Unsaturated and saturated saliency trends in fractional-slot concentrated-winding interior permanent magnet machines

This paper presents an investigation of trends in the unsaturated and saturated magnetic saliency values of interior permanent magnet (IPM) synchronous machines with fractional-slot concentrated windings (FSCW). This paper investigates alternative slot-pole combinations for FSCW-IPM machines, highlighting the key observation that the saliency of these machines is generally lower than their counterpart IPM machines with conventional distributed windings. The relative merits and challenges of FSCW-IPM machines are examined, with a focus on the contribution of reluctance torque to the total machine torque. A key design metric that proves useful in this discussion is “unsaturated saliency ratio”, defined as the ratio L_q/L_d in the limiting case of near zero stator current and “saturated saliency ratio”, defined as the ratio L_q/L_d at high stator current. An important objective is to use this parameter to help machine designers choose the most appropriate slot-pole configuration for an FSCW-IPM machine in order to achieve the desired performance requirements.