## 7 Conclusions
\begin{tabular}{c} Reducing congestion and increasing line loading (transmission loss and rescheduling cost) by employing three different curtailment strategies, \\ group, separate, and point-to-point \\ strategies, using UPFCs in modified \\ IEEE-14 bus and IEEE-30 bus systems. MMFO algorithms outperform MFO, PSO, GSA, GA \\ \end{tabular}  & The major benefit of MMFO is faster convergence and it outperforms MFO, PSO, GSA, and GA in terms of consistency and feasibility for minimizing transaction deviation and loss \\ \  
management, FACTS devices are a prominent solution for providing congestion management with NCFM methods compared to CFM methods because the marginal cost in NCFM is minimal. Moreover, the load-ability limits in deregulated power systems are increased by installing one or more FACTS devices. The latest generation of FACTS devices, such as the UPFC, is more effective for congestion management than the TCPST, TCVR, SVC, TCSC, SSSC, and STATCOM. However, cost remains a significant drawback for installation. Therefore, the TCSC is more commonly adopted for congestion management in parallel applications, whereas the SVC is selected for installation at weak buses with high voltage deviations in response to increased load-ability. FACTS devices are crucial for enhancing LFC, maintaining voltage stability, and alleviating congestion in deregulated power systems. Nonetheless, optimization techniques are equally significant for deriving optimal solutions or for the optimal placement of FACTS devices. Typically, meta-heuristic or hybrid optimization techniques are favored over classical, conventional, and analytical methods. Despite the practical advantages of classical control methods, such as ease of use and adaptability, they often demonstrate suboptimal performance against diverse system dynamics, non-linearities, and disturbances. Similarly, conventional optimization techniques, while possessing effective convergence characteristics, often struggle to manage constrained optimization problems. Furthermore, analytical approaches are inadequate for determining the optimal placement of FACTS devices in the networks. However, these aforementioned optimization techniques are effective when integrated with meta-heuristic techniques. Generally, FACTS controllers utilize existing resources of power networks that reflect their importance for present and future power systems, particularly hybrid or renewable-energy-based power systems. The authors believe that FACTS controllers have the ability to resolve multi-dimensional problems of existing power systems by more appropriate means. In addition, this review article will be very helpful to future researchers for determining the relevant references about the potential and behavior of FACTS controllers in deregulated power networks. In future, study should be extended to explore the impact of FACTS devices on hybrid or renewable-energy-based power systems. Moreover, exploring various machine-learning-based algorithms and artificial intelligence and their effect with FACTS devices on deregulated power systems is recommended. Conceptualization, J.A.S.-F. and P.Z. ; methodology. J.A.S.-F., M.F., P.Z. and M.A. ; software, M.A., M.F., P.Z. and J.A.S.-F.; validation, M.A., M.F., P.Z. and J.A.S.-F.; formal analysis, M.A., J.A.S.-F., P.Z. and M.F. ; investigation, M.A., M.F., P.Z. and J.A.S.-F.; resources, J.A.S.-F.; data curation, M.A., J.A.S.-F. and M.F. ; writing--original draft preparation, M.A., M.F., P.Z. and J.A.S.-F.; writing--review and editing, J.A.S.-F.; visualization, M.A., M.F. and J.A.S.-F.; supervision, J.A.S.-F. and P.Z. ; project administration, J.A.S.-F. and P.Z. ; funding acquisition, J.A.S.-F. All authors have read and agreed to the published version of the manuscript. This research was funded by Universidad Politecnica de Madrid, grant number RP2304330031. All the data supporting the reported results can be found in this paper and in the cited references. The authors declare no conflicts of interest.