Analysis of Fractional-Slot Concentrated Winding PM Vernier Machines With Regular Open-Slot Stators

Permanent magnet (PM) vernier (PMV) machines have been extensively researched for direct-drive applications due to their inherently high torque density. This paper presents a quantitative investigation on fractional-slot concentrated winding PMV (FSCW-PMV) machines with regular open-slot stator topology. Based on winding theory, the configuration of two winding types, i.e., nonoverlapping winding and FSCW with two-slot coil pitch are analytically derived for PMV machines, respectively. Through finite element analysis, comparative study of FSCW-PMV machines, regular integral slot winding PMV machines, and regular PM machines are performed. It is found that the flux modulation effect also exists in regular nonoverlapping winding PM machines. In other words, the regular nonoverlapping winding PM machine also belongs to the PMV machine family. The PMV machine with two-slot coil pitch is newly proposed, and turns out to be a promising PMV machine topology with competitive torque capability and power factor. Finally, a prototype of 18-slot, 14-rotor pole pair, and 4-stator pole pair PMV machine with two-slot coil pitch is built. Experimental results show that the torque density of the prototype can reach 20.0 kNm/m3 and the power factor is 0.91.