Wireless Power Transmission

Abstract

The power transmitter 101 comprises a driver 201 generating a drive signal for an output resonant circuit comprising a transmitter coil 103 generating a power transfer signal. A resonance detector 307 determines a coupled resonant frequency of the output resonant circuit, the coupled resonant frequency being a resonant frequency of the output resonant circuit of the transmitter coil 103 coupled to a receiver coil 107 which is part of a power transfer input resonant circuit of the power receiver 105. The quality factor of the input resonant circuit is 10 or greater. An estimation circuit 309 determines an estimate of a coupling coefficient for the coupling between the transmitter coil 103 and the receiver coil 107 depending on the first effective resonant frequency and, as the case may be, the uncoupled resonant frequency of the output resonant circuit or the input resonant circuit. An adapter 311 sets operating parameters depending on the estimate of the coupling coefficient.

Description

[Technical field]

[0001] The present invention relates to wireless power transfer systems, and in particular to the operation of a power transmitter to enable inductive power transfer to high power devices such as, but not limited to, kitchen appliances. [Background technology]

[0002] Most current electronic products require dedicated electrical contacts to be powered from an external power source. However, this is often impractical and requires the user to physically insert a connector or otherwise establish physical electrical contact. Power requirements also typically vary significantly, and most devices are now provided with their own dedicated power sources, so the typical user has many different power sources, each dedicated to a specific device. Although the use of an internal battery eliminates the need for a wired connection to a power source during use, this only provides a partial solution, as the battery must be recharged (or replaced). Furthermore, the use of a battery significantly increases the weight, and in some cases the cost and size, of the device.

[0003] To provide a significantly improved user experience, the use of wireless power sources has been proposed, where power is inductively transferred from a transmitter inductor in a power transmitter device to a receiver coil in an individual device.

[0004] Power transmission via magnetic induction is a well-known concept and is mainly used with transformers, with tight coupling between the primary transmitter inductor / coil and the secondary receiver coil. By separating the primary transmitter coil and secondary receiver coil between two devices, wireless power transfer between them is possible based on the principle of loosely coupled transformers.

[0005] Such a configuration allows wireless power transfer to the device without the need for any wires or physical electrical connections. Indeed, wireless power transfer allows the device to simply be placed adjacent to or on top of the transmitter coil in order to recharge or power it externally. The power transmitter device may be, for example, positioned with a horizontal surface on which the device can simply be placed in order to be powered.

[0006] Such wireless power transmission apparatus is further advantageous because it is designed so that the power transmitter device can be used with various power receiver devices. In particular, a wireless power transmission approach known as the Qi specification has been defined and is currently being further developed. This approach allows a power transmitter device that meets the Qi specification to be used with a power receiver device that also meets the Qi specification, and these devices do not need to be from the same manufacturer or proprietary to each other. The Qi standard further includes several features that allow the operation to be adapted to a specific power receiver device (e.g., depending on a specific power consumption).

[0007] The Qi specification is developed by the Wireless Power Consortium, and more information can be found, for example, on the Wireless Power Consortium website at http: / / www.wirelesspowerconsortium.com / index.html. In particular, the prescribed specification documents can be found here.

[0008] The Wireless Power Consortium is developing the Ki specification (also known as the Cordless Kitchen Specification), which is based on the Qi specification and aims to enable safe, reliable and efficient wireless power transfer to kitchen appliances. Ki supports much higher power levels, up to 2.2KW.

[0009] A possible challenge with wireless power transfer is that the performance of the power transfer is highly dependent on certain conditions. In particular, the power transfer performance in terms of efficiency, achievable power levels, compatible response time, etc., is often highly dependent on how the transmitter and receiver coils are positioned relative to each other. In general, placing the coils side-by-side and closer to each other often results in more efficient and reliable power transfer.

[0010] The performance of power transfer usually depends on the coupling coefficient or rate; the higher the coupling coefficient, the more efficient the power transfer.

[0011] Closer alignment and higher coupling coefficients can be achieved by designing the device such that the positioning of the power receiver device relative to the power transmitter device is severely restricted, e.g., constraining the power receiver to one specific location, but this is generally undesirable as it limits the practicality of the system. For example, in the case of a kitchen appliance where the power transmitter is implemented in a kitchen counter, it is preferable that the user can only place the appliance approximately close to the power transmitter coil, and the system then adapts accordingly. It is also preferable that the power transfer function is achieved without the need for mechanical or physical guide mechanisms that, for example, restrict the power receiver device. For example, it is desirable to be able to implement the power transmitter using a completely flat kitchen counter surface.

[0012] Power transfer is initiated at an initial operating point that provides acceptable performance for worst-case conditions to account for widely varying operating conditions. During power transfer, a control loop adapts the operating point to a more optimal operating point. Power transfer is specifically initiated at a low power level and then gradually increased during power transfer. Summary of the Invention [Problem to be solved by the invention]

[0013] However, such an approach is often suboptimal and does not provide ideal performance. Such an approach tends to introduce a delay before optimal performance is achieved. In many scenarios and conditions, this approach results in the optimal operating point not being reached, for example because the control loop settles into a local extremum instead of progressing to a global optimum.

[0014] Therefore, techniques that improve the operation of power transfer systems, and in particular those that can provide increased flexibility, reduced cost, reduced complexity, improved estimation of coupling coefficients, backward compatibility, increased suitability for the transmission of higher power levels, improved initialization of power transfer, increased suitability for particular operating conditions, and / or improved performance, would be beneficial.

[0015] SUMMARY OF THE DISCLOSURE Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination. [Means for solving the problem]

[0016] According to a first aspect of the present invention, there is provided a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter configured to wirelessly supply power to the power receiver via an inductive power transfer signal, the power transmitter comprising an output resonant circuit comprising a transmitter coil and at least one capacitor, a driver configured to generate a drive signal for the output resonant circuit and to generate the inductive power transfer signal, a resonance detector configured to determine a first coupled resonant frequency of the output resonant circuit during a resonance measurement period, the first coupled resonant frequency being a resonant frequency of the output resonant circuit of a transmitter coil coupled to a receiver coil of a power transfer input resonant circuit of the power receiver, and a resonance detector configured to determine a first coupled resonant frequency of the output resonant circuit during a resonance measurement period, the first coupled resonant frequency being a resonant frequency of the output resonant circuit of the transmitter coil coupled to a receiver coil of a power transfer input resonant circuit of the power receiver, and an adapter configured to set operating parameters in response to the estimated coupling coefficient, and the power receiver comprises a power transfer input resonant circuit having a power transmitter and a receiver coil configured to draw power from at least one capacitor, the power transfer input resonant circuit having a quality factor of 10 or greater during a resonant measurement period, and circuitry configured to switch from a power transfer mode in which the quality factor is not limited to 10 or greater to a measurement mode in which the quality factor is 10 or greater during the resonant measurement period when the power receiver is operating in the measurement mode.

[0017] The present invention, in many embodiments, allows for improved power transfer. In many embodiments, the present invention allows for improved initial performance and / or faster adaptation and convergence to a preferred operating point. In many embodiments, the approach increases the adaptability of the power transfer to changing operating conditions. The approach typically allows for a low complexity implementation while still achieving advantageous power transfer operation and performance. The approach allows for efficient, reliable, and / or accurate determination of coupling coefficients, which can increase the adaptability of parameters typically important in power transfer, thereby allowing for improved power transfer.

[0018] A particular advantage of this approach is that in many embodiments it is entirely power transmitter based, without necessarily performing specific estimation processes or calculations in the power receiver, which reduces costs in many scenarios, makes the approach easier to implement and / or more backward compatible.

[0019] The estimate of the coupling coefficient is an estimate of the change in the coupling coefficient.

[0020] The uncoupled resonant frequency of a resonant circuit is the resonant frequency when there is no inductive coupling from the resonant circuit to any inductors that are not part of the resonant circuit. The uncoupled resonant frequency of the output resonant circuit is the resonant frequency when the transmitter coil is not coupled to the receiver coil (or typically to any other inductors).

[0021] The first coupled resonant frequency is the resonant frequency of the output resonant circuit when the power receiver, with the output resonant circuit coupled to the receiver coil 107, is in a power transfer position for power transfer.

[0022] In some embodiments, the power transfer input resonant circuit has a quality factor of 20, 50, 100, or even 500 or more during the resonant measurement period.

[0023] The combined resonant frequency of the output resonant circuit corresponds to the resonant frequency of the drive signal, and more specifically to a maximum (or minimum, as the case may be) of the characteristic of the drive signal versus changing frequency of the drive signal.

[0024] In some embodiments, the estimation circuitry is further configured to determine an estimate of the coupling coefficient as a function of an uncoupled resonant frequency of the power transfer input resonant circuit.

[0025] In some embodiments, the uncoupled resonant frequency of the power transfer input resonant circuit is a predetermined frequency.

[0026] In some embodiments, the power transmitter further comprises a receiver for receiving data from the power receiver, the receiver being configured to receive data from the power receiver indicative of an uncoupled resonant frequency of the power transmission input resonant circuit.

[0027] In some embodiments, the estimation circuitry is further configured to determine an estimate of the coupling coefficient as a function of an uncoupled resonant frequency of the power transfer output resonant circuit.

[0028] In some embodiments, the uncoupled resonant frequency of the power transfer output resonant circuit is a predetermined frequency.

[0029] According to an optional feature of the invention, the resonance detector is further configured to measure a second coupling resonant frequency of the output resonant circuit during a resonance measurement period, the second coupling resonant frequency being another resonant frequency of the output resonant circuit in the presence of the power receiver, and the estimation circuit is further configured to determine an estimate of the coupling coefficient as a function of the second coupling resonant frequency.

[0030] This improves and / or facilitates estimation of the coupling coefficients in many embodiments, and in particular reduces sensitivity in many scenarios to changes in the operating environment, changing or unknown parameters of the components, power transmitters and / or power receivers, and / or measurement errors or inaccuracies.

[0031] According to an optional feature of the invention, the first coupling resonant frequency and / or the second coupling resonant frequency is a frequency at which a current of the drive signal exhibits a maximum value.

[0032] This may result in improved performance and / or operation and typically may facilitate or improve the estimation of the coupling coefficients.

[0033] The maximum value is the maximum value of the current of the drive signal with respect to the change in the frequency of the drive signal.

[0034] In some embodiments, the estimation circuit is configured to determine the coupling coefficient as a function of a ratio between the first coupling resonant frequency and the second coupling resonant frequency.

[0035] According to an optional feature of the invention, the estimator circuit is further configured to determine a coupling coefficient as a function of an uncoupled resonant frequency of the output resonant circuit and an uncoupled resonant frequency of the input resonant circuit.

[0036] This may result in improved performance and / or operation and typically may facilitate or improve the estimation of the coupling coefficients.

[0037] According to an optional feature of the invention, the estimator circuit is further configured to determine a coupling coefficient in response to a ratio of an uncoupled resonant frequency of the output resonant circuit to an uncoupled resonant frequency of the input resonant circuit.

[0038] This may result in improved performance and / or operation and may typically facilitate or improve the estimation of the coupling coefficients, particularly in many scenarios, making it less sensitive to changes in the operating environment, changing or unknown parameters of the components, power transmitters and / or power receivers, and / or measurement errors or inaccuracies.

[0039] In some embodiments, the estimation circuit is configured to determine a first ratio between the first coupled resonant frequency and the second coupled resonant frequency, and to determine a coupling coefficient that is a function of the ratio.

[0040] According to an optional feature of the invention, the estimation circuit is further configured to determine a coupling coefficient in response to a ratio between a sum of squares of the uncoupled resonant frequency of the output resonant circuit and the uncoupled resonant frequency of the input resonant circuit and a sum of squares of a second coupled resonant frequency, which is a resonant frequency of the output resonant circuit of the transmitter coil coupled to the receiver coil, and the first coupled resonant frequency.

[0041] This may result in improved performance and / or operation and may typically facilitate or improve the estimation of the coupling coefficients, particularly in many scenarios, making it less sensitive to changes in the operating environment, changing or unknown parameters of the components, power transmitters and / or power receivers, and / or measurement errors or inaccuracies.

[0042] According to an optional feature of the invention, the resonance detector is configured to determine an uncoupled resonance frequency of the output resonant circuit as a frequency at which a current of the drive signal exhibits a maximum value for an input resonant circuit having a quality factor of 2 or less, and the estimation circuit is configured to determine a coupling coefficient in response to the uncoupled resonance frequency of the output resonant circuit.

[0043] This improves the determination of the uncoupled resonant frequency of the output resonant circuit for the current conditions, and therefore improves the estimation of the coupling coefficient.

[0044] In some embodiments, the input resonant circuit has a quality factor of less than or equal to 0.5, 1, 3, or 5 when determining a maximum value corresponding to an uncoupled resonant frequency of the output resonant circuit.

[0045] The maximum value is the maximum value of the current of the drive signal with respect to the change in the frequency of the drive signal.

[0046] According to an optional feature of the invention, the resonance detector is configured to determine an uncoupled resonant frequency of the input resonant circuit as a frequency at which a current of the drive signal exhibits a local minimum for the input resonant circuit having a quality factor of 10 or greater, and the estimation circuit is configured to determine a coupling coefficient in response to the uncoupled resonant frequency of the input resonant circuit.

[0047] This improves the determination of the uncoupled resonant frequency of the input resonant circuit for the current conditions, and therefore improves the estimation of the coupling coefficient.

[0048] In some embodiments, the input resonant circuit has a quality factor of 5, 15, 20, or 30 or greater when determining a local minimum corresponding to an uncoupled resonant frequency of the input resonant circuit.

[0049] The minimum value is the minimum value of the current of the drive signal with respect to the change in the frequency of the drive signal.

[0050] The local minimum is determined during a resonance measurement period, specifically, using the same frequency sweep to determine both one or more coupled resonant frequencies of the output resonant circuit / drive signal and the uncoupled resonant frequency of the input resonant circuit.

[0051] In some embodiments, the resonance detector is configured to control the driver to generate a drive signal having a varying frequency during a resonance measurement period and determine the first coupled resonance frequency in response to at least one of a voltage of the drive signal, a current of the drive signal, and a phase difference between the voltage of the drive signal and the current of the drive signal.

[0052] This provides a particularly advantageous approach, resulting in a very efficient and practical determination of the coupling coefficients and therefore improved setting of the operating parameters.

[0053] In some embodiments, the resonance detector is configured to control the driver to perform a frequency sweep of the drive signal from a higher frequency to a lower frequency and determine a first coupled resonance frequency, which is a first detection frequency at which a criterion for resonance of the drive signal is met.

[0054] This, in many embodiments, allows for improved detection of the coupled resonant frequency of the output resonant circuit and therefore improved estimation of the coupling coefficient, leading to improved setting of operating parameters that result in improved power transfer.

[0055] According to an optional feature of the invention, the resonance measurement period is during initialization of the power transfer operation and the operating parameters are initial operating parameters for the power transfer operation.

[0056] This approach can improve the initialization of the power transfer, allowing faster and / or more reliable convergence towards a preferred operating point for the power transfer.

[0057] According to an optional feature of the invention, the driver is configured to generate the drive signal according to a repetitive time frame during the power transfer phase, the resonant measurement period being included in the measurement period, the resonant measurement period including at least one power transfer period and at least one measurement period.

[0058] This approach allows for greater adaptability to changes in operating conditions during power transfer, in particular greater adaptability to movement of the power receiver relative to the power transmitter.

[0059] In many embodiments, the duration of the measurement period is 5%, 10%, or 20% or more of the duration of the time frame. In many embodiments, the duration of the measurement period is 70%, 80%, or 90% or less of the time frame. The duration of the measurement period is 5 ms, 10 ms, or 50 ms or less in many scenarios.

[0060] In some embodiments, the operating parameter is a parameter that controls the power level of the power transmission signal.

[0061] The operating parameters provide particularly advantageous operation in many embodiments.

[0062] The parameters that control the power level of the power transmission signal are in particular parameters of the drive signal, such as the frequency, duty cycle, phase, current and / or voltage of the drive signal.

[0063] According to an optional feature of the invention, the operating parameter is a power loop parameter, which is a loop parameter of a power control loop configured to adapt a power level of the power transmission signal in response to a power control message received from the power receiver.

[0064] The operating parameters provide particularly advantageous operation in many embodiments by dynamically adapting and / or optimizing the control response of the power transfer to current conditions. This approach allows for faster control action in many scenarios while still ensuring control loop stability.

[0065] The loop parameters are specifically the loop gain and / or the loop delay.

[0066] In some embodiments, the estimation circuitry is further configured to determine an estimate of the coupling coefficient as a function of an uncoupled resonant frequency of the power transfer input resonant circuit.

[0067] This allows for improved estimation of the coupling coefficients in many scenarios, which makes the coupling coefficient estimates easier to determine.

[0068] The uncoupled resonant frequency of the power transfer input resonant circuit is the resonant frequency of the power transfer input resonant circuit when the receiver coil is not coupled to the transmitter coil (or typically to any other inductor).

[0069] According to some embodiments, the resonance detector is further configured to determine a second coupling resonant frequency of the output resonant circuit during the resonance measurement period, the second operating resonant frequency being another resonant frequency of the output resonant circuit in the presence of the power receiver, and the estimation circuit is further configured to determine an estimate of the coupling coefficient in response to the second operating resonant frequency.

[0070] This provides particularly advantageous and / or smooth operation and / or performance in many embodiments.

[0071] In some embodiments, the estimation circuitry is configured to determine the estimate of the coupling coefficient in response to at least one of the following equations:

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[0072] This provides particularly advantageous and / or smooth operation and / or performance in many embodiments.

[0073] The power receiver includes circuitry configured to switch from a power transfer mode, in which the quality factor is not limited to 10 or greater, to a measurement mode, in which the quality factor is 10 or greater, during a resonant measurement period when the power receiver is operating in the measurement mode.

[0074] This provides particularly advantageous and / or smooth operation and / or performance in many embodiments.

[0075] According to an optional feature of the invention, the power receiver further comprises circuitry configured to short-circuit the power transfer input resonant circuit during the resonant measurement period.

[0076] This provides particularly advantageous and / or smooth operation and / or performance in many embodiments.

[0077] According to another aspect of the present invention, there is provided a method of operation of a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter configured to wirelessly provide power to the power receiver via an inductive power transfer signal, the power transmitter comprising an output resonant circuit comprising a transmitter coil and at least one capacitor, the power receiver comprising a power transfer input resonant circuit comprising the power transmitter and a receiver coil configured to draw power from the at least one capacitor, the method comprising the steps of the power transmitter generating a drive signal for the output resonant circuit and generating the inductive power transfer signal, and determining a first coupled resonant frequency of the output resonant circuit during a resonance measurement period, the first coupled resonant frequency being in agreement with the power transmitter and the at least one capacitor. The method includes the steps of determining a first coupled resonant frequency, which is a resonant frequency of an output resonant circuit of a transmitter coil coupled to a receiver coil of a power transfer input resonant circuit of the receiver, and in which the power transfer input resonant circuit has a quality factor of 10 or greater during a resonant measurement period; determining an estimate of a coupling coefficient for coupling between the transmitter coil and the receiver coil in response to the first coupled resonant frequency; and setting operating parameters in response to the estimate of the coupling coefficient, the method further including the step of switching from a power transfer mode performed by the power receiver, in which the quality factor is not limited to 10 or greater, to a measurement mode in which the quality factor is 10 or greater during the resonant measurement period when the power receiver is operating in the measurement mode.

[0078] According to another aspect of the present invention, there is provided a power receiver for a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter configured to wirelessly supply power to the power receiver via an inductive power transfer signal, the power receiver comprising a power transfer input resonant circuit comprising the power transmitter and a receiver coil configured to draw power from at least one capacitor, and circuitry configured to switch from a power transfer mode in which the quality factor is not limited to 10 or greater to a measurement mode in which the quality factor is 10 or greater during a resonant measurement period when the power receiver is operating in the measurement mode.

[0079] According to another aspect of the present invention, there is provided a method of operating a power receiver for a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter configured to wirelessly supply power to the power receiver via an inductive power transfer signal, the power receiver comprising a power transfer input resonant circuit comprising the power transmitter and a receiver coil configured to draw power from at least one capacitor, the method including circuitry configured to switch from a power transfer mode in which the quality factor is not limited to 10 or greater to a measurement mode in which the quality factor is 10 or greater during a resonant measurement period when the power receiver is operating in the measurement mode.

[0080] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which: [Brief description of the drawings]

[0081] [Figure 1] FIG. 2 illustrates an example of elements of a power transfer system, according to some embodiments of the present invention. [Diagram 2] 2 is a diagram illustrating an example of an equivalent circuit of the power transmission system of FIG. 1. [Diagram 3] FIG. 2 illustrates an example of elements of a power transmitter according to some embodiments of the present invention. [Figure 4] FIG. 1 illustrates an example of a half-bridge inverter for a power transmitter. [Diagram 5] FIG. 1 illustrates an example of a full-bridge inverter for a power transmitter. [Figure 6] FIG. 2 illustrates an example of elements of a power receiver according to some embodiments of the present invention. [Figure 7] FIG. 4 illustrates an example of a response of the output resonant circuit of the power transmitter of FIG. [Figure 8] 4 illustrates an example of a coupling resonant frequency of the output resonant circuit of the power transmitter of FIG. 3 as a function of coupling coefficient. [Figure 9] 4 illustrates an example of a coupling resonant frequency of the output resonant circuit of the power transmitter of FIG. 3 as a function of coupling coefficient. [Figure 10]FIG. 4 illustrates an example of a response of the output resonant circuit of the power transmitter of FIG. [Figure 11] FIG. 4 illustrates an example of a response of the output resonant circuit of the power transmitter of FIG. [Figure 12] FIG. 4 illustrates an example of a response of the output resonant circuit of the power transmitter of FIG. [Figure 13] FIG. 4 illustrates an example of a response of the output resonant circuit of the power transmitter of FIG. [Figure 14] FIG. 4 illustrates an example of a response of the output resonant circuit of the power transmitter of FIG. [Figure 15] 2 is a diagram illustrating an example of a time frame of the wireless power transmission system of FIG. 1. [Figure 16] 2 is a diagram illustrating an example of an equivalent circuit of the power transmission system of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0082] The following description focuses on embodiments of the invention that are applicable to wireless power transfer systems that utilize power transfer techniques such as those known from the Qi or Ki specifications, but it will be appreciated that the invention is not limited to this application and has application to many other wireless power transfer systems.

[0083] 1 illustrates an example of a power transfer system according to some embodiments of the present invention. The power transfer system comprises a power transmitter 101 comprising (or coupled to) a transmitter coil / inductor 103. The system further comprises a power receiver 105 comprising (or coupled to) a receiver coil / inductor 107.

[0084] The system provides an induced electromagnetic wave power transmission signal that inductively transmits power from a power transmitter 101 to a power receiver 105. The power transmitter 101 specifically generates an electromagnetic signal that propagates as a magnetic flux from a transmitter coil or inductor 103. The power transmission signal typically has a frequency between about 20 kHz and about 500 kHz, and often typically ranges from 95 kHz to 205 kHz for Qi-compatible systems and from 20 kHz to 80 kHz for Ki-compatible systems. The transmitter coil 103 and the receiver coil 107 are loosely coupled, so that the receiver coil 107 receives (at least a portion of) the power transmission signal from the power transmitter 101. Thus, power is transmitted from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the receiver coil 107. The term power transmission signal is used primarily to refer to the induction signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the receiving coil 107, but it will be understood that it is also considered and used to refer to an electrical signal supplied to the transmitter coil 103 or received by the receiving coil 107.

[0085] In this example, power receiver 105 is specifically a power receiver that receives power via receiver coil 107. However, in other embodiments, power receiver 105 comprises a metallic element, such as a metal heating element, where the power transmission signal directly induces eddy currents, which in turn directly heat the element.

[0086] The system is configured to transmit significant power levels, and in particular the power transmitter supports power levels of 500mW, 1W, 5W, 50W, 100W, or greater in many embodiments. Power transmission, for example, for Qi-enabled applications, typically ranges from 1-5W power for low power applications (basic power profile), up to 15W for Qi specification version 1.2, up to 100W for higher power applications such as power tools, laptops, drones, robots, and beyond 100W up to 2000W+ for very high power applications, such as for Ki-enabled kitchen applications.

[0087] The operation of the power transmitter 101 and power receiver 105 will be described below with particular reference to embodiments generally in accordance with the Qi or Ki specifications (except for modifications and enhancements described (or resulting from) herein) or suitable for higher power kitchen specifications being developed by the Wireless Power Consortium. The power transmitter 101 and power receiver 105 specifically comply with or are substantially compatible with elements of the Qi specification versions 1.0, 1.1, 1.2, or 1.3 (except for modifications and enhancements described (or resulting from) herein).

[0088] Many wireless power transfer systems, especially high power systems such as Ki, utilize resonant power transfer, where the transmitter coil 103 is part of a resonant circuit, and typically the receiver coil 107 is also part of the resonant circuit. In many embodiments, the resonant circuit is a series resonant circuit, so that the transmitter coil 103 and the receiver coil 107 are coupled in series with corresponding resonant capacitors. Using a resonant circuit often results in more efficient power transfer.

[0089] In most power transmission systems, before power transmission begins, a communication channel is established between the power transmitter 101 and the power receiver 105. Once communication is set up and identification of the two devices is performed, the power transmitter 101 begins transmitting power to the power receiver 105.

[0090] An example of an electrical equivalent diagram of the power transfer function of the power transmitter 101 and the power receiver 105 is shown in Fig. 2. In a given system, there is a wide range of power transmitters and power receivers, which have significantly different characteristics and parameters. For example, the coil size, induction value, and load are significantly different. Therefore, the system parameters specifically shown in Fig. 2 will actually vary significantly due to various devices, mechanical structures, positioning, etc. In particular, the placement of the power receiver, and therefore the relative position of the receiver coil 107 and the transmitter coil 103, significantly affects the coupling between the coils, i.e., the primary (power transmitter side) inductor Lp and the secondary (power transmitter side) inductor Ls, and therefore significantly changes the system behavior.

[0091] The powered device may further have several different modes in which it operates, e.g., several loads may be switched on or off in various modes. For example, if the power receiver is a non-oil fryer appliance, the heating element may be switched on or off. This may result in, e.g., very large load steps, e.g., from 50 to 1200 W and vice versa. Furthermore, such load switching may be repeated during operation of the device to keep the temperature constant. The system may also include non-linear loads. For example, the power receiver may drive a motor, e.g., a food processor motor, rather than a resistive component. This may result in a completely different response of the system, which may have a significant impact on the design of the control system in particular.

[0092] Wireless power transfer systems typically use a power control loop to steer the system towards a suitable operating point. This power control loop varies the amount of power transmitted from the power transmitter to the power receiver. The received power (or voltage or current) can be measured and, together with a set-point power value, an error signal can be generated. The appliance sends this error signal, or sometimes the desired power set-point, to the power control function of the power transmitter to reduce the static error, ideally to zero.

[0093] However, the performance and operation of the system varies greatly depending on the combination and arrangement of the existing power transmitters and power receivers, so the appropriate operating point varies greatly, including the conditions at the start-up / initialization of the power transmission, so the optimal initial operating point also varies greatly.

[0094] One of the important parameters that affect operation is the coupling coefficient. The coupling coefficient also often depends on the positioning of the power receiver relative to the power transmitter (specifically, the receiver coil 107 relative to the transmitter coil 103), and therefore on the specific operating conditions. In contrast, most other parameters in FIG. 2 are often known and are often relatively constant for a particular power transmitter and receiver coil 107 combination. Therefore, almost all relevant system parameters are usually known, except for the coupling coefficient. The coupling coefficient depends on many parameters, including in particular the size / geometry of the coils, and the distance between the power transmitter and the power receiver.

[0095] In the system of FIG. 1, the system has the capability to estimate the coupling coefficient and adapt operating parameters in response to the coupling coefficient. Specifically, in many embodiments, parameters of the control loop, such as the open loop transfer function and / or loop gain, are adapted to optimize and control the performance of the closed loop. As another example, a preferred (usually initial) operating point, e.g., a power level, is adapted in response to the coupling coefficient. The measurement and adaptation may be performed before power transfer in some embodiments, or alternatively or additionally after power transfer.

[0096] As an exemplary operation, when a power receiver is placed on top of a power transmitter, communication is established between the power receiver and the power transmitter. This allows the power transmitter to start transmitting power, but first it needs to establish a suitable operating point. One option would be to select a very safe and reliable operating point that can ensure operation is possible even in the worst case scenario, and then gradually adapt the operating point during power transmission. However, such an approach is likely to be time-consuming and inefficient, and in fact, in many scenarios, gradually adapting to an optimal operating point is not practical (e.g., the system remains at a local maximum rather than going to a global maximum).

[0097] Therefore, it is preferable to determine a desired operating point and start operation at or near the desired operating point. The desired operating point can be estimated using all known system parameters. The known system parameters include (or consist of), for example, primary and secondary inductances, primary and secondary resonances, load resistance, power and voltage, and coupling coefficients. If all these parameters are known, the transfer function of the power path can be calculated and the initial operating point can be determined. However, while most of the parameters can be known by the power transmitter, for example based on the parameters of the power receiver transmitted from the power receiver, the coupling coefficients cannot be known in advance as they vary depending on the placement / misalignment of the devices.

[0098] The power transmitter therefore proceeds to measure / estimate the coupling coefficient in this example. This is done, for example, by determining one or more resonant frequencies of the power transmitter resonant circuit when loaded with the power receiver. The power receiver goes into a high Q mode during such measurement, and the resonant frequencies are determined by a frequency sweep of the signal driving the transmitter coil 103 at the power transmitter. The coupling coefficient is calculated based on the measured resonant frequencies, for example, based on the free running resonant frequencies of the power receiver and the power transmitter resonant frequencies.

[0099] This coupling coefficient can then be used to calculate the complete transfer function, and then calculate the initial operating point and the required operating parameters, such as initial power level and / or loop gain, etc. Setting the operating parameters to the calculated values, from the start of power transfer, the initial operating point can be reached, resulting in the appropriate power / current being delivered to the power receiver.

[0100] Indeed, by measuring the coupling coefficient of the power transmission system before power is transmitted, the system response can be better estimated. This allows the initial operating point (power signal frequency, duty cycle, loop gain, etc.) to be better selected. This allows the desired power level to be reached much more quickly. Such an approach further reduces the risk of overvoltage or overcurrent conditions occurring.

[0101] Additionally, measuring the coupling coefficient during power transfer and adapting operating parameters based on such measurements improves performance and typically allows for more accurate optimization and adaptation.

[0102] FIG. 3 shows elements of the power transmitter 101 of FIG. 1 in more detail.

[0103] The power transmitter 101 comprises a driver 301, which can generate a drive signal that is provided to the transmitter coil 103, which in return generates an electromagnetic power transmission signal, thereby achieving power transmission to the power receiver 105. The transmitter coil 103 is part of an output resonant circuit, which comprises the transmitter coil 103 and a capacitor 303. It will be appreciated that the output resonant circuit is a series resonant circuit in this example, although in other embodiments the output resonant circuit is a parallel resonant circuit. It will be appreciated that any suitable resonant circuit may be used, including a resonant circuit comprising multiple inductors and / or capacitors.

[0104] The driver 301 generates the current and voltage that are supplied to the output resonant circuit and thus to the transmitter coil 103. The driver 301 is typically a drive circuit in the form of an inverter that generates an AC signal from a DC voltage. The output of the driver 301 is typically a switch bridge that generates the drive signal by appropriate switching of the switches of the switch bridge. Figure 4 shows a half-bridge switch bridge / inverter. Switches S1 and S2 are controlled to never close at the same time. Alternately, S1 is closed while S2 is open and S2 is closed while S1 is open. The switches open and close at the desired frequency, which generates an AC signal at the output. The output of the inverter is typically connected to the transmitter inductor via a resonant capacitor. Figure 5 shows a full-bridge switch bridge / inverter. Switches S1 and S2 are controlled to never close at the same time. Switches S3 and S4 are controlled to never close at the same time. Alternately, switches S1 and S4 are closed while S2 and S3 are open, then S2 and S3 are closed while S1 and S4 are open, thereby producing a square wave signal at the output. The switches open and close at the desired frequency.

[0105] The power transmitter 101 further comprises a power transmitter controller 305 configured to control the operation of the power transmitter 101 according to a desired operating principle. The power transmitter 101 specifically has many of the functions necessary to perform power control according to the Qi or Ki specifications.

[0106] The power transmitter controller 305 is configured in particular to control the generation of the drive signal by the driver 301, and in particular can control the power level of the drive signal and thus the level of the generated power transmission signal. During the power transmission stage, the power transmitter controller 305 comprises a power loop controller that controls the power level of the power transmission signal in response to power control messages received from the power receiver 105.

[0107] The power transmitter controller 305 further comprises functionality for communicating with the power receiver 105. The power transmitter controller 305 is configured to transmit data to the power receiver 105, for example, by modulating the power transmission signal, and receive data from the power receiver 105, for example, by detecting load modulation of the power transmission signal. It will be understood that in other embodiments, other communication means are used, for example, another communication function is implemented, such as NFC communication.

[0108] It is well known that the use of a resonant circuit with the transmitter coil 103 allows for more efficient power transfer in many scenarios. Furthermore, having a power receiver that also uses a resonant circuit, in other words, where the receiver coil 107 is part of the resonant circuit, results in resonant power transfer that achieves many advantages including highly efficient power transfer and ease of control of the power transfer, for example by controlling the frequency of the drive signal.

[0109] FIG. 6 illustrates some example elements of the power receiver 105.

[0110] The receiver coil 107 is coupled to the power receiver controller 601 via a capacitor 603 which forms an input resonant circuit with the receiver coil 107. The power transfer is therefore a resonant power transfer between the resonant circuits.

[0111] The power receiver controller 601 specifically couples the receiver coil 107 to the load 605 via a switch 607 that can short the load 605. The power receiver controller 601 comprises a power control path that converts the power drawn by the receiver coil 107 into a power supply suitable for the load 605. In some embodiments, the power receiver controller 601 comprises a direct power path where the input resonant circuit is simply connected to the switch 607 or the load 605, i.e. the power path of the power receiver controller 601 is simply realized by two wires. In other embodiments, the power path comprises a rectifier, for example to provide a DC voltage, and possibly a smoothing capacitor. In still other embodiments, the power path comprises more complex functions, such as, for example, a voltage control circuit, an impedance matching circuit, a current control circuit, etc. It will be appreciated that the switch 607 is only present in some embodiments and in some embodiments the load 605 may be permanently coupled to the input resonant circuit.

[0112] The power receiver controller 601 additionally includes various power receiver controller functions necessary to perform a power transfer, in particular the functions necessary to perform a power transfer according to the Qi or Ki specifications.

[0113] The power receiver controller 601 further has functionality for communicating with the power transmitter 101. For example, it may be configured to decode and demodulate data modulated onto the power transmission signal, and may be configured to transmit data to the power transmitter 101 by load modulating the power transmission signal. In some embodiments, another communication functionality is used, such as an NFC communication functionality.

[0114] The system is configured to control the drive signal during operation such that the power transmission signal achieves preferred operating parameters / characteristics and such that the power transmission operates at a preferred operating point. To control the drive signal, the power transmitter is configured to control parameters of the drive signal using a power control loop in which the power characteristics of the power transmission signal / drive signal are controlled in response to power control error messages received from the power receiver.

[0115] The power receiver transmits a power control error message to the power transmitter at regular intervals, typically frequently. In some embodiments, a direct power set point change message is transmitted indicating the absolute power level desired (rather than a relative error message). The power receiver 105 has the functionality to accommodate such a power control loop. For example, the power receiver controller 601 continuously monitors the power or voltage of the load signal delivered to the load and detects whether it is above or below a desired value. The power receiver controller generates a power control error message at regular intervals requesting that the power level of the power transmission signal be increased or decreased, and transmits this power control error message to the power transmitter.

[0116] When the transmit controller 305 receives the power control error message from the power receiver, it determines how the drive signal parameters need to be modified to increase or decrease the power level of the power transmission signal as required. The transmitter controller then controls and adapts the drive signal parameters accordingly.

[0117] Therefore, a power control loop is used to control the power characteristics of the power transmission signal to obtain a desired operating point at the power receiver. The operation of the power transmission is therefore controlled by the power control loop, and it is important for the performance of the system that it operates effectively. It is therefore important to initialize or adapt the power control loop to the operating conditions in order to obtain optimal performance.

[0118] The power transmitter, in the described system, has the functionality to estimate the coupling coefficient and to adapt the operation of the power transfer system, and in particular the power control loop, based on the coupling coefficient.

[0119] The power transmitter is specifically configured to determine a coupling coefficient in response to detecting / measuring one or more resonant frequencies (and / or equivalent drive signals) of the output resonant circuit when coupled to a power receiver, specifically the receiver coil 107 and the input resonant circuit. The power transmitter then adapts the operation of the power transfer system accordingly.

[0120] The power transmitter 101 comprises a resonance detector 307 configured to determine at least one coupled operating resonance frequency of the output resonant circuit during a resonance measurement period, where the coupled resonance frequency is the resonance frequency of the output resonant circuit when a power receiver is present, i.e. when the transmitter coil 103 is coupled to the receiver coil 107 of the power receiver. The coupled resonance frequency therefore reflects the effective resonance frequency of the output resonant circuit when the transmitter coil 103 is coupled to the receiver coil 107. The effective inductance of the transmitter coil 103 is different from the self-inductance of the transmitter coil 103 when it is not coupled to any receiver coil 107 due to the coupling of the two coils. Similarly, the effective inductance of the receiver coil 107 is different from the self-inductance of the receiver coil 107 when it is not coupled to any transmitter coil 103. As a result, the effective resonance is different from the self-resonance when there is no coupling. Furthermore, the drive signal is subject to two (different) effective resonant frequencies due to the coupling of the two coils, and therefore the two resonant circuits, i.e. the output resonant circuit effectively has two resonant frequencies due to the coupling, the two resonant frequencies being different from the self (uncoupled) resonant frequency of the output resonant circuit.

[0121] In many embodiments, the resonance detector 307 is configured to determine both combined resonance frequencies.

[0122] The effective or coupled resonant frequency of the output resonant circuit will be different from its self-resonant frequency when not coupled to any other inductor, and the difference will depend on the coupling. Therefore, detecting the coupled or operating resonant frequency of the output resonant circuit provides information about the coupling with the receiver coil 107, which is used to estimate the coupling coefficient in the power transmitter 101.

[0123] The resonance detector 307 is coupled to an estimation circuit 309 configured to determine an estimate of a coupling coefficient for the coupling between the transmitter coil 103 and the receiver coil 107 based on at least the coupling resonance frequency.

[0124] In some embodiments, the estimation circuit 309 is configured to generate an estimate of the coupling coefficient based on only one measured coupling resonant frequency. The estimation circuit 309 includes, for example, a look-up table that provides a coupling estimate for an input address word that corresponds to the determined coupling resonant frequency. The look-up table is generated, for example, by measurements during manufacturing and design phase or based on theoretical calculations.

[0125] However, while such an approach is advantageous in many embodiments, it often does not provide an optimal estimate of the coupling coefficient when the parameters involved vary significantly, and therefore is typically limited to situations where the parameters involved (including the electrical parameters of the resonant circuit, the characteristics of the power transmitter and power receiver, etc.) are very limited.

[0126] In most embodiments, the estimation circuit 309 is therefore configured to further take into account additional parameters, and in many embodiments the estimation circuit 309 is configured to determine an estimate of the coupling coefficient based on also taking into account at least one of the second coupled resonant frequency of the output resonant circuit, the self-resonant frequency / uncoupled resonant frequency of the output resonant circuit, and the self-resonant frequency / uncoupled resonant frequency of the input resonant circuit.

[0127] In particular, the estimator 309 is configured in many embodiments to further take into account the uncoupled resonant frequency of the output resonant circuit when determining the estimate of the coupling coefficient.

[0128] The uncoupled frequency of the output resonant circuit is the resonant frequency of the output resonant circuit when it is not coupled to the receiver coil 107, and typically is the resonant frequency of the output resonant circuit when it is not coupled to any inductor. The uncoupled resonant frequency is also called the self-resonant frequency of the output resonant circuit.

[0129] The estimation circuit 309 is therefore in many embodiments configured to estimate a coupling coefficient based on the effect of the coupling between the transmitter coil 103 and the receiver coil 107 on the resonant frequency of the output resonant circuit.

[0130] The estimation circuit 309 is coupled to an adapter 311 configured to set an operating parameter depending on the estimated value of the coupling coefficient. In some embodiments, the setting is a relative setting or an absolute setting. The adapter 311 performs the relative setting of the operating parameter, for example, by increasing or decreasing the parameter value by a given amount, e.g., increasing or decreasing a power level from a current value.

[0131] In some embodiments, the adapter 311 is configured to adapt or set operating values ​​of power transmission signal parameters, in particular, to set parameter values ​​of the power transmission signal that control the power level of the power transmission signal, including the frequency (which affects the power level of the resonant power transmission system), phase, amplitude (current and / or voltage), or duty cycle of the power transmission signal.

[0132] For example, if the coupling coefficient is high, power transfer between the coils is efficient and a high power level can be set, but if the coupling coefficient is low, power transfer is less efficient and must be set at a lower level.

[0133] Thus, by estimating the coupling coefficient, a suitable power level can be determined, and when initiating a power transfer operation, the power transfer operation is initialized with the power level set to the desired value by appropriately setting the operating parameters of the power transfer signal.

[0134] The appropriate power levels are determined, for example, using a look-up table (LUT) generated during manufacturing. For example, based on measurements performed on different power receivers with different characteristics (e.g., coil dimensions, inductance values ​​of the power receivers, etc.), suitable power levels for different coupling coefficients are determined and stored in the LUT. During operation, when initializing a new power transfer with a new power receiver, the power receiver transmits the relevant parameter values ​​to the power transmitter, which further estimates the coupling coefficient. The resulting values ​​are used to perform a table lookup in the LUT, and the power transfer is initialized with the corresponding power level. The LUT outputs suitable values, in particular, of the frequency, duty cycle, and / or amplitude of the drive signal. The adapter 311 then, for example, supplies this information to the power transmitter controller 305, which controls the driver 301 to generate a drive signal with these characteristics. The system thus starts the power transfer with the suitable parameters and then performs the adaptation by the power control loop.

[0135] In some embodiments, the adapter 311 alternatively or additionally adapts power control loop parameters of a power control loop that controls the power level of the power transmission signal based on a power control message received from the power receiver (105).

[0136] The open-loop performance of the power control loop is highly dependent on the coupling coefficient, and hence the closed-loop performance is similar. In fact, in many scenarios, the closed loop is stable only for some values ​​of the coupling coefficient. The loop gain is usually substantially proportional to the coupling coefficient, and the more the coupling coefficient changes, the more the gain changes. Changes in the loop gain directly affect the time (and frequency) response of the closed loop, including the stability of the loop. The adapter 311 is configured to modify the loop gain to compensate for changes in the coupling coefficient so that the overall gain is at a desired level. This results in a faster operating loop, which provides optimized performance, since the loop gain does not need to be set to ensure stability in worst-case scenarios.

[0137] In some embodiments, more complex adaptation of the loop is performed, such as adjusting the delay or (open loop) frequency response. This allows for more flexible adaptation and allows the performance to be more closely individualized. For example, the filter response is adapted to prevent any possible self-oscillation and instability.

[0138] With respect to the power level of the power transfer signal, the parameters are determined, for example, by measurement and experimentation during design / manufacturing, with appropriate parameters stored in a LUT, in fact, parameters for both the control loop and the power level setting are stored in the same LUT.

[0139] It will be appreciated that the operating parameters that are adapted are not limited to power level parameters or loop parameters, and in some embodiments other parameters are set alternatively or in addition, such as foreign object detection parameters or communication parameters.

[0140] In various embodiments, the estimator 309 uses various techniques to determine the coupling coefficient. In particular, if the output resonant circuit is coupled to the input resonant circuit and is allowed to oscillate in a fully undamped manner, the output resonant circuit will in fact exhibit two coupled resonant frequencies rather than just one. In particular, if the input resonant circuit is completely undamped, such as when the series load / resistance is essentially zero due to a short circuit in the series resonant circuit, the output resonant circuit will exhibit two coupled resonant frequencies.

[0141] The response of the output resonant circuit when coupled to an input resonant circuit (which is fully undamped) is a two-resonant response, as shown in the example of Figure 7. Figure 7 shows an example of the response to typical system parameters (primary current amplitude and phase for a constant voltage amplitude of the drive signal) with an undamped input resonant circuit, and as can be clearly seen, the response contains two resonant peaks.

[0142] Figure 8 shows an example of how the resonant frequency of the coupled output resonant circuit changes for various coupling coefficients k. In this example, the uncoupled resonant frequencies of both the output and input resonant circuits are normalized to a frequency of 0.3×10 5 As can be seen, when coupled, the first resonant frequency is higher than the uncoupled frequency, and the second resonant frequency is lower than the uncoupled frequency. As can also be seen, the resonant frequencies are strongly dependent on the coupling coefficient, with the difference increasing as the coupling coefficient increases.

[0143] FIG. 9 shows an example that corresponds to the example of FIG. 8, but with a normalized average uncoupled resonant frequency of 0.268×10 5 and the normalized average uncoupled resonant frequency of the input resonant circuit is still 0.3 × 10 5 As can be seen, this results in slightly different combined resonant frequencies.

[0144] In some embodiments, measurements of such dependencies, shown in Figures 8 and 9, are made during the manufacturing / design stage of the associated power transmitter and receiver coil 107 combination. The results are stored in a LUT carried by the power transmitter (or, for example, stored centrally and retrieved when setting up a new power transfer). Following the determination of the coupling resonant frequency, the estimator 309 performs a table lookup to obtain the estimated coupling coefficient.

[0145] In some embodiments, the resonance detector 307 is configured to detect the coupling resonant frequency by varying the frequency of the drive signal during a resonance measurement period; specifically, the resonance detector performs a frequency sweep over a range of frequencies corresponding to a frequency interval within which the coupling resonant frequency is expected to be or within which the coupling coefficient is considered high enough to achieve acceptable power transfer. The resonance detector 307 then monitors the drive signal and detects, for example, extrema in the current or voltage amplitude. The resonance detector 307 controls the driver 301 to vary the frequency, for example, in the case of a series resonant circuit, with a constant voltage amplitude over a range. The resonance detector 307 then measures the current amplitude at various frequencies and determines the coupling resonant frequency at which the maximum current amplitude is determined. As another example, the resonance detector 307 detects when the phase difference between the current and the voltage of the drive signal becomes zero (or close to zero), i.e., when the load presented by the output resonant circuit becomes completely resistive. If the coupling resonant frequency is not detected within this frequency interval, this indicates that the coupling coefficient is not within a suitable interval for power transfer, and power transfer is discontinued.

[0146] In some embodiments, the frequency sweep of the drive signal goes from higher to lower frequencies, and the coupling resonant frequency is determined to be the first detected frequency where the criteria for resonance (e.g., an extremum in the current or voltage amplitude of the signal, or zero phase difference between the voltage and current) is met. Thus, for example, rather than finding a global extremum, the first local extremum is found.

[0147] Such an approach allows one to find the highest coupled resonant frequency of the two, and it has been recognized that it is usually advantageous to use the highest coupled resonant frequency, especially if only one coupled resonant frequency is used, since the largest change in coupled resonant frequency with respect to a change in coupling coefficient occurs at the highest coupled resonant frequency.

[0148] In some embodiments, both coupling resonant frequencies are detected and used to determine an estimate of the coupling coefficient, for example, two separate LUTs are provided for the lower and higher coupling resonant frequencies, respectively, and the estimate of the coupling coefficient is determined as the average of the lookup results of the two tables.

[0149] In other embodiments, other techniques are used to determine the combined resonant frequency of the output resonant circuit. For example, in some embodiments, a successive approximation technique is used. Such techniques may be very advantageous and useful when determining the resonant frequency based on frequency intervals. This technique may allow for rapid detection of one or more resonant frequencies.

[0150] In some embodiments, the power receiver communicates system parameters, such as the uncoupled resonant frequency and / or the inductance of the receiver coil, to the power transmitter, which are used to determine the coupling coefficient from the coupled resonant frequency. The LUT may, for example, depend on such power receiver elements, or different LUTs may be provided for different power receivers (indeed, in some embodiments, the LUTs are provided by the power receiver).

[0151] In some embodiments, the determination of the coupling coefficient is based on an analytical expression. The estimation circuit 309 is specifically configured to determine an estimate of the coupling coefficient according to at least one of the following expressions:

number

[0152] These equations apply to the coupled resonant circuit and are used (directly or indirectly) by the resonant detector 307.

[0153] In some embodiments, only one of the equations is used, and in fact the estimate of the coupling coefficient is based on only one of the coupled resonant frequencies. For example, as explained, the highest coupled resonant frequency is determined by finding the first peak in the sweep from a higher frequency to a lower frequency. Using the known values ​​of the uncoupled resonant frequencies of the input and output resonant circuits, based on the first equation above, the highest coupled resonant frequency is then used to calculate the estimate of the coupling coefficient.

[0154] The same approach is used to determine the coupling coefficient based on the lowest coupling resonant frequency.

[0155] In some embodiments, both the highest and lowest coupling resonant frequencies are measured and both equations are used. Two coupling coefficient values ​​are calculated, for example, using the first and second equations, respectively, and the respective measured coupling resonant frequencies, and an estimate of the coupling coefficient is generated as the average of the two coupling coefficients. In other embodiments, an estimate of the coupling coefficient is calculated as the value that minimizes the error between the above equations and the measurements.

[0156] In some embodiments, both coupled resonant frequencies and both equations are used, but the uncoupled resonant frequency of the input resonant circuit is not used. This variable is instead estimated using the above equation and the two coupled resonant frequencies. In such an approach, therefore, more complex estimates and calculations are used so that the power transmitter does not need to know the specific characteristics of the input resonant circuit. Such an approach is particularly useful in implementations in existing systems where some power receivers are not able to convey this information.

[0157] The described approach is based on estimating the coupling coefficient by considering the change in resonant frequency that occurs at the coupling between the output resonant circuit and the input resonant circuit. This change depends on the coupling coefficient, but also on the quality factor Q of the input resonant circuit. This change can be seen in Fig. 10 to Fig. 14, which show not only how the two coupled resonant frequencies change for various coupling coefficients (k=[0.1, 0.2, ~0.9] in each graph), but also how this change depends on the Q value (this can be seen by comparing the various graphs, which show graphs for Q=1000, 10, 3, 1, 0.1, respectively).

[0158] In this approach, the quality factor of the input resonant circuit during the resonance measurement period is at least 10, and typically higher. This makes the detection of the coupling resonance frequency reliable and reasonably accurate, and therefore the estimation of the coupling coefficient is reliable and accurate as well. This ensures a reliable adaptation of the operating point and efficient operation.

[0159] In some embodiments, high Q during the resonant measurement period is ensured by having the Q factor of the input resonant circuit always exceed 10, i.e. the power receiver is designed such that the input resonant circuit always has a quality factor exceeding 10. However, this is typically in contrast to the desire to provide adequate power to the load.

[0160] The Q factor, for example, for a Ki system, is typically less than 5, and often less than 2, due to the loading of the input resonant circuit with typical power values.

[0161] In many embodiments, the power receiver is therefore configured to switch its operating mode from a lower quality factor mode to a higher quality factor mode having a Q-factor that is at least 10 during the resonant measurement period interval, at least for some time outside the resonant measurement period, thereby allowing efficient power transfer and efficient estimation of the coupling coefficient. The power receiver is therefore configured to switch from a power transfer mode, in which the quality factor is not limited to be greater than 10, and in fact the quality factor is substantially less than 10, to a measurement mode, in which the quality factor is 10 or greater during the resonant measurement period, to allow efficient power transfer.

[0162] This is achieved, for example, by switch 607. For example, if the power path directly couples switch 607 and load 605 to the input resonant circuit outside the resonant measurement period, the switch couples the normal load 605 to the input resonant circuit. However, switch 607 disconnects load 605 during the resonant measurement period. In the case of an input parallel resonant circuit, switch 607 disconnects load 605, for example, so that no current is drawn from the input resonant circuit. In contrast, in the case of an input series resonant circuit, switch 607 disconnects the load by shorting load 605 during the resonant measurement period, thereby shorting the power transfer input resonant circuit.

[0163] In some embodiments, such a change in quality factor is made when the power receiver does not have a specific function. For example, in some embodiments, the load may have an inherently high Q input resonant circuit during start-up, which is a virtual short circuit, during the resonant measurement period before power transfer. For example, if the load is a motor, the load starts up in a near short circuit state. As another example, if there is a rectifier and a large power capacitor in the power path, when the capacitor is discharged, it will also act almost like a short circuit.

[0164] In many embodiments, a resonance measurement period (or at least one resonance measurement period) precedes power transmission. The determination of the coupling coefficient estimate and the setting of the operating parameters are specifically performed during initialization of the power transfer operation. The power transmitter thus determines the operating parameter values ​​suitable for the particular power receiver and the particular location of the power receiver prior to power transmission. The power transmitter then uses the parameter values ​​as the initial operating parameter values ​​and begins power transmission.

[0165] This approach is used, for example, in many embodiments to determine initial loop gain and power level values ​​for the power transfer signal. The system thus begins power transfer at a more likely near optimal operating point, rather than having to slowly adapt from an initial worst-case safe operating point. Thus, faster optimization can be achieved and the risk of not reaching the optimal operating point can be reduced.

[0166] Furthermore, the power receiver enters a measurement mode for coupling resonant frequency detection during coupling coefficient estimation, which is before power transfer. Specifically, the switch 607 shorts the load to achieve a high quality factor of the input resonant circuit. When the system enters the power transfer stage, the power receiver switches back to the normal power transfer operation mode, specifically, the short circuit is removed.

[0167] In some embodiments, this approach is alternatively or additionally applied to the power transfer stage. In such an approach, the estimation of the coupling coefficients is particularly useful for adapting loop parameters and performance. Such an approach is used, for example, to adapt loop parameters so as to achieve substantially the same control performance for different positions of the power receiver. Thus, the performance can be improved and, in particular, made less sensitive to differences in the positioning of the power receiver.

[0168] In many embodiments where this approach is used for the power transfer phase, the system is configured to operate in a time slotted mode, where the measurement and combined resonant frequency detection are performed during a measurement period, specifically during such short measurement periods of a repetitive time frame further including at least one power transfer period during which power is transferred to the power receiver.

[0169] The system therefore in such an embodiment utilizes time division for the power transfer phase, in particular the detection of the coupled resonant frequency and the power transfer are performed, for example, in separate time periods, which can significantly reduce interference between the detection and the power transfer.

[0170] In this example, the driver 301 and the transmitter coil 103 are configured to generate an electromagnetic power transmission signal for the purpose of transmitting power to the power receiver during a power transmission interval. In addition, the drive signal is used to detect the coupling resonance frequency during a measurement period to determine an estimate of the coupling coefficient. The power transmitter uses a repeating time frame for the drive signal during the power transmission phase, the time frame including at least one power transmission period and at least one resonance measurement period. An example of such a repeating time frame is shown in FIG. 15, where the power transmission period is indicated by PT and the measurement period is indicated by D (this period is also called the detection period). In this example, each time frame FRM includes only one resonance measurement period and one power transfer period, which (as well as the time frame itself) have the same duration in each frame. However, it will be understood that in other embodiments, other periods (such as, for example, communication intervals) may also be included in the time frame, or multiple resonance measurement periods and / or power transmission periods may be included in each time frame. Furthermore, in some embodiments, the duration of the various periods (and indeed the time frames themselves) varies dynamically.

[0171] Therefore, in this approach, the measurement, communication, and power transmission are separated in the time domain, thereby reducing the mutual interference from the power transmission to the measurement and coupling coefficient estimation. Therefore, the variability and uncertainty caused by the change in the operating conditions of the power transmission can be separated from the measurement and estimation, resulting in a more reliable and accurate estimation process. Furthermore, this approach allows the drive signal to be generated (and optimized) to detect the coupling resonance frequency. In particular, this approach allows the resonance detector 307 to perform a frequency sweep and perform operations suitable for this detection.

[0172] Moreover, this approach allows the power receiver to be specifically adapted to achieve improved or optimal detection characteristics. In particular, in many embodiments, the power receiver switches during power transfer from a power operation mode in which a load is coupled to the input resonant circuit (hence a low quality factor of the input resonant circuit) to a measurement mode in which a high quality factor of the input resonant circuit is ensured, for example by switch 607 shorting out the load.

[0173] Therefore, the time slot approach makes it possible or easy to perform an estimation of the coupling coefficients at the power transfer stage.

[0174] As described above, in many embodiments, an estimate of the coupling coefficient is determined based not only on at least one coupling resonant frequency, but also on a non-coupled / self-resonant frequency of an output resonant circuit (of a power transmitter) and / or an input resonant circuit (of an input resonant circuit).

[0175] In some embodiments, the uncoupled resonant frequency of the input resonant circuit and / or the output resonant circuit is a predetermined frequency. For example, in some embodiments, the power transmitter and / or the power receiver are strictly limited, for example, by the specifications and regulations of a suitable standard. For example, a wireless power transmission standard (such as, for example, the Ki specification) specifies that the power transmitter and the power receiver use an output resonant circuit and an input resonant circuit, respectively, having an uncoupled resonant frequency of, for example, 30 kHz. The estimator 309 is configured, in such an embodiment, to estimate an estimate of the coupling coefficient based on one or more coupled resonant frequencies and an assumed nominal value of the uncoupled resonant frequency.

[0176] In other embodiments, the system may tolerate some variation in, for example, the output resonant circuit. However, the power transmitter and estimator 309 may often know the uncoupled resonant frequency of the output resonant circuit. The output uncoupled resonant frequency may be stored in memory, for example, during manufacturing, and retrieved and used when determining the estimated value of the coupling coefficient. The uncoupled resonant frequency may simply be determined and stored in memory, for example, as the resonant frequency caused by the self-inductance of the transmitter coil and the capacitance value of the resonant capacitor.

[0177] In some embodiments, such a predetermined (non-constant) one is used in conjunction with an assumed uncoupled resonant frequency of the input resonant circuit of the power receiver, e.g. in scenarios where the uncoupled resonant frequency of the power receiver is specified in an appropriate standard.

[0178] In some embodiments, the estimator 309 is configured to determine the uncoupled resonant frequency of the input resonant circuit in response to data received from the power receiver. In some embodiments, the power transmitter comprises a data receiver 313 configured to receive data from the power receiver. Similarly, the power receiver comprises a data transmitter 609 that transmits data to the power transmitter. The communication is performed, for example, using load modulation or, for example, using NFC communication, as would be known to one skilled in the art.

[0179] In some embodiments, the data transmitter 609 transmits data to the data receiver 313 that is used to determine the uncoupled resonant frequency of the input resonant circuit. The power receiver transmits data that directly represents, for example, the uncoupled resonant frequency of the input resonant circuit. In other embodiments, the power receiver transmits data that characterizes or otherwise enables the power transmitter to determine the input resonant circuit.

[0180] The power receiver transmits data representing the parameters of the components of the input resonant circuit, such as, for example, in some embodiments, the self-inductance of the receiver coil and the capacitance of the resonant capacitor. The estimator 309 then calculates the uncoupled resonant frequency from the component values. The power receiver transmits, as another example, information regarding, for example, the type of input resonant circuit that the receiver is equipped with. For example, the characteristics of a set of possible input resonant circuits (specifically, the uncoupled resonant frequency) are specified by the system standard, and the power receiver indicates which type is equipped. The power transmitter stores the uncoupled resonant frequencies of various types of input resonant circuits and retrieves the value for the indicated type. In some embodiments, the uncoupled resonant frequency of the input resonant circuit is associated with the type or characteristics of the power receiver, which is communicated to the power transmitter, for example, during initialization of the power transfer. For example, different component values ​​are used for different power levels, and the power receiver transmits an indication of the required power level, which the power transmitter also uses to determine the uncoupled resonant frequency of the input resonant circuit.

[0181] The power transmitter therefore in some embodiments comprises a data receiver configured to receive data indicative of the uncoupled resonant frequency of the power transfer input resonant circuit from the power receiver, either directly representing the uncoupled resonant frequency or providing data from which the uncoupled resonant frequency can be determined (typically based on further information stored in the power transmitter).

[0182] However, such embodiments using a predetermined value of the uncoupled resonant frequency that is independent of the current situation / condition will provide advantageous performance in many embodiments, however, it has been recognized that improved performance may be achieved by estimating an estimate of the coupling coefficient using a dynamically measured uncoupled resonant frequency for the input and / or output resonant circuits.

[0183] In particular, it is recognized that changes in the uncoupled resonant frequency occur in various wireless charging conditions and scenarios, and this change is determined and taken into account when generating an estimate of the coupling coefficient. It is recognized that improved performance is achieved by using measurements of the uncoupled resonant frequencies of the input and / or output resonant circuits. It is further recognized that advantageous measurements can be made using the same techniques to determine the coupled resonant frequency, and in fact the coupled resonant frequency of the input resonant circuit is determined from measurements during the same frequency sweep used to determine the coupled resonant frequency.

[0184] In some embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient in response to a measurement of at least one of the natural resonant frequencies rather than a predetermined value.

[0185] In some embodiments, the resonance detector 307 is further configured to determine the uncoupled resonant frequency of the input resonant circuit as the frequency at which the current of the drive signal exhibits a local minimum for the input resonant circuit having a quality factor of 10 or greater. The uncoupled resonant frequency of the input resonant circuit, hereinafter also referred to as the input uncoupled resonant frequency, is determined by making a measurement of the drive signal when the input resonant circuit is substantially undamped. In many embodiments, the measurement and determination of the input uncoupled resonant frequency is performed when the load on the input resonant circuit is substantially zero, in particular when the (series) load of a series resonant circuit is shorted or the (parallel) load of a parallel resonant circuit is disconnected.

[0186] The resonance detector 307 performs the measurement, for example, by performing a frequency sweep with the input resonant circuit undamped and measuring the current of the drive signal. The resonance detector then determines the input uncoupled resonant frequency to be the frequency at which the current is at a minimum. In some embodiments, determining the frequency at which the current is at a minimum is more indirect, by measuring various parameters, such as that the phase between the voltage and current of the drive signal is zero, that the power of the drive signal is minimized, etc. In some embodiments, such a condition occurs when the current condition is at a minimum (because such a condition is caused by a resonant effect at that frequency).

[0187] In many embodiments, the determination of the input uncoupled resonant frequency is combined with the determination of the coupled resonant frequency. The resonance detector 307 performs the frequency sweep previously described to determine the coupled resonant frequency, which is in particular the frequency at which a local maximum in the current of the drive signal is detected. The resonance detector additionally determines, based on the same frequency sweep, the input uncoupled resonant frequency, which is the frequency at which the drive signal exhibits a minimum current. This determination is based on a direct measurement of the current of the drive signal, as mentioned, or by measurement of related parameters such as the phase, voltage, or power of the drive signal.

[0188] It has been recognized that the frequency for the minimum drive signal current provides a good estimate of the uncoupled resonant frequency of the input resonant circuit.

[0189] In some embodiments, the resonance detector 307 is further configured to determine the uncoupled resonant frequency of the output resonant circuit as the frequency at which the current of the drive signal exhibits a maximum relative to the input resonant circuit with a quality factor of 2 or less. The uncoupled resonant frequency of the output resonant circuit, hereafter also referred to as the output uncoupled resonant frequency, is determined by making measurements of the drive signal when the input resonant circuit is highly damped, or even fully damped. In many embodiments, the measurement and determination of the output uncoupled resonant frequency is performed when the input resonant circuit is very heavily loaded (possibly effectively infinite), in particular when the (series) load of a series resonant circuit is disconnected or the (parallel) load of a parallel resonant circuit is shorted.

[0190] The resonance detector 307 performs the measurement, for example, by performing a frequency sweep with the input resonant circuit fully damped so that resonance of the input resonant circuit does not occur, and measuring the current of the drive signal. The resonance detector then determines the output uncoupled resonant frequency as the frequency at which the current is at a maximum. In some embodiments, the determination of the frequency at which the current is at a maximum is more indirect, by measuring various parameters, such as the phase between the voltage and current of the drive signal being zero, the power of the drive signal being minimized, etc. In some embodiments, such a condition occurs when the current condition is at a maximum (because such a condition is caused by the resonant effect of the output resonant circuit at that frequency).

[0191] It has been recognized that the frequency for maximum current of the drive signal when the input resonant circuit is heavily damped allows a good estimate of the uncoupled resonant frequency of the output resonant circuit. Specifically, by heavily damping the input resonant circuit, the resonant effect of the input resonant circuit on the output resonant circuit can be eliminated or significantly reduced, allowing the uncoupled resonant frequency of the output resonant circuit to be measured. For example, by opening the series input resonant circuit, no current flows through the receiver coil and no power is drawn from the electromagnetic field. The input resonant circuit therefore has substantially no effect on the output resonant circuit, allowing the uncoupled resonant frequency of the output resonant circuit to be effectively measured.

[0192] The measurement of the uncoupled resonant frequency allows for substantially improved performance and more accurate estimation of the coupling coefficient. This approach mitigates and compensates for the effects of changes in the conditions, environment, and settings of the power transfer device, and in particular the effects of the characteristics of the power transmitter and power receiver. For example, the influence of the presence of the power receiver on the drive signal is not limited to the coupling between the transmitter coil and the receiver coil (and therefore between the resonant circuits), but is also influenced by other effects, such as the influence of metals in the power receiver and power transmitter devices. Such effects are independent of the coupling coefficient, but vary significantly, for example, depending on the specific characteristics of the device implementation and the positioning of other elements at or near the device. Such (usually unknown or inappropriate) effects therefore hinder the estimation of the coupling coefficient, making it less accurate. However, the current approach takes such dependencies and effects into account by determining the uncoupled resonant frequency by measuring its effective value in certain conditions and conditions. Thus, the use of measurements of at least one of the uncoupled resonant frequencies of the input or output resonant circuits provides a substantially improved estimation of the coupling coefficient.

[0193] The measured (condition / state dependent) uncoupled resonant frequency is also called the paired uncoupled resonant frequency.

[0194] The estimator 309 is configured, as previously described, in many embodiments to determine an estimate of the coupling coefficient as a function of both the first and second coupling resonant frequencies of the output resonant circuit / drive signal, for example by estimating an estimate of the coupling coefficient for two distinct coupling resonant frequencies using a predefined or measured coupling resonant frequency, as mentioned, and averaging the results.

[0195] In another embodiment, the two coupled resonant frequencies are determined and used together with the estimated uncoupled resonant frequency of the output resonant circuit to estimate the coupling coefficient without requiring knowledge of the coupled resonant frequency of the input resonant circuit. Specifically, the two formulas presented previously are used together to generate an estimate of the coupling coefficient based on the coupled resonant frequency of the output resonant circuit and the two uncoupled resonant frequencies.

[0196] It will also be appreciated that the exact mathematical formulas and expressions used to determine estimates of coupling coefficients will vary depending on individual embodiment specific choices and requirements. In many embodiments, manipulations and simplifications of the previously presented formulas, based on various assumptions or simplifications, result in advantageous and efficient approaches for generating estimates of coupling coefficients.

[0197] In many embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient as a function of the first coupling resonant frequency relative to the second coupling resonant frequency.

[0198] In particular, in many embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient as a function of the ratio between the first and second coupling resonant frequencies. In many embodiments, the estimate of the coupling coefficient is determined as a function of the ratio between the first and second coupling resonant frequencies. In some embodiments, the function only depends on either the first or second coupling resonant frequencies by depending on the ratio between the coupling resonant frequencies, and the function does not consider either the first or second coupling resonant frequencies separately. In some embodiments, the function is a function that can be manipulated or rearranged such that the first and second coupling resonant frequencies are included only as a ratio between the coupling resonant frequencies.

[0199] In many embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient that is a function of a dimensionless parameter determined from the first and second coupled resonant frequencies (e.g., a ratio between the frequencies), the dependence on the first and / or second coupled resonant frequencies being solely dependent on the dimensionless parameter, e.g., the ratio.

[0200] In particular, it is recognized that while the first and second coupled resonant frequencies vary significantly as a function of various parameters such as the load and effective quality factor at the time the measurement is performed, the characteristics of the coil, etc., such variations are mitigated and compensated for by determining an estimate of the coupling coefficient according to the relationship between the first and second coupled resonant frequencies, in particular the relationship between these relationships. In particular, the sensitivity of the input and output resonant circuits to variations in the uncoupled resonant frequencies when determining the estimate of the coupling coefficient is significantly reduced by determining an estimate of the coupling coefficient that is a function of the ratio between the first and second coupled resonant frequencies.

[0201] As an example, the coupling coefficient is determined in some embodiments using the following function:

number

[0202] This function has been found to provide particularly advantageous performance in situations where the uncoupled resonant frequencies of the input and output resonant circuits are substantially similar. In particular, the use of a ratio between the frequencies has been found to provide significantly less sensitivity to measurement errors and inaccuracies. Furthermore, the use of a simplified formula such as the above is easier to evaluate, which in turn makes it easier to implement and / or operate. For example, in some embodiments, only one LUT is provided, based on the ratio between the frequencies used as inputs to look up.

[0203] In many embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient as a function of the uncoupled resonant frequencies of the input resonant circuit and / or the output resonant circuit, as previously described, which is used, for example together with the determination of the estimate of the coupling coefficient based on the ratio between the coupled resonant frequencies, in particular to modify the above formula.

[0204] In many embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient as a function of the ratio of the uncoupled resonant frequency of the output resonant circuit to the uncoupled resonant frequency of the input resonant circuit. It has been recognized that taking into account the ratio between the uncoupled resonant frequencies allows for particularly advantageous operation, in particular reducing sensitivity to changing, often unknown, parameters.

[0205] In many embodiments, the estimate of the coupling coefficient is determined as a function of the ratio of the first coupled resonant frequency to the second coupled resonant frequency and the ratio between the uncoupled resonant frequencies of the input resonant circuit and the output resonant circuit.

number

[0206] A particularly advantageous function for estimating the coupling function is in particular the following:

number

number

number

[0207] For β=1, solving the previous equation now gives:

number

[0208] This function can alternatively be expressed as:

number

[0209] The following equations are derived from the previously presented equations with the input resonant circuit loaded shorted:

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

number

[0210] Another example of a particularly advantageous function for estimating the combination function is as follows:

number

[0211] Therefore, in some embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient depending on the ratio of the sum of the squares of the first and second uncoupled resonant frequencies to the sum of the squares of the first and second coupled resonant frequencies.

[0212] In many embodiments, the estimate of the coupling coefficient is determined as a function of the ratio of the sum of the squares of the uncoupled and coupled resonant frequencies, and in some embodiments, the function depends only on the resonant frequencies by depending on this ratio, and the function does not take into account the coupled or uncoupled resonant frequencies except for the ratio. In some embodiments, the function is one that can be manipulated or rearranged so that the resonant frequencies are included only as the ratio of the sum of the squares of the coupled and uncoupled resonant frequencies.

[0213] In many embodiments, the estimator 309 is configured to determine an estimate of the coupling coefficient, which is a function of a dimensionless parameter determined from the first and second coupled resonant frequencies and the first and second coupled resonant frequencies, in particular a ratio between the frequencies or between the squares of the frequencies, etc. The dependence on the first coupled resonant frequency and / or the second coupled resonant frequency and / or the first uncoupled resonant frequency and / or the second uncoupled resonant frequency depends only on the dimensionless parameter, in particular the ratio.

[0214] Such an approach has been found to be particularly advantageous, providing increased robustness and reduced sensitivity to environmental changes, component variations, measurement errors, and the like.

[0215] The above equation is specifically derived from the two equations presented earlier, using suitable assumptions and simplifications.

number

[0216] More specifically, starting from the system equation of the electrical equivalent circuit of FIG. 16, a First Harmonic Approximation is derived.

number

[0217] i t and i r The system equation for is determined and then the locations of the peaks and valleys in the transfer function are found based on the following equation:

number

[0218] Keep only the numerator of this equation and R L = 0 (i.e., short-circuit the load on the power receiver),

number

number

number

number

[0219] In this formula,

number

number

number

number

[0220] Setting the second term of this equation to zero will locate the valley (minimum), i.e., f=β, or equivalently, ω=ω'. r By setting the fourth term of this equation to zero, the positions of the two peaks (minima) are obtained. That is,

number

number

[0221] Dividing the two results and reworking to isolate the coupling coefficients gives us the following:

number

[0222] In this equation, T is the ratio of the two resonant frequencies (the solution with the plus sign divided by the solution with the minus sign).

[0223] Adding the two results together we get the following:

number

number

number

[0224] The uncoupled resonant frequency ω' of the output resonant circuit t is derived by measuring the peak position (maximum value) of the current in the output resonant circuit with the power receiver load disconnected. r is derived by measuring the position of the valley (minimum) between two resonant peaks of the current in the output resonant circuit.

[0225] It will be appreciated that deviations from assumptions and the like (e.g., replacing a short in the series input resonant circuit with a low value resistor) will cause some differences and possibly result in frequencies being determined that differ from the theoretical values. However, in many embodiments, such differences are tolerable or even negligible. In fact, it has been found that even in cases where the deviations are relatively large, this approach and the use of simplified mathematical expressions and relationships allows for advantageous and useful estimation of the coupling coefficients.

[0226] In some embodiments, the power transmitter is configured to determine an indication or degree of misalignment of the power receiver relative to the power transmitter (specifically, of the receiver coil 107 relative to the transmitter coil 103). Specifically, the lower the coupling coefficient, the greater the misalignment. Furthermore, in such embodiments, the power transmitter is configured to generate an output to the user indicative of the misalignment. Specifically, the power transmitter provides a warning to the user indicating that the power receiver needs to be repositioned when the coupling coefficient falls below a threshold.

[0227] It will be appreciated that the above description has, for clarity, described embodiments of the invention with reference to various functional circuits, units, and processors. However, it will be apparent that any suitable distribution of functionality between various functional circuits, units, or processors may be used without departing from the invention. For example, functionality shown to be performed by separate processors or controllers may be performed by the same processor or controller. Thus, references to specific functional units or circuits should not be considered as indicative of a strict logical or physical structure or organization, but merely as references to suitable means for achieving the described functionality.

[0228] The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention is optionally implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Functions may indeed be implemented in a single unit, in several units or as part of other functional units. The invention may thus be implemented in a single unit or may be physically and functionally distributed between different units, circuits and processors.

[0229] Although the present invention has been described in relation to some embodiments, it is not intended to be limited to the specific form described herein. Rather, the scope of the present invention is limited only by the appended claims. Furthermore, although features may appear to be described in relation to specific embodiments, those skilled in the art will recognize that various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0230] Furthermore, a plurality of means, elements, circuits, or method steps, although individually recited, may be implemented by, for example, only one circuit, unit, or processor. Moreover, although individual features are included in different claims, they may possibly be advantageously combined, and the inclusion in different claims does not imply that the combination of features is infeasible and / or disadvantageous. Moreover, the inclusion of a feature in one category of a claim does not imply a limitation to this category, but rather indicates that the feature may also be applied, as appropriate, to the other categories of claims. The inclusion of a feature in a dependent claim of an independent claim does not imply a limitation to this independent claim, but rather indicates that the feature may also be applied, as appropriate, to the other independent claims. Moreover, the order of features in the claims does not imply any particular order in which the features have to be performed, and in particular the order of individual steps in a method claim does not imply that the steps have to be performed in this order. Rather, the steps may be performed in any suitable order. In addition, reference to the singular does not exclude a plural. Thus, references to "first," "second," etc. do not exclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

[0231] In some scenarios, a power transmitter (101) is provided that wirelessly supplies power to a power receiver (105) via an inductive power transmission signal; The power transmitter (101) an output resonant circuit comprising a transmitter coil (103) and at least one capacitor (303); a driver (201) configured to generate a drive signal for the output resonant circuit (103) and generate an inductive power transfer signal; a resonance detector (307) configured to measure a first coupled resonant frequency of an output resonant circuit during a resonance measurement period, the first coupled resonant frequency being a resonant frequency of an output resonant circuit of a transmitter coil (103) coupled to a receiver coil (107) of a power transfer input resonant circuit of a power receiver (105), the power transfer input resonant circuit having a quality factor of 10 or greater during the resonance measurement period; an estimation circuit (309) configured to determine an estimate of a coupling coefficient for coupling between the transmitter coil (103) and the receiver coil (107) in response to the first coupling resonant frequency; and an adapter (311) configured to set operating parameters in response to the estimate of the coupling coefficient.

[0232] A method of operating a power transmitter (101) for wirelessly supplying power to a power receiver (105) via an inductive power transmission signal, the power transmitter (101) comprising an output resonant circuit comprising a transmitter coil (103) and at least one capacitor (303); This method is generating a drive signal for an output resonant circuit (103) to generate an inductive power transfer signal; determining a first coupled resonant frequency of the output resonant circuit during a resonance measurement period, the first coupled resonant frequency being a resonant frequency of an output resonant circuit of a transmitter coil (103) coupled to a receiver coil (107) of a power transfer input resonant circuit of a power receiver (105), the power transfer input resonant circuit having a quality factor of 10 or greater during the resonance measurement period; determining an estimate of a coupling coefficient for coupling between the transmitter coil (103) and the receiver coil (107) as a function of the first coupling resonant frequency; and setting operational parameters in response to the estimated coupling coefficients.

Claims

1. A wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter wirelessly providing power to the power receiver via an inductive power transfer signal; The power transmitter comprises: an output resonant circuit comprising a transmitter coil and at least one capacitor; a driver that generates a drive signal for the output resonant circuit and generates the inductive power transfer signal; a resonance detector that determines a first coupled resonant frequency of the output resonant circuit during a resonance measurement period, the first coupled resonant frequency being a resonant frequency of the output resonant circuit of the transmitter coil coupled to a receiver coil of a power transfer input resonant circuit of the power receiver; an estimation circuit that determines an estimate of a coupling coefficient for coupling between the transmitter coil and the receiver coil as a function of the first coupling resonant frequency; an adapter that sets operating parameters in response to the estimated coupling coefficient; Equipped with The power receiver, the power transfer input resonant circuit comprising the receiver coil drawing power from the power transmitter and at least one capacitor, the power transfer input resonant circuit having a quality factor of 10 or greater during the resonant measurement period; a circuit for switching from a power transfer mode in which the quality factor is not limited to 10 or greater to the measurement mode in which the quality factor is 10 or greater during the resonant measurement period when the power receiver is operating in the measurement mode; A wireless power transmission system comprising:

2. 2. The wireless power transfer system of claim 1, wherein the resonance detector further measures a second coupled resonant frequency of the output resonant circuit during the resonance measurement period, the second coupled resonant frequency being another resonant frequency of the output resonant circuit in the presence of the power receiver, and the estimation circuit further determines an estimate of the coupling coefficient in response to the second coupled resonant frequency.

3. The wireless power transmission system according to claim 2 , wherein the first coupled resonant frequency and the second coupled resonant frequency are frequencies at which a current of the drive signal exhibits a maximum value.

4. The wireless power transmission system apparatus according to claim 1 , wherein the estimation circuit is further configured to determine the coupling coefficient in response to an uncoupled resonant frequency of the output resonant circuit and an uncoupled resonant frequency of the power transmission input resonant circuit.

5. The wireless power transmission system apparatus according to claim 1 , wherein the estimation circuit is further configured to determine the coupling coefficient in accordance with a ratio of an uncoupled resonant frequency of the output resonant circuit to an uncoupled resonant frequency of the power transmission input resonant circuit.

6. 4. The wireless power transmission system device according to claim 1, wherein the estimation circuit further determines the coupling coefficient according to a ratio between a sum of squares of an uncoupled resonant frequency of the output resonant circuit and an uncoupled resonant frequency of the power transmission input resonant circuit and a sum of squares of a second coupled resonant frequency, which is a resonant frequency of the output resonant circuit of the transmitter coil coupled to the receiver coil, and the first coupled resonant frequency.

7. 7. The wireless power transmission system according to claim 1, wherein the resonance detector determines an uncoupled resonance frequency of the output resonant circuit as a frequency at which a current of the drive signal exhibits a maximum value with respect to the power transmission input resonant circuit having the quality factor of 2 or less, and the estimation circuit determines the coupling coefficient in response to the uncoupled resonance frequency of the output resonant circuit.

8. 8. The wireless power transmission system according to claim 1 , wherein the resonance detector determines an uncoupled resonant frequency of the power transmission input resonant circuit as a frequency at which the current of the drive signal exhibits a minimum value for the power transmission input resonant circuit having a quality factor of 10 or greater, and the estimation circuit determines the coupling coefficient in response to the uncoupled resonant frequency of the power transmission input resonant circuit.

9. The wireless power transfer system of claim 1 , wherein the resonance measurement period is during initialization of a power transfer operation, and the operating parameters are initial operating parameters of the power transfer operation.

10. 10. The wireless power transfer system of claim 1, wherein the driver generates the drive signal according to a repetitive time frame in a power transfer phase, the resonant measurement period being included in the measurement period, the resonant measurement period being included in the measurement period.

11. 11. The wireless power transmission system of claim 1, wherein the operating parameter is a power loop parameter, which is a loop parameter of a power control loop that adapts a power level of the inductive power transmission signal in response to a power control message received from the power receiver.

12. The wireless power transfer system of claim 1 , wherein the power receiver further comprises a circuit that shorts the power transfer input resonant circuit during the resonant measurement period.

13. 1. A method of operating a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter wirelessly providing power to the power receiver via an inductive power transfer signal; the power transmitter comprises an output resonant circuit comprising a transmitter coil and at least one capacitor, and the power receiver comprises a power transfer input resonant circuit comprising a receiver coil that draws power from the power transmitter and at least one capacitor; The method of operation includes the power transmitter: generating a drive signal for the output resonant circuit to generate the inductive power transfer signal; determining a first coupled resonant frequency of the output resonant circuit during a resonance measurement period, the first coupled resonant frequency being a resonant frequency of the output resonant circuit of the transmitter coil coupled to the receiver coil of the power transfer input resonant circuit of the power receiver, the power transfer input resonant circuit having a quality factor of 10 or greater during the resonance measurement period; determining an estimate of a coupling coefficient for coupling between the transmitter coil and the receiver coil as a function of the first coupling resonant frequency; setting operational parameters in response to the estimated coupling coefficients; Run The method includes the steps of: A method of operation comprising: switching from a power transfer mode, in which the quality factor is not limited to 10 or greater, to a measurement mode, in which the quality factor is 10 or greater during the resonant measurement period when the power receiver is operating in the measurement mode.

14. 1. A power receiver for a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter wirelessly providing power to the power receiver via an inductive power transfer signal, The power receiver, a power transfer input resonant circuit comprising a receiver coil that draws power from the power transmitter and at least one capacitor; a circuit for switching from a power transfer mode in which a quality factor is not limited to 10 or greater to said measurement mode in which said quality factor is 10 or greater during a resonant measurement period when said power receiver is operating in said measurement mode; A power receiver comprising:

15. A method of operating a power receiver for a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter wirelessly providing power to the power receiver via an inductive power transfer signal, the power receiver comprising a power transfer input resonant circuit comprising the power transmitter and a receiver coil drawing power from at least one capacitor; The method of operation includes switching a circuit from a power transfer mode, in which a quality factor is not limited to 10 or greater, to a measurement mode, in which the quality factor is 10 or greater when the power receiver is operating in the measurement mode during a resonant measurement period.

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