Adaptive rotor resistance estimation in the low-speed range of speed sensorless DTC controlled IM drives

In this paper, an adaptive flux observer is designed for a speed sensorless direct torque controlled induction motor drive in which the rotor resistance value is updating during operation and a new speed-adaptive law is given. By using robust control theory, the constant observer gain is obtained by solving two bilinear matrix inequalities. The stability of the flux observer is ensured in a sufficiently large symmetric interval include zero point. Therefore, the sensorless drive system is capable of steadily working in low speed range and exhibits good dynamic and steady-state performance. The impact of the rotor resistance change on the low-speed performance of speed sensorless direct torque control system is at first verified by simulation and then by extensive experimentation. The result shows that the variation of the rotor resistance has great influence on the performance of speed sensorless direct torque control system, and the proposed rotor resistance estimator is capable of modifying the estimated speed effectively.