Minkyun Noh, Wolfgang Gruber, David L. Trumper,
"Low-cost Eddy-current Position Sensing for Bearingless Motor Suspension Control"
: IEEE International Electric Machines and Drives Conference 2017, Miami, USA, 5-2017
Low-cost Eddy-current Position Sensing for Bearingless Motor Suspension Control
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IEEE International Electric Machines and Drives Conference 2017, Miami, USA
We present a low-cost position sensing module based on a commercial Inductance-to-Digital Converter (LDC) that is applied to bearingless motor suspension control. The sensing module uses four LDC evaluation boards to differentially measure the x- and y-positions of the rotor. Each of the evaluation boards consists of an LDC chip, a sensing coil, and an on-board capacitor. The LDC chip drives the sensing coil and the capacitor to their resonance, and streams out the instantaneous frequency values. As a conductive target approaches the sensing coil, the apparent inductance of the coil decreases due to the induced eddy-current, thereby increasing the resonance frequency. This frequency shift can be used for estimating the distance to the target. The sensing module exhibits a position resolution of 0.37 micrometers with the standard deviation of 0.31 micrometers at a
sampling rate of 2 kH. We have implemented this sensing module to our homopolar-biased hysteresis bearingless slice motor that drives a ring-shaped rotor made of D2 steel.