Inductive Power Foreign Object Detection Using Field-Synced 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 during detection.
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 simple subtraction of reference and operational time responses to detect foreign objects, thereby reducing interference and increasing sensitivity and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex signal processing methods are used for foreign object detection, then detection reliability is improved, but device complexity and processing time increase
Solution Approach 1:
The patent extracts and eliminates the interfering power transfer field from the detection signal by performing differential measurement. The measurement unit measures the detection cell response with and without the power transfer field active, then subtracts these signals to obtain a clean detection signal free from power transfer interference, achieving simple yet reliable foreign object detection
Solution Approach 2:
The system performs preliminary measurement of the detection cell response before activating the power transfer field, storing this as a reference signal. This preliminary action enables subsequent differential processing that eliminates the need for complex real-time signal processing during power transfer
2Reliability
If foreign object detection is performed during power transfer, then detection capability is improved, but power transfer efficiency decreases due to interference
Solution Approach 1:
The system implements periodic switching between measurement modes: during first time intervals, the power transfer field is active and detection measurements are taken; during second time intervals, the power transfer field is inactive and reference measurements are taken. This periodic action enables foreign object detection during power transfer while eliminating continuous interference
Solution Approach 2:
The control unit uses feedback from the measurement unit to dynamically adjust the power transfer field activation based on detected foreign objects. When a foreign object is detected through differential measurement, the system can adjust or terminate power transfer, creating a closed-loop control system that maintains efficiency while ensuring safety
3Ease of operation
If the stimulation signal is applied asynchronously, then system operation is simpler, but interference from the power transfer field increases and reduces detection sensitivity
Solution Approach 1:
The patent introduces an intermediary differential measurement process that mediates between the stimulation signal and the detection output. By measuring and subtracting the response with and without the power transfer field, the intermediary processing eliminates interference while maintaining simple asynchronous stimulation signal application
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 simplifies signal processing, enhances detection sensitivity, and maintains power transfer efficiency by converting the system into a time-invariant state, effectively reducing interference from the power transfer field.
Implementation Method 1
a primary resonator for generating a magnetic field for the inductive power transfer
Implementation Method 2
each detection cell comprises a sense coil, a stimulation unit connected to the current input for generating a stimulation signal
Implementation Method 3
Especially 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
Implementation Method 4
Especially 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
Figure 1~2
Figure 3~6
Figure 7a~7b
AI summary
A foreign object detection device (19) for a wireless power transfer arrangement for inductive power transfer from a primary part to a secondary part across an airgap, includes a sensor arrangement (20) 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 (21) and the time response of the detection cell is measured with a measurement unit (22) and compared to a reference time response of that detection cell that has been previously sensed by a control and signal processing unit (23). By synchronising the stimulation signal and the measurement of the time response to the magnetic field (9) for the power transfer of the wireless power transfer arrangement, which is detected by a detector (24), the interference from the magnetic power field (9) as well as other interference may be substantially reduced and the following signal analysis to detect foreign objects is considerably simplified.