Junction temperature and switching frequency prediction in direct torque controlled induction motor drives

This paper presents a new, accurate and simple calculation method to determine the switching frequency as well as semiconductor losses and junction temperatures in direct torque controlled induction motor drives. Instantaneous values of the switching frequency, semiconductor losses and junction temperature can be obtained on the basis of mechanical operating point data and the stator flux vector location. The proposed scheme substantially simplifies the thermal design of power semiconductors and cooling components in these drives by the avoidance of extensive and time consuming simulations and measurements. A comparison to precise simulations taking into account the semiconductor losses shows that the calculated junction temperature deviates from its real values by less than 2 degC. The scheme is verified by experimental investigations of a 44 kW induction motor drive.