Multivariable sliding mode approach with enhanced robustness properties based on the robust internal-loop compensator for a class of nonlinear mechanical systems
This paper proposes the synthesis of the integral sliding mode control (I-SMC) and the robust internal-loop compensator (RIC) for nonlinear multiple-input multiple-output (MIMO) systems, introducing a generalization of the well-known single-input single-output (SISO) case for linear systems. The new control term is introduced in order to incorporate a RIC structure with a multivariable I-SMC scheme for a class of nonlinear mechanical systems affected by perturbations. The finite-time stability of the closed-loop system is discussed using a Lyapunov based approach. The designed algorithm is used to control attitudes of the small-scale laboratory helicopter system, representing a nonlinear MIMO system with significant cross-couplings and inherently unstable characteristics. An excellent tracking performance and robustness properties of the proposed control method is demonstrated through both, computer simulation and experimental testing, even in the presence of additional internal and external disturbances.