Wireless Power Transfer Circuit for Metallic Object Detection
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Solution Overview
Problem
Wireless charging systems face challenges in efficiently detecting metallic objects within the charging field, which can lead to reduced efficiency and safety hazards due to the presence of foreign objects during power transmission.
Innovation Solution
A method involving the measurement of characteristics of the transmitter and receiver LC tanks during micro-slots, where the tanks are shorted to determine power loss, allowing for the detection of metallic objects by comparing the measured power loss with predetermined thresholds, and using a magnetic bitmap for distinguishing between friendly and foreign objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wireless power transmission is performed continuously, then power transfer efficiency is maintained, but metallic objects cannot be detected and safety hazards increase
Solution Approach 1:
The patent implements periodic interruption of wireless power transmission at defined slot periods to perform foreign object detection. During these interruption slots, the transmitter stops power transmission temporarily to measure transmitter and receiver signals, detect power loss, and identify metallic objects. This periodic action enables safety checks without completely abandoning continuous operation, resolving the contradiction between maintaining power transfer efficiency and ensuring safety through detection.
2Measurement precision
If the receiver LC tank is not shorted during measurement, then power reception continues, but accurate power loss measurement for object detection cannot be performed
Solution Approach 1:
The patent applies preliminary action by shorting the receiver LC tank before performing power loss measurements during interruption slots. This preliminary shorting action prepares the receiver in a known state, ensuring that any measured power loss is due to foreign objects rather than normal power reception variations. By pre-configuring the receiver state, the system achieves accurate measurement conditions while minimizing the duration and impact of power transmission interruptions.
3Reliability
If all metallic objects are detected and blocked, then safety is improved, but friendly objects cause unnecessary charging interruptions
Solution Approach 1:
The patent applies local quality by analyzing the spatial distribution and characteristics of detected metallic objects using magnetic bitmap data. Instead of treating all metallic detections uniformly, the system evaluates the location, size, and magnetic properties of each detected object to determine whether it is a foreign object requiring safety intervention or a friendly object that can be safely ignored. This localized differentiation enables selective charging continuation or interruption based on specific object characteristics rather than blanket safety protocols.
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 enables precise detection of metallic objects, preventing safety hazards and maintaining efficient wireless power transfer by distinguishing between friendly and foreign objects within the charging field.
Implementation Method 1
wirelessly transmitting power using a transmitter LC tank; wirelessly receiving power from the transmitter LC tank using a receiver LC tank
Implementation Method 2
during the slot period, shorting the receiver LC tank; during the slot period and after shorting the receiver LC tank, measuring a transmitter signal associated with the transmitter LC tank; determining a power loss associated with the wirelessly transmitting power based on the measured transmitter signal
Data Source
AI summary
In an embodiment, a method includes: wirelessly transmitting power using a transmitter LC tank; wirelessly receiving power from the transmitter LC tank using a receiver LC tank; interrupting wirelessly transmitting power for a slot period; during the slot period, shorting the receiver LC tank; during the slot period and after shorting the receiver LC tank, measuring a transmitter signal associated with the transmitter LC tank; determining a power loss associated with the wirelessly transmitting power based on the measured transmitter signal; and detecting a metallic object based on the determined power loss.