Nonlinear backstepping control for a three-stage servo valve-actuated cylinder with valve dynamics identification and ESO-based modeling error compensation

This research aims to enhance the tracking performance of an electro-hydraulic servo system (EHSS) controlled by a three-stage valve (TSV). In EHSS servo control, system models often simplify valve dynamics to facilitate controller design. To achieve a more precise characterization, this work focuses on modeling the TSV dynamics and investigating their influence on overall control performance. A complete dynamic model incorporating the identified TSV dynamics is established. The TSV model is obtained from frequency-sweep experiments and then integrated into the backstepping controller design. Based on this high-fidelity model, a backstepping controller integrated with a tracking differentiator (TD) is designed. Furthermore, an extended state observer (ESO) is introduced to estimate and compensate for the valve-dynamics modeling uncertainty, which represents the residual mismatch between the identified first-order valve model and the actual TSV dynamics. The combined TD-ESO-backstepping scheme is validated through co-simulations and experiments, demonstrating its feasibility and superior performance.