A systematic approach to the control of electrohydraulic servosystems

This paper develops a systematic methodology for the control of a class of feedback linearizable systems and applies it to an electrohydraulic servosystem. The class of systems to be dealt with are those that are single input and can be put in Strict Feedback Form. Additionally, it is assumed that the relative degree of these systems is greater than one and the zero dynamics are stable. For a system with relative degree, r, a series of r system errors are defined. An input-output feedback linearization method is then used to control each error through the use of synthetic inputs. Subsequently, the entire closed loop system is analyzed for stability. The approach is conceptually similar to previously developed Integrator Backstepping mehodologies. However, unlike some previous investigations which have relied exclusively on a Lyapunov analysis, this work presents a stability analysis including a Passivity formulation. There are two main advantages of the proposed approach which become significant during implementation. One practical advantage is that the resulting controller leads to synthetic inputs which are decoupled in a certain sense. This leads to a compartmentalization of modeling efforts associated with the controller development. A second advantage of this method is that the system model need not be differentiated in the control formulation. A class of modeling error is introduced and compensated for. The resulting control is able to guarantee specified boundary layer tracking. Finally, the approach is implemented on a hydraulic cylinder governed by a electronically controlled servovalve.