Robust active control of flexible systems with structured perturbations

The authors present a simple method to investigate robust stability and performance criteria for flexible systems under low-order observer-based controller designs. In the present approach, stability is defined in the internal sense, instead of the pure input-output (I/O) sense. This is superior to the usual methods based on I/O descriptions, in the sense that the situation for systems formulated in state-space models subject to joint structured unmodeled residuals and parametric perturbations can be treated simply