Techniques for detecting presence of a foreign object on a surface of a wireless charging transmitter by measuring a quality factor during a charging session

Abstract

An inductive charging system and method detects a wireless device on a charging surface of a wireless charging pad including a transmitter coil, determines a first quality factor of the transmitter coil and initiates a charging session, and periodically performs a foreign object detection (FOD) technique during the charging session, the FOD technique comprising: adjusting the operating point of the transmitter coil according to a specific sequence of operating points that reverse-biases a rectifier diode between a receiver coil and a receiver load of the wireless device to disconnect the receiver load from the receiver coil, and then determining a second quality factor of the transmitter coil; and detecting the presence of a foreign object on the charging surface based on a comparison between the first quality factor and the second quality factor.

Description

Technical Field

[0001] This disclosure generally relates to inductive charging, and more specifically, to a technique for detecting the presence of foreign objects on the surface of a wireless charging transmitter by measuring a quality factor during a charging session, particularly suitable for automotive applications. Background Technology

[0002] Inductive charging is a form of wireless power transfer that uses electromagnetic induction to power mobile or wireless devices, such as mobile phones. This is typically performed by placing the wireless device on a wireless charging pad that defines a charging surface and includes multiple transmitter coils configured to inductively couple with and transfer wireless power to the receiver coil of the wireless device. A potential risk of inductive or wireless charging (e.g., using inductive coupling frequencies between 80 kHz and 210 kHz) is that objects on or near the charging surface may be heated to potentially hazardous temperatures. Such "foreign objects" can be placed on or near the charging surface at any time, such as (i) before, (ii) while, or (iii) after the wireless device has been placed on the charging surface and the charging session has begun. Conventional inductive charging systems suffer from unreliable detection of foreign objects, especially small or ferrous objects, during a charging session. Therefore, while these conventional inductive charging systems do work for their intended purpose, there are opportunities for improvement in the related technology.

[0003] The background description provided herein is for the purpose of presenting the general context of this disclosure. The work of the inventors currently mentioned to the extent described in this background section, and aspects described at the time of filing as prior art, are neither expressly nor implicitly acknowledged as prior art to this disclosure. Summary of the Invention

[0004] According to one aspect of this disclosure, an inductive charging system is presented. In one exemplary embodiment, the inductive charging system includes: a transmitter coil configured to inductively transmit power to a receiver coil of a wireless device when activated, wherein the wireless device includes a rectifier diode located between the receiver coil and a receiver load; and a controller configured to: detect the wireless device on a charging surface proximate to the transmitter coil; determine a first quality factor of the transmitter coil and initiate a charging session in response to detecting the wireless device, during which the transmitter coil is activated to inductively couple with the receiver coil and inductively transmit electrical energy to the receiver coil; periodically perform a foreign object detection (FOD) technique during the charging session, the FOD technique including: adjusting the operating point of the transmitter coil according to a specific sequence of operating points, the specific sequence of operating points causing the rectifier diode to be reverse biased to disconnect the receiver load from the receiver coil; determining a second quality factor of the transmitter coil in response to adjusting the operating point of the transmitter coil according to the specific sequence; and detecting the presence of a foreign object on the charging surface based on a comparison between the first quality factor and the second quality factor.

[0005] In some embodiments, the controller is configured to detect the presence of a foreign object when the difference between a first quality factor and a second quality factor exceeds a threshold. In some embodiments, the controller is configured to initiate a specific sequence of transmitter coil operating points by increasing the transmitter coil's operating point from a normal level to a first level within a first time period, thereby causing the wireless device to send back a control error packet (CEP). In some embodiments, the controller is configured to subsequently decrease the transmitter coil's operating point from the first level to a second level for a second time period.

[0006] In some implementations, the duration of the second time period and the first level are determined such that the CEP is determined to prevent the wireless device from indicating that the power transfer contact has been disconnected. In some implementations, the controller is configured to subsequently increase the operating point of the transmitter coil from the second level to the first level for a third time period, and to determine a second quality factor. In some implementations, the controller is configured to subsequently decrease the operating point of the transmitter coil back to a normal level to complete a specific sequence of operating points of the transmitter coil. In some implementations, the controller is further configured to terminate the charging session in response to the detection of a foreign object.

[0007] According to another aspect of this disclosure, an inductive charging method is presented. In one exemplary embodiment, the inductive charging method includes: providing a wireless charging pad including a transmitter coil configured to inductively transmit power to a receiver coil of a wireless device when activated, wherein the wireless device includes a rectifier diode located between the receiver coil and a receiver load; detecting the wireless device on a charging surface proximate to the transmitter coil by a controller of the wireless charging pad; and, in response to detecting the wireless device, determining a first quality factor of the transmitter coil and initiating a charging session during which the transmitter coil is activated to inductively couple with and inductively transmit electrical energy to the receiver coil; and, during the charging session, periodically performing a FOD (Foreign Object Dependence) technique by the controller, the FOD technique including: adjusting the operating point of the transmitter coil according to a specific sequence of operating points, the specific sequence of operating points causing the rectifier diode to be reverse biased to disconnect the receiver load from the receiver coil; determining a second quality factor of the transmitter coil in response to adjusting the operating point of the transmitter coil according to the specific sequence; and detecting the presence of a foreign object on the charging surface based on a comparison between the first quality factor and the second quality factor.

[0008] In some implementations, the presence of a foreign object is detected when the difference between a first quality factor and a second quality factor exceeds a threshold. In some implementations, the FOD technique includes initiating a specific sequence of transmitter coil operating points by increasing the operating point of the transmitter coil from a normal level to a first level within a first time period, causing the wireless device to transmit back a CEP. In some implementations, the FOD technique includes subsequently decreasing the operating point of the transmitter coil from the first level to a second level for a second time period.

[0009] In some implementations, the duration of the second time period and the first level are determined such that the CEP is determined to cause the wireless device not to indicate that the power transfer contact has been disconnected. In some implementations, the FOD technique includes: subsequently increasing the operating point of the transmitter coil from the second level to the first level for a third time period, and determining a second quality factor. In some implementations, the FOD technique includes: subsequently lowering the operating point of the transmitter coil back to a normal level to complete a specific sequence of operating points of the transmitter coil. In some implementations, the method further includes: terminating the charging session by a controller in response to the detection of a foreign object.

[0010] According to another aspect of this disclosure, an inductive charging system is presented. In one exemplary embodiment, the inductive charging system includes: a transmitter coil arrangement for inductively transmitting power to a receiver coil of a wireless device when activated, wherein the wireless device includes a rectifier diode located between the receiver coil and a receiver load; and a controller arrangement for: detecting the wireless device on a charging surface proximate to the transmitter coil; determining a first quality factor of the transmitter coil and initiating a charging session in response to detecting the wireless device, during which the transmitter coil is activated to inductively couple with the receiver coil and inductively transmit electrical energy to the receiver coil; and periodically performing a FOD technique during the charging session, the FOD technique including: adjusting the operating point of the transmitter coil according to a specific sequence of operating points, the specific sequence of operating points causing the rectifier diode to be reverse biased to disconnect the receiver load from the receiver coil; determining a second quality factor of the transmitter coil in response to adjusting the operating point of the transmitter coil according to the specific sequence; and detecting the presence of a foreign object on the charging surface based on a comparison between the first quality factor and the second quality factor.

[0011] In some embodiments, the controller device detects the presence of a foreign object when the difference between a first quality factor and a second quality factor exceeds a threshold. In some embodiments, the controller device increases the operating point of the transmitter coil from a normal level to a first level for a first time period, causing the wireless device to send back a CEP (Content Transfer Error). It then decreases the operating point of the transmitter coil from the first level to a second level for a second time period, wherein the duration of the second time period and the first level are determined such that the CEP is determined so that the wireless device does not indicate that the power transfer contact has been broken. Subsequently, the operating point of the transmitter coil is increased from the second level to the first level for a third time period and a second quality factor is determined. Finally, the operating point of the transmitter coil is decreased back to a normal level to complete a specific sequence of transmitter coil operating points. In some embodiments, the controller device terminates the charging session in response to the detection of a foreign object.

[0012] Further applicability of this disclosure will become apparent from the specific embodiments provided below. It should be understood that the specific embodiments and examples are intended for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0013] This disclosure will be more fully understood through detailed description and the accompanying drawings, in which:

[0014] Figures 1A to 1BThis is a top view of an example wireless charging pad and an example wireless device according to some embodiments of the present disclosure, the example wireless charging pad including a plurality of transmitter coils arranged in a linearly overlapping arrangement, and the example wireless device including a receiver coil.

[0015] Figures 2A to 2C Example circuit diagrams illustrating the interaction between a wireless charging pad and a wireless device according to some embodiments of this disclosure, as well as diagrams showing specific sequences of transmitter operating points and their effects on receiver voltage levels; and

[0016] Figure 3 This is a flowchart of an example inductive charging method according to some embodiments of the present disclosure. Detailed Implementation

[0017] As discussed earlier, conventional inductive charging systems suffer from unreliable foreign object detection during charging sessions, especially of small or ferrous objects. One possible solution is foreign object detection (FOD) based on power loss accounting, which involves the wireless charging pad and the wireless device measuring the transmitted and received power, respectively. If the difference exceeds a threshold, a foreign object is assumed to be present. Another possible solution is FOD based on quality factor variation, which involves the wireless charging pad measuring the quality factor of (multiple) transmitter coils after the wireless receiver is placed on the charging surface, and a reference quality factor measured by the wireless device during a previous calibration process and subsequently provided to the wireless charging pad. If the difference between the two quality factors exceeds a threshold, a foreign object is assumed to be present. Both solutions are affected when detecting small or ferrous objects because the wireless receiver device typically has poor accuracy in measuring received power and a low reference quality factor, meaning that a foreign object may only cause a small change in the quality factor measured by the transmitter. This leads to the use of a larger threshold to reduce false positives, but there is a risk of failing to detect small or ferrous objects.

[0018] Another possible solution is FOD based on the reflected impedance change, which involves the wireless charging pad measuring its impedance and comparing it to a reference impedance previously measured during calibration. If the difference between the two impedances is higher than a threshold, the wireless charging pad can determine that the object is not the wireless device and thus assume the presence of a foreign object. This solution cannot be used during a charging session, i.e., the impedance is measured during the process prior to the charging session, and therefore, this method cannot be used to detect foreign objects placed on the charging surface simultaneously with or after the wireless device. It can be seen that even a combination of these possible solutions does not completely solve the problem of detecting small and ferrous objects during a charging session. Temporarily interrupting or stopping the charging session is also not ideal. Accordingly, improved FOD techniques are presented for use during charging and without interrupting power transmission. These techniques involve the wireless charging pad periodically performing a specific sequence during the charging session, in which the wireless charging pad raises and lowers its operating point (current, frequency, etc.) to reverse bias the rectifier diode in the wireless receiver device, which disconnects the receiver load of the wireless device from the receiver coil. When this occurs, the quality factor measured at the transmitter coils is unaffected by the receiver load and can be directly compared with the quality factor measured when the wireless device was initially placed on the charging surface of the wireless charging pad.

[0019] Figures 1A to 1B An example wireless charging pad 100 and an example wireless device 150 (e.g., a mobile phone) according to some embodiments of this disclosure are shown. The wireless charging pad 100 includes a housing 104 that houses a plurality of transmitter coils 108 arranged on top of a ferrite material sheet 112. Although a linearly overlapping configuration of a plurality of four transmitter coils 108 is shown and specifically discussed herein, it should be recognized that the techniques of this disclosure are applicable to other numbers and / or configurations of a plurality of transmitter coils (e.g., a two-dimensional array). A controller 116 controls the operation of the wireless charging pad 100, the operation primarily including monitoring electrical parameters of the plurality of transmitter coils 108 and selectively activating / deactivating the plurality of transmitter coils 108 (i.e., providing power to the plurality of transmitter coils 108). Although the wireless device 150 is shown as a mobile phone, it will be understood that the wireless device 150 can be any suitable device having a receiver coil configured to receive inductive power transmission. The wireless device 150 includes a housing 154 that houses various user-facing components (touch display 158, speaker / microphone 162, etc.) and a receiver coil 166 disposed on top of a ferrite material sheet 170.

[0020] Now for reference Figures 2A to 2CFigures 200, 250, and 270, illustrate an example circuit diagram of the interaction between a wireless charging pad 100 and a wireless device 150 according to some embodiments of the present disclosure, and specific sequences of transmitter operating points and their effects on receiver voltage levels. Figure 2A The diagram shows a simplified circuit diagram 200 of a transmitter / receiver system. The transmitter is a wireless charging pad 100 having one or more active transmitter coils 108 and an AC power supply 204. The receiver is a wireless device 150 having a receiver coil 166. AC This represents the peak AC voltage measured across receiver coil 166. (V) RECT This represents the DC voltage measured across the output of a full-wave rectifier 208, which includes four rectifier diodes 212-1…212-4 (collectively referred to as “rectifier diodes 208”). The wireless device 150 also includes a holding capacitor 216 and a resistive load 220 (also referred to herein as “wireless load 220”). For example, the wireless load 220 could be a battery of the wireless device 150.

[0021] Now for reference Figure 3 And continue to refer to Figures 2A to 2C A flowchart of an example inductive charging method 300 according to some embodiments of this disclosure. Although specifically referenced in Figure 1 and... Figure 2A The components are described, but it should be recognized that inductive charging method 300 is applicable to any suitable transmitter / receiver device. At 304, controller 116 detects whether wireless device 150 has been placed near or on top of the charging surface of transmitter coil(s) 108. If true, method 300 proceeds to 308. Otherwise, method 300 ends or returns to 304. At 308, controller 116 determines the first quality factor (QF1) of active transmitter coil(s) 108 and initiates a charging session. At 312, controller 116 determines whether a periodic FOD determination operation is about to occur. For example, FOD can be determined at a periodic rate throughout the charging session. If true, method 300 proceeds to 316. Otherwise, method 300 returns to 312. At 316, a specific sequence of operating points of the transmitter (wireless charging pad 100) begins, which causes receiver coil 166 to temporarily disconnect from wireless load 220.

[0022] If possible Figure 2B As seen in the diagram, controller 116 (e.g., in a stepped manner as shown) increases the operating point of wireless charging pad 100 from the normal level (s0) to the first level (s1) during a first time period (time t0 to time t1). This increase in the operating point of wireless charging pad 100 causes wireless device 150 to transmit a control error packet (CEP) within the target range. The CEP is related to the rectifier voltage V required to meet its voltage target.RECT is proportional to the change amount. The amplitude of the first level s1 is the target level, aiming to make the return of CEP within the target range (CEP 最小 to CEP 最大 ), thereby indicating that the rectified voltage V RECT is higher than its voltage target. The CEP target level and duration (t2 - t1) are selected or determined such that the wireless device 150 does not indicate that the power transfer contact has been disconnected (i.e., there is no visual, audible, or tactile indication to the user). At 320, the controller 116 reduces the operating point of the wireless charging pad 100 to the second level (s2, where 0 < s2 / s1 < 1) for a second time period (from time t1 to time t2). At 324, the controller 116 increases the operating point of the wireless charging pad 100 back to the first level s1 for a third time period (from time t2 to time t3).

[0023] It should also be noted that the rectifier voltage (V[[ID=eleven]] RECT ) never actually reaches the amplitude V2 of the AC voltage V AC at time t2. At time t2, the amplitude of the AC voltage V AC subsequently increases to the amplitude V1 in response to another operating point change, because this will cause the rectifier diode 212 (see below) to conduct current. Finally, at 328, the controller 116 determines the second quality factor (QF2) of the (multiple) active transmitter coils 108 and reduces the operating point of the wireless charging pad back to the original normal level s0. The purpose of this specific sequence of operating point changes is to reverse bias the receiver diode 212 and thereby disconnect the receiver coil 166 from the wireless load 220. When doing so, the (multiple) active transmitter coils 108 are not affected by the wireless device 150, which provides a highly accurate quality factor determination. At 332, the controller 116 determines whether the difference between the first quality factor and the second quality factor (QF1 - QF2) exceeds a threshold (TH) (such as a percentage). When true, it can be assumed that an external object has been placed on the charging surface during the charging session and has caused the quality factor to decrease, and the controller 116 can terminate the charging session at 336, and the method 300 can end or return to 304. Otherwise, the method 300 returns to 312 (e.g., until the charging session ends otherwise or another periodic FOD cycle occurs).

[0024] This method can be used regardless of whether the wireless power receiver supports FOD based on quality factor changes. Moreover, since this method only utilizes the measurements made by the transmitter, the accuracy of the receiver measurements does not affect the sensitivity of this method.

[0025] In yet another embodiment, in addition to the quality factor, the individual components of impedance (i.e., resistance and reactance) can also be used as a metric for FOD. By observing the individual components of impedance, the sensitivity of the FOD technique may be improved; however, some transmitter designs (e.g., wireless charging pads) cannot directly measure the individual components of impedance, in which case FOD based on the quality factor would be preferred.

[0026] Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope of protection to those skilled in the art. Numerous specific details, such as examples of specific components, devices, and methods, are set forth to provide a thorough understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that the example embodiments may be embodied in many different forms without requiring the specific details, and should not be construed as limiting the scope of this disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known techniques are not described in detail.

[0027] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may also be intended to include the plural forms unless the context clearly indicates otherwise. The terms “and / or” include any and all combinations of one or more of the associated listed items. The terms “comprises,” “comprising,” “including,” and “having” are inclusive and therefore specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless expressly identified as an order of execution, the method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown. It should also be understood that additional or alternative steps may be employed.

[0028] Although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or portion from another. Unless the context clearly indicates otherwise, terms such as “first,” “second,” and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or portion discussed below may be referred to as the second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0029] As used herein, the term "module" may refer to, be part of, or include: application-specific integrated circuits (ASICs); electronic circuits; combinational logic circuits; field-programmable gate arrays (FPGAs); storage of executable code or procedures in a processor or a distributed network of processors (shared, dedicated, or grouped) and a networked cluster or data center; other suitable components that provide the described functionality; or a combination of some or all of the foregoing, such as in a system-on-a-chip. The term "module" may also include memory (shared, dedicated, or grouped) storing code executed by one or more processors.

[0030] As used above, the term "code" can include software, firmware, bytecode, and / or microcode, and can refer to programs, routines, functions, classes, and / or objects. As used above, the term "shared" means that some or all of the code from multiple modules can be executed using a single (shared) processor. Additionally, some or all of the code from multiple modules can be stored in a single (shared) memory. As used above, the term "group" means that some or all of the code from a single module can be executed using a group of processors. Additionally, a set of memory can be used to store some or all of the code from a single module.

[0031] The techniques described herein can be implemented by one or more computer programs executed by one or more processors. The computer program includes computer-executable instructions stored on a non-transient tangible computer-readable medium. The computer program may also include stored data. Non-limiting examples of non-transient tangible computer-readable media are non-volatile memory, magnetic storage, and optical storage.

[0032] Certain parts of the above description present the techniques described herein based on the algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are means by which those skilled in the art of data processing effectively communicate the substance of their work to others skilled in the art. Although these operations are described functionally or logically, they should be understood as being implemented by computer programs. Furthermore, it has repeatedly proven convenient, without loss of generality, to arrange these operations as modules or to name them by function.

[0033] Unless otherwise specified, as is apparent from the foregoing discussion, it should be understood that the discussion throughout the specification using terms such as “processing,” “calculating,” “calculating,” “determining,” and “displaying” refers to the actions and processes of a computer system or similar electronic computing device that manipulate and transform data represented as physical (e.g., electronic) quantities within computer system memory and registers or other such information storage, transmission, or display devices.

[0034] Certain aspects of the described technology include processing steps and instructions described herein in algorithmic form. It should be noted that the described processing steps and instructions may be embodied in software, firmware, or hardware, and when embodied in software, may be downloaded to reside on and be operated from different platforms used by a real-time network operating system.

[0035] The foregoing description of embodiments has been provided for purposes of illustration and description. This description is not intended to be exhaustive or limiting of this disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable and may be used in selected embodiments where applicable, even if not specifically shown or described. The same parts may also be varied in various ways. Such variations are not considered a departure from this disclosure, and all such modifications are intended to be included within the scope of the invention.

Claims

1. An inductive charging system, comprising: A transmitter coil configured to inductively transmit power to a receiver coil of a wireless device when activated, wherein the wireless device includes a rectifier diode located between the receiver coil and a receiver load; as well as Controller, the controller is configured to: Detect the wireless device on a charging surface close to the transmitter coil; In response to detecting the wireless device, a first quality factor of the transmitter coil is determined and a charging session is initiated, during which the transmitter coil is activated to inductively couple with the receiver coil and inductively transfer electrical energy to the receiver coil; and During the charging session, foreign object detection (FOD) technology is periodically performed, the foreign object detection (FOD) technology including: The operating point of the transmitter coil is adjusted according to a specific sequence of operating points, which reverse-biases the rectifier diode to disconnect the receiver load from the receiver coil. In response to adjusting the operating point of the transmitter coil according to the specific sequence, a second quality factor of the transmitter coil is determined; and The presence of foreign objects on the charging surface is detected by comparing the first quality factor with the second quality factor.

2. The inductive charging system as described in claim 1, characterized in that, The controller is configured to detect the presence of the foreign object when the difference between the first quality factor and the second quality factor exceeds a threshold.

3. The inductive charging system as described in claim 1, characterized in that, The controller is configured to: initiate a specific sequence of operating points of the transmitter coil by increasing the operating point of the transmitter coil from a normal level to a first level within a first time period, thereby causing the wireless device to send back a control error packet (CEP).

4. The inductive charging system as described in claim 3, characterized in that, The controller is configured to subsequently reduce the operating point of the transmitter coil from the first level to the second level for a second time period.

5. The inductive charging system as described in claim 4, characterized in that, The duration of the second time period and the first level are determined such that the CEP is determined to cause the wireless device not to indicate that the power transmission contact has been disconnected.

6. The inductive charging system as described in claim 4, characterized in that, The controller is configured to: subsequently increase the operating point of the transmitter coil from the second level to the first level for a third time period, and determine the second quality factor.

7. The inductive charging system as described in claim 6, characterized in that, The controller is configured to subsequently lower the operating point of the transmitter coil back to the normal level to complete the specific sequence of operating points of the transmitter coil.

8. The inductive charging system as described in claim 2, characterized in that, The controller is further configured to terminate the charging session in response to detecting the presence of the foreign object.

9. An inductive charging method, comprising: A wireless charging pad is provided, the wireless charging pad including a transmitter coil configured to inductively transmit power to a receiver coil of a wireless device when activated, wherein the wireless device includes a rectifier diode located between the receiver coil and a receiver load; The controller of the wireless charging pad detects the wireless device on a charging surface that is close to the transmitter coil; In response to detecting the wireless device, the controller determines a first quality factor of the transmitter coil and initiates a charging session, during which the transmitter coil is activated to inductively couple with the receiver coil and inductively transfer electrical energy to the receiver coil; and During the charging session, the controller periodically performs Foreign Object Detection (FOD) technology, which includes: The operating point of the transmitter coil is adjusted according to a specific sequence of operating points, which reverse-biases the rectifier diode to disconnect the receiver load from the receiver coil. In response to adjusting the operating point of the transmitter coil according to the specific sequence, a second quality factor of the transmitter coil is determined; and The presence of foreign objects on the charging surface is detected by comparing the first quality factor with the second quality factor.

10. The inductive charging method as described in claim 9, characterized in that, The presence of the foreign object is detected when the difference between the first quality factor and the second quality factor exceeds a threshold.

11. The inductive charging method as described in claim 9, characterized in that, The FOD technology includes: initiating a specific sequence of operating points of the transmitter coil by increasing the operating point of the transmitter coil from a normal level to a first level within a first time period, thereby causing the wireless device to send back a control error packet (CEP).

12. The inductive charging method as described in claim 11, characterized in that, The FOD technology includes: subsequently reducing the operating point of the transmitter coil from the first level to the second level for a second time period.

13. The inductive charging method as described in claim 12, characterized in that, The duration of the second time period and the first level are determined such that the CEP is determined to cause the wireless device not to indicate that the power transmission contact has been disconnected.

14. The inductive charging method as described in claim 12, characterized in that, The FOD technology includes: subsequently increasing the operating point of the transmitter coil from the second level to the first level for a third time period, and determining the second quality factor.

15. The inductive charging method as described in claim 14, characterized in that, The FOD technique includes: subsequently lowering the operating point of the transmitter coil back to the normal level to complete the specific sequence of operating points of the transmitter coil.

16. The inductive charging method as described in claim 10, characterized in that, Further includes: In response to the detection of the foreign object, the controller terminates the charging session.

17. An inductive charging system, comprising: A transmitter coil assembly for inductively transmitting power to a receiver coil of a wireless device when activated, wherein the wireless device includes a rectifier diode located between the receiver coil and a receiver load; as well as A controller device, the controller device being used for: Detect the wireless device on a charging surface close to the transmitter coil; In response to detecting the wireless device, a first quality factor of the transmitter coil is determined and a charging session is initiated, during which the transmitter coil is activated to inductively couple with the receiver coil and inductively transfer electrical energy to the receiver coil; as well as During the charging session, foreign object detection (FOD) technology is periodically performed, the foreign object detection (FOD) technology including: The operating point of the transmitter coil is adjusted according to a specific sequence of operating points, which reverse-biases the rectifier diode to disconnect the receiver load from the receiver coil. In response to adjusting the operating point of the transmitter coil according to the specific sequence, a second quality factor of the transmitter coil is determined; and The presence of foreign objects on the charging surface is detected by comparing the first quality factor with the second quality factor.

18. The inductive charging system as described in claim 17, characterized in that, The controller device detects the presence of the foreign object when the difference between the first quality factor and the second quality factor exceeds a threshold.

19. The inductive charging system as described in claim 17, characterized in that, The controller device: During a first time period, the operating point of the transmitter coil is increased from the normal level to the first level, thereby causing the wireless device to send back a control error packet (CEP). The operating point of the transmitter coil is then lowered from the first level to the second level for a second time period, wherein the duration of the second time period and the first level are determined such that the CEP is determined to cause the wireless device not to indicate that the power transmission contact has been disconnected. The operating point of the transmitter coil is then increased from the second level to the first level for a third time period, and the second quality factor is determined. and The operating point of the transmitter coil is then lowered back to the normal level to complete the specific sequence of operating points of the transmitter coil.

20. The inductive charging system as described in claim 18, characterized in that, The controller device terminates the charging session in response to detecting the presence of the foreign object.

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