Wireless Charging Foreign Object Detection via Quality Factor Modulation
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Solution Overview
Problem
Conventional inductive charging systems fail to reliably detect foreign objects, particularly small or ferrous objects, during charging sessions due to limitations in power loss accounting, quality factor change, and reflected impedance change methods, which often result in false negatives or require interrupting the charging session.
Innovation Solution
The system employs a foreign object detection technique that periodically adjusts the operating point of the transmitter coil to reverse bias the rectifier diodes, allowing for a comparison of quality factors before and during the charging session to accurately detect foreign objects without interrupting power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional foreign object detection methods (power loss accounting, quality factor change, reflected impedance change) are used during charging sessions, then the system can detect some foreign objects, but small or ferrous objects cannot be reliably detected resulting in false negatives
Solution Approach 1:
The system dynamically adjusts the transmitter coil operating point during the charging session by modulating the drive signal amplitude. This creates time-varying operating conditions that cause rectifier diodes in the receiver to periodically reverse-bias and disconnect from the load, which in turn causes characteristic quality factor variations that reveal the presence of foreign objects that would otherwise be undetectable
Solution Approach 2:
The system implements periodic modulation of the transmitter coil operating point during the charging session. By periodically varying the drive signal amplitude and monitoring the resulting quality factor variations at specific frequencies, the system creates a detection mechanism that is sensitive to foreign objects while maintaining continuous power transfer to the receiver
2Measurement precision
If foreign object detection is performed during charging sessions using conventional methods, then detection capability is provided, but the charging session must be interrupted to perform detection
Solution Approach 1:
The system maintains continuous power transfer to the receiver throughout the charging session while simultaneously performing foreign object detection. By embedding detection within the ongoing charging process through operating point modulation, the system eliminates interruptions and ensures uninterrupted charging while maintaining foreign object detection capability
Solution Approach 2:
The transmitter coil serves dual functions: transferring power to the receiver and enabling foreign object detection. By modulating the operating point and monitoring quality factor variations, the same hardware infrastructure supports both charging and detection functions simultaneously without requiring separate detection hardware or interrupting the charging process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables reliable detection of foreign objects during charging sessions without power transfer interruption, improving the accuracy of foreign object detection and preventing potential overheating hazards.
Implementation Method 1
a transmitter coil configured to, when active, inductively transfer power to a receiver coil
Implementation Method 2
determining a second quality factor of the transmitter coil and detecting whether a foreign object is present on the charging surface based on a comparison between the first and second quality factors
Implementation Method 3
adjusting an operating point of the transmitter coil according to a specific sequence of operating points that causes the rectifier diodes to be reverse biased to disconnect the receiver load from the receiver coil
Data Source
AI summary
Inductive charging systems and methods detect a wireless device upon a charging surface of a wireless charging pad including a transmitter coil, determine a first quality factor of the transmitter coil and initiate a charging session, and during the charging session, periodically perform a foreign object detection (FOD) technique including adjusting an operating point of the transmitter coil according to a specific sequence of operating points that causes rectifier diodes between the receiver coil and a receiver load of the wireless device to be reverse biased to disconnect the receiver load from the receiver coil and then determining a second quality factor of the transmitter coil, and detecting whether a foreign object is present on the charging surface based on a comparison between the first and second quality factors.