*Review* **A Review of Recent Developments in Autotuning Methods for Fractional-Order Controllers**

**Cristina I. Muresan 1, Isabela Birs 1,2,3,\*, Clara Ionescu 1,2,3, Eva H. Dulf <sup>1</sup> and Robin De Keyser 2,3**


**Abstract:** The scientific community has recently seen a fast-growing number of publications tackling the topic of fractional-order controllers in general, with a focus on the fractional order PID. Several versions of this controller have been proposed, including different tuning methods and implementation possibilities. Quite a few recent papers discuss the practical use of such controllers. However, the industrial acceptance of these controllers is still far from being reached. Autotuning methods for such fractional order PIDs could possibly make them more appealing to industrial applications, as well. In this paper, the current autotuning methods for fractional order PIDs are reviewed. The focus is on the most recent findings. A comparison between several autotuning approaches is considered for various types of processes. Numerical examples are given to highlight the practicality of the methods that could be extended to simple industrial processes.

**Keywords:** direct autotuning methods; indirect autotuning methods; fractional-order controllers; simulation results
