Inductive Power Transfer Primary Unit Foreign Object Detection
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Solution Overview
Problem
Inductive power transfer systems face inefficiencies and parasitic loads issues, such as energy wastage when no secondary unit is present and heating due to foreign metal objects, which existing solutions fail to address effectively, especially in open systems that support multiple devices and arbitrary placements.
Innovation Solution
The method involves driving the primary unit to change the magnitude of its electrical drive signal and assessing the effect on power drawn to detect secondary units and foreign objects, allowing for efficient power management and prevention of heating by entering standby or shutdown modes as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the primary unit continuously operates to supply power, then power transfer capability is maintained, but energy is wasted when no secondary unit is present
Solution Approach 1:
The system performs preliminary detection by measuring power draw at different drive signal magnitudes before entering standby mode. This preliminary action identifies the presence of secondary units or foreign objects, allowing the system to avoid continuous operation when unnecessary, thus preventing energy waste while maintaining power transfer capability when needed.
Solution Approach 2:
The system dynamically adjusts its operating state based on detected conditions. It transitions between continuous operation, pulsed operation for detection, and standby mode. This dynamic behavior allows the system to maintain reliability when secondary units are present while minimizing energy consumption when they are absent.
2Productivity
If the primary unit operates at high power, then power transfer efficiency is improved, but foreign metal objects generate harmful heat
Solution Approach 1:
The system performs preliminary detection at reduced power levels by measuring power draw at different drive signal magnitudes. This allows identification of foreign objects before high-power operation begins, preventing harmful heating while maintaining the ability to achieve high power transfer efficiency when no foreign objects are present.
Solution Approach 2:
The system takes preliminary anti-action by detecting foreign objects through power draw measurement and preventing their exposure to high-power magnetic fields. By identifying foreign objects beforehand and avoiding continuous high-power operation when they are present, the system prevents the harmful heating effect while preserving high power transfer efficiency for legitimate secondary units.
3Loss of energy
If the primary unit enters standby mode to save energy, then energy waste is reduced, but detection of secondary units becomes less reliable
Solution Approach 1:
The system employs periodic detection by measuring power draw at different drive signal magnitudes at scheduled intervals rather than continuously. This periodic action maintains adequate detection reliability to identify secondary units while allowing the system to enter standby mode between measurements, significantly reducing energy waste compared to continuous operation.
4Measurement precision
If the system uses frequency sweeping to detect secondary units, then detection capability is improved, but EMC performance deteriorates
Solution Approach 1:
The system changes the parameter being measured (power draw at different drive signal magnitudes) instead of changing frequency. By maintaining a fixed operating frequency and varying only the drive signal magnitude for detection purposes, the system achieves reliable detection capability while avoiding the EMC interference problems associated with frequency sweeping.
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 efficient power transfer by distinguishing between secondary units and foreign objects without suspending power transfer, improving system capacity and EMC performance, and supporting multiple device scenarios.
Implementation Method 1
A primary unit having at least one primary coil, through which it drives an alternating current, creating a time-varying magnetic flux
Implementation Method 2
When the secondary coil is placed in proximity to the time-varying flux created by the primary coil, the varying flux induces an alternating current in the secondary coil
Implementation Method 3
Foreign objects made of metal may have eddy-currents induced therein. Such eddy currents tend to act to exclude the flux, but because the material has resistance, the flowing eddy currents may cause I2R losses that may cause heating of the object
Implementation Method 4
the flowing eddy currents may cause I2R losses that may cause heating of the object
Data Source
AI summary
A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.