Describing-Function-Based Identification of a Nonlinear Servo-Valve Model

With increasing demands on the performance of hydraulic actuators, the limitations due to servo-valve properties become most important. By means of nonlinear dynamic modelling, insight in these properties is obtained. Despite the presence of a static nonlinearity in a closed loop, the dynamics of the model can be identified by means of proper experiment design. Describing Function measurements are then used to identify the static nonlinearity. After validation of the nonlinear model of the servo-valve, the model is used to show, that the inherent properties of the servo-valve have a strong impact on the performance of the controlled servo-system.