System for controlling a synchronous electric motor

A control system included in a variable speed drive connected by output phases to a synchronous electric motor, the synchronous electric motor being controlled according to a control law implemented by the variable speed drive, a first speed of the synchronous electric motor being determined by a first speed estimator, the system comprising:

• a second speed estimator configured to determine a second speed of the synchronous electric motor;
• and
• a signal-generating module configured to generate a non-constant signal in terms of estimation current which gets added to a reference flux current to create a corrected reference flux current which is applied as an input to the control law, the control law being executed to determine voltages to be applied to the output phases;
• the second estimator configured to recover a response in terms of current on the output phases, to deduce therefrom the second speed of the synchronous electric motor.