We show that regulation to a constant value of the output of a process can be achieved robustly by designing a stabilizer for a model augmented with an integrator of the output and by having the model dynamics close enough to the process ones. This is nothing but the PI controller paradigm extended to the case of nonlinear systems. We recall also that the forwarding technique is well suited for this particular stabilizer design. Finally we illustrate our result with solving the problem of regulating the flight path angle of the longitudinal mode of a plane.

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