Balanced Detection Coils for Wireless Power Foreign Object Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current foreign object detection methods in wireless power transfer systems, particularly for higher power levels, suffer from inaccuracies, complexity, and high cost, leading to missed detections and false positives, and are not suitable for varying operating conditions.
Innovation Solution
A power transmitter system using balanced detection coils and a compensation circuit to generate a compensation drive signal that offsets the combined voltage of the detection coils, allowing for improved foreign object detection by minimizing interference during power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional foreign object detection methods are used in wireless power transfer systems, then power transfer can be performed, but detection accuracy is poor leading to missed detections and false positives
Solution Approach 1:
The detection system is segmented into multiple independent detection coils arranged in a balanced configuration. Each coil detects magnetic field changes independently, and their combined output provides more reliable foreign object detection by reducing false positives and missed detections through spatial diversity.
Solution Approach 2:
A compensation coil is introduced as an intermediary element to counteract the magnetic field generated by the power transmitter coil. This compensation coil carries a current that generates an opposing magnetic field, allowing the detection coils to operate in a reduced interference environment and improve detection accuracy.
2Power
If higher power levels are used in wireless power transfer, then power transfer capability is improved, but foreign object detection becomes more difficult and inaccurate
Solution Approach 1:
The compensation coil applies preliminary anti-action by generating an opposing magnetic field before foreign object detection is performed. This pre-compensation reduces the interference from the high-power transmitter coil, enabling accurate detection even at higher power levels where interference would normally prevent reliable detection.
Solution Approach 2:
The system changes operational parameters by introducing a compensation current with opposite polarity to the transmitter coil current. This parameter change (adding compensating current) modifies the magnetic field environment to enable accurate detection while maintaining high power transfer capability during normal operation.
3Measurement precision
If complex detection circuits are used to improve detection accuracy, then detection precision may be improved, but device complexity and cost increase
Solution Approach 1:
The detection system uses homogeneous detection coils with identical or similar construction and characteristics. This homogeneity simplifies the detection circuit design because all coils can be processed and calibrated in the same way, reducing the need for complex individual coil characterization and simplifying the overall detection electronics.
Solution Approach 2:
Multiple detection coils are merged into a single balanced detection system where their outputs are combined. This merging approach provides improved detection accuracy through spatial diversity while using relatively simple individual coil circuits, avoiding the need for complex individual processing of each coil.
4Productivity
If the transmitter coil generates strong magnetic field for power transfer, then power transfer efficiency is improved, but interference with detection coils increases
Solution Approach 1:
The compensation coil serves as an intermediary that counteracts the harmful magnetic field from the transmitter coil during detection phases. This allows the transmitter coil to operate at high power for efficient power transfer while the compensation coil temporarily reduces interference during foreign object detection intervals.
Solution Approach 2:
The system uses periodic action by alternating between power transfer mode (high transmitter power) and detection mode (with compensation active). This time-division approach allows high power transfer efficiency during power transfer intervals while minimizing magnetic interference during detection intervals through the compensation coil.
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 more accurate and reliable foreign object detection with reduced complexity and cost, suitable for higher power levels, while minimizing interference and improving detection accuracy.
Implementation Method 1
power is inductively transferred from a transmitter inductor in a power transmitter device to a receiver coil in the individual devices
Implementation Method 2
the magnetic flux generated by the transmitter coil will introduce eddy currents in the metal objects
Implementation Method 3
A power transmitter system using balanced detection coils and a compensation circuit to generate a compensation drive signal that offsets the combined voltage of the detection coils
Data Source
AI summary
A power transmitter (101) comprises a driver (201) generating a drive signal for a transmitter coil to generate a power transfer signal during a power transfer time interval and an electromagnetic test signal during a foreign object detection time interval. A set of balanced detection coils (207, 209) comprise two detection coils arranged such that signals induced in the two detection coils by an electromagnetic field generated by the transmitter coil compensate each other. A foreign object detector (205) is coupled to the detection coils and performs foreign object detection during the foreign object detection time interval. The foreign object detector (205) is arranged to detect a foreign object in response to a property of a signal from the detection coils meeting a foreign object detection criterion. A transformer (1101) has a primary winding and a secondary winding coupled in series with the set of balanced detection coils A compensation circuit (1103) is coupled to the primary winding and arranged to generate a compensation drive signal for the primary winding which offsets a combined voltage of the set of detection coils.