In recent years, fractional calculus has been applied in the modeling and control of various kinds of physical systems, as well known and documented in many control theories or in application literature.
In fact, the design of feedback controllers for fractional order systems (FOS) has been approached from generalizations of some classical design methods. For example, the fractional order PID controller can be seen as generalization of a traditional PID controller.
Various engineers designed fractional PID controllers using different designs and tuning methods. However, tuning of a fractional PID controller is a challenging work, because there are five parameters to tune, which means two more parameters than a classical PID controller.
So, Hyon Chung Il, a section head at the Faculty of Automation Engineering, has proposed a design method of a fractional order [proportional derivative] controller for a type of fractional order systems, and verified its effectiveness through comparisons with other controllers such as the traditional integer order PID controller and the fractional order proportional derivative controller.
The comparisons illustrate that the IO-PID controller designed may not always be stable enough to achieve the iso-damping specification and that the proposed FO-[PD] controller outperforms FO-PD controllers.
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