Online Decoupled Stator and Rotor Resistances Adaptation for Speed Sensorless Induction Motor Drives by a Time-Division Approach

The paper addresses the method for stator and rotor resistance identification in speed sensorless induction motor drives. The instability problem caused by pure integration of the voltage model (VM) of rotor flux is handled by introducing correction terms in the VM. It is, however, shown that the third-order persistent excitation (PE) condition for simultaneous identification of stator, rotor resistances and rotor speed can barely be satisfied even with extra excitations in rotor flux modulus command. And an adaptive observer that is not persistently excited may become instable when exposed to bounded disturbances. Hence, to design a robust flux observer, concept of time-division multiplexing is incorporated into the observer design. That is, stator resistance is identified as the flux modulus is flat, while rotor resistance is adapted as a ramp flux modulus command is applied. This relaxes PE condition to order two, and as a drawback, the ramp flux modulus command incurs speed ripples. The decoupled identifiability of stator resistance is designed and explained, a rigorous input-to-state stability analysis of both the mismatch [between VM and current model (CM)] and the error (between actual rotor flux and CM) is set forth, and a convergence analysis of parameters is elaborated. To validate the feasibility, simulation and experiment results are included in the text as well.