Power transmission device and method performed by the same

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 a wireless power transmission technology. [Background technology]

[0002] In recent years, technological development of wireless power transmission systems has been widely carried out. Patent Document 1 discloses a 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 signal for foreign object detection to a power receiving device and determines the presence or absence of a foreign object using an echo signal from the power receiving device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-56959 A [Patent Document 2] JP 2017-70074 A [Patent Document 3] JP 2015-27172 A 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 in order to detect a foreign object, which poses the problem of increased costs and reduced transmission efficiency, as it requires the addition of a circuit for transmitting the foreign object detection signal and time for transmitting the foreign object detection signal.

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

[0006] As one means for achieving the above object, a power transmitting 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 via a power transmitting antenna; A control means for controlling the power transmission by the power transmitting means; a measuring means for measuring a waveform attenuation rate of a transmitted wave in a state where the power transmission is stopped by the control means; a setting means for setting a threshold value used for detecting a foreign object between the power transmitting device and the power receiving device based on the measured waveform attenuation rate; a determination means for determining whether or not the foreign object is present based on the waveform attenuation rate measured by the measurement means and the threshold value after the threshold value is set by the setting means; has. Effect of the Invention

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

[0008] [Figure 1] 2 is a block diagram showing a configuration example of a power transmitting device. FIG. [Diagram 2] 2 is a block diagram showing a configuration example of a power receiving device; [Diagram 3] 4 is a block diagram showing an example of a functional configuration of a control unit of the power transmitting device. FIG. [Figure 4] FIG. 1 is a diagram illustrating a configuration example of a wireless power transmission system. [Diagram 5] FIG. 1 is a sequence diagram for power transmission according to the WPC standard. [Figure 6] 1A to 1C 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 of detecting a foreign object using radio wave transmission during power transmission. [Figure 8]1 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] 11A and 11B are diagrams for explaining a method of setting a foreign object detection threshold value using a waveform attenuation method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] [Embodiment 1] (Configuration of wireless power transmission system) FIG. 4 shows a configuration example of a wireless power transmission system (wireless charging system) in 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 called RX, and the power transmitting device 402 may be called TX. The RX is an electronic device that receives power from the TX and charges an internal battery. The TX is an electronic device that wirelessly transmits power to the RX placed on a charging stand 403, which is a part of the TX. Hereinafter, since the charging stand 403 is a part of the TX, "placed on the charging stand 403" may be "placed on the TX (power transmitting device 402)". The range 404 surrounded by a dotted line is a range in which the RX can receive power from the TX. The RX and the TX may have a function of executing an application 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 the TX may be a tablet, a storage device such as a hard disk device 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 defined by the WPC standard, and may be another method using an electromagnetic induction method, a magnetic field resonance method, an electric field resonance method, a microwave method, a laser, or the like. In addition, in this embodiment, wireless power transmission is used for wireless charging, but wireless power transmission may 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 a power value that is guaranteed to be output to a load (e.g., a charging circuit, a battery, etc.) of the power receiving device even if, for example, the positional relationship between the power receiving device and the power transmitting device changes 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 and transmits power so that it can output 5 watts to the load in the power receiving device, even if the positional relationship between the power receiving antenna and the power transmitting antenna changes and the power transmission efficiency decreases.

[0013] The WPC standard also specifies a method 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 transmitter antenna). More specifically, the standard specifies a power loss method for detecting a foreign object based on the difference between the power transmitted by the power transmitter and the power received by the power receiver, and a Q-factor measurement method for detecting a foreign object based on a change in the quality factor (Q-factor) of the power transmitter antenna (power transmitter coil) in the power transmitter. Foreign object detection using the power loss method is performed during power transmission (power transmission) (Power Transfer phase described later) based on data obtained in the calibration phase described later. Foreign object detection using the Q-factor measurement method is performed before power transmission (before sending a Digital Ping, Negotiation phase or Renegotiation phase described later).

[0014] The RX and TX according to this embodiment communicate for power transmission and reception control based on the WPC standard. In the WPC standard, a plurality of phases are defined, 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 phase before the power transmission may include a selection phase, a ping phase, an identification and configuration phase, a negotiation phase, and a calibration phase. In the following, the identification and configuration phase is called an I&C phase. The processing of each phase will be described below.

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

[0016] In the Ping phase, the TX transmits a Digital Ping with a 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. When the TX is notified of the received voltage value, it transitions to the I&C phase. In addition, before transmitting the Digital Ping, the TX measures the Q-factor of the power transmitting antenna (power transmitting coil). This measurement result is used when executing the foreign object detection process 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 this end, RX transmits an ID packet and a configuration packet. The ID packet contains the identifier information of RX, and the configuration packet contains the device configuration information (capability information) of RX. 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 RX and the power transmission capability of TX. In addition, TX performs foreign object detection processing using the Q-factor measurement method according to the request from RX. The WPC standard also specifies a method of once transitioning to the power transfer phase, and then performing the same processing as in the negotiation phase again at the request of RX. The phase transitioning from the power transfer phase and performing these processing is called the renegotiation phase.

[0019] In the calibration phase, calibration is performed based on the WPC standard. In addition, RX notifies TX of a predetermined received power value (received power value in a light load state / received power value in a maximum load state), and TX performs adjustments to transmit power efficiently. 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 full charge. For this power transmission and reception control, the TX and RX use the same power transmitting antenna (power transmitting coil) and power receiving antenna (power receiving coil) as those used when performing wireless power transmission 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 is possible between the TX and RX is almost the same as the range in which the TX can transmit power.

[0021] (Configuration of power transmitting device and power receiving device) Next, the configuration of the power transmitting device 402 (TX) and the power receiving device 401 (RX) according to this embodiment will be described. Note that the configuration described below is merely an example, and a part (or in some cases, the whole) of the configuration described may be replaced with another configuration performing a similar function or omitted, and further configuration may be added to the configuration described. Furthermore, one block shown in the following description may be divided into multiple blocks, or multiple blocks may be integrated into one block. In addition, although the functions of each functional block shown below are implemented as a software program, some or all of the components included in this functional block may be implemented as hardware.

[0022] Fig. 1 is a functional block diagram showing a configuration example 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 of these functional blocks may be implemented in 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 central processing unit (CPU) or a microprocessor unit (MPU). The control unit 101 may be configured with hardware such as an application specific integrated circuit (ASIC). The control unit 101 may also be configured with an array circuit such as a field programmable gate array (FPGA) compiled to execute a predetermined process. 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 the DC or AC power input from the power supply unit 102 into AC frequency power in a frequency band used for wireless power transmission, and generates electromagnetic waves for receiving power at the RX by inputting the AC frequency power to the power transmitting antenna 105. For example, the power transmitting unit 103 converts the DC voltage supplied by the power supply unit 102 into an AC voltage by a switching circuit in a half-bridge or full-bridge configuration using a FET (Field Effect Transistor). In this case, the power transmitting unit 103 includes a gate driver that controls ON / OFF of the FET.

[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 performs output control of AC frequency power so that power transmission from the power transmitting antenna 105 is started or stopped based on an instruction from the control unit 101. Furthermore, the power transmitting unit 103 is assumed to have a capacity to supply 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 performs communication with the RX for power transmission control based on the WPC standard as described above. The communication unit 104 modulates the 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 perform communication with the RX by communication based on a standard other than the WPC standard using an antenna other than the power transmitting antenna 105, or may perform communication with the RX by selectively using multiple communications.

[0028] The memory 106 can store the control program and also 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 one 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 a plurality of 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) being executed.

[0032] The control unit 201 may be configured with hardware such as an ASIC. The control unit 201 may be configured to include an array circuit such as an FPGA compiled to execute a predetermined process. The control unit 201 stores information to be stored during execution of various processes in the memory 208. The control unit 201 may 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, a speaker, a 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. Then, the power receiving unit 203 converts the AC power into DC or AC power of a predetermined frequency, and outputs the power to the charging unit 206 that performs processing for charging the battery 207. That is, 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 is assumed to have the capacity to supply power for the charging unit 206 to charge the battery 207 and to output 15 watts of power to the charging unit 206.

[0035] The switch unit 209 is for controlling whether or not the received power is supplied to the battery (load). It also has a function of controlling the value of the load. If the switch unit 209 connects the charging unit 206 and the battery 207, the received power is supplied to the battery 207. If the switch unit 209 disconnects the charging unit 206 and the battery 207 by the switch, the received power is not supplied to the battery 207. Note that the switch unit 209 is disposed between the charging unit 206 and the battery 207 in FIG. 2, but may be disposed between the power receiving unit 203 and the charging unit 206. Alternatively, the switch unit 209 is illustrated as one block in FIG. 2, but the switch unit 209 can be realized as a part of the charging unit 206. The communication unit 204 performs communication for power receiving control based on the WPC standard as described above with the communication unit 104 of the TX. The communication unit 204 demodulates the electromagnetic wave input from the power receiving antenna 205 to acquire information transmitted from the TX. The communication unit 204 performs communication with the TX by load modulating the input electromagnetic wave to superimpose a signal related to information to be transmitted to the TX on the electromagnetic wave. The communication unit 204 may communicate with the TX by communication according to a standard other than the WPC standard using an antenna other than the power receiving antenna 205, or may selectively use multiple communications to communicate with the TX.

[0036] The memory 208 stores the control program, as well as 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 transmission unit 103 and controls power transmission to the RX. The measurement unit 303 measures a waveform attenuation factor, which will be described later. In addition, the measurement unit 303 measures the power output to the RX via the power transmission unit 103, and measures the average output power per unit time. In addition, the measurement unit 303 measures the Q value of the power transmission antenna (power transmission 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 a calculation process.

[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 a foreign object detection process 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 a foreign object detection process using a counterpart device detection function according to the NFC standard. The foreign object detection unit 305 can also detect a change in the state of the TX as a function other than detecting a foreign object. 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 is 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 is a reference for determining the presence or absence of a foreign object, which is necessary when performing a foreign object detection process 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, the power transmission control unit 302, the measurement unit 303, the setting unit 304, and the 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 synchronizing 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 described with reference to the sequence diagram of Fig. 5. Fig. 5 is a sequence diagram for power transmission according to the WPC standard. Here, the explanation will be given by taking the power transmitting device 402 (TX) and the power receiving device 401 (RX) as examples.

[0041] The TX repeatedly transmits an Analog Ping of the WPC standard intermittently to detect an object present within the 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. The user of the RX brings the RX (e.g., a smartphone) close to the TX to charge the RX (F502). For example, the RX is brought close to the TX by placing the RX on the TX. When the TX detects that an object exists within the power transmission range (F503, F504), it transmits a Digital Ping of the WPC standard (F505). When the RX receives the Digital Ping, it can know that the TX has detected the RX (F506). When a predetermined response to the Digital Ping is received, the TX 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 is placed, the TX acquires the identification information and capability information from the RX through communication in the I&C phase defined by the WPC standard (F507). Here, the identification information of the RX includes a Manufacturer Code and a Basic Device ID. The capability information of the RX includes an information element capable of identifying the version of the WPC standard supported, a Maximum Power Value that is a value that identifies the maximum power that the RX can supply to a load, and information indicating whether or not the RX has a negotiation function in 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 be any other identification information capable of identifying an individual RX, such as a Wireless Power ID. The capability information may include information other than the above.

[0042] Next, TX determines the values ​​of RX and GP 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. Also, when TX acquires information indicating that RX does not support the negotiation phase (for example, in F507), it may not perform communication in the negotiation phase and may set the GP value to a small value (for example, predefined by 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). The first reference received power information in this embodiment 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) defined in the WPC standard, but other messages may be used. The TX judges whether or not to accept the first reference received power information based on the power transmission state of its own device. If the TX accepts, the TX transmits a positive response=ACK to the RX, and if not, the TX transmits a negative response=NAK to the RX.

[0044] Next, when RX receives an ACK from TX (F510), it is necessary to transmit information including the received power in a load connection state (load state in which the transmitted power is equal to or greater than the second threshold) to TX (hereinafter referred to as second reference received power information). 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) defined in the WPC standard, but other messages may be used. RX transmits a transmission 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 transmission power output change instruction and is able 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 transmission power output change instruction to suppress the transmission of power above the regulation (F515).

[0046] When the RX judges 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 connection state to the TX as second reference received power information (F516). The TX can calculate the amount of power loss between the TX and the RX based on the transmission power value of the TX and the received power value included in the first and second reference received power information, and can calculate the power loss value between the TX and the RX at all the transmission powers of the TX (in this case, the TX transmission power is from 250 milliwatts to 5 watts) by interpolating them (F517). The TX transmits an ACK in response to the second reference received power information from the RX (F518), and completes the calibration process. The TX, which judges that the charging process can be started, starts the power transmission process to the RX, and the charging of the RX starts. Then, the TX and the RX perform device authentication process (F519), and when it is found that the devices of both devices are compatible with a larger GP, the GP may be reset to a larger value, here 15 watts (F520).

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

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

[0049] In this way, during the power transfer phase, foreign object detection is performed using the power loss method. However, with only one foreign object detection method, there is a possibility of erroneous detection of a foreign object, or of erroneously determining that a foreign object is not present even though it is present. In order to further improve the accuracy of foreign object detection, it is generally desirable to perform a combination of multiple foreign object detection methods. In particular, the power transfer phase is a phase in which the TX transmits power, and if a foreign object is mixed between the TX and RX during power transmission, heat generation from the foreign object increases, so it is desirable to perform multiple foreign object detections in this phase to improve the accuracy of foreign object detection. Therefore, in this embodiment, a foreign object detection method different from 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 power transmission waveform, foreign object detection becomes possible without configuring a new signal for foreign object detection or the like. A method for detecting foreign objects using a power transmission waveform and based on the attenuation state of the transmission wave (hereinafter referred to as the waveform attenuation method) will be described with reference to FIG. 6. FIG. 6 is a diagram for explaining the principle of foreign object detection using the waveform attenuation method. Here, a power transmitting device 402 (TX) and a power receiving device 401 (RX) will be described as an example.

[0051] In FIG. 6, the waveform shows the time course of a voltage value 600 (hereinafter, simply referred to as voltage value) of a high-frequency voltage applied to a power transmitting antenna (power transmitting coil) of TX, with the horizontal axis being time and the vertical axis being voltage value. TX transmits power to RX via a power transmitting antenna, and stops power transmission at time T0, and application of the high-frequency voltage to the power transmitting antenna (power transmitting coil) is stopped. The frequency of the transmitting wave transmitted from TX is a predetermined (fixed) frequency. The frequency is between 85 kHz and 205 kHz used in the WPC standard. Point 601 is a part of the envelope of the high-frequency voltage, and is the voltage value at time T1. (T1, A1) in the figure indicates that the voltage value at time T1 is A1. Similarly, point 602 is a part of the envelope of the high-frequency voltage, and is the voltage value at time T2. (T2, A2) in the figure indicates that the voltage value at time T2 is A2. At this time, the quality factor (Q value) of the power transmitting antenna can be obtained based on the time change of the voltage value after time T0. Specifically, for example, it is calculated by Equation 1 based on the time, voltage value, and frequency f of the high frequency voltage at points 601 and 602 which are the envelope of the voltage value. Q = πf(T2-T1) / ln(A1 / A2) (Equation 1) When a foreign object is present between TX and RX, the Q value decreases. This is because a foreign object causes a loss of energy. Therefore, when the slope of the attenuation of the waveform is considered, the slope of the line connecting points 601 and 602 becomes steeper and the attenuation rate of the waveform becomes higher when a foreign object is present than when there is no foreign object, because a loss of energy occurs due to the foreign object. In other words, the waveform attenuation method judges the presence or absence of a foreign object from the attenuation state of points 601 and 602, and it is possible to judge the presence or absence of a foreign object by comparing some numerical value that represents this attenuation state. For example, the above-mentioned comparison of the Q value may be used. A lower Q value means that the waveform attenuation rate becomes higher. Alternatively, a comparison of the slope of the line connecting points 601 and 602 obtained from (A1-A2) / (T2-T1) may be used. Alternatively, if the time for observing the attenuation state of the waveform is fixed, a comparison of the value of (A1-A2) that represents the difference in voltage values ​​or the value of the ratio of voltage values ​​(A1 / A2) may be used. 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) until the voltage value A1 reaches 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 the power transmission is stopped, and there are multiple values ​​that represent the attenuation state. The value that represents this attenuation state is hereinafter referred to as the "waveform attenuation rate." As described above, the Q value calculated by Equation 1 is also a value that represents the attenuation state of the waveform, so it is included in the "waveform attenuation rate." Also, the vertical axis of FIG. 6 has been described as the voltage value applied to the power transmission antenna (coil), but even if it is the current value flowing through the power transmission antenna (coil), the attenuation state of the waveform changes depending on the presence or absence of a foreign object after the power transmission is stopped, as in FIG. 6, and if a foreign object is present, the attenuation rate becomes higher. Therefore, it is possible to determine the presence or absence of a foreign object and detect a foreign object from 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 value reaches a predetermined value, etc. by applying the above-mentioned method to the current value flowing through the power transmission antenna (coil). In the above, the TX measures the waveform attenuation rate when power transmission is stopped, but the power transmitting device may measure the waveform attenuation rate when the power transmission power (voltage, current) is reduced to a predetermined value.

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

[0054] When it is time to detect a foreign object, the TX stops transmitting power ("Power transmission stop" in FIG. 7). Then, the transmitting power waveform attenuates, and by calculating and using the waveform attenuation rate (Q value, or attenuation slope, etc.) from this attenuated waveform, it becomes possible to detect a foreign object ("Foreign object detection period" in FIG. 7). Then, after a predetermined time has elapsed, the TX resumes transmitting power ("Power transmission resumed" in FIG. 7). As described above, the transmitting power waveform is not stable during the transient response period ("Transient response period" in FIG. 7) immediately after the TX starts transmitting power ("Power transmission start" in FIG. 7). Therefore, during this transient response period when the transmitting power waveform is not stable, the RX controls the TX so that it does not communicate with the TX (communication by load modulation). Also, the TX controls the RX so that it does not 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 stop" in FIG. 7). Then, 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 elapsed, 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] (Treatment of power transmission equipment when applying the waveform attenuation method to the WPC standard) Next, we will briefly explain the processing of the power transmitting device when detecting a foreign object by applying this waveform attenuation method in the WPC standard. When detecting a foreign object 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 as a reference. The power transmitting device executes 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 in a state where no foreign object is present will be described. In the WPC standard, foreign object detection is performed in the negotiation phase using the Q-value measurement method as described above. If it is determined that no foreign object is present as a result of the foreign object detection, the process proceeds to the calibration phase and the power transfer phase. In other words, proceeding to the negotiation phase or later means that it is determined that no foreign object is present as a result of the foreign object detection using the Q-value measurement method. Therefore, if the waveform attenuation rate is measured in any of the negotiation phase, calibration phase, and power transfer phase, there is a high possibility that the waveform attenuation rate in a state where no foreign object is present can be measured (because it is determined that no foreign object is present in the negotiation phase by the foreign object detection using the Q-value measurement method). Therefore, the timing for measuring the waveform attenuation rate in a state where no foreign object is present may be any of the negotiation phase, calibration phase, and power transfer phase.

[0057] In this embodiment, a case where the measurement is performed during the power transfer phase will be described. The timing for measuring the waveform attenuation rate in a state where there is no foreign object is set to the first stage of the power transfer phase. The reason is that the more time passes, the higher the probability that a foreign object will be introduced between the power transmitting device and the power receiving device. Then, at the timing for foreign object detection designated 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 value calculated from the waveform attenuation rate in a state where there is no foreign object as described above, and determines whether or not there is 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, a description will be given taking the power transmitting device 402 (TX) and the power receiving device 401 (RX) as examples. As described above, in this embodiment, it is assumed that 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 the process of setting the threshold value for foreign object detection by the waveform attenuation method will be described. When the wireless power transmission system enters the power transfer phase, TX starts power transmission (S801, F1001), and RX starts power reception (S901). At this stage, RX turns off the switch unit 209 and disconnects the load of RX (battery 207) (F1002). Immediately after TX starts power transmission, RX determines whether or not a communication prohibition period (predetermined time) has elapsed (S902, F1003). This is because the transmission waveform is not stable until the communication prohibition period has elapsed, and therefore RX waits until it stabilizes to a steady state. After the communication prohibition period has elapsed, RX determines whether or not to measure the waveform attenuation rate (S903, F1004). If the threshold value 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, RX transmits an instruction to TX to measure the waveform attenuation rate via the communication unit 104 (S904, F1005). The instruction is a command to request TX to measure the waveform attenuation rate in order to set a threshold for detecting a foreign object using the waveform attenuation method. Then, RX disconnects the switch unit 209 and disconnects the load of RX (battery 207) (S905, F1006). Note that this disconnection of the switch unit 209 may be performed before the command transmission (S904).

[0060] Here, the reason for disconnecting the load of RX (battery 207) will be described. The waveform attenuation rate varies depending on the load of RX (battery 207) or the state of the power transmission 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), and then the measurement is performed. The TX judges whether or not an instruction to measure the waveform attenuation rate has been received from the RX through the communication unit 104 (S802). If an instruction has been received (YES in S802), the TX judges whether or not the content of the received instruction is the measurement of the waveform attenuation rate for determining the threshold value (S803, F1007). If the received instruction is a command requesting the measurement to set the threshold value for foreign object detection (YES in S803), the TX temporarily stops (instantaneous interruption) the 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 the 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 obtained 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 power transmission waveform becomes steady (S906, F1012). The reason for waiting for a predetermined time here is that if the power transmission waveform during power transmission is not stable (not in a steady state), there is a possibility that overpower may be applied to RX. After the predetermined time has passed, RX connects a load (battery 207) (S907, F1013). RX determines whether or not to request the power transmission to be stopped, for example, because the battery 207 is fully charged (S908). If it is determined that the power transmission is to be stopped (YES in S908), RX requests the power transmission to be stopped by transmitting an EPT (End Power Transfer) command to TX (S909) and ends the process (S910). If the power transmission is not to be stopped in S908 (NO in S908), RX starts power reception (S911). Through the above operations, the TX can measure the waveform attenuation rate when there is no foreign object, and use the results to set a threshold value required for determining whether or not there is a foreign object.

[0062] (2) Foreign object detection operation Next, the operation of detecting a foreign object will be described. TX is transmitting power (S801), and RX is receiving power (S901). RX judges whether the communication prohibition period has elapsed (S902, F1014). After the communication prohibition period has elapsed, RX judges whether to measure the waveform attenuation rate (S903, F1015). RX judges to measure the waveform attenuation rate in order to perform foreign object detection to confirm whether a foreign object exists. In this case, RX transmits an instruction to TX to perform waveform attenuation rate measurement via the communication unit 104 (S904, F1016). The instruction is a command to request TX to perform foreign object detection by the waveform attenuation method (to perform judgment on 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 the command transmission (S904). The reason for disconnecting the load of RX is as described above. The TX judges whether or not an instruction to perform waveform attenuation rate measurement has been received from the RX through the communication unit 104 (S802). If the instruction has been received (YES in S802), the TX judges whether or not the received instruction is for measuring the waveform attenuation rate to determine the threshold (S803, F1018). If the received instruction is a command requesting foreign object detection (determination of the presence or absence of a foreign object) using the waveform attenuation method (NO in S803), the TX temporarily stops (instantaneous interruption) the 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 the power transmission is stopped. Next, the TX compares the threshold calculated in S806 with the waveform attenuation rate measured in S810 to judge the presence or absence of a foreign object (S811, F1021). If it is determined that there is a foreign object (YES in S812), the TX stops power transmission (S815, F1023) and ends the process (S816). If it is determined that there is no foreign object (NO in S812), the TX determines whether or not there is an instruction to stop power transmission from the RX (whether an EPT command has been received) (S813). If there is an instruction to stop power transmission (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] RX waits for a predetermined time until 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 passed, RX connects a load (battery 207) (S907). RX determines whether or not to request power transmission to 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), RX requests power transmission to be stopped by transmitting an EPT command to TX, and ends the process (S910). Here, if TX determines that "foreign object is present" (YES in S812), and RX determines that power transmission from TX is not being performed, RX requests power transmission to be stopped by transmitting an EPT command to TX (F1024), and ends the process (S910). This allows power transmission to be normally ended. Alternatively, RX may end without transmitting an EPT command to TX (S910) and transition to a reset state (Stand-By state). In S908, if RX does not request that power transmission be stopped (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 rate, the load of RX is disconnected in advance to eliminate the influence of the load of RX beforehand, and then the measurement is performed. Alternatively, when measuring the waveform attenuation rate, the value of the load of RX may be controlled in advance to reduce the influence of the load of RX beforehand, and then the measurement may be performed. For example, this can be achieved by controlling the load so that the load of RX is in a light load state (light load state) so that only a small amount of power is supplied to RX.

[0065] In the above embodiment, the timing of the measurement of the waveform attenuation rate by the TX is realized by an instruction from the RX to the TX (S803). Alternatively, the timing can be determined by the TX and notified to the RX. Specifically, for example, instead of the processes of S802 and S803 in FIG. 8, the TX first determines whether or not the communication prohibition period has elapsed. After the communication prohibition period has elapsed, the TX determines whether or not to measure the waveform attenuation rate for determining the threshold value. Alternatively, the TX determines whether or not to measure the waveform attenuation rate for detecting the presence or absence of a foreign object. When the TX determines to measure the waveform attenuation rate, the TX determines the timing of the measurement of the waveform attenuation rate and notifies the RX of the timing. At the same time, the TX may notify the RX that the measurement of the waveform attenuation rate is for determining the threshold value if the measurement is for determining the threshold value, and may notify the RX that the measurement is for detecting the presence or absence of a foreign object if 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 of the measurement, and turns off the load of the RX (battery 207). Alternatively, the load of the RX (battery 207) is controlled so that the value of the load is in a light load state (light load state). In this way, the TX can measure the waveform attenuation rate. The timing of the measurement of the waveform attenuation rate by the TX may be configured to be performed 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 the value of the load is in a light load state (light load state). The TX may be configured to proceed to S804 when a user instructs to set a threshold value for foreign object detection, and to proceed to S809 when a user instructs to perform foreign object detection. The user's instruction can be realized by a predetermined input / operation to the TX.

[0066] In the above-described embodiment, the method has been described in which the TX measures the voltage applied to the TX 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, since 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, it is also possible for the RX to measure the voltage applied to the RX 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] Also, when the TX measures the waveform attenuation rate, the TX may notify the RX of the waveform attenuation rate or a threshold value calculated from the 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, the RX may notify the TX of the waveform attenuation rate or a threshold value calculated from the waveform attenuation rate. This allows the TX side to determine whether or not there is a foreign object.

[0068] In the above 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 the threshold value is calculated based on the measured waveform attenuation rate. Then, foreign object detection is performed using the waveform attenuation method, and if the measured waveform attenuation rate is greater than the threshold value, it is determined that "foreign object is present," and if the measured waveform attenuation rate is smaller than the threshold value, it is determined that "foreign object is not present." However, foreign object detection may be performed by comparing the measured waveform attenuation rate with a threshold value calculated from a previous waveform attenuation rate measured at a timing when it is assumed that no foreign object is present. For example, first, it is confirmed that no foreign object is present 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 it has been confirmed in advance that no foreign object is present 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. At this time, foreign object detection can be performed 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. In other words, when detecting a foreign object using the waveform attenuation method, it can also be realized by comparing the waveform attenuation rate with a waveform that is considered to have been measured in a state in which no foreign object is present, or with a threshold value.

[0069] In the above embodiment, the frequency of the transmitting wave transmitted from the TX is a predetermined (fixed) frequency. However, a plurality of frequencies may be used, and the operation for detecting a foreign object 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. By detecting a foreign object using not only the waveform attenuation rate at one predetermined (fixed) frequency, but also the waveform attenuation rates at a plurality of frequencies, it becomes possible to perform foreign object detection with higher accuracy.

[0070] In this embodiment, immediately after the TX stops transmitting power or immediately after it starts transmitting power, the transmitting power waveform is unstable due to a transient response, so a waiting time is provided before moving to each operation. However, the reason why the transmitting power waveform becomes unstable is caused by suddenly starting or stopping the transmitting power. Therefore, in order to alleviate this, the TX may control the transmitting power to increase in stages when starting the transmitting power. Alternatively, when stopping / pausing the transmitting power, the transmitting power may be controlled to decrease in stages.

[0071] [Embodiment 2] In the first embodiment, a method for controlling the power receiving device to measure the waveform attenuation rate after disconnecting the load of the power receiving device in order to eliminate the influence of the load of the power receiving device when the power transmitting device stops power transmission and measures the waveform attenuation rate of the transmitted wave is described. However, this method requires the power receiving device to disconnect and connect the load at a predetermined timing, which takes time and may cause a decrease in power transmission efficiency. In the present embodiment, a method for measuring the waveform attenuation rate while keeping the load of the power receiving device connected without disconnecting it is described.

[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 in each state (each transmission power value) of the load on the power receiving device side in a state in which there is no foreign object, and sets a threshold value used for determining the presence or absence of a foreign object in each state (each transmission power) of the load on the power receiving device side based on the measurement result. When detecting a foreign object, the power transmitting device measures the waveform attenuation rate without disconnecting the load of 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 process flow by the power transmitting device 402 (TX) and the power receiving device 401 (RX) will be described below. The configuration, process flow, and operation sequence of the TX and RX are basically the same as those in the first embodiment. The difference is in the method of measuring the waveform attenuation rate in S805 when the instruction received by the TX from the RX is a command requesting the implementation of measurement for setting the threshold for foreign object detection (YES in S803). The method by which the TX and RX in this embodiment implement measurement for setting 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 for explaining a method of setting a foreign object detection threshold by 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 a very small amount of power is supplied. The transmission power of TX at this time is Pt1. Then, TX stops power transmission in that state (S804) and measures the waveform attenuation rate (S805). The waveform attenuation rate at this time is δ1. At this time, TX associates the transmission power Pt1 (the power transmitting device recognizes the transmission power Pt transmitted by the power transmitting device) with the waveform attenuation rate δ1 and stores them in the memory (point 1100). Next, RX controls the load of RX to be in a load connected state (Connected Load state) so that the maximum power is supplied to the load of RX or a power equal to or greater than a predetermined threshold is supplied to the load of RX when power is transmitted from TX. The transmission power of TX at this time is Pt2. Then, the TX stops transmitting power in that state (S804) and measures the waveform attenuation rate (S805). At this time, the TX associates the transmission power Pt2 with the waveform attenuation rate δ2 and stores them in the memory (point 1101). Next, the TX linearly interpolates the points 1100 and 1101 to create a line 1102. The line 1102 shows the relationship between the transmission power and the waveform attenuation rate of the transmission wave in a state where there is no foreign object around the TX and RX. Therefore, the TX can predict the waveform attenuation rate of the transmission wave for each transmission power value in a state where there is no foreign object from the transmission power value and the line 1102. For example, when the transmission power value is Pt3, it can be predicted that the waveform attenuation rate is δ3 from the point 1103 on the line 1102 that indicates the transmission power value Pt3. Based on this line 1102, the TX can predict the waveform attenuation rate of the transmission wave for each transmission power value. Then, based on these, the TX can calculate a threshold value used for determining the presence or absence of a foreign object for each transmission power value in a state in which no foreign object is present.

[0075] In addition, RX may perform the control for the load to be in a no power supply / light load state (first control) and the control for the load to be in a load connection 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 disconnects the load of the RX when foreign object detection is performed (determining whether or not a foreign object is present). However, in the present embodiment, the RX does not need to disconnect the load when foreign object detection is performed (determining whether or not a foreign object is present). Since the TX can recognize the transmission power value transmitted by the TX when foreign object detection is performed (determining whether or not a foreign object is present), it is possible to determine whether or not a foreign object is detected by comparing the transmission power value with the threshold calculated from FIG. 11. That is, in the present embodiment, a threshold is set for each load (transmission power value), so that when foreign object detection is performed (determining whether or not a foreign object is present), 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 load of the RX as in the first embodiment.

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

[0078] In addition, the operation for calculating the threshold value used for determining the presence or absence of a foreign object for each load (each transmission 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 detecting a foreign object by 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 load connected state (connected load state). Therefore, the measurement of points 1100 and 1101 in FIG. 11 can be realized by measuring together when the RX is in a light load state (light load state) and a load connected state (connected load state) in the above-mentioned calibration phase. That is, when the TX receives the first reference received power information from the RX, in addition to the process to be performed in the calibration phase, the TX measures the point 1100. Also, when the TX receives the second reference received power information from the RX, in addition to the process to be performed in the calibration phase, the TX measures the point 1101. By doing so, it becomes unnecessary to provide a separate process for measuring points 1100 and 1101, and it becomes possible to measure points 1100 and 1101 in a shorter time.

[0079] [Embodiment 3] In the second embodiment, a method has been 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 which a threshold value for detecting a foreign object 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 in the second embodiment. Here, a description will be given taking 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 threshold value for detecting a foreign object is calculated by linearly interpolating (straight line 1102) the waveform attenuation rate when the TX transmission power is at its minimum (point 1100) and the waveform attenuation rate when the TX transmission power is at its maximum (point 1101) in a state where there is no foreign object. However, the linearly interpolated straight line 1102 in FIG. 11 may change when the state of the TX or RX changes. For example, this is the case when the temperature of the TX or RX rises. 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 the internal circuitry. Alternatively, when the RX is a mobile PC or a smartphone, the temperature may rise due to the use of an application or the like and data processing. The rise in temperature brings about a change in the shape of the TX or RX housing and a change in the electrical characteristics of each component of the electrical circuit. These occurrences cause the straight line 1102 in FIG. 11 to change, and the waveform attenuation rate in a state where there is no foreign object for each transmission power value changes. In this case, the foreign object detection threshold for each transmission power value must be calculated again. Or, even 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 in a state where there is no foreign object changes. In this case, the foreign object detection threshold for each transmission power value must be calculated again. Or, for example, as shown in F519 and F520 in FIG. 5, there is a possibility that the GP or maximum power to be transmitted may be changed when the devices authenticate each other. If the GP or maximum power is changed, it is necessary to plot the relationship between the transmission power and the waveform attenuation rate for a transmission power that is larger 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 the transmission power and the waveform attenuation rate shown in FIG. 11.

[0081] When the RX determines that there is a change in the state of the TX or the RX as described above and that it is necessary to update or add the threshold value used for foreign object detection, the RX transmits a command to the TX to request 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). Then, 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 rate is to be updated or added. When the TX receives the command, the TX suspends the power transmission (S804) and measures the waveform attenuation rate of the transmission wave (S805). Then, the TX associates the transmission power with the measured waveform attenuation rate and updates or adds the relationship between the transmission power and the waveform attenuation rate shown in FIG. 11. Then, the TX calculates the threshold value for foreign object detection based on the calculation, and updates or adds the threshold value. After that, the TX uses the threshold value to determine the presence or absence of a foreign object. In the above-mentioned embodiment, the determination of whether or not the threshold value used for foreign object detection needs to be updated or added is realized by the RX. Alternatively, the TX can perform the determination, and if it is determined that the threshold value used for foreign object detection needs to be updated or added as a result of the determination, it can be realized by notifying the RX of that effect. Specifically, for example, when the TX or RX state change occurs as described above and the TX 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 a measurement 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. When the RX receives the notification, it 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. When the load control is completed, the RX notifies the TX that the load control is completed. When the TX receives the notification, it suspends the power transmission (S804) and measures the waveform attenuation rate of the transmission wave (S805). Then, the TX associates the transmission power with the measured waveform attenuation rate and updates or adds the relationship between the transmission power and the waveform attenuation rate shown in FIG. 11. Then, the TX calculates the threshold value for detecting a foreign object based on the calculated threshold value, and updates or adds a new threshold value. After that, the TX uses the calculated 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 Fig. 8 to Fig. 10, in the above embodiment, the determination of the presence or absence of a foreign object by 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 the presence or absence of a foreign object during the power transfer phase, it transmits a command to the TX requesting the implementation of foreign object detection by the waveform attenuation method (implementation of the determination of the presence or absence of a foreign object). Then, the TX receives the command, performs foreign object detection, and determines the presence or absence of a foreign object.

[0084] On the other hand, the WPC standard specifies a foreign object detection method using the power loss method as a method for detecting a foreign object during the power transfer phase. Specifically, when the power receiving device determines that it is necessary to determine the presence or absence of a foreign object, the power receiving device transmits a command to the power transmitting device requesting the power loss method to detect a foreign object (to determine the presence or absence of a foreign object). The power transmitting device then receives the command, detects a foreign object, and determines the presence or absence of a foreign object.

[0085] As described above, if a foreign object is present between the power transmitting device and the power receiving device in the power transfer phase in which the power transmitting device transmits power, heat generation from the foreign object will increase, so it is desirable to perform multiple foreign object detections in this phase to improve the accuracy of foreign object detection. In consideration of this, in this embodiment, two methods, the power loss method and the waveform attenuation method, are combined to perform 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 the power loss method and the waveform attenuation method for foreign object detection during the power transfer phase. 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 for 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 depend on the foreign object detection results using a single method.

[0087] The second method is a method to stop power transmission when it is determined that there is a foreign object 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 detects foreign objects 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 using both methods, it controls to stop power transmission. Power transmission is stopped only when it is determined that there is a foreign object using both the power loss method and the waveform attenuation method, making it possible to reduce the probability of erroneously determining that there is a foreign object.

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

[0089] The fourth method is a method in which, when two foreign object detection methods give 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 power transmission control is appropriately performed. The TX performs foreign object detection using the power loss method, and even if the power loss method judges that "foreign object is present," foreign object detection is performed using the waveform attenuation method. Then, if the waveform attenuation method judges that "no foreign object is present," foreign object detection is performed again using either 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 judges that "no foreign object is present," foreign object detection is performed using the waveform attenuation method. Then, if the waveform attenuation method judges that "foreign object is present," foreign object detection is performed again using either 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" and "no foreign object" using the power loss method and the waveform attenuation method, respectively, and judges whether to continue or stop power transmission, and performs appropriate power transmission control. For example, the number of times a foreign object is determined to be present may be compared with the number of times a foreign object is determined to be absent, and the more of these may be used as the final determination result. Alternatively, for example, if there are cases in which a foreign object is determined to be present using both the power loss method and the waveform decay method, the final determination result may be "foreign object present." Alternatively, for example, if there are cases in which a foreign object is determined to be absent using both the power loss method and the waveform decay method, the final determination result may be "no foreign object." If the two methods produce different determination results regarding the presence or absence of a foreign object, foreign object detection may be performed again using one of the methods, and a comprehensive determination may be made based on the multiple determination results, making it possible to make an appropriate determination based on each determination result.

[0090] In the above-mentioned four methods, the case where two judgment results, "foreign object present" and "foreign object absent", are obtained as the judgment result of foreign object detection has been described. As described in the first, second and third embodiments, the judgment of foreign object detection is performed based on whether the measured value is greater or smaller than the calculated threshold value. However, even when it is judged that "foreign object absent", there may be a case where the margin for the threshold value is small and the presence of a foreign object is suspected. Even in the case where the presence of a foreign object is suspected, it is possible to perform more accurate foreign object detection by applying the above-mentioned four methods. Specifically, in the above-mentioned four methods, the process when it is judged that "foreign object present" is present may also be performed when it is judged that "foreign object presence is suspected". Here, the case where it is judged that "foreign object presence is suspected" can be realized by setting a new threshold value that is a predetermined margin added to the threshold value used for judging the presence or absence of a foreign object, and making a judgment based on the new threshold value. This enables more accurate foreign object detection. In addition, in the above-mentioned four methods, the foreign object detection is first performed by the power loss method, and then the foreign object detection is performed by the waveform attenuation method. The reason for this is as follows. The power loss method can be performed without stopping the power transmission from TX to RX, but the waveform attenuation method requires the power transmission from TX to RX to be temporarily stopped, which reduces the power transmission efficiency. Therefore, there are cases where the power transmission efficiency can be suppressed from decreasing by performing foreign object detection first using the power loss method and then using the waveform attenuation method. However, the same effect can be obtained by performing foreign object detection first using the waveform attenuation method and then using the power loss method in the above four methods.

[0091] [Embodiment 5] In the first embodiment, the timing for measuring the waveform attenuation rate in a state where no foreign object is present, which is necessary for creating a threshold (standard) for detecting foreign objects using the waveform attenuation method, is set to be any of the negotiation phase, calibration phase, and power transfer phase. In the WPC standard, foreign object detection using the Q-value measurement method is performed in the negotiation phase as described above, so that the fact that the phase has progressed beyond the negotiation phase means that the result of foreign object detection using the Q-value measurement method indicates that no foreign object is present. Therefore, if the waveform attenuation rate is measured in any of the negotiation phase, calibration phase, and power transfer phase, there is a high possibility that the waveform attenuation rate in a state where no foreign object is present can be measured.

[0092] However, if a foreign object is introduced between the power transmitting device and the power receiving device during the period from when it is confirmed that no foreign object is detected by the Q-value measurement method in the negotiation phase until the measurement of the waveform attenuation rate without the foreign object is performed in either the negotiation phase, the calibration phase, or the power transfer phase, the measurement of the waveform attenuation rate without the foreign object cannot be performed accurately. Therefore, ideally, it is desirable to confirm that there is no foreign object immediately before measuring the waveform attenuation rate without the foreign object. A method for achieving this will be described below. The following description will be given taking the power transmitting device 402 (TX) and the power receiving device 401 (RX) as an example.

[0093] For example, when RX detects that the state of TX or RX has changed and judges that it is necessary to update or add a threshold value used for foreign object detection by the waveform attenuation method (embodiment 3), RX transmits a command to TX to execute foreign object detection by the power loss method. TX executes foreign object detection by the power loss method and judges the presence or absence of a foreign object. As a result, when it is judged that there is no foreign object, TX notifies RX that there is no foreign object, and RX executes an operation to update or add a threshold value used for foreign object detection by the waveform attenuation method. That is, RX transmits a command to TX to request the execution of measurement to set a threshold value for foreign object detection by the waveform attenuation method as described in embodiments 1 and 2. Then, RX controls the load so that the transmission power is at a point where the relationship between the transmission power and the waveform attenuation rate is to be updated or added. When TX receives the command, it suspends power transmission and measures the waveform attenuation rate of the transmission wave. Then, TX uses the measured waveform attenuation rate to calculate a threshold value for foreign object detection by the waveform attenuation method and sets it as the threshold value.

[0094] In this way, when the RX decides to update / change the threshold for the waveform attenuation method, it checks for the absence of foreign objects using the power loss method immediately before performing the operation to update / change the threshold for the waveform attenuation method, and then performs the operation to update / change the threshold for the waveform attenuation method.This makes it extremely likely that there will be no foreign objects 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 of confirming the absence of foreign objects using the power loss method immediately before performing the operation to update or change the threshold value of the waveform attenuation method. However, the power loss method also has a threshold value for determining the presence or absence of foreign objects, and as with the waveform attenuation method, when the state of TX or RX changes, it becomes necessary to update or add the threshold value. This can also be done in the power transfer phase. Therefore, as with the above method, when RX decides to update or change the threshold value of the power loss method, it can also perform the operation to update or change the threshold value of the power loss method after confirming the absence of foreign objects using the waveform attenuation method immediately before performing the operation. In other words, for example, when RX detects that the state of TX or RX has changed and determines that it is necessary to update or add the threshold value used for foreign object detection using the power loss method, RX sends a command to TX to perform foreign object detection using the waveform attenuation method. TX performs foreign object detection using the waveform attenuation method and determines the presence or absence of foreign objects. If it is determined that no foreign object exists as a result, TX notifies RX that no foreign object exists, and RX performs the operation to update or add the threshold value used for foreign object detection using the power loss method. That is, in order to update or add a threshold value used for foreign object detection, RX sends a command requesting a measurement to set the foreign object detection threshold value using the power loss method. Then, RX controls the load so that the transmission power is the threshold value (point) to be updated or added. When TX receives the 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, making it possible to set a more accurate foreign object detection threshold value.

[0096] [Variations] The power loss method described in the above embodiment is an example of another foreign object detection method different from the waveform attenuation method. Therefore, another foreign object detection method may be used instead of the above power loss method. For example, a Q value measurement method may be used. As a method for measuring the Q value, there is a method of transmitting a signal of a resonance frequency (e.g., a sine wave, a square wave, etc.) and measuring the Q value at the resonance frequency. Alternatively, there is a method of transmitting signals of multiple frequencies near the resonance frequency multiple times and measuring their Q values. Alternatively, there is a method of transmitting a signal (e.g., a pulse wave) having all or some frequency components of multiple frequencies whose electrical characteristics are to be measured once, and performing arithmetic processing (e.g., Fourier transform) on the measurement result to measure the Q value at multiple frequencies. Alternatively, there is a method of transmitting a predetermined signal (not power transmission, but a signal) and then stopping the transmission, and measuring the attenuation state of the signal. Since the attenuation state of this signal is correlated with the Q value, foreign object detection may be performed based on this. Alternatively, a method of detecting a foreign object may be used by using the measurement results of the resonance frequency of the power transmitting antenna, the sharpness of the resonance curve, or the inductor 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. Furthermore, these methods may be used to determine the presence or absence of a foreign object based on the measurement results of the electrical characteristics at one frequency or multiple frequencies, and a method for measuring the electrical characteristics at multiple frequencies can be realized 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 the signal at each frequency. This method has the effect of enabling the measurement with a relatively small amount of calculation 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 is transmitted once, and calculation processing (e.g., Fourier transform) is performed on the measurement results, thereby calculating the electrical characteristics at multiple frequencies. Alternatively, a signal having some frequency components of the multiple frequencies at which the electrical characteristics are to be measured can be transmitted multiple times, and the measurement results can be processed (e.g., by Fourier transform) to calculate the electrical characteristics at multiple frequencies.This method has the advantage that the number of times signals for measurement are transmitted can be reduced, and therefore the measurement can be performed in a relatively short time. Alternatively, a method of detecting foreign objects using the measurement results of a sensor such as a photoelectric sensor, an eddy current type displacement sensor, a contact type displacement sensor, an ultrasonic sensor, an image discrimination sensor, or a weight sensor mounted on the power transmitting device may be used.

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

[0098] [Other embodiments] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a 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 implements one or more of the functions.

[0099] The invention is not limited to the above-described embodiments, and various modifications and variations are possible 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 transmitting device

Claims

[Claim 1] A power transmission device, A power transmitting means for wirelessly transmitting power to a power receiving device via a power transmitting antenna; A control means for controlling the power transmission by the power transmitting means; a measuring means for measuring a waveform attenuation rate of a transmitted wave in a state where the power transmission is stopped by the control means; a setting means for setting a threshold value used for detecting a foreign object between the power transmitting device and the power receiving device based on the measured waveform attenuation rate; a determination means for determining whether or not the foreign object is present based on the waveform attenuation rate measured by the measurement means and the threshold value after the threshold value is set by the setting means; A power transmitting device comprising:

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