Pulse turn-off method for starting of PMSM drive using back-emf position estimation technique

A new technique for change over from I-f method for starting to emf based sensorless vector control for normal operation of a PMSM drive is discussed in this paper. In I-f method, stator frequency is ramped up in a limited current operation. The sensorless control is implemented using a modified stator voltage integration method. When the machine picks up enough speed with I-f starting, a smooth transition to sensorless mode is performed with the proposed 'Pulse turn-off method'. Rotor position required for the transition is estimated by measuring the terminal voltage of the motor, which would be same as the back emf when the inverter switching pulses are off. The proposed method is validated experimentally.