**5. Conclusions**

This article presents the control of a grid-connected PV system using FO-SMC and FOsynergetic controllers. The mathematical model of a PV system connected to the main grid is presented together with the chain of intermediate elements: the DC-DC boost converter, the DC intermediate circuit, the DC-AC converter, the filtering block, and the transformer for the connection to the main grid, together with their control systems. The robustness and superior performance of an SMC-type controller for the control of *udc* voltage in the DC intermediate circuit are combined with the advantages provided by the flexibility of using synergetic control for the control of currents *id* and *iq*. In addition, these control techniques are suitable for the control of nonlinear systems, and it is not necessary to linearize the controlled system around a static operating point; thus, the control system achieved is robust to parametric variations and provides the required static and dynamic performance. Further, by approaching the synthesis of these controllers using the fractional calculus for integration and differentiation operators, this article proposes a control system based on FO-SMC/FO-SYN controllers. The validation of the synthesis of the proposed control system is achieved by comparing it with a benchmark for the control of a grid-connected PV system implemented in Matlab/Simulink.

**Author Contributions:** Conceptualization, M.N.; data curation, M.N. and C.-I.N.; formal analysis, M.N. and C.-I.N.; funding acquisition, M.N.; investigation, M.N. and C.-I.N.; methodology, M.N. and C.-I.N.; project administration, M.N.; resources, M.N. and C.-I.N.; software, M.N. and C.-I.N.; supervision, M.N.; validation, M.N. and C.-I.N.; visualization, M.N. and C.-I.N.; writing—original draft, M.N. and C.-I.N.; writing—review and editing, M.N. and C.-I.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** The paper was developed with funds from the Ministry of Education and Scientific Research—Romania as part of the NUCLEU Program: PN 19 38 01 03.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing not applicable. **Conflicts of Interest:** The authors declare no conflict of interest.
