Method and device for detecting a short circuit of a semiconductor switch element in an inverter for energizing an electric drive in an electric vehicle or hybrid vehicle; inverter comprising such a device

A method for detecting a short circuit of a semiconductor switch in an inverter that is designed to operate an electric drive in an electric vehicle or hybrid vehicle and comprises numerous semiconductor switches, wherein the semiconductor switches form a high side and a low side, wherein the high side and low side each comprise a plurality of semiconductor switches connected in parallel, wherein the high side and low side are connected in parallel to an intermediate circuit capacitor in the inverter, wherein the method comprises:

• measuring an intermediate circuit voltage at the intermediate circuit capacitor;
• determining an intermediate circuit capacitance in the intermediate circuit capacitor;
• determining a short circuit resistance in the inverter;
• setting a time constant from the intermediate circuit capacitance and the short circuit resistance by multiplying the intermediate circuit capacitance with the short circuit resistance;
• determining a change in the intermediate circuit voltage within the set time constant in order to calculate a speed of change;
• comparing the speed of change with a first threshold value;
• and
• determining that a short circuit of the semiconductor switch has occurred when the speed of change exceeds the first threshold value, and in response, switching the semiconductor switch off.