Zhili Wang

The bearingless slice motor employed in ventricular assist devices must deliver not only ultra-clean operation but also exceptionally low speed fluctuations to ensure precise flow control. While feed-forward compensation for cogging torque within the vector control framework can mitigate these fluctuations, the predictive accuracy of such strategies is limited by existing analytical models. These models, which are grounded in conventional magnetic field modulation theory, often neglect the critical modulation effect of stator saturation, leading to significant errors. To address this gap, this article introduces a novel analytical method for cogging torque based on a synchronous rotation saturation modulation (SRSM) factor. First, the modulation mechanism of the SRSM factor is analyzed. Second, the air gap permeance was reconstructed by introducing the SRSM factor, allowing for the complete and accurate determination of the harmonic pairs that generate cogging torque, thus achieving accurate analysis of cogging torque. Finally, experiments are conducted to verify the effectiveness and correctness of the proposed analytical method.

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.