Stability Analysis of Multi-Port MVDC Distribution Networks for All-Electric Ships

Advances in the power electronics technologies, over the years, have opened up the possibilities to consider medium-voltage dc (MVDC) distribution networks as possible evolutions of the existing medium-voltage ac (MVAC) distribution networks on large ships. The MVDC distribution networks provide the possibilities to increase fuel efficiency and remove bulky transformers. However, to implement industrial-scale MVDC distribution networks, some critical challenges exist, such as lack of standardized equipment and system-level stability. This paper studies the feasibility and stability of MVDC distribution networks when a distributed layout is considered. Due to the nature of the network, a multiple-input-multiple-output (MIMO) impedance stability approach is employed for modeling and assessment. The different components are modeled according to the existing industrial medium-voltage technologies. The theoretical analysis is verified by full-model time-domain simulations. As a summary of the contribution, the main features of the proposed study are: 1) the realistic identification of feasibility limits; 2) the definition of design rules for capacitance sizing and best placement; and 3) the evaluation of distances for dc distribution cables and their corresponding inductances.