| Abstract |
The use of AC-motors as controlled electrical drives, in spite or their nonlinear-multivariable characteristic, may be attractive using field orientation and microprocessors. To obtain a high performance with this scheme, it is important to know the instanteneous position of the rotor flux, which depends on the rotor time constant. In this paper, a self-adaptive scheme is described for automatically tracking the temperature and saturation-dependent rotor time constant. This scheme is based on a monitoring signal (PRBS) injected in the process. A cross-correlation function between this signal and the speed error indicates the Tr-changes in direction (increase or decrease) and magnitude. This very simple adaptive scheme presents unique characteristics: it doesn't use current or voltage sensors; it is not motor parameter dependent; the amplitude of the additional PRBS can be reduced with an increase on the speed sensor sensibility and so the interference in the drive performance can be controlled; it works either on steady- and dynamic transient-state. The proposed method needs some load to operate, but this condition is satisfied in all practical cases. Tests were conducted with a 1,2kW fourquadrant AC-drive, the control was implemented with a microcomputer and the motor was supplied by a voltage-source inverter with current control using IGBTs. Experimental and simulated results using this adaptive digital schemz for different loads and values of model Tr (representing a detuned operation) are presented showing very good response. Furthermore, the Tr influence in the induction motor dynamics is also presented. |
