Wireless Power Transfer Impedance Sensing for Foreign Object Detection
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Solution Overview
Problem
Existing wireless power transmission systems face challenges in detecting foreign substances within the transmission range, leading to unintended heating and increased costs due to the need for additional circuits to measure the Q-value of the power receiving antenna.
Innovation Solution
A power transmitting apparatus that uses impedance detection to differentiate between foreign substances and the power receiving apparatus by comparing initial and output impedance values, determining their presence based on impedance changes and communication responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a circuit for measuring the Q-value of the power receiving antenna is provided to detect foreign substances, then foreign substance detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The impedance detection circuit originally designed for power receiving apparatus detection is made multi-functional by enabling it to detect both power receiving apparatus and foreign substances through the same measurement mechanism. The circuit measures impedance at different frequencies (first and second frequencies) to distinguish between different types of objects in the power transmission range, eliminating the need for separate detection circuits.
Solution Approach 2:
The detection method changes the measurement parameter from single-frequency Q-value measurement to multi-frequency impedance measurement. By measuring impedance at first and second frequencies and comparing the results, the system can differentiate between power receiving apparatus (which responds at both frequencies) and foreign substances (which only respond at the resonant frequency), achieving enhanced detection capability without additional hardware.
2Measurement precision
If impedance detection is performed at multiple frequencies to differentiate foreign substances from power receiving apparatus, then detection accuracy is improved, but measurement time and processing complexity increase
Solution Approach 1:
The system performs periodic impedance measurements at first and second frequencies in a cyclic manner. The control unit alternates between measuring impedance at the first frequency and the second frequency, comparing results to determine object type. This periodic measurement approach allows for accurate detection while maintaining efficient timing, as measurements are conducted in regular intervals rather than continuously.
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 simple and effective foreign substance detection and appropriate power transmission control without the need for additional circuits, reducing costs and preventing unintended heating.
Implementation Method 1
power transmission means for performing wireless power transmission to a power receiving apparatus arranged within a predetermined power transmission range
Implementation Method 2
detection means for detecting the output impedance of the power transmission means when a predetermined detection signal has been transmitted by the power transmission means
Implementation Method 3
if a foreign substance such as a piece of metal is present in the range in which a power transmitting apparatus can transmit power, an eddy current will flow in the foreign substance and unintended heating will occur
Data Source
AI summary
Foreign substance detection can be performed with a simple configuration in a power transmission system. A power transmitting apparatus that wirelessly transmits power to a power receiving apparatus, the power transmitting apparatus comprises: determination means for, in a case where an initial impedance value and the detected output impedance value do not match and there is no change in the output impedance value between before and after the transmission of a predetermined detection signal, determining that a foreign substance is present within a predetermined power transmission range, and, in a case where the initial impedance value and the detected output impedance value do not match and there is a change in the output impedance value between before and after the transmission of the predetermined detection signal, determining that a power receiving apparatus is present within the predetermined power transmission range.