A Robust Fractional Order Parallel Control Structure for Flow Control using a Pneumatic Control Valve with Nonlinear and Uncertain Dynamics

Control of flow rate in industrial plants is an essential and crucial task, which is usually achieved by pneumatic control valves in industries. Use of these valves often incorporates nonlinear and uncertain dynamics in the control loop on account of its input-output characteristics, which may result in degradation of control loop performance. To address this concern, a robust and improved fractional order parallel control structure (FOPCS) for flow control is proposed in this paper. The proposed FOPCS is an extension of parallel control structure (PCS) with the help of fractional order calculus, to enhance the robustness in the control loop without compromising with control performance. Also, a global optimization technique, backtracking search algorithm was further employed to critically tune the parameters of control structures. This was done in order to obtain an optimized and enhanced performance from the control loop. Extensive runtime studies on a laboratory scale plant, using advanced data acquisition facilities, were carried out to showcase the effectiveness of developed FOPCS. Proposed FOPCS is thoroughly assessed in terms of servo, regulatory and robustness performance. A quantitative comparison of FOPCS with PCS is also made on the basis of integral of absolute error, integral of absolute rate of controller output and their algebraic summation. All the conducted experimental studies suggested that proposed FOPCS was able to address the issues pertaining to uncertain and nonlinear behaviour of pneumatic control valve in the flow control loop.