Method of monitoring a health state of a power semiconductor device by monitoring inverter case temperature during steady state loading

A method of monitoring health of a power semiconductor device including an inverter connected to a power consuming device to supply power to the power consuming device from a power source, the inverter having a case on which a temperature sensor is provided, the method comprising:

• determining a steady state loading of the power semiconductor device where a load on the inverter is determined to be steady;
• when determine that the power semiconductor device is under the steady state loading, monitoring a case temperature parameter relating to a temperature of the case of the inverter detected by the temperature sensor over a predetermined period;
• deriving a normalized parameter by normalizing the monitored case temperature parameter over the predetermined period;
• and
• determining a health state of the power semiconductor device based on the normalized parameter.