method multiple times, as described above, RX401 waits for a predetermined interval (predetermined time length) from the transmission of the foreign object detection execution request until the next foreign object detection execution request is sent. If the predetermined interval here is a short interval, power transmission control is executed by TX402 in a short period, and also in RX401, the load increases due to an increase in the processing related to the foreign object detection execution request. Therefore, it is desirable to set the waiting time long. After waiting for the predetermined interval in S803, RX401 sends a foreign object detection execution request to TX402 (S804). This foreign object detection execution request may be the above-mentioned Received Power Packet (mode0), or Received Power Packet (mode1), or Received Power Packet (mode2). After the transmission of the foreign object detection execution request in S804, RX401 determines whether the response packet from TX402 contains the possibility (probability of existence) of the presence of a foreign object (S805). The determination in S805 corresponds to the process of obtaining the possibility (probability of existence) of the presence of a foreign object from a predetermined number of power transmission control operations. If the power transmission control for the predetermined number of times has not been reached, the probability of the presence of a foreign object is not included in the response from TX402. This is realized by TX402 sending an ND (Not-Defined) packet indicating "do not judge" as a response to RX401. RX401 determines whether the power transmission control for the predetermined number of times has been completed based on the ND packet. In the case of an ND packet, it is determined that the power transmission control for the predetermined number of times has not been completed (NO in S805), and the process returns to S803, and waits for a predetermined interval to send the foreign object detection execution request again. If the possibility (probability of existence) of the presence of a foreign object is included in the response from TX402 (YES in S805), it is determined whether the notified possibility (probability of existence) of the presence of a foreign object is equal to or greater than the threshold value of the probability of existence (S806). If it is not equal to or greater than the threshold value of the probability of existence (NO in S806), the process returns to S803, and waits for a predetermined interval to send the foreign object detection execution request again.

[0107] When the existence probability is equal to or greater than the threshold (YES in S806), a determination is made as to whether the notified possibility of foreign object existence (existence probability) is clearly "there is a foreign object" (S807). In the present embodiment, as a way of representing the existence probability, "no foreign object" is represented by the numerical value 0, and "there is a foreign object" is represented by the numerical value 10. Therefore, when the value of the existence probability is 10, it is clearly determined that "there is a foreign object", and when it is not 10, it is clearly not determined that "there is a foreign object". Note that the present invention is not limited to this, and for example, a value of 8 may be set as the threshold used to clearly determine whether "there is a foreign object". In this case, when the value of the existence probability is greater than 8, it is clearly determined that "there is a foreign object", and when it is 8 or less, or less than 8, it is clearly not determined that "there is a foreign object". The threshold for clearly determining whether "there is a foreign object" at this time is a threshold greater than the threshold of the existence probability. Also, the way of representing the existence probability is not limited to the above, and values or ranges other than 0 to 10 may be used.

[0108] As a result of the determination, when it is clearly determined that "there is a foreign object" (YES in S807), power reception is stopped (S808). Note that S808 can be realized by transmitting an EPT (End Power Transfer) command (packet), which is a power transmission stop request command for RX401 to request TX402 to stop power transmission.

[0109] As a result of the determination in S807, when it is not clearly determined that "there is a foreign object", in order to adjust the waiting interval for transmitting the foreign object detection execution request, the current waiting interval is determined (S809). Specifically, it is determined whether the time length of the waiting time until the next foreign object detection execution request is transmitted can be made shorter than the current time length. When the waiting time for transmitting the foreign object detection execution request is not the shortest time length that RX401 can achieve (NO in S809), the waiting time until the foreign object detection execution request is transmitted is shortened (S810), and the transmission of the foreign object detection execution request is waited for until the shortened time has elapsed (S811). On the other hand, when the time length of the waiting time for transmitting the foreign object detection execution request is already the shortest time length (YES in S809), the waiting time for transmitting the foreign object detection execution request is not shortened, and the transmission of the foreign object detection execution request is waited for until the current waiting time has elapsed (S811).

[0110] As a method for determining a predetermined interval (the time length of the standby time) for transmitting a foreign object detection execution request, a method using a value determined in advance for at least one of the devices RX401 and TX402 may be used. Also, for example, as a method for determining a predetermined interval (the time length of the standby time), a method using a value determined by the power transmission output from TX402 may be used. Also, as the shortest time length, for example, it may be determined based on the shortest time length in which TX402 can execute the waveform attenuation method or the shortest time length in which RX401 can transmit a foreign object detection execution request. Also, for example, the predetermined interval may be determined by negotiation between RX401 and TX402. Also, this negotiation may be performed in the Negotiation phase.

[0111] Also, as a way to shorten the time length, there may be a method of shortening by a predetermined time length, a method of shortening to the shortest time length in one process, or a method of shortening by a time length corresponding to the power transmission output from TX402.

[0112] The processes from S811 to S813 are the same as the processes from S803 to S805, and the description thereof is omitted. When the possibility (existence probability) of the presence of a foreign object is included in the response from TX402 (YES in S813), RX401 determines whether the notified possibility (existence probability) of the presence of a foreign object clearly indicates "presence of a foreign object" (S814). As a result of the determination, if it is clearly "presence of a foreign object" (YES in S814), power reception is stopped (S808).

[0113] On the other hand, if the result of the determination is clearly "no foreign matter" (NO in S814), RX401 makes a determination as to whether it is clearly "no foreign matter" (S815). Here, being clearly "no foreign matter" means that the value of the existence probability is 0. If it is clearly "no foreign matter" (YES in S815), RX401 returns the time length of the waiting time for transmitting the shortened foreign matter detection execution request to the time length before shortening, returns to S803, and continues power reception (S816). On the other hand, if it is not clearly "no foreign matter" (NO in S815), RX401 determines whether it has continuously executed the transmission of the foreign matter detection execution request with the waiting time for transmitting the foreign matter detection execution request shortened for a predetermined number of times (S817). If it has been continuously executed for a predetermined number of times (YES in S817), since there is a possibility that a failure of the device or the like is suspected, RX401 stops power reception (S808). If it has not been continuously executed for a predetermined number of times (NO in S817), it returns to S809 and determines the current waiting interval in order to adjust the time length of the waiting time for transmitting the foreign matter detection execution request. Here, as a method for determining the predetermined number of times, a method using a value determined in advance for each RX401, a method using a value determined by the power transmission output from TX402, or the like may be used.

[0114] As described above, when the possibility (existence probability) of the presence of a foreign matter is higher than the threshold value of the existence probability and lower than the threshold value for determining whether there is clearly "foreign matter", RX401 controls so that the foreign matter detection execution request is transmitted at shorter intervals.

[0115] Note that, without performing the determination in S807, a configuration may be adopted in which the processing after S809 is performed when the existence probability is equal to or higher than the threshold value in S806. According to this configuration, when the existence probability is equal to or higher than the threshold value, by quickly transmitting the foreign matter detection execution request and performing foreign matter detection again, it is possible to quickly and surely confirm the presence or absence of a foreign matter.

[0116] Next, the processing flow in this embodiment of the power receiving device 401 (RX401) and TX402 (TX402) will be described using the sequence diagram of FIG. 9. FIG. 9 is the processing executed after the start of the power transmission processing of F528 in FIG. 5. Here, as an example of the processing, when TX402 performs the waveform attenuation method three times, the processing when foreign matter intrusion occurs during the power transmission power control in the waveform attenuation method will be described.

[0117] TX402 and RX401 start the power transmission process (F901). RX401 that has started power reception determines the threshold of the presence probability (F902). Here, it is assumed that power transmission of 15 watts determined in F527 is being performed, and RX401 that has determined that the received power is high determines the threshold so as to adjust the waiting time for waiting for the transmission of the foreign matter detection execution request even in the case of "low possibility of foreign matter presence".

[0118] In F902, RX401 that has determined the threshold waits for the waiting interval for the transmission of the foreign matter detection execution request (F903). Here, the waiting time is set to 2 seconds as the specified value of RX401. Also, the shortest waiting time for the transmission of the foreign matter detection execution request is set to 0.5 seconds. After the waiting time of F903 has elapsed, RX401 transmits a foreign matter detection execution request to TX402 (F904). TX402 that has received the foreign matter detection execution request from F904 performs power transmission power control and executes foreign matter detection (F905). Here, the number of times of the predetermined power transmission power control used by TX402 for detecting the possibility (presence probability) of foreign matter presence is three times.

[0119] In the power transmission power control of F905, since no foreign matter is present, it is clearly determined as "no foreign matter" as the possibility (presence probability) of foreign matter presence. In the power transmission power control of F905, since the number of times of the predetermined power transmission power control has not been reached, TX402 notifies RX401 of an ND packet (F906). RX401 that has received the notification of F906 waits until the waiting time elapses for the transmission of the next foreign matter detection execution request (F907). The processing from F908 to F911 is the same as the processing from F904 to F907, so the description is omitted.

[0120] Here, assume that a foreign object has entered the power transmission range of TX402 while F911 is in standby (F912). After the standby time of 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 power transmission control and executes foreign object detection (F914). In the power transmission control of F914, since a foreign object is present, "foreign object present" is clearly detected as the possibility (probability of existence) of a foreign object.

[0121] Since the number of times (=3) of a predetermined waveform attenuation method has been reached in the power transmission control of F914, TX402 determines the possibility (probability of existence) of a foreign object to be notified to RX401 based on the results of the power transmission controls of F905, F909, and F914 (F915). TX402 notifies RX401 of the possibility (probability of existence) of a foreign object determined in F915 (F916). RX401, which has received the notification in F916, determines whether the notified possibility (probability of existence) of a foreign object is equal to or greater than the probability threshold determined in F902 (F917). Here, RX401 compares the notified possibility (probability of existence) of a foreign object with the threshold and determines that the probability of existence is equal to or greater than the threshold.

[0122] Based on the result of the determination in F917, RX401 checks the current standby time for transmitting the foreign object detection execution request in order to shorten the standby time for transmitting the foreign object detection execution request (F918). As a result of F918, the current standby time for transmitting the foreign object detection execution request is 2 seconds, which is longer than the shortest standby time for transmitting the foreign object detection execution request, which is 0.5 seconds. Therefore, RX401 shortens the standby time for the foreign object detection execution request (F919). Here, RX401 determines 0.5 seconds, which is the shortest standby time, as the standby time. In this embodiment, the value is changed to the shortest value in one shortening, but a configuration that gradually shortens it may also be used.

[0123] RX401 waits (F920) for the waiting time for transmitting a foreign object detection execution request determined by F919. After the shortened waiting time of F920 has elapsed, RX401 transmits a foreign object detection execution request to TX402 (F921). As a result, TX402 receives the next foreign object detection execution request at an earlier timing compared to the case where these conditions are not met, when the possibility (probability of existence) of the presence of a foreign object due to foreign object detection is higher than the threshold value and it is not clearly determined that there is a foreign object. TX402, which has received the foreign object detection execution request transmitted in F921, performs power transmission control and executes foreign object detection (F922). Here, similar to F905, the number of times of the predetermined power transmission control used by TX402 for detecting the possibility (probability of existence) of the presence of a foreign object is set to three times.

[0124] In the power transmission control of F922, since a foreign object is present, it is clearly determined that there is a foreign object as the possibility (probability of existence) of the presence of a foreign object. In the power transmission control of F922, since the number of times of the predetermined power transmission control has not been reached, TX402 notifies RX401 of an ND packet (F923). RX401, which has received the notification of F923, waits again for the waiting interval for transmitting a foreign object detection execution request (F924). The processing from F925 to F930 is the same as the processing from F921 to F926, so the description is omitted.

[0125] In the power transmission control of F930, since the number of times of predetermined power transmission control has been reached, TX402 determines the possibility (probability of existence) of foreign object presence to be notified to RX401 from the results of the power transmission control of F922, F926, and F930 (F931). Here, TX402 determines to notify the probability of existence indicating "foreign object present" from the results of "foreign object present" in F922, "foreign object present" in F926, and "foreign object present" in F930. TX402 notifies RX401 of the possibility (probability of existence) of foreign object presence determined in F931 (F932). RX401 that has received the notification in F932 confirms that the notified possibility (probability of existence) of foreign object presence is "foreign object present", transmits an EPT (End Power Transfer) command (packet) to TX402, and stops power reception (F933). The above is an example of the processing when a foreign object is mixed in the foreign object detection based on a plurality of waveform attenuation methods.

[0126] Note that in this embodiment, as the intervals for waiting for the transmission of the foreign object detection execution request to be adjusted, there are two: the interval until the first foreign object detection execution represented by F903 and the interval between multiple power transmission controls represented by F907. In this embodiment, a method of adjusting both simultaneously is described, but only one of them may be adjusted.

[0127] With the above configuration, when RX401 is notified from TX402 that "there is a high possibility of a foreign object existing", it can shorten the transmission interval of the foreign object detection execution request. As a result, RX401 can shorten the time until the foreign object detection process is performed again when there is a high possibility of a foreign object existing. As a result, RX401 can quickly and clearly determine the presence or absence of a foreign object. Also, when there is no foreign object or when it is clearly notified that there is "no foreign object", RX401 sets the transmission time of the foreign object detection execution request to be longer than the shortest time length. Thereby, the processing load related to the waveform attenuation method can be reduced, and a safer and more efficient wireless power transmission system can be realized.

[0128] <Embodiment 2> In Embodiment 1, an example of applying foreign object detection by the waveform attenuation method a plurality of times in the WPC standard was described. In this embodiment, a method for performing more secure power transmission while using the method described in Embodiment 1 will be described.

[0129] (Processing of the power transmission device 402 and the power reception device 401) The flow of the processing of the power reception device 401 (RX401) in this embodiment will be described using the flowchart in FIG. 10. FIG. 10 is a flowchart showing the operation of RX401 executed after the start of the power transmission process of F528 in FIG. 5. Note that descriptions of the same processing content as in Embodiment 1 will be omitted.

[0130] The processing from S1001 to S1015 is the same as the processing from S801 to S815, so the description will be omitted. If it is not clearly "no foreign object" (NO in S1015), it is determined whether the transmission of the foreign object detection execution request with the waiting time shortened has been continuously executed for a predetermined number of times (S1017). If it has not been continuously executed for a predetermined number of times (NO in S1016), the process returns to S1009, and RX401 determines the current waiting time in order to adjust the waiting time for transmitting the foreign object detection execution request. The method for determining the predetermined number of times is the same as in Embodiment 1.

[0131] On the other hand, if it has been continuously executed for a predetermined number of times (YES in S1016), RX401 determines whether the current power transmitted from TX402 is the lower limit value that can be taken between TX402 and RX401 (S1017). If the power transmitted from TX402 is the lower limit value (YES in S1017), the process returns to S1009, and RX401 determines the current waiting time in order to adjust the waiting time for transmitting the foreign object detection execution request. If the power transmitted from TX402 is not the lower limit value (NO in S1017), RX401 transmits a power transmission power change request to TX402 to reduce the power transmission power (S1018).

[0132] After the completion of the transmission power change process of S1018, return to S1009. RX401 determines the current waiting time in order to adjust the waiting time for transmitting the foreign object detection execution request.

[0133] Also, when it is clearly determined that there is no foreign object in S1015 (YES in S1015), the waiting time for transmitting the shortened foreign object detection execution request is restored to the time length before shortening (S1019), and it is determined whether the transmission power of S1018 has been changed (S1020). If the transmission output has not been changed (NO in S1020), return to S803 and RX401 continues to receive power. On the other hand, if the transmission power has been changed (YES in S1020), RX401 sends a transmission output change request to TX402 to return the changed transmission power to the transmission power before the change (S1021), and then returns to S803 and continues to receive power.

[0134] By performing the above-described processing, the following effects are obtained. That is, when there is a high possibility that a foreign object exists, by reducing the transmission power, it is possible to avoid risks such as transmitting power to the foreign object and increasing the temperature of the foreign object. Also, the greater the transmission power, the greater the influence of the noise related to transmission can be. For this reason, when performing foreign object detection by the waveform attenuation method, there is also a high possibility that false detection of foreign objects occurs, where it is determined that there is a foreign object when there is no foreign object, or it is determined that there is no foreign object when there is a foreign object. Therefore, when it is determined that "there is a high possibility that a foreign object exists", by reducing the transmission power and performing foreign object detection again, it is possible to confirm the presence or absence of a foreign object in a more accurate state.

[0135] Next, the processing flow in this embodiment of the power receiving device 401 (RX401) and the power transmitting device 402 (TX402) will be described with reference to the sequence diagram of FIG. 11. FIG. 11 is the processing executed after the start of the power transmission process of F528. Here, as an example of the processing, when there is disturbance in the power transmission waveform during the power transmission control period due to temporary noise when performing power transmission power control in the waveform attenuation method, the processing will be described. Since the processing from F1101 to F1104 is the same as the processing from S901 to S904, the description will be omitted.

[0136] TX402 received from the foreign object detection execution request RX401 of F1104 performs power transmission control and executes foreign object detection (F1105). Here, it is assumed to be the number of times of a predetermined power transmission control that TX402 uses once for detecting the possibility (existence probability) of a foreign object. In the power transmission control of F1105, it is assumed that "the possibility of a foreign object existing is low" is detected as the possibility (existence probability) of a foreign object from the disturbance of the power transmission waveform during the power transmission control due to the influence of noise even though there is no foreign object. TX402 notifies the detection result of F1105 to RX401 (F1106). RX401 that has received the notification of F1106 determines whether the notified possibility (existence probability) of a foreign object is equal to or greater than the threshold value of the existence probability determined in F1102 (F1107). Here, RX401 compares the notified possibility (existence probability) of a foreign object with the threshold value and determines that it is equal to or greater than the threshold value of the existence probability.

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

[0138] Upon receiving the power transmission output change request of F1116, TX402 changes the power transmission power to 5 watts (F1117) and sends an ACK to notify RX401 that the change of the power transmission output is completed (F1118). In this embodiment, RX401 performs the process of changing to the lower limit value in one power transmission power change, but a configuration of gradually decreasing the power transmission power may also be used.

[0139] When the power transmission power is changed to the lower limit value, the noise that has affected the power transmission waveform disappears (F1119). After the noise disappearance of F1119, RX401 sends a foreign object detection execution request to TX402 (F1120). TX402 that has received the foreign object detection execution request of F1120 from RX401 performs power transmission power control in the waveform attenuation method and executes the detection of foreign objects (F1121). Here, since the noise that has affected the disturbance of the power transmission waveform during the power transmission power control period in S1119 has disappeared, it is clearly determined as "no foreign object" as the possibility (existence probability) of the presence of a foreign object. TX402 notifies RX401 of the existence probability based on the determination result of F1121 (F1122).

[0140] RX401 that has received the notification of F1122 repeats the execution of foreign object detection with the same processing from F1120 to F1122 and determines that no foreign object exists (F1123). In this embodiment, regarding the process of F1123, since the number of times of power transmission power control is 1, RX401 makes a determination based on the execution results of multiple foreign object detections in view of the influence of noise and the like, but a determination may also be made based on the execution result of one foreign object detection. RX401 that has determined that no foreign object exists in F1123 restores the transmission waiting time of the shortened foreign object detection execution request to the time length before shortening (S1124) and determines whether the power transmission power has been changed (S1125). In this embodiment, since the power transmission power has been changed from 15 watts to 5 watts, RX401 sends a power transmission power change request to TX402 to restore the power transmission output to 15 watts (S1126). TX402 that has received the power transmission output change request of F1126 changes the power transmission power to 15 watts (F1127) and sends an ACK to notify RX401 that the change of the power transmission power is completed (F1128).

[0141] In this way, when RX401 is notified of the "possibility of foreign matter" from TX402, the transmission time of the foreign object detection execution request is shortened and the power transmission power is reduced. As a result, RX401 and TX402 can prevent the power transmission from stopping due to false detection while reducing the possibility of the foreign object generating heat, and can continue the power transmission. In addition, by continuing the state in which the transmission time of the foreign object detection execution request is shortened, it is possible to quickly detect the mixing of foreign objects and realize a safer and more efficient wireless power transmission system.

[0142] <Other Embodiments> The contents of the above-described Embodiments 1 and 2 may be implemented in appropriate combination. Further, in the above-described embodiments, TX402 performs power transmission power control and detects foreign objects from its waveform attenuation index. As other methods for measuring the Q value, which is one of the waveform attenuation indexes, the following methods are conceivable. That is, there is also a method of transmitting a signal having a plurality of frequency components (for example, a pulse wave), measuring the amplitude or attenuation state of the waveform, and performing arithmetic processing (for example, Fourier transform) on the result to measure the Q value, and it is also possible to apply this to the above-described embodiments.

[0143] The present disclosure can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and causing one or more processors in the computer of the system or device to read and execute the program. Further, it can also be realized by a circuit (for example, ASIC, etc.) that realizes one or more functions. Further, the program may be recorded on a computer-readable recording medium and provided.

Explanation of Reference Numerals

[0144] 401 Power receiving device 201 Control unit 204 Communication unit 205 Coil

Claims

1. A power receiving device, A power receiving unit that wirelessly receives power from a power transmitting device; a transmission means for transmitting, at a predetermined interval, a signal for executing a detection process for detecting an object other than the power transmitting device and the power receiving device based on a voltage or current value at at least two points in time during a predetermined period during which the power transmitting device limits power transmission; a receiving means for receiving from the power transmitting device a response signal including a detection result based on the detection process executed in response to the signal transmitted by the transmitting means; a control means for controlling the transmission means to transmit the signal at an interval shorter than the predetermined interval when a detection result included in the response signal received by the receiving means satisfies a predetermined condition; A power receiving device comprising:

2. the response signal includes, as the detection result, information corresponding to a probability that an object different from the power transmitting device and the power receiving device is present; The power receiving device according to claim 1 , wherein the predetermined condition includes a case where the probability is higher than a threshold value.

3. The power receiving device according to claim 2 , wherein the predetermined condition includes a case where the probability is higher than the threshold and lower than another threshold that is higher than the threshold.

4. The power receiving device according to claim 3, characterized in that the control means controls the transmission means to transmit a signal to stop power transmitted from the power transmitting device when the probability is greater than the other threshold value.

5. The power receiving device according to any one of claims 1 to 4, characterized in that the control means does not change the specified interval at which the signal is transmitted by the transmitting means if the detection result contained in the response signal received by the receiving means does not satisfy a specified condition.

6. 6. The power receiving device according to claim 1, wherein the signal is a signal representing power received by the power receiving device.

7. The power transmitting device according to claim 6 , wherein the signal is a Received Power Packet defined by the Wireless Power Consortium standard.

8. The power receiving device described in any one of claims 1 to 7, characterized in that the control means controls the transmitting means to transmit a signal for changing the power transmitted by the power transmitting device to the power receiving device when the detection result contained in the response signal received by the receiving means satisfies a predetermined condition.

9. The power receiving device according to any one of claims 1 to 8, characterized in that the control means controls the transmitting means to transmit the signal at an interval shorter than the specified interval, and then, if the detection result contained in a response signal received by the receiving means satisfies another specified condition, controls the transmitting means to transmit the signal at the specified interval.

10. The power receiving device according to claim 9 , wherein the other predetermined condition includes a case where the detection result indicates that no object different from the power transmitting device and the power receiving device is present.

11. 11. The power receiving device according to claim 1, wherein the predetermined interval is a value that is determined in advance for at least one of the power receiving device and the power transmitting device.

12. 12. The power receiving device according to claim 1, wherein the predetermined interval is a value that is determined based on the power transmitted by the power transmitting device.

13. 13. The power receiving device according to claim 1, wherein the predetermined interval is a value that is determined based on negotiation between the power receiving device and the power transmitting device.

14. 14. The power receiving device according to claim 1, wherein the receiving means receives a response signal including a detection result based on a plurality of the detection processes.

15. a battery that stores the power received by the power receiving means; The power receiving device according to claim 1 , further comprising: a motor for driving wheels using electric power from the battery.

16. a battery that stores the power received by the power receiving means; 16. The power receiving device according to claim 1, further comprising: a display unit to which the power of the battery is supplied.

17. a battery that stores the power received by the power receiving means; a notification means for notifying the remaining capacity of the battery; The power receiving device according to claim 1 , further comprising:

18. A power transmission device, A power transmitting means for wirelessly transmitting power to a power receiving device; a receiving means for receiving a signal for executing a detection process for detecting an object other than the power transmitting device and the power receiving device based on a voltage or current value at at least two points in time during a predetermined period during which power transmission by the power transmitting means is restricted; a processing means for executing the detection process in response to a signal received by the receiving means; having When a detection result based on the detection process executed by the processing means in response to a first signal satisfies a predetermined condition, the receiving means receives a second signal, which is received after the first signal, at an earlier timing than when the detection result does not satisfy the predetermined condition. A power transmitting device comprising:

19. The power transmitting device according to claim 18 , further comprising a transmitting means for transmitting to the power receiving device a response signal including a detection result based on the detection process executed by the processing means.

20. 20. The power transmitting device according to claim 18, wherein the predetermined condition includes a case where a probability that an object different from the power transmitting device and the power receiving device exists is higher than a threshold value.

21. The power transmitting device according to claim 20 , wherein the predetermined condition includes a case where the probability is higher than the threshold and lower than another threshold that is higher than the threshold.

22. 22. The power receiving device according to claim 21, wherein the power transmitting means stops transmitting power to the power receiving device when the probability is greater than the other threshold value.

23. The vehicle has wheels and a battery.

23. The power transmitting device according to claim 18, wherein the power transmitting means wirelessly transmits power to the power receiving device using power from the battery.

24. 23. The power transmitting device according to claim 18, wherein the power transmitting device is installed in a vehicle.

25. A wireless power transmission method, comprising: a transmission step of transmitting, at a predetermined interval, a signal for executing a detection process for detecting an object other than the power transmitting device and the power receiving device based on a voltage or current value at at least two points in a predetermined period during which the power transmitting device limits power transmission to the power receiving device; a control step of controlling the signal to be transmitted at an interval shorter than the predetermined interval when a detection result based on a detection process executed in response to the signal transmitted in the transmission step satisfies a predetermined condition; A wireless power transmission method comprising:

26. A program for causing a computer to function as the power receiving device according to any one of claims 1 to 17 or the power transmitting device according to any one of claims 18 to 24.

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