Stator temperature estimation of open-loop controlled induction machines via active DC voltage injection

Thermal conditioning is a key component in the lifespan and efficiency of an induction machine, and appropriate thermal monitoring methods could help lengthen the lifetime of induction machines. The installation and purchase of potentially expensive and perishable temperature sensors are not the best option for manufacturers and businesses in today´s competitive market. This paper thus proposes a non-intrusive method for thermal estimation of induction motors operating under open-loop controlled systems widely used in industry. By superimposing dc values onto the three-phase voltage commands, the dc signal is injected into the stator windings of the induction machine. The stator winding temperature could thus be estimated upon the extraction of a dc resistance. This method is efficient and non-intrusive because it does not disturb the normal operations of the induction motor, nor does it involve any hardware changes. Also, this method is time efficient because the resistance and temperature estimations can be calculated within seconds after the injection has been made. The effectiveness of the proposed method is illustrated by simulations conducted under various motor conditions.