Comparative Study of Homopolar Inductor Machines with Different Rotor Structures for Flywheel Energy Storage System

In recent years, several novel homopolar inductor machine (HIM) topologies, such as rotors with the rectangular, arc-shaped, sinusoidal and triangle rotor slots, are developed. However, the influence of different rotor slots on the performance of HIM is not clear, and there is no basis for selecting rotor slots. Addressing this issue, a comprehensively comparative studies of these topologies with different rotor slot shapes are implemented. Firstly, the topology and operation principle of the HIM are illustrated. Then, the influences of rotor slot shape on the performance including the no-load air gap flux density, back electromotive force, inductance, torque, torque ripple and losses are systematically studied. Moreover, the stress distribution, modal and rotary inertia of rotor with four different rotor slots are analyzed. Based on the above analyses, the HIM with arc-shaped rotor slots is selected and its prototype is developed. Some electromagnetic performance indexes are tested to verify the rationality of analyses. This work clearly points out the advantages and disadvantages of HIMs with different rotor structures, which could be good reference for the selection of rotor slot shape.