Planar Air-Core Inductor Current Sensor for Thermal Reliability
Solution Overview
Problem
Existing current sensors for electric motors and power electronics fail due to poor thermal resistance, large size, and inability to respond to rapid current changes, leading to premature failure and inaccurate sensing.
Innovation Solution
A compact current sensor design featuring a substrate-based inductor with conductive traces and vias, coupled with a magnetic field sensor and filtering circuits, which separates alternating and direct current components and uses a sensor fusion circuit to determine aggregate current, including a current change detector and temperature sensor for enhanced accuracy and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a ferromagnetic core is used in the sensor, then the sensor can detect magnetic field signals, but self-heating from eddy currents and hysteresis losses causes premature failure
Solution Approach 1:
The patent extracts and removes the ferromagnetic core from the sensor design, replacing it with an air-core inductor. This eliminates the source of eddy currents and hysteresis losses while maintaining the sensing capability through alternative means (Hall effect sensor for DC component, inductor for AC component).
Solution Approach 2:
The patent substitutes the ferromagnetic core-based inductive sensing mechanism with a combination of air-core inductor and Hall effect magnetic field sensor. This replacement eliminates thermal issues while preserving measurement functionality across both AC and DC ranges.
2Reliability
If the sensor is designed to resist thermal stress, then reliability improves, but the sensor occupies larger than desired volume
Solution Approach 1:
The patent transitions from a three-dimensional ferromagnetic core structure to a planar air-core inductor implementation using PCB traces. This dimensional change reduces volume while maintaining inductance functionality and improving thermal characteristics through the distributed trace structure.
Solution Approach 2:
The patent employs thin film PCB traces to create the inductor structure, replacing bulky ferromagnetic components. The flexible trace layout on the PCB substrate achieves the required inductance in a compact form factor while providing excellent thermal management through the distributed structure.
3Measurement precision
If the sensor uses traditional inductive design, then it can sense current, but it fails to respond appropriately for rapid changes in current
Solution Approach 1:
The patent segments the current sensing function into two independent pathways: one for AC component detection (using the air-core inductor and high-pass filter) and one for DC component detection (using the Hall effect sensor). This segmentation allows each pathway to be optimized for its specific function, with the AC path capable of rapid response to current changes.
Solution Approach 2:
The patent implements dynamic signal processing with separate filtering circuits for AC and DC components. The high-pass filter for AC signals enables rapid response to current changes, while the low-pass filter for DC signals provides stable baseline measurement. The sensor fusion circuit dynamically combines these signals to achieve both speed and accuracy.
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 provides a compact, thermally resistant current sensor capable of accurately sensing both alternating and direct current components, including rapid changes, thereby improving longevity and reliability in high-temperature and high-frequency applications.
Implementation Method 1
an inductor for sensing an alternating current signal component of an observed signal
Implementation Method 2
a magnetic field sensor senses at least a direct current signal component of the observed signal
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A sensor (11) comprises an inductor (18) for sensing an alternating current signal component of an observed signal. The inductor (18) comprises a substrate, conductive traces associated with different layers of the substrate, and one or more conductive vias for interconnecting the plurality of conductive traces. A magnetic field sensor (20) senses a direct current signal component of the observed signal. A first filtering circuit (26) has a high-pass filter response. The first filtering circuit (26) is coupled to the inductor (18) to provide a filtered alternating current signal component. A second filtering circuit (28) has a low-pass filter response. The second filtering circuit (28) coupled to the magnetic field sensor (20) to provide a filtered direct current signal component. A sensor fusion circuit (30) determines an aggregate sensed current based on the filtered alternating current signal component and the filtered direct current signal component.