Patent ID: 8222856

Claim:
A control system (CS), without position sensors, for a synchronous, rotary electric motor (M), comprising: an electronic switch (TR) operatively connected in series with a stator winding (W) of the motor (M) between a first terminal and a second terminal (A, B) which are intended to be connected to a supply of an alternating voltage (V), first detector means suitable for providing an electrical signal (Vzc) indicative of the sign and of the zero-crossings of the alternating supply voltage (V), second detector means suitable for providing signals indicative of the sign and of the zero-crossings of the back-electromotive force which is developed in the stator winding (W) in operation, and control means (MC) connected to the electronic switch (TR) and to the first and second detector means and arranged to bring about the starting of the rotation of the rotor (R), starting from a predetermined initial position (θ 0 ), in accordance with a procedure comprising the steps of: a) driving the electronic switch (TR) in a manner such as to bring about the passage through the stator winding (W) of a first current pulse (I 1 ) which starts with a first predetermined delay (t 1 ) relative to the immediately preceding zero-crossing of the supply voltage (V), b) checking if the back-electromotive force (E) consequently developed in the stator winding (W) has a first zero-crossing within a predetermined period of time (T) which immediately precedes the third zero-crossing of the supply voltage (V) after the start of the first current pulse (I 1 ), c) when the above-mentioned check provides a positive outcome, driving the electronic switch (TR) in a manner such as to bring about the passage through the stator winding (W) of a second current pulse (I 2 ) of opposite sign or direction to the first (I 1 ), with a second predetermined delay (t 2 ) relative to the third zero-crossing of the supply voltage (V), and then supplying to the winding (W) a voltage at the frequency of the supply, and d) when the check provides a negative outcome, repeating the procedure of step a) given above from the beginning, reducing the duration of the first delay (t 1 ) if the first zero-crossing of the back-electromotive force (E) took place after the period of time (T), and increasing the duration of the first delay (t 1 ) if the first zero-crossing of the back-electromotive force (E) took place before the period of time (T).