Wireless Power Transmission System

Abstract

To provide a wireless power transmission system to solve a problem in which existence of a power transmission signal and the load can have adverse effect on the other operations such as foreign matter detection and communication behavior.SOLUTION: A power transmitter 101 for a wireless power transmission system has a transmission coil 103. A driver 201 adopts repetition time flame having power transmission time interval and reduction power time interval in which power level of a power transmission signal is reduced, and generates a driving signal for the transmission coil 103. The driver 201 generates the driving signal for the transmission coil 103 to generate the power transmission signal. A communication device 205 receives a message from a power receiver 105. An adapter 213 adapts timing characteristic of the reduction power time interval at least according to a first message received from the power receiver 105. A synchronizer 206 synchronizes foreign matter detection with generation of a test signal so as to be generated between the reduction power time interval.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to the operation of wireless power transfer systems, and more particularly to foreign object detection in wireless power transfer systems. [Background technology]

[0002] Many current electronic products require dedicated electrical contacts to be powered from an external source. However, this tends to be impractical, requiring the user to physically insert a connector or establish other physical electrical contact. Power requirements also typically vary widely, and most devices are currently provided with their own dedicated power source, resulting in a typical user having a number of different power sources, each dedicated to a specific device. While the use of an internal battery may eliminate the need for a wired connection to a power source during use, this is only a partial solution, as the battery still needs to be charged (or replaced). The use of batteries can also significantly increase the weight, potential cost and size of the device.

[0003] To provide a significantly improved user experience, wireless power devices have been proposed in which power is transferred inductively from a transmitting inductor in a power transmitting device to a receiving coil in an individual device.

[0004] Power transfer by magnetic induction is a well-known concept and is mainly applied to transformers with tight coupling between the primary transmitting inductor / coil and the secondary receiving coil. By separating the primary transmitting coil and secondary receiving coil between the two devices, wireless power transfer becomes possible using the principle of loosely coupled transformers.

[0005] Such a configuration allows wireless power transmission to the device without the need for wires or physical electrical connections. In fact, it simply allows the device to be placed adjacent to or above the transmitting coil to be charged or powered from the outside. For example, the power transmitting device can be configured to have a horizontal surface on which the device can simply be placed to be powered.

[0006] Moreover, such wireless power transmission configurations can be advantageously designed to allow a power transmitting device to be used with a variety of power receiving devices. In particular, a wireless power transmission approach known as the "Qi standard" has been defined and is currently being further developed. This approach allows a power transmitter conforming to the Qi standard to be used with a power receiver also conforming to the Qi standard, even if they are not from the same manufacturer or proprietary to each other. The Qi standard further includes several features to enable operation tailored to a specific power receiver (e.g., depending on a specific power drain).

[0007] The Qi standard is being developed by the Wireless Power Consortium, and further information can be found at the Wireless Power Consortium's website, http: / / www.wirelesspowerconsortium.com / index.html, where among other things the defined specifications can be found.

[0008] Power transfer systems such as Qi often generate very large electromagnetic fields to transmit the required levels of power to the power receiver. The presence of such strong fields can have an adverse effect on the environment in many situations.

[0009] For example, a potential problem with wireless power transmission is that power can be unintentionally transmitted to metallic objects or the like that happen to be near the power transmitting device. For example, if a foreign object such as a coin, key, ring, or the like is placed on the platform of a power transmitter configured to receive a power receiving device, the magnetic flux generated by the coil of the transmitter will induce eddy currents in the metallic object, causing the object to heat up. The heat rise can be significant and very inconvenient.

[0010] To reduce the risk of such scenarios occurring, it has been proposed to introduce foreign object detection, whereby the power transmitter can detect the presence of a foreign object and reduce transmission power and / or generate a user alert if a detection actually occurs. For example, the Qi system includes the ability to detect foreign objects and reduce power if a foreign object is detected. Specifically, Section 11 of the Qi standard version 1.2.1.1 describes various methods for foreign object detection.

[0011] One method for detecting such foreign objects is disclosed in WO20105018868A1. Another example is provided in WO 2012127335, which discloses an approach based on the determination of unknown power loss. In this approach, both the power receiver and the power transmitter measure their power, and the power receiver communicates the measured received power to the power transmitter. If the power transmitter detects that there is a significant difference between the power transmitted by the transmitter and the power received by the receiver, an unwanted foreign object may potentially be present, and power transmission may be scaled back or discontinued for safety reasons. This power loss scheme requires the power transmitter and power receiver to perform synchronized and accurate power measurements.

[0012] For example, in the Qi power transfer standard, a power receiver estimates its received power, e.g., by measuring the rectified voltage and current, multiplying them together, and adding an estimate of the power receiver's internal power losses (e.g., losses in the rectifier, the receiving coil, metal parts that are part of the power receiver, etc.). The receiver reports the determined received power to the power transmitter, e.g., at a minimum rate of every 4 seconds.

[0013] The power transmitter estimates its transmitted power by measuring the inverter's DC input voltage and current, multiplying them together, and correcting the result by subtracting an estimate of the transmitter's internal power losses, such as the estimated power losses in the inverter, the primary coil, and any metal parts that are part of the power transmitter.

[0014] The power transmitter can estimate the power loss by subtracting the reported received power from the transmitted power, and if the difference exceeds a threshold, the transmitter can determine that excess power is being dissipated in the foreign object and proceed to terminate power transmission.

[0015] Alternatively, it has been proposed to measure the quality or Q-factor of the resonant circuit formed by the primary and secondary coils and the corresponding capacitances and resistances. A reduction in the measured Q-factor may indicate the presence of a foreign object.

[0016] In practice, the methods described in the Qi standard tend to be difficult to achieve with sufficient detection accuracy, a difficulty exacerbated by the many uncertainties surrounding current specific operating conditions.

[0017] For example, a particular problem is the potential presence of friendly metals (i.e., metal parts of devices embodying power receivers or power transmitters), whose magnetic and electrical properties may be unknown (and vary between different devices) and therefore may be difficult to compensate for.

[0018] Furthermore, unwanted heating may result from the relatively small amounts of power dissipated in foreign metallic objects, which may make it necessary to detect even small power differences between transmitted and received power, which may be difficult, especially as the power levels of power transmission increase.

[0019] The reduced Q-factor approach may have better sensitivity for detecting the presence of metal objects in many scenarios, but it may still not provide sufficient accuracy and may be affected by friendly metals, for example.

[0020] The performance of foreign object detection depends on the specific operating conditions that exist when the test is actually performed. For example, when performing measurements for foreign object detection during the selection phase of the power transfer initialization process as described in the Qi specification, the signal provided by the power transmitter for the measurement must be small enough so as not to wake up the power receiver. However, such small signals generally have a poor signal-to-noise ratio, resulting in poor measurement accuracy.

[0021] The requirement for a small measurement signal can have other detrimental effects: a power receiver exposed to a small measurement signal may exhibit a leakage current that depends on the level of the measurement signal, the coupling between the primary and secondary coils, and the state of charge of the capacitor at the output of the rectifier. This leakage current may therefore vary depending on the actual conditions. Since the leakage current affects the reflected impedance at the power transmitting coil, the measurement of the quality factor also depends on the specific current conditions.

[0022] Another issue is that foreign object detection is typically a very sensitive test in which it is desirable to detect relatively small changes caused by the presence of a foreign object in an environment where the operating conditions and scenarios in which the test is performed can vary greatly.

[0023] Therefore, current algorithms tend to be sub-optimal and may not provide optimal performance in some scenarios or examples, in particular not detecting the presence of foreign objects or falsely detecting foreign objects when none are present.

[0024] The difficulty of accurate foreign object detection is particularly challenging in scenarios where the power transfer signal has high and / or fluctuating power levels. Thus, foreign object detection is particularly challenging during the power transfer phase, especially for powered devices that exhibit large and fluctuating loads.

[0025] Other operations of the power transmission system may also be susceptible to such effects. For example, in many situations, communication between a power transmitter and a power receiver may be adversely affected by large loads, especially large load variations.

[0026] In many systems, communication from the power receiver to the power transmitter can use load modulation, where the load of the power transmission signal varies depending on the data to be transmitted. However, such load modulation can be difficult to detect if the power transmission load of the power transmission signal varies at the same time. Similarly, communication from the power transmitter to the power receiver can be achieved by modulating (e.g., amplitude or frequency modulating) the power transmission signal, but interference to such modulation can be caused by fluctuations in the parameters of the power transmission signal due to the varying load.

[0027] Indeed, even when completely separate carriers are used for communication, such as in an NFC communication link, the very large and fluctuating electromagnetic fields caused by power transmission signals can cause substantial interference, albeit in very different frequency bands.

[0028] Thus, the presence of the power transmission signal and its loading can adversely affect other operations, such as foreign object detection and communication operations. Summary of the Invention [Problem to be solved by the invention]

[0029] Thus, improved operations for power transmission systems would be advantageous, and in particular, an approach that enables increased flexibility, reduced cost, reduced complexity, improved foreign object detection, improved communication, improved support for different loads, improved adaptability, backward compatibility, and / or improved performance would be advantageous. [Means for solving the problem]

[0030] SUMMARY OF THE DISCLOSURE Accordingly, the invention preferably seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0031] According to an aspect of the present invention, there is provided a power transmitter for wirelessly supplying power to a power receiver via an electromagnetic power transmission signal, the power transmitter comprising: a transmitter coil for generating the power transmission signal, the power transmission signal using a recurring time frame having at least a power transmission time interval and a reduced power time interval during a power transfer phase, wherein the power transmission signal has a power level reduced; a driver for generating a drive signal for the transmitter coil to generate the power transmission signal; a first communicator for receiving messages from the power receiver; an adapter for adapting timing characteristics of the reduced power time interval in response at least to a first message received from the power receiver; a synchronizer for synchronizing operation of the power transmitter to occur during the reduced power time interval; a test coil for generating an electromagnetic test signal; a test generator configured to generate a test drive signal for the test coil; and a foreign object detector configured to perform a foreign object detection test in response to parameters measured for the test drive signal during the reduced power time interval, the synchronizer configured to synchronize the test generator to provide the electromagnetic test signal during the reduced power time interval.

[0032] The present invention can provide improved performance in many embodiments and provide improved overall power transfer operations in many systems and embodiments. For example, in many embodiments, improved foreign object detection, and possibly communication, can be achieved by performing these operations during time intervals created to provide particularly favorable conditions for such operations.

[0033] This approach can reduce complexity in many embodiments and provide a high degree of backward compatibility in many systems, and may be particularly well suited to improving foreign object detection and communications in Qi wireless power transfer systems operating in accordance with Qi standard version 1.2 and earlier.

[0034] In many embodiments, the duration of a reduced power time interval is no more than 5%, 10%, or 20% of the duration of the time frame. In many embodiments, the duration of a reduced power time interval is no less than 70%, 80%, or 90% of the duration of the time frame.

[0035] The power transmitter, in some embodiments, can be configured to perform foreign object detection and possibly communication operations during the reduced power transmission time interval. In some embodiments, the power transmitter can be configured to time any of the foreign object detection and possibly communication operations to occur during the reduced power transmission time interval.

[0036] During the reduced power time interval, the power level of the power transmission signal is reduced corresponding to the reduced level of power transmitted from the power transmitter to the power receiver. The power level of the power transmitted from the power transmitter to the power receiver during the reduced power time interval may be considered to be reduced power level relative to the power level of the power transmitted from the power transmitter to the power receiver during a power transmission time interval (same as the reduced power time interval), and references to power and power level may be considered to relate specifically to actual power (IU-Cosφ).

[0037] According to an optional feature of the invention, the timing characteristic is the duration of a reduced power time interval.

[0038] The system may be configured to adapt the duration of the reduced power time interval in response to the communication from the power receiver to the power transmitter. This may allow for improved operation in many embodiments, allowing operations such as communication or foreign object detection to be performed during times of the day when conditions are particularly suitable for them. Adapting the duration of the reduced power time interval may ensure an improved trade-off between different conflicting requirements, for example requirements and preferences regarding the transmission of power from the power transmitter to the power receiver, and requirements and preferences regarding foreign object detection and communication.

[0039] The power transmitter may be configured to adapt the duration of the reduced power time interval subject to a minimum duration.

[0040] According to an optional feature of the invention, the timing characteristic is a duration between reduced power time intervals of successive recurring time frames.

[0041] In some embodiments the timing characteristic is the duration between successive repeating time frames.In some embodiments the timing characteristic is the duration of the repeating time frames.

[0042] The system may be configured to adapt the duration between the reduced power time intervals of successive repeating time frames in response to a communication from the power receiver to the power transmitter. This may allow for improved operation in many embodiments, allowing operations such as communication or foreign object detection to be performed during times of the day when conditions are particularly suitable for them. Adapting the duration between the reduced power time intervals of successive repeating time frames may ensure an improved trade-off between different conflicting requirements, e.g. requirements and preferences regarding the transmission of power from the power transmitter to the power receiver, and requirements and preferences regarding foreign object detection and communication.

[0043] The power transmitter may be configured to adapt the duration between reduced power transmission times of successive recurring time frames subject to the maximum duration.

[0044] According to an optional feature of the invention, the first communicator is configured to transmit a message to the power receiver, and the power transmitter is configured to transmit a message to the power receiver indicating at least one of a duration of the reduced power time interval and a period between the reduced power time intervals of successive recurring time frames prior to receiving the first message.

[0045] This can provide a particularly advantageous operation in many embodiments: the message can specify acceptable values, permissible values, restricted values ​​and / or preferred values.

[0046] The message may specifically be sent in response to a request for such information sent from the power receiver to the power transmitter.

[0047] According to an optional feature of the invention, the first message is a request message indicating a requested value for the timing characteristic, and the power transmitter is configured to accept or reject the requested value.

[0048] This can provide particularly advantageous operation in many embodiments, in particular allowing the power receiver to retain initiative or control of operation, which can be particularly advantageous in many scenarios.

[0049] According to an optional feature of the invention, the adapter is configured to determine the timing characteristics during an initialization phase prior to the power transfer phase.

[0050] This can provide particularly advantageous operation in many embodiments, and in particular can allow for low complexity operation in many embodiments.

[0051] According to an optional feature of the invention, the adapter is configured to dynamically adapt timing characteristics during the power transfer phase in response to a plurality of messages received from the power receiver during the power transfer phase.

[0052] This may provide particularly advantageous operation in many embodiments, allowing optimization specifically for current conditions.

[0053] According to an optional feature of the invention, the first communication device is configured to synchronize communication with the power receiver to occur during reduced power time intervals.

[0054] The present invention can, in many embodiments, allow for improved communication. This approach allows for improving the accuracy and / or reliability of communication between the power receiver and the power transmitter during the power transfer phase.

[0055] Note that communication synchronization may be performed only for a portion of communication, such as only power control communication, only communication from the power transmitter to the power receiver, or only communication from the power receiver to the power transmitter.

[0056] The power transmitter further has a test coil for generating an electromagnetic test signal, a test generator configured to generate a test drive signal for the test coil, and a foreign object detector arranged to perform a foreign object detection test in response to parameters measured for the test drive signal during the reduced power time interval, and a synchronizer configured to synchronize the test generator to provide the electromagnetic test signal during the reduced power time interval.

[0057] The present invention may, in many embodiments, enable improved foreign object detection. This approach may enable improved accuracy and / or reliability of foreign object detection testing during the power transfer phase. In many embodiments, this approach may reduce the uncertainty and variability of the foreign object detection testing, thereby improving performance. This approach may specifically reduce the impact of power transfer variability and operating conditions on foreign object detection. This approach may, for example, bias the system to operate at a particular, e.g., predetermined, reference scenario and operating point during foreign object detection. This may improve the consistency and predictability of foreign object detection testing. In particular, it may enable a more accurate and more reliable estimation of the power receiver's influence on the electromagnetic test signal, thus enabling the foreign object detector to improve compensation therefor.

[0058] This approach may introduce a foreign object detection time interval that allows the power receiver to operate at both high induced voltages but light loads, corresponding to, for example, high magnetic field strengths of the electromagnetic signal. In such a scenario, the impact of the foreign object may be more noticeable since the power induced in such objects will represent a higher percentage of the total power extracted. Indeed, a higher magnetic strength may result in a higher induced signal in the presence of any foreign object, and a reduced load may reduce the impact of the power receiver's presence in detecting whether a foreign object is present.

[0059] The foreign object detector may be configured to determine that the foreign object is detected if a difference between a power level of the electromagnetic test signal and a power received from the power receiver and indicated by a loading indicator indicative of an expected loading of the electromagnetic test signal is greater than or equal to a threshold value, and if the difference is less than or equal to a threshold value, the foreign object detector may determine that a foreign object is not detected.

[0060] The foreign object detector may be configured to determine that a foreign object is detected when a quality measurement of the resonant circuit including the test coil (determined from measurements of the drive signal) is below a threshold, which may typically depend on a message received from the power receiver.

[0061] In many embodiments, the test coil and the transmit coil may be the same coil. In many embodiments, the driver and test generator may be the same entity, and thus the same circuitry may generate both the drive signal and the test drive signal. In many embodiments, the power transmission signal and the test drive signal may share many parameter values, for example, they may have the same frequency.

[0062] According to an aspect of the present invention, there is provided a wireless power transmission system comprising the aforementioned power transmitter and further a power receiver, the power receiver comprising: a second communicator for communicating with the power transmitter; a request controller for sending a first message to the power transmitter, the first message comprising a request for a requested value of a timing characteristic; a response controller for receiving a request response from the power transmitter and determining the timing characteristic in response to the request response, the request response indicating whether the requested value has been accepted by the power transmitter; and a load controller for adapting the load of the power transmission signal to be reduced during a reduced power time interval.

[0063] The present invention can provide improved operation of wireless power transfer systems.

[0064] According to an optional feature of the invention, the request controller is configured to request a timing characteristic constraint from the power transmitter, the response controller is configured to receive a timing characteristic constraint indication from the power transmitter, and the request controller is configured to determine a requested value of the timing characteristic in response to the timing characteristic constraint.

[0065] This may allow for improved and / or easier operation in many embodiments.

[0066] According to an optional feature of the invention, the timing characteristic is a duration of a reduced power time interval, the request controller being configured to determine the required value of the timing characteristic subject to a maximum duration, and the adapter being configured to determine the value of the timing characteristic in response to a minimum duration.

[0067] This may allow for improved and / or easier operation in many embodiments.

[0068] In some embodiments, the power receiver may impose a maximum value and the power transmitter may impose a minimum value for the duration of a reduced power time interval.

[0069] According to an optional feature of the invention, the timing characteristic is a duration between reduced power transmission times of successive recurring time frames, and the request controller is configured to determine a required value of the timing characteristic subject to a minimum duration, and the adapter is configured to determine a value of the timing characteristic responsive to a maximum duration.

[0070] This may allow for improved and / or easier operation in many embodiments.

[0071] In some embodiments, the power receiver may impose a minimum value, and the power transmitter may impose a maximum value, for the period between reduced power transmission times of successive recurring time frames.

[0072] According to an aspect of the present invention, there is provided a method of operating a power transmitter for wirelessly supplying power to a power receiver via an electromagnetic power transmission signal, the method comprising the steps of: generating a power transmission signal by the power transmitter, the power transmission signal using a repetitive time frame having at least a power transmission time interval and a reduced power time interval during a power transmission phase, in which a power level of the power transmission signal is reduced; generating a drive signal for a transmitter coil to generate the power transmission signal; receiving a message from the power receiver; adapting timing characteristics of the reduced power time interval in response at least to a first message received from the power receiver; synchronizing operation of the power transmitter to occur during the reduced power time interval; generating a test drive signal for the test coil to generate an electromagnetic test signal; and performing a foreign object detection test in response to parameters measured for the test drive signal during the reduced power time interval, the synchronizing step comprising synchronizing the test drive signal to provide the electromagnetic test signal during the reduced power time interval.

[0073] According to an aspect of the invention, there is provided a method of operating a wireless power transfer system having a power transmitter wirelessly supplying power to a power receiver via an electromagnetic power transmission signal, the method comprising the steps of: generating a power transmission signal by the power transmitter, the power transmission signal using a recurring time frame having at least a power transmission time interval and a reduced power time interval during a power transfer phase in which a power level of the power transmission signal is reduced; generating a drive signal for a transmitter coil to generate the power transmission signal; receiving a message from the power receiver; adapting timing characteristics of the reduced power time interval in response at least to a first message received from the power receiver; synchronizing operation of the power transmitter to occur during the reduced power time interval; and transmitting a test signal to generate an electromagnetic test signal. generating a test drive signal for a test coil and performing a foreign object detection test in response to parameters measured for the test drive signal during a reduced power time interval, the synchronizing step comprising synchronizing the test drive signal to provide an electromagnetic test signal during the reduced power time interval, the method further comprising the steps of: the power receiver communicating with the power transmitter; transmitting a first message to the power transmitter, the first message having a request for a requested value of a timing characteristic; receiving a request response from the power transmitter; determining the timing characteristic in response to the request response, the request response indicating whether the requested value was accepted by the power transmitter; and adapting a load on the power transmission signal to be reduced during the reduced power time interval.

[0074] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. [Brief description of the drawings]

[0075] An embodiment of the present invention will now be described, by way of example only, with reference to the drawings, in which: [Figure 1] FIG. 1 illustrates example elements of a power transfer system according to some embodiments of the present invention. [Diagram 2] 1 illustrates example elements of a power transmitter according to some embodiments of the present invention. [Diagram 3] 2 illustrates example elements of a power receiver according to some embodiments of the present invention. [Figure 4] 1 illustrates example elements of a power receiver according to some embodiments of the present invention. [Diagram 5] FIG. 2 is a diagram showing an example of a time frame of the wireless power transmission system of FIG. [Figure 6] 1 illustrates an example time frame of a wireless power transfer system according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076] In the following description, the focus will be on embodiments of the invention applicable to wireless power transfer systems utilizing the power transfer approach as known from the Qi standard, however, it will be appreciated that the invention is not limited to this application and may be applied to many other wireless power transfer systems.

[0077] 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 transmit coil / inductor 103. The system further includes a power receiver 105 including (or coupled to) a receive coil / inductor 107.

[0078] In this embodiment, an electromagnetic power transmission signal is provided that can inductively transmit power from the power transmitter 101 to the power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal that is propagated as a magnetic flux by a transmitting coil or inductor 103. The power transmission signal may correspond to an electromagnetic power transmission component that represents the transfer of energy from the power transmitter to the power receiver, and may be considered to correspond to a component of the generated electromagnetic field that transfers power from the power transmitter to the power receiver. For example, without the loading of the receiving coil 107, no power would be extracted by the power receiver from the generated electromagnetic field (apart from losses). In such a scenario, the driving of the transmitting coil 103 may generate an electromagnetic field of potentially high field strength, but the power level of the power transmission signal would be zero (apart from losses). In some situations where a foreign object is present, the power transmission signal may be considered to include a component that corresponds to the transfer of power to the foreign object, and thus the power transmission signal may be considered to correspond to power extracted from the electromagnetic field generated by the power transmitter.

[0079] The power transmission signal may have a frequency generally between about 20 kHz and about 500 kHz, and is often typically in the range of 95 kHz to 205 kHz in Qi-enabled systems (or, for high-power kitchen applications, etc., the frequency may typically be in the range of 20 kHz to 80 kHz). The transmit coil 103 and receive coil 107 are loosely coupled, so that the receive coil 107 picks up (at least in part) the power transmission signal from the power transmitter 101. In this manner, power is transmitted from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmit coil 103 to the receive coil 107. It will be understood that the term power transmission signal is primarily used to refer to the inductive signal / magnetic field (magnetic flux signal) between the transmit coil 103 and the receive coil 107, but may also be considered and used in reference to an electrical signal provided to the transmit coil 103 or picked up by the receive coil 107.

[0080] In this example, 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 metal heating element, in which case the power transmission signal directly induces eddy currents that result in direct heating of the element.

[0081] The system is configured to transmit sufficient power levels, and specifically, the power transmitter may, in many embodiments, support power levels of 500mW, 1W, 5W, 50W, 100W, or greater than 500W. For example, Qi-enabled applications may range from 1-5W for low power applications (basic power profile), up to 15W for Qi standard version 1.2, up to 100W for high power applications such as power tools, laptops, drones, robots, and beyond 100W to over 1000W for ultra-high power applications such as kitchen applications.

[0082] The operation of the power transmitter 101 and the power receiver 105 is described below with specific reference to embodiments that conform generally to the Qi standard (except for modifications and extensions (or consequential) described herein) or that are suitable for higher power kitchen standards being developed by the Wireless Power Consortium. In particular, the power transmitter 101 and the power receiver 105 conform to or are substantially compatible with elements of the Qi standard version 1.0, 1.1 or 1.2 (except for modifications and extensions (or consequential) described herein).

[0083] The operation of the system in FIG. 1 will be specifically explained below, focusing on foreign object detection.

[0084] In wireless power transfer systems, the presence of objects (typically conductive elements that extract power from the power transfer signal and are not part of the power transmitter 101 or power receiver 105, i.e., elements that are unintended, unwanted, and / or interfere with the power transfer) can be highly detrimental to the power transfer. Such unwanted objects are known in the art as foreign objects.

[0085] Foreign objects not only reduce efficiency by adding power losses to the operation, but can also degrade the power transfer operation itself (e.g., by impeding the power transfer efficiency or by extracting power that is not directly controlled in a power transfer loop, etc.) Furthermore, the induction of electrical currents in the foreign object (specifically, eddy currents in the metallic parts of the foreign object) can result in heating of the foreign object, which is often highly undesirable.

[0086] To address such scenarios, wireless power transfer systems such as Qi are equipped with foreign object detection capabilities. Specifically, the power transmitter has the ability to try to detect the presence or absence of a foreign object. In that case, the power transmitter can, for example, terminate power transfer or reduce the maximum amount of power that can be transferred.

[0087] Current approaches proposed in the Qi standard are based on detecting power loss (by comparing the transmitted power with the reported received power) or on detecting degradation in the quality Q of the output resonant circuit. However, these currently used approaches have been found to provide suboptimal performance in many scenarios and, in particular, can result in inaccurate detection, resulting in missed detections, or even false positives, where a foreign object is detected when no such object is present.

[0088] Foreign object detection may be performed before the power receiver enters the power transfer phase (e.g., during initialization of the power transfer) or during the power transfer phase. Detection during the power transfer phase is often based on a comparison of the measured transmitted and received powers, whereas detection performed before the power transfer phase is often based on measuring the reflected impedance, for example by measuring the quality factor of the transmitting coil using a small measurement signal.

[0089] The inventors recognize that conventional foreign object detection operates less than optimally, in part due to variations and uncertainties in the particular operating conditions and scenarios in which foreign object detection is performed, including variations and uncertainties in power transmitter characteristics, power receiver characteristics, applied test conditions, etc.

[0090] One example of a foreign object detection test challenge is that a sufficiently accurate measurement must be made to achieve sufficiently reliable foreign object detection. For example, if a measurement for foreign object detection is made during the selection phase of the Qi power transfer initialization phase, the signal provided by the power transmitter for this measurement must be small enough so as not to wake up the power receiver. However, this typically results in a poor signal-to-noise ratio and reduced detection accuracy. Thus, detection performance may be sensitive to the particular signal level applied, and there are typically conflicting requirements.

[0091] A power receiver exposed to a small electromagnetic signal may exhibit a leakage current that depends on the level of the electromagnetic signal, on the coupling between the primary and secondary coils, and on the state of charge of the capacitor at the output of the rectifier. This leakage current may therefore vary with the actual conditions currently experienced and with the specific parameters of the individual power receiver (such as the characteristics of the capacitors). Since leakage currents affect the reflected impedance at the primary coil, the measurement of the quality factor also depends on the actual conditions and generally prevents optimal detection.

[0092] As yet another problem, detecting foreign objects based on reported received power indicators or the like at different loads or signal levels may be less reliable than desired because the relationship between transmitted power and received power varies with different loads and signal levels.

[0093] The system of FIG. 1 uses an approach for foreign object detection that aims to reduce sensitivity to uncertainty and variation, and accordingly aims to provide improved foreign object detection. This approach may provide improved foreign object detection in many embodiments, and in particular may provide more accurate and / or reliable foreign object detection in many embodiments. This approach may also allow for lower complexity and lower resource requirements. An advantage of this approach is that it may be suitable for incorporation into many existing systems, such as Qi wireless power transfer systems in particular, and indeed this may often be achieved with minor modifications.

[0094] Another operation that may be affected by the characteristics (especially variations in the characteristics) of the power transmission signal is communication (in either direction) between a power receiver and a power transmitter. As described below, communication from a power receiver to a power transmitter often uses load modulation, which varies the loading of the power transmission signal by the power receiver in response to the data to be transmitted. The power transmitter can then detect the resulting variations in the drive signal that generates the power transmission signal and decode the transmitted data from it. However, determining the effect of load modulation is difficult when the effective loading of the power transmission signal by the power receiver is very large, and becomes even more complicated when this loading varies.

[0095] The system of FIG. 1 uses an approach for communication that seeks to reduce uncertainty and sensitivity, and accordingly aims to provide improved communication performance, particularly for load modulated communication from the power receiver to the power transmitter. This approach can provide improved communication in many embodiments, and in particular, more accurate and / or reliable communication from the power receiver to the power transmitter in many embodiments. This approach may also allow for lower complexity and lower resource requirements. The advantages of this approach make it suitable for incorporation into many existing systems, such as Qi wireless power transmission systems in particular, and in fact this can often be achieved with minor modifications.

[0096] As described in more detail below, this approach utilizes a time-division approach during the power transfer phase, where operations such as foreign object detection and communication and power transfer are performed, for example, at different time intervals, thereby significantly reducing interference between them (specifically, the impact of power transfer on foreign object detection / communication).

[0097] Specifically, in a wireless power transfer system, the power transfer signal is subject to a repeating time frame having at least one power transfer time interval and one reduced power time interval.

[0098] The power level of the power transmission signal is reduced during the reduced power time interval relative to the power transmission time interval, and typically the maximum allowed power is 5, 10, or 50 times less at the power level during the reduced power time interval than during the power transmission time interval. The reduction in the power level can be caused as a result of an action at the power transmitter and / or the power receiver. For example, in some embodiments, the power transmitter may be configured to turn off the power transmission signal during the reduced power time interval and / or the power receiver may be configured to disconnect the load during the reduced power time interval.

[0099] The power transmitter (and typically the power receiver) may then arrange for one or more operations (functions, processes, procedures) to be performed during the reduced power time interval, i.e., it may synchronize the execution of one or more operations of the power transmitter to occur during the reduced power time interval. For example, it may typically synchronize the execution of foreign object detection, and possibly communication, to occur during the reduced power time interval. In this way, it is achieved that the impact of power transmission or power transmission signals on certain operations, specifically foreign object detection and communication, can be reduced, and in many cases minimized.

[0100] FIG. 2 shows elements of the power transmitter 101, and FIG. 3 shows elements of the power receiver 105 of FIG. 1 in more detail.

[0101] The power transmitter 101 includes a driver 201 capable of generating a drive signal that is provided to a transmitting coil 103, which in turn generates an electromagnetic power transfer signal capable of providing power transfer to a power receiver 105. The power transfer signal is provided (at least) during a power transfer time interval of a power transfer phase.

[0102] The driver 201 may typically constitute an output circuit in the form of an inverter formed by driving a full-bridge or a half-bridge, as is well known to those skilled in the art.

[0103] The power transmitter 101 further includes a power transmitter controller 203 configured to control operation of the power transmitter 101 according to a desired principle of operation. In particular, the power transmitter 101 may include many of the functions necessary to perform power control according to the Qi standard.

[0104] The power transmitter controller 203 is configured in particular to control the generation of the drive signal by the driver 201 and can specifically control the power level of the drive signal and therefore the level of the generated power transmission signal. The power transmitter controller 203 has a power loop controller that controls the power level of the power transmission signal in response to power control messages received from the power receiver 105 during a power control phase.

[0105] In order to receive data and messages from the power receiver 105, the power transmitter 101 has a first communicator 205 configured to receive data and messages from the power receiver 105 (a data message can provide one or multiple bits of information, as will be appreciated by those skilled in the art). In an embodiment, the power receiver 105 is arranged to load modulate the power transmission signal generated by the transmitter coil 103, and the first communicator 205 is configured to sense variations in the voltage and / or current of the transmitter coil 103 and demodulate the load modulation based thereon. Those skilled in the art are assumed to be aware of the principles of load modulation, as used, for example, in Qi wireless power transfer systems, and therefore will not be described in further detail here.

[0106] In many embodiments, the first communicator 205 is further configured to transmit data to the power receiver 105, and may be configured to modulate the power transmission signal using frequency, amplitude, or phase modulation.

[0107] In some embodiments, communication may occur using a separate communication channel, which may be accomplished using a separate communication coil, or in fact may occur using the transmitter coil 103. For example, in some embodiments, short-range communication may be implemented, or a high frequency carrier (e.g., having a carrier frequency of 13.56 MHz) may be overlaid onto the power transmission signal.

[0108] In the systems of Figures 1 to 3, communication is performed in reduced power time intervals during the power transfer phase. In particular, some or indeed all of the reduced power time intervals may be communication time intervals during which communication takes place between the power transmitter 101 and the power receiver 105. In particular, the transmission controller 203 may have / implement a synchronizer 206 configured to synchronize the first communicator 205 such that communication operations (typically both reception and transmission of data) are performed in the communication time intervals of the power transfer phase, i.e. the reduced power time intervals allocated for communication.

[0109] This makes it possible to significantly improve communication performance.

[0110] The power transmitter 101 further comprises a foreign object detector 207 configured to perform a foreign object detection test, i.e., to specifically detect whether any undesirable conductive elements may be present in the generated electromagnetic field.

[0111] In the present system, the foreign object detection test is based on measurements performed during the foreign object detection time interval, i.e. the reduced power time interval allocated to foreign object detection.

[0112] In this example, the electromagnetic power transmission signal and the electromagnetic test signal used for foreign object detection are generated by two different coils (driven by different drivers). Furthermore, these signals are referred to by different terms, i.e., the electromagnetic signal generated during the power transmission time interval is referred to as the power transmission signal, and the electromagnetic signal generated during the foreign object detection time interval is referred to as the electromagnetic test signal, or simply the test signal. However, it will be understood that in many embodiments the electromagnetic signal may be generated from the same coil during both the power transmission time interval and the foreign object detection time interval, and indeed the same driver, etc. may be used for both the power transmission time interval and the foreign object detection time interval. Indeed, references to the test signal may in many embodiments be considered to be equivalent to the power transmission signal during the foreign object detection time interval.

[0113] During the foreign object detection time interval, the power level of the power transmission signal is reduced, for example, by the power receiver disconnecting the load to reduce the overall loading of the power transmission signal. In many embodiments, the power receiver 105 may be configured to minimize the loading of the power transmission signal to accommodate only the loading resulting from friendly metal (metallic parts of the power receiver itself) and a small amount of power that may be used by the control functions of the power receiver. The power receiver can often completely disconnect the load of interest from the power transmission signal during the reduced power time interval. This can often reduce the loading of the power transmission signal from, for example, 5 to 50 W during the power transmission time interval to less than 500 mW during the reduced power time interval.

[0114] It should be noted that this allows the power level of the power transmission signal to be reduced without resulting in (or being caused by) a reduction in the strength of the generated electromagnetic field. For example, the power receiver decoupling the load reduces the amount of power extracted from the electromagnetic field and the power transmission signal, and thus the drive signal to the transmitter coil 103. However, this need not result in a reduction in the generated field strength, and in fact may result in a greater field strength since the opposing electromagnetic field due to the current flowing in the receiver coil 107 is reduced.

[0115] Thus, in many embodiments, the reduced power time interval is characterized by a reduced power transfer from the power transmitter to the power receiver compared to the power transfer during the power transfer time interval (or at least a reduced maximum possible / available power transfer from the power transmitter to the power receiver compared to the maximum possible / available power transfer during the power transfer time interval), although the strength of the electromagnetic field generated by the transmitter coil 103 may remain the same or may increase.

[0116] Indeed, in many embodiments where foreign object detection is based on measuring the loading of the electromagnetic field generated by the transmitter coil 103, it is desirable to adapt the drive signal so that the generated electromagnetic field has a suitable field strength to perform the intended operation during the reduced power interval. This may possibly be a higher field strength than during the power transfer interval, but typically reduces the amount of power transferred in order for the power receiver to disconnect the load.

[0117] Although in some embodiments it is possible to simply not change the drive signal parameters, the drive signal is typically adapted during reduced power intervals when the load on the power receiver is reduced. Unloading the load results in less damping of the transmitter coil 103, and accordingly, with the drive parameters unchanged, the current in the transmitter coil 103 / output resonant circuit increases. This leads to a higher induced voltage in the receiver coil 107, which may lead to an overvoltage condition in some circumstances. Such a scenario can be addressed, for example, by changing the drive signal parameters to reduce the amplitude of the drive signal during the reduced power intervals.

[0118] The reduced loading allows for more accurate foreign object detection in many scenarios: the power dissipated in the foreign object becomes a much larger percentage of the total power dissipation, and in fact typically exceeds the power dissipated in the power receiver, thereby making the power dissipation of the foreign object much easier to detect.

[0119] In many embodiments, the transmitter controller 203 is configured to reduce the power level of the power transmission signal during the foreign object detection time interval, and may in particular switch the power transmission signal off completely (particularly in examples using a coil for generating the power transmission signal and a different coil for generating the electromagnetic test signal for foreign object detection).

[0120] During the interval during which foreign object detection is performed, i.e., the foreign object detection time interval, the foreign object detector 207 may evaluate conditions to determine whether a foreign object is deemed to be present. During the foreign object detection time interval, the power transmitter 101 generates an electromagnetic test signal and evaluates features or characteristics of this signal to perform foreign object detection.

[0121] For example, the power level of (the power extracted from) the generated test signal may be used as an indication of the power extracted by a potential foreign object (typically by comparing it to the expected power extraction from the power receiver 105). The power level of the electromagnetic test signal reflects the power extracted from the electromagnetic test signal by the conductive elements in the electromagnetic field (including the receiver coil 107). It is therefore indicative of the power extracted by the combination of the power receiver 105 and any foreign objects that may be present. The difference between the power level of the electromagnetic signal and the power extracted by the power receiver 105 thus reflects the power extracted by any foreign object present. Foreign object detection may be a low-complexity detection, for example, where foreign object detection is deemed to have occurred if the power level of the electromagnetic signal (hereinafter referred to as the transmitted power level) exceeds the reported power extracted by the power receiver 105 (hereinafter referred to as the received power level).

[0122] In this approach, foreign object detection is responsive to a power level comparison between the transmitted power level and the reported received power level. The reaction upon detection of a foreign object may be different in different embodiments. However, in many embodiments, the power transmitter 101 can be configured to terminate power transmission (at least temporarily) in response to detection of a foreign object.

[0123] To generate the test signal, the power transmitter 101 has a test coil 209 coupled to a test generator 211. The test generator 211 is configured to generate a test drive signal for the test coil 209 to provide an electromagnetic test signal during the foreign object detection time interval. The test drive signal is an electrical signal provided to the test coil 209, resulting in the generation of the electromagnetic test signal, i.e., the test coil 209 generates a corresponding electromagnetic field having a field strength according to the test drive signal.

[0124] The test generator 211 may have substantially the same functionality as the driver 201, for example, the output of the test generator 211 may be a half-bridge inverter or a full-bridge inverter. Indeed, as mentioned above, in many embodiments, the test generator 211 may be implemented by the driver 201 and the test coil 209 may be implemented by the transmitter coil 103. Thus, in the following, all references to the test generator 211 and the test coil 209 may be appropriately considered as references to the driver 201 and the transmitter coil 103 for embodiments in which the same coils are used to generate both the power transfer signal and the electromagnetic test signal. In such a situation, the power of the generated electromagnetic signal may be adapted to a typically fixed reference level during the foreign object detection time interval.

[0125] The power transmitter further includes an adapter 213 configured to adapt timing characteristics of the reduced power time intervals in response to one or more messages received from the power receiver, as will be described in more detail below.

[0126] FIG. 3 illustrates some example elements of the power receiver 105.

[0127] The receiver coil 107 is coupled to a receiver controller 301 which couples the receiver coil 107 to a load 303 via a switch 305 (i.e., a switchable load 305). The power receiver controller 301 includes a power control path that converts the power extracted by the power receiver coil 107 into a supply suitable for the load. The power receiver controller 301 may also include various power receiver controller functions necessary to perform the power transfer, in particular functions necessary to perform the power transfer according to the Qi standard.

[0128] To support communication from the power receiver 105 to the power transmitter 101 , the power receiver 105 includes a second communicator 307 .

[0129] The second communicator 307 is configured to transmit data to the power transmitter 101 by varying the load of the receiver coil 107 in response to the data to be transmitted to the power transmitter 101. The load variation is then detected and demodulated by the power transmitter 101, as is known to those skilled in the art.

[0130] In an embodiment, the second communicator 307 is further configured to demodulate the amplitude, frequency and / or phase modulation of the power transmission signal to retrieve data transmitted from the power transmitter.

[0131] The power receiver controller 301 is further configured to control the second communicator 307 such that communication during the power transfer phase occurs during a communication time interval, i.e., a time interval during which the power level of the power transfer signal is reduced.

[0132] In this manner, just as the first communicator synchronizes its communications with the power receiver to occur during the reduced power time interval, the second communicator also synchronizes its communications with the power transmitter to occur during the reduced power time interval.

[0133] FIG. 4 is a circuit diagram of an example element of the power path of the power receiver 105. In this embodiment, the power receiver 105 has a receiver coil 107, designated LRX. In the embodiment, the receiver coil 107 is part of a resonant circuit, and therefore the power receiver 105 also includes a resonant capacitor CRX. The receiver coil 107 is exposed to an electromagnetic signal, and an AC voltage / current is induced in the coil in response. The resonant circuit is coupled to a rectifier bridge, and a smoothing capacitor C1 is coupled to the output of the bridge. In this way, a DC voltage is generated across the capacitor C1. The magnitude of the ripple in the DC voltage depends on the size of the smoothing capacitor as well as the load.

[0134] The bridge B1 and the smoothing capacitor C1 are coupled to a load 303, indicated by the reference RL, via a switch 305, illustrated by switch S1. The switch 305 can be used to connect or disconnect the load from the power path accordingly, and thus the load is a switchable load 305. Although the switch S1 is illustrated as a conventional switch, it will of course be understood that it may be implemented by any suitable means, typically including a MOSFET. Also, although the load 303 is illustrated as a simple passive port, it will of course be understood that it may be any suitable load. For example, the load 303 may be a battery to be charged, a mobile phone, or other communication or computing device, a simple passive load, etc. In fact, the load 303 need not be an external or dedicated internal load, but may include, for example, elements of the power receiver 105 itself. Thus, the load 303 illustrated in Figures 3 and 4 may be considered to represent any load of the receiving coil 107 / electromagnetic signal that can be disconnected by the switch 305 / S1, and thus also referred to as a switchable load 305.

[0135] 4 further illustrates a load modulation capacitor C2 that can be connected or disconnected in parallel with the resonant circuit based on switching of switch S2. The second communicator 307 can be configured to control switch S2 such that a load of the modulation capacitor C2 can be connected and disconnected depending on data to be transmitted to the power transmitter 101, thereby providing load modulation.

[0136] The power receiver 105 is configured to enter a reduced power mode during a reduced power time interval of each time frame during the power transfer phase. In an embodiment, the power receiver 105 has a load controller 309 that controls the switch 305 (equivalently, the switch 305 can be considered as part of the load controller). During the reduced power time interval, the load controller 309 can decouple the load 303 from the power receiver, i.e., decouple the load of the power receiver controller 301 and thus the load of the power receiver coil 107. In this way, the load controller 309 can reduce the load of the receiver coil 107 during the reduced power time interval. Furthermore, not only is the load of the power receiver 105 reduced, which makes it easier to detect other power losses or modulations, but often more importantly, the power receiver 105 enters a better defined or specific state in which the impact of load variations on the electromagnetic test signal is reduced.

[0137] It will be appreciated that the load of the receiver coil 107 may not be completely disconnected during the foreign object detection interval. For example, the power receiver 105 may still extract power, for example to operate some internal circuitry. In this way, the load controller 309 may be configured to disconnect the load from the load to the receiver coil 107 while allowing the receiver coil 107 to be loaded by one or more other loads. In fact, the loading of the receiver coil 107 can be considered to be composed of loads that are disconnected by the load controller 309 during the foreign object detection interval and loads that are not disconnected by the load controller 309. In this way, the load 303 can be considered to represent a load that is disconnected by the receiver coil 107 during the foreign object detection interval. This load may include both external or internal loads to which power transfer is established, but may also include, for example, internal control functions that are temporarily switched off during the foreign object detection interval.

[0138] In some embodiments, the switchable load may be disconnected, for example, by an inductive voltage drop at the input of rectifier B1, while at the same time maintaining a high voltage level at the output of the rectifier by the switchable load (which may be a battery) and / or the stored energy of capacitor C1, thereby stopping the current through rectifier B1 and thus effectively disconnecting the switchable load.

[0139] The power receiver 105 includes a power controller 311 configured to establish a power control loop with the power transmitter 101. Specifically, the power controller 311 transmits a power control message to the power transmitter 101, and in response, the power transmitter 101 can modify the power level of the power transmission signal during the power transmission time interval. Typically, the power controller 311 can generate a power control error message indicating to the power transmitter 101 to request an increase or decrease in the power level. The power controller 311 can determine an appropriate error message by comparing the measured value with a reference value. During the power transmission, the power controller 311 can compare the provided power level with the requested power level and request an increase or decrease in the power level based on the comparison.

[0140] As mentioned above, the system applies a recurring time frame during the power transfer phase, the time frame having at least one power transfer time interval and one reduced power time interval. An example of such a recurring time frame is shown in FIG. 5, where the power transfer time intervals are denoted by PT and the reduced power time intervals are denoted by D. In this example, each time frame FRM has only one reduced power time interval and one power transfer time interval. However, it will be understood that in other embodiments, other time intervals may be included in the time frame, or multiple reduced power time intervals and / or power transfer time intervals may be included in each time frame. In particular, the recurring time frame may have different types of reduced power time intervals, such as one or more foreign object detection time intervals and one or more communication time intervals.

[0141] In this approach, operations such as foreign object detection and communication can be performed in reduced power time intervals, so that foreign object detection / communication and power transfer can be separated in the time domain, reducing mutual interference from power transfer to foreign object detection / communication. In this way, variability and uncertainty due to variations in operating conditions for power transfer can be separated from foreign object detection / communication, resulting in more reliable and accurate foreign object detection / communication.

[0142] Then, in the power transmission phase, the power transmitter is configured to perform power transmission during the power transmission time intervals of the time frame of the power transmission phase. In particular, during these time intervals, the power transmitter and the power receiver may operate a power control loop (which may be based on communication within a communication time interval corresponding to the recurrence time interval). In this way, the level of the transmitted power can be dynamically changed.

[0143] In the reduced power interval of the time frame of the power transfer phase, the power level of the power transfer signal (specifically, the level of power transmitted to the power receiver) is reduced, often minimized. This can be accomplished, for example, by the power transmitter limiting the drive signal (e.g., turning it off completely) and / or the power receiver disconnecting the target load, etc.

[0144] In many embodiments, especially when the same coil is used for both the power transmission signal and the electromagnetic test signal used for foreign object detection, the power transmitter can be configured to reduce the level of the power transmission signal during the reduced power time interval relative to the level during the power transmission time interval. In many situations, the power level of the power transmission signal may be increased to a high level, for example up to a level of 10 to 100 W, and in many applications (e.g. for power transmission to kitchen appliances) even to a significantly higher level. However, during the reduced power time interval, the power level of the generated electromagnetic signal may be reduced to a predetermined level that is much lower than the current power or the maximum allowed power during the power transmission time interval. For example, the power level can be set to a predetermined level not exceeding 1 W. In other words, the power of the electromagnetic test signal during the foreign object detection time interval can be limited to a power level that is significantly (e.g. by a factor not less than 2, 5 or 10) lower than the maximum allowed power level of the power transmission signal during the power transmission time interval.

[0145] As mentioned above, a reduction in power level does not necessarily correspond to a reduction in the electric field strength of the generated electromagnetic field. For example, the power transfer level can be significantly reduced by reducing the loading of the field by the power receiver, for example by disconnecting the load 303. With reference to FIG. 4, this can be achieved, for example, by a small reduction in the electric field strength, so that the induced voltage (at LRX) remains below the voltage of the capacitor (C1), so that the rectifier bridge (B1) effectively isolates the capacitor (C1) from the receiver coil (LRX), thereby allowing an effective essential decoupling of the load (RL).

[0146] In order to measure sufficient power dissipation in a foreign object, and thus facilitate and improve foreign object detection, it may be preferable to keep the magnetic field strength relatively high.

[0147] Alternatively or additionally, the power receiver 105 may be configured to reduce the loading of the electromagnetic test signal / field generated during the reduced power time intervals compared to the level during the power transfer time intervals, i.e., the power receiver 105 may be configured to reduce the loading of the power receiver 105 of the electromagnetic test signal during the reduced power time intervals compared to the loading of the power transfer signal during the power transfer time intervals. Specifically, in the example of FIG. 3, the load controller 309 and switch 305 may be configured to disconnect the switchable load 303 during the foreign object detection time intervals and connect it during the power transfer time intervals. In this way, during the reduced power time intervals the power receiver 105 may (typically) switch off the main / target load, and indeed in many embodiments only the minimum loading required for continued operation of the power receiver 105 may be maintained.

[0148] 4, switch S1 may also be used to disconnect the load during the foreign object detection time interval. In embodiments where the switchable load 303 requires a more constant power supply, it will be appreciated that switch S1 may be placed before capacitor C1 or another energy reservoir may be provided after switch S1 to power the switchable load 303 during the foreign object detection time interval (or the previously described approach of simultaneously reducing the induced voltage at the input of rectifier B1 while maintaining a high voltage level at the output of rectifier B1 via stored energy in the switchable load (e.g., a battery) and / or stored energy in capacitor C1 may be used).

[0149] Thus, the power receiver 105 may reduce its loading during the reduced power time interval. Specifically, the loading of the electromagnetic test signal by the power receiver during the foreign object detection time interval will be less than the loading of the power transmission signal by the power receiver during the power transfer time interval (the loading can be considered, for example, as the effective resistive impedance of the transmitter coil 103 during the power transfer time interval and the test coil 209 during the foreign object detection time interval). Typically, the power transmission signal and the electromagnetic test signal have corresponding characteristics and thus both induce signals in the receiving coil 107. Thus, disconnecting the switchable load 303 during the foreign object detection time interval can relatively reduce the loading of the electromagnetic test signal compared to the loading experienced by the power transmission signal (and therefore the electromagnetic test signal) generated during the power transfer time interval when the load is connected.

[0150] The disconnection of the switchable load 303 not only reduces the loading of the electromagnetic test signal, but also makes this loading more predictable and reduces variability. Typically, the loading of the power transmitter by the power receiver can vary significantly from application to application, but also as a function of time for the same application and power transfer session. To accommodate such variations, a power control loop operates during the power transfer phase. However, by introducing a reduced power time interval during which the load can be disconnected (or otherwise set, for example, to a predefined level), it is possible to put the power receiver into a reference mode in which the loading of the electromagnetic field is more predictable. In this way, for example, a predefined loading of the electromagnetic test signal can be assumed, since a foreign object detection test can be performed, for example, on the assumption that the power receiver is in this reference or test mode. This approach therefore makes it possible not only to reduce the loading by the power receiver 105 (thereby improving accuracy by making the relative influence of any foreign object higher), but also to make this more predictable, thereby facilitating the compensation of the presence of the power receiver during the foreign object detection test.

[0151] 1-4 thus provides a much improved foreign object detection testing approach, which can be performed under more controlled conditions, thereby allowing more accurate and reliable foreign object detection testing to be performed, as well as providing an environment that allows for improved communications with less interference due to power transfer operations.

[0152] In many embodiments, the reduced power time intervals may include both communication time intervals and foreign object detection time intervals.

[0153] In the system of FIG. 1, the power transmitter and power receiver are configured to modify timing characteristics of reduced power time intervals of recurring time frames based on communications between the two entities.

[0154] In particular, the power transmitter has an adapter 213 for adapting timing characteristics of the reduced power time interval in response to at least a first message received from the power receiver.

[0155] In many embodiments, the power receiver can send one or more messages to the power transmitter requesting particular timing characteristics of the reduced power time intervals, and the power transmitter and power receiver can then proceed to apply these timing settings to their resulting operation.

[0156] In many embodiments, the power transmitter and power receiver can be configured to communicate to, among other things, establish the duration of a reduced power time interval and / or the period between reduced power time intervals, and typically the period between successive reduced power time intervals.

[0157] This approach may provide improved tradeoffs, and in particular may enable operation tailored to the particular characteristics of individual devices, and in many embodiments, to the particular characteristics of individual power transfer operations, e.g., timing may be adapted to reflect the power level of a power transfer.

[0158] This approach can address the fact that the duration of a reduced power time interval may affect the operation of the power transmitter and power receiver, as well as potentially an end load, such as a device powered by the power receiver.

[0159] Often, if the reduced power time interval is too long, the device may suffer from a drop in the effective supply voltage. This is particularly important if the device has limited energy storage, for example if the capacitor at the input of the device (output of the power receiver) is smaller than desired. The device must be able to ride out the time during which power transmission is interrupted, which typically requires a relatively large capacitor (note that in many embodiments the power receiver itself may have such a capacitor, as well as potential voltage regulation to provide a constant output voltage; however, this simply means that the described problem is related to the power receiver and not the external load device).

[0160] If the time slot is too short, the power transmitter may not be able to perform certain operations satisfactorily. For example, the power transmitter may not be able to perform FOD measurements with sufficient accuracy because the measurement signal is not stable when the measurement is performed or because a sufficient number of samples cannot be obtained. As another example, a reduced power time interval that is too short may not provide sufficient communication bandwidth, e.g., may not be able to communicate enough data to support the provision of power control reports and other measurement results.

[0161] The optimal duration of the reduced power time interval may therefore depend on many features and characteristics, such as the particular operating parameters and implementation of the power receiver. Thus, in some embodiments, the power receiver can send a message to the power transmitter, and the power transmitter can be configured to adapt the timing of the reduced power time interval in response to the message.

[0162] The message may be specifically and explicitly a request for a predefined duration of a reduced power time interval. In many embodiments, the power receiver may evaluate operating conditions, such as the power being drawn by the external load, and calculate the maximum time that the energy reservoir / capacitor can maintain sufficient charge to prevent the supply voltage to the load from dropping too low. For example, for a 1A load, the maximum duration may be twice as long as for a 2A load. Thus, the power receiver may send a request for twice the duration for a 2A load compared to a 1A load.

[0163] As another example, a suitable value for the duration of the reduced power time interval may be predefined for the power receiver, for example during the manufacturing stage. For example, the power receiver may be a battery charger with a maximum charging current. The corresponding duration during which an internal capacitor can hold a sufficient charge to provide the maximum charging current is determined at the design stage and permanently stored in the power receiver at the manufacturing stage. When initiating a power transfer with a power transmitter, the power receiver may read this value and send a request for the duration of the reduced power time interval to the power transmitter. The power transfer phase may then proceed using a repeating time frame with the reduced power time interval according to the stored value. Since power receivers may differ very widely in requirements and capabilities, this allows the power transmitter and power transfer operation to adapt to the individual characteristics of the power receiver.

[0164] In some embodiments, the system can be configured to set the duration between reduced power time intervals based on messages sent from the power receiver to the power transmitter. The system may specifically set the duration between reduced power time intervals for successive recurring time frames, effectively adapting the duration of the reduced power time intervals depending on the messages from the power receiver to the power transmitter.

[0165] In order to provide sufficient average power transfer, the peak power levels of the power transfer during power transfer time intervals are increased the shorter these periods are. In many embodiments, the power transfer level may be limited (by the power transmitter, or possibly by a power receiver that is only designed to extract a predetermined maximum amount of power). In such cases, the power receiver may transmit a request for a period between reduced power time intervals that is sufficient to ensure that the capacitor is fully charged before the start of the next repeating time interval (this is particularly suitable for embodiments in which the power transmitter turns off the power transfer signal during reduced power time intervals).

[0166] In some embodiments, a single request may be transmitted that relates to both the duration of the reduced power time intervals and the period between them, for example, in some embodiments, the recurring time frames may have a fixed duration and the power receiver may request a particular duty cycle to be applied.

[0167] In many embodiments, the power transmitter is configured to impose a minimum duration requirement on the duration of a reduced power time interval. This minimum duration can be used to ensure that operations to be performed during the reduced power time interval have enough time to actually achieve a desired result. For example, it can ensure that foreign object detection can be performed with sufficient reliability (including sufficient time for settling and stabilization of measurement signals). As another example, the power transmitter can be configured to require a minimum duration in order for communications to have sufficient bandwidth.

[0168] In many embodiments, the power transmitter is configured to impose a maximum duration requirement on the period between reduced power intervals. This maximum duration can be used to ensure that operations that should be performed in reduced power intervals are performed frequently enough. For example, it can ensure that foreign object detection is performed frequently enough to ensure that the appearance of a foreign object is detected before it is heated to an unacceptable level. As another example, it can ensure that communication occurs frequently enough (e.g., to allow a sufficient update rate for the power control loop).

[0169] As yet another example, in some embodiments, measurements for foreign object detection may be spread across multiple reduced power time intervals to improve accuracy and / or add some redundancy. This allows for more accurate foreign object detection. If the reduced power time intervals are short in duration, thus allowing only a small number of samples / measurements, the period between the reduced power time intervals may be shortened to allow a sufficient amount of samples / measurements to be taken within a given required time to compensate and ensure that a foreign object is detected before it is overheated.

[0170] Similarly, the power receiver may be configured to impose limits on timing values: for example, the power receiver may determine a desired value for the duration of a reduced power time interval subject to a maximum value that ensures that sufficient power can be provided to an external load without discharging an energy reservoir (typically a capacitor) resulting in an unacceptable voltage drop.

[0171] Similarly, as described above, the power receiver may determine a desired value for the period between reduced power intervals, subject to a minimum value that ensures that the power receiver's capacitor can be fully charged.

[0172] In many embodiments, the timing characteristics of the recurring time intervals will be subject to requirements imposed by both the power receiver and the power transmitter. Typically, both the power transmitter and the power receiver have requirements that must be met simultaneously in order for the timing values ​​to be adopted. For example, the setting of the duration of the recurring time interval and / or the period between successive recurring time intervals is subject to values ​​that meet the requirements of both the power transmitter and the power receiver.

[0173] Furthermore, in many embodiments, this typically means that one device (i.e., the power receiver or the power transmitter) can impose a limit on the maximum value and the other device can impose a limit on the minimum value for the timing characteristics that are set.

[0174] In particular, as explained above, in many embodiments the duration of a reduced power time interval will be subject to a minimum duration imposed by the power transmitter and a maximum duration imposed by the power receiver.

[0175] Similarly, in many embodiments, the duration between reduced power intervals will be subject to a maximum duration imposed by the power transmitter and a minimum duration imposed by the power receiver.

[0176] Such embodiments can, in many embodiments, impose efficient control of appropriate timing on the reduced power time intervals to ensure that the reduced power time intervals have timing characteristics that enable acceptable performance for both devices and thus the overall power transfer, independently, reducing complexity and enabling easier interoperation between both devices.

[0177] The actual approach and message exchanges used to set the timing characteristics of the reduced power time intervals will depend on the preferences and requirements of a particular implementation, and different approaches may be used in different systems.

[0178] However, many systems, such as Qi-type implementations, take the approach that the power receiver sends a request for the appropriate timing value and the power transmitter determines whether or not it accepts the requested value.

[0179] Thus, the power receiver of FIG. 3 comprises a request controller 311 arranged to send a request message to the power transmitter, the request message comprising a request for a requested value of a timing property.

[0180] For example, the power receiver can determine an appropriate value for the duration of the reduced power time interval. For example, it can estimate the external load and calculate therefrom the total power consumption (of both the target load and the power receiver itself). It can then calculate the time it takes for the energy storage to experience a voltage drop of a given tolerance value for that total power consumption. The resulting time corresponds to the maximum possible duration of the reduced power time interval. Typically, the power receiver can initially request a duration that is low enough to provide a sufficient margin and a safer operating point. For example, it may send a message to the power transmitter requesting a duration of the reduced power time interval of half the determined maximum value.

[0181] Upon receiving the message, the power transmitter can evaluate whether the requested duration is acceptable. For example, the requested duration can be compared to a pre-stored minimum time required to perform sufficiently accurate foreign object detection. If the requested duration exceeds this minimum time, the power transmitter proceeds to accept the requested duration, otherwise it rejects it.

[0182] The power transmitter may then transmit a response message to the power receiver including an indication of whether the requested value was accepted by the power transmitter, which response message is received by the response controller which proceeds to determine timing characteristics of the reduced power time intervals accordingly.

[0183] For example, the response message may include a single bit indicating whether the requested duration was accepted or rejected. If the requested duration is accepted, both devices then perform a power transfer phase using the agreed duration of the reduced power time interval (after completing an initialization process, in case there are further operations or negotiations to be performed before power transfer can begin). If the requested duration is rejected, the response controller 313 may control the request controller 311 to send a new request. For example, a duration of 75% of the maximum allowed value may be requested. This process may then be repeated until suitable timing characteristics are agreed upon.

[0184] If a common tolerance cannot be agreed upon, specifically if the power transmitter rejects a request for a duration of a reduced power time interval that corresponds to the maximum allowed duration calculated by the power receiver, the power receiver and power transmitter may terminate the power transmission process or may modify their operation, for example to allow the power receiver to increase the reduced power time interval (e.g., reduce the maximum power that can be provided to the external load).

[0185] It will be appreciated that a similar approach may be used to set the period between reduced power intervals.

[0186] In many embodiments, the power transmitter can transmit messages to the power receiver indicating preferred or acceptable values ​​of the timing characteristics. For example, the power transmitter may transmit one or more messages to the power receiver indicating the minimum acceptable duration of a reduced power time interval and / or the maximum acceptable duration between reduced power time intervals (of course, in some embodiments, only one of the timing parameters may be transmitted). The power receiver can then take these values ​​into account when determining the appropriate request values. Such an approach can facilitate operation in many embodiments and reduce the number of requests the power receiver needs to send. In particular, the power receiver can directly determine the request values ​​that the power transmitter has indicated can be tolerated, rather than guessing what values ​​the power transmitter will tolerate. Typically, the first requested value is accepted by the power transmitter, unless, for example, conditions at the power transmitter change.

[0187] In many such embodiments, the power transmitter can be configured to send messages indicating recommended / possible / acceptable values ​​to the power receiver in response to a request for such information from the power receiver. In this manner, the power receiver can remain the driver of, and maintain initiative and control over, message exchanges and operations.

[0188] Specifically, in many embodiments, the request controller 311 can control the second communicator to send a request therefor to the power transmitter to provide a timing characteristic constraint. The timing characteristic constraint indicates a constraint on a value of a given timing characteristic, such as a duration of a reduced power time interval or a period between successive reduced power time intervals. The timing characteristic constraint may indicate, for example, a maximum value, a minimum value, a tolerance range, a recommended range, and / or a preferred range, etc.

[0189] The power receiver can then proceed to determine required values ​​for timing characteristics to comply with this constraint if possible, for example, it may modify its operation or interface with an external load as necessary to satisfy the imposed constraint.

[0190] In many embodiments, the determination of the appropriate timing characteristics can be performed during an initialization phase prior to the power transfer phase. Thus, before starting a new power transfer operation, the power transfer system can enter an initialization phase during which appropriate timing characteristics are determined for the reduced power time interval as described above. The power transmitter and power receiver can then proceed to apply the determined characteristics during the power transfer phase. In particular, the determination of the appropriate timing characteristics of the recurring time frames may be determined during a negotiation phase performed during the initialization of the new power transfer operation.

[0191] This allows appropriate parameter determination while providing low complexity and reliable operation. In particular, timing characteristic values ​​determined in the initialization phase can be used without change or modification throughout the power transfer phase.

[0192] However, in some embodiments, the timing characteristics can be dynamically changed throughout the power transfer phase. In some embodiments, the power receiver can be configured to dynamically and repeatedly send messages to the power transmitter requesting values ​​of predetermined timing characteristics, e.g., durations of reduced power time intervals. The adapter 213 can be configured in such embodiments to dynamically adapt the timing characteristics during the power transfer phase in response to these messages.

[0193] For example, during the power transfer phase, the power receiver may continuously measure the power provided to the target load. If this is below the expected load agreed upon in the initialization phase, the power receiver may proceed to request a new reduced power time interval duration longer than the current value, reflecting a slower depletion of the storage capacitor. Conversely, if it detects that the power supply to the target load is increasing, the power receiver may proceed to request a reduced power time interval of shorter duration than the current duration. The power receiver may continuously measure these values ​​and continuously send request messages to the power transmitting device.

[0194] In response to receiving these messages, the power transmitter may either accept or reject the requested values: if accepted, a confirmation message is sent to the power receiver and the new values ​​are adopted, if rejected, a rejection message is sent to the power receiver and the previous values ​​are left unchanged.

[0195] The power receiver and power transmitter may, in some embodiments, effectively establish a control loop that adapts the timing characteristics of the reduced power time intervals.

[0196] It will be appreciated that dynamic modification of timing characteristics during the power transfer phase may be in addition to setting initial values ​​during the initialization phase. In other embodiments, the power transfer phase may instead begin with the same pre-defined timing characteristic values, without an initialization phase, determined based on worst case considerations, and dynamic control loop operation will adapt these to more appropriate values.

[0197] Below, the approach and considerations of a Qi-type power transfer system are described with a very specific example, in which the reduced power time intervals include reduced power time intervals corresponding to both foreign object detection time intervals and communication time intervals.

[0198] In the specific description, the following acronyms and abbreviations apply: PTx power transmitter PRx Power Receiver Devices containing device PRx, (partially) disconnectable loads, friendly metal Metal in the device that dissipates power when exposed to the magnetic field of the friendly metal PTx FO foreign body FOD foreign object detection ComCommunication PTx coil A single coil or set of coils in a PTx that supplies the AC voltage and current to generate a magnetic field (the power transmission signal) for the power receiver. A time slot corresponding to a TS time interval. FOD TS Foreign Object Detection Time Slot. A reduced power time interval is used for foreign object detection. A reduced power time interval is used for Com TS communications.

[0199] In a specific example, a time division approach and repeating time frames are used as shown in Figure 6. In the figure, NP denotes "No Power" which corresponds to a reduced power time interval, typically due to the power receiver disconnecting the target load, and PWR denotes a power transmission time interval.

[0200] [FOD time slot] The PRx disconnects the load, meaning that no (or almost no) power is delivered to the load. The PTx, for example, applies the saved settings of the measurement signal and measures the combined effect of the friendly metal and the FO. It compares this effect with the stored expected effect of the friendly metal to determine the effect of any FO. The determined effect of the FO may then be used to determine the maximum amplitude of the drive signal relative to the frequency at which the situation is considered safe, i.e., the frequency at which the temperature rise of the FO is expected to be within a safe range (or, in some embodiments, it may simply stop the power transfer if the effect is determined to be too large). The PTx then limits its drive signal to this maximum value and issues a warning if the PRx tries to control the drive signal beyond this maximum value.

[0201] If the PTx detects a change in the combined effects of friendly metal and FO, it may return to the initialization timeslot and re-establish the conditions for FOD measurements. To prevent premature triggering back to the initialization timeslot, the PTx may combine the results of multiple FOD timeslots (e.g., apply an averaging window) and / or adjust the drive signal within a certain margin.

[0202] [COM Time Slot] The PRx disconnects the load, which means that no (or very little) power is delivered to the load. The PRx can then communicate to: Power Control Information identification PRX measurements (e.g. power received, battery condition, housing temperature) PRx measurement results (e.g. coil current, power supply, component temperature)

[0203] [Initialization timeslot] Typically this occurs prior to the power transfer phase, but may occur during the power transfer phase, for example as part of each repeating time frame.

[0204] PRx disconnects a load, which means that no (or very little) power is delivered to that load.

[0205] PTx controls the drive signal to the PTx coil so that the following conditions are met. - The effect of the device's friendly metal on the magnetic field is known by PRx or can be accurately determined by PRx, e.g. the power loss of the friendly metal for a given amplitude and frequency of the magnetic field is known by PRx. - PTx can accurately measure the combined effects of nearby metals and FO. For example, the transmitted power can be accurately determined by PTx.

[0206] As a result, the system can accurately determine the effect of the FO on the magnetic field, which effect is preferably related to the expected increase in temperature caused by power dissipation in the FO caused by exposure to the magnetic field of the PTx coil when the PTx is powering the PRx.

[0207] To establish the above conditions, the PRx can provide information about the appropriate magnetic field, for example by communicating its type, the allowed frequency range, and optionally the required amplitude of the drive signal for the PTx coil. The latter of course depends on the design of the PTx coil. In addition, the PRx can have a measurement coil whose induced voltage gives a good indication of the magnetic field to which the friendly metal of the device is exposed. The PRx can then provide control information to the PTx for controlling the magnetic field to a level that allows the PRx to accurately determine the effect of the friendly metal.

[0208] Once the above conditions are met, the PTx stores the drive signal settings and the expected effect of the friendly metal as determined by the PRx.

[0209] By separating the measurement and communication in time, interference between them can be avoided.

[0210] In an embodiment, prior to power transfer, a negotiation / initialization phase is performed in which PTx and PRx negotiate the time constraints of different time slots. These timings include two parameters: the duration of each slot (SLOT_duration) and the time interval between different slots (SLOT_interval).

[0211] Below are provided some examples of power receiver and power transmitter considerations for individual timeslots.

[0212] [PTx considerations for FOD] - The PTx shall support a minimum FOD_duration (FOD_duration_min) that allows for at least one FOD measurement to be made for its FOD feature, and shall not support any shorter FOD_duration. - To achieve sufficient reliability of FOD, the PTx relies on a minimum number of FOD measurements (FOD_count_min). In order to react to the presence of FOD before excessive heating occurs, the PTx must be able to make the required FOD measurements within a maximum time (FOD_detection_max). - Once the PTx has negotiated the FOD_duration, it can calculate the number of FOD measurements that can be performed within an FOD slot (FOD_meas_nr) and derive the maximum FOD interval time (FOD_interval_max). FOD_interval_max = FOD_detection_max * FOD_meas_nr / FOD_count_min

[0213] [PTx considerations for COM] - PTx supports a minimum COM_duration (COM_duration_min) that allows at least one message to be sent / received, and does not support a shorter COM_duration. To enable the minimum number of messages, PTx relies on a minimum number of communication messages (COM_count_min). - Once PTx has negotiated COM_duration, it can calculate the number of communication messages (COM_mes_nr) that can be handled by a COM slot (and vice versa). - Once PTx has negotiated the number of communication messages (COM_mes_nr), it can calculate the maximum duration of a communication slot (COM_duration_max).

[0214] [PRx Considerations] - PRx allows a maximum FOD slot duration (FOD_duration_max) or a maximum COM slot duration (COM_duration_max) to ensure that dependent energy stores are not excessively discharged during either of these time slots. - PRx requires a minimum duration of a timeslot interval (FOD_interval_min or COM_interval_min) to ensure that the energy store is fully charged at the start of any timeslot.

[0215] Below are described some specific examples of message interactions between the power receiver and the power transmitter to establish timing parameters.

[0216] [FOD slot duration] - (PTx notifies PRx (at PRx's request) of FOD_duration_min) - PRx requests FOD_duration (for optimal FOD, PRx preferably requests FOD_duration close to FOD_duration_max). - PTx responds whether it accepts the proposed FOD_duration or not.

[0217] [FOD slot interval] - PTx calculates FOD_interval_max. - (PTx notifies PRx (at PRx's request) of FOD_interval_max) - PRx requires FOD_interval. -(For optimal FOD, PRx preferably requests FOD_interval close to FOD_interval_min). - PTx responds whether it accepts the proposed FOD_interval or not.

[0218] [Communication slot duration] - (PTx notifies PRx of COM_duration_min (at PRx's request).) - PRx requires: - Minimum COM_duration - Or, the minimum number of communication messages (COM_count_min). - PTx responds whether it accepts the proposed COM_duration or not.

[0219] [COM slot spacing] - PTx calculates COM_interval_max. - PTx notifies PRx of COM_interval_max (at PRx's request). - PRx requires COM_interval. - For optimal communication, PRx requests a COM_interval time that is preferably close to the FOD_interval_time. - PTx responds whether it accepts the proposed COM_interval or not.

[0220] It will be appreciated that for clarity, the above description has described embodiments of the invention with reference to different functional circuits, units, and processors. However, it will be apparent that any suitable distribution of functionality between different functional circuits, units, or processors may be used without detracting from the invention. For example, functions illustrated as being performed by separate processors or controllers may be performed by the same processor or controller. Thus, references to specific functional units or circuits are not intended to indicate a strict logical or physical structure or organization, but are merely to be regarded as references to suitable means for providing the described functionality.

[0221] The invention can 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 an embodiment 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. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units, circuits and processors.

[0222] Although the present invention has been described in relation to several embodiments, it is not intended that the present invention be limited to the specific embodiments described herein. Rather, the scope of the present invention is limited only by the appended claims. Moreover, although a feature may appear to be described in relation to a specific embodiment, a person 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.

[0223] It will be understood that the reference to the preferred value does not imply any limitation beyond that it is the value determined in the foreign object detection initialization mode, i.e., the preferred value as determined by the adaptation process. Reference to the preferred value may be replaced by a reference to the first value, for example.

[0224] Moreover, although individually recited, a plurality of means, elements, circuits or method steps may be implemented by, for example, a single circuit, unit or processor. Moreover, although individual features may be included in different claims, they may be advantageously combined, and the inclusion in different claims does not imply that the 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 may be equally applicable to other claim categories as well as appropriate. Moreover, the order of features in the claims does not imply a particular order in which the features must be operated, and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. Moreover, singular references do 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 are not to be construed as limiting the scope of the claims in any way.

Claims

1. A power receiver that is wirelessly supplied with power from a power transmitter via an electromagnetic power transmission signal, the power receiver comprising: a receiver coil for receiving the power transmission signal, the power transmission signal using a repetitive time frame having at least a power transmission time interval and a reduced power time interval during a power transfer phase in which a power level of the power transmission signal is reduced; a communicator for communicating with the power transmitter; a request controller for sending a first message to the power transmitter, the first message being a message to the power transmitter to adapt a timing characteristic of the reduced power time interval, the request controller having a requested value of the timing characteristic; a response controller for receiving a request response from the power transmitter and determining the timing characteristic in response to the request response, the request response indicating whether the requested value was accepted by the power transmitter; and a load controller for adapting the loading of the power transmission signal to be reduced during the reduced power time interval; having A power receiver, wherein the communication device is configured to receive a message from the power transmitter, and the power receiver is configured to receive a message from the power transmitter indicating at least one of a duration of the reduced power time interval and a period between reduced power time intervals of successive recurring time frames before transmitting the first message.

2. The power receiver of claim 1 , wherein the timing characteristic is a duration of the reduced power time interval.

3. 2. The power receiver of claim 1, wherein the timing characteristic is a duration between reduced power time intervals of successive recurring time frames.

4. 4. A power receiver as claimed in any preceding claim, wherein the communicator is configured to synchronise communication with the power transmitter to occur during the reduced power time interval.

5. A power receiver that is wirelessly supplied with power from a power transmitter via an electromagnetic power transmission signal, the power receiver comprising: a receiver coil for receiving the power transmission signal, the power transmission signal using a repetitive time frame having at least a power transmission time interval and a reduced power time interval during a power transfer phase in which a power level of the power transmission signal is reduced; a communicator for communicating with the power transmitter; a request controller for sending a first message to the power transmitter, the first message being a message to the power transmitter to adapt a timing characteristic of the reduced power time interval, the request controller having a requested value of the timing characteristic; a response controller for receiving a request response from the power transmitter and determining the timing characteristic in response to the request response, the request response indicating whether the requested value was accepted by the power transmitter; and a load controller for adapting the loading of the power transmission signal to be reduced during the reduced power time interval; having A power receiver, wherein the request controller is configured to request a timing characteristic constraint from the power transmitter, the response controller is configured to receive a timing characteristic constraint indicator from the power transmitter, and the request controller is configured to determine the requested value of the timing characteristic in response to the timing characteristic constraint.

6. A power receiver that is wirelessly supplied with power from a power transmitter via an electromagnetic power transmission signal, the power receiver comprising: a receiver coil for receiving the power transmission signal, the power transmission signal using a repetitive time frame having at least a power transmission time interval and a reduced power time interval during a power transfer phase in which a power level of the power transmission signal is reduced; a communicator for communicating with the power transmitter; a request controller for sending a first message to the power transmitter, the first message being a message to the power transmitter to adapt a timing characteristic of the reduced power time interval, the request controller having a requested value of the timing characteristic; a response controller for receiving a request response from the power transmitter and determining the timing characteristic in response to the request response, the request response indicating whether the requested value was accepted by the power transmitter; and a load controller for adapting the loading of the power transmission signal to be reduced during the reduced power time interval; having A power receiver, wherein the timing characteristic is a duration of the reduced power time interval, and the request controller is configured to determine the requested value of the timing characteristic to comply with a maximum duration.

7. A power receiver that is wirelessly supplied with power from a power transmitter via an electromagnetic power transmission signal, the power receiver comprising: a receiver coil for receiving the power transmission signal, the power transmission signal using a repetitive time frame having at least a power transmission time interval and a reduced power time interval during a power transfer phase in which a power level of the power transmission signal is reduced; a communicator for communicating with the power transmitter; a request controller for sending a first message to the power transmitter, the first message being a message to the power transmitter to adapt a timing characteristic of the reduced power time interval, the request controller having a requested value of the timing characteristic; a response controller for receiving a request response from the power transmitter and determining the timing characteristic in response to the request response, the request response indicating whether the requested value was accepted by the power transmitter; and a load controller for adapting the loading of the power transmission signal to be reduced during the reduced power time interval; having 11. A power receiver, wherein the timing characteristic is a duration between reduced power transmission times of successive recurring time frames, and the request controller is configured to determine the required value of the timing characteristic according to a minimum duration.

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