Patent ID: 8087259

Claim:
A system for controlling an electric power supply from an electric power source which can be connected to an electric motor ( 12 ) through a control unit ( 11 ), wherein the electric motor ( 12 ) can in turn be connected to a compression means ( 13 ), said system comprising: means for detecting a voltage of the electric power source; means for predetermining a desired operating speed of the electric motor ( 12 ); means for calculating a voltage signal which must be applied to windings of the electric motor ( 12 ) to reach the predetermined desired operating speed; and a PWM pulse width regulator ( 16 ) generating switching signals relating to the calculated voltage signal, to be applied to each of switching elements included in the control unit ( 11 ), so that the motor ( 12 ) reaches the desired operating speed, wherein the control unit ( 11 ) further includes energy conversion means ( 14 ) receiving energy from the electric power source, and the energy conversion means ( 14 ) comprise a switching element which is in a permanent cutoff mode when the voltage level demanded by the electric motor ( 12 ) is lower than or equal to the voltage level of the electric power source and in a modulation mode when the voltage level demanded by the electric motor ( 12 ) is greater than the voltage level of the electric power source.