Wireless power transfer

Abstract

A power receiver for a wireless power transmitter transmits (703) a request (107) for a power transfer phase when the power receiver is in a load state in which a load is disconnected from a power receiving coil. When receiving (705) the request, the power transmitter continues to measure (707) the power transmission parameter, and thereafter sends (709) and receives (711) an acknowledgement to the power receiver (105). In response, it continues to change (713) to a new load state in which the load is connected to the power receiving coil (107). It sends (715) a second request that, when received (717), causes the power transmitter (101) to perform another measurement (719) of the power transmission parameter. The power transfer is then started according to the measurement result (721). Improved initialization of the power transfer phase may be provided.

Description

Technical Field

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

[0002] Most current 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 plug in a connector or otherwise establish physical electrical contacts. Typically, power requirements also vary significantly, and most current devices are provided with their own dedicated power source, resulting in a typical user having a large number of different power sources, each dedicated to a specific device. Although 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 because the battery will need to be recharged (or replaced). The use of batteries can also significantly increase the weight and potential cost and size of the device.

[0003] In order to provide a significantly improved user experience, it has been proposed to use wireless power, where power is inductively transferred from a transmitter inductor in a power transmitter device to a receiver coil in the respective device.

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

[0005] This arrangement allows wireless power transfer to the device without the need to make any wired or physical electrical connections. In fact, it can simply allow the device to be placed near or on top of the transmitter coil to be recharged or powered externally. For example, the power transmitter device can be arranged with a horizontal surface, and the device can simply be placed on the horizontal surface to be powered.

[0006] Furthermore, such a wireless power transmission device can advantageously be designed so that a power transmitter device can be used with a range of power receiver devices. In particular, a wireless power transmission 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 having to be dedicated to each other. The Qi standard also includes some functions for allowing operation to be adapted to a specific power receiver device (e.g., depending on a specific power consumption).

[0007] The Qi specification was 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 Alliance continues to develop the Ki specification (also known as the Cordless Kitchen Specification) based on the Qi specification, which 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 including a function for detecting proximal foreign objects.

[0010] There can be a wide range of power transmitters and power receivers. For example, coil sizes, inductance values, and loads vary widely, so system parameters and power transfer operating parameters can vary significantly with specific equipment and mechanical configurations. In addition, the placement of the power receiver relative to the power transmitter can change the coupling and therefore change the power transfer properties.

[0011] Furthermore, the power receiver may have several modes of its operation, such as being able to switch several loads on or off. As an example, for a typical air fryer appliance powered by wireless power transfer, the heating element may be switched on and off, resulting in load steps between typical values ​​of about 50 to about 1200 W. This switching may be repeated during operation in order to keep the temperature of the heating element substantially constant for the air fryer.

[0012] Furthermore, the power transmission may include non-linear loads, for example, instead of resistive components, the powered device may include a motor (eg, a food processor). This often results in a completely different response of the system and can have a significant impact on the control system design.

[0013] The power transfer system will typically use a control loop to ensure that the correct operating point is reached. This control loop varies the amount of power transmitted to the power receiver. The received power (or voltage or current) can be measured by the power receiver, which can be compared to the expected value to generate an error signal. The power receiver can then transmit this error signal to the power control function in the power transmitter, which can dynamically adapt the generated power transfer signal in order to seek to reduce the static error to zero.

[0014] A key challenge for wireless power transfer systems is to ensure efficient and reliable initialization of the power transfer operation. For example, reaching a desired operating point by allowing a control loop to adapt the power transfer operation will typically be a slow process that tends to introduce significant delays in the power supply. For example, this can introduce a noticeable delay before a power device such as a powered appliance can start up.

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

[0016] Therefore, transitioning to the power transfer phase is a rather difficult and challenging process that requires many operations to be performed and certain conditions to be met before power transfer can begin. Current approaches are often suboptimal and do not provide ideal performance.

[0017] Accordingly, improved power transfer operation would be advantageous and in particular, methods allowing increased flexibility, reduced cost, reduced complexity, improved operation, more accurate power transfer operation, more flexible power transfer, improved suitability for higher power level transfers, improved and / or facilitated power transfer initialization and / or improved performance would be advantageous. Summary of the invention

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

[0019] According to one aspect of the present invention, a method for initiating power transfer in a wireless power transfer system is provided, the wireless power transfer system comprising a power transmitter, the power transmitter transmitting power to a power receiver using a power transfer signal, the power transfer signal inducing current in a power receiver coil of the power receiver, the method comprising: the power receiver transmitting a first request to the power transmitter during a non-power transfer phase, the first request being a request for transitioning from the non-power transfer phase to a power transfer phase; after transmitting the first request, the power receiver operating in a first load state, the load of the power receiver being decoupled from the power receiver coil when the power receiver operates in the first load state; the power transmitter receiving the first request; in response to receiving the first request, the power receiver A power transmitter performs a first measurement of a first power transfer parameter; after the first measurement, the power transmitter transmits a first confirmation to the power receiver; the power receiver receives the first confirmation; in response to receiving the first confirmation, the power receiver switches to a second load state, and when the power receiver operates in the second load state, the load of the power receiver is coupled to the power receiver coil; in conjunction with entering the second load state, the power receiver transmits a second request to the power transmitter, the second request being a request for power; the power transmitter receives the second request; in response to receiving the second request, the power transmitter performs a second measurement of a second system parameter; the power transmitter enters a power transfer phase of generating a power transfer signal based on the first measurement and the second measurement.

[0020] The present invention can provide improved and / or convenient performance and / or operation and / or implementation of wireless power transfer operations and systems. The method can provide improved conversion to power transfer and initialization of power transfer. In many scenarios, it can ensure safer and / or more reliable initialization and startup of power transfer.

[0021] The non-power transfer phase may not be a phase of the power transfer phase. In many embodiments, the power of the power transfer signal may be limited to a lower value in the non-power transfer phase than in the power transfer phase, and typically the maximum power level during the non-power transfer phase does not exceed 1%, 5%, 10% or 25% of the maximum power level during the power transfer phase.

[0022] The power transmitter may enter the power transfer phase for generating the power transfer signal based on the first measurement and the second measurement because it enters the power transfer phase for generating the power transfer signal based on the measured value of the first power transfer parameter and the measured value of the second power transfer parameter.

[0023] The first load state may also be referred to as a load decoupling state or an unloaded state. The first measurement may also be referred to as a load decoupling measurement. The second load state may also be referred to as a load coupling state or a loaded state. The second measurement may also be referred to as a load coupling measurement.

[0024] The power receiver may be arranged to operate in a second / loaded state in which the 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, as it may be a request for the start of a power transfer phase.

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

[0027] In many embodiments and scenarios, this may provide improved performance. It may allow for improved initialization of the power transfer phase, with an initial operating point that may be closer to a desired / optimal operating point.

[0028] When entering the power transfer phase, the property may specifically be an initial property of the power transfer phase.

[0029] According to an optional feature of the invention, the power transmitter is arranged to generate the power transfer signal to have a property that is dependent on at least one of the first measurement and the second measurement.

[0030] This may provide improved performance in many embodiments and scenarios.It may allow improved initialization of the power transfer phase with an initial operating point that may be closer to the desired / optimal operating point.

[0031] When entering the power transfer phase, the properties may specifically be initial properties of 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 the power transfer if the foreign object detection indicates the presence of a foreign object.

[0033] The method may provide a more reliable and improved initialisation of the power transfer phase. It may provide improved mitigation and / or risk reduction against the presence of foreign matter.

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

[0035] The method may provide a more reliable and improved initialisation of the power transfer phase. It may provide improved mitigation and / or risk reduction against the presence of foreign matter.

[0036] According to an optional feature of the invention, the power transmitter is arranged to send a second acknowledgement to the power receiver after the second measurement and before entering the power transfer phase.

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

[0038] According to an optional feature of the invention, the power transmitter is arranged to generate the power transfer signal with a maximum delay of 20 milliseconds in transmitting the second acknowledgement during a power transfer phase.

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

[0040] According to an optional feature of the invention, the power transmitter is arranged to synchronise the start of the power transfer phase with the timing of a cycle of a power supply signal to the power transmitter.

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

[0042] In some embodiments, the power transmitter may be arranged to synchronise the start of the power transfer phase with the timing of a cycle of a main power supply of the power transmitter.

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

[0044] In some embodiments, the power transmitter may be arranged to align the start of the power transfer phase with the timing of a cycle of a primary power supply of the power transmitter.

[0045] According to an optional feature of the invention, the power transmitter is arranged to terminate initiating the power transfer if no second request is received before expiry of a predetermined time interval.

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

[0047] According to an optional feature of the invention, the power transmitter is arranged to transmit a non-acknowledge message to the power receiver in response to termination of initiation of the power transfer.

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

[0049] According to one aspect of the invention, the load is a load of at least 10, 20, 50, 100, 500 or 1000 Watts. This may 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 transfer in a wireless power transfer system, the wireless power transfer system comprising a power transmitter, the power transmitter transmitting power to the power receiver using an inductive power transfer signal, the inductive power transfer signal inducing current in a power receiver coil of the power receiver, the method comprising: transmitting a first request to the power transmitter during a non-power transfer phase, the first request being a request to switch from the non-power transfer phase to a power transfer phase; operating in a first load state after transmitting the first request, when the power receiver operates in the first load state, the load of the power receiver is decoupled from the power receiver coil; receiving a first confirmation from the power transmitter; in response to receiving the first confirmation, switching to a second load state, when the power receiver operates in the second load state, the load of the power receiver is coupled to the power receiver coil; in conjunction with entering the second load state, transmitting a second request to the power transmitter, the second request being a request for power; entering a power transfer phase, wherein power is extracted by the power receiver from the power transfer signal.

[0051] According to one aspect of the present invention, there is provided a method for a power transmitter to initiate power transfer in a wireless power transfer system, the wireless power transfer system comprising a power transmitter, the power transmitter transmitting power to a power receiver using an inductive power transfer signal, the method comprising: receiving a first request, the first request being a request to switch from a non-power transfer phase to a power transfer phase; in response to receiving the first request, performing a first measurement of a first power transfer parameter; after the first measurement, sending a first confirmation to the power receiver; receiving a second request, the second request being a request for power and indicating that the power receiver has switched from a first load state to a second load state, wherein the load is decoupled from a power receiver coil of the power receiver when in the first load state, and is coupled to the power receiver coil when in the second load state; in response to receiving the second request, performing a second measurement of a second system parameter; and, entering a power transfer phase for generating a power transfer signal based on the first measurement and the second measurement.

[0052] According to one aspect of the present invention, there is provided a power receiver for a wireless power transmission system, the wireless power transmission system comprising a power transmitter, the power transmitter transmitting power to the power receiver using an inductive power transmission signal, the power receiver comprising: a power receiver coil, which is arranged to extract power from the power transmission signal by induction; a first transmitter, which is arranged to transmit a first request to the power transmitter during a non-power transmission phase, the first request being a request to switch from the non-power transmission phase to a power transmission phase; a mode processor, which is arranged to control the power receiver to operate in a first load state after transmitting the first request, when the power receiver operates in the first load state , the load of the power receiver is decoupled from the power receiver coil; a receiver, which is arranged to receive a first confirmation from the power transmitter; wherein the mode processor is also arranged to control the power receiver to switch to a second load state in response to receiving the first confirmation, when the power receiver operates in the second load state, the load of the power receiver is coupled to the power receiver coil; the transmitter is arranged to transmit a second request to the power transmitter in conjunction with entering the second load state, the second request is a request for power; and the power receiver also includes: a controller, which is arranged to enter a power transfer phase, wherein 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 DESCRIPTION OF THE DRAWINGS

[0054] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which

[0055] Figure 1 shows examples of elements of a power delivery system according to some embodiments of the present invention;

[0056] Figure 2 Shown for Figure 1 An example of an equivalent circuit of a power transmission system;

[0057] Figure 3 shows an example of elements of a power transmitter according to some embodiments of the present invention;

[0058] Figure 4 An example of a half-bridge inverter for a power transmitter is shown;

[0059] Figure 5 An example of a full-bridge inverter for a power transmitter is shown;

[0060] Figure 6shows examples of elements of a power receiver according to some embodiments of the present invention;

[0061] Figure 7 An example of a method of operation according to some embodiments of the present invention and a specific initialization of a power transfer phase are shown;

[0062] Figure 8 An example of a power transfer signal during initialization of a power transfer phase according to some embodiments of the present invention is shown. DETAILED DESCRIPTION

[0063] The following description focuses on an embodiment of the invention applicable to a wireless power transfer system utilizing a power transfer method such as known from the Qi specification or the Ki specification. However, it should be understood that the invention is not limited to this application but may be applied to many other wireless power transfer systems.

[0064] Figure 1 An example of a power transmission system according to some embodiments of the present invention is shown. The power transmission system comprises a power transmitter 101, which comprises (or is coupled to) a transmitter coil / inductor 103. The system also comprises a power receiver 105, which comprises (or is coupled to) a receiver coil / inductor 107.

[0065] The system provides an inductive electromagnetic signal that can inductively transfer power from the power transmitter 101 to the power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal that is propagated by the transmitter coil or inductor 103 as magnetic flux. 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 (and specifically to the receiver coil 107), and is referred to as the power transfer signal hereinafter. More generally, the term "power transfer signal" can refer to any electromagnetic signal / field generated by the transmitter coil 103 (including during the power transfer phase and outside the power transfer phase, such as in the standby / off / connect phase, and including signals / fields that are not generated for the specific purpose of powering the power receiver load, but for example, to perform measurements, communication, or provide standby power).

[0066] The power transfer signal may typically have a frequency between about 20 kHz and about 500 kHz, and typically in the range of 95 kHz to 205 kHz for Qi-compatible systems, or in the range of 20 kHz to 80 kHz for Ki-compatible systems. 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 portion 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 primarily used to refer to the induced 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 may also be considered and used as a reference to an electrical signal provided to the transmitter coil 103 or picked up by the power receiving coil 107.

[0067] In the example described, the power receiver 105 is specifically a power receiver that receives power via a receiver coil 107. However, in other embodiments, the power receiver 105 may comprise a metallic element, such as a metallic heating element, in which case the power transmission signal directly induces eddy currents resulting in direct heating of the element.

[0068] The system is arranged to transfer a number of power levels, and in particular, in many embodiments, the power transmitter may support power levels in excess of 500 mW, 1 W, 5 W, 50 W, 100 W or 500 W. For example, for Qi corresponding applications, the power transfer may typically be in the power range of 1-5 W for low power applications (basic power profile), in the power range of up to 15 W for Qi specification version 1.2, in the range of up to 100 W for higher power applications such as power tools, laptops, drones, robots, etc., and in excess of 100 W and up to over 2000 W for very high power applications such as Ki kitchen appliances.

[0069] Hereinafter, the operation of the power transmitter 101 and the power receiver 105 will be generally described with reference to the Qi or Ki specification (except for the modifications and enhancements described herein (or corresponding thereto) or with specific reference to the embodiment adapted for the higher power kitchen specification developed by the Wireless Charging Alliance. In particular, the power transmitter 101 and the power receiver 105 may comply with or be substantially compatible with elements of Qi specification version 1.0, 1.1 or 1.2 (except for the modifications and enhancements described herein (or corresponding thereto)).

[0070] For many wireless power transfer systems, particularly high power systems such as Ki, resonant power transfer is utilized, where the transmitter coil 103 is part of a resonant circuit, and typically the receiver coil 107 is also part of a resonant circuit. In many embodiments, the resonant circuit may be a series resonant circuit, and thus the transmitter coil 103 and the 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.

[0071] In most power transfer systems, before initiating power transfer, a communication channel is established between the power transmitter 101 and the power receiver 105. When communication has been established and recognition of the two devices has been achieved, the power transmitter 101 can begin transferring power to the power receiver 105.

[0072] Figure 2 An example of an electrical equivalent diagram of the power transfer function for the power transmitter 101 and the power receiver 105 is shown in FIG. A wide range of power transmitters and power receivers may exist in a given system, and these power transmitters and power receivers may have substantially different properties and parameters. For example, coil size, inductance, and load may vary significantly. Thus, as Figure 2 The system parameters specifically represented in can in practice vary significantly between different devices, mechanical configurations, positioning, etc. In particular, the placement of the power receiver and therefore the relative position of the receiver coil 107 and the transmitter coil 103 substantially affects the coupling between the coils (i.e., the primary (power transmitter side) inductor Lp and the secondary (power transmitter side) inductor Ls), and thus can significantly change the system performance.

[0073] Furthermore, power receiving devices may have several different modes in which they operate, such as powering a load at different voltage levels (5V, 12V, 20V).

[0074] Typically, wireless power transfer systems employ a power control loop in order to steer the system to an appropriate operating point. This power control loop varies the amount of power transmitted from a power transmitter to a power receiver. The received power (either voltage or current) can be measured, and an error signal can be generated along with a set point power value. The appliance sends this error signal to a power control function in the power transmitter to reduce the static error, ideally to zero.

[0075] However, since system performance and operation vary widely depending on the existing power transmitter and power receiver combination and placement, the appropriate operating point also varies widely. This includes the conditions at start-up / initialization of power transfer.

[0076] Figure 3 Shown in more detail Figure 1Elements of the power transmitter 101.

[0077] The power transmitter 101 includes a driver 301 that can generate a drive signal that is fed to the transmitter coil 103, which in turn generates an electromagnetic power transfer signal to provide power transfer to the 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, but it should be understood that in other embodiments, the output resonant circuit can be a parallel resonant circuit. It should be understood that any suitable resonant circuit can be used, including a resonant circuit including multiple inductors and / or capacitors.

[0078] The driver 301 generates a current and a voltage which is fed to the output resonant circuit and hence to the transmitter coil 103. The driver 301 is typically a drive circuit in the form of an inverter which generates an AC signal from a DC voltage. The output of the driver 301 is typically a switching bridge which generates a drive signal by appropriate switching of the switches of the switching bridge. Figure 4 A half-bridge switching bridge / inverter is shown. Switches S1 and S2 are controlled so that they are never closed at the same time. Alternatingly, S1 is closed when S2 is open, and S2 is closed when S1 is open. The switches are opened and closed at the desired frequency, generating an AC signal at the output. Typically, the output of the inverter is connected to the transmitter inductor via a resonant capacitor. Figure 5 A full-bridge switching bridge / inverter is shown. Switches S1 and S2 are controlled so that they are never closed at the same time. Switches S3 and S4 are controlled so that they are never closed at the same time. Alternatingly, switches S1 and S4 are closed when S2 and S3 are open, and then S2 and S3 are closed when S1 and S4 are open, creating a square wave signal at the output. The switches are opened and closed at the desired frequency.

[0079] The power transmitter 101 further comprises a power transmitter controller 305, which is arranged to control the operation of the power transmitter 101 according to a desired operating principle. In particular, the power transmitter 101 may comprise a number of functions required to perform power control according to the Qi specification or the Ki specification.

[0080] In particular, the power transmitter controller 305 is arranged to control the generation of the drive signal by the driver 301, 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 305 comprises a power loop controller that controls the power level of the power transfer signal in response to power control messages received from the power receiver 105 during the power transfer phase.

[0081] The power transmitter controller 305 may further include 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 it may receive data from the power receiver 105 by detecting the load modulation of the power transmission signal. It should be understood that in other embodiments, other communication means may be used, for example, a separate communication function may be implemented, such as NFC communication.

[0082] As is known, the use of a resonant circuit including the transmitter coil 103 provides more efficient power transfer in many scenarios, and the power transfer can be controlled by the frequency of the drive signal. In addition, having a power receiver that also employs a resonant circuit (i.e., where the receiver coil 107 is part of the resonant circuit) can result in resonant power transfer that achieves efficient power transfer.

[0083] Figure 6 Some exemplary elements of the power receiver 105 are shown.

[0084] The receiver coil 107 is coupled to the power receiver controller 601 via a capacitor 603, which together with the receiver coil 107 forms an input resonant circuit. Thus, the power transfer may be a resonant power transfer between the resonant circuits.

[0085] The power receiver controller 601 couples the receiver coil 107 to the load 605 via a switch 607, which may specifically be capable of connecting, disconnecting (or even short-circuiting) 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 suitable power supply for the load 605. In some embodiments, the power receiver controller 601 may 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 may be simply implemented by two wires. In other embodiments, the power path may include, for example, a rectifier and possible smoothing capacitors to provide a DC voltage. In other embodiments, the power path may include more complex functions, such as a voltage control circuit, an impedance matching circuit, a current control circuit, etc. Similarly, it should be understood that the switch 607 may only be present in some embodiments, and in some embodiments, the load 605 may be permanently coupled to the input resonant circuit.

[0086] Furthermore, the power receiver controller 601 may include various power receiver controller functions required to perform power transfer, in particular functions required to perform power transfer according to the Qi or Ki specifications.

[0087] The power receiver controller 601 may also include a communicator 609 for communicating with the power transmitter 101. For example, it may be arranged to decode and demodulate data modulated onto the power transfer signal, and it may be arranged to transmit the data to the power transmitter 101 by load modulating the power transfer signal. In some embodiments, a separate communication function may be employed, such as an NFC communication function.

[0088] In operation, the system is arranged to control the drive signal so that the power transfer signal reaches suitable operating parameters / properties and the power transfer operates at a suitable operating point. To do so, the power transmitter is arranged to control the parameters of the drive signal using a power control loop, wherein the power properties of the power transfer signal / drive signal are controlled in response to a power control error message received from the power receiver.

[0089] The power receiver transmits a power control error message to the power transmitter at regular and usually frequent intervals. The power receiver 105 includes functionality for supporting such a power control loop, for example, the power receiver controller 601 may continuously monitor the power or voltage of the load signal provided to the load, and detect whether this is higher or lower than an expected value. It may generate a power control error message at regular intervals, the power control error message requesting an increase or decrease in the power level of the power transfer signal, and it may transmit the power control error message to the power transmitter.

[0090] When a power control error message is received 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 transfer signal as requested. It can then control and adapt the drive signal parameters accordingly.

[0091] A power control loop is accordingly employed which controls the power properties of the power transfer signal to produce a desired operating point at the power receiver. Thus, the operation of the power transfer is controlled by the power control loop, and its efficient operation is critical to the performance of the system. Therefore, initializing or adapting the power control loop to the operating conditions is critical for optimal performance.

[0092] In many wireless power transfer systems, the establishment of a new power transfer setting includes different stages. In many cases, the detection of the presence of a power receiver by a power transmitter causes the setting to enter a state / stage in which the power transmitter and the power receiver are each aware of the presence of a complementary device and typically establish a (possibly dormant) communication link between them. However, in this stage / mode, the system may be in a standby state in which no power is transmitted and it does not automatically proceed to the power transfer stage. Such a stage may be referred to as a connection stage and may be a static stage in which the system remains until a specific event or action occurs. For example, when a kitchen appliance (e.g., a blender) is positioned for wireless power transfer, this may be detected by the power transmitter and may enter the connection stage. It may then remain in this stage, for example until the user switches the device (e.g., a blender) to the on position, in response to which the system may proceed to the active power transfer stage.

[0093] Transitioning from a passive connection phase, or from a state where there is no proximity of a power transmitter and a power receiver (e.g., no intermediate connection phase), to an active power transfer phase is a critical process with multiple steps and processes that may be performed to ensure safe, reliable, efficient, high-performance initialization of the power transfer phase.

[0094] In the following, reference will be made to Figure 1-Figure 6 The power delivery system of FIG. 1 describes specific advantageous methods that can generally achieve one or more of these preferences.

[0095] Figure 7 A flow chart showing elements / steps of a method of operation for a power transmission system. Specifically, Figure 7 A method of initializing a power transfer phase from, for example, a connection or other non-power phase may be shown.The figure shows steps performed by the system, in particular steps performed by both a power transmitter and a power receiver. Figure 8 The power transfer signal generated by the transmitter coil 103 during the initialisation process and during the initial part of the power transfer phase is shown.

[0096] In this example, the wireless power transfer system is initially in a non-power transfer phase, which may be, for example, a standby or connection phase, in which no power transfer occurs. However, in, for example, a connection phase, the power transmitter and the power receiver may be aware of each other and have established a bidirectional communication link that allows them to exchange data messages.

[0097] In this example, the method starts at step 701, where the power receiver is arranged to operate in a first load state, which may also be referred to as a low power load state, an unloaded state or a load decoupled state. In this first load state, the power receiver may specifically decouple the load 605 from the input resonant circuit. Therefore, the power transfer signal / electromagnetic field generated by the transmitter coil 103 may typically be very low (or even zero), such as Figure 8 shown.

[0098] The power receiver may also be operable to switch to a second load state, which may also be referred to as a low power load state, a load state or a load decoupling state. In the second load state, the power receiver may couple the load 605 from the input resonant circuit.

[0099] The power receiver may be arranged to operate in at least two different load states in which the power transmission signal and the drive signal of the power transmitter have different power loads. The difference between the two load states is that at least one load (component) is coupled to the input resonant circuit (and loaded with the power transmission signal / drive signal / electromagnetic field generated by the power transmitter / power transmitter coil) in one load state (the second load state), but is decoupled from the input resonant circuit (and not loaded with the power transmission signal / drive signal / electromagnetic field generated by the power transmitter / power transmitter coil) in another load state. Therefore, for the first load state and the second load state, the loading of the electromagnetic field (and therefore the drive signal) generated by the power transmitter by the power receiver is different.

[0100] Typically, the difference in loading between the first load state and the second load state may be significant.In many embodiments, the (power) loading in the first load state does not exceed 25%, 10%, 5% or even 2% of the loading in the second load state.

[0101] The power receiver may present substantially different loads to the power transmitter in two load states. In particular, the first load state may substantially correspond to a situation where no power is provided to the terminal load of the power receiver, and the second load state may substantially correspond to a situation where the terminal load is fully powered by the power transmitter and the 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, power is not fed to the load 605, and in the second load state, power is fed to the load 605.

[0102] It should be understood 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 and provided to power various control functions of the power receiver device). However, the amount of power extracted in the first load state and the second load state will tend to be substantially different.

[0103] Step 701 is followed by step 703, in which the power receiver enters the first load state (or remains in this state), and in step 703, the power receiver transmits a request (message) to the power transmitter, wherein the request is a request for the power transmitter to initiate a transition from the non-power transmission phase (connection phase) to the power transmission phase. Figure 8 As shown, at a certain time 801, the power receiver continues to transmit a request to the power transmitter to initiate a new power transfer operation.

[0104] For example, the power receiver may (e.g., as part of step 701 or 703) continuously monitor for events indicating that a power transfer is desired. For example, it may remain in the connection phase while continuously monitoring for user input indicating a desire to initiate a power transfer. For example, for a kitchen appliance, a user pressing an on button may be detected, resulting in the initiation of a power transfer. In other embodiments, other methods may be used, such as automatically detecting a change in the coupling factor between the power receiver and the power transmitter (e.g., movement of the power receiving device may result in the initiation of a power transfer) or automatically detecting a change in the environment (e.g., using motion detection).

[0105] When the power receiver decides that a power transfer operation should be initiated, it transmits a first request message to the power transmitter. The power transmitter receives the first request message in step 705. It should be understood that many different methods for transmitting messages / data from a power transmitter to a power receiver are known, and any suitable method may be used without impairing the methods and principles described.

[0106] In response to receiving the first request message, the power transmitter initiates a process of initialization of a power transfer operation. In the described method, in response to receiving the first request message, the power transmitter proceeds to step 707. In step 707, the measurement circuit / processor 309 of the power transmitter performs a first measurement of a first power transfer parameter. The power transfer parameter may specifically be a parameter that depends on / reflects the loading of the power receiver to the power transfer signal / electromagnetic field generated by the transmitter coil. Such operating parameters may include determination of a load level, a coupling factor, a size of the loading, etc.

[0107] Thus, when the power receiver is in the first decoupled load state, i.e. when the loading is reduced compared to the second (coupled / connected) load state, the first measurement is a measurement of the power transfer parameter. The first measurement may also be referred to hereinafter as a decoupled load measurement, and the measured power transfer parameter may be referred to as a decoupled power transfer parameter.

[0108] The power transmitter may then proceed to step 709, in which the power transmitter transmits a first confirmation to the power receiver. The first confirmation may be a message indicating to the power receiver that the first measurement has in fact been performed (successfully). Figure 8 As shown in , at a certain time 803, the power transmitter proceeds to transmit a confirmation (message) to the power receiver indicating that the first decoupling measurement has been performed.

[0109] In step 711, the power receiver receives the first confirmation, and in response, it proceeds to step 713, in which it switches from the first load state to the second load state. Thus, in a specific example, the power receiver is arranged to switch from the load-decoupled load state to the load-coupled load state in response to the power receiver receiving the first confirmation from the power receiver. Thus, the power transmitter performs a switch from operating in a mode where the loading of the power transmitter / power transfer signal is very low to a mode where the loading of the power transmitter / power transfer signal is very high, and in particular, it can switch from a shutdown or standby loading of the input resonant circuit / power transfer signal / electromagnetic field to full power stage loading.

[0110] After switching to the second load state, the power receiver proceeds to step 715, in which it transmits a second request (message). The second request may be a request for the power transmitter to start generating a power transfer signal for powering the power receiver. It may be a request to start a 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 the load is coupled to the input resonant circuit. Thus, as Figure 8 As shown, at some point in time 805, the power receiver proceeds to transmit a request to the power transmitter to begin a power transfer phase.

[0111] In step 717, the power transmitter proceeds to receive a second request, and in response, it proceeds to step 719, where the measurement circuit / processor 309 performs a second measurement of the power transmission parameter. The power transmission parameter may specifically be a parameter that depends on / reflects the loading of the power receiver to the power transmission signal / electromagnetic field generated by the transmitter coil. Such operating parameters may include determinations of load levels, coupling factors, size of loading, etc. In many embodiments, the power transmission parameter measured in the first measurement will be the same as the power transmission parameter measured in the second measurement, but in other embodiments, the two measurements may measure different power transmission parameters. Therefore, in step 707, a first measurement may be performed on the first power transmission parameter using a first measurement method (technique / algorithm). In step 719, a second measurement may be performed on the second power transmission parameter using a second measurement method (technique / algorithm). The first measurement, power transmission parameter, and / or measurement method (technique / algorithm) may be the same as the second measurement, power transmission parameter, and / or measurement method (technique / algorithm); or may be different.

[0112] Thus, when the power receiver is typically substantially in the second coupled load state, i.e. when the loading is increased compared to the first (decoupled) load state, the second measurement is a measurement of the power transfer parameter. The second measurement may also be referred to hereinafter as coupled load measurement, and the measured power transfer parameter may be referred to as coupled power transfer parameter.

[0113] Then, the power transmitter proceeds to step 721, in which it proceeds to enter a power transmission phase, in which the power transmitter generates a power transmission signal in order to transmit power to the power receiver. Figure 8 As shown, at a certain time 807, the power transmitter may proceed to enter the power transfer phase and generate a significant level of power transfer signal to transfer power to the power receiver. The power receiver further proceeds to maintain or enter the power transfer phase 723.

[0114] In some embodiments, the generated power transfer signal may be at a semi-constant level (e.g., changing only based on a power control loop). However, in other embodiments, such as Figure 8In an example of, a power transfer signal may be generated to follow the amplitude of a time-varying power signal to the driver. For example, the power supply voltage to the output circuit of the driver may be a signal derived directly from the mains as AC or a rectified but unsmoothed DC signal. In this case, the power transfer signal amplitude will vary over time according to the varying power supply signal. In addition, in some embodiments, the power transfer phase may include alternating time intervals for power transfer and for other functions such as foreign object detection and / or communication. Thus, the power transfer time intervals may typically be separated by short time intervals in which no power transfer signal is generated. Such intervals may typically be located at a minimum in the amplitude of the power transfer signal / power supply voltage. Figure 8 An example of this operation is shown during the power transfer phase.

[0115] In the method, the power transmitter is arranged to enter the power transfer phase in response to two measurements (i.e., depending on both the coupling measurement and the decoupling measurement, and in particular in many embodiments depending on the value of the measured power transfer parameter). In some embodiments, entering the power transfer phase may be conditional on the measurement, for example, the power transfer phase may only be entered if the measured coupling and / or decoupling 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, for example, the initial value of a parameter of the drive signal / power transfer signal may depend on the measured coupling and / or decoupling power transfer parameter values.

[0116] In many scenarios and embodiments, the method may provide a particularly advantageous initialization of a power transfer operation and a power transfer phase. The method provides an efficient and reliable method with reduced risk of errors and unexpected situations. The method provides reliable interaction and synchronization between a power transmitter and a power receiver when initializing the power transfer. In addition, the method includes performing power transmitter-side measurements of power transfer parameters for substantially different loads and operating points before entering the power transfer phase, and the power transfer phase may be entered based on the measurements. This may generally provide a more reliable and improved initialization of the power transfer phase, and may, for example, ensure that power transfer only starts when it is safe to do so and / or may start with initial properties that are closer to a desired operating point.

[0117] In many embodiments, the measurements may be performed with substantial differences in the loading of the drive signal / power transmitter / electromagnetic field / power transfer signal. In many embodiments, the power difference in loading between the first load state and the second load state, and thus between the first measurement and the second measurement, is not less than 5, 10, 15, 20, 50, 100, 500 or even 1000 Watts. Thus, information relating to very different operating points may be generated during initialization and may therefore result in an improved adaptation of operation and power transfer.

[0118] In some embodiments, the first measurement and / or the second measurement may be used to perform a foreign object detection test. If any of these foreign object detection tests results in a determination that a foreign object may potentially be present, the power transmitter may proceed to terminate initialization of the power transfer phase. The method may allow accurate foreign object detection for different operating points and may provide improved safety and more reliable initialization of the power transfer phase. In particular, foreign object detection performed at different operating points may provide more accurate foreign object detection.

[0119] In fact, advantageously, foreign object detection may first be performed for the decoupled load state. This test may be performed with a low level power transfer signal, which may result in a less accurate test. However, larger objects that extract a significant amount of power may still be detected, and the system will therefore only proceed to the second foreign object detection test, which is performed when in the coupled load state, if any foreign object is sufficiently benign so as not to be unsafe at the higher power level of the second measurement. However, due to the potentially higher power transfer signal level, the second measurement / coupled foreign object detection test may be substantially more accurate, so that even relatively small foreign objects may be detected. Therefore, the combination of the two foreign object detection tests, respectively in the coupled and uncoupled load states, may provide improved performance.

[0120] It will be appreciated that different methods for foreign object detection in wireless power transfer systems are known and any suitable method or algorithm may be used. The methods and algorithms may be the same for the first detection and the second detection, or may actually be different.

[0121] One possible approach is based on determining an unknown power loss. In this approach, the power transmitter can measure the generated power level and can compare it with the expected power loss of the power receiver. In a low-complexity embodiment, the power loss caused by the power receiver in the decoupled load state can simply be considered to be substantially zero. In other embodiments, a nominal power loss (e.g., caused by loading of harmless metal and / or standby circuits of the power receiver) can be expected and compared with the measured power transmitter power loss. Therefore, the first measurement can be a measurement of the power level of the drive signal, and the power level can therefore be compared with the expected value of the power receiver when it is in the decoupled load state. If the measured power exceeds the expected value margin / threshold, it can be considered that a foreign object is detected.

[0122] The power transmitter may estimate its 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 transmitter (e.g., estimated power losses in the inverter, primary coil, and metal components that are part of the power transmitter, etc.).

[0123] The power transmitter can estimate the resulting power loss by subtracting the expected extracted power from the transmitted power. If the difference exceeds a threshold, the transmitter will assume that too much power is being consumed in the foreign object, and it can then proceed to initiate termination of the power transfer.

[0124] The same approach can be used for coupled foreign object detection, where the expected power is increased and the receiver power loss is modified to include the expected power delivered to the load.

[0125] Therefore, in such an embodiment, the first measurement and / or the second measurement may be a measurement of a power level of a drive signal / power transfer signal for the power transmitter, and foreign object detection may be performed by comparing the measurement result with an expected value.

[0126] Another option is to measure the quality or Q factor of the resonant circuit formed by the transmitter coil 103 and the receiver coil 107 together with the corresponding capacitance and resistance. A decrease in the measured Q factor (compared to an expected value) may indicate the presence of a foreign object. Thus, in such an embodiment, the first measurement and / or the second measurement may be a measurement of the Q factor for the power transmitter and power receiver devices, and foreign object detection may be performed by comparing the measurement result with the expected value.

[0127] In some embodiments, the power transmitter may be arranged to generate a power transfer signal during the power transfer phase in dependence on the first measurement and / or the second measurement.

[0128] For example, an initial signal level for the power transfer phase when the power transfer phase starts may be set according to the power level measured during the second measurement. Thus, the coupling measurement may include measuring the power level of the drive signal when the power receiver is in a coupled load state. When initiating the power transfer phase, the power transmitter may, for example, set the power level (e.g., by controlling the voltage and / or current amplitude of the drive signal) to the same value, or possibly to another value determined as a fixed function thereof.

[0129] In some embodiments, the second request from the power receiver may include an indication of requested power transfer parameters, such as a requested power level specifically for the power transfer phase. The power transmitter may be arranged to set parameters of the drive signal / power transfer signal in accordance with the request.

[0130] For example, the power receiver may request that a power level be provided for the power transfer phase (e.g., twice the load during the second measurement period). The power transmitter may determine a suitable amplitude of the drive signal (e.g., current or voltage) based on the request and, for example, a value measured during the second measurement period (e.g., current or voltage). For example, the amplitude measured during the second measurement period may be scaled by a given scaling factor reflecting the increased power level.

[0131] In some embodiments, the first measurement and / or the second measurement may be a resonant frequency measurement. For example, a frequency sweep may be performed which allows the resonant frequency for power transfer to be determined by detecting peaks in, for example, the current or power of the drive signal. The performance at different loads may be used to provide information of the resonant frequencies at different loads. For example, such information may be used to determine a suitable operating frequency when starting a power transfer phase. For example, it may be arranged to adapt or select a suitable operating range for a power control loop which adapts the transfer power level by changing the drive / operating frequency. For example, the operating range may be set to be, for example, between 60% and 80% of the measured resonant frequency (or, for example, an average frequency of different measured resonant frequencies), wherein the initial operating frequency when starting the power transfer phase is set to the middle of the operating range (e.g., at 70% of the measured resonant frequency). As another example, the resonant frequencies at different loads may be used to determine a coupling factor between a transmitter coil and a receiver coil, and, for example, the initial power level when entering the power transfer phase may be set to reflect the determined coupling factor.

[0132] In some embodiments, the power transmitter may start power transfer in response to the second request by generating a drive signal and a power transfer signal with suitable parameters (such as frequency, current, voltage and / or power) to provide appropriate wireless power transfer. In many embodiments, the power receiver may simply enter a mode suitable for the power transfer phase when transmitting the second request. For example, it may connect the load to the power path and the input resonant circuit (or keep it connected) so that when a suitable power transfer signal is generated by the power transmitter entering the power transfer phase, suitable power is transferred to the load. For example, for a stirrer, the load may be a motor that is automatically started when the power transmitter generates a suitable power transfer signal.

[0133] In some embodiments, the power receiver may operate in a standby mode until it detects that the power transmitter has entered a power transfer phase. For example, the switch 607 may disconnect the load 605 until it detects that the power transfer signal / generated electromagnetic field strength / induced voltage is above a threshold, at which point it may switch to connect the load 605. For example, this may ensure that the load (which may include, for example, delicate electronic circuits) is not powered until full power is provided.

[0134] In some embodiments, the power transmitter may be arranged to transmit a second confirmation to the power receiver after the second measurement and in conjunction with entering the power transfer phase and, for example, before or after entering the power transfer phase. Figure 8 As shown, the power transmitter may transmit a second acknowledgement to the power receiver at a given time 809, which may typically be, for example, shortly before the power transfer phase begins.

[0135] The second confirmation may indicate to the power receiver that the second measurement (and indeed all other operations) has been successfully performed and that a power transfer phase is starting or has started. The power receiver may proceed in response to receiving the second confirmation to put the power receiver into a suitable power transfer phase mode, such as, for example, by switching switch 607 to connect load 605 to the input resonant circuit / power path.

[0136] In some embodiments, the power transmitter may be arranged to transmit a non-acknowledgement to the power receiver in response to termination of initiation of power transfer. This may allow the power receiver to terminate the power transfer phase operation. For example, it may switch to a minimum load and / or may generate and present a user indication (e.g., using a provided low level / standby power transfer signal or internal battery).

[0137] For example, if the first measurement or the second measurement results in an unsatisfactory value for the measured parameter, it can be decided that the power transfer phase should not continue and the initiation of the power transfer phase should be terminated (for example, if a foreign object is detected in the coupled load state or the decoupled load state, the initialization of the power transfer is terminated and a non-confirmation message is transmitted to the power receiver).

[0138] As another example, if a timeout occurs, such as due to not receiving an expected response or message in time, the power transmitter may proceed to terminate initialization of the power transfer phase and transmit a not-acknowledgement to the power receiver.

[0139] In some embodiments, the power transmitter may be arranged to synchronise the start of a power transfer phase with the timing of a cycle of the power transmitter's main power supply. This may be particularly advantageous in methods where the power transfer signal amplitude varies over time due to variations in the supply voltage generated from the mains supply to the driver.

[0140] For example, in many scenarios where the amplitude of the power transfer signal varies, for example due to changes in the power supply voltage, the start of the power transfer phase can be synchronized to start at the minimum amplitude of the power transfer signal. For example, if the power transfer signal amplitude depends directly on the power supply voltage, the start of the power transfer phase can be synchronized to start at the moment when the power supply voltage is minimum. In many embodiments, the start of the power transfer phase can be synchronized to occur at the moment of zero crossing of the AC signal from which the driver 301 is supplied (in some cases, a delay may be included). This approach can be applicable to scenarios where the AC power supply directly feeds the output of the inverter or when this power supply signal is completed after rectification. In fact, even if a smoothing capacitor is provided, the final power supply voltage will still tend to have a ripple that is synchronized with the AC signal, and therefore the minimum amplitude of the drive signal can still be synchronized with the AC signal (for example, with a delay related to the load). Therefore, in many embodiments, the start of the power transfer phase is synchronized with the AC signal (for example, the mains power signal), from which the voltage supply for the output circuit of the driver 301 is derived. Figure 8 An example is shown where the start 807 of the power transfer phase is synchronized with the minimum / zero crossing of the power and drive signal amplitudes.

[0141] In many cases, such an approach may provide a more gradual start of the power transfer phase, which may, for example, reduce power transients at the load when commencing power transfer.

[0142] In many embodiments, the process may include various timeouts for different operations and steps in the initialization process. This may allow for a reliable process that includes built-in provisions for terminating the process if there is a problem. Figure 8 Some examples of timeouts 811 that may be built into the system are shown:

[0143] Timeout A:

[0144] - In many embodiments, the time between the power receiver transmitting the first request to move into the power transfer mode and the power transmitter transmitting the first confirmation should not exceed 50, 100 or 200 ms.

[0145] -At this point, the power transmitter can perform foreign object detection, impedance checks, or other system measurements on the unloaded system.

[0146] Timeout B:

[0147] - In many embodiments, the time between the power transmitter acknowledgment message and the power receiver switching to the coupled load state and transmitting the second request should not exceed 20, 40 or 60 ms.

[0148] Timeout C:

[0149] - In many embodiments, the time between the second request and the power transmitter transmitting the second confirmation should not exceed 10, 20 or 30 ms.

[0150] - This is preferably as short as possible, since a lot of power can be transferred in this case.

[0151] - At this point, the power transmitter can perform foreign object detection, impedance checks or other system measurements on the load system (secondary side switch is closed, so the load is attached).

[0152] Timeout D:

[0153] - In many embodiments, the time between the power transmitter transmitting the second acknowledgement and the start of the power transfer phase should not exceed 10, 20 or 30 ms.

[0154] Timeout E:

[0155] - In many embodiments, 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.

[0156] Thus, the power transmitter and power receiver may be arranged to perform operations quickly enough to meet the timing described above, thereby allowing improved performance.

[0157] In many embodiments, the power transmitter and the power receiver may also be arranged to perform timeout detection. For example, if one of the above timings does not meet a margin of, for example, 0, 10, 20, 30, 50, 100 milliseconds (different margins may be used for different timeouts), the power transmitter and / or the power receiver may assume that a timeout / error has occurred and terminate the initialization of the power transfer. For example, this may include transmitting a power transfer termination message to the complementary device.

[0158] It should be understood that, for the sake of clarity, the above description has described embodiments of the present invention with reference to different functional circuits, units and processors. However, it is apparent that any suitable distribution of functions between different functional circuits, units or processors may be used without departing from the present invention. For example, functions shown as being performed by separate processors or controllers may be performed by the same processor or controller. Therefore, references to specific functional units or circuits are only considered references to suitable means for providing the described functions, rather than indicating a strict logical or physical structure or organization.

[0159] The present invention may be implemented in any suitable form, including hardware, software, firmware or any combination of these. 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 the embodiments of the present invention may be implemented physically, functionally and logically in any suitable manner. In fact, the functions may be implemented in a single unit, in multiple units or as a part of other functional units. In this way, the present invention may be implemented in a single unit, or may be physically and functionally distributed between different units, circuits and processors.

[0160] Although the present invention has been described in conjunction with some embodiments, the present invention is not intended to be limited to the specific form set forth herein. On the contrary, the scope of the present invention is limited only by the appended claims. In addition, although it seems that features have been described in conjunction with specific embodiments, it will be appreciated by those skilled in the art that the various features of the described embodiments may be combined according to the present invention. In the claims, the term includes does not exclude the presence of other elements or steps.

[0161] 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, it is possible to combine these features advantageously, and inclusion 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 indicates that the feature is also applicable to other claim categories. Including features in a dependent claim of an independent claim does not mean a limitation to the independent claim, but indicates that the feature is also applicable to other independent claims. 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 this order. On the contrary, these steps can be performed in any suitable order. In addition, singular references do not exclude multiple. Therefore, references to "one", "one", "first", "second", etc. do not exclude multiple. The figure marks in the claims are provided only as clear examples and should not be interpreted as limiting the scope of the claims in any way.

Claims

1. A method for initiating power transfer in a wireless power transfer system, the wireless power transfer system comprising a power transmitter (101), the power transmitter transmitting power to a power receiver (105) using a power transfer signal, the power transfer signal inducing a current in a power receiver coil (107) of the power receiver (105), the method comprising: During a non-power transfer phase, the power receiver (105) transmits (703) a first request to the power transmitter (101), the first request being a request to switch from the non-power transfer phase to a power transfer phase; After transmitting the first request, the power receiver (105) operates in a first load state (701), and when the power receiver (105) operates in the first load state, the load (605) of the power receiver is decoupled from the power receiver coil; The power transmitter (101) receives (705) the first request; In response to receiving the first request, the power transmitter (101) performs (707) a first measurement of a first power transfer parameter; After the first measurement, the power transmitter (101) transmits (709) a first acknowledgement to the power receiver (105); The power receiver (105) receives (711) the first confirmation; In response to receiving the first acknowledgement, the power receiver (105) switches (713) to a second load state, wherein when the power receiver (105) operates in the second load state, the load (605) of the power receiver (105) is coupled to the power receiver coil (107); In conjunction with entering the second load state, the power receiver (105) transmits (715) a second request to the power transmitter, the second request being a request for power; The power transmitter (101) receives (717) the second request; In response to receiving the second request, the power transmitter (101) performs (719) a second measurement of a second system parameter; The power transmitter (101) enters (721) a power transfer phase for generating a power transfer signal based on the first measurement and the second measurement.

2. The method according to claim 1, wherein: The power receiver (105) is arranged to include at least one requested power transfer parameter in the second request; and the power transmitter (101) is arranged to set at least one parameter of the power transfer signal according to the requested power transfer parameter.

3. A method according to any preceding claim, wherein: The power transmitter (101) is arranged to generate the power transfer signal to have a property that depends on at least one of the first measurement and the second measurement.

4. A method according to any preceding claim, wherein: The power transmitter (101) performs foreign object detection based on the first measurement and terminates initiating the power transfer if the foreign object detection indicates the presence of a foreign object.

5. A method according to any preceding claim, wherein: The power transmitter (101) performs foreign object detection based on the second measurement and terminates initiating the power transfer if the foreign object detection indicates the presence of a foreign object.

6. A method according to any preceding claim, wherein: The power transmitter (101) is arranged to transmit a second acknowledgement to the power receiver (105) after the second measurement and before entering the power transfer phase.

7. The method according to claim 6, wherein: The power transmitter (101) is arranged to generate the power transfer signal during the power transfer phase with a maximum delay of 20 milliseconds for transmitting the second acknowledgement.

8. A method according to any preceding claim, wherein: The power transmitter (101) is arranged to synchronize the start of the power transfer phase with the timing of a cycle of a power supply signal to the power transmitter (101).

9. A method according to any preceding claim, wherein: The power transmitter (101) is arranged to terminate initiating the power transfer if no second request is received before expiration of a predetermined time interval.

10. A method according to any preceding claim, wherein: The power transmitter (101) is arranged to transmit a non-acknowledgement message to the power receiver (105) in response to the termination of the initiation of the power transfer.

11. A method according to any preceding claim, wherein: The load is a load of at least 10 watts.

12. A method for a power receiver (105) to initiate power transfer in a wireless power transfer system, the wireless power transfer system comprising a power transmitter (101), the power transmitter transmitting power to the power receiver (105) using an inductive power transfer signal, the inductive power transfer signal inducing a current in a power receiver coil (107) of the power receiver, the method comprising: transmitting a first request to the power transmitter (101) 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, a load of the power receiver (105) being decoupled from the power receiver coil when the power receiver (105) is operating in the first load state; receiving a first confirmation from the power transmitter (101); In response to receiving the first acknowledgement, switching to a second load state, wherein when the power receiver (105) operates in the second load state, the load of the power receiver (105) is coupled to the power receiver coil; In conjunction with entering the second load state, transmitting a second request to the power transmitter (101), the second request being a request for power; Entering the power transfer phase, wherein the power receiver (105) extracts power from the power transfer signal.

13. A method for a power transmitter (101) to initiate power transmission in a wireless power transmission system, the wireless power transmission system comprising the power transmitter (101), the power transmitter transmitting power to a power receiver (105) using an inductive power transmission signal, the method comprising: receiving a first request, the first request being a request to switch from a non-power transfer phase to a power transfer phase; In response to receiving the first request, performing a first measurement of a first power transfer parameter; After the first measurement, sending a first acknowledgement to the power receiver (105); receiving a second request, the second request being a request for power and indicating that the power receiver (105) has switched from a first load state in which a load is decoupled from a power receiver coil (107) of the power receiver (105) to a second load state in which the load is coupled to the power receiver coil; In response to receiving the second request, performing a second measurement of a second system parameter; as well as A power transfer phase is entered for generating a power transfer signal based on the first measurement and the second measurement.

14. A power receiver (105) for a wireless power transmission system, the wireless power transmission system comprising a power transmitter (101), the power transmitter transmitting power to the power receiver (105) using an inductive power transmission signal, the power receiver (105) comprising: a power receiver coil (107) arranged to extract power from the power transfer signal by induction; a first transmitter (609) arranged to transmit a first request to the power transmitter (101) during a non-power transfer phase, the first request being a request to switch from the non-power transfer phase to a power transfer phase; a mode processor (601, 607) arranged to control the power receiver to operate in a first load state after the transmission of the first request, the load of the power receiver (105) being decoupled from the power receiver coil (107) when the power receiver (105) operates in the first load state; a receiver (609) arranged to receive a first acknowledgement from the power transmitter (101); in, The mode processor (601, 607) is further arranged to control the power receiver (105) to switch to a second load state in response to receiving the first confirmation, when the power receiver (105) operates in the second load state, the load of the power receiver (105) being coupled to the power receiver coil; The transmitter (609) is arranged to transmit a second request to the power transmitter (101) in conjunction with entering the second load state, the second request being a request for power; Furthermore, the power receiver (105) further comprises: A controller (601) is arranged to enter a power transfer phase, wherein power is extracted from the power transfer signal by the power receiver (105).

15. A power transmitter (101) for a wireless power transfer system, the wireless power transfer system comprising a power receiver (105), the power receiver being arranged to receive power from the power transmitter (101) using an inductive power transfer signal, the method comprising: a receiver (307) arranged to receive a first request, the first request being a request to switch from a non-power transfer phase to a power transfer phase; a measurement circuit (309) arranged to perform a first measurement of a first power transfer parameter in response to receiving the first request; a transmitter (307) arranged to transmit a first acknowledgement to the power receiver (105) after the first measurement; in, The receiver (307) is arranged to receive a second request, the second request being a request for power and indicating that the power receiver (105) has switched from a first load state, in which a load is decoupled from a power receiver coil (107) of the power receiver (105), to a second load state, in which the load is coupled to the power receiver coil; The measurement circuit (309) is arranged to perform a second measurement of a second system parameter in response to receiving the second request; Furthermore, the power transmitter (101) further comprises: A controller (305) is arranged to enter a power transfer phase generating a power transfer signal based on the first measurement and the second measurement.

16. A wireless power transmission system comprising the power transmitter (101) according to claim 15 and the power receiver (105) according to claim 14.

Images