Foreign object detection in wireless power transmission systems

Abstract

The transmitter 101 comprises a driver 201 that generates a drive signal for the transmitting coil to generate a power transfer signal during a power transfer time and to generate an electromagnetic test signal during a foreign object detection time. The set of balanced detection coils 207, 209 comprises two detection coils configured such that signals induced in the two detection coils by the electromagnetic field generated by the transmitting coil compensate each other. The foreign object detector 205 is coupled to the detection coils and performs foreign object detection during the foreign object detection time. The foreign object detector 205 is configured to detect a foreign object according to a foreign object detection criterion that requires that at least one signal from the set of balanced detection coils 207, 209 exceeds a first threshold and that the number of signals exceeding a second threshold is less than or equal to a given threshold, the foreign object detection criterion being at least two.

Description

[Technical field]

[0001] The present invention relates to foreign object detection in wireless power transfer systems, and in particular to foreign object detection for power transmitters providing inductive power transfer to high power devices such as, but not limited to, kitchen appliances. [Background technology]

[0002] Most of today's electronic products require dedicated electrical contacts to receive 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. Power requirements also typically vary widely, and since most devices now have their own dedicated power source, a typical user has many different power sources, each dedicated to a specific device. Using an internal battery could eliminate the need for a wired connection to a power source during use, but this is only a partial solution, as the battery would need to be recharged (or replaced). Using a battery can significantly increase the weight, and potentially the cost and size, of the device.

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

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

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

[0006] Moreover, such wireless power transfer configurations are advantageously designed to allow a power transmitting device to be used with a variety of power receiving devices. In particular, a wireless power transfer approach known as the Qi specification has been defined and is currently being further developed. This approach allows a power transmitting device that meets the Qi specification to be used with a power receiving device that also meets the Qi specification, without both devices having to be from the same manufacturer or proprietary to each other. The Qi standard also includes features for adapting operation to a particular power receiving device (e.g., depending on a particular power drain).

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

[0008] The Wireless Power Consortium is developing the Ki specification (also known as the Cordless Kitchen Specification) which is based on the Qi specification and aims to provide safe, reliable and efficient wireless power transfer for kitchen appliances. Ki will support much higher power levels up to 2.2KW.

[0009] A potential problem with wireless power transfer is that power may be unintentionally transferred to, for example, a metal object that happens to be in close proximity to the transmitter. For example, if a foreign object, such as a coin, key, or ring, is placed on a transmitter platform that is configured to receive a receiver, the magnetic flux generated by the transmitter coil will induce eddy currents in the metal object, causing the object to heat up. This temperature increase can be very noticeable and very undesirable.

[0010] To reduce the risk of such situations occurring, it has been proposed to introduce foreign object detection, where the transmitter can detect the presence of a foreign object and reduce transmitted power and / or generate a user warning when a foreign object is detected. For example, the Qi system includes the ability to detect foreign objects and reduce power if a foreign object is detected. Specifically, Section 11 of the Qi specification version 1.2.1 describes various methods for detecting foreign objects.

[0011] One method for detecting such foreign objects is disclosed in WO2015018868A1. Another example is provided in WO2012127335, which discloses an approach based on the determination of unknown power loss. In this approach, both the receiver and the transmitter measure the power, and the receiver communicates the measured received power to the transmitter. If the transmitter detects a large difference between the power sent by the transmitter and the power received by the receiver, an undesirable foreign object may be present, and power transmission is reduced or stopped for safety reasons. This power loss based approach requires synchronized and accurate power measurements to be performed by the transmitter and the receiver.

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

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

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

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

[0016] In practice, achieving sufficient detection accuracy using the methods described in the Qi specification tends to be difficult, a problem made all the more difficult by the large amount of uncertainty regarding the specific current operating conditions.

[0017] For example, the possible presence of friendly metals (i.e., metal parts of the devices embodying the receiver or transmitter) is particularly problematic because the magnetic and electrical properties of these metals are unknown (and vary from device to device) and therefore difficult to compensate for.

[0018] Furthermore, even a relatively small amount of power dissipated in the metallic foreign object will result in undesirable heating. Therefore, even small power discrepancies between transmitted and received power must be detected, which becomes particularly difficult when the power levels of the power transfer become high.

[0019] The Q-factor reduction approach is often more sensitive to detect the presence of metal objects, but this approach still does not provide sufficient accuracy and is subject to the effects of, for example, friendly metals.

[0020] The performance of foreign object detection depends on the specific operating conditions present when the test is actually performed. Furthermore, foreign object detection is typically a very sensitive test, where it is desired to detect relatively small changes caused by the presence of a foreign object in an environment where the operating conditions and scenarios in which the test is performed may vary widely.

[0021] This problem tends to get worse at higher power levels, where the foreign object detection algorithm needs to be more accurate to prevent the foreign object from heating beyond a safe temperature. In fact, since the temperature rise is a function of the absolute power level, the relative power loss that needs to be detected is greatly reduced at higher power levels.

[0022] Also, at higher power levels, the detection accuracy of foreign object detection becomes more important and therefore the requirements for accurate measurement techniques become more stringent. In fact, many of the foreign object detection techniques that are suitable for low power use are not suitable for detection for high power transmissions.

[0023] Current methods and measurement techniques for foreign object detection tend to be suboptimal and, in some scenarios and examples, may not detect the presence of a foreign object or may falsely detect a foreign object when none is present. Furthermore, more accurate methods tend to be complex and expensive. Summary of the Invention [Problem to be solved by the invention]

[0024] Improved object detection would therefore be advantageous, particularly techniques that allow for increased flexibility, reduced cost, reduced complexity, improved object detection, fewer false positives and negatives, backward compatibility, improved suitability for transmission of higher power levels, and / or improved performance.

[0025] SUMMARY OF THE DISCLOSURE Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination. [Means for solving the problem]

[0026] According to one aspect of the present invention, there is provided a power transmitter for wirelessly supplying power to a power receiver via an inductive power transmission signal, the power transmitter including a transmitting coil; a driver for generating a drive signal for the transmitting coil, the driver generating the drive signal for the transmitting coil to generate the inductive power transmission signal during at least one power transmission time of a recurring time frame and generating the drive signal for the transmitting coil to generate an electromagnetic test signal during at least one foreign object detection time of the recurring time frame; a plurality of sets of balanced detection coils coupled in series, each set of balanced detection coils including two detection coils, wherein signals induced in the two detection coils by an electromagnetic field generated by the transmitting coil compensate each other; and a plurality of sets of balanced detection coils coupled in series, each set of balanced detection coils including two detection coils, wherein signals induced in the two detection coils by an electromagnetic field generated by the transmitting coil compensate each other. and a foreign object detector coupled to the plurality of sets of balanced detection coils and performing foreign object detection during a foreign object detection time, the foreign object detector detecting a foreign object in response to signals from the plurality of sets of balanced detection coils satisfying a foreign object detection criterion, the foreign object detection criterion including a first requirement that a signal from at least one of the plurality of sets of balanced detection coils indicates that an imbalance between signals induced in two detection coils of the at least one set of the plurality of sets of balanced detection coils exceeds a first threshold, and a second requirement that a number of signals from the plurality of sets of balanced detection coils indicating that an imbalance between signals induced in two detection coils of the set of balanced detection coils exceeds a second threshold is less than a threshold number, the threshold number being at least two.

[0027] The present invention provides improved foreign object detection in many embodiments. More accurate foreign object detection is achieved in many scenarios and systems. The approach reduces complexity in many embodiments. In particular, the approach is particularly well suited to improving foreign object detection in power transfer systems at higher power levels.

[0028] This technique improves the accuracy and / or reliability of the foreign object detection test during the power transfer phase. In many embodiments, this technique improves the accuracy and / or reliability of the foreign object detection test. certainty This reduces the sensitivity and thereby improves performance.

[0029] The present invention provides improved and / or facilitated foreign object detection in many embodiments and scenarios. This approach provides a particularly efficient approach for improving detection accuracy when using balanced detection coils.

[0030] This approach reduces the risk of false foreign object detection in foreign object detection approaches that use balanced detection coils in many embodiments and scenarios, and in many embodiments, this approach allows for distinguishing between imbalances caused by foreign objects and imbalances caused by other events, such as movement of the receiving equipment / device.

[0031] The foreign object detection time of the repetitive time frame is specifically Reference and / or fluctuating (e.g. AC) supply voltage to the driver output stage. Amplitude It is timed to coincide with / include / synchronize with a zero crossing.

[0032] In many embodiments, the duration of the foreign object detection time is less than or equal to 5%, 10%, or 20% of the duration of the time frame. In many embodiments, the duration of the foreign object detection time is greater than or equal to 70%, 80%, or 90% of the time frame. The duration of the foreign object detection time is less than or equal to 5 ms, 10 ms, or 50 ms in many scenarios.

[0033] The detector coils are balanced in that they are configured such that the signals induced in the two detector coils by the electromagnetic field generated by the sending coil compensate each other. The combined voltage across the two balanced detector coils is less than the maximum of the respective voltages of the two balanced detector coils. The compensation is at least a partial cancellation of the two signals.

[0034] An electromagnetic test signal is also called a test field, and the terms are considered synonymous.

[0035] The imbalance between the signals induced in the two detector coils of a balanced detector coil set is the imbalance between the signals induced in the two detector coils by the electromagnetic test signal. Introduced into The signal imbalance is the imbalance between the signals induced in the two detector coils by the electromagnetic field generated by the sending coil. The set of balanced detector coils is not driven. The set of balanced detector coils is coupled to provide a net electrical energy output.

[0036] The transmitter is configured to supply no power / energy to the set of balanced detection coils. The set of balanced detection coils is coupled to receive energy only by induction. The only current flowing through the set of balanced detection coils is the current caused by induction.

[0037] The threshold number is less than or equal to the number of sets in the multiple sets of balanced detection coils. In many embodiments, the threshold number is less than or equal to one less than the number of sets in the multiple sets of balanced detection coils.

[0038] The detection coils as a set of balanced detection coils are coupled in series. When the detection coils / windings are coupled in series, the currents through them are identical.

[0039] In some embodiments, the frequency of the drive signal during the foreign object detection time is at least 50% higher than the frequency of the drive signal during the power transfer time.

[0040] This provides improved and / or facilitated foreign object detection in many embodiments, particularly as it reduces the effects of loading imposed by the receiver load resulting in detuning (e.g., resonant loading). Reducing the effects of loading results in more accurate foreign object detection in many embodiments.

[0041] In some embodiments, the frequency of the drive signal during the foreign object detection time is 100% higher, and in some cases 200% or more higher, than the frequency of the drive signal during the power transfer time.

[0042] In some embodiments, the voltage amplitude of the drive signal during the foreign object detection time is less than or equal to 50% of the voltage amplitude of the drive signal during the power transfer time.

[0043] This provides improved and / or facilitated foreign object detection in many embodiments, particularly reducing the effects of loading imposed by the receiver load resulting in detuning (e.g., resonant loading). Reducing the effects of loading results in more accurate foreign object detection in many embodiments.

[0044] In some embodiments, the voltage amplitude of the drive signal during the foreign object detection time is less than or equal to 25% or 10% of the voltage amplitude of the drive signal during the power transfer time.

[0045] In some embodiments, the voltage amplitude of the drive signal during the foreign object detection time is substantially constant.

[0046] This provides for improved and / or facilitated foreign object detection in many embodiments.

[0047] Each set of balanced detection coils includes two detection coils configured such that signals induced in the two detection coils by the electromagnetic field and signals generated by the sending coil offset / compensate / at least partially cancel each other in the signals from the balanced detection coil set.

[0048] A signal from a set of balanced detection coils is specifically a combined signal of induced signals from detection coils of the set of detection coils. The signal is a combined / summed voltage of the voltages induced in each detection coil (or includes such voltage contributions). Any imbalance between the signals induced in two detection coils of a given set of detection coils is indicated by the voltage of the signal, specifically the voltage amplitude and / or phase.

[0049] According to an optional feature of the invention, the threshold number is greater than or equal to three.

[0050] This provides particularly advantageous performance in many embodiments, particularly in many embodiments and scenarios where the cause of the first requirement may be a foreign object. and The receiver has been moved Make the distinction between the possibility of .

[0051] According to an optional feature of the invention, the threshold number is equal to the number of sets of balanced detection coils in the plurality of sets of balanced detection coils.

[0052] This provides particularly advantageous performance in many embodiments, particularly in many embodiments and scenarios where the cause of the first requirement may be a foreign object. and The receiver has been moved Make the distinction between the possibility of .

[0053] According to an optional feature of the invention, the power transmitter further comprises an adapter for adapting operating parameters of the power transmission in response to determining that the second requirement is met.

[0054] This provides particularly advantageous performance in many embodiments and scenarios. The operating parameters are, for example, power control loop parameters (e.g., loop gain, loop frequency response, or loop time constant), a maximum power limit of the power transmission signal, and / or a current power level of the power transmission signal.

[0055] According to an optional feature of the invention, the power transmitter further comprises an adapter for adapting operating parameters of the foreign object detection in response to determining that the second requirement is met.

[0056] This provides particularly advantageous performance in many embodiments and scenarios, and in many embodiments provides improved foreign object detection, and in particular more accurate foreign object detection, which typically has fewer false positives.

[0057] According to an optional feature of the invention, the operating parameter is a parameter of the first requirement.

[0058] This provides particularly advantageous performance in many embodiments and scenarios. In many embodiments, improved foreign object detection is provided, particularly more accurate foreign object detection, typically with fewer false positives. The operating parameter may be, for example, a first threshold value or may be part of a function / calculation / algorithm for determining an imbalance measurement that is compared to a threshold value, for example, from the signals of a set of detection coils.

[0059] According to an optional feature of the invention, the operating parameter is a parameter of the second requirement.

[0060] This provides particularly advantageous performance in many embodiments and scenarios. In many embodiments, improved foreign object detection is provided, particularly more accurate foreign object detection, typically with fewer false positives. The operating parameter may be, for example, a second threshold or may be part of a function / calculation / algorithm for determining an imbalance measurement that is compared to a threshold, for example, from the signals of a set of detection coils.

[0061] According to an optional feature of the invention, the transmitter further comprises a receiver for receiving data from the receiver, the data including physical characteristic data relating to a powered device comprising the receiver, for adapting operational parameters of the foreign object detection in response to the physical characteristic data.

[0062] This provides particularly advantageous performance in many embodiments and scenarios. In many embodiments, improved foreign object detection is provided, and in particular more accurate foreign object detection, typically with fewer false positives. The physical property data is indicative of a wide range of physical properties of the device that comprises the receiver. The physical property data may, for example, be indicative of size parameters and / or metal content parameters of the device.

[0063] The operating parameter is a parameter of the first requirement, e.g., a first threshold value or part of a function / calculation / algorithm for determining an imbalance measurement that is compared to a threshold value, e.g., from the signals of a set of detection coils.

[0064] According to an optional feature of the invention, the operating parameter is a parameter of the second requirement.

[0065] This provides particularly advantageous performance in many embodiments and scenarios. In many embodiments, improved foreign object detection is provided, particularly more accurate foreign object detection, typically with fewer false positives. The operating parameter may be, for example, a second threshold or may be part of a function / calculation / algorithm for determining an imbalance measurement that is compared to a threshold, for example, from the signals of a set of detection coils.

[0066] According to an optional feature of the invention, the transmitter further comprises a compensator that compensates signals from at least one set of balanced detection coils for an imbalance between the signals induced in the two detection coils when no foreign object is present.

[0067] This provides particularly advantageous performance in many embodiments and scenarios, and in particular provides improved foreign object detection in many embodiments.

[0068] The compensator is configured to determine a first signal from the first set of balanced detection coils when a foreign object is deemed not present, then determine a compensation signal that when combined with the first signal reduces the first signal, the compensation signal is combined with the first signal, and the combined signal is used to evaluate the first and second requirements of the foreign object detection criteria for the first set of balanced detection coils.

[0069] The compensation signal is generated to provide an offset / at least partial cancellation of the combined voltage from the detection coils of the set of balanced detection coils when no foreign object is present. The compensator is configured to adapt / compensate / alter a parameter of the drive signal, the parameter being at least one of a voltage amplitude and a phase of the drive signal.

[0070] According to an optional feature of the invention, the compensator initiates adaptation of the compensation in response to the second requirement being met.

[0071] This provides particularly advantageous performance in many embodiments and scenarios, and in particular provides improved foreign object detection in many embodiments, which allows for improved adaptation to current conditions and operating scenarios.

[0072] According to an optional feature of the invention, the compensator reduces a power level of the power transfer signal in response to detecting that compensation requires a compensation value that meets the criterion.

[0073] According to an optional feature of the invention, the transmitter further comprises an adapter for adapting operating parameters of the power transmission for at least two sets of balanced detection coils among the plurality of sets of balanced detection coils in response to an imbalance between signals induced in the two detection coils of the set of balanced detection coils.

[0074] According to an optional feature of the invention, the transmitter further comprises circuitry for generating a position change indication in response to determining that the second requirement is met, the position change indication being indicative of a change in position of the receiver.

[0075] According to an optional feature of the invention, the foreign object detection criteria includes a third requirement that the signal from at least one of the multiple sets of balanced detection coils indicates that an imbalance between the signals induced in the two detection coils of the at least one set of the multiple sets of balanced detection coils does not exceed a second threshold, the second threshold being greater than the first threshold.

[0076] This allows for improved foreign object detection performance, and in particular for reducing false positives in foreign object detection. In many embodiments, the second threshold is 2x, 3x, 5x, or 10x or more than the first threshold.

[0077] According to another aspect of the invention, there is provided a method of operating a power transmitter that wirelessly supplies power to a power receiver via an inductive power transmission signal, the power transmitter including a transmitting coil, a plurality of sets of balanced detection coils coupled in series, each set of balanced detection coils including two detection coils, where signals induced in the two detection coils by an electromagnetic field generated by the transmitting coil compensate each other, and a foreign object detector coupled to the plurality of sets of balanced detection coils, the method including: generating a drive signal for the transmitting coil to generate the inductive power transmission signal during at least one power transfer time of a recurring time frame; and generating a drive signal for the transmitting coil to generate an electromagnetic test signal during at least one foreign object detection time of the recurring time frame. and performing foreign object detection during a foreign object detection time, the detection of the foreign object being responsive to signals from the multiple sets of balanced detection coils satisfying a foreign object detection criterion, the foreign object detection criterion including a first requirement that a signal from at least one of the multiple sets of balanced detection coils indicates that an imbalance between signals induced in two detection coils of the at least one set of the multiple sets of balanced detection coils exceeds a first threshold, and a second requirement that a number of signals from the multiple sets of balanced detection coils indicating that an imbalance between signals induced in two detection coils of the at least one set of the multiple sets of balanced detection coils exceeds a second threshold is less than a threshold number, the threshold number being at least two.

[0078] These and other aspects, features and advantages of the invention will be elucidated and elucidated with reference to the embodiment(s) described hereinafter.

[0079] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which: [Brief description of the drawings]

[0080] [Figure 1] FIG. 2 illustrates an example of elements of a power transfer system according to some embodiments of the present invention. [Diagram 2]FIG. 2 illustrates an example of elements of a transmitter according to some embodiments of the present invention. [Diagram 3] FIG. 1 illustrates an example of a half-bridge inverter for a power transmitter. [Figure 4] FIG. 1 illustrates an example of a full bridge inverter for a power transmitter. [Diagram 5] 2 is a diagram illustrating an example of a time frame for the wireless power transmission system of FIG. 1. [Figure 6] FIG. 2 illustrates an example of a sensing coil for a transmitter according to some embodiments of the present invention. [Figure 7] FIG. 2 illustrates an example of an electromagnetic field and detection coil for a transmitter according to some embodiments of the present invention. [Figure 8] FIG. 2 illustrates an example of a drive signal for a transmitter according to some embodiments of the present invention. [Figure 9] FIG. 2 illustrates an example of a drive signal for a transmitter according to some embodiments of the present invention. [Figure 10] FIG. 2 illustrates an example of elements of a transmitter according to some embodiments of the present invention. [Figure 11] FIG. 2 illustrates an example of a sensing coil for a transmitter according to some embodiments of the present invention. [Figure 12] FIG. 2 illustrates an example of a sensing coil for a transmitter according to some embodiments of the present invention. [Figure 13] FIG. 2 illustrates an example of sensing coils for a receiver and transmitter according to some embodiments of the present invention. [Figure 14] FIG. 2 illustrates an example of sensing coils for a receiver and transmitter according to some embodiments of the present invention. [Figure 15] FIG. 2 illustrates an example of sensing coils for a receiver and transmitter according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0081] The following description focuses on embodiments of the invention that are applicable to wireless power transfer systems that utilize power transfer techniques as known from the Qi or Ki specifications, but it will be appreciated that the invention is not limited to this application and may be applied to many other wireless power transfer systems.

[0082] 1 illustrates an example of a power transfer system according to some embodiments of the present invention. The power transfer system comprises a transmitter 101 including (or coupled to) a transmitting coil / inductor 103. The system further comprises a receiver 105 including (or coupled to) a receiving coil / inductor 107.

[0083] The system provides an electromagnetic power transmission signal that inductively transmits power from the transmitter 101 to the receiver 105. Specifically, the transmitter 101 generates an electromagnetic signal that is propagated as a magnetic flux by a transmitting coil or inductor 103. The power transmission signal typically has a frequency of about 20 kHz to about 500 kHz, often typically in the range of 95 kHz to 205 kHz for Qi-enabled systems, or typically in the range of 20 kHz to 80 kHz for Ki-enabled systems. The transmitting coil 103 and the receiving coil 107 are loosely coupled, such that the receiving coil 107 picks up (at least a portion of) the power transmission signal from the transmitter 101. Thus, the power transmission signal from the transmitting coil 103 to the receiving coil 107 is Wireless Induction Via coupling, power is transmitted from the transmitter 101 to the receiver 105. It will be understood that the term power transmission signal is primarily used to refer to the induction signal / magnetic field (magnetic flux signal) between the transmitting coil 103 and the receiving coil 107, but is equally taken to refer to and used to refer to electrical signals provided to the transmitting coil 103 or picked up by the receiving coil 107.

[0084] In this example, the receiver 105 is specifically a receiver that receives power via a receiving coil 107. However, in other embodiments, the receiver 105 includes a metallic element, such as a metal heating element, in which case the power transmission signal directly induces eddy currents that result in direct heating of the metallic element.

[0085] The system is configured to transmit significant power levels, and specifically, in many embodiments, the transmitter supports power levels of 500 mW, 1 W, 5 W, 50 W, 100 W, or greater than 500 W. For example, for Qi-enabled applications, power transmission is typically in the range of 1-5 W power for low power applications (basic power profile), up to 15 W for Qi specification version 1.2, up to 100 W for high power applications such as power tools, laptops, drones, and robots, and greater than 100 W, up to greater than 2000 W for very high power applications such as, for example, Qi kitchen applications.

[0086] The operation of the transmitter 101 and receiver 105 is described below with specific reference to embodiments that generally conform to the Qi or Ki specifications (except for modifications and enhancements described (or resulting from) herein) or are suitable for the High Power Kitchen specification being developed by the Wireless Power Consortium. In particular, the transmitter 101 and receiver 105 conform to or are substantially compatible with elements of the Qi specification, versions 1.0, 1.1, or 1.2 (except for modifications and enhancements described (or resulting from) herein).

[0087] In a wireless power transfer system, the presence of objects (typically conductive elements that extract power from the power transfer signal and are not part of the transmitter 101 or receiver 105, i.e., unintended, undesired, and / or interfering elements with respect to the power transfer) is highly detrimental during power transfer. Such undesired objects are referred to in the art as foreign objects.

[0088] Foreign objects not only reduce efficiency by adding power losses to the operation, but also degrade the power transfer operation itself (e.g., by interfering with the power transfer efficiency or by extracting power that is not directly controlled, for example, by the power transfer loop.) Furthermore, the induction of currents in the foreign object (specifically, eddy currents in the metallic parts of the foreign object) often results in heating of the foreign object, which is highly undesirable.

[0089] To address such scenarios, wireless power transfer systems such as Qi or Ki include a foreign object detection feature. Specifically, the transmitter is equipped with a feature that attempts to detect whether a foreign object is present. If a presence is detected, the transmitter may, for example, terminate power transfer or reduce the maximum amount of power that can be transferred.

[0090] Foreign object detection is performed before the receiver enters the power transfer phase (e.g., during the initial setup of power transfer) or during the power transfer phase. Detection during the power transfer phase is often based on a comparison of measured transmitted and received power, while detection performed before the power transfer phase is often based on measuring the reflected impedance, for example by measuring the quality factor of the transmitting coil using a small measurement signal.

[0091] Current methods proposed by the Qi specification are based on detecting power loss (by comparing the transmitted power with the reported received power) or detecting a degradation in the quality Q of the output resonant circuit. However, these currently used methods have been found to provide suboptimal performance in many situations, in particular leading to inaccurate detection, resulting in missed detection of foreign objects, and / or false positives where a foreign object is detected when none is present.

[0092] Conventional foreign object detection tends to be suboptimal due in part to variations and uncertainties in the particular operating conditions and scenarios in which foreign object detection is performed, including variations and uncertainties in transmitter characteristics, receiver characteristics, applied test conditions, etc.

[0093] One example of a challenge in foreign object detection testing is the need to perform sufficiently accurate measurements to achieve sufficiently reliable foreign object detection. This leads to the desire to generate as strong a signal as possible to increase detection accuracy. However, generating a strong signal increases power consumption in the receiver and in any foreign object present. Detection performance is sensitive to the particular signal level applied, and there are usually conflicting requirements.

[0094] The system of Figure 1 employs a foreign object detection technique that aims to improve upon tradeoffs in foreign object detection, which in many embodiments provides improved foreign object detection, and in particular, in many embodiments, provides more accurate and / or reliable foreign object detection, and furthermore, which can have low complexity and resource requirements.

[0095] As described in more detail below, this approach utilizes a time-multiplexing approach during the power transfer phase: foreign object detection and power transfer are performed, for example, at separate times, which can significantly reduce interference between them (in particular, the effect of power transfer on foreign object detection).

[0096] The system of Figure 1 is described in more detail below. In this example, Electromagnetic power transmission signals and electromagnetic test signals used for foreign object detection are generated by the same coil, and the signals / fields are referred to by different terms, i.e., the electromagnetic signal / field generated during the power transfer time is referred to as the power transfer signal, and the electromagnetic signal / field generated during the foreign object detection time is referred to as the electromagnetic test signal, or simply the test signal.

[0097] FIG. 2 shows elements of the transmitter 101 of FIG. 1 in greater detail.

[0098] The transmitter 101 includes a driver 201 capable of generating a drive signal that is provided to the transmitting coil 103, which in turn generates an electromagnetic power transfer signal to provide power transfer to the receiver 105. The power transfer signal is provided during a power transfer time of a power transfer phase.

[0099] The driver 201 generates the current and voltage supplied to the transmitting inductor 103. The driver 201 is typically a drive circuit in the form of an inverter that generates an AC signal from a DC voltage. The output of the driver 201 is typically a switch bridge, generating the drive signal by appropriate switching of the switches of the switch bridge. Figure 3 shows a half-bridge switch bridge / inverter. Switches S1 and S2 are controlled so that they are not closed at the same time. Alternately, S1 is closed while S2 is open and S2 is closed while S1 is open. The switches open and close at a desired frequency, thereby generating an AC signal at the output. Typically, the output of the inverter is connected to the transmitting inductor via a resonant capacitor. Figure 4 shows a full-bridge switch bridge / inverter. Switches S1 and S2 are controlled so that they are not closed at the same time. Switches S3 and S4 are controlled so that they are not closed at the same time. Alternately, switches S1 and S4 are closed while S2 and S3 are open and S2 and S3 are closed while S1 and S4 are open, thereby generating a square wave signal at the output. The switches open and close at a desired frequency.

[0100] The transmitter 101 further comprises a transmitter controller 203 configured to control operation of the transmitter 101 in accordance with a desired operating principle. In particular, the transmitter 101 includes many of the functions necessary to perform power control in accordance with the Qi or Ki specifications.

[0101] The transmitter controller 203 is configured, among other things, to control the generation of the drive signal by the driver 201 and, in particular, may control the power level of the drive signal and thus the level of the generated power transmission signal. The transmitter controller 203 comprises a power loop controller that controls the power level of the power transmission signal in response to power control messages received from the receiver 105 during a power control phase.

[0102] The system of Figure 1 employs a foreign object detection technique that aims to adapt operations to improve foreign object detection tradeoffs. This technique, in many embodiments, provides improved foreign object detection, and in particular, in many embodiments, provides more accurate and / or reliable foreign object detection. Furthermore, this technique can have low complexity and resource requirements.

[0103] In this example, the driver 201 and the transmitting coil 103 are configured to generate both an electromagnetic power transmission signal for transmitting power to the receiver and an electromagnetic test signal used for foreign object detection. The transmitter uses a repeating time frame for the drive signal during the power transmission phase, the time frame including at least one power transmission time and one foreign object detection time. An example of such a repeating time frame is shown in FIG. 5. The power transmission time is indicated by PT and the foreign object detection time is indicated by D. In this example, each time frame FRM includes only one foreign object detection time and one power transmission time, both of which (and the time frame itself) have the same duration in each frame. However, it will be understood that in other embodiments, other times (e.g., communication intervals, etc.) are also included in the time frame, or multiple foreign object detection times and / or power transmission times are included in each time frame. Furthermore, in some embodiments, different time frames may be included in the time frame. (and indeed the time frame itself) duration Dynamically changes.

[0104] In this manner, this approach separates foreign object detection and power transfer in the time domain, thereby reducing the mutual interference from power transfer to foreign object detection, and therefore the variability and uncertainty due to variations in the operating conditions of power transfer can be isolated from foreign object detection, resulting in more reliable and accurate foreign object detection.

[0105] Thus, in the power transfer phase, the transmitter is configured to perform power transfer during the power transfer times of the time frame. In particular, during these times the transmitter 101 and the receiver 105 run a power control loop (based on communication during the power transfer times or based on communication outside the power transfer times, e.g. during dedicated communication times). For example, each foreign object time is separated by a number of alternating power transfer times and communication times. Thus, the level of the transmitted power changes dynamically. In the foreign object detection time of the time frame of the power transfer phase, typically at least one parameter of the drive signal, and therefore at least one parameter of the electromagnetic test signal, is set to a predefined value or to a value determined, for example, during an adaptation operation performed before the foreign object detection time. Thus, in the foreign object detection time, the parameter is set to a predefined value (i.e. a value determined before the foreign object detection time, often a value determined before the power transfer phase). In contrast, during the power transfer time, the parameter is not constrained to this predefined value.

[0106] For example, during the power transfer time, the system operates a power control loop that allows changing the power level of the power transmission signal in response to a power control message from the receiver. The power control loop controls / changes at least one of the current, voltage and frequency of the drive signal / power transmission signal. In contrast, the parameters changed by the power control loop during the power transfer time are set to predefined values ​​of current, voltage and / or frequency determined before the power transfer phase during the foreign object detection time.

[0107] In many embodiments, the drive signal is set to a constant (usually lower) amplitude (usually voltage) during the foreign object detection time. Additionally or alternatively, the drive signal during the foreign object detection time is set to a predetermined frequency, which is typically significantly higher than the drive signal during the power transfer time.

[0108] As a result, the power transmission signal, which is the electromagnetic signal generated during the power transfer time, typically has significantly different characteristics than the electromagnetic test signal, which is the electromagnetic signal generated during the foreign object detection time. The electromagnetic signal or field generated during the power transfer time is referred to as the power transmission signal, and the electromagnetic signal or field generated during the foreign object detection time is referred to as the electromagnetic test signal, or simply the test signal. However, it will be appreciated that in the system of FIG. 2, the electromagnetic signal is generated from the same coil during both the power transfer time and the foreign object detection time, and indeed the same driver, etc. is used during both the power transfer time and the foreign object detection time. Indeed, in many embodiments, reference to the test signal is considered equivalent to the power transmission signal during the foreign object detection time.

[0109] The transmitter 101 comprises a foreign object detector 205 configured to perform a foreign object detection test, i.e., in particular to detect whether there may be an undesirable conductive element in the generated electromagnetic field.

[0110] Thus, during the interval during which foreign object detection is performed, i.e., during the foreign object detection time, the foreign object detector 205 evaluates conditions to determine whether a foreign object is believed to be present. During the foreign object detection time, the transmitter 101 generates an electromagnetic test signal and foreign object detection is based on an evaluation of the features and characteristics of this signal.

[0111] In this system, foreign object detection is based on detecting a signal in a set of balanced detection coils induced by an electromagnetic test signal. The set of balanced detection coils includes at least two detection coils 207, 209 configured to negatively offset each other in the presence of a uniform magnetic field and an electromagnetic field generated by the sending coil 103, e.g., specifically in the presence of an electromagnetic test signal. Specifically, the transmitter includes a first detection coil 207 and a second detection coil 209 coupled such that the electromagnetic fields generated by the sending coil (at least partially) compensate each other. Has a set of balanced detection coils . A set of balanced detection coils is also called inductively balanced.

[0112] In the following, we first focus on operation for a single induction balance, i.e., for a single set of balanced detection coils as shown, for example, in FIG. 6. In the case of a set of balanced detection coils, the electromagnetic field generated by the sending coil 103 induces a signal in the first detection coil 207 and induces a signal in the second detection coil 209. However, since the induced voltages have opposite polarity to each other, the result is that the voltage (amplitude) of the series combination of the detection coils 207, 209 due to the electromagnetic field generated by the sending coil 103 is lower than at least the largest, and typically any, of the individual detection coils 207, 209 due to the electromagnetic field generated by the sending coil 103. Thus, the first detection coil 207 and the second detection coil 209 are coupled such that the induced voltages from the electromagnetic field generated by the sending coil 103 at least partially cancel each other out.

[0113] The detection coils are configured to correspond to at least two windings for which an opposite signal is generated by the electromagnetic test signal in the absence of a foreign object. The opposite signals therefore at least partially cancel each other out, and thus the level of the measured induced signal across the series combination of the detection coils 207, 209 is reduced, and in some cases substantially cancelled out. This allows for a significant increase in the magnetic field strength used for foreign object detection. In practice, in many embodiments and scenarios, the resulting induced voltage is (ideally) due solely to the difference in magnetic flux between the windings. Such a difference or asymmetry between the windings is due to the foreign object, and therefore in many scenarios the effect of the foreign object on the magnetic field (and therefore the induced signal) can be more accurately measured.

[0114] An example of a detector coil configuration is shown in FIG. 6. In this example, the first detector coil 207 is formed as a first winding L1 and the second detector coil 209 is formed as a second winding L2 coupled in (anti-)series. Thus, the composite voltages of the two windings are offset from each other with respect to a uniform electromagnetic field. In this example, the detector coils 207, 209 / windings L1, L2 are arranged symmetrically opposite each other with respect to a center point. Furthermore, these detector coils are formed in a plane, and the sending coil 103 is also formed in the same plane (or at least a substantially parallel plane). In this example, the detector coil 213 is formed inside the sending coil 103. Furthermore, the detector coils 213 are formed to have substantially the same outer shape and to cover substantially the same area.

[0115] As a result, the light passes through the two detection coils 213. electric The magnetic fluxes are substantially the same but in opposite directions. As a result, the induced voltages in the two sense coils 207, 209 are substantially the same but have opposite phase / polarity, and the combined voltage of the two series-coupled sense coils 213 cancels out and is substantially zero.

[0116] Thus, the sensing coils 207, 209 are configured such that in the presence of a uniform field and / or in the presence of an electromagnetic field generated by the sending coil 103 in the absence of other objects, the induced signals / voltages at least partially cancel / compensate each other, ideally resulting in a composite voltage of zero.

[0117] 2 and 6 are such that the induced signal in the first of the two detector coils has an opposite voltage to the induced signal in the second of the two detector coils. The induced signals in the two detector coils have opposite phases relative to a uniform magnetic field. The induced signals in the two detector coils have opposite phases. The two detector coils are coupled in series and in antiphase such that the induced signals have opposite polarities. These properties exist for a uniform field and for an undistorted field generated by the sending coil 103.

[0118] However, in the presence of a metallic foreign object, the magnetic field is distorted, which usually results in an asymmetry between the magnetic fields of the two detection coils 207, 209. Usually, in the case of a metallic foreign object, the generated electromagnetic test signal induces eddy currents, so that the foreign object generates an electromagnetic field such that the combined electromagnetic field is distorted compared to the electromagnetic field of the generated electromagnetic test signal. The generated asymmetric electromagnetic field induces different signals in the first detection coil 207 and the second detection coil 209, as shown in FIG. 7. Thus, in contrast to the situation in which no foreign object is present and the magnetic flux through the two detection coils 207, 209 is symmetrical, resulting in a composite voltage that is substantially zero, the presence of the foreign object results in an asymmetry and therefore a voltage. This difference in the induced signals of the two detection coils 207, 209 can be used to detect the presence of a foreign object.

[0119] In the system of Figure 2, the combined voltage of the pair of detection coils 207, 209 is measured directly and used to perform foreign object detection. In some embodiments, a more complex approach is used, such as coupling the detection coils in series with a transformer such that the current through the detection coils 207, 209 also flows through the primary winding of the transformer. Thus, the detection coils 207, 209 and the primary winding are part of a series circuit through which the current induced in the detection coils 207, 209 flows. The secondary winding is then coupled to the foreign object detector 205, e.g., the current through the secondary winding is measured and used as a measure of the imbalance between the induced signals in the two detection coils 207, 209.

[0120] The imbalance indicated by the signal from the inductive balance, specifically the output voltage, is used as an indication that a foreign object is present; specifically, if the signal from the set of balanced detection coils meets a criterion, for example that the absolute value exceeds a detection threshold, this is considered to be an indication that a foreign object is present.

[0121] This approach therefore implements foreign object detection utilizing a set of balanced detection coils 207, 209. In a particular example, the two detection coils 207, 209 are positioned opposite each other in the same magnetic plane as the sending coil 103. When such an inductive balance is exposed to a symmetric detection electromagnetic field generated by the sending coil 103, the voltage at the terminals of the detection coils 207, 209 will be substantially zero in the theoretical ideal case.

[0122] If a metal piece is placed on one side of the inductive balance, as in Figure 7, the density of the detected electromagnetic test signal / field will not be symmetrical and a voltage can be measured at the terminals of the inductive balance.

[0123] In this approach, a signal is induced in each detection coil, and in the case of a uniform magnetic field (as is typically the case when no foreign object is present), the balanced detection coils substantially compensate each other. The outputs of the detection coils 207, 209 are coupled to the foreign object detector 205. Thus, a signal is induced in the detection coils 207, 209 (by the electromagnetic field generated by the sending coil), and the resulting (difference) induced signal across the outputs of the balanced detection coils 207, 209 is provided to the foreign object detector 205. The resulting signal is then evaluated by the foreign object detector 205. Thus, the signal evaluated by the foreign object detector 205 is representative of the signals induced in the detection coils 207, 209, specifically the compensated difference / sum induced signal.

[0124] The foreign object detector is configured to detect a foreign object in response to a characteristic of the induction signal from the induction balance satisfying a foreign object detection criterion.

[0125] As mentioned above, the transmitter The drive signal is configured to be controlled to exhibit different parameters during a foreign object detection time and during a power transfer time. This is used, among other things, to reduce the loading effect and influence on the electromagnetic test signal by the receiver.

[0126] For this purpose, it has been proposed to disconnect the load of the receiver during the short foreign object detection time, for example by implementing the receiver with a switch that is actively opened. However, for higher power levels in the kW range, this solution is not ideal, since the disconnect switch would cause additional losses and increase costs. Indeed, in some high-power applications, it is simply not possible to implement such switching, for example when the load is an inductively heated metal element in which eddy currents are directly induced by the power transmission signal to cause heating.

[0127] Adaptation of the parameters of the drive signal during the foreign object detection time relative to the power transfer time is used to address this and mitigate the effect of receiver loading on foreign object detection.

[0128] In many embodiments, the driver 201 is configured to increase the frequency of the drive signal during the foreign object detection time compared to during the power transfer time, and in particular to set the drive signal frequency to be 50% or more higher than the frequency of the drive signal during the power transfer time. Thus, the driver 201 generates the electromagnetic test signal to have a significantly higher frequency than the power transfer signal.

[0129] In many scenarios, a significant increase in frequency improves detection and reduces the effect of the receiver load. For example, both the transmitter and receiver have resonant circuits formed for power transfer, e.g., the transmitter coil 103 and receiver coil 107 are both part of a resonant circuit with, e.g., a resonant frequency fres=25 kHz. Increasing the drive frequency (e.g., to 50 kHz) during the foreign object detection time causes the transmitter resonant circuit to operate in inductive mode, reducing the current in the transmitter coil 103. Furthermore, the receiver coil current also decreases, since the system is no longer tuned. This further reduces the transmitter current. The overall effect corresponds to that resulting from a partially disconnected load.

[0130] In many embodiments, the driver 201 is configured to reduce the voltage of the drive signal during the foreign object detection time relative to the power transfer time, and specifically, sets the voltage amplitude of the drive signal during the foreign object detection time to be 50% (or often 25%, and sometimes 10%) or less of the voltage amplitude of the drive signal during the power transfer time.

[0131] The reduced voltage generates a lower strength electromagnetic test signal, and thus the electromagnetic field generated during the foreign object detection time is lower than during the power transfer time, with a corresponding reduction in the load applied by the load. This allows for improved detection in many scenarios. In some embodiments, the reduced voltage is advantageous because it results in disconnection of the receiver load. For example, when the voltage drops to a certain level, a receiver that includes a rectifier and a battery does not have enough induced voltage for the rectifier to conduct, so the receiver is powered by a battery. This effectively disconnects the load from the electromagnetic test signal, improving foreign object detection performance.

[0132] In many embodiments, the driver 201 is configured to set the voltage amplitude of the drive signal constant during the foreign object detection time, resulting in a more uniform electromagnetic test signal, which improves foreign object detection based on the balanced detection coils 207, 209. For example, if the voltage amplitude varies over time, the detection signal will vary and detection accuracy will decrease unless this variation can be compensated for or taken into account.

[0133] In many embodiments, the driver 201 is configured to generate a drive signal during foreign object detection times that has a constant voltage amplitude that is at least 50% lower and a frequency that is at least 50% higher than the drive signal during power transfer times.

[0134] As an example, to transfer wireless power with high efficiency during the power transfer time, the drive signal is generated at a first operating frequency close to the resonant frequency of both the transmitter and receiver.

[0135] During the foreign object detection time, the first operating frequency of the drive signal is moved away from the resonant frequency of both the transmitter and the receiver and changed to a second, higher operating frequency, which is fixed at a predetermined value that is at least 1.5 times higher than the first operating frequency, i.e., the frequency of the power transmission signal.

[0136] Furthermore, the drive signal voltage Uinv is changed to a constant second amplitude (eg, supplied by a different voltage source) that is lower than during the power transfer time.

[0137] By using a drive signal having a second, higher operating frequency and a second, lower, constant voltage amplitude, the current through the sending coil 103 is significantly reduced and kept constant. Furthermore, because the driver current lags the driver signal voltage, the inverter at the output of the driver 201 operates in a zero voltage switching scenario, thereby significantly reducing switching noise.

[0138] An example of the drive signal amplitude in such a scenario is shown in Figure 8, where operation during power transfer time is shown as Mode 1 and operation during foreign object detection time is shown as Mode 2. In this example, the voltage amplitude is constant during power transfer time, e.g., because the inverter is supplied from a constant voltage source.

[0139] FIG. 9 shows a corresponding example in which the voltage amplitude is changed during the power transfer time. This is achieved, for example, by the inverter being supplied by a rectified (but not smoothed) AC voltage. The supply voltage during the foreign object detection time, which is synchronized with the zero crossings of the AC signal, is supplied via an alternative power supply that provides a substantially constant voltage. An example of a circuit for generating such a drive signal is shown in FIG. 10. In this circuit, the output inverter circuit (M1, M2, Cp1, Cp2) is driven by the rectified AC mains voltage, except when the rectified voltage is below a given voltage (48V in this example) of the smoothing capacitor C3, which is supplied by a second supply circuit (2nd Udc). During this time, the inverter circuit is supplied by the smoothing capacitor C3 via D5, resulting in a substantially constant supply voltage and therefore a constant voltage amplitude of the drive signal.

[0140] In such an example, the transmitting coil 103 generates an electromagnetic test signal corresponding to a substantially constant electromagnetic field for foreign object detection during the foreign object detection time, the electromagnetic test signal having a predetermined higher second operating frequency. The amplitude of the foreign object detection electromagnetic field / electromagnetic test signal is determined primarily by the second lower output voltage of the driver 201. In this case, the unisolated load of the receiver is effectively detuned from the transmitter and therefore has less impact on the electromagnetic field / electromagnetic test signal.

[0141] In the particular system described, the transmitter is equipped with multiple inductive balance, i.e. multiple sets of balanced detection coils, and foreign object detection is performed based on the output signals from two or more of these sets of balanced detection coils. Typically, foreign object detection is based on a criterion that takes into account the signals from all of the sets of balanced detection coils.

[0142] For example, as shown in Figure 11, a transmitter can be created that includes three sets of balanced detection coils, each set including two wedge coils. In this example, foreign object detection is performed by measuring the output signal from each of the three balanced detection coil pairs and using these signals to perform foreign object detection. The exact criteria used will depend on the preferences and requirements of a particular implementation, as will be described in more detail below.

[0143] In many embodiments, as is indeed the case in the example of Fig. 11, the balanced detection coil is located within the sending coil 103. This typically improves performance, in particular providing a uniform electromagnetic test signal / field for the different coils.

[0144] 2, the outputs of all the inductive balance / balanced detection coil sets are fed to foreign object detector 205, which measures the signals from all the inductive balances. Foreign object detector 205 determines the voltage and / or current for each of the balanced detection coil sets during the foreign object detection time, e.g., typically the voltage of each set of balanced detection coils is determined and used for foreign object detection.

[0145] The foreign object detector 205 is configured to apply foreign object detection criteria to signals from the inductive balance during a foreign object detection time. Each of these signals is also referred to hereafter for brevity as a detection signal. The foreign object detection criteria include at least two requirements that must be met for the foreign object detector 205 to determine that a foreign object has been detected.

[0146] The first requirement is that at least one detection signal indicates that for at least one of the set of balanced detection coils, the imbalance between the signals induced in the two detection coils exceeds a first threshold. This requirement applies to each detection signal independently of the other detection signals. The first requirement requires that the detection signal from at least one inductive balance indicates an imbalance that exceeds a threshold. The imbalance is indicative of a difference between the signals induced in the detection coils of the inductive balance.

[0147] The first requirement is assessed by determining a detection value from the detection signal, the detection value being indicative of the degree of imbalance between the signals induced in the detection coils. In many embodiments, the amplitude of the current and / or voltage of the detection signal is indicative of the imbalance, with an increase in amplitude indicating increased imbalance. Thus, in many embodiments, the detection value is determined as the amplitude value of the detection signal. directly , or as a monotonically increasing function of the amplitude 、 A monotonically increasing function is generated as follows: Complex This may be a function of the amplitude of the detected signal, or may be a simple scaling or amplification, for example.

[0148] In many embodiments, the first requirement is simply that the amplitude of the detection signals from at least one set of balanced detection coils exceed a detection threshold. Thus, the first requirement is evaluated by considering each detection signal in isolation and comparing the imbalance indication provided by each detection signal to a threshold.

[0149] In many embodiments, the detection coils are identical and symmetric with respect to translation / rotation. They are typically also symmetric and identical with respect to the sending coil 103 and other properties of the power transfer setup. Typically, the same threshold is applied to all sets of balanced detection coils. However, in some embodiments, the detection threshold is a function of which set of balanced detection coils is being evaluated. Thus, in some embodiments, the detection threshold varies and differs for different detection coils to compensate for differences in the physical properties of the detection coils or their relationship to the sending coil 103 and the generated test signal.

[0150] Thus, in this approach, the foreign object detection criteria includes a first requirement that at least one set of balanced detection coils have an imbalance. As previously discussed, such an imbalance is caused by the presence of a foreign object, and thus satisfaction of the first requirement is a strong indicator that a foreign object is present.

[0151] However, in this approach, the foreign object detection criterion does not only include this requirement: foreign object detection is not deemed to have occurred just because one of the detection signals exhibits a (sufficiently) high imbalance, but in addition a second requirement needs to be met that considers the detection signals (or at least some of the detection signals) together.

[0152] In practice, the foreign object detection criteria include a second requirement that the number of signals from the set of balanced detection coils indicating that the imbalance between the signals induced in the two detection coils of the set of balanced detection coils exceeds a second threshold (hereinafter also referred to as the detection number for brevity) is less than a threshold number, the threshold number being at least two.

[0153] The second requirement involves evaluating how many of the detection signals indicate an imbalance greater than a second threshold. This determination is performed similarly to the first requirement, e.g., by comparing the signal amplitude to a threshold to determine whether the amplitude exceeds the threshold. Like the first requirement, the second requirement depends on which set of balanced detection coils is being evaluated and therefore varies from set to set.

[0154] The number of induced balances whose imbalance exceeds a threshold is determined, and the second requirement is met only if this number is less than the threshold number, i.e., if the number of induced balances whose imbalance indicates an imbalance exceeding a second threshold is less than the threshold number.

[0155] In many embodiments, the first threshold and the second threshold are the same, and the process of evaluating the first requirement teeth , data allowing the determination of the number of detections too Provide directly.

[0156] Thus, the number of detections is compared to a threshold number, and only if the number of detections is less than the threshold number is the second requirement, and therefore the foreign object detection criterion, met.

[0157] Thus, according to this approach, satisfaction of the first requirement is deemed to indicate that a foreign object has probably been detected, but this determination is overridden by the second requirement if the number of applicable inductive balances does not fall below the threshold number. In effect, a foreign object detection that would occur if one of the sets of balanced detection coils detects an imbalance is overridden if this is true for a sufficiently large set of balanced detection coils.

[0158] In many embodiments, the threshold number is greater than or equal to three, and / or the threshold number is equal to the number of sets of balanced detection coils in the multiple sets of balanced detection coils.

[0159] 11, where the transmitter has three inductive balances, the second requirement uses a threshold number of three, resulting in the foreign object detection indication obtained from evaluating each detection signal individually being invalid if all detection signals indicate a sufficiently high unbalance, in which case the foreign object detector 205 will not detect the presence of a foreign object.

[0160] This approach improves performance in many embodiments and scenarios and significantly reduces the number of foreign object false positives that may occur based on balanced detection. In particular, it has been recognized that in many scenarios, the effect of a foreign object on a set of balanced detection coils can be separated from other events or causes by considering not only the individual signals from the set of balanced detection coils but also how they relate to each other. Thus, by including more holistic / integral considerations, many foreign object false positives can be avoided. In particular, it has been recognized that this approach allows for a distinction between a scenario in which a foreign object is present and a scenario in which a device or equipment that includes or forms the receiver is moved relative to the transmitter (specifically the transmitting coil 103 and the detection coils).

[0161] In many embodiments, a particularly efficient operation is achieved by a threshold number equal to the number of sets of balanced detection coils. In some embodiments, the second requirement overrides the foreign object detection of the first requirement only if all detection signals indicate a sufficiently high imbalance. This allows for more reliable foreign object detection in some embodiments by further weighting the detection of the presence of a foreign object detection, i.e., by biasing the detection. The override is restricted to be triggered only when an object large enough to affect all inductive balance is present, i.e., smaller devices are considered foreign objects. Since the receiving device / device is not only present during power transfer but also near the transmitting coil 103 (specifically, typically at the center of this), it is unlikely that a foreign object will be positioned to substantially affect all sets of balanced detection coils, and it is very unlikely that an imbalance of all sets of balanced detection coils will be caused by anything other than the movement of the receiving device / device. Such constraints are further weighted by, for example, the geometric characteristics of the detection coils and the transmitting coil 103.

[0162] Similarly, using a threshold number of three provides some specific advantages over using a threshold number of two. Specifically, while it is possible or even likely that a foreign object may be positioned to cause an imbalance in two sets of balanced detection coils (e.g., if a foreign object is positioned across the area of ​​two detection coils of different sets of balanced detection coils), it is much less likely that a foreign object may be positioned to strongly affect three sets of balanced detection coils. Indeed, such a strong effect on three sets of balanced detection coils would typically require the foreign object to extend across three different detection coils, but considering the need for the presence of a power receiver to effect power transfer, in many applications it is highly unlikely (or even impossible) that a foreign object would extend across three different detection coils.

[0163] In some embodiments, the foreign object detection criteria are: A signal from at least one of the plurality of inductive balances indicating an imbalance exceeding a given first foreign object detection threshold does not exceed a second threshold.and a third requirement that the second threshold is higher than the first foreign object detection threshold, typically an amplitude threshold that is 2, 3, 5, or 10 times or more the first foreign object detection threshold. Thus, if the imbalance is greater than a predetermined level, a foreign object is deemed to be present unless the imbalance is large enough to exceed the second threshold.

[0164] Such techniques therefore detect foreign objects by the imbalance they cause in the inductive coupling, but if the imbalance is very large, it is more likely that the imbalance is caused by the receiver being moved than by the presence of a foreign object.

[0165] Thus, in this example, foreign object detection is defeated not only by the second requirement that the imbalance must not affect multiple induced balances, but also by the third requirement that the imbalance must not be too large.

[0166] For example, if the imbalance signal not only becomes greater than a first threshold, but the amplitude of the imbalance signal also becomes greater than a second, higher threshold, it is assumed that the imbalance is due to the receiver having been moved, resulting in, for example, recalibrating the foreign object detection for the receiver's new position, instead of generating a foreign object detection.

[0167] It will be appreciated that a foreign object detection approach in which the foreign object detection criteria include the third requirement but not the second requirement is feasible and will provide advantageous performance in many systems and in many scenarios.

[0168] 2 further comprises a compensator 211 configured to compensate the signals from one, multiple, typically all, of the sets of balanced detection coils for imbalances between the signals induced in the two detection coils when no foreign object is present. In some embodiments, the compensation is a static compensation, e.g., compensating for differences in geometric characteristics of different detection coils within the same set of balanced detection coils. However, in most embodiments, the compensator 211 is configured to perform dynamic compensation, in which the compensation values ​​are adapted during operation, e.g., when certain events occur.

[0169] In practice, the detection coils 207, 209 are created to be as identical as possible and are designed to cancel induced signals as much as possible. However, in practice, it has been found that even in the absence of foreign objects, there tends to be some asymmetry and differences in the parameters of the detection coils 207, 209, and possibly the electromagnetic environment. Also, in many scenarios, the asymmetry and imbalance will cause the combined voltage across the detection coils 207, 209 to be of the same order of magnitude as the voltage caused by any foreign object that is desired to be detected. Thus, in some embodiments, even with balanced inductance / detection coils, detection performance is difficult or not ideal.

[0170] The compensator 211 is configured to compensate the signal by measuring a value during a foreign object detection time when it is assumed that no foreign object is present, i.e., the signal resulting from the test signal is determined when it is assumed that no foreign object is present. This assumption is deemed to be true, for example, as indicated by a successful foreign object detection resulting in no foreign object detection, or, for example, in response to a specific user input being provided indicating that no foreign object is present. For example, a user presses a button to initialize a calibration / compensation measurement. In some cases, compensation measurements are performed when a new powered device is detected and when a user placing a new powered device on the power transmitter indicates that they have confirmed that no foreign object is present.

[0171] Based on the measured imbalance (reflecting the signals from the set of balanced detection coils when no foreign object is present), a compensation value is determined and applied to each signal. Typically, the compensation value is the inverse of the measured imbalance. For example, the voltage or current amplitude of the output signal from the set of balanced detection coils is measured when no foreign object is present. This measured amplitude is then subtracted from the measured amplitude of the signal from the set of balanced detection coils to produce compensated signal amplitudes. These compensated signal amplitudes, rather than the measured amplitude of the signals, are then used to evaluate the foreign object detection criteria.

[0172] Specifically, compensator 211 generates a compensation value (with opposite phase / polarity) that offsets the signal value from the set of balanced detection coils measured when no foreign object is (assumed to be) present.

[0173] In some embodiments, the compensation is not a single value, such as a compensation current or voltage amplitude, but rather a compensation signal, such as a compensation signal having the same amplitude as the measurement signal but opposite phase (thus canceling the unbalanced signal). For example, the compensation signal is generated to have the same frequency as the measurement signal (and thus the same as the electromagnetic test signal). The phase and / or amplitude are set to values ​​that provide the desired compensation.

[0174] In some embodiments, the phase and / or amplitude are pre-determined values. For example, during manufacture or design, the asymmetry between the detection coils for the generated electromagnetic test signal is estimated (based on theoretical analysis and / or measurements) and suitable compensating drive signal parameter values ​​are determined. These are then applied during the foreign object detection time.

[0175] However, in many embodiments, the compensation circuit 1103 is configured to dynamically adapt parameters of the compensation signal, in particular to adapt the voltage amplitude and / or phase of the compensation signal.

[0176] This compensation improves foreign object detection in many embodiments. Indeed, even if the detection coils 207, 209 are perfectly balanced and / or perfectly characterized during the manufacturing stage, the electromagnetic field, and therefore the induced signal, also tends to vary depending on the particular environment, specifically, for example, which powered device is being used and where exactly it is located. Therefore, if the compensation can be dynamically adapted, specifically, calibrated to the current electromagnetic environment, performance is significantly improved. Compensation is useful to mitigate or reduce the imbalance between the detection coils and / or the environment around the detection coils. This improves performance in many scenarios, and in particular makes foreign object detection more accurate.

[0177] As an example, consider the configuration of FIG. 12 for a system in which foreign object detection is based on measuring the voltage amplitude Ufod from a set of balanced detection coils each including two detection coils (L1, L2), (L3, L4), and (L5, L6).

[0178] In this example, before starting the power transfer, a dynamic calibration of the foreign object detection system is performed to compensate / remove the original offsets from the voltages Ufod(L1-L2), Ufod(L3-L4), and Ufod(L5-L6). These offset voltages are due to a non-uniform detected H-field. In this example, the windings of the transmitting coil 103 are not perfectly circularly symmetrically mounted on the former. In this example, the inductive balances L3-L4 and L5-L6 capture more or less the same uniform detected H-field. However, the magnetic field captured by the inductive balance L1-L2 is not uniform due to the local wiring layout of the transmitting coil 103 under coil L2. For this condition, an active calibration is applied by compensating the voltage Ufod(L1-L2) of the inductive balance L1-L2 with a signal Ucomp(L1-L2) having the correct amplitude and phase with respect to the voltage U_Tx.

[0179] 13 illustrates another source of offset voltage: if the receiving device / appliance 1301 is misaligned and placed over the transmitter active area, the detected H field from the transmitting coil 103 is expected to become more distorted and inhomogeneous, especially if the apparatus contains metal parts.

[0180] In this example, an active offset calibration is also performed. Due to the size of the device 1301 relative to the size of the active area, it is believed that the distribution of the detected H field from the sending coil 103 will be non-uniform over a large area, possibly even across the entire area. As a result, all three inductive balances are affected and generate signals with offsets. In this situation, three independent compensation voltages Ucomp(L1-L2), Ucomp(L3-L4), and Ucomp(L5-L6) are determined and applied to the three inductive balances, respectively, each with the correct amplitude and phase with respect to the voltage induced offset unbalance signal.

[0181] In the example of FIG. 14, a foreign object FO is placed on the active area after active calibration has been performed and compensation has been applied. Due to its location on the active area, the detected H field from the transmitting coil 103 is expected to be inhomogeneous near the inductive balances L1-L2 and L5-L6. As a result, a detected voltage appears at both terminals of these inductive balances, and the first requirement of the foreign object detection criterion is met. However, the foreign object is unlikely to cause an imbalance in the third inductive balance L3-L4, and if the threshold number is set to the number of inductive balances, i.e., 3, the second requirement is also met. Thus, the foreign object detector 205 determines that a foreign object has been detected. Thus, as shown, the triple inductive balance system is capable of detecting a foreign object even when there is a misaligned device above the active area.

[0182] In the example of FIG. 15, no foreign object is present, but the device 1301 has been moved from its original position on the active area. This displacement results in a change in the distribution of the detection field (i.e., the test field) of the sending coil 103 across the entire detection area. If the triple inductive balance system is properly calibrated before this displacement, the balance state of all three inductive balances will be affected and detection voltages will be generated for all three inductive balances. In this case, the first requirement for foreign object detection is met, and therefore a foreign object is present. Possible A first indication is triggered. However, the second requirement is not met because all three inductive balances show a significant imbalance / detection signal. Therefore, the first indication is overridden and the foreign object detector 205 does not generate a foreign object detection. This avoids false foreign object detection.

[0183] The compensator 211 is configured to update / adapt / calibrate the compensation at different times and in different situations depending on the preferences and requirements of a particular embodiment. In many embodiments, the compensator 211 is configured to start adapting the compensation when it is detected that a new receiving device has been placed on the transmitter. This allows the compensation to be adapted not only to static characteristics, but also to the position of the receiving device on the transmitter, for example.

[0184] In some embodiments, the compensator 211 is configured to initiate a compensation adaptation in response to the second requirement of the foreign object detection criterion being met. Thus, if an imbalance is detected with more than a threshold number of inductive balances, often for all inductive balances, the compensator 211 initiates a new adaptation of the compensation. In particular, new values ​​of the signals (e.g., voltage and / or current amplitude and phase) from the different inductive balances are measured and used as new compensation signals going forward.

[0185] As mentioned before, an imbalance that affects all inductive loads may be due to a change in the position of the receiver rather than due to the presence of a foreign object. Similarly, if the imbalance is very high (higher than the second threshold, i.e. the third criterion is met), this indicates that the receiver has moved rather than that a foreign object is present. Thus, the adaptation of the compensation can be adapted to the new position allowing a more accurate measurement of the imbalance that may be caused by the foreign object, thus improving foreign object detection.

[0186] In some embodiments, the compensator 211 is configured to adapt the power transfer corresponding to the adaptation of the compensation. In some embodiments, the compensator 211 is configured to reduce or suppress the power level of the power transfer signal in response to detecting that the compensation requires a compensation value that meets a criterion. The criterion specifically corresponds to a criterion that one or more of the determined compensation values ​​(specifically the amplitude) exceed a threshold. If the threshold is met, it indicates that at least one imbalance is higher than a given threshold. This may be due to the presence of a foreign object, and therefore the power level is reduced. In many scenarios, a large imbalance occurs due to the position of the power receiving device being significantly shifted from the ideal central position. This prevents the power transfer, reduces the efficiency, etc. The power level is reduced accordingly. This is often recognizable by the user or actually provides a dedicated user instruction, which often leads the user to change the position of the power receiving device.

[0187] In many embodiments, the reduction in power level is specifically the termination or prevention of power transfer. For example, during the initial setup of the power transfer, the compensator 211 determines that the compensation value is , exceeding the detection threshold for one or more induced equilibriaIf it is detected that an imbalance is present, the initialization is terminated and the compensator 211 prevents the transmitter from entering the power transfer phase. If the transmitter is already in the power transfer phase, it is terminated. Thus, the compensation value is used to detect whether the current operating conditions are acceptable, in particular whether the power receiving device is suitably positioned over the transmitter active area.

[0188] In some embodiments, the transmitter is configured to adapt an operating parameter in response to detecting that a condition of a second requirement of the foreign object detection criterion is satisfied.

[0189] The operating parameters are the operating parameters of the power transmission, such as the power level, the frequency, the duty cycle, the duration of the power transmission time, etc. In particular, the detection that the second requirement is met, as well as the detection that the compensation value determined when adapting the compensation indicates an unbalance, results in a reduction of the power level. For example, a maximum power level is used for the power transmission, and this maximum power level is reduced if the second requirement is met.

[0190] As mentioned above, the second requirement may indicate that the powered device has been moved and different operating conditions may arise. In this case, the foreign object detector 205 will reduce the power level to ensure safe and reliable operation, and may actually terminate power transfer in certain cases. The powered device then continues into an operating mode where full power transfer is gradually achieved by gradually adapting the system to the new operating conditions (e.g., slow power control operation is used, or a full reinitialization of power transfer is performed if the ongoing power transfer is terminated).

[0191] In some embodiments, the parameters that are adapted are operational parameters of the foreign object detection, specifically the first requirement, the second requirement, or both.

[0192] Adaptation of the compensation value when the second requirement is met is an example of such an adaptation, since application of the compensation value is part of the evaluation of both the first requirement and the second requirement (because both comparisons are based on the compensated signal value).

[0193] As another example, in many embodiments, when it is detected that the second criterion is met, the detection threshold used for the first requirement and / or the second requirement is adapted.

[0194] For example, in some embodiments, the foreign object detector 205 starts with a predefined value as the threshold for the first requirement. When power transfer is ongoing and no foreign object is detected, e.g., the detected unbalance value is significantly smaller than the predefined threshold, the threshold is gradually reduced to increase the sensitivity of detection to smaller foreign objects. However, if the second requirement is met, the threshold is returned to the predefined threshold to reflect the uncertainty of the exact conditions of the new location. The same approach is used for the second requirement.

[0195] In some embodiments, the requirement includes a calculation or processing of a signal value, and the foreign object detector 205 is configured to adapt the calculation or processing when a second requirement is met and thus a possible movement of the powered device is detected.

[0196] In some embodiments, the adapter 213 may be, more generally, an inductively balanced , in particular in response to an imbalance between signals induced in at least two inductively balanced sensing coils, The power transfer operating parameters may be adapted to adapt, for example, the adaption of the operating parameters may not necessarily be in response to the same detection used for foreign object detection, for example, in some embodiments, a different threshold value is applied to determine whether the adaptation of the foreign object detection operation is performed than is used for the actual foreign object detection evaluation.

[0197] In many embodiments, the adapter 213 is configured to adapt parameters of the power transfer such that the power level is reduced if a measured imbalance of the inductive balance exceeds a given level. The measured imbalance is determined, for example, as an average or sum of the imbalance, or a maximum value of the imbalance.

[0198] In some embodiments, the transmitter comprises a receiver 215 configured to receive data from the receiver. In such embodiments, the receiver is configured to transmit physical property data to the transmitter, the physical property data being indicative of one or more physical properties of the receiver, in particular global physical properties. For example, the physical property data may be indicative of the size, extent, dimensions, etc. of the power receiving device. Thus, the physical property data is indicative of the spatially global properties of the power receiving device. In some embodiments, the physical property data may alternatively or additionally be indicative of the spatial extent or the amount of, for example, conductive material (metal) that is part of the power receiving device.

[0199] In such an embodiment, the physical property data is provided to an adapter 213 configured to adapt operational parameters of the foreign object detection in response to the physical property data. The operational parameters are in particular parameters of the first requirement and / or parameters of the second requirement. The parameters are in particular parameters of a function or algorithm used to determine a detection threshold for the requirement and / or a value to be compared to the detection threshold.

[0200] This approach is particularly advantageous for meeting the second requirement. For example, for a small power receiving device, the movement of the device does not cause a large imbalance in all the induction balances. Furthermore, a small power receiving device may have a large foreign object and may therefore be placed in a position that may cause an imbalance in all the induction balances comparable to the imbalance caused by the misalignment of the power receiving device. In contrast, for a sufficiently large power receiving device, it may be guaranteed that the misalignment and movement will affect all the induction balances and that the device is so large that any foreign object is too small to significantly affect all the induction balances. In such a case, if the physical characteristic data indicates a power receiving device having a size less than a given predetermined size, the second requirement is switched off (for example, by setting the detection threshold to a value that cannot occur) and switched on for the physical characteristic data indicating a size larger than the predetermined size.

[0201] In some embodiments, the physical property data is additionally or alternatively used to adapt the compensation, for example, adapting the compensation to determine a compensation value is performed only if the physical property data indicates that the power receiving device contains more than a given amount of metal.

[0202] In some embodiments, the power controller 203 is configured to generate a position change indication in response to the second requirement being satisfied. As previously discussed, satisfaction of the second criterion is considered to be an indication that the powered equipment / device has likely moved rather than that a foreign object is present. Thus, in some embodiments, satisfaction of the second requirement is used to indicate that a movement of the powered equipment has been detected (possibly independent of evaluation of the first requirement).

[0203] The movement indication is used differently in different embodiments, in some embodiments the movement indication is used to generate a user indication, such as an audio alarm, that indicates to the user that the powered device has been moved and should possibly be moved (by the user) back to a more optimal location for charging.

[0204] In other embodiments, the movement indication is used to adapt operating parameters of the power transfer, such as maximum power transfer levels. For example, if movement is detected, the power level is limited to a lower power limit immediately upon detection. The power level is then gradually increased to suit the new operating conditions while ensuring reliability and safety of the power transfer (e.g., by ensuring that no foreign object is detected for an extended period of time).

[0205] In some embodiments, the movement instruction is change It is used to indicate the loop gain, loop filter response, or loop time constant are adapted, for example. For example, during normal operation, the loop performance is optimized for the current operating scenario by slowly adapting the loop gain while ensuring loop stability. If the receiver is moved quickly, the change in coupling coefficient will cause a significant change in the loop behavior, which may lead to For the current loop parameters Potentially becoming unstable. Therefore, when a move instruction is generated, the power controller 203 changes the loop gain to a predetermined safe value that ensures stability of all coupling coefficients. The system then starts adapting the loop (specifically the loop gain) again to, for example, achieve a faster loop response while ensuring stability for the current conditions.

[0206] It will be appreciated that for clarity, the above description describes embodiments of the invention in terms of different functional circuits, units, and processors. However, it will be apparent that any suitable distribution of functionality between different functional circuits, units, or processors may be used without departing from the invention. For example, functionality described as being performed by separate processors or controllers may be performed by the same processor or controller. Thus, references to specific functional units or circuits should not be considered as indicative of a strict logical or physical structure or organization, but merely as references to suitable means for providing the described functionality.

[0207] The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention is optionally implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of the embodiments of the invention may be physically, functionally and logically implemented in any suitable way. In practice, functionality may be implemented in a single unit, in multiple units or as part of other functional units. Thus, the invention may be implemented in a single unit or may be physically and functionally distributed between different units, circuits and processors.

[0208] Although the present invention has been described in relation to several embodiments, it is not intended to limit the present invention to the specific form described herein. Rather, the scope of the present invention is limited only by the appended claims. Moreover, even if a feature appears to be described in relation to a particular embodiment, a person skilled in the art will recognize that various features of the described embodiments can be combined in accordance with the present invention. In the claims, the term "comprises" does not exclude the presence of other elements or steps.

[0209] It will be understood that the reference to a preferred value does not imply a limitation beyond the preferred value being a value determined in the foreign object detection initialization mode, i.e., preferred because it is determined in the fitting process. Reference to a preferred value may be substituted for a reference to a first value, for example.

[0210] Furthermore, although individually recited, a plurality of means, elements, circuits or method steps may be implemented by, for example, a single circuit, unit or processor. Furthermore, although individual features may be included in different claims, they may in some cases be advantageously combined, and the inclusion of such features in different claims does not imply that such a combination is infeasible and / or unadvantageous. Furthermore, the inclusion of a feature in one claim category does not imply that it is limited to this category, but indicates that the feature may be equally applicable to other claim categories, where appropriate. The inclusion of a feature in a dependent claim of an independent claim does not imply that it is limited to this independent claim, but indicates that the feature may be equally applicable to other independent claims, where appropriate. Furthermore, the order of features in the claims does not imply a particular order in which the features must be acted upon, and in particular the order of individual steps in a method claim does not imply that the steps must be performed in that order. Rather, the steps may be performed in any suitable order. Furthermore, the singular reference does not exclude the plural. Thus, reference to "first", "second", etc. does not exclude the plural. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

Claims

1. 1. A power transmitter for wirelessly supplying power to a power receiver via an inductive power transmission signal, the power transmitter comprising: A transmitting coil; a driver for generating a drive signal for the transmitting coil, the driver generating the drive signal for the transmitting coil to generate the inductive power transfer signal during at least one power transfer time of a repetitive time frame and generating the drive signal for the transmitting coil to generate an electromagnetic test signal during at least one foreign object detection time of the repetitive time frame; a plurality of sets of balanced detection coils coupled in series, each set of balanced detection coils including two detection coils, such that signals induced in the two detection coils by the electromagnetic field generated by the sending coil compensate each other; a foreign object detector coupled to the plurality of sets of balanced detection coils and performing foreign object detection during the foreign object detection time; The foreign object detector detects a foreign object in response to signals from the plurality of sets of balanced detection coils satisfying a foreign object detection criterion, the foreign object detection criterion comprising: a first requirement that a signal from at least one of the multiple sets of balanced detection coils indicates that an imbalance between signals induced in the two detection coils of the at least one set of the multiple sets of balanced detection coils exceeds a first threshold; and a second requirement that the number of signals from the multiple sets of balanced detection coils indicating that an imbalance between the signals induced in the two detection coils of the set of balanced detection coils exceeds a second threshold is less than a threshold number, the threshold number being at least two. Including, a power transmitter.

2. The power transmitter of claim 1 , wherein the threshold number is three or greater.

3. The transmitter of claim 1 , wherein the threshold number is equal to a number of sets of the balanced detection coils in the plurality of sets of balanced detection coils.

4. The power transmitter of claim 1 , further comprising an adapter for adapting operating parameters of a power transfer in response to determining that the second requirement is met.

5. The power transmitter of claim 1 , further comprising an adapter for adapting an operating parameter of the foreign object detection in response to determining that the second requirement is met.

6. The transmitter of claim 5 , wherein the operating parameter is a parameter of the first requirement.

7. The transmitter of claim 5 , wherein the operating parameter is a parameter of the second requirement.

8. The transmitter of claim 1 , further comprising a receiver for receiving data from the receiver, the data including physical property data relating to a power receiving device including the receiver, the data being for adapting operational parameters of the foreign object detection in response to the physical property data.

9. The transmitter of claim 8 , wherein the operating parameter is a parameter of the second requirement.

10. 10. The transmitter of claim 1, further comprising a compensator that compensates the signals from at least one set of balanced detection coils for an imbalance between the signals induced in the two detection coils when no foreign object is present.

11. The apparatus of claim 10 , wherein the compensator initiates adaptation of the compensation in response to the second requirement being met.

12. 12. The power transmitter of claim 10 or 11, wherein the compensator reduces a power level of the inductive power transfer signal in response to detecting that the compensation requires a compensation value that meets a criterion.

13. 13. The power transmitter of claim 1, further comprising an adapter for adapting operating parameters of power transmission for at least two sets of balanced detection coils among the plurality of sets of balanced detection coils in response to an imbalance between the signals induced in two detection coils of the set of balanced detection coils.

14. 14. The transmitter of claim 1, further comprising a circuit for generating a position change indication in response to determining that the second requirement is met, the position change indication indicating a change in position of the receiver.

15. The foreign object detection criterion is 15. The transmitter of claim 1, further comprising a third requirement that the signal from at least one of the multiple sets of balanced detection coils indicates that an imbalance between the signals induced in the two detection coils of the at least one of the multiple sets of balanced detection coils does not exceed a second threshold, the second threshold being greater than the first threshold.

16. 1. A method of operating a power transmitter that wirelessly supplies power to a power receiver via an inductive power transmission signal, comprising: A transmitting coil; a plurality of sets of balanced detection coils coupled in series, each set of balanced detection coils including two detection coils, and signals induced in the two detection coils by the electromagnetic field generated by the sending coil compensate each other; a foreign object detector coupled to the plurality of sets of balanced detection coils; The method of operation comprises: generating a drive signal for the transmitting coil to generate the inductive power transfer signal during at least one power transfer time of a repetitive time frame and generating the drive signal for the transmitting coil to generate an electromagnetic test signal during at least one foreign object detection time of the repetitive time frame; performing foreign object detection during the foreign object detection time; The foreign object detection is in response to signals from the plurality of sets of balanced detection coils satisfying a foreign object detection criterion, the foreign object detection criterion comprising: a first requirement that a signal from at least one of the multiple sets of balanced detection coils indicates that an imbalance between signals induced in the two detection coils of the at least one set of the multiple sets of balanced detection coils exceeds a first threshold; and a second requirement that the number of signals from the multiple sets of balanced detection coils indicating that an imbalance between the signals induced in the two detection coils of the set of balanced detection coils exceeds a second threshold is less than a threshold number, the threshold number being at least two. A method for operating a power transmitter, comprising:

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