Inductive Power Transmitter for Multi-Frequency Object Detection
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Solution Overview
Problem
Inductive power transmitters face challenges in accurately distinguishing between intended power receivers and foreign objects, particularly metallic items, which can heat due to eddy currents from the magnetic field, necessitating a method to prevent overheating by reliably detecting and differentiating these objects.
Innovation Solution
The solution involves generating object detection signals at two substantially different frequencies and measuring the inductance of the transmitting coil at each frequency to determine the presence and type of objects, leveraging the skin effect to differentiate between power receivers and foreign objects based on changes in inductance, without requiring communication with the receiver or additional circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single frequency detection method is used, then the device complexity is reduced, but the measurement precision for distinguishing foreign objects from power receivers deteriorates
Solution Approach 1:
The patent applies parameter changes by measuring inductance at multiple different frequencies (at least two distinct frequencies) rather than a single frequency. This allows the system to detect characteristic frequency responses that differentiate foreign objects from power receivers, improving measurement precision without requiring complex additional hardware beyond the existing coil and controller.
2Measurement precision
If communication with the receiver is required for detection, then the measurement precision improves, but the ease of operation deteriorates
Solution Approach 1:
The system performs self-service detection by measuring the electrical characteristics (inductance) of the coil itself at multiple frequencies. The controller analyzes changes in the coil's inductance to automatically identify foreign objects without requiring any communication, feedback, or interaction with the receiver device, thereby maintaining ease of operation while achieving accurate detection.
3Measurement precision
If additional circuitry is added for detection, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The existing transmitting coil serves multiple functions: it acts as both the power transmission coil and the detection coil for measuring inductance changes. The controller also performs dual roles by managing both power transmission control and foreign object detection analysis. This multi-functionality approach enables accurate detection without adding separate detection circuitry, maintaining system simplicity.
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 approach provides a robust, fast, and accurate method for foreign object detection, capable of distinguishing between metal and ferrous objects, ensuring safe power transfer and preventing overheating, without the need for calibration or modifications to the receiver.
Implementation Method 1
A charging mat is one way of providing a charging surface for a portable device, and has an interface surface incorporating a power transmitter with one or more transmitting coils that generate a time-varying magnetic field. The magnetic field induces an alternating current in a suitable receiving coil
Implementation Method 2
leveraging the skin effect to differentiate between power receivers and foreign objects based on changes in inductance
Data Source
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AI summary
An inductive power transmitter comprising: a converter configured to generate at least two object detection signals at substantially different frequencies, at least one transmitting coil configured to generate a magnetic field based on the object detection signals, and a controller configured to determine or measure circuit parameter(s) in relation to the coil to determine the inductance of the coil at each of the frequencies, and determine whether and/or what kind of object is present depending on a change in inductance between each of the frequencies.