Torque Analysis in an Alternating Flux-Barrier Permanent Magnet Vernier Machine

The Alternating Flux-Barrier Permanent Magnet Vernier Machine (AFBPMVM) is one of the promising topologies for low-speed direct-drive applications such as wind power generation. It was specially designed to mitigate the ‘flux-barrier’ effect which effectively offsets the benefits of flux-focusing associated with a spoke-type permanent magnet configuration. In previous studies, the improved torque capability of the AFBPMVM has been documented and has largely been attributed to the enhanced magnitude of the so-called effective (modulated) harmonic. However, the topology suffers from severe armature reaction and saturation effects. Consequently, there is a large discrepancy between the percentage increase in effective magnetic loading and the corresponding average torque. This paper presents an-depth analysis of the torque improvement mechanism from the perspective of radial and tangential airgap flux density components. It is revealed that the enhanced flux modulation effect in the AFBPMVM improves the contribution of the fundamental and its odd multiples, as well as several slot harmonics to the average torque. The analysis presented in this paper is validated using 2D Finite Element Analysis (FEA).