PM reluctance motor with two-part rotor

This paper relates to the selection and design of synchronous motors for variable-frequency operation to achieve wide constant-power speed range by field weakening. By analogy to conventional DC machines, the term "field weakening" is used to describe a process by which speed increase with falling torque may be obtained above base speed, using phase advance of stator currents to reduce the effective d-axis flux and the corresponding EMF. A number of rotor types have been applied in this way: surface permanent-magnets; reluctance rotors; sunken, or inset, permanent-magnet rotors; and buried-magnet rotors.