Backstepping design for controlling electrohydraulic servos

The backstepping technique is one of the tools which provides control Lyapunov functions (CLFs) and, therefore, control laws for automatic systems. In this paper, the backstepping design for position and force nonlinear electrohydraulic servos is investigated. Three control laws ensuring the asymptotic stability of references tracking are obtained by constructing CLFs on the errors concerning the state variables and theirs desired values. The possibility of converting a position servo into a force servo, with only minimal hard modification, is proved. An approach based on partitioning the state system into two subsystems-a first one stable, and a second one taken as framework of control synthesis by backstepping technique-was developed and used. Using as reference point a flight controls hydromechanical servo, numerical simulations were reported from viewpoint of servo time constant performance. Certain conjectures, concerning the behaviour of systems mathematical models, in connection with mathematical methodologies of control synthesis operating on them, are finally stressed.