A semi-physical model for pneumatic control valves

Abstract

Pneumatic control valves in practice are usually composed of three signal conversion processes that are associated with significant nonlinearities and dynamics. However, several physical, semi-physical, and data-driven models in the literature describe only one signal conversion process from the actuator force to the valve stem position. In this paper, a semi-physical model is proposed based on the physical principles of the three signal conversion processes. The proposed model contains two new components, namely, a backlash nonlinearity in the electric-pneumatic conversion process and an input-direction-dependent dynamics in the pneumatic-force conversion process. In addition, an updated model for the force-position conversion process is shown to be overdamped, instead of being the underdamped one in the literature. Experimental studies are provided to support the proposed semi-physical model and demonstrate the discrepancies of representatives of existing physical, semi-physical and data-driven models with experimental observations.