New Sensor Design for Rotor Displacement Measurement Based on the Coupled Oscillators Theory

Measurement of rotor position in bearingless motors and bearingless systems is of essence for proper operation. Insufficient resolution, sensor insensitivity and low sampling rate in measurement process leads unstable levitation and in worst case to the collision of rotor and stator which could end with motor destruction. Paper presents new concept for rotor position measurement based on Eddy current principle and Coupled oscillators theory in order to get accurate rotor position information. New concept is based on injection locking phenomena between coupled oscillators. Opposite pair of sensing oscillators are electrically coupled via resistor. In injection locking conditions phase shift between coupled oscillators is proportional to rotor movement. Phase shift was measured with Time to Digital Converter (TDC) and information is passed to Digital Signal Processor DSP over SPI communication link. DSP calculates the rotor position which is passed to power electronic circuit for rotor position control.