Multiplexed Sensing Circuit for Wireless Charging Object Detection
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Solution Overview
Problem
Inductive wireless charging systems for electric vehicles face challenges in efficiently detecting foreign metallic objects, living objects, and determining vehicle position due to high magnetic field strengths, which can lead to undesirable induction heating and exposure to electromagnetic fields, necessitating a multi-purpose detection circuit for safety and alignment purposes.
Innovation Solution
A multi-purpose detection circuit incorporating a combination of inductive and capacitive sense circuits with impedance matching elements, a measurement circuit for sequential electrical characteristic measurement, and a control and evaluation circuit to determine the presence of metallic objects, living objects, vehicle type, and vehicle position, using a time multiplexing scheme to optimize detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high magnetic field strength is used for sufficient power transfer, then power transfer efficiency is improved, but induction heating of metallic objects occurs
Solution Approach 1:
The system performs foreign object detection before initiating power transfer by measuring impedance characteristics of the power transfer coil. This preliminary detection identifies metallic objects in the power transfer region, preventing power transfer that would cause harmful induction heating while allowing efficient power transfer when safe
2Measurement precision
If separate detection circuits are used for foreign object detection, living object detection, and vehicle position determination, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The system uses a single impedance measurement circuit to perform multiple detection functions. By measuring impedance characteristics at different frequencies and analyzing different aspects of the impedance response, the system simultaneously detects foreign objects, living objects, and determines vehicle position, eliminating the need for separate dedicated circuits for each function
Solution Approach 2:
The system varies measurement parameters such as frequency and excitation signal characteristics to enable different detection functions with a single circuit. By changing the measurement frequency and analyzing different impedance components, the same hardware can detect metallic objects, living objects, and determine vehicle alignment
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 solution enables simultaneous detection of foreign objects and vehicle position determination, enhancing safety by preventing induction heating and ensuring efficient power transfer, while reducing hardware complexity and costs by integrating multiple functions into a single system.
Implementation Method 1
An alternating current passing through the coil e.g., of a primary wireless power transfer structure produces an alternating magnetic field. When a secondary wireless power transfer structure is placed in proximity to the primary wireless power transfer structure, the alternating magnetic field induces an electromotive force (EMF) into the secondary wireless power transfer structure according to Faraday's law
Implementation Method 2
metallic objects or other objects present in the magnetic field can experience undesirable induction heating
Implementation Method 3
Each of the plurality of capacitive sense circuits includes at least one capacitive sense element (e.g., a sense electrode) and an associated inductive element to compensate for the gross reactance as presented at the terminals of the at least one capacitive sense element at the sense frequency
Implementation Method 4
A multi-purpose detection circuit incorporating a combination of inductive and capacitive sense circuits with impedance matching elements, a measurement circuit for sequential electrical characteristic measurement, and a control and evaluation circuit to determine the presence of metallic objects, living objects, vehicle type, and vehicle position, using a time multiplexing scheme to optimize detection efficiency
Data Source
AI summary
A multi-purpose detection circuit for object detection and vehicle position determination is described. For example, the circuit is configurable for detecting foreign metallic objects, living objects, and a vehicle or type of vehicle above an inductive wireless power transmitter. The circuit is also configurable for determining the vehicle's position relative to the inductive wireless power transmitter. An example apparatus includes a measurement circuit including a multiplexer, electrically connected to a plurality of inductive and capacitive sense circuits, for measuring one or more electrical characteristics in each of the inductive and capacitive sense circuits according to a predetermined time multiplexing scheme. The apparatus further includes a control and evaluation circuit for evaluating the measured electrical characteristics and determining at least one of a presence of a metallic object, a living object, a vehicle, or a type of vehicle, and a vehicle position based on changes in the measured electrical characteristics.