Performance Assessment of a Hybrid Magnetic Bearing System for Rotary Centrifugal Blood Pump

Ren, Z., Hunsberger, A.Z., Jahanmir, S., Heshmat, H. and Walton II, J.F.  “Performance Assessment of a Hybrid Magnetic Bearing System for Rotary Centrifugal Blood Pump,” 54th Annual ASAIO Conference, June 19-21, 2008, San Francisco, California.

The performance of a proposed hybrid magnetic bearing system for a rotary blood pump is experimentally evaluated. The hybrid magnetic bearing system uses permanent magnets to provide passive radial support and electromagnetic coils to maintain rotor axial stability. The magnetic thrust bearing is actively controlled using a simple PID controller with zero-force balance algorithm. The proposed magnetic bearing system was fabricated and incorporated into a Left Ventricular Assist Device (LVAD). The performance of the hybrid magnetic bearing system with associated control algorithm was systematically evaluated under various operating conditions. Levitation tests were performed in air to ensure proper operation prior to closing the pump with the volute. The measured axial magnetic forces agreed with the predicted values. The zero-force balance system was also evaluated. The position reference in the closed loop control was continuously reset based on the feedback of electrical energy, thus using permanent magnets to carry all static loads and achieving zero-force balance. A current of less than 0.5 A was required for the bearing to operate. The closed prototype pump was then evaluated in vitro with a blood analogue and in vivo with an animal model. The results of both in vitro testing and in vivo animal studies demonstrated that the pump rotor can be completely levitated and spun up to the desired operating speed with low power loss and no mechanical contact.

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