Design of controllers using damping contours defined from closed loop systems based on fractional complex order integrators

Fractional complex order integrator is used since 1991 for the design of robust control-systems. In the CRONE control methodology, it permits the parameterization of open loop transfer function which is optimized in a robustness context. Sets of fractional order integrators that lead to a given closed loop damping ratio have also been used to build iso-damping contours on the Nichols plane. The objective of this paper is to present how these contours can be used to design robust controllers, not only CRONE controllers but also PD and QFT controllers.