Comparison of interior and surface permanent magnet machines with fractional slot concentrated windings for direct-drive wind generators

Large scale of wind generators is one of important methods to reduce the cost of the wind power system, and has been the growing trend of wind power market in recent years. In this paper, design strategies for large-scale permanent magnet (PM) generators with surface mounted PM (SPM) and V-shaped interior PM (IPM-V) are introduced. Since the weight and cost are the reference points for large-scale generators, influences of design parameters, such as pole number, magnet thickness, and yoke thickness, on total weights and costs are investigated. With the advantages of short end-windings and high torque density, fractional-slot concentrated windings (FSCWs) are adopted. Since the design parameters of the IPM generator are more than that of the SPM generator, the design flows of the IPM generator are also more complicated. Moreover, the performance of the optimal SPM and IPM wind generators with FSCWs are investigated respectively and compared, including flux density, back-electromotive force (EMF), power factor, torque density, torque ripple and losses. The capacities of anti-demagnetization of machines with both rotor types are also analyzed. Finite element analysis (FEA) is carried out in this paper to analyze and compare these performances.