| This paper analyzes a few aspects regarding the dynamic regime operation of the asynchronous motors supplied by variable frequency. The starting point is the conclusion that the stability is a quantitative feature of systems associated to their dynamic behaviour and that has imposed a method for the stability analysis, presented in this paper. The method has as a starting point the mathematical model of the motor written in per unit values. This model has been processed with the help of the Laplace transform. There has been obtained a block scheme with negative reaction which has been used for carrying out a Matlab program for stability analysis. With the help of the program there have been obtained some amplitude-pulsation, phase–pulsation, amplitude-phase characteristics and some hodographs corresponding to a low power asynchronous motor. Comparing the characteristics obtained when some motor parameters have been modified, the conclusions detailed in the final part of the paper have resulted. The notion of phase margin has had a special place for finalizing the analysis. This quantity shows the stability reserve of the machine until the stability limit is reached. The simulations have shown that the phase margin increases when the stator resistance value increases. On the other hand, when the rotor resistance value decreases, the phase margin decreases. |
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