NECESSARY AND SUFFICIENT CONDITIONS FOR QUADRATIC CONTROLLABILITY OF A CLASS OF UNCERTAIN SYSTEMS

We introduce a controllability notion for uncertain systems, namely, q uadratic controllability. For a specific class of norm bounded uncerta in systems, we show that this notion is equivalent to controllability of a nominal system and the satisfaction of a certain structural condi tion by the uncertainty. For systems in which the uncertain parameters affect all control inputs, this structural condition is simply the fa miliar matching condition commonly encountered in the literature on ro bust and adaptive control of uncertain systems.