Permanent Magnet Stepper Motor
The stator of PMSM consists salient pole with concentrated winding the rotor of this type of stepper motor is generally taken as cylindrical pole type which is made of permanent magnets and hence this motor is called permanent magnet stepper motor.
Figure A -2 pole PMSM.
When phase A is excited with the stator produced poles attract the rotor permanent magnet poles so that their magnetic axes coincide N- pole attract the rotor aligns with the phase a pole on the left. The rotor turns through 900 when phase A is de energized and phase B is excited with current in. If the above currents made negative the direction of rotation will be opposite. The sequence of exciting the stator phase winding is A, B, A, B, A......for clockwise rotor movement.
PMSM has high detent torque higher torque per ampere of stator current higher inertia and lower torque to inertia ration, slower acceleration and response. The major disadvantage of PMSM is that they cannot be constructed with PM rotors with large number of poles and small steps are not possible.