Adaptive Control for Nonlinear Uncertain Systems with Enhanced Transient Performance

Although adaptive control has been widely used to cope with unknown system parameters, a critical issue limiting its practical application is that the fast adaptation with a high learning rate for addressing uncertainties and obtaining rapid transient convergence can trigger high-frequency oscillations in the system and even cause system instability. To address this issue, we present two schemes to enhance the transient response of model reference adaptive control (MRAC) in this paper. The first idea is to incorporate a simple compensator into the control action, which can extract and eliminate the undesired residual dynamics in the transient process. The second idea is to introduce a modified adaptive law with a new leakage term, which contains the parameter estimation error, such that both the tracking error and estimation error will converge to zero exponentially. Apart from theoretical analysis, comparative simulation results based on a benchmark wing rock aircraft model verify the effectiveness of the proposed methods for addressing the system uncertainties and improving the transient responses.