Method for monitoring the starting of a three-phase synchronous motor with no commutator, said motor comprising: - a stator comprising teeth around which coils are wound, defining three electric phases (U, V, W), the supply of which defines a direction and a course of the polarisation of the stator, - a rotor disposed concentrically and facing the stator, said rotor comprising at least one pair of magnetic poles defining a magnetic polarisation of the rotor, and - an electronic board comprising a controller arranged to adjust the switching of the current in the different phases of the stator so as to define a variable direction of magnetic polarisation of the stator adapted to rotate the rotor, - one single position sensor of the logical type disposed on the bisector between two teeth of the stator and intended to deliver a signal to the controller, said signal comprising information on: - a course of magnetic polarisation of the rotor, and - a tilt instant of a course of magnetic polarisation from the rotor to another during the rotation of the rotor, said method comprising a step of aligning the direction and the course of the magnetic polarisation of the rotor with an alignment position defined by the direction and the course of the polarisation of the stator determined according to the information read from the position sensor relating to the course of the magnetic polarisation of the rotor, said method being characterised in that the alignment step has: - a duration at the end of which from any starting position of the rotor, the rotor is theoretically aligned for the first time with the alignment position, or - a duration at the end of which from any starting position of the rotor, the amplitude of the oscillations of the rotor around the alignment position is theoretically less than a predetermined threshold, or - a duration at the end of which the amplitude of the oscillations of the rotor for a theoretical starting position most distant from the alignment position is theoretically in a predetermined interval, or - a duration at the end of which from any starting position of the rotor, the speed of the rotor around the alignment position is theoretically less than a predetermined threshold, at least one of these theoretical durations being informed in a memory connected to the controller, these theoretical durations being deducted from a theoretical model of the oscillatory behaviour of the rotor around the alignment position of the rotor for different starting positions of the rotor. - a stator comprising teeth around which coils are wound, defining three electric phases (U, V, W), the supply of which defines a direction and a course of the polarisation of the stator, - a rotor disposed concentrically and facing the stator, said rotor comprising at least one pair of magnetic poles defining a magnetic polarisation of the rotor, and - an electronic board comprising a controller arranged to adjust the switching of the current in the different phases of the stator so as to define a variable direction of magnetic polarisation of the stator adapted to rotate the rotor, - one single position sensor of the logical type disposed on the bisector between two teeth of the stator and intended to deliver a signal to the controller, said signal comprising information on: - a course of magnetic polarisation of the rotor, and - a tilt instant of a course of magnetic polarisation from the rotor to another during the rotation of the rotor, - a course of magnetic polarisation of the rotor, and - a tilt instant of a course of magnetic polarisation from the rotor to another during the rotation of the rotor, - a duration at the end of which from any starting position of the rotor, the rotor is theoretically aligned for the first time with the alignment position, or - a duration at the end of which from any starting position of the rotor, the amplitude of the oscillations of the rotor around the alignment position is theoretically less than a predetermined threshold, or - a duration at the end of which the amplitude of the oscillations of the rotor for a theoretical starting position most distant from the alignment position is theoretically in a predetermined interval, or - a duration at the end of which from any starting position of the rotor, the speed of the rotor around the alignment position is theoretically less than a predetermined threshold,