Nonlinear Robust Adaptive Control of Electro-hydrostatic Actuators With Continuous Friction Compensation

Electro-hydrostatic actuators (EHAs) have gradually been applied in the flight control systems of multi-electric/all-electric aircraft due to the high power-to-volume ratio and the absence of throttling loss as well as overflow loss. However, the existence of high-order dynamics, system nonlinearities, and uncertainties significantly limits the tracking performance of EHAs. This article developed a robust adaptive controller with continuous friction compensation to improve the precise control performance of an EHA with a variable load, nonlinear friction, parametric uncertainties, and unmodeled disturbances. A nonlinear robust control law is used to attenuate various disturbances, and an adaptive law is adopted to cope with parametric uncertainties. Additionally, a continuous friction model is used to describe the friction behavior of an EHA to achieve effective friction compensation and further enhance the motion performance. Moreover, the upper bounds of the matched and mismatched uncertainties can be updated in real-time via adaptive laws, which can reduce design conservatism to some degree. The Lyapunov stability analysis reveals that asymptotic performance can be guaranteed despite the presence of unmodeled disturbances and parametric uncertainties. Furthermore, the applicability of the designed control algorithm with continuous friction compensation is demonstrated with experimental results.