Patent Publication Number: US-2022224166-A1

Title: Power transmitting apparatus, control method for power transmitting apparatus, and storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Patent Application No. PCT/JP2020/026059, filed Jul. 2, 2020, which claims the benefit of Japanese Patent Application No. 2019-156801, filed Aug. 29, 2019, both of which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Field 
     The present disclosure is related to a power transmitting apparatus, a control method for a power transmitting apparatus, and a storage medium. 
     Background Art 
     Development of technology relating to wireless power transmission systems such as wireless charging systems has been carried out extensively in recent years. For example, in Japanese Patent Laid-Open No. 2017-070074, a power transmitting apparatus is described which is compliant with a standard (hereinafter, referred to as the WPC standard) developed by the Wireless Power Consortium (WPC), a group for promoting wireless charging standardization. Also, in Japanese Patent Laid-Open No. 2017-070074, a calibration process is defined that increases the accuracy of the detection, near a power transmission antenna (coil), of an electrically conductive object (foreign object) such as a metal piece that is not an intended target for power transmission compliant with the WPC standard. 
     In the calibration process, a transmission power of a power transmitting apparatus and the corresponding received power of a power receiving apparatus are obtained when the power receiving apparatus is in two different states. Then, using these two sets of transmission power and received power, a parameter for calibrating the received power or the transmission power when power is actually transmitted wirelessly is calculated. This parameter is used in the processing for detecting a foreign object. In other words, for example, with respect to the received power when power is wirelessly transmitted by the power transmitting apparatus, the received power calibrated using the parameter can be estimated, and a power loss, which is the difference between the actual transmission power of the power transmitting apparatus and the estimated received power can be calculated. Then, in a case where the power loss is greater than a predetermined value, it can be determined that there is a power loss caused by a foreign object. 
     However, the transmission power of a power transmitting apparatus and the power loss between a power transmitting apparatus and a power receiving apparatus is not always constant. For example, a power transmitting unit of a power transmitting apparatus uses a switching circuit including a switching element (for example, a field effect transistor (hereinafter, referred to as an FET)) to convert a DC voltage or current to an AC voltage or current. For switching circuits, there are half bridge circuits including two FETs and full bridge circuits including four FETs. For the switching circuit of a power transmitting unit, it is widely known to operate while switching between these two circuits depending on the magnitude of the transmission power. Also, the electric power consumed by the switching circuit of the power transmitting unit in this operation or the electric power transmitted by the power transmitting antenna may fluctuate, temporarily increasing, and be unstable. Furthermore, for example, in a case where the power receiving apparatus placed on the power transmitting apparatus is a smart phone, it can be expected that vibrations or the like may cause misalignment and the received power may be unstable. When executing determination for foreign objects in the power transmitting process, if the parameter described above calculated using the transmission power and the received power under such conditions is used, a foreign object may be unable to be detected or a foreign object may be falsely detected. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Laid-Open No. 2017-070074 
       
    
     SUMMARY 
     In the present disclosure, technology is provided for improving the calculation accuracy of a parameter used to determine whether or not an object that is not the intended power transmission target exists. 
     According to one aspect of the present disclosure, there is provided a power transmitting apparatus, comprising: a power transmitting unit configured to wirelessly transmit power to a power receiving apparatus; a measuring unit configured to measure a transmission power transmitted by the power transmitting unit to the power receiving apparatus; an obtaining unit configured to obtain information representing a received power at the power receiving apparatus when power is transmitted to the power receiving apparatus by the power transmitting unit; a calculating unit configured to calculate a parameter used in determining whether or not an object not an intended power transmission target exists on the basis of a transmission power measured by the measuring unit when a received power at the power receiving apparatus is in a plurality of different states and a received power corresponding to the plurality of different states represented by information obtained by the obtaining unit; and a determining unit configured to determine whether or not an object not an intended power transmission target exists at a predetermined point in time on the basis of a parameter calculated by the calculating unit, a transmission power at the predetermined point in time measured by the measuring unit, and a received power corresponding to the predetermined point in time represented by information obtained by the obtaining unit, wherein in a case where at least one of a transmission power measured by the measuring unit in one state from among the plurality of different states or a received power represented by information obtained by the obtaining unit in the one state is unstable, the calculating unit does not use the transmission power and the received power in calculating the parameter. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the disclosure and, together with the description, serve to explain principles of the disclosure. 
         FIG. 1  is a block diagram illustrating an example configuration of a power transmitting apparatus according to an embodiment. 
         FIG. 2  is a block diagram illustrating an example configuration of a power receiving apparatus according to an embodiment. 
         FIG. 3  is a functional block diagram of a power transmitting apparatus according to an embodiment. 
         FIG. 4  is a diagram illustrating an example configuration of a wireless power transmission system according to an embodiment. 
         FIG. 5  is a flowchart illustrating a process executed by a power transmitting apparatus. 
         FIG. 6A  is a flowchart ( 1 ) illustrating a process executed by a power transmitting apparatus. 
         FIG. 6B  is a flowchart ( 2 ) illustrating a process executed by a power transmitting apparatus. 
         FIG. 7  is a flowchart illustrating a process executed by a power receiving apparatus. 
         FIG. 8A  is a diagram ( 1 ) illustrating an example of an operation sequence of a wireless power transmission system according to an embodiment. 
         FIG. 8B  is a diagram ( 2 ) illustrating an example of an operation sequence of a wireless power transmission system according to an embodiment. 
         FIG. 9A  is a diagram ( 1 ) illustrating an example of an operation sequence of a wireless power transmission system according to an embodiment. 
         FIG. 9B  is a diagram ( 2 ) illustrating an example of an operation sequence of a wireless power transmission system according to an embodiment. 
         FIG. 10  is a diagram illustrating an expected received power graph generated by a power transmitting apparatus. 
         FIG. 11  is a flowchart illustrating foreign object detection processing executed by a power transmitting apparatus. 
         FIG. 12  is a diagram illustrating the relationship between a measurement cycle and a measurement period in transmission power measurement processing in a power transmitting apparatus. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the present disclosure. Multiple features are described in the embodiments, but limitation is not made to the present disclosure that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. 
     Embodiments of the present disclosure are described below with reference to the drawings. Note that the embodiments described below are merely examples for describing the technical concept of the present disclosure, and the present disclosure is not limited by the configurations and methods described in the embodiments. 
     System Configuration 
       FIG. 4  is a diagram illustrating an example of the configuration of a wireless power transmission system (wireless charging system) according to the present embodiment. The present system includes a power transmitting apparatus  100  and a power receiving apparatus  200 . Hereinafter, the power transmitting apparatus will be referred to as TX, and the power receiving apparatus will be referred to as RX. The TX  100  is an electronic device that wirelessly transmits power to the RX  200  placed in a charging stand provided in the TX  100 . The RX  200  is an electronic device that charges a battery by receiving power via the TX  100 . In the example described below, the RX  200  is placed on the charging stand. However, for the TX  100  to transmit power to the RX  200 , as long as the RX  200  exists within the power-transmittal range (for example, the range representing by the dashed line in  FIG. 4 ) of the TX  100 , the RX  200  may not be placed on the charging stand. 
     Also, the RX  200  and the TX  100  may have a function of executing an application other than wireless charging. An example of the RX  200  is a smartphone, and an example of the TX  100  is an accessory device for charging the smartphone. The RX  200  and the TX  100  may be storage apparatuses, such as a hard disk or a memory device, or may be information processing apparatuses, such as a tablet, personal computer (PC), or the like. Also, the RX  200  and the TX  100 , for example, may be image input apparatuses, such as an image capture apparatus (a camera, a video camera, and the like) or a scanner, or may be image output apparatuses, such as a printer, copying machine, or a projector. Also, the TX  100  may be a smartphone. In this case, the RX  200  may be another smartphone or a wireless earphone. Also, the RX  200  may be a vehicle such as an automobile, and the TX  100  may be a charging stand placed on the console or the like of the automobile. 
     In the present system, wireless power transmission is performed using an electromagnetic induction method for wireless charging on the basis of the WPC standard. In other words, for the RX  200  and the TX  100 , wireless power transmission is performed between a power receiving antenna of the RX  200  and a power transmitting antenna of the TX  100  to perform a wireless charge based on the WPC standard. Note that the wireless power transmission system used in the present system is not limited to that defined in the WPC standard, and other systems may be used, such as other electromagnetic induction systems, magnetic field resonance systems, electric field resonance systems, microwave systems, lasers, and the like. Also, in the present embodiment, the wireless charging uses wireless power transmission. However, wireless power transmission may be used for a different purpose other than for wireless charging. 
     In the WPC standard, the magnitude of the power guaranteed when power is received by the RX  200  from the TX  100  is defined as a value called Guaranteed Power (hereinafter, referred to as GP). GP represents the power value of the guaranteed output to the load (for example, a circuit for charging) of the RX  200  even when the power transmitting efficiency between the power receiving antenna and the power transmitting antenna decreases due to the positional relationship between the RX  200  and the TX  100  changing, for example. For example, in a case where the GP is 5 watts, even when the positional relationship between the power receiving antenna and the power transmitting antenna changes and the power transmitting efficiency is reduced, the TX  100  controls the power transmission in a manner such that 5 watts is output to the load in the RX  200 . 
     Also, in the WPC standard, the method by which the TX  100  detects whether an object (foreign object) that is not the intended power transmission target exists near in the power transmitting antenna is specified. The methods specifically specified are a power loss method in which a foreign object is detected using the difference between the transmission power of the TX  100  and the received power of the RX  200  and a Q-factor measurement method in which a foreign object is detected using the change in the quality coefficient (Q-factor) of the power transmitting coil of the TX  100 . Foreign object detection using the power loss method is performed during power transmission (in a Power Transfer phase described below). Also, foreign object detection using the Q-factor measurement method is performed before power transmission (in a Negotiation phase or Renegotiation phase described below). 
     Also, The RX  200  and the TX  100  according to the present embodiment communicate to perform power transmission and reception control based on the WPC standard. The WPC standard defines a plurality of phases including a Power Transfer phase in which power is transmitted and one or more phases before actual power transmission. In these phases, communication is executed to control the transmitting and receiving of power as necessary. Pre-power transmission phases may include a Selection phase, a Ping phase, an Identification and Configuration phase, a Negotiation phase, and a Calibration phase. Note that hereinafter, the Identification and Configuration phase will be referred to as the I&amp;C phase. 
     In the Selection phase, the TX  100  intermittently transmits an Analog Ping and detects if an object is placed on the charging stand (for example, if the RX  200 , conductor piece, or the like is placed on the charging stand) of the TX  100 . The TX  100  detects at least a voltage value or a current value of a power transmitting antenna when the Analog Ping is transmitted, determines that an object exists in the case in which the voltage value is less than a threshold or the current value is greater than a threshold, and transitions to the Ping phase. 
     In the Ping phase, the TX  100  transmits a Digital Ping at a greater power than the Analog Ping. The power of the Digital Ping is sufficient enough to activate a control unit of the RX  200  placed on the charging stand of the TX  100 . The RX  200  notifies the TX  100  of the magnitude of the received voltage. In this manner, by receiving a reply from the RX  200  that received the Digital Ping, the TX  100  recognizes that the object detected in the Selection phase is the RX  200 . When the TX  100  receives a notification of the received voltage value, the process transitions to the I&amp;C phase. 
     In the I&amp;C phase, the TX  100  identifies the RX  200  and acquires device configuration information (capability information) from the RX  200 . Accordingly, the RX  200  transmits an ID packet and a Configuration packet to the TX  100 . The ID packet includes the identification information of the RX  200 , and the Configuration packet includes the device configuration information (capability information) of the RX  200 . The TX  100  having received the ID packet and the Configuration packet replies with an acknowledge (ACK, affirmative reply). Then, the I&amp;C phase ends. 
     In the Negotiation phase, the GP value is determined on the basis of the GP value requested by the RX  200 , the power transmission capability of the TX  100 , and the like. Also, the TX  100  executes foreign object detection processing using the Q-factor measurement method in accordance with the request from the RX  200 . Also, in the WPC standard, a method is specified in which, after the Power Transfer phase has been transitioned to, a similar processing to the Negotiation phase is again executed at the request of the RX  200 . The phase in which this processing is executed after transitioning from the Power Transfer phase is called the Renegotiation phase. 
     In the Calibration phase, on the basis of the WPC standard, the RX  200  notifies the TX  100  of a predetermined received power (value of received power in a light load state/value of received power in a high load state) and requests for calibration to be executed. The TX  100  obtains the transmission power value corresponding to the received power value, calculates the power loss on the basis of the transmission power value and the received power value, and associates together and stores the calculated power loss and the transmission power. Then, the TX  100  calculates a parameter for foreign object detection processing using the power loss method on the basis of at least two sets of the transmission power and the power loss. This parameter will be described below. In this manner, the calibration process may include processing to obtain the received power, obtain the transmission power corresponding to the received power and calculate the power loss, and associate together and store the transmission power and the power loss. Also, the calibration process may include processing to calculate the parameter for foreign object detection processing executed by the TX  100  from at least two sets of the transmission power and the power loss. Note that power loss is the power lost when power is transmitted from the TX  100  to the RX  200 . For example, in a case where the transmission power is 1 watt and the received power is 0.9 watt, the power loss is 0.1 watt. Note that instead of using the lost power value, the power loss ratio (for example, in this case, 10%) may be used as the power loss. 
     In the Power Transfer phase, control is performed to start power transmission, continue power transmission, stop power transmission due to detection of a foreign object or a full charge, and the like. 
     The TX  100  and the RX  200  perform communication using the same antenna (coil) used for wireless power transmission based on the WPC standard, for controlling the transmitting and receiving of power therebetween and superimposing a signal on the electromagnetic waves transmitted from the antenna. Note that the communicable range between the TX  100  and the RX  200  based on the WPC standard is roughly the same as the power-transmittal range (the range represented by the dashed line in  FIG. 4 ) of the TX  100 . 
     Next, the configuration of the power transmitting apparatus  100  (TX  100 ) and the power receiving apparatus  200  (RX  200 ) according to the present embodiment will be described. Note that the configuration described below is simply one example, and a part (or all parts) of the configuration described below may be replaced by other configurations with similar functions, may be omitted, or other configurations may be added in addition to the configurations described below. Furthermore, one block described in the description below may be one block divided into a plurality of blocks or may be a plurality of blocks merged as a single block. Also, for the functional blocks described below, the functions may be configured as software programs. However, a part or all parts included in each functional block may be configured as hardware. 
       FIG. 1  is a functional block diagram illustrating an example of the configuration of the TX  100  according to the present embodiment. The TX  100  includes a control unit  101 , a power source unit  102 , a power transmitting unit  103 , a communication unit  104 , a power transmitting antenna  105 , and a memory  106 . The control unit  101 , the power source unit  102 , the power transmitting unit  103 , the communication unit  104 , and the memory  106  are illustrated as separate units in  FIG. 1 . However, from among these, any number of the functional blocks may be mounted on the same chip. 
     The control unit  101 , for example, controls the entire TX  100  by executing a control program stored in the memory  106 . In other words, the control unit  101  controls the functional units illustrated in  FIG. 1 . Also, the control unit  101  executes control relating to power transmission control including communication for device authentication by the TX  100 . Furthermore, the control unit  101  may execute control for executing an application other than wireless power transmission. The control unit  101 , for example, includes one or more processors, such as a central processing unit (CPU), a microprocessing unit (MPU), or the like. Note that the control unit  101  may be configured as hardware dedicated to specific processing, such as an application specific integrated circuit (ASIC), or the like. Also, the control unit  101  may include an array circuit such as a field programmable gate array (FPGA) compiled so as to execute predetermined processing. The control unit  101  causes information stored during the execution of various types of processing to be stored in the memory  106 . Also, the control unit  101  is capable of measuring time using a timer (not illustrated). 
     The power source unit  102  supplies the power to the entire TX  100  required for the control, power transmission, and communication of the TX  100  by the control unit  101 . The power source unit  102 , for example, is a commercial power source or a battery. Power supplied from a commercial power source is stored in the battery. 
     The power transmitting unit  103  converts direct current or alternating current power input from the power source unit  102  to alternating current frequency power in a frequency band used for wireless power transmission and generates electromagnetic waves for reception by the RX  200  by inputting the alternating current frequency power into the power transmitting antenna  105 . For example, the power transmitting unit  103  converts DC voltage supplied by the power source unit  102  to AC voltage at a switching circuit with a half bridge or full bridge configuration using FETs. In this case, the power transmitting unit  103  includes a gate driver that controls switching the FETs on and off. Also, the power transmitting unit  103  is capable of changing the transmission power by changing these two switching circuits. 
     Also, the power transmitting unit  103  controls the intensity of the electromagnetic waves output by adjusting the voltage (transmission voltage) input to the power transmitting antenna  105 . If the transmission voltage is increased, the intensity of electromagnetic waves is increased, and if transmission voltage is decreased, the intensity of electromagnetic waves is decreased. As described below, the power transmitting unit  103  is capable of controlling the transmission power by changing the transmission voltage in accordance with a Control Error packet (hereinafter, referred to as a CE packet) periodically transmitted from the RX  200 . Note that the intensity of the output electromagnetic waves may be controlled by adjusting the current (transmission current) input to the power transmitting antenna  105  or both the transmission voltage and the transmission current. In addition, on the basis of an instruction from the control unit  101 , the power transmitting unit  103  performs output control of the alternating current frequency power to start or stop power transmission from the power transmitting antenna  105 . Also, the power transmitting unit  103  has the capability to supply power corresponding to outputting 15 watts (W) of power to a charging unit  206  ( FIG. 2 ) of the RX  200  power according to the WPC standard. 
     The communication unit  104  performs communication with the RX  200  for power transmission control based on the WPC standard as described above. The communication unit  104  performs communication including modulating the electromagnetic waves output from the power transmitting antenna  105  and transmitting information to the RX  200 . Also, the communication unit  104  demodulates the electromagnetic waves outputs from the power transmitting antenna  105  and modulated at the RX  200  to obtain the information transmitted by the RX  200 . In other words, communication performed by the communication unit  104  is performed by superimposition of a signal on electromagnetic waves transmitted from the power transmitting antenna  105 . Note that the communication unit  104  may perform communication with the RX  200  via a different communication method using an antenna other than the power transmitting antenna  105 . For example, communication may be performed via IEEE 802.11 standard series wireless LAN (for example, Wi-Fi (registered trademark), Bluetooth (registered trademark), ZigBee, near-field communication (NFC), or the like. Also, the communication unit  104  may perform communication with the RX  200  by selectively using a plurality of communication methods. 
     The memory  106  may store the control program as well as the state of the TX  100  and the RX  200  (received power value and the like). For example, the state of the TX  100  may be obtained by the control unit  101 , the state of the RX  200  may be obtained by a control unit  201  ( FIG. 2 ) of the RX  200 , and these may be received via the communication unit  104 . 
       FIG. 2  is a block diagram illustrating an example of the configuration of the power receiving apparatus  200  (RX  200 ) according to the present embodiment. The RX  200  includes the control unit  201 , a user interface (UI) unit  202 , a power receiving unit  203 , a communication unit  204 , a power receiving antenna  205 , the charging unit  206 , a battery  207 , and a memory  208 . 
     The control unit  201 , for example, controls the entire RX  200  by executing a control program stored in the memory  208 . In other words, the control unit  201  controls the functional units illustrated in  FIG. 2 . Furthermore, the control unit  201  may execute control for executing an application other than wireless power transmission. The control unit  201 , for example, includes one or more processors, such as a CPU, an MPU, or the like. Note that the entire RX  200  (in a case where the RX  200  is a smart phone, the entire smart phone) may be controlled in cooperation with the operating system (OS) executed by the control unit  201 . Also, the control unit  201  may be configured as hardware dedicated to a specific processing such as an ASIC. Also, the control unit  201  may include an array circuit such as an FPGA compiled so as to execute predetermined processing. The control unit  201  causes information stored during the execution of various types of processing to be stored in the memory  208 . Also, the control unit  201  is capable of measuring time using a timer (not illustrated). 
     The UI unit  202  outputs information in various manners to the user. Herein, outputting in various manners refers to an operation such as screen display, flashing or changing the color of LEDS, audio output via a speaker, vibration of the RX  200  body, and the like. The UI unit  202  includes an LED, a speaker, a vibration motor, and/or other notification devices. Also, the UI unit  202  may have a reception function of receiving operations of the RX  200  from the user. In this case, the UI unit  202 , for example, includes a button or keyboard, an audio input device such as a microphone, a motion detection device such as an acceleration sensor or gyro sensor, or another type of input device. Note that a device such as a touch panel may be used that is capable of both outputting information to the user and receiving operations from the user. 
     The power receiving unit  203 , at the power receiving antenna  205 , obtains AC power (AC voltage and AC current) generated by electromagnetic induction caused by electromagnetic waves emitted from the power transmitting antenna  105  of the TX  100 . Also, the power receiving unit  203  converts the AC power to DC or AC power of a predetermined frequency and outputs the power to the charging unit  206  that executes processing to charge the battery  207 . In other words, the power receiving unit  203  supplies power to a load in the RX  200 . GP as described above is a power value guaranteed to be output from the power receiving unit  203 . The power receiving unit  203  is capable of supplying power for the charging unit  206  to charge the battery  207  and supplying power corresponding to outputting 15 watts to the charging unit  206 . Furthermore, by the power receiving unit  203  notifying the control unit  201  of the current received power value, the received power value at any discretionary time can be known by the control unit  201 . 
     The charging unit  206  charges the battery  207  via power supplied from the power receiving unit  203 . Also, the charging unit  206  starts or stops charging of the battery  207  on the basis of control from the control unit  201  and adjusts the power used to charge the battery  207  on the basis of the charge state of the battery  207 . When the power used by the charging unit  206  changes, the power supplied from the power receiving unit  203 , i.e., the received power at the RX  200 , changes according to this change. Herein, the charging unit  206  is the load in the RX  200 . Accordingly, causing the charging unit  206  to start charging the battery  207  corresponds to connecting the load to the power receiving unit  203 . In a similar manner, stopping charging corresponds to disconnecting the load from the power receiving unit  203 . 
     The communication unit  204  performs communication for power reception control based on the WPC standard as described above with the communication unit  104  of the TX  100 . The communication unit  204  demodulates the electromagnetic waves received from the power receiving antenna  205  and obtains the information transmitted from the TX  100 . Also, the communication unit  204  performs communications with the TX  100  by superimposing, on electromagnetic waves, a signal relating to the information to be transmitted to the TX  100  via load modulation of the received electromagnetic waves. Note that the communication unit  204  may perform communication with the TX  100  via a different communication method using an antenna other than the power receiving antenna  205 . For example, communication may be performed via IEEE 802.11 standard series wireless LAN (for example, Wi-Fi (registered trademark), Bluetooth (registered trademark), ZigBee, NFC, or the like. Also, the communication unit  204  may perform communication with the TX  100  by selectively using a plurality of communication methods. 
     The memory  208  stores the control program as well as the state of the TX  100  and the RX  200 . For example, the state of the RX  200  may be obtained by the control unit  201 , the state of the TX  100  may be obtained by the control unit  101  of the TX  100 , and these may be received via the communication unit  204 . 
     Next, the functional block diagram of the control unit  101  of the TX  100  will be described next with reference to  FIG. 3 . The control unit  101  includes a communication processing unit  301 , a power transmitting processing unit  302 , a foreign object detection processing unit  303 , and a calculation processing unit  304 . 
     The communication processing unit  301  executes processing relating to the control communication with the RX  200  based on the WPC standard via the communication unit  104 . The power transmitting processing unit  302  controls the power transmitting unit  103  and executes processing relating to transmitting power to the RX  200 . 
     The foreign object detection processing unit  303  executes processing to detect a foreign object. Herein, a detected foreign object is a foreign object that exists in the power-transmittal range of the TX  100  and a foreign object placed on the placement surface (contact surface) where the RX  200  is placed. As long as a foreign object can be detected at a position that is affected when power is transmitted from the TX  100  to the RX  200 , its detection range is not limited. The foreign object detection processing unit  303  may implement a foreign object detection function via the power loss method and a foreign object detection function via the Q-factor measurement method. Also, the foreign object detection processing unit  303  may execute foreign object detection processing using another method. For example, in a case where the TX  100  has an NFC communication function, foreign object detection processing may be executed using an opposing device detection function using an NFC standard. 
     The calculation processing unit  304  measures the power output to the RX  200  via the power transmitting unit  103  and calculates the average transmission power value per unit time. The foreign object detection processing unit  303  executes foreign object detection processing using the power loss method on the basis of the calculation result from the calculation processing unit  304  and the received power information received from the power receiving apparatus via the communication processing unit  301 . 
     The functions of the communication processing unit  301 , the power transmitting processing unit  302 , the foreign object detection processing unit  303 , and the calculation processing unit  304  are implemented as programs operating via the control unit  101 . Each processing unit may be configured as an independent program and operate in parallel with the programs being in sync via event processing or the like. 
     Operations of Power Receiving Apparatus 
     Next, the operations of the RX  200  according to the present embodiment will be described using the flowchart of  FIG. 7 . The present processing can be implemented by the control unit  201  of the RX  200  executing a program read out from the memory  208 , for example. 
       FIG. 7  is a flowchart illustrating the processing executed by the RX  200  and illustrates the processing process for causing the TX  100  to calculate an estimation value of the power loss (hereinafter, also referred to as an estimated power loss) used in foreign object detection via the power loss method. The process in  FIG. 7  is executed after the Negotiation phase is completed at the RX  200  and before the charge processing for the battery  207  is executed. Specifically, the process is started after a packet requesting negotiation completion is transmitted by the RX  200  to the TX  100  and an affirmative reply (ACK packet) is received from the TX  100 . 
     Firstly, the RX  200  calculates the received power value in a low load (light load) state as reference received power information (step S 701 ). Note that herein, a low load state is a state in which the power receiving unit  203  is not connected to a load, or in other words, a state in which the received power is the minimum, with the power output to the power receiving unit  203  being approximately 500 mW. Then, the RX  200  uses a Received Power packet (hereinafter, referred to as an RP packet) in accordance with the WPC standard and sends a request to the TX  100  for calibration execution (step S 702 ). An RP packet includes the received power value at a low load state calculated as the reference power information and information corresponding to Mode=1 representing that a first item of calibration will be performed. 
     Note that though not illustrated, the RX  200  periodically transmits a CE packet for control of the transmission voltage (transmission power) of the TX  100  after the Negotiation phase is complete. For example, the CE packet corresponds to an instruction, such as +1 volt, −2 volt, 0 (maintain voltage), or the like. When calibration is performed, the CE packet is used for requesting fine adjustment of the transmission power to maintain the received power at a constant value (for example 500 mW). 
     When the RX  200  receives a NAK packet in response to the calibration request from the TX  100  (no in step S 703 ), the time from when the RP packet was first received in step S 702  is calculated, and whether or not time has run out is checked (step S 704 ). In the case of time out (yes in step S 704 ), the RX  200  notifies the user that an error has occurred (step S 705 ), and charge processing ends. In a case where the time has not run out (no in step S 704 ), again, the RX  200  calculates the received power value (step S 701 ) and transmits an RP packet (step S 702 ). 
     When an ACK packet is received in response to the calibration request from the TX  100  (yes in step S 703 ), the RX  200  instructs the TX  100  to raise the transmission voltage via a CE packet in order to calculate the received power value in a high load state (step S 706 ). Note that herein, a high load state is a state in which the power receiving unit  203  is connected to a load and the received power is the maximum, with the power output to the power receiving unit  203  being approximately 15 W, which is roughly the maximum power in the range according to the WPC standard. Note that when the received power is at the maximum, the maximum power capable of being supplied to the load by the RX  200 , the maximum power estimated to be required at the load in the time period from placement to charge completion, or a power based on the GP is set. The RX  200  may transmit a CE packet many times to measure the power output to the power receiving unit  203  and adjust output so that the output is approximately 15 W. The TX  100  may be configured to transmit a large power by switching the switching circuits when these CE packets are received. 
     After CE packet transmission, in a case where the received power is confirmed to has risen to approximately 15 W, in a similar manner to with the low load state, the RX  200  calculates the received power value as the reference received power information (step S 707 ) and sends a request for calibration using an RP packet (step S 708 ). Herein, a transmitted RP packet includes the received power value at a high load state and information corresponding to Mode=2 representing that a second item of calibration will be performed. 
     When the RX  200  receives a NAK packet in response to the second item of calibration request from the TX  100  (no in step S 709 ), the time from when the RP packet was received in step S 708  is calculated, and whether or not time has run out is checked (step S 710 ). In the case of time out (yes in step S 710 ), the RX  200  notifies the user that an error has occurred (step S 711 ), and charge processing ends. In a case where the time has not run out (no in step S 710 ), again, the RX  200  calculates the received power value (step S 707 ) and transmits an RP packet (step S 708 ). 
     When the RX  200  receives an ACK packet in response to the second item of calibration request from the TX  100  (yes in step S 709 ), processing to charge the battery  207  starts (step S 712 ). Note that after the second item of calibration is complete, the RX  200  periodically notifies the TX  100  of its own received power value via an RP packet. Thus, the RP packet transmitted in a case where there is no request for calibration execution includes the information corresponding to Mode=0. As described below, the TX  100  uses the received power value included in the RP packet in which Mode=0 received from the RX  200  and detects foreign objects via the power loss method. 
     Operations of Power Transmitting Apparatus 
     Next, the operations of the TX  100  according to the present embodiment will be described using the flowchart of  FIGS. 5 and 6 . The present processing can be implemented by the control unit  101  of the TX  100  executing a program read out from the memory  106 , for example. 
       FIG. 5  is a flowchart illustrating the processing operations of the calculation processing unit  304  operating in the control unit  101  and illustrating the processing process for calculating and storing the transmission power when the TX  100  transmits power to the RX  200 .  FIGS. 6A and 6B  are flowcharts illustrating the processing operations of the processing units operating in the control unit  101  and illustrating the processing process for calculating the estimated power loss using the foreign object detection processing via the power loss method by the TX  100 . The processes in  FIGS. 5, 6A, and 6B  are executed when the Negotiation phase described above is completed by the TX  100 . Specifically, the processes are started after the TX  100  receives a packet requesting negotiation completion from the RX  200  and an affirmative reply (ACK packet) is transmitted to the RX  200 . Also, the processes in  FIGS. 5, 6A , and  6 B operate independently and in parallel. 
     Firstly, the processing for measuring and storing the transmission power in  FIG. 5  will be described in detail. 
     The process from step S 502  to step S 508  is continuously executed after the Negotiation phase is completed by the TX  100  until the processing for transmitting power to the RX  200  is complete (yes in step S 501 ). Specifically, the process is repeatedly executed until the communication processing unit  301  receives an End Power Transfer packet (hereinafter, referred to as an EPT packet) from the RX  200  or the power transmitting process is unable to be continued due to an abnormality in the environment such as an increase in the temperature. 
     The calculation processing unit  304  of the TX  100  measures the transmission power value in a measurement period T 2  (no in step S 504 ) for each measurement cycle T 1  (yes in step S 502 ) (step S 503 ). Herein, the relationship between the measurement cycle T 1  and the measurement period T 2  will be described using  FIG. 12 . 
     In the diagram illustrated in  FIG. 12 , the horizontal axis represents time, the vertical axis represents the transmission power by the TX  100 , and a curved line  1210  represents the measurement value of the actual transmission power. The straight line at the bottom of the diagram represents the measurement period T 2  (the time period during which step S 503  is executed) of the transmission power value for the calculation processing unit  304 . 
       1220  represents the time at which the first measurement starts (the timing of the transition to yes in step S 502 ), and  1221  represents the time at which the first measurement ends (the timing of the transition to yes in step S 504 ).  1230  represents the time at which the second measurement starts, and  1231  represents the time at which the second measurement ends. Herein, the time interval from  1220  to  1221  and the time interval from  1230  to  1231  corresponds to the measurement period T 2 , and the time interval from  1220  to  1230  corresponds to the measurement cycle T 1 . As illustrated in  FIG. 12 , by setting the relationship between the measurement cycle T 1  and the measurement period T 2  to T 1 &lt;T 2 , the calculation processing unit  304  executes a plurality of processes in parallel to measure the transmission power at offset timings. In the present embodiment, T 1  is 3 msec and T 2  is 8 msec. Note that the relationship may be set to T 1 ≥T 2 . In this manner, the TX  100  periodically measures the transmission power value. Accordingly, regardless of when the received power value is reported by the RX  200  as described below, the transmission power value corresponding to the received power value can be derived. 
     Returning to the description of  FIG. 5 , when the measurement period T 2  elapses (yes in step S 504 ), the calculation processing unit  304  calculates the average value of the transmission power values measured in T 2  and the standard deviation as information representing the degree of variation in the transmission power values (step S 505 ). Also, the calculation processing unit  304  associates together the calculated average value (hereinafter, also referred to as the average transmission power value) of the transmission power values and the standard deviation and stores these as transmission power data in the memory  106  (step S 506 ). Note that in this example the standard deviation is used as information representing the degree of variation in the transmission power values. However, for example, the distribution or the difference between the maximum value and the minimum value may be used as the information representing the degree of variation. Also, the calculation processing unit  304  stores the pieces of transmission power data calculated in step S 505  in the memory  106  in order based on the measuring time. The stored data is managed as a ring buffer, and, in a case where the maximum storage number of the buffer is exceeded, the old data is overwritten with the new. 
     The calculation processing unit  304  determines whether or not there is a change request for a transmission voltage equal to or greater than a predetermined threshold using a CE packet transmitted from the RX  200  (step S 507 ). Here, there are cases in which a change request for a transmission voltage equal to or greater than the threshold, one example being a case where, in step S 706 , a CE packet is transmitted from the RX  200 . In this case, because the first item of calibration (calculation of the estimated power loss) is complete and the transmission power value prior to the transmission voltage change is not required, the transmission power data stored in step S 506  is deleted (step S 508 ). In another case, while the first item of calibration is being executed, it is plausible that the received power is made unstable due to the effects of misalignment of the RX  200  and the like and the amount of change in the voltage specified by the CE packet periodically transmitted from the RX  200  is increased. This may also occur while the second item of calibration is being executed, and in this case, the measurement of the transmission power is required to be redone. This makes the measurement results up until this point unnecessary, and the stored transmission power data is deleted in step S 508 . 
     In a case where, in step S 507 , there is not a change request for a transmission voltage of equal to or greater than the threshold or in a case where the transmission power data stored in the memory  106  is deleted in step S 508 , the process returns to step S 501 . Also, in a similar manner as to when the processing to transmit power to the RX  200  is complete (yes in step S 501 ), the calculation processing unit  304  deletes the transmission power data stored in the memory  106  in step S 506  (step S 509 ). By the data being deleted in steps S 508  and S 509 , the amount of data stored in the memory  106  can be reduced, and, even with a hardware configuration in which the memory  106  has a small capacity, the processing of the present embodiment can be executed. 
     In this manner, in the present embodiment, the TX  100  regularly executes processing to measure and calculate the transmission power. Thus, in the processes in  FIGS. 6A, 6B, and 11  described below, when the received power value is obtained from the RX  200 , the transmission power value corresponding to the received power value can be identified. 
     Next, the processing to calculate the estimated power loss will be described in detail using  FIGS. 6A and 6B . 
     The process from step S 602  to step S 620  is continuously executed after the Negotiation phase is completed by the TX  100  until the processing for transmitting power to the RX  200  is complete (yes in step S 601 ). 
     In this process, the communication processing unit  301  of the TX  100  waits to receive an RP packet (Mode=1 or 2) as the reference received power information transmitted from the RX  200  in step S 702  or step S 708  in  FIG. 7  and a CE packet as a transmission voltage change instruction. 
     In a case where the communication processing unit  301  receives an RP packet, in other words when a calibration request is received (yes in step S 602 ), the foreign object detection processing unit  303  checks the amount of time elapsed from when the switching circuit of the power transmitting unit  103  was last switched (step S 603 ). In a case where the predetermined amount of time has not elapsed from when the switching circuit was switched (yes in step S 603 ), the TX  100  determines that the transmission power output is not stable, and the communication processing unit  301  transmits a NAK packet to the RX  200  (step S 616 ). 
     In a case where the predetermined amount of time has elapsed from when the switching circuit was switched (no in step S 603 ), the foreign object detection processing unit  303  checks the change amount of the voltage requested by the CE packet most recently received from the RX  200  (step S 604 ). In a case where the change amount is equal to or greater than a predetermined threshold (yes in step S 604 ), the TX  100  determines that the received power at the RX  200  is not stable, and the communication processing unit  301  transmits a NAK packet to the RX  200  (step S 616 ). In a case where the change amount is less than a predetermined threshold (no in step S 604 ), the TX  100  determines that the received power at the RX  200  is stable. Note that the value checked in step S 604  may be determined on the basis of the value specified in most recent of the received plurality of CE packets. For example, in a case where the total change amount specified by the plurality of CE packets is equal to or greater than the threshold, the TX  100  may determine that the received power at the RX  200  is stable, and in a case where the total change amount is less than the threshold, the TX  100  may determine that the received power is not stable. Also, in a case where not one of the specified values (voltage change amount) of the CE packet received most recently a plurality of times is greater than the threshold, the TX  100  may determine that the received power at the RX  200  is stable, and in a case where even one is greater than the threshold, the TX  100  may determine that the received power is not stable. 
     In a case where the received power at the RX  200  is determined to be stable (no in step S 604 ), the foreign object detection processing unit  303  determines, from the transmission power data (the average value for the transmission power values and the standard deviation) stored in step S 506  by the calculation processing unit  304 , the data to use in calculating the power loss (step S 605 ). Specifically, the transmission power data with the calculation completion time closest to the time back by an amount of time T 3  from a point in time at which the RP packet was received is used. Herein, T 3  is a value calculated to be the time from when calculating the received power at the RX  200  is completed to when the TX  100  is notified of the value via an RP packet. In the present embodiment, T 3  is 8 msec. 
     In a case where the standard deviation of the transmission power values included in the transmission power data determined in step S 605  is equal to or greater than the threshold (yes in step S 606 ), the TX  100  determines that the transmission power is unstable, and the communication processing unit  301  transmits an NAK packet to the RX  200  (step S 616 ). In a case where the standard deviation included in the transmission power data determined in step S 605  is less than the threshold (no in step S 606 ), the foreign object detection processing unit  303  calculates the standard deviation of the average transmission power value used in step S 605  and n average transmission power values calculated before calculation of the data (step S 607 ). Note that herein, n is a predetermined integer value of one or greater and is a value equal to or less than the buffer number of the ring buffer where the transmission power data described above is stored. In the present embodiment, n is 5. 
     In a case where the standard deviation calculated in step S 607  is equal to or greater than the threshold (yes in step S 608 ), the TX  100  determines that the transmission power is unstable, and the communication processing unit  301  transmits an NAK packet to the RX  200  (step S 616 ). Also, in a case where the standard deviation calculated in step S 607  is less than the threshold (no in step S 608 ), the TX  100  determines that the transmission power is stable. Note that the value calculated and checked in steps S 607  and S 608  does not need to be a standard deviation. For example, the TX  100  may calculate the distribution, the difference value between the maximum value and the minimum value, and the total change amount for the calculated value each time and may determine that the transmission power is unstable if each value is equal to or greater than the threshold and determine that the transmission power is stable if each value is less than the threshold. Also, in a case where, for the average transmission power value of the transmission power data used in step S 605  and the average transmission power values of n transmission power data calculated before data calculation, not even one is greater than the threshold, the transmission power may be determined to be stable, and in a case where even one is greater than the threshold, the transmission power may be determined to be unstable. 
     In a case where the TX  100  determines that the transmission power is stable (no in step S 608 ), the foreign object detection processing unit  303  calculates the power loss lost between the TX  100  and the RX  200  (step S 609 ). Specifically, a value obtained by subtracting the received power value included in the RP packet received in step S 602  from the average transmission power value included in the transmission power data used in step S 605  corresponds to the power loss. Next, the foreign object detection processing unit  303  associates the calculated power loss with the average transmission power value used in step S 605  and stores it in the memory  106  (step S 610 ). 
     Here, the TX  100  determines whether or not the power loss for m times or more are stored. In a case where m times or more are not stored (no in step S 611 ), because there is a possibility that the power transmitting state between the TX  100  and the RX  200  is unstable, the communication processing unit  301  transmits a NAK packet to the RX  200  (step S 616 ). Herein, m is a predetermined integer value of two or greater, and in the present embodiment, m is three. 
     In a case where the power loss is stored m times or greater (yes in step S 611 ), the foreign object detection processing unit  303  calculates the standard deviation of the power loss calculated for the most recent m times (step S 612 ). As in the process from step S 606  to step S 608 , because the transmission power by the TX  100  is table, in a case where the standard deviation of the power loss is great, there may be variation in the received power at the RX  200 . This is thought to be caused by a problem in the RX  200  itself or caused by some kind of change in the power transmitting state (power transmitting environment) between the TX  100  and the RX  200 . In a case where the standard deviation is equal to or greater than the threshold (yes in step S 612 ), the received power by the RX  200  or the power transmitting state between the TX  100  and the RX  200  is determined to be unstable, and the communication processing unit  301  transmits a NAK packet to the RX  200  (step S 616 ). 
     In a case where the standard deviation is less than the threshold (no in step S 612 ), the power transmitting state between the TX  100  and the RX  200  is determined to be stable, and the foreign object detection processing unit  303  stores the estimated power loss in the memory  106  (step S 613 ). Specifically, the average value for the average transmission power value (Avtp) and for the power loss (Avloss) is calculated for the most recent m times stored in the memory  106 , and the estimated power loss when the transmission power is Avtp is stored as the Avloss. 
     Note that the value calculated and checked in step S 612  does not need to be a standard deviation. For example, the TX  100  may calculate the distribution, the difference value between the maximum value and the minimum value, and the total change amount for the calculated value each time and may determine that the power transmitting state with the RX  200  is unstable if each value is equal to or greater than the threshold and determine that the power transmitting state is stable if each value is less than the threshold. Also, in a case where the power loss calculated for the most recent m times is not once greater than the threshold, the TX  100  may determine that the power transmitting state with the RX  200  is stable, and in a case where the power loss is even once greater than the threshold, the TX  100  may determine that the power transmitting state is unstable. Also, in the example described above, in step S 612 , whether or not the power transmitting state is stable is determined on the basis of the calculated standard deviation of the power loss and the like. However, this may be determined on the basis of an obtained standard deviation of the received power. 
     Thereafter, the communication processing unit  301  transmits an ACK packet to the RX  200  (step S 614 ). Also, the foreign object detection processing unit  303  clears the unnecessary information including the power loss and the average transmission power value stored in the memory  106  in step S 610  (step S 615 ), and the process returns to step S 601 . 
     When the communication processing unit  301  receives a CE packet (yes in step S 617 ), the power transmitting processing unit  302  changes the voltage applied to the power transmitting unit  103  in accordance with the value instructed by the CE packet (step S 618 ). In a case where the change amount of the voltage instructed by the CE packet is equal to or greater than a predetermined threshold (yes in step S 619 ), the received power at the RX  200  is unstable and calibration needs to be performed again. Then, the foreign object detection processing unit  303  clears the information including the power loss and the average transmission power value stored in the memory  106  in step S 610  (step S 620 ). 
     When the processing for transmitting power from the TX  100  to the RX  200  is complete (yes in step S 601 ), the foreign object detection processing unit  303  clears the information including the power loss and the average transmission power value stored in the memory  106  in step S 610  and the estimated power loss information stored in step S 613  (step S 621 ). 
     Accordingly, in the present embodiment, in a case where the TX  100  receives a calibration request from the RX  200 , whether or not the state is one in which the estimated power loss is stable and measurement can be performed is checked. Specifically, whether the transmission power at the TX  100  is stable, whether the received power at the RX  200  is stable, and the like is checked. Also, when the state is one in which there is instability and measurement cannot be performed, the TX  100  replies with a NAK, and when the state changes to one in which there is stability and measurement can be performed, the estimated power loss is stored and the TX  100  replies with an ACK. Accordingly, the estimated power loss can be calculated with high accuracy, and the foreign object detection accuracy can be improved. 
     Next, the foreign object detection processing operations using the power loss method with the TX  100  of the present embodiment will be described using  FIGS. 10 and 11 . 
       FIG. 10  is a graph illustrating an expected received power graph  1000  generated by the TX  100 . The expected received power graph  1000  is a graph on which is plotted the expected received power (horizontal axis) against the transmission power (vertical axis) when power is transmitted from the TX  100  to the RX  200  in a state where a foreign object is not present. The graph is generated by the calculation processing unit  304  on the basis of the transmission power value Avtp and the estimated power loss Avloss stored in the memory  106  in step S 613  in  FIG. 6B  described above. 
       1010  and  1020  are plotted points based on the transmission power output Avtp and the estimated power loss Avloss, respectively, stored in step S 613 , with the values on the horizontal axis corresponding to the Avtp and the values on the vertical axis corresponding to Avtp−Avloss. In other words,  1010  is a point plotted on the basis of a calibration result in a low load state as described above, and  1020  is a point plotted on the basis of a calibration result in a high load state. The calculation processing unit  304  performs linear interpolation of the area between the measurement points plotted in step S 613 , and a calculation formula (graph) for obtaining an Avrp value with respect to a specific Avtp value is generated. In the present embodiment, the gradient and the intercept of the linear function represented by the graph corresponds to the parameters for the foreign object detection processing described above. 
     The calculation processing unit  304  continuously measures its own transmission power ( 1030 ) and calculates the corresponding expected received power value ( 1040 ). In a case where the difference between the received power value and the expected received power value reported by the RX  200  is equal to or greater than a predetermined threshold, the TX  100  determines that a foreign object exists near (in the power transmitting range) of the power transmitting antenna  105 . 
     Note that the method of generating the graph is not limited to the method of performing linear interpolation of the space between the measurement points and it is only required that a graph for obtaining one Avrp value with respect to one Avtp value is derived. For example, calibration may be performed for not only the two points described above, and the graph may be generated by performing linear interpolation of the space between three or more measurement points. Also, in a case where there are three or more measurement points, the graph may be generated using an approximation curve. 
       FIG. 11  is a flowchart of when foreign object detection processing is executed using the expected received power graph  1000  with the TX  100 . The process in  FIG. 11  is continuously executed after the process in  FIGS. 6A and 6B  are executed and while the TX  100  is in a Power Transfer phase. The present processing can be implemented by the control unit  101  of the TX  100  executing a program read out from the memory  106 , for example. 
     The calculation processing unit  304  of the TX  100  continuously calculates the expected received power value at the RX  200  with respect to its transmission power in accordance with the expected received power graph  1000  (step S 1101 ). 
     As described above, the RX  200  periodically notifies the TX  100  of its received power value via an RP packet (Mode=0) after the second item of calibration is complete. When the communication processing unit  301  receives the RP packet from the RX  200  (yes in step S 1102 ), the calculation processing unit  304  calculates the difference between the expected received power value obtained in step S 1101  and the received power value received via the RP packet (step S 1103 ). 
     In a case where the difference obtained in step S 1103  is equal to or greater than a threshold (yes in step S 1104 ), the TX  100  determines that a foreign object has been detected, the power transmitting process with respect to the RX  200  is stopped, and a Selection phase is transitioned to (step S 1105 ). Also, in a case where the difference obtained in step S 1103  is less than the threshold (no in step S 1104 ), the TX  100  stops in the Power Transfer phase and continues the power transmitting process. Note that the threshold used in the determination in step S 1104  may be a single fixed value or may be a value determined according to a measurement value that dynamically changes, such as the transmission power value, temperature, or the like. 
     Also, in the example described above, in step S 1101 , the expected received power value at the RX  200  with respect to the transmission power is continuously calculated. However, in step S 1102  when a Mode=0 RP packet is received, the corresponding transmission power may be obtained. Specifically, as in step S 605  in  FIG. 6A , the transmission power value with the calculation completion time closest to the time back by an amount of time T 3  from a point in time at which the RP packet was received may be used. 
     Wireless Power Transmission System Sequence 
     Next, a sequence of a wireless power transmission system including the TX  100  and the RX  200  will be described with reference to  FIGS. 8A and 8B and 9A and 9B .  FIGS. 8A and 8B and 9A and 9B  are diagrams illustrating an example of a communication sequence until the calibration between the TX  100  and the RX  200  is completed when the RX  200  is placed on the TX  100  with the RX  200  set to execute a charging function according to the WPC. 
       FIGS. 8A and 8B  are diagrams illustrating an example of a communication sequence in a case where the processing to calculate the estimated power loss at TX  100  can be executed under stable conditions. 
     Firstly, the TX  100  and the RX  200  execute the process from the Selection phase to the Negotiation phase in accordance with the WPC standard (step S 801 ). 
     When the Negotiation phase ends, the calculation processing unit  304  of the TX  100  starts the processing to measure and calculate the transmission power described using  FIG. 5  (step S 802 ). Thereafter, the TX  100  executes the processing to continuously measure and calculate the transmission power until the Power Transfer phase ends. 
     The RX  200  transmits, to the TX  100 , an RP packet (Mode=1) that specifies the received power value (approximately 500 mW) in a light load state as the first item of calibration request (step S 803 ). The TX  100  identifies the transmission power data corresponding to the received power value including in the RP packet. Then, the TX  100  calculates the power loss from the difference between the average transmission power value included in the transmission power data and the received power value included in the RP packet, stores this as the first calculation result (step S 804 ), and transmits a NAK packet to the RX  200  (step S 805 ). 
     The RX  200 , having received the NAK packet, again measures the received power value and transmits a RP packet (Mode=1) to the TX  100  (step S 806 ). The TX  100 , having received the RP packet, calculates the power loss in a similar manner, stores this as the second calculation result (step S 807 ), and transmits a NAK packet to the RX  200  (step S 808 ). Next, when the RX  200  again transmits an RP packet to the TX  100  (step S 809 ), the TX  100  calculates the power loss (step S 810 ), and calculates and stores the estimated power loss when 500 mW of power is being transmitted from the average of the first to third calculation results (step S 811 ). Then, the TX  100  transmits an ACK packet to the RX  200  and reports that, in response to the first item of calibration request, the calculation of the estimated power loss is a success (step S 812 ). 
     In order to calculate the estimated power loss at a high load state (when the received power is approximately 15 W), the RX  200 , having received the ACK packet, instructs the TX  100  to increase the transmission voltage by transmitting a CE packet (step S 813 ). 
     The TX  100 , having received the CE packet, controls the power transmitting unit  103  to increase the transmission voltage by the instructed change amount (step S 814 ). At this time, the power transmitting unit  103  controls turning on/off the FET, and the circuit is switched from a half bridge configuration to a full bridge configuration. The TX  100  activates a timer to measure the elapsed time from the circuit switching by the power transmitting unit  103  (step S 815 ). 
     Thereafter, the RX  200  transmits, to the TX  100 , an RP packet (Mode=2) that specifies the received power value (approximately 15 W) in a high load state as the second item of calibration request (step S 816 ). 
     At the time when the TX  100  receives the RP packet, the timer activated in step S 815  runs out, a predetermined amount of time from the circuit switching by the power transmitting unit  103  is determined to have elapsed. Thus, the TX  100  determines that power transmission is stable, calculates the power loss, and stores the calculation result as the first calculation result in a high load state (step S 817 ). Then, the TX  100  transmits a NAK packet to the RX  200  (step S 818 ). Thereafter, in a similar method to steps S 806  to S 810 , the second and the third power loss are calculated and stored (steps S 819  to S 823 ). 
     The TX  100  calculates and stores the estimated power loss when 15 W of power is being transmitted from the average of the first to third calculation results (step S 824 ). Then, the TX  100  transmits, to the RX  200 , an ACK packet that reports that, in response to the second item of calibration request, the calculation of the estimated power loss is a success (step S 825 ). 
       FIGS. 9A and 9B  are diagrams illustrating an example of a communication sequence in a case where the processing to calculate the estimated power loss at TX  100  is executed under unstable conditions.  FIGS. 9A and 9B  are diagrams illustrating a communication sequence based on the assumption that, corresponding to unstable conditions, an RP packet is transmitted from the RX  200  directly after the circuit switching by the power transmitting unit  103  of the TX  100 . 
     The process from steps S 901  to S 915  are the same as that from steps S 801  to S 815  described using  FIGS. 8A and 8B , and thus description thereof is omitted. 
     Directly after the CE packet is transmitted in step S 913 , the RX  200  transmits, to the TX  100 , an RP packet (Mode=2) that specifies the received power value (approximately 15 W) in a high load state (step S 916 ). At this time, the TX  100  determines that the power transmission is unstable due to a certain amount of time from the circuit switching by the power transmitting unit  103  not having elapsed (step S 917 ), does not calculate or record the power loss, and transmits a NAK packet to the RX  200  (step S 918 ). 
     Thereafter, when the RP packet is transmitted from the RX  200  after the timer activated in step S 915  has run out (step S 919 , the TX  100  calculates the power loss for the first time here, and stores the calculation result as the first calculation result in a high load state (step S 920 ). 
     The process from steps S 921  to S 928  are the same as that from steps S 818  to S 825  described using  FIG. 8B , and thus description thereof is omitted. 
     In this manner, according to the present embodiment, the TX  100  can execute the processing to measure and calculate the estimated power loss with the RX  200  under stable conditions. In other words, the transmission power or the received power which vary when sudden environmental changes or the like occur can be removed from the calculation source data of the estimated power loss. This means that, regarding the transmission power and the received power as described above, they are not used in calculating the parameter for foreign object detection. Accordingly, the power regularly lost during the power transmitting process executed thereafter can be estimated with a high accuracy, and the foreign object detection accuracy during the power transmitting process can be improved. 
     In the embodiment described above, the method for calculating the estimated power loss does not use the transmission power value measured and calculated directly after switching of the internal circuit at the power transmitting unit  103  of the TX  100  and the received power value corresponding to the transmission power value. Also, in a case where the standard deviation or the like of the transmission power continuously measured and calculated by the calculation processing unit  304  is measured and the value is equal to or greater than a threshold, the data is not used in the method for calculating the estimated power loss. With such a configuration, variation in the measurement and calculation with a cause inside the TX  100  can be taken into account. 
     In the embodiment described above, the method described includes, in the TX  100 , calculating the power loss on the basis of the received power value specified by an RP packet transmitted from the RX  200  and calculating the estimated power loss by averaging the calculation results. Also, in the method described above, at this time, the standard deviation or the like of the power loss or received power of a plurality of times calculated most recently is calculated, and in a case where the value is equal to or greater than a threshold, the data is not used in calculating the estimated power loss. With such a configuration, variation in the measurement and calculation data caused by the environment between the TX  100  and the RX  200  can be taken into account. For example, problems such as a value calculated when the contact surface between the TX  100  and the RX  200  gradually become misaligned due to small vibrations being used as the estimation value for when in a static state can be avoided. 
     In the method of the embodiment described above, in a case where the voltage change amount instructed by a CE packet from the RX  200  is equal to or greater than a threshold, the transmission power value used at that time by the TX  100  for measurement and calculation and the received power value corresponding to the transmission power value is not used in calculating the estimated power loss. Because the voltage change amount from the CE packet is determined as the result of processing and determination within the RX  200 , this configuration allows variation in the measurement and calculation data with a cause inside the RX  200  to be taken into account. 
     The embodiment described above is a representative example, and the present embodiment is not limited to the embodiments described in the specification and in the drawings and modifications that do not change the gist can be made as appropriate. 
     In the present embodiment, when the TX  100  receives a RP packet, in a case where there is instability and the estimated power loss cannot be calculated, a NAK is repeated. However, no such limitation is intended. In a configuration of another possible example, in a case where an ACK is not returned for a certain number of time or more or a certain amount of time or more, the TX  100  determines that the environment is one in which foreign object detection cannot be normally performed, stops transmitting power, and returns to the Selection phase. Such a configuration can prevent the processing to calculate the estimated power loss from being continuously performed in a condition where the transmission power output is always unstable. 
     In another possible configuration, in a case where an ACK is not returned for a certain number of times or more or a certain amount of time or more, the TX  100  determines that the state in which there is variation in the calculated value is a normal state, changes the thresholds described above to a large value, and determines whether or not there is stability. Also, in this case, the threshold (difference with the estimated power loss) of when foreign object detection processing is actually performed may be changed. With such a configuration, in an environment with regular vibrations such as in a moving vehicle, for example, power transmitting processing and foreign object detection processing can be executed in a suitable manner. 
     Also, in the present embodiment, as the method of determining whether or not the power transmitting process from the TX  100  to the RX  200  is stable, a method is used that uses the variations in the transmission power, the power loss, and the received power, the instructed change amount of the power, and the like. However, no such limitation is intended. For example, the TX  100  may be provided with a piece of hardware such as a vibration sensor or a magnetic sensor, and, in a case where the sensor detects vibration or magnetism equal to or greater than a threshold, the power transmitting process may be determined to be unstable and a NAK may be returned in response to an RP packet. Also, the TX  100  may be wirelessly connected to an external apparatus different from the RX  200 , and information representing whether or not the power transmitting process from an external apparatus is stable may be obtained and determination may be performed. Including the method described in the present embodiment, by combining these methods, the accuracy of the calculation processing of the estimated power loss can be further improved. 
     Also, in the example of the present embodiment described above, the estimated power loss is calculated at two points of power receiving states of the power receiving apparatus, a low load state and a high load state. However, no such limitation is intended. For example, the method described above may be used when calculating the estimated power loss using three or more points. Also, in the example described above, after the Negotiation phase is complete, the processes in  FIGS. 6A and 6B  are executed in the time before the charging processing is started. However, no such limitation is intended. For example, the processes in  FIGS. 6A and 6B  may be executed after the TX  100  transitions to the Power Transfer phase when a third estimated power loss is calculated. 
     Also in the example of the present embodiment described above, a CE packet is used as a request signal for controlling the transmission power of the TX  100 . However, no such limitation is intended. Also, in the example described above, an RP packet is used as a signal for the RX  200  to notify the TX  100  of the received power value. However, no such limitation is intended. In any case, another discretionary packet may be used for instruction and notification. Also, a plurality of packets may be used for instruction and notification, or a single packet may be used for two instructions or notifications. 
     In the present embodiment described above, the various thresholds and time out values are predetermined fixed values. However, no such limitation is intended. The values may dynamically change due to changes in the surrounding environment or the environment in which the software or hardware processing is executed, and for example, the values may be determined by negotiation between the TX  100  and the RX  200  in the Negotiation phase. 
     Also, in the present embodiment described above, in step S 613  in  FIG. 6B , the transmission power and the estimated power loss are associated together and stored, and this information is used to generate the graph in  FIG. 10 . However, other combinations may be used. For example, the received power and the estimated power loss may be associated together and stored and this information may be used to generate a graph, or the transmission power and the received power may be associated together and stored and this information may be used to generate a graph. Also, all three pieces of information may be stored. In other words, it is only required that at least two from among the transmission power, the received power, and the power loss are associated together and stored. Also, in the graph in  FIG. 10 , the horizontal axis represents the transmission power and the vertical axis represents the received power. However, any combination of the information including the transmission power, the received power, and the power loss may be used for the horizontal axis and the vertical axis. In a case of any such graph, the constant in the calculation formula representing the graph corresponds to a parameter for foreign object detection. 
     Also, at least a part of the processes illustrated in the flowcharts of  FIGS. 5 to 7 and 11  may be implemented by hardware. In the case of implementing processing by hardware, for example, using a predetermined compiler, the processing can be implemented by automatically generating a dedicated circuit on an FPGA from a program for implementing the steps. In addition, similarly to an FPGA, a gate array circuit may be formed and implemented as hardware. 
     According to the above embodiments, the calculation accuracy of a parameter used to determine whether or not an object that is not the intended power transmission target exists can be improved. 
     OTHER EXAMPLES 
     Embodiment(s) of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the present disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.