Intra-system magnetic coupling measurement for wireless power transfer

Abstract

To provide techniques for intra-system magnetic coupling measurement for wireless power transfer.SOLUTION: Determining an indication of coupling between a wireless power transmit coil of a wireless power transmitter and a wireless power receive coil of a wireless power receiver, wherein, with the wireless power receive coil substantially shorted: Measuring one or more circuit parameters of the wireless power transmitter, measuring the one or more circuit parameters of the wireless power transmitter with the wireless power receiver coil as an open circuit, and combining the one or more circuit parameters of the wireless power transmitter measured with the wireless power receiver coil substantially shorted and the one or more circuit parameters of the wireless power transmitter measured with the wireless power receiver coil as an open circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 669,517, filed July 10, 2024, entitled "SYSTEM MAGNETIC COUPLING MEASUREMENTS FOR WIRELESS POWER TRANSFER," and U.S. Provisional Patent Application No. 63 / 762,176, filed February 24, 2025, entitled "IN SYSTEM MAGNETIC COUPLING MEASUREMENTS FOR WIRELESS POWER TRANSFER," both of which are incorporated herein by reference. [Background technology]

[0002] Wireless power transmission is used in a variety of electronic devices. For example, smartphones, tablet computers, smart watches, wireless earbuds, styluses, etc. may employ wireless power transmission to facilitate charging of batteries within the devices. In some applications, estimating, calculating, or determining the coupling coefficient between a wireless power transmitter and a wireless power receiver may be desirable for purposes such as regulating power transmission, detecting foreign objects, etc. Summary of the Invention

[0003] The wireless power transmitter may include an inverter that generates an AC voltage upon receiving an input voltage, a wireless power transmit coil that receives the AC voltage from the inverter, the wireless power transmit coil being couplable with a wireless power receive coil of a wireless power receiver, and a controller circuit. With the wireless power receive coil in an open-circuit state, the controller circuit operates the inverter to wirelessly transfer power to the wireless power receiver using the wireless power transmit coil, and may determine an indication of coupling between the wireless power transmit coil and the wireless power receive coil by combining (i) one or more circuit parameters of the wireless power transmitter measured with the wireless power receive coil substantially shorted and (ii) one or more circuit parameters of the wireless power transmitter measured with the wireless power receive coil in an open-circuit state.

[0004] The indication of coupling may be a magnetic coupling coefficient determined according to an equation of the form:

number

number

number

[0005] The wireless power transmitter may further include a selectable tuning capacitance coupling the inverter to the wireless power transmitting coil. The selectable tuning capacitance may include one or more capacitors. The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially short-circuited may include one or more circuit parameters measured with a first value of the selectable tuning capacitance and one or more circuit parameters measured with a second value of the selectable tuning capacitance. The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil open-circuited may include one or more circuit parameters measured with the first value of the selectable tuning capacitance and one or more circuit parameters measured with the second value of the selectable tuning capacitance. Rx and L Rx may be determined by combining one or more circuit parameters measured using a first value of the selectable tuning capacitance and one or more circuit parameters measured using a second value of the selectable tuning capacitance.

[0006] C Rx and L Rx may be determined according to an equation of the form:

number

[0007] The indication of coupling may be a resistive coupling coefficient determined according to an equation of the form:

number

number

[0008] The wireless power transmitter may further include a selectable tuning capacitance coupling the inverter to the wireless power transmitting coil. The selectable tuning capacitance may include one or more capacitors. The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially short-circuited may include one or more circuit parameters measured with a first value of the selectable tuning capacitance and one or more circuit parameters measured with a second value of the selectable tuning capacitance. The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil open-circuited may include one or more circuit parameters measured with the first value of the selectable tuning capacitance and one or more circuit parameters measured with the second value of the selectable tuning capacitance. Rx and R Rx may be determined by combining one or more circuit parameters measured using a first value of the selectable tuning capacitance and one or more circuit parameters measured using a second value of the selectable tuning capacitance.

[0009] C Rx and R Rx is determined according to a formula of the form

number

[0010] A method of determining an indication of coupling between a wireless power transmitting coil of a wireless power transmitter and a wireless power receiving coil of a wireless power receiver, the method being performed by the wireless power transmitter, may include measuring one or more circuit parameters of the wireless power transmitter with the wireless power receiving coil substantially shorted, measuring one or more circuit parameters of the wireless power transmitter with the wireless power receiver coil open-circuited, and combining the one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted and the one or more circuit parameters of the wireless power transmitter measured with the wireless power receiver coil open-circuited.

[0011] The indication of coupling may be a magnetic coupling coefficient determined according to an equation of the form:

number

number

number

[0012] The method may further include measuring one or more circuit parameters of the wireless power transmitter with the wireless power receiving coil substantially shorted, including measuring one or more circuit parameters of the wireless power transmitter with a first value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted, and measuring one or more circuit parameters of the wireless power transmitter with a second value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted. The method may still further include measuring one or more circuit parameters of the wireless power transmitter with the wireless power receiver coil open-circuited, including measuring one or more circuit parameters of the wireless power transmitter with a first value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil open-circuited, and measuring one or more circuit parameters of the wireless power transmitter with a second value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil open-circuited. Rx and L Rx may be determined by combining one or more circuit parameters measured using a first value of the selectable tuning capacitance and one or more circuit parameters measured using a second value of the selectable tuning capacitance.

[0013] C Rx and L Rx is determined according to a formula of the form

number

[0014] The indication of coupling may be a resistive coupling coefficient determined according to an equation of the form:

number

number

[0015] The method may further include measuring one or more circuit parameters of the wireless power transmitter with the wireless power receiving coil substantially shorted, including measuring the one or more circuit parameters of the wireless power transmitter with a first value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted, and measuring the one or more circuit parameters of the wireless power transmitter with a second value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted. The method may further include measuring one or more circuit parameters of the wireless power transmitter with the wireless power receiver coil open-circuited, including measuring the one or more circuit parameters of the wireless power transmitter with a first value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil open-circuited, and measuring the one or more circuit parameters of the wireless power transmitter with a second value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil open-circuited. Rx and R Rx may be determined by combining one or more circuit parameters measured using a first value of the selectable tuning capacitance and one or more circuit parameters measured using a second value of the selectable tuning capacitance.

[0016] C Rx and R Rx may be determined according to an equation of the form:

number

[0017] The wireless power receiver may include a wireless power receiving coil that receives an AC voltage induced by a wireless power transmitting coil of a wireless power transmitter, a rectifier that converts the received AC voltage to a DC voltage, and a controller circuit that facilitates determining an indication of coupling between the wireless power receiving coil and the wireless power transmitting coil by the wireless power transmitter by selectively opening or substantially shorting the wireless power receiving coil and combining one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted with one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil open. The controller circuit may selectively substantially short-circuit the wireless power receiving coil using one or more switching devices of the rectifier. The controller circuit may selectively substantially short-circuit the wireless power receiving coil using one or more switching devices of the rectifier and one or more additional switching devices coupled between the wireless power receiving coil and ground.

[0018] The wireless power receiver may include a wireless power receiving coil configured to have an AC voltage induced by a wireless power transmitter, a rectifier that receives the AC voltage induced in the wireless power receiving coil and generates a DC rectifier output voltage, and a circuit that selectively shorts out the wireless power receiving coil to facilitate measurement by the wireless power transmitter of one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted.

[0019] The controller circuit for selectively shorting the wireless power receiving coil may include a counter that releases the selective shorting of the wireless power receiving coil upon counting a selected number of cycles of the AC voltage induced in the wireless power receiving coil. The circuit for selectively shorting the wireless power receiving coil may include a timer that releases the selective shorting of the wireless power receiving coil after a selected time. The circuit for selectively shorting the wireless power receiving coil may selectively short-circuit the wireless power receiving coil using one or more switching devices of a rectifier. The circuit for selectively shorting the wireless power receiving coil may be powered by a capacitor charged by the rectifier output voltage. The circuit for selectively shorting the wireless power receiving coil may be disabled upon discharge of the capacitor charged by the rectifier output voltage. The circuit for selectively shorting the wireless power receiving coil may be disabled in response to the rectifier output voltage corresponding to wireless power transfer from the wireless power receiver by the wireless power transmitter.

[0020] The circuitry for selectively shorting the wireless power receiving coil of the wireless power receiver may include at least one of a counter that releases the selective shorting of the wireless power receiving coil upon counting a selected number of cycles of the AC voltage induced in the wireless power receiving coil by the wireless power transmitter, and a timer that releases the selective shorting of the wireless power receiving coil after a selected time.

[0021] The circuitry may short-circuit the wireless power receiving coil to facilitate measurement by the wireless power transmitter of one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted. The circuitry may include both a counter that releases the selective short-circuiting of the wireless power receiving coil upon counting a selected number of cycles of an AC voltage induced in the wireless power receiving coil by the wireless power transmitter, and a timer that releases the selective short-circuiting of the wireless power receiving coil after a selected time.

[0022] The circuit may further include a comparator that generates an output having cycles corresponding to positive and negative half cycles of an AC voltage induced in the wireless power receiving coil by the wireless power transmitter, the output being provided to a counter. The circuit may selectively short-circuit the wireless power transmitting coil by turning on one or more switching devices of a rectifier of the wireless power transmitter. The circuit may further include a capacitor that charges from the rectifier of the wireless power transmitter to power the circuit. [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows a simplified block diagram of a wireless power transfer system.

[0024] [Figure 2A] 1 shows a simplified schematic diagram of a wireless power transfer system.

[0025] [Figure 2B] 1 shows an alternative simplified schematic diagram of a wireless power transfer system.

[0026] [Figure 3] 1 shows a flowchart of a coupling coefficient estimation technique.

[0027] [Figure 4A] 1 shows a timing sequence for a coupling coefficient estimation technique.

[0028] [Figure 4B] 10 illustrates an alternative timing sequence for a coupling coefficient estimation technique.

[0029] [Figure 5] 1 shows a schematic diagram of a circuit for selectively shorting wireless power receiver coils to perform coupling coefficient estimation.

[0030] [Figure 6] 10 illustrates exemplary waveforms associated with selectively shorting a wireless power receiver coil. DETAILED DESCRIPTION OF THE INVENTION

[0031] 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.

[0032] 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.

[0033] 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 configured using any suitable circuit topology (e.g., full bridge, half bridge, etc.) and implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., fabricated using silicon, silicon carbide, or gallium nitride devices).

[0034] The inverter 114 can deliver the generated AC voltage to the transmitter coil 112. In addition to the wireless coil that enables magnetic coupling to the receiver, the transmitter coil block 112 shown in FIG. 1 may include tuning circuit components, such as additional inductors and capacitors, that facilitate operation of the transmitter under different conditions, such as different degrees of magnetic coupling to the receiver or different operating frequencies. The wireless coil itself can be configured in a variety of different ways. In some embodiments, the wireless coil can be formed as a winding of wire wound around a suitable bobbin. In other embodiments, the wireless coil can be formed as a trace on a printed circuit board. Other arrangements are possible and can be used in conjunction with the various embodiments described herein. The wireless transmitter coil can also include a core of magnetically permeable material (e.g., ferrite) configured to affect the magnetic flux pattern of the coil in a manner suitable for a particular application. The teachings herein can be applied in conjunction with any of a wide variety of transmitter coil arrangements suitable for a given application.

[0035] The PTx controller / communications module 116 can monitor the power transmit 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 transmit coil (i.e., in-band communication) or via a separate communication channel (not shown, i.e., out-of-band communication). In the case of in-band communication, the controller / communications module 116 can detect and decode signals (such as voltage, frequency, or load variations) imposed on the magnetic link by the PRx to receive the information, and can instruct the inverter to modulate the delivered power by manipulating various parameters (such as voltage, frequency, etc.) of the generated voltage to transmit the information to the PRx. In some embodiments, the controller / communications module may be configured to communicate data to the PRx employing frequency shift keying (FSK) communications, in which the frequency of the inverter signal is modulated. The controller / communications module 116 may be configured to detect amplitude shift keying (ASK) communications or load modulation-based communications from the PRx. In either case, the controller / communications module 126 may be configured to vary the current drawn at the receiver 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.

[0036] 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.

[0037] The PTx device 110 may optionally include other systems and components, such as a separate communications module 118. In some embodiments, the communications module 118 can communicate with a corresponding module tag in the PTx via the power transfer coil. In other embodiments, the communications module 118 can communicate with a corresponding module using a separate physical channel 138.

[0038] 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.

[0039] The receiver coil 122 outputs an AC voltage induced therein by magnetic induction through the transmitter coil 112. This output AC voltage may be provided to a rectifier 124, which provides DC output power to one or more loads associated with the PRx device. The rectifier 124 may be controlled by a controller / communications module 126, which operates as described further below. In various embodiments, the rectifier controller and communications module may be implemented in a common system, such as a microprocessor-, microcontroller-, or other based system. In other embodiments, the rectifier controller may be implemented by a separate controller module and communications module having means for communication therebetween. The rectifier 124 may be configured using any suitable circuit topology (e.g., full bridge, half bridge, etc.) and may be implemented using any suitable semiconductor switching device technology (e.g., MOSFETs, IGBTs, etc., fabricated using silicon, silicon carbide, or gallium nitride devices).

[0040] The PTx controller / communications module 126 can monitor the receiver coil and use information derived therefrom to appropriately control the rectifier 124 depending on given circumstances. For example, the controller / communications module can be configured to operate the rectifier 124 to provide a given output voltage depending on a particular application. In some embodiments, the controller / communications module can be configured to transmit information to the PTx device to effectively control the power delivered to the receiver. This information can be received and transmitted via the power transmit 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.

[0041] 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 a power transfer coil. In other embodiments, the communications module 128 can communicate with a corresponding module or tag using a separate physical channel 138.

[0042] Many variations and extensions of the wireless power transmission system 100 described above are possible, and the teachings below are applicable to any such variations and extensions.

[0043] In a wireless power transfer system, it may be useful to know a magnetic coupling coefficient (also referred to as a “coupling coefficient,” and sometimes denoted as “k”) that indicates the degree of magnetic coupling between a PTx device and a PRx device. The coupling coefficient may be used for various purposes in a wireless power transfer system, such as to provide an indication of the degree of matching between a PTx device and a PRx device, an indication of the presence of a foreign object in proximity to the wireless power transfer device, etc. Accordingly, a wireless power transfer device may include a mechanism for calculating, estimating, or determining such a coupling coefficient, which may be understood with reference to the simplified schematic diagram of a wireless power transfer system shown in FIG. 2A .

[0044] FIG. 2A shows a simplified schematic diagram of a wireless power transfer system 200a. The PTx device is shown on the left side of the diagram, and an inverter 214, generally corresponding to the inverter 114 described above with reference to FIG. 1, can receive an input voltage Vinv. The inverter 214 can generate an AC output voltage that can be provided to a wireless power transfer coil 212 (corresponding to the coil 112 described above and represented in FIG. 2A as inductance LTx). The inverter 214 can be coupled to the wireless power transfer coil 212 by a tuning capacitance, represented in the schematic by capacitor CTx. In some embodiments, a selectable tuning capacitance can be provided to tune the circuit to different operating conditions.

[0045] With further reference to FIG. 2A , the wireless power transmission coil 212 may be magnetically or inductively coupled to the wireless power transmission coil 222 (corresponding to the coil 122 described above and represented as inductance LRx in FIG. 2A ) when the devices are physically close to each other. As a result of this magnetic or inductive coupling, represented by a coupling coefficient k, an AC voltage / current in the wireless power transmission coil 212 may induce a corresponding AC voltage / current in the wireless power transmission coil 222. This AC voltage / current may be coupled to the rectifier 224 by a tuning capacitance, represented in the schematic diagram by capacitor CRx. In some embodiments, a selectable tuning capacitance may be provided to tune the circuit to different operating conditions. In FIG. 2A , the rectifier 224 is shown as a full-bridge rectifier consisting of multiple switching devices S1-S4. The rectifier 224 may generate a DC output voltage Vrect, which may be used for various purposes within the PRx device, such as charging a battery or powering a receiver device system.

[0046] As mentioned above, estimating the coupling coefficient k can be useful for various purposes. In some prior art wireless power transfer systems, the estimated coupling coefficient value k est is determined according to the following formula:

number

[0047] It is desirable to determine the coupling coefficient k while enabling simplified measurements that can be performed in the field (i.e., after manufacturing) without extensive pre-manufacturing testing, etc. Such a technique may be based on measurements made with the receiver-side wireless power transmission coil 222 (represented by inductance LRx) short-circuited versus open-circuited. More specifically, the magnetic coupling coefficient k between two magnetically coupled coils may be given by:

number

number

number

[0048] Such techniques for coupling coefficient determination are based on being able to measure circuit parameters, including or corresponding to the inductance of the transmitter-side wireless power transmission coil, during operating conditions in which the receiver-side wireless power transmission coil is open-circuited and short-circuited, examples of which are described in more detail below. Generally, such measurements may be performed during what may be referred to as a “low power ping” or “LPP” phase of the wireless power transfer start-up sequence, which is described in more detail below with respect to FIG. 4A .

[0049] 2B, there is at least one alternative way in which the receiver-side wireless power transmission coil 222 can be substantially shorted. As used herein, "substantially shorted" means that either the coil or the resonant tank including the coil and any tuning capacitance is shorted, as will be explained in more detail below. One straightforward way is to short the receiver-side wireless power transmission coil 222, i.e., connect one terminal of the coil to ground, in particular by using an additional switch S sc (FIG. 2A). The other terminal can be shorted / connected to ground using rectifier switch S4. The advantage of such a configuration is that it completely shorts out the coil without including any other components in the circuit. A potential disadvantage of such a configuration, at least for some embodiments, is that it requires an additional switching device on the receiver side. In either case, such a circuit configuration can rely on the above equation for determining the coupling coefficient.

[0050] Alternatively, as shown in FIG. 2B, which illustrates a simplified schematic diagram of a wireless power transmission system 200b, another way in which the receiver-side wireless power transmission coil 222 can be substantially shorted is by closing rectifier switches S3 and S4. As in at least some embodiments, the tuning capacitance (tuning capacitance C in FIG. 2A) Rx The series-tuned capacitance C shown in FIG. 2B can correspond to series or parallel tuning capacitance C p ) the coil is sc As with the / S4 technology, the FET is effectively shorted. The same is essentially true if the tuning capacitance is large enough to be used more like a DC blocking capacitor than a tuning capacitor, which may be the case at least for some PRx device designs. Instead, the nominal series and / or parallel tuning capacitance (C series / C p ), which may be the case in at least some embodiments, the short circuit is actually a short circuit of the wireless power transmission coil and the tuning capacitance, which may be collectively described as a resonant tank. Thus, the short circuit is not just a short circuit of the receiver-side wireless power transmission coil, and the coupling coefficient equation above must be modified to account for the tuning capacitance.

[0051] In this alternative, the above equation may be adjusted to account for the fact that the receiver tuning capacitance and any parasitic capacitance may be included in the short circuit. More specifically, the coupling coefficient may be determined by:

number

[0052] 3 shows a flowchart 300 illustrating the coupling coefficient determination technique as described above. The steps of the flowchart may be performed by a controller circuit of a wireless power transmitter (as described above) or by any other suitable controller circuit in a wireless power transfer system. The illustrated flowchart illustrates the determination of the coupling coefficient by using a switchable transmitter-side tuning capacitance C Tx We show that we can determine both the magnetic coupling coefficient k and the resistive coupling coefficient kr for a wireless power transfer system that includes a tuning capacitance C Tx For example, C Tx1 and C Tx2 In some applications, the coupling coefficient k may be an indicator used to select a tuning capacitance value. Furthermore, the resistive coupling coefficient kr may be used to improve various aspects of operating or controlling the wireless power transfer system, such as improved foreign object detection. In any case, the flowchart 300 shows four separate measurement blocks 341-344. In block 341, a first transmitter-side tuning capacitance value C Tx1 At block 342, an open circuit measurement may be performed using a first transmitter tuning capacitance value C Tx1 In block 343, a short circuit measurement using a second transmitter tuning capacitance value C Tx2 At block 344, an open circuit measurement may be performed using a second transmitter tuning capacitance value C Tx2 Between blocks 342 and 343, a short circuit measurement can be performed using, for example, C Tx1 From C Tx2 A transition arrow 349 is shown corresponding to a change in the transmitter tuning capacitance to C. Tx The timing of the transitions is not important, and measurements may be performed in any order or at any time, as desired. One example of such a sequence is described in more detail below with respect to Figure 4A, and another example is described in Figure 4B.

[0053] In either case, the first measurement block 341 can generate two values: an open-circuit resonant frequency, denoted as Foc1, and an open-circuit resistance value, Roc1 (which can be used to determine the resistive coupling coefficient, as described in more detail below). Similarly, the second measurement block 342 can generate two additional values: a short-circuit resonant frequency, Fsc1, and a short-circuit resistance value, Rsc1 (which can be used to determine the resistive coupling coefficient, as described in more detail below). If the resistive coupling coefficient, kr, is not required for a particular application, the resistance measurement may be omitted. In either case, the measurements from the measurement blocks 341 and 342 can be provided to an initial calculation block 345. In the initial calculation block 345, the initial (magnetic) coupling coefficient can be calculated as described above, or more specifically, using the following equation:

number

number

[0054] The above calculations in the initial calculation block 345 provide magnetic and resistive coupling coefficient values ​​when there is no need to compensate for the transmitter-side tuning capacitance, such as when the receiver-side wireless power transmission coil can be shorted or when the transmitter-side tuning capacitance is large enough that its value is negligible. In other cases, the values ​​determined in the initial calculation block can be provided to a further calculation block 347, described in more detail below, to compensate for the tuning capacitance.

[0055] If the transmitter has an adjustable tuning capacitance, this capacitance value C Tx may be switched, and measurement blocks 343 and 344 may be performed. The third measurement block 343 may generate two values: an open-circuit resonant frequency, denoted as Foc2, and an open-circuit resistance value, Roc2, corresponding to a second transmitter-side tuning capacitance value. Similarly, the fourth measurement block 344 may generate two additional values: a short-circuit resonant frequency, Fsc2, and a short-circuit resistance value, Rsc2, both of which correspond to a second transmitter-side tuning capacitance value. If the resistive coupling coefficient, kr, is not required for a particular application, the resistance measurement may be omitted. In either case, the measurements from measurement blocks 343 and 344 may be provided to an initial calculation block 346, which may generally correspond to the initial calculation block 345 described above. In the initial calculation block 346, the initial (magnetic) coupling coefficient (corresponding to the second transmitter-side tuning capacitance value) may be calculated as described above, or more specifically, using the following equation:

number

number

[0056] The above calculations in the initial calculation block 346 provide magnetic and resistive coupling coefficient values ​​that can be used to compensate for the transmitter-side tuning capacitance when the receiver-side wireless power transmission coil cannot be shorted alone (e.g., when the resonant tank is shorted as a whole), or when the transmitter-side tuning capacitance is not large enough that its value can be ignored, etc. In such cases, the values ​​determined in the initial calculation block can be provided to a further calculation block 347.

[0057] Further calculation block 347 is executed to obtain the value L Rx C Rx (i.e., the product of the receiver inductance and capacitance) and R Rx C Rx (i.e., the product of the resistance and capacitance on the receiver side) can be determined and used to calculate the initial coupling coefficient value k determined above in initial calculation block 345. init_1 and kr init_1 More specifically, the amount L Rx C Rx may be given by:

number

number

[0058] The compensation parameter L calculated in the further calculation block 347 Rx C Rx and R Rx C Rx may then be provided to a compensation block 348, where the compensated (magnetic) coupling coefficient k may be determined by:

number

number

[0059] FIG. 4A illustrates a timing sequence 400a for a coupling coefficient estimation technique. The timing sequence 400a corresponds to a wireless power startup or initiation sequence that may be initiated by bringing a wireless power receiver (Rx) into proximity with a wireless power transmitter (Tx). The startup sequence may be performed according to an industry standard, such as the Qi family of standards promulgated by the Wireless Power Consortium (“WPC”). Alternatively, the startup sequence may be performed according to non-standard and / or proprietary techniques that may be fully or partially compatible with industry-standard startup sequences. In the illustrated example of FIG. 4A , the startup sequence may be initiated by bringing the Rx into proximity with the Tx, as indicated by block 0. A startup low-power ping “LPP” operation may then be performed, as indicated by block 1. This low-power ping may include an initial attempt at wireless power transmission by the wireless power transmitter, which may provide initial open-circuit measurements Foc1 and, optionally, Roc1, as described above with reference to FIG. 3. These values ​​may be provided to a coupling coefficient calculation block 2.7, described in more detail below. If the LPP indicates that an object is present in the vicinity of the wireless power transmitter, a digital ping may be initiated, as represented by block 2. This digital ping may include an attempt by Tx to initiate digital communication with Rx, for example, in-band communication by FSK (Frequency Shift Keying) of the drive signal provided by the inverter to the wireless power transmitter. If Rx receives an attempt to initiate digital communication, for example, by in-band communication using ASK (Amplitude Shift Keying) of the wireless power received by the rectifier, Tx may determine that a valid receiver device is present (block 451). Otherwise, the initiation process may resume at block 0 or 1, although such a process is beyond the scope of this disclosure.

[0060] If the digital ping process as described above results in a determination that a valid receiver is present, the determination of the coupling coefficient may proceed along the lines described above with respect to FIGS. 1-3. More specifically, the Rx may short-circuit the receiver-side wireless power transmission coil or resonant tank (block 2.1) to enable one or more resonant frequency or optional measurements to be made. In some embodiments, the Rx may, of course, automatically short-circuit the coil and / or tank at a predetermined time or sequence in the digital ping process. In some embodiments, the Rx may short-circuit the coil and / or tank in response to an instruction or communication received from the Tx. In either case, the Rx may short-circuit the coil and / or tank for a predetermined period of time (e.g., 100 ms). Optionally, the Rx may short-circuit the coil and / or tank until it receives a release command from the Tx. The period during which the Rx shorts the receiver-side wireless power transmission coil (whether fixed or terminated in response to a release command received from the Tx) is indicated by block 452 in FIG. 4A. Although 100 ms is one exemplary period, the period can be any desired value greater or less than 100 ms, such as 10 ms, 20 ms, 50 ms, 80 ms, 120 ms, 140 ms, 150 ms, 200 ms, etc.

[0061] In either case, during the short-circuit period, the Tx, e.g., the Tx controller circuit, can perform the short-circuit measurements described above. For example, a first short-circuit measurement can be performed during block 2.2, resulting in a first short-circuit resonant frequency (Fsc1) and, optionally, a first short-circuit resistance Rsc1, which may correspond to a first tuning capacitance value as described above with reference to FIG. 3. Then, in block 2.3, the Tx can change to a different resonant capacitance value, after which, in block 2.4, further measurements are taken. More specifically, a second short-circuit measurement can be performed during block 2.4, resulting in a second short-circuit resonant frequency (Fsc2) and, optionally, a second short-circuit resistance Rsc2, which may correspond to a second tuning capacitance value as described above with reference to FIG. 3. Then, in block 2.5, Rx may open the wireless power receiver coil and / or resonant tank circuit, allowing further measurements in block 2.6, resulting in a second open-circuit resonant frequency (Foc2) and optionally a second short-circuit resistance Roc2, which may correspond to a second tuning capacitance value as described above with reference to Figure 3. As described above, the first open-circuit measurements Fsc1 and Fsc2 may be performed following the start-up low power ping of block 1.

[0062] Once all of the measurements have been performed, the resulting measurements may be processed by the Tx, for example by its controller circuitry, in block 2.7 to determine the (magnetic) coupling coefficient k, and optionally the resistive coupling coefficient kr, which may proceed as described above with reference to Figure 3. The timing and sequencing of Figure 4A is merely an example, and other measurement sequences may be performed in any desired order to determine the particular parameters required in any given application.

[0063] FIG. 4B illustrates an alternative timing sequence 400b for the short and open circuit measurements described above. The sequence can begin with the wireless power receiver transmitting a KMEAS message 453 indicating that it wishes to perform the necessary measurements. This is acknowledged by an ACK message 454 from the wireless power transmitter, allowing the wireless power transmitter to begin a measurement interval, T_kmease. During this measurement interval, the wireless power transmitter can suspend power transmission for a T_terminate period. During the initial short interval, T_holdShort, the wireless power receiver can short-circuit the wireless power transmission coil (or resonant tank), allowing the wireless power transmitter to transmit analog pings 455a and 455b to perform the measurements described above. Between analog pings 455a and 455b, the wireless power transmitter can switch to an alternative transmitter tuning capacitance, Ctx, as described above with reference to FIG. 3. During a subsequent open-circuit interval T_holdOpen, the wireless power receiver can open-circuit the wireless power transmission coil (or resonant tank), allowing the wireless power transmitter to transmit analog pings 455c and 455d to perform the measurements described above. Between analog pings 455c and 455d, the wireless power transmitter can switch to an alternate transmitter tuning capacitance Ctx, as described above with reference to FIG. 3. After all measurements have been performed in conjunction with the analog pings, the wireless power transmitter can resume wireless power transmission, and the wireless power receiver can engage in subsequent ASK communications (457) as needed.

[0064] Other variations in the measurement timing sequence are possible, for example, a short circuit measurement can be performed after an open circuit measurement, a short and open circuit measurement for one tuning capacitance can be performed first, a short and open circuit measurement for a second tuning capacitance can be performed second, etc.

[0065] 5 shows a schematic diagram of a circuit 500 for selectively shorting a wireless power receiver coil to perform coupling coefficient estimation. Circuit 500 may be powered by the wireless power receiver's rectifier output voltage VRECT (see FIGS. 2A-2B) via circuit 561 that can selectively connect / disconnect the rectifier output voltage to the AUX bus that powers the circuit. For example, when Vrect is available, it may charge a source capacitor 562 that may be used to power the rest of the circuit when Vrect is not available. The illustrated arrangement of circuit 561 and source capacitor 562 is just one possible arrangement, and other configurations are possible.

[0066] Circuit 500 can also connect to the wireless power receiving coil via terminals AC1 and AC2 (see FIGS. 2A and 2B). As discussed above, this connection can allow for effective shorting of the wireless power receiving coil, which can include either shorting the coil alone or shorting the coil together with any tuning circuitry, as described above. As described in more detail below, circuit 500 can short-circuit the wireless power receiving coil in response to appropriate conditions to allow the wireless power transmitter to perform measurements within the circuit to determine the coupling coefficient, as described above. Circuit 500 can also disable the short-circuit under certain conditions to allow wireless power transmission to resume. For example, circuit 500 can remove the short-circuit in response to expiration of a timer, a specific number of cycles of the AC input, discharge of source capacitor 562, etc.

[0067] Circuit 500 can monitor the rectifier output voltage Vrect to determine whether the wireless power receiver is receiving power from the wireless power transmitter. If so, a RECT_PG (rectifier power good) signal applied to D flip-flop 570 (via inverter 571) can prevent shorting of the wireless power receive coil. Otherwise, if there is no Vrect voltage, wireless power transmission has stopped and receive coil shorting operation can be enabled. An additional input signal EnShort provided to D flip-flop 570 can further enable selective enabling or disabling of receive coil shorting operation. This EnShort signal can be provided, for example, by the wireless power receiver control circuitry described above with reference to FIG. 1.

[0068] In either case, when a condition occurs to trigger a coil short, the output of D flip-flop 570, an Apply_Short signal, may be provided to latch 569, which may be, for example, an SR flip-flop. This may trigger the latch, whose output signal (Short_On) may be applied to switches S3 / S4 (via driver circuit 576) to turn them on and effectively short-circuit the wireless power receiving coil. Switches S3 and S4 may be low-side rectifier switches (see FIGS. 2A and 2B) or may be separate switches for shorting the wireless power receiving coil as described above. In either case, once the wireless power receiving coil is short-circuited, the wireless power transmitter may use its inverter or other suitable circuitry to drive a wireless power transmitting coil, which may be magnetically coupled to the wireless power receiving coil, to perform measurements as described above to determine the coupling coefficient.

[0069] The voltage across the wireless power receiving coil, i.e., the voltage between terminals AC1 and AC2, can be provided to a comparator 563, which can deliver a positive output during the positive half-cycle of the AC waveform and a zero output during the negative half-cycle of the AC waveform (or vice versa). Thus, the output of comparator 563, the AC_Comp signal, can be a square wave having a frequency corresponding to the AC voltage across the wireless power receiving coil. This AC_Comp signal can be provided to a counter 566, which can count cycles associated with short-circuit measurements made by the wireless power transmitter. Counter 566 can be enabled by a control circuit (from the Ctl. signal) when a short circuit in the wireless power receiving coil is triggered. After a predetermined number of cycles has elapsed, the counter output goes high, which can trigger removal of the short circuit, as described in more detail below.

[0070] The removal of the short circuit may also be triggered in response to a timer 567. Timer 567 may be enabled by the control circuit and may receive as a clock input an output signal from oscillator 565, which may also be enabled by the control circuit. After a predetermined period of time has elapsed, the output of the timer goes high, which may trigger the removal of the short circuit, as described in more detail below.

[0071] Either counter 566 or timer 567 can trigger the release of the short circuit in response to either reaching its respective count or time threshold, which can be determined as appropriate for a particular application. For example, their outputs can be provided to OR gate 568, which in turn can be provided to the reset pin of latch 569 described above. This can reset the latch, which can deassert the Short_on signal provided to shorting switches S3 / S4, turning them off and thereby unshorting the wireless power receiving coil. The latch output signal can also be provided to D flip-flop 570 via delay element 572, resetting the flip-flop and thereby disabling circuit 500.

[0072] The short-circuit condition can also be released when the wireless power transmitter begins delivering power to the wireless power receiver. This action causes the rectifier output voltage Vrect to go high, which causes the RECT_PG signal described above to turn off the D flip-flop 570. Finally, the short-circuit condition can also be released when the source capacitor 562 discharges, thereby powering down the circuit 500 and deasserting the drive signal provided to the short-circuit switch S3 / S4.

[0073] FIG. 6 shows a plot 600 of example waveforms associated with selectively shorting a wireless power receiver coil, derived from a circuit simulation of circuit 500 described above. Waveform 681 shows the AC voltage across the wireless power transmission coil, indicated by waveform segments 681a-681f. Waveform segment 681a corresponds to the period during which the wireless power transmitter is delivering power to the wireless power receiver. This region is shown in solid line because the frequency of the AC voltage is substantially higher than the time scale of FIG. 6. Waveform segment 681b corresponds to the decay of the AC voltage when the wireless power transmitter stops delivering power to the wireless power receiver, eventually reaching a zero value when the wireless power receiver coil is shorted, as indicated by waveform segment 681c. Waveform segment 681d corresponds to a measurement performed by the wireless power transmitter as described above. Wireless power transmission then resumes, as indicated by waveform segment 681e, which may initially start at a lower voltage and then transition to a higher voltage, as indicated by waveform segment 681f.

[0074] Waveform 682 depicts the rectifier output voltage Vrect, shown in waveform segments 681a-681d. Waveform segment 682a depicts a constant value corresponding to the period when the wireless power transmitter is delivering power to the wireless power receiver. Waveform segment 682b depicts the rectifier output voltage Vrect when the wireless power transmitter is not delivering power, during which time the rectifier voltage decays (waveform segment 682c) until wireless power transmission resumes, at which point the rectifier voltage Vrect increases (waveform segment 682c) until it reaches its nominal constant value (waveform segment 682d).

[0075] Waveform 683 shows the voltage across capacitor 562, which powers circuit 500. As can be seen, the capacitor initially charges from the rectifier output voltage and then remains at a relatively constant level, thereby allowing capacitor 562 to power the operation of circuit 500, as described above with reference to FIG.

[0076] Waveform 684 corresponds to the value of counter 566 and is shown in segments 684a-684g. In waveform segment 684a, the counter is disabled, so the counter value is zero. When the wireless power receiving coil is shorted, waveform segment 684b shows a slight increase in the counter value, which may be associated with, for example, circuit ringing and / or open circuit measurements being performed by the wireless power transmitter. When the wireless power receiving coil stabilizes in the short circuit condition, the counter remains constant at a low level corresponding to waveform segment 684c. Then, when the wireless power transmitter begins its measurements (corresponding to waveform segment 681d above), the counter value increases accordingly. The counter may then stabilize at a value corresponding to waveform segment 684e until wireless power transmission resumes, at which point the counter again increases, as shown by waveform segment 684f. Finally, once the counter reaches its threshold (or the timer mentioned above reaches its timeout value), the short circuit condition can be removed, which can also cause the counter to reset, returning its value to zero, as shown by waveform segment 684g.

[0077] Waveform 685 illustrates the Short_On signal applied to the shorting switch, as shown in FIG. 5. During waveform segment 685a, the signal is low, indicating that shorting switch S3 / S4 has not yet been turned on. Waveform segment 685b corresponds to the interval when this signal is high, shorting out the wireless power receiving coil. Finally, when the short is released (based on one of the conditions described above, such as a counter or timer reaching a predetermined threshold), the signal returns to zero, turning off switch S3 / S4.

[0078] The foregoing describes various features and embodiments relating to calculating, estimating, or determining a coupling coefficient to improve wireless power transfer in a wireless power transfer system. 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, and the like. 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.

[0079] The above describes an exemplary embodiment of a wireless power transmission system capable of transmitting specific information between the PTx and PRx in the system. The present disclosure contemplates that the passing of this information may improve the ability of devices to provide wireless power signals to each other in an efficient manner that facilitates battery charging, such as by determining the level of inductive coupling between a wireless power transmitter and a wireless power receiver. Entities implementing the present technology should take care to ensure that well-established privacy policies and / or practices are adhered to, to the extent that 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 a 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 their devices on a power transmitter if the power transmitter is configured to poll for sensitive information from power receivers.

Claims

1. 1. A wireless power transmitter, comprising: an inverter that receives an input voltage and generates an AC voltage; a wireless power transmitting coil that receives the AC voltage from the inverter, the wireless power transmitting coil being couplable with a wireless power receiving coil of a wireless power receiver; a controller circuit, the controller circuit comprising: operating the inverter to wirelessly transfer power to the wireless power receiver using the wireless power transmit coil; A wireless power transmitter that determines an indication of coupling between the wireless power transmitting coil and the wireless power receiving coil by combining (i) one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially short-circuited, and (ii) one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil open-circuited.

2. The indication of the coupling is a magnetic coupling coefficient determined according to an equation of the form: [Equation 1] Here, L Tx,sc is the inductance of the wireless power transmitting coil measured with the wireless power receiving coil substantially short-circuited, and L Tx,oc 10. The wireless power transmitter of claim 1, wherein .times. ...

3. The indication of the coupling is an indication of a magnetic coupling coefficient determined according to an equation of the form: [Equation 2] where f sc is the resonant frequency measured with the wireless power receiving coil substantially short-circuited, and f oc 10. The wireless power transmitter of claim 1, wherein .lamda. is a resonant frequency measured when the wireless power receiving coil is in an open circuit state.

4. The indication of the coupling is an indication of a magnetic coupling coefficient determined according to an equation of the form: [Equation 3] where f sc is the resonant frequency measured with the wireless power receiving coil substantially short-circuited, and f oc is the resonant frequency measured when the wireless power receiving coil is in an open circuit state, and C Rx is the capacitance of the wireless power receiver, and L Rx 10. The wireless power transmitter of claim 1, wherein: is the inductance of the wireless power receiving coil.

5. a selectable tuning capacitance coupling the inverter to the wireless power transmit coil; the selectable tuning capacitance comprises one or more capacitors; The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted are: one or more circuit parameters measured using a first value of the selectable tuning capacitance; one or more circuit parameters measured using a second value of the selectable tuning capacitance; The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil in an open circuit state are one or more circuit parameters measured using the first value of the selectable tuning capacitance; one or more circuit parameters measured using the second value of the selectable tuning capacitance; C Rx and L Rx 5. The wireless power transmitter of claim 4, wherein is determined by combining one or more circuit parameters measured using the first value of the selectable tuning capacitance and one or more circuit parameters measured using the second value of the selectable tuning capacitance.

6. C Rx and L Rx is determined according to a formula of the form [Equation 4] where: k init_1 is a coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil open circuited; k init_2 is a coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil open circuited; ω sc_1 is the resonant frequency measured with the wireless power receiving coil substantially shorted and using the first value of the selectable tuning capacitance; ω sc_2 6. The wireless power transmitter of claim 5, wherein ≡(f) is a resonant frequency measured using the second value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted.

7. The indication of the coupling is a resistive coupling coefficient determined according to an equation of the form: [Equation 5] Here, R sc_1 is the resistance measured with the wireless power receiving coil substantially short-circuited, and R oc_1 10. The wireless power transmitter of claim 1, wherein Ω is the resistance measured when the wireless power receiving coil is in an open circuit state.

8. The indication of the coupling is a resistive coupling coefficient determined according to an equation of the form: [Equation 6] where: R sc_1 is the resistance measured with the wireless power receiving coil substantially shorted; R oc_1 is the resistance measured when the wireless power receiving coil is in an open circuit state, ω sc is the resonant frequency measured with the wireless power receiving coil substantially short-circuited, R Rx is the resistance of the wireless power receiver, C Rx 10. The wireless power transmitter of claim 1, wherein: is the capacitance of the wireless power receiver.

9. a selectable tuning capacitance coupling the inverter to the wireless power transmit coil; The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted are: one or more circuit parameters measured using a first value of the selectable tuning capacitance; one or more circuit parameters measured using a second value of the selectable tuning capacitance; The one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil in an open circuit state are one or more circuit parameters measured using the first value of the selectable tuning capacitance; one or more circuit parameters measured using the second value of the selectable tuning capacitance; C Rx and R Rx 9. The wireless power transmitter of claim 8, wherein is determined by combining one or more circuit parameters measured using the first value of the selectable tuning capacitance and one or more circuit parameters measured using the second value of the selectable tuning capacitance.

10. C Rx and R Rx is determined according to a formula of the form [Equation 7] where: kr init_1 is a resistive coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil open circuited; kr init_2 is a resistive coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil open circuited; ω sc_1 is the resonant frequency measured with the wireless power receiving coil substantially shorted and using the first value of the selectable tuning capacitance; ω sc_2 10. The wireless power transmitter of claim 9, wherein ≡(f) is a resonant frequency measured with the wireless power receiving coil substantially shorted and using the second value of the selectable tuning capacitance.

11. 1. A method for determining an indication of coupling between a wireless power transmitting coil of a wireless power transmitter and a wireless power receiving coil of a wireless power receiver, the method being performed by the wireless power transmitter, comprising: measuring the one or more circuit parameters of the wireless power transmitter with the wireless power receiving coil substantially shorted; measuring the one or more circuit parameters of the wireless power transmitter with the wireless power receiver coil in an open circuit state; combining the one or more circuit parameters of the wireless power transmitter measured with the wireless power receiver coil substantially short-circuited and the one or more circuit parameters of the wireless power transmitter measured with the wireless power receiver coil open-circuited; A method comprising:

12. The indication of the coupling coefficient is a magnetic coupling coefficient determined according to an equation of the form: [Equation 8] Here, L Tx,sc is the inductance of the wireless power transmitting coil measured with the wireless power receiving coil substantially short-circuited, and L Tx,oc 12. The method of claim 11, wherein ∑ i = 1 / 2 i ⁢ ...

13. The indication of the coupling is a magnetic coupling coefficient determined according to an equation of the form: [Equation 9] where f sc is the resonant frequency measured with the wireless power receiving coil substantially short-circuited, and f oc 12. The method of claim 11, wherein ≡(f) is the resonant frequency measured with the wireless power receiving coil in an open circuit state.

14. The indication of the coupling is a magnetic coupling coefficient determined according to an equation of the form: [Equation 10] where f sc is the resonant frequency measured with the wireless power receiving coil substantially short-circuited, and f oc is the resonant frequency measured when the wireless power receiving coil is in an open circuit state, and C Rx is the capacitance of the wireless power receiver, and L Rx 12. The method of claim 11, wherein: is the inductance of the wireless power receiving coil.

15. Measuring the one or more circuit parameters of the wireless power transmitter with the wireless power receiving coil substantially shorted includes: measuring one or more circuit parameters of the wireless power transmitter using a first value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted; measuring one or more circuit parameters of the wireless power transmitter using a second value of the selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted; Measuring the one or more circuit parameters of the wireless power transmitter with the wireless power receiver coil in an open circuit state includes: measuring one or more circuit parameters of the wireless power transmitter using the first value of the selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil in an open circuit state; measuring one or more circuit parameters of the wireless power transmitter using the second value of the selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil in an open circuit state; C Rx and L Rx 15. The method of claim 14, wherein is determined by combining one or more circuit parameters measured using the first value of the selectable tuning capacitance and one or more circuit parameters measured using the second value of the selectable tuning capacitance.

16. C Rx and L Rx is determined according to a formula of the form [0011] where: k init_1 is a coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil open circuited; k init_2 is a coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil open circuited; ω sc_1 is the resonant frequency measured with the wireless power receiving coil substantially shorted and using the first value of the selectable tuning capacitance; ω sc_2 16. The method of claim 15, wherein ≡(√{square root over ( ...

17. The indication of the coupling is a resistive coupling coefficient determined according to an equation of the form: [0012] Here, R sc_1 is the resistance measured with the wireless power receiving coil substantially short-circuited, and R oc_1 12. The method of claim 11, wherein ∑ is the resistance measured with the wireless power receiving coil in an open circuit state.

18. The indication of the coupling is a resistive coupling coefficient determined according to an equation of the form: [0013] where: R sc_1 is the resistance measured with the wireless power receiving coil substantially shorted; R oc_1 is the resistance measured when the wireless power receiving coil is in an open circuit state, ω sc is the resonant frequency measured with the wireless power receiving coil substantially short-circuited, R Rx is the resistance of the wireless power receiver, C Rx The method of claim 11 , wherein: is the capacitance of the wireless power receiver.

19. Measuring the one or more circuit parameters of the wireless power transmitter with the wireless power receiving coil substantially shorted includes: measuring one or more circuit parameters of the wireless power transmitter using a first value of a selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted; measuring one or more circuit parameters of the wireless power transmitter using a second value of the selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil substantially shorted; Measuring the one or more circuit parameters of the wireless power transmitter with the wireless power receiver coil in an open circuit state includes: measuring one or more circuit parameters of the wireless power transmitter using the first value of the selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil in an open circuit state; measuring one or more circuit parameters of the wireless power transmitter using the second value of the selectable tuning capacitance of the wireless power transmitter with the wireless power receiving coil in an open circuit state; C Rx and R Rx 20. The method of claim 18, wherein is determined by combining one or more circuit parameters measured using the first value of the selectable tuning capacitance and one or more circuit parameters measured using the second value of the selectable tuning capacitance.

20. C Rx and R Rx is determined according to a formula of the form [0014] where: kr init_1 is a resistive coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the first value of the selectable tuning capacitance with the wireless power receiving coil open circuited; kr init_2 is a resistive coupling coefficient determined using one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil substantially shorted, and one or more circuit parameters of the wireless power transmitter measured using the second value of the selectable tuning capacitance with the wireless power receiving coil open circuited; ω sc_1 is the resonant frequency measured with the wireless power receiving coil substantially shorted and using the first value of the selectable tuning capacitance; ω sc_2 20. The method of claim 19, wherein ≡(√{square root over ( ...

21. 1. A wireless power receiver, comprising: a wireless power receiving coil for receiving an AC voltage induced by a wireless power transmitting coil of a wireless power transmitter; a rectifier that converts the received AC voltage into a DC voltage; a controller circuit that selectively opens or substantially shorts the wireless power receiving coil and combines one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted with one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil open-circuited, thereby facilitating the wireless power transmitter to determine an indication of coupling between the wireless power receiving coil and the wireless power transmitting coil; A wireless power receiver comprising:

22. 22. The wireless power receiver of claim 21, wherein the controller circuit selectively substantially shorts out the wireless power receiving coil using one or more switching devices of the rectifier.

23. 22. The wireless power receiver of claim 21 , wherein the controller circuit selectively substantially shorts out the wireless power receiving coil using one or more switching devices of the rectifier and one or more additional switching devices coupled between the wireless power receiving coil and ground.

24. 1. A wireless power receiver, comprising: a wireless power receiving coil configured to have an AC voltage induced therein by a wireless power transmitter; a rectifier that receives the AC voltage induced in the wireless power receiving coil and generates a DC rectifier output voltage; a circuit for selectively shorting the wireless power receiving coil; A wireless power receiver comprising:

25. 25. The wireless power receiver of claim 24, wherein the circuit that selectively shorts the wireless power receiving coil selectively shorts the wireless power receiving coil to facilitate measurement by the wireless power transmitter of one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted.

26. 25. The wireless power receiver of claim 24, wherein the controller circuit that selectively shorts the wireless power receiving coil includes a counter that removes the selective shorting of the wireless power receiving coil upon counting a selected number of cycles of the AC voltage induced in the wireless power receiving coil.

27. 25. The wireless power receiver of claim 24, wherein the circuitry for selectively shorting the wireless power receiving coil includes a timer that releases the selective shorting of the wireless power receiving coil after a selected time.

28. 25. The wireless power receiver of claim 24, wherein the circuit for selectively shorting the wireless power receiving coil uses one or more switching devices of the rectifier to selectively short the wireless power receiving coil.

29. 25. The wireless power receiver of claim 24, wherein the circuit for selectively shorting the wireless power receiving coil is powered by a capacitor charged by the rectifier output voltage.

30. 29. The wireless power receiver of claim 28, wherein the circuit that selectively shorts the wireless power receiving coil is disabled upon discharging of the capacitor charged by the rectifier output voltage.

31. 25. The wireless power receiver of claim 24, wherein the circuit that selectively shorts the wireless power receiving coil is disabled in response to a rectifier output voltage corresponding to wireless power transfer from the wireless power receiver by the wireless power transmitter.

32. 1. A circuit for selectively shorting a wireless power receiving coil of a wireless power receiver, the circuit comprising: a counter that removes the selective short circuit of the wireless power receiving coil upon counting a selected number of cycles of an AC voltage induced in the wireless power receiving coil by a wireless power transmitter; and a timer that releases the selective shorting of the wireless power receiving coil after a selected time.

33. 33. The circuit of claim 32, wherein the circuit shorts out the wireless power receiving coil to facilitate measurement by the wireless power transmitter of one or more circuit parameters of the wireless power transmitter measured with the wireless power receiving coil substantially shorted.

34. 33. The circuit of claim 32, wherein the circuit comprises both the counter that removes the selective short circuit of the wireless power receiving coil upon counting the selected number of cycles of the AC voltage induced in the wireless power receiving coil by the wireless power transmitter, and the timer that removes the selective short circuit of the wireless power receiving coil after the selected time.

35. 33. The circuit of claim 32, further comprising a comparator that generates an output having cycles corresponding to positive and negative half cycles of the AC voltage induced in the wireless power receiving coil by the wireless power transmitter, the output being provided to the counter.

36. 33. The circuit of claim 32, wherein the circuit selectively shorts out the wireless power transmit coil by turning on one or more switching devices of a rectifier of a wireless power transmitter.

37. 33. The circuit of claim 32, further comprising a capacitor that charges from a rectifier of a wireless power transmitter to power the circuit.

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