Power Transfer Calculation for Wireless Power Transfer

Abstract

To provide a method of predicting power loss in order to take into account presence of foreign matters, and to provide a wireless power transmitter thereof, according to a power transmitter and / or a power receiver in a wireless power transmission system.SOLUTION: A method comprises the steps of: determining measured power loss associated with wireless power transmission; calculating predicted power loss, based on indication of a power receiver power associated with the wireless power transmission that includes a rectifier voltage or a rectifier current corresponding to a wireless power receiver, and one or more coefficients corresponding to baseline wireless power transmission between a wireless power transmitter and the wireless power receiver, or that is derived therefrom; and determining presence of foreign matters, when the measured power loss exceeds the predicted power loss by exceeding a threshold value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application is related to co-pending U.S. Provisional Patent Application No. 63 / 583,001, entitled "Power Transfer Accounting for Wireless Power Transfer," filed September 15, 2023; U.S. Provisional Patent Application No. 63 / 550,248, entitled "Power Transfer Accounting for Wireless Power Transfer," filed February 6, 2024; U.S. Provisional Patent Application No. 18 / 617,080, entitled "Power Transfer Accounting for Wireless Power Transfer," filed March 26, 2024; U.S. Provisional Patent Application No. 18 / 617,103, entitled "Power Transfer Accounting for Wireless Power Transfer," filed March 26, 2024; U.S. Provisional Patent Application No. 63 / 644,096, entitled "Power Transfer Accounting for Wireless Power Transfer," filed May 8, 2024; and U.S. Provisional Patent Application No. 63 / 644,096, entitled "Power Transfer Accounting for Wireless Power Transfer," filed July 16, 2024. This application claims priority to U.S. patent application Ser. No. 18 / 774,201, entitled "Power Transfer Accounting for Wireless Power Transfer," filed Jul. 29, 2024, and U.S. patent application Ser. No. 18 / 787,485, entitled "Power Transfer Accounting for Wireless Power Transfer," filed Jul. 29, 2024, each of which is incorporated herein by reference. [Background technology]

[0002] Wireless power transfer is becoming increasingly prevalent in a wide variety of electronic devices. For example, many electronic devices, such as smartphones, tablet computers, smartwatches, wireless earbuds, and styluses, may employ wireless power transfer to facilitate charging of batteries within the devices. In some applications, higher levels of wireless power transfer may be desired, for example, to provide faster charging. Such higher power transfer levels may benefit from techniques for detecting the presence of foreign objects within the electromagnetic fields associated with wireless power transfer. Summary of the Invention

[0003] A method performed by control circuitry of a wireless power transmitter to detect a foreign object affected by an electromagnetic field associated with wireless power transfer from a wireless power transmitter to a wireless power receiver may include receiving an indication of receiver power associated with the wireless power transfer from the wireless power receiver, the indication including or derived from a corresponding rectifier voltage and rectifier current of the wireless power receiver; determining a measured power loss associated with the wireless power transfer by comparing the indication of receiver power to a transmitter power measured by the wireless power transmitter; calculating a predicted power loss based on the indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage or rectifier current of the wireless power receiver and one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver; and determining that a foreign object is present if the measured power loss exceeds the predicted power loss by more than a threshold.

[0004] The received indication of the received power may be a rectifier voltage and a rectifier current, and the method may further include calculating a receiver power based on the rectifier voltage and the rectifier current. The rectifier voltage may be a rectifier output voltage, and the rectifier current may be a rectifier output current. The transmitter power may be calculated by the wireless power transmitter by multiplying the inverter input voltage by the inverter input current.

[0005] The method may further include calculating one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver by receiving, from the wireless power receiver, a plurality of indications of receiver power including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer; determining a plurality of measured power loss values ​​each corresponding to one of the plurality of indications of received power levels associated with the wireless power transfer by comparing the indications of the receiver power with corresponding transmitter powers measured by the wireless power transmitter; and performing a regression analysis on the received plurality of indications of receiver power and corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer and the determined plurality of measured power loss values ​​to calculate the one or more coefficients.

[0006] Receiving a plurality of indications of receiver power from a wireless power receiver associated with a wireless power transfer, the indications including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver, may include receiving a plurality of indications at three or more operating points. The three or more operating points may include an operating point at a minimum rectifier voltage and a maximum receiver power, an operating point at a nominal rectifier voltage and a nominal receiver power, and an operating point at a maximum rectifier voltage and a minimum receiver power. The plurality of indications at the three or more operating points may include a plurality of samples at each of the three or more operating points. The plurality of samples at each of the three or more operating points may include 25 or more samples at each of the three or more operating points.

[0007] The one or more coefficients include a first coefficient related to a rectifier voltage and a second coefficient related to a rectifier current.

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[0008] Performing a regression analysis on the received plurality of indications of receiver power and corresponding rectifier voltage and rectifier current of a wireless power receiver associated with the wireless power transfer, and the determined plurality of measured power loss values ​​to calculate one or more coefficients may include calculating a first plurality of coefficients corresponding to an initial operating period having a wireless power transfer level below a first threshold, during which the absence of a foreign object is indicated by another foreign object detection technique; calculating a second plurality of coefficients corresponding to a baseline capture period having a wireless power transfer level above the first threshold; and comparing the first plurality of coefficients to the second plurality of coefficients to determine whether a foreign object was introduced during the baseline capture period.

[0009] The method may further include mitigating the presence of the foreign object by reducing the power level of the wireless power transfer or by discontinuing the wireless power transfer if the foreign object is present.

[0010] A method performed by control circuitry of a wireless power transmitter to calculate one or more coefficients corresponding to a baseline wireless power transmission between a wireless power transmitter and a wireless power receiver for use in detecting a foreign object affected by an electromagnetic field associated with wireless power transfer from the wireless power transmitter to the wireless power receiver may include receiving, from the wireless power receiver, a plurality of indications of receiver power levels including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer; determining a plurality of measured power loss values ​​each corresponding to one of the plurality of indications of receiver power associated with the wireless power transfer by comparing the indications of receiver power with corresponding transmitter power measured by the wireless power transmitter; and performing a regression analysis on the received plurality of indications of receiver power including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer and the determined plurality of measured power loss values ​​to calculate the one or more coefficients.

[0011] The rectifier voltage may be the rectifier output voltage, and the rectifier current may be the rectifier output current. The transmitter power may be calculated by the wireless power transmitter by multiplying the inverter input voltage by the inverter input current. The one or more coefficients may include a first coefficient related to the rectifier voltage and a second coefficient related to the rectifier current.

[0012] Receiving a plurality of indications of receiver power from a wireless power receiver associated with a wireless power transfer, the indications including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver, may include receiving a plurality of indications at three or more operating points. The three or more operating points may include an operating point at a minimum rectifier voltage and a maximum receiver power, an operating point at a nominal rectifier voltage and a nominal receiver power, and an operating point at a maximum rectifier voltage and a minimum receiver power. The plurality of indications at the three or more operating points may include a plurality of samples at each of the three or more operating points. The plurality of samples at each of the three or more operating points may include 25 or more samples at each of the three or more operating points.

[0013] The method may further include calculating a predicted power loss based on the corresponding rectifier voltage and rectifier current and one or more coefficients, the predicted power loss being:

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[0014] Performing a regression analysis on the received plurality of indications of receiver power and corresponding rectifier voltages and rectifier currents of a wireless power receiver associated with a wireless power transfer and the determined plurality of measured power loss values ​​to calculate the one or more coefficients may further include performing a baselining procedure that includes determining that the plurality of indications of received power levels are linearly independent. The baselining procedure may include determining that the plurality of indications of received power levels lie in a two-dimensional plane.

[0015] The wireless power transmitter may include a wireless power transmitter coil configured to magnetically couple to a wireless power receiver coil of the wireless power receiver to wirelessly transfer power to the wireless power receiver, an inverter configured to receive input power and generate an output that drives the wireless power transmitter coil, and a controller and communication circuit coupled to the inverter and the wireless power transmitter coil to control the inverter to regulate wireless power transfer to the wireless power receiver. The controller and communications circuitry may include logic or programming to detect a foreign object affected by an electromagnetic field associated with wireless power transfer to the wireless power receiver by receiving from the wireless power receiver an indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage and rectifier current of the wireless power receiver; determining a measured power loss associated with the wireless power transfer by comparing the indication of receiver power to a transmitter power measured by the wireless power transmitter; calculating a predicted power loss based on the indication of receiver power associated with the wireless power transfer, the indication including or derived from the corresponding rectifier voltage and rectifier current of the wireless power receiver and one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver; and determining that a foreign object is present if the measured power loss exceeds the predicted power loss by more than a threshold value.

[0016] The rectifier voltage may be the rectifier output voltage, and the rectifier current may be the rectifier output current. The transmitter power may be calculated by the wireless power transmitter by multiplying the inverter input voltage by the inverter input current. The controller and communications circuitry may further include logic or programming to calculate one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver by receiving from the wireless power receiver a plurality of indications of receiver power including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer, determining a plurality of measured power loss values ​​each corresponding to one of the plurality of indications of receiver power associated with the wireless power transfer by comparing the indications of receiver power with corresponding transmitted wireless power levels measured by the wireless power transmitter, and performing a regression analysis on the plurality of received indications of receiver power including or derived from the corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer and the determined plurality of measured power loss values ​​to calculate the one or more coefficients.

[0017] Receiving a plurality of indications of receiver power from a wireless power receiver associated with a wireless power transfer, the indications including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver, may include receiving a plurality of indications at three or more operating points. The three or more operating points may include an operating point at a minimum rectifier voltage and a maximum receiver power, an operating point at a nominal rectifier voltage and a nominal receiver power, and an operating point at a maximum rectifier voltage and a minimum receiver power. The plurality of indications at the three or more operating points may include a plurality of samples at each of the three or more operating points. The plurality of samples at each of the three or more operating points may include 25 or more samples at each of the three or more operating points.

[0018] The one or more coefficients may include a first coefficient related to a rectifier voltage and a second coefficient related to a rectifier current.

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[0019] The controller and communication circuitry further includes logic or programming that mitigates the presence of the foreign object by reducing the power level of the wireless power transfer or by suspending the wireless power transfer if the foreign object is present.

[0020] The wireless power transmitter may include a wireless power transmitter coil configured to magnetically couple to a wireless power receiver coil of the wireless power receiver to wirelessly transfer power to the wireless power receiver, an inverter configured to receive input power and generate an output that drives the wireless power transmitter coil, and a controller and communication circuit coupled to the inverter and the wireless power transmitter coil to control the inverter to regulate wireless power transfer to the wireless power receiver. The controller and communications circuitry may further include logic or programming to calculate one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver by receiving a plurality of indications of receiver power from the wireless power receiver, the indications including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer; determining a plurality of measured power loss values, each corresponding to one of the plurality of indications of receiver power associated with the wireless power transfer, by comparing the indications of receiver power with corresponding transmitted wireless power levels measured by the wireless power transmitter; and performing a regression analysis on the plurality of received indications of receiver power, the plurality of measured power loss values ​​including or derived from the corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer, to calculate the one or more coefficients.

[0021] The rectifier voltage may be the rectifier output voltage, and the rectifier current may be the rectifier output current. The transmitter power may be calculated by the wireless power transmitter by multiplying the inverter input voltage by the inverter input current. The one or more coefficients may include a first coefficient related to the rectifier voltage and a second coefficient related to the rectifier current.

[0022] Receiving a plurality of indications of receiver power from a wireless power receiver associated with a wireless power transfer, the indications including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver, may include receiving a plurality of indications at three or more operating points. The three or more operating points may include an operating point at a minimum rectifier voltage and a maximum receiver power, an operating point at a nominal rectifier voltage and a nominal receiver power, and an operating point at a maximum rectifier voltage and a minimum receiver power. The plurality of indications at the three or more operating points may include a plurality of samples at each of the three or more operating points. The plurality of samples at each of the three or more operating points may include 25 or more samples at each of the three or more operating points.

[0023] The controller and communication circuitry may further include logic or programming for calculating a predicted power loss based on the corresponding rectifier voltage and rectifier current and one or more coefficients, the predicted power loss being:

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[0024] [Figure 1] FIG. 1 shows a simplified block diagram of a wireless power transfer system.

[0025] [Figure 2] 10 shows a plot of power measurements that may be used to detect foreign objects using power loss measurements in a wireless power transfer system.

[0026] [Figure 3] 1 shows a flowchart of a portion of a power loss foreign object detection technique for use in a wireless power transfer system.

[0027] [Figure 4] 10 shows plots of power measurements at various phases of a power loss foreign object detection technique.

[0028] [Figure 5] 10 shows plots of power measurements of the power loss foreign object detection technique at different temperatures.

[0029] [Figure 6] 10 shows a flow chart of a temperature compensation technique for a power loss foreign object detection technique.

[0030] [Figure 7] 1 shows a flowchart of a power loss foreign object detection technique for use in a wireless power transfer system.

[0031] [Figure 8] 10 shows plots of power measurements and estimated losses for use in power loss foreign object detection techniques.

[0032] [Figure 9] 10 shows a flowchart of an alternative power loss foreign object detection technique for use in a wireless power transfer system. DETAILED DESCRIPTION OF THE INVENTION

[0033] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed concepts. As part of this description, some of the drawings in this disclosure represent structures and devices in block diagram form in order to avoid obscuring the present invention. In the interest of clarity, not all features of an actual implementation are described in this specification. Moreover, the language used in this specification has been chosen solely for purposes of readability and explanation, and not to limit or restrict the disclosed subject matter. Rather, the appended claims are intended for such purposes.

[0034] Various embodiments of the disclosed concepts are illustrated in the accompanying drawings, by way of example, and not by way of limitation, wherein like reference numerals indicate like elements. For simplicity and clarity of illustration, where considered appropriate, reference numerals have been repeated among different drawings to indicate corresponding and / or similar elements. Additionally, numerous specific details have been described to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the relevant associated functionality being described. References to "an," "one," or "another" embodiment in the present disclosure do not necessarily refer to the same or different embodiments, but rather to at least one. A given drawing may be used to illustrate multiple embodiments or multiple species of the present disclosure, and not all elements in the drawing may be required for a given embodiment or species. A reference numeral, if provided in a given drawing, may refer to the same element throughout the drawings, but may not be repeated in all drawings. The drawings are not to scale unless otherwise indicated and the proportions of certain parts may be exaggerated to better show the details and features of the present disclosure.

[0035] FIG. 1 shows a simplified block diagram of a wireless power transfer system 100. The wireless power transfer system includes a power transmitter (PTx) 110 that transfers power wirelessly to a power receiver (PRx) 120, such as via inductive coupling 130. The power transmitter 110 can receive input power that is converted by an inverter 114 to an AC voltage having specific voltage and frequency characteristics. The inverter 114 can be controlled by a controller / communications module 116 that operates as described further below. In various embodiments, the inverter controller and communications module can be implemented in a common system, such as a system based on a microprocessor, microcontroller, or the like. In other embodiments, the inverter controller can be implemented by a separate controller module and communications module having means for communication therebetween. The inverter 114 can be configured using any suitable circuit topology (e.g., full bridge, half bridge, etc.) and implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., fabricated using silicon, silicon carbide, or gallium nitride devices).

[0036] The inverter 114 can deliver the generated AC voltage to the transmitter coil 112. In addition to the wireless coil that enables magnetic coupling to the receiver, the transmitter coil block 112 shown in FIG. 1 may include tuning circuit components, such as additional inductors and capacitors, that facilitate operation of the transmitter under different conditions, such as different degrees of magnetic coupling to the receiver or different operating frequencies. The wireless coil itself can be configured in a variety of different ways. In some embodiments, the wireless coil can be formed as a winding of wire wound around a suitable bobbin. In other embodiments, the wireless coil can be formed as a trace on a printed circuit board. Other arrangements are possible and can be used in conjunction with the various embodiments described herein. The wireless transmitter coil can also include a core of magnetically permeable material (e.g., ferrite) configured to affect the magnetic flux pattern of the coil in a manner suitable for a particular application. The teachings herein can be applied in conjunction with any of a wide variety of transmitter coil arrangements suitable for a given application.

[0037] The PTx controller / communications module 116 can monitor the power transmitter coil and use information derived therefrom to control the inverter 114 as appropriate for a given situation. For example, the controller / communications module can be configured to operate the inverter 114 at a given frequency or output voltage depending on a particular application. In some embodiments, the controller / communications module can be configured to receive information from the PRx device and control the inverter 114 accordingly. This information can be received via the power transmitter coil (i.e., in-band communication) or via a separate communication channel (not shown, i.e., out-of-band communication). In the case of in-band communication, the controller / communications module 116 can detect and decode signals (such as voltage, frequency, or load variations) imposed on the magnetic link by the PRx to receive the information, and can instruct the inverter to modulate the delivered power by manipulating various parameters (such as voltage, frequency, etc.) of the generated voltage to transmit the information to the PRx. In some embodiments, the controller / communications module may be configured to communicate data to the PRx employing frequency shift keying (FSK) communications, in which the frequency of the inverter signal is modulated. The controller / communications module 116 may be configured to detect amplitude shift keying (ASK) communications or load modulation-based communications from the PRx. In either case, the controller / communications module 126 may be configured to vary the current drawn at the receiver to manipulate the waveform seen on the Tx coil to deliver information from the PRx to the PTx. For out-of-band communications, additional modules may be provided to enable communication between the PTx and PRx, such as WiFi, Bluetooth, or other wireless links, or any other suitable communications channel.

[0038] As mentioned above, controller / communications module 116 may be, for example, a single module provided on a single integrated circuit, or may be constructed from multiple modules / devices provided on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of controller / communications circuitry.

[0039] The PTx device 110 may optionally include other systems and components, such as a separate communications module 118. In some embodiments, the communications module 118 can communicate with a corresponding module tag in the PTx via the power transfer coil. In other embodiments, the communications module 118 can communicate with a corresponding module using a separate physical channel 138.

[0040] As described above, the wireless power transmission system also includes a wireless power receiver (PRx) 120. The wireless power receiver may include a receiver coil 122 that may be magnetically coupled to the transmitter coil 112. Similar to the transmitter coil 112 described above, the receiver coil block 122 shown in FIG. 1 may include tuning circuit components, such as additional inductors and capacitors, to facilitate operation of the transmitter under different conditions, such as different degrees of magnetic coupling to the receiver or different operating frequencies. The wireless coil itself may be configured in a variety of different ways. In some embodiments, the wireless coil may be formed as a winding of wire wound around a suitable bobbin. In other embodiments, the wireless coil may be formed as a trace on a printed circuit board. Other arrangements are possible and may be used in conjunction with the various embodiments described herein. The wireless receiver coil may also include a core of magnetically permeable material (e.g., ferrite) configured to affect the magnetic flux pattern of the coil in a manner suitable for a particular application. The teachings herein may be applied in conjunction with any of a wide variety of receiver coil arrangements suitable for a given application.

[0041] The receiver coil 122 outputs an AC voltage induced therein by magnetic induction through the transmitter coil 112. This output AC voltage may be provided to a rectifier 124, which provides DC output power to one or more loads associated with the PRx device. The rectifier 124 may be controlled by a controller / communications module 126, which operates as described further below. In various embodiments, the rectifier controller and communications module may be implemented in a common system, such as a microprocessor-, microcontroller-, or other based system. In other embodiments, the rectifier controller may be implemented by a separate controller module and communications module having means for communication therebetween. The rectifier 124 may be configured using any suitable circuit topology (e.g., full bridge, half bridge, etc.) and may be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., fabricated using silicon, silicon carbide, or gallium nitride devices).

[0042] The PTx controller / communications module 126 can monitor the receiver coil and use information derived therefrom to appropriately control the rectifier 124 depending on given circumstances. For example, the controller / communications module can be configured to operate the rectifier 124 to provide a given output voltage depending on a particular application. In some embodiments, the controller / communications module can be configured to transmit information to the PTx device to effectively control the power delivered to the receiver. This information can be received and transmitted via the power transmitting coil (i.e., in-band communication) or can be transmitted via a separate communication channel (not shown, i.e., out-of-band communication). In the case of in-band communication, the controller / communications module 126 can transmit information to the PTx, for example, by modulating the load current or other electrical parameters of the received power. In some embodiments, the controller / communications module 126 can be configured to detect and decode signals (such as voltage, frequency, or load variations) applied by the PTx to the magnetic link in order to receive information from the PTx. In some embodiments, the controller / communications module 126 may be configured to receive frequency shift keying (FSK) communications, in which the frequency of the inverter signal is modulated to communicate data to the PRx. The controller / communications module 126 may be configured to generate amplitude shift keying (ASK) communications or load modulation-based communications from the PRx. In either case, the controller / communications module 126 may be configured to vary the current drawn at the receiver to manipulate the waveform seen on the Tx coil to deliver information from the PRx to the PTx. For out-of-band communications, additional modules may be provided to enable communication between the PTx and PRx, such as WiFi, Bluetooth, or other wireless links, or any other suitable communications channel.

[0043] As mentioned above, the controller / communications module 126 may be, for example, a single module provided on a single integrated circuit, or may be comprised of multiple modules / devices provided on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of controller / communications circuitry. The PRx device 120 may optionally include other systems and components, such as a communications (“comms”) module 128. In some embodiments, the communications module 128 can communicate with a corresponding module in the PTx via the power transfer coil. In other embodiments, the communications module 128 can communicate with a corresponding module or tag using a separate physical channel 138.

[0044] Many variations and extensions of the wireless power transmission system 100 described above are possible, and the following teachings are applicable to any such variations and extensions.

[0045] In wireless power transfer systems, it may be desirable to detect the presence of a conductive foreign object within the influence of a wireless power transfer magnetic field, for example, to mitigate undesired heating of such foreign object. There are numerous techniques for performing such foreign object detection. One class of such techniques may be based on power accounting. In power accounting techniques, a wireless power transmitter may receive a communication from a wireless power receiver indicating the amount of power received by the wireless power receiver. The receiver may calculate its received power by various techniques, such as monitoring its rectifier voltage and coil current. The received power may be calculated as the product of these values. The receiver may communicate this value back to the wireless power transmitter using in-band or out-of-band communication, as described above. In some cases, such communication may take a form specified by an industry standard, such as the Qi wireless power transfer standard promulgated by the Wireless Power Consortium, or by a proprietary protocol. The wireless power transmitter may compare the received power value of the wireless power receiver with the amount of power transmitted by the wireless power transmitter. The wireless power transmitter can calculate this value in a variety of ways, such as the product of the inverter output voltage and the wireless power transmitter coil current.

[0046] The difference between the power transmitted by the wireless power transmitter and the power received by the wireless power receiver is the power loss. This power loss may include losses associated with the so-called “friendly metal” of the wireless power transmitter and receiver, as well as any losses associated with potential foreign objects. Various techniques can be used to determine the friendly metal loss. For example, the wireless power receiver can provide the wireless power transmitter with information programmed into the wireless power receiver at the time of manufacture, allowing the wireless power transmitter to estimate the losses associated with the friendly metal of the wireless power receiver. Similarly, the wireless power transmitter can be programmed at the time of manufacture with information that allows it to estimate its own friendly metal loss. In some cases, additional calibration mechanisms can be provided that allow the friendly metal loss estimation parameters of the wireless power receiver and / or wireless power transmitter to be updated over time. In any case, once the friendly metal loss is determined, any remaining loss can be assumed to be associated with the presence of a foreign object. If the foreign object loss exceeds a threshold, which may be a predetermined static or dynamic threshold, wireless power transmission may be reduced or prohibited to prevent undesired heating of the foreign object.

[0047] Exemplary foreign object detection techniques based on power accounting are described in applicant's U.S. Provisional Patent Application No. 63 / 581,318, filed September 8, 2023, which is incorporated herein by reference, along with all references incorporated therein. Such techniques may be used in conjunction with additional foreign object detection techniques described below.

[0048] FIG. 2 shows plots 240 and 245 of power measurements that may be used to detect foreign objects using power loss measurements in a wireless power transfer system. The top plot 240 shows a series of wireless power receiver power measurements 241a-241d and 243a-243e taken over a period of time beginning with the initiation of wireless power transfer. As shown in plot 240, the power level may start at a level of 0 W and initially ramp up to a first value, such as 15 W (power measurement 241a), during an initial operating period 242. Assuming no foreign object is detected during this initial operating period 242, the received power level may continue to increase during a baseline recording period 247 to a higher (second) power level, e.g., 28 W, corresponding to power measurement 241d. This second higher value of the power level may correspond to a maximum power limit 244. Thereafter, operational received power measurements 243a-243e may be taken during a delta power loss active time period 249 (which may include or overlap with the baseline recording period 247) to be used along with baseline values ​​determined as described in more detail below to determine whether a foreign object is present. These power measurements 243a-243e may indicate a decrease in power over time as a battery being charged by the wireless power receiver approaches a fully charged state and, for example, the rate of charging is reduced accordingly, or may indicate when power is reduced to regulate battery temperature, for example.

[0049] The bottom plot 245 of FIG. 2 shows power loss measurements 246a-246d (from a baseline recording period, sometimes referred to as a baselining phase, when a baseline loss is determined) and 248a-248e (from a higher level power transfer operation period, when delta power loss measurements are taken and compared to the baseline value). These power loss measurements 246a-246d and 248a-248e correspond to the wireless power receive measurements 241a-241d and 243a-243e, respectively, described above. The power loss measurements 246a-246d and 248a-248e can be made by the wireless power transmitter according to the general principles and techniques described above and in the applicant's other patent applications referenced above. For example, the power loss measurements can be made by comparing the received power of the wireless power receiver with the transmitted power of the wireless power transmitter. Embodiments of the power loss regime described herein further optimize the power loss measurements to inherently account for associated friendly metal losses, as described in more detail herein. As a result, each wireless power receiver power measurement 241a-241d and 243a-243e can have an associated or corresponding power loss measurement 246a-246d and 248a-248e.

[0050] During the initial operating period 242, foreign object detection may be performed by techniques described in the applications incorporated by reference above, which provide indication of and protection against the introduction of a foreign object during the initial operating period 242. Once a first threshold power level of the initial operating regime is reached (e.g., 15 W received power measurement 241a), a power loss regime 249 may begin with a baseline recording period 247. During this baseline recording period, the transmitted power may be further increased to a second, higher (e.g., maximum) power level of the PTx and PRx system design. In the example of FIG. 2, the wireless power system is designed to operate below 30 W, as indicated by received power measurement 241d. In the illustrated example, 28 W and 30 W are used as the upper ends of the higher power operating regime, although other power levels for this boundary may also be implemented. At these threshold power levels and at one or more intermittent power levels corresponding to the received power measurements 241b, 241c, baseline power loss values ​​can be calculated, such that for each received power measurement 241a-241d, there is a corresponding power loss value 246a-246d derived by the wireless power transmitter. The baseline regime is complete when the maximum power limit 244 is reached (corresponding to the power measurement 241d and the power loss baseline value 246d). The measured baseline values ​​can be used to derive information, such as coefficients, that can be further used for foreign object detection, as described in more detail below with respect to FIGS. 3 and 4. More specifically, such coefficients can be used to predict power loss for a given received power measurement from the wireless power receiver. If the actual power loss determined by the wireless power transmitter exceeds the predicted power loss (i.e., power loss) based on the received power measurement by more than a predetermined threshold, a foreign object can be assumed to be present, and mitigating steps can be taken (such as reducing, pausing, and / or stopping wireless power transfer). For example, the power may be reduced to the first threshold level described above, for example, 15 W. This technique is further described below with reference to Figures 7 and 9.Additionally, based on any detected changes in operating conditions, the PRx device can request and / or the PTx device can initiate re-baselining. Such re-baselining may include returning to a first threshold level as an initial step. For example, the PRx may request re-baselining upon retuning its resonant circuit for power transfer and / or data communication optimization. Embodiment 1: P RECT 2 Based on measurements P LOSS Determine

[0051] FIG. 3 shows a process flow chart 300 for determining coefficients for a power-loss foreign object detection technique for use in a wireless power transfer system. FIG. 4 shows a plot 400 of power measurements at various phases of the power-loss foreign object detection technique. These two figures are discussed together to explain the process of determining coefficients for the power-loss foreign object detection technique. FIG. 4 plots the square of the received power measurements from a wireless power receiver on the x-axis.

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[0052] 4, which may correspond to the initial operating period 242 shown in FIG. 2, the wireless power transmitter may receive from the wireless power receiver a plurality of received power values ​​measured by the wireless power receiver, which correspond to the x-axis coordinates of data points 457a-457c. The wireless power transmitter may determine the power loss associated with each of these data points, which corresponds to the y-axis coordinates of data points 457a-457c. In one embodiment, the wireless power transmitter may then use a linear regression analysis on points 457a-457c to calculate the coefficient

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[0053] 4, which may correspond to the baseline recording period 247 shown in FIG. 2, the wireless power transmitter may receive from the wireless power receiver a further plurality of received power values ​​measured by the wireless power receiver, which correspond to the x-axis coordinates of data points 459a-459d. The wireless power transmitter may then determine the power loss associated with each of these data points, which corresponds to the y-axis coordinates of data points 459a-459d. In one embodiment, the wireless power transmitter may then use a linear regression analysis of points 459a-459d to determine the coefficients

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[0054] As indicated above, during the initial operating period 242 (region 456 of FIG. 4), the absence of a foreign object may be determined by operation of one or more foreign object detection techniques described in the applications incorporated by reference above.

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[0055] If it is determined (at block 353) that a foreign object was introduced during the baseline capture period, then wireless power transmission may be limited to a relatively low value, e.g., a first value of 15 W, as shown in block 354. In the illustrated example, 15 W is used as the upper bound of the low-power operating regime, although other power levels for this bound may also be implemented. Alternatively, if it is determined (at block 353) that a foreign object was not introduced during the baseline capture period, then coefficients α and α may be recalculated using all captured data points, e.g., data points 457a-457c captured during initial operating period 242 (region 456 of FIG. 4 ) and data points 459a-459d captured during baseline capture period 247 (region 458 of FIG. 4 ). Alternatively, a subset of the total number of data points may be used, if desired or appropriate for a given application.

[0056] In at least some applications, temperature can affect the relationship between the wireless power received and reported by a wireless power receiver and the losses measured by a wireless power transmitter. For example, an increase in transmitted power can cause an increase in losses, particularly when operating at higher transmitted power levels, that would otherwise affect the coefficients calculated as described above. FIG. 5 shows a plot 500 of power measurements of a power loss foreign object detection technique at different temperatures. More specifically, plot 500 shows the same power measurement at increasing temperatures T0, T1, and T2.

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[0057] The coefficients, particularly the α1 coefficient, can be updated as a function of temperature using power loss measurements taken at different temperatures. In practice, the actual operating temperature may not be known because both the wireless power transmitter and wireless power receiver have various components with different thermal masses and other heat transfer characteristics. However, as a general principle, the temperature increases during operation until it eventually reaches a thermal steady state at some point after the power transfer level has reached its steady state. Therefore, the coefficients can be updated periodically (i.e., at various times) until they stabilize at the steady-state operating temperature of the wireless power transmitter / wireless power receiver system.

[0058] 6 illustrates a process flow diagram 600 of a temperature compensation technique for power loss foreign object detection. The temperature compensation technique may optionally be used in conjunction with the coefficient determination techniques described above with respect to FIGS. 3 and 4. Beginning at block 664, a first (potentially unknown) temperature, Temp n The first time Time corresponding to n In block 664, fit coefficients can be calculated. This coefficient calculation can be as described above with reference to FIGS. 2-4. Then, after a period of time, it can be determined in block 665 whether a foreign object is present. This determination is made based on the predicted P calculated using the coefficients determined in block 664. LOSS The value is P RECT Measured P based on the current value of LOSSIf a foreign object is detected in block 665, the power may be reduced (block 666). Otherwise, if no foreign object is present, the temperature Temp n+1 Time corresponding to (also potentially unknown) n+1 New coefficients may be calculated in block 668. These coefficients may then be used to update the baseline by replacing the previously calculated coefficients from block 664 with the updated coefficients calculated in block 667 (block 668). This process may then be repeated, with further foreign object detection (block 665) and subsequent coefficient updates (block 667) occurring after another period of time. This may allow the baseline value to be updated to account for, for example, the temperature increase associated with continued operation at a higher power level along with the temperature decrease associated with operation at a reduced / lower power level, as shown in the right portion of FIG. 2. In some cases, the baseline update (block 668) may be skipped if the change in the calculated coefficients is relatively small, and / or the time interval between recalculations may be increased (or decreased if the difference in the coefficients is relatively large).

[0059] FIG. 7 shows a process flowchart 700 of a power-loss foreign object detection technique for use in a wireless power transfer system. Starting at block 771, a wireless power transmitter may receive data indicative of a received power level from a wireless power receiver. The wireless power receiver may determine the received power level by monitoring various voltages and / or currents, for example, the voltages or currents associated with the wireless power receiving coil and / or rectifier described above with reference to FIG. 1 . In some embodiments, the received power (also described herein as “receiver power”) may be determined (approximated) by the receiver multiplying the rectifier output voltage and the rectifier output current. While this is the rectifier output power, both the rectifier output voltage and the rectifier output current, being DC quantities, may simplify the measurement and calculation of the relevant values. In other embodiments, the rectifier input voltage and current or other suitable voltages and / or currents may be used as needed. In some embodiments, the wireless power receiver may transmit the calculated receiver power to the wireless power transmitter. In other embodiments, the wireless power receiver can convert underlying measurements such as voltage and current to the wireless power transmitter. Transmission of receiver power information can utilize in-band or out-of-band communication as described above.

[0060] At block 772, the wireless power transmitter calculates P corresponding to the received wireless power value, for example, by subtracting the receiver power from the transmitter's own measurement of the transmitter power. LOSS In some embodiments, transmitter power may be determined (approximated) by the transmitter multiplying the inverter input voltage and inverter input current. This is inverter input power, but both inverter input voltage and inverter input current, being DC quantities, may simplify the measurement and calculation of the associated values. In other embodiments, inverter output voltage and current or other suitable voltages and / or currents may be used as needed to determine transmitter power.

[0061] At block 773, the wireless power transmitter calculates the predicted P based on the fitness coefficients derived during the baseline measurement phase using a process such as that described above with respect to FIGS. 2-4. LOSS The coefficients may also be optionally temperature compensated using a process such as that described above with respect to FIGS. 5-6 or other suitable processes. LOSS Determination and predicted P LOSS The calculations of can be performed in any order or simultaneously, depending on the implementation.

[0062] In block 774, the wireless power transmitter LOSS value (i.e., the transmitted power value measured by the wireless power transmitter minus the received power value reported by the wireless power receiver) is the predicted P (calculated using the baseline model). LOSS It may be determined whether the value exceeds a threshold value. The threshold value may be static or dynamic, and may be predetermined and / or calculated or periodically updated, as needed. In either case, if the difference between the measured power loss and the predicted power loss is greater than such threshold value, it may be inferred that a foreign object is present, and mitigation steps may be taken (block 775). Such mitigation steps may include reducing the output power to a lower level selected to reduce or eliminate the possibility of undesired heating of such foreign object, or may include suspending or ceasing wireless power transfer entirely. Alternatively, if the difference between the measured power loss and the predicted power loss does not exceed the threshold value, it may be inferred that no foreign object is present (block 776), or if a foreign object is present, the temperature effect on the foreign object remains within acceptable limits, and therefore wireless power transfer may continue at the current level, and the process may be repeated as necessary (indicated by returning to block 771). Embodiment 2: V RECT 2 / I RECT 2 Based on P LOSS Measurements to determine

[0063] In the above example, the expected power loss of the wireless power transfer system is estimated as a function of the rectifier power (i.e.,

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[0064] In some embodiments, as illustrated using plot 800 in FIG. 8, the system losses are proportional to the square of the PRx rectifier voltage (V rect ) and the square of the rectifier current (I rect ) In other words, the loss can be estimated by:

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[0065] To verify the validity of the baselining point, an optional baselining procedure may be performed by the wireless power receiver and / or the wireless power transmitter, more particularly by one or more processors included in the control and communication circuitry of such devices. Baselining may optionally include two (or more) steps.

[0066] In a first step, the baselined points 877a, 877b, ..., 877c can be checked to determine that they define a plane. In other words, they are sufficiently non-collinear to define a single plane rather than an infinite number of planes. This check can be performed in a variety of ways. In one embodiment, the matrix A is calculated as follows: rect and I rect It can be constructed from measurements.

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[0067] A second baselining check can be performed to verify that the baselining points fit a sufficiently flat (i.e., two-dimensional) plane and not a paraboloid or other higher-order surface. In other words, the baselining points are expected to fit exactly (within a reasonable margin) on a two-dimensional plane. One way to check this is to check the compensated power loss P loss From the maximum absolute value of

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[0068] During power transfer, ΔP loss The value can be calculated as follows:

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[0069] As explained above, Figure 9 shows the V rect and I rect 9 is a flowchart 900 of an alternative power-loss foreign object detection technique for use in a wireless power transfer system incorporating a modified model utilizing (a) (b) (c). In block 981, a wireless power transmitter (PTx) can calculate transmitter power as described above. Similarly, in block 982, a wireless power receiver (PRx) can calculate receiver power in a similar manner (also described above). Alternatively, rather than calculating receiver power, the PRx device can report its associated voltage(s) and / or current(s) directly to the PTx. The PTx can then perform the power calculation itself. This reporting may be done, for example, over a wireless power link between the PTx and PRx using in-band communications such as ASK to transmit one or more data packets containing the associated voltage and current information. In block 983, the PRx can provide this calculated received power (and / or associated voltage and current parameters for calculating it) to the PTx device, which receives such data in block 984. In block 985, the PTx device may, for example, calculate the square of the rectifier voltage.

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[0070] At block 986, the calculated ΔP lossThe calculated ΔP can be compared to a threshold to determine if a foreign object is present. loss If ΔP exceeds a threshold, it can be inferred that a foreign object is present (block 987), and mitigation steps can be taken, such as limiting, reducing, suspending, and / or stopping power transfer. For example, the power can be reduced to the first threshold level described above, e.g., 15 W. Instead, the calculated ΔP loss If does not exceed the threshold, it can be inferred that no foreign object is present (block 988) and an increase in the power level can be permitted. Embodiment 3: V RECT 2 / I RECT 2 Based on the measured value ΔP LOSS Additional aspects of determining

[0071] As in the above embodiment, ΔP LOSS Calculating P may involve measuring the overall system loss at a single instance and comparing it to a baseline value. LOSS can be simply defined by calculating the difference between the transmitted and received power. P LOSS =P INV -P RECT where P LOSS is the power loss, and P INV is the transmission power (i.e., inverter power), and P RECT is the received power (i.e., the rectifier power).

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[0072] As briefly mentioned above with reference to Figure 8, V RECT 2 and I RECT 2 Based on the measured value ΔP LOSS Determining may include a baselining procedure. One purpose of the baselining procedure is to

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[0073] As an example, three baselined data points are RECT and P RECT These can be selected as three equally spaced points across the target range, e.g. ·

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[0074] In at least some embodiments, the PTx device can take these three points and fit the α and β coefficients to the following equation (corresponding to Equation 2 above):

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[0075] Linear baselining and fit error checks, as described below, can be used to ensure that the fit is well conditioned. A linear baselining check can be performed by checking how close the data is to a singular point. The following equations (similar to those described above with respect to embodiment 2) define the process: As noted above, matrix A is calculated by V rect and Irect It can be constructed from the measurements as follows:

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[0076] More specifically, if the determinant is zero, the baselined points are collinear, while a non-zero value indicates that the baselined points are not collinear. The matrix ATA is given by:

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[0077] To ensure a sufficient degree of non-collinearity, the determinant can be scaled by the number of points and compared to a threshold to determine whether the points are sufficiently non-collinear for baselining to be valid. In other words, the exemplary condition

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[0078] A second baselining check can be performed to verify that the baselining points fit a sufficiently flat (i.e., two-dimensional) plane and not a paraboloid or other higher-order surface. In other words, the baselining points are expected to fit exactly onto a two-dimensional plane, within a reasonable margin. Thus, after the α and β coefficients have been calculated, the maximum fit error can be calculated to confirm good baselining. One way to check this is to calculate the compensated power loss P loss_compensated From the maximum absolute value of

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[0079] ΔP LOSS ΔP can be evaluated (e.g., by PTx) upon receipt of its complementary packet (e.g., from PRx), and if a threshold is exceeded, the system can limit power, for example, by reverting to a 15W operating mode. LOSS can be given by:

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[0080] In the foregoing description, it is contemplated that the foreign object detection techniques described herein are performed by a wireless power transmitter, and more particularly by appropriately programmed or configured control circuitry in the wireless power transmitter, which may be constructed (for example) as described above with respect to FIG. 1. However, it may also be possible for all or part of the functionality to be performed by a wireless power receiver having appropriately programmed control circuitry. Such an arrangement may require slightly different control flows and communications, but would nevertheless be similar in structure and operation to the systems and methods described herein.

[0081] Additional terms: Item 1. A method performed by a control circuit of a wireless power transmitter for detecting a foreign object affected by an electromagnetic field associated with wireless power transfer from a wireless power transmitter to a wireless power receiver, the method comprising: receiving, from the wireless power receiver, an indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage and rectifier current of the wireless power receiver; determining a measured power loss associated with the wireless power transfer by comparing the indication of the receiver power to a transmitter power measured by the wireless power transmitter; calculating a predicted power loss based on an indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage or rectifier current of the wireless power receiver and one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver; and determining that a foreign object is present if the measured power loss exceeds the expected power loss by more than a threshold. Clause 2. The method of clause 1, wherein the received indication of the received power is a rectifier voltage and a rectifier current, and the method further includes calculating the receiver power based on the rectifier voltage and the rectifier current. Item 3. The method of item 1, wherein the rectifier voltage is the rectifier output voltage and the rectifier current is the rectifier output current. Clause 4. The method of clause 1, wherein the transmitter power is calculated by the wireless power transmitter by multiplying the inverter input voltage by the inverter input current. Section 5. One or more coefficients corresponding to a baseline wireless power transmission between a wireless power transmitter and a wireless power receiver, receiving, from a wireless power receiver, a plurality of indications of receiver power including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer; determining a plurality of measured power loss values, each corresponding to one of a plurality of indications of a received power level associated with the wireless power transfer, by comparing the indication of the receiver power with a corresponding transmitter power measured by the wireless power transmitter; The method of claim 1, further comprising: calculating one or more coefficients by performing a regression analysis on the received indications of receiver power and corresponding rectifier voltage and rectifier current of a wireless power receiver associated with the wireless power transfer, and the determined measured power loss values. Clause 6. The method of clause 5, wherein receiving a plurality of indications of receiver power from a wireless power receiver associated with a wireless power transfer, the indications including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver, includes receiving the plurality of indications at three or more operating points. Clause 7. The method of clause 6, wherein the three or more operating points include an operating point at a minimum rectifier voltage and a maximum receiver power, an operating point at a nominal rectifier voltage and a nominal receiver power, and an operating point at a maximum rectifier voltage and a minimum receiver power. Clause 8. The method of clause 6, wherein the plurality of indications at the three or more operating points includes a plurality of samples at each of the three or more operating points. Clause 9. The method of clause 8, wherein the plurality of samples at each of the three or more operating points includes 25 or more samples at each of the three or more operating points. Clause 10. The method of clause 5, wherein the one or more coefficients include a first coefficient related to a rectifier voltage and a second coefficient related to a rectifier current. Item 11. Estimated power loss is

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[0082] Various features and embodiments relating to foreign object detection in wireless power transfer systems have been described above. Such arrangements may be used in a variety of applications, but may be particularly advantageous when used with electronic devices such as mobile phones, tablet computers, laptop or notebook computers, and accessories such as wireless headphones, styluses, etc. Furthermore, while numerous specific features and various embodiments have been described, it should be understood that, unless otherwise stated as mutually exclusive, the various features and embodiments may be combined in various permutations in a particular implementation. Accordingly, the various embodiments described above are provided by way of example only and should not be construed as constituting the scope of the present disclosure. Various modifications and variations can be made to the principles and embodiments herein without departing from the scope of the present disclosure and without departing from the scope of the claims.

[0083] The above describes an exemplary embodiment of a wireless power transfer system capable of transmitting certain information between the PTx and PRx in the system. The present disclosure contemplates that the passing of this information improves the ability of devices to provide wireless power signals to each other in an efficient manner to facilitate battery charging, such as by sharing the devices' power handling capabilities with each other. Entities implementing the present technology should take care to ensure that well-established privacy policies and / or practices are adhered to, to the extent any sensitive information is used in a particular implementation. Specifically, such entities would be expected to implement and consistently apply privacy practices generally recognized as meeting or exceeding industry or government requirements for maintaining user privacy. Implementers should inform users of where personally identifiable information is expected to be transmitted in the wireless power transfer system and allow users to "opt in" or "opt out" of participation. For example, such information may be presented to users when they place a device on a power transmitter if the power transmitter is configured to poll for sensitive information from power receivers.

Claims

1. 1. A method, performed by control circuitry of a wireless power transmitter, for detecting a foreign object affected by an electromagnetic field associated with wireless power transfer from the wireless power transmitter to a wireless power receiver, the method comprising: receiving, from the wireless power receiver, an indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage and rectifier current of the wireless power receiver; determining a measured power loss associated with the wireless power transfer by comparing the indication of receiver power to a transmitter power measured by the wireless power transmitter; calculating a predicted power loss based on the indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage and rectifier current of the wireless power receiver, and one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver; determining that a foreign object is present if the measured power loss exceeds the predicted power loss by more than a threshold.

2. 2. The method of claim 1, wherein the received indication of received power is the rectifier voltage and rectifier current, the method further comprising calculating receiver power based on the rectifier voltage and rectifier current.

3. The method of claim 1 , wherein the rectifier voltage is a rectifier output voltage and the rectifier current is a rectifier output current.

4. 10. The method of claim 1, wherein the transmitter power is calculated by the wireless power transmitter by multiplying an inverter input voltage by an inverter input current.

5. The one or more coefficients corresponding to the baseline wireless power transmission between the wireless power transmitter and the wireless power receiver, receiving, from the wireless power receiver, a plurality of indications of receiver power including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer; determining a plurality of measured power loss values, each corresponding to one of the plurality of indications of received power level associated with the wireless power transfer, by comparing an indication of receiver power with a corresponding transmitter power measured by the wireless power transmitter; 2. The method of claim 1, further comprising: performing a regression analysis on the received indications of receiver power and corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer, and the determined measured power loss values, to calculate the one or more coefficients.

6. 6. The method of claim 5, wherein receiving from the wireless power receiver a plurality of indications of receiver power including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer comprises receiving the plurality of indications at three or more operating points.

7. 7. The method of claim 6, wherein the three or more operating points include an operating point at a minimum rectifier voltage and a maximum receiver power, an operating point at a nominal rectifier voltage and a nominal receiver power, and an operating point at a maximum rectifier voltage and a minimum receiver power.

8. The method of claim 6 , wherein the plurality of indications at three or more operating points comprises a plurality of samples at each of the three or more operating points.

9. The method of claim 8 , wherein the plurality of samples at each of the three or more operating points comprises 25 or more samples at each of the three or more operating points.

10. The method of claim 5 , wherein the one or more coefficients include a first coefficient related to the rectifier voltage and a second coefficient related to the rectifier current.

11. The predicted power loss is [Equation 1] 11. The method of claim 10, wherein the coefficient is of the form: where α is the first coefficient related to the rectifier voltage and β is the second coefficient related to the rectifier current.

12. 6. The method of claim 5, wherein performing the regression analysis on the plurality of indications of the received receiver power associated with the wireless power transfer and the determined plurality of measured power loss values ​​to calculate the one or more coefficients further comprises performing a baselining procedure that includes determining that the plurality of indications of receiver power are linearly independent.

13. The method of claim 12 , wherein the baselining procedure further comprises determining that the plurality of indications of receiver power lie in a two-dimensional plane.

14. performing the regression analysis on the received indications of receiver power and corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer, and the determined measured power loss values ​​to calculate the one or more coefficients; calculating a first plurality of coefficients corresponding to an initial period of operation having a wireless power transfer level below a first threshold during which another foreign object detection technique indicates the absence of a foreign object; calculating a second plurality of coefficients corresponding to a baseline capture period having a wireless power transfer level above the first threshold; and comparing the first plurality of coefficients to the second plurality of coefficients to determine whether a foreign object was introduced during the baseline capture period.

15. 10. The method of claim 1, further comprising, if a foreign object is present, mitigating the presence of the foreign object by reducing a power level of the wireless power transfer or by suspending the wireless power transfer.

16. A wireless power transmitter, a wireless power transmitter coil configured to be magnetically coupled to a wireless power receiver coil of a wireless power receiver to wirelessly transmit power to the wireless power receiver; an inverter configured to receive input power and generate an output that drives the wireless power transmitter coil; a controller and a communication circuit coupled to the inverter and the wireless power transmitter coil that controls the inverter to adjust wireless power transfer to the wireless power receiver, wherein the controller and communication circuit detects a foreign object that is affected by an electromagnetic field associated with wireless power transfer to the wireless power receiver by: receiving, from the wireless power receiver, an indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage and rectifier current of the wireless power receiver; determining a measured power loss associated with the wireless power transfer by comparing the indication of receiver power to a transmitter power measured by the wireless power transmitter; calculating a predicted power loss based on the indication of receiver power associated with the wireless power transfer, the indication including or derived from a corresponding rectifier voltage and rectifier current of the wireless power receiver, and one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver; and determining that a foreign object is present if the measured power loss exceeds the predicted power loss by more than a threshold.

17. A wireless power transmitter, a wireless power transmitter coil configured to be magnetically coupled to a wireless power receiver coil of a wireless power receiver to wirelessly transmit power to the wireless power receiver; an inverter configured to receive input power and generate an output that drives the wireless power transmitter coil; a controller and communication circuit coupled to the inverter and the wireless power transmitter coil that controls the inverter to adjust wireless power transfer to the wireless power receiver, wherein the controller and communication circuit is configured to: receiving, from the wireless power receiver, a plurality of indications of receiver power including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer; determining a plurality of measured power loss values, each corresponding to one of the plurality of indications of receiver power associated with the wireless power transfer, by comparing an indication of receiver power with a corresponding transmitted wireless power level measured by the wireless power transmitter; and performing a regression analysis on a plurality of indications of the received receiver power, including or derived from corresponding rectifier voltages and rectifier currents of the wireless power receiver associated with the wireless power transfer, and the determined plurality of measured power loss values ​​to calculate the one or more coefficients.

18. 1. A method performed by a control circuit of a wireless power transmitter for controlling wireless power transfer from the wireless power transmitter to a wireless power receiver, the method comprising: During an initial wireless power transfer period at or below the first power level, (i) The power received by the wireless power receiver (P rect ) and (ii) a plurality of indications of power (P inv ) corresponding rectifier voltages (V rect ) and rectifier current (I rect ) from the wireless power receiver; (i) the plurality of P rect and (ii) the corresponding V of the wireless power receiver. rect and I rect The power loss (P loss ) and determining the relationship is rect or I rect The power loss (P loss ) determining at least a first coefficient relating to the during a subsequent wireless power transfer period at or above a second power level that is higher than the first power level; The power P transmitted by the wireless power transmitter inv (iii) the power received by the wireless power receiver (P rect ), and (iv) a corresponding additional rectifier voltage (V rect ) and additional rectifier current (I rect ) and The power dissipation at the second power level (P inv -P rect and in response to determining that a power loss exceeds a power loss predicted from the relationship determined using (iii) and (iv) so as to indicate the presence of a foreign object, reducing power transmitted by the wireless power transmitter to a level equal to or less than the first power level.

19. Determining the relationship is a function of the relationship P inv -P rect = αV rect 2 +βI rect 2 20. The method of claim 18, comprising fitting (i) and (ii) according to:

20. P inv -P rect is the power loss (P loss 20. The method of claim 19, further comprising providing an indication of:

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