Novel coil arrangement of an integrated displacement sensor with reduced influence of suspension fluxes for a wide gap bearingless motor

Displacement sensors are necessary for bearingless motors and magnetic bearings. A sensor target ring is needed in a rotor shaft, thus, the axial length has to be extended. The shaft extension is considerable when a gap length is large because a wide gap sensor needs a large diameter in a sensor head coil. To solve this problem, search coils have been installed in a stator for rotor displacement estimation. However, there is the serious interference between suspension winding current and search coils. In this paper, the interference is theoretically and experimentally investigated. Two search coil connections are compared. Sensor output characteristics of one of the proposed connection are found to be effective in the interference elimination, even though suspension windings are driven by a three-phase inverter.