Lower-order robust controller design for smart structures

The low order controller has many advantages such as simple hardware implementation and high reliability and is very important for the successful integration of controllers with smart structures. Designing a controller with robustness to different uncertainties in smart structure always leads to a high order controller. In this paper, two low order controller design methods are proposed. One method is to design a low order controller based on the reduced plant model. The model error between the full order model and reduced order model is considered as an additive uncertainty in the controller design to reduce the spill-over effect. Another method, controller reduction, is to find a low order controller by reducing the full order controller. The effect of the controller reduction on the system performance is taken into account by selecting a maximum allowable controller reduction error for preserving the performance. The full order controller can be synthesized to provide optimal performance or maximum allowable controller reduction error. Linear matrix inequalities (LMIs) are utilized in those methods to design the low order controllers. The variations of structural parameters, natural frequencies and damping ratios are considered in the controller design as parametric uncertainties.