Theoretical and experimental comparison of two nonlinear controllers for current-fed induction motors

We present a theoretical and experimental comparison between two nonlinear controllers for speed regulation of current-fed induction motors: the passivity-based controller (PBC) and the observer-based adaptive controller (OBAC). The theoretical comparison centers on robust stability and performance, which can be easily assessed for the PBC given its exponential stability property. On the other hand, we show that, (as expected from a scheme based on nonlinearity cancellations), in the face of parameter mismatch OBAC may become unstable even in the state feedback case. For our experimental studies we used standard low-cost hardware readily available in a practical application. The conclusions of our experimental comparison may be summarized as follows: 1) the high computational requirements of the OBAC forced us to double the sampling period achievable for PBC with obvious ensuing performance degradation; 2) even at a lower sampling frequency, PBC systematically achieved better speed transient performance, faster load torque disturbance rejection, and enhanced robustness vis a vis uncertainty in the rotor resistance; and 3) commissioning of PBC was also simpler, because the performance of OBAC is more sensitive to parameter uncertainty and its control effort was larger. The latter factor considerably limited the range of operation of the scheme.