Pole placement direct adaptive control for time-varying ill-modeled plants

The problem is discussed of preserving the stability of pole placement direct adaptive control in spite of output bounded disturbances, time varying plant model parameters, and unmodeled dynamics, assumed to be small in the mean. The controller parameter estimates are shown to track, in the mean, their true (time varying) parameter values. Such a convergence property is achieved using an ad hoc, internally generated, excitation sequence that ensures persistent excitation. In the ideal case the convergence of the parameter estimates is exponential, avoiding, in particular, possible chaotic phenomena