Torque based model reference adaptive system updating rotor time constant in induction motor drives

Electromagnetic torque can be used to form a model reference adaptive system (MRAS) to achieve online identification of rotor time constant in an induction motor drive. The steady-state torque error caused by rotor time constant error is established in this paper. Based on the steady-state analysis, the converging relationship in the MRAS is found out to be lost for some operating points. Then the torque based adaptive scheme is further derived with Lyapunov theorem and the limitation of the scheme is also exposed, due to that Lyapunov stability criterion is not always satisfied. Besides, it is revealed that the torque model is more applicable to heavy-load operation. Experimental results are given to verify the proposed analysis.