**5. Conclusions**

In this paper, a fractional-order PID controller approximation was suggested to regulate voltage in a buck–boost converted. The model of the system was linearized through the small-signal technique around the equilibrium point. The resulting linearized plant was divided into minimum and non-minimum phase parts, which simplified the controller design, allowing us to focus it on the minimum phase part only. The controller design considered both performance and robustness, while a simple tuning method allowed us to determine directly appropriate gains to achieve stability margin requirements. Synthesized controllers effectively regulated voltage in both conversion modes with a stable, fast, and good tracking characteristic. Superior disturbance/perturbation and noise rejection characteristic was also determined.

By comparing performance parameters of typical PID controller with those obtained by the fractional-order PID approximation allowed us to determine quantitatively the proposed approach superiority in time and frequency domains. To corroborate the experimental viability, a generalization for the controller structure was derived. The resulting electrical arrangement is implementable easily through RC circuits and OPAMPs. Experimental results confirmed the proposed controller effectiveness and its viability, since the parameter values are all commercial.

Lastly, it is worth mentioning that numerical simulations not only predicted effectiveness of the controller but its actual effect, since the obtained experimental results confirmed data of Figure 5 and Table 4, column 2 for both conversion modes.

**Author Contributions:** Conceptualization, A.G.S.S.; Formal analysis, A.G.S.S. and E.T.-C.; Investigation, A.G.S.S., J.S.-V. and E.T.-C.; Methodology, A.G.S.S., J.S.-V. and E.T.-C.; Resources, A.G.S.S., E.T.-C. and M.A.R.-L.; Validation, A.G.S.S. and M.A.R.-L.; Visualization, A.G.S.S., E.T.-C. and M.A.R.-L.; Writing—original draft, A.G.S.S.; Writing—review & editing, A.G.S.S., E.T.-C. and M.A.R.-L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to thank CONACYT México for catedras 6782, 4155 and Josué Soto–Vega's M. Sc. scholarship.

**Conflicts of Interest:** The authors declare no conflict of interest.
