Sliding Mode Control of a 3-DOF Helicopter with State Dependent Regional Pole Placement

Sliding Mode Control methodologies are widely used to control uncertain and/or disturbed dynamical systems. The Sliding Mode Controller is designed so as the trajectories of the dynamical system are forced to stay on a stable hyper-surface which is pre-designed to shape the time response. This paper proposes a novel method confining the parameters (slopes) of the sliding surface while keeping the closed-loop system poles of the reduced order system without the control input expressing the null space dynamics in a desired region for a class of nonlinear systems. The traditional pole-placement approach attempts to locate the poles of the closed-loop system exactly at the desired locations. However, this approach provides a strict requirement for a nonlinear system since a nonlinear system usually shows different characteristics, mainly due to the uncertainties and state-dependent parameters. The proposed method eliminates this restriction by enabling the closed-loop system poles to stay inside a desired disk rather than force them to stay at some specific locations. The effectiveness of the proposed method and the effect of different disk parameters on the system responses are experimentally tested on the 3-DOF Helicopter test setup using three different disk parameters.