Foreign object detection in wireless power transfer systems

Abstract

A power transmitter for wirelessly providing power to a power receiver via an inductive power transfer signal. The power transmitter comprises a power transfer coil for generating the power transfer signal, a driver for generating a drive signal for the power transfer coil, the driver being arranged to generate the drive signal during a power transfer phase to adopt a repetitive time framework, the repetitive time framework comprising at least a power transfer time interval and a transfer foreign object detection time interval, a receiver for receiving a message from the power receiver, a foreign object detector arranged to perform a foreign object detection (FOD) test, a communication coil for generating a communication signal, and a communication unit arranged to generate a communication control signal for the communication coil to provide the communication signal during a communication period, the communication unit being arranged to set the communication control signal to a first value during the communication period and to a second value during a communication foreign object detection time interval, the communication foreign object detection time interval occurring during the communication period.

Description

Technical Field

[0001] This invention relates to foreign object detection in wireless power transmission systems, and particularly, but not exclusively, to foreign object detection in power transmitters used to provide inductive power transmission to higher power devices (e.g., kitchen appliances). Background Technology

[0002] Most existing electrical products require dedicated electrical contacts to draw power from an external power source. However, this is often impractical and requires the user to physically insert a connector or otherwise establish physical electrical contact. Power requirements also typically vary significantly, and most devices currently have their own dedicated power supplies, resulting in a typical user having a large number of different power supplies, each dedicated to a specific device. While using an internal battery avoids the need for a wired connection to a power source during use, this only provides a partial solution, as the battery requires charging (or replacement). Using a battery also substantially increases the weight of the device and potentially increases cost and size.

[0003] To provide a significantly improved user experience, the use of wireless power has been proposed, 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, primarily applied in 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 between them can be achieved based on the principle of a loosely coupled transformer.

[0005] This arrangement allows for wireless power transfer to the device without requiring any wiring or physical electrical connections. In fact, it simply allows the device to be placed in the vicinity or on top of the transmitter coil for external charging or power supply. For example, the power transmitter device can be arranged on a horizontal surface, allowing the device to be easily placed on that surface for power supply.

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

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

[0008] A potential problem with wireless power transfer is that power can be unintentionally transferred to, for example, a metallic object located near the power transmitter. For instance, if a foreign object (e.g., a coin, key, ring, etc.) is placed on a power transmitter platform arranged to receive power from a receiver, the magnetic flux generated by the transmitter coil will introduce eddy currents in the metallic object, causing it to heat up. This increase in heat can be significant and potentially highly detrimental.

[0009] To mitigate the risk of such scenarios, foreign object detection (FOD) has been proposed, whereby a power transmitter can detect the presence of a foreign object and reduce its transmission power and / or generate a user alarm upon detection. For example, the Qi system includes functions for detecting foreign objects and for reducing power upon detection. Specifically, Section 11 of Qi specification version 1.2.1 describes various methods for detecting foreign objects.

[0010] A method for detecting such foreign objects is disclosed in WO 2015018868 A1. Another example is provided in WO 2012127335, which discloses a method based on determining unknown power loss. In this method, both a power receiver and a power transmitter measure their power, and the receiver transmits its measured received power to the power transmitter. When the power transmitter detects a significant difference between the power transmitted by the transmitter and the power received by the receiver, an unwanted foreign object may be present, and power transmission can be reduced or stopped for safety reasons. This power loss method requires synchronized and accurate power measurements performed by the power transmitter and the power receiver.

[0011] For example, in the Qi power transmission standard, the power receiver estimates its received power, for instance, by measuring the rectified voltage and current, multiplying them, and adding an estimate of the power receiver's internal power losses (e.g., losses in the rectifier, receiver coils, 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, for example, every four seconds. This is commonly referred to as "power loss accounting."

[0012] The power transmitter estimates its transmit power, for example, by measuring the DC input voltage and current of the inverter, multiplying them, and correcting the result of the multiplication by subtracting an estimate of the internal power losses in the transmitter (e.g., the estimated power losses of the inverter, primary coil, and metal parts that are part of the power transmitter).

[0013] A power transmitter can estimate power loss by subtracting the reported received power from the transmitted power. If the difference exceeds a threshold, the transmitter will determine that too much power is being dissipated in the foreign object and can then terminate power transmission.

[0014] Alternatively, it has been proposed to measure the quality factor or quality factor of a resonant circuit formed by a primary and secondary coil, as well as the corresponding capacitance and resistance. A decrease in the measured quality factor can indicate the presence of a foreign object.

[0015] In practice, it is often difficult to achieve sufficient detection accuracy using the methods described in the Qi specification. Numerous uncertainties regarding current specific operating conditions exacerbate this difficulty.

[0016] For example, a particular problem may be the presence of metal-friendly materials (i.e., metal parts of devices that embody a power receiver or power transmitter) whose magnetic and electrical properties may be unknown (and vary between different devices), making them potentially difficult to compensate for.

[0017] Furthermore, even relatively small amounts of power dissipated within metallic foreign objects can cause unwanted heat generation. Therefore, it is even necessary to detect small power differences between transmitted and received power, which can be particularly difficult as the power level of the transmitted signal increases.

[0018] In many scenarios, the quality factor degradation method can have better sensitivity to detect the presence of metallic objects. However, it may still not provide sufficient accuracy and may also be affected by, for example, friendly metals.

[0019] The performance of foreign object detection (FOD) is affected by the specific operating conditions present during actual testing. For example, as described in the Qi specification, if a FOD measurement is performed during the selection phase of the power transmission initialization process, the signal provided by the power transmitter for that measurement must be small enough to prevent it from waking up the power receiver. However, for such a small signal, the signal-to-noise ratio is typically poor, leading to reduced measurement accuracy.

[0020] Another issue is that foreign object detection is typically a very sensitive test, where the expectation is to detect relatively small changes caused by the presence of a foreign object in an environment where the operating conditions and scenarios being tested may vary greatly.

[0021] Therefore, current algorithms are often suboptimal and may even provide worse performance than optimal performance in some scenarios. In particular, they may lead to undetected foreign objects or falsely detect foreign objects when they are not present.

[0022] Given that, for example, kitchen appliances may use very high power levels, foreign objects may heat up very quickly, so it is desirable to detect the presence of such objects as quickly and reliably as possible.

[0023] Therefore, it is advantageous to provide improved object detection, and in particular, to allow for methods that offer increased flexibility, reduced costs, reduced complexity, improved object detection, fewer false detections and missed detections, backward compatibility, and / or improved performance. Summary of the Invention

[0024] Therefore, the present invention seeks to mitigate, alleviate or eliminate one or more of the above-mentioned disadvantages, preferably in a single manner or in any combination thereof.

[0025] Therefore, a power transmitter is provided for wirelessly providing power to a power receiver via an inductive power transmission signal. The power transmitter 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 being arranged to generate the drive signal during a power transmission phase to employ a repetitive time frame, the repetitive time frame 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 (FOD) arranged to perform a foreign object detection (FOD) test; a communication coil for generating a communication signal; and a communication unit arranged to generate a communication control signal for the communication coil to provide the communication signal during a communication period, the communication unit being arranged to set the communication control signal to a first value during the communication period and to a second value during a communication FOD time interval, the communication FOD time interval occurring during the communication period.

[0026] The ability to perform foreign object testing during communication allows for the detection of foreign objects before power transmission begins. This reduces the risk of unwanted heating caused by any potentially present foreign objects. Such heating is particularly important in high-power applications, as even small objects can rapidly become hot and dangerous. The second value can be lower than the first value and can even be set to zero. By setting the second value to zero, interference from the communication signal to any foreign object testing can be significantly reduced.

[0027] In this embodiment, the communication period includes multiple communication foreign object detection time intervals, which include a longer communication foreign object detection time interval and a shorter communication foreign object detection time interval. The longer communication foreign object detection time interval is longer than the shorter foreign object detection time interval.

[0028] In this embodiment, longer FOD intervals allow for more accurate FOD testing and calibration, the data of which can be used for later FOD testing. They also provide opportunities to perform other tests, such as coupling coefficient tests. Shorter FOD intervals can be performed more frequently without interrupting communication signals for too long. Frequent FOD testing reduces the risk of placing foreign objects on the power transmitter between FOD tests.

[0029] In this embodiment, the longer foreign object detection (FOD) interval has a length of less than or equal to 100 ms, and the shorter FOD interval has a length of less than or equal to 10 ms, wherein the FOD interval occurs within a 200 ms time period. These values ​​allow sufficient time to perform the FOD test while maintaining the communication signal.

[0030] In one embodiment, there is a first long communication foreign object detection time interval, which is completed within 200ms of establishing communication with the power receiver, thereby allowing for the desired earlier FOD.

[0031] In this embodiment, the power transmitter is powered by an AC power supply with a zero-crossing point, and the foreign object detection time interval for power transmission is synchronized with the zero-crossing point. The zero-crossing point of the AC power supply is a convenient time because interference from the AC power supply will be lower.

[0032] In an embodiment, the first value of the communication signal is set to transmit sufficient power to the communication signal power harvester in the power receiver. Power can be harvested from the communication signal to power on and activate some basic functions of the power receiver (e.g., logic units for communication, and, where applicable, a user interface).

[0033] In this embodiment, the second value of the communication signal is set to reduce interference with the foreign object detection test, since the communication signal can also interfere with and reduce the reliability of the FOD test.

[0034] In this embodiment, the communication unit is used to perform the foreign object detection test, as this reduces the amount of hardware required.

[0035] In one embodiment, the power transmitter is configured to negotiate the frequency of the FOD time interval during the communication phase with the power receiver. This allows the system to find a potentially better trade-off between the time spent on FOD testing and the communication signal at default values.

[0036] A power receiver is provided for wirelessly receiving power via an inductive power transmission signal; the power receiver includes: a communication coil for receiving a received communication signal; a communication controller arranged to decode the received communication signal and generate a communication response signal for the communication coil; a communication signal power harvester arranged to: extract power from the received communication signal during a time interval in which the communication signal is at a first value, in order to power the communication controller; and store a portion of the extracted power, the portion of the extracted power being sufficient to maintain the communication controller (and user interface) in an operational state during a communication foreign object detection (FOD) 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 is able to maintain some of its hardware during the communication FOD time interval in order to continue cooperating with the power transmitter.

[0037] In one embodiment, the communication controller of the power receiver is configured to maintain a connection during the foreign object detection interval. This has the advantage that communication does not need to be renegotiated at each new communication interval.

[0038] In one embodiment, the power receiver includes a user interface and is arranged such that the extracted power is sufficient to power the communication controller and the user interface, wherein the communication signal has a duty cycle of 66% or less. Time spent on FOD testing and any other non-communication operations can occupy up to one-third of the communication time. Therefore, it is desirable for the power receiver to manage this.

[0039] In one embodiment, the power receiver is arranged to negotiate with the power transmitter about the frequency of foreign object detection time intervals that the power transmitter can support during the communication phase.

[0040] A wireless power transmission system is also provided, comprising a power transmitter and a power receiver, the power transmitter being configured to wirelessly provide power to the power receiver via an inductive power transmission signal. The power transmitter includes: a foreign object detector arranged to perform a foreign object detection test; a communication coil for generating a communication signal; a communication unit arranged to generate a communication control signal for the communication coil to provide the communication signal during a communication period, the communication unit being arranged to set the communication control signal to a first value during the 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; a transmitter coil for generating the power transmission signal; a driver for generating a drive signal for the transmitter coil, the driver being arranged to generate the drive signal during a power transmission phase to employ a repetitive time frame, the repetitive time frame including at least the power transmission time interval and the foreign object detection time interval; and a receiver for receiving messages from the power receiver. The power receiver includes: a communication coil for receiving a received 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, the portion of which is 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 for operating a power transmitter that wirelessly provides power to a power receiver via an inductive power transfer signal is also provided. The method includes: generating a communication signal, wherein the communication signal is set to a first value during a communication period and to a second value during a first foreign object detection (FOD) time interval, the first FOD time interval occurring during the communication period; applying the communication signal to a communication field; generating a power transfer signal; generating a drive signal for a transmitter coil, wherein during the power transfer phase, the drive signal employs a repetitive time frame, the repetitive time frame including at least the power transfer time interval and the second FOD time interval; and performing FOD detection during the first FOD time interval and the second FOD time interval; and receiving a message from the power receiver.

[0042] A method for operating a power receiver for wirelessly receiving power via an inductive power transmission signal is also provided, the method comprising: 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 powering a communication controller and a user interface, and storing a portion of the extracted power, the portion of the extracted power being sufficient to maintain the communication controller and the user interface in an operational state 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 the power transmitter via the communication coil.

[0043] A computer program product is also provided, which, when run on a processor located in a wireless power transmitter or wireless power receiver, causes the wireless power transmitter to operate accordingly. Attached Figure Description

[0044] Embodiments of the invention are described with reference to the accompanying drawings, which are merely examples, in which:

[0045] Figure 1 An example of the elements of a power transmission system according to an embodiment is illustrated.

[0046] Figure 2 An example of the elements of a power transmitter according to an embodiment is illustrated.

[0047] Figure 3a and Figure 3b Examples of half-bridge and full-bridge inverters for power transmitters are illustrated.

[0048] Figure 4 A power receiver according to an embodiment is illustrated.

[0049] Figure 5 An example of the elements of a power receiver according to an embodiment is illustrated.

[0050] Figure 6 The illustration shows the timeframe for the operation of the system according to an embodiment.

[0051] Figure 7 The diagram shows Figure 1 The operational phase of the wireless power transmission system.

[0052] Figure 8 The diagram illustrates the concept presented in a frame diagram. Figure 1 The operating time of the wireless power transmission system.

[0053] Figure 9 The illustrations depict some embodiments of the present invention. Figure 1The operational phase of the wireless power transmission system.

[0054] Figure 10 The illustrations are presented in a frame diagram according to some embodiments of the present invention. Figure 1 The operational phase of the wireless power transmission system. Detailed Implementation

[0055] The following description focuses on embodiments of the invention applicable to wireless power transmission systems utilizing power transmission methods known, for example, from the Qi specification. However, it will be appreciated that the invention is not limited to this application, but can be applied to many other wireless power transmission systems.

[0056] Figure 1 An example of a power delivery system 100 according to some embodiments of the present invention is illustrated. The power delivery system includes a power transmitter 101, which includes (or is coupled to) a transmitter coil / inductor 103. The system also includes a power receiver 105, which includes (or is coupled to) a receiver coil / inductor 107.

[0057] System 100 provides an electromagnetic power transmission signal that can be inductively powered 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 transmission signal typically has a frequency between about 20 kHz and about 500 kHz, and for Qi-compatible systems, the frequency range is typically 95 kHz to 205 kHz (or, for example, for high-power kitchen applications, the frequency range is typically between 20 kHz and 80 kHz). The transmitter coil 103 and the power receiving coil 107 are loosely coupled, so that the power receiving coil 107 picks up (at least a portion) of the power transmission signal from the power transmitter 101. Therefore, power is transmitted from the power transmitter 101 to the power receiver 105 via a wireless inductive coupling from the transmitter coil 103 to the power receiving coil 107. The term power transfer signal is primarily used to refer to the induced signal / magnetic field (magnetic flux signal) between the transmitter coil 103 and the power receiving coil 107, but it will be appreciated that the term power transfer signal can also be equivalently regarded as and used as a reference to the electrical signal provided to the transmitter coil 103 or picked up by the power receiving coil 107.

[0058] In this example, power receiver 105 specifically refers to a power receiver that receives power via receiver coil 107. However, in other embodiments, power receiver 105 may include a metallic element, such as a metallic heating element, in which case the power transmission signal directly induces eddy currents, resulting in direct heating of the element.

[0059] System 100 can be configured to transmit high power levels, and in particular, in many embodiments, power transmitter 101 can support power levels exceeding 500mW, 1W, 5W, 50W, 100W, or 500W. For example, for Qi-compliant applications, power transmission is typically within the 1-5W power range for low-power applications (basic power profile), up to 15W for Qi specification version 1.2, up to 100W for higher-power applications (e.g., power tools, laptops, drones, robots, etc.), and exceeding 1000W for ultra-high-power applications (e.g., kitchen appliances).

[0060] In the following description, the operation of power transmitter 101 and power receiver 105 will be specifically referenced to embodiments generally based on the Qi specification (other than the modifications and enhancements described herein) or suitable for use with higher power kitchen specifications developed by the Wireless Power Consortium. In particular, power transmitter 101 and power receiver 105 may conform to or be substantially compatible with Qi specification versions 1.0, 1.1, or 1.2 (other than the modifications and enhancements described herein).

[0061] In wireless power transmission systems, the presence of an object during power transmission (typically a conductive element that extracts power from the power transmission signal but is not part of the power transmitter 101 or power receiver 105, i.e., an unintended, unwanted, and / or interfering conductive element with power transmission) is highly detrimental. Such an unwanted object is referred to in the art as a foreign object.

[0062] Foreign objects not only reduce efficiency by increasing power loss during operation, but they can also degrade the power transmission operation itself (e.g., by interfering with power transmission efficiency or extracting power not directly controlled by the power transmission circuit). Furthermore, the induction of currents in foreign objects (especially eddy currents in the metal parts of the foreign object) can cause often highly undesirable heating of the foreign object. This concern is particularly acute when using high-power levels, such as those applicable to kitchen appliances, and when even small objects can undesirably heat up.

[0063] To address the problems in this scenario, wireless power transmission systems such as Qi include functions for foreign object detection. Specifically, the power transmitter 101 includes functions to detect the presence of foreign objects. If so, the power transmitter 101 can, for example, terminate power transmission or reduce the maximum amount of power that can be transmitted.

[0064] The current methods proposed in the Qi specification are based on detecting power loss (obtained by comparing the transmit power with the reported receive power) or detecting degradation of the quality Q of the output resonant circuit. However, in current use, these methods have been found to provide suboptimal performance in many scenarios, and they can particularly lead to inaccurate detection, resulting in missed detections and / or false positives (where a foreign object is detected even though it is not actually present).

[0065] Foreign object detection can be performed before the power receiver enters the power transfer phase (e.g., during power transfer initialization) or during the power transfer phase. Detection during the power transfer phase is typically based on a comparison of the measured transmit power with the received power, while detection occurring before the power transfer phase is typically based on a measurement of the reflected impedance (e.g., obtained by measuring the quality factor of the transmitter coil using a small measurement signal).

[0066] Conventional foreign object detection is often suboptimal, partly due to variations and uncertainties in the specific operating conditions and scenarios in which it is performed, including variations and uncertainties in power transmitter properties, power receiver properties, and applied test conditions.

[0067] An example of the challenges in foreign object detection testing is the requirement to perform sufficiently accurate measurements to achieve reliable foreign object detection. This leads to the desire for the strongest possible signal to improve detection accuracy. However, this increases power loss in the receiver and any foreign object present. Detection performance can be highly sensitive to specific signal levels applied, often resulting in conflicting requirements.

[0068] Figure 1 The system employs a method for foreign object detection that seeks to adjust operations to provide an improved trade-off for foreign object detection and facilitate earlier detection. In many embodiments, the method can provide improved foreign object detection, and in particular, in many embodiments, it can provide more accurate and / or reliable foreign object detection. The method also allows for low complexity and low resource requirements. An advantage of this method is its adaptability to many existing systems, particularly those included in Qi wireless power transmission systems; therefore, it can often be implemented with minimal modifications.

[0069] As will be described in more detail below, this method utilizes a time-division multiplexing approach during the power transfer phase, where foreign object detection and power transfer can be performed, for example, in separate time intervals, thereby allowing for a significant reduction in interference between foreign object detection and power transfer (especially the impact of power transfer on foreign object detection). Furthermore, the parameters of the generated electromagnetic signal can be adjusted for specific test scenarios. This can be achieved through an adjustment process, which can, for example, be performed before the system enters the power transfer phase.

[0070] The following text will describe this in more detail. Figure 1 The system. In this example, an electromagnetic power transfer signal and an electromagnetic test signal for foreign object detection are generated by two different coils (driven by different drivers). Furthermore, the signals will be referred to by different terms; that is, the electromagnetic signal generated during the power transfer time interval will be called the power transfer signal, and the electromagnetic signal generated during the foreign object detection time interval will be called the electromagnetic test signal, or simply the test signal. However, it will be appreciated that in many embodiments, the electromagnetic signal can be generated from the same coil both during the power transfer time interval and the foreign object detection time interval, and in fact, the same driver can be used for both the power transfer time interval and the foreign object detection time interval. In fact, in many embodiments, the reference to the test signal can be equivalently regarded as the power transfer signal during the foreign object detection time interval.

[0071] Figure 2 A more detailed illustration is provided. Figure 1 The power transmitter 101 is a component.

[0072] The power transmitter 101 includes a driver 201 capable of generating a (power transfer) drive signal, which is fed to a transmitter coil 103, which in turn generates an electromagnetic power transfer signal, thereby providing power transfer to the power receiver 105. The power transfer signal is provided during power transfer time intervals in the power transfer phase.

[0073] Driver 201 generates current and voltage fed to transmitter inductor 103. Driver 201 is typically a drive circuit in the form of an inverter that generates an AC signal based on a DC voltage. The output of driver 201 is typically a switched bridge that generates the drive signal by appropriate switching of the switches of a switched bridge. It should be understood that other components (e.g., matching circuitry) may be present. These components are within the skill of those skilled in the art and are not discussed in detail herein. Power transmitter 101 also includes power transmitter controller 203, which is arranged to control the operation of power transmitter 101 according to a desired operating principle. In particular, power transmitter 101 may include many functions required to perform power control according to the Qi specification.

[0074] The power transmitter controller 203 is specifically arranged to control the generation process of the drive signal generated by the driver 201, and is specifically capable of controlling the power level of the drive signal, and correspondingly controlling the level of the generated power transmission signal. The power transmitter controller 203 includes a power loop controller that controls the power level of the power transmission signal in response to a power control message received from the power receiver 105 during a power control phase.

[0075] To receive data and messages from power receiver 105, power transmitter 101 may include message receiver 205, which is arranged to receive data and messages from power receiver 105 via a power signal. As those skilled in the art will appreciate, a data message may provide one or more bits of information. In some cases, power receiver 105 is arranged to load modulate the power transmission signal generated by transmitter coil 103, and message receiver 205 is arranged to sense changes in the voltage and / or current of transmitter coil 103 and demodulate these load modulations based on those changes. Those skilled in the art will appreciate the principles of load modulation (e.g., as used in Qi wireless power transmission systems), and therefore these principles will not be described in more detail.

[0076] In some embodiments, communication can be performed using a separate communication channel, which can be implemented using a separate communication unit 207. In other embodiments, communication can be performed using a transmitter coil 103. When using a separate communication unit 207, this can have a communication coil or an antenna 209. The communication coil 209 is depicted as a loop antenna, but other forms may be suitable, and those skilled in the art can choose within their capabilities. For example, in some embodiments, near-field communication can be implemented by using a separate communication unit 207, or a high-frequency carrier (e.g., a carrier frequency of 13.56 MHz) can be superimposed on the power transmission signal. Communication protocols conforming to some or all of the ISO / IEC 18092 or ISO / IEC 14443 specifications can be used.

[0077] The power transmitter 101 may further include a foreign object detector 211, which is arranged to perform a foreign object detection test, specifically detecting whether any unwanted conductive element may be present in the generated electromagnetic field. The power transmitter 101 may include a test coil 213 coupled to a test generator 215, which is arranged to generate a test drive signal for the test coil 213 to provide an electromagnetic test signal during the foreign object detection time interval. The test drive signal is an electrical signal fed to the test coil 213 that causes the generation of the electromagnetic test signal; that is, the test coil 213 generates a corresponding electromagnetic field with a certain field strength according to the test drive signal.

[0078] Test generator 215 may include substantially the same functionality as driver 201; for example, test generator 215 may include a half-bridge or full-bridge inverter. In fact, as previously described, in many embodiments, test generator 215 may be implemented by driver 201, and test coil 213 may be implemented by transmitter coil 103. Therefore, in the following description, for embodiments in which the same coil is used for both generating power transfer signals and generating electromagnetic test signals, all references to test generator 215 and test coil 213 may, where appropriate, be regarded as references to driver 201 and test coil 213.

[0079] The power transmitter may also include an adapter / calibrator 217, which is arranged to determine suitable values ​​for one or more parameters of the test drive signal. These test drive signal parameter values ​​are then applied during at least one foreign object detection time interval in the power transmission phase.

[0080] In some embodiments, the communication unit 207 can also be used for foreign object detection (FOD). In this case, the test coil 213 and the test generator 215 are effectively integrated into the communication unit 207 and may not exist as separate units. The same coil or antenna may also be used for both communication and FOD in this configuration. In such an embodiment, the foreign object detector 211 communicates with the communication unit 207.

[0081] Figure 3a A schematic diagram of a half-bridge switching bridge / inverter used in an embodiment of the power transmitter 101 is shown. A DC voltage is applied across the input terminals V+ and V-. Switches S1 and S2 are controlled so that they are never closed simultaneously. The following operations are performed alternately: S1 is closed while S2 is open, and S2 is closed while S1 is open. The switches are opened and closed at a desired frequency, thereby generating an AC signal at the output. Typically, the inverter output is connected to the transmitter inductor 103 via a resonant capacitor Cres.

[0082] Figure 3b A schematic diagram of a full-bridge switched bridge / inverter used in an embodiment of power transmitter 101 is shown. A DC voltage is applied across the input terminals V+ and V-. In some operating modes, switches S1 and S2 are controlled so that they are never closed simultaneously. Switches S3 and S4 are controlled so that they are never closed simultaneously. The following operation is performed alternately: switches S1 and S4 are closed while S2 and S3 are open, and then S2 and S3 are closed while S1 and S4 are open, thereby creating a square wave signal at the output. The switches are turned on and off at a desired frequency. In another operating mode, S1 and S3 are open and S2 and S4 are closed for a portion of the time, and vice versa. This is often referred to as phase control.

[0083] Figure 4 The diagram shows Figure 1 Some exemplary components of the power receiver 105 are described below. Receiver coil 107 is coupled to power receiver controller 401, which couples receiver coil 107 to load 403 via load output circuit 405. Power receiver controller 401 and load output circuit 405 include a power control path that converts the power extracted by receiver coil 107 into suitable power for load 403. Additionally, power receiver controller 401 may include various power receiver controller functions required to perform power transfer, and in particular, specific functions required to perform power transfer according to the Qi specification.

[0084] To support communication from power receiver 105 to power transmitter 101, power receiver 105 may include load modulator 407. Load modulator 407 can be arranged to change the load of receiver coil 107 in response to data to be transmitted to power transmitter 101. Power transmitter 101 then detects and demodulates the load change, as those skilled in the art will know.

[0085] Power receiver 105 may include power controller 409, which is arranged to establish a power control loop with power transmitter 101. Specifically, power controller 409 is capable of transmitting power control messages to power transmitter 101, and in response, power transmitter 101 may change the power level of the power transmission signal during a power transmission time interval. Typically, power controller 409 may generate power control error messages indicating a request from power transmitter 101 to increase or decrease the power level. Power controller 409 can determine appropriate error messages by comparing measured values ​​with reference values. During power transmission, power controller 409 may compare the provided power level with the requested power level and request an increase or decrease in the power level based on this comparison. Power controller 409 may include a message controller, which is capable of generating appropriate messages and controlling a load modulator such that the power transmission signal is modulated according to the message, thereby allowing power transmitter 101 to detect the transmitted message.

[0086] Power receiver 105 may include a load controller 411. The load controller can be useful when power receiver 105 is arranged to enter a reduced power mode during reduced power time intervals in each frame(s) during a power transmission phase. In this example, power receiver 105 includes a load controller 411 that controls a load output circuit 405 (equivalently, the load output circuit 405 can be considered part of the load controller). During the reduced power time interval, load controller 411 can disconnect load 403 from the power receiver; that is, load controller 411 disconnects the load of power receiver controller 401, thereby disconnecting the load of receiver coil 107. Therefore, in this way, load controller 411 can reduce the load condition of receiver coil 107 during the reduced power time interval. Furthermore, not only can the load of power receiver 105 be reduced to make it easier to detect other power losses or modulation, but more often and more importantly, power receiver 105 enters a more clearly defined or specific state in which the effect of load changes on electromagnetic test signals is reduced. Moreover, the load controller can be used as part of the manner in which load modulation is performed.

[0087] It will be recognized that the load condition of receiver coil 107 may not be completely shut off during the foreign object detection interval. For example, power receiver 105 may still draw power for example, to operate some internal circuitry. Therefore, load controller 411 can be arranged to disconnect the load from receiver coil 107 carrying that load, while still allowing receiver coil 107 to carry a load condition provided by one or more other loads. In practice, the load condition of receiver coil 107 can be considered as including loads disconnected by load controller 411 during the foreign object detection interval as well as loads that load controller 411 does not disconnect. Therefore, load 403 can be considered as representing a load that can be disconnected from receiver coil 107 during the foreign object detection interval. This load can include both external or internal loads that establish power transfer, as well as internal control functions that are temporarily shut down, for example, during the foreign object detection interval.

[0088] The power receiver 105 may include a communication unit 413 and an associated communication coil or antenna 415. This can be used to communicate with the equivalent communication unit 207 in the power transmitter 101. The communication coil 415 is depicted as a loop antenna, but other forms may also be suitable, and those skilled in the art can choose within their capabilities. For example, in some embodiments, near-field communication may be implemented, or a high-frequency carrier (e.g., a carrier frequency of 13.56 MHz) may be superimposed on the power transmission signal. Communication protocols conforming to some or all of the ISO / IEC 18092 or ISO / IEC 14443 specifications may be used.

[0089] Foreign object detection testing can be based on measurements performed during foreign object detection intervals. During these foreign object detection intervals, the power transmitter 101 operates in a foreign object detection mode, in which operating conditions are set for the purpose of evaluating the presence of any foreign objects.

[0090] For example, in embodiments where power transmitter 101 uses different coils to generate the power transmission signal and the electromagnetic test signal, power transmitter 101 can completely shut off the power transmission signal and set the electromagnetic test signal to an appropriate value. In embodiments using the same coil to generate the power transmission signal and the electromagnetic test signal, the drive signal for the coil can be changed from an operating point suitable for power transmission to an operating point suitable for foreign object detection. Therefore, in many embodiments, the current, voltage, frequency, duty cycle, power, or level of the drive signal, and thus the power transmission signal and / or the electromagnetic test signal, change between the power transmission time interval and the foreign object detection time interval. In many embodiments, the power or level of the power transmission signal can be changed from a power level determined by the power transmission control loop function to a power level (e.g., a previously determined value) that is not determined by the power transmission control loop function (independent of the power transmission control loop function). In many embodiments, the power or level of the electromagnetic signal can be changed from a first power level to a second power level. The first power level can be a predetermined level or a nominal level (and in particular, can be zero) or can be determined, for example, by the power transmission power control loop. The second power level can be a previously determined level and can be independent of the power transmission power control loop.

[0091] During the interval of foreign object detection (i.e., during the foreign object detection time interval), the foreign object detector 211 therefore evaluates the conditions to determine whether a foreign object is considered to be present. During the foreign object detection time interval, the power transmitter 101 may generate an electromagnetic test signal, and the foreign object detection is based on the evaluation characteristics and properties of this signal.

[0092] For example, the power level of the test drive signal can reflect the power extracted from the generated electromagnetic test signal, and this can be used as an indication of the power extracted by a potential foreign object (typically achieved by comparing it to the expected power extracted 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 receiver coil 107). Therefore, the power level of the electromagnetic test signal indicates the power extracted by the combination of the power receiver 105 and any foreign object that may be present. The difference between the power level of the electromagnetic signal and the power extracted by the power receiver 105 correspondingly reflects the power extracted by any present foreign object. Foreign object detection can be, for example, low-complexity detection. For example, if the difference in the power level of the electromagnetic signal (hereinafter referred to as the transmit power level) exceeds the reported power extracted by the power receiver 105 (hereinafter referred to as the receive power level), it can be considered that a foreign object has been detected.

[0093] In this method, foreign object detection is performed based on a power level comparison between the transmitted power level and the reported received power level. In different embodiments, the response to foreign object detection can vary. However, in many embodiments, the power transmitter 101 can be arranged to (at least temporarily) terminate power transmission in response to the detection of a foreign object.

[0094] Figure 5 The diagram illustrates a circuit diagram of the components of an example power path for a power receiver 105. In this example, the power receiver 105 includes a receiver coil 107 referred to as LRX. In this example, the receiver coil 107 is part of a resonant circuit, and the power receiver 105 accordingly also includes a resonant capacitor 501 (CRX). The receiver coil 107 is subjected to an electromagnetic signal, and an AC voltage / current is induced in the coil accordingly. The resonant circuit is coupled to a rectifier bridge 503, which has a smoothing capacitor 505 (C1) coupled to the output of the bridge. Therefore, a DC voltage is generated across the capacitor 505. The amplitude of the ripple on the DC voltage will depend on the size of the smoothing capacitor and the load.

[0095] Bridge 503 and smoothing capacitor 505 are coupled to load 403 via switch 607. It will also be appreciated that load 403 is shown as a simple passive resistor, but it can certainly be any suitable load. For example, load 403 could be a battery to be charged, a mobile phone, or another communication or computing device; load 403 could be a simple passive load, etc. In fact, load 403 does not need to be an external load or a dedicated internal load, but can, for example, include components of the power receiver 105 itself. Therefore, Figure 4 and Figure 5 The load 403 shown can be considered as any load representing the receiver coil 107 / electromagnetic signal.

[0096] Figure 5 A load modulation capacitor 509 (C2) that can be connected or disconnected in parallel with the resonant circuit based on the switching of switch 511 is also shown. Load modulator 407 or message controller 409 can be arranged to control switch 511 such that the load of modulation capacitor C2 can be connected and disconnected in response to data to be transmitted to power transmitter 101, thereby providing load modulation.

[0097] Figure 6 The diagram illustrates the time intervals of the power transfer process. Power transfer can have two phases: communication phase 601 (annotated as "comm / neg / cal") and power transfer phase 603.

[0098] During communication phase 601, the power transmitter 101 and the power receiver 105 establish communication and negotiate their respective requirements and capabilities. Such a phase is described in the Qi specification. They can also execute calibration routines that can be used during subsequent operations.

[0099] During power transfer phase 603, system 101 applies a recurring timeframe 605, which includes at least one power transfer time interval 607 and a foreign object detection (FOD) time interval 609. The power transfer time interval is indicated by PT, and the FOD / COMM time interval is indicated by FOD / COMM. In this example, each timeframe 605 includes only one FOD time interval 609 and one power transfer time interval 607, and these time intervals (as well as the timeframe itself) have the same duration within each frame. The FOD time interval 609 can also be used for communication. It will be appreciated that in other embodiments, other time intervals (e.g., separate communication intervals) may also be included in the timeframe, or multiple FOD time intervals and / or power transfer time intervals may be included in each timeframe. In particular, some timeframes may include adjustment or calibration time intervals to allow calibration of the FOD system (211, 215, 207). Furthermore, in some embodiments, the duration of different time intervals (and indeed the timeframes themselves) may vary dynamically. It will also be appreciated that the length of the time period shown in the figure does not imply a ratio between the individual intervals.

[0100] In this method, foreign object detection and power transfer are thus separated in the time domain, reducing cross-interference between power transfer and foreign object detection. Therefore, the variability and uncertainty caused by changes in the operating conditions of power transfer can be isolated from foreign object detection, making foreign object detection more accurate and reliable.

[0101] During the power transmission time interval 607, the power transmitter is thus arranged to perform power transmission during the power transmission time interval within the time frame of the power transmission phase. Specifically, during these time intervals, the power transmitter 101 and the power receiver 105 can operate a power control loop (which may be based on communication within the power transmission signal time interval, or may be based, for example, on communication outside the power transmission signal time interval, such as a dedicated communication time interval. For example, each FOD time interval 609 may be separated by multiple alternating power transmission signal time intervals 607 and communication time intervals). Therefore, the transmitted power level can be dynamically changed. During the foreign object detection time interval 609 within 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 can be set to a value determined during an adjustment operation performed prior to the foreign object detection time interval. Thus, during the foreign object detection time interval, the parameter can be set to a predetermined value (i.e., a value determined prior to the foreign object detection time interval, and typically a value determined prior to the power transmission phase). In contrast, during the power transmission time interval, the parameter may not be constrained to this predetermined value.

[0102] For example, during power transfer time interval 607, the system can operate a power control loop that allows the power level of the power transfer signal to be changed in response to a power control message from the power receiver. The power control loop can control / change at least one of the current, voltage, and frequency of the drive signal / power transfer signal. In contrast, during FOD time interval 609, parameters changed by the power control loop during the power transfer time interval can be set to predetermined values ​​determined prior to the power transfer phase.

[0103] The power receiver 105 can conveniently reduce the load that occurs during the power transfer phase 603 during the FOD time interval 609.

[0104] In embodiments where the same coil is used for both power transmission signals and electromagnetic test signals, the power transmitter can be arranged to reduce the level of the power transmission signal relative to the power transmission time interval during the foreign object detection time interval. In many cases, the power level of the power transmission signal can be allowed to increase to a high level, such as 10-100W, or even to a fairly high level in many applications (e.g., for power transmission in kitchen appliances). However, during the foreign object detection time interval, the power level of the generated electromagnetic signal can be reduced to a predetermined level significantly lower than the predetermined level of current or maximum permissible power during the power transmission time interval. For example, the power level can be set to a predetermined level not exceeding 1W.

[0105] In high-power applications, even those using dedicated FOD systems (e.g., for power transfer in kitchen appliances), reducing the power transfer signal can be advantageous. The FOD system is expected to be highly sensitive enough to detect even small objects. In cases where the FOD system uses techniques requiring electromagnetic fields (e.g., quality factor variations), the presence of a high-power signal (i.e., a strong magnetic field) will necessitate a high dynamic range to still detect weak foreign object signals. Strong power signals can also reduce the signal-to-noise ratio (SNR) of FOD testing. When using power loss accounting methods, it can be difficult to accurately detect differences in absorbed power when a high-power signal is present (i.e., when a large amount of power is transferred), as these differences may not be significant compared to measurement errors. Therefore, the power level can be set to zero or very close to zero.

[0106] Figure 7 The illustration depicts a time interval and signal in a high-power application (e.g., with kitchen appliances). In this particular example, the power transmitter 101 is supplied with AC mains power. During the power transmission interval 709, the power signal has an envelope that follows a rectified version of the mains power supply's envelope. As shown, it operates at a frequency higher than the mains frequency. Figure 3a and Figure 3b The switching circuit. The FOD interval 707 is positioned at (or synchronized with) the zero-crossing point. The FOD interval 707 can be centered on the zero-crossing point, with intervals on either side of the zero-crossing point. The zero-crossing point of the mains power is a convenient time because interference from the mains power will be lower. A possible time width of the FOD interval is 1.6 ms, which should be sufficient to allow time for FOD testing and any communication. However, depending on the details of the system, other widths may also be preferred, and a technician will be able to make this determination. During the FOD interval, the power signal can be maintained at zero or below a level where the magnetic field will not interfere with the FOD test, up to any unacceptable level. Since most power is transmitted at high power levels, it is more convenient to set the power signal to zero during the FOD interval.

[0107] In addition to applying a timeframe that includes a specific foreign object detection time interval, the system may also employ a method in which the values ​​of one or more parameters (or properties) of the test signal are adjusted based on an adjustment process, which in many embodiments may be performed prior to the power transfer phase. Thus, the adjustment process determines preferred values ​​for one or more parameters / properties of the electromagnetic test signal before the power transfer phase, and then applies these preferred values ​​during the foreign object detection time interval of the subsequent power transfer phase. In some embodiments, the adjustment process may be repeated during the power transfer phase (e.g., at regular intervals).

[0108] In the case where the power transmitter 101 includes a dedicated FOD unit, the power transmitter 101 may include an adapter / calibrator 217, which is arranged to determine the test drive signal parameter values ​​during the adjustment time interval. This operation may be performed during and / or before the power transmission phase.

[0109] In high-power applications, potential foreign object (FOD) heating can be significant even in the first few power transfer intervals 607 of power transfer phase 603. Therefore, it is desirable to detect any FOD as quickly as possible (effectively before the start of power transfer phase 603). While the FOD interval 609 could be used to initiate power transfer phase 603, it is desirable to improve system safety, as there is a risk that the FOD test might miss the FOD (especially when the FOD is small), allowing power transfer to continue. It should be understood that all measurement methods have error and noise limitations, and these limitations can contribute to false negatives.

[0110] Figure 8 The illustration shows time intervals and signals in a power transmission system 101 according to an embodiment. As previously described, the communication phase precedes the power transmission phase 603. In the power transmission phase 603, there is a repeating time frame including a power transmission interval 607 and a FOD time interval 609. Additionally, a FOD time interval (or slot) 811 may exist during the communication phase 601.

[0111] Figure 9 The illustration shows time intervals during communication phase 601 according to an embodiment. 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 foreign objects. Moreover, having more FOD testing opportunities before power transmission begins reduces the risk of missing foreign objects. Having multiple FOD time intervals 903 during communication phase 601 is advantageous.

[0112] It is understandable that the communication phase can be quite long due to user actions (rather than system requirements). In many cases, for high-power applications (e.g., kitchen appliances), the user can place the appliance (power receiver 105) on the power transmitter 101 without immediately attempting to turn on high power. This provides additional opportunities for repeated FOD testing and can facilitate maintaining repeated FOD testing until the user performs some action to initiate the power transfer phase 603. In practice, this operation can be recommended because it caters to the situation where the foreign object is introduced after the first FOD test and before the power transfer phase 603. In practice, it can be expected that up to 5 FOD tests per second will be performed during the communication phase 601. The gain is less than 10 FOD tests per second.

[0113] The field used for communication (e.g., NFC) can also interfere with FOD testing to some extent, such as reducing the SNR of the measurement results. Therefore, it is expected that the communication signal (field) will be removed during the FOD time interval. However, removing the communication signal itself can cause problems. Power receivers rely on this signal to power their communication circuitry (since a power signal has not yet been established). Removing the signal for too long can cause instability or power failure in the active components of the receiver, and the consequence may be that communication must be reinitialized. It will also be appreciated that communication is impossible when no communication signal is present. “Removing the signal” may include reducing the signal power, and one percent of the level used during communication may be sufficient to reduce the interference with FOD testing to an acceptable level.

[0114] During communication phase 601, a certain amount of circuitry and hardware needs to be powered, and no power is transmitted via the mains power transmission system (i.e., coils 103, 107 and associated hardware). This circuitry can be a portion of the communication unit 413 and the logic unit of the power receiver controller 401 required for tasks such as negotiation, interval timing, and decision-making. A user interface (which may simply be a colored LED) may be present, and in at least some respects, the user interface can be conveniently powered. In the case of NFC used for communication, some energy from the NFC field can be harvested (or extracted) and used to power the aforementioned hardware. Since the NFC field can be removed (or at least significantly reduced) during the FOD time interval, the energy harvesting hardware of the power receiver 105 (which, if present, can be conveniently integrated into the communication unit 413) should be able to harvest and store sufficient energy to keep the required hardware powered during the FOD time interval 903. The communication signal (field) may only be present for 66% of the time. Therefore, it is advantageous for the power receiver 105 to keep the required hardware powered using a communication field with a duty cycle of less than 66%. The power receiver 105 can conveniently signal the power transmitter 101 to increase or decrease the power in the communication signal. This assumes that the communication unit 207 of the power transmitter is providing the communication signal. Under protocols conforming to one of the aforementioned ISO / IEC standards, power regulation can be performed when the communication unit 207 of the power transmitter initiates communication by providing a communication field and executing a read command.

[0115] Adding a capacitor to the receiver can help keep the power receiver powered in a relatively stable manner to some extent. However, it is desirable to keep this value to a minimum because the capacitor itself will be a load during the periods when power is present, thus "drawing power from the rest of the power receiver," meaning more power needs to be transferred compared to the case where only the receiver needs to be powered. Very large capacitors also impose size and cost penalties. Therefore, a trade-off needs to be made.

[0116] Therefore, a power transmitter 101 is provided for wirelessly providing power to a power receiver 105 via an inductive power transmission signal. The power transmitter 101 includes: foreign object detectors 207 and 215 arranged to perform a foreign object detection test; a communication coil 209 for generating a communication signal; a communication generator 207 arranged to generate a communication control signal for the communication coil 209 to provide the communication signal during a communication period, the communication generator 207 being arranged to set the communication control signal to a first value during the communication period and to a second value during a communication foreign object detection time interval, the communication foreign object detection time interval occurring during the communication period; 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 being arranged to generate the drive signal during a power transmission phase to employ a repetitive time frame, the repetitive time frame including at least a power transmission time interval and a transmission foreign object detection time interval; and receivers 205 and 207 for receiving messages from the power receiver 105. A power receiver 105 is arranged to wirelessly receive power via an inductive power transmission signal. The power receiver 105 includes: a communication coil 107 for receiving received communication signals; communication controllers 413, 407, 409 arranged to decode the received communication signals and generate communication response signals for the communication coils 415, 407; communication signal power harvesters 413, 107 arranged to: extract power from the received communication signals during a time interval when the communication signal is at a first value, to power the communication controllers and user interface; and store a portion of the extracted power sufficient to maintain the communication controllers and user interface in an operational state during a communication foreign object detection time interval; and message transmitters 413, 407 for transmitting messages to the power transmitters. The power receiver may also include a user interface, which may be more or less complex (e.g., from a simple LED to a display).

[0117] Typically, the first value will be higher than the second value, and the second value will be zero or nearly zero.

[0118] Therefore, the method of operating the power transmitter 101 (the power transmitter 101 wirelessly provides power to the power receiver 105 via an inductive power transfer signal) includes: generating a communication control signal, wherein 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 transfer signal; generating a drive signal for the transmitter coil (103), wherein during the power transfer phase, the drive signal employs a repetitive time frame, the repetitive time frame including at least the power transfer time interval and the second foreign object detection time interval; and performing foreign object detection during the first foreign object detection time interval and the second foreign object detection time interval; and receiving a message from the power receiver 105. On the power receiver 105 side, the method of operating the power receiver 105 (power receiver 105 for wirelessly receiving power via an inductive power transmission signal) includes: receiving a received communication signal via a 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 powering the communication controllers 413, 407, 409 and the user interface, and storing a portion of the extracted power, said portion of the extracted power being sufficient to keep the communication controllers and the user interface in an operational state 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.

[0119] A convenient way to perform FOD (Foreign Object Determination) is to apply a signal to observe the damping of the oscillations in the resonant circuit. Based on the damping, the real part of the system's reactance can be estimated. Since the real part of the reactance represents the amount of power absorbed by the system, the presence of a foreign object can be determined from the real part of the reactance. To successfully perform this operation, multiple cycles are required, and the more cycles (i.e., the longer the test), the more accurate the foreign object determination result.

[0120] Figure 10The illustration shows time intervals during communication 601 according to another embodiment. Communication phase 601 may begin with a first (initial) communication interval 1001. This first communication interval 1001 is followed by a longer FOD time interval 1003. This is then followed by a communication interval 1005 and a shorter FOD time interval 1007. The longer communication FOD time interval is longer than the shorter FOD time interval. The longer FOD time interval 1003 may be used for accurate FOD testing and / or for adjustment / calibration of the FOD system used by FOD testing (e.g., FOD testing performed later in communication phase 601 or FOD testing in power transfer phase 603). Other measurements (e.g., coupling coefficient measurements) may also be performed and the results used later. The shorter FOD time interval 1007 may be used to more quickly check for the presence of foreign objects. For example, this may be using calibration data acquired during the longer FOD time interval (where applicable), and / or this may be using a faster (but potentially less accurate) method. Longer FOD intervals can be 100ms or less, and shorter FOD intervals can be 10ms or less, typically around 2ms. These values ​​allow for variations between systems, such as differences in the actual resonant frequency or noise level in the measurement circuit. Therefore, if a user wishes to start using the appliance immediately upon placing it on the power transmitter 101, they will not experience a noticeable delay, and a longer FOD test can be conveniently completed within (approximately) 200ms of the initial connection. Compared to FOD test methods requiring longer intervals, using longer and shorter FOD intervals offers the advantages of: enabling the use of more FOD intervals without significantly reducing the duty cycle of the communication field.

[0121] Comparing this result to shorter FOD time intervals can be useful. If the results deviate from each other by more than a threshold, another longer FOD time interval can be used. An example of such comparison and threshold could be requiring measurements from a series of short FOD tests to be within ±5% of their average result.

[0122] It is understood that the power transmitter 101 and the power receiver 105 may also negotiate the timing, frequency, and / or duration of the FOD time intervals 903, 1001, and 1005 to occur during the communication phase 601 at the beginning of the communication phase 601. This allows the system 101 to set the FOD test frequency (or duration) as high as possible while allowing some margin to be maintained during energy harvesting operations.

[0123] It is understood that communication units 207, 413 and their respective coils 209, 415 can also be used for measurements other than foreign object detection. They can be used to measure the coupling factor. Such measurements can be performed during FOD time intervals 903, 1003, 1005 that occur during communication phase 601. This can have the benefit of allowing for more precise adjustment of the power signal. The hardware can also be used for coupling factor measurement when performing FOD testing of power transmission phase 603 using either communication unit 207 or a dedicated FOD tester 213. This will have the advantage of assisting power control (e.g., detecting slight movement of the appliance). This can be achieved by having the power receiver 105 indicate the maximum number of FOD time intervals it can support, and then having the power transmitter 101 conform to this.

[0124] It will be appreciated that, for clarity, the above description refers to different functional circuits, units, and processors to illustrate embodiments of the invention. However, it will be apparent that any suitable functional distribution among different functional circuits, units, or processors can be used without departing from the invention. For example, a function illustrated as being performed by a separate processor or controller can be performed by the same processor or controller. Therefore, references to specific functional units or circuits are to be considered merely as references to suitable modules for providing the described functions, and not as indications of a strict logical or physical structure or organization.

[0125] This invention can be implemented in any suitable form, including hardware, software, firmware, or any combination of these items. Optionally, the invention can be implemented at least partially as computer software running on one or more data processors and / or digital signal processors. Elements and components of embodiments of the invention can be implemented physically, functionally, and logically in any suitable manner. In practice, functionality can be implemented in a single unit, in multiple units, or as part of other functional units. Therefore, the invention can be implemented in a single unit, or it can be physically and functionally distributed among different units, circuits, and processors.

[0126] While the invention has been described in conjunction with some embodiments, it is not intended to be limited to the specific forms set forth herein. Rather, the scope of the invention is limited only by the claims. Furthermore, although features appear to have been described in conjunction with specific embodiments, those skilled in the art will recognize that various features of the described embodiments can be combined according to the invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0127] It will be appreciated that referencing a preferred value does not imply any limitation beyond the value determined in the foreign object detection initialization mode, i.e., preferably by determining the value during the adjustment process. A reference to a preferred value can replace a reference to, for example, a first value.

[0128] Furthermore, although listed separately, multiple modules, elements, circuits, or method steps may also be implemented by, for example, a single circuit, unit, or processor. Additionally, while individual features may be included in different claims, these features may be advantageously combined, and the inclusion of these features in different claims does not mean that such a combination is not feasible and / or advantageous. Moreover, the inclusion of a feature in a claim of one type does not mean that the feature is limited to that type of claim, but rather indicates that the feature is equivalently applicable to other types of claims where appropriate. Furthermore, the order of features in a claim does not mean that these features must be in any particular order of operation, and in particular, the order of steps in a method claim does not mean that the steps must be performed in that order. Rather, the steps can be performed in any suitable order. Additionally, singular references do not exclude plural. Therefore, references to “a,” “an,” “first,” “second,” etc., do not exclude plural. Reference numerals in the claims provided merely for clarification should not be construed as limiting the scope of the claims in any way.

Claims

1. A power transmitter (101) for wirelessly providing power to a power receiver (105) via an inductive power transmission signal, the power transmitter (101) comprising: A power transmission coil (103) is used to generate the power transmission signal; A driver (201) for generating a drive signal for the power transmission coil (103), the driver (201) being arranged to generate the drive signal during a power transmission phase to employ a repetitive time frame, the repetitive time frame including at least a power transmission time interval and a foreign object detection time interval. Foreign object detector (211) is configured to perform foreign object detection test; A communication coil (209) is used to generate communication signals; as well as A communication unit (207) is arranged to generate a communication control signal for the communication coil (209) to provide the communication signal during a communication phase prior to the power transmission phase, during which no power transmission signal is present, and during the communication phase, the communication unit (207) is arranged to set the communication control signal to a first value during a communication period and to a second value during a communication foreign object detection time interval, which occurs during the communication phase; The foreign object detector (211) is arranged to perform foreign object detection during both the transmission foreign object detection time interval and the communication foreign object detection time interval.

2. The power transmitter according to claim 1, wherein, The communication phase (601) includes multiple communication foreign object detection time intervals, including longer communication foreign object detection time intervals and shorter communication foreign object detection time intervals.

3. The power transmitter according to claim 2, wherein, The longer communication foreign object detection time interval has a length of less than or equal to 100 ms, and the shorter communication foreign object detection time interval has a length of less than or equal to 10 ms, wherein the communication foreign object detection time interval occurs within a time period of 200 ms.

4. The power transmitter according to claim 2 or 3, wherein, The first relatively long foreign object detection interval was completed within 200 ms of establishing communication with the power receiver.

5. The power transmitter according to any one of claims 1-3, wherein, The power transmitter is configured to be powered by an AC power supply with a zero-crossing point, and the power transmission foreign object detection time interval is configured to be synchronized with the zero-crossing point.

6. The power transmitter according to any one of claims 1-3, wherein, The first value of the communication signal is set so as to transmit sufficient power to the communication signal power harvester in the power receiver.

7. The power transmitter according to any one of claims 1-3, wherein, The second value of the communication signal is set to reduce interference with the foreign object detection test.

8. The power transmitter according to any one of claims 2-3, wherein, The foreign object detection test is performed using the communication unit.

9. The power transmitter according to any one of claims 1-3, wherein, The power transmitter is configured to negotiate the frequency and / or duration of foreign object detection (FOD) time intervals (903, 1003) during the communication phase (601) with the power receiver (105).

10. A wireless power transmission system (100) comprising a power transmitter according to any one of claims 1-9.

11. The wireless power transmission system of claim 10, further comprising a power receiver; and wherein, The power receiver (105) includes: A communication coil, used to receive received communication signals; A communication controller is configured to decode the received communication signal and generate a communication response signal for the communication coil; A communication signal power harvester is arranged to: extract power from the received communication signal during a time interval in which the communication signal is at a first value, in order to power the communication controller; and store a portion of the extracted power, the portion of the extracted power being sufficient to maintain the communication controller in an operational state during a communication foreign object detection time interval; A power receiving coil for extracting power from the power transmission signal; and A message transmitter for transmitting messages to the power transmitter (101).

12. The wireless power transmission system according to claim 11, wherein, The communication controller is configured to maintain a connection during the foreign object detection time interval.

13. The wireless power transmission system according to any one of claim 11 or 12, wherein, The power receiver is arranged such that the extracted power is sufficient to power the communication controller, wherein the communication signal has a duty cycle of 66% or less.

14. The wireless power transmission system according to any one of claims 11-12, wherein, The power receiver is configured to negotiate with the power transmitter the frequency and / or duration of foreign object detection time intervals (903, 1005) that the power transmitter can support during the communication phase (601).

15. A method of operating a power transmitter (101) that wirelessly supplies power to a power receiver (105) via an inductive power transmission signal, the method comprising: A communication signal is generated during a communication phase in which no power transmission signal is present. The communication signal is set to a first value during a communication period and to a second value during a first foreign object detection time interval, which occurs during the communication phase. Apply the communication signal to the communication field; Generate power transmission signals; A drive signal is generated for the transmitter coil, wherein, during the power transmission phase, the drive signal employs a repetitive time frame, the repetitive time frame including at least a power transmission time interval and a second foreign object detection time interval; and Foreign object detection tests are performed during the first foreign object detection time interval and the second foreign object detection time interval; Receive messages from the power receiver (105).

16. A computer program product that, when run on a processor located in and arranged to control a power transmitter according to any one of claims 1-9, causes the power transmitter to operate according to the method of claim 15.

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