Power transmission equipment and methods performed by power transmission equipment

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 those plurality of detection methods can be executed has not been established.

[0005] The present invention has been made in view of the above problems, The purpose is to appropriately control the foreign object detection process when performing wireless power transmission. [Means for solving the problem]

[0006] As one means to solve the above problems, the power transmission device of the present invention has the following configuration. That is, the power transmission device has a transmitting means for transmitting an Analog Ping, an acquiring means for obtaining a first quality coefficient from a first attenuation envelope of the voltage after transmitting an Analog Ping, and a second quality coefficient from a second attenuation envelope of the voltage after obtaining the first quality coefficient, a determination means for determining the presence or absence of foreign matter based on the result of comparing the first quality coefficient and the second quality coefficient, a power transmission means for wirelessly transmitting power to a power receiving device, and a negotiation means for negotiating with the power receiving device in the negotiation phase, wherein the acquiring means measures the voltage during a period when power transmission is restricted after obtaining the first quality coefficient and after the negotiation phase has ended, obtains the second quality coefficient from the second attenuation envelope of the voltage, and further has a receiving means for receiving identifier information from the power receiving device. [Effects of the Invention]

[0007] According to the present invention, when performing wireless power transmission The foreign object detection process can be appropriately controlled. [Brief explanation of the drawing]

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

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

[0010] [Configuration of a Wireless Power Transmission System] Figure 4 shows an example of the configuration of the wireless power transmission system (wireless charging system) in this embodiment. In one example, this system is configured to include a power receiving device 401 and a power transmitting device 402. The detailed configurations of the power receiving device 401 and the power transmitting device 402 will be described later using Figures 2 and 1. Hereinafter, the power receiving device 401 may be referred to as 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 its internal battery. TX is an electronic device that wirelessly transmits power to RX, which is placed on a charging base 403, which is part of TX. Hereinafter, since the charging base 403 is part of TX, "placed on the charging base 403" may be referred to as "placed on TX (power transmitting device 402)." The area 404 enclosed by the dotted line is the range in which 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 that smartphone. RX and TX may be tablets, storage devices such as hard disk drives and memory devices, or information processing devices such as personal computers (PCs). Furthermore, RX and TX may be, for example, imaging devices (cameras, video cameras, etc.), automobiles, robots, medical equipment, and printers.

[0011] In this system, wireless power transmission using the electromagnetic induction method for wireless charging is performed based on the WPC standard. That is, the RX and TX perform wireless power transmission for wireless charging based on the WPC standard between the power receiving antenna 205 of the RX and the power transmitting antenna 105 of the TX. Note that the wireless power transmission method applied to this system is not limited to the method defined by the WPC standard, and other electromagnetic induction methods, magnetic field resonance methods, electric field resonance methods, microwave methods, methods using lasers, etc. may also be used. Further, in this 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 magnitude of the 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 guaranteed for the output to the load (for example, a charging circuit, battery, etc.) of the power receiving device 401 even if the positional relationship between the power receiving device 401 and the power transmitting device 402 fluctuates 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 fluctuates 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 damage 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 and destruction of the foreign object can be prevented by stopping the power transmission when a foreign object is present. Specifically, a 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. In addition, a Q-value measurement method for detecting foreign objects based on changes in the quality factor (Q-value) of the power transmission antenna 105 (power transmission coil) in the power transmission device 402 is defined. Note that the foreign objects detected by the power transmission device 402 in the present embodiment are not limited to objects existing on the charging stand 403. The power transmission device 402 only needs to detect foreign objects located in the vicinity of the power transmission device 402. For example, it may be configured to detect foreign objects located within the range where the power transmission device 402 can perform power transmission.

[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 in FIG. 10 represents the power transmission power of the power transmission device 402, and the vertical axis represents the power reception power of the power reception device 401. Note that 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 metal piece having conductivity.

[0015] First, the power transmission device 402 performs power transmission to the power reception device 401 at the first power transmission power value Pt1. The power reception device 401 receives power at the first power reception power value Pr1 (this state is referred to as the Light Load state (light load state)). Then, the power transmission device 402 stores the first power transmission power value Pt1. Here, the first power transmission power value Pt1 or the first power reception power value Pr1 is a predetermined minimum power transmission or power reception power. 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 power reception 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] Next, the power transmission device 402 changes the transmission power value to the second transmission power value Pt2 and transmits power to the power receiving device 401. The power receiving device 401 receives power at the second received power value Pr2 (this state is called the Connected Load state). Then, the power transmission device 402 stores the second transmission power value Pt2. Here, the second transmission power value Pt2 or the second received power value Pr2 is a predetermined maximum transmission power or received power. At this time, the power receiving device 401 controls the load so that the power it receives is the maximum power. For example, the power receiving device 401 connects the receiving antenna 205 to the load so that the received power is supplied to the load. Next, the power receiving device 401 reports Pr2 to the power transmission device 402. Upon receiving Pr2 from the power receiving device 401, the power transmitting device 402 calculates that the power loss between the power transmitting device 402 and the power receiving device 401 is Pt2-Pr2 (=Ploss2), and can create a calibration point 1001 that shows the correspondence between Pt2 and Pr2.

[0017] The power transmission device 402 then creates a straight line 1002 by linear interpolation between calibration point 1000 and calibration point 1001. The straight line 1002 shows the relationship between transmitted power and received power when there are no foreign objects in the vicinity of the power transmission device 402 and the power receiving device 401. Based on the straight line 1002, the power transmission device 402 can predict the power value that the power receiving device 401 will receive when transmitting power at a predetermined transmission power in the absence of foreign objects. For example, if the power transmission device 402 transmits power at a third transmission power value Pt3, the third received power value that the power receiving device 401 will receive can be estimated to be Pr3 from point 1003 on the straight line 1002 corresponding to Pt3.

[0018] As described above, based on multiple combinations of the transmitted power value of the power transmission device 402 and the received power value of the power receiving device 401 measured while varying the load, the power loss between the power transmission device 402 and the power receiving device 401 according to the load can be determined. Furthermore, by interpolation from multiple combinations, the power loss between the power transmission device 402 and the power receiving device 401 for all loads can be estimated. In this way, the calibration process performed by the power transmission device 402 and the power receiving device 401 to obtain the combination of transmitted power value and received power value will be referred to below as the "Power Loss method Calibration process (CAL process)".

[0019] After calibration, when the power transmission device 402 actually transmits power to the power receiving device 401 using Pt3, the power transmission device 402 receives a power value Pr3' from the power receiving device 401. The power transmission device 402 calculates Pr3-Pr3' (=Ploss_FO) by subtracting the power value Pr3' actually received from the power receiving device 401 from the power value Pr3 in the absence of foreign objects. This Ploss_FO can be considered as power loss due to the power consumed by foreign objects when they are present near the power transmission device 402 and the power receiving device 401. Therefore, if the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold, it can be determined that a foreign object is present. Alternatively, the power transmission device 402 may pre-calculate the power loss Pt3-Pr3 (=Ploss3) between the power transmission device 402 and the power receiving device 401 from the power value Pr3 in the absence of foreign objects. Next, the power loss Pt3-Pr3' (=Ploss3') between the power transmission device 402 and the power receiving device 401 in the presence of foreign matter is calculated from the received power value Pr3' received from the power receiving device 401 in the presence of foreign matter. Then, Ploss3'-Ploss3 (==Ploss_FO) can be used to estimate the power Ploss_FO that would have been consumed by the foreign matter.

[0020] As described above, the power Ploss_FO, which is likely to have been consumed by the foreign object, can be calculated as Pr3-Pr3'(=Ploss_FO) or as Ploss3'-Ploss3 (=Ploss_FO). In this specification, we will primarily describe the method of calculating Ploss3'-Ploss3 (=Ploss_FO), but the contents of this embodiment can also be applied to the method of calculating Pr3-Pr3'(=Ploss_FO). This concludes the explanation of foreign object detection based on the power loss method.

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

[0022] In this embodiment, the RX and TX communicate for power transmission and reception control based on the WPC standard. The WPC standard defines multiple phases, including the Power Transfer phase in which power transmission is performed and one or more phases prior to actual power transmission, and necessary power transmission and reception control communication is performed in each phase. The phases prior to power transmission may include the Selection phase, Ping phase, Identification and Configuration phase, Negotiation phase, and Calibration phase. In the following, the Identification and Configuration phase will be referred to as the I&C phase. The processing of each phase will be described below.

[0023] In the Selection phase, the TX intermittently transmits Analog Pings to detect when an object is placed on the TX's charging base (for example, when an RX or conductor is placed on the charging base). The TX detects at least one of the voltage and current values ​​of the transmitting antenna 105 when the Analog Ping is transmitted, and determines that an object is present if the voltage value falls below 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 mounted on the TX. The RX notifies the TX of the magnitude of the received voltage. In this way, the TX recognizes that the object detected in the Selection phase is the RX by receiving the response from the RX that received the Digital Ping. Upon receiving notification of the received voltage value, the TX transitions to the I&C phase. Also, before transmitting the Digital Ping, the TX measures the Q-factor of the transmitting antenna 105. This measurement result is used when performing foreign object detection processing using the Q-factor measurement method.

[0025] In the I&C phase, the TX identifies the RX and obtains equipment configuration information (capability information) from the RX. The RX sends an ID Packet and a Configuration Packet. The ID Packet contains the RX's identifier information, and the Configuration Packet contains the RX's equipment configuration information (capability information). Upon receiving the ID Packet and Configuration Packet, the TX responds with an acknowledgment (ACK). The I&C phase then ends.

[0026] In the Negotiation phase, the GP value is determined based on the GP value requested by the RX and the transmission capacity of the TX. The TX also performs foreign object detection processing using the Q-value measurement method according to the request from the RX. Furthermore, the WPC standard specifies a method in which, after transitioning to the Power Transfer phase, the same processing as the Negotiation phase is performed again at the request of the RX. The phase in which these processes are performed after transitioning from the Power Transfer phase is called the Renegotiation phase.

[0027] During the Calibration phase, calibration is performed based on the WPC standard. The RX also notifies the TX of predetermined received power values ​​(received power value under light load conditions / received power value under maximum load conditions), and the TX makes adjustments to efficiently transmit power. The power received value notified to the TX can be used for foreign object detection processing using the Power Loss method.

[0028] During the Power Transfer phase, control is performed for initiating, continuing, and stopping power transmission due to errors or full charge. TX and RX communicate by superimposing signals onto electromagnetic waves transmitted from either the transmitting antenna 105 or the receiving antenna 205, using the transmitting antenna 105 and the receiving antenna 205, which are used for wireless power transmission based on the WPC standard, in order to control these transmission and reception. The range over which communication based on the WPC standard is possible between TX and RX is approximately the same as the transmission range of TX.

[0029] [Configuration of power transmission device 402 and power receiving device 401] Next, the configurations of the power transmission device 402 (TX) and the power receiving device 401 (RX) in this embodiment will be described. Note that the configuration described below is merely an example, and some (or all) of the described configurations may be replaced or omitted by other configurations that perform similar functions, and further configurations may be added to the described configurations. Furthermore, one block shown in the following description may be divided into multiple blocks, or multiple blocks may be integrated into one block. Also, each of the functional blocks shown below will be implemented as a software program, but some or all of the components included in this functional block may be implemented in hardware.

[0030] Figure 1 is a functional block diagram showing an example configuration of the power transmission device 402 (TX) according to this 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 resonant capacitor 107, and a switch 108. In Figure 1, the control unit 101, power supply unit 102, power transmission unit 103, communication unit 104, and memory 106 are shown as separate components, but any multiple functional blocks among these may be implemented on the same chip.

[0031] The control unit 101 controls the entire TX by executing a control program stored, for example, in memory 106. The control unit 101 also performs control related to power transmission control, including communication for device authentication in the TX. Furthermore, the control unit 101 may perform control for executing applications other than wireless power transmission. The control unit 101 is configured to include one or more processors, such as a CPU (Central Processing Unit) or an MPU (MicroProcessor Unit). The control unit 101 may also be configured to include hardware such as an Application Specific Integrated Circuit (ASIC). Additionally, the control unit 101 may include an array circuit such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processes. The control unit 101 stores information that should be stored during the execution of various processes in memory 106. The control unit 101 can also measure time using a timer (not shown).

[0032] The power supply unit 102 supplies power to each functional block. The power supply unit 102 is, for example, a commercial power source or a battery. The battery stores power supplied from the commercial power source.

[0033] The power transmission unit 103 converts the DC or AC power input from the power supply unit 102 into AC power in the frequency band used for wireless power transmission, and inputs this AC power to the power transmission antenna 105 to generate electromagnetic waves for the RX to receive power. For example, the power transmission unit 103 converts the DC voltage supplied by the power supply unit 102 into an AC voltage using a switching circuit with a half-bridge or full-bridge configuration using a FET (Field Effect Transistor). In this case, the power transmission unit 103 includes a gate driver that controls the ON / OFF state of the FET.

[0034] The power transmission unit 103 controls the intensity of the electromagnetic waves output by adjusting the voltage (transmission voltage) or current (transmission current), or both, input to the power transmission antenna 105. Increasing the transmission voltage or transmission current increases the intensity of the electromagnetic waves, while decreasing the transmission voltage or transmission current decreases the intensity of the electromagnetic waves. The power transmission unit 103 also controls the output of AC power so that power transmission from the power transmission antenna 105 is started or stopped based on instructions from the control unit 101. Furthermore, the power transmission unit 103 is assumed to have the capacity to supply enough power to output 15 watts (W) of power to the charging unit 206 of the power receiving device 401 (RX) compliant with the WPC standard.

[0035] The communication unit 104 communicates with the RX for power transmission control based on the WPC standard described above. The communication unit 104 modulates the electromagnetic waves output from the power transmission antenna 105 and transmits information to the RX to perform communication. The communication unit 104 also demodulates the electromagnetic waves transmitted from the power transmission antenna 105 that the RX has modulated to obtain the information transmitted by the RX. In other words, the communication performed by the communication unit 104 is carried out by superimposing a signal on the electromagnetic waves transmitted from the power transmission antenna 105. The communication unit 104 may also communicate with the RX using a different antenna than the power transmission antenna 105 and a different standard than the WPC standard, or it may selectively use multiple communication methods to communicate with the RX.

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

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

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

[0039] The control unit 201 controls the entire RX by executing a control program stored, for example, in the memory 208. In other words, the control unit 201 controls each of the functional units shown in Figure 2. Furthermore, the control unit 201 may perform control for executing applications other than wireless power transmission. An example of the control unit 201 is configured to include one or more processors such as a CPU or MPU. In addition, the control unit 201 may cooperate with the OS (Operating System) it is running to control the entire RX (or the entire smartphone if the RX is a smartphone).

[0040] Furthermore, the control unit 201 may be composed of hardware such as an ASIC. Alternatively, the control unit 201 may include an array circuit such as an FPGA compiled to perform predetermined processing. The control unit 201 stores information that should be stored during the execution of various processes in the memory 208. The control unit 201 may also measure time using a timer (not shown).

[0041] The UI unit 202 provides various outputs to the user. These outputs include screen displays, blinking and color changes of LEDs (Light Emitting Diodes), audio output from the speaker, and vibration of the RX unit. The UI unit 202 is implemented using an LCD panel, speaker, vibration motor, etc.

[0042] The power receiving unit 203 acquires AC power (AC voltage and AC current) generated by electromagnetic induction based on electromagnetic waves radiated from the TX's power transmitting antenna 105 via the power receiving antenna 205. The power receiving unit 203 converts the AC power into DC power or AC power of a predetermined frequency and outputs power to the charging unit 206, which performs processing for charging the battery 207. In other words, the power receiving unit 203 includes a rectifier and a voltage control unit necessary to supply power to the load in RX. The above-mentioned GP is the amount of power guaranteed to be output from the power receiving unit 203. The power receiving unit 203 is assumed to have the capacity to supply enough power for the charging unit 206 to charge the battery 207 and to output 15 watts of power to the charging unit 206.

[0043] The communication unit 204 communicates with the communication unit 104 of the TX for power receiving control based on the WPC standard as described above. The communication unit 204 demodulates the electromagnetic waves input from the power receiving antenna 205 and obtains the information transmitted from the TX. Then, the communication unit 204 communicates with the TX by superimposing a signal related to the information to be transmitted to the TX onto the electromagnetic waves by load modulation of the input electromagnetic waves. The communication unit 204 may also communicate with the TX using a different antenna than the power receiving antenna 205 and a communication standard different from the WPC standard, or it may selectively use multiple communication methods to communicate with the TX.

[0044] In addition to storing the control program, memory 208 also stores the states of TX and RX. For example, the state of RX can be obtained by the control unit 201, and the state of TX can be obtained by the TX control unit 101, and both 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 receiving antenna 205 is connected to the resonant capacitor 211. When the second switch unit 210 is turned ON and short-circuited, the receiving antenna 205 and the resonant capacitor 211 form a series resonant circuit and resonate at a specific frequency f2. At this time, current flows through the closed circuit formed by the receiving antenna 205, the resonant capacitor 211, and the second switch unit 210, but no current flows through the receiving unit. When the second switch unit 210 is turned OFF and opened, the power received by the receiving antenna 205 and the resonant capacitor 211 is supplied to the receiving unit 203.

[0046] The first switch unit 209 controls whether or not to supply the received power to the load, which is the battery. It also has the function of controlling the value of the load. When the first switch unit 209 connects the charging unit 206 and the battery 207, the received power is supplied to the battery 207. When the first switch unit 209 disconnects the connection between the charging unit 206 and the battery 207, the received power is not supplied to the battery 207. In Figure 2, the first switch unit 209 is located between the charging unit 206 and the battery 207, but it may also be located between the power receiving unit 203 and the charging unit 206. Alternatively, it may be located between the power receiving antenna 205, the resonant capacitor 211, and the closed circuit formed by the second switch unit 210 and the power receiving unit 203. In other words, the first switch unit 209 may also be for controlling whether or not to supply the received power to the power receiving unit 203. Furthermore, although Figure 2 shows the first switch unit 209 as a single block, it is also possible to implement the first switch unit 209 as part of the charging unit 206 or as part of the power receiving unit 203.

[0047] Next, the functions of the control unit 101 of the TX will be described with reference to Figure 3. Figure 3 is a block diagram showing an example of the functional configuration of the control unit 101 of the power transmission device 402 (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 a waveform attenuation index, which will be described later. It also measures the power transmitted to the RX via the power transmission unit 103 and measures the average transmitted power for each unit of time. The measurement unit 303 also measures the Q value of the power transmission antenna 105. The setting unit 304 sets a threshold value to be 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 foreign object detection functions using the Power Loss method, the Q-value measurement method, or the waveform attenuation method. The foreign object detection unit 305 may also have functions for performing foreign object detection processing using other methods. For example, in a TX equipped with NFC (Near Field Communication) communication functionality, the foreign object detection unit 305 may perform foreign object detection processing using the NFC standard's opposing device detection function. Furthermore, in addition to detecting foreign objects, the foreign object detection unit 305 can also detect changes in the state on the TX. For example, the TX can also detect increases or decreases in the number of power receiving devices 401 on the TX. The setting unit 304 sets thresholds that serve as criteria for determining the presence or absence of foreign objects when the TX performs foreign object detection using the Power Loss method, the Q-value measurement method, or the waveform attenuation method. The setting unit 304 may also have functions for setting thresholds that serve as criteria for determining the presence or absence of foreign objects, which are necessary when performing foreign object detection processing using other methods. Furthermore, the foreign object detection unit 305 can perform foreign object detection processing based on the threshold set by the setting unit 304 and the waveform attenuation index, power transmission power, and Q value measured by the measurement unit 303.

[0049] The communication control unit 301, power transmission control unit 302, measurement unit 303, setting unit 304, and foreign object detection unit 305 are implemented as programs that operate in the control unit 101. Each processing unit is configured as an independent program and can operate in parallel while synchronizing the programs through event processing, etc. However, two or more of these processing units may be incorporated into a single program.

[0050] [Processing flow for power transmission in accordance with WPC standards] The WPC standard specifies the Selection phase, Ping phase, I&C phase, Negotiation phase, Calibration phase, and Power Transfer phase. Below, the operation of the power transmission device 402 and the power receiving device 401 in these phases will be explained using the sequence diagram in Figure 5. Figure 5 is a sequence diagram for power transmission in accordance with the WPC standard. Here, the transmission device 402 (TX) and the receiving device 401 (RX) are used as examples.

[0051] The TX repeatedly and intermittently transmits Analog Pings according to the WPC standard to detect objects within its power transmission range (F501). The TX performs the processes defined as the Selection phase and Ping phase of the WPC standard and waits for the RX to be placed on it. The user of the RX brings the RX (e.g., a smartphone) closer to the TX to charge it (F502). For example, the RX is brought closer to the TX by loading it onto the TX. When the TX detects the presence of an object within its power transmission range (F503, F504), it transmits a Digital Ping according to the WPC standard (F505). When the RX receives the Digital Ping, it can understand that the TX has detected it (F506). The TX also determines that the detected object is an RX and that the RX has been placed on the charging cradle 403 when it receives a predetermined response to the Digital Ping. When the TX detects the placement of the RX, it obtains identification and capability information from the RX via I&C phase communication as defined by the WPC standard (F507). Here, the RX identification information includes the Manufacturer Code and Basic Device ID. The RX capability information includes information elements that can identify the version of the WPC standard it supports, the Maximum Power Value which is a value that identifies the maximum power the RX can supply to the load, and information indicating whether it has the WPC standard negotiation function. The TX may also obtain the RX identification and capability information by means other than the WPC standard I&C phase communication. Furthermore, the identification information may be any other identification information that can identify an individual RX, such as a Wireless Power ID. Capability information may also include information other than that described above.

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

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

[0054] Next, when RX receives an ACK from TX (F510), it processes information including the received power under load conditions (maximum load conditions, load conditions where the transmitted power exceeds the second threshold) (hereinafter referred to as second reference received power information) to transmit to TX. In this embodiment, since GP is 5 watts, the second reference received power information is the received power information of RX when the transmitted power of TX is 5 watts. Here, the second reference received power information is Received Power Packet (mode 2) as defined in the WPC standard, but other messages may be used. RX transmits a transmission output change instruction containing a positive value to increase the transmitted power from TX to 5 watts (F511).

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

[0056] When RX determines that it has reached the predetermined transmission power level by receiving a NAK from TX, it transmits information including the received power in the load-connected state to TX as second-reference received power information (F516). Based on the TX's transmission power value and the received power values ​​included in the first and second-reference received power information, TX can calculate the amount of power loss between TX and RX in the light-load state and the load-connected state. Furthermore, by interpolating between these power loss amounts, it can calculate the power loss value between TX and RX for all transmission power levels that TX can take (in this case, from 250 milliwatts to 5 watts) (F517). TX sends an ACK to RX for the second-reference received power information (F518) and completes the calibration process. When TX determines that it is ready to start charging and begins transmitting power to RX, charging of RX begins. Furthermore, before the start of power transmission processing, the TX and RX perform equipment authentication processing (F519), and if they determine that the equipment can handle a larger GP, they may reset the GP to a larger value, for example, 15 watts (F520).

[0057] In this case, RX and TX increase the transmission output using transmission output change instructions, ACK, and NAK to increase TX's transmission power to 15 watts (F521-F524). Then TX and RX perform calibration again for GP=15 watts. Specifically, RX transmits information including the received power in RX's load-connected state when TX's transmission power is 15 watts (hereinafter referred to as the third reference received power information) (F525). TX performs calibration based on the received power included in the first, second, and third reference received power information and can calculate the power loss between TX and RX for all transmission powers that TX can take (from 250 milliwatts to 15 watts in this case) (F526). TX sends an ACK to RX for the third reference received power information (F527) and completes the calibration process. Having determined that it is ready to start charging, TX starts the power transmission process to RX and moves to the Power Transfer phase (F528).

[0058] In the Power Transfer phase, the TX transmits power to the RX. Foreign object detection is also performed using the Power Loss method. In the Power Loss method, the TX first calculates the amount of power loss between the TX and RX in a state without foreign objects, based on the difference between the power transmitted by the TX and the power received by the RX, using the Calibration method described above. This calculated value corresponds to the standard amount of power loss in a normal state (without foreign objects) during power transmission. The TX then determines that "foreign objects are present" or "there is a possibility of foreign objects being present" if the amount of power loss between the TX and RX measured during power transmission after Calibration deviates by more than a threshold from the power loss in the normal state.

[0059] The above is an explanation of the Power Loss method. The Power Loss method detects foreign objects based on the measurement results of power loss during power transmission from the power transmission device 402 to the power receiving device 401. While 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, it has the advantage that it can maintain high power transmission efficiency because foreign object detection can be performed while power transmission continues.

[0060] Thus, foreign object detection can be performed during the Power Transfer phase using the Power Loss method. However, relying solely on the Power Loss method for foreign object detection carries the risk of false detection of foreign objects or incorrect determination of the absence of foreign objects when they are present. In particular, the Power Transfer phase is the phase in which the TX transmits power, and if foreign objects are present near the TX and RX during power transmission, heat generation from these objects will increase. Therefore, improving the accuracy of foreign object detection in this phase is required. Accordingly, in this embodiment, we consider implementing a foreign object detection method different from the Power Loss method in order to improve the accuracy of foreign object detection.

[0061] [Foreign object detection method using waveform attenuation] In the Power Transfer phase, the power transmission device 402 transmits power to the power receiving device 401. Therefore, if foreign object detection can be performed using the transmission waveform (voltage waveform or current waveform) related to this power transmission, foreign object detection will be possible without using newly defined foreign object detection signals, etc. A method of detecting foreign objects based on the attenuation state of the transmitted radio waves (hereinafter referred to as the waveform attenuation method) will be explained using Figure 6. Figure 6 is a diagram illustrating the principle of foreign object detection using the waveform attenuation method. Here, foreign object detection using the transmission waveform related to power transmission from the power transmission device 402 (TX) to the power receiving device 401 (RX) will be explained as an example.

[0062] In Figure 6, the waveform shows the change over time of the voltage value 600 (hereinafter simply referred to as the voltage value) of the high-frequency voltage applied to the TX's transmitting antenna 105. In Figure 6, the horizontal axis represents time, and the vertical axis represents the voltage value. The TX, which transmits power to the RX via the transmitting 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 transmitted radio waves related to power transmission from the TX is a predetermined frequency, for example, a fixed frequency between 85kHz and 205kHz used in the WPC standard. Point 601 is a point on the envelope of the high-frequency voltage and 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 transmitting antenna 105 can be determined based on the time change of the voltage value after time T0. For example, the Q value can be calculated using Equation 1 based on the time, voltage value, and frequency f of the high-frequency voltage at points 601 and 602 on the envelope of the voltage value. Q = πf(T2 - T1) / ln(A1 / A2) (Equation 1) If foreign matter is present near TX and RX, the Q value decreases. This is because energy loss occurs due to the presence of foreign matter. Therefore, focusing on the slope of voltage decay, the slope of the line connecting points 601 and 602 becomes steeper when foreign matter is present than when it is absent, as more energy is lost due to the foreign matter. This results in a higher attenuation rate of the waveform amplitude. In other words, the waveform attenuation method determines the presence or absence of foreign matter based on the voltage decay state between points 601 and 602. In practice, the presence or absence of foreign matter can be determined by comparing some numerical value that represents this attenuation state. For example, the above-mentioned Q value can be used for determination. A lower Q value means a higher waveform attenuation rate (the degree of decrease in waveform amplitude per unit time). Alternatively, the determination may be made using the slope of the line connecting points 601 and 602, which can be obtained from (A1-A2) / (T2-T1). Alternatively, if the time (T1 and T2) for observing the voltage decay state is fixed, the determination can also be made using the difference in voltage values ​​(A1-A2) or the ratio of voltage values ​​(A1 / A2). Alternatively, if the voltage value A1 immediately after the power transmission is stopped is constant, the determination can also be made using the value of voltage value A2 after a predetermined time has elapsed. Alternatively, the determination may be made using the value of the time (T2-T1) until the voltage value A1 becomes a predetermined voltage value A2.

[0063] As described above, the presence or absence of foreign matter can be determined by the voltage attenuation state during the power transmission outage, and there are multiple values ​​that represent this attenuation state. In this embodiment, these values ​​representing the attenuation state are called "waveform attenuation indices." For example, as mentioned above, the Q value calculated by Equation 1 is a value that represents the voltage attenuation state related to power transmission and is included in the "waveform attenuation indices." All waveform attenuation indices are values ​​that correspond to the waveform attenuation rate. In addition, in the waveform attenuation method, the waveform attenuation rate itself may be measured as the "waveform attenuation indices." In the following, we will mainly explain the case in which the waveform attenuation rate is used as the waveform attenuation indices, but the contents of this embodiment can be applied similarly when other waveform attenuation indices are used.

[0064] Furthermore, even if the vertical axis of Figure 6 represents the current value flowing through the power transmission antenna 105, the attenuation state of the current value during the power transmission stop period changes depending on the presence or absence of foreign matter, similar to the case of the voltage value. When foreign matter is present, the waveform attenuation rate is higher than when there is no foreign matter. Therefore, foreign matter can be detected by applying the above method to the time change of the current value flowing through the power transmission antenna 105. That is, the presence or absence of foreign matter can be determined and detected by using the Q value obtained from the current waveform, the slope of the current value attenuation, the difference in current values, the ratio of current values, the absolute value of the current value, and the time until a predetermined current value is reached, etc., as waveform attenuation indices. Alternatively, foreign matter detection may be performed based on both the attenuation state of the voltage value and the attenuation state of the current value, such as determining the presence or absence of foreign matter using an evaluation value calculated from the waveform attenuation index of the voltage value and the waveform attenuation index of the current value. In the above example, the waveform attenuation index was measured for the period when the TX temporarily stopped power transmission, but it may also be the case that the waveform attenuation index was measured for the period when the TX temporarily reduced the power supplied from the power supply unit 102 from a predetermined power level to a lower power level.

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

[0066] When it is time to detect a foreign object, the TX (transmission controller) temporarily suspends power transmission. During the foreign object detection period when power transmission is suspended, the amplitude of the transmitted wave is attenuated, and the TX calculates the waveform attenuation rate of this attenuated waveform. The TX then determines that a foreign object is present if the calculated waveform attenuation rate exceeds a predetermined threshold. After the predetermined foreign object detection period has elapsed, if no foreign object is detected, the TX resumes power transmission. After resuming power transmission, the TX repeatedly performs the above-described transient response period waiting, foreign object detection timing determination, power transmission suspension, and foreign object detection process. The above is the basic process of foreign object detection using the waveform attenuation method.

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

[0068] Furthermore, when measuring the waveform attenuation rate of a transmitting device, if elements such as the power transmission unit 103, communication unit 104, and power supply unit 102 are connected to the power transmission antenna 105 and resonant capacitor 107 of the power transmission device 402, the waveform attenuation rate of the attenuated waveform will be affected by the load from these elements. In other words, the waveform attenuation rate will change depending on the state of the power transmission unit 103, communication unit 104, and power supply unit 102. Therefore, even if the waveform attenuation rate is large, it becomes difficult to distinguish whether it is due to the influence of foreign objects or to the power transmission unit 103, communication unit 104, and power supply unit 102. For this reason, when measuring the waveform attenuation rate, the switch 108 may be turned ON to short-circuit it, causing current to flow in the closed loop formed by the power transmission antenna 105, resonant capacitor 107, and switch 108. This makes it possible to eliminate the influence of the power transmission unit 103, communication unit 104, and power supply unit 102. Alternatively, a switch may be provided between the closed-loop circuit formed by the transmitting antenna 105, the resonant capacitor 107, and the switch 108, and the power transmission unit 103. When detecting foreign objects, the switch disconnects the closed-loop circuit from the power transmission unit, thereby eliminating the influence of the power transmission unit 103, the communication unit 104, and the power supply unit 102. As described above, by turning the switch 108 ON to create a short circuit (connection), or by disconnecting the closed-loop circuit from the power transmission unit 103 with the switch, foreign object detection can be performed with high accuracy. Furthermore, by performing both turning the switch 108 ON to create a short circuit (connection) and disconnecting the closed-loop circuit from the power transmission unit 103 with the switch, high accuracy foreign object detection can also be achieved.

[0069] [Method for setting the foreign object detection threshold in waveform attenuation method] Figure 11 is a diagram illustrating the method for setting the foreign object detection threshold in the waveform attenuation method. First, the RX controls its load to a light load state so that when power is transmitted from the TX, no power or only very little power is supplied to the RX's load. Let the power transmitted by the TX at this time be Pt1. Then, the TX stops transmitting power in this state and measures the waveform attenuation rate. Let the waveform attenuation rate at this time be δ1. At this time, the TX recognizes the power transmitted Pt1 that it is transmitting and stores a calibration point 1100 in memory that associates the power transmitted Pt1 with the waveform attenuation rate δ1. Next, the RX controls its load to a load-connected state so that when power is transmitted from the TX, the RX's load is supplied with maximum power or power above a predetermined threshold. Let the power transmitted by the TX at this time be Pt2. Then, the TX stops transmitting power in this state and measures the waveform attenuation rate. At this time, the TX stores a calibration point 1101 in memory that associates the transmission power Pt2 with the waveform attenuation rate δ2. Next, the TX performs linear interpolation between calibration point 1100 and calibration point 1101 to create a line 1102. Line 1102 shows the relationship between the transmission power and the waveform attenuation rate of the transmitted signal when there are no foreign objects around the TX and RX. Therefore, the TX can estimate the waveform attenuation rate of the transmitted signal for each transmission power value in the absence of foreign objects from line 1102. For example, if the transmission power value is Pt3, the waveform attenuation rate can be estimated to be δ3 from point 1103 on line 1102 corresponding to the transmission power value Pt3. Based on the above estimation results, the TX can then calculate a threshold used to determine the presence or absence of foreign objects for each transmission power value. For example, a waveform attenuation rate that is a predetermined value (a value corresponding to the measurement error) greater than the estimated waveform attenuation rate in the case of no foreign matter at a given power transmission value may be set as the threshold for determining the presence or absence of foreign matter. The calibration process performed by the power transmission device 402 and the power receiving device 401 in order for the power transmission device 402 to acquire a combination of power transmission value and waveform attenuation rate will be referred to below as the "waveform attenuation method calibration process (CAL process)".

[0070] Furthermore, RX may perform control actions such as one that results in no power being supplied to the load / a light load state, and another that results in a load connection state, after notifying TX of its intention to perform these actions. Also, either of these two controls may be performed first.

[0071] Furthermore, the operation for calculating the threshold used to determine the presence or absence of foreign matter for each load (each transmission power value), as described in this embodiment, may be performed in the Calibration phase. As mentioned above, in the Calibration phase, TX acquires data necessary for foreign matter detection using the Power Loss method. At that time, TX acquires data on power loss when the RX is in a light load state and when it is in a load-connected state. Therefore, the measurement of calibration point 1100 and calibration point 1101 in Figure 11 may be performed in the Calibration phase described above, when RX is in a light load state and when it is in a load-connected state, together with the measurement of power loss. That is, when TX receives first reference received power information from RX, it measures calibration point 1100 in addition to the predetermined processing to be performed in the Calibration phase. Also, when TX receives second reference received power information from RX, it measures calibration point 1101 in addition to the predetermined processing to be performed in the Calibration phase. This eliminates the need to set aside a separate period for measuring calibration point 1100 and calibration point 1101, allowing measurements of calibration point 1100 and calibration point 1101 to be performed in a shorter time.

[0072] [Processing of power transmission equipment when the waveform attenuation method is applied to the WPC standard] Next, we will explain the processing performed by the power transmission device 402 when applying this waveform attenuation method to the WPC standard for foreign object detection. When performing foreign object detection using the waveform attenuation method, the power transmission device 402 first measures the waveform attenuation rate in the absence of foreign objects and calculates a threshold value based on that. Subsequently, the power transmission device 402 performs foreign object detection using the waveform attenuation method, and if the measured waveform attenuation rate is greater than the threshold value, it determines that "foreign objects are present" or "there is a possibility of foreign objects being present," and if it is smaller than the threshold value, it determines that "there are no foreign objects" or "there is a high possibility that there are no foreign objects."

[0073] This section explains the timing for pre-measuring the waveform attenuation rate in the absence of foreign matter. In the WPC standard, as mentioned above, foreign matter detection is performed in the Negotiation phase using the Q-value measurement method. If the foreign matter detection determines that there is no foreign matter, the process proceeds to the Calibration phase and then the Power Transfer phase. In other words, proceeding to the Negotiation phase or beyond means that the foreign matter detection using the Q-value measurement method has determined that there is no foreign matter. Therefore, measuring the waveform attenuation rate in any of the Negotiation, Calibration, or Power Transfer phases is highly likely to allow measurement of the waveform attenuation rate in the absence of foreign matter. Thus, the timing for measuring the waveform attenuation rate in the absence of foreign matter can be any of the Negotiation, Calibration, or Power Transfer phases.

[0074] In this embodiment, the timing for measuring the waveform attenuation rate in the absence of foreign matter is set to the first stage of the PowerTransfer phase. This is because the longer the time elapsed since it was determined that there was no foreign matter using the Q-value measurement method, the higher the probability that foreign matter will be placed near the power transmission device 402 and the power receiving device 401. Then, at the timing for foreign matter detection specified by the power receiving device 401 or the power transmission device 402, the power transmission device 402 measures the waveform attenuation rate of the transmitted radio waves. The power transmission device 402 then compares the measured waveform attenuation rate with a threshold calculated from the waveform attenuation rate in the absence of foreign matter described above, and determines whether or not there is foreign matter.

[0075] However, the waveform attenuation method has the disadvantage of causing a decrease in transmission efficiency due to the temporary suspension of power transmission, as the power transmission device 402 temporarily stops power transmission and observes the attenuation rate of the transmitted waves to detect foreign objects. On the other hand, it has the advantage of enabling highly accurate foreign object detection even when foreign object detection processing is performed while a large amount of power is being transmitted. In other words, even in situations where it is difficult to accurately detect foreign objects using the power loss method, foreign objects can be detected by using the waveform attenuation method.

[0076] In the embodiment described above, when foreign object detection is performed by the waveform attenuation method, the waveform attenuation rate in the absence of foreign objects is measured before the start of power transmission, and a threshold is calculated based on this. When performing foreign object detection by the waveform attenuation method, if the measured waveform attenuation rate is greater than the threshold, it is determined that "foreign objects are present" or "there is a possibility of foreign objects being present," and if it is smaller than the threshold, it is determined that "there are no foreign objects" or "there is a high possibility that there are no foreign objects." However, foreign object detection may also be performed using a threshold obtained from the waveform attenuation rate measured at a time when it is estimated that there are no foreign objects after the start of power transmission. For example, while the TX is transmitting power, it is confirmed that there are no foreign objects using the Power Loss method. Next, the TX performs the first waveform attenuation rate measurement and calculates a threshold based on the measured waveform attenuation rate. Since this first waveform attenuation rate measurement is performed immediately after it has been confirmed that there are no foreign objects using the Power Loss method, the measured waveform attenuation rate is estimated to be the waveform attenuation rate in the absence of foreign objects. Next, the TX resumes power transmission and performs a second waveform attenuation rate measurement at the time it is determined that foreign object detection should be performed. Then, by comparing the measurement result of the second waveform attenuation rate measurement with the measurement result of the first waveform attenuation rate measurement or a threshold calculated based on that result, it is possible to determine whether or not there is a foreign object present. In other words, when performing foreign object detection using the waveform attenuation method, the waveform attenuation rate measured at that time may be compared with the waveform attenuation rate or threshold measured in a previous state where there was no foreign object.

[0077] Furthermore, in the embodiment described above, the frequency of the transmitted radio waves related to power transmission from the power transmission device 402 was assumed to be a fixed frequency. However, the foreign object detection process described in this embodiment may be performed at each of multiple frequencies, and the presence or absence of foreign objects may be determined by combining the results. By performing foreign object detection using the waveform attenuation rates at multiple frequencies, not just one frequency, it becomes possible to perform foreign object detection with higher accuracy.

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

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

[0080] As described above, there are two methods for detecting foreign objects during power transmission from the power transmission device 402 to the power receiving device 401: the Power Loss method and the waveform attenuation method. In the Power Loss method, as explained using Figure 10, the power receiving device 401 notifies the power transmission device 402 of the power received value Pr3' measured by the power receiving device 401. The power transmission device 402 calculates Pr3-Pr3' (=Ploss_FO), which is the value obtained by subtracting the power received value Pr3' actually received from the power receiving device 401 from the power received value Pr3 in the absence of foreign objects. This Ploss_FO can be considered as power loss due to the power consumed by foreign objects when they are present in the vicinity of the power transmission device 402 and the power receiving device 401. Therefore, the power transmission device 402 can determine that foreign objects are present when the power Ploss_FO, which is likely to have been consumed by the foreign objects, exceeds a predetermined threshold. In other words, in the Power Loss method, when detecting foreign objects, communication takes place between the power transmission device 402 and the power receiving device 401 in order to notify the power transmission device 402 of the received power value Pr3' as described above. A communication error has already occurred between the power transmission device 402 and the power receiving device 401, and an error may occur in this communication for foreign object detection due to the same reason.

[0081] On the other hand, the waveform attenuation method involves the power transmission device 402 stopping power transmission and comparing the waveform attenuation rate at that time with the waveform attenuation rate measured in advance when no foreign objects are present to determine the presence or absence of foreign objects. Therefore, foreign object detection can be performed without communication between the power transmission device 402 and the power receiving device 401. Thus, in the event of a communication error, the power transmission device 402 performs foreign object detection using the waveform attenuation method, which does not require communication. This increases the likelihood of successful foreign object detection.

[0082] Furthermore, even if foreign objects are present near the power transmission device 402 and the power receiving device 401 during power transmission, communication errors may not occur. However, even if communication errors do not occur, the presence of foreign objects may cause problems such as significant power loss or overheating. Therefore, the power transmission device 402 periodically performs foreign object detection during the Power Transfer phase, which involves wireless power transmission, to check whether or not foreign objects are present near the power transmission device 402 and the power receiving device 401. If the waveform attenuation method is used for this periodic foreign object detection, power transmission from the power transmission device 402 will be temporarily stopped each time foreign object detection is performed, leading to a decrease in power transmission efficiency. On the other hand, if the Power Loss method is used, it is possible to detect foreign objects while continuing to transmit power from the power transmission device 402 to the power receiving device 401. Therefore, when no communication errors occur, the power transmission device 402 and the power receiving device 401 periodically perform foreign object detection using the Power Loss method during the Power Transfer phase. This allows for early detection of foreign objects while maintaining high power transmission efficiency.

[0083] The operation of the power transmission device 402 and power receiving device 401 using the above-described multiple foreign object detection methods will now be explained. Figure 8 shows an example of the operation of the power transmission device 402 during the Power Transfer phase. The process in Figure 8 starts when the power transmission device 402 detects the power receiving device 401 placed on the charging base 403, communicates with it, and the processing of each phase specified in the WPC standard is completed. The phases executed before the start of the process in Figure 8 are the Selection phase, Ping phase, I&C phase, Negotiation phase, and Calibration phase. However, the process in Figure 8 may start without performing at least some of the above 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 from the power receiving device 401 to perform foreign object detection using the Power Loss method. This command includes the power received value measured by the power receiving device 401. If this command is received, in S803, the power transmission device 402 performs foreign object detection using the Power Loss method based on the power received value from the power receiving device 401 and the power transmitted value measured by the power transmission device 402.

[0085] In S804, the power transmission device 402 determines whether or not a foreign object is present in its vicinity based on the results of the foreign object detection process. If it is determined that a foreign object is present, in S805, the power transmission device 402 sends a negative response (NAK), which is information indicating the presence of a foreign object, to the power receiving device 401. In S806, the power transmission device 402 either stops power transmission or controls the transmission power to decrease. On the other hand, if it is determined in S804 that no foreign object is present, the power transmission device 402 sends an acknowledgment (ACK), which is information indicating the absence of a foreign object, to the power receiving device 401, and continues power transmission, returning to S802.

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

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

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

[0089] Figure 9 shows an example of the operation of the power receiving device 401 during the Power Transfer phase. The process in Figure 9 starts at the same timing as the process in Figure 8. At S901, the power receiving device 401 starts receiving power during the Power Transfer phase. At S902, the power receiving device 401 sends a command to the power transmitting device 402 to execute foreign object detection using the Power Loss method, which is a command that should be sent periodically. This command is a notification from the power receiving device 401 to the power transmitting device 402 requesting foreign object detection processing using the Power Loss method.

[0090] In S903, the receiving device 401 determines whether a communication error has occurred in the communication between the transmitting device 402 and the receiving device 401. The receiving device 401 determines the communication error as follows: In accordance with the WPC standard, the receiving device 401 sends various commands to the transmitting device 402. When the transmitting device 402 receives a command from the receiving device 401, it responds to the receiving device 401 (such as an affirmative or negative response). For example, in order to periodically perform foreign object detection using the Power Loss method described above, the power receiving device 401 periodically sends a command to the power transmitting device 402 to execute foreign object detection using the Power Loss method. When the power transmitting device 402 receives this command, it responds to the power receiving device 401. The power receiving device 401 then determines that a communication error has occurred (i.e., detects a communication error) if it has sent a command to the power transmitting device 402 to execute foreign object detection using the Power Loss method but has not received a response from the power transmitting device 402. Furthermore, even if the power receiving device 401 receives a response from the power transmitting device 402, it determines that a communication error has occurred if the response contains an invalid packet. However, the method of detecting a communication error by the power receiving device 401 is not limited to this.

[0091] If a communication error is detected in S903, there is a possibility that a foreign object is present and that foreign object detection using the Power Loss method has not been performed correctly. Therefore, in S904, the receiving device 401 sends a command to the transmitting device 402 to execute foreign object detection using the waveform attenuation method. This command is a notification from the receiving device 401 to the transmitting device 402 requesting foreign object detection processing using the waveform attenuation method. The receiving device 401 then waits for a response from the transmitting device 402 according to the result of foreign object detection using the waveform attenuation method. If no communication error is detected in S903, the receiving device 401 waits for a response from the transmitting device 402 according to the result of foreign object detection using the Power Loss method.

[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. If a negative response is received, in S906, the power receiving device 401 sends an EPT (End Power Transfer) command to the power transmitting device 402, which is a command to terminate power transmission, and transitions to a state where it does not receive power. On the other hand, if no negative response is received in S905, for example, if an affirmative response is received, the power receiving device 401 continues receiving power and returns to S902.

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

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

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

[0096] Furthermore, if the power transmission device 402 measures the waveform attenuation rate, it may notify the power receiving device 401 of the measurement result of the waveform attenuation rate or a threshold value obtained from that measurement result. This allows the power receiving device 401 to determine the presence or absence of foreign matter based on the measurement results received from the power transmission device 402. Similarly, if the power receiving 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 a threshold value obtained from that measurement result. This allows the power transmission device 402 to determine the presence or absence of foreign matter based on the measurement results received from the power receiving device 401.

[0097] In the above explanation using Figures 8 and 9, the waveform attenuation method is employed to perform highly accurate foreign object detection when a communication error is detected. This allows the system to detect foreign objects and stop (or reduce) power transmission even if a foreign object is not detected by the periodic foreign object detection process using the Power Loss method, by performing the foreign object detection process using the waveform attenuation method in response to the communication error. However, if the power transmission device 402 and the power receiving device 401 wish to avoid a decrease in power transmission efficiency, they may perform foreign object detection using the Power Loss method in response to the detection of a communication error. In this case, the power transmission device 402, which detects a communication error in S808 of Figure 8, may perform foreign object detection using the Power Loss method in S809 instead of performing foreign object detection using the waveform attenuation method. Similarly, the power receiving device 401, which detects a communication error in S903 of Figure 9, may send a command to execute foreign object detection using the Power Loss method in S904 instead of sending a command to execute foreign object detection using the waveform attenuation method. When foreign object detection is performed using the Power Loss method in S809, the power transmission device 402 requests the power receiving device 401 to send a command including the received power value, and detects foreign objects based on the received power value and the transmitted power value measured by the power transmission device 402. When the power receiving device 402 sends a command to execute foreign object detection using the Power Loss method in S903, the power transmission device 401, upon receiving the command, performs foreign object detection using the Power Loss method. Through this process, even if a foreign object is not detected during the periodic foreign object detection process using the Power Loss method, the probability of detecting the foreign object is increased by performing the foreign object detection process again in response to a communication error.

[0098] Furthermore, when foreign object detection is performed using the Power Loss method in response to the detection of a communication error, communication for foreign object detection takes place between the power transmission device 402 and the power receiving device 401. However, there is a possibility that another communication error may occur during this communication, preventing the power transmission device 402 or the power receiving device 401 from receiving data, or receiving data containing invalid packets. If the foreign object detection execution command sent by the power receiving device 401 to the power transmission device 402 is lost due to a communication error, the power transmission device 402 will not recognize that foreign object detection has been requested and will not perform foreign object detection. Therefore, the power transmission device 402 will not send a response to the foreign object detection execution command to the power receiving device 401.

[0099] Therefore, if the power receiving device 401 suspects that another communication error has occurred, it may send an EPT command, which is a command to terminate power transmission, to the power transmitting device 402 and transition to a state where it is not receiving power. If the power transmitting device 402 receives the EPT, it will stop transmitting power. Alternatively, even if it does not receive the EPT, the power transmitting device 402 may detect that the power receiving device 401 has transitioned to a state where it is not receiving power, stop transmitting power, and transition to the Selection phase. If another communication error occurs in the communication for detecting foreign objects in response to the detection of a communication error, it is considered highly likely that a foreign object is present, or that there is another factor interfering with communication, given the high frequency of communication errors. Therefore, in such cases, by stopping power transmission or controlling the power transmission to reduce the power level as described above, it is possible to suppress the occurrence of malfunctions due to power transmission.

[0100] Furthermore, there is a possibility that foreign object detection may fail when foreign object detection is performed using the Power Loss method or the waveform attenuation method described above. For example, if the power receiving device 401 mounted on the power transmitting device 402 moves during the foreign object detection process, the measurement values ​​used for foreign object detection may become abnormal, causing foreign object detection to fail. In this case as well, since the conditions may not be suitable for wireless power transmission, the power transmitting device 402 and the power receiving device 401 may stop power transmission or reduce the power of the power transmission. This can suppress the occurrence of malfunctions due to power transmission.

[0101] [Foreign object detection processing in response to power drop] The above explanation using Figures 8 and 9 described the process 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. Next, we will explain the process when the power receiving device 401 performs foreign object detection in response to a decrease in received power.

[0102] If foreign matter is present near the power transmission device 402 and the power receiving device 401, this foreign matter may interfere with wireless power transmission between the power transmission device 402 and the power receiving device 401, potentially causing a decrease in the power received by the power receiving device 401. Therefore, if a decrease in the power received by the power receiving device 401 occurs, it is possible that foreign matter is present near the power transmission device 402 and the power receiving device 401, and the power transmission device 402 and the power receiving device 401 will perform control to detect the foreign matter.

[0103] The following describes the operation of the power transmission device 402 and the power receiving device 401 when foreign object detection is performed in response to the power transmission device 402 detecting a decrease in the power received by the power receiving device 401. The power transmission device 402 periodically receives the power received value Pr3' from the power receiving device 401 in order to perform foreign object detection using the Power Loss method during the Power Transfer phase. The power transmission device 402 then determines whether the power received by the power receiving device 401 has decreased based on the power received value Pr3' received from the power receiving device 401, or Ploss_FO, which is the difference between Pr3 and Pr3' that has been determined in advance. If the power received value Pr3' received from the power receiving device 401 falls below a certain threshold, or if Ploss_FO exceeds a certain threshold, the power transmission device 402 determines that the power received by the power receiving device 401 has decreased and performs foreign object detection using the waveform attenuation method.

[0104] In other words, the power transmission device 402 periodically detects foreign objects using the Power Loss method, which maintains high power transmission efficiency, and then performs foreign object detection using the waveform attenuation method, which has higher accuracy, in accordance with the power received from the power receiving device 401 for foreign object detection. For example, the power transmission device 402 may set a first threshold for determining whether there is a possibility of foreign object presence and a second threshold for determining whether foreign object presence exists, based on the value of Pr3' or Ploss_FO. When Pr3' or Ploss_FO exceeds the second threshold, the power transmission device 402 determines that foreign object has been detected by the Power Loss method and controls the power transmission to stop or reduce the power transmission. If Pr3' or Ploss_FO exceeds the first threshold but not the second threshold, the power transmission device 402 performs foreign object detection using the waveform attenuation method. This makes it possible to detect foreign objects even if they cannot be detected by the Power Loss method, by performing the waveform attenuation method with higher accuracy in accordance with the decrease in power received. The thresholds mentioned above may be set based on the data obtained from the Calibration process of the Power Loss method (straight line 1002 in Figure 10).

[0105] Furthermore, while the above explanation states that the power transmission device 402 performs foreign object detection in response to a decrease in the power received by the power receiving device 401, the power transmission device 402 may also perform foreign object detection in response to a change in the power transmitted by the power transmission device 402. The power transmission device 402 is capable of measuring the power transmitted value it is transmitting. Therefore, the power transmission device 402 may determine that there is a possibility of foreign object presence when the difference between this transmitted power value and a predetermined reference value is large compared to a certain threshold, and perform foreign object detection using the waveform attenuation method. This configuration also provides the same effect as when foreign object detection is performed in response to a decrease in power received.

[0106] Next, we will describe the operation of the power transmission unit 402 and the power receiving unit 401 when foreign object detection is performed in response to the power receiving unit 401 detecting a decrease in the power received by the power receiving unit 401. The power receiving unit 401 periodically measures the power it receives from the power transmission unit 402 during the Power Transfer phase. Based on the power received value measured periodically, the power receiving unit 401 determines whether or not the power received by the power receiving unit 401 has decreased. If the calculated power received value falls below a certain threshold, or if the difference between the calculated power received value and the reference value exceeds a certain threshold, the power receiving unit 401 determines that the power received by the power receiving unit 401 has decreased and requests the power transmission unit 402 to perform foreign object detection using the waveform attenuation method.

[0107] In other words, the power receiving device 401 periodically measures the received power value and, depending on the measurement result, requests the power transmitting device 402 to perform foreign object detection using the waveform attenuation method, which has high accuracy in detecting foreign objects. For example, if the difference between the measured received power and the reference value is below a predetermined threshold, the power receiving device 401 may send a command to execute foreign object detection using the Power Loss method. On the other hand, if the difference between the measured received power and the reference value exceeds a predetermined threshold, the power receiving device 401 may send a command to execute foreign object detection using the waveform attenuation method. With this configuration, if there is a high probability of foreign objects being present (when the received power is low), foreign objects can be detected using the highly accurate waveform attenuation method, and if not, foreign object detection can be performed using the Power Loss method while maintaining high power transmission efficiency.

[0108] Furthermore, if the decrease in the received power value exceeds a threshold, the receiving device 401 may determine that a foreign object is present and request the transmission device 402 to stop power transmission or reduce the transmitted power. The receiving device 401 may also set a first threshold for determining that there is a possibility of a foreign object being present in response to a decrease in the received power value, and a second threshold for determining that a foreign object is present. If the decrease in the received power value exceeds the first threshold but not the second threshold, the receiving device 401 requests the transmission device 402 to perform foreign object detection using the waveform attenuation method. If the decrease in the received power value exceeds the second threshold, the receiving device 401 may send an EPT command to the transmission device 402 to request the transmission device 402 to stop power transmission. Alternatively, it may send a command to the transmission device 402 requesting it to reduce the transmitted power.

[0109] As described above, the power transmission device 402 and the power receiving device 401 are controlled to perform foreign object detection using the waveform attenuation method when a decrease in power received by the power receiving device 401 is detected. This makes it possible to detect foreign objects early when there is a possibility that foreign objects are present in the vicinity of the power transmission device 402 and the power receiving device 401.

[0110] [Foreign object detection process based on calibration data] Next, we will describe the process for detecting foreign objects based on data obtained from the calibration process using the power loss method or the waveform attenuation method.

[0111] As described above, in foreign object detection using the Power Loss method and foreign object detection using the waveform attenuation method, a calibration process is performed to set a threshold value that will be used as a reference for determining the presence or absence of foreign objects. The reference data obtained from these calibration processes is expected to show the relationship between the transmitted power value and the received power value, or the relationship between the transmitted power value and the waveform attenuation rate, when there are no foreign objects. Therefore, if the reference data obtained from the calibration process does not show the predetermined relationship expected between the transmitted power value and the received power value, or between the transmitted power value and the waveform attenuation rate, there is a possibility that foreign objects are present near the power transmission device 402 and the power receiving device 401. For this reason, the power transmission device 402 and the power receiving device 401 perform control to execute foreign object detection.

[0112] First, we will describe the operation of the power transmission device 402 and the power receiving device 401 when foreign object detection is performed according to the data obtained from the calibration process of the Power Loss method. The power transmission device 402 and the power receiving device 401 perform a Power Loss Calibration process, which is a process for determining the threshold used in the Power Loss method. The data obtained from this Power Loss Calibration process should represent the relationship between transmitted power and received power in the absence of foreign matter, and it is possible to anticipate in advance the range of possible received power values ​​depending on the transmitted power value. Therefore, when the power transmission device 402 obtains data from the Power Loss Calibration process, it determines whether the received power value included in that data is within a predetermined range according to the transmitted power value. If it is outside the range, there is a possibility that foreign matter is present near the power transmission device 402 and the power receiving device 401, so the power transmission device 402 performs foreign matter detection using the waveform attenuation method. If foreign matter is determined to be present by the waveform attenuation method, the power transmission device 402 stops power transmission or controls the transmission power to reduce it. On the other hand, if the waveform attenuation method determines that no foreign matter is present, the power transmission device 402 performs the Calibration process of the Power Loss method again and updates the data.

[0113] In other words, the power transmission device 402 performs foreign object detection using a waveform attenuation method different from the Power Loss method, depending on the values ​​of the data obtained by the Calibration process of the Power Loss method. With this configuration, if the Calibration process of the Power Loss method determines that there is a possibility of foreign objects being present, foreign object detection using the waveform attenuation method can be performed to detect foreign objects at an early stage. Furthermore, if the accuracy of foreign object detection using the Power Loss method decreases due to inaccurate calibration data, foreign objects can be detected with high accuracy using the waveform attenuation method. Note that the decision to detect foreign objects based on the data obtained from the Calibration process may be made by the power receiving device 401.

[0114] Next, we will describe the operation of the power transmission device 402 and the power receiving device 401 when foreign object detection is performed according to the data obtained from the waveform attenuation method calibration process. The power transmission device 402 and the power receiving device 401 perform the waveform attenuation method calibration process, which is a process for determining the threshold used in the waveform attenuation method. The reference data obtained from this waveform attenuation method calibration process should represent the relationship between the transmitted power and the waveform attenuation rate in the absence of foreign objects, and it is possible to anticipate the range of data that can take place in advance. Therefore, the power transmission device 402 determines whether the waveform attenuation rate indicated by the reference data obtained from the waveform attenuation method calibration process is within a predetermined range. If the waveform attenuation rate is not within the predetermined range, there is a possibility that foreign objects exist near the power transmission device 402 and the power receiving device 401, so the power transmission device 402 performs foreign object detection using the Power Loss method. More specifically, the power transmission device 402 sends a command to the power receiving device 401 to notify it that it will perform the Power Loss method. Upon receiving the command, the power receiving device 401 sends a command to the power transmitting device 402 to execute foreign object detection using the Power Loss method, which includes the power received value measured by the power receiving device 401. When the power transmitting device 402 receives the command from the power receiving device 401, it executes foreign object detection using the Power Loss method.

[0115] If the Power Loss method determines that a foreign object is present, the power transmission device 402 stops power transmission or controls the transmission power to decrease. If the Power Loss method determines that there is no foreign object, the power transmission device 402 performs the waveform attenuation method calibration process again and updates the data. In this way, the power transmission device 402 performs foreign object detection using the Power Loss method, which is different from the waveform attenuation method, according to the value of the data obtained by the waveform attenuation method calibration process. With this configuration, if the waveform attenuation method calibration process determines that there is a possibility of a foreign object being present, it is possible to detect the foreign object early by performing foreign object detection using the Power Loss method. Note that the decision to detect a foreign object based on the data obtained by the calibration process may be made by the power receiving device 401.

[0116] [Foreign object detection process based on temperature rise] This section describes the process when foreign object detection is performed in response to the detection of a temperature rise in the power transmission device 402 or the power receiving device 401. Possible causes of the temperature rise in the power transmission device 402 or the power receiving device 401 include heat generated from electrical circuits, including antennas, and heat generated from the CPU due to various processing tasks. Furthermore, if a foreign object is present near the power transmission device 402 or the power receiving device 401, the foreign object will consume some of the energy of the transmitted power, causing it to generate heat, which in turn may cause the temperature of the power transmission device 402 or the power receiving device 401 in contact with the foreign object to rise. Therefore, if the temperature of the power transmission device 402 or the power receiving device 401 rises above a predetermined threshold, it is determined that a foreign object may be present near the power transmission device 402 or the power receiving device 401, and control is performed to enable foreign object detection in the power transmission device 402 and the power receiving device 401.

[0117] First, we will describe the operation of the power transmission device 402 and the power receiving device 401 when the power transmission device 402 detects a temperature rise. The power transmission device 402 has a temperature sensor, and when the temperature sensor detects that the temperature of the power transmission device 402 exceeds a predetermined threshold, the power transmission device 402 performs foreign object detection using the waveform attenuation method. If it is determined that a foreign object is present, the power transmission device 402 stops power transmission or controls the power transmission to reduce the power output.

[0118] The reason for using the waveform attenuation method instead of the power loss method for foreign object detection is as follows: In the power loss method, the power transmission device 402 needs to receive the power received value from the power receiving device 401, but in the waveform attenuation method, the power transmission device 402 does not need information from the power receiving device 401, so foreign object detection can be performed in a short time. Also, the waveform attenuation method can detect foreign objects with higher accuracy than the power loss method. In other words, when the temperature is high and there is a possibility of foreign objects being present, the power transmission device 402 can detect foreign objects early and with high accuracy using the waveform attenuation method. However, foreign object detection may also be performed using the power loss method. In this case, the power transmission device 402 will notify the power receiving device 401 that it will perform foreign object detection using the power loss method. Upon receiving this notification, the power receiving device 401 will send a command to the power transmission device 402 to execute foreign object detection using the power loss method, including the power received value measured by the power receiving device 401.

[0119] Next, we will describe the operation of the power transmission unit 402 and the power receiving unit 401 when the power receiving unit 401 detects a temperature rise. The power receiving unit 401 has a temperature sensor, and when the temperature sensor detects that the temperature of the power receiving unit 401 exceeds a predetermined threshold, the power receiving unit 401 sends a command to the power transmission unit 402 to execute foreign object detection using the waveform attenuation method. The power transmission unit 402 then performs foreign object detection using the waveform attenuation method, and if it determines that a foreign object is present, it stops power transmission or controls the power transmission to reduce the power output. Alternatively, foreign object detection may be performed using the power loss method instead of the waveform attenuation method. In this case, the power receiving unit 401 sends a command to the power transmission unit 402 to execute foreign object detection using the power loss method in response to the temperature information detected by the temperature sensor.

[0120] Furthermore, regarding the permissible temperature for power transmission or reception equipment, there may be prescribed values ​​stipulated by standards and national laws. Therefore, by setting the threshold for determining whether to perform the above-mentioned foreign object detection lower than these prescribed values, it becomes possible to detect foreign objects early, even if a temperature rise occurs due to foreign objects, before the temperature reaches the prescribed value.

[0121] [Foreign object detection processing based on power transmission level] Next, we will describe the process when foreign object detection is performed using a method selected according to the power transmitted from the power transmission device 402. As mentioned 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 receiving 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, it has the advantage that foreign object detection can be performed while power transmission continues, thus maintaining high power transmission efficiency. The waveform attenuation method, on the other hand, performs foreign object detection by observing the attenuation rate of the transmitted wave when the power transmission device 402 temporarily stops transmitting power, and has the disadvantage that power transmission efficiency decreases when power transmission is temporarily stopped. On the other hand, it has the advantage that foreign object detection can be performed with high accuracy even when a large amount of power is being transmitted.

[0122] Therefore, the power transmission device 402 and the power receiving device 401 are controlled to perform only foreign object detection using the Power Loss method when the power transmission value from the power transmission device 402 is below a predetermined threshold. This is because, when the power transmission value is low, the Power Loss method also has high accuracy in detecting foreign objects, making it advantageous for maintaining high power transmission efficiency. On the other hand, when the power transmission value from the power transmission device 402 is above a predetermined threshold, the power transmission device 402 and the power receiving device 401 are controlled to perform foreign object detection using both the Power Loss method and the waveform attenuation method, or to perform foreign object detection using only the waveform attenuation method. This is because, when the power transmission value is high, the accuracy of foreign object detection using the Power Loss method decreases, making it effective to use the waveform attenuation method, which has high accuracy in detecting foreign objects. In this way, by using multiple foreign object detection methods according to the power transmission value, it is possible to improve foreign object detection accuracy while maintaining high power transmission efficiency.

[0123] In the descriptions of the foreign object detection process in response to communication errors, foreign object detection process in response to power drops, foreign object detection process in response to calibration data, and foreign object detection process in response to temperature information, the focus was on cases where both the Power Loss method and the waveform attenuation method are used. However, when the transmitted power is lower than a predetermined threshold, foreign object detection may be performed using the Power Loss method at the same timing as when foreign object detection is performed using the waveform attenuation method in these embodiments. Furthermore, when the transmitted power is above a predetermined threshold, both the Power Loss method and the waveform attenuation method may be used, or foreign object detection may be performed using the waveform attenuation method at the same timing as when foreign object detection is performed using the Power Loss method in the embodiments described above.

[0124] In this embodiment, the description mainly focused on a case where the wireless power transmission system determines whether predetermined conditions relating to the state of at least one of the power transmission device 402 and the power receiving device 401 are met, and uses either the Power Loss method or the waveform attenuation method depending on the determination result. However, it is not limited to this, and at least one of the power transmission device 402 and the power receiving device 401 may use multiple foreign object detection methods, including foreign object detection methods other than those described above, depending on the conditions. Furthermore, the wireless power transmission system may combine multiple conditions, including the various conditions described above and other conditions, to select a foreign object detection method and control the foreign object detection process.

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

[0126] 401 Power receiving device 402 Power transmission equipment

Claims

1. A transmission means for transmitting Analog Ping, An acquisition means that obtains a first quality coefficient from the first attenuation envelope of the voltage after transmitting an Analog Ping, and obtains a second quality coefficient from the second attenuation envelope of the voltage after obtaining the first quality coefficient, A determination means for determining the presence or absence of foreign matter based on the result of comparing the first quality coefficient and the second quality coefficient, A power transmission means for wirelessly transmitting power to a power receiving device, Negotiation means for negotiating with the power receiving device in the Negotiation phase, It has, The acquisition means measures the voltage during the period when power transmission is restricted after acquiring the first quality coefficient and after the Negotiation phase has ended, and acquires the second quality coefficient from the second decay envelope of the voltage. Furthermore, a power transmission device having a receiving means for receiving identifier information from the power receiving device.

2. The power transmission device according to Claim 1, wherein the power transmission means restricts power transmission when the determination means determines that the foreign matter is present.

3. The power transmission device according to claim 1, wherein the power transmission means restricts the power transmission for the purpose of measurement.

4. A method performed by a power transmission device, The transmission process for sending Analog Ping, A first acquisition step involves obtaining a first quality factor from the first attenuation envelope of the voltage after transmitting an Analog Ping, A second acquisition step is to acquire a second quality factor from a second voltage decay envelope after obtaining the first quality factor, A determination step of determining the presence or absence of foreign matter based on a comparison of the first quality factor and the second quality factor, A power transmission process that wirelessly transmits power to a power receiving device, The negotiation phase includes a negotiation process in which negotiations are conducted with the power receiving device, Includes, The second acquisition step is to measure the voltage during the period when power transmission is restricted after obtaining the first quality coefficient and after the Negotiation phase has ended, and to obtain the second quality coefficient from the second attenuation envelope of the said voltage. A method further comprising a receiving step of receiving identifier information from the power receiving device.

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