A novel technique to estimate rotor time constant in vector controlled induction motor drives

This paper presents a new technique to estimate the rotor time constant of vector-controlled induction motors (IMs). The estimation is based on the comparison between the expected speed trajectory corresponding to constant acceleration and the actual speed trajectory of the drive. In fact, when the drive operates under vector control with constant torque reference and load, it is expected that the motor has constant acceleration and rectilinear speed trajectory. A simple optimization algorithm, implemented on the same microcontroller used for vector control, updates on-line the rotor time constant trying to minimize the difference between the expected and the actual speed trajectories of the IM. The main advantages of our approach are the complete independence from motor mathematical model, and possibility of implementation on low-cost microcontrollers. Simulation and experimental results are presented to prove the accuracy and the effectiveness of the estimation technique.