Initial Rotor Position Determination of a Soft Starter Driven Synchronous Motor

Abstract:
When connecting a permanent-magnet synchronousmachine directly to the line supply, a soft starter is needed for starting. The initial rotor position must be known when starting without a sensor. This paper describes a method to determine and verify the initial position. It is based on a pulsating current space vector in a predefined direction. During the motor’s orientation, the phase currents are utilised to monitor the correctness of the procedure. Measurements with different motors confirm the potential of the described method where motors not equipped with a sensor can be started using a soft starter.