Foreign Object Detection in Wireless Power Resonators
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Solution Overview
Problem
In wireless power transmission systems, the presence of metallic foreign objects between coils can cause eddy currents and heating, necessitating a reliable detection method to ensure safe and efficient power transfer.
Innovation Solution
A foreign object detector that uses a first resonator and a second resonator with a parallel resonant circuit, including a coil and a capacitor, to measure changes in input impedance at different frequencies, allowing for the detection of metallic foreign objects without requiring feedback from the power-receiving side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If efficiency measurement feedback from power-receiving side to power-transmitting side is implemented, then foreign object detection accuracy is improved, but system complexity and communication requirements increase
Solution Approach 1:
The patent extracts the foreign object detection function from the complex feedback-based system and implements it using only the power-transmitting side resources. By measuring input impedance changes at different frequencies (below and above resonant frequency) on the transmitting side alone, the system achieves foreign object detection without requiring feedback communication from the power-receiving side, thus reducing system complexity while maintaining detection accuracy
Solution Approach 2:
The patent introduces input impedance measurement as an intermediary parameter to detect foreign objects. By measuring how the input impedance of the transmitting coil changes when foreign objects are present (detected through frequency-dependent impedance variations), the system can infer foreign object presence without direct feedback from the receiving side, simplifying the overall system architecture
2Reliability
If foreign object detection is implemented, then safety is improved, but additional detection circuits and measurements increase device complexity
Solution Approach 1:
The patent makes the existing oscillator and measurement circuits multi-functional by using them for both power transmission characterization and foreign object detection. The same circuits that measure power transmission efficiency are also used to detect foreign objects by performing impedance measurements at different frequencies, eliminating the need for separate dedicated detection circuits and reducing overall device complexity
Solution Approach 2:
The patent changes the operating frequency parameter to enable foreign object detection. By measuring input impedance at frequencies both below and above the resonant frequency of the receiving coil, the system detects foreign objects through the differential impedance changes they cause, utilizing parameter variation rather than additional hardware
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
Enables safe and efficient wireless power transmission by accurately detecting metallic foreign objects between coils, preventing heating and ensuring reliable operation.
Implementation Method 1
an oscillator circuit capable of oscillating at a first frequency (f1) which is lower than a resonant frequency (fr) of the second resonator and at a second frequency (f2) which is higher than the resonant frequency (fr)
Implementation Method 2
a first resonator and a second resonator which is electromagnetically coupled to the first resonator
Implementation Method 3
a measurement circuit to measure changes in input impedance of the first resonator
Implementation Method 4
if a metallic foreign object exists between the power transmitting and power receiving coils, there is a risk of an eddy current occurring in the metallic foreign object, and resultant heating
Data Source
AI summary
A foreign object detector detects a metallic foreign object between a first resonator and a second resonator which is composed of a parallel resonant circuit including a coil and a capacitor. The foreign object detector includes the first resonator; an oscillator circuit capable of oscillating at a first frequency (f1) which is lower than a resonant frequency (fr) of the second resonator and at a second frequency (f2) which is higher than the resonant frequency (fr); and a measurement circuit to measure changes in input impedance of the first resonator. The measurement circuit detects a metallic foreign object between the first resonator and the second resonator based on: changes in input impedance of the first resonator as measured by the measurement circuit while the oscillator circuit is oscillating at the first frequency f1; and changes in input impedance of the first resonator as measured by the measurement circuit while the oscillator circuit is oscillating at the second frequency f2.