Saturating controllers for pressure control with an electrohydraulic servovalve

Electrohydraulic servovalves are the most commonly used control devices for hydraulic systems. However, electrohydraulic servo systems are difficult to control because they are in essence highly nonlinear. In this study, the pressure control loop including the electrohydraulic servovalve is modeled and the major nonlinearities are pointed out. A nonlinear transformation is presented to convert the system dynamics to a linear state space representation. Based on the flow saturation in the servovalve, a saturating controller is designed to control the pressure drop across a load. The derived control law is generalized and is shown to be Lyapunov stable. The performance of the proposed controllers is numerically analyzed and compared to a linear PID controller.