Wireless Power Foreign Object Detection Using Differential Coil Pairs
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Solution Overview
Problem
Existing wireless power transfer systems face inefficiencies and safety hazards due to inadequate detection of foreign metal objects, which can lead to undesired heating and disruption of power transfer, particularly in high-power applications.
Innovation Solution
A detection apparatus using a plurality of detection coils that measure differential currents between pairs of coils to identify foreign objects, with specific coil designs and layouts to enhance accuracy and distinguish between object presence and apparatus movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional detection techniques are used, then the system is simple, but foreign object detection accuracy is insufficient leading to safety hazards
Solution Approach 1:
The detection system is segmented into multiple independent detection coils arranged in a grid pattern, where each coil independently monitors its local region. This segmentation allows the system to achieve comprehensive coverage and high detection accuracy without requiring a single complex detection mechanism, thus resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The patent introduces detection coils as intermediary elements that mediate between the power transfer coils and the foreign objects. These coils detect changes in their electromagnetic fields caused by foreign objects and transmit this information to the control unit, enabling accurate detection without direct interaction between the power system and detection system, thereby maintaining reliability while managing complexity.
2Reliability
If detection coils are added to detect foreign objects, then detection accuracy improves, but interference with power transfer process increases
Solution Approach 1:
The system employs periodic foreign object detection during designated FOD periods, where detection coils are activated intermittently rather than continuously. This periodic operation allows the system to maintain high detection accuracy when needed while minimizing the time detection coils are active, thereby reducing their impact on power transfer efficiency and energy loss.
Solution Approach 2:
The detection system performs preliminary foreign object detection before initiating full power transfer and continues monitoring during designated periods. By detecting foreign objects in advance and during specific intervals, the system ensures safety without requiring constant detection activity, thus maintaining power transfer efficiency while achieving reliable detection.
3Area of stationary object
If multiple detection coils are used to cover large area, then detection coverage improves, but device complexity and cost increase
Solution Approach 1:
The detection system divides the monitoring area into multiple zones, each covered by individual detection coils arranged in a grid pattern. This segmentation allows the system to achieve large-area coverage through a modular arrangement of simpler components rather than using a single complex detection system, thereby expanding coverage while managing device complexity.
Solution Approach 2:
The detection coils serve multiple functions: they detect foreign objects, monitor power transfer conditions, and provide spatial information about detected objects. This multi-functionality allows the system to achieve comprehensive detection coverage using the same basic coil structure for multiple purposes, reducing the need for additional specialized components and thereby controlling device complexity while expanding effective coverage.
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
Accurately detects foreign objects before and during power transfer, minimizing interference with the power transfer process and preventing unsafe heating, while accounting for apparatus movement.
Implementation Method 1
The electromagnetic field may induce an electromotive force in a secondary coil of a wireless power reception apparatus when the secondary coil is placed in proximity to the primary coil
Implementation Method 2
when a foreign metal object (such as a key, a coin, a metallic can, or aluminum foil, among other examples) is in proximity of the electromagnetic field, the foreign metal object may be undesirably heated up due to eddy currents
Data Source
AI summary
This disclosure provides systems, methods and apparatuses for foreign object detection (FOD) in a wireless power transfer (WPT) system. Some implementations relate generally to the use of detection coils that are excited to measure and compare a differential current through a coil pair that includes at least two detection coils. A foreign object may cause a change in impedance for one or more detection coils compared to one or more other detection coils. By detecting the differential current of the coil pair, a detection apparatus may determine that a foreign object is in proximity to one of the detection coils of the coil pair. This disclosure provides several options for the design, construction, layout, and operations of detection coils to improve foreign object detection.