Algorithmes de commande des systèmes électrohydrauliques à dynamique variable

Abstract

This thesis proposes new control laws for electro-hydraulic servo-systems (EHSS) in the industrial context. Proportional-integral-derivative (PID) control is used extensively to control EHSS, but the closed-loop performance is limited using this approach, due to the nonlinear dynamics that characterize these systems. Recent studies have shown that feedback linearization is a viable control design technique that addresses the nonlinear dynamics of EHSS. However, it is important to establish the robustness of this method, given that hydraulic/mechanical parameters, friction and external load disturbances can vary significantly during operation. The first control law of this thesis focuses on supply pressure uncertainty. The supply pressure appears in a square-root term in the system model, and thus, standard adaptive techniques that require uncertain parameters to appear linearly in the system equations cannot be used. This issue is addressed by utilizing a switching control law, based on a feedbacklinearizing controller structure. In contrast to traditional adaptive control laws which update specific parameters, the proposed switching control law updates the function involving the unknown supply pressure. The second control law proposed in this research work addresses friction, torque load disturbances and the variation of multiple hydraulic parameters. Fuzzy and/or sliding mode versions of feedback-linearizing controllers have been used to compensate for bidirectional friction and external load disturbances. However, these robust versions are computationally complex and face limitations in terms of real-time implementation. In this thesis, an extended adaptive control law based on a feedback-linearizing structure is proposed to simultaneously reject load disturbances and friction, while compensating for uncertainty in hydraulic parameters. The real-time implementation of the proposed control laws is performed by numerically calculating the high-order derivatives of the measurement. Experimental results show that the control laws proposed in this thesis can be implemented in the presence of measurement noise, real-world friction effects, servovalve saturation and load variations. The numerical and the real-time experimental results indicate that the performance of the proposed controllers is superior to those of the PID and standard feedback-linearizing controllers. The present study is done considering a hydraulic rotational drive. The design is generic and allows for extension of the study herewith to other hydraulic drives.

Date	24 Aug 2011
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Jean-Pierre Kenné (Supervisor) & Ravinder Venugopal (Co-supervisor)