A 3-D Displacement Sensor System for Bearingless Motor Based on Hall Chip Array

In this paper, a three-dimensional displacement sensor system based on a Hall chip array and its signal-resolving algorithm is proposed for bearingless motors. The theoretical analysis of the magnetic field distribution around the cylindrical permanent magnet fixed on rotor is first provided. According to the mathematical model of the magnetic field, a sensor system based on a Hall array and its signal-resolving algorithm is proposed. The proposed sensor system can simultaneously measure the axial and radial displacements of a magnetically suspended rotor with a compact size and low cost. Additionally, due to the artfully designed sensor structure and its resolving algorithm, the proposed measurement scheme can minimize the impact of non-ideal characteristics of Hall chips on the X- and Y-axis displacement measurements, which is the most crucial for bearingless motors. To demonstrate the effectiveness of the proposed sensor system, the sensor system is compared with linear variable differential transformers (LVDTs) in steady states and eddy current sensors in dynamic states. A bearingless motor prototype equipped with the proposed sensor system is built to verify the proposed sensor system performance in a real bearingless motor. The experimental results prove that the proposed displacement sensor can accurately measure the displacement of the magnetically suspended rotor with high accuracy and good linearity.