A Simple Adaptive Scheme for Indirect Field Orientation of an Induction Motor

A self-adaptive scheme is described for automatically tracking the temperature and saturationdependent rotor time constant (Tr ) in indirect vector control. This method is based on a monitoring signal injected into the process. A cross-correlation function between the monitoring signal and the speed error indicates the Tr changes in direction (increase or decrease) and magnitude. The proposed identification algorithm presents unique characteristics: it doesn't use current or voltage sensors; it is not motor parameter dependent; the amplitude of the monitoring signal can be reduced but with an increase on the speed error sensibility to control interference in drive's performance and it works either on steadyand dynamic transient-state. It will need some load to operate but this condition is satisfied in all practical cases. Tests were conducted with a 1,2kW four-quadrant AC-drive. The adaptive indirect vector-control was implemented in a microcomputer with the motor supplied by a voltage-source inverter with current control using IGBTs. Experimental and simulated results using this adaptive digital scheme for different loads and values of model Tr (representing a detuned operation) are presented showing good performances.