Combined design of robust controller and disturbance observer in a fixed-order H. control framework

The disturbance observer (DOB) and H. based robust control methods are widely used in feedback control ap-plications due to their disturbance rejection capability and robustness improvement. However, the simultaneous synthesizing of DOB and H. controller considering the real uncertain parameters and dynamic uncertainties of the models is an open problem. This paper presents a new fixed-order 0-synthesis algorithm based optimization methodology for the combined design of DOB and robust controller in the presence of mixed uncertainty. The fixed-order robust H. control framework is adopted to optimize structured plant inverse, so-called Q filter and feedback controller. In order to guarantee the robust stability of the main feedback loop and inner DOB loop, the overall closed-loop system is considered with uncertainties during the design procedure. The proposed approach renders the need for an explicit plant inverse unnecessary. Thanks to this advantage and generality of 0-synthesis techniques, the proposed method can be directly applied to both the non-minimum phase and multiple-input and multiple-output (MIMO) uncertain systems without any approximation. The theoretical design approach is experimentally verified on an electromechanical control actuation system of an air vehicle and numerically on a non-minimum phase system.