Power transmission device and method performed by the power transmission device

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 wireless power transmission technology.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems 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 different from the power reception device, based on the measurement result of the power loss generated between the power transmission device and the power reception device during power transmission from the power transmission device to the power reception 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 the signal transmitted by the power transmission device. Thus, although a plurality of methods for detecting a foreign object in performing wireless power transmission are conceivable, a method for appropriately controlling the detection process when a plurality of these detection methods can be executed has not been established.

[0005] The present invention has been made in view of the above problems, and an object thereof is to appropriately control foreign object detection processing in performing wireless power transmission.

Means for Solving the Problems

[0006] As one means for solving the above problems, the power transmission device of the present invention has the following configuration. That is, the power transmission device includes transmission means for transmitting an Analog Ping, and after transmitting the Analog Ping, electricity Pressure acquires a first quality factor from a first attenuation envelope, and after acquiring the first quality factor, electricity Pressure acquisition means for acquiring a second quality factor from a second attenuation envelope, and based on the result of comparison between the first quality factor and the second quality factor Determine the presence or absence of foreign matter determination means for determining, Wirelessly to the power receiving device power transmission means for performing power transmission, and has After acquiring the first quality factor and after the Negotiation phase has ended, the voltage is measured during the period when the power transmission is restricted, and the second quality factor is acquired from the second attenuation envelope of the voltage it.

Effects of the Invention

[0007] According to the present invention, it is possible to appropriately control foreign object detection processing in performing wireless power transmission.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

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

[0010] [Configuration of Wireless Power Transmission System] FIG. 4 shows a configuration example of a wireless power transmission system (wireless charging system) according to the present embodiment. In one example, this system includes a power receiving device 401 and a power transmitting device 402. The detailed configurations of the power receiving device 401 and the power transmitting device 402 will be described later with reference to FIGS. 2 and 1. Hereinafter, the power receiving device 401 may be referred to as RX, and the power transmitting device 402 may be referred to as TX. RX is an electronic device that receives power from TX and charges a built-in battery. TX is an electronic device that wirelessly transmits power to RX placed on a charging stand 403 which is a part of TX. Hereinafter, since the charging stand 403 is a part of TX, "placed on the charging stand 403" may be referred to as "placed on TX (power transmitting device 402)". The range 404 surrounded by the dotted line is the range where RX can receive power from TX. Note that RX and TX may have functions to execute applications other than wireless charging. An example of RX is a smartphone, and an example of TX is an accessory device for charging the smartphone. RX and TX may be storage devices such as tablets, hard disk devices, and memory devices, or information processing devices such as personal computers (PCs). Also, RX and TX may be, for example, imaging devices (cameras, video cameras, etc.), automobiles, robots, medical devices, and printers.

[0011] In this system, wireless power transmission using an electromagnetic induction method for wireless charging is performed 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 other electromagnetic induction methods, magnetic field resonance methods, electric field resonance methods, microwave methods, methods using lasers, etc. Also, in the present embodiment, it is assumed that wireless power transmission is used for wireless charging, but wireless power transmission may be performed for uses other than wireless charging.

[0012] In the WPC standard, the amount of power guaranteed when the power receiving device 401 receives power from the power transmitting device 402 is defined by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates the power value that guarantees the output to the load (e.g., a charging circuit, a battery, etc.) of the power receiving device 401 even if, for example, 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 GP is 5 watts, even if the positional relationship between the power receiving antenna 205 and the power transmitting antenna 105 changes and the power transmission efficiency decreases, the power transmitting device 402 controls the power transmission so that it can output 5 watts to the load in the power receiving device 401.

[0013] Also, when power is transmitted from the power transmitting device 402 to the power receiving device 401, if there is a foreign object, which is an object other than the power receiving device 401, near the power transmitting device 402, there is a risk that the electromagnetic wave for power transmission will affect the foreign object and increase the temperature of the foreign object or destroy the foreign object. Therefore, in the WPC standard, a method for the power transmitting device 402 to detect the presence of a foreign object on the charging stand 403 is defined so that the temperature rise or destruction of the foreign object can be prevented by stopping the power transmission when a foreign object is present. Specifically, the Power Loss method for detecting a foreign object based on the difference between the power transmitted by the power transmitting device 402 and the power received by the power receiving device 401 is defined. Also, the Q-value measurement method for detecting a foreign object based on the change in the quality factor (Q-value) of the power transmitting antenna 105 (power transmitting coil) in the power transmitting device 402 is defined. Note that the foreign object detected by the power transmitting device 402 in this embodiment is not limited to an object existing on the charging stand 403. The power transmitting device 402 only needs to detect a foreign object located near the power transmitting device 402, and for example, it may detect a foreign object located within the range where the power transmitting device 402 can transmit power.

[0014] Regarding foreign object detection based on the Power Loss method defined in the WPC standard, it will be described with reference to FIG. 10. The horizontal axis of FIG. 10 is the power transmitted by the power transmission device 402, and the vertical axis is the power received by the power reception device 401. Here, a foreign object is an object other than the power reception device 401 that can affect the power transmission from the power transmission device 402 to the power reception device 401, such as an object like a conductive metal piece.

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

[0016] Subsequently, the power transmission device 402 changes the power transmission value to the second power transmission value Pt2 and performs power transmission to the power reception device 401. The power reception device 401 receives power at the second power reception value Pr2 (this state is referred to as the Connected Load state (load connection state)). Then, the power transmission device 402 stores the second power transmission value Pt2. Here, the second power transmission value Pt2 or the second power reception value Pr2 is the predetermined maximum power transmission or power reception. At this time, the power reception device 401 controls the load so that the received power becomes the maximum power. For example, the power reception device 401 connects the power reception antenna 205 and the load so that the received power is supplied to the load. Subsequently, the power reception device 401 reports Pr2 to the power transmission device 402. The power transmission device 402 that has received Pr2 from the power reception device 401 can calculate that the power loss between the power transmission device 402 and the power reception device 401 is Pt2 - Pr2 (= Ploss2) and create a calibration point 1001 indicating the correspondence between Pt2 and Pr2.

[0017] Then, the power transmission device 402 creates a straight line 1002 that linearly interpolates between the calibration point 1000 and the calibration point 1001. The straight line 1002 shows the relationship between the power transmission and the power reception in a state where there is no foreign object in the vicinity of the power transmission device 402 and the power reception device 401. Based on the straight line 1002, the power transmission device 402 can predict the power value received by the power reception device 401 when power is transmitted at a predetermined power transmission in a state without a foreign object. For example, when the power transmission device 402 transmits power at the third power transmission value Pt3, it can be inferred that the third power reception value received by the power reception device 401 is Pr3 from the point 1003 corresponding to Pt3 on the straight line 1002.

[0018] As described above, based on a plurality of combinations of the transmitted power value of the power transmission device 402 and the received power value of the power reception device 401 measured while changing the load, it is possible to obtain the power loss between the power transmission device 402 and the power reception device 401 according to the load. Further, by interpolation from the plurality of combinations, it is possible to estimate the power loss between the power transmission device 402 and the power reception device 401 corresponding to all loads. Thus, the calibration process performed by the power transmission device 402 and the power reception device 401 for the power transmission device 402 to obtain a combination of the transmitted power value and the received power value is hereinafter referred to as "Calibration Process (CAL Process) of the Power Loss Method".

[0019] After calibration, assume that when the power transmission device 402 actually transmits power to the power reception device 401 at Pt3, the power transmission device 402 receives a value Pr3' of the received power value from the power reception device 401. The power transmission device 402 calculates a value Pr3 - Pr3' (= Ploss_FO) obtained by subtracting the received power value Pr3' actually received from the power reception device 401 from the received power value Pr3 in a state where no foreign object exists. This Ploss_FO can be considered as the power loss due to the power consumed by the foreign object when a foreign object exists in the vicinity of the power transmission device 402 and the power reception device 401. Therefore, when the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold value, it can be determined that a foreign object exists. Alternatively, the power transmission device 402 may previously obtain the power loss Pt3 - Pr3 (= Ploss3) between the power transmission device 402 and the power reception device 401 from the received power value Pr3 in a state where no foreign object exists. Then, next, from the received power value Pr3' received from the power reception device 401 in a state where a foreign object exists, the power loss Pt3 - Pr3' (= Ploss3') between the power transmission device 402 and the power reception device 401 in a state where a foreign object exists is obtained. And the power Ploss_FO that would have been consumed by the foreign object may be estimated using Ploss3' - Ploss3 (== Ploss_FO).

[0020] As described above, as a method for obtaining the power Ploss_FO that would be consumed by foreign matter, it may be obtained as Pr3 - Pr3’ (= Ploss_FO), or it may be obtained as Ploss3’ - Ploss3 (= Ploss_FO). In the following description of this specification, basically, the method of obtaining it as Ploss3’ - Ploss3 (= Ploss_FO) will be described, but the content of this embodiment is also applicable to the method of obtaining it as Pr3 - Pr3’ (= Ploss_FO). The above is the explanation of foreign matter detection based on the Power Loss method.

[0021] Foreign matter detection by the Power Loss method is performed during power transmission (power transfer, to be described later) based on the data obtained by the Calibration phase to be described later. Also, foreign matter detection by the Q value measurement method is performed before power transmission (before Digital Ping transmission, Negotiation phase or Renegotiation phase to be described later).

[0022] The RX and TX according to this embodiment perform communication for power transmission and reception control based on the WPC standard. The WPC standard defines a plurality of phases including a Power Transfer phase in which power transmission is executed and one or more phases before actual power transmission, and communication for power transmission and reception control required in each phase is performed. The phases before power transmission may include a Selection phase, a Ping phase, an Identification and Configuration phase, a Negotiation phase, and a Calibration phase. Hereinafter, the Identification and Configuration phase will be referred to as the I&C phase. The processing of each phase will be described below.

[0023] In the Selection phase, the TX intermittently transmits an Analog Ping and detects that an object is placed on the charging stand of the TX (for example, an RX, a conductor piece, etc. is placed on the charging stand). The TX detects at least one of the voltage value and the current value of the power transmission antenna 105 when transmitting the Analog Ping, and determines that an object exists when the voltage value is lower than a certain threshold or the current value exceeds a certain threshold, and then transitions to the Ping phase.

[0024] In the Ping phase, the TX transmits a Digital Ping with higher power than the Analog Ping. The power of the Digital Ping is sufficient to activate the control unit of the RX placed on the TX. The RX notifies the TX of the magnitude of the received power voltage. In this way, the TX recognizes that the object detected in the Selection phase is the RX by receiving the response from the RX that has received the Digital Ping. When receiving the notification of the received power voltage value, the TX transitions to the I&C phase. Also, before transmitting the Digital Ping, the TX measures the Q value (Q-Factor) of the power transmission antenna 105. This measurement result is used when performing foreign object detection processing using the Q value measurement method.

[0025] In the I&C phase, the TX identifies the RX and acquires 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 that has received the ID Packet and the Configuration Packet responds with an acknowledge (ACK, positive response). Then, the I&C phase ends.

[0026] In the negotiation phase, the value of GP is determined based on the value of GP required by the RX, the power transmission capacity of the TX, etc. Also, the TX executes foreign object detection processing using the Q-value measurement method in accordance with the request from the RX. Further, in the WPC standard, after once shifting to the Power Transfer phase, a method of performing the same processing as in the Negotiation phase again according to the request of the RX is defined. The phase of performing these processes after shifting from the Power Transfer phase is called the Renegotiation phase.

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

[0028] In the Power Transfer phase, control for starting, continuing power transmission, and stopping power transmission due to errors or full charge is performed. The TX and the RX perform communication by superimposing a signal on the electromagnetic wave transmitted from the power transmission antenna 105 or the power reception antenna 205 using the power transmission antenna 105 and the power reception antenna 205 used when performing wireless power transmission based on the WPC standard for these power transmission and reception controls. Note that the range in which communication based on the WPC standard is possible between the TX and the RX is almost the same as the power transmission range of the TX.

[0029] [Configuration of Power Transmission Device 402 and Power Reception Device 401] Next, the configurations of the power transmission device 402 (TX) and the power reception device 401 (RX) in the present embodiment will be described. Note that the configurations described below are merely examples, and part (or in some cases, all) of the described configurations may be replaced with other configurations that perform the same functions or omitted, and additional configurations may be added to the described configurations. Further, one block shown in the following description may be divided into a plurality of blocks, or a plurality of blocks may be integrated into one block. Also, each functional block shown below is assumed to have its functions implemented as a software program, but part or all of the functional blocks may be implemented in hardware.

[0030] FIG. 1 is a functional block diagram showing a configuration example of the power transmission device 402 (TX) according to the present embodiment. The TX includes a control unit 101, a power supply unit 102, a power transmission unit 103, a communication unit 104, a power transmission antenna 105, a memory 106, a resonance capacitor 107, and a switch 108. In FIG. 1, the control unit 101, the power supply unit 102, the power transmission unit 103, the communication unit 104, and the memory 106 are shown as separate entities, but any plurality of these functional blocks may be implemented on the same chip.

[0031] The control unit 101 controls the entire TX by executing, for example, a control program stored in the memory 106. The control unit 101 also performs control related to power transmission control including communication for device authentication in the TX. Further, the control unit 101 may perform control for executing applications other than wireless power transmission. The control unit 101 includes one or more processors such as, for example, a CPU (Central Processing Unit) or an MPU (MicroProcessor Unit). Note that the control unit 101 may be configured by hardware such as an application specific integrated circuit (ASIC). Also, the control unit 101 may be configured to include an array circuit such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processing. The control unit 101 causes the memory 106 to store information to be stored during the execution of various processes. Also, the control unit 101 can 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. Electric power supplied from the commercial power supply is stored in the battery.

[0033] The power transmission 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 an electromagnetic wave for causing power reception in the RX by inputting the AC power to the power transmission antenna 105. For example, the power transmission unit 103 converts the DC voltage supplied by the power supply unit 102 into an AC voltage using a switching circuit having a half-bridge or full-bridge configuration using FETs (Field Effect Transisters). In this case, the power transmission unit 103 includes a gate driver that controls the ON / OFF of the FETs.

[0034] The power transmission unit 103 controls the intensity of the electromagnetic wave to be output by adjusting the voltage (transmission voltage) or current (transmission current), or both, input to the power transmission antenna 105. When the transmission voltage or transmission current is increased, the intensity of the electromagnetic wave becomes stronger, and when the transmission voltage or transmission current is decreased, the intensity of the electromagnetic wave becomes weaker. Also, the power transmission unit 103 performs output control of AC power so that power transmission from the power transmission antenna 105 is started or stopped based on an instruction from the control unit 101. Further, it is assumed that the power transmission unit 103 has the ability to supply power sufficient to output 15 watts (W) of power to the charging unit 206 of the power receiving device 401 (RX) compliant with the WPC standard.

[0035] The communication unit 104 communicates with the RX for power transmission control based on the WPC standard as described above. The communication unit 104 modulates the electromagnetic wave output from the power transmission antenna 105, transmits information to the RX, and performs communication. Also, the communication unit 104 demodulates the electromagnetic wave transmitted from the power transmission antenna 105 modulated by the RX and acquires the information transmitted by the RX. That is, the communication performed by the communication unit 104 is performed with a signal superimposed on the electromagnetic wave transmitted from the power transmission antenna 105. Also, the communication unit 104 may communicate with the RX by communication according to a standard different from the WPC standard using an antenna different from the power transmission antenna 105, or may communicate with the RX by selectively using a plurality of communications.

[0036] In addition to storing the control program, the memory 106 can also store the states of the TX and RX (such as the power transmission power value, power reception power value, etc.). For example, the state of the TX is acquired by the control unit 101, and the state of the RX is acquired by the control unit 201 of the RX and can be received via the communication unit 104.

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

[0038] FIG. 2 is a block diagram showing a configuration example of power receiving device 401 (RX) according to this embodiment. RX includes control unit 201, UI (user interface) unit 202, power receiving unit 203, communication unit 204, power receiving antenna 205, charging unit 206, battery 207, memory 208, first switch unit 209, second switch unit 210, and resonance capacitor 211. Note that a plurality of functional blocks shown in FIG. 2 may be realized as one hardware module.

[0039] Control unit 201 controls the entire RX by executing, for example, a control program stored in memory 208. That is, control unit 201 controls each functional unit shown in FIG. 2. Further, control unit 201 may perform control for executing applications other than wireless power transmission. An example of control unit 201 includes one or more processors such as a CPU or MPU. Note that the entire RX (the entire smartphone when RX is a smartphone) may be controlled in cooperation with the OS (Operating System) being executed by control unit 201.

[0040] Further, control unit 201 may be configured by hardware such as an ASIC. Also, control unit 201 may include an array circuit such as an FPGA compiled to execute predetermined processing. Control unit 201 stores information to be stored during execution of various processes in memory 208. Also, control unit 201 can measure time using a timer (not shown).

[0041] The UI unit 202 performs various outputs for the user. The various outputs here refer to operations such as screen display, blinking and color change of an LED (Light Emitting Diode), audio output by a speaker, and vibration of the RX main body. The UI unit 202 is realized by a liquid crystal panel, a speaker, a vibration motor, etc.

[0042] The power receiving unit 203 acquires alternating current power (alternating current voltage and alternating current) generated by electromagnetic induction based on the electromagnetic wave radiated from the power transmitting antenna 105 of the TX via the power receiving antenna 205. Then, the power receiving unit 203 converts the alternating current power into direct current or alternating current power of a predetermined frequency, and outputs the power to a charging unit 206 that performs a process of charging the battery 207. That is, the power receiving unit 203 includes a rectifying unit and a voltage control unit necessary for supplying power to the load in the RX. The above-mentioned GP is the amount of electric power guaranteed to be output from the power receiving unit 203. It is assumed that the power receiving unit 203 has the ability to supply power for the charging unit 206 to charge the battery 207 and supply power sufficient to output 15 watts of power to the charging unit 206.

[0043] The communication unit 204 performs communication for power reception control based on the WPC standard as described above with the communication unit 104 of the TX. The communication unit 204 demodulates the electromagnetic wave input from the power receiving antenna 205 to acquire the information transmitted from the TX. Then, the communication unit 204 performs communication with the TX by superimposing a signal regarding the information to be transmitted to the TX on the electromagnetic wave by load-modulating the input electromagnetic wave. Note that the communication unit 204 may communicate with the TX by a standard different from the WPC standard using an antenna different from the power receiving antenna 205, or may communicate with the TX by selectively using a plurality of communications.

[0044] The memory 208 stores not only the control program but also the states of the TX and RX, etc. For example, the state of the RX is acquired by the control unit 201, and the state of the TX is acquired by the control unit 101 of the TX 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 resonance capacitor 211. When the second switch unit 210 is turned on and short-circuited, the power receiving antenna 205 and the resonance capacitor 211 form a series resonance circuit and resonate at a specific frequency f2. At this time, a current flows through the closed circuit formed by the power receiving antenna 205, the resonance 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 resonance capacitor 211 is supplied to the power receiving unit 203.

[0046] The first switch unit 209 is for controlling whether to supply the received power to the battery as a load. It also has a function of controlling the value of the load. If the first switch unit 209 connects the charging unit 206 and the battery 207, the received power is supplied to the battery 207. If the first switch unit 209 disconnects the connection between the charging unit 206 and the battery 207, the received power is not supplied to the battery 207. In FIG. 2, the first switch unit 209 is arranged between the charging unit 206 and the battery 207, but it may also be arranged between the power receiving unit 203 and the charging unit 206. Alternatively, it may be arranged between the closed circuit formed by the power receiving antenna 205, the resonance capacitor 211, and the second switch unit 210 and the power receiving unit 203. That is, the first switch unit 209 may be for controlling whether to supply the received power to the power receiving unit 203. Also, in FIG. 2, the first switch unit 209 is described as one block, but it is also possible to realize the first switch unit 209 as a part of the charging unit 206 or a part of the power receiving unit 203.

[0047] Next, with reference to FIG. 3, the functions of the control unit 101 of the TX will be described. FIG. 3 is a block diagram showing a functional configuration example of the control unit 101 of the power transmission device 402 (TX). The control unit 101 includes a communication control unit 301, a power transmission control unit 302, a measurement unit 303, a setting unit 304, and a foreign object detection unit 305. 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 the power transmission to the RX. The measurement unit 303 measures the waveform attenuation index described later. Also, the power measured for transmission to the RX via the power transmission unit 103 is measured, and the average power transmission is measured per unit time. Further, the measurement unit 303 measures the Q value of the power transmission antenna 105. The setting unit 304 sets a threshold value used for foreign object detection based on the waveform attenuation index measured by the measurement unit 303, for example, by a calculation process.

[0048] The foreign object detection unit 305 can implement a foreign object detection function based on the Power Loss method, a foreign object detection function based on the Q value measurement method, and a foreign object detection function based on the waveform attenuation method. Also, the foreign object detection unit 305 may have a function for performing foreign object detection processing using other methods. For example, in a TX equipped with an NFC (Near Feald Communication) communication function, the foreign object detection unit 305 may perform foreign object detection processing using the opposing device detection function based on the NFC standard. Also, as a function other than detecting foreign objects, the foreign object detection unit 305 can detect that the state on the TX has changed. For example, the TX can also 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 serves as a criterion for determining the presence or absence of foreign objects when the TX performs foreign object detection based on the Power Loss method, the Q value measurement method, or the waveform attenuation method. Also, the setting unit 304 may have a function of setting a threshold value that serves as a criterion for determining the presence or absence of foreign objects, which is necessary for performing foreign object detection processing using other methods. Also, the foreign object detection unit 305 can perform foreign object detection processing based on the threshold value set by the setting unit 304 and the waveform attenuation index, power transmission, or Q value measured by the measurement unit 303.

[0049] 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 realize their functions as programs operating in the control unit 101. Each processing unit is configured as an independent program and can operate in parallel while synchronizing between programs through event processing or the like. However, two or more of these processing units may be incorporated into one program.

[0050] [Flow of processing for power transmission according to the WPC standard) In the WPC standard, a Selection phase, a Ping phase, an I&C phase, a Negotiation phase, a Calibration phase, and a Power Transfer phase are defined. Hereinafter, the operations of the power transmission device 402 and the power reception device 401 in these phases will be described using the sequence diagram of FIG. 5. FIG. 5 is a sequence diagram for power transmission according to the WPC standard. Here, the power transmission device 402 (TX) and the power reception device 401 (RX) will be described as examples.

[0051] TX repeatedly and intermittently transmits the Analog Ping of the WPC standard to detect objects within the power transmission range (F501). 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 closer to the TX to charge the RX (e.g., a smartphone) (F502). For example, the RX is brought closer to the TX by placing the RX on the TX. When TX detects that there is an object within the power transmission range (F503, F504), it transmits the Digital Ping of the WPC standard (F505). When the RX receives the Digital Ping, it can grasp that the TX has detected the RX (F506). Also, when there is a predetermined response to the Digital Ping, TX determines that the detected object is the RX and the RX is placed on the charging stand 403. When TX detects the placement of the RX, it 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 information elements that can identify the corresponding WPC standard version, the Maximum Power Value which is a value specifying the maximum power that the RX can supply to the load, and information indicating whether the RX has the Negotiation function of the WPC standard. Note that TX may acquire the identification information and capability information of the RX by methods other than communication in the I&C phase of the WPC standard. Also, the identification information may be any other identification information that can identify the individual RX, such as the Wireless Power ID. The capability information may include information other than the above.

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

[0053] After determining GP, TX performs Calibration based on the GP. In the Calibration process, first, RX transmits information including the received power in the light load state (load-disconnected state, load state where the transmission power is below the first threshold) to TX (hereinafter referred to as the first reference received power information) (F509). The first reference received power information in this embodiment is the received power information of RX when the transmission power of TX is 250 milliwatts. The first reference received power information is Received Power Packet (mode1) defined by the WPC standard, but other messages may also be used. TX determines whether to accept the first reference received power information based on its own transmission state. If TX accepts it, it sends an affirmative response = ACK to RX; if it does not accept it, it sends a negative response = NAK to RX.

[0054] Next, when RX receives ACK from TX (F510), it performs processing to transmit information including the received power in the load-connected state (maximum load state, load state where the transmission power is above the second threshold) to TX (hereinafter referred to as the second reference received power information). In this embodiment, since GP is 5 watts, the second reference received power information is the received power information of RX when the transmission power of TX is 5 watts. Here, the second reference received power information is Received Power Packet (mode2) defined by the WPC standard, but other messages may also be used. RX sends a transmission output change instruction including a positive value to increase the transmission power from TX to 5 watts (F511).

[0055] TX receives the power transmission output change instruction described above. When it is possible to increase the power transmission power, it responds with ACK and increases the power transmission power (F512, F513). Since the second reference received power information is the received power information when the power transmission power of TX is 5 watts, when TX receives a power increase request exceeding 5 watts from RX (F514), it responds with NAK to the power transmission output change instruction. Thereby, power transmission exceeding the regulation is suppressed (F515).

[0056] When RX determines that the predetermined power transmission power has been reached by receiving NAK from TX, it transmits information including the received power in the load connection state to TX as the second reference received power information (F516). TX can calculate the power loss amount between TX and RX in the light load state and the load connection state based on the power transmission power value of TX and the received power values included in the first and second reference received power information. Also, by interpolating between those power loss amounts, it is possible to calculate the power loss value between TX and RX at all power transmission powers that TX can take (in this case, from 250 mW to 5 watts) (F517). TX transmits ACK to the second reference received power information from RX (F518) and completes the Calibration process. When TX, which has determined that it is possible to start the charging process, starts the power transmission process to RX, the charging of RX is started. Before starting the power transmission process, TX and RX perform device authentication processing (F519). When it is determined that the mutual devices can support a larger GP, the GP may be reset to a larger value, for example, 15 watts (F520).

[0057] In this case, in order to increase the transmission power of the TX to up to 15 watts, the RX and TX use a transmission output change instruction, ACK, and NAK to increase the transmission output (F521 to F524). Then, the TX and RX perform the Calibration process again for GP = 15 watts. Specifically, the RX transmits information including the received power in the RX's load connection state when the TX's transmission power is 15 watts (hereinafter referred to as the third reference received power information) (F525). The TX performs Calibration based on the received power included in the first, second, and third reference received power information, and can calculate the power loss amount between the TX and RX at all possible transmission powers of the TX (in this case, from 250 milliwatts to 15 watts) (F526). The TX transmits an ACK to the third reference received power information from the RX (F527) and completes the Calibration process. The TX that determines that the charging process can be started starts the power transmission process to the RX and transitions to the Power Transfer phase (F528).

[0058] In the Power Transfer phase, the TX performs power transmission to the RX. Also, foreign object detection is performed by the Power Loss method. In the Power Loss method, first, the TX calculates the power loss amount between the TX and RX in the state without foreign objects from the difference between the transmission power by the TX and the received power by the RX through the above-mentioned Calibration. The calculated value corresponds to the reference power loss amount in the normal state (state without foreign objects) during the power transmission process. Then, when the power loss amount between the TX and RX measured during the power transmission after Calibration exceeds the threshold value from the power loss amount in the normal state, the TX determines that there is a foreign object or there may be a foreign object.

[0059] The above is the explanation of the Power Loss method. The Power Loss method performs foreign object detection based on the measurement results of power loss during power transmission from the power transmission device 402 to the power reception device 401. Foreign object detection by the Power Loss method has the disadvantage that the accuracy of foreign object detection decreases when the power transmission device 402 is transmitting a large amount of power. On the other hand, it has the advantage that power transmission efficiency can be kept high because foreign object detection can be performed while continuing power transmission.

[0060] Thus, during the Power Transfer phase, foreign object detection can be performed by the Power Loss method. However, relying solely on foreign object detection by the Power Loss method has the possibility of false detection of foreign objects and the possibility of false determination that there are no foreign objects even though there are foreign objects. In particular, the Power Transfer phase is the phase in which the TX performs power transmission. If foreign objects exist in the vicinity of the TX and RX during power transmission, heat generation from the foreign objects increases. Therefore, it is required 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, it is considered to implement a foreign object detection method different from the Power Loss method.

[0061] [Foreign Object Detection Method by Waveform Attenuation Method] During the Power Transfer phase, the power transmission device 402 is transmitting power to the power reception device 401. Therefore, if foreign object detection can be performed using the power transmission waveform (voltage waveform or current waveform) related to this power transmission, foreign object detection can be achieved without using a newly defined signal for foreign object detection or the like. A method of performing foreign object detection based on the attenuation state of the power transmission waveform (hereinafter referred to as the waveform attenuation method) will be described with reference to FIG. 6. FIG. 6 is a diagram for explaining the principle of foreign object detection by the waveform attenuation method. Here, foreign object detection using the power transmission waveform related to power transmission from the power transmission device 402 (TX) to the power reception device 401 will be described as an example.

[0062] In FIG. 6, the waveform shows the change in the voltage value 600 (hereinafter simply referred to as the voltage value) of the high-frequency voltage applied to the transmission antenna 105 of TX over time. The horizontal axis in FIG. 6 represents time, and the vertical axis represents the voltage value. TX, which is transmitting power to RX via the transmission antenna 105, stops transmitting power at time T0. That is, at time T0, the power supply for transmission from the power supply unit 102 is stopped. The frequency of the transmission waveform related to the transmission from 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 this transmission antenna 105 can be obtained based on the time change of the voltage value after time T0. For example, the Q value is calculated by Equation 1 based on the time, voltage value, and 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) (Equation 1) When there is a foreign object near TX and RX, this Q value decreases. This is because when a foreign object exists, energy loss occurs due to the foreign object. Therefore, focusing on the slope of the attenuation of the voltage value, when there is a foreign object, compared to when there is no foreign object, energy loss due to the foreign object occurs, so the slope of the straight line connecting point 601 and point 602 becomes steeper, and the attenuation rate of the waveform amplitude becomes higher. That is, the waveform attenuation method determines the presence or absence of a foreign object based on the attenuation state of the voltage value between this point 601 and point 602. In actually determining the presence or absence of a foreign object, it is possible to make a determination by comparing some numerical value representing this attenuation state. For example, determination can be made using the Q value described above. A decrease in the Q value means that the waveform attenuation rate (the degree of decrease in the amplitude of the waveform per unit time) becomes higher. Alternatively, determination may be made using the slope of the straight line connecting point 601 and point 602 obtained from (A1 - A2) / (T2 - T1). Alternatively, if the observation times (T1 and T2) of the attenuation state of the voltage value are fixed, determination can also be made using the value of (A1 - A2) representing the voltage value difference or the value of (A1 / A2) representing the voltage value ratio. Alternatively, if the voltage value A1 immediately after power transmission stops is constant, determination can also be made using the value of the voltage value A2 after a predetermined time has elapsed. Alternatively, determination may be made using the value of the time (T2 - T1) until the voltage value A1 becomes a predetermined voltage value A2.

[0063] As described above, the presence or absence of a foreign object can be determined based on the attenuation state of the voltage value during the power transmission stop period, and there are a plurality of values representing this attenuation state. In this embodiment, the values representing these attenuation states are called "waveform attenuation indicators". For example, as described above, the Q value calculated by Equation 1 is a value representing the attenuation state of the voltage value related to power transmission and is included in the "waveform attenuation indicator". All waveform attenuation indicators are values corresponding to the waveform attenuation rate. In the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation indicator". Hereinafter, the case where the waveform attenuation rate is used as the waveform attenuation indicator will be mainly described, but the content of this embodiment can be applied in the same way when other waveform attenuation indicators are used.

[0064] Note that, regarding the vertical axis in FIG. 6, even when the current value flowing through the power transmission antenna 105 is used, similar to the case of the voltage value, the attenuation state of the current value during the power transmission stop period changes depending on the presence or absence of a foreign object. When there is a foreign object, the waveform attenuation rate is higher than when there is no foreign object. Therefore, even when the above-described method is applied to the time change of the current value flowing through the power transmission 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 in current values, the ratio of current values, the absolute value of the current value, and the time until a predetermined current value is reached are used as waveform attenuation indicators to determine the presence or absence of a foreign object, and a foreign object can be detected. Further, foreign object detection based on both the attenuation state of the voltage value and the attenuation state of the current value may be performed, such as determining the presence or absence of a foreign object using an evaluation value calculated from the waveform attenuation indicator of the voltage value and the waveform attenuation indicator of the current value. In the above example, the waveform attenuation indicator during the period when TX temporarily stops power transmission is measured. However, it may be assumed that the waveform attenuation indicator during the period when TX temporarily reduces the power supplied from the power supply unit 102 from a predetermined power level to a lower power level is measured.

[0065] A method for detecting a foreign object based on the power transmission waveform during power transmission by the waveform attenuation method will be described with reference to FIG. 7. FIG. 7 shows the power transmission waveform when detecting a foreign object by the waveform attenuation method. The horizontal axis represents time, and the vertical axis represents the voltage value of the voltage applied to the power transmission antenna 105 or the resonance capacitor 107. Similar to FIG. 6, the vertical axis may represent the current value of the current flowing through the power transmission antenna 105. Immediately after TX starts power transmission, during the transient response period, the power transmission waveform is not stable. Therefore, during this transient response period when the power transmission waveform is not stable, RX controls not to communicate with TX (communication by load modulation). Also, TX controls not to communicate with RX (communication by frequency shift modulation).

[0066] When it is time to perform foreign object detection, TX temporarily stops power transmission. Then, since the amplitude of the power transmission waveform decays during the foreign object detection period when power transmission is stopped, TX calculates the waveform decay rate of this decaying waveform. And when the calculated waveform decay rate exceeds a predetermined threshold, TX determines that a foreign object is present. After the elapse of a predetermined foreign object detection period, if no foreign object is detected, TX resumes power transmission. After resuming power transmission, TX repeatedly executes the standby during the above-described transient response period, determination of the foreign object detection timing, power transmission stop, and foreign object detection process. The above is the basic process of foreign object detection by the waveform decay method.

[0067] Note that when measuring the waveform decay rate of the power transmission waveform, if elements such as the power receiving unit 203, charging unit 206, and battery 207 are connected to the power receiving antenna 205 and resonance capacitor 211 of the power receiving device 401, the waveform decay rate of the decaying waveform is affected by the load of these elements. That is, the waveform decay rate will change depending on the states of the power receiving unit 203, charging unit 206, and battery 207. Therefore, for example, even if the waveform decay rate is large, it is difficult to distinguish whether it is due to the influence of a foreign object or due to changes in the states of the power receiving unit 203, charging unit 206, battery 207, etc. Thus, when performing foreign object detection by observing the waveform decay rate, the first switch unit 209 may be disconnected. Thereby, it becomes possible to eliminate the influence of the battery 207. Alternatively, the second switch unit 210 may be turned ON and short-circuited so that a current flows in the closed loop formed by the power receiving antenna 205, resonance capacitor 211, and second switch unit 210. Thereby, it becomes possible to eliminate the influence of the power receiving unit 203, charging unit 206, and battery 207. As described above, by performing foreign object detection in a state where the first switch unit 209 is disconnected or in a state where the second switch unit 210 is turned ON and short-circuited (connected), highly accurate foreign object detection becomes possible. Also, highly accurate foreign object detection is possible by performing both disconnection of the first switch unit 209 and short-circuiting (connection) of the second switch unit 210.

[0068] Also, when measuring the waveform attenuation rate of the power transmission waveform, if elements such as the power transmission unit 103, the communication unit 104, and the power supply unit 102 are connected to the power transmission antenna 105 and the resonance capacitor 107 of the power transmission device 402, the waveform attenuation rate of the attenuation waveform is affected by the load of these elements. That is, the waveform attenuation rate will change depending on the states of the power transmission unit 103, the communication unit 104, and the power supply unit 102. Therefore, for example, even if the waveform attenuation rate is large, it becomes difficult to distinguish whether it is due to the influence of a foreign object or due to the power transmission unit 103, the communication unit 104, and the power supply unit 102. Thus, when measuring the waveform attenuation rate, the switch 108 may be turned ON to short-circuit, so that a current flows in the closed loop formed by the power transmission antenna 105, the resonance capacitor 107, and the switch 108. Thereby, it becomes possible to eliminate the influence of the power transmission unit 103, the communication unit 104, and the power supply unit 102. Alternatively, a switch may be provided between the closed loop circuit formed by the power transmission antenna 105, the resonance capacitor 107, and the switch 108, and the power transmission unit 103. And when performing foreign object detection, by disconnecting the closed loop circuit and the power transmission unit with the said switch, it becomes possible to eliminate the influence of the power transmission unit 103, the communication unit 104, and the power supply unit 102. As described above, by performing foreign object detection in a state where the switch 108 is turned ON to short-circuit (connect) or in a state where the closed loop circuit and the power transmission unit 103 are disconnected by a switch, highly accurate foreign object detection becomes possible. Also, even if both the state of turning the switch 108 ON to short-circuit (connect) and the state of disconnecting the closed loop circuit and the power transmission unit 103 by a switch are implemented, highly accurate foreign object detection becomes possible.

[0069] [Method for Setting Foreign Object Detection Threshold in 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, RX controls the load of RX to be in a light load state so that when power transmission occurs from TX, no power is supplied to the load of RX or only a very small amount of power is supplied. Let the transmission power of TX at this time be Pt1. Then, TX stops power transmission in that state and measures the waveform attenuation rate. Let the waveform attenuation rate at this time be δ1. At this time, TX recognizes the transmission power Pt1 that TX is transmitting and stores a calibration point 1100 associating the transmission power Pt1 and the waveform attenuation rate δ1 in the memory. Next, RX controls the load of RX to be in a load connection state so that when power transmission occurs from TX, maximum power is supplied to the load of RX or power equal to or higher than a predetermined threshold is supplied. Let the transmission power of TX at this time be Pt2. Then, TX stops power transmission in that state and measures the waveform attenuation rate. At this time, TX stores a calibration point 1101 associating the transmission power Pt2 and the waveform attenuation rate δ2 in the memory. Subsequently, TX linearly interpolates 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 waveform in a state where no foreign object exists around TX and RX. Therefore, TX can estimate the waveform attenuation rate of the transmission waveform for each transmission power value in a state without a 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, TX can calculate a threshold value for determining the presence or absence of a foreign object for each transmission power value. For example, a waveform attenuation rate that is larger than the estimation result of the waveform attenuation rate in the case of no foreign object at a certain transmission power value by a predetermined value (a value corresponding to the measurement error) may be set as the threshold value for determining the presence or absence of a foreign object. The calibration process performed by the transmission device 402 and the reception device 401 for the transmission device 402 to obtain a combination of the transmission power value and the waveform attenuation rate is hereinafter referred to as the "Calibration process (CAL process) of the waveform attenuation method".

[0070] Note that RX may perform control to bring the load into a state where no power is supplied or a light load state, and control to bring the load into a connected state, after notifying TX of each control to be performed. Also, either of the two controls may be performed first.

[0071] Note that the operation for calculating the threshold value used to determine the presence or absence of foreign matter for each load (for each power transmission power value) described in this embodiment may be performed in the Calibration phase. As described above, in the Calibration phase, TX acquires data required for foreign matter detection by the Power Loss method. At that time, TX acquires data related to power loss when the load state of RX is a light load state and when the load is connected. Therefore, the measurement of calibration point 1100 and calibration point 1101 in FIG. 11 may be performed together with the measurement of power loss when RX becomes a light load state and when the load is connected in the above-described Calibration phase. That is, when TX receives the first reference received power information from RX, in addition to the predetermined processing to be performed in the Calibration phase, TX measures calibration point 1100. Also, when TX receives the second reference received power information from RX, in addition to the predetermined processing to be performed in the Calibration phase, TX measures calibration point 1101. As a result, there is no need to separately provide a period for measuring calibration point 1100 and calibration point 1101, so calibration point 1100 and calibration point 1101 can be measured in a shorter time.

[0072] [Processing of Power Transmission Device When Applying Waveform Attenuation Method to WPC Standard] Next, the processing of the power transmission device 402 when this waveform attenuation method is applied to the WPC standard for foreign object detection will be described. When performing foreign object detection by the waveform attenuation method, the power transmission device 402 measures in advance the waveform attenuation rate in a state without foreign objects, and calculates a threshold value based on this. After that, the power transmission device 402 executes foreign object detection by the waveform attenuation method. If the measured waveform attenuation rate is greater than the threshold value when compared, it is determined that "there is a foreign object" or "there may be a foreign object", and if it is smaller than the threshold value when compared, it is determined that "there is no foreign object" or "the possibility of no foreign object is high".

[0073] The timing for measuring in advance the waveform attenuation rate in a state without foreign objects will be described. In the WPC standard, as described above, in the Negotiation phase, foreign object detection is performed by the Q value measurement method. And if as a result of the foreign object detection, it is determined that there is no foreign object, the process proceeds to the Calibration phase and the Power Transfer phase. That is, proceeding after the Negotiation phase means that as a result of the foreign object detection by the Q value measurement method, it has been determined that there is no foreign object. Therefore, if the waveform attenuation rate is measured in any of the Negotiation phase, the Calibration phase, and the Power Transfer phase, there is a high possibility of measuring the waveform attenuation rate in a state without foreign objects. Therefore, as the timing for measuring the waveform attenuation rate in a state without foreign objects, it may be any of the Negotiation phase, the Calibration phase, and the Power Transfer phase.

[0074] In this embodiment, the timing for measuring the waveform attenuation rate in a state without foreign matter is set at the first stage of the PowerTransfer phase. The reason is that as time elapses after it is determined by the Q-value measurement method that there is no foreign matter, the probability of a foreign object being placed near the power transmission device 402 and the power reception device 401 increases. Then, at the timing for foreign object detection specified by the power reception device 401 or the power transmission device 402, the power transmission device 402 measures the waveform attenuation rate of the power transmission waveform. After that, the power transmission device 402 compares the measured waveform attenuation rate with a threshold value calculated from the waveform attenuation rate in the state without the foreign matter described above, and determines the presence or absence of a foreign object.

[0075] Note that in the waveform attenuation method, since the power transmission device 402 temporarily stops power transmission and observes the attenuation rate of the power transmission waveform to detect foreign objects, there is a disadvantage of causing a decrease in power transmission efficiency due to the temporary stop of power transmission. On the other hand, there is an advantage that foreign objects can be detected with high accuracy even when foreign object detection processing is executed during power transmission of a large amount of power. That is, even in a situation where it is difficult to accurately detect foreign objects by the Power Loss method, foreign objects can be detected by using the waveform attenuation method.

[0076] In the above-described embodiment, when performing foreign object detection by the waveform attenuation method, the waveform attenuation rate in the state without foreign objects is measured before power transmission starts, and a threshold value is calculated based on this. Then, when the waveform attenuation rate measured during foreign object detection by the waveform attenuation method is greater than the threshold value, it is determined that "there is a foreign object" or "there may be a foreign object", and when it is smaller than the threshold value, it is determined that "there is no foreign object" or "the possibility of no foreign object is high". However, foreign object detection may be performed using the threshold value obtained from the waveform attenuation rate measured at the timing when it is estimated that there is no foreign object after power transmission starts. 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 the first measurement of the waveform attenuation rate and calculates a threshold value based on the measured waveform attenuation rate. Since this first measurement of the waveform attenuation rate is performed immediately after it has been confirmed by the Power Loss method in advance that there is no foreign object, the measured waveform attenuation rate is presumed to be the waveform attenuation rate in the state without foreign objects. Next, the TX resumes power transmission and performs a second measurement of the waveform attenuation rate at the timing when it is determined that foreign object detection should be performed. Then, by comparing the measurement result of the second measurement of the waveform attenuation rate with the measurement result of the first measurement of the waveform attenuation rate or the threshold value calculated based on it, it is possible to determine the presence or absence of a foreign object. That is, when performing foreign object detection by the waveform attenuation method, the waveform attenuation rate measured at that time may be compared with the waveform attenuation rate measured in the state without foreign objects before that or the threshold value.

[0077] Also, in the above-described embodiment, the frequency of the power transmission waveform related to the power transmission from the power transmission device 402 is assumed to be a fixed frequency. However, for each of a plurality of frequencies, the processing for foreign object detection described in this embodiment may be performed, and the results may be combined to determine the presence or absence of a foreign object. By performing foreign object detection using not only the waveform attenuation rate at one frequency but also the waveform attenuation rates at a plurality of frequencies, it becomes possible to perform more accurate foreign object detection.

[0078] Also, in this embodiment, immediately after the power transmission device 402 stops power transmission or immediately after starting power transmission, since the power transmission waveform is unstable due to transient response, a waiting time is provided before shifting to each operation. However, the cause of this unstable power transmission waveform is caused by suddenly starting or stopping power transmission. Therefore, in order to mitigate this, the power transmission device 402 may be controlled to increase the power transmission power step by step when starting power transmission. Alternatively, when stopping power transmission, it may be controlled to decrease the power transmission power step by step.

[0079] [Foreign object detection process according to communication error] As described above, the power transmission device 402 and the power reception device 401 perform communication for power transmission and reception control based on the WPC standard. This communication is performed wirelessly via the power transmission antenna 105 of the power transmission device 402 and the power reception antenna 205 of the power reception device 401. Therefore, if a foreign object exists in the vicinity of the power transmission device 402 and the power reception device 401 (for example, between the power transmission device 402 and the power reception device 401), the foreign object may interfere with the wireless communication between the power transmission device 402 and the power reception device 401, causing a communication error. Thus, in this embodiment, when a communication error occurs, since there may be a foreign object in the vicinity of the power transmission device 402 and the power reception device 401, the power transmission device 402 and the power reception device 401 perform control for foreign object detection.

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

[0081] On the other hand, the waveform attenuation method determines the presence or absence of a foreign object by the power transmission device 402 stopping power transmission and comparing the waveform attenuation rate at that time with the waveform attenuation rate in a state where no foreign object has been measured in advance. Therefore, foreign object detection can be performed without communicating between the power transmission device 402 and the power reception device 401. Thus, when a communication error occurs, the power transmission device 402 performs foreign object detection by the waveform attenuation method that does not require communication. Thereby, the possibility of successful foreign object detection can be increased.

[0082] Also, even if there is a foreign object near the power transmission device 402 and the power reception device 401 during power transmission, there may be no communication error. However, even if no communication error occurs, if there is a foreign object, problems such as a large power loss occurring due to the foreign object or the foreign object generating heat may arise. Therefore, the power transmission device 402 periodically performs a foreign object detection process during the Power Transfer phase of wireless power transmission to check whether there is a foreign object near the power transmission device 402 and the power reception device 401. If the waveform attenuation method is adopted for this periodic foreign object detection, each time the foreign object detection is executed, the power transmission from the power transmission device 402 is temporarily stopped, resulting in a decrease in power transmission efficiency. On the other hand, when the Power Loss method is adopted, it is possible to detect a foreign object while continuing to transmit power from the power transmission device 402 to the power reception device 401. Therefore, when no communication error has occurred, the power transmission device 402 and the power reception device 401 periodically perform foreign object detection by the Power Loss method during the Power Transfer phase. Thereby, it is possible to detect a foreign object at an early stage while maintaining a high power transmission efficiency.

[0083] The operations of the power transmission device 402 and the power reception device 401 that use the above-described plurality of foreign object detection methods will be described. FIG. 8 shows an example of the operation in the Power Transfer phase of the power transmission device 402. The process in FIG. 8 starts at the timing when the power transmission device 402 detects the power reception device 401 placed on the charging stand 403 and performs communication, and the processing of each phase defined by the WPC standard is completed. The phases executed before the start of the process in FIG. 8 include a Selection phase, a Ping phase, an I&C phase, a Negotiation phase, and a Calibration phase. However, the process in FIG. 8 may start without performing at least a part of the above-described phases.

[0084] In S801, the power transmission device 402 starts power transmission in the Power Transfer phase. In S802, the power transmission device 402 determines whether it has received a command for performing foreign object detection by the Power Loss method from the power reception device 401. This command includes the power reception value measured by the power reception device 401. When this command is received, in S803, the power transmission device 402 performs foreign object detection by the Power Loss method based on the power reception value received from the power reception device 401 and the power transmission value measured by the power transmission device 402.

[0085] In S804, the power transmission device 402 determines whether a foreign object exists in the vicinity of the power transmission device 402 based on the result of the foreign object detection process. When it is determined that a foreign object exists, in S805, the power transmission device 402 transmits a negative acknowledgment (NAK), which is information indicating the existence of a foreign object, to the power reception device 401. In S806, the power transmission device 402 stops power transmission or performs control to reduce the power transmission. On the other hand, when it is determined in S804 that no foreign object exists, the power transmission device 402 transmits an affirmative acknowledgment (ACK), which is information indicating the non - existence of a foreign object, to the power reception device 401, continues power transmission, and returns to S802.

[0086] When the power transmission device 402 does not receive a foreign object detection execution command by the Power Loss method in S802, in S808, the power transmission device 402 determines whether a communication error has occurred in the communication performed between the power transmission device 402 and the power reception device 401. The power transmission device 402 determines that a communication error has occurred (i.e., detects a communication error) when a command that should be transmitted from the power reception device 401 is not received by the power transmission device 402. For example, in order to periodically perform foreign object detection by the above - mentioned Power Loss method, the power reception device 401 periodically transmits a foreign object detection execution command by the Power Loss method to the power transmission device 402. The power transmission device 402 determines that a communication error has occurred when it does not receive the command that it should receive periodically or when it receives a command including an incorrect packet. However, the method for detecting a communication error by the power transmission device 402 is not limited to this.

[0087] If a communication error is detected in S808, since there may be a foreign object, in S809, the power transmission device 402 executes foreign object detection by the waveform attenuation method. Then, similar to the case where the power transmission device 402 executes foreign object detection by the Power Loss method, the power transmission device 402 performs the processes from S804 to S807 based on the result of the foreign object detection.

[0088]

[0088] If a communication error is not detected in S808, in S810, the power transmission device 402 determines whether it has received a foreign object detection execution command by the waveform attenuation method from the power reception device 401. The power reception device 401 transmits this command, for example, when the power reception device 401 detects a communication error as will be described later. When the power transmission device 402 receives this command, in S809, it executes foreign object detection by the waveform attenuation method. Then, the power transmission device 402 performs the processes from S804 to S807 based on the result of the foreign object detection.

[0089] FIG. 9 shows an example of the operation of the power reception device 401 in the Power Transfer phase. The process of FIG. 9 starts at the same timing as the process of FIG. 8. In S901, the power reception device 401 starts power reception in the Power Transfer phase. In S902, the power reception device 401 transmits a command for executing foreign object detection by the Power Loss method, which is a command to be periodically transmitted to the power transmission device 402. This command is a notification that the power reception device 401 requests the power transmission device 402 to perform foreign object detection processing by 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 determination of the communication error by the power receiving device 401 is performed as follows. In accordance with the WPC standard, the power receiving device 401 transmits various commands to the power transmitting device 402. Then, when the power transmitting device 402 receives a command from the power receiving device 401, it responds (such as a positive response or a negative response) to the power receiving device 401. For example, when periodically performing foreign object detection by the above-described Power Loss method, the power receiving device 401 periodically transmits a foreign object detection execution command by the Power Loss method to the power transmitting device 402. When the power transmitting device 402 receives the command, it responds to the power receiving device 401. Therefore, when the power receiving device 401 does not receive a response from the power transmitting device 402 even though it has transmitted a foreign object detection execution command by the Power Loss method to the power transmitting device 402, it determines that a communication error has occurred (that is, it detects a communication error). Also, even when the power receiving device 401 receives a response from the power transmitting device 402, if the response includes an incorrect packet, it determines that a communication error has occurred. However, the method for detecting a communication error by the power receiving device 401 is not limited to this.

[0091] When a communication error is detected in S903, there may be a foreign object present and there may be a possibility that the foreign object detection by the Power Loss method has not been executed normally. Therefore, in S904, the power receiving device 401 transmits a foreign object detection execution command by the waveform attenuation method to the power transmitting device 402. This command is a notification that the power receiving device 401 requests the power transmitting device 402 to perform foreign object detection processing by the waveform attenuation method. Then, the power receiving device 401 waits for a response according to the execution result of foreign object detection by the waveform attenuation method from the power transmitting device 402. When a communication error is not detected in S903, the power receiving device 401 waits for a response according to the execution result of foreign object detection by the Power Loss method from the power transmitting device 402.

[0092] In S905, the power receiving device 401 determines whether it has received a negative response from the power transmitting device 402, which is information indicating the presence of a foreign object. When a negative response is received, in S906, the power receiving device 401 transmits an EPT (End Power Transfer) command, which is a command for ending power transmission, to the power transmitting device 402 and shifts to a state where it does not receive power. On the other hand, when a negative response is not received in S905, for example, when an affirmative response is received, the power receiving device 401 continues power reception and returns to S902.

[0093] The above is an explanation of the operation examples of the power transmitting device 402 and the power receiving device 401. As described above, when a communication error in the communication between the power transmitting device 402 and the power receiving device 401 is detected, the power transmitting device 402 and the power receiving device 401 are controlled so that foreign object detection is performed by the waveform attenuation method. Thereby, when a foreign object exists near the power transmitting device 402 and the power receiving device 401, the foreign object can be detected early and power transmission can be stopped (or the transmitted power can be reduced), so that the probability of preventing extreme temperature rise or destruction of the foreign object can be increased. In the above description, it is assumed that 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, at the timing when the power transmitting device 402 performs foreign object detection by the waveform attenuation method, the switch 108 may be short-circuited, or the switch between the closed-loop circuit including the power transmission antenna 105 and the power transmission unit 103 may be disconnected. Thereby, the influence of the power transmission unit 103, the communication unit 104, and the power supply unit 102 on the attenuation waveform is eliminated, and more accurate foreign object detection becomes possible. Similarly, at the timing when the power receiving device 401 executes foreign object detection by the waveform attenuation method, the second switch unit 210 may be short-circuited, or the first switch unit 209 may be disconnected. Thereby, the influence of the power receiving unit 203, the charging unit 206, and the battery 207 on the attenuation waveform is eliminated, and more accurate foreign object detection becomes possible. In this case, the power transmitting device 402 and the power receiving device 401 perform communication for specifying the timing for performing foreign object detection.

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

[0096] Further, when the power transmission device 402 measures the waveform attenuation rate, it may notify the power reception device 401 of the measurement result of the waveform attenuation rate or the threshold value obtained from the measurement result. Thereby, the power reception device 401 can determine the presence or absence of a foreign object based on the measurement result and the like received from the power transmission device 402. Similarly, when the power reception device 401 measures the waveform attenuation rate, it may notify the power transmission device 402 of the measurement result of the waveform attenuation rate or the threshold value obtained from the measurement result. Thereby, the power transmission device 402 can determine the presence or absence of a foreign object based on the measurement result and the like received from the power reception device 401.

[0097] In the above description using FIGS. 8 and 9, when a communication error is detected, the waveform attenuation method is adopted to perform foreign object detection with high precision. Thereby, even if a foreign object is not detected in the foreign object detection process by the Power Loss method performed periodically, the foreign object can be detected by performing the foreign object detection process by the waveform attenuation method in response to the communication error, and power transmission can be stopped (or the power transmission power can be reduced). However, when the power transmission device 402 and the power reception device 401 want to avoid a decrease in power transmission efficiency, they may execute foreign object detection by the Power Loss method in response to the detection of a communication error. In this case, the power transmission device 402 that detects a communication error in S808 of FIG. 8 may execute foreign object detection by the Power Loss method instead of executing foreign object detection by the waveform attenuation method in S809. Also, the power reception device 401 that detects a communication error in S903 of FIG. 9 may transmit a foreign object detection execution command by the Power Loss method instead of transmitting a foreign object detection execution command by the waveform attenuation method in S904. When performing foreign object detection by the Power Loss method in S809, the power transmission device 402 requests the power reception device 401 to transmit a command including the received power value, and detects a foreign object based on the received power value received in response to the request and the power transmission value measured by the power transmission device 402. When the power reception device 402 transmits a foreign object detection execution command by the Power Loss method in S903, the power transmission device 401 that receives the command performs foreign object detection by the Power Loss method. By such processing, even if a foreign object is not detected in the foreign object detection process by the periodic Power Loss method, the probability of detecting the foreign object is increased by performing the foreign object detection process again in response to the communication error.

[0098] In addition, when performing foreign object detection by the Power Loss method in response to the detection of a communication error, communication for foreign object detection is performed between the power transmission device 402 and the power reception device 401. However, a communication error may occur again during this communication, and there is also a possibility that the power transmission device 402 or the power reception device 401 cannot receive data from the other party, or receives data including an incorrect packet. If the foreign object detection execution command transmitted from the power reception device 401 to the power transmission device 402 is lost due to a communication error, the power transmission device 402 cannot recognize that foreign object detection is requested, and thus does not perform foreign object detection. Therefore, a response to the foreign object detection execution command is not transmitted from the power transmission device 402 to the power reception device 401 either.

[0099] Therefore, when it is considered that such a communication error may occur again, the power reception device 401 may transmit an EPT command, which is a command to terminate power transmission to the power transmission device 402, and shift to a state where it does not receive power. When the power transmission device 402 can receive the EPT, it stops power transmission. Also, even when the power transmission device 402 cannot receive the EPT, it can detect that the power reception device 401 has shifted to a state where it does not receive power and stop power transmission, and may shift to the Selection phase. When a communication error occurs again even in the communication for performing foreign object detection in response to the detection of a communication error, since the frequency of occurrence of the communication error is high, it is considered that there is a high possibility that a foreign object exists, or there is a factor that interferes with communication other than the foreign object. Therefore, in such a case, by controlling to stop power transmission or reduce the power of power transmission as described above, it becomes possible to suppress the occurrence of problems due to power transmission.

[0100] In addition, when performing foreign object detection by the above-described Power Loss method or foreign object detection by the waveform attenuation method, there is also a possibility that the foreign object detection may fail. For example, if the power receiving device 401 placed on the power transmission device 402 moves during the foreign object detection process, it is conceivable that the measurement value used for the foreign object detection becomes an abnormal value and the foreign object detection fails. Also in this case, since there is a possibility that it is not in a state appropriate for performing wireless power transmission, the power transmission device 402 and the power receiving device 401 may stop power transmission or reduce the power of power transmission. Thereby, the occurrence of problems due to power transmission can be suppressed.

[0101] [Foreign Object Detection Processing in Response to Power Reduction] In the above description using FIGS. 8 and 9, the processing when the power transmission device 402 and the power receiving device 401 perform foreign object detection in response to the detection of a communication error has been described. Next, the processing when performing foreign object detection in response to a decrease in the received power of the power receiving device 401 will be described.

[0102] When a foreign object exists in the vicinity of the power transmission device 402 and the power receiving device 401, there is a possibility that the foreign object may interfere with the wireless power transmission between the power transmission device 402 and the power receiving device 401, causing a decrease in the received power in the power receiving device 401. Therefore, when a decrease in the received power of the power receiving device 401 occurs, since there is a possibility that a foreign object exists in the vicinity of the power transmission device 402 and the power receiving device 401, the power transmission device 402 and the power receiving device 401 perform control for performing foreign object detection.

[0103] The operations of the power transmission device 402 and the power reception device 401 when foreign object detection is performed in response to the power transmission device 402 detecting a decrease in the received power of the power reception device 401 will be described below. The power transmission device 402 periodically receives the received power value Pr3’ from the power reception device 401 in order to perform foreign object detection by the Power Loss method during the Power Transfer phase. Then, based on the received power value Pr3’ received from the power reception device 401 or Ploss_FO, which is the difference between Pr3 and Pr3’ specified in advance, the power transmission device 402 determines whether the received power of the power reception device 401 has decreased. When the received power value Pr3’ received from the power reception device 401 falls below a certain threshold or when Ploss_FO exceeds a certain threshold, the power transmission device 402 determines that the received power of the power reception device 401 has decreased and performs foreign object detection by the waveform attenuation method.

[0104] That is, the power transmission device 402 periodically performs foreign object detection by the Power Loss method that can maintain high power transmission efficiency, and based on the received power received from the power reception device 401 for this foreign object detection, performs foreign object detection by the waveform attenuation method with higher foreign object detection accuracy. For example, the power transmission device 402 may set a first threshold for determining that there may be a foreign object and a second threshold for determining that there is a foreign object with respect to the value of Pr3’ or Ploss_FO. When Pr3’ or Ploss_FO exceeds the second threshold, the power transmission device 402 determines that a foreign object has been detected by 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 but does not exceed the second threshold, the power transmission device 402 performs foreign object detection by the waveform attenuation method. As a result, even when a foreign object cannot be detected by the Power Loss method, it is possible to detect the foreign object by performing the waveform attenuation method with higher accuracy in response to a decrease in the received power. Note that each of the above-described thresholds may be set based on data (straight line 1002 in FIG. 10) obtained by the Calibration process of the Power Loss method.

[0105] Also, in the above description, the power transmission device 402 performs foreign object detection in response to a decrease in the received power of the power reception device 401. However, the power transmission device 402 may perform foreign object detection in response to a change in the transmitted power of the power transmission device 402. The power transmission device 402 is capable of measuring the transmitted power value that the power transmission device 402 is transmitting. Therefore, when the difference between this transmitted power value and a predetermined reference value is greater than a threshold value, the power transmission device 402 may determine that there may be a foreign object and perform foreign object detection by the waveform attenuation method. Even with such a configuration, the same effect as when performing foreign object detection in response to a decrease in received power can be obtained.

[0106] Next, the operations of the power transmission device 402 and the power reception device 401 when foreign object detection is executed in response to the power reception device 401 detecting a decrease in the received power of the power reception device 401 will be described. The power reception device 401 periodically measures the power received from the power transmission device 402 during the Power Transfer phase. Then, based on the periodically measured received power value, the power reception device 401 determines whether the received power of the power reception device 401 is decreasing. If the calculated received power value is below a certain threshold value, or if the difference between the calculated received power value and the reference value exceeds a certain threshold value, the power reception device 401 determines that the received power of the power reception device 401 is decreasing and requests the power transmission device 402 to execute foreign object detection by the waveform attenuation method.

[0107] That is, the power reception device 401 periodically measures the received power value and, according to the measurement result, requests the power transmission device 402 to perform foreign object detection by the waveform attenuation method with high foreign object detection accuracy. For example, when the difference between the measured received power and the reference value is less than or equal to a predetermined threshold value, the power reception device 401 may transmit a foreign object detection execution command by the Power Loss method. On the other hand, when the difference between the measured received power and the reference value exceeds a predetermined threshold value, the power reception device 401 may transmit a foreign object detection execution command by the waveform attenuation method. With such a configuration, when there is a high possibility of the presence of a foreign object (when the received power is decreasing), the foreign object can be detected by 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 by the Power Loss method.

[0108] In addition, when the received power value of the power receiving device 401 drops below a threshold value, it may be determined that a foreign object is present, and the power transmitting device 402 may be requested to stop power transmission or reduce the transmitted power. Further, the power receiving device 401 may be provided with a first threshold value for determining that there may be a foreign object in response to a decrease in the received power value, and a second threshold value for determining that a foreign object is present. When the decrease in the received power of the power receiving device 401 exceeds the first threshold value but does not exceed the second threshold value, the power receiving device 401 requests the power transmitting device 402 to perform foreign object detection by the waveform attenuation method. When the decrease in the received power exceeds the second threshold value, the power receiving device 401 may request the power transmitting device 402 to stop power transmission by transmitting an EPT command to the power transmitting device 402. Alternatively, a command may be transmitted to the power transmitting device 402 to request it to reduce the transmitted power.

[0109] As described above, when the power receiving device 401 detects a decrease in the received power, the power transmitting device 402 and the power receiving device 401 control so that foreign object detection is performed by the waveform attenuation method. As a result, when there may be a foreign object near the power transmitting device 402 and the power receiving device 401, it becomes possible to detect the foreign object at an early stage.

[0110] [Foreign Object Detection Processing According to Calibration Data] Next, the processing when foreign object detection is performed according to the data obtained in the Calibration process of the Power Loss method or the data obtained in the Calibration process of the waveform attenuation method will be described.

[0111] As described above, in foreign object detection by the Power Loss method and foreign object detection by the waveform attenuation method, a Calibration process is performed to set a threshold value that serves as a criterion for determining the presence or absence of a foreign object. The reference data obtained through these Calibration processes is assumed to indicate the relationship between the power transmission value and the power reception value in the absence of a foreign object, or the relationship between the power transmission value and the waveform attenuation rate. Therefore, if the reference data obtained through the Calibration process does not show a predetermined relationship expected between the power transmission value and the power reception value or between the power transmission value and the waveform attenuation rate, there may be a foreign object in the vicinity of the power transmission device 402 and the power reception device 401. For this reason, the power transmission device 402 and the power reception device 401 perform control for executing foreign object detection.

[0112] First, the operations of the power transmission device 402 and the power reception device 401 when foreign object detection is executed according to the data obtained through the Calibration process of the Power Loss method will be described. The power transmission device 402 and the power reception device 401 perform the Calibration process of the Power Loss method, which is a process for determining the threshold value used in the Power Loss method. The data obtained through this Calibration process of the Power Loss method should be data representing the relationship between the power transmission and the power reception in the absence of a foreign object, and it is possible to assume in advance the range within which the power reception value can take according to the power transmission value. Therefore, when the power transmission device 402 obtains data through the Calibration process of the Power Loss method, it determines whether the power reception value included in the data is within a range predetermined according to the power transmission value. If it is outside the range, since there may be a foreign object in the vicinity of the power transmission device 402 and the power reception device 401, the power transmission device 402 executes foreign object detection by the waveform attenuation method. Then, when it is determined that a foreign object is present by foreign object detection by the waveform attenuation method, the power transmission device 402 performs control to stop power transmission or reduce the power transmission power. On the other hand, when it is determined that no foreign object is present by the waveform attenuation method, the power transmission device 402 executes the Calibration process of the Power Loss method again to update the data.

[0113] That is, the power transmission device 402 executes foreign object detection by a waveform attenuation method different from the Power Loss method according to the value of the data obtained by the Calibration process of the Power Loss method. According to such a configuration, when it is determined that there may be a foreign object in the Calibration process of the Power Loss method, it is possible to detect the foreign object at an early stage by executing foreign object detection by the waveform attenuation method. Also, when the accuracy of foreign object detection by the Power Loss method decreases due to inaccurate calibration data, the foreign object can be detected with high accuracy by the waveform attenuation method. Note that the power receiving device 401 may make a determination of foreign object detection according to the data obtained in the Calibration process.

[0114] Next, the operations of the power transmission device 402 and the power receiving device 401 when foreign object detection is executed according to the data obtained by the Calibration process of the waveform attenuation method will be described. The power transmission device 402 and the power receiving device 401 perform the Calibration process of the waveform attenuation method, which is a process for determining the threshold value used in the waveform attenuation method. The reference data obtained by this Calibration process of the waveform attenuation method should be data representing the relationship between the power transmission power and the waveform attenuation rate in the state without a foreign object, and it is possible to assume in advance the range that the data can take. Therefore, the power transmission device 402 determines 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, since there may be a foreign object in the vicinity of the power transmission device 402 and the power receiving device 401, the power transmission device 402 executes foreign object detection by the Power Loss method. More specifically, the power transmission device 402 transmits a command for notifying the power receiving device 401 that the PowerLoss method is to be executed. The power receiving device 401 that has received the command transmits a foreign object detection execution command by the Power Loss method to the power transmission device 402, including the power reception power value measured by the power receiving device 401. When the power transmission device 402 receives a command from the power receiving device 401, it executes foreign object detection by the Power Loss method.

[0115] When it is determined that there is a foreign object by the Power Loss method, the power transmission device 402 stops power transmission or controls so that the transmitted power decreases. When it is determined that there is no foreign object by the Power Loss method, the power transmission device 402 executes the Calibration process of the waveform attenuation method again and updates the data. In this way, the power transmission device 402 executes foreign object detection by the Power Loss method different from the waveform attenuation method according to the value of the data obtained by the Calibration process of the waveform attenuation method. According to such a configuration, when it is determined that there may be a foreign object in the Calibration process of the waveform attenuation method, it is possible to detect the foreign object early by executing foreign object detection by the Power Loss method. Note that the determination of foreign object detection according to the data obtained in the Calibration process may be performed by the power reception device 401.

[0116] [Foreign object detection process according to temperature rise] The process when foreign object detection is executed in response to the detection of a temperature rise in the power transmission device 402 or the power reception device 401 will be described. As factors for the temperature rise of the power transmission device 402 or the power reception device 401, heat generation from an electric circuit including an antenna or the like included in the power transmission device 402 and the power reception device 401, and heat generation from the CPU by performing various processes can be considered. Further, when a foreign object exists in the vicinity of the power transmission device 402 and the power reception device 401, the foreign object consumes a part of the energy of the transmitted power, so that the foreign object generates heat, and accordingly, the temperature of the power transmission device 402 or the power reception device 401 in contact with the foreign object may also rise. Therefore, when the temperature of the power transmission device 402 or the power reception device 401 rises above a predetermined threshold value, there may be a foreign object in the vicinity of the power transmission device 402 and the power reception device 401, so the power transmission device 402 and the power reception device 401 perform control for performing foreign object detection.

[0117] First, the operations of the power transmission device 402 and the power reception device 401 when the power transmission device 402 detects a temperature increase will be described. The power transmission device 402 has a temperature sensor. When the temperature sensor detects that the temperature of the power transmission device 402 has exceeded a predetermined threshold value, the power transmission device 402 performs foreign object detection by the waveform attenuation method. And when it is determined that a foreign object exists, the power transmission device 402 controls to stop power transmission or reduce the transmitted power.

[0118] Here, the reason for performing foreign object detection by the waveform attenuation method instead of the Power Loss method is as follows. That is, in the Power Loss method, the power transmission device 402 needs to receive the received power value from the power reception device 401, but in the waveform attenuation method, the power transmission device 402 does not need information from the power reception 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 transmission device 402 is high and there may be a foreign object, the power transmission device 402 can detect the foreign object early and with high accuracy by the waveform attenuation method. However, foreign object detection may also be performed by the Power Loss method. In this case, the power transmission device 402 notifies the power reception device 401 of the implementation of foreign object detection by the Power Loss method. When the power reception device 401 receives the notification, it transmits a foreign object detection execution command by the Power Loss method including the received power value measured by the power reception device 401 to the power transmission device 402.

[0119] Next, the operations of the power transmission device 402 and the power reception device 401 when the power reception device 401 detects a temperature increase will be described. The power reception device 401 has a temperature sensor. When the temperature sensor detects that the temperature of the power reception device 401 has exceeded a predetermined threshold value, the power reception device 401 transmits a foreign object detection execution command using the waveform attenuation method to the power transmission device 402. Then, when the power transmission device 402 executes foreign object detection using the waveform attenuation method and determines that a foreign object exists, it controls to stop power transmission or reduce the transmitted power. Note that foreign object detection may be performed using the Power Loss method instead of the waveform attenuation method. In this case, the power reception device 401 transmits a foreign object detection execution command using the Power Loss method to the power transmission device 402 in response to the detection of temperature information by the temperature sensor.

[0120] Note that regarding the allowable temperature of the equipment that performs power transmission or reception, there may be predetermined specified values according to standards and laws of each country. Therefore, by setting the threshold value for determining the execution of the above-mentioned foreign object detection to be lower than those specified values, it is possible to detect foreign objects early before the temperature reaches the specified value even if a temperature increase due to a foreign object occurs.

[0121] [Foreign Object Detection Processing According to Transmitted Power] Next, the processing when foreign object detection is executed by a method selected according to the transmitted power transmitted from the power transmission device 402 will be described. As described above, the Power Loss method performs foreign object detection based on the power loss related to power transmission during power transmission from the power transmission device 402 to the power reception device 401, and has the disadvantage that the accuracy of foreign object detection decreases when the power transmission device 402 is transmitting a large amount of power. On the other hand, since foreign object detection can be performed while continuing power transmission, it has the advantage of maintaining high power transmission efficiency. Also, the waveform attenuation method observes the attenuation rate of the power transmission waveform when the power transmission device 402 temporarily stops power transmission to perform foreign object detection, so it has the disadvantage that the power transmission efficiency decreases due to the temporary stop of power transmission. On the other hand, it has the advantage that high-precision foreign object detection is possible even when performing during the transmission of a large amount of power.

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

[0123] In the description of the foreign object detection process according to the above communication error, the foreign object detection process according to the power reduction, the foreign object detection process according to the calibration data, and the foreign object detection process according to the temperature information, the case of using both the Power Loss method and the waveform attenuation method has been mainly described. However, when the power transmission is lower than a predetermined threshold, foreign object detection by the Power Loss method may be performed at the timing when foreign object detection is performed by the waveform attenuation method in these embodiments. Also, when the power transmission is equal to or greater than a predetermined threshold, both the Power Loss method and the waveform attenuation method may be used, or foreign object detection by the waveform attenuation method may be performed at the timing when foreign object detection is performed by the Power Loss method in the above embodiments.

[0124] In this embodiment, a case is mainly described in which a wireless power transmission system determines whether a predetermined condition regarding at least one of the states of a power transmission device 402 and a power reception device 401 is satisfied, and selectively uses the Power Loss method and the waveform attenuation method according to the determination result. However, the present invention is not limited to this, and at least one of the power transmission device 402 and the power reception device 401 may selectively use a plurality of foreign object detection methods including foreign object detection methods other than those described above according to conditions. Further, the wireless power transmission system may select a foreign object detection method and 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 that realizes one or more functions of the above-described embodiment to a system or device via a network or a storage medium, and causing one or more processors in a computer of the system or device to read and execute the program. Further, it can also be realized by a circuit (for example, an ASIC or the like) that realizes one or more functions. Further, the program may be recorded on a computer-readable recording medium and provided.

Explanation of Reference Numerals

[0126] 401 Power reception device 402 Power transmission device

Claims

1. A transmitting means for transmitting an Analog Ping; an acquisition means for acquiring a first quality factor from a first attenuation envelope of a voltage after transmitting an Analog Ping, and acquiring a second quality factor from a second attenuation envelope of the voltage after acquiring the first quality factor; a determination means for determining the presence or absence of a foreign object based on a result of a comparison between the first quality factor and the second quality factor; A power transmitting means for wirelessly transmitting power to a power receiving device; A negotiation means for negotiating with the power receiving device in a negotiation phase, The acquisition means measures a voltage during a period in which the power transmission is restricted after acquiring the first quality factor and after the negotiation phase ends, and acquires the second quality factor from a second attenuation envelope of the voltage.

2. The power transmitting device according to claim 1 , wherein the power transmitting means limits the power transmission when the determining means determines that the foreign object is present.

3. The power transmitting device according to claim 1 , wherein the power transmitting means limits the power transmission for the measurement.

4. A method performed by a power transmitting device, comprising: a transmitting step of transmitting an Analog Ping; a first obtaining step of obtaining a first quality factor from a first attenuation envelope of a voltage after transmitting an Analog Ping; a second obtaining step of obtaining a second quality factor from a second decay envelope of the voltage after obtaining the first quality factor; a determination step of determining the presence or absence of a foreign object based on a comparison between the first quality factor and the second quality factor; a power transmitting step of wirelessly transmitting power to a power receiving device; A negotiation step of negotiating with the power receiving device in a negotiation phase, The second acquisition step is a step of measuring a voltage during a period in which the power transmission is restricted after acquiring the first quality factor and after the negotiation phase ends, and acquiring the second quality factor from a second attenuation envelope of the voltage.

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