A Novel Heteropolar Bearingless Slice Motor With a PM-Free Rotor for Centrifugal Blood Pump Applications

We present a novel heteropolar bearingless slice motor (BELSM) with a PM-free rotor for a disposable centrifugal blood pump. The new motor adopts a triple-layer biased heteropolar magnetic field in the air gap, including two-layer sliced magnetic coupling generated by multipole ring magnets and a one-layer motor field. The biased motor field is induced by the PM sandwiched between the stator teeth and yoke for generating torque and the suspension force. Due to the unique triple-layer biased field, the motor possesses high passive stiffness in the axial and tilt directions. Additionally, a high torque density is achieved due to the biased heteropolar field induced by the permanent magnet, which allows bipolar current injection. As a result, the motor can transmit a greater amount of electromagnetic energy through the air gap. Thus, the motor achieves both a high torque density and high passive stiffness. Furthermore, the presence of a stationary biased flux enables the regulation of the suspension force generation to be independent of the rotor angle. This decoupling of the rotational and suspension control enables separate and simplified control strategies for the motor operation. FEA simulations were conducted to estimate the torque density and the passive stiffness of the BELSM. The results of the simulation were validated by tests on a prototype.