Robust control design of a hydraulic actuator using the QFT method

In this paper a control design study of a nonlinear hydraulic actuator is presented based on the Quantitative Feedback Theory (QFT). The model is linearized around an operating point and the uncertainty in the nominal plant is quantified. Using the robust design specifications, a robust QFT controller is designed using a novel fixed structure optimization algorithm. The resulting feedback controller has low complexity and, as shown via numerous simulations, is successful in meeting the robust stability and performance specifications of the design. The design illustrates the effectiveness of the proposed algorithm in achieving tight loop-shaping for a real system of medium complexity.