Modelling an Electro-hydraulic Proportional Valve in a Closed-Loop Control System using Matlab/Simulink

In this paper the main components of a hydraulic positioning unit are modelled and simulated using the software Matlab/Simulink. That includes the actuator, the pressure relief valve, connecting pipes and of course the proportional directional control valve. With this model the positioning unit was tested under different conditions to make predictions on how the system is going to react. The simulation of the proportional directional control valve was divided into a static and dynamic part. Based on flow, pressure and leakage curves given by the manufacturer, pseudo-section functions have been created. These functions characterize the relationship between normalized spool position and flow rate. For simulating dynamic behaviour, a non-linear Simulink model was created. The model was fitted to non-linear frequency response analysis (NFR) data points by using a Nelder-Mead simplex optimization algorithm. Several experiments were carried out to test the methodologies as well as the models with the manufacturer's data and experimentally verifying the adjustability of the results and the validation of the approach. The valve model shows high positioning accuracy and robust behaviour in both simulation and experimentation. The amplitude response curves for 10% and 25% showed some oscillation, but with a stable behaviour around the measurement. On the other hand, the amplitude curve for 100% of the coil path showed a very acceptable approximation and even coincided with the manufacturer's curve.