Air-Core Current Sensor Design for Thermal Stress Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing current sensors for electric motors fail due to poor resistance to thermal stress, occupy excessive volume, and fail to respond to rapid current changes, leading to inaccurate sensing and reduced longevity.
Innovation Solution
A compact current sensor design incorporating a Time Varying Flux Sensor (TVFS) coil and a Hall Effect sensor, with a ferrite structure to attenuate stray electromagnetic signals, allowing for accurate measurement of both alternating and direct current components without a ferromagnetic core, thus avoiding thermal heating issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ferromagnetic core is used in the sensor, then the sensor can measure current effectively, but self-heating from eddy currents and hysteresis losses causes thermal stress and premature failure
Solution Approach 1:
The patent removes the ferromagnetic core from the sensor design, extracting the source of thermal stress (eddy currents and hysteresis losses) while maintaining current sensing capability through alternative means (air-core inductor and Hall effect sensor combination)
Solution Approach 2:
The patent changes the material parameter from ferromagnetic to non-magnetic (air core), fundamentally altering the thermal and magnetic properties of the sensor to eliminate self-heating issues while preserving sensing function
2Volume of stationary object
If the sensor is designed to be compact, then the volume is reduced, but it becomes difficult to effectively address thermal stress while maintaining circuit density
Solution Approach 1:
By removing the ferromagnetic core, the patent eliminates the primary heat-generating component, allowing for a compact design that inherently addresses thermal stress without requiring additional cooling or spacing mechanisms
3Reliability
If the sensor uses traditional design, then it can measure current, but it fails to respond appropriately to rapid changes in current such as sudden short circuits
Solution Approach 1:
The patent divides the sensing function into two separate components: an air-core inductor for detecting rapid current changes (high-frequency component) and a Hall effect sensor for measuring steady-state current (low-frequency component), with each component optimized for its specific function
Solution Approach 2:
The patent implements dynamic response by using an air-core inductor that naturally responds to rapid current changes due to its low inductance and lack of magnetic saturation, enabling the sensor to track fast transient events
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 sensor provides reliable and accurate current measurement across a wide frequency range and temperature range, with a compact footprint, effectively addressing thermal stress and rapid current change detection limitations.
Implementation Method 1
an inductor for sensing an alternating current signal component of an observed signal in a conductor
Implementation Method 2
a Hall Effect sensor to sense a direct current signal component of the observed signal in the conductor
Implementation Method 3
with a ferrite structure to attenuate stray electromagnetic signals
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A sensor comprises primary ferrite members (362) spaced apart from the magnetic field sensor (20) on opposite sides of the magnetic field sensor to concentrate or steer an orientation of a magnetic field of the observed signal toward a target area (409) of the magnetic field sensor (20). A magnetic field sensor (20) senses a direct current signal component or lower frequency component of the observed signal. A first filtering circuit has a high-pass filter response. The first filtering circuit is coupled to the inductor to provide a filtered alternating current signal component. A second filtering circuit has a low-pass filter response. The second filtering circuit coupled to the magnetic field sensor to provide a filtered direct current signal component. A sensor fusion circuit determines an aggregate sensed current based on the filtered alternating current signal component and the filtered direct current signal component.