Method of starting a synchronous motor with a brushless dc exciter

A method of controlling startup of a synchronous motor having a brushless direct current exciter, comprising:

• using a variable frequency drive controller to deliver an initial magnetizing current to a stator of the motor and a field current to the exciter;
• holding the field current at a maximum permissible exciter stator current level for a time period;
• after a magnetizing state period, applying a torque current such that a rotor of the motor begins to rotate;
• increasing the torque current and motor speed to a predetermined level;
• when the torque current reaches the predetermined level, holding the torque current and motor speed at that level for a flux dwell time period;
• after a time period set by a phase-locked loop, closing a speed loop to regulate the torque current, thereby initiating a transition to operating the motor synchronously;
• closing a flux loop to reduce the magnetizing current to zero and to regulate the field current;
• and
• operating the motor as a synchronous motor.