Adaptive third-order super-twisting sliding mode control based on field-oriented control for three-phase induction motors satisfying power quality constraints

Robust control of the induction motor across a wide range of torque-speed operating points remains a challenge, particularly when the variable frequency drive (VFD) must satisfy stringent power quality constraints for motor insulation longevity. Therefore, this paper proposes an approach to implement an adaptive third-order sliding mode controller (ATOSMC) based on the third-order super-twisting algorithm (3-STA) on a three-phase squirrel-cage induction motor supplying a constant-torque mechanical load, e.g., elevators, hoists, cranes, etc. Field-oriented control (FOC) enables the system to independently control the rotor flux and the torque. The proposed ATOSMC provides the synchronously rotating voltage vectors to the space vector pulse width modulation (SVPWM) scheme. This ensures that not only are the control objectives achieved and the system remains on the sliding surface, but also the first and second derivatives of the sliding variable converge to zero. Results illustrate the superiority of the proposed adaptive control method over the conventional third-order super-twisting SMC algorithm, specifically in terms of reducing the chattering amplitude with the load variation. Moreover, the controller robustness against the DC-link voltage and the load demand is examined comprehensively.