Abstract
In this thesis a design methodology for multivariable control systems is developed to achieve performance robustness against plant uncertainty and multiple input saturation. Uncertainty in the plant model and actuator saturation nonlinearities are inherent in all practical control systems. A controller which is not able to deal plant uncertainty and actuator saturation may give rise to serious performance deterioration or, in the worst case, instability. The proposed design methodology is a two-stage design paradigm. In the first stage a quantitative robust performance design technique is developed by ignoring the saturation nonlinearities. To minimize the overdesign incurred in achieving robust performance, the cost of feedback (i.e. the effect of sensor noises at the plant input) is minimized subject to the constraints of robust performance specifications. With the obtained linear robust performance controllers, in the second stage an anti-windup (AW) compensation scheme is added to provide graceful degraded performance in the presence of input saturation while the linear performance is preserved. In this thesis two alternative anti-windup designs are developed for a wide class of applications. The first optimization-based approach has the advantage of providing good performance over an excessively large operating range but demands considerable computational effort. For the applications where a fast response speed is required, an optimal linear-time invariant (LTI) AW design which minimizes a weighted difference between the nonlinear saturated and the linear performance, and thereby maintain the output directionality in an optimal sense. The present design methodology merits itself in the following aspects: (i) The cost of feedback incurred in overdesign in achieving performance robustness is explicitly and efficiently minimized in the present quantitative robust performance design. (ii) The optimization-based AW design breaks the limits of achievable performance provided by most existing approaches. (iii) The optimal LTI AW design provides optimal saturated performance among existing LTI AW compensation schemes.