Wireless power transfer system and method for indicating foreign object detection fault condition

Abstract

The present disclosure provides a system, method, and apparatus for foreign object detection (FOD) in a wireless power transmission (WPT) system. An FOD protocol may be adjusted at different operational phases of a WPT system, such as an idle phase, a configuration phase, a connection phase, and a power transmission phase. An FOD assessment unit may perform a foreign object detection assessment as part of each operational phase. The FOD protocol may include an initial idle phase foreign object detection assessment in the idle phase to handle scenarios where a power receiver is placed on a power transmitter before the power transmitter is turned on. The FOD assessment unit may adjust an offset value used during each FOD assessment to improve accuracy of foreign object detection. The offset value may be adapted to accommodate movement of the power receiver after the initial idle phase foreign object detection assessment.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to wireless power. More specifically, this application relates to foreign object detection in wireless power transmission systems. [Background technology]

[0002] Technologies have been developed that allow for the transmission of power from a power transmitter (sometimes referred to as a "wireless power transmitter") to a power receiver (sometimes referred to as a "wireless power receiver"). The power receiver may be included in various types of devices, such as mobile devices, small electronic devices, computers, tablets, gadgets, home appliances (such as cordless blenders, kettles, or mixers), and some types of larger electronic devices, among other examples. Wireless power transmission may be referred to as contactless power transmission or contactless power transmission. Wireless power may be transmitted using inductive or resonant coupling between the power transmitter and the power receiver. For example, the power transmitter may include a primary coil that generates an electromagnetic field. The electromagnetic field may induce an electromotive force in a secondary coil of the power receiver when the secondary coil is placed in proximity to the primary coil. In this configuration, the electromagnetic field may wirelessly transmit power to the secondary coil.

[0003] In wireless power transmission systems, when a metallic foreign object (such as a key, a coin, a metal can, or aluminum foil, among other examples) is in the vicinity of an electromagnetic field, the metallic foreign object may be unnecessarily heated by eddy currents. This may result in safety hazards, such as a fire hazard. Furthermore, the efficiency of the wireless power transmission process may be inadvertently affected or disrupted. Conventional techniques for detecting foreign objects in wireless power transmission systems may be insufficient or ineffective in preventing such safety hazards. Summary of the Invention

[0004] The systems, methods, and devices of the present disclosure each have several innovative aspects, no one of which is solely responsible for the desirable attributes disclosed herein.

[0005] One innovative aspect of the subject matter described in this disclosure can be implemented as a method for foreign object detection (FOD) in a wireless power transfer (WPT) system. The method may include initializing an FOD evaluation unit prior to or as part of an idle phase in response to a user input to turn on the power transmitter. Initializing the FOD evaluation unit may include setting an FOD flag to a first value to indicate that an initial idle phase foreign object detection evaluation has not yet been performed. The method may include indicating an FOD fault condition if the power transmitter transitions from the idle phase to a different operating phase when the FOD flag is set to the first value.

[0006] Another innovative aspect of the subject matter described in this disclosure can be implemented as a system for FOD. The system may include a power transmitter configured to initialize an FOD evaluation unit prior to or as part of an idle phase in response to a user input to turn on the power transmitter. Initializing the FOD evaluation unit may include setting an FOD flag to a first value to indicate that an initial idle phase foreign object detection evaluation has not yet been performed. The system may include an FOD evaluation unit configured to indicate an FOD fault condition if the power transmitter transitions from the idle phase to a different operating phase when the FOD flag is set to the first value. [Brief description of the drawings]

[0007] The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. Please note that the overall dimensions of the following figures are not necessarily drawn to scale. [Figure 1] FIG. 1 is a block diagram of an example wireless power transfer (WPT) system. [Diagram 2]FIG. 1 is a block diagram of an example wireless power transfer system having a detection device for foreign object detection. [Diagram 3] FIG. 1 is a block diagram of an exemplary detection device in which detection values ​​are based on a comparison of coil circuits associated with a pair of detection coils. [Figure 4] 1 is a chart with example magnitudes of detection values; [Diagram 5] 1 is a block diagram of an exemplary sensing device in which the sensed value is based on a voltage induced by a differential current; [Figure 6] 1 is a diagram of multiple detection coils in an exemplary detection device. [Figure 7] FIG. 1 is a diagram of multiple coil pairs capable of distinguishing between power receiver movement and the presence of a foreign object. [Figure 8] 11 is an exemplary chart comparing the detected voltage of a coil pair due to power receiver movement versus the presence of a foreign object. [Figure 9] FIG. 13 is a block diagram of an example foreign object detection evaluation in which a detection value is adjusted based on an offset value. [Figure 10] FIG. 1 is a state diagram of the various operational phases of a WPT system. [Figure 11] FIG. 1 is a schematic diagram of foreign object detection evaluation associated with different operational phases of a WPT system. [Figure 12] FIG. 1 is a detailed view of foreign object detection evaluation associated with different operational phases of the WPT system. [Figure 13] FIG. 1 illustrates a process for foreign object detection evaluation. [Figure 14] FIG. 1 illustrates an example operation for foreign object detection (FOD) fault handling. [Figure 15] FIG. 1 is a flowchart diagram of an exemplary process for detecting foreign objects, according to some implementations. [Figure 16] 1 is a block diagram of an exemplary apparatus for use in a wireless power transfer system.Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A wireless power transmission (WPT) system may include a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device may include a power transmitter (sometimes referred to as a "PTx"). The wireless power transmitting device may include other elements. However, the terms "wireless power transmitting device" and "power transmitter" may be used interchangeably to represent all or a portion of the devices of a WPT system that transfer power to a wireless power receiving device via inductive or resonant coupling of an oscillating electromagnetic field. The wireless power receiving device may include a power receiver (sometimes referred to as a "PRx"). The wireless power receiving device may include other elements. However, the terms "wireless power receiving device" and "power receiver" may be used interchangeably to represent all or a portion of the devices of a WPT system that receive power via inductive or resonant coupling of an oscillating electromagnetic field. The mating surface may define a space between the power transmitter and the power receiver.

[0009] Occasionally, there may be a foreign object (sometimes referred to as a metallic foreign object) in the vicinity of an electromagnetic field, such as in or near a joint surface. A foreign object may be any object that is conductive or has detectable magnetic permeability and is not part of the WPT system but is inadvertently present in the operating environment of the WPT system. Non-limiting examples of foreign objects may include ferrous objects, metal cans, coins, metal spoons, keys, aluminum foil, or other conductive or ferrous objects. When a foreign object is in the vicinity of an electromagnetic field, it may interact with the electromagnetic field, which may adversely affect wireless power transmission or cause the foreign object to heat up unnecessarily.

[0010] The WPT system may include a foreign object detection system (sometimes referred to as a "detection device"). The detection device may include multiple detection coils that are used to obtain or generate values ​​(sometimes referred to as "detection values" or "FOD values") for foreign object detection (FOD) evaluation. Each detection value may represent a comparison of a current, a voltage, an impedance, or other electrical property between two coils of a coil pair. For example, the detection value may be a differential current, a differential voltage, or any value that indicates a difference in impedance associated with a pair of detection coils. As part of the FOD evaluation, the FOD evaluation unit may measure the detection value of each pair of detection coils while the detection coils are actively or passively excited with electrical energy. For example, the detection device may include a sensor or other circuitry for measuring or obtaining the detection value and transmitting the detection value to the FOD evaluation unit. The FOD evaluation unit may be part of a power transmitter (such as implemented within a controller of the power transmitter), part of a detection device (such as a control unit of the detection device), part of a home appliance that includes the power transmitter and the detection device (such as a processor of the home appliance), or an external processor, among other examples. The FOD assessment unit may compare the detection value to a detection threshold to determine whether a metal object is near one of the detection coils of the coil pairs. In some types of foreign object detection assessment, the FOD assessment unit may determine whether a detection value that exceeds the detection threshold is due to a foreign object or a movement of the power receiver based on how many coil pairs indicate the presence of a metal object. When fewer coil pairs (e.g., less than the threshold amount) detect the presence of a metal object, the metal object may be determined to be a foreign object. Conversely, when more coil pairs (e.g., more than the threshold amount) detect the presence of a metal object, the FOD assessment unit may determine that the metal object is a power receiver.

[0011] WPT systems operate in different phases, such as an idle phase, a configuration phase, a connection phase, and a power transmission phase. Technical specifications may define how the power transmitter and the power receiver can transition between operational phases. For example, a power transmitter typically starts in an idle phase after being turned on. Turning on the power transmitter refers to powering the controller, communication unit, driver, or other components of the power transmitter except the primary coil. The primary coil is only energized in the power transmission phase after communication has to take place between the power receiver and the power transmitter. When the power receiver is placed on the mating surface, the power transmitter's communication coil pings to detect the presence of the power receiver. A handshake process takes place between the power transmitter and the power receiver. Based on the success of the handshake, the power transmitter transitions from the idle phase to the configuration phase. The power transmitter and the power receiver communicate regarding the transition from the configuration phase to the connection phase and the power transmission phase. Conventional foreign object detection techniques are related to the power transmission phase, regardless of the unique scenarios that may occur in a particular operational phase, such as the idle phase.

[0012] The present disclosure provides systems, methods, and apparatus for foreign object detection in wireless power transmission systems operating in different operational phases. The type of foreign object detection evaluation performed at any particular time may depend on the operational phase of the power transmitter. Thus, the FOD evaluation unit may follow a protocol (sometimes referred to as an "FOD protocol") that defines how the FOD evaluation is performed in relation to various operational phases. For example, the FOD protocol may include an initial idle phase foreign object detection evaluation to detect foreign objects and mitigate scenarios in which a power receiver is placed on a power transmitter before the power transmitter is turned on. The FOD protocol may include subsequent foreign object detection evaluations (such as a pre-power foreign object detection evaluation and a power-on foreign object detection evaluation) as the power transmitter transitions to other operational phases toward the power transmission phase. The power transmitter (in coordination with the FOD evaluation unit) may prevent the WPT system from generating wireless power if a foreign object is introduced before or during each operational phase.

[0013] Each foreign object detection evaluation may be based on a comparison of the detection values ​​to a detection threshold, and in some operational phases, the foreign object detection evaluation is further based on a comparison of how many coil pairs indicate the presence of a metal object. According to aspects of the present disclosure, the FOD evaluation unit may adjust the detection values ​​using offset values ​​to improve the accuracy of foreign object detection in the WPT system. An offset value is added (or subtracted) to a corresponding one of the detection values ​​to compensate for changes in the system, such as mismatch of the detection coils, movement of the power receiver, and the presence of non-foreign objects (sometimes referred to as "friendly objects" or "friendly metal") in the WPT system, among other examples.

[0014] In some implementations, the FOD evaluation unit may be configured to perform an initial idle phase foreign object detection evaluation to detect a foreign object when the power transmitter is first turned on or initialized. The power transmitter may cause the FOD evaluation unit to perform an initial idle phase foreign object detection evaluation immediately after the power transmitter is first turned on and in conjunction with the idle phase. In the initial idle phase foreign object detection evaluation, the offset value (referred to as an "initial offset value") is based on a "calibration value" that may be pre-determined. For example, the calibration value may be measured in advance (referred to as "calibration" or "calibrated") at a moment when the mating surface is known to be free of the power receiver and foreign object, such as when the power transmitter is installed or maintained. The calibration value may be stored in a non-volatile memory of the power transmitter so as to remain available for the FOD evaluation unit when the power transmitter is first turned on. As part of the FOD initialization, the FOD evaluation unit determines a number of offset values ​​(as "initial offset values") based on the calibration value retrieved from the non-volatile memory. As described further herein, the initial idle phase foreign object detection evaluation may use different criteria for detecting foreign objects compared to other operational phases where a power receiver is already present at the interface. If a power receiver is already present when the power transmitter is turned on, the initial idle phase foreign object detection evaluation may prevent the power transmitter from transmitting wireless power until the FOD fault condition can be cleared. If a power receiver is not present when the power transmitter is turned on, the initial idle phase foreign object detection evaluation may successfully determine whether a foreign object is present.

[0015] After the initial idle phase foreign object detection evaluation, the FOD evaluation unit may perform subsequent foreign object detection evaluations, such as in other operational phases. In other operational phases, the FOD evaluation unit may adapt the offset values ​​to account for detected system changes. Adaptation (sometimes referred to as "recalibration") allows the FOD evaluation unit to update the offset values ​​(for use in subsequent foreign object detection evaluations) to account for system changes (such as movement of the power receiver) when the power receiver is detected and no foreign object is present. The updated offset values ​​(sometimes referred to as "adapted offset values") may be stored in a volatile memory so that they can be used while the power transmitter is on and deleted when the power transmitter is turned off. Each time the power transmitter is turned off and then on, the offset values ​​are reset to the calibrated values. Adaptation occurs after the FOD evaluation unit detects a power receiver present at the interface, such as in a configuration phase, connection phase, or power transfer phase. The FOD evaluation unit may perform adaptation in other operational phases to compensate for the presence or movement of the power receiver, or when no foreign object is detected.

[0016] For each foreign object detection evaluation, the FOD evaluation unit may indicate a fault condition (sometimes referred to as a "FOD fault") when a foreign object is detected. The power transmitter or power receiver may control operation in different phases based on the fault condition. This disclosure includes several examples of FOD fault handling that the FOD evaluation unit may use when determining an FOD fault depending on the current phase of the WPT system. For example, the FOD fault may be indicated by a user interface of the power transmitter, the power receiver, or both. In some implementations, the FOD evaluation unit may communicate a message to the power receiver, the power transmitter, or a processor of a home appliance that includes either the power transmitter or the power receiver, or both. In some implementations, user interaction (e.g., via a user interface of the PRx or PTx) may be used to disable or clear the FOD fault. Alternatively or additionally, the FOD fault condition may be cleared by user intervention to remove the foreign object and the PRx from the operating environment of the WPT system.

[0017] Certain implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages: Foreign object detection can be performed accurately at different operational phases of the WPT system. For example, the FOD evaluation unit can properly indicate an FOD fault when a foreign object is detected. And the FOD evaluation unit can properly adjust the detection value to account for the movement of the power receiver when no foreign object is present. Using the techniques of this disclosure, the WPT system can adjust the FOD procedure and operational phases. Furthermore, in some implementations, the FOD procedure can address some common user errors, such as placing a power receiver on a power transmitter before the WPT has a chance to check for a foreign object. Thus, implementations of the present disclosure can provide additional safety and reliability of the wireless power transfer system.

[0018] The following description is directed to a particular implementation for purposes of illustrating the innovative aspects of the present disclosure. However, those skilled in the art will readily recognize that the teachings herein may be applied in many different ways. The described implementations may be implemented in any means, device, system, or method for wireless power transmission.

[0019] FIG. 1 shows a block diagram of an exemplary wireless power transmission system 100. The wireless power transmission system may include a power transmitter 102 and a power receiver 118. The power transmitter 102 may include one or more primary coils 110 that transmit wireless energy (as a wireless power signal) to one or more corresponding secondary coils 120 in the power receiver 118. A primary coil refers to a wireless energy source in the power transmitter (such as induction or magnetic resonance energy that generates an electromagnetic field). The primary coil 110 may be associated with a power signal generator 106. The primary coil 110 may be a wire coil that transmits wireless power (which may also be referred to as wireless energy or a wireless power signal). The power signal generator and the primary coil together may generate a primary magnetic field during wireless power transmission. The power signal generator 106 may include components (not shown) that provide power to the primary coil 110 to cause the primary coil 110 to generate a wireless power signal. For example, the power signal generator 106 may include one or more switches, drivers, series capacitors, rectifiers, or other components. The power transmitter 102 may also include a transmit controller 108 (sometimes referred to as a PTX controller) that controls components of the power signal generator 106. For example, the transmit controller 108 may determine an operating point (such as a voltage or current) and control the power signal generator 106 according to the operating point.

[0020] In some implementations, the power signal generator 106, the transmit controller 108, and other components (not shown) may be collectively referred to as a power transmitter circuit. Some or all of the power transmitter circuit may be embodied as an integrated circuit (IC) that implements features of the present disclosure for controlling and transmitting wireless power to one or more power receivers. The transmit controller 108 may be implemented as a microcontroller, a dedicated processor, an integrated circuit, an application specific integrated circuit (ASIC), or any other suitable electronic device.

[0021] The power supply 112 may provide power to the power transmitter circuitry of the power transmitter 102. The power supply 112 may convert alternating current (AC) power to direct current (DC) power. For example, the power supply 112 may include a converter that receives AC power from an external power source (such as a mains power supply) and converts the AC power to DC power used by the power signal generator 106.

[0022] In some implementations, the first communication unit 142 may be coupled to components of the power signal generator 106 or the primary coil 110 to transmit or receive communications via the wireless power signal. The first communication unit 142 may include logic for controlling one or more switches and other components that cause the transmission and reception of wireless signals via the wireless power signal. For example, the first communication unit 142 may include a modulator or demodulator that converts information into a modulated signal added to the wireless power signal. In one example, the first communication unit 142 may convert data from the transmit controller 108 into a frequency shift key (FSK) modulated signal that is combined with the wireless power signal for communication from the power transmitter 102 to the power receiver 118. In another example, the first communication unit 142 may sense a load modulated amplitude shift key (ASK) signal from the power signal generator 106 or the primary coil 110 and demodulate the ASK signal to obtain the data that the first communication unit 142 provides to the transmit controller 108.

[0023] In some implementations, the power transmitter 102 may include a wireless communication interface 114. The wireless communication interface 114 may be connected to a first communication coil 116 (which may be a coil or a loop antenna). The wireless communication interface 114 may include logic for controlling one or more switches and other components that cause the transmission and reception of wireless communication signals through the first communication coil 116. In some implementations, the wireless communication interface 114 may support short-range radio frequency communication (such as Bluetooth™) or near field communication (NFC). NFC is a technology that transfers data at a carrier frequency of 13.56 MHz. The wireless communication unit 114 may also support any suitable communication protocol.

[0024] The transmit controller 108 may use various techniques to detect the presence or proximity of the power receiver 118. In some implementations, the presence or proximity of the power receiver 118 may be detected based on load changes in response to a periodic low power signal generated by the power signal generator 106 and the primary coil 110. In some implementations, the presence or proximity of the power receiver 118 may occur during a periodic ping process of the wireless communication interface 114 of the power transmitter 102.

[0025] The transmit controller 108 may control characteristics of the wireless power that the power transmitter 102 supplies to the power receiver 118. After detecting the power receiver 118, the transmit controller 108 may receive information from the power receiver 118. For example, the transmit controller 108 may receive information during a handshake process with the power receiver 118. The information may include information about the power receiver 118 (such as the power rating, load condition, manufacturer, model, or parameters of the receiver when operating with a standard transmitter, among other examples). The transmit controller 108 may use this information to determine at least one operational control parameter (such as frequency, duty cycle, voltage, etc.) of the wireless power it supplies to the power receiver 118. To configure the wireless power, the transmit controller 108 may modify the frequency, duty cycle, voltage, or any other suitable characteristic of the power signal generator 106.

[0026] The power receiver 118 may include a secondary coil 120, a rectifier 126, and a receiver controller 128. The secondary coil 120 may receive wireless energy via an electromagnetic field. When the secondary coil 120 aligns with the primary coil 110, the secondary coil 120 may generate an induced voltage based on the wireless power signal received from the primary coil 110. A capacitor (not shown) and a switch (not shown) may be in series between the secondary coil 120 and the rectifier 126. The rectifier 126 may rectify the induced voltage and provide the induced voltage to the load 130. In some implementations, the load 130 may be external to the power receiver 118 and coupled via a wire from the rectifier 126. In some implementations, the rectifier 126 may not be present and the induced voltage of the secondary coil 120 may be provided to an element in series with the secondary coil 120 and the load 130.

[0027] The receiver controller 128 may be connected to the rectifier 126 and the second communication unit 152. The second communication unit 152 may be coupled to components of the secondary coil 120 or the rectifier 126 to transmit or receive communications via the wireless power signal. The second communication unit 152 may include logic for controlling one or more switches and other components that cause the transmission and reception of communication signals via the wireless power signal. For example, the second communication unit 152 may include a modulator or demodulator that converts information into an ASK or FSK modulated signal. In one example, the second communication unit 152 may convert data from the receiver controller 128 into an ASK modulated signal that is used to load modulate the wireless power signal for communication from the power receiver 118 to the power transmitter 102. In another example, the second communication unit 152 may sense an FSK signal in the wireless power signal at the secondary coil 120 or the rectifier 126 and demodulate the FSK signal to obtain data that the second communication unit 152 provides to the receiver controller 128.

[0028] In some implementations, the power receiver 118 may include a wireless communication interface 132. The wireless communication interface 132 may include modulation and demodulation circuits for wireless communication via a second communication coil 134 (which may be a coil or a loop antenna). Thus, the receiver controller 128 may wirelessly communicate with the transmit controller 108 via the wireless communication interface 132 and the wireless communication interface 114 using NFC communication or Bluetooth.

[0029] In some conventional wireless power systems, the primary coil can transmit wireless energy to the secondary coil up to a rating predetermined by the wireless plan. For example, a low-power wireless power signal can carry five watts (5W), 9W, 12W, or 15W. Low-power wireless power systems can deliver up to 15 watts of energy, which is suitable for many electronic devices. Higher power wireless systems are being developed to support wireless power transmission to appliances or devices that require more power. For example, a high-power cordless kitchen transmitter can deliver as much as 2.2W of power.

[0030] The interface 180 (sometimes referred to as the "interface space") may define a space between the power transmitter and the power receiver. For example, the interface may include a surface of the power transmitter on which the power receiver may be disposed. The distance between the primary coil 110 and the secondary coil 120 may include a thickness of the interface surface. During wireless power transmission, the primary coil 110 may induce a magnetic field (referred to as the primary magnetic field) that passes through the interface and into the operating environment in which the secondary coil is disposed. Thus, the "operating environment" is defined by the primary magnetic field in the system, and the primary magnetic field of the primary coil 110 may detectably exist and detectably interact with the secondary coil or foreign object 190 (denoted as FO 190).

[0031] When a foreign object 190 is present in the operating environment of the WPT system, the foreign object 190 may experience an increase in temperature due to interaction with the magnetic field. Thus, when a foreign object is detected, the power transmitter may discontinue generating the primary magnetic field or otherwise prevent the power transmitter from transmitting a sufficient amount of energy to the foreign object to heat it beyond a safe level. The WPT system may include a detection device (sometimes referred to as a foreign object detection mat or "FOD mat"). In some implementations, the detection device may be integrated or coupled with the power transmitter 102 or the interface surface 180.

[0032] FIG. 2 illustrates a block diagram of an exemplary wireless power transfer system 200 having a detection device for foreign object detection. The wireless power transfer system 200 includes a power transmitter 102 (having a primary coil 110), a mating surface 180, and a power receiver 118 (having a secondary coil 120), as described with reference to FIG. 1. For brevity, other components of the power transmitter 102 and the power receiver 118 are not shown in FIG. 2. A detection device (such as the FOD mat 150 shown in FIG. 2 or a variation thereof) may include multiple detection coils 170 capable of detecting the presence of a foreign object according to some aspects of the disclosure. In some implementations, the detection device may include the FOD mat 150, and the detection coils may be constructed in or on the FOD mat 150. Although not shown in FIG. 2, in some implementations, the FOD mat may extend across the entire area of ​​the mating surface. Alternatively, the FOD mat (and the number or configuration of detection coils therein) may be sized based on technical specifications that define the size of the primary coil 110, the secondary coil 120, or both. Although the example of FIG. 2 shows the detection device deployed as a FOD mat 150 in or on a surface, in some implementations the detection device may be deployed on or in any surface or structure within the space between the primary coil 110 and the secondary coil 120.

[0033] The WPT system may include an FOD assessment unit 155. In some implementations, the FOD assessment unit 155 may be part of the power transmitter 102 (as shown in FIG. 2). In some other implementations, the FOD assessment unit 155 may be located elsewhere in the WPT system (in a detection device, an FOD control unit (not shown), or as part of a home appliance (not shown) that houses the power transmitter 102, among other examples). The FOD assessment unit 155 may be configured to detect a foreign object 190 in the vicinity of the detection coil 170 based on the detection value, as described further herein. In some implementations, the FOD assessment unit 155 may disable or enable wireless power transmission operation of the power transmitter 102 based on the FOD assessment result. The FOD assessment result may indicate whether the FOD assessment unit 155 has detected a foreign object 190 in the vicinity of the detection coil 170. In some implementations, the FOD evaluation unit 155 may communicate the FOD evaluation result to the power receiver 118 to cause the power receiver 118 to enable or disable the wireless power transmission operation of the power receiver 118 based on the FOD evaluation result. In some implementations, when the FOD evaluation result is that a foreign object is detected, the FOD evaluation result may be referred to as an FOD fault signal. Although only one FOD mat 150 is shown in FIG. 2, in some implementations, more than one FOD mat may be deployed in the WPT system. For example, the FOD evaluation unit 155 may perform foreign object detection using FOD mats (not shown) located in association with different primary coils or different power transmitters of a stove top or other wireless power appliance. Alternatively or additionally, one FOD mat may be located in association with the power transmitter and another FOD mat may be located in association with the power receiver. Each of the FOD mats may be connected to the same or different foreign object evaluation units (performing the functions described with reference to the FOD evaluation unit 155 of FIG. 2).

[0034] Techniques by which the FOD assessment unit 155 communicates the FOD assessment results with the power transmitter 102 or the power receiver 118 may vary. In some implementations, the FOD assessment unit 155 may be implemented in a transmit controller (not shown) of the power transmitter 102 and may provide the FOD assessment results as information processed by the transmit controller. In some other implementations, the FOD assessment unit 155 may have a wired communication link (not shown) to the transmit controller of the power transmitter 102. In some implementations, the FOD assessment unit 155 may communicate with the power transmitter 102 or the power receiver 118 or both by a wireless communication link (not shown). In implementations where the FOD assessment unit 155 is not integrated into the transmit controller of the power transmitter 102, the transmit controller may manage the timing of the FOD assessments performed by the FOD assessment unit 155. For example, the transmit controller may cause the FOD assessment unit 155 to perform FOD assessments during various operational phases of the WPT system. In some implementations, when the power transmitter 102 triggers an FOD assessment, the power transmitter 102 may provide the FOD assessment unit 155 with an indicator of the power transmitter's current operational phase or may indicate what type of FOD assessment the FOD assessment unit 155 will perform. In some implementations, the FOD assessment unit 155 may communicate the FOD assessment results to the power transmitter 102 or power receiver 118 using a memory storage unit, pin lines, or other control signals without the need for a communication protocol. In some implementations, the FOD assessment unit 155 may be located or implemented as software within a controller of the power transmitter 102 or power receiver 118.

[0035] The FOD mat 150 may be a flexible mat, a conformable mat, a rigid mat or a plug-and-play mat, a stand-alone mat, or a combination thereof. The substrate of the FOD mat 150 may be made of an electrically insulating material. In some implementations, the FOD mat 150 may further include a mechanical wear-resistant material to withstand movement of the power receiver thereon (such as when the power receiver 118 is a major appliance). In some implementations, the FOD mat 150 may be further designed for outdoor applications and may be designed to withstand temperature, humidity, and may be resistant to water ingress. The detection coil 170 may be disposed on the substrate of the FOD mat 150 or may be embedded in the substrate of the FOD mat 150 for user safety and aesthetics. In some other embodiments, the detection coil 170 may be printed, molded, woven, or additively manufactured on the substrate of the FOD mat 150.

[0036] The detection coils 170 may operate in pairs. The FOD assessment unit 155 may obtain detection values ​​(such as differential voltages, differential currents, or differential impedances, among other examples) associated with multiple coil pairs. Typically, the power receiver 118 is large enough to span multiple coil pairs at the same time. Conversely, the foreign object 190 may be smaller than the power receiver 118. The foreign object 190 may span only one coil or span two coils belonging to adjacent coil pairs. By comparing the difference in the detection values ​​in a pair of detection coils, the FOD assessment unit 155 can detect the presence of a foreign object in the vicinity of the coil pair. For example, a first detection coil 171 and a second detection coil 172 may form a coil pair. A foreign object 190 near the first detection coil 171 may cause the detection values ​​of the first detection coil 171 and the second detection coil 172 to be different. A detection device (such as FOD mat 150) may have several such coil pairs, and the FOD evaluation unit 155 may compare the respective detection values ​​for the coils of each coil pair.

[0037] In an implementation using active excitation, the FOD assessment unit 155 may cause a driver (not shown) to excite the first and second detection coils 171 and 172 using a high frequency (higher than frequencies typically used in primary magnetic fields, such as, by way of example, 200 kHz or higher). The coil pair may be coupled in a parallel circuit to a driver that simultaneously excites the detection coils of the coil pair. When present, a foreign object may cause the first detection coil 171 to experience a different impedance or current compared to the second detection coil 172 (without the foreign object). By comparing the current drawn through the first detection coil 171 and the second detection coil 172, the FOD assessment unit 155 may determine that a foreign object is present near the first detection coil 171 or the second detection coil 172. The difference in the current drawn by the coil pair may be referred to as a differential current.

[0038] In an implementation using passive excitation, the FOD assessment unit 155 may observe a voltage induced in the detection coil based on the magnetic field generated by the primary coil 110. The detection coils of a coil pair may be connected in series and terminated by a known impedance. When the primary coil 110 is excited by the power transmitter 102, the magnetic field generated by the primary coil 110 may induce a voltage in the detection coil of the coil pair. When no foreign object is present, the voltages in the detection coils are uniform and can be effectively cancelled out. Conversely, when a foreign object is present, the voltages in the detection coils are non-uniform, resulting in a measurable differential voltage. The differential voltage is an example of a detection value that can be adjusted using an offset value in various implementations of the present disclosure.

[0039] Thus, the techniques of this disclosure can be used with sensing devices that use active or passive excitation. For simplicity, many of the examples in this disclosure are based on active excitation, but the same or similar concepts apply to sensing devices that use passive excitation.

[0040] FIG. 3 shows a block diagram 300 of an exemplary detection device in which a detection value is based on a comparison of coil circuits associated with a pair of detection coils. FIG. 3 shows a coil pair comprising a first detection coil 171 and a second detection coil 172. The coil pair is connected in parallel to a driver 305. Thus, when one of the detection coils of the coil pair is excited, the other detection coil is also excited. The driver 305 may be operatively coupled to the coil pair (the first detection coil 171 and the second detection coil 172 in this example). The driver 305 may be configured to simultaneously excite the detection coils 171 and 172 of the coil pair using an alternating current signal through the coil circuits 311 and 312. For example, the first coil circuit 311 may include a current path from the driver 305 through the first detection coil 171, and the second coil circuit 312 may include a current path from the driver 305 through the second detection coil 172.

[0041] A sensing device (not shown) or FOD evaluation unit (not shown) may obtain a detection value 350 associated with the coil pair. For example, the detection value 350 may be a differential current, a differential voltage, or a differential impedance, among other examples. The detection value 350 represents a comparison of how currents conduct differently when comparing the first detection coil 171 and the second detection coil 172. For example, the detection value 350 may be a differential current representing the difference between a first current (referenced as "A" in FIG. 2) through the first coil circuit 311 and a second current (referenced as "B" in FIG. 2) through the second coil circuit 312.

[0042] The detection value 350 may be adjusted using an offset value according to the techniques of this disclosure. In some implementations, the impedance values ​​of the first detection coil 171 and the second detection coil 172 may be the same or similar when the foreign object 190 is not present. However, when the foreign object 190 is present, the foreign object 190 may cause an impedance change in one of the detection coils 171 and 172 such that the first detection coil 171 has a first impedance value and the second detection coil 172 has a second impedance value. The difference in impedance may cause the amount of current drawn through the coil circuits 311 and 312 to differ. A differential current may refer to a comparison of the current drawn through the coil circuits 311 and 312. When the foreign object 190 is not present and the impedances of the detection coils 171 and 172 are the same or similar, the amount of current drawn through the coil circuits 311 and 312 may be the same or similar. Thus, the detection value 350 may be a low value indicating little or no difference. Conversely, when a foreign object 190 is present near one of the first detection coils 171, the impedance of the first detection coil 171 changes, causing the detection value 350 to indicate a greater difference in the currents drawn through the coil circuits 311 and 312.

[0043] An FOD evaluation unit (not shown) can obtain detection values ​​(such as detection value 350) from multiple coil pairs of the detection coil. The FOD evaluation unit can distinguish between movement of the power receiver and the introduction of a foreign object based on how many coil pairs have a change in detection value. For example, when the detection values ​​for a threshold amount of the multiple coil pairs indicate a change in differential current or differential voltage, the FOD evaluation unit can determine that such change is due to movement of the power receiver. When the detection values ​​for one or two coil pairs (or less than the threshold amount) indicate a change in differential current or differential voltage, the FOD evaluation unit can determine that such change is due to the introduction of a foreign object. In such a case, the FOD evaluation unit can transmit an FOD evaluation result indicating an FOD fault condition. In some implementations, the FOD evaluation unit can modify or offset the detection values ​​of the multiple coil pairs in response to determining that a movement of the power receiver has occurred. Thus, for subsequent comparison of the detection values, the FOD evaluation unit can adjust the detection values ​​to account for the previous movement of the power receiver within the magnetic field of the WPT system. Thus, the accuracy of subsequent FOD assessments can be improved by accounting for the effects of the normal impedance of the power receiver, while still providing an accurate technique for detecting foreign objects.

[0044] 4 shows a chart 400 with example magnitudes of detection values. For example, FIG. 4 diagrammatically shows example magnitudes of differential currents 350A and 350B (as an example of differential current 350 of FIG. 3) and how the differential currents can be used to determine whether a foreign object is present. When no foreign object is present (as shown in graph 411), the magnitude of differential current 350A may be lower than detection threshold 420. When a foreign object is present (as shown in graph 412), the magnitude of differential current 350B may be higher than detection threshold 420. Detection threshold 420 may be a configurable parameter based on a desired sensitivity of the FOD assessment unit.

[0045] In the example shown in FIG. 4, a foreign object is detected when the differential current exceeds a detection threshold. In some implementations, the foreign object is detected based on the amount of change in the differential current. For example, the differential current may be higher during a baseline condition and drop below a threshold amount when a foreign object is detected. The differential current may be larger or smaller (compared to a previous measurement or a baseline measurement) when a foreign object is present. Thus, in some implementations, the amount of change in the differential current may indicate the presence of a foreign object. The change in the amount of the differential current may be compared to a detection threshold to determine whether the change is based on the introduction of a foreign object.

[0046] FIG. 5 shows a block diagram of an example detection device 500 in which the detection value is based on a voltage induced by a differential current. The example detection device may include detection coils arranged in pairs as described herein. For example, the example detection device may include a pair of detection coils 171 and 172 (referred to as a coil pair) as described with reference to FIG. 3. The detection device may include a driver (not shown) configured to simultaneously excite the coil pair during the FOD period. The presence (or lack thereof) of a foreign object 190 may induce differential currents in the coil circuits 311 and 312. FIG. 5 provides an example of a differential current sensing device that may be used to measure the differential current. The differential current sensing device may include a magnetic core 510 and a differential current sensing circuit 501, which operate in combination to provide a voltage that may be measured to obtain a detection value 545.

[0047] When the currents on the coil circuits 311 and 312 pass through the magnetic core 510, the difference in the currents creates a magnetic flux linkage in the magnetic core. The coil circuits 311 and 312 pass through the magnetic core in opposite directions such that equal currents in the coil circuits 311 and 312 create a smaller magnetic flux linkage, while a difference in the currents in the coil circuits 311 and 312 creates a larger magnetic flux linkage. The magnetic flux linkage in the magnetic core 510 can induce a corresponding electrical signal in the sensor coil 520 wound around the magnetic core 510. This induced electrical signal has an induced voltage 522 that is dependent (related or proportional) to the difference in the currents in the coil circuits 311 and 312 and represents a measure of the differential current between the coil pair of the sense coils 171 and 172, provided that the magnetic core 510 is not magnetically saturated.

[0048] The differential current sensing circuit 501 may also include a rectifier 530 that receives and rectifies the induced voltage signal to generate a DC voltage 545 (referred to as a sensed value 545). An optional filter 540 may filter the sensed voltage before transmitting it to the control unit 155. In one example, the filter 540 is configured to remove high frequency components from the measurement.

[0049] The FOD evaluation unit 155 may be configured to generate a foreign object detection evaluation result 580 (FOD result) indicative of the result of the foreign object detection evaluation using the detection value 545. In some implementations, the FOD evaluation unit 155 may include a comparator 560 configured to compare the absolute value of the detection value to a detection threshold 565. Based on the comparison of the detection value to the detection threshold 565, the FOD evaluation unit 155 may provide the FOD evaluation result 580 or other control signal to a component of the WPT system (power transmitter or power receiver). For example, when the absolute value of the detection value is greater than the detection threshold 565, the FOD evaluation unit 155 may provide the FOD evaluation result 580 indicative of a foreign object being present. Alternatively, the detection value in the presence of a foreign object may be lower than the detection value when the foreign object is not present. Thus, in some implementations, the change in the absolute value of the detection voltage from a previous or baseline measurement to a current measurement may be compared to a delta threshold, and a foreign object may be detected when the amount of change is greater than the delta threshold. The FOD assessment unit 155 may include a component (called an absolute value unit or ABS 555 ) for generating an absolute value (also called a magnitude) of the detection value 545 .

[0050] In some implementations, the FOD evaluation unit 155 may also include an adjustment unit 550 configured to add or subtract an offset value (sometimes referred to as "offset" for short) to the corresponding one of the detection voltages. For example, the offset value may be based on a normal difference in impedance of the coil pair of the detection coils 171 and 172, or may be based on the results of a previous foreign object detection evaluation. In some implementations, the initial offset value may be determined during or after manufacturing of the detection coils 171 and 172. Alternatively or additionally, the initial offset value may be determined by the FOD evaluation unit 155 or a test equipment (not shown) during a baseline measurement of the detection device when no foreign object is present. For example, the initial offset value may account for slight differences in impedance caused by other components of the FOD mat, power transmitter, or power receiver depending on where the detection device is installed. During calibration of the FOD evaluation unit 155, a calibration value may be measured and stored as an initial offset value. During an initial idle phase foreign object detection evaluation, the initial offset value (for each detection value) is subtracted from the actual detection value and passed to the ABS 555. Comparator 560 may compare the absolute value produced by ABS 555 to a detection threshold 565 to generate an FOD result 580.

[0051] In the idle phase, the initial idle phase foreign object detection evaluation utilizes a number of offset values, referred to as initial offset values, that are based on the calibration values. In other operational phases, the power receiver is present at the interface. The FOD evaluation unit 155 may adapt the number of offset values ​​to account for detection of movement of the power receiver on the interface when no foreign object is present. For example, the detected value may be used as an updated offset value associated with that coil pair for use in a subsequent foreign object detection evaluation (such as in the configuration phase, connection phase, or power transfer phase). The updated offset value may reflect a change in impedance due to movement of the power receiver. In subsequent foreign object detection evaluations, the updated offset value is used by the adjustment unit 550 to adjust the detection value 545.

[0052] FIG. 6 shows a diagram 600 of multiple detector coils in an exemplary detector device. Four coil pairs are shown. The first coil pair includes first and second detector coils 171 and 172. The second coil pair includes third and fourth detector coils 173 and 174. The third coil pair includes fifth and sixth detector coils 175 and 176. The fourth coil pair includes seventh and eighth detector coils 177 and 178. The example of FIG. 6 is provided for educational purposes, and it will be apparent that the detector device may have any of a variety of coil pairs. For simplicity, the detector coils 171, 172, 173, 174, 175, 176, 177, 178 are referred to as L1, L2, L3, L4, L5, L6, L7, and L8, respectively.

[0053] During a foreign object detection evaluation, one or more coil pairs may be actively or passively excited such that a detection value can be obtained for each coil pair. In some implementations, a coil pair may be excited in a sequential pattern such that its associated detection value may be measured without interference of other coil pairs. In some implementations, two or more coil pairs having non-adjacent detection coils may be excited and measured simultaneously.

[0054] 6 also shows an example where a foreign object 190 is located near coil L3. When the coil pair of coils L3 and L4 are energized, the detection coils draw different currents and the detection value may indicate that a foreign object is located near one of the coils.

[0055] FIG. 7 shows a diagram of multiple coil pairs that can distinguish between the movement of the power receiver and the presence of a foreign object. The layout of FIG. 7 utilizes the exemplary configuration of multiple coil pairs described with reference to FIG. 6. A primary coil (not shown) may be located below and in the center of the detection zone covered by coils L1-L8. A first example 701 shows a secondary coil (shown as a single circle for simplicity) moving over the array of detection coils from a first position 710 to a second position 720. Because the secondary coil includes metal and ferrite components, the secondary coil may cause a change in the impedance of the detection coil. Thus, when the detection values ​​of the coil pairs are measured, the secondary coil itself may cause a difference in the detection values ​​associated with some coil pairs. However, because the secondary coil is relatively large compared to the size of the detection coil, multiple coil pairs measure the change in the detection value. In comparison, a second example 702 shows a foreign object 190 introduced into the operating environment of the WPT system. The foreign object is relatively small compared to the size of the detection coil. Thus, perhaps one or two coil pairs may measure the change in the detection value due to the introduction of the foreign object. In some implementations, the size of the detection coils L1-L8 (and their sub-coils) may be selected based on a standard size (or sizes) of secondary coils that meet technical specifications. Similarly, the size of the detection coils L1-L8 may be selected based on the potential size of foreign objects likely to be introduced into the operating environment. For example, a detection device for use in a kitchen WPT system may include a detection coil of an appropriate size to detect spoons, forks, coins, keys, tin cans, or metal plates, among other examples. A detection device for use in an EV WPT system may include a detection coil of an appropriate size to detect wrenches, aluminum cans, gas tanks, washers, nuts, or screws, among other examples. A detection device for use in a desktop WPT system may include a detection coil of an appropriate size to detect foreign objects (such as pens, keys, computer parts, rings, or thumb drives, among other examples).

[0056] FIG. 8 illustrates an example chart 800 comparing detection values ​​of coil pairs due to movement of the power receiver versus the presence of a foreign object. In a first example 810, an FOD evaluation unit (such as the FOD evaluation unit 155 described with reference to any of the figures herein) may establish a baseline representation of the detection voltages (adjusted by an initial offset value based on a calibration value). For example, in an idle phase, the FOD evaluation unit may add an initial offset value to the detection value of each coil pair based on the calibration value. The detection values ​​811, 812, 813, and 814 may represent measurements of differential currents (or differential voltages) of multiple coil pairs. The FOD evaluation unit may determine that a foreign object is not present based on the detection values ​​(adjusted by the initial offset values). For example, the FOD evaluation unit may compare each detection value to a detection threshold and determine that a foreign object is not present for each coil pair. Alternatively or additionally, the detection FOD evaluation unit may compare the amount of change in each detection value to a delta threshold and determine that a foreign object is not present when the amount of change is less than the delta threshold. During other phases of operation when a power receiver is present and no foreign object is detected, the FOD assessment unit may adapt the offset values ​​based on changes in impedance caused by movement of the power receiver. During other phases of operation, the updated offset values ​​may be used to adjust the detection values ​​of the coil pairs during subsequent foreign object detection assessments.

[0057] In a second example 820 (e.g., a subsequent foreign object detection evaluation), the power receiver may have moved from a previous position associated with a previous evaluation. This movement may cause a change in the detection values ​​of the coil pairs. For example, detection values ​​821, 822, 823, and 824 may represent measurements of differential current (or differential voltage) of multiple coil pairs during a subsequent foreign object detection evaluation. In the second example, detection values ​​822, 823, and 824 corresponding to the second, third, and fourth coil pairs have changed. The changes in detection values ​​822, 823, and 824 are enclosed by 826, 827, and 828, respectively, for purposes of this explanation. Although shown as a decrease in detection values ​​(enclosed by 826, 827, and 828) for educational purposes, in some implementations the change may be an increase in detection values. Whether the change is an increase or decrease, the FOD evaluation unit may determine how many coil pairs had a change in detection value that is greater than the delta threshold. As the coil pairs that exceed the threshold have had a change in their respective detection values, the FOD evaluation unit may determine that the change is due to movement of the power receiver. The threshold amount may be a configurable parameter or may be predetermined. In some implementations, changes in three or more coil pairs may be considered to be due to movement of the power receiver during wireless power transmission. When the FOD evaluation unit determines that the change in the detection values ​​is due to movement of the power receiver, the FOD evaluation unit may adapt the offset value to account for the new position of the power receiver. In some implementations, the offset value may be adapted whenever the results of the foreign object detection evaluation are determined to be based on movement of the power receiver.

[0058] In a third example 830, a foreign object may be introduced into the operating environment during wireless power transmission. Detection values ​​831, 832, 833, and 834 may represent measurements of differential current (or differential voltage) of multiple coil pairs. In the third example, the detection value 832 of the second coil pair changes. The change in detection value 832 is circled at 836 for purposes of this description. Because the number of coil pairs having a change in detection value is less than a threshold amount, the FOD evaluation unit may determine that the change is due to a foreign object introduced in the vicinity of the detection coil of the second coil pair. The FOD evaluation unit may send an FOD fault signal or control signal to the WPT system to indicate that a foreign object may be present.

[0059] FIG. 9 illustrates an example foreign object detection evaluation block diagram 900 in which a detection value is adjusted based on an offset value. Block diagram 900 may illustrate features of an FOD evaluation unit (such as any of the FOD evaluation units described herein, including FOD evaluation unit 155). At some point prior to a foreign object detection evaluation (such as during installation or maintenance of the power transmitter), a calibration process 905 may be performed to determine a calibration value 910. The calibration value 910 represents a baseline measurement of the impedance difference between the coil pair at the moment when neither a foreign object nor a power receiver is present at the interface. The calibration value 910 may be stored in a non-volatile memory associated with the FOD evaluation unit such that it remains even when the power transmitter and FOD evaluation unit are turned off. When the power transmitter is turned on, the FOD evaluation unit undergoes FOD initialization 920 in which the calibration value 910 is retrieved from the non-volatile memory and used as an initial offset value for the corresponding adjustment units 921, 922, 923, and 924.

[0060] In the exemplary scenario described with reference to FIG. 9 , the FOD evaluation unit may be configured to receive detection values ​​911, 912, 913, and 914 associated with the first, second, third, and fourth coil pairs, respectively. For example, the detection values ​​may be differential voltages, differential currents, or differential impedances describing the difference in energy flowing through the detection coils of the actively or passively excited coil pairs. Each of the detection values ​​may be obtained using a sensing circuit associated with the coil pair. The detection values ​​911, 912, 913, and 914 may be adjusted using adjustment units 921, 922, 923, and 924, respectively. Each adjustment unit 921, 922, 923, and 924 may adjust the corresponding detection value 911, 912, 913, and 914 by adding or subtracting a corresponding offset value. In an initial idle phase foreign object detection evaluation, the offset values ​​(collectively referred to as offset values ​​970) may be based on an initial offset value obtained during FOD initialization 920. After the detection values ​​911, 912, 913, and 914 are adjusted by the adjustment units 921, 922, 923, and 924, respectively, the ABSs 951, 952, 953, and 954 may each generate an absolute value (magnitude) of the adjusted detection value. The comparator 960 may compare each adjusted detection value to a detection threshold 965 to determine whether a foreign object is located near the detection coil of a particular coil pair. In some implementations, if any one of the detection values ​​exceeds the detection threshold, such as in early idle phase foreign object detection, the comparator may transmit an FOD result 980 indicating an FOD fault signal. In other operational phases of foreign object detection evaluation, the comparator may determine the number of adjusted detection values ​​that exceed the detection threshold 965. For example, the comparator may determine a change number indicating how many of the adjusted detection values ​​(corresponding to each coil pair) exceed the detection threshold 965. If the change number exceeds a threshold amount 967, the comparator may determine that the change is due to movement of the power receiver. In this situation, the FOD assessment unit may perform an adaptation 990 to adapt the offset value 970 for use with subsequent foreign object detection assessments. Alternatively, if the number of changes falls below the threshold amount 967, the FOD assessment unit may determine that the FOD result 980 indicates the presence of a foreign object.In an initial idle phase foreign object detection evaluation, the threshold amount 967 may be disabled or otherwise set to a high value so that the number of changes is not interpreted as a movement of the power receiver. In the idle phase, when at least one of the adjusted detection values ​​exceeds the detection threshold 965, the FOD result 980 may indicate an FOD fault condition. In other operational phases, the threshold amount 967 may be a configurable value (such as 3 or 4) such that when more than one of the adjusted detection values ​​exceeds the detection threshold 965, the FOD evaluation unit may determine that the FOD result 980 indicates that no foreign object is present and perform adaptation 990 to update the offset value 970 for use in subsequent foreign object detection evaluations.

[0061] The FOD result 980 may include a first state indicating that no foreign object is detected and a second state indicating that a foreign object is detected. In some implementations, when the FOD result 980 indicates that a foreign object is detected, the FOD result 980 may also be referred to as an FOD fault condition signal, an FOD fault indication, or a term indicating an FOD fault to the power transmitter or power receiver. In some implementations, as a result of the FOD fault indication, the power transmitter stops or reduces power to the power receiver. In some implementations, the FOD fault indication may be presented via a user interface associated with either the power transmitter or the power receiver.

[0062] FIG. 10 illustrates a state diagram 1000 of the various operational phases of a WPT system. The state diagram 1000 illustrates the operational phases in which a WPT system may operate. Once a power receiver is placed within the mating surface of a power transmitter, the two begin communicating for the purpose of configuring and controlling power transfer. There may be four operational phases associated with a WPT system: an idle phase 1010 (sometimes referred to as a ping phase), a configuration phase 1020, a connection phase 1030, and a power transfer phase 1040. Technical specifications may define how the power transmitter and power receiver may transition between operational phases. For example, a WPT system typically begins with an idle phase 1010, and may transition from the idle phase 1010 to a configuration phase 1020. From the configuration phase 1020, the WPT system may transition to a connection phase 1030. From the connection phase 1030, the WPT system may transition to a power transfer phase 1040. Additionally, the WPT system can return to the idle phase 1010 from any of the other phases (configuration phase 1020, connection phase 1030, or power transfer phase 1040), such as when the power receiver is removed from the mating surface. Each of the operational phases is briefly described herein for reference.

[0063] In the idle phase 1010 (ping phase), the power transmitter attempts to establish communication with the power receiver. The power receiver may only be placed on the mating surface or may not be present during this operation phase. The power transmitter may attempt to communicate with or detect the presence of the power receiver. For example, the power transmitter may use analog ping, out-of-band communication (such as NFC), digital ping, or any combination thereof, to determine that a compatible power receiver is present. Once the WPT system determines that a power receiver is present (such as by verifying NFC communication), the WPT system may transition to a configuration phase 1020.

[0064] In the configuration phase 1020, the power receiver may transmit basic identification information and configuration data to the power transmitter. For example, the power transmitter may receive static configuration information from the power receiver via NFC communication. The power transmitter and the power receiver may use this information to verify that they both use compatible versions of a technical specification or protocol for wireless power transmission. The power transmitter and the power receiver may communicate basic settings or communicate regarding their respective capabilities. From the configuration phase 1020, the WPT system may transition to a connection phase 1030.

[0065] In the connection phase 1030, the power transmitter and the power receiver may exchange further communications to negotiate parameters governing the power transmission phase. After negotiating the parameters, the power transmitter may be prepared to transmit wireless power and the power receiver may be prepared to receive wireless power. However, the power transmitter may wait for a request or command from the power receiver before transitioning to the power transmission phase 1040. This may be useful, for example, when a cordless appliance (such as a blender, toaster, mixer, or microwave oven, among other examples) is configured to be used while waiting for user interaction. A user may initiate the power transmission phase 1040 by a user interface of the power receiver, and the power receiver communicates with the power transmitter to transition to the power transmission phase 1040.

[0066] In the power transmission phase 1040, the power transmitter may transmit wireless power to the power receiver. Typically, the power transmitter periodically performs a foreign object detection evaluation during the power transmission phase 1040. In some, the power transmitter may perform a foreign object detection evaluation to ensure that no foreign object is present before transitioning from the connection phase 1030 to the power transmission phase 1040. The power transmitter may also perform a periodic foreign object detection evaluation during the power transmission phase 1040.

[0067] The idle phase 1010, the configuration phase 1020, and the connection phase 1030 may be collectively referred to as the pre-power phase 1002, while the power transfer phase 1040 may be referred to as the powering phase 1004. Conventional implementations of WPT systems typically describe a foreign object detection evaluation in the powering phase 1004. However, such implementations may be insufficient to detect and appropriately handle issues that may occur due to the presence of a foreign object in the phase 1002. Furthermore, even when a foreign object detection evaluation is performed during one of the pre-power phases 1002 (such as the idle phase 1010), conventional WPT systems do not consider how the foreign object detection evaluation is coordinated between various operational phases as the power transmitter transitions between operational phases.

[0068] FIG. 11 illustrates a schematic diagram 1100 of foreign object detection evaluation associated with various operational phases of a WPT system. The schematic diagram 1100 includes an idle phase 1010, a configuration phase 1020, a connection phase 1030, and a power transfer phase 1040, as described with reference to FIG. 10. In accordance with the present disclosure, foreign object detection evaluation (shown as idle phase FOD evaluation 1110, pre-power FOD evaluation 1120 and 1130, and power FOD evaluation 1140) may be performed in association with multiple (or all) of the operational phases 1010, 1020, 1030, and 1040. In some implementations, the foreign object detection evaluation may be a prerequisite before moving to the next operational phase. If a foreign object is detected during any of the foreign object detection evaluations, the FOD evaluation unit may indicate an FOD fault. The present application describes various FOD fault handling 1180 options, some of which may depend on which operational phase the WPT system was performing when the foreign object was detected.

[0069] In some implementations, the FOD evaluation unit may perform a foreign object detection initialization 1108 after the power transmitter is turned on (shown in block 1106) and before (or as part of) the idle phase 1010. In some implementations, the power transmitter may initialize the FOD evaluation unit to prompt an idle phase FOD evaluation. During FOD initialization 1108, the FOD evaluation may obtain calibration values ​​(e.g., from non-volatile memory) and load these as initial offset values ​​in the FOD evaluation unit settings for the initial idle phase foreign object detection evaluation 1110. In some implementations, the foreign object detection initialization 1108 may include setting a status indicator (referred to as a FOD flag) to maintain a state regarding whether an initial idle phase foreign object detection evaluation has been performed. For example, the FOD evaluation unit may "set" the FOD flag to a first value (e.g., "1" or "true") to indicate that an initial idle phase foreign object detection evaluation (after turning on the power transmitter) has not yet been performed. Conversely, the FOD evaluation unit may "clear" the FOD flag by resetting it to a second value (such as "0" or "false") to indicate that an initial idle phase foreign object detection evaluation (after turning on the power transmitter) has been performed. The exemplary first and second values ​​of the FOD flag are provided here as non-limiting examples. The FOD flag (in addition to the FOD fault state) may control how the WPT system transitions between various operational phases.

[0070] In connection with the idle phase 1010 (particularly before the power receiver is placed on the interface of the power transmitter), the FOD evaluation unit may perform an idle phase FOD evaluation 1110. For the idle phase FOD evaluation 1110, the FOD evaluation unit may indicate a FOD fault condition when any one or more of the detection values ​​(adjusted by an initial offset value associated with a calibration value stored in non-volatile memory) exceed a detection threshold. Thus, the idle phase FOD evaluation 1110 may differ from the FOD evaluation in other operational phases (such as the pre-power FOD evaluations 1120 and 1130 or the on-power FOD evaluation 1140) in that the idle phase FOD evaluation 1110 does not attempt to take into account movement of the power receiver, and a lower threshold amount of detection value comparison triggers the FOD fault condition. If a foreign object is detected (block 1112), the FOD evaluation unit may indicate a FOD fault condition (as shown in block 1175) and proceed to one of several FOD fault handling options 1180, as further described with reference to FIG. 14. Alternatively, if no foreign object is detected (block 1112), the FOD evaluation unit may clear the FOD fault condition (and may also clear the FOD flag set during FOD initialization) so that the WPT system may continue to operate in the idle phase 1010 or transition to the configuration phase 1020 when the power receiver is placed on the interface. As a reminder, the FOD flag is used by the FOD evaluation unit to remember and indicate whether an initial idle phase foreign object detection evaluation has been performed after the power transmitter has been turned on. The FOD flag is set during FOD initialization (in conjunction with the power transmitter being turned on) and is cleared once an initial idle phase foreign object detection evaluation has been performed.

[0071] The FOD evaluation unit may include various scenarios, such as a first scenario where the power receiver is not placed on the interface before the power transmitter is turned on, and a second scenario where the power receiver is placed on the interface before the power transmitter is turned on. In both scenarios, the FOD evaluation unit may use an initial offset value (based on a calibration value) for idle phase FOD evaluation. In the idle phase FOD evaluation 1110, the FOD evaluation unit may indicate an FOD fault condition indication when it detects that a difference in at least one of the detection values ​​of any coil pair exceeds a detection threshold. In the scenario when the power receiver is placed on the interface before the power transmitter is turned on, the FOD evaluation unit does not clear the FOD flag that was set during FOD initialization and indicates an FOD fault condition that can be cleared either by a user action (such as using a switch or user interface) or by the user removing the power receiver (and foreign object, if any) for a short period of time and returning the power receiver after the FOD evaluation unit has performed an initial idle phase foreign object detection evaluation.

[0072] Recall that the idle phase FOD assessment 1110 may use an initial offset value based on a calibration value stored in non-volatile memory. The FOD assessment unit may perform foreign object detection assessments 1120, 1130, 1140 (and corresponding blocks 1122, 1132, 1142) in association with the configuration phase 1020, the connection phase 1030, and the power transfer phase 1040, respectively. In each operational phase other than the idle phase, a power receiver is present, and the FOD assessment unit may determine whether a foreign object is present based on criteria that can distinguish between a foreign object and a system change, such as movement of the power receiver. For example, movement of the power receiver may be detected when a number of the adjusted detection values ​​change (compared to a detection threshold). Conversely, a foreign object may be detected when one (or less than a threshold amount) of the adjusted detection values ​​changes (compared to a detection threshold). If the FOD assessment unit determines that a foreign object is not present, the FOD assessment unit may adapt the offset value to account for the system change. After adaptation, the updated offset values ​​may be used for subsequent foreign object detection evaluations, including those associated with later operational phases of the WPT system. In some implementations, the updated offset values ​​(based on adaptation for current system changes unrelated to the presence of a foreign object) may be retained in a volatile memory associated with the FOD evaluation unit.

[0073] FIG. 12 shows a detailed diagram 1200 of the foreign object detection evaluation associated with various operational phases of the WPT system. Elements in FIG. 12 having the same reference numbers as those in FIG. 11 describe similar features. At block 1106, the power transmitter may be turned on. For example, this may include operating a cookstove or oven in which one or more power transmitters are integrated. Once the power transmitter is turned on, the power transmitter may initialize the FOD evaluation unit. The power transmitter may initialize the FOD evaluation unit before or during the end of the idle phase. At block 1108, the FOD evaluation unit may set an FOD flag (indicating that an initial idle phase foreign object detection evaluation has not yet been performed) and an FOD fault condition. For example, the FOD flag may be set to a first value (e.g., “1”) to indicate that an initial idle phase foreign object detection evaluation has not yet been performed. Once the initial idle phase foreign object detection evaluation has been performed, the FOD flag may be cleared or set to a second value (e.g., “0”) to so indicate. Additionally, in block 1108, the FOD assessment unit may obtain calibration values ​​and use these to set initial offset values ​​for initial idle phase foreign object detection assessment.

[0074] At block 1210 (in the idle phase), the power transmitter may perform an NFC ping to determine whether a power receiver is present. If the power receiver is present and at least partially powered, the power transmitter's NFC ping will result in a communication from the power receiver to the power transmitter. Otherwise, if the power receiver is not present or its communication interface is not enabled, the power transmitter will not receive a communication in response to the NFC ping. If the power transmitter does not receive a response to the NFC ping at block 1212, the power transmitter may transition to a configuration phase at block 1220. Note that in one scenario, a user may have placed a power receiver on the power transmitter before turning on the power transmitter. Thus, in this scenario, the power transmitter may transition to a configuration phase before an initial idle phase foreign object detection evaluation is performed. As described in more detail below, the process described with reference to FIG. 12 can accommodate this scenario by not clearing the FOD flag and triggering an FOD fault condition, thereby preventing an inaccurate foreign object detection evaluation and potentially dangerous outcomes.

[0075] Briefly continuing with the idle phase, in block 1212, if the power transmitter does not receive a ping response, the process may continue to block 1110. In block 1110, the FOD evaluation unit may perform an idle phase FOD evaluation (as described with reference to FIG. 13). In block 1112, the FOD evaluation unit may check the results of the idle phase FOD evaluation 1110 to determine whether a foreign object has been detected. Note that in the idle phase, the FOD evaluation unit performs an initial idle phase foreign object detection evaluation, and a power receiver that does not respond to an NFC ping until after the power transmitter has received a ping response from the power receiver is also treated as a foreign object. If the FOD evaluation unit determines that a foreign object has been detected, the process continues to block 1215 where the FOD flag is set. From block 1215, the process may return to block 1210 to continue looping in the idle phase until an NFC ping response of the power receiver is detected. Alternatively, in some implementations (such as when the power transmitter or the appliance has a user interface), the process may proceed to block 1175 where the FOD evaluation unit indicates an FOD fault condition.

[0076] If no foreign object is detected in block 1112, the process continues to block 1214. In block 1214, the FOD evaluation unit may clear the FOD flag to indicate that an initial idle phase foreign object detection evaluation was performed and no foreign object was detected. From blocks 1214 and 1215, the process returns to block 1210 to again ping the presence of the power receiver and remain in the idle phase until such time as the power transmitter receives a ping response from the power receiver. If, after any of the idle phase FOD evaluations, the FOD flag was previously set and the foreign object was removed by the user, the process finally includes block 1214 where the FOD flag is cleared.

[0077] At some point, the power transmitter may receive a response to the NFC ping. From block 1212, the process may continue to block 1220 (also representing a change from the idle phase to the configuration phase). In block 1220, the power transmitter may receive configuration information from the power receiver. In block 1222, the power transmitter (or the FOD evaluation unit) may check the FOD flag. If the FOD flag is set to a first value (e.g., "1") indicating that an initial idle phase foreign object detection evaluation has not been performed or a foreign object has not been cleared prior to placement of the power receiver, the process may continue to block 1175. In block 1175, the FOD evaluation unit may indicate an FOD fault condition. This scenario occurs, for example, when the power receiver is placed on the power transmitter before an initial idle phase foreign object detection evaluation has been performed (e.g., before the power transmitter is turned on) or when a foreign object is detected in the idle phase and has not yet been removed to cause the FOD evaluation unit to clear the FOD flag. Because the FOD evaluation unit cannot confirm that a foreign object is not present, the FOD flag and FOD fault state may perform an idle phase foreign object detection evaluation and prevent the power transmitter from continuing operation until the FOD evaluation unit can confirm that a foreign object is not present. As described further herein, the FOD fault processing 1180 may include the user removing the power receiver for a short period of time so that the power transmitter can return to the idle phase (block 1210) and perform another idle phase FOD evaluation at block 1110 in the idle phase. For example, the FOD fault processing 1180 may include the user removing the foreign object or power receiver so that the idle phase FOD evaluation 1110 can verify that all foreign objects and power receivers at the interface are clear.

[0078] If the FOD flag is cleared at block 1222 (or if the idle phase foreign object detection evaluation otherwise indicates that no foreign object is present prior to placement of the power receiver), the process may continue to block 1221. At block 1221, the FOD assessment unit may perform adaptation to recalibrate the offset values. The FOD assessment unit may make new measurements of the detection values ​​and store these as adapted offset values. The adapted offset values ​​thus take into account the presence of the power receiver at the interface.

[0079] In block 1120, the FOD assessment unit may perform another foreign object detection assessment, this time with the power receiver positioned above the power transmitter. This operation in block 1120 may also be used to adapt offset values ​​that can be used in subsequent foreign object detection assessments to verify that a foreign object has not been introduced and to handle impedance changes due to movement of the power receiver at the interface. If a foreign object is detected in block 1122 (the configuration phase), the process may continue to block 1175 to indicate an FOD fault condition and abort the configuration operation phase. Otherwise, if no foreign object is detected in block 1122, the process may continue to block 1230. In some implementations, the FOD assessment unit may adapt offset values ​​(not shown) to account for system changes such as movement of the power receiver. After adaptation, the updated offset values ​​may be used in subsequent foreign object detection assessments, including those associated with subsequent operation phases of the WPT system.

[0080] In block 1230, the power transmitter may determine whether the power receiver is ready for operation. When the power receiver is operated, it is ready to receive wireless power transmissions. Typically, a user interface on the power receiver may control whether the power receiver is ready for operation, such as when a user presses a button to start the power receiver. If the power receiver is not ready for operation, the process may continue to block 1130. In block 1130, the FOD evaluation unit may perform a foreign object detection evaluation, and in block 1132, the FOD evaluation unit may determine whether a result of the foreign object detection evaluation indicates that a foreign object has been detected. If a foreign object is detected, the process continues to block 1175. If a foreign object is not detected, the process continues to block 1231. In block 1231, the FOD evaluation unit may adapt the offset value to account for system changes. For example, if the FOD evaluation unit detects the movement of the power receiver (e.g., based on the number of adjusted detection values ​​exceeding a threshold amount), the FOD evaluation unit may perform an adaptation to adapt the offset value for use in subsequent foreign object detection evaluations. Note that blocks 1230, 1130, 1132, and 1231 may form a loop such that the FOD evaluation unit may periodically or continuously monitor for foreign objects introduced into the power transmitter's operating environment when the power transmitter is in the connected phase and the power receiver is not operated. When the power receiver is ready for operation, the power receiver may communicate a message to the power transmitter to request a transition from the connected phase to the power transmission phase. Once the power receiver is ready for operation (as indicated by the message described above) in block 1230, the power transmitter may transition to the power transmission phase in block 1240.

[0081] In block 1240, the power transmitter may begin power transmission by energizing the primary coil of the power transmitter and generating an electromagnetic field to transfer power to the power receiver. During the power transmission phase, the power transmitter may periodically check that the power receiver is operated (shown in block 1242), and the FOD evaluation unit may periodically perform a foreign object detection evaluation (shown in block 1140). At any time when the power receiver is no longer operated (as determined in block 1242), the process may continue to block 1280. In block 1280, the power transmitter may determine whether the power receiver is still present. If so, the power transmitter may return to the connected phase in block 1230. If the power receiver is removed, the power transmitter may return to the idle phase in block 1210. During the power transmission phase, the FOD evaluation unit may periodically perform a foreign object detection evaluation (shown in block 1140). This allows the WPT system to react to the introduction of foreign objects in the operating environment. If the FOD assessment unit determines that a foreign object is present in block 1142, the process proceeds to block 1241 to adapt the offset value to account for system changes, if any. From block 1241, the process may return to block 1240 to continue wireless power transmission. If a foreign object is detected in block 1142, the process may continue to block 1244. In block 1244, the power transmitter may terminate or limit wireless power transmission. From block 1244, the process may continue to block 1175 to indicate an FOD fault condition.

[0082] At block 1175, the WPT system (such as the FOD evaluation unit, the power transmitter, or the power receiver, among other examples) may indicate an FOD fault condition. For example, the FOD fault condition may be presented via a user interface associated with the power transmitter, the power receiver, or both. In some implementations, the FOD fault condition may include a communication from the power transmitter to the power receiver (or vice versa) to communicate that an FOD fault condition has been indicated. At block 1180, there may be many ways to clear the FOD fault condition, such as those described with reference to FIG. 14 . For example, the user may remove the foreign object. In another example, the user may remove the power receiver to allow the FOD evaluation unit to perform an idle phase foreign object detection evaluation in the idle phase using an initial offset value before returning the power receiver. In some implementations, the user interface may allow for resetting the FOD fault condition by manual override or forcing an adaptation of the offset value to account for metals that are present in the operating environment and that are known to the user to be safe for use in the operating environment. Additionally, the user interface may allow manual initiation of a calibration procedure to measure new calibration values ​​that are stored in non-volatile memory for use the next time the power transmitter is turned on.

[0083] FIG. 13 shows a process 1300 for foreign object detection evaluation. In block 1310, the FOD evaluation unit may evaluate the detection value of each coil pair of detection coils. For example, in block 1312, the FOD evaluation unit may obtain the detection value (such as a differential current or a differential voltage). In block 1314, the FOD evaluation unit may adjust the detection value using an offset value for that coil pair. In an idle phase, the offset value may be an initial offset value based on a calibration value. In other operation phases, the offset value may be an adapted offset value based on a previous foreign object detection evaluation. In block 1316, the FOD evaluation unit may compare the adjusted detection value (or the absolute value of the adjusted detection value) to a detection threshold. In block 1318, if the adjusted detection value is above the detection threshold, the process may continue to block 1322. In block 1322, the FOD evaluation unit may determine that a metal object (possibly a foreign object or a power receiver) has been detected. In block 1322, the FOD evaluation unit may add the coil pair to the number of coil pairs that detected a metal object. The number of coil pairs is reset for each foreign object detection evaluation and represents the number of coils that were affected by the presence of a metal object during a particular iteration of the foreign object detection evaluation. The process may continue to block 1324, where the FOD evaluation unit continues to evaluate the next coil pair in the same manner as described with reference to block 1310. In block 1318, when the adjusted detection value is above the detection threshold, the FOD evaluation unit may determine that the coil pair is not affected by a metal object, and the process continues to block 1324 to evaluate the next coil pair. After evaluating multiple coil pairs in block 1310, the process may continue to block 1330.

[0084] In block 1330, in some implementations, the FOD evaluation unit may determine whether the magnitude of any adjusted detection value exceeds a safety limit. If so, the process may continue to block 1350, where the FOD evaluation unit may generate an FOD result indicating whether a foreign object was detected. Alternatively or additionally, the FOD evaluation unit may cause a user interface to request user feedback on whether the FOD evaluation should continue. The safety limit provides a mechanism to detect a faulty coil pair, a sensor, or a foreign object that may be present near one coil pair, even if multiple coil pairs also register the presence of a power receiver. For example, the safety limit may be higher than the detection threshold in block 1318. If none of the adjusted detection value magnitudes exceed the safety limit, the process may continue to block 1340.

[0085] In block 1340, the FOD evaluation unit may determine whether the number of coil pairs with metal detection (as accumulated in block 1322) exceeds a threshold amount. In some implementations, the threshold amount may depend on the operational phase of the power transmitter. For example, in an idle phase, when the power receiver is not present, the FOD evaluation unit triggers an FOD fault condition even if a single coil pair, or all coil pairs, have metal detection, and the process proceeds to block 1350. In a configuration phase, connection phase, or power transfer phase, the threshold amount may be set such that three or more coil pairs with metal detection may be interpreted as due to movement of the power receiver.

[0086] Returning to block 1340, if the number is below the threshold amount, the process may continue to block 1350. As a reminder, in block 1350, the FOD evaluation unit may generate an FOD result indicating that a foreign object has been detected. As an example, in block 1340, in the configuration phase, connection phase, or power transfer phase, if only one or two coil pairs detect a metal object (and the threshold amount is three coil pairs), the FOD evaluation unit may infer that the coil pair detected a metallic foreign object. Alternatively, in the configuration phase, connection phase, or power transfer phase, if multiple coil pairs (greater than a threshold amount, such as three) detect a change in the adjusted detection value, the FOD evaluation unit may infer that such change is due to movement of the power receiver. In block 1340, if the number of coil pairs with metal detection is above the threshold amount, the process may continue to block 1360. In block 1360, the FOD evaluation unit may perform an adaptation that updates the offset value so that the FOD evaluation unit accounts for movement of the power receiver. The updated offset value may then be used for subsequent foreign object detection evaluations. At block 1370, the FOD evaluation unit may generate an FOD result indicating that no foreign object has been detected.

[0087] 14 illustrates example operations 1400 for FOD fault handling. The example operations 1400 are provided as options, some of which may be omitted in various implementations. In block 1410, the power transmitter may indicate an FOD fault, such as via a user interface associated with the power transmitter. In block 1420, the power transmitter (or FOD evaluation unit) may communicate the FOD fault condition to the power receiver, which may then indicate the FOD fault, such as via a user interface associated with the power receiver.

[0088] In some implementations, user interaction (such as via a user interface associated with the power transmitter or power receiver) may cause the WPT system to disable the FOD fault. When user interaction disables the FOD fault in block 1430, the process may continue to block 1440. Otherwise, the process may continue to another FOD fault handling option, such as block 1470. Based on the user override in block 1440, the FOD evaluation unit may perform an adaptation in which the FOD evaluation unit updates the offset value based on the existing detection value. In block 1450, the FOD evaluation unit may clear the FOD fault condition. In block 1460, the FOD evaluation unit may reset the FOD flag. From there, the power transmitter may return to block 1120 of FIG. 12 (via reference character "B"). In some implementations, the user override may cause the power transmitter to return to block 1221 or block 1230 of FIG. 12 and then proceed to the connection phase.

[0089] In some implementations, the FOD fault condition may be cleared by removing the power receiver from the mating surface. In block 1470, once the power receiver is removed from the mating surface, the WPT system may return to the idle phase. In block 1452, the FOD evaluation unit may clear the FOD fault condition. In block 1462, the FOD evaluation unit may clear or reset the FOD flag. From there, the power transmitter may return to block 1210 of FIG. 12 (via reference character "A") and the idle phase.

[0090] FIG. 15 illustrates a flow chart diagram of an example process 1500 for detecting a foreign object, according to some implementations. The operations of the process 1500 may be performed by an FOD assessment unit described herein. For example, the operations of the process 1500 may be performed by an FOD assessment unit described with reference to FIGS. 2-14. In some implementations, the FOD assessment unit may be included in or part of a transmission controller of a power transmitter. Alternatively, the operations of the process 1500 may be performed by a power transmitter, a power receiver, or other components of a WPT system. For simplicity, the operations of the process 1500 are described as being performed by a device.

[0091] At block 1510, the device may initialize the FOD evaluation unit prior to or as part of the idle phase in response to a user input to turn on the power transmitter. Initializing the FOD evaluation unit may include setting an FOD flag to a first value to indicate that an initial idle phase foreign object detection evaluation has not yet been performed.

[0092] At block 1520, the device may indicate an FOD fault condition if the power transmitter transitions from an idle phase to a different operating phase when the FOD flag is set to a first value.

[0093] FIG. 16 illustrates a block diagram of an exemplary apparatus 1600 for use in a wireless power transfer system. In some implementations, the apparatus 1600 may be a detection apparatus, such as any of the detection apparatuses described herein. In some implementations, the apparatus 1600 may be an FOD evaluation unit, such as any of the FOD evaluation units. The apparatus 1600 may include a processor 1602 (possibly including multiple processors, multiple cores, multiple nodes, or multi-threading implementations, etc.). The apparatus 1600 may also include a memory 1606. The memory 1606 may be a system memory or any one or more of the possible implementations of the computer-readable media described herein. The apparatus 1600 may also include a bus 1611 (PCI, ISA, PCI-Express, HyperTransport®, InfiniBand®, NuBus®, AHB, AXI, etc.).

[0094] The apparatus 1600 may include one or more controllers 1662 configured to manage the excitation of multiple detection coils (such as a coil array 1664). In some implementations, the controller 1662 may be distributed within the processor 1602, the memory 1606, and the bus 1611. The controller 1662 may perform some or all of the operations described herein. For example, the controller 1662 may implement features of a driver controller described herein.

[0095] The memory 1606 may include computer instructions executable by the processor 1602 to implement the functionality of the implementations described with reference to Figures 1-15. Any one of these functions may be implemented partially (or fully) in hardware or in the processor 1602. For example, the functionality may be implemented in an application specific integrated circuit, logic implemented in the processor 1602, a co-processor on a peripheral or card, etc. Furthermore, an implementation may include fewer components or additional components not shown in Figure 16. The processor 1602, the memory 1606, and the controller 1662 may be coupled to a bus 1611. Although shown as being coupled to the bus 1611, the memory 1606 may also be coupled to the processor 1602.

[0096] The diagrams, operations, and components described herein are examples intended to aid in understanding of example implementations and should not be used to limit potential implementations or to limit the scope of the claims. Some implementations may perform additional operations, fewer operations, operations in parallel or in a different order, as well as some operations in a different manner.

[0097] The foregoing disclosure provides illustrations and explanations, but is not intended to be exhaustive or to limit the aspects to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects. Although aspects of the present disclosure have been described with reference to various examples, any combination of aspects from any of the examples is also within the scope of the present disclosure. The examples of the present disclosure are provided for educational purposes. Alternatively, or in addition to other examples disclosed herein, the examples include any combination of the following implementation options (listed as clauses for clarity): Terms

[0098] Clause 1. A method for foreign object detection (FOD) in a wireless power transfer (WPT) system, comprising: initializing an FOD evaluation unit prior to or as part of an idle phase in response to a user input to turn on a power transmitter, the initializing the FOD evaluation unit including setting an FOD flag to a first value to indicate that an initial idle phase foreign object detection evaluation has not yet been performed; and indicating an FOD fault condition if the power transmitter transitions from the idle phase to a different operating phase when the FOD flag is set to the first value.

[0099] Clause 2. The method of clause 1, further comprising the steps of performing an initial idle phase foreign object detection evaluation when the power transmitter is in an idle phase, setting an FOD flag to a second value when a result of the initial idle phase foreign object detection evaluation indicates that no foreign object has been detected, and indicating an FOD fault condition when a result of the initial idle phase foreign object detection evaluation indicates that a foreign object has been detected.

[0100] Clause 3. The method of clause 1, further comprising the step of determining that the power transmitter has transitioned from the idle phase to a different operational phase based on the presence of the power receiver before an initial idle phase foreign object detection evaluation is performed, the determination being based at least in part on an FOD flag being set to a first value when the power transmitter transitions from the idle phase to the different operational phase.

[0101] Clause 4. The method of clause 3, further comprising indicating an FOD fault condition to prompt removal of the power receiver from a mating surface associated with the power transmitter.

[0102] Clause 5. The method of any one of clauses 1 to 4, wherein the initial idle phase foreign object detection assessment is unique compared to the pre-power foreign object detection assessment and the on-power foreign object detection assessment associated with different respective operational phases.

[0103] Clause 6. The method of any one of clauses 1 to 5, wherein the step of performing an initial idle phase foreign object detection assessment includes the steps of obtaining a plurality of detection values, each detection value indicative of a difference between detection coils of a respective pair of detection coils; adjusting one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of a plurality of offset values, the plurality of offset values ​​being initial offset values ​​based on calibration of the FOD assessment unit; comparing each of the plurality of detection values ​​to a detection threshold; and determining that a foreign object is detected when at least one of the plurality of detection values ​​exceeds the detection threshold.

[0104] Clause 7. The method of clause 6, wherein the step of initializing the FOD evaluation unit further includes the steps of obtaining a calibration value from a non-volatile memory and determining an initial offset value based on the calibration value.

[0105] Clause 8. The method of clause 7, further comprising determining a calibration value as part of manufacturing, installation, or maintenance of the power transmitter, and storing the calibration value in non-volatile memory.

[0106] Clause 9. The method of any one of clauses 1-8, further comprising the steps of: setting an FOD flag to a second value when results of an initial idle phase foreign object detection evaluation indicate that no foreign object was detected; determining that the power transmitter has transitioned from the idle phase to the configuration phase in response to a communications handshake between the power transmitter and the power receiver; and adapting a plurality of offset values ​​for use in the pre-power foreign object detection evaluation.

[0107] Clause 10. The method of clause 9, wherein the step of adapting the FOD assessment unit includes the steps of obtaining a plurality of detection values, each detection value indicating a difference between a detection coil of a respective pair of detection coils, updating a plurality of offset values ​​based on the plurality of detection values, and storing the plurality of offset values ​​in a volatile memory of the power transmitter for use in subsequent foreign object detection assessments.

[0108] Clause 11. A method according to any one of clauses 1 to 10, further comprising the step of performing multiple foreign object detection assessments during two or more operational phases of the power transmitter, the multiple FOD assessments including at least a pre-power foreign object detection assessment performed during a configuration phase or a connection phase.

[0109] Clause 12. The method of clause 11, wherein the pre-power supply foreign object detection evaluation includes the steps of obtaining updated values ​​of the plurality of detection values, adjusting one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of the plurality of offset values, comparing each of the plurality of detection values ​​to a detection threshold, determining how many of the plurality of detection values ​​exceed the detection threshold, and indicating, when the number is less than the threshold amount, that the result of the pre-power supply foreign object detection evaluation is that a foreign object has been detected.

[0110] Clause 13. The method of clause 12, wherein the pre-power foreign object detection evaluation further includes a step of indicating that a result of the pre-power foreign object detection evaluation is that a foreign object has been detected when the magnitude of any one of the multiple detection values ​​exceeds a limit.

[0111] Clause 14. The method of clause 12, wherein the pre-power foreign object detection evaluation further includes a step of indicating that a result of the pre-power foreign object detection evaluation is that no foreign object is detected when the number is zero or when the number is equal to or greater than a threshold amount.

[0112] Clause 15. The method of any one of clauses 12-14, further comprising the steps of determining that the power receiver has moved when the number is equal to or greater than a threshold amount, and adapting the offset values ​​to generate updated offset values ​​based on the detection values ​​in response to determining that the power receiver has moved, such that the updated offset values ​​are usable in a subsequent foreign object detection evaluation.

[0113] Clause 16. The method of clause 15, further comprising storing the updated offset values ​​in a volatile memory such that the updated offset values ​​are maintained while the power transmitter is turned on and the updated offset values ​​are discarded while the power transmitter is turned off.

[0114] Clause 17. A method according to any one of clauses 1 to 16, wherein the step of indicating an FOD fault condition includes at least one of the following steps: causing an indication of the FOD fault condition to be presented on a user interface, the user interface being on the power transmitter, on a home appliance housing the power transmitter, or on a power receiver disposed on an interface of the power transmitter; or communicating the indication of the FOD fault condition via a communications interface associated with the power transmitter.

[0115] Clause 18. A method according to any one of clauses 1 to 17, further comprising the steps of receiving an indication of a user interaction to override the FOD fault condition, setting the FOD flag to a second value, and clearing the FOD fault condition.

[0116] Clause 19. The method of clause 18, further comprising adapting a plurality of offset values ​​for subsequent foreign object detection evaluation in response to said step of receiving an indication to override an FOD fault condition.

[0117] Clause 20. The method of clause 19, further comprising the steps of transitioning to an idle phase when the power receiver is removed from the mating surface, and performing an initial idle phase foreign object detection evaluation when the power transmitter is in the idle phase.

[0118] Clause 21. A system for foreign object detection (FOD), comprising: a power transmitter configured to initialize an FOD evaluation unit prior to or as part of an idle phase in response to a user input to turn on the power transmitter, wherein initializing the FOD evaluation unit includes setting an FOD flag to a first value to indicate that an initial idle phase foreign object detection evaluation has not yet been performed; and an FOD evaluation unit configured to indicate an FOD fault condition if the power transmitter transitions from the idle phase to a different operating phase when the FOD flag is set to the first value.

[0119] Clause 22. The system described in Clause 21, wherein the FOD evaluation unit is further configured to perform an initial idle phase foreign object detection evaluation when the power transmitter is in an idle phase, set the FOD flag to a second value when a result of the initial idle phase foreign object detection evaluation indicates that no foreign object has been detected, and indicate an FOD fault condition when a result of the initial idle phase foreign object detection evaluation indicates that a foreign object has been detected.

[0120] Clause 23. The system described in Clause 21, wherein the FOD assessment unit is configured to determine that the power transmitter has transitioned from the idle phase to a different operational phase based on the presence of the power receiver before an initial idle phase foreign object detection assessment is performed, the determination being based at least in part on an FOD flag being set to a first value when the power transmitter transitions from the idle phase to a different operational phase.

[0121] Clause 24. The system of clause 23, wherein the FOD assessment unit is configured to indicate an FOD fault condition to prompt removal of the power receiver from a mating surface associated with the power transmitter.

[0122] Clause 25. A system as described in any one of clauses 21 to 24, wherein the initial idle phase foreign object detection evaluation is unique compared to the pre-power foreign object detection evaluation and the on-power foreign object detection evaluation associated with different respective operational phases.

[0123] Clause 26. A system as described in any one of clauses 21 to 25, wherein during the idle phase, the FOD evaluation unit is configured to obtain a plurality of detection values, each detection value indicating a difference between detection coils of a respective pair of detection coils, adjust one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of a plurality of offset values, the plurality of offset values ​​being initial offset values ​​based on calibration of the FOD evaluation unit, compare each of the plurality of detection values ​​to a detection threshold, and determine that a foreign object is detected when at least one of the plurality of detection values ​​exceeds the detection threshold.

[0124] Clause 27. The system of clause 26, further comprising a non-volatile memory configured to store a calibration value, the FOD assessment unit configured to determine an initial offset value based on the calibration value.

[0125] Clause 28. A system as described in any one of clauses 21 to 27, wherein the FOD evaluation unit is configured to set the FOD flag to a second value when results of the initial idle phase foreign object detection evaluation indicate that no foreign object was detected, determine that the power transmitter has transitioned from the idle phase to the configuration phase in response to a communications handshake between the power transmitter and the power receiver, and adapt a plurality of offset values ​​for use in the pre-power supply foreign object detection evaluation.

[0126] Clause 29. The system described in Clause 28, wherein the FOD evaluation unit is further configured to obtain a plurality of detection values, each detection value indicating a difference between detection coils of a respective pair of detection coils, update a plurality of offset values ​​based on the plurality of detection values, and store the plurality of offset values ​​in a volatile memory of the power transmitter for use in subsequent foreign object detection evaluations.

[0127] Clause 30. A system described in any one of clauses 21 to 29, wherein the FOD assessment unit is configured to perform multiple foreign object detection assessments during two or more operational phases of the power transmitter, the multiple FOD assessments including at least a pre-power supply foreign object detection assessment performed during the configuration phase or the connection phase.

[0128] Clause 31. The system described in Clause 30, wherein the FOD evaluation unit configured to perform a pre-power foreign object detection evaluation includes an FOD evaluation unit configured to obtain updated values ​​of the plurality of detection values, adjust one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of the plurality of offset values, compare each of the plurality of detection values ​​to a detection threshold, determine a number of the plurality of detection values ​​that exceed the detection threshold, and when the number is less than the threshold amount, indicate a result of the pre-power foreign object detection evaluation that a foreign object has been detected.

[0129] Clause 32. The system described in Clause 31, wherein the FOD evaluation unit configured to perform a pre-power foreign object detection evaluation includes an FOD evaluation unit configured to indicate that a result of the pre-power foreign object detection evaluation is that a foreign object has been detected when the magnitude of any one of the multiple detection values ​​exceeds a limit.

[0130] Clause 33. The system described in clause 31, wherein the FOD assessment unit configured to perform a pre-power foreign object detection assessment includes an FOD assessment unit configured to indicate that a result of the pre-power foreign object detection assessment is that no foreign object is detected when the number is zero or when the number is greater than or equal to a threshold amount.

[0131] Clause 34. The system of any one of clauses 31 to 33, wherein the FOD assessment unit is further configured to determine that the power receiver has moved when the number is greater than or equal to a threshold amount, and to adapt the plurality of offset values ​​to generate updated plurality of offset values ​​based on the plurality of detection values ​​in response to determining that the power receiver has moved, such that the updated plurality of offset values ​​are usable in a subsequent foreign object detection assessment.

[0132] Clause 35. The system described in Clause 34, wherein the FOD evaluation unit is further configured to store the updated offset values ​​in a volatile memory such that the updated offset values ​​are maintained while the power transmitter is turned on and the updated offset values ​​are discarded while the power transmitter is turned off.

[0133] Clause 36. A system as described in any one of clauses 21 to 35, comprising an FOD evaluation unit configured to perform at least one of the following operations: causing an indication of the FOD fault condition to be presented on a user interface, the user interface being on the power transmitter, a home appliance housing the power transmitter, or a power receiver disposed on a mating surface of the power transmitter; or communicating the indication of the FOD fault condition via a communications interface associated with the power transmitter.

[0134] Clause 37. A system as described in any one of clauses 21 to 36, wherein the FOD evaluation unit is further configured to receive an indication of a user interaction to override the FOD fault condition, set the FOD flag to a second value, and clear the FOD fault condition.

[0135] Clause 38. The system described in Clause 37, wherein the FOD evaluation unit is further configured to adapt a plurality of offset values ​​for subsequent foreign object detection evaluation in response to the step of receiving an indication to disable an FOD fault condition.

[0136] Clause 39. The system described in clause 38, wherein the power transmitter is configured to transition to an idle phase when the power receiver is removed from the mating surface, and the FOD evaluation unit is configured to perform an initial idle phase foreign object detection evaluation when the power transmitter is in the idle phase.

[0137] Another innovative aspect of the subject matter described in this disclosure may be embodied as an apparatus. The apparatus may include a modem and at least one processor communicatively coupled to the at least one modem. The processor, together with the modem, may be configured to perform any one of the methods described above or features described herein.

[0138] Another innovative aspect of the subject matter described in this disclosure can be embodied as a computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform any one of the methods described above or features described herein.

[0139] Another innovative aspect of the subject matter described in this disclosure can be embodied as a system having means for performing any one of the methods or features described herein.

[0140] As used herein, phrases referring to "at least one of" or "one or more of" a list of items refer to any combination of those items, including singular ones. For example, "at least one of a, b, or c" is intended to cover the possibilities of a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and combinations of a, b, and c.

[0141] The various example components, logic, logic blocks, modules, circuits, operations, and algorithmic processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware, or software, including the structures disclosed herein and their structural equivalents. Interoperability of hardware, firmware, and software has been described generally in terms of functionality and illustrated in the various example components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented in hardware, firmware, or software depends on the particular application and design constraints imposed on the overall system.

[0142] The hardware and data processing devices used to implement the various example components, logic, logic blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed using general purpose single-chip or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices (PLDs), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration. In some implementations, certain processes, operations, and methods may be performed by circuitry specific to a given function.

[0143] As mentioned above, some aspects of the subject matter described herein can be implemented as software. For example, various functions of components disclosed herein, or various blocks or steps of methods, operations, processes, or algorithms disclosed herein, can be implemented as one or more modules of one or more computer programs. Such computer programs can include non-transitory processor-executable instructions or computer-executable instructions encoded on one or more processor-readable or computer-readable storage media for execution by, or for controlling the operation of, a data processing device, including components of the device disclosed herein. By way of example and not limitation, such storage media can include RAM, ROM, EEPROM, CD-ROM, or other optical disk storage, magnetic disk storage, or other magnetic storage devices, or any other medium that can be used to store program code in the form of instructions or data structures. Combinations of the above should also be included within the scope of storage media.

[0144] Various modifications of the implementations described in this disclosure may be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other implementations without departing from the scope of the present disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but should be accorded the widest scope consistent with the present disclosure, the principles, and novel features disclosed herein.

[0145] In addition, various features described herein in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any subcombination. Thus, although features may be described above as acting in a particular combination and initially claimed as such, one or more features from the claimed combination can, in some cases, be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination.

[0146] Similarly, although operations are depicted in the figures in a particular order, this should not be understood as requiring such operations to be performed in the particular order depicted, or in sequential order, or that all depicted operations be performed, to achieve desired results. Additionally, the figures may generally depict one or more exemplary processes in the form of a flow chart or diagram. However, other operations not depicted may be incorporated into the schematic depicted exemplary process. For example, one or more additional operations may be performed before, after, simultaneously with, or between any of the depicted operations. In some circumstances, multitasking and parallel processing may be advantageous. Also, it should be understood that the separation of various system components in the above-described implementations does not require such separation in all implementations, and that the described program components and systems may generally be integrated together in a single software product or packaged in multiple software products.

Claims

1. 1. A method for foreign object detection (FOD) in a wireless power transfer (WPT) system, comprising: initializing an FOD evaluation unit prior to or as part of an idle phase in response to a user input to turn on a power transmitter, said initializing the FOD evaluation unit including setting an FOD flag to a first value to indicate that an initial idle phase foreign object detection evaluation has not yet been performed; indicating a FOD fault condition if the power transmitter transitions from the idle phase to a different operational phase when the FOD flag is set to the first value; The method includes:

2. performing the initial idle phase foreign object detection assessment when the power transmitter is in the idle phase; setting the FOD flag to a second value when a result of the initial idle phase foreign object detection evaluation indicates that no foreign object was detected; indicating the FOD fault condition when the result of the initial idle phase foreign object detection evaluation indicates that a foreign object has been detected; The method of claim 1 further comprising:

3. 2. The method of claim 1, further comprising: determining that the power transmitter has transitioned from the idle phase to the different operational phase based on a presence of a power receiver before the initial idle phase foreign object detection evaluation is performed, the determination being based at least in part on the FOD flag being set to the first value when the power transmitter transitions from the idle phase to the different operational phase.

4. The method of claim 3 , further comprising indicating the FOD fault condition to prompt removal of the power receiver from a mating surface associated with the power transmitter.

5. The method of any one of claims 1 to 4, wherein the initial idle phase foreign object detection assessment is unique compared to pre-power and on-power foreign object detection assessments associated with different respective operational phases.

6. The step of performing an initial idle phase foreign object detection assessment comprises: obtaining a plurality of detection values, each detection value indicative of a difference between detection coils of a respective pair of detection coils; adjusting one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of a plurality of offset values, the plurality of offset values ​​being initial offset values ​​based on a calibration of the FOD assessment unit; comparing each of the plurality of detection values ​​to a detection threshold; determining that a foreign object is detected when at least one of the plurality of detection values ​​exceeds the detection threshold; The method according to any one of claims 1 to 5, comprising:

7. The step of initializing the FOD evaluation unit includes: retrieving a calibration value from a non-volatile memory; determining the initial offset value based on the calibration value; The method of claim 6 further comprising:

8. determining said calibration value as part of manufacturing, installation, or maintenance of a power transmitter; storing said calibration values ​​in a non-volatile memory; The method of claim 7 further comprising:

9. setting the FOD flag to a second value when a result of the initial idle phase foreign object detection evaluation indicates that no foreign object was detected; determining that the power transmitter has transitioned from the idle phase to a configuration phase in response to a communication handshake between the power transmitter and the power receiver; adapting a plurality of offset values ​​for use in a pre-power foreign object detection evaluation; The method of any one of claims 1 to 8, further comprising:

10. The step of adapting the FOD assessment unit comprises: obtaining a plurality of detection values, each detection value indicative of a difference between detection coils of a respective pair of detection coils; updating the offset values ​​based on the detected values; storing the plurality of offset values ​​in a volatile memory of the power transmitter for use in subsequent foreign object detection evaluations; 10. The method of claim 9, comprising:

11. The method of any one of claims 1 to 10, further comprising the step of performing a plurality of foreign object detection evaluations during two or more operational phases of the power transmitter, the plurality of FOD evaluations including at least a pre-power foreign object detection evaluation performed during a configuration phase or a connection phase.

12. The foreign object detection evaluation before power supply is obtaining updated values ​​of the plurality of detection values; adjusting one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of the plurality of offset values; comparing each of the plurality of detection values ​​to a detection threshold; determining how many of the plurality of detection values ​​exceed the detection threshold; indicating a result of the pre-power foreign object detection evaluation that a foreign object has been detected when the number is less than a threshold amount; The method of claim 11 , comprising:

13. The foreign object detection evaluation before power supply is indicating that a foreign object has been detected when a magnitude of any one of the plurality of detection values ​​exceeds a limit; The method of claim 12 further comprising:

14. The foreign object detection evaluation before power supply is indicating that the result of the pre-power foreign object detection evaluation is no foreign object detected when the number is zero or when the number is equal to or greater than the threshold amount. The method of claim 12 further comprising:

15. determining that the power receiver has moved when the number is greater than or equal to the threshold amount; adapting the offset values ​​to generate updated offset values ​​based on the detection values ​​in response to determining that the power receiver has moved, such that updated offset values ​​are usable in a subsequent foreign object detection evaluation; The method of any one of claims 12 to 14, further comprising:

16. 16. The method of claim 15, further comprising storing the updated offset values ​​in a volatile memory such that the updated offset values ​​are maintained while the power transmitter is turned on and the updated offset values ​​are discarded while the power transmitter is turned off.

17. The step of indicating a FOD fault condition comprises: causing a user interface to present an indication of the FOD fault condition, the user interface being on the power transmitter, a home appliance housing the power transmitter, or a power receiver disposed on an interface of the power transmitter; or communicating an indication of the FOD fault condition via a communications interface associated with the power transmitter; The method according to any one of claims 1 to 16, comprising at least one of the following:

18. receiving an indication of a user interaction to override the FOD fault condition; setting the FOD flag to the second value; clearing the FOD fault condition; The method of any one of claims 1 to 17, further comprising:

19. 20. The method of claim 18, further comprising adapting the plurality of offset values ​​for subsequent foreign object detection evaluation in response to receiving the indication to override the FOD fault condition.

20. transitioning to the idle phase when the power receiver is removed from the interface; performing the initial idle phase foreign object detection assessment when the power transmitter is in the idle phase; 20. The method of claim 19, further comprising:

21. 1. A system for foreign object detection (FOD), comprising: a power transmitter configured to initialize a FOD evaluation unit prior to or as part of an idle phase in response to a user input to turn on the power transmitter, the initializing the FOD evaluation unit comprising setting an FOD flag to a first value to indicate that an initial idle phase foreign object detection evaluation has not yet been performed; the FOD evaluation unit configured to indicate a FOD fault condition if the power transmitter transitions from the idle phase to a different operational phase when the FOD flag is set to the first value; A system comprising:

22. The FOD evaluation unit includes: performing the initial idle phase foreign object detection assessment while the power transmitter is in the idle phase; setting the FOD flag to a second value when the result of the initial idle phase foreign object detection evaluation indicates that no foreign object was detected; indicating the FOD fault condition when the result of the initial idle phase foreign object detection evaluation indicates that a foreign object has been detected.

22. The system of claim 21, further configured to:

23. 22. The system of claim 21, wherein the FOD assessment unit is configured to determine that the power transmitter has transitioned from the idle phase to the different operational phase based on the presence of a power receiver before the initial idle phase foreign object detection assessment is performed, the determination being based at least in part on the FOD flag being set to the first value when the power transmitter transitions from the idle phase to the different operational phase.

24. 24. The system of claim 23, wherein the FOD assessment unit is configured to indicate the FOD fault condition to prompt removal of the power receiver from a mating surface associated with the power transmitter.

25. A system according to any one of claims 21 to 24, wherein the initial idle phase foreign object detection assessment is unique compared to pre-power and on-power foreign object detection assessments associated with different respective operational phases.

26. During the idle phase, the FOD assessment unit: obtaining a plurality of detection values, each detection value indicative of a difference between detection coils of a respective pair of detection coils; adjusting one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of a plurality of offset values, the plurality of offset values ​​being initial offset values ​​based on a calibration of the FOD assessment unit; comparing each of the plurality of detection values ​​to a detection threshold; determining that a foreign object has been detected when at least one of the plurality of detection values ​​exceeds the detection threshold; The system according to any one of claims 21 to 25, configured as follows:

27. 27. The system of claim 26, further comprising a non-volatile memory configured to store a calibration value, the FOD assessment unit configured to determine the initial offset value based on the calibration value.

28. The FOD evaluation unit includes: setting the FOD flag to a second value when the result of the initial idle phase foreign object detection evaluation indicates that no foreign object was detected; determining that the power transmitter has transitioned from the idle phase to a configuration phase in response to a communication handshake between the power transmitter and a power receiver; Adapting a plurality of offset values ​​for use in a pre-power foreign object detection evaluation; The system according to any one of claims 21 to 27, configured as follows:

29. The FOD evaluation unit includes: obtaining a plurality of detection values, each detection value indicative of a difference between detection coils of a respective pair of detection coils; updating the offset values ​​based on the detection values; storing the plurality of offset values ​​in a volatile memory of the power transmitter for use in subsequent foreign object detection evaluations.

30. The system of claim 28, further configured to:

30. A system as described in any one of claims 21 to 29, wherein the FOD assessment unit is configured to perform multiple foreign object detection assessments during two or more operational phases of the power transmitter, the multiple FOD assessments including at least a pre-power foreign object detection assessment performed during a configuration phase or a connection phase.

31. The FOD assessment unit configured to perform the pre-power foreign object detection assessment comprises: obtaining updated values ​​of the plurality of detection values; adjusting one or more of the plurality of detection values ​​by adding or subtracting a corresponding one of the plurality of offset values; comparing each of the plurality of detection values ​​to a detection threshold; determining how many of the plurality of detection values ​​exceed the detection threshold; a result of the pre-power foreign object detection evaluation indicating that a foreign object has been detected when the number is less than a threshold amount; 31. The system of claim 30, comprising the FOD assessment unit configured to:

32. The FOD assessment unit configured to perform the pre-power foreign object detection assessment comprises: When the magnitude of any one of the plurality of detection values ​​exceeds a limit, the result of the pre-power supply foreign object detection evaluation indicates that a foreign object has been detected.

32. The system of claim 31 , comprising the FOD assessment unit configured to:

33. The FOD assessment unit configured to perform the pre-power foreign object detection assessment comprises: When the number is zero or when the number is equal to or greater than the threshold amount, the result of the pre-power foreign object detection evaluation indicates that no foreign object is detected.

32. The system of claim 31 , comprising the FOD assessment unit configured to:

34. The FOD evaluation unit includes: determining that the power receiver has moved when the number is equal to or greater than the threshold amount; adapting the plurality of offset values ​​to generate the updated plurality of offset values ​​based on the plurality of detection values ​​in response to determining that the power receiver has moved, such that the updated plurality of offset values ​​are usable in a subsequent foreign object detection evaluation. The system of any one of claims 31 to 33, further configured to:

35. The FOD evaluation unit includes:

35. The system of claim 34, further configured to store the updated offset values ​​in a volatile memory such that the updated offset values ​​are maintained while the power transmitter is turned on and the updated offset values ​​are discarded while the power transmitter is turned off.

36. The FOD assessment unit configured to indicate the FOD fault condition comprises: causing an indication of the FOD fault condition to be presented on a user interface, the user interface being on the power transmitter, on a home appliance housing the power transmitter, or on a power receiver disposed on an interface of the power transmitter; or communicating an indication of the FOD fault condition via a communications interface associated with the power transmitter; 36. The system of claim 21, comprising the FOD assessment unit configured to perform at least one of the following actions:

37. The FOD evaluation unit includes: receiving an indication of a user interaction to override the FOD fault condition; setting the FOD flag to the second value; clearing the FOD fault condition; The system of any one of claims 21 to 36, further configured to:

38. 38. The system of claim 37, wherein the FOD evaluation unit is further configured to adapt the plurality of offset values ​​for subsequent foreign object detection evaluation in response to receiving the indication to override the FOD fault condition.

39. the power transmitter is configured to transition to the idle phase when the power receiver is removed from the interface; 40. The system of claim 38, wherein the FOD assessment unit is configured to perform the initial idle phase foreign object detection assessment when the power transmitter is in the idle phase.

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