Wireless Power Transfer

Abstract

The power transmitter 101 includes a transmitting coil 103 that generates a power transmission signal during a power transfer phase. A driver 201 generates a drive signal for the transmitting coil 103 to generate the power transmission signal during the power transfer phase. A communicator 205 receives messages from the power receiver 105. The controller 203 generates low power time intervals during the power transfer phase, during which the power level of the power transmission signal is reduced. The low power time intervals are generated when the communicator 205 receives a low power time interval request message from the power receiver 105. The power receiver 105 can generate the request message, for example, when a change in operating mode occurs. The power receiver 105 can ensure that the request message, and therefore the low power time interval, is generated only if the power receiver can handle a power interruption in the power transmission signal.

Description

[Technical Field]

[0001] The present invention relates to wireless power transfer, and in particular, but not exclusively, to foreign object detection in wireless power transfer systems. [Background technology]

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

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

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

[0005] Such a configuration allows for wireless power transfer to a device without the need for wires or the establishment of a physical electrical connection. In fact, this may enable external charging or powering of a device simply by placing the device next to or on top of the transmitting coil. For example, the transmitting device may have a horizontal surface on which the device can simply be placed for powering.

[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 methodology known as the Qi specification has been defined and is currently being further developed. This methodology allows a power transmitting device compliant with the Qi specification to be used with a power receiving device that also complies with the Qi specification, without the devices needing to be from the same manufacturer or specifically designed for each other. The Qi standard also includes features for adapting operation to specific power receiving devices (e.g., depending on the specific power drain).

[0007] The Qi specification is developed by the Wireless Power Consortium and further information can be found, for example, on the organization's website (http: / / www.wirelesspowerconsortium.com / index.html), where, among other things, the prescribed specification documents can be found.

[0008] In power transfer systems such as Qi, the electromagnetic fields generated to transfer the required levels of power to the receiver are often very large, and the presence of such strong electromagnetic fields can have an adverse effect on the environment in many situations.

[0009] For example, a potential problem with wireless power transfer is the possibility of unintentional power transfer to metal objects or other objects that happen to be near the transmitter. For example, if a foreign object, such as a coin, key, or ring, is placed on the transmitter's base configured to support the receiver, the magnetic flux generated by the transmitting coil will induce eddy currents in the metal object, causing it to heat up. This temperature increase can be significant and can be very inconvenient.

[0010] To reduce the risk of this situation occurring, it has been proposed to introduce foreign object detection, whereby the transmitter can detect the presence of a foreign object and reduce transmission power and / or generate a user warning when a foreign object is detected. For example, the Qi system includes functionality to detect foreign objects and / or reduce power when a foreign object is detected. Specifically, Section 11 of the Qi Specification, Version 1.2.1, describes various foreign object detection methods.

[0011] One such foreign object detection method is disclosed in WO2012127335, which describes a technique based on determining unknown power loss. In this technique, both the receiver and transmitter measure power, and the receiver communicates the measured received power to the transmitter. If the transmitter detects a large difference between the power transmitted by the transmitter and the power received by the receiver, an undesired foreign object may be present, and power transmission may be reduced or stopped for safety reasons. This power loss method requires the transmitter and receiver to perform synchronized, accurate power measurements.

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

[0013] The transmitter estimates the transmitted power, for example, by measuring the inverter's DC input voltage and current, multiplying them, and correcting the result by subtracting an estimate of the transmitter's internal power losses (e.g., estimated power losses in the inverter, primary coil, and transmitter metal parts).

[0014] The transmitter can estimate the power loss by subtracting the reported received power from the transmitted power. If the difference exceeds a threshold, the transmitter may assume that too much power is being dissipated in the foreign object and may terminate power transmission.

[0015] Others have proposed measuring 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, achieving sufficient detection accuracy using the methods described in the Qi specification tends to be difficult, and the many uncertainties regarding specific current operating conditions make this even more difficult.

[0017] For example, one particular problem is the possible presence of friendly metals (i.e., metal components of devices that embody receivers or transmitters) that can be difficult to compensate for because the magnetic and electrical properties of these metals may be unknown (and may vary from device to device).

[0018] Furthermore, even relatively small amounts of power dissipated within the metallic foreign object can cause unwanted heating. Therefore, even small power discrepancies between transmitted and received power must be detected, which can be particularly difficult at high power levels of power transmission.

[0019] The Q-reduction approach may in many cases be more sensitive to detecting the presence of metal objects, but it may still not be accurate enough, for example, it may still be affected by friendly metals.

[0020] Foreign object detection performance depends on the specific operating conditions that exist when the test is actually performed. For example, as described in the Qi specification, when foreign object detection measurements are performed during the selection phase of the power transfer initialization process, the signal provided by the transmitter for measurement must be small enough to prevent the receiver from waking up. However, such small signals typically have poor signal-to-noise ratios, resulting in poor measurement accuracy.

[0021] The requirement for a small measurement signal can have other adverse effects. A 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 rectifier output. This leakage current may therefore vary depending on actual conditions. Because leakage current affects the reflected impedance at the 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, where 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 assumed by the test can vary widely.

[0023] Therefore, current algorithms tend to be suboptimal and may not achieve optimal performance in some scenarios or examples, particularly failing to detect the presence of foreign objects or falsely detecting foreign objects when none are present.

[0024] The difficulty of accurate foreign object detection is particularly pronounced when the power transmission signal has a high power level and / or when the power transmission signal is changing. Therefore, foreign object detection during the power transmission phase is particularly challenging, especially for power receivers that represent large and varying loads.

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

[0026] In many systems, communication from a power receiver to a power transmitter may use load modulation, where the load on the power transmission signal is changed in response to the data being transmitted. However, detecting such load modulation can be difficult if the power transmission load on the power transmission signal is also changing. Similarly, communication from a power transmitter to a power receiver may be achieved by modulating the power transmission signal (e.g., amplitude or frequency modulation), but variations in the parameters of the power transmission signal due to the varying load can cause interference with such modulation.

[0027] In fact, even if an entirely separate carrier is used for communication, such as an NFC communication link, the very large and fluctuating electromagnetic fields caused by the power transmission signals can cause significant interference, albeit in significantly different frequency bands.

[0028] Thus, the presence of and loads placed on the power transmission signal can adversely affect other operations, such as foreign object detection and communication operations.

[0029] To improve foreign object detection, WO18219793A1 discloses applying a recurring time frame to the power transmission signal. The recurring time frame is divided into a power transmission time interval and a foreign object detection time interval. In this approach, power transmission is stopped during the foreign object detection time interval and foreign object detection is performed using a dedicated foreign object detection signal.

[0030] However, while this may provide improved performance in many situations, it does not provide optimal performance in all situations or for all operations. For example, many approaches may result in reduced power transfer levels and / or efficiency. Also, interruptions in power transfer can impose significant constraints on the design of the receiver, as it is often required to provide continuous power to the load but must operate with an interrupted power source.

[0031] Therefore, improved operation of power transmission systems would be beneficial, and in particular techniques that enable increased flexibility, reduced cost, reduced complexity, improved operation of the power transmission system, improved foreign object detection, improved communication, increased adaptability, backward compatibility, and / or improved performance. Summary of the Invention

[0032] SUMMARY OF THE INVENTION Accordingly, the Invention seeks to preferably mitigate, reduce or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0033] According to one aspect of the present invention, there is provided a power transmitter for wirelessly supplying power to a power receiver via an inductive power transmission signal, the power transmitter comprising: a transmitting coil for generating the power transmission signal during a power transfer phase; a driver for generating a drive signal for the transmitting coil to generate the power transmission signal during the power transfer phase; a first communicator for receiving a message from the power receiver; and a controller for generating a low power time interval during the power transfer phase, wherein a power level of the power transmission signal is reduced during the low power time interval, and the controller generates the low power time interval upon receiving a low power time interval request message from the power receiver.

[0034] The present invention may provide improved performance in many embodiments and may provide improved overall power transfer operations in many systems and embodiments. For example, in many embodiments, improved foreign object detection and / or communication may be achieved by performing such operations during time intervals created to provide conditions particularly favorable for such operations.

[0035] This approach can provide a highly flexible way for the receiver to control the generation of low power intervals. This can, for example, improve transmission reliability and ensure that the receiver can supply power to the load during the low power intervals, or, for example, tolerate reduced power to the load. This approach can ensure that low power intervals are used only when it does not interfere with the receiver's acceptable support of the load.

[0036] During the low power time interval, the power level of the power transmission signal is reduced corresponding to the reduced power level transmitted from the transmitter to the receiver. During the low power time interval, the power level of the power transmitted from the transmitter to the receiver is reduced compared to the power level of the power transmitted from the transmitter to the receiver during a power transmission time interval adjacent to the low power time interval. Power level, and references to power and power level, may be considered to relate specifically to active power (I·U·Cosφ). In many embodiments, the transmitter may be configured not to provide a drive signal to the transmitting coil during the low power time interval.

[0037] According to an optional feature of the invention, the transmitter further comprises a foreign object detector for performing foreign object detection, the foreign object detector configured to perform a foreign object detection test during the low power time interval.

[0038] This approach may provide improved foreign object detection and may allow foreign object detection to be adapted to specific receiver preferences or requirements, for example, allowing precisely timed foreign object detection to be performed when the impact on power transfer can be reduced or minimized.

[0039] In accordance with an optional feature of the invention, the transmitter further comprises a reliability circuit that determines a reliability measure of the foreign object detection.

[0040] This can result in improved performance in many embodiments.

[0041] The reliability measure may indicate the reliability of the foreign object detection test, and in particular the reliability / certainty / confidence of the foreign object detection test results.

[0042] According to an optional feature of the invention, the reliability circuit transmits a foreign object detection result to the power receiver in response to determining that the reliability measure of the foreign object detection test meets the reliability criteria.

[0043] The foreign object detection result may be an indication of whether a foreign object is detected or not. The reliability criterion may be a criterion that indicates that the foreign object detection result is more reliable / confident than if the criterion is not met.

[0044] According to an optional feature of the invention, the reliability circuit transmits a request to the receiver requesting one or more low power time intervals in response to determining that the reliability measure of the foreign object detection test does not meet the reliability standard.

[0045] This may improve performance, for example, allowing the system to perform more reliable foreign object detection by using multiple low-power time intervals. This approach also allows the receiver to retain control over the operation and when such foreign object detection tests are performed.

[0046] According to an optional feature of the invention, the reliability circuitry transmits a request to the receiver requesting at least one additional low power time interval in response to the foreign object detection test.

[0047] In some embodiments, the transmitter further comprises a calibrator for performing a calibration of the foreign object detection, the calibration being dependent on a foreign object detection test.

[0048] This may provide improved performance in many embodiments and may allow for improved foreign object detection matching / calibration since this can be performed under conditions of high confidence that no foreign objects are present.

[0049] In some embodiments, the transmitter may include a calibrator for performing a calibration of the foreign object detection, the calibration being dependent on whether a foreign object is detected by a foreign object detection test.

[0050] In some embodiments, the transmitter may include a calibrator for performing a calibration of the foreign object detection, the calibration also being performed if the foreign object detection test indicates that no foreign object is present.

[0051] In some embodiments, the calibrator is configured to perform the calibration in response to the reliability measure.

[0052] This may improve performance and make foreign object detection fit and configuration more reliable. For example, the degree of fit achieved by calibration may depend on a confidence measure. The higher the confidence measure, the greater the degree of fit achieved by calibration. In some embodiments, foreign object detection calibration may only be performed if the confidence measure meets a confidence criterion (and typically results in no foreign object being present). The confidence criterion may be a criterion that indicates a higher degree of confidence / confidence in the foreign object detection result than if the criterion is not met.

[0053] In some embodiments, the foreign object detection is configured to perform foreign object detection using a first foreign object detection algorithm during the low power time interval and to perform foreign object detection using a different second foreign object detection algorithm during a power transfer time interval that is separate from the low power time interval, and the calibrator is configured to calibrate the second foreign object detection algorithm.

[0054] This may provide efficient, accurate, and reliable adaptation / calibration of foreign object detection performed during power transfer.

[0055] The first foreign object detection algorithm may be more accurate than the second foreign object detection algorithm, which may rely on the power transmission signal being absent or having a power level below a given threshold, while the second foreign object detection algorithm may not be based on such an assumption.

[0056] In some embodiments, the foreign object detection test includes determining whether a foreign object is present or not as a function of a decay time of a signal level of at least one of a current and a voltage of a resonant circuit including the transmitting coil.

[0057] Such an approach may provide particularly advantageous operation and may be particularly well suited for very short low power time intervals where the power transmission signal may be completely stopped.

[0058] According to an optional feature of the invention, the first communicator communicates with the receiver during the low power time interval.

[0059] According to an optional feature of the invention, the first communicator communicates with the power receiver using a communication carrier wave different from the power transmission signal.

[0060] The communication carrier may also be for another independent communication system, such as an NFC communication system.

[0061] According to an optional feature of the invention, the low power time interval request message is a dedicated message for requesting a low power time interval.

[0062] According to an optional feature of the invention, the low power time interval request message is a message including other data for power transfer, the data including data for power transfer operations to be performed outside the low power time interval.

[0063] The low power time interval request message may specifically be a power control message that is also used to provide feedback to the power control loop of the power transfer.

[0064] In some embodiments, the low power time interval request message is a power control message that includes control data for a power control loop for the power transmission signal.

[0065] According to an optional feature of the invention, the low power time interval request message is a power feedback message that includes data indicative of the power level to be drawn by the receiver.

[0066] The power feedback message may specifically be a received power data packet.

[0067] According to an optional feature of the invention, the low power time interval request message is a reserved field of the received power data packet.

[0068] In accordance with an optional feature of the invention, the received power data packet further includes at least one of a low power time interval start time and a low power time interval duration.

[0069] According to an optional feature of the invention, the low power time interval request message includes a data field for requesting an operating mode for power transmission from a set of operating modes, the set of operating modes including the low power time interval operating mode.

[0070] In some embodiments, the transmitter is configured to generate only one low power time interval per low power time interval request message.

[0071] In some embodiments, the transmitter is configured to generate a plurality of low power time intervals upon receiving a low power time interval request message.

[0072] In some embodiments, the low power time interval request message includes a timing indicator for the low power time interval, and the controller is configured to adjust the timing of the low power time interval in response to the timing indicator.

[0073] In some embodiments, the low power time interval request message includes an indication of the number of low power time intervals, and the controller is configured to select the number of low power time intervals to generate in response to receiving the low power time interval request message based on the indication of the number.

[0074] In some embodiments, the first communicator is configured to receive the second low power time interval request message in response to transmitting a response message to the receiver indicating that the reliability measure does not meet the reliability criterion.

[0075] In some embodiments, the transmitter is configured to cause the receiver to disconnect the load during the low power interval.

[0076] According to an optional feature of the invention, the low power time interval has a duration of 500 μs or less.

[0077] According to an optional feature of the invention, the transmitter further includes an initialization processor that initializes the power transfer phase before the start of the power transfer phase, the initialization processor determining characteristics of the low power time interval in response to communication with the receiver, and the controller generating the low power time interval to have the characteristics.

[0078] According to one aspect of the present invention, there is provided a wireless power transmission system including a power transmitter according to the above and a power receiver, the power receiver including a coil that extracts power from a power transmission signal, a power circuit that supplies the extracted power to a load, and a second communicator that transmits a low power time interval request message to the power transmitter.

[0079] According to an optional feature of the invention, the second communicator transmits a low power time interval request message to the transmitter in response to a change in at least one of the power being extracted from the power transmission signal, the current being supplied to the load, and the voltage being supplied to the load.

[0080] According to an optional feature of the invention, the second communicator receives a reliability indicator from the transmitter, the reliability indicator indicating reliability of a foreign object detection test performed during the low power time interval, and the second communicator transmits a further low power time interval request message in response to determining that the reliability indicator does not meet a reliability criterion.

[0081] The reliability criterion may be a criterion that indicates a foreign object detection result is more reliable / confident than if the criterion is not met.

[0082] According to an optional feature of the invention, the second communication device receives a reliability indicator from the transmitter, the reliability indicator being indicative of the reliability of the foreign object detection test performed during the low power time interval, and the receiver performs a calibration of the received power level measurement in response to determining that the reliability indicator meets the reliability criteria.

[0083] In some embodiments, the transmitter may transmit an indication of the transmit power estimate to the receiver, and the receiver may be configured to perform a calibration of the received power level measurement in response to the indication of the transmit power estimate.

[0084] The reliability criterion may be a criterion that indicates a foreign object detection result is more reliable / confident than if the criterion is not met.

[0085] In some embodiments, the second communicator is configured to transmit the second low power time interval request message in response to receiving a response message from the transmitter that the reliability measure does not meet the reliability criterion.

[0086] In some embodiments, the receiver is configured to decouple the load from the receiver during the low power interval.

[0087] According to an optional feature of the invention, the transmitter may transmit an indication of the detection of a suspected foreign object, and the receiver may transmit a request for a low power time interval upon receiving the indication of the detection of the suspected foreign object from the transmitter.

[0088] In some embodiments, the second communicator is configured to communicate with the transmitter during the low power interval.

[0089] In some embodiments, the second communicator communicates with the power transmitter using a different communication carrier than the power transmission signal.

[0090] According to one aspect of the present invention, there is provided a method of operating a power transmitter that wirelessly supplies power to a power receiver via an inductive power transmission signal, the method including the steps of: generating, by a transmitting coil, the power transmission signal during a power transfer phase; generating a drive signal for the transmitting coil to generate the power transmission signal during the power transfer phase; receiving a message from the power receiver during the power transfer phase; and generating a low power time interval during the power transfer phase, wherein a power level of the power transmission signal is reduced during the low power time interval, and wherein a controller generates the low power time interval upon receiving a low power time interval request message from the power receiver.

[0091] 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 explanation of the drawings]

[0092] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings: [Figure 1] FIG. 1 illustrates example elements of a power transfer system according to some embodiments of the present invention. [Figure 2] FIG. 2 illustrates example elements of a transmitter according to some embodiments of the present invention. [Figure 3] FIG. 3 illustrates example elements of a receiver according to some embodiments of the present invention. [Figure 4] FIG. 4 illustrates example elements of a transmitter according to some embodiments of the present invention. [Figure 5] FIG. 5 illustrates example elements of a receiver according to some embodiments of the present invention. [Figure 6] FIG. 6 illustrates an example of a signal after stopping a power transmission signal in a wireless power transmission system according to some embodiments of the present invention. [Figure 7] FIG. 7 illustrates an example of a signal after stopping a power transmission signal in a wireless power transmission system according to some embodiments of the present invention. [Figure 8] FIG. 8 illustrates an example of a message format for a message used in a wireless power transmission system according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0093] The following description focuses on embodiments of the invention applicable to wireless power transfer systems that utilize power transfer techniques such as those known from the Qi specification, but it will be appreciated that the invention is not limited to this application and can be applied to many other wireless power transfer systems.

[0094] 1 illustrates an example of a power transfer system according to some embodiments of the present invention. The power transfer system comprises a power transmitter 101 including (or coupled to) a transmitting coil / inductor 103. The system further comprises a power receiver 105 including (or coupled to) a receiving coil / inductor 107.

[0095] The system provides an electromagnetic power transmission signal that can inductively transfer power from a power transmitter 101 to a power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal that is propagated as magnetic flux by a coil or inductor 103. The power transmission signal may correspond to an electromagnetic power transmission component representing the transfer of energy from the power transmitter to the power receiver and can be considered to correspond to the component of the generated electromagnetic field that transfers power from the power transmitter to the power receiver. For example, if there is no load on the power receiver coil 107, the power receiver does not extract power from the generated electromagnetic field (except for losses). In such a case, the power level of the power transmission signal will be zero (except for losses), although driving the power transmitter coil 103 may potentially generate a high-intensity electromagnetic field. In some situations where a foreign object is present, the power transmission signal can be considered to include a component corresponding to power transfer to the foreign object, and therefore the power transmission signal can be considered to correspond to power extracted from the electromagnetic field generated by the power transmitter.

[0096] The power transmission signal may typically have a frequency of about 20 kHz to about 500 kHz, and for Qi-enabled systems, may often typically be in the range of 95 kHz to 205 kHz (or, for example, for high-power kitchen applications, the frequency may typically be in the range of 20 kHz to 80 kHz). Because the transmitting coil 103 and the receiving coil 107 are loosely coupled, the receiving coil 107 picks up (at least a portion of) the power transmission signal from the power transmitter 101. Thus, power is transmitted from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitting coil 103 to the receiving coil 107. The term power transmission signal is primarily used to refer to the inductive signal / magnetic field between the transmitting coil 103 and the receiving coil 107 (magnetic flux signal), but it can also be thought of and sometimes used to refer to an electrical signal provided to the transmitting coil 103 or picked up by the receiving coil 107.

[0097] The receiver 105 in this example is specifically a receiver that receives power via a receiving coil 107. However, in other embodiments, the receiver 105 may include a metal element, such as a metal heating element, in which case the power transmission signal directly induces eddy currents, thereby directly heating the metal element.

[0098] The system is configured to transmit significant power levels, and specifically, in many embodiments, the transmitter can support power levels of 500 mW, 1 W, 5 W, 50 W, 100 W, or greater than 500 W. For example, for Qi-enabled applications, power transmission may typically be in the power range of 1-5 W for low-power applications (basic power profile), up to 15 W for Qi specification version 1.2, up to 100 W for high-power applications such as power tools, laptops, drones, and robots, and potentially greater than 100 W, up to 1000 W, for very high-power applications such as kitchen applications.

[0099] The operation of transmitter 101 and receiver 105 is described below with specific reference to embodiments that generally conform to the Qi specification (except for modifications and enhancements described (or resulting therefrom) herein) or are suitable for the High Power Kitchen specification being developed by the Wireless Power Consortium. In particular, transmitter 101 and receiver 105 may conform to or substantially correspond to elements of the Qi specification version 1.0, 1.1, or 1.2 (except for modifications and enhancements described (or resulting therefrom) herein).

[0100] The operation of the system of FIG. 1 will now be described, with a particular focus on foreign object detection.

[0101] In a wireless power transfer system, the presence of objects (typically conductive elements that extract power from the power transfer signal and are not part of the transmitter 101 or receiver 105, i.e., elements that are unintended, unwanted, and / or interfere with the power transfer) can be very detrimental during power transfer. Such unwanted objects are referred to in the art as foreign objects.

[0102] Foreign objects not only reduce efficiency by adding power losses to the operation, but can also degrade the quality of the power transfer operation itself (e.g., by interfering with power transfer efficiency or extracting power that is not directly controlled (e.g., by a power transfer loop)). Furthermore, the induction of currents within the foreign object (specifically, eddy currents within the metal portions of the foreign object) can result in heating of the foreign object, which is often highly undesirable.

[0103] To address this situation, wireless power transmission systems such as Qi are equipped with a foreign object detection function. Specifically, the power transmitter is equipped with a function for detecting whether a foreign object is present. If the presence of a foreign object is detected, the power transmitter can, for example, terminate power transmission or reduce the maximum amount of power that can be transmitted.

[0104] Current techniques proposed by the Qi specification are primarily based on detecting power loss (by comparing the transmitted power with the reported received power) or detecting a reduction in the quality Q of the output resonant circuit. However, in current use, these techniques have been found to provide suboptimal performance in many situations and can lead to inaccurate detection, in particular missing foreign objects and / or false positives where a foreign object is detected when none is present.

[0105] Foreign object detection can be performed before the receiver enters the power transfer phase (e.g., during initial power transfer setup) or during the power transfer phase. Detection during the power transfer phase is often based on comparing measured transmitted and received power, while detection performed before the power transfer phase is often based on measuring reflected impedance, for example, by measuring the Q factor of the transmitting coil using a small measurement signal.

[0106] FIG. 2 illustrates an example of a power transmitter according to some embodiments of the present invention.

[0107] The transmitter 101 includes a driver 201 capable of generating a drive signal that is supplied to the transmitting coil 103, which in turn generates an electromagnetic force transmission signal that provides power transmission to the receiver 105. The power transmission signal is supplied during a power transmission time interval of a power transmission phase.

[0108] As is well known to those skilled in the art, the driver 201 may include an output circuit in the form of an inverter, typically formed by driving a full or half bridge.

[0109] The transmitter 101 further comprises a transmitter controller 203 configured to control operation of the transmitter 101 in accordance with desired operating principles. In particular, the transmitter 101 may include many of the functions necessary to perform power control in accordance with the Qi specification.

[0110] The transmitter controller 203 is configured, among other things, to control the generation of the drive signal by the driver 201, and in particular, can control the power level of the drive signal and therefore the level of the generated power transmission signal. The transmitter controller 203 includes a power loop controller that controls the power level of the power transmission signal in response to power control messages received from the receiver 105 during a power control phase.

[0111] To receive data and messages from the receiver 105, the transmitter 101 includes a first communicator 205 configured to receive data and messages from the receiver 105 (a data message may provide one or more information bits, as will be appreciated by those skilled in the art). In this example, the receiver 105 is configured to load modulate the power transmission signal generated by the transmitting coil 103, and the first communicator 205 is configured to sense variations in the voltage and / or current of the transmitting coil 103 and demodulate the power transmission signal based thereon. Those skilled in the art will be aware of the principles of load modulation, such as those used in Qi wireless power transfer systems, and therefore these will not be described in further detail.

[0112] As is well known to those skilled in the art, in many embodiments the first communicator 205 may also be configured to transmit data to the receiver 105, for example, by modulating the power transmission signal.

[0113] In some embodiments, communication may be performed using another communication channel, which may be achieved using another communication coil, or using the transmitting coil 103. For example, in some embodiments, near field communication (NFC) may be implemented, or a high frequency carrier wave (e.g., a carrier wave having a frequency of 13.56 MHz) may be superimposed on the power transmission signal.

[0114] FIG. 3 shows an example of some elements of the receiver 105.

[0115] The receiver coil 107 is coupled to a receiver controller 301, which couples the receiver coil 107 to a load 303 (i.e., a switchable load 305) via a switch 305. The receiver controller 301 includes a power control path that converts the power extracted by the receiver coil 107 into a supply suitable for the load. Additionally, the receiver controller 301 may include various receiver controller functions necessary to perform power transfer, particularly functions necessary to perform power transfer according to the Qi specification.

[0116] To support communication from the receiver 105 to the transmitter 101, the receiver 105 includes a second communicator 307. The second communicator 307 may specifically be a load modulator configured to vary the load of the receiver coil 107 in response to data to be transmitted to the transmitter 101. As known to those skilled in the art, the load variation is then detected and demodulated by the transmitter 101.

[0117] As known to those skilled in the art, the second communicator 307 may further be configured to receive data from the power transmitter 101, for example, by demodulating the modulation of the power transmission signal.

[0118] In many embodiments, the second communicator 307 is configured to communicate without using a power transmission signal and may in particular be for a separate communication system, for example an NFC communication unit.

[0119] According to many embodiments, the transmitter 101 includes a foreign object detector 207 configured to perform a foreign object detection test, i.e., configured specifically to detect whether there appears to be an undesirable conductive element present in the generated electromagnetic field.

[0120] In this system, some (or all) foreign object detection tests are based on measurements performed during low-power time intervals, which, when used for foreign object detection purposes, may also be referred to as foreign object detection time intervals. During these foreign object detection time intervals, the transmitter controller 203 is configured to reduce the power level of the power transmission signal. Indeed, in some embodiments, the transmitter 101 may use different coils to generate the power transmission signal and to generate the electromagnetic test signal used for foreign object detection during the foreign object detection time intervals. In many embodiments, the transmitter may completely shut off the power transmission signal during the foreign object detection time intervals.

[0121] Thus, during the interval during which foreign object detection is performed, ie, during the foreign object detection time interval, foreign object detector 207 may evaluate conditions to determine whether a foreign object is deemed to be present.

[0122] For example, during the foreign object detection time interval, the transmitter 101 may generate an electromagnetic test signal using a test signal coil, which may be a dedicated test coil, and foreign object detection may be based on evaluation of the features and characteristics of this signal.

[0123] 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. This may typically be done by comparing the actual extracted power to the expected power extraction from the test signal by the power receiver 105. The expected power extraction from the power receiver 105 may be, for example, the extracted power level reported by the power receiver.

[0124] In some embodiments, the power receiver 105 may be configured to turn off any external loads, and the expected power drawn by the power receiver may simply be the expected parasitic losses of the power receiver. In some cases, these may be estimated to be substantially zero or even considered to be substantially zero. In other embodiments, these may be estimated during normal operation, for example, during the power transfer phase (e.g., as the difference between the transmitted power and the reported received power, compensated for relative electromagnetic field strength levels).

[0125] An advantage of performing foreign object detection during low power time intervals is that the low power levels, specifically the cessation of the power transmission signal, may allow for more accurate and reliable foreign object detection tests to be performed. The foreign object detection tests may be based on the assumption that no strong electromagnetic force transmission signal is present, or on characteristics or conditions that result from the cessation of the power transmission signal.

[0126] For example, in some embodiments, a separate test coil can be used to generate a separate, dedicated electromagnetic test signal. The test signal can be optimized for foreign object detection testing, for example, by changing the test frequency to be different from the resonant frequency of the power transfer circuitry, including the transmit coil 103 and the receive coil 107, to minimize the influence of both coils. This approach can be used without the power transfer signal interfering with often sensitive measurements.

[0127] As a specific example, the foreign object detection test includes determining whether a foreign object is present based on the decay rate characteristics of at least one of the signal levels of the current and voltage of a resonant circuit including the transmitting coil. Specifically, foreign object detection may be configured to stop the drive signal to the resonant circuit and allow the resonant circuit to resonate (freewheel). The current and voltage levels in the resonant circuit decay / decrease due to losses, and the decay increases as the losses increase. Therefore, the decay performance and decay rate depend on the power extracted from the generated electromagnetic signal, and the decay rate increases as the extracted power increases. Therefore, in some embodiments, the timing of the decay, such as the time it takes for the voltage / current signal to decrease by a given amount, may be determined by foreign object detection and used to determine whether a foreign object is presumed to be present. For example, if the decay time or decay rate for a given decrease is below a given threshold, foreign object detection may determine that a foreign object is present.

[0128] Thus, in some embodiments, the presence of a foreign object can be detected by measuring the attenuation of the signal in an undriven resonant tank. U.S. Patent No. 7,554,316 B2 discloses attenuation measurements that are performed and used to control power transfer operation.

[0129] 4 shows an example of a driver output bridge driving an output resonant circuit including a transmitting coil 103 called LTx. To form the resonant circuit, the transmitter 101 includes a capacitor (CTx) in series with LTx. This resonant circuit is driven by a full-bridge inverter powered by a DC voltage.

[0130] Figure 5 shows a simplified diagram of the core elements of the power transmission path of the receiver 105. The receiver also includes a capacitor CRx that forms a resonant circuit with the receiver coil 107, referred to as LRx. The induced AC voltage in this circuit is rectified by a full-bridge rectifier and smoothed by capacitor C. A load 303, referred to as Rload, is shown coupled across capacitor C. The value of capacitor C, along with the resistance of the load Rload, determines the output voltage (U out ) ripple.

[0131] The power transmitter and the power receiver are inductively coupled via the power transmitting coil LTx and the power receiving coil LRx.

[0132] FIG. 6 shows the effect that can occur if the inverter stops driving the transmitter resonant circuit, shorting it out.

[0133] As shown, the voltage U across the resonant circuit / tank tank decays over time.

[0134] Initially, the induced voltage in the receiver resonant tank is still large enough for the rectifier to conduct, and the remaining current I LRx is fed through the rectifier to the capacitor. However, when energy is extracted from the resonant circuit by the receiver load, the induced voltage falls below the voltage on capacitor C and the load is effectively disconnected. Therefore, in this situation, the load Rload is powered from the energy stored in the capacitor rather than in the resonant circuit.

[0135] This isolates the resonant circuit from the load, so the damping performance is independent of the value of the load Rload, and therefore becomes more dependent on other characteristics, particularly the presence or absence of foreign objects.

[0136] To eliminate the effect of the load, the decay rate measurement can be delayed until the rectifier is not conducting. Thus, in many cases, the decay measurement starts after skipping the first cycle. Therefore, during the decay measurement, the load depends only on the energy stored in C. The output voltage U across the load out are C and R load The required value of C is kept relatively low, while U out The decay measurement time is preferably short to prevent τ from remaining sufficiently high.

[0137] Figure 7 shows the U in two situations: when there is no foreign object and when there is a foreign object. tank The decay rate is greater when a foreign object is present than when no foreign object is present. tank The amplitude of can be expressed as follows:

number

[0138] Instead of measuring over a fixed time t, it is also possible to measure over a fixed number of resonance cycles (n), for example. tank The amplitude of can be expressed as follows:

number

[0139] The approach of using low-power time intervals during which the power transmission signal may be stopped enables or supports the use of attenuation-based foreign object detection, which is a significant advantage in many systems and scenarios, as attenuation measurements have been found to provide very accurate and reliable detection in many embodiments.

[0140] Advantages of the damping method include that the transmitter does not need to force the signal to a predetermined value. For example, there is no need to apply a resonant frequency, as is the case with the quality factor foreign object detection method. The transmitter can simply switch the resonant tank from a driven to an undriven state without controlling the operating parameters to a predetermined setting. For example, there is no need to adapt the operating frequency. This allows for short interruptions in the power signal, which has the advantage of reducing disruption to the receiver's functionality. A notable advantage of this approach is that it is particularly suitable for very short foreign object detection time intervals.

[0141] Thus, in many situations and for various operations, the use of low power time intervals can improve performance. However, the use of low power time intervals also introduces a number of drawbacks, since it requires the receiver to be able to handle interrupted power transfer. This is typically addressed by applying a recurring time frame to one or more reduced power time intervals, such that reduced power time intervals of a predetermined duration occur at periodic intervals. This allows the receiver to be designed to accommodate interrupted power transfer, for example, by sizing the energy storage / capacitor specifically to maintain the load during the interruption.

[0142] However, in the described system, the receiver 105 is configured to control the generation of reduced power time intervals, and specifically, whether reduced power time intervals are generated. Thus, rather than generating predetermined or transmitter-controlled low power time intervals, the transmitter in the described system can generate low power time intervals under (and in some cases only under) the control of the receiver, and thus the receiver controls when to generate low power time intervals. This allows the receiver to generate low power time intervals when it can handle an interruption or when it particularly needs the benefits that low power time intervals can provide.

[0143] In particular, the receiver 105 is configured to transmit a request for a low power time interval during the power transfer phase, and the transmitter is configured to generate a low power time interval during the power transfer phase upon receiving the request. Thus, during the power transfer phase, the receiver can determine when a low power time interval is desired or permitted and can transmit a low power time interval request message to the transmitter, resulting in the generation of a low power time interval. In many embodiments, a low power time interval during the power transfer phase can be generated only in response to a low power time interval request message received from the receiver.

[0144] Thus, the transmitter may generate a low power time interval upon receiving a low power time interval request message from the receiver, and the low power time interval will not be generated if a low power time interval request message is not received. The transmitter may generate a low power time interval upon receiving a low power time interval request message from the receiver, which would not be generated if a low power time interval request message was not received from the receiver. Thus, a low power time interval exists only because the receiver transmits a low power time interval request message. In some embodiments, the generation of a low power time interval is conditional on receiving a low power time interval request message from the receiver.

[0145] This approach may enable asynchronous, ad-hoc, receiver-controlled generation of low-power time intervals during the power transfer phase. This may provide improved performance in many embodiments, for example, by preventing low-power time intervals from occurring at inappropriate times. For example, it may allow the receiver to prevent low-power time intervals from occurring when the power load is higher than nominal and the energy storage is in danger of being insufficient to maintain the voltage for the load. This approach may increase receiver design flexibility, for example, by allowing capacitors to be designed for nominal conditions rather than extreme worst-case scenarios.

[0146] This approach avoids many of the drawbacks and risks associated with the transmitter controlling when low power intervals are generated. For example, it can improve communication from the receiver to the transmitter because the receiver can control when communication interference is not present. This can prevent, for example, improper reception of control error messages, which can degrade power control performance. Similarly, it can prevent received power messages from not arriving / decoded. It can also prevent erroneous received power measurements due to sudden drops in power during slots. Furthermore, it can prevent, for example, unexpected received power behavior from causing the receiver's control logic to malfunction. By allowing the receiver to control when low power intervals occur, the effects of such power drops can be effectively avoided or compensated for because the receiver knows exactly when low power intervals will occur and can ensure that they only occur when acceptable.

[0147] The power level of the power transfer signal is reduced during the low power time intervals compared to the power transfer time intervals, and typically the maximum allowable power is 5, 10, or 50 times or more lower during the low power time intervals than during the power transfer time intervals of the power transfer phase.

[0148] The power transmitter (and typically the power receiver) may then prepare one or more operations (functions, processes, procedures) to be performed during the low power interval, i.e., synchronize the execution of one or more operations of the power transmitter to occur during the low power interval. For example, the power transmitter may typically synchronize the execution of foreign object detection and / or possibly communication to occur during the low power interval. In this manner, the impact of power transmission and power transmission signals on a given operation, specifically foreign object detection and communication, can be reduced, and often minimized.

[0149] As noted above, in many embodiments, the transmitter is configured to stop / disconnect the drive signal / resonant frequency from the transmitting coil 103 during the low power intervals. Additionally, in many embodiments, the transmitter may be configured to disconnect the load from the receiving coil 107 so that no power is directly transferred from the power transmission signal to the load during the low power intervals. In some embodiments, the disconnection may be only partial, such that the effective load is reduced during the low power intervals compared to other intervals. In many embodiments, the load of the power transmission signal applied by the receiver may be 100 mW, 200 mW, 500 mW, or 1 W or less during the low power intervals, while the power extraction during the power transfer intervals may be higher, typically significantly higher. In many embodiments, the power level of the power transmission signal may be 100 mW, 200 mW, 500 mW, or 1 W or less during the low power intervals, while the power level of the power transmission signal during the power transfer intervals may be higher, typically significantly higher.

[0150] In many embodiments, the reduced power time intervals may be very short, and in many embodiments, the low power time intervals have durations of 500 μs, 200 μs, or even 100 μs or less. This may provide an efficient way for the receiver to control the generation of low power time intervals that are very short but sufficient to perform efficient operations such as communication and foreign object detection, as described above. For example, attenuated foreign object detection may be performed by terminating the power transmission signal, and the accuracy of this detection may be further improved by the receiver disconnecting the load.

[0151] In many embodiments, the transmitter 101 further comprises a reliability circuit configured to determine a measure of reliability of foreign object detection tests performed during the low power time interval. In many embodiments, the reliability circuit is part of or coupled to the foreign object detector 207 and is configured to determine the reliability measure based on foreign object detection operations, parameters, values, and signals, which depend on the details of the particular embodiment.

[0152] The reliability measure indicates the reliability of the foreign object detection test, and more specifically, indicates the reliability / certainty / confidence of the foreign object detection test result. The reliability measure is also referred to as a confidence measure that indicates the reliability of the foreign object detection test result for the foreign object detection test performed during the low power time interval.

[0153] It will be appreciated that generating reliability / confidence values ​​for technical tests is well known for a variety of tests and algorithms. The specific approach for determining reliability / confidence values ​​for foreign object detection tests will vary depending on the specific test being performed. In many embodiments, foreign object detection is based on measurements to determine parameter values, and the likelihood of a foreign object being present depends monotonically on the parameter values, e.g., monotonically increasing or decreasing. In such embodiments, the confidence measure may be determined as the parameter values ​​or, for example, as a monotonic function of the parameter values.

[0154] For example, in the case of attenuation-based foreign object detection, the attenuation rate may indicate the probability that a foreign object is present, and therefore may also be used to indicate a confidence value. For example, a foreign object detection test may determine that a foreign object is present if the decay time is above a certain threshold, and that a foreign object is not present if it is not. Furthermore, the confidence of the determination may be given as a numerical difference between the actual decay rate value and the threshold. Thus, if the decay time is much higher than the threshold, there is a high confidence that a foreign object is present; if the decay time is much lower than the threshold, there is a high confidence that a foreign object is not present; and if the decay time is close to the threshold, this may indicate that a foreign object detection is present or absent depending on whether the threshold is exceeded, and the test result may be designated as having low confidence / confidence.

[0155] Similar approaches may be used for other foreign object detection tests, e.g., for a power loss test, the confidence measure may be a function of the difference between the power loss and the detection threshold, for a Q-factor foreign object detection test, the confidence measure may be a function of the difference between the power loss and the detection threshold, etc.

[0156] In many embodiments, the transmitter 101 may be configured to transmit data to the receiver to provide information regarding foreign object detection and / or foreign object detection reliability measures.

[0157] Specifically, in many embodiments, the transmitter 101 may be configured to transmit foreign object detection data to the receiver 105 depending on a reliability measure.

[0158] The power transmitter is arranged to transmit a foreign object detection test result of a foreign object detection test during a low power time interval in response to the confidence measure for the foreign object detection test / foreign object detection test result satisfying a confidence criterion indicating the confidence measure is above a certain confidence level. Thus, if the foreign object detection test produces a detection result that is deemed sufficiently reliable, the power transmitter 101 transmits an indication of the test result to the power receiver 105. Thus, if the confidence measure is sufficiently high, the power transmitter 101 transmits data to the power receiver 105 indicating whether a foreign object was detected.

[0159] In some embodiments, the transmitter may send a reliability measure in response to another message, such as received power, but not necessarily a request for a low power interval request.

[0160] Such a reliability measure may be transmitted for foreign object detection performed as part of a power transfer time interval, e.g., for power loss foreign object detection performed during power transfer. This may indicate that a suspect foreign object detection has occurred. As described in more detail below, this may result in the receiver transmitting a further low power time interval request message, which may result in more accurate foreign object detection, e.g., using attenuation-based measurements.

[0161] In some embodiments, the transmitter 101 may be configured to compare the reliability measure with a reliability criterion (which may be the same as or different from the reliability criterion used to determine whether to transmit the foreign object detection test results) and may transmit a request for one or more low power time intervals if the reliability criterion is not met.

[0162] As a result of evaluating the reliability criterion, it may be determined that the foreign object detection test results are not as reliable as desired. For example, if the reliability measure is below a threshold, it may be determined that the foreign object detection test is not sufficiently reliable. For example, if the attenuation rate is too close to the foreign object detection decision threshold, it may be determined that the foreign object detection test results are too uncertain to provide a sufficient definitive indication of whether a foreign object is present or not.

[0163] Thus, in this case, the power transmitter 101 may, in some embodiments, send requests for more low power time intervals to the power receiver. Thus, instead of instituting a low power time interval itself, for example by stopping the power transmission signal and disconnecting the load at the power receiver, the power transmitter 101 requests that the power receiver 105 take the initiative to introduce one or more new low power time intervals by generating a new request message.

[0164] Upon receiving such an indication from the power transmitter 101, the power receiver 105 may evaluate whether it is practical / possible to generate one or more new low power time intervals. For example, the current state of an energy storage device may be determined to determine whether sufficient energy is stored to support the load during the low power time interval. If so, a new request for a low power time interval may be generated and sent to the power transmitter. Thus, one or more subsequent low power time intervals may be generated using the same technique as the initial low power time interval.

[0165] The transmitter may be configured to perform additional foreign object detection tests during subsequent low-power time intervals to provide more accurate detection. The additional foreign object detection tests may be separate and independent tests, and the reliability and confidence of the foreign object detection test results may be assessed based on whether the tests in subsequent low-power time intervals are consistent. In other embodiments, the foreign object detection tests may combine different low-power time intervals. For example, the decay rate or power loss value may be averaged over multiple low-power time intervals before being compared to the detection threshold.

[0166] Thus, in some embodiments, the power transmitter 101 and the power receiver 105 may cooperate to dynamically and ad-hocly introduce sufficient low-power time intervals such that sufficiently reliable foreign object detection results are achieved. This may be achieved while maintaining operation under the control of the power receiver 105, specifically enabling the power receiver 105 to ensure that the low-power time intervals do not result in unacceptable power transfer.

[0167] In many embodiments, the communication of the confidence measure, the foreign object detection test result, and / or the request for a further low power time interval may be combined. For example, a single data parameter may be transmitted, with one value indicating that a reliable foreign object detection test indicated that a foreign object is not present, another value indicating that a reliable foreign object detection test indicated that a foreign object is present, and a third value indicating that the foreign object detection test was not reliable and that a further low power time interval should be initiated.

[0168] The transmitter 101 may be configured to perform other actions in response to the foreign object detection results. For example, in many embodiments, the transmitter 101 may be configured to terminate power transmission in response to detecting a foreign object. If an uncertain test result is obtained, the transmitter 101 may reduce the power level, for example, until a new foreign object detection test is performed in a subsequent low-power time interval. If a reliable foreign object detection test indicates that no foreign object is detected, the transmitter may continue power transmission without modification.

[0169] In some embodiments, foreign object detector 207 may be configured to not only perform foreign object detection during low power intervals, but also perform foreign object detection outside of low power intervals. In such embodiments, foreign object detection may also be performed while power transfer is ongoing during power transfer intervals. This may provide improved performance in many embodiments, often allowing foreign object detection to occur more quickly than if foreign object detection were performed only during asynchronous low power intervals. This approach may provide, for example, a combined effect of highly accurate detection during low power intervals and less accurate detection during power transfer intervals. This allows for accurate detection of small foreign objects while also allowing for very rapid detection of larger foreign objects.

[0170] The transmitter may decide to transmit data to the receiver indicating the reliability of foreign object detection outside of the low power interval. If the transmitter senses a need for more accurate foreign object detection, e.g., if the reliability is low or if the transmitter suspects a foreign object, the transmitter indicates such need to the receiver, and the receiver requests a low power interval at a moment convenient to the transmitter.

[0171] For example, the foreign object detector 207 may perform power loss foreign object detection during both the low power time interval and the power transfer interval, but during the low power time interval, a dedicated test signal may be used and the load may be disconnected, allowing for more accurate power loss detection performance.

[0172] In some embodiments, the power receiver may receive a reliability measure / indicator of the foreign object detection (foreign object detection may have been performed, e.g., during a low power interval, or may have been performed, e.g., during normal power transmission outside of a low power interval). The power receiver may determine whether to request the generation of additional low power intervals based on the reliability criterion. For example, if the reliability criterion is below a threshold, the power receiver may request the generation of a new low power interval to enable more accurate foreign object detection.

[0173] In some embodiments, both the receiver and transmitter may evaluate the reliability measure. For example, the transmitter may compare the reliability measure to a reference to determine whether to request more low power time intervals, and the transmitter may further transmit the reliability measure to the receiver, which may also perform an evaluation to determine, for example, whether to comply with the request. For example, the receiver may comply with the request only if it deems the reliability below a given threshold and reject the request otherwise. As another example, the threshold for not sending a request for a new low power time interval may be significantly higher when the transmitter sends a request for a new low power time interval than when it does not.

[0174] Such approaches may allow for a more complex decision process, for example, where the receiver generates a request for an additional low power time interval only if the reliability metric satisfies both the transmitter implementation criteria and the receiver implementation criteria. These approaches may allow tailoring the behavior of requesting a low power time interval to a specific pairing of a specific receiver and a specific transmitter (e.g., a new low power time interval may be generated only if both the receiver and transmitter deem it desirable).

[0175] In some embodiments, the transmitter further comprises a calibrator configured to perform a calibration of the foreign object detection, the calibration being dependent on the foreign object detection test.

[0176] In some embodiments, whether or not a calibration is performed may depend on a foreign object detection test, specifically, whether or not a foreign object is detected, and typically, calibration is performed only if the foreign object detection test indicates that no foreign object is present.

[0177] In many embodiments, the reliability of the foreign object detection test may also be taken into consideration. For example, calibration may be performed only if the foreign object detection test determines that no foreign object is present and the reliability measure indicates a sufficiently high degree of confidence that this is a correct determination. The reliability threshold for performing calibration may be different from the reliability threshold for other purposes, such as the threshold for sending a request for an additional low power time interval.

[0178] In some embodiments, the calibrator 211 may be configured to calibrate the foreign object detection for the low power time interval itself, i.e., to calibrate the algorithm used during the low power time interval itself. In other embodiments, the calibrator 211 may be configured to adapt / calibrate another foreign object detection, e.g., a foreign object detection algorithm executed during the power transfer time interval. For example, if accurate foreign object detection is performed during the low power time interval, it can be determined with high confidence that no foreign object is present (or that the impact of a foreign object present is very small). After the low power time interval, and immediately after power transfer resumes, the foreign object detection test and calibrator 211 may modify the foreign object detection to more accurately reflect the absence of a foreign object. For example, in the case of power loss foreign object detection, the power loss measured immediately after the low power time interval is most likely due to losses in the transmitter and receiver themselves (e.g., their metallic parts). Therefore, the calibrator 211 can introduce an offset into the power loss estimate to offset / compensate for this power loss. The compensation / offset is introduced for subsequent foreign object detection tests during the power transfer interval.

[0179] Thus, in many embodiments, the calibration is configured to calibrate foreign object detection performed during power transfer time intervals / outside low power time intervals.

[0180] Calibration may be an operation that changes parameters of foreign object detection operation. Specifically, calibration may be configured to adapt the foreign object detection algorithm to the current operating point / scenario. For example, calibration may compensate for variations in component values, relative positions between the transmitter and receiver, transmitter and / or receiver characteristics, power levels, etc. As another example, the average rate of signal decay at the beginning of a low-power time interval may be measured and averaged across multiple foreign object detection tests that indicate the absence of a foreign object, and the criteria may be adapted to reflect this average value. This may allow, for example, the foreign object detection algorithm to be adapted during the low-power time interval to be more deterministic and to detect smaller variations from the current operating point when a foreign object is not present.

[0181] In many embodiments, the transmitter may perform foreign object detection during both the low power time interval and the power transfer time interval, as described above, and the calibrator 211 may be configured to adapt the foreign object detection performed during the power transfer time interval depending on the results of the foreign object detection test during the low power time interval.

[0182] Thus, in a typical embodiment, foreign object detection performed during power transfer time intervals is different from foreign object detection performed during low power time intervals.

[0183] In some embodiments, the underlying foreign object detection operations performed may be the same, or may differ in that different detection criteria are applied. For example, power loss may be determined for both low power time interval foreign object detection and power transfer time interval foreign object detection, but the measured power loss may be compared to different detection thresholds. The detection thresholds for one or both foreign object detections may be adapted by the calibrator 211.

[0184] In many embodiments, different types of tests may be used for foreign object detection during power transfer time intervals and low power time intervals, and in particular, different parameters may be determined and evaluated to determine whether a foreign object is present.

[0185] As an example, in many embodiments, foreign object detector 207 may perform power loss during power transfer time intervals while performing attenuation-based or Q-factor foreign object detection during low-power time intervals. This may provide particularly advantageous performance in many embodiments where different foreign object detection algorithms are optimized or adapted for characteristics / conditions in different phases. Specifically, attenuation measurements may enable highly accurate and very short-term foreign object detection, but require the power transfer signal to be stopped. Therefore, they may be well-suited for short, low-power time intervals. In contrast, power loss tends to be more accurate for foreign object detection at higher, sustained power levels (especially if accurately calibrated and adapted to the specific current conditions). Q-factor methods that are not based on attenuation may provide high accuracy but may require longer times to stop power transfer. Thus, a combination of different foreign object detection algorithms (whether using simply different criteria or fundamentally different operation) may provide highly accurate foreign object detection throughout the power transfer phases, and adapting power transfer time interval operation based on foreign object detection tests during low-power time intervals may significantly improve performance.

[0186] As a specific example, the receiver may request a low-power time interval, and in response, the transmitter may cease the drive signal and perform a decay rate foreign object detection test. If a foreign object is detected with high confidence, power transfer may be terminated (e.g., subject to further foreign object detection tests indicating the presence of a foreign object). If the absence of a foreign object is detected with high confidence, the calibrator 211 may be activated to calibrate foreign object detection for subsequent power transfer time intervals. In this example, when the power transfer signal resumes and the power transfer time interval begins, the calibrator 211 performs measurements and, based on these measurements, adapts the foreign object detection algorithm that runs during the power transfer time interval. Thus, the power transfer foreign object detection algorithm is adapted based on the assumption that no foreign object was detected. For example, in the case of power loss detection, the current power loss, which is the power loss in the absence of a foreign object, is measured, and the decision threshold is adapted accordingly (or a compensation factor is introduced for the power loss).

[0187] If the reliability of the foreign object detection test based on the decay rate during the low power time interval results in a non-existent but unreliable detection of a foreign object, the system may be configured to continue power transfer, but the calibrator 211 may be configured not to calibrate the foreign object detection algorithm. This may reduce the risk that the calibration may adapt foreign object detection to a situation where a foreign object is actually present. For example, a small foreign object at some distance may not result in unacceptable power loss and may be an acceptable situation. However, the reliability of the detection of a foreign object being absent may be low (the parameter is close to the detection threshold), which may prevent the calibrator 211 from calibrating foreign object detection to a situation where a small foreign object is actually present.

[0188] Thus, in some embodiments, the operation of the transmitter in response to the low power time interval foreign object detection test may depend on both the detection result of whether or not a foreign object (FO) is present. For example, the following approach may be employed. Highly reliable +FO detection: Power transmission stop / reduction / limit Highly reliable +FO undetected: calibration. Additional data may be exchanged to support the calibration itself. Unreliable: Calibration postponed. Additional low-power intervals may be required.

[0189] This approach may therefore allow for improved interaction between two foreign object detection algorithms, with the first algorithm (one of the low power time intervals) typically being a significantly more reliable detector than the second algorithm (one of the power transfer time intervals). The accurate / reliable detection algorithm can be used to show with high confidence that no foreign object is present, and thus the less accurate / reliable detection algorithm can be calibrated under this assumption. A significantly improved overall foreign object detection can typically be achieved.

[0190] In many embodiments, calibration of foreign object detection during power transfer time intervals may depend on foreign object detection tests during low power time intervals, to the extent that calibration is performed only if no foreign object is detected (and in some cases, requires that the confidence measure be above a threshold), while in other embodiments it may depend more complexly on the test results and confidence. For example, in some embodiments, the degree of calibration / fit may depend on the confidence measure. For example, calibration may be configured to adjust the detection threshold by a relative offset from the current level. The magnitude of the offset may depend on the confidence measure, such that a detection that a foreign object is not present with high confidence may result in a larger change in the detection threshold than a lower confidence detection.

[0191] In some embodiments, the first communicator 205 may alternatively or additionally be configured to communicate with the receiver during the low power time intervals. In some embodiments, the communication may use a power transmission signal and / or the transmitting coil 103. In such embodiments, a drive signal may be generated, for example, at the same frequency as that used during the power transfer time intervals, and the drive signal may be modulated to transmit data.

[0192] In other embodiments, communication may be performed using an antenna / transmitting coil different from the transmitting coil 103. Also, the first communicator 205 may use a communication carrier different from the power transmission signal, typically a communication carrier having a different frequency.

[0193] In many embodiments, the communication may be via an entirely separate communication system, in particular a standardized short-range communication system such as a Near Field Communication (NFC) system.

[0194] In the described system, communication is performed in low-power time intervals during the power transfer phase. Specifically, some or all of the low-power time intervals may be communication time intervals during which communication between the transmitter 101 and the receiver 105 is performed. Specifically, the transmitter controller 203 may have a communication control function configured to synchronize the first communicator 205 so that communication operations (typically both transmitting and receiving data) are performed only during (typically only during) the communication time intervals of the power transfer phase, i.e., only during the low-power time intervals allocated for communication.

[0195] In many embodiments, the first communicator 205 is configured to transmit data to the receiver 105, and may be configured to modulate the power transmission signal using frequency, amplitude, or phase modulation. In some embodiments, this may be performed, for example, during low-power time intervals when the drive signal / power transmission signal is set to a low, constant level, which may result in better detection of amplitude fluctuations due to amplitude modulation.

[0196] In some embodiments, communication may be performed using another communication channel, which may be achieved using another communication coil, or using the transmitting coil 103. For example, in some embodiments, short-range wireless communication may be implemented, or a high-frequency carrier wave (e.g., a carrier wave having a frequency of 13.56 MHz) may be superimposed on the power transmission signal.

[0197] This may significantly improve communication performance, and specifically, may provide an environment that provides improved communication with less interference caused by power transmission operations. Furthermore, since the power transmission time interval is controlled by the power receiver, ad-hoc, dynamic, and asynchronous communication operations controlled by the power receiver can be achieved.

[0198] In many embodiments, the low power time interval may include both a communication time interval and a foreign object detection time interval.

[0199] In the described system, operations such as foreign object detection and / or communication may be performed in low-power time intervals. Therefore, foreign object detection / communication and power transfer can be separated in the time domain, reducing cross-interference from power transfer to foreign object detection / communication. Therefore, variability and uncertainty due to variations in power transfer operating conditions can be isolated from foreign object detection / communication, providing more reliable and accurate foreign object detection / communication.

[0200] Thus, in the power transmission phase, the power transmitter is configured to perform power transmission during power transmission time intervals. Specifically, during these time intervals, the power transmitter may provide information to the power receiver at a much higher bit rate, which would otherwise lead to an overload of low-bit-rate communication during the power transmission intervals. The power transmitter and the power receiver may (re)negotiate new operating parameters, such as a guaranteed power level. The power transmitter and the power receiver may also operate a power control loop (which may be based on communication during communication time intervals corresponding to low-power time intervals). Thus, the level of transmitted power may be dynamically changed.

[0201] Thus, an approach using low power time intervals for communication may provide significantly improved communications in many embodiments. Furthermore, by allowing the low power time intervals to be dynamic and ad hoc / asynchronous time intervals controlled by the receiver, a more efficient and adaptive approach may be realized. This allows the low power time intervals to be adapted to the specific needs, requirements, and preferences of individual receivers, including ensuring that the low power time intervals do not jeopardize reliable power delivery to the load.

[0202] The receiver may use different conditions and triggers to send a low power time interval request message to the transmitter in different embodiments.

[0203] In many embodiments, the power receiver may be configured to transmit a low power time interval request message in response to a change in the power extracted from the power transmission signal, the current supplied to the load, and / or the voltage supplied to the load. The change may be an actual change that has been detected or occurred, or may be a change that will occur in the future, for example, i.e., the power receiver may transmit a low power time interval request message before implementing the change.

[0204] As an example, the power receiver may change its operating point so that a different power, current, and / or voltage is delivered to the load. In particular, the power receiver may change its operating mode to deliver different power to the load, such as changing the charging of a battery from fast charging to normal or trickle charging.

[0205] The different power levels of these operating modes may have different effects on the power transfer signal, which may also affect the foreign object detection test during the power transfer time interval. For example, changing the power delivered to the load may significantly change the power loss measured at the transmitter, even if no foreign object is present. Therefore, it may be desirable to recalibrate the foreign object detection test, and a low power time interval request message may be generated and transmitted to the transmitter accordingly. This may initiate a new low power time interval, and a foreign object detection test, e.g., a decay rate test, may be performed during the low power time interval. As a result, if the absence of a foreign object is reliably indicated, the transmitter may perform a calibration of the power transfer time interval foreign object detection algorithm at the end of the low power time interval.

[0206] Such an approach is not limited to changing power levels, but can also be applied to changing between operating modes while keeping the power level the same. For example, a receiver may have the following operating modes: Operating mode 1: The receiver delivers 5W, 5V, and 1A to the load. Operating mode 2: The receiver delivers 5W, 10V, and 0.5A to the load.

[0207] The estimate of received power may be different in the two modes, and the estimate of transmitted power may also be different. The calculated power loss may be different for different operating modes, and the receiver may be configured to send a low power time interval request message when switching between these modes, so that a new low power time interval and foreign object detection calibration may be performed.

[0208] The system may behave differently depending on whether the power level is changed. In many embodiments, foreign object detection may utilize a calibrated power loss curve that shows the expected power loss at various power levels of the power transmission signal when no foreign object is present.

[0209] When the power level change is relatively small (typically no change in operating mode at the receiver), the current calibrated power loss curve can typically be reused and extended / improved for the new power level. However, in the case of an operating mode change (typically involving a change in the nominal voltage and / or current supplied to the load), the power loss curve should be updated, and thus multiple (two or more) power loss values ​​may be used. A different power loss curve may be maintained for each operating mode.

[0210] In some embodiments, the transmitter may be configured to transmit a request for a measurement and / or an indication of the detection of a suspected foreign object, and the receiver may be configured to transmit a request for a low power time interval in response to receiving the indication from the transmitter.

[0211] In some embodiments, the transmitter may be configured to transmit the indication by transmitting a negative (NACK) response to a message received from the receiver, which may be a power transmission message, such as specifically a received power or power control loop error message.

[0212] The transmitter may be configured to transmit an indication of the detection of a suspected foreign object in response to a result of a foreign object detection test, specifically a foreign object detection test performed during a power transfer time interval.

[0213] Specifically, in some embodiments, the transmitter may transmit an indication of suspected foreign object detection in response to a determination that the foreign object detection test did not result in a determination that the foreign object is not present with a confidence measure that meets the confidence criteria.

[0214] In particular, the transmitter, in some embodiments, may transmit an indication of a suspected foreign object detection in response to determining that a confidence measure of a foreign object detection test does not meet a confidence standard.

[0215] Thus, in some embodiments, the receiver may request a low-power time interval upon receiving an indication from the transmitter that it wishes to take measurements, which may occur specifically when the transmitter suspects the presence of a foreign object, for example, when the foreign object detection threshold is nearly reached or occasionally exceeded (e.g., during a single measurement event).

[0216] Upon receiving an indication of suspected foreign object detection, the power receiver may, for example, control power transmission to a lower level, thereby mitigating potential heating of the foreign object.

[0217] Alternatively or additionally, a more accurate test for the presence of a foreign object may be initiated. In such an example, the receiver may enable the transmitter to perform a more accurate test by requesting a low power time interval, and the transmitter may then perform an accurate foreign object detection test, such as a decay rate test. In some embodiments, the low power time interval request message may additionally or alternatively initiate a new calibration, as described above.

[0218] Specifically, a NAK sent in response to a received power message may indicate that the receiver should take action, such as reducing power consumption or requesting calibration, and may in particular indicate that a new low power time interval request message should be requested.

[0219] In an approach where operation is entirely controlled by the receiver, the transmitter relies on the receiver's acceptable operation during low power interval requests. However, this has associated challenges. For example, it can be difficult to ensure that sufficient compliance testing has been performed on such receiver options.

[0220] One approach may be to require the receiver to allow the transmitter to keep the power difference within a tighter range (i.e., lower power loss) than originally required, which places an implicit requirement on the receiver to allow the transmitter to calibrate the power difference, since otherwise achieving the tighter range is usually not practical.

[0221] In many systems, the transmitter may acknowledge / deny messages from the receiver. A negative acknowledgement (NAK) may also be used by the transmitter to alert the receiver to the (potential) presence of a foreign object. This means that the transmitter may cease power transmission if the receiver does not take action. The receiver's action may be to lower the receiver's power level request, thereby mitigating the potential risk of the foreign object heating.

[0222] Another approach may be for the receiver to request a low power time interval request message to allow the transmitter to perform more accurate foreign object detection.

[0223] In this context, a transmitter NAK may be considered an indicator that foreign object detection is not reliable / accurate enough, and therefore power transmission may cease.

[0224] Thus, the smart receiver may request a low power time interval to allow the transmitter to perform a more accurate foreign object detection test and / or perform a power difference calibration.

[0225] The receiver may be configured to request a low power interval in response to receiving a NAK response from the transmitter.

[0226] In some embodiments, the receiver may be further configured to perform a calibration, for example, if the receiver receives a confidence indicator for a low foreign object detection test from the transmitter. If the information indicates with a sufficiently high probability that a foreign object is not present, the receiver may calibrate the received power level measurement.

[0227] In such a case, the transmitter may, for example, transmit a measurement / estimate of its transmitted power, which the receiver may use to calibrate its received power to compensate for any difference between the two.

[0228] In some embodiments, the receiver may be configured to transmit low power time interval request messages with a maximum duration between them. For example, the maximum duration between two low power time intervals may be 100 ms, 500 ms, 1 s, or 2 s. In such embodiments, the receiver may transmit a low power time interval request message, for example, every time a change in operating mode occurs, or may transmit a low power time interval request message at a predetermined interval, for example, 500 ms, even if no change occurs.

[0229] In some embodiments, the low power time interval request message may be a dedicated message used solely for the purpose of requesting a low power time interval, e.g., simply in a predetermined bit pattern that, when detected by the transmitter's first communicator 205, is interpreted as a request to the transmitter to generate a low power time interval.

[0230] In some embodiments, the low power time interval request message may include data related to the low power time intervals, such as the proposed timing of the low power time intervals, the required maximum or minimum power levels, the duration, the number of low power time intervals required, etc. Such data may be provided as part of a dedicated message and as part of a composite message or a message also used for other purposes. In such embodiments, the transmitter may be configured to generate low power time intervals with such characteristics.

[0231] Thus, in some embodiments, the low power time interval request message may be a separate message used solely for the purpose of requesting a low power time interval. However, in some embodiments, the low power time interval request message may be a composite message, in particular, the request for a low power time interval may be piggybacked onto another existing message that is normally used for other purposes.

[0232] In some embodiments, the low power time interval request message is a message that includes other data for power transmission, the data being related to power transmission operations that are performed outside the low power time interval. The low power time interval request message may include data related to power transmission time interval operations. As a specific example, the low power time interval request message may be a power control message that includes control data for a power control loop for the power transmission signal.

[0233] Thus, instead of a dedicated or separate message, the low power time interval request message may be, for example, a power control error message. Such messages may be sent frequently, for example, every 250 ms, or faster. Many such messages may not include a low power time interval request, but may merely report a power control request, such as a power increase or power decrease request. However, some messages may include a data sequence that is interpreted as a request for a low power time interval.

[0234] In many embodiments, the low power time interval request message may be a power feedback message that includes data indicating the power level extracted by the receiver. The power feedback message may typically include data indicating the amount of power extracted by the receiver from the power transmission signal. The power feedback message may specifically be a received power data packet that indicates the power that has been (or will be) extracted from the power transmission signal by the receiver.

[0235] It will be appreciated that a variety of (existing) control messages can be modified to also function as low power time interval request messages that trigger low power time intervals. Examples include: Received Power Data Packet Uses a specific mode or reserved field to act as a low-power time interval request message (also called a trigger) Determine which modes also act as triggers All received power data packets act as triggers, regardless of mode A data packet in the negotiated set acts as a trigger A newly defined data packet acts as a trigger

[0236] This data packet may also include the actual slot start time and / or slot duration.

[0237] As a specific example, the low power time interval request message may be implemented as a Received Power Packet known from the Qi system. Such a data packet has a format as shown in FIG.

[0238] The bit pattern in a field called Mode provides additional information about the Received Power Value. This field can be modified so that certain bit patterns are also interpreted as low power time interval requests. For example, the following bit pattern may be defined: a bit pattern of "101" indicates that the Received Power Packet message is also a low power time interval request message. [Table 1]

[0239] In another example, a bit pattern of "011" may be defined that includes a request for a response from the transmitter. As noted above, the response may be a reliability measure. [Table 2]

[0240] In many embodiments, there may be a direct correspondence between low power time interval request messages and low power time intervals, such that each low power time interval request message may result in the transmitter generating only one low power time interval request message.

[0241] In some embodiments, a low power time interval may only be generated when a low power time interval request message is received from the receiver, so the receiver can rely on a low power time interval not occurring unless specifically requested.

[0242] In some embodiments, multiple low power time intervals may be generated by the transmitter in response to receiving a single low power time interval request message. For example, in some embodiments, receiving a low power time interval request message may cause the transmitter to generate a predetermined number of low power time intervals, e.g., having a predetermined duration and a predetermined interval. Thus, a single low power time interval request message may not result in the generation of a single low power time interval, but rather in the generation of a sequence or burst of potentially short low power time intervals.

[0243] In some embodiments, parameters of the low power time interval and the response to the low power time interval request message may be predetermined. For example, the duration of the low power time interval may be predetermined. However, in other embodiments, one, some, or more may be dynamically determined, for example, in response to data received in the low power time interval request message. The low power time interval request message may indicate, for example, the requested number and duration of low power time intervals.

[0244] In many embodiments, one or more parameters of the low power time interval or request process may be defined or determined during an initialization phase that occurs before the system enters the power transfer phase. For example, many wireless power transfer systems, such as Qi, include a negotiation phase that occurs as part of the initial setup of the power transfer phase. During such a phase, the receiver may request desired operating parameters or aspects, and the transmitter may agree or disagree with these requests. Power transfer may then proceed using the negotiated parameters.

[0245] In the described system, an initialization phase, specifically a negotiation phase, may be used to initialize the parameters of low power time interval operation.

[0246] Such a phase can be used to determine whether the transmitter and receiver can actually support such operation, and if so, how that operation should be implemented: whether low power time intervals are supported at all, whether only predetermined periodic low power time intervals based on predetermined recurring time frames are supported, or whether receiver-controlled low power time interval operation is fully supported.

[0247] In the latter case, negotiation may further be used to determine what message may be used as the low power time interval request message, such as whether a receive power packet or a dedicated message may be used.

[0248] Such an approach may allow for improved flexibility and, in particular, improved backward compatibility in many systems, allowing the described approach to be introduced into existing deployed systems.

[0249] The initialization / configuration / negotiation phase may additionally or alternatively determine parameters of the low power time interval, such as, for example, timing aspects (e.g., delay from low power time interval request message to start of low power time interval), duration, maximum power level, etc. In some embodiments, such negotiated parameters may be default parameters that can later be overwritten, for example, by dedicated data included in the low power time interval request message.

[0250] As a specific example during the negotiation (or configuration / negotiation) phase, the receiver may indicate whether it supports: Slotted operation (foreign object detection and / or communication) Low Power Time Interval Request Message (Slot Trigger) Implicit Slot Trigger Explicit Slot Triggers

[0251] During the power transfer phase, the transmitter can use this information to modify its operation as follows: [Table 3] Configuration Phase The receiver can indicate support for slotted FOD using a reserved bit in the configuration data packet (according to the table above) Negotiation Phase The receiver can indicate support for slotted FOD / communication using information messages in the negotiation phase. Messages can also be used to negotiate slot duration and slot interval.

[0252] It can also show how to generate a trigger using a message (Low Power Time Interval Request Message)

[0253] For clarity, the above description describes embodiments of the invention in terms of different functional circuits, units, and processors. However, it will be understood that functionality may be suitably distributed among different functional circuits, units, or processors without detracting from the invention. For example, functionality described as being performed by multiple separate processors or controllers may be performed by the same processor or controller. Thus, references to specific functional units or circuits should not be considered to indicate a strict logical or physical structure or organization, but rather to suitable means for providing the described functionality.

[0254] The present invention can be implemented in any suitable form including hardware, software, firmware, or any combination of these. The present invention may also be implemented at least in part as computer software running on one or more data processors and / or digital signal processors. The elements and components of embodiments of the present invention may be physically, functionally, and logically implemented in any suitable way. Indeed, functionality may be implemented in a single unit, in multiple units, or as part of other functional units. Thus, the present invention may be implemented as a single unit, or may be physically and functionally distributed among different units, circuits, and processors.

[0255] Although the present invention has been described in connection with several embodiments, the present invention is not limited to the specific forms set forth in the specification. The scope of the present invention is limited only by the appended claims. Furthermore, even if a feature appears to be described in connection with a particular embodiment, those skilled in the art will recognize that various features of the above embodiments may be combined in accordance with the present invention. In the claims, the terms "comprise," "include," and the like do not exclude the presence of other elements or steps.

[0256] It will be understood that reference to a preferred value does not imply any limitation beyond being a value determined in the foreign object detection initialization mode, i.e., preferred as determined in the fitting process. Reference to a preferred value may be replaced with a reference to a first value, for example.

[0257] Furthermore, although individually listed, a plurality of means, elements, circuits, or method steps may be implemented by, for example, a single circuit, unit, or processor. Furthermore, although individual features are included in different claims, they may be combined as desired, and their inclusion in different claims does not imply that a combination of features is infeasible and / or advantageous. Furthermore, the inclusion of a feature in one claim category does not necessarily limit the feature to that category, but the feature may equally apply to other claim categories, as appropriate. Furthermore, the order of features in the claims does not imply a particular order in which the features should be performed, and in particular the order of individual steps in method claims does not imply that the steps must be performed in that order. Steps may be performed in any suitable order. Furthermore, singular terms do not exclude plural terms; thus, the use of terms such as "first," "second," etc. does not exclude plural terms. Reference signs in the claims are merely for the sake of clarity and do not in any way limit the scope of the claims.

Claims

1. 1. A power transmitter for wirelessly supplying power to a power receiver via an inductive power transmission signal, the power transmitter comprising: a transmitting coil for generating a power transfer signal during a power transfer phase; a driver that generates a drive signal for the transmitting coil to generate the power transfer signal during the power transfer phase; a first communication device that receives a message from the power receiver; a controller configured to generate a low power time interval during the power transfer phase, during which a power level of the power transfer signal is reduced, the controller configured to generate the low power time interval upon receiving a low power time interval request message from the power receiver; a foreign object detector for performing foreign object detection; a confidence circuit for determining a confidence measure of said foreign object detection; the foreign object detection performs a foreign object detection test during the low power time interval; The reliability circuitry transmits a request to the power receiver requesting at least one additional low power time interval in response to determining that the reliability measure of the foreign object detection test does not meet a reliability standard.

2. The power transmitter of claim 1 , wherein the reliability circuitry transmits a foreign object detection result to the power receiver in response to determining that the reliability measure of the foreign object detection test meets a reliability standard.

3. The power transmitter of claim 1 , wherein the reliability circuitry is responsive to the foreign object detection test to send a request to the power receiver for at least one additional low power time interval.

4. The power transmitter of claim 1 , wherein the first communicator communicates with the power receiver during the low power time interval.

5. The power transmitter according to claim 4 , wherein the first communication device communicates with the power receiver using a communication carrier wave different from that of the power transmission signal.

6. The power transmitter of claim 1 , wherein the low power time interval request message is a dedicated message for requesting the low power time interval.

7. 6. The power transmitter of claim 1, wherein the low power time interval request message is a message including other data for power transmission, the data including data for power transmission operations to be performed outside the low power time interval.

8. The power transmitter of claim 7 , wherein the low power time interval request message is a power control message that provides feedback to a power control of the power transmission signal.

9. The power transmitter of claim 7 , wherein the low power time interval request message is a power feedback message that includes data indicative of a power level to be drawn by the power receiver.

10. The power transmitter of claim 7 , wherein the low power time interval request message is a reserved field of a received power data packet.

11. The power transmitter of claim 7 , wherein the low power time interval request message includes at least one of a low power time interval start time and a low power time interval duration.

12. 12. The power transmitter of claim 7, wherein the low power time interval request message includes a data field for requesting an operating mode for the power transmission from a set of operating modes, the set of operating modes including a low power time interval operating mode.

13. 13. The power transmitter of claim 1, further comprising an initialization processor that initializes the power transfer phase before the power transfer phase begins, the initialization processor determining characteristics of the low power time interval in response to communication with the power receiver, and the controller generating the low power time interval to have the characteristics.

14. A wireless power transmission system including the power transmitter according to any one of claims 1 to 13 and the power receiver, wherein the power receiver: a coil for extracting power from the power transmission signal; a power circuit configured to supply power extracted from the power transmission signal to a load; a second communicator that transmits the low power time interval request message to the power transmitter.

15. 15. The wireless power transfer system of claim 14, wherein the second communicator transmits the low power time interval request message to the transmitter in response to a change in at least one of power being extracted from the power transfer signal, a current being supplied to the load, and a voltage being supplied to the load.

16. 16. The wireless power transfer system of claim 14 or 15, wherein the second communicator receives a reliability indicator from the transmitter, the reliability indicator indicating reliability of a foreign object detection test performed during a low power time interval, and the second communicator transmits a further low power time interval request message in response to determining that the reliability indicator does not meet a reliability criterion.

17. 17. The wireless power transfer system of claim 14, wherein the power transmitter transmits an indication of a suspected foreign object detection, and the power receiver transmits a request for a low power time interval upon receiving the indication of the suspected foreign object detection from the power transmitter.

18. 1. A method of operating a power transmitter that wirelessly supplies power to a power receiver via an inductive power transmission signal, the method comprising: a transmitting coil generating a power transfer signal during a power transfer phase; generating a drive signal for the transmitting coil to generate the power transfer signal during the power transfer phase; receiving a message from the power receiver during the power transfer phase; generating a low power time interval during the power transfer phase, wherein a power level of the power transfer signal is reduced during the low power time interval, the controller generating the low power time interval upon receiving a low power time interval request message from the power receiver; performing foreign object detection, including performing a foreign object detection test during the low power time interval; determining a confidence measure of said foreign object detection; transmitting a request to the power receiver requesting at least one additional low power time interval in response to determining that the reliability measure of the foreign object detection test does not meet a reliability standard; A method comprising:

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