VSS theory-based disturbance estimation scheme for MIMO systems and its applications

Based on variable structure systems (VSS) theory, this paper presents a new method of estimating the disturbances (or system nonlinearities and any model uncertainties) for continuous-time multi-input multi-output (MIMO) minimum phase (with respect to the relation between the disturbance and the output) dynamical systems. The designed robust method requires only the input and output measurements of the system. Even for MIMO systems under the assumption that the partial states directly affected by the disturbances do not directly appear in the outputs (when it is considered in the state space), the disturbances can still be estimated by applying the proposed formulation. The estimated disturbances are then employed to construct a robust state observer. Further, the estimated disturbances and the state observer are applied to synthesize a controller to place the desired stable poles and to cancel the disturbances. A design example and simulation results are presented to show the practicality and effectiveness of the proposed algorithm.