Apparatus and method for wireless power transfer and improved foreign object detection

Abstract

A wireless power transmitter (101) or a power receiver (105) comprises a power transfer coil (103, 107) for receiving or generating a power transfer signal and a controller (201, 301) for controlling a device to perform power transfer during a power transfer phase. The power transfer phase comprises a power transfer interval at which power is transferred and a foreign object detection time interval during which the power level of the power transfer signal is reduced. A magnetic shielding element (503, 505) is positioned between the power transfer coil (103, 107) and a power transfer coil of a complementary device. The magnetic shielding element (503, 505) comprises a magnetic shielding material having a saturation point such that it operates in a saturated mode and a non-saturated mode during the power transfer interval and the foreign object detection time interval, respectively. The saturation point is higher than the magnetic field strength generated by the power transfer signal during the power transfer time interval and lower than the magnetic field strength generated during the foreign object detection time interval.

Description

Technical Field

[0001] The present invention relates to wireless power transfer systems and in particular, but not exclusively, to apparatus and methods for supporting high power wireless power transfer, for example for supporting kitchen appliances. Background Art

[0002] Most electrical products today require dedicated electrical contacts to be powered from an external power source. However, this is often impractical and requires the user to physically plug in a connector or otherwise establish physical electrical contact. Typically, power requirements also vary widely, and most current devices are provided with their own dedicated power source, resulting in a typical user having a large number of different power sources, each dedicated to a specific device. While the use of an internal battery can avoid the need for a wired connection to a power source during use, this only provides a partial solution as the battery needs to be recharged (or replaced). Using a battery can also significantly increase the weight and potential cost and size of the device.

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

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

[0005] Such an arrangement allows wireless power transfer to the device without having to make any wires or physical electrical connections. In fact, it can simply allow the device to be placed near or on top of the transmitter coil in order to be charged or powered from the outside. For example, the power transmitter device can be arranged with a horizontal surface on which the device can simply be placed in order to be powered.

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

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

[0008] In power transmission systems such as Qi, the electromagnetic fields generated to transmit the required power level to the power receiver are usually very large. In many cases, the presence of such strong magnetic fields may have an impact on the surrounding environment. For example, a potential problem with wireless power transmission is that power may be unintentionally transmitted to, for example, metal objects that happen to be near the power transmitter.

[0009] For example, if a foreign object (e.g., a coin, key, ring, etc.) is placed onto a power transmitter platform arranged as a receiving power receiver, the magnetic flux generated by the transmitter coil will induce eddy currents in the metal object, which will cause the object to heat up. The heat increase can be very significant and can be very undesirable.

[0010] To reduce the risk of this happening, it has been proposed to introduce foreign object detection, where the power transmitter is able to detect the presence of a foreign object and reduce the transmit power and / or generate a user alert when a positive detection occurs. For example, the Qi system includes functionality for detecting foreign objects and reducing power when a foreign object is detected. In particular, section 11 of the Qi specification version 1.2.1 describes various methods for detecting foreign objects.

[0011] WO2015018868A1 discloses a method for detecting such foreign matter. Another example is provided in WO2012127335, which discloses a method based on determining unknown power loss. In this method, the power receiver and the power transmitter both measure their power, and the receiver communicates its measured received power to the power transmitter. When the power transmitter detects a significant difference between the power transmitted by the transmitter and the power received by the receiver, there may be an unexpected foreign object, and for safety reasons, power transmission may be limited or aborted.

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

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

[0014] The power transmitter can estimate the power loss by subtracting the reported received power from the transmitted power. If the difference exceeds a threshold, the transmitter will assume that too much power is dissipated in the foreign object, and the transmitter can then terminate the power transfer. However, in practice, it has been found that this approach is less accurate than desired, and in particular errors and uncertainties in estimating the effects of internal power losses in the power transmitter and power receiver can cause suboptimal performance.

[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 capacitance and resistance.A decrease in the measured Q factor may indicate the presence of foreign matter.

[0016] In practice, it is often difficult to achieve adequate detection accuracy using the methods described in the Qi specification. This difficulty is exacerbated by the many uncertainties regarding the specific current operating conditions.

[0017] For example, a particular problem is the possible presence of friendly metals (ie metal parts of a device embodying a power receiver or power transmitter) which may be difficult to compensate for as their magnetic and electrical properties may be unknown (and vary between different devices).

[0018] Additionally, even relatively small amounts of power dissipated in a metallic foreign body can result in undesirable heating. It is therefore necessary to detect even small power differences between transmitted and received power, and this can be particularly difficult as the power level of the power transfer increases.

[0019] In many cases, the Q-factor degradation method may have better sensitivity for detecting the presence of metal objects. However, it may still not provide sufficient accuracy and may also be affected by friendly metals, for example.

[0020] As a result, current algorithms tend to be suboptimal and may provide less than optimal performance in some scenarios and examples. In particular, they may result in not detecting the presence of foreign objects or falsely detecting foreign objects when none are present.

[0021] Accurately performing foreign object detection is particularly difficult in scenarios where the power level of the power transfer signal is high and / or when the power level of the power transfer signal varies. Therefore, performing foreign object detection during the power transfer phase is particularly difficult.

[0022] Hence, improved operation for a power transfer system would be advantageous, and in particular methods allowing for increased flexibility, reduced cost, reduced complexity, improved foreign object detection, reduced sensitivity to changes in properties of a power receiver or power transmitter device, improved adaptability, improved backward compatibility and / or improved performance would be advantageous. In particular, methods providing an improved electromagnetic environment for detecting foreign objects would be advantageous. Summary of the invention

[0023] Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0024] Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

[0025] According to one aspect of the present invention, there is provided a device for wireless power transmission from a power transmitter to a power receiver using an electromagnetic power transmission signal, the device being one of the power transmitter and the power receiver, the device comprising: a power transmission coil for receiving or generating the power transmission signal; a controller for controlling the device to perform power transmission during a power transmission phase, the power transmission phase comprising a power transmission interval and a foreign object detection time interval, at which power is transmitted and during which the power level of the power transmission signal is reduced; a magnetic shielding element positioned between the power transmission coil and a power transmission coil of a complementary device during the power transmission operation, the complementary device being the other of the power receiver and the power transmitter; wherein the magnetic shielding element comprises a magnetic shielding material having a saturation point, so that it operates in a saturation mode during the power transmission interval and in a non-saturation mode during the foreign object detection time interval, the saturation point being higher than the magnetic field strength generated by the power transmission signal during the power transmission time interval and lower than the magnetic field strength generated during the foreign object detection time interval.

[0026] In many scenarios, the present invention can provide improved performance. In many embodiments, it can allow close coupling between power transfer coils while allowing effective and advantageous foreign object detection. In many embodiments, the method can provide improved foreign object detection and / or improved power transfer. The method can reduce or mitigate the effect of the power transfer coil on foreign object detection. The method can achieve separation between the foreign object detection antenna and the power transfer coil during foreign object detection without introducing unacceptable degradation of power transfer. In many embodiments, the effect of the power transfer coil on foreign object detection can be significantly reduced while introducing only a negligible effect on power transfer.

[0027] In many scenarios, the method may provide an electromagnetic environment that exhibits improved suitability for foreign object detection, and in particular may provide an electromagnetic environment in which the electromagnetic effects of foreign objects are more pronounced and more easily detected.

[0028] The magnetic shield element can be arranged to operate in a saturated mode during the power transfer interval and in a non-saturated mode during the foreign object detection time interval by having a saturation point, the saturation point corresponding to a magnetic field strength that is higher than the magnetic field strength generated by the foreign object detection antenna during the foreign object detection time interval and lower than the magnetic field strength generated by the power transfer coil during the power transfer time interval. The saturation point can be for a magnetic field strength that is higher than the maximum field strength generated in the magnetic shield element during the foreign object detection time interval but lower than the (minimum) field strength generated in the magnetic shield element during the power transfer time interval. In many embodiments, operation is achieved by designing the magnetic shield element to have a saturation point in the range from 100mT to 1T and typically in the range from 200mT to 400mT.

[0029] The saturation point of the magnetic shielding element may be the field strength in the magnetic shielding element for which the magnetic permeability decreases to 1 / 10 of the magnetic permeability for a magnetic field strength of 0 T.

[0030] A magnetic shielding material can generally be considered to be saturated if the field strength is above the saturation point, and unsaturated if the field strength is below the saturation point.

[0031] The foreign object detection antenna may overlap with the power coil such that at least a portion of the foreign object detection antenna is between the power transfer coil of the device and the power transfer coil of the complementary device for a nominal / optimal spatial position of the two devices for power transfer. The power transfer coil may have a central axis and may specifically have a substantially planar arrangement in a plane perpendicular to the axis. The foreign object detection antenna may overlap with the power coil such that at least a portion of the foreign object detection antenna falls within a 3D figure formed by translating the area of ​​the power transfer coil in the direction of the axis (the 3D figure may be considered to have a constant cross-section corresponding to the area of ​​the power transfer coil and extending along the axis).

[0032] The power transfer interval and the foreign object detection time interval are generally non-overlapping.

[0033] The power transfer coil and foreign object detection antenna are typically arranged so that the foreign object detection antenna is closer to the surface through which power transfer occurs than the power transfer coil. The arrangement is typically such that the foreign object detection antenna is positioned between the power transfer coil and a complementary power transfer coil of a complementary device during power transfer operation. The foreign object detection antenna may be positioned between the power transfer coil and a surface of the device for coupling to the complementary device.

[0034] In some embodiments, the foreign object detection antenna is not less than 30cm 2 A planar antenna of area.

[0035] In some embodiments, the area of ​​the power transmission coil is not less than 50 cm 2 .

[0036] In some embodiments, the foreign object detection antenna and the power transfer coil are planar coils.

[0037] In some embodiments, the foreign object detection antenna and the power transfer coil are coaxial.

[0038] In some embodiments, the power transmission interval and the foreign object detection time interval are non-consecutive.

[0039] In some embodiments, the saturation point corresponds to a magnetic field strength that is higher than the magnetic field strength generated by the foreign object detection antenna during the foreign object detection time interval and lower than the magnetic field strength generated by the power transfer coil during the power transfer time interval.

[0040] In some embodiments, the device further comprises a foreign object detection antenna and a foreign object detector, the foreign object detector being arranged to generate a drive signal to drive the foreign object detection antenna to generate a foreign object detection electromagnetic test signal during the foreign object detection time interval, and to perform foreign object detection in response to the drive signal.

[0041] According to an optional feature of the invention, the magnetic shielding element is a sheet element having a thickness of no more than 1 mm.

[0042] In many embodiments, this can provide an effective shielding effect and also allow for compact size and high coupling factors.

[0043] In some embodiments, the sheet element may have a thickness of no more than 0.5 mm, 2 mm, or 5 mm.

[0044] According to an optional feature of the invention, the magnetic shielding material is a ferrite material.

[0045] In many embodiments, this can provide particularly advantageous operation and performance.

[0046] According to an optional feature of the invention, the device is the power receiver and the complementary device is the power transmitter.

[0047] In many embodiments, the method may provide an improved power receiver.

[0048] According to an optional feature of the invention, the device is the power transmitter and the complementary device is the power receiver.

[0049] In many embodiments, the method may provide an improved power transmitter.

[0050] According to an optional feature of the present invention, the device also includes a foreign object detection antenna; and a foreign object detector, which is arranged to generate a drive signal to drive the foreign object detection antenna to generate a foreign object detection electromagnetic test signal during the foreign object detection time interval, and perform foreign object detection in response to the drive signal; and wherein the magnetic shielding element is positioned between the power transmission coil and the foreign object detection antenna.

[0051] In many embodiments, this can provide particularly advantageous operation and performance.

[0052] According to an optional feature of the invention, the foreign object detector is arranged to generate the drive signal to limit the electromagnetic field strength of the foreign object detection electromagnetic test signal in the magnetic shield element to below the saturation point.

[0053] In many embodiments, this can provide particularly advantageous operation and performance.

[0054] According to an optional feature of the invention, the foreign object detection antenna overlaps the power transmission coil.

[0055] According to an optional feature of the invention, the saturation point of the magnetic shielding element lies in the range from 100 mT to 1 T.

[0056] This may provide particularly efficient operation in many embodiments, and may specifically mean in many embodiments that the magnetic shielding material is arranged to operate in a saturated mode during the power transfer interval and in a non-saturated mode during the foreign object detection time interval.

[0057] According to an optional feature of the invention, the saturation point of the magnetic shielding element lies in the range from 200 mT to 400 mT.

[0058] This may provide particularly efficient operation in many embodiments, and may specifically mean in many embodiments that the magnetic shielding material is arranged to operate in a saturated mode during the power transfer interval and in a non-saturated mode during the foreign object detection time interval.

[0059] According to one aspect of the present invention, there is provided a wireless power transmission system for performing wireless power transmission from a power transmitter to a power receiver using an electromagnetic power transmission signal, the wireless power transmission system comprising: a first power transmission coil of the power transmitter, which is used to generate the power transmission signal; a second power transmission coil of the power receiver, which is used to receive the power transmission signal; a controller, which is used to control the power transmission system to perform power transmission during a power transmission phase, the power transmission phase comprising a power transmission interval and a foreign object detection time interval, at which power is transmitted and during which the power level of the power transmission signal is reduced; a magnetic shielding element, which is positioned between the first power transmission coil and the second power transmission coil during the power transmission operation; wherein the magnetic shielding element comprises a magnetic shielding material having a saturation point, so that it operates in a saturation mode during the power transmission interval and operates in a non-saturation mode during the foreign object detection time interval, the saturation point being higher than the magnetic field strength generated by the power transmission signal during the power transmission time interval and lower than the magnetic field strength generated during the foreign object detection time interval.

[0060] According to an optional feature of the present invention, at least one of the power transmitter and the power receiver includes a first foreign object test antenna, which is used to generate a foreign object detection electromagnetic test signal during the foreign object detection time interval; and the wireless power transmission system also includes a foreign object detector, which is arranged to perform foreign object detection in response to measurement of the foreign object detection electromagnetic test signal.

[0061] According to an optional feature of the invention, the measurement is a measurement of a parameter of a drive signal for the foreign object test antenna.

[0062] According to an optional feature of the present invention, the wireless power system also includes a foreign object detection antenna, and wherein the measurement is a measurement of a signal induced in the foreign object detection antenna during the foreign object detection time interval, and the foreign object test antenna and the foreign object detection antenna are in complementary devices of the power transmitter and the power receiver.

[0063] According to one aspect of the present invention, a method for wireless power transmission from a power transmitter to a power receiver using an electromagnetic power transmission signal is provided, wherein the device is one of the power transmitter and the power receiver, and the method includes: a power transmission coil receives or generates the power transmission signal; controlling the device to perform power transmission during a power transmission phase, wherein the power transmission phase includes a power transmission interval and a foreign object detection time interval, wherein power is transmitted at the power transmission interval, and during the foreign object detection time interval, the power level of the power transmission signal is reduced; providing a magnetic shielding element, wherein the magnetic shielding element is positioned between the power transmission coil and the power transmission coil of a complementary device during the power transmission operation, wherein the complementary device is the other device of the power receiver and the power transmitter; wherein the magnetic shielding element includes a magnetic shielding material, wherein the magnetic shielding material operates in a saturation mode during the power transmission interval and operates in a non-saturation mode during the foreign object detection time interval, and wherein a saturation point of the magnetic shielding element is higher than a magnetic field strength generated by the power transmission signal during the power transmission time interval and lower than a magnetic field strength generated during the foreign object detection time interval.

[0064] According to one aspect of the present invention, there is provided a method for operation of a wireless power transmission system, the wireless power transmission system performing wireless power transmission from a power transmitter to a power receiver using an electromagnetic power transmission signal, the wireless power transmission system comprising a first device, the first device being one of the power transmitter and the power receiver, the method comprising the first device performing the following steps: a first power transmission coil of the power transmitter generating the power transmission signal; a second power transmission coil of the power receiver receiving the power transmission signal; controlling the power transmission system to perform power transmission during a power transmission phase, the power transmission phase comprising a power transmission interval and a foreign object detection time interval, at which power is transmitted and during which the power level of the power transmission signal is reduced; providing a magnetic shielding element, the magnetic shielding element being positioned between the first power transmission coil and the second power transmission coil during the power transmission operation; wherein the magnetic shielding element comprises a magnetic shielding material, the magnetic shielding material operating in a saturation mode during the power transmission interval and operating in a non-saturation mode during the foreign object detection time interval, the saturation point of the magnetic shielding element being higher than the magnetic field strength generated by the power transmission signal during the power transmission time interval and lower than the magnetic field strength generated during the foreign object detection time interval.

[0065] In some embodiments, a wireless power transmission system may be provided, comprising a power transmitter and a power receiver, at least one of the power transmitter and the power receiver comprising: a power transmission coil for receiving or generating the power transmission signal; a controller for controlling the device to perform power transmission during a power transmission phase, the power transmission phase comprising a power transmission interval and a foreign object detection time interval, at which power is transmitted, and during which the power level of the power transmission signal is reduced; a magnetic shielding element, which is positioned between the power transmission coil and the power transmission coil of a complementary device during the power transmission operation, the complementary device being the other of the power receiver and the power transmitter; wherein the magnetic shielding element comprises a magnetic shielding material having a saturation point, so that it operates in a saturation mode during the power transmission interval and in a non-saturation mode during the foreign object detection time interval, the saturation point being higher than the magnetic field strength generated by the power transmission signal during the power transmission time interval and lower than the magnetic field strength generated during the foreign object detection time interval.

[0066] In such a system, at least one of the power transmitter and the power receiver includes: a foreign object detection antenna and a foreign object detector, the foreign object detector being arranged to generate a drive signal to drive the foreign object detection antenna to generate a foreign object detection electromagnetic test signal during the foreign object detection time interval, and to perform foreign object detection in response to the drive signal.

[0067] These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0069] Figure 1 illustrates examples of elements of a power delivery system according to some embodiments of the present invention;

[0070] Figure 2 illustrates an example of elements of a power transmitter according to some embodiments of the present invention;

[0071] Figure 3 illustrates examples of elements of a power receiver according to some embodiments of the present invention;

[0072] Figure 4 illustrates an example of a time frame for a power transmission system according to some embodiments of the present invention;

[0073] Figure 5illustrates an example of a coil arrangement for a power transmission system according to some embodiments of the present invention;

[0074] Figure 6 illustrates an example of a coil arrangement for a power transmission system according to some embodiments of the present invention;

[0075] Figure 7 illustrates an example of magnetic field distribution for a coil arrangement for a power transmission system according to some embodiments of the present invention;

[0076] Figure 8 illustrates an example of a coil arrangement for a power transmission system according to some embodiments of the present invention;

[0077] Fig. 9 illustrates an example of magnetic field distribution for a coil arrangement for a power transmission system according to some embodiments of the present invention;

[0078] Fig.10 illustrates an example of magnetic field distribution for a coil arrangement for a power transmission system according to some embodiments of the present invention;

[0079] Fig.11 Some performance characteristics of ferrite magnetic shields are illustrated;

[0080] Fig.12 illustrates an example of a coil arrangement for a power transmission system according to some embodiments of the present invention;

[0081] Fig.13 illustrates examples of elements of a power receiver according to some embodiments of the present invention; and

[0082] Fig.14 An example of a coil arrangement for a power transfer system according to some embodiments of the present invention is illustrated. DETAILED DESCRIPTION

[0083] The following description focuses on an embodiment of the invention applicable to a wireless power transfer system utilizing a power transfer method known, for example, from the Qi specification. However, it should be understood that the invention is not limited to this application but may be applied to many other wireless power transfer systems.

[0084] Figure 1 An example of a power transfer system according to some embodiments of the present invention is illustrated. The power transfer system comprises a power transmitter 101, which comprises (or is coupled to) a transmitter power transfer coil / inductor 103. The system also comprises a power receiver 105, which comprises (or is coupled to) a receiver power transfer coil / inductor 107.

[0085] The system provides an electromagnetic power transfer signal that can inductively transfer power from the power transmitter 101 to the power receiver 105. In particular, the power transmitter 101 generates an electromagnetic signal that is propagated as magnetic flux by the transmitter coil or inductor 103. The power transfer signal can correspond to an electromagnetic power transfer component representing the transfer of energy from the power transmitter to the power receiver, and can be considered to correspond to the component of the generated electromagnetic field that transfers power from the power transmitter to the power receiver. For example, if the receiving coil 107 is not loaded, the power receiver will not extract any power from the generated electromagnetic field (except for losses). In such a scenario, the driving of the transmitter power transfer coil 103 can generate an electromagnetic field with a potentially high field strength, but the power level of the power transfer signal will be zero (except for losses).

[0086] The frequency of the power transfer signal may typically be between about 20 kHz and about 500 kHz, and typically for Qi-compatible systems is typically in the range of 95 kHz to 205 kHz (or for high power kitchen applications, for example, the frequency may typically be in the range of between 20 kHz and 80 kHz, for example). The transmitter power transfer coil 103 and the receiver power transfer coil 107 are loosely coupled, and thus the receiver power transfer coil 107 picks up (at least part of) the power transfer signal from the power transmitter 101. Thus, power is transferred from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter power transfer coil 103 to the receiver power transfer coil 107. The term power transfer signal is primarily used to refer to the induced signal / magnetic field (magnetic flux signal) between the transmitter power transfer coil 103 and the receiver power transfer coil 107, but it should be understood that equivalently, the power transfer signal may also be considered and used as a reference for the electrical signal provided to the transmitter power transfer coil 103 or picked up by the receiver power transfer coil 107.

[0087] In this example, in particular, the power receiver 105 is a power receiver that receives power via a receiver power transfer coil 107. However, in other embodiments, the power receiver 105 may include a metal element, such as a metal heating element, in which case the power transfer signal directly induces eddy currents, thereby causing the element to heat directly (e.g., directly in a disc heating element).

[0088] The system is arranged to transfer substantial power levels, and in particular, in many embodiments the power transmitter may support power levels in excess of 500 mW, 1 W, 5 W, 50 W, 100 W or 500 W. For example, for Qi corresponding applications, the power transfer is typically in the 1-5 W power range for low power applications (basic power curve), up to 15 W for Qi specification version 1.2, in the range up to 100 W for higher power applications (e.g. power tools, portable computers, drones, robots, etc.), and in excess of 100 W and up to over 1000 W for ultra high power applications (e.g. kitchen applications).

[0089] Hereinafter, the operation of the power transmitter 101 and the power receiver 105 will be described with specific reference to embodiments generally in accordance with the Qi specification or adapted for use with a higher power kitchen specification being developed by the Wireless Power Alliance (except for modifications and enhancements described herein (or thereafter)). In particular, the power transmitter 101 and the power receiver 105 may comply with or be substantially compatible with elements of versions 1.0, 1.1 or 1.2 of the Qi specification (except for modifications and enhancements described herein (or thereafter)).

[0090] In order to improve the performance of wireless power transmission systems (such as Figure 1 In order to have the best performance in a wireless power transfer system of FIG. 1 , it is desirable that the power transfer coils 103, 107 of the power transmitter 101 and the power receiver 105 are closely aligned so that they share the maximum possible / feasible amount of magnetic flux. Therefore, it is desirable that the coils 103, 107 are geometrically aligned so as to maximize the coupling factor (κ) between the transmitter coil and the receiver coil.

[0091] Figure 2 The components of the power transmitter 101 are shown, and Figure 3 A more detailed illustration Figure 1 Elements of the power transmitter 105.

[0092] The power transmitter 101 comprises a driver 201 capable of generating a drive signal which is fed to the transmitter power transfer coil 103 which in turn generates an electromagnetic field and thus an electromagnetic power transfer signal providing a power transfer to the power receiver 105. The power transfer signal is provided (at least) during a power transfer phase.

[0093] The driver 201 may typically include an output circuit in the form of an inverter, which is typically formed by driving a full bridge or a half bridge as is known to those skilled in the art.

[0094] The power transmitter 101 further comprises a power transmitter controller 203 arranged to control the operation of the power transmitter 101 according to a desired operating principle. In particular, the power transmitter 101 may comprise many of the functions required to perform power control according to the Qi specification.

[0095] The power transmitter controller 203 is particularly arranged to control the generation of the drive signal by the driver 201, and the power transmitter controller 203 can particularly control the power level of the drive signal and correspondingly control the level of the generated power transfer signal / electromagnetic field. The power transmitter controller 203 includes a power loop controller that controls the power level of the power transfer signal in response to power control messages received from the power receiver 105 during the power control phase.

[0096] In the power receiver 105, the receiver coil 107 is coupled to a power receiver controller 301, which couples the receiver coil 107 to a load 303. The power receiver controller 301 includes a power control path that converts the power extracted by the receiver coil 107 into a suitable supply for the load 303. In addition, the power receiver controller 301 may include various power receiver controller functions required to perform power transfer, and in particular, functions required to perform power transfer in accordance with the Qi specification.

[0097] The power receiver 105 and the power transmitter 101 include functionality for communicating data such as power control messages. The communication may be achieved using the power transfer signal as a communication carrier, for example by the power transmitter 101 communicating data by frequency or phase modulation of the power transfer signal and the power receiver 105 communicating data by load modulation of the power transfer signal, as will be known to those skilled in the art.

[0098] Alternatively or additionally, communication may be performed via separate communication channels implemented using separate communication systems (typically including separate antennas). Using separate and dedicated communication systems means that communication and power transfer functions and operations may be optimized separately for their specific purposes. For example, signals for different functions may be optimized separately. As an example, for signals having relatively low frequencies in the range of, for example, 20 kHz to 500 kHz, efficient power transfer may generally be achieved, while for much higher frequencies (e.g., frequencies above 10 MHz or substantially much higher), efficient short-range communications may generally be achieved.

[0099] As a specific example, communication can be implemented using a short-range communication system such as NFC or RFID communication system. This communication method uses a frequency of 13.56 MHz, and a separate communication coil or antenna may be included and arranged to communicate using a carrier having this frequency and complying with a specific NFC or RFID standard.

[0100] Figure 1 The system also includes functionality for foreign object detection, and the following description will focus on foreign object detection performed by the power transmitter, but in some embodiments, foreign object detection may alternatively or additionally be performed by the power receiver.

[0101] In a wireless power transfer system, the presence of an object (typically a conductive element that extracts power from the power transfer signal and is not part of the power transmitter 101 or the power receiver 105, i.e., an element that is unintended, undesirable, and / or interfering with the power transfer) during power transfer can be highly detrimental. Such undesirable objects are referred to in the art as foreign matter.

[0102] Foreign matter can not only reduce efficiency by adding power losses to the operation, but can also degrade the power transfer operation itself (e.g., by interfering with the power transfer efficiency or extracting power that is not directly controlled by the power transfer loop, for example). In addition, the induction of currents in the foreign matter (particularly eddy currents in the metallic parts of the foreign matter) can lead to the often highly undesirable heating of the foreign matter.

[0103] To address such scenarios, wireless power transmission systems typically include functionality for foreign object detection. Specifically, the power transmitter may include functionality that seeks to detect whether a foreign object is present. If so, the power transmitter may, for example, terminate the power transmission or reduce the maximum amount of power that can be transmitted.

[0104] Typical approaches are based on detecting power loss (by comparing the transmitted power to the reported received power) or detecting degradation in the quality Q of the output resonant circuit that generates the power transfer signal. In some systems, a separate foreign object detection antenna may be used to generate a dedicated foreign object detection electromagnetic signal, where foreign object detection is based on detecting any effects on the foreign object detection electromagnetic signal that may be due to the presence of foreign objects.

[0105] exist Figure 2In the example of , the power transmitter 101 includes a foreign object detector 205, which is arranged to perform foreign object detection. The foreign object detector 205 is coupled to a foreign object detection antenna 207 and is arranged to generate a drive signal for it. The driver signal causes the foreign object detection antenna 207 to generate a foreign object detection electromagnetic test signal, that is, an electromagnetic field is generated by the foreign object detection antenna 207. The foreign object detector 205 is also arranged to determine / measure a parameter of the drive signal and perform a foreign object detection test in response to the parameter. Specifically, if the parameter meets a given standard, the foreign object detector 205 will consider that the potential presence of foreign object detection has been detected.

[0106] The determined parameter(s) and the specific foreign object detection criteria used will depend on the specific preferences and requirements of the various embodiments. Specifically, the foreign object detection methods previously mentioned and known from, for example, foreign object detection using a power transmission signal can also be used by the foreign object detector 205 based on the drive signal and the foreign object detection electromagnetic test signal (hereinafter also referred to as the test signal). Thus, specifically, if the amount of power extracted from the drive signal / test signal exceeds a given threshold, or if, for example, the damping of the resonant circuit including the foreign object detection antenna 207 exceeds a threshold, then a foreign object detection can be considered to be detected.

[0107] As will be described in more detail below, the described system utilizes a time division approach during the power transfer phase, wherein operations such as foreign object detection (and, for example, possible communication) and power transfer can be performed in different time intervals, thereby allowing interference between these (specifically, the impact of power transfer on foreign object detection / communication) to be significantly reduced.

[0108] Specifically, for a wireless power transmission system, the power transmission signal is subjected to the following conditions: Figure 4 The repetitive time frame shown includes at least a power transmission time interval PT and a foreign object detection time interval D.

[0109] The power level of the power transfer signal is reduced during the foreign object detection time interval relative to the power transfer time interval, and typically the maximum allowable power during the foreign object detection time interval is not less than 5 times, 10 times or 50 times lower than the power level during the power transfer time interval. The reduction in power level may be caused by an action at the power transmitter and / or at the power receiver. In some embodiments, the power transmitter may be arranged to turn off the power transfer signal during the foreign object detection time interval.

[0110] The power transmitter (and / or power receiver) can then be arranged for the foreign object detection time interval to be performed during the foreign object detection time interval. Specifically, the power transfer signal can be turned off during the foreign object detection time interval, and the foreign object detector 205 can instead continue to generate the drive signal / test signal and check for the presence of foreign objects. In this way, it can be achieved that the power transfer and the impact of the power transfer signal on foreign object detection can be reduced and generally minimized.

[0111] In the described system, a time division method is therefore applied, wherein power transmission and foreign object detection are performed in different time intervals. Specifically, the power transmitter controller 203 and the power receiver controller 301 are arranged to control the power transmitter and the power receiver, respectively, to perform power transmission during the power transmission interval and to perform foreign object detection during the foreign object detection time interval, wherein the power transmission interval and the foreign object detection time interval are generally non-consecutive and specifically non-overlapping. Figure 4 An example of a method is shown in , wherein a repeating time frame includes a power transfer interval PT in which power transfer is performed (and no foreign object detection) and a foreign object detection time interval D in which foreign object detection is performed (and no power transfer). Thus, in this example, the time frame is divided into a power transfer interval / time slot in which a power transfer signal is generated but a foreign object detection test signal is generally not generated and a foreign object detection time interval / time slot in which a power transfer signal is not generated and foreign object detection is performed (a foreign object detection test signal is generated). In this example, the transmitter power transfer coil 103 and the receiver power transfer coil 107 are active during the power transfer interval, and the foreign object detector 205 and the foreign object detection antenna 207 are active during the foreign object detection interval.

[0112] It should be understood that in some embodiments, the time interval can have a dynamically changing duration, and the time frame can have a dynamically changing duration. It should also be understood that the time frame can include other time intervals for performing other operations or combinations (e.g., a time frame can, for example, include a time slot for performing communication).

[0113] The separation of power transfer and foreign object detection in the time domain can provide a particularly effective separation of the impact of one operation on the other, and in particular, the interference caused by the power transfer signal on foreign object detection can be reduced or completely eliminated. However, even in this case, the separate foreign object detection and power transfer functions may have an impact on each other. In particular, the functions required to support the functions may have an impact. In particular, the presence of both the power transfer coil and the foreign object detection antenna may have an impact. In fact, the presence of the foreign object detection antenna may affect the positioning and the resulting distance between the power transfer coils. Similarly, the presence of a typically large power transfer coil may have a significant impact on the foreign object detection electromagnetic test signal. Therefore, the specific construction and design of the different functions are important challenges to be addressed.

[0114] The problem is exacerbated by the fact that both the power transfer coil and the foreign object detection antenna tend to have the same requirements, as they both need to generate an electromagnetic field in the environment external to the power transmitter.

[0115] In some embodiments, the foreign object detection antenna may be, for example, a foreign object detection test coil coaxial with the power transmission coil.The coils may have a common central axis around which they are distributed.

[0116] Figure 5 A cross section of such an arrangement for both a power transmitter and a power receiver is illustrated, wherein the devices are positioned in an (optimal) configuration for power transfer.In this example, the power receiver 105 is positioned on top of the power transmitter 101 .

[0117] The power transmitter 101 comprises a transmitter power transfer coil 103 which generates a power transfer signal. Figure 5 In the example of FIG. 1 , the transmitter power transfer coil 103 is illustrated by two regions, reflecting a cross-section of a region including a winding and reflecting a center region without a winding.

[0118] The foreign object detection antenna 207 is positioned on top of the transmitter power transmission coil 103 towards the power receiver 105 . Figure 5 The figure shows a typical example in which the foreign object detection antenna 207 is a coil that is significantly smaller than the transmitter power transmission coil 103. Figure 5 In the example of FIG. 2 , the windings of the foreign object detection antenna 207 also fill the central area.

[0119] The transmitter power transmission coil 103 and the foreign object detection antenna 207 are coaxial and symmetrically distributed around the central axis 501. They are also substantially invariant to rotation around the central axis 501.

[0120] Similarly, the power receiver 105 includes a receiver power transfer coil 107 for receiving the power transfer signal. Figure 5 In the example of FIG. 1 , the receiver power transmission coil 107 is illustrated with two regions, reflecting a cross-section of the region including the windings and reflecting a center region without the windings.

[0121] In the specific example, the receiver power transfer coil 107 is coaxial with the central axis of the power transmitter 101 and symmetrically distributed around the central axis (reflecting optimal positioning of the power receiver 105 on the power transmitter 101). It is also substantially invariant to rotation around the central axis 501 .

[0122] although Figure 5 An example is illustrated in which the power receiver is optimally placed relative to the power transmitter so that the central axis 501 is common to both the coil arrangement for the power transmitter and for the power receiver, but it will be appreciated that the power receiver will typically be placed with some misalignment and the central axis 501 will not be perfectly aligned for the power receiver to the power transmitter. However, it should be understood that although this may reduce the coupling by a certain amount, the method and operation will still be applicable and will still provide the advantages and benefits described as long as the misalignment is not too large. The exact misalignment that is acceptable will depend on the specific preferences and requirements of the individual embodiment (and, for example, the size of the coil).

[0123] Figure 5 The arrangement may be particularly useful for cordless kitchen appliances, wherein two large power transmission coils 103 , 107 are used to transmit power from a transmitter to a receiver. A foreign object detection antenna 207 is placed between the power transmission coils 103 , 107 .

[0124] This arrangement may provide very good coupling between the power transfer coils 103, 107 and good foreign object detection, since the foreign object detection antenna 207 is positioned close to the area between the power receiver and the power transmitter.

[0125] However, a problem with this arrangement is that even if time division is used between foreign object detection and power transfer, the presence of the coils may affect each other. In particular, a large metallic power transfer coil may have a significant impact on the performance of foreign object detection, and in particular on the generated foreign object detection electromagnetic detection signal.

[0126] Specifically, the presence of the power transfer coil may affect foreign object detection by losing a portion of the transmitted power in the power coil. The power transfer coil couples with the foreign object detection test signal and absorbs a portion of the power. This will behave like a foreign object, and therefore it may be difficult to separate the presence of the large power transfer coil 103, 107 from the presence of a foreign object. The power transfer coil (and its attached circuitry) may also add undesirable resonances in the foreign object detection system.

[0127] Typically, foreign object detection is relatively indiscriminate and essentially simply detects the presence of any conductive element that could substantially affect the generated test signal. However, this can be problematic in many scenarios. For example, power receivers and indeed power transmitters themselves often include various elements of conductive parts that are often referred to as friendly metal. There is a risk that such friendly metal may be detected as foreign object or otherwise degrade the accuracy of foreign object detection.

[0128] For example, Figure 6 An arrangement is illustrated in which foreign object detection is based on detecting power loss from the electromagnetic field generated by the transmitter coil 103. This can result in an effective detection area 601 (for a metallic object of a given size) that will allow a foreign object 603 to be detected. However, the metalness of both the transmitter coil 103 and the receiver coil 107 will also affect the loading of the generated test signal and must therefore be compensated for by the foreign object detection. This can be difficult, especially for a power receiver, as the foreign object detection of the power transmitter is designed without knowing the specific properties of the specific power receiver.

[0129] Still other conductive parts of the power transmitter and power receiver may affect the detection. For example, it may be difficult to detect the difference between the friendly metal 605, 607 and the foreign object 603 of the power receiver and power transmitter, respectively.

[0130] Figure 7 Shows Figure 6 Example of field lines of an example magnetic field of (only the right side of the arrangement is shown). Foreign object detection of a small foreign object 701 in the presence of a transmitter coil 103, a receiver coil 107 and a friendly metal 703 can be very difficult.

[0131] exist Figure 1-5 In a system, foreign object detection can be improved by including one or more magnetic shielding elements.

[0132] exist Figure 5 In the configuration of , the first magnetic shield element 503 is positioned between the power coil 103 and the foreign object detection antenna 207. Similarly, the second magnetic shield element 505 is positioned between the receiver coil 107 and the power transmitter 101. Thus, the two magnetic shield elements are positioned between their respective power coils and the complementary power device, and between their respective power coils and the foreign object detection antenna 207 (when in use).

[0133] The magnetic shielding element may specifically be a thin shielding sheet which does not significantly increase the height of the arrangement (eg it does not substantially increase the distance between the power transmission coils).

[0134] exist Figure 5In the arrangement of, the foreign object detection antenna 207 is positioned during power transfer operation so that it is the coil closest to both the receiver coil 107 and the transmitter coil 103. The transmitter coil 103 and the foreign object detection antenna 207 are arranged so that the foreign object detection antenna 207 is closer to the surface through which power transfer occurs than the transmitter coil 103. For both devices, the magnetic shielding element is positioned so that it is closer to the power transfer surface than the power transfer coil (but if the foreign object detection antenna 207 is present in the device, it is farther away from the power transfer surface than the foreign object detection antenna 207). This arrangement generally causes the foreign object detection antenna 207 and the magnetic shielding elements 503, 505 to be positioned between the power transfer coil of the device itself (power transmitter 101 or power receiver 105) and the power transfer coil of the other device (complementary device) during power transfer operation. The foreign object detection antenna 207 is specifically positioned between the transmitter coil 103 and the surface coupled to the power receiver 105.

[0135] The magnetic shielding element comprises a magnetic shielding material arranged such that it has a saturation point causing it to operate in a saturation mode during a power transfer interval and in a non-saturation mode during a foreign object detection interval. Thus, the magnetic shielding material is selected such that for higher magnetic field strengths during power transfer operation, saturation is reached, while for much lower field strengths during foreign object detection, the magnetic shielding material remains in its non-saturation mode.

[0136] It should be understood that different materials may be used in different embodiments, but in many embodiments, the magnetic shielding material may be ferrite, and the magnetic shielding element may be a thin ferrite sheet. Thus, in many embodiments, a thin ferrite sheet is placed between the foreign object detection antenna 207 and the power coil (possibly on both the transmitter side and the receiver side, but in many scenarios, only the power receiver or the power transmitter may utilize such a magnetic shielding element).

[0137] When a thin ferrite sheet is placed between the foreign object detection antenna 207 and the power transmission coil 103, 107, the foreign object detection antenna 207 and the test signal are much less affected by the power transmission coil 103, 107 or, in fact, by the metal elements on the remote side of the magnetic shielding element. The ferrite material has a high magnetic permeability μ for the low magnetic field strengths experienced during foreign object detection, and is therefore able to direct the flux of the test signal away from the power transmitter coil (e.g., made of copper) and friendly metals. The ferrite sheet can effectively create an artificial increase in the electromagnetic distance between the power transmission coil and the foreign object detection antenna 207 during foreign object detection. This can be considered as magnetic isolation of the foreign object detection antenna 207 from the conductive windings of the power coil.

[0138] Effectively, such as Figure 8As shown, the magnetic shielding elements can limit the foreign object detection electromagnetic test signal to the area 801 between the magnetic shielding elements. Therefore, a more focused and limited foreign object detection test can be performed. The magnetic shielding elements 505, 503 particularly reduce the influence of friendly metals from the power coils 103, 107 and as part of the power receiver or power transmitter. Therefore, the change in the parameters of the test signal and thus the detected drive signal is mainly determined by whether a foreign object is present, and thus improved foreign object detection, and in particular foreign object detection of smaller metal elements, can be achieved.

[0139] This can be done by Fig. 9 To illustrate, Fig. 9 The diagram illustrates how the electromagnetic test signal generated by the foreign object detection antenna 207 is concentrated in the area between the two magnetic shielding elements, resulting in a greater relative impact of small foreign objects (only the right side of the arrangement is shown).

[0140] However, during the power transfer time interval, the magnetic field is much stronger and the ferrite will saturate. This will effectively render the effect of the magnetic shielding element insignificant and it will effectively have the same effect as air / vacuum. In other words, the effect of the magnetic shielding element will disappear and power transfer will proceed as if the magnetic shielding element was not present.

[0141] Thus, in this approach, the magnetic shielding element can effectively behave like a switch and provide a very different effect and functionality during the foreign object detection time interval than during the power transfer time interval. This can provide the desired advantage of increasing the isolation between the foreign object detection antenna and the power transfer coil during the foreign object detection time interval without adversely affecting the power transfer.

[0142] The function during the foreign object detection interval can also be Fig.10 During such intervals, the foreign object detection antenna 207 generates a test signal for detecting foreign objects. During this operation, the ferrite sheet acts as a shield between the foreign object detection antenna 207 (and / or 307) and the power transmission coil. The ferrite sheet shields the foreign object detection antenna 207 from the power transmission coil, and the negative effects of the presence and proximity of the power transmission coil on the foreign object detection antenna are significantly reduced. Similarly, sensitivity to friendly metals is reduced.

[0143] like Fig.10 As shown, the field lines can be concentrated within the ferrite sheets 503, 505, resulting in a greatly reduced effect of the power transfer coils 103, 107. The magnetic flux lines are directed through the sheets and the copper planes of the power transfer coils are effectively shielded from the foreign object detection antenna 207. It can also be seen that an effect is achieved for both the power receiver and the power transmitter, where the magnetic flux lines are concentrated in the ferrite sheets and away from the windings of the power transfer coils. It should be noted that in Fig.10 In the example of FIG. 1 , the ferrite element 1001 is positioned close to the inner winding of the transmitter power transfer coil 103, and thus the magnetic flux lines are also directed through the element (it should also be understood that the transmitter power transfer coil 103 may include Fig.10 The outer winding is not shown in FIG.

[0144] Thus, in a particular example, during foreign object detection, the first magnetic shielding element 503 acts as a shield between the foreign object detection antenna 207 and the transmitter coil 103, whereby the negative impact of the power coil (and other friendly metals) on the test signal generated by the foreign object detection antenna 207 is significantly reduced. The sheet material is preferably selected to have positive characteristics at the frequency of the test signal (which is typically below 1 MHz, depending on the specific preferences and requirements of foreign object detection).

[0145] During power transfer, the inductive field from the transmitter coil 103 is much stronger than the field of the test signal and the shield will saturate immediately. When the shield is saturated, it will behave like air and will have minimal effect on the coupling and power transfer between the power coils 103, 107.

[0146] Thus, the first magnetic shield element 503 effectively behaves like a switch between operation in the power transfer time interval and in the foreign object detection time interval. This can provide the desired advantages for foreign object detection without introducing unacceptable degradation to the power transfer.

[0147] Similarly, the second magnetic shielding element 505 may provide shielding to the friendly metal of the power receiver 105 and in particular to the receiver coil 107 itself.

[0148] The thin ferrite sheets used to form the first magnetic shield element 503 and / or the second magnetic shield element 505 reduce the effect of friendly metals on foreign object detection. The high μ of the ferrite material allows this to direct flux around the friendly metal. It creates an artificial increase in distance between the foreign object detection antenna 207 and the friendly metal so it can be considered magnetically isolated. Foreign object detection is typically performed using relatively low frequencies (less than 100kHz), and ferrites can provide low losses and high permeability, which is particularly advantageous for the intended operation.

[0149] The disadvantage of shielding is that it reduces coupling between the power coils, but this can be significantly mitigated by keeping the sheets very thin and using materials that effectively saturate at the power levels used for power transfer.

[0150] The specific characteristics of the magnetic shielding elements and materials may depend on the preferences and requirements of an individual embodiment.

[0151] In many embodiments, a thin magnetic shielding element may be used, and typically it may have a thickness of no more than 1 mm (or for some requirements, no more than 0.5 mm, 2 mm, or even 5 mm). In many embodiments, this may provide a favorable tradeoff between the resulting distance between the power transfer coils and the magnetic shielding. It may typically provide effective shielding during foreign object detection without significantly affecting performance during power transfer.

[0152] Therefore, although the magnetic shielding element can reduce the coupling between the power transmission coils, this can be kept to a low level by using very thin sheets to form the magnetic shielding element. This allows the sheet to have a negligible effect on the power transmission while maintaining the advantages for foreign object detection / during foreign object detection. When the sheet is thin, it may also be more practical to implement a magnetic shielding element that operates in a saturated mode during power transmission and in a non-saturated mode during foreign object detection. The thickness of the sheet can be specifically designed so that foreign object detection does not cause the magnetic shielding element to be saturated by the antenna under any circumstances (e.g., maximum test signal power). At the same time, the thickness can be designed to be thin enough to allow it to saturate during power transmission.

[0153] Materials can also be selected and designed to achieve as close to optimal performance as reasonably possible. For example, a material can be selected to have high magnetic permeability and low losses for a given foreign object detection frequency.

[0154] For example, Fig.11 An example of the magnetic permeability μ' and the losses μ" of a ferrite material is illustrated, which is suitable for lower frequencies, for which the magnetic permeability μ' of the ferrite material is high and the losses μ" are low.

[0155] In different embodiments, the specific magnetic field strength at which the ferrite material saturates may be different.The magnetic shielding element may be arranged to operate in a non-saturated mode for power transfer levels below, for example, 0.5W, 1W, 5W or 10W.

[0156] Similarly, the magnetic shielding elements may be arranged to operate in saturation mode for power transfer levels above, for example, 0.5 W, 1 W, 5 W or 10 W. The power level corresponding to the saturation point will typically be below the minimum power transfer level allowed or expected during normal power transfer.

[0157] The magnetic field strength in the magnetic shielding element during the foreign object detection time interval is usually mainly given by the test signal. In fact, in most embodiments, the power transfer signal can be completely switched off during the foreign object detection time interval, i.e., wherein no power transfer signal is generated and no power transfer occurs during the foreign object detection time interval. Therefore, in this case, the field strength is only given by the generated electromagnetic test signal.

[0158] The foreign object detector 207 generates a drive signal that causes the test signal, and is arranged to generate the drive signal such that the electromagnetic field strength of the foreign object detection electromagnetic test signal in the magnetic shield is below a saturation point.

[0159] In many embodiments, this can be accomplished simply by generating a drive signal with an amplitude that ensures the resulting field strength will be below the saturation point. In some embodiments, this can include considering the maximum power transfer signal level that can be generated during the foreign object detection time interval.

[0160] Generally, the design is not critical, ie in many scenarios and embodiments it is possible to determine the amplitude such that for reasonably expected properties and positioning of the power receiver it will generate a field strength high enough to detect foreign objects but low enough to ensure that saturation does not occur.

[0161] In some embodiments, a dynamic and adaptive method can be used to control the amplitude of the drive signal. For example, a small detector coil can be positioned on the side of the power coil to measure the field strength during the foreign object detection time interval. The amplitude of the drive signal can then be set to a value just below the value at which the small detector coil detects the presence of the electromagnetic field.

[0162] Typically, the power transmitter may control the driving of the transmitter coil 103 and the foreign object detection antenna 207 such that the generated field strength ensures saturation during the power transmission time interval and non-saturation during the foreign object detection time interval.

[0163] In many embodiments, the saturation point corresponds to a magnetic field strength that is higher than the magnetic field strength generated by the foreign object detection antenna during the foreign object detection time interval and lower than the magnetic field strength generated by the power transfer coil during the power transfer time interval.

[0164] Typically, the difference between the power level / magnetic field strength generated during the foreign object detection time interval and during the power transfer time interval is high. For example, typical power levels for foreign object detection may be in the range of several hundred mW, whereas the power level during power transfer may be in the range from 10 W and above, and in practice for e.g. kitchen appliances it may be significantly higher. Therefore, it is typically possible to provide a magnetic shielding element that switches between a saturated mode and a non-saturated mode with a certain margin in the power transfer and foreign object detection time intervals, respectively.

[0165] In many embodiments, the saturation point of the magnetic shield element can be for magnetic field strengths in the range of 100mT to 1T. The saturation point in this range generally provides very efficient and reliable switching between a non-saturated mode in a foreign object detection time interval and a saturated mode in a power transfer time interval. This range generally provides such efficient switching for practical / typical power levels of typical foreign object detection and power transfer functions and operations. In many embodiments, particularly advantageous performance can be achieved for the saturation point of the magnetic shield element for magnetic field strengths in the range of 200mT to 400mT.

[0166] An advantage of the described arrangement is that it allows efficient operation and coupling for large coils, and indeed it allows both large foreign object detection coils and large power transfer coils.

[0167] In many embodiments, the area of ​​the foreign object detection coil implementing the foreign object detection antenna 207 is not less than 20 cm 2 (or for some purposes, may be no less than 10cm 2 、30cm 2 , 50cm 2 、100cm 2 In many embodiments, the area of ​​the power transmission coil is not less than 50 cm 2 (or for some purposes, may be no less than 30cm 2 、100cm 2 , 200cm 2 , 500cm 2 ). The area may be measured in the plane of the planar coil / antenna. The area may be the area of ​​the largest cross section of the coil / antenna.

[0168] The use of such a large coil provides many advantages in many scenarios and embodiments. For example, it provides high magnetic field strength over a large area and therefore provides increased freedom in the placement of the power receiver. It can also facilitate foreign object detection in a larger area.

[0169] Furthermore, high power transmission coils generally allow for efficient design for higher power levels (more windings, thicker wire), and are therefore particularly well suited for higher power levels, such as those experienced in, for example, kitchen applications.

[0170] The previous description has focused on embodiments in which foreign object detection is performed by the power transmitter 101. However, in other embodiments, the power receiver 105 may additionally or alternatively include functionality for performing foreign object detection.

[0171] For example, in some embodiments, the power receiver 105 may further include a foreign object detection antenna 1203 and a foreign object detector 1201, such as Fig.12In such an embodiment, the comments and descriptions of the operation of the foreign object detection antenna 207 and the foreign object detector 205 during the power transmission time interval may be equally applicable to the foreign object detection antenna 1203 and the foreign object detector 1201 of the power receiver 105 after appropriate modifications.

[0172] In such an embodiment, the second magnetic shielding element 505 may be positioned between the foreign object detection antenna 1203 and the receiver coil 107, such as Fig.13 shown.

[0173] It will therefore be appreciated that the description of foreign object detection of a power transmitter may be equally applicable to a corresponding / symmetrical implementation and arrangement in a power receiver.

[0174] Furthermore, in the previous examples, both the power transmitter and the power receiver included magnetic shielding elements, but it should be understood that in some embodiments, only the power transmitter or the power receiver may include magnetic shielding elements. Therefore, in some embodiments, the described arrangement and specifically the inclusion of magnetic shielding elements may be provided only in the power transmitter or the power receiver. Therefore, it should be appreciated that the previous description of the coil / antenna configuration in the power transmitter is independent of any particular coil / antenna configuration at the power receiver, and similarly, the previous description of the coil / antenna configuration in the power receiver is independent of any particular coil / antenna configuration at the power transmitter. The described method of using magnetic shielding elements is actually applicable to both power transmitter and power receiver embodiments individually.

[0175] In some embodiments, a separate antenna may be used to generate a foreign object detection electromagnetic test signal and to perform foreign object detection based on measurements of the foreign object detection electromagnetic test signal. In the previous example, the foreign object detection electromagnetic test signal has been generated by the foreign object detection antenna 207, and the effect of any potential foreign object on the test signal has been detected by measuring the effect on the drive signal used to generate the foreign object detection electromagnetic test signal (i.e., based on measurements by the foreign object detection antenna 207).

[0176] However, in some embodiments, the measurement of the effect on the foreign object detection electromagnetic test signal can be determined by different separate foreign object detection antennas, that is, one antenna can be a foreign object detection antenna that generates the foreign object detection electromagnetic test signal, and another foreign object detection antenna can be used to measure the foreign object detection electromagnetic test signal. Basically, the measurement of the effect on the foreign object detection electromagnetic test signal can be determined by measuring the signal induced in the foreign object detection antenna.

[0177] Furthermore, the foreign object test antenna and the foreign object detection antenna may be in different devices, ie, one may be in the power receiver and one may be in the power transmitter. Fig.14An example of an arrangement is illustrated in which the power transmitter includes a first foreign object antenna 1401 and the power receiver includes a second foreign object antenna 1403. In this example, one of the two foreign object antennas can be used as a foreign object test antenna that generates a foreign object detection electromagnetic test signal, and the other antenna can be used as a foreign object detection antenna that measures the foreign object detection electromagnetic test signal. The first foreign object antenna 1401 can correspond to the foreign object detection antenna 207, and the second foreign object antenna 1403 can correspond to the foreign object detection antenna 1203, wherein one of these antennas generates an electromagnetic test signal and the other measures the electromagnetic test signal.

[0178] For example, for a setup with a foreign object detection antenna 207, the second foreign object detection antenna 1403 can be an NFC antenna, and the system can measure the power transmitted by the Tx NFC antenna and the power received by the Rx NFC antenna. It can then check if the values ​​have changed, or if there is too much loss. If the difference between the received power and the transmitted power exceeds a threshold, a foreign object is considered to be detected.

[0179] Other types of antennas and different frequencies may be used in different embodiments.

[0180] Indeed, in some embodiments, the transmitter coil 103 and / or the receiver coil 107 may be used for one or both of the generation of the test signal and the detection of foreign objects.

[0181] For example, the power transmitter 101 may be arranged to generate a test signal for foreign object detection during a foreign object detection time interval. This signal may have a much lower value than during a power transmission time interval, and the reduced magnetic field strength at the second magnetic shielding element 505 may cause this to be in a non-saturated mode. In this way, the construction of the power receiver (and in particular the receiver coil 107) will be effectively shielded from the generated electromagnetic test signal.

[0182] However, since the first magnetic shielding element 503 is closer to the transmitter coil 103, the magnetic field strength may be significantly higher at the first magnetic shielding element 503, and in particular, the field strength may be higher such that the first magnetic shielding element 503 is in saturation mode. Therefore, the transmitter coil 103 generates an electromagnetic test signal that will be affected by foreign objects in the vicinity, such as in particular between the power transmitter and the power receiver. Therefore, foreign object detection may be performed at the power transmitter, for example, in response to the nature of the drive signal that generates the test signal. As a low complexity example, foreign object detection may be considered to have occurred if the power of the drive signal fed to the transmitter coil 103 during the foreign object detection time interval exceeds a given threshold.

[0183] It will be appreciated that the same considerations can be applied to a power receiver, and for example the power receiver can generate a test signal using the receiver coil 107 during a foreign object detection time interval, and detect the presence of a foreign object based on the properties of the corresponding drive signal (e.g., the extracted power level). Likewise, the signal level and saturation point can be selected so that the magnetic shielding element of the device generating the test signal is saturated, while the magnetic shielding element of the complementary device is not saturated.

[0184] In some embodiments, both the power transmitter and the power receiver may be arranged to perform foreign object detection as described, and indeed these operations may be performed in parallel and simultaneously.

[0185] In many embodiments, only one of the first magnetic shielding element 503 and the second magnetic shielding element 505 may be present, ie, only one of the power transmitter and the power receiver may include a magnetic shielding element.

[0186] For example, for an embodiment in which foreign object detection is performed by a power transmitter using the transmitter coil 103 as described above, the power transmitter may not include any magnetic shielding elements, and only the power receiver may include the magnetic shielding elements.

[0187] In many embodiments, this can still provide a very significant improvement. In particular, the foreign object detection of a device can often be adapted to compensate for specific properties of the device itself. However, if the device is used with a wide range of different devices, for example a power transmitter is used with a wide range of different power receivers, then the specific properties of currently existing devices are often not known with sufficient accuracy and therefore cannot be adequately compensated for. Therefore, the presence of a magnetic shielding element in such a device can shield the specific properties and provide greatly improved foreign object detection.

[0188] As a specific example, a power receiver having a magnetic shielding element is provided (e.g., by Figure 5 The power receiver 105 as illustrated in the drawings may support, enable and provide greatly improved foreign object detection by a conventional power transmitter which does not include any corresponding magnetic shielding elements or which simply exploits conventional foreign object detection using a transmitter coil 103, for example.

[0189] Therefore, in particular, even providing only a single magnetic shielding element in a power transmission device that does not itself perform any foreign object detection can provide significantly improved foreign object detection. The magnetic shielding element can provide an improved and suitable electromagnetic environment for more accurate foreign object detection, and in particular can provide an electromagnetic environment in which the electromagnetic effects of foreign objects are more significant and easier to detect.

[0190] It will be appreciated that, for clarity, embodiments of the present invention have been described above with reference to different functional circuits, units and processors. However, it will be apparent that any suitable distribution of functionality may be used between different functional circuits, units or processors without detracting from the present invention. For example, functions illustrated as being performed by separate processors or controllers may be performed by the same processor or controller. Therefore, references to specific functional units or circuits are merely considered references to suitable units for providing the described functionality, rather than indicating a strict logical or physical structure or organization.

[0191] The present invention can be implemented in any suitable form including hardware, software, firmware or any combination thereof. The present invention can be optionally implemented at least in part as computer software running on one or more data processors and / or digital signal processors. The elements and components of an embodiment of the present invention can be implemented physically, functionally and logically in any suitable manner. In fact, functions can be implemented in a single unit, in multiple units or as parts of other functional units. For this reason, the present invention can be implemented in a single unit, or can be physically and functionally distributed between different units, circuits and processors.

[0192] Although the present invention has been described in conjunction with some embodiments, the present invention is not intended to be limited to the specific forms set forth herein. Rather, the scope of the present invention is limited only by the claims. In addition, although it appears that features are described in conjunction with specific embodiments, those skilled in the art will recognize that the various features of the described embodiments can be combined according to the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0193] It will be appreciated that reference to a preferred value does not imply any restriction to it being other than a value determined in the foreign object detection initialisation mode, ie the preferred value is a value determined during the adjustment process. Reference to a preferred value may replace reference to, for example, the first value.

[0194] In addition, although listed separately, multiple units, elements, circuits or method steps can be implemented by, for example, a single circuit, unit or processor. In addition, although individual features can be included in different claims, these features can also be advantageously combined, and the inclusion of these features in different claims does not mean that the combination of features is not feasible and / or disadvantageous. Moreover, the inclusion of features in a type of claim does not mean a restriction on this type, but rather indicates that the feature can also be equally applicable to other claim types when appropriate. In addition, the order of features in the claims does not mean a specific order in which the features must work, and in particular, the order of individual steps in the method claims does not mean that the steps must be performed in this order. Instead, the steps can be performed in any suitable order. In addition, singular references do not exclude multiples. Therefore, references to "one", "one", "first", "second", etc. do not exclude multiples. The figure marks in the claims are provided only as illustrative examples and should not be interpreted as limiting the scope of the claims in any way.

Claims

1. A device for wireless power transmission from a power transmitter (101) to a power receiver (105) using an electromagnetic power transmission signal, the device being one of the power transmitter (101) and the power receiver (105), the device comprising: A power transmission coil (103, 107) for receiving or generating the power transmission signal; a controller (201, 301) for controlling the device to perform power transfer during a power transfer phase, the power transfer phase comprising a power transfer time interval at which power is transferred and a foreign object detection time interval during which a power level of the power transfer signal is reduced; Foreign object detection antenna; and a foreign object detector arranged to generate a drive signal to drive the foreign object detection antenna to generate a foreign object detection electromagnetic test signal during the foreign object detection time interval, and to perform foreign object detection in response to the drive signal; a magnetic shielding element (503, 505) positioned between the power transfer coil (103, 107) and a power transfer coil of a complementary device, the complementary device being the other of the power receiver (105) and the power transmitter (101) during a power transfer operation; wherein the magnetic shielding element (503, 505) is positioned between the power transmission coil (103, 107) and the foreign object detection antenna; in, The magnetic shielding element (503, 505) includes a magnetic shielding material having a saturation point so that it operates in a saturated mode during a power transfer time interval and in a non-saturated mode during a foreign object detection time interval, the saturation point being lower than a magnetic field strength generated by the power transfer signal during the power transfer time interval and higher than a magnetic field strength generated during the foreign object detection time interval.

2. The device according to claim 1, wherein: The magnetic shielding elements (503, 505) are sheet elements having a thickness not exceeding 1 mm.

3. The device according to any one of claims 1 to 2, wherein: The magnetic shielding material is a ferrite material.

4. The device according to any one of claims 1-2, wherein: The device is the power receiver (105) and the complementary device is the power transmitter (101).

5. The device according to any one of claims 1 to 2, wherein: The device is the power transmitter (101) and the complementary device is the power receiver (105).

6. The device according to claim 1, wherein: The foreign object detector is arranged to generate the drive signal to limit the electromagnetic field strength of the foreign object detection electromagnetic test signal in the magnetic shielding element (503, 505) to below the saturation point.

7. The device according to claim 1, wherein: The foreign object detection antenna (207, 307) overlaps with the power transmission coil (103, 107).

8. The device according to any one of claims 1 to 2, wherein: The saturation point of the magnetic shielding elements (503, 505) is in the range from 100 mT to 1 T.

9. The device according to any one of claims 1 to 2, wherein: The saturation point of the magnetic shielding elements (503, 505) is in the range from 200 mT to 400 mT.

10. A wireless power transmission system for performing wireless power transmission from a power transmitter (101) to a power receiver (105) using an electromagnetic power transmission signal, the wireless power transmission system comprising: A first power transmission coil (103) of the power transmitter, which is used to generate the power transmission signal; A second power transmission coil (107) of the power receiver, which is used to receive the power transmission signal; a controller (201, 301) for controlling the power transmission system to perform power transmission during a power transmission phase, the power transmission phase comprising a power transmission time interval at which power is transmitted and a foreign object detection time interval during which a power level of the power transmission signal is reduced; a foreign object detection antenna for generating a foreign object detection electromagnetic test signal during the foreign object detection time interval; a foreign object detector arranged to perform foreign object detection in response to measuring the foreign object detection electromagnetic test signal; a magnetic shielding element (503, 505) positioned between the first power transfer coil (103) and the second power transfer coil (107) during a power transfer operation; in, The magnetic shielding element (503, 505) includes a magnetic shielding material having a saturation point so that it operates in a saturated mode during a power transfer time interval and in a non-saturated mode during a foreign object detection time interval, the saturation point being lower than a magnetic field strength generated by the power transfer signal during the power transfer time interval and higher than a magnetic field strength generated during the foreign object detection time interval.

11. The wireless power transmission system according to claim 10, wherein: The measurement is a measurement of a parameter of a driving signal of the foreign object test antenna.

12. The wireless power transmission system according to claim 10, further comprising a foreign object detection antenna, and wherein The measurement is a measurement of a signal induced in the foreign object detection antenna during the foreign object detection time interval, the foreign object test antenna and the foreign object detection antenna being in complementary devices of the power transmitter and the power receiver.

13. A method of wireless power transmission from a power transmitter (101) to a power receiver (105) using an electromagnetic power transmission signal, the device being one of the power transmitter (101) and the power receiver (105), and the method comprising: The power transmission coil (103, 107) receives or generates the power transmission signal; controlling the device to perform power transfer during a power transfer phase, the power transfer phase comprising a power transfer time interval at which power is transferred and a foreign object detection time interval during which a power level of the power transfer signal is reduced; Provide foreign object detection antenna; The foreign object detector generates a driving signal to drive the foreign object detection antenna to generate a foreign object detection electromagnetic test signal during the foreign object detection time interval, and performs foreign object detection in response to the driving signal; providing a magnetic shielding element (503, 505) which is positioned between the power transfer coil (103, 107) and a power transfer coil of a complementary device, the complementary device being the other of the power receiver (105) and the power transmitter (101) during a power transfer operation; wherein the magnetic shielding element (503, 505) is positioned between the power transmission coil (103, 107) and the foreign object detection antenna; in, The magnetic shielding element (503, 505) includes a magnetic shielding material, which operates in a saturation mode during a power transmission time interval and in a non-saturation mode during a foreign object detection time interval, and the saturation point of the magnetic shielding element is lower than the magnetic field strength generated by the power transmission signal during the power transmission time interval and higher than the magnetic field strength generated during the foreign object detection time interval.

14. A method for operation of a wireless power transmission system, the wireless power transmission system performing wireless power transmission from a power transmitter (101) to a power receiver (105) using an electromagnetic power transmission signal, the wireless power transmission system comprising a first device, the first device being one of the power transmitter (101) and the power receiver (105), the method comprising the first device performing the following steps: The first power transmission coil (103) of the power transmitter generates the power transmission signal; The second power transmission coil (107) of the power receiver receives the power transmission signal; controlling the power transfer system to perform power transfer during a power transfer phase, the power transfer phase comprising a power transfer time interval at which power is transferred and a foreign object detection time interval during which a power level of the power transfer signal is reduced; The foreign object detection antenna generates a foreign object detection electromagnetic test signal during the foreign object detection time interval; The foreign object detector performs foreign object detection in response to measuring the foreign object detection electromagnetic test signal; providing a magnetic shielding element (503, 505) positioned between the first power transfer coil (103, 107) and the second power transfer coil during a power transfer operation; in, The magnetic shielding element (503, 505) includes a magnetic shielding material, which operates in a saturation mode during a power transmission time interval and in a non-saturation mode during a foreign object detection time interval, and the saturation point of the magnetic shielding element is lower than the magnetic field strength generated by the power transmission signal during the power transmission time interval and higher than the magnetic field strength generated during the foreign object detection time interval.

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