Time-delay compensation in active control of structures

A complete time-delay compensation method is derived. The sensitivity of the stability of the system to the estimation error of the initial condition and excitation, to the estimation error of the delay in the system, and to the specification of the controlled pole pairs are analyzed. Nondimensional formulas in two sets that indicated the conditions of instability are derived. An active control strategy that controls the absolute responses of the structure is presented as an illustration. The adoption of this control algorithm to the base-isolated structure is investigated and is shown to be effective even if the control force is exerted only to the base. Through varied allocation of the controlled poles, the control system shows variable performance. A stability problem is induced if the time-delay compensation method suggested in several papers is adopted. The locations of the controlled pole pairs should therefore be carefully specified and checked according to the characteristics of the system.