Robust controller design for nonlinear twin rotor control system using quantitative feedback theory

This paper presents a robust controller for twin rotor control system (TRCS) subject to parametric uncertainty. TRCS exemplifies a class of multiple-input-multiple-output (MIMO) system having complex nonlinearity and cross-coupling effects. The linearised form of TRCS model is decoupled into two single-input-single-output (SISO) systems. Using quantitative feedback theory (QFT), the robust controller and pre-filter are designed for the two SISO subsystems to satisfy minimum gain and phase margin, tracking specifications for robust performance, actuator saturation, fast convergence, input and output disturbance rejection and sensor noise attenuation. QFT is a new and innovative robust technique based on Nichols chart in frequency domain. This approach achieves desired robust controller design over a specified range of system parametric uncertainty in spite of input and output disturbances and noise. QFT-based controller and pre-filter are designed for the required specifications of robust stability and robust tracking. Additionally, a proportional-integral-derivative (PID) controller is augmented for the nonlinear model of TRCS to compare the results of the two controllers. A detailed comparative evaluation has been worked out between the two controllers applied to the nonlinear model of the TRCS with the help of simulation studies.