Stability analysis of a non-minimum phase Electro-Hydraulic Servo System (EHSS) and identification of parametric uncertainty

Abstract

The electro-hydraulic servo system (EHSS) is a common tool in a variety of modern-day industrial applications that mostly deal with aviation and vehicle manufacturing and operation. In this thesis, an electro-hydraulic servo system is presented which bears the characteristics of non-minimum phase (NMP) phenomenon. A discrete-time transfer function for investigating the EHSS-NMP features has been estimated using a revamped mathematical model of the EHSS with respect to existing model parameters. An optimal control strategy is then formulated based on discrete linear quadratic regulator (DLQR) that seemingly, optimizes the control issues associated with EHSS affected by NMP behavior. A comparative analysis shows that the EHSS stability response improves with the DLQR, but the NMP behavior still persists. This thesis also tries to identify parametric uncertainties through a comprehensive mathematical model of EHSS. The modeling constraints are then investigated to propose a finite frequency robust control technique to actuate an active suspension load subjected to road disturbances. Using various performance criteria, simulation results are able to determine an optimum trade-off between robust control and rejecting road disturbances at higher deflection frequencies. As a result, these studies have demonstrated that the proposed control technique may overcome the parametric uncertainties of an EHSS-driven active suspension load.