Nowadays, the development of power electronics has reached a level that encourages designers to consider the feasibility of DC-distribution power systems in various forms and application fields [1,2]. Some companies offer proven solutions for High Voltage DC (HVDC) transmission systems [3–۵]. However, at present few Medium Voltage DC (MVDC) power systems exist and most of them are in a prototyping or experimental stage [6], therefore in this market sector no or very few ready-to-use solutions can be found yet. Nevertheless, both public research centers and R & D units of leading private companies are working in this direction [7–۱۴]. A leading sector for the study and experimentation of MVDC power systems is the marine sector [15], where important investments have been and are being made to develop this technology [16]. At present the Integrated Power System (IPS) [17,18] of largest commercial vessels is characterized by a Medium Voltage AC (MVAC) distribution. A promising solution to improve IPS performance relies on moving from MVAC to MVDC power systems [19,20]. Compared to its MVAC counterpart, MVDC distribution has several advantages [21–۲۴] such as: • no need for phase angle synchronization of power sources, which simplifies connection and disconnection procedures for power generation and storage devices of different type and size; • reducing the size and ratings of on-board switchgear and cables and elimination of bulky low frequency transformers; • improved management of fault currents, system reconfiguration and power flow in transient and emergency conditions; • enhanced efficiency thanks to the elimination of reactive current and to the possibility of variable speed prime mover operation; • removal of frequency constraints from the design and operation of generator sets [25], leading to size and weight reduction for generators and reducing the running cost gap between gas turbines and diesel engines. This can make it more affordable to use gas turbines, which are known to produce much less polluting emissions than diesel engines [26]. Nevertheless, MVDC power systems pose several technical challenges [22–۲۴,۲۷], such as system protection [28] and network stability [29,30], and further development of industrial equipment for MVDC applications is needed in order for the transition to MVDC shipboard power systems to become a significant reality [31]. Actually, the convenience to use a MVDC distribution depends on the availability of three key components: reliable and efficient power sources, high power DC/DC converters with acceptable cost and efficiency to be employed as Solid State Transformers (SST) [32] (namely power converter systems serving the same purpose as power transformer in AC grids, i.e. to adapt voltage levels and ensure galvanic isolation) and protection systems against short circuits, which are much more critical than in AC systems mainly because it is not possible to take advantage of zero crossings for current interruption [33].