A combined direct, indirect, and variable structure method for robust adaptive control

Direct methods and indirect methods for the adaptive control of linear plants with unknown parameters are currently well known. Methods for combining direct and indirect methods have also been suggested. In the paper the latter method is combined with the variable structure method. New adaptive laws are suggested which overcome the principal drawbacks of the variable structure method. While the direct and indirect components of the new method assure stability, the variable structure component improves the transient response of the system. Simulation results are presented to show that the overall system is asymptotically stable in the ideal case, and exhibits robustness and improved performance in the presence of perturbations