Effect of Proportional Valves and Cylinders on the Behavior of Hydraulic Positioning Systems

Hydraulic positioning control systems are widely employed in several engineering fields such as industry, aerospace, vehicles, and electrical power plants. However, their design is not a straightforward engineering task because several configurations and sizes of valves and cylinders are available, the system components exhibit nonlinear behavior, and the aspects of both fluid mechanics and control theory need to be included for achieving a suitable design. Furthermore, each application has static and dynamic requirements that need to be fulfilled under uncertain loading conditions. Dynamic simulation is an important tool for the analysis and design of hydraulic positioning systems; however, the main characteristics of the components should be known beforehand so that the parameters and model structure can be defined. To overcome these constraints, comprehensive knowledge of the design problem is necessary to ensure appropriate sizing of the hydraulic components. In this regard, this paper presents a detailed study of the influences of the natural frequency and flow coefficient of the valves. The actuator natural frequency is also analyzed, and its modification according to the system requirements is described. The influence of these parameters on the behavior of a closed-loop hydraulic control system with a proportional controller is evaluated using a detailed mathematical model implemented in MATLAB®/Simulink®. Model validation is accomplished using a workbench.