High performance robust linear controller synthesis for an induction motor using a multi-objective hybrid control strategy

Two-degrees-of-freedom (2DOF) controller design is viewed as a standard technique capable of simultaneously addressing the performance objectives of the main operating modes - tracking and disturbance rejection - of an induction motor control system. However, in a typical industrial reduced cost controller implementation, the open-loop prefilter performance in the 2DOF topology could be severely degraded by the controller uncertainty, i.e., the mismatch between the dynamics of the analytical controller representation and its realization in software/hardware. This problem is addressed in the present work by a multi-objective hybrid control strategy. The latter consists in employing in each mode the corresponding optimally tuned One-degree-of-freedom (1DOF) design robust with respect to both the plant and the controller uncertainty, and organizing a rapid and smooth switching, or transfer, between the mode-specific controllers to provide sequencing of the operating modes, as necessary. Simulation results show that the technique proposed yields the fast switching robust controllers that provide the desired performance under rather significant controller uncertainty across the entire induction motor operating sequence, thereby offering an alternative, minimally affected by the reduced cost controller implementation, to a 2DOF design.