Analysis of impact of air-gap length and superconducting coil-to-stator distance in superconducting vernier machines

This paper investigates the influence of air-gap length ( lag ) and the distance between the superconducting coil and the stator ( lsc ) on the electromagnetic performance of a conventional Superconducting Machine (SCM) and a Superconducting Vernier Machine (SCVM). Both machines are partially superconducting (only rotor field windings are superconducting) and use iron stator and iron rotor (ISIR) topologies. They are designed for offshore wind power applications at a 10 MW power level. Key performance metrics—including cogging torque, induced EMF, air-gap flux density, average torque, torque ripple, efficiency, power factor and inductance are compared with respect to variations in lag and lsc . The finite element results show that the SCVM’s modulation effect is influenced by both lag and lsc . This modulation effect leads to increased average torque, reduced cogging torque and torque ripple compared with the conventional SCM. In contrast, for the conventional SCM, the electromagnetic performance is mainly influenced by lag . Moreover, the study indicates that the modulation effect of lag on SCVM is not only due to the fundamental component ( BPr ) but also other harmonics components, whereas the modulation effect of lsc is only due to BPr .