Wireless power transfer

Abstract

The power transmitter (101) wirelessly provides power to the power receiver (105) via a power transfer signal generated by the power transfer coil (103). The communication driver (209) generates a communication drive signal for the communication coil (207) to generate a communication carrier signal. During a standby phase in which the power transmission signal is not transmitted, the power transmitter generates a pulsed communication carrier signal. When there is a communication carrier signal, the power receiver (105) transmits an identification message during a standby phase. The identification message comprises a device identification for the power receiver (105). A power receiver (105) may request a power transfer operation by changing the device identification of the identification message, and in response to detecting a different device identification, a phase controller (203) of a power transmitter initializes a transition from the standby phase to a power transfer phase.

Description

Technical Field

[0001] The present invention relates to the operation of a wireless power transfer system arranged to wirelessly transfer power from a power transmitter to a power receiver, and in particular but not exclusively, to wirelessly transfer power to high-power devices such as kitchen appliances. Background Art

[0002] Currently, most electrical products require dedicated electrical contacts in order to be powered by an external power source. However, this is often impractical and requires the user to physically insert a connector or otherwise establish a physical electrical contact. Typically, the power requirements also vary significantly, and most current devices are provided with their own dedicated power source, resulting in the user typically having a large number of different power sources, each of which is dedicated to a specific device. Although the use of internal batteries can avoid the need for a wired connection to a power source during use, this only provides a partial solution since the batteries need to be recharged (or replaced). The use of batteries also significantly increases the weight and potential cost and size of the device.

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

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

[0005] This arrangement allows wireless power transfer to a device without the need for any wired or physical electrical connection. In fact, it can simply allow the device to be placed near or on top of the transmitter coil for external charging or power supply. For example, the power transmitter device can be arranged to have a horizontal surface on which the device can simply be placed to be powered.

[0006] Furthermore, such a wireless power transfer arrangement can advantageously be designed such that the power transmitter device can be used with a range of power receiver devices. In particular, a wireless power transfer method known as the Qi specification has been defined and is currently being further developed. This method allows a power transmitter device that meets the Qi specification to be used with a power receiver device that also meets the Qi specification, without having to be from the same manufacturer or without having to be dedicated to each other. The Qi standard also includes some functions for allowing operation adapted to a specific power receiver device (e.g., depending on a specific power consumption).

[0007] The Qi standard is developed by the Wireless Power Consortium, and more information can be found, for example, on its website: http: / / www.wirelesspowerconsortium.com.index.html, where, in particular, the defined specification documents can be found.

[0008] The Wireless Power Consortium continues to develop the Ki standard (also known as the cordless kitchen standard) based on the Qi standard, which aims to provide safe, reliable, and efficient wireless power transfer to kitchen appliances. Ki supports much higher power levels of up to 2.5 KW.

[0009] In many systems, such as specifically the Qi system, communication from the power receiver to the power transmitter can use load modulation, where the load of the power transfer signal varies according to the data to be transmitted. However, it may be difficult to detect whether the power transfer load of the power transfer signal changes simultaneously. Similarly, communication from the power transmitter to the power receiver can be achieved by modulating the power transfer signal (e.g., amplitude or frequency modulation), but interference to this modulation may be caused by parameter changes of the power transfer signal due to, for example, a varying load.

[0010] Therefore, in some systems, it has been proposed to use a completely independent communication method. Specifically, the Ki wireless power transfer system can use the Near Field Communication (NFC) standard to establish a two-way communication link. The communication is performed during the power transfer phase within a short time interval to avoid or reduce interference between power transfer and communication. The power receiver is arranged to detect the NFC carrier to perform communication during the short time interval.

[0011] The challenge of implementing a wireless power transfer system that provides a highly user-friendly, safe, and efficient operation and user experience lies in how to control the initialization and termination of the power transfer operation. Conventionally, when it is detected that the power receiving device is positioned close enough to the power transmitter (and specifically, the power transmitter coil), power transfer begins. The presence of the power receiver is detected by the power transmitter, and in response, the power transmitter starts the transfer of power to the power receiver. Then, the power receiver will continue to extract power, and the power transfer will continue.

[0012] Normally, this will continue until the power receiver is removed from the power transmitter. Similarly, the removal of the power receiver can be detected, and the power transmitter can terminate the power transfer accordingly and cut off the power transfer signal.

[0013] In some cases, the power receiver can simply be turned off without being removed from the power transmitter, and in fact, the power transfer operation can be terminated while the power receiver is still present. For example, a cordless kettle can be placed on top of the power transmitter, and after the operation of boiling water has been completed, the kettle can be turned off while still remaining on top of the power transmitter.

[0014] However, a particular challenge in this case is how to restart power transfer when needed subsequently. For example, if it is desired to re-boil the water in the kettle, an agency is needed to initialize a new power transfer operation. This is a particularly difficult challenge because the device is essentially in a state of not supplying power to the power receiver.

[0015] A current approach is based on requiring the user to actively provide user input to the power transmitter to make it start and initialize a new power transfer operation. However, this is not ideal in many cases. For example, for the user, it may seem highly counterintuitive that he needs to engage with the user interface of the power transmitter rather than, for example, the user appliance. It also hinders the user interface from being optimized and adapted to individual power receiving devices / appliances. It may also result in the activation physical location being suboptimal (e.g., being located on a workbench rather than on the appliance), etc.

[0016] Another option that has been proposed, particularly for Ki, is to require the user to first remove the power receiving device and then reposition it on the power transmitter. However, this is a very impractical and counterintuitive operation. It also requires frequent checking for the presence of the power receiver device.

[0017] Current methods tend to be suboptimal and require relatively complex functions and / or undesirable user operations.

[0018] Therefore, improved operation for a wireless power transfer system would be advantageous. In particular, methods that allow increased flexibility, reduced cost, reduced complexity, improved user experience, additional functionality, ease of operation, ease of user control, and / or improved performance would be advantageous. For example, an improved method for initializing power transfer to an already existing power receiver without requiring a power transmitter user interface and providing an improved user experience would be advantageous. SUMMARY OF THE INVENTION

[0019] Accordingly, the present invention seeks to preferably mitigate, alleviate, or eliminate one or more of the above disadvantages, either singly or in any combination.

[0020] According to one aspect of the present invention, there is provided a power transmitter for wirelessly providing power to a power receiver via an inductive power transfer signal, the power transmitter comprising: a power transfer coil arranged to generate the power transfer signal; a power transfer driver arranged to generate a power transfer drive signal for the power transfer coil, the power transfer driver being arranged to generate the power transfer drive signal during a power transfer phase; a communication coil arranged to generate a communication carrier signal; a communication driver arranged to generate a communication drive signal for the communication coil to generate the communication carrier signal, the communication driver being arranged to generate the communication drive signal to employ a repetitive time frame during a standby phase in the absence of the power transfer signal, each repetitive 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; a communication unit arranged to receive, during the standby phase, an identification message load-modulated onto the communication carrier signal during the communication time interval, each identification message in the identification messages including a device identification for the power receiver; a phase controller arranged to switch the power transmitter from the power transfer phase to the standby phase in response to termination of power transfer; and wherein the phase controller is arranged to compare a first device identification, which is the device identification of a first identification message, with a second device identification, which is the device identification of a second identification message received from the power receiver before the first identification message, and to remain in the standby phase if the first device identification matches the second device identification, and to initiate a transition from the standby phase to the power transfer phase in response to detecting that the first device identification does not match the second device identification.

[0021] In many embodiments, the present invention may allow for improved performance. In many systems and embodiments, it may allow for overall improved power transfer operation.

[0022] The method may allow for an efficient and generally ultra-low power standby phase, but still allow for reliable and user-friendly power initialization. The method may be particularly applicable to scenarios where the power receiver can remain positioned close to the power transmitter after termination of the power transfer operation. The method may provide an efficient and practical method with low complexity, allowing a user to interact with a user interface of the power receiver to initiate a new power transfer operation.

[0023] The method can also provide an efficient way to allow the execution of minimal functionality, e.g., by using a communication carrier signal to provide auxiliary power transfer to allow the start of a new power transfer operation, the communication carrier signal also being used to support communication during the standby phase.

[0024] In many embodiments, the method also provides reliable operation and allows additional flexibility and functionality by providing a way to ensure that a new power transfer operation is for a specific power receiver, and specifically, in many scenarios, it has a power receiver previously involved in a power transfer operation.

[0025] The method can provide an improved secondary / auxiliary power transfer path using the communication path during the standby phase, thus providing synergy and interoperability between communication and auxiliary power supply.

[0026] The power transfer driver can be arranged to generate a communication drive signal and thus generate a communication carrier signal that has a non-zero (usually constant / fixed) amplitude during a communication time interval and a zero amplitude during a non-communication time interval.

[0027] In many embodiments, the duration of the communication time interval does not exceed 5%, 10%, or 20% of the duration of the repeating time frame. In many embodiments, the duration of the non-communication time interval is not less than 70%, 80%, or 90% of the duration of the repeating time frame.

[0028] The detection of a first identification message including a changed device identification can be the detection that the first identification message includes a device identification different from the device identification of a previously (usually the previous) received identification message.

[0029] According to an optional feature of the invention, a second identification message is received during the same standby phase as the first identification message.

[0030] In many embodiments, this can allow improved operation and / or facilitate implementation and / or operation.

[0031] The method can allow particularly advantageous operation and generally can allow an efficient, reliable, and practical detection of a request for power transfer.

[0032] According to an optional feature of the invention, the second device identification is the device identification of the power receiver that received power during the power transfer phase immediately preceding the standby phase.

[0033] In many embodiments, this can allow improved operation and / or facilitate implementation and / or operation.

[0034] The method can allow particularly advantageous operation and generally can allow an efficient, reliable, and practical detection of a request for power transfer.

[0035] According to an optional feature of the present invention, a second identification message is received from the power receiver before entering the standby phase.

[0036] In many embodiments, this can allow for improved operation and / or facilitate implementation and / or operation.

[0037] The method can allow for particularly advantageous operation and generally allows for efficient, reliable, and practical detection of requests for power transfer.

[0038] In some embodiments, the second identification message is received before the standby phase of receiving the first identification message.

[0039] According to an optional feature of the present invention, the phase controller is arranged to: store the configuration parameters of the power receiver when entering the standby phase; retrieve the configuration parameters as part of the transition from the standby phase to the power transfer phase; and determine the operating parameters for the power transfer phase based on the configuration parameters.

[0040] In many embodiments, this can allow for particularly advantageous operation and / or implementation.

[0041] According to an optional feature of the present invention, the communication carrier signal is a Near Field Communication (NFC) carrier.

[0042] The method can allow for particularly advantageous operation and generally allows for efficient, reliable, and practical detection of requests for power transfer. It can also provide improved backward compatibility and applicability for many systems, specifications, and methods.

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

[0044] In many embodiments, the method can allow for particularly advantageous operation.

[0045] According to an optional feature of the present invention, the repetition time frame has a duration of not less than 50 milliseconds and not more than 10 seconds.

[0046] In many embodiments, this can allow for particularly advantageous operation and / or implementation.

[0047] In many embodiments, the repetition time frame can have a duration of not less than 50, 100, 250, 500, 1000 milliseconds. In many embodiments, the repetition time frame can have a duration of not more than 1, 2, 5, 10 seconds.

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

[0049] In many embodiments, this can allow for improved operation and / or facilitate implementation and / or operation.

[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 arranged to extract power from the power transmission signal during a power transmission phase; a communication coil for receiving a communication carrier signal; the communication drive signal adopting a repeating time frame during a standby phase in the absence of the power transmission signal, each repeating 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; a communication unit arranged to transmit an identification message by load modulation of the communication carrier signal during the communication time interval during the standby phase, each identification message in the identification messages including a device identification for the power receiver; a power extractor coupled to the communication coil and arranged to extract a power signal from the communication coil and supply power to a circuit of the communication unit through the power signal during the communication time interval; and a controller arranged to change the device identification for a first identification message relative to the device identification of a previous identification message in response to detecting a power request, the power request being an indication of a request to initiate a power transmission phase.

[0051] In many embodiments, the present invention can allow for improved performance. In many systems and embodiments, it can allow for overall improved power transmission operation.

[0052] The method can allow for an efficient and generally ultra-low power standby phase, but still allow for reliable and user-friendly power initialization. The method can be particularly applicable to scenarios where the power receiver can remain positioned close to the power transmitter after termination of the power transmission operation. The method can provide an efficient and practical method with low complexity, allowing user interaction with the user interface of the power receiver to initiate a new power transmission operation.

[0053] The method can allow the power receiver to control when to initiate a new power transmission while supporting ultra-low power operation during the standby phase.

[0054] The change in the device identification can include including a device identification different from any device identification previously transmitted by the power receiver during the standby phase in the first identification message.

[0055] According to an optional feature of the present invention, the power receiver further includes a user interface, and the controller is arranged to detect a power request in response to detecting user activation of the user interface.

[0056] In many embodiments, this can allow for improved operation and / or facilitate implementation and / or operation. The method can particularly allow for reduced complexity and facilitate implementation. The method can allow a user to access the user interface of the power receiver to initiate a new power transfer without, for example, moving the power receiver, and at the same time allow the standby phase to operate in an ultra-low power mode.

[0057] According to an optional feature of the present invention, the user interface is a passive user interface arranged to maintain a user activation indication of user activation for a duration exceeding a non-communication time interval.

[0058] In many embodiments, this can allow for particularly advantageous operation and / or implementation. The method can allow for very low power consumption during the power transfer phase while still allowing power transfer initialization to be controlled based on the user interface of the power receiver.

[0059] According to an optional feature of the present invention, the controller is arranged to: store a first user interface setting of 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] In many embodiments, this can allow for particularly advantageous operation and / or implementation.

[0061] According to an optional feature of the present invention, the controller is arranged to be powered only by the power supply signal during the communication time interval.

[0062] In many embodiments, this can allow for particularly advantageous operation and / or implementation. It can particularly allow for an ultra-low power standby phase.

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

[0064] According to one aspect of the present invention, there is provided an operating method for a power transmitter to wirelessly supply power to a power receiver via an inductive power transmission signal. The power transmitter includes: a power transmission coil arranged to generate the power transmission signal; and a communication coil arranged to generate a communication carrier signal. And the method further includes: generating a power transmission drive signal for the power transmission coil during a power transmission phase; generating a communication drive signal for the communication coil to generate the communication carrier signal, generating the communication drive signal to adopt a repetitive time frame during a standby phase in the absence of the power transmission signal, each repetitive 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; receiving, during the standby phase, an identification message load-modulated onto the communication carrier signal during the communication time interval, each identification message in the identification messages including a device identification for the power receiver; switching the power transmitter from the power transmission phase to the standby phase in response to termination of power transmission; and comparing a first device identification, which is the device identification of a first identification message, with a second device identification, which is the device identification of a second identification message received from the power receiver before the first identification message, and, if the first device identification matches the second device identification, remaining in the standby phase, and in response to detecting that the first device identification does not match the second device identification, initializing a transition from the standby phase to the power transmission phase.

[0065] According to one aspect of the present invention, there is provided an operating method for a power receiver to wirelessly receive power from a power transmitter via an electromagnetic power transmission signal. The power receiver includes: an inductive power extraction element arranged to extract power from the power transmission signal during a power transmission phase; and the method includes: a communication coil receiving a communication carrier signal; the communication drive signal adopting a repetitive time frame during a standby phase in the absence of the power transmission signal, each repetitive 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 an identification message during the communication time interval of the standby phase by load modulation of the communication carrier signal, each identification message in the identification messages including a device identification for the power receiver; extracting a power supply signal from the communication coil; powering a circuit of the communication unit with the power supply signal during the communication time interval; and changing the device identification for a first identification message relative to the device identification of a previous identification message in response to detecting a power request, the power request being an indication of a request to initiate a power transmission phase.

[0066] These and other aspects, features, and advantages of the present invention will become apparent from and will be elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Embodiments of the present invention will be described by way of example only with reference to the accompanying drawings, in which

[0068] Figure 1 an example of elements of a power transmission system according to some embodiments of the present invention is shown;

[0069] Figure 2 an example of elements of a power transmitter according to some embodiments of the present invention is shown;

[0070] Figure 3 an example of elements of a power receiver according to some embodiments of the present invention is shown;

[0071] Figure 4 an example of elements of a power transmission path for wireless power transmission operation is shown; and

[0072] Figure 5 an example of a repetitive time frame of a communication carrier signal in a wireless power transfer system according to some embodiments of the present invention is shown. DETAILED DESCRIPTION

[0073] The following description focuses on embodiments of the present invention applicable to a wireless power transfer system utilizing a power transfer method such as known from the Qi standard. However, it should be understood that the present invention is not limited to this application, but can be applied to many other wireless power transfer systems.

[0074] Figure 1 An example of a power transfer system according to some embodiments of the present invention is shown. The power transfer system includes a power transmitter 101, which includes (or is coupled to) a transmitter coil / inductor 103. The system also includes a power receiver 105, which includes (or is coupled to) a receiver coil / inductor 107.

[0075] The system provides an electromagnetic power transfer signal, which can inductively transfer power from the power transmitter 101 to the power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal, which propagates as a magnetic flux by the transmitter coil or inductor 103. The power transfer signal can correspond to an electromagnetic power transfer component representing the energy transfer from the power transmitter to the power receiver, and can 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 there is no load on the receiving coil 107, the power receiver will not extract power from the generated electromagnetic field (except for losses). In this case, driving the transmitter coil 103 can generate an electromagnetic field with a potentially high field intensity, but the power level of the power transfer signal will be zero (except for losses). In some cases where there is a foreign object, the power transfer signal can be considered to include a component corresponding to the power transfer to the foreign object, and thus the power transfer signal can be considered to correspond to the power extracted from the electromagnetic field generated by the power transmitter.

[0076] The power transfer signal can generally have a frequency between approximately 20 kHz and approximately 500 kHz, and for a Qi-compatible system, typically in the range between 20 kHz and 80 kHz. The transmitter coil 103 and the power receiving coil 107 are loosely coupled, and thus the power receiving coil 107 picks up (at least a part of) the power transfer signal from the power transmitter 101. Thus, power is transferred from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the power receiving coil 107. The term "power transfer signal" is mainly used to refer to the inductive signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the power receiving coil 107, but it should be understood that equivalently, it can also be considered and used as a reference for the electrical signal provided to the transmitter coil 103 or picked up by the power receiving coil 107.

[0077] In an example, the power receiver 105 is specifically a power receiver that receives power via the receiver coil 107. However, in other embodiments, the power receiver 105 may include a metal element, such as a metal heating element, in which case the power transfer signal directly induces eddy currents, resulting in direct heating of the element. Accordingly, the power receiver can provide a load to the power transfer signal by including an inductive power extraction element, which can specifically be a power extraction coil or an electronic (e.g., heating) element, where a current is induced by the power transfer signal.

[0078] The system is arranged to transfer a large number of power levels, and specifically, the power transmitter can support power levels of more than 50W, 100W, 500W, or 1kW. For example, for Ki-type applications, the power transfer can typically exceed 100W, and for very high power applications, it can be as high as more than 2500W.

[0079] Hereinafter, the operation of the power transmitter 101 and the power receiver 105 will be specifically described with reference to embodiments that generally conform to the specifications developed by the Wireless Power Consortium (except for the modifications and enhancements described herein (or the corresponding ones)). In particular, the power transmitter 101 and the power receiver 105 can follow the elements of the Ki standard or be substantially compatible with the elements of the Ki standard.

[0080] Many wireless power transfer systems (especially high-power systems such as Ki) utilize resonant power transfer, where the transmitter coil 103 is part of a resonant circuit, and typically the receiver coil 107 is also part of the resonant circuit. In many embodiments, the resonant circuit can be a series resonant circuit, and thus the transmitter coil 103 and the receiver coil 107 can be serially coupled with corresponding resonant capacitors. The use of resonant circuits tends to provide more efficient power transfer.

[0081] Figure 2 The elements of the power transmitter 101 are shown, and Figure 3 are shown in more detail Figure 1 the elements of the power receiver 105.

[0082] The power transmitter 101 includes a driver 201 that can generate a drive signal that is fed to the transmitter coil 103, which in turn generates an electromagnetic power transfer signal that provides power transfer to the power receiver 105. The power transfer signal is provided (at least) during a power transfer time interval of the power transfer phase.

[0083] The driver 201 can generally include an output circuit in the form of an inverter, which is typically formed by driving a full bridge or a half bridge, as will be well known to those skilled in the art.

[0084] The power transmitter 101 also includes a power transmitter controller 203, which is arranged to control the operation of the power transmitter 101 according to a desired operating principle. Specifically, the power transmitter 101 may include a number of functions required to perform power control according to the Qi or Ki specifications.

[0085] In particular, the power transmitter controller 203 is arranged to control the generation of a drive signal by the driver 201, and it may specifically control the power level of the drive signal and thus the level of the generated power transfer signal. The power transmitter controller 203 includes a power loop controller that controls the power level of the power transfer signal in response to a power control message received from the power receiver 105 during a power control phase.

[0086] To receive data and messages from the power receiver 105, the power transmitter 101 includes a first communicator 205, which is arranged to receive data and messages from the power receiver 105 and transmit data and messages to the power receiver 105 (as will be understood by those skilled in the art, data messages may provide information of one or more bits).

[0087] In the method, 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 arranged to generate a communication drive signal that is fed to the first communication coil 207 to generate a communication carrier signal. The communication driver 209 may generally be arranged to generate the communication drive signal / communication carrier signal to have a frequency significantly different from that of the power transfer drive signal / power transfer signal. In many embodiments, the frequency of the communication carrier signal may be not less than 10, 100, or 500 times higher than the frequency of the power transfer signal. In many embodiments, the frequency of the communication drive signal / communication carrier signal may have a frequency of not less than 500 kHz, 1 MHz, or 10 MHz. Specifically, for NFC implementations, the communication carrier signal frequency may be 13.56 MHz.

[0088] The first communicator 205 is coupled to the communication driver 209 and is arranged to control the communication driver 209 to modulate the communication drive signal / communication carrier signal in order to transmit data to the power receiver (in the following reference to the communication drive signal, an implicit reference to the communication carrier signal is also included, as appropriate).

[0089] In a specific example, the modulation is amplitude modulation of the communication drive signal, and specifically binary communication using amplitude shift keying (ASK) is employed. However, it should be understood that in other embodiments, the modulation may use other methods, such as phase or frequency modulation of the communication drive signal.

[0090] In some embodiments, the first communicator 205 may 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 fed to the communication driver 209. The control modulation signal may be, for example, a binary signal that matches the data to be transmitted, and the communication driver 209 may be arranged to generate a communication drive signal having a corresponding amplitude variation.

[0091] For communication from the power receiver to the power transmitter, the modulation of the communication drive signal may be load modulation. The power receiver may be arranged to modulate the communication carrier signal by changing the load of the communication carrier signal generated by the first communication coil 207 according to the data to be transmitted. The first communicator 205 may be arranged to sense changes in the voltage and / or current of the first communication coil 207 and demodulate the load modulation based thereon. Those skilled in the art will be aware of the principles of load modulation and will not be described in further detail herein.

[0092] In many embodiments, the communication may be in accordance with the near field communication NFC standard, 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 (at least) implement 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 (except for modulation).

[0093] The following description will focus on the example where the communication between the power transmitter and the power receiver is by NFC communication, and specifically where the modulation of the NFC carrier in the direction from the power transmitter to the power receiver is by amplitude shift keying (ASK), and the modulation of the NFC carrier in the direction from the power receiver to the power transmitter is by load modulation.

[0094] Figure 3 Some exemplary elements of the power receiver 105 are shown.

[0095] 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., it 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 suitable power supply for the load 303. Additionally, the power receiver controller 301 may include various power receiver controller functions required to perform power transfer, and in particular functions required to perform power transfer according to the Qi or Ki specifications.

[0096] To support communication from the power receiver 105 to the power transmitter 101, the power receiver 105 includes a second communicator 307 and a second communication coil 309. The second communication coil 309 is arranged to be coupled to the first communication coil 207, and thus a communication carrier signal induces a current (at least one electromagnetic field) in the second communication coil 309.

[0097] The second communicator 307 is coupled to the second communication coil 309 and is arranged to determine the amplitude variation of the induced signal and demodulate the amplitude modulation of the communication carrier signal. Thus, the second communicator 307 is arranged to decode the data transmitted from the power transmitter by the amplitude modulation of the communication carrier signal. It should be understood that in other embodiments, the second communicator 307 may be arranged to decode the data modulated onto the communication carrier signal using other modulation formats such as frequency or phase modulation.

[0098] The second communicator 307 is also arranged to perform load modulation on the communication carrier signal in order to transfer data from the power receiver to the power transmitter. Specifically, the second communicator 307 may include a load (such as a capacitor) that can be switched between being coupled to the second communication coil 309 and not being coupled to the second communication coil 309 according to the data to be transmitted. These load modulations can then be detected by the first communicator 205 of the power transmitter.

[0099] In a specific example, the second communication coil 309 and the second communicator 307 may provide NFC - compatible communication operation. Specifically, the second communication coil 309 may be arranged to provide a function corresponding to an NFC tag and decode the data that has been ASK - modulated onto the communication carrier signal according to the NFC specification.

[0100] Thus, the second communicator 307 is arranged to transfer data to the power transmitter by changing the load of the receiver coil 107 in response to the data to be transmitted to the power transmitter 101. Then, as is known to those skilled in the art, the power transmitter 101 detects and demodulates the load change.

[0101] In an example, the second communicator 307 is also arranged to demodulate an amplitude, frequency, and / or phase modulation of a communication carrier signal in order to retrieve data transmitted from the power transmitter.

[0102] In many embodiments, the wireless power transfer system and thus the power transmitter and / or the power receiver can be arranged to operate in different phases, and in particular it can operate in a power transfer phase in which a power transfer signal is generated and thus a power transfer operation of supplying power to the load 303 is performed. Additionally, the power transmitter can be arranged to operate in a standby phase in which the power transmitter does not generate a power transfer signal and thus there is no power transfer signal. In the standby phase, the power transfer driver 201 does not generate a power transfer drive signal and thus does not supply a drive signal to the transmitter coil 103. In the standby phase, the transmitter coil 103 does not generate a power transfer signal.

[0103] In many embodiments, such as for example many Ki-based embodiments, the wireless power transfer system and thus the power transmitter and / or the power receiver can be arranged 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 can include the following:

[0104] The first phase is the idle phase. In this phase, the power transmitter does not detect the presence of the power receiver. During the idle phase, no power transfer signal and no communication carrier signal are generated. In the idle phase, the power transmitter monitors the presence of the power receiver. In particular, the power transmitter can generate an electromagnetic detection signal at regular intervals, and if a load for that signal is detected, the power transmitter can assume the potential presence of a power receiver. When a power receiver is detected, the power transmitter can transition to the configuration phase. In some systems, the idle phase itself can be referred to by the term standby phase, e.g., in the Ki specification, the phase corresponding to the described idle phase is called the standby phase.

[0105] In the configuration phase, configuration information / data can be exchanged between the power transmitter and the power receiver. The configuration information / data can provide information about the attributes of the power receiver and the power transmitter to the complementary device. Each device can adapt its operating parameters based on the exchanged configuration data. Thus, the power transmitter and the power receiver can use the configuration phase to exchange specific information about the characteristics of the particular devices, thereby allowing them to adapt their operation to the specific pairing of the power transmitter and the power receiver.

[0106] If the configuration phase is not successful, such as for example if the power transmitter does not receive a suitable message from the power receiver or receives an explicit termination, the power transmitter can return to the idle phase.

[0107] If the configuration and communication are successfully completed, the power transmitter proceeds to the connection phase. During the connection phase, communication has been established between the power transmitter and the power receiver, and the devices can be adapted to each other. However, power transmission has not been initialized. During the connection phase, a communication carrier signal is generated, and it can specifically be continuously present during the connection phase. However, during the connection phase, no power transmission signal is generated. In addition, foreign object detection can be performed during the connection phase. Moreover, communication can be performed between the power transmitter and the power receiver. In many cases, the power receiver can be arranged to extract power from the communication carrier signal during the connection phase (e.g., to power the internal functions of the power receiver).

[0108] In many cases, the connection phase can last for a relatively long time, including several hours or more. For example, if a kitchen device (e.g., a blender) including the described wireless power receiver is placed on a workbench including the described power transmitter, they can go through the configuration phase and thus enter the connection phase in an adapted and connected mode. Then, the devices can remain in this state for a long time, corresponding to the device (e.g., the blender) being kept on the workbench ready to be activated but not actually turned on.

[0109] In response to detecting a suitable event, the power transmitter and the power receiver can transition from the connection phase to the power transmission phase. Usually, the event can be detected by the power receiver, which can transmit a message to the power transmitter to request entry into the power transmission phase. For example, if the user performs a suitable user action, such as pressing the on button, the power receiver can continue to transmit a request to the power transmitter in response to request entry into the power transmission phase.

[0110] Then, the power transmitter (and the power receiver) can continue to transition to power transmission.

[0111] During the power transmission phase, the power transmitter generates a power transmission drive signal and accordingly generates a power transmission signal. During the power transmission phase, power is provided / transmitted to the power receiver through the power transmission signal. As described above, the power transmission signal can use a time frame that provides the power transmission signal during the power transmission time interval, and the time frame also includes a communication time interval and / or a foreign object detection time interval. During the power transmission phase, when communication is performed during the communication time interval, a communication carrier signal can also be generated.

[0112] When power transmission terminates, the power transmitter and the power receiver can return to the standby phase, and thus specifically, it can return to the phase where no power transmission signal is generated.

[0113] The configuration phase and the connection phase can be collectively referred to as the initialization phase.

[0114] In Figure 2 the power transmitter, the power transmitter controller 203 is arranged to control the power transmitter to operate in different phases and transition between different phases. Further, as will be described in more detail later, the power transmitter and the power receiver are arranged to operate in a standby phase that supports the continuous presence of the power receiver while allowing the power transmitter to be powered off and operate in a very low power configuration. As described above, the described standby phase may specifically correspond to a modified standby phase and, in particular, to a modified idle or connected phase.

[0115] In addition to communication, the communication carrier signal can also be used to implement 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, for example, to power internal circuits such as user interfaces or power receiver control functions.

[0116] Accordingly, the communication carrier signal can 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 arranged to extract power from the communication carrier signal. In a specific example, the power extractor 311 can accordingly extract power from an NFC carrier signal.

[0117] The power extractor 311 is coupled to a load circuit 313, and the power that can be extracted from the communication carrier signal by the power extractor 311 provides the load circuit 313. The load circuit 313 can generally be the control logic / support function / circuit of the power receiver and / or can include the user interface of the power receiver. The load circuit 313 can, for example, include or be composed of elements of the power receiver controller 301 and / or the second communicator 307.

[0118] Accordingly, power can be provided from the power transmitter to the power receiver via communication carrier signal / NFC carrier power harvesting. This can supply power to low power levels and, for example, low voltage electronics such as NFC hardware or user interfaces. For example, for NFC implementations, the extracted power can be up to approximately 200 mW.

[0119] Auxiliary power supply can be provided especially during the standby phase, and thus the communication carrier signal can be used not only to provide (usually bilateral) communication channels between the power transmitter and the power receiver during the standby phase, but also to provide auxiliary power supply to the power receiver. Therefore, when there is no power transmission signal, the auxiliary power supply during the standby phase can provide a power source that can be used to power internal circuits (such as communication functions), for example. For example, during the traditional connection phase of the Ki system, power can be collected from the continuous NFC communication carrier signal.

[0120] The power extractor 311 can be relatively simple, and Figure 4 shows an example of a power extraction circuit / power path.

[0121] Figure 4 The circuit diagram of the elements showing an example of the power path of the power extractor 311 is shown. In this example, the second communication coil 309 is referred to by the name LRX, and when this is subjected to the communication carrier signal, a corresponding AC voltage / current is induced in the coil. In many embodiments, the power extractor 311 includes a capacitor CRX in parallel with the second communicator 307 / LRX, thus forming a resonant circuit that allows improved performance and power transfer.

[0122] The second communication coil 309 / LRX is coupled to a rectifier bridge B1, where a smoothing capacitor C1 is coupled to the output of the bridge. Thus, a DC voltage is generated across the capacitor C1. The amplitude of the ripple on the DC voltage will depend on the size of the smoothing capacitor and the load RL supplied by the power extractor 311.

[0123] The bridge B1 and the smoothing capacitor C1 are coupled to the load RL via a switch S1, and the switch S1 can be used to turn on and off power extraction / collection. It should be understood that in many embodiments, the power extractor 311 can be directly and permanently coupled to the load RL without a switch.

[0124] Figure 4 A load modulation capacitor C2 is also shown, which can be connected in parallel with or disconnected from the second communication coil 309 based on the switching of the switch S2. The second communicator 307 can control the switch S2 during the communication time interval to provide the desired load modulation.

[0125] Therefore, the power extractor 311 can be implemented with low-complexity and low-cost circuits.

[0126] Specific problems for many wireless power transfer are the management and initiation of power transfer and the switching between a standby phase and a power transfer phase. In particular, reliable and user-friendly operation is particularly challenging in situations where repeated power transfer operations may be desired without any physical movement or change of the power receiver to the power transmitter device.

[0127] For example, consider the scenario where a cordless kettle has been placed on top of a power transmitter to boil water. After the water has boiled, the kettle can be turned off but can remain on top of the power transmitter. The power transfer operation can be terminated, for example, by the power receiver transmitting a power transfer termination message to the power transmitter, and in response, the power transmitter enters the standby phase by turning off the power transfer signal.

[0128] In fact, since this state may persist for a very long time, it is important to minimize energy consumption, and thus the power receiver traditionally enters a fully powered-off mode where no power is extracted from the power transmitter and the power transmitter generates no power or communication signals. Specifically, as mentioned before, it can enter an idle phase.

[0129] In fact, for example, the regulations of Ki require the power transmitter to enter a fully powered-off standby mode after a certain duration, thus also requiring the shutdown of auxiliary power delivery and communication.

[0130] However, this poses a challenge if a new power transfer operation is desired for the same device. For example, after a period of time (which can be hours or even days), it may be desired to boil the water in the kettle again, and thus a new power transfer operation may be desired. However, since the kettle has not been physically moved or removed, the normal method of starting a new power transfer operation when the presence of the power receiver is detected is not applicable.

[0131] One solution that has been proposed is to simply require the user to remove the power receiver, such as the kettle, and reposition it on the power transmitter to start a new power transfer operation. However, this method is impractical and generally undesirable for the user. In addition, this method assumes that the power transmitter in the standby phase periodically measures, for example, the primary coil quality factor (or another parameter such as resonance frequency, impedance, etc.) to detect the removal and repositioning of the power receiver. This method requires a sufficiently high measurement frequency per second. If the user removes and reintroduces the appliance between two measurements, the change in the measured parameters may not be significant and may not meet the wake-up condition. Therefore, this method tends to be relatively complex and tends to consume more power than ideal.

[0132] Another solution is that the power transmitter provides a user interface that the user can activate to initiate a new power transfer operation. However, such an approach is useless for power transmitter operations that may not inherently have a user interface (such as a power transmitter installed as an integral part of a kitchen worktop). Additionally, having to use a user interface that is not part of the device being operated is often counterintuitive for the user. Another drawback is that it may prevent optimization of the user interface, as the power transmitter user interface typically needs to be generic enough to fit all possible power receiver devices, while the user interface of the device itself can be optimized for the device.

[0133] Figure 1 The wireless power transfer system (as well as Figure 2 and Figure 3 the power transmitter and / or power receiver) can employ methods that can provide improved performance, and the methods can generally facilitate the initialization of power transfer from the standby phase, and the methods can generally allow such initialization without movement of the power receiver or any user input to the power transmitter. It can also generally allow for an ultra-low power consumption standby phase.

[0134] In the method, the power transmitter is arranged to employ a repetitive time frame for a communication drive signal / communication carrier signal during the standby phase. The repetitive time frame is divided into communication time intervals and non-communication time intervals, where the power level of the power transfer signal is much lower during the non-communication time intervals than during the communication time intervals, and in fact the communication carrier signal is typically completely turned off during the non-communication time intervals. The non-communication time intervals can also be referred to as reduced power time intervals.

[0135] Typically, each repetitive time frame includes one communication time interval and one non-communication time interval.

[0136] The durations of the communication time interval and the non-communication time interval are substantially different, where the communication time interval is substantially shorter than the non-communication time interval, and specifically, the duration does not exceed 20% of the duration of the non-communication time interval, and typically does not exceed 10% or 5% of the duration of the non-communication time interval. The duration of the communication time interval is a relatively low fraction of the duration of the repetitive time frame. In many embodiments, the duration of the communication time interval does not exceed 20%, 10%, or 5% of the duration of the repetitive time frame.

[0137] Each repetitive time frame typically has the same duration and typically has the same configuration of communication time interval and non-communication time interval.

[0138] In many embodiments, the duration of each repeating time frame ranges from 50 milliseconds to 10 seconds, and particularly advantageously ranges from 200 milliseconds to 300 milliseconds. In the following, the description will focus on an example where each repeating time frame has a duration of 250 milliseconds and thus a frequency of 4 Hz, and where each time frame consists of a communication time interval with a duration of 20 milliseconds and a non-communication time interval with a duration of 230 milliseconds.

[0139] During the non-communication time interval, the power level of the communication drive signal / communication carrier signal is substantially lower than the power level of the communication drive signal / communication carrier signal during the communication time interval.

[0140] In many embodiments, during the non-communication time interval, the amplitude / power level of the communication drive signal does not exceed 10%, 5%, 2%, or even 1% of the power level and / or amplitude of the communication drive signal and / or communication carrier signal during the communication time interval. In cases where the amplitude / power level of the communication drive signal / communication carrier signal can vary during the repeating time frame, in many embodiments, the average amplitude / power level of the communication drive signal during the non-communication time interval does not exceed 10%, 5%, 2%, or even 1% of the average power level and / or amplitude of the communication drive signal and / or communication carrier signal during the communication time interval.

[0141] In many embodiments, the amplitude / power level of the communication drive signal / communication carrier signal is fixed within each communication time interval and / or within 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 within each non-communication time interval.

[0142] Thus, in the method described, the communication driver 209 is arranged to generate a communication drive signal / communication carrier signal during the standby phase, which employs a repeating time frame with a communication time interval and a non-communication time interval. Compared with the non-communication time interval, the communication time interval is shorter, but is generated with a substantially higher power / amplitude level. In fact, in most embodiments, the communication carrier signal is generated to exist only during the communication time interval, i.e., the communication drive signal / communication carrier signal can be completely turned off during the non-communication time interval. During the non-communication time interval, the amplitude power level of the communication drive signal / communication carrier signal can be zero.

[0143] During the standby phase, the power transmitter is thus arranged to generate short "bursts" of the communication carrier signal, but the level of the communication carrier signal is very low at other times and is typically completely turned off. Figure 5Shows an example of a communication carrier signal that can be generated during the standby phase.

[0144] In the method, the power receiver is arranged to provide specific communication to the power transmitter using bursts of the communication carrier signal, and thus can provide specific communication during the communication time interval.

[0145] Specifically, in the case where the power receiver remains in place after the termination of the power transfer operation, the power receiver can enter the standby phase, in which the power receiver continues to transmit an identification message to the power transmitter during the communication time interval. The power receiver transmits the identification message by load modulating the communication carrier signal generated by the power transmitter during the communication time interval of the standby phase.

[0146] The power receiver is arranged not to transmit any identification message or indeed any message during the non-communication time interval of the repeating time frame. In many embodiments, the power receiver is arranged not to transmit other messages than the identification message during the repeating time frame, and specifically, during the communication time interval, only the identification message can be transmitted.

[0147] Each identification message includes a device identification for the power receiver. Thus, the identification message includes the identification of the power receiver. The device identification can be a permanent or temporary identification for the power receiver. In some cases, the device identification can be dynamically assigned to the power receiver, and in other embodiments or scenarios, the device identification can be permanently assigned to the power receiver.

[0148] The device identification can be a data word, where different power receivers (or groups of power receivers) are assigned different device identifications / data words. The device identification can provide a distinction between different power receivers, and can specifically allow the power transmitter to distinguish the power receivers, and different power receivers can have different device identifications.

[0149] Accordingly, the device identifier allows the power receiver to identify itself to the power transmitter. The power receiver is arranged to repeatedly transmit an identification message having the device identifier to the power transmitter so as to identify itself to the power transmitter. Accordingly, the power transmitter is continuously notified not only of the presence of the power receiver, but also that the power receiver is in fact the same as the previous power receiver. In a scenario where the described standby phase has been entered from a previous power transfer phase in which power was provided to the power receiver, continuing to transmit the identification 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 where no physical change has occurred. For example, this can enable the power transmitter to determine that a new power transfer can be initiated without any new presence detection, etc. Thus, it allows the power transmitter to distinguish between a scenario where the same power receiver simply remains in the same location and a scenario where the power receiver is replaced by another power receiver.

[0150] In addition, in this arrangement, the power receiver is arranged to detect a power request and, in response, is arranged to change the device identifier of one or more identification messages. Accordingly, in response to detecting a request for power (from an internal or external source), the second communicator 307 may change the device identifier from the device identifier of the identification message with respect to the device identifier used in the previous (one or more) identification messages.

[0151] For example, a request for power may be automatically determined by the power receiver, such as due to time expiration, load level, or other electrical parameters such as a change in load. However, in many embodiments, as will be described in more detail later, the power request may be in response to user activation / input.

[0152] In response to the first communicator 205 receiving a different device identifier in the identification message, it may continue to notify the power transmitter controller 203. The power transmitter controller 203 may then continue to initialize the transition from the standby phase to the power transfer phase in response to detecting the first identification message including the changed device identifier.

[0153] In addition, the power receiver is arranged to transition to the power transfer phase. Generally, the power receiver may monitor the presence of the power transfer signal and the signal induced in the receiver coil 107. It may then continue to communicate with the power transmitter to initiate a new power transfer operation.

[0154] Thus, in the method, the power transmitter and the power receiver operate in a standby phase in which no power transfer signal is generated, and a burst communication carrier signal is provided in the standby phase to allow an identification message to be transmitted from the power receiver to the power transmitter. The identification message notifies the power transmitter that the same power receiver remains in place, and further provides a specific means for the power receiver to initiate the transition of the power transmitter to the power transfer phase. The method provides a very low-power standby phase but provides an effective means for allowing the same power receiver to remain in the same position and be able to initiate a new power transfer operation without, for example, any user interface at the power transmitter or any movement of the power receiver being required.

[0155] The power transmitter controller 203 may be arranged to control the power transmitter to perform power transfer initialization. For example, the power transfer initialization follows the same method as when initializing power transfer when the power receiver is in the first position at the power transmitter. Similarly, the power receiver may be arranged to perform the same power transfer initialization as when it is first positioned close to the power transmitter.

[0156] For example, the power transmitter and the power receiver may be arranged to perform power transfer initialization according to the Qi specification. For example, the power transmitter and the power receiver may continue to go through a configuration phase and possibly a connection phase to reach the power transfer phase.

[0157] However, in some embodiments, the power transmitter may be arranged to modify the operation of the power transfer phase and specifically the initialization of the power transfer phase compared to the case of initiating the power transfer phase with a new power receiver.

[0158] Specifically, in an example where a transition to the power transfer phase is performed in response to detecting a change in the received device identification, the initialization may take into account previously determined parameters for the power receiver, and specifically, at least one operating parameter depending on the stored attributes of the power receiver may be used to initiate the power transfer phase. For example, in some embodiments, a part of the configuration phase, in some cases the entire configuration phase, may be skipped, where the parameters of the previous power transfer operation are reused for the current power transfer operation.

[0159] Thus, in some embodiments, the power transmitter controller 203 may store configuration parameters for the power receiver when performing a power operation. These parameters may specifically include the configuration parameters that can be selected / determined / negotiated during the configuration or negotiation phase when initiating power transfer. For example, for the Qi system, a configuration phase is carried out in which the power transmitter and the power receiver communicate with each other to determine suitable parameters for power transfer. These parameters may be stored by the power transmitter controller 203 for future power transfer operations.

[0160] Parameters that can be determined and stored can include, for example, power level settings or levels, parasitic power loss parameters (e.g., for adapting foreign object detection), operation mode indications, load configuration indications, specific user interface settings, time attributes related to power transfer, and the like.

[0161] In some embodiments, various parameters can be determined and stored by the power transmitter controller 203 during the power transfer phase. For example, the power consumption of the power receiver can be monitored, and when the power transfer terminates, the minimum, maximum, and average power consumption can be stored, for example.

[0162] Configuration parameters can be stored at any suitable time, including before, during, or after a (previous) power operation.

[0163] In this case, when starting a new power transfer operation in response to detecting a changed device identity for the same power receiver, the power transmitter controller 203 can continue to retrieve the stored configuration parameters and apply these parameters. In fact, in some embodiments, the power transmitter can proceed to the power transfer phase without any communication or interaction with the power receiver regarding suitable operating parameters. Instead, it can, for example, simply restart the power transfer phase using the same operating parameters as when the previous power transfer terminated, or it can, for example, use the same initial operating parameters as the previous power transfer operation.

[0164] In many embodiments, the power transmitter controller 203 can be arranged to modify the power transfer initialization when, in response to detecting a changed device identity (from the same power receiver) relative to the power transfer initialization (when detecting the presence of a new power receiver).

[0165] In particular, it can be arranged to adapt the power transfer initialization process in response to detecting a changed identity. In many embodiments, it can be arranged, for example, to skip or bypass initialization operations performed for a new or unknown power receiver. For example, for the initialization of the power transfer phase performed in response to detecting a changed device identity, presence detection, authentication, or configuration operations included for the new power receiver may not be performed.

[0166] The specific details and attributes of the identification messages and device identifiers used can depend on the requirements and preferences of individual embodiments. The device identifier is specific to an individual power receiver, and different power receivers will (at least with high probability) have different identifiers. Thus, if a power receiver is replaced with another power receiver and the swap is fast enough to not detect the absence of the power receiver, any identification message transmitted from the new power receiver may not share the device identifier of the current power receiver, and thus the presence of the new rather than the old power receiver will be detected. Similarly, if a power receiver is removed and another power receiver happens to be close to the power transmitter, any identification message from that power receiver will not include the device identifier of the power receiver for the previous power transfer.

[0167] When the power receiver remains after power transfer termination, the transmission of identification messages with device identifiers provides highly reliable operation. The power transmitter can distinguish the presence of a persistent and a new power receiver.

[0168] In some embodiments, each power receiver can be assigned a unique and fixed device identifier, for example during manufacturing, and this identifier can be used as the device identifier. In fact, in some embodiments, for example during manufacturing, two unique and fixed device identifiers can be assigned to each power receiver. These identifiers can be used as the device identifiers for maintaining the standby phase and for requesting the start of the power transfer phase. In such a case, the permanent and unique device identifier can accordingly be used as the standby phase device identifier.

[0169] In some embodiments, the device identifier can be, for example, temporary and / or dynamically assigned or determined. For example, in some embodiments, each power transmitter can be assigned a series of device identifiers that can be assigned to power receivers. When a new power receiver is detected and power transfer is initiated, the power transmitter can, for example as part of the configuration phase, transmit one or two device identifiers to the power receiver, and then the power receiver can continue to use these device identifiers in subsequent power transfer phases. If the power transmitter and the power receiver detect that the power receiver has been removed from the power transmitter, they can both be arranged to delete the association between the device identifier and the power receiver. The device identifier can then be reused with another power receiver. For example, improved reliability can be achieved by the power transmitter using multiple device identifier (pairs) to ensure that there is some time between the reuse of the same (one or more) device identifiers.

[0170] In fact, in some embodiments, the power receiver itself can determine the device identifier and provide it to the power transmitter. For example, a random device identifier can be generated by the power receiver and transmitted to the power transmitter. Then, the power receiver can transmit the device identifier 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 identifier is long enough, it is extremely unlikely that a new power receiver will generate the same device identifier as an existing power receiver.

[0171] As described above, in many embodiments, the communication can be NFC communication, and the communication carrier signal can be an NFC carrier. In such embodiments, the identification message can be an NDEF message, and specifically an NDEF (NFC Data Exchange Format) static configuration message.

[0172] In this case, the identification message can specifically include an NDEF record, and the device identifier can be an NFC UID (User Identity). The UID is a number that is unique to the NFC device and cannot be deleted or changed.

[0173] Thus, specifically, the power transmitter can poll the power receiver during the standby phase by activating the communication carrier signal / NFC carrier, thereby implementing some power receiver operations. Device identification can be performed, for example, by reading the stored device identifier (such as the device UID or proprietary identification).

[0174] The power transmitter controller 203 is arranged to determine that a changed device identifier has been received and to continue initializing the power transfer operation in response to that detection.

[0175] In some embodiments, the power transmitter controller 203 can be arranged to store two device identifiers for the power receiver that exist at the start of the standby phase, where one of these device identifiers corresponds to no power transfer request, hereinafter referred to as the continuation device identifier, and one device identifier corresponds to a request for ongoing power transfer, hereinafter referred to as the power request device identifier. Then, the power transmitter controller 203 can compare the received device identifier of the identification message received during the standby phase with the stored device identifiers and proceed according to the result.

[0176] For example, in the case where the power receiver is assigned two device identifiers and the power transmitter knows these device identifiers, the power transmitter controller 203 can simply extract the device identifier from each identification message and compare it with the locally stored device identifier. If the extracted device identifier corresponds to the stored continuation device identifier, the power transmitter can continue with the operation suitable for the case where the power receiver remains in place and does not request power transfer. The power transmitter can, for example, continue to turn off the communication drive signal / communication carrier signal and terminate the communication time interval. It can set the time of the next communication time interval, indicating the time when the communication carrier signal is to be generated next. However, if the received device identifier matches the stored power request device identifier, the power transmitter controller 203 continues to initialize a new power transfer operation. If the received device identifier does not match any of the two stored device identifiers, the power transmitter can continue to modify the standby phase (and potentially subsequent power transfer operations) to reflect the presence of a new power receiver. In some cases, detecting a device identifier that does not match any device identifier associated with the power receiver of the previous power transfer phase may result in starting a new power transfer operation, but the initialization is adapted to reflect that it is for a new power receiver (e.g., performing a full configuration).

[0177] In some embodiments, the power receiver may be assigned two device identifiers that the power transmitter may know, for example, by being transmitted during a power transfer phase. These can then be stored separately as the continuation device identifier and the power request device identifier.

[0178] In other cases, the power request device identifier can be, for example, a predetermined device identifier. For example, the power transmitter controller 203 can store the predetermined device identifier corresponding to the power request, i.e., the power request device identifier can be a predetermined identifier. The predetermined device identifier can be common for different power receivers, while the continuation device identifier can be specific to an individual power receiver.

[0179] Thus, in some embodiments, the power transmitter controller 203 can compare the received device identifier with the stored device identifier for the power receiver, and if this is a match, it can continue without change. However, if the received device identifier corresponds to a predetermined power request device identifier (which can be common for different power receivers), the power transmitter controller 203 can initiate a power transfer operation. Similarly, if the received device identifier does not match any of these, the power transmitter can act appropriately for the presence of a new power receiver. The advantage of this method is that each power receiver can be assigned only one specific device identifier.

[0180] The power transmitter controller 203 may be arranged to compare the received device identifier with the device identifiers of previously received identification messages. For example, when first entering the standby phase, the device identifier of the first received identification message may be stored as a continuation device identifier. For subsequent identification messages, the device identifier is then compared with the continuation device identifier, and thus with the device identifier of the first received identification message in the standby phase. This method can be efficient and does not require any prior communication or determination of the device identifier associated with a particular power receiver.

[0181] In some embodiments, a continuation device identifier and / or a power request device identifier may be provided before entering the standby phase. For example, during a configuration phase of a previous power transfer initialization, and particularly during a power transfer initialization performed first for a given power receiver, the power receiver may report a device identifier that can be used as a continuation device identifier in a subsequent standby phase. The power transmitter may then store this device identifier as a continuation device identifier for later use. Similarly, in some embodiments, a power request device identifier may be provided and stored for potential subsequent standby phases.

[0182] The power receiver may specifically be arranged to change the device identifier in response to detecting a user input.

[0183] In many embodiments, the power receiver may include a user interface 315. Such a user interface may include user output devices, such as indicator lights, audio indicators, displays, etc. The user interface 315 may alternatively or additionally include user input devices, such as keyboards, voice recognition, user buttons, etc. In some embodiments, the user interface may simply consist of a single button.

[0184] The user interface 315 is coupled to an identification controller 315, which is arranged to detect the power for which the user has made a power request. The identification controller 315 may 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 button, the identification controller 315 may detect whether the user presses the button and regard this activation as a power request. In other embodiments, the user requesting power may enter, for example, via a keyboard or may make an oral statement that can be received via the user interface.

[0185] In response to detecting a power request and a user activation, the identification controller 315 may change the device identifier in the identification message to convey a request for power transfer to the power transmitter. Specifically, the identification controller 315 may generate an identification message in response to detecting a user activation, in which the device identifier indicating the power request is transmitted.

[0186] Thus, the method can allow for a highly reliable and secure standby phase from which power transfer can be easily and effectively re-initialized in response to a user providing a user input to the power receiver itself (e.g., simply pressing a button on the power receiver).

[0187] The user interface can specifically be a passive user interface and thus can specifically be a user interface that does not consume any power. Such a user interface can be implemented, for example, using a mechanical switch or button. The passive user interface can be implemented to minimize power consumption. It can be specifically arranged to ensure that no power needs to be extracted from the power receiver during the standby phase. It can specifically provide a continuous user interface where the user interface can always be interacted with by the user, regardless of or independent of when a communication carrier signal is present and when power can be provided. Thus, the operation of the user interface by the user can be at any time and is not affected by the burstiness of the communication carrier signal.

[0188] In many embodiments, such a passive user interface can be arranged to maintain a user activation indication for a duration exceeding a non-communication time interval and generally longer than the duration between two communication time intervals. In many embodiments, the user activation indication is maintained for a duration exceeding the duration of a repeating time frame.

[0189] In some embodiments, this can be achieved through a user input including, for example, a mechanical latching function. For example, a latching button can be used. In some cases, a mechanical activator with an instantaneous 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.

[0190] In such embodiments, the user interface can be activated at any time while allowing the circuit to detect the user activation, and in response, the adapted operation can be arranged to operate only during communication time intervals when a communication carrier signal is present and power can be extracted. For example, whenever a communication time interval is entered and a communication carrier signal is present, power can be extracted by the power extractor 311 and supplied to the second communicator 307 and the identification controller 315. The identification controller 315 can poll the user interface and select an appropriate device identification. For example, if no user activation corresponding to a power request is detected, the identification controller 315 selects the same device identification as in the previous message, otherwise it selects a different device identification (as described above) to indicate a request for a new power transfer to be initialized.

[0191] In many embodiments, the power receiver may not have any other power source other than the power delivery channel supplied by the power transmitter and may not have means for energy storage during non - communication time intervals in the standby phase. Thus, during at least a portion of the standby phase, the power receiver may be considered to be completely powered off. In such embodiments, the user interface may be passive and capable of maintaining a switched state (latching buttons and knobs, rotary switches) or ultra - low - power electronic circuits (e.g., bistable multivibrators).

[0192] In some embodiments, the identification controller 315 may be arranged to detect user activation in response to detecting that the settings of the user interface have changed and specifically have changed relative to the settings of the previous power transfer phase.

[0193] In some embodiments, the identification controller 315 may be arranged to store one or more settings of the user interface during the power transfer phase. For example, the setting of a switch may be stored. This may be done continuously throughout the power transfer phase, or may be done, for example, as part of the termination of the power transfer phase.

[0194] During the standby phase, the identification controller 315 may be arranged to compare the current setting(s) of the user interface with the stored settings. If a difference exists, the identification controller 315 may determine in response that a user activation has been performed. In some embodiments, any change may be considered a request for power transfer, and the identification controller 315 may change the device identification of the image data source 203 to indicate the power request to the power transmitter. In other embodiments, the identification controller 315 may determine whether a specific user interface setting has changed and change the device identification in response to that specific change.

[0195] In some embodiments, it may be advantageous if the power receiver compares the current user interface state / settings (e.g., rotary switch position) with the user interface state / settings that existed prior to entering the standby phase. In some embodiments, the power transmitter may transmit a message indicating that it is about to enter the standby phase, and in response, the power receiver may save the current user interface settings in non - volatile memory. This may facilitate operation and reduce the number of write cycles to the non - volatile memory. The stored user interface state is then compared with the actual user interface state during a polling interval that typically corresponds to the communication time interval. If a change in the user interface state is detected, the device identification of the identification message is changed to request initiation of a new power transfer.

[0196] Messages from the power transmitter may also be used by the power receiver to initiate standby phase operations of transmitting an identification message with the device identification during the communication time interval.

[0197] It should be understood that, for clarity, the above description has described embodiments of the present invention with reference to different functional circuits, units, and processors. However, it is obvious that any suitable functional distribution between different functional circuits, units, or processors may be used without departing from the present invention. For example, functions shown to be performed by separate processors or controllers may be performed by the same processor or controller. Thus, the reference to a particular functional unit or circuit is only considered as a reference to a suitable means for providing the said function, rather than indicating a strict logical or physical structure or organization.

[0198] The present invention may be implemented in any suitable form, including hardware, software, firmware, or any combination thereof. The present invention may optionally be implemented at least in part as computer software running on one or more data processors and / or digital signal processors. The elements and components of embodiments of the present invention may be physically, functionally, and logically implemented in any suitable manner. In fact, the functions may be implemented in a single unit, in multiple units, or as part of other functional units. Thus, the present invention may be implemented in a single unit, or may be physically and functionally distributed between different units, circuits, and processors.

[0199] Although the present invention has been described in connection with some embodiments, the present invention is not intended to be limited to the specific forms set forth herein. Instead, the scope of the present invention is limited only by the appended claims. Additionally, although features may seem to be described in connection with specific embodiments, those skilled in the art will recognize that the various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term includes the presence of other elements or steps without excluding them.

[0200] It should be understood that the reference to preferred values does not imply any limitation other than the values determined in the foreign object detection initialization mode, i.e., they are preferred as they are determined during the adaptation process. The reference to preferred values may be used in place of a reference to, for example, a first value.

[0201] In addition, although listed separately, multiple devices, elements, circuits or method steps can be implemented by, for example, a single circuit, unit or processor. In addition, although individual features can be included in different claims, these features may be advantageously combined, and being included in different claims does not mean that the combination of features is not feasible and / or advantageous. Moreover, including features in a category of claims does not mean a limitation to the category, but rather indicates that the feature is equally applicable to other claim categories. In addition, the order of features in the claims does not imply any specific order in which the features must work, and in particular, the order of the individual steps in the method claims does not imply that the steps must be performed in that order. On the contrary, the steps can be performed in any suitable order. In addition, singular references do not exclude multiples. Therefore, references to "one", "one", "first", "second", etc. do not exclude multiples. The figure marks in the claims are provided only as clarification examples and should not be interpreted as limiting the scope of the claims in any way.

[0202] In general, examples of a power transmitter and an operating method thereof, a power receiver and an operating method thereof, and a wireless power transmission system (and an operating method thereof) are indicated by the following embodiments.

[0203] Example:

[0204] Embodiment 1. A power transmitter (101) for wirelessly providing power to a power receiver (105) via an inductive power transfer signal, the power transmitter (101) comprising:

[0205] a power transfer coil (103) arranged to generate said power transfer signal;

[0206] a power transmission driver (201) arranged to generate a power transmission drive signal for the power transmission coil (103), the power transmission driver (201) being arranged to generate the power transmission drive signal during a power transmission phase;

[0207] a communication coil (207) arranged to generate a communication carrier signal;

[0208] A communication driver (209) arranged to generate a communication drive signal for the communication coil to generate the communication carrier signal, the communication driver (209) being arranged to generate the communication drive signal to employ a repeating time frame during a standby phase in the absence of a power transfer signal, each repeating 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;

[0209] A communication unit (205) arranged to receive, during the standby phase, an identification message that is load-modulated onto the communication carrier signal during a communication time interval, each identification message in the identification messages including a device identification for the power receiver;

[0210] A phase controller (203) arranged to switch the power transmitter from the power transfer phase to the standby phase in response to termination of power transfer, and to initiate a transition from the standby phase to the power transfer phase in response to detecting a first identification message including an altered device identification.

[0211] Example 2. The power transmitter according to Example 1, wherein the phase controller (203) is arranged to detect the altered device identification in response to a comparison of the device identification of the first identification message with the device identification of a second identification message received before the first identification message.

[0212] Example 3. The power transmitter according to Example 1 or 2, wherein the phase controller (203) is arranged to detect the altered device identification in response to a comparison of the device identification of the first identification message with a predetermined device identification.

[0213] Example 4. The power transmitter according to any of the foregoing examples, wherein the phase controller (203) is arranged to detect the altered device identification in response to a comparison of the device identification of the first identification message with the device identification of an identification message received from the power receiver (105) before entering the standby phase.

[0214] Example 5. The power transmitter according to any of the foregoing examples, wherein the phase controller (203) is arranged to: store configuration parameters for the power receiver (105) when entering the standby phase; retrieve the configuration parameters as part of the transition from the standby phase to the power transfer phase; and determine operating parameters for the power transfer phase based on the configuration parameters.

[0215] Example 6. The power transmitter according to any of the preceding embodiments, wherein the communication carrier signal is a Near Field Communication (NFC) carrier.

[0216] Example 7. The power transmitter according to any of the preceding embodiments, wherein the identification message is a Near Field Communication (NFC), NFC Data Exchange Format (NDEF) configuration message.

[0217] Example 8. The power transmitter according to any of the preceding embodiments, wherein the repetition time frame has a duration of not less than 50 milliseconds and not more than 10 seconds.

[0218] Example 9. The power transmitter according to any of the preceding embodiments, wherein the power transmitter controller 203 is arranged to adapt the operation of the power transfer phase initialization process in response to detecting the changed identification.

[0219] Example 10. A power receiver (105) for wirelessly receiving power from a power transmitter (101) via an electromagnetic power transfer signal, the power receiver (105) comprising:

[0220] An inductive power extraction element (107) arranged to extract power from the power transfer signal during a power transfer phase;

[0221] A communication coil (309) for receiving a communication carrier signal; the communication drive signal adopts a repetition time frame during a standby phase in the absence of the power transfer signal, each repetition 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;

[0222] A communication unit (307) arranged to transmit an identification message by load modulation of the communication carrier signal during the communication time interval during the standby phase, each identification message in the identification messages including a device identification for the power receiver (105);

[0223] A power extractor (311) coupled to the communication coil (309) and arranged to extract a power supply signal from the communication coil (309) and supply power to the circuit (313) of the communication unit during the communication time interval; and

[0224] A controller (315) arranged to change a device identifier for a first identification message relative to a device identifier of a previous identification message in response to detecting a power request, the power request being an indication of a request to initiate a power transfer phase.

[0225] Example 11. The power receiver (105) according to Example 10 further includes a user interface (317), and the controller (315) is arranged to detect the power request in response to detecting a user activation of the user interface (317).

[0226] Example 12. The power receiver (105) according to Example 11, wherein the user interface is a passive user interface arranged to maintain an indication of the user activation for a duration exceeding a non - communication time interval.

[0227] Example 13. The power receiver (105) according to any one of the previous Examples 10 - 12, wherein the controller is arranged to: store a first user interface setting for the 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.

[0228] Example 14. The power receiver (105) according to any one of the previous Examples 10 - 13, wherein the controller is arranged to be powered only by the power supply signal during a communication time interval.

[0229] Example 15. A wireless power transfer system including a power transmitter (101) according to any one of Examples 1 - 9 and a power receiver (105) according to Examples 10 - 14.

[0230] Example 16. A method of operating a power transmitter (101) that wirelessly provides power to a power receiver (105) via an inductive power transfer signal, the power transmitter (101) including:

[0231] A power transfer coil (103) arranged to generate the power transfer signal; and

[0232] A communication coil (207) arranged to generate a communication carrier signal;

[0233] And the method further includes:

[0234] Generating a power transfer drive signal for the power transfer coil (103) during a power transfer phase;

[0235] Generate a communication drive signal for the communication coil to generate the communication carrier signal, and generate the communication drive signal to adopt a repetitive time frame during a standby phase in the absence of a power transfer signal. Each repetitive time frame includes a communication time interval and a non-communication time interval. The duration of the communication time interval does not exceed 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 does not exceed 10% of the power level of the communication drive signal during the communication time interval;

[0236] During the standby phase, receive an identification message that is load-modulated onto the communication carrier signal during a communication time interval. Each identification message in the identification messages includes a device identification for the power receiver;

[0237] Switch the power transmitter from the power transfer phase to the standby phase in response to the termination of power transfer; and

[0238] In response to detecting a first identification message including the changed device identification, initialize the transition from the standby phase to the power transfer phase.

[0239] Example 17. A method of operating a power receiver (105) for wirelessly receiving power from a power transmitter (101) via an electromagnetic power transfer signal. The power receiver (105) includes:

[0240] An inductive power extraction element (107) arranged to extract power from the power transfer signal during a power transfer phase; and the method includes:

[0241] A communication coil (309) receives a communication carrier signal; the communication drive signal adopts a repetitive time frame during a standby phase in the absence of a power transfer signal. Each repetitive time frame includes a communication time interval and a non-communication time interval. The duration of the communication time interval does not exceed 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 does not exceed 10% of the power level of the communication drive signal during the communication time interval;

[0242] During the standby phase, transmit an identification message by load-modulating the communication carrier signal during a communication time interval. Each identification message in the identification messages includes a device identification for the power receiver (105);

[0243] Extract a power supply signal from the communication coil (309);

[0244] Power the circuitry (313) of the communication unit via the power signal during the communication time interval; and

[0245] In response to detecting a power request, change the device identifier for a first identification message relative to the device identifier of a previous identification message, the power request being an indication of a request to initiate a power transfer phase.

[0246] More specifically, the invention is defined by the appended claims.

Claims

1. A power transmitter (101) for wirelessly providing power to a power receiver (105) via an inductive power transfer signal, the power transmitter (101) comprising: A power transfer coil (103) arranged to generate the power transfer signal; A power transfer driver (201) arranged to generate a power transfer drive signal for the power transfer coil (103), the power transfer driver (201) being arranged to generate the power transfer drive signal during a power transfer phase; A communication coil (207) arranged to generate a communication carrier signal; A communication driver (209) arranged to generate a communication drive signal for the communication coil to generate the communication carrier signal, the communication driver (209) being arranged to generate the communication drive signal to employ a repeating time frame during a standby phase in which there is no power transfer signal, each repeating 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; A communication unit (205) arranged to repeatedly receive, during the standby phase, identification messages load-modulated onto the communication carrier signal during communication time intervals, each of the identification messages including a device identification for the power receiver; A phase controller (203) arranged to switch the power transmitter from the power transfer phase to the standby phase in response to power transfer termination; And Wherein the phase controller is arranged to compare a first device identification, which is the device identification of a first identification message, with a second device identification, which is the device identification of a second identification message received from the power receiver before the first identification message, and to remain in the standby phase if the first device identification matches the second device identification, and to initiate a transition from the standby phase to the power transfer phase in response to detecting that the first device identification does not match the second device identification.

2. The power transmitter according to claim 1, wherein, The second identification message is received in the same standby phase as the first identification message.

3. The power transmitter according to claim 1 or 2, wherein The second device identification is the device identification of a power receiver that received power during a power transfer phase immediately preceding the standby phase.

4. The power transmitter according to any one of the preceding claims, wherein, The second identification message is received from the power receiver (105) before entering the standby phase.

5. The power transmitter according to any one of the preceding claims, wherein, The phase controller (203) is arranged to store configuration parameters for the power receiver (105) upon entering the standby phase; retrieve the configuration parameters as part of the transition from the standby phase to the power transfer phase; and determine operating parameters for the power transfer phase based on the configuration parameters.

6. The power transmitter according to any one of the preceding claims, wherein, The communication carrier signal is a near field communication NFC carrier.

7. The power transmitter according to any one of the preceding claims, wherein, The identification message is a Near Field Communication (NFC), NFC Data Exchange Format (NDEF) configuration message.

8. The power transmitter according to any one of the preceding claims, wherein, The repetition time frame has a duration of not less than 50 milliseconds and not greater than 10 seconds.

9. The power transmitter according to any one of the preceding claims, wherein, The power transmitter controller (203) is arranged to adapt the operation of the power transfer phase initialization process in response to detecting a changed identification.

10. A power receiver (105) for wirelessly receiving power from a power transmitter (101) via an electromagnetic power transfer signal, the power receiver (105) comprising: An inductive power extraction element (107) arranged to extract power from the power transfer signal during a power transfer phase; A communication coil (309) for receiving a communication carrier signal; the communication drive signal adopts a repetition time frame during a standby phase in the absence of the power transfer signal, each repetition 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; A communication unit (307) arranged to transmit an identification message during the standby phase by load modulation of the communication carrier signal during the communication time interval, each identification message in the identification messages including a device identification for the power receiver (105); A power extractor (311) coupled to the communication coil (309) and arranged to extract a power supply signal from the communication coil (309) and supply power to a circuit (313) of the communication unit during the communication time interval via the power supply signal; And A controller (315) arranged to change the device identification for a first identification message relative to the device identification of a previous identification message in response to detecting a power request, the power request being an indication of a request to initiate a power transfer phase.

11. The power receiver (105) according to claim 10, further comprising a user interface (317), and the controller (315) is arranged to detect the power request in response to detecting a user activation of the user interface (317).

12. The power receiver (105) according to claim 11, wherein, The user interface is a passive user interface arranged to maintain a user activation indication of the user activation for a duration exceeding the duration of the non-communication time interval.

13. The power receiver (105) according to any one of the preceding claims 10 - 12, wherein, The controller is arranged to: store a first user interface setting of a power transfer phase before entering the 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. The power receiver (105) according to any one of the preceding claims 10-13, wherein, The controller is arranged to be powered only by the power supply signal during the communication time interval.

15. A wireless power transfer system includes a power transmitter (101) according to any one of claims 1 to 9 and a power receiver (105) according to any one of claims 10 to 14.

16. A method of operating a power transmitter (101) that wirelessly provides power to a power receiver (105) via an inductive power transfer signal, the power transmitter (101) including: A power transfer coil (103) arranged to generate the power transfer signal; And A communication coil (207) arranged to generate a communication carrier signal; And the method further includes: 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 the communication carrier signal, generating the communication drive signal to employ a repeating time frame during a standby phase in which there is no power transfer signal, each repeating 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, during the standby phase, identification messages that are load modulated onto the communication carrier signal during communication time intervals, each identification message including a device identification for the power receiver; Switching the power transmitter from the power transfer phase to the standby phase in response to termination of power transfer; and Comparing a first device identification that is the device identification of a first identification message with a second device identification that is the device identification of a second identification message received from the power receiver before the first identification message, and if the first device identification matches the second device identification, remaining in the standby phase and initializing a transition from the standby phase to the power transfer phase in response to detecting that the first device identification does not match the second device identification.

17. A method of operating a power receiver (105) that wirelessly receives power from a power transmitter (101) via an electromagnetic power transfer signal, the power receiver (105) including: An inductive power extraction element (107) arranged to extract power from the power transfer signal during a power transfer phase; And the method includes: A communication coil (309) receives a communication carrier signal; the communication drive signal employs a repeating time frame during a standby phase in which there is no power transfer signal, each repeating 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; During the standby phase, an identification message is transmitted by load modulation of the communication carrier signal during a communication time interval, and each identification message in the identification messages includes a device identification for the power receiver (105); Extract a power supply signal from the communication coil (309); During the communication time interval, supply power to the circuit (313) of the communication unit through the power supply signal; and In response to detecting a power request, change the device identification for the first identification message relative to the device identification of the previous identification message, where the power request is an indication of a request to initiate a power transfer phase.

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