The development of high-voltage direct current (HVDC) systems has been pivotal to the evolution of modern power systems, particularly in terms of providing an effective solution for long-distance, high-capacity power transmission, which has become increasingly important in the integration of renewable energy technologies. The integration of renewable energy sources into the grid requires the use of sophisticated tap-changing technology to ensure efficient extraction of power from HVDC lines. A critical review of the current status of the HVDC technology is presented in this paper. It synthesizes research findings on power flow optimization, grid expansion, and the challenges of designing HVDC grid substations. The development of modular multilevel converters (MMCs) and DC-DC converters, particularly for use in hybrid alternating current (AC)/direct current (DC) grids, is highlighted. These findings emphasize the importance of continuous research on the HVDC tap technology to improve the efficiency, reliability, and scalability of future power systems.