Disturbance observer in /spl Hscr//sub /spl infin// frameworks

A disturbance observer control scheme cannot be internally stabilized for unstable plants and nonminimum phase plants. Hence, we suggest the internally stabilizing disturbance observer which is derived from the concept of the Bezout identity and a coprime factorization, and it has some design constraints. The design constraints are derived from the small gain theorem and condition for good performance. The automatic design of an internally stabilizing disturbance observer is performed in /spl Hscr//sub /spl infin// frameworks, and it is induced from the stability constraint and condition for good performance. We show that the disturbance observer is equivalent to a /spl Hscr//sub /spl infin// control having a design parameter of Youla Q. The verification of an internally stabilizing disturbance observer is achieved for an unstable and nonminimum phase plant as the numerical example for a regulation problem.