Stability Margins of ${cal L}_{1}$ Adaptive Control Architecture

This technical note presents the L ₁ adaptive control architecture for systems in the presence of unknown high-frequency gain with known sign, time-varying unknown parameters and disturbances. The L ₁ adaptive controller leads to uniform performance bounds for the system´s input and output signals, which can be systematically improved by increasing the adaptation rate. For constant unknown parameters, this result leads to analytically computable time-delay margin of a semiglobal nature.