Abstract: The present invention relates to a method and an apparatus for controlling an electric motor by regulating at least the current Iout, the voltage Uout and the frequency fout to an input of said motor, where the number of revolutions of said electric motor is proportional to said frequency fout. If an available power Pin from an energy source is greater than or equal to the nominal requested power Pnom of said electric motor, the current Iout, voltage Uout and frequency fout are set to there corresponding nominal values Inom, Unom and fnom, respectively, to achieve said requested power Pnom and frequency fnom. If said available power Pin is less than the requester power Pnom, the voltage Uout and the frequency fout are reduced such that the relation between the voltage Uout and the frequency fout is essentially constant while said current Iout is kept at its nominal value Inom.

Abstract: A method and device (18) to control the temperature T in a refrigerator or freezer cabinet (10), which keep a set temperature in a space (12) in the cabinet. The space is refrigerated by an element (14) of an intermittently operating refrigerating machine (16). The refrigerator cabinet has a control gear (18), which consists of a first means (20) and a second means (22), a third means (24) and a fourth means (26). The first means is situated at the refrigerating element, which is placed in the space, and it measures a regulating temperature. The second means is arranged at a reference point in the space, and it measures a current temperature in the space. The third means compiles an average temperature of the current temperatures. The forth means compiles a discrepancy between the average temperature and a preset temperature.