Segregation of torque components in fractional-slot concentrated-winding interior PM machines using frozen permeability

Torque is produced in interior permanent magnet (IPM) machines as a result of stator current interactions with the rotor permanent magnets and rotor electromagnetic reluctance. Separation of the torque into its permanent magnet (PM) and reluctance components is helpful to machine designers but is complicated by the nonlinearity of magnetic saturation. This paper proposes a magnetic circuit model (MCM) to predict machine characteristics under frozen permeance conditions to help segregate machine torque components into PM and reluctance torques. Strengths and limitations of previously proposed techniques for performing this torque segregation are compared, including techniques based on finite element (FE) analysis. An alternative technique is proposed for delivering torque segregation results for fractional-slot concentrated-winding (FSCW) IPM machines that compares very well with the FE frozen permeability results but with significantly faster computation time. FE analysis is used to compare the characteristics of four alternative torque segregation techniques.