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

Abstract

The system is designed to allow for faster re-detection based on the results of the detection process for objects other than power transmission and receiving equipment. [Solution] The power receiving device 401 includes a coil 205 that wirelessly receives power from a power transmitting device, a communication unit 204 that transmits signals at predetermined intervals for performing a detection process to detect an object different from the power transmitting device and the power receiving device based on the voltage or current value at at least two points in time during a predetermined period in which the power transmitting device restricts power transmission, and receives a response signal from the power transmitting device that includes a detection result based on the detection process performed in response to the transmitted signal, and a control unit 201 that controls the transmission of signals at intervals shorter than predetermined intervals if the detection result included in the received response signal satisfies predetermined conditions.

Description

Technical Field

[0001] This disclosure relates to wireless power transmission technology.

Background Art

[0002] In recent years, the technological development of wireless power transmission systems has been widely carried out. Patent Document 1 discloses a method for foreign object detection in the Wireless Power Consortium standard (WPC standard). Further, Patent Document 2 discloses a foreign object detection method for detecting the presence of an object different from the power receiving device and the 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. Also, Patent Document 3 discloses a foreign object detection method in which a power transmitting device transmits a signal for foreign object detection to a power receiving device and determines the presence or absence of a foreign object using an echo signal from the power receiving device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In wireless power transmission, if a foreign object is detected, the power transmission device can stop power transmission, thereby suppressing the possibility of the foreign object overheating due to power being transmitted to it. Furthermore, the foreign object detection process is envisioned to be performed when the power transmission device receives a predetermined signal from the power receiving device. However, depending on the results of the foreign object detection process, it may not be clear whether or not a foreign object is present. In this case, there is a problem that the possibility of the foreign object overheating due to continued power transmission increases, or that power transmission is stopped even when no foreign object is present, reducing power transmission efficiency.

[0005] This disclosure has been made in view of the above-mentioned problems, and aims to enable faster re-detection processing depending on the results of the detection processing for detecting objects other than power transmission equipment and power receiving equipment. [Means for solving the problem]

[0006] The power receiving device of this disclosure includes: power receiving means for receiving power wirelessly from a power transmitting device; transmitting means for transmitting signals at predetermined intervals for performing a detection process to detect an object different from the power transmitting device and the power receiving device based on the voltage or current value at at least two points in time during a predetermined period in which the power transmitting device restricts power transmission; receiving means for receiving a response signal from the power transmitting device that includes a detection result based on the detection process performed in response to the signal transmitted by the transmitting means; and control means for controlling the transmitting means to transmit the signal at an interval shorter than the predetermined interval if the detection result included in the response signal received by the receiving means satisfies predetermined conditions. [Effects of the Invention]

[0007] According to this disclosure, a subsequent detection process can be performed more quickly depending on the result of the detection process for detecting an object different from the power transmission device and the power receiving device. [Brief explanation of the drawing]

[0008] [Figure 1]This figure shows an example of the configuration of a power transmission device. [Figure 2] This figure shows an example of the configuration of a power receiving device. [Figure 3] This is a block diagram showing an example of the functional configuration of the control unit of a power transmission device. [Figure 4] This is a diagram showing an example configuration of a wireless power transmission system. [Figure 5] This figure shows an example of the process for wireless power transmission. [Figure 6] This is a diagram illustrating foreign object detection using the waveform attenuation method. [Figure 7] This diagram illustrates a method for detecting foreign objects based on the power transmission waveform during power transmission. [Figure 8] This is a flowchart illustrating the operation of the power receiving device in Embodiment 1. [Figure 9] This is a diagram illustrating the operation of the power receiving device and the power transmitting device in Embodiment 1. [Figure 10] This is a flowchart illustrating the operation of the power receiving device in Embodiment 2. [Figure 11] This is a diagram illustrating the operation of the power receiving device and the power transmitting device in Embodiment 2. [Figure 12] This diagram illustrates how to set the threshold for foreign object detection using the Power Loss method. [Figure 13] This diagram illustrates how to set a threshold value in foreign object detection using the waveform attenuation method. [Figure 14] This diagram illustrates the processing when multiple waveform attenuation methods are applied. [Modes for carrying out the invention]

[0009] <Embodiment 1> The embodiments will be described in detail below with reference to the attached drawings. While several features are described in the embodiments, not all of these features are necessarily essential, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numeral.

[0010] (Configuration of a wireless power transmission system) Figure 4 shows an example of the configuration of the wireless power transmission system (wireless charging system) in this embodiment. In one example, this system is configured to include 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 using Figures 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 its built-in battery. TX402 is an electronic device that wirelessly transmits power to RX401, which is placed on a charging base 403, which is part of TX402. Hereinafter, since the charging base 403 is part of TX402, "placed on the charging base 403" may be referred to as "placed on TX402 (power transmitting device 402)". The area 404 enclosed by the dotted line is the range in which RX401 can receive power from TX402. Furthermore, the state of being "placed" does not necessarily mean that RX401 and TX402 are in contact, but rather refers to a state in which RX401 is included in 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. Also, 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. Also, 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 (camera, video camera, etc.). Also, RX401 may be an image input device such as a scanner, or an image output device such as a printer, a copier, a projector, etc. Also, RX401 may be a robot, a medical device, etc. 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. In such an automobile, the received power is supplied to a battery. The power of the battery may be supplied to a power generation unit (motor, electric unit) that drives the wheels, or may be used to drive a sensor used for driving assistance or a communication unit that communicates with an external device. 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 devices other than TX402.

[0014] Furthermore, RX401 may have a housing unit that houses a person. For example, as sensors, there are sensors used to measure 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 object, etc. that have a power generation unit 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 that charges 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 receiving device 401 (RX401) in this embodiment will be described. Note that the configuration described below is merely an example, and some (or in some cases all) of the described configuration may be replaced or omitted by other configurations that perform similar functions, and further configurations may be added to the described configuration. Furthermore, one block shown in the following description may be divided into multiple blocks, or multiple blocks may be integrated into one block. Also, each functional block shown below is assumed to be implemented as a software program, but some or all of the components included in this functional block may be implemented in hardware.

[0017] Figure 1 is a functional block diagram showing an example configuration of the TX402 according to this embodiment. The 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 Figure 1, the control unit 101, power supply unit 102, power transmission unit 103, communication unit 104, and memory 106 are shown as separate components, but any multiple functional blocks among these may be implemented on the same chip.

[0018] The control unit 101 controls the entire TX402, for example, by executing a control program stored in memory 106. The control unit 101 also 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 is configured to include one or more processors, such as a CPU (Central Processing Unit) or MPU (MicroProcessor Unit). The control unit 101 may also be configured to include hardware such as an Application Specific Integrated Circuit (ASIC). Additionally, the control unit 101 may include an array circuit such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processes. The control unit 101 stores information that should be stored during the execution of various processes in memory 106. The control unit 101 can also measure time using a timer (not shown).

[0019] The power supply unit 102 supplies power to each functional block. The power supply unit 102 is, for example, a commercial power source or a battery. The battery stores power supplied from the commercial power source.

[0020] The power transmission unit 103 converts the DC or AC power input from the power supply unit 102 into AC frequency power in the frequency band used for wireless power transmission, and inputs this AC frequency power to the power transmission antenna (coil) 105 to generate electromagnetic waves for the RX401 to receive power. 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 with a half-bridge or full-bridge configuration using a FET (Field Effect Transistor). In this case, the power transmission unit 103 includes a gate driver that controls the ON / OFF state of the FET.

[0021] The power transmission unit 103 controls the intensity of the electromagnetic waves output by adjusting the voltage (transmission voltage) or current (transmission current), or both, input to the power transmission antenna 105. Increasing the transmission voltage or transmission current increases the intensity of the electromagnetic waves, while decreasing the transmission voltage or transmission current decreases the intensity of the electromagnetic waves. The power transmission unit 103 also controls the output of AC frequency power so that power transmission from the power transmission antenna 105 is started or stopped based on instructions from the control unit 101. Furthermore, the power transmission unit 103 is assumed to have the capacity to supply enough power 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 modulates the electromagnetic waves output from the power transmission antenna 105 by frequency shift modulation and transmits information to the RX401 to perform communication. The communication unit 104 also demodulates the electromagnetic waves transmitted from the power transmission antenna 105, which have been amplitude modulated or load modulated by the RX401, to obtain the information transmitted by the RX401. In other words, the communication performed by the communication unit 104 is carried out by superimposing a signal onto the electromagnetic waves transmitted from the power transmission antenna 105. The communication unit 104 may also communicate with the RX401 using a communication standard different from the WPC standard using an antenna different from the power transmission antenna 105, or it may selectively use multiple communication methods to communicate with the RX401. Examples of such communication standards include Bluetooth® Low Energy (BLE) and NFC (Near Field Communication).

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

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

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

[0026] The control unit 201 controls the entire RX401 by executing a control program stored, for example, in the memory 208. That is, the control unit 201 controls each of the functional units shown in Figure 2. Furthermore, the control unit 201 may also perform control for executing applications other than wireless power transmission. An example of the control unit 201 is configured to include one or more processors such as a CPU or MPU. In addition, the control unit 201 may control the entire RX401 (or the entire smartphone if the RX401 is a smartphone) in cooperation with the OS (Operating System) it is running.

[0027] Furthermore, the control unit 201 may be composed of hardware such as an ASIC. Alternatively, the control unit 201 may include an array circuit such as an FPGA compiled to perform predetermined processing. The control unit 201 stores information that should be stored during the execution of various processes in the memory 208. The control unit 201 may also measure time using a timer (not shown).

[0028] The UI unit 202 provides various outputs to the user. These outputs include screen displays, blinking and color changes of LEDs (Light Emitting Diodes), audio output from the speaker, and vibration of the RX401 unit. The UI unit 202 is implemented using an LCD panel, speaker, vibration motor, etc.

[0029] The power receiving unit 203 acquires AC power (AC voltage and AC current) generated by electromagnetic induction based on electromagnetic waves radiated from the power transmitting antenna 105 of the TX402 via the power receiving antenna (coil) 205. The power receiving unit 203 then converts the AC power into DC or AC power of a predetermined frequency and outputs power to the charging unit 206, which performs processing for charging the battery 207. In other words, the power receiving unit 203 includes a rectifier and a voltage control unit necessary to supply power to the load in the RX401. The above GP is the amount of power guaranteed to be output from the power receiving unit 203. The power receiving unit 203 is assumed to have the capacity to supply enough power to the charging unit 206 to charge the battery 207 and to output 15 watts of power to the charging unit 206.

[0030] The communication unit 204 communicates with the communication unit 104 of the TX402 for power receiving control based on the WPC standard. The communication unit 204 demodulates the electromagnetic waves input from the power receiving antenna 205 and obtains the information transmitted from the TX402. Then, the communication unit 204 communicates with the TX402 by superimposing a signal related to the information to be transmitted to the TX402 onto the electromagnetic waves by amplitude modulation or load modulation. The communication unit 204 may also communicate with the TX402 using a different antenna than the power receiving antenna 205 and a communication standard different from the WPC standard, or it may selectively use multiple communication methods to communicate with the TX402. Examples of such communication standards include Bluetooth® Low Energy (BLE) and NFC (Near Field Communication).

[0031] In addition to storing the control program, memory 208 also stores the states of TX402 and RX401. 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 section 209 and the second switch section 210 are controlled by the control unit 201. The receiving antenna 205 is connected to the resonant capacitor 211. When the second switch section 210 is turned ON and short-circuited, the receiving antenna 205 and the resonant capacitor 211 form a series resonant circuit and resonate at a specific frequency f2. At this time, current flows through the closed circuit formed by the receiving antenna 205, the resonant capacitor 211, and the second switch section 210, but no current flows through the receiving section. When the second switch section 210 is turned OFF and opened, the power received by the receiving antenna 205 and the resonant capacitor 211 is supplied to the receiving section 203.

[0033] The first switch unit 209 controls whether or not to supply the received power to the load, which is the battery. It also has the function of controlling the value of the load. When the first switch unit 209 connects the charging unit 206 and the battery 207, the received power is supplied to the battery 207. When 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 Figure 2, the first switch unit 209 is located between the charging unit 206 and the battery 207, but it may also be located between the power receiving unit 203 and the charging unit 206. Alternatively, it may be located between the power receiving antenna 205, the resonant capacitor 211, and the closed circuit formed by the second switch unit 210 and the power receiving unit 203. In other words, the first switch unit 209 may also be for controlling whether or not to supply the received power to the power receiving unit 203. Furthermore, although Figure 2 shows the first switch unit 209 as a single block, it is also possible to implement the first switch unit 209 as part of the charging unit 206 or as part of the power receiving unit 203.

[0034] Next, the functions of the control unit 101 of the TX402 will be described with reference to Figure 3. Figure 3 is a block diagram showing an example of the functional configuration 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 the 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 the RX401. The measurement unit 303 measures the waveform attenuation index, which will be described later. It also measures the power transmitted to the RX401 via the power transmission unit 103 and measures the average transmitted power per unit time. The measurement unit 303 also measures the Q value of the power 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 calculation processing.

[0036] The foreign object detection unit 305 performs processing to detect foreign objects within the power transmission range of the TX402. Here, "foreign object" in this embodiment refers to an object different from the power receiving device and the power transmitting device. The foreign object detection unit 305 can implement foreign object detection functions using the Power Loss method, the Q value measurement method, and the waveform attenuation method, as described later. The foreign object detection unit 305 may also have a function to perform foreign object detection processing using other methods. For example, in a TX402 equipped with NFC (Near Field Communication) communication functionality, the foreign object detection unit 305 may perform foreign object detection processing using the NFC standard's opposing device detection function. In addition to detecting foreign objects, the foreign object detection unit 305 can also detect changes in the state on the TX402. For example, the TX402 can also detect increases or decreases in the number of RX401s on the TX402.

[0037] The setting unit 304 sets a threshold value that serves as a criterion for determining the presence or absence of foreign matter when TX402 performs foreign matter detection using methods such as the power loss method, the Q value measurement method, or the waveform attenuation method. The setting unit 304 may also have a function to set a threshold value that serves as a criterion for determining the presence or absence of foreign matter, which is necessary when performing foreign matter detection processing using other methods. Furthermore, the foreign matter detection unit 305 can perform foreign matter detection processing based on the threshold value set by the setting unit 304 and the waveform attenuation index, transmission power, and Q value measured by the measurement unit 303.

[0038] The communication control unit 301, power transmission control unit 302, measurement unit 303, setting unit 304, and foreign object detection unit 305 are implemented as programs that operate in the control unit 101. Each processing unit is configured as an independent program and can operate in parallel while synchronizing the programs through event processing, etc. However, two or more of these processing units may be incorporated into a single program.

[0039] In this embodiment, RX401 and TX402 perform wireless power transmission using an electromagnetic induction method for wireless charging, based on the WPC standard. Specifically, RX401 and TX402 perform wireless power transmission for wireless charging based on the WPC standard between the receiving antenna 205 of RX401 and the transmitting antenna 105 of TX402. The wireless power transmission method applied to this system is not limited to the method specified in the WPC standard, but may also be other methods such as electromagnetic induction, magnetic field resonance, electric field resonance, microwave, or laser. Furthermore, in this embodiment, wireless power transmission is used for wireless charging, but wireless power transmission may also be used for purposes other than wireless charging.

[0040] The WPC standard defines the amount of power that a receiving device is guaranteed to be able to output to its load (battery) when it receives power from a transmitting device, as defined by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates the power value that guarantees output to the load (e.g., charging circuit, battery, etc.) of RX401, even if the relative positions of RX401 and TX402 change and the power transmission efficiency between the receiving antenna 205 and the transmitting antenna 105 decreases. For example, if GP is 5 watts, even if the relative positions of the receiving antenna 205 and the transmitting antenna 105 change and the power transmission efficiency decreases, TX402 will be controlled to output 5 watts to the load within RX401 and continue power transmission.

[0041] Furthermore, when transmitting power from TX402 to RX401, if a foreign object other than RX401 is present near TX402, the electromagnetic waves used for power transmission may affect the foreign object, potentially raising its temperature or destroying it. Therefore, the WPC standard specifies a method for TX402 to detect the presence of a foreign object on the charging base 403, so that power transmission can be stopped if a foreign object is present to prevent temperature rise or destruction of the foreign object. Specifically, the Power Loss method is specified, which detects foreign objects based on the difference between the power transmitted by TX402 and the power received by RX401. Additionally, the Q-value measurement method is specified, which detects foreign objects based on the change in the Quality-Factor (Q-value) of the power transmitting antenna 105 in TX402. Note that the foreign objects detected by TX402 in this embodiment are not limited to objects present on the charging base 403. TX402 only needs to detect foreign objects located near TX402; for example, it may detect foreign objects located within the range to which TX402 can transmit power.

[0042] (Processing based on WPC standards) This section describes the processing performed by RX401 and TX402 according to this embodiment, based on the WPC standard. The WPC standard defines multiple phases, including the Power Transfer phase in which power transmission is performed and one or more phases prior to actual power transmission, and communication for necessary power transmission and reception control is performed in each phase. The phases prior to power transmission may include the Selection phase, Ping phase, Identification and Configuration phase, Negotiation phase, and Calibration phase. In the following, 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 Analog Pings to detect when an object is placed on the charging base of TX402 (for example, when RX401 or a conductive piece is placed on the charging base). TX402 detects at least one of the voltage and current values ​​of the transmitting antenna 105 when the Analog Ping is transmitted. If the voltage value falls below a certain threshold or the current value exceeds a certain threshold, it determines that an object is present and transitions to the Ping phase.

[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, which is mounted on top of TX402. RX401 notifies TX402 of the magnitude of the received voltage. In this way, TX402 recognizes that the object detected in the Selection phase is RX401 by receiving the response from RX401, which received the Digital Ping. Upon receiving notification of the received voltage value, TX402 transitions to the I&C phase. Also, before transmitting the Digital Ping, TX402 measures the Q value of the transmitting 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 equipment configuration information (capability information) from RX401. RX401 sends an ID Packet and a Configuration Packet. The ID Packet contains the identifier information of RX401, and the Configuration Packet contains the equipment configuration information (capability information) of RX401. Upon receiving the ID Packet and Configuration Packet, TX402 responds with an acknowledgment (ACK). The I&C phase then ends.

[0046] In the Negotiation phase, the GP value is determined based on the GP value requested by RX401 and the power transmission capacity of TX402. TX402 also receives an FOD Status Packet containing Reference Quality Factor Value information from RX401, adjusts and determines the threshold for the Q-value measurement method. Then, TX402 performs foreign object detection processing using the Q-value measurement method according to the request from RX401. Furthermore, the WPC standard specifies a method where, after transitioning to the Power Transfer phase, the same processing as the Negotiation phase is performed again at the request of RX401. The phase in which these processes are performed after transitioning from the Power Transfer phase is called the Renegotiation phase.

[0047] In the Calibration phase, calibration is performed based on the WPC standard. Additionally, RX401 notifies TX402 of predetermined received power values ​​(received power value under light load conditions / received power value under maximum load conditions), and TX402 performs adjustments for efficient power transmission. The received power values ​​notified to TX402 may be used for foreign object detection processing using the Power Loss method.

[0048] During the Power Transfer phase, control is performed for initiating, continuing, and stopping power transmission due to errors or full charge. TX402 and RX401 communicate using the transmitting antenna 105 and receiving antenna 205, superimposing signals onto electromagnetic waves transmitted from either antenna 105 or 205 for these power transmission and reception control operations. The range over which communication based on the WPC standard is possible between TX402 and RX401 is approximately the same as the power transmission range of TX402.

[0049] The above describes the processes performed by RX401 and TX402 in this embodiment. Below, the operation of RX401 and TX402 in each of the above-described phases will be explained using the sequence diagram in Figure 5. Figure 5 is a sequence diagram for power transmission in accordance with the WPC standard. Here, the transmission device 402 (TX402) and the receiving device 401 (RX401) will be used as examples.

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

[0051] When TX402 detects the presence of an object within its power transmission range using Analog Ping (F503, F504), it sends a WPC-compliant Digital Ping (F505). Upon receiving the Digital Ping, RX401 can understand that TX402 has detected RX401 (F506). Furthermore, when TX402 receives a predetermined response to the Digital Ping, it determines that the detected object is RX401 and that RX401 has been placed on the charging cradle 403. Upon detecting the placement of RX401, TX402 obtains identification information and capability information from RX401 via I&C phase communication as defined by the WPC standard (F507). Here, the identification information of RX401 includes the Manufacturer Code and Basic Device ID. The capability information of RX401 includes the following information: Specifically, this includes information elements that can identify the version of the WPC standard it supports, a Maximum Power Value that identifies the maximum power that the RX401 can supply to the load, and information indicating whether it has the WPC standard's Negotiation function. Note that the TX402 may obtain the identification and capability information of the RX401 by means other than the I&C phase communication of the WPC standard. Furthermore, the identification information may be any other identification information that can identify an individual RX401, such as a Wireless Power ID. Capability information may include information other than that mentioned above.

[0052] Next, TX402 determines the GP value with RX401 through communication in the Negotiation phase as defined in the WPC standard (F508). Note that F508 may perform other procedures to determine GP, not limited to communication in the Negotiation phase as defined in the WPC standard. Furthermore, if TX402 obtains information (for example in F507) indicating that RX401 does not support the Negotiation phase, it may choose not to perform communication in the Negotiation phase. In this case, TX402 may set the GP value to a small value (for example, one predetermined in the WPC standard). In this embodiment, GP = 5 watts.

[0053] After determining the GP, TX402 performs calibration based on the GP. In the calibration process, RX401 first transmits information to TX402 including the received power under light load conditions (load disconnection, or load conditions where the transmitted power is below the first threshold) (hereinafter referred to as the first reference received power information) (F509). In this embodiment, the first reference received power information is the received power information of RX401 when the transmitted power of TX402 is 250 milliwatts. The first reference received power information is a Received Power Packet (mode 1) as defined in the WPC standard, but other messages may be used. In the following, Received Power Packet (mode1) will also be referred to as "RP1". TX402 determines whether to accept the first reference power information based on the power transmission status of its own device. TX402 sends an acknowledgment (ACK) to RX401 if it accepts the information, and a negative acknowledgment (NAK) if it does not accept it.

[0054] Next, when RX401 receives an ACK from TX402 (F510), it processes information including the received power in the load-connected state (maximum load state, or load state where the transmitted power exceeds the second threshold) (hereinafter referred to as the second reference received power information) to send to TX402. 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 the Received Power Packet (mode2) as defined in the WPC standard, but other messages may be used. In the following, Received Power Packet (mode2) will also be referred to as "RP2". RX401 sends a transmission output change request containing a positive value to increase the transmitted power from TX402 to 5 watts (F511).

[0055] TX402 receives the above-mentioned power output change request and, if it is able to handle the increase in power, responds with an ACK and increases the power (F512, F513). Since the second reference received power information is the received power information when TX402's power output is 5 watts, if TX402 receives a power increase request from RX401 that exceeds 5 watts (F514), it responds with an NAK to the power output change request. This prevents the transmission of power exceeding the specified limit (F515).

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

[0057] If TX402 determines that it is ready to begin charging and starts transmitting power to RX401, charging of RX401 will begin. Before starting the power transmission process, TX402 and RX401 may perform device authentication (F519), and if they determine that the devices are capable of handling a larger GP, they may reset the GP to a larger value, for example, 15 watts (F520).

[0058] In this case, RX401 and TX402 increase the transmission output of TX402 to 15 watts using a transmission output change request, ACK, and NAK (F521-F524). Then TX402 and RX401 perform calibration again for GP=15 watts. Specifically, RX401 transmits information including the received power in the load-connected state of RX401 when TX402's transmission power 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. This allows TX402 to calculate the power loss between TX402 and RX401 for all possible transmission power levels of TX402 (from 250 milliwatts to 15 watts in this case) (F526). TX402 sends an ACK (acknowledgment) to RX401 for the third reference power information received (F527), completing the calibration process. Having determined that charging can begin, TX402 starts the power transmission process to RX401 and moves to the Power Transfer phase (F528). Note that processes F519 through F527 are not mandatory.

[0059] In the Power Transfer phase, TX402 transmits power to RX401. Foreign object detection is also performed using the Power Loss method. In the Power Loss method, TX402 first calculates the power loss between TX402 and RX401 in a state without foreign objects, based on the difference between the power transmitted by TX402 and the power received by RX401, as described in the Calibration section above. The calculated value corresponds to the standard power loss in a normal state (without foreign objects) during power transmission. Then, TX402 determines that "foreign object present" if the power loss between TX402 and RX401 measured during power transmission after Calibration deviates by a threshold from the normal power loss. A more detailed explanation of the Power Loss method will be provided later.

[0060] The Power Loss method detects foreign objects based on the measurement results of power loss during power transmission from TX402 to RX401. While the Power Loss method has the disadvantage of reduced accuracy when TX402 is transmitting a large amount of power, it has the advantage of maintaining high power transmission efficiency because it can detect foreign objects while continuing power transmission.

[0061] The above is the processing flow based on the WPC standard. In the power transmission process of the F528, if power transmission is to be terminated due to reasons such as the RX401 battery becoming fully charged or a foreign object being detected, the RX401 sends a power transmission termination request command to the TX402 requesting that power transmission be stopped. In this embodiment, the power transmission termination request command is an EPT (End Power Transfer) command (packet). This terminates the power transmission process.

[0062] (Power Loss Method) The detection of foreign objects based on the Power Loss method specified in the WPC standard will be explained using Figure 12. In Figure 12, the horizontal axis represents the power transmitted by TX402, and the vertical axis represents the power received by RX401. A foreign object is an object other than RX401 that may affect the power transmission from TX402 to RX401, and may be an object such as a conductive metal piece.

[0063] First, TX402 transmits power to RX401 at the first transmission power value Pt1. RX401 receives power at the first reception power value Pr1 (this state is called the Light Load state). Then, TX402 stores the first transmission power value Pt1. Here, the first transmission power value Pt1 or the first reception power value Pr1 is a predetermined minimum transmission power or reception power. At this time, RX401 controls itself so that the power it receives is 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 and battery, etc.). Subsequently, RX401 notifies TX402 of the power value Pr1 of the first reception power. Upon receiving Pr1 from RX401, TX402 calculates that the power loss between TX402 and RX401 is Pt1-Pr1(Ploss1), and can create calibration point 1200( which indicates the correspondence between Pt1 and Pr1).

[0064] Next, 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). 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 itself so that the power it receives is the maximum power. For example, RX401 controls the first switch unit 209 to connect the receiving antenna 205 and the load so that the received power is supplied to the load. Subsequently, RX401 notifies TX402 of Pr2. Upon receiving Pr2 from RX401, TX402 calculates that the power loss between TX402 and RX401 is Pt2-Pr2(Ploss2), and can create a calibration point 1001 that shows the correspondence between Pt2 and Pr2.

[0065] The TX402 then creates a linear interpolation line 1202 between calibration point 1200 and calibration point 1201. Line 1202 shows the relationship between transmitted power and received power when there are no foreign objects in the vicinity of the TX402 and RX401. Based on line 1202, the TX402 can predict the power value that the RX401 will receive when transmitting power at a predetermined transmission power in the absence of foreign objects. For example, if the TX402 transmits power at the third transmission power value Pt3, it can be inferred from point 1203 on line 1202, which corresponds to Pt3, that the third received power value that the RX401 will receive will be Pr3.

[0066] As described above, based on multiple combinations of the power transmission value of TX402 and the power reception value of RX401 measured while varying the load, the power loss between TX402 and RX401 according to the load can be determined. Furthermore, by interpolation from multiple combinations, the power loss between TX402 and RX401 for all loads can be estimated. In this way, the calibration process performed by TX402 and RX401 to obtain the combination of power transmission value and power reception value will be referred to below as the "Power Loss Method Calibration Process (CAL Process)".

[0067] After calibration, if TX402 actually transmits power to RX401 via Pt3, let's assume TX402 receives a power value Pr3' from RX401. TX402 calculates Pr3-Pr3' (=Ploss_FO) by subtracting the actual power value Pr3' received from RX401 from the power value Pr3 in the absence of foreign objects. This Ploss_FO can be considered as power loss due to the power consumed by foreign objects present near TX402 and RX401. Therefore, if the power Ploss_FO, which is likely to have been consumed by the foreign object, exceeds a predetermined threshold, it can be determined that a foreign object is present. Alternatively, TX402 may pre-calculate the power loss Pt3-Pr3 (Ploss3) between TX402 and RX401 from the power value Pr3 in the absence of foreign objects. Next, the power loss Pt3-Pr3'(Ploss3') between TX402 and RX401 in the presence of the foreign object is calculated from the received power value Pr3' received from RX401 in the presence of the foreign object. Then, Ploss3'-Ploss3 (=Ploss_FO) can be used to estimate the power Ploss_FO that would have been consumed by the foreign object.

[0068] As described above, the power Ploss_FO, which is likely to have been consumed by the foreign object, can be calculated as Pr3-Pr3'(=Ploss_FO) or as Ploss3'-Ploss3 (=Ploss_FO). In the following specification, the method of calculating Ploss3'-Ploss3 (=Ploss_FO) will be described in principle, but the contents of this embodiment can also be applied to the method of calculating Pr3-Pr3'(=Ploss_FO). The above is an explanation of foreign object detection based on the power loss method.

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

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

[0071] During the Power Transfer phase in the WPC standard, foreign object detection is performed using the Power Loss method. However, relying solely on the Power Loss method for foreign object detection carries the risk of false detection of foreign objects or incorrect determination of the absence of foreign objects when they are present. In particular, the Power Transfer phase is the phase in which TX402 transmits power, and if foreign objects are present near TX402 and RX401 during power transmission, heat generation from these objects will increase significantly. Therefore, improving the accuracy of foreign object detection in this phase is required. Accordingly, in this embodiment, we consider implementing a foreign object detection method different from the Power Loss method in order to improve the accuracy of foreign object detection.

[0072] (Foreign object detection method using waveform attenuation) In the Power Transfer phase, TX402 transmits power to RX401. Therefore, if foreign object detection can be performed using the transmission waveform (voltage waveform or current waveform) related to this power transmission, foreign object detection will be possible without using newly defined foreign object detection signals, etc. A method of detecting foreign objects based on the attenuation state of the transmitted radio waves (hereinafter referred to as the waveform attenuation method) will be explained using Figure 6. Figure 6 is a diagram illustrating the principle of foreign object detection using the waveform attenuation method. Here, foreign object detection using the transmission waveform related to power transmission from TX402 (TX402) to RX401 (RX401) will be explained as an example.

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

[0074] The transmission frequency for power transmission from TX402 is a predetermined frequency, for example, a fixed frequency between 85kHz and 205kHz used in the WPC standard. Point 601 is a point on the envelope of the high-frequency voltage and represents the voltage value at time T1. (T1, A1) in the figure indicates that the voltage value at time T1 is A1. Similarly, point 602 is a point on the envelope of the high-frequency voltage and represents the voltage value at time T2. (T2, A2) in the figure indicates that the voltage value at time T2 is A2. The quality factor (Q value) of this transmission antenna 105 can be determined based on the time change of the voltage value from time T0 onward. For example, the Q value can be calculated using Equation 1 based on the time, voltage value, and frequency f of the high-frequency voltage at points 601 and 602 on the envelope of the voltage value. Q = πf(T2 - T1) / ln(A1 / A2) (Equation 1)

[0075] If foreign matter is present near TX402 and RX401, the Q value decreases. This is because energy loss occurs due to the presence of foreign matter. Therefore, focusing on the slope of voltage decay, the slope of the line connecting points 601 and 602 becomes steeper when foreign matter is present than when it is absent, as more energy is lost due to the foreign matter. This results in a higher attenuation rate of the waveform amplitude. In other words, the waveform attenuation method determines the presence or absence of foreign matter based on the voltage decay state between points 601 and 602. In practice, the presence or absence of foreign matter can be determined by comparing some numerical value that represents this attenuation state. For example, the above-mentioned Q value can be used for determination. A lower Q value means a higher waveform attenuation rate (the degree of decrease in waveform amplitude per unit time). Alternatively, the determination may be made using the slope of the line connecting points 601 and 602, which can be obtained from (A1-A2) / (T2-T1). Alternatively, if the time (T1 and T2) for observing the voltage decay state is fixed, the determination can also be made using the difference in voltage values ​​(A1-A2) or the ratio of voltage values ​​(A1 / A2). Alternatively, if the voltage value A1 immediately after the power transmission is stopped is constant, the determination can also be made using the value of voltage value A2 after a predetermined time has elapsed. Alternatively, the determination may be made using the value of the time (T2-T1) until the voltage value A1 becomes a predetermined voltage value A2.

[0076] As described above, the presence or absence of foreign matter can be determined by the voltage attenuation state during the power transmission outage, and there are multiple values ​​that represent this attenuation state. In this embodiment, these values ​​representing the attenuation state are called "waveform attenuation indices." For example, as mentioned above, the Q value calculated by Equation 1 is a value that represents the voltage attenuation state related to power transmission and is included in the "waveform attenuation indices." All waveform attenuation indices are values ​​that correspond to the waveform attenuation rate. In addition, in the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation indices." In the following, we will mainly explain the case in which the waveform attenuation rate is used as the waveform attenuation indices, but the contents of this embodiment can be applied similarly when other waveform attenuation indices are used.

[0077] Furthermore, even if the vertical axis of Figure 6 represents 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 voltage values. When foreign matter is present, the waveform attenuation rate is higher than when it is not. Therefore, foreign matter can be detected by applying the above method to the time change of the current value flowing through the power transmission antenna 105. In other words, the Q value obtained from the current waveform, the slope of current attenuation, the difference in current values, the ratio of current values, the absolute value of the current value, and the time until a predetermined current value are reached can be used as waveform attenuation indicators to determine the presence or absence of foreign matter and to detect it.

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

[0079] A method for detecting foreign objects based on the power transmission waveform during power transmission using the waveform attenuation method will be explained with reference to Figure 7. Figure 7 shows the power transmission waveform when foreign object detection is performed using the waveform attenuation method, with the horizontal axis representing time and the vertical axis representing the voltage value of the power transmission antenna 105. Alternatively, as in Figure 6, the vertical axis may represent the voltage value of the power transmission antenna 105.

[0080] During the transient response period immediately following the start of power transmission by TX402, the transmitted power waveform is unstable. Therefore, during this transient response period when the transmitted power waveform is unstable, RX401 is controlled not to communicate with TX402 (communication via amplitude modulation or load modulation). Similarly, TX402 is controlled not to communicate with RX401 (communication via frequency shift modulation). Hereafter, this period will be referred to as the communication prohibition period. During this communication prohibition period, TX402 will transmit power to RX401. After the communication prohibition period, TX402 will resume power transmission to RX401. Hereafter, this period will be referred to as the power transmission period. When TX402 receives a foreign object detection execution request (command) from RX401, it will temporarily suspend power transmission after a predetermined period has elapsed, or temporarily reduce the transmitted power. This predetermined period will hereafter be referred to as the preparation period. This foreign object detection request may be the Received Power Packet (mode0), Received Power Packet (mode1), or Received Power Packet (mode2) mentioned above. The power transmission control unit 302 of TX402 then stops power transmission or temporarily reduces the power transmission. As a result, the amplitude of the transmitted radio wave is attenuated. The period from when TX402 temporarily stops or reduces the power transmission until power transmission is resumed will hereafter be called the power transmission control period. TX402 calculates a waveform attenuation index for this attenuated waveform, compares the calculated waveform attenuation index with a predetermined threshold, and determines the presence or absence of a foreign object, or the probability of a foreign object being present. The determination may be made during the power transmission control period, during the communication ban period, or during the power transmission period.

[0081] If no foreign objects are detected after the power transmission control period has elapsed, TX402 will resume power transmission. Immediately after power transmission is resumed, there is a transient response period during which the power transmission waveform is unstable, resulting in another communication ban period. Then, the system transitions to a power transmission period during which stably power is transmitted from TX402 to RX401.

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

[0083] Furthermore, if elements such as the power receiving unit 203, charging unit 206, and battery 207 are connected to the power receiving antenna 205 and resonant capacitor 211 of the RX401 during the power transmission control period, the waveform attenuation index of the attenuated waveform will be affected by the load from these elements. In other words, the waveform attenuation index will change depending on the state of the power receiving unit 203, charging unit 206, and battery 207. Therefore, even if the waveform attenuation index is large, it becomes difficult to distinguish whether it is due to the influence of foreign objects or due to changes in the state of the power receiving unit 203, charging unit 206, battery 207, etc. For this reason, when foreign object detection is performed by observing the waveform attenuation index, the first switch unit 209 of the RX401 may be disconnected 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 it, so that current flows through the closed loop formed by the power receiving antenna 205, resonant capacitor 211, and 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 RX401 sends a foreign object detection execution request (command) to TX402, it performs the above process. This enables highly accurate foreign object detection 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 and short-circuited (connected). Alternatively, during the above preparation period, RX401 may switch to a low power consumption mode or control the power consumption to be constant when the first switch unit 209 is turned ON and short-circuited, and the second switch unit 210 is turned OFF and disconnected. In other words, if the power consumed by RX401 is not constant, or if a large amount of power is consumed, the waveform attenuation index of the attenuated waveform will be affected by the fluctuations in power consumption. Therefore, in order to eliminate this, the following process may be performed. In other words, the power consumed by the RX401 is controlled by restricting or stopping the operation of software applications running on the RX401, or by putting the hardware function blocks of the RX401 into a low-power mode or an operation-stop mode. 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] Similarly, TX402 may also be configured to short-circuit the switch unit 108 by turning it ON during the preparation period when it receives a foreign object detection execution request (command) from RX401. In other words, TX402 may be configured to allow current to flow through the closed loop formed by the power transmitting antenna 105, the resonant capacitor 107, and the switch unit 108. This makes it possible to eliminate the influence of the power supply unit 102, the power transmitting unit 103, and the communication unit 104. Alternatively, a switch (not shown) can be provided between the power transmitting antenna and the power transmitting unit, and the influence of the power supply unit 102, the power transmitting unit 103, and the communication unit 104 can be eliminated by turning off the switch during the preparation period.

[0085] (Method for setting the foreign object detection threshold in waveform attenuation method) This section describes how to set a threshold for determining the presence or absence of foreign objects, or the probability of their presence, when performing foreign object detection using the waveform attenuation method. As mentioned above, the waveform attenuation method performs foreign object detection based on a "waveform attenuation index." The measured "waveform attenuation index" is compared with a predetermined threshold, and the presence or absence of foreign objects, or the probability of their presence, is determined based on the result. There are several ways to set this threshold. The first is for the TX402 to maintain a predetermined value as a common value that does not depend on the RX401 to which the power is being transmitted. This value may be the same in all cases, or it may be a value determined by the TX402 depending on the situation. As mentioned above, the waveform attenuation rate of the power transmission waveform during the power transmission control period increases when foreign objects are present. Therefore, the "waveform attenuation index" when it is considered that "no foreign objects are present" is maintained as a predetermined value, and this is used as the threshold to compare with the result of the measured "waveform attenuation index." If the measured waveform attenuation index is greater than the threshold, it is determined that "foreign objects are present" or "there is a high probability that foreign objects are present." For example, if the "waveform attenuation index" is defined as the Q value, the Q value measured by the TX402 is compared with a predetermined Q value (threshold) that indicates the absence of foreign matter. If the measured Q value is smaller than the threshold Q value, it is determined that "foreign matter is present" or "there is a high probability that foreign matter is present." If the measured Q value is larger than or approximately the same as the threshold Q value, it is determined that "no foreign matter is present" or "there is a low probability that foreign matter is present." In this way, foreign matter detection using the waveform attenuation method becomes possible using the first method.

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

[0087] For example, if the "waveform attenuation index" is defined as the Q value, the Q value measured by the TX402 when no foreign objects are present may differ depending on the RX401 placed on the TX402. Therefore, the RX401 stores the Q value information for each TX402 when it is placed on the TX402 without any foreign objects present, and notifies the TX402 of this Q value. The TX402 then adjusts and determines the threshold based on the Q value information received from the RX401. More specifically, in the Negotiation phase, TX402 receives an FOD Status Packet containing Reference Quality Factor Value information and adjusts and determines the threshold in the Q-value measurement method. This Reference Quality Factor Value corresponds to "Q-value information when RX401 is placed on TX402 without any foreign objects present." Therefore, the threshold for foreign object detection using 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, which originally measures the Q-value in the frequency domain. However, if the "waveform attenuation index" is used as the Q-value, although the method of deriving the Q-value is different, even using the waveform attenuation method, which measures the Q-value in the time domain, for example, from the waveform in Figure 6, Q = πf(T2 - T1) / ln(A1 / A2) As this makes it possible to determine the Q value, it is possible to set the Q value threshold for the waveform attenuation method based on the Reference Quality Factor Value. In this way, by having TX402 set the Q value threshold for the waveform attenuation method based on the information already transmitted from RX401 to TX402 during the Negotiation phase, new measurements and other processing for threshold setting become unnecessary. As a result, the threshold can be set in a shorter amount of time.

[0088] The TX402 compares the Q value measured with the threshold value determined by the method described above. If the measured Q value is smaller than the threshold Q value, it is determined that "foreign matter is present" or "there is a possibility of foreign matter being present." If the measured Q value is larger than or approximately the same as the threshold Q value, it is determined that "no foreign matter is present" or "there is a low possibility of foreign matter being present."

[0089] By doing so, it becomes possible to detect foreign objects using the waveform attenuation method with the second method.

[0090] The third method involves the TX402 measuring the waveform attenuation index in the absence of foreign objects, and then adjusting and determining the threshold based on the measurement results. The value of the "waveform attenuation index" may vary depending on the power transmission of the TX402. This is because the amount of heat generated, the characteristics of the TX402's electrical circuit, etc., change depending on the power transmission of the TX402, and these affect the value of the "waveform attenuation index". Therefore, by having the TX402 measure the waveform attenuation index for each power transmission level and adjusting and determining the threshold based on the results, more accurate foreign object detection becomes possible.

[0091] Figure 13 is a diagram illustrating how to set the foreign object detection threshold for each power transmission level of TX402 in the waveform attenuation method. First, RX401 controls its load to a light load state so that when power is transmitted from TX402, no power or only very little power is supplied to the load of RX401. Let the power transmission level of TX402 at this time be Pt1. Then, TX402 stops transmitting power in this state and measures the waveform attenuation index. Let the waveform attenuation index at this time be δ1. At this time, TX402 recognizes the power transmission level Pt1 that TX402 is transmitting and stores a calibration point 1300 in memory that associates the power transmission level Pt1 with the waveform attenuation index δ1. Next, RX401 controls its load to a load-connected state so that when power is transmitted from TX402, the maximum power or power above a predetermined threshold is supplied to the load of RX401. Let Pt2 be the power transmitted by TX402 at this time. Then, TX402 stops transmitting power in this state and measures the waveform attenuation index. At this time, TX402 stores in memory a calibration point 1301 that associates the power transmitted Pt2 with the waveform attenuation index δ2. Subsequently, TX402 linearly interpolates between calibration point 1300 and calibration point 1301 to create a line 1302. Line 1302 shows the relationship between the power transmitted and the waveform attenuation index of the transmitted radio wave type when there are no foreign objects around TX402 and RX401. Therefore, TX402 can estimate the waveform attenuation index of the transmitted radio wave type for each power transmitted value in the absence of foreign objects from line 1302. For example, if the power transmitted value is Pt3, the waveform attenuation index can be estimated to be δ3 from point 1303 on line 1302 corresponding to the power transmitted value Pt3. Based on the above estimation results, the TX402 can calculate a threshold value used to determine the presence or absence of foreign matter for each transmission power value. For example, a waveform attenuation index that is a predetermined value (a value corresponding to the measurement error) larger than the estimated waveform attenuation index for the case without foreign matter at a certain transmission power value may be set as the threshold value for determining the presence or absence of foreign matter.The calibration process performed by TX402 and RX401 to obtain a combination of transmission power value and waveform attenuation index will be referred to below as "waveform attenuation index calibration process (CAL process)". In the example above, measurements were taken at two points, Pt1 and Pt2, of the TX402's transmission power. However, to improve accuracy, measurements may be taken at three or more points to calculate the waveform attenuation index for each transmission power.

[0092] Furthermore, RX401 may perform the control that results in no power being supplied to the load / a light load state, and the control that results in a load connection state, after notifying TX402 of its intention to perform these controls. Also, the order in which the two controls are performed does not matter.

[0093] Furthermore, the operation described in this embodiment for calculating the threshold used to determine the presence or absence of foreign matter for each load (each transmitted power value) may be performed in the Calibration phase. As mentioned above, in the Calibration phase, TX402 acquires data necessary for detecting foreign matter using the Power Loss method. At that time, TX402 acquires data on power loss when the load state of RX401 is a light load state and when it is a load connected state. Therefore, the measurement of calibration point 1300 and calibration point 1301 in Figure 13 may be performed in the Calibration phase described above, when RX401 is in a light load state and when it is a load connected state. That is, when TX402 receives first reference received power information from RX401, it measures calibration point 1300 in addition to the predetermined processing to be performed in the Calibration phase. Also, when TX402 receives second reference received power information from RX401, it measures calibration point 1301 in addition to the predetermined processing to be performed in the Calibration phase. This eliminates the need to set aside a separate period for measuring calibration point 1300 and calibration point 1301, allowing measurements of calibration point 1300 and calibration point 1301 to be performed in a shorter time.

[0094] In this way, the TX402 adjusts and sets the threshold value for the waveform attenuation index of the waveform attenuation method for each power transmission based on the waveform attenuation index information measured by the TX402 for each power transmission. For example, if the waveform attenuation index is the Q value, the TX402 compares the Q value measured by the TX402 with the threshold value determined by the method described above. If the measured Q value is smaller than the threshold Q value, it determines that "foreign matter is present" or "there is a possibility of foreign matter being present." If the measured Q value is larger than or approximately the same as the threshold Q value, it determines that "there is no foreign matter" or "there is a low possibility of foreign matter being present." By doing so, it becomes possible to set threshold values ​​for each power transmission of the TX402, enabling more accurate foreign matter detection.

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

[0096] Furthermore, when performing foreign object detection, it may not be possible to perform accurate detection by simply executing the foreign object detection process once. For example, when performing foreign object detection using the waveform attenuation method, if the presence or absence of a foreign object, or the possibility (probability of presence) of a foreign object, is determined from the waveform attenuation index after performing a single power transmission control, there is a possibility that the power transmission waveform will be disturbed during the power transmission control period. Possible causes of disturbance in the power transmission waveform during the power transmission control period include the introduction of other noise during the power transmission control period, or the position of the RX401 mounted on the TX402 shifting for some reason. As a result, the waveform attenuation index obtained from the power transmission waveform during a single power transmission control period will not be an accurate value due to the disturbance in the conductive waveform, and as a result, there is a possibility of misjudging foreign object detection. To prevent this, it is conceivable to perform multiple power transmission control cycles, measure the waveform attenuation index from the power transmission waveforms during multiple power transmission control periods, and perform foreign object detection based on the results.

[0097] (Foreign object detection using multiple waveform attenuation methods) The waveform attenuation method described above involved the TX402 performing a single Q-value measurement and then performing foreign object detection based on the result. However, there are cases where the TX402 performs multiple Q-value measurements and then performs foreign object detection based on the results. The process of detecting foreign objects based on the results of multiple Q-value measurements will be explained using Figure 14. In Figure 14, the TX402 is assumed to perform two Q-value measurements using the waveform attenuation method and then perform foreign object detection based on the results.

[0098] First, RX401 sends RP0 to TX (F636). Upon receiving RP0, TX402 performs a Q-factor measurement using the waveform attenuation method (F637). Here, we can see that the Q-factor measurement performed by TX402 (F637) is the first of two. Therefore, as a response to RP0 (F636), TX402 sends a packet to RX401 indicating that it "does not determine" the presence or absence of foreign matter at this time (F638).

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

[0100] RX401 retransmits RP0 (F640). Upon receiving RP0, TX402 performs Q-factor measurement using the waveform attenuation method (F641).

[0101] Here, we can see that the Q-value measurement (F641) performed on TX402 was the second of two attempts. TX402, T window Assume that the transmitted power value is stable during the specified period, and that the third foreign object detection system determines that there is a high probability that no foreign objects are present. In that case, TX402 determines the presence or absence of foreign objects and, based on the determination result, sends a response signal to RX401 that includes the probability of foreign object presence (probability of presence) (F642).

[0102] Here, we will explain an example of a method for deriving the probability of foreign object presence using multiple waveform attenuation methods. For example, the probability of foreign object presence is derived based on the difference between the Q value obtained by one waveform attenuation method and the threshold. This process is performed for multiple waveform attenuation methods, and the average value of the presence probability is derived. This obtains the probability of foreign object presence based on the results of multiple waveform attenuation methods. Another example is a method of weighting the total value of the probability of foreign object presence from multiple methods. A third is a method of measuring the number of waveform attenuation methods in which a probability of foreign object presence above a certain value was detected. In this embodiment, when notifying the RX401 of the probability of foreign object presence, "no foreign object" is replaced with the value 0, and "foreign object present" is replaced with the value 10, and the average value of the presence probability from multiple methods is notified to the RX401. Alternatively, the decimal part of the average value may be rounded up.

[0103] Furthermore, in this embodiment, RX401 controls the interval between sending RP0, which is a foreign object detection execution request, in order to control the timing at which TX402 limits power transmission related to multiple waveform attenuation methods. When RX401 sends multiple RP0s as foreign object detection execution requests to TX402, it waits for a predetermined interval after sending RP0 and then sends the next RP0. However, if the probability of foreign object presence (existence probability) satisfies predetermined conditions, RX401 controls the timing between sending RP0 and sending the next RP0. This process will be described later.

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

[0105] RX401 begins receiving power transmitted from TX402 (S801). After starting to receive power, RX401 determines the threshold for the probability of presence (S802). Here, the threshold for the probability of presence is the threshold used to determine whether there is a possibility of a foreign object being present. For example, if the probability of presence obtained by the foreign object detection process is greater than the threshold for the probability of presence, it is determined that "there is a high probability of a foreign object being present." Also, for example, if the probability of presence obtained by the foreign object detection process is less than the threshold for the probability of presence, it is determined that "there is a low probability of a foreign object being present." Furthermore, the threshold for the probability of presence is a value used to determine whether or not to adjust the interval at which RX401 waits for the transmission of a foreign object detection execution request, as described later. The method for determining the threshold for the probability of presence may be to use a value predetermined for each RX401, or to use a value determined by the power output from TX402.

[0106] RX401 waits for a predetermined interval before sending a request to TX402 to execute foreign object detection (S803). In this embodiment, TX402 performs foreign object detection based on multiple waveform attenuation methods, so as described above, RX401 waits for a predetermined interval (a predetermined time length) between sending a foreign object detection execution request and sending the next foreign object detection execution request. If the predetermined interval here is short, TX402 will perform power transmission control in a short period of time, and RX401 will also be burdened by the increased processing related to foreign object detection execution requests, so it is desirable to set the waiting time to be 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 Received Power Packet (mode0), Received Power Packet (mode1), or Received Power Packet (mode2) described above. After sending the foreign object detection execution request in S804, RX401 determines whether the response packet from TX402 contains the possibility (probability) of foreign object presence (S805). The determination in S805 corresponds to the process of determining the possibility (probability) of foreign object presence from a predetermined number of power transmission control cycles. If the predetermined number of power transmission control cycles has not been reached, the response from TX402 does not contain the probability of foreign object presence. This is achieved by TX402 sending an ND (Not-Defined) packet to RX401 as a response, indicating that it "does not make a judgment". Based on the ND packet, RX401 determines whether the predetermined number of power transmission control cycles have been completed. If it is an ND packet, it determines that the predetermined number of power transmission control cycles have not been completed (NO in S805), returns to S803, and waits for a predetermined interval before sending the foreign object detection execution request again. If the response from TX402 includes the possibility (probability) of foreign object presence (YES in S805), it is determined whether the notified possibility (probability) of foreign object presence is greater than or equal to the probability threshold (S806). If it is not greater than or equal to the probability threshold (NO in S806), it returns to S803 and waits for a predetermined interval before sending another request to perform foreign object detection.

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

[0108] If the detection result clearly indicates "foreign object present" (YES in S807), power reception is stopped (S808). Note that S808 can be achieved by RX401 sending an EPT (End Power Transfer) command (packet), which is a power transmission stop request command, to TX402 to request the cessation of power transmission.

[0109] If the result of the S807 determination does not clearly determine that "foreign object is present," the current waiting interval is determined in order to adjust the waiting interval for sending the foreign object detection execution request (S809). Specifically, it is determined whether the length of the waiting time until the next foreign object detection execution request is sent can be shortened from the current length. If the waiting time for sending the foreign object detection execution request is not the shortest length that RX401 can achieve (NO in S809), the waiting time until sending the foreign object detection execution request is shortened (S810), and the sending of the foreign object detection execution request is waited until the shortened time has elapsed (S811). On the other hand, if the length of the waiting time for sending the foreign object detection execution request is already the shortest length (YES in S809), the waiting time for sending the foreign object detection execution request is not shortened, and the sending of the foreign object detection execution request is waited until the current waiting time has elapsed (S811).

[0110] Furthermore, the method for determining the predetermined interval (waiting time) for sending a foreign object detection execution request may be to use a value predetermined for at least one of the RX401 and TX402 devices. Alternatively, for example, the method for determining the predetermined interval (waiting time) may be to use a value determined by the power output from TX402. The shortest time length may also be determined based on, for example, the shortest time length for which TX402 can perform the waveform attenuation method, or the shortest time length for which RX401 can send a foreign object detection execution request. Alternatively, for example, the predetermined interval may be determined by negotiation between RX401 and TX402. This negotiation may also be performed in the Negotiation phase.

[0111] Furthermore, methods for shortening the time duration include shortening it by a predetermined time duration, shortening it to the shortest possible time duration in a single process, or shortening it by a time duration corresponding to the power output from TX402.

[0112] The processing from S811 to S813 is the same as the processing from S803 to S805, so the explanation is omitted. If the response from TX402 includes the possibility (probability) of foreign matter being present (YES in S813), RX401 determines whether the notified possibility (probability) of foreign matter being present clearly indicates "foreign matter present" (S814). If the determination result is clearly "foreign matter present" (YES in S814), power reception is stopped (S808).

[0113] On the other hand, if the determination does not clearly indicate "foreign object present" (NO in S814), RX401 determines whether there is clearly "no foreign object" (S815). Here, "no foreign object" means that the probability of presence is 0. If there is clearly "no foreign object" (YES in S815), RX401 returns the shortened waiting time for sending the foreign object detection execution request to its original length and returns to S803 to continue receiving power (S816). On the other hand, if there is not clearly "no foreign object" (NO in S815), RX401 determines whether it has continuously sent the foreign object detection execution request with the shortened waiting time for sending the foreign object detection execution request a predetermined number of times (S817). If it has been continuously executed a predetermined number of times (YES in S817), RX401 stops receiving power because there is a possibility of equipment failure, etc. (S808). If the predetermined number of executions has not been performed consecutively (NO in S817), the process returns to S809, and the current waiting interval is determined in order to adjust the length of the waiting time for sending the foreign object detection execution request. Here, the method for determining the predetermined number of executions may be to use a value predetermined for each RX401, or to use a value determined by the power output from TX402.

[0114] As described above, RX401 controls the system so that if the probability of foreign object presence (probability of presence) is higher than the probability threshold but lower than the threshold for clearly determining whether a foreign object is present, foreign object detection requests are sent at shorter intervals.

[0115] Alternatively, the system may be configured to perform the processing from S809 onward if the probability of presence in S806 is above a threshold, without performing the determination in S807. With this configuration, if the probability of presence is above a threshold, the transmission of the foreign object detection execution request is expedited and foreign object detection is performed again, thereby quickly and reliably confirming the presence or absence of a foreign object.

[0116] Next, the processing flow of the power receiving devices 401 (RX401) and TX402 (TX402) in this embodiment will be explained using the sequence diagram in Figure 9. Figure 9 shows the processing that is executed after the start of the power transmission process at F528 in Figure 5. Here, as an example of processing, we will explain the processing that occurs when foreign matter is introduced during the power transmission control in the waveform attenuation method when TX402 performs the waveform attenuation method three times.

[0117] TX402 and RX401 begin the power transmission process (F901). RX401, having begun receiving power, determines the threshold for the probability of presence (F902). Here, assuming that 15 watts of power determined in F527 is being transmitted, RX401, having determined that the received power is high, determines the threshold to adjust the waiting time for sending a foreign object detection request, even when the "possibility of foreign object presence is low."

[0118] In F902, RX401, having determined the threshold, waits for the duration of the waiting interval before sending a foreign object detection execution request (F903). Here, the default waiting time for RX401 is set to 2 seconds. The shortest waiting time for sending a foreign object detection execution request is set to 0.5 seconds. After the waiting time in F903 has elapsed, RX401 sends a foreign object detection execution request to TX402 (F904). Upon receiving the foreign object detection execution request from RX401 in F904, TX402 performs power transmission control and executes foreign object detection (F905). Here, 3 is set as the predetermined number of power transmission control operations that TX402 uses to detect the possibility (probability) of foreign object presence.

[0119] In the F905 power transmission control, since no foreign object is present, the probability of foreign object presence is clearly determined to be "no foreign object". In the F905 power transmission control, since the predetermined number of power transmission control cycles has not been reached, TX402 notifies RX401 of an ND packet (F906). Upon receiving notification of F906, RX401 waits for the waiting period to elapse before sending the next foreign object detection execution request (F907). The processes from F908 to F911 are the same as those from F904 to F907, so the explanation is omitted.

[0120] Here, we assume that a foreign object enters the power transmission range of TX402 while F911 is in standby mode (F912). After the standby time for F911 has elapsed, RX401 sends a request to TX402 to perform foreign object detection (F913). Upon receiving the foreign object detection request from RX401 in F913, TX402 performs power transmission control and performs foreign object detection (F914). In the power transmission control in F914, since a foreign object is present, the possibility (probability) of the presence of a foreign object is clearly detected as "foreign object present".

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

[0122] Based on the result of the F917 determination, RX401 checks the current waiting time for sending the foreign object detection execution request in order to shorten the waiting time for sending the foreign object detection execution request (F918). As a result of F918, the current waiting time for sending the foreign object detection execution request is 2 seconds, which is longer than the shortest waiting time for sending the foreign object detection execution request, which is 0.5 seconds, so RX401 shortens the waiting time for sending the foreign object detection execution request (F919). Here, RX401 decides on the shortest waiting time of 0.5 seconds as the waiting time. In this embodiment, the waiting time was changed to the shortest value in one step, but a configuration in which it is shortened gradually is also possible.

[0123] RX401 waits for the duration determined in F919 for sending the foreign object detection execution request (F920). After the shortened waiting time in F920 has elapsed, RX401 sends the foreign object detection execution request to TX402 (F921). As a result, if the probability of foreign object presence (existence probability) detected by foreign object detection is higher than the threshold and it is not clearly determined that "foreign object is present", TX402 receives the next foreign object detection execution request at an earlier timing than if these conditions were not met. Upon receiving the foreign object detection execution request sent in F921, TX402 performs power transmission control and executes foreign object detection (F922). Here, as with F905, 3 is set as the predetermined number of power transmission control operations that TX402 uses to detect the possibility (existence probability) of foreign object presence.

[0124] In the F922 power transmission control, since a foreign object is present, the possibility (probability) of the presence of a foreign object is clearly determined to be "foreign object present". In the F922 power transmission control, since the predetermined number of power transmission control cycles has not been reached, TX402 notifies RX401 of an ND packet (F923). Upon receiving notification of F923, RX401 waits for the waiting interval for sending another foreign object detection execution request (F924). The processes from F925 to F930 are the same as the processes from F921 to F926, so the explanation is omitted.

[0125] During power transmission control by F930, the predetermined number of power transmission control cycles has been reached, so TX402 determines the probability of foreign object presence (probability of presence) to notify RX401 based on the power transmission control results of F922, F926, and F930 (F931). Here, TX402 decides to notify RX401 of the probability of foreign object presence (probability of presence) determined in F922, F926, and F930. TX402 notifies RX401 of the probability of foreign object presence (probability of presence) determined in F931 (F932). Upon receiving notification from F932, RX401 confirms that the notified probability of foreign object presence (probability of presence) is "foreign object present," sends an EPT (End Power Transfer) command (packet) to TX402, and stops power reception (F933). The above is an example of how to handle foreign matter contamination in foreign matter detection based on multiple waveform attenuation methods.

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

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

[0128] <Embodiment 2> Embodiment 1 described an example of applying foreign object detection using multiple waveform attenuation methods in the WPC standard. This embodiment describes a method for achieving safer power transmission while using the method described in Embodiment 1.

[0129] (Processing of power transmission device 402 and power receiving device 401) The processing flow of the power receiving device 401 (RX401) in this embodiment will be explained using the flowchart in Figure 10. Figure 10 is a flowchart showing the operation of RX401 that is executed after the start of the power transmission process F528 in Figure 5. The processing content that is the same as in Embodiment 1 will not be explained.

[0130] The processing from S1001 to S1015 is the same as the processing from S801 to S815, so the explanation is omitted. If it is not clearly "no foreign object" (NO in S1015), it is determined whether the transmission of a foreign object detection execution request with a shortened waiting time for transmission of the foreign object detection execution request has been performed consecutively for a predetermined number of times (S1017). If it has not been performed consecutively for the 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 transmission of 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 the process has been executed for a predetermined number of consecutive times (YES in S1016), RX401 determines whether the current power transmitted from TX402 is the lower limit that can be set between TX402 and RX401 (S1017). If the power transmitted from TX402 is the lower limit (YES in S1017), the process returns to S1009, and RX401 determines the current waiting time in order to adjust the waiting time for sending the foreign object detection execution request. If the power transmitted from TX402 is not the lower limit (NO in S1017), RX401 sends a power transmission change request to TX402 to reduce the power transmission (S1018).

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

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

[0134] The above-described process has the following effects: Specifically, when there is a high probability of foreign matter being present, reducing the transmission power can avoid dangers such as the foreign matter's temperature rising due to power being transmitted to it. Furthermore, the higher the transmission power, the greater the influence of noise related to power transmission. Therefore, when foreign matter detection is performed using the waveform attenuation method, there is a higher possibility of false detection of foreign matter, such as determining that "foreign matter is present" when no foreign matter is present, or determining that "no foreign matter is present" when foreign matter is present. For this reason, when it is determined that "there is a high probability of foreign matter being present," reducing the transmission power and performing foreign matter detection again allows for a more accurate confirmation of the presence or absence of foreign matter.

[0135] Next, the processing flow of the power receiving device 401 (RX401) and the power transmitting device 402 (TX402) in this embodiment will be explained using the sequence diagram in Figure 11. Figure 11 shows the processing that is executed after the start of the power transmission process in F528. Here, as an example of processing, we will explain the processing that occurs when the power transmission waveform is disturbed during the power transmission control period due to temporary noise when performing power transmission control using the waveform attenuation method. The processing from F1101 to F1104 is the same as the processing from S901 to S904, so the explanation will be omitted.

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

[0137] The processes from F1108 to F1111 are the same as those from F918 to F921, so their explanation is omitted. The processes from F1112 and F1113 are the same as those from F1105 and F1106, so their explanation is omitted. While the foreign object detection is repeatedly performed using the same process as from F1110 to F1113, with a shortened waiting interval for sending the foreign object detection execution request, 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 is set to the lower limit (F1115). In this embodiment, the lower limit of the power transmission is set to 5 watts, and the current power transmission output is set to 15 watts. Therefore, the F1115 judgment determines that the current transmission power is not at the lower limit, and RX401 sends a transmission power change request to TX402 to set the transmission power to the lower limit of 5 watts (F1116).

[0138] Upon receiving the power output change request F1116, TX402 changes the power output to 5 watts (F1117) and sends an ACK to notify RX401 that the power output change has been completed (F1118). In this embodiment, RX401 changed the power output to the lower limit in a single change, but a configuration that gradually reduces the power output is also possible.

[0139] When the transmission power is changed to the lower limit, the noise that was affecting the transmission waveform disappears (F1119). After the noise disappearance in F1119, RX401 sends a request to TX402 to perform foreign object detection (F1120). Upon receiving the foreign object detection request in F1120 from RX401, TX402 performs transmission power control using the waveform attenuation method and performs foreign object detection (F1121). Here, because the noise that was affecting the disturbance of the transmitted signal shape during the transmission power control period in S1119 has disappeared, the possibility (probability of presence) of foreign objects is clearly determined to be "no foreign objects". TX402 notifies RX401 of the probability of presence based on the determination result in F1121 (F1122).

[0140] Upon receiving notification of F1122, RX401 repeatedly performs foreign object detection using the same process as from F1120 to F1122, and determines that no foreign object is present (F1123). In this embodiment, regarding the processing of F1123, since the number of power transmission control operations was only one, RX401 makes a decision based on the results of multiple foreign object detection operations, taking into account the influence of noise, etc. However, it may also make a decision based on the result of a single foreign object detection operation. Having determined in F1123 that no foreign object is present, RX401 returns the shortened waiting time for sending the foreign object detection execution request to its original length (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 return the power transmission output to 15 watts (S1126). Upon receiving the power output change request F1126, TX402 changes the power output to 15 watts (F1127) and sends an ACK to notify RX401 that the power output change has been completed (F1128).

[0141] In this way, when RX401 receives notification from TX402 that "there is a possibility of a foreign object being present," it shortens the transmission time of the foreign object detection request and reduces the power transmission. As a result, RX401 and TX402 can reduce the possibility of the foreign object generating heat, prevent power transmission interruptions due to false detection, and continue power transmission. Furthermore, by maintaining a shortened transmission time for the foreign object detection request, foreign object contamination can be detected more quickly, resulting in a safer and more efficient wireless power transmission system.

[0142] <Other Embodiments> The contents of Embodiments 1 and 2 described above may be combined as appropriate. In the embodiments described above, the TX402 performed power transmission control and detected foreign objects from its waveform attenuation index. As an alternative method for measuring the Q value, which is one of the waveform attenuation indices, the following method can be considered. That is, a signal having multiple frequency components (e.g., a pulse wave) is transmitted, the amplitude or attenuation state of the waveform is measured, and the Q value is measured by performing calculation processing (e.g., Fourier transform) on the result, and this method can also be applied to the embodiments described above.

[0143] This disclosure can also be implemented by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be implemented by a circuit (e.g., an ASIC) that implements one or more functions. Furthermore, the program may be recorded on a recording medium readable by a computer and provided. [Explanation of Symbols]

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

Claims

[Claim 1] A power receiving device, A power receiving means for receiving power wirelessly from a power transmission device, A transmitting means that transmits signals at predetermined intervals for performing a detection process to detect an object different from the power transmission device and the power receiving device based on the voltage or current value at at least two points in time during a predetermined period in which the power transmission device restricts power transmission, A receiving means receives a response signal from the power transmission device that includes a detection result based on the detection process performed in response to the signal transmitted by the transmitting means, If the detection result included in the response signal received by the receiving means satisfies a predetermined condition, the control means controls the transmitting means to transmit the signal at an interval shorter than the predetermined interval. A power receiving device characterized by having the following features.

Images