Inductive Foreign Object Detection With Synchronized Time Response
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Solution Overview
Problem
Existing wireless power transfer systems face challenges in efficiently and reliably detecting foreign objects, which can cause heating and safety issues due to unintentional energy conversion, especially with magnetic and conductive objects, and current methods often require complex signal processing or reduce power transfer efficiency.
Innovation Solution
A foreign object detection device that synchronizes the application of a stimulation signal with the magnetic field during inductive power transfer, allowing for simplified signal processing by comparing time responses at the same trigger point, thereby reducing interference and enhancing detection robustness and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If inductive power transfer is performed using a magnetic field, then wireless energy transfer is achieved, but foreign objects in the magnetic field heat up due to induced eddy currents and hysteresis losses causing safety dangers
Solution Approach 1:
The system performs foreign object detection before initiating full power transfer by applying a preliminary stimulation signal at a different frequency. This preliminary action identifies the presence of foreign objects that would otherwise heat up during normal operation, allowing the system to prevent harmful heating before it occurs.
Solution Approach 2:
A separate detection coil system acts as an intermediary between the power transfer system and foreign objects. This intermediary detection system uses a different frequency (e.g., 6.78 MHz) than the power transfer frequency, allowing it to detect foreign objects through eddy current effects without causing the harmful heating that occurs at the power transfer frequency.
2Measurement precision
If sensors are used to detect foreign objects, then detection capability is provided, but sensors are disturbed by environmental influences and non-metallic objects
Solution Approach 1:
The system changes the frequency parameter of the detection signal to 6.78 MHz, which is optimized for detecting metallic foreign objects through eddy current effects. This frequency parameter change makes the detection less sensitive to environmental influences and non-metallic objects that do not conduct electricity, thereby improving both detection precision and reliability.
Solution Approach 2:
The patent replaces traditional capacitive or optical sensors with an inductive detection system using coils. This substitution uses electromagnetic induction principles that are inherently more robust against environmental factors like dirt and moisture, while being specifically sensitive to metallic foreign objects through eddy current effects.
3Measurement precision
If arrays of sensor coils are used to increase detection area, then detection sensitivity is improved, but device complexity increases
Solution Approach 1:
The detection coils serve multiple functions: they detect foreign objects during power transfer operation, provide preliminary detection before power transfer, and can operate independently of the power transfer system. This multi-functionality reduces the need for separate dedicated detection systems, thereby managing complexity while maintaining high detection sensitivity across the entire power transfer area.
4Reliability
If foreign object detection is performed during power transfer, then continuous monitoring is achieved, but interference from the power transfer field complicates signal processing
Solution Approach 1:
The system uses periodic stimulation signals at a specific frequency (6.78 MHz) that is distinct from the power transfer frequency. This periodic action at a different frequency creates a clear spectral separation, allowing the detection system to periodically sample for foreign objects during power transfer without the measurement being corrupted by the much stronger power transfer magnetic field.
Solution Approach 2:
A separate detection coil system acts as an intermediary that measures the magnetic field at the frequency of interest (6.78 MHz) while being insensitive to the power transfer frequency. This intermediary measurement system provides continuous monitoring capability without direct interference from the power transfer field, simplifying signal processing.
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 approach significantly reduces interference from the power transfer field, enabling efficient and reliable foreign object detection without compromising power transfer efficiency, thus ensuring safer and more accurate detection of foreign objects.
Implementation Method 1
a primary resonator for generating a magnetic field for inductive power transfer
Implementation Method 2
one kind of inductive sensors detects the reduction of the inductance of a coil due to induced eddy currents in the object to be detected
Implementation Method 3
magnetic and conductive objects such as for example coins, keys, tools, cans or other objects, can heat up in a magnetic field quickly by induced eddy currents and hysteresis losses
Data Source
AI summary
A foreign object detection device for a wireless power transfer system for inductive power transfer from a primary part to a secondary part across an airgap, includes a sensor module with a multitude of detection cells. In order detect a foreign object near a detection cell, a stimulation signal is applied to a detection cell by means of a stimulation unit and the time response of the detection cell is measured with a measurement unit and compared to a reference time response of that detection cell that has been previously sensed by a control and signal processing unit.