Foreign Object Detection in Wireless Power Transfer
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Solution Overview
Problem
Current wireless power transfer systems face challenges in detecting foreign objects, such as metal, human bodies, and animals, with high precision over a wide range, particularly in the height direction, due to limitations in magnetic field distribution and detection coil configurations, which can lead to heat generation and safety concerns.
Innovation Solution
A foreign object detecting device comprising three adjacent coils with a foreign object detecting circuit that generates a combined magnetic field by outputting signals with opposite polarities to the outer coils, allowing for precise detection of foreign objects above the center coil by measuring impedance changes, thereby increasing the detection range and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single detecting coil is used in conventional wireless power transfer systems, then the device complexity is low, but the detection precision and detection range are insufficient
Solution Approach 1:
The detecting coil is divided into three separate coils (first coil, second coil, third coil) arranged adjacently. Each coil contributes to detecting foreign objects in different spatial regions, thereby improving overall detection precision and range while maintaining manageable system complexity through modular architecture
Solution Approach 2:
The three coils are combined to generate a composite magnetic field that extends across all three coils. By merging the detection capabilities of multiple coils and processing their combined output, the system achieves superior detection performance compared to a single coil while keeping the overall device structure integrated and coherent
2Area of stationary object
If the power transmitting coil size is increased to widen charging area, then the charging area is expanded, but the detection range for foreign objects remains limited in the height direction
Solution Approach 1:
Instead of merely increasing coil size in the horizontal plane, the invention extends the magnetic field coverage in the vertical (height) direction by using three adjacently arranged coils. This dimensional approach to field distribution improves detection range in the height direction while maintaining the expanded charging area provided by the large coil configuration
3Reliability
If conventional single-coil detection is used, then the system is simple and cost-effective, but foreign objects cannot be detected with high precision over a wide range
Solution Approach 1:
The detection system is segmented into three coils with distinct functions: the first and third coils generate magnetic fields, while the second coil primarily detects foreign objects. This segmentation improves detection reliability by distributing detection responsibilities across multiple components, reducing the risk of undetected foreign objects
Solution Approach 2:
The system continuously monitors impedance changes in the second coil and compares them against threshold values to determine the presence of foreign objects. This feedback mechanism ensures reliable detection and enables the system to respond appropriately by preventing power transmission when foreign objects are detected
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
The solution enhances the range and precision of foreign object detection, particularly in the height direction, while maintaining a simple and cost-effective design, preventing heat generation and ensuring safety by accurately identifying objects before power transmission.
Implementation Method 1
a first detecting signal having a first predetermined waveform to the first terminal of the first coil and also outputs a second detecting signal having a second predetermined waveform to the fifth terminal of the third coil, thereby generating a combined magnetic field extending over the first and third coils
Implementation Method 2
a foreign object detecting circuit... measures an amount of change of an impedance value of the second coil with respect to a change in the combined magnetic field due to the presence of a foreign object
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A foreign object detecting device includes first, second, and third coils (11a,11b,11c) and a foreign object detecting circuit (10). The foreign object detecting circuit outputs a first detecting signal (S1) having a first predetermined waveform to a first terminal (T1) of the first coil (11a) and outputs a second detecting signal (S2) having a second predetermined waveform, which is an inverted form of the first predetermined waveform, to a fifth terminal (T5) of the third coil to cause a combined magnetic field extending over the first and third coils. The foreign object detecting circuit (10) measures an amount of change of the impedance value of the first or third coil with respect to a change in the combined magnetic field in the case of the presence of a foreign object (20). The amount of change exceeds a predetermined value, the foreign object detecting circuit determines that there is a foreign object above the second coil.