Model Reference Robust Adaptive Control without a Priori Knowledge of the High Frequency Gain

This paper propose a new model reference robust adaptive controller that does not require a priori knowledge of the high frequency gain sign. The scheme is applicable to minimum phase plants of arbitrary relative degree and ensures that, in the absence of unmodelled dynamics, the tracking error converges to zero and all the signals remain bounded. The control law uses a particular projected parameter vector instead of the current estimates to avoid division by zero.