Future MVDC shipboard power systems will be characterized by a progressive employment of power converters. In this paper, starting from a real case-study, the focus is on two AC/DC power conversion stages forming the MVDC bus of a shipboard power system. A preliminary design of the AC/DC power conversion stages and their control system is provided in order to verify feasible operations. A coordination strategy based on the droop control technique is adopted achieving load power sharing. Simulation results verify proper operation also in case of pulsating loads.

Voltage stability is an important problem in Medium Voltage DC (MVDC) power systems. A previous paper analyzed a model of a power system with one controlled load converter, achieving useful stability conditions on the controller bandwidth connected to system parameters. In this paper, a further study has been carried on, concerning the stability analysis of the two converters (the feeder buck and the load buck) with simple integral controls. The above-mentioned power system, composed by two cascaded DC-DC converters, is modelled using a fourth-order nonlinear system of differential equations. Then, the system is linearized around its equilibrium point and the input admittance is found. The Routh-Hurwitz criterion is applied to find the conditions on both controllers bandwidths that assure stability. The results are simple and of simple application. They may be very useful for what concerns the system stability analysis because the influence of the feeder controller on the load controller is made clear. Small-signals numerical simulations are used to validate the proposed model.

Voltage stability is a fundamental issue to be addressed in the future All-Electric Ships (AESs) based on DC distribution. Focusing on a cascade-connected MVDC power system (i.e. a feeder DC-DC converter supplying a load DC-DC converter), the small-signal analysis is the first study to be accomplished for investigating the effect of load converter's control bandwidth on the system stability. Albeit such an evaluation may be performed on the complete fifth order model by determining the Routh-Hurwitz coefficients, a convenient model reduction can simplify this study. In such a way, it is possible to provide an analytical and simple formula for defining the minimum acceptable time constant (i.e. the maximum load converter control bandwidth). Once identified such a minimum time constant, some simulations show how the complete and reduced models work in presence of three different filter arrangements on the load converter side.

The concept of an all-electric ship, while offering unprecedented advantages from the point of view of efficiency and flexibility of operation, has introduced new challenges in terms of stability and power flow control. The advent of a full power electronics power system has raised new questions from the point of view of system dynamics, particularly when dealing with the new medium-voltage direct current distribution. The overall goal of guaranteeing a secure operation of the power system has brought researchers to consider two main approaches: reducing the dynamics of the large load to operate in a range of dynamics compatible with traditional generation systems, or making the generator set smarter through its power electronics interface. This paper compares these approaches to stable operation, focusing on the latter considered more in line with the progress of technology and in general more appealing.

The articles in this special issue provides a comprehensive treatment of the history of electric ship propulsion, the present status of both commercial and military electric ships, and the ongoing research that will lead to the fully integrated all-electric ship.

This contribution starts with a review of the state of the art of existing high-voltage shore connection (HVSC) systems in terms of principles, rules, publications, technologies, and relevant installations. Then, tutorial sections present the main technical aspects of HVSC systems as ship-to-shore interface, shore equipment (transformers, converters, etc.), onboard devices (cubicles, shore switchboard, etc.), operating sequences, and feasibility aspects, for both commercial and military applications. Finally, some technical challenges are presented, concerning intentional/unintentional bonding, interactions between HVSC bonding and cathodic protection systems, bonding opportunity, and electrical safety aspects related to bonding issues in case of large earth fault currents in port facilities.