The linear control system for LTI (linear time invariance) plant has a limitation in control performance. So far, many approaches such as nonlinear control, intelligent control, fractional order, etc. to break this limitation have been proposed. Among them, the approach based on fractional order description provides great possibility to improve the control performance by greatly expanding the control area of the controller and the control targets.
It is expected that most design methods for linear control systems provide positive effects if they are extended to fractional order version.
Pak Se Yang, a section head at the Faculty of Automatics, who was motivated by such expectation, conducted a study to extend the robust controller design method in the frequency domain under study, into the fractional order controller.
The controller has the structure of linear combination of fractional basis transfer functions with respect to parameters. The problem for controller design is solved by finding the parameters which satisfy the approximated linear inequalities corresponding to H∞ norm condition for the robust criterions.
He investigated the problem to design the fractional PI and PID controllers through a simulation, which verified the validity of the proposed method.
You can find the details in his paper “Data-Driven Design of Fractional Order H∞ Controller by Convex Optimization” in “International Journal of Dynamics and Control” (EI).