Wireless Power Transmission

Abstract

A power receiver for a wireless power transmitter transmits (703) a request for a power transfer phase while the power receiver is in a load state in which the load is disconnected from the power receiving coil 107. Upon receiving (705) the request, the power transmitter proceeds to measure (707) power transfer parameters, after which an acknowledgment is sent (709) and received (711) by the power receiver 105. In response, the power receiver proceeds to change (713) to a new load state in which the load is connected to the power receiving coil 107. The power receiver transmits (715) a second request, which, upon receiving (717), causes the power receiver to perform another measurement of the power transfer parameters, and power transfer is initiated (721) in response to the measurement results. Improved initialization of the power transfer phase is provided.

Description

[Technical Field]

[0001] The present invention relates to wireless power transfer systems, and particularly, but not exclusively, to the operation of power transmitters to provide inductive power transfer to high power devices such as kitchen appliances. [Background technology]

[0002] Most current electrical products require dedicated electrical contacts to receive power from an external power source. However, this tends to be impractical, requiring the user to physically insert a connector or otherwise establish physical electrical contact. Power requirements also typically vary widely, and currently most devices are provided with dedicated power sources, resulting in a typical user having numerous different power sources, each dedicated to a specific device. However, while the use of an internal battery can avoid the need for a wired connection to a power source during use, this only provides a partial solution, as the battery requires recharging (or replacement). Additionally, using a battery can substantially increase the weight and potential cost and size of the device.

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

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

[0005] Such a configuration allows for wireless power transmission to a device without the need for a wired or physical electrical connection. Indeed, a device can simply be placed adjacent to or on top of the transmitter coil for external recharging or powering. For example, the power transmitter can be configured to have a horizontal surface onto which a device can simply be placed to receive power.

[0006] Furthermore, such wireless power transmission configurations can be advantageously designed so that the power transmitter can be used with a range of power receiving devices. In particular, a wireless power transmission approach known as the Qi standard has been defined and is currently being further developed. This approach allows power transmitter devices that meet the Qi standard to be used with power receiver devices that meet the Qi standard, without the need for them to be from the same manufacturer or proprietary to each other. The Qi standard also includes several features that allow operation to be tailored to specific power receiving devices (e.g., depending on a specific power drain).

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

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

[0009] EP 3 661 015 A1 discloses an example of a wireless power transmission system that includes functionality for detecting nearby foreign objects.

[0010] A wide variety of power transmitters and receivers exist. For example, coil sizes, induction values, and loads vary widely, and therefore system parameters and power transfer operating parameters can vary significantly depending on the particular device and mechanical configuration. Additionally, the placement of the power receiver relative to the power transmitter can change the coupling and therefore the power transfer characteristics.

[0011] Additionally, the power receiver may have several modes in which it operates, for example, several loads may be switched on and off. As an example, in a typical air fryer appliance powered by wireless power transmission, the heating element is turned on and off, resulting in a load that varies between typical values of about 50 to about 1200 W. This switching is repeated during operation in order for the air fryer to maintain a substantially constant temperature of the heating element.

[0012] Also, the power transfer can include nonlinear loads, for example, instead of resistive components, the powered device can include a motor (e.g., a food processor). This typically results in a completely different response of the system, which can have significant implications for control system design.

[0013] Power transfer systems typically use a control loop to ensure the correct operating point is reached. This control loop varies the amount of power transferred to the power receiver. The received power (or voltage or current) can be measured by the power receiver and compared to a desired value to generate an error signal. The power receiver can then send this error signal to a power control function in the power transmitter, which can dynamically adapt the generated power transfer signal to attempt to reduce the static error to zero.

[0014] A key challenge for wireless power transfer systems is ensuring efficient and reliable initialization of power transfer operations. For example, reaching a desired operating point by allowing a control loop to adapt power transfer operations is typically a slow process that tends to introduce substantial delays in power delivery. This can result in a noticeable delay before a powered device, such as an electrically powered machine, can start up.

[0015] Other challenges include that power transfer should be initiated safely and with minimal risk of creating unacceptable operating conditions. Furthermore, it is desirable that power transfer be initiated quickly with as little delay as possible, and with low complexity and reduced communication overhead.

[0016] Therefore, the transition to the power transfer phase is quite difficult and is a challenging process that requires several actions to be performed and specific conditions to be met before power transfer can begin. Current approaches are not optimal and tend to not provide ideal performance. Summary of the Invention [Problem to be solved by the invention]

[0017] Therefore, improved power transfer operation would be advantageous, and in particular, an approach that allows for increased flexibility, reduced cost, reduced complexity, improved operation, more accurate power transfer operation, more flexible power transfer, improved suitability for the transfer of higher power levels, improved and / or expedited power transfer initialization, and / or improved performance. [Means for solving the problem]

[0018] Accordingly, the Invention seeks to preferably mitigate, reduce or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0019] According to one aspect of the present invention, there is provided a method for initiating power transmission in a wireless power transmission system including a power transmitter that transmits power to a power receiver using a power transmission signal that induces a current in a power receiving coil of the power receiver, the method comprising the steps of: the power receiver transmitting a first request to the power transmitter in a non-power transmission phase, the first request being a request to transition from the non-power transmission phase to a power transmission phase; the power receiver operating in a first load state after transmitting the first request, wherein the load of the power receiver is decoupled from the power receiving coil when the power receiver is operating in the first load state; the power transmitter receiving the first request; the power transmitter performing a first measurement of a first power transmission parameter in response to receiving the first request; the power transmitter transmitting a first acknowledgement to the power receiver after the first measurement; the power receiver receiving the first acknowledgement; and the power receiver switching to a second load state in response to receiving the first acknowledgement. The method includes the steps of: a load of the power receiver being coupled to the power receiving coil when the power receiver is operating in a second load state; the power receiver transmitting a second request to the power transmitter in association with entering the second load state, the second request being a request for power; the power transmitter receiving the second request; the power transmitter performing a second measurement of a second system parameter in response to receiving the second request; and the power transmitter entering a power transfer phase in which the power transmitter generates a power transmission signal depending on the first and second measurements.

[0020] The present invention can provide improved and / or accelerated performance and / or operation and / or implementation of wireless power transfer operations and systems. The approach can provide improved transition to and initialization of power transfer. In many scenarios, it can ensure safer and / or more reliable initialization and start-up of power transfer.

[0021] A non-power transfer phase is a phase that is not a power transfer phase. The power of the power transfer signal can be limited to a lower value in the non-power transfer phase than in the power transfer phase, and typically the maximum power level in the non-power transfer phase can be no more than 1%, 5%, 10%, or 25% of the maximum power level in the power transfer phase in many embodiments.

[0022] The power transmitter enters a power transfer phase in which it generates a power transfer signal dependent on the measurement of the first power transfer parameter and the measurement of the second power transfer parameter, in that it enters a power transfer phase in which it generates a power transfer signal dependent on the measured value of the first power transfer parameter and the measured value of the second power transfer parameter.

[0023] The first load condition may also be referred to as a non-load coupled condition or an unloaded condition. The first measurement may also be referred to as a load-separated measurement. The second load condition may also be referred to as a load coupled condition or a loaded condition. The second measurement may also be referred to as a load coupled measurement.

[0024] The power receiver can be configured to operate in a second / loaded state in which a load is connected to the power path of the input resonant circuit, and in a first / unloaded state in which the load is disconnected from the power path of the input resonant circuit.

[0025] The second request is a request for power in that it is a request to initiate the power transfer phase.

[0026] According to an optional feature of the invention, the power receiver is configured to include at least one requested power transfer parameter in the second request, and the power transmitter is configured to set at least one parameter of the power transfer signal in response to the requested power transfer parameter.

[0027] This can provide improved performance in many embodiments and scenarios: it allows for improved initialization of the power transfer phase with an initial operating point that may be closer to the desired / optimal operating point.

[0028] The characteristic may specifically be an initial characteristic of the power transfer phase when entering the power transfer phase.

[0029] According to an optional feature of the invention, the power transmitter is configured to generate the transmission signal to have a characteristic that depends on at least one of the first measurement and the second measurement.

[0030] This can provide improved performance in many embodiments and scenarios: it allows for improved initialization of the power transfer phase with an initial operating point that can be closer to the desired / optimal operating point.

[0031] The characteristic may specifically be an initial characteristic of the power transfer phase when entering the power transfer phase.

[0032] According to an optional feature of the invention, the power transmitter performs foreign object detection based on the first measurement and terminates initiating power transmission if the foreign object detection indicates the presence of a foreign object.

[0033] This approach can provide a more reliable and improved initialization of the power transfer phase, which can provide improved risk mitigation and / or reduction for the presence of foreign objects.

[0034] In accordance with an optional feature of the invention, the power transmitter performs foreign object detection based on the second measurement and terminates initiating power transmission if the foreign object detection indicates the presence of a foreign object.

[0035] This approach can provide a more reliable and improved initialization of the power transfer phase, which can provide improved risk mitigation and / or reduction for the presence of foreign objects.

[0036] According to an optional feature of the invention, the power transmitter is configured to transmit a second acknowledgement of power reception following the second measurement and before entering the power transmission phase.

[0037] This can provide improved performance in many embodiments and scenarios.

[0038] According to an optional feature of the invention, the power transmitter is configured to generate the power transmission signal during the power transmission phase with a maximum delay of up to 20 msec from transmitting the second acknowledgement.

[0039] This can provide improved performance in many embodiments and scenarios.

[0040] In accordance with an optional feature of the invention, the power transmitter is configured to synchronize the start of a power transmission phase with the timing of a cycle of a power supply signal to the power transmitter.

[0041] This can provide improved performance in many embodiments and scenarios.

[0042] In some embodiments, the power transmitter can be configured to synchronize the start of the power transmission phase with the timing of a cycle of the main power supply to the power transmitter.

[0043] In some embodiments, the power transmitter is configured to align the start of the power transmission phase with the timing of a cycle of a power supply signal to the power transmitter.

[0044] In some embodiments, the power transmitter can be configured to align the start of the power transfer phase with the timing of a cycle of the main power supply to the power transmitter.

[0045] According to an optional feature of the invention, the power transmitter is configured to terminate the initiation of power transmission if the second request is not received before the expiration of a predetermined time interval.

[0046] This can provide improved performance in many embodiments and scenarios.

[0047] In accordance with an optional feature of the invention, the power transmitter is configured to transmit a negative acknowledgement message to the power receiver in response to completion of the initiation of power transmission.

[0048] This can provide improved performance in many embodiments and scenarios.

[0049] According to one aspect of the invention, the load is at least a 10, 20, 50, 100, 500 or 1000 watt load, which can provide improved performance in many embodiments and scenarios.

[0050] According to one aspect of the present invention, there is provided a method for a power receiver to initiate power transmission in a wireless power transmission system including a power transmitter that transmits power to the power receiver using an inductive power transmission signal that induces a current in a power receiving coil of the power receiver, the method comprising the steps of: sending a first request to the power transmitter in a non-power transfer phase, the first request being a request to transition from the non-power transmission phase to a power transmission phase; operating in a first load state after sending the first request, wherein when the power receiver is operating in the first load state, the load of the power receiver is decoupled from the power receiving coil; receiving a first acknowledgement from the power transmitter; and switching to a second load state in response to receiving the first acknowledgement, wherein when the power receiver is operating in the second load state, the load of the power receiver is coupled to the power receiving coil; sending a second request to the power transmitter in connection with entering the second load state, the second request being a request for power; and entering a power transfer phase in which power is extracted by the power receiver from the power transmission signal.

[0051] According to one aspect of the present invention, a power transmitter method of initiating power transmission in a wireless power transmission system in which the power transmitter transmits power to a power receiver using an inductive power transmission signal includes the steps of receiving a first request to transition from a non-power transmission phase to a power transmission phase, performing a first measurement of a first power transmission parameter in response to receiving the first request, and sending a first acknowledgment to the power receiver following the first measurement, receiving a second request for power indicating that the power receiver has switched from a first load state to a second load state, the load being decoupled from the power receiving coil of the power receiver in the first load state and coupled to the power receiving coil in the second load state, performing a second measurement of a second system parameter in response to receiving the second request, and entering the power transmission phase generating a power transmission signal depending on the first and second measurements.

[0052] According to one aspect of the present invention, there is provided a power receiver for a wireless power transfer system including a power transmitter that transfers power to a power receiver using an inductive power transfer signal, the power receiver having a power receiving coil configured to extract power from the power transfer signal by induction, a first transmitter configured to transmit a first request to the power transmitter during a non-power transfer phase, the first request being a request to transition from the non-power transfer phase to a power transfer phase, a mode processor configured to control the power receiver to operate in a first load state after transmitting the first request, wherein a load of the power receiver is decoupled from the power receiving coil when the power receiver is operating in the first load state, and a receiver configured to receive a first acknowledgement from the power transmitter, the mode processor further configured to control the power receiver to switch to a second load state in response to receiving the first acknowledgement, the load of the power receiver being coupled to the power receiving coil when the power receiver is operating in the second load state, and the transmitter configured to transmit a second request to the power transmitter in connection with entering the second load state. The second request is a request for power, and the power receiver further comprises a controller configured to enter a power transfer phase in which power is extracted by the power receiver from the power transfer signal.

[0053] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief explanation of the drawings]

[0054] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which: [Figure 1] FIG. 2 illustrates an example of elements of a power transfer system according to some embodiments of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of an equivalent circuit of the power transmission system of FIG. 1. [Figure 3] FIG. 2 illustrates an example of elements of a power transmitter according to some embodiments of the present invention. [Figure 4] FIG. 1 illustrates an example of a half-bridge inverter for a power transmitter. [Figure 5] FIG. 1 illustrates an example of a full-bridge inverter for a power transmitter. [Figure 6] FIG. 2 illustrates an example of elements of a power receiver according to some embodiments of the present invention. [Figure 7] 10A-10C illustrate examples of power transfer phase operation and specific initialization methods according to some embodiments of the present invention. [Figure 8] 4A-4C illustrate examples of power transfer signals during power transfer phase initialization according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0055] The following description focuses on embodiments of the invention applicable to wireless power transfer systems that utilize power transfer approaches such as those known from the Qi or Ki standards, however, it will be understood that the invention is not limited to this application and may be applied to many other wireless power transfer systems.

[0056] 1 illustrates an example of a power transfer system according to some embodiments of the present invention. The power transfer system includes a power transmitter 101 including (or coupled to) a transmitter coil / inductor 103. The system further includes a power receiver 105 including (or coupled to) a receiver coil / inductor 107.

[0057] The system provides an inductive electromagnetic signal capable of inductively transferring power from a power transmitter 101 to a power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal, which is propagated as magnetic flux by a transmitter coil or inductor 103. The electromagnetic signal is a signal generated by the transmitter coil 103 in response to a drive signal provided to the transmitter coil 103. During power transfer, the electromagnetic signal transfers power to the power receiver 105 (specifically, the receiver coil) and is hereinafter referred to as a power transfer signal. More generally, the term power transfer signal may refer to any electromagnetic signal / field generated by the transmitter coil 103 (including both during the power transfer phase and outside of the power transfer phase, such as during a standby / off / connected phase, and including signals / fields generated not for the specific purpose of powering a power receiver load, for example, for performing measurements, communicating, or providing standby power).

[0058] The power transmission signal may typically have a frequency between about 20 kHz and about 500 kHz, typically in the range of 95 kHz to 205 kHz for Qi-compatible systems, and typically in the range of 20 kHz to 80 kHz for Ki-compatible systems. The transmitter coil 103 and the receiving coil 107 are loosely coupled, and thus the receiving coil 107 picks up (at least a portion of) the power transmission signal from the power transmitter 101. Thus, power is transmitted from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the receiving coil 107. While the term power transmission signal is primarily used to refer to the induction signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the receiving coil 107, it will be understood that it may equally be considered and used to refer to an electrical signal supplied to the transmitter coil 103 or picked up by the receiving coil 107.

[0059] In an embodiment, power receiver 105 is specifically a power receiver that receives power via receiver coil 107. However, in other embodiments, power receiver 105 may include a metallic element, such as a metallic heating element, where the power transmission signal directly induces eddy currents that result in direct heating of the element.

[0060] The system is configured to transmit substantial power levels, and specifically, the power transmitter, in many embodiments, can support power levels of 500 mW, 1 W, 5 W, 50 W, 100 W, or greater than 500 W. For example, for Qi-enabled applications, power transmission can typically range from 1 to 5 W for low-power applications (basic power profile), up to 15 W for Qi standard version 1.2, up to 100 W for high-power applications such as power tools, laptops, drones, robots, etc., and powers greater than 100 W or even greater than 2000 W for very high-power applications such as kitchen applications.

[0061] The operation of power transmitter 101 and power receiver 105 is described below with particular reference to embodiments that generally conform to the Qi or Ki standard (except for the modifications and extensions described (or resulting from) herein) or are suitable for higher power kitchen specifications being developed by wireless power consortia. In particular, power transmitter 101 and power receiver 105 may conform to or be substantially compatible with elements of Qi standard version 1.0, 1.1, or 1.2 (except for the modifications and extensions described (or resulting from) herein).

[0062] Many wireless power transfer systems, particularly 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 may be a series resonant circuit, such that the transmitter coil 103 and receiver coil 107 may be coupled in series with corresponding resonant capacitors. The use of a resonant circuit tends to provide more efficient power transfer.

[0063] In most power transmission systems, before power transmission begins, a communication channel is established between the power transmitter 101 and the power receiver 105. Once communication is set up and identification of the two devices is achieved, the power transmitter 101 can begin transmitting power to the power receiver 105.

[0064] FIG. 2 shows an example of an electrical equivalent diagram of the power transfer function of the power transmitter 101 and power receiver 105. Various power transmitters and receivers may be present in a given system, and these may have significantly different characteristics and parameters. For example, coil size, induction, and load may vary significantly. Thus, system parameters may in practice vary significantly between different devices, mechanical configurations, positioning, etc., as specifically shown in FIG. 2. In particular, the placement of the power receiver, and therefore the relative positions of the receiver coil 107 and transmitter coil 103, may substantially affect the coupling between the coils, i.e., the primary (transmitting) inductor Lp and the secondary (transmitting) inductor Ls, and therefore significantly change system behavior.

[0065] Additionally, the power receiving device may have several different modes, for example, operating at different voltage levels (5V, 12V, 20V) to power a load.

[0066] Typically, wireless power transfer systems use a power control loop to steer the system toward a suitable operating point. This power control loop varies the amount of power transmitted from the power transmitter to the power receiver. The received power (or voltage or current) can be measured, and an error signal can be generated depending on the set power value. The device sends this error signal to the power control function of the power transmitter, reducing this static error, ideally to zero.

[0067] However, system performance and operation vary greatly depending on the combination and placement of existing power transmitters and receivers, and therefore the appropriate operating point, including the conditions at the start / initialization of power transfer.

[0068] FIG. 3 shows elements of the power transmitter 101 of FIG. 1 in more detail.

[0069] The power transmitter 101 includes a driver 301 capable of generating a drive signal that is supplied to a power transmitter coil 103, which in return generates an electromagnetic power transmission signal, thereby providing power transmission to a power receiver 105. The transmitter coil 103 is part of an output resonant circuit that includes the transmitter coil 103 and a capacitor 303. In this example, the output resonant circuit is a series resonant circuit, although it will be understood that in other embodiments the output resonant circuit can be a parallel resonant circuit. It will be understood that any suitable resonant circuit may be used, including one that includes multiple inductors and / or capacitors.

[0070] The driver 301 generates the current and voltage supplied to the output resonant circuit and thus to the transmitter coil 103. The driver 301 is typically a drive circuit in the form of an inverter that generates an AC signal from a DC voltage. The output of the driver 301 is typically a switch bridge that generates the drive signal by appropriate switching of the switches of the switch bridge. Figure 4 shows a half-bridge switch bridge / inverter. Switches S1 and S2 are controlled so that they are never closed simultaneously. Alternately, S1 is closed while S2 is open, and S2 is closed while S1 is open. The switches are opened and closed at a desired frequency, thereby generating an AC signal at the output. Typically, the inverter output is connected to the transmitter inductor via a resonant capacitor. Figure 5 shows a full-bridge switch bridge / inverter. Switches S1 and S2 are controlled so that they are never closed simultaneously. Switches S3 and S4 are controlled so that they are never closed simultaneously. Alternately, switches S1 and S4 are closed while S2 and S3 are open, and switches S2 and S3 are closed while S1 and S4 are open, thereby producing a square wave signal at the output. The switches are opened and closed at the desired frequency.

[0071] The power transmitter 101 further includes a power transmitter controller 305 configured to control the operation of the power transmitter 101 according to a desired operating principle. Specifically, the power transmitter 101 may include many of the functions necessary to perform power control according to the Qi or Ki standards.

[0072] The power transmitter controller 305 is particularly configured to control the generation of the drive signal by the driver 301 and is particularly able to control the power level of the drive signal and therefore the level of the generated power transmission signal. The power transmitter controller 305 comprises a power loop controller that controls the power level of the power transmission signal in response to power control messages received from the power receiver 105 during the power transfer phase.

[0073] The power transmitter controller 305 may further comprise a communicator 307 for communicating with the power receiver 105. For example, the communicator 307 may control the driver 301 / power transmitter controller 305 to transmit data to the power receiver 105 by modulating the power transmission signal, and may receive data from the power receiver 105 by detecting load modulation of the power transmission signal. It will be understood that in other embodiments, other communication means may be used, such as, for example, a separate communication function may be implemented, such as NFC communication.

[0074] The use of a resonant circuit that includes the transmitter coil 103 is well known to provide more efficient power transfer in many scenarios, allowing for control of the power transfer by the frequency of the drive signal. Furthermore, having a power receiver that also uses a resonant circuit, i.e., the receiver coil is part of the resonant circuit, results in resonant power transfer, which allows for very efficient power transfer.

[0075] FIG. 6 shows some exemplary elements of the power receiver 105.

[0076] The receiver coil 107 is coupled to the power receiver controller 601 via a capacitor 603 which forms an input resonant circuit with the receiver coil 107. Thus, the power transfer is a resonant power transfer between resonant circuits.

[0077] The power receiver controller 601 couples the receiver coil 107 to the load 605, particularly via a switch 607 that can connect and disconnect (or short) the load 605. The power receiver controller 601 includes a power control path that converts the power extracted by the receiver coil 107 into a supply suitable for the load 605. In some embodiments, the power receiver controller 601 can provide a direct power path that simply connects / couples the input resonant circuit to the switch 607 or the load 605, i.e., the power path of the power receiver controller 601 can be implemented by simply two wires. In other embodiments, the power path can include, for example, a rectifier and possibly a smoothing capacitor to provide a DC voltage. In still other embodiments, the power path can include more complex functionality, such as, for example, a voltage control circuit, an impedance matching circuit, a current control circuit, etc. Similarly, it will be understood that the switch 607 may only be present in some embodiments, and that in some embodiments the load 605 may be permanently coupled to the input resonant circuit.

[0078] Additionally, the power receiver controller 601 may include various power receiver controller functions required to perform power transfer, particularly functions required to perform power transfer according to the Qi or Ki standards.

[0079] The power receiver controller 601 may further comprise a communicator 609 for communicating with the power transmitter 101. For example, it may be configured to decode and demodulate data modulated onto the power transmission signal and to transmit data to the power transmitter 101 by load modulating the power transmission signal. In some embodiments, a separate communication function, such as an NFC communication function, may be employed.

[0080] During operation, the system is configured to control the drive signal such that the power transmission signal achieves appropriate operating parameters / characteristics and the power transmission operates at an appropriate operating point. To do so, the power transmitter is configured to control parameters of the drive signal using a power control loop in which the power characteristics of the power transmission signal / drive signal are controlled in response to power control error messages received from the power receiver.

[0081] At regular, typically frequent intervals, the power receiver transmits a power control error message to the power transmitter. The power receiver 105 may include functionality to support such a power control loop; for example, the power receiver controller 601 may continuously monitor the power or voltage of the load signal supplied to the load and detect whether it is above or below a desired value. At regular intervals, it may generate a power control error message requesting that the power level of the power transmission signal be increased or decreased, and it may transmit this power control error message to the power transmitter.

[0082] Upon receiving the power control error message from the power receiver, the transmit controller 305 can determine how the drive signal parameters should be modified to increase or decrease the power level of the power transmission signal as required, and it can control and adapt the drive signal parameters accordingly.

[0083] Therefore, a power control loop is used to control the power characteristics of the power transmission signal to produce a desired operating point at the power receiver. The operation of the power transmission is therefore controlled by the power control loop, and its effective operation is important to the performance of the system. Therefore, initializing or adapting the power control loop to the operating conditions is important for optimal performance.

[0084] In many wireless power transfer systems, setting up a new power transfer configuration involves different phases. Often, detection of the presence of a power receiver by a power transmitter enters a state / phase in which the power transmitter and power receiver each recognize the presence of a complementary device, and a (potentially dormant) communication link is typically established between them. However, in this phase / mode, the system may be in a standby state in which no power is transferred and does not automatically proceed to the power transfer phase. Such a phase is sometimes called a connected phase, and is a static phase in which the system remains until a specific event or action occurs. For example, when a kitchen appliance, such as a blender, is placed in a location for wireless power transfer, this can be detected by the power transmitter and it can enter the connected phase. It can then remain in that phase until, for example, a user switches the appliance (e.g., blender) to the on position, and upon switching to the on position, the system can proceed to the active power transfer phase.

[0085] The transition from a passive connected phase, or from a state in which there is no proximity between the power transmitter and power receiver (e.g., without an intervening connected phase), to an active power transfer phase is a non-trivial process involving several steps and processes that can be performed to ensure a safe, reliable, efficient, and high performance initialization of the power transfer phase.

[0086] Certain advantageous approaches that typically achieve one or more of these preferences are described below with reference to the power transfer systems of FIGS. 1-6.

[0087] FIG. 7 shows a flowchart of elements / steps of a method of operating a power transfer system. In particular, FIG. 7 illustrates a method of initializing a power transfer phase, for example, from a connected phase or other non-power phase. The diagram illustrates steps performed by the system, and in particular, steps performed by both the power transmitter and the power receiver. FIG. 8 illustrates the power transfer signal generated by the transmitter coil 103 during the initialization process and in the early part of the power transfer phase.

[0088] In this example, the wireless power transfer system is initially in a non-power transfer phase, e.g., a standby or connected phase in which no power transfer is occurring. However, for example, in the connected phase, the power transmitter and power receiver are aware of each other and have established a bidirectional communication link that allows them to exchange data messages.

[0089] In this example, the method begins in step 701, where the power receiver is configured to operate in a first load state, also referred to as a low power load state, a no load state, or a load isolation state. In this first load state, the power receiver can, among other things, isolate the load 605 from the input resonant circuit. Thus, the power transfer signal / electromagnetic field generated by the transmitter coil 103 can generally be very low (or even zero), as shown in FIG.

[0090] The power receiver is also operable to switch to a second load state, sometimes referred to as a low power load state, a load state, or a no-load state, in which the power receiver can couple the load 605 from the input resonant circuit.

[0091] The power receiver can be configured to operate in at least two different load states that differ in power loading of the power transmission signal and drive signal of the power transmitter. The two load states differ by at least one load (component) being coupled to the input resonant circuit (loading the power transmission signal / drive signal / electromagnetic field generated by the power transmitter / power transmitter coil) in one load state (second load state) and decoupled from the input resonant circuit (not loading the power transmission signal / drive signal / electromagnetic field generated by the power transmitter / power transmitter coil) in the other load state. Thus, the loading by the power receiver of the electromagnetic field (and therefore the drive signal) generated by the power transmitter differs between the first load state and the second load state.

[0092] Typically, the difference in load between the first and second load conditions is significant, and in many embodiments, the (power) load at the first load condition is no more than 25%, 10%, 5%, or even 2% of the load at the second load condition.

[0093] The power receiver presents substantially different loads to the power transmitter in two load states. In particular, the first load state can substantially correspond to a situation in which no power is supplied to the power receiver's terminating load, while the second load state can substantially correspond to a situation in which the terminating load is fully powered by the power transmitter and power receiver. In a specific example, the first load state is a state in which the switch 607 disconnects the load 605 from the power path, and the second load state is a state in which the switch 607 connects the load 605 to the power path. In the first load state, no power is supplied to the load 605, and in the second load state, power is supplied to the load 605.

[0094] It will be appreciated that in some embodiments, when the power receiver is in the first load state, some power may still be extracted from the electromagnetic field / power transmitter (e.g., some standby power may be extracted to power various control functions of the power receiver device), however, the amount of power extracted in the first and second load states is likely to differ quite significantly.

[0095] Step 701, in which the power receiver enters (or remains in) a first load state, is followed by step 703, in which the power receiver sends a request (message) to the power transmitter, which is a request to the power transmitter to initiate a transition from a non-power transmitting phase (connected phase) to a power transmitting phase. Thus, as shown in Figure 8, at some point 801 the power receiver proceeds to send a request for the power transmitter to start a new power transmission operation.

[0096] For example, the power receiver may continuously monitor (e.g., as part of step 701 or 703) for an event indicating a need for power transfer. For example, it may remain in the connected phase while continuously monitoring for user input indicating a desire to initiate power transfer. For example, in the case of a kitchen appliance, it may be detected that an on button has been pressed by a user, resulting in power transfer being initiated. In other embodiments, other approaches may be used, such as, for example, automatic detection of a change in the coupling coefficient between the power receiver and the power transmitter (e.g., movement of the power receiver may result in power transmission initiation) or automatic detection of a change in the environment (e.g., using motion detection).

[0097] When the power receiver determines that a power transfer operation should be initiated, it transmits a first request message to the power transmitter. In step 705, the power transmitter receives the first request message. Many different approaches for transmitting messages / data from a power transmitter to a power receiver are known, and it will be appreciated that any suitable approach may be used without detracting from the approaches and principles described.

[0098] In response to receiving the first request message, the power transmitter begins the process of initializing power transmission operation. In the described approach, the power transmitter proceeds to step 707 in response to receiving the first request message. In step 707, the power transmitter's measurement circuit / processor 309 performs a first measurement of a first power transmission parameter. The power transmission parameter can be, in particular, a parameter that depends on / reflects the loading by the power receiver of the power transmission signal / electromagnetic field generated by the power transmission coil. Such operating parameters can include determining the level of loading, coupling coefficient, size of the load, etc.

[0099] Thus, the first measurement is a measurement of the power transfer parameter when the power receiver is in a first uncoupled load state, i.e., when the load is reduced compared to the second (coupled / connected) load state. In the following, the first measurement may also be referred to as an uncoupled load measurement, and the measured power transfer parameter may also be referred to as an uncoupled power transfer parameter.

[0100] The power transmitter then proceeds to step 709, where the power transmitter transmits a first acknowledgement to the power receiver. This first acknowledgement is a message indicating to the power receiver that the first measurement has indeed been (successfully) performed. Thus, as shown in Figure 8, at some point 803, the power transmitter proceeds to transmit an acknowledgement (message) to the power receiver indicating that the first uncoupled measurement has been performed.

[0101] In step 711, the power receiver receives the first acknowledgement and, in response, proceeds to step 713, where the power receiver switches from a first load state to a second load state. Thus, in a particular example, the power receiver is configured to switch from a no-load-coupled load state to a load-coupled load state in response to the power receiver receiving the first acknowledgement from the power transmitter. Thus, the power transmitter can switch from operating in a mode where the power transmitter / power transmission signal load is very low to a mode where it is high, specifically, from an input resonant circuit / power transmission signal / electromagnetic field off or standby load to a full power phase load.

[0102] Following the switch to the second load state, the power receiver proceeds to step 715, where it transmits a second request (message). This second request may be a request for the power transmitter to begin generating a power transmission signal to power the power receiver. It may be a request to begin the power transfer phase. The second request also confirms to the power transmitter that the power receiver has switched to the second (load coupled) load state in which a load is coupled to the input resonant circuit. Thus, as shown in FIG. 8, at point 805, the power receiver proceeds to transmit a request to the power transmitter to begin the power transfer phase.

[0103] The power transmitter proceeds to receive the second request in step 717 and, in response, proceeds to step 719 where the measurement circuit / processor 309 performs a second measurement of the power transfer parameter. The power transfer parameter can be, in particular, a parameter that depends on / reflects the loading by the power receiver of the power transfer signal / field generated by the transmitter coil. Such operating parameters can include determining the level of loading, coupling coefficient, size of the load, etc. In many embodiments, the power transfer parameter measured in the first measurement is the same as the power transfer parameter measured in the second measurement, although in other embodiments the two measurements can measure different power transfer parameters. Thus, in step 707, a first measurement of the first power transfer parameter can be performed using a first measurement approach (technique / algorithm). In step 719, a second measurement of the second power transfer parameter can be performed using a second measurement approach (technique / algorithm). The first measurement, power transfer parameter, and / or measurement approach (technique / algorithm) can be the same as or different from the second measurement, power transfer parameter, and / or measurement approach (technique / algorithm).

[0104] Thus, the second measurement is typically substantially a measurement of the power transfer parameter when the power receiver is in a second coupled load condition, i.e., when the load is increased compared to the first (uncoupled) load condition. In the following, the second measurement may also be referred to as a coupled load measurement, and the measured power transfer parameter may be referred to as a coupled power transfer parameter.

[0105] The power transmitter then proceeds to step 721 and enters a power transmission phase in which the power transmitter generates a power transmission signal to transmit power to the power receiver. As shown in Figure 8, at some point 807 the power transmitter enters the power transmission phase and can generate a significant level of the power transmission signal to transmit power to the power receiver. The power receiver then either remains in or proceeds to enter the power transmission phase 723.

[0106] In some embodiments, the generated power transfer signal can be at a quasi-steady level (e.g., varying only based on a power control loop). However, in other embodiments, as in the example of FIG. 8, the power transfer signal may be generated to follow the amplitude of a time-varying supply signal to the driver. For example, the supply voltage to the driver's output circuitry may be a signal derived directly from the mains, such as AC, or a signal that is a rectified but unsmoothed DC signal. In such cases, the amplitude of the power transfer signal will time-vary along with the varying supply signal. Furthermore, in some embodiments, the power transfer phase may include alternating time intervals for power transfer and other functions, such as foreign object detection and / or communication. Thus, power transfer time intervals may typically be separated by short time intervals during which the power transfer signal is not generated. Such intervals may typically be located at minimum values of the amplitude of the power transfer signal / supply voltage. FIG. 8 illustrates an example of such operation during a power transfer phase.

[0107] In this approach, the power transmitter is configured to enter the power transfer phase in response to two measurements, i.e., both coupled and uncoupled measurements, specifically, in many embodiments, depending on the values of the measured power transfer parameters. In some embodiments, the power transfer phase may be entered conditionally on the measurements, e.g., only if the measured coupled and / or uncoupled parameter values meet appropriate criteria. In some embodiments, parameters, properties, or characteristics of the power transfer operation during the power transfer phase, such as initial parameter values, may depend on the measurements, e.g., the initial values of the parameters of the drive signal / power transfer signal may depend on the measured coupled and / or uncoupled power transfer parameter values.

[0108] This approach can provide particularly advantageous initialization of power transfer operation and the power transfer phase in many scenarios and embodiments. This approach provides an efficient and reliable approach with reduced risk of errors and undesirable conditions. This approach provides reliable interaction and synchronization between the power transmitter and the power receiver when initializing power transfer. Furthermore, this approach can include power transmitter-side measurements of power transfer parameters for substantially different loads and operating points performed before entering the power transfer phase, and can enter the power transfer phase depending on the measurements. This can typically provide more reliable and improved initialization of the power transfer phase, for example, ensuring that power transfer is initiated only when safe and / or with initial characteristics closer to the desired operating point.

[0109] In many embodiments, measurements are performed with significant differences in the load of the drive signal / power transmitter / electromagnetic field / power transfer signal. In many embodiments, the difference in power of the load between the first and second load conditions, and therefore the first and second measurements, is 5, 10, 15, 20, 50, 100, 500, or even 1000 watts or more. Thus, information about significantly different operating points can be generated during initialization, thereby resulting in improved adaptation of operation and power transfer.

[0110] In some embodiments, the first and / or second measurements can be used to perform foreign object detection tests. If any of these foreign object detection tests lead to a determination that a foreign object may potentially be present, the power transmitter can proceed to terminate the initialization of the power transfer phase. This approach can enable accurate foreign object detection for different operating points and provide improved safety and more reliable initialization of the power transfer phase. In particular, foreign object detection performed at different operating points can provide more accurate foreign object detection.

[0111] In fact, foreign object detection can be advantageously performed first in the isolated load state. This test can be performed using a low-level power transmission signal, resulting in a less accurate test. However, larger objects that draw large amounts of power may still be detected, and the system proceeds to the second foreign object detection test performed in the coupled load state only if any foreign object is sufficiently benign that it is not dangerous, even at the higher power level of the second measurement. However, the second measurement / coupled foreign object detection test is potentially substantially more accurate due to the higher power transmission signal level, and therefore even relatively small foreign objects can be detected. Therefore, the combination of the two foreign object detection tests in the coupled and uncoupled load states can provide improved performance.

[0112] It will be appreciated that different approaches for foreign object detection in wireless power transfer systems are known, and any suitable approach or algorithm may be used. The approaches and algorithms may be the same for the first and second detections, or may actually be different.

[0113] One possible approach is based on determining the unknown power loss. In this approach, the power transmitter can measure the generated power level and compare it to the expected power loss for the power receiver. In a low-complexity embodiment, the power loss caused by the power receiver in an uncoupled load state is simply assumed to be substantially zero. In other embodiments, a nominal power loss (e.g., caused by the power receiver's friendly metal and / or loading-by-standby circuitry) can be expected and compared to the measured power transmitter power loss. Thus, the first measurement is a measurement of the power level of the drive signal, and the power level is then compared to the expected value for the power receiver in an uncoupled load state. If the measured power exceeds the expected value by more than a margin / threshold, a foreign object can be considered detected.

[0114] The power transmitter can estimate the transmitted power, for example, by measuring the DC input voltage and current of the inverter, multiplying them, and correcting the result by subtracting an estimate of internal power losses in the power transmitter, such as estimated power losses in the inverter, primary coil, and metal components that are part of the power transmitter.

[0115] The power transmitter can estimate the resulting power loss by subtracting the expected extracted power from the transmitted power, and if the difference exceeds a threshold, the transmitter can assume that excess power is being dissipated in the foreign object and proceed to terminate power transfer initialization.

[0116] The same approach can be used for coupled foreign object detection, with the addition that the expected power receiver power loss is modified to include the expected power provided to the load.

[0117] Thus, in such an embodiment, the first and / or second measurement is a measurement of the power level of the drive signal / power transmission signal of the power transmitter, and foreign object detection can be performed by comparing this measurement with an expected value.

[0118] Another option is to measure the quality or Q-factor of the resonant circuit formed by the transmitter coil 103 and receiver coil 107, along with the corresponding capacitance and resistance. A decrease in the measured Q-factor (compared to an expected value) indicates the presence of a foreign object. Thus, in such an embodiment, the first and / or second measurement is a measurement of the Q-factor of the power transmitter and power receiver arrangement, and foreign object detection can be performed by comparing this measurement with an expected value.

[0119] In some embodiments, the power transmitter can be configured to generate a power transfer signal during the power transfer phase in response to the first and / or second measurements.

[0120] For example, an initial signal level for the power transfer phase when the power transfer phase begins can be set depending on the power level measured during the second measurement. Thus, the coupled measurement includes measuring the power level of the drive signal when the power receiver is in a coupled load state. Once the power transfer phase begins, the power transmitter can, for example, set the power level to the same value (e.g., by controlling the voltage and / or current amplitude of the drive signal) or to another value, possibly determined as a fixed function thereof.

[0121] In some embodiments, the second request from the power receiver may include an indication of desired power transfer parameters, such as a specifically desired power level for the power transfer phase, and the power transmitter may be configured to set the parameters of the drive signal / power transfer signal in response to this request.

[0122] For example, the power receiver may request that a power level twice the power level of the load during the second measurement be provided for the power transfer phase. The power transmitter may determine an appropriate amplitude (e.g., current or voltage) of the drive signal based on this request and, for example, a value (e.g., current or voltage) measured during the second measurement. For example, the amplitude measured during the second measurement may be scaled by a given scale factor to reflect the increased power level.

[0123] In some embodiments, the first and / or second measurement can be a resonant frequency measurement. For example, a frequency scan can be performed to determine the resonant frequency for power transfer by detecting peaks in the current or power of the drive signal. Results at different loads can be used to provide information about the resonant frequency at different loads. Such information can be used, for example, to determine an appropriate operating frequency when initiating the power transfer phase. For example, it can be configured to adapt or select an appropriate operating range for a power control loop that adapts the transmitted power level by changing the drive / operating frequency. For example, the operating range can be set to be 60% to 80% of the measured resonant frequency (or the average frequency of each measured resonant frequency), and the initial operating frequency when initiating the power transfer phase can be set to the middle of the operating range (e.g., 70% of the measured resonant frequency). As another example, the resonant frequency at different loads can be used to determine a coupling coefficient between the transmitter coil and the receiver coil, and the initial power level, e.g., when entering the power transfer phase, can be set to reflect the determined coupling coefficient.

[0124] In some embodiments, the power transmitter can initiate power transmission in response to the second request by generating a drive signal and a power transmission signal with appropriate parameters, such as frequency, current, voltage, and / or power, to provide appropriate wireless power transmission. In many embodiments, the power receiver can enter a mode appropriate for the power transmission phase simply upon sending the second request. For example, it can connect (or maintain connection) the load to the power path and input resonant circuit such that appropriate power is transmitted to the load when an appropriate power transmission signal is generated by the power transmitter entering the power transmission phase. For example, in the case of a blender, the load can be a motor that automatically starts when the power transmitter generates an appropriate power transmission signal.

[0125] In some embodiments, the power receiver can operate in standby mode until it detects that the power transmitter has entered a power transfer phase. For example, the switch 607 can disconnect the load 605 until a power transfer signal / generated electromagnetic field strength / induced voltage above a threshold is detected, at which point the switch can switch to connect the load 605. This ensures, for example, that the load (which may include, for example, sensitive electronic circuitry) is not powered until sufficient power is provided.

[0126] In some embodiments, the power transmitter can be configured to transmit a second acknowledgment to the power receiver following the second measurement in connection with entering the power transfer phase, e.g., before or upon entering the power transfer phase. For example, as shown in FIG. 8, the second acknowledgment can typically be transmitted by the power transmitter to the power receiver at a given time 809, e.g., just prior to the start of the power transfer phase.

[0127] The second acknowledgement may indicate to the power receiver that the second measurement (and indeed all other operations) was successfully performed and that the power transfer phase will or has begun. In response to receiving the second acknowledgement, the power receiver may proceed to enter the appropriate power transfer phase mode, such as by switching switch 607 to connect load 605 to the input resonant circuit / power path.

[0128] In some embodiments, the power transmitter can be configured to transmit a negative acknowledgment to the power receiver in response to ceasing to initiate power transmission. This allows the power receiver to terminate the power transmission phase operation. For example, it can switch to a minimum load and / or generate and present user instructions (e.g., using a provided low-level / standby power transmission signal or an internal battery).

[0129] For example, if the first or second measurement results in an unsatisfactory value of the measured parameter, it can be determined that the power transfer phase should not proceed and that the initiation of the power transfer phase should be terminated (e.g., if a foreign object is detected in either a coupled load state or a non-coupled load state, the initialization of the power transfer is terminated and a negative acknowledgement message is sent to the power receiver).

[0130] As another example, if a timeout occurs, for example due to an expected response or message not being received in time, the power transmitter may terminate initialization of the power transmission phase and proceed to send a negative response to the power receiver.

[0131] In some embodiments, the power transmitter can be configured to synchronize the start of the power transfer phase to the timing of the cycle of the mains power supply to the power transmitter, which is particularly advantageous in approaches where the amplitude of the power transfer signal varies in time due to variations in the supply voltage to the driver generated from the mains power supply.

[0132] For example, in many scenarios where the amplitude of the power transmission signal varies, e.g., due to fluctuations in the supply voltage, the start of the power transfer phase can be synchronized to begin at the minimum amplitude of the power transmission signal. For example, if the amplitude of the power transmission signal depends directly on the supply voltage, the start of the power transfer phase can be synchronized to begin at the moment when the supply voltage is minimum. In many embodiments, the start of the power transfer phase is synchronized (possibly with a delay) to occur at the zero-crossing moment of the AC signal supplied to the driver 301. Such an approach would be suitable for scenarios where the AC source is fed directly to the output of the inverter or is fed by a rectified supply signal. In fact, even with a smoothing capacitor, the resulting supply voltage still tends to have ripples that are synchronous with the AC signal, and therefore the minimum amplitude of the drive signal would still be synchronized with the AC signal (e.g., with a load-dependent delay). Therefore, in many embodiments, the start of the power transfer phase is synchronized to an AC signal (e.g., a mains signal) from which the voltage supply for the output circuit of the driver 301 is derived. FIG. 8 shows an example where the start 807 of the power transfer phase is synchronized with the minimum / zero crossing of the supply and drive signal amplitudes.

[0133] Such an approach can often provide a more gradual start of the power transfer phase, for example, reducing power surges at the load when power transfer begins.

[0134] In many embodiments, the process can include various timeouts for various operations and steps in the initialization process. This can allow for a reliable process with built-in conditions for terminating the process if something fails. Figure 8 shows some examples of timeouts 811 that can be built into the system:

[0135] Timeout A: The time between the power receiver sending the first request to enter power transmission mode and the power transmitter sending the first acknowledgement should not exceed 50, 100 or 200 ms in many embodiments. During this time, the power transmitter can perform foreign object detection, impedance checks or other system measurements on the unloaded system.

[0136] Timeout B: The time between the power transmitter's confirmation message and the power receiver switching to the coupled load state and sending the second request should not exceed 20, 40 or 60 ms in many embodiments.

[0137] Timeout C: In many embodiments, the time between the second request and the power transmitter sending the second acknowledgement should not exceed 10, 20 or 30 ms. - This is preferably as short as possible since substantial power is transferred in this situation. At this time, the power transmitter can perform foreign object detection, impedance checks or other system measurements on the load system (with the secondary switch closed and therefore the load attached).

[0138] Timeout D: The time between the power transmitter sending the second acknowledgement and the start of the power transfer phase should not exceed 10, 20 or 30 ms in many embodiments.

[0139] Timeout E: The duration of the entire initialization process time from the first request to the start of the power transfer phase should not exceed 100, 150, 180, 200, 250, or 500 ms in many embodiments.

[0140] Thus, the power transmitter and power receiver can be configured to perform operations fast enough so that the above timings are met, thereby allowing for improved performance.

[0141] In many embodiments, the power transmitter and power receiver are configured to perform timeout detection. For example, if one of the above timings is not met, for example, with a margin of 0, 10, 20, 30, 50, or 100 msec (different margins may be used for different timeouts), the power transmitter and / or power receiver may consider a timeout / error to have occurred and terminate the power transfer initialization. This may include, for example, sending a power transfer termination message to the complementary device.

[0142] It will be understood that, for clarity, the above description has described embodiments of the invention with reference to different functional circuits, units, and processors. However, it will be apparent that any suitable distribution of functionality between different functional circuits, units, or processors may be used without departing from the invention. For example, functionality shown to be performed by separate processors or controllers may be performed by the same processor or controller. References to specific functional units or circuits should therefore be seen only as references to suitable means for providing the described functionality, rather than to indicative of a strict logical or physical structure or organization.

[0143] The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of embodiments of the invention may be physically, functionally, and logically implemented in any suitable way. Indeed, functionality may be implemented in a single unit, in multiple units, or as part of other functional units. Thus, the invention may be implemented in a single unit, or may be physically and functionally distributed between different units, circuits, and processors.

[0144] Although the present invention has been described in connection with several embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the appended claims. Furthermore, while certain features may appear to be described in connection with particular embodiments, those skilled in the art will recognize that various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0145] Furthermore, although individually listed, a plurality of means, elements, circuits, or method steps may be implemented by, for example, a single circuit, unit, or processor. Furthermore, although individual features may be included in different claims, these may be advantageously combined in some cases, and their inclusion in different claims does not imply that a combination of features is not feasible and / or advantageous. Moreover, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate. The inclusion of a feature in a dependent claim of one independent claim does not imply a limitation to this independent claim, but rather indicates that the feature is equally applicable to other independent claims, where appropriate. Furthermore, the order of features in the claims does not imply a particular order in which the features must operate, and in particular the order of individual steps in method claims does not imply that the steps must be performed in this order. Rather, steps may be performed in any suitable order. Furthermore, a reference to the singular does not exclude a plurality. Thus, references to "a," "an," "first," "second," etc. do not exclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

Claims

1. 1. A method for initiating power transmission in a wireless power transmission system including a power transmitter transmitting power to a power receiver using a power transmission signal that induces a current in a power receiving coil of the power receiver, comprising: the power receiver transmitting a first request to the power transmitter during a non-power transmission phase, the first request being a request to transition from the non-power transmission phase to a power transmission phase; operating the power receiver in a first load state after transmitting the first request, wherein a load of the power receiver is isolated from the power receiving coil when the power receiver is operating in the first load state; receiving the first request by the power transmitter; performing, by the power transmitter, a first measurement of a first power transfer parameter in response to receiving the first request; the power transmitter sending a first acknowledgement to the power receiver after the first measurement; receiving the first acknowledgement by the power receiver; switching the power receiver to a second load state in response to receiving the first acknowledgement, the load of the power receiver being coupled to the power receiving coil when the power receiver is operating in the second load state; transmitting a second request to the power transmitter in connection with the power receiver entering the second load state, the second request being a request for power; receiving the second request by the power transmitter; performing, by the power transmitter, a second measurement of a second system parameter in response to receiving the second request; entering a power transmission phase in which the power transmitter generates a power transmission signal dependent on the first measurement and the second measurement; A method having the following.

2. 2. The method of claim 1, wherein the power receiver is configured to include at least one requested power transfer parameter in the second request, and the power transmitter is configured to set at least one parameter of the power transfer signal depending on the requested power transfer parameter.

3. 3. The method of claim 1, wherein the power transmitter is configured to generate the power transmission signal to have a characteristic that depends on at least one of the first measurement and the second measurement.

4. The method of claim 1 , wherein the power transmitter performs foreign object detection based on the first measurement and refrains from initiating power transmission if the foreign object detection indicates the presence of a foreign object.

5. The method of claim 1 , wherein the power transmitter performs foreign object detection based on the second measurement and refrains from initiating power transmission if the foreign object detection indicates the presence of a foreign object.

6. 6. The method of claim 1, wherein the power transmitter is configured to send a second acknowledgement to the power receiver after the second measurement and before entering the power transfer phase.

7. 7. The method of claim 6, wherein the power transmitter is configured to generate the power transmission signal during a power transmission phase with a maximum delay of 20 ms from transmission of the second acknowledgement.

8. 8. The method of claim 1, wherein the power transmitter is configured to synchronize the start of the power transfer phase with the timing of a cycle of a power supply signal to the power transmitter.

9. 9. The method of claim 1, wherein the power transmitter is configured to refrain from initiating power transmission if a second request is not received before expiry of a predetermined time interval.

10. The method of claim 1 , wherein the power transmitter is configured to send a negative acknowledgement message to the power receiver in response to ceasing to initiate power transmission.

11. 11. The method of claim 1, wherein the load is at least a 10 W load.

12. 1. A method of initiating power transmission in a wireless power transmission system including a power transmitter transmitting power to a power receiver using an inductive power transmission signal that induces a current in a power receiving coil of the power receiver, the method comprising: sending a first request to the power transmitter during a non-power transfer phase, the first request being a request to transition from the non-power transfer phase to a power transfer phase; operating in a first load state after transmitting the first request, wherein a load of the power receiver is isolated from the power receiving coil when the power receiver is operating in the first load state; receiving a first acknowledgement from the power transmitter; switching to a second load state in response to receiving the first acknowledgement, the load of the power receiver being coupled to the power receiving coil when the power receiver is operating in the second load state; sending a second request to the power transmitter in association with entering the second load state, the second request being a request for power; entering a power transfer phase in which power is extracted from the power transfer signal by the power receiver; A method having the following.

13. 1. A method of initiating power transmission in a wireless power transmission system including a power transmitter that transmits power to a power receiver using an inductive power transmission signal, comprising: receiving a first request to transition from a non-power transfer phase to a power transfer phase; performing a first measurement of a first power transfer parameter in response to receiving the first request; sending a first acknowledgement to the power receiver after the first measurement; receiving a second request for power indicating that the power receiver has switched from a first load state to a second load state, wherein a load is decoupled from a power receiving coil of the power receiver when in the first load state and a load is coupled to the power receiving coil when in the second load state; performing a second measurement of a second system parameter in response to receiving the second request; entering a power transfer phase generating a power transfer signal dependent on the first measurement and the second measurement; A method having the following.

14. 1. A power receiver for a wireless power transfer system including a power transmitter that transmits power to the power receiver using an inductive power transfer signal, a power receiving coil configured to extract power from the power transmission signal by induction; a transmitter configured to send a first request to the power transmitter during a non-power transmission phase, the first request being a request for a transition from the non-power transmission phase to a power transmission phase; a mode processor configured to control the power receiver to operate in a first load state after transmitting the first request, wherein a load of the power receiver is decoupled from the power receiving coil when the power receiver is operating in the first load state; and a receiver configured to receive a first acknowledgement from the power transmitter; and the mode processor is further configured to control the power receiver to switch to a second load state in response to receiving the first acknowledgment, the load of the power receiver being coupled to the power receiving coil when the power receiver is operating in the second load state; the transmitter is configured to send a second request to the power transmitter in association with entering the second load state, the second request being a request for power; The power receiver further comprises a controller configured to enter a power transfer phase during which power is extracted by the power receiver from the power transmission signal.

15. 1. A power transmitter for a wireless power transmission system including a power receiver that receives power from a power transmitter using an inductive power transmission signal, a receiver configured to receive a first request to transition from a non-power transfer phase to a power transfer phase; a measurement circuit configured to perform a first measurement of a first power transfer parameter in response to receiving the first request; a transmitter configured to transmit a first acknowledgement to the power receiver after the first measurement; and the receiver is configured to receive a second request for power indicating that the power receiver has switched from a first load state to a second load state, a load being decoupled from a power receiving coil of the power receiver when in the first load state and a load being coupled to the power receiving coil when in the second load state; the measurement circuitry is configured to perform a second measurement of a second system parameter in response to receiving the second request; the power transmitter further comprising: a controller configured to enter a power transfer phase to generate a power transfer signal dependent on the first measurement and the second measurement; Power transmitter.

16. A wireless power transmission system comprising the power transmitter according to claim 15 and the power receiver according to claim 14.

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