The Eddy-Current Sensor-Free Control for a Bearingless Slice Motor With the PM’s Third Harmonic

Eddy-current sensor-free control based on reusing Hall sensors of a bearingless slice motor system can reduce the volume, cost, weight, and the impact of shear on transmitted liquid. However, the algorithm will fail in the presence of the PM’s third harmonic. Hence, this article presents the eddy-current sensor-free control algorithm based on the two negative sequence coordinate transformation in parallel with different frequencies (TNSPDF). The random and disordered signal in the Hall output is modulated into asymmetrical component about the displacement vector angle through negative sequence coordinate transformation at different electrical frequencies, achieving decoupling between the displacement vector angle and the motor electrical frequency. The interference signal does not lead to any pulsation in the estimated displacement; rather, it evolves into a significant coefficient for the purpose of displacement identification. The validity and effectiveness of the proposed method are verified through experiments on a bearingless permanent magnet slice motor system.