Protection of power semiconductor components

A method and a system for protecting the power semiconductor components used in the power stages of power electronics devices, such as frequency converters, wherein calculation modeling the degree of heating of the semiconductor junction of the power components (V11-V16) is used, wherein the degree of heating of the power components between the measurable outer surface or cooler and the internal semiconductor junction is determined on the basis of the dissipation power and a thermal network model of the component, wherein the temperature of the outer surface of the power component or the temperature of the cooler is measured, wherein the modeled temperature of the semiconductor junction is the sum of the measured temperature of the outer surface or cooler and the calculated degree of heating, and wherein, based on the modeled junction temperature, an alarm is issued or some other protective action is taken. In the method, the temperature of the semiconductor junction is calculated in real time, at least at time intervals equal to the shortest time constant in the thermal network model, on the basis of the heating caused by the dissipation power pulse produced during each current conduction cycle.