MVDC technology is a promising solution to avoid installation of new AC networks. MVDC can provide optimum integration of large-scale renewable energy sources, the interconnection of different voltage levels of DC and AC grids with the ancillary services. The development in MVDC depends significantly on the DC-DC converters. Such converters support the modern trends of utilising medium-frequency transformers in power networks. Research on isolated converters technology is in its infancy and limited by the conversion ratio and component ratings. Besides, there is no standards exist covering specific aspects of isolated converter product. Thus, a review of such converters is needed. This work presents, for the first time, a review of the DC-DC power converter families in MVDC grids including the leading families which are isolated and nonisolated converters, as well as other subfamilies comparing the specifications and characteristics. Also, the applications of these converters are provided by focusing on the essential requirements for each application. Index Terms-MVDC grids, DC-DC power converters, dual active bridge (DAB), multilevel converter. TABLE I RECOMMENDED CLASSES FOR MVDC VOLTAGE MVDC Class (kV) Nominal Rated Voltage (kV) Maximum Rated Voltage (kV)

The extensive use of electric vehicles (EVs) needs ultra-fast-charging stations with high charging power greater than 22 kW (PCharging >22kW). Medium voltage direct current (MVDC) grids can provide the best solution for the high demand of EVs and fast-charging stations infrastructures with the existing distribution grids. The resonant bidirectional dual active bridge (DAB) DC-DC converter can be a promising technology in integrating an electric vehicle charging station (EVCS) with MVDC grid. This work focuses on the converter design with voltage control and stability by applying two different control strategies mainly: PI control and sliding mode control (SMC). All simulations will be performed in order to present the feasibility of the proposed solution and compare the results of each control methods. This comparison, for the first time, in the medium voltage level can open new insights for using nonlinear control methods such as SMC to ensure stability and obtain better dynamic performance

Transferring bulk power via high voltage direct current (HVDC) transmission is dominated by line commutated converters (LCC). This is due to the robustness and higher ratings of the thyristors as well as the higher converter efficiency. Nevertheless, most of these transmission networks are point to point. This is due to the challenges of allowing multi-terminal LCC based networks and power reversal. This paper introduces a new dc-dc converter topology that allows connecting two independent LCC networks. The proposed converter is based on insulated gate commutated thyristors (IGCTs). Utilizing IGCTs allow mimicking similar control and performance as in insulated gate bipolar transistor (IGBT) based voltage source dc-dc converters. However, IGCTs have more superior features over IGBTs such as higher efficiency, higher short circuit current and higher power ratings. Detailed analysis and simulations are provided to validate the proposed converter topology, which confirms its potential in connecting HVDC-LCC networks.