A nonintrusive thermal monitoring method for closed-loop drive-fed induction machines

Closed-loop induction motor drives have wide applications in electric traction system and industrial processes. Accurate thermal monitoring not only protects the induction machines from overheating, but also boosts the usage and performance of the overall drive system. State-of-the-art thermal monitoring scheme for induction machines utilize simple thermal models, which is generally far too conservative. This paper proposes a nonintrusive thermal monitoring scheme for induction motors fed by closed-loop inverter drives. By applying an offset to the controllers in the motor drive, DC currents can be injected into the stator windings of the machine. The stator winding temperature can thus be monitored based on the estimated DC stator resistance. The method is nonintrusive because it eliminates the thermocouples and requires no hardware change to the existing motor drive. This proposed method is validated both by simulation and real-time experimental results.