Two-degrees-of-freedom Fractional Control Method for DC Position Servo System

To improve the control performance in DC-position servo systems, we propose a two-degrees-of-freedom (2DOF) fractional-order control method. By designing a 2DOF control structure, we achieve decoupling control of the system's set-point tracking and disturbance rejection responses. Then, we develop a design method for the set-point tracking and disturbance rejection controllers by choosing a fractional-order filter by combining internal model control (IMC) and fractional control. Based on the control performance requirements, we use the system's cut-off frequency and maximum sensitivity index to analytically tune the parameters of the 2DOF controller. Simulation and experimental results show that the fractional-order 2DOF controller has good set-point tracking characteristics and disturbance rejection capability.