A MRAC for multivariable plants with zero residual tracking error

In almost all model-reference adaptive control (MRAC) schemes proposed in the literature the tracking error cannot be guaranteed to go to zero in the presence of plant unmodeled dynamics and/or bounded disturbances. It is shown that when an MRAC scheme is combined with a variable-structure control law, the tracking error goes to zero asymptotically with time in the presence of unmodeled dynamics and bounded disturbances for a class of multi-input, multi-output plants whose modified left interactor matrix is strictly positive real