Finder metal loss estimation for

Abstract

A method for estimating friendly metal loss associated with wireless power transfer from a wireless power transmitter to a wireless power receiver may include obtaining an indication of received power including a rectifier voltage and a rectifier current of the wireless power receiver; and calculating a friendly metal power loss based on the indication of a rectifier voltage and a 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. The rectifier voltage may be a rectifier output voltage, and the rectifier current may be a rectifier output current. Calculating the friendly metal power loss may use an equation of the form where b is a coefficient related to the rectifier current, c is a coefficient related to the rectifier voltage, and a is a coefficient related to the transmitter current ITX.

Description

BACKGROUND

[0001] Wireless power transfer is used in a variety of electronic devices. For example, smart phones, tablet computers, smart watches, wireless earphones, stylus pens, and the like can employ wireless power transfer to facilitate charging of a battery within the device. In some applications, a higher level of wireless power transfer can be desirable, e.g., to provide faster charging. Such higher power transfer levels can benefit from techniques for improving estimation of losses, including losses associated with “friendly metal” associated with wireless power transmitter and / or wireless power receiver devices. SUMMARY

[0002] A wireless power transmitter can include a wireless power transfer coil configured to magnetically couple to a wireless power transfer coil of a wireless power receiver to wirelessly transfer power to the wireless power receiver, an inverter configured to receive input power and generate an output to drive the wireless power transfer coil, and a controller and communication circuit coupled to the inverter and the wireless power transfer coil, the controller and communication circuit controlling the inverter to regulate the wireless power transfer to the wireless power receiver, wherein the controller and communication circuit estimate a friendly metal loss associated with the wireless power transfer to the wireless power receiver by receiving, from the wireless power receiver, an indication of received power including a rectifier voltage and a rectifier current of the wireless power receiver associated with the wireless power transfer, calculating a friendly metal power loss based on the received rectifier voltage and the received rectifier current of the wireless power receiver and one or more coefficients corresponding to a baseline wireless power transfer between the wireless power transmitter and the wireless power receiver, and using the friendly metal power loss to regulate the wireless power transfer to the wireless power receiver.

[0003] The rectifier voltage can be a rectifier output voltage and the rectifier current can be a rectifier output current. The one or more coefficients corresponding to a baseline wireless power transfer between the wireless power transmitter and the wireless power receiver can have been derived by performing a regression analysis to calculate the one or more coefficients on a plurality of received indications of received power including corresponding rectifier voltages and rectifier currents of another wireless power receiver associated with another wireless power transfer, or received power derived therefrom, and a plurality of measured power loss values determined therefrom. The one or more coefficients can include a first coefficient related to the rectifier current and a second coefficient related to the rectifier voltage.

[0004] Calculating the friendly metal power loss can use an equation having a form of:

[0005]

[0006] where b is a first coefficient related to the rectifier current, c is a second coefficient related to the rectifier voltage, a is a coefficient related to the transmitter current, and ITX is the transmitter current.

[0007] The controller and communication circuitry can further estimate the friendly metal loss by: receiving one or more power loss scaling factors from the wireless power receiver; and calculating the friendly metal power loss in response to the one or more power loss scaling factors, where the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and the actual wireless power transmitter or the actual wireless power receiver.

[0008] The controller and communication circuitry can further estimate the friendly metal loss by: receiving one or more power loss scaling factors from the wireless power receiver; and calculating the friendly metal power loss in response to the one or more power loss scaling factors, where the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and the actual wireless power transmitter or the actual wireless power receiver.

[0009] A method performed by control circuitry of a wireless power transmitter or a wireless power receiver for estimating a friendly metal loss associated with a wireless power transfer from the wireless power transmitter to a wireless power receiver can include: obtaining an indication of a received power including a rectifier voltage and a rectifier current of the wireless power receiver; and calculating a friendly metal power loss based on the indication of the rectifier voltage and the 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 using the friendly metal power loss to adjust the wireless power transfer; where the rectifier voltage is a rectifier output voltage and the rectifier current is a rectifier output current; and calculating the friendly metal power loss using an equation having the form:

[0010]

[0011] where b is a first coefficient related to the rectifier current, c is a second coefficient related to the rectifier voltage, a is a coefficient related to the transmitter current, and ITX is the transmitter current.

[0012] The rectifier voltage can be a rectifier output voltage, and the rectifier current can be a rectifier output current. The one or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and the wireless power receiver can have been derived by performing a regression analysis to calculate the one or more coefficients on a received power and a received plurality of indications of corresponding rectifier voltages and rectifier currents of another wireless power receiver associated with another wireless power transfer.

[0013] The method can also include receiving one or more power loss scaling factors from the wireless power receiver, wherein calculating the friendly metal power loss is based on the one or more power loss scaling factors, wherein the one or more power loss scaling factors can be based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and the actual wireless power transmitter or the actual wireless power receiver.

[0014] A wireless power transmitter can include a wireless power transfer coil configured to magnetically couple to a wireless power transfer coil of a wireless power receiver to wirelessly transfer power to the wireless power receiver, an inverter configured to receive input power and generate an output to drive the wireless power transfer coil, and a controller and communication circuit coupled to the inverter and the wireless power transfer coil, the controller and communication circuit controlling the inverter to regulate the wireless power transfer to the wireless power receiver. The controller and communication circuit can estimate a friendly metal loss associated with the wireless power transfer to the wireless power receiver by receiving, from the wireless power receiver, an indication of a received power including a rectifier voltage and a rectifier current of the wireless power receiver, calculating the friendly metal power loss based on the rectifier voltage and the 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 regulating the wireless power transfer to the wireless power receiver using the friendly metal power loss. The rectifier voltage can be a rectifier output voltage, and the rectifier current can be a rectifier output current. Calculating the friendly metal power loss can use an equation having the form:

[0015]

[0016] where b is a first coefficient related to the rectifier current, c is a second coefficient related to the rectifier voltage, a is a coefficient related to the transmitter current, and ITX is the transmitter current.

[0017] One or more coefficients corresponding to a baseline wireless power transmission between the wireless power transmitter and another wireless power receiver may have been derived by performing a regression analysis on a plurality of received indications, including corresponding rectifier voltages and rectifier currents of the other wireless power receiver associated with another wireless power transfer, or received power derived therefrom, and a plurality of determined measured power loss values ​​derived therefrom to calculate the one or more coefficients. The controller and communication circuitry may further estimate the friendly metal loss by receiving one or more power loss scaling factors from the wireless power receiver; and calculating the friendly metal power loss in response to the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or reference wireless power receiver and an actual wireless power transmitter or actual wireless power receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A simplified block diagram of a wireless power transfer system is illustrated.

[0019] Figures 2A to 2C Various configurations of wireless power transfer systems are illustrated.

[0020] Figure 3 A simplified flow chart of the foreign object detection technology based on power accounting is depicted.

[0021] Figure 4 A flow chart illustrating the friendly metal loss estimation technique.

[0022] Figures 5A to 5B The circuit model and associated equations of a wireless power transfer system are illustrated.

[0023] Figure 6 is a circuit diagram of an exemplary wireless power system according to one embodiment.

[0024] Figure 7 is a flow diagram of illustrative operations associated with utilizing a device in a wireless power system, according to an embodiment.

[0025] Figure 8 is a flow diagram of illustrative operations associated with utilizing a device in a wireless power system, according to an embodiment.

[0026] Figure 9 Aspects of an ecosystem scaling arrangement for a wireless power transfer system are illustrated.

[0027] Figure 10 Some combinations of monitorable parameters that can be used for friendly metal loss estimation in a wireless power transfer system are illustrated. DETAILED DESCRIPTION

[0028] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed concept. As part of this description, some of the diagrams in the drawings are presented in block diagram form representing structural and device implementations. For the purposes of clarity, not all of the features of the actual implementation are described in this disclosure. Further, the language used in this disclosure has been principally selected for readability and instructional purposes and it can not have been selected to delineate or circumscribe the disclosed subject matter. Rather, the appended claims are intended to define the disclosed subject matter as accurately as possible.

[0029] Various embodiments of the disclosed concept are illustrated by way of example in the drawings and are not intended to be limited by the specific arrangements and instrumentalities shown. Like reference numerals in the various drawings indicate like elements, and the drawings are not to scale (with scale emphasis on certain components). For simplicity and clarity, the detailed description reproduces portions of the drawings in greater detail, where appropriate. In addition, numerous specific details are set forth in order to provide a thorough understanding of the specific implementations described herein. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant function being described. References in this disclosure to “one” or “another” embodiment or implementations are not necessarily to the same or different embodiments, and this means at least one. A given drawing can be used to illustrate more than one embodiment or more than one category of features, and not all of the elements illustrated in a given drawing can be required for a given embodiment or category. When provided in a given drawing, reference numerals are used consistently throughout the several drawings to refer to the same element, but they can not be repeated in every drawing. The drawings are not to scale, and the proportions of certain components can be exaggerated to better illustrate the details and features of the present disclosure. Unless specifically stated otherwise, the drawings are not to scale and the proportions of certain components can be exaggerated to better illustrate the details and features of the present disclosure.

[0030] Wireless power transfer

[0031] Figure 1A simplified block diagram of a wireless power transfer system 100 is illustrated. The wireless power transfer system includes a power transmitter (PTx) 110 that wirelessly transmits power to a power receiver (PRx) 120, such as via an inductive coupling 130. The power transmitter 110 can receive input power that is converted by an inverter 114 into an AC voltage having particular voltage and frequency characteristics. The inverter 114 can be controlled by a controller / communication module 116 that operates as further described below. In various embodiments, the inverter controller and communication module can be implemented in a common system, such as a microprocessor, microcontroller, or the like based system. In other embodiments, the inverter controller can be implemented by separate controller module and communication module with a communication device therebetween. The inverter 114 can be constructed using any suitable circuit topology (e.g., full-bridge, half-bridge, etc.) and can be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc. manufactured using silicon, silicon carbide, or gallium nitride devices).

[0032] The inverter 114 can deliver the generated AC voltage to a transfer coil 112. In addition to allowing for magnetic coupling to a receiver's wireless coil, Figure 1 The illustrated transfer coil block 112 can include tuning circuitry, such as additional inductors and capacitors, that facilitate operation of the transmitter under different conditions, such as different degrees of magnetic coupling to a receiver, different operating frequencies, etc. The wireless coil itself can be constructed in a variety of different ways. In some embodiments, the wireless coil can be formed as a metal wire winding 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 transfer coil can also include a magnetically permeable material (e.g., ferrite) core that is configured to influence the 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 variety of transfer coil arrangements suitable for a given application. In some contexts, the transfer coil 112 can be described as a transmitting or transmitter coil. In some embodiments, a device can be capable of bidirectional operation, i.e., transmitting or receiving wireless power, and thus the wireless power transfer coil of such a device can be capable of transmitting or receiving power, depending on the mode of operation.

[0033] The PTx controller / communication module 116 can monitor the transfer coil and use information derived therefrom to control the inverter 114 to suit a given situation. For example, the controller / communication module can be configured to cause the inverter 114 to operate at a given frequency or output voltage depending on the particular application. In some embodiments, the controller / communication 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 transfer coil (i.e., in-band communication) or can be received via a separate communication channel (not shown, i.e., out-of-band communication). For in-band communication, the controller / communication module 116 can detect and decode signals (such as voltage, frequency, or load variations) imposed by the PRx on the magnetic link to receive information, and can instruct the inverter to modulate the power delivered by manipulating various parameters of the generated voltage (such as voltage, frequency, etc.) to convey information to the PRx. In some embodiments, the controller / communication module can be configured to employ frequency shift keying (FSK) communication to communicate data to the PRx, in which the frequency of the inverter signal is modulated. The controller / communication module 116 can be configured to detect amplitude shift keying (ASK) communication or load modulation based communication from the PRx. In either case, the controller / communication module 126 can be configured to vary the current drawn on the receiver side to manipulate the waveform seen on the Tx coil, delivering information from the PRx to the PTx. For out-of-band communication, an additional module allowing communication between the PTx and the PRx can be provided, such as WiFi, Bluetooth, or other wireless radio link, or any other suitable communication channel.

[0034] As noted above, the controller / communication module 116 can be a single module, e.g., provided on a single integrated circuit, or can be constructed from multiple modules / devices provided on different integrated circuits or a combination of integrated and discrete circuits with analog components, digital components, and / or programmable components that can be field programmable or updatable. The teachings herein are not limited to any particular arrangement of controller / communication circuitry.

[0035] The PTx device 110 can optionally include other systems and components, such as a separate communication module 118. In some embodiments, the communication module 118 can communicate with a corresponding module in the PRx via the power transfer coil. In other embodiments, the communication module 118 can use a separate physical channel 138 to communicate with the corresponding module.

[0036] As mentioned above, the wireless power transfer system also includes a wireless power receiver (PRx) 120. The wireless power receiver can include a transfer coil 122 that can be magnetically coupled 130 to the transfer coil 112. As with the transfer coil 112, discussed above, Figure 1The illustrated transfer coil block 122 can include tuning circuitry, such as additional inductors and capacitors, that facilitates operation of the transmitter under different conditions, such as different degrees of magnetic coupling to the receiver, different operating frequencies, etc. The wireless coil itself can be constructed in a variety of different ways. In some embodiments, the wireless coil can be formed as a metal wire winding 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 transfer coil can also include a magnetically permeable material (e.g., ferrite) core configured to influence the 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 variety of transfer coil arrangements suitable for a given application. In some contexts, the transfer coil 122 can be described as a receive or receiver coil. In some embodiments, a device can be capable of bidirectional operation, i.e., transmitting or receiving wireless power, and thus the wireless power transfer coil of such a device can be capable of transmitting or receiving power, depending on the mode of operation.

[0037] The transfer coil 122 outputs an AC voltage induced therein via magnetic induction by the transfer coil 112. The output AC voltage can be provided to a rectifier 124, which provides a DC output power to one or more loads associated with the PRx device. The rectifier 124 can be controlled by a controller / communication module 126, which operates as further described below. In various embodiments, the rectifier controller and communication module can be implemented in a common system, such as a microprocessor, microcontroller, etc. based system. In other embodiments, the rectifier controller can be implemented by separate controller module and communication module with communication means therebetween. The rectifier 124 can be constructed using any suitable circuit topology (e.g., full-bridge, half-bridge, etc.) and can be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc. fabricated using silicon, silicon carbide, or gallium nitride devices).

[0038] The PRx controller / communication module 126 can monitor the receiver coil and use information derived therefrom to control the rectifier 124 to adapt to a given situation. For example, the controller / communication module can be configured to cause the rectifier 124 to provide a given output voltage depending on the particular application. In some embodiments, the controller / communication module can be configured to transmit information to the PTx device to effectively control the power delivered to the receiver. This information can be transmitted via the power transmission coil (i.e., in-band communication) or can be transmitted via a separate communication channel (not shown, i.e., out-of-band communication). For in-band communication, the controller / communication module 126 may, for example, modulate the load current or other electrical parameter of the received power to transmit information to the PTx. In some embodiments, the controller / communication module 126 can be configured to detect and decode signals (such as voltage, frequency, or load variations) imposed on the magnetic link by the PTx to receive information from the PTx. In some embodiments, the controller / communication module 126 can be configured to receive frequency shift keying (FSK) communication in which the frequency of the inverter signal has been modulated to convey data to the PRx. The controller / communication module 126 can be configured to generate amplitude shift keying (ASK) communication or load modulation based communication from the PRx. In either case, the controller / communication module 126 can be configured to vary the current drawn on the receiver side to manipulate the waveform seen on the Tx coil to deliver information from the PRx to the PTx. For out-of-band communication, an additional module allowing communication between the PTx and the PRx can be provided, such as a WiFi, Bluetooth, or other radio link, or any other suitable communication channel.

[0039] As noted above, the controller / communication module 126 can be a single module, e.g., provided on a single integrated circuit, or can be constructed from multiple modules / devices provided on different integrated circuits or a combination of integrated and discrete circuits with analog components, digital components, and / or programmable components that can be field programmable or updatable. The teachings herein are not limited to any particular arrangement of controller / communication circuitry. The PRx device 120 can optionally include other systems and components, such as a communications ("comms") module 128. In some embodiments, the comms module 128 can communicate with a corresponding module in the PTx via the power transfer coil. In other embodiments, the comms module 128 can communicate with a corresponding module or tag using a separate physical channel 138.

[0040] Many variations and enhancements of the wireless power transmission system 100 described above are possible, and the following teachings apply to any of such variations and enhancements.

[0041] Improved friendly metal loss estimation

[0042] In some applications, it can be desirable to increase the rate of power transfer from a wireless power transmitter to a wireless power receiver. One approach for accomplishing this can be to use a magnetic power profile (“MPP”) as described in the Qi 2.0 specification promulgated by the Wireless Power Consortium (“WPC”). The MPP can employ a magnet to provide improved alignment between respective wireless power transfer coils of the wireless power transmitter and the wireless power receiver. This improved alignment can be one aspect that facilitates higher levels of power transfer. Another aspect that can enable higher levels of power transfer can include improved techniques for foreign object detection and losses associated therewith. In some cases, the presence of a foreign object in the vicinity of the wireless power transmitter and / or receiver can absorb power and result in undesirable heating of the foreign object. Mitigating these effects can be based on power loss accounting (“PLA”) techniques, where a comparison between the power transmitted by the wireless power transmitter, the power received by the wireless power receiver can be used to determine power losses associated with the wireless power transfer.

[0043] By modeling the expected losses for a given level of wireless power transfer, if the actual losses experienced exceed the expected losses by some threshold amount, the presence of a foreign object can be inferred. The expected losses can come from a variety of sources, including losses associated with the circuitry of the wireless power transmitter and / or receiver, “friendly metal” in the housing or other structure of the wireless power transmitter and / or receiver, etc. In the event that the actual losses experienced (e.g., measured) exceed the expected level based on the modeling, mitigation techniques can be employed, such as reducing or stopping power transfer, providing an audio or visual indication (or other feedback) to the user, etc.

[0044] Introduction to Friendly Metal Loss Estimation

[0045] Exemplary friendly metal loss modeling and estimation techniques are described in Applicant’s co-pending U.S. Patent Application No. 18 / 166,839, entitled “Friendly Metal Loss Estimation,” filed February 9, 2023, which is incorporated by reference in its entirety and certain teachings of which are reproduced below.

[0046] Wireless power transfer as described above depends on the degree of electromagnetic coupling between the PTx and the PRx. For example, in an inductive charging system, the transfer coil 112 and the transfer coil 122 can be viewed as a loosely coupled transformer. Thus, the relative position of the PTx and the PRx can affect the degree of magnetic coupling between the PTx and the PRx, which in turn can affect the power transfer capability of the system. Figure 2AA simplified diagram of a PTx (110)-PRx (120) system is shown. The two devices are shown in plan view (upper portion of the figure) and in edge cross-sectional view (lower portion of the figure). The PTx device 110 includes a transfer coil 112, and the PRx device 120 includes a transfer coil 122. In some embodiments, the PTx device 110 can be a wireless charging pad, mat, or stand (or other wireless power transfer device), and the PRx device 120 can be a mobile phone, tablet computer, smart watch (or other wireless power receiver device). Although the respective devices are depicted as having a generally rectangular shape with a generally circular charging coil, it should be understood that other configurations are possible.

[0047] Figure 2B The "optimal" alignment of PTx 110 and PRx 120 is shown. Figure 2B In the embodiment of the present invention, the device (more specifically, its wireless power transfer coil) is aligned horizontally (as depicted in plan view), vertically, and as close as possible (as shown in cross-section). In this context, horizontal and vertical are used only as terms of convenience, and the actual orientation of the system may vary, and the following description applies to systems in any such orientation, although "horizontal" and "vertical" will continue to be used for clarity of context. Figure 2C The devices are shown with a slight misalignment. More specifically, there is a radial displacement "r," which can be understood by noting that the centers of coils 112 and 122 no longer coincide in the plan view. Such radial displacement can be caused by any number of things, such as slightly misaligning the phone relative to the charging pad. Additionally, there is a vertical displacement "z," which can be understood by noting the separation between the PTx device 110 and the PRx device 120 in the cross-sectional view. This vertical displacement can also be caused by any number of things, such as the phone being enclosed in a housing or cover. The cross-sectional view also shows a lateral / radial displacement. It should be understood that in some cases, there may be only radial displacement or only vertical displacement.

[0048] The above-described offset can reduce the degree of magnetic coupling between the PTx and PRx devices. Reduced magnetic coupling can limit the amount of power that can be delivered from the PTx 110 to the PRx 120. More specifically, reduced coupling between the PTx 110 and PRx 120 reduces the portion of the power transmitted from the PTx 110 that is received by the PRx 120. Additionally, the degree of magnetic coupling between the PTx 110 and PRx 120 can be reduced, at least in part, by corresponding retuning of the receiver (or transmitter) circuitry. For example, one or more tuning capacitors can be included between the inverter 114 and transmitter coil 112 in the PTx circuitry. Likewise, one or more tuning capacitors can be included between the rectifier 124 and receiver coil 122 in the PRx circuitry. The function of these respective capacitors is to tune the circuitry by adjusting the resonant frequency of the respective circuitry, and these capacitors can include, for example, series resonant capacitors in series with the respective coil, or parallel resonant capacitors in parallel with the respective coil, depending on the particular design mode of operation of the circuitry. To this end, a plurality of selectable capacitors can be provided on the PTx 110 and / or PRx 120, and the appropriate tuning capacitor can be selected by the respective device based on a coupling factor estimate derived from various observable circuit parameters, such as voltage, current, etc.

[0049] In a wireless power transfer system, it can be desirable to detect the presence of "foreign objects." For example, an item (such as a coin, key, paperclip, etc.) that is brought into proximity with the wireless power transfer coils can receive a portion of the power transmitted by the PTx 110, which not only limits the power available to the PRx 120, but can also cause induced eddy currents in the foreign object. Wireless power transfer systems can employ a variety of foreign object detection ("FOD") techniques. One class of FOD techniques is based on power accounting. The basic principle of power accounting is as follows: the power transmitted by the PTx 110 minus the power received by the PRx 120 is the "loss" power. This loss power can be considered to flow to one of three places. Some of the power can be absorbed by so-called "friendly metal" of the PTx 110. Some of the power can be absorbed by friendly metal of the PRx 120. Some of the power can be absorbed by a foreign object. In this context, "friendly metal" refers to metal or other conductive structures that make up the PTx and PRx. The metal or other conductive structures can be frame or housing portions, internal circuit elements, magnets, etc. These elements are designated as friendly metal because they are known and accounted for in the design of the wireless power transfer system. Losses that are not associated with friendly metal can be assumed to be associated with foreign objects.

[0050] Figure 3A simplified flowchart of the foreign object detection technique 330 based on power accounting is depicted. Starting from block 331a, the PTx 110 calculates the power transmitted by the PTx. This can be done by multiplying the output voltage of the inverter 114 by the current flowing through the transmit coil 112. In some implementations, the power that is considered to be transmitted by the PTx is the output voltage multiplied by the current minus the losses in the transmit coil. Further, what is needed to use is the output side values. Sometimes, these values (e.g., as an AC output RMS current) can be more difficult to measure. As an alternative, the input voltage (and / or current) can be used, but then the inverter and / or coil losses can be subtracted to improve accuracy. Accordingly, block 331b calculates the power received by the PRx 120. In some implementations, this can be done by multiplying the current through the transfer coil 122 by the input voltage of the rectifier 124. In some applications, it can be difficult to make these measurements on the AC side of the PRx rectifier. As an alternative, the received power can be calculated as the power at the output (not the input) of the rectifier of the PRx 120 plus the estimated losses of the rectifier and coil 122. Additionally or alternatively, the power estimation can be made using the power measurements or estimates on the PTx side. These PTx side measurements can be based on the DC input power of the PTx 110, or AC measurements of the output of the inverter 114. In summary, the power transmitted by the PTx 110 or received by the PRx 120 can be estimated by directly measuring the current flowing through the respective wireless power transfer coil (112 / 122), or indirectly using the input DC current of the transmitter or the output DC current of the receiver. The respective voltages and currents can be monitored by sensors coupled to the respective controller circuitry located in the controllers as well as the communication modules 116 (for the PTx 110) and 126 (for the PRx 120). Implementations of such measurement systems are well known to those skilled in the art, and thus are not described in further detail herein.

[0051] In block 332b, PRx 120 can communicate the received power value to PTx 110, which receives the power value as shown in block 332a. The discussion assumes that foreign object detection is performed by PTx 110, e.g., by circuitry located in controller / communication module 126. However, in some applications, the foreign object detection process can run on PRx 120, in which case PTx 110 can send its measured power value to PRx 120. In either case, this can be done through in-band communication (involving modulation of the transmitted voltage, current, frequency, phase, etc. wireless power) or out-of-band communication using separate communication modules 118 / 128 and separate communication channels 138, which can be near field communication (NFC), Bluetooth communication, WiFi communication, etc., as described above. Alternatively, the devices can send the underlying measurements (e.g., voltage and current measurements) rather than sending the computed power value, which can allow the counterpart device to compute the respective power.

[0052] In either case, in block 333, PTx (or PRx, if it is performing foreign object detection) can compute the measured power loss as the difference between the transmitted power and the received power. As described above, this measured power loss can include two components: a friendly metal loss (associated with PTx 110 or PRx 120) and a foreign object loss. Thus, in block 334, PTx (or PRx, if it is performing foreign object detection) estimates the friendly metal loss. Exemplary friendly metal loss estimation techniques will be discussed in more detail below. For the purposes of this discussion, the estimation of the friendly metal loss can be viewed as a computation based on observable circuit parameters (voltage, current, coupling factor, etc.) and predetermined parameters relating these observable circuit parameters to the resulting loss. These parameters can be part of a model that can be analytically or empirically derived during the design process of a particular wireless power transfer device. These model parameters can be stored in memory associated with the controller of the respective wireless power transfer device and used by the device to estimate its friendly metal loss, or provided to the counterpart device to allow the device to estimate the friendly metal loss of its counterpart. Figure 4

[0053] ​Once the friendly metal loss is estimated / determined (block 334), the device performing the foreign object detection can calculate a net foreign object loss (block 335), which can be the difference between the calculated measured power loss (block 333) and the estimated friendly metal loss (block 334). The net foreign object loss can then be compared to a net loss threshold (block 336). If the net foreign object loss is less than the threshold, it can be inferred that no foreign object is present (block 338), and no mitigation measures are needed. Alternatively, if the net foreign object loss is greater than the threshold (block 336), it can be inferred that a foreign object is present (block 337), and some mitigation measures can be taken. Such mitigation measures can include reducing or limiting the amount of power delivered, interrupting power delivery, providing an alert to the user (such as an audiovisual alert), etc.

[0054] In high-performance wireless power transfer systems, even relatively low levels of foreign object loss can be significant, and it is desirable to be able to detect such losses at levels that can be slightly below the friendly metal loss. It is therefore desirable to ensure the accuracy of the estimated friendly metal loss. For example, if the estimated friendly metal loss is higher than the actual friendly metal loss, unnecessary eddy currents can be induced in foreign objects. Alternatively, if the estimated friendly metal loss is lower than the actual friendly metal loss, the system can unnecessarily take mitigation measures, such as those described above. However, these mitigation measures can result in a poor user experience, such as slower charging speeds or complete interruption of charging, false user interface messages, etc. Moreover, as typical wireless power levels increase from relatively low levels (e.g., around 5 W) to relatively high levels (e.g., 20 W or more), all of these issues can become more pronounced.

[0055] One method of estimating the friendly metal loss is as a function of the current flowing through the PTx transmit coil 112. The friendly metal loss can be measured as a linear function of the transmit coil current squared, i.e.,

[0056] P FM = a FM (I TX ) 2 + b FM

[0057] where P FM is the estimated friendly metal loss, a FM is a first coefficient, and b FM is a second coefficient. As described above, these coefficients can be derived analytically or empirically, e.g., based on measurements of P TX 2The regression model is linear in the above. However, the model can be further optimized in two ways. First, a more accurate estimate of the friendly metal loss can be obtained by modeling the loss as a function of voltage, not just current. Second, the friendly metal loss model can be modified to account for different coupling factors.

[0058] Regarding the first optimization, in addition to the transmit coil current I TX , the DC input voltage V in of the inverter can also be included to improve the friendly metal loss model. (As an alternative, the inverter output voltage or other suitable voltage can also be used. Thus, the estimated friendly metal loss can be expressed as:

[0059] P FM = a FM (I TX ) 2 + b FM + g FM V in + d FM

[0060] where P FM is the estimated friendly metal loss, a FM is a first coefficient related to the transmit coil current, g FM is a second coefficient related to the inverter voltage, and b FM and d FM are combinable DC offset terms (coefficients). As described above, these coefficients can be analytically or empirically derived, e.g., based on a multiple regression model that is linear in the two independent variables I TX (I 2 the square of the transmit coil current) and V in the inverter input voltage (or voltage other suitable, such as V in 2 or V rect , if applicable). This optimization can significantly improve the accuracy of the friendly metal loss estimate. This is an example of a PTx-side only friendly metal loss estimate.

[0061] Regarding the second optimization, different model coefficients can be provided for different coupling conditions. For example, a first set of coupling coefficients can be used for high coupling conditions, where the coupling factor k between the PTx 110 and the PRx 120 is above a threshold; a second set of coupling coefficients can be used for low coupling conditions, where the coupling factor k between the PTx 110 and the PRx 120 is below the threshold. Thus, if both the first and second optimizations are employed, the estimated friendly metal loss can be expressed as:

[0062]

[0063]

[0064] where P FM is the estimated friendly metal loss, and are model coefficients for low coupling conditions, and are model coefficients for high coupling conditions, k is the coupling coefficient, and k th is a threshold coupling coefficient, which is the boundary between the low coupling conditions and the high coupling conditions. In some applications, additional higher order terms (e.g., V in 2 , V in 3 , etc.) or lower order terms (e.g., I TX ) can be included in the model with appropriate coefficients. Although defined in terms of low and high coupling conditions, more than two coupling conditions and appropriate coefficients can be used in some implementations, such as a three-level system with low, medium, and high degrees of coupling and associated coefficients, or a larger number of coupling conditions and corresponding number of coefficients.

[0065] Such an arrangement can utilize existing logic and functionality in the control circuit of the wireless power transmitter (or receiver). For example, as noted above, some wireless power transfer devices can include a controller circuit that measures certain circuit parameters (e.g., voltage and current) and estimates the coupling factor k based on these values. The controller circuit can then select one (or more) tuning capacitors to provide appropriate tuning for the circuit for such a coupling factor. The same calculations can also be used to select appropriate coefficients for the friendly metal loss estimation model.

[0066] Figure 4 A flowchart illustrating the friendly metal loss estimation technique 440 is shown. Beginning at block 441, the FOD system can measure observable parameters of the wireless power transfer system. These measurements can be performed by the PTx 110 if the PTx 110 implements the FOD system, or by the PRx 120 if the PRx 120 implements the FOD system. These observable parameters can include wireless power transfer voltage, current, phase shift, frequency, impedance, etc., as well as parameters that can be derived therefrom, such as power consumption, efficiency, coupling coefficient, etc. As noted above, a device implementing the FOD system can perform these measurements using appropriate sensors in conjunction with the device's control circuit.

[0067] In block 442b, the FOD system implemented by the PTx 110 can receive the friendly metal parameters from the PRx 120 (block 442a). If the FOD system is implemented by the PRx 120, the situation can be reversed. The communication can be made using in-band or out-of-band communication, as described above. The transmitted friendly metal parameters can include model coefficients as described above, including model parameters related to current, voltage, and coupling factor. In one embodiment, the PRx can transmit a list of parameters including current and voltage parameters for a first coupling coefficient and current and voltage parameters for a second coupling coefficient. For wireless power transfer systems that can operate at different power transfer frequencies, it can be appropriate to include different parameters for different operating frequencies. In some applications, the communication can be made according to a predetermined industry standard, such as the Qi standard for wireless power transfer / charging published by the Wireless Power Consortium organization.

[0068] In block 443, the FOD system can estimate the friendly metal loss according to the observable values obtained in block 441 and the parameters received from the opposite end device. The FOD system can also have its own associated friendly metal loss modeling parameters, which can correspond to different coupling factors and / or operating frequencies of the received friendly metal loss modeling parameters from the opposite end device. Then, in block 444, the estimated friendly metal loss can be provided to the FOD system, such as described above with respect to Figure 3 the system for foreign object detection described.

[0069] Described below is an improved MPP power loss accounting (MPLA) technique that can be used to further improve the accuracy of the expected loss estimate. The MPLA as defined in the Qi v2.0 specification makes assumptions for the modeling of the friendly metal loss (P FM ) in a wireless power system. To improve accuracy, a new model for the friendly metal loss is proposed to account for the variations in the rectified voltage and current.

[0070] Further friendly metal loss discussion

[0071] The MPLA power loss estimate starts by estimating the power delivered to the foreign object by estimating the difference between the power transmitted by the wireless power transmitter and the power received by the wireless power receiver. In at least some embodiments, this comparison can be performed by controller circuitry located in the wireless power transmitter, but in some embodiments it can be performed by controller circuitry located in the wireless power receiver. In either case, the comparison can be represented by the following equation:

[0072] P FO = P PT -P PR

[0073] (P FO: Equation 1) where P FO is the power dissipated in foreign objects, P PT is the power transmitted by the wireless power transmitter, and P PR is the power received by the wireless power receiver. Further, the power transmitted by the wireless power transmitter can be represented as:

[0074] P PT = V IN I IN - P circuit loss,TX - P coil loss,TX - P FM loss

[0075] (p pt : Equation 2) where V IN and I IN are the input voltage and current of the inverter of the wireless power transmitter, P circuit loss,TX represents circuit losses associated with the wireless power transmitter circuit, P coil loss,TX represents losses associated with the wireless power transfer coil of the wireless power transmitter, and P FM loss represents losses associated with the friendly metal of the wireless power transmitter. As described above, the "friendly metal" is the metal or other conductive structure associated with the wireless power transmitter and receiver device itself, such as a housing, internal structure, etc. Similarly, the power received by the wireless power receiver can be represented as:

[0076] P PR = V RECT I RECT + P circuit loss,RX + R coil loss,RX

[0077] (P PR : Equation 3) where V RECT and I RECT are the output voltage and current of the rectifier of the wireless power receiver, P circuit loss,RX represents circuit losses associated with the wireless power receiver circuit, P coil loss,RX represents losses associated with the wireless power transfer coil of the wireless power receiver.

[0078] In some applications, various improvements to wireless power transfer can be achieved by varying the rectifier voltage VRECT, i.e., the output voltage of the rectifier 124 in the wireless power receiver. (See, e.g., 124; Figure 1 ). In such cases, it can be desirable to extend the friendly metal loss term P FM loss to account for the variability of the voltage and current of the rectification (V RECT and I RECT ). For example, the friendly metal loss can be represented as:

[0079]

[0080] where g FM,ITX , g FM,IRECT , and g FM,VRECT are ecosystem scaling terms (such as described in more detail below), and a FM,ITX , a FM,IRECT , and a FM,VRECT are coefficients related to circuit and magnetic circuit parameters (physical and / or equivalent) characterizing the wireless power transfer system. Such coefficients can be described in a variety of ways, some of which are described in more detail herein. More generally, the friendly metal loss can be modeled in the form:

[0081]

[0082] where P FM is the estimated friendly metal loss, I TX is the DC current at the input of the inverter of the wireless power transmitter, I RECT is the DC current at the output of the rectifier of the wireless power receiver, and V RECT is the DC output voltage of the rectifier of the wireless power receiver, where a, b, and c are fitting coefficients characterizing a particular wireless power transfer system. The model described above does not require a DC bias term as in some existing power loss accounting techniques.

[0083] Figure 5A and Figure 5B illustrates the derivation of the model described above. More specifically, Figure 5A depicts an equivalent circuit 500 that can be used to model a wireless power transfer system. In the equivalent circuit 500, the inverter input voltage is represented by a voltage source Vin, and the load on the wireless power receiver is represented by a resistor R L . The wireless power transmitter current i TX flows through: a capacitor C TX representing the tuning capacitor of the wireless power transmitter; a resistor R CONN_TX representing the conduction losses associated with the wireless power transmitter circuit; a resistor R COIL_TX representing the losses in the wireless power transfer coil of the wireless power transmitter; a resistor R FM_TX representing the friendly metal losses associated with the metal or other conductive structures in the wireless power transmitter; and an inductance L TX_LK representing the leakage inductance of the wireless power transfer coil of the wireless power transmitter. The wireless power transmitter current i TX can then be modeled as being split into a magnetization current i M and a receiver current iRX magnetization current i M flowing through inductance L M and resistance R M representing the magnetization effect of the wireless power transfer coil. Receiver current i RX flowing through: inductance L RX_LK representing the leakage inductance of the wireless power transfer coil of the wireless power receiver; R FM_RX representing the friendly metal loss associated with metal or other conductive structures in the wireless power receiver; R COIL_RX representing losses in the wireless power transfer coil of the wireless power receiver; resistance R CONN_RX representing conduction losses associated with the wireless power receiver circuit; and capacitance C RX representing the tuning capacitance of the wireless power receiver. The circuit elements described above can represent such devices and / or can be lumped parameters representing or modeling multiple physical components or structures, rather than specific physical devices.

[0084] Further reference to Figure 5A Equation 501 describes the interrelationships between the various circuit elements and parameters of the equivalent circuit model 500. These equations can be combined to produce equation 502. Then, further reference to Figure 5B These equations can be further manipulated to produce equation 503, which represents losses in terms of and similar to the form of equations 4 and 5 above.

[0085] Although the above description models friendly metal losses in terms of transmitter current squared receiver rectifier voltage squared and receiver rectifier current squared such losses can be modeled in other ways based on other orders of such variables, such as transmitter current (I TX ), rectifier voltage (V RECT ), and rectifier current (I RECT ), and / or can be modeled in conjunction with other voltages, currents, or other circuit parameters.

[0086] In Applicant’s co-pending U.S. Patent Application No. 18 / 617,103, filed March 26, 2024, entitled “Power Transfer Accounting for Wireless Power Transfer,” described in terms of rectifier voltage V RECT and rectifier current I RECTThe patent application is incorporated by reference in its entirety for the additional aspects of power loss accounting (including loss attributable to friendly metal).

[0087] Ecosystem scaling

[0088] The accuracy of friendly metal loss estimation can vary depending on different possible wireless power transmitter and wireless power receiver pairings. In some implementations, for example, at the time of manufacture, baseline values and / or adjustments (e.g., such as scaling factors, offsets, etc.) can be determined for various pairs of wireless power transmitters and wireless power receivers and stored in one or more of the wireless power transmitter and receiver devices. However, as the number of potential transmitter-receiver pairs becomes larger, this can quickly become infeasible. Thus, it can be desirable to provide one or more baseline values pairs for each transmitter based on one or more “reference” or “golden” receiver pairings. Each receiver can then be characterized relative to one or more of the reference / golden receivers, and each receiver can be provided with its own stored value corresponding to such characterization. For example, this can be implemented as various scaling factors relative to the reference / golden receivers. The wireless power receiver can then provide its scaling factor to the wireless power transmitter, which can then adjust its friendly metal estimation based on the stored reference value and the scaling factor, which accounts for differences in the magnetic parameters of the particular wireless power transfer devices (such as the inductance (L) of the wireless power transfer coils, the quality factor (Q) of the coils, etc.).

[0089] Example techniques for loss measurement scaling are described in Applicant’s U.S. Patent Application 17 / 681,363, entitled “Wireless Power Systems with Shared Inducive Loss Scaling Factors,” filed February 25, 2022, the teachings of which are reproduced below in their entirety, which is incorporated by reference herein in its entirety.

[0090] To accurately estimate power loss values, various potential sources of power loss in a wireless power system should be considered. Some power losses exhibited by a power transmitter and a power receiver are independent of the magnetic properties of the transmitter and receiver (e.g., switching losses, losses dependent on the drain-source resistance of field effect transistors in inverters and rectifiers, etc.). Losses such as these can be accounted for by characterizing the relevant device components (e.g., by determining transistor drain-source resistance using measurements made during manufacturing testing and / or other testing).

[0091] Transmitters and receivers also exhibit power losses that depend on the inductive properties of the transmitter and receiver (e.g., losses that depend on the magnetic properties of the coupled transmitter and receiver, sometimes referred to as matching dependent losses, inductive losses, magnetic losses, etc.). Examples of power losses that depend on the magnetic properties of the transmitter and receiver include: 1) coil losses that depend on the alternating current (AC) resistance of the matched transfer coil, 2) friendly metal losses (e.g., power losses due to eddy currents induced in the metal casing of the receiving device), and 3) foreign object losses that occur in the presence of foreign objects between the transmitter and receiver. These power losses, such as those that depend on the magnetic properties of the transmitter and receiver, can sometimes be characterized in terms of the LQK magnetic parameters, where L refers to the inductance of the transfer coil, Q refers to the quality factor of the coil, and K refers to the magnetic coupling of the coil.

[0092] In a wireless power ecosystem with numerous different transmitters and receivers, each pairing between a given one of the transmitters and a given one of the receivers will result in a potentially different set of magnetic properties, thereby challenging accurate assessment of power losses that depend on the magnetic properties of the coupled transmitter-receiver pair. To facilitate accurate transmitter and receiver power loss estimation, various models of the transmitter and receiver can be used with measurements between the transmitter and receiver and a reference unit (e.g., a reference transmitter and a reference receiver) to determine magnetic power loss parameters associated with the transmitter and receiver. Characteristic information from measurements by the reference transmitter and / or the reference receiver can be stored in each different model of the device and subsequently used to help ensure accurate power loss estimation when a particular transmitter model is paired with a particular receiver model.

[0093] Figure 6 Exemplary wireless power circuitry in a wireless power transfer system 608 in an illustrative scenario in which a wireless power transmitting device has been paired with a wireless power receiving device is shown. In some examples, the system 608 implements the wireless power circuitry of the wireless power transfer system 100 discussed above with reference to FIG. 1. Figure 1 The design of the wireless power transfer system 100 discussed above with reference to FIG. 1 is discussed. Figure 6 The wireless power circuitry of the wireless power transfer system 100 discussed above with reference to FIG. 1 includes wireless power transmitting circuitry 652 in a wireless power transmitting device 612 and wireless power receiving circuitry 654 in a wireless power receiving device 624. During operation, a wireless power signal 644 is transmitted by the wireless power transmitting circuitry 652 and received by the wireless power receiving circuitry 654. Figure 6 The configuration of the wireless power transfer system 100 discussed above with reference to FIG. 1 includes a single transfer coil 636 and a single transfer coil 648 (as an example). In other implementations, the voltage across the measurement capacitor 670 is measured and the current through the coil is inferred from the measurement.

[0094] As discussed above with reference to FIG. 1, the wireless power transfer system 100 includes a wireless power transmitting device 612 and a wireless power receiving device 624. Figure 6As shown, the wireless power transmit circuit 652 includes an inverter circuit 661. The inverter circuit (inverter) 661 can be used to provide a signal to the coil 636. During wireless power transmission, the control circuit of the device 612 provides a signal to a control input 682 of the inverter 661 that causes the inverter 661 to provide an alternating drive signal to the coil 636. As Figure 6 As shown, a circuit component such as a capacitor 670 can be coupled in series with the coil 636. A measurement circuit 641 in the device 612 can make measurements of operating current and voltage in the device 612. For example, a voltage sensor 641A can be used to measure the coil voltage across the coil 636, and a current sensor 641B can be used to measure the coil current through the coil 636.

[0095] When an alternating current signal is supplied to the coil 636, a corresponding alternating electromagnetic signal (wireless power signal 644) is transmitted to a nearby coil, such as the exemplary coil 648 in the wireless power receive circuit 654. This induces a corresponding alternating (AC) current signal in the coil 648. A capacitor such as the capacitor 672 can be coupled in series with the coil 648. The rectifier 650 receives the AC current from the coil 648 and produces a corresponding direct current power (e.g., a direct voltage Vrect) at an output terminal 676. This power can be used to power a load. A measurement circuit 643 in the device 624 can make measurements of operating current and voltage in the device 624. For example, a voltage sensor 643A can measure Vrect (the output voltage of the rectifier 650), or a voltage sensor can measure the coil voltage across the coil 648. A current sensor 643B can measure the rectifier output current of the rectifier 650, or a current sensor can measure the current of the coil 648.

[0096] The measurements made by the measurement circuits 641 and 643 can be processed to extract magnetic loss properties (e.g., coefficients or other parameters that characterize the amount of power loss in the devices 612 and 624 and that depend on the magnetic properties of the transmitter and receiver). These measurements can be stored within each device and can be exchanged between devices, so that the device 612 (and, if desired, the device 624) can use this information to accurately estimate the operating conditions of the wireless power transfer system. power loss.

[0097] For example, these measurements can be used to estimate how well the transmitter and receiver are able to transfer wireless power, and thus estimate whether to inform the user that the wireless power transfer operation is proceeding normally. As another example, these measurements can be used to estimate the magnetic coupling coefficient k, the wireless power transfer efficiency, the estimated power loss, and / or other properties of the matched transmitter-receiver pair. As an addition or alternative to estimating the power loss to determine whether a foreign object is present and thus whether to continue the wireless power transfer, the system 608 can use this information (e.g., the estimated foreign object power loss and / or related coupling and / or efficiency information) to determine whether to present a confirmation message to the user of the system 608 to inform the user that the wireless power transfer is proceeding properly (e.g., to inform the user that this process has not been impeded by the presence of a poor coupling due to the presence of a foreign object, possible misalignment, or other factors). Exemplary confirmation messages include audio outputs, such as a chime presented on the device 624 and / or visual outputs to reassure the user that the charging operation is proceeding normally.

[0098] Consider an example in which the following equations are used to determine the amount of power potentially absorbed by a foreign object in the system 10 after measurements are made with the circuits 641 and 643:

[0099] PFO = PIN - POUT - PLOSSTX - PLOSSRX

[0100] (PFO: Equation 6)

[0101] In Equation 6, PFO represents the amount of power absorbed by a present foreign object, if any. POUT represents the output power (e.g., the output power of the rectifier 650), PIN represents the input power (e.g., the input power to the coil 636), PLOSSTX represents the power loss attributable to the PTx wireless power transmitter 612, and PLOSSRX represents the power loss attributable to the wireless power receiver 624. The values of POUT and PIN can be measured (e.g., using the circuits 641 and 643). As discussed above with reference to Equations 2 and 3, the power loss attributable to the devices 612 and / or 624 can include losses to friendly metals. Mathematical models can be used to produce relational expressions for PLOSSTX and PLOSSRX, and these expressions can be evaluated using measured operating parameters, such as measurements made using the circuits 641 and 643. For example, for one illustrative modeling implementation, PLOSSTX and PLOSSRX can be calculated using Equations 7a and 8a, respectively.

[0102] PLOSSTX = b * RAIRTX * (ITX) 2

[0103] (PLOSSTX: Equation 7a)

[0104] PLOSSRX = m * RAIRRX * (IRX) 2 + a * (IRX) 2 + aDC

[0105] (PLOSSRX: Equation 8a)

[0106] In Equations 7a and 8a, ITX represents the transmitter current (e.g., coil current) and IRX represents the receiver current (e.g., rectifier output current, or in some implementations, the transfer coil current). The values of RAIRTX and RAIRRX represent the measured AC coil resistance of coils 636 and 648, respectively. The values of b, m, a, and aDC are model parameters (sometimes referred to as magnetic power loss coefficients) that characterize the performance of the coupled transmitter and receiver pair in system 608. In this example, transmitter power loss PLOSSTX is due to transfer coil power loss in the model of Equation 7a, and receiver power loss PLOSSRX has a first component due to transfer coil power loss (the first term of Equation 8a), and has a second component (consisting of the last two terms in Equation 8a) that represents friendly metal losses (e.g., losses due to eddy currents induced in the receiver while power is being transferred). Parameter b can sometimes be referred to as a transmitter transfer coil loss parameter or coefficient. Parameter m can sometimes be referred to as a receiver transfer coil loss parameter or coefficient, and parameters a and aDC can sometimes be referred to as friendly metal loss parameters or friendly metal loss coefficients. Parameters b, m, a, and aDC depend on the magnetic interaction between devices 612 and 624 when coupled, and can therefore sometimes be referred to as magnetic loss parameters or magnetic loss coefficients.

[0107] In an ecosystem in which there are multiple different models of wireless power transmitting devices available to a user (e.g., different models of device 612) and multiple different models of wireless power receiving devices available to a user (e.g., different models of device 624), the magnetic loss parameters will vary depending on which particular transmitter and receiver are paired together. For example, if a model I transmitter is paired with a model J receiver, the amount of power loss in each device will be different than the amount of power loss experienced when those devices are paired with different devices. To account for these variations, Equations 7a and 8a can be replaced by Equations 7b and 8b, respectively.

[0108] PLOSSTX = gb * bR * RAIRTX * (ITX) 2

[0109] (PLOSSTX: Equation 7b)

[0110] PLOSSRX = gm * mR * RAIRRX * (IRX) 2+ g a * a R * (IRX) 2 + g a * a R * (IRX)

[0111] (PLOSS RX : Equation 8b)

[0112] In Equation 7b, the transmitter transfer coil loss parameter b is replaced by a reference transmitter transfer coil loss value bR (sometimes referred to as a transmitter transfer coil loss coefficient) that is associated with the transmitter loss measured when the reference transmitter is coupled to the reference receiver, and then scaled using a scaling factor gb. In Equation 8b, the receiver transfer coil loss parameter m is replaced by mR (sometimes referred to as a receiver transfer coil loss coefficient) that is associated with the receiver transfer coil loss measured when the reference receiver and reference transmitter are coupled, and then scaled using a scaling factor gm. In Equation 8b, the friendly metal loss parameters a and aDC are replaced by reference friendly metal loss parameters (coefficients) aR and aRDC, respectively, that are extracted using measurements made with the reference transmitter and reference receiver. The reference friendly metal loss parameters are scaled by the respective scaling factors g a and g aDC. By using the scaling factors in the calculation of PLOSSTX (see, e.g., Equation 7b) and PLOSSRX (see, e.g., Equation 8b), Equation 6 can be evaluated satisfactorily across various permutations of pairs of wireless power transmitter and receiver models.

[0113] In Figure 7 the flowchart in FIG. 8 illustrates exemplary operations involved in using a measurement wireless power transmitter and receiver to determine their scaling parameters. The operations in Figure 7 are performed at design time, and the resulting scaling factors are stored in the production unit. The operations in Figure 8 are performed at run time (e.g., when a transmitter is paired with a receiver in preparation for transmitting wireless power between the transmitter and receiver). The operations in Figure 8 are performed at run time (e.g., when a transmitter is paired with a receiver in preparation for transmitting wireless power between the transmitter and receiver). The operations in Figure 7 and Figure 8 In the example of FIGS. 7 and 8, it is assumed that the scaling factors for a particular transmitter model (Model I transmitter) and a particular receiver model (e.g., Model J receiver) are obtained using reference device measurements, and subsequently used when a Model I transmitter is paired with a Model J receiver. In general, it is desirable to perform this process for numerous transmitter models (models other than Model I) and numerous receiver models (models other than Model J). Furthermore, a user can typically pair any of the various different transmitter models that have been characterized with any of the various different receiver models that have been characterized. This is because not all users own the same transmitter model and not all users own the same receiver model. In this example, an exemplary user has a Model I transmitter and a Model J receiver. Figure 8 pairing a model I transmitter with a model J receiver during operation.

[0114] In Figure 7 The operations involved in measuring the magnetic power loss parameter scaling factors for a model I transmitter and a model J receiver are shown in FIG. 8. During operation of block 790, a reference wireless power receiving device is paired with a reference wireless power transmitting device (either physically or via a simulation pairing, such as a finite element analysis simulation pairing). The physical reference devices can be obtained from a centralized source or can be constructed by different device manufacturers according to a common distributed reference design. Once paired, the reference transmitter and reference receiver can begin transferring power. Specifically, during operation of block 790, the reference transmitter can transmit a wireless power signal to the reference receiver while measuring and storing internal operating parameters (e.g., transmitter and receiver currents and voltages). From these measurements, the reference magnetic loss parameters are extracted (e.g., values for the reference magnetic loss parameters bR, mR, aR, and aRDC are obtained). In scenarios where a simulation pairing is used instead of measurements on physical paired devices, finite element analysis simulations are used to determine the LQK of the coupled transmitter-receiver pair, and then circuit simulations are used to determine the expected currents and voltages. These simulated currents and voltages can then be used to determine the magnetic loss parameters.

[0115] After the reference magnetic loss parameters have been determined (either through physical measurements or simulations), a model J receiver is paired with the reference transmitter. When these devices are paired in simulation or when these devices are physically paired and wireless power is being transferred from the reference transmitter to the model J receiver, loss parameter measurements for the model J receiver can be obtained. Specifically, during operation of block 792, the model J loss parameters (coefficients) bRj, mRj, aRj, and aRjDC are obtained. The “J” in each of these parameters and the R (for “reference”) in each of these parameters indicates that the loss parameters are specific to scenarios where the model J receiver is operating with the reference transmitter. The scaling factor gb (Equation 7b) for the model J receiver can then be calculated using Equation 9 and stored in the model J wireless power receiving device (e.g., during manufacturing or later using an update).

[0116] gb = bRj / bR

[0117] (gb: Equation 9)

[0118] During operation of block 794, a model I transmitter is paired with the reference receiver. Power is transmitted wirelessly while transmitter operating parameters (e.g., currents and voltages) are measured. From these measurements or simulations, the magnetic loss parameters miR, biR, aiiR, and aiiRDC for the model I transmitter are obtained. Using Equations 10, 11, and 12, the scaling factors gm, g, and g for the model I transmitter can then be calculated.

[0119] gm= miR / mR

[0120] (gm: Equation 10)

[0121] ga= aiR / aR

[0122] (ga: Equation 11)

[0123] gaDC= aiRDC / aRDC

[0124] (gaDC: Equation 12)

[0125] The scaling factors of the Model I transmitter are then stored in the Model I transmitter (e.g., during manufacturing or later using an update).

[0126] In the flowchart of FIG. 8, exemplary operations involved in using the scaling factors of the Model I transmitter and Model J receiver in a scenario in which a user pairs the Model I transmitter and Model J receiver are shown. In the operations of FIG. 8, a user with a Model J receiver and Model I transmitter who wishes to wirelessly transfer power from the Model I transmitter to the Model J receiver pairs the Model I transmitter and Model J receiver during the operations of block 800 (e.g., by magnetically attaching the Model I charging puck to the Model J cell phone, as just one example). Figure 8 Figure 8 During the operations of block 802, the Model I transmitter and Model J receiver exchange information such as their scaling factors (e.g., using low power in-band communication or other wireless communication) and will transfer power. For example, the Model J receiver sends to the Model I transmitter the value of the scaling factor gmobtained from the Model J measurements made with the reference transmitter at block 792 of FIG. 7. The Model I transmitter communicates to the Model J receiver the values of the scaling factors gm, ga, and gaDCobtained from the Model I measurements made with the reference receiver at block 794 of FIG. 7.

[0127] During the operations of block 802, the Model I transmitter and Model J receiver exchange information such as their scaling factors (e.g., using low power in-band communication or other wireless communication) and will transfer power. For example, the Model J receiver sends to the Model I transmitter the value of the scaling factor gmobtained from the Model J measurements made with the reference transmitter at block 792 of FIG. 7. The Model I transmitter communicates to the Model J receiver the values of the scaling factors gm, ga, and gaDCobtained from the Model I measurements made with the reference receiver at block 794 of FIG. 7. Figure 7 Figure 7 During the operations of block 802, the Model I transmitter and Model J receiver exchange information such as their scaling factors (e.g., using low power in-band communication or other wireless communication) and will transfer power. For example, the Model J receiver sends to the Model I transmitter the value of the scaling factor gmobtained from the Model J measurements made with the reference transmitter at block 792 of FIG. 7. The Model I transmitter communicates to the Model J receiver the values of the scaling factors gm, ga, and gaDCobtained from the Model I measurements made with the reference receiver at block 794 of FIG. 7.

[0128] When wirelessly transferring power from the Model I transmitter to the Model J receiver, the measurement circuit 641 in the transmitter and the measurement circuit 643 in the receiver can measure operating parameters of the transmitter and receiver (e.g., coil currents and voltages, rectifier output voltages and currents, etc.). If desired, current and voltage measurements can be exchanged between the transmitter and receiver (e.g., using in-band wireless communication). The information measured by the circuits 641 and 643 can be used in conjunction with the exchanged scaling factors to calculate PLOSSRXand PLOSSTXusing Equations 7b and 8b.

[0129] ​​For example, during operation of block 804, model J receiver can measure rectifier current and rectifier voltage (the product of which is POUT), and can use the measurements in conjunction with the scaling factors gm, ga, and gaDC received from model I transmitter during operation of block 802 to evaluate equation 8b and thereby estimate PLOSSRX. The scaling factors received from model I transmitter provide model J receiver with information about the expected operating characteristics of model I transmitter with respect to receiver transfer coil losses and friendly metal losses.

[0130] As one example, consider receiver transfer coil losses. If receiver J were to pair with the reference transmitter, the value of the scaling factor gm would be 1.0. The receiver could then use the first term in equation 8b to determine receiver transfer coil losses (1.0 * mR * RAIRRX * (IRX)2), where the values of mR, RAIRRX, and receiver current IRX are known for the receiver. However, in the current case, receiver J is not pairing with the reference transmitter, but rather with transmitter I. It can have previously been determined that transmitter I causes lower coil losses in a matching receiver compared to the reference transmitter, so the value of gm that transmitter I communicates to model J receiver during block 802 can be 0.9 (as an example). When model J receiver evaluates equation 8b using the scaling factor value of 0.9 received from model I transmitter, model J receiver will accurately estimate a slightly reduced value of PLOSSRX (due to the presence of model I transmitter, which is known to cause a lesser amount of receiver transfer coil losses compared to the reference transmitter). As this example demonstrates, by using the scaling factors received from model I transmitter, the magnetic loss parameters that the receiver uses to calculate PLOSSRX can be appropriately scaled to reflect the presence of model I transmitter instead of the reference transmitter, thereby enhancing the accuracy of the value of PLOSSRX that is estimated.

[0131] During operation of block 806, model I transmitter uses the measured value of transmitter transfer coil current ITX, the known values of bR and RAIRTX, and the scaling factor gb received from the receiver to evaluate equation 7b to estimate PLOSSTX. The scaling factor gb is a reflection of how the receiver of model J is expected to affect transmitter transfer coil losses in a transmitter that is paired with model J receiver instead of the reference receiver. As one example, model J receiver can tend to cause a paired transmitter to exhibit more transmitter transfer coil losses compared to the reference receiver. Thus, the value of the scaling factor gb that model I transmitter receives from model J receiver can be 1.1 (as an example). This increased scaling factor will help transmitter I account for the fact that model I transmitter is coupled to model J receiver when evaluating equation 7b, and thus should expect greater transmitter transfer coil losses than when coupled to the reference receiver.

[0132] During operation of block 807, the PLOSSRX value calculated at block 804 can be transmitted to the paired transmitter. During operation of block 808, the system 608 evaluates the value of PFO (e.g., estimates the foreign object power loss, if any) using Equation 6. By using the scaling factor information received from the model J receiver to accurately estimate PLOSSTX and by receiving an estimate of PLOSSRX from the model J receiver, the model I transmitter will have both PLOSSTX and PLOSSRX for Equation 6. The transmitter can obtain the value of PIN by calculating the product of the transmitter transfer coil current (ITX) and the voltage from the measurement circuit 641. The transmitter can obtain the value of POUT by calculating the product of the rectifier output current IRX and the rectifier output voltage received from the measurement circuit 643 or by receiving POUT from the receiver.

[0133] After determining the value of PFO during operation of block 808, the transmitter can compare PFO to a threshold power loss value (TH) (block 810). Appropriate actions can then be taken by the system 608. For example, in response to determining that PFO is less than TH, it can be inferred that no foreign object is present and that the power transfer operation can proceed normally (e.g., so that power can be transferred to charge the battery 658). In response to determining that PFO is greater than TH, the power transfer operation can be limited. Examples of power transfer limitations that can be implemented include abandoning all power transfer operations and / or suspending power transfer if already underway, limiting the maximum amount of power that can be transferred (e.g., to a predetermined relatively low power level that is lower than the normal maximum power transfer capability of the system 608), and / or issuing a visual, audible, and / or vibratory alert to the user. If desired, the alert (e.g., a warning and / or other information content that informs the user that the power transfer operation is not proceeding normally because a foreign object has been detected) can be presented to the user using an output device in the device 612 and / or in the device 624. For example, the control circuit in the device 612 can wirelessly communicate with the control circuit in the device 624 to issue a visual alert that is presented on a display in the device 624.

[0134] Further ecosystem scaling discussions

[0135] In an ecosystem in which there are multiple different models of wireless power transmitting devices and multiple different models of wireless power receiving devices available to a user (e.g., different models of either device), the electrical and / or magnetic loss parameters can vary depending on which particular wireless power transmitter and wireless power receiver are paired together. For example, if a model I transmitter is paired with a model J receiver, the amount of power loss in each device will be different than the amount of power loss experienced when these devices are paired with different devices.

[0136] To account for these variations and thereby ensure accurate estimates of friendly metal, foreign object, and / or other power losses, electrical and magnetic power loss parameter scaling factors (sometimes referred to as power loss coefficient scaling factors) may be used. By using such scaling factors when calculating the various parameters, the loss equations may be satisfactorily evaluated regardless of which models of the transmitter and receiver are paired with each other. The example of such scaling parameters between various wireless power transfer devices may be considered to provide "ecosystem scaling" because it expands the "ecosystem" of devices that may collaborate to provide wireless power transfer and foreign object detection. This ecosystem scaling may be extended to the context-friendly metal loss estimation described above.

[0137] Techniques for performing ecosystem scaling to generate friendly metal loss estimates may include Figure 9 From the various aspects described in Figure 9 Starting with FIG901 of FIG901 , on the wireless power transmitter (PTx) side, various gain factors g may be calculated for various parameters based on the pairing between a “golden” or “reference” wireless power transmitter GTx and a “golden” or “reference” wireless power receiver GRx and an actual wireless power transmitter PTx and an actual wireless power receiver PRx. More specifically, a scaling or proportional factor (a) may be used to scale the measured GG, as between the golden or reference transmitter GTx and the golden or reference receiver GRx, to correspond to the measured GR, as between the golden transmitter GTx and the actual receiver PRx. Similarly, a scaling or proportional factor (b) may be used to scale the measured TR, as between the actual wireless power transmitter PTx and the actual wireless power receiver PRx, to the measured TR, as between the actual power transmitter PTx and the golden wireless power receiver GRx. Thus, as depicted in the equation below FIG901 , the gain factor g associated with the wireless power transmitter transfer coil g is coil,TX The associated gain may be calculated as a value that may be stored on the wireless power transmitter.

[0138] like Figure 9scaling can similarly be performed for the wireless power receiver. More specifically, various gain factors g can be computed for various parameters based on the pairing between the "golden" or "reference" wireless power transmitter GTx and the "golden" or "reference" wireless power receiver GRx and the actual wireless power transmitter PTx and the actual wireless power receiver PRx. More specifically, a scaling or proportionality factor (a) can be used to scale the measurements as between the golden or reference transmitter GTx and the golden or reference receiver GRx, so as to correspond to the measurements as between the golden receiver GRx and the actual transmitter PTx. Similarly, a scaling or proportionality factor (b) can be used to scale the measurements as between the actual wireless power transmitter PTx and the actual wireless power receiver PRx to the measurements as between the actual power receiver PRx and the golden wireless power transmitter GTx. Thus, as depicted in the equations below the diagram 902, the relevant gains for the wireless power receiver transfer coil g coil,RX The relevant gains can be computed as values that can be provided to the wireless power receiver and / or can be stored on the wireless power transmitter. Similarly, the gain parameters for ecosystem scaling can be computed based on the transmitter current (g FM,ITX ), the rectifier current (g FM,IRECT ), and the rectifier voltage (g FM,VRECT ) similarly to the coefficients described above related to the friendly metal loss estimation. These gain parameters for ecosystem scaling can be computed by the wireless power transmitter and retained on the wireless power transmitter, but in some embodiments they can also be computed by and / or provided to the wireless power receiver.

[0139] Figure 10 A table 1000 is illustrated that depicts some combinations of the monitorable parameters that can be used for friendly metal loss estimation in a wireless power transfer system. The parameters that can be used can include the DC modeling parameter (DC), the transmitter current (square) ITX 2 , the rectifier current (square) IRECT 2 , the inverter input voltage (Vin), and the rectifier voltage (square) VRECT 2 . The above description focuses on the use of the combination of the transmitter current square, the rectifier current square, and the rectifier voltage square, as depicted in row 1041 of the table 1000. However, the inventors have experimented with models that incorporate two to four of the variables in various combinations, as depicted in rows 1042 through 1051, and have observed different accuracies of the various models depending on the particular implementation. Thus, for a given implementation, it can be desirable to employ one or more models that incorporate different combinations of such variables that are appropriate for the given application. In any case, a model equation can be selected, and the corresponding coefficients can be fitted based on power transfer measurements as described above and in the incorporated applications.

[0140] The various features and implementations described above relating to improving friendly metal loss estimation to improve wireless power transfer in a wireless power transfer system. Such arrangements can be used in a variety of applications, but can be particularly advantageous when used in conjunction with electronic devices such as mobile phones, tablets, laptop or notebook computers, and accessories such as wireless headsets, styluses, etc. In addition, although a number of specific features and various implementations have been described, it should be understood that the various features and implementations can be arranged in various permutations and combinations in a particular implementation, unless otherwise stated as mutually exclusive. Thus, the various implementations described above are provided merely as illustrative examples and should not be construed as limiting the scope of the disclosure. Various modifications and changes can be made to the principles and implementations described herein without departing from the scope of the disclosure and without departing from the scope of the claims.

[0141] The example implementations of a wireless power transfer system described above are capable of sending certain information between the PTx and PRx in the system. The disclosure contemplates that such transfer of 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 ecosystem scaling parameters of the devices with each other. Entities implementing the technology should note that the extent to which any sensitive information is used in a particular implementation depends on the nature of the information, that this disclosure is not, in any way, authorizing the commission of any acts of privacy violation, and that appropriate precautions should be taken to ensure compliance with established privacy policies and / or privacy practices. In particular, it would be desirable for such entities to implement and consistently apply privacy practices generally recognized to satisfy or exceed privacy requirements imposed by industry or government to maintain user privacy. Implementers should inform users where in the wireless power transfer system personally identifiable information is expected to be sent and allow users to “opt in” or “opt out” of participation. For example, if a power transmitter is configured to poll for sensitive information from a power receiver, such information can be presented to the user when the user places the device on the power transmitter.

Claims

1. A wireless power transmitter comprising: a wireless power transfer coil configured to magnetically couple to a wireless power transfer coil of a 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 transfer coil; and a controller and communication circuit coupled to the inverter and the wireless power transfer coil, the controller and communication circuit controlling the inverter to regulate wireless power transfer to the wireless power receiver, wherein the controller and communication circuit estimate a friendly metal loss associated with wireless power transfer to the wireless power receiver by: receiving, from the wireless power receiver, an indication of received power including a rectifier voltage and a rectifier current of the wireless power receiver associated with the wireless power transfer; calculating a friendly metal power loss based on the received rectifier voltage and the received 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 using the friendly metal power loss to regulate wireless power transfer to the wireless power receiver.

2. The wireless power transmitter of claim 1, wherein the rectifier voltage is a rectifier output voltage and the rectifier current is a rectifier output current.

3. The wireless power transmitter of claim 1, wherein the controller and communication circuit derive the one or more coefficients corresponding to the baseline wireless power transmission between the wireless power transmitter and the wireless power receiver by: performing a regression analysis to calculate the one or more coefficients on a plurality of received indications of received power including a corresponding rectifier voltage and rectifier current of another wireless power receiver associated with another wireless power transfer or a received power derived therefrom and a plurality of measured power loss values determined therefrom.

4. The wireless power transmitter of claim 3, wherein the one or more coefficients include a first coefficient related to the rectifier current and a second coefficient related to the rectifier voltage.

5. The wireless power transmitter of claim 4, wherein calculating the friendly metal power loss uses an equation having a form of:

6. The wireless power transmitter of claim 5, wherein the controller and communication circuit further estimate the friendly metal loss by receiving, from the wireless power receiver, one or more power loss scaling factors and calculating the friendly metal power loss in response to the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and an actual wireless power transmitter or an actual wireless power receiver. ​ where b is the first coefficient related to the rectifier current, c is the second coefficient related to the rectifier voltage, a is a coefficient related to the transmitter current, and I TX is the transmitter current. ​ 7. The wireless power transmitter of claim 1, wherein the friendly metal power loss is calculated using an equation having the form: where b is a first coefficient related to the rectifier current, c is a second coefficient related to the rectifier voltage, a is a coefficient related to the transmitter current, and I TX is the transmitter current.

8. The wireless power transmitter of claim 7, wherein the controller and communication circuitry further estimates the friendly metal loss by receiving one or more power loss scaling factors from the wireless power receiver and calculating the friendly metal power loss in response to the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or reference wireless power receiver and an actual wireless power transmitter or actual wireless power receiver.

9. The wireless power transmitter of claim 1, wherein the controller and communication circuitry further estimates the friendly metal loss by receiving one or more power loss scaling factors from the wireless power receiver and calculating the friendly metal power loss in response to the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or reference wireless power receiver and an actual wireless power transmitter or actual wireless power receiver.

10. A method performed by control circuitry of a wireless power transmitter or wireless power receiver for estimating a friendly metal loss associated with wireless power transfer from the wireless power transmitter to a wireless power receiver, the method comprising: obtaining an indication of received power including a rectifier voltage and a rectifier current of the wireless power receiver; and calculating a friendly metal power loss based on the indication of 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 using the friendly metal power loss to adjust wireless power transfer; wherein: the rectifier voltage is a rectifier output voltage and the rectifier current is a rectifier output current; and the friendly metal power loss is calculated using an equation having the form: where b is a first coefficient related to the rectifier current, c is a second coefficient related to the rectifier voltage, a is a coefficient related to the transmitter current, and I TX is the transmitter current.

11. The method of claim 10, wherein the rectifier voltage is a rectifier output voltage and the rectifier current is a rectifier output current.

12. The method of claim 10, wherein the one or more coefficients corresponding to the baseline wireless power transmission between the wireless power transmitter and the wireless power receiver are derived by: performing a regression analysis on a plurality of indications of received power and corresponding rectifier voltage and rectifier current of another wireless power receiver associated with another wireless power transfer to calculate the one or more coefficients, and a plurality of measured power loss values determined therefrom.

13. The method of claim 12, further comprising: receive one or more power loss scaling factors from the wireless power receiver, wherein calculating the friendly metal power loss is based on the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and an actual wireless power transmitter or an actual wireless power receiver.

14. The method of claim 10, further comprising: receive one or more power loss scaling factors from the wireless power receiver, wherein calculating the friendly metal power loss is based on the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and an actual wireless power transmitter or an actual wireless power receiver.

15. A wireless power transmitter, the wireless power transmitter comprising: a wireless power transfer coil configured to magnetically couple to a wireless power transfer coil of a 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 transfer coil; and a controller and communication circuit coupled to the inverter and the wireless power transfer coil, the controller and communication circuit controlling the inverter to regulate wireless power transfer to the wireless power receiver, wherein the controller and communication circuit estimate a friendly metal loss associated with wireless power transfer to the wireless power receiver by: receiving, from the wireless power receiver, an indication of received power including a rectifier voltage and a rectifier current of the wireless power receiver; calculating a friendly metal power loss based on the rectifier voltage and the 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 using the friendly metal power loss to regulate wireless power transfer to the wireless power receiver; wherein: the rectifier voltage is a rectifier output voltage and the rectifier current is a rectifier output current; and the friendly metal power loss is calculated using an equation having a form:

16. The wireless power transmitter of claim 15, wherein the one or more coefficients corresponding to the baseline wireless power transmission between the wireless power transmitter and another wireless power receiver are derived by: where b is a first coefficient related to the rectifier current, c is a second coefficient related to the rectifier voltage, a is a coefficient related to the transmitter current, and I TX is the transmitter current. performing a regression analysis on a plurality of received indications of received power including corresponding rectifier voltages and rectifier currents associated with another wireless power transfer or received power derived therefrom, and a plurality of measured power loss values determined therefrom to compute the one or more coefficients. ​ 17. The wireless power transmitter of claim 16, wherein the controller and communication circuitry further estimates the friendly metal loss by receiving one or more power loss scaling factors from the wireless power receiver and calculating the friendly metal power loss in response to the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and an actual wireless power transmitter or an actual wireless power receiver.

18. The wireless power transmitter of claim 15, wherein the controller and communication circuitry further estimates the friendly metal loss by receiving one or more power loss scaling factors from the wireless power receiver and calculating the friendly metal power loss in response to the one or more power loss scaling factors, wherein the one or more power loss scaling factors are based on a pairing between a reference wireless power transmitter or a reference wireless power receiver and an actual wireless power transmitter or an actual wireless power receiver.

19. The wireless power transmitter of claim 15, wherein the rectifier voltage is a rectifier output voltage and the rectifier current is a rectifier output current.

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