To solve the problem of detuning due to parameter variations in the current decoupled control of a direct stator-flux-oriented induction motor (IM) drive, two approaches for the rotor time-constant estimation are presented in this study. The first approach is based on the model reference adaptive system (MRAS) using an energy function, and the second approach is based on the sliding mode technique. The estimated rotor time-constant is used in the current decoupled controller, which is designed to decouple the torque and flux in the stator flux field-oriented control. To increase the accuracy of the estimated rotor time-constant, the estimation methods are implemented using a digital signal processor (DSP). The effectiveness of the proposed estimation methods are demonstrated by some simulation and experimental results.