On global stability of adaptive systems using an estimator with parameter freezing

The results of R. Kosut and B. Friedlander (1985) on robust global stability of direct adaptive controllers using an integral adaptation law are extended to the case where the adaptation algorithm includes a parameter freezing mechanism, i.e. the control parameters are held constant at certain time intervals. The authors´ main concern is to propose an estimator with freezing capabilities which preserve the property needed for the global stability analysis, namely, that it defines a passive operator. In an adaptive control context, the additional degree of freedom provided by the freezing imposes no further assumptions for global stability. A crucial requirement for the analysis is that the number of freezing intervals is finite.<>