Wireless power transfer

Abstract

A power transmitter (101) comprises: a transmitter coil (103) for generating a power transfer signal during a power transfer phase; a driver (201) for generating a drive signal for the transmitter coil (103) to generate the power transfer signal during the power transfer phase; a communicator (205) for receiving a message from the power receiver (105); and a controller (203) arranged to generate a reduced power time interval during the power transfer phase, during which the power level of the power transfer signal is reduced, wherein the reduced power time interval is generated in response to the communicator (205) receiving a reduced power time interval request message from the power receiver (105). The power receiver (105) may generate the request message when, for example, an operating mode changes. The power receiver (105) may ensure that the request message is generated only when the power receiver is able to handle a power interruption for the power transfer signal, thereby generating the reduced power time interval.

Description

Technical Field

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

[0002] Most existing electrical products require dedicated electrical contacts in order to obtain power from an external power source. However, this is often impractical and requires the user to physically insert a connector or otherwise establish physical electrical contact. Typically, power requirements also vary significantly, and most current devices have their own dedicated power supply, resulting in a typical user having a large number of different power sources, each of which is dedicated to a specific device. Although using an internal battery can avoid the need for a wired connection to a power source during use, this only provides a partial solution because the battery needs to be charged (or replaced). Using a battery also substantially increases the weight of the device and potentially increases cost and size.

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

[0004] Power transmission via magnetic induction is a well-known concept that primarily applies to transformers with tight coupling between a primary transmitter inductor / coil and a secondary receiver coil. By separating the primary transmitter coil and the secondary receiver coil between the two devices, wireless power transfer between the two devices can be achieved based on the principle of loosely coupled transformers.

[0005] This arrangement allows for wireless power transfer to devices without requiring any wires or physical electrical connections. In practice, it can simply allow a device to be placed adjacent to or on top of the transmitter coil for external charging or powering. For example, the power transmitter device can be placed on a horizontal surface, where the device can simply be placed for power.

[0006] Furthermore, such wireless power transmission devices can be advantageously designed to enable the power transmitter device to be used with a range of power receiver devices. In particular, a wireless power transmission method known as the Qi specification has been defined and is currently under further development. This method allows a power transmitter device that complies with the Qi specification to be used with a power receiver device that also complies with the Qi specification, without requiring the power transmitter device and the power receiver device to be from the same manufacturer or to be specific to each other. The Qi standard also includes certain features that allow operation to be adjusted for a specific power receiver device (e.g., depending on the specific power consumption).

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

[0008] In power transmission systems such as Qi, the electromagnetic fields generated to transmit the required power levels to the power receiver are often very large. In many cases, the presence of such strong fields can have an impact on the surrounding environment.

[0009] For example, a potential problem with wireless power transmission is that power may be unintentionally transferred to, for example, a metal object that is located near the power transmitter. For example, if a foreign object (e.g., a coin, key, ring, etc.) is placed on a power transmitter platform that is arranged to receive a power receiver, the magnetic flux generated by the transmitter coil will induce eddy currents in the metal object, which will cause the object to heat up. The heat increase can be very significant and can be highly undesirable.

[0010] To mitigate the risk of such scenarios, foreign object detection has been proposed, whereby a power transmitter can detect the presence of a foreign object and, upon detection, reduce transmit power and / or generate a user alert. For example, the Qi system includes functionality for detecting foreign objects and for reducing power when a foreign object is detected. Specifically, Section 11 of the Qi specification, Version 1.2.1, describes various methods for detecting foreign objects.

[0011] WO 2012127335 discloses a method for detecting such foreign objects, which involves determining an unknown power loss. In this method, both a power receiver and a power transmitter measure their power, and the receiver transmits its measured received power to the power transmitter. If the power transmitter detects a significant difference between the power transmitted by the transmitter and the power received by the receiver, an unwanted foreign object may be present, and power transmission may be reduced or terminated for safety reasons. This power loss method requires synchronized and accurate power measurements performed by the power transmitter and the power receiver.

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

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

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

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

[0016] Another example of foreign object detection is provided in EP 3528364 A1, wherein foreign object detection is performed during a reduced power time interval of a repeating time frame. US 2016 / 301261 ​​A1 discloses a system for wireless transmission, wherein the transmitted power is compared with the received power, wherein if the power loss exceeds a maximum value, no power phase occurs.

[0017] In practice, achieving sufficient detection accuracy using the methods described in the Qi specification is often difficult, a difficulty exacerbated by numerous uncertainties regarding the specific operating conditions at hand.

[0018] For example, a particular issue is the possible presence of friendly metals (i.e., metal parts of a device embodying a power receiver or power transmitter), as the magnetic and electrical properties of these metal parts may be unknown (and vary between different devices) and therefore may be difficult to compensate for.

[0019] Additionally, even relatively small amounts of power dissipated in metallic foreign objects can cause undesirable heating. Consequently, it is necessary to detect even small power differences between transmitted and received power, and this can be particularly difficult as the power level of the power transfer increases.

[0020] In many scenarios, the quality factor degradation method can have better sensitivity to detect the presence of metal objects. However, it may still not provide sufficient accuracy and may also be affected by friendly metals, for example.

[0021] The performance of foreign object detection is affected by the specific operating conditions present when the test is actually performed. For example, as described in the Qi specification, if the foreign object detection measurement is performed during the select phase of the power transfer initialization process, the signal provided by the power transmitter for this measurement must be small enough to prevent it from waking up the power receiver. However, for such a small signal, the signal-to-noise ratio is typically poor, resulting in reduced measurement accuracy.

[0022] The requirement for a small measurement signal can lead to other adverse effects. A power receiver exposed to a small measurement signal may exhibit leakage current, depending on the measurement signal level, the coupling between the primary and secondary coils, and the charge state of the capacitor at the rectifier's output. Consequently, this leakage current can vary depending on the actual situation. Because leakage current affects the reflected impedance at the power transmitter coil, the quality factor measurement will also depend on the specific current conditions.

[0023] Another problem is that foreign object detection is typically a very sensitive test, where it is desired to detect relatively small changes due to the presence of a foreign object in an environment where there may be wide variations in the operating conditions and scenarios under which the test is being performed.

[0024] As a result, current algorithms are often suboptimal and may provide worse than optimal performance in some scenarios. In particular, they may result in undetected foreign objects or falsely detect foreign objects when none are present.

[0025] The difficulty in accurately detecting foreign objects is particularly pronounced in scenarios where the power level of the power transfer signal is high and / or when the power level of the power transfer signal varies. Consequently, foreign object detection is particularly difficult during the power transfer phase, and this is especially true for power receivers that present large and varying loads.

[0026] Furthermore, other operations of the power transfer system may also be sensitive to such effects. For example, in many cases, communication between a power transmitter and a power receiver may be negatively affected by large loads, and especially by large load variations.

[0027] In many systems, communication from a power receiver to a power transmitter can use load modulation, where the load of the power transfer signal varies depending on the data being transmitted. However, this load modulation can be difficult to detect if the power transfer load of the power transfer signal also varies. Similarly, communication from a power transmitter to a power receiver can be achieved by modulating the power transfer signal (e.g., amplitude or frequency modulation), but changes in the parameters of the power transfer signal caused by the varying load can interfere with this modulation.

[0028] In fact, even if a completely independent carrier wave is used for communication (e.g., an NFC communication link), the very large and varying electromagnetic fields caused by the power transfer signal, albeit in a very different frequency band, may cause considerable interference.

[0029] Therefore, the presence of the power transfer signal and its load condition may adversely affect other operations (eg, foreign object detection and communication operations).

[0030] To improve foreign object detection, WO 18219793 A1 discloses applying a repetitive time frame to the power transmission signal. The repetitive time frame is divided into a power transmission interval and a foreign object detection interval. In this method, power transmission is turned off during the foreign object detection interval, and foreign object detection is performed using a dedicated foreign object detection signal.

[0031] However, while this can provide improved performance in many situations, it does not provide optimal performance in all situations or for all operations. For example, it can result in reduced power transfer levels and / or efficiency in many methods. Interrupted power transfer can also impose significant constraints on the design of power receivers, as it requires operating under interrupted power supply while often requiring continuous power to the load.

[0032] Therefore, improving the operation of power transfer systems would be advantageous, and in particular methods allowing for increased flexibility, reduced cost, reduced complexity, improved operation of power transfer system operation, improved foreign object detection, improved communications, increased adaptability, backward compatibility and / or increased performance would be advantageous. Summary of the Invention

[0033] Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0034] According to one aspect of the present invention, there is provided a power transmitter for wirelessly providing power to a power receiver via an inductive power transfer signal; the power transmitter comprising: a transmitter coil for generating the power transfer signal during a power transfer phase; a driver for generating a drive signal for the transmitter coil to generate the power transfer signal during the power transfer phase; a first communicator for receiving a message from the power receiver; and a controller arranged to generate a reduced power time interval during the power transfer phase, during which the power level of the power transfer signal is reduced, the controller being arranged to generate the reduced power time interval in response to receiving a reduced power time interval request message from the power receiver; a foreign object detector arranged to perform foreign object detection, the foreign object detection being arranged to perform a foreign object detection test during the reduced power time interval; and a reliability circuit arranged to determine a reliability metric for the foreign object detection; wherein the reliability circuit is arranged to send a request for at least one or more reduced power time intervals to the power receiver in response to determining that the reliability metric for the foreign object detection test does not meet a reliability criterion.

[0035] The present invention can provide improved performance in many embodiments and can provide overall improved power transfer operation in many systems and embodiments. For example, in many embodiments, improved foreign object detection and / or communication can be achieved by performing such operations during time intervals that create particularly favorable conditions for such operations.

[0036] This method can provide a highly flexible approach in which the power receiver controls the generation of reduced power time intervals. This can, for example, allow for improved reliability of transmission and can allow the power receiver to ensure that it can provide power to the load during the reduced power time intervals, or, for example, can tolerate providing reduced power to the load. This method can ensure that reduced power time intervals are only used when this does not prevent the power receiver from being able to acceptably support the load.

[0037] During the reduced power time interval, the power level of the power transfer signal is reduced correspondingly to the degree of reduction in the power level transmitted from the power transmitter to the power receiver. During the reduced power time interval, the power level transmitted from the power transmitter to the power receiver is reduced relative to the power level transmitted from the power transmitter to the power receiver during the power transfer time interval adjacent to the reduced power time interval. Power levels, and references to power and power levels, can be specifically considered to be related to actual power (I·U·cosφ). In many embodiments, the power transmitter can be arranged to not provide a drive signal to the transmitter coil during the reduced power time interval.

[0038] The power transmitter further comprises a foreign object detector for performing foreign object detection, the foreign object detector being arranged to perform a foreign object detection test during the reduced power time interval.

[0039] The method may provide improved foreign object detection and may allow it to be tailored to specific power receiver preferences or requirements, for example to perform timely and accurate foreign object detection when the impact on power transfer can be reduced or minimized.

[0040] The power transmitter further comprises a reliability circuit arranged to determine a reliability metric for the foreign object detection.

[0041] This may provide improved operation in many embodiments.

[0042] The reliability metric may indicate the reliability of the foreign object detection test, and may particularly indicate the reliability / certainty / confidence of the foreign object detection test results.

[0043] According to an optional feature of the invention, the reliability circuit is arranged to send a foreign object detection result to the power receiver in response to determining that the reliability metric for the foreign object detection test satisfies a reliability criterion.

[0044] The foreign object detection result may be an indication of whether a foreign object is detected. The reliability criterion may be a criterion indicating that the reliability / confidence of the foreign object detection result is higher than if the criterion is not met.

[0045] The reliability circuit is arranged to send a request for one or more reduced power time intervals to the power receiver in response to determining that the reliability metric for the foreign object detection test does not satisfy a reliability criterion.

[0046] This may provide improved performance and may, for example, allow the system to continue to perform more reliable foreign object detection by using multiple reduced power time intervals.The method also allows the power receiver to retain control of operation and control of when such foreign object detection testing may be performed.

[0047] According to an optional feature of the invention, the reliability circuit is arranged to send a request to the power receiver for at least one or more reduced power time intervals in response to the foreign object detection test.

[0048] In some embodiments, the power transmitter further comprises a calibrator for performing calibration of the foreign object detection, the calibration being dependent on the foreign object detection test.

[0049] This may provide improved performance in many embodiments and may allow for improved foreign object detection adaptation / calibration, as this can be performed with a high degree of confidence that no foreign objects are present.

[0050] In some embodiments, the power transmitter may include a calibrator for performing calibration of the foreign object detection, the calibration being dependent on whether the foreign object detection test detects a foreign object.

[0051] In some embodiments, the power transmitter may include a calibrator for performing calibration of the foreign object detection, the calibration being performed only when the foreign object detection test indicates that no foreign object is present.

[0052] In some embodiments, the calibrator is arranged to perform the calibration in response to the reliability measure.

[0053] This can provide improved performance and more reliable foreign object detection adaptation and calibration. For example, the degree of adaptation performed by the calibration can depend on the reliability metric. For an increased reliability metric, a higher degree of adaptation can be performed by the calibration. In some embodiments, foreign object detection calibration can be performed only when the reliability metric meets the reliability criterion (and typically if the result is that no foreign object is present). The reliability criterion can be a criterion that indicates that the reliability / confidence of the foreign object detection result is higher than if the criterion is not met.

[0054] In some embodiments, the foreign object detection is arranged to perform foreign object detection using a first foreign object detection algorithm during a reduced power time interval and to perform foreign object detection using a different second foreign object detection algorithm during a power transmission time interval that does not intersect the reduced power time interval, and wherein the calibrator is arranged to calibrate the second foreign object detection algorithm.

[0055] This may provide for efficient, accurate and reliable adaptation / calibration of foreign object detection performed during power transfer.

[0056] The first foreign object detection algorithm may be more accurate than the second foreign object detection algorithm. The first foreign object detection algorithm may depend on the absence of a power transmission signal at a power level or a power transmission signal having a power level below a given threshold, while the second foreign object detection algorithm may not be based on such an assumption.

[0057] In some embodiments, the foreign object detection test includes determining whether a foreign object is present responsive to a decay time property of a signal level for at least one of a current and a voltage of a resonant circuit including the transmitter coil.

[0058] Such an approach may provide particularly advantageous operation and may be particularly well suited for very short reduced power time intervals (wherein the power transfer signal may be completely switched off).

[0059] According to an optional feature of the invention, the first communicator is arranged to communicate with the power receiver during the reduced power time interval.

[0060] According to an optional feature of the invention, the first communicator is arranged to communicate with the power receiver using a different communication carrier than the power transfer signal.

[0061] The communication carrier may be used for a separate independent communication system, for example, an NFC communication system.

[0062] According to an optional feature of the invention, the reduced power time interval request message is a dedicated message for the purpose of requesting the reduced power time interval.

[0063] According to an optional feature of the invention, the reduced power time interval request message is a message comprising further data for power transfer, the data comprising data for power transfer operations performed outside the reduced power time interval.

[0064] The reduced power time interval request message may specifically be a power control message which is also used to provide feedback to a power control loop of the power transmission.

[0065] In some embodiments, the reduced power time interval request message is a power control message including control data for a power control loop for the power transfer signal.

[0066] According to an optional feature of the invention, the reduced power time interval request message is a power feedback message comprising data indicative of a power level drawn by the power receiver.

[0067] The power feedback message may specifically be a received power data packet.

[0068] According to an optional feature of the invention, the reduced power time interval request message is a reserved field of the received power data packet.

[0069] According to an optional feature of the invention, the received power data packet further comprises at least one of a reduced power time interval start time and a reduced power time interval duration.

[0070] According to an optional feature of the invention, the reduced power time interval request message comprises a data field for requesting an operating mode for the power transfer from a set of operating modes, the set of operating modes including the reduced power time interval operating mode.

[0071] In some embodiments, the power transmitter is arranged to generate only one reduced power time interval per reduced power time interval request message.

[0072] In some embodiments, the power transmitter is arranged to generate a plurality of reduced power time intervals in response to receiving a reduced power time interval request message.

[0073] In some embodiments, the reduced power time interval request message comprises a timing indication for the reduced power time interval, and the controller is arranged to adjust the timing of the reduced power time interval in response to the timing indication.

[0074] In some embodiments, the reduced power interval request message comprises an indication of a number of reduced power intervals, and the controller is arranged to select the number of reduced power intervals to be generated in response to receiving the reduced power interval request message based on the number indication.

[0075] In some embodiments, the first communicator is arranged to receive the second reduced power time interval request message in response to sending a response message to the power receiver indicating that the reliability metric does not meet the reliability criterion.

[0076] In some embodiments, the power transmitter is arranged to decouple the power receiver from the load during the reduced power time interval.

[0077] According to an optional feature of the invention, the reduced power time interval has a duration of no more than 500 microseconds.

[0078] According to an optional feature of the invention, the power transmitter further comprises an initialisation processor arranged to initialise the power transfer phase before the power transfer phase begins, the initialisation processor being arranged to determine properties of the reduced power time interval in response to communication with the power receiver, and the controller being arranged to generate the reduced power time interval to have the properties.

[0079] According to one aspect of the present invention, a wireless power transmission system is provided, comprising a power transmitter according to the above description and a power receiver, wherein the power receiver comprises: a coil for extracting power from the power transmission signal; a power circuit for providing the power extracted from the power transmission signal to a load; and a second communicator arranged to send the reduced power time interval request message to the power transmitter.

[0080] According to an optional feature of the invention, the second communicator is arranged to send the reduced power time interval request message to the power transmitter in response to a change in at least one of: power being extracted from the power transfer signal, current being provided to the load, and voltage being provided to the load.

[0081] According to an optional feature of the invention, the second communicator is arranged to receive a reliability indication from the power transmitter, the reliability indication indicating the reliability of a foreign object detection test performed during the reduced power time interval, and wherein the second communicator is arranged to send a further reduced power time interval request message in response to determining that the reliability indication does not meet a reliability criterion.

[0082] The reliability criterion may be a criterion indicating that the reliability / confidence of the foreign matter detection result is higher than a case where the criterion is not satisfied.

[0083] According to an optional feature of the invention, the second communicator is arranged to receive a reliability indication from the power transmitter, the reliability indication indicating the reliability of a foreign object detection test performed during the reduced power time interval, and wherein the power receiver is arranged to perform calibration of the received power level measurements in response to determining that the reliability indication satisfies a reliability criterion.

[0084] In some embodiments, the power transmitter may transmit an indication of the transmit power estimate to the power receiver, and the power receiver may be arranged to perform calibration of the received power level measurements in response to the indication of the transmit power estimate.

[0085] The reliability criterion may be a criterion indicating that the reliability / confidence of the foreign matter detection result is higher than a case where the criterion is not satisfied.

[0086] In some embodiments, the second communicator is arranged to send the second reduced power time interval request message in response to receiving a response message from the power transmitter that the reliability metric does not satisfy the reliability criterion.

[0087] In some embodiments, the power receiver is arranged to decouple the load from the receiver coil during the reduced power time interval.

[0088] According to an optional feature of the invention, the power transmitter is arranged to send an indication of suspected detection of a foreign object, and the power receiver may be arranged to send the request for a reduced power time interval in response to receiving the indication of the suspected detection of a foreign object from the power transmitter.

[0089] In some embodiments, the second communicator is arranged to communicate with the power transmitter during the reduced power time interval.

[0090] In some embodiments, the second communicator is arranged to communicate with the power transmitter using a different communication carrier than the power transfer signal.

[0091] According to one aspect of the present invention, there is provided a method for operating a power transmitter to wirelessly provide power to a power receiver via an inductive power transfer signal; the method comprising: a transmitter coil generating the power transfer signal during a power transfer phase; generating a drive signal for the transmitter coil to generate the power transfer signal during the power transfer phase; receiving a message from the power receiver during the power transfer phase; and generating a reduced power time interval during the power transfer phase, during which the power level of the power transfer signal is reduced, the controller being arranged to generate the reduced power time interval in response to receiving a reduced power time interval request message from the power receiver; performing foreign object detection, including performing a foreign object detection test during the reduced power time interval; determining a reliability metric for the foreign object detection; and sending a request for at least one or more reduced power time intervals to the power receiver in response to determining that the reliability metric for the foreign object detection test does not meet a reliability criterion.

[0092] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0094] Figure 1 illustrates examples of elements of a power delivery system according to some embodiments of the present invention;

[0095] Figure 2 illustrates an example of elements of a power transmitter according to some embodiments of the present invention;

[0096] Figure 3 illustrates examples of elements of a power receiver according to some embodiments of the present invention;

[0097] Figure 4 illustrates an example of elements of a power transmitter according to some embodiments of the present invention;

[0098] Figure 5 illustrates examples of elements of a power receiver according to some embodiments of the present invention;

[0099] Figure 6 illustrates an example of a signal after a power transmission signal is turned off in a wireless power transmission system according to some embodiments of the present invention;

[0100] Figure 7 illustrates an example of a signal after a power transmission signal is turned off in a wireless power transmission system according to some embodiments of the present invention; and

[0101] Figure 8 Illustrated are examples of message formats for messages used in a wireless power transfer system according to some embodiments of the present invention. DETAILED DESCRIPTION

[0102] The following description focuses on embodiments of the invention applicable to wireless power transfer systems utilizing power transfer methods known, for example, from the Qi specification. However, it will be appreciated that the invention is not limited to this application but may be applied to many other wireless power transfer systems.

[0103] Figure 1 An example of a power transmission system according to some embodiments of the present invention is shown. The power transmission system includes a power transmitter 101, which includes (or is coupled to) a transmitter coil / inductor 103. The system also includes a power receiver 105, which includes (or is coupled to) a receiver coil / inductor 107.

[0104] The system provides an electromagnetic power transfer signal that can be inductively transferred 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 transmitter coil or inductor 103. The power transfer signal can correspond to an electromagnetic power transfer 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 the receiving coil 107 is unloaded, the power receiver will not extract power from the generated electromagnetic field (other than losses). In such a scenario, the driving action of the transmitter coil 103 can generate an electromagnetic field with a potentially high field strength, but the power level of the power transfer signal will be zero (other than losses). In some situations where a foreign object is present, the power transfer signal can be considered to include a power component corresponding to the power transferred to the foreign object, and thus the power transfer signal can be considered to correspond to power extracted from the electromagnetic field generated by the power transmitter.

[0105] The power transfer signal may typically have a frequency between about 20 kHz and about 500 kHz, and for Qi-compatible systems, the frequency range of the power transfer signal is typically 95 kHz to 205 kHz (or, for example, for high-power kitchen applications, the frequency range of the power transfer signal is typically between 20 kHz and 80 kHz). The transmitter coil 103 and the power receiving coil 107 are loosely coupled, so that the power receiving coil 107 picks up (at least part of) the power transfer signal from the power transmitter 101. Thus, power is transferred from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the power receiving coil 107. The term power transfer signal is primarily used to refer to the induced signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the power receiving coil 107, but it will be appreciated that the term power transfer signal can also be equivalently considered and used as a reference to the electrical signal provided to the transmitter coil 103 or picked up by the power receiving coil 107.

[0106] In this example, the power receiver 105 is specifically a power receiver that receives power via the receiver coil 107. However, in other embodiments, the power receiver 105 may include a metal element, for example, a metal heating element, in which case the power transmission signal directly induces eddy currents, thereby causing direct heating of the element.

[0107] The system is arranged to transmit high power levels, and in particular, in many embodiments, the power transmitter can support power levels exceeding 500 mW, 1 W, 5 W, 50 W, 100 W, or 500 W. For example, for Qi-compliant applications, power transmission can 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, in the range of up to 100 W for higher power applications (e.g., power tools, laptops, drones, robots, etc.), and up to over 1000 W for ultra-high power applications (e.g., kitchen appliances).

[0108] Hereinafter, the operation of the power transmitter 101 and the power receiver 105 will be described with specific reference to embodiments generally in accordance with the Qi specification (except as modified and enhanced herein (or thereafter)) or adapted for use with the higher power kitchen specification developed by the Wireless Power Alliance. In particular, the power transmitter 101 and the power receiver 105 may conform to or be substantially compatible with elements of Qi specification versions 1.0, 1.1, or 1.2 (except as modified and enhanced herein (or thereafter)).

[0109] In the following, we will focus on foreign body detection to describe Figure 1 operation of the system.

[0110] In a wireless power transfer system, the presence of an object (typically a conductive element that extracts power from the power transfer signal but is not part of the power transmitter 101 or the power receiver 105, i.e., a conductive element that is unintended, undesirable, and / or interferes with the power transfer) during power transfer can be highly disadvantageous. Such undesirable objects are referred to in the art as foreign matter.

[0111] Foreign matter not only reduces efficiency by adding power losses to the operation, but can also degrade the power transfer operation itself (e.g., by interfering with power transfer efficiency or extracting power that is not directly controlled by the power transfer loop). Additionally, inducing currents in foreign matter (particularly eddy currents in metallic parts of the foreign matter) can lead to heating of the foreign matter, which is often highly undesirable.

[0112] To address this issue, wireless power transmission systems such as Qi include functionality for foreign object detection. Specifically, the power transmitter includes functionality that seeks to detect the presence of a foreign object. If so, the power transmitter can, for example, terminate the power transfer or reduce the maximum amount of power that can be transmitted.

[0113] Current methods proposed by the Qi specification are primarily based on detecting power loss (by comparing the transmitted power to the reported received power) or detecting degradation of the output resonant circuit's quality, Q. However, in current use, these methods have been found to provide suboptimal performance in many scenarios, and they can specifically lead to inaccurate detection, resulting in missed detections and / or false positives (where a foreign object is detected despite the absence of such an object).

[0114] Foreign object detection can be performed before the power receiver enters the power transfer phase (e.g., during initialization of the power transfer) or during the power transfer phase. Detection during the power transfer phase is typically based on a comparison of the measured transmit power with the received power, while detection occurring before the power transfer phase is typically based on a measurement of the reflected impedance (e.g., by measuring the quality factor of the transmitter coil using a small measurement signal).

[0115] Figure 2 An example of a power transmitter according to some embodiments of the present invention is illustrated.

[0116] The power transmitter 101 includes a driver 201 capable of generating a drive signal that is fed to the transmitter coil 103, which in turn generates an electromagnetic power transfer signal that is capable of providing power transfer to the power receiver 105. The power transfer signal is provided during a power transfer time interval of a power transfer phase.

[0117] The driver 201 may generally include an output circuit in the form of an inverter, which is typically formed by driving a full bridge or a half bridge, as is well known to those skilled in the art.

[0118] The power transmitter 101 further comprises a power transmitter controller 203 arranged to control the operation of the power transmitter 101 according to a desired operating principle. In particular, the power transmitter 101 may comprise many of the functions required to perform power control according to the Qi specification.

[0119] The power transmitter controller 203 is specifically arranged to control the generation of the drive signal generated by the driver 201 and is capable of controlling in particular the power level of the drive signal and, accordingly, the level of the generated power transfer signal. The power transmitter controller 203 comprises a power loop controller that controls the power level of the power transfer signal in response to power control messages received from the power receiver 105 during the power control phase.

[0120] In order to receive data and messages from the power receiver 105, the power transmitter 101 includes a first communicator 205, which is arranged to receive data and messages from the power receiver 105 (as will be appreciated by those skilled in the art, the data message may provide one or more bits of information). In this example, the power receiver 105 is arranged to load modulate the power transfer signal generated by the transmitter coil 103, and the first communicator 205 is arranged to sense changes in the voltage and / or current of the transmitter coil 103 and demodulate these load modulations based on these changes. The skilled person will be aware of the principles of load modulation (e.g., as used in Qi wireless power transfer systems), and therefore these principles will not be described in further detail.

[0121] In many embodiments, the first communicator 205 may also be arranged to send data to the power receiver 105 (eg by modulating the power transfer signal), as is known to those skilled in the art.

[0122] In some embodiments, communication may be performed using a separate communication channel, which may be achieved by using a separate communication coil or indeed using the transmitter coil 103. For example, in some embodiments, near field communication (NFC) may be implemented, or a high frequency carrier (e.g., having a carrier frequency of 13.56 MHz) may be superimposed on the power transfer signal.

[0123] Figure 3 Some exemplary elements of the power receiver 105 are illustrated.

[0124] The receiver coil 107 is coupled to a power receiver controller 301, which couples the receiver coil 107 to a load 303 via a switch 305 (i.e., it is a switchable load 305). The power receiver controller 301 includes a power control path that converts the power extracted by the receiver coil 107 into a suitable power supply for the load. In addition, the power receiver controller 301 may include various power receiver controller functions required to perform power transfer, particularly the functions required to perform power transfer in accordance with the Qi specification.

[0125] To support communication from the power receiver 105 to the power transmitter 101, the power receiver 105 includes a second communicator 307. The second communicator 307 may specifically be a load modulator that is arranged to change the load condition of the receiver coil 107 in response to data to be sent to the power transmitter 101. The power transmitter 101 then detects and demodulates the load change, as will be known to those skilled in the art.

[0126] In many embodiments, the second communicator 307 may also be arranged to receive data from the power transmitter 101 (eg by demodulating the modulation of the power transfer signal), as will be known to those skilled in the art.

[0127] In many embodiments, the second communicator 307 is arranged to communicate without using a power transmission signal, and in particular, the second communicator 307 may be used for a separate communication system, for example, the second communicator 307 may be an NFC communication unit.

[0128] According to many embodiments, the power transmitter 101 further comprises a foreign object detector 207 arranged to perform a foreign object detection test, ie specifically to detect whether any unwanted conductive elements may be present in the generated electromagnetic field.

[0129] In this system, some (or possibly all) foreign object detection tests are based on measurements performed during reduced power time intervals, which, when used for the purpose of foreign object detection, may also be referred to as foreign object detection time intervals. During these foreign object detection time intervals, the transmitter controller 203 is arranged to reduce the power level of the power transfer signal. In fact, in some embodiments, the power transmitter 101 may use different coils to generate the power transfer signal and to generate the electromagnetic test signal for foreign object detection during the foreign object detection time interval. In many embodiments, the power transmitter may completely shut down the power transfer signal during the foreign object detection time interval.

[0130] During intervals when foreign object detection is being performed (ie, during a foreign object detection time interval), the foreign object detector 207 may evaluate conditions to determine whether a foreign object is believed to be present.

[0131] For example, during the foreign object detection time interval, the power 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 evaluating characteristics and properties of the signal.

[0132] For example, the power level of the generated test signal (the power extracted from the generated test signal) can be used as an indication of the power being extracted by a potential foreign object. This can typically be done by comparing the power actually extracted by the power receiver 105 with the power that the power receiver 105 is expected to extract from the test signal. The power expected to be extracted from the power receiver 105 can, for example, be the extracted power level reported by the power receiver.

[0133] In some embodiments, the power receiver 105 may be arranged to turn off any external loads, and the power that the power receiver is expected to draw may simply be the expected parasitic losses in the power receiver. In some cases, these expected parasitic losses may be estimated to be substantially zero or even assumed to be substantially zero. In other embodiments, these expected parasitic losses may be estimated, for example, during normal operation in a power transfer phase (e.g., as the difference between the transmitted power and the reported received power, compensated for the relative field strength levels).

[0134] An advantage of implementing foreign object detection during a reduced power time interval is that the reduced power level (particularly turning off the power transfer signal) can allow for a more accurate and reliable foreign object detection test to be performed. The foreign object detection test can be based on the assumption that a strong electromagnetic power transfer signal is not present, or can be based on properties or conditions resulting from turning off the power transfer signal.

[0135] 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 a frequency different from the resonant frequency of the power transfer circuitry including transmitter coil 103 and receiver coil 107 to minimize the effects of these factors. This approach can be used without the power transfer signal interfering with typically sensitive measurements.

[0136] As a specific example, a foreign object detection test includes determining the presence of a foreign object in response to a decay time property of a signal level of at least one of a current and a voltage of a resonant circuit comprising a transmitter coil. The foreign object detection can be specifically arranged to shut off the drive signal to the resonant circuit, thereby allowing the resonant circuit to resonate (freewheel). Due to losses, this will cause the current and voltage levels in the resonant circuit to decay / decrease, wherein the decay increases with increasing losses. The decay behavior and decay rate therefore depend on the power extracted from the generated electromagnetic signal, wherein the decay rate increases with increasing power extracted. In some embodiments, the timing of the decay (e.g., the time it takes for the voltage / current signal to decrease by a given amount) can therefore be determined by the foreign object detection and used to determine whether to estimate the presence of a foreign object. For example, if the decay time or decay rate for a given decrease is less than a given threshold, the foreign object detection can determine the presence of a foreign object.

[0137] Thus, in some embodiments, the presence of a foreign object can be detected by measuring the signal attenuation in an undriven resonant tank.US 7554316 B2 discloses attenuation measurements being performed and used to control power transfer operations.

[0138] Figure 4 The figure shows an example of an output bridge of a driver that drives an output resonant circuit (referred to as LTx) including a transmitter coil 103. The power transmitter 101 includes a capacitor (CTx) in series with LTx to form a resonant circuit. The resonant circuit is driven by a full-bridge inverter powered by a DC voltage.

[0139] Figure 5 A simplified schematic diagram of the core elements of the power transfer path for the power receiver 105 is shown. The power receiver also includes a capacitor CRx to form a resonant circuit (referred to as LRx) with the receiver coil 107. The induced AC voltage on this circuit is rectified by a full-bridge rectifier and smoothed by capacitor C. The load 303 (referred to as Rload) is shown (simplified) as being coupled across capacitor C. The value of capacitor C and the resistance of load Rload determine the output voltage (U out ) on the ripple.

[0140] The power transmitter and the power receiver are inductively coupled via a transmitter coil LTx and a receiver coil LRx.

[0141] Figure 6 The diagram illustrates the effects that may occur when the inverter interrupts the drive to the resonant circuit of the power transmitter and shorts it out.

[0142] As shown in the figure, the voltage U across the resonant circuit / tank tank Decay over time.

[0143] Initially, the induced voltage at the receiver resonant tank is still high enough to turn on the rectifier and the residual current I LRx Flows through the rectifier to the capacitor. However, after energy is extracted from the resonant circuit by the load of the power receiver extracting power, the induced voltage drops below the voltage of the capacitor C), effectively disconnecting the load. Therefore, in this case, the load Rload is fed by the energy stored in the capacitor rather than the energy stored in the resonant circuit.

[0144] This isolates the resonant circuit from the load, so the attenuation behavior does not depend on the value of the load Rload. Because of this, the relative dependence on other properties (especially the presence of foreign objects) is higher.

[0145] To eliminate the influence of the load, the decay rate measurement may be delayed so that the rectifier is not conducting. Therefore, the decay measurement is often started after the first cycle has been skipped. Therefore, during the decay measurement, the load depends only on the energy stored in C. The output voltage U across the load out The drop depends on the value of C and R load In order to keep the required C value relatively low and still prevent U out Keep it high enough and the decay measurement time is preferably short.

[0146] Figure 7 The diagram shows U tank The decay behavior in two situations, one in which there is no foreign object and the other in which there is a foreign object. The decay in the presence of a foreign object is sharper / larger / faster than in the absence of a foreign object, i.e. the decay rate is greater. The voltage U can be described by the following formula tank Amplitude:

[0147]

[0148] in,

[0149] U(0) = U at the start of attenuation measurement tank Amplitude

[0150] U(t) = U at the end of attenuation measurement tank Amplitude

[0151] Q = quality of the resonant circuit

[0152] ω = angular frequency

[0153] Instead of measuring over a fixed time t, it is also possible to measure over a fixed number of resonance cycles (n), for example. U can be described by the following formula tank Amplitude:

[0154]

[0155] Where T is the number of resonance cycles.

[0156] The use of a reduced power time interval during which the power transmission signal can be turned off allows or facilitates the use of attenuation-based foreign object detection. This is an important advantage in many systems and scenarios, as attenuation measurements have been found to provide very accurate and reliable detection in many embodiments.

[0157] Advantages of the attenuation method include the fact that the power transmitter does not need to drive the signal to a predefined value. For example, for the quality factor foreign object detection method, no resonant frequency needs to be applied. The power transmitter can simply switch from a driven resonant tank to an undriven resonant tank without controlling operating parameters to predetermined settings. For example, there is no need to adjust the operating frequency. This allows for brief interruptions in the power signal, which has the advantage of reducing interference with the power receiver's operation. A particular advantage of this method is its suitability for very short foreign object detection intervals.

[0158] Therefore, in many situations and indeed for different operations, using reduced power time intervals can provide improved performance. However, using reduced power time intervals also presents a number of disadvantages, as it requires the power receiver to be able to handle interrupted power transmission. This can typically be handled by imposing a repeating time frame with one or more reduced power time intervals, such that reduced power time intervals of predetermined duration occur at periodic intervals. This allows the power receiver to be designed to cope with interrupted power transmission, for example by specifically designing the dimensions of the accumulator / capacitor to sustain the load during the interruption.

[0159] However, in the described system, the power receiver 105 is arranged to control the generation of the reduced power time intervals, and in particular to control whether the reduced power time intervals are generated. Thus, rather than predetermined generation of reduced power time intervals or generation of reduced power time intervals controlled by the power transmitter, the power transmitter of the described system can (possibly only) generate reduced power time intervals under the control of the power receiver, whereby the power receiver controls when the reduced power time intervals are generated, thereby allowing the reduced power time intervals to be generated only when the power receiver can handle an interruption or when the advantages that can be provided by the reduced power time intervals are particularly needed.

[0160] In particular, the power receiver 105 is arranged to send a request for a reduced power time interval during the power transfer phase, and the power transmitter is arranged to generate a reduced power time interval during the power transfer phase in response to receiving the request. Thus, during the power transfer phase, the power receiver can determine when a reduced power time interval is desired or permitted, and can send a reduced power time interval request message to the power transmitter, which will cause the message to be generated. In many embodiments, a reduced power time interval can be generated during the power transfer phase only in response to receiving a reduced power time interval request message from the power receiver.

[0161] Thus, the power transmitter may generate a reduced power time interval in response to receiving a reduced power time interval request message from the power receiver, wherein if the reduced power time interval request message has not been received, the reduced power time interval is not generated. The power receiver may generate a reduced power time interval in response to receiving a reduced power time interval request message from the power receiver, wherein if the reduced power time interval request message has not been received from the power receiver, the reduced power time interval is not generated. Thus, the reduced power time interval only exists due to the power receiver sending the reduced power time interval request message. In some embodiments, the generation of the reduced power time interval is conditional on the receipt of the reduced power time interval request message from the power receiver.

[0162] This method can allow asynchronous, self-organized, power receiver-controlled generation of reduced power intervals during the power transfer phase. This can provide improved performance in many embodiments and, for example, prevent reduced power intervals from occurring at inappropriate times. For example, it can allow the power receiver to ensure that reduced power intervals do not occur when the power load is above nominal, which could potentially result in the accumulator being insufficient to maintain the voltage for the load. This method can allow greater flexibility in the design of the power receiver, for example, allowing capacitors to be designed for nominal conditions rather than extreme worst-case scenarios.

[0163] This approach can avoid many of the drawbacks and risks associated with a power transmitter controlling when reduced power intervals are generated. For example, it can improve communication from the power receiver to the power transmitter, as the power receiver can control when there are no communication interferences. This can prevent, for example, power control performance degradation caused by improperly received control error messages. Similarly, received power messages may not arrive or may not be decoded. It can also avoid errors in received power measurements caused by sudden power reductions in a time slot. It can also prevent, for example, control logic at the receiver from malfunctioning due to unexpected behavior in received power. By allowing the power receiver to control when reduced power intervals occur, it can effectively avoid or compensate for the effects of such power reductions, as it knows exactly when they will occur and can ensure they only occur when acceptable.

[0164] The power level of the power transfer signal during the reduced power time interval is reduced relative to that during the power transfer time interval, and typically the maximum allowed power during the reduced power time interval is not less than 1 / 5, 1 / 10 or 1 / 50 of the maximum allowed power during the power transfer time interval during the power transfer phase.

[0165] The power transmitter (and typically the power receiver) can then be arranged to execute one or more operations (functions, processes, procedures) during the reduced power time interval. That is, it can synchronize the execution of one or more operations of the power transmitter to occur during the reduced power time interval. For example, it can typically synchronize the execution of foreign object detection and / or possibly communication to occur during the reduced power time interval. In this way, the impact of power transfer and power transfer signals on a given operation (particularly on foreign object detection and communication) can be reduced, and often minimized.

[0166] As previously mentioned, in many embodiments, the power transmitter is arranged to decouple the drive signal from the transmitter coil 103 / resonant frequency during the reduced power time intervals. Furthermore, in many embodiments, the power receiver can be arranged to decouple the load from the receiver coil 107, such that no power is directly transferred from the power transfer signal to the load during the reduced power time intervals. In some embodiments, the decoupling can be only partial, such that the effective load during the reduced power time intervals is reduced relative to that outside of these time intervals. In many embodiments, the load of the power receiver from the power transfer signal during the reduced power time intervals may not exceed 100 mW, 200 mW, 500 mW, or 1 W, while the power draw during the power transfer time intervals may be higher, and typically significantly higher. In many embodiments, the power level of the power transfer signal during the reduced power time intervals may not exceed 100 mW, 200 mW, 500 mW, or 1 W, while the power level of the power transfer signal during the power transfer time intervals may be higher, and typically significantly higher.

[0167] In many embodiments, the reduced power time interval can be very short, and in many embodiments, the reduced power time interval has a duration of no more than 500 microseconds, 200 microseconds, or even 100 microseconds. This can provide an efficient method in which the power receiver can control the generation of very short reduced power time intervals, but which are sufficient to perform effective operations, such as communication or foreign object detection, as described above, due to the reduced power time interval. For example, turning off the power transfer signal allows for attenuated foreign object detection to be performed, and the accuracy of attenuated foreign object detection can be further improved by disconnecting the load from the power receiver.

[0168] In many embodiments, power transmitter 101 further comprises a reliability circuit that is arranged to determine a reliability metric for a foreign object detection test performed during the reduced power time interval. In many embodiments, the reliability circuit is part of or coupled to foreign object detector 207 and is arranged to determine the reliability metric based on foreign object detection operations, parameters, values, and signals, depending on the details of the particular embodiment.

[0169] The reliability metric indicates the reliability of the foreign object detection test and, in particular, the reliability / certainty / confidence of the foreign object detection test results. The reliability metric may also be referred to as a confidence metric that indicates the confidence of the foreign object detection test results of the foreign object detection test performed during the reduced power time interval.

[0170] It will be appreciated that the generation of reliability / confidence values ​​for technical tests is well known for different tests and algorithms. The specific method used to determine the reliability / confidence value for a foreign object detection test depends on the specific test being performed. In many embodiments, foreign object detection is based on measuring a parameter value, where the likelihood of the presence of a foreign object is monotonically dependent on the parameter value, e.g., monotonically increasing or monotonically decreasing. In such embodiments, the reliability metric can be determined as the parameter value, or, for example, as a monotonic function thereof.

[0171] For example, for decay-based foreign object detection, the decay rate can indicate the probability that a foreign object is present, and therefore the decay rate can also be used to indicate a confidence value. For example, if the decay time is above a certain threshold, the foreign object detection test can determine that a foreign object is present, otherwise it can be determined that a foreign object is not present. In addition, the confidence of the determination can be given as the numerical difference between the actual decay rate value and the threshold. Therefore, if the decay time is well above the threshold, the confidence that a foreign object is present is high, if the decay time is well below the threshold, the confidence that a foreign object is not present is high, and for cases where the decay time is close to the threshold, this can indicate the presence of a foreign object or the absence of a foreign object, depending on whether the threshold is exceeded, and the test result can be designated as having low confidence / reliability.

[0172] Similar methods can be used for other foreign object detection tests. For example, for a power loss test, the confidence metric can be a function indicating how much the power loss differs from the detection threshold, and for a Q-factor foreign object detection test, the confidence metric can be a function indicating how much the power loss differs from the detection threshold.

[0173] In many embodiments, the power transmitter 101 may be arranged to send data to the power receiver, providing information about foreign object detection and / or about a measure of foreign object detection reliability.

[0174] In particular, in many embodiments, the power transmitter 101 may be arranged to send foreign object detection data to the power receiver 105 according to a reliability metric.

[0175] The power transmitter is arranged to transmit a foreign object detection test result for the foreign object detection test in the reduced power time interval in response to the reliability metric / result for the test satisfying a reliability criterion indicating that the reliability metric exceeds the reliability level. Thus, if the foreign object detection test result is a detection result that is deemed sufficiently reliable, the power transmitter 101 will transmit an indication of the test result to the power receiver 105. Thus, if the reliability metric is sufficiently high, the power transmitter 101 transmits data to the power receiver 105 indicating whether a foreign object has been detected.

[0176] In some embodiments, the power transmitter may send the reliability metric in response to another message (eg, received power), which is not necessarily a request for a reduced power interval request.

[0177] This reliability metric can be sent for foreign object detection performed as part of a power transfer interval (e.g., power loss foreign object detection performed during power transfer). This can indicate that a suspected foreign object has been detected. As will be described in more detail later, this can cause the power receiver to send another reduced power interval request message, thereby causing more accurate foreign object detection to be performed using, for example, attenuation-based measurements.

[0178] In some embodiments, the power transmitter 101 may be arranged to compare the reliability metric to a reliability criterion (which may be the same or different than the reliability criterion used to determine whether to send a foreign object detection test result), and if the reliability criterion is not met, the power transmitter 101 may continue to send requests for one or more reduced power time intervals.

[0179] Evaluation of the reliability criterion may determine that the confidence level of the foreign object detection test result is not as high as desired. For example, if the reliability metric is below a threshold, the foreign object detection test may be determined to be insufficiently reliable. For example, if the decay rate is too close to the foreign object detection decision threshold, the foreign object detection test result may be determined to be too uncertain to clearly indicate the presence of a foreign object.

[0180] In this case, the power transmitter 101 may therefore continue to send requests for more reduced power time intervals to the power receiver in some embodiments. Thus, rather than the power transmitter 101 itself introducing a reduced power time interval by, for example, shutting down the power transfer signal that causes load decoupling at the receiver, the power transmitter 101 continues to request the power receiver 105 to actively introduce one or more new reduced power time intervals by generating new request messages.

[0181] Upon receiving such an indication from power transmitter 101, power receiver 105 may proceed to evaluate whether generating one or more new reduced power time intervals is feasible / possible. For example, power receiver 105 may determine the current state of the energy accumulator to determine whether sufficient energy is stored to support the load during the reduced power time interval. If so, power receiver 105 may proceed to generate a new request for a reduced power time interval and send this new request to the power transmitter. Thus, one or more subsequent reduced power time intervals may be generated using the same method as for the first reduced power time interval.

[0182] The power transmitter can be arranged to perform additional foreign object detection tests during subsequent reduced power time intervals to obtain more accurate detection. The additional foreign object detection tests can be separate and independent tests, and the reliability and confidence of the foreign object detection test results can be evaluated based on whether the tests in subsequent reduced power time intervals are consistent. In other embodiments, foreign object detection tests can be combined over different reduced power time intervals. For example, the decay rate or power loss value can be averaged over multiple reduced power time intervals before being compared to the detection threshold.

[0183] Therefore, in some embodiments, the power transmitter 101 and the power receiver 105 can communicate with each other to dynamically and self-organize to introduce sufficient reduced power time intervals to ensure that sufficiently reliable foreign object detection results are achieved. This can be achieved while still allowing the power receiver 105 to control the operation, and in particular, it allows the power receiver 105 to ensure that the reduced power time intervals do not result in unacceptable power transfer.

[0184] In many embodiments, the communication of a reliability metric, a foreign object detection test result, and / or a request for an additional reduced power time interval may be combined. For example, a single data parameter may be sent with one value indicating that a reliable foreign object detection test indicates the absence of a foreign object, another value indicating that a reliable foreign object detection test indicates the presence of a foreign object, and a third value indicating that the foreign object detection test is unreliable and that an additional reduced power time interval should preferably be initiated.

[0185] The power transmitter 101 may be arranged to perform other operations in response to the foreign object detection result. For example, in many embodiments, it may be arranged to terminate power transmission in response to the detection of a foreign object. If an inconclusive test result is obtained, the power level may continue to be reduced, for example until a new foreign object detection test is performed in a subsequent reduced power time interval. If a reliable foreign object detection test indicates that no foreign object is detected, the power transmitter may continue power transmission without change.

[0186] In some embodiments, foreign object detector 207 can be arranged to perform foreign object detection not only during the reduced power time interval, but also outside of the reduced power time interval. In such embodiments, foreign object detection can also be performed during the power transfer interval and while power transfer is ongoing. This can provide improved performance in many embodiments and can often allow for faster detection of foreign objects than if foreign object detection were performed only during the asynchronous reduced power time interval. This approach can, for example, provide a combined effect of highly accurate detection during the reduced power time interval and less accurate detection during the power transfer interval. This can allow for accurate detection of very small foreign objects while also allowing for very rapid detection of large foreign objects.

[0187] The transmitter may decide to send data to the receiver indicating the reliability of foreign object detection outside of the reduced 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 the presence of a foreign object), the transmitter may thereby indicate this need to the receiver, allowing the receiver to request a reduced power interval at the appropriate time for the receiver.

[0188] For example, the foreign object detector 207 can perform power loss foreign object detection during both the reduced power time interval and the power transfer interval. However, during the reduced power time interval, a dedicated test signal can be used and the load can be decoupled, allowing for more accurate power loss detection performance.

[0189] In some embodiments, a power receiver may receive a reliability metric / indication of foreign object detection (which may be performed, for example, during a reduced power time interval or during normal power transfer outside of a reduced power time interval). The power receiver may determine whether to request generation of an additional reduced power time interval based on the reliability criterion. For example, if the reliability criterion is below a threshold, the power receiver may request generation of a new reduced power time interval to allow for more accurate foreign object detection.

[0190] In some embodiments, both the power receiver and the power transmitter can evaluate the reliability metric. For example, the power transmitter can compare the reliability metric with a criterion to determine whether to request more reduced power time intervals. Additionally, the power transmitter can send the reliability metric to the power receiver, which can also perform an evaluation to, for example, determine whether to comply with the request. For example, the power receiver can only comply with the request if the power receiver determines that the reliability is below a given threshold; otherwise, the power receiver can reject the request. As another example, the threshold for not sending a request for a new reduced power time interval can be much higher if the power transmitter sends a request for a new reduced power time interval than if the power transmitter does not send a request for a new reduced power time interval.

[0191] Such methods may, for example, allow for a more complex decision process, where the power receiver continues to generate requests for additional reduced power time intervals only when the reliability metric satisfies both criteria implemented by the power transmitter and criteria implemented by the power receiver. These methods may generally allow the operation of requesting reduced power time intervals to be tailored to a specific pairing of a specific power receiver and a specific power transmitter (e.g., a new reduced power time interval is generated only if both the power receiver and the power transmitter consider it desirable to generate a new reduced power time interval).

[0192] In some embodiments, the power transmitter further comprises a calibrator arranged to perform calibration for foreign object detection, wherein the calibration is dependent on a foreign object detection test.

[0193] In some embodiments, whether calibration is performed may depend on a foreign object detection test. In particular, whether calibration is performed may depend on whether a foreign object is detected, and calibration is typically performed only when the foreign object detection test indicates that no foreign object is present.

[0194] In many embodiments, the reliability of the foreign object detection test may also be considered. For example, calibration may be performed only if the foreign object detection test determines that no foreign object is present (where the reliability metric indicates a sufficiently high confidence level that this is a correct determination). The reliability threshold used to perform calibration may be different from the reliability threshold used for other purposes, such as the threshold used to send a request for an additional reduced power time interval.

[0195] In some embodiments, the calibrator 211 can be arranged to calibrate the reduced power time interval foreign object detection itself, that is, the calibrator 211 can be arranged to calibrate the algorithm used during the reduced power time interval itself. In other embodiments, the calibrator 211 can be arranged to adjust / calibrate another foreign object detection, such as a foreign object detection algorithm performed during the power transmission time interval. For example, if accurate foreign object detection is performed during the reduced power time interval, it can be determined with very high reliability that a foreign object is not present (or that any foreign object present will have a very small impact). Immediately after the reduced power time interval and power transmission is resumed, the foreign object detection test and calibrator 211 can continue to modify the foreign object detection to make it more accurately reflect the absence of a foreign object. For example, for power loss foreign object detection, the power loss measured immediately after the reduced power time interval is most likely due to losses in the power transmitter and power receiver themselves (e.g., losses in metal parts of the power transmitter and power receiver). The calibrator 211 can accordingly continue to introduce an offset to the power loss estimate that offsets / compensates for this power loss. This compensation / offset is then introduced during the power delivery interval for subsequent foreign object detection tests.

[0196] Thus, in many embodiments the calibration is arranged to calibrate foreign object detection performed during the power transmission time intervals / outside the reduced power time intervals.

[0197] Calibration can be an operation that changes the parameters of the foreign object detection operation, and in particular, calibration can be arranged to adjust the foreign object detection algorithm for the current operating point / scenario. For example, calibration can compensate for changes in component values, the relative position between the power transmitter and the power receiver, the properties of the power transmitter and / or the power receiver, the power level, etc. As another example, the average decay rate of the signal at the beginning of the reduced power time interval indicating the absence of a foreign object can be measured and averaged over multiple foreign object detection tests, and the decision criteria can be adjusted to reflect the average value. This can, for example, allow the foreign object detection algorithm in the reduced power time interval to be adjusted to be more discerning and able to detect smaller changes from the current operating point when no foreign object is present.

[0198] In many embodiments, as described, the power transmitter is capable of performing foreign object detection during both the reduced power time interval and the power transfer time interval, and the calibrator 211 can be arranged to adjust the foreign object detection performed during the power transfer time interval based on the results of the foreign object detection test during the reduced power time interval.

[0199] In typical embodiments, foreign object detection performed during power transmission time intervals is therefore different from foreign object detection performed during reduced power time intervals.

[0200] In some embodiments, the same underlying foreign object detection operation can be performed, but different detection criteria can be applied. For example, power loss can be determined for both reduced power time intervals and power transfer time intervals for foreign object detection, but the measured power loss can be compared to different detection thresholds. The detection thresholds for one or both foreign object detections can be adjusted by the calibrator 211.

[0201] In many embodiments, different types of tests can be used for foreign object detection during the power transmission time interval and during the reduced power time interval. In particular, different parameters can be determined and evaluated to determine whether a foreign object is present.

[0202] As an example, in many embodiments, foreign object detector 207 may perform power loss during the power transfer interval, but perform attenuation-based foreign object detection or Q-factor foreign object detection during the reduced power interval. This can provide particularly advantageous performance in many embodiments, where different foreign object detection algorithms are optimized or adjusted for the properties / conditions of different phases. In particular, attenuation measurement can allow highly accurate and very short foreign object detection, but requires shutting down the power transfer signal. Therefore, it may be well suited for short reduced power intervals. In contrast, at higher sustained power levels, power loss is often very accurate for foreign object detection, especially when accurately calibrated and adjusted for the specific current conditions. Non-attenuation-based Q-factor methods can provide high accuracy, but may require a longer time to shut down power transfer. Therefore, a combination of different foreign object detection algorithms (whether simply using different criteria or fundamentally different operations) can provide highly accurate foreign object detection throughout the power transfer phase, and adjusting the power transfer interval operation based on foreign object detection testing performed during the reduced power interval can significantly improve performance.

[0203] As a specific example, the power receiver can request a reduced power time interval, and in response, the power transmitter can continue to turn off the drive signal and perform a decay rate foreign object detection test. If a foreign object is detected with high reliability in this way, the power transfer can be terminated (e.g., subjected to another foreign object detection test indicating the presence of a foreign object). If it detects with high reliability / confidence that there is no foreign object, it can start the calibrator 211 to perform calibration for foreign object detection in the subsequent power transfer time interval. In this example, when the power transfer signal is turned back on and the power transfer time interval is started, the calibrator 211 performs measurements and adjusts the foreign object detection algorithm executed during the power transfer time interval based on these measurements. Therefore, the power transfer foreign object detection algorithm is adjusted based on the assumption that no foreign object is detected. For example, for power loss detection, the current power loss is measured (which is the power loss without a foreign object) and the decision threshold is adjusted accordingly (or a compensation factor is introduced into the power loss).

[0204] If the reliability of the foreign object detection test based on the decay rate during the reduced power time interval results in the detection of the absence of a foreign object but with low reliability, the system can be arranged to continue power transfer, but the calibrator 211 can be arranged not to calibrate the foreign object detection algorithm. This can reduce the risk of the calibration potentially adjusting the foreign object detection for a situation where a foreign object is actually present. For example, if a small foreign object is present at a certain distance, it may not result in an unacceptable power loss and is therefore an acceptable situation. However, this will result in a less reliable detection of the absence of a foreign object (the parameter will be closer to the detection threshold) and this may prevent the calibrator 211 from calibrating the foreign object detection for a situation where a small foreign object is actually present.

[0205] In some embodiments, the operation of the power transmitter in response to the reduced power time interval foreign object detection test may therefore also depend on the detection result of whether a foreign object (FO) is present. For example, the following method may be used:

[0206] Reliable+FO detected: stop / reduce / limit power transfer

[0207] Reliable + No FO detected: calibration. Additional data can be exchanged to support the calibration itself

[0208] Unreliable: Postpone calibration. Additional reduced power intervals may be required.

[0209] This method can thus allow for improved interaction between two foreign object detection algorithms, wherein the first algorithm (one of the reduced power time intervals) is typically a significantly more reliable detector than the second algorithm (one of the power transmission time intervals). The accurate / reliable detection algorithm can be used to indicate the absence of a foreign object with high confidence, and thus the less accurate / reliable detection algorithm can be calibrated under this assumption. Typically, significantly more accurate overall foreign object detection can be achieved.

[0210] While in many embodiments, calibration of foreign object detection during power transmission time intervals may depend on foreign object detection testing during reduced power time intervals, to the extent that calibration is performed only when no foreign object is detected (and possibly also requiring a reliability metric to be above a threshold), in other embodiments, it may depend on test results and reliability in a more complex manner. For example, in some embodiments, the extent of calibration / adjustment may depend on a reliability metric. For example, calibration may be arranged to adjust the detection threshold by a relative offset from a current level. The magnitude of the offset may depend on the reliability metric, so that when the absence of a foreign object is detected with high confidence, the change in the detection threshold is greater than when the confidence is lower.

[0211] In some embodiments, the first communicator 205 may be arranged to communicate with the power receiver during the reduced power time interval, alternatively or additionally. In some embodiments, the communication may use a power transfer signal and / or the transmitter coil 103. In such embodiments, the drive signal may be generated, for example, at exactly the same frequency as used during the power transfer time interval, and may be modulated to transmit data.

[0212] In other embodiments, communication may be performed using an antenna / transmitter coil that is different from the transmitter coil 103. Furthermore, the first communicator 205 may use a communication carrier that is different from the power transfer signal, and typically a communication carrier having a different frequency.

[0213] In many embodiments, the communication may be a completely independent communication system, and may in particular be a standardized short-range communication system, such as a Near Field Communication (NFC) system.

[0214] In the described system, communication is performed in reduced power time intervals during the power transfer phase. In particular, some or indeed all reduced power time intervals may be communication time intervals during which communication between the power transmitter 101 and the power receiver 105 is performed. In particular, the transmitter controller 203 may include a communication control function that is arranged to synchronize the first communicator 205 so that communication operations (typically both receiving data and transmitting data) are performed in (and typically only in) the communication time intervals of the power transfer phase (i.e., in the reduced power time intervals allocated for communication).

[0215] In many embodiments, the first communicator 205 is arranged to send data to the power receiver 105 and may in particular be arranged to modulate the power transfer signal using frequency, amplitude or phase modulation. In some embodiments, this may be done during a reduced power time interval, where, for example, a low and constant level is set for the drive signal / power transfer signal, which may, for example, improve the detection of amplitude changes caused by the amplitude modulation.

[0216] In some embodiments, communication may be performed using a separate communication channel, which may be accomplished using a separate communication coil or indeed using the transmitter coil 103. For example, in some embodiments, near field communication may be implemented, or a high frequency carrier (e.g., having a carrier frequency of 13.56 MHz) may be superimposed on the power transfer signal.

[0217] This can significantly improve communication performance and, in particular, can provide a favorable environment in which improved communication is provided while reducing interference caused by power transfer operations. In addition, since the power transfer time interval is controlled by the power receiver, dynamic and asynchronous communication operations controlled by the self-organizing power receiver can be achieved.

[0218] In many embodiments, the reduced power time interval may include a communication time interval and a foreign object detection time interval.

[0219] In the described system, operations such as foreign object detection and / or communication can be performed in reduced power time intervals, so foreign object detection / communication and power transmission can be separated in the time domain, thereby reducing cross-interference from power transmission to foreign object detection / communication. Consequently, variability and uncertainty caused by changes in operating conditions of power transmission can be isolated from foreign object detection / communication, resulting in more accurate and reliable foreign object detection / communication.

[0220] During the power transfer phase, the power transmitter is therefore arranged to perform power transfers during power transfer intervals. In particular, during these intervals, the power transmitter can provide information to the power receiver at a much higher bit rate, which would otherwise overload the low-bit-rate communication during the power transfer intervals. The power transmitter and the power receiver can (re)negotiate new operating parameters, such as guaranteed power levels. The power transmitter and the power receiver can also operate a power control loop (which can be based on communications during communication intervals corresponding to the reduced power intervals). Thus, the power level being transferred can be dynamically changed.

[0221] Thus, in many embodiments, methods for communicating using reduced power time intervals can provide significantly improved communications. Additionally, by allowing the reduced power time intervals to be dynamic and self-organizing / asynchronous time intervals controlled by the power receiver, a more efficient and adaptive approach can be achieved, thereby allowing the reduced power time intervals to be tailored to the specific needs, requirements, and preferences of individual power receivers, including specifically ensuring that the reduced power time intervals do not jeopardize the reliable supply of power to the load.

[0222] In different embodiments, the power receiver may use different conditions and triggers to send the reduced power time interval request message to the power transmitter.

[0223] In many embodiments, the power receiver may be arranged to send a reduced power time interval request message in response to a change in the power being extracted from the power transfer signal, the current being supplied to the load, and / or the voltage being supplied to the load. The change may be an actual change that has been detected or has already occurred, or may be an impending change, for example, i.e., the power receiver may send the reduced power time interval request message before implementing the change.

[0224] For example, a power receiver may occasionally change its operating point to deliver different power, current, and / or voltage to a load. In particular, it may change its operating mode to deliver different power to a load, such as when changing the battery's charging from fast charging to normal charging or trickle charging.

[0225] Different power levels for such operating modes may have different effects on the power transfer signal, which may in turn affect the foreign object detection test during the power transfer interval. For example, changing the power supplied to the load may result in a very different power loss being measured at the power transmitter, even when no foreign object is present. Therefore, it may be desirable to recalibrate the foreign object detection test, and thus a reduced power interval request message may be generated and sent to the power transmitter, causing a new reduced power interval to be initiated and a foreign object detection test, such as a decay rate test, to be performed during the reduced power interval. If this results in a reliable indication that a foreign object is not present, the power transmitter may continue to calibrate the foreign object detection algorithm for the power transfer interval at the end of the reduced power interval.

[0226] Such an approach is not limited to changes in power levels, but can also be applied when changing between operating modes at the same power level.

[0227] For example, a power receiver may have the following operating modes:

[0228] Operation Mode 1: The power receiver provides power to the load. 5W , 5V, 1A.

[0229] Operation Mode 2: The power receiver provides power to the load. 5W , 10V, 0.5A.

[0230] The received power evaluation results may be different for the two modes, and the transmitted power evaluation results may also be different. The calculated power loss may be different in the different operating modes, and the power receiver may be arranged to send a reduced power time interval request message when switching between different operating modes, thereby causing a new reduced power time interval and foreign object detection calibration to be performed.

[0231] Depending on whether the power level changes, the system may behave differently.In many embodiments, foreign object detection may utilize a calibrated power loss curve that shows the expected power loss for different power levels of the power transfer signal when no foreign object is present.

[0232] In the case of relatively small changes in power levels (typically no changes in operating mode at the receiver), the currently calibrated power loss curve can generally be reused and expanded / improved with the new power level(s). However, for changes in operating mode (typically including changes in the nominal voltage and / or current supplied to the load), the power loss curve should be updated so that multiple (2 or more) power loss values ​​are used. A different power loss curve can be maintained for each operating mode.

[0233] In some embodiments, the power transmitter may be arranged to send a request for measurement and / or an indication of suspected detection of a foreign object, and the power receiver may be arranged to send a request for a reduced power time interval in response to receiving the indication from the power transmitter.

[0234] In some embodiments, the power transmitter may be arranged to send the indication by sending a non-acknowledgement (NACK) response to a message received from the power receiver. The message may be a power transfer message, such as in particular a receive power or power control loop error message.

[0235] The power transmitter may be arranged to transmit an indication of suspected detection of a foreign object in response to a result of a foreign object detection test, in particular a result of a foreign object detection test performed during a power transfer time interval.

[0236] In some embodiments, the power transmitter may transmit an indication of suspected detection of a foreign object specifically in response to determining that the foreign object detection test did not determine that a foreign object is not present if the reliability metric satisfies the reliability criterion.

[0237] In some embodiments, the power transmitter may transmit an indication of suspected detection of a foreign object, particularly in response to determining that a reliability metric for a foreign object detection test does not satisfy a reliability criterion.

[0238] In some embodiments, the power receiver may therefore request a reduced power time interval when it receives an indication from the power transmitter to perform a measurement. This may particularly occur when the power transmitter suspects the presence of a foreign object (e.g., the foreign object detection threshold is nearly reached, or the foreign object detection threshold is occasionally exceeded (e.g., for a single measurement event)).

[0239] In response to receiving an indication that a foreign object is suspected of being detected, the power receiver may, for example, control power transmission to a lower level to mitigate potential heating of the foreign object.

[0240] Alternatively or additionally, it may initiate a more accurate test for the presence of a foreign object. In such an example, the power receiver may enable the power transmitter to perform a more accurate test by requesting a reduced power time interval, which may cause the power transmitter to perform an accurate foreign object detection test, such as a decay rate test. In some embodiments, the reduced power time interval request message may additionally or alternatively initiate a new calibration, as previously described.

[0241] In particular, a NAK sent in response to a received power message may indicate that the receiver should take action, eg reduce its power consumption or request a calibration, in particular requesting a new reduced power time interval request message.

[0242] In an approach where the power receiver fully controls operation, the power transmitter relies on the power receiver to operate acceptably when requesting reduced power intervals. However, this can also present associated challenges. For example, it can be difficult to ensure that sufficient compliance testing has been performed on such an option for the power receiver.

[0243] One approach may be to require the power receiver to enable the power transmitter to keep the power difference within a tighter range (i.e., lower power loss) than originally required. This places an implicit requirement on the power receiver to enable the power transmitter to calibrate the power difference, otherwise achieving a tighter range is generally impractical.

[0244] In many systems, the power transmitter can acknowledge / unacknowledge messages from the power receiver. A power transmitter can also use a non-acknowledgement (NAK) to alert the power receiver to the (possible) presence of a foreign object. This means that if the power receiver does not take action, the power transmitter stops power transmission. The power receiver's action could be to reduce its power level requirements, thereby mitigating the potential danger of heating the foreign object.

[0245] Another method may be that the power receiver requests a reduced power time interval request message to enable the power transmitter to perform more accurate foreign object detection.

[0246] In this context, a NAK from the power transmitter can be considered an indication that the reliability / accuracy of foreign object detection is insufficient, thus halting power transfer.

[0247] The smart power receiver can therefore request a reduced power time interval to enable the power transmitter to perform a more accurate foreign object detection test and / or perform calibration of the power difference.

[0248] The power receiver may be arranged to request a reduced power interval in response to receiving a NAK response from the power transmitter.

[0249] In some embodiments, the power receiver may also be configured to perform calibration. This may be the case, for example, if the power receiver receives a reliability indication for a reduced foreign object detection test from the power transmitter. If this information indicates with a sufficiently high probability that a foreign object is not present, the power receiver may proceed with calibrating the received power level measurements.

[0250] In this case, the power transmitter may, for example, send a measurement / estimation of the transmit power, and the power receiver may use this to calibrate its received power in order to compensate for the difference between them.

[0251] In some embodiments, the power receiver may be arranged to send reduced power time interval request messages with a maximum duration between these reduced power time interval request messages. For example, the maximum duration between two reduced power time intervals may be 100 ms, 500 ms, 1 second, or 2 seconds. In such an embodiment, the power receiver may, for example, send a reduced power time interval request message when the operating mode changes, but if no change occurs, it may send reduced power time interval request messages at predetermined intervals of, for example, 500 milliseconds.

[0252] In some embodiments, the reduced power time interval request message may be a dedicated message for the sole purpose of requesting a reduced power time interval. The message may, for example, simply contain a predetermined pattern of bits that, if detected by the first communicator 205 of the power transmitter, is interpreted as a request for the power transmitter to generate a reduced power time interval.

[0253] In some embodiments, the reduced power time interval request message may include data related to the reduced power time interval, such as a suggested timing for the reduced power time interval, a required maximum or minimum power level, a duration, a number of required reduced power time intervals, etc. Such data may be provided as part of a dedicated message, as part of a combined message, or as a message also used for other purposes. In such embodiments, the power transmitter may be arranged to generate a reduced power time interval having such properties.

[0254] Thus, in some embodiments, the reduced power time interval request message is a separate message that is used only for the specific purpose of requesting a reduced power time interval. However, in some embodiments, the reduced power time interval request message may also be a combined message, and in particular, the request for a reduced power time interval may be piggybacked onto another existing message that is typically used for other purposes.

[0255] In some embodiments, the reduced power interval request message is a message that includes additional data related to power transfer operations performed outside of the reduced power interval. The reduced power interval request message may include data related to power transfer interval operations. As a specific example, the reduced power interval request message may be a power control message that includes control data for a power control loop of a power transfer signal.

[0256] Thus, the reduced power time interval request message is not a dedicated or separate message, but may be, for example, a power control error message. Such a message may be sent frequently (e.g., every 250 milliseconds or faster). Many such messages may not include any reduced power time interval requests, but may only report power control requests, such as power-up requests or power-down requests. However, some messages may include a data sequence that is interpreted as a request for a reduced power time interval.

[0257] In many embodiments, the reduced power time interval request message may be a power feedback message that includes data indicating the power level extracted by the power receiver. The power feedback message may generally include data indicating the amount of power extracted by the power receiver from the power transfer signal. The power feedback message may specifically be a received power data packet that indicates the power extracted (or to be extracted) by the power receiver from the power transfer signal.

[0258] It will be appreciated that many different (existing) control messages may be modified to also function as reduced power time interval request messages to trigger a reduced power time interval. Examples include:

[0259] Received power data packet

[0260] Use a specific pattern or reserved field to serve as a reduced power time interval request message (also known as a trigger)

[0261] Determine which of the patterns in the pattern are also used as triggers

[0262] Regardless of mode, all received power packets are used as triggers

[0263] The packet in the negotiation set is used as a trigger

[0264] Newly defined data packets are used as triggers

[0265] The data packet may also contain the actual slot start time and / or slot duration

[0266] As a specific example, the reduced power time interval request message may be implemented as a received power packet known from a Qi system. Such a packet has a value such as Figure 8 The format shown.

[0267] The bit pattern in the 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 reduced power time interval requests. For example, a bit pattern of "101" can be defined to indicate that a received power packet message is also a reduced power time interval request message.

[0268] model illustrate ‘000’ Normal value; request response ‘001’ Light load calibration value; request response ‘010’ Connect load calibration value; request response ‘011’ reserve ‘100’ Normal value; no response expected ‘101’ Normal value; trigger for FOD slot; no response expected ‘110’ reserve ‘111’ reserve

[0269] In another example, a bit pattern of "011" may be defined that includes a request for a response from the transmitter. The response can be a reliability metric as previously described.

[0270] model illustrate ‘000’ Normal value; request response ‘001’ Light load calibration value; request response ‘010’ Connect load calibration value; request response ‘011’ Normal value; trigger for FOD time slot; expected response ‘100’ Normal value; no response expected ‘101’ reserve ‘110’ reserve ‘111’ reserve

[0271] In many embodiments, there may be a direct correspondence between the reduced power time interval request messages and the reduced power time intervals, such that each reduced power time interval request message causes the power transmitter to generate one and only one reduced power time interval request message.

[0272] In some embodiments, the reduced power time interval may be generated only in response to a reduced power time interval request message received from the power receiver, so the power receiver can rely on reduced power time intervals not occurring unless specifically requested.

[0273] In some embodiments, in response to receiving a single reduced power time interval request message, the power transmitter may generate more than one reduced power time interval. For example, in some embodiments, receiving a reduced power time interval request message may cause the power transmitter to generate a predetermined number of reduced power time intervals, which may, for example, have a predetermined duration and a predetermined interval. Thus, rather than a single reduced power time interval request message causing a single reduced power time interval to be generated, the single reduced power time interval request message may cause a sequence or burst of potentially shorter reduced power time intervals to be generated.

[0274] In some embodiments, the parameters of the reduced power time intervals and the response to the reduced power time interval request message can be predetermined, for example, the duration of the reduced power time interval can be predetermined. However, in other embodiments, one, some, or more reduced power time intervals can be dynamically determined, for example, in response to data received in the reduced power time interval request message. The reduced power time interval request message can, for example, indicate the requested number and duration of the reduced power time intervals.

[0275] In many embodiments, one or more parameters of the reduced power time interval or request process can be defined or determined during an initialization phase performed before the system enters the power transfer phase. For example, many wireless power transfer systems (e.g., Qi) include a negotiation phase performed as part of the initialization of the power transfer phase. During such a phase, the power receiver can request desired operating parameters or aspects, and the power transmitter can agree or disagree with these requests. Power transfer can then proceed using the negotiated parameters.

[0276] In the described system, the initialization phase, and in particular the negotiation phase, may be used to initialize parameters for the reduced power time interval operation.

[0277] Such a stage can be used to determine whether the power transmitter and power receiver are indeed capable of supporting such operation, and if so, how the operation should be implemented. It can determine whether reduced power time intervals are fully supported, whether only predetermined periodic reduced power time intervals based on a predetermined repeating time frame are supported, or whether fully power receiver-controlled reduced power time interval operation is supported.

[0278] In the latter case, the negotiation may also be used to determine which message may be used as the reduced power time interval request message, such as whether a received power packet can be used, whether a dedicated message can be used, and so on.

[0279] Such an approach may allow for increased flexibility and may in particular allow for improved backward compatibility in many systems and may enable the described approach to be introduced into existing deployed systems.

[0280] The initialization / configuration / negotiation phase may additionally or alternatively determine parameters of the reduced power time interval, such as timing aspects (e.g., delay from the reduced power time interval request message to the start of the reduced power time interval), duration, maximum power level, etc. In some embodiments, such negotiated parameters may be default parameters, which can subsequently be overwritten, for example, by dedicated data included in the reduced power time interval request message.

[0281] As a specific example of the negotiation (or configuration / negotiation) phase, the power receiver can indicate whether it supports:

[0282] Time-slot operation (foreign object detection and / or communication)

[0283] Reduced Power Time Interval Request Message (Time Slot Trigger)

[0284] Implicit time slot trigger

[0285] Explicit time-slot trigger

[0286] During the power transfer phase, the power transmitter can use this information to modify its behavior as follows:

[0287]

[0288] Configuration phase

[0289] The power receiver can use the reserved bits in the configuration packet to indicate its support for slotted FOD (according to the table above)

[0290] Negotiation stage

[0291] The power receiver can indicate its support for slotted FOD / communication using information messages during the negotiation phase

[0292] It is also able to use messages to negotiate slot duration and slot interval

[0293] Additionally, it can use messages to indicate how it will generate triggers (Reduce Power Interval Request messages)

[0294] It will be appreciated that, for the sake of clarity, the above description describes embodiments of the present invention with reference to different functional circuits, units, and processors. However, it will be apparent that any suitable distribution of functionality between different functional circuits, units, or processors may be used without departing from the present invention. For example, functions illustrated as being performed by separate processors or controllers may be performed by the same processor or controller. Therefore, references to specific functional units or circuits are merely to references to appropriate modules for providing the described functionality, rather than to indications of a strict logical or physical structure or organization.

[0295] The present invention can be implemented in any suitable form comprising any combination of hardware, software, firmware or these projects. The present invention can optionally be implemented at least in part as the computer software running on one or more data processors and / or digital signal processors. The elements and components of an embodiment of the present invention can be implemented physically, functionally and logically in any suitable manner. In fact, function can be implemented in a single unit, in multiple units or as the part of other functional units. Just for this reason, the present invention can be implemented in a single unit, or can be distributed between different units, circuits and processors physically and functionally.

[0296] While the present invention has been described in conjunction with certain embodiments, it is not intended that the invention be limited to the specific forms set forth herein. Rather, the scope of the invention is limited solely by the claims. Furthermore, while features may appear to be described in conjunction with specific embodiments, those skilled in the art will recognize that various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0297] It will be appreciated that reference to a preferred value does not imply any restriction beyond the value determined in the foreign object detection initialisation mode, ie preferably by determining the value during the adjustment process. Reference to a preferred value may replace reference to eg the first value.

[0298] In addition, although listed separately, multiple modules, elements, circuits or method steps can also be implemented by, for example, a single circuit, unit or processor. In addition, although individual features may be included in different claims, these features can be advantageously combined, and the inclusion of these features in different claims does not mean that the combination of these features is not feasible and / or advantageous. Moreover, the inclusion of a feature in one type of claim does not mean that the feature is limited to that type of claim, but rather indicates that the feature can be equally applicable to other types of claims when appropriate. In addition, the order of features in the claims does not mean that the features must be in any specific order in which they work, and in particular, the order of the individual steps in a method claim does not mean that the steps must be performed in that order. Instead, the steps can be performed in any appropriate order. In addition, singular references do not exclude pluralities. Therefore, references to "one", "first", "second", etc. do not exclude pluralities. The reference numerals in the claims provided solely for the purpose of clarifying the examples should not be interpreted as limiting the scope of the claims in any way.

Claims

1. A power transmitter (101) for wirelessly providing power to a power receiver (105) via an inductive power transfer signal; the power transmitter (101) comprising: a transmitter coil (103) for generating the power transfer signal during a power transfer phase; a driver (201) for generating a drive signal for the transmitter coil (103) to generate the power transfer signal during the power transfer phase; a first communicator (205) for receiving a message from the power receiver (105); as well as a controller (203) arranged to generate a reduced power time interval during the power transfer phase, during which the power level of the power transfer signal is reduced, the controller being arranged to generate the reduced power time interval in response to receiving a reduced power time interval request message from the power receiver; a foreign object detector (207) arranged to perform foreign object detection, said foreign object detection being arranged to perform a foreign object detection test during said reduced power time interval; reliability circuitry (209) arranged to determine a reliability metric for said foreign object detection; wherein the reliability circuit (209) is arranged to send a request for at least one or more reduced power time intervals to the power receiver in response to determining that the reliability metric for the foreign object detection test does not meet a reliability criterion.

2. The power transmitter according to claim 1, wherein: The reliability circuit (209) is arranged to send a foreign object detection result to the power receiver (105) in response to determining that the reliability metric for the foreign object detection test satisfies a reliability criterion.

3. The power transmitter according to claim 1, wherein: The reliability circuit (209) is arranged to send a request for at least one or more reduced power time intervals to the power receiver in response to the foreign object detection test.

4. The power transmitter according to any one of claims 1 to 3, wherein: The first communicator (205) is arranged to communicate with the power receiver during the reduced power time interval.

5. The power transmitter according to claim 4, wherein: The first communicator (205) is arranged to communicate with the power receiver using a communication carrier different from the power transfer signal.

6. The power transmitter according to any one of claims 1 to 3, wherein: The reduced power time interval request message is a dedicated message for the purpose of requesting the reduced power time interval.

7. The power transmitter according to any one of claims 1 to 3, wherein: The reduced power time interval request message is a message including other data for power transfer, the data including data for a power transfer operation performed outside the reduced power time interval.

8. The power transmitter according to claim 7, wherein: The reduced power time interval request message is a power control message that provides feedback to power control for the power transfer signal.

9. The power transmitter according to claim 7, wherein: The reduced power time interval request message is a power feedback message comprising data indicative of a power level drawn by the power receiver.

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

11. The power transmitter according to claim 7, wherein: The reduced power time interval request message includes at least one of a reduced power time interval start time and a reduced power time interval duration.

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

13. The power transmitter according to any one of claims 1 to 3, further comprising an initialisation processor arranged to initialise the power transfer phase before the power transfer phase begins, the initialisation processor being arranged to determine properties of the reduced power time interval in response to communication with the power receiver, and the controller being arranged to generate the reduced power time interval to have the properties.

14. A wireless power transmission system comprising a power transmitter (101) according to any preceding claim and a power receiver (105), the power receiver (105) comprising: a coil (107) for extracting power from the power transfer signal; A power circuit (301, 305) for providing power extracted from the power transmission signal to a load (303); A second communicator (307) is arranged to send the reduced power time interval request message to the power transmitter (103).

15. The wireless power transmission system according to claim 14, wherein: The second communicator (307) is arranged to send the reduced power time interval request message to the power transmitter (101) in response to a change in at least one of: power being extracted from the power transfer signal, current being provided to the load (303), and voltage being provided to the load (303).

16. The wireless power transmission system according to claim 14, wherein: The second communicator (307) is arranged to receive a reliability indication from the power transmitter (101), the reliability indication indicating the reliability of a foreign object detection test performed during a reduced power time interval, and wherein the second communicator (307) is arranged to send a further reduced power time interval request message in response to determining that the reliability indication does not meet a reliability criterion.

17. The wireless power transmission system according to any one of claims 14 to 16, wherein: The power transmitter (101) is arranged to send an indication of suspected detection of a foreign object, and the power receiver (105) is arranged to send the request for a reduced power time interval in response to receiving the indication of the suspected detection of a foreign object from the power transmitter (101).

18. A method for operating a power transmitter (101) to wirelessly provide power to a power receiver (105) via an inductive power transfer signal; the method comprising: generating the power transfer signal during a power transfer phase via a transmitter coil (103); generating a drive signal for the transmitter coil (103) to generate the power transfer signal during the power transfer phase; receiving a message from the power receiver (105) during the power transfer phase; generating a reduced power time interval during the power transfer phase, wherein a power level of the power transfer signal is reduced during the reduced power time interval; generating the reduced power time interval in response to receiving a reduced power time interval request message from the power receiver (105); performing foreign object detection, including performing a foreign object detection test during the reduced power time interval; determining a reliability metric for the foreign object detection; and A request for at least one or more reduced power time intervals is sent to the power receiver in response to determining that the reliability metric for the foreign object detection test does not satisfy reliability criteria.

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