Power transmission device and power reception device

Abstract

This power transmission device wirelessly transmits power and has: a receiving means for receiving, from a power reception device, a received power value and a request for calculating a Q-value; a stopping means for stopping voltage applied to a power transmission coil; a calculation means for calculating the Q-value on the basis of the aging variation of the electric characteristics of the power transmission coil during stopping period; and a transmission means for, when the aging variation of the electric characteristics of the power transmission coil during the stopping period decreases monotonically, transmitting, to the power reception device, whether or not to use the received power value to detect an object different from the power reception device on the basis of the Q-value calculated by the calculation means and for, when the aging variation of the electric characteristics of the power transmission coil during the stopping period does not decrease monotonically, transmitting, to the power reception device, a notification indicating that it is not determined whether or not to use the received power value to detect the object.

Description

Power transmitting device and power receiving device

[0001] The present disclosure relates to a power transmitting device, a power receiving device, a control method, and a program.

[0002] The Wireless Power Consortium (WPC) has established a standard for wireless charging called the WPC standard, which is widely known. In such a wireless power transmission system, when an object (foreign object) other than the power receiving device is present within a range where a power transmitting device can transmit power, it is essential to detect the foreign object and control power transmission and reception.

[0003] Patent Literature 1 describes a technology for detecting a foreign object near a power transmitting / receiving device that complies with the WPC standard and restricting power transmission / reception. Patent Literature 2 discloses a technology for detecting a foreign object by short-circuiting a coil in a wireless power transmission system. Patent Literature 3 describes a technology for detecting a foreign object by measuring a change in the quality factor (Q factor) of a power transmitting coil of a wireless power transmission system by applying a high-frequency signal to the power transmitting coil for a certain period of time.

[0004] JP 2017-70074 A JP 2017-34972 A JP 2017-22999 A

[0005] An object of the present disclosure is to enable a power transmitting device to detect an object different from a power receiving device with high accuracy.

[0006] The power transmitting device is a power transmitting device that transmits power wirelessly, and has a receiving means that receives a request to calculate a Q value and a received power value from the power receiving device, a stopping means that stops the voltage applied to the power transmitting coil, a calculation means that calculates the Q value based on changes over time in the electrical characteristics of the power transmitting coil when stopped, and a transmitting means that, if the changes over time in the electrical characteristics of the power transmitting coil when stopped are monotonically decreasing, transmits to the power receiving device whether or not to use the received power value for detecting an object other than the power receiving device based on the Q value calculated by the calculation means, and, if the changes over time in the electrical characteristics of the power transmitting coil when stopped are not monotonically decreasing, transmits to the power receiving device a notification indicating that it will not determine whether or not to use the received power value for detecting the object.

[0007] According to the present disclosure, it is possible to enable a power transmitting device to detect an object different from a power receiving device with high accuracy.

[0008] 1 is a diagram illustrating an example of the configuration of a wireless power transmission system. FIG. 2 is a diagram illustrating an example of the hardware configuration of a power receiving device. FIG. 3 is a diagram illustrating an example of the hardware configuration of a power transmitting device. FIG. 4 is a diagram illustrating an example of the functional configuration of a power transmitting device. FIG. 5 is a diagram illustrating an example of the functional configuration of a power receiving device. FIG. 6 is a sequence diagram illustrating the operation of a power transmitting device and a power receiving device. FIG. 7 is a flowchart of a second Q-value measurement process. FIG. 8 is a flowchart of a second Q-value measurement process. FIG. 9 is a flowchart of a third foreign object detection process. FIG. 10 is a flowchart of a third foreign object detection process. FIG. 11 is a diagram illustrating a determination in the third foreign object detection process. FIG. 12 is a flowchart of a power receiving device. FIG. 13 is a diagram illustrating a method for measuring a Q-value in the time domain. FIG. 14 is a diagram illustrating a method for measuring a Q-value in the time domain. FIG. 15 is a diagram illustrating a method for measuring a Q-value in the time domain. FIG. 16 is a diagram illustrating foreign object detection by a power loss method.

[0009] Hereinafter, embodiments will be described with reference to the drawings. Note that the following embodiments do not limit the scope of the claims. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential, and multiple features may be combined arbitrarily. Furthermore, in the drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] [First Embodiment] (System Configuration) Fig. 1 is a diagram illustrating an example of the configuration of a wireless power transmission system 102 according to a first embodiment. In one example, the wireless power transmission system 102 includes a power transmission device 100 and a power receiving device 101. The power transmission device 100 and the power receiving device 101 comply with the Wireless Power Consortium (WPC) standard. The power transmission device 100 is, for example, an electronic device that wirelessly transmits power to a power receiving device 101 placed on the power transmission device 100. The power transmission device 100 wirelessly transmits power to the power receiving device 101 via a power transmission coil. The power receiving device 101 is, for example, an electronic device that receives power from the power transmission device 100 and charges a built-in battery. In addition, the power transmitting device 100 and the power receiving device 101 may be built into other devices (cameras, smartphones, tablet PCs, laptops, automobiles, robots, medical equipment, printers) and supply power to these devices.

[0011] The power receiving device 101 and the power transmitting device 100 may have a function for executing applications other than wireless charging. An example of the power receiving device 101 is an information processing terminal such as a smartphone, and an example of the power transmitting device 100 is an accessory device for charging the information processing terminal. For example, the information terminal device has a display unit (display) that displays information to a user and receives power from a receiving coil (antenna). Furthermore, the power received from the receiving coil is stored in a power storage unit (battery), and power is supplied from the battery to the display unit. In this case, the power receiving device 101 may have a communication unit that communicates with other devices different from the power transmitting device 100. The communication unit may be compatible with communication standards such as NFC communication or the fifth-generation mobile communication system (5G). In this case, the communication unit may communicate by receiving power from the battery. Furthermore, the power receiving device 101 may be a tablet terminal, a storage device such as a hard disk drive or a memory device, or an information processing device such as a personal computer (PC). The power receiving device 101 may be, for example, an imaging device (such as a camera or a video camera). The power receiving device 101 may be an image input device such as a scanner, or an image output device such as a printer, a copier, or a projector. The power receiving device 101 may be a robot, a medical device, or the like. The power transmitting device 100 may be a device for charging the above-mentioned devices.

[0012] The power transmitting device 100 may be a smartphone. In this case, the power receiving device 101 may be another smartphone or a wireless earphone.

[0013] The power receiving device 101 in this embodiment may also be a vehicle such as an automobile. For example, the automobile serving as the power receiving device 101 may receive power from a charger (power transmitting device 100) via a power transmitting antenna installed in a parking lot. The automobile serving as the power receiving device 101 may also receive power from the charger (power transmitting device 100) via a power transmitting coil (antenna) embedded in the road. In such an automobile, the received power is supplied to a battery. The battery power may be supplied to a driving unit (motor, electric unit) that drives the wheels, or may be used to drive a sensor used for driving assistance or a communication unit that communicates with an external device. In other words, in this case, the power receiving device 101 may include, in addition to the wheels, a battery, a motor or sensor that is driven using the received power, and even a communication unit that communicates with devices other than the power transmitting device 100. Furthermore, the power receiving device 101 may have a storage unit for accommodating a person. For example, the sensor may be a sensor used to measure the distance between vehicles or the distance to other obstacles. The communication unit may be compatible with, for example, the Global Positioning System (GPS). The communication unit may also be compatible with communication standards such as the fifth generation mobile communication system (5G). The vehicle may also be a bicycle or a motorcycle. The power receiving device 101 is not limited to a vehicle, and may also be a moving object or an aircraft having a power generating unit that is driven using power stored in a battery.

[0014] Furthermore, the power receiving device 101 in this embodiment may be an electric tool, a home appliance, or the like. These devices, which are the power receiving device 101, may have a battery and a motor that is driven by the received power stored in the battery. These devices may also have a notification means that notifies the user of the remaining battery charge, etc. These devices may also have a communication unit that communicates with other devices different from the power transmitting device 100. The communication unit may be compatible with communication standards such as NFC and the fifth generation mobile communication system (5G).

[0015] Furthermore, the power transmission device 100 in this embodiment may be an in-vehicle charger that transmits power to a mobile information terminal device, such as a smartphone or tablet, that supports wireless power transmission within the vehicle. Such an in-vehicle charger may be installed anywhere within the vehicle. For example, the in-vehicle charger may be installed in the console of the vehicle, on the instrument panel (instrument panel, dashboard), between passenger seats, on the ceiling, or in the door. However, it is preferable that the charger not be installed in a location that interferes with driving. Furthermore, although the power transmission device 100 has been described as an example of an in-vehicle charger, such a charger is not limited to being installed in a vehicle, but may also be installed in transportation vehicles such as trains, airplanes, and ships. In this case, the charger may also be installed between passenger seats, on the ceiling, or in the door.

[0016] Furthermore, a vehicle such as an automobile equipped with an on-board charger may be the power transmitting device 100. In this case, the power transmitting device 100 has wheels and a battery, and supplies power to the power receiving device 101 via a power transmitting circuit unit and a power transmitting coil (antenna) using power from the battery.

[0017] 2 is a diagram illustrating an example of the hardware configuration of the power receiving device 101. The power receiving device 101 includes, for example, a control unit 200, a power receiving coil 201, a rectification unit 202, a voltage control unit 203, a communication unit 204, a charging unit 205, a battery 206, a resonance capacitor 207, and a switch 208.

[0018] The control unit 200 controls the entire power receiving device 101. The control unit 200 has one or more processors, such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The control unit 200 may also include one or more storage devices, such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The control unit 200 performs each process described below by, for example, executing a program stored in the storage device using the processor.

[0019] The receiving coil 201 is a coil used when receiving power from the transmitting coil 303 ( FIG. 3 ) of the power transmitting device 100. The rectifier 202 converts the AC voltage and AC current received via the receiving coil 201 into DC voltage and DC current. The voltage control unit 203 converts the level of the DC voltage input from the rectifier 202 to a DC voltage level appropriate for the operation of the control unit 200, the charging unit 205, and the like (neither too high nor too low). The voltage control unit 203 also supplies the converted voltage to the charging unit 205. The charging unit 205 charges the battery 206 with the voltage supplied from the voltage control unit 203. The communication unit 204 performs wireless charging control communication with the power transmitting device 100 based on the WPC standard. This control communication is performed by load modulation of the AC voltage and AC current received by the receiving coil 201.

[0020] Furthermore, receiving coil 201 is connected to resonant capacitor 207 and is configured to resonate at a specific frequency F2. Switch 208 is a switch for shorting receiving coil 201 and resonant capacitor 207, and is controlled by control unit 200. When switch 208 is turned on, receiving coil 201 and resonant capacitor 207 form a series resonant circuit. At this time, current flows only through the closed circuit of receiving coil 201, resonant capacitor 207, and switch 208, and no current flows through rectifier unit 202 or voltage control unit 203. On the other hand, when switch 208 is turned off, current flows through rectifier unit 202 and voltage control unit 203 via receiving coil 201 and resonant capacitor 207.

[0021] 3 is a diagram illustrating an example of the hardware configuration of the power transmitting device 100. The power transmitting device 100 includes, for example, a control unit 300, a power supply unit 301, a power transmitting unit 302, a power transmitting coil 303, a communication unit 304, a memory 305, a resonant capacitor 306, and a switch 307.

[0022] The control unit 300 controls the entire power transmission device 100. The control unit 300 has one or more processors, such as a CPU or an MPU. The control unit 300 performs each process described below by, for example, executing a program stored in a memory 305 (described below) or a storage device built into the control unit 300 using the processor. The power supply unit 301 supplies a power supply voltage to each component. The power supply unit 301 is, for example, a commercial power supply or a battery. The battery stores power supplied from the commercial power supply, for example.

[0023] The power transmitting unit 302 converts DC power or AC power input from the power supply unit 301 into AC power in a frequency band used for wireless power transmission and inputs the AC power to the power transmitting coil 303. This causes the power transmitting coil 303 to generate electromagnetic waves for receiving power at the power receiving device 101. For example, the power transmitting unit 302 converts the DC voltage supplied from the power supply unit 301 into an AC voltage using a half-bridge or full-bridge switching circuit that uses FETs (Field Effect Transistors). In this case, the power transmitting unit 302 includes a gate driver that controls the on / off of the FETs. The power transmitting unit 302 also controls the intensity and frequency of the electromagnetic waves to be output by adjusting at least one of the voltage (power transmitting voltage) and current (power transmitting current) input to the power transmitting coil 303, or the frequency. For example, the power transmitting unit 302 increases the intensity of the electromagnetic waves by increasing the transmission voltage or the transmission current, and decreases the intensity of the electromagnetic waves by decreasing the transmission voltage or the transmission current. Here, the power transmitting unit 302 is assumed to have the capacity to supply at least 15 watts (W) of power to the charging unit 205 of the power receiving device 101 that complies with the WPC standard. Furthermore, the power transmitting unit 302 controls the output of AC power based on instructions from the control unit 300 so that the output of electromagnetic waves from the power transmitting coil 303 is started or stopped.

[0024] The communication unit 304 communicates with the power receiving device 101 via the power transmitting coil 303 for power transmission control based on the WPC standard. The communication unit 304 modulates the AC voltage and AC current output from the power transmitting unit 302 using frequency modulation (FSK (Frequency Shift Keying)) and transmits information to the power receiving device 101. The communication unit 304 also demodulates the AC voltage and AC current modulated by load modulation by the communication unit 204 of the power receiving device 101 to acquire information transmitted by the power receiving device 101. That is, the communication unit 304 superimposes information to be transmitted to the power receiving device 101 on electromagnetic waves transmitted from the power transmitting unit 302 and detects a received signal superimposed by the power receiving device 101 on the electromagnetic waves, thereby communicating with the power receiving device 101. The communication unit 304 may communicate with the power receiving device 101 according to a standard different from the WPC standard by using a coil (or antenna) different from the power transmitting coil 303. The communication unit 304 may communicate with the power receiving device 101 by selectively using a plurality of communication functions.

[0025] The memory 305 stores, for example, a control program executed by the control unit 300 and information such as the states of the power transmitting device 100 and the power receiving device 101. For example, the state of the power transmitting device 100 is acquired by the control unit 300. The state of the power receiving device 101 is acquired by the control unit 200 of the power receiving device 101 and transmitted from the communication unit 204, and the power transmitting device 100 acquires information indicating this state via the communication unit 304.

[0026] Furthermore, the power transmitting coil 303 is connected to a resonant capacitor 306 and is configured to resonate at a specific frequency F1. The switch 307 is a switch for shorting the power transmitting coil 303 and the resonant capacitor 306, and is controlled by the control unit 300. When the switch 307 is turned on, the power transmitting coil 303 and the resonant capacitor 306 form a series resonant circuit. At this time, current flows only through the closed circuit of the power transmitting coil 303, the resonant capacitor 306, and the switch 307. When the switch 308 is turned off, power is supplied from the power transmitting unit 302 to the power transmitting coil 303 and the resonant capacitor 306.

[0027] 4 is a diagram illustrating an example of the functional configuration of the power transmitting device 100. The power transmitting device 100 operates as each functional unit by the control unit 300 executing a program. The power transmitting device 100 includes a first Q-value measurement unit 400, a second Q-value measurement unit 401, a calibration processing unit 402, a first foreign object detection processing unit 403, a second foreign object detection processing unit 404, a third foreign object detection processing unit 405, and a power transmission processing unit 406. Note that, in the present disclosure, a foreign object refers to, for example, a metal piece, a paper clip, an IC card, or the like. Among objects that are integral parts of a power receiving device and a product incorporating the power receiving device, or a power transmitting device and a product incorporating the power transmitting device, objects that may unintentionally generate heat when exposed to wireless power transmitted by a power transmitting antenna are not considered foreign objects.

[0028] The first Q-value measurement unit 400 measures the Q-value in the frequency domain (first Q-value measurement) as described below. The second Q-value measurement unit 401 measures the Q-value in the time domain (second Q-value measurement) as described below. The calibration processing unit 402 acquires calibration data points and creates a calibration curve as described below. The first foreign object detection processing unit 403 performs foreign object detection processing (first foreign object detection processing) based on the first Q-value measured by the first Q-value measurement unit 400. The second foreign object detection processing unit 404 performs foreign object detection processing (second foreign object detection processing) based on a power loss method as described below. The third foreign object detection processing unit 405 performs foreign object detection processing (third foreign object detection processing) based on the second Q-value measured by the second Q-value measurement unit 401. The power transmission processing unit 406 performs processing related to starting and stopping power transmission and increasing and decreasing the transmitted power of the power transmission unit 302. Each functional unit shown in Fig. 4 is realized, for example, by a plurality of independent programs, and these programs operate in parallel while being synchronized with each other through event processing or the like.

[0029] 5 is a diagram illustrating an example of the functional configuration of the power receiving device 101. The power receiving device 101 operates as each functional unit by the control unit 200 executing a program. The power receiving device 101 has a second Q-value measurement unit 501 and a third foreign object detection processing unit 500.

[0030] The second Q-factor measurement unit 501 measures the Q-factor in the time domain (second Q-factor measurement) as described below. The third foreign object detection processing unit 500 executes foreign object detection processing (third foreign object detection processing) based on the second Q-factor measured by the second Q-factor measurement unit 501. Each functional unit shown in Fig. 5 is realized by an independent program, and operates in parallel while maintaining synchronization between the programs through event processing or the like.

[0031] (Foreign object detection method in WPC standard) Next, a foreign object detection method defined in the WPC (Wireless Power Consortium) standard will be described using the power transmitting device 100 and the power receiving device 101. Here, a foreign object detection method based on a Q value measured in the frequency domain (first foreign object detection method) and a foreign object detection method based on a power loss technique (second foreign object detection method) will be described.

[0032] (1) Foreign Object Detection Method Based on Q-Factor Measured in the Frequency Domain (First Foreign Object Detection Method) In the first foreign object detection method, first, the power transmitting device 100 measures the Q-factor, which changes due to the influence of a foreign object, in the frequency domain (first Q-factor measurement). This measurement is performed between the time when the power transmitting device 100 transmits an Analog Ping in step F600 of FIG. 6 and the time when it transmits a Digital Ping in step F602 of FIG. 6 (see step F601 of FIG. 6). For example, to measure the Q-factor, the power transmitting unit 302 sweeps the frequency of the wireless power output by the power transmitting coil 303, and the first Q-factor measurement unit 400 measures the voltage value at the end of the resonant capacitor 306 connected in series (or parallel) with the power transmitting coil 303. Then, the first Q value measuring unit 400 searches for the resonant frequency at which the voltage value reaches its peak, and calculates the Q value of the transmitting coil 303 from the frequency indicating a voltage value that is 3 dB lower than the peak voltage value measured at the resonant frequency and the resonant frequency.

[0033] Alternatively, the first Q-factor measuring unit 400 may measure the Q-factor using another method. For example, the power transmitting unit 302 sweeps the frequency of the wireless power output by the power transmitting coil 303, and the first Q-factor measuring unit 400 measures the voltage value at the ends of the resonant capacitor 306 connected in series with the power transmitting coil 303 to search for the resonant frequency at which the voltage value reaches a peak. The first Q-factor measuring unit 400 then measures the voltage value at both ends of the resonant capacitor 306 at the resonant frequency and calculates the Q-factor of the power transmitting coil 303 from the ratio of the voltage values ​​at both ends.

[0034] After calculating the Q value of the power transmitting coil 303, the first foreign object detection processing unit 403 of the power transmitting device 100 acquires the Q value, which is a criterion for determining foreign object detection, from the power receiving device 101 via the communication unit 304. For example, the first foreign object detection processing unit 403 receives from the power receiving device 101 the Q value (first characteristic value) of the power transmitting coil when the power receiving device 101 is placed on a certain power transmitting coil specified by the WPC standard. This Q value is stored in a Foreign Object Detection (FOD) Status packet transmitted by the power receiving device 101, and the power transmitting device 100 acquires this Q value by receiving this FOD Status packet. From the acquired Q value, the first foreign object detection processing unit 403 estimates the Q value of the power transmitting coil 303 when the power receiving device 101 is placed on the power transmitting device 100. In this embodiment, the estimated Q value is referred to as a first reference Q value. The Q value stored in the FOD Status packet is stored in advance in a non-volatile memory (not shown) of the power receiving device 101. That is, the power receiving device 101 notifies the power transmitting device 100 of the Q value stored in advance. This Q value corresponds to Q1, which will be described later.

[0035] The first foreign object detection processing unit 403 of the power transmitting device 100 compares the first reference Q value with the Q value measured by the first Q value measurement unit 400, and determines the presence or absence of a foreign object based on the comparison result. For example, the first foreign object detection processing unit 403 sets a Q value that is lower than the first reference Q value by a % (first percentage) as a threshold value, and determines that there is a high possibility that there is a foreign object if the measured Q value is lower than the threshold value, and otherwise determines that there is a high possibility that there is no foreign object.

[0036] (2) Foreign object detection method based on power loss technique (second foreign object detection method) Next, a foreign object detection method based on the power loss technique defined in the WPC standard will be described with reference to Fig. 13. Fig. 13 is an explanatory diagram of foreign object detection using the power loss technique, in which the horizontal axis indicates the transmitted power value of the power transmitting device 100 and the vertical axis indicates the received power value of the power receiving device 101. Note that the transmitted power by the power transmitting unit 302 of the power transmitting device 100 is controlled by the power transmission processing unit 406.

[0037] First, the power transmitting unit 302 of the power transmitting device 100 transmits a Digital Ping to the power receiving device 101. Then, the communication unit 304 of the power transmitting device 100 receives a received power value Pr1 (referred to as Light Load) of the power receiving device 101 by a Received Power Packet (mode 1). Note that Received Power Packet (mode 1) will be referred to as "RP1" below. The received power value Pr1 is the received power value when the power receiving device 101 is not supplying received power to a load (such as the charging unit 205 and the battery 206). The control unit 300 of the power transmitting device 100 stores the relationship between the received power value Pr1 and the transmitted power value Pt1 at which the received power value Pr1 was obtained (point 1300 in FIG. 13 ) in the memory 305. This allows the power transmitting device 100 to recognize that the amount of power loss between the power transmitting device 100 and the power receiving device 101 when transmitting power of the transmitted power value Pt1 is Pt1-Pr1 (=Ploss1).

[0038] Next, the communication unit 304 of the power transmitting device 100 receives the value of the received power value Pr2 (referred to as Connected Load) of the power receiving device 101 from the power receiving device 101 in a Received Power Packet (mode 2). Note that Received Power Packet (mode 2) will be referred to as "RP2" below. The received power value Pr2 is the received power value when the power receiving device 101 is supplying received power to a load. Then, the control unit 300 of the power transmitting device 100 stores in the memory 305 the relationship between the received received power value Pr2 and the transmitted power value Pt2 when the received power value Pr2 is obtained (point 1301 in FIG. 13 ). This allows the power transmitting device 100 to recognize that the amount of power loss between the power transmitting device 100 and the power receiving device 101 when transmitting power of the transmission power value Pt2 is Pt2-Pr2 (=Ploss2).

[0039] Then, the calibration processing unit 402 of the power transmitting device 100 linearly interpolates between the points 1300 and 1301 to create a line 1302. The line 1302 corresponds to the relationship between the transmitted power and the received power in a state where no foreign object is present around the power transmitting device 100 and the power receiving device 101. Therefore, the power transmitting device 100 can predict the received power value in a state where there is a high possibility that no foreign object is present, from the transmitted power value and the line 1302. For example, for a transmitted power value Pt3, the power transmitting device 100 can predict the received power value Pr3 from a point 1303 on the line 1302 that corresponds to the transmitted power value Pt3.

[0040] Here, assume that the power transmitting unit 302 of the power transmitting device 100 transmits power to the power receiving device 101 at a transmission power value Pt3, and the communication unit 304 receives a received power value Pr3' from the power receiving device 101. The second foreign object detection processing unit 404 of the power transmitting device 100 calculates a value Pr3-Pr3' (=Ploss_FO) by subtracting the received power value Pr3' actually received from the power receiving device 101 from the received power value Pr3 in a state where no foreign object is present. This Ploss_FO can be considered to be the amount of power loss consumed by a foreign object if a foreign object is present between the power transmitting device 100 and the power receiving device 101. Therefore, the second foreign object detection processing unit 404 can determine the presence of a foreign object if the power value Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold. This threshold value is derived based on the relationship between point 1300 and point 1301, for example.

[0041] Furthermore, the second foreign object detection processing unit 404 of the power transmitting device 100 previously calculates the amount of power loss Pt3-Pr3 (Ploss3) between the power transmitting device 100 and the power receiving device 101 from the received power value Pr3 in a state where no foreign object is present. Then, the second foreign object detection processing unit 404 calculates the amount of power loss Pt3-Pr3' (=Ploss3') between the power transmitting device 100 and the power receiving device 101 in a state where a foreign object is present from the received power value Pr3' received from the power receiving device 101 in a state where it is unknown whether a foreign object is present. The second foreign object detection processing unit 404 then calculates Ploss3'-Ploss3, and can determine that a foreign object is present if this value exceeds a predetermined threshold. Note that Ploss3'-Ploss3 = Pt3-Pr3'-Pt3+Pr3 = Pr3-Pr3'. Therefore, the second foreign object detection processing unit 404 can also estimate the power Ploss_FO that is predicted to be consumed by the foreign object by comparing the amounts of power loss.

[0042] As described above, the power value Ploss_FO that would have been consumed by the foreign object may be calculated as the difference in received power Pr3-Pr3', or may be calculated as the difference in power loss Ploss3'-Ploss3 (=Ploss_FO).

[0043] After the calibration processing unit 402 acquires the straight line 1302, the second foreign object detection processing unit 404 of the power transmitting device 100 periodically receives the current received power value (for example, the above-mentioned received power value Pr3′) from the power receiving device 101 via the communication unit 304. The current received power value periodically transmitted by the power receiving device 101 is transmitted to the power transmitting device 100 as a Received Power Packet (mode 0). The second foreign object detection processing unit 404 of the power transmitting device 100 performs foreign object detection based on the received power value stored in the Received Power Packet (mode 0) and the straight line 1302. Note that Received Power Packet (mode 0) will be referred to as "RP0" below.

[0044] In this embodiment, points 1300 and 1301 for obtaining a straight line 1302 that represents the relationship between the transmitted power value and the received power value when no foreign object is present around the power transmitting device 100 and the power receiving device 101 are called "calibration data points." Also, a line segment (straight line 1302) obtained by interpolating at least two calibration data points is called a "calibration curve." The calibration data points and calibration curve (second criterion) are used for foreign object detection processing by the second foreign object detection processing unit 404.

[0045] (Q-Factor Measurement Method in the Time Domain) A method for measuring a Q-factor in the time domain will be described with reference to FIGS. 11A and 11B. FIGS. 11A and 11B are diagrams for explaining a method for measuring a Q-factor in the time domain (second Q-factor measurement). In this embodiment, the foreign object detection method based on the second Q-factor is referred to as a third foreign object detection method. The second Q-factor measurement is performed by the second Q-factor measurement unit 401. Furthermore, the control of the transmitted power by the power transmission unit 302 of the power transmission device 100 is performed by the power transmission processing unit 406. In the second Q-factor measurement, the power transmission device 100 and the power receiving device 101 turn on their switches for the same period, causing a momentary interruption in power transmission and preventing the received power from being delivered to the load. This results in, for example, an exponential decrease in the voltage applied to the coil. The second Q-factor is then calculated based on the manner in which this decrease occurs.

[0046] Waveform 1100 in FIG. 11A shows the value of the high-frequency voltage applied to the end of the power transmitting coil 303 or the resonant capacitor 306 of the power transmitting device 100 over time (hereinafter simply referred to as the "voltage value of the power transmitting coil"). Note that in FIGS. 11A and 11B, the horizontal axis represents time, and the vertical axis represents the voltage value. At time T0, the application of the high-frequency voltage (power transmission) is stopped. Point 1101 is a point on the envelope of the high-frequency voltage (in other words, a point of maximum value), and is the high-frequency voltage at time T1. (T1, A1) in FIG. 11A indicates that the voltage value at time T1 is A1. Similarly, point 1102 is a point on the envelope of the high-frequency voltage, and is the high-frequency voltage at time T2. (T2, A2) in FIG. 11A indicates that the voltage value at time T2 is A2.

[0047] The Q value is measured based on the change in the voltage value over time after time T0. For example, the Q value is calculated using Equation 1 based on the time, voltage value, and frequency f of the high-frequency voltage (hereinafter, f is referred to as the operating frequency) of points 1101 and 1102 that are the envelope of the voltage value.

[0048]

[0049] That is, the Q value here is an electrical characteristic determined by the relationship between the time elapsed in the power transmission coil 303 after power transmission is limited (stopped) and the amount of voltage drop at that time.

[0050] Next, the process for measuring the Q-factor in the time domain by the power transmitting device 100 in this embodiment will be described with reference to FIG. 11B . Waveform 1103 shows the value of the high-frequency voltage applied to the power transmitting coil 303, and its frequency is between 110 kHz and 148.5 kHz, as used in the Qi standard. Points 1104, 1105, 1106, and 1107 are part of the voltage envelope. The power transmitting unit 302 of the power transmitting device 100 stops power transmission from time T0 to T5. The second Q-factor measuring unit 401 of the power transmitting device 100 measures the Q-factor based on the voltage value A3 (point 1104) at time T3, the voltage value A4 (point 1105) at time T4, the operating frequency of the high-frequency voltage, and Equation 1. The power transmitting unit 302 of the power transmitting device 100 resumes power transmission at time T5. In this way, the second Q value is measured by the power transmitting device 100 momentarily interrupting power transmission and measuring the Q value based on the elapsed time, voltage value, and operating frequency. Similarly, the power receiving device 101 measures the second Q value as an electrical characteristic determined by the relationship between the elapsed time of the power receiving coil 201 after power transmission is limited (stopped) and the amount of voltage drop at that time.

[0051] (Operation of a general power transmitting device and a power receiving device) Figure 6 is a diagram showing the operation when a power transmitting device 100 and a power receiving device 101 that comply with the WPC standard perform a first foreign object detection process, a second foreign object detection process, and a third foreign object detection process.

[0052] In step F600, the power transmitting device 100 transmits an analog ping to detect an object present near the power transmitting coil 303. The analog ping is pulsed power for detecting an object. Even if the power receiving device 101 receives the analog ping, the analog ping is so small that it cannot start the control unit 200. The power transmitting device 100 detects the object by using the analog ping to detect a shift in the resonant frequency of the voltage value inside the power transmitting coil 303, which is caused by an object present near the power transmitting coil 303, or a change in the voltage value and current value flowing through the power transmitting coil 303.

[0053] In step F601, when the power transmitting device 100 detects an object by Analog Ping, it measures the Q value of the power transmitting coil 303 by the first Q value measurement described above. Then, in step F602, following the first Q value measurement, the power transmitting device 100 starts transmitting Digital Ping. Digital Ping is power for starting the control unit 200 of the power receiving device 101 and is greater in power than Analog Ping. Digital Ping is transmitted continuously thereafter. That is, the power transmitting device 100 continues to transmit power equal to or greater than Digital Ping from the time it starts transmitting Digital Ping in step F602 until it receives an EPT packet (described later) from the power receiving device 101 in step F622. EPT stands for End Power Transfer.

[0054] In step F603, when the power receiving device 101 receives a Digital Ping and starts up, it stores the voltage value of the received Digital Ping in a Signal Strength packet and transmits the packet to the power transmitting device 100. Next, in step F604, the power receiving device 101 transmits to the power transmitting device 100 an ID packet storing an ID including version information of the WPC standard to which the power receiving device 101 complies and device identification information. Furthermore, in step F605, the power receiving device 101 transmits to the power transmitting device 100 a Configuration packet including information such as the maximum value of power that the voltage control unit 203 supplies to the load (charging unit 205). The power transmitting device 100 receives the ID packet and the Configuration packet. In step F606, if the power transmitting apparatus 100 determines from these packets that the power receiving apparatus 101 supports the extended protocol of WPC standard v1.2 or later (including Negotiation, which will be described later), it responds with an ACK (acknowledgment).

[0055] Upon receiving the ACK, the power receiving device 101 transitions to a negotiation phase in which negotiations are performed regarding the power to be transmitted and received. First, in step F607, the power receiving device 101 transmits an FOD Status packet to the power transmitting device 100. In this embodiment, this FOD Status packet is referred to as "FOD(Q1)." The power transmitting device 100 performs foreign object detection using a first foreign object detection method based on the Q value (first characteristic value) stored in the received FOD(Q1) and the Q value measured in the first Q value measurement. Then, in step F608, if the power transmitting device 100 determines that there is a high possibility that a foreign object is not present, it transmits an ACK indicating the determination result to the power receiving device 101.

[0056] When the power receiving device 101 receives the ACK, it negotiates a Guaranteed Power (GP), which is the maximum value of the power value that the power receiving device 101 requests to receive. The Guaranteed Power indicates the load power of the power receiving device 101 (the power consumed by the battery 206) agreed upon with the power transmitting device 100. This negotiation is realized by the power receiving device 101 transmitting a packet that stores the requested Guaranteed Power value to the power transmitting device 100 in step F609 of a Specific Request defined in the WPC standard. In this embodiment, this packet is called an "SRQ (GP)." The power transmitting device 100 responds to the SRQ (GP) taking into consideration the power transmitting capability of its own device, etc.

[0057] In step F610, if the power transmitting device 100 determines that the guaranteed power is acceptable, the power transmitting device 100 transmits an ACK indicating that the request has been accepted. In this embodiment, it is assumed that the power receiving device 101 has requested 15 watts as the guaranteed power by an SRQ (GP).

[0058] In step F611, when the negotiation of multiple parameters including the Guaranteed Power is completed, the power receiving device 101 transmits an "SRQ (EN)" of the Specific Requests requesting the end of the negotiation to the power transmitting device 100. The end of the negotiation is End Negotiation. Then, in step F612, the power transmitting device 100 transmits an ACK in response to the SRQ (EN), ends the negotiation, and transitions to a Power Transfer phase in which the power receiving device 101 transmits and receives power determined by the Guaranteed Power.

[0059] Next, the power transmitting device 100 creates a calibration curve for performing foreign object detection based on the above-described power loss technique (second foreign object detection method). First, in step F613, the power transmitting device 100 receives RP1 from the power receiving device 101. This RP1 includes an information element by which the power receiving device 101 requests the power transmitting device 100 to perform a second Q-value measurement. For example, a 1-bit field indicating whether or not the second Q-value measurement is requested is provided in a reserved area of ​​the Received Power Packet. The power receiving device 101 stores "1" in that bit if the second Q-value measurement is requested, and stores "0" if the second Q-value measurement is not requested. In this embodiment, this bit is referred to as a "request bit." In this embodiment, RP1 with "1" stored in the request bit is referred to as RP1(FOD).

[0060] In step F614, upon receiving RP1 (FOD), the power transmitting device 100 performs a second Q-value measurement according to the procedure already described and performs a third foreign object detection process. Here, the response to RP1 (FOD) is determined based on two factors. One is the result of the third foreign object detection process. The other is a Control Error Packet (hereinafter referred to as CE) that the power receiving device 101 sends to the power transmitting device 100 to request an increase or decrease in the receiving voltage (or receiving current, receiving power). CE stores an integer with a + sign if the power receiving device 101 requests an increase in the receiving voltage, an integer with a - sign if the power receiving voltage is requested to be decreased, or "0" if the power transmitting device 100 wants to maintain the current receiving voltage. The power transmitting device 100 promptly performs power transmission control based on the sign and integer stored in CE. Specifically, the power transmission device 100 quickly increases the transmission voltage when an integer with a + sign is stored, quickly decreases the transmission voltage when an integer with a - sign is stored, and maintains the transmission voltage when "0" is stored.

[0061] In step F615, the power transmitting device 100 determines to accept the received power value stored in RP1 (FOD) and the transmitted power value of the power transmitting device 100 when the received power was obtained as a calibration data point (corresponding to point 1300 in FIG. 13 ). Then, the power transmitting device 100 transmits an ACK to the power receiving device 101.

[0062] Next, in step F616, the power receiving device 101 transmits CE(+), which indicates that the power should be increased, to the power transmitting device 100. Upon receiving CE(+), the power transmitting device 100 changes the setting value of the power transmitting unit 302 to increase the transmitted power. When the received power increases in response to CE(+), the power receiving device 101 supplies the received power to a load (the charging unit 205 or the battery 206).

[0063] Next, in step F617, the power receiving device 101 transmits RP2 (FOD) with "1" stored in the request bit to the power transmitting device 100. In step F618, upon receiving RP1 (FOD), the power transmitting device 100 performs a second Q-value measurement and performs a third foreign object detection process. In step F619, the power transmitting device 100 determines to accept the received power value stored in RP2 (FOD) and the transmitted power value of the power transmitting device 100 when the received power was obtained as calibration data points (corresponding to point 1301 in FIG. 13 ). Then, the power transmitting device 100 transmits an ACK to the power receiving device 101.

[0064] In step F620, the power receiving device 101 transmits RP0 to the power transmitting device 100. Upon receiving RP0, the power transmitting device 100 performs foreign object detection based on the second foreign object detection method described above. In step F621, if the power transmitting device 100 determines that there is a high possibility that no foreign object is present as a result of foreign object detection, the power transmitting device 100 transmits an ACK to the power receiving device 101. Thereafter, in step F622, when charging of the battery 206 is completed, the power receiving device 101 transmits an EPT (End Power Transfer) packet to the power transmitting device 100 to request that power transmission be stopped.

[0065] As described above, wireless power transmission is performed between the power transmitting device 100 and the power receiving device 101 based on the first foreign object detection process, the second foreign object detection process, and the third foreign object detection process.

[0066] (Issues of the Present Embodiment) Consider the case where the voltage waveforms of the transmitting coil 303 and the receiving coil 201 when performing the second Q-factor measurement are as shown in Figure 11C. Figure 11C shows a case where the amplitude of the voltage of the transmitting coil 303 during an instantaneous power outage does not monotonically decrease over time. Here, when the absolute value of the amplitude (maximum value) at time Ta on the voltage waveform is Aa and the absolute value of the amplitude (maximum value) at time Tb is Ab, if the relationship "if time Ta < Tb, then amplitude Aa > Ab" holds, in the present embodiment, the voltage is said to monotonically decrease.

[0067] Regarding points 1109 and 1110 in FIG. 11C, time T9<T10, but amplitude A9>A10 is not, so the voltage waveform in FIG. 11C is not monotonically decreasing. Let's assume that the Q value is calculated for points 1109 (T9, A9) and 1110 (T10, A10) based on Equation 1. Since T9<T10, the numerator sign is +. On the other hand, as shown in FIG. 11C, A9<A10, so the denominator sign in Equation 1 is -, and therefore the Q value sign is -. The Q value should normally be +, which contradicts the definition of the Q value. This means that the Q value cannot be measured unless the waveform is monotonically decreasing. Furthermore, if the waveform is not monotonically decreasing, it is possible that the maximum points will have the same value at different times. For example, the amplitudes of points 1109 and 1111 are the same, A9. In this case, the Q value calculated using points 1108 and 1109 and the Q value calculated using points 1108 and 1111 have the same denominator in Equation 1 but different numerators. This means that if the waveform is not monotonically decreasing, the calculated Q value will vary depending on which local maximum point is used as the measurement point. In other words, if the voltage waveform is not monotonically decreasing, the Q value (second Q value) cannot be calculated with high accuracy, and therefore third foreign object detection, which determines the presence or absence of a foreign object based on the second Q value, cannot be performed with high accuracy.

[0068] (Explanation of Operation of Second Q-Factor Measuring Unit) FIG. 7A is a flowchart showing processing performed by the second Q-factor measuring unit 401 of this embodiment to solve the problem that third foreign object detection cannot be performed with high accuracy.

[0069] In step S700, the second Q value measurement unit 401 limits the power transmission of the power transmission unit 302. Subsequently, in step S701, the second Q value measurement unit 401 turns on the switch 307 for short-circuiting the power transmission coil 303 and the resonant capacitor 306, and performs short-circuit processing.

[0070] Then, in step S702, the second Q-value measurement unit 401 determines whether the voltage waveform of the transmitting coil 303 is monotonically decreasing. The voltage waveform at this time is shown in Fig. 11C. Since the voltage waveform in Fig. 11C is not monotonically decreasing (NO in S702), the second Q-value measurement unit 401 proceeds to step S708.

[0071] In step S708, the second Q-value measuring unit 401 determines that the presence or absence of a foreign object cannot be determined using the second Q-value calculated based on the voltage waveform. Then, in step S706, the second Q-value measuring unit 401 turns off the switch 307 to cancel the short-circuiting process. Thereafter, in step S707, the second Q-value measuring unit 401 cancels the restriction on power transmission by the power transmitting unit 302.

[0072] 11B, the voltage waveform of the transmitting coil 303 is assumed to be monotonically decreasing. In this case, the second Q-factor measuring unit 401 determines that the voltage waveform of the transmitting coil 303 is monotonically decreasing (YES in S702), and therefore proceeds to step S703.

[0073] In step S703, the second Q-value measuring unit 401 determines that the presence or absence of a foreign object can be determined using the second Q-value calculated based on the voltage waveform. Then, in step S704, the second Q-value measuring unit 401 acquires, for example, a voltage value A3 of the power transmitting coil 303 at time T3 and a voltage value A4 at time T4. In step S705, the second Q-value measuring unit 401 calculates the second Q-value from the frequency, time, and voltage value based on Equation 1.

[0074] After that, in step S706, the second Q-value measuring unit 401 turns off the switch 307 to release the short-circuiting process. In step S707, the second Q-value measuring unit 401 releases the restriction on the power transmission of the power transmitting unit 302.

[0075] In this way, the second Q value measuring unit 401 determines whether or not the presence or absence of a foreign object can be determined using the second Q value based on the voltage waveform of the power transmitting coil 303 .

[0076] (Explanation of Operation of Third Foreign Object Detection Processing Unit) Fig. 8A is a flowchart showing processing of the third foreign object detection processing unit 405 based on the determination of the second Q-value measuring unit 401 in Fig. 7A. A control method of the power transmitting device 100 will be described below.

[0077] In step S800, the third foreign object detection processing unit 405 receives RP1 from the power receiving device 101.

[0078] In step S801, if the request bit included in RP1 is "0" (NO in S801), the third foreign object detection processing unit 405 ends the processing of the flowchart in FIG. 8A and waits for reception of RP1 in the next step S800. Also, if the request bit included in RP1 is "1" (YES in S801), the third foreign object detection processing unit 405 proceeds to step S802. In step S802, the second Q-factor measurement unit 401 performs the processing of the flowchart in FIG. 7A (second Q-factor measurement).

[0079] In step S803, the third foreign object detection processing unit 405 determines whether the presence or absence of a foreign object can be determined using the second Q value calculated based on the voltage waveform, based on Fig. 7A. If the voltage waveform of the power transmitting coil 303 does not monotonically decrease, the third foreign object detection processing unit 405 determines that the calculated second Q value cannot be used to determine the presence or absence of a foreign object (NO in S803), because the calculated second Q value may not be accurate, and proceeds to step S808.

[0080] Furthermore, if the voltage waveform of the transmitting coil 303 monotonically decreases, the third foreign object detection processing unit 405 determines that the calculated second Q value is likely to be accurate, and therefore the presence or absence of a foreign object can be determined using the calculated second Q value (YES in S803), and proceeds to step S804.

[0081] Here, possible methods for detecting foreign matter using the second Q value include a method in which the presence or absence of foreign matter is determined based on the results of a single second Q value measurement, and a method in which the second Q value measurement is performed multiple times and the determination is made based on the results of the multiple measurements.

[0082] In step S804, if the third foreign object detection processing unit 405 determines whether or not a foreign object is present based on a single second Q-value measurement (YES in S804), the process proceeds to step S805. On the other hand, if the third foreign object detection processing unit 405 determines whether or not a foreign object is present based on the measurement results of multiple second Q-value measurements (NO in S804), the process proceeds to step S807.

[0083] In step S807, if the second Q-value measurement performed in step S802 is the final second Q-value measurement (YES in S807, for example, the third measurement if three second Q-value measurements are used), the third foreign object detection processing unit 405 proceeds to step S805. Also, if the second Q-value measurement performed in step S802 is not the final second Q-value measurement (NO in S807), the third foreign object detection processing unit 405 proceeds to step S808 because it will not determine the presence or absence of a foreign object until the final second Q-value measurement is performed.

[0084] In step S808, the third foreign object detection processing unit 405 transmits data indicating that it is unable to determine the presence or absence of a foreign object as a response to RP1, terminates the processing of the flowchart in FIG. 8A, and waits for reception of RP1 in the next step S800.

[0085] In step S805, if the calculated second Q value is greater than the threshold value (YES in S805), the third foreign object detection processing unit 405 proceeds to step S806, and if the calculated second Q value is not greater than the threshold value (NO in S805), the third foreign object detection processing unit 405 proceeds to step S809.

[0086] In step S806, the third foreign object detection processing unit 405 transmits an ACK to RP1, and ends the processing of the flowchart in Fig. 8A. In step S809, the third foreign object detection processing unit 405 transmits a NAK to RP1, and ends the processing of the flowchart in Fig. 8A, and waits for reception from RP1 in the next step S800.

[0087] As described above, the power transmitting device 100 does not determine the presence or absence of a foreign object based on the second Q-value measurement if there is a possibility that the second Q-value measurement will be inaccurate depending on whether the voltage waveform of the power transmitting coil 303 at the time of the second Q-value measurement is monotonically decreasing. This has the effect of enabling the presence or absence of a foreign object to be determined with high accuracy.

[0088] (Explanation of Other Operations of the Third Foreign Object Detection Processing Unit) The determination performed by the third foreign object detection processing unit 405 as to whether or not the presence or absence of a foreign object can be determined using the second Q value may be determined by adding the magnitude of an integer included in CE (hereinafter referred to as Control Error Value: CEV) as an additional condition.

[0089] FIG. 9 is a diagram illustrating the conditions. Condition 900 is a CEV condition. |CEV|≦2 indicates that the absolute value of CEV is 2 or less. This indicates a state in which the voltage value of the transmitting coil 303 is stable. On the other hand, |CEV|>2 indicates that the absolute value of CEV is greater than 2. This indicates a state in which the voltage value of the transmitting coil 303 is unstable because the power transmitting unit 302 increases or decreases the transmission voltage based on the CE. Note that while FIG. 9 illustrates a case in which the absolute value of CEV is compared with 2, this may be any integer. Naturally, the CEV value may be compared with any integer with a positive or negative sign.

[0090] Condition 901 is a case where the third foreign object detection processing unit 405 determines that the presence or absence of a foreign object can be determined using the second Q value, and the second Q value is smaller than a threshold value. Condition 902 is a case where the third foreign object detection processing unit 405 determines that the presence or absence of a foreign object can be determined using the second Q value, and the second Q value is larger than a threshold value. Condition 903 is a case where the third foreign object detection processing unit 405 determines that the presence or absence of a foreign object cannot be determined using the second Q value.

[0091] 9, let us consider a state in which |CEV|≦2 and the voltage value of the transmitting coil 303 is stable. If the second Q value is smaller than the threshold value, the third foreign object detection processing unit 405 transmits a NAK to RP1, if the second Q value is larger than the threshold value, it transmits an ACK to RP1, and if it is not possible to determine the presence or absence of a foreign object using the second Q value, it transmits a message indicating that the determination is not possible.

[0092] On the other hand, when |CEV|>2 and the voltage value of the power transmitting coil 303 is unstable, the third foreign object detection processing unit 405 transmits a NAK regardless of other conditions. This is because, when the voltage value is unstable, the second Q-factor measurement may not be performed accurately.

[0093] Fig. 8B is a flowchart showing the processing of the third foreign object detection processing unit 405 taking into consideration the determination in Fig. 9. Fig. 8B is obtained by adding step S810 to Fig. 8A. After step S800, the third foreign object detection processing unit 405 proceeds to step S810.

[0094] In step S810, if the most recent voltage value of the power transmitting coil 303 is not stable (NO in S810), the third foreign object detection processing unit 405 proceeds to step S809. On the other hand, if the most recent voltage value of the power transmitting coil 303 is stable, the third foreign object detection processing unit 405 proceeds to step S802.

[0095] In step S809, the third foreign object detection processing unit 405 transmits a NAK to RP1, terminates the processing of the flowchart in Fig. 8A, and waits for reception of RP1 in the next step S800. From step S802 onwards, the third foreign object detection processing unit 405 performs the same processing as in Fig. 8A.

[0096] As a result, the third foreign object detection processing unit 405 can make an accurate judgment by sending a NAK when the second Q value happens to be larger than the threshold value because the second Q value was calculated when the voltage value of the transmitting coil 303 was not stable.

[0097] 10 is a flowchart showing the processing of the power receiving device 101 when the third foreign object detection processing unit 405 determines the presence or absence of a foreign object by one second Q-value measurement. A control method of the power receiving device 101 will be described below.

[0098] In step S1001, the power receiving device 101 waits until it receives a response to any one of RP1 (FOD), RP2 (FOD), and RP0 (FOD), and if it receives a response (YES in S1001), it proceeds to step S1002.

[0099] In step S1002, if the response indicates that "the presence or absence of a foreign object cannot be determined using the second Q value" (YES in S1002), the power receiving device 101 proceeds to step S1003. On the other hand, if the response does not indicate that "the presence or absence of a foreign object cannot be determined using the second Q value" (NO in S1002), the power receiving device 101 proceeds to step S1007.

[0100] In step S1007, if the response is a NAK (YES in S1007), the power receiving apparatus 101 proceeds to step S1003, and if the response is not a NAK (NO in S1007), the power receiving apparatus 101 proceeds to step S1008.

[0101] In step S1008, the power receiving device 101 ends the processing of the flowchart in FIG. 10 because the response is an ACK and the calibration data points have been accepted.

[0102] In step S1003, the power receiving device 101 determines whether the response has been received A times in succession. If the power receiving device 101 has not received the response A times in succession (NO in S1006), the process proceeds to step S1006. If the power receiving device 101 has received the response A times in succession (YES in S1006), the process proceeds to step S1004.

[0103] In step S1006, the power receiving apparatus 101 again sets the request bit to "1" and transmits RP1 to the power transmitting apparatus 100, and ends the processing of the flowchart in FIG.

[0104] In step S1004, the power receiving device 101 determines that the calibration has failed, and proceeds to step S1005. In step S1005, the power receiving device 101 limits the received power. For example, to limit the received power, the power receiving device 101 may transmit an EPT packet or may reduce the power consumption of the load to a value greater than 0 (for example, 5 watts). Thereafter, the power receiving device 101 ends the processing of the flowchart in FIG. 10.

[0105] In this way, the power transmitting device 100 transmits power wirelessly. In step S800, the third foreign object detection processing unit 405 functions as a receiving unit and receives from the power receiving device 101 a request bit for calculating the Q value and the received power value of RP1.

[0106] In step S700, the second Q-value measurement unit 401 functions as a stopping unit and stops applying voltage to the power transmitting coil 303. In step S705, the second Q-value measurement unit 401 functions as a calculation unit and calculates the Q-value based on changes over time in the electrical characteristics of the power transmitting coil 303 when the measurement is stopped. The electrical characteristics of the power transmitting coil 303 are the voltage values ​​of the power transmitting coil 303.

[0107] In step S803, if the change over time in the electrical characteristics of the power transmitting coil when stopped is a monotonous decrease, the third foreign object detection processing unit 405 proceeds to step S804. If the change over time in the electrical characteristics of the power transmitting coil when stopped is not a monotonous decrease, the third foreign object detection processing unit 405 proceeds to step S808.

[0108] In steps S806 and S809, the third foreign object detection processing unit 405 functions as a transmitting unit and transmits to the power receiving device 101 whether or not to use the received power value of RP1 for foreign object detection based on the Q value calculated in step S705.

[0109] In step S806, if the Q value calculated in step S705 is greater than the first threshold, the third foreign object detection processing unit 405 transmits an ACK to the power receiving device 101 indicating that the received power value of RP1 will be used for foreign object detection. This ACK indicates that the received power value of RP1 will be accepted as a calibration data point.

[0110] In step S809, if the Q value calculated in step S705 is not greater than the first threshold, the third foreign object detection processing unit 405 transmits a NAK to the power receiving device 101, indicating that the received power value of RP1 will not be used for foreign object detection. This NAK indicates that the received power value of RP1 will not be accepted as a calibration data point.

[0111] In step S808, the third foreign object detection processing unit 405 functions as a transmitting unit and transmits a notification to the power receiving device 101 indicating that it is not determining whether or not to use the received power value of RP1 for foreign object detection.

[0112] 8B , if the absolute value of the increase / decrease value CEV of the voltage value that the power receiving device 101 requests the power transmitting device 100 to increase / decrease is equal to or less than the second threshold, the third foreign object detection processing unit 405 proceeds to step S801. If the absolute value of the increase / decrease value CEV of the voltage value that the power receiving device 101 requests the power transmitting device 100 to increase / decrease is greater than the second threshold, the third foreign object detection processing unit 405 proceeds to step S809.

[0113] The power receiving device 101 wirelessly receives power. In step S800, the power receiving device 101 functions as a transmitter and transmits to the power transmitting device 100 a request bit for calculating a Q value based on a change over time in the electrical characteristics of the power transmitting coil 303 and the received power value of RP1.

[0114] 10, the power receiving device 101 receives a response to the above transmission. In step S1002, if the power receiving device 101 receives a response notifying the power receiving device 101 that it will not determine whether to use the received power value of RP1 for foreign object detection based on the Q value, the power receiving device 101 proceeds to step S1003.

[0115] In step S1006, the power receiving device 101 functions as a transmitter and again transmits to the power transmitting device 100 a request bit for calculating the Q value based on the change over time in the electrical characteristics of the power transmitting coil 303 and the received power value of RP1.

[0116] In step S1005, the power receiving device 101 functions as a limiting unit and limits the received power when it receives a notification response indicating that it will not determine whether or not to use the received power value of RP1 for foreign object detection based on the Q value a threshold number of times in succession.

[0117] Second Embodiment A second embodiment will be described. There are cases where the voltage waveform of the power transmitting coil 303 contains multiple frequency components. The operation of the second Q-factor measuring unit 401 in such a case will be described with reference to FIGS. 11C, 12A, and 12B.

[0118] In Fig. 11C, the voltage waveform of the transmitting coil 303 is not monotonically decreasing, but may be a superposition of monotonically decreasing voltage waveforms. For example, Fig. 12A shows the voltage waveform of the frequency component of the resonant frequency F1 when the transmitting coil 303 and the resonant capacitor 306 are short-circuited from the voltage waveform of Fig. 11C. Fig. 12B shows the voltage waveform of the frequency component of the resonant frequency F2 when the receiving coil 201 and the resonant capacitor 207 are short-circuited from the voltage waveform of Fig. 11C.

[0119] 7B is a flowchart showing the processing performed by the second Q-factor measurement unit 401 on the voltage waveform of the frequency components of the resonant frequencies F1 and F2. In FIG. 7B, step S702 is deleted and steps S709 to S711 are added to FIG. 7A. Differences between the second embodiment and the first embodiment will be described below.

[0120] After step S701, the second Q value measurement unit 401 proceeds to step S709. In step S709, the second Q value measurement unit 401 separates the voltage waveform of the power transmitting coil 303 shown in Fig. 11C into a frequency component of the resonant frequency F1 of the power transmitting device 100 shown in Fig. 12A and a frequency component of the resonant frequency F2 of the power receiving device 101 shown in Fig. 12B.

[0121] In step S710, the second Q value measurement unit 401 determines whether the voltage waveform having the frequency component of the resonant frequency F1 of the power transmitting device 100 in Fig. 12A is monotonically decreasing. If the voltage waveform having the frequency component of the resonant frequency F1 is monotonically decreasing as in Fig. 12A (YES in S710), the second Q value measurement unit 401 proceeds to step S711. If the voltage waveform having the frequency component of the resonant frequency F1 is not monotonically decreasing (NO in S710), the second Q value measurement unit 401 proceeds to step S708.

[0122] In step S711, the second Q value measurement unit 401 determines whether the voltage waveform having the frequency component of the resonant frequency F2 of the power receiving device 101 in Fig. 12B monotonically decreases. If the voltage waveform having the frequency component of the resonant frequency F2 monotonically decreases as in Fig. 12B (YES in S711), the second Q value measurement unit 401 proceeds to step S703. If the voltage waveform having the frequency component of the resonant frequency F2 does not monotonically decrease (NO in S711), the second Q value measurement unit 401 proceeds to step S708.

[0123] In step S703, the second Q value measuring unit 401 determines that the presence or absence of a foreign object can be determined using the second Q value calculated based on the voltage waveform, as in Fig. 7A . In step S708, the second Q value measuring unit 401 determines that the presence or absence of a foreign object cannot be determined using the second Q value calculated based on the voltage waveform, as in Fig. 7A .

[0124] As described above, the second Q-value measuring unit 401 separates the voltage waveform of the power transmitting coil 303 into a frequency component of the resonant frequency F1 of the power transmitting device 100 and a frequency component of the resonant frequency F2 of the power receiving device 101. The second Q-value measuring unit 401 then determines whether or not the presence or absence of a foreign object can be determined based on whether or not each of the voltage waveform having the frequency component of the resonant frequency F1 and the voltage waveform having the frequency component of the resonant frequency F2 monotonically decreases. In this way, the second Q-value measuring unit 401 can determine the presence or absence of a foreign object using the second Q-value even when a voltage waveform that does not appear to monotonically decrease, as shown in FIG. 11C , is observed.

[0125] 7B, the second Q-value measuring unit 401 determines that the presence or absence of a foreign object can be determined when both the voltage waveform having the frequency component of the resonant frequency F1 and the voltage waveform having the frequency component of the resonant frequency F2 monotonically decrease. However, this is not limited to this. For example, the second Q-value measuring unit 401 may determine that the presence or absence of a foreign object can be determined if the voltage waveform having the frequency component of the resonant frequency F1 monotonically decreases, regardless of the voltage waveform having the frequency component of the resonant frequency F2. Furthermore, the second Q-value measuring unit 401 may determine that the presence or absence of a foreign object can be determined if the voltage waveform having the frequency component of the resonant frequency F2 monotonically decreases, regardless of the voltage waveform having the frequency component of the resonant frequency F1. The second Q-value measuring unit 401 may receive the resonant frequency F2 of the power receiving device 101 from the power receiving device 101.

[0126] 11B , the second Q value measurement unit 401 measured the second Q value once using two points, points 1104 and 1105, when the power transmission unit 302 stopped power transmission from time T0 to time T5. Note that the second Q value measurement unit 401 may measure the second Q value multiple times using multiple points from time T0 to time T5. Specifically, the second Q value measurement unit 401 may calculate the second Q value a total of two times using, for example, points 1104 and 1107 and points 1106 and 1105 out of the four points obtained by adding points 1104 and 1105 to points 1106 and 1107.

[0127] 7C is a flowchart showing an example of a method for determining a second Q value when the second Q value is calculated multiple times. In step S712, the second Q value measurement unit 401 selects the calculated multiple second Q values. In step S713, the second Q value measurement unit 401 calculates the median value of the selected multiple second Q values ​​and determines the median value as the second Q value. Alternatively, the second Q value measurement unit 401 may determine the second Q value using either one or a combination of a method of averaging the multiple second Q values ​​or a method of determining the second Q value by excluding outliers from the multiple second Q values.

[0128] In step S705, the second Q-factor measurement unit 401 calculates multiple Q-factors based on multiple points of time-dependent changes in the electrical characteristics of the power transmitting coil 303 when the power transmitting coil 303 is stopped. In steps S806 and S809, the third foreign object detection processing unit 405 transmits to the power receiving device 101, based on the multiple Q-factors, whether or not to use the received power value of RP1 for foreign object detection.

[0129] Furthermore, when receiving RP1, the second Q-value measurement unit 401 may cause the power transmission unit 302 to stop and resume power transmission multiple times. The second Q-value measurement unit 401 may perform the second Q-value measurement once or multiple times for each cycle of power transmission stop and restart, and calculate the second Q-value based on the results of the multiple cycles for each cycle using the configuration shown in FIG. 7A or 7B and already described. The second Q-value measurement unit 401 may then determine whether the presence or absence of a foreign object can be determined. Specifically, the second Q-value measurement unit 401 may determine the second Q-value using the method of determining the second Q-value excluding the median value, average value, or outliers, as already described, or a combination thereof.

[0130] In step S700, the second Q-value measurement unit 401 repeatedly stops and restarts the application of voltage to the power transmitting coil 303. In step S705, the second Q-value measurement unit 401 calculates multiple Q-values ​​based on changes over time in the electrical characteristics of the power transmitting coil 303 during the multiple stops. In steps S806 and S809, the third foreign object detection processing unit 405 transmits to the power receiving device 101, based on the multiple Q-values, whether or not to use the received power value of RP1 for foreign object detection.

[0131] Furthermore, when the second Q-value measurement unit 401 performs the second Q-value measurement process multiple times (N times), if it determines that "the presence or absence of a foreign object cannot be determined" even once out of the N times, it may determine that "the presence or absence of a foreign object cannot be determined" after the N times. Furthermore, if the second Q-value measurement unit 401 determines that "the presence or absence of a foreign object can be determined" even once out of the N times, it may determine that "the presence or absence of a foreign object can be determined" after the N times. Furthermore, the second Q-value measurement unit 401 may set a threshold value for the number of times it determines that "the presence or absence of a foreign object cannot be determined" (e.g., M times, M≦N), and determine that "the presence or absence of a foreign object cannot be determined" if the number of times it determines that "the presence or absence of a foreign object cannot be determined" exceeds M times. Conversely, the second Q-value measurement unit 401 may set a threshold value for the number of times it determines that "the presence or absence of a foreign object can be determined" (e.g., M' times, M'≦N), and determine that "the presence or absence of a foreign object can be determined" if the number of times it determines that "the presence or absence of a foreign object can be determined" exceeds M' times.

[0132] 8A , the third foreign object detection processing unit 405 is described as transmitting data indicating that it is unable to determine the presence or absence of a foreign object using the second Q value calculated based on the voltage waveform, but this is not limiting. The third foreign object detection processing unit 405 may transmit data indicating that it is unable to determine whether to accept, as calibration data points, the received power value stored in RP1 (FOD) and the transmitted power value of the power transmitting device 100 when the received power value was obtained.

[0133] 8B, the third foreign object detection processing unit 405 determines whether the voltage value of the power transmitting coil 303 is stable. This determination may be made based on whether the CEV value is near "0," or may be made by actually observing whether the voltage value of the power transmitting coil 303 is stable.

[0134] In the present embodiment, the power transmitting device 100 is described as measuring the second Q value. However, the second Q value measurement unit 501 ( FIG. 5 ) of the power receiving device 101 may measure the second Q value. Specifically, the second Q value measurement unit 501 may perform the process of FIG. 7A or 7B , and the third foreign object detection processing unit 500 may perform the process of FIG. 8A or 8B . In this case, the power receiving device 101 may receive information regarding the resonant frequency F1 of the power transmitting device 100 from the power transmitting device 100. The power transmitting device 100 is described as transmitting data indicating that a determination cannot be made in step S808. Here, this data has two meanings. One is that when the power transmitting device 100 performs the second Q value measurement multiple times and makes a determination based on the results of the multiple measurements, the power transmitting device 100 determines the presence or absence of a foreign object based on the last second Q value measurement, and therefore transmits information indicating that a determination cannot be made (no determination will be made) based on any other than the last second Q value measurement. The other meaning is that when the power transmitting device 100 performs the second Q-value measurement once and makes a judgment based on the result of the single measurement, the second Q-value cannot be calculated because the voltage waveform of the power transmitting coil 303 does not monotonically decrease. To distinguish between the two meanings, the power transmitting device 100 may transmit different data for each of the two meanings. Specifically, when making a judgment based on the result of multiple measurements, the power transmitting device 100 may transmit data indicating that a judgment cannot be made (no judgment) based on any measurement other than the last second Q-value measurement. Furthermore, when making a judgment based on the result of a single Q-value measurement and the voltage waveform of the power transmitting coil 303 does not monotonically decrease, the power transmitting device 100 may transmit a message indicating that the calculation is not possible (NC: Not Calculated). This enables more precise control.

[0135] In the present embodiment, the second Q-value measuring unit 401 and the third foreign object detection processing unit 405 determine whether or not the presence of a foreign object can be determined using the second Q-value, but the present invention is not limited to this. The second Q-value measuring unit 401 and the third foreign object detection processing unit 405 may also determine the possibility of the presence of a foreign object (presence probability).

[0136] Also, in step S800, the third foreign object detection processing unit 405 has been described as receiving RP1, but it may also receive either RP2 or RP0.

[0137] Furthermore, in the present embodiment, the second Q-value measurement unit 401 determines that the presence or absence of a foreign object cannot be determined using the second Q-value based on whether the voltage waveform of the power transmitting coil 303 monotonically decreases, but this is not limiting. The second Q-value measurement unit 401 may also make the determination based on the results of actually measuring the second Q-value. Specifically, for example, as described with reference to FIG. 11B , when the power transmitting unit 302 stops power transmission from time T0 to time T5, the second Q-value measurement unit 401 calculates the second Q-value multiple times using multiple points. Then, if the multiple calculation results fall within a certain range, the second Q-value measurement unit 401 may determine that the presence or absence of a foreign object can be determined using the second Q-value. Otherwise, the second Q-value measurement unit 401 may determine that the presence or absence of a foreign object cannot be determined using the second Q-value.

[0138] Furthermore, when the second Q-value measurement unit 401 performs the second Q-value measurement process multiple times (N times) to make the above determination, it actually calculates the second Q-value N times. If the multiple calculation results fall within a certain range, the second Q-value measurement unit 401 may determine that the second Q-value can be used to determine whether or not a foreign object is present, and if not, may determine that the second Q-value cannot be used to determine whether or not a foreign object is present.

[0139] 7B , the second Q-value measurement unit 401 separates the change over time in the electrical characteristics of the power transmitting coil 303 during shutdown into two or more frequency components. If the change over time in the electrical characteristics having at least one of the separated frequency components is a monotonically decreasing change, the second Q-value measurement unit 401 proceeds to step S703. If the change over time in all of the electrical characteristics having the separated frequency components is not a monotonically decreasing change, the second Q-value measurement unit 401 proceeds to step S708.

[0140] The present disclosure can also be realized by a process in which a program that realizes one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present disclosure can also be realized by a circuit (e.g., an ASIC) that realizes one or more functions.

[0141] At least a part of the processing shown in the above flowchart may be implemented by hardware. When implementing by hardware, for example, a specific compiler may be used to automatically generate a dedicated circuit on an FPGA from a program for implementing each step. FPGA stands for Field Programmable Gate Array. Alternatively, a gate array circuit may be formed in the same manner as an FPGA and implemented as hardware.

[0142] The power transmitting device and the power receiving device may be, for example, an image input device such as an imaging device (such as a camera or a video camera) or a scanner, or an image output device such as a printer, a copier, a projector, etc. Furthermore, they may be storage devices such as a hard disk drive or a memory device, or information processing devices such as a personal computer (PC) or a smartphone.

[0143] The power receiving device of the present disclosure may also be an information terminal device. For example, the information terminal device has a display unit (display) that receives power from a power receiving antenna and displays information to a user. The power received from the power receiving antenna is stored in a power storage unit (battery), and power is supplied from the battery to the display unit. In this case, the power receiving device may have a communication unit that communicates with another device different from the power transmitting device. The communication unit may be compatible with communication standards such as NFC communication and the fifth generation mobile communication system (5G).

[0144] The power receiving device of the present disclosure may also be a vehicle such as an automobile. For example, the automobile serving as the power receiving device may receive power from a charger (power transmitting device) via a power transmitting antenna installed in a parking lot. The automobile serving as the power receiving device may also receive power from the charger (power transmitting device) via a power transmitting antenna embedded in the road. In such an automobile, the received power is supplied to a battery. The battery power may be supplied to a driving unit (motor, electric unit) that drives the wheels, or may be used to drive a sensor used for driving assistance or a communication unit that communicates with an external device. In other words, in this case, the power receiving device may include, in addition to the wheels, a battery, a motor or sensor that is driven using the received power, and even a communication unit that communicates with devices other than the power transmitting device. Furthermore, the power receiving device may have a storage unit for accommodating a person. For example, the sensor may be a sensor used to measure the distance between vehicles or the distance to other obstacles. The communication unit may be compatible with, for example, the Global Positioning System (GPS), or may be compatible with a communication standard such as the fifth generation mobile communication system (5G). The vehicle may be a bicycle or a motorcycle.

[0145] The power receiving device of the present disclosure may also be an electric tool, a home appliance, or the like. These devices, which are power receiving devices, may have a battery and a motor that is driven by the received power stored in the battery. These devices may also have a notification means for notifying the remaining battery charge, etc. These devices may also have a communication unit that communicates with other devices different from the power transmitting device. The communication unit may be compatible with communication standards such as NFC and the fifth generation mobile communication system (5G).

[0146] The power transmission device of the present disclosure may also be an on-board charger that transmits power to a mobile information terminal device, such as a smartphone or tablet, that supports wireless power transmission within the vehicle. Such an on-board charger may be installed anywhere within the vehicle. For example, the on-board charger may be installed in the console of the vehicle, on the instrument panel (instrument panel, dashboard), between passenger seats, on the ceiling, or in the door. However, it is preferable that the on-board charger not be installed in a location that interferes with driving. Furthermore, although the power transmission device has been described using the example of an on-board charger, such a charger is not limited to being installed in a vehicle, but may also be installed in transportation such as a train, airplane, or ship. In this case, the charger may also be installed between passenger seats, on the ceiling, or in the door.

[0147] The power transmitting device may also be a vehicle such as an automobile equipped with an on-board charger. In this case, the power transmitting device has wheels and a battery, and supplies power to the power receiving device via a power transmitting circuit unit and a power transmitting antenna using power from the battery.

[0148] It should be noted that the above-described embodiments merely illustrate specific examples of implementing the present disclosure, and the technical scope of the present disclosure should not be construed as being limited by these embodiments. In other words, the present disclosure can be implemented in various forms without departing from its technical concept or main features.

[0149] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0150] This application claims priority based on Japanese Patent Application No. 2021-152002, filed on September 17, 2021, the entire contents of which are incorporated herein by reference.

[0151] 300 Control unit 301 Power supply unit 302 Power transmission unit 303 Power transmission coil 304 Communication unit 305 Memory 306 Resonant capacitor 307 Switch 400 First Q value measurement unit 401 Second Q value measurement unit 402 Calibration processing unit 403 First foreign object detection processing unit 404 Second foreign object detection processing unit 405 Third foreign object detection processing unit 406 Power transmission control processing unit

Claims

1. A power transmission device that wirelessly transmits power, a receiving means for receiving a request to calculate a Q value and a received power value from the power receiving device; a stopping means for stopping the voltage applied to the power transmitting coil; a calculation means for calculating a Q value based on a change over time in the electrical characteristics of the power transmitting coil when the power transmitting coil is stopped; a transmitting means for transmitting to the power receiving device, when the change over time in the electrical characteristics of the power transmitting coil when the power transmitting device is stopped is a monotonous decrease, whether or not to use the received power value for detecting an object different from the power receiving device, based on the Q value calculated by the calculating means, and, when the change over time in the electrical characteristics of the power transmitting coil when the power transmitting device is stopped is not a monotonous decrease, transmitting to the power receiving device a notification indicating that it will not determine whether or not to use the received power value for detecting the object; A power transmitting device comprising:

2. The power transmitting device according to claim 1, characterized in that if the Q value calculated by the calculation means is greater than a first threshold, the transmitting means transmits to the power receiving device a message that the received power value will be used to detect the object, and if the Q value calculated by the calculation means is not greater than the first threshold, the transmitting means transmits to the power receiving device a message that the received power value will not be used to detect the object.

3. The power transmitting device according to claim 1, characterized in that, when the absolute value of the increase / decrease in the voltage value requested by the power receiving device to the power transmitting device is equal to or less than a second threshold value and the change over time in the electrical characteristics of the power transmitting coil when stopped is a monotonically decreasing value, the transmitting means transmits to the power receiving device whether or not to use the received power value for detecting the object based on the Q value calculated by the calculation means, and when the absolute value of the increase / decrease in the voltage value requested by the power receiving device to the power transmitting device is equal to or less than the second threshold value and the change over time in the electrical characteristics of the power transmitting coil when stopped is not a monotonically decreasing value, the transmitting means transmits to the power receiving device a notification indicating that it will not determine whether or not to use the received power value for detecting the object.

4. The power transmitting device according to claim 3, characterized in that the transmitting means transmits to the power receiving device a message that the received power value will not be used to detect the object if the absolute value of the increase / decrease in voltage value requested by the power receiving device to the power transmitting device is greater than the second threshold value.

5. The power transmitting device according to claim 1, characterized in that the transmitting means separates the change over time of the electrical characteristics of the transmitting coil when stopped into two or more frequency components, and if the change over time of the electrical characteristics having at least one of the separated frequency components is monotonically decreasing, transmits to the power receiving device a notification indicating whether or not to use the received power value for detecting the object based on the Q value calculated by the calculation means, and if the change over time of all of the electrical characteristics having each of the separated frequency components is not monotonically decreasing, transmits to the power receiving device a notification indicating that it will not determine whether or not to use the received power value for detecting the object.

6. the calculation means calculates a plurality of Q values ​​based on a plurality of points of time-dependent changes in the electrical characteristics of the power transmitting coil when the power transmitting coil is stopped; The power transmitting device according to claim 1 , wherein the transmitting means transmits to the power receiving device information on whether or not the received power value is to be used for detecting the object based on the plurality of Q values.

7. the stopping means repeatedly stops and restarts the voltage applied to the power transmission coil a plurality of times; the calculation means calculates a plurality of Q values ​​based on changes over time in the electrical characteristics of the power transmission coil when the power transmission coil is stopped a plurality of times; The power transmitting device according to claim 1 , wherein the transmitting means transmits to the power receiving device information on whether or not the received power value is to be used for detecting the object based on the plurality of Q values.

8. The power transmitting device according to claim 1 , wherein whether or not the received power value is used for the object detection indicates whether or not the received power value is accepted as a calibration data point.

9. The power transmitting device according to claim 1 , wherein the electrical characteristic of the power transmitting coil is a voltage value of the power transmitting coil.

10. a wheel; and a battery; 2. The power transmitting device according to claim 1, wherein the power transmitting means wirelessly transmits power to the power receiving device using the power of the battery.

11. 2. The power transmitting device according to claim 1, wherein the power transmitting device is installed in a vehicle.

12. A power receiving device that receives power wirelessly, a transmitting means for transmitting a request to calculate a Q value based on a change over time in the electrical characteristics of the power transmitting coil and a received power value to the power transmitting device; The receiving device is characterized in that when the transmitting means receives a notification response indicating that it will not determine whether or not to use the received power value to detect an object other than the receiving device based on the Q value in response to the transmission, it again transmits to the transmitting device a request to calculate the Q value based on changes over time in the electrical characteristics of the transmitting coil and the received power value.

13. The power receiving device described in claim 12, further comprising a limiting means for limiting the received power when a notification response indicating that a determination will not be made as to whether or not the received power value will be used to detect the object based on the Q value is received a threshold number of times in succession in response to the transmission.

14. a battery that stores the power received by the power receiving means; The power receiving device according to claim 12, further comprising: a motor for driving wheels using the electric power of the battery.

15. a battery that stores the power received by the power receiving means; 13. The power receiving device according to claim 12, further comprising: a display unit to which power from the battery is supplied.

16. a battery that stores the power received by the power receiving means; The power receiving device according to claim 12 , further comprising: a notification unit that notifies the user of the remaining charge of the battery.

17. A control method for a power transmission device that wirelessly transmits power, comprising: a receiving step of receiving a request to calculate a Q value and a received power value from the power receiving device; a stopping step of stopping the voltage applied to the power transmitting coil; a calculation step of calculating a Q value based on a change over time in the electrical characteristics of the power transmitting coil when the power transmitting coil is stopped; If the change over time in the electrical characteristics of the power transmitting coil when stopped is a monotonous decrease, a signal indicating whether or not to use the received power value for detecting an object other than the power receiving device is transmitted to the power receiving device based on the Q value calculated in the calculation step, and if the change over time in the electrical characteristics of the power transmitting coil when stopped is not a monotonous decrease, a transmitting step of transmitting a notification to the power receiving device indicating that it will not be determined whether or not to use the received power value for detecting the object; A control method for a power transmitting device, comprising:

18. A control method for a power receiving device that wirelessly receives power, comprising: a first transmission step of transmitting a request to calculate a Q value based on a change over time in an electrical characteristic of the power transmitting coil and a received power value to the power transmitting device; a second transmission step of transmitting to the power transmitting device a request to calculate the Q value based on a change over time in the electrical characteristics of the power transmitting coil and the received power value again when a notification response indicating that it is not determined whether or not the received power value is to be used for detecting an object different from the power receiving device based on the Q value is received as a response to the transmission; A control method for a power receiving device, comprising:

19. A program for causing a computer to function as the power transmitting device according to any one of claims 1 to 11.

20. A program for causing a computer to function as the power receiving device according to any one of claims 12 to 16.