Electromagnetic levitation control with sensorless large air gap detection for translational motion application using measured current-ripple slope

In this paper, sensorless magnetic levitation for large air gap translational motion is investigated. Most of the research in this field has been for magnetic bearings whose system characteristics and control requirements are different from a translational moving vehicle. An obvious difference is the range of operational air gap. Furthermore, the quality of magnetic materials, in terms of laminations, saturation, etc. used is also different. Therefore, well developed sensorless methods for magnetic bearings cannot be directly applied to large air gap applications. Thus, a novel method is proposed for detecting air gap by injecting high frequency signal into the magnetic coil and measuring either rising or falling current-ripple slope (single slope detection) using high speed sampler. Resistance is simultaneously estimated as well. Finally, stable levitation using the detected air gap signal as control feedback is demonstrated experimentally.

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