A Study on Improving Superconducting Machine Performance by Focusing on End Windings

The current topology for superconducting machines aligns the effective stator length with the straight section of the rotor racetrack magnet, resulting in wasted superconducting material at the magnet's ends. Moreover, the ends of the superconducting magnet produce a substantial magnetic field, resulting in significant electromagnetic forces on the stator winding ends under rated operating conditions. This paper comprehensively analyzes and addresses the above issues in superconducting machines by proposing two improved stator end structures. Firstly, the difference between non-superconducting and superconducting machines on the stator side electromagnetic force is summarized by theoretical analysis. Then, based on the H-formulation, a three-dimensional numerical model reveals that the minimum critical current in traditional superconducting machines occurs at the end of the racetrack winding's straight section. The improved design in this paper increases it effectively. Moreover, it is demonstrated that without any modification of the high price of superconducting materials employed for the rotor, the output power of the proposed two structures can be effectively increased by 11.3% and 25.9%, respectively, while minimizing electromagnetic force at the stator end winding. A comprehensive comparison of the two proposed design modifications indicates that extending the stator's effective length and incorporating partial magnetic teeth at its ends is the more advantageous strategy. Finally, the experiment indicates that the proposed structure in this study enhances the critical current and mitigates the issue of stator end electromagnetic force.