Foreign Object Detection in Inductive Power Transfer
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Solution Overview
Problem
Existing inductive power transfer devices face challenges in detecting foreign metal objects without causing power losses and potential heating, as the varying magnetic field induces current in foreign objects, and existing detection methods are either complex or fail to accurately detect objects across varying air gaps.
Innovation Solution
Switching to a specific frequency where the current curves for minimum and maximum air gaps intersect allows for a single threshold to detect foreign objects, reducing power losses and improving detection accuracy regardless of air gap width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single frequency is used for power transfer and foreign object detection, then device complexity is reduced, but foreign object detection accuracy deteriorates due to power losses and heating
Solution Approach 1:
The patent applies periodic action by alternating between power transfer mode and detection mode at different frequencies. During detection mode, a higher frequency is used to detect foreign objects without excessive heating, while during power transfer mode, a lower frequency is used for efficient power transmission. This periodic switching resolves the contradiction by separating the conflicting requirements of detection accuracy and power efficiency into different time periods.
Solution Approach 2:
The patent changes the frequency parameter based on the operational mode. A higher frequency is used specifically for foreign object detection to minimize power losses and heating effects, while a lower frequency is used for power transfer. This dynamic parameter adjustment allows the system to optimize detection accuracy without suffering from the power losses that would occur if the same frequency were used continuously.
2Loss of energy
If a higher frequency is used during foreign object detection, then power losses are reduced, but detection accuracy across varying air gaps deteriorates
Solution Approach 1:
The patent employs feedback mechanisms to adjust detection thresholds based on the operating frequency and air gap conditions. By monitoring the system response at the higher detection frequency and comparing it against dynamically adjusted thresholds, the system maintains accurate foreign object detection across varying air gaps while benefiting from reduced power losses at the higher frequency.
Solution Approach 2:
The patent makes the detection system dynamic by adjusting detection parameters such as thresholds and timing based on the higher operating frequency and detected air gap conditions. This dynamic adaptation allows the system to maintain detection accuracy across varying air gaps while operating at the higher frequency that reduces power losses.
3Power
If the operating frequency is lowered to increase current and power delivery, then power transfer efficiency is improved, but foreign object heating increases
Solution Approach 1:
The patent uses periodic action by implementing distinct power transfer phases and detection phases. During power transfer phases, a lower frequency is used to maximize power delivery to the secondary coil. During detection phases, a higher frequency is used to minimize foreign object heating. This periodic switching between frequencies resolves the contradiction by ensuring that high power delivery and low heating requirements are met at different times.
Solution Approach 2:
The patent segments the operational cycle into separate power transfer intervals and detection intervals, each using optimally different frequencies. This segmentation allows the system to use low frequency for power transfer (reducing heating during this phase) and high frequency for detection (minimizing power losses and heating during detection), thereby resolving the contradiction between power delivery and heating prevention.
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 unambiguous detection of foreign objects with reduced power losses and improved accuracy, as the current threshold remains consistent across different air gaps, preventing damage and inefficiencies.
Implementation Method 1
The primary coil generates a magnetic field. A secondary unit separable from the primary unit comprises a secondary coil. When the secondary coil is placed in proximity to the varying magnetic flux created by the primary coil, the varying magnetic flux induces an alternating current in the secondary coil thus transferring power inductively
Implementation Method 2
The varying magnetic field in the primary coil may induce current in the foreign objects made of metal. Such currents may cause power losses that may also cause heating of the object
Data Source
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AI summary
A primary device for inductive power transfer to a secondary device is disclosed. The primary device includes a primary coil, the primary device being configured to (i) operate in a first mode during which the primary coil transfers power through inductive coupling to the secondary device, and (ii) operate in a second mode during which a foreign object is detected. The primary device further includes a primary controller configured to operate the primary coil (i) using a first frequency during the first mode, and (ii) using a second frequency during the second mode. A method to detect a foreign object which is in proximity of an inductively coupled environment of a primary device is also disclosed.