Permanent magnet excited synchronous motors

FRACTIONAL-HORSEPOWER synchronous motors are generally available for quantity production in only the reluctance or hysteresis types. The reasons for this are: the simplicity of their rotor constructions, because of the omission of d-c excitation; and the possibility of assembling the rotors of either type in standard induction motor frames. Unfortunately, these advantages are offset by inferior performance characteristics, such as low efficiency, low-power factor, and low output, when compared to that of the same size induction motor. The locked rotor torque is also low and in the reluctance type, extremely variable.