The control circuit keeps the SCR-1 from firing until the induced field current frequency is very low, representing a close approach to synchronous speed, and then fires the rectifier SCR-1 at the proper time and applies excitation to the synchronous motor field. At the same time, the field discharge resistor is removed from the circuit. This is done by the inherent operating characteristics of silicon controlled rectifier SCR-2. This frequency sensitive part of the control circuit assures that field excitation is applied at the proper pull-in speed for successful synchronizing and at the proper polarity to give maximum pull-in torque with minimum line disturbance