Fuzzy variable structure control of induction motors with sag ride-through capability

In this paper, indirect rotor field oriented control (FOC) of an induction motor for speed control is presented. It is proposed to use variable structure control (VSC) strategy for the inner current loop while the rotor speed is controlled via a proportional-integral (PI) type outer controller. To reduce ´chattering´ in the motor currents owing to the VSC, a variable control input voltage consisting of an equivalent control voltage component and a fuzzy controlled component is proposed. The fuzzy controlled component is nonlinearly dependent on the current error level. The philosophy behind this control approach is to modulate the current feedback error gain in the sliding surface by fuzzy approach. With this approach, reaching mode to the sliding surface is unaffected while chattering in the sliding mode is reduced. Moreover, a sag ride-through control method using regeneration is proposed. Simulated and experimental results are presented to show the efficacy of the proposed control strategy.