Foreign object detection in wireless power transmission systems

Abstract

A power transmitter for wirelessly providing power via an inductive power transmission signal to a power receiver includes: a power transmission coil for generating the power transmission signal; a driver for generating a drive signal for the power transmission coil, the driver configured to generate the drive signal to use a recurring time frame during a power transmission phase that includes at least a power transmission time interval and a transmitting foreign object detection time interval; a receiver for receiving messages from the power receiver; a foreign object detector configured to perform a foreign object detection (FOD) test; a communications coil for generating a communications signal; and a communications unit configured to generate a communications control signal for the communications coil that provides the communications signal during a communications period, the communications unit configured to set the communications control signal to a first value during the communications period and to set the communications control signal to a second value during the communicating foreign object detection time interval, the communicating foreign object detection time interval occurring during the communications period.

Description

[Technical field]

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

[0002] Most today's electronic products require a dedicated electrical contact in order to be powered from an external power supply. However, this tends to be impractical, requiring the user to physically insert a connector or otherwise establish physical electrical contact. Typically, power requirements also vary significantly, and most devices now have their own dedicated power supplies, with the result that a typical user has many different power supplies, each dedicated to a particular device. The use of an internal battery avoids the need for a wired connection to the power supply during use, but this only provides a partial solution, as the battery requires recharging (or replacement). The use of a battery also significantly increases the weight, potential cost, and size of the device.

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

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

[0005] Such a configuration allows wireless power transmission to the device without the need for any wires or physical electrical connections to be established. In fact, the device only needs to be placed adjacent to or on the transmitter coil to be externally recharged or powered. For example, the power transmitter device is configured to have a horizontal surface on which the device simply needs to be placed to be powered.

[0006] Furthermore, such a wireless power transmission configuration: Various Advantageously, power transmitter devices are designed to be used in conjunction with power receiver devices. In particular, a wireless power transmission approach known as the Qi specification has been defined and is currently being further developed. This approach allows power transmitter devices conforming to the Qi specification to be used in conjunction with power receiver devices also conforming to the Qi specification, without these needing to be from the same manufacturer or proprietary to each other. The Qi standard specifies that a particular power receiver device (e.g., a particular power consumption It further has several features to allow the operation to be adapted (depending on

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

[0008] A potential problem with wireless power transmission is the unintentional transmission of power to, for example, a metal object that happens to be in the vicinity of the power transmitter. For example, if a foreign object, such as a coin, key, or ring, is placed on the platform of the power transmitter that is configured to receive the power receiver, the magnetic flux generated by the transmitter coil will induce an eddy current in the metal object, which will heat up the object. The heat rise can be very significant and extremely undesirable.

[0009] To reduce the risk of such a scenario occurring, it has been proposed to introduce foreign object detection (FOD) such that the power transmitter may detect the presence of a foreign object and may reduce the transmission power when a positive detection occurs and / or generate a warning to the user. For example, the Qi system has the functionality to detect foreign objects and to reduce the power if a foreign object is detected. Specifically, section 11 of the Qi specification version 1.2.1 describes various methods of detecting foreign objects.

[0010] One method of detecting such foreign objects is disclosed in WO2015018868A1. Another example is provided in WO2012127335, which discloses an approach based on determining an unknown power loss. In this approach, both the power receiver and the power transmitter 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 sent by the transmitter and the power received by the receiver, an unwanted foreign object is potentially present, and power transmission is reduced or stopped for safety reasons. This power loss approach requires synchronized and accurate power measurements performed by the power transmitter and the power receiver.

[0011] For example, in the Qi power transfer standard, the power receiver estimates its received power, e.g., 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 4 seconds. This is commonly referred to as "power loss accounting."

[0012] 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, such as the estimated power losses in the inverter, the primary coil, and metal parts that are part of the power transmitter.

[0013] The power transmitter may estimate the power loss by subtracting the reported received power from the transmitted power, and if the difference exceeds a threshold, the transmitter may assume that too much power has been dissipated in the foreign object and proceed to terminate power transmission.

[0014] Alternatively, it has been proposed to measure the quality or Q-factor of the resonant circuit formed by the primary and secondary coils and the corresponding capacitances and resistances. A reduction in the measured Q-factor indicates the presence of a foreign object.

[0015] In practice, achieving sufficient detection accuracy using the methods described in the Qi specification tends to be difficult, a difficulty exacerbated by some uncertainty about the specific current operating conditions.

[0016] For example, a particular problem is the potential presence of intimate metals (i.e., metallic parts of the devices embodying the power receiver or power transmitter), whose magnetic and electrical properties are unknown (and vary for different devices) and therefore difficult to compensate for.

[0017] Furthermore, even relatively small amounts of power dissipated in a foreign metal object can result in unwanted heating. Therefore, it is necessary to detect even small power discrepancies between transmitted and received power, which is particularly difficult as the power level of the power transmission increases.

[0018] The Q-factor degradation approach has better sensitivity for detecting the presence of metal objects in many scenarios. However, it still does not provide sufficient accuracy and is still vulnerable to metal-affinity, e.g. Aggravated by .

[0019] The performance of foreign object detection is affected by the specific operating conditions that exist when the test is actually performed. For example, as described in the Qi specification, if measurements for foreign object detection are performed during the selection phase of the power transfer initialization process, the signal that the power transmitter provides for the measurement must be small enough to prevent the signal from waking up the power receiver. However, such small signals typically have a poor signal-to-noise ratio, resulting in a reduced accuracy of the measurement.

[0020] Another problem is that foreign object detection is typically a very sensitive test where it is desirable to detect relatively small changes caused by the presence of a foreign object in potentially large variations in the operating environment and scenario in which the test is being performed.

[0021] Therefore, current algorithms tend to be suboptimal and provide less than optimal performance in some scenarios and implementations, in particular resulting in failure to detect the presence of a foreign object or falsely detecting a foreign object when none is present. Summary of the Invention [Problem to be solved by the invention]

[0022] With potentially high power levels, such as those used for kitchenware, heating of foreign objects can be very rapid, and it is desirable to detect the presence of such foreign objects as early and as reliably as possible.

[0023] Accordingly, improved foreign object detection would be advantageous, particularly techniques that enable increased flexibility, reduced cost, reduced complexity, improved object detection, fewer false positives and negatives, backward compatibility, and / or improved performance.

[0024] Therefore, the present invention preferably comprises any of the above-mentioned compounds, either alone or in any combination. Lack The aim of the present invention is to reduce, alleviate or eliminate one or more of the above mentioned points. [Means for solving the problem]

[0025] Thus, there is provided a power transmitter for wirelessly providing power via an inductive power transmission signal to a power receiver, the power transmitter comprising: a power transmission coil for generating the power transmission signal; a driver for generating a drive signal for the power transmission coil, the driver configured to generate the drive signal to use a repetitive time frame during a power transmission phase including at least a power transmission time interval and a transmission foreign object detection time interval; a receiver for receiving messages from the power receiver; a foreign object detector configured to perform a foreign object detection (FOD) test; a communications coil for generating a communication signal; and a communications unit configured to generate a communications control signal for the communications coil providing the communications signal during a communication period, the communications unit configured to set the communications control signal to a first value during the communication period and to set the communications control signal to a second value during the communication foreign object detection time interval, the communication foreign object detection time interval occurring during the communication period.

[0026] The ability to perform a foreign object test during communication allows detection of a foreign object before power transmission begins. This reduces the risk of unwanted heating of any foreign object that may be present. Heating of such objects in the field of high power applications is of particular concern since even small objects can become dangerously hot very quickly. The second value may be lower than the first value and set to zero. By setting the second value to zero, interference of the communication signal with any foreign object test is significantly reduced.

[0027] In an embodiment, the communication period includes a plurality of foreign object detection time intervals, the plurality of foreign object detection time intervals including a longer foreign object detection time interval and a shorter foreign object detection time interval, the longer foreign object detection time interval being longer than the shorter foreign object detection time interval.

[0028] In embodiments, longer FOD time intervals allow for more accurate FOD testing and calibration, and the data is used for subsequent FOD tests. They also provide an opportunity to perform other tests, such as coupling coefficient tests. Shorter FOD time intervals can be performed more frequently without interrupting the communication signal for an excessively long period of time. Performing frequent FOD tests reduces the risk that a foreign object will be placed on the power transmitter between FODs.

[0029] In an embodiment, the longer foreign object detection time interval has a length less than or equal to 100 ms, the short foreign object detection time interval has a length less than or equal to 10 ms, and the foreign object detection time intervals occur at a period of 200 ms, these values ​​allowing sufficient time to perform FOD testing while maintaining a communication signal.

[0030] In an embodiment, there is a first long communication foreign object detection time interval that is completed within 200 ms of establishing communication with the power receiver, thus allowing for early FOD detection as desired. Possibly do.

[0031] In an embodiment, the power transmitter is powered by a power mains supply having a zero crossing point, and the power transmission foreign object detection time interval is synchronized with the zero crossing point, which is a convenient time since there is lower interference from the power mains supply.

[0032] In an embodiment, the first value of the communication signal is set to transmit sufficient power to the communication signal power capture in the power receiver. Some basic functions of the power receiver (logic for communication circuit , and, where applicable, a user interface, etc.), power is harvested from the communication signal.

[0033] In an embodiment, the second value of the communication signal is set to reduce interference with foreign object detection testing, since the communication signal also interferes with FOD testing, reducing its reliability.

[0034] In an embodiment, the foreign object detection test is performed using the communication unit because this reduces the amount of hardware.

[0035] In an embodiment, the power transmitter is frequency This means that the system is configured to negotiate with the power receiver: Better possible time between time spent on FOD and time to turn on communication signal than the default value. It allows you to find trade-offs.

[0036] A power receiver for wirelessly receiving power via an inductive power transmission signal is provided, the power receiver including a communication coil for receiving a received communication signal, and a communication controller configured to decode the received communication signal and generate a communication response signal for the communication coil; communicationThe system includes a communications signal power harvester configured to extract power from the received communications signal to power the communications controller during a time interval in which the signal is at a first value and to store a portion of the extracted power sufficient to maintain the communications controller (and the user interface) in operation during a communications foreign object detection time interval, a power receiving coil for extracting power from the power transmission signal, and a message transmitter for transmitting a message to the power transmitter, the power receiver being capable of maintaining some of its hardware such that it can continue to cooperate with the power transmitter during the communications FOD time interval.

[0037] In an embodiment, the communication controller of the power receiver is configured to maintain the connection state during the communication foreign object detection time interval, which has the advantage that renegotiation of communication is not required at each new communication time interval.

[0038] In an embodiment, the power receiver includes a user interface and is configured such that the extracted power is sufficient to power the communications controller and the user interface with a received communications signal having a duty cycle of 66% or less. The time used for FOD testing and any other non-communicative operations can take up to 1 / 3 of the time of the communications period. It is therefore desirable for the power receiver to be able to manage this.

[0039] In an embodiment, the power receiver may support a foreign object detection time interval during the communication phase. frequency The power supply is configured to negotiate with the power transmitter regarding

[0040] Also provided is a wireless power transfer system comprising a power transmitter and a power receiver for wirelessly providing power via an inductive power transmission signal to a power receiver, the power transmitter comprising a foreign object detector configured to perform a foreign object detection test, a communication coil for generating a communication signal, a communication unit configured to generate a communication control signal for the communication coil providing the communication signal during a communication period, the communication unit configured to set the communication control signal to a first value during the communication period and to set the communication control signal to a second value during a first foreign object detection time interval, the first foreign object detection time interval occurring during the communication period, a transmitter coil for generating the power transmission signal, a driver for generating a drive signal for the transmitter coil, the driver configured to generate the drive signal to employ a repetitive time frame during a power transfer phase that includes at least a power transfer time interval and a foreign object detection time interval, and a receiver for receiving messages from the power receiver. The power receiver comprises a communication coil for receiving an incoming communication signal, a communication controller configured to decode the received communication signal and generate a communication response signal for the communication coil, a communication signal power harvester configured to extract power from the received communication signal to power the communication controller and store a portion of the extracted power sufficient to maintain the communication controller and the user interface in an operational state, and a message transmitter for transmitting a message to the power transmitter.

[0041] A method of operating a power transmitter that wirelessly provides power via an inductive power transmission signal to a power receiver is also provided, the method comprising the steps of generating a communication signal, the communication signal being set to a first value during a communication period and set to a second value during a first foreign object detection time interval, the first foreign object detection time interval occurring during the communication period; applying the communication signal to a communication field; generating a power transmission signal; generating a drive signal for a transmitter coil, wherein during the power transfer phase the drive signal uses a repetitive time frame that includes at least the power transfer time interval and a second foreign object detection time interval; performing a foreign object detection test during the first and second foreign object detection time intervals; and receiving a message from the power receiver.

[0042] A method of operating a power receiver to wirelessly receive power via an inductive power transmission signal is also provided, the method comprising the steps of receiving a received communication signal via a communication coil, decoding the received communication signal and generating a communication response signal for the communication coil, extracting power from the received communication signal and storing a portion of the extracted power sufficient to power a communication controller and a user interface and maintain the communication controller and user interface in operation during a first foreign object detection time interval, extracting power from the power transmission signal using the power transmission coil, and transmitting a message to a power transmitter via the communication coil.

[0043] A computer program product is also provided which, when executed on a processor of a wireless power transmitter or a power receiver, causes the wireless power transmitter to operate the respective method.

[0044] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which: [Brief description of the drawings]

[0045] [Figure 1] 1 illustrates an example of elements of a power transfer system according to an embodiment. [Diagram 2]1 illustrates an example of elements of a power transmitter according to an embodiment. [Figure 3a] 1 illustrates an embodiment of a half-bridge inverter for a power transmitter. [Figure 3b] 1 illustrates an embodiment of a full bridge inverter for a power transmitter. [Figure 4] 1 illustrates a power receiver according to an embodiment. [Diagram 5] 1 illustrates an example of elements of a power receiver according to an embodiment. [Figure 6] 4 illustrates a time frame for operation of a system according to an embodiment. [Figure 7] 2 illustrates phases of operation of the wireless power transfer system of FIG. 1. [Figure 8] 2 shows periods of operation of the wireless power transfer system of FIG. 1 presented as a frame diagram. [Figure 9] 2 illustrates phases of operation of the wireless power transfer system of FIG. 1 according to some embodiments of the present invention. [Figure 10] 2 illustrates periods of operation of the wireless power transfer system of FIG. 1 presented as a frame diagram according to some embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] The following description focuses on embodiments of the invention that are applicable to wireless power transfer systems utilizing power transfer techniques such as those known from the Qi specification, however, it will be appreciated that the invention is not limited to this application and applies to many other wireless power transfer systems.

[0047] 1 illustrates an example of a power transfer system 100 according to some embodiments of the present invention. The power transfer system comprises a power transmitter 101 including (or coupled to) a transmitter coil / inductor 103. The system further comprises a power receiver 105 including (or coupled to) a receiver coil / inductor 107.

[0048] The system 100 provides an electromagnetic power transfer signal that inductively transfers power from a power transmitter 101 to a power receiver 105. Specifically, the power transmitter 101 generates an electromagnetic signal that is propagated as magnetic flux by a transmitter coil or inductor 103. The power transfer signal typically has a frequency between about 20 kHz and about 50 kHz. frequency For Qi-compatible systems, the typical frequency range is often 95kHz to 205kHz. frequency (or, for example, for high power kitchen applications, frequency (e.g., typically in the range of 20 kHz to 80 kHz). The transmitter coil 103 and the power receiving coil 107 are loosely coupled, and thus the power receiving coil 107 picks up (at least a portion of) the power transmission signal from the power transmitter 101. Thus, power is transferred from the power transmitter 101 to the power receiver 105 via wireless inductive coupling from the transmitter coil 103 to the power receiving coil 107. It will be understood that the term power transmission signal is primarily used to refer to the inductive signal / magnetic field between the transmitter coil 103 and the power receiving coil 107 (magnetic flux signal), but is equivalently also considered and used as a reference to the electrical signal provided to the transmitter coil 103 or the electrical signal picked up by the power receiving coil 107.

[0049] In this example, the power receiver 105 is specifically a power receiver that receives power via a receiver coil 107. However, in other embodiments, the power receiver 105 includes a metallic element, such as a metallic heating element, in which case the power transmission signal directly induces an eddy current, resulting in direct heating of the element.

[0050] System 100 is configured to transmit significant power levels, and specifically, in many embodiments, power transmitter 101 supports power levels of 500 mW, 1 W, 5 W, 50 W, 100 W, or greater than 500 W. For example, for Qi-enabled applications, power transmission typically ranges from 1-5 W power for low power applications (basic power profile), up to 15 W for Qi specification version 1.2, up to 100 W for higher power applications such as power tools, laptops, drones, robots, and beyond 100 W, even exceeding 1000 W, for very high power applications such as kitchen applications.

[0051] The operation of power transmitter 101 and power receiver 105 is described below with particular reference to an embodiment generally in accordance with the Qi specification (except for modifications and enhancements described herein (or resulting therefrom)) or an embodiment suitable for a higher power kitchen specification being developed by the Wireless Power Consortium. In particular, power transmitter 101 and power receiver 105 conform to or are substantially compatible with elements of the Qi specification version 1.0, 1.1 or 1.2 (except for modifications and enhancements described herein (or resulting therefrom)).

[0052] In wireless power transfer systems, the presence of objects (typically conductive elements that extract power from the power transfer signal but are not part of the power transmitter 101 or power receiver 105, i.e. elements that are unintended, unwanted and / or interfere with the power transfer) is highly undesirable during power transfer. Such unwanted objects are known in the art as foreign objects.

[0053] Foreign objects not only reduce efficiency by adding power losses to the operation, but also degrade the power transfer operation itself (e.g., by interfering with the power transfer efficiency or by extracting power without being directly controlled, for example, by the power transfer loop). In addition, the induction of currents in the foreign object (specifically, current surges in the metal parts of the foreign object) often results in heating of the foreign object, which is highly undesirable. This concern becomes particularly acute when high power levels are used, such as those applicable to kitchen appliances, and even small objects can become undesirably hot.

[0054] To address such scenarios, wireless power transmission systems such as Qi have a feature for foreign object detection. Specifically, the power transmitter 101 has a feature that tries to detect whether a foreign object is present. If a foreign object is present, the power transmitter 101 may, for example, terminate power transmission or reduce the maximum amount of power that can be transmitted.

[0055] Current approaches proposed by the Qi specification are based on detecting power loss (by comparing the transmitted power with the reported received power) or on detecting a degradation in the quality Q of the output resonant circuit. However, in current use, these approaches have been found to provide suboptimal performance in many scenarios, in particular leading to inaccurate detection, resulting in missed detections and / or false positive detections where a foreign object is detected despite no such object being present.

[0056] Foreign object detection is performed before the power receiver enters the power transfer phase (e.g., during initialization of the power transfer) or during the power transfer phase. Detection during the power transfer phase is often based on a comparison of measured transmitted and received powers, while detection performed before the power transfer phase is often based on measuring the reflected impedance, for example by measuring the quality factor of the transmitter coil using a small measurement signal.

[0057] Conventional foreign object detection tends to be suboptimal due in part to variations and uncertainties in the particular operating conditions and scenarios in which foreign object detection is performed, such as variations and uncertainties in power transmitter characteristics, power receiver characteristics, applied test conditions, etc.

[0058] An example of a challenge to foreign object detection testing is the requirement to perform sufficiently accurate measurements to achieve sufficiently reliable foreign object detection. This leads to a desire to generate as strong a signal as possible to increase detection accuracy. However, this increases power consumption in the power receiver and any foreign objects present. Detection performance is sensitive to the particular signal level applied, and typically there are conflicting requirements.

[0059] The system of FIG. 1 employs an approach for foreign object detection that adapts operations to provide improved tradeoffs for foreign object detection and seeks to facilitate early detection of foreign objects. This approach provides improved foreign object detection in many embodiments, and in particular, more accurate and / or more reliable foreign object detection in many embodiments. Furthermore, this approach allows for low complexity and low resource requirements. An advantage of this approach is that it is suitable for inclusion within many existing systems, such as in particular Qi wireless power transfer systems, and in practice this is often achieved with minor modifications.

[0060] As will be described in more detail below, this approach utilizes a time division approach during the power transfer phase, where foreign object detection and power transfer are performed, for example, in separate time intervals, thereby allowing interference between them (specifically, the effect of power transfer on foreign object detection) to be significantly reduced. Furthermore, the parameters of the generated electromagnetic signal are adapted to the specific test scenario. This can be achieved, for example, through an adaptation process performed before the system enters the power transfer phase.

[0061] In the following, the system of FIG. 1 is described in more detail. In an embodiment, the electromagnetic power transfer signal and the electromagnetic test signal used for foreign object detection are generated by two different coils (driven by different drivers). Furthermore, the signals are referred to by different terms, i.e., the electromagnetic signal generated during the power transfer time interval is referred to as the power transfer signal, and the electromagnetic signal generated during the foreign object detection time interval is referred to as the electromagnetic test signal or simply the test signal. However, it will be understood that in many embodiments, the electromagnetic signal may be generated from the same coil in both the power transfer time interval and the foreign object detection time interval, and in fact the same driver or the like may be used for both the power transfer time interval and the foreign object detection time interval. In fact, in many embodiments, reference to the test signal is considered to be equivalent to the power transfer signal during the foreign object detection time interval.

[0062] FIG. 2 shows elements of the power transmitter 101 of FIG. 1 in more detail.

[0063] The power transmitter 101 includes a driver 201 that may generate a (power transmission) drive signal that is provided to a transmitter coil 103, which generates an electromagnetic power transmission signal, thereby providing a power transmission to a power receiver 105. The power transmission signal is provided during a power transmission time interval of a power transmission phase.

[0064] The driver 201 generates the current and voltage provided to the transmitter inductor 103. The driver 201 is typically a drive circuit in the form of an inverter that generates an AC signal from a DC voltage. The output of the driver 201 is typically a switch bridge that generates the drive signal by appropriate switching of the switches of the switch bridge. It is understood that other components such as matching circuits may be present. These are within the understanding of those skilled in the art and will not be discussed in detail herein. The power transmitter 101 further comprises a power transmitter controller 203 configured to control the operation of the power transmitter 101 according to a desired operating principle. In particular, the power transmitter 101 includes many of the functions required to perform power control according to the Qi specification.

[0065] The power transmitter controller 203 is particularly configured to control the generation of the drive signal by the driver 201 and may in particular control the power level of the drive signal and therefore the level of the generated power transmission signal. The power transmitter controller 203 comprises a power loop controller that controls the power level of the power transmission signal in response to power control messages received from the power receiver 105 during a power control phase.

[0066] To receive data and messages from the power receiver 105, the power transmitter 101 comprises a message receiver 205 configured to receive data and messages from the power receiver 105 via a power signal. As will be understood by those skilled in the art, a data message provides one or more bits of information. In some cases, the power receiver 105 is configured to load modulate the power transmission signal generated by the transmitter coil 103, and the message receiver 205 is configured to sense variations in the voltage and / or current of the transmitter coil 103 and demodulate the load modulation based thereon. Those skilled in the art are aware of the principles of load modulation used, for example, in Qi wireless power transmission systems, so these will not be described in further detail.

[0067] In some embodiments, communication is performed using a separate communication channel achieved using a separate communication unit 207. In other examples, communication is performed using the transmitter coil 103. If a separate communication unit 207 is used, it comprises a communication coil or antenna 209. The communication coil 209 is depicted as a loop antenna, although other configurations are suitable and the selection is within the capabilities of one of ordinary skill in the art. For example, in some embodiments, near field communication is performed or high frequency communication is performed. frequency Carrier (e.g. 13.56MHz carrier frequency ) is superimposed on the power transmission signal using a separate communication unit 207. A communication protocol compliant with some or all of the ISO / IEC 18092 or ISO / IEC 14443 specifications may be used.

[0068] The power transmitter 101 further comprises a foreign object detector 211 configured to perform a foreign object detection test, i.e., specifically configured to detect whether any undesired conductive elements may be present in the generated electromagnetic field. The power transmitter 101 comprises a test coil 213 coupled to a test generator 215. The test generator 215 is configured to generate a test drive signal for the test coil 213 to provide an electromagnetic test signal during a foreign object detection time interval. The test drive signal is an electrical signal that is supplied to the test coil 213, resulting in the generation of an electromagnetic test signal. That is, the test coil 213 generates a corresponding electromagnetic field having a field strength according to the test drive signal.

[0069] The test generator 215 has substantially the same functionality as the driver 201, for example the test generator 215 comprises a half or full bridge inverter. Indeed, as previously mentioned, in many embodiments the test generator 215 may be realized by the driver 201 and the test coil 213 may be realized by the transmitter coil 103. Hence, in the following all references to the test generator 215 and the test coil 213 will be taken as references to the driver 201 and the test coil 213, where appropriate, for embodiments in which the same coils are used for generation of both the power transfer signal and the electromagnetic test signal.

[0070] The power transmitter further comprises an adapter / calibrator 217 configured to determine appropriate values ​​for one or more parameters of the test drive signal, which values ​​of the parameters of the test drive signal are then applied during (at least one) foreign object detection time interval of the power transfer phase.

[0071] In some embodiments, the communications unit 207 is also used for foreign object detection (FOD). In such cases, the test coil 213 and test generator 215 are effectively incorporated within the communications unit 207 and do not exist as separate units. In such configurations, the same coil or antenna is used for both communications and FOD. In such embodiments, the foreign object detector 211 communicates with the communications unit 207.

[0072] FIG. 3a illustrates a schematic of a half-bridge switched bridge / inverter used in an embodiment of the power transmitter 101. A DC voltage is applied to the input terminals V+ and V-. Switches S1 and S2 are controlled such that they are never closed at the same time. Alternately, S1 is closed while S2 is open and S2 is closed while S1 is open. The switches are switched to the desired frequency The inverter outputs a resonant capacitor Cres connected to the transmitter inductor 103, which is connected to the output of the inverter.

[0073] FIG. 3b illustrates a schematic of a full-bridge switched bridge / inverter used in an embodiment of the power transmitter 101. A DC voltage is applied to input terminals V+ and V−. In some modes of operation, switches S1 and S2 are controlled such that they are never closed at the same time. Switches S3 and S4 are controlled such that they are never closed at the same time. Alternately, switches S1 and S4 are closed while S2 and S3 are open, then S2 and S3 are closed while S1 and S4 are open, thereby producing a square wave signal at the output. The switches are controlled to switch the desired frequency In another mode of operation, part of the time S1 and S3 are open and S2 and S4 are closed, or vice versa. This is often referred to as phase control.

[0074] Figure 4 illustrates some example elements of the power receiver 105 of Figure 1. The receiver coil 107 is coupled to a power receiver controller 401, which couples the receiver coil 107 to a load 403 via a load output circuit 405. The power receiver controller 401 and the load output circuit 405 include a power control path that converts the power extracted by the receiver coil 107 into an appropriate supply to the load 403. In addition, the power receiver controller 401 has various power receiver controller functions required to perform a power transfer, and in particular, has functions required to perform a power transfer according to the Qi specification.

[0075] To support communication from the power receiver 105 to the power transmitter 101, the power receiver 105 includes a load modulator 407. The load modulator 407 may be configured to vary the load application of the receiver coil 107 in response to data to be transmitted to the power transmitter 101. The load variation is then detected and demodulated by the power transmitter 101 as known to those skilled in the art.

[0076] The power receiver 105 includes a power controller 409 configured to establish a power control loop with the power transmitter 101. Specifically, the power controller 409 may transmit a power control message to the power transmitter 101, in response to which the power transmitter 101 changes the power level of the power transmission signal during the power transmission time interval. Typically, the power controller 409 generates a power control error message indicating a request to the power transmitter 101 to increase or decrease the power level. The power controller 409 determines an appropriate error message by comparing a measurement value with a reference value. During power transmission, the power controller 409 compares the provided power level with a required power level and requests an increase or decrease in the power level based on the comparison. The power controller 409 includes a message controller that may be configured to generate an appropriate message and control the load modulator such that the power transmission signal is modulated according to the message, thereby enabling the power transmitter 101 to detect the transmitted message.

[0077] The power receiver 105 comprises a load controller 411. The load controller is useful when the power receiver 105 is configured to enter a reduced power mode during a reduced power time interval of each time frame during the power transfer phase. In this embodiment, the power receiver 105 comprises a load controller 411 that controls the load output circuit 405 (equivalently, the load output circuit 405 can be considered as part of the load controller). During the reduced power time interval, the load controller 411 can disconnect the load 403 from the power receiver, i.e., disconnect the load of the power receiver controller 401 and thus the load of the receiver coil 107. Thus, in this way, the load controller 411 reduces the load application of the receiver coil 107 during the reduced power time interval. Furthermore, the loading of the power receiver 105 is reduced, making other power loss detection or modulation detection easier, and often more importantly, the power receiver 105 is in a better defined or reliable state with reduced impact of load variations on the electromagnetic test signal. A load controller may also be used as part of the manner in which load modulation is implemented.

[0078] It will be appreciated that the loading of the receiver coil 107 does not have to be completely switched off during a foreign object detection interval. For example, the power receiver 105 may still extract power, for example to operate some internal circuitry. Thus, the load controller 411 may switch off the load of the receiver coil 107 while still allowing the receiver coil 107 to be loaded from one or more other loads. Certain The load 403 is configured to disconnect the load from the load application to the receiver coil 107. In practice, the load application to the receiver coil 107 may be considered to be composed of loads that are disconnected by the load controller 411 during the foreign object detection interval and loads that are not disconnected by the load controller 411. Thus, the load 403 may be considered to represent a load that is disconnected from the receiver coil 107 during the foreign object detection interval. This load includes both external or internal loads for which power transfer is established, but also internal control functions that are, for example, temporarily switched off during the foreign object detection interval.

[0079] The power receiver 105 comprises a communication unit 413 and an associated communication coil or antenna 415 that is used to communicate with an equivalent communication unit 207 in the power transmitter 101. The communication coil 415 is depicted as a loop antenna, although other configurations are suitable and the selection of which is within the capabilities of one of ordinary skill in the art. For example, in some embodiments near field communication is implemented or high frequency communication is implemented. frequency Carrier (e.g. 13.56MHz carrier frequency ) is superimposed on the power transmission signal. A communication protocol conforming to some or all of the ISO / IEC 18092 or 14443 specifications may be used.

[0080] The foreign object detection tests are based on measurements made during foreign object detection time intervals during which the power transmitter 101 operates in a foreign object detection mode in which operating conditions are set to assess whether any foreign objects are present.

[0081] For example, in embodiments where the power transmitter 101 uses different coils to generate the power transmission signal and the electromagnetic test signal, the power transmitter 101 switches off the power transmission signal completely and sets the electromagnetic test signal to an appropriate value. In embodiments where the same coil is used to generate the power transmission signal and the electromagnetic test signal, the drive signal for the coil is changed from an operating point suitable for power transmission to an operating point suitable for foreign object detection. Thus, in many embodiments, the current, voltage, frequency, duty cycle, power or level is changed between the power transfer time interval and the foreign object detection time interval. In many embodiments, the power or level of the power transfer signal is changed from a power level determined by the power transfer control loop function to a power level not determined by (independent of) the power transfer control loop function, such as a predetermined value. In many embodiments, the power or level of the electromagnetic signal is changed from a first power level to a second power level. The first power level is a predetermined or nominal level (e.g., may be zero) or is determined, for example, by the power transfer power control loop. The second power level is a predetermined level and is independent of the power transfer power control loop.

[0082] Thus, during an interval during which foreign object detection is performed, i.e., during a foreign object detection time interval, the foreign object detector 211 evaluates conditions to determine whether a foreign object is deemed to be present. During the foreign object detection time interval, the power transmitter 101 generates an electromagnetic test signal and foreign object detection is based on an evaluation of the features and characteristics of this signal.

[0083] For example, the power level of the test drive signal reflects the power extracted from the generated electromagnetic test signal, which is used as an indication that power is being extracted by a potential foreign object (typically by comparing this to the expected power extraction from the power receiver 105). The power level of the electromagnetic test signal reflects the power extracted from the electromagnetic test signal by conductive elements in the electromagnetic field (including the receiver coil 107). Thus, this is indicative of the power extracted by the combination of the power receiver 105 and any foreign object that may be present. Accordingly, the difference between the power level of the electromagnetic signal and the power extracted by the power receiver 105 reflects the power extracted by any foreign object present. Foreign object detection, for example, is a low complexity detection. For example, a foreign object detection is deemed to have occurred when the difference in the power level of the electromagnetic signal (hereafter referred to as the transmit power level) exceeds the reported power extracted by the power receiver 105 (hereafter referred to as the receive power level).

[0084] Therefore, in this approach, foreign object detection is based on a power level comparison between the transmit power level and the reported received power level. The response to the detection of a foreign object varies in different embodiments. However, in many embodiments, the power transmitter 101 is configured to terminate (at least temporarily) power transmission in response to the detection of a foreign object.

[0085] FIG. 5 shows a circuit diagram of an embodiment of the power path of the power receiver 105. In an embodiment, the power receiver 105 comprises a receiver coil 107, referenced by the symbol LRX. In an embodiment, the receiver coil 107 is part of a resonant circuit, and therefore the power receiver 105 also includes a resonant capacitor 501 (CRX). The receiver coil 107 is exposed to an electromagnetic signal, and therefore an AC voltage / current is induced in the coil. The resonant circuit is coupled to a rectifier bridge 503 with a smoothing capacitor 505 (C1), which is coupled to the output of the bridge. This generates a DC voltage on the capacitor 505. The magnitude of the ripple in the DC voltage depends on the size of the smoothing capacitor and the load.

[0086] The bridge 503 and the smoothing capacitor 505 are coupled to the load 403 via a switch 607. Although the load 403 is shown as a simple passive resistor, it will of course be understood that it may be any suitable load. For example, the load 403 may be a battery to be charged, a mobile phone, or another communication or computing device, may be a simple passive load, etc. In practice, the load 403 need not be an external load or a dedicated internal load, but may include, for example, elements of the power receiver 105 itself. Thus, the load 403 shown in Figures 4 and 5 may be taken to represent any load of the receiver coil 107 / electromagnetic signal.

[0087] 5 further illustrates a load modulation capacitor 509 (C2) that can be connected or disconnected in parallel to the resonant circuit based on the switching of a switch 511. The load modulator 407 or message controller 409 is configured to control the switch 511 such that the load of the modulation capacitor C2 can be connected or disconnected depending on the data to be transmitted to the power transmitter 101, thereby providing load modulation.

[0088] 6 illustrates figuratively the duration of the power transfer process. The power transfer has two phases: a communication phase 601 (annotated as "comm / neg / cal") and a power transfer phase 603.

[0089] During the communication phase 601, the power transmitter 101 and the power receiver 105 establish communication and perform negotiations regarding their respective requirements and capabilities. Such a phase is described in the Qi specification. They also perform a calibration routine that is used during subsequent operation.

[0090] During the power transfer phase 603, the system 101 applies recurring time frames 605, which include at least one power transfer time interval 607 and one foreign object detection time interval 609. The power transfer time intervals are denoted by PT, and the foreign object detection time intervals are denoted by FOD / COMM. In an embodiment, each time frame 605 includes only one FOD time interval 609 and one power transfer time interval 607, which (and the time frame itself) have the same duration in each frame. The FOD time interval 609 is also used for communication. It will be understood that in other embodiments, the time frames may also include other time intervals (e.g., separate communication intervals), or each time frame may include multiple foreign object detection time intervals and / or power transfer time intervals. In particular, some time frames include an adaptation or calibration time interval that allows calibration of the FOD system (211, 215, 207). Moreover, in some embodiments, the duration of the various time intervals (and, indeed, the time frames themselves) varies dynamically, and it will also be understood that the lengths of the periods shown do not imply a proportional relationship between the various intervals.

[0091] Thus, in this approach, foreign object detection and power transfer are separated in the time domain, thereby resulting in reduced cross-interference from power transfer to foreign object detection. Thus, variability and uncertainty resulting from variations in operating conditions for power transfer can be isolated from foreign object detection, resulting in more reliable and accurate foreign object detection.

[0092] Thus, in the power transmission time intervals 607, the power transmitter is configured to perform power transmission during the power transmission time intervals of the time frame of the power transmission phase. In particular, during these time intervals, the power transmitter 101 and the power receiver 105 operate a power control loop. (The power control loop is based on communication within the power transmission signal time interval or based on communication outside the power transmission signal time interval, e.g., in a dedicated communication time interval. For example, each FOD time interval 609 is separated by a number of alternating power transmission signal time intervals 607 and communication time intervals.) Thus, the level of power being transmitted is dynamically varied. In the foreign object detection time interval 609 of the time frame of the power transmission phase, at least one parameter of the drive signal, and therefore at least one parameter of the electromagnetic test signal, is set to a value determined during an adaptation operation performed before the foreign object detection time interval. Thus, during the foreign object detection time interval, the parameter is set to a predefined value (i.e., a value determined before the foreign object detection time interval and often before the power transmission phase). In contrast, during the power transfer time interval, the parameter is not constrained to this predetermined value.

[0093] For example, during the power transfer time interval 607, the system operates a power control loop that allows the system to vary the power level of the power transfer signal in response to power control messages from the power receiver. The power control loop controls the current, voltage, and frequency In contrast, during the FOD time interval 609, the parameters varied by the power control loop during the power transfer time interval are set to pre-defined values ​​determined before the power transfer phase.

[0094] It is convenient for the power receiver 105 to reduce its load during the FOD time intervals 609 that occur during the power transfer phase 603 .

[0095] In embodiments where the same coil is used for both the power transmission signal and the electromagnetic test signal, the power transmitter is configured to reduce the level of the power transmission signal during the foreign object detection time interval compared to the power transmission time interval. In many situations, the power level of the power transmission signal may be increased to a high level, such as a level of 10-100 W, or in many applications (e.g., for power transmission to kitchen appliances) to a significantly higher power level. However, during the foreign object detection time interval, the power level of the generated electromagnetic signal is reduced to a predetermined level that is much lower than the current or maximum allowed power during the power transmission time interval. For example, the power level is set to a predetermined level not exceeding 1 W.

[0096] In high power applications where dedicated FOD systems are used (e.g. for power transmission to kitchen appliances), it is advantageous to reduce the power transmission signal. It is desirable for the FOD system to be sensitive to detect even small objects. FOD systems are often used in technologies that require electromagnetic fields (such as high Q-factors). change When using a magnetic field such as a 1000 Hz FOD sensor, the presence of a large power signal (i.e., a strong magnetic field) requires the FOD system to have a high dynamic range in order to still be able to detect the weak signal of the foreign object. The strong power signal also reduces the signal-to-noise ratio (SNR) of the FOD test. When a power loss accounting method is used, the presence of a large power signal, i.e., when a large amount of power is being transmitted, it is difficult to accurately detect the differences in absorbed power because these differences are not large compared to the measurement error. Therefore, the power level is set to zero or very close to zero.

[0097] FIG. 7 illustrates time intervals and signals in a high power application such as a kitchen appliance. In this particular embodiment, the power transmitter 101 comprises an AC mains supply. During the power transfer interval 709, the power signal has an envelope that follows the envelope of a rectified version of the mains supply. As shown, the switching circuitry of FIGS. 3a and 3b frequency Higher than frequency The FOD interval 707 is operated at (or synchronized with) the zero crossing point. The FOD interval 707 is centered on the zero crossing point with an interval on either side. The zero crossing point of the main supply is a convenient time since interference from the main supply is lower. A possible time width for the FOD interval is 1.6 ms, which is sufficient to allow time for FOD testing and any communications. However, other time widths are also preferred depending on the details of the system, and one skilled in the art can make this determination. During the FOD interval, the power signal is kept at zero or below a level such that the magnetic field does not cause an unacceptable level of interference with the FOD testing. Since most of the power is transmitted at high power levels, it is more convenient to set the power signal to zero during the FOD interval.

[0098] In addition to applying a time frame that includes a particular foreign object detection time interval, the system also applies a technique in which values ​​of one or more parameters (or characteristics) of the test signal are adapted based on an adaptation process that in many embodiments is performed before the power transfer phase. Thus, this adaptation process determines a preferred value for one or more of the parameters / characteristics of the electromagnetic test signal before the power transfer phase and then applies this preferred value during the foreign object detection time interval of the subsequent power transfer phase. In some embodiments, the adaptation process is repeated during the power transfer phase, for example at regular intervals.

[0099] If the power transmitter 101 is equipped with a dedicated FOD unit, the power transmitter 101 may perform a FOD during a power transmission phase and / or during a matching time interval that is performed before the power transmission phase. To An adapter / calibrator 217 is provided that is configured to determine parameter values ​​of the test drive signal.

[0100] For high power applications, the potential heating of a foreign object can be significant even during just the first few power transfer intervals 607 of the power transfer phase 603. It is therefore desirable to detect any foreign object as soon as possible, and in fact before the power transfer phase 603 begins. The power transfer phase 603 is initiated by a FOD time interval 609, which is the time when the FOD test is performed to detect a foreign object. This is desirable for improving the safety of the system in that there is a risk of missing a foreign object, especially if the object is very small and allows power transmission to continue. It is understood that all measurement methods have error and noise limitations, and that these contribute to false negative results.

[0101] 8 illustrates time intervals and signals in a power transfer system 101 according to an embodiment. As before, a communication phase precedes a power transfer phase 603. In the power transfer phase 603, there is a recurring time frame that includes a power transfer interval 607 and an FOD time interval 609. Additionally, there is an FOD time interval (or slot) 811 during the communication phase 601.

[0102] 9 illustrates time intervals during a communication phase 601 according to an embodiment. The communication phase 601 includes a series of communication time intervals 901 and FOD time intervals 903. Performing FOD testing during the communication phase allows for earlier detection of a foreign object. Also, having more opportunities for FOD testing before power transfer begins reduces the risk of missing a foreign object. Having multiple FOD time intervals 903 during the communication phase is advantageous.

[0103] It can be seen that the communication phase is in practice very long due to the user's behavior (as opposed to the system's requirements). In many cases of high power applications (e.g. kitchen appliances), the user is not going to switch on the high power immediately after placing the appliance (power receiver 105) on the power transmitter 101. This provides further opportunities for repeated FOD tests, and it is advantageous to keep the FOD test repetitions until the user does something to start the power transfer phase 603. In practice, this is expedient as it answers the requirement for the situation where a foreign object is introduced after the first FOD test and before the power transfer phase 603. In practice, it is desirable to perform 5 FOD tests per second during the communication phase 601. There is little additional benefit to performing more than 10 FOD tests per second.

[0104] Fields used for communication (e.g., NFC) also interfere to some extent with the FOD test, for example degrading the SNR of the measurement. It is therefore desirable to remove the communication signal (field) during the FOD time interval. However, removing the communication signal can itself cause problems. The power receiver relies on this signal to power its communication circuitry (as the power signal has not yet been established). If the signal is removed for too long, the active part of the receiver may become unstable or power down, with the result that communication must be started again. It will also be appreciated that communication is not possible while the communication signal is not present. "Removing the signal" consists of reducing the signal power, less than 1 percent of the level used during communication being sufficient to keep interference with the FOD test to an acceptable level.

[0105] During the communication phase 601, some circuitry and hardware needs to be powered up, which does not involve the transfer of power via the main power transfer system (i.e., coils 103, 107 and associated hardware). Such circuitry includes the communication unit 413 and logic in the power receiver controller 401 required for the tasks of negotiation, interval timing and determination. circuit4. A user interface (which may be as simple as a colored LED) may be present, convenient for powering at least some of this. If NFC is used for communication, some of the energy of the NFC field may be harvested (or extracted) and used to power the hardware mentioned above. Since the NFC field is removed (or at least significantly reduced) during the FOD time interval, the energy harvesting hardware of the power receiver 105 (which may be conveniently incorporated in the communication unit 413, when present) must be able to harvest enough energy and store this energy to be able to keep the required hardware powered during the FOD time interval 903. The communication signal (field) may only be present 66% of the time. It is therefore advantageous for the energy harvester of the power receiver 105 to be able to keep the required hardware powered using a communication field that has a duty cycle of less than 66%. The power receiver 105 The power transmitter 101 Increasing or decreasing the power in a communication signal like , it is convenient to be able to send a signal to the power transmitter 101. This assumes that the communication unit 207 of the power transmitter is providing the communication signal. In the case of a protocol compliant with one of the above mentioned ISO / IEC standards, the power adjustment is performed when the communication unit 207 of the power transmitter starts the communication by providing a communication field and implementing a READ command.

[0106] Providing a capacitor at the receiver can help the power receiver to remain stably powered to some extent. However, it is desirable to keep this value to a minimum, since it presents a load in itself during the period when power is present, and therefore takes power away from the rest of the power receiver, i.e. more power needs to be transferred than if only the receiver were powered. A very large capacitor also carries a size and cost penalty. Hence, a trade-off is made.

[0107] Thus, there is a power transmitter 101 for wirelessly providing power via an inductive power transmission signal to a power receiver 105, the power transmitter 101 comprising a foreign object detector 207, 215 configured to perform a foreign object detection test, a communication coil 209 for generating a communication signal, a communication generator 207 configured to generate a communication control signal for the communication coil 209 providing the communication signal during a communication period, the communication generator 207 configured to set the communication control signal to a first value during the communication period and to set the communication control signal to a second value during a communication foreign object detection time interval, the communication foreign object detection time interval occurring during the communication period, the communication generator 207 configured to generate a power transmission signal, a power transmission coil 103 for generating a power transmission signal, a driver 201 for generating a drive signal for the power transmission coil 103, the driver 201 configured to generate the drive signal to use a repetitive time frame including at least a power transmission time interval and a transmission foreign object detection time interval during a power transmission phase, and a receiver 205, 207 for receiving messages from the power receiver 105. The power receiver 105 is configured to wirelessly receive power via an inductive power transmission signal, the power receiver 105 comprising a communication coil 107 for receiving the received communication signal, a communication controller 413, 407, 409 configured to decode the received communication signal and generate a communication response signal for the communication coil 415, 407, a communication signal power harvester 413, 107 configured to extract power from the received communication signal for powering the communication controller and the user interface during a time interval in which the communication signal is at a first value and to store a portion of the extracted power sufficient to keep the communication controller and the user interface in an operational state during a communication foreign object detection time interval, the power receiver coil 107 for extracting power from the power transmission signal, a foreign object detection controller 411 for reducing the load of the power receiver during the transmission foreign object detection time interval, and a message transmitter 413, 407 for transmitting a first message to the power transmitter. The power receiver also comprises a more or less complex user interface (e.g. from a simple LED to a display).

[0108] Often, the first value is higher than the second value and the second value is zero or substantially zero.

[0109] Thus, there is also provided a method of operating a power transmitter 101 that wirelessly provides power via an inductive power transmission signal to a power receiver 105, the method comprising the steps of generating a communication control signal, where the communication control signal is set to a first value during a communication period and to a second value during a first foreign object detection time interval, the first foreign object detection time interval occurring during the communication period; generating a communication signal by applying the communication signal to a communication field; generating a power transmission signal; and generating a drive signal for a transmitter coil (103), where during the power transmission phase the drive signal uses a repetitive time frame that includes at least the power transmission time interval and the second foreign object detection time interval; performing a foreign object detection test during the first and second foreign object detection time intervals; and receiving a message from the power receiver 105. On the power receiver 105 side, a method of operating the power receiver 105 to wirelessly receive power via an inductive power transmission signal includes receiving a received communication signal via the communication coil 107, decoding the received communication signal and generating a communication response signal for the communication coil 107, extracting power from the received communication signal and storing a portion of the extracted power sufficient to power the communication controller 413, 407, 409 and the user interface and maintain the communication controller and the user interface in operation during a first foreign object detection time interval, extracting power from the power transmission signal using the power transmission coil 107, reducing the load on the power receiver during a second foreign object detection time interval, and transmitting a message to the power transmitter via the communication coil.

[0110] A convenient way of performing FOD is by applying a signal to observe the damping of oscillations in a resonant circuit. From the damping, the real part of the reactance of the system can be deduced. Since the real part of the reactance represents the amount of power absorbed by the system, the presence of a foreign object can then be determined. For this to be successful, a number of cycles are required, the more cycles (i.e. the longer the test), the more accurate it will be.

[0111] 10 shows time intervals during communication 610 according to a further embodiment. The communication phase 601 starts with a first (initial) communication interval 1001. This first communication interval 1001 is followed by a long FOD time interval 1003. Then, a communication interval 1005 and a shorter FOD time interval 1007 follow. The longer communication foreign object detection time interval is longer than the shorter foreign object detection time interval. The longer FOD time interval 1003 is used for accurate FOD testing and / or for adapting / calibrating the FOD system used by a later FOD test, such as a FOD test performed in the communication phase 601 or a FOD test in the power transfer phase 603. Other measurements, such as coupling coefficients, may also be performed and the results used later. The shorter FOD time interval 1007 is used for a quicker check for the presence of a foreign object. For example, this may be by using calibration data acquired during a longer FOD time interval (if applicable) and / or by using a faster (but perhaps less accurate) method. A longer FOD time interval may be 100 ms or less, a shorter FOD time interval may be 10 ms or less, and typically be around 2 ms long. This value may take into account system-wide variations such as differences in the actual resonant frequency or noise levels in the measurement circuitry. To allow a user to place an appliance on the power transmitter 101 and immediately begin using the appliance without experiencing any noticeable delay. It is convenient to complete the longer FOD test within (approximately) 200 ms from the start of the connection. An advantage of using longer and shorter FOD time intervals may be that more FOD time intervals may be used without unduly reducing the duty cycle of the communication field, compared to using FOD test methods that require longer intervals.

[0112] It is useful to compare results from shorter FOD time intervals. If the results deviate from each other by more than a threshold, another longer FOD time interval can be used. An example of this comparison and threshold is that measurements from a series of short FOD tests must be within ±5 percent of their average result.

[0113] The power transmitter 101 and the power receiver 105, during the beginning of the communication phase 601, determine the timing of the FOD time intervals 903, 1001, 1005 occurring during the communication phase 601, frequency It is understood that negotiations may also be conducted regarding the duration and / or duration of the FOD test. This allows the system 101 to perform the FOD test while allowing some margin in the operation of the energy harvesting. frequency (or duration) can be set as high as possible.

[0114] The communication units 207, 413 and their respective coils 209, 415 can also be used for other measurements besides foreign object detection. May be It will be appreciated that the FOD tester 105 may be used to measure the coupling coefficients. Such measurements may be performed during FOD time intervals 903, 1003, 1005 occurring during the communication phase 601. This has the benefit of allowing more accurate adjustment of the power signal. If the FOD test of the power transfer phase 603 is performed using either or both the communication unit 207 or a dedicated FOD tester 213, this hardware may also be used for the coupling coefficient measurements. This has the advantage of aiding in power control, for example by detecting when the appliance has moved slightly. This may be achieved by having the power receiver 105 indicate the maximum number of FOD time intervals it can support and then adapting the power transmitter 101 to that.

[0115] It will be appreciated that for clarity, the above description has described embodiments of the invention with reference to various functional circuits, units and processors. However, it will be apparent that any suitable distribution of functionality between various functional circuits, units or processors may be used without detracting from the invention. For example, functionality shown to be performed by separate processors or controllers may be performed by the same processor or controller. Thus, references to specific functional units or circuits should not be considered as indicative of a strict logical or physical structure or organization, but merely as references to suitable means for providing the described functionality.

[0116] The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and / or digital signal processors. The elements and components of the embodiments of the invention may be physically, functionally and logically implemented in any suitable way. Indeed functionality may be implemented in a single unit, in multiple units or as part of other functional units. Thus, the invention may be implemented in a single unit or may be physically and functionally distributed between different units, circuits and processors.

[0117] Although the present invention has been described in connection with certain embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the appended claims. Moreover, while features may appear to be described in connection with certain embodiments, those skilled in the art will recognize that various features of the described embodiments may be combined in accordance with the present invention. In the claims, the term "comprises," "includes," "has," "has" does not exclude the presence of other elements or steps.

[0118] It will be understood that the reference to a preferred value does not imply any limitation beyond it being the value determined in the foreign object detection initialization mode, i.e., it is preferred because it was determined in the fitting process. The reference to a preferred value may be replaced with a reference to a first value, for example.

[0119] Furthermore, a number of means, elements, circuits and method steps, although individually recited, may be implemented by, for example, a single circuit, unit or processor. Moreover, although individual features are included in different claims, they may be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not possible / advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is applicable to other claim categories as well, as appropriate. Furthermore, the order of features in the claims does not imply any particular order in which the features should be performed, and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, references in the singular do not exclude a plurality. Thus, references to the singular, "first", "second", etc. do not exclude a plurality. Reference signs in the claims are provided merely as examples for clarity and should not be construed as limiting the scope of the claims in any way.

Claims

1. 1. A power transmitter for wirelessly providing power via an inductive power transmission signal to a power receiver, the power transmitter comprising: a power transmission coil for generating the power transmission signal; a driver for generating a drive signal for the power transmission coil, the driver generating the drive signal to use a repetitive time frame during a power transmission phase that includes at least a power transmission time interval and a transmitted foreign object detection time interval, the drive signal being generated such that a level of the power transmission signal during the transmitted foreign object detection time interval is reduced compared to a level of the power transmission signal during the power transmission time interval; a foreign object detector for performing a foreign object detection test; a communication coil for generating a communication signal; a communication unit generating a communication control signal for the communication coil providing the communication signal during a communication phase preceding the power transmission phase, wherein no power transmission signal is present during the communication phase, and during the communication phase, the communication unit sets the communication control signal to a first value during a communication period and sets the communication control signal to a second value lower than the first value during a foreign object sensing time interval, the foreign object sensing time interval occurring during the communication phase; The power transmitter is configured such that the foreign object detector performs foreign object detection tests during both the transmission foreign object detection time interval and the communication foreign object detection time interval.

2. The power transmitter of claim 1 , wherein the communication period includes a plurality of foreign object detection time intervals, the plurality of foreign object detection time intervals including a longer foreign object detection time interval and a shorter foreign object detection time interval.

3. 3. The power transmitter of claim 2, wherein the longer foreign object sensing time interval has a length less than or equal to 100 ms, the short foreign object sensing time interval has a length less than or equal to 10 ms, and the foreign object sensing time intervals occur at a period of 200 ms.

4. 4. The power transmitter of claim 2 or 3, wherein the first longer communication foreign object detection time interval is completed within 200 ms of establishing communication with the power receiver.

5. 5. The power transmitter of claim 1, wherein the power transmitter is powered by a mains power supply having a zero crossing point, and the transmission foreign object detection time interval is synchronized with the zero crossing point.

6. The power receiver comprises a communications signal power harvester configured to extract and store power from a received communications signal; 6. The power transmitter of claim 1, wherein the first value of the communication signal is set such that the communication signal power capturer can extract sufficient power from the communication signal received during the communication period of the communication phase to maintain communication during the communication foreign object detection time interval of the communication phase.

7. The power transmitter of claim 1 , wherein the second value of the communication signal is set to reduce interference with a foreign object detection test.

8. The power transmitter of claim 2 , wherein the foreign object detection test is performed using the communication unit.

9. 9. The power transmitter of claim 1, wherein the power transmitter negotiates with the power receiver the frequency and / or duration of foreign object detection (FOD) time intervals during a communication phase.

10. 1. A power receiver for wirelessly receiving power via an inductive power transmission signal, the power receiver comprising: a communication coil for receiving an incoming communication signal; a communication controller for decoding the received communication signal and generating a communication response signal for the communication coil; a communications signal power harvester that extracts power from the received communications signal to power the communications controller during a time interval in which the received communications signal is at a first value and that stores a portion of the extracted power sufficient to maintain the communications controller in an operational state during a communicating foreign object detection time interval; a power receiving coil for extracting power from the power transmission signal; a message transmitter for transmitting a message to the power transmitter; A power receiver comprising:

11. The power receiver according to claim 10 , wherein the communication controller maintains a connection state during the foreign object detection time interval.

12. 12. The power receiver of claim 10 or 11, wherein the power extracted is sufficient to power the communications controller with the received communication signal having a duty cycle of 66% or less.

13. 13. The power receiver of claim 10, wherein the power receiver negotiates with the power transmitter the frequency and / or duration of foreign object detection time intervals that it can support during a communication phase.

14. 1. A wireless power transfer system comprising a power transmitter for wirelessly providing power via an inductive power transfer signal to a power receiver, the power transmitter comprising: a foreign object detector for performing a foreign object detection test; a communication coil for generating a communication signal; a communication unit generating a communication control signal for the communication coil providing the communication signal during a communication phase preceding a power transmission phase, wherein no power transmission signal is present during the communication phase, the communication unit setting the communication control signal to a first value during a communication period and setting the communication control signal to a second value lower than the first value during a communication foreign object detection time interval, the communication foreign object detection time interval occurring during the communication phase; a transmitter coil for generating the power transmission signal; a driver for generating a drive signal for the transmitter coil, the driver generating the drive signal to use a repetitive time frame during the power transfer phase that includes at least a power transfer time interval and a transmission foreign object detection time interval, the drive signal being generated such that a level of the power transfer signal during the transmission foreign object detection time interval is reduced compared to a level of the power transfer signal during the power transfer time interval; Equipped with the foreign object detector is configured to perform a foreign object detection test during both the transmission foreign object detection time interval and the communication foreign object detection time interval; The power receiver includes: a communication coil for receiving an incoming communication signal; a communication controller for decoding the received communication signal and generating a communication response signal for the communication coil; a communications signal power harvester that extracts power from the received communications signal to power the communications controller and stores a portion of the extracted power sufficient to maintain the communications controller and a user interface in an operational state; a message transmitter for transmitting a message to the power transmitter; A wireless power transmission system comprising:

15. 1. A method of operating a power transmitter that wirelessly provides power via an inductive power transmission signal to a power receiver, the method comprising: generating a communication signal during a communication phase preceding a power transfer phase, wherein no power transfer signal is present during the communication phase, the communication signal being set to a first value during a communication period and set to a second value lower than the first value during a first foreign object detection time interval, the first foreign object detection time interval occurring during the communication phase; applying said communication signal to a communication field; generating a power transfer signal; generating a drive signal for a transmitter coil, during the power transfer phase, the drive signal using a repetitive time frame including at least a power transfer time interval and a second foreign object detection time interval, the drive signal being generated such that a level of the power transfer signal during the second foreign object detection time interval is reduced compared to a level of the power transfer signal during the power transfer time interval; conducting a foreign object detection test during both the first and second foreign object detection time intervals; receiving a message from the power receiver; The method comprising:

16. 1. A method of operating a power receiver for wirelessly receiving power via an inductive power transmission signal, the method comprising: receiving an incoming communication signal via a communication coil; decoding the received communication signal and generating a communication response signal for the communication coil; extracting power from the received communication signal and storing a portion of the extracted power sufficient to power a communications controller and a user interface and maintain the communications controller and the user interface in operation during a first foreign object detection time interval; extracting power from the power transmission signal using a power transmission coil; transmitting a message to a power transmitter via the communication coil; The method comprising:

17. A computer program which, when executed on a processor controlling a wireless power transmitter according to any one of claims 1 to 9, causes the wireless power transmitter to perform a method according to claim 15.

18. A computer program which, when executed on a processor controlling a wireless power receiver according to any one of claims 10 to 13, causes the wireless power receiver to perform a method according to claim 16.

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