Power transmission device and method to be performed by the same

Abstract

To appropriately control the detection process in a case where multiple detection methods can be executed for detecting an object different from a receiving device when performing wireless power transmission.SOLUTION: A wireless power transmission system transmits power from a power transmission device to a power receiving device via wireless transmission. The system periodically executes detection processing using a first detection method for detecting an object different from the receiving device. The system also determines whether a predetermined condition regarding the status of at least one of the power transmission device and the power receiving device has been satisfied. The system then executes detection processing of the object using a second detection method that differs from the first detection method in accordance with the results of the predetermined condition determination.SELECTED DRAWING: Figure 8

Description

[Technical field]

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

[0002] In recent years, technical development of wireless power transmission systems has been widely carried out. Patent Document 1 discloses a foreign object detection method in the Wireless Power Consortium (WPC) standard. Patent Document 2 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 2017-70074 A [Patent Document 2] JP 2015-27172 A Summary of the Invention [Problem to be solved by the invention]

[0004] The foreign object detection method (power loss method) disclosed in Patent Document 1 detects a foreign object, which is an object other than a power receiving device, based on the measurement result of the power loss occurring between the power transmitting device and the power receiving device during power transmission from the power transmitting device to the power receiving device. On the other hand, the foreign object detection method disclosed in Patent Document 2 detects a foreign object based on the measurement result of the attenuation state of a signal transmitted by the power transmitting device. Thus, although there are several possible methods for detecting a foreign object when performing wireless power transmission, a method for appropriately controlling the detection process when the several detection methods are feasible has not been established.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to appropriately control the detection process when multiple detection methods for detecting an object other than a power receiving device can be executed when performing wireless power transmission. [Means for solving the problem]

[0006] As one means for solving the above problem, the power transmission device of the present invention has the following configuration: That is, the power transmission device has a power transmission means for wirelessly transmitting power to a power receiving device, a first detection means for periodically executing a detection process by a first detection method for detecting an object different from the power receiving device based on a power loss related to power transmission by the power transmission means, a determination means for determining whether a predetermined condition related to at least one of the states of the power transmission device and the power receiving device is satisfied, and a second detection means for executing a detection process by a second detection method for detecting the object based on at least one of a voltage attenuation state and a current attenuation state related to power transmission by the power transmission means according to a result of the determination by the determination means. Effect of the Invention

[0007] According to the present invention, when a plurality of detection methods for detecting an object other than a power receiving device are executable for wireless power transmission, it is possible to appropriately control the detection process. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram illustrating a configuration example of a power transmitting device. [Diagram 2] FIG. 2 illustrates an example of the configuration 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. 11 is a sequence diagram illustrating an example of a process for performing wireless power transmission. [Figure 6] 11A and 11B are diagrams for explaining foreign object detection by a waveform attenuation method. [Figure 7]11A and 11B are diagrams for explaining a method of detecting a foreign object based on a power transmission waveform during power transmission. [Figure 8] 11 is a flowchart illustrating an example of processing in a power transfer phase of a power transmitting device. [Figure 9] 11 is a flowchart illustrating an example of processing in a power transfer phase of a power receiving device. [Figure 10] 11 is a diagram for explaining a method of setting a threshold value in foreign object detection by the Power Loss method. FIG. [Figure 11] 11A and 11B are diagrams for explaining a method of setting a threshold value in foreign object detection using a waveform attenuation method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Although the embodiments include a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. In addition, in the accompanying drawings, the same reference numerals are used to refer to the same or similar components.

[0010] [Wireless power transmission system configuration] 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. Detailed configurations of the power receiving device 401 and the power transmitting device 402 will be described later with reference to FIG. 2 and FIG. 1. In the following, 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. In the following, since the charging stand 403 is a part of the TX, "placed on the charging stand 403" may be called "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 applications other than wireless charging. An example of the RX is a smartphone, and an example of the TX is an accessory device for charging the smartphone. The RX and TX may be a storage device such as a tablet, a hard disk device, or a memory device, or may be an information processing device such as a personal computer (PC). The RX and TX may also be, for example, an imaging device (a camera, a video camera, etc.), an automobile, a robot, a medical device, a printer, etc.

[0011] In this system, wireless power transmission is performed using an electromagnetic induction method for wireless charging based on the WPC standard. That is, RX and TX perform wireless power transmission for wireless charging based on the WPC standard between the power receiving antenna 205 of RX and the power transmitting antenna 105 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 a method using other electromagnetic induction method, magnetic field resonance method, electric field resonance method, microwave method, laser method, etc. Also, 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 magnitude of power guaranteed when the power receiving device 401 receives power from the power transmitting device 402 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 401 even if the positional relationship between the power receiving device 401 and the power transmitting device 402 changes and the power transmission efficiency between the power receiving antenna 205 and the power transmitting antenna 105 decreases. For example, when the GP is 5 watts, the power transmitting device 402 performs power transmission by controlling so as to output 5 watts to the load in the power receiving device 401, even if the positional relationship between the power receiving antenna 205 and the power transmitting antenna 105 changes and the power transmission efficiency decreases.

[0013] Furthermore, when transmitting power from the power transmitting device 402 to the power receiving device 401, if a foreign object other than the power receiving device 401 is present near the power transmitting device 402, there is a risk that the electromagnetic waves for transmitting power will affect the foreign object, raising the temperature of the foreign object or destroying the foreign object. Therefore, the WPC standard specifies a method for the power transmitting device 402 to detect the presence of a foreign object on the charging stand 403 so that the power transmitting device 402 can prevent the foreign object from increasing in temperature or being destroyed by stopping power transmission when the foreign object is present. Specifically, the WPC standard specifies a power loss method for detecting a foreign object based on the difference between the transmitted power in the power transmitting device 402 and the received power in the power receiving device 401. In addition, the WPC standard specifies a Q-factor measurement method for detecting a foreign object based on a change in the quality factor (Q-factor) of the power transmitting antenna 105 (power transmitting coil) in the power transmitting device 402. Note that the foreign object detected by the power transmitting device 402 in this embodiment is not limited to an object present on the charging stand 403. The power transmitting device 402 only needs to detect a foreign object located in the vicinity of the power transmitting device 402, and may detect a foreign object located within a range where the power transmitting device 402 can transmit power, for example.

[0014] Foreign object detection based on the power loss method defined in the WPC standard will be described with reference to Fig. 10. The horizontal axis of Fig. 10 represents the transmitted power of the power transmitting device 402, and the vertical axis represents the received power of the power receiving device 401. Note that a foreign object is an object other than the power receiving device 401 that may affect the power transmission from the power transmitting device 402 to the power receiving device 401, such as an object such as a metal piece having electrical conductivity.

[0015] First, the power transmitting device 402 transmits power to the power receiving device 401 at a first transmission power value Pt1. The power receiving device 401 receives power at a first reception power value Pr1 (this state is called a light load state). Then, the power transmitting device 402 stores the first transmission power value Pt1. Here, the first transmission power value Pt1 or the first reception power value Pr1 is a predetermined minimum transmission power or reception power. At this time, the power receiving device 401 controls the load so that the received power is the minimum power. For example, the power receiving device 401 may disconnect the load from the power receiving antenna 205 so that the received power is not supplied to the load (such as a charging circuit and a battery). Next, the power receiving device 401 reports the power value Pr1 of the first reception power to the power transmitting device 402. The power transmitting device 402, which receives Pr1 from the power receiving device 401, calculates that the power loss between the power transmitting device 402 and the power receiving device 401 is Pt1-Pr1 (=Ploss1), and can create a calibration point 1000 that shows the correspondence between Pt1 and Pr1.

[0016] Next, the power transmitting device 402 changes the transmission power value to the second transmission power value Pt2 and transmits power to the power receiving device 401. The power receiving device 401 receives power at the second receiving power value Pr2 (this state is called a connected load state). Then, the power transmitting device 402 stores the second transmission power value Pt2. Here, the second transmission power value Pt2 or the second receiving power value Pr2 is a predetermined maximum transmission power or receiving power. At this time, the power receiving device 401 controls the load so that the received power becomes the maximum power. For example, the power receiving device 401 connects the power receiving antenna 205 to the load so that the received power is supplied to the load. Next, the power receiving device 401 reports Pr2 to the power transmitting device 402. The power transmitting device 402, which receives Pr2 from the power receiving device 401, calculates that the power loss between the power transmitting device 402 and the power receiving device 401 is Pt2-Pr2 (=Ploss2), and can create a calibration point 1001 showing the correspondence between Pt2 and Pr2.

[0017] Then, the power transmitting device 402 creates a straight line 1002 that linearly interpolates between the calibration point 1000 and the calibration point 1001. The straight line 1002 indicates the relationship between the transmitted power and the received power in a state where no foreign object is present near the power transmitting device 402 and the power receiving device 401. Based on the straight line 1002, the power transmitting device 402 can predict the power value that the power receiving device 401 will receive when transmitting power at a predetermined transmitted power in a state where no foreign object is present. For example, when the power transmitting device 402 transmits power at a third transmitted power value Pt3, it can be inferred from a point 1003 on the straight line 1002 that corresponds to Pt3 that the third received power value received by the power receiving device 401 will be Pr3.

[0018] As described above, the power loss between the power transmitting device 402 and the power receiving device 401 according to the load can be obtained based on multiple combinations of the transmission power value of the power transmitting device 402 and the reception power value of the power receiving device 401 measured while changing the load. In addition, the power loss between the power transmitting device 402 and the power receiving device 401 according to all loads can be estimated by interpolating from multiple combinations. In this way, the calibration process performed by the power transmitting device 402 and the power receiving device 401 for the power transmitting device 402 to acquire combinations of the transmission power value and the reception power value is hereinafter referred to as "calibration process (CAL process) of the power loss method."

[0019] After the calibration, it is assumed that the power transmitting device 402 actually transmits power to the power receiving device 401 at Pt3, and the power transmitting device 402 receives a value of a received power value Pr3' from the power receiving device 401. The power transmitting device 402 calculates a value Pr3-Pr3' (=Ploss_FO) by subtracting the received power value Pr3' actually received from the power receiving device 401 from the received power value Pr3 in a state where no foreign object is present. This Ploss_FO can be considered as a power loss due to power consumed by a foreign object when a foreign object is present near the power transmitting device 402 and the power receiving device 401. Therefore, when the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold value, it is possible to determine that a foreign object is present. Alternatively, the power transmitting device 402 calculates in advance the power loss Pt3-Pr3 (=Ploss3) between the power transmitting device 402 and the power receiving device 401 from the received power value Pr3 in a state where no foreign object is present. Next, the power loss Pt3-Pr3' (=Ploss3') between the power transmitting device 402 and the power receiving device 401 in the presence of the foreign object is calculated from the received power value Pr3' received from the power receiving device 401 in the presence of the foreign object. Then, the power Ploss_FO that would have been consumed by the foreign object may be estimated using Ploss3'-Ploss3 (==Ploss_FO).

[0020] As described above, the power Ploss_FO that would have been consumed by a foreign object may be calculated as Pr3-Pr3' (=Ploss_FO) or as Ploss3'-Ploss3 (=Ploss_FO). In the following specification, the method of calculating Ploss3'-Ploss3 (=Ploss_FO) will basically be described, but the contents of this embodiment are also applicable to the method of calculating Pr3-Pr3' (=Ploss_FO). This concludes the explanation of foreign object detection based on the Power Loss method.

[0021] Foreign object detection using the Power Loss method is performed during power transmission (Power Transfer phase described below) based on data obtained in the Calibration phase described below. Foreign object detection using the Q-value measurement method is performed before power transmission (before sending a Digital Ping, Negotiation phase or Renegotiation phase described below).

[0022] 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.

[0023] In the Selection phase, the TX transmits Analog Pings intermittently and detects 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 105 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.

[0024] 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 105. This measurement result is used when executing a foreign object detection process using a Q-factor measurement method.

[0025] In the I&C phase, the TX identifies the RX and obtains device configuration information (capability information) from the RX. The RX transmits an ID packet and a configuration packet. The ID packet contains the identifier information of the RX, and the configuration packet contains the device configuration information (capability information) of the RX. The TX, having received the ID packet and the configuration packet, responds with an acknowledgement (ACK, positive response). Then, the I&C phase ends.

[0026] 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.

[0027] In the calibration phase, calibration is performed based on the WPC standard. In addition, RX notifies TX of a predetermined receiving power value (receiving power value in a light load state / receiving power value in a maximum load state), and TX performs adjustments to transmit power efficiently. The receiving power value notified to TX can be used for foreign object detection processing using the Power Loss method.

[0028] In the power transfer phase, control is performed for starting and continuing power transmission, and stopping power transmission due to an error or full charge. For this power transmission and reception control, the TX and RX use the power transmitting antenna 105 and the power receiving antenna 205 used when performing wireless power transmission based on the WPC standard to perform communication by superimposing a signal on the electromagnetic wave transmitted from the power transmitting antenna 105 or the power receiving antenna 205. The range in which communication based on the WPC standard is possible between the TX and RX is almost the same as the power transmission range of the TX.

[0029] [Configuration of power transmitting device 402 and power receiving device 401] Next, the configurations of the power transmitting device 402 (TX) and the power receiving device 401 (RX) in this embodiment will be described. Note that the configurations described below are merely examples, and a part (or in some cases, the whole) of the configurations described may be replaced with other configurations that perform similar functions or may be omitted, and further configurations may be added to the configurations described. Furthermore, one block described below may be divided into multiple blocks, or multiple blocks may be integrated into one block. In addition, although the functions of each of the functional blocks described below are implemented as a software program, some or all of the components included in the functional blocks may be implemented as hardware.

[0030] 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, a resonant capacitor 107, and a switch 108. In Fig. 1, the control unit 101, the power supply unit 102, the power transmitting unit 103, the communication unit 104, and the memory 106 are depicted as separate entities, but any of a plurality of these functional blocks may be implemented in the same chip.

[0031] The control unit 101 controls the entire TX by executing a control program stored in the memory 106, for example. The control unit 101 also controls power transmission control including communication for device authentication in the TX. The control unit 101 may also control the execution of applications other than wireless power transmission. The control unit 101 includes one or more processors, such as a CPU (Central Processing Unit) or an MPU (Microprocessor Unit). The control unit 101 may also be configured with hardware such as an application specific integrated circuit (ASIC). The control unit 101 may also be configured with an array circuit such as an FPGA (Field Programmable Gate Array) 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).

[0032] 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.

[0033] The power transmitting unit 103 converts the DC or AC power input from the power supply unit 102 into AC power in a frequency band used for wireless power transmission, and generates electromagnetic waves for receiving power at the RX by inputting the AC 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.

[0034] 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 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 of the power receiving device 401 (RX) that complies with the WPC standard.

[0035] 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.

[0036] The memory 106 can store the control program and also the TX and RX states (transmitted power value, received 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, and can be received via the communication unit 104.

[0037] The switch 108 is controlled by the control unit 101. The power transmitting antenna 105 is connected to the resonant capacitor 107, and when the switch 108 is turned on and short-circuited, the power transmitting antenna 105 and the resonant capacitor 107 form a series resonant circuit and resonate at a specific frequency f1. At this time, a current flows through a closed circuit formed by the power transmitting antenna 105, the resonant capacitor 107, and the switch 108. When the switch 108 is turned off and opened, power is supplied from the power transmitting unit 103 to the power transmitting antenna 105 and the resonant capacitor 107.

[0038] Fig. 2 is a block diagram showing a configuration example 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, a first switch unit 209, a second switch unit 210, and a resonance capacitor 211. Note that a plurality of functional blocks shown in Fig. 2 may be realized as one hardware module.

[0039] 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.

[0040] 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).

[0041] 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.

[0042] The power receiving unit 203 acquires AC power (AC voltage and AC current) generated by electromagnetic induction based on electromagnetic waves radiated from the power transmitting antenna 105 of TX via the power receiving antenna 205. 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 includes a rectification unit and a voltage control unit required for supplying power to the load in RX. The above-mentioned GP is the amount of power guaranteed to be output from the power receiving unit 203. It is assumed that the power receiving unit 203 has 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.

[0043] The communication unit 204 communicates with the communication unit 104 of the TX for power receiving control based on the WPC standard as described above. The communication unit 204 demodulates the electromagnetic wave input from the power receiving antenna 205 to obtain information transmitted from the TX. The communication unit 204 then performs load modulation on the input electromagnetic wave to superimpose a signal related to information to be transmitted to the TX on the electromagnetic wave, thereby communicating with the TX. Note that the communication unit 204 may communicate with the TX by communication based on 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.

[0044] 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.

[0045] The first switch unit 209 and the second switch unit 210 are controlled by the control unit 201. The power receiving antenna 205 is connected to the resonant capacitor 211, and when the second switch unit 210 is turned on and short-circuited, the power receiving antenna 205 and the resonant capacitor 211 form a series resonant circuit and resonate at a specific frequency f2. At this time, a current flows through a closed circuit formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210, and no current flows through the power receiving unit. When the second switch unit 210 is turned off and opened, the power received by the power receiving antenna 205 and the resonant capacitor 211 is supplied to the power receiving unit 203.

[0046] The first switch unit 209 is for controlling whether or not the received power is supplied to the battery, which is a load. It also has a function of controlling the value of the load. When the first switch unit 209 connects the charging unit 206 and the battery 207, the received power is supplied to the battery 207. When the first switch unit 209 disconnects the connection between the charging unit 206 and the battery 207, the received power is not supplied to the battery 207. Note that the first 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 first switch unit 209 may be disposed between the closed circuit formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210, and the power receiving unit 203. In other words, the first switch unit 209 may be for controlling whether or not the received power is supplied to the power receiving unit 203. In addition, while first switch unit 209 is illustrated as one block in FIG. 2, first switch unit 209 can also be realized as part of charging unit 206 or as part of power receiving unit 203 .

[0047] Next, the function of the control unit 101 of the TX 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 index, which will be described later. In addition, the measurement unit 303 measures the power transmitted to the RX via the power transmission unit 103, and measures the average transmission power per unit time. In addition, the measurement unit 303 measures the Q value of the power transmission antenna 105. The setting unit 304 sets a threshold value used for foreign object detection based on the waveform attenuation index measured by the measurement unit 303, for example, by a calculation process.

[0048] 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 401 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 detection unit 305 can perform foreign object detection processing based on the threshold value set by the setting unit 304 and the waveform attenuation index, the transmission power, and the Q value measured by the measurement unit 303.

[0049] 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. However, two or more of these processing units may be incorporated into one program.

[0050] [Process flow for power transmission according to WPC standards) The WPC standard specifies a Selection phase, a Ping phase, an I&C phase, a Negotiation phase, a Calibration phase, and a Power Transfer phase. The operations of the power transmitting device 402 and the power receiving device 401 in these phases will be described below with reference to the sequence diagram of Fig. 5. Fig. 5 is a sequence diagram for power transmission according to the WPC standard. Here, the power transmitting device 402 (TX) and the power receiving device 401 (RX) will be described as examples.

[0051] 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 the Manufacturer Code and the 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 the RX has a negotiation function of the WPC standard. The TX may acquire the identification information and capability information of the RX through a method other than communication in the I&C phase of the WPC standard. The identification information may 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.

[0052] Next, the TX determines the GP value with the RX through communication in the negotiation phase defined by the WPC standard (F508). Note that in F508, other procedures for determining the GP may be executed, not limited to communication in the negotiation phase of the WPC standard. Also, when the TX acquires information indicating that the RX does not support the negotiation phase (for example, in F507), the TX 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, the GP is set to 5 watts.

[0053] 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.

[0054] Next, when RX receives an ACK from TX (F510), it performs processing to transmit information (hereinafter referred to as second reference received power information) including the received power in a load connection state (maximum load state, a load state in which the transmitted power is equal to or greater than the second threshold) to TX. 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).

[0055] When the TX receives the above-mentioned transmission 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 output change instruction. This prevents the transmission of power above the specified level (F515).

[0056] When the RX judges that the predetermined transmission power has been reached by receiving a NAK from the TX, it transmits information including the received power in the load-connected state to the TX as the second reference received power information (F516). The TX can calculate the amount of power loss between the TX and the RX in the light load state and the load-connected state based on the transmission power value of the TX and the received power value included in the first and second reference received power information. In addition, by interpolating between these power loss amounts, it is possible to calculate the power loss value between the TX and the RX for all possible transmission powers of the TX (250 milliwatts to 5 watts in this case) (F517). The TX transmits an ACK in response to the second reference received power information from the RX (F518) and completes the calibration process. When the TX judges that the charging process can be started and starts the power transmission process to the RX, the charging of the RX starts. Before starting the power transmission process, TX and RX perform device authentication processing (F519). If it is determined that each device can support a larger GP, the GP may be reset to a larger value, for example, 15 watts (F520).

[0057] In this case, 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). Then, TX and RX perform calibration processing again for GP=15 watts. Specifically, RX transmits information including the received power 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 can calculate the amount of power loss between TX and RX for all possible transmission powers of TX (250 milliwatts to 15 watts in this case) (F526). TX transmits ACK in response to the third reference received power information from RX (F527) and completes the calibration processing. TX, which has determined that charging processing can be started, starts the power transmission processing to RX and transitions to the Power Transfer phase (F528).

[0058] 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 the amount of power loss between the TX and RX in a state where 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 corresponds to the reference amount of power loss in a normal state (a state where there is no foreign object) during power transmission processing. Then, the TX determines that there is a "foreign object" or that there is a "possibility of a foreign object being present" if the amount of power loss between the TX and RX measured during power transmission after calibration deviates from the amount of power loss in the normal state by more than a threshold value.

[0059] This concludes the description of the power loss method. In the power loss method, foreign object detection is performed based on the measurement results of power loss while power is being transmitted from power transmitting device 402 to power receiving device 401. Foreign object detection using the power loss method has a drawback in that the accuracy of foreign object detection decreases when power transmitting device 402 is transmitting large power, but has an advantage in that foreign object detection can be performed while continuing power transmission, thereby maintaining high power transmission efficiency.

[0060] In this way, foreign object detection can be performed using the power loss method during the power transfer phase. However, foreign object detection using only the power loss method may result in erroneous detection of a foreign object or erroneous determination that there is no foreign object even though there is one. In particular, the power transfer phase is a phase in which the TX transmits power, and if a foreign object is present near the TX and RX during power transmission, heat generation from the foreign object increases, so it is necessary to improve the accuracy of foreign object detection in this phase. Therefore, in this embodiment, in order to improve the accuracy of foreign object detection, a foreign object detection method other than the power loss method is considered.

[0061] [Foreign object detection method using waveform attenuation method] In the power transfer phase, the power transmitting device 402 transmits power to the power receiving device 401. Therefore, if foreign object detection can be performed using a power transmission waveform (voltage waveform or current waveform) related to this power transmission, foreign object detection can be performed without using a newly defined foreign object detection signal or the like. A method for detecting foreign objects based on the attenuation state of a transmitted wave (hereinafter referred to as a 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, foreign object detection using a power transmission waveform related to power transmission from the power transmitting device 402 (TX) to the power receiving device 401 (RX) will be described as an example.

[0062] In FIG. 6, the waveform shows the change over time of the voltage value 600 (hereinafter simply referred to as the voltage value) of the high frequency voltage applied to the power transmitting antenna 105 of the TX. The horizontal axis of FIG. 6 shows the time, and the vertical axis shows the voltage value. The TX, which is transmitting power to the RX via the power transmitting antenna 105, stops transmitting power at time T0. That is, at time T0, the power supply for power transmission from the power supply unit 102 is stopped. The frequency of the transmitting wave for power transmission from the TX is a predetermined frequency, for example, a fixed frequency between 85 kHz and 205 kHz used in the WPC standard. Point 601 is a point on the envelope of the high frequency voltage, and is the voltage value at time T1. (T1, A1) in the figure indicates that the voltage value at time T1 is A1. Similarly, point 602 is a point on the envelope of the high frequency voltage, and is the voltage value at time T2. (T2, A2) in the figure indicates that the voltage value at time T2 is A2. The quality factor (Q value) of the power transmitting antenna 105 can be obtained based on the time change in the voltage value after time T0. For example, the Q value is calculated by Equation 1 based on the time, the voltage value, and the frequency f of the high-frequency voltage at points 601 and 602 on the envelope of the voltage value. Q=πf(T2-T1) / ln(A1 / A2) (Formula 1) When a foreign object is present near TX and RX, the Q value decreases. This is because a foreign object causes energy loss when the foreign object is present. Therefore, when paying attention to the slope of the attenuation of the voltage value, the slope of the line connecting points 601 and 602 becomes steeper and the attenuation rate of the waveform amplitude becomes higher when a foreign object is present than when there is no foreign object, because energy loss occurs due to the foreign object. In other words, the waveform attenuation method judges the presence or absence of a foreign object based on the attenuation state of the voltage value between 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 judgment can be made using the above-mentioned Q value. A lower Q value means a higher waveform attenuation rate (the degree of reduction in the waveform amplitude per unit time). Alternatively, the judgment may be made using the slope of the line connecting points 601 and 602, which is calculated from (A1-A2) / (T2-T1). Alternatively, if the time (T1 and T2) for observing the attenuation state of the voltage values ​​is fixed, the judgment can be made using the value of (A1-A2) representing the difference in the voltage values ​​or the value of the ratio of the voltage values ​​(A1 / A2). Alternatively, if the voltage value A1 immediately after the power transmission is stopped is constant, the judgment can be made using the value of the voltage value A2 after a predetermined time has elapsed. Alternatively, the judgment can be made using the value of the time (T2-T1) until the voltage value A1 reaches the predetermined voltage value A2.

[0063] As described above, the presence or absence of a foreign object can be determined by the attenuation state of the voltage value during the power transmission stop period, and there are multiple values ​​that represent the attenuation state. In this embodiment, the values ​​that represent these attenuation states are called "waveform attenuation indexes." For example, as described above, the Q value calculated by Equation 1 is a value that represents the attenuation state of the voltage value related to power transmission, and is included in the "waveform attenuation index." All waveform attenuation indexes are values ​​that correspond to the waveform attenuation rate. Note that in the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation index." The following description will focus on the case where the waveform attenuation rate is used as the waveform attenuation index, but the contents of this embodiment can be applied to the case where other waveform attenuation indexes are used.

[0064] In addition, even if the vertical axis of FIG. 6 is the current value flowing through the power transmitting antenna 105, the attenuation state of the current value during the power transmission stop period changes depending on the presence or absence of a foreign object, as in the case of the voltage value. And, when a foreign object is present, the waveform attenuation rate is higher than when a foreign object is not present. Therefore, even if the above-mentioned method is applied to the time change of the current value flowing through the power transmitting antenna 105, a foreign object can be detected. That is, the Q value obtained from the current waveform, the slope of the attenuation of the current value, the difference of the current values, the ratio of the current values, the absolute value of the current value, the time until the current value reaches a predetermined current value, and the like can be used as waveform attenuation indexes to determine the presence or absence of a foreign object and detect the foreign object. In addition, foreign object detection may be performed based on both the attenuation state of the voltage value and the attenuation state of the current value, such as determining the presence or absence of a foreign object using an evaluation value calculated from the waveform attenuation index of the voltage value and the waveform attenuation index of the current value. In the above example, the waveform attenuation index is measured during the period when the TX temporarily stops power transmission, but the waveform attenuation index may be measured during the period when the TX temporarily reduces the power supplied from the power supply unit 102 from a predetermined power level to a power level lower than that.

[0065] A method of detecting a foreign object based on a power transmission waveform during power transmission using the waveform attenuation method will be described with reference to FIG. 7. FIG. 7 shows a power transmission waveform when detecting a foreign object using the waveform attenuation method, with the horizontal axis representing time and the vertical axis representing the voltage value of the voltage applied to the power transmission antenna 105 or the resonant capacitor 107. As in FIG. 6, the vertical axis may represent the current value of the current flowing through the power transmission antenna 105. During the transient response period immediately after the TX starts power transmission, the power transmission waveform is not stable. Therefore, during this transient response period when the power transmission waveform is not stable, the RX is controlled so as not to communicate with the TX (communication by load modulation). Also, the TX is controlled so as not to communicate with the RX (communication by frequency shift keying).

[0066] When it is time to detect a foreign object, the TX suspends power transmission. Then, since the amplitude of the transmitted wave attenuates during the foreign object detection period when power transmission is stopped, the TX calculates the waveform attenuation rate of this attenuated waveform. Then, the TX determines that a foreign object is present when the calculated waveform attenuation rate exceeds a predetermined threshold. If no foreign object is detected after the predetermined foreign object detection period has elapsed, the TX resumes power transmission. After resuming power transmission, the TX repeatedly executes the above-mentioned waiting for the transient response period, determining the timing of foreign object detection, stopping power transmission, and foreign object detection processing. The above is the basic processing of foreign object detection using the waveform attenuation method.

[0067] When measuring the waveform attenuation rate of the transmitting wave, if elements such as the power receiving unit 203, the charging unit 206, and the battery 207 are connected to the power receiving antenna 205 and the resonant capacitor 211 of the power receiving device 401, the waveform attenuation rate of the attenuated waveform is affected by the load of these elements. That is, the waveform attenuation rate changes depending on the state of the power receiving unit 203, the charging unit 206, and the battery 207. Therefore, even if the waveform attenuation rate is large, it is difficult to distinguish whether it is due to the influence of a foreign object or due to a change in the state of the power receiving unit 203, the charging unit 206, the battery 207, etc. Therefore, when observing the waveform attenuation rate to detect a foreign object, the first switch unit 209 may be disconnected. This makes it possible to eliminate the influence of the battery 207. Alternatively, the second switch unit 210 may be turned on to short-circuit the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210, so that a current flows through a closed loop formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210. This makes it possible to eliminate the effects of power receiving unit 203, charging unit 206, and battery 207. As described above, highly accurate foreign object detection is possible by performing foreign object detection with first switch unit 209 disconnected or with second switch unit 210 turned on and short-circuited (connected). Highly accurate foreign object detection is also possible by performing both disconnection of first switch unit 209 and short-circuit (connection) of second switch unit 210.

[0068] In addition, when measuring the waveform attenuation rate of the transmitting wave, if elements such as the power transmitting unit 103, the communication unit 104, and the power supply unit 102 are connected to the power transmitting antenna 105 and the resonant capacitor 107 of the power transmitting device 402, the waveform attenuation rate of the attenuated waveform is affected by the load of these elements. That is, the waveform attenuation rate changes depending on the state of the power transmitting unit 103, the communication unit 104, and the power supply unit 102. Therefore, even if the waveform attenuation rate is large, it is difficult to distinguish whether it is due to the influence of a foreign object or the power transmitting unit 103, the communication unit 104, and the power supply unit 102. Therefore, when measuring the waveform attenuation rate, the switch 108 may be turned on to short-circuit the power transmitting antenna 105, the resonant capacitor 107, and the switch 108, so that a current flows through a closed loop formed by the power transmitting antenna 105, the resonant capacitor 107, and the switch 108. This makes it possible to eliminate the influence of the power transmitting unit 103, the communication unit 104, and the power supply unit 102. Alternatively, a switch may be provided between the power transmitting unit 103 and a closed loop circuit formed by the power transmitting antenna 105, the resonant capacitor 107, and the switch 108. When detecting a foreign object, the switch is used to disconnect the closed loop circuit from the power transmitting unit, thereby making it possible to eliminate the influence of the power transmitting unit 103, the communication unit 104, and the power supply unit 102. As described above, highly accurate foreign object detection is possible by performing foreign object detection with the switch 108 turned on to establish a short-circuit (connection) state, or with the closed loop circuit and the power transmitting unit 103 disconnected by the switch. Also, highly accurate foreign object detection is possible by implementing both the switch 108 turned on to establish a short-circuit (connection) state and the closed loop circuit and the power transmitting unit 103 disconnected by the switch.

[0069] [How to set the foreign object detection threshold in the waveform attenuation method] FIG. 11 is a diagram for explaining a method of setting a foreign object detection threshold in the waveform attenuation method. First, when power is transmitted from TX, RX controls the load of RX to be in a light load state so that no power is supplied 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 this state and measures the waveform attenuation rate. The waveform attenuation rate at this time is δ1. At this time, TX recognizes the transmission power Pt1 transmitted by TX, and stores in memory a calibration point 1100 that associates the transmission power Pt1 with the waveform attenuation rate δ1. Next, RX controls the load of RX to be in a load connection state so that when power is transmitted from TX, the maximum power is supplied to the load of RX or power equal to or greater than a predetermined threshold is supplied. The transmission power of TX at this time is Pt2. Then, TX stops power transmission in this state and measures the waveform attenuation rate. At this time, the TX stores in the memory a calibration point 1101 that associates the transmission power Pt2 with the waveform attenuation rate δ2. Next, the TX performs linear interpolation between the calibration point 1100 and the calibration point 1101 to create a straight line 1102. The straight 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 estimate the waveform attenuation rate of the transmission wave for each transmission power value in a state where there is no foreign object from the straight line 1102. For example, when the transmission power value is Pt3, it can be estimated that the waveform attenuation rate is δ3 from the point 1103 on the straight line 1102 corresponding to the transmission power value Pt3. Then, based on the above estimation result, the TX can calculate a threshold value used to determine the presence or absence of a foreign object for each transmission power value. For example, a waveform attenuation rate that is greater than the estimated waveform attenuation rate at a certain transmission power value by a predetermined value (a value corresponding to a measurement error) when no foreign object is present may be set as the threshold for determining the presence or absence of a foreign object. The calibration process performed by the power transmitting device 402 and the power receiving device 401 for the power transmitting device 402 to acquire a combination of the transmission power value and the waveform attenuation rate is hereinafter referred to as "calibration process of the waveform attenuation method (CAL process)."

[0070] In addition, RX may perform the control to put the load into a no power / light load state and the control to put the load into a connected state after notifying TX of the control to be performed. Also, either of the two controls may be performed first.

[0071] The operation for calculating the threshold value used to determine 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 on power loss when the load state of the RX is a light load state and when the load is connected. Therefore, the measurement of the calibration point 1100 and the calibration point 1101 in FIG. 11 may be performed together with the measurement of power loss when the RX is in a light load state and a load connected 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 predetermined processing to be performed in the calibration phase, the TX measures the calibration point 1100. Also, when the TX receives the second reference received power information from the RX, in addition to the predetermined processing to be performed in the calibration phase, the TX measures the calibration point 1101. This eliminates the need to provide a separate period for measuring the calibration points 1100 and 1101, and therefore allows the measurements of the calibration points 1100 and 1101 to be performed in a shorter time.

[0072] [Treatment of power transmission equipment when applying the waveform attenuation method to the WPC standard] Next, the process of the power transmitting device 402 when detecting a foreign object by applying this waveform attenuation method to the WPC standard will be described. When detecting a foreign object using the waveform attenuation method, the power transmitting device 402 measures the waveform attenuation rate in advance when there is no foreign object, and calculates a threshold value based on that. After that, the power transmitting device 402 performs foreign object detection using the waveform attenuation method, and if the measured waveform attenuation rate is greater than the threshold value, it determines that "foreign object is present" or "there is a possibility that a foreign object is present," and if it is less than the threshold value, it determines that "no foreign object is present" or "there is a high possibility that there is no foreign object."

[0073] The timing for measuring the waveform attenuation rate in advance in a state where there is no foreign object will be described. In the WPC standard, foreign object detection is performed in the negotiation phase by the Q-value measurement method as described above. If it is determined that there is no foreign object 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 there is no foreign object as a result of the foreign object detection by 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 there is no foreign object can be measured. Therefore, the timing for measuring the waveform attenuation rate in a state where there is no foreign object may be any of the negotiation phase, calibration phase, and power transfer phase.

[0074] In this embodiment, the timing for measuring the waveform attenuation rate in the absence of a foreign object is set to the first stage of the power transfer phase. The reason is that the more time that passes after it is determined by the Q-value measurement method that there is no foreign object, the higher the probability that a foreign object will be placed near the power transmitting device 402 and the power receiving device 401. Then, at the timing for foreign object detection designated by the power receiving device 401 or the power transmitting device 402, the power transmitting device 402 measures the waveform attenuation rate of the transmitted wave. The power transmitting device 402 then compares the measured waveform attenuation rate with a threshold value calculated from the waveform attenuation rate in the absence of the above-mentioned foreign object, and determines the presence or absence of a foreign object.

[0075] In the waveform attenuation method, the power transmitting device 402 temporarily stops transmitting power and observes the attenuation rate of the transmitted radio wave to detect a foreign object, which has the disadvantage of reducing the power transmission efficiency due to the temporary suspension of power transmission. On the other hand, the method has the advantage that foreign objects can be detected with high accuracy even when the foreign object detection process is executed while transmitting a large amount of power. In other words, even in situations where it is difficult to accurately detect a foreign object using the power loss method, foreign objects can be detected by using the waveform attenuation method.

[0076] In the above embodiment, when foreign object detection is performed by the waveform attenuation method, the waveform attenuation rate in a state where there is no foreign object is measured before the start of power transmission, and the threshold value is calculated based on the measured value. Then, when the waveform attenuation rate measured when performing foreign object detection by the waveform attenuation method is larger than the threshold value, it is determined that "foreign object is present" or "there is a possibility that there is a foreign object", and when it is smaller than the threshold value, it is determined that "no foreign object is present" or "there is a high possibility that there is no foreign object". However, foreign object detection may be performed using a threshold value obtained from the waveform attenuation rate measured at a timing when it is estimated that there is no foreign object after the start of power transmission. For example, while the TX is transmitting power, it is confirmed that there is no foreign object by the power loss method. Next, the TX performs a first waveform attenuation rate measurement and calculates a threshold value based on the measured waveform attenuation rate. This first waveform attenuation rate measurement is performed immediately after it has been confirmed that there is no foreign object by the power loss method in advance, so the measured waveform attenuation rate is estimated to be the waveform attenuation rate in a state where there is no foreign object. Next, the TX resumes power transmission and performs a second waveform attenuation rate measurement at a timing when it is determined that foreign object detection should be performed. The presence or absence of a foreign object can be determined by comparing the result of the second waveform attenuation rate measurement with the result of the first waveform attenuation rate measurement or with a threshold value calculated based on that result. In other words, when detecting a foreign object using the waveform attenuation method, the waveform attenuation rate measured at that time may be compared with the waveform attenuation rate measured previously in a state where no foreign object was present, or with a threshold value.

[0077] In the above-described embodiment, the frequency of the transmission wave for power transmission from the power transmitting device 402 is a fixed frequency. However, the process for foreign object detection described in this embodiment may be performed for each of a plurality of frequencies, 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 frequency, but also the waveform attenuation rate at a plurality of frequencies, it is possible to perform foreign object detection with higher accuracy.

[0078] In this embodiment, immediately after the power transmitting device 402 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 power transmission. Therefore, in order to alleviate this, the power transmitting device 402 may control the transmitting power to increase in stages when starting the power transmission. Alternatively, when stopping the power transmission, the transmitting power may be controlled to decrease in stages.

[0079] [Foreign object detection process in response to communication errors] As described above, the power transmitting device 402 and the power receiving device 401 communicate for power transmission and reception control based on the WPC standard. This communication is performed wirelessly via the power transmitting antenna 105 of the power transmitting device 402 and the power receiving antenna 205 of the power receiving device 401. Therefore, if a foreign object is present near the power transmitting device 402 and the power receiving device 401 (for example, between the power transmitting device 402 and the power receiving device 401), the foreign object may interfere with wireless communication between the power transmitting device 402 and the power receiving device 401, causing a communication error. Therefore, in this embodiment, when a communication error occurs, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401, so that the power transmitting device 402 and the power receiving device 401 perform control to detect the foreign object.

[0080] As described above, the power loss method and the waveform attenuation method are used to detect a foreign object during power transmission from the power transmitting device 402 to the power receiving device 401. In the power loss method, as described with reference to FIG. 10, the power receiving device 401 notifies the power transmitting device 402 of the received power value Pr3' measured by the power receiving device 401. The power transmitting device 402 calculates Pr3-Pr3' (=Ploss_FO), which is a value obtained by subtracting the received power value Pr3' actually received from the power receiving device 401 from the received power value Pr3 in a state in which no foreign object is present. This Ploss_FO can be considered as a power loss due to power consumed by a foreign object when a foreign object is present near the power transmitting device 402 and the power receiving device 401. Therefore, the power transmitting device 402 can determine that a foreign object is present when the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold value. That is, in the power loss method, when foreign object detection is performed, as described above, communication is performed between the power transmitting device 402 and the power receiving device 401 in order to notify the power transmitting device 402 of the received power value Pr3'. A communication error has already occurred between the power transmitting device 402 and the power receiving device 401, and an error may occur for the same reason in the communication for foreign object detection.

[0081] On the other hand, the waveform attenuation method determines the presence or absence of a foreign object by stopping the power transmitting device 402 from transmitting power and comparing the waveform attenuation rate at that time with a waveform attenuation rate measured in advance when no foreign object is present. Therefore, foreign object detection can be performed without communication between the power transmitting device 402 and the power receiving device 401. Therefore, when a communication error occurs, the power transmitting device 402 performs foreign object detection using the waveform attenuation method, which does not require communication. This can increase the possibility of successful foreign object detection.

[0082] In addition, even if a foreign object is present near the power transmitting device 402 and the power receiving device 401 during power transmission, a communication error may not occur. However, even if a communication error does not occur, if a foreign object is present, there is a possibility that a malfunction such as a large power loss due to the foreign object or heat generation may occur. Therefore, the power transmitting device 402 periodically performs a foreign object detection process during the power transfer phase in which wireless power transmission is performed, and checks whether or not a foreign object is present near the power transmitting device 402 and the power receiving device 401. If the waveform attenuation method is adopted for this periodic foreign object detection, power transmission from the power transmitting device 402 is temporarily stopped every time foreign object detection is performed, which leads to a decrease in power transmission efficiency. On the other hand, if the power loss method is adopted, it is possible to detect a foreign object while continuing power transmission from the power transmitting device 402 to the power receiving device 401. Therefore, when no communication error occurs, the power transmitting device 402 and the power receiving device 401 periodically perform foreign object detection by the power loss method during the power transfer phase. This allows foreign objects to be detected early while maintaining high power transmission efficiency.

[0083] The operation of the power transmitting device 402 and the power receiving device 401 using the above-mentioned multiple foreign object detection methods will be described. Fig. 8 shows an example of the operation of the power transmitting device 402 in the Power Transfer phase. The process of Fig. 8 is started when the power transmitting device 402 detects the power receiving device 401 placed on the charging stand 403, communicates with it, and the process of each phase defined by the WPC standard is completed. Phases that are executed before the process of Fig. 8 starts include a Selection phase, a Ping phase, an I&C phase, a Negotiation phase, and a Calibration phase. However, the process of Fig. 8 may be started without performing at least some of the above phases.

[0084] In S801, the power transmitting apparatus 402 starts power transmission in the power transfer phase. In S802, the power transmitting apparatus 402 determines whether or not a command to execute foreign object detection using the power loss method has been received from the power receiving apparatus 401. This command includes the received power value measured by the power receiving apparatus 401. If this command has been received, in S803, the power transmitting apparatus 402 executes foreign object detection using the power loss method based on the received power value received from the power receiving apparatus 401 and the transmitted power value measured by the power transmitting apparatus 402.

[0085] In S804, the power transmitting device 402 determines whether or not a foreign object is present near the power transmitting device 402 based on the result of the foreign object detection process. If it is determined that a foreign object is present, in S805, the power transmitting device 402 transmits a negative acknowledgement (NAK) which is information indicating the presence of a foreign object to the power receiving device 401. In S806, the power transmitting device 402 performs control to stop power transmission or reduce the transmission power. On the other hand, if it is determined that no foreign object is present in S804, the power transmitting device 402 transmits an acknowledgement (ACK) which is information indicating the absence of a foreign object to the power receiving device 401, continues power transmission, and returns to S802.

[0086] If the power transmitting device 402 does not receive a foreign object detection execution command using the Power Loss method in S802, the power transmitting device 402 determines in S808 whether a communication error has occurred in communication between the power transmitting device 402 and the power receiving device 401. If the power transmitting device 402 does not receive a command that should be transmitted from the power receiving device 401, the power transmitting device 402 determines that a communication error has occurred (i.e., detects a communication error). For example, in order to periodically execute foreign object detection using the Power Loss method described above, the power receiving device 401 periodically transmits a foreign object detection execution command using the Power Loss method to the power transmitting device 402. If the power transmitting device 402 does not receive the command that should be received periodically, or if it receives a command including an invalid packet, it determines that a communication error has occurred. However, the method of detecting a communication error by the power transmitting device 402 is not limited to this.

[0087] If a communication error is detected in S808, there is a possibility that a foreign object is present, so in S809, the power transmitting device 402 performs foreign object detection using the waveform attenuation method. Then, the power transmitting device 402 performs the processes from S804 to S807 based on the result of foreign object detection, similar to the case where foreign object detection is performed using the power loss method.

[0088] If no communication error is detected in S808, the power transmitting device 402 determines in S810 whether a command to execute foreign object detection using the waveform attenuation method has been received from the power receiving device 401. The power receiving device 401 transmits this command when, for example, the power receiving device 401 detects a communication error, as described below. If the power transmitting device 402 receives this command, it executes foreign object detection using the waveform attenuation method in S809. Then, the power transmitting device 402 performs the processes from S804 to S807 based on the result of foreign object detection.

[0089] Fig. 9 shows an example of the operation of the power receiving device 401 in the power transfer phase. The process in Fig. 9 starts at the same timing as the process in Fig. 8. In S901, the power receiving device 401 starts power reception in the power transfer phase. In S902, the power receiving device 401 transmits a command to execute foreign object detection using the power loss method, which is a command to be periodically transmitted to the power transmitting device 402. This command is a notification from the power receiving device 401 to the power transmitting device 402 requesting foreign object detection processing using the power loss method.

[0090] In S903, the power receiving device 401 determines whether a communication error has occurred in the communication between the power transmitting device 402 and the power receiving device 401. The power receiving device 401 determines whether a communication error has occurred as follows. In accordance with the WPC standard, the power receiving device 401 transmits various commands to the power transmitting device 402. When the power transmitting device 402 receives a command from the power receiving device 401, the power receiving device 401 responds (positive response, negative response, etc.) to the power receiving device 401. For example, in periodically executing foreign object detection using the above-mentioned Power Loss method, the power receiving device 401 periodically transmits a foreign object detection execution command using the Power Loss method to the power transmitting device 402. When the power transmitting device 402 receives the command, the power receiving device 401 responds to the power receiving device 401. Therefore, when the power receiving device 401 transmits a foreign object detection execution command using the Power Loss method to the power transmitting device 402 but does not receive a response from the power transmitting device 402, the power receiving device 401 determines that a communication error has occurred (i.e., detects a communication error). Furthermore, even if the power receiving apparatus 401 receives a response from the power transmitting apparatus 402, if the response includes an invalid packet, the power receiving apparatus 401 determines that a communication error has occurred. However, the method of detecting a communication error by the power receiving apparatus 401 is not limited to this.

[0091] If a communication error is detected in S903, there is a possibility that a foreign object is present and foreign object detection using the power loss method has not been performed normally. Therefore, in S904, the power receiving device 401 transmits a command to execute foreign object detection using the waveform attenuation method to the power transmitting device 402. This command is a notification from the power receiving device 401 to the power transmitting device 402 requesting foreign object detection processing using the waveform attenuation method. Then, the power receiving device 401 waits for a response from the power transmitting device 402 according to the result of execution of foreign object detection using the waveform attenuation method. Note that if a communication error is not detected in S903, the power receiving device 401 waits for a response from the power transmitting device 402 according to the result of execution of foreign object detection using the power loss method.

[0092] In S905, the power receiving apparatus 401 determines whether or not a negative response, which is information indicating the presence of a foreign object, has been received from the power transmitting apparatus 402. If a negative response has been received, in S906 the power receiving apparatus 401 transmits an EPT (End Power Transfer) command, which is a command for ending power transmission, to the power transmitting apparatus 402, and transitions to a state in which power is not received. On the other hand, if a negative response has not been received in S905, for example, if a positive response has been received, the power receiving apparatus 401 continues power reception and returns to S902.

[0093] The above is an explanation of an example of the operation of the power transmitting device 402 and the power receiving device 401. In this way, the power transmitting device 402 and the power receiving device 401 control to perform foreign object detection by the waveform attenuation method when a communication error is detected in communication between the power transmitting device 402 and the power receiving device 401. This makes it possible to detect a foreign object early and stop power transmission (or reduce the transmission power) when a foreign object is present near the power transmitting device 402 and the power receiving device 401, thereby increasing the probability of preventing an extreme temperature rise or destruction of the foreign object. In the above explanation, both the power transmitting device 402 and the power receiving device 401 perform error detection, but either the power transmitting device 402 or the power receiving device 401 may perform error detection.

[0094] As already described, the power transmitting device 402 may short-circuit the switch 108 or disconnect the switch between the power transmitting unit 103 and the closed loop circuit including the power transmitting antenna 105 at the timing of performing foreign object detection by the waveform attenuation method. This eliminates the influence of the power transmitting unit 103, the communication unit 104, and the power supply unit 102 on the attenuated waveform, enabling more accurate foreign object detection. Similarly, the power receiving device 401 may short-circuit the second switch unit 210 or disconnect the first switch unit 209 at the timing of performing foreign object detection by the waveform attenuation method. This eliminates the influence of the power receiving unit 203, the charging unit 206, and the battery 207 on the attenuated waveform, enabling more accurate foreign object detection. In this case, the power transmitting device 402 and the power receiving device 401 communicate with each other to identify the timing of performing foreign object detection.

[0095] In the above-described embodiment, when detecting a foreign object using the waveform attenuation method, the power transmitting device 402 measures the attenuation rate of the voltage applied to the power transmitting antenna 105 or the current flowing through the power transmitting antenna 105 as the attenuation state of the transmitted wave related to wireless power transmission. However, since the power transmitting antenna 105 and the power receiving antenna 205 face each other and are electromagnetically coupled, the electromagnetic energy of the power transmitting antenna 105 is also excited in the power receiving antenna 205. Therefore, foreign object detection using the waveform attenuation method can also be realized by the power receiving device 401 measuring the attenuation rate of the voltage applied to the power receiving antenna 205 or the current flowing through the power receiving antenna 205 as the attenuation state of the received wave related to wireless power transmission.

[0096] Furthermore, when the power transmitting device 402 measures the waveform attenuation factor, it may notify the power receiving device 401 of the measurement result of the waveform attenuation factor or a threshold value calculated from the measurement result. This allows the power receiving device 401 to determine the presence or absence of a foreign object based on the measurement result, etc. received from the power transmitting device 402. Similarly, when the power receiving device 401 measures the waveform attenuation factor, it may notify the power transmitting device 402 of the measurement result of the waveform attenuation factor or a threshold value calculated from the measurement result. This allows the power transmitting device 402 to determine the presence or absence of a foreign object based on the measurement result, etc. received from the power receiving device 401.

[0097] In the above description using Fig. 8 and Fig. 9, the waveform attenuation method is adopted to perform foreign object detection with high accuracy when a communication error is detected. As a result, even if a foreign object is not detected in the foreign object detection process using the power loss method that is periodically performed, the foreign object detection process using the waveform attenuation method is performed in response to the communication error, so that the foreign object can be detected and power transmission can be stopped (or the transmission power can be reduced). However, when it is desired to avoid a decrease in power transmission efficiency, the power transmitting device 402 and the power receiving device 401 may perform foreign object detection using the power loss method in response to the detection of a communication error. In this case, the power transmitting device 402 that detects a communication error in S808 of Fig. 8 may perform foreign object detection using the power loss method instead of performing foreign object detection using the waveform attenuation method in S809. Also, the power receiving device 401 that detects a communication error in S903 of Fig. 9 may transmit a foreign object detection execution command using the power loss method instead of transmitting a foreign object detection execution command using the waveform attenuation method in S904. When foreign object detection is performed using the power loss method in S809, the power transmitting device 402 requests the power receiving device 401 to transmit a command including a received power value, and detects a foreign object based on the received power value received in response to the request and the transmitted power value measured by the power transmitting device 402. When the power receiving device 402 transmits a foreign object detection execution command using the power loss method in S903, the power transmitting device 401 that receives the command performs foreign object detection using the power loss method. With this processing, even if a foreign object fails to be detected in periodic foreign object detection processing using the power loss method, the probability of detecting a foreign object increases by performing the foreign object detection processing again in response to a communication error.

[0098] When foreign object detection is performed using the power loss method in response to detection of a communication error, communication for foreign object detection is performed between the power transmitting device 402 and the power receiving device 401. However, a communication error may occur again in this communication, and the power transmitting device 402 or the power receiving device 401 may not be able to receive data from the other device, or may receive data including an unauthorized packet. If a foreign object detection execution command transmitted by the power receiving device 401 to the power transmitting device 402 is lost due to a communication error, the power transmitting device 402 does not recognize that foreign object detection is being requested, and therefore does not perform foreign object detection. Therefore, no response to the foreign object detection execution command is transmitted from the power transmitting device 402 to the power receiving device 401.

[0099] Therefore, when it is considered that such a communication error has occurred again, the power receiving device 401 may transmit an EPT command, which is a command to end power transmission, to the power transmitting device 402 and transition to a state in which power is not received. When the power transmitting device 402 receives the EPT, the power transmitting device 402 stops power transmission. Even if the power transmitting device 402 cannot receive the EPT, the power transmitting device 402 may detect that the power receiving device 401 has transitioned to a state in which power is not received, stop power transmission, and transition to the Selection phase. When a communication error occurs again in communication for detecting a foreign object in response to the detection of a communication error, it is considered that there is a high possibility that a foreign object exists or that there is a factor that interferes with communication other than a foreign object, since the frequency of communication errors is high. Therefore, by controlling the power transmission to be stopped or the power of the power transmission to be reduced in such a case, it is possible to suppress the occurrence of problems due to power transmission.

[0100] Furthermore, when foreign object detection is performed using the above-mentioned power loss method or waveform attenuation method, foreign object detection may fail. For example, if the power receiving device 401 placed on the power transmitting device 402 moves during the foreign object detection process, the measurement value used for foreign object detection may become abnormal, causing foreign object detection to fail. In this case, too, since the state may not be suitable for wireless power transmission, the power transmitting device 402 and the power receiving device 401 may stop power transmission or reduce the power of the power transmission. This can prevent problems caused by power transmission.

[0101] [Foreign object detection process in response to power drop] 8 and 9, the process of detecting a foreign object when the power transmitting device 402 and the power receiving device 401 detect a communication error has been described. Next, the process of detecting a foreign object when the power receiving device 401 detects a decrease in the received power will be described.

[0102] If a foreign object is present near the power transmitting device 402 and the power receiving device 401, the foreign object may interfere with wireless power transmission between the power transmitting device 402 and the power receiving device 401, and may cause a drop in the received power in the power receiving device 401. Therefore, when a drop in the received power of the power receiving device 401 occurs, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401, and therefore the power transmitting device 402 and the power receiving device 401 perform control to detect the foreign object.

[0103] The operation of the power transmitting device 402 and the power receiving device 401 when foreign object detection is performed in response to the power transmitting device 402 detecting a decrease in the received power of the power receiving device 401 will be described below. The power transmitting device 402 periodically receives the received power value Pr3' from the power receiving device 401 in order to perform foreign object detection by the power loss method during the power transfer phase. The power transmitting device 402 then determines whether the received power of the power receiving device 401 has decreased based on the received power value Pr3' received from the power receiving device 401 or Ploss_FO, which is a difference between Pr3 and Pr3' determined in advance. When the received power value Pr3' received from the power receiving device 401 falls below a certain threshold value or when Ploss_FO exceeds a certain threshold value, the power transmitting device 402 determines that the received power of the power receiving device 401 has decreased and performs foreign object detection by the waveform attenuation method.

[0104] That is, the power transmitting device 402 periodically performs foreign object detection using the power loss method that can maintain high power transmission efficiency, and performs foreign object detection using the waveform attenuation method that has higher foreign object detection accuracy according to the received power received from the power receiving device 401 for the foreign object detection. For example, the power transmitting device 402 may set a first threshold value for determining that a foreign object may exist and a second threshold value for determining that a foreign object exists for the value of Pr3' or Ploss_FO. Then, when Pr3' or Ploss_FO exceeds the second threshold value, the power transmitting device 402 determines that a foreign object has been detected using the power loss method, and controls to stop power transmission or reduce the transmitted power. Also, when Pr3' or Ploss_FO exceeds the first threshold value but does not exceed the second threshold value, the power transmitting device 402 performs foreign object detection using the waveform attenuation method. As a result, even if a foreign object cannot be detected using the power loss method, it is possible to detect a foreign object by performing the waveform attenuation method with higher accuracy according to a decrease in the received power. Each of the above-mentioned threshold values ​​may be set based on data obtained by the calibration process of the power loss method (straight line 1002 in FIG. 10).

[0105] In the above description, the power transmitting device 402 detects a foreign object in response to a drop in the received power of the power receiving device 401, but the power transmitting device 402 may detect a foreign object in response to a change in the transmitted power of the power transmitting device 402. The power transmitting device 402 is capable of measuring the transmitted power value transmitted by the power transmitting device 402. If the difference between the transmitted power value and a predetermined reference value is greater than a certain threshold value, the power transmitting device 402 may determine that a foreign object may be present and perform foreign object detection using a waveform attenuation method. With such a configuration, the same effect as when foreign object detection is performed in response to a drop in received power can be obtained.

[0106] Next, the operation of the power transmitting device 402 and the power receiving device 401 in the case where foreign object detection is executed in response to the power receiving device 401 detecting a decrease in the received power of the power receiving device 401 will be described. The power receiving device 401 periodically measures the power received from the power transmitting device 402 during the power transfer phase. The power receiving device 401 then determines whether the received power of the power receiving device 401 has decreased based on the periodically measured received power value. If the calculated received power value falls below a certain threshold value, or if the difference between the calculated received power value and a reference value exceeds a certain threshold value, the power receiving device 401 determines that the received power of the power receiving device 401 has decreased, and requests the power transmitting device 402 to execute foreign object detection using a waveform attenuation method.

[0107] That is, the power receiving device 401 periodically measures the received power value, and requests the power transmitting device 402 to detect a foreign object using the waveform attenuation method, which has high foreign object detection accuracy, depending on the measurement result. For example, the power receiving device 401 may transmit a foreign object detection execution command using the power loss method when the difference between the measured received power and the reference value is equal to or less than a predetermined threshold. On the other hand, the power receiving device 401 may transmit a foreign object detection execution command using the waveform attenuation method when the difference between the measured received power and the reference value exceeds the predetermined threshold. With this configuration, when there is a high possibility that a foreign object is present (when the received power is low), a foreign object is detected using the highly accurate waveform attenuation method, and when this is not the case, foreign object detection can be performed while maintaining high power transmission efficiency using the power loss method.

[0108] In addition, when the decrease in the received power value exceeds a threshold, the power receiving device 401 may determine that a foreign object is present and may request the power transmitting device 402 to stop transmitting power or to reduce the transmitted power. In addition, the power receiving device 401 may set a first threshold for determining that a foreign object may be present with respect to the decrease in the received power value and a second threshold for determining that a foreign object is present. Then, when the decrease in the received power exceeds the first threshold but does not exceed the second threshold, the power receiving device 401 requests the power transmitting device 402 to execute foreign object detection using a waveform attenuation method. In addition, when the decrease in the received power exceeds the second threshold, the power receiving device 401 may request the power transmitting device 402 to stop transmitting power by transmitting an EPT command to the power transmitting device 402. Alternatively, the power receiving device 401 may transmit a command to the power transmitting device 402 requesting that the transmitted power be reduced.

[0109] As described above, when the power transmitting device 402 and the power receiving device 401 detect a drop in the received power of the power receiving device 401, they control so that foreign object detection is performed by the waveform attenuation method. This makes it possible to detect a foreign object early when there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401.

[0110] [Foreign object detection processing according to calibration data] Next, a process for detecting foreign matter based on data obtained by calibration processing using the power loss method or data obtained by calibration processing using the waveform attenuation method will be described.

[0111] As described above, in foreign object detection using the power loss method and the waveform attenuation method, a calibration process is performed to set a threshold value that is a reference used to determine the presence or absence of a foreign object. It is assumed that the reference data obtained by these calibration processes indicates the relationship between the transmission power value and the reception power value, or the relationship between the transmission power value and the waveform attenuation rate, in a state in which there is no foreign object. Therefore, if the reference data obtained by the calibration process does not indicate a predetermined relationship that is assumed between the transmission power value and the reception power value or between the transmission power value and the waveform attenuation rate, there is a possibility that a foreign object exists near the power transmitting device 402 and the power receiving device 401. Therefore, the power transmitting device 402 and the power receiving device 401 perform control to execute foreign object detection.

[0112] First, the operation of the power transmitting device 402 and the power receiving device 401 when foreign object detection is performed according to data obtained by the calibration process of the power loss method will be described. The power transmitting device 402 and the power receiving device 401 perform the calibration process of the power loss method, which is a process for determining a threshold value used in the power loss method. The data obtained by the calibration process of the power loss method should be data that represents the relationship between the transmitted power and the received power in a state where there is no foreign object, and it is possible to pre-estimate the range of the received power value according to the transmitted power value. Therefore, when the power transmitting device 402 obtains data by the calibration process of the power loss method, it determines whether the received power value included in the data is within a range that is predetermined according to the transmitted power value. If it is outside the range, there is a possibility that a foreign object exists near the power transmitting device 402 and the power receiving device 401, so the power transmitting device 402 performs foreign object detection by the waveform attenuation method. If the presence of a foreign object is determined by the waveform attenuation method, the power transmitting device 402 stops transmitting power or controls to reduce the transmitted power. On the other hand, if the absence of a foreign object is determined by the waveform attenuation method, the power transmitting device 402 executes the calibration process by the power loss method again and updates the data.

[0113] That is, the power transmitting device 402 performs foreign object detection using a waveform attenuation method different from the power loss method, depending on the value of data obtained by the calibration process using the power loss method. With this configuration, when it is determined in the calibration process using the power loss method that there is a possibility of a foreign object being present, it is possible to detect the foreign object early by performing foreign object detection using the waveform attenuation method. Also, when the accuracy of foreign object detection using the power loss method is reduced due to inaccurate calibration data, it is possible to detect a foreign object with high accuracy using the waveform attenuation method. Note that the power receiving device 401 may determine whether or not to detect a foreign object depending on the data obtained by the calibration process.

[0114] Next, the operation of the power transmitting device 402 and the power receiving device 401 when foreign object detection is performed according to data obtained by the calibration process of the waveform attenuation method will be described. The power transmitting device 402 and the power receiving device 401 perform the calibration process of the waveform attenuation method, which is a process for determining a threshold value used in the waveform attenuation method. The reference data obtained by the calibration process of the waveform attenuation method should be data that indicates the relationship between the transmitted power and the waveform attenuation rate in a state where there is no foreign object, and it is possible to pre-estimate the range of the data. Therefore, the power transmitting device 402 judges whether the waveform attenuation rate indicated by the reference data obtained by the calibration process of the waveform attenuation method is within a predetermined range. If the waveform attenuation rate is not within the predetermined range, there is a possibility that a foreign object exists near the power transmitting device 402 and the power receiving device 401, so the power transmitting device 402 performs foreign object detection by the Power Loss method. More specifically, the power transmitting device 402 transmits a command to notify the power receiving device 401 that the Power Loss method will be performed. The power receiving apparatus 401 that has received the command transmits to the power transmitting apparatus 402 a foreign object detection execution command using the power loss method, including the received power value measured by the power receiving apparatus 401. Upon receiving the command from the power receiving apparatus 401, the power transmitting apparatus 402 executes foreign object detection using the power loss method.

[0115] If the power loss method determines that a foreign object is present, the power transmitting device 402 stops power transmission or controls the power transmission to be reduced. If the power loss method determines that no foreign object is present, the power transmitting device 402 executes the calibration process using the waveform attenuation method again to update the data. In this way, the power transmitting device 402 executes foreign object detection using a power loss method different from the waveform attenuation method, depending on the value of the data obtained by the calibration process using the waveform attenuation method. With this configuration, if the calibration process using the waveform attenuation method determines that a foreign object may be present, foreign object detection using the power loss method can be executed to detect the foreign object early. Note that the power receiving device 401 may determine whether a foreign object is detected depending on the data obtained by the calibration process.

[0116] [Foreign object detection process according to temperature rise] A process of detecting a foreign object in response to detection of a temperature rise of the power transmitting device 402 or the power receiving device 401 will be described. Possible causes of a rise in temperature of the power transmitting device 402 or the power receiving device 401 include heat generation from an electric circuit including an antenna or the like of the power transmitting device 402 and the power receiving device 401, and heat generation from a CPU due to various processes. In addition, if a foreign object is present near the power transmitting device 402 and the power receiving device 401, the foreign object may consume part of the energy of the transmitted power and generate heat, which may cause the temperature of the power transmitting device 402 or the power receiving device 401 in contact with the foreign object to rise. Therefore, if the temperature of the power transmitting device 402 or the power receiving device 401 rises above a predetermined threshold, there is a possibility that a foreign object is present near the power transmitting device 402 and the power receiving device 401, and therefore the power transmitting device 402 and the power receiving device 401 perform control to detect a foreign object.

[0117] First, the operation of the power transmitting device 402 and the power receiving device 401 when the power transmitting device 402 detects a temperature rise will be described. The power transmitting device 402 has a temperature sensor, and when the temperature sensor detects that the temperature of the power transmitting device 402 exceeds a predetermined threshold, the power transmitting device 402 executes foreign object detection using a waveform attenuation method. When it is determined that a foreign object is present, the power transmitting device 402 stops power transmission or controls the transmission power to be reduced.

[0118] Here, the reason why foreign object detection is performed using the waveform attenuation method rather than the power loss method is as follows. That is, in the power loss method, the power transmitting device 402 needs to receive the received power value from the power receiving device 401, but in the waveform attenuation method, the power transmitting device 402 does not need information from the power receiving device 401, so foreign object detection can be performed in a short time. Also, the waveform attenuation method can perform foreign object detection with higher accuracy than the power loss method. That is, when the temperature of the power transmitting device 402 is high and there is a possibility that a foreign object is present, the power transmitting device 402 can detect a foreign object early and with high accuracy using the waveform attenuation method. However, foreign object detection may be performed using the power loss method. In this case, the power transmitting device 402 notifies the power receiving device 401 that foreign object detection will be performed using the power loss method. When the power receiving device 401 receives the notification, it transmits a foreign object detection execution command using the power loss method to the power transmitting device 402, including the received power value measured by the power receiving device 401.

[0119] Next, the operation of the power transmitting device 402 and the power receiving device 401 when the power receiving device 401 detects a temperature rise will be described. The power receiving device 401 has a temperature sensor, and when the temperature sensor detects that the temperature of the power receiving device 401 exceeds a predetermined threshold, the power receiving device 401 transmits a foreign object detection execution command using the waveform attenuation method to the power transmitting device 402. Then, the power transmitting device 402 executes foreign object detection using the waveform attenuation method, and when it is determined that a foreign object is present, it stops power transmission or controls so as to reduce the transmitted power. Note that foreign object detection may be performed using a power loss method instead of the waveform attenuation method. In this case, the power receiving device 401 transmits a foreign object detection execution command using the power loss method to the power transmitting device 402 in response to temperature information detected by the temperature sensor.

[0120] In addition, there may be cases where the allowable temperature of a device that transmits or receives power is specified by standards or the laws of each country. Therefore, by setting the threshold value for determining whether to perform the above foreign object detection lower than these specified values, even if a temperature rise occurs due to a foreign object, it is possible to detect the foreign object early before the temperature reaches the specified value.

[0121] [Foreign object detection processing according to transmission power] Next, a process will be described in which foreign object detection is performed by a method selected according to the transmission power transmitted from the power transmitting device 402. As described above, the power loss method detects a foreign object based on the loss of power related to power transmission during power transmission from the power transmitting device 402 to the power receiving device 401, and has a disadvantage that the accuracy of foreign object detection decreases when the power transmitting device 402 is transmitting large power. On the other hand, it has an advantage that the power transmission efficiency can be kept high because foreign object detection can be performed while continuing power transmission. In addition, the waveform attenuation method detects a foreign object by observing the attenuation rate of the transmitted wave when the power transmitting device 402 temporarily stops transmitting power, and therefore has a disadvantage that the power transmission efficiency decreases due to a temporary suspension of power transmission. On the other hand, it has an advantage that a foreign object can be detected with high accuracy even when it is performed during power transmission of large power.

[0122] Therefore, when the transmission power value from the power transmitting device 402 is less than a predetermined threshold, the power transmitting device 402 and the power receiving device 401 are controlled to perform foreign object detection only using the power loss method. This is because, when the transmission power is low, the power loss method also has high foreign object detection accuracy, so the power loss method, which can maintain high power transmission efficiency, is advantageous. On the other hand, when the transmission power from the power transmitting device 402 is equal to or greater than a predetermined threshold, the power transmitting device 402 and the power receiving device 401 are controlled to perform foreign object detection using both the power loss method and the waveform attenuation method, or to perform foreign object detection only using the waveform attenuation method. This is because, when the transmission power is high, the accuracy of foreign object detection using the power loss method decreases, so it is effective to use the waveform attenuation method, which has high foreign object detection accuracy. In this way, by using a plurality of foreign object detection methods according to the transmission power, it is possible to improve foreign object detection accuracy while maintaining high power transmission efficiency.

[0123] In the above-mentioned explanations of the foreign object detection process in response to a communication error, the foreign object detection process in response to a power drop, the foreign object detection process in response to calibration data, and the foreign object detection process in response to temperature information, the explanations were focused on the cases where both the power loss method and the waveform attenuation method are used. However, when the transmission power is lower than a predetermined threshold, the foreign object detection may be performed by the power loss method at the timing when the foreign object detection is performed by the waveform attenuation method in these embodiments. Also, when the transmission power is equal to or higher than a predetermined threshold, both the power loss method and the waveform attenuation method may be used, or the foreign object detection may be performed by the waveform attenuation method at the timing when the foreign object detection is performed by the power loss method in the above-mentioned embodiments.

[0124] In the present embodiment, the wireless power transmission system determines whether a predetermined condition related to the state of at least one of the power transmitting device 402 and the power receiving device 401 is satisfied, and selectively uses the power loss method and the waveform attenuation method depending on the determination result. However, the present invention is not limited to this, and at least one of the power transmitting device 402 and the power receiving device 401 may selectively use a plurality of foreign object detection methods, including foreign object detection methods other than those described above, depending on the conditions. Furthermore, the wireless power transmission system may select a foreign object detection method or control foreign object detection processing by combining a plurality of conditions, including the various conditions described above and other conditions.

[0125] The present invention can also be realized by supplying a program for implementing one or more of the functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC, etc.) that implements one or more of the functions. The program may also be provided by recording it on a computer-readable storage medium. [Explanation of symbols]

[0126] 401 Power receiving device 402 Power transmission equipment

Claims

1. A power transmission device, A power transmitting means for wirelessly transmitting power to a power receiving device; a first detection means for periodically executing a detection process by a first detection method for detecting an object other than the power receiving device based on a power loss related to the power transmission by the power transmission means; a determination means for determining whether a predetermined condition related to a state of at least one of the power transmitting device and the power receiving device is satisfied; A power transmission device characterized by having a second detection means that executes a detection process using a second detection method to detect the object based on at least one of a voltage attenuation state and a current attenuation state related to power transmission by the power transmission means, in accordance with the result of judgment by the judgment means.

2. The power transmitting device according to claim 1 , wherein the predetermined condition includes at least one of a condition related to accuracy of detection of the object by the first detection method and a condition related to a possibility that the object is present.

3. the predetermined condition includes a condition that a communication error occurs in at least one of the power transmitting device and the power receiving device, The power transmitting device according to claim 1 , wherein the second detecting means executes the detection process by the second detection method when the determining means determines that the predetermined condition is satisfied.

4. the predetermined condition includes a condition that a received power value of the power receiving device in response to power transmission by the power transmitting device is less than a predetermined threshold value; The power transmitting device according to claim 1 , wherein the second detecting means executes the detection process by the second detection method when the determining means determines that the predetermined condition is satisfied.

5. the predetermined condition includes a condition that, in a combination of a transmission power value of the power transmitting device acquired as reference data for the first detection method and a reception power value of the power receiving device corresponding to the power transmission by the power transmitting device, the reception power value is not included in a range predetermined according to the transmission power value; The power transmitting device according to claim 1 , wherein the second detecting means executes the detection process by the second detection method when the determining means determines that the predetermined condition is satisfied.

6. the determination means determines whether at least one of a voltage attenuation state and a current attenuation state related to the power transmission by the power transmitting means, which are acquired as reference data for the second detection method, is outside a predetermined range of attenuation states; The power transmitting device according to claim 5 , wherein the first detecting means executes the detection process by the first detection method when the determining means determines that the attenuation state is outside the predetermined range.

7. the predetermined condition includes a condition that the temperature of at least one of the power transmitting device and the power receiving device is equal to or higher than a predetermined threshold; The power transmitting device according to claim 1 , wherein the second detecting means executes the detection process by the second detection method when the determining means determines that the predetermined condition is satisfied.

8. the predetermined condition includes a condition that a transmission power value of the power transmitting device is equal to or greater than a predetermined threshold value, The power transmitting device according to claim 1 , wherein the second detecting means executes the detection process by the second detection method when the determining means determines that the predetermined condition is satisfied.

9. The power transmission device according to claim 8, characterized in that when the determination means determines that the specified condition is not satisfied, the first detection means performs detection processing using the first detection method and the second detection means does not perform detection processing using the second detection method.

10. A power transmission device as described in any one of claims 1 to 9, characterized in that in the first detection method, the object is determined to be present when a power loss based on the transmission power value of the power transmission device and the received power value of the power receiving device in response to power transmission by the power transmission device exceeds a threshold value.

11. The power transmission device according to any one of claims 1 to 10, characterized in that in the second detection method, the object is determined to be present when the attenuation rate of the amplitude of at least any of the voltage waveform related to power transmission, the current waveform related to power transmission, the voltage waveform related to power reception, and the current waveform related to power reception during a period in which the power transmission device temporarily suspends power transmission during power transmission exceeds a threshold value.

12. 12. The power transmitting device according to claim 1, wherein the power transmitting means transmits power to the power receiving device in accordance with a Wireless Power Consortium (WPC) standard.

13. A power receiving device, a power receiving unit that receives power wirelessly transmitted from a power transmitting device; a first request means for periodically requesting the power transmitting device to perform a detection process using a first detection method for detecting an object other than the power receiving device based on a power loss related to power transmission from the power transmitting device; a determination means for determining whether a predetermined condition related to a state of at least one of the power transmitting device and the power receiving device is satisfied; A power receiving device characterized by having a second request means that requests the power transmitting device to perform a detection process using a second detection method that detects the object based on at least one of a voltage attenuation state and a current attenuation state related to the power transmission from the power transmitting device in accordance with the result of the judgment by the judgment means.

14. The power receiving device according to claim 13 , wherein the predetermined condition includes at least one of a condition related to accuracy of detection of the object by the first detection method and a condition related to a possibility that the object exists.

15. A control method for a wireless power transmission system having a power transmitting device and a power receiving device, comprising: a power transmitting step of wirelessly transmitting power from the power transmitting device to the power receiving device; a first detection process of periodically executing a detection process by a first detection method for detecting an object other than the power receiving device based on a power loss related to the power transmission in the power transmitting process; a determination step of determining whether a predetermined condition related to a state of at least one of the power transmitting device and the power receiving device is satisfied; A control method characterized by having a second detection process of executing a detection process using a second detection method that detects the object based on at least one of the voltage attenuation state and the current attenuation state related to the power transmission in the power transmission process, depending on the result of the judgment in the judgment process.

16. 16. The control method according to claim 15, wherein the predetermined condition includes at least one of a condition related to accuracy of detection of the object by the first detection method and a condition related to a possibility that the object exists.

17. A program for causing a computer to function as each of the means of the power transmitting device according to any one of claims 1 to 12 or the means of the power receiving device according to claim 13 or 14.

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