A motor control system for controlling the speed of a threephase wound-rotor induction-type electric motor. Silicon controlled rectifiers are connected in circuit with the rotor windings of the motor for controlling the current flow therein. A control circuit is connected to the gate electrode of each of the silicon controlled rectifiers for firing same. These control circuits are responsive to the rotor winding voltages for determining the phase angles at which the silicon controlled rectifiers are fired. This control action acts to hold the motor speed constant under varying load conditions. Adjustable bias circuit means are connected to each of the control circuits for changing the basic operating speed of the motor.