Power transmission device and method performed by the power transmission device

Abstract

To provide a further appropriate foreign matter detection technique.SOLUTION: A power transmission device 402 measures a waveform attenuation rate of a power transmission waveform in a power transmission antenna 105 in a state where power transmission is stopped, sets a threshold used for detecting foreign matters between the power transmission device 402 and a power reception device 401 based on the measured waveform attenuation rate, and determines whether or not there are foreign matters between the power transmission device 402 and the power reception device 401 based on the waveform attenuation rate measured after the threshold is set and the threshold.SELECTED DRAWING: Figure 10

Description

[Technical Field]

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

[0002] In recent years, technological development of wireless power transmission systems has been widespread. Patent Document 1 discloses a power transmitting device and a power receiving device that comply with the WPC standard established by the Wireless Power Consortium (WPC), a standardization organization for wireless charging standards. Patent Document 2 discloses a foreign object detection method in the WPC standard. Patent Document 3 discloses a foreign object detection method in which a power transmitting device transmits a foreign object detection signal to a power receiving device and determines the presence or absence of a foreign object using an echo signal from the power receiving device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-56959 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-70074 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-27172 Summary of the Invention [Problem to be solved by the invention]

[0004] The foreign object detection method disclosed in Patent Document 3 requires the transmission of a foreign object detection signal to detect a foreign object, which necessitates the addition of a circuit for transmitting the foreign object detection signal and the time required to transmit the foreign object detection signal, resulting in increased costs and reduced transmission efficiency.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a more appropriate foreign object detection technology. [Means for solving the problem]

[0006] As a means for achieving the above object, a power transmission device of the present invention has the following configuration: A power transmission device, a power transmitting means for wirelessly transmitting power to a power receiving device; receiving means for receiving identification information of the power receiving device from the power receiving device; a measuring means for measuring a transmission waveform after the power transmitting means transmits a ping to detect an object and before a power transfer phase; an acquisition means for acquiring a quality factor based on an envelope curve indicating the attenuation of the measured transmission wave; a setting means for setting information relating to the acquired quality factor and transmission power, and setting a threshold value based on the information; a determining unit that determines whether a foreign object is present based on the set threshold value during the power transfer phase after the set threshold value is set by the setting unit; It has. [Effects of the Invention]

[0007] According to the present invention, a more appropriate foreign object detection technique can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a block diagram illustrating a configuration example of a power transmission device. [Figure 2] FIG. 2 is a block diagram illustrating a configuration example of a power receiving device. [Figure 3] FIG. 2 is a block diagram illustrating an example of a functional configuration of a control unit of the power transmitting device. [Figure 4] FIG. 1 is a diagram illustrating a configuration example of a wireless power transmission system. [Figure 5] FIG. 1 is a sequence diagram for power transmission according to the WPC standard. [Figure 6] 1A and 1B are diagrams illustrating the principle of foreign object detection using a waveform attenuation method. [Figure 7] 10A and 10B are diagrams for explaining a method for detecting a foreign object using radio wave transmission during power transmission. [Figure 8] 10 is a flowchart of a process performed by a power transmitting device in some embodiments. [Figure 9] 1 is a flowchart of a process performed by a power receiving device in some embodiments. [Figure 10] FIG. 2 is a sequence diagram of a power transmitting device and a power receiving device according to some embodiments. [Figure 11] 10A and 10B are diagrams for explaining a method for setting a foreign object detection threshold using a waveform attenuation method. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

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

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

[0012] In the WPC standard, the amount of power guaranteed when a power receiving device receives power from a power transmitting device is specified by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates the power value that is guaranteed to be output to a load (e.g., a charging circuit, battery, etc.) of the power receiving device, even if the relative positions of the power receiving device and the power transmitting device change and the power transmission efficiency between the power receiving antenna and the power transmitting antenna decreases. For example, if the GP is 5 watts, the power transmitting device controls power transmission so that it can output 5 watts to the load in the power receiving device, even if the relative positions of the power receiving antenna and the power transmitting antenna change and the power transmission efficiency decreases.

[0013] The WPC standard also specifies methods for a power transmitter to detect the presence of an object (foreign object) other than a power receiver around the power transmitter (near the power transmitting antenna). More specifically, the standard specifies the power loss method, which detects foreign objects based on the difference between the power transmitted by the power transmitter and the power received by the power receiving device, and the Q-factor measurement method, which detects foreign objects based on changes in the quality factor (Q-factor) of the power transmitting antenna (power transmitting coil) in the power transmitter. Foreign object detection using the power loss method is performed during power transmission (power transmission) (the power transfer phase, described below) based on data obtained in the calibration phase, described below. Foreign object detection using the Q-factor measurement method is performed before power transmission (before sending a digital ping, or in the negotiation or renegotiation phase, described below).

[0014] In this embodiment, the RX and TX communicate for power transmission and reception control based on the WPC standard. The WPC standard defines multiple phases, including a power transfer phase in which power transmission is performed and one or more phases before the actual power transmission, and communication for the necessary power transmission and reception control is performed in each phase. The phases before power transmission may include a selection phase, a ping phase, an identification and configuration phase, a negotiation phase, and a calibration phase. Note that the identification and configuration phase will be referred to as the I&C phase below. The processing in each phase will be described below.

[0015] In the Selection phase, the TX intermittently transmits Analog Pings to detect that an object has been placed on the TX's charging base (for example, that the RX or a conductor piece has been placed on the charging base). The TX detects at least one of the voltage and current values ​​of the power transmitting antenna when it transmits Analog Pings, and if the voltage value is below a certain threshold or the current value exceeds a certain threshold, it determines that an object is present and transitions to the Ping phase.

[0016] In the Ping phase, the TX transmits a Digital Ping with higher power than the Analog Ping. The power of the Digital Ping is sufficient to start the control unit of the RX placed on the TX. The RX notifies the TX of the magnitude of the received voltage. In this way, the TX recognizes that the object detected in the Selection phase is the RX by receiving a response from the RX that received the Digital Ping. Upon receiving notification of the received voltage value, the TX transitions to the I&C phase. In addition, before transmitting the Digital Ping, the TX measures the Q-factor of the transmitting antenna (transmitting coil). This measurement result is used when performing foreign object detection processing using the Q-factor measurement method.

[0017] In the I&C phase, TX identifies RX and obtains device configuration information (capability information) from RX. To do this, RX transmits an ID packet and a configuration packet. The ID packet contains the RX's identifier information, and the configuration packet contains the RX's device configuration information (capability information). Upon receiving the ID packet and configuration packet, TX responds with an acknowledgement (ACK, positive response). Then, the I&C phase ends.

[0018] In the Negotiation phase, the GP value is determined based on the GP value requested by the RX and the power transmission capability of the TX. The TX also performs foreign object detection processing using the Q-factor measurement method in response to a request from the RX. The WPC standard also specifies a method in which, after transitioning to the Power Transfer phase, the same processing as in the Negotiation phase is performed again at the request of the RX. The phase in which these processing steps are performed after transitioning from the Power Transfer phase is called the Renegotiation phase.

[0019] In the calibration phase, calibration is performed based on the WPC standard. RX notifies TX of a predetermined received power value (received power value under light load / received power value under maximum load), and TX adjusts the power transmission for efficient power transmission. The received power value notified to TX can be used for foreign object detection processing using the Power Loss method.

[0020] In the Power Transfer phase, control is performed to start and continue power transmission, and to stop power transmission due to errors or when the device is fully charged. To control power transmission and reception, the TX and RX use the same power transmitting antenna (power transmitting coil) and power receiving antenna (power receiving coil) that are used when transmitting wireless power based on the WPC standard, and communicate by superimposing a signal on the electromagnetic waves transmitted from the power transmitting antenna or power receiving antenna. The range in which communication based on the WPC standard between the TX and RX is possible is approximately the same as the range in which the TX can transmit power.

[0021] (Configuration of power transmitting device and power receiving device) Next, the configurations of the power transmitting device 402 (TX) and the power receiving device 401 (RX) according to this embodiment will be described. Note that the configurations described below are merely examples, and part (or in some cases the whole) of the described configurations may be replaced with other configurations that perform similar functions or may be omitted, or additional configurations may be added to the described configurations. Furthermore, one block described below may be divided into multiple blocks, or multiple blocks may be integrated into one block. Furthermore, although the functions of each functional block described below are implemented as a software program, some or all of the components included in the functional blocks may be implemented as hardware.

[0022] Fig. 1 is a functional block diagram showing an example of the configuration of a power transmitting device 402 (TX) according to this embodiment. The TX has a control unit 101, a power supply unit 102, a power transmitting unit 103, a communication unit 104, a power transmitting antenna 105, a memory 106, and an antenna switching unit 107. In Fig. 1, the control unit 101, the power supply unit 102, the power transmitting unit 103, the communication unit 104, the memory 106, and the antenna switching unit 107 are depicted as separate entities, but any two or more of these functional blocks may be implemented on the same chip.

[0023] The control unit 101 controls the entire TX by executing a control program stored in the memory 106, for example. The control unit 101 also controls power transmission control, including communication for device authentication in the TX. The control unit 101 may also control the execution of applications other than wireless power transmission. The control unit 101 includes one or more processors, such as a CPU (Central Processing Unit) or an MPU (Microprocessor Unit). The control unit 101 may also be configured with hardware, such as an ASIC (Application Specific Integrated Circuit). The control unit 101 may also be configured with an array circuit, such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processes. The control unit 101 stores information to be stored during the execution of various processes in the memory 106. The control unit 101 may also measure time using a timer (not shown).

[0024] The power supply unit 102 supplies power to each functional block. The power supply unit 102 is, for example, a commercial power supply or a battery. The battery stores power supplied from the commercial power supply.

[0025] The power transmitting unit 103 converts DC or AC power input from the power supply unit 102 into AC frequency power in a frequency band used for wireless power transmission, and inputs the AC frequency power to the power transmitting antenna 105 to generate electromagnetic waves for receiving power at the RX. For example, the power transmitting unit 103 converts the DC voltage supplied by the power supply unit 102 into an AC voltage using a switching circuit with a half-bridge or full-bridge configuration using FETs (Field Effect Transistors). In this case, the power transmitting unit 103 includes a gate driver that controls the ON / OFF of the FETs.

[0026] The power transmitting unit 103 controls the intensity of the electromagnetic waves to be output by adjusting the voltage (power transmission voltage) or current (power transmission current), or both, input to the power transmitting antenna 105. Increasing the power transmission voltage or power transmission current increases the intensity of the electromagnetic waves, and decreasing the power transmission voltage or power transmission current decreases the intensity of the electromagnetic waves. Furthermore, the power transmitting unit 103 controls the output of AC frequency power so as to start or stop power transmission from the power transmitting antenna 105 based on instructions from the control unit 101. Furthermore, the power transmitting unit 103 is assumed to be capable of supplying enough power to output 15 watts (W) to the charging unit 206 (FIG. 2) of the power receiving device 401 (RX) that complies with the WPC standard.

[0027] The communication unit 104 communicates with the RX for power transmission control based on the WPC standard as described above. The communication unit 104 modulates electromagnetic waves output from the power transmitting antenna 105 and transmits information to the RX to perform communication. The communication unit 104 also demodulates the electromagnetic waves modulated by the RX and transmitted from the power transmitting antenna 105 to acquire information transmitted by the RX. That is, the communication performed by the communication unit 104 is performed by superimposing a signal on the electromagnetic waves transmitted from the power transmitting antenna 105. The communication unit 104 may also communicate with the RX using an antenna different from the power transmitting antenna 105 and based on a standard different from the WPC standard, or may communicate with the RX by selectively using multiple communication methods.

[0028] The memory 106 can store the control program as well as the TX and RX states (transmission power value, reception power value, etc.). For example, the TX state is acquired by the control unit 101, and the RX state is acquired by the RX control unit 201 (FIG. 2) and can be received via the communication unit 104.

[0029] The power transmitting antenna 105 has a plurality of antennas (coils). The antenna switching unit 107 selects and switches one of the plurality of antennas (coils). Alternatively, the power transmitting antenna 105 may have a single power transmitting antenna 105 instead of a plurality of antennas. In this case, the antenna switching unit 107 is not necessary.

[0030] Fig. 2 is a block diagram showing an example of the configuration of a power receiving device 401 (RX) according to this embodiment. The RX includes a control unit 201, a UI (user interface) unit 202, a power receiving unit 203, a communication unit 204, a power receiving antenna 205, a charging unit 206, a battery 207, a memory 208, and a switch unit 209. Note that the multiple functional blocks shown in Fig. 2 may be realized as one hardware module.

[0031] The control unit 201 controls the entire RX by executing a control program stored in the memory 208, for example. That is, the control unit 201 controls each functional unit shown in FIG. 2. Furthermore, the control unit 201 may perform control for executing applications other than wireless power transmission. An example of the control unit 201 is configured to include one or more processors such as a CPU or an MPU. Note that the control unit 201 may control the entire RX (if the RX is a smartphone, the entire smartphone) in cooperation with an OS (Operating System) that it is running.

[0032] The control unit 201 may also be configured with hardware such as an ASIC. The control unit 201 may also be configured to include an array circuit such as an FPGA compiled to execute predetermined processes. The control unit 201 stores information to be stored while executing various processes in the memory 208. The control unit 201 may also measure time using a timer (not shown).

[0033] The UI unit 202 performs various outputs to the user. The various outputs referred to here include screen display, blinking or color changes of LEDs (Light Emitting Diodes), audio output from a speaker, vibration of the RX main unit, etc. The UI unit 202 is realized by a liquid crystal panel, speaker, vibration motor, etc.

[0034] The power receiving unit 203 acquires, at the power receiving antenna 205, AC power (AC voltage and AC current) generated by electromagnetic induction caused by electromagnetic waves radiated from the power transmitting antenna 105 of the TX 402. The power receiving unit 203 then converts the AC power into DC or AC power of a predetermined frequency, and outputs the power to the charging unit 206, which performs processing to charge the battery 207. In other words, the power receiving unit 203 supplies power to the load in the RX. The above-mentioned GP is the amount of power guaranteed to be output from the power receiving unit 203. The power receiving unit 203 supplies power for the charging unit 206 to charge the battery 207, and is assumed to have the capacity to supply enough power to output 15 watts of power to the charging unit 206.

[0035] The switch unit 209 controls whether or not the received power is supplied to the battery (load). It also has a function of controlling the load value. When the switch unit 209 connects the charging unit 206 and the battery 207, the received power is supplied to the battery 207. When the switch unit 209 disconnects the charging unit 206 and the battery 207 with the switch, the received power is not supplied to the battery 207. Note that although the switch unit 209 is arranged between the charging unit 206 and the battery 207 in FIG. 2, it may be arranged between the power receiving unit 203 and the charging unit 206. Alternatively, although the switch unit 209 is illustrated as a single block in FIG. 2, the switch unit 209 can also be realized as part of the charging unit 206. The communication unit 204 communicates with the communication unit 104 of the TX for power reception control based on the WPC standard as described above. The communication unit 204 demodulates electromagnetic waves input from the power receiving antenna 205 and acquires information transmitted from the TX. The communication unit 204 then performs load modulation on the input electromagnetic waves to superimpose a signal related to information to be transmitted to the TX onto the electromagnetic waves, thereby communicating with the TX. Note that the communication unit 204 may communicate with the TX using a standard other than the WPC standard and using an antenna other than the power receiving antenna 205, or may communicate with the TX by selectively using multiple communication standards.

[0036] The memory 208 stores the control program and also stores the TX and RX states. For example, the RX state is acquired by the control unit 201, and the TX state is acquired by the TX control unit 101 and can be received via the communication unit 204.

[0037] Next, the function of the control unit 101 of the TX 402 will be described with reference to FIG. 3. FIG. 3 is a block diagram showing an example of the functional configuration of the control unit 101 of the power transmitting device 402 (TX). The control unit 101 has a communication control unit 301, a power transmission control unit 302, a measurement unit 303, a setting unit 304, and a foreign object detection unit 305. The communication control unit 301 performs control communication with the RX based on the WPC standard via the communication unit 104. The power transmission control unit 302 controls the power transmitting unit 103 to control power transmission to the RX. The measurement unit 303 measures a waveform attenuation factor, which will be described later. It also measures the power output to the RX via the power transmitting unit 103 and measures the average output power per unit time. It also measures the Q value of the power transmitting antenna (power transmitting coil). The setting unit 304 sets a threshold value used for foreign object detection based on the waveform attenuation factor measured by the measurement unit 303, for example, by calculation processing.

[0038] The foreign object detection unit 305 can realize a foreign object detection function using a power loss method, a foreign object detection function using a Q-value measurement method, or a foreign object detection function using a waveform attenuation method. The foreign object detection unit 305 may also have a function for performing foreign object detection processing using other methods. For example, in a TX equipped with an NFC (Near Field Communication) communication function, the foreign object detection unit 305 may perform foreign object detection processing using an opposite device detection function according to the NFC standard. The foreign object detection unit 305 can also detect changes in the state of the TX, in addition to detecting foreign objects. For example, the TX can detect an increase or decrease in the number of power receiving devices on the TX. The setting unit 304 sets a threshold value that serves as a reference for determining the presence or absence of a foreign object when the TX performs foreign object detection using the power loss method, the Q-value measurement method, or the waveform attenuation method. The setting unit 304 may also have a function for setting a threshold value that serves as a reference for determining the presence or absence of a foreign object, which is necessary when performing foreign object detection processing using other methods. Furthermore, the foreign object detector 305 can perform foreign object detection processing based on the threshold value set by the setting unit 304 and the waveform attenuation rate, output power, and Q value measured by the measuring unit 303 .

[0039] The functions of the communication control unit 301, power transmission control unit 302, measurement unit 303, setting unit 304, and foreign object detection unit 305 are realized as programs that run in the control unit 101. Each processing unit is configured as an independent program, and can run in parallel while maintaining synchronization between the programs through event processing or the like.

[0040] (Process flow for power transmission according to WPC standards) Next, the operations of the power transmitting device and the power receiving device in the Selection phase, Ping phase, I&C phase, Negotiation phase, Calibration phase, and Power Transfer phase defined in the WPC standard will be explained using the sequence diagram in Fig. 5. Fig. 5 is a sequence diagram for power transmission according to the WPC standard. Here, the explanation will be given using the power transmitting device 402 (TX) and the power receiving device 401 (RX) as examples.

[0041] The TX repeatedly and intermittently transmits Analog Pings conforming to the WPC standard to detect objects within its power transmission range (F501). The TX executes the processes defined as the Selection phase and Ping phase of the WPC standard, and waits for the RX to be placed on it. The user of the RX brings the RX (e.g., a smartphone) close to the TX to charge it (F502). For example, the RX is brought close to the TX by placing it on the TX. When the TX detects the presence of an object within its power transmission range (F503, F504), it transmits Digital Pings conforming to the WPC standard (F505). When the RX receives the Digital Ping, it knows that the TX has detected the RX (F506). Furthermore, when the TX receives a predetermined response to the Digital Ping, it determines that the detected object is the RX and that the RX has been placed on the charging stand 403. When the TX detects that the RX has been placed, it acquires identification information and capability information from the RX through communication in the I&C phase specified by the WPC standard (F507). The identification information of the RX includes a Manufacturer Code and a Basic Device ID. The capability information of the RX includes information elements that can identify the version of the WPC standard that the RX supports, a Maximum Power Value that specifies the maximum power that the RX can supply to a load, and information indicating whether the RX has the negotiation function of the WPC standard. The TX may acquire the identification information and capability information of the RX through a method other than communication in the I&C phase of the WPC standard. The identification information may also be any other identification information that can identify an individual RX, such as a Wireless Power ID. The capability information may include information other than the above.

[0042] Next, TX determines the GP value with RX through communication in the negotiation phase defined by the WPC standard (F508). Note that in F508, other procedures for determining GP may be executed, not limited to communication in the negotiation phase defined by the WPC standard. Furthermore, if TX acquires information indicating that RX does not support the negotiation phase (for example, in F507), it may not execute communication in the negotiation phase and may set the GP value to a small value (for example, defined in advance in the WPC standard). In this embodiment, GP = 5 watts.

[0043] After determining the GP, the TX performs calibration based on the GP. In the calibration process, first, the RX transmits information (hereinafter referred to as first reference received power information) including the received power in a light load state (load disconnected state, load state in which the transmitted power is equal to or less than the first threshold) to the TX (F509). In this embodiment, the first reference received power information is the received power information of the RX when the transmitted power of the TX is 250 milliwatts. The first reference received power information is the Received Power Packet (mode 1) specified in the WPC standard, but other messages may also be used. The TX determines whether to accept the first reference received power information based on the power transmission state of its own device. If the TX accepts, it transmits an acknowledgment (ACK) to the RX, and if not, it transmits a negative acknowledgment (NAK).

[0044] Next, when RX receives an ACK from TX (F510), it needs to transmit to TX information (hereinafter referred to as second reference received power information) including the received power in a load connection state (a load state in which the transmitted power is equal to or greater than the second threshold). In this embodiment, since GP is 5 watts, the second reference received power information is the received power information of RX when the transmitted power of TX is 5 watts. Here, the second reference received power information is the Received Power Packet (mode 2) specified in the WPC standard, but other messages may also be used. RX transmits a transmitted power output change instruction including a positive value to increase the transmitted power from TX to 5 watts (F511).

[0045] When the TX receives the above-mentioned instruction to change the transmission power output, and if it is possible to increase the transmission power, it responds with an ACK and increases the transmission power (F512, F513). Since the second reference received power information is the received power information when the transmission power of the TX is 5 watts, when the TX receives a power increase request exceeding 5 watts from the RX (F514), it responds with a NAK to the instruction to change the transmission power output, thereby preventing the transmission of power above the specified level (F515).

[0046] When the RX determines that the predetermined received power has been reached by receiving a NAK from the TX, it transmits information including the received power in the load-connected state to the TX as second reference received power information (F516). The TX can calculate the amount of power loss between the TX and RX based on the TX's transmitted power value and the received power values ​​included in the first and second reference received power information. Furthermore, by interpolating these values, it can calculate the power loss value between the TX and RX for all TX transmitted powers (in this case, the TX transmitted power is between 250 milliwatts and 5 watts) (F517). The TX transmits an ACK in response to the second reference received power information from the RX (F518), completing the calibration process. Having determined that charging can be started, the TX starts transmitting power to the RX, and charging of the RX begins. The TX and RX then perform device authentication (F519). If it is determined that both devices are compatible with a higher GP, the GP may be reset to a higher value, 15 watts in this case (F520).

[0047] As described above, the RX and TX increase the transmission power output using a transmission power output change command, ACK, and NAK to increase the TX transmission power to 15 watts (F521 to F524). The TX and RX then perform calibration again for GP = 15 watts. Specifically, the RX transmits information including the received power information for the RX load connection state when the TX transmission power is 15 watts (hereinafter referred to as third reference received power information) (F525). The TX performs calibration based on the received power included in the first, second, and third reference received power information, making it possible to calculate the amount of power loss between the TX and RX for all TX transmission powers (in this case, the TX transmission power is from 250 milliwatts to 15 watts) (F526). The TX then transmits an ACK in response to the third reference received power information from the RX (F527), completing the calibration process. When TX determines that charging can be started, it starts power transmission to RX and moves to the Power Transfer phase (F528).

[0048] In the power transfer phase, TX transmits power to RX. Foreign object detection is also performed using the power loss method. In the power loss method, TX first uses the calibration described above to calculate in advance the amount of power loss between TX and RX when there is no foreign object, based on the difference between the power transmitted by TX and the power received by RX. This calculated value is taken as the reference amount of power loss in the normal state (when there is no foreign object) during power transmission processing. Then, TX determines that there is a foreign object if the amount of power loss between TX and RX calculated during subsequent power transmission deviates from the amount of power loss in the normal state by more than a threshold value.

[0049] Thus, foreign object detection is performed using the power loss method during the power transfer phase. However, using only one foreign object detection method may result in erroneous foreign object detection or in a false determination that a foreign object is not present when it is. To further improve the accuracy of foreign object detection, it is generally desirable to combine multiple foreign object detection methods. In particular, the power transfer phase is the phase in which the TX transmits power. If a foreign object is introduced between the TX and RX during power transmission, heat generation from the foreign object will increase. Therefore, it is desirable to perform multiple foreign object detection methods during this phase to improve the accuracy of foreign object detection. Therefore, in this embodiment, a foreign object detection method other than the power loss method is considered.

[0050] (Foreign object detection method using waveform attenuation method) In the power transfer phase, the power transmitting device transmits power to the power receiving device. Therefore, if foreign object detection can be performed using this transmitted power waveform, foreign object detection becomes possible without creating a new signal for foreign object detection. A method for detecting foreign objects using a transmitted power waveform based on the attenuation state of the transmitted power waveform (hereinafter referred to as the waveform attenuation method) will be described with reference to FIG. 6. FIG. 6 is a diagram illustrating the principle of foreign object detection using the waveform attenuation method. Here, the explanation will be given using a power transmitting device 402 (TX) and a power receiving device 401 (RX) as examples.

[0051] In FIG. 6, the waveform shows the time course of a voltage value 600 (hereinafter simply referred to as voltage value) of the high-frequency voltage applied to the power transmitting antenna (power transmitting coil) of the TX. The horizontal axis represents time, and the vertical axis represents voltage value. The TX transmits power to the RX via the power transmitting antenna. At time T0, the power transmission stops, and the application of the high-frequency voltage to the power transmitting antenna (power transmitting coil) is stopped. The frequency of the power transmitting wave transmitted from the TX is a predetermined (fixed) frequency. This frequency is between 85 kHz and 205 kHz, as specified by the WPC standard. Point 601 is part of 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 part of 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. At this time, the quality factor (Q value) of this power transmitting antenna can be calculated based on the time change of the voltage value after time T0. Specifically, for example, it is calculated using Equation 1 based on the time, voltage value, and frequency f of the high-frequency voltage at points 601 and 602 on the envelope of the voltage value. Q=πf(T2-T1) / ln(A1 / A2) (Equation 1) If a foreign object is present between TX and RX, the Q factor decreases. This is because the presence of the foreign object causes energy loss. Therefore, focusing on the slope of the waveform attenuation, the presence of a foreign object causes more energy loss due to the foreign object than the absence of a foreign object. Therefore, the slope of the line connecting points 601 and 602 becomes steeper, resulting in a higher waveform attenuation rate. In other words, the waveform attenuation method determines the presence or absence of a foreign object based on the attenuation state between points 601 and 602. The actual presence or absence of a foreign object can be determined by comparing some numerical value representing this attenuation state. For example, the above-mentioned Q factor comparison may be used. A lower Q factor indicates a higher waveform attenuation rate. Alternatively, the slope of the line connecting points 601 and 602, calculated from (A1-A2) / (T2-T1), may be compared. Alternatively, if the time period for observing the waveform attenuation state is fixed, the value (A1-A2), which represents the difference in voltage values, or the voltage ratio (A1 / A2) may be compared. Alternatively, if the voltage value A1 during power transmission is constant, the voltage value A2 after a predetermined time has elapsed may be compared, or the time (T2-T1) required for the voltage value A1 to reach the predetermined voltage value A2 may be compared.

[0052] As described above, the presence or absence of a foreign object can be determined by the attenuation state of the waveform after power transmission is stopped, and there are multiple values ​​that represent this attenuation state. Hereinafter, this value representing the attenuation state will be referred to as the "waveform attenuation rate." As mentioned above, the Q value calculated using Equation 1 also represents the attenuation state of the waveform, and therefore is included in the "waveform attenuation rate." While the vertical axis in Figure 6 represents the voltage applied to the power transmitting antenna (coil), the attenuation state of the waveform also changes for the current value flowing through the power transmitting antenna (coil) after power transmission is stopped, as in Figure 6, depending on the presence or absence of a foreign object. The presence of a foreign object results in a higher attenuation rate. Therefore, by applying the above-described method to the current value flowing through the power transmitting antenna (coil), it is possible to determine the presence or absence of a foreign object and detect the foreign object based on the Q value obtained from the current waveform, the slope of the attenuated waveform, the difference in current values, the ratio of current values, the current value, the time until the current reaches a predetermined value, and other factors. In the above, the TX measures the waveform attenuation rate when power transmission is stopped, but the power transmission device may also measure the waveform attenuation rate when the power transmission power (voltage, current) is reduced to a predetermined value.

[0053] A method for detecting a foreign object using a transmitted wave form during power transmission using the waveform attenuation method will be described with reference to FIG. 7. FIG. 7 is a diagram for explaining a method for detecting a foreign object using a transmitted wave form during power transmission. FIG. 7 shows the transmitted power waveform when detecting a foreign object using the waveform attenuation method, with the horizontal axis representing time and the vertical axis representing the voltage value of the power transmitting antenna (power transmitting coil). As with FIG. 6, the vertical axis may represent the current value flowing through the power transmitting antenna. The TX starts transmitting power ("Power Transmission Start" in FIG. 7). During the transient response period ("Transient Response Period" in FIG. 7) immediately after the TX starts transmitting power ("Power Transmission Start" in FIG. 7), the transmitted power waveform is unstable. Therefore, during this transient response period when the transmitted power waveform is unstable, the RX is controlled so as not to communicate with the TX (communication by load modulation). The TX is also controlled so as not to communicate with the RX (communication by frequency shift keying).

[0054] When it is time to detect a foreign object, the TX stops transmitting power ("Power transmission stopped" in Figure 7). Then, the transmitted power waveform attenuates, and by calculating and using the waveform attenuation rate (Q value, attenuation slope, etc.) from this attenuated waveform, it becomes possible to detect a foreign object ("Foreign object detection period" in Figure 7). Then, after a predetermined time has elapsed, the TX resumes transmitting power ("Power transmission resumed" in Figure 7). As described above, the transmitted power waveform is unstable during the transient response period ("Transient response period" in Figure 7) immediately after the TX starts transmitting power ("Power transmission start" in Figure 7). Therefore, during this transient response period when the transmitted power waveform is unstable, the RX is controlled not to communicate with the TX (communication by load modulation). In addition, the TX is controlled not to communicate with the RX (communication by frequency shift keying). When it is time to detect a foreign object, the TX stops transmitting power ("Power transmission stopped" in Figure 7). As a result, the transmitted power waveform attenuates, and by calculating and using the waveform attenuation rate from this attenuated waveform, it becomes possible to detect a foreign object ("Foreign object detection period" in Figure 7). Then, after a predetermined time has passed, the TX resumes power transmission ("Power transmission resumed" in Figure 7). This is the basic principle of foreign object detection using the waveform attenuation method.

[0055] (Processing of power transmission equipment when applying the waveform attenuation method to the WPC standard) Next, we will briefly explain the processing of a power transmitting device when applying this waveform attenuation method in accordance with the WPC standard to perform foreign object detection. When performing foreign object detection using the waveform attenuation method, the power transmitting device measures the waveform attenuation rate in advance when there is no foreign object and calculates a threshold value based on that. The power transmitting device performs foreign object detection using the waveform attenuation method, and if the measured waveform attenuation rate is greater than the threshold value, it determines that there is a foreign object, and if it is less than the threshold value, it determines that there is no foreign object.

[0056] The timing for measuring the waveform attenuation rate in advance when there is no foreign object will be explained. In the WPC standard, foreign object detection is performed using the Q-value measurement method in the negotiation phase as described above. If it is determined that no foreign object is present as a result of foreign object detection, the system proceeds to the calibration phase and power transfer phase. In other words, proceeding to the negotiation phase or later means that the Q-value measurement method has determined that no foreign object is present as a result of foreign object detection. Therefore, if the waveform attenuation rate is measured in either the negotiation phase, calibration phase, or power transfer phase, there is a high possibility that the waveform attenuation rate in a foreign object-free state can be measured (because the Q-value measurement method has determined that no foreign object is present in the negotiation phase). Therefore, the timing for measuring the waveform attenuation rate in a foreign object-free state may be any of the negotiation phase, calibration phase, or power transfer phase.

[0057] In this embodiment, a case where this is performed during the power transfer phase will be described. The timing for measuring the waveform attenuation rate in the absence of a foreign object is set at the beginning of the power transfer phase. This is because the probability of a foreign object being introduced between the power transmitting device and the power receiving device increases as time passes. Then, at the timing for foreign object detection specified by the power receiving device or the power transmitting device, the power transmitting device measures the waveform attenuation rate of the transmitted wave. The power transmitting device then compares the measured waveform attenuation rate with a threshold calculated from the waveform attenuation rate in the absence of a foreign object as described above, to determine the presence or absence of a foreign object.

[0058] (Processing flow in the first embodiment) A specific flow of foreign object detection processing by the power transmitting device and the power receiving device will be described with reference to Figs. 8 to 10. Fig. 8 is a flowchart of processing executed by the power transmitting device in this embodiment, and Fig. 9 is a flowchart of processing executed by the power receiving device in this embodiment. Fig. 10 is a sequence diagram of the power transmitting device and the power receiving device. Below, the power transmitting device 402 (TX) and the power receiving device 401 (RX) will be described as examples. As described above, in this embodiment, the foreign object detection processing is performed during the power transfer phase.

[0059] (1) Setting the threshold for detecting foreign objects using the waveform attenuation method First, the flow of processing for setting a threshold for foreign object detection using the waveform attenuation method will be described. When the wireless power transmission system enters the Power Transfer phase, TX starts transmitting power (S801, F1001), and RX starts receiving power (S901). At this stage, RX turns off the switch unit 209, disconnecting the RX load (battery 207) (F1002). Immediately after TX starts transmitting power, RX determines whether a communication prohibition period (predetermined time) has elapsed (S902, F1003). This is because the transmitted power waveform does not stabilize until the communication prohibition period has elapsed, and so RX waits until it stabilizes to a steady state. After the communication prohibition period has elapsed, RX determines whether to measure the waveform attenuation rate (S903, F1004). If the threshold for the waveform attenuation rate for foreign object detection has not yet been set (calculated), RX determines to measure the waveform attenuation rate. In this case, the RX transmits an instruction to the TX to measure the waveform attenuation rate via the communication unit 104 (S904, F1005). This instruction is a command requesting the TX to measure the waveform attenuation rate in order to set a threshold for foreign object detection using the waveform attenuation method. The RX then disconnects the switch unit 209 and disconnects the load of the RX (battery 207) (S905, F1006). Note that the switch unit 209 may be disconnected before the command is transmitted (S904).

[0060] Here, the reason for disconnecting the load of RX (battery 207) will be described. The waveform attenuation rate fluctuates depending on the state of the load of RX (battery 207) or the power transmission state of TX. Therefore, when measuring the waveform attenuation rate, the load is disconnected in advance to eliminate the influence of the load of RX (battery 207). The TX determines, via the communication unit 104, whether or not an instruction to measure the waveform attenuation rate has been received from the RX (S802). If an instruction has been received (YES in S802), the TX determines whether the received instruction is to measure the waveform attenuation rate for determining a threshold value (S803, F1007). If the received instruction is a command requesting measurement to set a threshold value for foreign object detection (YES in S803), the TX temporarily stops (instantaneous interruption of) power transmission (S804, F1008). Then, the TX measures the waveform attenuation rate after a predetermined time has elapsed (S805, F1009). The reason for waiting for the passage of a predetermined time here is that the transient response is unstable immediately after power transmission is stopped. Next, the TX calculates a threshold value from the waveform attenuation rate measured in S805 (S806, F1010). For example, the TX calculates a value by adding a predetermined margin to the measured waveform attenuation rate as the threshold value. Then, the TX stores the calculated threshold value in the memory 106 (S807, F1011). Then, the TX resumes power transmission (S808).

[0061] RX waits for a predetermined time until TX resumes power transmission and the transmission waveform reaches a steady state (S906, F1012). The reason for waiting for the predetermined time is that if the transmission waveform during power transmission is unstable (not in a steady state), excessive power may be applied to RX. After the predetermined time has passed, RX connects a load (battery 207) (S907, F1013). RX determines whether to request the power transmission to stop (for example, because the battery 207 is fully charged) (S908). If it is determined that the power transmission should be stopped (YES in S908), RX requests the power transmission to stop by sending an EPT (End Power Transfer) command to TX (S909), and ends the process (S910). If the power transmission is not requested to stop (NO in S908) in S908, RX starts power reception (S911). Through the above operation, the TX can measure the waveform attenuation rate when there is no foreign object, and from the results, set the threshold value required to determine whether or not there is a foreign object.

[0062] (2) Foreign object detection operation Next, the operation of foreign object detection will be described. TX is transmitting power (S801), and RX is receiving power (S901). RX determines whether the communication prohibition period has elapsed (S902, F1014). After the communication prohibition period has elapsed, RX determines whether to measure the waveform attenuation rate (S903, F1015). RX determines to measure the waveform attenuation rate in order to perform foreign object detection to confirm the presence or absence of a foreign object. In this case, RX transmits an instruction to TX to perform waveform attenuation rate measurement via the communication unit 104 (S904, F1016). This instruction is a command requesting TX to perform foreign object detection using the waveform attenuation method (to determine the presence or absence of a foreign object). Then, RX disconnects the switch unit 209 and disconnects the load of RX (battery 207) (S905, F1017). Note that this disconnection of the switch unit 209 may be performed before transmitting the command (S904). The reason for disconnecting the load of RX is as described above. The TX determines whether or not it has received an instruction to measure the waveform attenuation rate from the RX through the communication unit 104 (S802). If it has received the instruction (YES in S802), the TX determines whether or not the received instruction is to measure the waveform attenuation rate to determine a threshold (S803, F1018). If the received instruction is a command requesting foreign object detection using the waveform attenuation method (determining whether or not a foreign object is present) (NO in S803), the TX temporarily stops (instantaneously interrupts) power transmission (S809, F1019). Then, the TX measures the waveform attenuation rate after a predetermined time has elapsed (S810, F1020). The reason for waiting for the predetermined time to elapse here is that the transient response is unstable immediately after power transmission is stopped. Next, the TX compares the threshold calculated in S806 with the waveform attenuation rate measured in S810 to determine whether or not a foreign object is present (S811, F1021). If it is determined that a foreign object is present (YES in S812), the TX stops power transmission (S815, F1023) and ends the process (S816). If it is determined that no foreign object is present (NO in S812), the TX determines whether an instruction to stop power transmission has been received from the RX (whether an EPT command has been received) (S813). If an instruction to stop power transmission has been received (YES in S813), the TX stops power transmission (S815) and ends the process (S816).If there is no instruction to stop power transmission (NO in S813), the TX resumes power transmission (S814).

[0063] The RX waits for a predetermined time to elapse until the TX resumes power transmission and the power transmission waveform reaches a steady state (S906). The reason for waiting for a predetermined time is as described above. After the predetermined time has elapsed, the RX connects a load (battery 207) (S907). The RX determines whether or not to request that power transmission be stopped, for example, because the battery 207 is fully charged (S908). If it is determined that power transmission is to be stopped (YES in S908), the RX requests that power transmission be stopped by sending an EPT command to the TX, and ends the process (S910). Here, if the TX determines that "foreign object is present" (YES in S812), and the RX determines that power transmission from the TX is not being performed, the RX requests that power transmission be stopped by sending an EPT command to the TX (F1024), and ends the process (S910). This allows power transmission to be ended normally. Alternatively, RX may end the process without sending an EPT command to TX (S910) and transition to a reset state (Standby state). If RX does not request that power transmission be stopped in S908 (NO in S908), it starts power reception (S910). Through the above operations, TX can determine the presence or absence of a foreign object between TX and RX by utilizing the waveform attenuation rate of the transmitted wave.

[0064] In the above-described embodiment, when measuring the waveform attenuation factor, the RX load is disconnected in advance to eliminate the influence of the RX load before measurement. Alternatively, when measuring the waveform attenuation factor, the RX load value may be controlled in advance to reduce the influence of the RX load before measurement. For example, this can be achieved by controlling the load so that the RX load is in a light load state (light load state) so that only a small amount of power is supplied to the RX.

[0065] In the above-described embodiment, the timing for measuring the waveform attenuation rate by the TX is determined by an instruction from the RX to the TX (S803). Alternatively, the TX can determine the timing and notify the RX of that timing. Specifically, for example, instead of the processes of S802 and S803 in FIG. 8, the TX first determines whether the communication prohibition period has elapsed. After the communication prohibition period has elapsed, the TX determines whether to measure the waveform attenuation rate for determining a threshold value. Alternatively, the TX determines whether to measure the waveform attenuation rate for detecting the presence or absence of a foreign object. If the TX determines to measure the waveform attenuation rate, the TX determines the timing for measuring the waveform attenuation rate and notifies the RX of that timing. If the measurement of the waveform attenuation rate is for determining a threshold value, the TX may simultaneously notify the RX that the measurement is for determining the threshold value, or if the measurement is for detecting the presence or absence of a foreign object, may notify the RX that the measurement is for detecting the presence or absence of a foreign object. Then, the RX turns off the switch unit 209 at the timing for measuring the waveform attenuation rate and disconnects the RX load (battery 207). Alternatively, the load (battery 207) of the RX is controlled so that its load value is in a light load state (light load state). As a result of the above, the TX is able to measure the waveform attenuation rate. The timing of the measurement of the waveform attenuation rate by the TX may be configured to be executed at a predetermined timing. At the predetermined timing, the TX measures the waveform attenuation rate, and the RX disconnects the load or controls the load so that its load value is in a light load state (light load state). The TX may also be configured to proceed to S804 when a user instructs the TX to set a threshold for foreign object detection, or to proceed to S809 when a user instructs the TX to perform foreign object detection. The user's instruction can be implemented by a predetermined input / operation on the TX.

[0066] In the above-described embodiment, the TX measures the voltage applied to the TX's power transmitting antenna (power transmitting coil) or the attenuation rate of the current flowing through the power transmitting antenna (power transmitting coil) to determine whether a foreign object has been detected. However, because the power transmitting antenna (power transmitting coil) and the power receiving antenna (power receiving coil) face each other and are electromagnetically coupled, the electromagnetic energy of the power transmitting antenna is also excited in the power receiving antenna. Therefore, the RX can also measure the voltage applied to the RX's power receiving antenna (power receiving coil) or the attenuation rate of the current flowing through the power receiving antenna (power receiving coil) to determine whether a foreign object has been detected.

[0067] Furthermore, when the TX measures the waveform attenuation rate, it may notify the RX of that waveform attenuation rate or a threshold value calculated from that waveform attenuation rate. This allows the RX side to determine whether or not there is a foreign object. Alternatively, when the RX measures the waveform attenuation rate, it may notify the TX of that waveform attenuation rate or a threshold value calculated from that waveform attenuation rate. This allows the TX side to determine whether or not there is a foreign object.

[0068] In the above-described embodiment, when foreign object detection is performed using the waveform attenuation method, the waveform attenuation rate in a state where no foreign object is present is measured in advance, and a threshold value is calculated based on the measured waveform attenuation rate. Foreign object detection is then performed using the waveform attenuation method. If the measured waveform attenuation rate is greater than the threshold value, a "foreign object is present" is determined; if it is smaller than the threshold value, a "foreign object is not present" is determined. However, foreign object detection may also be performed by comparing the measured waveform attenuation rate with a threshold value calculated from a previous waveform attenuation rate measured at a time when no foreign object is expected to be present. For example, the absence of a foreign object is first confirmed using the power loss method. Next, a first waveform attenuation rate measurement is performed using the waveform attenuation method, and a threshold value is calculated. In this case, since the absence of a foreign object has been confirmed in advance using the power loss method, this waveform attenuation rate or threshold value is considered to be a value in a state where no foreign object is present. Next, a second waveform attenuation rate measurement is performed using the waveform attenuation method, and a threshold value is calculated. In this case, foreign object detection can be achieved by comparing the measurement result of the first waveform attenuation rate measurement with the threshold value. This is because the measurement result of the first waveform attenuation rate measurement and the threshold value are those in a state where no foreign object is present. That is, when foreign matter detection is performed using the waveform attenuation method, it can also be realized by comparing the waveform attenuation rate with a threshold value or a waveform attenuation rate that is considered to have been measured in the absence of foreign matter.

[0069] In the above-described embodiment, the frequency of the power transmission wave transmitted from the TX is a predetermined (fixed) frequency. However, multiple frequencies may be used, and the foreign object detection operation described in this embodiment may be performed at each frequency, and the presence or absence of a foreign object may be determined by combining the results. Performing foreign object detection using the waveform attenuation rate of multiple frequencies, rather than just the waveform attenuation rate of one predetermined (fixed) frequency, enables more accurate foreign object detection.

[0070] In this embodiment, immediately after the TX stops or starts transmitting power, the transmission waveform is unstable due to a transient response, so a waiting time is provided before proceeding to each operation. However, this instability in the transmission waveform is caused by a sudden start or stop of power transmission. Therefore, to alleviate this, the TX may be controlled to increase the transmission power in stages when starting power transmission. Alternatively, when stopping / pausing power transmission, the TX may be controlled to decrease the transmission power in stages.

[0071] [Embodiment 2] In the first embodiment, a control method was described in which, when the power transmitting device stops power transmission and measures the waveform attenuation rate of the transmitted wave, the load on the power receiving device is disconnected before measuring the waveform attenuation rate in order to eliminate the influence of the load on the power receiving device. However, this method requires the power receiving device to disconnect and connect the load at a predetermined timing, which takes time and may result in a decrease in power transmission efficiency. In the present embodiment, a method is described in which the load on the power receiving device is kept connected without being disconnected when measuring the waveform attenuation rate.

[0072] The transmission power of the power transmitting device varies depending on the state of the load (battery) of the power receiving device. In other words, the power receiving device can control the transmission power from the power transmitting device by controlling the state of the load of the power receiving device. The power transmitting device measures in advance the waveform attenuation rate for each state (each transmission power value) of the load on the power receiving device when there is no foreign object, and sets a threshold value used to determine the presence or absence of a foreign object for each state (each transmission power) of the load on the power receiving device based on the measurement results. When detecting a foreign object, the power transmitting device measures the waveform attenuation rate without disconnecting the load on the power receiving device, and determines the presence or absence of a foreign object by comparing it with a threshold value corresponding to the value of the transmission power.

[0073] The processing flow by the power transmitting device 402 (TX) and the power receiving device 401 (RX) will be described below. The configurations, processing flow, and operation sequence of the TX and RX are basically the same as those in the first embodiment. The difference is the method of measuring the waveform attenuation rate in S805 when the instruction received by the TX from the RX is a command requesting measurement to set the threshold for foreign object detection (YES in S803). The method by which the TX and RX in this embodiment perform measurement to set the threshold for foreign object detection using the waveform attenuation method will be described with reference to FIGS. 8 and 11.

[0074] FIG. 11 is a diagram illustrating a method for setting a foreign object detection threshold using the waveform attenuation method. First, when power is transmitted from TX, RX controls the load of RX to be in a light load state (light load state) so that no power is supplied (disconnected) to the load of RX or only very small power is supplied. The transmitted power of TX at this time is defined as Pt1. Then, TX stops transmitting power in this state (S804) and measures the waveform attenuation rate (S805). The waveform attenuation rate at this time is defined as δ1. At this time, TX associates the transmitted power Pt1 (the power transmitting device recognizes the transmitted power Pt that it is transmitting) with the waveform attenuation rate δ1 and stores them in memory (point 1100). Next, when power is transmitted from TX, RX controls the load of RX to be in a connected load state (connected load state) so that maximum power or power equal to or greater than a predetermined threshold is supplied to the load of RX. The transmitted power of TX at this time is defined as Pt2. Then, the TX stops transmitting power in this state (S804) and measures the waveform attenuation rate (S805). At this time, the TX associates the transmitted power Pt2 with the waveform attenuation rate δ2 and stores them in memory (point 1101). Next, the TX linearly interpolates points 1100 and 1101 to create line 1102. Line 1102 represents the relationship between the transmitted power and the waveform attenuation rate of the transmitted wave when there are no foreign objects around the TX and RX. Therefore, the TX can predict the waveform attenuation rate of the transmitted wave for each transmitted power value when there are no foreign objects, from the transmitted power value and line 1102. For example, if the transmitted power value is Pt3, the waveform attenuation rate can be predicted to be δ3 from point 1103 on line 1102, which represents the transmitted power value Pt3. Based on this line 1102, the TX can predict the waveform attenuation rate of the transmitted wave for each transmitted power value. Then, based on these, the TX can calculate a threshold value to be used for determining the presence or absence of a foreign object for each transmission power value in a state where no foreign object is present.

[0075] Note that RX may perform the control to put the load into a no-power / light-load state (first control) and the control to put the load into a load-connected state (second control) after notifying TX of the control to be performed. Also, either of the two controls may be performed first.

[0076] In the first embodiment, the RX disconnected its load when foreign object detection was performed (determining whether a foreign object is present or not). However, in this embodiment, the RX does not need to disconnect its load when foreign object detection is performed (determining whether a foreign object is present or not). The TX can recognize the transmission power value transmitted by the TX when foreign object detection is performed (determining whether a foreign object is present or not), and can therefore determine whether a foreign object is detected or not by comparing it with the threshold calculated from FIG. 11. That is, in this embodiment, a threshold is set for each load (transmission power value), so when foreign object detection is performed (determining whether a foreign object is present or not), it is sufficient to compare the waveform attenuation rate of the load (transmission power value) at that time with the threshold corresponding to that load (transmission power value). Therefore, it is not necessary to disconnect the RX load as in the first embodiment.

[0077] This eliminates the need for the RX to connect or disconnect a load when the TX measures the waveform attenuation rate to perform foreign object detection (determine whether a foreign object is present or not), making it possible to perform foreign object detection without reducing power transmission efficiency.

[0078] Note that the operation for calculating the threshold value used to determine the presence or absence of a foreign object for each load (each transmitted power value) described in this embodiment may be performed in the calibration phase. As described above, in the calibration phase, the TX acquires data required for foreign object detection using the power loss method. At that time, the TX acquires data when the load state of the RX is a light load state (light load state) and a connected load state (connected load state). Therefore, the measurements of points 1100 and 1101 in FIG. 11 can be realized by simultaneously measuring when the RX is in a light load state (light load state) and a connected load state (connected load state) in the calibration phase described above. That is, when the TX receives first reference received power information from the RX, it measures point 1100 in addition to the processing to be performed in the calibration phase. Furthermore, when the TX receives second reference received power information from the RX, it measures point 1101 in addition to the processing to be performed in the calibration phase. By doing so, it is no longer necessary to provide a separate process for measuring points 1100 and 1101, and it is therefore possible to measure points 1100 and 1101 in a shorter time.

[0079] [Embodiment 3] In the second embodiment, a method was described in which a threshold value used to determine the presence or absence of a foreign object is set for each load of the power receiving device (for each transmission power value transmitted by the power transmitting device), thereby eliminating the need to disconnect the load. In this embodiment, a method will be described in the second embodiment in which a foreign object detection threshold value is updated or added when the state of the power transmitting device or the power receiving device changes or when the maximum value of the transmission power is changed. Here, the explanation will be given using the power transmitting device 402 (TX) and the power receiving device 401 (RX) as examples.

[0080] As shown in FIG. 11 , in the second embodiment, the foreign object detection threshold is calculated by linearly interpolating (line 1102) the waveform attenuation rate when the TX power transmission is at its minimum (point 1100) and the waveform attenuation rate when the TX power transmission is at its maximum (point 1101) in a state where no foreign object is present. However, the linearly interpolated line 1102 in FIG. 11 can change when the state of the TX or RX changes. For example, this can occur when the temperature of the TX or RX increases. The higher the power transmitted by the TX and the longer the transmission time, the higher the temperature of the TX or RX housing or internal circuitry. Alternatively, if the RX is a mobile PC or smartphone, the use of applications and data processing can also cause a temperature rise. The temperature rise can lead to changes in the shape of the TX or RX housing and changes in the electrical characteristics of each component in the electrical circuit. These occurrences cause the line 1102 in FIG. 11 to change, and the waveform attenuation rate in a state where no foreign object is present for each transmitted power value changes. In this case, the foreign object detection threshold for each transmission power value must be recalculated. Alternatively, if the RX placed on the TX moves, the line 1102 in FIG. 11 changes, and the waveform attenuation rate for each transmission power value when no foreign object is present also changes. In this case, the foreign object detection threshold for each transmission power value must be recalculated. Alternatively, as shown in F519 and F520 in FIG. 5, the devices may perform device authentication with each other, and the GP or maximum power to transmit may change. If the GP or maximum power changes, it is necessary to plot the relationship between transmission power and waveform attenuation rate for a transmission power greater than the transmission power Pt2 in FIG. 11. In other words, when the state of the TX or RX changes, it is necessary to update or add the relationship between transmission power and waveform attenuation rate shown in FIG. 11.

[0081] When the RX determines that a change in the state of the TX or RX as described above has occurred and that the threshold value used for foreign object detection needs to be updated or added, the RX sends a command to the TX requesting measurement to set the threshold value for foreign object detection using the waveform attenuation method, as described in the first and second embodiments (YES in S803). The RX then controls the load so that the transmission power is at the point where the relationship between the transmission power and the waveform attenuation factor is to be updated or added. Upon receiving the command, the TX temporarily suspends power transmission (S804) and measures the waveform attenuation factor of the transmitted wave (S805). The TX then associates the transmission power with the measured waveform attenuation factor and updates or adds the relationship between the transmission power and the waveform attenuation factor shown in FIG. 11. The TX then calculates the foreign object detection threshold value based on the calculation and updates or adds the threshold value. Subsequently, the TX uses the calculated threshold value to determine the presence or absence of a foreign object. In the above-described embodiment, the RX determines whether the threshold value used for foreign object detection needs to be updated or added. Alternatively, the TX can perform the determination and, if it determines that the threshold value used for foreign object detection needs to be updated or added, notify the RX accordingly. Specifically, for example, if the TX or RX state changes as described above and determines that the threshold value used for foreign object detection needs to be updated or added, the TX notifies the RX that it will perform measurements to set the threshold value for foreign object detection using the waveform attenuation method in order to update or add the threshold value used for foreign object detection. Upon receiving this notification, the RX controls the load so that the transmission power is at the point where the relationship between the transmission power and the waveform attenuation factor is to be updated or added. Upon completing the load control, the RX notifies the TX that the load control is complete. Upon receiving this notification, the TX temporarily suspends power transmission (S804) and measures the waveform attenuation factor of the transmitted wave (S805). The TX then associates the transmission power with the measured waveform attenuation factor and updates or adds the relationship between the transmission power and the waveform attenuation factor shown in FIG. 11. Then, based on this, the TX calculates the threshold value for detecting foreign objects, updates or adds the threshold value, and thereafter, the TX uses this threshold value to determine whether or not a foreign object is present.

[0082] According to this embodiment, even if the state of the power transmitting device or the power receiving device changes, it is possible to set a foreign object detection threshold appropriate for that state.

[0083] [Embodiment 4] As described with reference to Figures 8 to 10, in the above-described embodiment, the determination of whether or not a foreign object has been detected using the waveform attenuation method is performed during the power transfer phase, in which the power transmitting device 402 (TX) transmits power. Specifically, when the power receiving device 401 (RX) determines that it is necessary to determine whether or not a foreign object is present during the power transfer phase, it transmits a command to the TX requesting that foreign object detection be performed using the waveform attenuation method (determine whether or not a foreign object is present). The TX then receives the command, performs foreign object detection, and determines whether or not a foreign object is present.

[0084] Meanwhile, the WPC standard specifies a foreign object detection method using the power loss method as a method for detecting foreign objects during the power transfer phase. Specifically, when the power receiving device determines that it needs to determine whether or not a foreign object is present, the power receiving device transmits a command to the power transmitting device requesting foreign object detection using the power loss method (determining whether or not a foreign object is present). The power transmitting device then receives the command, detects the foreign object, and determines whether or not a foreign object is present.

[0085] As described above, if a foreign object is present between the power transmitting device and the power receiving device during the power transfer phase in which the power transmitting device transmits power, heat generation from the foreign object will increase. Therefore, it is desirable to perform multiple foreign object detections during this phase to improve the accuracy of foreign object detection. Taking this into consideration, this embodiment combines two methods, the power loss method and the waveform attenuation method, to achieve more accurate foreign object detection. A specific method will be described below. Here, the power transmitting device 402 (TX) and the power receiving device 401 (RX) will be described as an example.

[0086] The first method is to periodically alternate between two methods for foreign object detection during the power transfer phase: the power loss method and the waveform attenuation method. The RX instructs the TX to periodically alternate between the power loss method and the waveform attenuation method, and the TX performs foreign object detection using each method. If the TX determines that a foreign object is present using either method, it stops power transmission. This allows for more accurate foreign object detection, as it does not rely on the foreign object detection results of a single method.

[0087] The second method is to stop power transmission when a "foreign object presence" is determined using both the power loss method and the waveform attenuation method. The TX periodically detects foreign objects using the power loss method, and if it determines that there is no foreign object, it continues power transmission. The TX periodically detects foreign objects using the power loss method, and if it determines that there is a "foreign object" using the power loss method, it performs foreign object detection using the waveform attenuation method, and if it determines that there is a "foreign object" using the waveform attenuation method, it stops power transmission. In other words, if it determines that there is a "foreign object presence" using both methods, it controls power transmission to stop. Power transmission is stopped only when it determines that there is a "foreign object presence" using both the power loss method and the waveform attenuation method, making it possible to reduce the probability of incorrectly determining that there is a "foreign object presence."

[0088] The third method is to continue power transmission if both the power loss method and the waveform attenuation method determine that there is no foreign object. The TX periodically performs foreign object detection using the power loss method, and if the power loss method determines that there is a foreign object, it stops power transmission. Alternatively, the TX periodically performs foreign object detection using the power loss method, and if the power loss method determines that there is no foreign object, it performs foreign object detection using the waveform attenuation method, and if the waveform attenuation method determines that there is a foreign object, it stops power transmission. If the waveform attenuation method detects a foreign object and determines that there is no foreign object, the TX continues power transmission. Power transmission can only be continued if both the power loss method and the waveform attenuation method determine that there is no foreign object, which makes it possible to reduce the probability of incorrectly determining that there is no foreign object.

[0089] The fourth method is a method in which, when the two foreign object detection methods produce different judgment results on the presence or absence of a foreign object, foreign object detection is performed again using one of the methods, a comprehensive judgment is made based on the multiple judgment results, and appropriate power transmission control is performed. The TX performs foreign object detection using the power loss method, and even if the power loss method determines that a foreign object is present, foreign object detection is performed using the waveform attenuation method. If the waveform attenuation method determines that a foreign object is not present, foreign object detection is performed again using one of the methods (power loss method or waveform attenuation method). Alternatively, the TX performs foreign object detection using the power loss method, and even if the power loss method determines that a foreign object is not present, foreign object detection is performed again using the waveform attenuation method. If the waveform attenuation method determines that a foreign object is present, foreign object detection is performed again using one of the methods (power loss method or waveform attenuation method). The TX performs a comprehensive judgment based on the judgment results of ``foreign object present'' or ``foreign object not present'' using the power loss method and the waveform attenuation method, and determines whether to continue or stop power transmission, and appropriately controls power transmission. For example, the number of times a "foreign object is present" determination is compared with the number of times a "foreign object is absent" determination is made, and the greater number is used as the final determination result. Alternatively, for example, if there are cases in which a "foreign object is present" determination is made using both the power loss method and the waveform attenuation method, the final determination result may be "foreign object present." Alternatively, for example, if there are cases in which a "foreign object is absent" determination is made using both the power loss method and the waveform attenuation method, the final determination result may be "foreign object is absent." If the two methods produce different determination results regarding the presence or absence of a foreign object, foreign object detection can be performed again using one of the methods, and a comprehensive determination can be made based on the multiple determination results, making it possible to make an appropriate determination based on each determination result.

[0090] In the four methods described above, two foreign object detection results, "foreign object present" and "foreign object absent," have been described. As described in the first, second, and third embodiments, foreign object detection is determined based on whether the measured value is greater or smaller than a calculated threshold value. However, even when a "foreign object absent" determination is made, there may be cases where the margin for the threshold value is small, and the presence of a foreign object is suspected. Applying the four methods described above to cases where the presence of a foreign object is suspected can also enable more accurate foreign object detection. Specifically, the processing performed when a "foreign object present" determination is made in the four methods described above may also be performed when a "foreign object presence is suspected." Here, the "foreign object presence is suspected" determination can be achieved by setting a new threshold value that adds a predetermined margin to the threshold value used to determine the presence or absence of a foreign object and making a determination based on the new threshold value. This enables more accurate foreign object detection. Furthermore, in the four methods described above, foreign object detection is first performed using the power loss method, and then using the waveform attenuation method. The reason for this is as follows. The power loss method can be performed without stopping power transmission from TX to RX, but the waveform attenuation method requires power transmission from TX to RX to be temporarily stopped, which reduces power transmission efficiency. Therefore, in some cases, a configuration in which foreign object detection is performed first using the power loss method and then using the waveform attenuation method can suppress the reduction in power transmission efficiency. However, the same effect can be achieved by first performing foreign object detection using the waveform attenuation method and then using the power loss method in the four methods described above.

[0091] [Embodiment 5] In the first embodiment, the timing for measuring the waveform attenuation rate in a foreign object-free state, which is necessary for creating a threshold (standard) for detecting foreign objects using the waveform attenuation method, is set to be during either the negotiation phase, the calibration phase, or the power transfer phase. In the WPC standard, foreign object detection using the Q-factor measurement method is performed in the negotiation phase as described above. Therefore, the progression of the phase beyond the negotiation phase means that the result of foreign object detection using the Q-factor measurement method is that no foreign object is detected. Therefore, if the waveform attenuation rate is measured in either the negotiation phase, the calibration phase, or the power transfer phase, there is a high possibility that the waveform attenuation rate in a foreign object-free state can be measured.

[0092] However, if a foreign object is introduced between the power transmitting device and the power receiving device between the time when the absence of a foreign object is confirmed by the Q-factor measurement method in the negotiation phase and the time when the waveform attenuation rate is measured without a foreign object in the negotiation phase, calibration phase, or power transfer phase, the waveform attenuation rate cannot be accurately measured without a foreign object. Therefore, ideally, it is desirable to confirm the absence of a foreign object immediately before measuring the waveform attenuation rate without a foreign object. A method for achieving this is described below. The following explanation uses the power transmitting device 402 (TX) and the power receiving device 401 (RX) as an example.

[0093] For example, when the RX detects a change in the state of the TX or the RX and determines that the threshold value used for foreign object detection using the waveform attenuation method needs to be updated or added (Embodiment 3), the RX sends a command to the TX to perform foreign object detection using the power loss method. The TX performs foreign object detection using the power loss method and determines whether a foreign object is present. If it determines that no foreign object is present, the TX notifies the RX that a foreign object is not present, and the RX performs an operation to update or add the threshold value used for foreign object detection using the waveform attenuation method. That is, the RX sends a command to the TX requesting measurement to set the threshold value for foreign object detection using the waveform attenuation method, as described in Embodiments 1 and 2. The RX then controls the load so that the transmission power is at the point where the relationship between the transmission power and the waveform attenuation rate is to be updated or added. Upon receiving this command, the TX suspends power transmission and measures the waveform attenuation rate of the transmitted wave. The TX then uses the measured waveform attenuation rate to calculate the threshold value for foreign object detection using the waveform attenuation rate and sets it as the threshold value.

[0094] In this way, when the RX determines that the threshold for the waveform attenuation method should be updated or changed, it confirms the absence of foreign objects using the power loss method immediately before performing the operation to update or change the threshold for the waveform attenuation method.This makes it extremely likely that no foreign objects will be present when the measurement to set the threshold for foreign object detection using the waveform attenuation method is performed, making it possible to set a more accurate foreign object detection threshold.

[0095] In the above example, we described a method for confirming the absence of foreign objects using the power loss method immediately before updating or changing the threshold value for the waveform attenuation method. However, the power loss method also has a threshold for determining the presence or absence of foreign objects, and just like the waveform attenuation method, if the status of the TX or RX changes, it becomes necessary to update or add this threshold. This can also be done during the power transfer phase. Therefore, as with the method described above, if the RX determines that the threshold value for the power loss method needs to be updated or changed, it can confirm the absence of foreign objects using the waveform attenuation method immediately before performing the operation to update or change the threshold value for the power loss method. That is, for example, if the RX detects a change in the status of the TX or RX and determines that the threshold value used for power loss method foreign object detection needs to be updated or added, the RX sends a command to the TX to perform foreign object detection using the waveform attenuation method. The TX performs foreign object detection using the waveform attenuation method and determines whether or not a foreign object is present. If the result indicates that no foreign object is present, the TX notifies the RX that a foreign object is not present, and the RX performs the operation to update or add the threshold value used for power loss method foreign object detection. That is, in order to update or add a threshold value used for foreign object detection, RX sends a command requesting measurement to set the foreign object detection threshold value using the power loss method. RX then controls the load so that the transmission power is equal to the threshold value (point) to be updated or added. When TX receives this command, it calculates the foreign object detection threshold value using the power loss method and sets it as the threshold value. This makes it extremely likely that there will be no foreign object when the measurement to set the foreign object detection threshold value using the power loss method is performed, enabling a more accurate foreign object detection threshold value to be set.

[0096] [Variations] The power loss method described in the above embodiment is an example of a foreign object detection method different from the waveform attenuation method. Therefore, other foreign object detection methods may be used instead of the power loss method. For example, a Q-factor measurement method may be used. One method for measuring the Q-factor is to transmit a signal at a resonant frequency (e.g., a sine wave, a square wave, etc.) and measure the Q-factor at that resonant frequency. Another method is to transmit signals at multiple frequencies near the resonant frequency multiple times and measure their Q-factors. Another method is to transmit a signal (e.g., a pulse wave) once containing all or some of the frequency components of multiple frequencies whose electrical characteristics are to be measured, and then perform arithmetic processing (e.g., Fourier transform) on the measurement results to measure the Q-factor at multiple frequencies. Another method is to transmit a predetermined signal (not power transmission, but a signal) and then stop the transmission and measure the attenuation state of the signal. Because the attenuation state of this signal is correlated with the Q-factor, foreign object detection may be performed based on this. Alternatively, a foreign object detection method may be used that uses measurement results of the resonant frequency of the power transmitting antenna, the sharpness of the resonant curve, the inductance value of the power transmitting antenna, the coupling coefficient between the power transmitting antenna and an object placed on the power transmitting device, the electrical characteristics of the power transmitting unit including the power transmitting antenna of the power transmitting device, etc. These methods may determine the presence or absence of a foreign object based on measurement results of electrical characteristics at one frequency or multiple frequencies. A method for measuring electrical characteristics at multiple frequencies can be achieved by transmitting a signal (e.g., a sine wave, a square wave, etc.) at each frequency whose electrical characteristics are to be measured multiple times and measuring the electrical characteristics of each signal at each frequency. This method has the advantage of enabling measurements with relatively little computational processing in the power transmitting device. Alternatively, a signal (e.g., a pulse wave) having all frequency components of the multiple frequencies whose electrical characteristics are to be measured can be transmitted once, and computational processing (e.g., Fourier transform) can be performed on the measurement results to calculate the electrical characteristics at multiple frequencies. Alternatively, a signal having some frequency components of the multiple frequencies at which electrical characteristics are to be measured can be transmitted multiple times, and the measurement results can be subjected to arithmetic processing (e.g., Fourier transform) to calculate the electrical characteristics at multiple frequencies.This method has the advantage of being able to reduce the number of times signals for measurement are transmitted, thereby enabling measurements to be made in a relatively short time. Alternatively, foreign objects may be detected using the results of measurements made by sensors such as photoelectric sensors, eddy current displacement sensors, contact displacement sensors, ultrasonic sensors, image discrimination sensors, and weight sensors mounted on the power transmitting device.

[0097] Furthermore, the contents described in the above-described embodiments can be combined as appropriate.

[0098] [Other embodiments] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0099] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0100] 101 control unit, 103 power transmission unit, 105 power transmission antenna, 303 measurement unit, 304 setting unit, 305 foreign object detection unit, 401 power receiving device, 402 power transmission device

Claims

1. A power transmission device, a power transmitting means for wirelessly transmitting power to a power receiving device; receiving means for receiving identification information of the power receiving device from the power receiving device; a measuring means for measuring a transmission waveform after the power transmitting means transmits a ping to detect an object and before a power transfer phase; an acquisition means for acquiring a quality factor based on an envelope curve indicating the attenuation of the measured transmission wave; a setting means for setting information relating to the acquired quality factor and transmission power, and setting a threshold value based on the information; a determining unit that determines whether a foreign object is present based on the set threshold value during the power transfer phase after the threshold value is set by the setting unit; A power transmission device comprising:

2. A power transmission device as described in claim 1, characterized in that the transmission waveform is a waveform of the voltage applied to the coil versus time.

3. A power transmission device as described in claim 1, characterized in that the transmission waveform is a waveform of the transmission current flowing through the coil over time.

4. A power transmission device described in any one of claims 1 to 3, characterized in that the information is information representing the relationship between transmitted power and quality factor.

5. A method performed by a power transmission device, comprising: a receiving step of receiving identification information of the power receiving device from the power receiving device; a measuring step of measuring a transmission waveform after transmitting a Ping for detecting an object by a power transmitting means that wirelessly transmits power to a power receiving device and before a Power Transfer phase; an acquisition step of acquiring a quality factor based on an envelope curve indicating the attenuation of the measured transmitted wave; a setting step of setting information related to the acquired quality factor and transmission power, and setting a threshold value based on the information; a determining step of determining whether or not a foreign object is present in the power transfer phase based on the set threshold value after the threshold value is set in the setting step; A method performed by a power transmission device, comprising: