THERMISCHES SCHUTZVERFAHREN FÜR LEISTUNGSEINRICHTUNG IN EINEM FREQUENZUMRICHTER

A method for thermal protection of a frequency converter and a frequency converter that comprises means for controlling the output current of the frequency converter. The method comprises the steps of determining beforehand two or more data points ( I sw1, T sink1 , I sw1, T sink2 , I sw1, T sink3 ) which define a thermal current limit for a semiconductor component of the frequency converter at specific temperatures ( T sink1 , T sink2 , T sink3 ) at two or more switching frequencies ( f sw1 , f sw2 , f sw3 ), determining beforehand two or more data points ( I f out, 0, T sink1 , I f out, 0, T sink2 , I f out, 0, T sink3 ) which define a thermal current limit for the semiconductor component at specific temperatures ( T sink1 , T sink2 , T sink3 ) at a zero converter output frequency, measuring the temperature ( T sink ) of the semiconductor component, determining the switching frequency ( f sw ) of the frequency converter, determining the output frequency ( f out ) of the frequency converter, determining the highest allowable thermal current ( I th ) as a function of measured temperature ( T sink ), determined switching frequency ( f sw ) and determined output frequency ( f out ) on the basis of the defined data points, and limiting the output current of the frequency converter to the determined highest allowable thermal current ( I th ).