A novel approach to the linearization of motor-driven valves in process control systems

An approach based on input/output feedback linearization has been developed for the linearization of motor-driven valves in process systems. The development of a nonlinear mathematical model for a general class of motor-driven valves is given. This model is used to derive an input/output feedback linearization scheme for the valve system. A comparison between the valve performance using the linearization scheme developed in this work and that obtained using a conventional PID controller is presented. The performance of the linearization scheme is superior to the conventional approach, especially in the range of low flow rate where the nonlinear characteristics of the valve system are dominant. Furthermore, in the low flow operating regime the nonlinear characteristics of the valve system are such that even a feedforward inverse of the nonlinear characteristics of the valve fails to linearize the valve sufficiently to provide reasonable control. A simulation of a temperature process which includes a cascade temperature-flow control system and the motor-driven valve and the proposed linearizing control scheme is used to further study the robustness of the proposed scheme to process and measurement noise