Using polytopic uncertainty to model linearization errors for hydraulic actuator position control

The objective of this paper is to study an electro-hydraulic servo system (EHSS) with the task of position control, giving special attention to its uncertainty representation. For this purpose, first, the nonlinear equations of the EHSS are derived. It is shown that an uncertain linear model can be derived from the nonlinear model, capturing the nonlinearity in the form of polytopic uncertainty. Special attention is given to reducing the conservativeness of this approach. The resulting model is used to synthesize an output-feedback H_∞ controller for the EHSS using a Linear Matrix Inequality (LMI)-based approach. The effectiveness of this method is demonstrated after providing simulation and experimental results.