Foreign Object Detection in Wireless Power Transfer Using Weakly Coupled Coils
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Solution Overview
Problem
Existing wireless power transfer systems face challenges in detecting foreign objects, particularly in high-power applications where energy loss is low, making it difficult to accurately detect small objects that can cause hazardous heat generation, and are sensitive to mechanical variations and non-dissipating magnetic materials, leading to complex and unreliable detection systems.
Innovation Solution
A system with a power transfer coil and a foreign object detecting device featuring detection coils that are weakly coupled to the power transfer coil, allowing for continuous foreign object detection without interfering with the primary magnetic field, using a driver circuit and control unit to maintain a steady magnetic field and measure damping, and positioned to minimize magnetic coupling, enabling detection during active power transfer and reducing sensitivity to mechanical variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the difference between transmitted power and received power is used to detect foreign objects, then the detection method is simple, but it becomes difficult to detect foreign objects in high power applications where energy loss is low
Solution Approach 1:
The patent introduces an intermediary detection coil that is weakly coupled to the power transfer coil. This intermediary coil acts as a mediator to sense the magnetic field changes caused by foreign objects without being directly affected by the high power transmission, enabling detection in high power applications where direct power difference measurement fails.
Solution Approach 2:
The patent changes the detection parameter from power difference (which is insensitive in high power applications) to magnetic field coupling characteristics. By measuring the change in magnetic coupling between the power transfer coil and the detection coil, the system can detect foreign objects even when energy loss is minimal.
2Reliability
If auxiliary coils are used for foreign object detection, then detection can be performed when power transfer is not active, but the system complexity and cost increase due to requiring two sets of coils
Solution Approach 1:
The detection coil serves multiple functions: it acts as a power receiver during active power transfer and simultaneously functions as a foreign object detector by sensing magnetic field changes. This multi-functionality eliminates the need for separate auxiliary coils, reducing system complexity while maintaining detection reliability.
Solution Approach 2:
The patent merges the power reception function and foreign object detection function into a single integrated system using the same coils. The detection coil and power receiver coil are combined, allowing the system to perform both power transfer and foreign object detection without requiring separate auxiliary coil sets.
3Measurement precision
If detector coils are used for foreign object detection, then the presence of foreign objects can be measured, but the system becomes very sensitive to mechanical variations and non-dissipating magnetic materials, leading to false triggers
Solution Approach 1:
The patent changes the detection approach from measuring absolute magnetic field strength (which is sensitive to mechanical variations) to measuring the change in magnetic coupling characteristics. By focusing on coupling changes rather than absolute field levels, the system maintains sensitivity to foreign objects while becoming insensitive to mechanical variations and ferrite positioning.
Solution Approach 2:
The system uses feedback from the weakly coupled detection coil to monitor changes in magnetic coupling. This feedback mechanism allows the system to distinguish between genuine foreign object presence (which causes characteristic coupling changes) and mechanical variations (which do not produce the same coupling signature), reducing false triggers.
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 system provides reliable and continuous foreign object detection with reduced complexity and cost, improved detection range, and robustness against mechanical variations, allowing for safe and efficient wireless power transfer.
Implementation Method 1
In wireless power transfer by means of induction an electromagnetic field is generated by a transmitter coil
Implementation Method 2
a control unit, which may be coupled to the driver circuit, and is configured to measure a value or quantity representative of a damping of the magnetic field
Data Source
Figure 1
Figure 2
Figure 3a~4c
AI summary
Apparatus for wireless power transfer, comprising a power transfer coil (111) configured for inductive power transfer and defining a first plane, a foreign object detecting device comprising at least one detection coil (31) defining a second plane substantially parallel to the first plane. The foreign object detecting device comprises a driver circuit (22) coupled to the at least one detection coil for generating a magnetic field with the at least one detection coil and a control unit (24) coupled to the driver circuit and configured to measure a value representative of a damping of the magnetic field. The control unit is configured to measure an electrical power supplied to the at least one detection coil and to control the electrical power to maintain the magnetic field at a steady magnitude.