Robust controller design for twin rotor system using quantitative feedback theory with parametric uncertainty

This paper presents quantitative feedback theory (QFT) based control, input disturbance rejection and tracking of a twin rotor system. Twin rotor system is a class of multiple-input multiple-output (MIMO) system having complex nonlinearity. QFT is a robust frequency domain technique based on Nichols chart. This technique achieves desired robust design over a specified range of plant uncertainty. QFT is used for the design of robust controllers for the plants with uncertainty in the parameters, input and output disturbances and noises. The twin rotor system with two inputs and two outputs having parametric uncertainty is divided into two equivalent single-input single-output (SISO) sub-systems. Based upon the performance, input disturbance rejection and tracking specifications, bounds are determined. After determining the bounds, controller and pre-filter are designed for each SISO sub-system which fulfills the necessary control, input disturbance rejection and tracking specifications. Simulation results demonstrate the effectiveness of the proposed robust controller.