An Effective Disturbance-Observer-Based Nonlinear Controller for a Pump-Controlled Hydraulic System

Abstract

Researches for improving the control performance of hydraulic systems in both control accuracy and energy efficiency have never stopped in aerospace and industrial applications. The existence of nonlinearities, uncertainties, and unknown terms in the system dynamics, however, significantly limits the desired performance. To realize improvements by dealing with these problems, an advanced position controller incorporated with effective disturbance observers (DOs) applied for a pump-controlled hydraulic system is proposed in this article. Here, uncertainties are considered as certainties (nominal terms) and their deviations. To eliminate certain nonlinearities in the system dynamics, the proposed controller is designed based on a simplified robust sliding-mode-backstepping scheme. The lumped unknown terms, which mainly degrade the performance of the controller, in pressure dynamics and force dynamics are expanded by using equivalent nonautonomous models. To effectively approximate the terms and to ensure usability of the estimated results inside the control framework, two different high-order DOs are developed. Asymptotic convergences of these observers are achieved by adopting nonlinear combinations of the estimation errors. Effectiveness and feasibility of the designed observers and the closed-loop system for an asymptotically tracking performance in the presence of bounded time-varying disturbances are then confirmed by Lyapunov-based proofs and extensive experiments.