Exponential Tracking Control of a Hydraulic Proportional Directional Valve and Cylinder via Integrator Backstepping

Hydraulic systems are widely used in manufacturing processes and transportation systems where energy intensive operations are performed and “machine” control is vital. A variety of flow control products exist including manual directional control valves, proportional directional control valves, and servo-valves. The selection of a control valve actuation strategy is dependent on the system response requirements, permissible pressure drop, and hardware cost. Although high bandwidth servo-valves offer fast response times, the higher expense, susceptibility to debris, and pressure drop may be prohibitive. Thus, the question exists whether the economical proportional directional control valve’s performance can be sufficiently enhanced using nonlinear control strategies to begin approaching that of servo-valves. In this paper, exponential tracking control of a hydraulic cylinder and proportional directional control valve, with spool position feedback, is achieved for precise positioning of a mechanical load. An analytical and empirical mathematical model is developed which describes the transient behavior of the integrated components. A nonlinear backstepping control algorithm is designed to accommodate inherent system nonlinearities.