Process and an apparatus for controlling an electric motor

A process for controlling an electric motor supplied with a voltage, the process comprising the steps of

• a) providing a functional relationship, which associates a first and a second quantity of actual torque delivered by the electric motor and of said voltage respectively, with a speed parameter of the electric motor, wherein the speed parameter is a limit output speed associated with mechanical characteristics unique to the electric motor, wherein the speed parameter increases with the second quantity according to said functional relationship,
• b) determining a pair of values of the first and of the second quantity in association with a current time instant,
• c) determining a value of a third quantity in association with the current time instant, wherein the third quantity is indicative of an output speed of the electric motor,
• d) determining a value of the speed parameter corresponding to said pair of values through the functional relationship,
• e) determining a value of a fourth quantity indicative of a difference between the value of the speed parameter and the value of the third quantity,
• f) determining a target value for the first quantity in association with the current time instant as a function of the value of the fourth quantity, and
• g) controlling the electric motor according to the determined target value such that the output speed of the electric motor does not exceed the limit output speed, wherein exceeding the limit output speed causes the electric motor to operate uncontrollably.