**5. Conclusions**

In this paper, a mixed AC/DC Power Flow (PF) algorithm for the steady-state interaction of the large-scale MT-HVDC systems is investigated. This algorithm is an improved sequential AC/DC PF algorithm, which uses the Newton-Raphson method to solve the DC PF problem. Different operational constraints and control strategies along with contingency analysis in the hybrid AC/DC grids are considered in this study. Fast convergence and high accuracy are the main advantages of the mixed AC/DC PF algorithm. In addition, it is a powerful tool for sensitivity analysis and congestion managemen<sup>t</sup> in power systems. Various cases are studied in this paper to evaluate the performance of the mixed AC/DC PF algorithm. The obtained results demonstrate the robustness and effectiveness of the mixed AC/DC PF algorithm for power system operation and planning studies.

**Author Contributions:** F.M. was responsible for methodology, collecting resources, data analysis, writing—original draft preparation, and writing—review and editing. G.-A.N. and M.S. were responsible for the supervision, and writing—review and editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** M. Saif acknowledges the financial support of Natural Sciences and Engineering Research Council (NSERC) of Canada, as well as National Science Foundation of China under gran<sup>t</sup> number 61873144.

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