An Axial Gap Type self-bearing Motor with Separated Winding for An Implantable Maglev Pediatric Ventricular Assist Device

Magnetically levitated motors have been applied as non-contact impeller suspension mechanisms in adult ventricular assist devices (VADs), indicating excellent blood compatibility. Recently, application of magnetic levitation in implantable pediatric VADs has been studied. However, miniaturization for small pediatric patients is difficult due to requirements of magnetic core shape, permanent magnet design, and winding arrangement in limited space. Therefore, magnetically levitated pediatric VADs are not clinically available yet. We have developed a self-bearing motor with an outer diameter of 22 mm and height of 43 mm using two 6-slot 4-pole permanent magnet synchronous motors for pediatric VADs. In previous research, an integrated winding was used for magnetic suspension and rotation, achieving non-contact impeller suspension. This configuration has high magnetomotive force but requires 12 windings excited independently by single-phase PWM current amplifiers, increasing size and power cable diameter. In this study, two insulated windings are arranged for each stator slot to construct a separated winding motor with two three-phase windings. Using four three-phase inverters, the total number of wires is reduced to 12. One winding is excited with four-pole control current, and the other with two-pole control current. The effect of this winding configuration on magnetic suspension stability was investigated. In this paper, the current control characteristics of the fabricated three-phase inverter are evaluated, and magnetic levitation tests are conducted using the separated winding motor and the three-phase inverter, The three-phase inverter has a bandwidth of 700 Hz. A maglev centrifugal blood pump with the separated winding motor was constructed and tested in a closed loop circulation circuit. Axial oscillation amplitude was suppressed within 0.06 mm, and inclination amplitude was less than 0.7 degrees. Non-contact suspension was achieved at all operating points. Future work will optimize the turns ratio of separated windings to enhance magnetic suspension performance and energy efficiency.