A Multi-Layer Framework for Reliability Assessment of Shore-to-Ship Fast Charging System Design

In this paper, a multi-layer framework is proposed to assess the reliability of Shore-to-Ship Charging (S2SC) systems, considering the potential for failures of the main elements, such as power converters and batteries. The proposed reliability model enables evaluating a S2SC system with redundancy, multi-state system availability, and multi-variable design scenarios, based on a recursive algorithm. Instead of conventional Markov-chain multi-state models, a reduced order state-space model is established from a set of specific sub-systems with a predefined configuration complying with the design requirements. A modular approach is taken, and the probabilistic characteristics of the sub-systems are established by developing a Universal Generating Function considering the available charging power and energy balance constraints. Then, the sub-systems are integrated into the system configuration to assess a set of proposed application-specific system-level reliability indices. Thus, the modular approach enables expansion to the power system dimensions without extra complexity. Finally, a case study based on an operating 4-MW dc S2SC system is performed by the proposed framework, and design suggestions are given based on a figure of merit defined for evaluation of reliability and energy efficiency. These design suggestions include resizing the charging system by installing onshore batteries, modularization, and introduction of redundancy in the sub-systems.