Power transmission device and method

Abstract

To suppress the reduction in detection accuracy in a case where foreign object detection is performed on the basis of measurement results of voltage or current during a period when power transmission is stopped.SOLUTION: A power transmission device 101 has a communication unit 206 that communicates wirelessly using a power receiving device and an antenna, a power transmission unit 203 that transmits power wirelessly to the power receiving device using the antenna, a detection unit 204 for measuring at least one of a voltage and current output from the antenna during a period in which power transmission is stopped and communication by the communication unit 206 is not performed to determine that an object other than the power receiving device is present on the basis of the measurement result, and a control unit 201 that restricts the transmission of power when it is determined that an object other than the power receiving device is present.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power transmission device.

Background Art

[0002] In recent years, the technological development of wireless power transmission systems has been widely carried out. Patent Document 1 discloses a power transmission device and a power reception device compliant with the standard (hereinafter referred to as the WPC standard) formulated by the Wireless Power Consortium (WPC), a standardization organization for wireless charging standards. Communication between the power transmission device and the power reception device is realized by superimposing a signal on the transmitted power using an antenna used during wireless power transmission.

[0003] Patent Document 1 discloses a method of identifying the presence of a foreign object when an object different from the power reception device (hereinafter referred to as a foreign object) exists within the range where the power transmission device can transmit power, and restricting the power transmission based on the identification result.

[0004] Further, Patent Document 2 discloses a method of determining whether an object exists in the vicinity of a power transmitter based on the attenuation amount of the voltage value of the power transmitter during a period in which the voltage of the power transmitter gradually decreases after the power transmission is stopped.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When using an antenna used for wireless power transmission in the communication between a power transmission device and a power reception device, the method disclosed in Patent Document 2 has the following problems. That is, when measuring the voltage during a period when power transmission is stopped, if communication is performed using the antenna used for wireless power transmission, the amplitude change of the signal is reflected in the power, that is, the measured voltage. Therefore, the measured voltage is affected not only by the object but also by communication. And when determining the presence of an object based on this measured voltage, there is a problem that the detection accuracy of the object decreases, such as not being detected when the object is present or being erroneously detected even though the object is not present. And when this method is applied to the detection of foreign objects, the detection accuracy of foreign objects may decrease. This problem also occurs when the measurement target is current.

[0007] The present invention has been made in view of the above problems. The object is to suppress a decrease in detection accuracy when foreign object detection is performed based on the measurement result of voltage or current during a period when power transmission is stopped.

Means for Solving the Problems

[0008] One aspect of the power transmission device according to the present invention includes a communication means for performing wireless communication with a power reception device using an antenna, a power transmission means for wirelessly transmitting power to the power reception device using the antenna, a measurement means for measuring at least one of the voltage and current of the antenna during a period when the power transmission by the power transmission means is stopped and the communication by the communication means is not performed, a determination means for determining that an object different from the power reception device exists based on the measurement result by the measurement means, and a restriction means for restricting the power transmission by the power transmission means when the determination means determines that an object different from the power reception device exists.

Effects of the Invention

[0009] According to the present invention, when foreign object detection is performed based on the measurement results of voltage or current during a period in which power transmission is stopped, it is possible to suppress a decrease in detection accuracy.

Brief Description of the Drawings

[0010]

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Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the components described in the following embodiments are examples of embodiments of the present invention, and the present invention is not limited thereto.

[0012] (First Embodiment) FIG. 1 shows a configuration example of a wireless power charging system (wireless power transmission system) according to the present embodiment. In one example, this system includes a power transmission device 101 and a power reception device 102. Hereinafter, the power reception device may be referred to as RX, and the power transmission device may be referred to as TX. RX 102 is an electronic device that receives power from TX 101 and charges a built-in battery. TX 101 is an electronic device that wirelessly transmits power to RX 102 placed on the charging stand 103. RX 102 can receive power from TX 101 within the range 104. An example of RX 102 is a smartphone, and an example of TX 101 is an accessory device for charging the smartphone. Note that RX 102 and TX 101 may be storage devices such as a hard disk device or a memory device, or may be information processing devices such as a personal computer (PC). Also, RX 102 and TX 101 may be, for example, image input devices such as an imaging device (camera, video camera, etc.) or a scanner, or may be image output devices such as a printer, a copier, or a projector. Further, RX 102 and TX 101 may have a function of executing applications other than wireless charging. Also, TX 101 may be a smartphone. In this case, RX 102 may be another smartphone or a wireless earphone. Also, RX 102 may be an automobile. Also, TX 101 may be a charger installed in a console or the like inside an automobile.

[0013] In addition, in the present embodiment, although one TX 101 and RX 102 are shown, it can also be applied to a configuration in which a plurality of RX 102 are powered from one TX 101 or from separate TX 101s respectively.

[0014] This system shall perform wireless power transmission using the electromagnetic induction method for wireless charging based on the standard for wireless charging (WPC standard) defined by the Wireless Power Consortium (WPC). That is, RX102 and TX101 perform wireless power transmission for wireless charging based on the WPC standard between the power receiving coil (power receiving antenna) of RX102 and the power transmitting coil (power transmitting antenna) of TX101. Note that the wireless power transmission method is not limited to the method defined by the WPC standard, and other electromagnetic induction methods, magnetic field resonance methods, electric field resonance methods, microwave methods, methods using lasers, etc. may be used. Also, in this embodiment, it is assumed that wireless power transmission is used for wireless charging, but wireless power transmission may be performed for uses other than wireless charging.

[0015] In the WPC standard, the magnitude of the power guaranteed when RX102 receives power from TX101 is defined by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates the power value that is guaranteed to be output to the load (charging circuit, etc.) in RX102 even if, for example, the positional relationship between RX102 and TX101 changes and the power transmission efficiency between the power receiving coil and the power transmitting coil decreases. For example, when GP is 5 watts, even if the positional relationship between the power receiving coil and the power transmitting coil changes and the power transmission efficiency decreases, TX101 controls the power transmission so that it can output 5 watts to the load in RX102.

[0016] RX102 and TX101 according to this embodiment perform communication for power transmission and reception control based on the WPC standard. Here, the communication for power transmission and reception control will be described. In the WPC standard, a plurality of phases are defined, including a Power Transfer phase in which power transmission is executed and a phase before power transmission. The phase before power transmission includes (1) Selection phase, (2) Ping phase, (3) Identification & Configuration phase, (4) Negotiation phase, and (5) Calibration phase. Hereinafter, the Identification and Configuration phase will be referred to as the I&C phase.

[0017] (1) In the Selection phase, TX101 intermittently transmits an Analog Ping to detect the presence of an object within the power transmission range (for example, the presence of the power receiving device 102 or a conductor piece on the charging stand 103). That is, the Analog Ping is a detection signal for detecting the presence of an object. TX101 transmits the Analog Ping by applying a voltage or current to the power transmission coil. Then, when an object is placed on the charging stand 103 and when no object is placed, a change occurs in the voltage or current applied to the power transmission coil. Therefore, TX101 detects at least one of the voltage value and current value of the power transmission coil when transmitting the Analog Ping, and determines that an object is present when the voltage value is below a certain threshold or the current value exceeds a certain threshold, and transitions to the Ping phase.

[0018] (2) In the Ping phase, TX101 transmits a Digital Ping with higher power than the Analog Ping. The magnitude of the Digital Ping is sufficient power for the control unit of RX102 placed on the charging stand 103 to start up. RX102 notifies TX101 of the magnitude of the received power voltage. That is, RX102 transmits a Signal Strength packet (hereinafter referred to as the "SS packet") to TX101. In this way, by receiving the response from RX102 that has received its Digital Ping, TX101 recognizes that the object detected in the Selection phase is RX102. When receiving the notification of the received power voltage value, TX101 transitions to the I&C phase.

[0019] (3) In the I&C phase, TX101 identifies RX102 and acquires device configuration information (capability information) from RX102. Therefore, RX102 transmits an ID packet and a Configuration packet to TX101. The ID Packet contains the identification information of RX102, and the Configuration packet contains the device configuration information (capability information) of RX102. TX101 that has received the ID packet and the Configuration packet responds with an acknowledge (ACK). Then, the I&C phase ends.

[0020] (4) In the Negotiation phase, the value of GP is determined based on the value of GP required by RX102, the power transmission capability of TX101, etc.

[0021] (5) In the calibration phase, based on the WPC standard, RX102 uses the Received Power packet to notify TX101 of the received power value. Accordingly, TX101 acquires the transmission power corresponding to the received power and stores it in association with the received power. Then, based on at least two sets of received power and transmission power, TX101 calculates and stores parameters for the foreign object detection process based on power loss. In this embodiment, even in the Power Transfer phase described later, parameters for the foreign object detection process are calculated and stored. Foreign object detection is a process of determining whether there is an object different from RX102 (hereinafter referred to as a foreign object) within the power transmission range of TX101 or whether there may be a foreign object.

[0022] In the Power Transfer phase, control for starting, continuing power transmission, and stopping power transmission due to foreign object detection or full charge is performed.

[0023] TX101 and RX102 superimpose signals related to communication for these power transmission and reception controls on the power using the same antenna (coil) as wireless power transmission based on the WPC standard. Thereby, TX101 and RX102 can perform communication for power transmission and reception control using the same antenna (coil) as wireless power transmission. Note that the range within which communication based on the WPC standard is possible between TX101 and RX102 is substantially the same as the power transmission range. That is, in FIG. 1, range 104 represents the range within which wireless power transmission and communication are possible with the power transmission and reception coils of TX101 and RX102.

[0024] <Device Configuration> Subsequently, the configurations of the power transmission device 101 (TX101) and the power reception device 102 (RX102) according to this embodiment will be described. Note that the configurations described below are merely examples, and a part (in some cases, all) of the described configurations may be replaced with other configurations that perform the same functions or omitted, and additional configurations may be added to the described configurations. Furthermore, one block shown in the following description may be divided into a plurality of blocks, or a plurality of blocks may be integrated into one block.

[0025] FIG. 2 is a diagram showing a configuration example of a power transmission device 101 (TX101) according to the present embodiment. TX101 includes a control unit 201, a power supply unit 202, a power transmission unit 203, a detection unit 204, a power transmission coil 205, a communication unit 206, an output unit 207, an operation unit 208, a memory 209, and a timer 210.

[0026] The control unit 201 controls the entirety of TX101 by executing, for example, a control program stored in the memory 209. That is, the control unit 201 controls each functional unit shown in FIG. 2. Further, the control unit 201 performs control related to power reception control in TX101. In one example, the control unit 201 performs device authentication in TX101 and control necessary for power transmission. The control unit 201 may perform control for executing applications other than wireless power transmission. The control unit 201 includes, for example, one or more processors such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). Note that the control unit 201 may be configured by dedicated hardware for specific processing such as an ASIC (Application Specific Integrated Circuit). Further, the control unit 201 may include an array circuit such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processing. The control unit 201 stores in the memory 209 information that should be stored during the execution of various processes. Further, the control unit 201 can measure time or a time point using the timer 210. Further, when the detection unit 204 described later detects a foreign object, the control unit 201 restricts the power transmission performed by the power transmission unit 203 described later based on the detection of the foreign object.

[0027] The power supply unit 202 transmits power necessary for control, power transmission, and communication to the entire TX101. The power supply unit 202 is, for example, a commercial power supply or a battery. Electric power transmitted from the commercial power supply is stored in the battery.

[0028] The power transmission unit 203 converts the DC or AC power input from the power supply unit 202 into AC frequency power in the frequency band used for wireless power transmission. Further, by inputting the AC frequency power to the power transmission coil 205, an electromagnetic wave for causing power reception by the RX102 is generated. Note that the frequency of the AC power generated by the power transmission unit 203 is about several hundred kHz (for example, 110 kHz to 205 kHz).

[0029] Based on the instruction of the control unit 201, the power transmission unit 203 inputs AC frequency power to the power transmission coil 205 so as to output an electromagnetic wave for power transmission from the power transmission coil 205 to the RX102. Further, the power transmission unit 203 controls the intensity of the output electromagnetic wave by adjusting the voltage (transmission voltage) or current (transmission current) input to the power transmission coil 205. When the transmission voltage or transmission current is increased, the intensity of the electromagnetic wave becomes stronger, and when the transmission voltage or transmission current is decreased, the intensity of the electromagnetic wave becomes weaker. Further, based on the instruction of the control unit 201, the power transmission unit 203 performs output control of the AC frequency power so that power transmission from the power transmission coil 205 is started or stopped. The power transmission unit 203 of the RX102 in the present embodiment has a switch on the circuit connected to the power transmission coil 205. When measuring the Q value (Quality factor) described later, the power transmission unit 203 switches a switch inside the power transmission unit 203 and disconnects the connection with the power transmission coil 205, thereby stopping the application of voltage to the power transmission coil 205. Note that the switch may be located outside the power transmission unit 203. For example, a switch may be provided between the power transmission unit 203 and the detection unit 204 in FIG. 2, or between the detection unit 204 and the power transmission coil 205.

[0030] The detection unit 204 detects whether an object exists in the range 104 by measuring the voltage or current of the power transmission coil 205. For example, the detection unit 204 detects the voltage or current of the power transmission coil 205 when the power transmission unit 203 transmits an Analog Ping of the WPC standard via the power transmission coil 205. Then, the detection unit 204 can determine that an object exists in the range 104 when the voltage is below a predetermined voltage value or the current value exceeds a predetermined current value. Also, whether this object is RX102 or another foreign object is determined to be RX102 when a predetermined response is received for the Digital Ping subsequently transmitted by the communication unit 206. Further, the detection unit 204 measures the voltage of the power transmission coil 205 when obtaining the Q value described later, and detects foreign objects using the Q value obtained based on the measurement result. Details will be described later.

[0031] The communication unit 206 performs control communication based on the WPC standard as described above with RX102. The communication unit 206 modulates the electromagnetic wave output from the power transmission coil 205 and transmits information to RX102. Also, the communication unit 206 demodulates the electromagnetic wave output from the power transmission coil 205 and modulated at RX102 to obtain the information transmitted by RX102. That is, the communication performed by the communication unit 206 is performed by being superimposed on the power transmission from the power transmission coil 205.

[0032] The output unit 207 provides information to the user by any method such as visual, auditory, or tactile means. The output unit 207 notifies the user, for example, of the state of TX101 and information indicating the state of the wireless power transmission system including TX101 and RX102 as shown in FIG. 1. The output unit 207 is configured to include, for example, a liquid crystal display, an LED (Light Emitting Diode), a speaker, a vibration generation circuit, and other notification devices.

[0033] The operation unit 208 has a reception function for receiving operations on TX101 from the user. The operation unit 208 includes, for example, buttons, a keyboard, a voice input device such as a microphone, a motion detection device such as an acceleration sensor or a gyro sensor, or other input devices. Note that a device in which the output unit 207 and the operation unit 208 are integrated, such as a touch panel, may be used.

[0034] The memory 209 stores various information. Note that the memory 209 may store information obtained by a functional unit different from the control unit 201. The timer 210 measures time, for example, by a count-up timer that measures the elapsed time from the start time, a count-down timer that counts down from the set time, or the like.

[0035] FIG. 3 is a diagram showing a configuration example of the power receiving device 102 (RX102) according to the present embodiment. RX102 includes a control unit 301, a battery 302, a power receiving unit 303, a detection unit 304, a power receiving coil 305, a communication unit 306, an output unit 307, an operation unit 308, a memory 309, a timer 310, and a charging unit 311.

[0036] The control unit 301 controls the entire RX102 by, for example, executing a control program stored in the memory 309. In one example, the control unit 301 performs device authentication in RX102 and control necessary for power reception. The control unit 301 may perform control for executing applications other than wireless power transmission. The control unit 301 includes, for example, one or more processors such as a CPU or an MPU. Note that the control unit 201 may include dedicated hardware for specific processing such as an ASIC or an array circuit such as an FPGA compiled to execute predetermined processing. The control unit 301 causes the memory 309 to store information that should be stored during the execution of various processes. Further, the control unit 301 can measure time using the timer 310.

[0037] The battery 302 transmits the power necessary for control, power reception, and communication to the entire RX102. The battery 302 also stores the power received via the power receiving coil 305. In the power receiving coil 305, an induced electromotive force is generated by the electromagnetic wave radiated from the power transmitting coil 205 of the TX101, and the power receiving unit 303 acquires the power generated in the power receiving coil 305.

[0038] The power receiving unit 303 acquires the AC power generated by electromagnetic induction in the power receiving coil 305. Then, the power receiving unit 303 converts the AC power into DC power or AC power of a predetermined frequency and outputs the power to the charging unit 311 that performs a process for charging the battery 302. That is, the power receiving unit 303 transmits power to the load in the RX102. The above-mentioned GP is the amount of power guaranteed to be output from the power receiving unit 303.

[0039] The detection unit 304 detects whether the RX102 is placed within the power reception range 104 from the TX101. The detection unit 304 detects, for example, the voltage or current of the power receiving coil 305 when the power receiving unit 303 receives a Digital Ping conforming to the WPC standard via the power receiving coil 305. Then, the detection unit 304 can determine that the RX102 is placed within the range 104, for example, when the detected voltage is lower than a predetermined voltage threshold or when the detected current value exceeds a predetermined current threshold.

[0040] The communication unit 306 performs the above-described control communication based on the WPC standard by superimposing signals using the same antenna (coil) for wireless power transmission as that for communication with the TX101 based on the WPC standard. The communication unit 306 acquires the information transmitted from the TX101 by demodulating the electromagnetic wave input from the power receiving coil 305. The communication unit 306 further superimposes the information to be transmitted to the TX101 on the electromagnetic wave by load-modulating the electromagnetic wave, thereby performing communication with the TX101. That is, the communication by the communication unit 306 can be performed by being superimposed on the power transmission from the power transmitting coil 205 (FIG. 2) of the TX101.

[0041] The output unit 307 provides information to the user by any method such as visual, auditory, or tactile means. The output unit 307 notifies the user of, for example, the state of RX102 or the state of the wireless power transmission system including TX101 and RX102 as shown in FIG. 1. The output unit 307 is configured to include, for example, a liquid crystal display, an LED, a speaker, a vibration generation circuit, and other notification devices.

[0042] The operation unit 308 has a reception function for receiving an operation on RX102 from the user. The operation unit 308 is configured to include, for example, buttons, a keyboard, a voice input device such as a microphone, a motion detection device such as an acceleration sensor or a gyro sensor, or other input devices. Note that a device in which the output unit 307 and the operation unit 308 are integrated, such as a touch panel, may be used.

[0043] The memory 309 stores various information. Note that the memory 309 may store information obtained by a functional unit different from the control unit 301. The timer 310 measures time, for example, by an up-counter timer that measures the elapsed time from the start time or a down-counter timer that counts down from a set time.

[0044] Next, the processes performed by the power transmission device 101 (TX101) and the power reception device 102 (RX102) according to the present embodiment will be described with reference to the drawings.

[0045] <Processing in the Power Transmission Device> FIG. 4 is a flowchart showing the process executed by the power transmission device 101 (TX101) in the present embodiment. The flowchart shown in FIG. 4 can be realized by the control unit 201 of TX101 executing a control program stored in the memory 209 and performing operations on information, processing of information, control of each hardware, and the like.

[0046] In F401, the control unit 201 executes processes defined as the Selection phase and the Ping phase of the WPC standard. Then, for example, RX102 detects that it is placed on the charging stand 103 of TX101 by detecting the Digital Ping from TX101. And when RX102 detects the Digital Ping, it transmits an SS packet including the value of the received voltage to TX101. RX102 detects that it is placed within the power transmission range of TX101.

[0047] In F402, the control unit 201 acquires identification information and capability information from RX102 by performing communication in the I&C phase via the communication unit 206. The identification information of RX102 may include a Manufacturer Code and a Basic Device ID. The capability information of RX102 may include information capable of specifying the version of the corresponding WPC standard, a Maximum Power Value indicating the maximum value of the power that RX102 can receive, and information indicating whether RX102 has a Negotiation function of the WPC standard. Note that TX101 may acquire the identification information and capability information of RX102 by methods other than communication in the I&C phase. Also, the identification information may include information capable of identifying the individual of RX102, such as a Wireless Power ID. Thus, the identification information may include information other than the above, and similarly, the capability information may also include information other than the above.

[0048] In F403, the control unit 201 determines the value of GP based on the value of GP requested by RX102 and the like by performing communication in the Negotiation phase via the communication unit 206.

[0049] In F404, the control unit 201 starts the processing in the Calibration phase (hereinafter referred to as calibration processing). Here, the calibration processing is a process of calibrating the correlation between the value measured inside TX101 (transmission power) and the value measured inside RX102 (received power) for the power transmitted from TX101 to RX102. In the Calibration phase, TX101 performs power transmission for obtaining communication of information in the calibration processing and the above-described power correlation.

[0050] The steps from F404 to F407 are the processing performed in the Calibration phase. Here, measurement of the Q value is performed to confirm that there is no foreign object within the power transmission range. Using FIG. 7(a), the method for measuring the Q value in the time domain will be described. The waveform shown in FIG. 7(a) shows the change over time of the measured value of the voltage inside the transmission coil 205 of TX101 (hereinafter referred to as voltage value), where the horizontal axis represents time and the vertical axis represents the voltage value. Waveform 700 is the voltage value of the high-frequency voltage applied to the transmission coil 205. Time T0 indicates the time when the application of the high-frequency voltage to the transmission coil 205 is stopped. Point 701 is a part of the envelope of the voltage value indicated by waveform 700. (T1, A1) corresponding to point 701 indicates that the voltage value at time T1 is A1. Similarly, point 702 is a part of the envelope of the voltage value indicated by waveform 700, and (T2, A2) corresponding to point 702 indicates that the voltage value at time T2 is A2.

[0051] The Q value is measured based on the change in the voltage value after the application of the high-frequency voltage to the transmission coil 205 is stopped. In the example shown in FIG. 7(a), 0 the Q value is obtained by measuring the change amount of the voltage value after time T. In the case of FIG. 7(a), for example, the voltage values A1 and A2 at times T1 and T2, which are times within the period after time T0 when the application of the high-frequency voltage is stopped, are measured. Based on these times and the measured voltages, the Q value is calculated by Equation 1.

[0052] Q = ω(T2 - T1) / 2ln(A1 / A2) (Equation 1) In this way, the Q value is calculated based on the time duration from time T1 to time jT2 and the ratio of the voltage value A1 corresponding to time T1 to the voltage value A2 corresponding to time T2. Here, ω represents the angular velocity of the high-frequency voltage 700 (obtained by multiplying the frequency by 2π).

[0053] Next, the process for TX101 in this embodiment to measure the Q value will be described with reference to FIG. 7(b). Waveform 703 is the high-frequency voltage applied to the power transmission coil 205 by the power transmission unit 203, and its frequency is within the range of 110 kHz to 148.5 kHz used in the WPC standard. During the period from time T0 to time T5, the power transmission unit 203 switches the switch and disconnects the connection with the power transmission coil 205, thereby stopping the application of the high-frequency voltage. Note that the period from time T0 to time T5 is a very short period compared to when TX101 performs power transmission to RX102.

[0054] Points 704 and 705 are parts of the envelope of the voltage value indicated by waveform 703. The power transmission unit 203 stops power transmission during the period from time T0 to time T5, and the detection unit 204 measures the voltage values at time T3 during this period and at time T4 after a predetermined time has elapsed from time T3. In the example shown in FIG. 7(b), the voltage values at time T3 and time T4 are A3 and A4, respectively. TX101 calculates the Q value according to Equation 1 using time T3, time T4, voltage value A3, voltage value A4, and the angular velocity of the high-frequency voltage. In this way, the detection unit 204 in TX101 measures the voltage value and calculates the Q value while the power transmission unit 203 stops power transmission to RX102. TX101 switches the switch in the power transmission unit 203 at time T5 and resumes power transmission.

[0055] By the method described above, TX101 in the present embodiment acquires a Q value. Further, TX101 performs foreign object detection based on the acquired Q value and confirms that there is no foreign object within the power transmission range. At this time, TX101 stores in advance, as a reference value, the Q value measured in a state where there is no foreign object within the power transmission range. When power transmission is performed when there is a foreign object such as a conductor piece within the power transmission range, not only RX102 but also the foreign object consumes power. As a result, when there is a foreign object, it is assumed that the voltage value when TX101 stops power transmission attenuates more significantly than when there is no foreign object. Accordingly, it is assumed that the value of the Q value based on Equation 1 when there is a foreign object becomes smaller than the Q value when there is no foreign object. Therefore, TX101 determines (detects a foreign object) that there is a foreign object based on the fact that the acquired Q value is smaller than the reference value. At this time, TX101 calculates the difference between the acquired Q value and the reference value, and determines that there is a foreign object when the difference is larger than a predetermined threshold value. Further, when the difference between the acquired Q value and the reference value is smaller than the predetermined threshold value, TX101 can confirm that there is no foreign object within the power transmission range.

[0056] Here, the communication unit 206 of TX101 in this embodiment communicates information with RX102 by modulating or demodulating the electromagnetic wave generated by the voltage applied by the power transmission unit 203 to the power transmission coil 205. Also, the communication unit 306 of RX102 communicates information with TX101 by load-modulating the electromagnetic wave received by the power reception coil 305. Therefore, even if the voltage value is measured while the communication by the communication unit 206 and the communication unit 306 is being performed, a voltage value suitable for obtaining the Q value used for foreign object detection may not be measured. For example, if load modulation is performed during the period from T0 to T5 when TX101 stops applying voltage in FIG. 7(b), the voltage value may change compared to the case where no load modulation is performed. As a result, the values of voltage A3 and voltage A4 at time T3 and time T4 when load modulation is performed may be larger or smaller than the voltage value when no load modulation is performed. If the Q value obtained based on this voltage value is used for foreign object detection, there is a possibility that a foreign object may not be detected when a foreign object is present, or that a false detection may occur when no foreign object is present.

[0057] For the above reasons, it is desirable that during the period when the power transmission device measures the Q value, communication of information by TX101 and RX102 is not performed. During the calibration process, power reception power information for notifying TX101 of the received power and information for requesting an increase or decrease in the received power are transmitted from RX102 to TX101. RX102 in the present embodiment does not perform communication during a specific period defined in the WPC standard as a period during which a power receiving device must not transmit a signal. The period during which RX102 does not perform communication is, for example, a period defined in the WPC standard as a period during which a power receiving device must not transmit a preamble of the next packet from the end of a packet transmitted by the power receiving device. That is, the period during which RX102 does not perform communication is a period until a predetermined time elapses after a signal is transmitted by the power receiving device and it is defined that the next signal must not be transmitted. Also, for example, the period during which RX102 does not perform communication is a period defined in the WPC standard as a period during which a power receiving device must not transmit a preamble of the next packet from the end of a packet transmitted by the power transmission device. That is, the period during which RX102 does not perform communication is a period until a predetermined time elapses after a signal is received by the power receiving device from the power transmission device and it is defined that the power receiving device must not transmit the next signal. Therefore, TX101 in the present embodiment measures the Q value using the period during which RX102 does not perform communication as described above. At this time, TX101 also does not transmit a signal to RX102. TX101 in the present embodiment waits until information is transmitted from RX102 (F405), and after receiving the information transmitted from RX102, measures the voltage value of the power transmission coil 205 during the period when information transmission by RX102 is not performed (F406). In the following description, measuring the voltage value of the power transmission coil 205 to calculate the Q value used for foreign object detection is simply expressed as measuring the Q value, but the process of calculating the Q value based on Equation 1 may be performed during a period when communication is being performed. TX101 in the present embodiment performs at least voltage value measurement during a period when communication is not performed.

[0058] Note that foreign object detection based on the measurement result of the Q value can be used in combination with foreign object detection based on power loss. However, foreign object detection based on power loss cannot be executed unless the processing in the Calibration phase for calculating the parameters used for foreign object detection is completed. That is, foreign object detection based on power loss cannot be used in the Calibration phase. If a foreign object exists within the power transmission range at the Calibration phase, inappropriate parameters may be obtained, and the accuracy of foreign object detection based on power loss in the subsequent Power Transfer phase may decrease. In contrast, foreign object detection based on the measurement result of the Q value can be executed even in the Calibration phase, so it is possible to determine whether a foreign object exists at the Calibration phase. As a result, TX101 can determine that there is a foreign object at the Calibration phase and restrict the power transmission.

[0059] In F407, TX101 performs foreign object detection by comparing the Q value measured in F406 with a reference value stored in advance. If a foreign object is detected (Yes in F407), TX101 stops power transmission (F414). If no foreign object is detected (No in F407), the calibration process is terminated (F408).

[0060] In F409, TX101 shifts to the Power Transfer phase and starts power transmission for wireless charging to RX102. Even after starting the power transmission for charging, TX101 periodically receives the received power information from RX102. Therefore, in F410, TX101 monitors whether predetermined information is transmitted from RX102. The predetermined information includes the received power information for notifying the above-mentioned power and the information for requesting an increase or decrease in the received power.

[0061] In F410, when receiving predetermined information, TX101 measures the Q value by using the period during which information is not transmitted by RX102 (F411). In F411, foreign object detection based on the measurement result of the Q value and foreign object detection based on the loss of the transmitted power are performed. The foreign object detection based on the power loss is a process of determining that a foreign object exists when the value of the power transmitted by TX101 is lost more than a predetermined amount. The foreign object detection based on the power loss is performed by RX102 notifying TX101 of the received power. By performing foreign object detection in F411, it is possible to detect that a foreign object is placed within the power transmission range during charging. Note that the foreign object detection executed here may be either one of the foreign object detection based on the measurement result of the Q value and the foreign object detection based on the loss of the transmitted power. Also, in F411, at least the process of measuring the voltage value of the power transmission coil 205 may be performed during the period when communication is not performed. That is, since the calculation of the Q value based on the measured voltage value of the power transmission coil 205 and the process of foreign object detection based on the Q value can be performed even when communication is being performed, for example, it may be executed after F411. Also, since the foreign object detection based on the power loss can also be performed during communication, as long as RX102 notifies TX101 of the received power, it may be performed in a process other than F411.

[0062] Here, the combined use of foreign object detection based on the measurement result of the Q value and foreign object detection based on the power loss will be described. When both the result of foreign object detection based on the measurement result of the Q value and the result of foreign object detection based on the power loss are "no foreign object exists", TX101 determines that no foreign object exists. On the other hand, when at least one of the result of foreign object detection based on the measurement result of the Q value and the result of foreign object detection based on the power loss is "a foreign object exists", TX101 determines that a foreign object exists (with a high possibility). Thereby, TX101 can suppress erroneously determining that no foreign object exists when a foreign object exists and transmitting power.

[0063] In addition, when the results of foreign object detection based on the measurement result of the Q value and the results of foreign object detection based on power loss are different, TX101 may prioritize the results of either one of the foreign object detections. For example, when prioritizing the results of foreign object detection based on power loss, assume that in the foreign object detection based on the measurement result of the Q value, it is determined that "no foreign object exists", and in the foreign object detection based on power loss, it is determined that "a foreign object exists". In this case, TX101 prioritizes the results of foreign object detection based on power loss and determines that "a foreign object exists". Similarly, the results of foreign object detection based on the measurement result of the Q value may be prioritized. In the case of the method where TX101 determines that "a foreign object exists" when at least one of the plurality of foreign object detections described above determines that "a foreign object exists", the situation of transmitting power even though a foreign object exists is suppressed. However, this method may also limit power transmission frequently. Therefore, when using a plurality of foreign object detection methods, it can be expected that power transmission will not be frequently restricted by determining in advance which foreign object detection result to prioritize.

[0064] When a foreign object is detected in F412, TX101 stops the charging process (Yes in F414). The processes from F410 to F412 are repeatedly executed until a charging completion notification transmitted from RX102 is received. TX101 does not receive predetermined information in F410 (No in F410), and when receiving a notification indicating charging completion transmitted from RX102 (Yes in F413), TX101 stops power transmission for charging (F414).

[0065] <Processing in the power receiving device> FIG. 5 is a flowchart showing the processing executed by the power receiving device 102 (RX102) in the present embodiment. The flowchart shown in FIG. 5 can be realized by the control unit 301 of RX102 executing a control program stored in the memory 309 and performing calculation of information, processing of information, and control of each hardware.

[0066] In F501, RX102 is loaded within the power transmission range of TX101 by a user or the like. In F502, the communication unit 306 transmits identification information and capability information to TX101 through communication in the I&C phase. In F503, the control unit 301 determines the value of GP with TX101 through communication in the Negotiation phase via the communication unit 306. Note that in F503, other procedures for determining GP different from the communication in the Negotiation phase may be executed.

[0067] In F504, the communication unit 306 executes calibration processing for configuring the correlation between the power transmission power and the power reception power with TX101. When the calibration processing is completed, in F505, the power reception processing for charging RX102 is started. Note that in the steps of the calibration processing and the power reception processing, RX102 transmits to TX101 power reception power information for notifying the received power, information for requesting an increase or decrease in the power reception power, and the like. When the charging of RX102 is completed, RX102 transmits a notification indicating that the charging is completed to TX101 (F506).

[0068] <Operation Sequence of Power Transmission Device and Power Reception Device> FIG. 6 shows the operation sequence of the power transmission device 101 (TX101) and the power reception device 102 (RX102). In order to detect an object existing within the power transmission range, TX101 intermittently transmits an Analog Ping conforming to the WPC standard (S601). RX102 is placed within the power transmission range of TX101 by a user or the like (S602). TX101 detects that the voltage of the power transmission coil 205 becomes smaller than a predetermined value or the current of the power transmission coil 205 becomes larger than a predetermined value when transmitting the Analog Ping. Thereby, TX101 detects that an object exists within the power transmission range (S603, S604). After detecting that an object exists within the power transmission range, TX101 transmits a Digital Ping conforming to the WPC standard (S605). RX102 receives the Digital Ping and recognizes that it has been detected by TX101 (S606). When there is a predetermined response to the Digital Ping, TX101 detects that the detected object is RX102 and RX102 is placed on the charging stand 103.

[0069] When TX101 detects that RX102 is placed, it acquires identification information and capability information from RX102 by performing communication in the I&C phase conforming to the WPC standard (S607). TX101 determines the value of GP with RX102 by performing communication in the Negotiation phase conforming to the WPC standard (S608). Note that in S608, other procedures for determining GP different from the communication in the Negotiation phase conforming to the WPC standard may be executed. Also, when RX102 does not correspond to the Negotiation phase of the WPC standard, it transmits information indicating non-correspondence to TX101 at the timing of S607 or the like. At this time, when TX101 acquires information indicating that RX102 does not correspond to the Negotiation phase of the WPC standard, it may determine GP without performing communication in the Negotiation phase. The value of GP determined at this time is, for example, a value defined in the WPC standard. In the example of FIG. 6, GP = 5 W (watts) is determined in S608.

[0070] Subsequently, calibration processing is performed. First, RX102 transmits first reference power information to TX101 (S609). Here, the reference power information is information indicating the power received by RX102. After transmitting the reference power information, RX102 does not perform communication (information transmission) until a predetermined time elapses based on the WPC standard (S610). When TX101 receives the reference power information transmitted from RX102, TX101 performs Q-value measurement using the period during which RX102 does not perform communication (S611). TX101 checks whether there is a foreign object within the power transmission range based on the measurement result of the Q value. If a foreign object is detected, TX101 ends the power transmission process to RX102.

[0071] In S609, RX102 transmits information indicating that it has received power of 500 mW (milliwatts) as the first reference power information. The first reference power information is information indicating the power received by the power transmission coil 305 measured in a state where the power receiving unit 303 and the charging unit 311 are not connected. TX101 determines whether to accept the first reference power information based on the power transmission state of its own device. TX101 transmits an affirmative response (ACK) to RX102 if it accepts, and a negative response (NAK) if it does not accept. At this time, TX101 can accept the first reference power information if it determines that the power indicated by the first reference power information can be stably transmitted, and not accept it if it determines that the power cannot be stably transmitted. In the example of FIG. 6, TX101 determines that the power transmission state is stable and transmits ACK to RX102 (S612). If TX101 transmits NAK, RX102 measures the received voltage value again and transmits new first reference power information to TX101.

[0072] Here, the execution timing of S611 (measurement of Q value) and S612 (transmission of ACK) is mentioned. If the processes of S611 and S612 overlap, for the reasons described above, it may not be possible to measure the voltage value suitable for obtaining the Q value used for foreign object detection. Also, if TX101 stops applying voltage during the transmission of ACK, the ACK data may be damaged. Therefore, the processes of S611 and S612 are preferably carried out so as not to overlap. Also, since the period when RX102 does not perform communication is a period of waiting for a response from TX101, when RX102 acquires an ACK or NAK transmitted from TX101, RX102 resumes communication. Therefore, TX101 measures the Q value before transmitting the ACK. Note that the process of determining whether a foreign object exists based on the measurement result of the Q value may be before or after the transmission of the ACK.

[0073] After receiving the ACK from TX101, RX102 performs a process to request TX101 to transmit power of the value of GP. In the example of FIG. 6, since GP = 5W, RX102 transmits instruction information indicating an instruction to change the power transmission output (S613) in order to increase the power transmission power by TX101 up to 5W. This instruction information may include a value (positive value) indicating the amount of power increase. Even after transmitting the instruction information, RX102 does not perform communication until a predetermined time elapses based on the WPC standard. TX101 measures the Q value using the period when communication by RX102 is not performed, and performs foreign object detection based on the Q value (S615). After measuring the Q value, TX101 transmits an ACK to RX102 as a response indicating that it can respond to the instruction to increase the power indicated by the instruction information, and changes the power transmission output based on the instruction information (S616, S617).

[0074] In S618, RX102 transmits, as the second reference power information, information indicating that it receives power of 5W. The second reference power information is information indicating the power received by the power receiving coil 305, which is measured in a state where the power receiving unit 303 and the charging unit 311 are connected. TX101 performs measurement of the Q value and foreign object detection by using a period during which communication is not performed after RX102 transmits the second reference power information (S619, S620). Further, TX101 calculates an estimated value of the power loss in power transmission based on at least either the voltage value or the current value of the power transmission coil 205 when the own device performs power transmission, and the first and second reference power information. TX101 performs foreign object detection based on the calculated estimated value of the power loss (S621). Further, TX101 transmits an ACK to RX102 as a response indicating that it accepts the second reference power information transmitted from RX102 (S622). Note that the processing of S621 and S622 may be reversed. Through the processing up to S622, TX101 determines that the calibration processing is completed and the charging processing can be started, starts the power transmission processing to RX102, and the charging of RX102 is started.

[0075] Here, referring to the operations after S623 in FIG. 6, the operation sequence when the GP that has been once determined is changed (redetermined) will be described. For example, TX101 and RX102 perform an authentication process for authenticating each other's devices (S623), and based on the authentication result, determine whether the mutual devices can support a GP larger than the current GP (5W). If it is determined that they can support a larger GP, the GP is redetermined to, for example, 15W (S624). Note that when determining whether they can support a larger GP, the determination may be based on a method other than the authentication process. RX102 transmits instruction information for increasing the power transmission output in order to increase the power transmission output of TX101 up to 15W. TX101 transmits ACK or NAK to RX102 as a response to the instruction information. When TX101 transmits ACK, it increases the power transmission output based on the instruction information. Also in this step, TX101 measures the Q value and performs foreign object detection using the period during which communication is not performed after RX102 transmits information. Further, foreign object detection based on the estimated value of power loss similar to S621 is also performed (S625 to S630).

[0076] TX101 and RX102 perform the calibration process again. RX102 transmits to TX101 information indicating that it has received the re-determined GP = 15W as the third reference power information (S631). TX101 measures the Q value and performs foreign object detection using the period during which communication is not performed after RX102 transmits the third reference power information (S633). Also, TX101 performs foreign object detection by calculating an estimated value of power loss based on at least either the voltage value or the current value of the power transmission coil 205 when the device itself performs power transmission, and the first, second, and third reference power information (S634). Further, TX101 transmits an ACK to the third reference power information transmitted from RX102 (S635) and starts the power transmission process. Regarding S631, if TX101 cannot respond to the third reference power information within a predetermined time, power transmission may be performed at 15W while withholding the transmission of the ACK, or power transmission may be continued at a power transmission power of up to 5W. At this time, TX101 and RX102 may display a screen for allowing the user to select whether to perform charging at 15W or 5W on the output unit 207 and the output unit 307 that each has. Also, the user may specify which to select by operating the operation unit 208 or the operation unit 308, or may specify by operating the operation screen displayed on the output unit 207 or the output unit 307.

[0077] As described above, TX101 measures the voltage value of the power transmission coil 205 when the application of voltage to the power transmission coil 205 is stopped during the period when communication is not performed after RX102 transmits information, and calculates the Q value. Also, TX101 performs foreign object detection based on the calculated Q value, and stops power transmission if a foreign object is detected. This suppresses the continuation of power transmission even when a conductive foreign object exists within the power transmission range. Also, by combining the above method with foreign object detection based on power loss, TX101 can perform more reliable foreign object detection. Note that as the processing of TX101 when a foreign object is detected, it may be restricted to stop power transmission as described above, or it may be restricted so that the power transmission power becomes smaller than when no foreign object is detected.

[0078] Also, as a process when a foreign object is detected, a configuration in which GP is re-determined between TX101 and RX102 may be adopted. When TX101 determines that RX102 has the ability to perform re-negotiation regarding GP, TX101 transmits a signal instructing RX102 to perform re-negotiation for re-determining GP. At this time, TX101 may notify the power receiving device of the maximum value of the negotiable GP. Also, the maximum value of the negotiable GP may be limited to 5W. Further, when TX101 determines that RX102 does not have the ability to perform re-negotiation regarding GP, TX101 performs processing such as limiting so that the power transmission power becomes smaller than the time when no foreign object is detected, changing the value of the power transmission power to a predetermined value (for example, 5W), or stopping.

[0079] (Second Embodiment) In the following description, the differences from the first embodiment will be mainly described. Since the configurations of the power transmission device 101 (TX101) and the power receiving device 102 (RX102) are the same as those in the first embodiment, the description thereof will be omitted.

[0080] <Processing in the Power Transmission Device> FIG. 8 is a flowchart showing the processing executed by the power transmission device 101 (TX101) in the second embodiment. The flowchart shown in FIG. 8 can be realized by the control unit 201 of TX101 executing the control program stored in the memory 209 and performing calculation of information, processing of information, and control of each hardware. Since the processing from F801 to F804 is the same as the processing from F401 to F404 in FIG. 4, the description thereof will be omitted.

[0081] When the calibration process is started in F804, power reception information for notifying the received power to TX101 from RX102 and information for requesting an increase or decrease in the received power are transmitted (F405). TX101 makes a response such as ACK to the received information. At this time, TX101 adds information that enables identification of the timing for measuring the Q value to the ACK data and transmits it (F806). As an example, TX101 adds time information indicating the time when the Q value is measured using a data format as shown in FIG. 11. The time information may be, for example, a value based on the elapsed time from the time when TX101 is activated, or a value indicating the offset time from the time when ACK is transmitted. When applying a value based on the elapsed time, TX101 and RX102 are set to perform processing based on the same time. For example, TX101 and RX102 share the time when TX101 is activated, the time elapsed since TX101 was activated, etc. in the I&C phase or the like, and are set to match the processing times. Then, RX102 acquires ACK from TX101 and stops communication at the time indicated by the time information. Also, when applying a value indicating the offset time, RX102 acquires ACK from TX101 and stops communication until the offset time indicated by the time information has elapsed.

[0082] TX101 adds the time information as described above to the ACK and transmits it, and measures the Q value during the period when RX102 does not perform communication based on the time information. Since the processing from F808 to F810 is the same as the processing from F407 to F409, the description is omitted. At F811, TX101 monitors whether or not predetermined information (such as received power information for notifying power and information for requesting an increase or decrease in received power) has been transmitted from RX102. At F811, when the predetermined information is received, TX101 transmits an ACK as a response to the predetermined information. At this time, TX101 adds, for example, the time information as described above to the ACK and transmits it (F812). At F813, TX101 measures the Q value based on the timing indicated by the transmitted time information and performs foreign object detection wp (F813). At this time, TX101 may perform foreign object detection based on power loss. The foreign object detection based on power loss may be configured to be performed in a step other than F813, or may be configured not to be performed as a whole process. Note that the method for measuring the Q value and the method for foreign object detection are assumed to be the same as those in the first embodiment. Since the processing from F814 to F816 is the same as the processing from F412 to F414, the description is omitted.

[0083] As described above, TX101 can make it possible that communication is not performed during the measurement of the Q value by transmitting information that enables RX102 to specify the timing of measuring the Q value. Note that the information added to the ACK only needs to be information that enables TX101 to specify the timing of measuring the Q value, and is not limited to the above. For example, instruction information for instructing RX102 to stop communication may be transmitted, and RX102 may not perform communication until a predetermined time has elapsed after acquiring the instruction information. The predetermined time at this time may be set in advance based on the time required for measuring the Q value and the delay time related to the communication between RX102 and TX101, or may be included in the instruction information. Further, the predetermined time may be determined by the communication in the Negotiation phase in F803. Further, TX101 may individually transmit time information, instruction information, etc. without adding information to the ACK. Further, it may be combined with a method of measuring the Q value during a period in which communication is not performed after predetermined information is transmitted from RX102 as in the first embodiment. For example, TX101 may be configured to use the method described in this embodiment from F805 to F807 and use the method described in the first embodiment in the steps after F810. These modifications are similarly applicable in the following description.

[0084] <Processing in the power receiving device> FIG. 9 is a flowchart showing the processing executed by the power receiving device 102 (RX102) in the second embodiment. The flowchart shown in FIG. 9 can be realized by the control unit 301 of RX102 executing a control program stored in the memory 309 and performing arithmetic operations on information, information processing, and control of each hardware. Since the processing from F901 to F905 is the same as that from F501 to F505 in FIG. 5, the description thereof is omitted. When the power receiving process is started, RX102 performs power receiving power information for notifying the received power, data transmission for requesting an increase or decrease in the received power, etc. (F906). RX102 receives an ACK or the like from TX101 as a response to the transmitted information (F907). At this time, since time information for specifying the timing at which TX101 measures the Q value is added to the ACK, RX102 extracts the time information (F908). RX102 restricts communication from being performed based on the time information (F909). Thereafter, RX102 repeatedly executes the processing from F906 to F909 until charging is completed. When charging is completed (F910), RX102 transmits a notification indicating that charging is completed to TX101 (F911).

[0085] <Operation sequence of power transmission device and power receiving device> FIG. 10 shows the operation sequence of the power transmission device 101 (TX101) and the power receiving device 102 (RX102) in the second processing example. Since the processing from S1001 to S1008 is the same as that from S601 to S608 in FIG. 6, the description of these processes is omitted.

[0086] When TX101 determines the value of GP with RX102, it starts the calibration process. First, RX102 transmits, as the first reference power information, information indicating the power received by the power receiving coil 305 in a state where the power receiving unit 303 and the charging unit 311 are connected to TX101 (S1009). In the example of FIG. 10, the first reference power information is 500 mW. TX101 determines whether to accept the first reference power information based on its own power transmission state. If it determines to accept, it transmits ACK to RX102, and if it determines not to accept, it transmits NAK to RX102. In the example of FIG. 10, TX101 determines that it can stably transmit the power indicated by the first reference power information and transmits ACK to RX102.

[0087] TX101 sets the timing for measuring the Q value and transmits the time information as information that can identify the timing by adding it to ACK (S1010, S1011). RX102 that has received ACK extracts the time information added to ACK and restricts communication based on this time information (S1012). TX101 measures the Q value based on the timing indicated by the time information and performs foreign object detection (S1013).

[0088] After restricting communication for a predetermined period based on the time information, RX102 transmits, as the second reference power information, information indicating the power received by the power receiving coil 305 in a state where the power receiving unit 303 and the charging unit 311 are connected to TX101. In the example of FIG. 10, since GP = 5 W, the second reference power information is 5 W. RX102 transmits instruction information for instructing a change in the power transmission output in order to increase the power transmission power by TX101 to 5 W (S1014). TX101 receives the instruction information transmitted from RX102 and increases the power transmission power if it can respond to the increase in the power transmission power (S1015).

[0089] Even when responding to the indication information, TX101 adds time information for specifying the timing of measuring the Q value to the ACK and transmits it (1016, S1017). RX102 that has received the ACK extracts the time information added to the ACK and restricts communication from being performed based on this time information (S1018). TX101 measures the Q value based on the timing indicated by the time information and performs foreign object detection (S1019).

[0090] Thereafter, RX102 transmits second reference power information (5W) to TX101 (S1020). TX101 calculates an estimated value of power loss based on the received power included in the first and second reference power information and performs foreign object detection (S1021). Also, TX101 transmits an ACK to the second reference power information from RX102. Also in this case, TX101 performs Q value measurement, but since the method is the same as that from S1010 to S1013, the description is omitted (S1022 to S1025). Through the above processing, TX101 and RX102 complete the calibration process and start charging RX102.

[0091] Here, the processing when the GP once determined in this embodiment is changed (redetermined) will be described with reference to FIG. 10. TX101 and RX102 perform, for example, the authentication process of the device (S1026). When it is determined that the mutual devices can support a larger GP, the GP is redetermined to 15W (S1027). Thereafter, TX101 and RX102 perform a recalibration process for increasing the transmission power of TX101 to 15W in the same manner as the processes from S1014 to S1017 (S1028 to S1031). Also, RX102 transmits a value of 15W as the third reference power information. TX101 transmits a response to the third reference power information to RX102. During this period, TX101 also adds time information to the ACK and transmits it, measures the Q value based on the timing indicated by the time information, and performs foreign object detection (S1033 to S1038). TX101 confirms that no foreign object is present and starts power transmission for charging. Regarding S1033, if TX101 cannot respond to the third reference power information within a predetermined time, power transmission may be performed at 15W while withholding the transmission of the ACK, or power transmission may be continued at a transmission power of up to 5W. Also at this time, TX101 and RX102 may perform a screen display for allowing the user to select whether to perform charging at 15W or 5W on the output unit 207 and the output unit 307 they each have. Further, the user may specify which to select by operating the operation unit 208 or the operation unit 308, or may specify it by operating the operation screen displayed on the output unit 207 or the output unit 307.

[0092] As described above, TX101 can prevent communication from occurring during the measurement of the Q value by transmitting, for example, time information or the like as a signal for specifying the timing of measuring the Q value. Note that the timing at which TX101 measures the Q value may be notified to RX102 using another configuration. TX101 stores information that enables the specification of the timing of measuring the Q value in a Power Transmitter Capability packet defined by the WPC standard as a packet for notifying the power receiving device of information regarding the capabilities of the power transmission device. TX101 can notify RX102 of the timing of measuring the Q value by transmitting a packet in which instruction information, time information, and the like are stored to RX102. Also, for example, in the Negotiation phase, RX102 may request TX101 to transmit information that enables the specification of the timing of measuring the Q value in order to specify the timing of measuring the Q value. In this case, TX101 transmits an affirmative response (ACK) and time information or the like to RX102 in response to the request, or transmits a negative response (NAK) to RX102. Also, for example, RX102 may transmit time information or the like to TX101 in order to specify the timing of measuring the Q value to TX101.

[0093] (Third Embodiment) In this embodiment, a configuration for restricting communication from occurring by having the power receiving device 102 (RX102) detect the measurement of the Q value performed by the power transmission device 101 (TX101) will be described. The detection unit 304 of RX102 detects that the application of the voltage has been stopped by TX101 for measuring the Q value by measuring at least one of the voltage or current of the power receiving coil 305. For example, when RX102 measures the voltage of the power receiving coil 305 and detects a decrease in the voltage, RX102 determines that TX101 is measuring the Q value and restricts communication from occurring until a predetermined time has elapsed. The predetermined time can be set in advance based on, for example, the length of time required for measuring the Q value. With this configuration, RX102 can prevent communication from occurring while TX101 measures the Q value.

[0094] Note that, as for the situation where RX102 detects a voltage drop in the power receiving coil 305, there are cases where TX101 measures the Q value and cases where power transmission stops due to an error such as TX101 malfunctioning. Therefore, when RX102 detects a voltage drop in the power receiving coil 305, it waits without communicating for a predetermined time required for measuring the Q value. If power transmission does not resume even after the predetermined time has elapsed, it may be configured to transmit a signal for requesting power transmission. By doing so, RX102 can also handle the stop of power transmission during a failure.

[0095] (Other Embodiments) TX101 in the above-described embodiment measures the Q value based on the passage of time of the voltage inside the power transmission coil 205, but is not limited to this method, and it is also possible to measure the Q value based on the passage of time of the current inside the power transmission coil 205. In this case, TX101 measures the current value A3 at T3 and the current value A4 at time T4, and calculates the Q value based on Equation 1 using the measured current values and the frequency of the high-frequency current.

[0096] Further, TX101 may perform foreign object detection without calculating the Q value. In the case of Fig. 7(b), for example, TX101 measures the voltage values A1 and A2 at time T3 and time T4 during the period when the application of the voltage to the power transmission coil 205 is stopped. Based on the measurement results, TX101 determines whether a foreign object is present based on the difference (slope) of the voltage values during the period from time T3 to time T4. When a foreign object exists within the power transmission range, it is assumed that the voltage value of the power transmission coil 205 decays more significantly than when no foreign object is present. Therefore, when the measured voltage difference (slope) is greater than or equal to a certain value compared to the reference value (the difference in voltage at two times) obtained when no foreign object is present, TX101 determines that a foreign object is present. Also, TX101 can perform foreign object detection by obtaining the ratio of the voltage value A1 to the voltage value A2. For example, when the ratio of the voltage A1 at time T1 to the voltage A2 at time T2 is greater than or equal to a certain value compared to the reference value (the ratio of the voltages at two times) obtained when no foreign object is present, TX101 determines that a foreign object is present.

[0097] Note that when performing foreign object detection without calculating the Q value as described above, the calculated voltage difference and ratio may vary depending on the magnitude of the voltage applied to the power transmission coil 205 and the timing of voltage measurement. Therefore, by matching the magnitude of the voltage and the timing of voltage measurement with the conditions when the reference value was obtained, it becomes possible to perform foreign object detection more reliably.

[0098] Also, TX101 in the above-described embodiment measures at least one of the voltage or current output by the power transmission coil 205 and performs foreign object detection based on the measurement results, but is not limited thereto. For example, another device connected to the outside of TX101 may measure and calculate the voltage, current, power output by the power transmission coil 205, and the energy stored in the capacitor in TX101, etc., and provide the obtained values to TX101. TX101 can perform foreign object detection based on the values provided by another device.

[0099] Also, the TX101 in the above-described embodiment is configured to stop applying voltage to the power transmission coil 205 by switching the switch in the power transmission unit 203 to disconnect the connection with the power transmission coil 205 when measuring the Q value, but it is not limited thereto. For example, the power transmission unit 203 may stop applying voltage by setting the power transmission voltage to 0 when measuring the Q value. Also, when measuring the Q value, a configuration may be adopted in which the power transmission voltage is not completely set to 0 but switched to a lower voltage value. However, since the Q value measurement method in this embodiment calculates the Q value based on the degree of attenuation of the voltage value, the Q value can be measured without completely stopping the voltage application by reducing the voltage value to at least a voltage value at which the attenuation of the voltage value can be observed. At this time, if the period during which the voltage is reduced exceeds a certain time, there is a possibility that an error is determined to have occurred in TX101 on the RX102 side. Therefore, it is desirable to set the reduction width of the voltage value such that the attenuation of the voltage can be measured during a period when TX101 is not determined to be abnormal by RX102.

[0100] Also, the TX101 in the above-described embodiment performs foreign object detection by measuring the Q value after stopping the voltage. However, in any embodiment, the possibility that an error is determined to have occurred in TX101 on the RX102 side when the voltage is stopped is conceivable. Therefore, when the RX102 is placed within the power transmission range of the TX101, a method for solving the above problem will be described by the RX102 acquiring information regarding the TX101.

[0101] RX102 transmits a signal to TX101 to instruct it to transmit information about TX101, for example, through communication in the Negotiation phase. The information about TX101 includes TX101's version information, information about the standards TX101 complies with, and information such as the method of foreign object detection used by TX101. TX101 transmits information about TX101 to RX102, and RX102 recognizes based on the acquired information that TX101 stops the voltage for a predetermined period for Q value measurement. Thereby, when TX101 stops applying the voltage for Q value measurement, it is possible to suppress RX102 from erroneously determining that an error has occurred in TX101, and the charging process can be stably continued. Also, when transmitting information for specifying the timing at which TX101 performs Q value measurement, for example, as in the second embodiment, by sharing the information format, RX102 can appropriately perform communication restrictions.

[0102] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and having one or more processors in the computer of the system or apparatus read and execute the program. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Explanation of Reference Numerals

[0103] 102 Power transmission device 201 Control unit 203 Power transmission unit 204 Detection unit 205 Power transmission coil 206 Communication unit

Claims

1. A communication means for wirelessly communicating using a power receiving device and an antenna; a power transmitting unit that transmits power wirelessly to the power receiving device using the antenna; a measuring means for measuring at least one of a voltage and a current output from the antenna during a period in which the power transmission means stops transmitting power and the communication means does not perform the communication; A determination means for determining that an object other than the power receiving device is present based on a measurement result by the measurement means; a limiting means for limiting transmission of power by the power transmitting means when the determining means determines that an object other than the power receiving device is present.

2. A method performed by a power transmitting device, comprising: It communicates wirelessly using a power receiving device and an antenna, The antenna is used to wirelessly transmit power to the power receiving device; measuring at least one of a voltage and a current output from the antenna during a period in which the transmission of power is stopped in the power transmitting step and the communication is not performed in the communication step; determining, based on a measurement result of the measurement performed in the measuring step, that an object other than the power receiving device is present; The method further comprising: limiting the transmission of power in the power transmitting step when it is determined in the determining step that an object other than the power receiving device is present.

3. A program for causing a computer to execute the method according to claim 2.

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