Influence of Number of Turns Per Coil in Fractional-Slot PM Brushless Machines

An investigation of electromagnetic performance on fractional-slot PM Brushless Machines which slot-number and pole-number differs by one using 2-D finite-element analysis is presented. The investigation is motivated by the rise of Unbalanced Magnetic Force (UMF) resulted by asymmetric disposition of phase windings. It can be seen that a significant reduction of UMF is possibly achieved by employing uneven number of turns per coil. However, a slight reduction of torque performance exists which could be due to higher saturation on stator magnetic path at rated condition. It is also shown that the significant reduction of UMF is mainly due to the reduction of radial force density component while the tangential force density component remains unchanged.