Patent ID: 8238131

Claim:
A method in connection with a frequency converter, the frequency converter being arranged for periodic recurrent use, wherein the method comprises steps of: determining and storing in a memory a magnitude of an average temperature rise of a power semiconductor in the frequency converter, caused by one loading period; determining a temperature limit from the determined temperature rise and a highest allowed temperature of the power semiconductor; determining the temperature of the power semiconductor in the frequency converter; and changing the operation mode of the frequency converter by reducing a torque limit on-line when the temperature of the power semiconductor exceeds the temperature limit when transferring to a loading period, wherein the determining of the magnitude of the average temperature rise caused by one loading period comprises: (i) determining the magnitude of the temperature before the start of the loading period; (ii) determining the magnitude of the temperature after the loading period; (iii) calculating the difference of the determined temperatures; and (iv) repeating steps (i)-(iii) and calculating the mean of the differences of the determined temperatures.