Performance Evaluation and Comparison of Three-Phase and Six-Phase Winding in Ultrahigh-Speed Machine for High-Power Application

This article investigates the influence of multiphase winding topologies in high-power ultrahigh-speed machines (HP-UHSM) of 500 kr/min. At this speed level, increasing the rotor's magnetic loading excites its critical bending resonances and leads to structural breakdown. On the other hand, increasing the stator's electric loading using the three-phase winding increases unwanted vibrations in a slotted stator and reduces the electromagnetic interaction of the stator and rotor in a slotless stator. Consequently, the maximum output power level of UHSM (500 kr/min or more) is limited to a few hundred watts only in the state-of-the-art. To over-come such a critical limitation, this article proposes a new design methodology for HP-UHSM, where the rotor's bending resonances and centrifugal stresses are restricted by limiting the maximum aspect ratio (L/D), and an optimal multiphase winding is adopted in the slotless stator to increase the power level by effective electric loading. Also, a multiphysics optimization is utilized to obtain the optimum magnetic loading and electric loading, where the bending resonance and other system limits are defined using multidisciplinary design constraints. It is observed that the multiphase winding provides an added degree of freedom to increase the power level of UHSM without exciting the rotor's bending resonances and structural breakdown. Using the proposed method, a multiphase 2 kW 500 kr/min HP-UHSM has been designed for the safety-critical AMEBA system and compared its multiphysics performance with the three-phase machine having the same volume. Finally, extensive experiments are performed on both prototypes to validate the effectiveness of the proposed method. It is shown that the multiphase HP-UHSM has no critical bending resonance below the 500 kr/min, and it has 16.3% higher output power with 1.18% higher efficiency and 28.6% lower back-EMF than the three-phase design.