Sensor Resonant Circuit for Small Metal Object Detection in Inductive Charging
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Solution Overview
Problem
Existing methods for detecting electrically conductive foreign bodies during inductive energy transmission, such as inductive charging of electric vehicles, are inadequate for detecting small objects with low power dissipation and are unreliable due to environmental influences and changes in the operating point of the primary circuit.
Innovation Solution
A method and apparatus using a sensor coil connected to a capacitor to form a closed resonant circuit matched to the excitation frequency of the primary coil, which detects phase shifts in the current to identify foreign bodies, allowing for reliable detection of small conductive objects by forming a sensor resonant circuit with significantly lower inductance than the primary coil and calibrating for changes in the operating point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensor coils are used to detect foreign bodies during inductive energy transmission, then detection capability is improved, but detection accuracy for small objects with low power dissipation deteriorates
Solution Approach 1:
The patent segments the detection function by using a separate sensor coil arrangement independent of the primary and secondary coils. This sensor coil is specifically designed for detection purposes only, allowing it to be optimized for sensitivity without interfering with the main energy transmission function. The sensor coil measures the real component of its impedance, which changes when foreign bodies are present, enabling accurate detection of even small objects with low power dissipation.
Solution Approach 2:
The sensor coil acts as an intermediary detection element that indirectly senses the presence of foreign bodies through changes in its electrical impedance. Instead of directly measuring foreign body properties, the sensor coil's impedance changes serve as a mediator that indicates foreign body presence. This intermediary approach enhances detection sensitivity while maintaining system reliability.
2Measurement precision
If detection sensitivity is increased to detect small foreign bodies, then detection accuracy is improved, but susceptibility to environmental influences and operating point changes worsens
Solution Approach 1:
The patent implements feedback by continuously monitoring the real component of the sensor coil's impedance and comparing it against reference values or thresholds. The evaluation device processes the sensor signal and provides feedback control, enabling the system to distinguish between impedance changes caused by foreign bodies and those caused by environmental variations or operating point changes. This feedback mechanism maintains detection reliability while preserving high sensitivity.
Solution Approach 2:
The patent changes the detection parameter from measuring power dissipation or temperature to measuring the real component of electrical impedance. This parameter change makes the detection more sensitive to foreign bodies while being less susceptible to environmental influences. The impedance measurement approach allows for better differentiation between foreign body effects and normal operating variations through appropriate threshold setting and evaluation.
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
Enables the accurate and reliable detection of small electrically conductive foreign bodies with low power dissipation, independent of the operating point and transmission power, by using a highly sensitive phase shift detection mechanism that adapts to changes in the primary circuit's operating conditions.
Implementation Method 1
In an alternating magnetic field, electrically conductive foreign bodies are heated by induced eddy currents and remagnetisation
Implementation Method 2
In an alternating magnetic field, electrically conductive foreign bodies are heated by induced eddy currents and remagnetisation
Data Source
AI summary
In a method and an apparatus for detecting electrically conductive foreign bodies during inductive energy transmission between a primary coil (1) and a secondary coil (2), at least one sensor coil (5) is arranged between the primary coil (1) and the secondary coil (2), and a current flowing in the sensor coil (5) due to the induced voltage during the energy transmission is detected and evaluated. In this case, the sensor coil (5) is connected to at least one capacitor to form a resonant circuit which is matched to the excitation frequency of the primary coil (1). The phase position of the current in the resonant circuit in relation to a reference signal is then used to determine whether there are electrically conductive foreign bodies (4) between the primary coil (1) and the secondary coil (2). A high degree of sensitivity, also in relation to small electrically conductive foreign bodies within the energy transmission path, is achieved by means of the method and the apparatus.