Wireless Power Transmission

Abstract

The power transmitter 101 wirelessly supplies power to the power receiver 105 via a power transmission signal generated by the power transmission coil 103. The communication driver 209 generates a communication drive signal for the communication coil 207 to generate a communication carrier signal. In the standby phase when the power transmission signal is not transmitted, the power transmitter generates a pulsed communication carrier signal. The power receiver 105 transmits an ID message during the standby phase when the communication carrier signal is present. The ID message includes the device ID of the power receiver 105. The power receiver 105 can request power transmission operation by changing the device ID in the ID message, and in response to detecting a different device ID, the power transmitter's phase controller 203 initiates a transition from the standby phase to the power transmission phase.

Description

[Technical Field]

[0001] The present invention relates to the operation of a wireless power transfer system configured to transfer power wirelessly from a power transmitter to a power receiver, particularly, but not exclusively, to transfer power wirelessly to high power devices such as kitchen appliances. [Background technology]

[0002] Most electronic products today require dedicated electrical contacts to be powered from an external source. However, this tends to be impractical, requiring the user to physically insert a connector or establish physical electrical contact. Power requirements also typically vary widely, and most devices now have their own dedicated power sources, meaning the typical user owns many different power sources, each dedicated to a specific device. While using an internal battery could eliminate the need for a wired connection to a power source during use, this is only a partial solution, as the battery will need to be recharged (or replaced). Using a battery can significantly increase the weight of the device, as well as its cost and size.

[0003] To significantly improve the user experience, it has been proposed to use wireless power sources in which power is inductively transferred from a transmitting inductor in a power transmitting device to a receiving coil in an individual device.

[0004] Power transfer via magnetic induction is a well-known concept and is primarily applied to transformers with tight coupling between the primary transmitter inductor / coil and the secondary receiver coil. Separating the primary transmitter coil and secondary receiver coil between the two devices allows wireless power transfer between them based on the principle of a loosely coupled transformer.

[0005] Such a configuration allows for wireless power transfer to the device without the need for wires or physical electrical connections. In fact, the device can be externally charged or powered simply by being placed next to or above the transmitter coil. For example, the power transmission device may be placed on a horizontal surface where the device can be powered simply by being placed on it.

[0006] Moreover, such wireless power transmission configurations may be advantageously designed to allow a power transmitting device to be used with a variety of power receiving devices. In particular, a wireless power transmission approach known as the Qi standard has been defined and is currently being further developed. This approach allows a Qi-compliant power transmitting device to be used with a similarly Qi-compliant power receiving device, without the devices needing to be from the same manufacturer or proprietary to each other. The Qi standard further includes several features that allow it to adapt its operation to specific power receiving devices (e.g., depending on their specific power consumption).

[0007] The Qi standard was developed by the Wireless Power Consortium, and more information can be found in the specific specification document on the consortium's website (http: / / www.wirelesspowerconsortium.com / index.html).

[0008] The Wireless Power Consortium has been developing the Qi standard (also known as the Cordless Kitchen standard), which builds on the Qi standard and aims to provide safe, reliable, and efficient wireless power transmission to kitchen appliances. Ki supports much higher power levels, up to 2.5KW.

[0009] Many systems, particularly Qi systems, may use load modulation in communication from a power receiver to a power transmitter. In load modulation, the load of the power transmission signal varies depending on the data being transmitted. However, detecting such load modulation can be difficult if the power transmission load of the power transmission signal also fluctuates. Similarly, communication from a power transmitter to a power receiver can be achieved by modulating the power transmission signal (e.g., amplitude modulation or frequency modulation), but interference with such modulation can occur due to fluctuations in the parameters of the power transmission signal, for example, due to load fluctuations.

[0010] Some systems have proposed using a completely independent communication approach. Specifically, the Ki wireless power transfer system can establish a bidirectional communication link using the Near Field Communication (NFC) standard. Communication is performed at short time intervals during the power transfer phase to avoid or reduce interference between power transfer and communication. The power receiver is configured to detect the NFC carrier to perform communication during the short time intervals.

[0011] A challenge in implementing a wireless power transfer system that provides a highly user-friendly, safe, and efficient operation and user experience is how to control the initialization and termination of power transfer operations. Traditionally, power transfer is initiated when a power receiving device is detected to be positioned sufficiently close to a power transmitter, specifically the power transmitter's coil. The presence of a power receiver is detected by the power transmitter, which in response initiates power transfer to the power receiver. The power receiver then proceeds to extract power, and power transfer proceeds.

[0012] Typically, this continues until the power receiver is removed from the power transmitter, which again can be detected and the power transmitter can accordingly terminate power transmission and turn off the power transmission signal.

[0013] In some cases, the power receiver may simply be switched off without being removed from the power transmitter, and the power transmission operation may actually be terminated while the power receiver is still present. For example, a cordless kettle may be placed on the power transmitter, and after the operation of boiling water is completed, the kettle may be turned off while still placed on the power transmitter.

[0014] However, a particular challenge in this case is how to resume power transfer later if needed. For example, if you want to re-boil the water in the kettle, you need a mechanism to initialize a new power transfer operation. This is particularly challenging because the device is essentially in a state where the power receiver has no power.

[0015] One current approach is to require the user to actively provide user input to the power transmitter, which activates power transmission and initializes a new power transmission operation. However, this is not ideal in many situations. For example, having to interact with the power transmitter's user interface rather than the user equipment can be very counter-intuitive for the user. It also prevents the user interface from being optimized and adapted to individual power-receiving devices / equipment. It can also result in a suboptimal physical location of activation (e.g., placed on a workbench rather than on the equipment).

[0016] Another option that has been proposed, especially for the Ki, is that the user must first remove the power-receiving device and then reposition it over the power transmitter, but this is highly impractical and counterintuitive behavior, and requires frequent checks for the presence of the power-receiving device. Summary of the Invention [Problem to be solved by the invention]

[0017] Current approaches tend to be suboptimal, requiring relatively complex functionality and undesirable user behavior.

[0018] Therefore, improvements in the operation of wireless power transfer systems would be advantageous, particularly approaches that allow for increased flexibility, reduced cost, reduced complexity, improved user experience, additional functionality, facilitated operation, facilitated user control, and / or improved performance. For example, an improved approach for initializing power transfer for an already existing power receiver without requiring a user interface on the power transmitter, providing an improved user experience, would be advantageous. [Means for solving the problem]

[0019] Accordingly, the Invention seeks to preferably mitigate, reduce or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0020] According to one aspect of the present invention, there is provided a power transmitter for wirelessly supplying power to a power receiver via an inductive power transmission signal, the power transmitter comprising: a power transmission coil arranged to generate a power transmission signal; and a power transmission driver arranged to generate a power transmission drive signal for said power transmission coil; said power transmission driver being arranged to generate the power transmission drive signal during a power transmission phase; a communication coil arranged to generate a communication carrier signal; and a communication driver arranged to generate a communication drive signal for said communication coil generating said communication carrier signal; and a communication driver arranged to generate a communication drive signal employing repeat time frames during a standby phase in which said power transmission signal is not present, and a communication unit arranged to receive ID messages load modulated onto a communication carrier signal during the communication time intervals during a standby phase, wherein the duration of the communication time intervals does not exceed 20% of the duration of a non-communication time interval and a power level of the communication time intervals does not exceed 10% of the power level of the communication drive signal during the non-communication time interval; each ID message in the ID messages indicating a device ID of the power receiver; and a phase controller arranged to switch the power transmitter from the power transmission phase to the standby phase in response to termination of power transmission, the phase controller comparing a first device ID, which is the device ID of the first ID message, with a second device ID, which is the device ID of a second ID message received from the power receiver prior to the first ID message, and remaining in the standby phase if the first device ID matches the second device ID, and switching from the standby phase to the power transmission phase in response to detecting that the first device ID does not match the second device ID.

[0021] The present invention allows for improved performance in many embodiments, which allows for improved overall power transfer operation in many systems and embodiments.

[0022] This approach allows for an efficient, often ultra-low power standby phase and enables reliable and user-friendly power initialization. This approach may be particularly suitable for scenarios where the power receiver may remain in proximity to the power transmitter after the end of a power transfer operation. This approach provides a low-complexity, efficient, and practical approach, allowing the user to interact with the power receiver's user interface to initialize a new power transfer operation.

[0023] This approach may further provide an efficient way to provide auxiliary power transmission using a communications carrier signal that is also used to support communications during the standby phase, for example, to enable minimal functionality to be performed to allow a new power transmission operation to be initiated.

[0024] The approach in many embodiments further provides reliable operation and allows for additional flexibility and functionality by providing an approach that ensures that a new power transfer operation is intended for a specific power receiver, particularly in many scenarios for a power receiver that was previously involved in a power transfer operation.

[0025] This approach provides an improved secondary / auxiliary power transmission path that utilizes the communication path during the standby phase, thereby providing synergistic interoperability between communication and auxiliary power supply.

[0026] The power transfer driver can be configured to generate the communications drive signal, and therefore the communications carrier signal, to have a non-zero (often constant / fixed) amplitude during communications time intervals and a zero amplitude during non-communications time intervals.

[0027] In many embodiments, the duration of the communication time interval is less than or equal to 5%, 10%, or 20% of the duration of the recurring time frame. In many embodiments, the duration of the non-communication time interval is greater than or equal to 70%, 80%, or 90% of the duration of the recurring time frame.

[0028] The detection that the first ID message includes a changed device ID may be the detection that the first ID message includes a device ID that is different from the device ID of a previously (typically previously) received ID message.

[0029] According to an optional feature of the present invention, the second ID message is received in the same standby phase as the first ID message.

[0030] This allows for improved operation and / or eases implementation and / or operation in many embodiments.

[0031] This approach can be particularly advantageous and typically allows for very efficient and reliable detection of practical power transfer requirements.

[0032] According to an optional feature of the invention, the second device ID is the device ID of a power receiver that receives power in a power transfer phase immediately preceding the standby phase.

[0033] This allows for improved operation and / or eases implementation and / or operation in many embodiments.

[0034] This approach can be particularly advantageous and typically allows for very efficient and reliable detection of practical power transfer requirements.

[0035] In accordance with an optional feature of the invention, a second ID message is received from the power receiver before entering the standby phase.

[0036] This allows for improved operation and / or eases implementation and / or operation in many embodiments.

[0037] This approach can be particularly advantageous and typically allows for very efficient and reliable detection of practical power transfer requirements.

[0038] In some embodiments, the second ID message is received prior to the standby phase in which the first ID message is received.

[0039] According to an optional feature of the invention, the phase controller is configured to store configuration parameters of the power receiver upon entering the standby phase, to retrieve the configuration parameters as part of the transition from the standby phase to the power transfer phase, and to determine operating parameters of the power transfer phase in response to the configuration parameters.

[0040] This allows for particularly advantageous operation and / or implementation in many embodiments.

[0041] In accordance with an optional feature of the invention, the communications carrier signal is a Near Field Communication (NFC) carrier.

[0042] This approach can be particularly advantageous and typically allows for highly efficient and reliable detection of practical power transfer requirements, further enhancing backward compatibility and compatibility with many systems, standards and approaches.

[0043] According to an optional feature of the invention, the ID message is a Near Field Communication (NFC) Data Exchange Format (NDEF) structured message.

[0044] This approach allows for particularly advantageous operation in many embodiments.

[0045] In accordance with an optional feature of the invention, the recurring time frame has a duration of not less than 50 milliseconds and not more than 10 seconds.

[0046] This allows for particularly advantageous operation and / or implementation in many embodiments.

[0047] In many embodiments, the repeating time frames can have a duration of 50, 100, 250, 500, 1000 milliseconds or more. In many embodiments, the repeating time frames can have a duration of 1 second, 2 seconds, 5 seconds, 10 seconds or less.

[0048] According to an optional feature of the invention, power transmitter controller 203 is configured to adapt operation of the initialization process of the power transfer phase in response to detecting a changed ID.

[0049] This allows for improved operation and / or eases implementation and / or operation in many embodiments.

[0050] According to one aspect of the present invention, there is provided a power receiver for wirelessly receiving power from a power transmitter via an electromagnetic power transmission signal, the power receiver comprising: an inductive power extraction element configured to extract power from the power transmission signal during a power transmission phase; a communications coil for receiving a communications carrier signal, the communications drive signal employing recurring time frames during a standby phase in which the power transmission signal is absent, each recurring time frame including a communications time interval and a non-communication time interval, the duration of the communications time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communications drive signal in the non-communication time interval not exceeding 10% of the power level of the communications drive signal in the communications time interval; and a communications unit configured to transmit ID messages by load modulation of the communications carrier signal during the communications time intervals during the standby phase, each ID message including a device ID of the power receiver. The device includes a power extractor coupled to the communication coil and configured to extract a power supply signal from the communication coil and power a circuit of the communication unit with the power supply signal during a communication time interval, and a controller configured to change the device ID of the first ID message relative to the device ID of the previous ID message in response to detecting a power request, wherein the power request is an indication of a request to start a power transfer phase.

[0051] This can provide improved performance in many embodiments, which allows for improved overall power transfer behavior in many systems and embodiments.

[0052] This approach allows for an efficient, often ultra-low power standby phase and enables reliable and user-friendly power initialization. This approach may be particularly suitable for scenarios where the power receiver may remain in proximity to the power transmitter after the end of a power transfer operation. This approach provides a low-complexity, efficient, and practical approach, allowing the user to interact with the power receiver's user interface to initialize a new power transfer operation.

[0053] This approach allows the power receiver to control when new power transfers are initiated while simultaneously supporting ultra-low power operation during the standby phase.

[0054] Changing the device ID may include including a device ID in the first ID message that is different from a device ID previously transmitted by the power receiver during the standby phase.

[0055] In accordance with an optional feature of the invention, the power receiver further comprises a user interface, and the controller is configured to detect the power request in response to detecting user activation of the user interface.

[0056] This allows for improved operation and / or ease of implementation and / or operation in many embodiments. This approach can, among other things, reduce complexity and ease implementation. This approach can, for example, allow a user to access a user interface on the power receiver to initiate a new power transfer without requiring movement of the power receiver and while allowing the standby phase to operate in an ultra-low power mode.

[0057] In accordance with an optional feature of the invention, the user interface is a passive user interface configured to maintain a user-activated indication of a user activation for a duration that exceeds the duration of the non-communication time interval.

[0058] This allows for particularly advantageous operation and / or implementation in many embodiments: this approach allows for very low power consumption during the power transfer phase, while still allowing a power receiver-based user interface to control the initialization of the power transfer.

[0059] According to an optional feature of the invention, the controller is configured to store a first user interface setting for the power transfer phase before entering the standby phase, determine a second user interface setting during the standby phase, and detect user activation in response to detecting a difference between the first user interface setting and the second user interface setting.

[0060] This allows for particularly advantageous operation and / or implementation in many embodiments.

[0061] In accordance with an optional feature of the invention, the controller is configured to be powered by the power supply signal only during the communication time interval.

[0062] This allows for particularly advantageous operation and / or implementation in many embodiments, in particular allowing for an ultra-low power standby phase.

[0063] According to one aspect of the present invention, there is provided a wireless power transmission system including the power transmitter and power receiver described above.

[0064] According to one aspect of the present invention, there is provided a method of operating a power transmitter that wirelessly supplies power to a power receiver via an inductive power transmission signal, the power transmitter having a power transmission coil configured to generate the power transmission signal and a communication coil configured to generate a communication carrier signal, the method comprising the steps of generating a power transmission drive signal for the power transmission coil during a power transmission phase, and generating a communication drive signal for the communication coil to generate the communication carrier signal, the communication drive signal being generated to employ recurring time frames during a standby phase in which the power transmission signal is not present, each recurring time frame including a communication time interval and a non-communication time interval, a duration of the communication time interval not exceeding 20% ​​of a duration of the non-communication time interval, and a power level of the communication drive signal during the non-communication time interval. receiving, during a communication time interval of the standby phase, ID messages load-modulated onto a communication carrier signal, each ID message including a device ID of the power receiver; switching the power transmitter from the power transmission phase to the standby phase in response to termination of the power transmission; comparing a first device ID, which is the device ID of the first ID message, with a second device ID, which is the device ID of a second ID message received from the power receiver before the first ID message, and remaining in the standby phase if the first device ID matches the second device ID; and initializing a transition from the standby phase to the power transmission phase in response to detecting that the first device ID does not match the second device ID.

[0065] According to one aspect of the present invention, there is provided a method of operating a power receiver that receives power wirelessly from a power transmitter via an electromagnetic power transmission signal, the power receiver comprising: an inductive power extraction element arranged to extract power from the power transmission signal during a power transmission phase; a communication coil that receives a communication carrier signal; and a communication drive signal using a repeat time axis during a standby phase in which the power transmission signal is not present, each repeat time frame comprising the communication time interval and a non-communication time interval, a duration of the communication time interval not exceeding 20% ​​of the duration of the non-communication time interval, a power level of the communication drive signal during the non-communication time interval, and a power level of the communication drive signal during the non-communication time interval not exceeding 10% of the power level; and the communication drive signal during the communication time interval. transmitting ID messages by load modulation of a communication carrier signal during a communication time interval during a standby phase, each ID message indicating a device ID of the power receiver; extracting a power signal from a communication coil and supplying the power signal to circuitry of the communication unit during the communication time interval; and changing the device ID of a first ID message to the device ID of a previous ID message in response to detecting a power request, the power request indicating a request to begin a power transfer phase.

[0066] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief explanation of the drawings]

[0067] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which: [Figure 1] FIG. 2 illustrates an example of elements of a power transfer system according to some embodiments of the present invention. [Figure 2] FIG. 1 illustrates an example of elements of a power transmitter according to some embodiments of the present invention. [Figure 3] FIG. 1 illustrates an example of elements of a power receiver according to some embodiments of the present invention. [Figure 4]FIG. 2 is a diagram showing an example of elements of a power transmission path in a wireless power transmission operation. [Figure 5] 2A and 2B illustrate examples of recurring time frames of a communication carrier signal in a wireless power transfer system according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0068] The following description focuses on embodiments of the invention applicable to wireless power transfer systems utilizing the power transfer approach as known from the Ki standard, however, it will be understood that the invention is not limited to this application and may be applied to many other wireless power transfer systems.

[0069] 1 illustrates an example of a power transfer system according to some embodiments of the present invention. The power transfer system includes a power transmitter 101 including (or coupled to) a transmitter coil / inductor 103. The system further includes a power receiver 105 including (or coupled to) a receiver coil / inductor 107.

[0070] The system provides an electromagnetic power transmission signal capable of inductively transmitting power from a power transmitter 101 to a power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal, which is propagated as magnetic flux by a transmitter coil or inductor 103. The power transmission signal may correspond to an electromagnetic power transmission component representing the transfer of energy from the power transmitter to the power receiver, and may be considered to correspond to the component of the generated electromagnetic field that transfers power from the power transmitter to the power receiver. For example, if the receiver coil 107 is unloaded, no power is extracted (apart from losses) from the electromagnetic field generated by the power receiver. In such a scenario, driving the transmitter coil 103 can generate an electromagnetic field of potentially high field strength, but the power level of the power transmission signal (apart from losses) would be zero. In some situations where a foreign object is present, the power transmission signal can be considered to include a component corresponding to the transfer of power to the foreign object, and therefore the power transmission signal can be considered to correspond to power extracted from the electromagnetic field generated by the power transmitter.

[0071] The power transmission signal may typically have a frequency between about 20 kHz and about 500 kHz, and for Ki-compatible systems, may typically have a frequency in the range of 20 kHz to 80 kHz. The transmitter coil 103 and the receiving coil 107 are loosely coupled, and thus the receiving coil 107 picks up (at least a portion of) the power transmission signal from the power transmitter 101. Thus, power is transmitted from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the receiving coil 107. While the term power transmission signal is primarily used to refer to the induction signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the receiving coil 107, it will be understood that, equivalently, it may also be considered and used to refer to an electrical signal supplied to the transmitter coil 103 or picked up by the receiving coil 107.

[0072] In an embodiment, power receiver 105 is specifically a power receiver that receives power via receiver coil 107. However, in other embodiments, power receiver 105 may include a metallic element, such as a metallic heating element, where the power transmission signal directly induces eddy currents that result in direct heating of the element. Consequently, the power receiver may load the power transmission signal by including an inductive power extraction element, specifically a power extraction coil or an electrical (e.g., heating) element in which a current is induced by the power transmission signal.

[0073] The system is configured to transmit significant power levels; specifically, the power transmitter can support power levels of 50 W, 100 W, 500 W, or even greater than 1 kW. For example, for Ki-type applications, power transfer is often greater than 100 W, and can exceed 2500 W for very high power applications.

[0074] The operation of the power transmitter 101 and the power receiver 105 is described below with particular reference to embodiments that generally conform to the standards being developed by the Wireless Power Consortium (except for modifications and enhancements described therein or resulting therefrom). In particular, the power transmitter 101 and the power receiver 105 conform to or are substantially compatible with elements of the Ki standard.

[0075] Many wireless power transfer systems, particularly high-power systems such as Ki, use resonant power transfer, where the transmitter coil 103 is part of a resonant circuit and typically the receiver coil 107 is also part of the resonant circuit. In many embodiments, the resonant circuit may be a series resonant circuit, such that the transmitter coil 103 and receiver coil 107 are coupled in series with corresponding resonant capacitors. The use of a resonant circuit tends to provide more efficient power transfer.

[0076] FIG. 2 illustrates elements of the power transmitter 101, and FIG. 3 illustrates elements of the power receiver 105 of FIG. 1 in more detail.

[0077] The power transmitter 101 includes a driver 201 operable to generate a drive signal that is provided to a transmitting coil 103, which in turn generates an electromagnetic power transmission signal that transmits power to a power receiver 105. The power transmission signal is provided at least during a power transmission time interval of a power transmission phase.

[0078] The driver 201 may comprise an output circuit in the form of an inverter, typically formed by driving a full or half bridge, as is well known to those skilled in the art.

[0079] The power transmitter 101 further comprises a power transmitter controller 203 configured to control the operation of the power transmitter 101 according to a desired operating principle. Specifically, the power transmitter 101 may include many of the functions necessary to perform power control according to the Qi or Ki standards.

[0080] The power transmitter controller 203 is particularly configured to control the generation of the drive signal by the driver 201 and is particularly able to control the power level of the drive signal and therefore the level of the generated power transmission signal. The power transmitter controller 203 comprises a power loop controller that controls the power level of the power transmission signal in response to power control messages received from the power receiver 105 during a power control phase.

[0081] To receive data and messages from the power receiver 105, the power transmitter 101 comprises a first communicator 205 configured to receive data and messages from the power receiver 105 and to transmit data and messages to the power receiver 105 (as will be appreciated by those skilled in the art, a data message may provide one or more bits of information).

[0082] In this approach, communication is performed by modulating a communication carrier signal generated by the first communication coil 207. The power transmitter specifically includes a communication driver 209 coupled to the first communication coil 207. The communication driver 209 is configured to generate a communication drive signal that is supplied to the first communication coil 207 to generate the communication carrier signal. The communication driver 209 can typically be configured to generate a communication drive signal / communication carrier signal having a frequency significantly different from that of the power transmission drive signal / power transmission signal. In many embodiments, the frequency of the communication carrier signal can be 10 times or more, 100 times or more, or 500 times or more the frequency of the power transmission signal. In many embodiments, the frequency of the communication drive signal / communication carrier signal is no less than 500 kHz, 1 MHz, or 10 MHz. In particular, for NFC implementations, the communication carrier signal frequency is 13.56 MHz.

[0083] The first communicator 205 is coupled to the communication driver 209 and configured to control it to modulate a communication drive signal / communication carrier signal to transmit data to the power receiver (references to the communication drive signal below also include implicit references to the communication carrier signal, where appropriate).

[0084] The modulation is illustratively amplitude modulation of the communication drive signal, specifically binary communication using Amplitude Shift Keying (ASK), although it will be appreciated that other approaches may be used in other embodiments, such as phase modulation or frequency modulation of the communication drive signal.

[0085] In some embodiments, the first communicator 205 can receive, for example, data to be transmitted to the power receiver from the power transmitter controller 203 and, in response, generate a control modulation signal that is provided to the communication driver 209. The control modulation signal can be, for example, a binary signal that corresponds to the data to be transmitted, and the communication driver 209 can be configured to generate the communication drive signal to have a corresponding amplitude variation.

[0086] In communication from the power receiver to the power transmitter, modulation of the communication drive signal can be load modulation. The power receiver can be configured to modulate the communication carrier signal by varying the load of the communication carrier signal generated by the first communication coil 207 according to the data to be transmitted. The first communication device 205 can be configured to detect fluctuations in the voltage and / or current of the first communication coil 207 and demodulate the load modulation based on these. Those skilled in the art will be familiar with the principles of load modulation, and therefore will not be described in further detail.

[0087] In many embodiments, the communication may conform to Near Field Communication (NFC) standards, and the power receiver may specifically include NFC functionality. In many embodiments, the first communicator 205, the communication driver 209, and the first communication coil 207 may implement (at least) the functionality of an NFC reader. Thus, in many embodiments, the communication drive signal / communication carrier signal is a 13.56 MHz signal at a constant level (excluding modulation).

[0088] In the following description, we will focus on an example in which the communication between the power transmitter and the power receiver is NFC communication, and more specifically, the modulation of the NFC carrier in the direction from the power transmitter to the power receiver is amplitude shift keying (ASK), and the modulation of the NFC carrier in the direction from the power receiver to the power transmitter is load modulation.

[0089] FIG. 3 shows some exemplary elements of the power receiver 105.

[0090] The receiver coil 107 is coupled to a power receiver controller 301, which couples the receiver coil 107 to a load 303 via a switch 305 (i.e., is a switchable load 305). The power receiver controller 301 includes a power control path that converts the power extracted by the receiver coil 107 into a supply suitable for the load 303. Additionally, the power receiver controller 301 can include various power receiver controller functions required to perform power transfer, particularly functions required to perform power transfer according to the Qi or Ki standards.

[0091] To support communication from the power receiver 105 to the power transmitter 101, the power receiver 105 includes a second communication coil 309 and a second communication coil 309. The second communication coil 309 is configured to couple with the first communication coil 207 such that a communication carrier signal induces a current (at least an electromotive force) in the second communication coil 309.

[0092] The second communicator 307 is coupled to the second communication coil 309 and is configured to determine the amplitude change of the induced signal and demodulate the amplitude modulation of the communication carrier signal. In this manner, the second communicator 307 is configured to decode data transmitted from the power transmitter by amplitude modulation of the communication carrier signal. It will be appreciated that in other embodiments, the second communicator 307 may be configured to decode data modulated onto the communication carrier signal using other forms of modulation, such as frequency modulation or phase modulation.

[0093] The second communicator 307 is further configured to load modulate the communication carrier signal to transmit data from the power receiver to the power transmitter. Specifically, the second communicator 307 may have a load (such as a capacitor) that can be switchably coupled or not coupled to the second communication coil 309 depending on the data to be transmitted. These load modulations are detected by the first communicator 205 of the power transmitter.

[0094] In a specific example, the second communication coil 309 and the second communication device 307 can provide an NFC-compatible communication operation. Specifically, the second communication coil 309 can provide functionality compatible with NFC tags and be configured to decode data ASK-modulated onto a communication carrier signal in accordance with the NFC standard.

[0095] The second communicator 307 is then configured to transmit data to the power transmitter 101 by varying the load on the receiver coil 107 according to the data to be transmitted to the power transmitter 101. The load variation is then detected and demodulated by the power transmitter 101, as known to those skilled in the art.

[0096] In an embodiment, the second communicator 307 is further configured to demodulate the amplitude, frequency and / or phase modulation of the communication carrier signal to retrieve the data transmitted from the power transmitter.

[0097] In many embodiments, the wireless power transfer system, and thus the power transmitter and / or power receiver, can be configured to operate in different phases, in particular a power transfer phase in which a power transfer signal is generated and thus a power transfer operation to provide power to the load 303 occurs. Additionally, the power transmitter can be configured to operate in a standby phase in which a power transfer signal is not generated by the power transmitter and thus can be configured to operate in the absence of a power transfer signal. In the standby phase, the power transfer driver 201 does not generate a power transfer drive signal, and therefore no drive signal is provided to the transmitter coil 103. In the standby phase, no power transfer signal is generated by the transmitter coil 103.

[0098] In many embodiments, e.g., many Ki-based embodiments, the wireless power transmission system, and thus the power transmitter and / or power receiver, is configured to operate in different phases during the standby phase, i.e., the standby phase itself can be divided into different (sub)phases. These phases / modes include:

[0099] The first phase is the idle phase. During this phase, the power transmitter does not detect the presence of a power receiver. During the idle phase, neither a power transmission signal nor a communication carrier signal is generated. During the idle phase, the power transmitter monitors the presence of a power receiver. Specifically, the power transmitter can generate an electromagnetic detection signal at regular intervals. If a load on this signal is detected, the power transmitter can assume that a power receiver is potentially present. Once a power receiver is detected, the power transmitter can transition to the configuration phase. The idle phase may itself be referred to as a standby phase in some systems; for example, in the Ki standard, the phase corresponding to the described idle phase is called the standby phase.

[0100] During the configuration phase, configuration information / data can be exchanged between the power transmitter and the power receiver. The configuration information / data can provide the complementary device with information about the characteristics of the power receiver and the power transmitter. Each device can adapt its operating parameters based on the exchanged configuration data. Thus, the configuration phase is used by the power transmitter and the power receiver to exchange specific information about the characteristics of a particular device, thereby adapting operation to the particular pairing of the power transmitter and the power receiver.

[0101] If the configuration phase is not successful, for example, if the power transmitter does not receive an appropriate message from the power receiver or if an explicit termination is received, the power transmitter may return to the idle phase.

[0102] Upon successful completion of configuration and communication, the power transmitter proceeds to the connection phase. During the connection phase, the power transmitter and power receiver have established communication and the devices are adapted to each other, but power transmission has not yet begun. During the connection phase, a communication carrier signal is generated, which may be present continuously during the connection phase. However, no power transmission signal is generated during the connection phase. Foreign object detection may also be performed during the connection phase. Communication may also occur between the power transmitter and the power receiver. The power receiver may often be configured to extract power from the communication carrier signal (e.g., to power internal functions of the power receiver) during the connection phase.

[0103] The connection phase can last for a significant period of time, including several hours or more, in many scenarios. For example, when a kitchen appliance equipped with a power receiver as described, such as a blender, is placed on a countertop equipped with a wireless power transmitter as described, it can go through a setup phase and then enter the connection phase in an adapted connection mode. The device can then remain in this state for a lengthy period corresponding to the device, e.g., a blender, remaining on the countertop ready to be operated but not actually switched on.

[0104] In response to detecting an appropriate event, the power transmitter and power receiver can transition from the connection phase to the power transfer phase. This event is typically detected by the power receiver, which can send a message to the power transmitter to request entry into the power transfer phase. For example, if a user performs an appropriate user action, such as pressing an on button, the power receiver can responsively send a request to the power transmitter to enter the power transfer phase.

[0105] The power transmitter (and power receiver) can then proceed to transition to power transmission.

[0106] During the power transmission phase, the power transmitter generates a power transmission drive signal and generates a power transmission signal in response. During the power transmission phase, power is supplied / transmitted to the power receiver by the power transmission signal. As described above, the power transmission signal uses a time frame in which the power transmission signal is provided in a power transmission time interval, which also includes a communication time interval and / or a foreign object detection time interval. During the power transmission phase, a communication carrier signal can also be generated when communication occurs in the communication time interval.

[0107] Once the power transmission has ended, the power transmitter and power receiver can return to a standby phase, and therefore specifically to a phase in which no power transmission signal is generated.

[0108] The setup phase and connection phase are sometimes collectively referred to as the initialization phase.

[0109] In the power transmitter of Figure 2, the power transmitter controller 203 is configured to control the power transmitter to operate in different phases and transition between different phases. Additionally, as described in more detail below, the power transmitter and power receiver are configured to operate in a standby phase that supports continued presence of the power receiver and allows the power transmitter to power down to operate in an ultra-low power configuration. The standby phases described may correspond, among other things, to modified standby phases, particularly modified idle phases or connection phases, as described above.

[0110] In addition to communication, the communication carrier signal can also be used to enable auxiliary power supply from the power transmitter to the power receiver. The auxiliary power transmission / path can provide a low level power supply that can be used to power internal circuitry such as a user interface or power receiver control functions.

[0111] The communication carrier signal can accordingly be used to provide a secondary / auxiliary low-level power transmission path from the power transmitter to the power receiver. To support this, the power receiver includes a power extractor 311 configured to extract power from the communication carrier signal. In a specific example, the power extractor 311 can suitably extract power from an NFC carrier signal.

[0112] The power extractor 311 is coupled to a load circuit 313 that can be powered by power extracted from the communications carrier signal by the power extractor 311. The load circuit 313 may typically be the control logic / support functions / circuitry of the power receiver and / or may include a user interface for the power receiver. The load circuit 313 can include or consist of elements of the power receiver controller 301 and / or the second communicator 307, for example.

[0113] Therefore, power can be provided from a power transmitter to a power receiver via communication carrier signal / NFC carrier power harvesting. This allows for powering low-power electronics or user interfaces, such as low-voltage NFC hardware. For example, in an NFC implementation, the extracted power can be up to approximately 200mW.

[0114] The auxiliary power supply may be provided particularly during the standby phase, such that the communication carrier signal during the standby phase can be used not only to provide a (typically bidirectional) communication channel between the power transmitter and the power receiver, but also to provide an auxiliary power supply to the power receiver. Thus, the auxiliary power supply during the standby phase can provide supply power that can be used to power internal circuits, such as communication functions, when the power transmission signal is not present. For example, in the conventional connection phase of a Ki system, power can be harvested from the continuous NFC communication carrier signal.

[0115] The power extractor 311 is relatively simple and an example of the power extraction circuit / path is shown in FIG.

[0116] 4 shows a circuit diagram of an example power path element of the power extractor 311. In this example, the second communication coil 309 is referenced by the symbol LRX, and when a communication carrier signal is applied to it, a corresponding AC voltage / current is induced in the coil. The power extractor 311 includes a capacitor CRX in parallel with the second communication coil 307 / LRX, thereby forming a resonant circuit that allows for improved performance and power transfer in many embodiments.

[0117] The second communication coil 309 / LRX is coupled to a rectifier bridge B1 with a smoothing capacitor C1 coupled to the output of the bridge. A DC voltage is therefore generated across capacitor C1. The magnitude of the ripple in the DC voltage is determined by the size of the smoothing capacitor and the load RL supplied by the power extractor 311.

[0118] Bridge B1 and smoothing capacitor C1 are coupled to load RL via switch S1, which can be used to turn power extraction / harvesting on and off. It will be appreciated that in many embodiments, power extractor 311 can be directly and permanently coupled to load RL without a switch.

[0119] 4 further shows a load modulation capacitor C2 that can be connected or disconnected in parallel with the second communication coil 309 based on the switching of switch S2. The second communication device 307 can control switch S2 during the communication time interval to provide the desired load modulation.

[0120] Therefore, the power extractor 311 can be implemented with low complexity and low cost circuitry.

[0121] A problem inherent in many wireless power transfers is the management and initiation of power transfer, and switching between standby and power transfer phases. A reliable and user-friendly operation is particularly challenging in situations where repeated power transfer operation is desired without any physical movement or change in the placement of the power receiver to the power transmitter.

[0122] For example, consider a scenario in which a cordless kettle is placed on a power transmitter to boil water. After the water boils, the kettle may be switched off but left on the power transmitter. The power transmission operation can be terminated, for example, by the power receiver sending a power transmission end message to the power transmitter, which in response turns off the power transmission signal, causing the power transmitter to enter a standby phase.

[0123] In fact, since this state can last for a very long time, it is important to minimize energy consumption, and therefore the power receiver conventionally goes into a complete power-down mode in which no power is extracted from the power transmitter and no power or communication signals are generated by the power transmitter. Specifically, it can enter an idle phase as described above.

[0124] Indeed, regulations such as Ki require that power transmitters enter a completely powered-down standby mode after a certain time, thus shutting down auxiliary power supplies and communications as well.

[0125] However, this presents a challenge if it is desired to initiate a new power transfer operation for the same device. For example, after some time (which could be hours or days), it may be desired to re-boil the water in the kettle, and therefore a new power transfer operation may be desired. However, because the kettle has not been physically moved or removed, the usual approach of initiating a new power transfer operation when the presence of a power receiver is detected is not applicable.

[0126] One proposed solution is to require the user to remove and relocate a power receiver, such as a kettle, to the power transmitter in order to initiate a new power transmission operation. However, this approach is impractical and typically undesirable for users. Furthermore, this approach assumes that the standby-phase power transmitter detects the removal and relocation of the power receiver by periodically measuring, for example, the quality factor of the primary coil (or another parameter, such as resonant frequency or impedance). This method requires a sufficiently high measurement frequency per second. If the user removes and reinserts the device between two measurements, the change in the measured parameter may not be significant, and the wake-up condition may not be met. Therefore, this approach tends to be relatively complex and consumes more power than is ideal.

[0127] Another solution is for the power transmitter to provide a user interface that the user can activate to initiate a new power transfer operation. However, such an approach is not useful for power transmitter operations that may not naturally have a user interface, such as a power transmitter mounted as an integral part of a kitchen countertop. Furthermore, having to use a user interface that is not part of the device being operated tends to be counterintuitive for the user. Another drawback is that the power transmitter's user interface typically needs to be generic enough to fit all power-receiving devices, whereas the device's own user interface can be optimized for the device, potentially hindering user interface optimization.

[0128] The wireless power transfer system of FIG. 1 (and the power transmitter and / or power receiver of FIGS. 2 and 3) can employ an approach that may provide improved performance, typically facilitating initialization of power transfer from a standby phase, and typically enabling such initialization without requiring movement of the power receiver or any user input to the power transmitter. Typically, an ultra-low power standby phase can further be enabled.

[0129] In this approach, the power transmitter is configured to employ recurring time frames for the communication drive signal / communication carrier signal during the standby phase. The recurring time frames are divided into communication time intervals and non-communication time intervals, during which the power transmission signal has a much lower power level than during the communication time intervals; in fact, the communication carrier signal is typically turned off entirely during the non-communication time intervals. The non-communication time intervals are sometimes referred to as low-power time intervals.

[0130] Typically, each repeating time frame consists of one communication time interval and one non-communication time interval.

[0131] The durations of the communication time interval and the non-communication time interval may differ significantly, with the communication time interval being significantly shorter than the non-communication time interval, specifically, its duration not exceeding 20%, often not exceeding 10% or 5% of the duration of the non-communication time interval. The duration of the communication time interval is a relatively low percentage of the duration of the recurring time frame. In many embodiments, the duration of the communication time interval does not exceed 20%, 10%, or 5% of the duration of the recurring time frame.

[0132] Typically, each repeating time frame has the same duration and the same composition of communication and non-communication time intervals.

[0133] The duration of each recurring time frame is in many embodiments in the range of 50 ms to 10 seconds, and particularly advantageously in the range of 200 ms to 300 ms. In the following, we will focus on an example in which each recurring time frame has a duration of 250 ms, hence a frequency of 4 Hz, and each time frame consists of one communication time interval of 20 ms and one non-communication time interval of 230 ms.

[0134] The power level of the communication drive signal / communication carrier signal during the non-communication time interval is significantly lower than the power level of the communication drive signal / communication carrier signal during the communication time interval.

[0135] The amplitude / power level of the communication drive signal during the non-communication time interval in many embodiments does not exceed 10%, 5%, 2%, or 1% of the power level and / or amplitude of the communication drive signal and / or communication carrier signal during the communication time interval. Where the amplitude / power level of the communication drive signal / communication carrier signal may vary during recurring time frames, the average amplitude / power level of the communication drive signal during the non-communication time interval in many embodiments does not exceed 10%, 5%, 2%, or 1% of the average power level and / or amplitude of the communication drive signal and / or communication carrier signal during the communication time interval.

[0136] In many embodiments, the amplitude / power level of the communication drive signal / communication carrier signal is fixed within each communication time interval and / or each non-communication time interval. In some embodiments, the amplitude / power level of the communication drive signal / communication carrier signal can be set to a predetermined level within each communication time interval and / or each non-communication time interval.

[0137] In the described approach, the communications driver 209 is configured to generate a communications drive signal / communications carrier signal during the standby phase that employs a recurring time frame of communications time intervals and non-communications time intervals. The communications time intervals are shorter than the non-communications time intervals, but are generated at a significantly higher power / amplitude level. Indeed, in most embodiments, the communications carrier signal is generated to be present only during the communications time intervals; i.e., during the non-communications time intervals, the communications drive signal / communications carrier signal can be turned off entirely. The amplitude power level of the communications drive signal / communications carrier signal can be zero during the non-communications time intervals.

[0138] During the standby phase, the power transmitter is configured to generate short "bursts" of the communications carrier signal in response, while at other times the communications carrier signal is at a very low level, or typically turned off entirely. Figure 5 shows an example of a communications carrier signal that may be generated during the standby phase.

[0139] In this approach, the power receiver is configured to provide specific communications to the power transmitter using bursts of the communications carrier signal, and is therefore able to provide specific communications during a communication time interval.

[0140] Specifically, in a scenario where the power receiver remains in place after the power transmission operation has ended, the power receiver can enter a standby phase in which it proceeds to transmit an ID message to the power transmitter during a communication time interval. The power receiver transmits the ID message by load modulating a communication carrier signal generated by the power transmitter during the communication time interval of the standby phase.

[0141] The power receiver is configured not to transmit any ID messages, or indeed any messages, during the non-communication time intervals of the recurring time frames. In many embodiments, the power receiver is configured not to transmit any messages other than ID messages during the recurring time frames, and in particular only ID messages may be transmitted during the communication time intervals.

[0142] Each ID message includes the device ID of the power receiver. Thus, the ID message includes the ID of the power receiver. The device ID can be a permanent or temporary ID of the power receiver. In some cases, the device ID can be dynamically assigned to the power receiver, and in other embodiments or scenarios, the device ID can be permanently assigned to the power receiver.

[0143] The Device ID can be a data word, and each power receiver (or group of power receivers) is assigned a different Device ID / data word. The Device ID provides a distinction between different power receivers, and in particular allows a power transmitter to communicate appart to a power receiver, each power receiver having a different Device ID.

[0144] Thus, the device ID allows the power receiver to identify itself to the power transmitter. The power receiver is configured to repeatedly transmit an ID message containing the device ID to the power transmitter, thereby identifying itself to the power transmitter. Thus, the power transmitter is continuously notified not only that a power receiver is present, but also that this power receiver is indeed the same as before. In the scenario of entering the described standby phase from a previous power transmission phase that provided power to the power receiver, the continuous transmission of the ID message during the standby phase notifies the power transmitter that the same power receiver is still present, and thus notifies the power transmitter of a scenario in which no physical change has occurred. This allows, for example, the power transmitter to determine that a new power transmission may be initiated without a new presence detection, etc. Thus, the power transmitter can distinguish between a scenario in which the same power receiver is simply left in the same location and a scenario in which the power-receiving device is replaced with a different power receiver.

[0145] Further, in this configuration, the power receiver is configured to detect a power request and, in response, to change the device ID of one or more ID messages. Thus, in response to detecting a power request (from an internal or external source), the second communicator 307 can change the device ID from the device ID of the ID message to the device ID used in the previous ID message.

[0146] The request for power may be determined automatically by the power receiver, for example, by expiration of time, load level, or other electrical parameter of the load changing, etc. However, in many embodiments, the power request may be in response to user activation / input, as described in more detail below.

[0147] The first communicator 205, in response to receiving the different device ID in the ID message, can proceed to notify the power transmission controller 203. And the power transmitter controller 203, in response to detecting the first ID message including the changed device ID, can proceed to initiate a transition from the standby phase to the power transmission phase.

[0148] The power receiver is also configured to transition to the power transfer phase. Typically, the power receiver can monitor for the presence of a power transfer signal and the signal induced in the receiver coil 107. It can then proceed to interact with the power transmitter to initiate a new power transfer operation.

[0149] Thus, in this approach, the power transmitter and power receiver operate in a standby phase in which no power transmission signal is generated, and a bursty communication carrier signal is provided to enable communication of an ID message from the power receiver to the power transmitter. The ID message notifies the power transmitter that the same power receiver remains in place and further provides a specific means for the power receiver to transition the power transmitter to the power transmission phase. This approach provides a very low power standby phase and an efficient means for the same power receiver to remain in place, but does not require a user interface on the power transmitter or movement of the power receiver to initiate a new power transmission operation.

[0150] The power transmitter controller 203 can be configured to control the power transmitter to perform power transmission initialization, which can follow the same approach as when a power receiver initializes power transmission when it is first placed near the power transmitter, for example. Similarly, the power receiver can be configured to perform the same power transmission initialization when it is first placed near the power transmitter.

[0151] For example, the power transmitter and the power receiver can be configured to perform power transfer initialization according to the Ki standard, for example, the power transmitter and the power receiver can go through a setup phase, possibly a connection phase, and then reach the power transfer phase.

[0152] However, in some embodiments, the power transmitter can be configured to change the operation of the power transfer phase, particularly the initialization of the power transfer phase, compared to the situation where the power transfer phase is initiated with a new power receiver.

[0153] In particular, in examples where the transition to the power transfer phase occurs in response to detecting a change in the receiving device ID, the initialization can take into account predetermined parameters for the power receiver, and in particular, the power transfer phase can be initiated with at least one operating parameter dependent on stored characteristics of the power receiver. For example, in some embodiments, part of the setup phase, or even the entire setup phase, can be skipped, and parameters from a previous power transfer operation can be reused for the current power transfer operation.

[0154] Thus, in some embodiments, the power transmitter controller 203 can store configuration parameters of the power receiver when performing a power operation. These parameters may specifically include configuration parameters that can be selected / determined / negotiated during a configuration or negotiation phase when initiating a power transfer. For example, in the case of a Ki system, a configuration phase occurs in which the power transmitter and power receiver interact to determine appropriate parameters for the power transfer. These parameters can be stored by the power transmitter controller 203 for use in future power transfer operations.

[0155] Parameters that may be determined and stored may include, for example, power level settings or levels, parasitic power loss parameters (e.g., used to adapt foreign object detection), operating mode indicators, load setting indicators, specific user interface settings, time characteristics associated with power transfer, etc.

[0156] In some embodiments, various parameters can be determined during the power transfer phase and stored by the power transmitter controller 203. For example, the power consumption of the power receiver can be monitored and, when the power transfer is completed, the minimum, maximum, and average power consumption, for example, can be stored.

[0157] The configuration parameters can be stored at any suitable time, such as before, during or after the (previous) power operation.

[0158] In such a case, the power transmitter controller 203 can proceed to retrieve the stored configuration parameters and apply them when initiating a new power transfer operation in response to detecting a changed device ID for the same power receiver. Indeed, in some embodiments, the power transmitter can proceed to the power transfer phase without communication or interaction with the power receiver for the appropriate operating parameters. Rather, the power transmitter can simply resume the power transfer phase using the same operating parameters as when the previous power transfer ended, e.g., using the same initial operating parameters as the previous power transfer operation.

[0159] In many embodiments, the power transmitter controller 203 can be configured to modify power transmission initialization when responding to detecting a changed device ID (from the same power receiver) relative to power transmission initialization when responding to detecting the presence of a new power receiver.

[0160] In particular, the power transfer initialization process can be configured to adapt in response to the detection of a changed ID. In many embodiments, for example, the power transfer initialization process can be configured to skip or bypass initialization operations performed for a new or unknown power receiver. For example, presence detection, authentication, or configuration operations included for a new power receiver may not be performed for the power transfer initialization phase performed in response to the detection of a changed device ID.

[0161] The specific details and characteristics of the ID message and device ID used depend on the requirements and preferences of individual implementations. The device ID is unique to each individual power receiver, and each power receiver will (at least with a high probability) have a different ID. Thus, if a power receiver is replaced with another power receiver and this replacement is fast enough that the absence of the power receiver is not detected, the ID message that may be sent from the new power receiver will likely not share a device ID with the current power receiver, and therefore the presence of the new power receiver, rather than the old one, will be detected. Similarly, if a power receiver is removed and another power receiver happens to be near the power transmitter, the ID message from this power receiver will not include the device ID of the power receiver from the previous power transmission.

[0162] The transmission of the ID message containing the device ID provides highly reliable operation if the power receiver remains after the power transmission has ended: the power transmitter can distinguish between its continued presence and the presence of a new power transmitter.

[0163] In some embodiments, each power receiver can be assigned a unique, fixed device ID, e.g., during manufacturing, and this ID can be used as the device ID. Indeed, in some embodiments, each power receiver can be assigned two unique, fixed device IDs, e.g., during manufacturing. These IDs can be used as device IDs for maintaining the standby phase and requesting the initiation of the power transfer phase. In such cases, the persistent, unique device ID can be used as the device ID for the standby phase.

[0164] In some embodiments, device IDs can be assigned or determined, for example, temporarily and / or dynamically. For example, in some embodiments, each power transmitter can be assigned a range of device IDs that can be assigned to power receivers. When a new power receiver is detected and power transmission begins, the power transmitter can transmit one or two device IDs to the power receiver, for example, as part of a setup phase, which the power receiver can then use in subsequent power transmission phases. If the power transmitter and power receiver detect that the power receiver has been removed from the power transmitter, they can both be configured to delete the association between the device ID and the power receiver. The device ID can then be reused with another power receiver. For example, reliability can be improved by the power transmitter using multiple device IDs (pairs) and ensuring a certain amount of time between reuse of the same device ID.

[0165] Indeed, in some embodiments, the power receiver can determine its own device ID and provide it to the power transmitter. For example, a random device ID can be generated by the power receiver and transmitted to the power transmitter. The power receiver can then transmit this device ID to the power transmitter during a subsequent standby phase. Thus, the power transmitter can determine that the same power receiver remains in place. As long as the device ID is long enough, it is unlikely that a new power receiver will generate the same device ID as an existing power receiver.

[0166] As previously mentioned, the communication can be an NFC communication in many embodiments, and the communication carrier signal can be an NFC carrier. In such embodiments, the ID message can be an NDEF message, particularly an NDEF (NFC Data Exchange Format) static configuration message.

[0167] In such a case, the ID message may specifically include an NDEF record, and the device ID may be an NFC UID (User IDentity), a number that is unique to the NFC device and cannot be deleted or changed.

[0168] Thus, specifically, the power transmitter may activate a communication carrier signal / NFC carrier to poll the power receiver during the standby phase, thereby enabling some power receiver operation. Device identification may be performed by reading a stored device ID, such as the device UID or unique ID.

[0169] The power transmitter controller 203 is configured to determine that a changed device ID has been received and to proceed to initialize power transmission operations in response to this detection.

[0170] In some embodiments, power transmitter controller 203 can be configured to store two device IDs of power receivers present when starting the standby phase, one corresponding to no request for power transmission, hereinafter referred to as the continuing device ID, and one corresponding to a request for power transmission, hereinafter referred to as the power supply requesting device ID. Power transmitter controller 203 can then compare the received device IDs of ID messages received during the standby phase with the stored device IDs and proceed accordingly.

[0171] For example, in a situation where a power receiver is assigned two device IDs known to the power transmitter, the power transmitter controller 203 can simply extract the device ID from each ID message and compare it to the locally stored device ID. If the extracted device ID corresponds to the stored persistent device ID, the power transmitter can continue operation appropriate for a situation where the power receiver remains in place and no power transmission is requested. The power transmitter can, for example, proceed to turn off the communication drive signal / communication carrier signal and end the communication time interval. This can set the time of the next communication time interval indicating when the communication carrier signal should next be generated. However, if the received device ID matches the stored power request device ID, the power transmitter controller 203 proceeds to initialize a new power transmission operation. If the received device ID does not match either of the two stored device IDs, the power transmitter can proceed to change the standby phase (and potential subsequent power transmission operation) to reflect the presence of a new power receiver. In some cases, detection of a device ID that does not match any of the device IDs associated with the power receiver from the previous power transfer phase may initiate a new power transfer operation, but with this initialization adjusted to reflect that it is for a new power receiver (e.g., a full configuration is performed).

[0172] In some embodiments, the power receiver can be assigned two device IDs known to the power transmitter, for example, by being communicated during the power transmission phase, and these can be stored as the persistent device ID and the power requesting device ID, respectively.

[0173] In other cases, the power requesting device ID may be, for example, a predetermined device ID. For example, the power transmitter controller 203 may store a predetermined device ID corresponding to a power request, i.e., the power requesting device ID may be a predetermined ID. The predetermined device ID may be common to different power receivers, and the persistent device ID may be unique to each individual power receiver.

[0174] Thus, in some embodiments, the power transmitter controller 203 can compare the received device ID with the power receiver's stored device ID, and if it matches, can proceed without change. However, if the received device ID corresponds to a predetermined power request device ID that is common to different power receivers, the power transmitter controller 203 can proceed to initiate a power transmission operation. Again, if the received device ID does not match any of these, the power transmitter can proceed appropriately for any new power receivers that may be present. The advantage of such an approach is that each power receiver can be assigned only one specific device ID.

[0175] The power transmitter controller 203 can be configured to compare the received device ID with the device ID of a previously received ID message. For example, when first entering the standby phase, the device ID of the first received ID message can be stored as the persistent device ID. For subsequent ID messages, the device ID is compared with the persistent device ID, i.e., the device ID first received in the standby phase. Such an approach is efficient in that it does not require prior communication or determination of the device ID associated with a particular power receiver.

[0176] In some embodiments, a persistent device ID and / or a power-requesting device ID can be provided prior to entering a standby phase. For example, during the setup phase of a previous power transmission initialization, particularly the first initialization performed for a given power receiver, the power receiver can report a device ID that can be used as a persistent device ID in a subsequent standby phase. The power transmitter can then store this device ID as a persistent device ID for later use. Similarly, in some embodiments, a power-requesting device ID can be provided and stored for use in a potential subsequent standby phase.

[0177] The power receiver may be particularly configured to change the device ID in response to detecting a user input.

[0178] In many embodiments, the power receiver may include a user interface 315. Such a user interface may include user output means such as indicator lights, audio indicators, a display, etc. Alternatively or additionally, the user interface 315 may include user input means such as a keyboard, voice recognition, user buttons, etc. In some embodiments, the user interface may simply consist of a single push button.

[0179] The user interface 315 is coupled to an ID controller 315 configured to detect a request for power made by a user. The ID controller 315 can detect the request in response to detecting a user activation of the user interface. For example, in a simple example where the user interface 317 is simply a push button, the ID controller 315 can detect whether the user presses the button and consider this activation a request for power. In other embodiments, a request for power by a user can be made by, for example, keyboard entry or a voice statement that can be received via the user interface.

[0180] In response to detecting a power request and user activation, the ID controller 315 can modify the device ID in the ID message to communicate to the power transmitter that a power transmission is requested. Specifically, in response to detecting user activation, the ID controller 315 can proceed to generate an ID message in which a device ID indicating a power request is transmitted.

[0181] This approach therefore enables a reliable and safe standby phase, allowing power transfer to be easily and efficiently reinitialized in response to a user providing user input to the power receiver itself (e.g., simply pressing a button on the power receiver).

[0182] The user interface may be, in particular, a passive user interface, and therefore, in particular, a user interface that does not consume power. Such a user interface may be implemented, for example, using a mechanical switch or a push button. A passive user interface may be implemented to minimize power consumption. In particular, it may be configured so that it does not need to draw power from the power receiver during a standby phase. In particular, it may provide a continuous user interface that can be constantly interacted with by a user, without considering or depending on when a communications carrier signal is present and power can be supplied. Thus, user operation of the user interface can occur at any time and is not affected by the burstiness of the communications carrier signal.

[0183] In many embodiments, such passive user interfaces can be configured to maintain a user-activated indication for a duration that exceeds the duration of a non-communication time interval, and that is typically longer than the duration between two communication time intervals. In many embodiments, the user-activated indication is maintained for a period that exceeds the duration of a recurring time frame.

[0184] In some embodiments, this can be accomplished by a user input that includes, for example, a mechanical latching function. For example, a latching push button can be used. In some cases, for example, a mechanical activator with a momentary on and delayed off function (or vice versa) can be used. In some cases, the user interface can simply utilize a switch with different positions, for example.

[0185] In such an embodiment, the user interface may be activated at any time, while the circuitry that detects user activation and adapts its operation accordingly may be configured to operate only during a communication time interval when a communications carrier signal is present and power can be extracted. For example, whenever a communication time interval is entered and a communications carrier signal is present, power may be extracted by power extractor 311 and provided to second communicator 307 and ID controller 315. ID controller 315 may poll the user interface and select an appropriate device ID. For example, if no user activation corresponding to a power request is detected, ID controller 315 may proceed to select the same device ID as the previous message; otherwise, it may select a different device ID (as described above) to indicate a request for a new power transfer to be initiated.

[0186] In many embodiments, the power receiver may have no power source other than the power supply channel provided by the power transmitter and no means for energy storage during the non-communication intervals of the standby phase. Thus, the power receiver is considered to be completely power-starved during at least a portion of the standby phase. The user interface, in such embodiments, may be passive and maintain switching states (latched buttons and knobs, rotary switches) or ultra-low-power electronic circuits (e.g., bistable multivibrators).

[0187] In some embodiments, the ID controller 315 can be configured to detect user activation in response to detecting that a user interface setting has been changed, particularly relative to the setting of a previous power transfer phase.

[0188] In some embodiments, the ID controller 315 can be configured to save one or more settings of the user interface during the power transfer phase. For example, switch settings can be saved. This can be done continuously, for example, throughout the power transfer phase, or as part of the end of the power transfer phase, for example.

[0189] During the standby phase, the ID controller 315 can be configured to compare the current settings of the user interface with the stored settings. If there is a difference, the ID controller 315 can accordingly determine that a user activation has occurred. In some embodiments, any change is considered a request for power transmission, and the ID controller 315 can proceed to change the device ID of the image data source 203 to indicate a power request to the power transmitter. In other embodiments, the ID controller 315 can determine whether a particular user interface setting has changed and change the device ID in response to this particular change.

[0190] In some embodiments, it is advantageous for the power receiver to compare the current user interface state / settings (e.g., rotary switch position) with those that existed before entering the standby phase. The power transmitter, in some embodiments, can send a message to the power receiver indicating that it is entering the standby phase, and the power receiver can proceed to save the current user interface settings in non-volatile memory in response. This can facilitate operation and reduce the number of non-volatile memory write cycles. The stored user interface state is then compared with the actual user interface state during a polling interval (which typically corresponds to the communication time interval). If a change in the user interface state is detected, the device ID in the ID message is changed and a new power transmission is requested to begin.

[0191] The message from the power transmitter can also be used by the power receiver to initiate a standby phase operation, which transmits an ID message with the device ID during the communication time interval.

[0192] It will be appreciated that, for clarity, the above description has described embodiments of the invention with reference to different functional circuits, units, and processors. However, it will be apparent that any suitable distribution of functionality between different functional circuits, units, or processors may be used without departing from the invention. For example, functionality shown to be performed by separate processors or controllers may be performed by the same processor or controller. References to specific functional units or circuits should therefore be seen merely as references to suitable means for providing the described functionality, rather than to indicative of a strict logical or physical structure or organization.

[0193] The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of embodiments of the invention may be physically, functionally, and logically implemented in any suitable way. Indeed, functionality may be implemented in a single unit, in multiple units, or as part of other functional units. Thus, the invention may be implemented in a single unit, or may be physically and functionally distributed between different units, circuits, and processors.

[0194] Although the present invention has been described in connection with several embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the appended claims. Furthermore, while certain features may appear to be described in connection with particular embodiments, those skilled in the art will recognize that various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0195] It will be understood that the reference to a preferred value does not imply any limitation beyond it being the value determined in the foreign object detection initialization mode, i.e., it is preferably determined in the adaptation process. Reference to a preferred value can be used instead of a reference to, for example, the first value.

[0196] Furthermore, although individually listed, a plurality of means, elements, circuits, or method steps may be implemented by, for example, a single circuit, unit, or processor. Furthermore, although individual features may be included in different claims, these may be advantageously combined in some cases, and their inclusion in different claims does not imply that a combination of features is not feasible and / or advantageous. Moreover, the inclusion of a feature in one category of claims does not imply limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, where appropriate. Furthermore, the order of features in the claims does not imply a particular order in which the features must operate, and in particular the order of individual steps in method claims does not imply that the steps must be performed in this order. Rather, steps may be performed in any suitable order. Furthermore, a reference to the singular does not exclude a plurality. Thus, references to "a," "an," "first," "second," etc. do not exclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

[0197] In general, examples of a power transmitter and its operating method, a power receiver and its operating method, and a wireless power transfer system (and its operating method) are provided in the following embodiments. Embodiments: Embodiment 1. A power transmitter (101) for wirelessly supplying power to a power receiver (105) via an inductive power transmission signal, the power transmitter (101) comprising: a power transmission coil (103) configured to generate a power transmission signal; a power transfer driver (201) configured to generate a power transfer drive signal for the power transfer coil (103), the power transfer driver being configured to generate the power transfer drive signal during a power transfer phase; a communication coil (207) configured to generate a communication carrier signal; a communication driver (209) configured to generate a communication drive signal for a communication coil to generate a communication carrier signal, the communication driver configured to generate the communication drive signal to employ recurring time frames during a standby phase in which no power transmission signal is present, each recurring frame including a communication time interval and a non-communication time interval, the duration of the communication time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communication drive signal during the non-communication time interval not exceeding 10% of the power level of the communication drive signal during the communication time interval; a communication unit (205) configured to receive ID messages load modulated onto a communication carrier signal during a communication time interval during a standby phase, each ID message including a device ID of a power receiver; and a phase controller (203) configured to switch the power transmitter from the power transmission phase to the standby phase in response to an end of power transmission, and to initiate a transition from the standby phase to the power transmission phase in response to detecting a first ID message including a changed device ID. Embodiment 2. The power transmitter of embodiment 1, wherein the phase controller (203) is configured to detect a changed device ID in response to a comparison of a device ID of a first ID message with a device ID of a second ID message received prior to the first ID message. Embodiment 3. The power transmitter of embodiment 1 or 2, wherein the phase controller (203) is configured to detect a changed device ID in response to a comparison of the device ID of the first ID message with a predetermined device ID. Embodiment 4. The power transmitter of any preceding embodiment, wherein the phase controller (203) is configured to detect a changed device ID in response to a comparison of the device ID of the first ID message with the device ID of the ID message received from the power receiver (105) before entering the standby phase. Embodiment 5. The power transmitter of any preceding embodiment, wherein the phase controller (203) is configured to store configuration parameters of the power receiver (105) upon entering the standby phase, to read the configuration parameters as part of the transition from the standby phase to the power transfer phase, and to determine operating parameters of the power transfer phase in dependence on the configuration parameters. Embodiment 6. The power transmitter of any previous embodiment, wherein the communications carrier signal is a near field communication (NFC) carrier. Embodiment 7. The power transmitter of any previous embodiment, wherein the ID message is a Near Field Communication (NFC) Data Exchange Format (NDEF) structured message. Embodiment 8. The power transmitter of any previous embodiment, wherein the recurring time frame has a duration of not less than 50 milliseconds and not more than 10 seconds. Embodiment 9. A power transmitter as described in any previous embodiment, wherein the power transmitter controller (203) is arranged to adapt operation of the power transmission phase initialization process in response to detecting a changed ID. Embodiment 10. A power receiver (105) for wirelessly receiving power from a power transmitter (101) via an electromagnetic power transmission signal, the power receiver (105) comprising: an inductive power extraction element (107) arranged to extract power from the power transmission signal during the power transfer phase; a communications coil (309) for receiving a communications carrier signal, the communications drive signal employing recurring time frames during a standby phase in which no power transmission signal is present, each recurring time frame including a communications time interval and a non-communication time interval, the duration of the communications time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communications drive signal during the non-communication time interval not exceeding 10% of the power level of the communications drive signal during the communications time interval; a communication unit (307) configured to transmit ID messages by load modulation of a communication carrier signal during a communication time interval during a standby phase, each ID message including a device ID of a power receiver (105); a power extractor (311) coupled to the communication coil (309) and configured to extract a power supply signal from the communication coil (309) and to power a circuit (313) of the communication unit with the power supply signal during a communication time interval; a controller (315) configured to change a device ID of a first ID message relative to a device ID of a previous ID message in response to detecting a power request, wherein the power request is an indication of a request to commence a power transfer phase. Embodiment 11. The power receiver of embodiment 10, further comprising a user interface (317), wherein the controller (315) is configured to detect a power request in response to detecting user activation of the user interface (317). Embodiment 12. The power receiver (105) of embodiment 11, wherein the user interface is a passive user interface configured to maintain a user activation indication of user activation for a duration that exceeds the duration of the non-communication time interval. Embodiment 13. The controller is configured to store a first user interface setting for a power transfer phase before entering a standby phase, the controller is configured to determine a first user interface setting before entering a standby phase, a second user interface setting during the standby phase, and to detect user activation in response to detecting a difference between the first user interface setting and the second user interface setting. Embodiment 14. The power receiver (105) according to any of the preceding embodiments 10 to 13, wherein the controller is configured to be powered by the power supply signal only during the communication time interval. Embodiment 15. A wireless power transmission system comprising a power transmitter (101) according to any one of the first to ninth embodiments and a power receiver (105) according to any one of the tenth to fourteenth embodiments. Embodiment 16. A method of operating a power transmitter (101) that wirelessly supplies power to a power receiver (105) via an inductive power transmission signal, the power transmitter (101) comprising: a power transmission coil (103) configured to generate the power transmission signal; a communication coil (207) configured to generate a communication carrier signal; The method comprises: generating a power transfer drive signal for the power transfer coil (103) during a power transfer phase; generating a communication drive signal for the communication coil to generate a communication carrier signal, the communication drive signal being generated to employ recurring time frames during a standby phase in which no power transmission signal is present, each recurring frame including a communication time interval and a non-communication time interval, the duration of the communication time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communication drive signal during the non-communication time interval not exceeding 10% of the power level of the communication drive signal during the communication time interval; receiving ID messages load modulated onto a communications carrier signal during a communication time interval during a standby phase, each ID message including a device ID of a power receiver; switching the power transmitter from the power transmission phase to a standby phase in response to the end of the power transmission; and initiating a transition from the standby phase to the power transfer phase in response to detecting a first ID message that includes a changed device ID. Embodiment 17. A method of operating a power receiver (105) that wirelessly receives power from a power transmitter (101) via an electromagnetic power transmission signal, the power receiver (105) comprising: an inductive power extraction element (107) configured to extract power from the power transmission signal during the power transfer phase; a communications coil (309) for receiving a communications carrier signal, the communications drive signal employing recurring time frames during a standby phase in which no power transmission signal is present, each recurring time frame including a communications time interval and a non-communication time interval, the duration of the communications time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communications drive signal during the non-communication time interval not exceeding 10% of the power level of the communications drive signal during the communications time interval; transmitting ID messages by load modulation of a communications carrier signal during a communication time interval during a standby phase, each ID message including a device ID of the power receiver (105); Extracting a power supply signal from a communication coil (309); powering said communication unit circuitry (313) with a power supply signal during a communication time interval; and changing the device ID of the first ID message relative to the device ID of the previous ID message in response to detecting a power request, the power request indicating a request for initiation of a power transfer phase.

[0198] More particularly, the present invention is defined by the following claims.

Claims

1. 1. A power transmitter for wirelessly supplying power to a power receiver via an inductive power transmission signal, the power transmitter comprising: a power transfer coil configured to generate the power transfer signal; a power transfer driver configured to generate a power transfer drive signal for the power transfer coil, the power transfer driver configured to generate the power transfer drive signal during a power transfer phase; a communications coil configured to generate a communications carrier signal; a communication driver configured to generate a communication drive signal for the communication coil to generate the communication carrier signal, the communication driver configured to generate the communication drive signal to employ recurring time frames during a standby phase in which the power transmission signal is not present, each recurring time frame including a communication time interval and a non-communication time interval, a duration of the communication time interval not exceeding 20% ​​of a duration of the non-communication time interval, and a power level of the communication drive signal during the non-communication time interval not exceeding 10% of a power level of the communication drive signal during the communication time interval; a communication unit configured to repeatedly receive ID messages load modulated onto the communication carrier signal during a communication time interval during the standby phase, each ID message including a device ID of the power receiver; a phase controller configured to switch the power transmitter from a power transmission phase to a standby phase in response to an end of power transmission; a power transmitter configured such that the phase controller compares a first device ID, which is a device ID of a first ID message, with a second device ID, which is a device ID of a second ID message received from a power receiver before the first ID message, and remains in a standby phase if the first device ID matches the second device ID; and initiates a transition from the standby phase to a power transmission phase in response to detecting that the first device ID does not match the second device ID.

2. 2. The power transmitter of claim 1, wherein the second ID message is received during the same standby phase as the first ID message.

3. 3. The power transmitter according to claim 1, wherein the second device ID is a device ID of a power receiver that received power in a power transmission phase immediately before the standby phase.

4. 4. The power transmitter of claim 1, wherein the second ID message is received from the power receiver before entering a standby phase.

5. 5. The power transmitter of claim 1, wherein the phase controller is configured to store configuration parameters of the power receiver when entering a standby phase, to retrieve the configuration parameters as part of a transition from the standby phase to the power transfer phase, and to determine operating parameters of the power transfer phase in dependence on the configuration parameters.

6. The power transmitter of claim 1 , wherein the communication carrier signal is a near field communication (NFC) carrier.

7. The power transmitter of claim 1 , wherein the ID message is a message in an NFC Data Exchange Format (NDEF) structure for Near Field Communication (NFC).

8. 8. A power transmitter according to claim 1, wherein the recurring time frames have a duration of at least 50 milliseconds and at most 10 seconds.

9. 9. The power transmitter of claim 1, wherein the phase controller is configured to adapt operation of an initialization process of the power transfer phase in response to detecting a changed ID.

10. 1. A power receiver that wirelessly receives power from a power transmitter via an electromagnetic power transmission signal, the power receiver comprising: an inductive power extraction element configured to extract power from the power transmission signal during a power transfer phase; a communications coil for receiving a communications carrier signal, the communications drive signal employing recurring time frames during a standby phase in which the power transmission signal is not present, each recurring time frame including a communications time interval and a non-communication time interval, the duration of the communications time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communications drive signal during the non-communication time interval not exceeding 10% of the power level of the communications drive signal during the communications time interval; a communication unit configured to transmit ID messages by load modulation of the communication carrier signal during communication time intervals during a standby phase, each ID message including a device ID of a power receiver; a power extractor coupled to the communication coil and configured to extract a power supply signal from the communication coil and to power circuitry of the communication unit with the power supply signal during the communication time interval; a controller configured to change a device ID of a first ID message relative to a device ID of a previous ID message in response to detecting a power request, the power request being an indication of a request to start a power transmission phase; and

11. The power receiver of claim 10 , further comprising a user interface, the controller configured to detect the power request in response to detecting user activation of the user interface.

12. 12. The power receiver of claim 11, wherein the user interface is a passive user interface configured to maintain a user-activated indication of a user activation for a duration that exceeds a duration of the non-communication time interval.

13. 13. The power receiver of claim 10, wherein the controller is configured to store a first user interface setting for a power transfer phase before entering a standby phase, determine a second user interface setting during the standby phase, and detect the user activation in response to detecting a difference between the first user interface setting and the second user interface setting.

14. 14. A power receiver according to any one of claims 10 to 13, wherein the controller is configured to be powered by the power supply signal only during the communication time interval.

15. A wireless power transmission system comprising the power transmitter according to any one of claims 1 to 9 and the power receiver according to any one of claims 10 to 14.

16. 1. A method of operating a power transmitter that wirelessly supplies power to a power receiver via an inductive power transmission signal, the power transmitter having a power transmission coil configured to generate the power transmission signal and a communication coil configured to generate a communication carrier signal, the method comprising: generating a power transfer drive signal for the power transfer coil during a power transfer phase; generating a communication drive signal for the communication coil to generate the communication carrier signal, the communication drive signal is generated to employ recurring time frames during a standby phase in which the power transmission signal is not present, each recurring time frame including a communication time interval and a non-communication time interval, the duration of the communication time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communication drive signal during the non-communication time interval not exceeding 10% of the power level of the communication drive signal during the communication time interval; repeatedly receiving ID messages load modulated onto the communication carrier signal during the communication time interval of the standby phase, each ID message including a device ID of a power receiver; switching the power transmitter from the power transmission phase to the standby phase in response to the end of power transmission; comparing a first device ID, which is the device ID of a first ID message, with a second device ID, which is the device ID of a second ID message received from a power receiver prior to the first ID message, and if the first device ID matches the second device ID, remaining in the standby phase; and initializing a transition from the standby phase to the power transmission phase in response to detecting that the first device ID does not match the second device ID.

17. 1. A method of operating a power receiver that receives power wirelessly via an electromagnetic power transmission signal from a power transmitter, the power receiver having an inductive power extraction element configured to extract power from the power transmission signal during a power transfer phase, the method comprising: receiving a communication carrier signal with a communication coil, the communication drive signal employing recurring time frames during a standby phase in which the power transmission signal is not present, each recurring time frame including a communication time interval and a non-communication time interval, the duration of the communication time interval not exceeding 20% ​​of the duration of the non-communication time interval, and the power level of the communication drive signal during the non-communication time interval not exceeding 10% of the power level of the communication drive signal during the communication time interval; transmitting ID messages by load modulation of the communication carrier signal during the communication time intervals during the standby phase, each ID message including a device ID of the power receiver; extracting a power supply signal from the communication coil; powering circuitry of the communication unit with said power supply signal during said communication time interval; and changing the device ID of the first ID message to the device ID of a previous ID message in response to detecting a power request, the power request indicating a request to start a power transfer phase.

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