Synchronous motor startup configuration to synchronous mode at a field zero-crossing

A method of monitoring a start of a multi-phase electric motor, comprising:

• obtaining stator phase current signals from each phase of current supplied to a stator of the multi-phase electric motor;
• calculating a representative current from the stator phase current signals;
• calculating a frequency of the representative current;
• inducing current asymmetry in the representative current using an asymmetry inducing module of a rotor of the multi-phase electric motor;
• detecting the current asymmetry in the representative current;
• calculating a zero crossing of a voltage of field windings of the rotor using the detected current asymmetry;
• and
• controlling a configuration of the motor from induction mode to synchronous mode when the frequency of the representative current falls below a threshold and the zero crossing is detected;
• by connecting a direct-current power source to the field windings of the rotor of the motor.

A system for starting a multi-phase electric motor, comprising:

• a stator of the multi-phase electric motor, comprising multi-phase current inputs;
• a rotor of the multi-phase electric motor, comprising:
• a field winding configurable between induction mode and synchronous mode;
• and
• a switching device for selectively connecting a current asymmetry inducing module with the field winding;
• and;
• an intelligent electronic device (IED) in communication with the multi-phase current inputs and the switching device, the apparatus configured to:
• obtain stator phase current signals from the multi-phase current inputs;
• calculate a representative current from the stator phase current signals;
• calculate a frequency of the representative current;
• detect current asymmetry induced on the stator phase current signals by the current asymmetry inducing module;
• calculate a zero crossing of a voltage of field windings of the rotor using the detected current asymmetry;
• and
• control a configuration of the motor from the induction mode to the synchronous mode when the frequency of the representative current falls below a threshold and the zero crossing is detected.