Adaptive Output Feedback for Nonsquare Systems with Arbitrary Relative Degree

This article considers adaptive output-feedback control problem for nonsquare multi-input-multi-output systems (MIMO) with arbitrary relative degree. The proposed controller, based on the \mathcal {L}_1 adaptive control architecture, is designed using the right interactor matrix and a suitably defined projection matrix. A state-output predictor, a low-pass filter, and adaptive laws are introduced that achieve output tracking of a desired reference signal. It is shown that the proposed control strategy guarantees closed-loop stability with arbitrarily small steady-state errors. The transient performance in the presence of nonzero initialization errors is quantified in terms of decreasing functions. Rigorous mathematical analysis and illustrative examples are provided to validate the theoretical claims.