Power transmission device, method, and program

Abstract

To appropriately detect an object different from a power-transmitting device and a power-receiving device.SOLUTION: When a command for giving a notice of the end of a Negotiation phase before exchange of the command required for executing foreign matter detection by a waveform attenuation method in the Negotiation phase is completed, it is made possible to transmit a message of requesting an inquiry, to continue communication in such a manner that a message of a transmission request of a command that is insufficient as response of an inquiry command thereof is transmitted, and to complete the exchange of the command required for executing the foreign matter detection by the waveform attenuation method.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power transmission device, a control method for a power transmission device, and a program. [Background technology]

[0002] In recent years, there has been widespread technological development in wireless power transmission systems. In wireless power transmission systems, it is crucial to detect foreign objects (hereinafter referred to as "foreign objects") that are not present in the range within which the power transmission device can transmit power, and to control power transmission and reception accordingly. Patent Document 1 discloses a method for detecting foreign objects and restricting power transmission and reception when they are present near power transmission and reception devices compliant with the WPC (Wireless Power Consortium) standard.

[0003] Furthermore, as another method for detecting foreign objects, Patent Document 2 discloses a method for detecting the presence of an object based on changes in energy attenuation or resonant frequency of a power transmission coil and a resonant circuit integrated with or coupled to the power transmission coil. In this method, the power transmission device transmits a signal for detecting foreign objects to the power receiving device, and the presence or absence of a foreign object is determined using the echo signal from the power receiving device. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-70074 [Patent Document 2] Japanese Patent Publication No. 2015-27172 [Overview of the project] [Problems that the invention aims to solve]

[0005] When detecting foreign objects using changes in energy waveform attenuation, as disclosed in Patent Document 2, it is required that the waveform attenuation does not cause problems in both the power transmission and receiving equipment. Considering this, when implementing this method of foreign object detection in the WPC standard, it is conceivable that the power transmission and receiving equipment exchange information regarding their ability to handle the attenuation period during the Negotiation phase. However, even a power receiving equipment compliant with the WPC standard may request the termination of the Negotiation phase before all the necessary information exchange for executing this method of foreign object detection is complete. If the Negotiation phase is terminated while information exchange is interrupted, a request for foreign object detection may be made even if detection is impossible, or a request for foreign object detection may not be made even if detection is possible, resulting in malfunctions.

[0006] In light of the aforementioned problems, this disclosure aims to appropriately detect objects other than power receiving equipment and power transmitting equipment. [Means for solving the problem]

[0007] The power transmission device according to this disclosure is a power transmission device that wirelessly transmits power to a power receiving device, and is characterized by comprising: detection means for detecting whether or not an object other than the power transmission device and the power receiving device exists; communication means for exchanging information with the power receiving device for performing the detection by the detection means; and request means for making a request to the power receiving device to continue the exchange of information if the power receiving device requests the termination of the exchange of information before the exchange of information necessary for performing the detection by the detection means is completed. [Effects of the Invention]

[0008] According to this disclosure, it is possible to appropriately detect objects other than power receiving devices and power transmitting devices. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing an example of the internal configuration of a power transmission device according to an embodiment. [Figure 2] It is a block diagram showing an example of the internal configuration of the power receiving device according to the embodiment. [Figure 3] It is a block diagram showing an example of the functional configuration in the control unit of the power transmission device. [Figure 4] It is a diagram showing an example of the configuration of the wireless power transmission system in the embodiment. [Figure 5] It is a diagram for explaining a sequence for power transmission according to the WPC standard. [Figure 6] It is a diagram for explaining the principle of foreign object detection by the waveform attenuation method. [Figure 7] It is a diagram for explaining each period when performing foreign object detection by the waveform attenuation method. [Figure 8] It is a diagram for explaining a foreign object detection method by the power loss method. [Figure 9] It is a diagram for explaining the waveform attenuation rate according to the transmitted power. [Figure 10] It is a flowchart showing an example of a basic processing procedure performed by the power receiving device for performing foreign object detection by the waveform attenuation method. [Figure 11] It is a flowchart showing an example of a basic processing procedure performed by the power transmission device for performing foreign object detection by the waveform attenuation method. [Figure 12] In the embodiment, it is a flowchart showing an example of an exceptional processing procedure performed by the power receiving device in the Negotiation phase. [Figure 13] In the embodiment, it is a flowchart showing an example of the processing procedure of the power transmission device in the Negotiation phase. [Figure 14] In the embodiment, it is a flowchart showing another example of an exceptional processing procedure performed by the power receiving device in the Negotiation phase.

Embodiments for Carrying Out the Invention

[0010] 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.

[0011] [Configuration of a Wireless Power Transmission System] Figure 4 shows an example configuration of the wireless power transmission system (wireless charging system) 400 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.

[0012] The power receiving device 401 is an electronic device that receives power from the power transmitting device 402 and charges its built-in battery. The power transmitting device 402 is an electronic device that wirelessly transmits power to the power receiving device 401, which is placed on the charging base 403. Hereinafter, being placed on the charging base 403 will be simply referred to as being placed on the power transmitting device 402. The area 404 enclosed by the dotted line is the range in which the power receiving device 401 can receive power from the power transmitting device 402. Note that the power receiving device 401 and the power transmitting device 402 have functions to perform applications other than wireless charging. Furthermore, in the following description, any object different from the power transmitting device 402 and the power receiving device 401 that is included in the power transmission range of the power transmitting device 402 will be referred to as a foreign object.

[0013] In the following explanation, "the power receiving device 401 is placed on the power transmitting device 402" means "the power receiving device 401 is included in the power transmission range of the power transmitting device 402." The power transmission range of the power transmitting device 402 is the range in which power can be transmitted to the power receiving device 401 using the power transmission coil. Furthermore, the state in which the power receiving device 401 is placed on the power transmitting device 402 does not necessarily mean that the power receiving device 401 and the power transmitting device 402 are in contact. For example, the state in which the power receiving device 401 is included in the power transmission range of the power transmitting device 402 without being in contact with it will also be considered as "the power receiving device 401 is placed on the power transmitting device 402." In addition, the power receiving device 401 may be configured to be placed on the side of the power transmitting device 402, for example, instead of being placed on top of the power transmitting device 402.

[0014] The power receiving device 401 and the power transmitting device 402 may have functions to perform applications other than wireless charging. An example of the power receiving device 401 is an information processing terminal such as a smartphone, and an example of the power transmitting device 402 is an accessory device for charging that information processing terminal. For example, the information terminal device has a display unit that displays information to the user, and is supplied with power received from a power receiving coil (antenna). The power received from the power receiving coil is stored in a power storage unit (battery), and power is supplied to the display unit from the battery. In this case, the power receiving device 401 may have a communication unit that communicates with other devices different from the power transmitting device 402. The communication unit may support communication standards such as NFC communication or fifth-generation mobile communication systems (5G). In this case, the communication unit may perform communication by being powered from the battery. Furthermore, the power receiving device 401 may be a tablet terminal, a storage device such as a hard disk drive and memory device, or an information processing device such as a personal computer (PC). Furthermore, the power receiving device 401 may be, for example, an imaging device (such as a camera or video camera). The power receiving device 401 may also be an image input device such as a scanner, or an image output device such as a printer, copier, or projector. The power receiving device 401 may also be a robot, medical equipment, etc. The power transmitting device 402 may be a device for charging the aforementioned equipment.

[0015] Furthermore, the power transmission device 402 may be a smartphone. In this case, the power receiving device 401 may be another smartphone or wireless earphones.

[0016] Furthermore, the power receiving device 401 in this embodiment may be a vehicle such as an automobile. For example, the automobile, which is the power receiving device 401, may receive power from a charger (power transmission device 402) via a power transmission antenna installed in a parking lot. Alternatively, the automobile, which is the power receiving device 401, may receive power from a charger (power transmission device 402) via a power transmission coil (antenna) embedded in the road. In such an automobile, the received power is supplied to a battery. The power from the battery may be supplied to a drive unit (motor, electric unit) that drives the wheels, or it may be used to drive sensors used for driving assistance or a communication unit that communicates with external devices. In other words, in this case, the power receiving device 401 may have a battery, motors and sensors that are driven using the received power, and a communication unit that communicates with devices other than the power transmission device 402, in addition to the wheels. Furthermore, the power receiving device 401 may have a dwelling for accommodating people. For example, sensors may be used to measure the distance between vehicles or the distance to other obstacles. The communication unit may, for example, be compatible with the Global Positioning System (Global Positioning Satellite, GPS). The communication unit may also be compatible with communication standards such as 5G. The vehicle may be a bicycle or a motorcycle. Furthermore, the power receiving device 401 is not limited to a vehicle, but may be a mobile or flying object having an activation unit that uses power stored in a battery for propulsion.

[0017] Furthermore, the power receiving device 401 in this embodiment may be a power tool, a home appliance, or the like. These devices, which are the power receiving device 401, may have a battery, as well as a motor driven by the power received from the battery. These devices may also have a notification means for notifying the remaining battery level, etc. These devices may also have a communication unit that communicates with other devices different from the power transmitting device 402. The communication unit may support communication standards such as NFC or fifth-generation mobile communication systems (5G).

[0018] Furthermore, the power transmission device 402 in this embodiment may be an in-vehicle charger that supplies power to portable information terminal devices such as smartphones and tablets that support wireless power transmission within the vehicle. Such an in-vehicle charger may be installed anywhere in the vehicle. For example, the in-vehicle charger may be installed on the vehicle's console, on the instrument panel (dashboard), between passenger seats, on the ceiling, or on the doors. However, it is preferable not to install it in a location that would interfere with driving. In addition, although the power transmission device 402 has been described using the example of an in-vehicle charger, such chargers are not limited to those installed in vehicles, but may also be installed in transport vehicles such as trains, aircraft, and ships. In this case, the charger may also be installed between passenger seats, on the ceiling, or on the doors.

[0019] Alternatively, the power transmission device 402 may be a vehicle such as an automobile equipped with an on-board charger. In this case, the power transmission device 402 has wheels and a battery, and uses the power from the battery to supply power to the power receiving device 401 via a power transmission circuit and a power transmission coil (antenna).

[0020] [Configuration of power transmission device 402 and power receiving device 401] Next, the configurations of the power transmission device 402 and the power receiving device 401 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 is assumed to be implemented as a software program, but some or all of the components included in this functional block may be implemented in hardware.

[0021] Figure 1 is a block diagram showing an example of the internal configuration of a power transmission device 402 according to this embodiment. Figure 2 is a block diagram showing an example of the internal configuration of a power receiving device 401 according to this embodiment. The power transmission device 402 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.

[0022] The control unit 101 controls the entire power transmission device 402 by executing a control program stored in, for example, memory 106. The control unit 101 also performs control related to power transmission control, including communication for equipment authentication in the power transmission device 402. 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 MPU (Micro Processor 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 also measures time using a timer (not shown).

[0023] 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.

[0024] The power transmission unit 103 converts the DC or AC power input from the power supply unit 102 into AC frequency power in the frequency band used for wireless power transmission, and outputs this AC frequency power to the power transmission antenna 105, thereby generating electromagnetic waves for the power receiving device 401 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.

[0025] Furthermore, 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, output 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. In addition, the power transmission unit 103 controls the output of AC frequency 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, which complies with the WPC (Wireless Power Consortium) standard.

[0026] The communication unit 104 communicates with the power receiving device 401 for power transmission control based on the WPC standard. The communication unit 104 modulates the electromagnetic waves output from the power transmitting antenna 105 by frequency shift modulation and transmits information to the power receiving device 401 to perform communication. The communication unit 104 also demodulates the electromagnetic waves transmitted from the power transmitting antenna 105, which have been amplitude modulated or load modulated by the power receiving device 401, to obtain the information transmitted by the power receiving device 401. 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 transmitting antenna 105. The communication unit 104 may also communicate with the power receiving device 401 using a communication standard different from the WPC standard using an antenna different from the power transmitting antenna 105, or it may selectively use multiple communication methods to communicate with the power receiving device 401. Examples of such communication standards include BLE (Bluetooth® Low Energy) and NFC (Near Field Communication).

[0027] In addition to storing the control program, the memory 106 also stores the status of the power transmission device 402 and the power receiving device 401 (transmission power value, power receiving power value, etc.). For example, the status of the power transmission device 402 is acquired by the control unit 101, and the status of the power receiving device 401 is acquired by the control unit 201 of the power receiving device 401 and received via the communication unit 104.

[0028] 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.

[0029] Next, an example of the internal configuration of the power receiving device 401 according to this embodiment will be described with reference to Figure 2. The power receiving device 401 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.

[0030] The control unit 201 controls the entire power receiving device 401 by executing a control program stored, for example, in the memory 208. That is, the control unit 201 controls each of the functional units shown in Figure 2. Furthermore, the control unit 201 may also 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 entire power receiving device 401 may be controlled in cooperation with the OS (Operating System) that the control unit 201 is running.

[0031] 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).

[0032] The UI unit 202 provides various outputs to the user. These outputs include screen displays, flashing and color changes of LEDs (Light Emitting Diodes), audio output from the speaker, and vibration of the power receiving device 401. The UI unit 202 is implemented using an LCD panel, speaker, vibration motor, etc.

[0033] The power receiving unit 203 acquires AC power (AC voltage and AC current) generated by electromagnetic induction based on electromagnetic waves radiated from the power transmitting antenna 105 of the power transmitting device 402 via the power receiving antenna 205. The power receiving unit 203 then 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 the power receiving device 401. The power receiving unit 203 is assumed to have the capacity to supply enough power to the charging unit 206 to charge the battery 207 and to output 15 watts of power to the charging unit 206.

[0034] The communication unit 204 communicates with the communication unit 104 of the power transmission device 402 for power receiving control based on the WPC standard described above. The communication unit 204 demodulates the electromagnetic waves input from the power receiving antenna 205 and obtains information transmitted from the power transmission device 402. Then, the communication unit 204 communicates with the power transmission device 402 by superimposing a signal related to the information to be transmitted to the power transmission device 402 onto the electromagnetic waves by amplitude modulation or load modulation. The communication unit 204 may also communicate with the power transmission device 402 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 power transmission device 402. Examples of such communication standards include BLE and NFC as mentioned above.

[0035] In addition to storing the control program, the memory 208 also stores information relating to the status of the power transmission device 402 and the power receiving device 401. For example, the status of the power receiving device 401 is acquired by the control unit 201, and information relating to the status of the power transmission device 402 is acquired by the control unit 101 of the power transmission device 402 and received via the communication unit 204.

[0036] The first switch section 209 and the second switch section 210 are controlled by the control unit 201. The receiving antenna 205 is connected to the resonant capacitor 211. When the second switch section 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 section 210, but no current flows through the receiving section. When the second switch section 210 is turned OFF and opened, the power received by the receiving antenna 205 and the resonant capacitor 211 is supplied to the receiving section 203.

[0037] 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.

[0038] Next, with reference to Figure 3, the functions of the control unit 101 of the power transmission device 402 will be described. Figure 3 is a block diagram showing an example of the functional configuration of the control unit 101 of the power transmission device 402. 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.

[0039] The communication control unit 301 performs control communication with the power receiving device 401 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 power receiving device 401. The measurement unit 303 measures the waveform attenuation index, which will be described later. It also measures the power transmitted to the power receiving device 401 via the power transmission unit 103 and measures the average transmitted power per unit time. The measurement unit 303 also measures the quality coefficient (Q value) of the power transmission antenna (power transmission coil) 105.

[0040] The foreign object detection unit 305 implements foreign object detection using the power loss method, foreign object detection using the Q value measurement method, and foreign object detection utilizing changes in the attenuation of the energy waveform (hereinafter referred to as foreign object detection using the waveform attenuation method). Details of the power loss method, Q value measurement method, and waveform attenuation method will be described later. In addition, the foreign object detection unit 305 may have functions for performing foreign object detection processing using other methods. For example, in a power transmission device 402 equipped with NFC 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 power transmission device 402. For example, the power transmission device 402 can also detect increases or decreases in the number of power receiving devices 401 on the power transmission device 402.

[0041] The setting unit 304 sets thresholds that serve as criteria for determining the presence or absence of foreign objects when the power transmission device 402 performs foreign object detection using the power loss method, Q-value measurement method, or waveform attenuation method. For example, the setting unit 304 sets thresholds used for foreign object detection based on the waveform attenuation index measured by the measurement unit 303. The setting unit 304 may also have a function to set 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. As a result, the foreign object detection unit 305 can perform foreign object detection processing based on the thresholds set by the setting unit 304 and the waveform attenuation index, power transmission power, and Q-value measured by the measurement unit 303.

[0042] 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.

[0043] In this system, wireless power transmission is performed using an electromagnetic induction method for wireless charging, based on the WPC standard. Specifically, the power receiving device 401 and the power transmitting device 402 perform wireless power transmission for wireless charging based on the WPC standard between the power receiving antenna 205 of the power receiving device 401 and the power transmitting antenna 105 of the power transmitting device 402. The wireless power transmission method applied to this system is not limited to the method specified in the WPC standard, but may also be other methods such as electromagnetic induction, magnetic field resonance, electric field resonance, microwave, or laser. Furthermore, in this embodiment, wireless power transmission is used for wireless charging, but wireless power transmission may also be used for purposes other than wireless charging.

[0044] The WPC standard specifies that the amount of power guaranteed when the receiving device 401 receives power from the transmitting device 402 is defined by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates the power value at which the output to the load of the receiving device 401 (e.g., charging circuit, battery, etc.) is guaranteed, even if the relative positions of the receiving device 401 and the transmitting device 402 change and the power transmission efficiency between the receiving antenna 205 and the transmitting antenna 105 decreases. For example, if the GP is 5 watts, even if the relative positions of the receiving antenna 205 and the transmitting antenna 105 change and the power transmission efficiency decreases, the transmitting device 402 will be controlled to output 5 watts of power to the load inside the receiving device 401 and will continue to transmit power.

[0045] Furthermore, when transmitting power from the power transmission device 402 to the power receiving device 401, if a foreign object other than the power receiving device 401 is present near the power transmission device 402, the electromagnetic waves used for power transmission may affect the foreign object, potentially raising its temperature or destroying it. Therefore, the WPC standard specifies a method for the power transmission device 402 to detect the presence of a foreign object on the charging base 403, so as to prevent the foreign object from overheating or being destroyed by stopping power transmission if a foreign object is present. Specifically, the WPC standard specifies a power loss method that detects foreign objects based on the difference between the power transmitted by the power transmission device 402 and the power received by the power receiving device 401. The WPC standard also specifies a Q-value measurement method as a foreign object detection method, which detects foreign objects by changing the quality coefficient (Q-value) of the power transmission antenna (power transmission coil) 105 in the power transmission device 402. It should be noted that the foreign objects detected by the power transmission device 402 in this embodiment are not limited to objects present on the charging base 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 detect foreign objects located within the range in which the power transmission device 402 can transmit power.

[0046] [Foreign object detection method based on the power loss method] Next, we will explain the foreign object detection method based on the power loss method specified in the WPC standard, using Figure 8. In Figure 8, the horizontal axis represents the power transmitted by the power transmission device 402, and the vertical axis represents the power received by the power receiving device 401. Here, a foreign object is an object other than the power receiving device 401 that may affect the transmission of power from the power transmission device 402 to the power receiving device 401, such as a conductive metal piece.

[0047] First, the power transmission device 402 transmits power to the power receiving device 401 at a first transmission power value Pt1. The power receiving device 401 receives power at a first reception power value Pr1 (this state is called the Light Load state). Then, the power transmission device 402 stores the first transmission power value Pt1. Here, the first transmission power value Pt1 or the first reception power value Pr1 is a predetermined minimum transmission power or reception power. At this time, the power receiving device 401 controls the load (charging circuit, battery, etc.) so that the power received is the minimum power. For example, the power receiving device 401 may disconnect the load from the power receiving antenna 205 so that the received power is not supplied to the load.

[0048] Next, the power receiving device 401 reports the first power received value Pr1 to the power transmitting device 402. Upon receiving the information of the first power received value Pr1 from the power receiving device 401, the power transmitting device 402 calculates the power loss Pt1-Pr1(P between the power transmitting device 402 and the power receiving device 401. loss1 The following is calculated: Then, calibration point 800 is created that shows the correspondence between the first transmission power value Pt1 and the first reception power value Pr1.

[0049] 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). The power transmission device 402 then 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.

[0050] Next, the power receiving device 401 reports the second power received value Pr2 to the power transmitting device 402. Upon receiving the information of the second power received value Pr2 from the power receiving device 401, the power transmitting device 402 calculates the power loss Pt2-Pr2(P) between the power transmitting device 402 and the power receiving device 401. loss2 The following is calculated: Then, a calibration point 801 is created that shows the correspondence between the second transmission power value Pt2 and the second reception power value Pr2.

[0051] The power transmission device 402 then creates a straight line 802 by linearly interpolating between calibration point 800 and calibration point 801. The straight line 802 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 802, 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 803 on the straight line 802 corresponding to Pt3.

[0052] As described above, based on a plurality of combinations of the power transmission power value of the power transmission device 402 and the power reception power value of the power reception device 401 measured while changing the load, the power loss between the power transmission device 402 and the power reception device 401 corresponding to the load can be obtained. Further, by interpolation from a plurality of combinations, the power loss between the power transmission device 402 and the power reception device 401 corresponding to all loads can be estimated. Thus, the calibration process performed by the power transmission device 402 and the power reception device 401 for the power transmission device 402 to obtain a combination of the power transmission power value and the power reception power value is hereinafter referred to as "calibration process of the power loss method (CAL process)".

[0053] After the CAL process, when the power transmission device 402 actually transmits power to the power reception device 401 at the third power transmission power value Pt3, it is assumed that the power transmission device 402 receives the power reception power value Pr3' from the power reception device 401. The power transmission device 402 calculates a value Pr3 - Pr3' (= P loss _FO) obtained by subtracting the power reception power value Pr3' actually received from the power reception device 401 from the third power reception power value Pr3 in a state where no foreign object exists. This power value P loss _FO can be considered as the power loss consumed by the foreign object when a foreign object exists near the power transmission device 402 and the power reception device 401. Therefore, when the power value P loss _FO consumed by the foreign object exceeds a predetermined threshold value, it can be determined that a foreign object exists.[[ID=ll]]

[0054] Alternatively, the power transmission device 402 previously obtains the power loss Pt3 - Pr3 (P loss 3) between the power transmission device 402 and the power reception device 401 from the third power reception power value Pr3 in a state where no foreign object exists. Then, the power transmission device 402 obtains the power loss Pt3 - Pr3' (P loss 3') between the power transmission device 402 and the power reception device 401 in a state where a foreign object exists from the power reception power value Pr3' received from the power reception device 401 in a state where a foreign object exists. Then, P loss 3' - P loss 3 (= P loss _FO) can be used to estimate the power value P loss _FO that would be consumed by the foreign object.

[0055] As described above, the power value P consumed by the foreign object. loss The way to find _FO is Pr3-Pr3'(=P loss You can also obtain it as _FO) or P loss 3'-P loss 3(=P loss It may also be calculated as _FO). In this embodiment, basically P loss 3'-P loss 3(=P loss I will explain the method of obtaining it as _FO), but Pr3-Pr3'(=P loss The method of obtaining it as _FO) is also applicable.

[0056] After the linear 802 is acquired through the calibration process, the foreign object detection unit 305 of the power transmission device 402 periodically receives the current received power value (for example, the above received power value Pr3') from the power receiving device 401 via the communication unit 104. The current received power value transmitted periodically by the power receiving device 401 is sent to the power transmission device 402 as Received Power Packet (mode0) (hereinafter, RP0). The foreign object detection unit 305 of the power transmission device 402 performs foreign object detection based on the received power value stored in RP0 and the linear 802.

[0057] [Explanation of each phase leading up to power transmission] 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).

[0058] In this embodiment, the power receiving device 401 and the power transmitting device 402 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 include the Selection phase, Ping phase, Identification and Configuration phase, Negotiation phase, and Calibration phase. Hereafter, the Identification and Configuration phase will be referred to as the I&C phase. The basic processing of each phase will be described below.

[0059] In the Selection phase, the power transmission device 402 intermittently transmits Analog Pings to detect when an object is placed on the power transmission device 402 (for example, when a power receiving device 401 or a conductor piece is placed on the charging base 403). The power transmission device 402 detects at least one of the voltage and current values ​​of the power transmission antenna 105 when it transmits the Analog Ping, 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.

[0060] In the Ping phase, the power transmitter 402 transmits a Digital Ping with higher power than the Analog Ping. The power of the Digital Ping is sufficient to activate the control unit 201 of the power receiver 401, which is mounted on top of the power transmitter 402. The power receiver 401 notifies the power transmitter 402 of the magnitude of the received voltage. In this way, the power transmitter 402 recognizes that the object detected in the Selection phase is the power receiver 401 by receiving the response from the power receiver 401 that received the Digital Ping. Upon receiving notification of the received voltage value, the power transmitter 402 transitions to the I&C phase. Also, before transmitting the Digital Ping, the power transmitter 402 measures the Q-factor of the power transmitting antenna (power transmitting coil) 105. This measurement result is used when performing foreign object detection processing using the Q-factor measurement method.

[0061] In the I&C phase, the power transmission device 402 identifies the power receiving device 401 and obtains equipment configuration information (capacity information) from the power receiving device 401. The power receiving device 401 transmits an ID Packet and a Configuration Packet. The ID Packet contains the identifier information of the power receiving device 401, and the Configuration Packet contains the equipment configuration information (capacity information) of the power receiving device 401. Upon receiving the ID Packet and Configuration Packet, the power transmission device 402 responds with an acknowledgment (ACK). The I&C phase then ends, and the system moves on to the next Negotiation phase.

[0062] In the Negotiation phase, the GP value is determined based on the GP value requested by the power receiving device 401 and the power transmission capacity of the power transmission device 402. The power transmission device 402 receives an FOD Status Packet containing Reference Quality Factor Value information from the power receiving device 401, and the setting unit 304 adjusts the threshold in the Q-value measurement method to determine the final threshold. Then, the power transmission device 402 performs foreign object detection processing using the Q-value measurement method via the foreign object detection unit 305 in accordance with the request from the power receiving device 401. Here, the Reference Quality Factor Value information is the Q-value information when the power receiving device 401 is placed on the power transmission device 402 in a state where no foreign objects are present. Furthermore, the WPC standard specifies a method in which, after transitioning to the Power Transfer phase described below, the same processing as the Negotiation phase is performed again at the request of the power receiving device 401. Hereafter, the phase in which these processes are performed after transitioning from the Power Transfer phase will be called the Renegotiation phase.

[0063] In the Calibration phase, calibration is performed based on the WPC standard. The power receiving device 401 also notifies the power transmission device 402 of a predetermined power received value (power received value under light load conditions / power received value under maximum load conditions), and the power transmission device 402 makes adjustments to efficiently transmit power. The power received value notified to the power transmission device 402 is used for foreign object detection processing using the power loss method.

[0064] In the Power Transfer phase, control is performed for starting and continuing power transmission, as well as stopping power transmission due to errors or full charge. The power transmission device 402 and the power receiving device 401 communicate by superimposing signals onto electromagnetic waves transmitted from the power transmission antenna 105 and power receiving antenna 205, which are used when performing wireless power transmission based on the WPC standard, for the purpose of controlling power transmission and reception. The range in which communication based on the WPC standard is possible between the power transmission device 402 and the power receiving device 401 is approximately the same as the power transmission range of the power transmission device 402.

[0065] [Processing flow for power transmission in accordance with WPC standards] As described above, 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 diagram illustrating the sequence for power transmission in accordance with the WPC standard. Here, the power transmission device 402 and the power receiving device 401 will be used as examples.

[0066] First, the power transmission device 402 repeatedly and intermittently transmits Analog Ping according to the WPC standard to detect objects within the power transmission range (F501). The power transmission device 402 performs the processes defined as the Selection phase and Ping phase of the WPC standard and waits for the power receiving device 401 to be placed on it. The user of the power receiving device 401 brings the power receiving device 401 closer to the power transmission device 402 in order to charge the power receiving device 401 (e.g., a smartphone) (F502). For example, the power receiving device 401 is brought closer to the power transmission device 402 by loading the power receiving device 401 onto the power transmission device 402.

[0067] When the power transmission device 402 detects the presence of an object within the power transmission range via the transmitted Analog Ping (F503, F504), it transmits a Digital Ping according to the WPC standard (F505). When the power receiving device 401 receives the Digital Ping, it understands that the power transmission device 402 has detected the power receiving device 401 (F506). Furthermore, when the power transmission device 402 receives a predetermined response to the Digital Ping, it determines that the detected object is the power receiving device 401 and that the power receiving device 401 has been placed on the charging base 403. When the power transmission device 402 detects the placement of the power receiving device 401, it obtains identification information and capability information from the power receiving device 401 via I&C phase communication as defined in the WPC standard (F507).

[0068] Here, the identification information of the power receiving device 401 includes the Manufacturer Code and Basic Device ID. The capability information of the power receiving device 401 includes information elements that can identify the version of the WPC standard it supports, and a value that identifies the maximum power that the power receiving device 401 can supply to the load (Maximum Power Value). Furthermore, the capability information of the power receiving device 401 also includes information indicating whether or not it has the Negotiation function of the WPC standard. Note that the power transmitting device 402 may obtain the identification information and capability information of the power receiving device 401 by means other than the I&C phase communication of the WPC standard. In addition, the identification information may be any other identification information that can identify an individual power receiving device 401, such as a Wireless Power ID. Capability information may also include information other than that described above.

[0069] Next, the power transmission device 402 determines the GP value with the power receiving device 401 through communication in the Negotiation phase as defined in the WPC standard (F508). Note that in F508, other procedures for determining GP may be performed in addition to the communication in the Negotiation phase as defined in the WPC standard. Furthermore, if the power transmission device 402 obtains information, for example, during the acquisition of information in F507, indicating that the power receiving device 401 does not support the Negotiation phase, it may not perform the Negotiation phase communication and may set the GP value to a small value (for example, one predetermined in the WPC standard). In this embodiment, GP is determined to be 5 watts in F508.

[0070] After determining the GP, the power transmission device 402 moves to the Calibration phase and performs calibration processing based on the determined GP. In the calibration processing, first, the power receiving device 401 transmits information (first reference power receiving information) to the power transmission device 402, including the power received under light load conditions (load disconnection state, load condition where the transmitted power is below the first threshold) (F509). In this embodiment, the first reference power receiving information is the power received by the power receiving device 401 when the power transmitted by the power transmission device 402 is 250 milliwatts. The first reference power receiving information is stored and transmitted in a Received Power Packet (mode 1) (hereinafter, RP1) as defined in the WPC standard, but other messages may be used. The power transmission device 402 determines whether or not to accept the first reference power receiving information based on the power transmission status of its own device. The power transmission device 402 sends an acknowledgment (ACK) to the power receiving device 401 if it accepts the signal, or a negative response (NAK) if it does not accept the signal (F510).

[0071] Next, when the receiving device 401 receives an ACK from the transmitting device 402, it processes information (second reference receiving power information) including the received power in the load connection state (maximum load state, load state where the transmitted power is equal to or greater than the second threshold) to the transmitting device 402. In this embodiment, since the GP is currently 5 watts, the second reference receiving power information is the received power information of the receiving device 401 when the transmitted power of the transmitting device 402 is 5 watts. Here, the second reference receiving power information is stored in Received Power Packet (mode 2) (hereinafter, RP2) as defined in the WPC standard, but other messages may be used. First, as a step before transmitting the second reference receiving power information, the receiving device 401 sends a transmission output change instruction (F511) containing a positive value in order to increase the transmitted power from the transmitting device 402 to 5 watts.

[0072] When the power transmission unit 402 receives the above-mentioned power output change instruction, if it is able to handle the increase in power transmission, it responds with an ACK and increases the power transmission (F512, F513). Subsequently, steps F511 to F513 are repeated to increase the power transmission. Since the second reference received power information is the received power information when the power transmission unit 402's transmission power is 5 watts, if the power transmission unit 402 receives a power increase request exceeding 5 watts from the power receiving unit 401 (F514), it responds with an NAK to the power output change instruction (F515). This prevents the transmission of power exceeding the specified amount.

[0073] The receiving device 401 recognizes that it has reached a predetermined transmission power level by receiving NAK from the transmitting device 402. The receiving device 401 then stores information including the received power in the load-connected state (second reference received power information) in RP2 and transmits it to the transmitting device 402 (F516). The transmitting device 402 can calculate the power loss between the transmitting device 402 and the receiving device 401 in the load-disconnected state and the load-connected state based on the transmission power value of the transmitting device 402 and the received power values ​​included in the first and second reference received power information. Furthermore, by interpolating between these power losses, the power loss value between the transmitting device 402 and the receiving device 401 can be calculated for all transmission power levels that the transmitting device 402 can take (in this case, from 250 milliwatts to 5 watts) (F517). The power transmission device 402 sends an ACK (F518) to the second reference power information from the power receiving device 401, and completes the calibration process.

[0074] When the power transmission device 402 determines that it is ready to start the charging process and begins transmitting power to the power receiving device 401, the process moves to the Power Transfer phase and charging of the power receiving device 401 begins. Before the power transmission process begins, the power transmission device 402 and the power receiving device 401 perform equipment authentication (F519), and if they determine that their equipment can handle a larger GP, they may reset the GP to a larger value, for example, 15 watts (F520).

[0075] In this case, the receiving device 401 and the transmitting device 402 perform the same processing as in F511 to F515 (F521 to F524) in order to increase the transmitting power of the transmitting device 402 to 15 watts. Then, the transmitting device 402 and the receiving device 401 perform calibration processing again for GP = 15 watts. Specifically, the receiving device 401 transmits information (third reference receiving power information) including the received power in the load-connected state of the receiving device 401 when the transmitting power of the transmitting device 402 is 15 watts (F525). Based on the received power included in the first, second and third reference receiving power information, the transmitting device 402 calculates the power loss between the transmitting device 402 and the receiving device 401 for all possible transmitting powers (from 250 milliwatts to 15 watts) of the transmitting device 402 (F526). Then, the power transmission device 402 sends an ACK to the third reference power information from the power receiving device 401 (F527) and completes the calibration process. Having determined that it is possible to start the charging process, the power transmission device 402 starts the power transmission process to the power receiving device 401 and moves to the Power Transfer phase (F528).

[0076] In the Power Transfer phase, the power transmission device 402 transmits power to the power receiving device 401. Foreign object detection is also performed using the power loss method. In the power loss method, the power transmission device 402 first calculates the power loss P between the power transmission device 402 and the power receiving device 401 in the absence of foreign objects, based on the difference between the power transmitted by the power transmission device 402 and the power received by the power receiving device 401, as determined by the calibration process described above. loss Calculate 3. The calculated value corresponds to the standard power loss under normal conditions (no foreign matter) during power transmission. Then, the power transmission device 402 measures the power loss P between the power transmission device 402 and the power receiving device 401 during power transmission after calibration processing. loss 3' is determined to be "foreign object present" if it deviates by more than a threshold from the power loss in the normal state.

[0077] 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 foreign object detection can be performed while power transmission continues, thus maintaining high power transmission efficiency.

[0078] 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 power transmission device 402 transmits power, and if foreign objects are present near the power transmission device 402 and the power receiving device 401 during power transmission, heat generation from the foreign objects will increase. Therefore, it is necessary to improve the accuracy of foreign object detection in this phase. Accordingly, in this embodiment, in order to improve the accuracy of foreign object detection, the waveform attenuation method is implemented as a foreign object detection method different from the power loss method.

[0079] [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. Below, a method for detecting foreign objects based on the attenuation state of the transmitted radio waves (waveform attenuation method) will be explained using Figure 6. Figure 6 is a diagram for explaining the principle of foreign object detection using the waveform attenuation method. Here, we will explain using foreign object detection using the transmission waveform related to power transmission from the power transmission device 402 to the power receiving device 401 as an example.

[0080] 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 transmitting antenna 105 of the power transmission device 402. In Figure 6, the horizontal axis represents time, and the vertical axis represents the voltage value. The power transmission device 402 transmits power to the power receiving device 401 via the transmitting antenna 105, and is assumed to stop transmitting power at time T0. That is, at time T0, the power supply for power transmission from the power supply unit 102 is stopped. The frequency of the transmitted radio waves related to power transmission from the power transmission device 402 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 represents the voltage value at time T1. (T1, A1) at point 601 indicates that the voltage value at time T1 is A1. Similarly, point 602 is also a point on the envelope of the high-frequency voltage and represents the voltage value at time T2. At point 602, (T2, A2) 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 from time T0 onward. 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) (Formula 1)

[0081] If foreign matter is present near the power transmission device 402 and the power receiving device 401, this Q value decreases. This is because, when foreign matter is present, energy loss occurs due to that foreign matter. Therefore, focusing on the slope of voltage attenuation, when foreign matter is present, more energy loss occurs due to the foreign matter than when it is absent, so the slope of the line connecting points 601 and 602 becomes steeper, and the attenuation rate of the waveform amplitude increases. In other words, the waveform attenuation method determines the presence or absence of foreign matter based on the voltage attenuation state between points 601 and 602, and 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 to make the determination.

[0082] 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 attenuation state is fixed, the determination may 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 may be made using the value of the 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 the predetermined voltage value A2.

[0083] As described above, the presence or absence of foreign matter can be determined by the voltage attenuation state during the power transmission interruption period, 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.

[0084] 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 voltage values. 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 Q value obtained from the current waveform, the slope of the current 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 can be used as waveform attenuation indices to determine the presence or absence of foreign matter and to detect it. Thus, the waveform attenuation method is a method of detecting foreign matter by measuring the voltage or current value at at least two points in time during a predetermined period in which the power transmission device 402 restricts power transmission. Note that measurements at three or more points in time may also be used.

[0085] Furthermore, foreign object detection may be performed based on both the voltage attenuation state and the current attenuation state, such as by using an evaluation value calculated from the voltage waveform attenuation index and the current waveform attenuation index to determine the presence or absence of foreign objects. In the above example, the waveform attenuation index was measured for the period during which the power transmission device 402 temporarily suspended power transmission, but the waveform attenuation index may also be measured for the period during which the power transmission device 402 temporarily reduced the power supplied from the power supply unit 102 from a predetermined power level to a lower power level.

[0086] Next, 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 of the power transmission antenna 105. As with Figure 6, the vertical axis may also represent the current value of the current flowing through the power transmission antenna 105.

[0087] During the transient response period immediately following the start of power transmission by the power transmission device 402, the transmitted waveform is unstable. Therefore, during this transient response period in which the transmitted waveform is unstable, the power receiving device 401 is controlled not to communicate with the power transmission device 402 (communication by amplitude modulation or load modulation). Similarly, the power transmission device 402 is controlled not to communicate with the power receiving device 401 (communication by frequency shift modulation). Hereafter, this period will be referred to as the communication prohibition period. During this communication prohibition period, the power transmission device 402 will continue to transmit power to the power receiving device 401. After the communication prohibition period has elapsed, the power transmission device 402 will continue to transmit power to the power receiving device 401. Hereafter, this steady-state period will be referred to as the power transmission period.

[0088] When the power transmission device 402 receives a foreign object detection execution request packet (command) from the power receiving device 401, it temporarily suspends power transmission after a predetermined period of time has elapsed, or temporarily reduces the transmission power. Hereinafter, this predetermined period will be referred to as the preparation period. Note that this foreign object detection execution request packet may be RP0, RP1, or RP2 as described above. Then, the power transmission control unit 302 of the power transmission device 402 stops power transmission or temporarily reduces the transmission power after the preparation period has elapsed. As a result, the amplitude of the transmitted radio wave is attenuated. Hereinafter, the period from when the power transmission device 402 temporarily suspends or reduces the transmission power until it resumes power transmission will be referred to as the power transmission control period. The power transmission device 402 calculates a waveform attenuation index of this attenuated waveform, compares the calculated waveform attenuation index with a threshold, and determines the presence or absence of a foreign object, or the probability of a foreign object being present. This determination may be performed during the power transmission control period, the communication prohibition period, or the power transmission period.

[0089] If no foreign objects are detected after the power transmission control period has elapsed, the power transmission device 402 resumes power transmission. During the transient response period immediately following the resumption of power transmission, the transmission waveform is unstable, and therefore, a communication ban period is imposed again. Then, the system transitions to a power transmission period in which power is stably transmitted from the power transmission device 402 to the power receiving device 401.

[0090] As described above, the power transmission device 402 repeatedly starts and stops power transmission after a communication ban period, a power transmission period, a preparation period, and a power transmission control period. The power transmission device 402 then calculates a waveform attenuation index of the attenuated waveform at a predetermined timing, compares the calculated waveform attenuation index with a threshold, and determines the presence or absence of foreign matter, or the probability of foreign matter being present.

[0091] Furthermore, if elements such as the power receiving unit 203, the charging unit 206, and the battery 207 are connected to the power receiving antenna 205 and resonant capacitor 211 of the power receiving device 401 during the power transmission control period, the waveform attenuation index may be affected by the load from these elements. In other words, the waveform attenuation index may change depending on the state of the power receiving unit 203, the charging unit 206, and the battery 207. Therefore, even if the waveform attenuation index is large, it may be difficult to distinguish whether it is due to the influence of foreign objects or due to changes in the state of the power receiving unit 203, the charging unit 206, the battery 207, etc.

[0092] Therefore, when detecting foreign objects by observing the waveform attenuation index, the power receiving device 401 may disconnect the first switch unit 209 during the above preparation period. 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 it, causing current to flow through the closed loop formed by the power receiving antenna 205, the resonant capacitor 211, and the second switch unit 210. This eliminates the influence of the power receiving unit 203, the charging unit 206, and the battery 207, and by performing foreign object detection based on the waveform attenuation index of the waveform observed in this state, highly accurate foreign object detection becomes possible.

[0093] Furthermore, during the above preparation period, the power receiving device 401 may switch to a low-power mode or be controlled to maintain a constant power consumption when the first switch unit 209 is turned ON to short-circuit and the second switch unit 210 is turned OFF to disconnect. If the power consumed by the power receiving device 401 is not constant or if a large amount of power is consumed, the waveform attenuation index of the attenuated waveform will be affected by these fluctuations in power consumption. Therefore, in order to eliminate such effects, the power consumed by the power receiving device 401 is controlled. Specifically, the operation of applications running on the power receiving device 401 may be restricted or stopped, or the hardware functions of the power receiving device 401 may be put into a low-power mode or an operation stop mode. By performing foreign object detection based on the waveform attenuation index of the waveform observed in such a state, highly accurate foreign object detection becomes possible.

[0094] Similarly, the power transmission device 402 may also be short-circuited by turning on switch 108 during the above preparation period, allowing current to flow through 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 supply unit 102, power transmission unit 103, and communication unit 104. Alternatively, a switch (not shown) can be provided between the power transmission antenna 105 and the power transmission unit 103, and this switch can be turned off during the above preparation period to eliminate the influence of the power supply unit 102, power transmission unit 103, and communication unit 104.

[0095] [Method for determining each period when using the waveform attenuation method as a foreign object detection method] Next, the method for determining the preparation period described above will be explained. The preparation period may be determined by a predetermined fixed value (time). Alternatively, the power transmission device 402 may determine the time according to the status of the power transmission device 402 and notify the power receiving device 401 of the determined time. Or, the power receiving device 401 may determine the time according to the status of the power receiving device 401 and notify the power transmission device 402 of the determined time.

[0096] Alternatively, the time can be determined by the transmission device 402 and the receiving device 401 communicating with each other and exchanging information. For example, the transmission device 402 may determine the maximum preparation time and notify the receiving device 401, while the receiving device 401 may determine the minimum preparation time and notify the transmission device 402. The receiving device 401 may then determine the preparation period within a range (time) set by the transmission device 402 and the receiving device 401, and notify the transmission device 402 of that value. The relationship between the transmission device 402 and the receiving device 401 may also be reversed. By determining the preparation period to an appropriate time, it is possible to prevent the waveform during the power transmission control period from becoming distorted.

[0097] Next, the method for determining the power transmission control period described above will be explained. In determining the power transmission control period, it is important to determine a power transmission control period that can be handled by both the power transmission device 402 and the power receiving device 401. Therefore, in the negotiation phase, the power transmission device 402 and the power receiving device 401 notify each other of their capabilities for handling power transmission control periods, and the actual power transmission control period is determined from a common range between the two. Specifically, this is achieved by two types of commands issued by the power receiving device 401.

[0098] Firstly, the receiving device 401 issues a command (hereinafter referred to as the "minimum power transmission control period request command") to obtain information on the minimum power transmission control period that can be generated by the power transmission device 402 (hereinafter referred to as the "minimum power transmission control period"). Here, the minimum power transmission control period that can be generated by the power transmission device 402 shall include at least the period necessary for the power transmission device 402 to perform foreign object detection using the waveform attenuation method. Secondly, the receiving device 401 issues a command (hereinafter referred to as the "maximum power transmission control period notification command") to notify information on the maximum power transmission control period that the receiving device 401 can handle (hereinafter referred to as the "maximum power transmission control period"). Here, the maximum power transmission control period that the receiving device 401 can handle is defined as a period within which power transmission is not judged to have been stopped.

[0099] These two commands allow the receiving device 401 and the transmitting device 402 to understand each other's capabilities regarding the power transmission control period. Then, if the condition "(minimum power transmission control period that can be generated by the transmitting device 402) ≤ (maximum power transmission control period that the receiving device 401 can handle)" is met, the power transmission control period can be determined from within that range. In addition, in the above exchange, if you do not want to perform foreign object detection using the waveform attenuation method, you can notify the other party of your intention not to perform foreign object detection using the waveform attenuation method by setting the value of the minimum power transmission control period or the maximum power transmission control period set in the RP packet to "0".

[0100] Here, we will explain the relationship between the transmitted power transmitted from the power transmission device 402 and the power transmission control period. In the exchange of information between the power transmission device 402 and the power receiving device 401, in addition to the method described above, the power transmission control period is determined such that the greater the transmitted power transmitted by the power transmission device 402, the shorter the power transmission control period becomes. When power transmission is resumed after the power transmission control period, ringing occurs in the transmitted waveform at the time of resumption of power transmission. The greater the difference in the peak of the transmitted power before and after the resumption of power transmission, the greater the ringing that occurs. Therefore, in order to reduce the ringing, it is necessary to reduce the difference in the peak of the transmitted power before and after the resumption of power transmission.

[0101] Shortening the power transmission control period allows for the resumption of power transmission with less waveform attenuation, resulting in a smaller peak-to-peak difference in transmitted power and suppressing ringing. Thus, the larger the transmitted power, the smaller the peak-to-peak difference in transmitted power upon resumption, and the more effective it is to shorten the power transmission control period to suppress ringing. Conversely, the power transmission control period can also be made longer as the transmitted power increases. Higher transmitted power requires more accurate foreign object detection, so when the transmitted power is high, the power transmission control period can be extended to observe the attenuation state for a longer period. This makes it possible to achieve more accurate foreign object detection than when the transmitted power is low.

[0102] Next, the method for determining the communication prohibition period described above will be explained. Since ringing occurs in the power transmission waveform after power transmission is resumed, stable communication is achieved by not performing communication when ringing occurs. The method for determining the communication prohibition period may be the same as the method for determining the preparation period, which is a predetermined fixed value (time). Alternatively, the power transmission device 402 may determine the time according to the state of the power transmission device 402 and notify the power receiving device 401 of the determined time. Or, the power receiving device 401 may determine the time according to the state of the power receiving device 401 and notify the power transmission device 402 of the determined time.

[0103] Alternatively, the transmission device 402 and the receiving device 401 may communicate with each other and exchange information to determine the time. For example, the transmission device 402 may determine the maximum time of the communication ban period and notify the receiving device 401, while the receiving device 401 may determine the minimum time of the communication ban period and notify the transmission device 402. The receiving device 401 may then determine the communication ban period within a range (time) set by the transmission device 402 and the receiving device 401, and notify the transmission device 402 of that value. The relationship between the transmission device 402 and the receiving device 401 may also be reversed. In this case, the transmission device 402 or the receiving device 401 may determine the minimum time within the range set by the transmission device 402 and the receiving device 401 as the communication ban period. Alternatively, the transmission device 402 or the receiving device 401 may determine the maximum time within the range set by the transmission device 402 and the receiving device 401 as the communication ban period.

[0104] Here, we will explain the relationship between the power transmitted from the power transmission device 402 and the communication blackout period. In the exchange of information between the power transmission device 402 and the power receiving device 401, in addition to the method described above, the communication blackout period is determined such that the longer the power transmitted by the power transmission device 402, the greater the communication blackout period. As described above, the greater the difference in power levels before and after the resumption of power transmission, the greater the ringing will be, so the communication blackout period is set to be long enough to cause the ringing to converge or become sufficiently small. This makes it possible to perform stable communication between the power transmission device 402 and the power receiving device 401. Conversely, the communication blackout period may be shortened as the power transmitted is greater.

[0105] Next, the relationship between the power transmission control period and the communication blackout period will be explained. In the exchange of information between the power transmission device 402 and the power receiving device 401, in addition to the method described above, the communication blackout period is determined such that the longer the power transmission control period, the longer the communication blackout period. As described above, the greater the difference in the power transmission level before and after power transmission restart, the greater the ringing. Therefore, as the power transmission control period increases, the attenuation of the transmitted radio waves also increases, resulting in a larger difference in the power transmission level at the time of power transmission restart, and thus greater ringing. By making the communication blackout period longer as the power transmission control period increases, communication can be performed after the ringing has converged or become sufficiently small, enabling stable communication between the power transmission device 402 and the power receiving device 401. Conversely, the communication blackout period may be made shorter as the power transmission control period increases.

[0106] Next, the method for determining the power transmission period described above will be explained. The method for determining the power transmission control period may be a predetermined fixed value (time), similar to the method for determining the preparation period and the communication prohibition period. Alternatively, the power transmission device 402 may determine the time according to the state of the power transmission device 402 and notify the power receiving device 401 of the determined time. Or, the power receiving device 401 may determine the time according to the state of the power receiving device 401 and notify the power transmission device 402 of the determined time.

[0107] Alternatively, the transmission device 402 and the receiving device 401 may communicate with each other and exchange information to determine the time. For example, the transmission device 402 may determine the maximum transmission period and notify the receiving device 401, and the receiving device 401 may determine the minimum transmission period and notify the transmission device 402. Then, the receiving device 401 may determine the transmission period within a range (time) set by the transmission device 402 and the receiving device 401, and notify the transmission device 402 of that value. The relationship between the transmission device 402 and the receiving device 401 may also be reversed.

[0108] Here, we will explain the relationship between the power transmitted from the power transmission device 402 and the transmission period. In the exchange of information between the power transmission device 402 and the power receiving device 401, in addition to the method described above, the transmission period is determined such that the transmission period becomes shorter as the power transmitted by the power transmission device 402 increases. As described above, the higher the power transmitted, the higher the accuracy of foreign object detection required. Therefore, by shortening the transmission period as the power transmitted is higher, the number of power transmission control periods within a predetermined time is increased. This makes it possible to increase the number of times waveform attenuation is observed and increase the opportunities for foreign object detection, enabling high-precision foreign object detection. On the other hand, conversely, the transmission period may be made longer as the power transmitted is higher. This makes it possible to transmit power from the power transmission device 402 to the power receiving device 401 without reducing the transmission efficiency of the power transmitted.

[0109] [Method for setting thresholds for foreign object detection in waveform attenuation method] Next, we will explain how to set a threshold for determining the presence or absence of a foreign object, or the probability of its presence, when performing foreign object detection using the waveform attenuation method. As mentioned above, the waveform attenuation method performs foreign object detection based on a waveform attenuation index. In other words, the measured waveform attenuation index is compared with a predetermined threshold, and the presence or absence of a foreign object, or the probability of its presence, is determined based on the result. The following methods can be used to set this threshold.

[0110] The first method involves the power transmission device 402 maintaining a predetermined fixed value as a threshold, which is a common value independent of the receiving device 401 to which the power is transmitted. This fixed value may be the same in all cases, or it may be a value determined by the power transmission device 402 depending on the situation. As mentioned above, the waveform attenuation rate of the transmitted waveform during the power transmission control period increases if foreign matter is present. Therefore, a predetermined value for the waveform attenuation index when it is considered that no foreign matter is present is maintained in advance, and this is used as a threshold to compare with the measured waveform attenuation index result. If the measured waveform attenuation index is greater than the threshold, it is determined that foreign matter is present or that there is a high probability that foreign matter is present.

[0111] For example, if the waveform attenuation index is defined as the Q value, the Q value measured by the power transmission device 402 is compared with a predetermined Q value (threshold) that indicates the absence of foreign matter. If the measured Q value is smaller than the threshold, it is determined that foreign matter is present or there is a possibility of foreign matter being present. If the measured Q value is larger than or approximately the same as the threshold, it is determined that there is no foreign matter or the possibility of foreign matter being present is low. In this way, foreign matter detection by the waveform attenuation method becomes possible using the first method.

[0112] The second method involves the setting unit 304 of the power transmission device 402 adjusting a threshold based on information transmitted from the power receiving device 401 to determine the final threshold. Similar to the first method, a predetermined value for the waveform attenuation index when no foreign matter is considered to be present is stored in advance and used as the threshold, which is then compared with the measured waveform attenuation index result. If the measured waveform attenuation index is greater than the threshold, it is determined that there is foreign matter or a high probability that foreign matter is present. Here, the value of the measured waveform attenuation index may differ depending on the power receiving device 401 to be transmitted, which is mounted on the power transmission device 402. This is because the electrical characteristics of the power receiving device 401 coupled via the power transmission antenna 105 of the power transmission device 402 affect the value of the waveform attenuation index.

[0113] For example, if the waveform attenuation index is defined as the Q value, the Q value measured by the power transmission device 402 when no foreign matter is present may differ depending on the power receiving device 401 placed on the power transmission device 402. Therefore, the power receiving device 401 stores information on the Q value when the power receiving device 401 is placed on the power transmission device 402 when no foreign matter is present, and communicates this Q value to the power transmission device 402. The power transmission device 402 then adjusts the threshold based on the Q value information received from the power receiving device 401 to determine the final threshold.

[0114] As described above, in the Negotiation phase, the power transmission device 402 receives an FOD Status Packet containing information on the Reference Quality Factor Value and adjusts the threshold in the Q-value measurement method. Then, it determines the final threshold in the Q-value measurement method. Similarly, for the threshold in foreign object detection using the waveform attenuation method, the power transmission device 402 adjusts the threshold based on this Reference Quality Factor Value to determine the final threshold.

[0115] In the Negotiation phase, the Reference Quality Factor Value transmitted from the power receiving device 401 to the power transmitting device 402 is information originally used for foreign object detection in the Q-value measurement method, which measures the Q-value in the frequency domain. On the other hand, when the waveform attenuation index is used as the Q-value, although the method of deriving the Q-value is different, it is also possible to determine the Q-value from the waveform in Figure 6, for example, using Equation 1 described above, even using the waveform attenuation method, which measures the Q-value in the time domain. Therefore, it is possible to set the threshold value of the Q-value in the waveform attenuation method based on the Reference Quality Factor Value. In this way, by setting the threshold value of the Q-value in the waveform attenuation method based on the information already transmitted from the power receiving device 401 to the power transmitting device 402 in the Negotiation phase, the power transmitting device 402 eliminates the need for new measurements or other processing for threshold setting. Therefore, it is possible to set the threshold in a shorter time.

[0116] The Q value measured by the power transmission device 402 is compared with the threshold value determined by the method described above. If the measured Q value is smaller than the threshold value, it is determined that there is a foreign object present or that there is a possibility of a foreign object being present. On the other hand, if the measured Q value is larger than the threshold value or is approximately the same, it is determined that there is no foreign object present or that the possibility of a foreign object being present is low. In this way, foreign object detection by waveform attenuation method becomes possible using the second method.

[0117] The third method involves the measurement unit 303 of the power transmission device 402 measuring the waveform attenuation index in the absence of foreign matter, and the setting unit 304 of the power transmission device 402 adjusting the threshold based on the measurement results to determine the final threshold. The value of the waveform attenuation index may differ depending on the power transmission power of the power transmission device 402. This is because the amount of heat generated, the characteristics of the electrical circuits of the power transmission device 402, etc., change depending on the magnitude of the power transmission power of the power transmission device 402, and these affect the value of the waveform attenuation index. Therefore, by having the power transmission device 402 measure the waveform attenuation index for each power transmission power, adjust the threshold based on the results, and determine the final threshold, more accurate foreign matter detection becomes possible.

[0118] Figure 9 is a diagram illustrating the method for setting thresholds for foreign object detection for each transmitted power of the power transmission device 402 in the waveform attenuation method. First, when power is transmitted from the power transmission device 402, the power receiving device 401 is controlled to be in a light load state where no power is supplied to the load of the power receiving device 401, or only a very small amount of power is supplied. The transmitted power of the power transmission device 402 at this time is denoted as Pt1. Then, the power transmission device 402 stops transmitting power in that state and measures the waveform attenuation index. The waveform attenuation index at this time is denoted as δ1. At this time, the power transmission device 402 recognizes the transmitted power Pt1 that it is transmitting and stores a calibration point 900 in the memory 106 that associates the transmitted power Pt1 with the waveform attenuation index δ1.

[0119] Next, the power receiving device 401 controls itself so that when power is transmitted from the power transmitting device 402, the load connection state is such that the maximum power is supplied to the load of the power receiving device 401, or power exceeding a predetermined threshold is supplied. The power transmitted by the power transmitting device 402 at this time is denoted as Pt2. Then, the power transmitting device 402 stops transmitting power in this state and measures the waveform attenuation index. The waveform attenuation index at this time is denoted as δ2. At this time, the power transmitting device 402 stores a calibration point 901 in the memory 106 that associates the transmitted power Pt2 and the waveform attenuation index δ2.

[0120] Next, the power transmission device 402 performs linear interpolation between calibration point 900 and calibration point 901 to create a line 902. Line 902 shows the relationship between the transmitted power and the waveform attenuation index of the transmitted radio wave type when there are no foreign objects around the power transmission device 402 and the power receiving device 401. From this, the power transmission device 402 can estimate the waveform attenuation index of the transmitted radio wave type for each transmitted power value in the absence of foreign objects from line 902. For example, if the transmitted power value is Pt3, the waveform attenuation index can be estimated to be δ3 from point 903 on line 902 corresponding to the transmitted power value Pt3. Based on the above estimation results, the power transmission device 402 can then calculate a threshold used to determine the presence or absence of foreign objects for each transmitted power value.

[0121] For example, a waveform attenuation index that is larger by a value corresponding to the measurement error than the estimated waveform attenuation index for a given transmission power value in the case of no foreign matter may be set as the threshold for determining the presence or absence of foreign matter. The calibration process performed by the transmission device 402 and the receiving device 401 in order for the transmission device 402 to acquire a combination of transmission power value and waveform attenuation index will be referred to below as the "waveform attenuation index calibration process (CAL process)". In the example above, measurements were taken at two points, Pt1 and Pt2, of the transmission power of the transmission device 402, but in order to improve accuracy, measurements may be taken at three or more points to calculate the waveform attenuation index for each transmission power.

[0122] Furthermore, the power receiving device 401 may perform two separate controls: one to create a light-load state where no power is supplied to the load, and another to create a load-connected state, after notifying the power transmission device 402 of its intention to perform these controls. Also, either of these two controls may be performed first.

[0123] 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 above, may also be performed in the Calibration phase. As mentioned above, in the Calibration phase, the transmission device 402 acquires the data necessary for detecting foreign matter using the power loss method. At that time, the transmission device 402 acquires data on power loss for both the light load state and the load-connected state of the receiving device 401. Therefore, the measurement of calibration point 900 and calibration point 901 in Figure 9 may be performed together with the measurement of power loss described above. In this case, when the transmission device 402 receives the first reference received power information from the receiving device 401, it measures calibration point 900 in addition to the processing that should be performed in the Calibration phase described above. Also, when the transmission device 402 receives the second reference received power information from the receiving device 401, it measures calibration point 901 in addition to the processing that should be performed in the Calibration phase described above. This eliminates the need to set aside a separate period for measuring calibration point 900 and calibration point 901, allowing measurements of calibration point 900 and calibration point 901 to be performed in a shorter time.

[0124] In this way, the power transmission device 402 adjusts the threshold value of the waveform attenuation index for each power transmission method based on the waveform attenuation index information measured by the power transmission device 402, and sets the final threshold value. For example, if the waveform attenuation index is the Q value, the power transmission device 402 compares the Q value measured by the power transmission device 402 with the threshold value determined by the method described above, and determines that there is a foreign object present or that there is a possibility of a foreign object present if the measured Q value is smaller than the threshold value. On the other hand, if the measured Q value is larger than the threshold value or is approximately the same, it determines that there is no foreign object present or that the possibility of a foreign object present is low. In this way, it becomes possible to set a threshold value for each power transmission of the power transmission device 402, enabling more accurate foreign object detection.

[0125] [Basic processing of the power receiving device 401 and the power transmitting device 402] The basic processing flow of the power receiving device 401 and the power transmitting device 402 for executing the above-mentioned content will be explained with reference to the flowchart of the power receiving device 401 in Figure 10 and the flowchart of the power transmitting device 402 in Figure 11. The flowcharts in Figures 10(a) and 11(a) relate to the information exchange process that takes place in the Negotiation phase between the power transmitting device 402 and the power receiving device 401 in order to perform foreign object detection using the waveform attenuation method. The flowcharts in Figures 10(b) and 11(b) relate to the process of requesting foreign object detection using the waveform attenuation method with respect to the RP.

[0126] Figure 10(a) is a flowchart showing an example of a basic processing procedure in the Negotiation phase by a power receiving device ideal for foreign object detection using the waveform attenuation method. In this embodiment, it is also possible to support a power receiving device that sends a command notifying the end of the Negotiation phase before sending a minimum power control period request command or a maximum power control period notification command. The processing procedure for such a power receiving device will be described later with reference to Figures 12 and 14.

[0127] First, in S1001, the control unit 201 of the power receiving device 401 sends a minimum power transmission control period request command to the power transmitting device 402. Here, the command transmission process in the power receiving device 401 can be achieved by the control unit 201 sending the request command via the communication unit 204. Then, in S1002, the control unit 201 waits until it receives a response from the power transmitting device 402. The reception of the response in the power receiving device 401 can be achieved by the control unit 201 polling the communication unit 204, or by the communication unit 204 raising an interrupt to the control unit 201. The received response is then transferred to and stored in the memory 208.

[0128] Upon receiving a response from the power transmission device 402, in S1003, the control unit 201 saves the information contained in the response regarding the minimum power transmission control period that can be generated by the power transmission device 402. In S1004, the control unit 201 sends a maximum power transmission control period notification command to the power transmission device 402. Then, in S1005, the control unit 201 waits until it receives a response from the power transmission device 402. The implementation method for these processes is the same as in S1001 and S1002.

[0129] Here, there are several methods for setting the maximum transmission power control period that the power receiving device 401 can handle. The maximum transmission power control period is the maximum value of the transmission power control period that the power receiving device 401 can tolerate. This maximum value indicates how long the power receiving device 401 will not consider the power transmission to have been stopped if it is temporarily stopped due to foreign object detection by the waveform attenuation method, and it is a value that can change depending on various conditions of the power receiving device 401.

[0130] One possible method is to set a predetermined fixed value as the maximum period of power transmission control that the power receiving device 401 can handle. It is also possible to set a predetermined value based on the specifications of the modules involved in power receiving, such as the power receiving unit 203, the power receiving antenna 205, the second switch unit 210, and the resonant capacitor 211.

[0131] As a second method, a value calculated from the operating mode of the power receiving device 401 and its dependence on the power receiving power source, taking into account power consumption, may be set as the maximum transmission power control period that the power receiving device 401 can handle. For example, if the battery 207 is removed and the power receiving device 401 is operating solely on power received via wireless power transmission, if the period of power transmission being stopped is long, the power stored in the resonant capacitor 211 will be consumed, leading to a power loss. In this situation, if the operating mode of the power receiving device 401 is high load mode, the time during which power is lost from the resonant capacitor 211 during the transmission power control period will be shorter, and consequently, the allowable transmission power control period will also be shorter. In such cases where the power receiving device 401 is highly dependent on the power receiving power, the smallest possible value should be selected as the maximum transmission power control period. Furthermore, if the battery 207 is installed and there is sufficient reserve power, and the degree of dependence on the received power is not very high, a large value is selected as the maximum period for power transmission control to improve the reliability of foreign object detection using the waveform attenuation method. In this way, it is also possible to set the maximum period for power transmission control considering the operating mode of the power receiving device 401 and the degree of dependence on the power receiving power, taking into account the power consumption.

[0132] Upon receiving a response from the power transmission device 402, in S1006, the control unit 201 transmits other commands necessary for the Negotiation phase to the power transmission device 402. These commands include commands related to the GP requested by the power receiving device 401, and commands necessary for executing foreign object detection processing using the Q-value measurement method. Then, in S1007, the control unit 201 waits until it receives a response to the transmitted commands.

[0133] Upon receiving a response from the power transmission device 402, in S1008, the control unit 201 determines whether the command sent in S1006 was a command notifying the end of the Negotiation phase. If the result of this determination is that the command notifying the end of the Negotiation phase is indeed a command, this flowchart is terminated. Otherwise, the process returns to S1006, and the control unit 201 sends the next command required in the Negotiation phase.

[0134] Figure 11(a) is a flowchart illustrating an example of the basic processing procedure of a power transmission device during the Negotiation phase. The processing shown in Figure 11(a) assumes that a minimum power control period request command and a maximum power control period notification command are sent from the power receiving device, followed by a command notifying the end of the Negotiation phase. The power transmission device 402 according to this embodiment can also handle cases where a command notifying the end of the Negotiation phase is sent before the minimum power control period request command or the maximum power control period notification command is sent, but the processing procedure for that will be described later. Figure 11(a) illustrates the basic processing of the power transmission device during the Negotiation phase for foreign object detection using the waveform attenuation method.

[0135] First, in S1101, the power transmission device waits until it receives a command from the power receiving device. Receiving a command in the power transmission device may be achieved by the control unit polling the communication unit, or by the communication unit raising an interrupt to the control unit. The received command is then transferred to and stored in memory.

[0136] Upon receiving a command from the power receiving device, in S1102, the power transmitting device determines whether the received command is a minimum power transmission control period request command. If the result of this determination is that the received command is a minimum power transmission control period request command, the process proceeds to S1103.

[0137] In S1103, the power transmission device sets the minimum power transmission control period that it can generate and generates a response containing that information. In this process, the control unit interprets the command held in memory and generates the corresponding response in memory. The minimum power transmission control period set here may be a fixed value for the power transmission device, or it may be determined in consideration of the method for determining the power transmission control period, as described above. For example, the minimum power transmission control period that the power transmission device can generate may be set based on the relationship between the power transmitted from the power transmission device and the power transmission control period.

[0138] On the other hand, if the result of the determination in S1102 is that the received command is not a minimum power transmission period request command, then in S1106, the power transmission device determines whether the received command is a maximum power transmission period notification command. If the result of this determination is that the received command is a maximum power transmission period notification command, the process proceeds to S1107.

[0139] In S1107, the power transmission device obtains the maximum power transmission period from the received command and stores this information in memory. Then, in S1108, the power transmission device generates a response to the power transmission maximum period notification command.

[0140] On the other hand, if the result of the determination in S1106 is that the received command is not a command notifying the maximum period of power transmission control, then in S1109 the power transmission device determines whether the command received in S1101 is a command notifying the end of the Negotiation phase. If the result of this determination is that it is a command notifying the end of the Negotiation phase, the process proceeds to S1110.

[0141] In S1110, the power transmission unit activates the Negotiation phase termination flag. This process can be achieved by the control unit setting information in a predetermined area of ​​memory. Then, in S1111, the power transmission unit generates a response to the command notifying the termination of the Negotiation phase.

[0142] On the other hand, if the result of the determination in S1109 is that the received command is not a command that notifies the end of the Negotiation phase, then in S1112 the power transmission device performs processing according to the received command. For example, if the received command is a command related to GP, the power transmission device determines the value of GP based on the GP value requested by the power receiving device and the power transmission capacity of the power transmission device. Also, if the received command is an FOD Status Packet containing information on Reference Quality Factor Value, the power transmission device adjusts the threshold in the Q value measurement method to determine the final threshold. Then, in S1113, the power transmission device generates a response according to the received command.

[0143] In S1104, the power transmission device sends the generated response to the power receiving device. Then, in S1105, the power transmission device determines whether the Negotiation phase termination flag is valid or not. The determination of the termination flag can be achieved by the control unit checking the information held in memory. If the Negotiation phase termination flag is valid as a result of this determination, this flowchart is terminated. On the other hand, if the Negotiation phase termination flag is invalid, the process returns to S1101.

[0144] Next, we will explain the process of requesting foreign object detection using the waveform attenuation method with various Received Power Packets based on the results of the Negotiation phase described above. The power receiving device 401 requests foreign object detection using the waveform attenuation method by adding information about the power transmission control period as an argument to various RP packets (RP0, RP1, RP2). In other words, foreign object detection using the waveform attenuation method can only be performed during the Calibration phase or the Power Transfer phase, when RP packets can be transmitted.

[0145] Figure 10(b) is a flowchart showing an example of the processing procedure for detecting foreign objects using the waveform attenuation method in the power receiving device 401. First, in S1009, the control unit 201 of the power receiving device 401 determines whether the maximum power transmission control period that the power receiving device 401 can handle is greater than or equal to the minimum power transmission control period that the power transmission device 402 can generate. This process can be achieved by the control unit 201 checking the maximum power transmission control period in the response held in memory 208 and comparing it with the information on the maximum power transmission control period for the power receiving device 401, also held in memory 208. If the result of this determination does not satisfy the condition of being greater than or equal to the minimum power transmission control period that the power transmission device 402 can generate, the process proceeds to S1010. On the other hand, if the condition of being greater than or equal to the minimum power transmission control period that the power transmission device 402 can generate is satisfied, the process proceeds to S1011.

[0146] In S1010, the control unit 201 sets the power transmission control period to be set in the RP packet to zero. This means that foreign object detection using the waveform attenuation method will not be performed. On the other hand, in S1011, the control unit 201 sets a value selected from the available power transmission control periods as the power transmission control period and stores that value in the memory 208.

[0147] The usable power transmission control period here is, as mentioned above, any value between the minimum power transmission control period that can be generated by the power transmission device 402 and the maximum power transmission control period that the power receiving device 401 can handle. There are several methods for selecting the power transmission control period.

[0148] One method is to uniformly determine the maximum, minimum, and median values ​​of the selected range according to predetermined rules. Another method is to select a value calculated from the operating mode of the power receiving device 401 and its dependence on the power receiving power source, taking into account its power consumption. As mentioned above, if the battery 207 is removed and the device is operating solely on power received via wireless power transmission, the smallest possible value will be selected as the maximum power transmission control period, and consequently, the allowable power transmission control period will also be shorter. Thus, if the power receiving device 401 has a high dependence on the power receiving power, the smallest possible value should be selected. On the other hand, if the battery 207 is installed and there is sufficient stored energy, and the dependence on the power receiving power is not so high, a larger value can be selected as the maximum power transmission control period, and therefore a larger power transmission control period can also be selected. In this way, it is also possible to select the power transmission control period by considering the operating mode of the power receiving device 401 and its dependence on the power receiving power source, taking into account its power consumption.

[0149] Next, in S1012, the control unit 201 generates an RP packet with the information of the power transmission control period determined in S1010 or S1011 as an argument and sends it to the power transmission device 402. Then, in S1013, the control unit 201 waits until it receives an ACK response from the power transmission device 402. If it does not receive an ACK response after waiting for a predetermined period, it returns to S1012 and retransmits the RP packet. Similarly, if it receives an ND (No Decision) response from the power transmission device 402 (as described later), it returns to S1012 and retransmits the RP packet.

[0150] If an ACK response is received from the power transmission device 402, in S1014 the control unit 201 processes the notification of foreign object detection. Then, in S1015, the control unit 201 determines, based on the received notification of foreign object detection, whether a foreign object is present or whether there is a high probability of a foreign object being present. If the result of this determination indicates that a foreign object is present or there is a high probability of a foreign object being present, the process proceeds to S1016; otherwise, this flowchart ends.

[0151] In S1016, the control unit 201 performs a predetermined process in response to the presence of a foreign object, and then terminates this flowchart. Examples of predetermined processes in response to the presence of a foreign object include issuing a warning to the user and stopping wireless power transmission.

[0152] Figure 11(b) is a flowchart showing an example of a processing procedure for detecting foreign objects using the waveform attenuation method in the power transmission device 402. First, in S1114, the control unit 101 of the power transmission device 402 checks whether the received RP packet contains information about the power transmission control period. If the RP packet does not contain information about the power transmission control period, then foreign object detection using the waveform attenuation method is not required, and the process proceeds to S1120, which will be described later. On the other hand, if the RP packet contains information about the power transmission control period, the process proceeds to S1115.

[0153] Next, in S1115, the control unit 101 checks whether the power transmission control period in the received RP packet is zero. If the power transmission control period is zero as a result of this check, it means that foreign object detection using the waveform attenuation method will not be performed, and the process proceeds to S1120, which will be described later. On the other hand, if the power transmission control period is not zero, the process proceeds to S1116.

[0154] Next, in S1116, the control unit 101 (power transmission control unit 302) starts stopping power transmission for foreign object detection using the waveform attenuation method, according to the acquired information on the power transmission control period. Then, in S1117, the control unit 101 (foreign object detection unit 305) performs foreign object detection using the waveform attenuation method described above.

[0155] Next, in S1118, the control unit 101 determines whether or not the probability of foreign object presence has been determined. There are several ways to determine the probability of foreign object presence. For example, if the power transmission unit 103 has a function to calculate the probability of foreign object presence from the results of foreign object detection by waveform attenuation, the control unit 101 can obtain this information to determine the probability of foreign object presence. If such a function is not available, the probability of foreign object presence may be calculated from the statistical results after repeating foreign object detection by waveform attenuation several times. In this case, the results of foreign object detection by waveform attenuation can be stored in the memory 106 and statistically analyzed by the control unit 101. However, if the number of repetitions of foreign object detection by waveform attenuation is small, the probability of foreign object presence cannot be determined, so it is necessary to have the power receiving device 401 resend the RP packet each time foreign object detection by waveform attenuation is performed.

[0156] If the determination in S1118 does not determine the probability of the presence of a foreign object, in S1119, the control unit 101 sends an ND (No Decision) response to the power receiving device 401 to request that the RP packet be retransmitted. Then, it returns to S1114 and waits for the retransmitted RP packet. On the other hand, if the determination in S1118 determines the probability of the presence of a foreign object, the process proceeds to S1120.

[0157] In S1120, the control unit 101 processes the corresponding RP packet. Then, in S1121, it sends an ACK as a response to the power receiving device 401. Subsequently, in S1122, the control unit 101 determines whether or not foreign object detection using the waveform attenuation method was performed in S1117. If the result of this determination is that foreign object detection using the waveform attenuation method was not performed, this flowchart is terminated. On the other hand, if foreign object detection using the waveform attenuation method was performed, in S1123, the control unit 101 sends a foreign object detection result notification, including information such as the probability of foreign object presence, to the power receiving device 401, and this flowchart is terminated.

[0158] The above describes the basic processes performed in foreign object detection using the waveform attenuation method. In the flowchart in Figure 10(a), the instructions explain that the minimum power transmission period request command is sent in S1001, followed by the maximum power transmission period notification command in S1004, but the order may be reversed.

[0159] [Exception handling for power receiving device 401 and power transmitting device 402] Next, assuming that the basic process of foreign object detection using the waveform attenuation method described in Figures 10(a) and 11(a) is the normal process, the exceptional process in the Negotiation phase in this embodiment will be described. As mentioned above, in the Negotiation phase, the receiving device basically sends a minimum power control period request command and a maximum power control period notification command, and then sends a command notifying the end of the Negotiation phase. On the other hand, the WPC standard allows the receiving device to request the end of the Negotiation phase at any time, even if the exchange of commands related to foreign object detection using the waveform attenuation method is not yet complete. In other words, depending on the type of receiving device installed on the power transmission device, there may be situations where, for example, a command notifying the end of the Negotiation phase is sent before the maximum power control period notification command is sent. Also, if the transmission order of the minimum power control period request command and the maximum power control period notification command is reversed, there may be situations where a command notifying the end of the Negotiation phase is sent before the minimum power control period request command is sent. In this embodiment, the processing procedures in the power transmission device 402 and the power receiving device 401 in such a situation will be explained below using the flowcharts in Figures 12 and 13.

[0160] Figure 13 is a flowchart showing an example of the processing procedure of the power transmission device 402 during the Negotiation phase in this embodiment. Note that each process shown in Figure 13 is performed by the control unit 101 of the power transmission device 402, and the processes S1301 to S1309 in Figure 13 are the same as S1101 to S1109 in Figure 11, so their explanation is omitted.

[0161] If the result of the determination in S1309 is that the received command is a command notifying the end of the Negotiation phase, the process proceeds to S1310. In S1310, the control unit 101 checks whether the exchange of commands necessary for performing foreign object detection using the waveform attenuation method has been completed. The control unit 101 of the power transmission device 402 records the history of the exchange of commands necessary for foreign object detection using the waveform attenuation method in the memory 106, and by checking the history, it is possible to check whether there are any missing commands. In this embodiment, the commands necessary for foreign object detection using the waveform attenuation method are the power transmission power control minimum period request command and the power transmission power control maximum period notification command. If the result of the check in S1310 is that the exchange of commands necessary for performing foreign object detection using the waveform attenuation method has been completed, the process proceeds to S1311. The processing in S1311 and S1312 is the same as S1110 and S1111 in Figure 11, respectively.

[0162] On the other hand, if the confirmation in S1310 indicates that the necessary command exchange for performing foreign object detection using the waveform attenuation method has not been completed, the process proceeds to S1313. In S1313, the control unit 101 generates a message requesting the power receiving device 401 to make an inquiry. This message conveys that the power transmission device 402 intends to initiate communication with the power receiving device 401 and requests the power receiving device 401 to send an inquiry command. This message may also include information indicating that the exchange of the minimum power transmission period request command or the maximum power transmission period notification command has not been completed.

[0163] On the other hand, if the result of the determination in S1309 is that the received command is not a command that notifies the end of the Negotiation phase, the process proceeds to S1314. In S1314, the control unit 101 determines whether the command received in S1301 is an inquiry command. If the result of this determination is that the received command is not an inquiry command, the process proceeds to S1316. The processing in S1316 and S1317 is the same as S1112 and S1113 in Figure 11, respectively.

[0164] On the other hand, if the result of the determination in S1314 indicates that the received command is an inquiry command, the process proceeds to S1315. In S1315, the control unit 101 generates a message requesting the transmission of a command whose exchange has not been completed. Specifically, it generates a message requesting the transmission of either a minimum power transmission control period request command or a maximum power transmission control period notification command.

[0165] Figure 12 is a flowchart showing an example of an exceptional processing procedure performed by the power receiving device 401 during the Negotiation phase in this embodiment. Below, an example will be described in which the power receiving device 401 sends a command notifying the end of the Negotiation phase before sending the maximum power transmission period notification command. Note that the processing from S1201 to S1203 in Figure 12 is the same as the processing from S1001 to S1003 in Figure 10(a). Also, the processing from S1204 to S1206 in Figure 2 is the same as the processing from S1006 to S1008.

[0166] If the result of the determination in S1206 is that the command sent in S1204 is a command notifying the end of the Negotiation phase, the process proceeds to S1207. In S1207, the control unit 201 checks whether the response received in S1205 is a message requesting an inquiry command. If the result of this check is that the received response is not a message requesting an inquiry command, it can be considered a response to a command notifying the end of the Negotiation phase, and the Negotiation phase ends there.

[0167] On the other hand, if the confirmation in S1207 indicates that the received response is a message requesting an inquiry command, the process proceeds to S1208. In S1208, the control unit 201 sends an inquiry command to the power transmission unit 402. This process can be achieved by the control unit 201 writing the inquiry command to the communication unit 204. Then, in S1209, the control unit 201 waits until it receives a response to the inquiry command.

[0168] When a response is received from the power transmission device 402, in S1210, the control unit 201 checks whether the received response is a message requesting the transmission of a power transmission power control maximum period notification command. If the result of this check is that the received response is a message requesting the transmission of a power transmission power control maximum period notification command, the process proceeds to S1211. The processing in S1211 and S1212 is the same as S1004 and S1005 in Figure 10(a), respectively. When a response is received from the power transmission device 402 in S1212, the process returns to S1204, but essentially it has responded to the inquiry from the power transmission device 402. Therefore, in S1204, the control unit 201 may resend a command notifying the end of the negotiation phase. On the other hand, if the result of the check in S1210 is that the received response is not a message requesting the transmission of a power transmission power control maximum period notification command, the process proceeds to S1213. Then, in S1213, the control unit 201 performs processing corresponding to the content of the message, and then returns to S1204.

[0169] Figure 14 is a flowchart showing another example of an exceptional processing procedure performed by the power receiving device 401 during the Negotiation phase in this embodiment. Below, we will describe an example in which the power receiving device 401 sends a command notifying the end of the Negotiation phase before sending the minimum power transmission period request command. The processes S1401 and S1402 in Figure 14 are the same as S1004 and S1005 in Figure 10, respectively. Also, the processes S1403 to S1408 in Figure 14 are the same as S1204 to S1209 in Figure 12, respectively.

[0170] When a response is received from the power transmission device 402 in S1408, in S1409 the control unit 201 checks whether the received response is a message requesting the transmission of a minimum power transmission control period request command. If the result of this check is that the received response is a message requesting the transmission of a minimum power transmission control period request command, the process proceeds to S1410. The processing in S1410 to S1412 is the same as S1001 to S1003 in Figure 10(a), respectively. After saving the information on the minimum power transmission control period that can be generated by the power transmission device 402, which is included in the response in S1412, the process returns to S1403, but essentially this means that the inquiry from the power transmission device 402 has been addressed. Therefore, in S1403, the control unit 201 may resend a command notifying the end of the negotiation phase. On the other hand, if the result of the check in S1409 is that the received response is not a message requesting the transmission of a minimum power transmission control period request command, the process proceeds to S1413. Then, in S1413, the control unit 201 performs processing corresponding to the content of the message, and then returns to S1403.

[0171] As described above, this embodiment can also handle cases where a command notifying the end of the Negotiation phase is sent before the exchange of commands necessary to perform foreign object detection using the waveform attenuation method is completed in the Negotiation phase. Specifically, the power transmission device 402 sends a message requesting an inquiry, and in response to that inquiry command, it sends a message requesting the transmission of any missing commands. This allows communication to continue even when a command notifying the end of the Negotiation phase is sent, and the exchange of commands necessary to perform foreign object detection using the waveform attenuation method can be completed. In this way, this embodiment can reliably establish an environment in which it is possible to correctly determine whether or not to perform foreign object detection using the waveform attenuation method.

[0172] In the example shown in Figure 13, if the receiving device 401 sends a command notifying the end of the Negotiation phase before the transmission power control minimum period request command is sent, the transmission device 402 sends a message requesting an inquiry. Alternatively, to shorten subsequent processing, instead of sending a message requesting an inquiry, the transmission device 402 may set a minimum transmission power control period that it can generate and directly send a response containing that information. In this case, in S1313 of Figure 13, the transmission device 402 performs the same processing as in S1303 and enables the Negotiation phase end flag instead of generating a message requesting an inquiry. The receiving device 401 also considers the response containing the information on the minimum transmission power control period sent from the transmission device 402 as a response to the command notifying the end of the Negotiation phase. The control unit 201 then saves the information on the minimum transmission power control period and terminates the processing shown in Figure 14.

[0173] Furthermore, if the receiving device 401 does not send either a minimum power control period request command or a maximum power control period notification command, but instead sends a command notifying the end of the Negotiation phase, the transmission device 402 will basically follow the processing procedure shown in Figure 13. In this case, a message is generated requesting that both the minimum power control period request command and the maximum power control period notification command be sent in response to a single query command.

[0174] Furthermore, in the power receiving device 401, based on the processing procedure in Figure 14, processing begins from S1403. Then, after saving the minimum transmission power period in S1412, processing in S1401 and S1402 is performed, and the process returns to S1403.

[0175] Furthermore, in this embodiment, the power transmission device 402 continued communication in the Negotiation phase by sending a message requesting an inquiry. However, depending on the type of power receiving device, it may intentionally send a command notifying the end of the Negotiation phase while one of the commands has not been executed. In such a power receiving device, even if the power transmission device 402 sends a message requesting an inquiry, it may refuse to continue communication and send another command notifying the end of the Negotiation phase. As a result, the exchange between the command notifying the end of the Negotiation phase and the message requesting an inquiry is repeated, resulting in a situation that never ends.

[0176] Therefore, to address such situations, the control unit 101 of the power transmission device 402 may record in memory 106 the number of times it has generated a message requesting an inquiry in S1313. Then, after the number of times the message requesting an inquiry has been generated reaches a predetermined number, it forcibly enables the Negotiation phase termination flag. This prevents the exchange between the command notifying the end of the Negotiation phase and the message requesting an inquiry from continuing indefinitely.

[0177] (Other embodiments) In the embodiment described above, the power transmission device 402 performed power transmission control and detected foreign matter from its waveform attenuation index. Another method for measuring the Q value, which is one of the waveform attenuation indices, is to transmit a signal having multiple frequency components (e.g., a pulse wave), measure the amplitude or attenuation state of the waveform, and perform calculation processing (e.g., Fourier transform) on the results to measure the Q value. This method can also be applied to the embodiment described above.

[0178] This disclosure can also be implemented by supplying a program that implements one or more of the functions of the embodiments described above 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 implemented by a circuit (e.g., an ASIC) that implements one or more functions. [Explanation of Symbols]

[0179] 101 Control unit, 104 Communication unit

Claims

1. A power transmitting means for wirelessly transmitting power to a power receiving device; A detection means for performing a process for detecting a foreign object; a communication means for transmitting a request to continue the negotiation to the power receiving device when the power receiving device requests the end of the negotiation regarding the detection process before the end of the negotiation; A power transmitting device comprising:

2. The communication means includes: requesting transmission of an inquiry command as a request to continue the negotiation; The power transmitting device according to claim 1 , further comprising: a transmission request for information lacking for performing the detection process, which is transmitted to the power receiving device in response to the inquiry command.

3. A power transmission device as described in claim 1 or 2, characterized in that the detection process is a process of detecting the foreign object based on a quality coefficient measured during a period in which the power transmission is restricted.

4. The power transmission device described in Claim 3, characterized in that the communication means transmits to the power receiving device a request to send a command requesting a minimum value for the period for limiting the power transmission when the power receiving device requests termination of the negotiation before receiving a command from the power receiving device requesting a minimum value for the period for limiting the power transmission.

5. The power transmission device described in Claim 3 or 4, characterized in that the communication means transmits to the power receiving device a request to send a command notifying the maximum value of the period for limiting the power transmission when the power receiving device requests termination of the negotiation before receiving a command from the power receiving device notifying the maximum value of the period for limiting the power transmission.

6. A power transmission device as described in any one of claims 1 to 5, characterized in that the communication means transmits a response to the power receiving device indicating acceptance of a request to terminate the negotiation from the power receiving device when the number of times a request to continue the negotiation has been sent to the power receiving device reaches a predetermined number.

7. A method performed by a power transmission device, comprising: A detection step of performing a foreign object detection process; a request step of making a request to the power receiving device to continue the negotiation when the power receiving device requests the end of the negotiation before the end of the negotiation regarding the detection process; The method according to claim 1, further comprising:

8. A program for causing a computer to execute the method according to claim 7.

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