WIRELESS POWER TRANSFER

Abstract

An energy transmitter (101) comprises an actuator (201) that generates a drive signal for an output resonant circuit comprising a transmitter coil (103) that generates an energy transfer signal. A resonant detector (307) determines a coupled resonant frequency for the output resonant circuit, where the coupled resonant frequency is a resonant frequency for the output resonant circuit for the transmitter coil (103) that is coupled to a receiver coil (107) that is part of an energy transfer input resonant circuit of the energy receiver (105). The input resonant circuit has a quality factor of not less than ten.An estimation circuit (309) determines an estimate of the coupling factor for the coupling between the transmitting coil (103) and the receiving coil (107) in response to the first effective resonant frequency and possibly an uncoupled resonant frequency of the output resonant circuit or the input resonant circuit. An adapter (311) configures an operating parameter in response to the estimated coupling factor.

Description

WIRELESS POWER TRANSFER Field of invention The invention relates to a wireless power transfer system and in particular, but not exclusively, to the operation of a power transmitter that provides inductive power transfer to high-power devices, such as, e.g., kitchen appliances. Background of the invention Most modern electrical products require a dedicated electrical outlet to draw power from an external source. However, this tends to be impractical, requiring the user to physically insert connectors or establish a physical electrical connection in some other way. Power requirements also typically vary significantly, and most devices now come with their own dedicated power supply, resulting in a large number of different power supplies for the average user, each dedicated to a specific device. While using internal batteries can eliminate the need for a wired connection to a power source during use, this only provides a partial solution, as the batteries will eventually need to be recharged (or replaced).The use of batteries can also substantially increase the weight and potentially the cost and size of the devices. To provide a significantly better user experience, it has been proposed to use a wireless power supply where energy is inductively transferred from a transmitting inductor in a power transmitting device to a receiving coil in the individual devices. RZRRnn / eznz / B / YiAi Power transmission through magnetic induction is a well-known concept, primarily applied in transformers with a tight coupling between a primary transmitting coil / inductor and a secondary receiving coil. When the primary transmitting coil and the secondary receiving coil are separated between two devices, wireless power transfer between them becomes possible based on the principle of a loosely coupled transformer. RZRRnn / eznz / B / YiAi This arrangement allows for wireless power transfer to the device without requiring cables or physical electrical connections. In fact, a device can simply be placed adjacent to, or on top of, the transmitter coil to recharge or receive external power. For example, power transmitters can be arranged with a horizontal surface upon which a device can simply be placed to receive power. Furthermore, these wireless power transfer arrangements can be advantageously designed so that the power-transmitting device can be used with a range of power-receiving devices. In particular, a wireless power transfer approach, known as the Qi specification, has been defined and is currently under development. This method allows Qi-compliant power-transmitting devices to be used with Qi-compliant power-receiving devices without requiring them to be from the same manufacturer or dedicated to each other. The Qi specification also includes features to allow operation to be tailored to the specific power-receiving device (e.g., dependent on the specific power draw). The Qi specification is developed by the Wireless Power Consortium and further information can be found, e.g., on their website: http: / / www.wirelesspowerconsortium.com / index.html, where, in particular, the documents of the defined Specification can be found. AZRRnn / eznz / B / YiAi The Wireless Power Consortium, building upon the Qi specification, developed the Ki specification (also known as the Wireless Kitchens Specification) which aims to provide safe, reliable, and efficient wireless power transfer to kitchen appliances. Ki supports much higher power levels, up to 2.2 kW. A potential problem with wireless power transfer is that power transfer performance can depend significantly on specific conditions. In particular, power transfer performance in terms of efficiency, achievable power levels, adaptation response times, etc., tends to depend heavily on how the transmitting and receiving coils are positioned relative to each other. Generally, more efficient and reliable power transfer is achieved when the coils are aligned and closer together. Typically, energy transfer performance depends on the coupling factor or coefficient, and the higher the coupling factor, the more efficient the energy transfer. While closer alignment and higher coupling factors can be achieved by designing devices in such a way that the positioning of the energy-receiving device relative to the energy-transmitting device is severely limited, e.g., by restricting the energy receiver to a specific position, this is generally undesirable as it restricts the system's functionality. For example, for kitchen appliances where the energy transmitter is implemented in a countertop, it is preferable that the user can simply position the appliance approximately near a coil of the energy transmitter, with the system then adapting accordingly. It is also preferable for the energy transfer function to be implemented without requiring, e.g., mechanical or physical guiding features that limit the energy-receiving device.It is desired that the power transmitter can be implemented using a completely flat countertop surface. AZRRnn / eznz / B / YiAi To account for the fact that operating conditions can vary substantially, the power transfer can be initiated with an initial operating point that provides acceptable performance under the worst-case scenario. During the power transfer, control loops can adjust the operating point to a more optimal level. Specifically, the power transfer can begin at low power levels and then be gradually increased during the transfer. However, such approaches tend to be suboptimal and do not provide ideal performance. There is often a delay before optimal performance is achieved. In many scenarios and situations, the approach may not result in reaching the optimal operating point, e.g., due to the control loop settling at a local endpoint instead of proceeding to an optimal global level. Therefore, an improved operation for a power transfer system would be advantageous, and in particular, an approach that allows for better flexibility, reduced cost, reduced complexity, better estimation of the coupling factor, backlash compatibility, better suitability for higher power level transfers, better power transfer initialization, better adaptation to specific operating conditions, and / or better performance would be advantageous. Brief description of the invention Therefore, the invention is intended, preferably, to mitigate, alleviate or eliminate one or more of the disadvantages mentioned above, either individually or in any combination. RZRRnn / eznz / B / YiAi According to one aspect of the invention, a wireless power transfer system is provided comprising a power transmitter and a power receiver; the power transmitter is arranged to wirelessly supply power to the power receiver by means of an inductive power transfer signal; the power transmitter comprises: an output resonant circuit comprising a transmitter coil and at least one capacitor;an actuator arranged to generate a drive signal for the resonant circuit to generate the inductive energy transfer signal; a resonant detector arranged to determine a first coupled resonant frequency for the output resonant circuit during a resonant measurement time interval; the first coupled resonant frequency being a resonant frequency for the output resonant circuit for the transmitting coil to couple to a receiving coil of an energy transfer input resonant circuit of the energy receiver; an estimation circuit arranged to determine an estimate of the coupling factor for coupling between the transmitting coil and the receiving coil in response to the first coupled resonant frequency; and an adapter arranged to set an operating parameter in response to the estimated coupling factor.and the energy receiver comprising an energy transfer input resonance circuit comprising a receiving coil arranged to draw energy from the energy transmitter and at least one capacitor; the energy transfer input resonance circuit having a quality factor of not less than ten during the resonance measurement time interval; and a circuit arranged to switch from an energy transfer mode in which the quality factor is not restricted to being not less than ten to a measurement mode during the resonance measurement time interval, the quality factor being not less than ten when the energy receiver is operating in the measurement mode. RZRRnn / eznz / B / YiAi The invention can provide improved energy transfer in many ways. In many ways, it can provide better initial performance and / or faster adaptation and convergence to a preferred operating point. In many ways, the approach can provide better adaptation of energy transfer to changing operating conditions. The approach can typically provide advantageous energy transfer operation and performance while allowing for low-complexity implementation. The approach can allow for efficient, reliable, and / or accurate determination of a coupling factor, which can enable better adaptation of typically critical energy transfer parameters, thereby enabling improved energy transfer. A particular advantage of this approach is that in many modes it can be a completely energy-based transmitter, without any specific calculations or estimation processes necessarily performed on the energy receiver. This can reduce costs in many scenarios. It can also simplify implementation and / or provide better recoil compatibility. The coupling factor estimate can be an estimate of the coupling factor change. An uncoupled resonant frequency for a resonant circuit can be a resonant frequency when there is no inductive coupling from the resonant circuit to an inductor that is not part of the resonant circuit. An uncoupled resonant frequency for the output resonant circuit can be a resonant frequency when the transmitting coil is not coupled to the receiving coil (nor typically to any other inductor). The first coupled resonance frequency can be a resonance frequency of the output resonance circuit when it is coupled to the receiving coil 107 and when the power receiver is in a power transfer position for power transfer. RZRRnn / eznz / B / YiAi In some modalities, the power transfer input resonance circuit has a quality factor of no less than 20, 50, 100 or even 500 during the resonance measurement time interval. A coupled resonant frequency for the output resonant circuit corresponds to a resonant frequency for the drive signal, and may specifically correspond to a local maximum (or possibly a local minimum) for a property of the drive signal for varying drive signal frequencies. In some modalities, the estimation circuit is further arranged to determine the estimated coupling factor in response to an uncoupled resonant frequency of the power transfer input resonant circuit. In some modes, the uncoupled resonant frequency of the power transfer input resonant circuit is a predetermined frequency. In some embodiments, the power transmitter further comprises a receiver for receiving data from the power receiver, and the receiver is arranged to receive data indicating the uncoupled resonant frequency of the power transfer input resonant circuit of the power receiver. In some modalities, the estimation circuit is further arranged to determine the estimated coupling factor in response to an uncoupled resonant frequency of the power transfer output resonant circuit. In some modes, the uncoupled resonant frequency of the power transfer output resonant circuit is a predetermined frequency. AZRRnn / eznz / B / YiAi According to an optional feature of the invention, the resonance detector is further arranged to measure a second coupled resonance frequency for the output resonance circuit during the resonance measurement time interval; the second coupled resonance frequency is a different resonance frequency for the output resonance circuit in the presence of the energy receiver; and the estimation circuit is further arranged to determine the estimated coupling factor in response to the second coupled resonance frequency. This can provide an improved and / or facilitated coupling factor estimate in many modalities and can specifically provide in many scenarios reduced sensitivity to variations in the operating environment, components, variable or unknown parameters of the energy transmitter and / or energy receiver, and / or measurement errors or inaccuracies. According to an optional feature of the invention, the first coupled resonant frequency and / or the second coupled resonant frequency are frequencies for which a drive signal current exhibits a local maximum. This can provide improved performance and / or operation, and typically an easier or improved coupling factor estimate can be achieved. The local maximum can be a local maximum of the drive signal current for varying drive signal frequencies. In some modalities, the estimation circuit is arranged to determine the coupling factor in response to a ratio between the first coupled resonance frequency and the second coupled resonance frequency. According to an optional feature of the invention, the estimation circuit is arranged to further determine the coupling factor in response to an uncoupled resonant frequency for the output resonant circuit and an uncoupled resonant frequency for the input resonant circuit. This can provide improved performance and / or operation, and typically an easier or improved coupling factor estimate can be achieved. According to an optional feature of the invention, the estimation circuit is arranged to further determine the coupling factor in response to a ratio between an uncoupled resonant frequency for the output resonant circuit and an uncoupled resonant frequency for the input resonant circuit. This can provide improved performance and / or operation, and typically an easier or improved coupling factor estimate can be achieved. Specifically, in many scenarios, it can provide reduced sensitivity to variations in the operating environment, components, variable or unknown parameters of the RZRRnn / eznz / B / YiAi energy transmitter and / or energy receiver, and / or measurement errors or inaccuracies. RZRRnn / eznz / B / YiAi In some modalities, the estimation circuit is arranged to determine a first relationship between the first coupled resonance frequency and the second coupled resonance frequency, and to determine the coupling factor as a function of the relationship. According to an optional feature of the invention, the estimation circuit is arranged to further determine the coupling factor in response to a ratio between a sum of squares of the uncoupled resonant frequency for the output resonant circuit and an uncoupled resonant frequency for the input resonant circuit and a sum of squares of the first coupled resonant frequencies and a second coupled resonant frequency that is a resonant frequency for the output resonant circuit for the transmitting coil to couple to a receiving coil. This can provide improved performance and / or operation, and typically results in a simplified or improved coupling factor estimate. Specifically, in many scenarios, it can provide reduced sensitivity to variations in the operating environment, components, variable or unknown parameters of the energy transmitter and / or energy receiver, and / or measurement errors or inaccuracies. According to an optional feature of the invention, the resonance detector is arranged to determine an uncoupled resonance frequency for the output resonance circuit as a frequency for which a current of the drive signal exhibits a local maximum for the input resonance circuit that has a quality factor of no more than two; and the estimation circuit is arranged to determine the coupling factor in response to the uncoupled resonance frequency for the output resonance circuit. This can provide an improved determination of the uncoupled resonant frequency of the output resonant circuit for the current conditions, which can result in an improved estimate of the coupling factor. In some modes, the input resonance circuit may have a quality factor of no more than 0.5, 1, 3, or 5 when determining the local maximum corresponding to the uncoupled resonance frequency of the output resonance circuit. RZRRnn / eznz / B / YiAi The local maximum can be a local maximum of the drive signal current for varying drive signal frequencies. According to an optional feature of the invention, the resonance detector is arranged to determine an uncoupled resonance frequency for the input resonance circuit as a frequency for which a current of the drive signal exhibits a local minimum for the input resonance circuit having a quality factor of not less than ten; and the estimation circuit is arranged to determine the coupling factor in response to the uncoupled resonance frequency for the input resonance circuit. This can provide an improved determination of the uncoupled resonant frequency of the input resonant circuit for the current conditions, which can result in an improved estimate of the coupling factor. In some modes, the input resonance circuit may have a quality factor of no less than 5, 15, 20 or 30 when determining the local minimum corresponding to the uncoupled resonance frequency of the input resonance circuit. The local minimum can be a local minimum of the drive signal current for varying drive signal frequencies. The local minimum can be determined during the resonance measurement time interval, and the same frequency sweep can be used specifically to determine one or more coupled resonance frequencies of the output / drive signal resonance circuit as well as the uncoupled resonance frequency of the input resonance circuit. In some embodiments, the resonance detector is arranged to control the actuator to generate the actuation signal to have a variable frequency during the resonance measurement time interval and to determine the first coupled resonance frequency in response to at least one of an actuation signal voltage, an actuation signal current, and a phase difference between the actuation signal voltage and the actuation signal current. This can provide a particularly advantageous approach and can lead to a highly effective and practical determination of the coupling factor and, therefore, a better configuration of the operating parameter. In some embodiments, the resonance detector is arranged to control the actuator to perform a frequency sweep of the actuation signal from higher frequencies to lower frequencies, and to determine the first coupled resonance frequency as a first detected frequency for which a resonance criterion for the actuation signal is met. RZRRnn / eznz / B / YiAi This can, in many ways, provide better detection of the coupled resonant frequency for the output resonant circuit and, therefore, a better estimate of the coupling factor and a better operating parameter setting that leads to better power transfer. According to an optional feature of the invention, the resonance measurement time interval is found during an initialization of a power transfer operation, and the operating parameter is an initial operating parameter for the power transfer operation. This approach may allow for improved initialization of a power transfer. It may also allow for faster and / or more reliable convergence to a preferred operating point for the power transfer. RZRRnn / eznz / B / YiAi According to an optional feature of the invention, the actuator is arranged to, during an energy transfer phase, generate the actuation signal according to a repetitive time period comprising at least one energy transfer time interval and at least one measurement time interval, and wherein the resonance measurement time interval is comprised within a measurement time interval. This approach may allow for better adaptation to changing operating conditions during a power transfer, such as specifically better adaptation to the movements of the power receiver relative to the power transmitter. In many modalities, the duration of the measurement time interval is no less than 5%, 10%, or 20% of the time period. In many modalities, the duration of the measurement time interval(s) is no greater than 70%, 80%, or 90% of the time period. The duration of the measurement time interval(s) may, in many scenarios, not exceed 5 ms, 10 ms, or 50 ms. In some modes, the operating parameter is a parameter that controls an energy level of the energy transfer signal. This can provide a particularly advantageous operation in many modalities. The parameter that controls a power level of the energy transfer signal can specifically be a parameter of the drive signal such as a frequency, duty cycle, phase, current and / or voltage of the drive signal. According to an optional feature of the invention, the operating parameter is a power loop parameter that is a loop parameter of a power control loop arranged to adapt a power level of the power transfer signal in response to power control messages received from the power receiver. This can provide particularly advantageous operation in many modes. It can allow the power transfer control response to be dynamically adapted and / or optimized for current conditions. In many scenarios, this approach can enable faster control operation while still ensuring the stability of the control loop. The loop parameter can specifically be a loop gain and / or loop delay. In some modalities, the estimation circuit is also available RZRRnn / eznz / B / YiAi to determine the estimated coupling factor in response to an uncoupled resonance frequency of the power transfer input resonance circuit. This can allow for an improved estimation of the coupling factor in many scenarios. This can facilitate the determination of the coupling factor estimate. The uncoupled resonant frequency of the power transfer input resonant circuit can be a resonant frequency of the power transfer input resonant circuit when the receiving coil is not coupled to the transmitting coil (nor typically to any other inductor). In some embodiments, the resonance detector is further arranged to determine a second coupled resonance frequency for the output resonance circuit during the resonance measurement time interval; the second operative resonance frequency is a different resonance frequency for the output resonance circuit in the presence of the energy receiver; and the estimation circuit is further arranged to determine the estimated coupling factor in response to the second operative resonance frequency. This can provide particularly advantageous and / or facilitated operation and / or performance in many ways. In some configurations, the estimation circuit is arranged to determine the estimated coupling factor in response to at least one of the following equations: Fresl := — RZRRnn / eznz / e / YiAi I Ί Ί > II Ί Ί > “ Ί Ί I Ί > 'fp* - fs';- 'j 'íp* ~ fs*1' - 4-fp'fs*·11 - k'; - k* RZRRnn / CZnZ / B / Y • Ί Ί · I j Λ Λ · - Λ Ί । Λ1fp · fs' - J'fp~ · fs' - - fp~fs~11 - k' Fres? =-----------------3----------------------------------1 - k' where fPes is the uncoupled resonance frequency of the resonant output circuit, fses is an uncoupled resonance frequency of the power transfer input resonant circuit, Fresl is the first coupled resonance frequency, Fres2 is a second coupled resonance frequency, and k is the coupling factor. This can provide a particularly advantageous and / or facilitated operation and / or performance in many modalities. The power receiver comprises a circuit arranged to switch from a power transfer mode in which the quality factor is not restricted to being no less than ten to a measurement mode during the resonance measurement time interval, the quality factor being no less than ten when the power receiver is operating in measurement mode. This can provide particularly advantageous and / or facilitated operation and / or performance in many ways. According to an optional feature of the invention, the energy receiver further comprises a circuit arranged to cause a short circuit in the energy transfer input resonance circuit during the resonance measurement time interval. This can provide particularly advantageous and / or facilitated operation and / or performance in many ways. According to another aspect of the invention, a method of operation is provided for a wireless power transfer system comprising a power transmitter and a power receiver. The power transmitter is arranged to wirelessly supply power to the power receiver by means of 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 an input resonant power transfer circuit comprising a receiver coil arranged to draw power from the power transmitter and at least one capacitor. The method of operation comprising the power transmitter performs the steps of: generating a drive signal for the output resonant circuit to generate the inductive power transfer signal,Determine a first coupled resonant frequency for the output resonant circuit during a resonant measurement time interval; the first coupled resonant frequency is a resonant frequency for the output resonant circuit so that the transmitting coil is coupled to a receiving coil of an input resonant energy transfer circuit of the energy receiver; the input resonant energy transfer circuit has a quality factor of not less than ten during the resonant measurement time interval; determine an estimate of the coupling factor for a coupling between the transmitting coil and the receiving coil in response to the first coupled resonant frequency.and configuring an operating parameter in response to the estimated coupling factor; and the method further comprising the power receiver performing the step of: switching from a power transfer mode in which the quality factor is not restricted to being not less than ten to a measurement mode during the resonance measurement time interval, the quality factor being not less than ten when the power receiver is operating in measurement mode. RZRRnn / eznz / e / YiAi According to another aspect of the invention, a power receiver is provided for a wireless power transfer system comprising a power transmitter and the power receiver. The power transmitter is arranged to wirelessly supply power to the power receiver by means of an inductive power transfer signal. The power receiver comprises: a power transfer input resonant circuit comprising a receiver coil arranged to draw power from the power transmitter and at least one capacitor; and a circuit arranged to switch from a power transfer mode in which the quality factor is not restricted to being at least ten to a measurement mode during a resonant measurement time interval. The quality factor is at least ten when the power receiver is operating in the measurement mode. RZRRnn / eznz / B / YiAi According to another aspect of the invention, a method of operation is provided for a power receiver for a wireless power transfer system comprising a power transmitter and the power receiver. The power transmitter is arranged to wirelessly supply power to the power receiver by means of an inductive power transfer signal. The power receiver comprises: a power transfer input resonant circuit comprising a receiver coil arranged to draw power from the power transmitter and at least one capacitor. The method comprises: a circuit arranged to switch from a power transfer mode in which the quality factor is not restricted to being at least ten to a measurement mode during a resonant measurement time interval. The quality factor is at least ten when the power receiver is operating in the measurement mode. Brief description of the figures The embodiments of the invention will be described, by way of example only, with reference to the figures, in which Figure 1 illustrates an example of elements of an energy transfer system according to some embodiments of the invention; Figure 2 illustrates an example of an equivalence circuit for the energy transfer system of Figure 1; Figure 3 illustrates an example of elements of a power transmitter according to some embodiments of the invention; Figure 4 illustrates an example of a half-bridge inverter for a power transmitter; Figure 5 illustrates an example of a full-bridge inverter for a power transmitter; RZRRnn / eznz / B / YiAi Figure 6 illustrates an example of elements of an energy receiver according to some embodiments of the invention; Figure 7 illustrates an example of a resonant output circuit response of the power transmitter of Figure 3; Figure 8 illustrates an example of coupled resonant frequencies of a power transmitter output resonant circuit from Figure 3 as a function of the coupling factor; Figure 9 illustrates an example of coupled resonant frequencies of an output resonant circuit of the power transmitter of Figure 3 as a function of the coupling factor; Figure 10 illustrates an example of a resonant output circuit response of the power transmitter of Figure 3; Figure 11 illustrates an example of a resonant output circuit response of the power transmitter of Figure 3; Figure 12 illustrates an example of a resonant output circuit response of the power transmitter of Figure 3; Figure 13 illustrates an example of a resonant output circuit response of the power transmitter of Figure 3; Figure 14 illustrates an example of a resonant output circuit response of the power transmitter of Figure 3; Figure 15 illustrates an example of a time period for the wireless power transfer system of Figure 1; and Figure 16 illustrates an example of an equivalence circuit for the power transfer system of Figure 1. RZRRnn / pznz / e / YiAi Detailed description of the modalities The following description focuses on embodiments of the invention applicable to a wireless power transfer system using a power transfer approach as known from the Qi specification or the Ki specification. However, it will be appreciated that the invention is not limited to this application, but can be applied to many other wireless power transfer systems. Figure 1 illustrates an example of an energy transfer system according to some embodiments of the invention. The energy transfer system comprises an energy transmitter (PTX) 101 that includes (or is coupled to) a transmitter coil / inductor 103. The system further comprises an energy receiver 105 (PRX) that includes (or is coupled to) a receiver coil / inductor 107. AZRRnn / eznz / B / YiAi The system provides an electromagnetic signal for inductive energy transfer, which can inductively transfer energy from the energy transmitter 101 to the energy receiver 105. Specifically, the energy transmitter 101 generates an electromagnetic signal, which propagates as a magnetic flux through the transmitting coil or inductor 103. The energy transfer signal typically has a frequency between approximately 20 kHz and approximately 500 kHz, and frequently, for Qi-compatible systems, typically in the range of 95 kHz to 205 kHz, or for Ki-compatible systems, typically in the range of 20 kHz to 80 kHz. The transmitting coil 103 and the energy receiving coil 107 are weakly coupled, and therefore the energy receiving coil 107 collects (at least part of) the energy transfer signal from the energy transmitter 101.Therefore, energy is transferred from energy transmitter 101 to energy receiver 105 by means of wireless inductive coupling from the transmitting coil 103 to the energy receiving coil 107. The term energy transfer signal is mainly used to refer to the inductive signal / magnetic field between the transmitting coil 103 and the energy receiving coil 107 (the magnetic flux signal), but it will be appreciated that by equivalence it can also be considered and used as a reference for an electrical signal supplied to the transmitting coil 103 or picked up by the energy receiving coil 107. In the example, the energy receiver 105 is specifically an energy receiver that receives energy through the receiving coil 107. However, in other embodiments, the energy receiver 105 may comprise a metallic element, such as a metallic thermal element, in which case the energy transfer signal directly induces eddy currents, resulting in direct heating of the element. RZRRnn / eznz / B / YiAi The system is designed to transfer substantial levels of energy, and specifically, the power transmitter can support power levels exceeding 500 mW, 1 W, 5 W, 50 W, 100 W, or 500 W in various configurations. For example, for corresponding Qi applications, power transfers can typically be in the 1–5 W power range for low-power applications (the reference power profile), up to 15 W for Qi specification version 1.2, up to 100 W for higher-power applications such as power tools, laptops, drones, robots, etc., and in excess of 100 W and up to more than 2000 W for very high-power applications such as Qi cooking applications. In what follows, the operation of the power transmitter 101 and power receiver 105 will be described with specific reference to a mode generally in accordance with the Qi or Ki specification (except for the modifications and improvements described (or resulting from) this description) or suitable for the higher-power cooking specification developed by the Wireless Power Consortium. In particular, the power transmitter 101 and power receiver 105 may follow, or be substantially compatible with, elements of version 1.0, 1.1, 1.2, or 1.3 of the Qi Specification (except for the modifications and improvements described (or resulting from) this description). Many wireless power transfer systems, and in particular high-power systems such as Ki, utilize resonant power transfer where the transmitting coil 103 is part of a resonant circuit, and typically, the receiving coil 107 is also part of a resonant circuit. In many configurations, the resonant circuits can be series resonant circuits, and therefore the transmitting coil 103 and the receiving coil 107 can be coupled in series with a corresponding resonant capacitor. The use of resonant circuits tends to provide more efficient power transfer. In most power transfer systems, before power transfer begins, a communication channel is established between power transmitter 101 and power receiver 105. Once communication is established and the two devices have been identified, power transmitter 101 can begin transmitting power to power receiver 105. An example of an electrical equivalence diagram for the energy transfer function of energy transmitter 101 and energy receiver 105 is illustrated in Figure 2. A wide range of energy transmitters and energy receivers may exist in a given system, and these may have substantially different properties and parameters. For example, coil sizes, inductance values, and loads may vary considerably. Consequently, the system parameters, as specifically represented in Figure 2, may vary significantly in practice between different devices, mechanical constructions, positioning, and so on.In particular, the placement of the power receiver and, therefore, the relative positions of the receiving coil 107 and the transmitting coil 103, substantially affect the coupling between the coils, i.e., the primary inductor Lp (power transmitter side) and the secondary inductor Ls (power transmitter side), and can therefore significantly change the behavior of the system. RZRRnn / eznz / B / YiAi Furthermore, power receiving devices can have several different operating modes, such as switching various loads on and off. For example, in an air fryer, the heating element might switch on and off. This could result in a very substantial load switching, from, say, 50 to 1200 W and vice versa. Moreover, such load switching can be repeated during device operation to maintain a constant temperature. RZRRnn / eznz / B / YiAi Systems can also contain nonlinear loads; for example, instead of a resistive component, the power receiver can drive a motor, such as, for example, a motor in a food processor. This results in a completely different system response and has a significant impact on the design of the control system. Typically, a wireless power transfer system uses a power control loop to direct the system to the appropriate 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 along with the setpoint power value, an error signal can be generated. The appliance sends this error signal, or possibly the desired power setpoint, to the power control function in the power transmitter to reduce the static error, ideally to zero. However, since system performance and operation vary greatly depending on the existing combination and placement of the power transmitter and receiver, the appropriate operating point also varies considerably. This includes the conditions at the start / initialization of a power transfer, and therefore the optimal initial operating point also varies greatly. One of the key parameters affecting operation is the coupling factor. Furthermore, the positioning of the power receiver relative to the power transmitter (and specifically the receiving coil 107 relative to the transmitting coil 103) and, therefore, depends on the specific operating conditions. In contrast, most of the other parameters in Figure 2 tend to be known and relatively constant for the specific combination of power transmitter and receiving coil 107. Thus, typically, almost all relevant system parameters can be known except for the coupling factor. The coupling factor depends on several parameters, including, in particular, the coil sizes / geometry and the distance between the power transmitter and the power receiver. In the system shown in Figure 1, the system includes functionality for estimating a coupling factor and for adapting an operating parameter in response to that factor. Specifically, in many configurations, a control loop parameter, such as the open-loop transfer function and / or loop gain, can be adapted to optimize and control closed-loop performance. As another example, the preferred operating point (typically the initial one), such as the power level, can be adapted depending on the coupling factor. In some configurations, the measurement and adaptation can be performed before energy transfer, or alternatively or additionally after energy transfer. As an illustrative example, when a power receiver is placed on a power transmitter, communication can be established between them. This allows the power transmitter to begin 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 for which operation can be guaranteed under the worst-case scenarios, followed by a gradual adjustment of the operating point during power transfer. However, such an approach tends to be slow and inefficient, and in fact, in many RZRRnn / eznz / B / YiAi scenarios may not be feasible to gradually adapt to the optimal operating point (e.g., the system may get stuck at a local maximum instead of proceeding to a global maximum). Therefore, it may be preferable to determine a desired operating point and initiate operation at, or near, this desired operating point. The desired operating point can be estimated using all known system parameters. For example, these may include (or consist of): primary and secondary induction; primary and secondary resonance; load resistance, power, and voltage; and coupling factor. With all these parameters known, the transfer function for the power path can be calculated, and an initial operating point can be determined. However, while most parameters can be known by the power transmitter, e.g., based on communication of the power receiver parameters from the power receiver, the coupling factor depends on the placement / misalignment of the devices and, therefore, cannot be known in advance. In the example, the power transmitter can therefore proceed to measure / estimate the coupling factor. This can be done, for example, by determining one or more resonant frequencies for the power transmitter's resonant circuit when loaded by the power receiver. The power receiver can be put into a high-Q mode during such a measurement, and the resonant frequency can be determined by the power transmitter by a frequency sweep of the signal driving the transmitter coil 103. Based on the measured resonant frequency(ies), the coupling factor can be calculated, e.g., based on the free-running resonant frequencies of the power receiver's resonant frequency and the power transmitter's resonant frequency. This coupling factor can then be used to calculate the RZRRnn / eznz / B / YiAi complete transfer function and then to calculate the initial operating point and the necessary operating parameters, such as the initial power level and / or loop gain. Setting the operating parameters to the calculated values ​​can allow the initial operating point to be reached from the start of the energy transfer, resulting in the appropriate energy / current being supplied to the energy receiver. In fact, by measuring the coupling factor of a power transfer system before power is transferred, a better estimate of the system's response can be made. This can lead to a better selection of the initial operating point (frequency, power signal duty cycle, loop gain, etc.). This can allow the desired power level to be reached much faster. Furthermore, such an approach can reduce the risk of overvoltage or overcurrent conditions. Also, measuring the coupling factor during power transfer and adapting the operating parameter(s) based on such measurement can provide better performance and can typically provide more accurate optimization and adaptation. Figure 3 illustrates elements of the power transmitter 101 from Figure 1 in greater detail. The energy transmitter 101 includes an actuator 301 that can generate an actuation signal which is fed to the transmitter coil 103, which, in turn, generates the electromagnetic energy transfer signal that thus provides energy transfer to the energy receiver 105. The transmitter coil 103 is part of an output resonant circuit comprising the transmitter coil 103 and a capacitor 303. In the example, the output resonant circuit is a series resonant circuit, but it will be seen that in other configurations, the output resonant circuit can be a single-resonant circuit. AZRRnn / eznz / B / YiAi parallel. It will be appreciated that any suitable resonant circuit including one or more inductors and / or capacitors can be used. Actuator 301 generates the current and voltage that are fed to the output resonant circuit and, therefore, to the transmitter coil 103. Actuator 301 is typically a drive circuit in the form of an inverter that generates an alternating signal from a DC voltage. The output of actuator 301 is typically a switch bridge that generates the drive signal by appropriately switching the switches in the switch bridge. Figure 4 shows a half-bridge / inverter with switches. Switches SI and S2 are controlled so that they are never closed at the same time. Alternatingly, SI is closed while S2 is open, and S2 is closed while SI is open. The switches open and close at the desired frequency, thus generating an alternating signal at the output.Typically, the inverter output is connected to the transmitter inductor via a resonant capacitor. Figure 5 shows a full-bridge inverter with switches. Switches S1 and S2 are controlled so that they are never closed simultaneously. Switches S3 and S4 are also controlled so that they are never closed simultaneously. Alternately, switches S1 and S4 are closed while S2 and S3 are open, and then S2 and S3 are closed while S1 and S4 are open, thus creating a square wave signal at the output. The switches open and close at the desired frequency. The energy transmitter 101 further comprises an energy transmitter controller 305, which is arranged to control the operation of the energy transmitter 101 according to the desired operating principles. Specifically, the energy transmitter 101 may include many of the functionalities required to perform the AZRRnn / eznz / B / YiAi energy control according to the Qi specification or the Ki specification. RZRRnn / eznz / B / YiAi The energy transmitter controller 305 is specifically designed to control the generation of the drive signal by the actuator 301 and can specifically control the power level of the drive signal and, consequently, the level of the generated energy transfer signal. The energy transmitter controller 305 comprises an energy loop controller that controls the power level of the energy transfer signal in response to energy control messages received from the energy receiver 105 during the energy transfer phase. The energy transmitter controller 305 may further include functionality for communicating with the energy receiver 105. For example, the energy transmitter controller 305 may be configured to transmit data to the energy receiver 105 by modulating the energy transfer signal and to receive data from the energy receiver 105 by detecting the load modulation of the energy transfer signal. It will be appreciated that in other configurations, other means of communication may be used, such as, for example, a separate communication functionality, such as NEC communication. The use of a resonant circuit that includes the transmitting coil 103 is well known for providing more efficient power transfer in many scenarios. Furthermore, having a power receiver that also uses a resonant circuit—that is, where the receiving coil 107 is part of a resonant circuit—can result in resonant power transfer, which provides several advantages, including highly efficient power transfer and ease of control, such as, for example, by controlling the frequency of the drive signal. Figure 6 illustrates some illustrative elements of the 105 energy receiver. The receiving coil 107 is coupled to a power receiving controller 601 through a capacitor 603, which, together with the receiving coil 107, forms an input resonant circuit. Therefore, the power transfer can be a resonant power transfer between resonant circuits. RZRRnn / eznz / B / YiAi The power receiver controller 601 couples the receiver coil 107 to a load 605 through a switch 607 that may be specifically capable of short-circuiting the load 605. The power receiver controller 601 includes a power control path that converts the energy drawn by the receiver coil 107 into a suitable supply for the load 605. In some embodiments, the power receiver controller 601 may provide a straightforward power path that simply connects the input resonant circuit to the switch 607 or load 605; that is, the power path of the power receiver controller 601 may be implemented using only two wires. In other embodiments, the power path may include, for example, rectifiers and possibly damping capacitors to provide a DC voltage. Still in other embodiments, the power path may include more complex functions, such as, for example,Voltage control circuit system, impedance matching circuit system, current control circuit system, etc. Similarly, it will be seen that switch 607 may only be present in some modes and that in some modes the load 605 may be permanently coupled to the input resonance circuit. In addition, the 601 energy receiver controller may include various energy receiver controller functionalities required to perform energy transfer, and in particular the functions required to perform energy transfer in accordance with Qi or Ki specifications. The energy receiver controller 601 may also include functionality for communicating with the energy transmitter 101. For example, it may be configured to decode and demodulate data modulated onto the energy transfer signal and may be configured to transmit data to the energy transmitter 101 via the load that modulates the energy transfer signal. In some configurations, a separate communication function, such as an NEC communication function, may be employed. In operation, the system is configured to control the drive signal so that the energy transfer signal reaches appropriate operating parameters / properties and so that the energy transfer operates at a suitable operating point. To achieve this, the energy transmitter is configured to control a parameter of the drive signal using an energy control loop where an energy property of the energy transfer / drive signal is monitored in response to energy control error messages received from the energy receiver. At regular and typically frequent intervals, the power receiver transmits a power control error message to the power transmitter. In some configurations, a direct power setpoint change message indicating a desired absolute power level (instead of a relative error message) may be transmitted. The power receiver 105 includes functionality to support such a power control loop; for example, the power receiver controller 601 can continuously monitor the power or voltage of a load signal supplied to the load and detect whether it is above or below the set point. RZRRnn / eznz / B / YiAi of a desired value. It can at regular intervals generate a power control error message requesting that the power level of the power transfer signal be increased or decreased, and can transmit this power control error message to the power transmitter. When it receives a power control error message from the power receiver, the 305 transmission controller can determine how the drive signal parameter should be modified to increase or decrease the power level of the energy transfer signal as requested. It can then monitor and adjust the drive signal parameter accordingly. Consequently, a power control loop is used to regulate a specific energy property of the power transfer signal, resulting in the desired operating point at the power receiver. The power transfer operation is therefore controlled by this loop, and its effective operation is critical to system performance. Initiating or adapting the power control loop to the operating conditions is thus essential for optimal performance. In the described system, the power transmitter includes functionality to estimate the coupling factor and to adapt the operation of the power transfer system and, specifically, the power control loop, based on the coupling factor. The power transmitter is specifically designed to determine the coupling factor in response to the detection / measurement of one or more resonant frequencies for the output resonant circuit (and / or equivalently for the drive signal) when coupled to the power receiver, and specifically to the receiver coil 107 and the input resonant circuit. It can then adapt the RZRRnn / eznz / B / YiAi operation of the energy transfer system, accordingly. The energy transmitter 101 comprises a resonance detector 307 arranged to determine at least one coupled operational resonant frequency for the output resonant circuit during a resonant measurement time interval, where the coupled resonant frequency is a resonant frequency for the output resonant circuit in the presence of the energy receiver, i.e., when the transmitting coil 103 is coupled to the receiving coil 107 of the energy receiver. Consequently, the coupled resonant frequency reflects an effective resonant frequency of the output resonant circuit when the transmitting coil 103 is coupled to the receiving coil 107. Due to the coupling of the two coils, the effective inductance of the transmitting coil 103 is different from the self-inductance of the transmitting coil 103 when it is not coupled to any receiving coil 107.Similarly, the effective inductance of the receiving coil 107 is different from the self-inductance of the receiving coil 107 when it is not coupled to any transmitting coil 103. As a result, the effective resonances will be different from the self-resonances when there is no coupling. Furthermore, due to the coupling of the two coils and, therefore, the two resonant circuits, the drive signals will effectively experience two (different) resonant frequencies; that is, due to the coupling, the output resonant circuit will effectively have two resonant frequencies, and these will be different from the (uncoupled) self-resonant frequency of the output resonant circuit. RZRRnn / eznz / B / YiAi In many configurations, the 307 resonance detector can be arranged to determine both coupled resonance frequencies. The effective or coupled resonant frequency of the output resonant circuit will differ from the self-resonant frequency of the output resonant circuit when it is not coupled to any other inductor, and this difference will depend on the coupling. Therefore, detecting the coupled or operating resonant frequency of the output resonant circuit can provide information about the coupling to the receiving coil 107, and this can be used in the power transmitter 101 to estimate the coupling factor. The resonance detector 307 is coupled to an estimation circuit 309 which is arranged to determine an estimate of the coupling factor for the coupling between the transmitting coil 103 and the receiving coil 107 based on at least the coupled resonance frequency. In some embodiments, the estimation circuit 309 can be configured to generate the coupling factor estimate based on only a single measured coupled resonant frequency. For example, the estimation circuit 309 may include a lookup table that, for an input address word corresponding to a given coupled resonant frequency, provides a coupling estimate. The lookup table may be generated, for example, by measurements during a manufacturing and design stage or based on theoretical calculations. However, while it may be advantageous in many modalities, such an approach tends to provide a less than optimal estimate of the coupling factor when the parameters involved can vary substantially and is therefore typically limited to situations where the parameters involved (including the electrical parameters of the resonant circuits, the properties of the power transmitter and power receiver, etc.) are very restricted. In most modes, estimation circuit 309 is arranged accordingly to consider additional parameters, and in many modes estimation circuit 309 can be arranged to determine the coupling factor estimate based also on considering at least one of a second resonant frequency RZRRnn / eznz / e / YiAi coupled output resonance circuit, a self-resonant frequency / uncoupled resonance frequency of the output resonance circuit, and a self-resonant frequency / uncoupled resonance frequency of the input resonance circuit. In particular, estimator 309 can, in many ways, be arranged to also consider the uncoupled resonance frequency of the output resonance circuit when determining the coupling factor estimate. 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 is typically 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. RZRRnn / cznz / e / YiAi Therefore, in many modalities, the estimation circuit 309 is arranged to estimate the coupling factor based on the effect that the coupling between the transmitting coil 103 and the receiving coil 107 has on a resonant frequency of the output resonant circuit. The estimation circuit 309 is coupled to an adapter 311, which is configured to set an operating parameter in response to the estimated coupling factor. In some configurations, the setting can be either relative or absolute. For example, the adapter 311 can perform a relative setting of an operating parameter by increasing or decreasing a parameter value by a given amount; for instance, it can increase or decrease the power level of the current value. In some configurations, the 311 adapter can be used to adapt or configure an operating value for a power transfer signal parameter, and specifically to configure a parameter value for the power transfer signal that controls the power level of the power transfer signal. Such parameter values ​​may include a frequency (which affects the power level for a resonant power transfer system), a phase, amplitude (current and / or voltage), or duty cycle for the power transfer signal. For example, for a high coupling factor, the energy transfer between the coils can be efficient and therefore a high power level can be set, whereas for a low coupling factor the energy transfer is less efficient and therefore it must be set to a lower level. Therefore, by estimating the coupling factor, it is possible to determine a suitable power level, and when starting a power transfer operation, this can be initiated with that power level set to a desired value by setting the operating parameters of the power transfer signal appropriately. Appropriate power levels can be determined, for example, using a lookup table (LUT) generated during manufacturing. For instance, based on measurements taken for different energy receivers with varying properties (e.g., coil type, energy receiver inductance values, etc.), appropriate power levels can be determined for different coupling factors and stored in an LUT. During operation, when a new energy transfer is initiated with a new energy receiver, the energy receiver can transmit relevant parameter values ​​to the energy transmitter, which can then estimate the coupling factor. The resulting values ​​can be used to populate the LUT with a lookup table, and the transfer The RZRRnn / eznz / B / YiAi power supply can be initiated with the corresponding power level. The LUT can specifically output suitable values ​​for the frequency, duty cycle, and / or amplitude of the drive signal. Then, the adapter 311 can, for example, provide this information to the power transmitter controller 305, which can control the actuator 301 to generate a drive signal with these properties. Therefore, the system can initiate power transfer with appropriate parameters after adaptation is performed via the power control loop. In some modes, the 311 adapter can alternatively or additionally adapt a power control loop parameter of the power control loop that controls the power level of the power transfer signal based on the power control messages received from the power receiver (105). The open-loop performance of the power control loop is strongly dependent on the coupling factor, and consequently, so is the closed-loop performance. In fact, in many cases, the closed loop can only be stable for certain values ​​of the coupling factor. Typically, the loop gain is substantially proportional to the coupling factor, and since the coupling factor can vary substantially, so can the gain. Variations in loop gain directly affect the time response (and frequency) of the closed loop, including loop stability. The 311 adapter can be configured to modify the loop gain to compensate for variations in the coupling factor so that the overall gain can be at a desired level.This can provide optimized performance with a faster action loop since it is not necessary to set the loop gain to ensure stability in the worst possible scenario. In some modalities, more complex loop adaptations can be made, such as adjusting the frequency response (open loop). RZRRnn / eznz / B / YiAi or delay. This can provide more flexible adaptation that can allow performance to be customized more precisely. For example, the filter response can be adapted to avoid any self-oscillation and potential instability. Regarding the power level of the energy transfer signal, the parameters can be determined, for example, through measurements and experiments during the design / manufacturing phase, with the appropriate parameters stored in a LUT (Layout Unit Tool). In fact, the same LUT can store parameters for both the control loop and the power level configuration. It will be appreciated that the operating parameters that can be adapted are not limited to power level parameters or loop parameters, but that other parameters can be set alternatively or additionally in some modes such as, for example, a foreign object detection parameter or a communication parameter. In different configurations, estimator 309 can use different approaches to determine the coupling factor. In particular, when the output resonant circuit is coupled to the input resonant circuit, with the latter being able to oscillate sufficiently undamped, the output resonant circuit will effectively exhibit two coupled resonant frequencies instead of just a single coupled resonant frequency. Specifically, when the input resonant circuit is completely undamped, such as when a series resonant circuit is shorted so that the series load / resistance is substantially zero, the output resonant circuit will exhibit two coupled resonant frequencies. As illustrated by the example in Figure 7, the response of the output resonant circuit when coupled to the circuit of The AZRRnn / eznz / B / YiAi input resonance (with this being sufficiently undamped) is one that includes two resonances. Figure 7 shows an example of a response (amplitude and phase of the primary current for a constant voltage amplitude of the drive signal) for typical system parameters with the input resonance circuit being undamped, and as clearly illustrated, the response comprises two resonance peaks. Figure 8 illustrates an example of how the resonant frequencies of the coupled output resonant circuit vary for different coupling coefficients k. In the example, the uncoupled resonant frequencies of both the output and input resonant circuits are at a normalized frequency of 0.3 × 10⁵. As can be seen, the coupled case results in a first resonant frequency above the uncoupled frequencies and a second resonant frequency below the uncoupled frequencies. Also as can be seen, there is a strong dependence of the resonant frequencies on the coupling factor, with the difference increasing for a higher coupling factor. Figure 9 illustrates a corresponding example to that of Figure 8, but with the normalized average uncoupled resonant frequency of the output resonant circuit at 0.268xl05 and the normalized average uncoupled resonant frequency of the input resonant circuit still at 0.3xl05. As can be seen, this results in slightly different coupled resonant frequencies. RZRRnn / eznz / B / YiAi In some configurations, measurements of such dependencies, as shown in Figures 8 and 9, can be made during a manufacturing / design phase for relevant combinations of the power transmitter and receiver coil 107. The results can be stored in the LUTs included in the power transmitter (or, e.g., stored centrally and retrieved when a new power transfer is established). After determining a coupled resonant frequency, a lookup table can be generated using the estimator 309 to derive an estimated coupling factor. RZRRnn / eznz / B / YiAi In some configurations, the resonance detector 307 can be arranged to detect the coupled resonant frequency during the resonance measurement time interval by varying the frequency of the drive signal. Specifically, it can perform a frequency sweep over a range of frequencies that may correspond to the frequency range in which the coupled resonant frequency is expected to be found, or within which the coupling factor can be considered sufficiently high to provide acceptable power transfer. The resonance detector 307 can then monitor the drive signal and detect an extreme of, for example, the current or voltage amplitude. For instance, for series resonant circuits, the resonance detector 307 can control the drive 301 to vary the frequency over a range and with a fixed voltage amplitude.Next, you can measure the current amplitude at different frequencies and determine the coupled resonant frequency at which the highest current amplitude occurs. As another example, the 307 resonant detector can detect when the phase difference between the current and voltage of the drive signal is zero (or close to zero), meaning when the load on the output resonant circuit is purely resistive. If the coupled resonant frequency is not detected within the specified frequency range, this may indicate that the coupling factor is not within a suitable range for power transfer, and power transfer may be terminated. In some modes, the frequency sweep of the drive signal can be from higher to lower frequencies, and the coupled resonant frequency can be determined as the first detected frequency for which a resonance criterion is met (e.g., extremes for current amplitude or signal voltage, or zero phase difference between voltage and current). Therefore, instead of, for example, detecting the global extreme, the first local extreme can be detected. This approach allows for the detection of the higher of the two coupled resonant frequencies. The inventors have discovered that the greatest variation in the coupled resonant frequency for a variable coupling factor occurs at the higher coupled resonant frequency, and therefore this can be used to typical and advantageous effect, especially if only one coupled resonant frequency is used. RZRRnn / eznz / B / YiAi In some modalities, both coupled resonant frequencies can be detected and used to determine the estimated coupling factor. For example, two separate LUTs can be provided for the lower and higher coupled resonant frequencies, and the estimated coupling factor can be determined as the average of the two results from the lookup table. In other modalities, different approaches can be used to determine the coupled resonant frequency of the output resonant circuit. For example, in some modalities, a successive approximation approach can be used. Such an approach would be highly advantageous and useful when basing the determination of the resonant frequency on frequency intervals. This approach can allow for rapid detection of the resonant frequency or frequencies. In some configurations, the power receiver can communicate system parameters, such as the uncoupled resonant frequency and / or the receiver coil inductance, to the power transmitter, which can then be used to determine the coupling factor of the coupled resonant frequency. For example, LUTs can also be dependent on these power receiver factors, or different LUTs can be provided for different power receivers (in fact, in some configurations, a LUT can be provided by the power receiver). RZRRnn / eznz / B / YiAi In some configurations, the coupling factor can be determined using analytical formulas. Specifically, estimation circuit 309 can be used to determine the estimated coupling factor in response to at least one of the following equations: Fresl I Ί η I | Ί η · Ί Ί | Ί. 'fp* - fs*' - ψίρ* - fs*'' - 4-fp'fs*·11 - k' 1fp~ ~ fs* - J'fp* - fs* - 4 fp*fs* ' 1 - k* Fres? =-----------------1---------------------------------1 - k* where fPes is the uncoupled resonance frequency of the resonant output circuit, fses is an uncoupled resonance frequency of the power transfer input resonant circuit, Fresl is the first higher coupled resonance frequency, Fres2 is a second lower coupled resonance frequency, and k is the coupling factor. These equations apply to coupled resonant circuits and can be used by the 307 resonant detector (either directly or indirectly). In some configurations, only one of the equations can be used, and, in fact, the coupling factor estimate can be based on only one of the coupled resonant frequencies. For example, as described, the highest coupled resonant frequency can be determined by detecting the first peak in a sweep from higher to lower frequencies. Based on the first equation above, and using known values ​​for the uncoupled resonant frequencies of the input and output resonant circuits, respectively, this highest coupled resonant frequency can then be used to calculate the coupling factor estimate. The same approach can be used to determine the coupling factor based on the lowest coupled resonance frequency. In some modalities, both the highest and lowest coupled resonance frequencies can be measured, and both equations can be used. For example, two coupling factor values ​​can be calculated using the first and second equations and the respective measured coupled resonance frequencies, and the coupling factor estimate can be generated as the average of these. In other modalities, the coupling factor estimate can be calculated as the value that results in the lowest errors between the above equations and the measured values. In some configurations, both coupled resonant frequencies can be used in both equations, but the uncoupled resonant frequency of the input resonant circuit is not used. Instead, this variable can be estimated using the equations above and the two coupled resonant frequencies. In such an approach, a more complex estimation and calculation can be used to avoid the need for the energy transmitter to know the specific properties of the input resonant circuit. This approach can be particularly useful for implementation in an existing system where some energy receivers may not be able to communicate this information. RZRRnn / eznz / B / YiAi The described approach is based on estimating a coupling factor by considering the change in resonant frequency caused by coupling the output resonant circuit to the input resonant circuit. This change depends on the coupling factor but also on the quality factor (Q) of the input resonant circuit. This can be seen in Figures 10-14, which show how the two coupled resonant frequencies vary for different coupling factors (within each graph, k = [0.1, 0.2, ..., 0.9]), and also how the change depends on the Q value (as can be seen by comparing the different graphs showing Q = 1000, 10, 3, 1, and 0.1, respectively). In this approach, the quality factor of the input resonant circuit during the resonant measurement time interval is no less than ten and can typically be higher. This can result in the detection of coupled resonant frequency(ies) that are reliable and reasonably accurate, and therefore, the estimated coupling factor is similarly reliable and accurate. Consequently, it can be ensured that the operating point matching is reliable and can enable efficient operation. RZRRnn / eznz / B / YiAi In some modalities, a high Q during the resonance measurement time interval can be ensured by the Q value for the input resonance circuit as long as it is above ten, i.e., by the power receiver being designed for the input resonance circuit that always has a quality factor above 10. However, this is typically in contrast to the desire to provide the appropriate power to the load. For example, for Ki systems, loading an input resonant circuit by typical energy values ​​results in Q values ​​that are typically less than 5 and often less than 2. In many configurations, the energy receiver can be arranged to switch its operating mode from a lower quality factor mode for at least some time outside the resonance measurement time interval to a higher quality factor mode with a Q value of at least 10 during the resonance measurement time interval. This allows for efficient energy transfer and an efficient coupling factor estimation. Therefore, the energy receiver can be configured to switch from an energy transfer mode in which the quality factor is not restricted to being above 10, and during which it may in fact be substantially less than 10 to allow for efficient energy transfer, to a measurement mode during the resonance measurement time interval where the quality factor is no less than ten. This can be achieved, for example, by using switch 607. For instance, if the power path connects switch 607 and load 605 directly to the input resonant circuit, the switch can connect the normal load 605 to the input resonant circuit outside of the resonant measurement time interval(s). However, during the resonant measurement time interval(s), switch 607 can disconnect load 605. For a parallel input resonant circuit, switch 607 can, for example, disconnect load 605 so that no current is drawn from the input resonant circuit. In contrast, for a series input resonant circuit, switch 607 can disconnect the load by short-circuiting load 605, thereby short-circuiting the power transfer input resonant circuit during the resonant measurement time interval. In some modes, such a variation in the quality factor can occur without the power receiver understanding a specific function. For example, in some modes, the load can inherently and essentially create a short circuit during operation. RZRRnn / eznz / B / YiAi startup that can allow a resonance measurement time interval before power transfer inherently has a high-Q input resonance circuit. For example, when the load is a motor, it can start up almost like a short circuit. As another example, when a rectifier and a large output capacitor are present in the power path, it will also behave almost like a short circuit when the capacitor discharges. In many modes, the resonant measurement time interval (or at least one resonant measurement time interval) can precede the energy transfer. Specifically, the determination of the coupling factor estimate and the configuration of the operating parameter can be performed during the initialization of an energy transfer operation. Therefore, prior to the energy transfer, the energy transmitter can determine an appropriate operating parameter value for the specific energy receiver and its specific positioning. It can then initiate the energy transfer using this parameter value as the initial operating parameter value. For example, in many applications, this approach can be used to determine the initial loop gain and power level values ​​for the energy transfer signal. Consequently, the system can initiate energy transfer in a state that is more likely to be close to the optimal operating point, eliminating the need for a slow, gradual adjustment from a worst-case initial safe operating point. Therefore, faster optimization can be achieved, and the risk of failing to reach the optimal operating point can be reduced. Furthermore, during the estimation of the pre-power transfer coupling factor, the power receiver can be entered into a measurement mode for frequency detection. RZRRnn / eznz / B / YiAi coupled resonance. Specifically, switch 607 can short-circuit the load to provide a high-quality factor for the input resonance circuit. When the system enters the power transfer phase, the power receiver can be switched back to normal power transfer operating mode, and specifically, the short circuit can be removed. In some configurations, this approach can be applied alternatively or additionally during the energy transfer phase. In such an approach, estimating the coupling factor can be particularly useful for adapting loop parameters and performance. For example, it can be used to adapt loop parameters so that substantially the same control performance can be achieved for different energy receiver positions. Therefore, improved performance, and in particular reduced sensitivity to variations in the energy receiver's positioning, can be achieved. In many modes where the focus is used during an energy transfer phase, the system can be configured to operate in a time-slotted mode, with measurements and coupled resonance frequency detection performed during measurement time intervals. The resonance measurement time interval can be specifically performed during such reduced measurement time intervals within a repetitive time period that also includes at least one energy transfer time interval during which energy is transferred to the energy receiver. In such modes, the system can therefore use time division during the energy transfer phase. In particular, the detection of coupled resonant frequencies and the energy transfer can be performed, for example, in separate time intervals, thereby substantially reducing the interference between them. AZRRnn / eznz / B / YiAi In the example, actuator 301 and transmitter coil 103 are arranged during the energy transfer intervals to generate an electromagnetic energy transfer signal for the purpose of transferring energy to the energy receiver. Additionally, the actuation signal can be used during a measurement time interval to detect coupled resonant frequencies in order to determine the estimated coupling factor. The energy transmitter can use a repetitive time period for the actuation signal during the energy transfer phase, where the time period comprises at least one energy transfer time interval and one resonant measurement time interval.An example of such a repetitive time period is illustrated in Figure 15, where energy transfer time intervals are denoted by PT and measurement time intervals are denoted by D (the time intervals may also be called detection time intervals). In the example, each FRM time period comprises only one resonance measurement time interval and one energy transfer time interval, and these (as well as the time period itself) are of the same duration in each period. However, it will be appreciated that in other modalities, other time intervals may also be included in a time period (such as, e.g., communication intervals), or a plurality of resonance measurement time intervals and / or energy transfer time intervals may be included in each time period.Furthermore, the duration of different time intervals (and indeed the period itself) can in some modalities vary dynamically. In this approach, measurements, communication, and energy transfer are separated in the time domain, resulting in less cross-interference from energy transfer to the coupling factor estimation. Therefore, the variability and uncertainty arising from variations in operating conditions for energy transfer can be isolated from the measurement and estimation, resulting in a more reliable and accurate estimation process. Furthermore, it allows the signal of The AZRRnn / eznz / B / YiAi drive is generated (and optimized) for the detection of the coupled resonant frequency. In particular, it allows the 307 resonant detector to perform a frequency sweep and carry out operations suitable for this detection. Furthermore, it allows the energy receiver to be specifically adapted to provide enhanced or optimal properties for detection. In particular, in many modes, the energy receiver can switch from an energy operating mode during the energy transfer time intervals, during which the load couples to the input resonant circuit (and therefore the quality factor of the input resonant circuit is low), to a measurement mode where a high quality factor of the input resonant circuit is ensured, e.g., by using switch 607, which shorts the load. Therefore, the time-slotted approach may enable or facilitate the performance of coupling factor estimation during the power transfer phase. As described above, in many modalities, the coupling factor estimate is determined based on at least one coupled resonant frequency as well as based on the non-coupling / self-resonance of the output resonant circuit (of the power transmitter) and / or the input resonant circuit (of the input resonant circuit). In some modes, the uncoupled resonant frequency of the input resonant circuit and / or the output resonant circuit is a predetermined frequency. For example, in some modes, the power transmitters and / or power receivers may be tightly restricted, for example, by the specifications and requirements of a suitable standard. For example, a wireless power transfer standard (such as, e.g., the Specification) RZRRnn / eznz / B / YiAi Ki) may prescribe that power transmitters and power receivers may employ an output resonant circuit and an input resonant circuit respectively with uncoupled resonant frequencies of, e.g., 30 kHz. In such modalities, estimator 309 may be arranged to estimate the coupling factor based on the coupled resonant frequency or frequencies and the assumed nominal value of the uncoupled resonant frequencies. RZRRnn / eznz / B / YiAi In other configurations, the system may allow some variation in, for example, the output resonant circuit. However, the uncoupled resonant frequency of the output resonant circuit can often be known for the power transmitter and estimator 309. For example, during manufacturing, the uncoupled output resonant frequency can be stored in memory for retrieval and use when determining the coupling factor estimate. The uncoupled resonant frequency can be determined, for example, simply as the resonant frequency resulting from the self-inductance values ​​of the transmitter coil and the capacitance of the resonant capacitor and stored in memory. In some modalities, such a predetermined (non-fixed) frequency may be used in conjunction with an assumed uncoupled resonant frequency of the power receiver's input resonant circuit, such as, e.g., in scenarios where the uncoupled resonant frequency of the power receiver is prescribed by the appropriate standard. In some embodiments, the estimator 309 may be arranged to determine the uncoupled resonant frequency of the input resonant circuit in response to data received from the energy receiver. In some embodiments, the energy transmitter may comprise a data receiver 313 arranged to receive data from the energy receiver. Similarly, the energy receiver may comprise a data transmitter 609 to transmit data to the energy transmitter. Communication may, for example, use charge modulation or, e.g., be implemented using NFC communication, as will be known to the person skilled in the art. In some configurations, the data transmitter 609 can transmit data to the data receiver 313 that can be used to determine the uncoupled resonant frequency of the input resonant circuit. For example, the power receiver can transmit data that directly represents the uncoupled resonant frequency of the input resonant circuit. In other configurations, the power receiver can transmit data that indicates properties or otherwise allows the power transmitter to determine the input resonant circuit. For example, in some modes, the power receiver can transmit data describing parameters of the input resonant circuit components, such as the self-inductance of the receiving coil and the capacitance of the resonant capacitor. The estimator 309 can then calculate the uncoupled resonant frequency from these component values. As another example, the power receiver can transmit information about, for instance, a type of input resonant circuit implemented by the receiver. For example, a set of possible input resonant circuit properties (specifically uncoupled resonant frequencies) may be specified by system standards, and the power receiver can indicate which type is implemented.The energy transmitter can store the uncoupled resonant frequency for different types of input resonant circuits and can retrieve the value for the specified type. In some modes, the uncoupled resonant frequency of the input resonant circuit can be linked to a type or property of the energy receiver, and this can be communicated to the energy transmitter, e.g., during energy transfer initialization. For example, different component values ​​can be used for different energy levels. The RZRRnn / eznz / B / YiAi power receiver can transmit an indication of the required power level, which can also be used by the power transmitter to determine the uncoupled resonant frequency of the input resonant circuit. RZRRnn / eznz / e / YiAi Therefore, in some embodiments, the power transmitter includes a data receiver configured to receive data from the power receiver indicating the uncoupled resonant frequency of the power transfer input resonant circuit. The data may either directly represent the uncoupled resonant frequency or provide data that allows it to be determined (typically based on additional information stored in the power transmitter). Although such methods use predetermined values ​​for uncoupled resonant frequencies that are independent of the current context / situation, they can provide advantageous performance in many applications. However, the inventors have realized that improved performance can be achieved by estimating the coupling factor using dynamically measured uncoupled resonant frequencies for the input resonant circuit and / or the output resonant circuit. In particular, the inventors have realized that variations in uncoupled resonant frequencies can occur for different wireless charging situations and scenarios, and that these variations can be determined and accounted for when generating the coupling factor estimate. The inventors have realized that improved performance can be achieved using measured values ​​of the uncoupled resonant frequencies of the input resonant circuit and / or the output resonant circuit. Furthermore, they have realized that advantageous measurements can be made using the same approaches as for determining the coupled resonant frequencies, and that the coupled resonant frequency of the input resonant circuit can clearly be determined from measurements taken during the same frequency sweep used to determine the coupled resonant frequencies. RZRRnn / cznz / e / YiAi In some modalities, the estimator 309 can be arranged to determine the coupling factor estimate in response to measured values ​​of at least one of the natural resonance frequencies instead of predetermined values. In some configurations, the 307 resonance detector can be further arranged to determine the uncoupled resonant frequency for the input resonant circuit as a frequency at which a drive signal current exhibits a local minimum for the input resonant circuit that has a quality factor of at least ten. The uncoupled resonant frequency for the input resonant circuit, hereafter also referred to as the input uncoupled resonant frequency, is determined by making measurements of the drive signal in a situation where the input resonant circuit is substantially undamped.In many modalities, measurements and determination of the input uncoupled resonant frequency can be made for the input resonant circuit load that is substantially zero, and specifically with the (series) load of a series resonant circuit that is short-circuited or the (parallel) load of a parallel resonant circuit that is disconnected. The 307 resonance detector can, for example, perform measurements by sweeping frequencies for a situation where the input resonant circuit is undamped and measuring the drive signal current. It can then determine the input uncoupled resonant frequency as the frequency at which the current is at a minimum. In some configurations, determining the frequency at which the current is at a minimum can be more indirect by measuring different parameters such as the phase difference between the drive signal voltage and current (which is zero), the drive signal power (which is minimized), and so on. In some configurations, such conditions occur to achieve a minimum current (due to resonance effects at that frequency). In many configurations, determining the input uncoupled resonant frequency can be combined with determining the coupled resonant frequencies. Specifically, the 307 resonance detector can perform a frequency sweep, as described above, to determine the coupled resonant frequencies as those at which a local maximum of the drive signal current is detected. Furthermore, it can use the same frequency sweep to determine the input uncoupled resonant frequency as the frequency at which the drive signal exhibits a minimum current. As mentioned, this determination can be based on a direct measurement of the drive signal current or on the measurement of a related parameter, such as the phase, voltage, or energy of the drive signal. The inventors have realized that the frequency for the minimum current of the drive signal provides a good estimate for the uncoupled resonant frequency of the input resonant circuit. In some embodiments, the 307 resonance detector can be further arranged to determine the uncoupled resonant frequency for the output resonant circuit as a frequency at which a current of the drive signal exhibits a local maximum for the input resonant circuit that has a quality factor of no more than two. The uncoupled resonant frequency for the output resonant circuit, hereafter also referred to as the output uncoupled resonant frequency, is determined by doing RZRRnn / eznz / B / YiAi measurements of the drive signal in a situation where the input resonant circuit is a heavily damped, and possibly fully damped, circuit. In many modalities, measurements and determination of the uncoupled output resonant frequency can be made for the input resonant circuit load that is very high (and possibly in effect infinite), and specifically with the (series) load of a series resonant circuit that is disconnected or the (parallel) load of a parallel resonant circuit that is short-circuited. RZRRnn / eznz / B / YiAi The 307 resonance detector can, for example, perform measurements by sweeping frequencies in a situation where the input resonant circuit is fully damped, preventing resonance of the input circuit, and measuring the drive signal current. It can then determine the output uncoupled resonant frequency as the frequency at which the current is maximum. In some configurations, determining the maximum current frequency can be more indirect, by measuring different parameters such as the zero phase difference between the drive signal voltage and current, the minimized drive signal energy, and so on. In some configurations, such conditions occur that result in the maximum current (due to resonance effects of the output resonant circuit at that frequency). The inventors have realized that the frequency of the maximum drive current for a heavily damped input resonant circuit provides 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 substantially attenuated, thus allowing the measurement of the uncoupled resonant frequency of the output resonant circuit. For example, with open circuits in a series input resonant circuit, no current will flow through the receiving coil, which will therefore not extract any energy from the electromagnetic field.The input resonance circuit may not affect the output resonance circuit, which substantially allows the measurement to be effectively the uncoupled resonance frequency of the output resonance circuit. Measurements of uncoupled resonant frequencies can provide substantially improved performance and a more accurate estimate of the coupling factor. This approach can mitigate and compensate for the effects of variations in the context, environment, and configuration of the power transfer array, and in particular, it can mitigate and compensate for the impact of the properties of the power transmitter and receiver. For example, the impact on the drive signal of the presence of the power receiver is not limited to the coupling between the transmitting and receiving coils (and therefore between the resonant circuits) but can also be affected by other effects such as the impact of metal on the power receiver and transmitter devices, etc. Such effects are not dependent on the coupling factor but can vary substantially with, for example,The specific properties of the device implementation and the positioning of the devices or other elements in the adjacent area can affect the estimation of the coupling factor. Therefore, the estimation of the coupling factor can be hindered and made less accurate due to such effects (typically unknown or unqualified). However, in the current approach, such dependencies and effects can be taken into account when determining the uncoupled resonant frequencies by measuring the effective values ​​in the specific context and situation. Therefore, A substantially improved coupling factor estimate can be achieved using measured values ​​for at least one of the uncoupled resonant frequencies of the input resonant circuit or the output resonant circuit. Measured uncoupled resonance frequencies (context / situation dependent) may also be called paired uncoupled resonance frequencies. As described above, the 309 estimator can, in many ways, be configured to determine the coupling factor estimate in response to both the first and second coupled resonant frequencies of the output resonant circuit / drive signal. As mentioned, this can be done, for example, by estimating the coupling factor estimates for the two different coupled resonant frequencies using predetermined or measured coupled resonant frequencies and averaging the results. In other configurations, the two coupled resonant frequencies can be determined and used in conjunction with an estimated uncoupled resonant frequency of the output resonant circuit to estimate the coupling factor without requiring knowledge of the coupled resonant frequency of the input resonant circuit. Specifically, the two formulas provided above can be used together to generate a coupling factor estimate based on the coupled resonant frequency of the output resonant circuit and the two uncoupled resonant frequencies. It will also be appreciated that the exact formulas and equations used to determine the estimated coupling factor can vary and depend on the specific preferences and requirements of the individual modality. In many modalities, manipulations and simplifications of the equations provided above, based on various assumptions or simplifications, can lead to RZRRnn / eznz / B / YiAi advantageous and efficient approaches to generating the coupling factor estimate. In many modalities, the estimator 309 can be arranged to determine the estimated coupling factor in response to the first coupled resonance frequency relative to the second coupled resonance frequency. RZRRnn / eznz / B / YiAi In particular, in many modalities, estimator 309 can be used to determine the coupling factor estimate in response to the ratio between the first coupled resonant frequency and the second coupled resonant frequency. In many modalities, the coupling factor estimate can be determined as a function of the ratio between the first coupled resonant frequency and the second coupled resonant frequency. In some modalities, the function depends only on either the first or second coupled resonant frequency by being dependent on the ratio between them, and the function does not consider either the first or second coupled resonant frequency separately.In some modalities, the function may be a function that can be manipulated or rearranged in such a way that the first coupled resonance frequency and the second coupled resonance frequency are included only as a ratio between coupled resonance frequencies. In many forms, estimator 309 can be used to determine the coupling factor estimate as a function of a dimensionless parameter determined from the first coupled resonance frequency and the second coupled resonance frequency (specifically, a ratio between the frequencies). The dependence on the first coupled resonance frequency and / or the second coupled resonance frequency can only be expressed as a dimensionless parameter, and specifically as a ratio. The inventors have realized that while the first and second coupled resonant frequencies can vary significantly as a function of various parameters, such as the load and effective quality factor at the time of measurement, coil properties, etc., such variation can be mitigated and compensated for by determining the coupling factor estimate in response to the ratio between the first and second coupled resonant frequencies, and specifically the ratio between these frequencies. Specifically, the sensitivity to variations in the uncoupled resonant frequencies of the input and output resonant circuits when determining the coupling factor estimate can be substantially reduced by determining the coupling factor estimate as a function of the ratio between the first and second coupled resonant frequencies. As a specific example, the coupling factor can, in some modalities, be determined using the following function: RZRRnn / eznz / B / YiAi where El is the first coupled resonant frequency and F2 is the second coupled resonant frequency. The function has been found to provide a highly accurate estimate of the coupling factor for a variety of scenarios and parameters. The 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. Specifically, the use of relationships between these frequencies has been found to substantially reduce sensitivity to measurement errors and inaccuracies. Furthermore, using a simplified equation such as the one above is simpler to evaluate, which can facilitate implementation and / or operation. For example, in some modalities, a single LUT can be implemented based on the relationship between the frequencies used as input for the query. In many configurations, estimator 309 is available, as described above, to determine the coupling factor estimate in response to the uncoupled resonant frequencies of the input resonant circuit and / or the output resonant circuit. This can be used, for example, in relation to determining the coupling factor estimate based on the ratio between the coupled resonant frequencies, and can be used especially to modify the equation above. In many embodiments, the estimator 309 can be arranged to determine the estimated coupling factor in response to a ratio between an uncoupled resonant frequency for the output resonant circuit and an uncoupled resonant frequency for the input resonant circuit. The inventors have realized that considering the ratio between the uncoupled resonant frequencies can provide particularly advantageous operation and, in particular, reduced sensitivity to variable and often unknown parameters. In many modalities, the coupling factor estimate can be determined as a function of the ratio between the first and second coupled resonant frequencies and the ratio between the uncoupled resonant frequencies of the input resonant circuit and the output resonant circuit; where fre is the uncoupled resonance frequency of the input resonance circuit, ft is the uncoupled resonance frequency of the output resonance circuit, Fi is the highest coupled resonance frequency, and F2 is the lowest coupled resonance frequency. A particularly advantageous function for estimating the coupling function might be specifically: (l + β2)2T β2(T + l)2' RZRRnn / eznz / B / YiAi fr / Fi\2where β = — and T = I — I ft For β = 1 this reduces to the previous equation: T- 1k _T + 1' The function can be alternatively expressed as ( / t2+ f2)2f2f2 A2A2(f2+ f2)2 which is derived from the previous equation by replacing β and T with the corresponding functions of the appropriate frequencies and some direct manipulation. The equations can be derived from the equations provided above and with the input resonant circuit load being shorted: =f2+ f2± V(f2+ f2)2- 4f2f2(1 - k2) 2(1-k2) Replacing the frequencies with the relationship fr= pft: ft2+ f2= ft2(1 + β2) ft2fr2= β2se obtains the following: ft2(1 + β2) ± J(ft2(l + β2))2- 4ίϊ4β2(1 - R2)res =2(1 — k2) ft2(1 + β2) ± Vft4(l + β2)2- 4(4β2(1 - k2) 2(1-k2)=ft2(l + β2) ± Vf4((l + β2)2- 4β2(1 - k2)) 2(1-k2) ft2(1 + β2) ± 12ν(1 + β2)2-4β2(1-Κ2) 2(1-k2) + β2± 7(1 + β2)2- 4β2(1 - k2)fres=ft-----------2(Ϊ^Ρ)----------Using the relationship of the left (negative) and right (positive) peak of fres, T = = γγγ- (i.e., fright= fres(+) = yf]eft= fres(-) = F2), 'rleft7 rresl ) we obtain f21 + β2+ 7(1 + β2)2- 4β2(1 - k2) _____________________ 2(1 —k2) 1 + β2+ 7(1 + β2)2- 4β2(1 - k2)21 + β2- 7(1 + β2)2-4β2(1 -k2) 1 + β2- 7(1 + β2)2-4β2(1 -k2) 2(1 —k2) This formula has the form T = ^-^,cona = 1 + β2y b = 7(1 + β2)2— 4β2(1 — k2) a + b T =--ra — b T(a — b) = a + b Ta — Tb = a + b —Tb — b = a — Ta b(—T — 1) = a(l -T) 1-T T-1 b = a------= a----T - 1 T + 1 RZRRnn / eznz / B / YiAi This proportion of the equal sign: the following formula with k only on the left side T — 1 V(1 + β2)2— 4β2(1 — k2) = (1 + β2)—— / T - 1\2(1 + β2)2- 4β2(1 - k2) = (1 + β2)2J / Τ - 1\2—4β2(1 — k2) = (1 + β2)2- (1 + β2)2(! + β2)2(τττ) -α + β2)2) —4β2 -k2 Al simplificar resultado (τ-ι)2-(τ+ι)2(τ+ι)2 Τ2-2Τ+1-Τ2-2Τ-1 —4Τ (Τ + 1)2(Τ+1)2da como (1 + β2)2—4Τ ϊβ2(Τ + I)2, _ -, (1 + β2)2T fr / fderecha J β2(T + i)2'conpftyTvizquierda For β = 1, when both primary and secondary resonances are similar: (1 + β2)2T β2(T + l)2(1 +1)2T _ 4T Ϊ (T + l)2“ J1(T + l)2(T + l)2- 4T (T + l)2 T2 + 2T + 1-4T_ T2-2T + 1 _ (T - l)2 J σ + d2 J (T +1)2λ (T + l)2 T- 1 k =-----, with β = 1 T + 1H(1 + β2)2T fr“A1—=f \2•right \ f I •left / By replacing them again in the formulas: right left (T+ l)2( / right + left') (Jt + fr )2right)left ft2fr (f2+ f2)2 V right1J left J Another example of a particularly advantageous function for estimating the coupling function is the following: A2+fr21 F? + F¿ AZRRnn / CZnZ / B / Y Therefore, in some modalities, the estimator 309 can be arranged to determine the coupling factor estimate in response to a ratio between a sum of squares of the first and second uncoupled resonance frequencies and a sum of squares of the first and second coupled resonance frequencies. In many modalities, the coupling factor estimate can be determined as a function of the ratio of the sums of squares of the uncoupled and coupled resonant frequencies. In some modalities, the function is dependent on the resonant frequencies only insofar as it depends on this ratio, and the function does not consider the coupled or uncoupled resonant frequencies except within this ratio. In some modalities, the function may be manipulated or rearranged so that the resonant frequencies are included only as a ratio of the sum of squares of the coupled resonant frequencies to the sum of squares of the uncoupled resonant frequencies. In many forms, estimator 309 can be used to determine the coupling factor estimate as a function of a dimensionless parameter determined from the first and second coupled resonance frequencies (specifically, a ratio between the frequencies or the squares of the frequencies). The dependence on the first coupled resonance frequency and / or the second coupled resonance frequency and / or the first uncoupled resonance frequency and / or the second uncoupled resonance frequency can only be expressed as a dimensionless parameter, and specifically as a ratio. Such approaches have been found to be particularly advantageous, providing greater robustness and less sensitivity to variations in the environment, component variations, measurement errors, etc. The above equations can be derived specifically from the two equations provided above using appropriate assumptions and simplifications: Fresl I Ί Ί > II Ί Ί > “ Ί Ί I Ί > 'fp* - fs*· --J'fp* - fs*;- 4-fp*fs*·'1 - k*' ϊ 1 - k* 'fp* - fs* - J'fp* ~ fs* - 4 fp*fs* ' 1 - k* - k* with fPft, fS= fr, Fresl Fl, and Fresl = fl. In more detail, from the system equations for the electrical equivalent circuit in Figure 16, the first harmonic approximation (FHA) can be derived: / 1 q ja>M = Lr\Jü)L'rH---h Rr+ \ ywCr In these equations, ut represents the voltage applied to the output resonant circuit; ω represents the operating angular frequency; AZRRnn / eznz / B / YiAi represents the current in the output resonance circuit; ir represents output; the current in the resonant circuit of L't represents output; the inductance in the resonant circuit of Ct represents output; the capacitance in the resonant circuit of Rt represents output; the resistance in the resonant circuit of L'r represents output; the inductance in the resonant circuit of Cr represents output; the capacitance in the resonant circuit of Rr represents output; the resistance in the resonant circuit of T?L represents output; and M represents the resistance in the mutual inductance. The system equations can be determined for ty iry, then the peak and valley positions in the transfer function can be found based on the expression: δϊζ δω Keep only the numerator of this expression, set T?L= 0 (i.e., causing a short circuit in the energy receiver load), ii ignore the terms proportional to ^7, 1 factor the Qr' ' Qr result, and setting it equal to zero produces the following equation: f ( / ? - n (β+n (r4fc2- / 4+β2^2+r2- β2 / (3 / ?2 / 4fc2- f6k2+ β4β2- 2β2β4+ f6+ β4- 2β2β2+ f4) = 0 RZRRnn / CZnZ / B / Y In this equation, f = —7r with ü)t = — , represents the operating frequency JP dimensionless; and β =—7, with ω(= *—, represents the ratio of the uncoupled resonance frequencies. Setting the second term of this equation to zero yields the position of the valley (local minimum), i.e., f = β or equivalently ω = . Setting the fourth term of this equation to zero yields the positions of the two peaks (local minima), i.e., 2 =1 + β2± V(l+ / ?2)2-4(l- / c2)^2' 2(1 — / c2) or equivalently ω(2+ ω,'2+ (ω(2+ ω'2)2— 4(1 — A2)ω(2ω'2 ω =2(1-fc2) Dividing the two results and rearranging to isolate the coupling factor yields: _ 7(T2+ 1)β2- {β4+ 1)Tk~ (T + 1) / ? In this equation T is the ratio of the two resonance frequencies (solution with the plus sign divided by the solution with the minus sign). Adding the two results gives Airs)+ / z + β2 - k2 RZRRnn / eznz / B / YiAi and after rearranging , .12 I , J2 (júf- τ COr(res)2(res)2 The uncoupled resonant frequency of the output resonant circuit (ü'tse) is deduced by measuring the peak (local maximum) position of the output resonant circuit current with the power receiver load disconnected. The uncoupled resonant frequency ω(.) is deduced by measuring the valley (local minimum) position between the two resonant peaks of the current in the output resonant circuit. It will be noted that deviations from the assumptions, etc. (e.g., the short circuit of the series input resonance circuit being replaced by a low resistance value) may result in some variations and may possibly cause the determined frequencies to differ from the theoretical values. However, in many cases, such variations may be acceptable or even negligible. In fact, even for relatively large deviations, the approach and use of simplified formulas and relationships have been found to provide an advantageous and useful estimate of the coupling factor. In some configurations, the power transmitter may be configured to determine an indication or measurement of misalignment between the power receiver and the power transmitter (specifically, between the receiving coil 107 and the transmitting coil 103). Specifically, the lower the coupling factor, the greater the misalignment. Furthermore, in such configurations, the power transmitter may be configured to generate a user output indicative of the misalignment. Specifically, it may provide a user alert indicating that the power receiver should be repositioned if the coupling factor falls below a certain threshold. It will be appreciated that, for clarity, the preceding description has described embodiments of the invention with reference to different functional circuits, units, and processors. However, it will be evident that any suitable distribution of functionality among the different functional circuits, units, or processors may be used without departing from the invention. For example, functionality illustrated as being executed by separate processors or controllers may be executed by the same processor or controllers. Therefore, references to specific functional units or circuits should be considered only as references to suitable means for providing the described functionality rather than indicating a strict logical or physical structure or organization. The invention can be implemented in any suitable form, including hardware, software, firmware, or any combination thereof. The invention can optionally be implemented, at least partially, 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 can be implemented physically, functionally, and logically in any suitable manner. In fact, the functionality can be implemented in a single unit, in a RZRRnn / eznz / e / YiAi plurality of units or as part of other functional units. As such, the invention can be implemented in a single unit or can be physically and functionally distributed among different units, circuits, and processors. RZRRnn / cznz / e / YiAi Although the present invention has been described in relation to some embodiments, it is not intended to be limited to the specific embodiment described herein. Rather, the scope of the present invention is limited only by the appended claims. Furthermore, although a feature may appear to be described in relation to particular embodiments, a person skilled in the art would recognize that several features of the described embodiments can be combined according to the invention. In the claims, the expression "comprising" does not exclude the presence of other elements or steps. Furthermore, although listed individually, a plurality of means, elements, circuits, or method steps may be implemented, e.g., by a single circuit, unit, or processor. Moreover, although individual features may be included in different claims, they may possibly be advantageously combined, and inclusion in different claims does not imply that a combination of features is neither feasible nor advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to that category, but rather indicates that the feature is equally applicable to other categories of claims as appropriate. The inclusion of a feature in a dependent claim of an independent claim does not imply a limitation to that independent claim, but rather indicates that the feature is equally applicable to other independent claims as appropriate.Furthermore, the order of the features in the claims does not imply any specific order in which the features must function, and in particular, the order of the individual steps in a claim of the method does not imply that the steps must be carried out in that order. Rather, the steps may be performed in any suitable order. Moreover, singular references do not preclude plurality. Thus, references to a, an, first, second, etc., do not preclude plurality. The reference symbols in the claims are provided simply as an illustrative example and shall not be construed in any way as limiting the scope of the claims. RZRRnn / eznz / B / YiAi In some scenarios, the following may be provided: A power transmitter (101) for wirelessly supplying power to a power receiver (105) by means of an inductive power transfer signal; the power transmitter (101) comprising: an output resonance circuit comprising a transmitter coil (103) and at least one capacitor (303); an actuator (201) arranged to generate an actuation signal so that the output resonant circuit (103) generates the inductive power transfer signal; a resonance detector (307) arranged to measure a first coupled resonance frequency for the output resonance circuit during a resonance measurement time interval, the first coupled resonance frequency being a resonance frequency for the output resonance circuit so that the transmitting coil (103) is coupled to a receiving coil (107) of an energy transfer input resonance circuit of the energy receiver (105), the energy transfer input resonance circuit having a quality factor of not less than ten during the resonance measurement time interval; an estimation circuit (309) arranged to determine an estimate of the coupling factor for a coupling between the transmitting coil (103) and the receiving coil (107) in response to the first coupled resonant frequency; and an adapter (311) arranged to configure an operating parameter in response to the estimated coupling factor. RZRRnn / eznz / B / YiAi A method of operating a power transmitter (101) that wirelessly provides power to a power receiver (105) by means of an inductive power transfer signal; the power transmitter (101) comprising: an output resonance circuit comprising a transmitter coil (103) and at least one capacitor (303); and the method comprising: generate a drive signal so that the output resonant circuit (103) generates the inductive power transfer signal; determine a first coupled resonant frequency for the output resonant circuit during a resonant measurement time interval, the first coupled resonant frequency is a resonant frequency for the output resonant circuit so that the transmitting coil (103) is coupled to a receiving coil (107) of an energy transfer input resonant circuit of the energy receiver (105), the energy transfer input resonant circuit having a quality factor of not less than ten during the resonant measurement time interval; determine an estimate of the coupling factor for a coupling between the transmitting coil (103) and the receiving coil (107) in response to the first coupled resonant frequency; and set an operating parameter in response to the estimated coupling factor.

Claims

1. A wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter being arranged to wirelessly supply power to the power receiver (105) by means of an inductive power transfer signal; the power transmitter (101) comprising: an output resonant circuit comprising a transmitter coil (103) and at least one capacitor (303); an actuator (201) arranged to generate a drive signal for the output resonant circuit (103) to generate the inductive power transfer signal;a resonance detector (307) arranged to determine a first coupled resonance frequency for the output resonance circuit during a resonance measurement time interval, the first coupled resonance frequency being a resonance frequency for the output resonance circuit for the transmitting coil (103) to couple to a receiving coil (107) of an energy transfer input resonance circuit of the energy receiver (105); an estimation circuit (309) arranged to determine an estimate of the coupling factor for coupling between the transmitting coil (103) and the receiving coil (107) in response to the first coupled resonance frequency; and an adapter (311) arranged to set an operating parameter in response to the estimated coupling factor;and the energy receiver comprises: an energy transfer input resonance circuit comprising a receiving coil (107) arranged to draw energy from the energy transmitter and at least one capacitor; the energy transfer input resonance circuit RZRRnn / eznz / B / YiAi having a quality factor of not less than ten during the resonance measurement time interval; and a circuit arranged to switch from an energy transfer mode in which the quality factor is not restricted to being not less than ten to a measurement mode during the resonance measurement time interval, the quality factor being not less than ten when the energy receiver is operating in measurement mode. RZRRnn / eznz / B / YiAi; 2. The wireless power transfer system of any preceding claim characterized in that the resonance detector (307) is further arranged to measure a second coupled resonance frequency for the output resonance circuit during the resonance measurement time interval, the second coupled resonance frequency being a different resonance frequency for the output resonance circuit in the presence of the power receiver (105); and the estimation circuit (309) is further arranged to determine the estimated coupling factor in response to the second coupled resonance frequency.

3. The wireless power transfer system of claim 2 characterized in that the first coupled resonant frequency and the second coupled resonant frequency are frequencies for which a drive signal current exhibits a local maximum.

4. The wireless power transfer system apparatus of any of claims 1-3 characterized in that the estimation circuit (309) is arranged to further determine the coupling factor in response to an uncoupled resonant frequency for the output resonant circuit and an uncoupled resonant frequency for the input resonant circuit.

5. The wireless power transfer system apparatus of any of claims 1-3, characterized in that the estimation circuit (309) is arranged to further determine the coupling factor in response to a ratio between an uncoupled resonant frequency for the output resonant circuit and an uncoupled resonant frequency for the input resonant circuit. RZRRnn / eznz / B / YiAi 6. The wireless power transfer system apparatus of any of claims 1-3 characterized in that the estimation circuit (309) is arranged to further determine the coupling factor in response to a ratio between a sum of squares of an uncoupled resonant frequency for the output resonant circuit and an uncoupled resonant frequency for the input resonant circuit and a sum of squares of the first coupled resonant frequencies and a second coupled resonant frequency which is a resonant frequency for the output resonant circuit so that the transmitting coil (103) is coupled to a receiving coil (107).

7. The wireless power transfer system of any preceding claim characterized in that the resonance detector (307) is arranged to determine an uncoupled resonance frequency for the output resonance circuit as a frequency for which a current of the drive signal exhibits a local maximum for the input resonance circuit having a quality factor of no more than two; and the estimation circuit is arranged to determine the coupling factor in response to the uncoupled resonance frequency for the output resonance circuit.

8. The wireless power transfer system of any preceding claim characterized in that the resonance detector (307) is arranged to determine an uncoupled resonance frequency for the input resonance circuit as a frequency for which a drive signal current exhibits a local minimum for the input resonance circuit having a quality factor of not less than ten; and the estimation circuit is arranged to determine the coupling factor in response to the uncoupled resonance frequency for the input resonance circuit.

9. The wireless power transfer system of any preceding claim, characterized in that the resonance measurement time interval is during the initialization of a power transfer operation, and the operating parameter is an initial operating parameter for the power transfer operation. RZRRnn / eznz / B / YiAi 10. The wireless power transfer system of any preceding claim characterized in that the actuator (201) is arranged, during a power transfer phase, to generate the drive signal according to a repetitive time period comprising at least one power transfer time interval and at least one measurement time interval, and wherein the resonance measurement time interval is comprised within a measurement time interval.

11. The wireless power transfer system of any preceding claim characterized in that the operating parameter is a power loop parameter which is a loop parameter of a power control loop arranged to adapt a power level of the power transfer signal in response to power control messages received from the power receiver (105).

12. The wireless power transfer system of any preceding claim characterized in that the power receiver further comprises a circuit arranged to cause a short circuit in the power transfer input resonance circuit during the resonance measurement time interval.

13. A method of operation for a wireless power transfer system comprising a power transmitter and a power receiver, the power transmitter arranged to wirelessly supply power to the power receiver (105) by means of an inductive power transfer signal; the power transmitter (101) comprising an output resonant circuit comprising a transmitter coil (103) and at least one capacitor (303), and the power receiver comprising an input power transfer resonant circuit comprising a receiver coil (107) arranged to draw power from the power transmitter and at least one capacitor; the method of operation comprising the power transmitter performing the steps of: generating a drive signal for the output resonant circuit (103) to generate the inductive power transfer signal,Determine a first coupled resonant frequency for the output resonant circuit during a resonant measurement time interval; the first coupled resonant frequency is a resonant frequency for the output resonant circuit so that the transmitting coil (103) is coupled to a receiving coil (107) of an energy transfer input resonant circuit of the energy receiver (105); the energy transfer input resonant circuit has a quality factor of not less than ten during the resonant measurement time interval; determine an estimate of the coupling factor for a coupling between the transmitting coil (103) and the receiving coil (107) in response to the first coupled resonant frequency.and RZRRnn / eznz / B / YiAi configure an operating parameter in response to the estimated coupling factor; and the method further comprising the power receiver (105) performs the steps of: switching from a power transfer mode in which the quality factor is not restricted to being not less than ten to a measurement mode during the resonance measurement time interval, the quality factor being not less than ten when the power receiver is operating in measurement mode.

14. A power receiver for a wireless power transfer system comprising a power transmitter and the power receiver, the power transmitter arranged to wirelessly supply power to the power receiver (105) by means of an inductive power transfer signal; the power receiver (105) comprising: a power transfer input resonant circuit comprising a receiving coil (107) arranged to draw power from the power transmitter and at least one capacitor; and a circuit arranged to switch from a power transfer mode in which the quality factor is not restricted to being not less than ten to a measurement mode during a resonant measurement time interval, the quality factor being not less than ten when the power receiver is operating in the measurement mode.

15. A method of operation for a power receiver for a wireless power transfer system comprising a power transmitter and the power receiver, the power transmitter arranged to wirelessly supply power to the power receiver (105) by means of an inductive power transfer signal; the power receiver (105) comprising: a power transfer input resonant circuit comprising a receiver coil (107) arranged to draw power from the power transmitter and at least one capacitor; the method comprising: a circuit arranged to switch from a power transfer mode in which the quality factor is not restricted to being not less than ten to a measurement mode during a resonant measurement time interval, the quality factor being not less than ten when the power receiver is operating in the measurement mode.

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