A controller continually updates rotor time constant estimation of an induction machine by interrogating the induction machine with a small signal oscillation and monitoring the response. The small signal oscillation is injected onto the d-axis current command signal, and is generated at a frequency that represents the most recent estimate of the rotor time constant (i.e., rotor time constant equal the inverse of the frequency). The controller monitors rotor flux generated in response to the small signal oscillation, and updates the most recent estimate of the rotor time constant based on the monitored rotor flux. This process is repeated continuously to allow for the continuous updating of the rotor time constant.