Abstract
Structural controllability of a linear time-invariant system is considered using the representation called an intermediate standard form (ISF), descriptor form, or semistate equation. This unorthodox representation is employed instead of the ordinary state equation to express structure of physical systems in their mathematical descriptions in a straight-forward manner so that a major drawback in the structural consideration using state equations is resolved. As a definition, a system is said to be structurally controllable if its state equation, which can be obtained from the ISF representation, is controllable for almost all nonzero parameters in the ISF. The necessary and sufficient condition for structural controllability is presented both in algebraic and graph-theoretic terms, which is applied to ISF.
