On fractional-order PID controllers

A new Fractional Order Proportional-Integral (FOPI) controller tuning method is proposed in this paper for process control systems. This is achieved by combining Biggest Log-modulus Tuning (BLT) method and Internal Model Control (IMC) method of designing conventional PID controllers to tuning FOPI controllers for multivariable processes. Unlike the conventional PID case, internal model control method is first used to design the FOPI controller and obtain preliminary values of controller parameters. This yields simple formulae for setting controller gains. Thereafter, the FOPI controller gains are adjusted using a single detuning factor (F) until a biggest log modulus of 2n dB is obtained where n is the number of loops. Extended simulation studies show that good compromise between performance and robustness can be achieved for multiloop process control applications with the proposed FOPI controller.