Adaptive linear regulation for systems with multiple zeros at the origin

We consider the problem of asymptotic rejection of exogenous harmonic inputs having unknown amplitudes, phases, and frequencies on the output for a class of uncertain and nonminimum-phase linear systems. Special emphasis is given to the case in which the controlled system has multiple zeros at the origin. It is shown how the method recently proposed to design internal models by means of regression arguments, combined with control strategies based on the redesign of the zero dynamics of the system through redefinition of the output, can be successfully used to solve the problem in presence of plant parameter uncertainties.