Power calculation for wireless power transmission

Abstract

Power calculations for wireless power transfer are provided. [Solution] Operating a wireless power transmission system can include initiating a temporary pause in wireless power transmission using a wireless power transmitter control circuit, providing a stimulus signal to induce a resonant voltage in the wireless power transmitter coil during the temporary pause in wireless power transmission, using the resonant voltage to measure or characterize one or more parameters that characterize the wireless power transmission link between the wireless power transmitter and the wireless power receiver via the wireless power receiver coil, and then resuming wireless power transmission by ending the temporary pause in wireless power transmission.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Application No. 63 / 549,736, entitled "Power Accounting for Wireless Power Transfer," filed February 5, 2024, which is incorporated herein by reference in its entirety. [Background technology]

[0002] Wireless power transfer is used in electronic devices such as smartphones, tablet computers, smartwatches, wireless earbuds, styluses, etc. to facilitate charging of batteries within the devices. In some applications, higher levels of wireless power transfer may be desired, for example, to provide faster charging. Such higher power transfer levels can benefit from techniques to adjust system characteristics and operating parameters to improve operating efficiency, voltage regulation, foreign object detection, etc. Summary of the Invention

[0003] The wireless power transmitter may include a boot housing an inverter and a wireless power transmitter control circuit, a puck housing a wireless power transmitter coil, and a cable disposed between the boot and the puck, the cable having two or more conductors including a conductor that conducts AC current between the inverter and the wireless power transmitter coil in normal wireless power transmission operation. The pack may further house a resonant capacitor and a plurality of switching devices operable to selectively provide a resonant current circulation path between the wireless power transmitter coil and the resonant capacitor during a remote ping operation. The wireless power transmitter control circuit in the boot may further include logic and circuitry for selectively activating the plurality of switching devices to provide a resonant current circulation path between the wireless power transmitter coil and the resonant capacitor in a remote ping operation via one of the two or more conductors, and an analog measurement circuit for measuring a resonant voltage associated with the wireless power transmitter coil and the resonant capacitor via one of the two or more conductors.

[0004] The remote ping operation may be separate from normal wireless power transfer operation and may enable the wireless power transmitter control circuitry to measure or characterize one or more electrical, magnetic, or electromagnetic parameters characterizing a wireless power transfer link between the wireless power transmitter and an external object based on a resonant voltage associated with the wireless power transmit coil and the resonant capacitor. The one or more electrical, magnetic, or electromagnetic parameters characterizing the wireless power transfer link may be used to detect a wireless power receiver. The one or more electrical, magnetic, or electromagnetic parameters characterizing the wireless power transfer link may be used to detect a foreign object. The resonant voltage associated with the wireless power transmit coil and the resonant capacitor may be a ringing signal induced by a stimulus provided by the inverter at the initiation of the remote ping operation. The logic and control circuitry may selectively activate multiple switching devices via a third conductor of the two or more conductors, and the analog measurement circuitry may measure the resonant voltage associated with the wireless power transmit coil and the resonant capacitor via one of the two or more conductors that conducts AC current between the inverter and the wireless power transmit coil during normal wireless power transfer operation.

[0005] The wireless power receiver may include a wireless power receiver coil; a rectifier having a rectifier input coupled to the wireless power receiver coil, the rectifier receiving an AC voltage induced by a wireless power transmitter coupled to the wireless power receiver via the wireless power receiver coil and generating a DC rectifier output voltage at the rectifier output for one or more receiver loads coupled to the rectifier output; and a wireless power receiver control circuit that detects cessation of wireless power transmission initiated by the wireless power transmitter to measure or characterize one or more parameters that characterize a wireless power transmission link between the wireless power transmitter and the wireless power receiver via the wireless power receiver coil, wherein the wireless power receiver control circuit detects cessation of wireless power transmission by detecting a change in one or more power transmission voltage, current, and frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter.

[0006] The wireless power receiver control circuit can detect a pause in wireless power transmission by detecting a drop in the DC rectifier output voltage. The rectifier can be a synchronous rectifier, and the wireless power receiver control circuit can detect a pause in wireless power transmission by detecting a cessation of switching of the synchronous rectifier. The wireless power receiver control circuit can detect a pause in wireless power transmission by a change in the waveform shape of the voltage appearing across the wireless power receiver coil from a square wave shape associated with inverter switching in the wireless power transmitter to a sinusoidal wave shape associated with a power pause. In response to detecting a pause in wireless power transmission, the wireless power receiver control circuit can temporarily pause at least one of one or more receiver loads coupled to the rectifier output. The wireless power receiver control circuit can further detect an end of the pause in wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics in the wireless power receiver, independent of communication with the wireless power transmitter. In response to detecting an end of the pause in wireless power transmission, the wireless power receiver control circuit can resume at least one of the one or more receiver loads coupled to the rectifier output that was paused in response to detecting the pause in wireless power transmission. At least one of the one or more receiver loads coupled to the rectifier output can be paused in response to detecting a pause in wireless power transmission and can include a switching converter. The wireless power receiver control circuit can resume at least one of the one or more receiver loads coupled to the rectifier output that was paused in response to detecting a pause in wireless power transmission by ramping up a switching duty cycle of the switching converter to avoid an overshoot or overvoltage of the DC rectifier output voltage.Ramping up the switching duty cycle of the switching converter to avoid overshoot or overvoltage of the DC rectifier output voltage may include storing a pre-power-down duty cycle value and using the pre-power-down duty cycle value as a feedforward signal to accelerate the ramp-up of the switching converter duty cycle.

[0007] The wireless power transfer system may include a wireless power transmitter including an inverter driving a wireless power transmitter coil, a wireless power receiver including a wireless power receiver coil magnetically coupled to the wireless power transmitter coil, and a rectifier having a rectifier input coupled to the wireless power receiver coil and a rectifier output coupled to one or more wireless power receiver loads. A method of operating the wireless power transfer system may include initiating a temporary pause in wireless power transfer using a wireless power transmitter control circuit, providing a stimulus signal to induce a resonant voltage in the wireless power transmitter coil during the temporary pause in wireless power transfer, using the resonant voltage to measure or characterize one or more parameters that characterize the wireless power transfer link between the wireless power transmitter and the wireless power receiver through the wireless power receiver coil, and then resuming wireless power transfer by ending the temporary pause in wireless power transfer. The method may further include detecting a temporary pause in wireless power transmission using a wireless power receiver control circuitry by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter; temporarily pausing at least one of the one or more receiver loads coupled to the rectifier output in response to detecting the temporary pause in wireless power transmission; detecting a resumption of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter; and resuming at least one of the one or more receiver loads coupled to the rectifier output that was paused in response to detecting the temporary pause in wireless power transmission in response to the resumption of wireless power transmission.

[0008] The wireless power transmitter may include a boot housing an inverter and a wireless power transmitter control circuit, a pack housing a wireless power transmitter coil, a resonant capacitor, and multiple switching devices operable to selectively provide a resonant current circulation path between the wireless power transmitter coil and the resonant capacitor during a remote ping operation, and a cable disposed between the boot and the pack, the cable having at least three conductors including first and second conductors that conduct AC current between the inverter and the wireless power transmitter coil during normal wireless power transfer operation, and a third conductor that enables the wireless power transmitter control circuit to selectively activate the multiple switching devices. Measuring or characterizing one or more parameters that characterize the wireless power transfer link between the wireless power transmitter and the wireless power receiver using the resonant voltage may include selectively activating the multiple switching devices during a remote ping operation. Measuring or characterizing one or more parameters that characterize the wireless power transfer link between the wireless power transmitter and the wireless power receiver using the resonant voltage may include detecting a foreign object. At least one of detecting a temporary cessation of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter and detecting a resumption of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter can include detecting a drop in a rectifier output voltage. At least one of detecting a temporary cessation of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter and detecting a resumption of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter can include detecting a cessation of rectifier switching. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows a simplified block diagram of a wireless power transfer system.

[0010] [Figure 2] 1 illustrates an alternative embodiment of a wireless charger device.

[0011] [Figure 3] 1 shows a simplified schematic diagram of a wireless charger device.

[0012] [Figure 4] Techniques are presented for pausing wireless power transfer to perform measurements that characterize wireless links in a wireless power transfer system.

[0013] [Figure 5] 1 illustrates the operation of a wireless power receiver during a quiescent period in a wireless power transmission system to perform measurements that characterize a wireless link in the wireless power transmission system.

[0014] [Figure 6] 1 shows a simplified flowchart of the operation of a wireless power transmitter and a wireless power receiver during a quiescent period in a wireless power transmission system to perform measurements to characterize a wireless link in the wireless power transmission system. DETAILED DESCRIPTION OF THE INVENTION

[0015] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed concepts. As part of this description, some of the drawings in this disclosure represent structures and devices in block diagram form in order to avoid obscuring the present invention. In the interest of clarity, not all features of an actual implementation are described in this specification. Moreover, the language used in this specification has been chosen solely for purposes of readability and explanation, and not to limit or restrict the disclosed subject matter. Rather, the appended claims are intended for such purposes.

[0016] Various embodiments of the disclosed concepts are illustrated in the accompanying drawings, by way of example, and not by way of limitation, wherein like reference numerals indicate like elements. For simplicity and clarity of illustration, where considered appropriate, reference numerals have been repeated among different drawings to indicate corresponding and / or similar elements. Additionally, numerous specific details have been described to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the relevant associated functionality being described. References to "an," "one," or "another" embodiment in the present disclosure do not necessarily refer to the same or different embodiments, but rather to at least one. A given drawing may be used to illustrate multiple embodiments or multiple species of the present disclosure, and not all elements in the drawing may be required for a given embodiment or species. A reference numeral, if provided in a given drawing, may refer to the same element throughout the drawings, but may not be repeated in all drawings. The drawings are not to scale unless otherwise indicated and the proportions of certain parts may be exaggerated to better show the details and features of the present disclosure.

[0017] FIG. 1 shows a simplified block diagram of a wireless power transfer system 100. The wireless power transfer system includes a power transmitter (PTx) 110 that transmits power wirelessly to a power receiver (PRx) 120, such as via inductive coupling 130. The power transmitter 110 can receive input power, which is converted by an inverter 114 to an AC voltage having specific voltage and frequency characteristics. The inverter 114 can be controlled by a controller / communications module 116, which operates as described further below. In various embodiments, the inverter controller and communications module can be implemented in a common system, such as a system based on a microprocessor, microcontroller, or the like. In other embodiments, the inverter controller can be implemented by a separate controller module and communications module having means for communication therebetween. The inverter 114 can be 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).

[0018] The inverter 114 can deliver the generated AC voltage to the transmitter coil 112. In addition to the wireless coil that enables magnetic coupling to the receiver, the transmitter coil block 112 shown in FIG. 1 may include tuning circuit components, such as additional inductors and capacitors, that facilitate operation of the transmitter under different conditions, such as different degrees of magnetic coupling to the receiver or different operating frequencies. The wireless coil itself can be configured in a variety of different ways. In some embodiments, the wireless coil can be formed as a winding of wire wrapped around a suitable bobbin. In other embodiments, the wireless coil can be formed as a trace on a printed circuit board. Other configurations are possible and can be used in conjunction with the various embodiments described herein. The wireless transmitter coil can also include a core of magnetically permeable material (e.g., ferrite) configured to affect the magnetic flux pattern of the coil in a manner suitable for a particular application. The teachings herein can be applied in conjunction with any of a wide variety of transmitter coil configurations suitable for a given application.

[0019] The PTx controller / communications module 116 can monitor the power transmission coil and use information derived therefrom to control the inverter 114 as appropriate for a given situation. For example, the controller / communications module can be configured to operate the inverter 114 at a given frequency or output voltage depending on a particular application. In some embodiments, the controller / communications module can be configured to receive information from the PRx device and control the inverter 114 accordingly. This information can be received via the power transmission coil (i.e., in-band communication) or via a separate communication channel (not shown, i.e., out-of-band communication). In the case of in-band communication, the controller / communications module 116 can detect and decode signals (such as voltage, frequency, or load variations) imposed on the magnetic link by the PRx to receive the information, and can command the inverter to modulate the delivered power by manipulating various parameters (such as voltage, frequency, etc.) of the generated voltage to transmit the information to the PRx. In some embodiments, the controller / communications module may be configured to communicate data to the PRx employing frequency shift keying (FSK) communications, in which the frequency of the inverter signal is modulated. The controller / communications module 116 may be configured to detect amplitude shift keying (ASK) communications or load modulation-based communications from the PRx. In either case, the controller / communications module 126 may be configured to vary the current drawn at the receiver side to manipulate the waveform seen on the Tx coil to deliver information from the PRx to the PTx. For out-of-band communications, additional modules may be provided to enable communication between the PTx and PRx, such as WiFi, Bluetooth, or other wireless links, or any other suitable communications channel.

[0020] As noted above, controller / communications module 116 may be, for example, a single module located on a single integrated circuit, or may be comprised of multiple modules / devices located on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of controller / communications circuitry.

[0021] The PTx device 110 may optionally include other systems and components, such as a separate communications module 118. In some embodiments, the communications module 118 can communicate with a corresponding module in the PTx via the power transfer coil. In other embodiments, the communications module 118 can communicate with a corresponding module using a separate physical channel 138.

[0022] As described above, the wireless power transmission system also includes a wireless power receiver (PRx) 120. The wireless power receiver may include a receiver coil 122 that may be magnetically coupled to the transmitter coil 112. Similar to the transmitter coil 112 described above, the receiver coil block 122 shown in FIG. 1 may include tuning circuit components, such as additional inductors and capacitors, to facilitate operation of the transmitter under different conditions, such as different degrees of magnetic coupling to the receiver or different operating frequencies. The wireless coil itself may be configured in a variety of different ways. In some embodiments, the wireless coil may be formed as a winding of wire wound around a suitable bobbin. In other embodiments, the wireless coil may be formed as a trace on a printed circuit board. Other arrangements are possible and may be used in conjunction with the various embodiments described herein. The wireless receiver coil may also include a core of magnetically permeable material (e.g., ferrite) configured to affect the magnetic flux pattern of the coil in a manner suitable for a particular application. The teachings herein may be applied in conjunction with any of a wide variety of receiver coil arrangements suitable for a given application.

[0023] The receiver coil 122 outputs an AC voltage induced therein by magnetic induction through the transmitter coil 112. This output AC voltage may be provided to a rectifier 124, which provides DC output power to one or more loads associated with the PRx device. The rectifier 124 may be controlled by a controller / communications module 126, which operates as described further below. In various embodiments, the rectifier controller and communications module may be implemented in a common system, such as a system based on a microprocessor, microcontroller, or the like. In other embodiments, the rectifier controller may be implemented by a separate controller module and communications module having means of communication therebetween. The rectifier 124 may be constructed using any suitable circuit topology (e.g., full bridge, half bridge, etc.) and may be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., fabricated using silicon, silicon carbide, or gallium nitride devices).

[0024] The PTx controller / communications module 126 can monitor the receiver coil and use information derived therefrom to appropriately control the rectifier 124 depending on given circumstances. For example, the controller / communications module can be configured to operate the rectifier 124 to provide a given output voltage depending on a particular application. In some embodiments, the controller / communications module can be configured to transmit information to the PTx device to effectively control the power delivered to the receiver. This information can be received or 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). In the case of in-band communication, the controller / communications module 126 can transmit information to the PTx, for example, by modulating the load current or other electrical parameters of the received power. In some embodiments, the controller / communications module 126 can be configured to detect and decode signals (such as voltage, frequency, or load variations) applied by the PTx to the magnetic link in order to receive information from the PTx. In some embodiments, the controller / communications module 126 may be configured to receive frequency shift keying (FSK) communications, in which the frequency of the inverter signal is modulated to communicate data to the PRx. The controller / communications module 126 may be configured to generate amplitude shift keying (ASK) communications or load modulation-based communications from the PRx. In either case, the controller / communications module 126 may be configured to vary the current drawn at the receiver to manipulate the waveform seen on the Tx coil to deliver information from the PRx to the PTx. For out-of-band communications, additional modules may be provided to enable communication between the PTx and PRx, such as WiFi, Bluetooth, or other wireless links, or any other suitable communications channel.

[0025] As mentioned above, the controller / communications module 126 may be, for example, a single module provided on a single integrated circuit, or may be comprised of multiple modules / devices provided on different integrated circuits, or a combination of integrated circuits and discrete circuits having both analog and digital components. The teachings herein are not limited to any particular arrangement of controller / communications circuitry. The PRx device 120 may optionally include other systems and components, such as a communications (“comms”) module 128. In some embodiments, the communications module 128 can communicate with a corresponding module in the PTx via the power transfer coil. In other embodiments, the communications module 128 can communicate with a corresponding module or tag using a separate physical channel 138.

[0026] Many variations and extensions of the wireless power transmission system 100 described above are possible, and the following teachings are applicable to any such variations and extensions.

[0027] FIG. 2 illustrates an alternative embodiment of a wireless charger device. More specifically, wireless charger 201 is a wireless charger capable of providing power to a wireless power receiver (PRx) device 220. Wireless charger 201 can include a puck 231 that can be coupled to PRx 220, a cable 234, and a boot 232. In some embodiments, puck 231 can be secured to PRx 220 by a magnet or other securing mechanism. Boot 232 can include an electrical connection for coupling to a power source. For example, the electrical connection can be a USB connection that can be coupled to a corresponding USB (Universal Serial Bus) port on a power adapter or on a device such as a desktop computer, laptop computer, tablet, or the like. In some embodiments, boot 232 can include a DC-DC converter 235 that converts voltage received from the power source to a level suitable for use by the components in pack 231. Components in pack 231 can include an inverter (DC / AC converter) 214 and a wireless power transmit coil 212. As described above, wireless power transmit coil 212 can be coupled to a corresponding wireless power receive coil (not shown) in PRx 220.

[0028] The above-described configuration results in DC current flowing from the DC-DC converter 235 located in the boot 232 of the wireless charger 201 to the inverter 214 located in the pack 231 of the wireless charger 201. When configured in this manner, the power transfer capability to the PRx 220 may be limited by thermal limitations associated with the inverter 214 located in the pack 231. More specifically, there may be certain losses associated with the operation of the inverter 214, as well as certain losses associated with the wireless power receiver circuitry located in the PRx 220 (as described above with reference to FIG. 1 ). In some cases, there may also be losses associated with charging a battery (not shown) located in the PRx 220. Each of these losses is located in relatively close physical proximity, and therefore, the combination of these losses may present thermal conditions that limit the amount of power that can be supplied by the wireless charger 201 to the PRx 220.

[0029] One way to address such losses may be to relocate the inverter 214 from the pack 231 to the boot 232, as shown with respect to the wireless charger 202. As a result, heat corresponding to losses associated with inverter operation can be moved from the vicinity of the other losses mentioned above, providing more headroom for increased levels of power transfer. This change in configuration results in AC current (generated by the inverter 214) being sent via the cable 234. Furthermore, the pack 231 in such an embodiment includes the power transmit coil 212 as the only component of the wireless power transfer chain. Note that other sensing and control components (i.e., non-power carrying components) associated with a wireless power transfer system, such as the various components described above with respect to FIG. 1 and below with respect to FIG. 3, may also be located within the pack 231.

[0030] Wireless power transmission systems can incorporate features that rely on “pings” initiated by the wireless power transmitter to characterize the magnetic link between the wireless power transmitter and receiver, detect the presence of the wireless power receiver, detect the presence of a foreign object, etc. The general nature of these pings is that the wireless power transmitter provides some type of stimulus signal to a resonant LC tank corresponding to the magnetic link. This results in some type of response, e.g., a ringing signal, that can be characterized in terms of its frequency, duration, decay envelope, etc., to identify the electrical and / or magnetic properties of the magnetic link. For example, the Q factor of the wireless power transmitter coil can be measured, which is affected by various objects (e.g., the wireless power receiver and / or foreign object) magnetically and / or electrically coupled to the wireless power transmitter coil. Additionally or alternatively, parameters other than Q factor can be measured, such as effective inductance, coupling coefficient, or other electrical, magnetic, and / or electromagnetic parameters or characteristics of the wireless link. These various parameters may be used for various purposes, such as detecting the presence of a wireless power receiver, detecting the presence of a foreign object, detecting an object and determining whether the detected object is a wireless power receiver or a foreign object, and estimating the degree of coupling or matching between the wireless power receiver and the wireless power transmitter, which may affect the level of power transmission.

[0031] These pings initiated by the wireless power transmitter may be affected by changes in the wireless charger configuration described above with reference to FIG. 2 in that the pings characterize an AC current path. By relocating the inverter from the pack to the boot, the cable 234 (now carrying an AC signal) becomes part of the AC circuit characterized by the ping signal. This can add increased resistance associated with the cable 234, distorting the measurements. Furthermore, the impedance of the cable can change with use, aging, temperature, wear, etc. All of these factors can potentially make such measurements more difficult to use for all desired purposes. Therefore, in at least some embodiments, it may be desirable to provide a mechanism that enables “ping” measurements such that the additional impedance presented by the cable 234 can be removed.

[0032] FIG. 3 shows a simplified schematic diagram of a wireless charger 300 capable of remote pinging, which can eliminate the effects of cable impedance, overcoming the aforementioned problems. More specifically, the wireless charger 300 includes a boot 232, a pack 231, and a cable 234, as described above with respect to FIG. 3. The boot 232 may include a DC-DC converter (not shown). The boot 232 may also include an inverter in the form of two switching bridges (A-bridge and B-bridge), each consisting of a high-side switching device (214a / 214c) and a low-side switching device (214b / 214d). Other inverter topologies may also be used. The boot 232 may also include a resonant capacitor Cres that can resonate with the wireless power transmit coil 212 located in the pack 231 during normal wireless power transfer operation. Furthermore, in addition to the components and functions described above with respect to the controller / communications module 116, the boot 232 may include a control circuit 316 that can implement analog measurement circuitry and logic 336 and remote ping control circuitry and logic 337, as described in more detail below.

[0033] The cable 234 may include a cable for carrying power and signals between the boot 232 and the pack 231. The illustrated cable 234 includes two power conductors 234a and 234b that couple the inverter to the wireless power transmitter coil 212 located within the pack. Each of these conductors may have an associated impedance, shown in FIG. 3 as AC resistances Rac1 and Rac2. In at least some embodiments, the AC resistance of these conductors may be considered the dominant component of the cable's impedance; however, parasitic inductance and capacitance associated with the cable and its length may also be present. However, the effect of impedance of any nature may be mitigated by techniques described below. The cable 234 may also include a remote signal conductor 234c that is used as part of a remote ping process, described in more detail below. The cable 234 may also include other conductors used with sensing components (e.g., temperature sensors) or other components (not shown) that may be located within the pack 231. Finally, the cable 234 may also include a shield 234d that may be coupled to the ground references of both the boot 232 and the pack 231.

[0034] The pack 231 may include the wireless power transmission coil 212, as described above. The wireless power transmission coil 212 may be coupled to the inverter in the boot 232 by a cable 234, specifically conductors 234a / 234b. The pack 231 may also include a capacitor Cping and switching devices S1, S2 used for remote ping operations. More specifically, during normal operation, switches S1 and S2 may be open, disconnecting capacitor Cping from the circuit and enabling normal operation. Switches S1 and S2 may be controlled by a remote switch controller 337, which may be circuitry and / or logic integrated into the control circuit 316, as described above. Thus, during a remote ping operation, which may occur before wireless power transfer inverter operation, or during quiescence of wireless power transfer inverter operation (as described in more detail below), the remote switch controller 337 may close switches S1 and S2, effectively providing a current path 339 for a ringing signal in the resonant circuit formed by the wireless power transmitter coil 212 and resonant capacitor Cping.

[0035] During this remote ping period, the ringing voltage at the terminal forming the junction between the wireless power transmit coil 212 and the resonant capacitor Cping may be measured via the analog measurement circuitry and logic 336 (described above), to which this node is coupled by conductor 234b. The analog measurement circuitry and logic 336 may include an analog-to-digital converter (A / D converter) for converting the measured voltage into a digital value that can be used by one or more processors of the control circuitry 316 or other digital control circuitry. The analog measurement circuitry 336 may also, or alternatively, include other signal conditioning circuitry (buffer amplifiers, error amplifiers, etc.) that enables the signal to be used by the control circuitry 336. In either case, the analog measurement circuitry 336 may present a very high impedance such that little current flows in conductor 234b, and as a result, the impedance associated with the cable 234 does not affect the measurement associated with the remote ping operation.

[0036] FIG. 3 also shows signal plots 301 and 302 illustrating further aspects of remote ping operation. Plot 301 shows output 341 of inverter low-side switch 214b, illustrating the switch-off transition associated with stopping inverter operation. Plot 301 also shows output 342 of inverter high-side switch 214a, which may be a pulse supplying inverter input voltage V to wireless power transmitter coil 212. This may be the "ping" or stimulus signal discussed above. Finally, plot 301 also shows output 343 of remote switch controller 337, which closes after the stimulus signal to provide the ringing current circulation path discussed above. Plot 302 shows ringing signal V appearing at the junction between wireless power transmitter coil 212 and resonant capacitor C, as discussed above, and measured by analog measurement circuitry and logic 336 via conductor 234b. The signal includes an initial portion 344 corresponding to the stimulus pulse and a response portion 345 corresponding to the ringing period. This ringing signal measured by the analog measurement circuitry and logic 316 may be processed to determine the Q factor of the wireless power transmitter coil 212 or other electrical, magnetic, or electromagnetic properties that may be used to characterize the wireless link between the wireless power transmitter and receiver, to detect the presence of a wireless power receiver, to detect the presence of a foreign object, etc.

[0037] FIG. 4 illustrates a technique for quiescing wireless power transmission to perform measurements that characterize the wireless link in a wireless power transmission system. FIG. 4 includes a first simplified schematic diagram 401 illustrating a wireless power transmission system in normal power transmission operation. FIG. 4 also includes a second simplified schematic diagram 402 illustrating a wireless power transmission system in a power quiescing mode, which allows for measurement of resonant circuit ringing. This measurement may, but need not, use a remote ping configuration, as described above. FIG. 4 also includes a plot 403 illustrating the rectifier output voltage Vrect / 447 and the resonant capacitor voltage V_Ctx / 448 during a power quiescing period 449.

[0038] Referring to the first schematic diagram, a wireless power transmission system 401 in normal operation can include a wireless power transmitter and a wireless power receiver as described above. The wireless power transmitter can include an inverter 114 including switching devices Q1-Q4. The topology shown is merely exemplary, and other inverter topologies can be used. The wireless power transmitter also includes an inductor L corresponding to the inductance and resistance of the wireless power transmitter coil, respectively. TX and R TX The wireless power transmitter coil may include a resonant capacitor C TX may be coupled to the inverter 114 by

[0039] The wireless power receiver may include a rectifier 124, shown in block diagram form, which may include any of a variety of rectifier bridge configurations, such as a half-bridge, a full-bridge, etc. Additionally, the rectifier may include "passive" rectifier devices, such as diodes or active rectifier devices, including switching devices such as MOSFETs, JFETs, IGBTs, BJTs, etc. The switching devices may be implemented using any suitable semiconductor technology, such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), etc. In at least one embodiment, the rectifier 124 may be a full-bridge active (synchronous) rectifier formed from MOSFET switches. The input of the rectifier 124 may be coupled to the wireless power receiver coil, and in FIG. 4 , an inductor L corresponds to the inductance and resistance of the wireless power receiver coil, respectively. RX and resistor R RX The rectifier 124 and the wireless power receiver coil are represented by a series combination of resonant capacitor C RX The magnetic coupling between the wireless power transmitter and the wireless power receiver can be achieved by an inductor L TX and L RXThe output of the rectifier 124 is a DC voltage Vrect that is supplied to a receiver load 446. In some cases, the receiver load 446 may be a further regulator / converter that provides one or more regulated voltages to various receiver system loads. The rectifier output capacitor C DC may be provided for output bus filtering, load hold-up, etc.

[0040] Referring to a second schematic diagram 402, a wireless power transmission system (including the same components as those described above with reference to schematic diagram 401) can operate in a "power pause" mode to measure characteristics of the magnetic link between the wireless power transmitter and receiver corresponding to the "ping" operation described above. This power pause involves stopping the switching of inverter switching devices Q1-Q4 to stop the supply of power from the wireless power transmitter to the wireless power receiver. The power pause opens the upper switching devices Q1 / Q2, closes the lower switching devices Q2 / Q4, and turns on the capacitor C TX and the wireless power receiver coil. In some embodiments, this short circuit can be performed using a remote ping configuration as described above with respect to FIGS. 2 and 3. In either case, the stimulus provided to the resonant tank is the previous power transfer and its cessation for power quiescence. This can be understood with reference to plot 403 in FIG. 4.

[0041] Plot 403 shows the rectifier output voltage V rect is shown as curve 447, and the resonant capacitor C TX The voltage V_Ctx across V is plotted as curve 448. The power pause interval 449 begins when the inverter stops switching. Before this moment, V rectcan be at its nominal value, and the voltage V_Ctx can be a sinusoidal voltage with a DC offset. When the inverter stops switching, V_Ctx begins a damped ringing. This also removes the DC offset from this signal. During this same interval, V rect The wireless power receiver circuitry can detect a power outage using various techniques, which will be described in more detail below. When the wireless power receiver detects a power outage, it starts to decay the rectifier output / rectifier output capacitor C DC The receiver load 446 can be controlled to stop drawing power from the rectifier output voltage V. For example, a battery charger or other switching converter / regulator can be disabled. rect The decay of V can be stopped. rect may be held below its nominal value. After the wireless power transmitter completes its measurements characterizing the magnetic link between the wireless power transmitter and the receiver, the wireless power transmitter may resume normal operation and restore normal switching of the inverter. This results in the restoration of the DC offset in curve 448, as well as the reversal of the decaying / ringing signal, by returning V_Ctx to its normal DC offset sinusoidal waveform. Additionally, the rectifier output voltage V rect begins to increase and eventually returns to its nominal value. At the same time, the wireless power receiver can detect the end of the power hibernation using various techniques, described in more detail below, and allow the receiver load 446 to resume normal operation. Further details of these power hibernation operations are described in more detail below with reference to FIGS. 5 and 6.

[0042] FIG. 5 illustrates the operation of a wireless power receiver during periods of quiescence in wireless power transmission, enabling a wireless power transmitter to perform measurements that characterize the wireless link in a wireless power transmission system. The illustration in FIG. 5 includes a plot 500 of various receiver-side waveforms. The first plotted waveform 551 is the rectifier output voltage Vrect, as described above with reference to FIG. 4. The second plotted waveform 552 illustrates the power drawn from the rectifier (Prect), for example, by the receiver load 446, as described above. The third plotted waveform 553 is an exemplary enable / disable signal for the receiver load 446, which, for purposes of this example, is a switching regulator / converter that converts the rectifier output to one or more regulated voltages or currents for various other loads. In some embodiments, this may be a battery charger, but may also be another converter / regulator. The fourth plotted waveform 554 is an exemplary switching duty cycle of the receiver load 446.

[0043] Prior to time t1, which indicates the start of the power sleep interval, the wireless power transfer system may be operating in normal power transfer mode 555. Thus, the rectifier output voltage Vrect may be at its nominal value. This nominal value may be determined based on system requirements, available input voltage, power transfer level, and other factors. In some embodiments, this may be a voltage of 28V, although other voltages such as 5V, 9V, 10V, 12V, 15V, 18V, 19V, 20V, 24V, 25V, 30V, etc. may be used as appropriate. Also, during this interval prior to time t1, the power drawn from the rectifier may be the nominal value required by the wireless power receiver and its associated system. In some embodiments, this may correspond to a power level of 5W, 7.5W, 10W, 12W, 15W, 20W, 25W, 30W, 35W, 40W, 50W, etc. Similarly, the receiver load converter may be enabled during this time period, and the receiver load converter may operate at a duty cycle corresponding to its input voltage (i.e., rectifier output voltage Vrect), its output voltage and / or current, the power required by various loads downstream of the converter, etc.

[0044] At time t1, a power pause interval may be initiated by the wireless power transmitter stopping normal inverter switching and shorting the wireless power transmitter coil to measure the characteristics of the electromagnetic link between the wireless power transmitter and the receiver. As a result, power drawn from the rectifier stops, as shown by curve 552. During the power pause interval, no power is supplied from the wireless power transmitter to the wireless power receiver. However, as shown by curve 553, the receiver load converter remains enabled, and the receiver load converter duty cycle continues at its nominal value, determined by downstream load requirements as described above. This results in a decay of the rectifier output voltage Vrect, as the output capacitor VDC supplies the energy required by the receiver load 446.

[0045] At time t2, the rectifier output voltage decays to a lower limit vlim as a result of the receiver load continuing to draw power from the rectifier output capacitor VDC. At time t2, the receiver can detect a power outage and disable the receiver load converter (as shown by curve 553), which will result in the receiver load converter having a zero duty cycle (as shown by curve 554). A receiver controller (e.g., the receiver-side controller / communications module 126 described above) can perform both this detection of a power outage and a corresponding shutdown of the receiver load, such as receiver load converter 446.

[0046] The receiver controller can detect a power outage in various ways. For example, the receiver controller can detect a decay of the rectifier output voltage Vrect to a reduced level vlim. This value may be a fixed voltage value less than the nominal rectifier output voltage, or may be a percentage of the nominal rectifier output voltage. As an example, for a nominal Vrect voltage of 28V, the vlim limit voltage may be 23.5V, although other values ​​are possible. Such a value may be 90%, 85%, 80%, 75%, 70%, etc. of the nominal voltage, or any other suitable value in particular embodiments, a percentage between any of the foregoing, e.g., 85-90%, 80-85%, 75-80%, 70-75%, etc.

[0047] The receiver controller may also detect other signals resulting from the cessation of switching of the active / synchronous rectifier 124 or a power outage. Such signals may include, but are not limited to, a drop in voltage or current level, a change in frequency, or a change in waveform shape (e.g., from a square wave associated with normal switching to a sine wave associated with transmitter-side power outage / ringdown), which may be detected by the wireless power receiver coil (L RX / R RX ) and / or receiver capacitor C RXThis may include changes in the nature of the waveform that appears over time. In some embodiments, the receiver controller may also receive a communication from the wireless power transmitter indicating a power pause, although in some cases, in-band communication between the wireless power transmitter and receiver may be slow enough that the transmitter needs to notify (or begin notifying) the wireless power receiver in advance of a power pause, allowing time to send the packets / bits necessary to convey such a message. Therefore, it may be preferable for the wireless power receiver controller to be able to detect a power pause based on one or more characteristics of the power transmission voltage, current, or frequency without relying on typical in-band communication mechanisms.

[0048] At time t3, when the wireless power transmitter completes its measurements, the wireless power transmitter can resume normal inverter operation and wireless power transmission. In some embodiments, the time required for the power pause may be on the order of 10 microseconds to 100 microseconds, although other intervals are possible. Such a short duration suggests the desirability of the receiver directly detecting the power pause rather than relying on a communication from the wireless power transmitter, which may take somewhat longer than the pause depending on the in-band communication implementation. In either case, the resumption of inverter switching and wireless power transmission can cause the rectifier output voltage (Vrect) and the power drawn from the rectifier (Prect) to begin ramping up, as shown by curves 551 and 552 in FIG. 5 during the interval between t3 and t4. During this interval, the power drawn from the rectifier is applied to the rectifier output capacitor C DCAt time t4, the wireless power receiver (i.e., receiver control circuitry) can detect that wireless power transmission has resumed. One possible trigger for such detection can be an increase in the rectifier output voltage Vrect to a threshold Vth greater than the lower limit vlim but less than the nominal value of Vrect (e.g., the value before power was suspended). In some embodiments, such as the 28V embodiment described above, the threshold voltage Vth can be 26V, although other suitable values, including values ​​within the ranges of the above-mentioned percentages, may be used.

[0049] In either case, detection of this increase can trigger the wireless power receiver controller to re-enable the receiver load converter, as shown by curve 553. This decision can also (alternatively or additionally) be triggered by detection of other voltage, current, frequency, or waveform characteristics indicative of resumption of wireless power transfer, with a time delay after the rectifier output voltage Vrect or output power Prect begins to increase. As a result, during the interval from time t4 (when the receiver controller detects resumption of wireless power transfer) to t5, the receiver controller can ramp up the switching duty cycle of the receiver load converter sufficiently quickly to avoid overshoot / overvoltage of the rectifier output voltage. This can be accomplished in various ways, such as by the receiver controller storing the pre-power pause duty cycle value and using it as a feedforward signal to accelerate the ramp-up of the load converter duty cycle. In either case, it may be desirable for the load converter to have resumed its nominal power transfer level before full recovery of the rectifier output voltage (Vrect) and rectifier output power (Prect), which corresponds to the interval between times t5 and t6 in FIG. 5 .

[0050] FIG. 6 shows a simplified flowchart 600 of the operation of a wireless power transmitter (PTx) and a wireless power receiver (PRx) during a quiescence period in a wireless power transmission system to perform measurements to characterize the wireless link in the wireless power transmission system. Starting at block 661, the wireless power transmitter may quiesce power transmission. The wireless power transmitter may then send a “ping” to the wireless power transmitter coil (block 663). This “ping” may include, for example, providing a stimulus signal to the coil using an inverter. In some cases, the stimulus signal may be the cessation of wireless power transmission itself. Thereafter (block 665), the wireless power transmitter may measure a Q factor or other electrical, magnetic, or electromagnetic property that characterizes the link between the wireless power transmitter and the wireless power receiver. These measurements may be performed using the remote ping technique described above or by shorting the wireless power transmission coil using an inverter switch.

[0051] In either case, the resulting measurements and characterizations may then be used to detect the presence of the wireless power receiver and / or foreign object and set an appropriate wireless power transmission level based at least in part thereon. Additionally or alternatively, these measurements and characterizations may be used to determine the degree of coupling between the wireless power transmitter and the wireless power receiver and set an appropriate power transmission level based at least in part thereon. After completing the measurements / characterizations, the wireless power transmitter may resume wireless power transfer (block 667). These PTx-side operations may be performed by control circuitry associated with the wireless power transmitter, such as the controller / communications module 116 described above.

[0052] On the receiver (PRx) side, when the transmitter (PTx) pauses power transmission, the receiver can detect the pause in power transmission (block 662). This can be substantially simultaneous with a ping initiated by the transmitter and / or measurements made on the wireless power transmitter side. In either case, after detecting the power pause, the wireless power receiver controller can disable the load converter (block 664). As described above, this can be responsive to various signals measured by the receiver controller on the receiver side without receiving communication from the wireless power transmitter. When the wireless power transmitter resumes wireless power transmission (block 667), the receiver controller can detect the resumed power transmission (block 666) and, in response, can re-enable and ramp up the load converter (block 668), as described above. These PRx-side operations can be performed by control circuitry associated with the wireless power transmitter, such as the controller / communications module 126 described above.

[0053] The operations described above refer to various voltage levels and thresholds, power levels and thresholds, etc. The descriptions herein may be applied to various systems operating at different voltage levels, different power levels, etc. For example, in some embodiments, the input voltage may be controllable, whether by manipulation of a control signal for the DC-DC converter or not, to be in a range between approximately 16 V and 20 V. Such a voltage range may, but need not, correspond to a USB-PD power supply providing a 20 V input voltage to such a DC-DC converter. However, operation at other voltage ranges corresponding to other USB-PD voltage levels may also be appropriate. For example, an input voltage range between approximately 10 V and 15 V or 12 V and 15 V may be used with a 15 V USB-PD power supply. Alternatively, if a buck-boost converter is used to provide V from a power source, the upper limit of the supplied voltage range may exceed the voltage supplied to such a DC-DC converter. Similarly, with respect to power thresholds, a 15 W power threshold may serve as a boundary between a low-power regime and a high-power regime. Operating above this threshold can be used to selectively enable or disable features such as input voltage reduction before initiating capacitance changes on either the PTx or PRx side. However, 15 W is merely one example of such a threshold; the threshold could be 10 W, 12 W, 16 W, 18 W, 20 W, 22 W, 25 W, 28 W, 30 W, 32 W, 35 W, 38 W, 40 W, 45 W, 50 W, or any other suitable value. If some degree of hysteresis is desired, an additional power threshold can be used to indicate a return to a low-power regime. Such a threshold could be 9 W, although any value below the high-power threshold could be used, such as 12 W, 10 W, 7.5 W, 5 W, etc. Unless otherwise specified herein or in the appended claims, any of the above values ​​can be used. However, in at least some applications, there may be advantageous reasons for adopting a particular threshold.

[0054] Various features and embodiments relating to systems and operating parameter measurement in wireless power transmission systems have been described above. Such configurations may be used in a variety of applications, but may be particularly advantageous when used with electronic devices such as mobile phones, tablet computers, laptop or notebook computers, and accessories such as wireless headphones, styluses, etc. Furthermore, while numerous specific features and various embodiments have been described, it should be understood that, unless otherwise stated as mutually exclusive, the various features and embodiments may be combined in various permutations in a particular implementation. Accordingly, the various embodiments described above are provided by way of example only and should not be construed as constituting the scope of the present disclosure. Various modifications and variations can be made to the principles and embodiments herein without departing from the scope of the present disclosure and without departing from the scope of the claims.

[0055] The above describes an exemplary embodiment of a wireless power transmission system capable of transmitting certain information between the PTx and PRx in the system. The present disclosure contemplates that the passing of this information improves the ability of devices to provide wireless power signals to each other in an efficient manner to facilitate battery charging, such as by sharing the devices' power handling capabilities with each other. Entities implementing the present technology should take care to ensure that well-established privacy policies and / or practices are adhered to, to the extent any sensitive information is used in a particular implementation. Specifically, such entities would be expected to implement and consistently apply privacy practices generally recognized as meeting or exceeding industry or government requirements for maintaining user privacy. Implementers should inform users of where personally identifiable information is expected to be transmitted in the wireless power transmission system and allow users to "opt in" or "opt out" of participation. For example, such information may be presented to users when they place a device on a power transmitter if the power transmitter is configured to poll for sensitive information from the power receiver.

Claims

1. 1. A wireless power transmitter, comprising: a boot housing an inverter and wireless power transmitter control circuitry; a puck containing a wireless power transmitter coil; a cable disposed between the boot and the pack, the cable having two or more conductors, including a conductor that conducts AC current between the inverter and the wireless power transmitter coil in normal wireless power transmission operation.

2. the pack further houses a resonant capacitor and a plurality of switching devices operable to selectively provide a resonant current circulating path between the wireless power transmitter coil and the resonant capacitor during a remote ping operation; The wireless power transmitter control circuit in the boot logic and circuitry for selectively activating the plurality of switching devices to provide the resonant current circulation path between the wireless power transmitter coil and the resonant capacitor in the remote ping operation via one of the two or more conductors; an analog measurement circuit that measures a resonant voltage associated with the wireless power transmitting coil and the resonant capacitor via one of the two or more conductors.

3. 3. The wireless power transmitter of claim 2, wherein the remote ping operation is separate from normal wireless power transmission operation and enables the wireless power transmitter control circuitry to measure or characterize one or more electrical, magnetic, or electromagnetic parameters that characterize a wireless power transmission link between the wireless power transmitter and an external object based on the resonant voltage associated with the wireless power transmitting coil and the resonant capacitor.

4. The wireless power transmitter of claim 3 , wherein the one or more electrical, magnetic, or electromagnetic parameters characterizing a wireless power transmission link are used to detect a wireless power receiver.

5. The wireless power transmitter of claim 3 , wherein the one or more electrical, magnetic, or electromagnetic parameters characterizing a wireless power transmission link are used to detect foreign objects.

6. 4. The wireless power transmitter of claim 3, wherein the resonant voltage associated with the wireless power transmitting coil and the resonant capacitor is a ringing signal induced by a stimulus provided by the inverter at the initiation of the remote ping operation.

7. 3. The wireless power transmitter of claim 2, wherein the logic and control circuit selectively activates the plurality of switching devices via a third conductor of the two or more conductors, and the analog measurement circuit measures the resonant voltage associated with the wireless power transmitting coil and the resonant capacitor via one of the two or more conductors that conducts the AC current between the inverter and the wireless power transmitter coil in normal wireless power transfer operation.

8. 1. A wireless power receiver, comprising: a wireless power receiver coil; a rectifier having a rectifier input coupled to the wireless power receiver coil, the rectifier receiving an AC voltage induced by a wireless power transmitter coupled to the wireless power receiver via the wireless power receiver coil, and generating a DC rectifier output voltage at a rectifier output for one or more receiver loads coupled to the rectifier output; a wireless power receiver control circuit that detects a pause in wireless power transmission initiated by the wireless power transmitter and measures or characterizes, via the wireless power receiver coil, one or more parameters that characterize a wireless power transmission link between the wireless power transmitter and the wireless power receiver; A wireless power receiver, wherein the wireless power receiver control circuit detects the cessation of wireless power transmission by detecting a change in one or more power transmission voltage, current, and frequency characteristics in the wireless power receiver, independent of communication with the wireless power transmitter.

9. The wireless power receiver of claim 8 , wherein the wireless power receiver control circuit detects the pause in wireless power transmission by detecting a drop in the DC rectifier output voltage.

10. 9. The wireless power receiver of claim 8, wherein the rectifier is a synchronous rectifier, and the wireless power receiver control circuit detects the pause in wireless power transmission by detecting cessation of switching of the synchronous rectifier.

11. 10. The wireless power receiver of claim 8, wherein the wireless power receiver control circuit detects the pause in wireless power transmission by a change in waveform shape of a voltage appearing across the wireless power receiver coil from a square wave shape associated with inverter switching in the wireless power transmitter to a sinusoidal wave shape associated with a power pause.

12. 9. The wireless power receiver of claim 8, wherein in response to detecting the pause in the wireless power transmission, the wireless power receiver control circuit temporarily pauses at least one of the one or more receiver loads coupled to the rectifier output.

13. the wireless power receiver control circuitry further detects the end of the pause in wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver, independent of communication with the wireless power transmitter; 9. The wireless power receiver of claim 8, wherein in response to detecting the end of the pause in the wireless power transmission, the wireless power receiver control circuit resumes the at least one of the one or more receiver loads coupled to the rectifier output that was paused in response to detecting the pause in the wireless power transmission.

14. the at least one of the one or more receiver loads coupled to the rectifier output that is paused in response to detecting the pause in the wireless power transfer includes a switching converter; 14. The wireless power receiver of claim 13, wherein the wireless power receiver control circuitry re-enables the at least one of the one or more receiver loads coupled to the paused rectifier output in response to detecting the pause in the wireless power transmission by ramping up the switching duty cycle of the switching converter to avoid overshoot or overvoltage of the DC rectifier output voltage.

15. 14. The wireless power receiver of claim 13, wherein ramping up the switching duty cycle of the switching converter to avoid overshoot or overvoltage of the DC rectifier output voltage comprises storing a pre-power pause duty cycle value and using the pre-power pause duty cycle value as a feedforward signal to accelerate ramp-up of the switching converter duty cycle.

16. 1. A method of operating a wireless power transmission system having a wireless power transmitter including an inverter driving a wireless power transmitter coil, a wireless power receiver including a wireless power receiver coil magnetically coupled to the wireless power transmitter coil, and a rectifier having a rectifier input coupled to the wireless power receiver coil and a rectifier output coupled to one or more wireless power receiver loads, comprising: Using the wireless power transmitter control circuit, initiating a temporary pause in wireless power transmission; providing a stimulus signal to induce a resonant voltage in the wireless power transmitter coil during the temporary pause in wireless power transmission; using the resonant voltage to measure or characterize one or more parameters that characterize a wireless power transmission link between the wireless power transmitter and the wireless power receiver through the wireless power receiver coil; thereafter, restarting the wireless power transmission by ending the temporary suspension of the wireless power transmission; Using the wireless power receiver control circuit, detecting the temporary cessation of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter; temporarily pausing at least one of the one or more receiver loads coupled to the rectifier output in response to detecting the temporary pause in wireless power transmission; and detecting a resumption of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics at the wireless power receiver independent of communication with the wireless power transmitter; and in response to resuming wireless power transmission, resuming the at least one of the one or more receiver loads coupled to the rectifier output that was paused in response to detecting the temporary pause in wireless power transmission.

17. the wireless power transmitter includes: a boot housing the inverter and the wireless power transmitter control circuitry; a pack housing the wireless power transmitter coil, a resonant capacitor, and a plurality of switching devices operable to selectively provide a resonant current circulation path between the wireless power transmitter coil and the resonant capacitor during a remote ping operation; and a cable disposed between the boot and the pack, the cable having at least three conductors including a first conductor and a second conductor for conducting AC current between the inverter and the wireless power transmitter coil, and a third conductor for enabling the wireless power transmitter control circuitry to selectively operate the plurality of switching devices during a normal wireless power transmission operation; 17. The method of claim 16, wherein using the resonant voltage to measure or characterize one or more parameters that characterize a wireless power transmission link between the wireless power transmitter and the wireless power receiver comprises selectively activating the plurality of switching devices during the remote ping operation.

18. 17. The method of claim 16, wherein using the resonant voltage to measure or characterize one or more parameters that characterize a wireless power transmission link between the wireless power transmitter and the wireless power receiver comprises detecting a foreign object.

19. 17. The method of claim 16, wherein at least one of detecting the temporary cessation of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics in the wireless power receiver independent of communication with the wireless power transmitter and detecting a resumption of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics in the wireless power receiver independent of communication with the wireless power transmitter comprises detecting a drop in a rectifier output voltage.

20. 17. The method of claim 16, wherein at least one of detecting the temporary cessation of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics in the wireless power receiver independent of communication with the wireless power transmitter and detecting a resumption of wireless power transmission by detecting a change in one or more power transmission voltage, current, or frequency characteristics in the wireless power receiver independent of communication with the wireless power transmitter comprises detecting a cessation of switching of the rectifier.

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