Power transmission device and method performed by power transmission device

Abstract

To provide a technique for suppressing a decrease in the accuracy of foreign substance detection.SOLUTION: A power transmission device measures a Q-value of power transmission means that performs wireless power transmission to a power reception device, and determines the presence or absence of an object different from the power reception device on the basis of a reference Q-value received from the power reception device and the measured Q-value. The power transmission device acquires a first index value related to a predetermined physical quantity different from the reference Q-value after the measurement of the Q-value, acquires a second index value related to the predetermined physical quantity before starting power transmission to the power reception device after determining the absence of the object different from the power reception device in the determination, and determines the presence or absence of the object different from the power reception device on the basis of the first index value and the second index value.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a power receiving device and a power receiving device in wireless power transmission, a control method thereof, and a program.

Background Art

[0002] The technology of wireless power transmission systems has been widely developed. Patent Document 1 describes a method for detecting foreign objects during power transmission and reception in accordance with a standard (WPC standard) established by the Wireless Power Consortium (WPC), a standardization organization for wireless charging standards. In Patent Document 1, the Q value (quality factor value) of the coil of the wireless power transmission system is measured before the start of power transmission and reception, and foreign object detection is performed based on the measured Q value and the reference Q value received from the power receiving device. When it is determined that no foreign object exists by foreign object detection based on the Q value, subsequently, an estimated value of the power loss between the power transmission and reception device and the power receiving device is calculated. After the start of power transmission and reception, foreign object detection is performed based on the difference between the estimated value and the measured value of this power loss. A foreign object is an object different from the power receiving device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the WPC standard, following the measurement of the Q value by the power transmission device, the exchange of identification information and capability information, and the negotiation of various parameters related to power transmission and reception are carried out between the power transmission device and the power reception device. Thereafter, the power transmission device performs foreign object detection based on the reference Q value and the measured Q value, and calculates an estimated value of power loss if no foreign object is detected. Therefore, if a foreign object enters during the time from the measurement of the Q value to the calculation of the estimated value of power loss, the power transmission device cannot detect the foreign object. Further, if a foreign object enters during this time, the estimated value of power loss is calculated in a state where there is a foreign object, resulting in a decrease in accuracy in foreign object detection based on the power loss after the start of power transmission.

[0005] The present invention provides a technique for suppressing a decrease in the accuracy of foreign object detection.

Means for Solving the Problems

[0006] The power transmission device according to one aspect of the present invention has the following configuration. That is, Power transmission means for performing wireless power transmission to the power reception device, Measurement means for measuring the Q value of the power transmission means, First acquisition means for acquiring a first index value related to a predetermined physical quantity different from the Q value after the measurement of the Q value, First determination means for determining the presence or absence of an object different from the power reception device based on the Q value indicated by the information received from the power reception device and the Q value measured by the measurement means, Second acquisition means for acquiring a second index value related to the predetermined physical quantity after it is determined by the first determination means that there is no object different from the power reception device and before starting wireless power transmission to the power reception device, Second determination means for determining the presence or absence of an object different from the power reception device based on the first index value and the second index value.

Effects of the Invention

[0007] According to the present invention, it is possible to suppress a decrease in the accuracy of foreign object detection.

Brief Description of the Drawings

[0008]

Figure 1

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Figure 10

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0010] <First Embodiment> (Configuration of the System) FIG. 1 shows a configuration example of a wireless charging system (wireless power transmission system) according to the present embodiment. In one example, this system is configured to include a power receiving device 101 and a power transmitting device 102. Hereinafter, the power receiving device 101 may be referred to as RX, and the power transmitting device 102 may be referred to as TX. RX is an electronic device that receives power from TX and charges a built-in battery. TX is an electronic device that wirelessly transmits power to RX placed on a charging stand 103. The range 104 indicates a power transmission range in which RX can receive the power transmitted from TX. Note that RX and TX may have functions to execute applications other than wireless charging. RX is, for example, a smartphone, and TX is, for example, an accessory device for charging the smartphone. RX and TX may be storage devices such as a hard disk device and a memory device, or may be information processing devices such as a personal computer (PC). Also, RX and TX may be, for example, image input devices such as an imaging device (a camera, a video camera, etc.) and a scanner, or may be image output devices such as a printer, a copier, and a projector. TX may be a smartphone or the like. In this case, for example, RX may be another smartphone or a wireless earphone. Also, RX may be a vehicle such as an automobile or a transporter, or TX may be a charger installed in a console or the like of a vehicle such as an automobile or a transporter.

[0011] This system performs wireless power transmission using an electromagnetic induction method for wireless charging based on the WPC standard defined by the Wireless Power Consortium (WPC). That is, RX and TX perform wireless power transmission for wireless charging based on the WPC standard between the power receiving coil of RX and the power transmitting coil of TX. Note that the wireless power transmission method is not limited to the method defined by the WPC standard, and may be other electromagnetic induction methods, magnetic field resonance methods, electric field resonance methods, microwave methods, methods using lasers, etc. Also, in the present embodiment, it is assumed that wireless power transmission is used for wireless charging, but wireless power transmission may be performed for uses other than wireless charging.

[0012] In the WPC standard, the amount of power guaranteed when the RX receives power from the TX 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 of the RX, such as a charging circuit, even if, for example, the positional relationship between the RX and the TX changes and the power transmission efficiency between the power receiving coil and the power transmitting coil decreases. For example, when GP is 15 watts, even if the positional relationship between the power receiving coil and the power transmitting coil changes and the power transmission efficiency decreases, the TX controls the power transmission so that 15 watts can be output to the load in the RX. Also, in the WPC standard, a method for the TX to detect the presence of an object (foreign object) that is not a power receiving device (near the power receiving antenna) around the TX is defined. More specifically, a method for detecting a foreign object based on a change in the quality factor (Q value) of the power transmitting antenna (power transmitting coil 303) in the TX and a power loss method for detecting a foreign object based on the difference between the power transmitted in the TX and the power received in the RX are defined. The foreign object detection based on the Q value is performed before power transmission (Negotiation phase or Renegotiation phase). Also, the foreign object detection by the power loss method is performed during power transmission (Power Transfer phase, described later) based on the data obtained by performing Calibration, which will be described later. Details will be described later. Note that the foreign object is, for example, a conductive object such as a metal piece or an IC card.

[0013] The RX and TX according to this embodiment perform communication for power transmission and reception control based on the WPC standard and communication for device authentication. Here, the communication for power transmission and reception control based on the WPC standard will be described.

[0014] In the WPC standard, multiple phases are defined, including the Power Transfer phase in which power transmission is executed and the phases before actual power transmission. Communication for power transmission and reception control required in each phase is performed. The phases before power transmission may include the Selection phase, Ping phase, Identification and Configuration phase, Negotiation phase, and Calibration phase. Hereinafter, the Identification and Configuration phase will be referred to as the I&C phase.

[0015] In the Selection phase, the TX intermittently transmits an Analog Ping to detect the presence of an object within the power transmission range (for example, an RX or a conductor piece is placed on the charging stand 103). In the Ping phase, the TX transmits a Digital Ping with higher power than the Analog Ping. The power of the Digital Ping is sufficient to activate the control unit of the RX placed on the TX. The RX notifies the TX of the magnitude of the received voltage via a Signal Strength Packet. In this way, the TX recognizes that the object detected in the Selection phase is an RX by receiving a response from the RX (a packet notifying the received voltage) that is a response to the Digital Ping transmitted by the TX itself. When the TX receives a notification of the received voltage from the RX, it transitions to the I&C phase. Also, before transmitting the Digital Ping, the TX measures the Q value (Q-Factor) of the power transmission antenna (power transmission coil 303). This measurement result is used when performing foreign object detection processing using the Q value.

[0016] In the I&C phase, the TX identifies the RX and acquires device configuration information (capability information) from the RX. Therefore, the RX transmits an ID Packet and a Configuration Packet. The ID Packet contains the identifier information of the RX. The Configuration Packet contains the device configuration information (capability information) of the RX. The TX that has received the ID Packet and the Configuration Packet responds with an acknowledge (ACK, positive response). Then, the I&C phase ends.

[0017] In the Negotiation phase, the value of GP is determined based on the value of GP requested by the RX, the power transmission capability of the TX, etc. Also, the TX executes foreign object detection processing using the Q value based on the reference Q value (described later) based on the Q value included in the request from the RX and the measured Q value. Further, in the WPC standard, once the Power Transfer phase has been entered, a method of performing the same processing as in the Negotiation phase again according to the request of the RX is defined. The phase of performing these processes after migrating from the Power Transfer phase is called the Renegotiation phase. In the Calibration phase, based on the WPC standard, the RX notifies the TX of predetermined received power values (for example, the received power value in the light load state and the received power value in the maximum load state), and the TX performs adjustments for efficient power transmission. These received power values notified to the TX can also be used for foreign object detection processing by the power loss method.

[0018] In the power transfer phase, power transmission is continued and control is performed for reasons such as power transmission stop due to errors or full charge. TX and RX perform communication for these power transmission and reception controls based on the WPC standard. In this embodiment, this communication is performed by in-band communication in which signals are superimposed using the same antenna (coil) as wireless power transmission. Note that the range in which in-band communication based on the WPC standard is possible between TX and RX is almost the same as the power transmission possible range. Therefore, in FIG. 1, range 104 represents the range in which wireless power transmission is possible and the range in which in-band communication is possible by the power transmission and reception coils of TX and RX. In the following description, "the RX is placed on the charging stand 103" means that the RX has entered the inside of range 104, and actually includes a state where the RX is not placed on the charging stand 103.

[0019] (Configuration of the power receiving device 101 and the power transmitting device 102) Next, the configurations of the power receiving device 101 (RX) and the power transmitting device 102 (TX) according to this embodiment will be described. Note that the configurations described below are merely examples, and part (or in some cases, all) of the described configurations may be replaced with other configurations that perform the same functions or omitted, and additional configurations may be added to the described configurations. 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.

[0020] ·Configuration of RX FIG. 2 is a block diagram showing a configuration example of the RX according to this embodiment. The RX of this embodiment complies with the WPC standard. In one example, the RX includes a control unit 200, a power receiving coil 201, a rectifying unit 202, a voltage control unit 203, a communication unit 204, a charging unit 205, a battery 206, a resonance capacitor 207, a switch 208, a memory 209, and a timer 210.

[0021] The control unit 200 controls the entire RX by executing, for example, a control program stored in the memory 209. The control unit 200 may perform control for executing applications other than wireless power transmission. The control unit 200 includes one or more processors such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). Note that the control unit 200 may include dedicated hardware for specific processing such as an application-specific integrated circuit (ASIC), or an array circuit such as an FPGA (Field Programmable Gate Array) compiled to execute predetermined processing. The control unit 200 stores in the memory 209 the information that should be stored during the execution of various processes. Also, the control unit 200 can measure time using the timer 210.

[0022] The power receiving coil 201 receives power from the power transmission coil of the power transmission device. Also, the power receiving coil 201 is connected to the resonance capacitor 207 and resonates at a specific frequency. The rectifying unit 202 converts the AC voltage and AC current from the power transmission coil received via the power receiving coil 201 into a DC voltage and a DC current. The voltage control unit 203 converts the level of the DC voltage input from the rectifying unit into the level of the DC voltage at which the control unit 200, the charging unit 205, etc. operate. The communication unit 204 performs control communication based on the WPC standard as described above by in-band communication with the TX. The communication unit 204 demodulates the electromagnetic wave input from the power receiving coil 201 to acquire the information transmitted from the TX, and superimposes the information to be transmitted to the TX on the electromagnetic wave by load-modulating the electromagnetic wave, thereby performing communication with the TX. That is, the communication performed by the communication unit 204 is performed superimposed on the power transmission from the power transmission coil of the power transmission device. The battery 206 supplies power necessary for control, power reception, and communication to the entire RX. Also, the battery 206 stores the power received via the power receiving coil 201.

[0023] Switch 208 is a switch for short - circuiting the power - receiving coil 201 and the resonance capacitor 207, and is controlled by the control unit 200. When switch 208 is turned on, the power - receiving coil 201 and the resonance capacitor 207 form a series resonance circuit. At this time, current flows only through the closed circuit of the power - receiving coil 201, the resonance capacitor 207, and the switch 208, and no current flows through the rectifying unit 202 and the voltage - control unit 203. When switch 208 is turned off, current flows through the rectifying unit 202 and the voltage - control unit 203 via the power - receiving coil 201 and the resonance capacitor 207. Memory 209 stores various information as described above. Note that memory 209 may store information obtained by a functional unit different from the control unit 200. Timer 210 includes, for example, an up - counter timer that measures the elapsed time from the start time, a down - counter timer that counts down from a set time, etc., and performs timing using these.

[0024] ·Configuration of TX FIG. 3 is a diagram showing a configuration example of the TX according to the present embodiment. The TX of the present embodiment complies with the WPC standard. In one example, the TX has a control unit 300, a power supply unit 301, a power - transmission unit 302, a power - transmission coil 303, a communication unit 304, a resonance capacitor 305, a switch 306, a memory 307, and a timer 308.

[0025] The control unit 300 controls the entire TX by, for example, executing a control program stored in the memory 307. The control unit 300 may perform control for executing applications other than wireless power transmission. The control unit 300 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 300 may include dedicated hardware for specific processing such as an ASIC (Application - Specific Integrated Circuit) or an array circuit such as an FPGA (Field - Programmable Gate Array) compiled to execute predetermined processing. The control unit 300 causes the memory 307 to store information that should be stored during the execution of various processes. Also, the control unit 300 can measure time using the timer 308.

[0026] The power supply unit 301 supplies the power necessary for control, power transmission, and communication to the entire TX. The power supply unit 301 is, for example, a commercial power supply or a battery. The power transmission unit 302 converts the DC or AC power input from the power supply unit 301 into AC power in the frequency band used for wireless power transmission, and generates an electromagnetic wave for power reception by the RX by inputting the AC power into the power transmission coil 303. Note that the frequency (AC frequency) of the AC power generated by the power transmission unit 302 is about several hundred kHz (for example, 110 kHz to 205 kHz). Based on the instruction of the control unit 300, the power transmission unit 302 inputs the AC power of the above AC frequency into the power transmission coil 303 so as to output an electromagnetic wave for power transmission from the power transmission coil 303 to the RX. In addition, the power transmission unit 302 controls the intensity of the output electromagnetic wave by adjusting the voltage (transmission voltage) or current (transmission current) input to the power transmission coil 303. 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 300, the power transmission unit 302 performs output control of the AC frequency power so that the power transmission from the power transmission coil 303 is started or stopped. The power transmission coil 303 is connected to the resonance capacitor 305 and resonates at a specific frequency.

[0027] The communication unit 304 performs control communication based on the WPC standard as described above through in-band communication with the RX. The communication unit 304 modulates the electromagnetic wave output from the power transmission coil 303 to transmit information to the RX. Also, the communication unit 304 demodulates the electromagnetic wave output from the power transmission coil 303 and modulated at the RX to obtain the information transmitted by the RX. That is, the communication performed by the communication unit 304 is superimposed on the power transmission from the power transmission coil 303. The switch 306 is a switch for short-circuiting the power transmission coil 303 and the resonance capacitor 305, and is controlled by the control unit 300. When the switch 306 is turned on, the power transmission coil 303 and the resonance capacitor 305 form a series resonance circuit. At this time, current flows only in the closed circuit of the power transmission coil 303, the resonance capacitor 305, and the switch 306. When the switch 306 is turned off, power is supplied to the power transmission coil 303 and the resonance capacitor 305 from the power transmission unit 302. The memory 307 stores various information as described above. Note that the memory 307 may store information obtained by a functional unit different from the control unit 300. The timer 308 measures time, for example, by an up-counter that measures the elapsed time from the start time, a down-counter that counts down from the set time, or the like.

[0028] ·Regarding the functional configuration of the TX Next, the functional configuration of the control unit 300 of the TX will be described with reference to FIG. 4. The control unit 300 includes a communication processing unit 401, a power transmission processing unit 402, a foreign object detection processing unit 403, and a calculation processing unit 404.

[0029] The communication processing unit 401 performs control communication with the RX based on the WPC standard via the communication unit 304. The power transmission processing unit 402 controls the power transmission unit 302 and controls the power transmission to the RX based on the WPC standard.

[0030] The foreign object detection processing unit 403 measures the power loss between the power transmission device and the power reception device, and the Q value of the power transmission antenna (power transmission coil 303) to detect foreign objects. The foreign object detection processing unit 403 can implement a foreign object detection function based on the power loss method and a foreign object detection function based on the Q value. These foreign object detection functions will be described later. Note that the foreign object detection processing unit 403 may perform foreign object detection processing using other methods. For example, in a TX equipped with an NFC communication function, foreign object detection processing may be performed using the opposing device detection function according to the NFC standard. Note that NFC is an abbreviation for Near Feald Communication. Also, the foreign object detection processing unit 403 can measure the Q value in the time domain and detect foreign objects based on the measurement result. The Q value measurement in the time domain will be described later. Furthermore, as a function other than detecting foreign objects, the foreign object detection processing unit 403 can also detect that the state on the TX has changed. For example, it is also possible to detect an increase or decrease in the number of power reception devices in the range 104.

[0031] The calculation processing unit 404 measures the power output to the RX via the power transmission unit 302 and calculates the average output power value for each unit time. The foreign object detection processing unit 403 performs foreign object detection processing based on the power loss method using the calculation result by the calculation processing unit 404 and the received power value received from the power reception device via the communication processing unit 401. The communication processing unit 401, the power transmission processing unit 402, the foreign object detection processing unit 403, and the calculation processing unit 404 have their functions realized as programs operating in the control unit 300. Each processing unit is configured as an independent program and can operate in parallel while synchronizing between programs by event processing or the like.

[0032] (Regarding the foreign object detection method) ·Foreign object detection method based on Q value Next, a foreign object detection method based on the Q value defined in the WPC standard, which is executed by the foreign object detection unit 403, will be described. First, the TX measures the Q value that changes due to the influence of foreign objects in the frequency domain (Q value measurement). This Q value measurement is performed after transmitting the Analog Ping and before transmitting the Digital Ping. Specifically, the power transmission unit 302 sweeps the frequency of the wireless power output by the power transmission coil 303, and measures the voltage value at the end of the resonance capacitor 305 connected in series (or in parallel) with the power transmission coil 303. The power transmission unit 302 searches for the resonance frequency (f1) at which this voltage value peaks, and calculates the Q value (f1 / (f2 - f3)) of the power transmission coil using the frequencies (f2, f3) indicating the voltage values that are 3 dB lower than the peak voltage value (the voltage value measured at the resonance frequency). As another example of the Q value measurement method, the following method can be mentioned. That is, the power transmission unit 302 sweeps the frequency of the wireless power output by the power transmission coil 303, measures the voltage value at the end of the resonance capacitor 305 connected in series with the power transmission coil 303, and searches for the resonance frequency at which the voltage value peaks. Then, the power transmission unit 302 measures the voltage values across the resonance capacitor 305 at that resonance frequency, and calculates the Q value of the power transmission coil 303 from the ratio of those measured voltage values.

[0033] Next, TX acquires the Q value, which serves as the criterion for foreign object detection, from RX. Specifically, TX receives from RX the Q value of the power transmission coil 303 when RX is placed within the power transmission range 104 achievable by the power transmission coil 303 defined in the WPC standard. This Q value is stored in the FOD (Foreign Object Detection) Status Packet received from RX. TX infers the Q value of the power transmission coil 303 when RX is placed at TX from the Q value (the Q value held by RX) stored in the FOD Status Packet. The Q value thus inferred is referred to as the reference Q value in this embodiment. It is assumed that the Q value stored in the FOD Status Packet is pre-stored in the non-volatile memory (e.g., memory 209) of RX. Then, the foreign object detection unit 403 of TX compares the reference Q value with the actually measured Q value and determines the presence or absence of a foreign object based on the comparison result. More specifically, with a Q value reduced by a% with respect to the reference Q value as the threshold, if the actually measured Q value is lower than the threshold, it is determined that there is a foreign object, and if not, it is determined that there is no foreign object.

[0034] ·Foreign object detection method based on the power loss method Next, a foreign object detection method based on the power loss method defined in the WPC standard, which is executed by the foreign object detection processing unit 403, will be described with reference to FIG. 7. The horizontal axis in FIG. 7 represents the transmission power of the TX, and the vertical axis represents the received power of the RX. The TX acquires the received power value Pr1 received by the RX. The received power value Pr1 is transmitted from the RX, for example, stored in Received Power Packet (mode1) and received by the TX. At this time, the RX is not supplying the received power to the load (such as a charging circuit and a battery), and the received power value Pr1 indicates the received power value in a light load state. The TX stores the received power value Pr1 and the transmission power value Pt1 at that time in the memory 307 (point 700). The TX recognizes that the power loss amount between the TX and the RX when transmitting the power of the transmission power value Pt1 is Pt1 - Pr1 (Ploss1). Next, the TX acquires the received power value Pr2 received by the RX. The received power value Pr2 is transmitted from the RX, for example, stored in Received Power Packet (mode2) and received by the TX. The received power value Pr2 is the received power value in a state where the RX is supplying the received power to the load (connected load). The TX stores the received power value Pr2 and the transmission power value Pt2 at that time in the memory 307 (point 701). The TX recognizes that the power loss amount between the TX and the RX when transmitting the power of the transmission power value Pt2 is Pt2 - Pr2 (Ploss2).

[0035] Thereafter, TX linearly interpolates between point 700 and point 701 to create line 702. Line 702 is treated as indicating the relationship between the transmitted power and the received power in a state where there is no foreign object around TX and RX. TX can predict the received power value in a state where there is a high probability of no foreign object from the transmitted power value and line 702. For example, when the transmitted power value is Pt3, TX predicts that the received power value at RX will be Pr3 from point 703 on line 702. Here, assume that when TX transmits power to RX at a transmitted power of Pt3, TX receives a received power value Pr3' from RX. TX calculates a value Pr3 - Pr3' (= Ploss_FO) obtained by subtracting the actually received power value Pr3' from RX from the estimated received power value Pr3 in a state where there is no foreign object. This Ploss_FO can be considered as the power loss consumed by the foreign object when there is a foreign object between TX and RX (for example, within range 104). Therefore, when the power Ploss_FO that would have been consumed by the foreign object exceeds a predetermined threshold value, TX determines that there is a foreign object.

[0036] Note that the procedure for detecting a foreign object is not limited to the above procedure. For example, the following procedure may be used. That is, TX obtains in advance the power loss amount Pt3 - Pr3 (Ploss3) between TX and RX from the received power value Pr3 in a state where there is no foreign object. Next, from the received power value Pr3' received from RX in a state where there is a foreign object, the power loss amount Pt3 - Pr3' (Ploss3') between the transmitting device and the receiving device in a state where there is a foreign object is obtained. Then, Ploss3' - Ploss3 (= Ploss_FO) may be used to obtain the power Ploss_FO that would have been consumed by the foreign object. As described above, as a method for obtaining the power Ploss_FO that would have been consumed by the foreign object, it may be obtained as Pr3 - Pr3' (= Ploss_FO), or it may be obtained as Ploss3' - Ploss3 (= Ploss_FO).

[0037] After obtaining the straight line 702, the power transmission device periodically receives the current received power value (Pr3') from the power reception device. The current received power value periodically transmitted by the power reception device is transmitted to the power transmission device as Received Power Packet (mode0). The power transmission device performs foreign object detection based on the received power value stored in the Received Power Packet (mode0) and the straight line 702. The above is the explanation of foreign object detection based on the power loss method. Incidentally, in this embodiment, the points 700 and 701 for obtaining the straight line 702, which is the relationship between the transmitted power and the received power when there is no foreign object around the power transmission device and the power reception device, are expressed as Calibration data Point. Also, the line segment (straight line 702) obtained by interpolating at least two Calibration data Points is expressed as a Calibration curve. Although the name curve is used, a part or the whole of the Calibration curve may be a straight line.

[0038] (Flow of processing by the power transmission device 102) Subsequently, an example of the flow of processing executed by the TX will be described. FIG. 5 shows an example of the flow of processing executed by the TX. This processing can be realized, for example, by the control unit 300 of the TX executing a program read from the memory 307. Note that at least a part of the following procedures may be realized by hardware. In this case, the hardware can be realized, for example, by automatically generating a dedicated circuit using a gate array circuit such as an FPGA from a program for realizing each processing step using a predetermined compiler. Also, this processing can be executed in response to the power of the TX being turned on, in response to the user of the TX inputting an instruction to start the wireless charging application, or in response to the TX being connected to a commercial power supply and receiving power supply. Also, this processing may be started by other triggers.

[0039] First, TX starts the process defined as the Selection phase of the WPC standard. In the Selection phase, TX repeatedly transmits intermittent Analog Pings of the WPC standard to detect objects existing inside the power transmission range 104 (S501). When TX detects that there is an object within range 104, it measures the Q value (measurement of the Q value in the frequency domain) for foreign object detection based on the Q value described above and stores the result (S502). After measuring the Q value, TX transitions to the Ping phase of the WPC standard and transmits a Digital Ping. When there is a predetermined response to the Digital Ping, TX determines that the detected object is RX and RX is placed on the charging stand 103 (S503). When TX detects that RX is placed on the charging stand 103, it calculates the power loss (Ploss0) (S504). Here, the power loss is calculated by the difference between the received power value received from RX and the power transmission power value at TX at that time. Note that the power loss calculated at this time corresponds to the value calculated in a state where the power received by RX is not supplied to the load (Light Load).

[0040] After calculating the power loss, TX transitions to the I&C phase of the WPC standard and acquires the identifier information and capability information of RX (S505). The identifier information of RX may include the Manufacturer Code and Basic Device ID of the WPC standard. Also, the capability information of RX includes an information element specifying the corresponding WPC standard version, a value (Maximum Power Value) specifying the maximum power that RX can supply to the load, and information indicating whether RX has the Negotiation function of the WPC standard. Note that these are just examples, and the identifier information and capability information of RX may be replaced by other information or may include other information in addition to the above information. For example, the identifier information may include any other identifier information that can identify the individual of RX, such as Wireless Power ID. Also, TX may acquire the identifier information and capability information of RX by methods other than communication in the I&C phase.

[0041] Subsequently, TX transitions to the Negotiation phase of the WPC standard, receives the FOD Status Packet from RX, and obtains the reference Q value based on its content (S506). When TX obtains the reference Q value, it performs the above-described "foreign object detection based on Q value" (S507) and determines whether there is a foreign object in the range 104 (S508). Specifically, TX determines the presence or absence of a foreign object by comparing the Q value measured in S502 with the reference Q value obtained in S503. If TX determines that a foreign object is present (YES in S508), it stops the process (S515). On the other hand, if TX determines that no foreign object is present (NO in S508), it determines the value of GP with RX (S509). Note that in S509, not only the communication in the Negotiation phase of the WPC standard but also other procedures for determining GP may be executed. If RX does not support the Negotiation phase, TX may not perform the communication in the Negotiation phase and set the value of GP to a predetermined value, for example, predefined in the WPC standard. TX can determine whether RX supports the Negotiation phase based on the information obtained, for example, in S505 (I&C phase).

[0042] After the GP's decision, TX transitions to the Calibration phase of the WPC standard and calculates the first reference power loss for creating the Calibration curve described above (S510). The first reference power loss is the power loss (Ploss1) in the state where the power received by RX is not supplied to the load (Light Load). As described above with reference to FIG. 7, it is calculated from the received power value Pr1 received from RX and the transmission power value Pt1 at that time. After calculating the first reference power loss, TX performs foreign object detection based on the power loss (Ploss0) calculated in S504 and the first reference power loss (Ploss1) (S511), and determines whether a foreign object exists (S512). Here, whether a foreign object exists is determined by calculating the difference (Ploss1 - Ploss0) between the power loss calculated in S504 and the first reference power loss, and checking whether the difference is equal to or greater than the threshold value. If it is determined that a foreign object exists (YES in S512), TX stops the process (or transmission) (S515).

[0043] On the other hand, if it is determined that no foreign object exists (NO in S512), TX calculates the second reference power loss (S513). The second reference power loss is the power loss (Ploss2) in the state where the power received by RX is supplied to the load (Connected Load). As described above, it is calculated from the received power value Pr2 received from RX and the transmission power value Pt2 at that time. After calculating the second reference power loss, TX creates a Calibration curve from the first reference power loss (Ploss1) and the second reference power loss (Ploss2), and executes transmission (S514). The transmission by TX is performed by the processing in the Power Transfer phase of the WPC standard. However, it is not limited to this, and transmission may be performed by a method other than the WPC standard.

[0044] (Flow of the process executed in the system) With reference to FIG. 6, the operation sequence of the system (TX and RX) according to the first embodiment will be described. Note that, as an initial state, it is assumed that the RX is not placed within the power transmission range of the TX, and the TX has sufficient power transmission capacity to execute power transmission at the GP required by the RX. Hereinafter, a case where a foreign object has entered after the TX has detected the placement of the RX and performed the measurement of the Q value (S502) and the calculation of the power loss (S504) will be described. In this case, since the measurement of the Q value is performed before the foreign object has entered, the "foreign object detection method based on the Q value" determines that no foreign object is present, and the processing in the Calibration phase is executed. However, since the difference between the first reference power loss (S510) and the power loss (S504) calculated when the placement of the RX is detected is equal to or greater than the threshold value, the TX determines that a foreign object is present and stops the processing before starting power transmission. Hereinafter, the description will be made with reference to FIG. 6.

[0045] The TX waits for an object to be placed by Analog Ping (S501, F601). When the RX is placed on the charging stand 103 (F602), a change occurs in the Analog Ping (F603). By detecting this change, the TX detects that some object has been placed on the charging stand 103 (F604). When the TX detects that an object has been placed on the charging stand 103, it measures the Q value of the power transmission coil (S502, F605). Thereafter, the TX transmits a Digital Ping as a placement detection request (S503, F606). When the RX receives the Digital Ping and detects that it has been placed on the charging stand 103 of the TX (F607), it transmits a packet (received power voltage notification) for notifying the received power voltage value (F608). By receiving the received power voltage notification, which is a response to the Digital Ping (F608), the TX detects that the placed object is the RX (F609). Here, for example, a Signal Strength Packet of the WPC standard can be used for the received power voltage notification.

[0046] Next, when TX adjusts the transmitted power and receives a received power notification indicating that the received power value from RX is 250 milliwatts (F610), it calculates the power loss (Ploss0) from the difference between the transmitted power value at that time and the received received power value (S504, F611). At this time, the power transmitted from TX and received by RX is sufficient power for the control unit 200 of RX to activate. Also, the power loss calculated at this time may correspond to the power loss in the state (Light Load) where RX does not supply the received power to the load, that is, the first reference power loss (Ploss1). Note that for this received power notification, the Received Power Packet (mode0) of the WPC standard can be used. However, it is not limited to this, and for example, a Specific Request defined in the WPC standard may be used. Also, the received power value may be included in the received voltage notification of F608, that is, the Signal Strength Packet and notified. In this case, the received power notification of F610 may be omitted.

[0047] Subsequently, through communication in the I&C phase, TX acquires identification information and capability information from RX (S505, F612). At this time, it is assumed that a foreign object has entered the range 104 where TX can transmit power (F613). Subsequently, when TX acquires a reference Q value based on the Q value notified from RX (S506, F614), it performs foreign object detection based on the Q value measured in F605 and the reference Q value (S507, F615). Since a foreign object has entered after the Q value was measured in F605, it is determined in this foreign object detection that no foreign object exists (NO in S508, F616).

[0048] Next, GP is determined by communication during the Negotiation phase between TX and RX (S509, F617). In this example, GP = 15 watts is determined. Subsequently, TX adjusts the transmission power and receives the first reference received power notification by communication during the Calibration phase (F618). Here, the transmission power is adjusted to be equivalent to the transmission power when receiving a received power notification of 250 mW, for example, at F610. In the example of FIG. 6, since a foreign object has invaded (F613), a first reference received power notification with a received power value = 100 milliwatts is received from RX. TX calculates the power loss (Ploss1) from the difference between the received power value stored in the received first reference received power notification and its own transmission power value (S510, F619), and transmits an ACK, which is a response indicating acceptance (F620). When TX transmits the ACK, TX performs foreign object detection based on the difference between the power loss (Ploss0) calculated at F611 and the first reference power loss (Ploss1) calculated at F619 (S511, F620). In the example of FIG. 6, due to the invasion of a foreign object, the difference between the power loss calculated at F611 and the power loss calculated at F619 becomes equal to or greater than the threshold value. TX determines that a foreign object exists (YES at S512, F622), and transmits an EPT (End Power Transfer Packet) to RX to stop the process (F623).

[0049] As described above, according to the first embodiment, after TX measures the Q value for foreign object detection, TX acquires the power loss as an index value of a predetermined physical quantity different from the Q value for foreign object detection. Then, TX performs foreign object detection based on the power loss acquired during the Calibration phase performed after foreign object detection based on the Q value and the power loss acquired after measurement of the Q value. Since the above-mentioned power loss acquired after measurement of the Q value is implemented within a short period after measurement of the Q value, when it is determined that no foreign object exists by foreign object detection based on the Q value, it can be said that the power loss is acquired in a state where the possibility of a foreign object existing is extremely low. Therefore, even if a foreign object invades during the period from after measurement of the Q value until the start of the processing in the Calibration phase, it is possible to detect the foreign object with a high probability, and a safer wireless power transmission system can be realized.

[0050] (Modification example) In the above example, after measuring the Q value, the power loss (Ploss0) in the state where the power received by RX is not supplied to the load (Light Load) is obtained, and foreign object detection is performed based on the difference from the first reference power loss (Ploss1). Also, when obtaining the power loss (Ploss0), the transmission power of TX is adjusted so that the received power notification received from RX indicates 250 milliwatts. However, it is not limited to these. For example, the state of RX may be set to the state where the received power is supplied to the load (Connected Load), and after increasing the transmission output of TX until the received (transmitted) power value equivalent to GP is reached, the power loss may be obtained using the received power indicated by the received power notification. In this case, foreign object detection may be performed based on the difference between the power loss obtained after Q value measurement and the second reference power loss (Ploss2). Also, the power loss may be obtained after TX adjusts the transmission output until a predetermined received (transmitted) power value is reached (after increasing the transmission power output). In this case, for example, foreign object detection can be performed based on the difference between the power loss after Q value measurement and the power loss at a predetermined received (transmitted) power value on the Calibration curve obtained in the Calibration phase. Also, foreign object detection may be performed by obtaining the power loss at a predetermined received (transmitted) power value during the process of increasing the transmission output during the Calibration phase (during the generation of the Calibration curve). That is, the received power value received from the power receiving device when generating the Calibration curve can be used for foreign object detection. Thereby, since foreign object detection is performed based on the power loss at a received (transmitted) power value larger than the state where the power received by RX is not supplied to the load (Light Load), stable foreign object detection with relatively suppressed influence of outliers due to noise or the like can be performed.

[0051] Also, in the above example, as the power loss after the Q value measurement, the power loss at one received (transmitted) power value is obtained, but the power losses at a plurality of received (transmitted) power values may be obtained. In this case, after the processing of the Calibration phase is completed, foreign object detection can be performed by comparing the sum, average value, median value, etc. of the differences from the power losses at the plurality of received (transmitted) power values on the obtained Calibration curve. Also, by measuring the power losses at a plurality of different received (transmitted) power values after the Q value measurement, a curve (referred to as an estimated curve) representing the correspondence between the power value and the power loss may be generated. In this case, the presence or absence of foreign objects may be detected by comparing the estimated curve with the Calibration curve. For example, an estimated curve is obtained by linearly interpolating a plurality of measurement values, and the slope of the estimated curve is compared with the Calibration curve. If the difference or ratio of the slopes is equal to or greater than a threshold value, it can be determined that a foreign object is present. Note that, similar to the Calibration curve, a part or the whole of the estimated curve may be a straight line.

[0052] Furthermore, in obtaining the power loss after the Q value measurement, the Calibration curve may be obtained by obtaining Calibration data Points (Ploss1, Ploss2) as the power losses of a plurality of received (transmitted) power values. In this case, if it is determined that no foreign object exists in the foreign object detection based on the Q value, it can be judged that the Calibration curve has also been obtained in a state where the possibility of the presence of a foreign object is extremely low. Therefore, the processing of the Calibration phase can be omitted. As described above, even when a foreign object intrudes after the Q value measurement, it becomes possible to detect the foreign object by foreign object detection based on the power loss method implemented during power transmission, and a safer wireless power transmission system can be realized.

[0053] Also, when it is determined in S508 that there is no foreign object, the power loss obtained in S504 may be used as a point constituting the Calibration curve. That is, the power loss obtained in S504 may be set as the first reference power loss. In this case, S511 and S512 can be skipped. This is because when it is determined that there is no foreign object by foreign object detection based on the Q value, it is highly likely that there is no foreign object at the time when the Q value is measured in S502 and there is also no foreign object in S504. If there is a high concern that a foreign object may enter between S502 and S504, as described above, in S510, the TX may obtain the received power from the RX again.

[0054] Also, S504 may be performed before the negotiation between the TX and the RX. For example, the TX may obtain the received power value from the RX before obtaining the identification information and the capability information from the RX in the I&C phase.

[0055] Also, the step of obtaining the received power value from the RX in S504 may be performed between S503 and S505, and the step of calculating the power loss in S504 may be performed after S505. That is, if the transmitted power corresponding to the received power value obtained from the RX is stored, the calculation of the power loss may be performed after S505.

[0056] <Second Embodiment> In the first embodiment, an example was shown in which power loss is used as an index of a predetermined physical quantity for foreign object detection, which is different from the Q value. However, foreign object detection based on power loss is easily affected by heat generation and the like, and the possibility of false detection of foreign objects and the possibility of false determination in which it is determined that there is no foreign object despite the presence of a foreign object cannot be denied. Therefore, in order to further improve the accuracy of foreign object detection, it is conceivable to perform foreign object detection using another physical quantity different from power loss as the predetermined physical quantity. In the second embodiment, a measured value for detecting an electrical change in the power transmission coil 303 when the power transmission unit 302 stops power transmission is used as an index value. Hereinafter, as an example thereof, a method for performing foreign object detection based on an index (Q value in the time domain) representing the attenuation state of the power transmission waveform will be described. Note that the configuration of the wireless power transmission system, the configuration of the power receiving device, and the configuration of the power transmission device in the second embodiment are the same as those in the first embodiment (FIGS. 1 to 4).

[0057] First, a method for measuring the Q value in the time domain will be described. The waveform shown in FIG. 8(a) shows the passage of time of the voltage value at the end of the power transmission coil 303 or the resonant capacitor 305 of the TX (hereinafter referred to as the voltage value of the power transmission coil unit), the horizontal axis is time, and the vertical axis is the voltage value. Waveform 800 indicates the high-frequency voltage applied to the power transmission coil 303. When the application of the high-frequency voltage is stopped at time T0, the voltage value of the power transmission coil unit decays with the passage of time. Point 801 is a part of the envelope of the decaying high-frequency voltage and is the voltage value of the power transmission coil unit at time T1. (T1, A1) in the figure indicates that the voltage value at time T1 is A1. Similarly, point 802 is a part of the envelope of the high-frequency voltage and is the voltage value of the power transmission coil unit at time T2. (T2, A2) in the figure indicates that the voltage value at time T2 is A2. The Q value in the time domain is obtained based on the time change of the voltage value after time T0. More specifically, the Q value in the time domain is calculated by Equation 1 based on the times and voltage values of points 801 and 802 on the envelope of the voltage value and the frequency f of the high-frequency voltage (hereinafter referred to as the operating frequency). Q = πf(T2 - T1) / ln(A1 / A2) (Equation 1)

[0058] Next, the process for the TX to measure the Q value in the time domain in this embodiment will be described with reference to FIG. 8(b). The waveform 803 indicates the high-frequency voltage applied to the power transmission coil, and its frequency is between 110 kHz and 148.5 kHz used in the Qi standard. Also, the points 804 and 805 are part of the envelope of the voltage value. The TX stops power transmission in the section from time T0 to T5. At this time, the RX turns on the switch 208 to short-circuit the power receiving coil 201 and the resonance capacitor 207 to form a series resonance circuit and stop power reception. The TX turns on the switch 306 to short-circuit the power transmission coil 303 and the resonance capacitor 305 to form a series resonance circuit and stop power transmission. The TX measures the Q value based on the voltage value A3 (point 804) of the power transmission coil section at time T3, the voltage value A4 (point 805) of the power transmission coil section at time T4, and the operating frequency f of the high-frequency voltage and Equation 1. Note that the TX resumes power transmission at time T5. Thus, the Q value calculated based on the passage of time, the voltage value, and the operating frequency while the TX is intermittently powering off is referred to as the second Q value in this embodiment.

[0059] Even if the Q value in the time domain is not assumed, by measuring (T3, A3) and (T4, A4), the presence or absence of a foreign object can be detected. That is, as shown in (Equation 1), by using an index based on the value of T4 - T3 and the ratio of A4 to A3 (A4 / A3) or the ratio of A3 to A4 (A3 / A4), the presence or absence of a foreign object may be detected. Specifically, the presence or absence of a foreign object may be detected by comparing the index with a threshold value.

[0060] Alternatively, instead of the voltage value, the current value may be measured, and the presence or absence of a foreign object may be detected using an index based on the ratio of the current values. That is, the current value at T3 and the current value at time T4 may be measured. Also, the second Q value may be obtained based on the current value.

[0061] (Flow of processing by the power transmission device) Next, an example of the processing flow executed by the TX when the second Q value described above is applied as a second value different from the Q value will be described. FIG. 9 shows an example of the processing flow executed by the TX according to the second embodiment. This processing can be realized, for example, by the control unit 300 of the TX executing a program read from the memory 307. Note that at least a part of the following procedures may be realized by hardware. In this case, the hardware can be realized, for example, by automatically generating a dedicated circuit using a gate array circuit such as an FPGA from a program for realizing each processing step using a predetermined compiler. Further, this processing can be executed in response to the power of the TX being turned on, in response to the user of the TX inputting an instruction to start a wireless charging application, or in response to the TX being connected to a commercial power supply and receiving power supply. Further, this processing may be started by other triggers.

[0062] In S901 to S903, the same processing as S501 to S503 (FIG. 5) of the first embodiment is performed. When the TX detects in S903 that the RX is placed, it measures the second Q value according to the procedure described above with reference to FIG. 8(b) (S904). The second Q value measured in S904 is hereinafter referred to as the reference second Q value. After finishing the measurement of the reference second Q value, the TX shifts to the I&C phase of the WPC standard and acquires the identifier information and capability information of the RX (S905). In S905 to S909, the same processing as S505 to S509 (FIG. 5) of the first embodiment is performed.

[0063] After the GP's decision, the TX transitions to the Calibration phase of the WPC standard and calculates the first reference power loss (Ploss1) (S910). Then, the TX calculates the second reference power loss (Ploss2) (S911). And the TX obtains a Calibration curve from the first reference power loss (Ploss1) and the second reference power loss (Ploss2). Also, the TX measures the second Q value according to the procedure described in S904 (S912). The TX performs foreign object detection based on the reference second Q value measured in S904 and the second Q value measured in S912 (S913), and determines whether a foreign object exists (S914). Here, the foreign object detection based on the second Q value can be performed by determining whether the difference between the reference second Q value and the second Q value is greater than or equal to a threshold value. If the TX determines that a foreign object exists (YES in S914), it stops the process (or power transmission) (S916). On the other hand, if the TX determines that no foreign object exists (NO in S914), it executes power transmission (S915). The power transmission is performed by the processing in the Power Transfer phase of the WPC standard. However, it is not limited to this, and power transmission may be performed by a method other than the WPC standard. Note that in the above, the processing of S912 is executed after the Calibration phase, but it is not limited to this. For example, the processing of S912 may be executed before the start of the Calibration phase.

[0064] (Flow of the process executed in the system) Using FIG. 10, the operation sequence of the system (TX and RX) when the second Q value (Q value in the time domain) is applied as an index of a physical quantity of a type different from the Q value in the frequency domain will be described. Note that, as an initial state, it is assumed that the RX is not placed on the TX, and the TX has sufficient power transmission ability to execute power transmission in the GP required by the RX. In the second embodiment, a case where a foreign object enters after the TX detects the placement of the RX and measures the Q value and the reference second Q value will be described. Since the Q value is measured before the foreign object enters, it is determined that there is no foreign object in the foreign object detection based on the Q value. The TX measures the second Q value after obtaining the Calibration curve. Due to the entry of a foreign object, the difference between the measured second Q value and the reference second Q value measured when the RX is placed becomes equal to or greater than the threshold value. As a result, the TX determines that a foreign object is present. Hereinafter, it will be described in detail with reference to FIG. 10.

[0065] F1001 to F1008 are the same processes as F601 to F608 (FIG. 6) of the first embodiment. When the RX transmits a power reception voltage notification, after the first period has elapsed, the control unit 200 turns on the switch 208 to short-circuit the power reception coil 201 and the resonance capacitor 207 to form a series resonance circuit and stop power reception (F1009). Similarly, when the TX receives the power reception voltage notification, after the first period has elapsed, the control unit 300 turns on the switch 306 to short-circuit the power transmission coil 303 and the resonance capacitor 305 to form a series resonance circuit and stop power transmission (F1010). The first period is a period for the TX and the RX to synchronously stop power transmission and reception, and can be set to a predetermined fixed value. When the TX stops power transmission, it measures the second Q value (S904, F1011) and stores it in the memory 307 as the reference second Q value. After the second period has elapsed since the TX stopped power transmission in F1010, the TX turns off the switch 306 to resume power transmission (F1012). Similarly, after the second period has elapsed since the RX stopped power reception in F1009, the RX turns off the switch 208 to resume power reception (F1013). The second period is a period for the TX and the RX to synchronously resume power transmission and reception, and can be set to a predetermined fixed value.

[0066] F1014 to F1022 are the same processes as F612 to F620 (FIG. 6) in the first embodiment. Subsequently, TX receives a second reference received power notification with a received power value = 13 watts from RX (F1023). TX calculates a second reference power loss (Ploss2) from the difference between the received power value stored in the received second reference received power notification and its own transmitted power value (S911, F1024). TX obtains a Calibration curve based on the first reference power loss (PLoss1) and the second reference power loss (Ploss2) (F1025). When TX obtains the Calibration curve, it transmits an ACK, which is a response indicating approval, to RX (F1026).

[0067] Next, after the first period has elapsed since the transmission of ACK, TX turns on switch 306 to stop power transmission (F1027). Similarly, after the first period has elapsed since the reception of ACK, RX turns on switch 208 to stop power reception (F1028). When TX stops power transmission, it measures the second Q value (S912, F1029). Then, after the second period has elapsed since the stop of power transmission, TX turns off switch 306 to resume power transmission (F1030). Similarly, after the second period has elapsed since the stop of power reception, RX turns off switch 208 to resume power reception (F1031). TX performs foreign object detection based on the difference between the reference second Q value calculated in F1011 and the second Q value calculated in F1027 (S913, F1032). In this example, due to the intrusion of a foreign object, the difference between the reference second Q value and the second Q value becomes equal to or greater than the threshold value, and TX determines that a foreign object is present (YES in S914, F1033), and transmits an EPT to stop power transmission (F1034).

[0068] As described above, according to the second embodiment, the TX measures the reference second Q value after measuring the Q value, and performs foreign object detection based on the second Q value measured after obtaining the Calibration curve and the reference Q value. The time interval from the measurement of the Q value to the measurement of the reference second Q value is short. Therefore, when it is determined that there is no foreign object in the foreign object detection based on the Q value, the second Q value is measured in a state where the possibility of the presence of a foreign object is extremely low. Therefore, by performing foreign object detection using such a reference second Q value, even if a foreign object enters after the measurement of the Q value, it is possible to detect the foreign object with a high probability, and a safer wireless power transmission system can be realized.

[0069] (Modification example) In the above example, the second Q value is measured in a state where the RX stops power reception, that is, in a state where the switch 208 is turned on and the power reception coil 201 and the resonance capacitor 207 are short-circuited. However, it may be measured in a non-shorted state. In this case, since current flows through the rectifying unit 202 and the voltage control unit 203 via the power reception coil 201 and the resonance capacitor 207, the measured second Q value may be affected by the operating frequency at the time of power transmission stop. Therefore, when performing foreign object detection using the second Q value in a state where the RX is not short-circuited, it is desirable to measure the second Q value at a plurality of frequencies.

[0070] For example, in S904, within the frequency range from 110 kHz to 148.5 kHz, the second Q value is measured at three points where the operating frequencies are 110 kHz, 125 kHz, and 145 kHz, and the measured values at these three points are interpolated with respect to the frequency. For example, TX linearly interpolates the Q values between the three points obtained by plotting the respective Q values when the operating frequencies are 100 kHz, 125 kHz, and 145 KHz on a graph with frequency on the horizontal axis and Q value on the vertical axis, and acquires the interpolation data as a reference value. In S912, TX acquires the Q value corresponding to the operating frequency when the second Q value is measured from the interpolation data, and performs foreign object detection based on the measured second Q value and the second Q value acquired from the interpolation data. Thereby, when the second Q value is measured in a state where RX does not stop power reception, even if a foreign object enters after the Q value measurement, it becomes possible to detect the foreign object, and a safer wireless power transmission system can be realized.

[0071] Also, in the above, in S904 and S912, the second Q value was acquired under the same operating conditions (for example, power transmission with the same frequency and power value (voltage)) of the power transmission unit 302, but it is not limited to this. For example, in S904, TX may acquire a plurality of second Q values under a plurality of different operating conditions and acquire an estimated curve showing the relationship between the operating conditions and the second Q value. In this case, in S913, TX acquires the second Q value corresponding to the operating conditions of the power transmission unit 302 when the second Q value is acquired again in S912 from the estimated curve generated in S904. Then, TX determines the presence or absence of a foreign object based on the second Q value acquired in S912 and the second Q value acquired from the estimated curve.

[0072] Note that, although an example in which the second Q value is used as an index value for detecting an electrical change in the power transmission coil 303 has been described, other measurable electrical characteristics may be used as the index value. For example, it may be the slope of the voltage value (A4 - A3 / T4 - T3) between point 804 and point 805. In this case, in S904 and S912, the TX calculates the slope of the voltage value from the time and the measured voltage value instead of the second Q value. Further, it is not limited to the slope of the voltage value. For example, the slope of the current value may be calculated, or a value calculated from the voltage value and the current value (impedance, load resistance, power) may be used. Furthermore, in S904 and S912, the TX may acquire a coupling coefficient representing the strength of the coupling between the power transmission coil and the power reception coil. Any configuration has an effect equivalent to the effect already described.

[0073] As described above, according to the first and second embodiments, even if a foreign object intrudes after the Q value measurement and before the estimated value of the power loss is calculated, the foreign object can be detected and power transmission can be stopped.

[0074] <Other Embodiments> In the first and second embodiments, either the power loss or the second Q value is used as an index value of a physical quantity different from the Q value to detect a foreign object. However, both of them (that is, the power loss and the second Q value) may be used in combination. For example, after the Q value is measured, the power loss and the second Q value are acquired, and foreign object detection based on the Q value, foreign object detection based on the power loss (F621), and foreign object detection based on the second Q value (F1032) may be performed in this order. Further, the execution order of the foreign object detection is not limited to this, and the foreign object detection based on the second Q value (F1032) may be performed before the foreign object detection based on the power loss (F621). By combining a plurality of foreign object detection methods in this way, it becomes possible to detect a foreign object with a higher probability and to realize a safer wireless power transmission system.

[0075] Also, in the first and second embodiments, when TX detects a foreign object by foreign object detection, it stops the process (or power transmission) (S515, S916), but it is not limited to this. For example, TX may perform power transmission to RX, but suppress the power transmission output so that the received power value at RX becomes a small value (for example, 5 watts or less). Also, when TX receives a received power notification from RX including a value exceeding the received power value = 5 watts, TX may request RX to suppress the received power value to 5 watts or less by transmitting a NAK which is a rejection response. At this time, if RX does not reduce the received power value to 5 watts or less thereafter, TX itself may reduce the power transmission output or stop the power transmission. Also, the communication in the Negotiation phase may be executed again between TX and RX, and the GP may be re-determined to a small value (for example, 5 watts or less) to limit the power that can be transmitted and received. Thereby, power transmission and reception at an appropriate power transmission output can be continued while assuming that a foreign object may exist.

[0076] Also, in the first and second embodiments, it has been described that RX can perform the processes necessary for foreign object detection based on an index value related to a predetermined physical quantity different from the Q value. However, if RX cannot perform this, TX may omit the processes related to foreign object detection based on an index related to a predetermined physical quantity. For example, when using power loss as an index related to a predetermined physical quantity, it is a case where TX cannot receive a received power notification (F608) from RX within a predetermined time after detecting the placement of RX. In this case, TX may suppress the power transmission. For example, TX may not increase the power transmission output so that the received power value at RX becomes a small value (for example, 5 watts or less). Also, for example, the value of GP determined by the communication in the Negotiation phase between TX and RX may be made a small value (for example, 5 watts or less). Thereby, even when RX cannot perform foreign object detection using a second value different from the Q value, power transmission and reception at an appropriate power transmission output can be continued while assuming that a foreign object may exist.

[0077] Also, in the first and second embodiments, calculations or measurements for obtaining an index different from the Q value are performed after the placement of the RX is detected, that is, triggered by receiving a Signal Strength Pakcet for Digital Ping. However, it is not limited to this. For example, it may be any time after the placement of the RX is detected, such as after the processing of the I&C phase is completed and before the processing of the Calibration phase starts. Even if an index value different from the Q value is obtained at any timing, foreign object detection can be performed with a high probability compared to the case where foreign object detection is not performed based on the index value. That is, according to each of the above embodiments, it becomes possible to more accurately determine the intrusion of foreign objects that occurred before the estimated value of power loss is calculated, and the reliability of foreign object detection is improved.

[0078] 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 device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

[0079] The present invention is not limited to the above-described embodiments, and various changes and modifications are possible without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to disclose the scope of the present invention.

Description of Reference Numerals

[0080] 101: Power receiving device, 102: Power transmitting device, 300: Control unit, 302: Power transmitting unit, 304: Communication unit

Claims

1. A power transmission device, comprising: power transmission means for wirelessly transmitting power to a power receiving device; measurement means for measuring the Q value of the power transmission means; first acquisition means for acquiring a first index value related to a predetermined physical quantity different from the Q value after measuring the Q value; first determination means for determining the presence or absence of an object different from the power receiving device based on the Q value indicated in the information received from the power receiving device and the Q value measured by the measurement means; second acquisition means for acquiring a second index value related to the predetermined physical quantity after it is determined by the first determination means that there is no object different from the power receiving device and before starting wireless power transmission to the power receiving device; A power transmission device, comprising second determination means for determining the presence or absence of an object different from the power receiving device based on the first index value and the second index value.

2. The power transmission device according to claim 1, wherein the first index value and the second index value are values of power loss calculated from the power transmission power value by the power transmission means and the power reception power value notified from the power receiving device.

3. The power transmission device according to claim 2, wherein the power reception power value for obtaining the first index value is included in a power reception voltage notification packet received from the power receiving device in the Ping phase of the WPC standard, or a power reception power notification packet received from the power receiving device following the power reception voltage notification.

4. Further comprising generation means for generating a Calibration curve for estimating power loss corresponding to the power transmission power using the power reception power value notified from the power receiving device; The power transmission device according to claim 2 or 3, wherein the second acquisition means uses the power reception power value notified from the power receiving device when generating the Calibration curve as the power reception power value for obtaining the second index value.

5. Further comprising generation means for generating a Calibration curve for estimating power loss corresponding to the power transmission power using the power reception power value notified from the power receiving device; The power transmission device according to claim 2 or 3, wherein the second acquisition means obtains the second index value by estimating the power loss at the power transmission power when the first index value is acquired from the Calibration curve.

6. The first acquisition means acquires a plurality of power losses for a plurality of different power transmission powers. In the Calibration phase, the second acquisition means generates a Calibration curve representing the relationship between the transmission power and the power loss based on a plurality of received power values notified from the power receiving device for a plurality of different transmission powers. The second determination means determines the presence or absence of an object different from the power receiving device based on the plurality of power losses acquired by the first acquisition means and the power losses obtained from the Calibration curve. The power transmission device according to claim 2 or 3.

7. Before the start of the Calibration phase of the WPC standard, the first acquisition means generates an estimated curve representing the relationship between the transmission power and the power loss based on a plurality of received power values notified from the power receiving device for a plurality of different transmission powers. In the Calibration phase, the second acquisition means generates a Calibration curve representing the relationship between the transmission power and the power loss based on a plurality of received power values notified from the power receiving device for a plurality of different transmission powers. The second determination means determines the presence or absence of an object different from the power receiving device based on a comparison between the estimated curve and the Calibration curve. The power transmission device according to claim 2 or 3.

8. The first index value and the second index value are index values for detecting an electrical change in the transmission coil included in the transmission means when the transmission means stops power transmission. The power transmission device according to claim 1.

9. The first acquisition means and the second acquisition means acquire the first index value and the second index value under the same operating conditions of the transmission means. The power transmission device according to claim 8.

10. The first acquisition means acquires an estimated curve showing the relationship between the operating conditions and the first index value based on a plurality of first index values acquired under a plurality of different operating conditions. The power transmission device according to claim 9.

11. The second determination means acquires an index value corresponding to the operating condition of the transmission means when the second acquisition means acquires the second index value from the estimated curve. The power transmission device according to claim 10, wherein the presence or absence of an object different from the power receiving device is determined based on the second index value acquired by the second acquisition means and the index value acquired from the estimated curve.

12. The power transmission device according to any one of claims 8 to 11, wherein the index value is a Q value in a time domain based on an attenuation state of a power transmission waveform of the power transmission means when the power transmission means stops power transmission.

13. The power transmission device according to claim 12, wherein the first acquisition means and the second acquisition means configure a resonance circuit including a power transmission coil and a capacitor in the power transmission means, and measure the Q value in the time domain.

14. The power transmission device according to any one of claims 8 to 11, wherein the index value is a measured value based on at least one of a voltage value, a current value, a power value, and a load resistance.

15. The power transmission device according to any one of claims 1 to 14, wherein the first acquisition means acquires the first index value before starting a Calibration phase of the WPC standard.

16. The power transmission device according to any one of claims 1 to 15, wherein the second acquisition means acquires the second index value after the end of a Calibration phase of the WPC standard.

17. A power receiving device, a power receiving means for receiving power transmitted by wireless power transmission from a power transmission device; a notification means for notifying the power transmission device of a Q value held by the power receiving device and an index value related to a predetermined physical quantity different from the Q value before negotiating with the power transmission device regarding wireless power transmission.

18. A power receiving device for receiving power transmitted by wireless power transmission from a power transmission device, a transmission means for transmitting a received power voltage value as a response to a placement detection request from the power transmission device; a control means for stopping power reception for a predetermined period after a predetermined time has elapsed after transmitting the received power voltage value and after a predetermined time has elapsed after receiving a predetermined signal transmitted before the power transmission device starts power transmission.

19. A control method for a power transmission device having a power transmission means for performing wireless power transmission to a power receiving device, a measurement step of measuring a Q value of the power transmission means; a first acquisition step of acquiring a first index value related to a predetermined physical quantity different from the Q value after measuring the Q value; a first determination step of determining the presence or absence of an object different from the power receiving device based on the Q value indicated by the information received from the power receiving device and the Q value measured in the measurement step; After it is determined by the first determination step that there is no object different from the power receiving device and before starting wireless power transmission to the power receiving device, a second acquisition step of acquiring a second index value regarding the predetermined physical quantity; A control method for a power transmission device, comprising: a second determination step of determining the presence or absence of an object different from the power receiving device based on the first index value and the second index value.

20. A control method for a power receiving device having a power receiving means for receiving power transmitted by wireless power transmission from a power transmission device, A control method for a power receiving device, comprising: a notification step of notifying the power transmission device of a Q value held by the power receiving device and an index value regarding a predetermined physical quantity different from the Q value before performing negotiation regarding wireless power transmission with the power transmission device.

21. A program for causing a computer to function as the power transmission device according to any one of claims 1 to 16 or the power receiving device according to claim 17 or 18.

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