Abstract: A method and apparatus for connecting a converter to an asynchronous machine whose rotor is rotating with respect to the stator before and/or during the connection at some unknown rotation speed is disclosed. According to the present invention, a current is forced to flow, a rotor flux model vector and a stator current model vector are calculated as a function of a stator voltage and of an estimated rotation speed value. An error (e) is determined as a function of these calculated values and of a determined actual stator current vector, and the estimated rotation speed value is changed in such a manner that the determined error turns to zero. A method and apparatus are thus obtained for connecting a converter to an asynchronous machine, with the estimated rotation speed value converging in a very short time, starting from an initial value, to the actual mechanical rotation speed.