Design of Robust Fractional Controller for Unstable Linear Systems Based on Phase Shaper Method

This paper is on the design of fractional controller for a class of undamped unstable linear plants. In the absence of the adequate damping the derivative control term is necessary for controlling these class of plants. The required performance specifications of the controlled system is first represented in terms of bode loop transfer function which is actually a fractional order integrator. The optimal control parameters of the controller is obtained by proper tuning of the fractional order of the integration and differentiation. The parameters of the fractional order controller is tuned using genetic algorithm. The inclusion of disturbance rejection, noise attenuation and robustness to plant gain variations as constraints of the optimization problem, guarantees robustness action of controller.