Hybrid Inductive-Capacitive Sensing for WPT Foreign Object Detection
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Solution Overview
Problem
Inductive wireless power transfer systems for electric vehicles face challenges in efficiently detecting and discriminating between metallic and living objects, as well as determining vehicle position, due to high magnetic field strengths that can cause induction heating and electromagnetic exposure, necessitating separate detection circuits for each function which increases hardware complexity and cost.
Innovation Solution
A hybrid inductive and capacitive sensing system using a common detection circuit that includes inductive and capacitive sense elements to detect foreign objects, living objects, and determine vehicle position, by measuring electrical characteristics through time multiplexing and impedance changes, allowing for shared hardware components across multiple detection functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high magnetic field strength is used for power transfer, then power transfer efficiency is improved, but induction heating of foreign objects worsens
Solution Approach 1:
The system continuously monitors the detection signals from both inductive and capacitive sensing circuits during power transfer operation. When a foreign object is detected or when abnormal heating is indicated by changes in the sensing signals, the control circuit automatically reduces or shuts off the power transfer to prevent harmful induction heating, while maintaining high efficiency during normal operation.
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 hybrid system effectively detects and discriminates between metallic and living objects, and determines vehicle position, reducing hardware complexity and cost while ensuring safety and efficiency in wireless power transfer.
Implementation Method 1
A first sense circuit includes a first electrical conductor forming a loop of an inductive sense element
Implementation Method 2
A second sense circuit includes a second electrical conductor forming an electrode of a capacitive sense element
Implementation Method 3
An alternating current passing through the coil e.g., of a primary WPT structure produces an alternating magnetic field. When a secondary WPT structure is placed in proximity to the primary WPT structure, the alternating magnetic field induces an electromotive force (EMF) into the secondary WPT structure according to Faraday's law
Implementation Method 4
metallic objects or other objects present in the magnetic field can experience undesirable induction heating due to eddy current loss effects
Data Source
AI summary
In aspects, techniques for detecting and discriminating foreign objects near an inductive wireless power transfer system is disclosed. The method is based on hybrid inductive and capacitive sensing. The apparatus includes a sensing system, a measurement circuit, and a controller. The sensing system senses the object based on at least one of an inductive or a capacitive effect. The sensing system includes an inductive sense element, which has an electrical characteristic that changes in a presence of the object based on the inductive effect. The sensing system further includes a capacitive sense element, which has an electrical characteristic that changes in the presence of the object based on the capacitive effect. The measurement circuit measures the electrical characteristics in the inductive and capacitive sense circuits. The controller determines the presence of the object, and discriminates between metallic and non-metallic objects based on the change in the measured electrical characteristics.