Smart valve actuation for dynamic fluid flow control with constraints in the power unit

Perfect reference tracking by peripheral subsystems is a common requirement in industry, but it is often limited by system non-linearities. In fluid flow control systems, non-linearities are mainly caused by the characteristic curve of a valve. Such a curve describes the steady state relation between the valve opening and the flow rate but is significantly modified when installing the valve in a pipeline. Traditionally, the valve is adjusted to the pipe by design, an expensive and very complicated approach. In contrast, in the mechatronic approach a powerful, high-dynamic actuator is used within a control loop to realize perfect tracking in dynamic conditions from the input of the overall process control system to the actual flow rate. This approach is cost-effective, easy exchangeable and allows a simple expansion of existing plants. In this paper, the mechatronic approach is developed and validated. Firstly, a modular, mathematical model of the hydraulic power unit, the hydraulic cylinder, the valve and the fluid flow in the pipe is derived. Subsequently, a model-based control concept is employed to invert the model and compensate system non-linearities in dynamic conditions. Finally, the approach is validated numerically with respect to challenging test cases employing industrial devices and recalling industrial needs. The results attained prove that the mechatronic approach allows extending the range of perfect tracking of valves, and that useful insights for the development of such systems can be provided.