Variable structure control for MRAC systems with feedforward filter

The variable structure control (VSC) scheme is robust to parameter uncertainty, external disturbance, and un-modeled dynamics, and it is widely applied to designing the robust model reference adaptive control (MRAC) systems. The main drawback of VSC is the phenomena of chattering. To improve system performance and to eliminate chattering, a new VSC with feedforward filter is designed in the paper. The proposed stable feedforward filter makes the control switching with sign functions to produce a continuous and measurable signal so that the actual control law is smooth. The auxiliary signals and normalized signals with memory functions are introduced to the controller design and the estimation of uncertainties. With a suitable choice of controller parameters, it is shown that even when the uumodeled dynamics exists,, the proposed VSC guarantees the closed-loop global stability and arbitrary smallness of the tracking error. Simulation validates the proposed VSC scheme.