Robust MRAC augmented baseline LQR for tracking control of 2 DoF helicopter

This paper proposes a novel in-line direct adaptive Linear Quadratic Regulator (LQR) using Model Reference Adaptive Control (MRAC) scheme for tracking control of a 2 DoF helicopter. LQR is one of the most preferred controllers for flight control applications due to its inherent robustness and stability characteristics. However, the tracking performance of LQR gets degraded when the system is perturbed or subjected to model uncertainty. To address this issue, by cascading the adaptive control law with the baseline LQR, an adaptive controller framework is synthesized using an inverse Lyapunov function. The key advantage of the proposed framework is that it widens the operating horizon which significantly increases the stability and robustness of the system to accommodate both uncertainty and disturbance. The efficacy of the controller framework is tested on the benchmark 2 DoF helicopter testbed. The command tracking and maneuvering responses of the 2 DoF helicopter under nominal and perturbed operating conditions are assessed. The tracking responses accentuate that MRAC augmented LQR can result in quicker convergence with improved stability.