In order to control the speed of the rotor of a three-phase, synchronous motor of a sinusoidal type (M) driving a yarn-winding drum (R) for feeding a yarn (F) to a user machine (MF) under a desired tension, the motor is controlled instant-by-instant as a function of the instant position of the rotor (θrif), which is calculated by integrating a reference speed value (ωrif) and deriving from the latter an excitation angular parameter for the motor.