Design of an Optimal Fractional Order PID for Constant Tension Control System

Winding system is a production system commonly used in industry. Its control goal is to achieve constant tension control of the system by controlling motor torque, and to cope with various external disturbances in industrial environment. The Fractional Order PID (FOPID) controller is well known for its simplicity with better tuning flexibility as well as robustness with respect to disturbances. Thus, this paper proposes a control strategy based on FOPID to achieve the control objectives. First, a linear approximation model is established for the constant tension control system. Then, a FOPID controller is designed based on the model. Four non-linear constraints and an objective function of the controller are proposed based on the frequency domain. Five tunable parameters of FOPID are determined by combining genetic algorithm (GA) with FMINCON non-linear optimization. Finally, through the simulation of MATLAB, the performance of the controller is compared with the classic integer order PID. The results show that the FOPID controller has better control characteristics and robustness.