Power receiving device and method

Abstract

To prevent a reduction in the accuracy of foreign substance detection processing based on power loss even if an output voltage to a load is changed in a power receiving device.SOLUTION: A power receiving device receives power wirelessly transmitted from a power transmitting device, supplies the received power to a load by using a preset voltage, determines a voltage for power supply to the load while the power is supplied to the load, and requests update of a parameter used by the power transmitting device for foreign substance detection processing based on the voltage used for the supply of power to the load and the determined voltage.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] In recent years, technological development of wireless power transmission systems such as wireless charging systems has been widely carried out. Patent Document 1 describes a power transmitting device and a power receiving device that comply with the standard (hereinafter referred to as the "WPC standard") established by the Wireless Power Consortium (WPC), a standardization organization for wireless charging. Patent Document 1 also describes a calibration process defined in the WPC standard to improve the accuracy of detection of conductive objects (foreign objects) such as metal pieces.

[0003] In the calibration process, the received power of the power receiving device and the power loss at that time are acquired in each of two different states. The power loss is calculated as the difference between the transmitted power in the power transmitting device and the received power of the power receiving device. Then, using the pair of the received power and the power loss in these two states as parameters, the power loss expected from the received power notified by the power receiving device in wireless power transmission is calculated, and the actual power loss is compared with the expected power loss. If the difference between the actual power loss and the expected power loss exceeds a predetermined value, it is possible to determine that there is a power loss due to a foreign object, i.e., that a foreign object is present.

[0004] Meanwhile, Universal Serial Bus Power Delivery (USB PD) is becoming popular as a standard for supplying power via wired connections for rapid charging of batteries, etc. With USB PD, when the power supplied to the load increases, the voltage output to the load is increased accordingly. This keeps the current low even when the power supplied increases, suppressing losses and heat generation in the circuit and enabling power to be supplied to the load while maintaining high efficiency. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-070074 A Summary of the Invention [Problem to be solved by the invention]

[0006] In a power receiving device for wireless power transmission, when the output voltage to a load is changed in response to a change in the received power, the state of power loss in the power receiving device changes before and after the output voltage is changed. For this reason, if a pair of the received power and the power loss acquired before the output voltage is changed is used as a parameter for foreign object detection to perform foreign object detection after the output voltage is changed, the accuracy of foreign object detection may decrease.

[0007] The present invention provides a technique for suppressing a decrease in accuracy of foreign object detection processing due to power loss even when an output voltage to a load in a power receiving device is changed. [Means for solving the problem]

[0008] A power receiving device according to one aspect of the present invention has the following configuration. A power receiving device, Power is transmitted wirelessly from the power transmission device. exchange A power receiving means for receiving power; A communication means for communicating with the power transmitting device; A conversion means for converting the AC power into DC power; The above Output of the conversion method A voltage changing means for changing the voltage; having The communication means transmits a first received power packet including information indicating a value of a first received power to the power transmitting device; The change means, after the first receiving power packet is transmitted, in , and Authentication of the power transmitting device After To , Guaranteed Power has been changed, The above output Change the voltage, The communication means ,beforeNote output After the voltage is changed, a second received power packet including information indicating a value of the second received power is transmitted to the power transmitting device. Effect of the Invention

[0009] According to the present invention, even if the output voltage to the load in the power receiving device is changed, it is possible to suppress a decrease in the accuracy of the foreign object detection process due to power loss. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a wireless charging system according to an embodiment. [Diagram 2] FIG. 1 is a block diagram showing a configuration example of a power receiving device according to a first embodiment; [Diagram 3] 1 is a block diagram showing an example of the configuration of a power transmitting device according to a first embodiment. [Figure 4A] 5 is a flowchart showing an example of a processing flow of the power receiving device according to the first embodiment. [Figure 4B] 5 is a flowchart showing an example of a processing flow of the power receiving device according to the first embodiment. [Figure 5A] 5 is a flowchart showing an example of a processing flow of the power transmitting device according to the first embodiment. [Figure 5B] 5 is a flowchart showing an example of a processing flow of the power transmitting device according to the first embodiment. [Figure 6A] FIG. 4 is a diagram showing an example of a flow of processes executed in the wireless charging system. [Figure 6B] FIG. 4 is a diagram showing an example of a flow of processes executed in the wireless charging system. [Figure 7] (A) is a diagram showing the communication sequence in the I&C phase, (B) is a diagram showing the communication sequence in the negotiation phase, and (C) is a diagram showing the communication sequence in the calibration phase. [Figure 8] FIG. 4 is a diagram showing the contents of parameters for foreign object detection processing according to the first embodiment. [Figure 9] 5A to 5C are diagrams illustrating linear interpolation in the foreign object detection processing according to the first embodiment. [Figure 10](A) is a diagram showing the relationship between the GP and the output voltage to the charging unit, and (B) is a diagram showing the relationship between the GP and the input voltage to the transmission unit. [Figure 11] 10 is a flowchart showing an example of a processing flow of a power receiving device according to a second embodiment. [Figure 12] 13 is a diagram showing the relationship between the power consumption of a charging unit and the output voltage to the charging unit according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0012] <First embodiment> (System Configuration) FIG. 1 shows an example of the configuration of a wireless charging system (wireless power transmission system) according to this embodiment. This system includes a power receiving device 101 and a power transmitting device 102. Hereinafter, the power receiving device may be called RX, and the power transmitting device may be called TX. The TX102 is an electronic device that wirelessly transmits power to the RX101 placed on a charging stand 103. The RX101 is an electronic device that receives power wirelessly transmitted from the TX102 and charges an internal battery. Below, a case where the RX101 is placed on the charging stand 103 will be described as an example. However, when the TX102 transmits power to the RX101, the RX101 only needs to be present within a power transmitting range of the TX102, and the RX101 does not necessarily have to be placed on the charging stand 103.

[0013] Each of RX101 and TX102 may have a function of executing an application other than wireless charging. An example of RX101 is a mobile information device that operates on a rechargeable battery, such as a laptop PC (Personal Computer), a tablet PC, or a smartphone. An example of TX102 is an accessory device for charging the mobile information device. RX101 and TX102 may be a storage device such as a hard disk device or a memory device, or an information processing device such as a personal computer (PC). RX101 and TX102 may be an image input device such as an imaging device (camera, video camera, etc.) or a scanner, or an image output device such as a printer, a copier, or a projector. TX102 may be a mobile information device. In this case, RX101 may be another mobile information device or a wireless earphone. RX101 may be an automobile. TX102 may be a charger installed in a console or the like in the automobile.

[0014] In addition, in this embodiment, one RX 101 and one TX 102 are shown, but the present invention is not limited to this. The present invention can also be applied to a configuration in which multiple RX 101 receive power transmitted from one TX 102 or from separate TXs 102.

[0015] This system performs wireless power transmission using an electromagnetic induction method for wireless charging based on the WPC standard. That is, RX101 and TX102 perform wireless power transmission for wireless charging based on the WPC standard between the receiving coil of RX101 and the transmitting coil of TX102. Note that the wireless power transmission method (non-contact power transmission method) applied to this system is not limited to the method defined by the WPC standard, and may be other electromagnetic induction method, magnetic field resonance method, electric field resonance method, microwave method, method using laser, etc. Also, in this embodiment, wireless power transmission is used for wireless charging, but wireless power transmission may be performed for purposes other than wireless charging.

[0016] In the WPC standard, the magnitude of power guaranteed when the RX101 receives power from the TX102 is stipulated by a value called Guaranteed Power (hereinafter referred to as "GP"). GP indicates the power value guaranteed for the output to the load of the RX101 (e.g., a charging circuit, etc.) even if the positional relationship between the RX101 and the TX102 fluctuates and the power transmission efficiency between the receiving coil and the transmitting coil decreases. For example, if the GP is 5 watts, the TX102 controls the power transmission so that it can output 5 watts to the load in the RX101, even if the positional relationship between the receiving coil and the transmitting coil fluctuates and the power transmission efficiency decreases.

[0017] The RX101 and TX102 according to this embodiment perform communication for power transmission and reception control based on the WPC standard. The WPC standard specifies a number of phases including a power transfer phase in which power transmission is performed and a phase before power transmission is performed, and communication for power transmission and reception control is performed in each phase. The phase before power transmission includes a selection phase, a ping phase, an identification and configuration phase, a negotiation phase, and a calibration phase. In the following, the identification and configuration phase is referred to as an I&C phase.

[0018] In the Selection phase, the TX102 repeatedly transmits Analog Pings intermittently to detect that an object has been placed on the charging stand 103 (for example, that the RX101 or a conductor piece has been placed on the charging stand 103). The Analog Ping is a detection signal for detecting the presence of an object. The TX102 transmits Analog Pings by applying a voltage or current to the power transmitting coil. When the charging stand 103 changes from a state in which no object is placed on it to a state in which an object is placed on it, a change occurs in the voltage or current applied to the power transmitting coil. The TX102 detects at least one of the voltage value and current value of the power transmitting coil when the Analog Ping is transmitted, and when the voltage value is below a certain threshold value or the current value exceeds a certain threshold value, it determines that an object is present and transitions to the Ping phase.

[0019] In the Ping phase, the TX102 transmits a Digital Ping with a higher power than the Analog Ping. The power of the Digital Ping is sufficient to start up the control unit of the RX101 placed on the charging stand 103. The RX101 notifies the TX102 of the magnitude of the received voltage. That is, the RX101 transmits a Signal Strength packet (hereinafter referred to as an "SS packet") to the TX102. The TX102 recognizes that the object detected in the Selection phase is the RX101 by receiving a response from the RX101 that received the Digital Ping that it transmitted. When the TX102 is notified of the received voltage value, it transitions to the I&C phase.

[0020] In the I&C phase, TX102 identifies RX101 and acquires device configuration information (capability information) from RX101. To this end, RX101 transmits an ID packet and a configuration packet to TX102. The ID packet contains the identification information of RX101, and the configuration packet contains the device configuration information (capability information) of RX101. Upon receiving the ID packet and configuration packet from RX101, TX102 responds by transmitting an acknowledgement (ACK) to RX101. Then, the I&C phase ends. When the I&C phase ends, TX102 transitions to the negotiation phase. In the negotiation phase, the GP value is determined based on the GP value requested by RX101, the power transmission capability of TX102, etc. When the negotiation phase ends, TX102 transitions to the calibration phase.

[0021] In the calibration phase, RX101 notifies TX102 of the received power by using a Received Power Packet. At this time, at least two different received powers are notified. For example, the received power when no load is connected and the received power when a load is connected and power close to GP is received are notified. TX102 acquires the transmitted power of its own device corresponding to the two received powers, calculates the power loss from the difference between the notified received power and the acquired transmitted power, and stores it in association with the received power. In this way, pairs of received power and power loss are stored in TX102 for at least two states of RX101. In the subsequent Power Transfer phase (described later), TX102 performs foreign object detection processing using the pair of received power and power loss stored as described above as parameters.

[0022] Here, a method for performing foreign object detection processing using two sets of received power and power loss as parameters in TX102 will be described. For example, TX102 stores a pair of two sets of received power and power loss through communication in the Calibration phase. Let this be (received power = RP1, power loss = PL1) and (received power = RP2, power loss = PL2). When TX102 performs foreign object detection processing in the Power Transfer phase, first, from RX101, the current received power = P received is obtained. Subsequently, TX102 calculates the expected value PL cal of the power loss at this time by linear interpolation between the two points (RP1, PL1) and (RP2, PL2). Assume that RP1 < RP2. For example, the expected value PL cal of the power loss can be obtained by the following Equation 1. [Equation 1] PL cal = (PL2 - PL1) / (RP2 - RP1)·(P received - RP1)+PL1

[0023] The current power loss PL is calculated by the following Equation 2 from the current transmission power P transmitted in TX102 and the received power = P received notified from RX101. When the current power loss PL of TX102 exceeds the expected value PL cal by a predetermined value or more, it is determined that power is consumed due to the foreign object value, resulting in an increase in power loss, that is, a foreign object is detected. [Equation 2] PL = P transmitted - P received

[0024] In the above-mentioned method, the expected value of the current power loss is calculated by linear interpolation using the previously acquired power loss value as a parameter. This is expressed as calibrating the power loss. Note that the object to be calibrated may be the received power of RX101 instead of the power loss of RX101, or the transmitted power of TX102. The method of calculating the expected value of the power loss, that is, the method of calibration, is not limited to linear interpolation, and may be, for example, nonlinear interpolation using a power series. Also, three or more sets of information (for example, a pair of received power and transmitted power) may be used as parameters. An example of using three or more sets of information as parameters is a broken line linear interpolation connecting (RP1, PL1) and (RP2, PL2), and (RP2, PL2) and (RP3, PL3). Here, (RP3, PL3) is the information of the third pair of received power and power loss, and RP2 <RP3であるとする。

[0025] In the power transfer phase, control is performed for starting and continuing power transmission, and stopping power transmission due to foreign object detection or full charge. In this embodiment, in the power transfer phase, processing is further performed for changing GP to a larger value, changing the output voltage to the load of the power receiving device, and requesting reacquisition or addition of parameters for foreign object detection. Details of these processing will be described later.

[0026] The TX102 and the RX101 perform communication based on the WPC standard for these power transmission and reception control by superimposing a signal on the transmission power using the same antenna (coil) as the wireless power transmission. The TX102 and the RX101 may perform communication for power transmission and reception control using an antenna (coil) different from that used for wireless power transmission. An example of communication using an antenna (coil) different from that used for wireless power transmission is a communication method conforming to the Bluetooth (registered trademark) Low Energy standard. In addition, communication may be performed by other communication methods such as wireless LAN (e.g., Wi-Fi (registered trademark)) of the IEEE802.11 standard series, ZigBee, and NFC (Near Field Communication). Communication using an antenna (coil) different from that used for wireless power transmission may be performed at a frequency different from that used for wireless power transmission.

[0027] (Device configuration) Next, the configuration of the power receiving device 101 (RX101) and the power transmitting device 102 (TX102) according to this embodiment will be described. Note that the configuration described below is merely an example, and a part (or in some cases, the whole) of the configuration described below may be replaced with another configuration performing a similar function or may be omitted, or further configuration may be added to the configuration described below. Furthermore, one hardware block shown in the following description may be divided into multiple blocks, or multiple blocks may be integrated into one block.

[0028] 2 is a diagram showing an example of the configuration of the RX101 according to this embodiment. The RX101 has a control unit 201, a battery 202, a power receiving unit 203, a placement detection unit 204, a power receiving coil 205, a communication unit 206, a notification unit 207, an operation unit 208, a memory 209, and a timer 210. The RX101 also has a charging unit 211, a variable voltage circuit 212, a voltage acquisition unit 213, a voltage determination unit 214, a parameter re-acquisition request unit 215, and a parameter addition request unit 216.

[0029] The control unit 201 controls the entire RX101 by executing a control program stored in the memory 209, for example. That is, the control unit 201 controls each functional unit shown in FIG. 2. The control unit 201 also performs control related to power reception control in the RX101. Furthermore, the control unit 201 may perform control for executing applications other than wireless power transmission. The control unit 201 includes one or more processors, such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The control unit 201 may be configured with hardware dedicated to a specific process, such as an application specific integrated circuit (ASIC). The control unit 201 may also be configured with an array circuit, such as a field programmable gate array (FPGA) compiled to execute a specific process. The control unit 201 stores information to be stored during execution of various processes in the memory 209. The control unit 201 may measure time using a timer 210.

[0030] The battery 202 supplies the entire RX 101 with power required for the control of each part of the RX 101 by the control unit 201 and for power reception and communication. The battery 202 also stores the power received via the power receiving coil 205.

[0031] In the power receiving coil 205, an induced electromotive force is generated by the electromagnetic waves radiated from the power transmitting coil of the TX102. The power receiving unit 203 acquires the power generated in the power receiving coil 205. The power receiving unit 203 acquires the AC power generated by electromagnetic induction in the power receiving coil 205, converts the AC power into a direct current or an AC power of a predetermined frequency, and outputs the power to the charging unit 211 that performs processing for charging the battery 202. That is, the power receiving unit 203 supplies power to a load in the RX101, and the charging unit 211 and the battery 202 are examples of such loads. The above-mentioned GP is power that is guaranteed to be output from the power receiving unit 203. Furthermore, the power receiving unit 203 notifies the control unit 201 of the current received power. This allows the control unit 201 to know the received power at any timing. Note that the measurement of the received power and the notification of the received power to the control unit 201 may be configured to be performed by a unit other than the power receiving unit 203.

[0032] The placement detection unit 204 detects that the RX101 is placed on the charging stand 103 based on the WPC standard. The placement detection unit 204 detects, for example, at least one of the voltage value and the current value of the power receiving coil 205 when the power receiving unit 203 receives a Digital Ping of the WPC standard via the power receiving coil 205. The placement detection unit 204 determines that the RX101 is placed on the charging stand 103 when, for example, the voltage value is below a predetermined voltage threshold or the current value exceeds a predetermined current threshold.

[0033] The communication unit 206 performs control communication based on the WPC standard as described above with the TX 102. The communication unit 206 demodulates the electromagnetic waves input from the power receiving coil 205 to obtain information transmitted from the TX 102, and performs communication with the TX 102 by superimposing information to be transmitted to the TX 102 on the electromagnetic waves through load modulation of the electromagnetic waves. That is, the communication performed by the communication unit 206 is performed by being superimposed on the electromagnetic waves transmitted from the power transmitting coil of the TX 102.

[0034] The notification unit 207 notifies the user of information by any method such as visual, auditory, or tactile. The notification unit 207 notifies the user of, for example, the charging state of RX101 and the state related to power transmission of the wireless power transmission system including TX102 and RX101 as shown in FIG. 1. The notification unit 207 includes, for example, a liquid crystal display, an LED, a speaker, a vibration generating circuit, and other notification devices. The operation unit 208 has a reception function for receiving an operation on RX101 from the user. The operation unit 208 includes, for example, a voice input device such as a button, a keyboard, or 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 notification unit 207 and the operation unit 208 are integrated, such as a touch panel, may be used. The memory 209 stores various information such as identification information and device configuration information, control programs, and the like, as described above. Note that the memory 209 may store information obtained by a functional unit different from the control unit 201. The timer 210 measures time using, for example, a count-up timer that measures the elapsed time from the time it was started, or a count-down timer that counts down from a set time.

[0035] The charging unit 211 charges the battery 202 with power supplied from the power receiving unit 203. The charging unit 211 starts or stops charging the battery 202 based on the control of the control unit 201, and adjusts the power used to charge the battery 202 based on the charging state of the battery 202. When the power used by the charging unit 211 changes, the power supplied from the power receiving unit 203, i.e., the received power in the RX101, also changes accordingly. As described above, the charging unit 211 is a load in the RX101. Note that the charging unit 211 and the battery 202 may exist as separate devices outside the RX101. The device may be, for example, a device that operates with power supplied based on the USB PD standard. In that case, the control unit 201 may acquire information on the amount of power required by the charging unit 211 from the charging unit 211 through communication based on the USB PD standard.

[0036] Variable voltage circuit 212 sets an output voltage for supplying power from power receiving unit 203 to charging unit 211, i.e., a load, based on the control of control unit 201. Voltage acquisition unit 213 acquires the voltage output to charging unit 211. This voltage value can be read by control unit 201 at any timing. Voltage determination unit 214 determines the voltage to be set in variable voltage circuit 212.

[0037] The parameter reacquisition request unit 215 uses the communication unit 206 to request the TX 102 to reacquire parameters for foreign object detection processing. The parameters for foreign object detection processing are the pair of received power and power loss described in the above description of the calibration phase. The parameter addition request unit 216 uses the communication unit 206 to request the TX 102 to add parameters for foreign object detection processing. This is a request to add and store a third pair when, for example, two pairs are already held in the TX 102. Note that the voltage determination unit 214, the parameter reacquisition request unit 215, and the parameter addition request unit 216 may be configured to operate in whole or in part on a processor separate from the control unit 201, or may be executed by a program operating on the control unit 201. The voltage determination unit 214, the parameter reacquisition request unit 215, and the parameter addition request unit 216 may be realized by, for example, the control unit 201 executing a program stored in the memory 209.

[0038] 3 is a diagram showing an example of the configuration of the TX 102 according to the present embodiment. In one example, the TX 102 includes a control unit 301, a power supply unit 302, a power transmission unit 303, a placement detection unit 304, a power transmission coil 305, a communication unit 306, a notification unit 307, an operation unit 308, a memory 309, a timer 310, and a variable voltage circuit 311.

[0039] The control unit 301 controls the entire TX 102 by executing a control program stored in the memory 309, for example. That is, the control unit 301 controls each functional unit shown in FIG. 3. The control unit 301 also performs control related to power transmission control in the TX 102. Furthermore, the control unit 301 may perform control for executing applications other than wireless power transmission. The control unit 301 includes one or more processors, such as a CPU or an MPU. The control unit 301 may include hardware dedicated to a specific process, such as an application specific integrated circuit (ASIC), or an array circuit, such as an FPGA, compiled to execute a specific process. The control unit 301 stores information to be stored during execution of various processes in the memory 309. The control unit 301 may also measure time using a timer 310.

[0040] The power supply unit 302 supplies the entire TX 102 with power required for the control of the TX 102 by the control unit 301 and for power transmission and communication. The power supply unit 302 is, for example, a commercial power source or a battery. The battery stores power supplied from the commercial power source.

[0041] The power transmitting unit 303 converts the DC or AC power input from the power supply unit 302 into AC frequency power in a frequency band used for wireless power transmission, and inputs the AC frequency power to the power transmitting coil 305 to generate electromagnetic waves for receiving power in the RX101. The frequency of the AC power generated by the power transmitting unit 303 is, for example, about several hundred kHz (for example, 110 kHz to 205 kHz). Based on an instruction from the control unit 301, the power transmitting unit 303 inputs the AC frequency power to the power transmitting coil 305 so that the power transmitting coil 305 outputs electromagnetic waves for transmitting power to the RX101. The power transmitting unit 303 also controls the intensity of the electromagnetic waves to be output by adjusting the voltage (power transmitting voltage) or current (power transmitting current) input to the power transmitting coil 305, or both. Increasing the power transmitting voltage or power transmitting current increases the intensity of the electromagnetic waves, and decreasing the power transmitting voltage or power transmitting current decreases the intensity of the electromagnetic waves. Furthermore, the power transmitting unit 303 performs output control of AC frequency power so that power transmission from the power transmitting coil 305 is started or stopped based on an instruction from the control unit 301. Furthermore, the power transmitting unit 303 notifies the control unit 301 of the current transmitted power. This allows the control unit 301 to know the transmitted power at any timing. Note that the measurement of the transmitted power and the notification to the control unit 301 may be performed by a device other than the power transmitting unit 303.

[0042] The placement detection unit 304 detects whether an object is placed on the charging stand 103 based on the WPC standard. Specifically, the placement detection unit 304 detects whether an object is placed on the interface surface of the charging stand 103. For example, the placement detection unit 304 detects at least one of the voltage value and the current value of the power transmitting coil 305 when the power transmitting unit 303 transmits an Analog Ping of the WPC standard via the power transmitting coil 305. The placement detection unit 304 may detect a change in impedance. Then, the placement detection unit 304 may determine that an object is placed on the charging stand 103 when the voltage value falls below a predetermined voltage value or the current value exceeds a predetermined current value. Whether the object is a power receiving device or another foreign object is determined based on the presence or absence of a predetermined response to the Digital Ping transmitted by the communication unit 306. That is, if the TX102 receives a predetermined response, it determines that the object is the power receiving device (RX101), and if not, it determines that the object is an object different from the power receiving device.

[0043] The communication unit 306 performs control communication with RX101 based on the WPC standard as described above. The communication unit 306 modulates the electromagnetic waves output from the power transmitting coil 305 and transmits information to RX101 to perform communication. The communication unit 306 also demodulates the electromagnetic waves output from the power transmitting coil 305 and modulated in RX101 to acquire information transmitted by RX101. That is, the communication performed by the communication unit 306 is superimposed on the electromagnetic waves transmitted from the power transmitting coil 305.

[0044] The notification unit 307 notifies the user of information by any method such as visual, auditory, or tactile. The notification unit 307 notifies the user of, for example, the charging state of the TX102, or the state related to power transmission of the wireless power transmission system including the TX102 and the RX101 as shown in FIG. 1. The notification unit 307 includes, for example, a liquid crystal display, an LED, a speaker, a vibration generating circuit, and other notification devices. The operation unit 308 has a reception function for receiving an operation on the TX102 from the user. The operation unit 308 includes, for example, a voice input device such as a button, a keyboard, or a microphone, a motion detection device such as an acceleration sensor or a gyro sensor, or other input device. Note that a device in which the notification unit 307 and the operation unit 308 are integrated, such as a touch panel, may be used.

[0045] Memory 309 stores various information such as identification information and capability information, control programs, etc. Note that memory 309 may store information obtained by a functional unit other than control unit 301. Timer 310 measures time, for example, by a count-up timer that measures the elapsed time from the time of activation, or a count-down timer that counts down from a set time.

[0046] Variable voltage circuit 311 sets an input voltage for supplying power from power supply unit 302 to power transmission unit 303 under the control of control unit 301. Note that power supply unit 302 and variable voltage circuit 311 may exist as separate devices outside TX102. The device may be a power adapter that supplies power based on the USB PD standard. In this case, control of variable voltage circuit 311 by control unit 301 may be performed through communication based on the USB PD standard.

[0047] (Processing flow) Next, an example of the flow of processes executed by the RX 101 and the TX 102 will be described.

[0048] [Processing in the power receiving device] 4A and 4B are flowcharts showing an example of processing executed by RX101. This processing can be realized, for example, by the control unit 201 of RX101 executing a program read from the memory 209. This processing also includes processing in the voltage determination unit 214, the parameter reacquisition request unit 215, and the parameter addition request unit 216. At least a part of the procedure of this processing described below may be realized by hardware. In this case, the hardware can be realized, for example, by using a predetermined compiler to automatically generate a dedicated circuit using a gate array circuit such as an FPGA from a program for realizing each processing step. This processing can be started in response to the power supply of RX101 being turned on, in response to the start of RX101 by power supply from the battery 202 or TX102, or in response to the user of RX101 inputting an instruction to start a wireless charging application. This processing may also be started by another trigger.

[0049] After starting processing related to power transmission and reception, RX101 executes processing defined as the Selection phase and Ping phase of the WPC standard, and waits for its own device to be placed on TX102 (S401). Then, RX101 detects that it has been placed on the charging stand 103 of TX102, for example, by detecting a Digital Ping from TX102. When RX101 detects a Digital Ping, it transmits an SS packet including a receiving voltage value to TX102. When RX101 detects that its own device has been placed on the charging stand 103 of TX102, it executes processing defined as the I&C phase of the WPC standard by the communication unit 206, and transmits identification information and device configuration information (capability information) to TX102 (S402).

[0050] 7(A) shows the flow of communication in the I&C phase. In the I&C phase, the RX101 transmits an Identification Packet (ID Packet) to the TX102 (F701). The ID Packet stores the Manufacturer Code and Basic Device ID, which are identification information for the RX101, as well as information elements that can specify the version of the WPC standard supported as capability information for the RX101. The RX101 further transmits a Configuration Packet to the TX102 (F702). The Configuration Packet contains the following information as capability information for the RX101. That is, the Maximum Power Value, which is a value that specifies the maximum power that the RX101 can supply to a load, and information indicating whether or not the RX101 has a negotiation function of the WPC standard.

[0051] When TX102 receives these packets, it transmits an ACK (F703), and the I&C phase ends. Note that RX101 may notify TX102 of its identification information and device configuration information (capability information) by a method other than the I&C phase communication of the WPC standard. Furthermore, the identification information of RX101 may be the Wireless Power ID of the WPC standard, or any other identification information capable of identifying an individual RX101. The capability information may include information other than the above.

[0052] Returning to FIG. 4A, RX101 negotiates with TX102 through communication in the negotiation phase to determine the GP (S403). FIG. 7(B) shows an example of the flow of the negotiation phase. The GP is determined by a Specific Request Packet from RX101 and a response thereto from TX102. First, RX101 notifies TX102 of the requested GP value by transmitting a Specific Request Packet to TX102 (F711). RX101 determines the requested GP value based on the power required by its own device. It is assumed that this value is stored in advance in the memory 209. An example of the GP value is 5 watts.

[0053] Based on the power transmission capacity of the own device, the TX102 judges whether or not to accept the request from the RX101, and transmits an ACK (positive response) to the RX101 if the request is accepted, or transmits a NAK (negative response) to the RX101 if the request is not accepted. Note that FIG. 7B shows an example in which the TX102 transmits an ACK (F712). When the TX102 transmits an ACK, the value of the GP is determined as the same as the value requested by the RX101, and is stored in the memories of both the RX101 and the TX102. On the other hand, when the TX102 transmits a NAK, the value of the GP is set to a small default value, for example, a value of 5 watts or less. In one example, the default value is stored in advance in the memories of both the RX101 and the TX102. Note that the method of determining the GP described above is one example, and the GP may be determined by other methods.

[0054] Returning to FIG. 4A, the RX101 determines the output voltage for supplying power from the power receiving unit 203 to the charging unit 211 based on the GP determined in S403 (S404). In addition, if there is an output voltage already stored in S404, the stored output voltage is adopted as the output voltage for supplying power from the power receiving unit 203 to the charging unit 211 regardless of the determined GP. An example of an output voltage determined based on the GP is shown in table 1001 in FIG. 10(A). By referring to table 1001, for example, the output voltage can be determined to be 5 volts when the GP is 5 watts, and 9 volts when the GP is 15 watts. Here, each value in table 1001 is a value determined in advance to efficiently charge the battery 202 based on the electrical characteristics of the charging unit 211 of the RX101. Table 1001 is held in the memory 209, for example. In addition, when the charging unit 211 is an external device that operates based on the USB PD standard, the power receiving unit 203 may acquire the output voltage from the charging unit 211 through communication, or the output voltage may be stored in the memory 209 as a table defined by the USB PD standard.

[0055] Returning to FIG. 4A, the RX101 sets the output voltage determined in S404 in the variable voltage circuit 212, and waits until the actually output voltage stabilizes (S405). Next, the RX101 requests the TX102 to obtain parameters for foreign object detection processing, thereby requesting the TX102 to perform the above-mentioned calibration phase (S406). Note that by waiting until the output voltage stabilizes in S405, it is possible to perform the calibration phase processing in S406 with the output voltage stabilized. As a result, the obtained parameters for foreign object detection processing are not affected by temporal fluctuations in the output voltage, enabling more accurate foreign object detection.

[0056] 7C shows the flow of processing in the calibration phase. The RX101 transmits a Received Power Packet via the communication unit 206 (F721). The Received Power Packet includes a Received Power Value, which is the current received power. It also includes information Mode=1, which indicates the start of the calibration phase. The TX102 stores the received power information included in the Received Power Packet as a foreign object detection processing parameter, and then returns an ACK (F722). The TX102 also detects the start of the calibration phase by detecting Mode=1, and discards any foreign object detection processing parameters that have already been stored up to that point. Details of other processing in the TX102 will be described later.

[0057] In the calibration phase, the RX101 notifies the received power in two different states: a state where no load is connected, i.e., a state where the power is close to 0 watts, and a state where the power is close to GP. That is, the communication of the Received Power Packet and ACK shown in FIG. 7(C) occurs at least twice, and the TX102 stores information on the two received powers. Furthermore, when the GP value exceeds 5 watts, the RX101 notifies the received power at voltage value intervals of about 5 watts. For example, when the GP value is 15 watts, the RX101 notifies the received power in a state where about 0 watts, about 5 watts, about 10 watts, and about 15 watts are received. Note that the voltage value intervals for notifying the received power by the RX101 do not have to be 5 watts, and do not have to be constant. The TX102 stores all the received powers notified by the RX101 as parameters for foreign object detection processing.

[0058] Returning to FIG. 4A, RX101 connects the charging unit 211, which is a load, to the power receiving unit 203 and starts power reception in the power transfer phase (S407). After starting power reception, RX101 acquires the power required by the charging unit 211 (S408). This value may be stored in advance in the memory 209, or if the charging unit 211 is an external device, it may be acquired from the external device via communication. If the power required by the charging unit 211 is within the range of the current GP, RX101 determines that it is not necessary to change the GP (NO in S409) and continues power reception for a predetermined time (S419 in FIG. 4B). The predetermined time is, for example, one second. After that, if charging of the battery 202 by the charging unit 211 is completed (YES in S420), RX101 disconnects the load and stops power reception. If charging is not completed (NO in S420), the process returns to S408 to continue charging.

[0059] Here, while continuing power reception in S419, RX101 notifies TX102 of the current received power periodically and repeatedly. TX102 performs foreign object detection based on the received power notified from RX101. The Received Power Packet is used to notify the current received power. As described above, the Received Power Packet is also used to notify parameters for foreign object detection processing. For this reason, RX101 provides information to distinguish whether the notification is a parameter for foreign object detection processing, that is, a notification requesting TX102 to store it, or a notification of the current received power for performing foreign object detection processing in TX102. This information is stored, for example, in the Mode value of the Received Power Packet. In this embodiment, when Mode=0, it means that the notification is the received power for foreign object detection processing. When requesting TX102 to store it as a parameter, the Mode value is set to a value other than 0. For example, in the above-mentioned calibration phase, the Mode value of the Received Power Packet is set to 1.

[0060] When it becomes necessary to change the GP (YES in S409) as a result of obtaining the power required by the charging unit 211 (S408), the RX101 negotiates with the TX102 and changes the GP (S410). When attempting to change the GP to a value greater than a predetermined value, the RX101 may perform device authentication of the TX102 through communication. By performing device authentication, it is possible to receive power greater than or equal to a predetermined value only from a TX102 that is guaranteed to meet conditions such as the WPC standard. One example of device authentication is challenge-response type communication using an electronic certificate.

[0061] Next, RX101 determines the output voltage to the charging unit 211 based on the updated GP (S411 in FIG. 4B). The output voltage to the charging unit 211 is determined based on table 1001 in FIG. 10(A). After that, RX101 compares the output voltage determined in S411 with the current output voltage (S412). If the result of the comparison is that the determined output voltage is the same as the current output voltage (NO in S412), RX101 requests TX102 to add parameters for foreign object detection processing (S418). This request is made by sending a Received Power Packet after setting the received power to a value close to the updated GP. Here, Mode=2 is used as a Mode value other than 0. For example, when changing the GP from 5 watts to 10 watts, RX101 sets the received power to about 10 watts and then sends a Received Power Packet (Mode=2). Note that when reducing the GP, it is not necessary to send an additional request. Furthermore, if the updated GP becomes very large (if the difference from the current GP becomes larger than a predetermined value), the Received Power Packet may be transmitted multiple times in multiple received power states, for example, at intervals of about 5 watts.

[0062] The TX 102 adds the information on the received power notified in S418 to the memory 309 as a foreign object detection processing parameter and stores it therein. In order to distinguish from the start of the calibration phase and the notification of the received power, the value of Mode in the Received Power Packet for the request to add parameters for foreign object detection processing is set to a value other than 0 or 1. As described above, in this embodiment, Mode=2 is used. After that, the process proceeds to S419. The process from S419 onwards is as described above.

[0063] On the other hand, if the output voltage determined in S411 differs from the current output voltage (YES in S412), the communication unit 206 is used to request the TX102 to reacquire the foreign object detection processing parameters (S413), and a response from the TX102 is awaited. This reacquisition request is different from the request for adding foreign object detection processing parameters in S418 described above. In other words, the reacquisition request requests the TX102 to discard the foreign object detection processing parameters held in the memory 309, and to save the foreign object detection processing parameters newly notified from the RX101.

[0064] This reacquisition request may be made by transmitting a packet conforming to the WPC standard, or may be made by transmitting another packet that the TX102 can recognize. In the WPC standard, the response of the TX102 is one of ACK (Acknowledge), ND (Not Defined), and NAK (Not-Acknowledge). ACK is a positive response indicating that the TX102 has accepted the reacquisition request. ND is a response indicating that the packet is undefined, that is, that the TX102 does not have the function of accepting the reacquisition request. NAK is a negative response indicating that the reacquisition request is rejected. If the response of the TX102 is a positive response (ACK) (ACK in S414), the RX101 disconnects the load and stops receiving power, and then returns to S405 (S415). In S405 to which the RX101 has returned, the RX101 sets the output voltage determined in S411 in the variable voltage circuit 212. Then, in S406, the RX101 performs the process of the calibration phase with the set output voltage. The process from S406 onwards is as described above. In S412, the determination of whether the determined output voltage is the same as or different from the current output voltage may be replaced with whether the difference between the determined output voltage and the current output voltage is greater than or equal to a predetermined threshold. Here, the threshold is ≧0. Furthermore, the threshold may be determined based on the magnitude of the output voltage determined in S411. For example, it may be a value that increases as the output voltage determined in S411 increases. Also, for example, the threshold may be set to 10% of the magnitude of the output voltage determined in S411.

[0065] On the other hand, if the response from the TX102 indicates undefined (ND) (ND in S414), the RX101 stores the value of the GP updated in S410 in the memory 209 (S416) and requests the TX102 to stop power transmission (S417). After that, the process returns to S401, and the RX101 waits for a Digital Ping. The request to stop power transmission is made, for example, by the RX101 transmitting an End Power Transfer Packet of the WPC standard to the TX102. Note that instead of the request to stop power transmission, a request to limit the transmission power to a small value equal to or less than a predetermined value may be used. When the process returns to S401, S401 to S402 are immediately executed since the mounted state continues, and in S403, the RX101 negotiates with the TX102 so that the GP updated in S410 is set. As a result, the output voltage from the variable voltage circuit 212 becomes the output voltage determined in S411 (S404), and with this output voltage stable (S405), the calibration phase processing is performed (S406). As described above, in the calibration phase, the foreign object detection processing parameters already stored in the TX102 are discarded, and a Received Power Packet (Mode=1) is issued with the received power in the state of 0 watts to 5 watts increments. The TX102 newly stores the received power notified by these Received Power Packets as foreign object detection processing parameters. The subsequent processing is as described above.

[0066] In this way, even if the response from TX102 to the parameter re-acquisition request from RX101 is ND, foreign object detection processing parameters are re-acquired by RX101 and TX102. Therefore, even if TX102 does not respond to the request to re-acquire parameters for foreign object detection processing and the response in S414 is ND, it is possible to re-acquire parameters for foreign object detection processing in the state of the output voltage determined in S411.

[0067] In S414, if the response from the TX102 is NAK (NAK in S414), the RX101 requests the addition of parameters for foreign object detection processing based on the GP updated in S410 (S418). In this case, the output voltage does not change. This makes it possible to prevent the output voltage from being changed if the TX102 rejects the change in the output voltage.

[0068] [Processing in power transmission device 102] Next, an example of the flow of the process executed by the TX102 will be described with reference to FIG. 5A to FIG. 5B. This process can be realized, for example, by the control unit 301 of the TX102 executing a program read from the memory 309. At least a part of the following procedure may be realized by hardware. In this case, the hardware can be realized, for example, by using a predetermined compiler to automatically generate a dedicated circuit using a gate array circuit such as an FPGA from a program for realizing each processing step. This process can be executed in response to the power supply of the TX102 being turned on, in response to the user of the TX102 inputting an instruction to start a wireless charging application, or in response to the TX102 being connected to a commercial power source and receiving power supply. This process may also be started by another trigger.

[0069] First, the TX102 executes the processes defined as the Selection phase and Ping phase of the WPC standard, and waits for the RX101 to be placed on it (S501). Specifically, the TX102 repeatedly and intermittently transmits an Analog Ping of the WPC standard to detect the presence or absence of an object placed on the charging stand 103. Then, when the TX102 detects that an object has been placed on the charging stand 103, it transmits a Digital Ping. When there is a predetermined response (Signal Strength Packet) to the Digital Ping, the TX102 determines that the detected object is the RX101, and that the RX101 has been placed on the charging stand 103.

[0070] When the TX102 detects that the RX101 has been placed, the TX102 executes communication in the I&C phase described above using the communication unit 306, and acquires identification information and device configuration information (capability information) from the RX101 (S502). Then, the TX102 executes communication in the Negotiation phase with the RX101, and determines the GP based on the request of the RX101 (S503). Specifically, as described in the processing of the power receiving device, this is performed using the Specific Request Packet shown in FIG. 7(B) and the response thereto.

[0071] Returning to FIG. 5A, the TX102 determines an input voltage for supplying power from the power supply unit 302 to the power transmission unit 303 based on the GP determined in S503, and sets the input voltage in the variable voltage circuit 311 (S504). An example of the input voltage to the power transmission unit 303 determined based on the GP is shown in table 1002 in FIG. 10(B). By referring to table 1002, the TX102 can determine, for example, an input voltage of 5 volts when the GP is 5 watts, and an input voltage of 9 volts when the GP is 15 watts. Each value in table 1002 is a value determined in advance for efficient power transmission based on the electrical characteristics of the power transmission unit 303 of the TX102, and is stored in the memory 309. Note that the power supply unit 302 and the variable voltage circuit 311 may be external devices that operate based on the USB PD standard. In that case, the input voltage to the power transmission unit 303 may be acquired by communication from the external device (power supply unit 302), or may be stored in the memory 309 as a table defined by the USB PD standard. The table 1002 held by the TX 102 and the table 1001 held by the RX 101 may be the same or different.

[0072] Returning to FIG. 5A, after setting the input voltage, the TX102 acquires foreign object detection processing parameters by processing in the calibration phase (S505). The processing in the calibration phase is started by receiving a Received Power Packet including Mode=1 from the RX101. When this packet is received, the TX102 discards any foreign object detection processing parameters that have already been stored. The TX102 associates the received power included in the Received Power Packet (Mode=1) received from the RX101 with the power loss, which is the difference between the transmitted power in the power transmitting unit 303 at that time, and stores them in the memory 309. Note that the transmitted power may be stored in association with the received power instead of the power loss, or both the power loss and the transmitted power may be stored in association with the received power.

[0073] Table 800 in Fig. 8 shows an example of the contents of foreign object detection processing parameters stored in memory 309. For example, the information in row 801 indicates that the power loss is 0.6 watts when the received power notified from RX101 is 0.1 watts. Thereafter, every time TX102 receives a Received Power Packet (Mode = 2) from RX101, it adds a row to table 800. However, as described above, when Mode = 0, TX102 does not add a row. Also, when Mode = 1, TX102 clears the contents of table 800 up to that point.

[0074] Returning to FIG. 5A, the TX102 starts foreign object detection processing and power transmission (S506, S507). The foreign object detection processing in the TX102 is a processing that is periodically executed while wireless power transmission is being performed, and is performed, for example, as follows. First, the TX102 periodically acquires information on the current received power from the RX101. As described above, the RX101 periodically transmits information on the received power in a Received Power Packet including Mode=0 (S419), and the TX102 acquires this information. Then, the TX102 calculates the expected value of the power loss in the acquired received power by linear interpolation of each point using the parameters for foreign object detection processing in table 800 in FIG. 8. For example, the above formula 1 can be used for the linear interpolation. The TX102 calculates the power loss from the difference between the measured transmitted power and the acquired received power. Then, when the difference between the calculated power loss and the calculated expected value exceeds a predetermined threshold, the TX102 determines that there is a power loss due to a foreign object such as a metal piece, and determines that there is a foreign object in the power transmission range. When it is determined that there is a foreign object in the power transmission range, the control unit 201 of the TX102 limits the power transmission to the RX101. Specifically, the control unit 201 controls the power transmitting unit 303 to stop the power transmission or to reduce the transmission power. In addition, the control unit 201 may notify the RX101 of the presence of a foreign object via the communication unit 306. Furthermore, the control unit 201 may notify that the transmission power will be limited.

[0075] Here, the foreign object detection process will be described in more detail, taking as an example a case where the contents of the foreign object detection process parameters are those shown in rows 801 and 802 of table 800 in Fig. 8. When rows 801 and 802 are plotted on a graph with received power and power loss as axes, they become points A and B in Fig. 9(A), respectively. The TX 102 obtains the expected value of power loss at the current received power by linear interpolation using a straight line connecting points A and B. For example, when the value of the current received power (RP) is 2.5 watts, the numerical values ​​of row 801 (RP1 = 0.1 watts, PL1 = 0.6 watts) and row 802 (RP1 = 4.9 watts, PL2 = 1.6 watts) are applied to the above formula 1. In this case, the expected value PL of power loss is as follows: PL=(1.6-0.6) / (4.9-0.1)*(2.5-0.1)+0.6=1.1 Then, the TX 102 calculates the power loss from the difference between the current transmission power and the current reception power (RP=2.5 watts). If the difference between the calculated power loss value and the expected value (PL=1.1 watts) is equal to or greater than the threshold, the TX 102 determines that power is being lost in the foreign object and that the foreign object is within the power transmission range. The threshold may be an absolute value such as 1 watt, or a relative value such as 50 percent of the expected value. Information regarding this threshold is stored in the memory 309. The threshold may also change in stages according to the expected value of the received power or the power loss.

[0076] Returning to FIG. 5A, the TX102 accepts GP negotiation from the RX101 even during power transmission. When GP negotiation is accepted from the RX101, the GP is updated (S508). If there is no GP negotiation, S508 is simply skipped. Also, as described above, there are cases where a request to reacquire parameters for foreign object detection processing is received from the RX101. When a request to reacquire parameters for foreign object detection processing is received (YES in S509), the TX102 returns an ACK (S510), and the process returns to S504. Thus, in response to the reacquisition request from the RX101, the TX102 resets the input voltage to the variable voltage circuit 311 and reacquires parameters for object detection processing in the calibration phase.

[0077] On the other hand, if a request to reacquire the foreign object detection processing parameters has not been received (NO in S509), the process proceeds to S511 in FIG. 5B. If there is a request from RX101 to add foreign object detection processing parameters, the TX102 adds the foreign object detection processing parameters (S511). In the process of adding the foreign object detection processing parameters, the TX102 receives from RX101 a received power value greater than the value of the conventional GP, calculates the difference between the received power and the transmitted power at that time as a power loss, associates the received power with the calculated power loss, and adds and holds it in the table 800. For example, if the transmitted power when receiving a received power of 9.9 watts from RX101 is 13.4 watts, the TX102 obtains the difference between the two, 3.5 watts, as the power loss. The TX102 associates the received power of 3.5 watts with the power loss of 9.9 watts, and holds it as an additional foreign object detection processing parameter. This state is shown in row 803 of table 800 in Fig. 8. Row 803 corresponds to point C in Fig. 9(B). This allows the TX102 to more accurately calculate the expected value of power loss when the received power becomes greater than the conventional GP value, and to more accurately detect foreign objects. Note that if there is no request from the RX101 for additional parameters for foreign object detection processing, S511 is skipped.

[0078] Returning to FIG. 5B, the TX102 judges whether a power transmission stop request has been received from the RX101 or whether a foreign object has been detected (S512). If a power transmission stop request has not been received or a foreign object has not been detected (NO in S512), the process returns to S508 in FIG. 5A, and the TX102 continues power transmission by repeating the above-mentioned process. If a power transmission stop request has been received or a foreign object has been detected (YES in S512), the TX102 stops power transmission (S513). After that, the TX102 judges whether or not to end the process (S514), and if it is judged that the process should be ended (YES in S514), this process ends. On the other hand, if the process should not be ended (NO in S514), the process returns to S501, and the above-mentioned process is repeated. Whether or not to end the process is determined based on, for example, the operation content of the operation unit 308 by the user.

[0079] [System Operation] The operation sequence of RX101 and TX102 explained using Fig. 4A-Fig. 4B and Fig. 5A-Fig. 5B will be explained using Fig. 6A-Fig. 6B. In Fig. 6A-Fig. 6B, time flows from top to bottom. In the initial state, RX101 is not placed on TX102, and the load (charging unit 211) of RX101 is not connected to the power receiving unit 203. In addition, the power required by the charging unit 211 of RX101 is initially 5 watts, which increases to 10 watts and 15 watts after the start of the Power Transfer phase.

[0080] First, TX102 transmits an Analog Ping and waits for an object to be placed on the charging stand 103 (F601, S501). When RX101 is placed (F602), a change occurs in the voltage or current of the Analog Ping (F603). This change causes TX102 to detect the placement of an object (F604). When the placement of an object is detected, TX102 transmits a Digital Ping (F605). By receiving this Digital Ping, RX101 detects that its own device has been placed on TX102 (F606). Furthermore, TX102 detects that the object placed on the charging stand 103 is RX101 by the response to the Digital Ping. Next, by communication in the I&C phase, RX101 transmits identification information and device configuration information (capability information) to TX102 (F607, S402, S502).

[0081] Next, GP is determined between RX101 and TX102 (F608, S403, S503). RX101 initially requests the necessary power of 5 watts, so GP here is 5 watts. Since GP is 5 watts, RX101 refers to table 1001 and sets the output voltage to 5 volts (F609, S404, S405). Similarly, TX102 refers to table 1002 and sets the input voltage to 5 volts (F610, S504). Next, by processing in the calibration phase, foreign object detection processing parameters from GP = 0 watts to 5 watts are acquired and held in TX102 (F611, S406, S505). At this stage, the foreign object detection processing parameters held by TX102 correspond to those shown in FIG. 9(A). Next, the RX 101 starts power reception (F612, S407), and the TX 102 starts foreign object detection processing and power transmission (F613, S506, S507).

[0082] After that, power transmission / reception and foreign object detection processing continue with GP = 5 watts for a while (F614, a loop of NO in S408 → S409 → NO → S419 → S420 → NO → S408, and a loop of NO in S508 → S509 → S511 → S512 → NO → S508). When 10 watts is required by the charging unit 211 (YES in F615, S408, S409), GP is updated to 10 watts between RX101 and TX102 (F616, S410, S508). When GP is updated to 10 watts, RX101 refers to table 1001 and determines to maintain the output voltage at 5 volts (F617, S411). Since the current output voltage continues, RX101 requests the addition of parameters for foreign object detection processing in the range of 5 to 10 watts (F618, NO in S412, S418). As a result, point C in Fig. 9B is added to the foreign object detection processing parameters held by the TX 102. Note that since the calibration processing for points A and B has already been performed by F611, the results are maintained.

[0083] After that, power transmission / reception and foreign object detection processing continue for a while with GP = 10 watts (F619, a loop of NO in S408 → S409 → NO → S419 → S420 → NO → S408, and a loop of NO in S508 → S509 → S511 → S512 → NO → S508). When 15 watts is required by the charging unit 211 (YES in F620, S408, S409), GP is updated to 15 watts between RX101 and TX102 (F621, S410, S508). When GP is updated to 15 watts, RX101 refers to table 1001 and decides to change the output voltage to 9 volts (F622, S411). Since the output voltage will change, RX101 requests TX102 to reacquire parameters for foreign object detection processing (YES in F623, S412). If an ACK is returned in response to this (F624, YES in S414, YES in S509, S510), the RX101 disconnects the load and stops receiving power (F625, S415).

[0084] Next, the RX101 sets the determined output voltage=9 volts in the variable voltage circuit 212 and waits for the output voltage to stabilize (F626, S405). Meanwhile, after transmitting ACK, the TX102 changes the input voltage to the power transmitting unit 303 to 9 volts by referring to table 1002 based on GP=15 watts (F627, S504). Then, the calibration phase process for GP=0 to 15 watts is performed (F628, S406, S505). At the beginning of the calibration phase, the TX102 clears the foreign object detection processing parameters that it has held up to that point. Then, when the output voltage to the load of the RX101 becomes 9 volts, the TX102 again acquires information on each of the points of 0 watts, 5 watts, 10 watts, and 15 watts as parameters for the foreign object detection process. Furthermore, at this time, the variable voltage circuit 212 of RX101 and the variable voltage circuit 311 of TX102 are set to 9 volts, which is a voltage based on the GP. That is, the electrical state is different from when the foreign object detection processing parameters are updated in F611 or F618. Therefore, as a result of the calibration process in F628, points A', B', C', and D' in Fig. 9(C) are obtained, which are different from points A, B, and C in Fig. 9(B).

[0085] After that, the RX101 connects the load and starts receiving power (F629, S407), and thereafter, power transmission / reception and foreign object detection processing continue at GP=15 watts (F630).

[0086] In the above-described operation, the RX101 changes the GP to 5 watts, 10 watts, and 15 watts based on the power required by the charging unit 211, which is the load. When the RX101 increases the GP from 5 watts to 10 watts, the output voltage remains unchanged at 5 volts, and a request is made for additional parameters for foreign object detection processing (F618). When the GP is increased from 10 watts to 15 watts, the RX101 changes the output voltage to 9 volts and requests reacquisition of parameters for foreign object detection processing (F623). That is, the RX101 selects an appropriate output voltage based on the power required by the load, and when the output voltage changes, it controls so that the parameters for foreign object detection are reacquired with the output voltage after the change. As a result, even if the output voltage changes and the electrical state of the RX101 changes, foreign object detection can be performed more accurately using parameters updated according to that state. Furthermore, when the output voltage does not change but the GP increases, the RX101 performs additional calibration processing in the area where the GP has increased. This allows more accurate foreign object detection when the received power and power loss change nonlinearly.

[0087] In addition, the RX101 may add information on the output voltage determined in S411 to a request for reacquisition of foreign object detection processing parameters, and the TX102 may store this output voltage information in the memory 309 in association with the table 800 in FIG. 8. That is, the TX102 holds the table 800 for each output voltage included in the reacquisition request in the memory 309. Then, when a reacquisition request is received from the RX101, if there is a table 800 that matches the output voltage included in the request, the TX102 may use the information of the table 800 corresponding to the output voltage in the memory 309 as a parameter. This prevents repeated reacquisition of foreign object detection processing parameters corresponding to output voltages previously acquired, and allows the foreign object detection processing parameters to be set efficiently. As a result, the efficiency of the charging process for the battery 202 is improved.

[0088] Furthermore, in the RX 101, information indicating the reason for reacquisition may be added to the request for reacquisition of the foreign object detection processing parameters. This allows the TX 102 to notify the user of the reason for reacquisition via the notification unit 307. Furthermore, this notification allows the user to know that power transmission has been temporarily stopped due to a change in output voltage.

[0089] <Second embodiment> In the first embodiment, the RX101 determines the output voltage based on the GP (S411 in FIG. 4B). In the second embodiment, the RX101 determines the output voltage based on the current power consumption in the charging unit 211, which is a load, instead of the GP. FIG. 11 shows the processing by the RX101 in the second embodiment. Note that the processing shown in FIG. 11 replaces part of the processing in the first embodiment (the processing shown in FIG. 4B). That is, the difference from the first embodiment is that S411 in FIG. 4B is replaced by S1101, and that the processing proceeds to S1101 if NO in S409 (if there is no need to change the GP). Furthermore, in the RX101 in the second embodiment, the voltage acquisition unit 213 can also acquire the magnitude of the power supplied to and consumed by the charging unit 211.

[0090] In FIG. 11, the RX101 starts the power transfer phase by the same process as in the first embodiment (S401 to S408). Next, the RX101 determines the GP based on the power required by the charging unit 211 (S408, S409, S410). After that, regardless of whether the GP has been changed, the RX101 acquires the current power consumption in the charging unit 211 and determines the output voltage to the charging unit 211 based on the value (S1101). Here, the RX101 determines the output voltage by referring to table 1201 in FIG. 12(A). Table 1201 lists the power consumption in the charging unit 211 and the output voltage to the charging unit 211 that is efficient for that power consumption. It is also assumed that table 1201 is held in advance in the memory 209. According to the configuration of the second embodiment, the output voltage can be determined based on the current power consumption in the charging unit 211. Therefore, for example, even if the charging unit 211 and the battery 202 are external devices and necessary power information cannot be frequently obtained from the charging unit 211 in S408, an appropriate output voltage can be quickly determined.

[0091] If the output voltage determined in S1101 is different from the current output voltage (YES in S412), the process proceeds to S413. The process from S413 onwards is the same as that of the first embodiment. However, if S405 is executed because it is determined in S414 that an ACK response has been received, the output voltage determined in S1101 is set in the variable voltage circuit 212. Also, if S416 is executed because it is determined in S414 that an ND response has been received, the output voltage set in S404 is the output voltage determined in S1101. On the other hand, if it is determined that the output voltage determined in S1101 is the same as the current output voltage, the process proceeds to S418. If the GP has been changed in S410, the RX101 requests the TX102 to add a parameter for foreign object detection processing, as in the first embodiment. However, if the GP has not been changed, the process of S418 is skipped. The process from S419 onwards is the same as that of the first embodiment.

[0092] Note that the RX101 may determine the output voltage to the charging unit 211 based on table 1202 shown in Fig. 12(B) instead of table 1201. In table 1202, the power consumption threshold is different for increasing and decreasing the output voltage. This makes it possible to prevent the output voltage from being changed and the associated foreign object detection processing parameter reacquisition processing from occurring frequently when the power consumption in the charging unit 211 has characteristics that vary from large to small in a short period of time. Furthermore, as another method for solving the same problem, the RX101 may use the timer 210 to prevent the output voltage from being changed for a predetermined period of time after the output voltage is changed.

[0093] <Other embodiments> The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0094] At least a part of the processes shown in the flowcharts of Figures 4A to 4B, 5A to 5B, and 11 may be realized by hardware. When the processes are realized by hardware, for example, a specific compiler may be used to automatically generate a dedicated circuit on the FPGA from a program for realizing each process. Also, a gate array circuit may be formed in the same manner as the FPGA, and the processes may be realized as hardware.

[0095] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention. [Explanation of symbols]

[0096] 101: power receiving device, 203: power receiving unit, 213: voltage determination unit, 215: parameter reacquisition request unit

Claims

1. A power receiving device, A power receiving unit that receives AC power wirelessly transmitted from a power transmitting device; A communication means for communicating with the power transmitting device; A conversion means for converting the AC power into DC power; A change means for changing an output voltage of the conversion means; having The communication means transmits a first received power packet including information indicating a value of a first received power to the power transmitting device; the change means changes a Guaranteed Power and changes the output voltage after the first received power packet is transmitted and after authentication of the power transmitting device; The power receiving device, characterized in that the communication means transmits a second received power packet including information indicating a value of a second received power to the power transmitting device after the output voltage is changed.

2. 2. The power receiving device according to claim 1, wherein the change unit changes the output voltage based on power required by a load that consumes the power received by the power receiving unit.

3. 3. The power receiving device according to claim 2, further comprising a negotiation means for negotiating the Guaranteed Power based on the power required by the load.

4. 4. The power receiving device according to claim 1, wherein a calibration process is started by transmitting the first received power packet.

5. The power receiving device according to claim 4 , wherein the transmission of the second received power packet restarts a calibration process.

6. 6. The power receiving device according to claim 4, wherein the calibration process acquires parameters used in a foreign object detection process performed by the power transmitting device.

7. The power receiving device according to claim 1 , wherein the authentication is based on an electronic certificate.

8. A method performed by a power receiving device, comprising: a first transmission step of transmitting a first received power packet including information indicating a value of the first received power to the power transmitting device; a changing step of changing a Guaranteed Power after the first transmission step and after authentication of the power transmitting device, and changing an output voltage after converting the AC power received by the power receiving device into DC power; A method comprising: after the changing step, a second transmitting step of transmitting a second received power packet to the power transmitting device, the second received power packet including information indicating a value of a second received power.

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